The origin of enigmatic sedimentary structures in the Neoproterozoic Noonday dolomite, Death Valley, California: A paleoenvironmental, petrographic, and geochemical investigation

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Content THE ORIGIN OF ENIGMATIC SEDIMENTARY STRUCTURES IN THE NEOPROTEROZOIC NOONDAY DOLOMITE, DEATH VALLEY, CA: A PALEOENVIRONMENTAL, PETROGRAPHIC, AND GEOCHEMICAL INVESTIGATION by Katharine Nicole Woods A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE (GEOLOGICAL SCIENCE) May 2003 Copyright 2003 Katharine Nicole Woods Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1416586 Copyright 2003 by Woods, Katharine Nicole All rights reserved. ® UMI UMI Microform 1416586 Copyright 2003 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY O F S O U T H E R N CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA S 0 0 0 7 This thesis, written by Ka^thaxine^Nicole^Woods under the direction of h.HP. Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements fo r the degree of THESIS COMMITTEE Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ii Acknowledgements Dr. David Bottjer, my advisor at USC, told me of strange structures lurking in our geologic backyard when I arrived at USC in the fall of 1998. Although I initially had my heart set on working in the Mesoproterozoic, the Noonday and its tubes were too bizarre to ignore. These rocks soon won me over to their mid- Neoproterozoic world, and I haven’t looked back since. Thank you, Dave, for presenting me with a project idea as fascinating and challenging as this one and trusting me with the room to do with it as I chose, while always helping me to reign in my urges to try to solve all the unanswered questions all at once. This has been a great intellectual and personal experience for me. Dr. Donn Gorsline and Dr. Robert Douglas, my committee members, have provided me with insight and resources, not to mention countless grant proposal recommendations, during my time at USC. Thank you for your time, patience, and insights. In addition to my committee, a number of people have been instrumental in development of this research. For well over five years, Dr. Julie Bartley, University of West Georgia, has been a continuous font of knowledge on all things Precambrian and a prominent figure in my academic development in ways both professional and personal. Dr. Frank Corsetti, USC, has been a sounding board and a source of information on the geology of the Death Valley area and the Snowball Earth hypothesis. Dr. Linda Kah, University of Tennessee, kindly found Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the time to help me with dolomite and its related geochemistry, as well as the wily ways of academia. Dr. Maria Mutti, Stuttgart, introduced me to the wonders of carbonate sedimentology, dolomite, and fieldwork. Dr. Andy Knoll, Harvard University, took me into his lab in 1997, gave me a senior thesis project, and through it not only showed me how to conduct research in historical sciences but also provided the example of a scientist that I strive to emulate to this day (though I doubt I’ll ever reach that goal). Dr. Steve Gould opened the door to the study of earth sciences for me, for which I owe him more than I can express. Early on, Bob Vieth, University of Connecticut, taught me both that research at its best is a creative endeavor, and that if you only have a driving curiosity to unlock the mysteries of the world, the rest will follow. Thank you all for your inspiration. Many peers have listened to me think out loud, often providing excellent and useful feedback, in the course of this project. Thank you Tran Huynh, Nicole Fraser, Masha Prokopenko, Bob Gaines, and Seth Finnegan for your insights and patience with my ramblings about tubes, dolomite, and the wonders of the Proterozoic. Thanks also to my field assistants: Tran Huynh, Whitey Hagadorn, and Dan Woods, some of whom now know too well that it does rain in Death Valley. No acknowledgement would be complete without thanking my parents, Dan and Ellen Woods. They have always taught me to be myself, and I may have Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iv learned the lesson a little too well, often to their dismay. And while they’ve told me to follow my heart, they have always been there for me when I find myself suddenly lost in unfamiliar territory. Thank you for your unending support and love. Trace metals analyses and isotope distillation were conducted under the gracious hospitality of the University of West Georgia Department of Geoscience with the help of Dr. Julie Bartley. Drs. Jean Morrison and Keegan Schmidt kindly aided in running and calculating stable isotope data at the University of Southern California Department of Earth Sciences. Funding was provided by student research grants from the Wrigley Institute for Environmental Studies, the Paleontological Society, and the USC Department of Earth Sciences. Occasional accommodations in the field were provided by the SHEAR House, Shoshone, CA. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V Table of Contents A cknow ledgements.............................................................................................................ii List of T ables......................................................................................................................vii L ist of Figures................................................................................................................... viii Abstract............................................................................................................................... xii Chapter 1: Introduction .................................................................................................1 1.1: General Introduction..................................................................................... 1 1.2: The Noonday Formation ...............................................................................2 1.2.1: The Noonday Form ation.................................................................2 1.2.2: Previous W o rk ............................................................................. 13 1.2.3: Related S ections........................................................................... 17 1.3: M icrobial Mats and Stromatolites...............................................................23 1.4: Skolithos, Root Casts, and The Early History of B ioturbation...........29 1.5: Neoproterozoic Deposits and The Snowball Earth H ypothesis...........37 1.5.1: The O bservations.......................................................................... 37 1.5.2: Distribution of F eatu res...............................................................41 1.5.3: The E xplanations.......................................................................... 43 1.6: Focus of this S tu d y ........................................................................................46 1.7: Possible Im plications................................................................................... 49 Chapter 2: D ata ............................................................................................................. 51 2.1: Methods of Study ......................................................................................... 51 2.2: Field D ata......................................................................................................... 51 2.3: Hand Sam ples................................................................................................. 67 2.4: P etrography.....................................................................................................69 2.4.1: S taining ........................................................................................... 70 2.4.2: Light M icroscopy.......................................................................... 70 2.4.3: Cathodolum inescence.................................................................. 79 2.5: Macerations (Organic E xtractions)........................................................... 80 2.6: Geochemical A nalyses................................................................................. 82 2.6.1: General Procedures (ICP and M S)............................................ 82 2.6.2: Trace Metal Analyses (IC P ).......................................................82 2.6.3: Stable Isotope Analyses (M S )................................................... 85 2.6.4: X-Ray D iffraction......................................................................... 87 Chapter 3: D isc u ssio n ......................................................................................................90 3.1: The Enigmatic S tructures..............................................................................90 3.1.1: Summary of important observations........................................90 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vi 3.1.2: Comparison of observations with suggested mechanisms of formation....................................................... 91 3.1.3: Suggested process of formation............................................94 3.2: Is the Noonday a Cap Carbonate?........................................................96 Chapter 4: C onclusions and Issues for Further St u d y ............................. 98 Refe r e n c e s..............................................................................................................100 Appendicies: Appendix A: Locale Information.......................................................................... 108 Appendix B: Sample Information........................................................................... 109 Appendix C: Trace Metals Data Calibrations.........................................................113 Appendix D: Stable Isotope Data Calibrations.................................................... 114 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Tables Table 1. Table of Trace Metals Data and Useful Ratios, pg.86. Table 2. Stable Isotope Data Table, pg. 88. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. viii List of Figures Figure 1. Fault map of Death Valley area (from Wright, etal., 1974), pg.3. Figure 2. Depositional map of the Death Valley area (from Wright, et al., 1974), Pg-4- Figure 3. Stratigraphic column of Precambrian/Cambrian in the Death Valley area (from Wright, et al., 1974), pg. 6. Figure 4. Stratigraphic column with common features of Precambrian/Cambrian in the Death Valley area (from Awramik, et al., 2000), pg. 7. Figure 5. Geologic Map of Death Valley, with inset map of Noonday (from Wright, etal., 1974), pg. 8. Figure 6. Sequential stratigraphic cross section showing depositional process from the Lower Crystal Springs (LCS) to the Noonday (ND) (from Link, 1992) and stratigraphic cross section showing depositional summary through the Noonday (from Wright, et al., 1974), pg. 10. Figure 7. Detailed stratigraphic column of the Noonday members (from Cloud, et al., 1974), pg. 11. Figure 8. Evolution of mounds in Noonday dolomite (from Wright, et al., 1978), pg. 15. Figure 9. Diagram of mound from Panamint Range, with features (from Cloud, et al., 1974), pg. 16. FigurelO. Correlative strata with succession labels (from Link, et al., 1992), pg. 18. Figure 11. Correlative strata with thickness variations (from Link, et al., 1992), pg. 19. Figurel2. Stratigraphic column of related Namibian sections (from Hoffman, et al., 1998), pg. 21. Figurel3. Related Australian sections (from Kennedy, 1996), pg. 22. Figure 14. Stromatolite forms (from Walter, et al., 1992), pg. 26. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ix Figure 15. Stromatolite diversity through time (from Grotzinger and Knoll, 1999), pg. 28. Figure 16. Stromatolite abundance through time (from Awramik, 1971) 28 Figure 17. Selected marine traces (from Bromley, 1996), pg. 30. Figure 18. Selected non-marine traces (from Bromley, 1996), pg. 31. Figure 19. Common trace fossils in the late Precambrian (from Crimes, 1992), pg. 33. Figure 20. Trace fossil diversity over time, (from Bottjer and Droser, 1994), pg. 33. Figure 21. Ichnofabric index for Skolithos dominated nearshore facies (from Bottjer and Droser, 1989), pg. 35. Figure 22. Banded iron formation distributions over time, (from Klein and Beukes, 1992), pg. 38. Figure 23. Variations in 8I3 C over time, (from Kaufman, et al., 1997), pg. 40. Figure 24. Map of Southern Death Valley area (from Awramik, et a l, 2000), pg. 52. Figure 25. Sperry Hills, pg. 53. Figure 26. Saddle Peak Hills, pg. 53. Figure 27. Kingston Peak/Noonday Contact in Sperry Hills, pg. 54. Figure 28. Kingston Peak Diamictite with large dropstone to the field assistant’s left, pg. 56. Figure 29. Kingston Peak Diamictite, pg. 56. Figure 30. Kingston Peak/Noonday contact, pg. 56. Figure 31. Lower Noonday, sharp contact, pg. 57. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. X Figure 32. Lower Noonday, graded contact, pg. 57. Figure 33. Lower Noonday, massive dolomite, pg. 57. Figure 34. Noonday/Crystal Springs contact (bottom of Noonday marked with tape “X’s”), Nopah Range, pg. 59. Figure 35. Massive Noonday in Nopah Range, pg. 59. Figure 36. Upper Noonday/Johnnie contact, Saddle Peak Hills, pg. 61. Figure 37. Tubes in Alexander Hills, plan view, pg. 63. Figure 38. Tubes in Alexander Hills, cross section view, pg. 63. Figure 39. Variety of talus, original orientation unknown, Nopah Range, pg. 64. Figure 40. Layers of material, Panamint Range, pg. 65. Figure 41. Pockets of material, Panamint Range, pg. 65. Figure 42. Tubes of material, Panamint Range, pg. 65. Figure 43. Large domal stromatolite with tube field, Panamint Range, pg. 66. Figure 44. Polished slab with tubes, cross section, pg. 68. Figure 45. Polished slab with tubes, plan view, pg. 68. Figure 46. Clotted dolomitic matrix fabric (at 2.5x (top), lOx (middle), and 25x (bottom)), pg. 72. Figure 47. Matrix fabric with detrital iron (at 25x (top) and 50x (bottom)), pg. 73. Figure 48. Meniscoid infill (2.5x), pg. 74. Figure 49. Infill material with detrital iron particles (at 2.5x (top), lOx (middle), and 25x (bottom)), pg. 75. Figure 50. Matrix -tube boundary (25x), pg. 77. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 51. Sparry pocket (at 2.5x (above) and lOx (below)), pg. 78. Figure 52. Organic residue from matrix material (2.5x), pg. 81. Figure 53. Drilled slabs, pg. 83. Figure 54. Flowchart of sample processing, pg. 84. Figure 55. Stable Isotope Data Graph, pg. 89. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Abstract The lower member platform facies of the Noonday Formation (Neoproterozoic, California) is primarily a domal dolomite containing laminates interspersed with pockets of fine-grained material. This material comes in many forms — layers, irregular pockets, and distinctive tubular structures. These structures have formerly been interpreted as stromatolites, bioturbation, out- gassing tubes, and many other types of structures. This study employed field, petrographic, and geochemical methods to elucidate the nature of these structures; and the previous suggestions of stromatolites, root casts, Skolithos, out-gassing tubes, selective diagenetic alteration, and post depositional fluid flow have been eliminated. The collected evidence indicates that these fabrics are the result of a balance between microbial mat growth and contemporaneous abiotic sedimentation. Data also confirmed an interpretation of the Noonday as a Marinoan-type cap carbonate. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 Chapter 1: Introduction 1.1: General Introduction The Middle Neoproterozoic has recently been the focus of intense research interest. As more and more data accumulates, it is becoming increasingly clear that this is a period in Earth’s history marked by dramatically different conditions than those of the modern Earth. During this time, 81 3 C values, and the rapidity of their extreme excursions, dwarf isotopic values and excursions seen in the Phanerozoic (Kaufman and Knoll, 1995, e.g.). A brief return of banded iron formation deposition is seen after a nearly billion year hiatus, after which BIF’s are not seen again (Klein and Beukes, 1992). Unusual deposits of odd carbonates with irregular fabrics are seen globally at this time, as well (Hoffman, etal., 1998; Kennedy, 1996, e.g.). The Noonday Formation, or Noonday Dolomite, of the Death Valley Region, CA, is one of these odd carbonate units from the mid-Neoproterozoic (Cloud, et al., 1974; Wright, et al., 1978; e.g.). Among the most interesting characteristics of this unit are nearly cylindrical tube structures that have been, through the years, suggested to be produced by a number of causes including, but not limited to, stromatolite growth, bioturbation, and outgassing (Cloud, et al., 1974). To attempt to elucidate the nature and process of formation of these tubes seen in the Noonday Formation, a multidisciplinary set of data was collected and, in combination, analyzed. Field studies were conducted to survey the extent and variety of tube morphology and distribution. Petrographic studies via light microscopy and cathodoluminscence were conducted on collected samples to determine tube/matrix relationships. Lastly, geochemical studies of trace metals and stable isotopes provided additional data related to the tube/matrix relationships. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 This chapter provides the general geologic and historical framework of the Noonday Formation; introduces the background on the previously suggested possibilities for the formation of the tubes; discusses the Snowball Earth hypothesis, its competing theories, and its suggested implications on Neoproterozoic deposits like the Noonday; and addresses the current state of understanding of dolomite deposition in general. 