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Structure and origin of echinoid beds, unique biogenic deposits in the stratigraphic record

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Structure and origin of echinoid beds, unique biogenic deposits in the stratigraphic record

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Content INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. 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 bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI 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. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. 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STRUCTURE AND ORIGIN OF ECHINOID BEDS, UNIQUE BIOGENIC DEPOSITS IN THE STRATIGRAPHIC RECORD by Heather Ann Moffat A Thesis Presented to the FACULTY OFTHE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER IN SCIENCE (Earth Sciences) August 1996 Copyright 1996 Heather Ann Moffat Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1381599 UMI Microform 1381599 Copyright 1996, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY O F SOUTHERN CALIFORNIA TH E GRADUATE SCHOOL. UNIVERSITY PARK LOS A N Q C L tt. CALIFORNIA * 0 0 0 7 This thesis, w ritten by H eather Ann MoCfat_______________ under the direction of h§s£ Thesis C om m ittee, and approved by all its members, has been pre sented to and accepted by the D ean of The Graduate School, in partial fulfillm ent of the requirements fo r the degree of Mas t e r o f S c ie n c e Dem lOMMITTEE th e; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This thesis is dedicated to my mother and father for their unconditional love and support Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS I wish to acknowledge the generosity of the following sponsors: the AMOCO Corporation, the Paleontological Society, Sigma Xi, The U.S.C. Trojan League and the U.S.C. Department of Earth Science's Graduate Student Research Fund. I would also like to thank the Twisselman family for permission to explore the Buttonbed localities on their beautiful ranch. I extend my appreciation to the many people who have invested both time and energy in helping me complete this project, especially Ben Greenstein, A 1 Fischer, Jean Morrison, Kathy Campbell and Sherman Suter. Also, I would like to thank my field assistants, Stephen Schellenberg, Anne Koob, Deanne Sabarese, and Michael Neumann, for their patience and enthusiasm on those long, hot days. There were many friends and colleagues at U.S.C. who were supportive during my stay, particularly my lab mates: Nicole Fraser (who has been an invaluable contributor to both my academic career and personal sanity for many years) Whitey Hagadom, Stephen Schellenberg, Carol Tang (who has often held my hand and answered my endless questions this semester), Adam Woods, and Karen Whittlesey. I could always get a quick and humorous (if not correct) answer from any one of them. I also wish to thank my roommates, Becky Robinson and Julia Smith, for making our home such a happy sanctuary during this past year. My days at the beach will be among my favorite memories of my time here. Lastly, I wish to thank my advisor, David Bottjer, for his endless patience and support His encouragement and incredible repetoire of puns made many of the "difficult times" seem quite manageable. I thank Dave for his great advice and support throughout this project particularly during the crazy final semester. With that, I also Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. thank my other committee members, Donn Gorsline and Loren Smith, for their advice and cooperation in these final months. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V TABLE OF CONTENTS DEDICATION...................................................................................................................ii ACKNOWLEDGEMENTS...............................................................................................iii LIST OF FIGURES..........................................................................................................vii LISTOFTABLES............................................................................................................ x ABSTRACT...................................................................................................................... xi CHAPTER 1: INTRODUCTION.................................................................................... 1 The Echinoid Fossil Record................................................................................. 2 Preservation Potential and the Echinoid Fossil Record......................................... 3 Echinoid Concentration Beds................................................................................4 CHAPTER 2: BUTTONBED SANDSTONE ECHINOID BED..................................... 11 Historical Background on the Temblor Formation, San Joaquin Basin, CA......................................................................................................................... 11 The Geology and Stratigraphy of the Type Temblor Formation............................13 Geology and Stratigraphy of the Buttonbed Sandstone Member..........................23 Field Methods and Sampling Strategies................................................................31 Laboratory Methods of Data Collection................................................................37 Stratigraphy and Sedimentology of the Buttonbed Sandstone Echinoid Bed........................................................................................................................ 41 Sedimentary Petrography of the Echinoid Bed..................................................... 55 Faunal Components of the Buttonbed Sandstone Echinoid Bed..........................70 Composition............................................................................................. 70 Paleobiological Analysis of Vaquerosella merriami.................................. 73 Test Shape and Proportions...........................................................76 Petal Development........................................................................77 Food Groove Pattern....................................................................77 Pillars............................................................................................77 Summary...................................................................................... 78 Abundance and Distribution Patterns........................................................78 Taphonomy...............................................................................................91 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vi CHAPTER 3: THE VIRGIN LIMESTONE ECHINOID BED........................................94 Geology and Stratigraphy of the Moenkopi Formation, southwestern Nevada..................................................................................................................94 Virgin Limestone Member of the Moenkopi Formation, Lost Cabin Springs, Nevada................................................................................................... 100 Reid Observations and Sampling Strategies..........................................................108 Laboratory Methods of Data Collection................................................................ 110 Stratigraphy and Sedimentology of the Virgin Limestone Echinoid Bed...............119 Sedimentary Petrography of the Echinoid Bed......................................................121 Faunal Components of the Virgin Limestone Echinoid Bed................................. 127 Composition.............................................................................................. 127 Abundance and Distribution Patterns........................................................ 132 Taphonomy............................................................................................... 142 Petrographic Examination of the Virgin Limestone Echinoid Bed.............................................................................................................146 CHAPTER 4: DISCUSSION...........................................................................................152 Comparison of the Two Echinoid Beds.................................................................152 Echinoid type.............................................................................................152 Depositional environment.......................................................................... 153 EvoIutionaryTiming.................................................................................. 154 Accumulation Processes.............................................................................155 Echinoid-rich deposits of the fossil record............................................................ 164 Virgin Limestone Echinoid Bed of S t George, Utah................................ 164 Merriamaster Bed, Kettleman Hills North Dome, CA...............................166 The Impact of Preservational Style and Taxonomic Wealth on the Classification of Echinoid Deposits....................................................................... 167 Implications and Future Research..........................................................................169 CHAPTER 5: CONCLUSIONS......................................................................................172 BIBLIOGRAPHY.............................................................................................................176 APPENDICES.................................................................................................................. 188 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vii LIST OF FIGURES Figure 1. Schematic diagrams of the geometry of plate sutures within the echinoid corona. A = Flexible or imbricated test (e.g. Archaeocidaris). Arrows indicate relative motion of plates. B = Rigid test (e.g. cidaioids after the Late Ttiassic). C = Rigid test with strongly interlocking trabeculae or peg and socket structures (e.g. Meoma). D = Rigid test of Clypeaster with double wall (From Donovan, 1991)......................................................................................................5 Figure 2. General locality map of the two echinoid bed study sites. CMC = Buttonbed Sandstone echinoid bed at Chico Martinez Creek, CA. LCS = Virgin Limestone echinoid bed at Lost Cabin Springs, NV.................................. 8 Figure 3. Locality map of the Miocene Buttonbed Sandstone Member of the Temblor Formation of the western San Joaquin Basin, CA. CMC = Chico Martinez Creek locality.......................................................................................................14 Figure 4. Outcrop of Temblor strata in vicinity of type area. Geology from Dibblee (1977), from Carter (1990)................................................................................. 16 Figure 5. Stratigraphy of the Temblor Formation and surrounding formations (Modified from Carter, 1985b)........................................................................ 18 Figure 6. Diagrammatic cross-section illustrating the lenticularity of the Buttonbed Sandstone member (from Carter, 1985a).........................................................24 Figure 7. Photograph of outcrop of the Buttonbed Sandstone on Buttonbed Hill near Chico Martinez Creek. The three lithofacies are labeled as follows: A = lower bioturbated sandstone lithofacies, B = thick sandwave interval, and C = the Buttonbed coquina................................................................................................ 27 Figure 8. Schematic illustrations of relative packing categories for skeletal material greater than 2 mm (Kidwell and Holland, 1991)................................................. 32 Figure 9. Held fossil abundance point-count technique for Buttonbed sand dollars. w X”s mark the sampling positions. Note: not to scale........................................35 Figure 10. Examples of percent-volume charts for bioclasts of different shapes (From Kidwell and Holland, 1991; Schafer, 1969)............................................. 39 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. viii Figure 11. Measured sections of the Buttonbed echinoid bed from Stations B1-B9 at the Chico Martinez Creek locality. Scale in meters..........................................42 Figure 12. Photomicrograph showing the edge of a recrystallized sand dollar from sample BID, Station B7. Plate boundaries are marked by the black arrows. Held of view is 2.6 mm. Above is plane light; below is polarized lig h t................................................................................................................................ 59 Figure 13. Photomicrograph of glauconitic (A) nodules and (B) ooids from sample P5, Station B5. Held of view is 2.6 mm, plane light........................................61 Figure 14. Photomicrograph of articulated pecten with infilling geopetal structure from sample Flh- Reid of view is 2.6 mm, plane light.................................67 Figure 15. Illustration of the two species of VaqueroseUa observed in the Buttonbed Sandstone Member. A - V . andersoni (Twitchell). B = V . merriami (Anderson). Note scale (Modified from Addicott, 1972)................................ 74 Figure 16. Photograph of poorly sorted sand dollars located near Station B7. Specimens range in size from 0.5 to 2 cm in diameter.....................................................86 Figure 17. Triassic stratigraphy of the western United States. The Moenkopi Formation of southwestern Nevada is marked with arrows (From Schubert, 1993)................................................................................................................................95 Figure 18. Map showing simplified regional paleoenvironments (From Schubert, 1989)................................................................................................................98 Figure 19. Locality map of the Triassic Virgin Limestone Member of the Moenkopi Formation study site at Lost Cabin Springs, NV............................................101 Figure 20. Outcrop photograph of the Virgin Limestone Member at Lost Cabin Springs, Nevada. Location of the Virgin Limestone echinoid bed is marked by the white arrow.............................................................................................. 103 Figure 21. Measured section of Schubert's Unit 15 from Lost Cabin Springs, NV (Modified from Schubert, 1989)................................................................ 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ix Figure 22. Measured sections of the Virgin Limestone echinoid bed from Stations 1 ,2 ,4 ,5 , and 6 at Lost Cabin Springs. Scale is in meters...............................112 Figure 23. Photomicrograph of ragged silicification of a echinoid spine from sample 5B Lower, Station 5. The silicified region is marked by the black arrow. Reid of view is 2.6 mm, plane lig h t...................................................................123 Figure 24. Photograph of silicified spines in outcrop at Station 2. Three of the spines are marked by white arrows. Swiss army knife below for scale..................... 130 Figure 25. Photograph showing spine distribution within the Virgin Limestone echinoid bed near Station 5. Scale is in cm.....................................................134 Figure 26. Schematic ternary diagram of genetic types of shell beds (From Kidwell, Fiirsich and Aigner, 1986)..................................................................................156 Figure 27. Expected relative abundances of shell bed types along an onshore-offshore transect in a marine setting dominated by terrigenous sedimentation (Rom Kidwell, Fiirsich and Aigner, 1986)............................................. 162 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. X LIST OF TABLES Table 1. Petrographic information for samples examined from the Buttonbed Sandstone echinoid bed and the underlying sandwave lithofacies................................... 56 Table 2. Macrofauna from the Buttonbed Sandstone Member (Modified from Carter, 1985).....................................................................................................................71 Table 3. Results of field analysis of fossil abundance, packing, relative orientation and taphonomic condition............................................................................... 79 Table 4. Held and hand sample results from fossil abundance analysis.......................88 Table 5. Results from hand sample analysis of fossil abundance, packing and orientation...........................................................................................................................136 Table 6. Results of fossil abundance analysis using random and nonrandom sampling techniques......................................................................................................... 140 Table 7. Results of taphonomic analysis of degrees of spine striations and presence/absence of spine tips..........................................................................................143 Table 8. Petrographic information for samples examined from the Virgin Limestone echinoid bed and the surrounding lithologies................................................. 147 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Echinoid concentrations provide insight into the role of shell composition and taphonomic resilience in the formation of shell bed types. The two groups of echinoids, regular and irregular, have very different taphonomic characteristics, such as hydrodynamic structure and post-mortem skeletal resilience, and result in distinct types of fossil accumulations. Examination of the different types and reconstruction of their accumulation histories provides a better understanding of these unique fossil concentrations. It has been hypothesized that much of the diversity of the echinoid fossil record comes from specimens that occur in shell beds rich in echinoid material. It is therefore important to understand the depositional histories of echinoid-rich deposits (echinoids as >50% of macroscopic fossil material observed in the deposits) to better decipher the biases of the echinoid fossil record. This study focuses on two echinoid concentrations which represent extreme examples of echinoid-rich fossil beds (echinoids >75% of macroscopic fossil material). The Buttonbed Sandstone coquina of the Miocene Temblor Formation (central California) ranges in thickness from 1 to 4.1 m.. The echinoid bed is composed primarily of the sand dollar Vaquerosellamerriami (0.5 and 2 cm in diameter), but pecten and barnacle fragments are also present In general, the coquina can be subdivided into an upper hash layer of sand dollar fragments and a lower coarse grained sandstone comprised of more complete specimens. Fossil abundance, distribution and taphonomic conditions are highly variable both laterally and vertically within the lower subunit, with sand dollars comprising up to 80% of the bed. This lower subunit is a multiple event concentration produced by significant reworking of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xii fossil material, perhaps by current winnowing and/or storm activity. The upper hash layer results from additional reworking of the lower subunit Taphonomy of individual specimens within the coquina reinforces the conclusion that this shell bed is a product of multiple high energy events which incorporated many generations of V. merriami into a winnowed, coarse-grained fossiliferous deposit The Virgin Limestone Member echinoid bed (1-2.5 m thick) is a LowerTriassic sea urchin spine bed located in the Moenkopi Formation of southwestern Nevada. The concentration appears to be a monospecific accumulation of regular echinoid spines; although unidentified echinoderm, bivalve and microgastropod material have been identified in petrographic analysis, no other fossil material has been observed on the macroscopic level. The spines (1-6 mm in diameter) appear to belong to an undescribed echinoid genus. They are partially silicified and increase in abundance upsection within the limestone unit. Spines show no consistent orientation relative to the bedding plane and their distribution varies both laterally and vertically with occasional lenses and stringers, suggesting significant reworking of the deposit The spines are the only megascopic skeletal component to remain intact as the other megascopic fossil material was eliminated by taphonomic processes. The two very different echinoid beds provide insight into the variety of factors which lead to the formation of echinoid-rich deposits. The Buttonbed coquina is a coarse-grained deposit which formed as a result of a combination of physical and biological controls; it is clear that V. merriami was abundant within the area but the overall stratigraphy of the bed results from physical processes acting upon the depositional environment In contrast the Virgin Limestone echinoid bed is the only unit within the study area which is comprised of echinoid spines, suggesting a primarily biological control on the nature of the bed. The spines are partially silicified, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. indicating a strong diagenetic influence on the deposit's appearance. Stratigraphic, sedimentologic and taphonomic characteristics of the bed, however, indicate that its formation is a result of sedimentologic processes. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 CHAPTER 1: INTRODUCTION For paleontologists, bioclastic deposits are often "the key to the past." Clues within the deposits provide information which enables a reconstruction of ancient environments and their depositional histories. Shell beds have been a prominent topic of paleontological research in recent years (Seilacher, 1982; Kidwell and Jablonski, 1983; Kidwell, 1985; Kidwell etal, 1986; Davies etal., 1989a, 1989b; Kidwell, 1991a, 1991b, Kidwell and Bosence, 1991; Kidwell and Holland, 1991; Ketcher and Allmon; 1993). Such accumulations are very diverse with many forms present in the stratigraphic record. In fact, the term "shell bed" is applied to any concentration of invertebrate skeletal parts within a terrigenous or carbonate matrix. Composition varies greatly within shell beds to include all invertebrate skeletal material exceeding 2 mm in diameter (skeletal material less than 2 mm in diameter is considered matrix; Kidwell, 1991). Although shell bed workers have stated the importance of factors such as faunal types and life habits of fossils in the reconstruction of accumulation histories and the interpretation of depositional environments (e.g. Kidwell, 1991a and Kidwell and Hoffman, 1991), no one has included composition as a discriminating part of their classification systems. Shell bed composition is equally important as life mode information in understanding the history of a fossil concentration. Different shell beds (composed of different types of "shells") hold distinct characteristics relative to the shell types they contain. For example, a concentration of rudist bivalves will exhibit very different characteristics (e.g. bed geometry, degree of articulation) than an encrinite which underwent similar conditions. Shell bed workers must understand the importance of shell features on the overall fossil accumulation, such as the relationship Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. between shell dimension and relative packing within a bed (Kidwell and Holland, 1991). Also, it is vital that they recognize that shell types are affected differently by taphonomic processes and that the taphonomic characteristics of shells will produce very different kinds of accumulations. Knowledge of how individual fossil elements are affected by different processes and/or different durations in the Taphonomically Active Zone (orTAZ; Davies et al„ 1989a) is necessary in order to accurately reconstruct the accumulation histories of the concentration which the elements comprise. Echinoid-rich accumulations provide an excellent example of the importance of shell composition in understanding shell bed formation. The two groups of echinoids, regular and irregular, have very different taphonomic characteristics, such as hydrodynamic structure and post-mortem skeletal resilience, and result in distinct types of fossil accumulations. Because it is relatively difficult to preserve echinoids (particularly regular echinoids), concentrations of these fossils offer unique insight into the deposits' histories. Taphonomic, stratigraphic and sedimentologic characteristics of echinoid beds are important tools in the interpretation of the depositional environments and accumulation histories of the beds. The Echinoid Fossil Record Class Echinoidea has a long and abundant fossil record. Echinoids first appeared in the Upper Ordovician and reached a Paleozoic diversity peak in the Upper Carboniferous (Smith, 1984; Bambach, 1985). Following this peak in diversity, the class experienced a steady decline in diversity, reaching its lowest point at the Permian- Triassic boundary. Only two genera and three species of echinoid are recorded for the Upper Permian and only two species are reported for the Lower Triassic (Kier, 1977b; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Smith, 1990). Species numbers begin to increase beginning in the Upper Triassic marking the start of a radiation which continued through the Mesozoic and Cenozoic to present day. The radiation of Echinoidea is thought to have resulted from two factors: (a) the conserved diversity (with replacement) of cidaroids and (b) the immense diversification of the subclass Euechinoidea, which includes all irregular echinoids (Bambach, 1985; Smith, 1984; Greenstein, 1992). Irregular echinoids first appeared in the early Jurassic and rapidly diversified as they exploited previously unoccupied niches, infaunal soft bottom ecospaces (Smith, 1984). The most recent group of echinoids to evolve was the clypeasteroids, including the sand dollars, which first appeared in the Paleocene (Smith, 1984). Preservation Potential and the Echinoid Fossil Record There appears to be a preservational bias in the echinoid fossil record which favors preservation of irregular echinoid fossil material over that of regular echinoids. Kier (1977) documented that the regular echinoid record is poor compared to the irregular echinoid record. He found that only 20% of known echinoids from the Tertiary are regular echinoids whereas today 53% of all living echinoids are regular echinoids. Smith (1984) identified two sources of bias leading to the dramatic difference in preservation potential between the two groups. First, the type of environments that the two groups evolved and diversified in are quite different Regular echinoids evolved and diversified as grazers and most prefer shallow water, firm ground or rocky strata (Smith, 1984; Barnes, 1987). Such environments are the site of active erosion and would disfavor preservation. Irregulars, however, evolved and diversified as deposit feeders and most prefer to live on or in unconsolidated Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sediments (Smith, 1984; Barnes, 1967). Such environments are areas of active sedimentation, which would promote preservation. The second factor which accounts for the difference in preservation potential between the two groups is the rigidity of their tests. There are a wide variety of test structures found among echinoids which each exhibit different degrees of resilience during life and post-mortem (Figure 1). Preservation potential is greater for those organisms with more rigid tests. Overall, regular echinoids tend to have less resilient tests than irregulars. Recent actualistic studies have aided in understanding the disarticulation threshold of regular echinoid test material and have concluded that test resilience is highly variable even within families (Kidwell and Baumiller, 1989; Greenstein, 1990,1991). Differences in test rigidity, as well as environmental preferences, have changed over the evolutionary history of the Echinoideaand as a result, knowledge of post-Paleozoic echinoids is greater than what is understood of the Paleozoic history of this group. Echinoid Concentration Beds As little previous research has been done on the description and interpretation of echinoid concentration beds, it is necessary to provide a list of working terminology regarding echinoid-rich deposits. This study expands upon Kidwell, Fiirsich and Aigner's (1986) definition of a shell concentration ("any relatively dense accumulation of biologic hardparts, irrespective of taxonomic composition, state of preservation, or degree of post-mortem modification") to include relative compositional abundance as a discriminating factor in determining an "echinoid-rich deposit" from an "echinoid bed." For this study, an "echinoid-rich deposit" is a shell bed in which at least 50% of the megascopic fossil material (greater than 2 mm) is echinoid material. Within this Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 Figure 1. Schematic diagrams of the geometry of plate sutures within the echinoid corona. A = Flexible or imbricated test (e.g. Archaeocidaris). Arrows indicate relative motion of plates. B = Rigid test (e.g. cidaroids after the Late Triassic). C = Rigid test with strongly interlocking trabeculae or peg and socket structures (e.g. Meoma). D = Rigid test of Clypeaster with double wall (From Donovan, 1991). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. same classification scheme, an "echinoid bed" is herein described as a shell bed in which over 75% of the megascope fossil material is echinoid material. Because of the high percentage of taphonomically responsive fossil components within them, echinoid beds provide particularly important insight into the role of shell composition in the formation of different types of shell beds. This study focused on two echinoid beds: an irregular echinoid (sand dollar) bed within the Miocene Buttonbed Sandstone (Temblor Formation) of central California and a regular echinoid (sea urchin) spine bed within the Triassic Virgin Limestone (Moenkopi Formation) of southwestern Nevada (Figure 2). The two fossil accumulations provide very different examples of an echinoid bed. They are comprised of different types of echinoids which were deposited in very different environments (siliciclastic vs. carbonate) during different stages in the evolutionary history of echinoids (the prosperous Cenozoic vs. slow recovery from the Permian-Triassic mass extinction). The purpose of this study is to examine the two echinoid beds in order to better understand the unique characteristics and depositional histories of echinoid beds. To achieve this objective, this thesis will: 1) Describe the stratigraphic, sedimentologic, paleontologic and petrographic characteristics of the two echinoid concentrations and assess the information that these features provide about the echinoid beds themselves. 