UC Santa Barbara

This dissertation utilizes a combination of field geology, geochronology, and geochemistry to contextualize stratigraphic and chemostratigraphic data in both time and space, and to assess the relative influence of local, regional, and global drivers on sedimentary records during periods of global change. In my first project chapter, I develop a source-to-sink test of two prevalent hypotheses for the generation of the Great Unconformity by interrogating Tonian-Cambrian stratigraphic records from the distal Cordilleran margin of Laurentia. I utilize a combination of geological mapping, U-Pb zircon geochronology, and stable carbon isotope chemostratigraphy to build a new chronostratigraphic framework for the Tonian-Cryogenian Trout Creek Sequence and Ediacaran McCoy Creek Group of eastern Nevada and western Utah. Integration of these data into a tectonic subsidence model demonstrates that these strata were accommodated by a single rifting event and a Cryogenian transition to thermal subsidence on a passive margin. I show that the distal sedimentary record of western Laurentia records the progressive erosion of the Proterozoic sedimentary cover of Laurentia throughout the Tonian-Cambrian, consistent with extant thermochronological data documenting diachronous erosion and exhumation across Laurentia over hundreds of millions of years along the Great Unconformity. My next chapter utilizes similar observational and analytical approaches to assess putative drivers and mechanisms of phosphogenesis across the Ediacaran-Cambrian boundary. I amalgamate field observations, U-Pb zircon geochronology, and carbonate chemostratigraphy into a new stratigraphic framework, age model, and tectonostratigraphic model for the Cryogenian-Cambrian Khuvsgul Group of northern Mongolia, which hosts one of the largest sedimentary phosphate deposits on Earth. These data demonstrate that phosphorites of the Khuvsgul Group were deposited in a proforeland basin between 534-531 Ma, and that tectonically-mediated basinal evolution and paleotopography controlled the timing, locus, and style of phosphogenesis in the Khuvsgul region. Furthermore, this work suggests that taphonomic effects associated with redox-mediated shifts in phosphogenic environment, rather than changes in marine phosphate concentration, were responsible for the apparent global increase in phosphorite abundance across the Ediacaran-Cambrian boundary. In my final thesis chapter, I present a radiometrically-constrained test of hypotheses linking organic carbon burial in circum-Pacific basins to Miocene climate change. I utilize high-precision U-Pb zircon geochronology to generate a new chronostratigraphic framework for the organic-carbon-rich Miocene Monterey Formation of central California, which I combine with total organic carbon data to constrain the timing and tempo of organic carbon burial in the Monterey Formation. Rather than driving climate, organic carbon burial in the Monterey Formation was controlled by changes in sedimentation rate, which was in turn controlled by a combination of local tectonics and eustasy. Thus, I demonstrate that organic carbon deposition in the Monterey Formation was largely a response to basin formation and climate change.