Provenance and geochemistry of upper Proterozoic strata in California and other areas of the western United States: Paleogeographic and biogeochemical implications

This dissertation summarizes a collection of research projects conducted on upper Proterozoic strata in the Great Basin and other areas of the western United States. The objectives were to test specific assumptions in prevailing stratigraphic models and to develop new analytical tools that improve paleogeographic and biogeochemical interpretation. The late Proterozoic was a time of global tectonic reorganization and severe climate change that created the biogeochemical conditions that led to the Cambrian faunal radiation. The stratigraphic record from this period reflects multiple episodes of rifting and gives ambiguous indications of North America's position within the Rodinia supercontinent. Biogeochemistry of the marine reservoir during Neoproterozoic glaciations is also an area of controversy. New forms of geochemical data are needed to assess how organic and inorganic carbon reservoirs may have affected the diversity of plankton and other eukaryotes in the aftermath of Neoproterozoic glaciation.; Chapter 1 is an overview of upper Proterozoic stratigraphic interpretations in western North America with regard to the Rodinia and Snowball Earth models. The second chapter is concerned with detrital zircon age signatures of upper Proterozoic units from western North America and describes a strategy for rigorous analysis of large detrital zircon age datasets. Using principal component analysis, chapter 2 identifies the independently-varying subpopulations of detrital zircon ages that characterize upper Proterozoic units in western North America and compares them to local and regional sediment sources. Chapter 3 is a study of trace element distributions in cap carbonate units from Death Valley that describes a significant negative correlation between trace element concentrations and carbon isotopic composition. The correlation suggests that anoxic overturn was a mechanism that created the large volume of isotopically light carbonate units found in most Neoproterozoic sections. Chapter 4 is an inventory of biomarkers in samples from the Neoproterozoic Chuar and Uinta Mountain Groups, comparing them with biomarkers from the Middle Cambrian Burgess Shale. Sterane patterns of the Kwagunt and Red Pine samples show extreme enrichment of the C₂₇ isomer suggesting that biological diversity was restricted among eukaryotes during the Neoproterozoic. Methylalkane patterns suggest a significant prokaryotic biomass similar to that found in present day cyanobacterial mats.