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Characterization of geochemical and lithologic variations in Milankovitch cycles: Green River Formation, Wyoming
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Characterization of geochemical and lithologic variations in Milankovitch cycles: Green River Formation, Wyoming
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CHARACTERIZATION OF GEOCHEMICAL AND LITHOLOGIC VARIATIONS IN MILANKOVITCH CYCLES; GREEN RIVER FORMATION, WYOMING by Stan C. Teerman A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (DEPARTMENT OF EARTH SCIENCES) May 2005 Copyright 2005 Stan C. Teerman Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3180382 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3180382 Copyright 2005 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS My graduate advisor Alfred Fischer contributed to this project in a variety o f ways. First, a deep understanding of the impact that orbital cyclicity has on depositional systems including organic-rich lacustrine sediments. From this, a geochemical project of Green River cyclicity was initiated. Second, he seriously challenged me to find and consider multi-disciplinary alternatives concerning the origin of Green River cyclicity. Third, without his patience and support in completing this project, I would have never finished because of too many other commitments. In addition, I want to acknowledge my thesis committee - David Bottjer, Doug Capone, and Frank Corsetti who provided knowledge and insight in their respective fields. Their contribution provided a much more integrated outcome to this work. Thanks are also given to the contributions by Donn Gorsline and Bob Douglas. As I labored in the completion of this work, the patient consideration of David Bottjer as co-chair will always be appreciated. Acknowledgement also goes to the United States Geological Survey (USGS) for use of their core facility and sampling. Thanks are given to John Dyni (USGS) for providing permission to sample Green River Formation cores. He also provided background and data from previous studies of Green River oil shales. ChevronTexaco helped support some of the analytical work. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I owe everything to my wife Shu for supporting me to continue in this project. I may never fully grasp her patience in allowing me to work long hours combined with completing this dissertation. I also owe my daughter Hanna many missed days of play and visits to the park. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ii LIST OF TABLES viii LIST OF FIGURES xi ABSTRACT xix CHAPTER 1 INTRODUCTION AND DISSERTATION ORGANIZATION 1 Background 1 Dissertation Organization 6 CHAPTER 2 BACKGROUND-GREEN RIVER FORMATION GEOLOGY AND CYCLICITY 9 Green River Formation 9 Geologic Setting and Tectonic History 9 Stratigraphy and Geologic History 12 Luman Tongue 14 Tipton Shale Member 14 Wilkins Peak Member 15 Laney Member 16 Biostratigraphy and Age Dates 17 Paleoclimate-Green River Formation Southwest Wyoming 18 Existing Green River Lacustrine Models 21 Lacustrine Geochemical Studies-Green River Formation 22 Solar and Orbital Cyclicity 23 Concept and Historical Background 23 Cyclicity-Green River Formation 26 CHAPTER 3 OBJECTIVES, STUDY LOCATION, SAMPLING, METHODOLOGIES AND DEFINITIONS 32 Objectives 32 Study Location and Stratigraphic Intervals 33 Selection of Cycles for Evaluation 39 Analyses, Methods and Techniques 40 Fischer Assay Oil-Yields-Procedure and Application 40 Time-Series and Spectral Analysis 42 Geochemical Evaluation and Analytical Techniques 43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Total Organic Carbon and Rock-Eval Pyrolysis 43 Total Sulfur 44 Pyrolysis-Gas Chromatography 44 Maceral Analyses-Organic Petrography 45 Solvent Extraction 47 Liquid Chromatography 47 Gas Chromatography-Bitumen 47 Gas Chromatography-Mass Spectrometry 48 Carbon Isotope Analysis (Kerogen and Bitumen) 49 Stable 8 13 and 8 18 O Measurements-Carbonate Matrix 50 X-Ray Mineralogy 51 Definition and Terms Used in This Study 51 CHAPTER 4 CYCLICITY - TIPTON AND WILKINS PEAK MEMBER 55 Introduction 55 Observations and Results 55 Milankovitch Cycles - Tipton Member 55 Log Identification o f Cyclicity 55 Cyclical Properties, Patterns and Depositional Period 58 Milankovitch Cycles - Wilkins Peak Member 65 Wilkins Peak Precessional Cycles-Occurrence and Properties 69 Lithologic Successions-Precessional Cycles 73 Oil-Yield Pattems-Precessional Cycles 76 Sub-Milankovitch Cycles-Tipton and Wilkins Peak Members 82 Time Series and Spectral Analysis-Tipton and Wilkins Peak 91 Discussion 95 Litho-Organic Signatures-Applications to Cyclicity 96 Cyclicity-Tipton Member 96 Cyclicity -Wilkins Peak Member 97 Long-Term Eccentric and Sub-Milankovitch Cyclicity 101 Half-Precessional Cycles 102 Century-Level Cycles 103 Variations in Milankovitch Cycles-Tipton and Wilkins Peak 105 Precession Index and Short- and Long-term Cyclicity 105 Paleoclimate and T ectonics 106 Episodic Depositional Distortions 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page CHAPTER 5 GEOCHEMICAL EXPRESSION AND PROPERTIES OF CYCLICITY-TIPTON MEMBER 111 Introduction 111 Results 111 Discussion 146 Geochemical Properties, Cyclical Trends and Mechanisms 146 Organic-Rich Cycle Base - Geochemical Expression and Processes 146 Mid-Cycle-Geochemical Expression and Processes 149 Half-Cycle and Cycle Top-Geochemical Signatures 155 Geochemical Comparison-Scheggs and Rife Precessional Cycles 156 CHAPTER 6 GEOCHEMICAL EXPRESSION AND PROPERTIES OF WILKINS PEAK CYCLICITY 159 Introduction 159 Results 159 Discussion 195 Cyclical Geochemical Patterns and Processes 195 Precessional Geochemical Pattern 1 Oil Shale- Mudflat F acies 197 Carbon Isotope Enrichment and Excursions-Lerogen 202 Precessional Geochemical Pattern 2-Oil Shale Occurrence and Variations 209 Pattern 3-Variations Mudflat Facies - Organic Microfacies 217 CHAPTER 7 GREEN RIVER ORBITAL CYCLICITY-ORIGIN, IMPRINT, AND APPLICATIONS 219 Introduction 219 Cyclical-Driven Depositional Models - Tipton and Wilkins Peak 224 Tipton Scheggs and Paleolate Stages 226 Wilkins Peak Playa Lake 231 Wilkins Peak “Wet and Dry Mudflat” Microfacies 236 Spectrum of Lacustrine Facies, Cyclical Expression and Litho- organic Signatures - Application to Orbital Cyclicity 241 Spectrum of Green River Lacustrine Facies 241 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Expression of Cyclicity in the Spectrum of Tipton and Wilkins Peak Facies 244 Litho-Organic Signatures-Applications of Geochemistry to Orbital Cyclicity 252 Orbital Cyclicity and its Transfer into the Sedimentary Record 256 Eocene Greenhouse Conditions-Organic Rich Cyclical Deposition 257 Imprint Mechanisms - Precessional Cycles 259 Imprint Mechanisms - Eccentricity Cycles 262 Obliquity Cycle 265 Half-Precessional Cycles 265 Applications to the Origin of Organic-Rich Green River Sediments 267 CHAPTER 8 SUMMARY AND CONCLUSIONS 271 REFERENCES 280 Appendix 1 305 Appendix 2 310 Appendix 3 323 Appendix 4 333 Appendix 5 334 Appendix 6 335 vii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Page Table 1. Classification of individual macerals and organic constituents used for organic petrography analyses of Tipton and Wilkins Peak samples. 46 Table 2. Summary o f precessional cycle dimensions and properties, Scheggs and Rife Beds; Tipton Member, Blacks Fork-1. 64 Table 3. Whole rock X-ray diffraction results for selected samples from the Scheggs and Rife Beds in the Tipton Member, Blacks Fork-1. 6 6 Table 4. Precessional cycle dimensions and maximum oil-yield for individual cycles, Wilkins Peak Member, Blacks Fork-1. 71 Table 5. Dimensions and calculated depositional interval representing half- precessional cycles in the Tipton Member, Blacks Fork-1. 84 Table 6 . Occurrence o f half-precessional cycles in the Wilkins Peak Member, Black Fork-1. 85 Table 7. Examples of episodic depositional distortions and their depositional disruption and imprint described for the Tipton and Wilkins Peak Members. 108 Table 8 . Fischer assay oil-yields for selected precessional cycles in The Scheggs and Rife Beds, Tipton Member; Blacks Fork-1. 113 Table 9. Geochemical summary of rock and kerogen properties for Scheggs and Rife precessional cycles, Tipton Member, Blacks Fork-1. 114 Table 10. Geochemical summary of extractable organic matter (bitumen) for Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. 116 Table 11. Total organic carbon (TOC), complete Rock-Eval pyrolysis and weight percent total sulfur data, Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. 126 viii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Table 12. Organic petrographic results for selected samples from Scheggs and Rife precessional cycles, Tipton Member, Blacks Fork-1. 128 Table 13. Carbon isotope composition for saturate and aromatic fractions of solvent extracts from the Tipton and Wilkins Peak Members, and quantities of C29-C35 hopanes of saturate fraction, Blacks Fork-1. Table 14a. Summary o f selected quantitative gas chromatography (GC) results for extracts from Scheggs and Rife precessional cycles, Tipton Member, Blacks Fork-1. Table 14b. GCMS biomarker data listing terpane ratios and (3-carotane content for extracts from Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. Table 14c. GCMS biomarker data listing quantity of individual steranes And methyl steranes for extracts from Scheggs and Rife precessional Cycles, Tipton Member; Blacks Fork-1. Table 14d. GCMS thermal maturation data for extracts from the Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. Table 15. Fischer assay oil-yields for measured intervals in selected precessional cycles, eccentricity cycles A and E, Wilkins Peak Member, Blacks Fork-1. Table 16. Geochemical summary of kerogen and rock properties for selected Wilkins Peak precessional cycles; Blacks Fork-1. Table 17. Geochemical summary of extractable organic matter for Wilkins Peak precessional cycles; Blacks Fork-1. Table 18. Total organic carbon (TOC), Rock-Eval pyrolysis and total sulfur for selected precessional cycles, Wilkins Peak Member; Blacks Fork-1. 173 Table 19. Organic petrographic results for select Wilkins Peak samples, eccentricity A and E, Blacks Fork-1. 175 Table 20a. Summary of gas chromatography (GC) parameters for individual Wilkins Peak precessional cycles; Blacks Fork-1. 189 ix 129 130 131 132 133 169 170 172 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Table 20b. GCMS-biomarker data listing terpane ratios for extracts from individual precessional cycles in the Wilkins Peak Member, Blacks Fork-1. Table 20c. GCMS-biomarker data including sterane distributions and content (ppm) for extracts from individual precessional cycles in the Wilkins Peak Member, Blacks, Fork-1. Table 20d. GCMS-biomarker thermal maturation data for extracts from individual precessional cycles in the Wilkins Peak Member, Blacks Fork-1. Table 21. Properties and description of lacustrine systems and geologic expression of precessional cyclicity in the Tipton Scheggs and Rife Beds, and Lower and Middle Wilkins Peak Members. Table 22. Geochemical properties expression of precessional cycles in Tipton Scheggs and Rife Beds, and Lower and Middle Wilkins Peak. Table 23. Description o f major climatic and lacustrine conditions and processes that imprint Tipton and Wilkins Peak precessional cycles, precessional cycles. Table 24. Role of different mechanisms that influenced organic productivity, preservation and sedimentation, and their effect on organic accumulation associated with cyclical deposition in the Tipton and Wilkins Peak Members. Table 25. Common litho-organic signatures in Tipton and Wilkins Peak: depositional paleoclimatic significance, applications and interpretation for orbital mechanism and imprint. 190 191 192 221 222 223 225 253 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Page Figure 1. General elements of lake systems and lacustrine processes that control organic matter accumulation. Figure 2. The occurrence of the Green River Formation in Utah, Colorado and Wyoming. 10 Figure 3. Map of major structural features, greater Green River Basin, Wyoming and Colorado. 11 Figure 4. Generalized stratigraphic section of Eocene sediments in the greater Green River Basin. 13 Figure 5. Summary of calendar, solar, Milankovitch, and possible longer cycles. 25 Figure 6 . Cyclicity in the Tipton and Wilkins Peak Members, Green River Basin. 28 Figure 7. North-south section illustrating stratigraphy and the 77 precessional cycles in the Wilkins Peak Member, as identified by Roehler (1991). 29 Figure 8 . Energy Research and Development Administration Blacks Fork Corehole Number 1. 30 Figure 9. Isopach map of the Scheggs Bed of Tipton Shale Member, Green River Formation. 34 Figure 10. Isopach map of the Rife Bed of Tipton Shale Member. 35 Figure 11. Isopach map o f the lower part of the Wilkins Peak Member, Green River Formation. 36 Figure 12. Isopach map of the middle part of the Wilkins Peak Member, representing precessional cycles 12-67. 37 Figure 13. Isopach map o f the upper part of the Wilkins Peak Member, representing precessional cycles 68-77. 38 X I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 14. Wilkins Peak study intervals in Energy Research and Development Administration Blacks Fork Number 1. 41 Figure 15. Gamma and sonic log for Tipton Member, El Paso-1 illustrates the occurrence of precessional and eccentricity cycles. 56 Figure 16. Scheggs precessional cycles defined by Fischer assay oil-yield, Blacks Fork-1. 59 Figure 17. Occurrence of precessional cycles in Rife Beds of the Tipton Member, Blacks Fork-1. 60 Figure 18. Representative oil-yield patterns in Tipton precessional cycles. 61 Figure 19. Range in thickness of precessional cycles as defined by oil-yield, Tipton Member, Blacks Fork-1. 63 Figure 20. Gamma and sonic log, Wilkins Peak Member, El Paso-1. 67 Figure 21. Various imprints of orbital cyclicity in the Wilkins Peak Including precessional and short-and-long eccentricity cycles. 6 8 Figure 22. Variation in thickness of precessional cycles, Wilkins Peak Member, Blacks Fork-1. 70 Figure 23. Thickness of individual Wilkins Peak precessional cycles in relation to eccentricity cycles, Blacks Fork-1. 74 Figure 24. Five different lithologic successions are identified in precessional cycles that represent the paleogeographic lake center in the Wilkins Peak Member. 75 Figure 25. Precessional patterns in Wilkins Peak Member. 77 Figure 26. Comparison cycle thickness and corresponding oil shale, And maximum oil-yield for individual precessional cycles, Wilkins Peak Member, Blacks Fork-1. 79 xii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 27. Thickness of oil shales in individual precessional cycles versus depth, Wilkins Peak Member, Blacks Fork-1. 80 Figure 28. Maximum oil-yield of individual Wilkins Peak precessional cycles, Blacks Fork-1. 81 Figure 29. Dry, intermediate and wet precessional cycles in Wilkins Peak eccentricity E. 83 Figure 30. Identification of sub-Milankovitch, half-precessional enrichment in oil-yield that occurs somewhere in the middle of Tipton precessional cycles (H), Black Fork-1. 84 Figure 31. Expression of Wilkins Peak half-precessional cycle patterns defined by oil-yield, Blacks Fork-1. 85 Figure 32. Occurrence of likely half-precessional cycles throughout the Wilkins Peak, Blacks Fork-1. 8 6 Figure 33. Example of thin organic-rich bands that sometimes occurs in the Mudflat facies in the Wilkins Peak Member, Blacks Fork-1. 8 8 Figure 34. Spectral analysis results for cycle properties from Blacks Fork-1 Illustrating Milankovitch cyclicity in the Tipton Member. 92 Figure 35. Spectral analysis illustrating Milankovitch cyclicity in the Wilkins Peak Member. 93 Figure 36. Precessional cycles in the Tipton Member, Blacks Fork-1 are defined from Fischer assay oil-yield and total organic carbon patterns. 112 Figure 37. Lithologic description, oil-yield and geochemical patterns versus depth for Scheggs cycle 7 (1628.2-1633.5 ft), Blacks Fork-1. 118 Figure 38. Lithologic description, and oil-yield and geochemical patterns, versus depth for Scheggs cycle 3 (1650.9-1656.5 ft), Blacks Fork-1. 119 Figure 39. Lithologic description, and oil-yield and geochemical pattern versus depth for Scheggs cycle 4 (1645.6-1650.9 ft), Blacks Fork-1. 120 xiii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 40. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 7 (1531.0-1541.1 ft), Blacks Fork-1. 121 Figure 41. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 6 (1541.1-1548.7 ft), Blacks Fork-1. 122 Figure 42. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 5 (1548.7-1556.6 ft), Blacks Fork-1. 123 Figure 43. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 3 (1561.7-1572.0 ft), Blacks Fork-1. 124 Figure 44. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 1 (1582.1-1587.5 ft), Blacks Fork-1. 125 Figure 45. Gas chromatograms of saturate fraction of extracts from Scheggs cycle 7 (1628.2-1633.5 ft). 136 Figure 46. Gas chromatograms of saturate fraction of extracts from Scheggs cycle 4 (1645.6-1650.9 fit), Blacks Fork-1. 137 Figure 47. Gas chromatograms of saturate fraction of extracts from Scheggs cycle 3 (1650.9-1656.5 ft). 138 Figure 48. Terpane mass chromatograms (m/z 191) from GCMS analysis of saturate fraction of extracts, Scheggs cycle 3. 139 Figure 49. Gas chromatograms of saturate fraction of extracts from Rife cycle 7. 141 Figure 50. Terpane mass chromatograms (m/z 191) from GCMS analysis of saturate fraction of extracts from Rife cycle 7. 142 Figure 51. Gas chromatograms of saturate fraction of extracts, Rife cycle 6 . 143 Figure 52. Terpane mass chromatograms (m/z 191) from GCMS analysis of saturate fraction of Rife cycle 6 extract (1541.1-1548.7 ft). 144 XIV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 53. Sterane distribution of saturate fraction of extracts from Rife cycles 6 and 7. 145 1 ^ Figure 54. Comparison of the A8 C of the aromatic and saturate fraction, and C29- C35 hopane content of the extracts. 154 Figure 55. The C27-C28-C29 sterane distribution of the saturate fraction of extracts from Scheggs cycles 3, 4, and 7. 158 Figure 56. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak precessional cycle 1 (1486.6-1502.0 ft), Blacks Fork-1. 161 Figure 57. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 3 (1458.7-1468.6 ft), Blacks Fork-1. 162 Figure 58. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 5 (1425.9-1440.5 ft), Blacks Fork-1. 163 Figure 59. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 20 (1229.2-1250.8 ft), Blacks Fork-1. 164 Figure 60. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 21 (1217.8.2-1229.2 ft), Blacks Fork-1. 165 Figure 61. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 22 (1204.5-1217.8 ft), Blacks Fork-1. 166 Figure 62. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 23 (1193.6-11204.5 ft), Blacks Fork-1. 167 X V Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 63. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 24 (1179.0-1193.6 ft), Blacks Fork-1. 168 Figure 64. Gas chromatography (GC) trace of saturate fraction of extracts from oil shale and mudflat facies; cycle 1, Blacks Fork-1. 177 Figure 65. Gas chromatography-mass spectrometry (GCMS) results for saturate fraction of extracts from cycle 1. 178 Figure 6 6 . GC traces o f saturate fraction o f mudflat and oil shale extracts from cycle 5. 179 Figure 67. GC traces of saturate fraction of oil shale, mudflat and trona extracts from cycle 2 2 . 180 Figure 6 8 . GCMS biomarker parameters for saturate fraction of extracts, cycle 2 2 . 181 Figure 69. GC traces of saturate fraction of extracts from cycle 23. 182 Figure 70. GCMS biomarker ratios of saturate fracture of extracts from cycle 23. 183 Figure 71. GC traces for saturate fraction o f oil shale and mudflat facies from cycle 24. 184 Figure 72. GCMS biomarker parameters of saturate fracture extracts from cycle 24. 185 Figure 73. Various biomarker parameters document differences in Precursor input between the mudflat and oil shale facies, Wilkins Peak Member; Blacks Fork-1. 187 Figure 74. Differences in biomarker parameters between saturate fraction extracts from the mudflat and oil shale facies, Wilkins Peak Member; Blacks Fork-1. 188 X V I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 75. Differences in weight percent total organic carbon (TOC) and Rock-Eval pyrolysis SI + S2 for “wet mudflat” and “dry mudflat” microfacies. 196 Figure 76. Relationship between 8 1 3 C kerogen and TOC and HI of Wilkins Peak sediments, Blacks Fork-1. 203 Figure 77. Solubility of carbon dioxide in aqueous solutions decreases with increasing sodium chloride and temperature. 205 Figure 78. Carbon isotopic fractionation in C3 plants (tomato) and aquatic algae utilizing the C3 pathway in response to CO2 pressure in ambient air. 206 Figure 79. Relationship between carbon isotopic composition of kerogen and the matrix carbonate. 208 Figure 80. Linear correlation between TOC and Rock-Eval SI + S2 indicates similar Type I/II kerogen for most oil shale in the Wilkins Peak. 211 Figure 81. Relationship between TOC and Rock-Eval HI suggests organic matter degradation is not a major cause of the lower organic carbon content in most oil shales and select organic-rich mudstones. 213 Figure 82. Comparison of lateral variation in oil-yield and TOC between White Mountain-1 and Blacks Fork-1 for precessional cycles 21 -23. 215 Figure 83. Precessional-driven lake cycle for Scheggs Beds. 227 Figure 84. Precessional-driven lake cycle for Rife Beds. 228 Figure 85. Precessional-driven playa lake stages for Wilkins Peak oil shale facies. 232 Figure 8 6 . Depositional setting of “wet and dry mudflat” microfacies, Wilkins Peak Member. 238 xvii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Page Figure 87. Summary of likely paleoclimatic, tectonic and orbital factors that influenced lake levels in the spectrum of Tipton and Wilkins Peak lacustrine systems. 242 Figure 8 8 . Similar lithological and geochemical precessional patterns in the Tipton and Wilkins Peak precessional cycles confirm parallel trends in relative moisture availability. 245 Figure 89. Similarities in the lithological and geochemical expression of precessional cycles, and their occurrence in the Tipton and Wilkins Peak Members. 246 Figure 90. Lithological and geochemical differences in expression of cyclicity with the evolving Tipton and Wilkins Peak lake systems. 247 Figure 91. Different climatic and lacustrine mechanisms associated with the Tipton and Wilkins Peak lacustrine spectrum and their effects on the imprint of cyclicity. 251 xviii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT This study defines how changing lacustrine conditions driven by Milankovitch cyclicity imprinted lithologic and organic properties in the Eocene Green River Formation, Wyoming. The Scheggs and Rife Beds in the Tipton Member represent perennial freshwater and brackish/saline facies, respectively; the Wilkins Peak Member consists of a hypersaline playa lake, and trona-mudflat. Lithologically uniform Tipton precessional cycles consist of an organic-rich base with a reduced organic content in the remainder of the cycle. The cycle base contains an algal-dominated, aliphatic-rich kerogen sometimes depleted in 13C; deposition occurred during the rainy precessional phase when an expanded, nutrient-rich lake enhanced productivity and elevated stratification. The remainder o f the cycle contains a greater proportion of bacterial input; deposition occurred during the dry precessional phase with reduced lake levels, eutrophication, and stratification. In Wilkins Peak precessional cycles, lithologic, oil-yield, and geochemical patterns define the depositional character of the rainy and dry phases based on: ( 1) sharp geochemical changes between the basal oil shale and trona-mudflat, (2 ) cyclical trends in playa lake expansion-contraction, and (3) “dry and wet mudflat” microfacies. These cyclical lithologic and organic signatures help reconstruct the changing paleolimnology and orbital imprint. An orbital-driven two-stage lake with similar temporal trends in net moisture availability is recorded in both members. The precession-eccentricity signals dictated lacustrine conditions that continuously imprinted sediments. Yet, these evolving lake xix Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. systems simultaneously modified lacustrine processes, resulting in different cyclical expressions. A half-precessional cycle is sometimes identified in both members. The orbital signals were transferred into the organic-bearing sediments by changes in net moisture, inflow, lake size, nutrient availability, productivity, precursor input, organic flux, stratification and preservation, and organic dilution. During the precessional rainy phase, which appears to correspond to the winter perihelion, increased precipitation and reduced evaporation enhanced inflow and organic accumulation. Periods of minimal eccentricity likely extended lake duration and oil shale deposition. Greenhouse conditions and the paleogeographic setting of paleolake Gosiute appear to have magnified the orbital-derived changes in net moisture. Cyclical changes in lake level were essential for deposition of both rich oil shales and organic-lean lithologies, and helps explain sedimentary and geochemical variations in the Green River Formation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 1 INTRODUCTION AND DISSERTATION ORGANIZATION Background The effects of orbital changes on solar radiation and the Earth’s climate have been recognized for over a century, and numerically analyzed for decades (Croll, 1875; Gilbert, 1895; Milankovitch 1941; Hays et al., 1976). Numerous publications from the 1980’s and 1990’s document that orbital forcing was a dominant mechanism in the deposition of cyclical stratigraphic intervals in all geologic ages. Yet, ongoing research in orbital-forced stratigraphy reveals that critical questions remain concerning the variation in solar insolation reaching the Earth’s surface, and how these changes are imprinted in the sedimentary record (Hinnov, 2000). Part of the challenge in addressing these questions involves using different analytical and modeling techniques to refine the analysis of orbital forcing, and the connection to inter-related climatic and sedimentological processes. Most geochemical studies of cyclicity have been limited to the successful application of carbon and oxygen isotopes in marine sediments. Further application of organic geochemical parameters in a high-resolution stratigraphic context can help define relationships between orbital-forced solar radiation, paleoclimate and depositional processes, and the sedimentary record. Classical limnology studies have demonstrated that lakes occur in a wide range of settings, exhibit different water chemistries and sediment properties, and are products of inter-related climatic, biological, chemical, hydrological, tectonic and other geological 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. processes (Forel, 1901; Hutchinson, 1957; Frey, 1974; Kelts, 1988; Bohacs et al., 2000). Requirements for lakes include a basin and a hydrological balance where inflow exceeds outflow plus evaporation. Lacustrine sediments comprise a small part of the existing stratigraphic record; furthermore, only a small percentage of these are organic-rich indicating that these sediments were deposited under unique conditions. Primary controls on the formation of organic-bearing lacustrine sediments include topographic setting, morphology, climate, hydrology, organic productivity, preservation, and sedimentation (Katz, 1990). Most lakes have common biological, chemical, geological and physical conditions that are important in the production and preservation versus the destruction of organic mater (Figure 1). Combined climatic and structural-topographic factors control lake levels and fluctuations that affect productivity, preservation, and sedimentation, all of which control the quantities and properties of organic matter, and the thickness and lithology of the accumulating lacustrine sequence. Most lakes display laterally and temporally complex sedimentation and organic accumulation patterns (Hue et al., 1990). Geologic investigations have identified solar and orbital cyclicity, and the record of periodic climate change in various types of lacustrine deposits (Van Houten, 1962; Anderson and Kirkland, 1960; Olsen, 1986; Fischer and Roberts, 1991; Glenn and Kelts, 1991). However, much still needs to be learned about the intertwined physical and biochemical lacustrine processes that transfer and record cyclical climatic signals in different types of lake systems. In contrast to marine settings, lacustrine environments are relatively shallow and small and quickly respond to environmental change, and thus can provide a near instantaneous indicator of climatic variation. Also, lake sediments often 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O l i # i c < 3 0 G reenetal, 197 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 1 . General elements o f la k e systems a n d lacustrine processes th at control organic m atter accumulation. display a high degree of temporal and spatial heterogeneity because climatic and other environmental perturbations are amplified in continental systems. Because lakes are often stratified and contain annual productivity cycles, lacustrine settings have the potential to provide a good record of cyclicity. Thus, cyclical lacustrine sections that contain a complete record of environmental change provide a good laboratory to further the study of how Milankovitch forced changes in insolation are transferred through climate and lake systems and into the sedimentary record. Recent studies have made significant strides in understanding the deposition, biogeochemistry, and properties of organic-rich lacustrine sediments (Powell, 1986; Scholz and Rosendahl, 1988; Katz, 1990; Collister et al., 1994). Because geochemical parameters are effective tools for reconstructing changing lacustrine conditions, they can help decipher different types of depositional variations. Multiple studies have meticulously described geochemical variations in lacustrine sediments and their implications to environmental and depositional processes (McKenzie, 1985; Hwang et al., 1989; Katz and Mertani, 1989; Collister et al., 1992; Burwood et al., 1992; Curiale and Stout, 1993; Curiale and Gibling, 1994; Carroll, 1998). However, only a few studies have described geochemical properties in lacustrine Milankovitch cycles (Kruge et al., 1990a and b). Even more significant, no investigations have systematically characterized the geochemical expression of lacustrine Milankovitch cyclicity to reconstruct orbital- driven lake conditions. Although geochemical studies have recorded variations based on lithologic and secular constraints (Barron et al., 1985), few studies have concentrated on short-term orbital time scales. Characterization of lithologic and geochemical signatures 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. associated with cyclical lacustrine intervals will help define the orbital imprint by reconstructing the changing limnology and climatic conditions. The Eocene Green River Formation in the Green River Basin of Wyoming provides an ideal setting to document how orbital and other types of cyclicity imprint the lithologic and geochemical properties of lacustrine sediments. The Green River Formation represents one of the world’s largest accumulations of lacustrine sediments deposited in a series of intermontane basins under different depositional conditions. The early Eocene in the Rocky Mountain region represents a unique paleoclimatic chapter containing: ( 1) global greenhouse conditions, and (2 ) evidence for rapid regional climate change. The Green River region also underwent tectonic changes that contributed to changing lake systems. The well documented occurrences of different types of cyclicity in the Tipton and Wilkins Peak Members of the Green River Formation indicate that they were a product of periodic climate change, rather than random deposition (Fischer and Roberts, 1991; Roehler, 1993). The Tipton Scheggs and Rife Beds provide a setting to evaluate cyclicity in a large perennial lake that evolved from freshwater to brackish- saline. The Wilkins Peak provides a depositional interval to evaluate cyclical variations in a contracted, saline to hypersaline playa lake, salt pan, and mudflat. Thus, these intervals provide opportunities to lithologically and geochemically characterize the record of orbital cyclicity in a spectrum of climatic- and tectonic-derived lacustrine facies. The occurrence of varves and re-occurring lithologic properties in these intervals provides temporal control for the study of climatically imprinted secular variations. 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This study builds on the abundance of Green River geological, chemical, biological, and paleoclimatic studies from the 1800’s to present (Anonymous, 1980; Smith, 1990; Roehler, 1992a), which provides a strong foundation for additional investigation of lacustrine cyclicity. Although the Green River lake systems are well studied, many questions remain abut the origin of these unique organic-rich sediments, especially the relationship between orbital cyclicity and lacustrine deposition. The purpose of this study is to define how climatic-controlled lacustrine conditions driven by Milankovitch and other types of cyclicity imprinted lithological and geochemical properties in different lacustrine facies. This study: (1) identifies lacustrine conditions and processes in which orbital-forced changes in insolation were transferred into the sedimentary record, and (2 ) evaluates the relationship between orbital cyclicity and Tipton and Wilkins Peak deposition to further ascertain the origin of these sediments. Results from this can be applied to three different disciplines: (1) Solar and orbital cyclicity, and its relationship to paleoclimatic studies; (2) Lacustrine studies; (3) Geochemistry and the study of organic-rich sediments. Dissertation Organization This dissertation is divided into 8 chapters including this introductory chapter. Chapter 2 provides background information on the geologic setting, and stratigraphic, tectonic, and paleoclimatic history of the Green River Formation in western Wyoming. Descriptions of existing Green River lacustrine models and pertinent 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. geochemical studies are provided. Background about solar and orbital cycles are described along with their occurrence in the Green River Formation. Chapter 3 lists the specific objectives for this study. Descriptions of the study location, cyclicity, and sample selection are included. The second part of the chapter describes the techniques and analytical geochemical methodologies used to evaluate samples. Definitions of terms used in this study are also included. Chapter 4 provides a description of the occurrence and properties of different types of Milankovitch and sub-Milankovitch cycles in the Tipton and Wilkins Peak. The study of these cycles is based on lithologic descriptions, log analysis, Fischer assay oil- yield data and spectral analysis. Ideas are presented to explain variations in the properties of these cycles. Chapter 5 describes the geochemical properties and expression of precessional cycles from the Tipton Member. Variations in geochemical parameters are used to define precessional patterns in the Scheggs and Rife cycles. Lacustrine processes that result from orbital-driven climate change during Tipton deposition are described. Chapter 6 describes the geochemical properties and expression of Wilkins Peak precessional and eccentricity cycles. Geochemical variations in the oil shale, trona, and mudflat facies define precessional patterns. Climatic-driven lake and mudflat conditions involved in the deposition of Wilkins Peak precessional cycles are described. Chapter 7 presents five topics that describe how orbital-forced changes in insolation were translated into the Green River sedimentary record, and helps ascertain the origin of these organic-rich sediments. This includes: 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1) Orbital-driven lake models that describe how climatic controlled lacustrine conditions imprint the lithologic and geochemical properties of Tipton and Wilkins Peak cycles; (2) The lithologic and geochemical pattern of Milankovitch cyclicity is described, and how the orbital imprint is expressed in an evolving spectrum of paleoclimatic conditions and lake systems; (3) Application of litho-organic signatures that record changes in moisture availability and lake conditions, which help decipher mechanisms involved in the imprint of orbital variations; (4) Identification of how the different orbital variations were transferred through various paleoclimatic and lacustrine processes into the different lake systems represented in the Green River record; (5) Defining the relationship between orbital cyclicity and Tipton and Wilkins Peak deposition to provide additional insight into the origin of organic-rich Green River sediments. Chapter 8 provides a list and description of conclusions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2 BACKGROUND - GREEN RIVER FORMATION GEOLOGY AND ORBITAL CYCLICITY Green River Formation Geologic Setting and Tectonic History The early to middle Eocene Green River Formation in the tri-state area of Utah, Colorado and Wyoming represents a widespread lacustrine system. A series of lakes formed from a combination of tectonic, climatic, and hydrographic conditions in the Laramide intermontane basins. Paleolake Gosiute sediments were deposited in the Green River, Great Divide, Washakie and Sand Wash Basins, collectively named the greater Green River Basin (Figures 2 and 3). Paleolake Uinta occupied the greater Uinta- Piceance Basins in northwestern Colorado and northeastern Utah. This study concentrates on the Green River Formation in the western part of the greater Green River Basin in Wyoming. The greater Green River Basin is bounded by the Wyoming thrust belt to the west, the Rawlins Uplift and Sierra Madre to the east, the Wind River Mountains and Sweetwater arch to the north, and the Uinta Mountains to the south (Figure 3). Intra-basin anticlines divide it into four structural and topographic sub-basins. The greater Green River Basin is divided by the Rock Springs Uplift; the Green River Basin occurs in the western half, and the Great Divide, Washakie and Sand Wash Basins to the east. 9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ' k Big Huey ■ »sS * ■ ■ H M h W y o « f ! n o . R xk Spring ■ m i fY 4 v v , s , « ♦ ; — ¥ « & » » * . » »“*- Colorado Vernal Pioeance, K c t f a k \ M i i l » 10 a tQ 20 30 Km 1 C 0 10 20 30 M > cH f» - 4 - ■ f^o ^Sr Qrani} Junction mm River . .rmatfon Figure 2. The occurrence of the Green River Formation in Utah, Colorado and Wyoming. The greater Green River Basin includes the Green River, Washakie, Great Divide, and Sand Wash Basins. This study focused on the Green River Formation in the western part of the greater Green River Basin. 10 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. nr R A W LIN S i U PLIFT •BOUNDARY OF GREATER GREEN RIVER BASIN ■ S f e g f t S Y N C U N E _ ^ ^ WYOMING^- :OLORAD<V-- ^ ' 1 \ W S i p / i ' J iS c w ThRuS tJ § 'M O U N T A IN S - S | S / s i:> 'V-A---: \ / m - l S i f* Y < Figure 3. Map of major structural elements in the greater Green River Basin, Wyoming and Colorado. Figure from Roehler (1992a). 1 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The greater Green River Basin formed during the late Cretaceous to Eocene Laramide Orogeny. The structural formation involved intermittent uplifts in the surrounding mountains, flank thrusting at the basin margins, local folding and faulting, and rapid subsidence of synclinal depocenters in the basin. The major east-west depositional axis was located along the Uinta Mountains where as much as 10,000 ft of lacustrine, fluvial, paludal, and volcanic sediments were deposited. The end of the Laramide Orogeny coincided with the end of basin subsidence in the greater Green River Basin near the close of the Eocene. After this time, the basin has only been slightly modified by regional uplift, faulting and volcanism. Stratigraphy and Geologic History The Green River Formation in the greater Green River Basin is composed of the Luman Tongue, and the Tipton, Wilkins Peak, and Laney Members (Figure 4). These units were deposited over an approximate 5 million year (m.y.) period, and represent distinct changes in climate, tectonic events and resulting lake conditions (Surdam and Stanley, 1979; Smith, 2003). Paleolake Gosiute began as an open freshwater lake (Luman Tongue), expanded into a widespread lacustrine system that evolved into a brackish- saline lake (Tipton Member), contracted to a saline-hypersaline playa lake (Wilkins Peak Member), then expanded again to form a stratified lake (Laney Member). Changes in water chemistry correspond to lake expansions and contractions, derived from climatic and tectonic driven changes in inflow. The Green River Formation intertongues with the underlying alluvial-fluvial Wasatch Formation and overlying fluvial deposits of the Bridger Formation. Detailed stratigraphic relationships and subdivisions of the Green 12 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ftP.fito Figure 4. Generalized stratigraphic section o f Eocene sediments in the greater Green River Basin. This study concentrates on the Tipton and Wilkins Peak Members in the Green River Formation. The Tipton Member consists of the Scheggs and Rife Beds. Figure from Roehler (1992c). River Formation have been described by Bradley (1925,1926,1948,1959, and 1964); Eugster and Surdam (1973); Eugster and Hardie (1975); Wolfbauer (1973); Surdam and Wolfbauer (1975); Sullivan (1980); Surdam and Stanley (1979); and Roehler (1965, 1968,1992a-c and 1993). Luman Tongue. Pipiringos (1955) originally defined the Luman Tongue as a member of the Green River Formation. It has a maximum thickness of 455 ft in the Washakie Basin and contains low-grade oil shales, sandstone, and limestone. Deposition occurred in freshwater lakes fringed by swamps that developed on a broad, subsiding Wasatch alluvial plain (Pipiringos, 1962; Wolfbauer, 1971). The Luman lake(s) were initially confined to the north flank of the Uinta Mountains and then extended eastward across the Rock Springs Uplift. Cyclicity related to lake-level fluctuation is subtle or absent, consistent with its open lake hydrology (Carroll and Bohacs, 2001). Tipton Shale Member. The Tipton Shale Member, which is up to 500 feet thick, was originally named by Schultz (1920) and revised by Roehler (1965 and 1968). Later, Roehler (1991) subdivided the Tipton Member into the Scheggs and Rife Beds (Figure 4). During the freshwater Scheggs phase, paleolake Gosiute expanded and covered more than 75% of the greater Green River Basin. As the lake deepened and became stratified, oil shales were deposited. At the end of Scheggs deposition, the outlet closed and the lake began to slowly contract, as a result, brackish to saline conditions developed. This is recorded by the disappearance of fish scales and freshwater mollusks (such as Goniobasis tenera, Viviparus sp. and Lampsilis sp.), and the presence of saline minerals (Hanley, 1975; Roehler, 1990 and 1991). The Rife lake became progressively more saline based 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. on: (1) the disappearance of the gastropod Gyraulus militaris about 35 feet above the basal Rife, and (2) the occurrence of thin evaporites near the top of the Rife Beds. The Rife is generally unfossiliferous except for the occurrence of Gyraulus militaris, an air- breathing gastropod that could survive in saline waters (Baker, 1945). The Farson Sandstone, which consists of lacustrine deltaic and shoreline sediments derived from the Wind River Mountains, was deposited contemporaneously with the upper Scheggs (Roehler, 1992a-c). Surdam and Wolfbauer (1975) describe three Tipton zones; the top zone consists of thin beds of algal stromatolites (less than 6 ft), indicating a shallow, shrinking lake and transition to the Wilkins Peak. Wilkins Peak Member. The Wilkins Peak Member was originally named by Bradley (1959) for the distinct lacustrine interval above the Tipton Member in the Green River Basin. This member represents a contracted playa lake/mudflat sequence consisting of oil shale, trona, and marlstones and mudstones up to 1300 feet thick. The oil shales are some of the richest in the Green River Formation of Wyoming. A variety of studies have provided a good stratigraphic, lithological and depositional knowledge of the Wilkins Peak (Roehler, 1965; Culbertson, 1961,1966,1969, and 1971; Deardorff, 1963; Textoris, 1963; Bradley, 1964; Bradley and Eugster, 1969; Eugster and Hardie, 1975; Surdam and Wolfbauer, 1975; Smoot, 1978; Sullivan 1980; Buchheim and Surdam, 1981; Mott and Drever, 1983). The Wilkins Peak was deposited in a shallow, saline to hypersaline playa lake and surrounding carbonate mudflats (Eugster and Surdam, 1973). During relatively wet periods, with precipitation exceeding evaporation, the lake expanded and oil shales were 15 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. deposited in the basin center. In arid periods, evaporation approached or exceeded precipitation and the lake contracted; bedded trona was deposited from alkaline-rich lake water. With continued drying of the lake to broad mudflats, dolomitic mudstones were deposited. These expansion and contraction episodes are arranged in well-defined, laterally continuous cycles. At the basin margins, flat-pebble conglomerates, rippled sandstones, oil shales and laminated mudstone often accumulated (Eugster and Hardie, 1975). Roehler (1993) subdivided the Wilkins Peak Member into three parts. The lower Wilkins Peak Member was deposited across the southern part of the Green River Basin and extended eastward across most of the Great Divide, Washakie, and Sand Wash Basins. Deposition of the middle Wilkins Peak was restricted to an area west of the Rock Springs Uplift due to a regional east-to-west tilting. During upper Wilkins Peak deposition, paleolake Gosiute doubled in size as a more wet climate developed and tectonic activity opened an outlet of the lake to the east of the Uinta Mountains. Evaporite deposition ended as the lake expanded northward in the Green River Basin, and into the western Washakie and Sand Wash Basins (Surdam and Stanley, 1979). Laney Member. The Laney Shale Member was named by Schultz (1920) and redefined by Bradley (1959). It was divided into a lower oil shale named the LaClede Bed, and an upper volcaniclastic Sand Butte Bed (Roehler, 1973a). During Laney deposition, a chemically stratified lake expanded over most of the greater Green River Basin due to influx of water from the Wind River Basin, which was related to a more moist climate and tectonic modification of drainage (Surdam and Stanley, 1979; Boyer, 1982; Roehler, 16 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1991). Over time, the lake gradually freshened and recorded in reverse order the increasing salinity that took place in the Rife Beds. Biostratigraphv and Age Dates The ages of the Tipton and Wilkins Peak Members have been defined by fossil mammals, potassium-argon (K-Ar) and argon (4 0 Ar/3 9 Ar) dating, and magnetostratigraphy. The Scheggs and Rife Beds have been dated as Late Early Eocene based on vertebrate fossils and mammal teeth (Honey, 1988; Roehler, 1992a-c). This age is consistent with lateral equivalent units and intervals above and below the Tipton, including the Godiva Member, Cottonwood Creek Delta, and Bridger Formation (Roehler, 1992a). The chronostratigraphic terms early, middle, and late Eocene are used in preference to faunal terms (Roehler, 1992c). Zonneveld et al., (2000) used fossil vertebrates to delineate the Wasatchian/Bridgerian boundary in the southwestern Green River Basin. In the past, K-Ar ages obtained from biotites have been questionable and difficult to establish from tuffs located in the Wilkins Peak. A tuff located a few feet below the top of the Wilkins Peak has been dated at 46.6 Ma (O’Neil, 1980). Roehler (1993) calculated the total depositional time for the Wilkins Peak at 1.6 m.y. (48.2-46.6 Ma) using K-Ar dates, stratigraphic thickness, and oil shale varve counts. Alternatively, Wilf (2000) lists recalibrated K-Ar dates of 50.1 and 50.2 Ma in the middle-upper part of the Wilkins Peak. Refined age dating based on 4 0 Ar/3 9 Ar measurements using laser fusion of sanidine phenocrysts from tuffs has provided ages of 51.25 Ma for an approximate middle Rife; and 49.96 and 49.70 Ma for the respective Main and Sixth tuffs near the top of the 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wilkins Peak (Smith et al., 2003). Machlus et al. (2004) reports ages of 50.4 and 49.1 Ma for the Main and Sixth tuffs using a different 4 0 Ar/3 9 Ar approach. Clyde et al. (1997 and 2001) established a magneto-biostratigraphic framework that correlates the Geomagnetic Polarity Time Scale (GPTS) to the North American Land Mammal ages (NALMA). Their GPTS correlation using radiometric ages places the Wasatchian/Bridgerian boundary in chron 23r at about 52 Ma. The revised age model by Smith et al. (2003) suggests the Green River spans an approximate 5 m.y. period from 53.5 to 48.5 Ma, which encompasses magnetic chrons 24n through 21r. From this, they assign the Wasatchian/Bridgerian boundary to an age of 50.55 Ma, which occurs in the lower-middle Wilkins Peak. Machlus et al. (2004) place the Wasatchian/Bridgerian boundary in chron C23r at 51 Ma. These age dates and correlations are continuing to be refined by ongoing work. Paleoclimate-Green River Formation. Southwest Wyoming Global paleoclimatic evidence indicates the development of increasing greenhouse conditions and reduced latitudinal temperature gradients in the early Eocene. A Cenozoic global temperature maximum occurred at the Wasatchian/Bridgerian boundary (Wing et al., 1991; Wing and Greenwood, 1993). Deposition of the Green River Formation spans the Eocene climatic optimum as defined by the global marine oxygen isotope records from benthic foraminifera (Zachos et al., 2001). Then, global cooling extended into the Oligocene. Paleobotanical records and assemblages of fossil vertebrates in the greater Green River Basin indicate fairly rapid variations in paleoclimate from temperate to arid to 18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. warm and sub-tropical (Leopold and MacGinitie, 1972; Hutchinson, 1982; and Wing and Greenwood, 1993). Paleofloral results are based on a comparison of fossil flora and pollen records with southeast Asia, and are consistent with the expansions and contractions of paleolake Gosiute’s sedimentary record. Mean annual temperatures in the greater Green River Basin inferred from paleofloral data varied between 15 and 25 °C, and mean annual precipitation ranged from 75 to 150 cm/year (Wilf et al., 1998; Wilf, 2000). Although a tight correlation between rainfall, temperature, and lake size does not exist, paleobotanical and isotopic studies document decreasing precipitation and temperature between the Early Tipton and Middle Wilkins Peak (Wing et al., 1998; Wilf et al., 2000). A combination of increased aridity and seasonality are proposed as likely causes of changes in Wasatchian/Bridgerian flora (Wilf, 2000). Paleobotanical results suggest that during Green River deposition, winter continental temperatures remained above freezing, indicating an equable Eocene climate with reduced seasonal variation (Greenwood and Wing, 1995). In contrast, initial paleoclimatic modeling suggested Eocene winters with freezing temperatures. However, when paleoclimatic simulations included greenhouse gases, topography, vegetation, heat capacity of a large hypothetical lake, and variation in insolation from orbital forcing, modeling results were in good agreement with paleoclimate proxy data (Sloan and Barron, 1992; Sloan and Rea, 1995; Sloan and Morrill, 1998). The apparent rapid climatic shifts between the Tipton, Wilkins Peak, and Laney Members are difficult to explain. Major variations in precipitation are not evident elsewhere in the United States, and drying periods do not occur in west coast floras. A 19 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. proposed rain shadow formed from a tectonic orographic event (Axelrod, 1968), does not explain the rapid climatic shifts and reversal. A shift in the jet stream, or the amount of moisture carried into the greater Green River Basin region from storm tracts could explain the rapid changes in climate and precipitation. Early Eocene paleobotanical and isotopic data from the Bighorn Basin, Wyoming indicate that the mean annual temperature decreased 7.4 °C in less than 700,000 years, then increased 11.4 °C over the subsequent 700,000 years (Wing et al., 1998). The sharp changes in moisture availability may have been derived or magnified by tectonic events that affected drainage and inflow into the Green River Basin (Surdam and Stanley, 1979; Bohacs and Carroll, 1999). Previous estimates of the paleolatitude of paleolake Gosiute range from 40 to 46 °N, which is comparable to or slightly higher than present day (Matthews and Perlmutter, 1994; Sloan and Rea, 1995; Wilf, 2000; Morrill et al., 2001). The paleoaltitude of the greater Green River Basin during the Eocene is estimated to have been about 450-1000 ft above sea level (Bradley, 1929a; Sloan and Barron, 1992; Wing and Greenwood, 1993). The elevation of the surrounding mountains was originally estimated between 1,500 and 7,000 ft (Bradley, 1963; MacGinitie, 1969). Altitudes of more than 10,000 ft have been proposed based on isotopically depleted §1 8 0 values of the carbonate matrix from the upper Wilkins Peak that indicate a snow melt contribution to paleolake Gosiute (Norris et al., 1996 and 2000). Paleobotanical studies used to define paleoaltitude of the Green River Formation support these isotopic inferences (Wolfe et al., 1998). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Existing Green River Lacustrine Models Although numerous studies describing lacustrine Green River deposition have been published, two end-member models predominate: (1) a relatively deep, perennial, stratified lake; and (2) a shallow, expanding-contracting playa lake. The permanently stratified lake model was initially proposed by Bradley (1929a and 1948). The expansive, meromictic lakes were deeper than 20-30 meters and contained a thermocline where water column mixing did not occur in the hypolimnion (Bradley and Eugster, 1969; Desborough, 1978; Sullivan, 1980). The oil shale facies was derived from abundant productivity in the photic zone and an anoxic water bottom with high preservation potential. Bradley (1963) estimated paleolake Gosiute plankton production to have been 270 g/m2 /year, which classifies it as a hypertrophic setting (Green et al., 1976). Varves consisting of alternating organic matter and carbonate lamina formed as a result of increased photosynthetic productivity and flux, and then warmer water in summer resulting in carbonate precipitation (Bradley, 1925 and 1929b). Eugster and Surdam (1973) proposed the playa lake model to explain shallow water features that conflicted with a deeper, stratified lake. Their evidence included subaerial and shallow water sedimentary features, the predominance of dolomite compared to calcite, and evaporites in the hydrographic center of the Wilkins Peak phase of paleolake Gosiute. Oil shales and trona accumulated in shallow lakes maintained by runoff, and springs. The high productivity that resulted from abundant nutrients was preserved by hypersaline conditions that limited metazoan grazers. The fluctuating playa lake was surrounded by carbonate mudflats, which were areas of high evaporation and 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. deposition of dolomitic and calcareous mudstones. Bromide studies of Wilkins Peak evaporites indicate stratified lake conditions with dense, hypersaline bottom waters and an overlying less saline water (Higley, 1983). Boyer (1982) proposed an intermediate ectogenic-meromictic lake model for the Laney Member, in which the lake was chemically stratified, rather than a thermally- dependent meromictic lake. Freshwater from an extra-basinal source was added to existing brines in the playa lake. This resulted in a dense, saline, anoxic hypolimnion overlain by an oxygenated, biota-inhabited epilimnion. Evidence for this lake setting includes well-laminated oil shales with fossilized fish, and freshwater mollusks and ostracodes. Bohacs et al. (2000) proposed that the Green River lakes originated and were modified primarily from tectonic influence rather than climatic control. The Scheggs, Rife, and Wilkins Peak respectively represent overfilled, balanced-fill and underfilled lake types. These lake systems are classified based on the climate-controlled supply of water and sediment compared to accommodation space linked to tectonic subsidence. Lacustrine Geochemical Studies-Green River Formation Included in the abundant geochemical investigations of the Green River since the early 1900’s, are a number of studies that provide a foundation to characterize variations in lacustrine conditions. Dean and Anders (1991) described relationships between geochemical parameters, lacustrine conditions and organic precursors. Collister (1989) 13 and Collister et al. (1994) used the relative distribution and 8 C composition of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. individual molecular components to identify different types of kerogen precursors: (1) cyanobacteria, (2) phytoplankton, (3) chemoautotrophic bacteria, (4) heterotrophic bacteria, and (5) terrestrial plant waxes. Other studies have identified precursors of Green River biomarkers and their relation to lacustrine conditions (Schoell et al., 1994a; Ruble et al., 1994). Reconstruction of the biogeochemistry of the Green River setting indicates distinct nitrogen cycles for the meromictic and playa lake stages (Collister and Hayes, 1991). Identification of sulfur cycles are correlated to changing depositional conditions (Dyni, 1983; Tuttle and Goldhaber, 1991). Oxygen and carbon isotopic (S1 8 0 and 81 3 C) studies help define the origin and effects of environmental influences on the formation of Green River carbonates (Pitman, 1996; Norris et al., 2000). Numerous organic and inorganic studies have documented that highly dynamic temporal and spatial lake fluctuations affect sedimentation and organic matter accumulation, and result in geochemically heterogeneous lacustrine intervals. Solar and Orbital Cyclicity Concept and Historical Background The concept of astronomical influences and their climatic imprint on sedimentary sequences has been widely documented. As summarized by Imbrie and hnbrie (1979) and Berger (1988), astronomers in the early-to-mid 1800’s began to identify orbital variations. Croll (1875) was the first to calculate the effects of the Earth’s eccentricity, obliquity, and precession on solar insolation. Gilbert (1895) suggested that Late Cretaceous carbonate-marl cycles in Colorado were the result of astronomical forcing, thus providing a chronostratigraphic reconstruction. Milankovitch (1941) further Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. developed the concept of orbital influences on climate by examining the relationship between astronomical parameters and the ice ages. From this pioneering work, other researchers began to document and interpret sedimentary cyclicity, thus furthering the study of cyclostratigraphy (Schwarzacher, 1947; Anderson, 1961; Van Houten, 1964; Fischer, 1964,1980 and 1986). In lacustrine sections, the identification of solar and Milankovitch cycles extends back to the Paleozoic (Glenn and Kelts, 1991). Astronomical forcing of climate and its potential sedimentary imprint depends on the changing position of the Earth’s axis and the variation in its orbital path around the Sun (Figure 5). These variations primarily result from the interaction of gravitational forces in the rotating planetary system. The precessional cycle results from the gyration of the Earth’s axis due to the combined effects of the solar and lunar attraction on the Earth’s equatorial bulge. Although the modes of the Earth’s precession are about 19 and 23 k.y., extremes of 14 and 28 k.y. are recognized (Berger, 1988). The precession leads to regular and predictable changes in the distribution of insolation over the Earth. The obliquity of the Earth’s axis is its angle of tilt with respect to the perpendicular of the ecliptic, or its orbital plane around the sun. The obliquity varies between 22.1 and 24.5°, and has a mean period of 41 k.y. The short eccentricity represents the Earth’s elliptical path around the Sun, where the average period is 100 k.y. Variations in the larger eccentricity also occur at approximately 400 and 1300 k.y., and 2 m.y. (De Boer and Smith, 1994). The precessional-eccentricity syndrome as defined by Berger (1988), expresses non-linear changes in insolation for a specific latitude from the combination of the precession (carrier cycle) and the short- or long-term eccentricity (modulator). This 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. < r ... < 3 z 3 < o >- >- t— > - o — C xC <ut 3 f— 1 — a z z UJ UJ o u so i j U o UJ UJ o o u u z z X X U J UJ 4 $ 8 ^ 6 yyyyyyy Milankovi'tch Band i —rrr-i ----- ° YEARS 1 x 4 0 2 x Calendar Band Solar Band \ / $ / r precession 19,000 - 26,000 obliquity 41 .0 0 0 eccentricity 10 0,0 00 4 0 0, 08 0 Figure 5. Summary of calendar, solar, Milankovitch and possible longer cycles. Approximate duration of cycle is listed. Figure modified from Fischer and Bottjer (1991). to U i precession index is a major force of climate change in mid-latitudes where deviation from existing seasonality can occur by variation between maximum and minimum eccentricity. Milankovitch cycles in the sedimentary record result from variations in the spatial distribution of solar energy that reaches the Earth’s surface (Berger, 1978b and 1988). With changes in orbital position, differences in the amount of insolation reaching a given latitude affects the degree of seasonality, and the boundary between dry and wet climates due to differential heating and the migration of Hadley circulation cells. At low- to mid latitudes (20-40°), changes in solar energy modifies the latitudinal boundary between dry and wet climates by up to 30°, and changes monsoon intensity resulting in variable precipitation over the precessional period (Kutzbach and Otto-Bliesner, 1982). The monsoonal intensity varies most at low- to mid-latitudes, especially over continental landmasses; it is greatest during times of enhanced heating corresponding to perihelial positions of the precession and eccentricity. Climatic modeling demonstrates that precipitation and lake level are strongly influenced by orbital cyclicity and the resulting north-south migration of wet and dry climatic belts (Rossignol-Strick, 1983; Kutzbach and Street-Perrott, 1985). Rotational changes of the Earth driven by astronomical cycles have also been suggested to alter gravity potential, atmospheric shielding, and differential rotation affecting paleomagnetics, all of which could hypothetically imprint the sedimentary record (Momer, 1994). Cvclicitv-Green River Formation Several studies have described exogenetically-driven climatic cyclicity in the Green River Formation. Bradley (1929a) proposed an 11-year cyclicity in the Uinta Basin 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. based on visual variation in varve thickness. He attributed oil shale and marlstone alternations in the Piceance Creek Basin to precessional cyclicity by the extrapolation of varves. Crowley et al. (1986) used spectral analysis to identify a weak cyclicity of 5.4 and 10.8 years in the Uinta Basin. Studies by Roberts (1988), Fischer and Roberts (1991), and Ripepe et al. (1991) identified seven types of cycles including solar, sub-Milankovitch and Milankovitch cyclicity in the Green River Formation of the greater Green River Basin. In the Tipton and Laney, they used image analysis to determine varve thickness and thereby define El Nino (4.8-5.6 years), sunspot (10.4-14.7 years), and cycles with a 30-year periodicity. In the Laney, they defined a 3,300-year periodicity based on the occurrence of rich oil shales with 40 cm spacing. These spacings are divided into 5 couplets of 600 years. In the Tipton and Wilkins Peak, gamma ray and sonic logs record precessional cyclicity and an approximate 5:1 bundling defines the 100,000-year eccentricity cycle (Figure 6). In the Tipton, more than 20 oscillations in gamma ray and sonic velocity logs are identified with a mean 7.7 ft spacing of 19,350 years, based on varve thickness. In the Wilkins Peak, oil shale-marlstone doublets or oil shale-trona-marlstone triplets correspond to the precessional log response, with a mean thickness of 12.2 ft. Roehler (1991 and 1993) used the identification of precessional and eccentricity cycles by Fischer and Roberts (1991) as a basis to define and correlate 77 Wilkins Peak precessional cycles across the greater Green River Basin (Figures 7 and 8). The 77 cycles are grouped into eccentricity bundles that contain between 4 and 6 precessional cycles, but average 5. Furthermore, Roehler (1993) grouped Wilkins Peak eccentricity cycles 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W ILKINS PEAK TIPTON Marlstone CYCLE Trona, Halite Oil Shale Figure 6. Cyclicity in the Tipton and Wilkins Peak Members, Green River Formation, greater Green River Basin. Sonic and gamma log oscillations define Tipton and Wilkins Peak precessional cycles. Log plots illustrate the grouping of precessional cycles into 100 k.y. eccentricity bundles (A-D). Figure from Fischer and Roberts (1991). 28 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NORTH Blue Rim-1 White Mountain-1 Blacks Fork-1 El Paso-1 SOUTH Sand Butta Bed of Laney M ember of Green River Formation Ham Cabin Bed of Laney Member of Green River Formation LaCiede Bed of Laney Member of Green River Formation 77 7 6 10 15 20 MILES EXPLANATION Lacu&trlne sandstone Thick lacustrine olt-shale beds Thin lacustrine oil-shaie beds in the Wilkins Peak Member Mosily gray and green fluvial sandstone and mudstone Mostly red fluvial sandstone and mudstone Unconformity Figure 7. North-south section illustrates stratigraphy and the 77 precessional cycles in the Wilkins Peak Member, as identified by Roehler (1991). This section of the Green River Formation in the western part of the Green River Basin shows the location of Blacks Fork-1 and surrounding wells. This figure is modified from Roehler (1993). 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fischer assay (gal/ton) ( F T ) 1 .300 1 .500 1 .500 III > II Figure 8. Energy Research and Development Administration Blacks Fork Corehole Number 1. Section illustrates Tipton and Wilkins Peak Members. In the Wilkins Peak Member, 77 processional cycles and 17 eccentricity cycles (A-Q) have been identified. Two-and-one-half superbundles (I-III) were defined by Roehler (1993). Figure modified from Roehler (1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. into two-and-one-half superbundles containing seven eccentricity cycles. A 20 k.y. chronology of Wilkins Peak cycles defined by Fisher and Roberts (1991) and Roehler (1993) using different approaches further confirms the Green River record of the astronomical precession. The obliquity cycle has also been identified in the Green River Formation in Wyoming (Machlus et al., 2001). Conversely, Smith et al. (2003) and Pietras et al. (2003) reject the approximate 21 k.y. precessional period for the Wilkins Peak based on 4 0 Ar/3 9 Ar age dates of the Rife to Upper Wilkins Peak interval. In the Laney Member, 3 to 10 ft parasequences that record lake expansion- contraction cycles in the LaClede Bed have been suggested to record precessional forcing (Surdam and Stanley, 1979; Horsfield et al., 1994). Although Rhodes et al. (2002); and Smith et al. (2003) reject precessional forcing in the Wilkins Peak, they state that a 21 k.y. precessional forcing is acceptable for cycles in the Laney. Simulation of Eocene paleoclimate in the Green River region that includes orbital variations produces a range of continental temperatures (Sloan and Rea, 1995; Sloan and Morrill, 1998). These results infer that orbital forcing affected climatic conditions during Green River deposition. Paleoclimatic modeling by Lawrence et al. (2003) that correlates temperature and precipitation to orbital forcing suggests an absence of dramatic climate swings throughout precessional intervals. Based on paleoclimatic modeling of orbital forcing for the Eocene Green River, Morrill et al. (2001) proposed that changes in shortwave radiation throughout the precessional cycle affects lake evaporation, and thus controlled lake level fluctuation to a greater extent than variation in precipitation. 31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3 OBJECTIVES, STUDY LOCATION, SAMPLING, METHODOLOGIES AND DEFINITIONS Objectives The overall objective of this dissertation is to define how climatic-controlled lacustrine conditions that were driven by Milankovitch and other types of cyclicity imprinted sedimentary and geochemical properties in the Tipton and Wilkins Peak Members of the Green River Formation. This includes evaluation of the relationship between orbital cyclicity and Tipton and Wilkins Peak deposition to further ascertain the origin of organic-rich Green River sediments. To meet this objective requires completion of the following specific objectives: (1) Characterize variations in lithologic properties, as well as the quantity, composition, and molecular properties of organic matter in Tipton and Wilkins Peak precessional cycles. Relate these lithological and geochemical variations to the eccentricity and other occurrences of cyclicity. (2) Define cyclical variations in lacustrine conditions and processes involved in the accumulation of organic matter that are associated with the perennial, freshwater, overfilled Scheggs and brackish-saline, balanced-fill Rife lakes, and the contracted, saline-hypersaline, underfilled Wilkins Peak playa lake and mudflat facies. (3) Identify orbital-driven paleoclimatic variations and processes in the Green River region, and their effect on lacustrine conditions. This includes identifying lithological and geochemical signatures that help decipher climatic variations. 32 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (4) Identify lacustrine depositional processes in which orbital-forced changes in insolation were transferred into the Green River sedimentary record, which represents evolving climate and lake systems. These objectives were met by using lithologic descriptions, Fischer assay oil- yields, and geochemical and petrographic data to characterize sedimentary and organic matter properties. Geochemical analyses were completed to define the quantity and type of organic matter, including precursor input, productivity and preservation. Petrographic analyses were completed to identify the type, distribution, and properties of organic matter in the sediment. Study Location and Stratigraphic Intervals This study examined cyclicity in the Tipton and Wilkins Peak Members from the Energy Resource and Development Administration Blacks Fork-1 corehole in the Green River Basin. Blacks Fork-1 is located in section 24, Township 16 north and Range 108 west, Wyoming (Figure 9). This location is near the paleogeographic basinal center of the Scheggs, Rife, and Wilkins Peak phases of paleolake Gosiute. The evaluation of cyclicity in a basinal sequence reduced the effects of non-cyclical and external depositional events that may have altered the cyclical imprint. Isopach maps of the Scheggs and Rife Beds, and the lower, middle, and upper Wilkins Peak are shown in Figures 9-13. This study also used geological and geochemical data, and samples from White Mountain-1 and Union Pacific El Paso-1, which are respectively northeast and southwest of Blacks Fork-1 (Figure 9). 33 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N D * GREAT DIVIDB BASIN <jo 42‘ RAWLINS' I UPLIFT S J W t ROCK SPRINGS 'BOUNDARY OF GREATER GREEN RIVER BASIN U PL IFT I Paso ipo. m WYOMING ____ COLORADO 4? 41* »A N Q I Q < 1 5 5 s H O S O MltlS J 2 5 . 1 0 Figure 9. Isopach map of the Scheggs Bed of the Tipton Shale Member, Green River Formation. Isopach interval is 50 ft. The Blacks Fork-1 corehole is located in the Green River Basin in southwest Wyoming. Data from White Mountain-1 and El Paso-1 were also used in this study. Map from Roehler (1992). 34 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RA W O NS t UPLIFT ROCK BOUNDARY O r GREATER GREEN RIVER 8ASIN W Y O M IN G _____ COLORADO ■£. SAND WASH ‘ .. BASIN U I N T A «0°N T A I N S K S Figure 10. Isopach map of the Rife Bed of the Tipton Shale Member. Isopach contour interval is 50 ft. Map from Roehler (1992). 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in* n o * J O S ' IG R E A T P W O E i ? sB A S IN i h 5 S 2 RAWLINS i UPLIFT BOUNDARY OF GREATER GREEN RIVER BASIN 5 3 M IL E S 0 25 i. Figure 11. Isopach map of the lower part of the Wilkins Peak Member, Green River Formation. The lower Wilkins Peak represents precessional cycles 1-11 as originally defined by Roehler (1991). Isopach contour interval is 50 ft. Map is from Roehler (1992). 36 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U T A H IDAHO 1 1 0 “ BOUNDARY OF GREATER GREEN RIVER BASIN /ASHAKIE BASIN SAND WASH h?BASlN u sn ta m o u n t a in s a j Figure 12. Isopach map o f the middle part of the Wilkins Peak Member, representing precessional cycles 12-67 as originally defined by Roehler (1991). Isopach contour interval is 100 ft. Map from Roehler (1992). 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GftEAT qiVlDE [nVfiStj* < o BOUNDARY OF GREATER GREEN RIVER BASIN jjy_ C irv#nR iy^e , WVOMfNO ____ V. COLORADO % , FOUNTAINS ( 3 a Figure 13. Isopach map of the upper part of the Wilkins Peak Member representing precessional cycles 68-77 as originally defined by Roehler (1991). Isopach contour interval is 50 ft. Map is from Roehler (1992). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Approximately 175 ft of the Tipton Member and 1050 feet of the Wilkins Peak Member are represented in Blacks Fork-1. This corehole allows the direct comparison of cyclicity in the Tipton and Wilkins Peak Members. Although Roehler (1991 and 1993) described Wilkins Peak precessional and eccentricity cycles in Blacks Fork-1, he did not complete any studies of cyclicity in the Tipton Member. The Tipton and Wilkins Peak Members represented in Blacks Fork-1 have been stratigraphically correlated with other wells and outcrops in the Green River Basin of western Wyoming (Roehler, 1991). Oil- yields and lithologic descriptions for the Blacks Fork-1 section are available from unpublished open file data and published reports (Trudell, 1979; Roehler, 1991). Other geochemical studies have been completed using the Blacks Fork-1 core (Dean and Anders, 1991; Collister and Hayes, 1991; Tuttle and Goldhaber, 1991). Selection of Cycles for Evaluation Fischer assay oil-yields and lithologic properties were utilized in this study to initially identify precessional cycles in the Scheggs and Rife Beds. Intervals containing relatively abundant volcanic ash or detrital sediments were not sampled. Eccentricity cycles are difficult to lithologically identify in the Tipton Member. Gamma and sonic logs are not available from Blacks Fork-1 to identify Milankovitch cyclicity using log signatures, as described by Fischer and Roberts, (1991). Although well logs are available from El Paso-1 and nearby wells, they do not contain core. Lithologic core descriptions for selected Scheggs and Rife precessional cycles from Blacks Fork-1 are provided in Appendix 1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In the Lower and Middle Wilkins Peak, precessional cycles 1 through 5 and 20 through 24 representing eccentricity cycles A and E respectively were selected for this study (Figure 14). Eccentricity cycle A was deposited in a more wet and subaqueous setting than eccentricity C, which is consistent with the apparent decrease in moisture availability between the Early Tipton and Middle Wilkins Peak. Regional tilting at the end of the Lower Wilkins Peak reduced drainage and lake inflow (Roehler, 1993). Based on lithology, oil shale occurrence, oil-yields, and bundling of precessional cycles, eccentricity A and E represent typical Wilkins Peak 100 k.y. cycles. They contain limited evidence of detrital tongues and other non-cyclical imprints, or anomalous effects from longer-term eccentricity cycles. Lithologic descriptions of Wilkins Peak precessional cycles from Blacks Fork-1 used in this study are provided in Appendix 2. Samples were collected from the United States Geological Survey (USGS) core storage facility in Denver, Colorado. Slabbed core samples of 0.1 ft in length and approximately % inch thick were collected throughout selected Tipton and Wilkins Peak precessional cycles. Sample selection was based on oil-yields, lithologic variations, and representative spacing throughout individual cycles. Procedures and terminology for lithologic descriptions are from Tmdell et al. (1973). Analyses, Methods and Techniques Fischer Assay Oil-Yields-Procedure and Application Fischer assay oil-yields provide a standardized measure of the richness of Green River oil shales. Oil-yields were completed using the Fischer assay procedure American 40 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fischer assa y (g a l/to n ) DEPTH (FT) 1 .O O O 1 .200 1 ,300 1 .500 1 ,500 III > II > I Figure 14. Wilkins Peak study intervals in Energy Research and Development Administration Blacks Fork Number 1 (arrows). Roehler (1991) originally identified 77 precessional cycles and 17 eccentricity cycles in the Wilkins Peak. Precessional cycles 1-5 and 20-24 in the Lower and Middle Wilkins Peak, respectively were selected for this study. Figure modified from Roehler (1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Standard of Testing Materials (ASTM Designation D 3904-80). This retort method has been a standard test to measure a rock’s ability to generate oil (Stanfield and Frost, 1949). The sedimentary kerogen is converted by distillation into a “low-quality” crude oil that provides an empirical measure of the rock’s potential to yield oil and water. The oil and water yields are expressed as both weight percent, and as gallons per short ton of rock (2,000 pounds). A USGS database of oil-yields is available from coreholes in the greater Green River Basin that were assayed at the United States Bureau of Mines Energy Research Center, Laramie, Wyoming. The Blacks Fork-1 core was collected, and originally described and analyzed between 1976 and 1980. The unpublished oil-yield data for Blacks Fork-1 were obtained from John Dyni at the USGS in Denver, Colorado. Continuous Fischer assay data in Blacks Fork-1 and nearby coreholes were used to define patterns and trends in oil-yield throughout the entire Tipton and Wilkins Peak Members. Although Fischer assay data provide generalized stratigraphic trends, oil-yields were sometimes measured on irregular or wide sample intervals (0.4-5.0 ft), and thus were not always sufficient for defining detailed patterns and trends within individual precessional cycles. Time-Series and Spectral Analysis Time-series and spectral analysis were completed to test for the occurrence of Milankovitch periodicity in the Tipton and Wilkins Peak Members. To test for the occurrence of orbital-related frequencies, oil-yields, and the thickness of the precessional 42 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cycle and oil shale from Blacks Fork-1 were transformed into a geological time-series. Spectral analysis was completed to evaluate statistical relationships with the frequency domain of the orbital cyclicity. Dr. Al Fischer and Alessandro Grippo (USC Department of Earth Sciences) completed the initial work for this study. Time-series analysis was completed using AnalySeries, a Macintosh application designed by Martinson et al. (1987) to study paleoclimatic records. The spectral analysis was completed using the multitaper method (MTM) developed and documented by Thompson (1982). The MTM method is incorporated in the AnalySeries software. Geochemical Evaluation and Analytical Techniques Organic and inorganic geochemical and petrographic analyses were completed on representative samples throughout individual precessional cycles. The quantity, type, precursors and properties of insoluble and soluble organic matter (kerogen and bitumen, respectively) were evaluated. Inorganic geochemical analyses were completed to characterize variations in lake chemistry and diagenesis. An approximate 6 mm sample split for geochemical analyses was taken to represent an approximate double sunspot period. This provided a consistent sample thickness, and helped average any potential geochemical anomalies that may be associated with individual El Nino or sunspot cycles. Larger samples were required for solvent extraction and organic petrology. Total Organic Carbon and Rock-Eval Pyrolysis. Weight percent total organic carbon (TOC) and Rock-Eval pyrolysis were completed to evaluate organic content and define variations in the type and nature of the kerogen. TOC and Rock-Eval pyrolysis were Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. completed using a Rock-Eval VI instrument at Humble Instruments; Houston, Texas. Representative splits of rock samples were pulverized to minus 200 mesh. TOC was completed using both LECO and Rock-Eval pyrolysis methods. Between 10 and 100 mg of pulverized rock was used for pyrolysis, depending on organic content. Calibration of the Rock-Eval instrument was completed using a Green River rock standard. Standard Rock-Eval pyrolysis procedures as described by Espitalie et al. (1977) were employed. Total Sulfur. Weight percent total sulfur was measured using high temperature combustion with oxidation of the sulfur to SO2. An infrared detection based on ASTM method D-4239 was used. The rock sample was ground to a standard minus 200 mesh to provide a homogenous sample. Pyrolysis-Gas Chromatography. Pyrolysis-Gas Chromatography (Py-GC) was completed to help define kerogen composition and properties. The analyses were completed at Humble Instruments, using a gas chromatograph (GC), equipped with a custom inlet furnace to perform flash pyrolysis at 550 °C. Depending on weight percent TOC, between 1 and 10 mg of cmshed rock was placed in a quartz liner and inserted into the furnace at 550 °C for 1.85 minutes. Approximately 0.3-1.0 mg of an adamantine/aluminum oxide mixture was added to samples as an internal standard. The pyrolyzate was cryofocused and then subsequently separated using a Varian 3400 gas chromatograph equipped with a 50 m x 0.20 mmDB-1 column that used hydrogen as the carrier gas. The gas chromatograph oven program was set at 4 minutes isothermal starting at 35 °C, and then heated at a rate of 4 °C/minute to a final temperature of 350 °C, and held isothermally for 15 minutes. 44 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Maceral Analyses-Organic Petrology. Organic petrographic analyses were completed to evaluate the type, relative abundance, and properties of individual organic components or macerals in the kerogen assemblage. The following macerals were identified: lamalginite, bituminite-amorphous, structured lipitinite, liptodetrinite, vitrinite, inertinite and bitumen. A description of these individual macerals and organic constituents, and their origin and properties is provided in Table 1. Polished thin sections and strew-mount slides were prepared. Petrographic analyses of the polished thin sections were completed to define the occurrence and properties of organic constituents in relation to the sedimentary matrix. Polished thin sections, which are approximately 50 microns (pm) thick, were made using procedures similar to the preparation of thin sections, except that the surface was polished. Strew-mount slides were prepared from isolated kerogen to study properties of the unstructured amorphous organic matter and individual structured liptinites. Demineralization of the kerogen was completed by using alternating hydrochloric (HC1) and hydrofluoric (HF) acid baths according to techniques described by Durand and Nicise (1980). Isolated kerogen was mounted on glass slides, similar to palynological analysis. For select samples, the isolated wet kerogen was sieved at minus 20 pm to identify structured material embedded in large particles of amorphous organic matter (lamalginite or bituminite). A Leitz Orthoplan microscope equipped with white and ultraviolet- fluorescence light sources was used for maceral analysis. Polished thin sections and strew-mount slides were analyzed in epi-illumination and transmitted light using oil immersion at magnifications o f200 and 500x. 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M a c e ra l/O rg a n ic C o m p o n e n t S u b C a te g o ry O rig in P e tro g ra p h ic P ro p e rtie s Lam alqinite M atrix Lam alqinite Planktonic Alqal C om ponents M a k e s up S edim ent Matrix Alqal/Bacterial M a t Precursors Fluorescent A m orphous Filam ent Lam alqinite Individual Planktonic Precursors Thin, Filam entous Bitum inite-Am orphous Fluorescent Bacterial Lipids & D egradation V arious A m orphous Textures N on Fluorescent Oxidized Bituminite Physically/Bioloqically D eqraded Bituminite Oxidized Hum ic Precursors Structured Liptinite Alqinite Pediastrum , etc Structured Algal Bodies Sporinite Spore-Pollen Cutinite Cuticle Vitrinite C arbonaceous M aterial W o o d y T exture W o o d y Tissues H om ogenous G el Consolidated Bacterial M at M aterial? Inertinite Fossil Charcoal O xidized W oo d y M aterial Bitumen Fluorescent Indigenous Bitum en Soluble - Insoluble in O rganic Solvents Non Fluorescent/ Early G enerated Bitum en Products? Insoluble Table 1. Classification of individual macerals and organic constituents used for organic petrographic analyses of Tipton and Wilkins Peak samples. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Solvent Extraction. Soxhlet extraction was completed to obtain solvent extractable organic matter or bitumen for gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), and isotopic analyses. Samples were ground to a minus 60 mesh sieve, weighed into a porous thimble, and extracted with dichloromethane for 24 hours. Copper beads were added to the solvent flask to remove elemental sulfur. After extraction, the solvent was removed using a turbovap at room temperature to help retain the light molecular components (<nCis) within the extract. The bitumen was transferred to a tared vial and then weighed to quantify the amount of extract. Liquid Chromatography. Medium pressure liquid chromatography (MPLC) of the solvent extract was completed to separate the bitumen into the saturate, aromatic and polar fractions. The MPLC utilized a deactivated silica pre-column and a main activated silica column as the stationary phases; n-pentane was used as the mobile phase. The extract was passed through a deactivated silica pre-column and then to the main column. The saturate fraction was not absorbed and thus easily eluted from the columns with the mobile phase, while the aromatics were retained near the head of the main column. By reversing the flow of n-pentane in the main column, the aromatics were back-flushed from the column and directed to the fraction collector. Polars were adsorbed by the deactivated silica pre-column. The polars were later flushed from the pre-column with a 50:50 mix of dichloromethane/methanol using a separate pump. The saturate, aromatic and polar fractions were weighed after evaporation of the solvent. Gas Chromatography-Bitumen. The saturate fraction of the bitumen was analyzed by an Hewlett Packard HP-5890A chromatograph, equipped with a split/splitless injector 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and high resolution capillary column. The bitumen was diluted in cyclohexane and automatically injected. The chromatograph was heated from 40 to 320 °C using helium as the carrier gas. A 30 m J&W Scientific DB-5 capillary column with a 0.25 mm internal diameter (ID), and a 0.20 micron was used. The temperature program used the following: 40 °C (2 minutes) 40 °C to 320 °C at 2.5 °C/minute 320 °C (18 minutes) Data acquisition was completed using a Hewlett Packard Chemstation. Gas Chromatography-Mass Spectrometry (GCMS). GCMS was completed to identify and determine concentrations of selected molecular components (biomarkers) in the saturate fraction of the extracts. A volume of 0.1 microliter (pL) of the saturate fraction was injected into a Hewlett Packard 6890 Series Plus GC System that is coupled to a Hewlett Packard 5973 Series Mass Selective Detector (MSD). A 60 m DB-5 capillary gas chromatography column was utilized for the analysis. Helium was used as the carrier gas. A selected ion monitoring technique was used where specific ions were selected for identification and measurement (SIM mode). Ions were collected in two different time windows: window 1 ranges from 5.00 to 30.00 minutes; window 2 extends from 30.00 to 118.50 minutes. The dwell time was set at 20 milliseconds for each ion in both windows. The components were quantified relative to an internal standard that was added to the saturate fraction after the MPLC separation. The concentration in parts per million (ppm) of each reported molecular component was calculated and compared with the known value. A multiplier was calculated based on the standard, which converted the 48 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. measured value to the known value for each component. The specific multipliers were applied to each sample until the standard was run again. 1 < 3 Carbon Isotope Analysis (Kerogen and Bitumen). Carbon isotope (8 C) measurements were completed on kerogen, whole-bitumen, and the saturate and aromatic fractions of the bitumen. For kerogen, a 5 mg portion of solvent extracted and thoroughly crushed and decarbonated rock was placed in a quartz tube with cupric oxide and a silver strip, then sealed under vacuum. The tube was combusted at 850 °C under vacuum for four hours in the presence of cupric oxides and silver in order to fix sulfur species. The resulting CO2 was collected and purified by differential temperature transfer using a cryogenic high vacuum glass preparation line. The whole-bitumen and extract fractions were converted to CO2 on a combustion line, which had the water removed. Analysis of the samples was completed using a Finnigan MAT 252 mass spectrometer. The analyses were performed at Coastal Laboratories, Austin, Texas. The 1 3 C/1 2 C ratio was determined through ionization of CO2 and monitoring of 1 2 C02 mass charge (m/z) 44 and of 1 3 C02 (m/z 45). Measurements were compared to the PDB standard (belemnite carbonate, Peedee Formation, Upper Cretaceous, South Carolina, USA) and reported as 81 3 C (% ) = [1 3 C/1 2 C (sample) - 1 3 C/1 2 C (standard)] / [1 3 C/1 2 C (standard)] x 103. Special preparation techniques were used to thoroughly decarbonate the kerogen samples because of the wide variety of relatively abundant carbonate minerals in Green River sediments. Rock samples were crushed to minus 200 mesh. Decarbonation was completed using multiple “doses” of hot HC1 acid. The pH of the remaining acid was 49 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. checked to ensure complete removal of all carbonate minerals. Selected isolated kerogens were compared with representative splits of decarbonated rock to verify results of the preparation procedure. Stable 5°C and 5lsO Measurements-Carbonate Matrix. Sediments were crushed to minus 200 mesh and solvent rinsed to remove all extractable organic matter. Stable isotope analyses of CO2 gas released from the carbonate matrix during reaction with 103% phosphoric acid at 25 °C under vacuum was measured using a Finnigan MAT 251 triple collecting dual inlet gas isotope ratio mass spectrometer. The analyses were performed at Coastal Laboratories; Austin, Texas. The results are reported as S1 3 C in parts per mil (%o) relative to the PDB standard. The oxygen isotope ratio (1 8 0 /1 6 0 ) of the bulk matrix carbonate is reported as the per mil deviation from the international PDB isotopic standard. The carbonate collected for isotopic analyses represents various types and proportions of calcium, magnesium and iron carbonate minerals. Therefore, a timed- dissolution procedure based on different reaction rates for chemically distinct carbonate phases was used to measure the carbon isotope ratios. The inability to physically separate discrete carbonate phases in most samples led to attributing CO2 evolved in the first hour to calcium carbonate (calcite), and CO2 evolved after several hours to magnesium and iron carbonates (dolomite, ankerite and siderite). Calcite was assumed to be the first phase derived from the acid digestion. Carbonate phases including dolomite and siderite take much longer and therefore, were not captured in the initial acid digestion. This procedure is similar to the approach employed by Pitman (1996) to measure the 81 3 C of 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Green River carbonates. Potential variability in the isotopic composition could reflect the difference between calcite and dolomite. However, only small differences between calcite and dolomite in paired samples (average AS O = -0.98 % o) were observed from a suite of Green River Formation samples from Colorado and Wyoming by Pitman (1996). X-Ray Mineralogy. X-ray mineralogy was completed at ChevronTexaco Laboratories; Houston, Texas. Whole rock mineral identification was based on correspondence of experimental d-values with the diagnostic hkl reflections from the International Center for Diffraction Data (1993), (ICDD) reference file. The quantitative analysis method is based on a modification by Srodon et al. (2001) and Mystkowski et al. (2002) of the matrix- flushing technique by Chung (1974). Concentration values were determined in weight percent and then reported as normalized to 100 percent. Zero values indicate the phase was not detected. Samples for X-ray analysis were solvent extracted. However the significant amount of remaining kerogen caused possible problems with analyzing the mineralogy. Definitions and Terms Used in This Study Oil Shale - Represents any sedimentary rock that when heated, yields significant amounts of liquid hydrocarbons by the thermal breakdown of “solid” organic matter. Although the sedimentary properties and mineralogy of Green River oil shales are variable, they often consist of marls with a high carbonate content, rather than clay-rich shales. 51 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Organic-Rich Mudstone - Includes mudstone or marlstone with oil-yields less than oil shale, usually 5 to 15 gallons/ton. Organic-rich mudstones often represent a gradation in organic content between oil shale and mudflat sediments. Tipton and Wilkins Peak mudstones are usually highly calcareous. Organic Facies - A sedimentary unit whose organic constituents are defined and distinguished on the basis of their chemical composition, lithologic and petrographic properties, and paleodepositional setting (Curiale and Lin, 1991). This description is modified from many of the traditional definitions of organic facies summarized in Jones (1988) because it implies both organic geochemical properties and depositional character. Organic facies identified in this study include: (1) Oil Shale Facies - Consists of organic-rich sediments including different types of oil shales and organic-rich mudstones. (2) Mudflat Facies - Consists of various sediments deposited in mudflats dominated by either shallow subaqueous, or subaerial conditions. Mudflat sediments contain reduced amounts of organic matter in comparison to the oil shale facies. (3) Trona-Saltpan Facies - Represents the evaporative, organic-lean to -barren interval that consists of trona, and/or other evaporites. Organic Microfacies - Represent sub-divisions of the different organic facies. Microfacies are defined from small but consistent and discemable differences in lithology, bulk and molecular geochemical, and petrographic properties. These differences usually result from relatively small but consistent changes in depositional 52 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. conditions. This description is modified from the original definition by Brown (1943), which employed the facies concept on a microscopic scale. Kerogen Types-Kerogen is classified into Types I-IY based on the van Krevelen atomic hydrogen/carbon and oxygen/carbon diagram (Tissot et al., 1974). Type I is very hydrogen-rich and oil prone. Type II is oil prone, Type III is gas prone, and Type IV is inert and contains limited amounts of hydrogen. Classification of kerogen types can be inferred from the Rock-Eval pyrolysis method by using the hydrogen index (Espitalie et al., 1977). Net Moisture-Represents precipitation minus the evaporation, and is the moisture available for potential runoff and/or lake accumulation. Rainy Precessional Phase - Represents the part of the precessional cycle with more precipitation and/or reduced evaporation leading to higher net moisture and lake levels. Dry Precessional Phase - Represents the part of the precessional cycle that has less precipitation and/or higher evaporation leading to reduced net moisture and lake levels. Episodic Depositional Distortions - Represent episodic, non-cyclical processes and events that alter the orbital record of deposition. These events and processes are separate from cyclical-driven deposition, and can originate from intra-basinal, regional, or global processes. Litho-organic Signatures - Represent a combination of trends, patterns, or excursions in lithology, organic content, and other geochemical parameters that record 53 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. variations in water depth and lacustrine depositional conditions. These signatures can help unravel changes in net moisture, cyclical versus non-cyclical deposition, and reconstruct paleoclimatic and paleoenvironmental conditions. Brackish, Saline and Hypersaline - Terms that represent relative levels of water salinity rather than imply specific solute concentrations. Prokaryote - Eukaryote Terminology - Where applicable, prokaryote terminology as defined by Fox et al. (1980) was utilized. Therefore, informal terms like blue-green algae were avoided. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 4 CYCLICITY - TIPTON AND W ILKINS PEAK M EM BERS Introduction Sonic and gamma logs, Fischer assay oil-yields and lithologic properties were utilized to identify and define the Tipton and Wilkins Peak cyclicity. In order to further evaluate the Milankovitch periodicity o f these cycles, as described by Fischer and Roberts (1991) and Roehler (1993), calculation of depositional periods and time series and spectral analysis were completed. Results were utilized to evaluate: (1) cyclical-driven climatic and depositional patterns throughout the precessional and eccentricity cycles, (2) variability in cycle properties related to cyclical and non- cyclical processes, and (3) the occurrence of sub-Milankovitch cyclicity. Observations and Results Milankovitch Cvcles-Tipton Member Visual identification of Milankovitch or other cyclicity in the Tipton is difficult because of the lithologically uniform oil shales. However, precessional cycles in the Scheggs and Rife Beds are defined from electric log signatures and oil- yield patterns. Log Identification of Cyclicity. Small-scale gamma ray and sonic velocity oscillations define Tipton precessional cycles in the depocenter of the Green River Basin. A log from Union Pacific El Paso-1 identifies twenty sonic oscillations representing precessional cycles that range between about 6 and 10 ft (Figure 15). Small-scale gamma ray oscillations, which are sometimes slightly offset compared to 55 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gamma Ray A P I U N IT S Interval Ttansit Time MICROSECONDS PER FOOT 0 160 140 90 40 too 3® 240 190 140 D E P T H 4 S t Oil Yield (Gallons/Ton) 18.0 19.7 > Rife Scheggs 18.0 < > 2,7 2300 18.® Data from Trudell (1975) Figure 15. Gamma and sonic log for Tipton Member, El Paso-1 illustrates the occurrence of precessional and eccentricity cycles. Sonic oscillations define precessional cycles. Slower sonic travel time generally correlates with increased oil- yield. Gamma ray response that forms undulating and reversed log pattern in packages of approximately 4 to 6 individual precessional cycles defines short eccentricity. Precessional cycles in El Paso-1 correlate with Blacks Fork-1. 56 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the sonic peaks, also define precessional cycles. The cycle pattern and thickness is similar to the cyclicity described by Fischer and Roberts (1991) in the Washakie Basin (Figure 6). Complete logs from Blacks Fork-1 are not available; however, stratigraphic correlation by Roehler (1991) indicates that precessional cycles are stratigraphically equivalent and laterally continuous between Blacks Fork-1 and El Paso-1. The occurrence of short (approximate 100 k.y.) eccentricity cycles in the Tipton can also be identified from their log signature. Small-scale precessional gamma ray oscillations form packages of four or five in a longer spaced, undulating, and often reversed log response (Figure 15). This eccentricity log pattern is similar to descriptions by Fischer and Roberts (1991). It is difficult to identify long eccentricity (~400 k.y.) cycles due to the short depositional period of the Tipton Member. Sonic log travel time and oil-yields in El Paso-1 display a good correlation. Most sonic peaks, which represent a higher interval travel time, correspond to high oil-yields (Figure 15). The sonic log is a measure of the travel time defined in milliseconds (ms) divided by the distance penetrated from the borehole into the formation. Transit times in the Tipton range from 75 to 125 ms/ft, which are similar to values in other oil shales (Rider, 1986; Crain, 1986; Bennett, 1991). The sonic log travel time primarily reflects variation in the density of the oil shale. High-interval transit times represent organic-rich zones, whereas low interval transit times equate to reduced organic content and well-consolidated zones (Selley, 1985). 57 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Gamma ray spikes are sometimes offset compared to the sonic oscillations throughout the Tipton interval. The gamma ray response is influenced by several different compositional properties, including potassium-rich clays, carbonate content, volcanic ash, analcime, and uranium and thorium. Many of the minerals that contribute to natural radioactivity such as volcanic ash and analcime are not directly related to orbital cyclicity. Therefore, the application of gamma logs to define cyclical patterns is sometimes difficult. The higher gamma response immediately above the base of some cycles likely results from greater amounts of radioactive elements associated with the higher organic content. An increase in the gamma response at the base of some cycles may correspond to an initial flooding and influx of potassium-rich clay and volcanic ash. Most marlstones and dolomite-rich oil shales have a lower gamma ray response because they contain less clay. Cyclical Properties, Patterns and Depositional Period. Most Scheggs and Rife precessional cycles can be defined from Fischer assay patterns, which consist of a high oil-yield base with reduced yields in the middle and upper parts of the cycle (Figures 16 and 17). The cycle base contains the highest oil-yields in the precessional interval and ranges from 0.5 to 3.3 ft thick. Directly above this base, a marked reduction in oil-yield occurs, which sometimes represents the lowest yields in the cycle. A variable oil-yield occurs in the remainder of the cycle. Although oil- yield patterns in Tipton precessional cycles are expressed in different ways, most cycles display this two-stage signature (Figure 18). As defined from oil-yield 58 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D ep th Cycle # 1591.0- 1592.0 1593.0- 1594.0 1595.0- 1596.3 1597.6- 1599.0 1600.0- 1601.0 1602.0- 1603.0 1604.0- 1605.0 1606.0- 1607.0 1608.0- 1609.0 1610.0- 1611.0 1612.0- 1613.0 1614.0- 1615.0 1616.0- 1617.0 1617.9- 1618.6 1619.6- 1620.8 1622.1- 1623.1 1624.1- 125.6 1626.9- 1628.2 1929.2- 1630.2 1631.2- 1632.2 1633.5- 1634.8 1636.2- 1637.2 1638.2- 1639.4 1640.6- 1641.7 1642.7- 1643.6 1644.6- 1645.6 1646.6- 1647.7 1648.8- 1649.9 1650.9- 1652.0 1653.2- 1654.3 1655.4- 1656.5 1657.5- 1658.5 1659.5- 1660.5 1661.5- 1662.6 1663.6- 1664.6 1665.6- 1666.6 1667.6- 1668.1 1668.6- 1669.2 1670.8- 1671.4 1672.4- 1674.2 1676.2- 1676.6 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 O il Y ield Figure 16. Scheggs precessional cycles defined by Fischer assay oil-yield, Blacks Fork-1. Most precessional cycles (arrows) contain a high oil-yield base with lower yields in the middle and upper part of the cycle. Oil-yield is expressed in gallons/ton. 59 rson SS Equivalent Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D ep th Cycle # 1508.4-1509 1510.4-1511 1512.4-1513 1514.5-1515 1518.7-1517 1519. 1-1520 1521.8-1523 1524.0-1525 1526.0-1527 1528.0-1529 1530.0-1531 1532.0-1533 1534.0-1535 1536.0-1537 1538.0-1539 1540.0-1541 1542.2-1543 1544.4-1545 1546.7-1547 1548.7-1550 1551.0-1552 1553.5-1555 1555.5-1556 f 1557.8-1558 1559.8-1560 1562.6-1563 1565.2-1566 1567.7-1568 1569.7-1570 1571.7-1572 1573.2-1574 1575.2-1576 1578.2-1578 1579.9-1581 1582.1-1583 1584.1-1585 1586.5-1587 Farson Equivale 1588.7-1590 Oil Y ield 40.0 Figure 17. Occurrence o f precessional cycles (arrows) in Rife Beds o f the Tipton Member, Blacks Fork-1. Distinctive, repetitive oil-yield patterns define precessional cycles. Rife precessional cycles display a similar oil-yield pattern as the Scheggs Bed with a high-yield cycle base. 60 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 0 35 S 1 0 IS 2 0 m m : . - i .. .... 1 .. ,_ _ l— : s Half Cycle S houlder Peak . . " ' 1 R educed Yield Above Base - . - I , - . . . : , : ... _!-----------------1 -----------------i_ to p Transition ^ I -1 042.7 16 2S 3 0 3 6 0 5 1 0 O il 7 1 * 1 4 (G allTon) O HV KW IOtfTon) Figure 18. Representative oil-yield patterns in Tipton precessional cycles. Most cycles display characteristic pattern consisting of: (1) high oil-yield base, (2) reduced yield in middle and upper part of cycle, (3) approximate mid-cycle increase in oil-yield, and (4) transitional increase in oil-yields to overlying cycle. Some cycles display unique patterns in part due to episodic depositional distortions. 61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. patterns, Scheggs and Rife precessional cycles range from 4.2 to 12.4 ft in Blacks Fork-1, with a respective mean thickness of 6.8 and 8.6 ft (Figure 19 and Table 2). Overall, oil-yields in Tipton cycles range from less than 5 to 34 gallons/ton. The range in oil-yields for individual cycles is variable throughout the Scheggs and Rife (Figures 16 and 17). Precessional cycles with the highest oil-yields occur in the center of the Scheggs and Rife Beds. Individual oil-yields for the Tipton Member are listed in Appendix 3. The depositional period for Tipton precessional cycles as defined from oil- yield patterns and the application of varves, ranges from 12,725 to 28,900 years. Although variability exists, the mean depositional period for Scheggs and Rife cycles are calculated at 17,350 and 21,750 years, respectively (Table 2). When calculated by using a 120 pm annual varve thickness, these depositional periods further confirm the 21 k.y. precessional cycle. Some of the variation in depositional age may result from non-cyclical effects and the imprint from shorter- and longer-term cyclicity. A mean depositional period of 19,358 years was defined for Tipton cycles using sonic and gamma log signatures in the Washakie Basin (Fischer and Roberts, 1991). Because most Tipton cycles consist of an organic-rich base and overlying interval with reduced oil-yields, a constant varve thickness of 120 pm is assumed to represent annual deposition for these two types of oil shales. Caution must be used in the application of varve thickness to define depositional time. Changes in the number of yearly varves and their lateral thickness can occur. Oil shale varves can range from 62 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. <0 [0,2) [2,4) [4,6) [6,8) [8,10) [10,12) [12,14) [14,16) >=16 Feet Figure 19. Range in thickness of precessional cycles as defined by oil- yield, Tipton Member, Blacks Fork-1. The mean thickness o f precessional cycles in Scheggs and Rife Beds are 6.8 and 8.6 ft, respectively. 63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Bed/Cycle Top Depth Base Depth Cycle Thickness Oil-Yield Range Depositional Period* Comments (Feet) (Feet) (Feet) (Gallon/Ton) (Ka-Years) Scheggs1 1662.6 1669.2 6.6 5.3-16.3 16800 Early development of Scheggs Lake Scheggs 2 1656.5 1662.6 6.1 7.0-18.7 15525 Scheggs 3 1650.9 1656.5 5.6 10.5-34.2 14250 Scheggs 4 1645.6 1650.9 5.3 7.4-18.6 13500 Scheggs 5 1639.4 1645.6 6.2 20.4-31.6 15800 Abundant volcanic ash Scheggs 6 1633.5 1639.4 5.9 14.4-28.8 15050 Scheggs 7 1628.2 1633.5 5.3 17.3-26.3 13500 Scheggs 8 1619.6 1628.2 8.6 6.6-26.1 21800 Scheggs 9 1611.0 1619.6 8.6 7.2-19.5 21887 Scheggs 10 1604.0 1611.0 7.0 6.7-17.2 17800 Influence from Farson Sandstone Scheggs11 1597.6 1604.0 6.4 4.6-10.5 16300 Influence from Farson Sandstone Scheggs 12 1587.5 1597.6 10.1 0.7-16.3 25700 Influence from Farson Sandstone Rife 1 1582.1 1587.5 5.4 8.3-19.0 13750 Influence from Farson Sandstone Rife 2 1573.2 1582.1 8.9 8.2-16.4 22650 Rife 3 1560.8 1573.2 12.4 3.2-27.6 31500 Rife 4 1556.6 1560.8 4.2 14.1-24.0 10700 Rife 5 1548.7 1556.6 7.9 12.0-30.2 20105 Rife 6 1540.0 1548.7 8.7 18.7-31.8 22100 Rife 7 1531.0 1540.0 9.0 8.8-32.9 22860 Rife 8 1521.8 1531.0 9.2 9.9-21.0 23400 Rife 9 1510.4 1521.8 11.4 23.8-32.0 28900 Average Cycle Thickness Scheggs Bed - 6.8 Feet Rife Bed - 8.6 Feet Depositional period based on cycle thickness and 120 micron annual varve Table 2. Summary of precessional cycle dimensions and properties, Scheggs and Rife Beds; Tipton Member, Blacks Fork-1. Depositional period defined from approximate varve thickness. 64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 to 500 (im, depending on organic content, biological productivity, sedimentation, and origin (Bradley, 1929a). X-ray diffraction indicates a subtle increase in carbonate composition between the base and the middle of Rife cycles (Table 3). Mineralogical trends are less evident in the Scheggs. In Scheggs cycle 4, an increase in quartz and total clay occurs in the organic-rich mudstone at the top of the cycle (1646.4 ft). Variation in mineralogy through the Scheggs and Rife cycles is consistent with the results reported by Robb and Smith (1976) that documented significant small-scale (1-2 ft) variations in the mineralogical composition in the Blacks Fork-41-23 corehole. Because of the large quantities of kerogen, analcime and associated volcanic ash, additional work is required to quantify Tipton mineral fractions in Blacks Fork-1. Milankovitch Cvcles-Wilkins Peak Member Precessional cycles in the Wilkins Peak consist of either basal oil shale and mudstone doublets, or oil shale, trona and mudstone triplets. Cyclical log signatures include: (1) gamma values that are low in trona, intermediate but variable in the mudstone, and high in the oil shale, and (2) sonic interval transit times that are low in trona and high in oil shales. Documentation of this log response from El Paso-1 is shown in Figure 20, and is similar to the description by Fischer and Roberts (1991). In Blacks Fork-1, 17 eccentricity cycles are identified in the Wilkins Peak that range between 34.1 and 75.6 ft thick with a mean thickness of 63.0 ft (Figure 21). Eccentricity boundaries consist of mudstone, marlstone, siltstone, and very fine 65 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Bed/Cvcle Depth (ft.) Qtz Kspar Plag Cal Dol *Ank Dol+ Ank Total Carb Pyr Halite Analcime Fluorapatlte SUM NON CLAY 2:1 CLAY+MICA SUM CLAY Total Normalized Rife 7 1537.0 11 12 13 0 9 11 20 20 1 0 23 1 80 20 20 100 Rife 7 1540.0 14 13 11 0 5 2 7 7 0 0 17 5 6 7 33 33 100 Rife 6 1542.8 11 15 9 0 1 18 19 19 0 0 14 4 72 28 28 100 Rife 6 1545.2 8 9 4 0 8 4 13 13 0 0 33 5 73 27 27 100 Rife 6 1547.9 14 12 2 3 3 6 9 12 1 0 19 6 6 6 34 3 4 100 Scheags 4 1646.4 26 4 7 2 1 4 11 2 0 1 0 4 5 55 55 100 Scheggs 4 1650.0 21 4 6 0 22 22 28 2 0 0 0 56 44 4 4 100 Scheggs 3 1652.0 20 4 18 1 4 4 23 4 0 1 1 54 47 47 100 Scheags 3 1654.0 18 2 3 21 2 5 8 28 3 0 0 1 5 6 44 43 100 Scheggs 3 1656.1 20 4 6 4 7 12 20 23 2 0 1 1 58 43 43 100 Q tz = quartz A nk = ankerite Kspar = K feldspar P y r » pyrite Plag = plagiociase feldspar 2:1 clav + m ica = dioctahedral illite, m ixed-layer illite-smectite, sm ectite, and possibly mica. Cal = calcite i I i i Dol = dolomite Shortite = N a 2 C a 2 (C 0 3 )3 i ........ i....: i ........ I I 'N ote: ankerite likely represents acatcium -rich dolomite, additional analyses are required to m ake the distinction i ............r ............................................................................... i i Table 3. Whole rock X-ray diffraction results for selected samples from the Scheggs and Rife Beds in the Tipton Member, Blacks Fork-1. Results normalized to 100 percent. 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTERVAL TRANSIT TIME M fC ftO S ttO N D S H t fO Q l G A M M A RAY Cycle 24 Mudstone Oil Shale Cycle 22 Trona Oil Shale Trona Cycle 19 Oil Shale Mudstone Cycle 14 Trona Oil Shale Cycle 10 Cycle 5 Trona Oil Shale Figure 20. Gamma and sonic log, Wilkins Peak Member, El Paso-1. Gamma is low in trona, intermediate but variable in the mudflat facies and high in the oil shale. Sonic velocities are fast in trona and slow in oil shales. Precessional cycle number is listed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fischer assay (gal/ton) 1 o 60 i—i—1 .100 .200 .300 1 ,400 1.500- '1 .600 M o d ifie d Inflow > in Increased Net Moisture Tectonic & Climatic? > ix S u p e rb u n d le Minimum Net Moisture I > i S u p e rb u n d le Regional Tilting - Change in Drainage Rapid Decrease Net Moisture Tectonic & Climatic? Figure 21. Various imprints of orbital cyclicity in the Wilkins Peak including precessional and short-and-long eccentricity cycles. Likely tectonic and long-term climatic effects, and the influence of potential longer term cyclicity are illustrated. Figure modified from Roehler (1993). 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. grained sandstone that extends from the underlying precessional cycle. The thick organic-barren detrital intervals between eccentricity cycles G and H, and N and O have been described as 700 k.y. superbundles by Roehler (1993). Two superbundles and part of a third appear to occur based on packages of eccentricity cycles (Figure 21). Wilkins Peak Precessional Cvcles-Occurrence and Properties Lithologies in the basal oil shale facies include oil shale and organic-rich mudstone. The trona-salt pan facies occurs in approximately 40 of the originally 77 identified precessional cycles in Blacks Fork-1, which records evaporite deposition. The mudflat facies consists of dolomitic or silty mudstone, marlstone, carbonate, siltstone, and fine-grained sandstone. Volcanic ash, shortite, phosphatic beds, halite, lime sandstone, dolomite, and regular and flat pebble conglomerates sporadically occur throughout the Wilkins Peak in Blacks Fork-1. In Blacks Fork-1, Wilkins Peak precessional cycles range from 5 to more than 35 ft thick, with a mean thickness of 13.25 ft (Figure 22, Table 4). About 75% of the cycles range between 8 and 16 ft. Relatively thin precessional cycles usually occur in the middle of eccentricity cycles and contain less silty sediments. Most cycles that are more than 15 ft thick are adjacent to an eccentricity boundary. Excluding precessional cycles that contain thick eccentricity boundaries, the mean cycle thickness is 11.1 ft. Cycles 34 and 67, which are associated with the proposed superbundle boundaries, are the thickest (39.4 and 57.1 ft, respectively). The 69 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75% of Precessional Cycles Cycle Thickness Figure 22. Variation in the thickness o f precessional cycles, Wilkins Peak Member, Blacks Fork-1. The mean thickness o f Wilkins Peak precessional cycles is 13.3 ft. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wilkins Peak Cycle Thickness Oil Shale Thickness Maximum Oil-Yield Comments Cycle # Feet Feet (Gallons/Ton) 74 14.0 11.1 27.3 73 6.8 2.5 16.1 72 7.8 3.5 28.1 71 14.0 3.4 26.8 70 6.2 3.0 25.4 Associated volcanic tuff 69 6.9 2.2 30.9 68 7.0 0.6 34.6 67 39.4 2.4 25.6 66 10.9 8.3 9.8 Oil shale contains 0.5' tuff 65 11.7 2.9 36.4 Poorly defined cycle 64 5.7 2.6 13.5 Contains tuff & marlstone 63 8.2 6.0 9.1 Several breaks 62 11.0 2.0 11.6 61 34.3 5.3 16.8 60 11.6 11.6 Poorly defined cycle 59 9.7 2.5 8.5 Poorly defined cycle 58 15.4 3.4 25.9 57 5.6 2.3 22.6 56 9.0 1.8 29.1 55 12.2 2.9 29.9 54 8.8 1.9 32.3 53 10.0 0.9 27.7 52 15.0 Negligible oil shale 51 9.9 1.5 31.4 50 8.6 2.3 23.6 49 6.7 3.1 18.8 48 6.9 2.9 11.6 47 22.9 2.3 8.9 Organic-rich marlstone 46 12.5 11.9 13.3 45 12.5 3.1 26.3 44 11.5 0.8 14.3 43 13.3 Negligible Oil Shale 42 13.8 3.0 17.4 Organic-rich marlstone 41 12.2 7.0 21.1 40 6.7 0.9 25.9 39 16.5 0.9 7.2 Poorly developed cycle 38 20.6 1.4 30.2 37 10.8 4.5 4.6 36 5.0 1.2 19.3 Cycle contains conglomerate 35 12.6 Negligible Oil Shale 34 57.0 2.5 13.1 33 13.6 3.1 7.2 32 7.1 3.4 9.1 Poorly defined cycle base 31 7.5 3.8 13.6 30 6.2 3.2 11.2 29 14.9 3.4 4.6 28 17.5 7.9 36.3 27 9.7 1.5 40.6 Table 4. Precessional cycle dimensions and maximum oil-yield for individual cycles, Wilkins Peak Member, Blacks Fork-1. The mean thickness of Wilkins Peak precessional cycles is 13.3 ft, when cycles with thick eccentricity boundaries are excluded, the mean thickness is 11.1 ft. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wilkins Peak Cycle Thickness Oil Shale Thickness Maximum Oil Yield Comments Cycle# Feet Feet (Gallons/Ton) 26 7.4 3.2 25.1 ------- 2 5 ------- S 3 : ? § : S ------2 9 :3 ----- 23 10.9 1.4 37.2 22 13.3 6.2 30.8 21 11.4 2.6 13.8 20 21.6 1.7 26.3 Contains Volcanic Tuff 19 20.3 3.7 31.6 18 15.1 10.4 17.0 17 8.2 3.0 12.6 16 8.2 2.1 15.1 15 6.9 1.0 5.3 14 13.8 4.9 6.1 13 12.5 2.2 5.6 12 7.8 1.4 4.1 11 20.4 2.7 5.0 10 13.5 2.5 14.6 9 13.0 3.4 12.5 8 9.8 3.1 21.3 7 9.2 2.5 12.7 6 16.4 2.2 19.7 5 14.6 5.1 14.0 4 18.2 5.7 20.2 3 9.9 4.2 28.2 2 18.0 3.7 21.0 1 15.6 4.5 31.8 Notes: 1. Wilkins Peak precessional cycle numbers and intervals from Roehler (1991 and 1993) 2. Some cycle intervals adjusted based on oil yields and lithologies defined in this study 3. Some precessional cycles may represent sub-Milankovitch intervals and require modification I Table 4 (Continued). Precessional cycle dimensions and maximum oil-yield for individual cycles, Wilkins Peak Member, Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. thickness of most precessional cycles is influenced primarily by the amount of mudflat sedimentation and secondarily by oil shale deposition. Distinct trends in the thickness of precessional cycles are not evident throughout the Wilkins Peak (Figure 23). Lithologic Successions-Precessional Cycles. Five lithologic successions are identified in Wilkins Peak precessional cycles in the Blacks Fork-1 section (Figure 24). These precessional patterns include: (1) Oil Shale, Trona, and Mudstone - This is the most common succession in Blacks Fork-1, and is equivalent to the “Type IV” cycle described by Eugster and Hardie (1975). In some cycles, the halite or trona may be less than several inches thick or occur as thin, multiple layers. (2) Oil Shale and Mudstone - The mudstone can range from dolomitic to sandy with variable oil-yields that range from 0 to 6 gallons/ton. Trona is absent. (3) Oil Shale, Mudstone, and Siltstone or Sandstone - The middle and upper part of the mudflat facies contains siltstone, very fine grained sandstone or inter bedded siltstone and mudstone. (4) Oil Shale, Carbonate, and Mudstone - This is similar to the first succession but contains carbonate instead of evaporite. The carbonate is usually organic-lean and may occur as thin bands. (5) Organic-rich Mudstone, Mudstone, and Silty Mudstone - This succession is similar to successions 2 or 3, but the basal oil shale facies consists of an 73 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Eccentricity cycle U pper W ilkins P e a k Lower W ilkins P e a k 10 1 5 T hickness 20 (FeetP 30 35 40 Figure 23. Thickness o f individual Wilkins Peak precessional cycles and relation to eccentricity cycles (A-P), Blacks Fork-1. The absence o f distinct trends in precessional cycle thickness throughout the Wilkins Peak indicates a dominant, consistent orbital imprint. 74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. B Marlstone/ Mudstone Mudstone 3 S Z B I ------------ Trona = = = = = Oil Shale 2 S ^ = = = Oil Shale 3 Siltstone/ Sandstone Mudstone Oil Shale = = = = = Mudstone Carbonate Oil Shale Silty Mudstone/ Siltstone Mudstone Organic-Rich Mudstone Figure 24. Five different lithologic successions are identified in precessional cycles that represent the paleogeographic lake center in the Wilkins Peak Member. Thickness o f individual lithologic units and facies are variable. Mineralogy of mudstone is variable. Descriptions are primarily based on the Blacks Fork-1 corehole. 75 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. organic-rich mudstone that is often greenish-gray and has oil-yields less than the oil shales. Silty lithologies sometimes occur in the middle and top of this cyclical succession. 011-Yield Patterns-Precessional Cycles. Distinct precessional patterns in Fischer assay oil-yields occur throughout the oil shale and trona-mudflat facies (Figure 25). The most common oil-yield pattern consists of: (1) a 1-3 ft oil shale with oil-yields > 12-15 gallons/ton, (2) small to negligible yields in trona, (3) a thin organic-bearing mudstone with yields of 2-10 gallons/ton, and (4) the overlying mudflat facies with yields <0.1-2 gallons/ton. Other oil-yield patterns in precessional cycles include: (1) Thick Low-Yield Cycle - A thick, low-to-moderate yield oil shale that grades to an organic-rich mudstone (Blacks Fork-1 Cycles 9,17,18, 41, 59, and 61). Trona is usually absent or occurs in thin layers. (2) Double Cycle - An oil shale interval or “shoulder peak” defined by increasing oil-yields, usually at the top of the oil shale facies or directly above the trona (Cycles 22,25 and 28). This double cycle is identified from a variable, but often subtle, increase in oil-yield. (3) Climbing Cycle - The base of the cycle consists of a low-to-moderate yield, organic-rich mudstone that grades upward into oil shale (Cycles 3, 18, 41,46, 49, and 74). The highest oil-yields often occur near the top of the oil shale facies. Identification of the cycle base is sometimes difficult because of the gradual increase increase in oil-yield. 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ■ .. ■ ■ ■ f 1 1 1 1 i i I i i i i i i. I i I s 1 1 i 1 I i I ■ i ' " I |. I. 1 . 1 . 1 . 1 . 8.. ,| Figure 25. Precessional patterns in Wilkins Peak Member. Patterns defined from Fischer-assay oil-yields (gallons/ton). These patterns document different precipitation-evaporation and depositional histories for individual precessional cycles. Descriptions are primarily based on the Blacks Fork-1 corehole. (4) Thin High-Yield Cycle - The oil shale is often thin (< 1-2 ft) but displays some of the highest yields (>30 gallons/ton) in the Wilkins Peak (Cycles 23, 38, 51, and 68). Above the oil shale, the trona-mudflat facies is similar to most cycles. (5) Low-Yield Cycle - The cycle usually contains a thin, organic-rich mudstone or oil shale with low yields (<10-12 gallons/ton). There is usually a sharp transition to the overlying mudflat facies, which often has low to negligible oil-yields (Cycles 15, 29,35, 39, and 43). Basal oil shales associated with each precessional cycle range from less than 1 to 8 ft thick; most are between 1 and 4 ft (Figures 26 and 27). Some cycles are dominated by oil shales, others by the mudflat facies. Oil shales in eccentricity A are generally thicker than those in eccentricity E. The thickest oil shales usually occur in precessional cycles in the middle of eccentricity bundles. Cycles with low-yield oil shales often contain thick, silty mudflat sediments and limited amounts of trona. Packages of high- and low-yield oil shales occur throughout the Wilkins Peak. Generally, thicker but lower yield oil shales occur in precessional cycles 9-14,29-34, and 59-64 (Figures 21, 27-28). Overall, there is no direct correlation between the thickness of individual oil shales and maximum oil-yield, which ranges from approximately 5 to 40 gallons/ton (Figure 26 and Table 4). Individual Wilkins Peak oil-yields are listed in Appendix 3. The mudflat facies consists of two end-member lithologies and corresponding sedimentary features. A brecciated to massive mudstone, which can be silty or sandy, 78 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Oil Shale T hickness 9 8 7 6 Eccentricity B o u n d aries 4 3 ♦ ♦ 2 1 0 19 21 23 25 1 1 13 15 17 7 9 5 Total Precessional Cycle Thickness (Feet) 9 ♦ 8 ♦ 7 ’ ♦ ♦ 6 ♦ ♦ ♦ 5 ♦ ♦ ♦ ♦ ♦ ♦ 4 ♦ ♦ ♦ ♦ ♦ ^ ♦ ♦ ♦ ♦ ♦ 3 ♦ V ♦ ♦ ♦ ♦ ♦ ♦ ♦ ▲ 2 ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ 4 ♦ ♦ ♦ ♦ 1 ♦ ♦ ♦ ♦ 0 ♦ 0 5 10 15 20 25 30 35 40 45 Maximum OH Yield Gal/Ton Figure 26. Comparison o f cycle thickness and corresponding oil shale, and maximum oil- yield for individual precessional cycles, Wilkins Peak Member, Blacks Fork-1. Most oil shales range between 1 and 4 ft thick. Some cycles show a correlation between thickness o f the oil shale and the total cycle. 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 1 1 . 2 5 3 3 .0 5 4 6 .1 5 9 2 . 5 6 7 4 . 5 6 9 5 . 8 7 1 6 . 8 7 3 8 . 0 7 5 6 . 8 7 8 1 . 7 7 9 7 . 0 8 2 6 . 8 8 6 4 . 7 9 2 8 . 0 5= 9 5 1 .2 1 0 7 4 . 2 1 0 8 7 . 11 0 7 .9 1 1 35.1 1 1 6 3 .7 1 2 0 4 . 5 1 2 2 9 . 2 1 2 7 3 . 0 1 2 9 4 . 4 1 3 0 9 . 5 1 3 3 5 . 8 1 3 6 2 . 7 1 3 9 0 . 5 1 4 0 9 . 5 1 4 4 0 . 5 1 4 7 1 .0 1 5 0 1 .5 3 .0 4 .0 5.0 T h i c k n e s s (Feet) Figure 27. Thickness o f oil shales in individual precessional cycles versus depth, Wilkins Peak Member, Blacks Fork-1. Note variation in thickness of individual oil shales throughout specific eccentricity cycles. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0 5 1 0 1 5 2 ) 2 5 3 3 35 43 45 Yield (Galons/Ton) Figure 28. Maximum oil-yield of individual Wilkins Peak precessional cycles, Blacks Fork-1. Packages o f high- and low-yield oil shales occur throughout the Wilkins Peak. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. often displays disrupted bedding and remnant mudcracks. A silty texture is evident in thin section. This end-member usually has negligible oil-yields and is often adjacent to eccentricity boundaries. In contrast, a homogenous massive to laminated mudstone usually has oil-yields greater than 1-2 gallons/ton (Figure 29). Petrographically, this end-member often displays a fine grain calcareous nature with evidence of dispersed to laminated kerogen. Sub-Milankovitch Cvcles-Tipton and Wilkins Peak Members Twelve of the 21Tipton precessional cycles display a half-cycle organic enrichment. In the middle of most Rife and some Scheggs cycles, there is a thin interval that displays up to a 30% increase in oil-yield compared to the underlying oil shale (Figure 30). The expression of this half-precessional organic enrichment or “shoulder peak” is often variable and subtle, and sometimes identified by a slower sonic log velocity response (Figure 15). Some Wilkins Peak precessional cycles contain an organic-enriched zone located near the top of the oil shale or trona, or in the lower part of the mudflat facies. Such zones of organic enrichment range from a high-yield, double oil shale to thin, organic-rich layers encased in mudstone (Figure 31). Precessional cycles that contain a thick, low-yield or climbing oil shale may also record a half-cycle organic- enrichment (Figure 25). Approximately 18 of the identified 77 precessional cycles display evidence of a half-precessional enrichment (Figure 32). 82 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dry Cycles Intermediate Cycles Thin Low-Yield Oil Shale Negligible Oil-Yields in Mudflats A bundant Siltstone/Sandstone Negligible Trona Cycle 24 Cycle 20 “ OiSWe Cycle 21 Wet Cycles Marlstane 0 1 S h a l e 0 1 S h a l e Cycle 23 Cycle 22 Thick Oil Shale Organic-Rich Mudflats with Oii-Yields > 1 -2 gallons/ton Trona feBHHMnMHH CflflXinatS i s d i i l s s - s - s - d S s h r n rira tiiiH iS is . Typical Lithological Succession Mudflat Oil-Yields 1 2 l (1-2 gallons/ton) Figure 29. Dry, intermediate and wet precessional cycles in Wilkins Peak eccentricity E. Silty, brecciated mudflat lithologies have negligible oil-yields where-as massive-laminated mudstone/marlstones typically have yields up to 2 gallons/ton. Precessional cycle variation partly related to the precession index. 8 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7848^239792^176^096674483268 5515 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 30. Identification o f sub-Milankovitch, half-precessional enrichment in oil-yield that occurs somewhere in the middle o f Tipton precessional cycles (H), Blacks Fork-1. Expression of organic enrichment is often subtle and variable. These half-cycles are more common in the brackish-saline Rife compared to the freshwater Scheggs Beds. O O 4 ^ Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. I 1 I I 1 I I I I I 1 1 - 1 w I I I I I I ~ r i D “ T 1 i i S I I I i I I 1 1 ! ! S I I 1 B I 1 I ! I I I I I I I Figure 31. Expression o f Wilkins Peak half-precessional cycle patterns defined by oil-yield, Blacks Fork-1. Variable increase in oil-yield in the middle of the cycles corresponds to thin organic-rich layers. 00 L A 50 0 - 700 i 4 d 300 a . 1.000 1.500 Figure 32. Occurrence o f likely half-precessional cycles throughout the Wilkins Peak Member, Blacks Fork-1. Half-cycle pattern based on organic-enrichment defined as strong (S), moderate (M) or weak (W). Precessional cycles with questionable (?) half-cycle enrichment also shown. Figure modified from Roehler (1993) 86 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Generally, one precessional cycle in each 100 k.y. eccentricity bundle displays evidence of a half-precessional cycle; this usually occurs near the middle of the eccentricity bundle. In the Tipton, the half-cycle depositional period ranges from 8,630 to 15,240 years, with a mean of 10,730 years based on a varve thickness of 120 pm (Table 5). In the Wilkins Peak, the depositional period between the precessional cycle base and the mid-cycle organic enrichment ranges from 6,750 to 13,850 years, with a mean of 9,900 years (Table 6). This calculated depositional period uses an average 120 pm for oil shale varves, but 300 pm for the organic-lean mudflat (Bradley, 1929a). This sedimentation rate is consistent with other studies that document that mudflat accumulation can be up to 3 times faster than the playa lake facies (Bobst et al., 2001; Smith et al., 2003). Variation in the half-precessional depositional period is the result of variation in sedimentation rates and non-cyclical events. In the Wilkins Peak mudflat, thin organic-rich bands (0.15 to 0.3 ft) sometimes occur (Figure 33). These consist of a sharp, medium-dark green laminated mudstone base that grade upward to a light gray massive mudstone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 4 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 Mudstone; Md-lt green gray. Org-rich intervals. Mudstone: Md-lt green gray silty in parts. Org-rich intervals up to 0.2”. Mudstone; Oreen gray-green haBte(0.1)@1448.9. O H Shale; M-d-dk green gray-brown gray Oil Shale; Dk green gray-brown gray O H Shale: Md green gray. Dk brown gray Total Organic Carbon Content _ Organic-Rich BaseHB Organic-Rich Base •'f* _ Figure 33. Example of thin organic-rich bands that sometimes occur in the mudflat facies in the Wilkins Peak Member, Blacks Fork-1. A sharp increase in organic carbon occurs at the base of the cycle with upward gradation to a lower organic content. These may represent “century-level” cycles. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Cycle/Bed Cycle Base Base Half Cycle Depositional Period* Comments (Feet) (Feet) (K a) Scheggs1 1669.2 1665.6 9144 Early development of Scheggs Lake Scheggs 2 1662.6 1659 9144 Scheggs5 1645.6 1641.7 9906 Abundant volcanic ash Scheggs 9 1619.6 1615.0 11680 Scheggs10 1611.0 1607.0 10160 D etrital influence from Farson Sandstone Rifel 1587.5 1584.1 8636 D etrital influence from Farson Sandstone Rife 2 1582.1 1576.9 13208 Rife 3 1573.2 1569.7 8890 Rife 5 1556.6 1552 11684 Rife 6 1548.7 1544.4 10922 Rife 7 1541.1 1535 15240 M ay represent two cycles Rife 8 1531.0 1527 10160 Table 5. Dimensions and calculated depositional interval representing half-precessional cycles in the Tipton Member, Blacks Fork-1. A 120 pm annual varve thickness was used to calculate depositional periods. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wilkins Peak P r e c e s s io n a l Cycle Depth C y cle B ase Half C y c le B ase O il S h a le T hickness Oil Shale D e p o s itio n a l Period M u d flat Thickness Mudflat D e p o s itio n a l Period Half-Cycle D e p o s itio n a l Period* Com m ents (Feet) (Feet) (Feet) (Years) (Feet) (Years) (Years) 6 1425.4 1418.5 2 5080 4.9 4978 10058 9 1390.5 1382.5 3.8 9600 4.2 4260 13860 16 1302.6 1297.9 1.1 3076 3.6 3658 6734 19 1271.6 1266.5 1.6 4065 3.5 3556 7621 18 1294.4 1289 3.3 8382 2.1 2133 10515 22 1217.8 1212.8 5 12700 0 12700 25 1159.8 1154 4.2 10650 1.6 1600 12250 28 1125.4 1121 3 7620 1.4 1422 9042 40 934.7 927.9 0.6 1524 6.6 6300 7824 42 915.8 911.2 2.5 6350 2.1 2134 8484 44 877.2 869.2 0.8 2032 7.2 7315 9347 45 863.9 857.5 2.3 5842 4.1 4166 10008 50 790.3 785.7 2.3 5842 2.3 2337 8179 56 725.8 720.8 1.8 4572 3.2 3252 7824 62 640 633 1.2 3048 5.8 5893 8941 65 613.4 605.7 2.4 6096 5.3 5385 11481 71 533 524 1.2 3048 7 7112 10160 Minus 0.8' tuff 76 483.6 477 4.4 11176 2.2 2235 13411 * Defined from oil shale and mudflat depositional period using respective varve thickness I I I I I I Table 6. Occurrence of half-precessional cycles in the Wilkins Peak Member, Blacks Fork-1. Depositional period is calculated from interval between cycle base and half-cycle organic enrichment using oil shale and mudflat varve thickness. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Time-Series and Spectral Analvsis-Tipton and Wilkins Peak Time-series and spectral analysis were completed to further evaluate the occurrence of discrete cycles possessing Milankovitch periodicity. To test for the occurrence of orbital-related frequencies, the measured core data from Blacks Fork-1 was transformed into a geological time-series. If it is assumed that the oil- yield reflects orbital changes in climate, especially precessional variations, then it is expected to have registered the short and long eccentricity cycles, as well as an obliquity signal if present. The Fourier analysis evaluated the statistical relationships between the oil-yield and the frequency domain of the orbital cyclicity. Input data is listed in Appendix 3. Dr. Al Fischer and Alessandro Grippo completed this analysis. The Fourier spectrum obtained from the oil-yield corresponds to the predicted periodicities of the Milankovitch-band model in the Tipton and Wilkins Peak. Results of the spectral analysis indicate that the precession, short and long eccentricity cycles, and a weak obliquity signal are present (Figures 34 and 35). The strength of the precessional and eccentricity spectral peaks is much greater than noise signals. This cyclicity documents the orbital-driven climatic imprint in these lacustrine sediments, indicating it is unlikely that this occurred by chance through some type of non-Milankovitch forcing mechanism. Smaller spectral peaks appear to represent the obliquity; however, they are at a level that is barely considered significant. A “double-beat,” half-precession signal is evident, consistent with the half-cycle observed in oil-yield values. The remainder of the series is categorized simply under the heading of “noise.” However, this may not be an entirely accurate 91 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ‘ d .m > tso 50 e 0 p . p TIFTOM BLACKS FOUR V ? p i V 2 p ? CORE 1 * > ■ ! ' } « y p s* 0,1 «»« Q.SS Figure 34. Spectral analysis results for cycle properties tfom Blacks Fork-1 illustrating Milankovitch cyclicity in the Tipton Member. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I'l WILKINS PEAK BLACKS FORK 1/2p, l/?.p,C C R E I 1 1 U m 2,1 m E e 0 p , p > v z p i V ? p , W IUtlM S PEAK CtJttREMT CREEK RIOGE CORE I 11 m , n t i? i 3 • 1 1 I I as m WMm ibubS a.t o,m Figure 35. Spectral analysis results illustrating Milankovitch cyclicity in the Wilkins Peak Member. Results based on analysis from Blacks Fork-1 and Currant Creek-1. 93 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. description of the Green River data set in that this lumped noise may represent the sum effects of a number of aperiodic, non-Milankovitch phenomena. In the Tipton, the limited depositional period does not allow identification of the 404 k.y. long eccentricity. The characteristic bimodal pattern o f the short eccentricity cycle with modes at 123 and 96 k.y. displays well-defined low frequency peaks. Identification of the short eccentricity provides a good fit for the placement of the other predicted cycles. There are strong multi-modal peaks evident for the precession, and an indication of signals for the half-precession. The Wilkins Peak series is extensive enough to resolve the long eccentricity. Spectral results from a more basinal facies in Currant Creek-1 (Figure 35) illustrate two appropriate peaks for the eccentricity cycles as defined by Fischer et al. (2004). Aligning the predicted values with the eccentricity provides a good fit to a single peak for the precession, a smaller one for the half-precession, and a weak obliquity. In the Blacks Fork-1 core, the precessional peaks are not only multiplied but appear displaced. The reason for this is that sedimentation in the silty mudflat facies was more rapid compared to the oil shales and introduced variability that is recorded as noise in the spectra, especially at higher frequencies. Correlation by Fischer et al. (2004) of these Milankovitch periods to most of the Tipton and Wilkins Peak argon dates defined by Smith et al. (2003) further confirms the traditional orbital-derived time-scale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although variability exists between individual precessional and eccentricity cycles, consistent cyclical patterns defined from log properties, lithology, and oil- yields throughout the Tipton and Wilkins Peak confirm a continuous orbital imprint. Discussion Although variability exists between individual precessional and eccentricity cycles, consistent cyclical patterns defined from log properties, lithology, and oil- yields throughout the Tipton and Wilkins Peak confirm a continuous orbital imprint. The time-series spectra defined from the statistical correlation with oil-yield confirms the suite of Milankovitch cyclicity. Documentation of the short- and long- eccentricity from the spectral analysis is interpreted to verify the occurrence of the precessional cycle. Furthermore, the approximate 5:1 bundling of the short- eccentricity verifies the occurrence of the precessional cycle, consistent with the approximate 21 k.y. depositional periodicity defined from varves. The consistent, well-pronounced Milankovitch imprint indicates that orbital cyclicity provided significant influence on lake conditions throughout Tipton and Wilkins Peak deposition. Each precessional cycle began with increased precipitation compared to evaporation, and is defined as the rainy phase that led to elevated lake levels. Then, during the dry precessional phase, net moisture decreased with lower precipitation, and a similar or increased evaporation that resulted in lower lake levels. 95 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Litho-Organic Signatures-Applications to Cyclicity Cyclical variations in oil-yield and lithology provide litho-organic signatures that document the sensitive response of the Tipton and Wilkins Peak lake systems and facies to environmental change. Litho-organic signatures represent a combination of patterns, excursions and cyclical trends in lithology, sedimentary features, and oil-yield (organic content). These signatures record changes in net moisture and help reconstruct paleoclimatic and lacustrine conditions, and unravel cyclical versus non-cyclical imprints. The interpretation of these different litho- organic signatures helps define the origin and mechanisms involved in the Tipton and Wilkins Peak cyclicity. Geochemical definitions of these litho-organic signatures and their applications are discussed in Chapter 7. Cvclicitv-Tipton Member In the rainy and dry precessional phases, the respective rise and decline in Tipton lake levels created differences in the lake ecology, water column conditions, and sedimentation, all of which influenced organic accumulation and sedimentation. Distinct but cyclical changes in oil-yield at the precessional time scale confirm the repetitive changes in lacustrine conditions for both the open, overfilled Scheggs and closed, balanced-fill Rife lakes. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cvclicitv-Wilkins Peak Member Changes in precipitation and evaporation controlled the Wilkins Peak playa lake expansion and contraction, and variation in salinity, and sedimentation. At the start of the rainy precessional phase, the mudflat lake expanded to form a perennial playa lake conducive to organic accumulation. Then, during the dry precessional phase, the playa lake shoaled back to shallow, contracted salt pan and mudflat conditions. The oil shale facies grades vertically and laterally into the salt pan and mudflat sediments. In the paleogeographic lake center, litho-organic patterns representing the different lithologic successions ascertain dynamic, climatic-driven deposition during the rainy and dry precessional phases. In comparison to the single basinal depositional sequence described by Eugster and Hardie (1975), these different lithologic successions document a distinct set of climatic and possibly tectonic conditions during playa lake and mudflat deposition (Figure 24). Trona beds are the products of large playa lakes that became increasingly saline through multiple episodes of the accumulation, evaporation, and concentration of brines. Conversely, the absence of trona can indicate the limited development of an expanded and stratified playa lake. Trona may also be absent because it was re-dissolved or eroded after deposition, or because it occurs in a laterally equivalent interval. Directly above the oil shale facies, organic-lean carbonates, which are products of shallow, oxygenated lakes with limited brine concentration and detrital input, represent an intermediate water depth between the expanded playa and contracted mudflat lakes. 97 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. At the top of some precessional cycles, there is a gradational increase in oil-yield to as much as 5-8 gallons/ton, which indicates the onset to the next rainy phase. The different litho-organic patterns defined from Fischer assay oil-yields further indicate distinct paleoclimatic histories for individual precessional cycles. These patterns help define the onset, duration, and intensity of the rainy precessional phase, and moisture availability during mudflat deposition (Figure 25). Cycles with an organic-rich basal mudstone instead of oil shale and trona indicate limited net moisture and playa lake development. The thick, low-yield, double, and climbing patterns indicate an extended rainy phase that sustained oil shale deposition. The thin, high and low oil-yield patterns record short-lived rainy phases. The variation in oil shale thickness documents differences in the duration of the playa lake and length of the rainy precessional phase. For example using a 120 pm varve, the 1.0 ft of oil shale in cycle 24 is approximately equivalent to 2,540 years of playa lake deposition, and the 6.2 ft of oil shale in cycle 22 represents 15,750 years. Throughout many of the Wilkins Peak 100 k.y. eccentricity bundles, precessional cycles display an alternating “wet, dry, and intermediate” litho-organic character. “Wet” precessional cycles generally contain a thick oil shale, and trona, and the mudflat facies has oil-yields of 1-2 gallons/ton or more (Figure 29). “Dry” cycles display the following characteristics: (1) thin oil shales, (2) trona beds that are thin or absent, (3) an organic-barren, silty mudflat facies, (4) usually adjacent to eccentricity boundaries, and (5) often greater than 15-20 ft thick. “Intermediate” cycles usually display a typical succession of oil shale, trona, and mudstone that is 98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. near average cycle thickness, and oil-yields in the mudflat of approximately 1 gallon/ton. These alternating wet-dry precessional patterns are found in eccentricity cycles D, E, G, H, I, J, K, L and N in Blacks Fork-1 (Figure 21). The wet-dry litho- organic pattern is difficult to detect in eccentricity cycles near the Tipton - Wilkins Peak and Wilkins Peak - Laney boundaries (Eccentricity cycles A, B, C, 0 , P, and Q), which represent a more moist setting. In the mudflat facies, subtle litho-organic signatures defined by differences in lithology, sedimentary features and oil-yields identify depositional variations that resulted from changes in precipitation and evaporation during the dry precessional phase. Brecciated to massive mudstones with negligible oil-yields indicate low precipitation-evaporation ratios that define a “dry mudflat” microfacies. Deposition was dominated by subaerial conditions, desiccation, aeolian transport, and limited seasonal flooding that provided short-lived, shallow, ephemeral lakes. This microfacies, which is most common in the Middle Wilkins Peak, is often associated with “dry” precessional cycles. In contrast, the “wet mudflat” microfacies consists of massive to laminated marlstones with oil-yields of 1-2 gallons/ton or more. Mudflat deposition consisting of micritic muds was dominated by stable, primarily subaqueous conditions that resulted from higher precipitation-evaporation ratios. The “wet mudflat” microfacies is common in the lower Wilkins Peak due to the topographically enhanced drainage and retention of water. In the middle Wilkins Peak, the “wet mudflat” is associated with “wet” precessional cycles, or the oil shale-mudflat transition. These mudflat microfacies are modified from formal 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. descriptions by Hardie et al. (1978) and Warren (1986) in order to help identify paleoclimatic and depositional signatures. Silt and fine-grained sand in “dry mudflats” are derived from distal tongues of ephemeral, braided streams and reworked by aeolian transport. Sheetwash sediments were deposited from rapid, episodic flooding that delivered distal pulses of detrital sediments from the sparsely vegetated playa fringes (Van Houten, 1964; Hardie et al., 1978). Fine-grained cross-bedded sands support the occurrence of thin, ephemeral stream deposits formed under shallow water (Picard and High, 1972). Some laminated siltstones may reflect the existence of ephemeral mudflat lakes. Sparse occurrences of biogenic traces may record the episodic input of relatively freshwater. The burrowing probably originated from the transport and colonization of invertebrates that were associated with the rapid flooding and short lived expansion of a mudflat lake. Yet, the overall absence of biogenic structures indicates that mudflat conditions were dominated by brine-rich groundwater and short-lived alkaline lakes that were rarely suitable for invertebrate burrowers. Subaerial desiccation and mud-cracking may have partially erased the limited record of biogenic traces. The thick eccentricity boundaries appear to represent periods of extended aridity, yet increased sedimentation. The thick, brecciated, dolomitic or silty mudstones represent periods of below-average precipitation with sporadic seasonal flooding, lake evaporation and desiccation, and evaporative pumping. This process resulted in the precipitation of calcareous mudstone at a greater rate than the oil shale 100 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. facies. In addition, distal tongues of detrital input from sporadic flooding contributed to the increased sedimentation rate. Oil-yields provide a proxy for lake level and changes in water depth. Furthermore, mudcracks and cross-bedding, and other lithologic and sedimentary properties compliment oil-yields to define small variations in water depth. Individual mudflat microfacies can be used to identify variations in precipitation and evaporation throughout an individual precessional or eccentricity cycle. These litho- organic signatures provide a foundation for additional interpretation of the orbital imprint presented in the following chapters. Long-Term Eccentricity and Sub-Milankovitch Cyclicity In the Wilkins Peak, identification of the 400 k.y. eccentricity cycle is based on likely packages o f 100 k.y. cycles consisting o f thick low-yield oil shales. This pattern is seen in Blacks Fork short eccentricity cycles 9-14, 29-34 and 59-64. Higher yield oil shales usually occur between these packages (Figures 21 and 28). Throughout the Wilkins Peak, the changing thickness and yield of the oil shale facies may reflect moisture availability related to the climatic-derived effects of the long- eccentricity. The approximate 1.6 m.y. Wilkins Peak interval and apparent superbundle boundaries limit the manifestation of 400 k.y. cycles. The proposed 700 k.y. superbundle boundary in the Wilkins Peak could represent episodic detrital tongues, or a cyclical event. When these superbundles were proposed by Roehler (1993) an orbital mechanism was unavailable. 101 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Subsequently, Olsen and Kent (1999) described a 700 k.y. eccentricity in the Newark Basin representing a longer-period modulation related to the behaviour of the inner planets. In addition, Wing et al. (1998) described a late Paleocene to early Eocene cool-warm-cool climatic oscillation in the Rocky Mountain region that may equate to an approximate 700 k.y. periodicity. Additional work is required to characterize this potential cyclicity, and evaluate the relationship of its frequency domain to orbital cyclicity. The potential 700 k.y. cyclicity may have contributed to the arid imprint associated with eccentricity cycles G and H. Half-Precessional Cycles. The organic enrichment in the middle of some Tipton and Wilkins Peak precessional cycles suggests a mid-cycle increase in net moisture. The relatively abundant and consistent record of this half-precessional event in both members implies a cyclical mechanism. The occurrence of half-precessional cycles is consistent with previous studies that have identified 10-12 k.y. sub-Milankovitch cycles (Willis et al., 1999). An approximate 11 k.y. cycle over the past million years has been resolved at DSDP sites in the North Atlantic and equatorial Pacific (Hagelberg et al., 1994). These cycles are recorded as productivity events, and as increased deposition of carbonate, opal, and terrigenous components. Half-cycle precipitation events are best recorded in the brackish-to- hypersaline lake systems of the Rife and Wilkins Peak. In these lakes, a small increase in net moisture could have contributed to lake expansion and enhanced the accumulation of organic matter. Descriptions of carbonate partings in Wilkins Peak trona beds at the basin margin (Bradley and Eugster, 1969) may also represent half- 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. precessional precipitation events. The origin and orbital imprint of these cycles is further discussed in Chapter 7. In contrast to these Wilkins Peak half-cycles identified by an organic enrichment, Pietras et al. (2003) proposes that the previously identified precessional cycles may actually represent a 10 k.y. cyclicity based on 40Ar/3 9 Ar ages. He attributes this cyclicity to either a potential orbital-forced mechanism, or tectonic modification of drainage. Based on the identification of Tipton and Wilkins Peak half-cycles in this study, Roehler (1991 and 1993) may have over-estimated the number of Wilkins Peak precessional cycles. Some of Roehlers’ precessional cycles that contain a thin, poorly defined, low-yield oil shale and reduced mudflat interval may actually represent half-precessional cycles. Re-evaluation of the Wilkins Peak cyclicity, as represented in Blacks Fork-1, indicates that there may only be about 65 cycles with a definite precessional period. Century-Level Cycles. The occasional thin, organic-rich bands o f mudstone in the Wilkins Peak mudflat facies may represent cycles that are associated with century- level precipitation events. These appear to have originated from a sudden expansion of the ephemeral mudflat lake, which facilitated deposition of laminated mudstone. These expanded, possibly stratified, but relatively short-lived mudflat lakes were smaller and more susceptible to environmental change compared to the playa lakes. As the precipitation event diminished, the lake quickly contracted to a shallow, subaqueous mudflat setting. 103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In silty, “dry mudflats,” thin, dark-green mudstones (<0.1 ft) may also indicate short-lived precipitation events. Other precipitation events that may represent century-level cycles include occasional thin oil shales in trona and thin 8lsO excursions in the Upper Wilkins Peak. These negative 51 8 0 anomalies suggest abundant snowfall in the mountains surrounding paleolake Gosiute (Norris et al., 1996 and 2000). Because the record of these century-level precipitation events is sporadic, it is difficult to ascertain if they were cyclical, periodic, or random. If cyclical, these precipitation events may have only been recorded in mudflat settings in which small to moderate amounts of additional moisture could modify sedimentation and overcome the threshold for organic accumulation. The length of these precipitation events is difficult to define because of the gradation of lithology and organic content. Based on a 120 pm varve typical of oil shales, these bands potentially represent a 600-year cycle as described in the Laney Member (Fischer and Roberts, 1991). However, an approximate 200-year cycle, defined by a 300 pm varve more realistically corresponds to the organic-rich mudstone. These century-level events may correlate to the widespread occurrence of an approximate 200-year cycle that is related to variations in solar irradiance (Leventer et al., 1996; Anderson, 1992). Studies support a 200-year solar-oceanic link that affects global sea surface temperatures, storm intensity, and atmospheric temperatures (Peterson et al., 1991; Tinsley, 1994). Additional identification of these century-level events is required to determine their duration and origin. 104 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Variations in Milankovitch Cycles - Tipton and Wilkins Peak Tipton and Wilkins Peak precessional and eccentricity cycles in Blacks Fork- 1 and nearby coreholes document considerable variations in the thickness, and litho- organic properties, indicating a “noisy” cyclical record. Differences in thickness and oil-yields between individual Tipton precessional cycles are related to factors associated with organic accumulation and sedimentation. Wilkins Peak precessional cycles display variability in their thickness, and lithologic and oil-yield patterns due to the sensitivity of the playa lake and mudflat to changing environmental signals. A range of sedimentation rates likely occurred between the oil shale and mudflat facies, and between individual mudflat intervals. A closer evaluation of the dimensions and properties of these cycles identifies a hierarchy of cyclical and non-cyclical processes that can explain most of the variations in precessional cycles. These include: (1) interaction between short- and long-term cyclicity, especially the precession index, (2) variations in lake systems and facies related to regional paleoclimatic changes and tectonic activity, and (3) episodic depositional distortions. Precession Index and Short- and Long-Term Cyclicity. When precessional cycles are placed into 100 k.y. precessional-eccentricity bundles, a pattern for much of the cyclical variation, especially in the Wilkins Peak, becomes evident. The modulation of the precession by the eccentricity and the resulting changes in the magnitude of seasonality affect the precipitation-evaporation ratio (Berger, 1988). This influenced the size, duration, and chemistry of the playa and mudflat lakes. This dynamic affected the extent and nature of oil shale, trona, and mudflat deposition, which 105 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. controlled the lithologic and oil-yield patterns, and the resulting cycle thickness (Figure 29). These differences are often recorded as the alternating “wet, intermediate, and dry” precessional imprint that occurs throughout most eccentricity cycles. These variations are relatively subdued in the perennial Tipton lake(s). The character of Wilkins Peak precessional cycles is also a product of short- and long-term cyclicity. The low oil-yields in eccentricity cycles C, G and M may represent boundaries that are associated with the approximate 400 k.y. eccentricity cycle (Figure 21). The apparent 700 k.y. superbundle boundaries contribute to mudflat intervals with a poorly-developed oil shale facies. Precipitation events associated with the half-precessional and century-level cycles contribute to variations in the lithology, oil-yield, and cycle thickness. Paleoclimate and Tectonics. An evolving paleoclimate, combined with tectonic derived structural-topographic modifications of the lake basin, also contributed to cyclical variations (Figure 21). An east-to-west structural tilting of the greater Green River Basin at the end of the Lower Wilkins Peak reduced drainage and lake size (Roehler, 1993). Deposition during the Lower Wilkins Peak occurred during a period of decreasing moisture availability between the Tipton and Wilkins Peak. The reduced oil shale thickness associated with precessional cycles 30-40 appears to represent a period of lowest net moisture. Larger amounts of oil shales in eccentricity cycles P and Q in the upper Wilkins Peak are derived from increased lake inflow related to intertwined tectonic and more moist paleoclimatic conditions (Surdam and 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Stanley, 1980; Roehler, 1993). Paleoclimatic changes are both local and regional, and are separate from orbital-derived climatic changes. Episodic Depositional Distortions. Episodic depositional distortions are non- cyclical events and processes that alter the uniform repetition of cyclical organic accumulation and sedimentation derived from orbital forcing. These distortions originate from intra-basinal, regional, and globally derived processes that can be near instantaneous or longer-term events. The effects of episodic distortions on the cyclical record include variations in lithology, oil-yields, and the thickness of the entire cycle or an individual facies within the cycle. These depositional distortions influence the continuity and apparent length of cycle deposition. The effect of episodic depositional distortions varies throughout the Tipton and Wilkins Peak, depending on variations in water depth and lacustrine facies, tectonic activity and paleoclimatic conditions. These distortions may have also erased parts of the cyclical record. In the Tipton, episodic depositional distortions primarily consist of sediment dilution, volcanic ash, rapid non-cyclical changes in water column conditions, and short-term climatic effects, all of which lead to differences in sedimentation rate and organic occur (Table 7). Episodic depositional distortions are most effectively recorded during Tipton lake lowstands, usually as rare but sporadic thin bands of mudstone, siltstone, or dolomite. Detrital input and possible oxygenation associated with the Farson Sandstone contributed to reduced oil-yields and poorly defined precessional boundaries in the upper Scheggs and lower Rife. 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Process/Event Effect Depositional Disruption/Imprint Example Volcanism Ash Deposits Volcanic Tuffs & Ash layers A sh-Nutrient Input-Productivity S edim ent Diluted Oil Shales Cycle 20 C ooler Clim ate O rganic Rich Thicker Oil Shales C ycle 25? Flooding Events O rganic M atter Dilution V ariable Cycle thickness Farson Sandstone Detrital Influx O rganic-Lean Cycle Intervals Cycles 35 -3 6 Event Sedim entation Distal Detrital Tongues O rganic-Barren Partings (Precipitation Pulses) Short-Term M udflat Lakes S andstone & Silt Layers C onglom erates, Lenses C arbonaceous Lam ina Localized Sedim entation Algal Lim estones Local Lithological Variations C ycle 13 C hem ical Deposition Basin Floor Flooding Phosphate & Chert Bands W ilkins P eak Mudflat G roundw ater Pumping Dolomite Erosion/Dissolution W ind Erosion Dry Mudflat Variations in M udflat Thickness W ilkins P eak Mudflat Dissolution of Trona R educed Cycle Thickness Diagenesis Diagenetic C arbonates Variations in M udflat Thickness Shortite Recrystalization Tectonics & Subsidence Shift in Depositional Center Thicker/Thinner Oil Shales Cycles 1-11 vs. 12-67 C hange in W a te r Inflow M udflat O rganic Content Cycles 68 -7 5 Short-Term Clim atic Events Dolomitic Bands Tipton Rapid C hanges W a te r Colum n Bioturbation Burrowing, Lam ina Disruption M asks Sedim entary-G eochem ical C ycle 24 Signal Table 7. Examples of episodic depositional distortions and their depositional disruption and imprint described for the Tipton and Wilkins Peak Members. 108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. with the Farson Sandstone contributed to reduced oil-yields and poorly defined precessional boundaries in the upper Scheggs and lower Rife. Episodic distortions in the Wilkins Peak include detrital tongues, volcanic ash, storm deposits, diagenesis, chemical deposition, short-term climatic events, bioturbation, depositional hiatus’, erosional surfaces, and localized variations in sedimentation. In addition to eccentricity boundaries, organic-barren silty and sandy intervals throughout the Wilkins Peak may indicate detrital influx. Episodic depositional distortions related to short-term tectonic events include the periodic failure of a basin outlet or drainage network instability that sporadically affected lake inflow (Pietras et al., 2003). The expanding and contracting shallow playa lake and mudflat easily record episodic depositional distortions. The depositional record of the Tipton and Wilkins Peak are products of the interaction between cyclicity of various frequencies, regional climatic changes, tectonic activity, and episodic deposition. The identification and removal of non- cyclical climatic, tectonic, and depositional effects is important in the reconstruction of the orbital-driven climatic signal, and its transfer into the sedimentary record of these different lake systems. Because of these variations, a complete interpretation of lacustrine cyclicity requires an understanding of the following: (1) the depositional facies, (2) the lateral stratigraphic variability of the facies, and (3) the imprint from lower and higher frequency cycles. It is essential to eliminate episodic depositional distortions by studying the paleogeographic lake center. Overall, the Tipton and 109 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Wilkins Peak contain a relatively limited record of episodic sedimentation, erosion, bioturbation, and diagenesis that distorted the orbital signal. Therefore, these intervals provide a good setting for evaluating the variations in lithologic and geochemical signatures derived from orbital signals. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 5 GEOCHEMICAL EXPRESSION AND PROPERTIES OF CYCLICITY - TIPTON MEMBER Introduction This chapter describes the geochemical expression of precessional cycles in the Scheggs and Rife Beds of the Tipton Member, as represented in Blacks Fork-1. Geochemical and petrographic results combined with Fischer assay oil-yields and lithologic descriptions are used to define the cyclical expression. Cyclical lacustrine processes are described that are the result of orbital-driven climatic variations that occurred during deposition of the freshwater and brackish-saline phases of paleolake Gosiute. Results Although the Tipton Member is lithologically uniform, precessional cycles can be defined from weight percent total organic carbon (TOC) and Fischer assay oil-yields (Figure 36). Cyclical patterns in Rock-Eval pyrolysis Hydrogen Index (HI), and the maceral, pyrolysate, isotopic, and biomarker compositions, which are sometimes subtle, parallel the organic content. The geochemical expression o f Rife precessional cycles is usually magnified compared to those in the Scheggs Beds. Fischer assay oil-yields and geochemical summaries of rock, kerogen, and solvent extract data for individual cycles are listed in Tables 8-10. This data includes IT 18 TOC, HI, carbon and oxygen isotope composition (8 C and 8 O), weight percent total sulfur, and selected parameters from gas chromatography (GC) and 111 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 36. Precessional cycles in the Tipton Member, Blacks Fork-1 are defined from Fischer assay oil-yield and total organic carbon patterns. Cycles consist of an organic-rich base and a reduced organic content in the remainder of the cycle. Although organic content varies throughout the Scheggs and Rife Beds, a similar two-stage cyclical pattern occurs for most cycles. Boundaries of individual cycles that are based on organic content are generally consistent with sonic and gamma log signatures. Tipton Cycle Depth Interval Oil-Yield Tipton Cycle Depth Interval Oil Yield (Bed/Cycle) (Feet) (Gallons/Ton) (Bed/Cycle) (Feet) (Gallons/Ton) Rife 7 1531.0-1532.0 15.9 Scheggs 7 1628.2-1629.2 18.8 1532.0-1533.0 16.6 1929.2-1630.2 17.3 1533.0-1534.0 15.2 1630.2-1631.2 21.1 1534.0-1535.0 17.6 1631.2-1632.2 26.3 1535.0-1536.0 8.8 1632.2-1633.5 24.3 1536.0-1537.0 11.4 1537.0-1538.0 12.0 1538.0-1539.0 13.0 Scheggs 4 1645.6-1646.6 7.4 1539.0-1540.0 31.5 1646.6-1647.7 10.7 1540.0-1541.1 32.9 1647.7-1648.8 14.8 1648.8-1649.9 17 1649.9-1650.9 18.6 Rife 6 1541.1-1542.2 23.4 1542.2-1543.3 21.0 1543.3-1544.4 23.3 Scheggs 3 1650.9-1652.0 10.5 1544.4-1545.5 18.7 1652.0-1653.2 11.6 1545.5-1546.7 19.7 1653.2-1654.3 12.2 1546.7-1547.7 30.6 1654.3-1655.4 20.4 1547.7-1548.7 31.8 1655.4-1656.5 34.2 Rife 5 1548.7-1550.0 17.6 1550.0-1551.0 25.5 1551.0-1552.0 17.3 1552.0-1553.5 12.0 1553.5-1555.0 27.3 1555.0-1555.5 30.1 1555.5-1556.6 30.2 Rife 3 1560.8-1562.6 7.7 1562.6-1563.8 3.2 1563.8-1565.2 4.7 1565.2-1566.7 8.1 1566.7-1567.7 10.2 1567.7-1568.7 19.8 1568.7-1569.7 17.6 1569.7-1570.7 11.6 1570.7-1571.7 12.5 1571.7-1572.2 27.6 Rife 1 1582.1-1583.1 9.3 1583.1-1584.1 10.9 1584.1-1585.5 8.3 1585.5-1586.5 19.0 1586.5-1587.5 13.1 Table 8 . Fischer assay oil-yields for selected precessional cycles in the Scheggs and Rife Beds, Tipton Member; Blacks Fork-1. See Figure 36. Complete Fischer assay oil-yields for the Tipton Member in Blacks Fork-1 are listed in Appendix 3. 113 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bed/Cycle Depth TOC H I 81 3 C Kerogen S1 3 C Carbonate 51 8 0 Carbonate Total Sulfur Tmax (Feet) w t. % mg HC/g OC %. %. w t. % °c Rife 7 1531.00 8.54 856.0 -33.6 6.1 -8.9 445 Rife 7 1532.00 6.80 850.0 -31.6 4.9 -7.8 Rife 7 1534.00 7.11 846.0 -31.7 0.8 441 Rife 7 1535.00 6.89 804.0 -31.1 7.5 -6.9 437 Rife 7 1535.90 4.66 676.0 -30.7 6.0 -6.9 0.33 431 Rife 7 1537.00 4.45 786.0 420 Rife 7 1537.90 5.78 776.0 -30.3 8.3 -4.6 432 Rife 7 1538.70 6.04 793.0 -30.8 9.3 -4.0 0.22 429 Rife 7 1539.00 14.48 747.0 445 Rife 7 1539.10 14.29 843.0 -33.9 0.46 446 Rife 7 1539.55 8.49 922.0 -33.5 0.28 442 Rife 7 1540.00 23.07 701.0 -34.1 9.7 -3.3 0.50 442 Rife 7 1540.45 -33.6 8.8 -3.7 Rife 6 1541.30 15.58 759.3 -33.7 8.4 -3.2 0.34 448 Rife 6 1541.70 12.42 701.3 -32.8 443 Rife 6 1543.20 5.99 805.0 -31.1 9.2 -5.7 0.52 430 Rife 6 1544.30 9.03 721.2 -30.9 9.5 -2.7 434 Rife 6 1545.15 10.54 588.3 -29.7 9.1 -5.5 0.55 423 Rife 6 1546.05 10.09 852.0 424 Rife 6 1546.45 10.32 733.0 417 Rife 6 1547.00 16.53 814.0 -31.1 9.8 -1.0 431 Rife 6 1547.35 13.89 821.0 -33.0 0.64 442 Rife 6 1548.00 27.78 937.5 -34.3 5.6 -2.5 7.33 448 Rife 6 1548.00 30.7 650.0 440 Rife 6 1548.20 12.51 832.1 -32.8 0.32 443 Rife 5 1549.00 6.81 863.0 -29.6 8.2 -2.5 441 Rife 5 1550.90 13.41 764.0 -29.9 5.6 -6.7 439 Rife 5 1552.00 5.90 859.0 -31.2 436 Rife 5 1553.10 11.78 958.0 -34.0 7.2 -1.3 446 Rife 5 1554.00 9.10 894.0 -30.3 Rife 5 1554.80 17.62 797.0 -30.6 434 Rife 5 1555.55 18.45 825.0 -30.3 434 Rife 5 1556.05 18.85 697.0 429 Rife 5 1556.40 9.74 812.0 -29.9 10.9 -1.5 436 Rife 5 1556.50 8.57 866.0 429 Rife 3 1563.00 2.10 636.0 -30.5 6.5 -1.6 0.69 435 Rife 3 1565.10 2.88 733.3 -30.2 7.5 -0.9 0.89 436 Rife 3 1567.45 4.70 784.0 -30.8 7.3 -1.6 438 Rife 3 1568.15 10.83 703.0 434 Rife 3 1568.85 10.56 797.3 -29.4 435 Rife 3 1570.10 6.27 755.3 -30.3 439 Rife 3 1570.90 6.51 767.0 0.75 440 Rife 3 1571.90 12.92 964.0 -30.5 8.1 -1.9 0.26 445 Table 9. Geochemical summary of rock and kerogen properties for Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. Results include TOC, Rock-Eval pyrolysis Hydrogen Index (HI), and 51 3 C and 61 8 0 data for kerogen and the carbonate matrix. 114 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bed/Cycle Depth TOC HI 81 3 C Kerogen 61 3 C Carbonate 51 s O Carbonate Total Sulfur Tmax (Feet) w t. % mg HC/g OC % 0 % > %. w t. % °c Rife 1 1583.15 6.85 786.0 -30.3 437 Rife 1 1583.65 5.81 721.0 437 Rife 1 1584.50 4.84 683.0 -31.2 437 Rife 1 1585.00 -30.6 Rife 1 1585.80 8.01 772.0 438 Rife 1 1586.40 7.46 760.0 435 Rife 1 1587.15 5.30 1019.0 -31.7 443 Scheqqs 7 1628.90 9.75 917.0 -30.5 7.0 -0.3 445 Scheggs 7 1630.00 6.01 887.0 -30.0 4.7 -1.8 2.16 434 Scheggs 7 1631.00 10.52 871.0 431 Scheggs 7 1631.55 9.28 919.0 -31.3 2.91 441 Scheqqs 7 1632.00 11.70 917.0 -31.0 7.7 -1.2 2.59 445 Scheqgs 4 1645.70 2.44 589.8 -30.3 2.5 -2.2 438 Scheqqs 4 1646.10 3.42 763.0 434 Scheqqs 4 1646.50 4.25 739.0 -29.2 430 Scheqqs 4 1646.90 6.55 643.4 428 Scheggs 4 1648.00 6.12 748.0 -27.2 Scheqqs 4 1648.80 7.76 686.0 -27.6 1.6 -3.8 431 Scheggs 4 1650.00 9.30 951.8 -29.5 3.9 -2.2 435 Scheqqs 4 1650.60 9.15 748.0 -28.9 434 Scheqgs 3 1651.85 7.42 669.0 -29.1 1.5 -5.8 2.54 385 Scheggs 3 1652.95 6.70 693.7 -30.1 1.8 -5.5 2.11 439 Scheqqs 3 1654.10 7.07 738.3 -30.8 439 Scheggs 3 1654.40 6.30 746.5 1.77 440 Scheqqs 3 1654.55 7.40 764.3 -31.1 2.5 -3.1 439 Scheggs 3 1655.00 9.54 998.0 430 Scheggs 3 1655.60 10.68 990.0 -30.9 1.4 -3.2 2.67 442 Scheggs 3 1656.10 10.77 986.0 -30.0 4.5 -3.0 2.63 437 Scheggs 3 1656.50 11.29 943.0 0.3 -2.7 426 TOC - Weight Percent Total Organic Carbon H I - Hydrogen Index Rock-Eval P'rrolysis Tmax - Rock-Eval Pyrolysis Table 9 (Continued). Geochemical summary of rock and kerogen properties for Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. 115 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bed/Cycle Depth s1 3 c S aturate 613C A rom atic P ristan e/ Phytane C 29/C 27 S teran es S teranes/ H opanes G am m acerane/ H opane C19/C23 Tricyclic T erpanes C23/C 24 Tricyclic T erpanes C26/C 25 Tricyclic T erpanes C24Tetracyclic/ C2s Tricyclic T erpanes (Feet) %. Rife 7 1534.90 •31.8 •31.3 0.40 5.90 0.89 0.56 0.06 1.29 2.80 0.08 Rife 7 1535.80 •33.6 -30.9 0.52 Rife 7 1537.90 •36.5 •30.8 2.84 0 .2 2 0.58 0.09 1.17 2.70 0.14 Rife 7 1539.00 •35.7 •31.2 0.56 4.81 0.63 0.86 0.00 1.29 4.40 0.21 Rife 7 1540.00 •34.6 •32.7 0.61 11.20 3.53 0.28 0.11 0.99 1.80 0.41 Rife 6 1541.30 •34.0 •32.0 0.55 5.63 1.37 0.54 0.09 1.04 2.14 0.26 Rife 6 1543.20 -37.1 -30.7 0.49 2.63 0.24 1.18 0.12 1.08 2.54 0.21 Rife 6 1545.05 •35.8 -30.7 0.42 2.80 0.30 1.64 0.09 1.07 2.98 0.12 Rife 6 1547.80 -34.0 •32.9 0.33 11.90 4.26 0.47 0.11 0.99 1.78 0.41 Scheggs 7 1630.00 •31.7 -30.4 0.23 2.06 0.73 1.41 0.06 1.13 1.72 0.34 Scheggs 7 1632.00 -30.8 -31.1 0.21 3.17 1.55 2.75 0.06 1.01 1.55 0.56 Scheggs 4 1646.10 -31.5 -30.6 0.39 1.69 1.27 1.05 0.09 0.99 1.18 1.08 Scheggs 4 1650.50 -31.6 -30.3 0.29 1.23 1.03 0.42 0.13 1.03 1.22 1.62 Scheggs 3 1651.90 •32.6 -30.5 0.32 1.03 1.17 0.41 0.13 1.17 1.09 2.55 Scheggs 3 1654.50 -31.7 -30.7 0.25 1.77 3.47 1.54 ND 0.99 0.86 1.06 Scheggs 3 1656.10 -31.9 -31.1 0.24 2.18 3.24 1.54 0.06 1.11 0.91 1.09 Table 10. Geochemical summary of extractable organic matter (bitumen) for Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. Results include carbon isotope composition of the saturate and aromatic fractions, and summary of select biomarker ratios. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. gas chromatography-mass spectrometry (GCMS). Tables 11-14 provide complete geochemical data, which includes all Rock-Eval pyrolysis data, maceral and isotopic compositions, and GC and GCMS results. Additional geochemical data and results are listed in Appendix 4. The primary geochemical pattern in Tipton precessional cycles consists of an organic-rich base and a reduced but variable organic content in the remainder of the cycle. A sharp reduction of up to 60% in organic content occurs directly above the 0.5-3.3 ft cycle base (Figures 36-44). Although the range in organic content can significantly vary between individual cycles and throughout the Tipton Member, this distinct two-stage signature in organic content occurs in almost all precessional cycles (Figure 36). In some precessional cycles, other patterns in organic content occur, including: (1) thin, high TOC zones within the organic-rich basal oil shale; (2) a half-precessional enrichment; (3) a small gradational increase in organic content at the top of the cycle; and (4) a reduced organic content in mudstone in the upper parts of some cycles (Figures 37-41, and 44). Unlike oil-yields that are averaged over intervals of 0.5-1.8 ft, TOC values help define short temporal variations in organic content throughout individual cycles. Kerogen composition generally parallels the two-stage cyclical pattern in organic content. The organic-rich cycle base contains Type I kerogen with HI values that are usually greater than 800 mg HC/g OC. Intervals with a reduced organic content above the cycle base mostly contain a Type I-I/II kerogen with HI values that are usually less than 700-800 mg HC/g OC. Half-precessional zones 117 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1 630 1631 1632 1633 TOC wt.% Oil Shale: M d-dk grayish b ro w n , faint to distinct lam inae. Oil Shale: Dk-md b ro w n ish g ra y , som e light b ro w n is h g ra y in lo w e r p a rt. 1 6 3 0 .5 - 1 6 3 1 .5 grayish b ro w n . Oil Shale: Tan to dark b ro w n ish g ra y , som e blade, dolomitic. Distinct to faint lam inae, ra re thin b ands. H I mg HC/g OC 13C Kero per mil 13C Carb per mil Total Sulfur wt.% 3 5 o 1 5 soo 1 0 0 0 -3 5 -2 5 0 Figure 37. Lithologic description, oil-yield and geochemical patterns versus depth for Scheggs cycle 7 (1628.2-1633.5 ft), Blacks Fork-1. Cycle base contains elevated oil-yields. The 1 3 C enriched carbonate matrix suggests methanogenesis within the sediments. Samples from cycle base were not available. A4687/+::...:..::...:^^55.759.//////^^ Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ^ m & m s s Figure 38. Lithologic description, and oil-yield and geochemical patterns versus depth for Scheggs cycle 3 (1650.9- 1656.5 ft), Blacks Fork-1. Decrease in organic content and Hydrogen Index (HI) occurs above cycle base. Kerogen in cycle base consists of lamalginite and the pyro lysate contains C5 + aliphatic-rich pyrolysate compared to the overlying interval that consists of a mixed bituminite and lamalginite organic assemblage. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. s-S & S - g l ' l Figure 39. Lithologic description, and oil-yield and geochemical pattern versus depth for Scheggs cycle 4 (1645.6-1650.9 ft), Blacks Fork-1. Systematic decrease in oil-yield and TOC occurs upward to mudstone at the top of the cycle. The organic composition and geochemical properties o f the kerogen in the mudstone are similar to the oil shale. t —* K > O m i\ 098999999999999999999999997999999999^ Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 Oil Y ield Oal/Ton T O C Wt.% HI mg HC/g OC 1 3 C K ero per mil 13C G arb per mil 1 0 O C a rb p er mil T o ta l S u lfu r W t% . = = O B Shale: Dk-md brownish gray some olive gray, dolomitic. = = Oil Shale: Dk-md brownish gray. Thin analcime stringer ert 1533.2. .............= = Oil Shale: Dk brownish gray, dolomitic. = Oil Shale: Dk-md brownish gray. Tan silty tuff at 1536.6- 1536.7. , 1 ....~ ~ Oil Shale: Dk to rare md brownish gray. Brownish-gray tuff at 1S3B.25-1530.65. — ........ .................... Oil Shale: Md-dk brownish gray. 35 0 25 500 1000 -35 -25 0 10 -10 0 0 Figure 40. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 7 (1531.0-1541.1 ft), Blacks Fork-1. Kerogen in cycle base between 1539 and 1541 ft is depleted in 1 3 C. to Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. m is Figure 41. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 6 (1541.1-1548.7 ft), Blacks Fork-1. A thin, organic-rich zone occurs in cycle base suggesting a lacustrine highstand. Above cycle base, the lower organic content equates with a greater proportion o f bituminite and a pyrolysate that contains reduced amounts o f C5 + n-aliphatics compared to internal standard (IS). Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. O il Yield Gal/Ton T O C HI 13C Kero 1 3 C C a rb Wt.% mg HC/g OC perm it perm it 1549 1551 1552 1553 1554 1555 1556 ................— Oil Shale: Md-dk grayish brow n. 1 “tuft stringer at 1549.4 " .:'= = = = Oil Shale: Ok and rare md brow nish gray to som e black. . '= = = = Oil Shale: Dk brow nish gray to md grayish brow n. • = = Oil Shale: Dk-md brow nish to slightly olive gray. 3/4“ brow nish-gray tuff at 1552.8 pyritic stre a k s. .............. ■.■■=== Oil Shale: Dk and som e md brow nish gray, som e black. < < < < < < ■ < < < ■ < < < < < Tuff: Md light grayish brow n, siiy . Contains --------------------------------- , V 9 / .......................... - = Oil Shale: Dk-md brow nish gray to black, faintly laminated. 35 0 20 500 1000 -35 -25 0 10 t o O J Figure 42. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 5 (1548.7-1556.6 ft), Blacks Fork-1. Interval of increased oil-yield and elevated TOC at 1550.9 ft represents a half-precessional organic enrichment. 7 3 CD ■ o - 5 o Q . C o CD Q . ■ o CD C / ) ( J ) o' 3 O O o ■ O c q ' 3. CD CD ■o - 5 o Q. C a o o ■ O -5 o CD Q. ■o CD «£■ 4 jjK - C / ) c / ) Figure 43. Lithologic description, and oil-yield and geochemical patterns versus depth for Rife cycle 3 (1561.7-1572.0 ft), Blacks Fork-1. Note half-cycle organic-enrichment and reduced organic content in upper part o f cycle. 1583 1584 1585 1586 1587 V V V V V V V V V \ V V V V V Tuff .................• = Oil Shale: Dk-md b ro w n , silty oil shale. ..................... .............. . ■ ■ ■ ■ ■ ■ - — - —................. Oil Shale: Black, m assive-lam inated. < < < < < Tuff: Tan. ---------------- " —• = = = = = Oil Shale: Md b row n. V ' V ' V ' V ' V ' V V V v \ V V V V V Tuff: Light b row n. .......... ——= Oil Shale: Black, laminated. ............. = Oil Shale: Black to dk g ray . O il Y ield G a l/T o n T O C HI 1 3 C K e ro W t.% m g H C /g O C p e r m i t 35 0 10 500 1000 -35 -25 125 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4 4 . Lithologic description, a n d oil-yield a n d geochemical patterns versus depth fo r Rife cycle 1 (1582.1- 1587.5 ft). Limited geochemical variations occur compared t o other R ife precessional cycles. T i p t o n D e p t h T O C S 1 S 2 S 3 H I O l T M A X S 2 / S 3 P I S 1 / T O C T o t a l S u l f u r C y c le (Feet) w t. % mg HC/g Rk mg HC/g Rk mg COj/g Rk mg HC/g OC mg COj/g OC °c w t.% R ife 7 1 5 3 1 .0 0 8 .5 4 1 .7 6 7 3 .0 6 1.11 8 5 6 13 4 4 5 6 5 .8 2 0 .0 2 2 1 .0 0 R ife 7 1 5 3 2 .0 0 6 .8 0 8 5 0 R ife 7 1 5 3 4 .0 0 7.11 2.61 6 0 .1 3 0 .7 9 8 4 6 11 441 7 6 .1 1 0 .0 4 3 7 .0 0 0 .8 0 R ife 7 1 5 3 5 .0 0 6 .8 9 2 .3 5 5 5 .3 8 1 .3 7 8 0 4 2 0 4 3 7 4 0 .4 2 0 .0 4 3 4 .0 0 R ife 7 1 5 3 5 .9 0 4 .6 6 3 .0 8 3 1 .4 8 1.41 6 7 6 30 431 2 2 .3 3 0 .0 9 6 6 .0 0 0 .3 3 R ife 7 1 5 3 7 .0 0 4 .4 5 4.01 3 4 .9 7 1 .5 4 7 8 6 35 4 2 0 2 2 .7 1 0 .1 0 9 0 .0 0 R ife 7 1 5 3 7 .9 0 5 .7 8 2 .8 3 4 4 .8 6 1 .4 9 7 7 6 26 4 3 2 3 0 .1 1 0 .0 6 4 9 .0 0 R ife 7 1 5 3 8 .7 0 6 .0 4 3 .0 0 4 7 .9 0 1 .1 6 7 9 3 19 4 2 9 4 1 .2 9 0 .0 6 5 0 .0 0 0 .2 2 R ife 7 1 5 3 9 .0 0 1 4 .4 8 1 .2 5 1 0 8 .1 3 2 .9 0 7 4 7 20 4 4 5 3 7 .2 9 0.01 9 .0 0 R ife 7 1 5 3 9 .1 0 1 4 .2 9 3 .3 8 1 2 0 .4 8 2.21 8 4 3 15 4 4 6 5 4 .5 2 0 .0 3 2 4 .0 0 0 .4 6 R ife 7 1 5 3 9 .5 5 8 .4 9 2 .9 2 7 2 .3 4 1 .2 6 8 5 2 15 4 4 2 5 7 .4 1 0 .0 4 3 4 .0 0 0 .2 8 R ife 7 1 5 3 9 .7 5 8 .4 4 2 .0 8 7 7 .8 4 1 .4 2 9 2 2 17 4 3 6 5 4 .8 1 0 .0 3 2 5 .0 0 R ife 7 1 5 4 0 .0 0 2 3 .0 7 4 .3 2 1 6 1 .7 7 2 .5 6 701 11 4 4 2 6 3 .1 9 0 .0 3 1 9 .0 0 0 .5 0 R ife 6 1 5 4 1 .3 0 1 5 .5 8 4 .4 0 1 1 8 .3 0 2 .9 0 7 5 9 19 4 4 8 4 0 .7 9 0 .0 4 2 8 .2 4 0 .3 4 R ife 6 1 5 4 1 .7 0 1 2 .4 2 4 .5 5 8 7 .1 0 2 .3 3 701 19 4 4 3 3 7 .3 8 0 .0 5 3 6 .6 3 R ife 6 1 5 4 3 .2 0 5 .9 9 3 .5 4 4 8 .2 0 0 .8 8 8 0 5 15 4 3 0 5 4 .7 7 0 .0 7 5 9 .0 0 0 .5 2 R ife 6 1 5 4 4 .3 0 9 .0 3 5 .1 6 6 5 .1 2 0 .7 9 721 9 4 3 4 8 2 .4 3 0 .0 7 5 7 .1 4 R ife 6 1 5 4 5 .1 5 1 0 .5 4 5 .2 3 6 2.01 0 .8 4 5 8 8 8 4 2 3 7 3 .8 2 0 .0 8 4 9 .6 2 0 .5 5 R ife 6 1 5 4 6 .0 5 1 0 .0 9 5 .0 7 8 5 .9 8 1 .2 7 8 5 2 13 4 2 4 6 7 .7 0 0 .0 6 6 5 .0 0 R ife 6 1 5 4 6 .4 5 1 0 .3 2 7 .5 7 7 5 .6 6 1 .4 8 7 3 3 14 4 1 7 5 1 .1 2 0 .0 9 7 3 .0 0 R ife 6 1 5 4 7 .0 0 2 4 .4 2 8 .7 5 8 6 .9 6 1 .0 9 3 5 6 4 431 7 9 .7 8 0 .0 9 3 5 .8 3 R ife 6 1 5 4 7 .1 0 1 6 .5 3 6 .8 0 1 3 4 .5 2 3.31 8 1 4 2 0 4 3 4 4 0 .6 4 0 .0 5 4 1 .0 0 R ife 6 1 5 4 7 .3 5 1 3 .8 9 5 .0 7 1 1 4 .0 5 1 .5 9 821 11 4 4 2 7 1 .7 3 0 .0 4 3 7 .0 0 0 .6 4 R ife 6 1 5 4 7 .8 0 2 7 .7 8 4 .6 4 2 6 0 .4 5 3 .3 0 9 3 8 12 4 4 8 7 8 .9 2 0 .0 2 1 6 .7 0 7 .3 3 R ife 6 1 5 4 8 .0 0 3 0 .7 0 6.21 1 9 9 .5 7 2 .3 6 6 5 0 8 4 5 0 8 4 .5 6 0 .0 3 6.21 R ife 6 1 5 4 8 .2 0 12.51 3 .4 3 1 0 4 .0 9 2 .8 0 8 3 2 2 2 4 4 3 3 7 .1 8 0 .0 3 2 7 .4 2 0 .3 2 R ife 5 1 5 4 9 .0 0 6.81 2 .2 9 5 8 .8 0 1 .5 7 8 6 3 23 441 3 7 .4 5 0 .0 4 3 4 .0 0 R ife 5 1 5 5 0 .9 0 13.41 4 .2 4 1 0 2 .4 8 1 .6 0 7 6 4 12 4 3 9 6 4 .0 5 0 .0 4 3 2 .0 0 R ife 5 1 5 5 0 .9 0 13.41 4 .2 4 1 0 2 .4 8 1 .6 0 7 6 4 12 4 3 9 6 4 .0 5 0 .0 4 3 2 .0 0 R ife 5 1 5 5 2 .0 0 5 .9 0 2 .2 0 5 0 .6 6 0 .7 8 8 5 9 13 4 3 6 6 4 .9 5 0 .0 4 3 7 .0 0 R ife 5 1 5 5 3 .1 0 1 1 .7 8 3.31 1 1 2 .8 8 1 .0 6 9 5 8 9 4 4 6 1 0 6 .4 9 0 .0 3 2 8 .0 0 R ife S 1 5 5 4 .8 0 1 7 .6 2 7 .5 0 140.51 1 .3 9 7 9 7 8 4 3 4 1 0 1 .0 9 0 .0 5 4 3 .0 0 R ife 5 1 5 5 5 .5 5 1 8 .4 5 7 .4 6 1 5 2 .1 4 1 .3 0 8 2 5 7 4 3 4 1 1 7 .0 3 0 .0 5 4 0 .0 0 R ife 5 1 5 5 6 .0 5 1 8 .8 5 5 .3 0 1 3 1 .3 7 1 .5 7 6 9 7 8 4 2 9 8 3 .6 8 0 .0 4 2 8 .0 0 R ife 5 1 5 5 6 .4 0 9 .7 4 3 .1 4 7 9 .0 6 0 .9 6 8 1 2 10 4 3 6 8 2 .3 5 0 .0 4 3 2 .0 0 R ife 5 1 5 5 6 .5 0 8 .5 7 8 6 6 4 3 3 R ife 3 1 5 6 3 .0 0 2 .1 3 0 .7 7 1 3 .5 5 0 .9 4 6 3 6 4 4 4 3 5 14.41 0 .0 5 3 6 .0 0 0 .6 9 R ife 3 1 5 6 5 .1 0 2 .8 8 0 .6 9 2 1 .1 2 0 .6 9 7 3 3 24 4 3 6 3 0 .6 1 0 .0 3 2 3 .9 6 0 .8 9 R ife 3 1 5 5 6 .5 0 8 .5 7 2 .6 2 7 4 .2 2 0 .9 6 8 6 6 11 4 2 9 7 7 .3 1 j 0 .0 3 3 1 .0 0 R ife 3 1 5 6 7 .4 5 4 .7 0 1 .2 5 3 6 .8 5 0 .8 3 7 8 4 18 4 3 8 4 4 .4 0 0 .0 3 2 6 .6 0 R ife 3 1 5 6 8 .1 5 1 0 .8 3 3 .1 6 7 6 .1 3 1 .5 7 7 0 3 14 4 3 4 4 8 .4 9 0 .0 4 2 9 .1 8 R ife 3 1 5 6 8 .8 5 1 0 .5 6 2.51 8 4 .1 9 1.91 7 9 7 18 4 3 5 4 4 .0 8 0 .0 3 2 3 .7 7 R ife 3 1 5 7 0 .1 0 6 .2 7 1 .0 8 4 7 .3 6 0.81 7 5 5 13 4 3 9 5 8 .4 7 0 .0 2 1 7 .2 2 R ife 3 1 5 7 0 .9 0 6.51 0 .9 6 4 9 .9 4 1 .0 3 7 6 7 16 4 4 0 4 8 .4 9 0 .0 2 1 5 .0 0 0 .7 5 R ife 3 1 5 7 1 .9 0 1 2 .9 2 2 .6 7 1 2 4 .5 5 2 .0 7 9 6 4 16 4 4 5 6 0 .1 7 0 .0 2 2 0 .6 7 0 .2 6 R ife 2 1 5 7 2 .3 0 4 .7 0 0 .6 3 3 3 .0 7 0.41 7 0 4 9 4 3 5 8 0 .6 6 0 .0 2 2 0 .0 0 R ife 2 1 5 7 3 .2 0 6 .3 7 3 .2 3 5 2 .2 7 0 .5 7 821 9 4 4 0 9 1 .7 0 0 .0 6 5 0 .7 1 R ife 1 1 5 8 3 .1 5 6 .8 5 1 .2 5 5 3 .8 2 0 .8 5 7 8 6 12 4 3 7 6 3 .3 2 0 .0 2 1 8 .0 0 R ife 1 1 5 8 3 .6 5 5.81 1 .0 5 41.91 0.71 721 12 4 3 7 5 9 .0 3 0 .0 2 1 8 .0 0 R ife 1 1 5 8 4 .5 0 4 .8 4 0 .9 5 3 3 .0 5 1.0 6 6 8 3 2 2 4 3 7 3 1 .1 8 0 .0 3 2 0 .0 0 R ife 1 1 5 8 5 .8 0 8.01 2 .0 6 6 1 .8 3 0 .7 5 7 7 2 9 4 3 8 8 2 .4 4 0 .0 3 2 6 .0 0 R ife 1 1 5 8 6 .4 0 7 .4 6 1 .0 7 5 6 .7 3 0 .8 7 7 6 0 12 4 3 5 6 5 .2 1 0 .0 2 1 4 .0 0 R ife 1 1 5 8 7 .1 5 5 .3 0 0 .8 3 5 3 .9 9 0 .7 8 1 0 1 9 15 4 4 3 6 9 .2 2 0 .0 2 1 6 .0 0 Table 11. Total organic carbon (TOC), complete Rock-Eval pyrolysis and weight percent total sulfur data, Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. T i p t o n D e p t h T O C S 1 S 2 S 3 HI O l T M A X S 2 / S 3 PI S 1 / T O C T o t a l S u l f u r C y c le (Feet) WL % mg HC/g Rk mg HC/g Rk mg COj/g Rk mg HC/g OC mg COj/g OC •c W t.% S c h e g g s 7 1 6 2 7 .5 0 9 .4 7 6 .9 6 7 9 .8 9 1 .2 8 8 4 4 14 4 2 5 6 2 .4 1 0 .0 8 7 3 .0 0 1.11 S c h e q q s 7 1 6 2 8 .9 0 9 .7 5 2.21 8 9 .4 3 1 .7 8 9 1 7 18 4 4 5 5 0 .2 4 0 .0 2 2 3 .0 0 S c h e q q s 7 1 6 3 0 .0 0 6 .0 1 2 .3 8 5 3 .3 1 1 .0 6 8 8 7 18 4 3 4 5 0 .2 9 0 .0 4 4 0 .0 0 2 .1 6 S c h e q q s 7 1 6 3 1 .0 0 1 0 .5 2 3 .3 6 9 1 .5 8 1 .2 7 871 12 431 7 2 .1 1 0 .0 4 4 3 .0 0 S c h e q q s 7 1 6 3 1 .5 5 9 .2 8 2.51 8 5 .3 0 1 .1 0 9 1 9 12 441 7 7 .5 5 0 .0 3 2 7 .0 0 2.91 S c h e q q s 7 1 6 3 2 .0 0 1 1 .7 0 3 .7 3 1 0 7 .2 8 1 .2 2 9 1 7 10 4 4 5 8 7 .9 3 0 .0 3 3 2 .0 0 2 .5 9 S c h e g g s 4 1 6 4 5 .7 0 2 .4 4 1 .1 6 1 4 .3 9 0 .3 5 5 9 0 14 4 3 8 4 1 .1 1 0 .0 7 4 7 .5 4 S c h e q q s 4 1 6 4 6 .1 0 3 .4 2 0 .5 8 2 6 .1 1 0 .3 9 7 6 3 11 4 3 4 6 6 .9 5 0 .0 2 1 7 .0 0 S c h e q g s 4 1 6 4 6 .5 0 4 .2 5 0 .9 7 3 1 .4 1 0 .5 7 7 3 9 13 4 3 0 5 5 .1 1 0 .0 3 2 3 .0 0 S c h e g q s 4 1 6 4 6 .9 0 6 .5 5 1 .6 4 4 2 .1 4 0 .7 6 6 4 3 12 4 2 8 5 5 .4 5 0 .0 4 2 5 .0 4 S c h e q q s 4 1 6 4 8 .8 0 7 .7 6 2 .0 0 5 3 .2 3 0 .5 4 6 8 6 7 431 9 8 .5 7 0 .0 4 2 5 .7 7 S c h e q q s 4 1 6 5 0 .0 5 9 .3 0 2 .7 2 8 8 .5 2 1 .7 9 9 5 2 19 4 3 5 4 9 .4 5 0 .0 3 2 9 .2 5 S c h e q q s 4 1 6 5 0 .6 0 9 .1 5 2 .3 2 6 8 .4 5 0 .8 6 7 4 8 9 4 3 4 7 9 .5 9 0 .0 3 2 5 .0 0 S c h e g g s 3 1 6 5 1 .8 5 7 .4 2 1 .6 9 4 9 .6 6 0 .6 5 6 6 9 9 3 8 5 7 6 .4 0 0 .0 3 3 .0 0 2 .5 4 S c h e g g s 3 1 6 5 2 .9 5 6 .7 0 1 .9 9 4 6 .4 8 0 .5 8 6 9 4 9 4 3 9 8 0 .1 4 0 .0 4 2 9 .7 0 2.11 S c h e q q s 3 1 6 5 4 .1 0 7 .0 7 1 .7 6 5 2 .2 0 0 .5 6 7 3 8 8 4 3 9 9 3 .2 1 0 .0 3 2 4 .8 9 S c h e q q s 3 1 6 5 4 .4 0 6 .3 0 1 .5 0 4 7 .0 3 0 .5 6 7 4 7 9 4 4 0 8 3 .9 8 0 .0 3 2 3 .8 1 1 .7 7 S c h e q q s 3 1 6 5 4 .5 5 7 .4 0 2 .3 5 5 6 .5 6 0 .9 9 7 6 4 13 4 3 9 5 7 .1 3 0 .0 4 3 1 .7 6 S c h e q q s 3 1 6 5 5 .0 0 9 .5 4 4 .0 8 9 5 .2 2 0 .8 4 9 9 8 9 4 3 0 1 1 3 .3 6 0 .0 4 4 3 .0 0 S c h e q q s 3 1 6 5 5 .6 0 1 0 .6 8 3 .6 7 1 0 5 .7 6 0 .8 9 9 9 0 8 4 4 2 1 1 8 .8 3 0 .0 3 3 4 .0 0 2 .6 7 S c h e q q s 3 1 6 5 6 .1 0 1 0 .7 7 3 .7 4 1 0 6 .2 3 1.01 9 8 6 9 4 3 7 1 0 5 .1 8 0 .0 3 3 5 .0 0 2 .6 3 S c h e g g s 3 1 6 5 6 .5 0 1 1 .2 9 4 .8 0 1 0 6 .5 2 0 .7 9 9 4 3 7 4 2 6 1 3 4 .8 4 0 .0 4 4 2 .0 0 T O C - T o ta l O r g a n ic C a rb o n W e iq h t P e rc e n t I R o c k E v a l P y ro ly s is S 1 - m q H C /q R o c k S 2 - m g H C /g R o c k S 3 - m g C 0 2/g R o ck H I - H y d ro q e n In d e x (m q H C /q T O C ) O l - O x y g e n In d e x (m g C 0 2/g T O C ) T m a x °C | P I = S 1 /S 1 + S 2 i T o ta l S u lfu r W e ig h t P e rc e n t i Table 11 (Continued). Total organic carbon (TOC), complete Rock-Eval pyrolysis and weight percent total sulfur data, Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. 127 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D e p th In te rv a l C y c le L a m a lg in ite A m o r p n o u s B itu m in ite s tr u c t u r e d L ip tin ite L ip to d e trin ite V itin ite In e rtin ite B itu m e n C o m m e n ts S cheaas 1e d s 1645.60 4 s A T M T T Pediastrum ? 1646.10 4 S A T M T T Pediastrum ? 1646.50 4 A A T M T T Pediastrum ? 1649.95 4 A S T T T T 1652.95 1653.05 3 A A T M T T Pediastrum ? 1656.10 3 D R T M T T Rife Beds 1538.70 7 S A T T T T 1539.90 7 D M T T T Matrix Lamalginite 1544.30 1544.40 6 A S T T T T Pediastrum ? 1547.00 1547.10 6 A S T T M T 1547.70 1547.80 6 D M T T T T Matrix Lamalginite 1565.10 3 S A T T R T 1567.35 1567.45 3 A A T T T T 1570.10 3 A A T M T T 1571.80 1571.90 3 D M T T T D ■ Dominant A = Abundant S * Some M = Minor R = Rare T = Trace Table 12. Organic petrographic results for selected samples from Scheggs and Rife precessional cycles; Tipton Member, Blacks Fork-1. 128 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Depth (Feet) Member/ Cycle S1 3 C Saturate (%o) 81 3 C Aromatic (%o) A 8 ,JC Aromatic- Saturate Total Hopanes C2 9-C3 5 (ppm) 1534.90 Rife 7 -31.8 -31.3 0.5 29964 1537.90 Rife 7 -36.5 -30.8 5.7 70962 1539.00 Rife 7 -35.7 -31.2 4.5 54534 1540.00 Rife 7 -34.6 -32.7 1.9 23383 1541.30 Rife 6 -34.0 -32.0 2.0 35424 1543.20 Rife 6 -37.1 -30.7 6.4 87759 1545.05 Rife 6 -35.8 -30.7 5.1 48298 1547.80 Rife 6 -34.0 -32.9 1.1 16279 1630.00 Scheggs 7 -31.7 -30.4 1.3 4788 1632.00 Scheggs 7 -30.8 -31.1 0.3 3776 1646.10 Scheggs 4 -31.5 -30.6 0.9 4550 1650.50 Scheggs 4 -31.6 -30.3 1.3 2686 1651.90 Scheggs 3 -32.6 -30.5 2.1 29405 1654.50 Scheggs 3 -31.7 -30.7 1.0 12491 1656.10 Scheggs 3 -31.9 -31.1 0.8 20342 1192.00 Wilkins Peak E -29.1 -27.1 2.0 11443 1192.90 Wilkins Peak E -28.5 -30.9 2.4 11293 1193.40 Wilkins Peak E 9294 1193.80 Wilkins Peak E -29.5 -28.2 1.3 8031 1201.4 Wilkins Peak E -27.6 •26.0 1.6 5942 1203.42 Wilkins Peak E -31.9 -30.9 1.0 15733 1204.10 Wilkins Peak E -31.4 -30.9 0.5 14902 1205.1 Wilkins Peak E -27.9 -26.0 1.9 2859 1210.80 Wilkins Peak E -30.9 -29.5 1.4 16395 1211.50 Wilkins Peak E 39758 1213.90 Wilkins Peak E -30.4 -28.8 1.6 17149 1217.00 Wilkins Peak A -30.9 -29.6 1.3 9752 1435.30 Wilkins Peak A -31.4 -29.0 2.4 8957 1437.85 Wilkins Peak A -31.7 -29.3 2.4 12830 1498.00 Wilkins Peak A -34.9 -32.6 2.3 26416 1501.00 Wilkins Peak A -34.8 -33.0 1.8 25341 1502.00 Wilkins Peak A -32.3 -30.0 2.3 21100 Table 13. Carbon isotope composition for saturate and aromatic fractions of solvent extracts from the Tipton and Wilkins Peak Members, and quantities of C2 9 -C3 5 hopanes of saturate fraction, Blacks Fork-1. Tipton samples with a large A5°C correspond to a high C2 9 -C3 5 hopane content. Wilkins Peak data from eccentricity A and E cycles are provided for comparison. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Depth (Feet) 1534.90 1537.90 1539.00 1540.00 1541.30 1543.20 1545.05 1547.80 1630.00 1632.00 1646.10 1650.50 1651.90 1654.50 1656.10 Bed/Cycle Rife 7 Rife 7 Rife 7 Rife 7 Rife 6 Rife 6 Rife 6 Rife 6 Scheggs 7 Scheggs 7 Scheggs 4 Scheggs 4 Scheggs 3 Scheggs 3 Scheggs 3 GC Parameter Pristane/ Phytane 0.40 0.52 0.56 0.61 0.55 0.49 0.43 0.33 0.23 0 . 2 1 0.29 0.39 0.32 0.25 0.24 nC17/CM 0.36 0.44 0.53 0.81 0.44 0.47 0.42 1.71 2.80 4.80 0.94 2.14 0.64 0.26 0.73 nC1 7 / Pristane 0 . 2 0 0.15 0.18 0 . 2 0 0.15 0.17 0.18 0.78 0 . 8 6 1.04 1.16 1.08 1.04 0.89 1.19 Table 14a. Summary of selected quantitative gas chromatography (GC) results for extracts from Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. o Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Depth (Feet) 1 5 3 4 .9 0 R ife 7 1 5 3 7 .9 0 1 5 3 9 .0 1 5 4 0 .0 1 5 4 1 .3 0 1 5 4 3 .2 0 1 5 4 5 .0 5 1 5 4 7 .8 0 16 3 0 .0 0 16 3 2 .0 0 1 6 4 6 .1 0 16 5 0 .5 0 1651.90 1654.50 16 5 6 .1 0 Bed/Cycle R ife 7 R ife 7 Rife 7 R ife 6 Rife 6 Rife 6 Rife 6 Scheggs 7 Scheggs 7 S cheggs 4 S cheggs 4 Scheggs 3 Scheggs 3 S cheggs 3 Terpanes (m/z 191) Cis/Cft Tricyclic Terpanes 0 .0 6 0 .0 9 0 . 0 0 0 . 1 1 0 .0 9 0 . 1 2 0 .0 9 0 . 1 1 0 .0 6 0 .0 6 0 .0 9 0 .1 3 0 .1 3 nd 0 .0 6 C23/C24 Tricyclic Terpanes 1.29 1.17 1.29 0 .9 9 1.04 1.08 1.07 0.9 9 1.13 1 . 0 1 0 .9 9 1 .0 3 1.17 0 .9 9 1 . 1 1 Cjg/C^ Tricyclic Terpanes 2 .7 6 2 .1 7 4 .4 2 1.80 2 .1 9 2 .5 4 2 .9 8 1.78 1.72 1 .5 5 1 .1 8 1 . 2 2 1 .0 9 0 . 8 6 0.91 <j2 4 1 etracyciic/u26 mcyciic Terpanes 0 .0 8 0 .1 4 0 . 2 1 0.41 0 .2 3 0 . 2 1 0 .1 3 0.41 0 .3 4 0 .5 6 1 .0 8 1 .6 2 2 .5 5 1 .0 6 1.0 9 Terpanes and Steranes Oleanane/Hopane 0 . 0 2 0 . 0 0 0 . 0 1 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 0 0 . 0 1 0 .0 3 0 .0 6 0 .0 6 0 .0 5 0 .0 8 0 .0 8 Gammacerane/Hopane 0 .5 6 0 .5 8 0 . 8 6 0 .2 8 0 .6 5 1 .1 8 1.64 0.4 7 1.41 2 .7 5 1 .0 5 0 .4 2 0.41 1 .5 4 1 .5 4 Moretane/(Moretane+Hopane) 0 .3 2 0 .3 0 0 .2 8 0 .2 9 0.2 7 0 .2 6 0 .2 9 0 .3 0 0 .1 6 0 .1 9 0 . 2 0 0 .1 8 0 .1 8 0 . 2 2 0 . 2 1 H35/H34 Homohopanes nd nd nd nd nd nd nd nd 1.41 1 . 2 2 1 . 8 8 1 .5 7 1.63 1 .3 4 1.45 Steranes/H opanes 0 .8 9 0 . 2 2 0.6 3 3 .5 3 1 . 2 0 0 .2 4 0 .3 0 4 .2 6 0 .7 3 1.55 1 .2 7 1 .0 3 1.17 3 .4 7 3 .2 4 Tricyclic Terpanes/Hopanes 0 .9 5 0.1 8 0 .1 5 0 .5 3 0.31 0 .1 5 0 .3 3 0.7 7 0 . 2 1 0 .3 5 0 . 1 2 0 .0 9 0 .0 4 0 .0 7 0 . 1 1 Tricyclic Terpanes/Steranes 1.07 0 .8 3 0.2 4 0 .1 5 0 .2 6 0 .6 3 1 . 1 1 0.1 8 0.2 8 0 . 2 2 0 . 1 0 0 .0 8 0 .0 4 0 . 0 2 0 .0 3 Other (ppm) P-carotane 6 4 0 6 1 7 4 0 2 8 9 3 6 1 2 146 2 2 0 2 2 2 3 3 9 4 1 5 192 52 1 4 691 56 3 4 3 3 2 1 3 2 8 3 891 109 5 Table 14b. GCMS biomarker data listing terpane ratios and p-carotane content for extracts from Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. Depth (Feet) 1534.9 1537.9 1539.0 1540.0 1541.3 1543.2 1545.05 1547.8 1630.00 1632.00 1646.1 1650.5 1651.9 1654.5 1656.1 Bed/Cycle Rife 7 Rife 7 Rife 7 Rife 7 Rife 6 Rife 6 Rife 6 Rife 6 Scheggs 7 Scheaqs 7 Scheggs 4 Scheggs 4 Scheggs 3 Scheaas 3 Scheaqs 3 Steranes (ppm) m/z 217 C2 7 aa 20S 190.6 162.9 525.8 355.7 216.3 169.5 115.8 176.5 41.3 64.3 46.8 26.2 268.7 2807.6 575.8 C3 , aa 20R 3205.6 3085.6 4357.5 7612.4 5150.0 3706.7 2391.7 4836.4 1167.1 1827.9 2340.0 944.7 11624.4 13193.5 21976.1 C2 7 PP 20S 105.0 88.6 77.5 87.6 78.9 91.4 57.9 93.8 6.3 12.0 12.6 9.3 92.0 70.8 97.7 C2 7 pp 20R 111.7 95.5 93.3 121.6 105.4 104.8 55.6 120.4 21.5 32.2 50.3 29.2 140.8 212.4 351.6 C2 7 Total 3612.9 3432.6 5054.1 8177.3 5550.6 4092.4 2621.0 5227.1 1236.2 1936.4 2449.7 1009.4 12125.9 16284.3 23001.0 C2 a aa 20S 280.0 224.2 312.5 596.4 340.4 323.8 256.4 506.8 99.1 149.9 70.7 29.7 186.6 460.5 819.2 C2 4 aa 2QR 4847.8 3728.0 8355.0 19406.2 10699.4 5431.4 3264.7 18071.0 807.0 1452.7 1382.1 648.6 4468.7 5120.5 8731.0 C„ PP 20S 238.9 153.8 184.2 286.1 218.7 215.2 130.1 371.0 12.6 30.6 22.9 17.2 165.2 172.4 282.6 C2 . PP 20R 401.1 340.2 467.5 964.5 670.5 544.8 412.8 1098.1 165.0 261.1 154.5 67.8 763.7 831.9 1431.0 Cji Total 5767.8 4446.2 9319.2 21273.2 11929.0 6515.2 4064.0 20046.9 1083.7 1894.3 1630.2 763.3 5564.2 6585.3 11263.8 C2 » aa 20S 2096.1 1001.5 2738.3 7530.0 3377.7 1301.9 1130.1 4679.6 106.9 271.7 202.9 103.4 545.3 1003.8 1676.1 C2 # aa 20R 12448.3 4915.9 13715.0 35248.5 22356.0 7057.1 5294.0 32198.8 805.3 1572.1 1961.8 1171.6 11743.3 15598.9 24996.7 C2 « PP 20S 570.6 240.9 365.8 923.2 436.1 276.2 159.4 904.3 15.2 16.7 24.5 17.4 131.8 134.1 235.2 C2I pp 20R 1943.3 940.9 1880.0 5329.4 3331.9 1309.5 1172.2 4792.6 134.5 288.6 438.7 259.0 1933.3 2650.3 4377.9 C2 $ Total 17058.3 7099.2 18699.1 49031.1 29501.7 9944.7 7755.7 42575.3 1061.9 2149.1 2627.9 1551.4 14353.7 19387.1 31285.9 Total Steranes C^.Cm.Cm (ppm) 26439.0 14978.0 33072.4 78481.6 46981.3 20552.3 14440.7 67849.3 3381.8 5979.8 6707.8 3324.1 32063.8 42256.7 65550.7 % C2 7 /C2 7 +C2 »+C2 I 0.137 0.229 0.153 0.104 0.118 0.199 0.182 0.077 0.366 0.324 0.365 0.304 0.378 0.385 0.351 % C jg/C j7+ C 2j+ C 2| 0.218 0.297 0.282 0.271 0.254 0.317 0.281 0.295 0.320 0.317 0.243 0.230 0.174 0.156 0.172 % c 2 */c2 7 +c2 «+c2 1 0.645 0.474 0.565 0.625 0.628 0.484 0.537 0.627 0.314 0.359 0.392 0.467 0.448 0.459 0.477 aaaR Steranes m/2 217 C2 7 aa 20R 3206.6 3085.6 4357.5 7612.4 5150.0 3706.7 2391.7 4836.4 1167.1 1827.9 2340.0 944.7 11624.4 13193.5 21976.1 C2t aa 20R 4847.8 3728.0 8355.0 19406.2 10699.4 5431.4 3264.7 18071.0 807.0 1452.7 1382.1 648.6 4468.7 5120.5 8731.0 C2 »aa20R 12448.3 4915.9 13715.0 35248.5 22356.0 7057.1 5294.0 32198.8 805.3 1572.1 1961.8 1171.6 11743.3 15598.9 24996.7 % c 2 7 /c2 7 +c2l+c2 # 0.1564 0.26306 0.1649 0.12225 0.1348 0.22888 0.21841 0.08777 0.419911 0.376677 0.411689 0.341676 0.417597 0.389041 0.3945171 % c 2l/c2 7 +c2l+c2 » 0.2365 0.31783 0.3181 0.31166 0.28005 0.33537 0.29814 0.32793 0.29035 0.299359 0.243161 0.234584 0.160534 0.15099 0.1567398 % C2 j/C2 7 +C2t+Cj, 0.6072 0.41911 0.519 0.56609 0.58515 0.43575 0.48345 0.5843 0.289739 0.323964 0.34515 0.42374 0.421868 0.45997 0.4487432 % c 2 7 15.638 26.3063 16.489 12.2254 13.4798 22.8876 21.8412 8.77651 41.99108 37.66769 41,16892 34.1676 41.75971 38.90407 39.451707 %CM 23.646 31.7831 31.615 31.1661 28.0049 33.5371 29.8135 32.793 29.03504 29.93591 24.31605 23.45835 16.05344 15.09897 15.673976 % C2 , 60.718 41.9106 51.897 56.6085 58.5153 43.5753 46.3453 58.4304 28.97388 32.3964 34.51503 42.37405 42.18685 45.99695 44.874317 Methvlsteranes (ppm) C «4a 39.4 87.1 0 201 134.3 0 0 73.5 25.8 147.4 689 631 4560.7 3271.4 5559.6 213.3 148.5 0 434 456.6 0 0 738.9 72.2 218.7 232.5 159.9 1122.4 1637.8 2610.3 Cjo 4a 265.6 54.5 93.3 179.4 185.5 663.8 436.8 483.3 75.2 370.5 644.6 551.3 2493 1733.5 2987.8 Total Methvlsteranes C2 »,C2 # ICJ0 (ppm) 518.3 290.1 93.3 814.4 778.4 663.8 436.8 1295.7 173.2 736.6 1566.1 1342.2 8176.1 6642.7 11157.7 % C2 j/C2 j+C2 2 +Cjo 0.076 0.300 0.000 0.247 0.173 nd nd 0.057 0.149 0.200 0.440 0.470 0.558 0.492 0.498 % C2 »/C2 0+C2 j+Cj(i 0.412 0.512 0.000 0.533 0.588 nd nd *0.570 0.417 0.297 0.148 0.119 0.137 0.247 0.234 % C 3 O /C 2l+ C 29+C30 0.512 0.188 1.000 0.220 0.239 nd nd 0.373 0.434 0.503 0.412 0.411 0.305 0.261 0.266 Table 14c. GCMS biomarker data listing quantity o f individual steranes and methyl steranes for extracts from Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. 132 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Depth (Feeef| 1 5 3 4 .9 0 1 5 3 7 .9 0 1 5 3 9 .0 1 5 4 0 .0 1 5 4 1 .3 0 1 5 4 3 .2 0 1 5 4 5 .0 5 1 5 4 7 .8 0 1 6 3 0 .0 0 1 6 3 2 .0 0 1 6 4 6 .1 0 1 6 5 0 .5 0 1 6 5 1 .9 0 1 6 5 4 .5 0 1 6 5 6 .1 0 Bed/Cyclfle R ife 7 R ife 7 R ife 7 R ife 7 R ife 6 R ife 6 R ife 6 R ife 6 S c h e g g s 7 S c h e g g s 7 S ch eg g s 4 S c h e g g s 4 S c h e g g s 3 S c h e g g s 3 S ch eg g s 3 Steraness C a 2 0 S ( 2 0 S + 2 - 9 R ) 0 .1 4 0 .1 7 0 .1 7 0 .1 8 0 .1 8 0 .1 6 0 .1 8 0 .1 3 0 .1 2 0 .1 5 0 .0 9 0 .0 7 0 .0 4 0 .0 6 0 .0 6 C M pp/(aa+ f |p) 0 .1 5 0 .1 7 0 .1 2 0 .1 3 0 .1 6 0 .1 6 0 .1 7 0 .1 3 0 .1 4 0 .1 5 0 .1 6 0 .1 6 0 .1 4 0 .1 4 0 .1 5 Terpanees T s /T m 0 .0 6 nd 0 .0 9 nd 0 .0 5 nd nd nd 0 .0 7 0 .0 7 0 .0 9 0 . 1 1 0 .1 5 0 .1 0 . 1 C 2 9 T s /T n rra 0 .1 5 0 .0 9 0 .1 2 0 .2 2 0 . 1 1 0 . 2 0 .2 3 0 .2 7 0 .0 6 0 .0 7 0 .0 8 0 .0 7 0 .0 9 0 .2 1 0 .2 3 H3 2 S (S + R ) H o m o b t e p a n e s nd nd 0 .2 4 0 .2 8 0 .4 3 nd nd 0 .2 9 0 .1 3 0 .0 9 0 .4 3 0 .4 0 .3 1 0 .4 6 0 .4 9 Table 14d. CGCMS thermal maturation data for extracts from the Scheggs and Rife precessional cycles, Tipton Member; Blacks Fork-1. that have higher TOC values often correspond to small increases in HI (Figure 40). Differences in the maceral composition and properties that make up the kerogen are identified in the two-stage precessional pattern. The cycle base usually contains a highly fluorescent, dense amorphous material equivalent to matrix lamalginite (Table 12). The overlying parts of the cycle usually contain a moderate fluorescing amorphous material typical of bituminite with associated liptodetrinite, and mixed with some lamalginite. A small number of planktonic precursors (structured alginite) are identified in these cycles based on morphology and fluorescence, which may represent pediastrum, as reported by Bradley (1964). Planktonic precursors in the middle and upper parts of these cycles are often different compared to the cycle base. Pyrolysate composition, which is measured by pyrolysis-gas chromatography, also identifies compositional differences in kerogen between the two precessional cycle stages. Pyrolysates generated from samples representing the cycle base contain a greater quantity o f C5-C29 n-alkane/alkenes or n-aliphatics (Figures 38-39, and 41). In contrast, pyrolysates from the middle and upper parts of the cycle contain relatively lower quantities of C5-C29 n-aliphatics and a small increase in the proportion of light aromatics. Quantitative pyrolysis-gas chromatography data are listed in Appendix 5. Variations in the 8 1 3 C composition of the Rife kerogen, extracts, and carbonate matrix are consistent with other precessional patterns. Kerogen depleted in 1 3 C (-32.8 to -34.3 % o versus -29.1 to -31.6 % o ) occurs in the organic-rich base of 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. some Rife cycles (Figures 40 and 41, Table 9). The organic enriched zones at the top of some cycles also contain kerogen depleted in 13C. Above the base of the Rife 1 T cycles, the saturate extract fraction displays a depletion in C compared to the aromatic fraction (A8 1 3 C [aromatic-saturate] > 4). In contrast, the organic-rich cycle 1 ^ base and top have A5 C values [aromatic-saturate] less than 2 (Table 13). In the 1 ^ basal part of some Scheggs cycles, the 8 C composition of the matrix carbonate is enriched (+3.9 to +7.7 % o) compared to the remainder of the cycle (Figures 37-39, Table 9). Throughout individual Rife cycles, the matrix carbonate is usually enriched in 1 3 C, with values between +4 and +10 % o. GC and GCMS-biomarker parameters from analyses of the saturate fraction of extracts throughout Tipton cycles further define cyclical patterns. Overall, GC patterns of Scheggs extracts display variable patterns in their n-alkane profile and low Pr/Ph ratios (Figure 45-47). In extracts above the base in Scheggs cycle 3, there is an increase in the proportion of nC25-C3i alkanes with a strong odd-to-even carbon predominance (Figure 47). The mudstone at the top of Scheggs cycle 4 contains a greater proportion of nC25-C3i than nCi5-Ci9 range alkanes, which is reflected in its lower nCn/nC 29 ratio compared to the cycle base (Figure 46). A decrease in the sterane/hopane, C29/C27 steranes, gammacerane/C3o hopane, and C29/C30 methyl sterane ratios occur between the middle and upper parts of Scheggs cycles 3 and 7 (Figures 45 and 48). Small changes in the C24 tetracyclic/C26 tricyclic and C26/C25 tricyclic terpane ratios further confirm molecular changes in the extracts between the middle and top parts of these cycles. 135 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. copyright owner. Further reproduction prohibited without permission. O il Y ield 8 1 3 C Bitumen Fraction/ GCMS Param eters 1630.0 Ft Pr/Ph 0.23 Saturate -31.7%o Oil Shale nCiy/C29 2.80 Aromatic -30.4%o Ph nC1 7 /Pr 0.86 Steranes/Hopanes C2 9/O2 7 Steranes Gamm/Hopane Pr C 2g lC 2 5 Tricyclic I C2 4 Tet/C26 Tricyclic _ 1 . a 8 1 .1 .1 1 1 L S 1 S - 111]5 Hi ifjllL xJ7 1 0 2o 3 0 4'0 50 60 0.73 2.06 1.41 1.72 0.34 1632.0 Ft Oil Shale Pr/Ph 0.21 nC^/Cjg 4.8C nC1 7 /Pr 1.04 e ! o Saturate -3 0 .8 % o Aromatic - 3 1 .1 % o Steranes/Hopanes C29/C2 7 Steranes Gamm/Hopane C -2^C2 5 Tricyclic C2 4 Tet/Cje Tricyclic 1 . 5 5 3 . 1 7 2 . 7 5 1 . 5 5 0 . 5 6 Figure 45. Gas chromatograms o f saturate fraction of the extracts from Scheggs cycle 7 (1628.2-1633.5 ft). Subtle differences occur in n-alkane profile. GCMS analysis of saturate fraction of extract in middle/upper part o f the cycle has reduced sterane/hopane, C2 9/C 2 7 sterane and gammacerane/hopane ratios reflecting differences in source input. The A51 3 C [aromatic- saturate] values are relatively small. Complete name and definition of biomarker ratios are provided in Table 10 and Appendix 6 . U ) ON Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. a > c o c t j c r » o r * IP Figure 46. Gas chromatograms o f saturate fraction o f extracts from Scheggs cycle 4 (1645.6-1650.9 ft), Blacks Fork-1. A greater proportion of nC2 5-C3i compared to nCi5 -Ci9 alkanes occurs in the mudstone extract at 1646.1 ft. The A51 3 C [aromatic-saturate] values are relatively small. 55555555505J55555555555555555558555555 Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 3 > GO 3 B 2 - < i o cUj n 't Q ) P P Figure 47. Gas chromatograms of saturate fraction o f extracts from Scheggs cycle 3 (1650.9-1656.5 ft). Basal extract contains less nC2 5-C3 i alkanes compared to overlying interval suggesting a reduced proportion o f land-plant input. Compared to Rife cycles, the §1 3 C composition o f the saturate and aromatic fractions o f bitumen are similar suggesting absence of methanogenic input. u > 00 513C Bitum en Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ■ * F O O O O C O - ^ ^ <r> I r n .7 3 ^ ■ s O O O O C O £ M SS cS“ - H O 5 O S <"> C~ > CT 5 C~> CO ^ C ~ > g rC ~ > 3 C D s ^ CO r o Figure 48. Terpane mass chromatograms (m/z 191) from GCMS analysis o f saturate fraction of extracts, Scheggs cycle 3. The gammacerane/C3 0 hopane ratio for extract at top of cycle is reversed compared to lower samples. Saturate fraction o f extract in upper part of cycle also has lower sterane/hopane and C2 9/C2 7 sterane ratios. Differences in these ratios and other parameters confirm changes in precursor input between middle and top of cycle. Complete name and definition of biomarker ratios are provided in Table 10 and Appendix 6 . L O V O 449999999999999999999999999999999999999994454 Extracts from the base of Rife cycles are characterized by high 11C17/C 29 alkane, sterane/hopane, C29/C27 sterane, C2 4 tetracyclic/C26 tricyclic terpane, and low gammacerane/hopane, and C26/C25 tricyclic terpanes ratios compared to the overlying parts of the cycles (Figures 49-52; Tables 10 and 14). Lower amounts of ( 5- carotane, total hopane and gammacerane occur in extracts from the cycle base. The C27-C28-C29 sterane distribution of extracts from the cycle base, half-cycle enrichment, and top of the cycle documents that they are enriched in C29 steranes (Figure 53 and Table 14). This enrichment is reflected in the higher C29/C27 sterane ratios. Above the cycle base, the sharp decrease in the C29/C27 sterane ratio coincides with a decrease in the sterane/hopane ratios (Figures 50 and 52). Generally, an increase in C29 methyl steranes occur in extracts from the cycle base compared to most of the overlying interval (Table 14). The extract from the base of Rife cycle 6 (1547.8 ft) has a lower pristane/phytane (Pr/Ph) ratio and contains more nCi9-C25 alkanes compared to the nC25-C29 alkane range than other extracts in the cycle (Figure 52). Geochemical variations in the Tipton kerogen and bitumen-extracts are independent of their narrow range of thermal maturity in these precessional cycles. Therefore, they document changes in organic matter properties throughout individual cycles. Low Rock-Eval pyrolysis Tmax, and C 2 9 20S/R and Ts/Tm values of the bitumen further confirm the thermal immaturity o f the Tipton Member in Blacks Fork-1 (Tables 9 and 14). 140 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Figure 49. Gas chromatograms o f saturate fraction of extracts from Rife cycle 7. Subtle decrease in Pr/Ph and nC 17/C 2 9 occurs upward in cycle. Highest content o f P-carotane ((3) occurs in middle of cycle with reduced organic carbon. The 51 3 C depleted composition o f the saturate compared to aromatic fraction of extracts in middle o f cycle indicates methanogenic input. ueuinMW Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. c ~ > c? < p > O O O CD O < r > a ? . c ~ > *3 o Figure 50. Terpane mass chromatograms (m/z 191) from GCMS analysis o f saturate fraction of extracts from Rife cycle 7. Organic-rich base has a lower gammacerane/C3 o hopane ratio compared to middle part o f cycle. Measurable differences in the sterane/hopane and C 2g/C27 sterane ratios occur above the cycle base indicating differences in precursor input. These molecular differences are consistent with changes in other terpane ratios. 4 ^ ts J G C M S Parameters Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ? s' Figure 51. Gas chromatograms of saturate fraction o f extracts, Rife cycle 6 . Differences in Pr/Ph, nCi7/C2 9 alkane ratios, and p-carotane (P) content occur in the extract from organic-rich cycle base (1547.8 ft) compared to overlying parts o f the cycle. The 51 3 C depleted composition o f the saturate fraction compared to the aromatic fraction of extracts in the middle o f the cycle indicates methanogenic input. 4^ 15999999999999999999999999999999999999999999999999^ Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. ST s P s P |? e s P W § * s£! W § *SZ W S - S T1, 0 ; rc~ 5 m ^ 1 | ^ jp * 3 _ [p* S jb. - P l p * = ^ Ie ~ P s . fSF~ie S . P s 1 o g I K ° 5 1 5 2 I S ’ ■§ ^ & 1 ^ - 3 1 1 § §= 1 ^ - a "S S -S 1 § ° i - a @ , = = “S 5 a g = ■ § - g _ "■ M ^ - 3 ?=r ~ i i i t S - Q . _ _ ^ o — «=z>ro—-iso<=> <=> r-» :—'“ r * 0 S <=> r > o « = » o n SiiioK b jg 2 s g ^ S » s “ B ? 3 £ S £ g 3 Figure 52. Terpane mass chromatogram (m/z 191) from GCMS analysis o f saturate fraction o f Rife cycle 6 extract (1541.1-1548.7 ft).Organic-rich cycle base and top o f cycle display a lower gammacerane/C3 0 hopane ratio compared to middle parts o f cycle. Decrease in sterane/hopane and C2 9/C 2 7 sterane ratios occur above the cycle base. This cycle displays a similar molecular pattern as Rife cycle 7. The C2 (JC 2 5 tricyclic terpane and C2 4 tetracyclic/C2 6 tricyclic terpane ratios of the extract from the cycle base are distinct compared to the overlying parts o f the cycle. C28 © Rife 71S34.91 & p n % T \ s a .v «Rife71H9.0- QRlfe71540.0' C27 C29 C28 4 (We 61541.3' C27 Figure 53. Sterane distribution of saturate fraction of extracts from Rife cycles 6 and 7. Extracts from cycle base have different C2 7-C2 8 -C2 9 sterane distribution than samples from the middle of the cycle. 145 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Discussion Geochemical Properties. Cyclical Trends and Mechanisms Geochemical and petrographic parameters provide additional definition to the Tipton precessional cycles defined from variations in oil-yields, and sonic and gamma logs. The distinct two-stage geochemical signature in Scheggs and Rife cycles represents a limnological response to the rainy and dry precessional phases. Much of the geochemical heterogeneity that is apparent over short intervals in the Tipton Member can be attributed to these orbital-driven variations in lacustrine conditions. The differences in the expression of geochemical patterns between the Scheggs and Rife cycles are a result of evolving lacustrine conditions in the different lake systems. Organic-Rich Cycle Base - Geochemical Expression and Processes The cycle base represents distinct climatic-derived lacustrine conditions compared to most of the overlying precessional interval. The organic enriched cycle base equates to enhanced productivity and preservation, as well as different types of precursor input. The onset of the rainy precessional phase led to increased eutrophic to hypertrophic algal productivity. The abundant matrix lamalginite, which is consistent with high HI values (>750 - 950 mg HC/g OC) and an n-aliphatic-rich pyrolysate, originated from a high organic flux of planktonic algal precursors that underwent negligible amounts of degradation (Cook et al., 1981). However, specific biological precursors of the lamalginite can not be ascertained possibly due to 146 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. their fragile character, syndepositional alteration, or absence o f a resistant cyst. The high algal productivity and extended trophic levels that occurred during deposition of the cycle base is supported by the high sterane/hopane ratios, and greater amounts of C29 sterane and methyl sterane composition. Steranes originate from sterols in eukaryotic organisms including dinoflagellates, zooplankton, and other higher organisms (Mackenzie et al., 1982). In contrast, hopanes are derived from hopanoids in prokaryotic organisms such as bacteria (Simoneit, 1986; Ourisson et al., 1979). Although it has been reported that small amounts of sterols are produced by cyanobacteria, steranes are almost exclusively derived from eukaryotic organisms (Ourisson et al., 1987). Organic-rich intervals in these cycles also contain an increase in the total C28, C29, and C30 methyl sterane content, suggesting a greater proportion of algal input (Hwang et al., 1989). The higher C29/C27 sterane ratios in extracts from the cycle base compared to other parts of the cycle are probably related to the different types of algal species associated with changing lake conditions. Kerogens in the cycle base that are depleted in 1 3 C are primarily a product of precessional-driven changes in water column stratification. High photic zone productivity resulted in an increase in organic flux. As the biomass descended through the upper water column, oxidative decay depleted the oxygen content. As a result, the chemoocline rose in the water column, probably reaching into the lower part of the photic zone, as has occurred in other hypertrophic lakes (Mckenzie, 1985; Koopmans et al., 1996). Bacterial degradation of the biomass in the lower photic zone produced recycled, 12C-enriched CO2 that became available for photosynthesis. 147 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 7 . The incorporation of the C-enriched CO2 resulted in the isotopically depleted kerogen. In modem stratified lakes, gradients in the 8 1 3 C composition of dissolved CO2 become more negative with depth because of the decay of the biomass (Oana 1 9 and Deevy, 1960; Torgersen et al., 1981). In the Rife lake, recycled C-enriched CO2 may have also been transported by diffusion upward through the short stagnant water column into the photic zone. Later in the precessional period, as productivity, organic flux, and the rate of biomass decay decreased, the chemocline fell to lower levels in the water column, and less 12C-enriched CO2 was available for photosynthesis in the lower photic zone. The rise and drop in the chemocline and the 11 resulting variation in the availability of C-depleted CO2 could have been seasonal or taken place over a period of years compared to slowly changing anoxic marine systems (Saelen et al., 1998). Basal intervals in Tipton cycles that do not contain Sl3C depleted kerogen were the result of the limited amounts of recycled CO2 that could enter the photic zone, probably related to a lower chemocline. The positive 5l3C carbonate matrix (+3.9 to +7.7 % o) in the basal parts of some Scheggs cycles suggests a moderate-to-strong methanogenic input or diagenetic origin compared to the rest of the cycle (Figures 37 and 38). Precipitation of isotopically heavy carbonate from pore water originates when methanogenic bacteria via acetate metabolism form isotopically light methane and associated heavy CO2 (Irwin et al., 1977; Pitman, 1996). Methanogenesis occurs when the rapid reduction of sulfate that accompanies a large organic flux causes an increase in the alkalinity of the anoxic pore water. The l3C-enriched carbonate matrix (+5.6 to +9.8 148 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. % o) throughout Rife cycles confirms that methanogenesis was a continuous process below the sediment/water interface, which was saturated with alkaline pore water. At I 3 the top of Rife cycle 7 and base of Rife cycle 6 , lower 8 C values in the carbonate matrix suggest reduced methanogenesis, which could be related to greater eukaryotic input or a less alkaline pore water. Although Tipton precessional cycles display a distinct two-stage signature, small geochemical variations indicate temporal variability existed within each of the precessional phases. In both the rainy and dry phases, dynamic and variable climatic conditions affected short-term lake level, productivity, and water column conditions. Thin, high TOC zones in the cycle base represent periods of optimal organic accumulation, a product of hypertrophic productivity and enhanced stratification during the rainy phase. These thin zones indicate that even during the rainy phase, considerable variation in lake inflow, productivity, stratification and organic matter accumulation occurred. Mid-Cvcle-Geochemical Expression and Processes The decrease in organic content, the sterane/hopane and C29/C27 sterane ratios, as well as changes in kerogen composition directly above the cycle base equates with the dry precessional phase. The lake quickly shifted toward more eutrophic-mesotrophic conditions as a result o f reduced inflow and lake size. The following changes in lake ecology occurred: ( 1) lower algal productivity in the photic zone, (2 ) an increase in bacterial input from different positions in the water 149 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. column, and (3) an increase in the degradation of the descending biomass through the upper and middle water column. Above the cycle base, a shift to a Type I-I/II kerogen with a reduced nC5-C29 aliphatic pyrolysate composition corresponds to a greater proportion of bacterial hopanoid precursors and slightly reduced preservation. This shift is consistent with a change from a lamalginite-dominated kerogen to a mixed bituminite and lamalginite assemblage. Bituminite and liptodetrinite originate from bacterial input and the biological reworking of algal precursors, which results in lower HI values than in algal-derived kerogen (Gutjahr, 1983). The petrographic occurrence of bituminite is consistent with the lower sterane/hopane ratios. The reduced algal productivity and flux during the dry phase allowed different communities of bacterial precursors to exist at deeper levels in the water column. In addition, a greater proportion of the upper and middle water column contained adequate oxygen for bacterial reworking and degradation. In addition to the decline in algal productivity, the type of eukaryotic and prokaryotic precursors also changed. In extracts from above the cycle base, lower C29/C27 sterane ratios coincide with reduced sterane/hopane ratios, indicating different types of algal precursors. Algal precursors differ in their steroid composition in terms of chemical structure and carbon number (Huang and Meinschein, 1979; Withers, 1983). Reduced amounts and a different distribution of 4-methyl steranes in extracts from the middle and upper cycle compared to the cycle base further confirm changes in the type of algal precursors (Fu Jiamo et al., 1990). 150 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The increase in C2JC 25 tricyclic terpanes above the cycle base also indicates differences in the type of microbial input (Zumberge, 1987; Aquino Neto et al., 1983). The decrease in the C24 tetracyclic/C26 tricyclic terpanes above the Rife cycle base is probably related to increased salinity (Palacas et al., 1984; Connan et al., 1986) and corresponding changes in microbial precursors. These molecular variations reflecting a change in precursor input originated from a different water column ecology that developed from climatic-derived changes in nutrient concentrations, water chemistry, temperature, and bioproductivity (Taylor, 1987; Withers, 1987). The increase in the gammacerane/C3o hopane ratio above the Rife cycle base further documents changes in bioproductivity and water column conditions (Figures 50 and 52). Traditionally, an increase in gammacerane suggested more saline lake conditions (Peters and Moldowan, 1993). However, recent studies indicate that gammacerane records input from bacterivorous ciliates living at or below the chemocline in stratified lakes (Schoell et al., 1994a; Sinninghe Damste’ et al., 1995). These anaerobic ciliates feed on photosynthetic purple and green sulfur bacteria, as well as sulphide-oxidizing bacteria. Gammacerane is formed from tetrahymanol, which is only produced when ciliates rely entirely on prokaryotic food sources and their diet is deprived of sterols (ten Haven et al., 1989; Harvey and McManus, 1991). Thus, the reduced algal flux and greater proportion of bacterial input contributed to the larger amount of gammacerane. During the dry precessional phase, an increase in the brackish-saline conditions in the Rife lake may have also contributed to the 151 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. increase in gammacerane. Lower amounts of gammacerane in extracts from the cycle base are related to a high flux of algal-derived sterol precursors. In contrast, the reduced quantity o f gammacerane in the upper parts of Scheggs cycles 3 and 7 may be due to increased mixing and a less stratified water column, and thus a reduced input of ciliate precursors. The variation in gammacerane content in Tipton cycles is similar to other lacustrine settings where salinity changes are documented (Fu Jiamo et al., 1986). An increase in P-carotane above the base of Rife cycles further indicates reduced algal flux, a lower chemocline, and possibly elevated salinity, all of which are consistent with reduced lake levels. P-carotane is derived from algae and some phototrophic bacteria that occur in deeper portions of the photic zone (Hall and Douglas, 1983; Schoell et al., 1994a; Ruble et al., 1994). The specific precursors include halophilic eukaryotic algae (.Dunaliella), which flourish close to the halocline and are capable of synthesizing carotenoids (Loeblich, 1982). As algal input from the upper photic zone decreased at the end of the rainy phase, precursors of p-carotane began to constitute a larger proportion of the organic flux. The lower P- carotane content in the organic-rich cycle base may also be related to the following conditions: ( 1) the occurrence of the chemocline above the base of the photic zone, and/or (2) a less brackish-saline water chemistry. The small increase in P-carotane in the middle of Scheggs cycles 3 and 7 may be related to a reduced algal flux from the upper photic zone. 152 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Above the Rife cycle base, a positive correlation exists between extracts with large A8 1 3 C [aromatic-saturate] values and hopane abundance (Figures 49, 51, and 54 and Table 13). This correlation indicates an increased methanotrophic archea i t input into the soluble biomass. The C depletion in the saturate fraction is primarily controlled by the isotopic composition of hopane compounds that are derived from methanogenic archea (Collister and Wavrek, 1996). The 13C-depleted methane (CH4 8 1 3 C = -50 to -65 % o or less) that is produced by fermentation in lake sediments is used as a carbon source for microaerophilic methylotrophs (hopane precursors) living at the aerobic-anaerobic boundary (Hayes et al., 1987). Methanogenic archea become an important contributor to the biomass after sulfate-reducing bacteria are subdued due to depletion of sulfate (Collister et al., 1992). The methanogenic archea contribution is consistent with sterane/hopane ratios less than 1.0 , changes in other biomarkers indicating greater prokaryote input, and a lower n-aliphatic pyrolysate composition. Because methanotrophic archea thrive at the chemocline (Hanson, 1980), the occurrence of a hopane-rich saturate fraction depleted in 1 3 C provides evidence for a stratified water column, as described in other lakes (Freeman et al., 1989). The absence of a methanogenic signature in Rife extracts from the cycle base is due to the eukaryote-dominated flux that overwhelms the methanotrophic archea input. The absence o f 513C-depleted methanotrophic signature in kerogen from the middle of Rife cycles is because the bitumen is probably derived from free lipids that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. AAA A A ( II . ! - 4 - ._L. - 4 - ■4 - - 4 - Figure 54. Comparison o f the A51 3 C of the aromatic and saturate fraction, and the C2 9 -C3 5 hopane content of the extracts. High values in the middle parts o f Rife cycles indicate methanogenic input compared to the Scheggs. Wilkins Peak extract data from eccentricity cycles A and E are included for comparison. 1 ^ are separate from the kerogen macromolecule (Collister et al., 1992). The 5 C signature of the kerogen represents contributions from a wide range of non- methanogenic precursors (e. g., n-alkanes). These extracts represent the hydrolysis products of lipids formed at the beginning of diagenesis rather than the thermal cracking of kerogen (Anders and Robinson, 1973). Half-Cvcle and Cycle Top-Geochemical Signatures The half-precessional zone and the top of the cycle are sometimes geochemically similar to the organic-rich base. Similarities include: elevated TOC i ^ 1 and HI values, and sterane/hopane ratios, C depleted kerogen, and reduced AS C [aromatic-saturate] of extracts. An increase in lake inflow corresponding to a half- precessional event and transition to the overlying cycle led to increased algal productivity and anaerobic conditions in the upper water column. Thus, the resulting geochemical signature is similar to the organic-rich cycle base. An increase in the C25-C29 alkane content of the extract from the half-cycle peak in Rife cycle 7 (1534.9 ft) suggests greater landplant input, related to increased inflow (Figure 49). The increase in organic content and preservation in the half-cycle zone and transition to the overlying cycle may suggest that relatively small changes in net moisture and inflow triggered eutrophic conditions in the Tipton lakes. Similar geochemical signatures associated with the Tipton half-cycle enrichment further supports a cyclical process. 155 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The occurrence of mudstones near the top of some Scheggs and Rife cycles result primarily from sediment dilution and reduced organic productivity. An increase in quartz and total clay at the top of some Tipton cycles based on x-ray and petrographic analyses indicates sedimentary dilution of the accumulating organic matter (Table 9). Although these intervals have reduced TOC values (< 3-5 wt %), similar HI values, and maceral and pyrolysate compositions compared to the underlying oil shale indicate a similar level of preservation (Figure 39). The occurrence of anaerobic conditions in the lower water column and below the sediment/water interface provided adequate organic preservation. Geochemical Comparison-Scheggs and Rife Precessional Cycles Compared to the Scheggs, the two-stage geochemical signature in Rife cycles is usually more pronounced. This magnified Rife signature is characterized by greater differences in TOC, S1 3 C composition of kerogen, methanogenic input, sterane distribution, and the gammacerane/C3o hopane and sterane/hopane ratios. The greater geochemical contrast in Rife cycles is a result of the relatively larger changes in lake conditions between the rainy and dry precessional phases. The Scheggs cycles have a higher total sulfur content than the Rife, which is probably related to increased inflow and a greater availability of sulfate. The larger amounts of methyl steranes in the Scheggs extracts are consistent with freshwater algal blooms, which are the likely precursors of C30 4-methyl steranes (Boon et al., 1979; de Leeuw et al., 1983; Robinson et al., 1984). Compared to the Rife, Scheggs 156 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cycles also contain abundant ostracodes, consistent with the freshwater lake. Surprisingly, the Pr/Ph ratio o f extracts from the freshwater Scheggs is similar to or lower than those from the brackish-saline Rife. This is probably a result of adequate anaerobic conditions in the Scheggs lake. Rife extracts are enriched in C29 steranes compared to the Scheggs (Figures 53 and 55). The absence of a methanogenic signature in the aromatic and saturate fractions of extracts from Scheggs cycles may be the result of a greater availability of sulfate and abundant algal input. Additional sulfate introduced into the Scheggs lake may have suppressed methanogenesis, if it was not completely reduced by sulfate-reducing bacteria. Reduced stratification and greater oxygenation in the upper and middle water column may have also limited methanogenic input. The reduced S1 3 C composition of the matrix carbonate (< 3-4 % o) in the middle and upper part of the Scheggs cycles compared to the Rife indicates less methanogenic activity in the sediment pore water, which is consistent with a reduced carbon flux, as well as less alkaline and anoxic conditions. The reduced amount of C20-C25 tricyclics, P-carotane, and gammacerane in the Scheggs compared to the Rife is related to the absence o f a halocline and more mixing in the upper and middle water column. This probably helped to disseminate bacterial precursors. The absence of 13C-depleted kerogen in the base of Scheggs cycles is related to a lower chemocline and less recycling of CO2 in the basal photic zone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C28 © Scheggs 71630.0* 71632.0* E 3 Scheggs 41650.50* U S Scheggs 31651.9* * Scheggs 31654.5* X Scheggs 31656. T C27 Figure 55. The C2 7-C2 8-C2 9 sterane distribution o f the saturate fraction of extracts from Scheggs cycles 3, 4, and 7. Note distinct sterane distribution compared to Rife cycles shown in Figure 53. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 6 GEOCHEMICAL EXPRESSION AND PROPERTIES OF WILKINS PEAK CYCLICITY Introduction This chapter describes the geochemical expression of precessional cycles in Wilkins Peak eccentricity cycles A and E, as represented in Blacks Fork-1. Geochemical and petrographic results combined with Fischer assay oil-yields and lithologic properties are used to define precessional cycle patterns. Cyclical lacustrine processes are described that result from orbital-driven climatic variations that occurred during deposition of the oil shale, trona, and mudflat facies. Results Three different geochemical patterns in Wilkins Peak precessional cycles are identified from variations in organic content and other geochemical parameters. First, the oil shale and mudflat facies are distinguished by significant differences in 1 T organic content and composition, and by a carbon isotope (8 C) excursion. Second, the oil shale facies in individual cycles displays three different signatures based on variations in organic content and thickness. Third, the mudflat consists of two end- member microfacies defined from organic content and composition. These three geochemical patterns usually correlate with lithologic properties in individual precessional cycles. 159 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lithologic descriptions, Fischer assay oil-yields, and various geochemical parameters are summarized for precessional cycles 1, 3, 5, and 20-24. Oil-yields and geochemical summaries of rock, kerogen and solvent extract data for individual cycles are listed in Tables 15-17. This includes weight percent (wt. %) total organic carbon (TOC), Rock-Eval pyrolysis Hydrogen Index (HI), carbon and oxygen n 1 o isotope composition (8 C and 8 O), weight percent total sulfur, and selected parameters from gas chromatography (GC) and gas chromatography-mass spectrometry (GCMS). Complete Rock-Eval pyrolysis data are listed in Table 18. Sharp changes in organic content and composition, precursor input and preservation parallel the oil shale and mudflat lithofacies. Most cycles display a significant decrease in oil-yield and TOC values, either near the top or directly above the oil shale facies (Figures 56-63). In most oil shales, oil-yields range between 10 and 40 gallons/ton, and TOC between 5 and 29 wt. %. In the mudflat facies, oil-yields range between 0 and 6 gallons/ton, and TOC values are generally < 3 wt. %. Oil shales have high HI values (> 600 mg HC/g OC), and are primarily composed of lamalginte with some bituminite (Table 19). Overall, the mudflat facies has a lower but wide range of HI values (<100 up to 600 mg HC/g OC), depending on the mudflat microfacies. Kerogen in the mudflat is composed of poor-to-well preserved bituminite and contains variable proportions of terrestrial components. A few zones in the mudflat facies have HI values between 600 and 750 mg HC/g OC and contain a mixture of bituminite and lamalginite. The pyrolysate composition of the mudflat kerogen, which is measured by pyrolysis-gas chromatography, contains 160 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Oil Yield G allo n T O C HI 13C K ero 1 3 C C a rb T otal Sulfur W t.% m g H C /g G G p e r m il p e r m il W t.% 1487 1488 1489 149D 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 Mudstone: Md-K.gray. Sharp break from □live gray-green mudstone to gray mudstone @1489.6. Lt -Md gray pebble conglomerate near 1489'. O il Shale: Md-dk olive gray. Nahcolite: With thin oil shale. Oil Shale: Md-dk olive gray. Grades to mudstone with depth. 20 300 1000 -35 -25 0 Figure 56. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak precessional cycle 1 (1486.6-1502.0 ft), Blacks Fork-1. Data includes total organic carbon (TOC), Rock-Eval Hydrogen Index (HI), and carbon isotope composition (51 3 C) o f the kerogen and carbonate matrix. Sharp changes in geochemical properties occur at the oil shale-mudflat boundary (1497.2 ft). Note organic-rich zone at 1501.0 ft suggesting a lacustrine highstand event. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1 4 5 9 1 4 6 0 1 4 6 1 1 4 6 2 1 4 6 3 1 4 6 4 1 4 6 5 1 4 6 6 1 4 6 7 1 4 6 6 Mudstone: Md-lt olive gray. Mudstone: Olive gray. Oil Shale: Black to dk brow n gray. Oil Shale Oil Shale: Md-dk olive gray. Oil Y ield G airran T O C W t.% HI m g H C /g O C 1 3 C K e r o p er mil 3 5 □ 20 500 1000 -35 -25 O N to Figure 57. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 3 (1458.7-1468.6 ft), Blacks Fork-1. Note 81 3 C variation in oil shale. The “wet mudflat” microfacies contains oil-yields o f 2-6 gallons/ton and Type II/III kerogen with relatively limited geochemical contrast compared to the oil shale facies. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1426 1427 1426 1429 1430 1431 1432 1433 1434 1435 1436 1437 1436 1439 1440 Mudstone: Md greenish grey. Top of cycle grad es to oil shale above 1427.4- 1427.6 light grey: 1429.2-1429.4 light grey; 1429.5 pebble conglomerate; 1429.9-1430.3 light gray. Mudstone: Greenish gray. Mudstone: Md grey to oilve gray. 1434.5- 1434.9 occasional thin tr ana. Oil Shale: Md-dk olive gray. G rades from black at 1436 to green at 1435.5. Oil Shale: Md olive gray, som e : laminations. Oil Shale: Md-dk alive grey to olive 1437.3- 1439.3. Oil shale md- dk olive grey 1439.3- 1440.5. Oil Yield Gal/Tan T O C W t .% 35 a HI mg HC/g GC ! ■ 13C Kero per mil 10 300 1000 -35 Total Sulfur W t .% -25 0 C \ Figure 58. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 5 (1425.9-1440.5 ft), Blacks Fork-1. Oil shale facies consists o f organic-rich mudstone with oil-yields < 1 5 gallons/ton and TOC values < 6 wt. %. Limited geochemical contrast in HI and the 51 3 C occurs between oil shale and “wet mudflat” microfacies. ^ Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Oil Y ield Gal/Ton T O C Wt.% HI mg HC/gOC 1 3 C K ero par mil 123 0 1231 123 2 123 3 1 23 4 123 5 123 6 1 23 7 123 6 123 9 124 0 1241 124 2 124 3 124 4 1 2 4 5 1 2 4 6 1 2 4 7 1 2 4 8 1 2 4 9 1 2 5 0 Siltstone: Md-lt greenish gray. 1229.2 algal dolomite layerB 1229.2.1230.0-1233.1 gray green muddy siltstone. Siltstone: Contains some vfg sandstone, bedding is common, carbonaceous lamina, burrow s? 1234.1-1234.3 dk green mudstone, silty. 1235.05-1235.25 dk green mudstone, silty. 1237.0-1237.5 dk green mudstone, silty. 1239.2-1239.9 dk green mudstone, silty. 1 I I I I 1 . . . . . . . . . . . . 1 1 1 1 1 1 1 1 1 ! 1 1 . . . . . . . . . . . i. i - i - i -i. i - i- i - i. i. i - i . . . . . . . . . . . . 1 1 1 1 1 1 1 1 1 1 1 1 . . . . . . . . . . . 1 1 1 1 1 1 I 1 1 1 1 . . . . . . . . . . . . 1 1 1 1 1 1 t 1 1 1 1 1 . . . . . . . . . . . I'lllll'll'lll I -1 -1-1 -1-1■ I ■ I -1' I ■ I ■ I Mudstone: Md-lt alive gray, some siltstone. 1234.4-1243.7 banded. 1245.0-1247.0 dk green mudstone. Marlstone: Lt-md brownish gray. Mudstone: G rades to oil shale. Oil Shale: Md blk, brownish gray. > > > > > > > > > Tuff K A Git Shale: B lack J 4 0 0 1 5 Q 1 0 0 0 -3 5 -2 5 0\ 4 ^ Figure 59. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 20 (1229.2- 1250.8 ft), Blacks Fork-1. The “dry mudflat” microfacies contains minor amounts o f Type III/IV kerogen and consists o f a silty mudstone. A 51 3 C enrichment in kerogen occurs above oil shale. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1218 1 2 1 9 1220 1222 1223 1224 122S 1227 1228 1229 - Mudstone: Md-lt green, marly, massive, relatively uniform. 1219.75 halite band 1 Q ". Mudstone: Md green gray. G rades to thin organic-rich mudstone layers in places. Mudstone: Dk green. 1226.Q-1226.7 Mudstone almost grades to oil shale. Carbonate: Md olive gray and brownish gray. Some banded layered mudstone with carbonate. Oil Shale: Md dive gray, almost mudstone. Oil Shale: Md olive gray to brow n gray. Increasing organic content with depth. Oil Y ield G allon T O C Wt.% i i i i j ! I ; ; s I i i i ! I HI mg HC/g OC > j 1 : i : • 5 i i i : i r - 1 ? i i i l i i i i I I i : : I i i * j * ■ i mi 1 3 C K ern per mil 40 o 15 300 1QQ0 .35 -25 Figure 60. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 21 (1217.8 - 1229.2 ft), Blacks Fork-1. Oil shale facies consists o f organic-rich mudstone rather than oil shale based on low organic content. Note sharp 51 3 C enrichment in kerogen above the oil shale facies. Top of mudflat facies (1218 ft) represents geochemical transition to overlying cycle. 0\ U i Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 207.3 Ft IS C5 ‘ C2949.5 wt. 1210 bftswn 0 1 S & G k - t S c tx m m . O r a t S s s t o qSive g ra y a t b a s e . Ca S h a f e r - # iirowrvgray.cksctes to btacs » base. 8wfe£ia and J - J U J a * J~ '210.95 Ft Cj-Cjg 72.2 Wt. % : lVf.iUkliihliAUHu 1211.6 Ft Cs-Cjg' 90.1 w t.' ! 1217.1 Ft Figure 61. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 22, (1204.5-1217.8 ft) Blacks Fork-1. Thick oil shale facies displays small variations in TOC, HI, and S1 3 C kerogen. Pyrolysate from mudflat facies contains reduced C5 + n-aliphatics compared to oil shale. The 1 3 C kerogen enrichment in mudflat facies parallels TOC. Note geochemical expression of half-precessional cycle at top of oil shale facies. IS= internal standard o\ O s Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1196 1198 1 2 0 1 1204 Mudstone: Dk-olive-green, m assive. Laminated mustone @ 1 1 9 4 .5 -1 1 9 4 .7 . Marlstone: Dk-olive-cp'een, m assive laminated tu ff in low er part. Carbonate: Dk green-gray w iththin oil shale. Mudstone: Dk-green, very thin bedded to varved , interbedded, dolomite. Thin bed o ftro n a at 1 ,199.7. Oil shale appearance in places. Trona: B row n, finely crystalline, thin interbedded oil shale v e rv e s at 1 ,2 0 1 .3 ,1 ,2 0 1 .4 ,a n d 1 ,2 0 2.2-1,202.4. Oil Shale: 2" thick Oil Yield G a l/T o n Oil Shale: Black, varved , dolam ie lenses in lo w er part. I i i i ! I i I ! i i t : I ; I i i : i 1 ! ; i ; i i I i i ! i I ; I : : : : i . ill; I ; i ; TOC W t.% H I m g H C /g O C 13C Kero p e r m il ' j i i : • I I I ; ; 1 1 1! ! : I i i ! ; : ; : ' : ; I i I ! I Total Sulfur wt.% 100 0 -3 5 Figure 62. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 23 (11931- 1204.5 ft), Blacks Fork-1. Cycle contains thin oil shale and high TOC zone (1204.1-1204.4 ft) indicating an optimal organic accumulation event. Oil shale that is directly below trona (1203.4 ft) is geochemically similar to main oil shalek thin oil shale (1202.2-1202.4 ft) occurs in trona bed and contributes to its oil-yield. < i Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. O ccassonsS %mS$ « j* io itTMtk. D f c ’ iroiM fehgray. g r a y s L a s i k s a e c e r t a i n s - $ m z o f g a r i t e maKer, : * * < > w f t . 9 r e * n M a ta * * * # ) tftitfstone:Cfc^eesv O E C S S S a O f s a l & S P f f i ? b e J & J d s t c e s E t & M i k b r o w n i s h g r a y th fe S s a e sih e a n d c a lc a f e e u s a v te k m b m v i* . 1 1 9 1 .5 4 1 9 2 0 0 * S h afer 1 1 9 2 .0 4 1 S 2 8 < * g r e e * . 1 1 9 2 .8 4 SS 3.5 & b r o w n lo fcfeek 1 1 S 3 .4 4 1 ® 3 ,? d S i g r e e n , 03 Yield O a i f T o r t T O C W t .% HI 13C Kero TwalSuSur m sH O a o c p » tM m % IS 1192.0 Ft is Pyrolysis-GC C5 -C2 9 45.7 wt % 1192.92 Ft C5 -C2 g 79.6 wt 1193.70 Ft Cc-Coq 58.5 w t1 IS 1 0 0 0 * 3 5 - 2 5 0 Figure 63. Lithologic description, and oil-yield and geochemical patterns versus depth for Wilkins Peak cycle 24 (1179.0 - 1193.6 ft), Blacks Fork-1. Only 0.8 ft of oil shale facies has yields > 5 gallons/ton. A sharp 5 % o 1 3 C enrichment in kerogen occurs at the top of the oil shale facies. The 1 3 C-enriched sample at 1188.0 ft consists o f carbonaceous material. Pyrolysate from organic-rich zone (1192.9-1193.0 ft) is aliphatic-rich compared to samples at the top and base o f the oil shale that have lower HI values and consist of bituminite. IS = internal pyrolysate standard. OO Wilkins Peak Eccentricity E (1164.8-1250.8 Feet Depth Oil-Yield Depth Oil-Yield Depth Oil-Yield Depth Oil-Yield (Feet) Gallons/Ton (Feet) Gallons/Ton (Feet) Gallons/Ton (Feet) Gallons/Ton Cycle 20 Cycle 21 Cycle 22 Cycle 23 1229.2-1233.1 0 . 1 1217.8-1219.0 0.5 1204.5-1205.5 1.5 1193.6-1194.7 5.4 1233.1-1237.5 0 . 1 1219.0-1221.5 0 . 0 1205.5-1206.5 1.9 1194.7-1195.7 0.5 1237.5-1241.8 0 . 1 1221.5-1224.0 0 . 1 1206.5-1207.5 1.3 1195.7-1196.7 0 . 2 1241.8-1244.6 0 . 1 1224.0-1225.6 0.4 1207.5-1209.0 1 . 8 1196.7-1197.9 1 . 2 1244.6-1247.0 0 . 1 1225.6-1226.7 1 . 6 1209.0-1209.5 4.3 1197.9-1199.0 1 . 1 1247.0-1248.0 1 . 1 1226.7-1227.9 2 . 2 1209.5-1210.5 0 . 1 1199.0-1200.0 1.3 1248.0-1249.0 2 . 1 1227.9-1228.6 3.8 1210.5-1211.6 4.7 1 2 0 0 .0 -1 2 0 1 . 0 1 . 1 1249.0-1249.7 9.7 1228.6-1229.2 13.8 1 2 1 1 .6 - 1 2 1 2 . 6 29.2 1 2 0 1 .0 -1 2 0 2 . 1 1.7 1249.7-1250.3 12.5 1212.6-1213.9 1 2 . 2 1202.1-1203.4 1 0 . 2 1250.3-1250.8 26.3 1213.9-1215.2 11.5 1203.4-1204.5 37.2 1215.2-1215.9 22.3 1215.9-1216.8 30.8 1216.8-1217.8 27.8 Cycle 24 1164.8-1166.3 0.4 1166.3-1167.7 0 . 0 1167.7-1170.0 0 . 0 1170-1175.0 0 . 1 1175.0-1180.0 0 . 0 1180.0-1184.0 0 . 0 1184.0-1185.1 0 . 1 1185.1-1187.4 0 . 0 1187.4-1190.0 0 . 1 1190.4-1192.0 2 . 6 1192.0-1192.8 4.9 1192.8-1193.6 23.8 Wilkins Peak Eccentricity A (1502.2-1425.9 Feet) I Depth Oil-Yield Depth Oil-Yield Depth Oil-Yield Depth Oil-Yield (Feet) Gallons/Ton (Feet) Gallons/Ton (Feet) Gallons/Ton (Feet) Gallons/Ton Cycle 1 Cycle 2 Cycle 3 Cycle 4 1486.6-1488.0 1.4 1468.6-1469.6 1 2 . 0 1458.7-1460.0 4.1 1440.5-1441.9 7.9 1488.0-1491.0 1.7 1469.6-1471.0 6.4 1460.0-1462.4 2 . 6 1441.9-1443.6 5.0 1491.0-1493.6 0.3 1471.0-1474.9 3.8 1462.4-1464.8 2 . 8 1443.6-1445.8 9.3 1493.6-1496.2 0 . 8 1474.9-1476.5 1.9 1464.8-1465.6 6.4 1445.8-1448.4 4.0 1496.2-1497.2 1 . 2 1476.5-1478.2 3.0 1465.6-1466.7 28.2 1448.4-1450.2 8 . 2 1497.2-1498.7 19.9 1478.2-1481.0 8.9 1466.7-1467.7 26.3 1450.2-1452.0 6 . 6 1498.7-1499.7 24.6 1481.0-1483.9 1 1 . 1 1467.7-1468.6 15.3 1452.0-1453.0 8.5 1499.7-1500.6 14.4 1483.9-1484.9 17.4 1453.0-1454.2 13.9 1500.6-1501.5 31.8 1484.9-1485.6 2 1 . 0 1454.2-1455.2 13.4 1501.5-1502.2 13.2 1485.6-1486.6 9.6 1455.2-1456.2 17.4 1456.2-1457.0 16.2 1457.0-1457.8 2 0 . 2 1457.8-1458.7 14.8 Cycle 5 1425.9-1428.3 2.4 1428.3-1430.7 1.7 1430.7-1432.7 1.7 1432.7-1434.4 2 . 0 1434.4-1435.4 1.9 1435.4-1436.1 1 2 . 8 1436.1-1437.3 14.0 1437.3-1438.3 13.0 1438.3-1439.3 12.4 1439.3-1440.5 12.3 Table 15. Fischer assay oil-yields for measured intervals in selected precessional cycles, in eccentricity cycles A and E, Wilkins Peak Member; Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle Depth TOC HI 81 3 C Kerogen 81 3 C Carbonate 51 s O Carbonate Total Sulfur Tmax (F e e t) wt. % m g H C /g O C % . wt.% °c 24 1166.2 0.14 79.0 534 1169 0.11 200.0 417 1172.3 0.11 145.0 406 1179.9 0.21 71.0 . . . 1180.0 0.18 194.4 -25.9 0.3 -5.2 0.20 345 1181.2 0.15 40.0 -26.4 432 1182.85 0.14 14.0 298 1187.0 0.15 40.0 368 1188.0 0.24 158.3 -25.6 1.7 -4.7 417 1189.0 0.26 73.1 -26.0 401 1191.0 0.82 546.0 -26.4 1191.95 1.52 548.0 -27.6 <0.01 429 1192.05 2.23 543.0 -26.8 2.0 -3.3 425 1192.5 3.48 677.0 432 1192.92 23.18 877.3 -31.9 3.1 -1.6 0.15 447 1192.98 7.65 729.7 437 1193.4 13.34 731.0 0.16 446 1193.7 4.69 680.6 -31.8 2.9 -3.6 0.06 438 23 1194.05 1.68 671.0 -27.3 1.3 -6.7 428 1194.3 2.01 571.1 426 1194.65 4.44 694.6 -29.0 1.7 -5.8 439 1194.95 0.39 323.1 -25.8 0.68 429 1196.25 0.36 358.3 -26.0 0.62 429 1197.2 0.61 696.7 435 1198.35 0.65 427.7 -25.5 1.7 -5.8 432 1199.75 0.42 762.0 -25.4 0.02 421 1200.5 0.58 741.0 421 1200.85 1.87 567.0 -26.2 0.03 425 1201.25 0.29 255.2 -25.7 0.1 -5.8 431 1201.4 0.85 746.0 -27.9 427 1202.15 17.65 719.8 -29.8 0.48 444 1202.18 10.38 783.0 448 1203.4 0.97 800.0 -30.1 436 1203.4 9.02 833.6 -31.3 -0.1 -5.8 0.44 440 1203.55 16.9 955.6 443 1204.1 29.1 876.7 -30.4 0.9 -0.3 1.20 439 1204.4 26.18 847.8 447 1204.5 3.69 590.2 3.2 -2.4 0.34 439 22 1205.1 1.22 614.0 431 1205.5 1.13 611.0 434 1206.15 -24.7 1207.3 1.33 530.1 -25.8 2.6 -3.2 0.27 431 1209.0 2.7 625.9 -26.6 2.5 -3.6 0.04 428 1209.45 3.16 770.0 -27.5 3.2 -3.2 427 1210.7 10.67 741.0 -32.1 2.7 -3.4 446 1210.95 -30.1 1211.6 14.44 805.0 2.3 -2.8 445 1211.6 14.75 785.0 447 1212.0 17.19 866.8 -30.4 3.2 -2.0 1.23 445 1212.5 11.42 802.7 441 1213.1 7.47 657.7 -29.7 438 1214.1 6.43 763.6 0.27 437 1215.0 7.24 846.4 -29.8 2.6 -4.0 449 1215.45 10.37 798.0 445 1216.1 14.99 801.3 -30.9 1.01 443 1216.5 13.89 748.0 437 1217.1 19.73 872.8 -30.7 2.4 -2.8 1.32 442 1217.55 9.52 755.0 -30.3 439 1217.75 11.69 808.0 426 Table 16. Geochemical summary o f kerogen and rock properties for selected Wilkins Peak precessional cycles; Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle Depth TOC HI 81 3 C Kerogen 81 3 C Carbonate 81 8 0 Carbonate Total Sulfur Tmax (Feet) wt.% mg H C /g O C % . % « wt.% “C 21 1217.9 1.2 576.7 -29.9 435 1220.0 0.10 234.0 411 1223.0--046- 296.0 -25.0 436 1226.4 1.50 629.0 -27.8 444 1227.0 1.07 593.0 -27.9 441 1228.0 1.61 750.9 437 1228.45 2.49 716.0 -29.6 439 12128.8 4.52 827.0 432 1229.0 10.7 792.7 -33.8 440 1229.15 9.05 691.0 441 20 1230.95 0.47 134.0 -27.6 433 1235.0 0.15 40.0 -25.8 359 1237.1 0.52 121.2 424 1239.6 1.62 84.0 -25.8 438 1241.0 0.18 44.4 414 1242.9 0.25 128.0 -26.6 425 1246.0 0.42 233.3 -28.1 430 1247.2 1.62 700.0 432 1248.4 0.11 227.0 -31.2 430 1248.48 1.92 673.0 429 1249.2 5.45 900.0 -32.7 442 1250.4 15.98 949.4 -33.3 446 1250.65 11.05 834.0 447 1250.75 0.13 38.0 408 5 1426.0 1.34 528.0 -30.6 1.3 -5.5 0.07 437 1428.0 1.45 659.0 -33.3 426 1430.0 0.94 503.0 -28.9 0.7 -5.8 0.01 435 1430.4 -30.0 1430.95 0.85 481.0 434 1432.0 1.01 557.0 -29.9 441 1434.1 2.03 618.0 -29.8 438 1435.4 2.51 688.0 0.07 435 1436.0 5.7 791.0 -32.1 2.0 -4.6 439 1436.9 5.85 787.0 0.55 435 1437.9 5.03 790.0 -31.3 437 1440.0 3.05 736.0 -34.0 0.05 436 3 1460.9 0.93 501.0 -31.0 428 1463.0 1.76 665.0 -30.9 431 1466.1 13.04 738.0 -31.0 439 1467.0 14.05 765.0 -31.8 440 1467.5 18.2 764.0 436 1467.9 7.17 792.0 -34.7 446 1 1488.8 2.04 326.0 -31.8 0.9 -6.5 1.15 431 1490.9 1.12 434.0 -31.3 2.5 -6.1 0.16 433 1493.0 0.7 330.0 -30.6 433 1495.0 0.59 427.0 -31.3 3.7 -4.2 0.22 434 1497.0 1.24 527.0 0.05 425 1497.9 10.64 813.0 -34.3 3.2 -5.5 445 1498.85 9.74 761.0 -32.5 1.06 439 1499.95 17.74 841.0 -34.8 3.3 -6.0 444 1501.05 19.28 778.0 -34.5 443 1501.6 19.87 818.0 -34.6 2.9 -6.5 1.20 448 1502.2 4.95 646.0 -33.3 1.59 439 Table 16 (Continued). Geochemical summary of kerogen and rock properties for selected Wilkins Peak precessional cycles; Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5,3c S a tu ra te s 13c A ro m a tic ? 513C A ro m a tic - S a tu ra te C 2 9-C3 B T o ta l H o p a n e s P ris ta n e / P h y ta n e C 2 9 /C 2 7 S te ra n e s S te ra n e s / H o p a n e s G a m m a c e ra n e / H o p a n e c « / c „ T ric y c lic T e rp a n e s C M/C M T ric y c lic T e rp a n e s C 26/C M T ric y c lic T e rp a n e s C M T e tra c y c lic / C jjT r ic y c llc T e rp a n e s % 0 % Q (ppm ) -29.1 -27.1 2 .0 1 1 4 4 3 0 .7 6 11.9 3.2 0.07 0 .2 5 0 .4 4 2.1 0 .4 6 -2 8 .5 -3 0 .9 2 .4 1 1 2 9 3 0 .8 9 12.5 3 .4 9 0 .0 9 0 .3 6 0.51 1.91 0 .7 7 nd nd nd 9 2 9 4 0 .9 5 10.5 3 .3 2 0 .1 2 0 .3 8 0 .5 6 1.75 0 .7 8 -2 9 .5 -2 8 .2 1.3 8031 0 .8 7 9.7 3 .5 0.1 0 .2 8 0 .5 9 1.79 0 .7 nd nd nd 4471 0 .5 6 11.3 4 .1 2 0 .0 3 0.61 1.61 0 .9 9 3 .5 -2 7 .6 -2 6 .0 1.6 5 942 0 .2 9 19.5 4 .7 0 .0 7 0 .6 9 1.4 1.3 3 .8 -3 1 .9 -3 0 .9 1.0 1 5 7 3 3 0 .1 9 10.0 3 .2 6 0 .2 0 .0 9 0 .9 9 1.9 0 .2 8 -3 1 .4 -3 0 .9 0.5 1 4 902 0 .1 9 11.5 3 .3 9 0.21 0.1 1 .0 5 1.94 0 .2 6 -2 7 .9 -2 6 .0 1.9 "2859 0 .6 5 8 . 2 3 .2 6 0 . 1 1 0.3 6 1.45 F 1.15 2 .6 3 8.8 3 .3 0.11 0 .3 6 1.45 nd nd nd 0.81 9 5 .3 0.18 0 .3 8 1.06 0 .9 8 2 .0 7 -3 0 .9 -2 9 .5 1.4 1 6 395 0 .3 11.7 3 .8 6 0 .1 7 0.11 0 .3 5 2 .0 4 0 .2 5 nd nd nd 3 9 7 5 8 0 .3 4 9.7 1.69 0 .2 9 0.1 0 .5 3 2 .3 6 0 .1 8 -3 0 .4 -2 8 .8 1.6 1 7 149 0 .3 10.0 2 .5 5 0.18 0 .0 9 0 .4 6 2 .0 6 0 .2 2 -3 0 .9 -2 9 .6 1.3 9 7 5 2 0 .3 5 9.1 2.11 0.24 0 .0 9 0.5 2 2.11 0 .2 nd nd nd 12 3 3 1 .8 0 .3 6 1 0 .6 7 4 .3 5 0 .0 5 0 .6 7 1.25 1.13 7 .2 2 nd nd nd 8 947 0.31 6.6 3 .1 4 0.21 0 .2 4 0 .1 9 1.77 0 .5 2 -3 1 .7 -2 9 .3 2 .4 1 2 8 3 0 0 .3 6 .6 4 3.31 0 .2 0 .2 3 0 .1 8 1 .7 4 0 .4 6 -3 0 .2 -28.1 2.1 9521 0 .8 4 3 .5 3 .5 3 0.27 0 .6 5 1.69 1.01 8 .5 9 -3 4 .9 -3 2 .6 2 .3 2 6 4 1 6 0 .3 4 2 .3 2.31 0.22 0 .1 7 1.29 2 .3 6 0 .3 9 -3 4 .8 -3 3 .0 1.8 25341 0 .3 5 2 .8 2.81 0 .2 5 0 .2 2 1.33 2 .3 4 0 .5 8 -3 2 .3 -3 0 .0 2 .3 2 1 1 0 0 0 .3 5 3.0 3 .0 2 0 .2 9 0 .2 7 1.26 2 .1 7 0 .8 4 nd - not determ ined Table 17. Geochemical summary of extractable organic matter for Wilkins Peak precessional cycles; Blacks Fork-1. Carbon isotope composition of saturate and aromatic fractions, and select biomarker ratios o f saturate fraction of extracts. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle Depth TOC S1 S2 S3 TMAX HI Ol S2/S3 PI S1/TOC Total S ulfur fFeet) W t. % mg HC/g Rk mg HC/g Rk mg COj/g Rk °C mg HC/g OC mg COj/g OC wt. % 24 1165 3.61 1.43 27.83 1.52 424 771.00 42.00 18.31 0.05 40.00 1165.1 2.69 1.23 19.01 2.54 426 707.00 94.00 7.48 0.06 46.00 1166.2 0.14 0.04 0.11 0.79 534 79.00 564.00 0.14 0.27 29.00 1169.0 0.11 0.09 0.22 0.43 417 200.00 391.00 0.51 0.28 79.00 1172.3 0.11 0.12 0.16 0.6 406 145.00 545.00 0.27 0.42 106.00 1179.9 0.21 0.06 0.15 0.47 — 71 224 0.32 0.29 29 1180.0 0.18 0.09 0.35 0.76 345 194.44 422.22 0.46 0.20 50.00 0.2 1181.2 0.15 0.06 0.06 1.18 432 40.00 786.67 0.05 0.50 40.00 1182.85 0.14 0.04 0.02 0.68 298 14.00 486.00 0.03 0.67 29.00 1187.0 0.15 0.05 0.06 1.4 368 40.00 933.33 0.04 0.45 33.33 1187.95 0.24 0.13 0.38 0.83 417 158.33 345.83 0.46 0.25 54.17 1189.0 0.26 0.1 0.19 0.6 401 73.08 230.77 0.32 0.34 38.46 1191.95 1.52 0.71 8.33 0.89 429 548.00 59.00 9.36 0.08 47.00 <0.01 1192.05 2.23 1.22 12.1 2.16 425 543.00 97.00 5.60 0.09 54.70 1192.5 3.48 1.1 23.56 0.86 432 677 25 27.4 0.04 32 1192.92 23.18 3.59 203.36 4.06 447 877.31 17.52 50.09 0.02 15.49 0.15 1192.98 7.65 1.17 55.82 2.09 437 729.67 27.32 26.71 0.02 15.29 1193.4 13.34 3.54 97.49 3.48 446 731 26 28.01 0.04 27 0.16 1193.7 4.69 0.8 31.92 1.41 438 680.60 30.06 22.64 0.02 17.06 1193.85 0.06 23 1194.05 1.68 0.57 11.28 0.75 428 671 45 15.04 0.05 34 1194.3 2.01 0.84 11.48 1.14 426 571.14 56.72 10.07 0.07 41.79 1194.65 4.44 0.98 30.84 1.76 439 694.59 39.64 17.52 0.03 22.07 1194.95 0.39 0.26 1.26 1.06 429 323.08 271.79 1.19 0.17 66.67 0.68 1196.25 0.36 0.16 1.29 1.06 429 358.33 294.44 1.22 0.11 44.44 0.62 1197.2 0.61 0.33 4.25 1.16 435 696.72 190.16 3.66 0.07 54.10 1198.35 0.65 0.21 2.78 1.53 432 427.69 235.38 1.82 0.07 32.31 1199.75 0.42 0.19 3.20 0.54 421 762.00 129.00 5.93 0.06 45.00 0.02 1200.5 0.58 0.33 4.30 0.77 421 741.00 133.00 5.58 0.07 57.00 1200.85 1.87 0.93 10.6 1.1 425 567.00 59.00 9.64 0.08 50.00 0.03 1201.3 0.29 0.09 0.74 18.19 431 255.17 6272.41 0.04 0.11 31.03 1201.35 0.85 0.32 6.34 26.36 427 746.00 3101.00 0.24 0.05 38.00 1202.15 17.65 4.6 127.05 3.33 444 719.83 18.87 38.15 0.03 26.06 0.48 1202.18 10.38 4.98 81.28 3.35 448 783.00 32.00 24.26 0.06 47.68 1203.4 0.97 0.21 7.76 12.8 436 800.00 1319.59 0.61 0.03 21.65 23 1203.4 9.02 2.37 75.19 18.58 440 833.59 205.99 4.05 0.03 26.27 0.44 1203.55 16.9 3.69 161.5 2.51 443 955.62 14.85 64.34 0.02 21.83 1204.1 29.1 8.54 255.11 2.9 439 876.67 9.97 87.97 0.03 29.35 1.2 1204.4 26.18 7 221.96 3.03 447 847.82 11.57 73.25 0.03 26.74 1204.5 3.69 3.52 21.78 0.98 439 590.24 26.56 22.22 0.14 95.39 0.34 22 1205.1 1.22 0.32 7.5 1.52 431 614.00 125.00 4.92 0.04 26.00 1205.5 1.13 0.38 6.91 1.51 434 611.00 133.00 4.59 0.05 34.00 1207.3 1.33 0.51 7.05 1.65 431 530.08 124.06 4.27 0.07 38.35 0.27 1209.0 2.7 1.7 16.9 3.72 428 625.93 137.78 4.54 0.09 62.96 0.04 1209.45 3.16 1.19 24.34 2.02 427 770.00 64.00 12.05 0.05 38.00 1210.7 10.67 4.45 79.04 2.05 446 741.00 19.00 38.56 0.05 41.71 1211.6 14.44 4.63 116.23 2.88 445 805 20 40.36 0.04 32 1211.6 14.75 3.65 115.78 2.11 447 785.00 14.00 54.87 0.03 24.75 1211.95 17.19 3.6 149.01 4.18 445 866.84 24.32 35.65 0.02 20.94 1.23 1212.5 11.42 3.39 91.67 2.1 441 802.71 18.39 43.65 0.04 29.68 1213.1 7.47 2.96 49.13 1.25 438 657.70 16.73 i_39.30 0.06 39.63 1214.1 6.43 1.99 49.1 1.37 437 763.61 21.31 35.84 0.04 30.95 0.27 1214.95 7.24 1.51 61.28 1.91 449 846.41 26.38 32.08 0.02 20.86 1215.45 10.37 3.27 82.78 2.07 445 798 20 39.99 0.04 32 1216.1 14.99 3.02 120.12 2.14 443 801.33 14.28 56.13 0.02 20.15 1.01 1216.5 13.89 2.33 103.88 3.12 437 748.00 22.00 0.02 17.00 1217.08 19.73 4.51 172.2 4.44 442 872.78 22.50 38.78 0.03 22.86 1.32 1217.55 9.52 4.05 71.87 2.78 439 755 29 25.85 0.05 43 1217.75 11.69 6.61 94.49 2.96 426 808 25 0.07 57 21 1217.9 1.2 1.59 6.92 1.33 435 576.67 110.83 5,20 0.19 132.50 1220.0 0.10 0.19 0.23 1.36 411 234 1360 0.17 0.45 190 1222.0 0.16 0.14 0.47 1.75 436 294 1094 0.27 0.23 88 1224.0 0.25 0.17 1.09 1.11 439 436 444 0.98 0.13 68 1226.4 1.50 0.43 9.44 1.46 444 629.00 97.00 6.47 0.04 29.00 1227.0 1.07 0.42 6.35 0.6 441 593 56 10.58 0.06 39 1228.0 1.61 0.64 12.09 1.26 437 750.93 78.26 9.60 0.05 39.75 1228.45 2.49 0.62 17.82 1.45 439 716 58 12.29 0.03 25 1229.0 10.7 1.95 84.82 1.63 440 792.71 15.23 52.04 0.02 18.22 1229.15 9.05 2.16 62.50 2.27 441 691.00 25.00 27.53 0.03 24.00 20 1230.95 0.47 0.13 0.63 1.2 433 134.04 255.32 0.53 0.17 27.66 1235.0 0.15 0.05 0.06 2.14 359 40.00 1426.67 0.03 0.45 33.33 1237.1 0.52 0.1 0.63 2.48 424 121.15 476.92 0.25 0.14 19.23 1239.6 1.62 0.19 1.36 1.28 438 83.95 79.01 1.06 0.12 11.73 1241.0 0.18 0.05 0.08 2.12 414 44.44 1177.78 0.04 0.38 27.78 1242.9 0.25 0.07 0.32 1.65 425 128.00 660.00 0.19 0.18 28.00 1245.95 0.42 0.14 0.98 0.78 430 233.33 185.71 1.26 0.13 33.33 1248.4 0.11 0.06 0.25 0.65 430 227.00 591.00 0.38 0.19 55.00 1248.48 1.92 0.67 12.93 1.89 429 673.00 98.00 6.84 0.05 2.87 1249.2 5.45 1.43 49.05 1.66 442 900.00 30.46 29.55 0.03 26.24 1250.4 15.98 3.32 151.71 2.26 446 949.37 14.14 67.13 0.02 20.78 1250.65 11.05 2.1 92.11 2.56 447 834 23 35.98 0.02 19 1250.75 0.13 0.02 0.05 1.52 408 38.00 1169.00 0.03 0.29 15.00 Table 18. Total organic carbon (TOC), Rock-Eval pyrolysis and total sulfur for selected precessional cycles, Wilkins Peak Member, Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth Interval (JydO # Lam algfnite A m o rp n o u s Bftum lte s tru c tu re d Llptlnlte Liptodetlnite Vitrinlte Inertinlte B itum en C o m m en ts 1190.90 1191.00 24 M A T s M T Liptodetinite consists of degraded algalbodies? OM occurs as non-continuous lamina 1192.00 1192.10 24 M A T s M OM occurrs as bands and discontlnous layers 1192.90 1193.00 24 D M T M T M Matrix Lamalginite 1193.70 1193.80 24 S A T M M T 1194.20 23 s A T M M T 1194.60 1194.75 23 A S T T T 1198.35 1198.55 23 M D T M T T 1202.15 1202.20 23 A S M M M Matrix & indivual lamafginite 1203.40 1203.50 23 A S T 87 T M Matrix lamalginite with variable fluorescence 1204.40 1204.50 23 D M R S M M Matrix lamalginite 1206.95 1207.05 22 D A S T M Matrix & indivual lamalginite. 1207.30 1207.46 22 S A T M T T? Indivdual stringers of lamalginite Also some matrix lamalginite 1210.70 1210.80 22 D M T? 1211.50 1211.65 22 A S M S M Bacterial mat-like material? 1211.95 1212.10 22 A S T S Matrix-band lamalatginite; lamalginite-bituminite; Bacterial mat-like material 1214.85 1215.05 22 D s T M T Transition to bituminite from matrix lamalginite 1217.00 1217.10 22 D s T S M Bitumen filling voids Alternating matrix lamalinite and bituminite 1217.50 22 A A M M S 1241.00 1241.10 20 S D Siltstone with vitrinHic material 1248.40 1248.50 20 S A S M Matrix bituminite-lamalginite gradation 1249.20 1249.30 20 D S T T S M 1250.40 1250.50 20 D s T M T? M 1435.10 5 S A T T M T 1436.90 5 A S T T M T 1492.90 M A T M M T 1499.00 D S T T M T 1501.50 D T T M T T = Dominant : Abundant 3 = Some 4 * Minor R = Rarel r = T race I Table 19. Organic petrographic results for select Wilkins Peak samples, Eccentricity A and E, Blacks Fork-1. 175 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. significantly less nCs-C29 alkanes/alkenes (n-aliphatics) compared to the aliphatic- rich oil shales (Figures 61 and 63). Quantitative pyrolysis-GC results are listed in Appendix 5. Highest values of total sulfur occur in oil shales (1.0-1.6 wt. %), whereas most mudflat intervals contain less than 0.3 wt. % (Tables 16 and 18). A sharp 1 3 C enrichment in kerogen occurs at the top of the oil shale, or lower part of the mudflat in most cycles (Figures 56, and 59 to 63). The maximum 1 3 C enrichment in mudflat kerogen as compared to the oil shale, ranges between 5.5 and 8.9 % o in cycles 20-24. A 5 % o enrichment in kerogen occurs over a one-foot interval at the top of the oil shale facies in cycle 24 (Figure 63). In cycles 22 and 23, the 1 3 C composition of kerogen generally parallels the TOC and HI values in the mudflat facies (Figures 61 and 62). In eccentricity A, up to a 4.0 % o 8 1 3 C enrichment occurs I between the oil shale and mudflat facies. Overall, the 8 C composition of Wilkins Peak kerogen in Blacks Fork-1 ranges between -24.8 and -34.7 % o, similar to previous studies (Dean and Anders, 1991). The aromatic fraction of extracts from the • 1 3 mudflat facies is enriched in C compared to those in the oil shale (Figures 64 and Table 17). The saturate fraction of mudflat extracts display consistent differences in molecular properties compared to the oil shale facies (Figures 64-72). Mudflat extracts usually have higher pristane/phytane (Pr/Ph) ratios and a larger proportion of nC25-C29 alkanes. GCMS results document that mudflat extracts often have higher sterane/hopane, tricyclic terpanes/steranes, C24 tetracyclic/C23 tricyclic and C 19/C23 tricyclic terpane biomarker ratios, as well as lower C26/C25 tricyclic terpanes and C30 176 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Pr/Ph 0.84 O il Y ield 1490.9 Ft P h 1 4 8 ? n C . 1488 480 1498.0 Ft Pr/Ph 0.34 4 91 483 Pr/Ph 0.35 nC1 7 /C29 1.51 nC1 7 /P r 0.50 1501.0 Ft 484 495 4% 497 498 Pr/Ph 0.35 nC1 7 /C29 0.70 nC1 7 /P r 0.40 1502.0 Ft' 502 513C Bitum en Fraction S aturate -30.2%o Aromatic -28.1%o S aturate -34.9%o Arom atic -32.6%o S aturate -34.8%o Aromatic -33.0%o S aturate -32.3%o Aromatic -30.0%o Figure 64. Gas chromatography (GC) trace o f saturate fraction o f extracts from oil shale and mudflat facies; cycle 1, Blacks Fork-1. The extract from the mudflat facies has a higher pristane/phytane (Pr/Ph) ratio and negligible p-carotane (P) content compared to oil shale extracts. Note 1 3 C enrichment of saturate and aromatic fractions o f extract from the base o f oil shale and the mudflat facies. -j Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 48? . i » * i * 1 1 ■ 1 1 :. r Steranes/ C2 9 /C2 7 Gammacerane/ C2 3 /C2 4 C2 6 /C2 5 C2 4 Tetracyclic/ C1 9 /C2 3 Hopanes Steranes Hopane Tricyclic Tricyclic C2 6 Tricyclic Tricyclic 3.5 14.6 0.30 2.3 5.9 0.27 2.8 6.4 0.29 3.0 8.0 0.33 1.6 1.3 1.3 1.4 1.0 2.1 2.0 2.2 8.9 0.40 0.60 0.95 0.51 0.15 0.16 0.21 Figure 65. Gas chromatography-mass spectrometry (GCMS) results for saturate fraction of extracts from cycle 1. Although GCMS-biomarker results o f oil shales are generally similar, minor variations occur. Terpane and sterane biomarker ratios of extracts from the mudflat facies (1490 ft) indicate a different source input compared to oil shale facies. Complete name and definition of biomarker ratios are provided in Table 20 and Appendix 6. -j O O Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 1427.0 Ft Pr/Ph 0.36 nC1 7 /C2 9 0.60 nC1 7 /Pr 0.88 Ph 1427 1426 1429. Ft Pr/Ph 0.36 1431 1432 1433 Pr/Ph 0.31 nC^/Ggg 0.54 nC1 7 /Pr 0.60 1435.3 Ft 1434 1435 01 Shale 143? 1437.85 Ft Pr/Ph nC1 7 /C: nC1 7 /Pr 0.56 0.30 0.27 1440 Figure 66. GC traces of saturate fraction of mudflat and oil shale extracts from cycle 5. Extracts from “wet mudflat” microfacies have similar Pr/Ph ratios as oil shale extract however, they do not contain p-carotane (P). Note strong odd/even n- alkane predominance in C2 5 -C3 0 range consistent with landplant input. VO Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. O il Yield 120$ 1206 1207 1208 1208 1210 1211 1212 1214 1215 1216 1217 tvlaristone U v . V 4 A » \ A A - ' . - v , . v \ a a 4 a - \ - \ A ' b ta r ls to n e M a r te tc n e O il S t a l e Trona < » S t a t e Q 1 S t a l e ................................. — .........r - - r ^ : r ! r " r r " : : : : : r r r : r r r r r : : r r r r r r : : '— : : : = = = e : .... . ...... 01 S t a l e ...........................— 0 1 S t a l e = = = = = 1209.0 Ft Pr Ph i 'Si* JJJJLii nC ,- [25 | J . Pr/Ph 0.81 nC1 7 /C2 9 2.38 nC1 7 /Pr 0.81 51 3 C Bitumen Fraction 1210.8 Ft 1 , 1 I ' 1 Pr/Ph 0.3CJ nC1 7 /C2 9 1.80 nC1 7 /Pr 1.20 P Saturate -30.9%o Aromatic -29.5%o 1213.9 Ft i,i i' j l .I . I . I i i 1 'iiL ' Pr/Ph 0.30 nC1 7 /C2 9 1.64 nC1 7 /Pr 1.18 Saturate -30.4%o Aromatic -28.8%o 1217.0 Ft i i i . » V i 1 1 . I !i !, J J j j L li _ L i i Pr/Ph 0.35 nC17/C29 1.17 nC17/Pr 1.24 IlLi. V I -L * I i Saturate -30.9%o Aromatic -29.6%o Figure 67. GC traces o f saturate fraction o f oil shale, mudflat and trona extracts from cycle 22. Note higher Pr/Ph and odd/even predominance in nC2 5-C3 0 range of mudflat extract (1209.0 ft) indicating greater landplant input and likely more oxidizing conditions compared to oil shale facies. Content o f p-carotane (P) varies throughout oil shale facies. OO o o f th e copyright owner. Further reproduction prohibited without permission. 1205 1206 120? 1208 1203 1210 1211 1212 1213 1214 1215 121$ 1217 eggs a ' t S g i f SteranesI C2 9 /C2 7 Gammacerane/ C2 3 /C2 4 C2 6 /C2 5 C2 4 Tetracyclic/ C1 9 /C2 3 Hopanes Steranes Hopane Tricyclic Tricyclic C2 6 Tricyclic Tricyclic 3.3 8.8 0.11 5.3 9.0 0.18 5.2 11.7 0.18 2.3 9.7 0.27 2.6 10.0 0.18 1.45 1.15 1.06 0.98 0.34 2.0 0.54 2.3 0.46 2.1 2.63 2.07 0.25 0.19 0.22 0.36 0.38 0.11 0.10 0.09 2.6 9.1 0.25 0.49 2.1 0.20 0.09 0 0 Figure 68. GCMS biomarker parameters for saturate fraction of extracts, cycle 22. Note overall similarity in biomarker parameters of oil shale extracts. Solvent extracts associated with the trona and mudflat have a higher sterane/hopane ratio suggesting different source input. Complete name and definition of biomarker ratios are provided in Table 20 and Appendix 6. Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. Oil Yield 1194 11SS 1197 119 8 1199 1200 1 2 0 1 1202 1203 1204 1201.4 Ft Pr/Ph 0.29 nC1 7 /C2 9 1.26 nC1 7 /Pr 0.67 [ i ii is II I 1203.4 Ft Pr/Ph 0.19 nC1 7 /C2 9 1.49 nC1 7 /Pr 0.68 S I: 'i S 2 S S S S 1204.1 Ft Pr/Ph 0.19 nC1 7 /C2 9 1.94 nC1 7 /Pr 0.69 Mudst 8 8 I f | 1 6 * , i .i iQiJ'ji; t n a i * * i 1204.8 Ft 0.65 1.06 nC1 7 /Pr 0.44 Pr/Ph x S l Shale nCi7/C 2 9 Trona « Shale i I 1 * ■ I 8 1 I I i I i H I' 51 3 C Bitumen Fraction Saturate -27.6%o Aromatic -26.0%o Saturate Aromatic -31.9%o ■30.9% o Saturate -31.4%o Aromatic -30.9%o Saturate -27.9%o Aromatic -26.0%o Figure 69. GC traces o f saturate fraction of extracts from cycle 23. Extract from trona contains negligible p-carotane (P), a higher Pr/Ph ratio and different n-alkane profile compared to oil shale. Note 1 3 C enrichment in the saturate and aromatic fractions of the trona extract. 00 h J Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. 1194 1195 1 1% 1197 1198 11% 1 2% 1201 1202 1 2 0 3 1204 SS SiS S S S i SteranesI C^IC2 7 Gammacerane/ C2 3 /C2 4 C2 6 /C2 S C2 4 Tetracyclic/ C1 9 /C2 3 Hopanes Steranes Hopane Tricyclic Tricyclic C2 8 Tricyclic 4.7 19.5 0.07 1.4 1.3 3.8 Tricyclic 0.69 4.2 10.0 4.4 11.5 4.2 8.2 0.23 0.23 0.12 1.0 1.0 1.5 1.8 1.7 1.1 0.26 0.26 2.62 0.08 0.08 0.24 Figure 70. GCMS biomarker ratios o f saturate fraction o f extracts from cycle 23. Mudflat extracts directly underlying oil shale at base o f cycle 23 (1204.8 ft) and overlying trona (1200.6 ft) have higher C2 9 /C27 ratios, and consistent differences in tricyclic and tetracyclic terpanes compared to oil shale. 00 U ) 891499 Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. Oil Yield 61 3 C Bitumen Fraction 1192.0 Ft 1181 Saturate -29.1%o Aromatic -27.1%o 1182 1183 Pr/Ph 0.89 nC1 7 /C2 9 7.65 nC1 7 /Pr 1.40 1192.0 Ft 1184 Saturate -28.5%o Aromatic -30.9%o 118? Pr/Ph 0.95 nC1 7 /C2 9 9.45 nC1 7 /Pr 1.51 1193.4 Ft ire fere 1188 Pr/Ph 0.87 nC1 7 /C2 9 4.07 nC1 7 /Pr 1.08 1193.8 Ft 1191 Saturate -29.5%o Aromatic -28.2%o 1192 1193 Figure 71. GC traces for saturate fraction of oil shale and mudflat facies from cycle 24. Note increase in squalane (S) and possible C2 5 isoprenoid (I) at top o f oil shale facies. Compared to other cycles, oil shale extracts have higher Pr/Ph ratios. The S1 3 C o f the aromatic fraction o f the extract from the mudflat and basal oil shale is enriched compared to the saturate fraction. O O 4 ^ Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. 90 Iteranes/ C2 9 /C2 7 Gammacerane/ C2 3 /C2 4 C2 6 /C2 5 C2 4 Tetracyclic/ Ci9/C2 3 lopanes Steranes Hopane Tricyclic Tricyclic C2 6 Tricyclic Tricyclic 4.4 11.9 0 .1 0 0.40 1 .8 0.50 0.19 4.7 12.5 0 .1 2 0.49 2 .0 0.77 0.28 4.5 10.5 0.16 0.57 1 .8 0.79 0.28 4.6 9.7 0.14 0.60 1.9 0.74 0 .2 1 Figure 72. GCMS biomarker parameters o f saturate fraction extracts from cycle 24. Similarity in the molecular character of extracts from organic-rich and lean zone of oil shale facies suggests similar source input. 00 L /l moretane/C3o hopane ratios compared to oil shales (Figures 65,68,70,72-74, and Table 20). Larger amounts of squalane, which is a biomarker derived from halophilic bacteria, occurs in extracts from the mudflat, and the top and base of some oil shales. Small-to-moderate amounts of P-carotane are identified in the oil shale extracts; whereas, negligible-to-trace amounts occur in the mudflat extracts. Although measurable differences in the biomarker composition occur, extracts from both oil shales and mudflats are characterized by a dominance of C29 steranes and low gammacerane/hopane ratios. Three different oil shale signatures are identified in individual cycles based on variation in organic content, and its thickness. First, some oil shales contain a relatively thin organic-rich zone (>20 wt. % TOC) encased in lower TOC intervals (Figures 56, 61- 63). In cycle 24, less than 0.5’ of the oil shale has TOC values > 20 wt. %. These zones usually represent some of the highest TOC values in the Wilkins Peak. Although these organic-rich zones sometimes occur in thick oil shales, they are most pronounced in thin oil shales. Second, some cycles contain a thick oil shale (> 3 ft), which often displays small, closely spaced variations in TOC, HI, maceral 1 ^ composition and properties, and 8 C (Figures 56 and 61). Variations in p-carotane are identified throughout a single oil shale (Figure 67). A subtle enrichment in the 8 1 3 C and 8 lsO composition of the carbonate matrix sometimes occurs upward through the oil shale facies (Figure 56 and Table 16). Third, the oil shale facies in some cycles consists of an organic-rich mudstone with maximum oil-yields and TOC values less than 15 gallons/ton and 10 wt. %, respectively (Figures 186 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.5 ♦ Oil S hale ■ M udflat 0.5 0 -I-------------------------- 1 ---------------------------1 -------------------------- 1 -------------------------- 1 -------------------------- 1 -------------------------- 1 -------------------------- 1 -------------------------- 1 --------------------------- 0 1 2 3 4 5 6 7 8 9 C24Tetracyclic/C23Tricyclic T erpanes ♦ Oil S h ale ■ Mudflat 0.3 0.4 0.5 C19/C23 Tricyclic T e rp an es Figure 73. Various biomarker parameters document differences in precursor input between the mudflat and oil shale facies, Wilkins Peak Member; Blacks Fork-1. Extracts are from the “wet mudflat” microfacies due the difficulty in obtaining extractable material from the “dry mudflat” microfacies. 1 8 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.45 0.4 0.35 0.3 0.25 0.2 0.05 ♦ O il S h a le ■ M u d flat 1.5 2.0 2.5 3.5 Steranes/Hopane 4.0 4.5 5.0 ♦ O il S h a le H M u d flat • 0.4 0.2 3.5 S te ra n e /H o p a n e 5.0 5.5 Figure 74. Differences in biomarker parameters between saturate fraction extracts from the mudflat and oil shale facies, Wilkins Peak Member; Blacks Fork-1. Distinct differences in sterane/hopane, moretane/(moretane + hopane), and tricyclic terpanes/steranes suggest differences in precursor input and depositional conditions between two facies. 1 8 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. Sample/Depth (Ft) 1192.00 1192.90 1193.40 1193.80 1198.35 1200.60 1201.40 1202.40 1203.40 1204.80 1209.00 1210.80 1211.50 1213.90 1217.00 Precessional Cycle 24 24 24 24 23 23 23 23 23 23 22 22 22 22 22 Pristane/Phytane 0.76 0.89 0.95 0.87 0.56 0.67 0.29 0.22 0.19 0.65 0.81 0.3 0.34 0.3 0.35 nC1 7 /C2 S 2.77 7.65 9.45 4.07 1.66 1.45 1.26 1.53 1.49 1.06 2.38 1.8 2.86 1.64 1.17 nC1 7 /Pristane 0.91 1.4 1.51 1.08 0.71 0.72 0.67 0.77 0.68 0.44 0.81 1.2 1.38 1.18 1.24 Sample/Depth (Ft) 1427.00 1429.20 1435.30 1437.85 1490.90 1498.00 1501.00 1502.00 Precessional Cycle 5 5 5 5 1 1 1 1 Pristane/Phytane 0.36 0.36 0.31 0.3 0.84 0.34 0.35 0.35 nC1 7 /C2 9 0.6 0.31 0.54 0.27 1.3 1.22 1.51 0.7 nC1 7 /Pristane 0.88 0.69 0.6 0.56 0.33 0.46 0.5 0.4 Table 20a. Summary o f gas chromatography (GC) parameters for individual Wilkins Peak precessional cycles; Blacks Fork-1. Reproduced w ith permission o f the copyright owner. Further reproduction prohibited without perm ission. Sam ple Depth (Feet) 1192.0 1193 1193.4 1193.8 1198.35 1 2 0 0 .6 1203.42 1204.1 1205.1 1209.0 1 2 1 0 .8 1211.5 1213.9 1217.00 1429.2 1435.3 1437.85 1490.90 1498.00 1501.00 1502.00 Precessional Cycle 24 24 24 24 23 23 23 23 2 2 2 2 2 2 2 2 2 2 2 2 5 5 5 1 1 1 1 Terpanes C19/C23 Tricyclic Terpanes m/z191 0.25 0.36 0.38 0.28 0.61 0.69 0.09 0 .1 0 0.36 0.38 0 .1 1 0 . 1 0 0.09 0.09 0.67 0.24 0.23 0.65 0.17 0 .2 2 0.27 C23/C24 Tricyclic Terpanes m/z 191 0.44 0.51 0.56 0.59 1.61 1.36 0.99 1.05 1.45 1.06 0.35 0.53 0.46 0.52 1.25 0.19 0.18 1.69 1.29 1.33 1.26 C2S/C25 Tricyclic Terpanes m/z 191 2 . 1 0 1.91 1.75 1.79 0.99 1.32 1.90 1.94 1.15 0.98 2.04 2.36 2.06 2 .1 1 1.13 1.77 1.74 1 .0 1 2.36 2.34 2.17 C24 Tetracyclic/C^ Tricyclics m/z 191 0.46 0.77 0.78 0.70 3.50 3.78 0.28 0.26 2.63 2.07 0.25 0.18 0 .2 2 0 . 2 0 7.22 0.52 0.46 8.59 0.39 0.58 0.84 Oleanane/Hoparte m/z 191 0 .0 1 0 .0 2 0 .0 2 0 .0 2 0.04 0.04 0.03 0.03 0.05 0.05 0 .0 2 0 . 0 2 0 .0 1 0 .0 1 0 .0 1 0 .0 2 0 . 0 2 0 .0 2 0 .0 1 0 .0 1 0 .0 2 Gam macerane/Hopane m/z 191 0.07 0.09 0 .1 2 0 .1 0.03 0.07 0 .2 0 .2 1 0 .1 1 0.18 0.17 0.29 0.18 0.24 0.05 0 .2 1 0 .2 0.27 0 . 2 2 0.25 0.29 Moretane/(Moretane+Hopane) m/z 191 0.46 0.46 0.47 0.46 0.32 0.17 0.53 0.53 0.4 0.29 0.49 0.52 0.5 0.51 0.32 0.44 0.45 0.27 0.52 0.51 0.47 H35/H34 H om ohopanes m/z 191 nd nd nd nd 0.75 1.08 1.9 1.85 nd 1.04 nd 1.17 nd nd 0.62 1.55 1.3 nd 1.37 1.58 1.47 Steranes/H opanes m/z 191 3.2 3.49 3.32 3.5 4.12 4.65 3.26 3.39 3.26 5.25 3.86 1.69 2.55 2 .1 4.35 3.14 3.31 3.53 2.31 2.81 3.02 Tricyclic Terpanes/Steranes m/z 191 0.23 0.39 0.36 0.26 0.04 0.03 0.32 0.34 0 .1 1 0.05 0.37 0.39 0.38 0.34 0 .1 0.17 0.13 0.13 0 .2 0 .2 2 0.16 Tricyclic Terpanes/Hopanes m/z 191 0.07 0 .1 1 0 .1 1 0.07 0.17 0.13 0 .1 0 .1 0.35 0.27 0 .1 0.23 0.15 0.16 0 .0 2 0.52 0.43 0.04 0.09 0.08 0.05 Other (ppm) Squalane m/z 183 1070 628 340 491 nd 1773 142 154 546 1071 303 nd 180 17 497.5 174.1 379 nd nd nd nd C2S R egular Isoprenoid m/z 183 135 123 80 85 nd 393 39 38 182 159 2 2 nd 51 71 75.1 29.9 44.3 nd nd • nd nd p-carotane m/z125 1687 425 354 956 127 1455 1861 1829 81 270 2613 3853 2845 880 281.4 1426.7 3809.6 81 10,500 8355 5478 nd = not determined Table 20b. GCMS-biomarker data listing terpane ratios for extracts from individual precessional cycles in the Wilkins Peak Member, Blacks Fork-1 VO O Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Depth (Feet) 1192.00 1192.90 1193.40 1193.80 1198.35 1200.60 1203.42 1204.10 1205.1 1209.00 1210.80 1211.50 1213.90 1217.00 1429.2 1435.3 1437.85 1490.90 1498.00 1501.00 1502.00 Precessional Cycle 24 24 24 24 23 23 23 23 22 22 22 22 22 22 5 5 1 1 1 1 S teranes (ppm) m/z 217 C?r n o 20S 100.30 119.20 90.10 73.00 44.00 79.30 168.00 183.30 28.30 72.20 146.80 240.90 121.40 50.50 144.10 121.70 192.90 191.30 273.20 301.90 258.10 C27 a a 20R 2489.70 2707.40 2011.60 1542.40 855.00 1099.70 5200.00 5371.60 723.40 920.10 4057.40 6905.90 3957.60 1859.10 7874.30 5667.80 8429.20 3134.50 4768.80 4772.20 3784.40 C * P P 20S 0.00 0.00 0.00 0.00 27.30 0.00 0.00 0.00 0.00 91.10 0.00 0.00 34.90 21.50 31.80 40.80 40.20 42.60 36.30 C „ p p 2 0 R 0.00 0.00 0.00 0.00 69.40 0.00 0.00 0.00 0.00 149.50 0.00 0.00 94.00 41.70 67.50 51.60 85.70 91.70 95.00 C „ Total 2590.00 2626.60 2101.70 1615.40 899.00 1275.70 5368.00 5554.90 751.70 992.30 4204.20 7387.40 4079.00 1909.60 8147.30 5852.70 8721.40 3418.20 5167.90 5208.40 4173.80 Ca a a 20S 546.00 568.30 463.70 401.90 427.00 701.00 548.10 576.80 161.50 570.30 671.30 816.50 429.80 198.70 586.00 229.90 363.90 545.60 554.50 793.50 911.90 C 2gaa20R 11387.70 13516.30 10529.10 9107.00 5118.00 12349.30 14826.80 14181.40 2914.00 920.10 16969.00 17500.60 11454.70 5740.60 12011.00 6116.30 9151.20 8719.20 16175.90 19403.70 18011.30 c » pp 20S 252.80 300.60 212.80 177.00 174.00 353.60 136.90 146.30 73.10 175.10 233.90 271.40 160.50 80.20 209.00 119.80 193.30 112.20 174.10 188.00 209.00 c » p p 20R 1950.10 2102.60 1716.00 1543.80 926.00 2639.10 1533.40 1505.30 580.20 1070.50 2182.30 2702.40 1553.40 696.60 1287.00 1434.50 661.70 1038.70 827.70 1172.20 1661.30 C „ Total 14136.60 16467.80 12921.60 11229.70 6645.00 16043.00 17045.20 16409.80 3728.80 2736.00 20056.50 21290.90 13598.40 6716.10 14093.00 7900.50 10370.10 10415.70 17732.20 21557.40 20793.50 C a a a 20S 2445.70 2450.30 1964.50 1861.10 1262.40 1933.90 3962.20 4053.50 616.80 1593.80 5492.90 4822.50 2978.30 1238.30 4559.00 1394.40 2059.00 3574.90 4002.70 5413.90 5509.40 C a a a 20R 13829.30 14186.50 11294.80 10981.60 7187.00 7327.60 20844.10 20659.40 2878.60 7432.90 27601.90 26124.90 18980.30 8784.20 19644.00 11795.60 17858.10 12219.20 29130.40 33716.70 28142.50 C » p p 20S 325.50 334.90 236.00 209.20 214.00 35.50 298.30 275.90 91.30 322.10 390.60 427.70 258.30 98.40 289.40 119.60 160.80 265.90 242.90 281.50 295.00 C a PP20R 1781.50 1742.90 1370.30 1319.70 1385.00 61.80 2353.00 2311.00 423.40 650.10 3254.20 3574.10 2071.50 882.00 2483.60 1434.50 2162.00 1592.70 3115.20 3481.50 3258.10 C a Total 18382.00 18714.60 14865.60 14371.60 10048.40 9358.80 27457.60 27299.80 4010.10 9998.90 36739.60 34949.20 24288.40 11002.90 26976.00 14744.30 22259.90 17652.70 36491.20 42893.60 37205.00 Total S teranes (ppm) 35108.60 36029.00 29688.90 27216.70 17592.40 26677.50 49870.80 49264.50 8490.6G 13727.20 61000.30 63627.50 41965.80 19628.60 49216.30 28497.50 41351.40 31486.60 59391.30 69659.40 62172.30 %C2 7 /C27+ C a+C a 0.07 0.07 0.07 0.06 0.06 0.05 0.11 0.11 0.09 0.07 0.07 0.12 0.10 0.10 0.17 0.21 0.21 0.11 0.09 0.07 0.07 %Ca/C27+C a+C a 0.40 0.43 0.43 0.41 0.41 0.60 0.34 0.33 0.43 0.20 0.33 0.33 0.32 0.34 0.29 0.28 0.25 0.33 0.30 0.31 0.33 %C»/C27+C a+C a 0.52 0.49 0.50 0.53 0.53 0.35 0.55 0.55 0.48 0.73 0.60 0.55 0.58 0.56 0.55 0.52 0.54 0.56 0.61 0.62 0.60 Table 20c. GCMS-biomarker data including sterane distributions and content (ppm) for extracts from individual precessional cycles in the Wilkins Peak Member, Blacks Fork-1. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Sample Depth (Feet) 1192.0 1192.9 1193.4 1193.8 1198.35 1 2 0 0 .6 1203.42 1204.1 1205.1 1209.0 1 2 1 0 .8 1211.5 1213.9 1217.0 1429.2 1435.3 1437.9 1490.9 1498.0 1501.0 1502.0 Precessional Cycle 24 24 24 24 23 23 23 23 2 2 2 2 2 2 2 2 2 2 2 2 5 5 5 1 1 1 1 Steranes (m/z 217) Css 20S(20S+20R) 0.18 0.17 0.15 0.17 0.15 0 . 2 1 0.16 0.16 0.18 0.18 0.17 0.16 0.14 0 .1 2 0.19 0 . 1 1 0 . 1 0.23 0 .1 2 0.14 0.16 m«*+m 0.15 0.15 0 . 1 1 0 . 1 1 0.16 0.14 0 . 1 0.09 0.13 0 .1 2 0 . 1 0 . 1 1 0 . 1 0.09 0 . 1 0 . 1 1 0 . 1 1 0 . 1 1 0.09 0.09 0 . 1 Terpanes (m/z 191) Ts/Tm 0.06 0.05 0.07 0 . 1 1 0.05 0.09 0.06 0.07 0.04 0.08 0.06 0.03 0.08 0.06 0.03 0.05 0.04 nd nd nd 0.07 C29 Ts/Tm 0 .2 0.18 0.18 0 .2 2 0 .2 0 .1 2 0.26 0.25 0 . 1 1 0.15 0.29 0.13 0 .2 0.18 0.17 0 .2 2 0.23 0 .1 2 0.24 0.26 0 .2 2 H3 2 S(S + R) Homohopanes 0.36 0.3 0.33 0.32 0.24 0.38 0.3 0.28 0.35 0.3 0.37 0.52 0.37 0.42 0.25 0.38 0.37 0.24 0.33 0 .2 2 0.18 Table 20d. GCMS-biomarker thermal maturation data for extracts from individual precessional cycles in the Wilkins Peak Member, Blacks Fork-1 58 and 60). Half-precessional cycles are often expressed by an increase in organic content at the top of the oil shale (Figure 61). Organic matter composition in the oil shale facies often displays cyclical influenced patterns. Zones of organic-rich oil shale contain Type I kerogen (HI >750-800 mg HC/g OC) composed of dense, highly-fluorescing matrix lamalginite. Corresponding pyrolysates contain abundant nCs+ aliphatic components (Figures 61 and 63). These organic-rich zones are often surrounded by intervals that have slightly reduced TOC’s but are composed of kerogen with similar HI values, and maceral composition. In contrast, lower TOC zones near the base and top o f many oil shales consist of Type I/II or II kerogen (HI ~ 600 -800 mg HC/g OC) that contains a greater proportion of bituminite and terrestrially-derived organic matter. The corresponding pyrolysates contain reduced amounts of nCs+ aliphatics and a greater proportion of light aromatics. In cycles where the oil shale facies consists o f an organic-rich mudstone, there is a Type I/II-II kerogen with HI values in the range of 600-800 mg HC/g OC. Lower nC^/Pr, and nCn/C29 ratios occur at the base and/or top of some oil shales. The apparent cyclical variations in these ratios correspond to increased amounts of both nCn and/or nC25-C29 alkanes (Figures 64, 67, 69 and 71). Most GC and GCMS parameters do not display distinct patterns throughout the oil shale facies. The 8 1 3 C composition of kerogen within individual oil shales can vary by up to 2.9 % o. When present, isotopically depleted kerogens (<-33 % o) often occur near the cycle base or associated with an increase in organic content (Figures 57-60). 193 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Organic matter in the mudflat facies can be sub-divided into two end-member assemblages. The first organic assemblage in the mudflat usually occurs in brecciated to massive mudstones and siltstones, and has TOC values and oil-yields less than 0.5 wt. % and 1.5 gallons/ton, respectively (Figures 59-60, and 63). This assemblage consists of Type III-IV kerogen (HI < 100 mg HC/g OC) that is primarily composed of a non-fluorescent, oxidized, amorphous assemblage (bituminite) with minor amounts of dull-fluorescing liptodetrinite. This “amorphous dust” is finely disseminated throughout the sediment. Sporadic carbonaceous material also occurs in certain silty and sandy zones. The low TOC values o f these samples often results in anomalous HI values. The second end-member organic assemblage in the mudflat commonly occurs in massive to laminated mudstones and has TOC values between 0.5 and 2.0 wt. %, consistent with oil-yields of 1-2 gallons/ton (Figures 56, 57, and 61). This assemblage consists of Type II-II/III kerogen (HI ~ 300-750 mg HC/g OC) that is composed of fluorescing bituminite, liptodetrinite, and small amounts of lamalginite, vitrinite and planktonic algae (pediastrum?). The sedimentary occurrence, composition and fluorescence of the semi-laminated kerogen can significantly vary over several millimeters. The GC profile and character of the saturate fraction of extracts is often similar to the oil shale facies (Figure 6 6 ). This assemblage also occurs in mudflat intervals directly above or below the oil shale facies where TOC and oil-yields can be up to 5 wt. % and 6 gallons/ton, respectively (Figures 57, 60 194 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and 62). The two mudflat microfacies are distinguished by organic content and the amount of organic matter that can be converted to hydrocarbons (Figure 75). Rare occurrences o f organic lamina and thin oil shales (<1-3 inches) are found in trona (Figures 61 and 62). At a multi-lamina scale, the occurrence and fluorescence o f the kerogen can be highly variable. Thin “stringers” of organic lamina (<1/4 inch thick) encased in trona in cycles 22 and 23 display a relatively wide range in 8 13C. Variations in kerogen properties are independent of the narrow range of thermal maturity in eccentricity cycles A and E, and therefore document differences in organic matter properties throughout individual precessional cycles. Low Rock- Eval pyrolysis Tmax, and C29 20S/R and Ts/Tm values of the bitumen confirm the thermal immaturity of the Wilkins Peak Member in Blacks Fork-1 (Tables 16 and 2 0 d). Complete geochemical data, including Rock-Eval pyrolysis, maceral composition, and additional GC and GCMS parameters, are provided in Tables 18- 20. Additional geochemical data are listed in Appendix 4. Discussion Cyclical Geochemical Patterns and Processes These high-resolution geochemical profiles provide additional definition to the Wilkins Peak precessional cycles defined by the oil shale, trona and mudflat lithofacies. Pronounced orbital-derived changes in water level resulted in distinct 195 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. 35 30 25 o o 0)20 o 10 ■ I 1 iB m ■ 4 'T T ' ■4 ♦ Dry Mudflat ■ Wet Mudflat 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Wt. % TOC 3.5 4.0 4.5 Figure 75. Differences in weight percent total organic carbon (TOC) and Rock-Eval pyrolysis SI + S2 for “wet mudflat” and “dry mudflat” microfacies. Low TOC values and negligible Rock Eval SI + S2 yields in the “dry mudflat” are the result of an oxidized and desiccated setting. 5.0 'O 0\ depositional processes and patterns between the oil shale and mudflat, and within these two facies. Variations in geochemical parameters throughout individual cycles help define changes in playa lake size, lacustrine processes and mudflat conditions. Although most of these geochemical patterns are a product of orbital-driven changes in net moisture, they are also influenced by non-cyclical climatic, tectonic and other depositional factors. Precessional Geochemical Pattern 1 Oil Shale-Mudflat Facies The sharp changes in bioproductivity, precursors and oxidation-reduction between the oil shale and mudflat are a product of rapid but cyclical variations in net moisture and chemistry. These changes also controlled lithologic properties including chemical deposition and detrital input. In contrast to the good-to-optimal conditions for organic accumulation in the playa lake, the mudflat consisted of limited productivity, different precursors, and moderate to severe organic degradation. Limited preservation in the mudflat also controlled the record of organic input by the preferential destruction of lipids and concentration o f residual humic material. The degree of lithologic and geochemical contrast between the oil shale and mudflat is primarily a result of how mudflat conditions controlled productivity, preservation-desiccation and sedimentation. The reduced geochemical contrast between the oil shale and mudflat in eccentricity cycle A results from subaqueous-dominated conditions that enhanced preservation. 197 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The mudflat facies contains different types of precursors and a larger proportion of terrestrial input compared to the underlying oil shales. Lower p- carotane, C26/C25 tricyclic terpanes and tricyclic terpane/sterane ratios of mudflat extracts compared to the oil shale indicate differences in precursor input (Figures 73 and 74). Higher C24 tetracyclic/C23 tricyclic terpane ratios in mudflat extracts are an indication of input from prokarotes, bacterial mat and terrestrial material, and a suggestion of increased salinity (Palacas et al., 1984; Connan et al., 1986; Mello and Maxwell, 1990; Yawanarajah and Kruge, 1994). Preferential concentration of terrestrial material in the mudflat is consistent with an increase in the nC25-C29 alkane content, and higher C19/C23 tricyclic terpanes ratios (Zumberge, 1987). The higher Pr/Ph ratios in some of the mudflats are consistent with increased oxidizing conditions and a greater proportion of terrestrial material. The increase in squalane in mudflat extracts indicates a greater input from halophilic bacterial precursors associated with hypersaline conditions (Tornabene, 1978; ten Haven et al., 1988a). Tentative identification of increased amounts of the C 2 5 isoprenoid in mudflat extracts further supports a harsh, saline water chemistry (Waples et al., 1974). These hardy, resistant bacterial precursors represent a limited number of biota that can exist in shallow, harsh, ephemeral, alkaline-rich mudflat lakes. Although the moretane/hopane ratio defines thermal maturity, the higher moretane content in the oil shale compared to the adjacent mudflat suggests facies differences due to the less alkaline playa lake (Figure 74). This results in an 198 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. increased rate of isomerization that is controlled by acidic catalytic activity (Horsfield et al., 1994). Differences in planktonic versus benthic input between the oil shale and mudflat facies is a product of variations in water depth, water column chemistry and ecology, and selective preservation. Other precursor input in the oil shale and mudflat facies appears to originate primarily from cyanobacteria. However, the oil shale contains a mix of benthic and planktonic input, where-as mudflat kerogen was primarily derived from benthic precursors along with the increase in humic input. The absence of p-carotane in extracts from the mudflat compared to the oil shale is due to limited precursor input from a stratified water column (Roble et al., 1994; ten Haven et al., 1989). P-carotane is mainly produced by the phototrophic, oxygenic, primarily planktonic, unicellular algae Dunaliella, and is never found in microbial mats (Javor, 1989; Santos Neto et al., 1998). Small amounts of planktonic components are petrographically identified in the oil shale but are rare in the mudflat. Although lamalginite is not identifiable as planktonic or benthic in origin, the small amounts of lamalginite in the mudflat display an elongate stylolitic • • • 1 'X • • character suggestive of a benthic mat origin. The C-enriched mudflat kerogen is consistent with shallow-water cyanobacteria benthic mat precursors (Boon et al., 1983; Faure and Cole, 1999), as described later. Additional pyrolysis and biomarker analyses are required to identify specific organic precursors in the oil shale and mudflat. 199 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although the total sulfur content is low, elevated values occur in the oil shale compared to the mudflat. The small variations in sulfur throughout individual precessional cycles are a result of changing lake conditions. Sulfate was transported into the basin either dissolved in inflow waters from dissolution of pre-existing evaporite minerals or absorbed onto volcanic ash, and reduced by sulfate-reducing bacteria that formed H2S. In expanded playa lakes, the H2S that formed in either the anoxic water column or below the sediment water interface reacted with available iron and formed iron sulfides. High porewater pH prevented rapid sulfidization of iron, which contributed to some incorporation of organo-sulfur into the kerogen (Tuttle and Goldhaber, 1991). The H2S helped inhibit aerobic destruction o f organic matter in the playa lake. In the shallow, ephemeral mudflat lakes, oxidizing conditions limited H2S formation. The small amounts of H2S that formed probably escaped into the atmosphere (Dyni, 1983), resulting in the near absence of primary sulfate minerals. In organic-rich mudstones, the low total sulfur is consistent with limited formation of H2S. The contraction of the playa lakes to an evaporated salt pan that represented conditions below the necessary threshold for organic matter accumulation appears to have been a rapid event. With increasing salinity, biological precursors were unable to avoid desiccation by osmosis and continue photosynthesis due to a reduced CO2 concentration (Kirkland and Evans, 1981). Immediately below most oil shale-trona contacts, there is a sharp drop in TOC, and a switch from lamalginite-bituminite to an oxidized organic assemblage. There is no evidence for a transitional geochemical 200 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. signature indicating the occurrence of an ultrasaline, ecologically stressed lake that represents a long-term, gradual shrinkage of the playa lake. After oil shale deposition ceased, the water-saturated, organic-rich material below the sediment/water interface retained the hypersaline, anoxic pore waters, which helped exclude aerobic bacteria and preserve the hydrogen-rich kerogen. The high organic content at the top of the oil shale in cycle 2 2 and sharp contact with the overlying trona suggests a strong half-precessional precipitation event that was quickly terminated. Properties of organic matter encased in trona are highly variable because it reflects a harsh but variable setting. Some thin organic “stringers” display evidence of unique or ecologically stressed biota. For example, thin organic “stringers” encased in trona in cycle 22 (1210.9 ft) contain petrographically unique “flattened” t algal bodies that have a higher sterane/hopane ratio, and a 8 C depleted kerogen composition (-32.2 % o) compared to the underlying oil shale (Figure 61). The pyrolysate composition of this kerogen displays a subtle stair-step pattern in the nCi7-Cig range that is similar to descriptions of environmentally stressed and desiccated Laney Member kerogen (Horsfield et al., 1994). Small-scale variation in the occurrence and fluorescence at a multi-lamina scale suggests that the type and preservation of organic matter deposited during salt pan deposition varied rapidly and sporadically. Identification of P-carotane in an extract from organic material encased in trona (cycle 2 2 , 1 2 1 0 . 8 ft) suggests periodic development o f a photic zone and stratification of the salt lake (Schoell et al., 1994a). 201 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Carbon Isotope Enrichment and Excursions - Kerogen 1 3 The occurrence and extent of the C-enriched kerogen in the mudflat facies is controlled by water level and chemistry. This enrichment is primarily a result of: ( 1) composition of the mudflat kerogen, and (2 ) a reduced CO2 concentration in the mudflat lake that lowered the isotopic fractionation factor. An altered carbon assimilatory pathway and differences in precursor input may have also made a 11 subordinate contribution to the 8 C excursion. The mudflat facies contains a greater proportion of landplant input and degraded organic matter compared to the oil shales. This increase in humic input including occasional thin lamina of carbonaceous material results from both detrital influx and its preferential concentration due to oxidation in the mudflat (Figure 63). I -3 Landplant derived kerogen tends to have 8 C values of approximately -24 to -27 %o, similar to worldwide values of Type III kerogen and modem C-3 terrestrial vegetation (Whiticar, 1996). Lacustrine reeds and sedges can be important sources of C-4 type vegetation (Talbot and Livingstone, 1989). However, these plants do not make a major contribution to the 13C-enriched kerogen because terrestrially dominated organic matter assemblages in the Wilkins Peak are not isotopically heavy enough (8 1 3 C > -25 % o ) to document a major C-4 contribution. The 13C-enriched kerogen is also a product of degradation of the mudflat organic matter. Most kerogens that are isotopically heavier than -29 % o have TOC, and HI values less than 3-4 wt. % and 600 mg HC/g OC, respectively (Figure 76). Organic constituents in these kerogens usually consist of non-to-poorly fluorescing 202 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. - 25.0 -26.0 -27.0 -28.0 % -29.0 O) g O - 30.0 O « - 31.0 - 32.0 - 33.0 - 34.0 - 35.0 — I- V * . _ M | . 'm -4-1 ♦ I •I" - l _ - ► 4 ♦ Eccentricity A ■ Eccentricity E 10 15 Wt. % TOC 20 25 - 25.0 - 27.0 5 - 29.0 O ) O k _ 0) O « - 31.0 - 33.0 -35.0 30 ® y p I ■ 1 a ■ _____II ■ ■ ■ ■ ■ " m ■ ■ 1 1 ! 1 1 1 --------1 --------1 _ ------i-------h----- -------1 --------1 ------- ■ I i | ■ J ■ I 1 1 I■ 1 1 1 ■ ■ 1 J_ J. _ L it - \- 1 1 1 1 I ! 1 1 1 ! 1 1 ♦ ■ 1 , ■ 1 1 i I ♦ 1 I ♦ ■ 1 II ! _ r r*“T — •*- ..♦ ............ 1 1 i ♦ i i H I _ ♦ J ■ 1 ■ ♦ , 1 1 1 1 1 1 ♦ 1 1 1 4- 4 4 4 - ^ ♦ ♦ t | | h 1 1 ■ ♦ Eccentricity A 1 1 1 ♦ \ 1 ■ Eccentricity E 1 1 1 *« !♦ ♦ 1 0 100 200 300 400 500 600 700 800 900 1000 Hydrogen Index (mg HC/g OC) Figure 76. Relationship between 51 3 C kerogen and TOC and HI o f Wilkins Peak sediments, Blacks Fork-1. Most samples with 81 3 C values heavier than - 29 % o have less than 3 wt. %TOC and HI values less than 600 mg HC/g OC. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bituminite, liptodetrinite, or oxidized amorphous material in addition to humic precursors. Pyrolysates display a preferential reduction in their n-aliphatic content 1 ^ suggesting organic degradation (Figure 61 and 63). The C enrichment coincides with a reduced water level and enhanced subaerial desiccation, similar to desiccation events described in other lacustrine settings (Benson et al., 1991; Talbot and Johannessen, 1992). Physical desiccation preferentially destroyed the isotopically lighter lipid precursors resulting in an oxidized, amorphous assemblage. Biological reworking of lipid precursors leading to the formation of bituminite also produces an isotopic enrichment as described by (DeNiro and Epstein, 1978; Hayes et al., 1989; Gutjhar, 1983). However, it is unlikely that desiccation processes contributed to more than a 3 % o enrichment in the 8 1 3 C because: (1) even complete organic degradation usually results in an enrichment of only 2-3 % o (Hayes, 1993), and (2) some 13C-enriched kerogens display limited degradation with HI values between 500 and 800 mg HC/g OC (Figure 76). The 1 3 C enriched mudflat kerogen is also a product o f environmental adaptation to CO2 depletion in heliothermal brines in the shallow, alkaline-rich lakes with elevated temperatures. Previous studies document that a lower fractionation factor results from a lower concentration of dissolved aqueous CO2 due to an increase in salinity and/or pH, and temperature, as shown in Figure 77 (Deuser et al., 1968; Degens, 1969; Schidlowski et al., 1984; Schoell et al., 1994b). This leads to a reduction in the biological carbon isotopic fractionation and thus an enriched 51 3 C composition (Figure 78). The biomass becomes isotopically 204 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. j ? t z « e _ 0 8 * “ 3 ° a s c f M 8 0.4 Figure 77. Solubility o f carbon dioxide in aqueous solutions decreases with increasing sodium chloride and temperature (PCO2 =760 Torr). Figure from Schidlowski et al. (1984). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. T O M A T O - 20 ALGAE -22 1.0 1.5 Figure 78. Carbon isotope fractionation in C3 plants (tomato) and aquatic algae utilizing the C3 pathway in response to C 02 pressure in ambient air. The reduced C 02 pressures lead to a profound effect on diffusion controlled fractionation by aquatic algae. Figure from Schidlowski et al. (1984) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. enriched from the reduced sum of all fractionations (Ep) associated with the transfer and assimilation o f CO2 by the photosynthetic organism. The low aqueous CO2 content is a likely result of a reduced volume of water relative to the high photosynthetic productivity that often occurs in cyanobacterial mats (Bauld, 1981). The S1 3 C composition o f the carbonate matrix in the Wilkins Peak mudflat is not 1 - 2 enriched compared to the oil shale facies, and does not correlate with the 8 C of 1 ■ ! kerogen (Figure 79). Therefore, a limited variation in the 8 C composition of the CO2 reservoir in the playa and mudflat lakes does not appear to explain differences in the S1 3 C composition of the respective kerogens. Conversely, preferential incorporation of 1 3 C versus 1 2 C during high levels of photosynthesis has been attributed to carbon isotope excursions in some microbial mats (Des Marais et al., 1989). In harsh, shallow water settings with low aqueous CO2, HCO3 pumping may also contribute to a 13C-enriched kerogen. Laboratory studies have demonstrated that certain types of opportunistic algae can adopt a bicarbonate pumping strategy to continue photosynthesizing in low CO2 aqueous settings (Badger, 1987). If no additional isotopic fractionation processes occur during bicarbonate assimilation, the S1 3 C and Ep values should reflect the relative percentage of the isotopically heavier bicarbonate that is added to the organic carbon pool (Hollander and McKenzie, 1991; Hayes, 1993). Exceptionally 13C-enriched organic carbon has been documented in sabkha and brine-rich lakes where cyanobacteria mats predominate (Behrens and Frishman, 207 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 3 C Kerogen - 25.0 • Oil Shale-Eccentricity A ■ Oil Shale Eccentricity E A Mudflat A ♦ Mudflat E X Trona - 26.0 - 27.0 - 28.0 - 29.0 - 30.0 - 31.0 - 32.0 -33.0 - 34.0 - 35.0 5.0 3.0 4.0 2.0 1.0 0.0 - 1.0 13C Carbonate Figure 79. Relationship between 51 3 C of the kerogen and the matrix carbonate. The absence o f a correlation suggests limited variation in the §I3C composition of the CO2 reservoir. Arrow represents hypothetical correlation of two parameters. 208 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1971; Schidlowski et al., 1984). In ecologically stressed settings, a different biological precursor may contribute to a lower fractionation factor. In some high salinity settings, certain organic precursors show evidence of isotopically enriched lipids (Grice et al., 1998). However, these precursors are unlikely to have been a major contributor in the Wilkins Peak because kerogen associated with trona does 1 ‘ I i -7 not usually display a significant C enrichment. The absence of a significant C kerogen enrichment (> -29 % o) in mudflats from eccentricity A is consistent with stable, almost perennial, expanded mudflat lakes. The elevated water levels resulted in adequate organic preservation, a reduced landplant input, lower brine concentrations and sufficient aqueous CO2. Precessional Geochemical Pattern 2-Oil Shale Occurrence and Variations The three different oil shale signatures result from differences in playa lake conditions and net moisture availability during the precessional rainy phase. First, thin organic-rich zones in the oil shale facies represent optimal organic accumulation events during lacustrine highstands. Maximum expansion of the playa lake provided ideal conditions for organic productivity and preservation, combined with reduced sediment dilution. Second, cycles with thick oil shales (>3 ft) record an extended rainy phase that usually equates with “wet” precessional cycles. Third, in cycles where the oil shale facies consists of organic-rich mudstone it is primarily the result of reduced organic productivity combined with sediment dilution. 209 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Overall similarities in HI, biomarker, pyrolysate and maceral composition between organic-rich and adjacent zones with lower TOC values indicate similar source input and generally equivalent levels of preservation (Figure 61). Elevated primary productivity was a result of increased nutrient availability and development of enhanced photic zone conditions in the playa lake. Saline lakes often are settings of high plankton productivity due to concentration of nutrients, specialized biota and elimination of grazing organisms (Kirkland and Evans, 1981). The linear correlation between TOC and Rock-Eval SI + S2 indicates a similar type of homogenous Type I-I/II kerogen consisting primarily of lamalginite and some bituminite (Figure 80). The general similarity in the biomarker composition and distribution of extracts throughout individual oil shales suggests a relatively homogeneous input of precursors throughout the life of the playa lake. Therefore, variation in organic input is not a major cause of the geochemical heterogeneity in these oil shales. However, these extracts represent hydrolysis products of lipids formed at the beginning of diagenesis rather than thermal cracking of kerogen due to the thermally immature nature of these oil shales (Anders and Robinson, 1973). Therefore, molecular characterization of artificially generated pyrolysates throughout the oil shale facies could help identify small differences in precursor input related to variation in playa lake conditions. Primary productivity is an important contributor to variations in organic content throughout the oil shale facies. Zones with more than 20 wt. % TOC that 210 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W eight % TOC 30 25 20 15 10 5 0 0 50 100 150 200 250 Rock Eval S1 + S2 Figure 80. Linear correlation between TOC and Rock-Eval SI + S2 indicates a similar Type I/II kerogen for most oil shale in the Wilkins Peak. Samples with low values represent the mudflat facies. Data for individual samples are listed in Table 18. 1 1 1 1 ± J 1 I 1 1 1 L 1 I 1 1 _L ♦ !♦ ! \ ♦ i i ---------------------- , ---------------- ^ 1 -i 1 1 itfi* f 1 “ T 1 1_____________ 1 - * * ' 1 -I ! ........... ! .......................... L 1 1 — 1 ---------------- _L 1 ! -----1 ---------------------- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. consist of dense, highly fluorescing matrix lamalginite are a product of elevated primary productivity and organic flux. In the expanded phase o f these playa lakes, a highly efficient export of biomass from the photic zone to the anaerobic lake bottom eliminated any organic degradation. During prodigious algae blooms, the playa lake surface probably became “soupy” with cyanobacterial precursors (Bradley, 1970). The flocculation of this gel-like biomass facilitated a rapid settling of ungrazed aggregates that propelled a massive self-sedimentation, similar to other aqueous settings (Grimm et al., 1997). Because of the limited time required for the biomass to settle through the thin, oxygenated upper water column, negligible destruction of the organic flux occurred (Katz, 1990 and 1995). These processes are consistent with the identification of thick, irregular kerogen lamina in certain zones in Wilkins Peak oil shales. Overall, the process of organic destruction does not limit organic accumulation in the oil shale facies. Degradation of organic matter is limited to a small number of zones at the top and base of some oil shales. Oil shale intervals that have a lower TOC and HI (<10 wt. % and 750 mg HC/g OC, respectively) usually contain a larger proportion of bituminite, and the pyrolysates contain a lower n- aliphatic content (Figure 81). The slightly lower HI values are primarily attributed to preferential degradation of aliphatic-rich components rather than to incorporation of hydrogen-poor source input. In very shallow playa lake settings, constant mixing throughout much of the water column contributed to organic degradation even at the sediment/water interface. 212 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hydrogen Index 1000 900 800 700 600 500 400 300 200 100 Oil Shales p Wilkins Pea sy __ k X " + -u .j Jk 'A k ^ 4 ♦ ■ ■ u + x t- * x " ♦ P + M • - ♦ ♦ X ▲ p .— W~" ♦ A l ♦ BF Cycle 24 ■ BF Cycle 23 A BF Cycle 22 XBF Cycle 21 X BF Cycle 20 ♦ WM Cycle 23 +WM Cycle 22 - BF Cycle 5 — BF Cycle 3 ♦ BF Cycle 1 10 15Wt % TOC 2 0 25 30 Figure 81. Relationship between TOC and Rock-Eval HI suggests organic matter degradation is not a major cause of the lower organic carbon content in most oil shales and select organic-rich mudstones. Arrows indicate area o f degradation. Data are from Blacks Fork-1 and White Mountain-1. 213 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dilution of the accumulating organic matter by sediment influx contributed to a reduced organic content in parts of the oil shale facies. A lower organic content in precessional cycles 21-23 at White Mountain-1 as compared to Blacks Fork-1 suggest that greater sediment dilution occurred in the playa lake cycle due to its proximity to the basin-edge (Figure 82). Sediment dilution at the base o f oil shales is further supported by fine-grained shoreline transgressive sands directly underlying oil shales in the White Mountain-1 core, and other basin margin locations (Pietras et al., 2003). Although these sands are usually absent under oil shales in Blacks Fork-1, silts or sandy lamina sometimes occur. In Blacks Fork-1 cycle 20, low TOC values in oil shale directly above the volcanic tuff indicate sediment dilution (Figure 59). Evidence of increased landplant input in some extracts at the base and top of oil shales are consistent with increased detrital influx (Figure 6 6 ). Seasonal influx of sediment from the adjacent mudflats likely occurred during expansion and contraction of the playa lake. Suspended sediment in the playa lake probably limited light penetration and photosynthetic production of planktonic and benthic organisms at certain lake stages. Geochemical heterogeneity throughout individual oil shales suggest fluctuations in lake size and water column conditions. Small, closely spaced variations in TOC, HI, 8 1 3 C composition of kerogen, and lamalginite fluorescence . suggest a combination o f rapid fluctuations in productivity, small-to-moderate changes in preservation and sediment dilution. Differences in HI o f up to 200 mg HC/g OC often correlate with TOC and variation in the petrographic occurrence and 214 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. White Mountain*! Shale TOC -29.1 jwt % ; Oil 3.7 Cycle 23 Oil Shale TOC 3.2 -19.7 W t % Oil & hale tO C 2.1 411.3 W t % Cycle 22 Cycle 21 4.0 B A 100 0. 0 Figure 82. Comparison o f lateral variation in oil-yield and TOC between White Mountain-1 and Blacks Fork-1 for precessional cycles 21-23. Lower oil-yields and TOC in White Mountain cycles suggest sediment dilution. White Mountain-1 occurs closer to the basin edge. 215 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. preservation of lamalginite, rather than dilution by hydrogen-poor terrestrial material 1 -3 (Figure 61). Occasional C depletion of kerogen in individual oil shales suggests variation in the CO2 pool available in the water column (McKenzie, 1985; Hwang et el., 1989). The 13C-depleted kerogen may be related to an increase in organic flux and episodic release of isotopically light, recycled CO2 related to the intermittent breakdown of the fragile stratification. Variations in the amount of P-carotane in individual oil shales suggest differences in the development and stability of water column conditions, and the resulting precursor ecology (Schoell et al., 1994a; Ruble et al., 1994). The closely-spaced geochemical variability documents fluctuating playa lake size and conditions. Distinct playa lake conditions appear to have developed in individual Wilkins Peak precessional cycles. Although the GC and GCMS properties of extracts throughout individual oil shales are usually similar, extracts from different cycles often display distinct molecular characteristics. Oil shales in cycles associated with trona usually have Pr/Ph ratios less than 0.35 consistent with higher salinity (ten Haven et al., 1988b). The higher Pr/Ph ratios (0.76 - 0.95) in extracts from cycle 24 compared to other cycles are probably related to a more oxygenated and less saline lake. A larger nCn content in extracts from cycles 22 and 24 suggests a greater proportion of cyanobacterial input (Parker and Leo, 1965; Collister et al., 1994). Oil shale extracts from cycles 1 and 22, which represent “wet cycles,” have lower sterane/hopane ratios than cycles 23 and 24 suggesting greater prokaryotic input. During the rainy phase, a different water column ecology formed in each developing playa lake as a result o f lake size and 216 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. chemistry, inflow and the expansion-contraction episodes. Molecular variations in black shales from individual precessional lakes in the Upper Triassic Lockatang Formation of the Newark Basin are common (Kruge et al., 1990a). Pattern 3 - Variations Mudflat Facies - Organic Microfacies Identification of geochemical patterns and processes in the mudflat further define the “dry and wet mudflat” microfacies. The “dry mudflat” microfacies is consistent with the organic-lean-to-barren, brecciated to massive silty mudstones. Negligible to small quantities of Type III-IV kerogen represent oxidation products of limited amounts of lipid precursors. The shallow, short-lived mudflat lakes only allowed thin, filamented, oscillatoracia type algal/bacterial mats to develop (Schreiber et al., 2001). Subsequent subaerial exposure led to physical and biological degradation of the benthic precursors before, during, and after burial. Ongoing desiccation preferentially destroyed lipid precursors by ( 1) oxidation from subaerial exposure and aeolian reworking of recently deposited organic precursors, and (2 ) heat fixation o f kerogen precursors to form a gelified material during and after burial (Bradley, 1973). The occurrence of oxidized, non-fluorescent “amorphous dust” that is finely disseminated in the mudflat is consistent with these degradation processes. During arid periods, subaerial exposure and desiccation could have destroyed multi year records o f organic accumulation. The massive-to-laminated mudstones in the “wet mudflat” consist o f an organic-bearing, moderate-well preserved Type II/III kerogen. The dominantly 217 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. subaqueous mudflat conditions provided sufficient organic productivity and preservation, and protection from subaerial desiccation. Continual growth of cyanobacteria mats, and occasional development of water column conditions suitable for planktonic precursors provided organic input. The development o f a cohesive, thick, filamentous and gelatinous matrix of benthic mat precursors enhanced organic preservation at and below the sediment/water interface (Bauld, 1981). The high resistance of cyanobacteria precursors to decay further contributed to its well- preserved nature (Bradley, 1970). The common occurrence of laminated or semi laminated organic matter indicates that the sediment/water interface was protected from abundant grazing and organic degradation. Adequate preservation is consistent with fluorescing bituminite, Pr/Ph ratios similar to oil shales, small-to-moderate amounts of nCs+ aliphatics in mudflat pyrolysates. This microfacies also occurs in the transition between the oil shale and mudflat facies where short-term expanded mudflat lakes promoted organic accumulation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 7 GREEN RIVER ORBITAL CYCLICITY - ORIGIN, IMPRINT, AND APPLICATIONS Introduction Discounting occasional clastic tongues, a 7-to-15 ft cyclicity consistently occurs throughout the Tipton and Wilkins Peak Members. Using separate approaches, Fischer and Roberts (1991) and Roehler (1993) calculated that these oscillations represent the 21 k.y. precessional periodicity. The grouping of these precessional cycles into larger sets reveals the occurrence of 100 and 400 k.y. eccentricity cycles. Spectral analysis by Machlus et al. (2001) also documents the occurrence of Milankovitch cyclicity in the Tipton and Wilkins Peak. However, based on argon dates (40Ar/39Ar), Smith et al. (2003) rejects the traditional precessional time-scale in the Wilkins Peak. Pietras et al. (2003) proposes an approximate 1 0 k.y. cyclicity with an origin that could have been related to the tectonic control o f drainage. In this study, spectral analysis using the Blacks Fork-1 and Currant Creek-1 coreholes defines the short and long eccentricity, half and full precession and a weak obliquity. Results from the time-series analysis combined with the elimination of erroneous (40Ar/39Ar) dates confirm the traditional precessional time-scale (Fischer et al., 2004). Furthermore, the 21 k.y. precessional periodicity is supported by: ( 1) varve counts, (2 ) half-precessional organic- enrichments, (3) eccentricity bundling, and (4) the consistent precessional pattern throughout the Green River Formation. The potential dichotomy in the duration of 219 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. this cyclicity was the result of: ( 1) corruption of the precessional record by higher frequency cycles, (2) evaluation of the cyclicity away from the basin-center, and (3) episodic depositional distortions. Although this cyclicity displays variation, the consistent occurrence of the full suite of Milankovitch cycles throughout the Tipton and Wilkins Peak documents that orbital-driven climatic change dictated lacustrine deposition in these different lake systems. Tipton and Wilkins Peak precessional cycles consist of a two-stage pattern defined from lithologic and geochemical signatures. This cyclicity consists of an organic-enriched basal oil shale that records lake level maxima, and a reduced organic content throughout the remainder of the cycle. Precessional fluctuations in lake level were the result of orbital-driven variations in net moisture (precipitation- evaporation), and other factors affecting lake inflow (Kutzbach and Otto-Bliesner 1982; Benson, 1981; Morrill et al., 2001). Although a well defined, continuous orbital imprint occurs throughout the Tipton and Wilkins Peak, lithologic and geochemical patterns of cyclicity display a progressive change related to the hydrologic evolution of paleolake Gosiute (Tables 21-23). The Scheggs phase represented an expanded, perennial, freshwater, overfilled lake system; the Rife, a brackish-saline, balanced-fill lake; and the Wilkins Peak, a contracted, underfilled, hypersaline, playa-mudflat (Carroll and Bohacs, 1999). Attempts to correlate these oscillations to orbital forcing raise questions about the climatic and depositional mechanisms involved in the cyclical imprint, including which orbital phases were associated with higher and lower amounts of net 220 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Green River M e m b e r Lacustrine S y s t e m & S e t t i n g L lt h o l o g y Log S i g n a t u r e Facies I n d i c a t o r s ) O i l - Y i e l d M id d le W ilk in s P e a k M u d fia t F acies: S u b a q u e o u s to S u b a e ria l E xp o s u re M u d s to n e M a rls to n e S H tstone T ro n a -H a lite In term . G a m m a T ro n a : L o w S o n ic L o w G a m m a M u d c ra c k s A e o lia n S e d im e n ts S h e e tw a s h E v a p o rlte s M u d fla t W e t M ic ro fa c ie s : 1-3 G a llo n s /T o n D ry M ic ro fa c ie s : <1 G a llo n s /T o n P la y a L a k e F acies: H y p e rs a l i n e-S al 1 ne S o m e S tra tific a tio n E x p a n s io n -C o n tra c tio n O il S h ale O rg a n ic -R ic h M u d s to n e H ig h S o n ic H ig h G a m m a C a lc a re o u s Oil S h a le O rg a n ic -R ic h O il S h a le /O rg a n ic -R ic h M u d s to n e : 1 5 -3 7 G a lio n s /T o n V a ria b le O il S h a le C h a ra c te r L o w e r W ilk in s P e a k M u d fla t F acies: S u b a q u e o u s R a re S u b a e ria l E x p o s u re M a rls to n e M u d s to n e R a re -M o d . T ro n a R a re S ilts to n e In term . G a m m a T ro n a : L o w S o n ic L o w G a m m a R a re M u d c ra c k s S o m e E va p o rlte s O rg a n ic -B e a rin g S e d im e n ts M u d fia t: O il-Y ie ld s : 1 -9 G a llo n s flo n P laya L a k e F acies: S a lin e -H y p e rs a lin e E x p a n s io n -C o n tra c tio n S o m e S tra tific a tio n O il S h a le O rg a n ic -R ic h M u d s to n e H ig h S o n ic H ig h G a m m a C a lc a re o u s O il S h a le O rg a n ic -R ic h U n fo s s ilife ro u s O il S h a le /O rg a n ic -R ic h M u d s to n e : 1 0 -3 0 G a ilo n s /T o n V a ria b le O il S h a le C h a ra c te r T ip to n R ife B ed s B a la n c e d -F ill L ake P e re n n ia l L ake B ra c k is h -S a lin e S tra tifie d (O x y c lin e a n d H a lo c lin e ) O il S h a le (H o m o g e n o u s ) R a re M a rls to n e V o lc a n ic A sh R a re E v a p o rlte s S o n ic: C y c le B a s e -H ig h G a m m a : C y c le B a s e -H ig h G e n e ra lly U n fo s s ilife ro u s R are E va p o rlte s R are M u d s to n e s H o m o g e n o u s O il S h a le C y c le B ase: O rg a n ic -R ic h B a s a l O il S h a le (M o s t > 2 5 -3 0 G a llo n s H o n ) L o w e r/M id d le & U p p e r C ycle: R e d u c e d O il-Y ie ld (1 0 -2 0 G a llo n s /T o n ) H a lf-P re c e s s io n a l C ycle: In c . O il-Y ie ld T ip to n S c h e g g s B ed s O p e n L a k e /O v e rfille d E x p a n d e d , P e re n n ia l L ake F re s h w a te r S tra tifie d - T h e rm o c lin e (O x y c lin e ) O il S h a le (H o m o g e n o u s ) R a re M u d s to n e V o lc a n ic A sh S o n ic: C y c le B a s e -H ig h G am m a: C y c le B a s e -H ig h F re s h w a te r M o llu s k s (O s tra c o d e s ) C y c le B ase: O rg a n ic -R ic h B asal O il S h ale: (1 5 -2 5 G a llo n s /T o n ) L o w e r/M id d le & U p p e r C ycle: V a ria b le O il-Y ie ld s U p w a rd In C ycle: (1 0 -2 0 G a llo n s /T o n ) H a lf-P re c e s s io n a l C ycle: In c O il-Y ie ld Table 21. Properties and description o f lacustrine systems and geologic expression o f precessional cyclicity in the Tipton Scheggs and Rife Beds, and Lower and Middle Wilkins Peak Members. 221 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Green River Member Geochemical Patterns & Properties of Precessional Cycles Kerogen Bitumen Middle Wilkins Peak Top Oil Shale - Mudflat: 3-9 % o 1 3 C Enrichment Aliphatic-Rich Pyrolysate In High TOC Oil Shale Lower Aliphatic Pyrolysate-Lean Oil Shale & Mudflat Geochemical Signatures In Oil Shales: (1) Highstand, (2) Organic-Rich Mudstone, (3) Thick Oil Shale w/ Variable Geochemical Properties Mudflat: (Compared to Oil Shale) Increased Squalane & nC2!-C3 , Alkane Content Reduced p-carotane, Different Terpane Ratios Different Sterane/Hopane & C^Ctt Sterane Ratios Oil Shale: Variable nC^-Cj, Alkane Content-Base and Top of Oil Shales Variable p-carotane Content Lower Wilkins Peak Top Oil Shale - Mudflat Occasional 2-4 % o 1 5 C Enrichment Mudflat vs. Oil Shale: Decrease In Oil-Yield and TOC Moderate Decrease in Hydrogen Index (H I) Increase in Bituminite Content Occasional Depletion in S1 3 C Values Mudflat: (Compared to Oil Shale) Higher Pr/Ph, nC25-C3 i Alkane Content Different Terpane Ratios & GCMS Pattern Reduced p-carotane Content Greater Landplant Input Oil Shale: Variable p-carotane Content Tipton Rife Beds Cycle Base and Other Organic-Rich Intervals: 1-4 % >,3C Depletion Matrix Lamalginlte, High H I & Aliphatic-Rich Kerogen Upper/Middle Part of Cycle: (Compared to Base) Reduced Organic Content Reduced Hydrogen & Aliphatic Content Increase in Bituminite Content Cycle Base and Other Organic-Rich Intervals: High Sterane/Hopane & Cj7/C2 » Sterane Ratios Low Gamm/Hopane, CM /C2! Tricyclic Terpane Ratios Reduced nCjj-Cj, Alkane Content? Upper/Middle Part of Cycle: Inc. Methanogenic Input; Large AS1 3 C Aromatic-Saturate Inc. p -carotane and Gammacerane Tipton Scheggs Beds Cycle Base and Other Organic-Rich Intervals: Elevated TOC & H I Matrix Lamalginite, Aliphatic-Rich Pyrolysate Occasional Methanogenic Imprint-Carbonate Middle & Top of Cycle: (Compared to Base) Reduced Organic and Aliphatic Content, and H I Increase in Bituminite Content Cycle Base and Other Organic-Rich Intervals: Reduced nC^-C^ Alkane Content Higher Sterane/Hopane, C27/C20 Sterane Middle & Top of Cycle: Different Terpane Ratios and General GCMS Patterns Methyl Steranes Throughout Cycle Table 22. Geochemical properties and expression o f precessional cycles in Tipton Scheggs and Rife Beds, and Lower and Middle Wilkins Peak. 222 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Green River Member Precessional Cycle Imprint - Lacustrine Conditions & Geochemical Processes M id d le W ilk in s P e a k O il S h a le : In c . N e t M o is tu re (P re c ip ita tio n - E v a p o ra tio n ) & E x p a n d e d P la y a L a k e : In c re a s e d C a p a c ity fo r O rg a n ic A c c u m u la tio n M a x im u m P re c ip ita tio n a n d H ig h s ta n d s , V a ria b le S a lin ity S tra tific a tio n , S e d im e n t T ra p p in g , P ro d u c tiv ity E v e n ts O il S h a le V a ria tio n s : L e n g th & In te n s ity o f P re c ip ita tio n E v e n ts a n d L a k e S iz e M u d fla t: In c re a s e d S u b a e ria l E x p o s u re - S h a llo w S e a s o n a l L a k e s K e ro g e n 13C E n ric h m e n t: R a p id C h a n g e to E v a p o ra tio n -P re c ip ita tio n In c re a s e d L a n d p ia n t in p u t & O rg a n ic D e g ra d a tio n R e d u c e d C 0 2 in B rin e -R ic h M u d fla t L e a d s to In c re a s e d F ra c tio n a tio n , P o s s ib le H C 0 3 P u m p in g H a rs h M u d fla t S e ttin g : H a lo p h ilic In p u t; O x id iz in g C o n d itio n s a n d O c c a s io n a l D e trita l In p u t " W e t & D ry M u d fla t" M ic ro fa c ie s : C lim a tic F lu c tu a tio n s R e la te d to P re c e s s io n -E c c e n tric ity S y n d ro m e L o w e r W ilk in s P e a k O il S h a le : In c re a s e d N e t M o is tu re & P la y a L a k e E x p a n s io n G o o d C o n d itio n s fo r O rg a n ic A c c u m u la tio n - V a ria b le W a te r C o lu m n S tra tific a tio n L a k e In flo w & D e trita l In p u t (? ) F ro m S tru c tu ra l-T o p o g ra p h lc a lly E n h a n c e d D ra in a g e M u d fla t: P rim a rily S u b a q u e o u s , M o d e ra te -G o o d O rg a n ic M a tte r P re s e rv a tio n , S o m e 13C E n ric h m e n t T ip to n R ife B e d s C y c le B a s e - In c N e t M o is tu re & L a k e E x p a n s io n : A b u n d a n t E u tro p h ic to H y p e rtro p h ic A lg a l B lo o m s & H ig h O rg a n ic F lu x E n h a n c e d P re s e rv a tio n • C h e m o c lin e R is e s in to L o w e r P h o tic Z o n e , C 0 2 R e c y c lin g ; H a lo c lin e D e v e lo p s M id d le -U p p e r C y c le : R e d u c e d N e t M o is tu re , L o w e r L a k e L e v e l A b u n d a n t b u t R e d u c e d A lg a l P ro d u c tiv ity (E u tro p h ic C o n d itio n s ) C o m p a re d to C y c le B a s e L o w e r C h e m o c lin e a n d In c re a s e d D e g ra d a tio n in U p p e r W a te r C o lu m n G re a te r B a c te ria l C o n trib u tio n In c lu d in g M e th a n o g e n ic S o u rc e s fro m B a s a l P h o tic Z o n e & M id d le W a te r C o lu m n H a lf P re c e s s io n C y c le a n d E n d o f C y c le T ra n s itio n • P re c ip ita tio n E v e n t(s )? , In c re a s e d P ro d u c tiv ity T ip to n S c h e g g s B e d s C y c le B a s e - In c re a s e d N e t M o is tu re : In c re a s e d N u trie n t in flu x , H y p e rtro p h ic -E u tro p h ic A lg a l P ro d u c tiv ity & H ig h O rg a n ic F lu x S ta b le E le v a te d T h e rm o c lin e ; S o m e M e th a n o g e n ic C o n trib u tio n B e lo w S e d im e n t/W a te r In te rfa c e (S W I) M id d le /U p p e r C y c le : R e d u c e d N e t M o is tu re , R e d u c e d L a k e S iz e & W a te r D ep th A b u n d a n t b u t L o w e r O rg a n ic P ro d u c tiv ity (E u tro p h ic -M e s o tro p h ic C o n d itio n s ) a n d O rg a n ic F lu x O rg a n ic P re c u rs o rs C o n s is t o f G re a te r B a c te ria l In p u t; D iffe re n t A lg a l P re c u rs o r in p u t C o m p a re d to C y c le B a s e L o w e r T h e rm o c lin e , In c re a s e d W a te r C o lu m n M ix in g & D e g ra d a tio n ; S u b tle In c re a s e D e trita l/L a n d p la n t In p u t H a lf-C y c le P re c ip ita tio n E v e n t is S u b tle a n d O fte n N o t R e c o rd e d Table 23. Description of major climatic and lacustrine conditions and processes that imprint Tipton and Wilkins Peak precessional cycles. 223 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. moisture. To define how these orbital signals were translated into the Green River sediments requires that the cyclical record and its origin are accurately 1 interpreted. First, the cyclicity needs to be defined in terms of orbital-driven environmental changes that controlled lacustrine conditions. Second, the changing expression of cyclicity in this spectrum of lacustrine facies needs to be understood to identify the different depositional mechanisms that produced the orbital imprint. Third, the influence of Eocene paleoclimatic conditions and the paleogeographic setting on lacustrine conditions and processes must be defined. A better understanding of the relationship between orbital cyclicity and lacustrine deposition will help ascertain the origin of the organic-rich Green River sediments. Cyclical-Driven Depositional Models-Tipton and Wilkins Peak Because organic-rich lacustrine systems represent dynamic depositional processes, their origin needs to be defined in terms o f the environmental changes that controlled lake size, water column conditions, organic matter accumulation, and sedimentation. During the deposition of the Tipton and Wilkins Peak precessional intervals, these lakes underwent a two-stage lifecycle that corresponded to the precession-driven rainy and dry phases. These climatic variations had profound, but repetitive and predicable changes in the limnology and sedimentation of the lakes. Cyclical changes in organic accumulation are characterized in terms of lacustrine processes that influenced organic productivity, precursors, preservation, organic matter composition, and sedimentation (Tables 23 and 24). 224 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Lower Upper W ilkins P eak W ilkins Peak S ch eg g s B eds Rife Beds Productivity Rainy Phase: High Nutrient Input Slgnflcant Baslnal Flushing (External Input)- Snowmelt + Convective Precipitation Erosion of Phosphatic/Calcareous Sediments Some Self-Fertlllzatlon & Nutrient Recycling From Upper Water Column & Lake Margins Rainy Phase: High Nutrient Input Moderate Baslnal Flushing Self-Fertilization from Playa Lake Margins Significant Nutrient Recycling In Lake Enhanced Water Column and Photic Zone Preservation Rainy Phase: Mid/Upper Water Column to Sediment/Water Interface is Anoxic Elevated and Stable Thermocline (Scheggs) Elevated Chemocline from Oxidative Degradation (Rife) Development of Halocline (Rife) Rainy Phase: Rapid, Short Flux and Self Sedimentation of Biomass Halocline and Reduced Water Column Mixing Anoxic Conditions: Water & Sediment Water Interface Sedimentation (Organic Dilution) Dry Phase: Additional Precipitation of Carbonate (?) Lowstand ■ Minor Detrital Input Rainy Phase: Detrital Dilution from Surrounding Mudflat- Durlng Initial Lake Expansion & Lake Contraction Dry Phase: Sporadic Input - Distal Detrital Tongues Aeolian Transport Storm and Sheetwash Deposits Table 24. Role of different mechanisms that influenced organic productivity, preservation and sedimentation, and their effect on organic accumulation associated with cyclical deposition in the Tipton and Wilkins Peak Members. 225 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Organic accumulation in lacustrine sediments is a function of productivity minus the destruction of the organic matter divided by its dilution (Bohacs, 1998). A large number of factors influence the temporal and spatial variations in the production and degradation of sedimentary organic matter (Brylinsky and Mann, 1973; Demaison and Moore, 1980; Pedersen and Calvert, 1990; Powell, 1986; Kelts, 1988; Katz, 1990; Hollander, 1990; Bohacs et al., 2000). Dilution by sediments decreases the proportion of organic matter relative to the inorganic matrix. Tipton Scheggs and Rife Paleolate Stages The lithological and geochemical patterns in Tipton precessional cycles define dynamic but repetitive conditions in this perennial lacustrine setting. Tipton precessional and half-precessional lake cycles modified the size, chemistry, and water column conditions in these perennial lakes, and influenced organic precursors and productivity (Figures 83 and 84). At the start of the rainy precessional phase, increased runoff caused lake expansion and deepening. Simultaneously, the increased net moisture enhanced chemical weathering throughout the drainage area. Runoff from the adjacent Precambrian terrain expanded to a larger drainage area consisting of Paleozoic and Mesozoic marine carbonates and siliclastics, and Tertiary volcanics (Rhodes et al., 2002). Lake inflow was rich in soluble nutrients that were derived from phosphatic-rich sediments in the drainage basin and recycled from the productive lake margins. Continuous nutrient inflow from seasonal runoff and basinal flushing initiated and sustained eutrophic-to-hypertrophic planktonic algal blooms. As an 226 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W ater Colum n H y p e rtro p h ic A ig a l B lo o m s P h o tic Zo n e M id W a te r B a c te ria l M ass (M in o r) E p ilim n io n Prevailing T h e rm o c lin e H y p o lim n io n N e g lig ib le O rg a n ic D e g ra d a tio n Rainy Phase M e th a n o g e n ic B a c te ria SWI H ig h O rg a n ic A c c u m u la tio n O rg a n ic & A lip h a tic R ich P h o tic Z o n e ia a l Blooms (M o d e r a te ) M id W a te r B a c te ria l B io m a s s (M o d e ra te C o n trib u tio n ) M in o r O rg a n ic D e g ra d a tio n D ry Phase rhermocline R e d u c e d O rg a n ic C o n te n t S W I M o d e ra te - H ig h O rg a n ic M a tte r A c c u m u la tio n Figure 83. Precessional-driven lake cycle for Scheggs Beds. Precessional rainy and dry phases controlled water column conditions during Scheggs stage o f paleolake Gosiute. 227 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. W ater Colum n Hypertrophic Algal Blooms Photic Zone Recycled CO2 Seasonal Chemocline Mid Water Bacterial Mass X M inor)' E p illm n io n Therm ocline Prevailing Hypollmnion Negligible Organic Degradation Rainy Phase Methanogenic Bacteria High Organic Accumulation O rg a n ic & A lip h a tic R ich P h o tic Z o n e Jgal Blooms (M oderate) Mid W ater Bacterial Biomass (Significant Contribution) Minor Organic Degradation D ry Phase Methylotrophs M ethanogenic & Fermentative Input R e d u c e d O rg a n ic C o n te n t G re a te r B a c te ria l In p u t SWI Moderate - High Organic Matter Accumulation Figure 84. Precessional-driven lake cycle for Rife Beds. Precessional rainy and dry phases controlled water column conditions during Rife stage o f paleolake Gosiute. 228 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. example, deposition of organic-rich lacustrine sediments in West Africa has been linked to a high flux of dissolved carbonate (Harris et al., 2004). During seasonal periods of increased dissolved nitrogen in Big Soda Lake, Nevada, phytoplankton productivity increased by about 30-fold (Oremland et al., 1988). The alkaline Rife lake helped support a higher level of primary production than in waters of neutral pH because of the abundance of available CO3 ions in addition to atmospheric CO2 during photosynthesis (Kelts, 1988). The expanded lake combined with abundant photic zone productivity elevated and strengthened the existing stratification. With expansion of the Scheggs lake, which was primarily thermally stratified, an elevated and more stable stratification developed. The Rife lake however, may have started as a thermally stratified lake but developed a halocline. With the expanded water column, the base of the photic zone probably reached deeper into the lower epilimnion. Oxidative degradation of the increased organic flux in the lower photic zone consumed the dissolved oxygen, which caused the chemocline to rise in the water column, at least on a seasonal basis. Any oxygen that was introduced into this part of the water column was quickly consumed. The buildup of dissolved organic carbon in the bottom waters of these lakes further enhanced the stability of stratification. Because most of the expanded water column was anoxic, the increased flux of algal- planktonic precursors was protected from destructive degradation by aerobic and even sulfate-reducing bacteria. 229 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The expanded lake helped trap sediments and reduce detrital dilution of the accumulating organic matter. Suspended sediments were trapped by vegetation in marginal lacustrine settings. This lake stage is consistent with high total organic carbon (TOC) and hydrogen index (HI) values, and the occurrence of well-preserved lamalginite. The high sterane/hopane ratios further confirm the algal-dominated precursor input. At the start of the dry precessional phase, less precipitation and increased evaporative conditions caused lake levels to decline. Planktonic productivity in the photic zone declined as runoff and the input of nutrients including essential trace metals (iron, etc.) decreased. Similar relationships are documented in modem lakes (Axler et al., 1978). Lake productivity shifted from a eutrophic-hypertrophic to a eutrophic-mesotrophic state. The changes in nutrient balance and photic zone ecology led to not only a reduced algal productivity, but also different types and proportions of planktonic precursors. As the planktonic flux declined, more light was able to penetrate the water column and sustain bacterial photosynthesis in the lower photic zone and directly above the chemocline. This probably formed a seasonal bacterial plate at a stratified interface, which is similar to other lacustrine settings (Oremland et al., 1988). A deeper thermocline and chemocline in these lakes led to a slight increase in organic degradation as the flux passed thorough the water column. During the winter, an increased mixing in a greater proportion of the water column resulted in slightly more organic degradation, especially in the Scheggs. However, a complete lake overturn was unlikely, or limited to brief episodes during lowstand 230 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. events. Increased summer evaporation led to greater carbonate precipitation, which further diluted the already reduced accumulation of organic carbon. The slightly lower TOC and HI values compared to the cycle base are primarily a result of reduced productivity combined with a slight increase in water column degradation. The reduced sterane/hopane ratio and the increased proportion o f bituminite are consistent with a greater proportion of bacterial input and degradation compared to the rainy phase. Wilkins Peak Plava Lake As the Wilkins Peak stage of paleolake Gosiute transgressed and regressed great distances across the playa, oil shale deposition occurred in evolving stages throughout the precessional rainy phase (Figure 85). The generally similar precursor input throughout the life of the playa lake indicates that variations in the oil shale are products of changing productivity, preservation, and sediment dilution, all of which were derived from fluctuations in lake size and depth. At the start of the rainy phase, the shallow, contracted lake started to expand with an increased capacity for organic matter accumulation. Stable subaqueous conditions allowed for increased organic productivity from mostly benthic but some planktonic precursors. However, episodic lake contraction, water column mixing, and aeration of the substrate still occurred on a seasonal or multi-year scale, which resulted in organic degradation. Some fluctuations in lake conditions during the rainy phase may have been related to short-term cyclicity (Fischer and Roberts, 1991). The increased runoff transported fine-grained sediment into the expanding lake from the 231 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. O nset Rainy Phase: O rganic-B earing M udstone * < ^ T T 1 Shallow Playa Lake Form s Increased Productivity & Preservation Dilution of Organic M atter Highstand -O ptim al Organic Accumulation Event_ _ E utroph ic-H ypertroph ic P rod u ctivity H igh F lu x Expanded ’hotic Self-Sedim entation Chem ocline? ke Contraction - Salt Pan Or Mudflat Lake Evaporation~>Precipitation Poisoned or Restricted Productivity < D co G D S-, W ) g 0 C O c d a 1 tX < L > o ,c3 a o •a o P h < l > W ) G < t > % C S $ c u G O > G O 0> o a P m in 00 .£ P S 232 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. accumulation o f organic matter, (B) continued lak e expansion leading t o lacustrine highstand a n d optimal organic accumulation, ( C ) lake contraction resulting i n formation o f a salt p a n o r mudflat lake. P arts o f th e figure a r e f r o m Roehler (1993). surrounding mudflats and drainage areas. Dilution of the accumulating organic matter was a dominant process during the initial expansion of the playa lake because of an increased mobilization of sediment stored in the surrounding mudflat and basin margins. A hypersaline bottom brine began to form as a result of a rapid rise in lake level that was fed from runoff of the surrounding alkaline mudflats combined with seasonal evaporation and concentration (Sassen and Moore, 1988). The increased inflow of fresh water into the hypersaline lake promoted ectogenic meromixis and salinity stratification as defined by Boyer (1982). With continued expansion, larger amounts of better-preserved organic matter were deposited in comparison to the underlying mudflat. This is reflected in higher TOC and HI values. The continued expansion and deepening of the playa lakes provided improved conditions for organic matter accumulation. During periods of maximum precipitation and inflow, development of a lacustrine highstand corresponded to high nutrient influx, productivity, lake expansion and stratification, and reduced organic degradation and detrital dilution (Figure 85). Roehler (1992c and 1993) inferred that the maximum depth of the playa lakes was tens of feet, rather than hundred’s of feet as in the Tipton. A low diversity of specialized halotolerant biota associated with the saline-hypersaline lake contributed to the high productivity (Kirkland and Evans, 1981). Photosynthetic sulfur bacteria and cyanobacteria were probably the dominant precursors because they prefer high salinities, whereas the algal community was limited to a few primary species. Seasonal precipitation and flushing of the drainage basin provided continual replenishment of nutrients that triggered high organic 233 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. productivity. Furthermore, recycling of nutrients and self-fertilization of the lake occurred as decomposition products of benthic mats at the periphery of the playa lake were transported basinward. Evaporative conditions also helped concentrate nutrients in the playa lake. The saline lake provided for an increased solubility of phosphorous, as well as other nutrients that promoted productivity (Hammer, 1981; Kelts, 1988). Although the playa lakes were alkaline, seasonally freshened surface water probably provided salinities of less than 250 per mil, which were conducive for prolific plankton blooms under conditions otherwise too saline (Warren, 1986). The expanded playa lake provided the following conditions for enhanced photic zone productivity: ( 1) a deeper water column, which increased the zone of primary productivity and provided protection for planktonic organisms from ultraviolet light; and (2 ) a reduced influx of suspended sediment, which allowed greater penetration of sunlight for photosynthetic activity (Kirkland and Evans, 1981). During the maximum expansion of the playa lakes, a large proportion of the water column was in the highly productive photic zone. Warm summer temperatures further promoted high rates of organic productivity. The expanded playa lake provided optimal preservation that enhanced organic accumulation. A seasonal influx of magnesium and calcium from distal alkaline mudflats was toxic to potential metazoan grazers. They are greatly reduced in diversity and number at salinities above 1 0 0 per mil, leaving only brine shrimp (DeDeckker and Geddes, 1980). Most organisms were restricted due to the osmotic stress as elevated concentrations of salt limited the ability o f the water to absorb 234 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oxygen. In comparison, brine shrimp in modem lakes quickly graze phytoplankton to very low densities when salinity is reduced (Stephens, 2002). During periods of highest runoff, oxygenated, less saline water floated on the dense bottom brine, which promoted stable ectogenic meromictic lakes (Boyer, 1982; Higley, 1983). An established halocline was maintained by runoff and the seasonal flooding of alkali deposited at the lake margins, which is similar to Great Salt Lake (Spencer et al., 1984). The presence of a dense, hypersaline bottom layer reduced water column mixing that might have been associated with wind stress. Rapid transport of the abundant biomass through the thin epilimnion limited water column degradation, and thus helped preserve the organic matter. The slow rate of oxygen advection below the halocline further protected against organic degradation. Also, trapped sediments at the expanded lake margins reduced the detrital dilution of the accumulating organic matter. The closely-spaced geochemical variability documents fluctuating playa lake conditions in responses to changes in net moisture during the rainy phase. These relatively short periods of maximum lake expansion represented optimal organic accumulation events, in which high productivity, organic flux, preservation potential, and reduced sediment dilution operated in tandem. The highstand and optimal organic accumulation is geochemically recorded by a significant increase in TOC, and HI values that correspond to a lamalginite- and aliphatic-rich kerogen. Biomarker distributions reflect a low diversity of precursor organisms associated with harsh conditions. 235 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. As the decreasing rate of precipitation approached evaporation, the lake rapidly contracted, reducing the potential for organic matter accumulation (Figure 85). Productivity and organic flux declined as inflow and nutrients diminished along with deterioration o f the photic zone. A reduced organic flux and oxidative degradation, and increased water column mixing due to shallowing conditions provided more potential for organic degradation. However, a complete overturn of the lake was unlikely. Sporadic runoff supplied sediments from the encroaching mudflat that diluted the reduced amounts of accumulating organic matter. Eventually, as productivity and preservation declined, the threshold for oil shale accumulation could not be maintained. This lake stage is often recorded by lower TOC and HI values, and a kerogen with a lower aliphatic content. With further reduction in net moisture and lake size, the small amount of remaining organic productivity was poisoned by concentration of alkali material due to seasonal cycles of evaporation (April, 1981). The increased aridity caused the lake to become supersaturated and to precipitate trona. The high trona content indicates that the lake did not completely evaporate during its transition to a shallow ephemeral mudflat lake (Higley, 1983). Therefore, the occurrence of trona indicates a significant decrease in moisture but not a net moisture deficit. Wilkins Peak “Wet and Dry Mudflat” Microfacies Overall, mudflat deposition during the dry precessional phase consisted of reduced precipitation combined with evaporative conditions, which limited lake 236 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. formation and duration. Chemical deposition of calcareous and alkaline-rich sediments predominated during periods of reduced runoff. The “dry and wet” microfacies originated from short-lived seasonally flooded to almost perennial mudflat lakes. Small variations in moisture availability influenced the size and duration of the mudflat lake, and controlled the quantity and properties of organic matter, which often varies over short vertical intervals. Orbital-derived climatic variations, structural-topographic modifications, evolving climatic conditions, variable sedimentation, and episodic depositional distortions contributed to variations in organic and lithologic properties of the mudflat facies (Figure 8 6 ). Many of the sub-environments that have been described in the Wilkins Peak mudflat by Smoot (1978) are often represented in a single short eccentricity cycle. The “dry mudflat” microfacies was deposited during periods o f evaporative conditions and minimum but sporadic inflow, which led to organic-lean to -barren sediments, especially in the middle Wilkins Peak. Deposition took place in small, shallow lakes that evaporated to form subaerially exposed mudflats during much of the year. These ephemeral mudflat lakes developed during sporadic seasonal flooding or from spring-fed water. The mudflat floor probably occurred in the capillary fringe just above the watertable. Limited productivity from cyanobacteria mats occurred in the ecologically-stressed shallow lakes that consisted of heliothermal brine-rich water. As these fragile lakes evaporated, the small amounts of organic matter underwent oxidation. Desiccation, mud-cracking, deflation, and aeolian transport further destroyed the organic matter. The geochemical signature of 237 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dry Microfacies P»rawilal Perennial fA a m m in A tk s H m ^Sjreams^Jffnts Intense E v a p o r a tio n . £ : A . Wet Microfacies Sub-Aerial Dominated Thin-Fragile Benthic M ats Repeated Desiccaticr Sporadic Runoff Aeolian Transport E vap o ratio n Air f C a p illa ry D raw o f P o re W ater Traditional Wilkins Peak M odel Sub-Aqueous Dominated Conditions Stable Benthic Mats Protected from Desiccation/Oxidation Evaporation * | * L a k e f Surfcc© Planktonic? *«-• A % a l< 5 r o w th Figure 86. Depositional setting o f “wet and dry mudflat” microfacies, Wilkins Peak Member. The “dry mudflat” microfacies is a product o f high evaporation and reduced precipitation associated with the precession index, and arid phases during the Middle Wilkins Peak. The “wet mudflat” is a product of increased net moisture including structural-topographic effects that enhanced drainage during the Lower Wilkins Peak. Parts of figure are from Eugster and Hardie (1975). 238 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the “dry mudflat” includes TOC values less than 0.5 wt. % and HI values less than 100 mg HC/g OC, which is characteristic of a Type III-IV oxidized and inertinitic kerogen. Brecciated to massive dolomitic mudstones were the products of reworked silt and micritic mud that underwent repeated mudcracking. Evaporative pumping formed proto-dolomite and interclasts of carbonate. Mudflat intervals consisting of silts and fine grained sands were deposited from episodic runoff that delivered distal detrital pulses from the sparsely vegetated playa fringes during infrequent precipitation. The limited amounts of biogenic structures indicate that the mudflat was dominated by alkaline-rich conditions, which were rarely suitable for invertebrate burrowers. The “wet mudflat” microfacies consist of organic-bearing marly mudstones that were deposited in a predominantly subaqueous setting. In the lower Wilkins Peak, “wet mudflat” deposition was associated with relatively moist climatic conditions, and a structural-topographic setting that enhanced drainage and retention of water to provide almost perennial mudflat lakes. In comparison, “wet mudflats” in the Middle Wilkins Peak were associated with stable subaqueous dominated conditions related to “wet” precessional cycles. Although benthic mats were the dominant organic precursors, planktonic organisms occasionally occurred during temporal flooding. Periodic short-term stratification of the mudflat lake may have partially developed from saline groundwater springs feeding into it (Staffers and Heckly, 1978). The highly alkaline water bottoms combined with an anoxic zone directly above the sediment/water interface protected organic matter from biological 239 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. degradation. Transported micritic muds and dissolved calcium derived from the margins of the mudflat lake were seasonally deposited as laminated-to-massive calcareous mudstones, which further helped preserve organic matter. The larger mudflat lake may have reduced sporadic detrital input. This microfacies is consistent with TOC’s up to 2 wt. % and H i’s between 300 and 700 mg HC/g OC. The moderate- to well-preserved Type II-III kerogen documents the mudflat was flooded for extended periods. The abundance of this microfacies and geochemical properties are contrary to most existing Wilkins Peak mudflat models (Eugster and Hardie, 1975; Smoot, 1978). These cyclical-derived patterns demonstrate that the Scheggs, Rife, and Lower and Middle Wilkins Peak lacustrine systems underwent a two-stage lake cycle corresponding to the precessional rainy and dry phases. Geochemical and lithological differences between these two phases can be defined in terms o f precessional-driven changes in lacustrine conditions. This two-stage lake was further modified by the eccentricity. These models compliment existing Tipton and Wilkins Peak depositional studies by explaining: ( 1) how cyclical-driven climatic variations controlled lake conditions and processes, (2 ) the occurrence of different lacustrine facies and microfacies, (3) the expression of the orbital imprint in the sedimentary record, and (4) mechanisms involved in the origin of these organic-rich sediments. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Spectrum of Lacustrine Facies, Cyclical Expression and Litho-organic Signatures - Applications to Orbital Cyclicity Spectrum of Green River Lacustrine Facies The spectrum of lacustrine facies that occurs between the Scheggs and Middle Wilkins Peak is the result of an expanded, perennial, freshwater lake that contracted to an ephemeral, hypersaline, playa-mudflat. Evolution of these lake systems is documented by increasing organic-lean sediments, evaporites and a shallow, subaerial dominated lithofacies. Geochemical evidence of this evolution includes a change from freshwater to brackish-saline input, increasing bacterial and benthic precursors, and greater oxidation. Although a significant change in lake conditions occurred at the end of the Tipton, occasional evaporites and mudstone in the Rife, stromatolites at the top of the Tipton, and a decreasing organic content in the lower to middle Wilkins Peak mudflats document a continuously evolving lake system. Distinguishing between the tectonic and climatic effects on the water depth of paleolake Gosiute is difficult and the subject o f current debate. The evolving lake systems appear to represent interrelated responses to both structural-topographic changes and regional paleoclimatic trends (Figure 87). During Wilkins Peak deposition, active fault movement at the northern and southern basin margins probably provided additional accommodation space and diverted some drainage away from the basin that contributed to the hydrologically-closed lake (Roehler, 241 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Scheggs Rife L. Wilkins Peak M. Wilkins Peak Fresh/Perennial —► Brackish/Perennial — ► Ephemeral/Hvpersaline Plava ____________ Greenhouse Conditions O to Decreasing Mean Annual Precipitation 120-80 cm J ____________Decreasing Mean Annual Temperature 23-20 °C______ , ° Mnist/Ri ih-trnpicai___________________ Warm Temperate-Hot/Arid) Overfilled — ► Balanced ► Underfilled --------- Lake Closure? Fault Movement .... . D. ..'.... Northern & Southern Basin Margins Wind River Uplift . . . . .. a r Increased Accommodation East-West Basin Tilt > > ;o T 5 > O Figure 87. Summary o f likely paleoclimatic, tectonic and orbital factors that influenced lake level in the spectrum of Tipton and Wilkins Peak lacustrine systems. It is difficult to unravel the influence of tectonic and climatic effects on these lake systems. “Long-Term” Orbital Cyclicity (-1.2 m.y. Eccentricity/Other Cyclicity?) Com piled From: Carroll et al., 2 0 0 2 Roehler, 1993 W ilf, 2 0 0 0 M acGinitie, 1969 Bohacs et al., 2 002 Laskar, 1989 Matthew s & Perlm utter, 1994 242 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1993; Pietras et al., 2003). Although a tight correlation between rainfall, temperature and lake size does not exist, paleobotanical and isotopic studies document decreasing precipitation and temperature between the Early Tipton and Middle Wilkins Peak (Leopold and MacGinitie, 1972; Wing et al., 1998; W ilf et al., 2000). Regional paleoclimatic change is indicated from 40Ar/3 9 Ar results, which indicate the Wilkins Peak-Laney boundary is synchronous with a saline-evaporite to freshwater transition in the Piceance and Uinta Basins (Machlus et al., 2002). Increasing aridity and decreasing temperatures in the Rocky Mountain region during the Early Eocene appear to have occurred in several pulses with short-term reversals. Tectonic activity and intrabasinal sills may have magnified paleoclimatic changes. The evolution from the deep Scheggs lake to the Wilkins Peak playa-mudflat could have been influenced by the effects of a long-period eccentricity. These contrasting lake systems may reflect near end-member climatic conditions associated with an approximate 2 m.y. eccentricity (Laskar, 1990 and 1999; Olsen and Kent, 1999). Earth and Mars appear to go into resonance at intervals ranging between 2.0 and 2 .8 m.y., in which the eccentricity cycle is greatly reduced for several hundred thousand years. The expanded Scheggs and Laney paleolake stages may have been a product of this low eccentricity. Further work is required to evaluate the imprint of a long-period eccentricity. Regardless of the mechanisms involved in the contraction of paleolake Gosiute, the early Tipton to middle Wilkins Peak interval provides an opportunity to evaluate how cyclicity is recorded and expressed in an evolving lake system. 243 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Expression of Cyclicity in the Spectrum of Tipton and Wilkins Peak Facies Although declining lake levels occurred between the Scheggs and Middle Wilkins Peak, parallel precessional patterns in organic content indicate similar trends in net moisture throughout the 21 k.y. interval. Similarities include: (1) a sharp transition to the organic-enriched cycle base from the underlying cycle; (2 ) thickness of the cycle base; (3) thin, organic-rich highstands in some basal oil shales; (4) sharp lithologic and geochemical changes above the cycle base; and (5) a half-precessional organic enrichment. The similar range in thickness of the cycle base in both members suggests a consistent precessional rainy phase (Figure 8 8 ). These consistent litho-organic patterns throughout the Tipton and Wilkins Peak cycles were the result of common lacustrine conditions derived from the continual precessional shift in rainy and dry conditions (Figure 89). Although a continuous orbital imprint occurs throughout the Tipton and Wilkins Peak, the expression of cyclicity progressively changes in response to evolving lake conditions. Reduced lake levels between the overfilled Scheggs and the underfilled Middle Wilkins Peak produced an increasing lithological and geochemical contrast between the rainy and dry precessional phases (Figure 90). A higher sedimentation rate in the playa lake and mudflat corresponds to an increase in the average cycle thickness for the Wilkins Peak (13.3 ft) in comparison to the Rife (8 .6 ft) and Scheggs (6.4 ft). Enhanced organic productivity and preservation in the Rife contributed to an increased cycle thickness compared to the Scheggs. The magnified lake contractions at the end of the rainy phase(s) in the Wilkins Peak 244 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Wilkins Peak 0 ) in n £ O L > U T ransition to O verlying Cycle M id/U pper Cycle Reduced Net M oisture Evaporative C onditions? H alf-Precessional C ycle O rganic E nrichm ent Sharp Decrease i i 1 O rganic C ontent 1 1 [ O rganic-R ich H ighstand ; 1 ! M axim um Net M oisture 1 1 Sharp Onset i n O rganic-R ich — 3 t Cycle Base C y clical Im p rin t t * u * X > 1 + i 0. - 3 0 ■ o ' £ E l i O .1 245 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 88. Similar lithological a n d geochemical patterns i n th e Tipton a n d Wilkins P eak precessional cycles confirm parallel trends in relative moisture availability. 964781^022520^47951263^8959^42^^^532566^0088^546851021842^01 B837C Tipton Scheggs Beds Tipton Rife Beds Lower Wilkins Peak Middle Wilkins Peak Moist/ Sub-Tropical Temperate/ Arid ■ Hot Perennial Lake Freshwater Perennial Lake Brackish-Saline Playa Lake Saline-Hypersaline Subaqueous Mudflat Playa Lake Hypersaline-Saline Dry-Moist Mudflat Sharp Increase in Organic Content at Cycle Base-Onset to Rainy Precessional Phase ____________________________________In c r e a s e d N e t M o is tu re : P ro d u c tiv ity - R e d o x E v e n tfs t_________________________ Organic-Rich Cycle Base In crea se d Nutrient F lu y F n h an ce d P hntic 7 n n e an d High O rganic F lliy _______________________ O r g a n ic -R ic h C y c le B a s e - E n h a n c e d W a t e r C o lu m n S tra tific a tio n & P r e s e r v a tio n ______________ O r n a n ic -R ic h H in h s ta n d : M a x im u m N e t M o is tu r e A O n tim a l P ro d u c tiv ity in R a in y P h a s e r _____________ H a lf-C y c le E n ric h m e n t: In c r e a s e d N e t M o is tu r e . L a k e I e v a l A O r g a n ic A c c u m u la tio n ------------ Rainy - Dry Phase Boundary - Lower Organic Content: Reduced Lake Level, Productivity & Preservation Figure 89. Similarities in the lithological and geochemical expression o f precessional cycles, and their occurrence throughout the Tipton and Wilkins Peak Members. These similarities are a result of common lacustrine conditions and processes that occurred in the different lake systems. Properties of the different lake systems and apparent climatic conditions are shown at the top of the figure. Dry Phase: Reduced Organic Content: Lower Productivity & Preservation 246 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Scheggs Beds Moist/ Sub-tropical Tipton Rife Beds Lower Wilkins Peak Middle Wilkins Peak Temperate/ Arid-Hot Perennial Lake Freshwater Perennial Lake Brackish-Saline Piaya Lake Saline-Hype rsaline Subaqueous Mudflat Playa Lake Hypersaline-Saline Dry-Moist Mudflat Pronounced Wet/Dry Precessional Cycles Increased Cycle Thickness___________________________^ Increased Lithological & Geochemical Contrast Between Rainy & Dry Phases Increased Litholooic Contrast-Eccentricitv Boundaries________ ^ Organic-Lean Oxidized Sediments - Dry Precessional Phase r __________Increased Mudstone/Marlstone________________ Increased Trona & Siltstone fSubaerial Exposure! ( Pronounced Organic-Rich Hiahstands___________^ S u h tla D e c r e a s e in B a s a l O il S h a le T h ic k n e s s 1 3 C-Depleted Kerogen in Cycle Base Enhanced Expression of Half-Cvcle Increase in Rectorial ft Benthic Precursor Input - Dry Phase Absence of Methanotrophic Input Figure 90. Lithological and geochemical differences in the expression of cyclicity with the evolving Tipton and Wilkins Peak lake systems. 247 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. compared to the Tipton resulted in precipitation of evaporites and calcareous sediments. The increased depositional contrast between the rainy and dry phases in the playa lake-mudflat resulted in the more pronounced eccentricity bundling in the Wilkins Peak. A decrease in available net moisture and inflow between the Lower and Middle Wilkins Peak limited the temporal extent of the rainy precessional phase and duration of the playa lake, which reduced the thickness of the oil shale. The increase in subaerial conditions in the Middle Wilkins Peak resulted in increased amounts of organic-barren, brecciated mudstone and detrital mudflat sediments that contributed to the cyclical contrast. As the size of these lakes diminished, episodic depositional distortions contributed to greater variations in the cyclical record. The harsh, subaerial and possibly erosive mudflat conditions in the Middle Wilkins Peak may have erased some of the detail of the cyclical record during the dry phase. Geochemical patterns of cyclicity progressively change in response to the evolving lacustrine conditions. The geochemical expression of Rife cyclicity is magnified compared to the Scheggs because the larger precessional fluctuations in the size and water column conditions of the balanced-fill lake optimized changes in productivity, precursors and preservation. The ecology of the overfilled, open Scheggs lake was less sensitive to precessional-driven changes in water depth. In comparison to the Scheggs, Rife sediments contain a relative abundance of P- carotane, gammacerane, 1 3 C depleted kerogen, and methanotrophic bacterial input that reflects the presence of a chemocline and halocline. Reduced HI values in the 248 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. upper parts of some Scheggs cycles are the result of increased organic degradation in the less stratified lake. Compared to the Tipton, an increased geochemical contrast between the rainy and dry phases in the Wilkins Peak is the result of magnified changes in lake level. The rainy and dry phases in the Tipton correspond to alternating eutrophic- hypertrophic and mesotrophic - eutrophic conditions, respectively; whereas in the Wilkins Peak, these respective phases correspond to mesotrophic to hypertrophic and oligotrophic conditions. Between the Tipton and Wilkins Peak, organic precursors in the dry phase shifted from planktonic to benthic. Temporal fluctuations in net moisture during the rainy phase in the Wilkins Peak had a large impact on lake expansion and contraction, which are recorded as highstands and closely-spaced geochemical variations. In the Tipton, various proportions o f water column anoxicity controlled preservation potential, whereas in the Wilkins Peak, the chemocline 1 ^ ranged from well above to below the sediment water interface. The absence of a C- enriched carbonate matrix in Wilkins Peak sediments indicates that below the sediment/water interface methanogenesis was inhibited partly due to hypersalinity (Lupton et al., 1984). In the Middle compared to the Lower Wilkins Peak mudflat, the greater occurrence of oxidized, 13C-enriched kerogen is the product of increasing shallow, evaporative conditions. The pronounced highstands in the Middle as opposed to the Lower Wilkins Peak resulted from magnified episodes of lake expansion and a well- developed halocline. The greater amounts of p-carotane and 13C-depleted kerogen in 249 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oil shales from the Lower Wilkins Peak suggest stable stratification and a better developed photic zone. Although the saline-hypersaline Middle Wilkins Peak would be expected to have relatively abundant P-carotane and gammacerane, their low abundances appear to be related to the shallow, poorly stratified and oxidizing setting. In these different lake systems, the precessional-eccentricity signal dictated repetitive climatic-driven lacustrine processes that continuously imprinted sediments with a consistent signature. Conversely, evolving lake conditions simultaneously modified, magnified, or suppressed other lacustrine processes, resulting in different lithologic and geochemical expressions of cyclicity. The continuous orbital signals were transferred into sediments through different lacustrine processes and depositional pathways associated with these changing lake systems. The changing patterns of cyclicity result from the effects of different lacustrine conditions on productivity, precursors, stratification, redox-oxidation, biochemical versus detrital sedimentation, and desiccation in response to the rainy-dry shift (Figures 90 and 91). Therefore, the cyclical imprint must be interpreted in the context of the depositional response to changes in the lake system. The identification of cyclical patterns associated with this spectrum of lacustrine facies can be used to reconstruct the climatic and depositional history, and thus understand how orbital signals were recorded. Reconstruction of the different climatic mechanisms and lake conditions that produced the lacustrine processes 250 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Tipton Scheggs Beds Moist/ Sub-tropical P erennial Lake Freshw ater Tipton Rife Beds Lower Wilkins Peak Perennial Lake B rackish-Saline Middle Wilkins Peak T em perate/ Arid-Hot Playa Lake Saline-H ypersaline S u b aq u eo u s Mudflat Playa Lake H ypersaline-Saline Dry-Moist Mudflat o > in n • c a. > » c S . A bundant External Nutrient Flux P lanktonic Algal Productivity E levated T herm odine G reater Internal N utrient Recycling Benthic + Planktonic Productivity E nh an ced Photic Z one Conditions Productivity-Flux-Preservation E nhanced Halocline & C h em o d in e Halocline G reater Sensitivity to C h an g e s in Precipitation/Evaporation R educed W ater Colum n Stratification £ D In creased C arbonate Precipitation? Limited Benthic Productivity Shallow Suboxic/Oxic Conditions & S ubaerial D esiccation G reater R ole of Evaporation D etrital Influx/Reworking Figure 91. Different climatic and lacustrine mechanisms associated with the Tipton and Wilkins Peak lacustrine spectrum, and their effects on the imprint of cyclicity. 251 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. associated with these cyclical patterns better defines how the orbital signal was translated in the sedimentary record. With the moist-to-arid hydrologic shift, the greater cyclical contrast in water column conditions, redox-oxidation, and desiccation-sedimentation played increasing roles in the orbital imprint. Organic accumulation in the rainy phase was maintained by an increasing reliance on internal recycling of nutrients in the lake and salinity stratification. The stronger expression of the precession-eccentricity syndrome in the Wilkins Peak is a result of the shallow lakes being more responsive to small changes in seasonality that produced increasing contrasts in oxidation-reduction and sedimentation. In contrast, the deeper Tipton lakes buffered the seasonality signal. Different orbital signals may preferentially affect different components of organic accumulation in a lake system. Precessional changes magnify precipitation and nutrient inflow, thus affecting water column productivity; where-as, changes in the eccentricity reduce evaporation, which extends lake duration and preserves stratification. Litho-Organic Signatures - Applications of Geochemistry to Orbital Cvclicitv The sensitive response of these lake systems to environmental change provides litho-organic signatures that help reconstruct changes in net moisture, climatic mechanisms, and unravel cyclical versus non-cyclical imprints (Table 25). Litho-organic signatures document the increased precipitation in the Green River region during deposition of the precessional cycle base. Deposition of the organic- 252 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Litho-Organic Signature Occurrence (Member) Interpretation - Application T h in O rg a n ic -R ic h H ig h s ta n d s W ilk in s P eak: C o m m o n M a x im u m P re c ip ita tio n -E v a p o ra tio n , L a k e E x p a n s io n , O p tim a l T ip to n : R are - O c c a s io n a l O rg a n ic A c c u m u la tio n ; M axim u m P re c e s s io n a l P o s itio n fo r P re c ip ita tio n ? O rg a n ic -E n ric h e d T ip to n & W ilk in s P eak In creased N e t M o is tu re & O rg a n ic A c c u m u la tio n : H alf-P re c e s s io n a l C ycles A b u n d a n t in R ife B eds A p p ro x im a te 10 k.y. S u b -M iia n k o v itc h M e c h a n is m O rg a n ic -R ic h A lg al D o m in ated T ip to n E xp an d ed Lake, E u tro p h ic -H y p e rtro p h ic P ro d u c tiv ity & E n h a n c e d P reservatio n B asal O il S h ale R a in y P re c e s s io n a l P h ase w ith E le v a te d P re c ip ita tio n M e s o -E u tro p h ic O il S h ales T ip to n R ed u ced L ake S ize, N u trie n t In flo w , O rg a n ic P ro d u c tiv ity & P res e rv a tio n E levated B acterial In p u t D ry P recessio n al S tag e: R ed u c e d M o is tu re & In c re a s e d E v a p o ra tio n 1iC E n ric h e d M u d fla t K ero g en C o m m o n M . W ilk in s P eak H u m lc In p u t, L im ite d A q u e o u s C 0 2, O rg a n ic D e g ra d a tio n R a re L. W ilk in s P eak S h a llo w E v a p o ra tiv e C o n d itio n s D ry P recessio n al P h ase Lo w T O C B re c ia te d M u d s to n e M id d le W ilk in s P eak S e a s o n a l F lo o d in g o f M u d fla t, S u b aerial E x p o s u re , D e s ic c a tio n & M u d c ra c k in g Dry M u d ffa t M ic ro fa c ie s R a re L. W ilk in s P eak D ry P re c e s s io n a l C ycle H o m o g e n o u s O rg a n ic -B e a rin g W ilk in s Peak S ta b le , S h a llo w S u b a q u e o u s D o m in a te d M u d fla t C o n d itio n s M u d flat S u ffic ie n t P ro d u c tiv ity a n d P reservatio n W e t M u d fla t M ic ro fa c ie s W e t P recessio n al C ycles R elated to P re c e s s io n In d ex O rg a n ic -R ic h *S C D e p le te d R ife M a x im u m P recip itatio n , P ro d u c tiv ity , E le v a te d C h e m o c lin e , R e c y c le d C 0 2 O il S h ales L o w e r W ilk in s P eak In P h o tic Z o n e ; R a in y P recessio n al P hase M u d s to n e , S ilty M u d s to n e , S ilt W ilk in s P e a k -C o m m o n M a x im u m S e a s o n a lity & E ccen tricity E c c e n tric ity B o u n d a rie s T ip to n - R are C o o l D ry W in te rs w ith O x id iz in g C o n d itio n s H o t E v a p o ra tiv e S u m m e rs w ith S p o ra d ic b u t In te n s e P re c ip ita tio n W e t • D ry P re c e s s io n a l C ycles W ilk in s P eak P recessio n al V a ria tio n in L ith o to g y & O rg a n ic M a tte r P ro p erties P ro d u c t o f P re c e s s io n In d ex H o m o g e n o u s T ro n a W ilk in s P eak S h a llo w U ltra -s a lin e L ake - R estricted b u t P o s itiv e N e t M o is tu re O rg a n ic M a tte r in T ro n a W ilk in s P eak P recip itatio n E ven ts? S h arp R a in y -D ry P re c e s s io n a l T ip to n R ap id C h a n g e s in L ake L e v e l an d Lake E c o lo g y P hase B o u n d a rie s (M id C ycle) W ilk in s P eak O rb ital T h re s h o ld s T rig g e re d N e t M o is tu re C h a n g e Ic h n o fa c ie s & B u rro w in g W ilk in s P e a k • R are H igh P recip itatio n F re s h w a te r Input B io tu rb atio n O rg a n ic -R ic h M u d s to n e in W ilk in s Peak R estricted L ake S ize & P ro d u ctivity; D e trita l D ilu tio n O il S h a le Facies T ip to n • R are D ry P re c e s s io n a l C ycles T h ick, L o w O il-Y ie ld W ilk in s P eak W e t P re c e s s io n a l C ycle P recessio n al C ycle M in im al E c c en tricity? T h in H ig h O il-Y ie ld W ilk in s P eak D ry P re c e s s io n a l C ycle w ith S h o rt-L iv e d M a x im u m P re c ip ita tio n P recessio n al C ycle T h in L o w O il-Y ie ld W ilk in s P eak D ry P re c e s s io n a l C ycle P recessio n al C ycle V a ria b le L ith o lo g ic S u c c e s s io n s W ilk in s P eak D iffe re n t P laya L a k e M u d fla t C o n d itio n s - C lim a tic & S tru c tu ra l T o p o g ra p h ic (P recessio n al C ycle) C o n d itio n s C e n tu ry L e v e l C ycles W ilk in s P eak S h o rt C y c lic a l? ) P re c ip ita tio n E v e n t (<1 k.y.) Table 25. Common litho-organic signatures in the Tipton and Wilkins Peak: depositional paleoclimatic significance, applications and interpretation for orbital mechanism and imprint. 253 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rich cycle base required increased lake inflow for the eutrophic-hypertrophic algal productivity. Highstands embedded in the basal oil shales document maximum precipitation-evaporation, lake expansion and organic accumulation that equates to maximum precessional moisture. In contrast to paleoclimatic models that suggest Green River lake levels were primarily controlled by evaporation (Morrill et al., 2001), these litho organic signatures document increased precipitation. If summer perihelion lake levels were reduced by higher rates of evaporation, then these organic-rich signatures suggest maximum precipitation during the winter perihelion. In individual Wilkins Peak eccentricity bundles, the increased litho- organic heterogeneity in “dry” compared to “wet” precessional cycles suggests greater seasonality. The homogenous “wet cycle,” which usually occurs near the middle of the eccentricity bundle, is a product of reduced evaporation and relatively uniform annual precipitation that equates to minimal seasonality. Conversely, the greater heterogeneity in “dry cycles” that reflects increased depositional variation equates to greater seasonality. Evidence of maximum seasonality associated with thick eccentricity boundaries include: ( 1) detrital silts and sands that are the product of sporadic, short but intense episodes of precipitation; and (2 ) desiccation and aeolian features, and organic-lean, calcareous mudstone that are products of increased evaporation. Litho-organic signatures document that Green River cyclicity represents orbital derived changes in moisture, rather than a quasi-repetitious tectonic 254 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. modification of drainage, as proposed by Pietras et al. (2003). The consistent, well- defined cyclical and temporal pattern in organic-content in both members documents a continuous orbital-driven availability of net moisture (Figure 8 8 ). The reoccurring “wet-intermediate-dry” eccentricity bundling further confirms the role of orbital- derived variations in net moisture. Tipton and Wilkins Peak litho-organic signatures suggest these cyclical patterns are products of sensitive lacustrine environments. Although sharp boundaries between the rainy and dry precessional phases record differences in moisture availability, they do not necessarily indicate dramatic changes in precipitation-evaporation. The geochemical similarity between half-cycle enrichments, the transition at the top of some cycles, and the organic-rich cycle base suggests that a small-to-moderate increase in net moisture quickly transformed the lake into a eutrophic setting. Century-level cycles also document the rapid transformation of the mudflat into a small playa lake. Extensive expansion of the playa lakes during the rainy phase was limited to short-lived highstands; this suggests that large scale changes in moisture availability throughout the cycle were of limited duration. In part, these signatures are consistent with paleoclimatic modeling that suggests the climatic swings across the Wilkins Peak precessional interval were minor (Lawrence et al., 2003). Geochemical parameters further complement oil-yields as a proxy for water depth, since they provide additional detail about variations in lake conditions. Although oil-yield defines the two-stage Tipton lake history, isotopic, maceral and 255 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. molecular variations further define subtle changes in lake conditions, which further elucidates variations in climatic conditions throughout the precessional interval. In the Wilkins Peak oil shale-mudstone doublets, the Rock-Eval HI, 8 13C, and maceral compositions in combination with sedimentary features further identify small variations in water depth and playa-mudflat conditions. These litho-organic signatures record changes in dynamic lake conditions that can be used to identify and reconstruct orbital-driven climatic manifestations and their imprint. The evaluation of the temporal association of litho-organic signatures with lithofacies boundaries help distinguish cyclical and non-cyclical imprints. These signatures help determine if a paleoclimatic reconstruction fits the observed data throughout a cyclical interval, which helps decipher how orbital variations were transferred into the sedimentary record. Orbital Cyclicity and its Transfer into the Sedimentary Record Deposition of organic-rich Tipton and Wilkins Peak sediments switched on at a relatively constant rate over one part o f the precession, then diminished over the remaining interval as the orbital-controlled insolation reached a specific threshold. The two-stage precessional signature consisting of differences in organic content and properties primarily represents a moisture-driven productivity cycle, but also more subtle precursor and preservation cycles (Figure 8 8 ). In the Wilkins Peak, redox- desiccation and detrital-sedimentation cycles also parallel the productivity cycle. Eccentricity-driven climatic effects modulated this imprint by magnifying or Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. suppressing the precessional signal. In order to define the origin of this cyclical imprint, it must be determined how the precessional-eccentricity signal controlled net moisture availability and lacustrine conditions that affected organic accumulation in the context of the Green River climatic and topographic setting. Eocene Greenhouse Conditions-Organic Rich Cyclical Deposition The unique existence of paleolake Gosiute during greenhouse conditions in a modified North American topographic setting was conducive for the orbital-driven deposition of organic-rich sediments. The greenhouse world reduced latitudinal temperature gradients and annual temperature variations, which suppressed the detrimental effects of seasonal climatic extremes associated with the mid-latitude continental interior. The large paleolake Gosiute provided moderate temperatures and frost-free conditions that further suppressed seasonality. Global greenhouse conditions likely magnified the amount and seasonal patterns of precipitation. In all likelihood, a greenhouse-derived poleward shift in climatic belts, including the Hadley-Ferrel circulation cells, suppressed zonal circulation patterns and allowed the transport of more moisture into the mid-latitudes. The reduced latitudinal temperature gradients and increased atmospheric CO2 likely enhanced the intensity o f storm tracks (Prell and Kutzbach, 1992). More important, paleoclimatic modeling results of the Green River region that includes orbital parameters indicate that maximum precipitation occurred in spring and summer, regardless of a northern hemisphere summer or winter perihelion position (Lawrence et al., 2003). The 257 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. similarity in the amount and seasonal patterns of precipitation was due to the consistent dominance of onshore, monsoonal-like winds that flowed in from the Gulf of Mexico. In comparison to the present, a greater number and intensity of southerly storms were able to move into the continental interior due to the larger Mississippi embayment (Sewell et al., 2000). Conversely, other studies indicate that Pacific- derived winter storms delivered precipitation to Western North America (Spaulding and Graumlich, 1986). In contrast to low-latitude monsoons, Gulf of Mexico storm tracts transported moisture into the Laramide region, where they collided with cool Artic-derived northerlies to form convective precipitation. Eocene coals in the Hanna and Powder River Basins of Wyoming further attest to this regionally transported moisture. In comparison to the present, a potentially higher elevation ( - 1 0 ,0 0 0 ft) in the Cordillera and mountains surrounding paleolake Gosiute (Morrill et al., 2001) may have facilitated adiabatic cooling of the moist air and promoted greater rainfall. Seasonal changes in wind direction, and heating and cooling over mountain ranges produce strong density contrasts in the atmosphere that are commonly accompanied by periods of heavy rainfall (Norris et al., 2000). A larger Laramide drainage basin may have contributed to increased spring and early summer snowmelt, which helped maintain lake levels. Snowmelt is supported by light 51 8 0 signatures in the Wilkins Peak (Norris et al., 1996). To date, incorporation of detailed Rocky Mountain topography and airflow has not yet been realistically simulated in paleoclimatic models. 258 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Greenhouse-elevated pCC> 2 and vegetation promoted low-level clouds that further reduced the evaporative potential already associated with the convective- derived cloud cover (Sloan and Rea, 1995). The saline nature of the Rife and Wilkins Peak lakes may have further reduced summer evaporation, which contributed to lake level preservation (Morrill et al., 2001). In contrast to lower evaporation during the rainy phase, adiabatic warming of less moist air that descended into the lake basin during the dry precessional phase may have increased the rate of evaporation, similar to processes described by Manspeizer (1985). Imprint Mechanisms-Precessional Cycles Although litho-organic signatures document the importance of moisture transport in the origin of the Tipton and Wilkins Peak precessional patterns, it is difficult to identify which precessional phase provided the elevated lake levels. Summer perihelion-derived monsoons that elevated lakes in low-latitudes (< 20°) are difficult to apply to paleolake Gosiute because of zonal barriers in transporting large amounts of tropical-derived moisture into the mid-latitudes. Increased evaporation associated with the summer perihelion may have reduced lake levels. The summer perihelion model is viable only if the greenhouse world sufficiently broadened the latitudinal migration of the Hadley circulation cells that were associated with the para-tropical dry belt. Such broadening would have potentially allowed adequate monsoonal moisture from low-latitudes to travel northward along an Atlantic- Caribbean corridor and into the Gulf of Mexico. 259 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A more likely scenario for elevated levels of paleolake Gosiute was the combined effects of a winter perihelion climatic setting and precipitation associated with the Gulf of Mexico storm tracts. The winter perihelion facilitated Pacific- derived winter precipitation, provided snowpack, and reduced seasonality and evaporation. Paleoclimatic modeling indicates less spring and summer evaporation in the Green River region during the aphelion summer precession due to reduced insolation and slightly lower temperatures (Sewall et al., 2000). Although the simulated rainfall associated with the winter precession only increased by about 1 0%, the combined effects of precipitation and evaporation, which change in opposite directions, led to as much as a 40% increase in net moisture. The greater winter moisture and runoff, and less evaporative conditions provided an increased infiltration rate of the soil and a higher runoff coefficient (runoff/precipitation) in the drainage basin that led to an increased lake inflow. The cooler summer aphelion increased latitudinal temperature gradients that provided more convective Laramide precipitation. Thus, the winter-early spring runoff combined with spring-summer convective rainfall provided the elevated lakes. It is essential to place the summer versus winter precession models of net moisture availability into the context of circulation patterns that operated in the Eocene greenhouse and topographic settings. These lithologic- and geochemical-defined mechanisms of orbital imprint will be tested and modified by ongoing paleoclimate and paleogeographic studies, which simulate increasingly sophisticated models for a specific region. 260 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The consistent two-stage precessional pattern with an organic-rich base confirms a strong link between organic productivity and a precession-derived increase in net moisture. Elevated lake levels enhanced the photic zone ecology, especially in the Wilkins Peak. Basinal flushing associated with spring-early summer snowmelt and pulses of convective precipitation, provided a continual replenishment of nutrients for eutrophic-hypertrophic bloom events. Upper water column mixing associated with convective circulation and winter storms helped to recycle nutrients from the middle and lower photic zone and extend periods of high organic productivity, which is similar to modem lakes (Bradbury et al., 1993). Conversely, during the summer perihelion, a small reduction in precipitation, as well as increased evaporation resulted in smaller less productive lakes in this sensitive depositional setting. Variations in geochemical signatures throughout the precessional cycle can be used to link orbital-driven climatic and lake mechanisms to redox and preservation. Precessional-derived lake expansion provided an elevated and stable perennial thermocline in the hydrologically-open Scheggs lake. Reduced water column mixing and degradation was an important contributor to the organic-rich Scheggs cycle base. Salinity stratification in the Rife and Wilkins Peak lakes was enhanced during the rainy phase by freshening of the surface layer. The elevated chemocline in the Rife lake, which was derived from an increased lake level and organic productivity, limited degradation of the biomass in the upper water column. The development of a meromictic Wilkins Peak playa lake highstand allowed the 261 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rapid export of the biomass from the highly productive photic zone to the underlying halocline. Increased runoff from the distal alkaline mudflats surrounding the playa lake introduced toxins that suppressed organic degradation from the higher levels of the food chain. Although less inflow occurred during the dry precessional phase, reduced sediment trapping at the margins of the contracted lakes contributed to greater organic dilution. This further accelerated the decline in organic accumulation that resulted from reduced productivity and preservation. Increased lake temperatures and summer evaporation during the dry precessional phase probably enhanced carbonate precipitation and organic dilution. Imprint Mechanisms - Eccentricity Cycles The eccentricity is a major force of climate change in mid-latitude regions in which deviation from existing seasonality can occur (Fischer et al., 1991). This climatic imprint is pronounced in the Wilkins Peak, since “wet, intermediate, and dry” precessional cycles define an approximate 5:1 bundling due to the modulation of the precession by the eccentricity (Berger, 1988; Fischer, 1991). In the Tipton, higher sonic velocities and a lower gamma ray response at the eccentricity boundaries correspond to a reduced organic content in oil shales and the occasional occurrence of marlstone and mudstone. These boundaries likely reflect the maximum eccentricity that reduced lake level, lowered organic productivity, and 262 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. increased water column mixing and degradation. In addition, episodic storms appear to have contributed to sediment dilution, consistent with lower lake levels. During Wilkins Peak deposition, periods of minimum eccentricity and reduced seasonality provided greater amounts of winter rain and lower summer evaporation. Extended periods of moist conditions sustained the temporal existence of the playa lakes, which resulted in the formation of relatively thick oil shales and “wet” precessional cycles. The thick, low-yield oil shales associated with the long eccentricity appear to represent extended moist conditions associated with minimal eccentricity instead of short periods of maximum precipitation that are likely related to greater seasonality. During mudflat deposition that was associated with minimal eccentricity and uniform seasonality, the greater potential for winter precipitation and a relative reduction in summer evaporation provided stable, almost perennial, shallow mudflat lakes. This setting is consistent with the homogenous “wet mudflat” microfacies. The deposition of thick trona in individual precessional cycles may have been associated with periods of minimum eccentricity when the temporal and spatially expanded playa lake underwent greater contraction and evaporation. As maximum eccentricity was approached, deposition of thin, sediment- diluted oil shales and a “dry mudflat” microfacies occurred. Reduced winter precipitation and increased summer evaporation limited the temporal extent and size of the playa lakes, which limited the duration of oil shale deposition. Sporadic, near monsoon-like runoff that was associated with the perihelial position caused detrital dilution of the accumulating oil shale. Thin, high-yield oils shales, however, may 263 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. indicate intense but short-lived precipitation associated with an increased eccentricity. The desiccated signature in the “dry mudflat” could be related to the near zero net moisture in summer months (Lawrence et al., 2003). A signature of aridity and lithologic variability corresponds with periods of maximum seasonality and eccentricity related to reduced aphelia precipitation and increased perihelial evaporation. The thick eccentricity boundary, similar to a “dry mudflat” microfacies is a product of the highly evaporative setting in association with a perihelial position during maximum eccentricity. Sporadic perihelial-derived precipitation initiated detrital runoff into the central mudflat. Reduced precipitation during the cool aphelial winter facilitated subaerial exposure and oxidation. Aeolian transport of detrital sediments across the barren mudflat further contributed to the rapid sedimentation. Rapid marlstone deposition sometimes occurred from the occasional summer perihelial precipitation combined with the high degree of evaporation. Alternatively, maximum eccentricity could have provided increased precipitation and elevated lake levels similar to those described in the Newark Basin (Olsen and Kent, 1996). However, this scenario would have required an efficient monsoonal transport of moisture into the Green River region with an increased cloud cover for lowered evaporation. Lacustrine lowstands in underfilled lake systems usually consist of chemical and biogenic sediments. However, the occurrence of sporadic, thin tongues of detrital sediment in the Wilkins Peak can be explained by periods of maximum eccentricity and episodic runoff. Episodic storms transported sediments into the 264 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. basin center that were desiccated by the evaporative conditions. This process provides a “dry monsoonal” record. These “dry” cycle regressive phases that extend toward the basin center are similar to detrital cycles in the Newark Group (Van Houten, 1962, 1964, and 1969). Silts and detrital intervals that represent 400 k.y. boundaries and the proposed 700 k.y. superbundle by Roehler (1993) were also products of maximum eccentricity. Obliquity Cycle The time-series analysis defines a weak obliquity signal throughout the Tipton and Wilkins Peak based on an increased oil-yield. Obliquity-driven changes in insolation influenced the latitudinal migration of the wet versus dry belts, and magnified the effects of the rainy precessional phase (Berger, 1978a and b ). The resulting increase in net moisture, runoff, lake level and stratification enhanced organic matter accumulation. The relatively weak obliquity signal in the Green River region may have been overprinted by the more dominant low- to mid-latitude climatic effects that were associated with the precession and eccentricity. Half-Precessional Cycles The consistent occurrence of half-cycles throughout the Tipton and Wilkins Peak suggests a Milankovitch related forcing mechanism. This approximate 10 k.y. cyclicity has been observed in deep sea sediments and might be related to a non- 265 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. linear response of the climate system to astronomical forcing (Pestiaux et al., 1988; Park et a l, 1993). A signature of this mechanism is the appearance of significant spectral power at twice the precessional frequency. Half-cycles appear to have originated from the doubling and rectification of the precession. This was in response to the biannual migration of the zone of maximum heating across the equator, which amplified the temperature and precipitation response, and forced climatic changes in the inter-tropical zone. This response has been demonstrated to be out-of-phase by a half-precession cycle (Berger and Loutre, 1997). Alternatively, a statistically significant phase coupling indicates that the variability in precessional solar insolation is transferred to a 10-12 k.y. band (Hagelberg et al., 1994: McIntyre et al., 1989). The occurrence of half-precessional cycles in equatorial regions suggests that their origin is connected to a precessional-driven monsoonal mechanism (Short et al., 1991). The identification of these cycles in mid- and high-latitudes (Park et al., 1993; Hagelberg et al., 1994) may indicate moisture transport from low-latitudes. The relatively common occurrence of Tipton and Wilkins Peak half-cycles may be a result of the equitable greenhouse climate that enhanced the transport of moisture from the tropics, representing a distal monsoonal effect. Although zonal effects probably restricted tropical-derived moisture from reaching paleolake Gosiute, the high potential heat capacity of the Caribbean ocean could have allowed some moisture from the precessional extremes to reach the continental interior. 266 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Alternatively, the association of half-cycles with “wet and intermediate” precessional cycles in the Wilkins Peak suggests an origin related to a reduced eccentricity. If the winter precessional perihelion provided maximum net moisture, potentially a summer perihelion could have provided a subordinate pulse of precipitation that was only recorded during minimal eccentricity. In addition to reduced evaporation, minimal eccentricity provided increased winter rain, which elevated lake levels. A small increase in precipitation and reduced evaporation may have been sufficient for the subtle half-precessional organic enrichment. Applications to the Origin of Organic-Rich Green River Sediments Many questions remain about the origin of the unique, organic-rich Green River sediments, including the role of tectonic versus climatic mechanisms and what relationship they had to lacustrine processes. Tectonism has been recognized to have controlled the overall basin configuration and sedimentary thickness (Bradley, 1964; Bradley and Eugster, 1969). Paleoclimate studies by MacGinitie (1969) and Leopold and MacGinitie (1972) concluded that the deposition of the Green River Formation was accompanied by climatic changes, which has been used to explain the different lake facies. Conversely, Bohacs et al., (2000) proposed that the Green River lake systems are primarily a product o f tectonic-controlled sediment and water supply. Bradley (1929a) suggested that cyclical variation in Green River oil shales originated from solar and Milankovitch cyclicity. Recent investigations using lithology, log properties, stratigraphic correlations and time-series analysis provide well- 267 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. documented evidence of Milankovitch cyclicity in several of the basins containing the Green River Formation (Bennett, 1989; Fisher and Roberts, 1991; Roehler, 1993; Machlus et al., 2001; Cole, 2002). Results form this study illustrate that a well- defined, continuous, but progressively changing orbital imprint occurs with the evolving lake facies. An understanding o f the relationship between orbital cyclicity and lacustrine deposition complements the permanently stratified and playa lake models that have explained the properties of Green River oil shales (Bradley and Eugster, 1969; Eugster and Surdam, 1973). Lithological and geochemical characterization of Milankovitch cycles in the Tipton and Wilkins Peak demonstrate that orbital-driven climatic variations caused significant but repetitive changes in lacustrine conditions. The rainy and dry precessional phases created a two-stage cyclical variation in lake size, biomass productivity, water column ecology, stratification and preservation, and sedimentation. The eccentricity further modified the precession-controlled lithologies and amount and type of organic matter that accumulated. The rainy precessional phase was essential for the deposition of the organic- enriched cycle base including optimal organic accumulation events. Even in intervals of Green River oil shales that are attributed to tectonics (Surdam and Stanley, 1980) precession-eccentricity derived maximum net moisture enhanced organic accumulation. In the overfilled and balanced-fill, permanently stratified Tipton lakes, increased inflow combined with reduced evaporation triggered higher productivity and elevated stratification that protected the abundant organic flux from degradation. 268 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In the underfilled Wilkins Peak, the orbital-derived increase in precipitation- evaporation transformed the desiccation-dominated mudflat to a stable, productive, stratified playa lake, leading to optimal organic accumulation. Without the precessional-derived increase in precipitation-to-evaporation, only a small, shallow, oligotrophic lake dominated by water column mixing, degradation, and occasional desiccation would have existed. The hypothetical, non-cyclical sedimentary record would have consisted of an organic-lean to moderate calcareous mudstone, with only sporadic, thin, aerially limited oil shale. The deposition of small volumes of oil shale would have been dependent on episodic lake expansion derived from tectonic or non-cyclical climatic events. Throughout the Wilkins Peak rainy and dry precessional phases, the playa- mudflat lake underwent large aerial expansions and contractions that radically changed sedimentologic and biotic conditions. The pronounced lateral and vertical lithofacies successions were a product of orbital-driven changes combined with sensitive depositional thresholds. Lake salinity was controlled by precessional- derived inflow that contained solutes, and the subsequent evaporative concentration that led to the deposition of evaporites. During the dry precessional phase, large- scale carbonate mudflat deposition was predominant throughout the basin. Then at the start of the rainy phase, sediment that accumulated in drainage areas during the dry phase was mobilized and transported basinward as a result of increased runoff (Perlmutter and Matthews, 1989). 269 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Regardless of the tectonic versus climatic origin of the different Green River lake systems, the Milankovitch imprint explains the occurrence of end-member lithologies that consist o f organic-enriched oil shale and desiccated, detrital, and chemical-derived sediments. Furthermore, these orbital-driven depositional mechanisms reveal the dynamic nature of the existing deep stratified and playa lake models. Application of an orbital-driven climatic model can explain and predict much of the lithological and geochemical variation in these lake systems of diverse origins. Orbital-driven moisture availability significantly influenced the occurrence and properties of these organic-rich sediments. Additional work is required to understand how long period eccentricity cycles (>400 k.y.) may have influenced the occurrence of the different Green River lake systems. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 8 SUMMARY AND CONCLUSIONS (1) During deposition of the Green River Tipton and Wilkins Peak Members, paleolake Gosiute evolved from an overfilled, expanded, freshwater, perennial lake in a moist climatic setting to an underfilled, contracted, saline-hypersaline playa lake-mudflat associated with apparent arid conditions. Throughout this spectrum of lacustrine facies, a well-defined and continuous record of cyclicity is identified from a combination of lithology, log patterns, Fischer assay oil-yields, and geochemical patterns as represented in Blacks Fork-1 and nearby coreholes in the Green River Basin, Wyoming. Results from time-series and spectral analysis, and varve counts combined with eccentricity bundling define the full suite of Milankovitch cyclicity. In the Tipton, spectral analysis based on oil-yields defines the short-eccentricity and precession. In the Wilkins Peak, the short- and long-eccentricity and a somewhat noisy precession are documented from spectral analysis of oil-yield results. A weak obliquity and a sub-Milankovitch half-precessional cycle are also identified in both members. (2) In the lithologically uniform Tipton oil shales, oscillations in the sonic and gamma logs, and oil-yield and geochemical patterns define precessional cycles. Almost all Tipton cycles contain a 0.5-3.3 ft base with high oil-yields and reduced but variable yields in the remainder of the cycle. In Blacks Fork-1, about 21 Scheggs 271 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and Rife precessional cycles range from 4.2 to 12.4 ft, with a respective mean thickness of 6’ .8 and 8.6 ft. Sonic log peaks at the cycle base, which indicate higher travel time, correspond to increased oil-yields, and thus provide an indication of organic content and cyclicity. Based on a 120 pm varve thickness, respective mean depositional periods for Scheggs and Rife cycles of 17,350 and 21,750 years support the 21 k.y. precessional cyclicity. (3) Wilkins Peak precessional cycles consist of an oil shale-mudflat doublet or oil shale-trona-mudflat triplet that ranges from 5 to 35 ft thick, with a mean thickness of 13.2 ft. Five different lithologic successions in the paleogeographic lake center provide sensitive indicators of climatically controlled playa lake and mudflat depositional responses during individual precessional periods. Different oil-yield patterns define variations in the onset, intensity and duration of the rainy and dry precessional phases. Wilkins Peak precessional cycles display an alternating “wet, intermediate and dry” litho-organic character throughout many o f the short 100 k.y. eccentricity bundles. “Wet” precessional cycles generally have thicker oil shales and higher organic content in the mudflat facies compared to “dry” cycles. (4) Considerable variation in the thickness, lithology, and oil-yields of precessional cycles occurs throughout the Tipton and especially the Wilkins Peak. Much o f this variation can be attributed to: (1) the interaction between short- or long term cyclicity, including the precession index, (2) a combination of tectonic activity and regional paleoclimatic changes, and (3) episodic depositional distortions, which represent non-cyclical depositional imprints caused by short-term climatic events, volcanic ash, erosion, and event sedimentation, etc. Variations in the Wilkins Peak 272 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cyclicity are magnified because of the shallow lake system and different sedimentation rates in the trona-mudflat compared to the oil shale. (5) The primary geochemical pattern in Tipton precessional cycles consist of an organic-rich base with a reduced but variable organic content in the remainder of the overlying interval. The bulk chemical, maceral, isotopic, and molecular composition of the kerogen and bitumen generally parallels the two-stage cyclical pattern in organic content. In the cycle base, algal-dominated precursor input is defined from Type I, aliphatic-rich kerogen that consists of lamalginite. The saturate fraction of solvent extracts contains high sterane/hopane ratios. Kerogens depleted in 1 3 C result from high photic zone productivity and an elevated chemocline that rises into the lower photic zone, where recycled 1 2 C-enriched CO2 was available for photosynthesis. Above the cycle base, a Type I/II kerogen with a slightly reduced aliphatic content consists of a greater proportion of bituminite. This corresponds to extracts that have lower sterane/hopane ratios and a methanogenic bacterial signature. (6) Three main geochemical patterns are identified in Wilkins Peak precessional cycles. First, sharp changes in organic content and properties occur at the oil shale-mudflat boundary. Compared to the oil shale, the mudflat contains small amounts of Type II to III/IV kerogen that are the products of reduced productivity and preservation. A larger proportion of benthic precursors and terrestrial input occurs in the mudflat facies. In most cycles, a 1 3 C-enriched mudflat kerogen of up to 8.9%o occurs directly above the oil shale. This 1 3 C enrichment results from: (1) a greater proportion of terrestrial input in the kerogen, (2) increased organic 273 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. degradation, and (3) a reduced CO2 concentration in the mudflat lake, which lowered the isotopic fractionation factor and may have altered the carbon-assimilatory pathway. Second, distinct patterns in the thickness, organic content, and composition of individual oil shales are the result of differences in available net moisture. Thin, organic-rich zones in the oil shale represent optimal organic accumulation events that equate to lacustrine highstands. Cycles with 3 to 6 ft of oil shale record an extended rainy phase that usually corresponds to “wet” precessional cycles. The oil shale facies sometimes consists of organic-rich mudstone rather than actual oil shale that resulted from reduced net moisture, lake size, and organic productivity, and sedimentary dilution of the accumulating organic matter. Third, the mudflat consists of “dry and wet” microfacies, which are products of the precession index, and changes in the regional paleoclimate and structural- topographic setting. The “dry mudflat” consists of brecciated-to-massive, silty mudstones, and contains negligible-to-small quantities of oxidized Type III-IV kerogen. This microfacies was deposited in short-lived, seasonally flooded mudflats dominated by subaerial conditions. Conversely, the “wet mudflat” contains small-to- moderate quantities of Type II-III kerogen in massive-to-laminated calcareous mudstones. This microfacies is a product of increased organic productivity and preservation, and corresponds to a setting dominated by shallow subaqueous conditions. (7) In the Tipton and Wilkins Peak, a two-stage lake corresponding to the rainy and dry precessional phases dictated lacustrine conditions. During the rainy 274 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. phase, increased accumulation of organic matter occurred. Increased inflow, nutrient input and recycling, and lake size promoted eutrophic-to-hypertrophic productivity. The expanded lakes developed or strengthened stratification, which enhanced preservation. Sediments trapped at the basin margins reduced organic dilution, especially in the Wilkins Peak. At the start of the dry phase, a reduction in net moisture and nutrients led to lower organic productivity and a shift to a greater proportion of bacterial input. Reduced stratification and water column anoxicity in the Tipton lakes, and the occurrence of shallow mudflat lakes in the Wilkins Peak led to an increased oxidative degradation of the biomass. This cyclical two-stage lake model compliments existing depositional studies by documenting how orbital-driven climatic variations: (1) drive lake conditions that produce changes in lacustrine processes, (2) imprint the sedimentary record through temporal, dynamic lacustrine conditions, and (3) explain the occurrence of different Green River facies and microfacies. (8) Throughout the Tipton and Wilkins Peak, the precessional-eccentricity signal dictated lacustrine conditions that continuously imprinted sediments with a consistent orbital signature. Yet, the evolving Green River lake systems simultaneously modified, magnified, or suppressed lacustrine processes, which resulted in different lithologic and geochemical expressions of cyclicity. The evolving pattern of cyclicity resulted from the influence of changing lacustrine conditions on productivity, precursors, stratification, redox-oxidation, desiccation and sedimentation. Shallowing lacustrine conditions between the Scheggs and middle Wilkins Peak resulted in an increasing lithological and geochemical contrast 275 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. between the rainy and dry precessional phases. The geochemical expression of precessional cyclicity in the balanced-fill Rife lake interval is more pronounced than cycles associated with the overfilled Scheggs because of increased stratification, and greater fluctuation in lake size and water column ecology throughout the precessional interval. Although an evolving pattern of cyclicity occurs in the Tipton- Wilkins Peak, parallel trends in the organic content throughout precessional cycles define a similar temporal pattern of relative net moisture availability. (9) The sensitive response of the Tipton and Wilkins Peak lakes to environmental change provides lithologic and geochemical signatures that help reconstruct paleoclimatic and depositional conditions. These litho-organic signatures are a combination of lithologic and geochemical patterns, excursions and cyclical trends that record variations in lake conditions. These signatures help unravel changes in net moisture, identify cyclical versus non-cyclical imprints, and decipher how orbital variations were transferred into the sedimentary record. (10) Organic productivity and preservation are linked to the precession- derived increase in net moisture. Increased precipitation and reduced evaporation, which appears to have occurred during the winter perihelion, elevated Green River lake levels. Regional storm tracks from the Gulf of Mexico provided spring-summer convective precipitation regardless of a summer or winter precessional perihelion. However, during the winter perihelion, increasing moisture was available from Pacific derived storms that provided additional winter rainfall and spring snowmelt. This not only elevated lake levels but increased the runoff coefficient for the spring- summer precipitation. The winter perihelion also provided a reduced evaporation rate 276 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that enhanced runoff and preserved lake levels. A continual replenishment of nutrients and elevated lake levels enhanced the photic zone ecology that provided eutrophic-to-hypertrophic algal productivity. In the hydrologically-open Scheggs lake, the expanded lake provided an elevated and stable thermocline, which reduced water column mixing and degradation. Increased runoff enhanced salinity stratification in the Rife and Wilkins Peak lakes. Higher productivity and oxidative degradation in the Rife lake elevated the chemocline. With elevated stratification, the rapid export of biomass from the photic zone to the underlying anaerobic water column enhanced preservation. The expanded lakes reduced dilution of the accumulating organic matter. (11) Periods of minimum eccentricity and seasonality appear to have resulted in less evaporation and greater amounts of winter rain. This helped extend the temporal duration of these paleolakes and the accumulation o f organic matter associated with the rainy precessional phase. In contrast, times of maximum eccentricity represented greater seasonality, increased evaporation, and reduced winter rains. The reduced duration, extent, and stratification of these lakes limited the accumulation of organic matter. The “wet and dry mudflats” appear to be important products of minimum and maximum eccentricity, respectively. (12) Sub-Milankovitch half-precessional cycles are identified as organic- enriched zones near the middle of some Tipton and Wilkins Peak precessional cycles. Most Rife precessional cycles display a half-precessional organic- enrichment, where-as only some Sheggs cycles display a half-cycle. About one- fourth of Wilkins Peak precessional cycles display some type of organic enrichment 277 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. near the top of the oil shale or in the lower part o f the trona-mudflat. These half- precessional cycles are most common near the middle of Wilkins Peak eccentricity bundles. The mean depositional period for Tipton and Wilkins Peak half-cycles based on varve thickness and sedimentation rate is about 10,700 and 9,900 years, respectively. These half-cycles may originate from an orbital feedback mechanism that infers moisture transport from low-latitude regions. Alternatively, the occurrence of half-cycles in “wet and intermediate” Wilkins Peak precessional cycles suggests an origin related to a reduced eccentricity. First, increased winter rainfall associated with the minimal eccentricity contributed to elevated lake levels. Second, as the winter precessional perihelion provided maximum net moisture, the summer perihelion could have provided a subordinate pulse of precipitation, which was only recorded as higher lake levels during periods of reduced eccentricity and evaporation. (13) Lithological and geochemical characterization of Tipton and Wilkins Peak cycles demonstrate that orbital-driven climatic variations had repetitive and predicable changes in the limnology of different Green River lake systems. The precessional rainy phase was an essential element for deposition of organic-rich oil shales that occur in the cycle base. In the Wilkins Peak, without the orbital-enhanced runoff, only a small, shallow, well-mixed, oligotrophic lake would have existed. The result would have been deposition of organic lean-to-moderate sediments. Oil shale deposition would have been sporadic, thin, and aerially limited. Milankovitch mechanisms were also essential for the deposition of desiccated, detrital and chemical-derived sediments. When combined with non-cyclical processes, these 278 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. orbital-driven climatic variations can explain much of the lithologic and geochemical variability in Green River sediments. 279 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCES American Society for Testing and Materials, 1980, Standard method of test for oil from oil shale: Annual Book of ASTM Standards, Part 25, Designation D 3904-80, p. 513-515. Anders, D. E., and Robinson, W. E., 1973, Geochemical aspects of the saturated hydrocarbon constituents of Green River oil shale - Colorado No. 1 core: U.S. Bureau of Mines, Report of Investigations 7737, 23 p. Anderson, R. Y., 1961, Solar-terrestrial climatic patterns in varved sediments: Annals of the New York Academy of Sciences, v. 95, p. 424-435. Anderson, R. Y., and Kirkland, D. W., 1960, Origin of varves, and cycles of Jurassic Todilto Formation, New Mexico: American Association of Petroleum Geologists Bulletin, v. 44, p. 27-52. Anderson, R. Y., 1992, Possible connection between surface winds, solar activity and the Earth’s magnetic field: Nature, v. 358, p. 51-53. Anonymous, 1980, A bibliography of publications dealing with oil shale and shale oil from U. S. Bureau of Mines, 1917-1974, the ERDA Laramie Energy Research Center, 1975-1976, and the DOE Laramie Energy Research Center, 1977-1979: Springfield, VA, National Technological Information Service, U. S. Department of Commerce, 58 p. April, R. H., 1981, Trioctahedral smectite and interstratified chlorite/smectite in Jurassic strata of the Connecticut Valley: Clays and Clay Minerals, v. 29, p. 31-39. Aquino Neto, F. R., Trendel, J. M., Restle, A., Connan, J., and Albrecht, P. 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J., 1996, Stable isotope geochemistry of coals, humic kerogen and related gases: International Journal of Coal Geology, v. 32, p. 191-215. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Wilf, P., 2000, Late Paleocene-early Eocene climate changes in Southwestern Wyoming: Paleobotanical analysis: Geological Society of America Bulletin, v. 112, p. 292-307. Wilf, P., Wing, S. L., Greenwood, D. R., and Greenwood, C. L., 1998, Using fossil leaves as paleoprecipitation indicators: an Eocene example: Geology, v. 26, p. 203-206. Willis, K. J., Kleckowski, A., Briggs, K. M., and Gilligan, C. A., 1999, The role of sub-Milankovitch climatic forcing in the initiation of the northern hemisphere glaciation: Science, v. 285, p. 568-571. Wing, S. L., Bao, H., and Koch, P. L., 1998, An early Eocene cool period? Evidence for continental cooling during warmest part of the Cenozoic, in Huber, et al., eds. 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Appendix 1 Lithologic Description of Core from Black Forks-1, Tipton Member Select Precessional Cycles - Scheggs and Rife Beds Rife Cycle 1 (1582.1-1587.5’) Tipton Member Blacks Fork-1 1582.1-1582.4 Tuff, Light to medium gray, gray buff near top 1582.4-1583.0 Oil Shale, dark brown 1583.0-1583.3 Oil Shale, medium brown, silty oil shale 1583.3-1584.15 Oil Shale, black, massive-laminated 1584.15 -1584.3 Marlstone, buff (or ash?) 1584.3-1584.8 Oil Shale, medium brown 1584.8- 1585.1 Tuff, Medium to light gray and slightly brownish gray 1585.1- 1586.5 Oil Shale, black, well laminated 1586.5-1587.5 Oil Shale, black to dark gray, organic-rich. Lost core 1586.5-1587.7? R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Rife Cycle 3 (1561.7 -1572.0’) Tipton Member, Black Forks-1 1561.7-1562.5 Oil Shale, medium brown to tan. Generally laminated. Contains lighter bands up to 1” in several places; also contains dark brown bands in places. 1562.4-1563.8 Marlstone, light brownish gray with faint lamina. 1563.8-1566.7 Marlstone, light to medium brown, uniform grades to oil shale below. 1566.7-1567.7 Oil Shale, medium olive gray grades to darker more organic-rich with depth. 1567.7-1568.7 Oil Shale, dark brown gray to black. Decreasing silt content with depth? 1568.7-1573.2 Oil Shale, dark medium brownish gray to black. 1570.8-1571.4 Oil Shale, dark olive gray 1572.4-1572.6 Oil Shale, medium olive gray 1572.6-1573.8 Dolomitic Band?? 1573.2-1572.0 Oil Shale, medium-light brownish gray. Sharp contact with above. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Rife Cycle 5 (1548.7-1556.6’) Tipton Member Blacks Fork-1 1548.7-1550.0 Oil Shale Medium to dark grayish brown 1550.0-1551.0 Oil Shale Dark and rare medium brownish gray to some black 1551.0-1552.0 Oil Shale Dark brownish gray to medium grayish brown 1552.0-1553.5 Oil Shale Dark to medium brownish to slightly olive gray 1553.5-1555.0 Oil Shale Dark and some medium brownish gray to some black 1555.0-1555.45 Tuff Medium to rare light grayish brown, silty to fine sandy textured 1555.45-1556.6 Oil Shale Dark and rare medium brownish gray to black Rife Cycle 6 (1541.1-1548.7’) Tipton Member Blacks Fork-1 1541.1-1541.9 Oil Shale, medium-dark brownish gray. 1541.9-1544.2 Oil Shale, medium-dark brown to black, laminated. 1542.0-1542.3 Black 1542.3-1542.9 Dark Brown 1542.9-1543.8 Black 1543.8-1544.2 Dark Brown 1544.2-1547.6 Oil Shale, Dark brownish gray to Black, uniform, well laminated to massive but predominantly laminated. Grades to black color with depth? 1547.6-1548.7 Oil Shale Dark green to dark brown to black, very silty. Sharp contact with overlying interval (1544.2-1547.6’). 307 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Rife Cycle 7 (1531.0-1541.0’) Tipton Member Blacks Fork-1 1531.0-1532.0 Oil Shale dark to medium brownish gray and some olive gray 1532.0-1534.0 Oil Shale Dark to medium brownish gray 1534.0-1535.0 Oil Shale Dark brownish gray 1535.0-1538.0 Oil Shale Dark to medium brownish gray 1538.0- 1539.0 Oil Shale Dark to rare medium browinish gray 1539.0-1541.1 Oil Shale Medium to dark brownish gray Scheggs Cycle 3 (1650.9-1656.5’) Tipton Member Blacks Fork-1 1650.9-1651.5 Mudstone, medium gray silty similar to 1646.0? Grades to oil shale below. 1651.5-1654.3 Oil Shale, dark brown to black. Subtle gradation to medium brownish gray at 1653.5. 1653.5-1654.3 Medium brownish gray 1654.3-1654.55 Oil Shale 1654.55-1656.5 Oil Shale? Medium brownish gray, mudstone organic-rich? Silty in parts? R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Scheggs Cycle 4 (1645.6-1650.9’) Tipton Member Blacks Fork-1 1645.6-1646.6 Mudstone, medium gray to brown, organic-poor, silty in parts. Grades to oil shale below. 1646.6-1647.3 Oil Shale, medium to dark gray to brown. Displays lighter color than below. 1647.3-1650.9 Oil Shale, dark brown to black, laminated, uniform subtle variations. Contains some light intervals up to 0.1? Dark gray brown at several locations: 1650.2 and 1649.3? Scheggs Cycle 7 (1628.2-1633.5’) Tipton Member Blacks Fork-1 1628.2-1630.2 Oil Shale, medium grayish brown and medium to dark brownish gray. Faint to fairly distinct laminae. 1630.2-1632.2 Oil Shale, dark to medium brownish gray, some light brownish gray in lower part. Faintly laminated; distinctly laminated in light zones at 1631.2-1631.4 and 1631.8-1631.9. Regular to irregular thick to medium parting 1630.5-1631.5 Grayish brown stringer 1632.2-1633.5 Oil Shale, buff and tan to dark brownish gray and some black dolomitic. Distinct to faint irregular to regular laminae and rare thin bands. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Appendix 2 Lithologic Descriptions of Core from Blacks Fork-1, Wilkins Peak Member Precessional Cycles 1,2,3,4,5,20,21,22,23,24 Cycle 1 (1486.6-1502.2’) Wilkins Peak Member, Blacks Fork-1 1486.6-1497.2 Mudstone, medium - light gray, slightly olive. Mudstone with thin trona at ~ 1497.0? @ 1489.6 sharp break from olive gray-green mudstone to gray mudstone Faint lamina from 1487.0-1488.0 Lt-Md gray pebble conglomerate near 1489’ Subtle decrease in organic content with depth 1497.2-1500.0 Oil Shale, medium-dark olive gray to brownish gray. Massive oil shale around 1498’, some lamina near 1499 1500.0-1500.6 Nahcolite, contains thin oil shale 1500.6-1501.5 Oil Shale, medium to dark olive gray 1501.5-1502.2 Oil Shale, lean oil shale grades to relatively more of a mudstone R eproduced with perm ission of the copyright owner. Further reproduction prohibited without perm ission. Cycle 2 (1468.6-1486.6’) Wilkins Peak Member, Blacks Fork-1 1468.6-1471.0 Mudstone, marly. Organic-rich mudstone in upper part. Mudstone, greenish gray 1471.0-1476.5 Mudstone, medium olive gray. Faint streaked bedding, some discontinuous to regular lamina. Some carbonate lamina? And carbonate layers? 1476.5-1478.2 Mudstone, medium-dark olive gray, some lamina. 1478.2-1484.9 Mudstone, medium olive gray. Grades to lean oil shale. Uniform appearance. Below 1480.5 appearance of lean oil shale, olive gray with increasing organic matter and lamina in spots, ie. 1484.1-1484.5 and 1484.9-1485.6’ 1484.9-1485.6 Oil shale, medium dark olive gray. Variable laminations and density 1485.6-1486.6 Oil shale-mudstone, medium olive gray. Sharp break to overlying oil shale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 3 (1458.7-1468.6’) Wilkins Peak Member, Blacks Fork-1 1458.7-1464.8 Mudstone, medium-light olive gray. Lamina generally occurs but variation in density of lamina. Most of the mudstone is laminated. Contains some carbonate layers. Occasional organic barren light gray mudstone band(s) up to 1 4 ” in several places Carbonate layers 1460.5-1460.7 up to 0.1’ Tuff 1462.2-1462.4 Laminated mudstone near 1463’ Thin sparse carbonate layers at 1464.5 1464.8-1465.6 Mudstone, olive gray, marly. Mudstone displays laminations. Grades to lean oil shale below. Contains very thin carbonate lamina at 1464.8-1464.9’ also shortite? 1465.6-1467.7 Oil Shale, black to dark brown gray. Primarily black massive texture with minor lamina. 1467.7-1468.6 Oil Shale, medium-dark olive gray. Grades to richer oil shale above. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 4 (1440.5-1458.7’) Wilkins Peak Member, Blacks Fork-1 1440.5-1445.8 Mudstone, medium - light olive gray. Minor cycle 1445.0-1445.8 organic-rich laminated base grades to “dry and lean” at top. 1445.8-1448.4 Mudstone, medium-light olive gray, silty in parts. Minor cycle 1447.2-1447.9, same as above. Other organic-rich intervals?? 1448.4-1453.0 Mudstone, olive gray to olive green. Generally uniform appearance and texture. Thick partings? Halite band at 1448.9,1 inch. White, crystalline? 1449.2-1449.4 dry lean light gray mudstone Minor cycle 1449.1-1449.7, same as above? Interval may contain some more minor cycles. 1453.0-1454.2 Oil Shale, green-gray, uniform? Lean oil shale at base? 1454.2-1457.0 Oil Shale, medium-dark olive gray to brownish gray. Laminated? 1457.0-1457.8 Oil Shale, dark olive gray to brown gray. 1457.8-1458.7 Oil Shale Medium olive gray to dark brown gray. Grades to partially laminated oil shale at base? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 5 (1425.9-1440.5’) Wilkins Peak Member, Blacks Fork-1 1425.9-1430.7 Mudstone, medium greenish gray. Massive texture? Contains possible minor cycles top of cycle grades to oil shale above 1427.4-1427.6 Light Gray 1429.2-1429.4 Light Gray 1429.5 Pebble Conglomerate 1429.9-1430.3 Light Gray 1429.9-1430.4 - Minor cycle ranges from “dry to mod dry”? 1430.7-1432.7 Mudstone, greenish gray. 1432.7-1435.4 Mudstone, medium gray to olive gray. Massive texture in places? 1434.5-1434.9 Occasional trona and shortitie layers? 1435.4-1436.1 Oil Shale, medium dark olive gray. Some green mudstone? Gradation from black oil shale at 1436 to green oil shale at 1435.5 1436.1-1437.3 Oil shale, medium olive gray, displays some laminations. Dark -Medium olive gray? 1439.3-1440.5 Oil Shale, medium dark olive gray-olive green. 1440.5-1440.6 halite layer? 314 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 20 (1229.2-1250.8’) Wilkins Peak Member, Blacks Fork-1 1229.2-1233.1 Siltstone, medium-light greenish gray. 1229.2 Algal dolomite layer at top of cycle directly below overlying oil shale 3 / 4” thick. White-pink laminated appearance. 1229.2-1230.0 Siltstone- 1230.0-1233.1 Gray green mudy siltstone almost becoming mudstone, with dark green mudstone at 1230.8-1231.2. Grades to siltstone from 1232.0-1233.1. 1233.1-1241.8 Siltstone, light gray to olive gray. Contains som vfg sandstone, cross bedding is common throughout the interval. 1234.1-1234.3 Dark green mudstone, silty 1236.05-1236.25 Dark green mudstone, silty 1237.0-1237.5 Dark green mudstone, silty 1239.2-1239.9 Dark green mudstone, silty Interval contains plant/carbonaceous lamina, burrows, and wispy lamina in parts. 1241.8-1247.0 Mudstone, medium-light olive gray, minor color variations. Interval contains some siltstone. 1234.4-1243.7-banded 1245.0-1247.0 Dark green mudstone? 1247.0-1248.0 Shortite and marlstone, light-medium brownish gray. 315 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1248.0-1249.0 Shortite and mudstone, Very rich mudstone almost grading to oil shale. Mudstone layers u to 0.6? Mudstone increases upward in interval. Consists of banded carbonate/mudstone. 1249.0-1249.7 Oil Shale, medium black, brownish gray. Interval contains some ash. 1249.7-1250.3 Tuff 1249.8-1249.9 Oil shale 1250.3-1250.8 Oil shale Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 21 (1217.8-1229.2’) Wilkins Peak Member, Blacks Fork-1 1217.8-1224.0 Mudstone, Medium-light green, marly. Subtle variations in color. Mudstone is massive, relatively uniform, no bedding, limited laminations. Occasional faint laminations in several zones (1220-1221). 1219.75 halite band-V z” 1224.0-1225.6 Mudstone, medium green gray, marly. Grades to organic-rich mudstone in places. Decrease in carbonate & shortite and OM going upward? 1225.6-1226.7 Mudstone, dark green. Uniform? 1226.0-1226.7 Mudstone grades to almost oil shale. Brown, olive gray. 1226.7-1227.9 Carbonate/shortite, medium olive gray and brownish gray. ‘Some bands of oil shale? Grades upward to mudstone. Some banded, layered mudstone with carbonate. 1227.9-1228.6 Oil Shale, medium olive gray, almost mudstone. 1228.6-1229.2 Oil shale, medium olive gray to brown gray. Increasing organic content with depth. Dark green mudstone grades to oil shale at base of interval. Algal mat directly below base of oil shale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cycle 22 (1204.5-1217.8’) Wilkins Peak Member, Blacks Fork-1 1204.5-1205.8 Marlstone, medium olive gray. Color grades with depth, to medium- dark green gray. Relatively uniform but with minor lamina. Abundant shortite minerals in select parts of interval. Sharp transition to overlying oil shale. Grades to interval below. 1205.8-1208.1 Marlstone and shortite, medium-dark olive gray. Highly variable. Contains relatively abundant homogenous bands of mudstone (up to 1.5”) where shortite is absent. Some irregular layers. 1206.8-1207.0 Marlstone dark greenish brown with abundant shortite and irregular layers, mudstone bands are rare. 1207.8-1208.1 Limestone/carbonate, greenish brown gray, rare mudstone bands 1208.1-1209.0 Marlstone and Shortite, Medium-dark brownish gray. Mottled and irregularly layered with relatively abundant fine-coarse grain shortitie. Contains occasional irregular brown dolomitic mudstone layers that range from 1/8” to 1/2”. More bedding with depth. Sharp contact with oil shale below. 1209.0-1209.5 Oil shale, md olive gray, displays mudstone appearance. Abundant shortite, fine to very coarse grain; some minor trona crystals. Texture dominated by shortite. Faint streaked bedding. Sharp contact with underlying trona. 1209.5-1211.6 Trona, medium gray, brown, massive. Texture based on core face. Contains some oil shale. 1210.7-1210.8 Oil shale in trona, dark brown to black. Contains abundant shortite. Sharp contacts above and below. 1210.9-1211.0 organic mudstone layers and lamina in trona. Algal-bacterial mats? 1211.5-1211.6 Lost Core 318 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1211.6-1212.6 Oil shale, black-dark brown. Grades to medium olive gray at base of interval with appearance of decreasing organic content with depth. Faint lamina and thin bands in places. Shortite or trona crystals at base of interval. 1212.6-1215.2 Oil Shale, medium olive gray to brownish gray. Some minor variation in color throughout interval corresponding to OM content. Some bedding and lamination through interval; sometimes with “breaks” in color and OM content. Massive texture at 1214.0. 1215.2-1215.9 Oil shale, medium dark brown-gray. Grades to black at base. Bedding and laminations are evident. Occasionally irregular laminations. Some shortite. Noticeable contact with oil shale interval below. 1215.9-1217.8 Oil shale, dark brown gray to black. Some individual lamina and dense lamina, massive in select locations. Some minor lamina and small lenses of ash in oil shale, especially at base of interval. 1216.5 Sharp break from dark brownish black to black oil shale 1216.6 massive texture, 2” thick 1217.65 1” tuff, massive. Light tan. Below ash, oil shale with very sharp break to mustone/marlstone below. Cycle 24 (1163.7-1193.6’) Wilkins Peak Member, Blacks Fork-1 1163.7-1164.8 Silty mudstone ranging from mudstone to siltstone, light greenish gray to gray. Increasing silt content with depth. Rare to moderate mudstone lamina and rare mudstone partings up to 0.5 inch. Minor cross-laminations in places. Micaceous, possibly contains some volcanic ash. Sharp contact with overlying oil shale. 1164.8-1165.0 Core loss 1165.0-1166.1 Siltstone, gray to light greenish gray. Uniform. Contains some vfg sandstone and rare mudstone lamina. Displays occasional cross-bedding, laminations, and “wavy or streaked” laminations. Micaceous. 319 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1166.1-1167.7 Mudstone with siltstone in places, gray to light greenish gray. Possibly some silty limestone. Increasing mudstone content with depth. Mudstone is often uniform. Gradational with units above and below. Indistinct and disrupted bedding in several locations. 1166.1-1166.3 lamina with organic matter 1166.9-1167.7 mudstone contains specks of carbonaceous? Organic matter 1167.7-1171.0 Mudstone, light to medium olive gray. Generally massive and uniform with occasional thin lamina. Faintly mottled in places. 1169.4-1169.8 Silty mudstone in places with occasional faint lamina 1169.9-1171.0 Medium-dark green mudstone, massive 1170.1-1170.3 Core Loss 1171.0-1172.6 Siltstone, olive gray. Almost muddy in certain parts. Streaked bedding and laminations , which increase with depth. Contains white appearing mineral spots? in places. Gradational with below. 1172.6-1176.4 Mudstone, medium olive gray. Rare dark olive gray. Silty in parts. Thin silt lamina are common throughout interval? Tan to brownish gray lamina in places (ash?). 1172.8-1173.1 Distinct well laminated interval containing OM. Minor cycle? 1173.1-1175.3 Medium - dark gray green mudstone generally uniform with some thin silt lamina at 1174.0 1175.3-1176.4 Medium green mudstone with abundant tan bands and laminations (ash?) 1176.4-1184.4 Dark green to very dark green mudstone with silt lamina that are up to V ” thick? 1176.7-1177.1-Core Loss 1178.4-1178.8 Medium green mudstone with tan laminations 1179.0-1182.8 Dark green uniform mudstone. Very dark green from 1179.0- 1181.1, occasional organic-rich bands up to ‘ A” thick. This may represent an additional cycle base in the eccentricity break? 320 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1182.8-1183.5 Medium-dark green. Some partial and disrupted lamina with cross-beds. 1184.4-1185.1 Mudstone, silty, dark to medium brownish gray, marly, increasing silt content with depth. 1185.1-1187.4 Siltstone, light gray With some vfg sandstone Interval is uniform throughout. Micaeous Streaked -laminated bedding throughout. Lamina contains organic matter probably carbonaceous. Some faint cross-bedding in parts. 1185.9-1186.3 Core Loss 1187.2-1187.4 Silty mudstone. Increasing laminations. 1187.4-1188.6 Mudstone, medium brown-green gray. Uniform. Decreasing silt content with depth. Some carbonaceous partings, especially at top of interval. 1188.6— 1190.4 Mudstone, dark green, generally massive, minor bedding. Occassional faint bedding and lamina in places throughout interval. Micaeous, minor carbonaceous material? 1190.4-1192.0 Mudstone and limestone, Medium green-dark brownish gray. Highly variable. 1190.4-1191.0 Mudstone with thin limestone and calcareous mudstone bands. Variable 1191.0-1191.17 Core Loss 1191.17-1191.5 Same as 1190.4-1191.0 1191.5-1192.0 Limestone, dark gray brown with thin mudstone bands/laminations and some oil shale lamina. Variable. Grades to oil shale below. 1192.0-1193.7 Oil shale 1192.0-1192.2 Oil Shale, dark green. Contains thin bands of calcareous mudstone, organic-rich. 1192.2-1192.8 Oil Shale, dark green uniform except several thin bands of calcareous mudstone. Increasing dark green color with depth. 321 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1192.8-1192.95 Oil Shale, black very organic rich, banded, difficult to define upper boundary, Gradational? 1192.95-1193.4 Very dark brown-green to black laminated, Contains shortite minerals? Discontinuous organic-rich streaks - mat material? 1193.4 - 1193.5 Oil Shale dark brown to black, organic-rich banded 1193.5-1193.7 Oil Shale very dark green, grades to organic-rich mudstone. Oil shale grades to a mudstone in underlying cycle. Difficult to identify cycle base. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Appendix 3 D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) (G allons/T on) 447.3 447.8 3.2 505.5 506.6 2.9 447.8 449.6 0.4 506.6 507.7 4.5 449.6 451.2 0.4 507.7 508.7 4.3 451.2 452.2 1.2 508.7 509.7 6.5 452.2 453.2 2.1 509.7 511.2 16.1 453.2 454.5 6.5 511.2 . 512.1 5.1 454.5 456.3 22.2 512.1 512.9 3.7 456.3 457.5 11.9 512.9 513.8 3.1 457.5 458.5 1.0 513.8 514.7 4.6 458.5 459.9 2.7 514.7 515.6 7.3 459.9 461.0 6.9 515.6 517.2 28.1 461.0 462.0 6.1 517.2 518.0 9.7 462.0 463.0 6.7 518.0 519.0 1.8 463.0 464.0 3.9 519.0 520.1 1.4 464.0 465.0 3.7 520.1 521.4 4.2 465.0 466.8 1.8 521.4 522.7 9.5 466.8 467.4 0,3 522.7 524.0 8.8 . 467.4 468.6 2.2 524.0 525.1 3.2 468.6 469.7 1.9 525.1 526.3 1.1 469.7 470.8 2.0 526.3 527.5 0.2 470.8 471.8 2.2 527.5 528.5 1.1 471.8 472.8 1.9 528.5 529.6 1.5 472.8 474.0 4.6 529.6 530.7 4.0 474.0 475.0 7.9 530.7 532.0 16.3 475.0 476.0 7.7 532.0 533.0 26.8 476.0 477.0 9.7 533.0 534.0 7.4 477.0 478.0 8.5 534.0 535.1 5.6 478.0 479.2 7.4 535.1 536.2 5.5 479.2 480.6 14.6 536.2 537.2 18.1 480.6 481.6 20.7 537.2 538.2 25.4 481.6 482.6 17.0 538.2 539.2 '21.4 482.6 483.6 11.2 539.2 540.2 6.6 483.6 485.0 7.0 540.2 541.5 2.5 485.0 486.5 6.1 541.5 542.7 1.6 486.5 487.8 17.5 542.7 543.9 1.5 487.8 489.0 21.4 543.9 545.0 11.9 489.0 490.2 12.9 545.0 546.1 30.9 490.2 491.3 2.0 546.1 547.1 1.4 491.3 492.3 3.8 547.1 548.3 0.2 492.3 493.3 3.0 548.3 • 549.3 0.4 493.3 494.5 4.4 549.3 550.4 0.7 494.5 496.0 5.8 550.4 551.5 2.1 496.0 497.0 16.6 551.5 552.5 2.3 497.0 498.0 27.3 552.7 553.7 7.1 498.0 499.0 25.3 553.1 554.1 0.1 499.0 500.0 21.5 554.1 556.7 0.1 500.0 501.0 14.2 556.7 559.5 0.1 501.0 502.1 7.4 559.5 560.8 0.1 502.1 503.3 10.6 560.8 561.7 0.1 503.3 504.4 11.4 561.7 562.5 0.1 504.4 505.5 5.2 562.5 563.5 0.1 323 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) G allons/T on) 563.5 564.6 0.1 634.9 636.0 1.1 564.6 565.6 0.0 636.0 637.0 2.0 565.6 569.7 0.0 637.0 638.0 3.2 569.7 573.8 0.0 638.0 639.0 6.6 573.8 575.5 0.1 639.0 640.0 11.6 575.5 576.5 0.1 640.0 641.3 5.4 576.5 578.0 0.1 641.7 642.7 3.1 578.0 580.0 0.1 642.7 644.3 1.9 580.0 582.0 0.1 644.3 645.5 3.1 582.0 584.0 0.1 645.5 647.8 2.5 584.0 585.0 0.1 647.8 650.1 2.5 585.0 587.0 0.1 650.1 651.1 2.0 587.6 590.1 0.6 651.1 652.9 2.9 590.1 591.1 6.0 652.9 654.7 2.8 591.1 592.5 25.6 654.7 659.0 2.5 592.5 593.5 8.8 659.0 663.5 ’ 1.7 593.5 594.9 1.8 663.5 664.5 1.0 594.9 596.3 0.3 664.5 668.2 3.0 596.3 597.4 1.1 668.2 669.2 4.6 597.4 598.9 1.9 669.2 670.3 6.3 598.9 600.8 3.8 670.3 671.5 6.6 600.8 602.7 9.8 671.5 672.6 14.3 602.7 603.4 4.7 672.6 673.5 16.8 603.4 603.9 0.1 673.5 674.5 10.2 603.9 605.7 1.3 674.5 677.2 2.3 605.7 607.6 0.6 677.2 679.9 2.2 607.6 609.6 0.8 679.9 682.0 3.5 609.6 611.0 2.6 682.0 683.4 6.3 611.0 612.2 33.0 684.9 686.1 11.6 612.2 613.4 36.4 686.1 689.0 6.3 613.4 613.9 11.3 689.0 692.0 7.7 613.9 615.1 1.2 692.0 693.4 6.7 615.1 616.1 0.1 693.4 694.8 8.1 616.1 617.2 0.2 694.8 695.8 8.5 617.2 618.3 0.6 695.8 697.0 4.6 618.3 619.3 1.5 697.0 699.1 2.5 619.3 620.8 13.5 699.1 701.1 1.5 620.8 622.4 3.9 701.1 703.1 1.8 622.4 623.9 0.6 703.1 704.7 2.5 624.6 625.2 1.7 704.7 706.0 4.2 625.2 626.5 1.3 706.0 707.8 4.5 626.5 627.8 7.1 707.8 708.8 12.7 627.8 629.0 9.1 708.8 710.2 17.5 629.0 629.8 0.4 710.2 711.2 25.9 629.8 631.4 3.6 711.2 712.3 5.0 631.9 632.9 2.2 712.3 713.5 2.9 632.9 633.9 1.0 713.5 714.5 3.4 633.9 634.9 0.8 714.5 715.5 10.2 .... 324 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) (G allons/T on) 715.5 716.8 22.6 786.7 788.0 1.5 716.8 718.0 2.9 788.0 789.4 23.6 718.0 720.0 1.8 789.4 790.3 13.3 720.0 721.6 3.5 790.3 791.7 1.8 721.6 723.0 2.6 791.7 793.0 1.4 723.0 724.0 0.1 793.0 794.0 2.6 724.0 724.6 14.0 794.0 795.0 18.8 724.6 725.8 29.1 795.0 796.0 17.7 725.8 727.0 3.8 796.0 797.0 10.0 727.0 728.2 2 .2 797.0 798.0 6.2 728.2 729.4 2.4 798.0 799.0 1.8 729.4 730.4 2.3 799.0 800.0 1.4 730.4 731.4 1.1 800.0 801.5 1.0 731.4 733.2 0.1 801.5 802.9 3.6 733.2 735.0 0.1 802.9 803.9 11.6 735.0 736.0 15.4 803.9 805.9 0.1 736.0 737.0 29.9 805.9 807.9 0.1 737.0 738.0 28.3 807.9 809.0 0.1 738.0 739.0 27.2 809.0 813.0 0.1 739.0 740.0 6.7 813.0 817.0 0.1 740.0 741.1 5.6 817.0 820.0 0.1 741.1 742.5 1.5 820.0 821.8 0.1 742.5 743.5 3.7 821.8 823.0 0.1 743.5 744.9 4.1 823.0 824.3 0.1 744.9 746.8 32.3 824.3 825.8 1.9 746.8 748.0 2.4 825.8 826.8 8.9 748.0 751.5 0.4 826.8 828.2 0.1 751.5 754.9 0.9 828.2 831.3 0.1 754.9 755.9 3.9 831.3 834.4 0.1 755.9 756.8 27.7 834.4 838.4 0.0 756.8 757.4 2.0 838.4 840.3 0.1 757.4 759.0 0.1 840.3 842.1 0.1 759.0 761.7 0.1 842.1 843.6 0.2 761.7 764.5 0.1 843.8 845.3 1.7 765.0 767.0 0.8 845.3 846.6 1.0 767.0 770.0 1.0 846.6 847.8 1.1 770.0 771.8 0.9 847.8 849.2 13.3 771.8 775.2 0.1 849.2 850.2 9.7 775.3 776.7 0.8 850.2 85-1.2 8.3 776.7 777.7 1.3 851.2 852.2 8.0 777.7 778.7 1.8 852.2 853.3 7.7 778.7 780.2 1.7 853.3 854.3 4.2 780.2 780.8 4.1 854.3 855.7 3.0 780.8 781.7 31.4 855.7 856.8 1.0 781.7 783.2 1.0 856.8 858.0 1.2 783.2 784.2 0.3 858.0 859.3 1.3 784.7 785.7 2.1 859.3 860.6 1.9 785.7 786.7 2.5 860.6 861.6 3.9 325 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) [G allons/T on) 861.6 862.7 26.3 930.4 931.5 1.3 862.7 863.9 21.1 931.5 932.6 0.8 863.9 864.7 7.6 932.6 933.9 2.6 864.7 865.6 1.2 933.9 934.7 25.9 865.6 866.9 1.1 934.7 936.0 1.5 866.9 868.3 0.8 936.0 937.2 0.9 868.3 869.7 3.2 937.2 938.2 1.1 869.7 871.6 0.7 938.4 942.0 0.1 871.6 872.5 1.7 942.0 946.0 0.0 872.5 874.2 0.6 946.0 950.3 0.1 874.2 875.8 0.3 950.0 951.2 7.2 875.8 876.4 3.0 951.2 955.0 0.0 876.4 877.2 14.3 955.0 959.3 0.0 877.2 878.3 3.1 959.3 963.5 0.1 878.3 879.4 1.4 963.5 967.5 0.1 879.4 881.2 1.4 967.5 968.8 0.5 881.2 883.0 0.1 968.8 970.4 1.7 883.0 884.9 0.1 970.4 970.9 30.2 884.9 886.0 0.3 970.9 971.6 1.4 886.0 887.3 4.7 971.6 972.2 0.1 887.3 888.7 2.5 972.2 973.7 0.1 888.7 890.1 0.1 973.7 975.3 0.2 890.1 893.0 0.1 975.3 976.5 2.4 893.0 898.0 0.0 976.5 977.7 1.3 898.0 902.0 0.0 977.7 978.9 2.9 902.0 906.4 0.0 978.9 980.8 4.1 906.4 908.2 0.0 980.8 982.8 4.6 908.2 909.4 0.1 982.8 985.6 0.1 909.4 910.6 0.1 985.6 986.6 4.6 910.6 911.8 0.5 986.6 987.6 19.3 911.8 912.8 0.5 987.6 992.0 0.1 912.8 913.8 7.8 992.0 997.3 0.1 913.8 914.8 17.1 997.3 1001.6 0.1 914.8 915.8 17.4 1001.6 1003.6 0.1 915.8 916.8 1.9 1003.6 1004.6 0.1 916.8 918.0 0.8 1004.6 1005.7 0.1 918.0 919.0 1.0 1005.7 1007.4 0.8 919.0 920.0 1.5 1007.4 1008.0 0.1 920.0 921.0 3.2 1008.0 1011.0 0.1 921.0 922.0 11.4 1011.0 1015.0 0.1 922.0 923.0 21.1 1015.0 1020.0 0.1 923.0 923.8 11.7 1020.0 1025.0 0.1 923.8 924.9 6.5 1025.0 1030.0 0.1 924.9 925.9 6.7 1030.0 1035.0 0.1 925.9 926.9 7.3 1035.0 1040.0 0.0 926.9 927.9 15.9 1040.0 1045.0 0.1 927.9 929.1 6.3 1045.0 1048.3 0.1 929.1 930.4 2.9 1048.3 1051.3 0.0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) (G allons/T on) 1051.3 1052.6 0.1 1112.0 1113.0 1.8 1052.6 1053.6 0.1 1113.0 1114.2 1.2 1053.6 1054.6 0.2 1114.2 1115.8 5.0 1054.6 1055.6 0.8 1115.8 1116.7 5.9 1055.6 1056.6 2.7 1116.7 1118.0 2.7 1056.6 1057.6 13.1 1118.0 1119.0 17.2 1057.6 1058.6 6.1 1119.0 1120.0 18.5 1058.6 1059.7 0.4 1120.0 1121.1 24.1 1059.7 1060.9 0.5 1121.1 1122.6 5.4 1060.9 1062.0 0.1 1122.6 1124.3 36.3 1062.0 1063.2 0.2 1124.3 1125.4 24.0 1063.2 1064.7 0.3 1125.4 1126.4 3.4 1064.7 1066.1 1.1 1126.4 1128.0 0.7 1067.6 1068.7 1.9 1128.0 1129.4 1.2 1068.7 1069.8 3.0 1129.4 1130.9 1.4 1069.8 1071.2 6.6 1130.9 1132.4 2.6 1071.2 1072.2 7.2 1132.4 1133.3 0.1 1072.2 1073.2 5.0 1133.3 1133.9 7.2 1073.2 1074.2 4.3 1133.9 1135.1 40.6 1074.2 1075.4 0.8 1135.1 1136.1 2.3 1075.4 1076.6 2.2 1136.1 1138.1 2.3 1076.6 1077.9 7.0 1138.1 1139.8 6.1 1077.9 1079.3 9.1 1139.8 1140.6 13.7 1079.3 1080.3 4.3 1140.6 1141.4 18.5 1080.3 1081.4 2.0 1141.4 1142.5 25.1 1081.4 1082.5 1.5 1142.5 1143.5 6.8 1082.5 1083.7 1.7 1143.5 1144.5 1.8 1083.7 1084.9 2.5 1144.5 1145.5 1.4 1084.9 1085.9 4.2 1145.5 1146.6 1.7 1085.9 1086.8 13.6 1146.6 1147.6 3.6 1086.8 1087.8 4.2 1147.6 1149.5 0.1 1087.8 1088.8 1.2 1149.5 1151.4 0.1 1088.8 1089.8 0.4 1151.4 1152.1 19.5 1089.8 1090.8 1.1 1152.1 1152.8 16.6 1090.8 1091.9 10.2 1152.8 1154.0 19.5 1091.9 1093.0 11.2 1154.0 1155.4 6.4 1093.0 1094.0 4.2 1155.4 1156.8 10.4 1094.0 1095.3 0.0 1156.8 1157.8 19.6 1095.3 1097.6 0.3 1157.8 1158.8 30.7 1097.6 1101.0 0.0 1158.8 1159.8 23.5 1101.0 1104.0 0.1 1159.8 1160.8 2.8 1104.0 1105.7 1.7 1160.8 1162.0 1.6 1105.7 1106.9 1.5 1162.0 1163.1 0.6 1106.9 1107.9 4.6 1163.1 1163.7 11.4 1107.9 1109.0 2.0 1163.7 1164.8 0.4 1109.0 1110.0 1.4 1164.8 1166.3 0.0 1110.0 1111.0 1.9 1166.3 1167.7 0.0 1111.0 1112.0 1.3 1167.7 1170.0 0.0 327 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth F rom D epth To Oil Yield (Feet) (Feet) (Gallons/Ton) (Feet) (Feet) G allons/T on) 1170.0 1175.0 0.1 1249.7 1250.3 12.5 1175.0 1180.0 0.0 1250.3 1250.8 26.3 1180.0 1184.0 0.0 1250.8 1253.5 0.1 1184.0 1185.1 0.1 1253.5 1256.3 0.1 1185.1 1187.4 0.0 1256.3 1257.7 0.1 1187.4 1190.4 0.1 1257.7 1259.2 0.1 1190.4 1192.0 2.6 1259.2 1261.4 0.1 1192.0 1192.8 4.9 1261.4 1263.6 0.1 1192.8 1193.6 23.8 1263.6 1264.6 0.4 1193.6 1194.7 5.4 1264.6 1265.8 1.3 1194.7 1195.7 0.5 1265.8 1267.0 1.9 1195.7 1196.7 0.2 1267.0 1268.2 0.1 1196.7 1197.9 1.2 1268.2 1269.2 4.6 1197.9 1199.0 1.1 1269.2 1270.5 7.6 1199.0 1200.0 1.3 1270.5 1271.1 31.6 1200.0 1201.0 1.1 1271.1 1271.6 10.3 1201.0 1202.1 1.7 1271.6 1273.0 2.9 1202.1 1203.4 10.2 1273.0 1274.4 1.6 1203.4 1204.5 37.2 1274.4 1275.8 2.6 1204.5 1205.5 1.5 1275.8 1277.2 1.5 1205.5 1206.5 1.9 . 1277.2 1278.2 0.1 1206.5 1207.5 1.3 1278.2 1278.7 1.9 1207.5 1209.0 1.8 1278.7 1279.9 0.1 1209.0 1209.5 4.3 1279.9 1281.0 3.9 1209.5 1210.5 0.1 1281.0 1282.2 8.2 1210.5 1211.6 4.7 1282.0 1283.2 13.8 1211.6 1212.6 29.2 1283.2 1284.2 6.1 1212.6 1213.9 12.2 1284.2 1285.2 10.6 1213.0 1215.2 11.5 1285.2 1286.2 17.0 1215.2 1215.9 22.3 1286.2 1287.2 11.5 1215.9 1216.8 30.8 1287.2 1288.2 10.9 1216.8 1217.8 27.8 1288.2 1289.3 7.2 1217.8 1219.0 0.5 1289.3 1290.4 5.0 1219.0 1221.5 0.0 1290.4 1291.4 3.1 1221.5 1224.0 0.1 1291.4 1292.4 10.8 1224.0 1225.6 0.4 1292.4 1293.4 11.1 1225.6 1226.7 1.6 1293.4 1294.4 12.6 1226.7 1227.9 2.2 1294.4 1295.6 1.7 1227.9 1228.6 3.8 1295.6 1296.8 1.5 1228.6 1229.2 13.8 1296.8 1298.0 1.1 1229.2 1233.1 0.1 1298.0 1299.0 2.1 1233.1 1237.5 0.1 1299.0 1300.5 1.5 1237.5 1241.8 0.1 1300.5 1301.5 5.8 1241.8 1246.6 0.1 1301.5 1302.6 15.1 1246.6 1247.0 0.1 1302.6 1303.6 2.8 1247.0 1248.0 1.1 1303.6 1304.7 1.1 1248.0 1249.0 2.1 1304.7 1305.8 1.0 1249.0 1249.7 9.7 1305.8 1306.8 1.4 328 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (F eet) (Feet) (G allons/T on) (Feet) (Feet) (G allons/T on) 1306.8 1308.5 4.2 1387.8 1388.9 12.5 1308.5 1309.5 5.3 1388.9 1390.5 12.1 1309.5 1310.5 0.1 1390.5 1391.5 3.8 1310.5 1312.1 0.2 1391.5 1393.0 3.0 1312.1 1313.7 0.5 1393.0 1394.6 4.1 ' 1313.7 1315.3 0.6 1394.6 1396.2 4.1 1315.3 1316.8 0.9 1396.2 1397.2 7.3 1316.8 1318.4 1.0 1397.2 1398.2 12.9 1318.4 1319.7 2.4 1398.2 1399.7 21.3 1319.7 1321.0 4.2 1399.7 1400.3 6.6 1321.0 1322.3 3.8 1400.3 1401.6 2.6 1322.3 1323.3 6.1 1401.6 1403.2 1.7 1323.3 1324.4 0.6 1403.2 1404.8 2.6 1324.4 1326.0 0.7 1404.8 1406.5 3.8 1326.0 1329.3 0.3 1406.5 1407.8 6.9 1329.3 1332.6 1.8 1407.8 1408.5 11.4 1332.6 1333.6 1.5 1408.5 1409.5 12.7 1333.6 1334.7 5.1 1409.5 1410.5 4.5 1334.7 1335.8 5.6 1410.5 1413.1 0.6 1335.8 1337.0 2.3 1413.1 1415.8 0.3 1337.0 1338.0 0.4 1415.8 1419.3 4.5 1338.0 1339.0 0.1 1419.3 1422.7 1.5 1339.0 1340.1 0.5 1422.7 1424.2 11.1 1340.1 1341.2 2.1 1424.2 1425.4 19.7 1341.2 1342.4 4.1 1425.4 ' 1425.9 9.5 1342.4 1343.6 2.6 1425.9 1428.3 2.4 1343.6 1345.5 1.4 1428.3 1430.7 1.7 1345.5 1347.2 0.5 1430.7 1432.7 1.7 1347.2 1350.0 0.4 1432.7 1434.4 2.0 1350.0 1355.0 0.3 1434.4 1435.4 1.9 1355.0 1360.0 1.7 1435.4 1436.1 12.8 1360.0 1361.6 2.6 1436.1 1437.3 14.0 1361.6 1362.7 5.0 1437.3 1438.3 13.0 1362.7 1364.0 2.0 1438.3 1439.3 12.4 1364.0 1367.0 1.6 1439.3 1440.5 12.3 1367.0 1370.0 1.1 1440.5 1441.9 7.9 1370.0 1373.5 2.2 1441.9 1443.6 5.0 1373.4 1375.0 3.7 1443.6 1445.8 9.3 1375.0 1376.3 14.6 1445.8 1448.4 4.0 1376.3 1377.5 14.2 1448.4 1450.2 8.2 1377.5 1378.6 6.3 1450.2 1452.0 6.6 1378.6 1379.6 4.3 1452.0 1453.0 8.5 1379.6 1381.0 4.4 1453.0 1454.2 13.9 1381.0 1382.5 4.9 1454.2 1455.2 13.4 1382.5 1383.7 3.9 1455.2 1456.2 17.4 1383.7 1385.2 3.7 1456.2 1457.0 16.2 1385.2 1386.7 8.3 1457.0 1457.8 20.2 1386.7 1387.8 12.5 1457.8 1458.7 14.8 329 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allo n s/T o n ) (Feet) (Feet) (G allons/T on) 1458.7 1460.0 4.1 1526.0 1527.0 11.9 1460.0 1462.4 2.6 1527.0 1528.0 9.9 1462.4 1464.8 2.8 1528.0 1529.0 15.7 1464.8 1465.6 6.4 1529.0 1530.0 19.2 1465.6 1466.7 28.2 1530.0 1531.0 21.0 1466.7 1467.7 26.3 1531.0 1532.0 15.9 1467.7 1468.6 15.3 1532.0 1533.0 16.6 1468.6 1469.6 12.0 1533.0 1534.0 15.2 1469.6 1471.0 6.4 1534.0 1535.0 17.6 1471.0 1474.9 3.8 1535.0 1536.0 8.8 1474.9 1476.5 1.9 1536.0 1537.0 11.4 1476.5 1478.2 3.0 1537.0 1538.0 12.0 1478.2 1481.0 8.9 1538 1539.0 13.0 1481.0 1483.9 11.1 1539 1540.0 31.5 1483.9 1484.9 17.4 1540.0 1541.1 32.9 1484.9 1485.6 21.0 1541.1 1542.2 23.4 1485.6 1486.6 9.6 1542.2 1543.3 21.0 1486.6 1488.0 1.4 1543.3 1544.4 23.3 1488.0 1491.0 1.7 1544.4 1545.5 18.7 1491.0 1493.6 0.3 1545.5 1546.7 19.7 1493.6 1496.2 0.8 1546.7 1547.7 30.6 1496.2 1497.2 1.2 1547.7 1548.7 31.8 1497.2 1498.7 19.9 1548.7 1550.0 17.6 1498.7 1499.7 24.6 1550.0 1551.0 25.5 1499.7 1500.6 14.4 1551.0 1552.0 17.3 1500.6 1501.5 31.8 1552.0 1553.5 12.0 1501.5 1502.2 13.2 1553.5 1555.0 27.3 1502.2 1503.6 3.1 1555.0 1555.5 30.1 1503.6 1505.2 1.0 1555.5 1556.6 30.2 1505.2 1506.3 0.1 1556.6 1557.8 17.9 1506.3 1507.4 1.0 1557.8 1558.8 24.0 1507.4 1508.4 0.1 1558.8 1559.8 14.2 1508.4 1509.4 0.1 1559.8 1560.8 14.1 1509.4 1510.4 7.6 1560.8 1562.6 7.7 1510.4 1511.4 23.3 1562.6 1563.8 3.2 1511.4 1512.4 24.8 1563.8 1565.2 4.7 1512.4 1513.4 28.1 • 1565.2 1566.7 8.1 1513.4 1514.5 29.4 1566.7 1567.7 10.2 1514.5 1515.6 28.1 1567.7 1568.7 19.8 1515.6 1516.7 30.1 1568.7 1569.7 17.6 1516.7 1517.9 32.0 1569.7 1570.7 11.6 1517.9 1519.1 31.4 1570.7 1571.7 12.5 1519.1 1520.1 28.8 1571.7 1572.2 27.6 1520.1 1521.8 28.0 1572.2 1573.2 16.2 1521.8 1523.0 12.5 1573.2 1574.2 8.4 1523.0 1524.0 13.4 1574.2 1575.2 10.6 1524.0 1525.0 13.7 1575.2 1576.9 10.5 1525.0 1526.0 11.8 1576.9 1578.2 8.2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Depth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) [G allons/Ton) 1526.0 1527.0 11.9 1578.2 1578.8 12.4 1527.0 1528.0 9.9 1578.8 1579.9 12.2 1528.0 1529.0 15.7 1579.9 . 1581.0 16.4 1529.0 1530.0 19.2 1581.0 1582.1 16.1 1530.0 1531.0 21.0 1582.1 1583.1 9.3 1531.0 1532.0 15.9 1583.1 1584.1 10.9 1532.0 1533.0 16.6 1584.1 1585.5 8.3 1533.0 1534.0 15.2 1585.5 1586.5 19.0 1534.0 1535.0 17.6 1586.5 1587.5 13.1 1535.0 1536.0 8.8 1587.5 1588.7 1.4 1536.0 1537.0 11.4 1588.7 1590.0 1.1 1537.0 1538.0 12.0 1590.0 1591.0 0.7 1538 1539.0 13.0 1591.0 1592.0 1.2 1539 1540.0 31.5 1592.0 1593.0 2.4 1540.0 1541.1 32.9 1593.0 1594.0 6.0 1541.1 1542.2 23.4 1594.0 1595.0 4.9 1542.2 1543.3 21.0 1595.0 1596.3 6.3 1543.3 1544.4 23.3 1596.3 1597.6 16.3 1544.4 1545.5 18.7 1597.6 1599.0 8.3 1545.5 1546.7 19.7 1599.0 1600.0 6.3 1546.7 1547.7 30.6 1600.0 1601.0 9.6 1547.7 1548.7 31.8 1601.0 1602.0 10.5 1548.7 1550.0 17.6 1602.0 1603.0 7.7 1550.0 1551.0 25.5 1603.0 1604.0 9.9 1551.0 1552.0 17.3 ' 1604.0 1605.0 6.2 1552.0 1553.5 12.0 1605.0 1606.0 4.6 1553.5 1555.0 27.3 1606.0 1607.0 9.6 1555.0 1555.5 30.1 1607.0 1608.0 7.7 1555.5 1556.6 30.2 1608.0 1609.0 6.7 1556.6 1557.8 17.9 1609.0 1610.0 6.9 1557.8 1558.8 24.0 1610.0 1611.0 11.5 1558.8 1559.8 14.2 1611.0 1612.0 10.1 1559.8 1560.8 14.1 1612.0 1613.0 11.5 1560.8 1562.6 7.7 1613.0 1614.0 12.2 1562.6 1563.8 3.2 1614.0 1615.0 17.2 1563.8 1565.2 4.7 1615.0 1616.0 10.9 1565.2 1566.7 8.1 1616.0 1617.0 7.2 1566.7 1567.7 10.2 1617.0 1617.9 11.9 1567.7 1568.7 19.8 1617.9 1618.6 19.5 1568.7 1569.7 17.6 1618.6 1619.6 19.2 1569.7 1570.7 11.6 1619.6 1620.8 11.7 1570.7 1571.7 12.5 1620.8 1622.1 6.6 1571.7 1572.2 27.6 1622.1 1623.1 10.4 1572.2 1573.2 16.2 1623.1 1624.1 11.4 1573.2 1574.2 8.4 1624.1 1625.6 17.0 1574.2 1575.2 10.6 1625.6 1626.9 20.2 1575.2 1576.9 10.5 1626.9 1628.2 26.1 1576.9 1578.2 8.2 1628.2 1629.2 18.8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. D epth From D epth To Oil Yield D epth From D epth To Oil Yield (Feet) (Feet) (G allons/T on) (Feet) (Feet) (G allons/T on) 1929.2 1630.2 17.3 1630.2 1631.2 21.1 1631.2 1632.2 26.3 1632.2 1633.5 24.3 1633.5 1634.8 18.4 1634.8 1636.2 14.5 1636.2 1637.2 14.4 1637.2 1638.2 20.6 1638.2 1639.4 28.8 1639.4 1640.6 27.5 1640.6 1641.7. 31.6 1641.7 1642.7 27.7 1642.7 1643.6 23.8 1643.6 1644.6 20.4 1644.6 1645.6 25.4 1645.6 1646.6 7.4 1646.6 1647.7 10.7 1647.7 1648.8 14.8 1648.8 1649.9 17 1649.9 1650.9 18.6 1650.9 1652.0 10.5 1652 1653.2 11.6 1653.2 1654.3 12.2 1654.3 1655.4 20.4 1655.4 1656.5 34.2 1656.5 1657.5 18.7 1657.5 1658.5 16.1 1658.5 1659.5 10.4 1659.5 1660.5 7.0 1660.5 1661.5 8.7 1661.5 1662.6 17.6 1662.6 1663.6 10.9 1663.6 1664.6 7.7 1664.6 1665.6 8.7 1665.6 1666.6 5.9 1666.6 1667.6 5.3 1667.6 1668.1 19.2 1668.1 1668.6 11.1 1668.6 1669.2 16.3 1669.2 1670.8 2.6 1670.8 1671.4 15.6 1671.4 1672.4 0.1 1672.4 1674.2 0.1 1674.2 1676.2 0.1 1676.2 1676.6 | 4.1 I 332 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission i ! I ' I I I E x tra c t F ra c tio n W e ig h t (m g) E x tra c t C o m p o s itio n (Wt%) D ep th (Ft) C ycle R o c k W t( g ) E x tra c t W t(g W t % B itu m en S a tu ra te A ro m a tic N SO A s p h a lte n e S a tu ra te A ro m atic N SO A s p h a lte n e S a tu ra te /A ro m a tii 1534.9 Rife 7 8.267 0.0669 0.809 7.30 3 .30 45 .9 0 4 .10 12.12 5 .48 76.21 6 .19 2.21 1535.8 Rife 7 7.885 0.0625 0.793 8.00 2 .60 31 .5 0 14.00 14.45 4 .7 0 56 .9 2 23.93 3.08 1537.9 Rife 7 11.377 0.1 3 2 5 1.165 9.80 3 .6 0 3 4 .9 0 4 .1 0 18.76 6 .8 9 66 .8 2 7.52 2 .7 2 1539 Rife 7 7.200 0.0664 0.922 12.80 4 .7 0 42.8 0 1.90 2 0 .5 9 7.56 6 8 .8 5 3.00 2 .72 1540 Rife 7 6.061 0 .0 2 9 9 0.493 7.20 2 .70 15.70 1.20 2 7 .0 3 10.14 58.9 4 3.90 2 .6 7 1541.3 Rife 6 0 .0 5 2 8 11.00 3.90 36.6 0 2 .5 0 20 .4 0 7 .2 0 6 7 .8 0 4 .60 2.82 1543.2 Rife 6 13.037 0.2746 2.106 10.30 3 .90 37 .7 0 7.90 17.39 6:59 6 3 .6 6 12.36 2 .64 1545.05 Rife 6 0 .0 4 0 2 5.20 2.8 27 .4 0 5 .00 12.9 6 .9 6 7 .8 0 12.40 1.86 1547.8 Rife 6 9.059 0.0418 0.461 11.30 4 .50 18.60 0.60 32.35 12.88 53 ,2 5 1.52 2.51 1630 S ch e g g s 7 3.8 20 0.0191 0.500 1632 S c h e g g s 7 5.9 0 9 0 .0 2 8 2 0.4 8 0 1646.1 S c h e g g s 4 11.503 0.0571 0.5 0 0 1650.5 S c h e g g s 4 14.672 0.0851 0.580 1651.9 S c h e g g s 3 13.562 0.1683 1.241 10.80 1.50 30 .2 0 0 .30 25 .2 9 3.51 7 0 .7 2 0.48 7 .20 1654.5 S c h e g g s 3 14.132 0.0922 0.6 5 2 6.40 1.30 21.20 0 .80 21 .7 4 4 .4 2 72 .0 0 1.85 4 .92 1656.1 S c h e g g s 3 19.415 0.2631 1.355 9.40 2.20 20.00 0 .50 29 .4 3 6 .8 9 6 2 .6 2 1.06 4 .2 7 Topping performed a t 60C under nitrogen stream A sphaltenes:Pentane insoluble, m ethylene chloride soluble traction Oil: Pentane soluble fraction | | Residual*: Pentane and m ethylene chloride Insoluble fraction (* Includes weight loss during processing and/or sed im en t) Appendix 4. Bitumen yields and composition of extracts from Tipton Member, Blacks Fork-1. U 1 CO CO Appendix 4 Appendix 5 M e m b e r/B e d D e p th W e ig h t P e r c e n t (T o tal P y ro ly s a te A re a ) (C y cle) (F e e t) 0 1 o C 5-C 29 BTEX T ipton Rife C ycle 6 1 5 4 4 .3 0 4 3 .5 4 8 .2 8.3 T ipton Rife C ycle 6 1 5 4 7 .0 0 4 .7 81.1 14.1 Tipton Rife C ycle 6 1 5 4 7 .8 0 2 8 .2 6 8 .7 3.1 T ipton Rife C ycle 3 1 5 6 5 .0 0 38.5 6 1 .5 4.2 T ipton Rife C ycle 3 1 5 7 0 .1 0 13.8 67.8 2.1 T ipton Rife C ycle 3 1 5 7 1 .9 0 2 2 .8 74 3 Tipton S c h e g g s C ycle 4 1 6 4 6 .1 0 Tipton S c h e g g s C ycle 4 1 6 4 6 .5 0 T ipton S c h e g g s C ycle 4 1 6 5 0 .0 5 19.9 74.6 5.43 T ipton S c h e g g s C ycle 3 1 6 5 2 .9 5 2 6 .9 69.5 3.5 Tipton S c h e g g s C ycle 3 1 6 5 6 .2 0 17.6 8 0.5 1.9 W ilkins P e a k C ycle 24 1 1 9 2 .0 5 4 7 .5 4 5.7 6.8 W ilkins P e a k C ycle 24 1 1 9 2 .9 2 16.9 79.6 3.5 W ilkins P e a k C ycle 24 119 3 .7 0 34.4 5 8.5 7 W ilkins P e a k C ycle 22 1 2 0 7 .3 0 4 7 .4 4 9 .5 3.1 W ilkins P e a k C ycle 22 12 1 0 .9 5 19 7 2.2 8.7 W ilkins P e a k C ycle 2 2 121 1 .6 0 5.8 90.1 4.1 W ilkins P e a k C ycle 2 2 1 2 1 7 1 .1 0 36.5 60.7 2.8 BTEX is th e su m of b e n z e n e , to lu e n e , x y len es a n d e th y lb e n ze n e. Appendix 5. Quantitative pyrolysis-gas chromatography results for selected Tipton and Wilkins Peak samples; Blacks Fork-1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Appendix 6 P aram eter Form ula Steranes (m/z 217; 218) S/(S+R) (Czgctaa) (217) PP/(aa+3P)(C») (217) S teranes (otppS) (218) D iaster/aaa Ster (C2 7 ) (217) Terpanes (m/z 191) Oleanane/Hopane G am m acerane/H opane N orhopane/Hopane D iahopane/Hopane Moretane/(M oretane+Hopane) Ts/Tm trisnorhopanes Ts/(Ts+Tm) trisnorhopanes H32 S/(R+S) H om ohopanes H35/H34 H om ohopanes H35/H34 H om ohopanes H35/H34 H om ohopanes H35/H34 H om ohopanes H35/H34 H om ohopanes H35/H34 H om ohopanes Com bined (m /z 191; 217) [Steranes]/[Hopanes] [Tricyclic terpanesJ/[Hopanes] [Tricyclic terpanes]/[Steranes] jlVlethylsteranes m/z 231 C28 M ethylsteranes C29 M ethylsteranes C 30 Methylsteranes C29S/(C29S+C29R) (C29BBR+C29BBS)/(C29S+C29BBR+C29BBS+C29R) C29ABBS/C27ABBS (DIA27S+DIA27R)/(C27S+C27R) OL/H30 GAM/H30 H29/H30 DH30/H30 M30/(M30+H30) TS/TM TS/(TS+TM) H32S/(H32R+H32S) (H35R+H35S)/(H34R+H34S) (Desehop)/H30 (Desehop)/(TR26A+TR26B) Tr23/Tr24 Tr19/Tr23 (TR26A+TR26B)/(TR25A+TR25B) (DIA27S+DIA27R+DIA28SA+DIA28SB+DIA28RA+OIA28RB+C27S+BB_D29S+C27BBS+C27R+DIA29R+ C28S+C28BBR+C28BBS+C28R+C29S+C29BBR+C29BBS+C29R)/(TS+TM+H28+H29+C29TS+DH30+H30+ H31R+H31S+H32R+H32S+H33R+H33S+H34R+H34S+H35R+H35S) (TR19+TR20+TR21+TR22+TR23+TR24+TR25A+TR25B+TR26A+TR26B+TR28A+TR28B+TR29A+TR29B+ TR30A+TR30B)/(TS+TM+H28+H29+C29TS+DH30+H30+H31R+H31S+H32R+H32S+H33R+H33S+H34R+ H34S+H35R+H35S) (TR19+TR20+TR21+TR22+TR23+TR24+TR25A+TR25B+TR26A+TR26B+TR28A+TR28B+TR29A+TR29B+ . TR30A+TR30B)/(DlA27S+DIA27R+DlA2BSA+DIA28SB+DlA28RA+D!A2BRB+C27S+BB_D29S+C27BBS+ C27R+DIA29R+C28S+C28BBR+C28BBS+C28R+C29S+C29BBR+C29BBS+C29R) C28 4 a Methyisterane C29 4 a Methyisterane C30 4 a Methyisterane Total H opane C29-C35 (ppm)* C2917a(H )2ip(H )-30-norhopane (L) C2917f3(H)21a(H)-30-nomnoretane (M) C3017a(H)21p(H)-hopane (N) C3117a(H)21p(H)22S,22R hom ohopane (P) C3217a(H )2ip(H )22S,22R hom ohopane (Q) C3317a(H )2ip(H )22S,22R hom ohopane (R) C3417a(H)21p(H)22S,22R hom ohopane (S) C3517a(H)21p(H)22S,22R hom ohopane (T) C29Tm 17aH21p(H)-norhopane C29 norm oretane C30 17a(H )-hopane r D efined from C arrol e t al., 1993 Appendix 6 Definitions and form ulas for GCMS biomarker param eters. 335 * Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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Teerman, Stan Carl
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Characterization of geochemical and lithologic variations in Milankovitch cycles: Green River Formation, Wyoming
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