Incorporation, Morphology, and Extinction of Framework-Building
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University of Wisconsin Milwaukee UWM Digital Commons Theses and Dissertations May 2019 Incorporation, Morphology, and Extinction of Framework-Building Metazoans in Early Cambrian Reef Ecosystems from the Western Usa and Mongolia and Their Effects on Reef Diversity David Russell Cordie University of Wisconsin-Milwaukee Follow this and additional works at: https://dc.uwm.edu/etd Part of the Ecology and Evolutionary Biology Commons, Geology Commons, and the Paleontology Commons Recommended Citation Cordie, David Russell, "Incorporation, Morphology, and Extinction of Framework-Building Metazoans in Early Cambrian Reef Ecosystems from the Western Usa and Mongolia and Their Effects on Reef Diversity" (2019). Theses and Dissertations. 2055. https://dc.uwm.edu/etd/2055 This Dissertation is brought to you for free and open access by UWM Digital Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of UWM Digital Commons. For more information, please contact [email protected]. INCORPORATION, MORPHOLOGY, AND EXTINCTION OF FRAMEWORK-BUILDING METAZOANS IN EARLY CAMBRIAN REEF ECOSYSTEMS FROM THE WESTERN USA AND MONGOLIA AND THEIR EFFECTS ON REEF DIVERSITY by David Russell Cordie A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Geosciences at The University of Wisconsin-Milwaukee May 2019 ABSTRACT INCORPORATION, MORPHOLOGY, AND EXTINCTION OF FRAMEWORK-BUILDING METAZOANS IN EARLY CAMBRIAN REEF ECOSYSTEMS FROM THE WESTERN USA AND MONGOLIA AND THEIR EFFECTS ON REEF DIVERSITY by David Russell Cordie The University of Wisconsin-Milwaukee, 2019 Under the Supervision of Professor Stephen Q. Dornbos The early Cambrian represents an important transition in the evolution of life, perhaps most vividly exemplified by reef ecosystems as they changed from microbial-supported to metazoan-supported framework reefs. Microbial reefs were initially composed of Renalcis- and Epiphyton-group calcifying microbes. Subsequent reefs began to incorporate archaeocyathan sponges within this framework. This represents a shift in the source of carbonate production, which can be quantified using thin section point counts. In archaeocyathan reefs from the western USA, carbonate contribution from metazoan framework builders increased from zero to 29.7%. Similar reefs from Mongolia increased from zero to 5.0%. Increases in Laurentian archaeocyath contributions are not associated with shifts in carbon isotopic composition or changes in global redox conditions, while Gondwana examples might be associated with a negative carbon isotopic excursion and increase in redox sensitive elements. The incorporation of metazoan framework builders is not associated with an increase in reef dwellers, as one might expect based on the niche supporting roles that framework builders play in modern reefs. ii To further explore the timing of reef dweller biodiversity, a literature survey was conducted that shows an increase in reef-dweller abundance (17.9% in the Cambrian to 28.8% considered “frequent” in the Ordovician), functional richness (3.8 to 5.9 functional groups), and skeletonization. Furthermore, archaeocyath gross morphologies are also highly constrained to a few (3-6 categories) simple morphologies and smaller body sizes compared to lithistid and modern demosponges. It therefore may not be unusual for early Cambrian reefs to have reduced reef-dweller diversity, potentially due to a combination of low ocean productivity and restricted morphological diversity. Archaeocyaths went extinct at the end of Stage 4 of the Cambrian. This ushered in a period of low reef carbonate contribution from metazoans. This post-archaeocyath interval is preserved in western Nevada, but this locality does not contain substantial evidence of either metazoan or microbial framework building. As archaeocyaths were an important framework builder, their extinction may have resulted in a local reef eclipse. This work highlights the early Cambrian as a transitional period between the minimal diversity of the Proterozoic and high diversity reefs of the later Paleozoic. iii © Copyright by David Russell Cordie, 2019 All Rights Reserved iv To my grandparents Robert “Gramps” Cordie (1932-2018) and Marilyn “Nana” Cordie (1930-2018) v TABLE OF CONTENTS List of Figures ............................................................................................... viii List of Tables ................................................................................................ x Acknowledgments ....................................................................................... xi Chapter I. Introduction ................................................................................................. 1 Purpose of study and synopsis .............................................................. 1 Background ............................................................................................ 3 References ............................................................................................. 12 Increase in carbonate contributions from framework-building II. metazoans in microbial-archaeocyathan reefs from the early 20 Cambrian of the western USA and Mongolia ............................................. Introduction to carbonate contributions in reefs ................................. 20 Geologic settings ................................................................................... 23 Materials and methods ......................................................................... 29 Results ................................................................................................... 35 Sedimentological observations ............................................................. 52 Discussion .............................................................................................. 64 Geochemical diagenetic and chemostratigraphic interpretations ....... 72 Conclusions ............................................................................................ 76 References ............................................................................................. 77 Depauperate skeletonized reef-dwelling fauna of the early Cambrian: III. 92 a literature survey to determine the timing of reef-dweller diversity ....... Typical reef dwellers of the early Cambrian ......................................... 94 Materials and methods ......................................................................... 96 Results ................................................................................................... 98 Discussion .............................................................................................. 102 Conclusions ............................................................................................ 106 References ............................................................................................. 106 vi Restricted morphospace occupancy of early Cambrian reef-building IV. 119 archaeocyaths .............................................................................................. Cambrian morphospace occupancy and sponge morphology .............. 119 Materials and methods ......................................................................... 122 Results ................................................................................................... 126 Discussion .............................................................................................. 133 Conclusions ............................................................................................ 143 References ............................................................................................. 144 Exploring the Cambrian metazoan reef gap in the Mule Spring V. 157 Limestone of Nevada ................................................................................... The Cambrian “reef gap” ....................................................................... 157 Geologic setting ..................................................................................... 160 Materials and methods ......................................................................... 162 Results and discussion ........................................................................... 165 Conclusions ............................................................................................ 187 References ............................................................................................. 188 VI. Conclusions .................................................................................................. 200 Outcome of started goals ...................................................................... 200 Shifts towards metazoan reefs .............................................................. 201 Delayed biodiversity of Cambrian reefs ................................................ 204 Cambrian reefs are different ................................................................. 204 Future directions ................................................................................... 205 Appendix A: Point count data ..................................................................... 211 Appendix B: Geochemical data ................................................................... 216 Appendix C: Literature survey data ............................................................ 221 Appendix D: Morphological data ...............................................................