2) Interpret the depositional environment and accumulation histories of the two examined beds. 3) Compare and contrast the two echinoid beds in order to make general observations about the formation of echinoid beds. The two echinoid beds are placed within Kidwell, Fiirsich and Aigner's (1986) genetic classification scheme based on the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2. General locality map of the two echinoid bed study sites. CMC = Buttonbed Sandstone echinoid bed at Chico Martinez Creek, CA. LCS Virgin Limestone echinoid bed at Lost Cabin Springs, NV. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission 10 primary factors (biogenic, sedimentologic, diagenetic, or a combination) which influenced their formation. 4) Discuss the characteristics and accumulation histories of several other prominent examples of echinoid-rich deposits in the stratigraphic and fossil record. 5) Discuss the role which echinoid-rich deposits, such as echinoid beds, play in the interpretation of the echinoid fossil record. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 CHAPTER 2: BUTTONBED SANDSTONE ECHINOID BED Historical Background on the Temblor Formation, San Joaquin Basin, CA The Temblor Formation represents a series of depositional sequences which outcrop over 100 miles across the western portion of the San Joaquin Basin. The Tertiary-aged formation includes rocks from the early Oligocene (lower Zemorrian) to the late early Miocene (lower Relizian). Although the "Temblor" rocks have been described in the stratigraphic literature for over 90 years (Anderson, 1905), it is only within the last 25 years that the ambiguous nomenclature surrounding the Temblor Formation has begun to be clarified. Much of the confusion surrounding the terminology comes from the application of the terms " Vaqueros" and "Temblor" for the generally sandy, fossiliferous, Oligo- Miocene sequences found along the western North American coast (Arnold, 1909; Clark, 1921,1929; Clark and Clark, 1935; Kleinpell, 1938; Weaver etal, 1944; Corey, 1954; Durham, 1954; Dibblee, 1968,1973; Bandy and Amal, 1969). "Vaqueros" was originally applied to sandstones of the Santa Lucia Range (Hamlin, 1904) around the same time that Anderson applied the term "Temblor" to similar rocks of the Coast Ranges. Due to the similarity of the sequences which the two terms designated, "Vaqueros" and "Temblor" have often been used inconsistently and interchangeably, resulting in a confusing collection of literature (see Graham, 1985; Calloway, 1988). In 1973, Dibblee attempted to clarify the nomenclatural ambiguity by proposing a division based on geographic position relative to the San Andreas Fault: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 Oligo-Miocene rocks located west of the San Andreas Fault would be from the "Vaqueros" while those located east of the fault would be "Temblor". Biostratigraphic studies of the Oligo-Miocene rocks of the western North American Coastal Ranges both clarified and further confused the issue. Both provincial molluscan stages (Addicott, 1972) and foraminiferal zonations (Kleinpell, 1938) aided in the determination and correlation of the ages of the marine Tertiary strata of the region. Unfortunately, the studies categorized the biostratigraphic stages into the "Vaqueros" stage (provincial upper Oligocene to lower Miocene) and the "Temblor" stage (provincial middle Miocene). Thus, both terms are not only pertaining to the lithostratigraphy of the area but also to the biostratigraphy of the Coastal Ranges. In addition to his geographic designations, Dibblee (1973) also tried to resolve the nomenclature! problem by describing a type section for the Temblor Formation. This type area is located between Cameras and Zemorra Creeks in the western margin of the San Joaquin Basin and is the locality in which this study's focus, the upper member of the formation, lies. Dibblee's type section allowed for a first detailed description of type members of the Temblor Formation. It should be noted, however, that until the mid-1980s, his description was still fit into the old biostratigraphic framework of the "Vaqueros" and "Temblor" stages, thus maintaining nomenclatural confusion. Beginning in the mid-1980s, a renewed interest in the geology and stratigraphy of the San Joaquin Basin produced an explosion of new literature on the Temblor Formation and its surrounding formations, including numerous papers and at least four SEPM volumes on the geology, structure and stratigraphy of the basin. The vigorous research activity, led primarily by Steven Graham and his students from Stanford University, has greatly clarified the nomenclatural problem, leading to better correlation Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 of the Oligo-Miocene rocks of the Pacific Coast of North America. In addition, the extensive Held and subsurface studies on the stratigraphy and depositional environments of the Temblor Formation have led to an increasing understanding of the formation of the Oligo-Miocene sequences within it (Cooley, 1982, Kuespert, 1983; Bate, 1984; Bent, 1985; Carter, 1985a; Pence, 1985 and others). The Geology and Stratigraphy of the Type Temblor Formation The type area of the Temblor Formation is located on the western side of the San Joaquin Basin, within the eastern foothills of the Temblor Range (Figures 3 and 4). The formation is present in eight mappable units which span from Cameras to Zemorra Creeks and comprise four partial and complete depositional sequences: (1) the lower Zemorrian Cymric Shale sequence; (2) the lower and upper Zemorrian Wygal Sandstone and lower Santos Shale sequence; (3) the Saucesian sequence; and (4) the basal portion of the Monterey sequence, which is represent by the Relizian Buttonbed Sandstone (Figure 5). Together, the four depositional sequences document the major tectonic uplifts which affected the Coastal Range during the Oligo-Miocene, thus reflecting the rapidly changing dynamics of the active continental margin of the Tertiary Pacific Coast of North America. The first depositional sequence in the Temblor Formation, the lower Zemorrian Cymric Shale sequence, is comprised of one member, the Cyrmic Shale. The shale member is poorly exposed and heavily weathered, making it difficult to identify small scale lithologic features. The Cymric Shale contains a high percentage of sand and silt and a foraminiferal assemblage which suggests a lower to middle bathyal range of 1500 to 2000 m during deposition. The abundance of BidimneUacurta, an outer shelf Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 Figure 3. Locality map of the Miocene Buttonbed Sandstone Member of the Temblor Formation of the western San Joaquin Basin, CA. CMC = Chico Martinez Creek locality. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 figure 4. Outcrop of Temblor strata in vicinity of type area. Geology from Dibblee (1977), from Carter (1990). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 T28S R19E T29S R19E T28S R20E N nT29S R20E \ 1800 Ridge \ / Little Hill Buttonbed Hill C Cameras Creek CMC Chico Martinez Creek D Devilwater Creek M Media Agua Creek S Salt Creek SC Stone Corral Canyon SN Santos Creek ST Slratigraphic Trench T Temblor Creek Z Zemorra Creek / / Z ' “ /S T O P 1-1 y 'tP O iM T OF f RO CK S) 1 nl 1 Ion Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 Figure 5. Stratigraphy of the Temblor Formation and surrounding formations (Modified from Carter, 1985b). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SERIES 8TAOE AND ZONE FORM ATION A N D M EM BER Z UPPER MONTEREY FORMATION N «J HI C c HI * o BUTTONBED S3 0-61ia HI Z HI O 0 1 5 c NVI8390V8 UPPER M EDIA SH 7Sm < HI * MIDDLE I g Ik B O .1 S P CARNEROS 8 8 62m-178m T s U. 8ANTOS6H 10m AQUA 8 8 Sm-SOtn 1 O Z < S K o ! L. SANTOS 8H 88m o s 3 o s K c £ WYOAL 8 8 4£(n 61 rti o .J CYMRIC SH 0m-18m U1Q refuqian TUMEY SH Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 form (Ingle, 1980), combined with the sedimentology of the Cymric Shale suggests a downslope displacement by gravity-slope processes (Carter, 1985a). Carter proposes that the overall lack of turbidite beds (ex’any environmentally diagnostic sedimentary structures) within the member is the result of a slow sedimentation rate and rapid homogenization by bioturbators in the well-oxygenated bottom waters. The Zemorrian Cymric Shale is unconformably overlain by the Wygal Sandstone-Lower Santos Shale sequence, which followed a cycle of tectonic uplift and erosion. The lower member of the sequence, the Wygal Sandstone, is lower Zemorrian in age and is subdivided into three lithofacies: a sporadically-occurring basal sandstone, a highly fossiliferous sandy siltstone, and an upper unit of glauconitic and phosphatic sandstone. The coarse-grained nature and faunal composition of the basal sandstone is indicative of a high energy, inner neritic environment (Carter, 1985a). The faunal composition of the unit, including well-rounded shark teeth, bone fragments and a Crassostrea oyster reef, confirms a shallow marine origin, perhaps less than 18 m (Addicott, 1973). The highly fossiliferous siltstone lithofacies is characterized by a large molluscan assemblage indicative of deposition in the upper part of the inner sublittoral zone, between 18 and 37 m (Addicott, 1973). The third lithofacies, the glauconitic and phosphatic sandstone, is over 75% glauconite grains in some areas. The combination of the presence of abundant glauconite and phosphate and the composition and low diversity of the sandstone's foraminiferal assemblage suggests that this unit represents a long depositional hiatus in the reducing environment of an outer shelf or upper bathyal setting. The second member of the sequence, the lower Santos Shale, records an abrupt change to deposition in middle bathyal depths. Changes in the foraminiferal assemblages of the clayey shale member document a progressive shoaling during Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 deposition from middle bathyal depths of 1500 to 2000 m to upper bathyal depths of 150 to 200 m, which is thought to reflect the initial phase of the next cycle of uplift (Tipton et al, 1973; Carter, 1985a). The degree of shoaling appears to be too great (over 1000 m) to result from sediment infilling or a eustatic fall in sea level. The lower Santos Shale is unconformably overlain by the third depositional sequence of the Temblor Formation, the Saucesian sequence. This depositional sequence is comprised of four members: the Agua Sandstone (latest Zemorrian), the upper Santos Shale (lower Saucesian), the Cameras Sandstone (middle Saucesian) and the Media Shale (upper Saucesian). The uplift which preceded the deposition of the relatively shallow marine Agua Sandstone is most likely a continuation of the uplift which began during the deposition of the lower Santos Shale (Carter, 1985a). The Agua Sandstone is the basal transgressive sand in the sequence and is characterized by in situ Crassostrea reefs in the northern portion of the type area, suggestive of a shallow marine inner neritic environment (Addicott, 1973). Toward the southern portion of the type area, however, the Agua Sandstone is present as a condensed phosphatic sandstone, indicative of a sediment-starved outer shelf or an inner neritic sandstone in the northern portion of the type area and a condensed, outer shelf inner or upper slope. The upper Santos Shale rests conformably on the Agua Sandstone and is early Saucesian (earliest Miocene) in age (Foss and Blaisdell, 1968). Foraminiferal evidence within the shale indicates that the unit marks the return to deposition at middle to lower bathyal depths (Tipton et al, 1973). The unit is comprised of a heavily bioturbated, silty clay shale which is consistent with a middle to lower bathyal interpretation. The Cameras Sandstone member is a thick series of sandstones and interbedded shales which represent the relatively deep marine setting of an inner to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 2 middle submarine fan facies (Graham et al, 1982; Carter, 1985a). Presence of lenticular conglomerates within the proximal submarine fan deposits of the Cameras Sandstone represent an abrupt influx of coarse elastics, perhaps due to an early to middle Saucesian orogenic event to the northwest (Carter, 1985b). Vail et al's (1977) sea level curve for the Miocene indicates that the Saucesian was a time of gradual rise in sea level, therefore indicating that tectonic, rather than eustatic controls, were the primary controls on the deposition of the Cameras Sandstone. Overlying the Cameras Sandstone is the Media Shale, the fourth and final member of the Saucesian depositional sequence. The shale member can be subdivided into two portions: the lower part of the Media Shale, which is a massive clayey shale containing the occasional finely laminated intervals of silt and very fine sand, and the upper part of the unit, which is more siliceous, platy and laminated than the lower portion. Foraminiferal evidence from the lower Media Shale indicate deposition at a middle bathyal depth of 500 to 2000 m (Tipton et al, 1973). Sedimentation of the lower portion was clearly dominated by pelagic processes. The siliceous upper Media Shale is mostly likely biogenic in origin, reflecting an increase in diatom production (Carter, 1985b). Abundant phosphatic nodules within the upper Media Shale are supporting evidence of an organic-rich environment Progressive shoaling from a slope environment to a higher shelf-break setting is documented within the upper Media Shale through the changes in distribution of the phosphatic nodules; the first occurrence of phosphatic nodules within the upper Media is within turbidite layers, which came from the starved shelf and nearby banktops, and later occurrences place the nodules in situ in laminated dolomites (Carter, 1985a). This shoaling within the Media Shale is indicative of initial stages of the next and final cycle of uplift recorded in the Temblor Formation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 Following the tectonic uplift and erosion initialed during the deposition of the Media Shale, the Buttonbed Sandstone member was deposited. It is evident that the deposition of this youngest member of the Temblor Formation postdated a period of significant tectonic deformation and uplift' the Buttonbed lies unconformably upon several different members in different areas of its distribution, including the middle Eocene Point of Rocks sandstone, the lower Santos Shale, the Agua Sandstone, the upper Santos Shale and, in the type area, the Media Shale. This sandstone is the basal transgressive sand of the Monterey depositional sequence and is conformably overlain by the bathyal Gould Shale, the oldest member of the Monterey Formation (Kleinpell, 1938; Stinemeyer et al, 1959; Dibblee, 1973; Carter, 1985a; Calloway, 1988). The following section describes the youngest member of the type Temblor Formation in greater detail. Geology and Stratigraphy of the Buttonbed Sandstone Member The Buttonbed Sandstone member outcrops for a distance of approximately 31 km along the western margin of the San Joaquin Basin, from Packwood Creek in the northwest to Zemorra Creek in the south (Heikkila and MacLeod, 1951). The sandstone member is highly lenticular in nature, ranging in outcrop thickness from 0 to 245 m and up to 180 m thick in the subsurface (Wharton, 1943). This lenticularity suggests that the fold-related paleotopography of the early Relizian had some influence, at least locally, on the deposition of the sandstone member (Carter, 1985a; see Figure 6). The Buttonbed Sandstone is an important reservoir rock within the basin, extending as far northeast as the Lost Hills Oil Field, which is located 30 km from the type area (see Figure 4). Several oil fields utilize the Buttonbed Sandstone within the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 Figure 6. Diagrammatic cross-section illustrating the lenticularity of the Buttonbed Sandstone member (from Carter, 1985a). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 iU < / > O ui w o vj Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 6 San Joaquin valley, including Antelope Hills, North Antelope Hills. McDonald Anticline and North Belridge (Carter, 1985a). The Buttonbed Sandstone member is late early Miocene in age. Biostratigraphic studies based on provincial molluscan stages have placed the member in the "Temblor" Stage (Smith, 1912; Loel and Corey, 1932; Addicott, 1973). Foraminiferal analysis of the sandstone has led to its placement into the Siphoeenerina huehesi Zone of the Relizian Stage, giving it an approximate age of 17 to 18 million years (Stinemeyer et al, 1959; Foss and Blaisdell, 1968). This study will focus on the uppermost portion of this Relizian deposit. The study area is the Chico Martinez Creek locality within the type area (see Figure 4). The best outcrop exposures of the Buttonbed Sandstone are on two knolls, Buttonbed Hill and "1800" Ridge. Buttonbed Hill is a low knoll situated between the Chico Martinez and Zemorra Creeks at the southern end of the type area (Figure 7). Up to 60 vertical m of the Buttonbed Sandstone is exposed on this hill. Located 1220 m north of Buttonbed Hill, the north-south trending" 1800" Ridge (named for its height of 1800 ft) exhibits approximately 40-45 m of the sandstone member (Carter, 1985a). Approximately midway between the two hills is a smaller knoll informally called the "Little Hill". It also displays some exposures' of the sandstone member, but only the uppermost portion of the member is represented. The Buttonbed Sandstone of the Chico Martinez Creek locality can be divided into three lithofacies: (a) a lower bioturbated sandstone, (b) a thick interval of sandwave cross-stratified sandstone, and (c) an upper coquina (see Figure 7). The lower heavily bioturbated unit is a poorly sorted, very fine to fine grained sandstone. This lithofacies comprises up to two-thirds of the "1800" Ridge and approximately Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 7 Figure 7. Photograph of outcrop of the Buttonbed Sandstone on Buttonbed Hill near Chico Martinez Creek. The three lithofacies are labeled as follows: A = lower bioturbated sandstone lithofacies, B = thick sandwave interval, and C = the Buttonbed coquina. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 9 one-half of Buttonbed Hill (Carter, 1985a). The unit is so heavily bioturbated that many portions are almost completely homogenized. This well-homogenized fabric suggests that the lower bioturbated sandstone was deposited in relatively quiet waters some distance offshore where infaunal reworking exceeded sediment influx. Its fine grained composition also supports a quiet setting, free of current winnowing. On " 1800" Ridge, there are a series of storm lag deposits found toward the base of this lower unit containing colonial barnacle fragments, pectens, oyster valves, echinoids, phosphate nodules, and pholad-bored dolomite and sandstone clasts. The fossiliferous beds are surrounded by the characteristically unfossiliferous fine-grained sandstone and are indicative of debris lags which were deposited into the quiet setting by storm- generated currents. The lower lithofacies is succeeded by the lenticular sandwave lithofacies (26 m thick on Buttonbed Hill and 5.5 m on 1800 Ridge). The contact between the two lithofacies is sharp but there is no evidence of erosional scour. Throughout most of the sandwave interval, the sandstone is well-sorted and medium- to coarse-grained. Amplitudes exceed 8 m and appear to decrease in size upsection to a maximum of 1-3 m. By using the empirical estimate of the maximum ratio sandwave height to water depth (1:3), the minimum water depth for the paleoenvironment can be approximated at 25 m (for the 8 m amplitudes; Belderson et al., 1982; Carter, 1985b). The paleocurrent analysis of the cross-stratification appears to indicate unidirectional current flow to the south-southwest This sandwave interval has been interpreted to document a progressive shoaling on the Relizian shelf (Carter, 1985a). The only body fossils observed in the sandwave interval are occasional whole and fragmented sand dollars. Ichnofossil abundance is greater within this lithofacies; distinct unnamed conical burrows are quite common throughout the unit The conical Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 0 burrows are typically 6 to 10 cm in length and 6 cm wide, with 1 to 4 branches which branch upward. The burrows are often infilled with coarser sand than that which surrounds them. Similar burrows have been described from foreshore-nearshore deposits of the Cretaceous Cape Sebastian Sandstone in Oregon (Bourgeois, 1979). The uppermost lithofacies of the Buttonbed Sandstone member is the accumulation for which the youngest Temblor member was named: the Buttonbed coquina. This upper unit of the Buttonbed Sandstone was deposited in a relatively shallow marine environment resulting from the shoaling of the underlying sandwave interval. It is a highly fossiliferous, coarse to very coarse sandstone composed primarily of sand dollars, Vaquerosellamerriami. In the following sections, the stratigraphy, sedimentology, and paleontology of the Buttonbed coquina will be described in order to document the highly concentrated echinoid accumulation and to aid the reconstruction of its accumulation history. In summary, the three lithofacies of the Buttonbed Sandstone represent subenvironments on an early Relizian (late early Miocene, 17-18 my) shelf. First, the lower bioturbated lithofacies is fine-grained sandstone which represents deposition in quiet waters some distance offshore. The coarse fossil/pebble deposits within this first lithofacies were most likely brought from nearby shoals by storm activity. Overlying the lower sandstone, the sandwave lithofacies represents continued shoaling as sandwaves migrating south to southwest built up (possibly creating ridges) in the early Relizian regression. This shoaling exposed a broad area to high energy shallow marine conditions, such as vigorous current or wave action, which led to the deposition of the coarsest sandstone lithofacies, the Buttonbed echinoid coquina Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 Field Methods and Sampling Strategies In order to assess the stratigraphy of the Buttonbed coquina, vertical sections of the bed were measured and recorded as graphic columnar logs at nine stations along the echinoid bed. Stations were located between the northern point of ” 1800 Ridge" and the southern point of Buttonbed Hill (Appendix 1). Five sites were described from "1800 Ridge" (Stations Bl-5), three from Buttonbed Hill (Stations B6-8) and one from the "Little Hill" (Station B9). Due to the lenticular nature of the coquina, stations were chosen on the basis of outcrop exposure. At each site, lithologic features (color, composition, friability, etc.) and changes in weathering profile were recorded. Also, general lithologies of the surrounding facies were noted and contacts above and below the echinoid coquina were examined and recorded in the graphic logs. In addition to lithologic information, sedimentological factors were also examined in the field. Sedimentary and ichnological structures within the bed were recorded. The relationship of size and abundance of body fossils to matrix was described. Only skeletal or clastic materials exceeding 2 mm were categorized as grains; components less than 2 mm were considered matrix. Packing and sorting of fossils within the sandstone was determined using Kidwell and Holland's (1991) schematic scale of relative packing. The semi- qualitative scale distinguishes between three relative degrees of shell bed fabrics: densely packed, loosely packed and dispersed (Figure 8). Variations in packing and sorting distributions (both vertically and horizontally) throughout the stratigraphic sections were described based on specimen distribution. Packing of all fossil material (including fragments) was also noted. Paleontological observations were made based on surface exposures. Fossil composition and diversity were described for each section. Also, fossil distribution Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 2 Figure 8. Schematic illustrations of relative packing categories for skeletal material greater than 2 mm (Kidwell and Holland, 1991). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 3 CLOSE-PACKING densely packed bioclast-supported, biodast/biodast contacts common loosely packed most biodasts within one body length of each other, a few in direct contact dispersed most biodasts are more than one body length away from each other Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 4 patterns and orientation relative to bedding were described. Fossil abundance was measured for the coquina at each station by point-counting specimens using a stratified random sampling scheme (Bakus, 1990). The exposures were laterally measured and divided into 12 10-cm intervals (Figure 9). Each interval was assigned a number (1- 12) and a pair of dice was rolled to choose which lateral portion of the bed to examine. Next, a 100 cm2 grid was placed at the base of the selected area. The fossil abundance of the selected portion of the outcrop was determined by counting the number of fossils within the grid. The grid was placed on the outcrop at 20 cm vertical intervals and an abundance count was completed for each interval. All fossil elements greater than 2 mm were counted but only sand dollar material in which the tests' diameters could be observed were considered "whole specimens". Fossil composition was noted within the grids and the taphonomic condition of the fossils was qualitatively assessed. Degrees of ornamentation (e.g. presence of petal structure) were described for all whole specimens within the selected blocks. Also, types of breakage (e.g. along or across plate boundaries) observed among whole specimens and degrees of rounding of fossil fragments were described. Multiple samples (range: 3-7; total: 37) were chiseled out of the bed within each station site, including samples throughout the echinoid bed and one below the bed at some stations. Ideally, the sampling strategy consisted of a stratified random sampling scheme. However, the fossiliferous rock was very difficult to extract from the outcrops, making it hard to collect samples. Collection, therefore, was based primarily on accessibility of samples. This strategy results in a sampling bias of over represented friable, hash samples and under-represented densely fossiliferous samples. Fossil abundance data from hand samples was therefore used to supplement the information obtained from the field. This sampling bias is addressed further in the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 Figure 9. Field fossil abundance point-count technique for Button bed sand dollars. “X”s mark the sampling positions. Note: not to scale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 E o o \ k " V * o \ * ¥ % k * 2 * \ % s? * * . 4 " • * a % ■IE/£3B5I£d!liBt2;lLflfc3 r 0 * >4 \ • * < p £ * > * V. — T % * « 0 * % * V * * Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 7 "Faunal Components of the Buttonbed Sandstone Coquina" section. Samples were collected at various heights throughout the stratigraphic section and their relative positions were recorded and marked on the graphic logs. In addition to the 37 samples chiseled directly from the coquina, one sample (Frn) was collected as float from the Little Hill. Laboratory Methods of Data Collection The 38 samples were first examined for fossil composition and diversity. Next, fossil abundance was determined. A fossil point-count was conducted using a random sampling technique similar to that which was used for abundance analysis in the field. A 100 cm2 grid was placed above the largest outcrop surface of each hand sample, which was oriented in its original position relative to the bedding plane. The grid was subdivided into four 25 cm2 blocks, which were numbered 1-4. Four numbered, folded pieces of paper were drawn from an opaque container, which was shaken between each trial. The number drawn determined which quadrant of the grid would be examined. If the sample surface did not fill the chosen quadrant, the grid was moved until the entire space was occupied. Fossil material (larger than 2 mm) observed within the 100 cm2 block was counted and recorded. This technique provided a standard unit from which to compare the samples' surficial fossil densities. In addition to fossil abundance, the degrees of packing observed within the selected blocks were recorded using Kidwell and Holland's (1991) field scale. Degrees of ornamentation and breakage among whole specimens were described to supplement field information. Orientation of fossils relative to bedding was also noted. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 8 Petrographic informatioti about the fossil composition and abundance of the echinoid bed was obtained by examining thin sections made from several samples. A total of seven thin sections (six standard and one oversized) from samples from three stations (one from Station B5, one from Station B7, four from Station B9 and one from float located near Station B9) were analyzed to provide many vertical and lateral views into the bed. Samples B9A-B9D represent the complete vertical section at Station B9. Sample B7D was collected from a concentrated layer of sand dollars located just above the lower meter at Station B7. Sample B5S was collected from the pitted sandstone which underlies the echinoid accumulation at Station 5. Sample Ftk is from the Little Hill and represents a condensed pecten layer and surrounding sand dollar concentrations located midway through the portion of the echinoid bed near Station 9. Each thin section was studied in detail and fossil composition was recorded. Fossil abundance was determined through visual estimations of the percent-volume of fossils within the rocks using percent-volume charts, such as those provided by Schafer (1969) and Kidwell and Holland (1991; Figure 10). Abundance measurement sites on the slides were chosen through a random sampling technique. Slides were subdivided into equal portions (x=6, y=8 for oversized slides and x=6, y=6 for standards). For standard slides, a die was rolled twice for each slide (once for each axis) to determine where fossil abundance was measured. For oversized slides, a die was rolled once (for the x-axis) and a number (written on folded paper; 1 through 8) was picked from an opaque shaken container for the y-axis. Each slide was adjusted to the specified site, fossils were identified within the microscopic field of view and a visual estimation of percent-volume was recorded. Relative sorting of microfossils within the selected site was also noted. In addition to fossil composition, abundance Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 9 Figure 10. Examples of percent-volume charts for bioclasts of different shapes (From Kidwell and Holland, 1991; Schafer, 1969). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40 'J 1 h H 9 < 0 O O 9 < 0 C ® ■ o > 5 in Q . 1 0 9 " D M ■ s P « » O « o ( 0 O o 9 < 0 O O v? 0 s 9 < 0 9 m O < 0 C M O c 9 ■ o 9 ( 0 o 9 o < 0 V ® C 9 T 3 in in 9 1 0 c 9 • o t I * « . * 1 • M W * •#/» r t S m o N 9 1 0 C 9 ■ D fi*a % t Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 and sorting information, petrographic analysis of the Buttonbed Sandstone thin sections provided information about size variability of fossils throughout the bed, degrees of rounding of skeletal grains, and possible orientations of microfossils relative to bedding. Sedimentological aspects of the thin sections which were also examined include matrix and cement compositions, inorganic detrital composition, grain sizes, grain fabric and the degree of grain rounding. Also, thin sections were analyzed for porosity types and other diagenetic features of the rocks. In addition, the ratio of grains to matrix was assessed, using visual estimation charts. Stratigraphy and Sedimentology of the Buttonbed Sandstone Echinoid Bed Nine stratigraphic sections were described and recorded over the distance between the northern peak o f" 1800" Ridge and the southern tip of Buttonbed Hill (Figure 11; Appendix 1). The best exposures of the Buttonbed coquina are located on these two prominently ridged hills. Buttonbed Hill, a low knoll situated between Chico Martinez and Zemorra Creeks, exhibits the most vertically extensive exposures of the coquina (see Figure 7). Located 1220 m north of Buttonbed Hill, the north-south trending" 1800" Ridge provides extensive lateral exposure of the coquina The vertical extent of the echinoid bed exposure is rather limited in most areas of the ridge, with several meters of coverage separating the coquina outcrop from the underlying sandwave outcrop. Stratigraphic and environmental interpretations of the other less well-exposed sections of the coquina were based largely on the information provided in the three best exposed sections (Stations B3, B6 and B8) measured on the two hills. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 2 Figure 11. Measured sections of the Buttonbed echinoid bed from Stations B1-B9 at the Chico Martinez Creek locality. Scale in meters. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. KEY: Sand dollar tests Cross-stratification Pitted weathering Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 11 (continued). 3 m — i 2.5 m — -Covered B1C -Coquina hash of coarse sand dollar ( Vaquerosella merrlaml) fragments with large fragments and occasional whole specimens (average 1 cm in diameter); top of unit Is fairly friable (2 m thick). 2 m - 1.5 m B1B 1 m 0.5 m B1A -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 11 (continued). 45 3 m 2.5 m 2m B2B 1 m B2A •Covered -Coquina hash of coarse sand dollar (Vaquerosella merrfaml) fragments. Not as consistently coarse as Station 1, also not as many whole specimens (average 1 cm In diameter); (1.77 m thick). -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 Figure 11 (continued). 4.S m ' 4m — 3.5 m — 3m — 2.5 m — 2m — 1.5 m — 1m — 0.5 m — I & *2 * S ’ A -B 3C , -B 3 B -B 3A -Covered T18 ’ -Upper subunit of coquina composed of hash of coarse sand dollar ( Vaquerosella merrfaml) fragments; rare barnacle fragments present; (2 m thick). -Lower subunit of coquina composed of more complete sand dollars (0.5 to 2 cm In diameter) within a medlum-to- coarse sandstone matrix (2.1 m thick). -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 Figure 11 (continued). 3 in 2.5 m 2m 1.5 m B4C 1 m B4B 0.5 m B4A -Covered -Coquina with patchy coarseness. Increased coarseness at bottom and top of outcrop, with finest fragments located around 0.5 m. Lateral variability with more complete specimens located In coarser areas; (1 m thick). •Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 Figure 11 (continued). 4m — B5D 3.5 m 3 m — 2.5 m — 2m — -B 5 C -B 5 B 1.5 m — * 1 m - 0.5 m — -Covered. -Coquina with weathered layers; very coarse with abundant whole specimens (0.5 to 2 cm in diameter); rare barnacle fragments present; hash to massive to hash composition (2.4 m thick). -B 5 A -Medium, well-sorted sandstone with tabular cross-stratification with amplitudes up to 5.5. m; pitted weathering present; (1.2 m thick). -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 11 (continued). 4 m 3.5 m 3 m 2.5 m B6B 2m / • « . * & ^ ^ # * _ a . < * y / * <3 B6A 1 m 0.5 m -Covered •Upper subunit of coquina composed of hash of coarse sand dollar (Vaquerosella merriami) fragments; rare barnacle fragments present (1 m thick). •Lower subunit of coquina composed of more complete sand dollars (mostly 2 cm In diameter) within a medium-to- coarse sandstone matrix (2 m thick); phosphate granules present approximately 1.05 m from bottom. •Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 11 (continued). 2.5 m — 2m — 1.5 m — 1m — 0.5 m — -Covered -B 7C -Coquina hash of coarse sand dollar (Vaquerosella merrlaml) fragments wtth"medium" abundance of whole specimens; specimens are in no orientation and appear abraded (0.5 to 2 cm in diameter); (0.75 m thick). - B7D, B7E B7B1, .L0W er subunit contains abundant whole specimens, well-sorted and closely packed in most areas; the 2 subunits are separated by a concentrated layer of whole sand dollars approx. 3-12 cm In thickness; (1 m thick). B7B2 -B7A1, B7A2 -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 11 (continued). 51 4m — 3.5 m — 3 m — - B8E1, B8E2 2.5 m — 2m — 1.5 m — 1 m — 0.5m< -B 8 C -B 8 B -B 8 A -Covered -Upper subunit of coquina composed of hash of coarse sand dollar (Vaquerosella merrfaml) fragments, with few whole specimens (0.65 m thick). -Lower subunit of coquina composed of more complete sand dollars (average 0.5 cm in diameter) within a medium-to-coarse sandstone matrix (2.5 m thick); specimens in stringers and lenses; subunits within the bed appear layered (weakly x-stratified); rare barnacles are present; underlying sandstone is x-bedded below with ledges of echinoid material within interbedded sandstone subunits. -X-bedded sandstone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 2 Figure 11 (continued). 4 m B9D, B9E Z F l & k ' l t 3.5 m B9C 3 m 2.5 m 2 m B9B 1 m B9A 0.5 m -Covered - At the base of the echinoid bed, there is a 15-cm-thick layer of abundant whole specimens; above this densely packed layer is a fragment-rich layer (with few, if any, whole specimens); the bed is distinctly layered; approximately 3 m upsection, whole echinoids are more abundant and barnacle fragments are observed; within the upper meter of the echinoid bed, abundant whole echinoids and large fragments (as well as barnacle fragments) are present; specimens within the top of the bed are not oriented, vary in size (0.75 to 2 cm In diameter) and exhibit various taphonomlc conditions. (3.68 m thick). -There is a well-defined contact between the echinoid bed and the underlying sandstone. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 The Buttonbed coquina is lenticular in nature, ranging in thickness between 0 to 4.1 m in outcrop. In general, the coquina can be divided into two subunits: a coarse upper hash layer which caps the sandstone member and a lower layer composed of more complete sand dollars. Within the measured sections which exhibit both subunits, the upper hash unit ranges in thickness between 0.65 to 2 m while the lower specimen-rich unit ranges between 1 to 2.5 m thick. Sections which consist only of the upper hash subunit display a maximum thickness of 2 m. It should be noted that all such hash sections are located o n " 1800” Ridge and that the earlier deposited sandwave interval of the Buttonbed member is the closest underlying outcrop, which is separated from the base of the hash exposure by several meters, perhaps suggesting the presence of the lower specimen-rich subunit under the surficial coverage. In outcrops where both subunits are present, there is a sharp contact between the two subunits which is marked, in some areas, by concentrated fossil lag deposits. For example, one portion of the coquina exposure on Buttonbed Hill contains a prominent condensed accumulation of flat-lying, whole sand dollar tests located at the contact between the two subunits (Station B7). There is also a dense pecten layer separating the coquina subunits on an area of the Little Hill (Sample Flh). Such condensed deposits represent periods of low sedimentation and relatively little reworking. Fossils within the condensed intervals are predominately horizontal relative to bedding and show little signs of taphonomic destruction. Fossil composition, abundance and distribution patterns observed in the Buttonbed coquina are further discussed within the "Faunal Components of the Buttonbed Sandstone Echinoid Bed" section which follows. Trough sets (with amplitudes of 5-20 cm) and occasional tabular sets (with amplitudes of 20-40 cm) of cross-strata are found within the coquina. Paleocurrent Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 4 work completed by Carter ( 1985a) reveals a strong southwestern trend on Buttonbed Hill and a wide scatter in directi cm o n " 1800" Ridge. Physical sedimentary structures present within the lower portion of the coquina include occasional small scale lenticular lag deposits which are often infilled with sand dollar tests. The lag "holes" average 1-2 m in length and 5-10 cm in depth. Tests are not oriented in any consistent direction within the lag holes, suggesting rapid infill due to storm activity. Other small scale structures within the lower subunit of the Buttonbed echinoid concentration include several specimens of an unnamed conical burrow, which is 15-25 cm deep and 6-15 cm in diameter, located near the base of the coquina The burrows are often infilled with coarser sand, precluding identification. All recognizable traces are vertical and have been assigned to the Skolithos ichnofacies, indicating a high- energy shallow marine paleoenvironment (Carter, 1985a). Dade brown, granule-sized (1-4 mm) phosphatic nodules are scattered throughout the coquina, with several concentrated zones. For example, a 10 cm-thick concentrated layer of phosphatic nodules at Station B6 comprises more than 5% of the rock volume within that portion of the bed. Nodular phosphorite typically forms in reduced, organic-rich offshore environments (Tucker, 1991; Williams etal., 1982). The abundance of phosphatic nodules present in the sandstone suggests proximity to their place of origin; the concentrations of phosphatic nodules probably represent allochthonous storm lag deposits (Carter, 1985a). The phosphatic nodules most likely formed in quieter deeper marine surroundings and were later exposed and transported in by storm activity. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 5 Sedimentary Petrography of the Echinoid Bed The Buttonbed coquina's inorganic composition is predominately quartz with smaller amounts of glauconite and feldspars (Table 1). Within the six thin sections examined for petrographical information, the quartz grain percent volume averaged approximately 25%, glauconite 5% volume, and feldspars less than 1%. It should be noted that the mineralogical content is anomalously low within the Flh sample. This sample represents a concentrated pecten accumulation found between the two coquina subunits on Little Hill and is indicative of the hiatal concentration bed. Within the echinoid bed, quartz grain sizes vary between 0.05 to 2 mm and show no size distribution patterns (i.e. coarsening or fining upward) or evidence of preferential sorting. Degrees of rounding of grains varied throughout the bed, with no apparent pattern. Overall, there was no evidence of consistent orientation of clasts within the examined thin sections, with the exception of the pecten layer observed in Sample Fm . The following is a brief description of the six coquina samples and one sandwave sample which were petrographically examined. The descriptions include information regarding both the inorganic and organic components of the coquina, concentrating more on the inorganic elements and their implications. Consult the following "Faunal Components of the Buttonbed Sandstone Coquina" section for further discussion of the microscopic fossil contents within the coquina. Sample B7D was collected from the boundary between the coquina's two subunits at Station B7 (Figure II) and represents the condensed sand dollar interval which marks the boundary. Fossil material dominates the sample, accounting for 30- 35% of the randomly selected petrographic view. Fossil components include fully Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 6 Table 1. Petrographic information for samples examined from the Buttonbed Sandstone echinoid bed and the underlying sandwave lithofacies. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. < 0 < 0 ( 0 CM CM O O c m CM cn CM CM CM CM < 0 CM 9 CM CM < n m A CM O Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 articulated sand dollar tests (with pillar structures visible), echinoderm debris, bryozoan and barnacle fragments, bivalve debris, and one benthic foraminifera. Sand dollar tests have been completely recrystallized by coarse calcite crystals which have each replaced the individual echinoid plates (they lack any signs of original internal structure). Plate suturing is still present (Figure 12). Spaces between the pillar structures within some tests have been filled with a sparry cement. Or, in some cases, the calcite crystals which have replaced the original test material encompass both the test material and the spaces between the pillars. In Sample B7D, quartz grains comprise approximately 20% of the petrographic view and vary between 0.3 to 1.5 mm in size. Other materials present include glauconite (5%) and rare feldspars (<1%). The glauconite can be observed as both nodules and ooids, which display a spectrum of weathering stages ranging from " fresh" characteristically green aggregates to dark brown limonitic aggregates resulting from oxidation (Figure 13). The pellets and ooids range in size from 0.05 to 0.5 mm in diameter. Diagenetic evidence within the sample includes intercrystal porosity in some sand dollar plates. Other evidence is the partial dissolution of the edges of some sand dollar tests and occasional fractured glauconite aggregates. Calcite syntaxial overgrowths on echinoderm debris are common. The syntaxial overgrowths can also be observed between two adjacent sand dollar tests. Dolomite cement (in the form of euhedral crystals) has replaced secondary (intracrystalline) pore space within the recrystallized plates of some sand dollar tests. Samples B9A-B9D represent the complete vertical section of the bed at Station B9 (Figure 11) and therefore, provide successive windows of the accumulation at that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 Figure 12. Photomicrograph showing the edge of a recrystallized sand dollar from sample B7D, Station B7. Plate boundaries are marked by the black arrows. Field of view is 2.6 mm. Above is plane light; below is polarized light Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 Figure 13. Photomicrograph of glauconitic (A) nodules and (B) ooids from sample P5, Station B5. Reid of view is 2.6 mm, plane light Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 site. It should be noted that the exposure of the Buttonbed coquina at Station B9 is not clearly subdivided into the two subunits generally observed in the bed. This section provides a more complex picture of the accumulation with several densely fossiliferous layers separated by hash layers. Sample B9A was located within the lowest meter of the section and is comprised of a coarse-grained hash (Figure 11). On the microscopic scale, the sample consists primarily of quartz grains and fossils, with a 55-60% grain to matrix relationship. The grain fabric within the rock is not densely packed (i.e. most grains are not in point contact). Quartz grains account for 25-30% of the selected petrographic view and vary in size from 0.65-1.2 mm. Fossil components account for approximately 20% of the petrographic view and include echinoderm material (fragments), bryozoan debris, barnacle fragments, and rare microgastropods. No whole sand dollars were observed in thin section. Glauconite pellets and ooids are also present, making up to 6% of the selected view. Feldspar is rarely present, accounting for less than 1% of the view. Within B9A, the grains are separated by a microcrystalline calcite matrix. Syntaxial overgrowths on echinoderm debris by calcite are highly common. Other diagenetic evidence within the sample includes occasional examples of interparticle and intraparticle porosity (in the case of voids within bryozoan structures) within the rock. Sample B9B was located in the middle of the Station B9 section, approximately 1 m above B9A's position (Figure 11). It is a hash comprised primarily of quartz and fossils, with approximately 50% grains relative to matrix. Similar to B9A, sample B9B's grain fabric is also only moderately packed on the microscopic level, with only occasional grains in point contact Quartz grains comprise 30% of the petrographic view and range from 0.2-1.1 mm in size. Fossil elements account for Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 4 15% of the petrographic view and include echinoderm debris, bryozoan and barnacle debris, bivalve fragments, and rare microgastropods and benthic foraminifera. No whole sand dollar specimens were observed in the thin section. Glauconite pellets and ooids at various weathering degrees are also present in this sample, comprising approximately 6% of the selected petrographic view. Feldspar grains are rarely present, representing less than 1% of the petrographic view. The grains within Sample B9B are surrounded by microcrystalline calcite matrix. There is presence of interparticle porosity as well as rare occurrences of elongate pore spaces and partial dissolution of echinoderm debris. At least one quartz grain is fractured within the thin section. As is observed in Sample B9A, syntaxial overgrowths on echinoderm debris by calcite are very common within the B9B thin section. Sample B9C was located approximately 1.5 m above B9B's position within the section and is a coarse-grained hash (Figure 11). The grain fabric of this sample is more closely packed than those previously described from the station; point contacts between grains are fairly common. The grain vs. matrix relationship is 40-50%. Quartz grains make up approximately 25-30% of the petrographic view and exhibit a wide range in size between 0.05 and 1.2 mm. Fossil material is less common in this sample, accounting for 5-10% of the petrographic view. Those elements present include echinoderm debris, barnacle and bryozoan debris and bivalve fragments. No whole sand dollars were present within the thin section. Glauconite pellets and ooids present in various weathering stages, making up 6% of the petrographic view. Feldspar grains are present in small amounts (<1%). The matrix surrounding the grains within this sample is microcrystalline calcite and shows signs of interparticle porosity. Secondary porosity evidence includes Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 5 presence of rare honeycombed grains and fractured grains. Calcite syntaxial overgrowth is very common within the sample, particularly on echinoderm debris. Sample B9D is the final thin section examined from Station B9 and was collected from the upper boundary of the Buttonbed coquina (Figure 11). This sample contains more fossiliferous material than the previously described samples from Station B9; there are more abundant whole specimens found within the sample than within the lower hashy samples. The grain fabric is closely packed with point contacts between grains. There is a 50-55% presence of grains versus matrix within the sample. Quartz grains comprise approximately 15-20% of the petrographic view and range in size from 0.4 to 2 mm. Fossil elements are the predominant component within the rock, accounting for 30-35% of the petrographic view. This increase in percentage can be related to both size and abundance of the material. Fossils include echinoderm fragments, fully articulated sand dollar tests, bryozoan and barnacle fragments, and bivalve material (including one articulated bivalve). As observed in Sample B7D, sand dollar tests have been completely reciystallized into a series of sparry calcite crystals (lacking all original internal structure) but retain the suture contacts between the crystals which have replaced the individual plates. Glauconite pellets and ooids are present as approximately 6% of the petrographic view. Feldspars are also present but are extremely rare. Both interparticle and intercrystal porosity is observed within the B9D thin section. Rare fractured grains are present, including one fractured glauconite nodule. Calcite syntaxial overgrowth on echinoderm debris is common. Partial dissolution of sand dollar test material is observable and, in some cases, the secondary pore space has been partially infilled by euhedral dolomite crystals. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 Sample Flh was collected as float from the Little Hill but most certainly represents the concentrated pec ten zone which occurs between the coquina's two subunits in a portion of the small knoll. Examination of the slide provides information about the transition between the sand dollar coquina and the pecten concentration found within it Such information can also be used as a basis of comparison between the two different forms of shell bed. Sample Flh is comprised primarily of fossils, particularly articulated pecten shells, single pecten valves, articulated sand dollar tests, echinoderm fragments, and occasional bryozoan debris. The pecten material is concentrated within a zone which is surrounded by the other, more dispersely packed fossil elements. There is a distinct decrease in quartz grain abundance within the pecten zone, which consists of fine grained (micritized) sediments. The petrographic view which was randomly selected for detailed examination of the thin section focuses on a portion of the pecten concentration. Therefore, the following information pertains to the pecten bed only, and not the surrounding sand dollar coquina, and aids in comparing the two shell beds. Fossil materials comprise 25-30% of the petrographic view, whereas quartz grains, glauconite aggregates and feldspars represent approximately 5%, 2% and 1% respectively. Quartz grains present within the pecten zone are relatively small, ranging from 0.06 to 0.5 mm in size. The pecten material is often enveloped in spar, separating the fossils from the micritic matrix. Articulated pecten shells exhibit classic geopetal structures with fine-grained (micritic) sediments below drusy spar calcite, suggesting that the pecten accumulation was not winnowed by strong current or wave activity. The fact that the pecten shells are still articulated indicates little reworking of the layer (Figure 14). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 7 Figure 14. Photomicrograph of articulated pecten with infilling geopetal structure from sample Flh. Field of view is 2.6 mm, plane light Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission 69 Sample B5S also provides a basis of comparison for the Buttonbed sand dollar coquina, this time with the underlying sandwave lithofacies. The sample was collected from a portion of the underlying sandwave interval located at Station B5 and was located approximately 2 m below the lower boundary of the coquina (Figure 11; Appendix 1). The sandstone is grain-supported; it has a moderately compact fabric with some point contact The percentage of grains versus matrix is greater than 50%. Quartz grains comprise 30% of the petrographic view and range in size between 0.3 and 0.65 mm. Glauconite aggregates and ooids are the next most abundant grain, accounting for approximately 11% of the examined view. This amount of glauconite is much higher than that found within the overlying coquina, perhaps suggestive of a larger clay ratio within the sandwave interval. Smaller amounts of glauconite in the overlying coquina may result from current or wave winnowing within the higher energy depositional setting than that present during the deposition of the sandwave lithofacies. Compared to the Buttonbed coquina samples, fossils are less abundant within Sample B5S. Fossil materials account for 10% of the petrographic view and include echinoderm debris, bryozoan and barnacle fragments, bivalve debris, and benthic foraminifera. Feldspars are present but represent less than 1% of the selected petrographic view. The surrounding matrix in Sample B5S is microcrystalline calcite. Both interparticle and intraparticle porosity can be observed. Diagenetic evidence also includes calcite syntaxial overgrowths on echinoderm debris and the micritization of some bivalve fragments within the rock. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 0 Faunal Components of the Buttonbed Sandstone Echinoid Bed Composition As its name suggests, the Buttonbed coquina is faunally dominated by the button-iike sand dollar, VaqueroseUamerriami. These irregular echinoids, which range in size from 0.5 to 2 cm in diameter, comprise up to 80% of the bed in some outcrop areas. The only other macrofaunal components observed in the Buttonbed coquina at the Chico Martinez Creek locality are pecten shells and the occasional fragments of an unidentified barnacle. Pecten fossils (possibly Leptopectenanderstoni) are found both in scarce abundance scattered throughout the coquina and within a densely concentrated pecten zone (6 cm thick) located on the Little Hill. When the microscopic scale is considered, the faunal diversity of the Buttonbed coquina from this study's locality increases. The list of fossil material identified in thin section includes the macroscopically recognized articulated sand dollar tests, articulated pecten shells, and barnacle fragments, but expands to include echinoderm debris, bryozoan fragments, bivalve fragments, microgastropods, and foraminifera. It should be mentioned here that according to fossil deposit criteria (Embry and Klovan, 1972; Kidwell and Holland, 1991 and others), no fossil material under 2 mm in size is considered a fossil component of the accumulation. Although much of the more diverse fossil assemblage observed in the petrographic analysis is of no use in categorizing the shell bed type, it is of interest in reconstructing the depositional environment and accumulation history of the bed. A diverse assemblage of macrofauna has been recognized from several Buttonbed sandstone localities in the central Temblor Range (Anderson, 1905; Addicott, 1970,1972,1973). Table 2 compiles the list of fossils, which consists of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 Table 2. Macrofauna from the Buttonbed Sandstone Member (Modified from Carter, 1985). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 2 Buttonbed Megafauna* Localities 5159 M2632 M3986 M3987 1800R Bathymetric range of genera In the modem environment** Echlnolds: VaqueroseUa andersoni (Twitcheli) X i ? VaqueroseUa merriami (Anderson) X X Bivalves: Amussiopecten vamfedd (Arnold) X drenomvtilus enpansusfArnold) X O oslnia cf. D. margatilana Loel & Corey X D osinia merriami Clark X X Leptopectea anderson/fAmotd) ? X X X Ludnoma ac</t(t/nea(a(Conrad) X Intertidal -150 m Lvmpeden crass/cardofConrad) X 5 -10 m Macoma eopelamt Wiedey X Intertidal -1545 m M ilth a aanctaocrvc& L Arnold) ? X Nuculana PcftsnenfAnderson & Martin) X 5 * 3660 m P a nopea abruptafConrad) ? X X Intertidal - 20 m I .§ I X Intertidal-440 m Trachvcanfium vaouerosense(Amold) X X Intertidal -120 m O strea so. Intertidal - 35 m dastrODods: Brvdarkia barfcedanafCoooer) X Brudaritfa oraoonensafCanrad) X dancallaria cf. £. orsgonensMConrad) X 25-550 m draptduia /ssfnuh(6onrad} X Intertidal -165 m Motopophorva anoonanr/stAnderson) X Nassanua amoMtAnderson) X Intertidal - 365 m Nassarkrs harraUensis Addicott X Intertidal - 365 m Nassarius oosoensis Addicott X Intertidal* 365m dcenebm oab<Wana<Andersonl X X Intertidal -150 m 1 1 ! X X Intertidal • 90 m □ X Intertidal • 100 m Tembra cl. r. cooped Anderson X ' Intertidal-55 m tmpboaveon kemiammUCoooer) X X Turtfcufa olerce* Arnold) X furritelia ocovana Conrad — X • 20 -185 m bthers: unidentified bamade “ X unidentified coral fragments X Localities 5159; SW., NE. sec. 16, T.28S., R-19E^ Shale Point quad. M2632: 600 It S., 1400 ft E. of NW cor. sea 27, T.27S.. R.18E.. Pacfcwood Creek quad. M3986: 2600 It N.t 750 ft E. of SW cor. sea 32. T.27S.. R19E.. Shale Point quad. 1800R: 1800ftN.. 1500ftE.of SWcor.sea4.T.29S., R20E., Cameras Rocks quad. •The bulk of this 1st is taken from Addtooft, 1972. ••Keen and Coen, 1974. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 thirty-three species and twenty-eight genera. It is important to note that this list summarizes the fauna collected throughout the Buttonbed Sandstone member (encompassing all three lithofacies: the bioturbated sandstone, sandwave interval and the coquina). Therefore, the list is useful in confirming the overall paleoenvironmental conditions of the member but should not be used in direct correlation with the coquina's faunal composition or diversity, particularly that from only the Chico Martinez Creek locality. In general, the Buttonbed Sandstone fauna confirms that the member represents a shallow-marine depositional setting. Table 2 includes the bathymetric ranges of modern representatives of the genera present in the Buttonbed Sandstone member. At least eleven of the modem representatives are restricted to shelfal environments (from the intertidal zone to 165 m maximum water depth) and none are restricted to slope or basinal settings (Carter, 1985a). Thus, the assemblage appears to represent a fully marine, shelfal deposit The sedimentology and stratigraphy of the Buttonbed Sandstone reinforces this conclusion. Although two species of VaqueroseUa, V. merriami and V. andersoni, have been described in the Buttonbed Sandstone member of the central Temblor Range, only V. merriami was observed in the Buttonbed coquina at Chico Martinez Creek. The two species are distinctive, particularly in cross section, allowing for easy identification (Figure 15). The Buttonbed coquina at the study locality appears to be a relatively monospecific VaqueroseUamerriami accumulation on the macrofossil scale. Paleobiological Analysis of VaqueroseUa merriami The overwhelming abundance of whole specimens of VaqueroseUamerriami within the Buttonbed coquina suggests that the sand dollars once lived in great Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 Figure 15. Illustration of the two species of VaqueroseUa observed in the Buttonbed Sandstone Member. A = V. andersoni (Twitchell). B = V . merriami (Anderson). Note scale (Modified from Addicott, 1972). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 x 1 x 11/2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 6 numbers in the area. In order to interpret how the organisms functioned in their environment, the functional morphology of complete V. merriami specimens was considered as part of this study. Characteristics of the specimens (e.g. test shape, plate structure and food groove patterns) were analyzed in hand sample. Cross-sections of V. merriami were examined for internal structures, such as pillars. In addition to laboratory analysis, this paleobiological component of the study included a literature survey of the morphology of V. merriami. The majority of the V . merriami specimens were not preserved well enough to closely examine their features. Therefore, the literature survey served as a vital basis for examining many of the fossils' structures. Interpretations of some of the organisms’ functions and life habits were made through a comparison of Recent homologous/analogous features. Test Shape and Proportions The V. merriami of the Buttonbed Sandstone are relatively small sand dollars, ranging in size from 0.5 to 2 cm in diameter. Test width of the species is slightly greater than its length (see Figure 15). These proportions may have allowed them to plough a wider stretch as they moved through the sediment (Seilacher, 1979). Also, the relatively flat oral surface of V. merriami probably increased efficiency of locomotion by bringing more spines in contact with the seafloor. The low test profile (Harness) of V. merriami would have proved beneficial for stability in currents. The periproct of this species is located on the marginal edge of the oral surface. The periproct of all irregular echinoids is located on the oral side (not the aboral surface as with regular echinoids). This migration from aboral to oral surface results in the prevention of fouling of the aboral respiratory area and also decreases the likelihood of redigesting sediment (Smith, 1984). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 Petal Development The petals of V. merriami are slightly raised with an open anterior petal and closed paired petals. The petals are relatively long, approximately 0.7 to 0.75 the length of the radius. Such developed petals allowed maximum room for respiratory tube feet Generally, petal development in irregular echinoids can be related to seawater temperature (Zoeke, 1951; Smith, 1984). An increase in temperature increases the echinoid’s metabolism requiring more oxygen. Irregular echinoids living in warmer temperatures often have longer petals than those in colder environments in order to accommodate more respiratory tube feet V. merriami had ample room for many respiratory tube feet and would probably have been able to tolerate relatively warm temperatures. Food Groove Pattern V. merriami has a very simple food groove pattern on its oral surface. The grooves are split irregularly distal to five long primary trunks which lead to the mouth. This pattern is not as efficient for tube feet access as a more complex branched pattern; there are not as many grooves over the oral surface in the simpler pattern. V. merriami would probably not have faired well in areas of sparse organic content Pillars Pillar structures are well-defined in many of the V. merriami specimens examined in this study. These internal supports are well-sutured together so that impact loading can be transmitted to adjacent plates on the same surface as well as through the pillars to the opposite side. These structures are very beneficial to V. merriami as they provide the support that a flat test would require against loading stress. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Summary The functional morphologic study of V. merriami yielded some important information about the sand dollar’s life habits. Due to the Harness of its oral surface and its overall test proportions, it probably moved rather efficiently. Also, it could probably have withstood current flows because of its relatively flat test shape. Its well- developed petals allowed for ample room for respiratory tube feet This suggests that the organism could have maintained a relatively high metabolic rate and may have been capable of living in warm environments. Its simple food groove pattern suggests that it probably needed to live in areas where sediment contained sufficient amounts of organic content This would be particularly true if the organism’s metabolic rate was indeed relatively high. Abundance and Distribution Patterns Fossil abundance varies both vertically and laterally within the Buttonbed coquina. Table 3 summarizes the results of the field abundance analysis, which also recorded relative packing, orientation and taphonomic conditions at each station (also see Appendix 2). Fossil abundance and distribution patterns are highly variable within the accumulation but general observations can be made which correlate the amount of fossil content to the bed's stratigraphy. Stations B1, B2 and B4 each represent the upper hash subunit of the coquina and exhibit a general decrease in sand dollar specimen abundance from the base to the top of the exposures. The coquina is represented as a densely packed hash of sand dollar fragments at each of the stations. Considering only fossil material greater than 2 mm in size, the exposures represent an accumulation of dispersed to loosely packed sand dollars. Sand dollar specimens do not appear to have any consistent orientation Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 Table 3. Results of field analysis of fossil abundance, packing, relative orientation and taphonomic condition. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 0 Station # Sampling position Abundance (per 100 cm ) Packing Packing (w/fragments) Orientation Degree of Ornamentation B 1 (B A ) (1) base 20 ots D no no (2) 20 cm up 16 DIS/L D no no (3) 20 cm up 19 DIS/L D no no (4) 20 cm up 22 DIS/L D no no (5) 20 cm up 6 ots D no no ■ > B2 (1) 20 cm up 14 0 6 0 no no (2) 20 cm up 4 ots D no no (3) 20 cm up 2 ots 0 . _ yes • (4) 20 cm up 2 D C S D no * (5) 20 cm up 0 • D • B3 (1) base 0 . D . (2) 20 cm up 5 D C S D no (3) 20 cm up 1 0 6 D no (4) 20 cm up 13 DIS/L D no (5) 20 cm up 8 0 6 D no plates visible (6) 20 cm up 2 DIS(L) D ves no (7) 20 cm up 0 0 6 D . - (8) 20 cm up 4 0 6 D no petals visible (9) 20 cm up (10) 20 cm up 0 • 0 (11) 20 cm up 0 • D (12) 20 cm up 0 • D . (13) 20 cm up 0 • D . B4 (1) base 7 L/DIS 0 no • (2) 20 cm up 4 0 6 D no (3) 20 cm up 17 D6 D no - (4) 20 cm up 0 0 6 D . - BS (1) base 4 0 6 D no - (2) 20 cm up 4 0 6 D no - (3) 20 cm up 3 0 6 D no - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 Table 3 (continued). Station # Sampling position Abundance (per 100 cm ) Packing Packing (w/ fragments) Orientation (surface) Degree of Ornamentation B6 (1) 20 cm up 3 OS D horiz. no (2) 20 cm up 11 D/L (cl) D no petals visible (3) 20 cm up 0 - D . (4) 20 cm up 9 D/D/L D no (5) 20 cm up 10 L D horiz. (6) 20 cm up 9 L D horiz. (7) 20 cm up 1 L/D/D D horiz. (8) 20 cm up 1 D no no (9) 20 cm up 5 OS D no B7 (1) 10 cm up 11 L/DIS D no (2) 20 cm up 7 UDIS D horiz. no (3) 20 cm up 23 L/D (cl) D no - (4) 20 cm up 5 L/DIS D horiz. petal visible (5) bet. 3 & 4 39 D/D/L D most horiz. petal visible B9 (1) base 10 OS D most horiz. (2) 20 cm up 0 D . • . (3) 20 cm up 0 • D . • (4) 20 cm up 0 D . • (5) 20 cm up 5 0 6 D no • (6) 20 cm up 2 0 6 D horiz. up . (7) 20 cm up 9 L/DIS D no plates/petals (8) 20 cm up 6 D/D/L D no plates visible B IO (1) base 3-film 0 6 D no . (2) 20 cm up 18 D/D/L D no no (3) 20 cm up 5 D6 D no no (4) 20 cm up 0 0 6 D . . (5) 20 cm up 7 UDIS D no no (6) 20 cm up 0 D _ - (7) 20 cm up 0 - D - - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 2 within the sections at the three stations, with the exception of a small lens of specimens which are oriented upside down but horizontal to the bedding plane. This overall lack of orientation within the hash bed suggests significant reworking of the material. Both subunits of the Buttonbed coquina are exposed at Stations B3, B6, B7, and B10. Fossil abundance analyses at each station show a decrease in sand dollar specimens found in the lower subunit versus those from the upper hash subunit; the boundaries between the two subunits can be seen in the changes in fossil abundance recorded in the field. At Station B3, the transition between the two subunits is well marked between the sampling positions (5) and (6) and can clearly be seen in the change in fossil abundance observed in the grid samples recorded above and below the transition (averages of 0.75 specimens and 5.4 specimens, respectively; Table 3). Similarly, the transition at Station B6 is marked between sampling positions (6) and (7) and is easily observed in the relative fossil abundances recorded above and below the two sampling positions (averages of 7 specimens and 2.33 specimens, respectively). The two subunits at Station B 10 are clearly subdivided between sampling positions (3) and (4) and show this transition in the relative fossil abundance within the two subunits. The lower subunit at Station BIO has an average of 9.66 sand dollar specimens whereas the upper hash subunit displays an average of 1.75 specimens. Station B7 also shows this decreasing trend in fossil abundance, with an average of 13.66 specimens in the lower subunit and 5 specimens in abundance analysis of the upper hash. It should be noted that the boundary between the two subunits is between sampling positions (3) and (4) and that the abundance count from sampling position (5) was measured directly above sampling position (3) and represents the condensed interval of complete sand dollars which marks the boundary at that station (see Table 3 and Figure 11). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 The overall pattern of decreasing abundance of sand dollar tests upsection within the Buttonbed coquina accompanied by an increased abundance of fragments indicates a significant amount of reworking of the fossil material as time progressed. The combination of progressively shallower marine high energy conditions with periodic storm-intensified reworking could lead to an increase in test destruction. The ever-present overwhelming abundance of sand dollars within the bed supports the conclusion that changes in VaqueroseUamerriami specimen abundance within the coquina are the result of physical, and not biological, factors. The sand dollars are present in the underlying sandwave interval, suggesting that the fossils are not specific to only the coquina bed. Their overwhelming abundance within the coquina when combined with the winnowed fabric of the bed point to a strong physical control on the final deposition of the bed. The shallow marine paleoenvironment would have been much affected by high energy processes, particularly during storm events. Stations B5 and B9 represent portions of the Buttonbed coquina which do not show a clear subdivision of the echinoid bed into two layers. These two stations display vertical sections of the accumulation which consist of many alternating layers and lenses of whole sand dollars mixed with a sand dollar fragment-rich hash. The fossil distribution at Station B9 differs greatly from that of previously described sections; whole V. merriami specimens are abundant within the top and bottom of the outcrop separated by approximately 3 m of coarse hash. The fossil abundance analysis conducted at Station B9 reveals this pattern, with 10 specimens per 100 cm2 at the base, 0 specimens from the middle of the vertical section and an average of 5.5 specimens per 100 cm2 toward the top of the section. The majority of specimens found at the base of the section occur within a 15 cm interval and were deposited horizontal to the bedding plane, suggesting relatively little reworking before their final Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 4 burial. In contrast, the overlying hash contained no whole sand dollar tests but was comprised of coarse sand dollar fragments (1-3 mm in size). Although the abundant V. merriami specimens found at the top of the section were not deposited in any consistent orientation, they display a wide range of sizes (0.5-3 cm) and taphonomic conditions, suggesting that they were only affected by moderate transport and reworking. A majority of the specimens observed in this poorly-sorted top portion of the outcrop display their original petal structure and plate sutures, indicating relatively little interaction with destructive taphonomic processes. This well-preserved top layer of echinoid material most likely represents a recent influx of material, which had not yet been significantly reworked within the high energy regime. It should be emphasized that although some lenses and stringers of sand dollar tests do appear to have been deposited horizontal to the bedding plane, the majority of fossil material in the Buttonbed coquina was not deposited in any consistent orientation (Table 3). Most of the V. merriami specimens observed in the accumulation appear jumbled together, deposited in every direction relative to the seafloor surface. This observation further supports the conclusion that this echinoid concentration bed is the result of high energy reworking, perhaps by a combination of current (or wave) action and periodic storm events. Another line of evidence supporting a high energy reworking scenario is the range of degrees of packing and sorting which characterize the Buttonbed coquina. In general, packing of V. merriami within the coquina is highly variable, both laterally and vertically. Densely-packed areas and more dispersed areas with occasional lenses and stringers are observed. When the presence of sand dollar fragments is considered, the degree of packing on the accumulation changes dramatically. Every observed outcrop exhibiting a dispersed sand dollar test fabric was classified as a densely-packed Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 accumulation when sand dollar fragments (1-3 mm in size) were taken into account; the Buttonbed coquina represents a dense accumulation of sand dollar material (Table 3). The dense packing of this coarse-grained echinoid concentration bed is indicative of winnowing events which removed the finer grained material from the area and reworked the coarser fossil material, packing it together. Within the Buttonbed coquina, sorting of the fossil material is also highly variable, both vertically and laterally. In fact, well-sorted areas with sand dollar tests of approximately equal size and poorly sorted areas with tests ranging from 0.5 to 3 cm in diameter (Figure 16) can be found in close proximity in some portions of the bed. Overall, no sorting pattern could be distinguished. The exception to this finding is the poorly sorted, well-preserved top portion of the accumulation at Station B9 (see previous section on fossil abundance and distribution at Station B9). Variation in fossil abundance within the Buttonbed coquina can be observed by comparing the information on fossil abundance and distribution obtained from the field grid analyses with that obtained from hand samples from the nine stations (Table 4). It should be noted that the two scales of measurement within the analyses are different; fossil abundance from hand samples is based on 25 cm2 grid view whereas field analysis is based on a 100 cm2 view. The more limited view used to examine the hand samples may account for the comparatively small number of sand dollar tests recorded in the rocks versus those recorded in the outcrop. Another possible explanation for the difference in magnitude may be the friable nature of the rocks which were collected; perhaps this friability (necessary for collection purposes) resulted in a biased sampling of relatively specimen-poor material. Regardless of the examination scales used in the two abundance analyses, comparison of the relative changes in abundance recorded by the two procedures Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 16. Photograph of poorly sorted sand dollars located near Station B7. Specimens range in size from 0.5 to 2 cm in diameter. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4. Field and hand sample results from fossil abundance analysis. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 9 OUTCROP ANALYSIS: Station f Roid SanipHng position Abundance (per 100 cm ) B1 (BA) (1) base 20 (2) 20 cm up 16 (3) 20 cm up 19 (4) 20 cm up 22 (5) 20 cm up 6 HAND SAMPLE ANALYSIS: Sample # Abundance (per 25 cm ) B1A 1 B1B 1 B1C 3 B2 (1) 20 cm up 14 (2) 20 cm up 4 (3) 20 cm up 2 (4) 20 cm up 2 (5) 20 cm up 0 B2A 0 B2B 0 B2C 0 83 (1) base 0 (2) 20 cm up 5 (3) 20 cm up 1 (4) 20 cm up 13 (S) 20 cm up 8 (6) 20 cm up 2 (7) 20 cm up 0 (8) 20 cm up 4 (9) 20 cm up (10) 20 cm up 0 (11) 20 cm up 0 (12) 20 cm up 0 (13) 20 cm up 0 B3A 1 B3B 0 BSC 0 B4 (1) base 7 (2) 20 cm up 4 (3) 20 cm up 17 (4) 20 cm up 0 B4A 0 B4B 0 B4C.1 3 B4C.2 5 BS (1) base 4 (2) 20 cm up 4 (3) 20 cm up 3 BSA 4 B5B 0 BSC 0 B5D 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 T able 4 (continued). OUTCROP ANALYSIS: Station # Sampling position Abundance (per 100 cm ) B6 (1) 20 cm up 3 (2) 20 cm up 11 (3) 20 cm up 0 (4) 20 cm up 9 (5) 20 cm up 10 (6) 20 cm up 9 (71 20 cm up 1 (8) 20 cm up 1 (9) 20 cm up S HAND SAMPLE ANALYSIS: Sample # Abundance (per 25 cm ) B6A 0 B6B 2 B6C 1 B7 (1) 10 cm up 11 (2) 20 cm up 7 (3) 20 cm up 23 (4) 20 cm up 5 (5) bet 3 4 4 39 B7A.1 0 B7A.2 0 B7B.1 0 B7B.2 0 B7C 0 B9 (1) base 10 (2) 20 cm up 0 (3) 20 cm up 0 (41 20 cm up 0 (5) 20 cm up S (6) 20 cm up 2 (71 20 cm up 9 (81 20 cm up 6 B9A 1 B9B 2 B9C 0 090 0 B9E 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 illustrates the degree of fossil distribution variability which occurs both vertically and laterally within the bed. Table 4 shows that some of the stations show similar trends of decreasing abundance (B3 and B5) or mixed abundance (B9) upsection, while others, such as B1 and B4, show an opposing trend of increasing abundance upsection in hand samples and decreasing abundance upsection in outcrop. As an extreme example, Station B7 is one of the most abundant V. merriami outcrop sites but no sand dollar tests were observed within the hand samples collected from the station. These differences in abundance may result from the high variability of fossil distribution within the accumulation or may be a product of both distribution variability and sampling bias. Taphonomv The majority of the Vaquerosellamerriami examined in the accumulation are present in cross-section only. This view made taphonomic assessment nearly impossible, except to note that the sand dollar tests were intact enough to preserve a cross-sectional view. The specimens of V. merriami which are present with observable aboral or oral views exhibit a variety of preservational states, ranging from those which are relatively "pristine" with original petal structures and individual sutured plates still visible, to those which have partially smoothed surfaces and breakage along plate boundaries, to those specimens which have completely smoothed surfaces and breakage across plate boundaries (Table 3). Overall, the taphonomic conditions of the specimens exhibiting aboral or oral views indicate signs of multiple reworking, perhaps by sandwave or current winnowing, with fewer well-preserved specimens among the majority of heavily abraded individuals. The taphonomy of the Buttonbed coquina supports the conclusion that the echinoid concentration bed was affected by periodic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 2 storm-intensified events which incorporated many generations of V. merriami into a winnowed, coarse-grained fossiliferous deposit In summary, the Buttonbed coquina provides an extreme example of an echinoid-rich deposit It is comprised primarily of the sand dollars, V. merriami, with occasional pectens and barnacle fragments. The accumulation is generally observed as two subunits: a coarse upper hash layer which caps the sandstone member and a lower layer composed of more complete specimens. Presence of the upper hash subunit which is composed primarily of coarse sand dollar fragments, is interpreted to represent substantial reworking of the underlying better preserved accumulation. Fossil abundance and distribution varies both laterally and vertically within the lower portion of the bed. Abundance of V. merriami within the echinoid bed suggests that these organisms lived in great numbers (for many generations) in the area and were only affected by moderate transport Overall, the fossils exhibit no consistent orientation and appear jumbled together in many areas, indicating that the accumulation is the product of significant reworking and not an intact paleocommunity. Both packing and sorting vary greatly within the bed. Densely-packed areas and more dispersed areas with occasional lenses and stringers of specimens are present Sorting is variable with well-sorted areas and poorly sorted areas in close proximity. These packing and sorting characteristics further suggest reworking and influx through a series of high energy events. The taphonomic conditions of the fossils also indicate signs of multiple reworking, perhaps by sandwave or current winnowing, with fewer well-preserved specimens among the majority of heavily abraded individuals. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Buttonbed coquina was obviously formed in a shallow marine environment, as is indicated by paleontologic, sedimentologjc and stratigraphic evidence. During the Relizian, the Buttonbed area was a shallow shelfal environment elevated by the sandwave interval which preceded deposition of the coquina. Populations of V . merriami thrived in the surroundings for many generations. High energy conditions, such as storm events and winnowing by current action produced the generally jumbled accumulation observed in the lower portion of the Buttonbed coquina. The complexity of this subunit of the concentration bed suggests that it is the result of multiple reworking events, which preserved the massive amount of sand dollar material in a variety of stratigraphic and taphonomic styles. Additional reworking of the overlying hash subunit probably occurred as a result of current winnowing, a product of an increasingly shallower marine environment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 4 CHAPTER 3: THE VIRGIN LIMESTONE ECHINOID BED The Early Triassic was a time of recovery for most marine faunas. The Permian-Triassic mass extinction devastated much of ocean life. Almost 50% of all marine families and as many as an astronomical 90% of marine genera went extinct at the end of the Permian (e.g., Erwin, 1993, 1994). The Virgin Limestone member of the Moenkopi Formation represents a time several million years after the mass extinction event The Moenkopi Formation has been identified as Scythian in age based on its Tirolites ammonoid fauna (Larson, 1966). The Virgin Limestone has been dated as Spathian, placing its deposition approximately 4 million years after the Permian-Triassic event (Poborski, 1954; Larson, 1966; Harland etal., 1989). Studies of the member provide valuable information about the aftermath of the Permian-Triassic event (Larson, 1966; Schubert, 1989,1993; Schubert and Bottjer, 1995). The following section addresses the geological history of the Moenkopi Formation and in particular, the Virgin Limestone, in order to provide a historical background for this chapter's focus, the Virgin Limestone echinoid bed. Later discussion will address the echinoid bed in the context of its deposition in the early Triassic. Geology and Stratigraphy of the Moenkopi Formation, southwestern Nevada The Lower Triassic Moenkopi Formation of southwestern Nevada is comprised of three limestone members, the Timpoweap, Virgin and Schnabkaib Limestones, separated by three red members (Figure 17). Within the Great Basin, the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 Figure 17. Triassic stratigraphy of the western United States. The Moenkopi Formation of southwestern Nevada is marked with arrows (From Schubert, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 6 W'CEHTOAJ. UTAH (WaaUlmu. W luncti lute.) NORTHEAST UTAH (East Uintaa) SOUTHEAST UTAH CLARK COUNTY Ankara* Formation qirwGrit Cninia Formation SMnanins - m m Form ation Kamabun PERUlAM Form ation Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^743763498836455 9 7 contact between the Moenkopi and the underlying Upper Permian strata is nonconformable, due to erosion or nondeposition in the latest Permian or earliest Triassic (Reeside, etal., 1957; Schubert etal., 1992). In fact, the lowest member of the Moenkopi, the Timpoweap, is commonly very thin or absent in portions of the Great Basin (Larson, 1966). This nonconformity may have resulted from uplift of much of Nevada and Utah associated with the accretion of the Sonomian Terrane (Hinze, 1973; Collinson etal., 1976). Subsidence following the tectonic activity resulted in an elongate epicontinental basin in the western portion of the Great Basin (Larson, 1966; Bissel, 1970). The three limestone members were deposited during sea level transgression from the north into the arid epicontinental seaway and are progressively thicker to the west, indicating deeper marine conditions (Bissel, 1969; Figure 18). Rief and Slatt (1979) have interpreted intercalating red members of the Moenkopi as a broad tidal complex deposited during increased terrigenous sediment supply from eastern and southern sources. The red members are accordingly thicker to the east of the basin, proximal to the ancient shoreline (Larson, 1966). As mentioned, the oldest limestone member of the formation, the Timpoweap, is absent or very thin in some areas of the basin. Where it is present, the member is represented by a very sparsely fossiliferous, mainly fluvial or marginal marine deposit It is comprised of an assortment of interbedded conglomerates, gypsum and calcareous mudstones and siltstones (Larson, 1966). The middle limestone member of the Moenkopi, the Virgin Limestone, is comprised of limestone units intercalated with fine-grained siliciclastics and sandstone. At the Lost Cabin Springs locality, the member's limestone units are thought to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 8 Figure 18. Map showing simplified regional paleoenvironments (From Schubert, 1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 9 v % V & A V * V m u \\\V \V \> > > V > > > > , m m m m w m m ® W ;ns r a m \ \ \ v \ \ \ \ \ \ \ \ \ avwLTSB v \ \ \ v \ I J&M, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 represent shelfal settings below normal wave base. The Virgin Limestone of Lost Cabin Springs will be described in greater detail in the following section. In the southwestern Nevada area, the Middle Red Member of the Moenkopi pinches out, so that the Schnabkaib Limestone lies conformably over the Virgin Limestone. The Schnabkaib Limestone is an unfossiliferous deposit which is mainly comprised of gypsum, gypsiferous shales, mudstones, dolomites, and limestones (Larson, 1966). In most areas, this upper limestone member is overlain by the Upper Red Member, the youngest member of the Moenkopi Formation. The formation is unconformably overlain by the sandstone and fine conglomerate of the upper T riassic Shinarump Formation. Virgin Limestone Member of the Moenkopi Formation, Lost Cabin Springs, Nevada This study focuses on a portion of the Virgin Limestone Member located at the Lost Cabin Springs site in the Spring Mountains of southwestern Nevada (Figures 19 and 20) At this locality, the member is a series of limestone units interbedded with terrigenous shales and mudstones, which represent periods of influx of terrigenous elastics. Virgin Limestone units within the study area are much thicker than those found to the east, suggesting a more basinal setting to the west (Larson, 1966; Schubert, 1989). The member is comprised of a number of fossiliferous units which vary greatly in thickness, from 1 cm to several meters. Fossil material found within the limestone units is predominantly bivalves and crinoid ossicles but also includes echinoid spines and stromatolites. Extensive paleoecological work done by Schubert (1989) yielded general paleoenvironmental information about the Virgin Limestone member of Lost Cabin Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 Figure 19. Locality map of the Triassic Virgin Limestone Member of the Moenkopi Formation study site at Lost Cabin Springs, NV. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 UTAH NEVADA C lark County Virgin River Lake Mead Lost Cabin Springs L as Vegas 160 Colorado River ARIZONA CALIFORNIA Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 Figure 20. Outcrop photograph of the Virgin Limestone Member at Lost Cabin Springs, Nevada Location of the Virgin Limestone echinoid bed is marked by the white arrow. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 Springs. Over 84 m of limestone units were examined at the study area (Schubert, 1989). Measured sections of the overall sequence of limestones and intercalating terrigenous intervals were interpreted to represent the distal portion of a shelfal setting (Schubert, 1989). The limestone units themselves are comprised of a series of fossiliferous beds separated by thin-bedded carbonate mudstones. The mudstones show signs of horizontal bioturbation, physical reworking, and pressure solution (Schubert, 1989). The fossiliferous units, however, are typically devoid of sedimentary structures and may have erosive boundaries with the surrounding mudstones, suggesting that they are distal storm deposits (Schubert, 1989). Thin fossiliferous beds are more common within the member but deposits up to several meters are observed. The size range of the fossil units may result from the magnitudes of the storms which deposited them. The Virgin Limestone echinoid bed and its surrounding lithologies can be correlated to the upper portion of Unit 15 of Schubert's (1989) stratigraphic section of the Virgin Limestone at Lost Cabin Springs (Figure 21). Within Unit 15, the echinoid concentration is described as a massive bed of abundant echinoid spines underlain by laminated beds of sand-sized skeletal fragments and coated grains and overlain by a slope of rubble-covered non-resistant material (Schubert, 1989). The stratigraphic aspect of this study provides a more detailed picture of the echinoid accumulation and its surrounding units. The remainder of this section will focus on the units above and below the echinoid deposit Next the following sections will address the stratigraphy, sedimentology and paleontology of the echinoid accumulation itself. The Virgin Limestone echinoid bed is part of a shallowing-upward sequence. In most sections, it is underlain by a series of laminated beds, which appear devoid of macroscopic fossils, and overlain by a microgastropod bed. The echinoid unit is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 Figure 21. Measured section of Schubert's Unit 15 from Lost Cabin Springs, NV (Modified from Schubert, 1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 KEY; CsSsiAwtn ^ V S » .V V S « 1 r«r. 56S68Q kvS&aa E M ; ! • « < • • • « ••••4 U U 4 4 M M M H s USHb ] c o v e r e d I n t e r v a l m atrix-dom inated m ottled carbonate mudstone carbonate mudstone ichno fabric index S carbonate mudstone Ichno fabric index 4 carbonate mudstone ichnofabric index 2 -3 thin-bedded carbonate mudstone m assive carbonate mudstone fossiliferous bed containing bivalves fossiliferous bed containing bivalves and crinoid ossicles fossiliferous bed containing crinoid ossicles fossiliferous bed containing echinoid spines finely laminated bed containing sand-sized skeletal fragments massive bed containing sand-sized skeletal fragments massive bad of sand-sizad carbonate grains bod with low-angle cross-bedded sand sized skeletal fragments m assive o r rippled siltstone stro m ato lites UNIT 15 » // // /// /( ,w /v w w . >V,VAV/V, vVAV.V/V, l / v V W / V W V/VAV/V/ ,V,V/V,V/' vV,V/,W/i >VVV;VV>'A . V \ ^ * V v\ ///////ZZi V W \ \ b \ \ > ^ W > V ,A VAVAVA] V \ V \ V a \ \ \ <<//■/.>»</ note; m easurem ents a re rounded off to the n e a re st 5 cm interval Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 separated from its surrounding lithologies by sharp erosional boundaries. In some sections, the laminated beds are missing and the echinoid bed is underlain by a mudstone containing abundant carbonate "blebs" (small, discrete zones of carbonate mud which are a darker shade of gray than the carbonate mud matrix; Schubert, 1989). When present, the underlying laminated mudstone varies in thickness between 29 to 100 cm in outcrop. In some sections, it is underlain by the "blebby" mudstone, which varies in exposure between 30 and 80 cm. The echinoid accumulation is overlain by a microgastropod-rich limestone unit, which varies in thickness between 1.5 to 3.5 m. The two fossiliferous limestones are both dark gray in color and exhibit similar surficial weathering styles. The sharp contact between the two units aids in distinguishing them, as well as the change in fossil composition. No echinoid spine material was observed within the overlying accumulation; microgastropods are the only faunal component visible in outcrop. The unit lacks any internal sedimentary structures and the microgastropods do not appear to have been deposited in any consistent orientation. Further discussion of the paleontological and sedimentological aspects of the microgastropod limestone are addressed in the "Sedimentary Petrography" section. Field Observations and Sampling Strategies In order to determine the stratigraphy of the Virgin Limestone echinoid bed, vertical sections of the bed were measured and recorded as graphic columnar logs at Five of six stations along the unit. Stations were located along the western portion of the Virgin Limestone Member exposures at the Lost Cabin Springs locality. At each site, lithologic features (color, composition, friability, etc.) and changes in weathering profile were recorded. Also, general lithologies of the surrounding facies were noted Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 and contacts above and below the echinoid coquina were examined and recorded in the graphic logs. In addition to lithologic information, sedimentological factors were also described in the field. The bed was examined for any sedimentary and ichnological structures. Also, the relationship of size and abundance of body fossils to matrix was noted. Only skeletal or clastic materials exceeding 2 mm were categorized as grains; components less than 2 mm were considered matrix. Packing and sorting of fossils within the limestone were determined using Kidwell and Holland's schematic scales of relative packing (1991; see Figure 8). Variations in packing and sorting distributions (both vertically and horizontally) throughout the stratigraphic sections were described at each station. In the field, paleontological observations were made based on surface exposures. Fossil composition, diversity and abundance were described for each stratigraphic section. Also, fossil distribution patterns and orientation relative to bedding were described. Taphonomic condition of spines was observed on the weathered surfaces of the echinoid bed and noted to supplement more detailed lab analysis. Multiple samples were chiseled out of the bed along the six stations. Between three to six samples were collected at each site, including a minimum of three from within the echinoid bed and one from each of the surrounding units at some stations. Originally, this study's sampling strategy consisted of a stratified random sampling scheme (as suggested in Bakus, 1990). Ideally, samples were to be taken from portions of each station which were selected using a random numbers table. However, the fossiliferous rock was very difficult to extract from outcrops, making it hard to collect samples. Collection, therefore, was based primarily on accessibility of samples. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 1 0 A total of 26 samples were collected at various heights throughout the stratigraphic section and their relative positions were recorded and marked on the graphic logs. Laboratory Methods of Data Collection At the macroscopic scale, samples were examined for paleontological information, including fossil composition, abundance and distribution. In order to ensure unbiased results, a random sampling procedure was used to determine which portion of each rock would be examined. For each sample, a 100 cm2 grid, subdivided into four numbered 25 cm2 quadrants, was placed over the rock, which was oriented in its original position relative to the outcrop's bedding plane. Four numbered, folded pieces of paper were drawn from an opaque container, which was shaken between each trial. The number drawn determined which quadrant of the grid would be examined. If the sample surface did not fill the chosen quadrant, the grid was moved until the entire space was occupied. Within the selected quadrant, the sample was examined for fossil composition and diversity. Only fossil materials greater than 2 mm were considered specimens and were described. Fossil abundance within each sample quadrant was determined by counting the number of specimens found within the quadrant Spine abundance results were compared to the results of similar methods which did not account for random sampling procedures. A second set of abundance data was generated by simply placing the 100 cm2 grid on the largest surface of each sample and examining it Comparison of the nonrandom generated data and that obtained from the random sampling methods provides information about the biases of sampling. In addition to spine abundance, packing and orientation patterns were noted for the selected 25 cm2 blocks. Packing within each grid was assessed using Kidwell and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 111 Holland's (1991) schematic charts of relative packing. Orientation of spines was determined by noting the general longitudinal direction (perpendicular/parallel to bedding) of individual specimens and recording any directional trends observed in mote than 50% of specimens within the grids. For each sample, the taphonomic condition of the spines was observed and quantified using a qualitative 3-point index. The taphonomic index was used to quantify the degree of ornamentation on the fossils' surfaces. The three categories consisted of: 1-well preserved with striations, 2-some striations present, and 3-smoothed or abraded surface with no striations present Another taphonomic feature which was noted was the abundance of spines with observable tips present on the sample surfaces. Data on the abundance of spine tips was collected with the knowledge that the surficial exposures examined only provide a glimpse of the spines present in the bed and data, therefore, should be used cautiously. Absence of spine tips may result from a number of factors. Presence of abundant spine tips, however, would suggest a relatively short time within the TAZ (Davies et al., 1989a), as tips would be most vulnerable to abrasive processes. The Virgin Limestone echinoid bed was also examined on a microscopic scale. Seven thin sections (three standard and four oversized) were made from hand samples from Stations 1 and 5 for petrographic analysis of the echinoid bed and its surrounding facies. Samples collected from Station 5 represent the complete vertical section of the bed at that site and therefore, provide successive vertical windows into the accumulation (Figure 22). Sample 1A1 was taken from the base of the echinoid bed and contains a portion of a chert layer which marks the base (Figure 22). Samples 5A Lower, 5A Upper, 5B Lower, 5B Upper and 5B+ were taken from within the echinoid Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 Figure 22. Measured sections of the Virgin Limestone echinoid bed from Stations 1, 2,4,5, and 6 at Lost Cabin Springs. Scale is in meters. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 KEY: xs n * f t v Echinoid spines Microgastropods Carbonate ,fblebs,f Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 Figure 22 (continued). 5m 4.5 m 4 m - 3.5 m 3 m - U m - 2m _ 1.5 m - 1 m - 0.5 m - & & — 1D \* /\ - / I ■ I / • / , . . A - / ; : < \\ ^ -r / * „C • / i . • - / .1.. \ < »•%. . I i ' /»< • • • i • / ^ ^ • * • / * f ! \ j s . -i V • ' ^ V ~ J'N < - r * « ■ • I \ * V % >. " ^ v l « ^s. / ,• \ • \ - < • J / . — IB •Microgastropod bed (1.5 m thick); caps ridge. — 1C.1.1C2 -Miocldaris spine bed (225 m thick); spines increase in abundance up section, most noticably 20 cm above the chert layers; degrees of packing vary laterally and vertically; orientation and spine diameter (1mnrt»mm) also vary. t S e » < i < j f 1A.1,1A2 -Chert layers (2 layers and blebs), each approximately 2 J S cm thick, found at 10 cm Intervals near the base of echinoid bed; fossil-free mudstone (30 cm thick) found below cherts. •Laminated mudstone (29 cm thick). •Mudstone with carbonate "blebs* (50 cm thick) -Covered Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 Figure 22 (continued). 5 m - 4.5 m 4 m - 3.5 m - 3m NN ZSm - 2m — 1.5 m — 1m — 0.5 m — & % I fc 4 V /./v ' w /y-.v r •.,'■< w: - ' < - • * > • - < /' V ^ ' ■ / C /t / =r- ' >> v > < t . < .o '- * * '. '• v > v .;i \ v - . ' / r , . . - _ i i * — .> ; • . - s . - . • • ✓//* \-> • •< «. . v . ' .• * V v v - * - « ■ ' / / / ^ ' ' V ^ ^ I v ^ 'N *1 " - , v 0<3 U 6 « 0 * <9 0 <? O — 2C — 28 — 2A •Microgastropod bed (1.5 m thick); this limestone unit caps ridge. •Miocldaris spine bed (2£5 m thick); spines Increase in abundance up section, most noticably 23 cm above the top chert layers; degrees of packing vary laterally and vertically; orientation and spine diameter (1mm-5mm) also vary; some stringers of spines visible In upper half. -Fossil-free mudstone (30 cm thick) below chert layers (each 1.5 cm thick). -Mudstone with carbonate "blebs” (30 cm thick). -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 116 Figure 22 (continued). 5.5 m 5 m 4C 4.5 m - — -"•<« 4D 4 m 48 3.5 m 4A — V"*/ i s m — / ^ < . '/ V 2m — / . - W . x V 4E 1 m 0.5 m -Microgastropod bed (1.5 m thick); caps ridge. -Miocldarfs spine bed (2.5 m thick); spines increase In abundance up section, most noticably 25 cm above the chert layers; degrees of packing vary laterally and vertically; orientation and spine diameter (1mm-6mm) also vary. •Chert layers (2 cm thick each) found near the base of the echinoid bed; fossil-free mudstone below cherts (25 cm thick). -Laminated mudstone (1 meter thick). -Covered Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 22 (continued). 117 4m — i 3.5 m — 3m — 2.6m - 2m _ & & 4 4 1.5 m - 1m — 0.5 m — e’c ° t a ^ •Microgastropod bed (1.5 m thick); this limestone unit caps ridge. -5 C —P5 -5B + 5B 5A -Mlocldarfs spine bed (1.15 m thick); spines Increase In abundance up section, most noticably 34 cm above the chert layer; degrees of packing vary laterally and vertically; orientation and spine diameter (1mm-6mm) also vary; some stringers of spines visible In upper half. -Fossil-free mudstone (30 cm thick) below chert layer (1.5 cm thick). -Mudstone with carbonate "blebs" (30 cm thick). -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 22 (continued). 118 4m — 3.5 m — 3m — 2.5 m - 2 m — 1.5 m 1m — OJm- & & 'y S * ~ .* • V / x . . , • .* • ' • - ' — \ * * * - • v • • • * > — A- # * . x \ , • > << " x y .s . • / • -» /"••; v •— '< i_ • : . - _ ^ * V - — 6b \ /■ • * ■ V •Microgastropod bed (1.5 m thick); this limestone unit caps ridge. - 6 A • -6 C -Miocldaris spine bed (1.25 m thick); spines Increase in abundance up section, most noticably 20 cm above the chert layers; degrees of packing vary laterally and vertically; orientation and spine diameter (1mm-6mm) also vary; some stringers of spines visible In upper half; fossil-free mudstone with chert layer and blebs (each approximately 2J S cm thick) found 8 cm above lower contact (30 cm). •Laminated mudstone (30 cm thick). •Mudstone with carbonate "blebs” (80 cm thick). -Covered. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 accumulation (in ascending order). Sample P5 was taken from the overlying microgastropod bed at Station 5 (Figure 22). Each thin section was studied in detail and fossil composition was recorded. Fossil abundance was determined through visual estimations of the percent-volume of fossils within the rocks using percent-volume charts such as those provided by Schafer (1969) and Kidwell and Holland (1991; see Figure 10). Abundance measurement sites on the slides were chosen through the same random sampling technique used for the Buttonbed echinoid bed thin sections (see "Laboratory Methods of Data Collection" in Chapter 2). After each slide was adjusted to the specified site, fossils were identified within the microscopic field of view and a visual estimation of percent-volume was recorded. Relative sorting of fossils within the selected site was also noted. In addition to fossil composition, abundance and sorting information, petrographic analysis of the Virgin Limestone thin sections provided information about size variability of fossils throughout the bed, degrees of rounding of skeletal grains, and possible orientations of fossils relative to bedding. Slides from each sample were also examined to determine sedimentological aspects of the rocks, including matrix composition, porosity types, the ratio of grains to matrix, and degree of diagenesis of the rocks. Stratigraphy and Sedimentology of the Virgin Limestone Echinoid Bed Stratigraphic logs were constructed at five stations (Stations 1,2,4,5, and 6) along 322 m of the western portion of the Virgin Limestone echinoid bed at Lost Cabin Springs and are shown in Figure 22 (also see Appendix 3). Only the western portion of the unit's exposure was analyzed because the steep topography of the eastern portion of the outcrop precluded stratigraphic analysis and sample collecting. Examination of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120 accessible exposures on the eastern portion of the study area provided information which was consistent with that recorded from the western exposures. The Virgin Limestone echinoid bed is part of a larger dark gray limestone unit, which ranges in thickness between 1.46 and 2.89 m and is relatively uniform in shape (Figure 20). At its base, the unit is comprised of 25-30 cm of unfossiliferous limestone overlain by one to three black chert layers. The chert layers are quite laterally extensive, typically following the length of the echinoid bed. Also, the layers are fairly uniform in thickness and distribution, with occasional pinching out The bedded cherts range in thickness between 1.5 to 2.5 cm and are each separated by 10 cm intervals of unfossiliferous limestone. The cherts are massive and show no internal sedimentary structures. (For further discussion about the chert layers, see the petrographic analysis of Sample 1A1 described in the following section.) Above the chert layer(s) lies the echinoid accumulation, which accounts for most of the thickness of the limestone unit (between 1.15 - 2.5 m of the overall range of 1.46 - 2.89 m). Spines first appear within this section of the unit approximately 20 to 30 cm above the uppermost chert layer and remain present throughout the rest of the unit. It is important to note that, with the exception of the chert layers, the echinoid spines are the only macroscopic features observed in the limestone unit. No physical or biogenic structures were found within the unit Lack of obvious bioturbation within the unit strongly contrasts with the bioturbated nature of the carbonate mudstones within the Virgin Limestone member. It is suggested that the lack of biogenic and sedimentary structures within the limestone unit indicates it was deposited as a storm bed (Schubert, 1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 121 Sedimentary Petrography of the Echinoid Bed Petrographic analysis of seven thin sections from samples throughout the study area provides important information about the echinoid bed and the lithologies surrounding it The following is a brief description of the seven sample which were petrographically examined. Taken from the base of the echinoid accumulation, Sample 1A1 appears void of fossils, except possibly for one silicified echinoid spine seen only in thin section. The unfossiliferous limestone is composed of large calcite crystals, measuring between 0.6 and 0.8 mm. Small stylolites are present within the limestone with glauconite concentrated along them, suggesting the previous presence of argillaceous material within the limestone. Slide 1A1 includes the chert layer preserved at the base of the echinoid bed (Figure 22). The chert is composed of microcrystalline quartz, which is occasionally transected by clear microscopic veins of coarser quartz. The bedded chert appears to be biogenic in origin, with very poorly preserved sponge spicules and radiolarians observable under high magnification (A.G. Fischer, pers. comm., 1996). Although many radiolarian-rich bedded cherts are interpreted as deeper marine deposits (below the CCD), some cherts may be formed in shallower marine environments if there is a paucity of calcareous plankton and terrigenous detrital influx. Tucker (1991) suggests that such cases in the Paleozoic and Mesozoic may be present because coccoliths, one of the main calcareous planktonic organisms, did not evolve until the Mesozoic. Variations in the CCD could also result in deposition of biogenic siliceous-rich sediments in shallower water. Slide "5A Lower" (Figure 22) is matrix-supported and contains only echinoderm material: echinoid spines, echinoderm fragments, and, occasionally, fairly Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 2 complete crinoid ossicles. Fossil abundance is approximately 30%. Skeletal grains range from 0.3 to 0.8 mm in size. It should be noted that no echinoid spines were observed in this portion of hand sample 5A. Within the thin section, grain sorting is fairly mixed with small grains next to larger ones. Skeletal material is sub- to well- rounded, suggesting exposure to taphonomic conditions which wore down the originally straight edges. There is no evidence of a consistent orientation of material relative to overall bedding. Large interlocking calcite crystals separate the fossil material within Slide "5A Lower". The crystals range in size between 0.35 and 1.7 mm. Calcite syntaxial overgrowths on echinoderm debris are quite common. Small stylolites are also present with glauconite concentrated along them. Other than its concentration along stylolites, the mineral glauconite is very rarely present within the rock, accounting for less than 1% Like "5A Lower", Slide "5A Upper" (Figure 22) is also matrix-supported with large interlocking calcite crystals (0.6 to 1.6 mm). Small stylolites with concentrated glauconite are also present. Slide "5A Upper" contains echinoderm fragments, echinoid spines, bivalve fragments and a few microgastropods. Fossil abundance within this portion of the sample is approximately 25-30% (predominantly echinoderm material). Echinoderm grains range from 0.3 to 1.15 mm in size and bivalve grains range in size from 0.1 to 1.30 mm longitudinally. The two microgastropods measure between 0.7 and 0.8 mm in size. Grain sorting is poor within this slide; grain size is highly variable. Both echinoderm and bivalve fragments exhibit rounded edges, suggesting reworking of material. The echinoid spines have been recrystallized by coarse calcite and are surrounded by ragged quartz, indicating surficial silicification of the fossil material (Figure 23). Calcite syntaxial overgrowths on echinoderm debris are Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 123 Figure 23. Photomicrograph of ragged silicification of a echinoid spine from sample 5B Lower, Station 5. The silicified region is marked by the black arrow. Field of view is 2.6 mm, plane light. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 125 common within the sample. Although there does not appear to be any sedimentological evidence of orientation within the slide (e.g . no geopetal structure), many of the bivalve fragments are oriented parallel to the bedding plane, suggesting that environmental conditions (on the microscopic scale) allowed for settling of the skeletal material. Slide "5B Lower" (Figure 22) is very similar to "5A Upper." It is matrix- supported and contains echinoid spines, echinoderm fragments, bivalve fragments, and one microgastropod. Fossil abundance was measured at 20% (predominantly echinoderm material), slightly lower than "5A Upper." Grain sizes vary as follows: echinoderms 0.15 to 7.5 mm, bivalves 0.2 to 2.9 mm, and gastropod 0.5 mm. Sorting is poor and grains appear rounded. Bivalve fragments are generally oriented parallel to the bedding plane The slide shows that Sample "5B Lower” is matrix-supported, with coarse interlocking calcite crystals (0.4 to 1.4 mm) and some micrite. Calcite syntaxial overgrowths on echinoderm debris are quite common. Recrystallized spines are silicified on their surfaces, as is evident by the ragged quartz surrounding the spines. As observed in the previous slides, small stylolites with concentrated glauconite are present, indicating the original presence of argillaceous material. Slide "5B Upper" (Figure 22) is the most fossiliferous slide, containing 40- 45% (predominantly bivalve material). It includes echinoid spines, echinoderm fragments and abundant bivalve fragments. Echinoderm grains range from 0.2 to 2.8 mm and bivalve fragments from 0.12 to 4 mm. Sorting is poor and grain edges are rounded. A majority of the bivalves are oriented parallel with respect to bedding but curved shells are not preferentially convex or concave. Slide "5B Upper" shows the same mineralogic properties as Slide "5B Lower"; it is matrix-supported with both large interlocking calcite crystals, ranging between 0.6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 6 to 1.5 mm, and micrite. Small stylolites with concentrated glauconite grains are present. Isolated glauconite crystals are also observed in the rock, accounting for less than 1% of the petrographic view. Also, the calcite syntaxial overgrowth on echinoderm debris and the ragged silicificadon of recrystallized spines are quite prominent Slide "5B+" (Figure 22) represents the composition and abundance of fossil material at the Virgin Limestone echinoid bed's upper contact Compositionally, it is very similar to the previously described slides: echinoid spines, echinoderm fragments, abundant bivalve fragments, and occasional microgastropods within a matrix-supported rock. Fossil abundance is approximately 30% (predominantly bivalve material). Skeletal grains range from 0.2 to 5.2 mm for echinoderms and 0.15 to 1.6 mm for bivalves. One gastropod was measured at approximately 0.8 mm in size. Sorting is poor and grain edges are rounded. As with previous samples, many of the bivalve fragments in "5B+" appear to rest horizontal to the bedding plane. Inorganic components of the sample are also similar to the two previously described samples. Large interlocking calcite crystals, ranging from 0.35 to 1.7 mm, separate fossil material in some areas. Ragged silicilication of the surfaces of recrystallized spines is observed within the sample. There are no stylolites found in the thin section. Slide "P5" (Figure 22) gives a view of the petrographic composition within the overlying microgastropod bed. The sample is matrix-supported but contains a different assortment of fossil material. Fossil composition includes abundant microgastropods and bivalves, echinoderm fragments (only one echinoid spine was observed), and one relatively large algae specimen. Fossil abundance was measured at approximately 20% (predominantly microgastropods and bivalves). Skeletal grain sizes vary as follows: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 7 0.5-1.5 mm for microgastropods, 0.15-2.75 mm for bivalve fragments and 0.3-2.5 mm for echinoderm material. One cross section of an articulated bivalve was observed, measuring approximately 2.75 mm in size. The algae specimen was approximately 3.15 mm. Sorting is poor and grains appear sub- to well-rounded. Some of the bivalves appear to be oriented parallel to the bedding plane but the trend is definitely not as strong as the pattern exhibited in the underlying echinoid bed. This sample is more micritic than previous samples. A vast majority of the fossil material has micritized and thus lacks any of its original shell structure. Small stylolites are present within the sample with concentrations of weathered glauconite along them. Glauconite is more abundant within the microgastropod bed, making up to 5% of the petrographic view. The mineral can be observed as isolated crystals and as replacement in some of the microgastropod shells. Faunal Components of the Virgin Limestone Echinoid Bed Composition The Virgin Limestone echinoid bed is a monospecific spine accumulation. Interestingly, the regular echinoid spines which comprise the fossil bed appear to belong to an undescribed species of Early Triassic echinoids. This is not highly unusual considering the patchiness of the Triassic echinoid fossil record. In fact, within the vast majority of Triassic type species of Cidaridae, the only family traditionally thought to have survived the Permian-Triassic mass extinction, is described from spine material (Greenstein, 1992). Articulated test material is rarely preserved among the early post-Paleozoic echinoids because many of them had imbricated tests, which disarticulated rapidly after death (Smith, 1990). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 128 Imbricated tests consist of plates embedded in a thick layer of connective tissue which overlap (like tiles on a roof). The skeletons cannot rapidly transmit impact shocks to adjacent plates (thus dissipating the stress). The evolution of sutural plating, which resulted in a more rigid structure, was significant in allowing post-Paleozoic echinoids to invade more turbulent shallow water niches (Smith, 1984). The early post-Paleozoic echinoids exhibiting the imbricated plate structure probably could not live in very turbulent environments. Post-mortem decay of the connective tissues binding the plates would result in quick disarticulation of the imbricated plates (see Kidwell and Baumiller, 1990; Greenstein, 1990, 1991; Donovan, 1991 for further discussions of decay and disarticulation of regular echinoid tests). It would be expected that spine material would be predominant in fossil assemblages involving the taphonomically fragile early post-Paleozoic echinoids. Spines are the most resilient skeletal component of the echinoid test and would remain intact while more taphonomically fragile test material was disarticulated. Moderate reworking in a depositional setting would preclude preservation of articulated test material without inhibiting spine preservation. In his 1977 compilation of Triassic echinoids, Kier described only those species whose test morphologies were known in sufficient detail; all the rest were considered nominal species and were left undescribed. For the Early Triassic echinoids, Kier (1977b) only lists two species, M iocidarispakistanensis and Leniicidaris utahensis (now known as Miocidaris', Paul, 1988). Upon comparison of primary spine material, it became obvious that the spines of the Virgin Limestone echinoid bed do not belong to either of the described species. The spines found at Lost Cabin Springs range in size from 1 to 6 mm in diameter. No total length for the spines could be determined, as specimens could not Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 129 be removed from the limestone. The maximum (partial) spine length observed in the rock was 2 cm. The spines appear silicifled on weathered surfaces, giving them a darker color than the surrounding and infilling carbonate (Figure 24). Where spine tips are present, the spines appear to taper gently to the terminal point Longitudinal striations are observed on some of the relatively pristine specimens. In contrast the primary spines of M iocidaris utahensis are much thinner than the spines found at Lost Cabin Springs, with a maximum observed width of 1.5 mm in diameter. For this study, the M . utahensis type specimens catalogued in the Smithsonian Institution's Springer Collection at the National Museum of Natural History were examined over the course of several days. Interestingly, these type specimens come from an echinoderm iagerstatten located within the Virgin Limestone of S t George, Utah (see the "Echinoid-Rich Deposits from the Fossil Record" section for further discussion). Examination of the M . utahensis type specimens confirm that the long slender spines of the exquisitely preserved M . utahensis are dramatically different from the thicker spines found at the Lost Cabin Springs locality. The M . utahensis spines are long, straight and appear to be longitudinally striated. The maximum spine length observed within the St. George collection was 27 mm. This length is approximately equal to the horizontal diameter of the corona of M . utahensis, which averages 25 mm. A literature review of M iocidaris pakistanensis revealed that the primary spines of M. pakistanensis also appear to be quite different from the spines found at Lost Cabin Springs. Although the M. pakistanensis spines are closer in size to the spines found in the Virgin Limestone echinoid bed, they appear to be more fusiform in shape. The largest spines observed in the holotype of M. pakistanensis have a maximum width of 5 mm. They appear to be subfusiform; they are widest in their middle portions and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 130 figure 24. Photograph of silicified spines in outcrop at Station 2. Three of the spines are marked by white arrows. Swiss army knife below for scale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 sharply taper to rounded tips (Smith, 1990). This shape differs from the gently tapering shape and pointed tips of the Lost Cabin Springs spines. Also, the M . pakistanensis spines are smooth whereas the spines from Lost Cabin Springs have striations. M iocidaris is the only genus of echinoids known to have survived the Permian- Triassic mass extinction and has therefore been considered ancestral to all post- Paleozoic echinoids (Kier, 1974; Paul, 1988; Smith, 1984). Recent studies suggest, however, that two lineages, the cidaroids (represented by Miocidaris) and the euechinoids, diverged prior to the end of the Permian and therefore, both crossed the Permian-Triassic boundary (Smith and Hollingsworth, 1990). Although this is presently the general sentiment among echinoid workers, there has been no direct fossil evidence of euechinoids within the Early Triassic echinoid fossil record; the two species of Miocidaris remain the only documented echinoids from the beginning of the Mesozoic. The following sections describe the field observations and laboratory analyses of the paleontologic components of the Virgin Limestone echinoid bed. The fossil abundance, distribution patterns, taphonomy, and microfaunal components of the bed will be addressed. Reconstruction of the accumulation history of the spine bed will then be discussed using the information revealed in this study. Abundance and Distribution Patterns As previously mentioned, the Virgin Limestone echinoid bed's spines are the only fossils observed macroscopically within the dark gray limestone. The spines first appear within the unit approximately 20-30 cm above a series of bedded cherts. There Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 133 is an overall increase in spine abundance upsection within the bed (Figure 25). Held observations record high variability in spine distribution both laterally and vertically within the unit, with occasional densely packed lenses and stringers present among more dispersed areas. Spines appear to be poorly sorted, with various diameters (1-6 mm) visible in outcrop. This range of spine sizes may indicate the presence of several types of spines or may simply be an artifact of examining a two-dimensional view. Identical spines would display varying diameters depending on which portions were cut As a result, sorting may appear poorer than it actually is due to the nature of the observed view. The Virgin Limestone echinoid bed spines were not deposited in any consistent orientation; they are oriented in every direction with respect to the bedding plane (see hand sample analysis results in Table 5). Uncommonly horizontally bedded stringers are present within the bed but the vast majority of the fossil material shows no consistent trend. This common jumbled appearance suggests that the formation of the spine bed was influenced by significant reworking of the depositional area Some spines are even oriented perpendicular to the bedding plane. This lack of orientation relative to the bedding plane could be result from either relatively high energy physical processes (e.g., storm activity; see Middleton, 1967; Greensmith and Tucker, 1969; Kidwell, 1991b) or bioturbation. It should be noted that many of the bivalve fragments observed in thin sections of the echinoid bed are oriented parallel to the bedding plane. It is unlikely that the seemingly random orientation of spines within the bed is a product of bioturbation, since the smaller, more fragile bivalves surrounding the spines were apparently unaffected by the local mixing. Examination of spine abundance and distribution patterns within hand samples confirms the above-described field observations. Table 5 summarizes the results of the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 134 Figure 25. Photograph showing spine distribution within the Virgin Limestone echinoid bed near Station 5. Scale is in cm. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 135 DNAG Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 136 Table 5. Results from hand sample analysis of fossil abundance, packing and orientation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sample # Packing Abundance (per 100 cm ) Orientation (surface) 1 A - 0 1B - 1 perpendicular to beddinq 1C.1 DIS 13 on bedding plane. 1C.2 OS 18 none 2A DIS 3 perpendicular to bedding 2B DIS 14 none 2C - 0 - 3A.1 - 1? . 3A .2 DIS 3 none 3B • 0 _ 3C - 0 - 4A L 4 none 4B • 0 . 4D L 3 4 none 5A DIS 19 none 5B L 2 0 none 5B+ DIS 10 none 6A • 0 . 6B DIS 13 none Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 hand sample analysis of spine abundance, packing and orientation within the echinoid bed. Recall that sample letters progress (A, B, C, etc.) from the base to the top of the bed at most stations,with the exception of Station 4 (Figure 22; Appendix 3). The overall trend of vertical increase in spine abundance within the bed is well-documented in the hand sample analysis; most stations show a definite increase in spine abundance from bottom to top. There is an interesting correlation between the absolute spine abundance recorded within each randomly selected view of the samples and the relative packing assessed for each selected view. Relative packing of the spines does not appear to be a factor of spine abundance as much as it is affected by the elongate spine shapes. For example, the number of spines within Samples 2A and 4A only differs by one (3 spines/25 cm2 vs. 4 spines/25 cm2, respectively) but the relative packing of the two samples is markedly different due to the cut of the exposed spines. Sample 4A contains more longitudinal exposures of spine material, resulting in a more closely packed fabric. The difference in the relative packing of Samples 5A and 5B, which also differ in absolute spine abundance by 1 spine, similarly results from the biases of two-dimensional analysis. When conducting relative abundance analyses on two- dimensional subjects, it is therefore important to recognize the potential impact that fossil shape has on the information, particularly in the case of very irregularly shaped fossils deposited in an inconsistent orientation. Another comparison using the absolute spine abundance information contained in Table 5 explores the potential bias of a nonrandomized sampling technique. Samples were examined for absolute spine abundance (by simply placing a grid down on the largest surface) and the results were compared to Table 5s results, which were obtained through examination of randomly selected views (Table 6). Note that the two Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 3 9 scales of raw abundance are different with the "Abundance by Nonrandom Method” column based cm an examination view of 100 cm2, four times that of the "Abundance by Random Method" column. A third column, "Nonrandom Adjusted", modifies the abundance results of the nonrandomized method so they are based on a 25 cm2 field of view. It was predicted that the abundance recorded by the nonrandomized method would noticeably exceed the abundance recorded through randomized procedures, as the former results would be based on wherever the surveyor's eyes preferred to place the grid. The table confirms that this pattern is present but is not as exaggerated as expected. It appears that only the samples which had very large numbers of spines on their surfaces were greatly affected by the predicted sampling bias. For example, Samples 3A.1,3A.2 and 4A appear much more fossiliferous when a non-random approach was taken. Samples with only moderate spine abundance may not have "tempted" the surveyor's eye and, therefore, do not exhibit very different results between the two methods. It should be noted that the difference in the two results illustrates the high variability of spine abundance found within the bed, even at such a small scale. Like fossil abundance, spine orientation is another feature which produced similar results in both hand sample and field analyses. No consistent orientation of spines could be determined in the hand samples. Table 5 records the various patterns of orientation observed in the hand samples. A directional "trend" was described when at least half of the total number of spines within the grid view exhibited the same general orientation (e.g., perpendicular, parallel) relative to the bedding plane. As was described in the field observations, the majority of spines (8 of 11 samples) show no consistent orientation relative to the bedding plane. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140 Table 6. Results of fossil abundance analysis using random and nonrandom sampling techniques. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 141 Sample# Abundance by ’Nonrandom* Method (per 100 cm ) ’Nonrandom* Adjusted (per 25 cm \ Abundance by ‘Random* Method (per 25 c m ) 1A 0 0 0 1B 4 1 1 1C.1 77 19.25 13 1C.2 61 15.25 18 2A 15 3.75 3 2B 47 11.75 14 2C 1 0.25 0 3A.1 89 22.25 1? 3 A. 2 70 17.5 3 3B 2 0.5 0 3C 0 0 0 4A 67 16.75 4 4B 6 1.5 0 40 68 17 34 SA 23 5.75 19 SB 43 10.75 20 5B+ 10 2.5 10 6A 2 0.5 0 6B 41 10.25 13 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 142 Taphonomv A taphonomic analysis was conducted on the spines present within the hand samples. Degree of striations on spine surfaces was assessed through the use of a three-point semi-qualitative index, in which "I" described well preserved spines with striations, "2" described those with some striations present, and "3" represented spines with smoothed or abraded surfaces with no striations present Results show that most of the examined spines were well-abraded with no striations present (Table 7). The echinoid bed contains spines exhibiting various degrees of abrasion, with relatively pristine specimens mixed with more abundant heavily abraded specimens (e.g. Samples 1C, 2B, 5B, and 6B). In addition to the degree of surficial ornamentation of the spines, the abundance of spines with observable tips was noted. Presence of abundant spine tips would suggest a relatively short exposure time before burial as tips would be most vulnerable to abrasive processes. Table 7 shows that most spines exposed on the weathering surfaces of the echinoid bed do not exhibit their terminal points. In fact, many of the observed spines are broken across their shorter axis. Absence of spine tips may result from a number of factors, including predepositional abrasion or breakage, post- depositional abrasion or breakage, or perhaps even, exposure of the middle portions of spines (i.e., the points are present but are imbedded in the limestone). The rare presence of spine tips reveals relatively sharp points, suggesting that the spines were not exposed long enough to significantly round their sharp points. In addition to examining the degrees of spine ornamentation and presence of spine tips within the Virgin Limestone echinoid bed, it is important to discuss the partially silicified nature of the spines observed in the unit It is appears that the larger spines (greater than 2 mm in size) have been preferentially silicified; smaller spines Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 7. Results of taphonomic analysis of degrees of spine striations and presence/absence of spine tips. 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. Sample# Degree of Ornamentation Spine points (# pres/abs) Comments 1A • no spines on surface IB 3 abs smooth 1C 2, 3 abs 2 spines partially striated, rest smooth 2A 3 ?no seines abs well worn, if present 2B 3 .2 2 points 2 spines with end points present 2C - no spines on surface 3A 3 abs 3B • a no spines on surface 3C - - no spines on surface 4A 3 abs 4B . a no spines on surface 4D 3 2 points 2 spines with end points present 5A 3 abs SB 3. 2 abs one compressed Is partially striated 5B+ 3 ■ badly worn 6A 3 . badly worn 6B 3. 1 abs one compressed Is partially to well striated 145 seen in thin section do not appear silicified. Ragged cryptocrystalline silicification has replaced the outer portions of the larger carbonate fossil material (see Figure 23). The immediate source of silica for the echinoid bed is most likely the underlying chert layers. It is interesting to note the influence which the silicified nature of the spines has in recognizing the bed; silicification of the spines' surfaces results in a distinctive weathering color contrast leading to easy identification of the fossil material within the unit The partially silicified spines on the weathered surfaces of the unit are the only macroscopically diagnostic feature of the bed. All the larger spines (greater than 2 mm) observed in thin section (and in hand sample with a hand lens) appear to be surficially silicified and there is no increasing or decreasing trend in silicification of other fossil material. This suggests that the distribution of silicified material is not the result of the specimens' position relative to the underlying chert. Apparently, the larger spines are preferentially silicified according to their composition or size and not due to a silicification gradient within the echinoid bed. If the abundance of silicified spines was related to a silicification gradient, it would be expected that a decrease of silicified material upsection would be observed. However, an increase in silicified spine abundance is witnessed, suggesting that the larger spines are being preferentially silicified throughout the unit Primary skeletal structure has been shown to play an important part in the determination of silicification sites (Elorza, 1987; Crowley, 1988; Carson, 1991; Tucker, 1991). The large crystal size of the spines may cause a cryptocrystalline crust to form, as the carbonate material is dissolved slower than the silica is precipitated (see Holdaway and Clayton, 1982; Carson, 1991). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 146 Petroeraphic Examination of the Virgin Limestone Echinoid Bed The petrographic information revealed in this study provides important information about the fossiliferous deposit which is considered to be the Virgin Limestone echinoid spine bed. Macroscopically, the Virgin Limestone accumulation appears as a monospecific spine bed; according to the commonly accepted shell bed criteria of 2 mm maximum grain size, this fossil accumulation is simply a spine-rich limestone. Examination of the bed at a finer scale, however, reveals that the fossil content and accumulation history of this deposit are more complex than the macroscopic scale would indicate. The shell bed is more faunally diverse than it appears. The abundance patterns observed in the petrographic analyses (Table 8) can be compared to those patterns observed both in the field and in hand samples. The limestone portion of both Sample and Slide" 1A1" is unfossiliferous. Directly above " 1A1", Sample "5A Lower" marks the beginning of a fossiliferous deposit The hand sample itself does not display any macroscopic fossil material but the slide gives insight into the amount of echinoderm debris which is present within the rock. There are echinoderm fragments and microscopic echinoid spines observed within the limestone layer before the larger, easily recognizable silicified spines appear in any significant numbers. Interestingly, the microscopic abundance values from the bottom to the top of the echinoid bed do not provide the clear up-section increasing trend that was observed in hand sample. In fact, as echinoid spine material generally increases upsection on the macro-scale, the relative abundance of echinoderm material to bivalve material decreases on the micro-scale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 8. Petrographic information for samples examined from the Virgin Limestone echinoid bed and the surrounding Iithologies. 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. SAMPLE# FOSSIL COMPOSmON ABUNDANCE (% ) G R A IN SIZES SO R T IN G R O U N D IN G 1A1 - 0% ?? - - 5A Lower echinoderm fragm ents 30% 0.3-0.8 mm poor sub to well echinoderm plates echinoid spines 5A Upper echinoderm fragm ents 25-30% 0.3-1.15 mm poor rounded echinoderm plates echinoid spines bivalve fragm ents 1% 0.1-1.3 mm m icrogastropods <1% 0.7; 0.8 mm 5B Lower echinoderm fragm ents 20% 0.15-7.5 mm poor rounded echinoid spines bivalve fragm ents <5% 0.2-2.9 mm m icrogastropods <1% 0.5 mm 56 Upper echinoderm fragm ents 20% 0.2-2.8 mm poor rounded echinoid spines bivalve fragm ents 25% 0.12-4 mm 5B+ echinoderm fragm ents 10% 0.2-5.2 mm poor rounded echinoid spines bivalve fragm ents 25% 0.15-1.6 mm m icrogastropods <1% 0.8 mm 5P m icrogastropods 10% 0.5-1.5 mm poor rounded bivalve fragm ents 5% 0.15-2.75 mm echinoderm fragm ents <5% 0.3-2.5 mm echinoid spines algae <1% 3.15 mm 149 There is a definite compositional difference between the Virgin Limestone echinoid bed and the overlying microgastropod unit This is evident in field, hand sample, and petrographic analyses. Both macroscopic and microscopic views display a marked decrease in echinoderm material, which is replaced by abundant microgastropod specimens ( see Table 8; Sample P5 represents the microgastropod bed). The microscopic fossil information obtained from the Virgin Limestone echinoid bed generally confirms compositional and abundance patterns observed at the macroscopic scale: (1) fossil composition changes between the echinoid bed and its surrounding lithologies, and (2) echinoderm distribution is variable within the bed. In summary, the Virgin Limestone echinoid bed is an Early Triassic sea urchin spine bed. The concentration appears to be a monospecific accumulation of regular echinoid spines; although echinoderm, bivalve and microgastropod material have been identified in petrographic analysis, no other fossil material has been observed on the macroscopic level. The spines are 1-6 mm in diameter and some exhibit longitudinal striations. They appear to belong to an undescribed echinoid species. In general, spine abundance increases upsection within the limestone unit The echinoid bed most likely represents a storm debris bed which was deposited into the distal portion of a shelfal setting. Many of the fossiliferous limestone units of the Virgin Limestone at Lost Cabin Springs have been identified as distal storm deposits (Schubert, 1989). Overall, Virgin Limestone units display several characteristics described in the storm bed literature including intraclasts, erosional boundaries, gutter casts, the absence of internal sedimentary structure, and concave- down bivalve orientation (Schubert, 1989; see summary storm bed descriptions in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150 Kriesa, 1981; Norris, 1986; Parsons etal., 1988). The echinoid bed is thicker than most of the described storm beds from Lost Cabin Springs but its size has been interpreted to reflect the magnitude of the storm which deposited it (Schubert, 1989). Although the Virgin Limestone spine bed does not display some of the classic signs of storm bed deposition, such as rip-up clasts, it does exhibit evidence of high energy depositional conditions. The echinoid bed has an erosional base, separating it from the underlying bioturbated mudstone unit Lack of internal sedimentary structures within the bed also is indicative of some storm beds (Kriesa, 1981; Kidwell, 1982; Aigner, 1985; Norris, 1986). Petrographic analysis reveals that many of the bivalve fragments observed in the bed are oriented parallel to the bedding plane, suggesting that this lack of sedimentary structure is not due to the homogenization of the deposit by bioturbation. Active bioturbation would affect the orientation of both the spines and the bivalve material surrounding them. With this petrographic evidence in mind, lack of spine orientation appears to be the result of physical processes and not the result of movement by bioturbation. Perhaps the difference in orientation patterns between the spines and the delicate bivalves is a result of the different sizes and densities of the two fossil types. The less dense, smaller bivalve fragments would have been hydrodynamically different from the dense, large spines. The accumulation represents a mix of allochthonous echinoid material and parautochthonous fossil debris {e.g., delicate, thin-shelled bivalve fragments; see Aigner, 1985 and Schubert, 1989). Regular echinoids tend to prefer shallow water, firm ground or rocky strata (Smith, 1984; Barnes, 1987). It is likely that the spines were brought into the depositional area from the shallower eastern part of the shelf. The spine bed is the only portion of the Virgin Limestone at Lost Cabin Springs which exhibits echinoid spine material, supporting an allochthonous origin. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 Taphonomic condition of the spines suggests that the spine bed was comprised of fewer relatively pristine specimens among more abundant heavily abraded individuals. This could be the result of differential abrasion due to storm activity or perhaps reflects a time-averaged deposit including both significantly reworked material and fresher material. Presence of spine tips suggests that the spines were not reworked to the degree that terminal points were completely worn down or removed. The amount of matrix and fine-grained fossil material (£ 2 mm) within the bed suggests that the accumulation was not greatly physically reworked (e.g., winnowed) after deposition. This would seem logical as the energy regime within the distal portion of the shelf is typically low (see onshore-offshore storm bed morphologies in Kidwell etal., 1986; Norris, 1986; Parsons etal., 1988). The echinoid bed was probably deposited from the east into the quieter, deeper setting below normal wave base. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 152 CHAPTER 4: DISCUSSION Comparison of the Two Echinoid Beds The two echinoid concentrations described in this study provide very different examples of echinoid beds and how they form. There are many ways in which the two beds vary, the most prominent being that (1) they are comprised of different types of echinoids, 2) they were deposited in different marine environments, and (3) they are from very different stages in the evolutionary history of echinoids. The following section discusses several of the key differences between the two examined echinoid beds. Also, it addresses the primary factors which influenced the formation of the two beds. Echinoid type As mentioned in the introduction to this paper, we know from the echinoid fossil record that different echinoid test morphologies have different degrees of post mortem resilience (see Figure 1). Two end members on the spectrum of test strength are present in the Buttonbed Sandstone and the Virgin Limestone. Clypeasteriods, which include sand dollars, have the most well-structured or resilient tests of all the echinoids, with interlocking sutured plates and supportive internal pillars (Seilacher, 1979; Smith, 1984; Donovan, 1991). Vaquerosellamerriami's test enabled it to withstand relatively high energy regimes during life and proved fairly resistant to post mortem taphonomic processes. In contrast to the test morphology of the sand dollar, the regular echinoid test is weak against taphonomic destruction (Kier, 1977a; Smith, 1984; Donovan, 1991; Greenstein, 1992). The Triassic was a time in which regular echinoid test structures Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 5 3 were evolving from the imbricated variety to more rigid designs (Kier, 1977b; Smith, 1990; Smith and Hollingworth, 1990). Both described regular echinoids from the Early Triassic had imbricated tests (Durham and Melville, 1957; Kier, 1974,1977b; Smith, 1984). Although no articulated test material was found in relation to the Virgin Limestone spines at Lost Cabin Springs, it can be inferred that the corresponding tests were probably imbricated. These early post-Paleozoic echinoid tests would have disarticulated soon after death when decay and/or scavengers had removed the connective tissue joining the test plates. The most taphonomically resilient parts of the echinoids, the spines, are the only intact macroscopic evidence of the presence of regular echinoids in the Virgin Limestone at Lost Cabin Springs. Depositional environment The fossil components of the two echinoid beds strongly reflect the relative preservational potential of the two types of echinoids, particularly considering the different types of environments in which the echinoids were deposited. The Buttonbed coquina was formed in a shallow marine siliciclastic environment, as is evident in the stratigraphic and sedimentologic analysis of the bed. The echinoid concentration was shaped by current winnowing and periodic storm activity in the shallow setting, producing the coarse-grained fossiliferous deposit Although sand dollar fragments are abundant within the lower subunit, many of the sand dollar specimens present in this lower portion of the bed remained intact despite the winnowing action. As the environment became increasingly shallow over time, the high energy processes continued to rework the concentration, resulting in an upper hash unit The carbonate depositional environment of the Virgin Limestone was deeper marine than the siliciclastic Buttonbed and, therefore, was not subject to the same Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154 reworking intensity. Presence of microscopic fossil material, such as delicate bivalve fragments, indicates that the bed was not reworked significantly enough to remove the finer material from the accumulation. Horizontal orientation of the bivalve material suggests that the bed was not bioturbated. Spines, the largest grain component of the bed, do not appear to have been deposited in any consistent orientation. Instead, they are oriented in numerous directions relative to the bedding plane. This lack of orientation may be a product of storm deposition (see previous section). Lack of internal structure, including bioturbation and sedimentary features, in the limestone suggests that the unit was deposited as a storm debris bed. Evolutionary Timing It is of interest to note the very different stages of echinoid evolutionary history represented by the two examined echinoid beds. The Virgin Limestone spine bed was deposited following the most devastating mass extinction in the history of life. An estimated 90% of all marine genera present in the Upper Permian went extinct at the Permian-Triassic boundary (e.g., Erwin, 1993, 1994). As previously mentioned, only one genus of echinoid, Miocidaris, is reported for the Early Triassic. This was a crucial time of recovery for the class. It is also a time in the evolutionary history of echinoids that is poorly understood by paleontologists. Knowledge of the echinoid fauna of the Early Triassic is very patchy and present information, such as diversity patterns based on taxonomic counts, may be greatly biased by the relatively poor quality of the fossil record (Smith, 1990). The Virgin Limestone spine bed exhibits a preservational style quite typical of the Early Triassic (Greenstein, 1990,1992). In sharp contrast, the dense sand dollar accumulation of the Miocene Buttonbed Sandstone was deposited well into the radiation of echinoids, which began to flower in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 155 the Jurassic. Clypeasteriods had been steadily increasing in diversity since the Paleocene (Smith, 1984). This echinoid bed represents a prosperous time in the evolutionary history of echinoids. Clypeasteriods were particularly prosperous, accounting for408 of the 924 species of irregular echinoids recorded from the Miocene (Kier, 1977a). Accumulation Processes When reconstructing the accumulation histories of shell beds, it becomes important to recognize the relative importance of biological and sedimentological factors in bed formation. Both biological and physical agents contribute to the accumulation of a fossiliferous deposit; identification of the relative degrees in which these processes influence the bed's deposition is crucial in accurately understanding how the bed was formed. In order to evaluate the processes which affected the accumulation of the echinoid beds examined in this study, it is first important to provide working definitions of the processes involved. There are many genetic classification schemes based on accumulation processes (Johnson, 1960; Aepler and Rief, 1971; Seilacher andWestphal, 1971; Aigner etal., 1978; Ftirsich, 1982; Kidwell, 1982; Strauch, 1990; and others). This study uses the Kidwell, Filrsich and Aigner (1986) classification scheme which divides all concentrations into three categories: biogenic, sedimentologic and diagenetic. The three concentration types can be seen as a schematic ternary diagram of the three end members and three intermediate types of accumulations (Figure 26). For the purposes of this study, only four of the six types will be discussed: biogenic, sedimentologic, diagenetic, and the combination of biogenic and sedimentologic concentrations. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 156 Figure 26. Schematic ternary diagram of genetic types of shell beds (From Kidwell, Fiirsich and Aigner, 1986). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 BIOGENIC GENETIC TYPES OF SKELETAL ACCUMULATIONS SEDIMENTOLOGIC DIAGENETIC flip iS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 158 Biogenic concentrations (area 1 on Figure 26) can be either intrinsically or extrinsically biogenic. Intrinsic biogenic concentrations result from the gregarious behavior (in life or death) of the shell producers. These fossil accumulations are typically autochthonous or parautochthonous and can record preferential larval colonization, single colonization events by opportunistic groups, and dense ephemeral groupings associated with feeding, spawning or moulting (Kidwell etal., 1986). Extrinsic biogenic concentrations are produced when other organisms interact with the shell producers or their shells. These accumulations are typically parautochthonous or allochthonous. Examples of such concentrations include shell-filled pits produced by predators (or scavengers) and burrows selectively lined or backfilled with shell material (see Kidwell etal., 1986, for detailed references). Sedimentologic concentrations (area 2 on Figure 26) are produced by physical, primarily hydraulic, processes. In the accumulation of the bed, the fossil components act as sedimentary grains within a matrix which is either reworked or never accumulates. Kidwell etal. (1986) subdivide sedimentologic concentrations into three accumulation types: (a) parautochthonous lags which result from concentration of fossil material by hydraulic sorting or preferential removal of finer sediments; (b) autochthonous/parautochthonous concentrations produced by gradual accumulation during periods of low net sedimentation; and (c) autochthonous/parautochthonous/ allochthonous concentrations which combine transported exotic shells into the parautochthonous or autochthonous depositional setting. Examples of sedimentologic concentrations include fossiliferous storm deposits and shell-paved turbidites (see Kidwell etal., 1986, for detailed references). Diagenetic concentrations (area 3 on Figure 26) are defined as fossil concentrations in which the fossil density is significantly increased as a result of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 159 diagenesis (Kidwell etal., 1986). Two main diagenetic processes which produce concentrations are compaction, which increases the close-packing of fossil material, and selective pressure solution of matrix in fossiliferous limestones (see Kidwell etal., 1986 for detailed references). The fourth type of genetically classified concentration relevant to this study is the concentration of mixed origin, which combines both the biogenic and sedimentologic processes (area 4 on Figure 26). These types of concentrations result from the interplay of the two kinds of processes or from the overprinting of one type of process over the other (Kidwell et al., 1986). The authors propose two different scenarios for the formation of mixed origin concentrations. First, a primarily biogenic accumulation may later be reworked by physical agents to produce a parautochthonous concentration. The overprint of sedimentologic processes over the initially biogenic concentration is often significant enough to obscure the original nature of the concentration. It is important to note factors in the bed, such as gregarious behavior of the shell producers, in order to accurately assess its accumulation history. It is suggested that if reworked skeletal material is deemed allochthonous then the concentration should be classified as sedimentologic, and not mixed, in origin (Kidwell etal., 1986). The second type of mixed origin concentration may be produced by the recolonization of initially sedimentologic concentrations. The settling of sessile organisms on sedimentologically produced shell concentrations could result in either parautochthonous or parautochthonous/allochthonous fossil accumulations. Examination of the stratigraphy, sedimentology and paleontology of the two echinoid beds of this study reveals that the two accumulations were formed by different primary processes. By the above described terminology, the Buttonbed Sandstone coquina would be classified as a concentration of mixed origin. V. merriami Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 populations were abundant within the area, as is evident by their presence in the underlying sandwave lithofacies and their overwhelming abundance in the coquina. Sand dollars are typically gregarious in nature; the masses of V. merriami were initially locally deposited as biogenic concentrations. Physical reworking of the area by shallow marine high energy processes greatly overprinted the original biogenic fabric of the bed by winnowing and extensively reworking it It is a parautochthonous fossil accumulation which was produced by both biogenic and sedimentologic agents. Unlike the Buttonbed coquina, the Virgin Limestone echinoid bed does not contain fossils found in other surrounding units; the spines present in the echinoid bed are only found within the unit This is important in understanding the biological control of the accumulation. The spine bed represents an area of very low diversity and very abundant regular echinoids within the epicontinental seaway. It is these biological controls which deline the fossil accumulation. The resulting deposit presents a unique fossil component to the Virgin Limestone member. It is also important to recognize that diagenetic controls help define the Virgin Limestone spine bed. The partial silicification of the spine material has aided in identifying the echinoid bed; the color contrast of dark brown partially silicified spines and the gray limestone is the primary macroscopic feature of the bed. Without the silicification, the spine bed would take on a very different macroscopic appearance. Although the spine bed is certainly the product of both biologic and diagenetic factors, it is not a biogenic or diagenetic concentration. The bed does not directly result from the behavior of shell producers or organisms interacting with the shell material. Nor is its final concentration primarily the product of the diagenetic processes. According to the ternary scheme, this bed would more accurately be classified as a sedimentologic concentration. The limestone unit is a storm deposit which brought Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 161 regular echinoid material from a shallower area to the more distal portion of the shelf. The fact that there is no evidence of the spines elsewhere in the study area reinforces the conclusion that they are allochthonous in origin. Within the employed classification scheme, the Virgin Limestone echinoid bed should therefore be classified as a sedimentologic concentration. Comparative analysis of controlling processes along environmental gradients confirms this study's evaluation of the beds (Figure 27). Kidwell etal. (1986) suggest that the nearshore shelfal environments, such as the depositional setting on the Buttonbed coquina, can typically be comprised of concentrations which are primarily sedimentologic in origin or combine both sedimentologic and biogenic agents. This depositional environment is dominated by sedimentologic concentrations due to its high energy regime but also includes sedimentologically overprinted biogenic concentrations similar to the Buttonbed Sandstone echinoid bed. Further offshore, biogenic agents are more controlling of the shell concentrations, as seafloor energy dynamics decrease. Sedimentologic concentrations found in the distal portion of the shelf area are thought to result from rare intense storm events (Kidwell et al., 1986). The Virgin Limestone echinoid bed is most likely an example of this type of concentration, which was preserved in a relatively low energy setting. Bulk deposition of the accumulation during a storm event could explain the lack of bioturbation within the unit, as well as the poorly sorted fossil components and overall lack of consistent orientation of spines within the bed. Together the two concentrations provide examples of very different echinoid beds. It is important to recognize that these examples are only two of a wide variety of forms that echinoid concentrations can exhibit Examination of other echinoid-rich Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 162 Figure 27. Expected relative abundances of shell bed types along an onshore- offshore transect in a marine setting dominated by terrigenous sedimentation (From Kidwell, Fiirsich and Aigner, 1986). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 164 accumulation in the literature allows for a larger view of what comprises an echinoid bed and how these interesting fossil accumulations can form. Echinoid-rich deposits of the fossil record The following section discusses the characteristics and depositional environments of two prominent examples of echinoid-rich deposits in the stratigraphic and fossil record. These samples of echinoid concentrations are not limited to any particular type of echinoid, time period or marine depositional environment; they were chosen solely because they are known to yield abundant echinoid fossils. The concentrations were selected to provide several additional examples of what an echinoid concentration can be. Virgin Limestone Echinoid Bed of S t George. Utah This echinoid bed was originally chosen for study because it is coeval to the Virgin Limestone spine bed and was thought to be a better preserved assemblage of the Triassic echinoids found at Lost Cabin Springs. However, examination of the specimens from both localities revealed that the two echinoid beds differ not only in preservational style but also in echinoid composition. The echinoid accumulation of S t George has yielded more than 200 specimens of Miocidaris utahensis (Kier, 1968). The ammonite, Tirolites, and several other molluscs have also been described from the locality (Kier, 1977b) but none were observed in the slabs examined from the Smithsonian collections. According to the fossil composition of the slabs, the echinoid bed is a monospecific bed of M. utahensis. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 6 5 For this study, the Smithsonian slabs were examined over the course of several days in order to assess the preservational style of the echinoid concentration. The slabs vary in thickness from 6-50 mm and echinoids are abundant on bedding surfaces and throughout the thickness of the samples. Specimens present on the slab surfaces are exquisitely preserved. Most exhibit intact or slightly crushed tests with primary and secondary spines still attached. Periproctal and peristomal plates, which are typically among the first skeletal elements to be taphonomically removed, are commonly observed on the specimens. Lantern structures are also often preserved in place. On some of the echinoids, plates have been weathered away exposing the lantern structures and the interior of the tests. Cross-sectional views of specimens (located in the vertical portions of the slabs) also show articulated tests with spines and lanterns still attached. There are numerous echinoid test-rich layers within the slabs suggesting the burial of multiple generations of M. utahensis over time. It is obvious that this echinoid bed represents many generations of a community of echinoids which were either buried alive or very soon after their demise. Presence of intact imbricated tests with attached spines and internal skeletal components indicate that the organisms' remains were barely exposed to taphonomic processes. Such extraordinary preservation, particularly for the Triassic, demands a rapid burial scenario. These echinoids are preserved in the eastern portion of the Virgin Limestone, which is interpreted as a quiet shallow subtidal to intertidal setting (Schubert, 1989). Kier (1968) has identified their depositional unit as a fine-grained sandstone representing a subtidal to intertidal environment The M. utahensis populations living in this shallow potion of the epicontinental seaway would have experienced relatively intense and frequent storms which would account for their quick burial. This biogenic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 166 bed clearly represents multiple generations of echinoids which were each buried by rapid storm events, leading to their exquisite preservation. Merriamaster Bed. Kettleman Hills North Dome. CA Examination of the Merriamaster-rich accumulation from the Kettleman Hills was done primarily through a literature review. Previous work, particularly by J. R. Dodd and R.J. Stanton Jr., on the echinoid bed and its surrounding units provided much of the depositional history of the accumulation. Personal observations from a field trip to the North Dome supplement the information obtained from the literature. This irregular echinoid bed is located within the late Pliocene Pecten "Zone" of the San Joaquin Formation (Woodring etal., 1940). The unit varies in thickness between 30 cm to 6 m and laterally extents for at least 16 km (Dodd and Stanton, 1975). The sand dollar Merriamaster predominates in the accumulation with rare bivalves and gastropods. Sand dollar tests range in size from a few millimeters to 45 mm in diameter, suggesting that both juveniles and adults were present in the assemblage (Durham, 1978). The taphonomic conditions of the Merriamaster sped mens vary greatly. Most specimens are preserved as spineless tests but a few have been observed with spines still attached (see photographs in Durham, 1978). Of the spineless specimens, many are in relatively pristine condition (petal structures and plate boundaries are visible) while others are heavily abraded or corroded. Most specimens display intact tests but some appear badly crushed (but still distinguishable). This sand dollar bed has been interpreted to have been deposited in the outer portion of a marine embayment (Stanton and Dodd, 1970,1976). The unit is a well- sorted, commonly cross-bedded sandstone indicative of a current-swept environment Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 (Dodd etal., 1965). Stratigraphic studies by Dodd and Stanton (1975) suggest that the lenticular sandstone unit represents a series of sand lenses or bars. The low diversity of the fossil assemblage (similar to that of the Buttonbed Sandstone echinoid bed) may reflect the stress conditions of a mobile sand substrate. The abundance of Merriamaster within the bed (approximately 8 specimens per 28 mm of vertical exposure according to Durham, 1978) suggests that many generations of the sand dollar lived in the depositional area. Variability in the preservational conditions of the specimens indicates that some sand dollars were buried quickly, perhaps during intense storms, while others were reworked until heavily abraded. The paleodepth of the depositional area, which has been determined to be only a few tens of meters (Dodd etal., 1985), supports the conclusion that these sand dollars were deposited in a relatively high energy environment which would have been impacted by storm activity. It should be noted that it is likely that the area was not reworked to the extent that all the underlying accumulation was exhumed, as is suggested by the presence of those specimens with attached spines. The Impact of Preservational Style and Taxonomic Wealth on the Classification of Echinoid Deposits The working definition of an "echinoid bed" used in this paper is based on the relative abundance of echinoid material in a shell bed. It is important to recognize that extraordinary preservation and/or high diversity are not discriminating criteria of this classification scheme. During the selection process for echinoid-rich deposits, one example was repeatedly suggested by various echinoid workers: the St. Cassian Beds of the Italian Alps. Thousands of echinoid specimens have been collected from the St. Cassian. Smith (1990) classifies the fossil beds as Echinoderm Lagerstatten. It is with Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 6 8 this knowledge that the beds were chosen for description in this study. Examination of the literature, however, revealed that the proclaimed wealth of echinoids found within the beds is based on exquisite preservational style and taxonomic abundance but does not take into account the abundance of the echinoids relative to the overall fauna. The S t Cassian Beds do yield a significant amount of well-preserved echinoid species. In fact 12 genera and 23 species (and an additional 24 nominal species based solely on spine morphologies) have been identified from the beds and almost all of the Triassic cidaroid type species come from these fossiliferous deposits (Smith, 1990). Preservation of echinoid tests is extraordinary as is evident by the thousands of beautiful specimens (not to mention the innumerable spines) found in these deposits (see Ftirsich and Wendt 1977; Kier, 1977b; Smith, 1990). But the S t Cassian Beds are not echinoid-rich deposits. They include an extremely diverse fossil assemblage including bivalves, calcareous sponges, corals, gastropods, brachiopods, and echinoderms, as well as ammonoids, algae, foraminiferaand ostracods (Ftirsich and Wendt 1977; Kier, 1977b). As of 1977, the total number of invertebrate species which have been described from the beds was 1000,400 of which were gastropod species (Ftirsich and Wendt 1977). The S t Cassian Beds represent a sequence of carbonate environments ranging from back-reef areas to a central basin. They also include numerous cipit boulders, which were originally part of the shallow water carbonate platform but were transported into the deeper water basinal area. For the purposes of this study, only information pertaining to in situ facies (or "beds") is discussed. Fossil assemblages vary within different facies but none of the facies is echinoid-dominant According to relative compositional abundance studies conducted Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169 for the different environments, echinoids comprise a maximum of less than 2% total fossil abundance (see Tables I - X in Ftirsich and Wendt, 1977). It is obvious that the fossiliferous deposits of the S t Cassian Beds are important to the echinoid fossil record and should be considered "prolific" echinoid accumulations in the sense that they have provided a great deal of information about Triassic echinoids. Their amazing preservational style and high species diversity does indeed qualify them as "the best echinoid fauna in the Triassic" (Smith, 1990). They should not, however, be mistakenly classified as echinoid beds due to the fact that they are unusual echinoid deposits in the fossil record. The term "echinoid bed" must imply an echinoid-dominated fossil accumulation, not simply a shell concentration which includes an exquisitely preserved or highly diverse echinoid fauna. Relative compositional abundance must be considered. Implications and Future Research This study proposes the hypothesis that much of the diversity of the overall echinoid fossil record comes from specimens which occur in shell beds rich in echinoid material. This idea seems intuitive; paleontologists tend to go where the fossils are. It would seem reasonable that many echinoid descriptions would come from accumulations which had attracted paleontologists by their high echinoid fossil content Take for example the four echinoid-rich deposits described in this study. Each was chosen because of its abundant echinoids. With the exception of the St George Virgin Limestone lagerstatten which was chosen because of its possible correlation to the Virgin Limestone spine bed, taxonomic information was not considered in composing the list of echinoid bed examples. When taxonomic information is taken into account, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 170 it is discovered that all three concentrations which contain described echinoids have yielded the type specimens for the echinoids found within them. If the majority of described fossil echinoids does indeed come from echinoid- rich deposits, then an understanding of the formation of these accumulations is vital in interpreting the nature and biases in the echinoid fossil record. The accumulation histories of these echinoid-rich deposits must be carefully reconstructed in order to better understand the nature of the overall echinoid fossil record. Determining the relative importance of echinoid concentrations in interpreting the echinoid fossil record requires further study of both echinoid accumulations and the echinoid fossil record. Future work should include: 1) Examination of additional echinoid concentrations from stratigraphic, sedimentologic, petrographic, paleontologic and taphonomic perspectives. Well- rounded studies of the concentrations will allow for accurate reconstructions of the beds' accumulation histories. This information, in turn, will provide the basis for understanding the many facets of echinoid beds and their formation. Are there significant changes in the preservational styles of echinoid-rich deposits relative to environmental or temporal parameters? How do such changes relate to the general preservational styles documented for echinoid groups (e.g. Greenstein's 1992 cidaroid study)? 2) A literature survey exploring the preservational style of type species of echinoids. Accumulating data on the kind of deposits which yield type specimens will aid in determining the importance of the role which echinoid concentrations play in the interpretation of the echinoid fossil record. What percentage of the described echinoid record comes from echinoid-rich deposits? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 171 3) Data compilation on general fossil echinoid occurrences of those groups which have type specimens described from echinoid-rich deposits. A comparison of the preservational styles of the general occurrences and the type beds would determine if the preservational style of an echinoid-rich deposit yielding a type specimen is a reasonable proxy for the entire group. 4) Comparison of the preservational styles and accumulation histories of echinoid-rich deposits which contain different types of echinoids to further understand the relationship between test morphology and the overall nature of the echinoid accumulation. Do predictable patterns appear? Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 CHAPTER 5: CONCLUSIONS 1. Echinoid beds are here defined as fossil concentrations in which at least 75% of the macroscopic fossil material (greater than 2 mm) is echinoid material. Echinoid-rich faunas are defined as shell beds in which at least 50% of the macroscopic fauna is echinoid material. This working terminology is based on relative compositional abundance and does not consider taphonomic condition or taxonomic diversity of the fossil material. 2. The two echinoid concentrations examined in this study provided information about the characteristics and accumulation histories of echinoid beds. Both deposits represent nearly monospecific echinoid beds. 3. Stratigraphy and sedimentology of the Buttonbed Sandstone echinoid bed indicates that the deposit represents a nearshore high energy shelfal environment. The coarse-grained fabric of the unit suggests significant reworking and winnowing of the depositional area. Petrographic analysis of the Buttonbed coquina supports this conclusion. 4. The Buttonbed echinoid bed is generally subdivided into two subunits: an upper hash layer of sand dollar fragments and a lower coarse-grained sandstone comprised of more complete specimens. Fossil abundance, distribution and taphonomic conditions are highly variable both laterally and vertically within the lower subunit This lower subunit is a multiple event concentration produced by significant Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 173 reworking of fossil material, perhaps by current winnowing and/or storm activity. The upper hash layer results from additional reworking of the lower subunit 6. The preservational style of the abundant V. merriami observed in the echinoid bed indicates that many generations of the sand dollar were buried and reworked within the area. Variability in the degree of ornamentation suggests that this accumulation is a product of multiple high energy events which incorporated the many generations into a winnowed, time-averaged fossiliferous deposit. 7. Stratigraphy and sedimentology of the Virgin Limestone echinoid bed suggest that it is a storm bed deposited in the distal portion of a shelfal setting. Lack of sedimentary structures supports this conclusion. The parallel orientation of many bivalve fragments observed in petrographic analysis suggests that the bed was not significantly reworked by bioturbation. Lack of consistent orientation of spines is therefore thought to result from physical processes. 8. Spine abundance and distribution varies both laterally and vertically with occasional lenses and stringers, suggesting reworking of the deposit The spines are the only skeletal component to remain intact as the other macroscopic fossil material was broken down or eliminated by taphonomic processes. 9. It appears that the larger spines within the Virgin Limestone echinoid bed were preferentially silicified. Smaller fossil material, including echinoid spines, were not silicified in the bed. Skeletal structure of the recrystallized spines may be the determining factor for the partial silicification of fossil material within the bed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 7 4 10. Petrographic examination of the echinoid bed shows a more diverse faunal assemblage of the bed. Presence of microscopic fossil material, such as delicate bivalve fragments, suggests that the bed was not reworked to the extent that the finer material was removed from the accumulation. The thin-shelled bivalve fragments are most likely parautochthonous in origin. 11. The low diversity faunal assemblage combined with the high abundance of echinoid spines in the bed suggests that the Virgin Limestone echinoid bed represents a once-thriving community dominated by regular echinoids which was reworked and later transported by storm activity. 12. Spines within the Virgin Limestone echinoid bed appear to belong to an undescribed species. Spine characteristics observed in the bed differ significantly from those of the only two known Triassic echinoids, Miocidaris utahensis and Miocidaris paJdstanensis. 13. The two echinoid beds provide examples of how different types of echinoids are preserved in different marine environments. The more resilient sand dollar tests of the Buttonbed coquina proved fairly resistant to high energy neritic processes whereas the taphonomically fragile regular echinoid tests of the Virgin Limestone bed were destroyed and eventually deposited in a relatively deeper marine setting. 14. The two echinoid beds represent very different periods in the evolutionary history of Gass Echinoidea. The Virgin Limestone bed was deposited during the class' slow recovery from the end of the Permian. The echinoid fossil record is very patchy for Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175 this time period, particularly due to the imbricated test morphology of early post- Paleozoic echinoids. The preservational style of the Virgin Limestone spine bed is typical of the Triassic. In contrast, the Buttonbed echinoid bed represents a prolific time in the evolutionary history of echinoids. Clypeasteriods reached their zenith in the Miocene. 15. The two very different echinoid beds provide insight into the variety of factors which lead to the formation of echinoid-rich deposits. The Buttonbed coquina formed as a result of a combination of physical and biological controls; it is clear that Vaquerosellamerriami was abundant within the area but the overall stratigraphy of the bed results from physical processes acting upon the depositional environment The Virgin Limestone echinoid bed is macroscopically comprised of only echinoid spines, suggesting a strong biological control on the fossil concentration. The partial silicification of the spine material is also an important factor in the definition of the echinoid bed. The final deposition of the bed, however, is a product of sedimentologic processes. The Virgin Limestone echinoid bed was deposited as an allochthonous storm bed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176 BIBLIOGRAPHY Addicott, W.O., 1970, Miocene gastropods and biostratigraphy of the Kern River area, California, United States Geological Survey Professional Paper 642,174 p. Addicott, W.O., 1972, Provincial middle and late tertiary molluscan stages, Temblor Range, California, Proceedings of the Pacific Coast Miocene Biostratigraphic Symposium, Forty-seventh annual Pacific Section S.EP.M. Convention, Bakersfield, CA, p. 1-26. 