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Depositional Environments and Paleoecology of the Lower Ordovician Pogonip Group, Opd Unit, Arrow Canyon Range, Clark County, Nevada

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Depositional Environments and Paleoecology of the Lower Ordovician Pogonip Group, Opd Unit, Arrow Canyon Range, Clark County, Nevada UNLV Theses, Dissertations, Professional Papers, and Capstones 8-1992 Depositional Environments and Paleoecology of the Lower Ordovician Pogonip Group, Opd Unit, Arrow Canyon Range, Clark County, Nevada Jeffrey K. Donovan University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Geology Commons, Paleontology Commons, and the Sedimentology Commons Repository Citation Donovan, Jeffrey K., "Depositional Environments and Paleoecology of the Lower Ordovician Pogonip Group, Opd Unit, Arrow Canyon Range, Clark County, Nevada" (1992). UNLV Theses, Dissertations, Professional Papers, and Capstones. 1116. http://dx.doi.org/10.34917/2493857 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Theses, Dissertations, Professional Papers, and Capstones by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. DEPOSITIONAL ENVIRONMENTS AND PALEOECOLOGY OF THE LOWER ORDOVICIAN POGONIP GROUP, Opd UNIT, ARROW CANYON RANGE, CLARK COUNTY, NEVADA by Jeffrey K. Donovan A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology Department of Geoscience University of Nevada, Las Vegas August, 1992 i The thesis of Jeffrey K. Donovan for the degree of Master of science in Geology is approved. Cha1rperson, s. M. Rowland, Ph.D. Exam1ning Comm1ttee Member, F. w. Bachhuber, Ph.D. Examining Committee Member, D. L. Weide, Ph.D. Graduate Faculty Representat1ve, J. B. Case, Ph.D. Graduate Dean, R. w. Smith, Ph.D. University of Nevada, Las Vegas August, 1992 ii ABSTRACT The Opd Unit of the Pogonip Group is a slope-forming carbonate sequence that crops out in the Arrow Canyon Range 75 miles north of Las Vegas, Nevada. It is composed mainly of grainstones, packstones, and intraformational conglomerates and also contains Calathium-bearing bioherms composed dominantly of wackestones.. These rocks were deposited in a shallow-water, high-energy, subtidal, tropical marine environment. Nuia and Nuia-crinoid shoals developed on this shallow ramp and the area was frequently disturbed by storms. Calathium-dominated carbonate mudmounds emerged on the Nuia and Nuia-crinoid shoals. Although Calathium dominated the mounds on a macroscopic scale, the mounds were build by unpreserved microorganisms. Calathium simply lived in the mounds and may have acted as sediment bafflers. Other mound dwellers included trilobites, crinoids, gastropods, nautiloids, brachiopods, and bryozoa. The bioherms of the Opd Unit represent the transition from bioconstructions dominated by microorganisms during the Middle and Late Cambrian to those dominated by sessile benthonic macroorganisms during the Middle Ordovician. iii TABLE OF CONTENTS ABSTRACT iii TABLE OF CONTENTS . iv LIST OF FIGURES AND TABLES v AtKNOWLEDGEMENTS vi INTRODUCTION • • • 1 Purpose of This study 1 Distribution and study Area 1 Access . .. 3 Previous Work • 5 Objectives • . • 10 METHODS AND DESCRIPTIONS 11 Methods • • • . • • 11 Rock Descriptions . 13 Stratigraphic Column Description 25 DEPOSITIONAL ENVIRONMENTS . • . 28 Paleogeography . • • . • . 28 Depositional Environments of the Opd Unit 31 MOUND PALEOECOLOGY 46 Guild Concept 46 Bioherms • • . 47 COMPARISONS AND DISCUSSION • 61 Other Ordovician Buildups 61 Early Paleozoic Reef Evolution 67 CONCLUSIONS 70 REFERENCES 71 APPENDIX A 77 APPENDIX B 81 APPENDIX C 86 iv LIST OF FIGURES AND TABLES Figure 1. study area location map. 2 2. Photographs of the Opd Unit. • . 4 3. Correlation of southern Nevada Ordovician rocks. 7 4. Pogonip Group at the Arrow Canyon Range. 8 5. Measured column locarions. 12 6. Dunham's classification of carbonate rocks 14 7. Nuia grainstone/packstone. 15 8. Nuia-crinoid grainstone/packstone. 17 9. Intraclastic grainstone/packstone. 18 10. Mudstone . 20 11. Fenestral fabric mudstone. 21 12. Bioclastic wackestone. 23 13. Crystalline carbonate. 24 14. Generalized stratigraphic column . 27 15. North America during the Early Ordovician .... 29 16. ordovician lithofacies of western North America. 30 17. Depositional setting of the Opd Unit 32 is. Intraformational conglomerate. 37 19. Rose diagrams. 39 20. Bioturbated rock . 44 21. Calathium. • . 49 22. Calathium holdfast . 49 23. Calathium meromes. 50 24. Calathium overgrowths. 50 25. Bioherm. 52 2 6. Large bioherm. 52 27. Bioherm serial sections. 54 28. Sharp bioherm boundary . • 57 29. Draping of sediments between bioherms. 57 30. Downwarping of sediments below bioherm 58 31. Cavity in bioherm with geopetal sediment 58 32. Guild diagram of Opd Unit mound. 60 33. Map of locations of work by other authors. 62 34. Comparison of Ordovician carbonate buildups. 63 Table 1. Summary of Calathium orientations. 40 2. Volumetric analysis of bioherms ..• . 55 v ACKNOWLEDGEMENTS I would like to express my appreciation to Jack Deibert, Susan Panttaja, Lance Larsen, Jeff Nejedly, Lynn Oliver, Joel Hayworth, Alan Titus, Sharlynn Jeffrey, and John Watkins for their help in measuring sections and collecting samples during my hospitalization and illness. I would like to thank Dr. Margaret Rees for organizing the above mentioned people and providing valuable assistance and advice. Thanks goes to Dr. Steve Rowland for his unwavering support during the long process of completing this thesis and for suggesting this project. I am indebted to the UNLV Graduate Student Association and to Lilly and Wing Fong for their generous financial support. vi 1 INTRODUCTION Purpose of This Study The Early Ordovician is an important time in the history of reef evolution because it represents a transition from reefs dominated by microorganisms to reefs built by skeletal macroorganisms. Bioherms that occur in the Lower Ordovician Pogonip Group and are exposed in the Arrow canyon Range are one of the few examples of Early Ordovician bioherms anywhere and are the only examples from southern Nevada. The purpose of this study is to describe and interpret the depositional environments and paleoecology of these bioherms in order to further our understanding of this critical period in the history of reef evolution. Distribution and Study Area The Pogonip Group is a Lower Ordovician carbonate sequence composed dominantly of limestones and dolomites. It crops out in a variety of locations in southeastern California, southern and central Nevada, and western Utah. The primary location for this study is the Arrow Canyon Range, approximately 75 km north of Las Vegas, Nevada (Fig. 1). At this locality the Pogonip Group crops out on the western slope of the Arrow Canyon Range where Langenheim and 2 / Study Area Arrow / Canyon / Ra n g e / / / / las • Vegas cIa ---­r k ...... 0 2 0 ...... County ...... -km ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... Figure 1. study area location map. 3 others (1962) divided it into six units designated Opa through Opf (Fig. 2). The Opd Unit, which is described in this study, is a slope-forming carbonate unit ranging from 75 to 100 meters thick; it is composed of grainstones, packstones, and intraformational conglomerates. The unit also contains numerous bioherms dominated by Calathium, a problematical organism presently grouped with receptaculitids (Nitecki, 1986). These bioherms are important in the history of Paleozoic reef evolution because they were among the first with a skeletal component to appear after the virtual extinction of the archaeocyatha at the end of the early Cambrian. Access To reach the study area, travel north from Las Vegas, Nevada on Interstate 15 approximately 20 miles to Highway 93. Travel north on Highway 93 to mile marker 77. Travel another 0.4 miles to an unmarkerd dirt road on the right. Turn right and go east 1.5 miles to another dirt road. Turn right an travel south slightly over 0.2 miles. Turn left on another dirt road and travel east to southeast for as far as the road goes. The study area is located on the west-facing cliff of the Arrow Canyon Range near the location where the Ope Unit cliff dips into the subsurface (Fig. 2). 4 A Figure 2. Opd Unit at the Arrow canyon Range. A) West face of the Arrow Canyon Range. B) Opd Unit showing its bench-forming characteristic. View is to the south. 5 Previous Work The term "Pogonip" was first used by King (1878) in his report of the 1876 geological expedition of the 40th parallel (as reported in Smith, 1962). He used the name Pogonip Limestone for a sequence of carbonates at Pogonip Mountain near White Pine, Nevada. This sequence was identified as Silurian in age because the Ordovician had not yet been accepted as a part of the geologic time table. Hague (1883) in his work on the geology of the Eureka District of Nevada redefined the Pogonip Limestone to include all the rocks occurring between the Cambrian Hamburg Shale and the Eureka Quartzite. Hague also collected and described over seventy fossil species from the Pogonip. The loose term "Pogonip Limestone" was redefined by Hintze (1951) as the Pogonip Group, consisting of six Ordovician formations
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