1.2: The Noonday Formation 1.2.1: The Noonday Formation The Noonday Formation is a mid-Neoproterozoic dolomite succession that is unique to, but ubiquitous within, the central portion of the southern Great Basin (Stewart, 1970; Wright, et al. 1974). It is seen only in the Death Valley Region, a structurally complex area bounded by the Basin and Range Province to the east and the San Andreas fault system to the west (ibid.). (Figs. 1, 2) The Noonday crops out from the Kingston Range in the east to Death Valley and at a few sites in the Panamint Range to the west. It pinches out gradually northward, with the most northerly occurrence a thin layer of sandy dolomite in the Funeral Mountains. South of the Kingston Range there are only a few isolated outcrops of the basinal facies near Clark Mountain (Stewart, 1970). Before the early 1980’s, both the Noonday and Ibex Formations were together referred to as the Noonday Formation or the Noonday Dolomite. In a series of publications such as Troxel (1982) and Wright, et al. (1984), the former Noonday was separated into a basinal and a shelf facies; the former renamed the Ibex Formation and the latter retaining the moniker Noonday Formation or Noonday Dolomite. The Ibex Formation is very limited in extent and only appears in the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 EX PLA N A TIO N Normal fault, bar and bail on downthrown side__________ » « * Thrust fault, barbs on overriding plate (older units over younger units)_____ Strike slip fault, arrows show relative displacement. Compiled by Lauren A. Wright Pennsylvania State University University Park, Pennsylvania 16802 Cartography by Robert J. Tex ter. I 7 % & : 1 . ‘ ^ Figure 1. Fault map of the Death Valley Area (from Wright,et al., 1974) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 E X P L A N A T I O N Q uaternary alluvn. P lio c e n e - P le isto c e n e B i n I I - a n d e s i t e l n r j h t ) Mesoioic volcanic * n d _ , sedim entary rocks. . .UJill Later P iecam lin an Tertiary volcanic ioc k Tertiary sedim entary ru c k * and sedimentary rocks . m and Paleoioic k * .E Z 3 L a te r P ra c a tttb ria n 1 I 1 P a h ru m p C ro u p , m ost- In- |y s e d im e n ta ry rock*,, Earlier Precambrian metamorphie and KTfeti ig n eo u s r o c k * ............... Compiled by Lauren A. Wright Pr-mcylvania State Univerilty University Park, Pennsylvania 168C Cirtosrapny by Robert J. Texter. t. Mesoioic -Tertiary granitic locks (?) dionte gp : SOM iiai Figure 2. Depositional map of the Death Valley Area (from Wright, et al. 1974) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. center of the Amaragosa Basin, and it is sometimes seen overlain by the Noonday Formation {ibid.). Where conformable, the Noonday Formation lies above the upper diamictite beds of the Kingston Peak Formation (Awramik, et al., 1994), which is the uppermost unit of the Pahrump Group, a classic Proterozoic thick sedimentary-sequence- dominated rift basin deposit (Grotzinger and Ingersoll, 1992). The blocks found in the Kingston Peak diamictite are composed mostly of pieces from the Crystal Spring and Beck Spring Formations, which directly underly the glacial deposit (Link, et al., 1993). Miller (1985) conducted extensive work on the Kingston Peak Formation, including the glacial origin of the diamicties therein. The lower contact of the Noonday, however, is not conformable at most outcrops due to its deposition in an active rift basin (Link, et al., 1993). This syn- depositional rifting to the Northwest created an increasing angular unconformity toward the northeast (Stewart, 1970). In this direction, the lower unit of the Noonday angularly overlies progressively older strata, to the gniesses and schists of the older Precambrian basement in the most north-easterly outcrops {ibid). (Figs. 3,4,5) Again, Miller (1987) and others have investigated the nature and implications of the Noonday/Kingston Peak contact in relation to tectonics and paleoenvironment, suggesting that the deposition of the Noonday over the Kingston Peak and lower units is the result of the end stage “sealing off’ of both the lower units and the tectonic results of the rift system, namely thermal subsidence and normal faulting (Link, etal., 1993). The Noonday Formation is approximately 450 m thick and at the type section in the Southern Nopah Range is composed of two members (Stewart, 1970; Awramik, et al., 1994). The lower of these is the algal dolomite member, a light tan to gray massive dolomite with microbial laminae, large domal stromatolites, and an Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 Quarttit*. groaralty locally eongtomarattsi in lowar part Dotomit*. tllWona and landnont Mxad aadimamaty rock* Ouanaita, clartic dotomit* and goaraitit Momtta, ptobty oongtomacata, tMatona, dotomha, limanon* * abundantly erooM kM , minor dokimit Ciaytlc rMomrta— qMartrit* nx* atxrodantty i * Algal dotemrw ggM b i Cla*t« doiomi»--<}U»rti rock 'Alfptl (M anila with law than on* pamMM ioaotubtaa dactJc, linwnon*, thWy baddad -Ark one Hndnona and rilttton* Conglonwtu (diarmetila), *nd Bandstona, and lubotdlnat* iltertowfr HHf tfrnthr: ymfr1 if f # toada and gigantic daaa common; nay b* « m o* w 1800m. Odck Coogtonwrat* idtamMw) and lindnona. ganaralty poor hr baddad Saoditona and dttitoot; wall landntttd to maad** maawra; orXitte i Miitad aadknannry rocki: ModRooa, dtetoM . dud*, dolomite; minor wogicmarat* . 'v i t f l f e S i i i i '! . I CMrl Umattona, ttromatolrttc Oolomil*. dttcaour -mudttoo* - faidapathk landiton* and dluton* Arkoric conglomcrat* randmofl* and-dJtttoha: Motlly granitic gnans Figure 3. Stratigraphic column of Precambrian/Cambrian in the Death Valley area (fromWright, etal., 1974) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 0 C l Cl Z > o N O w C D C 0 c C O _Q E C O o 0 73 73 0 O O N O 0 o V - 0. O N O 0 o i m . CL O (1 ) O ( /) 0 ) Nopah (partial) Bonanza King Carrara Zabriskie Wood Canyon i co n tin u es HI® ^ Stirling Johnnie Noonday J o h n n ie o o lite goi a dz ^ a a a v v v v Fe r 'u n n a m e d lim e sto n e " T^j1 T^rl'1 S oL jrdotJoh lim e sto n e " y A A A Fe?® <^ C O Ch S 'C L O C O v wl .08 Ga t K1*WA stromatolites u n n am ed d o m es and colum ns H I throm bolites 1 Boxonia oncoids $ Conophyton f Baicalia & m eg a-d o m es trace fossils arthropod ^ tra c e fossils Treptichnus pedum > 0 first tra c e fossils Ediacarans @ Ernietta Sm Swartpuntia fossils with shells & trilobites p hyolithellids ^ a rc h a e o c y a th s Cloudina microfossils £i2 Dzhelindia f microfossils (in chert) lithologlc symbols [i 11 1 i j 1 L im estone f. . .-1 Q uartzite D olom ite Diamictite 11 ^ 1 C on g lo m erate □ S h ale | | In terb ed d ed qu arzite a n d siltstone r ; i M etam orphic/granitic b a s e m e n t rocks \ [ J D ia b a se sills an d d ikes " '" ''S Fe ▲ ▲ a glacial unit iron-rich stra ta v v v v volcanics | abiotic? 0 vertical tu b e s fault-active / during d e p o sition probable disconform ity 5 0 0 m Basement 1.4-1.7 Ga Figure 4. Stratigraphic column with common features of Precambrian/ Cambrian in the Death Valley area (from Awramik, et al., 2000) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 Nd . NOONDAY DOL. K P . KINGSTON PK. PM. :K^b b s R ; > s pr; ;D o u : ; : C S -C R Y S T A L SPR . FM. p-P - PRE- PAHRUMP COMPLEX: N.B. Palinspaslically unrestoredj ;in g s t o n RNG , LEGEND :.E 3 :“ mainly; ^ q u a te r n a r y - alluvium' ; . E f / r L s s t -p Xh T O p ! S e 6 im E n t a r y : : f k j c x s : M tahruw: s : cmp3? O P R E - P A R R N M P ;;'W S E M 6 N T '': :: Figure 5. G eologic map of Death Valley, with inset map o f Noonday (from Wright, et al., 1974) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 assortment of strange tube and pocket features. It comprises about two thirds of the thickness of the section and is often mounded in overall appearance (Stewart, 1970). The upper third is the sandy dolomite, a pink cross-bedded silicicalstic rich dolomite. This same combination of lithologies is seen in the eastern Kingston Range west to Death Valley and in the southern Panamint Range (ibid.). (Fig. 6) To the south and west of this transect, there is a unit in-between the algal and sandy members called the clastic wedge. It is composed of shales and graywackes and it thickens to the southwest (Stewart, 1970). In the central to northern Panamint Range, there is a different interfingering unit seen. It is a sandy/silty limestone first identified by Murphy (1932), prior to Hazzard’s (1937) naming of the Noonday. Murphy (1932) called his Panamint Range lower algal dolomite the Sentinel Dolomite, the interfingering unit the Radcliff Formation, and the upper portion (with some of the Johnnie) the Redlands Dolomitic Limestone. Now, the lower and upper portions have been reassigned to the algal and sandy members of the Noonday, respectively, and the interfingering unit is called the Radcliff (Stewart, 1970). The Radcliff and the clastc wedge occupy the same stratigraphic position; however, they have different lithologies and are separated by a region in which the sandy member directly overlies the algal member without any intervening unit (ibid.). (Fig. 7) The Noonday is consistently conformably overlain by the Johnnie Formation. The lower Johnnie Formation is a pink sandy dolomite as is the upper Noonday. This often presents problems in clearly defining the boundary between the two units. The problem is resolved by marking the formation division at the point at which thicker bedded, more carbonate rich strata give way to thinner bedded strata that have a more even carbonate/clastic content (Stewart, 1970). Still, this division is hardly distinct in the field. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 . arkose LCS TT7- * — "—- .». • • % .............. K^$&m$a£; & w m Figure 6. Sequential stratigraphic cross section showing depositional process from the Lower Crystal Spring (LCS) to the Noonday (ND) (to the left, from Link, 1992) and stratigraphic cross section showing depositional summary through the Noonday (below, from Wright, et al., 1974) UKP-ND . -^^ollalostrom e ; ^ \ r J \ ~ 1 Q M Q 14,0® - 6.001) ft t-4 o e o ti . -H aoooti J Bkro NOONDAY DOLOMITE tPl^lf!i.'m tfepcrtl) AY - EQUIVALENT UNITS CBednal deposits) ' Y , v ; » ............." r , ' 7 7 \ . . ■ ■ ■ • ; — . . , . 1 1 r • — * * ** *.*•• *• * * 1 - KINGSTON PFAK 1 . ’ • ' * ** /* * *. * • o’ . formation * .* * • 1 , • ' | 1 1 •*, * ’****»*** : BIU S EARLIER PRECAMBRIAN CRYSTALLINE Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 <v- o o N O V C Ill K o Of a. < K U f o sc 3 o > * z o fr» < s < c o u . UJ z z z o TRANSITIONAL MEMBER {Stftwtirt, isroi 150 m. faj £ 5 o _ j o a > < a z o o z UPPER MEMBER 120m ± MIDDLE MEMBER 0 - 100m + LOWER MEMBER 130- 330m . ± LOCALLY SAKOr OOLOM1TE WITH LARGE d o m a l s t r o m a t o l i t e s W AVY-BEDDED STRUCTURES ______ ' ~ silty” oolomTt e a ' - ^ OOLOMITIC ' - SILTSTOHE g i a n t d o m a l STROMATOLITES o p p u r e MICROGRANULAR DOLOMITE WITH SUS VERTICAL TU B ES AND SPARRY IN T E R S P A C E S RISING FROM 8A S A L ALGAL DOLOMITE Z UJ 2 UJ CD < C D PAHRUMP GRP CRYSTAL SPG FM. PRE -PAHRUMP METAMQRPHJC AND IGNEOUS ROCKS • 7 / / V Figure 7. Detailed stratigraphic column of the Noonday members (from Cloud, etal., 1974) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 12 The Noonday was deposited in a deepening upward nearshore shelf system (transgressive), starting with intertidal deposits at the base through to subtidal deposits as it grades into the Johnnie Formation (Link, et al., 1993). This resulted in the production of a shallow marine carbonate platform system in the interim, represented by the Noonday Dolomite (ibid). It has been suggested (Awramik, et al., 1994) that the mounded portions of the Noonday may questionably be the oldest mud mounds in the record, however there has been little evidence to corroborate this hypothesis to date. The Noonday’s sister formation, the Ibex, is comprised of carbonate detritus shed from the platform interfingered with arkosic clastic strata that prograde south to north (Troxel, 1982; Link, et al., 1993). The southern Great Basin as a whole is a structurally complex region. It has many resultant tight folds and a variety of high and low angle faults (Stewart, 1970). Consequently, much of the outcrop seen in the region is highly metamorphosed. In its southeasterly outcrops, however, the Noonday has experienced little to no metamorphism (Link, et al., 1993) and is thus perhaps the best place to sample the unit. The age of the Noonday is not well defined. The earliest researchers considered it Cambrian in age (Hazzard, 1937; Hewett 1940). Later, it was reassigned to the Precambrian (Hunt and Mabey, 1966; Stewart, 1970) based upon biostratigraphic evidence — in its westernmost exposures, the Noonday occurs over 2300m below the lowest Olenellid trilobites and archaeocyaths, and about 1700m below the oldest conclusive trace fossils. Correlations have more recently been based upon global comparisons of glacial deposits combined with biostratigraphic and carbon isotopic data. The Kingston Peak Formation, interpreted as a glaical diamitctite with abundant dropstones, is tentatively dated as ~ 750 ma (Awramik, et al., 1994), which would Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 place it within the Sturtian glacial events. The upper Noonday is overlain by the Ediacaran-fauna containing Wood Canyon Formation, generally dated to ~580 ma {ibid.). Therefore, sediments of both the lower and upper overlying Noonday could have been deposited anytime from 750 to 580 ma. As recently as 1994, the age was still only loosely constrained to this 750-580 ma window {ibid.). The possible discovery of two distinct, not one massive, diamictite in the Kingston Peak Formation may suggest that the Noonday falls at the younger end of this window, although this is still under scrutiny (Prave, 1999; Labotka, et al., 2000). Chemostratigraphic data, however, may add support to this interpretation of the Noonday as younger, rather than older (Corsetti, 2000). Conservatively though, this leaves the age of the Noonday, outside of a general window of the Mid- Neoproterozoic, currently undecided. 1.2.2: Previous Work The Noonday was named by Hazzard (1937) in his USC PhD dissertation, however, that was not the first work done on the unit. Murphy (1932) noted the same units in the Panamint Range, naming the lower unit the Sentinel Dolomite. With the subsequent study of the same units by Hazzard (1937) Murphy’s (1932) sections were re-assigned to the Noonday. Since these initial observations, a plethora of work has been done on the area, not least amongst these the work of Hunt and Mabey (1966), Stewart (1970), Troxel (1982), Miller (1985, 1987), Williams, et al., (1974) Awramik and Corsetti (2000), Cloud, et al. (1974), and Wright, et al. (1978). Hunt and Mabey (1966) surveyed the stratigraphy and structure in the region, and were the first to associate the Noonday tubes with Skolithos trace fossils. Stewart (1970), in his extensive U.S. Geological Survey Professional Paper, divided and named the upper and lower members, and primarily investigated the upper sandy dolomites as Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. part of his general survey of the late Proterozoic of the Great Basin. Williams, et al. (1974) investigated primarily the depositional environment of the Noonday and related units. Troxel (1982) published extensively on the Noonday and related units, including geologic mapping, facies correlations, and the naming of the Ibex Formation. Miller (1987) investigated the nature and implications of the Kingston Peak Noonday contact, in addition to her work on the Kingston Peak itself (1985). Recently, Awramik, Corsetti, Kaufman and others have together done extensive work on the general stratigraphy, chemostratigraphy, and general sedimentology of the region. Corsetti and Kaufman (1998, 2000) have published extensive chemostratigraphic data not only for the Death Valley Region, but also the nearby White-Inyo area. Awramik, Corsetti, and Shapiro (2000) overviewed the sedimentology, also describing stromatolite forms seen, throughout the Death Valley and White-Inyo sections in their paper for the San Bernardino Museum. While the Noonday has been extensively studied stratigraphically, sedimentologically, and structurally, unfortunately there have been few researchers working directly on the possible modes of formation of the tubular structures of the Noonday. Cloud, et al. (1974), and Wright, et al. (1978), though, tackle both the paleoenvironment that created the Noonday and the possible origin of the tube structures. Cloud, et al. (1974) worked more extensively on the lower domed tubular member, documenting the structures in detail as well as preliminarily suggesting a number of tentative hypothetical alternate explanations for their origins, as did Wright, etal. (1978). The Wright, et al. (1978) paper more broadly addresses the unit as a whole, providing a paleoenvironmental analysis of the growth of the large mounds (Fig. 8). Cloud, et al. (1974) describe the tubes in detail and then systematically discuss possible alternatives for their formation. First, they detail the characteristics of the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 15 BA SIN M A R G IN STABLE PLATFORM SEMISTAHJE PLATFORM L A M IN A T E D D O L O M IT E PU f-’A H IU M F CSWAIL.NI COM A ex O U lF T W A TE R \ ' ' ’ . V t h in l y A N D EVENLY 5 E 3 D 5 D S H T 5 T O N E AND SB.TY DOLOMITE OUrgT W A T S * SHTY OCLOMHE Wirn W A V Y LAM INATION S SM A L L D C M A L T O RIP*LF SHAPED STROM ATOLITES MASSIVE OOlOM fTE QUARTZ SA N D STO N E W A 7F F 1 IN M006RATE M C T K 3 N Jar* " -x 1 — V • - - - - I S’ L T W DC! 0M(7= WIT* L ARG E OUARTi D O LO M ITE SA N D STO N E CROSSBEDOED D O M A L STR O M A TO LITES W A TER IN STRONG M O T IO N * * w v-isrt z — w " \QUQit.'. Figure 8. Evolution of the mounds in Noonday dolomite (from Wright, et al., 1978) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 Hi , -1 ---- » i „ , .--- 1 --------1 --------1 _ > 8 ? . S____ 8 - S t, Figure 9. Diagram of mound from Panamint Range, with features (from Cloud, et al., 1974) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 large microbial mounds, verifying their biotic mediation. (Fig. 9) They then describe four tube-like structure types in the unit. Two of these are clearly post-depositional features that are a product of a combination of jointing, differential solution, and other diagenetic and small scale structural effects: vertical lineations expanded by weathering, and gray tubes often continuous with these lineations found in the lower portions of the mounds. They also describe tube-like structures filled with coarse crystalline spar that are likely the product of diagenetic dissolution and reprecipitation or secondary precipitant infilling of pore spaces in the algal mats. Lastly, they describe tube-like structures in the upper and central parts of the mounds. These have a concave upward laminated infill of rusty brown to tan dolomite, and sometimes have upward lateral spreading. They suggest a variety of possible interpretations for the last of these tube structures including Skolithos, root casts, dissolution structures, stromatolites, and outgassing pipes. Using field and petrographic evidence, they conclude that they are, in fact, defluidization channels. They suggest that the tubes were formed through the upward movement of fluids through the mounds, and then later filled in with sediment from above (Cloud, et al, 1974). 1.2.3: Related Sections: The Noonday has a few regional broadly correlative sections seen in western North America. (Figs. 10, 11) In keeping with the divisions made by Young, et al. (1979) in the Canadian Cordillera and Canadian Arctic — in which they separated the mid to late Proterozoic rocks seen there into three tectonically bounded successions: A, B, and C — the Noonday, with its overlying Johnnie and Sterling Formations, correlates with the upper part of succession C. Succession C also broadly includes the Windermere and Hamill Groups of Northeast Washington, the Brigham Group of Idaho and Utah, the McCoy Creek Group and Prospect Mountain Quartzite Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 n g j OKttOM ioswam I I i K i s itJ A s n ? % tM * m ■ _____ ! ! # W a i o z o H U Q & r m s M Figure 10. Correl ative strata with succession labels (from Link, et al., 1992) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 J J I . i l l Ilfll M 1 11 u s i n Iii i *M < *1 * i I it u y h i D I O Z O a a i Q H d 3 1 0 Q J W xnoax ill J ! ¥ I s it ij li ? H i i i \ i i i s i ______ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ & w l* S f« i m * 8.... ... a i v i Figure 11. Correlative strata with thickness variations (from Link, et al., 1994) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 of Nevada, the Grand Canyon’s Tapeats Sandstone and lower Bright Angel Shale (Link, et al., 1993). All of these are syn- and post-rift deposits which resulted in deposition in rift basins, in epicontinental seas, and on the east sides of west facing continental margins {ibid.). The Noonday fits this general depositional model, as it was deposited towards the end of a local active rifting event (Grotzinger and Ingersoll, 1992). Succession C begins around 800ma and ends with the Early Cambrian transgression and general onlapping event (Link, et al., 1993). The Noonday correlates locally to very little outcrop. To the east of the Death Valley Region, there was either no deposition at the time or the material has been subsequently eroded away. To the west, all strata seen are definitely younger than the Noonday (Stewart, 1970). There are units described as similar to the Noonday that are seen in the mid- to late Neoproterozoic of Namibia (Fig. 12). One of these is the Bildah Member of the Kuibis Subgroup, Nama Group that is dated to ~650ma. This member is a light gray peritidal microbial laminated dolomite up to 50 m thick (Hoffman, et al., 1998; Hegenberger, 1987). It contains sub-vertical tube structures that are from 0.5 to 2.5 cm in diameter and from one to several meters long. These tubes have a meniscate infill that is made of large carbonate crystals (spar), rarely of chert, and are thought to have originally been filled with a carbonate mud (Hegenberger, 1987). They are sub-perpendicular to the microbial laminae which have a downward dip at the tube contacts, and appear to occur in a facies dependent manner {ibid.). These tubes have been interpreted as fluid escape structures, more specifically, as either de-gassing structures related to mat decay or as paths of artesian egression (Hegenberger, 1987; Hoffman, et al., 1998). There is also the Noab Formation of the Damara Group, also of Namibia. This formation also contains a massive, microbially laminated tidal dolomite with Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1100 •oco 1900 - CHUOS FM KEILBERG MB QNAUBFM : LITHOFACIES microbiaiaminlte | : : ! ; Q r ^ r t 9 t S 0 6 '' il l stromatolite^ : water [ribbon rock d*P» [ rhythmite • sequence boundary ||Jdlairilctit0 Q siliciclastic Figure 12. Stratigraphic column of related Namibian sections (from Hoffman, et al., 1998) 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. 3 1 C T Q * c l - t c d U > C D S C D P * > P £ * C D o o’ 3 1 7 > 3 3 £ a > 3 3 n > a. ^ 3 M 3 M 3 O N ■ 4 3 0 fWOkm KIMBERLEY REGION Ranford Formation Moonlight Valley Ttilite W irara Form ation /F rank River^ l Low er C ap L im estone yF argoo 8 1 Landrigan Tillrlo Ngalia Basin 2 2 ^ 2 .^M t Doreen Formation Rinkabeena Shale Lower Cap Limestone Nii'burula Formation Basement ADELAIDE GEOSYNCLINE ABC R an g o Q uartzitc B rachina Form ation ^ V ^ N u c c a i o o n a Form ation Elatina Form ation . ; : j Tappley Hill Form ation ■ r C ap L im estone Sturt Tillite Aralka Form ation ADELAIDE Dolomite M M Lim estone rr'ifv iT f ■ -«.r- S an d y Lim estone S an d sto n e Glacigenic D eposits ‘ it!?; 1 , Siltstone AMADEUS BASIN ■ < > = if P ertatatak a Form ation V^VVn V *. ^ U pper C ap Dolomite Olympic Form ation Lower C ap L im estone A reyonga Form ation to to 23 tube structures (Hoffman, et al., 1998). These tubes are 1.5 cm in diameter and 10 cm long {ibid.). They are filled with quartz and carbonate spars. Both ends of these tubes pass into beds that are parallel to carbonate veins, and therefore they were interpreted as possible infilled sheet cracks (ibid.). The Maieberg Formation, also of the Damara Sequence again has similar tube structures seen in a massive, pale, microbiolaminated dolomite. In this case, as with the Bildah, they have been interpreted as fluid escape structures, but this time as gas escape tubes associated with post-Snowball de-gassing (Hoffman, et al., 1998). It must be noted, however, that due to the problems assigning a meaningful date to the Noonday, it is unclear which of these Namibian units is most correlative. In the Amadeus Basin in Australia, there is also a similar sort of sequence, but without tube structures (Kennedy, 1996). (Fig. 13) Here the “upper cap dolostone” is 0-30m thick and is made of a light tan to gray dolomite{ibid.). It is comprised of rhythically laminated beds of silty dolomite near the base and iron rich stromatolites near the top {ibid.). There are also chemical sediments such as large barite crystals seen near the top {ibid.). This unit overlies a glacial deposit, the Areyonga Formation. Nearby correlative sections in the Kimberley Region, Adelaide Geosyncline, and Ngalia Basin, as well as a lower unit in the Amadeus Basin, also have “postglacial carbonates,” but in these cases the carbonate is usually limestone, not dolomite {ibid.). 1.3: Microbial Mats and Stromatolites Modem constructive mat communities are seen in limited environments today, and these have been extensively studied as the proxy for microbial build ups in the geologic record. Microbial mats are defined as “accretionary cohesive microbial communities which are often laminated and found growing at the sediment Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 interface...stabiliz(ing) unconsolidated sediment (Pierson, 1992);” the key to this definition being the biogenicity of the related deposits, which, since they are seen during formation, can be conclusively proved. The degree of cohesion varies, as does the organic material-sediment ratio, but in all cases they produce laminated sediments that have slight irregularities. They usually contain many metabolically distinct species that live in microenvironments within the mats. Many of these communities have alternating periods of growth and sedimentation corresponding to seasonal variations (Pierson, 1992; Bauld, et al., 1992). A few simple megascopic morphologies exist in modern mat communities, including smooth, domal, tufted, columnal, and pustular and each is relatively well correlated with specific environmental constraints and in some cases, combinations of microbes. Each type also can undergo similar post-depositional deformation due to burial, compaction, dessication, etc.; and often, mat types that at the time of growth and deposition are distinct appear very similar after depositional effects. The amount of relief created in any one place is based upon a variety of factors including rate of growth, amount of grazing, water chemistry, and level of energy in the environment. It is interesting to note that laminations are more apparent and defined in structures formed by filamentous microbes (Pierson, 1992; Bauld et al, 1992). Researchers have also observed a list of complex biotic and environmental factors that directly influence microbial mat communities. Amongst these, salinity, temperature, and pH are major factors as are light, dissolved oxygen, sulfide and sediment input. It appears that environmental factors determine which organisms grow in a mat community initially, and preservation/growth to an accretionary stage is dependant upon a lack of grazing and disruptive bioturbation, with physical Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 dynamics such as wind direction, water depth, and current velocity also having an impact. Feedback relationships between the biotic and abiotic factors seem to have the most control over development of mat-built structures. In addition to the studies of the microenvironments within mat communities, much work has been done in developing an understanding of the roles of photosynthesis, decomposition, and chemotrophy in mat growth and preservation (Pierson, 1992; Bauld et al., 1992; Jorgensen, etal., 1992). Many laminated sedimentary structures in the fossil record have been categorized as of microbial origin, although this categorization is the subject of debate. There are two basic camps when it comes to ancient stromatolites, and each has a primary definition upon which its investigations are based. The first group believes that stromatolites must be, by definition, biogenic structures. As Walter (1976) would suggest, they feel that “(s)tromatolites are organosedimentary stmctures produced by sediment trapping, binding, and/or precipitation as a result of the growth and metabolic activity of microorganisms, principally cyanophytes.” Therefore, this definition excludes any structure not produced biotically, and assumes the ability to determine the mode of formation from fossil evidence (Grotzinger and Knoll, 1999). In some cases, the presence of microfossils is used to infer biogenicity of the stromatolite, as it is assumed that the fossils are preserved in situ. Many of the earliest microfossils are preserved in cherty portions of carbonate stromatolites. Fossils include filaments, chains, rods, and other forms as well (Walter, et al., 1992). When actual organic or permineralized remnants are not present the microfabric of biotically mediated stromatolites is thought to have a characteristic mottled, or clotted, texture distinct from even, non-biotic laminae often called dzellindia (or Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 M ODE OF O C C U R R E N C E L ilhotw rm * /3 (liotwfintl 0* O T M L ith o ttro m at I FLAN O U TLIN E | ! Q t t f t t a t m t | O 0*< M f I NO N CO LU M N A R i _ N on b rm e h in g r«r*'r Crftfftfw*' ft/nto*#** i B r m tm n o siv i* ' B ra n ch in g r ATTITUDE 1 v a r i a b i l i t y LA M IN A E TYRE U m frm A»ff#0 i C m iM M LAM INA SHARE u m M v f f lm tt Figure 14. Stromatolite forms (from Walter, et al., 1992) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 gellindia) (Cloud, et al., 1978). The microbiotas of the stromatolites themselves are often accompanied by trapped planktonic fossil forms (Walter, et al., 1992). When describing stromatolites, form-genera and form-species have typically been used (as in trace fossils) by those working within the purely biogenic definition. In this mode of description the primary focus is on the relationship of the laminae to each other. This is because it is thought that the way in which laminae stack combined with the horizontal extent of a mat determines the form of the stromatolite (Walter, et al., 1992). There are two basic growth patterns: litho/bioherms and litho/biostromes (Fig. 14). Lithoherms have populations made of defined separate entities, while lithostromes are extensive buildups, often with little to no internal differentiation (ibid.). As can also be seen in Figure 14, there are also two basic form divisions of bioherms: columnar and non-columnar. Columnar stromatolites have a wide variety of forms, with varied size, angle, branching, and lamina shape. Biostromes, especially tabular ones, and non-columnar stromatolites are sometimes not termed stromatolites at all, but are simply called microbially laminated sediments. Overall, over 800 fossil forms from over 200 basins have been described and categorized, and these have been widely used for biostratigraphic basin correlations in the Proterozoic (Walter, et al., 1992). This is all often a bit problematic, though. Microfossils found in stromatolites may have not been preserved in situ and may have been planktonic during their lifespan, only to settle out after death. In addition, not all laminated, discrete sedimentary structures have clotted fabrics or other sedimentological features that can link them with modern microbial mats and modem stromatolite structures. Many researchers, therefore, have adopted another definition of stromatolite that does not require biogenicity. Instead, stromatolites are defined by some as “attached, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 (b) « ■ ) 2500 ■ ? 0 0 i 1 iCokimfw; cnty* F T ...... 1 * . I i s e j & . b I S ■| : 2 - s a l W aitar ar-n) S e y s, t«gg; 2S0| £ 0 0 b 1 6 0 ] I A w ram ik ?9f*2 Figure 15. (to the left) Stromatolite diversity through time, according to different studies (from Grotzinger and Knoll, 1999) u n Semkhajov and Raaoaty *§95 b . £ 1 S » y I •| t o o P A lg Q P R O T S R Q Z G C S a r i y P m t a r c z o i c M e S O P R Q T g R Q Z G s C j Saify R i j a i i e a r v :N E Q -- Figure 16. (to the right) Stromatolite abundance through time (from Awramik, 1971) t.o E fti; 2 0 2.5 30 "If 40 W ife * S t W ir* CAIMOZOIC 1 3 MESOZOIC (% LA £02O IC CAMBRIAN 2 < o J l U i 1 p N it r U k * 0 c u . 0 tr a . RIPHEAN MIDDLE RIPHEAN LOWER RIPHEAN P flE - RIPHEAN ARCHEAN no rock record 4.6 Origin of Earth STROMATOLITES Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 laminated, lithified, sedimentary growth structure(s), accretionary away from a point or limited surface of initiation (Semikhatov, et al., 1979)”. Perhaps the most important implication of this definition, other than the lack of the need for biotic mediation, is that specific stromatolite forms are not linked to specific populations or types of organisms. Here the role of environmental conditions is at least of equal importance as the type of microbe present (or even the presence of microbes at all) (Grotzinger and Knoll, 1999). The debate about definitions aside, stromatolites and other preserved microbial mat communities are a common feature in the Proterozoic record. At some point in the history of the earth, stromatolites, biotic or not, occupied every paleoenvironment from terrestrial to intertidal to reef and shelf settings (Walter, et al., 1992). Depending upon which definition of stromatolite is used, and upon which features stromatolites are differentiated, these varied and complex sedimentary structures reached a maximum diversity of ~50 to ~250 genera around 1000 ma (Fig. 15) (Grotzinger and Knoll, 1999). Stromatolite abundance peaked later, near the end of the Neoproterozoic (Fig. 16) (Awramik, 1971). 1.4: Skolithos, Root Casts, and The Early History of Bioturbation Trace fossils, also known as ichnofossils, are biogenic sedimentary structures that record organism-sediment interactions (Bromley, 1996). These can range from surface structures related to grazing, moving, or attaching to the bottom to burrowing structures related to feeding, home-building, breeding, or a host of other activities. It also includes footprints, coprolites, root-created structures, and a suite of other examples (Bromley, 1996; Pemberton, etal., 1992). (Fig. 17, Fig. 18) Basically, if any sedimentary structure was created by an organism in the course of it doing anything at all - even simply resting - it is a trace fossil. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 Planolites Thaiassinoides 'Zoophycos \Miondi ;tes Figure 17. Selected marine traces (from Bromley, 1996) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 ALLUVIAL FAN AEOLIAN DUNE FLUVIAL CHANNEL FLOOD PLAIN LAKE k ............. LAGOON DELTA BACKSHORE SALT MARSH 1 : , 1 1 U v 7 ' k m ' 2 ' f £ 12 k * * - 9 ' ‘ '> > V : * ' J t- . ---------------- j j j j g T ~ ^ p n p r ~ j L JL 15 t • hi/ rv ® \ 22 \ s B ® H .. 19 D D istrib u tio n o f so m e tra c e fossils in n o n -m a rin e e n v iro n m e n ts (m o d ified after P o lla rd in G o ld rin g 1991). 1, P a leoh cku ra (sc o rp io n track w ay ); 2. M eskh n iu m (in sect tra c k w ay); 3 Entradichnus (ex o g en ic in sect traces); 4. A cripes (c ru stac ea n trac k w a y ); 5, Cruziana pra h lem a tica (b ra n c h io p o d c ru sta c e a n b u rro w ); 6. C uchikhnus, 7, Scoven ia gracilis: 8. Siske- m ia (a rth r o p o d trac k w a y ); 9. Kouphichnium (x ip h o su ra n trac k w a y ); 10, Undichnus (fish sw im m in g traces); 11. rep tile trac k ; 12. b ird track s; 13, a m p h ib ia n trac k ; 14, ro o ts; 15, Bea- conites: 16. in sect b u rro w s; 17, Spongcliom orpha curlsbcrgi (insect b u rro w ); 18. L o ck eia sili- quaria: 19, Fuerxkhnus communis: 20. D iplocraicrion parallelum : 21, Skoliihos: 22. P silonichnus a n d o th e r c ra b b u rro w s. Figure 18. Selected non-marine traces (from Bromley, 1996) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 In the case of these ichnofossils, there are many unique issues to address. From the difficulties in dividing and defining taxa - whether descriptively, preservationally, or behaviorally - to how to actually determine that a given trace was biogenically produced, uncertainties abound. Generally, ichnologists attempt to solve a number of these problems by trying to relate fossil traces to modern organism processes whenever possible (Bromley, 1996; Savazzi, 1994). This process is not, though, fool-proof by any means. Many problematica and dubiofossils exist in the Proterozoic record that have been assigned as trace fossils at one time or another. Usually, these associations with more modern traces are not well supported, although there is rarely enough evidence to fully support or refute such an interpretation. Proterozoic dubiofossils come in many forms, from surface phenomena like spindles, ropes, and discoids; to vertical traces such as cylinders and U-shaped structures (Hofmann, 1992). For example, there are a series of pre-Vendian structures reported as possible trace fossils. There are billion year old “burrows” in the Zambian Copperbelt, later shown to be modern termite galleries (Fedonkin and Runnegar, 1992). There are tube structures in the 2 ba Medicine Peak Quartzite of Wyoming, originally argued to possibly be burrows that are more likely fluid pathways (Fedonkin and Runnegar, 1992; Kauffman and Steidtmann, 1981). Others, such as the structures in the 2.2 ba upper Huronian of Ontario, were later determined to be mud cracks (Crimes, 1994). There are also rocks that were originally mis-dated as Proterozoic that are, in fact Paleozoic, such as some burrows found in the Ukraine (Fedonkin and Runnegar, 1992). In addition, there are many completely unexplained phenomena such as Brooksella in the Nankoweap of the Grand Canyon and bead shaped structures seen in the early Proterozoic in Michigan that may, in the future, be found to be traces. There is not, however, enough information to assign them as such yet {ibid.). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 Restricted Range Long Range | Lower Cambrian | f l i «9 3 > 0 S W W S q o im w tic iy o n M ite a d w y o a C a s m o / h g p h e O & f t c h n t e * L. . * » . 1 9 -----1 if ............ ? 9 f Owto fiu s o fih tftu i C tm d r fK * O t f r t i x x M e r b n c < 0 T) C 2 D S l « n i 0 ■ * . * 0 c m K ) 0 « « f f f tjv a d iw I 'f f f p d a f o w i d V f a i V / * * I t o f c W r A u t f i ' c g 1 » .» 1 5 t .....S.„---! ? . tn t r H e s H v fy tv tlb C a M M v H fi B e r g t o t t i * . A f a n o m f o t M c i t i l t i f o o p a i * Figure 19. (above) Common traces in the late Precambrian (from Crimes 1992) 0 m p w aur tom * Balhynwlrically mdapandanl torm* 60 40 .« 30 PC Ichnogeneric diversity from the Precambrian to die Tertiary (from Crimes, 1992; data from Crimes, 1974). Key: PC * Precambrian; -6 = Cambrian; 0 = Ordovician; S = Silurian; 0 = Devonian; C = Carboniferous; P « Permian; T = Triassic; J = Jurassic; K * Cretaceous; Tr = Tertiary. Figure 20. (above) Trace fossil diversity over time (from Bottjer and Droser, 1994) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The oldest clearly biogenic structures co-occur at the Same time or are stratigraphically just below the Ediacaran fauna (Fedonkin and Runnegar, 1992). They are all surface phenomena, like Planolites, with the exception of one shallow anemone burrow, Beltanelliformis (ibid.). These surface structures are likely grazing forms left by early metazoans consuming microbial mat material off of the sea floor (Hagadorn and Bottjer, 1999). A diversity of spatial distribution of traces, and the appearance of vertical, or infaunal, traces, does not arise until after the Vendian-Cambrian boundary. At that point, vertical traces such as Skolithos and Arenicolites as well as arthropod traces begin to be apparent in the record (Fedonkin and Runnegar, 1992; Bottjer and Droser, 1994). Common trace fossils from the late Precambrian are detailed in figure 19 and trace fossil diversity through time is shown in figure 20. Skolithos is a common trace fossil from the Early Cambrian to the modern (Bottjer and Droser, 1994). It is a tube-shaped vertical trace, 2mm-3cm in diameter and up to 3m long. This trace is usually a straight tube, non-branching and non joining with a relatively regular width and a generally round cross section. It is often found with a clay (or other) lining (spreite) and internally often has a meniscate infill. It is generally from a shelf environment, usually siliciclastic, but can be found rarely in carbonates, and is usually seen in relatively well oxygenated conditions. The upper end of a population of tubes is often associated with a bedding plane; and there is usually disruption of immediate matrix around the tube created in the process of burrowing (Bromley, 1996; Vossler and Pemberton, 1988; Droser, 1991). While Skolithos is usually thought to be the result of burrowing into substrate, the suggestion has also been made that in some cases this trace may be the remnant tubes of polychaete worms (Ekdale and Lewis, 1993; Skoog, et al., 1994). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 Figure 21. Ichnofabric index for Skolithos dominated nearshore facies (from Bottjer and Droser, 1989) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 Skolithos piperock (Fig. 21) is a monospecific ichnofabric made of high density assemblages of Skolithos traces (Droser, 1991; Droser and Bottjer, 1993). Ichnofabrics, in general, are the total records of sedimentary rock fabric that result from biotic activity, including everything from discrete traces to obliterated textures. Often discrete tiers of traces are apparent, with surface, moderate, vertical and deep infaunal traces presenting a view of life on and in the paleosediment. They are usually judged in vertical cross section and are assigned an index number with 0 or 1 being no traces to 5 being extensive bioturbation and complete to near complete original bed obliteration (Droser and Bottjer, 1993). The Skolithos ichnofabric is most common from the Early Cambrian to end Paleozoic in high energy nearshore environments. It is primarily associated with siliciclastic facies with hummocky cross stratification. Overall, it has a bimodal ichnofabric index measurement of around 1/5 (periods of no bioturbation, periods of much bioturbation) and this bimodality is associated with bedding planes (Droser, 1991; Pemberton, et al. 1992; Bottjer and Droser, 1993). Root casts are traces left in paleosols and some freshwater deposits by the downward growth of roots. They can be found preserved from terrestrial and swampy paleoenvironments, as well as in weathered reef rock and caliches (Behrensmeyer and Hook, 1992), but not in normal marine settings. These traces incrementally decrease in size with depth, tapering downward; and they often fork downward and branch multiple times at high angles. This can lead to extensive horizontal, interlocking networks of roots (Klappa, 1990; Ekdale, et al., 1984). Root casts can range from 0.1mm to 20cm in diameter and from a few centimeters to several meters in length (ibid.). They usually compact and disrupt surrounding sediments during growth; and root hairs often interfinger with matrix sediment. Residual characteristic organic material is often seen in the tube areas, with increased Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 concentrations toward the center of the tube and clear secondary in situ crystal formation around it as secondary lining (Sarjeant, 1975). These structures are seen from the Upper Devonian onward in the fossil record (ibid.). 1.5: Neoproterozoic Deposits and The Snowball Earth Hypothesis Globally, sections of rock from the mid- to late Neoproterozoic repeatedly exhibit any number of a set of abnormal features in conjunction with one another. These features include iron rich glaciogenic diamictites, banded iron formations, cap carbonates, and large excursions of carbon isotopic values. Any to all of them are seen at a host of sites globally, including Africa, Australia, and North America. Attempts to elucidate the phenomenon/phenomena that produced these geological products has sparked heated debate recently, and a conclusive answer has yet to emerge. 1.5.1: The Observations A number of distinct diamictites are seen throughout the mid- to late Neoproterozoic. They have abundant dropstones (some with striations) that disrupt underlying depositional laminae, and thus are deemed glaciogenic. Two features of these tillites are of interest here - their high iron content, and the fact that paleomagnetic data places some of them at apparently low latitudes during deposition (Sohl, et al., 1999; Hoffman, et al., 1998; e.g.). A return of Banded Iron Formations, or BIFs, is seen briefly in the Neoproterozoic. BIFs are thinly bedded or laminated chemical sediments, usually containing chert, that have distinct layers with high iron content. They appear in the Archean and are mostly noted in the Paleoproterozoic and early Mesoproterozoic. They disappear around 1700 ma and re-appear briefly and globally around 800 ma (Fig 22). Interestingly, the banded iron formations of the Neoproterozoic have a 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. ° x II 5 „ flt w — (B ® (C LL I L CD CD Q . = * o 2 < D O = S ' a > ® T J » C Jr 3 ® JQ E < « Canadian greenstone belts Yilgarn Block, W.A Zimbabwe.S. Africa; Ukraine, U.S.S.R; Venezuela; Western Australia isua, West ~\ Greenland ^ _______ I _ _ m Hamer sley Group, W.A. ~ 4.5 4.0 Transvaal Supergroup,S.Africa Lake Superior Region, USA Krivoy Rog series, U.S.S.R Labrador Trough, Canada Rapitan Group, Canada; Urucum Region, Brazil; Da mar a Supergroup, Namibia J Q a V O V O o to “ 21 r ! « 2 3 c C T Q § 0 a. g. B « § W C D o y | o to to 3 o * C D a- U > 00 39 distinctly different composition from the earlier iron formations, in that they are mainly hematite and chert, while earlier versions tend to have more siderite. In addition, the earlier ones have more strikingly different alternating laminae, while later ones can be more mottled (Klein and Beukes, 1992). The exact ways in which banded iron formations form, and the chemistry involved in their production, are still not well understood. Cap carbonates are massive carbonate units (often dolomite) that overly, or cap, glacial deposits and have both anomalous fabrics and abnormal carbon isotopic values (Kennedy, 1996). There are two types of caps seen in the Neoproterozoic, an early, or “Sturtian-type,” and a later, or “Marinoan-type.” Both types fit all of the criteria for a cap carbonate, but have different sets of features beyond that distinction. Sturtian-type caps are a group of these carbonates that are also associated with ironstones/BIF’s, have a dark, organic rich composition, slightly heavier carbon isotopic values, and rhythmic laminae. Marinoan-type caps are organic poor, and have sheet cracks, tube structures, crystal fans, and lighter carbon isotope values (Kennedy, et al., 1998). The proliferation of chemostratigraphic data within the past few decades has revealed a curious pattern of many drastic globally recorded shifts in the carbon isotope record in the mid- to late Neoproterozoic (Kaufman and Knoll, 1995; Kaufman, et al., 1997; Kennedy, et al., 1998; Walter, et al., 2000). (Fig. 23) As measured in carbonate, positive values, indicating deposits enriched in 1 3 C, reach up to 10%c (relative to PBD), and are followed rapidly by negative (depleted) values of as much as -9 % o a number of times, although the number of these excursions is the subject of controversy (Kaufman, et al, 1997; Kennedy, et al., 1998; Knoll, 2000; Walter, et al., 2000). This data is used both to attempt stratigraphic correlation and to aid in deciphering the environmental nature of the event(s) that produced it. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Phanerozoic i Proterozoic 4 0 (puesnoyj jad sped) 3 g Figure 23. Carbon isotope ratios through tine (from Kaufman, et al., 1997). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 Both strontium and sulfur istotope data has been accumulated for this time; however, in both cases it is both harder to gather and less reliable than carbon data due to initial scarcity and diagenetic and metamorphic susceptibility (Knoll, 2000). Strontium isotope data is used primarily for chemostratigraphy and correlation of sections; although it has been employed for other uses as well, including estimation of the amount and type of weathering occurring at a given time (Knoll, 2000; Walter, et al., 2000). The strontium data shows two positive excursions from background in the Neoproterozoic. The first is a small spike occurring between what has been interpreted as two major glacial events (discussed further in 1.5.2 and 1.5.3) and the second is a large, more gradual excursion temporally placed after the last of these events (Walter, et al., 2000). Sulfur ratios indicate one positive excursion around 700 ma that has been used to correlate sections in Namibia, China, and Australia (Walter, et al., 2000); and may also indicate a separate excursion later in the Neoproterozoic, although data to this effect is still tentative (Knoll, 2000). 1.5.2; Distribution of Features Globally, some or all of these features are seen on nearly every continent today. The sections of primary interest occur in Australia (e.g., Kennedy, 1996), Namibia (e.g., Hoffman, et al., 1998), and Western North America (e.g., Awramik, et al., 2000); however, sections with some features have also been observed at sites including ones in Oman, South Africa, the Volta Basin, Guinea, Greenland/ Spitzbergen, Poland, Siberia, Mongolia, Eastern North America, South America, and China (Walter, e ta l, 2000). Glacial deposits have been observed at most of these locales; however, only a few are identified as low-latitude at the time of deposition. The best paleomagnetic data indicating low-latitude position comes from the sections seen in Australia, where primary outcrops occur in the Adelaide Geosyncline (Whyalla Formation and Elatina Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 2 Formation), Central Australia (including the Amadeus and Ngalia Basins) and the Kimberly region (an assortment of tillites) (Kennedy, 1996; Kennedy, et al., 1998). Current data places these, and all other contemporaneous Australian deposits, at ~8 degrees from the equator (Sohl, et al., 1999). Other low to mid-latitude glacial deposits include those in the Chuos and Ghaub Formations of Namibia (Hoffman, et al., 1998), the Kingston Peak Formation of California (Awramik, et al., 2000), and the Rapitan Group of Canada (Walter, et al., 2000). The major banded iron formations seen in the Neoproterozoic are in the Rapitan Group in Canada and the Damara Supergroup in Namibia (Chuos). Their distinctly different composition from the earlier iron formations (hematite and chert, while Archean and Paleoproterozoic versions tend to have more siderite) has been suggested to be related to the possible association between the Neoproterozoic BIF’s and glacial cycling (Klein and Beukes, 1992). Sturtian-type cap carbonates include those seen in Namibia, where the Rasthof caps the Chuos (Hoffman, et al., 1998); in the Areyonga Formation of Australia (Kennedy, 1996); and in the Rapitan of Canada (Kennedy, et al., 1998). All of these have dark, organic-rich laminate carbonates, and both the Chuos and Rapitan are associated with the previously mentioned BIF’s (ibid.). Marinoan-type caps include again those in Namibia, with the Maieberg Formation and the Bildah (Hoffman, et al., 1998); in Australia, in the Elatina (Kennedy, 1996), and in Canada, with the Icebrook (Aiken, 1991). Of these, only the Maieberg and Bildah contain dolomites with tube structures (Hoffman, et al., 1998; Kennedy, etal., 1998). All of these, though, do have features such as crystal fans and sheet cracks, and none are organic rich (Kennedy, et al., 1998). Isotopic data has been collected globally for carbon, strontium, and sulfur depending upon the availability of necessary types of deposits at different locales Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 (Kaufman, et al., 1997; Knoll, 2000; Walter, et al., 2000; e.g.). Walter, et al. (2000) produced the most comprehensive global correlation of sections to date based up a combination of this data from sites on all continents, and is combined with biostratigraphic data Knoll (2000). 1.5.3: The Explanations A suite of explanations have been provided for some or all of this combination of interesting sedimentological and geochemical features. These include obliquity-oblateness changes in the Earth, true polar wander (TPW), effects from impacts, near-normal sized glaciation with ocean stagnation and overturn, and the Snowball Earth hypothesis. All of these, with the exception of the impact ejecta hypothesis, involve glaciation of some form in their explanations. Rampino’s (1994) ejecta hypothesis, on the other hand, suggests that the diamictites are not of glacial origin, but instead are the result of the ejecta produced during large extra-terrestrial impacts. This explanation, though, does not account for the striated clasts in the diamictites, nor for any of the associated features, such as the iron formations, cap carbonates, and isotopic data. This leaves a variety of alternate explanations involving glaciation. The obliquity-oblateness hypothesis (Bills, 1998; Williams, et al., 1998) and the inertial interchange true polar wander hypothesis (IITPW) (Kirschvink, et al., 1997; Evans, et al., 1998) both suggest that there was no actual low-latitude glaciation at this time. Instead, these hypotheses both have alternate ways of making actual high- and mid-latitude glacial deposits appear paleomagnetically to have formed at low latitudes. The obliquity-oblateness hypothesis achieves this through the suggestion that the obliquity (slant of the rotational axis) of the Earth was 54 degrees, instead of the modern 23.5 degrees. This would slant the Earth such that climatic reversals would Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 4 occur due to the angle of rotation combined with the angle of incidence of the sun, and ice covered areas would be located a magnetically low latitudes, although the high latitudes would likely be ice-free (Bills, 1998; Williams, et al., 1998). This does not, however, explain the drastic carbon isotopic shifts nor the cap carbonates or BIFs seen in the record. The inertial interchange true polar wander (IITPW) hypothesis, originally formulated for the Cambrian (Kirschvink, et al., 1997), has been applied to the Neoproterozoic situation as well (Evans, et al., 1998). This hypothesis suggests that the lithosphere of the Earth will rotate to align bulks of mass along the equator when the moment of interia is imbalanced. Basically, it suggests that when large amounts of land mass are focused at the poles with substantially less mass at the equator, the lithosphere will move over the asthenosphere such that the excess mass is redistributed away from the poles to the equator (Kirschvink, et al., 1997), much like a centrifugal force type motion. In this way, glacial deposits could have been deposited while the land masses were pole-ward, and then cap carbonates were deposited in tropical areas after IITPW. It does not, though, account for BIFs or the isotopic record. Another hypothesis is that there was a stratified ocean and modern style glaciation during this period (Grotzinger and Knoll, 1995; Knoll, et al., 1996). This, deemed the “ocean overturn model” suggests that ocean circulation stagnated, producing a stratified column where anoxic bottom waters were not upwelled for a period of time. This would produce an unstable system that, when mixed (or “overturned”) would release these anoxic, likely iron-rich waters onto continental shelves (ibid.) This could produce drastic carbon isotope shifts as organic carbon is buried and released, which could also greatly effect carbonate deposition, and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 5 mixing of iron rich-anoxic waters with shelf waters could produce BIFs {ibid.). This hypothesis does not explain the low latitude glacial deposits, though. Lastly, the Snowball Earth hypothesis was initially developed by Kirschvink (1992) to explain the abundance of globally distributed low latitude glacial deposits in the mid-Neoproterozoic. The hypothesis suggests that there were a number of times in Earth’s history when glacial cycles were so intense that all of the oceans were frozen over. By a process of positive feedback due mostly to extreme albedo effects, once oceanic ice sheets reached 30 degrees from the equator it is thought that a runaway effect would cause total ice cover {ibid.). This does not, though, preclude ice free continents. In fact, land masses are thought to remain ice free during the glaciation. Ice cover is suggested to have lasted from 4 to 30 million years before enough C 0 2 could build up in the atmosphere by normal means (primarily mantle outgassing, deep sea carbonate dissolution, and continental weathering) to create a greenhouse atmosphere and sufficient global warming to start ice break-up. Once melting started, it is hypothesized that it would create another positive feedback, rapidly melting the ice sheets in a geologic instant, regenerating ocean circulation, raising sea level, and releasing anoxic gases from the ocean floor (Kirschvink, 1992; Hoffman, etal., 1998). It is suggested that one would expect to see a suite of features in the rock record to corroborate this hypothesis, which are generally represented in the record. Amongst these would be the presence of a glacial diamictite overlain by a massive cap carbonate, anoxia related sediments such as iron formations, a strontium isotopic excursion towards mantle values, and possible outgassing structures. Hoffman, with his more recent work in Namibian successions, re-introduced the hypothesis bolstered with the presence of these expected observations (Hoffman, et al., 1998). In addition, this hypothesis could also explain the dramatic isotopic shifts seen Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 6 globally in this time period, by providing a reservoir for long term sequestering of large amounts of organic carbon (Hoffman, et al., 1998; Kaufman, et al., 1997). This theory has taken on many forms in recent years, with slight variations to the process and explanations of effects seen; however, the general idea remains the same. One of the major sources of debate, though, is to how many individual events of this type may have occurred. Kennedy, et al. (1998) suggest that there were only two glacial episodes, as does Walter, et al., (2000); however, they disagree as to the timing of these two events. Knoll (2000) suggests three episodes, and Kaufman, et al. (1997) suggests four episodes, as does Corsetti (2001, pers. comm.). Braiser, et al. (2000) and Hoffman, et al. (1998) see at least two, but perhaps more. In the end, this determination will be highly dependent upon the strength of global section correlations, as well as the accuracy of individual glacial sequence identification in the field. 1.6: Focus of this study This work is focused on determining the method of formation of the odd, semi-cylindrical sedimentary structures (referred to generally as “tubes” in previous work) in the lower unit of the Noonday Formation/Noonday Dolomite. Field observations, petrography, and geochemical studies are combined to attempt a complete profile of the matrix material, the “tubes,” and their interrelation in the hopes of elucidating their mode of formation. Specifically, five sites where the Noonday crops out were investigated, samples were collected and compared, thin sections were made and observed by light microscopy and cathodoluminescence, slabs were stained for carbonate type, trace metal content (Ca, Mg, Sr, Mn, Fe) was analyzed by inductively coupled plasma spectroscopy, stable isotopic ratios (51 3 C, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 7 81 8 0) were measured by distillation and mass spectroscopy, and x-ray diffraction was used to verify the mineral content. There are a number of possible alternatives to explore, and expected observations for each if they are the mechanism by which the structures were formed. While it is always best to gather data and then objectively come to a conclusion as to the data’s implications, it is perhaps useful in this case to look at the previously suggested (and in some cases previously ruled out) possibilities to set the stage for the analysis of collected data. First, are they early diagenetic products such as dissolution pipes? If this is the case one would expect to see a set of specific petrographic and diagenetic indicators such as luminosity differentials and independant geochemical signatures for the tubes and the matrix materials. Are the tubes and pockets, in themselves, stromatolites? Stromatolites have a particular collection of features that define them, all of which would be necessary for this conclusion. First, their deposition would need to be microbially mediated, according to one definition (Walter, 1976). This could be easily verified through the identification of classic microbial fabrics under light microscopy. Secondly, in macrostructure do they form definitive entities, that is, are they lithohermal, or do they lack a limited surface or point of intiation (Semikhatov, 1979; Walter, et al., 1992)? If not, are they simply interspaces between stromatolites, later filled in with mud? For this to be the case, the matrix material would also need to be stromatolitic, and therefore fit the aforementioned criteria. Are they the product of some sort of metazoan activity, such as the trace fossil Skolithos or root casts? In both of these cases, a suite of characteristics should be present. For an infaunal trace fossil, like Skolithos, one would expect to see: vertical tubes, up to 3 cm wide with a circular cross section, disruption of the matrix fabric, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 8 possibly pieces of matrix material broken and redepostited in the meniscate infill, no upward or downward branching, and likely with a clay lining (Droser, 1991; Droser and Bottjer, 1993; Bromley, 1996). More specifically, if the dense assemblages of tubes seen in some places are not only Skolithos, but “Skolithos Piperock,” the rock would likely have been deposited in a high energy, nearshore environment and have clear hummocky cross stratification, a distinct common upper bedding plane, and have high density, closely packed populations of monospecific (in this case, Skolithos) traces (Droser, 1991). Both of these, as well, are nearly always seen primarily in siliclastics (Droser, 1991; Droser and Bottjer, 1993; Bromley, 1996 ). In the case of root casts, one would expect only downward, often high angle, branching, disruption of the matrix material, likely much organic residue in the tubes, probably a common upper bedding plane as an upper termination to an abundance of tubes, tubes tapering downward, and indications of deposition in a terrestrial environment (Klappa, 1980; Ekdale, et al., 1984; Behrensmeyer and Hook, 1992). Are they, as suggested by Cloud (1978), Hegenberger (1987), and others, outgassing pipes of some sort? If they are, then a different set of features would be expected. Sedimentologically, the force of outgassing would have disrupted the surrounding matrix material and likely dislodged pieces of it in the process. These pieces could be expected to be seen re-deposited in the infill in the tubes. If the outgassing was the result of massive, rapid outflow, there should be an identifiable source point from which the gases were emitted, and thus also a common starting point or bed for the structures. In addition, infill of the tubes would necessarily have been secondary to the growth of the matrix material, thus creating a situation in which there was a downward filling of the tubes. This would result in concave up, or meniscate, infill that would have a clear boundary and be distinct from the matrix petrographically. Geochemically, the infill material should be different from Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 9 the matrix material. It should have a different isotopic signature due to the influence of the released gasses upon the chemistry of the source water. In addition, it could, but not necessarily, be expected that there may be some slight difference in trace metal contents, due to solubility changes resulting from outgassing. 1.7: Possible Implications The many possible interpretations of these sedimentary structures hold a range of implications. Currently the oldest marine trace fossils are Vendian surface phenomena (Bottjer and Droser, 1994). Infaunal traces indicating burrowing activities below the surface are thought to infer that the organisms that created the traces likely had some skeletized hard parts with which to move sediment (Savazzi, 1994). Therefore, an interpretation of the tubes as Skolithos (or other some trace) would not only increase the length of the record of metazoans, but specifically of skeletized metazoans capable of deep burrowing. It would also indicate that sub surface oxygenation levels would have been relatively high (Bottjer and Droser, 1993). In relation to this, the oldest definitive root casts currently date to the Devonian (Sarjeant, 1975). If the Noonday in fact contains root casts, then this also drastically increases the length of recorded land plant activity. If they are stromatolites, they are a rare and interesting case that could help in the understanding of the mechanics and the relative roles of physical and biological factors in stromatolite growth. These structures are very tall and have a small cross sectional area, and they also branch and anastimose, which while not previously unseen, is uncommon (Walter, et al., 1992). Both an interpretation of the tubes as stromatolites or as the interspaces between stromatolites that were then, at a later time infilled, would have interesting implications for the study of stromatolite growth mechanics. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 0 If they are outgassing pipes, especially with point source or bed, this would corraborate the interpretations of Hegenberger (1987) and Hoffman (1998) for the similar structures in the Namibian correlates and provide another piece of consistent evidence for Snowball Earth. With all of this in mind, there is also the possibility that the structures are the product of a mechanism other than those defined to this point. This possibility would require an alternate process to be developed for the formation of these structures. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 Chapter 2: Data 2.1: Methods of Study A set of sites was chosen based upon a variety of factors including accessibility, paleospatial distribution, and ability to observe lower contacts with a variety of underlying units, upper contacts, and a variety of representative tube/ pocket morphologies. Sites were surveyed, roughly mapped, and key areas were heavily investigated. Samples were collected where permissible. These samples were slabbed, thin and thick sections were prepared for petrographic observation, and microsamples were drilled for geochemical analyses. 2.2: Field Data A variety of sites where the Noonday crops out were observed in and around southern Death Valley. (Fig. 24) The lower conformable contact with the Kingston Peak Formation through most of the lower unit of the Noonday was observed in the Sperry Hills (north of the Dumont Dunes) and in the Saddle Peak Hills. (Figs. 25, 26) A non-conformable lower contact with the Crystal Springs Formation, up through the lower Noonday, was observed in the Southern Nopah Range and in the Southern Panamint Range. An upper contact with the upper Noonday, through to the Johnnie Formation was also observed in the Saddle Peak Hills. The lower Noonday was observed in isolation in the Alexander Hills. Precise locale descriptions and sample lists are in Appendix A and B, respectively. As described by previous workers (Hazzard, Stewart, Wright, Cloud, etc.), the lower Noonday is, for the most part, a massive, cliff forming tan to gray microbial dolomite with large stromatolites and vertical tubes. It is easily recognizable throughout the southern Death Valley region. This, however, only begins to fully 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. e r a s l-S North to Beatty D eath Park Furnaco' Creek -O 3 (O Pahrump Las Vegas, S hoshone, :te3gcopa Shoshone Inyo Co. t-- K in g s to n . R a n g e r~ Tecopa w ' San B e rnardino Co. Baker A l e x a n d e r H i l ls Keiso Barstow 10 km ~“ T Outcrop map of Proterozoic-Cambrian Strata (after Stewart, 1970) 50 kilometers L A to 53 Figure 25. Sperry Hills Figure 26. Saddle Peak Hills Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 Figure 27. Kingston Peak/Noonday contact in Sperry Hills Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 describe the unit. First, it is important to note that this region is extremely structurally complex, with multiple events of deformation impacting it since the deposition of the unit, in addition to the observation that the Noonday itself was syndepositional with a local rifting event, thus creating the widening angular unconformity to the N/NW. This should be kept in mind especially when attempting lateral and temporal correlation of observed sections. The lower contact, as observed in the Sperry Hills, is a complex progression from the underlying Kingston Peak Diamictite into the Noonday. (Fig.27) Here, the Kingston Peak is easily recognizable, with abundant large dropstones (up to 2 m or more in diameter, see Fig. 28) in a laminated variably silty to sandy, reddish to dark siliciclastic matrix. Towards the upper contact, dropstones are smaller and the matrix sandstone is more uniform in size (sand-sized particles) and color (rusty red), while also being more massively laminated (see Fig. 29). The contact itself is characterized by a sharp demarcation of a change in lithology, from the sandy red siliciclastic below to a fine grained, dark gray, cherty carbonate above. (Fig. 30) This is the lowest of the Noonday lithologies, and this cherty, dark, iron rich, bedded carbonate continues upward in the section for ~ 1-1.5 m (variable), with generally thin (a few mm), friable laminae interspersed with more massive (a few cm or more), higher carbonate-containing beds. All of these lithologies also contain red to black iron-rich micro-layers. Above this there is a locally sharp contact with a massive gray dolomite unit. The contact between these units is not level or uniform. In places there appears to be a pinching and swelling of the underlying laminae around the base of the massive unit, and even some sort of distinct separate contact here between an apparently rapidly lithified fine bedded material and the massive upper section. (Fig. 31) In other places, only a few meters away, the progression from the laminated beds to the massive dolomite is more gradational (while still seemingly Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 6 Figure 28. Kingston Peak Diamictite with large dropstone to the field assistant’s left Figure 29. Kingston Peak Diamictite Figure 30. Kingston Peak/ Noonday contact Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 7 Figure 31. Lower Noonday, sharp contact Figure 32. Lower Noonday, graded contact Figure 33. Lower Noon day, massive dolomite Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 rapid). (Fig. 32) This massive bed continues upward for the remainder of the outcrop at this site (10 m or more). In the lower 2-3 m, the dolomite is dark, massive and in some places looks possibly microbial, with some vuggy patches filled with a redder material with a larger crystal size also present. Distinct microbial fabrics (irregular laminations, etc.) become apparent about 3 m up in the massive portion of the unit, and it is about at this point that pockets and layers, are seen, although not in high concentrations. (Fig. 33) A few miles away, in the Saddle Peak Hills, this lower contact is different. While still a seemingly conformable contact with the Kingston Peak, here the progression lacks the finely laminated cherty carbonate portion of the Lower Noonday seen in the Sperry Hills. In most places, there is a simple sharp contact with reddish sandy conglomerate underlying a massive gray dolomite. There are, however, some odd quartzite lenses seen in a few places in the Saddle Peak Hills. These lenses are longer than they are high, but are no more than a few meters in either direction. They are comprised of a chunky gray quartzite that appears almost brecciated in some cases. These lenses are seen between the Kingston Peak and the Noonday, that is, they appear to be an additional, small, rare sub-unit that either caps the Kingston Peak or begins the Noonday at this locale, and may be the Ibex Formation. Much like in the Sperry Hills, in the Saddle Peak Hills the massive gray dolomite at the base of the Noonday continues for a number of meters upward before distinct microbial structures and pockets, tubes, etc. start to be seen in the unit. This probably represents an early deposition of the Noonday basinal facies, or Ibex Formation, then overlain by the shallow water deposition of the classic Noonday facies. The lower contact at the Southern Nopah and Southern Panamint sites shows the Noonday unconformably overlying the Crystal Springs Formation. In the Nopah Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 9 Figure 34. Noonday/Crystal Springs contact (bottom of Noonday marked with tape “X’s”), Nopah Range ..>* * r .& JIk m TSS L : i’ J » F > i^ Q ^ S W i ... - m . *w, M M S Figure 35. Massive Noonday in Nopah Range Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 0 Range, there is a sharp erosive angular unconformity delineating the clear boundary between the Crystal Springs and the Lower Noonday, (Fig. 34) which is presented, again, as a massive gray dolomite at the base of the section, that gradually, over a number of meters vertically, grades into a more microbially textured dolomite that contains the layer, pocket and tube structures. In the Nopah Range, the uppermost Crystal Springs seen before the erosional unconformity consists of cherty metamorphosed shales that are variably bedded, which may be any of a number of units seen in this formation, as it has many alternating and varied lithologies. The Noonday above this contact is massive, gray-tan and has no pockets or tubes until higher in the section. (Fig. 35) In the Panamint Range, the lower contact is equally as sharp, but less angular offset has occurred. Here, the uppermost Crystal Springs that is seen is a dark pink carbonate that is very stromatolite rich, primarily with closely packed stromatolites. Above the sharp contact, the Lower Noonday is seen again as a massive gray dolomite, but here the pockets, layers, and tubes are seen within a meter of the contact and large, domal stromatolites are present as well upward through the unit. The upper contact with the Upper Noonday through to the Johnnie Formation is progressive. As seen in the Saddle Peak Hills (Fig. 36), the upper Noonday is a darker pink, sandy dolomite, sometimes with cross-bedding. This grades quickly and conformably into the lower Johnnie Formation, which is more sandy/silty and darker in color than the upper Noonday. In between, the Lower Noonday has a number of interesting structures that vary both laterally and vertically. While previous researchers focused primarily on the “tubes” seen in some places in the unit, this is by far not the only character worth investigation. Wright, et al. (1978) classified the “tubes” into four types (see 1.2.2); however, more than just tubes are seen. Pockets and layers of the same material seen Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 E - V . /tiff I m ^ - ^ 4 ■asr Figure 36. Upper Noonday/ Johnnie contact, Saddle Peak Hills (seated field assistant for scale) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 2 as infill in the tubes are often also present in the unit. In addition, the differentiations made by Wright, et al. (1978) neglect to rule out structural features, such as jointing, before labeling a feature a “tube.” In the Alexander Hills, mostly massive dolomite without disruptions and dolomite with closely packed, nearly parallel tubes are seen. These tubes are ~2cm in diameter, of regular size, are generally evenly spaced ~3cm apart, are up to 3 m long, and are filled with a fine grained, orange-tan material that preferentially weathers (Figs. 37, 38). Sometimes, tubes are seen to branch and anastimose at this site, and these structures are found in large pockets of several meters, surrounded by non-tubed massive dolomite. These pockets, however, do not have a bedding plane at the base or top at which most tubes either start or end. Instead, tubes begin and end intermittently within the spatial range of the “tube field.” In the Southern Nopah Range, near the War Eagle and Noonday mines, and in the Panamint Range, in the Galena Canyon area, a full variety of forms are seen both in situ and in talus (Fig. 39). Layers of preferentially weathered, darker orange material appear interspersed with gray-tan apparently microbial dolomite (Fig. 40). Pockets of the same material are seen in various shapes (spherical to oblong to irregular) and sizes (less than 1 cm to ~6 cm in diameter) (Fig. 41). There are also the characteristic tubes, again ~2cm in diameter, up to 3 m in length. As in the Alexander Hills, tubes branch and anastamose in places, and are seen in large pockets where they are found in dense concentrations. (Fig. 42) Interestingly, these “tube fields” are often seen in conjunction with large, domal stromatolites. In these cases, the tubes do not infiltrate the stromatolite at all, and no disruption of any kind is apparent within the stromatolite. (Fig. 43) All three forms of material are spatially related in a variety of ways. Most commonly, layers and pockets are often seen within a few centimeters of each other, and tubes are sometimes seen to spread out Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 37. Tubes in Alexander Hills, plan view (penny for scale) Figure 38. Tubes in Alexander Hills, cross section view (penny for scale) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 4 Figure 39. Variety of talus, original orientation unknown, Nopah Range Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 Figure 40. Layers of material, Pana- mint Range Figure 41. Pockets of material, Pana- mint Range Figure 42. Tubes of material, Panamint Range Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 Figure 43. Large domal stromatolite with tube field, Panamint Range Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 at their tops into layers of the orange material. Again, as in the Alexander Hills, there appear to be no common upper or lower bedding planes at which a majority of tubes begin or end. In the Saddle Peak Hills, on the Northeast side of the hills, and in the Sperry Hills, near the access road to the Dumont Dunes, tubes and pockets are not seen in accessible areas of in situ outcrop. Large talus blocks with all three features, however, are seen in both of these areas in washes upslope in the hills. Therefore, the tubes, pockets and layers are present at these sites, but not within 100 or more meters of the base of the unit. 2.3: Hand Samples Samples with a stratigraphic context were collected at the Sperry Hills, Alexander Hills, and Nopah Range sites. Talus samples were collected at these sites as well as from near route 127 by the Saddle Peak Hills. Samples from the Saddle Peak Hills themselves, as well as from the Panamint Range site were not collected due to the placement of these sites within Death Valley National Park. Samples were taken back to the lab for further observation, slabbing, and thin sectioning. A list and description of key samples is in Appendix B. Samples of a variety of macro-fabric types were collected to attempt to accurately represent the diversity of forms seen in the field; however, complications did arise due to the placement of the Saddle Peak Hills and the Southern Panamint Range within the Death Valley National Park boundaries, and also due to difficulties sampling the very hard dolomite while standing on shear cliffs. For the most part, though, the same features are seen in hand samples as are seen in the field; and even if talus samples had to be collected in place of in situ samples in some cases, it was easy to determine their original orientations. There are a variety of pocket Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68 Figure 44. Polished slab with tubes, cross section Figure 45. Polished slab with tubes, plan view Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 morphologies, from layers to irregular pockets to tubes, all filled with the same orange colored, fine grained, usually finely laminated material. When the samples are cut to reveal fresh surfaces and then wet or polished, they reveal the same features, only more pronounced. In all cases, the bulk of any sample is composed of a gray-tan dolomite, often irregularly laminated. Pockets of a variety of sizes contain a fine grained, orange colored material that sometimes has a small amount of small-scale coarsening-upward graded bedding. Layers have the same material present, with the same bedding feature. Tubes of the same material display this bedding in a more pronounced manner, with a meniscate (concave downward) curve seen in vertical cross section (Fig. 44). Also, the tubes are again seen to fork both upwards and downwards, and begin or end independently of each other, sometimes into pockets or layers. In horizontal cross section, the plan view of the tubes is less circular and more irregular than they appear when presented on a weathered surface (Fig. 45) The boundaries between the gray matrix material and the orange material are not marked by any pore space, lining, or other material. Large rhombs of secondary-pore filling dolomite are seen overprinting both matrix and pocket/tube material. 2.4: Petrography Three petrographic procedures were used to help describe the samples taken from the Noonday. Samples were stained to determine carbonate type. Thin sections were cut and examined under light microscopy to evaluate the fabrics of the samples. Polished thick sections were examined by cathodoluminescence to help infer diagenetic history. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 0 2.4.1: Staining An assortment of talus hand samples of the Noonday from various sites were cut into small slabs. These were then rinsed in distilled water and allowed to air dry. They were dyed by the Alizarin red-S process as outlined by Dixon (1965). This staining process involves first etching the surface of the slab with dilute HC1 so that it will better accept the stain. Then, a two step staining process is used. This not only separates calcites from dolomites, but also differentiates ferroan and non-ferroan products. With this, a suite of color results are possible: pale pink to red for calcite, both pale pink to red and pale blue to dark blue for ferroan calcite, no stain color for dolomite, and pale to deep turquoise for ferroan dolomite (in which the depth of color indicates ferrous content). In the case of these samples, in all cases staining resulted in no color, thus they are composed entirely of regular (non-ferroan) dolomite with some slight light turquoise seen in clearly re-crystallized rhomboid filled pockets. 2.4.2: Light Microscopy Thin sections were cut from a variety of the samples collected in the field. A series of petrographic sections were made that contained layers, pockets, and tubes and the surrounding material, as well as a series of representative samples from the different lithologies found at the base of the section in the Sperry Hills. These samples, 1-6 (talus from near the Saddle Peak Hills; 1-2 have no tubes or pockets); Tl-3 (talus from the Alexander Hills), Pl-2 (from the Nopah Range) and DD4-8 (in situ samples from base of Noonday, just above Kingston Peak contact, Sperry Hills) are described, with collection information, in Appendix B. A sample of non related dolomite, taken from the early Cambrian Reed Dolomite in the White-Inyo Mountains, was used as a basis of comparison. The Reed Dolomite is a likely non- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 microbial, highly overprinted dolomite. These samples were observed under a Zeiss light Microscope and fabric types and relationships were noted. The Reed Dolomite “control” is a sparry dolomite. Any original fabrics have been obliterated in the dolomitization process. There are many large, multiphased rhombs seen in secondary pore spaces. The various samples from the massive portion of the Noonday that contain pockets, tubes and layers, showed a set of common features. For the most part, three different fabrics are present: a matrix fabric, a tube/pocket fabric, and a pore fabric. The matrix fabric consists of a classic “clotted microbial fabric” commonly called dzhellindia (Corsetti, 2000), that is, as the name indicates, thought to be the result of microbially mediated carbonate deposition. It is a mix of cloudy fine grained micritic pockets interspaced with more sparry clearer areas. (Fig. 46) In the case of the Noonday, there are also occasional hematitic grains seen in the clotted fabric, more commonly in the micritic material than in the sparry material, but with a maximum concentration of -5% in some places. Some of these grains appear to be altered pyrite grains, as they retain the pyrite’s framboid shape, and some also appear to be multiphased. (Fig. 47) The fabric seen in the tubes, pockets, and layers - seen as an orange colored, sometimes meniscate-layered “infill” in hand sample — has another fabric (Fig. 48). This fabric is seen in all cases of the orange material, regardless of the macro shape in which it is found. This fabric is a relatively uniform, but slightly layered, coarsening-upward, micrite with abundant hematite grains (Fig. 49). These grains appear to be the same as those found in the matrix material, but more abundant, up to 15% locally in some places. They also often have a framboidal shape that indicates that they were likely originally pyrite. The subtle meniscate layers seen in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 2 Figure 46. Clotted dolomitic matrix fabric (at 2.5x (top), lOx (middle, and 25x(bottom)) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 47. Matrix fabric with detrial iron (at 25x (above) and 50x (below)) # ■ ■ ill ■ ■ I ill m Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74 Figure 48. Meniscoid infill (2.5x) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 Figure 49. Infill material with detrital iron parti cles (at 2.5x (top), lOx (middle), and 25x (bottom)) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 6 hand sample are no longer visible under higher magnification, and there appears to be no petrographic difference between these layers. In addition, no pieces of clotted fabric are incorporated into the tube material. At the contact between these two fabrics, the “walls of the tubes” per se, there is not a wall or lining, or other such clear demarcation. There is no gap, primary or secondary porosity, or disruption in either fabric at the boundary (Fig. 50). In fact, often the boundary is indistinct except for a rise in amount of detrital hematite, especially where micritic portions of the clotted fabric abut a tube or pocket. In addition, there is often a third fabric seen in many of these thin sections. These are sparry pockets with large, multi-phased dolomite crystals. These crystals often have layers of hematite in between crystal growth phases (Fig. 51). These spar filled pores, as well as sparry veins, cross cut both the microbial matrix and micritic tube fabrics. Samples 1 and 2 are sections from non tube or pocket-containing talus samples of the Noonday. Sample 1 is a mottled small-scale combination of three fabrics: a partially silicified micrite, a recrystalized dolomite spar, and a finer-grained, little- to non- silicified micrite. The last of these sometimes, but not exclusively, appears in discrete fine layers of less than 0.5 mm. Sample 2, whatever its original composition, has been dolomitized and subsequently silicified. Most of this sample is made of wide (~2-4 mm) layers of chert that contain some dolomite filled pores. The intervening layers (variable but ~lmm wide) are made of partially silicified sparry dolomite. There are micro veins crosscutting both of these fabrics which are filled with an iron rich carbonate. The series of samples studied from the base of the section reveal a very different set of petrographic characteristics. DD4 is comprised of a mostly silicified carbonate (chert) with very thin, incomplete layers of hematite seen at close Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 7 Figure 50. Matrix-tube boundary (25x) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 Figure 51. Sparry pocket (at 2.5x (above) and lOx (below)) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 9 (<0.5mm) intervals. It is unclear as to whether these are originally pyritic or not. DD5, again, is mostly highly silicified carbonate with iron rich layers, likely hematite. There are also small veins filled with dolomite that cross-cut both the chert and hematite layers. DD6 is composed of a less layered combination of silicified carbonate (chert) and hematite pockets, with more dolomite veins cross-cutting both. 2.4.3: Cathodoluminescence Polished thick sections that were mirror images to some of the thin sections (specifically 1-6, T l, T3, and DD4-8) observed under light microscopy were observed using cathodoluminescence, a process by which the small slabs of rock were sealed into a vacuumed vessel, exposed to an X-ray beam which releases electrons from the surface of the slab, and the luminosity patterns were noted. This process reveals much about the post-depositional influences on the rock by indicating areas of hydrothermal alteration, high diagenetic change, chertification, etc. These patterns can be compared to the fabric patterns seen under light microscopy to interpret diagenetic history. Diagrams of the luminosity patterns observed, superimposed over the fabric types, can be found in Appendix B. Overall, the luminosity patterns in the pocket/tube slabs are independent of petrographic patterns, that is, the matrix/tube differences noted both in hand sample and under light microscopy. These samples have a pink glow, with some variety of intensities. Most of the area of these slabs has a low luminosity, with the pore spaces, which have the zoned dolomite crystals, highly luminous. Otherwise, in the few cases where there is a rise from background luminosity, the distribution of high regions does not mimic the distribution of micritic or sparry areas. In the slabs from the base of the section, DD4-6, and in the non-tube- containing talus samples 1 and 2, the luminosity patterns closely track petrographic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 0 differences. There is an overall high luminosity in the cherty areas. Hematite layers appear dark, with no luminosity seen. Veins, where present, have a very high luminosity. Samples 1 and 2, the non-tubular massive Noonday samples, are overall highly luminescent. Sample 1 is very bright, except for the areas with the fine micrite fabric, which is less luminous. In sample 2, the sparry layers are extremely bright, with very bright chert layers and non luminescent veins. 2.5: Macerations (Organic Extractions) Maceration is a palynological procedure that has also been used to extract Precambrian organic walled microfossils such as acritarchs and algae. It dissolves both silicates and carbonates to leave semi-resistant and resistant organic material. 2.5.1: Procedure Small (-10 mg) crushed samples of tube and matrix materials were powdered by mortar and pestle. The powders were then placed in plastic beakers, rinsed with distilled water, and dried. The beakers were then half filled with 30% HC1 and topped off with distilled water, to dissolve the carbonates. After three days, the samples were drained, rinsed and the acid-water mix was repeated, this time with -10ml of 40% HF to remove any siliciclastic material. After another 3 days, the samples were drained, washed, and any resultant material was spread onto glass slides for viewing under light microscopy (modified from Wellman and Axe, 1999). 2.5.2: Results Both the matrix and tube materials, when macerated, yielded small amounts of very decayed organic material. In a few cases, some of this decayed matter has a baggy spheroidal appearance, and may be the remnants of an unadorned unidentified type of acritarch. Overall, the amount of organic material present is negligible, however more was seen from the matrix material than from the fill (Fig. 52). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 Figure 52. Organic residue from matrix material (2.5x) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 2.6: Geochemical Data 2.6.1: General Procedures (ICPand MS) The thin sections that were prepared from samples 1-6 (variety of talus from Saddle Peak Hills site); T l, T3 (in situ talus from Alexander Hills site); and DD4-8 (in situ samples taken from the base of the Noonday in the Sperry Hills) were selected for further analysis because together they represent a variety of the fabrics seen in the rock unit, examples of similar structures from different sites, and a measured portion of the base of the unit as it grades upward into the massive microbial dolomite (DD4-8). Polished thick sections mirroring the thin sections from these samples were studied under cathodoluminescence and the luminosity patterns were noted. (See Ch.2.4) Both petrographic fabrics and luminosity patterns were considered when choosing microdrilling sites, and an attempt was made to represent all petrographic fabrics as well as varied luminosities during micro sampling. (See Fig. 53 for pictures of slabs, Fig. 54 for a flow chart of procedures, and Appendix B for sample information) Ten to fifteen milligram samples were drilled of each unique diagenetic phase and petrographic texture seen in each thick section using a Servo microdrill with Lapcraft micromite 1 mm diamond drill bits. The bits were changed with every sample drilled and cleaned with nitric acid before re-use. The resultant powder was utilized in both ICP trace metals analyses and C 02 distillation for MS stable isotope analyses. 2.6.2: Trace Metals Analyses (Inductively Coupled Plasma Spectroscopy) Inductively coupled plasma spectroscopy (ICP) was chosen to analyze for trace metal concentrations in the carbonate of the samples because of its speed, ease, and accuracy even at very small (parts per billion) amounts. Analytes were calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), and strontium (Sr). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 Figure 53. Drilled slabs Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 4 Hand samples Thin Sections Petrography Polished Thick sections t e M M R R a L ilh o io g t e Heterogeneity a R H Heterogeneity "* Select Sam pling Site* OHII w/ 1mm b i t s Microsampled Powders 1 - 5 m g powder* ♦ 10m L H N 0 3 2-Smg powttJeru * 1Q2SH3PGMI reacted tn rented lube # S O ^ C Dissolved Sample D'ssoivod S a m p le Sampio Solution ‘CP-US C r y o g e n ic •i t: .1!p n CO; PRISM Ca. Mg. Mn, Fa, Sr d,80, 513C ppm *«*>P D 0 . Figure 54. Flowchart of sample processing Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 85 Approximately 5 mg of each powdered sample was measured into 20ml plastic tubes (exact amounts are recorded in Appendix D). Ten ml of 2.5% H N 03 (TM grade) was added to each tube and the tubes were capped and shaken to dissolve and distribute ions. This only puts the carbonate associated metals into solution, not any detrital/particulate matter. Thus, the hematized pyrite seen in thin sections is not represented in these results. Low and high standards of known concentration were prepared, as well as blanks of HN03 , a set of primary standards (Lincoln Limestone), and internal standards to monitor machine drift during processing. The machine was calibrated with in-house standards both before and after processing. The standards, controls and samples were run through an automated process that first involved homogenization and concentration with an ultrasonic nebulizer before being sent to the Perkin Elmer Plasma 400 Argon-fed plasma torch and emission spectrophotometer. Samples were read in triplicate and the concentration amounts averaged. A ninety-nine second delay between samples ensured that the previous sample had cleared the line before reading of each new sample began. Data was re-calibrated for machine drift over the course of each run as well as normalized between the two runs by standards. Calculations/ calibrations of the data are listed in Appendix C. Table 1 shows sample number, sample descriptions, site collected, and trace metals concentrations (Ca, Mg, Mn, Sr, and Fe) for all samples as well as the calculated Mg/Ca, Mn/Sr and Sr/Mn (xlO-4) ratios. 2.6.3: Stable Isotope Analyses (Mass Spectroscopy) Samples were cryogenically distilled to extract carbon dioxide at the University of West Georgia Department of Geoscience. Two to six milligrams of sample powder were reacted with abundant anhydrous H3 P 04 in vacuum sealed pyrex y-tubes at 90 degrees Celsius for a minimum of two hours. The carbon dioxide was then harvested on a pyrex line kept at or below 2 millibars of atmosphere, equipped Reproduced with permission of the copyright owner. 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(/) u . 0 > o 0 • + — J ' C > * CL 0 4— » k_ 0 T3 o J O o E i _ 3 Q . o £ C c c C c o o o o o ' - 4 — < o o " - I — » o 4— » o 4 — » o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 J OJ OJO J O J O 3 3 3 3 3 » • * — > 4— > 4— < C c c c c O o o o o c c c c c C O C O -Q C O JD O o o o 0 0 0 0 0 0 X E E X * 1 b . 4— * 0 0 * u . 4— * 0 J O J O 0 E 3 3 4-* E c C c c o o o o o o o o 0 0 0 0 0 0 0 0 0 0 0 0 J O J O J O J O 3 3 3 3 4— > 4-^ J O O 0 J O CM CM CO CO i — i — T — 1— Table 1. Table of trace metals data and useful ratios Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 3 c tu b e section spar Winter’s Hill P a ss 1 .2 5 1 .3 4 70.93 98.86 0 .0 4 0.72 31.25 0.40 87 with a regularly replenished ethanol and liquid nitrogen water trap. Sample gas was trapped in sealed pyrex tubes. Carbon and oxygen data was gathered using the VG Isotech PRISM Mass Spectrometer in Jean Morrison’s Lab in the University of Southern California Department of Earth Sciences. A number of samples, however, were unusable for a variety of reasons. Samples 7a, 7b, and lib had too little sample to read. Sample 6c must have had a leak when sealed, as it was flooded with atmosphere. Sample 3d produced irregular traces that perhaps indicated the presence of non-condensable organics with a mass to charge ratio of 45/+ that were not filtered out during extraction. Controls and corrections/calibrations are in Appendix D. The relevant data - sample number, type, locale, carbon ratio and oxygen ratio — is presented in both a table and a graph (Table 2, Fig. 55). 2.6.4: XRD (X-Ray Diffraction) Bulk samples of rock from the Alexander Hills site (chosen because of its apparently lesser amounts of diagenesis and hydrothermal alteration under CL) containing both matrix and pocket fabrics were crushed into chips and the two materials manually separated based upon color. The sorted chips were then sequentially pulverized into fine powders, yielding ~lkg of each material. This powder was then sputtered onto a filter that was put into the analyzer. Analysis indicated that the material, in both cases, was dolomite with negligible levels of opaque minerals. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 Smp # Sample Type Site Collected 813C 8180 la non-tube section micrite Saddle Peak Hills -2.739 -8.445 lb non-tube section spar Saddle Peak Hills -2.849 -9.27 2a non-tube section micrite Saddle Peak Hills -2.076 -5.583 2b non-tube section spar Saddle Peak Hills -2.865 -11.093 3a tube section matrix, low lum Saddle Peak Hills -2.446 -7.272 3b tube section matrix, med lum Saddle Peak Hills -2.649 -7.516 3c tube section zoned spar Saddle Peak Hills -3.145 -10.356 5a tube section tube material Saddle Peak Hills -2.53 -8.12 5b tube section matrix Saddle Peak Hills -2.557 -7.24 5c tube section zoned spar Saddle Peak Hills -4.083 -9.348 6a tube section tube material Saddle Peak Hills -2.597 -7.762 6b tube section matrix Saddle Peak Hills -2.473 -7.209 8a BIF grey material Sperry Hills -2.817 -5.995 9a non-tube section opaque grey Sperry Hills -2.819 -6.477 9b non-tube section dark spar Sperry Hills -1.373 -12.125 10a non-tube section blocky spar Sperry Hills -1.431 -15.185 10b non-tube section opaque grey Sperry Hills -2.73 -6.843 10c non-tube section purply spar Sperry Hills -2.819 -6.737 11a non-tube section opaque grey Sperry Hills -2.776 -7.016 12a tube section spar Winter’s Hill Pass -2.811 -12.451 12b tube section matrix Winter’s Hill Pass -2.832 -7.045 12c tube section tube material Winter’s Hill Pass -2.559 -7.778 13a tube section tube material Winter’s Hill Pass -2.601 -8.097 13b tube section matrix Winter’s Hill Pass -2.802 -6.714 13c tube section spar Winter’s Hill Pass -3.768 -9.532 Table 2. Table of stable isotope data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Carbon a n d O^gen Isotope Values for Carbonate Samples 89 I (a d d ) s ;h*»A uo q ieo Figure 55. Graph of stable isotope data Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Oxygen values (PDB) 9 0 Chapter 3: Discussion 3.1: The Enigmatic Structures 3.1.1: Summary of important observations The Noonday Dolomite from the Mid to Late Neoproterozoic of Death Valley, CA, is a massive gray to tan carbonate unit with an assortment of interesting sedimentary structures apparent in places throughout the unit. Among these are orange-tan structures that come in a number of forms: tubes, pockets, and layers. Tubes are 1-3 cm in diameter, up to 3 meters long, and appear in relatively closely packed assemblages and in conjunction sometimes with layers. They have irregularly circular cross sections, concave-up graded laminae, and often branch and come together vertically. They do not have a common upper or lower bedding plane. Pockets are irregular sizes and shapes and also can have concave-up graded laminae. Layers of graded laminated material also appear. In all cases, the internal material is a preferentially weathering, orange-tan micritic dolomite with abundant detrital iron grains. There is no lining or other intervening material in between the contact of the mat matrix and the tube/pocket/layer material. The mat material is not disrupted near the interface with the micrite, nor are there pieces of mat material seen in the micrite. In addition, sometimes laminae divisions carry across the matrix-micrite boundary. The gray matrix material has a clotted microbial texture often described by others (Cloud, et al., 1974, e.g) as dzhellindia (or gellindia), some detrital iron grains, and some extractable organic matter. Spars and veins seen in samples cross-cut both the matrix and micritic fabrics, and luminosity variations do not coincide with variations between these two fabrics. Mg/Ca ratios and XRD analysis indicate that both the matirx and micritic matter are dolomitic. Trace metal data, oxygen isotope Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 data, and carbon isotope data for the matrix and the micrite cluster within a small, overlapping range of values, while powders of spars from the same samples have very different signatures in all cases. The 81 3 C data for both matrix and fill clusters closely around ~-2.7%o. 3.1.2: Comparison of observations with suggested mechanisms A variety of means by which the structures in the Noonday could have formed have been suggested over the years. Those warranting consideration are that the tubes are the product of diagenesis, or are trace fossils, dissolution pipes, outgassing structures, stromatolites, or stromatolite interspaces. (Fig. 67) If the structures were the product of diagenesis or are dissolution pipes, one would expect them to have specific petrographic and diagenetic indicators. These should include luminosity differentials that track petrographic changes, different oxygen isotopic ratios for the two materials, and different trace metal signatures - specifically, higher Sr and lower Mn and Fe for the less altered phase (the mat in this case). With the Noonday, the luminosity patterns do not track with the petrographic patterns, other than in the case of the sparry pore infills. The oxygen isotopic values for the matrix and the micrites cluster, with the sparry material serving as an outlier and a control for comparison. Lastly, the trace metal signatures for the two fabrics in question again cluster together. Outgassing structures would also be expected to have a different isotopic signature due to the influence of the released gasses upon the chemistry of the source water. If the unit is a seep of some sort, the carbon isotopic values would be extremely negative, as methane has an average isotopic value of -40 %o. In addition, it could, but not necessarily, be expected that there may be some slight difference in trace metal contents, due to solubility changes resulting from outgassing. Sedimentologically, the force of outgassing would have disrupted the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 2 surrounding matrix material and likely dislodged pieces of it in the process. Not only should this disruption of the mat matrix be seen, but these pieces could be expected to be seen re-deposited in the infill in the tubes. Also, there may be an identifiable source point from which the gasses were emitted, and thus also a common starting point or bed for the structures. In addition, infill of the tubes would necessarily have been secondary to the growth of the matrix material, thus creating a situation in which there was a downward filling of the tubes after the growth of most or all of the vertical section of mat material. This would result in concave up, or meniscate, infill that would have a clear boundary and be distinct from the matrix petrographically and laminae should not carry over from mat material to micritic material. Of these features, only the concave-up infill is seen. In all other cases, the evidence for outgassing tubes is not present in the Noonday. In addition, the carbon isotope values are, while negative, only slightly so at ~-2.7%o and thus do not provide strong evidence for methane output. The two possible trace fossils suggested as explanations for the tubes are Skolithos and root casts. If the tubes are Skolithos, they should be vertical tubes, up to 3 cm wide with a circular cross section, that disrupt the matrix fabric (Droser, 1991). Pieces of matrix material might be seen broken and re-deposited in the meniscate infill, if the matrix was sufficiently consolidated prior to burrowing. (Skolithos, however, are usually formed in unconsolidated sediments.) No upward or downward branching should be seen, and they likely would have a clay lining and a higher concentration of organic matter in the tube than outside the tube (ibid.). More specifically, if the dense assemblages of tubes seen in some places are not only Skolithos, but “Skolithos Piperock,” the matrix rock would likely have been deposited in a high energy, nearshore environment and have clear hummocky cross stratification and likely be siliciclastic. In addition, the tubes would have a distinct Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 common upper bedding plane, appear in high density, closely packed populations (ibid.). Although they are found in dense assemblages and are the requisite size, the tubes in the Noonday do not have a clear upper bedding plane, nor do they have linings. Extractable organic material in the Noonday was found more abundantly in the matrix, not the micrite. The matrix material is carbonate, not siliciclastic, and it is not disrupted (nor are pieces of it seen in the micrite), and the tubes of the Noonday in fact do branch and come together - they are not independent pipes. If they are root casts, they should have only downward, often high angle, branching, disruption of the matrix material, likely much organic residue in the tubes, probably a common upper bedding plane as an upper termination to an abundance of tubes, tubes tapering downward, and indications of deposition in a terrestrial environment (Klappa, 1980; Ekdale, et al., 1984; Behrensmeyer and Hook, 1992). Of these features, only downward branching, but not at a high angle, is seen. If the tubes were stromatolites, there would need to be evidence of rapid lithification of the micritic material and, according to one of the definitions of stromatolites, evidence of biogenicity (Walter, 1976). Neither is the case in the Noonday. In addition, the matrix material would need to be shown to be a secondary deposition that occurred progressively after the tubes were formed to indicate the growth of the tubes as independent structures. The concave-up internal lamination is not consistent with this finding. Both definitions of “stromatolite” (Walter, 1976; Semikhatov, et al., 1979) currently in use suggest that they have a limited point or bed of initiation. The matrix material surrounding the tubes, although apparently microbial and rapidly lithified, covers a large lateral area (many meters), and except in the cases of the large domal stromatolites seen interspersed in the same matrix material (which are not surrounded by the micrite alone), does not have discemable individual forms. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 4 Perhaps most importantly in relation to all of these proposed mechanisms, tubes are not the only feature of its kind seen in the Noonday. The same orange colored, detrital-iron-rich, fine-grained micritic, slightly coarsening-upward bedded material is found in a variety of other forms in the unit. The presence of layers and a variety of pockets of this material requires that any mechanism for the formation of the tubes also explain these other morphologies. Neither trace fossil suggested also produces bedding parallel layers nor pocket material. Dissolution pipes, outgassing structures, and stromatolites imply a directional movement or growth, and thus again pockets and layers are not consistent with these explanations. 3.1.3: Suggested process of formation The odd pockets and tubes in the Noonday Formation, Death Valley, CA are not the product of diagenesis or dissolution, nor are they trace fossils (such as Skolithos or root casts), outgassing structures, stromatolites or stromatolite interspaces. So, then, what are they? This last explanation, of stromatolite interspaces, although not sufficient, perhaps comes closest to a useful start to describe the process of formation. The matrix material around the tube, pocket, and layer structures of the Noonday does have features consistent with microbially mediated carbonate deposition, such as irregular small scale lamination, clotted fabric (dzhellindia) characteristic of microbial mediation, and some residual organic matter. The extensive lateral extent and lack of a limited layer or point source of initiation of these layers in the matrix, however, excludes the possibility that the matrix is a stromatolite. This matrix, though, is clearly microbially mediated, in contrast to the tubes, pockets, and layers, whose deposition has no features of biotic mediation. These pockets, layers and tubes, then, are suggested to have formed from inorganic detrital carbonate input that was occurring at the same time as the mat growth. The form seen (layer, pocket, or tube) is a product of the difference between Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the rate of mat growth and the rate of input. As the extensive mat system was growing on the sea floor, detrital carbonate was raining down upon it. When the rate of mat growth far outpaced input, no features are seen. At slightly higher comparative rates of input to mat growth, the detrital material could inhibit mat growth where it collected in large enough amounts. Detrital material would likely collect at natural points of low relief in the mats, as mat growth is not generally uniform over lateral area. If the mat compensated after a short time, a pocket of detrital material would be formed. When input inhibited mat growth at various points and the mat could not compensate, the points would remain inhibited and provide a positive feedback system by which more detrital input would be deposited in the low points without mat growth. As long as this was maintained for a length of time, tubes of detrital material would be produced. Layers of detrital material would be produced when input far outpaced mat growth. This mechanism explains all of the features seen in the Noonday. If this mechanism is consistent, the matrix material should have characteristics of microbial mediation and the tubes/pockets/layers should not. This is the case. The isotope and trace metal data for the tubes/pockets/layers and the matrix should be similar, as they all originated from the same source waters. The geochemical signatures of both the matrix and these forms are the same. All diagenetic features such as veins, reprecipitation pockets, chertification, and luminosity patterns should effect and cross-cut both tubes/layers/pockets and matrix material, which they do. In addition, variable detrital input from above can easily account for both the graded nature of the material seen as well as concave up curvature of laminations in the material. It also accounts for the variety of forms seen containing the fine-grained material, and for the lack of any of these forms within the large, domal stromatolites. These discrete stromatolites may have been produced by a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 6 slightly different combination of microbes that produced more resistant independent structures that grew more rapidly than surrounding mat material, thus inhibiting tube/pocket/layer formation within the structures. 3.2: Is the Noonday a Cap Carbonate? A cap carbonate, by definition, is a massive carbonate unit with anomalous fabrics and negative carbon isotopic values that overlies a glacial unit (Kennedy, 1996). The Noonday is a massive dolomite unit that overlies (in conformable locales) the upper Kingston Peak diamictite, which has abundant dropstones and other glacial features. It has the enigmatic sedimentary structures described in 3.1, and it has carbon isotope values in the -2.7%o range. Therefore, it is by definition a cap carbonate. Is it, though, a Sturtian-type or a Marinoan-type? Sturtian-type caps, like the Chuos of Namibia (Hoffman, et al., 1998), the Areyonga of Austrailia (Kennedy, 1996), and the Rapitan of Canada (Aitken, 1991), are associated with iron-rich deposits, have rhythmic laminae, and have a dark, organic rich composition that has heavier carbon isotope values than the Marinoan- type caps. Marinoan-types, such as the Ghaub (Maiberg Cap) of Namibia, (Hoffman, et al., 1998), the Elatina of Australia (Kennedy, 1996), and the Icebrook of Canada (Aitken, 1991), have more negative carbon values, little to no organic matter, and often have crystal fan and tube-rocks fabrics (Kennedy, et al., 1998). Interestingly, while Kennedy, et al. (1998) could clearly divide all of the caps they observed into these two distinct “phyla,” the Noonday exhibits some features of each. Like the older, Surtian-type caps, the Noonday has a rhythmic portion to its base, as seen in the Sperry Hills, and has an apparently BIF-like unit of small extent just below its base at one site. As seen in Marinoan-type caps, the Noonday is extremely organic poor, has light carbon composition, has the depositional tube Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 7 features, and contains large domal stromatolites like those in the upper units in Australia and Namibia (Kennedy, 1996; Hoffman, et al., 1998). The Noonday, therefore, has a combination of the features of older and younger caps; however, more evidence points to it being a Marinoan-type, rather than a Sturtian-type, cap. Cap carbonates in general have been suggested to have formed in a variety of ways anomalous to modem processes for carbonate deposition. Two primary suggestions are that they are some type of seep deposit that resulted from the release of large amounts of gas hydrates (Kennedy, et al., 2001), or that the dolomite is deposited rapidly (on the scale of 100 Ky) in a post-Snowball accommodation space facilitated by sudden, increased C 02 exchange with a C 0 2 rich atmosphere (Hoffman, et al., 1998; e.g.). While there is no direct evidence as to the duration of time represented by the Noonday, the carbon isotopic values, while negative, are orders of magnitude higher than those seen in documented seeps. Carbon values for carbonates from fossil seeps are highly variable, at —20 to -80%o (Roberts and Aharon, 1994; Campbell and Bottjer, 1995), but the values found in the Noonday carbonate is only about l/10th the lowest of these values. In addition, the tube structures were not produced through emission and later infill, but syndepositionally with the matrix, as evidenced most notably by the discrete laminae that can be carried from the matrix, through the tube, and back into the matrix. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 Chapter 4: Conclusions and Issues for Further Study The Noonday Formation consists of a massive gray microbial dolomite that contains a variety of related tube, pocket, and layered structures composed of a fine-grained, orange material that often displays small scale graded bedding in concave up layers. These features are the result of a variation in the balance between the microbial mat growth and accretion and detrital carbonate input and are therefore different expressions of a purely sedimentary phenomenon. In addition, the Noonday is indeed a cap carbonate, as it is a massive carbonate unit that overlies a diamictite and it has anomalous fabrics and negative carbon isotopic signatures o f— 2.7%o. There remain many avenues for exploration with the Noonday. First, the sedimentation process that would produce the structures should be able to be mathematically modeled to produce the same variety of outcomes. In addition, the relationship of the “regular” mat material to the domal stromatolites and their relative resistance to detrital input should be investigated. These avenues of research could help to shed further light on the mechanisms involved in stromatolite growth, specifically, the relative roles of the organisms in the mat and the outside environment in the resultant forms seen. In addition, the source of the different carbonates in the unit remains to be elucidated. Was the carbonate in the matrix accreted, or precipitated with the aid of biotic microenvironmental conditions in the mat? Where was the detrital carbonate formed, and how? How, also, was the unit dolomitized, and what can this infer about the role o f mat communities and micro-environment water chemistry on in situ diagenesis? Secondly, the source of the detrital iron is still unexplained, and may provide greater insight into the ocean chemistry at the time of deposition, as will further Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 9 research into the rapid dolomitization process apparent in this unit, as well as further work on cap carbonates and their isotopic signatures in general. Proterozoic ocean chemistry was likely very different from the modem, even under non-glaciated conditions. What was the ocean chemistry like? What implications does that have on atmospheric conditions? On the evolution of life? Discovering the source and process of formation of the iron in the Noonday, as well as the abundant iron in the underlying Kingston Peak, could help to answer some of these questions. The depositional environment of the Noonday - that of an active rift basin - is also of further interest. Many of the suggested glacial diamictites and cap carbonates were produced near active rift margins. It is unclear how many of the effects of rifting, including those related to thermal subsidence, debris flows, and increased local mantle outgassing, can be conclusively distinguished in all cases from a possible Snowball. The Noonday, in addition to the Namibian and Australian correlates, taken together can help to not only further investigate the plausibility of a Snowball Earth cycle, but also help us to better understand the influences that active rifting has on depositional environments. Lastly, the Noonday, as a likely Marinoan-type cap carbonate, provides another unit in addition to the classic Namibian section through which to study the mechanism of cap carbonate formation. With its low metamorphic grade, moderate lateral extent, accessibility, and large thickness, it is an excellent choice for further exploration of this subject, as well. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 References Aitken, J.D. 1991. The Icebrook Formation and the post-Rapitan, Late Proterozoic glaciation, Mackenzie Mountains, Northwest Territories: Geological Survey of Canada Bulletin 404,43 p. Awramik, S.M. 1971. Precambrian columnar stromatolite diversity: reflection of metazoan appearance: Science 174:825-27. Awramik, S.A., Corsetti, F.A. and Shapiro, R.S. 1994. Death Valley International Stromatolite Symposium: Pre-Symposium Excursion: Death Valley Region:42 pp. Awramik, S.A., Corsetti, F.A. and Shapiro, R.S. 2000. Stromatolites and the Pre- Phanerozoic to Cambrian History of the Area Southeast of Death Valley: SBCMA Quarterly 47:65-74. Bauld, J., D’Amelio, E. and Farmer, J. 1992. Modem microbial mats in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 261-269. Behrensmeyer, A.K. and Hook, R.W. 1992. Paleoenvironmental contexts and taphonomic modes in Behrensmeyer, A.K, Damuth, J.D., DiMichele, W.A., Pots, R., Sues, H. and Wing, S., eds., Terrestrial Ecosystems Through Time: Evolutionary Paleoecologv of Terrestrial Plants and Animals: The University of Chicago Press, Chicago, p. 15-136. Bills, B.G. 1998. An oblique view of climate: Nature 396:405-406. Bottjer, D.J. and Droser, M.L. 1994. The history of Phanerozoic bioturbation in Donovan, S.K., ed., The Palaeobiologv of Trace Fossils: John Wiley &Sons, Chichester, p. 155-176. Brasier, M., McCarron, G., Tucker, R., Leather, J., Allen, P. and Shields, G. 2000. New U-Pb zircon dates for the Neoproterozoic Ghubrah glaciation and for the Huqf Supergroup, Oman: Geology 28:175-178. Bromley, R.G. 1996. Trace Fossils: Biology, taphonomv and applications: Chapman &Hall, London, 361 pp. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 Campbell, K.A., and Bottjer, D J. 1995. Brachiopods and chemosymbiotic bivalves in Phanerozoic hydrothermal vent and cold seep environments '.Geology 23:321-324. Cloud, P.E., Wright, L.A., Williams, E.G., Diehl, P., Walter, M.R. 1974. Giant Stromatolites and Associated Vertical Tubes from the Upper Proterozoic Noonday Dolomite, Death Valley Region, Eastern California: GSA Bull. 85:1869-1882. Corsetti, F.A. 1998. Regional correlation, age constraints, and geologic history of the Neoproterozoic-Cambrian strata, southern Great Basin, USA; integrated carbon isotope stratigraphy, biostratigraphy, and lithostratigraphy [Doctoral thesis]: Santa Barbara, CA, University of California Santa Barbara. Corsetti, F.A., Awramik, S.M., Pierce, D.L., and Kaufman, A.J. 2000. Using chemostratigraphy to correlate and calibrate unconformities in Neoproterzoic strata from the southern Great Basin of the United States: International Geology Review 42:516-533. Corsetti, F.A., and Hagadorn, J.W. 2000. Precambrian-Cambrian transition; Death Valley, United States: Geology 28:299-302. Corsetti, F.A., 2000-2001. personal communication. Crimes, P.T. 1992. Changes in the Trace Fossil Biota Across the Proterozoic- Phanerzoic Boundary: Journal of the Geological Society 149:637-46. Crimes, P.T. 1994. The period of early evolutionary failure and the dawn of evolutionary success: The record of biotic changes across the Precambrian- Cambrian boundary in Donovan, S.K., ed., The Palaeobiologv of Trace Fossils: John Wiley &Sons, Chichester, p. 105-133. Dixon, J.A.D. 1965. A modified staining technique for carbonates in thin section: Nature 4971:587. Droser, M.L. 1991. Ichnofabric of Paleozoic Skolithos ichnofacies and the nature and distribution of Skolithos piperock: Palaios 6:316-325. Droser, M.L. and Bottjer, D.J. 1989. Ichnofabric of sandstones deposited in high-energy nearshore environments; measurement and utilization: Palaios 4:598-604. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 Droser, M.L. and Bottjer, D.J. 1993. Trends and patterns of Phanerozoic ichnofarics: Annu. Rev. Earth Planet. Sci. 21:205-25. Ekdale, A.A. and Lewis, D.W. 1993. Sabellariid reefs in Ruby Bay, New Zealand: A modem analogue of Skolithos “piperock” that is not produced by burrowing activity: Palaios 8:614-620. Ekdale, A.A., Bromley, R.G. and Pemberton, S.G. 1984. Ichnologv: Trace Fossils in Sedimentologv and Stratigraphy: Society of Economic Paleontologists and Minerologists, Tulsa, OK, 317 pp. Evans, D.A., Ripperdan, R.L. and Kirschvink, J.L. 1998. Cambrian drift of Gondwana; plate tectonics and TPW?: Journ. Afr. Earth Sci. 27:67-69. Fedonkin, M.A. and Runnegar, B.N. 1992. Proterozoic metazoan trace fossils in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 389-395. Grotzinger, J.P. and Ingersoll, R.V. 1992. Proterozoic sedimentary basins in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 47-50. Grotzinger, J.P. and Knoll, A.H. 1995. Anomalous carbonate precipitates; is the Precambrian the key to the Permian? Palaios 10:578-596. Grotzinger, J.P. and Knoll, A.H. 1999. Stromatolites in Precambrian carbonates: Evolutionary mileposts or environmental dipsticks?: Annu. Rev. Earth Planet. Sci. 27:313-58. Hagadorn, J.W. and Bottjer, D.J. 1999. Restriction of a Late Neoproterozoic biotope: suspect-microbial structures and trace fossils at the Vendian- Cambrian transition: Palaios 14:73-85. Hazzard, J.C. 1937. The Paleozoic section in the Nopah and Resting Springs Mountains, Inyo County, California: Ph.D. Thesis, University of Southern California, Los Angeles, CA. Hegenberger, W. 1987. Gas escape stmctures in Precambrian peritidal carbonate rocks: Geological Survey of Namibia Communications 3:49-55. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 Hewett, D.F. 1940. New formation names to be used in the Kingston Range, Ivanpah Quadrangle, California: Journal of the Washington Academy of Sciences 30:239-240 Hoffman, P.F., Kaufman, A J. and Halverson, G.R 1998. Comings and goings of global glaciations on a Neoproterozoic tropical platform in Namibia: GSA Today 8:1-9. Hoffman, P.F., Kaufman, A.J., Halverson, G.P. and Schrag, D.P. 1998. A Neoproterozoic Snowball Earth: Science 281:1342-1346. Hofmann, H.J. 1992. Megascopic dubiofossils in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, UK, p. 413-419. Hunt, C.B. and Mabey, D.R. 1966. General geology of Death Valley. California: stratigraphy and structure: U. S. Geological Survey Professional Paper: U.S. Geological Survey, Reston, VA, A1-A165. Jorgensen, B.B., Castenholz, R.W. and Pierson, B.K. 1992. The microenvironment within modem microbial mats in Schopf, J.W. and Klein, C., eds., The Pro terozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 271-285. Kauffman, E. G. and Steidtmann, J.R. 1981. Are these the oldest metazoan trace fossils?: J. ofPaleo. 55:923-947. Kaufman, A.J. and Knoll, A.H. 1995. Neoproterozoic variations in the C-isotopic compositions of seawater: stratigraphic and biogeochemical implications: Precam. Res. 73:27-49. Kaufman, A.J., Knoll, A.H. and Narbonne, G.M. 1997. Isotopes, ice ages, and terminal Proterozoic Earth history: Proc. Natl. Acad. Sci. USA 94:6600-6605. Kennedy, M.J. 1996. Stratigraphy, sedimentology and isotopic geochemistry of Australian Neoproterozoic post-glacial cap dolostones: deglaciation, 81 3 C excursions and carbonate precipitation: Jour. Sed. Res. 66:1050-1064. Kennedy, M.J., Runnegar, B., Prave, A.R., Hoffmann, K.-H., Arthur, M.A. 1998. Two or four Neoproterozoic glaciations?: Geology 26:1059-1063. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 Kennedy, M.J., Christie-Blick, N., Sohl, L.E. 2001. Are Proterozoic carbon isotopic anomalies related to climatically driven changes in the global gas hydrate budget? Geology 29:443-446. Kirschvink, J. L. 1992. Late Proterozoic low-latitude global glaciation: the Snowball Earth in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 51-52. Kirschvink, J.L., Ripperdan, R.L., Evans, D.A. 1997. Evidence for a large-scale reorganization of Early Cambrian continental masses by inertial interchange true polar wander: Science 277:541-545. Klappa, C.F. 1980. Rhizoliths in terrestrial carbonates: classification, recognition, genesis and significance: Sedimentol. 27:613-629. Klein, C. and Beukes, N.J. 1992. Time distribution, stratigraphy and sedimentological setting and geochemistry of Precambrian iron-formations in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 139-146. Knoll, A.H. 2000. Learning to tell Neoproterozoic time: Precam. Res. 100:3-20. Knoll, A.H., Bambach, R.K., Canfield, D.E. and Grotzinger, J.P. 1996. Comparative Earth history and Late Permian mass extinction: Science 273:452-457. Labotka, T. C., Bergfeld, D., Nabelek, P. I., Prave, A.R. 2000. Two diamictites, two cap carbonates, two 81 3 C excursions, two rifts; the Neoproterozoic Kingston Peak Formation, Death Valley, California; discussion and reply: Geology 28:191-192. Link, P.K., Christie-Blick, N., Devlin, W.J., Elston, D.P., Horodyski, R.J., Levy, M., Miller, J.M., Pearson, R.C., Prave, A., Stewart, J.H., Winston, D., Wright, L.A., Wrucke, C.T. 1993. Middle and Late Proterozoic stratified rocks of the western U.S. Cordillera, Colorado Plateau and Basin and Range province in The G eology of America Volume C-2: Precambrian Conterminous U.S.: The Geological Society of America, Boulder, CO, p. 462-596. Miller, J.G. 1985. Glacial and syntectonic sedimentation; the upper Proterozoic Kingston Peak Formation, southern Panamint Range, eastern California: GSA Bull. 96:1537-1553. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 Miller, J.G. 1987. Paleotectonic and stratigraphic implications of the Kingston Peak- Noonday contact in the Panamint Range, eastern California: Journ. ofGeol. 95:75-85 Murphy, F.M. 1932. Geology of a part of the Panamint Range, California:California Jour. Mines and Geol. 28:329-356. Pemberton, S.G., Frey, R.W., Ranger, M J. and MacEachern, J. 1992. The conceptual framework of ichnology in Applications of ichnologv to petroleum explora tion: a core workshop: Society of Economic Paleontologists and Mineralo gists, Tulsa, OK, p. 1-32. Pierson, B.K. 1992. Summary and conclusions: The current status of studies of modern microbial mat-building communities and their relevance to interpretation of Proterozoic stromatolites in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisciplinary Study: Cambridge University Press, Cambridge, p. 341-342. Prave, A.R. 1999. Two diamictites, two cap carbonates, two 81 3 C excursions, two rifts; the Neoproterozoic Kingston Peak Formation, Death Valley, California: Geology 27:339-342. Rampino, M.R. 1994. Tillites, diamictites, and ballistic ejecta of large impacts: Journ. ofGeol. 102:439-456. Roberts, H.H., and Aharon, P. 1994. Hydrocarbon-derived carbonate buildups of the northern Gulf of Mexico: A review of submersible investigations: Geo-marine Letters 14:135-148. Sarjeant, W.A.S. 1975. Plant trace fossils in Frey, R.W.. ed.. The Study of Trace Fossils: A Synthesis of Principles. Problems and Procedures in Ichnology: Springer-Verlag, London, p. 163-179. Savazzi, E. 1994. Functional morphology of boring and burrowing invertebrates in The palaeobiologv of trace fossils: Johns Hopkins University Press, Baltimore, MD, p. 43-82. Semikhatov, M.A., Gebelein, C.D., Cloud, P., Awramik, S.M., Benmore, W.C. 1979. Stromatolite morphogenesis -progress and problems: Can. J. Earth Sci. 19:992-1015. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 Skoog, S.Y., Venn, C. and Simpson, E.L. 1994. Distribution of Diopatra cuprea across modern tidal flats: implications for Skolithos: Palaios 9:188-201. Sohl, L.E., Christie-Blick, N. and Kent, D.V. 1999. Paleomagnetic polarity reversals in Marinoan (ca. 600 Ma) glacial deposits of Australia; implications for the duration of low-latitude glaciation in Neoproterozoic time: GSA Bull. 111:1120-1139. Stewart, J. H. 1970. Upper Precambrian and Lower Cambrian strata in the southern Great Basin: U.S. Geological Survey Professional Paper 620, U. S. Geologi cal Survey, Reston, VA, 206 pp. Troxel, B.W. 1982. Basin facies (Ibex Formation) of the Noonday Dolomite, southern Saddle Peak Hills, southern Death Valley, California in Cooper, J. D., Troxel, B.W. and Wright, L.A., eds., Geology of selected areas in the San Bernardino Mountains, western Mojave Desert and southern Great Basin. California (Geological Society of America. Cordilleran Section. Guidebook Field Trip No. 9): Death Valley Publ. Co., Shohone, CA, p. 43-48. Vossler, S.M. and Pemberton, S.G. 1988. Skolithos in the Upper Cretaceous Cardium Formation: an ichnofossil example of opportunistic ecology: Lethaia 21:351-362. Walter, M.R., ed. 1976. Stromatolites: Elsevier, New York, 790 pp. Walter, M.R., Grotzinger, J.P. and Schopf, J.W. 1992. Proterozoic stromatolites in Schopf, J.W. and Klein, C., eds., The Proterozoic Biosphere: A Multidisci plinary Studv: Cambridge University Press, Cambridge, p. 253-260. Walter, M.R., Veevers, J.J., Calver, C.R., Gorjan, P. and Hill, A.C. 2000. Dating the 840-544 Ma Neoproterozoic interval by isotopes of strontium, carbon, and sulfur in seawater, and some interpretative models: Precam. Res. 100:371-433. Wellman, C.H. and Axe, L. 1999. Extracting plant mesofossils and megafossils by bulk acid maceration, in Jones, T.P. and Rowe, N.P., eds., Fossil Plants and Spores: Modern Techniques: The Geological Society, London, p. 11-14. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 Williams, E. G., Wright, L.A., Troxel, B.W 1974. The Noonday Dolomite and equivalent stratigraphic units, southern Death Valley region, California in Guidebook: Death Valley region. California and Nevada fGeological Society of America. Cordilleran Section. Field Trip No. 1): Death Valley Publ. Co., Shoshone, CA, p. 73-77. Williams, D.M., Kasting, J.F., and Frakes, L.A. 1998. Low-latitude glaciation and rapid changes in the Earth’s obliquity explained by the obliquity-oblateness feedback: Nature 396:453-455. Wright, L.A., Troxel, B.W., Williams, E.G., Roberts, M.T. and Diehl, RE. 1974. Precambrian sedimentary environments of the Death Valley Region, Eastern California in Guidebook: Death Valiev region. California and Nevada (Geo logical Society of America. Cordilleran Section. Field Trip No. 11: Death Valley Publ. Co., Shoshone, CA, p. 27-36. Wright, L.A., Williams, E.G. and Cloud, P.E. 1978. Algal and cryptalgal structures and platform environments of the late pre-Phanerozoic Noonday Dolomite, eastern California: GSA Bull. 89:321-333 . Wright, L.A., Williams, E. G. and Troxel, B. W. 1984. Appendix II; Type section of the newly-named Proterozoic Ibex Formation, the basinal equivalent of the Noonday Dolomite, Death Valley region, California: Map Sheet - California Division of Mines and Geology, 34:25-31. Young, G.M., Jefferson, C.W., Delaney, G.D. and Yeo, G.M. 1979. Middle and Late Proterozoic evolution of the northern Canadian Cordillera and Shield: Geology 7:125-128. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 Appendix A: Locale Information Locality 1 - Alexander Hills/Winters Pass: San Bernardino County, California. Low hills south-southwest of dirt road sub-parallel off of Excelsior Mine Road, 25 miles north from the Cima Road off-ramp of US 15; southeast comer of section T. 19 N., R. 11 E., U.S. Geological Survey 7.5 minute series Blackwater Mine Quadrangle. Locality 2 - Southern Nopah Range: Inyo County, California. Upslope from War Eagle and Noonday Mines, north on dirt road off of Furnace Creek Road, ~6 miles after turn-off from Old Spanish Trail; sections 14 and 23, T. 20 N., R. 8 E., U.S. Geological Survey 7.5 minute series Tecopa Pass Quadrangle. Locality 3 - Saddle Peak Hills: San Bernardino County, California. Along the west side of Route 127, west half of U.S. Geological Survey 7.5 minute series Saddle Peak Hills Quadrangle. Locality 4 - Sperry Hills: San Bernardino County, California. Along the north side of the Dumont Dunes access road, on the east side of Route 127 from the Saddle Peak Hills, east half of U.S. Geological Survey 7.5 munite series Saddle Peak Hills Quadrangle, northwest quarter of 7.5 minute series Dumont Dunes Quadrangle. Locality 5 - Panamint Range: Inyo County, California. Up wash to the right of dead end on Galena Canyon Road, west up Southern Panamints from West Side Road in Death Valley; from location description by Cloud, et al., 1974, the exposure is found atT. 22 S., R. 47 E., U.S. Geological Survey Bennetts Well Quadrangle. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 Appendix B: Sample Information Samples Collected: Alexander Hills/Winters Pass: Fall 1998/Spring 1999:Assorted talus samples, tubes and other fabrics Southern Nopah Range: ll/12Sept99: Just S. of War Eagle Mine, up slope from access road: WEMl(a,b) - Crystal Springs, 0.5m below contact, shaley WEM2(a,b) - Crystal Springs, at contact, shaley WEM3 - sample at contact, likely caliche WEM4 - Noonday dolomite, at contact WEM5 - Noonday dolomite, 0.5m above contact Assorted talus samples 26Nov99: Around War Eagle Mine/Gunsight Mine: WEM7 - Crystal Springs at contact gneissic WEM8 - Noonday dolomite with contact surface WEM9 - Noonday dolomite, midway in section, no irregular fabric WEM10 - Noonday dolomite, loose in-place, irregular fabric WEM11 - Noonday dolomite, loose in-place, irregular fabric Saddle Peak Hills: 9/10Oct99: North end of hills, near microwave tower: SPH1 - Noonday dolomite, no irregular fabric SPH2 - Noonday dolomite, no irregular fabric SPH3 - Noonday dolomite, talus, irregular fabric 12/13Feb00: South end of hills: Assorted talus with irregular fabrics 18/19MarOO: Mid area of hills, nearest road: Assorted talus samples, variety of fabric morphologies Sperry Hills: 4/5Mar00: Up hill nearest access road to Dumont Dunes: DD1 - Kingston Peak sandstone, 0.25 m below contact DD2 - Kingston Peak siltstone, at contact DD3 - Noonday(?) BIF(?) at contact DD4 - Noonday/?) BIF(?) 1 m up from Kingston Peak DD5 - Noonday (?) friable cherty material 0.25m below second “contact” DD6 - Noonday dolomite, massive, no irregular fabric DD7 - Noonday dolomite, irregular fabric DD8 - Noonday dolomite, irregular fabric Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Samples Thin Sectioned/Slabbed: 110 Samples cut for thin sections, CL and gechemical analyses were chosen from the hand samples to provide a representative sample of fabrics and locations. These were: - Six (6) Noonday talus samples, variety of fabrics, from Saddle Peak Hills and Southern Nopah Range: Called 1, 2, 3, 4, 5, and 6. 1 - grey clotted dolomite with tan micritic layers 2 - grey dolomite with some sparry layers and red veining 3 - plan-view cut of through tube 4 - cut parallel with tube length, through tube 5 - oblique cut through tube 6 - through pocket material, but mostly of matrix - Three (3) Noonday talus samples, tubed fabric, from Alexander Hills/Winters Pass: Called T l, T2, and T3 (T2 was improperly processed for CL). T1 - oblique cut through tube T2 - plan-view cut through tube T3 - cut parallel with tube length - Five (5) samples from the base of the Noonday from Sperry Hills: Called (after the hand sample names) DD4, DD5, DD6, DD7, and DD8. DD4 - Possible BIF material, cut perpendicular to bedding DD5 - Friable material, cut perpendicular to bedding DD6 - Massive cherty dolomite, cut perpendicular to base of section DD7 - Dolomite with odd crystal layers, cut perpendicular to base of section DD8 - Massive dolomite, cut perpendicular to base of section Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ill Luminosity Patterns: 3-. 't'7\ r r " , ’ b - ' X > P .S T - ^ . : Z Z . a . g S — V : xk.. • - - ................... .5 ' ' .. v* \ £t f L ’ tk Z U -tsJ r i T J. ■ \Z '? \i<J 7^ - Slabs are numbered, ^sampling sites are marked with sample number/letter. In some cases, “H,” “M,” and “L” indi- . cate areas of high, .•medium, and low luminosity. i < - ,IW3 0 o. '0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 Drilled Samples: These intentification tags correspond to the labels on the CL diagrams. Samples 1-6 are from slabs 1-6; samples 7-11 are from slabs DD4-DD8; and samples 12 and 13 are from slabs T1 and T3, respectively. A complete description of each microsample follows: la: tan micritic layer lb: clotted grey 2a: fine grained fill 2b: sparry layer 3a: clotted grey matrix 3b: tan/brown tube fill 3c: highly luminescent zoned spar 3d: mid-luminescent zone in matris 3e: darker orange tube fill 4a: orange/tan layer 4b: clotted grey matrix 5a: orange tube fill 5b: clotted grey matrix 5c: spar 6a: orange tube fill 6b: clotted grey matrix 6c: spar 7a: tan/grey opaque 7b: black/dark red layers 8a: tan/grey material 9a: opaque tan/grey 9b: dark spar 10a: spar 10b: opaque grey/white 10c: purply spar 11a: opaque grey 1 lb: red spar 12a: spar 12b: clotted grey matrix 12c: orange tube fill 13a: orange tube fill 13b: clotted grey matrix 13c: spar Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 Appendix C: Trace Metals Data Calibrations ICP outputs were in mg/L, these values were adjusted accordingly to reflect slight variations in amounts of sample in each solution. A blank and two standards, a high and a low, were run before and after each run (there were two runs performed). The low standard contained 100 ppm Ca, 0.50 ppm Mg, 0.10 ppm Fe, 0.08 ppm Mn, and 0.08 ppm Sr. The high standard contined 200 ppm Ca, 100 ppm Mg, 4.0 ppm Fe, 2.0 ppm Mn, and 2.0 ppm Sr. The blanks and standards provided good data with expected values and repeated results across and between runs for all elements except Ca. The measured concentrations of the blank, low, and high standards (in all cases except that of Ca) plotted linearly with R-squareds and slopes of ~ 1. Calcium, however, did not plot linearly and the values measured at the begin ning and end of runs, as well as between runs, varied. First of all, a correction was applied to all Ca measurements to account for machine drift over and between runs. Secondly, it appeared that the high standard, at 200 ppm, was approching the detection limit of the machine. At lower concentrations, Ca was showing a linear relationship like those of the other metals, so two separate correction factors were used — one for values within the linear range and one for those approching the detection limit. These corrections satisfactorily adjusted the known values of the standards and was then applied to all data. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 Appendix D: Stable Isotope Data Calibrations During the process of analysis of the extracted carbon dioxide, a few samples did not provide usable data. Both sample 7a and 7b (from the questionable BIF) and 1 lb did not have enough carbon dioxide present to be measurable. Sample 6c had atmosphere in it, and thus must not have been sealed properly. Sample 3d (from cherty section) produced a strange trace pattern, wherein the carbon had normal traces, but the oxygen traces for the sample were disrupted. It is most likely that this was produced by non-condensible organics with a mass to charge ratio of 45/+ present in the sample that were not dissolved or trapped in the extraction procedure. In addition, the sample run after 3d (3e) showed some residual disruption. The carbon data were reported as measured, no corrections applied. Since all of the oxygen from the carbonate does not go to carbon dioxide in the extraction process, a correction factor specific to the type of carbonate and temperature of reaction was applied. This fractionation factor, in this case with dolomite reacted at 90 degrees C measured in PDB, is: 1.00895 = (1000 + 51 8 0 measured) / (1000 + 81 8 0 actual) The quality of the stable isotope data was measured both with reference to process standards (Lincoln Limestone 1: three (3) samples of this standard were processed and run along with the unknowns) and the machine reference gas. The data measured matched the known values within normal limits. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Creator Woods, Katharine Nicole (author)

Core Title The origin of enigmatic sedimentary structures in the Neoproterozoic Noonday dolomite, Death Valley, California: A paleoenvironmental, petrographic, and geochemical investigation

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