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Kier, P.M., 1974, Evolutionary trends and their functional significance in the post- Paleozoic echinoids, Journal of Paleontology, v. 48 (supplement): Paleontological Society Memoir 5, p. 1-95. Kier, P.M., 1977a, The poor fossil record of the regular echinoid, Paleobiology, v. 3, p. 168-174. Kier, P.M., 1977b, Triassic echinoids, Smithsonian Contributions to Paleobiology, v. 30, p. 1-80. Kleinpell, R.M., 1938, Miocene stratigraphy of California: American Association of Petroleum Geologists, Tulsa, OK, 450 p. Kreisa, R.D., 1981, Storm-generated sedimentary structures, Journal of Sedimentary Petrology, v. 51, p. 823-848. Kuespert, J.G., 1983, The depositional environments and provenance of the Temblor Formation and associated Oligo-Miocene units in the vicinity of Kettleman North Dome, San Joaquin Valley, California, M.S. thesis, Stanford University, 105 p. Kuespert, J.G., 1985, The depositional environments and sedimentary history of the Miocene Temblor Formation and associated Oligo-Miocene units in the vicinity of Kettleman North Dome, San Joaquin Valley, California, in Graham, S.A., ed., Geology of the Temblor Formation Western San Joaquin Basin, California: Pacific Section, Society of Economic Paleontologists and Mineralogists, p. 53- 67. Larson, A.R., 1966, Stratigraphy and paleontology of the Moenkopi Formation in southern Nevada, unpublished Master's thesis, University of California, Los Angeles, 257 p. Loel, W. and Corey, W.H., 1932, The Vaqueros Formation, lower Miocene of California, California University Publications, Dept of Geology Bulletin, v. 10, no. 18, p. 293-326. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 4 Middleton, G.V., 1967, The orientation of concave-convex particles deposited from experimental turbidity currents, Journal of Sedimentary Petrology, v. 37, p. 229- 232. Norris, R.D., 1986, Taphonomic gradients in shelf fossil assemblages: Pliocene Purisima Formation, California, Palaios, v. 1, p. 256-270. Parsons, K.M., Brett, C.E., and Miller, K.B., 1988, Taphonomy and depositional dynamics of Devonian shell-rich mudstones, Paiaeogeography, Palaeoclimatology, Palaeoecology, v.636, p. 106-140. Paul, C.R.C., 1988, Extinction and Survival of in the Echinoderms, p. 155-170, in Larwood, G.P. (ed.), Extinction and Survival in the Fossil Record: The Systematic Association Special Volume No. 34, Oxford Science Publications, Oxford, 365 p. Pence, J.J., 1985, Sedimentation and tectonics of the upper Oligocene to middle Miocene Temblor Formation of the northern Temblor Range, Kem and San Luis Obispo Counties, California, M.S. thesis, Stanford University. Poborski, S.J., 1954, Virgin Formation (Triassic) of the St. George, Utah area, Geological Society of America Bulletin, v. 65, p. 971-1006. Reeside, J.B., Jr., Applin, P.L., Colbert, E.H., Gregory, J.T., Hadley, H.D., Kummel, B., Lewis, P.J., Love, J.D., Maldonado-Koerdell, M., McKee, E.D., McLaughlin, D.B., Muller, S.W., Reinemund, J.A., Rodgers, J., Sanders, J., Silberling, N.J., and Waagd, K., 1957, Correlation of the Triassic formations of North America exclusive of Canada, Geological Society of America Bulletin, v. 68, p. 1451-1514. Rief, D.M. and Slatt, R.M., 1979, Red bed members of the Lower Triassic Moenkopi Formation, southern Nevada, sedimentology and paleogeography of muddy tidal deposits, Journal of Sedimentary Petrology, v. 49, p. 869-889. Schafer, W., 1969, Vergleichs-Schaubilderzur Bestimmung des Allochemgehaltes bioklastischerKarbonategesteine, N. Jb. Geol. Palaont. Mh., p. 173-184. Schubert, J.K., 1989, Paleoecology of the Lower Triassic Virgin Member, (Moenkopi Formation, southeastern Nevada and southwestern Utah, unpublished M.S. thesis, University of Southern California, 234 p. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 185 Schubert, J.K., 1993, Rebound from the Permian-Triassic mass extinction event: paleoecology of Lower Triassic carbonates in the western United States, unpublished Ph.D. dissertation, University of Southern California, 396 p. Schubert, J.K. and Bottjer, DJ., 1995, Aftermath of the Permian-Triassic mass extinction event: Paleoecology of Lower Triassic carbonates in the western USA, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 116, p. 1-39. Schubert, J.K., Bottjer, D.J. and Simms, M.J., 1992, Paleobiology of the oldest known articulate crinoid, Letbaia, v. 25, p. 97-110. Seilacher, A., 1979, Constructional morphology of sand dollars, Paleobiology, v. 5, p. 191-221. Seilacher, A., 1982, General remarks about event deposits, in Einsele, G. and Seilacher, A., eds., Cyclic and Event Stratification: Springer-Verlag, Berlin, p. 161-174. Seilacher, A. and Westphal, F., 1971, Fossi 1-Lagerstatten, in Sedimentology of Parts of Central Europe, Guidebook 8th International Sedimentological Congress, Heidelberg, p. 327-335. Smith, A.B., 1984, Echinoid Paleobiology: George Allen and Unwin, London, 190 P- Smith, A.B., 1990, Echinoid evolution from the Triassic to lower Liassic, Cahiers de llnstitut Catholique de Lyon, Series Science, v. 3, p. 79-115. Smith, A.B. and Hollingworth, N.T.J., 1990, Tooth structure and phylogeny of the upper Permian echinoid M iocidaris keyserlingi, Proceedings of the Yorkshire Geological Society, v. 48, p. 47-60. Smith, J.P., 1912, Geological range of Miocene invertebrate fossils of California, California Academy of Sciences Proceedings, series 4, v. 3, no. 8, p. 161-182. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 186 Stanton, R.J., Jr. and Dodd, J.R., 1970, Paleoecologic techniques-comparison of fauna! and geochemical analyses of Pliocene pdeoenvironments, Kettleman Hills, California, Journal of Paleontology, v. 44, p. 1092-1121. Stanton, R.J., Jr. and Dodd, J.R., 1976, The application of trophic structure of fossil communities in paleoenvironmental reconstruction, Lethaia, v. 9, p. 327-342. Stinemeyer, E.S., Beck, R.S., Ortalda, R.A., Espenscheid, E.K., Bainton, J.D., and O'Keefe, M.S., 1959, Guidebook for Chico Martinez Creek area field trip, San Joaquin Geological Society, 15 p. Tipton, A., Kleinpell, R.M., and Weaver, D.W., 1973, Oligocene biostratigraphy, San Joaquin Valley, California, University of California Publications in Geological Sciences, v. 105. Tucker, M.E., 1991, Sedimentary Petrology: Blackwell Scientific Publications, Oxford, 260 p. Vail, P.R., Mitchum, R.M., Jr., and Thompson, S., Ill, 1977, Global cycles of relative changes of sea level, in Payton, C.E., ed., Seismic Stratigraphy— applications to hydrocarbon exploration, American Association of Petroleum Geologists Memoir 26,87 p. Weaver, C.E., Beck, S., Bramlette, M.N., Carlson, S., Clark, B.L., Dibblee, Jr., T.W., Durham, W., Ferguson, G.C., Forest, L.C., Grant, VI, U.S., Hill, M., Kelley, F.R., Kleinpell, R.M., Kleinpell, W.D., Marks, J., Putnam, W.C., Schenck, H.G., Taliaferro, N.L., Thorup, R.R., Watson, E., and R.T., 1944, Correlation of the marine Cenozoic formations of the Western North America, Geological Society of America Bulletin, vol. 55, p. 569-598. Wharton, J.B., Jr., 1943, Belridge oil field (California), California Dept. Nat Res., Div. Mines Bulletin, v. 118, p. 502-504. Williams, L.A., Cooley, S.A., Graham, S.A., and Phillips, L., 1982, Road Log: Monterey Formation and associated coarse clastic rocks, Central San Joaquin Basin, California, Pacific Section, Society of Paleontologists and Mineralogists, p. 74-95. Williams, H., Turner, F.J., and Gilbert, C.M., 1982 (2nd ed.), Sedimentary Rocks, Part Two, in Petrography: An Introduction to the Study of Rocks in Thin Section: W.H. Freeman and Company, San Francisco, p. 277-427. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 187 Woodring, W.P., Stewart, R. and Richards, R.W., 1940, Geology of the Kettleman Hills oilfield, California: stratigraphy, paleontology, and structure, U.S. Geological Survey Professional Pfcper 195, p. 1-170. Zoeke, E., 1951, Etude des plaques des Hemiaster, Bull. Mus. Natn. Hist. Nat, v. 23, p. 696-705. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 188 Appendix 1. Station and Sample Information from the Chico Martinez Creek locality. Samples are lettered up-section (i.e., A to B from bottom to top). STATION Bl: Located on the highest northern point of the 1800 Ridge. 200 cm thick. Covered above and below. It is a hash of coarse fragments with large fragments and whole specimens (ave. 1 cm diameter) within the medium sandstone. Specimens are abraded with no ornamentation present Sample # Descriptions A Bottom of exposure, fairly friable B 85 cm from the bottom of exposure C Top of exposure STATION B2: Located 20.5 m from Station B1. Not as consistently coarse as Station B1; possibly weathering bias(?). 177 cm thick with coverage above and below. Also, a coarse hash, although not as many whole echinoids (ave. I cm diameter). Specimens are abraded with no ornamentation present Sample # Descriptions A 52 cm from bottom B 92 cm from bottom C Top of exposure STATION B3: Located 28.7 m from Station B2. 4.1m thick. Coarse hash with more abundant whole echinoids (1 cm diameter). No orientation; all mixed up. Lots of lateral and vertical variation, esp. in lower meter. Rare barnacles. Upper meter appears to have less whole echinoids with very rare whole specimens near the very top (see sample B3Q. Specimens are abraded with no ornamentation present Sample# Descriptions A 40 cm from bottom B 2 m from top (or 2.1 m from bottom) C Top of exposure Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 189 OBSERVATIONS between STATIONS B3 and B4: Approx. 42 m from Station 3, sparse whole echinoids in coarse fragment hash. 3 meters from that area, much more abundant whole specimens, ranging from .5 to 1.5 cm diameter. Not clumped or oriented. (Obvious example oflateral variability within the bed.) STATION B4 Located 82 m from Station B3. lm thick. Patchy coarseness within exposure with finest fragments around 50 cm (lateral variability present). Also vertical variability with coarser bottom and top of the bed. More whole specimens on bottom and top of bed. Sample# Descriptions A 2 cm from bottom B 35 cm from bottom Cl Top of exposure C2 Top of exposure OBSERVATIONS between STATIONS B4 and B5: Bed loses ridge form (i.e., becomes very poorly exposed, approx. 34 m south of B4); Bed still poorly exposed 100m south of B4 with 70 cm thick outcrop showing a few whole echinoids interspersed with coarse fragments (S8,9); Bed is similar at 150 m south of B4 as it is at 100m (52 cm thick with interspersed whole echinoids); Bed shows layered subunits approx. 177.5 m south of B4. Rare barnacles found at each observed site. STATION B5 Located 220 m from STATION B4. 240 cm thick with direct contact with 140 cm- thick underlying pitted sandstone (with interspersed sandstone cherts). Layers with prominent weathering (layers vary from coarse hash to more massive beds to thin hash concentrations). [Appears to be most abundant site thus far on 1800 Ridge] Lots of whole echinoids ranging from .5 to 2.5 cm in diameter. Rare barnacles present Sample # Descriptions A 15 cm from bottom B 95 cm from bottom C 1 m from top (or 1.4 m from bottom) D Top of exposure (two pieces; note: if fine-grained) S Underlying sandstone 2 m below contact OBSERVATIONS 31m south of STATION 5: Whole echinoids still very abundant within the bed (ranging from .5 to 1.5 cm in diameter), poorly sorted. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 190 STATION 6 Located at the top of the Buttonbed Hill. 3 m thick. The bed caps BBH with presence of erosional contact at lower boundary. Upper 1 m is composed mostly of fragments with rare whole specimens. The lower two meters contain abundant whole sand dollars (unoriented and mostly 2 cm in diameter). Many well-preserved specimens on face exposures (approx. 30% of specimens exhibit petal structures). Granules are dispersed throughout a somewhat concentrated zone 105 cm from bottom of bed. Sample# Descriptions________________________________________________ A 1 m from bottom B 2 m from bottom C Top of exposure STATION 7 Located 80 m North of Station 6 (backtracked toward van). 175 cm thick. Upper 75 cm consists of fragments with a medium abundance of whole specimens. Specimens are in no orientation and appear abraded (0.5 to 2.5 cm in diameter). The lower 1 m contains abundant whole specimens (unoriented), well-sorted and closely packed in most areas. The two subunits are separated by a concentrated layer of whole sand dollars approx. 3-12 cm in thickness. Sample# Descriptions A1 Bottom of exposure A2 Bottom of exposure B1 lm from bottom B2 1 m from bottom C Top of exposure D Stringer (conc. bed) E Stringer (conc. bed) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STATION 8 Located South of Station 6 before the bed pinches out under covering. The bed caps the ridge with coverage below. 3.1S m thick. The upper 65 cm is hash with a few whole specimens. The lower 2.5 m, whole specimens (unoriented, abraded and differing in size; 0.5 cm in diameter ave.?) are more abundant, in stringers and pods/lenses. Subunits within the bed appear layered (weakly stratified?). Rare barnacles are present Underlying sandstone is x-bedded below echinoid bed with ledges of echinoid material within interbedded sandstone subunits. Sample# Descriptions A 50 cm from bottom B 90 cm from bottom C 1.5 m from bottom D 2 m from bottom El 2.8 from bottom (35 cm from top) E2 2.8 from bottom (35 cm from top) S Top of underlying sandstone STATION 9 Located on the LH. 3.68 m thick. There is well-defined contact between the echinoid bed and the underlying sandstone. At the base of the echinoid bed, there is a 15-cm- thick layer of abundance whole echinoids. Above this densely packed layer is a fragment-rich layer (with few, if any, whole specimens). The bed is distinctly layered. Approximately 3 m upsection, whole echinoids are more abundant and barnacle fragments are observed. Within the upper m, abundant whole echinoids and large fragments (as well as barnacle fragments) are present Specimens within the top of the bed are not oriented, vary greatly in size (0.75 to 2 cm in diameter) and exhibit various taphonomic degrees (from well-preserved to “yuck”). Sample# Descriptions A 49 cm from bottom B 162 cm from bottom C 3 m from bottom (note barnacle fragments in sample) D Top of exposure E Top of exposure Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 192 Appendix 2. Buttonbed Sandstone Held Notes from Abundance and Composition Analysis Composition, abundance and taphonomic analyses of the stations on 1800 Ridge were completed using a random sampling technique involving a 400 cm2 grid. The grid was placed at 20 cm intervals and observations were made from within one box within the grid. It should be noted that these field observations are to supplement the information found in the "BBST Held Data Forms" which follow. Also, it should be recognized that although the composition/abundance information was collected at each station at which previous strati graphic columns were constructed, the sections selected for the fossil analyses are not necessarily the exact stations which were measured for the stratigraphic logs. Therefore, measurements of the two sections for each station may not match. Station Bl: Grid 1 - taken from the base of the bed. Fossil comp, includes sand dollars (1 cm in diameter ave.), SD fragments (ave. 1-2 mm), and 2 barnacle fragments (each approx. 2 cm long). 20 SDs were counted ("SD" is used to designate whole specimens; which are those which show the test diameter). Edges of the SDs are broken/worn, no ornamentation. Grid 2 - 20 cm up from Grid 1. Fossil comp, includes SDs (1 cm ave), SD frag.s (1 mm ave) and 2 barnacle frag.s. 16 SDs present within the 10 cm x 10 cm grid. No ornamentation, jumbled with no consistent orientation. SD edges were broken. Grid 3 - 20 cm up from Grid 2. Fossil comp, includes SDs (approx. 1 cm ave), SD frags (1-3 mm). 19 SDs counted. Grid 4 - Fossil comp, includes SDs (1 cm), SD frag.s (1-2 mm). 22 SDs counted. Grid S - Fossil comp. SDs and SD frags. 6 SDs counted. Station B2: in general, a hash with whole SDs and large barnacle fragments (incl. 1 in xsec), and 1 oyster fragment Grid 1 - 20 cm up from base. Fossil comp, includes SDs (0.5-0.8 cm), SD frags., pecten frag., barnacle frag. (3 mm?) and occasional phosphate nodules. Total SDs counted = 14. Grid 2 - 20 cm up from Grid 1. Hashy; lots of SD frags. Few whole SDs (4) and 1 large (2.5 cm) barnacle fragment Grid 3 - 20 cm up from Grid 2. Hash; SD frag.s and 2 SDs (0.5, 1 cm). Grid 4 - 20 cm up from Grid 3. Hash; SD frag.s and rare SDs (2; 0.85, 1 cm). Frag.s approx. 1 mm; appear smaller than those in Grids 1-3. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 193 Grid 5 - 20 cm up from Grid 4. Laterally adjacent to Sample B2C (top of the bed). Fossil comp, includes SD frag.s only (1-2.5 mm). NO SDs. Station B3: Grid 1 - from base. Smooth weathering; hard to see specimens. Fossil comp, includes bam frag. (3 mm), and SD frags (ave. 2 mm). No SDs. Grid 2 - 20 cm up from Grid 2. Fossil comp, includes SD frag.s, rare SDs (5 total), and 1 barnacle frag (2 mm). Smooth weathering of rock surface. No orientation of SDs. Xsectional views but edges not broken. No ornamentation; smooth surfaces. Grid 3 - 20 cm up from Grid 3. Very abundant SD fragments (1-3 mm) and 1 SD (0.8 cm). Grid 4 - 20 cm up from Grid 3. Many SD fragments, 1 barnacle frag. (1 cm) and whole SDs (4 mm - 1 cm). Grid 5 - 20 cm up from Grid 4. Hash with many SD frag.s (1 mm) and many SDs (1 cm). General condition of SDs: edges are broken, 2 show plate sutures. Grid 6 - 20 cm up from Grid 5. Many SD frag.s, phosphate nodules, rare whole SDs (2 in xsection) and possible pecten. Grid 7 - 20 cm up from Grid 6. Many SD frag.s (2-3 mm) and occasional phosphate nodules. Grid 8 - 20 cm up from Grid 7. Fossil comp: SD frag.s (1-2.5 mm), 4 whole SDs (0.7-1 cm). Rare phosphate nodules. One SD with obs. face has experienced post- dep. weathering (dissolution/abrasion; is missing portion of top) but has one petal present Grid 9 - 20 cm up from Grid 8. Massive lichen coverage makes observations very difficult Grid 10 - 20 cm up from Grid 9. Definitely a sandstone... SD frag.s are ave. 1 mm. NO whole SDs. Grid 11 - 20 cm up from Grid 10. 2 barnacle frag.s (4 mm), large SD frag.s (1-4 mm). NO whole SDs. Some lichen coverage. Grid 12 - 20 cm up from Grid 11. SD frag.s (1-4 mm) and phosphate nodules (1mm). NO whole SDs. Grid 13 - 20 cm up from Grid 12. SD frag.s (1-3 mm) and phosphate nodules (1-3 mm). NO whole SDs. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 194 Station B4: Grid 1 - from base. SD frag.s and 7 SDs (0.7-1 cm). Well-weathered specimens; SDs showing faces appear to be worn in half (top portion gone). Grid 2 - 20 cm up from Grid 1. 4 SDs counted (0.4-0.8 cm). All in xsection. Grid 3 - 20 cm up from Grid 2. Mostly SD frag.s (£ 1 mm), rare phosphate nodules (1 mm). Possibly 1 SD. Grid 4 - 20 cm up from Grid 3. Coarse-grained sandstone. SD frag.s (1-2 mm) and rare phosphate nodules. NO whole SD. Station B5: Grid 1 - from base. Fossil comp.: SD frag.s (1-3 mm) and SDs (1 cm). Grid 2 - 20 cm up from Grid 1. Fossil comp.: SD frag.s (1-3 mm) and SDs (1 cm). Grid 3 - 20 cm up from Grid 2 and 20 cm from top of bed. SD frag.s (1-3 mm), 2 barnacle frag.s (3 mm, 1 cm) and rare SD. Station B6: Approximately 30-35 m south of B10. Grid 1-20 cm from bottom. Fossil comp.: 3 SD (2 cm). All SDs present with obs. faces have plate sutures preserved. Heavy weathering/carbonate film. Grid 2 - 20 cm up from Grid 1. Large barnacle (2cm x 5cm) adjacent to grid. SDs (1.5-2 cm; ave. 1.5 cm). Sd frag.s (2-5 mm; more 5 mm). Grid 3 - 20 cm up from Grid 2. Fossil comp.: SD frag.s (<1-6 mm). Heavy weathering/possible film. 10 phosphate nodules. About 10 cm up from grid is a 10- cm thick phosphate concentration. Grid 4 - 20 cm up from Grid 3. Fossil comp.: 9 SDs (1.5-2 cm), SDfrag.s (0.1-1 cm). Block adjacent has 1 SD with obs. face which has petal structure present. Weathered. 72 phosphate nodules (2-3 mm) are subrounded to angular. Grid 5 - 20 cm up from Grid 4. SDs (2 cm). No phosphate nodules. Heavy weathering. Grid 6 - 20 cm up from Grid 5. Fossil comp.: SDs (2 cm), SD frag.s (1-6 mm). 5 phosphate nodules (2-4 mm) present Grid 7 - 20 cm up from Grid 6. Fossil comp.: large SD frag.s (6 mm), 1 whole SD (2.5 cm). 15 phosphate nodules (2-3 mm). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 195 Grid 8 - 20 cm up from Grid 7. Many SD frag.s (2-7 mm; ave. 4.5 mm). 1 SD (2 cm), heavy weathering. 5 phosphate nodules (1-2 mm). Grid 9 - 20 cm up from Grid 8. Fossil comp.: SDs (1-2 cm), SD frag.s, 1 barnacle frag.s (2-3 mm). 1 SD with obs. face, well worn. "Micro-pitted" weathering. Carbonate film. Station B7: Grid 1 - from base. Fossil comp, includes 11 SDs (1-2 cm), SD frag.s (1-2 mm). Abundant phosphate nodules (39). Heavy weathering/ carbonate film makes specimens hard to see. Grid 2 - 20 cm up from Grid 1. Fossil comp, includes SD (0.6-1.5 cm), SD frag.s (0.1-1 cm). Some phosphate nodules (5). Heavy weathering/carbonate film makes specimens hard to see. Grid 3 - 20 cm up from Grid 2. Local erosional contact 8 cm from top of grid. Fossil comp, includes 23 SDs (0.5-2 cm), SD frag.s (<1 mm to 5 mm). 16 phosphate nodules on either side of the division. Most small SD below l.e.c. and larger ones above. Grid 4 - 20 cm up from Grid 3. Fossil comp, includes SDs (1.7-2 cm), SD frag.s (<1- 5 mm). 2 phosphate nodules. Smaller SDs above grid. Largest SD (2 cm) has obs. face with top half missing (dissolved/weathered), and 1 petal showing. Breakage along sutures. Top surface of the station has SDs with sizes varying 0.5-3 cm. They are poorly sorted; dense in spots. Grid 5 - Located between Grids 3 and 4 in the concentrated SD zone (which is 8-10 cm thick). 39 SDs (ave. 1.8 cm but some 1 cm). SD frag.s (2-4mm). No phosphate nodules. Most SDs in xsection, 1 face up has petal structure. Station B9: Grid 1 - from base. Fossil comp.: 10 SDs (1-1.5 cm; 1 SD is 2 cm), SD frag.s (1-2 mm). All SDs in xsection. 30 phosphate nodules (ave. 2 cm). Grid 2 - 20 cm up from Grid 1. Many SDs frag.s (<1-3 mm). NO whole SDs. Grid 3 - 20 cm up from Grid 2. Hash of SD frag.s (1-3 mm). NO whole SDs. 3 phosphate nodules (1-2 mm). Grid 4 - 20 cm up from Grid 3. SD frag.s (1-2.5 mm). NO whole SDs. Heavy weathering/carbonate film. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 196 Grid 5 - 20 cm up from Grid 4. SD frag.s (2-3 mm). 5 SDs (0.5-1 cm; 2 of 5 are 0.5 cm). Grid 6 - 20 cm up from Grid 5. Hash of SD frag.s (1-2 mm). 2 SDs (1, 1.5 cm). Grid 7 - 20 cm up from Grid 6. 9 SDs (1-3 cm), 1 barnacle frag. (3 mm), SD frag.s (<1-4 mm). Grid 8 - 20 cm up from Grid 7. SD bits (1-1.5 cm) ; do not show full diameter. SD frag.s (1-5 mm). 2 barnacle frag.s (1 cm). Ornamentation observed on SDs in adjacent boxes. Station B10: Bottom meter is covered by lichen/grass. There is a definite stratigraphic (erosional) boundary between the lower and upper subunits. Lower subunit has abundant whole SDs in xsection. General description: 2 subunits. Upper subunit (1.6 m) has cross-bedding. Hashy toward top. On bottom of upper subunit, horizontal layers of SDs. All in xsection. Patches of SDs look like small slumps. Taphonomic conditions vary. Ave. SD size is 2 cm in diameter. Occasional barnacle fragments. There is a local erosional feature 90 cm from top of bed. Lower subunit is 1.75 m (1 m is covered) thick. SDs are abundant; all in xsection. Well-weathered. No orientation of SDs. Phosphate nodules present Grid 1 - from base. Fossil comp, includes 3 SDs (1 cm), SD frag.s. Phosphate nodules (2-5 mm). Heavy weathering/carbonate film present on surface. Grid 2 - 20 cm up from Grid 1. Fossil comp, includes SDs (ave. 2 cm; range 1-2.5 cm), SD frag.s (1-6 mm), 1 barnacle frag. (2 cm). Phosphate nodules (1-3 mm; 3 mm ave.). Heavy weathering/dissolution. Grid 3 - 20 cm up from Grid 2; from top of erosional layer. Fossil comp, includes 5 SDs (1 cm), SD frag.s (1-5 mm), 1 barnacle frag.s (2 cm). Phosphate nodules (2-3 mm). Very worn SDs. One with obs. face is heavily wean but not along sutures (2 cm in size, mixed with 1 cm specimens). One with obs. face about 10 cm away from grid has petal structure and breakage along sutures. Grid 4 - 20 cm up from Grid 3. Mostly hash. Fossil comp, includes SD frag.s (1 mm), 1 barnacle frag. (1 cm). 3 pieces of SD (each 1 cm). NO whole SDs. Heavy weathering/carbonate film. Grid 5 - 20 cm up from Grid 4. Fossil comp.: rare SD (0.8-2 cm), SD frag.s (<1-5 mm). Phosphate nodules (1-2 mm). Heavy weathering. Grid 6 - 20 cm up from Grid 5. Fossil comp.: SD frag.s (l-3mm, ave. 1 mm), possibly 3(1 cm) SDs. No whole SDs. Possibly phosphate nodules (<1 mm). Grid 7 - 20 cm up from Grid 6. Fossil comp.: possibly 2 SD bits (1.5 cm). No whole SDs. 3 phosphate nodules (2 mm). Heavy weathering/carbonate film. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 197 SMon f Sampans ooaMon Atoundinci (Mr 100 a n ) tegraaaf Omiwntioon Ortonifltlon (surfaeo) Commend (sea grid notee (or delale) B1 (B A ) (1) DM* OB 20 no no m m SDs: hmh 0 (* 1-2 nun Indudad) (?) 20 cm uo DtS/L 16 no no m l SDK Imh 0 ((1-2 mm Indudad) (3) 20 cm ud w a v 19 no no attm SO«: ham 0 «1-3 mm include!) (4) 20 cm ue w a v 22 no no Btnai SDs: ham □ m 1-3 mm mctudad) (!) 20 cm uo 0 5 6 no no SOa not aa aDundant B2 (1) 20 on uo 0 6 14 no no (2) 20 cm ud 0 6 4 no no 1 obeatvad laca adh too ootdon 'dfeaolvoditootn* (3) 20 cm ud 06 2 vw both SOa m mac. hndznmal adh bottom u d (4) 20 cm uo 06 2 - no (!) 20 cm ua . 0 a! baaa. 1-2.5 mm B3 (l)baaa. . _ 0 . no SO: emoodi aaadwdna (2) 20 cm ud 0 6 5 xaaca ontv: smooth aaadiadna (3) 20 cm ud 0 6 1 latara»y mote abundant than In odd (4) 20 cm ud WS/L 13 . araat aiza variabUtv (!) 20 cm ud 0 6 0 2 SO ahoat olaaa aulutaa (!) 20 cm ud WS(U 2 no v m both SO hotlzomal adh too u d (7) 20 cm ud 06 0 SOa otaaant totatadv (outsida odd) not brefcan but aom (8) 20 cm uo 0 6 4 1 aiW i aba. laca la btokan but natal attuctuia ntaaant ( 2 ) 20 cm uo maaaiwa Ichan oouetaae* 0 0 ) 20 cm ud . 0 . (11) 20 cm ud 0 lama SO Itaaa 1-4 mm (12) 20 cm ud 0 SO bane 1-4 mm (13) 20 cm ud 0 m m fltam N B D N U lO C O D O n B4 (1) baaa uws 7 no SOa adh aba. tacae ata atom m had (2) 20 cm ud 06 4 . . alS O ah aec (3) 20 cm ud 06 17 . tara oftce nomdaa (4) 20 cm ud 0 6 0 . . no article 80e B5 0) baaa 0 6 4 _ adSOatisaee (2) 20 cm ud OB 4 . . 1 oba. laca - had aom (3) 20 cm ud 0 6 3 no nmnoQ onm non B8 (1) 20 cm ud 06 3 no hotlz. taaratwiaSOa (2) 20 cm ud M . (d) 11 no 1 oba. laca shoal amm natal atracaim (3) 20 cm ud 0 _ noatuieSOe (4) 20 cm u d D/D/L 9 no a lln a a e (!) 20 cm ud L 10 hotlz. a! In aaac ad. SOa not in odd ata not hotlz. (!) 20 cm ud L 9 hodx. aam oac ( 7 ) 20 cm ud L/D/D 1 hodz. bodom un odenL: teat adcaa ptaaam (not aom ofl) (8) 20 cm ud 1 no . laca natlladv vtadrte ( S ) 20 cm ud DB S no 1 oba. laca - a m i aaalhatad B7 (1) 10 cm ud UDIS 1 1 . aimxaac (2) 20 cm ud uw s 7 no hotlz. net nac. too uo (canl m due to weathered audaca) ( 3 ) 20 cm ud UD (d) 23 no all m t u c local eras, contact 8 cm bom bottom In odd ( 4 1 20 cm ud UWS 5 1 D O t d hotlz. bottom ua (Indians la alona auturaal ( ! ) bat 3 A 4 D/0/L 39 mad hotlz. most In saac; 1 laca shows petal stnjetuta Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (Appendix 2 Table continued) 198 SMIan ( SompBig DoiWon Paddng Abundance (oar 100 cm ) OagrM rf Omamentalon Orientation (aurfaca) Comments (aaa grtd notes for duals) BS fi> dm* OS 10 moat hodr. aH nxsec (21 20 cm uo . 0 no whole SOa (31 20 em uo . 0 . no whole SOs (41 20 o n uo . 0 no whole SOs (51 20 em uo OB s . whdo SDa a n fabiy complete (81 20 em uo OB 2 hortz. uo a* m » a c ; loo 1 0 at tfflerant lave* (71 20 em uo in n s 0 VM no M e suturaa and Mtal struefuiaa m ea n t (8) 20 em uo D/D/L 6 V O * no smootfied auvfsoee BIO <1J6o»o_ . OS . no a l in sane (21 20 em uo o/on. no no til In » a c : 1 baefcaida obs. (31 20 em uo OB no no haavtv worn (41 20 em uo OB • no whole SOa (51 20 em uo UD 4S no no a l in n e e heavy weatfierina (81 20 em uo . no whale SOs (71 20 cm uo . - - no 't M o SO c heavy wealharmo (cart). Hm) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 199 Appendix 3. Station and Sample Information from the Lost Cabin Springs locality. Samples are lettered up-section (i.e., A to B from bottom to top). STATION 1 : Located 2 m to the right of the landmark tree. 2.25 m thick. Sample # Locations in Strat Section 1A Including part of the chert IB 70 cm above chert 1C.I 150 cm above chert 1C.2 150 cm above chert and 75 cm from top of bed ID Overlying gastropod bed; 70 cm above echinoid bed STATION 2: Located 18 m left (south) of Station 1. 2.35 m thick. Sample# Locations in Strat Section 2A 5 cm above chert 2B 100 cm above 2A or 105 cm above chert 2C 230cm above 2a or 235 cm above chert STATION 3: Located 42 m left (south) of Station 1 or 24 m south of Station 2. 1.85 m thick (?). Sample# Locations in Strat Section 3A 70 cm above chert 3B 171 cm above chert 3C 185 cm above chert STATION 4: Located 66 m left (south) of Station 1 or 24 m south of Station 3. 2.5 m thick. Sample # Locations in Strat Section 4A 175 cm above chert 4B 70 cm above 4A or 245 cm above chert 4C 60 cm above 4B or 305 above chert; from top of or possibly above bed 4D 40 cm below 4C or 265 cm above chert 4E underlying laminated mudstone, approx. 20 cm below chert Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 0 STATION 5: Located 84 m left (south) of Station 1 or 18 m south of Station 4. 1.15 m thick. Sample # Locations in Strat Section______________________________ 5A Directly above chert and right beneath 5B 5B 123 cm above the chert, 8 cm from top of the bed 5C 150 cm above chert, from 35 cm above the bed +5B Behind and directly above 5B, shows upper contact P5 115 cm above chert or 35 cm below 5C, above/laterally adj. to +5B, shows upper contact and above gastropod bed STATION 6: Located 112 m left (south) of Station 1 or 28 m south of Station 5. 1.25 m thick. Sample # Locations in Strat Section________________________________ 6A 20 cm above chert 6B 100 cm above chert 6C Portion of the chert Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Asset Metadata

Creator Moffat, Heather Ann (author)

Core Title Structure and origin of echinoid beds, unique biogenic deposits in the stratigraphic record

Degree Master of Science

Degree Program Earth Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag OAI-PMH Harvest,paleoecology,paleontology

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-5820

Unique identifier UC11337447

Identifier 1381599.pdf (filename),usctheses-c16-5820 (legacy record id)

Legacy Identifier 1381599.pdf

Dmrecord 5820

Document Type Thesis

Rights Moffat, Heather Ann

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA