Causes and consequences of marine carbon burial: Examples from the Cretaceous Niobrara Formation and the Permian Brushy Canyon Formation

The stratigraphic record of the Phanerozoic provides key evidence of temporal changes in the global carbon cycle over the past 560 myr of Earth history. Measurements of carbon concentrations in ancient marine sediment, in conjunction with a chronological framework, provide a means to reconstruct burial flux history and, thus, evaluate mass exchange between surface reservoirs of the carbon cycle. The goal of this study is to evaluate the controls on carbon enrichment in ancient marine sediment and to constrain burial fluxes of the two major carbon-bearing components in marine depositional systems, organic and inorganic carbon.; The research is conducted through a series of case studies. The first addresses longterm oscillations in carbonate mineralogy through the Phanerozoic and modeling results suggest that on these timescales alkalinity changes, potentially derived from variations in riverine runoff, may have been an important aspect to the saturation state of carbonate minerals in seawater. The second study evaluates hypotheses of Milankovitch cyclicity in limestone-shale rhythms of the Upper Cretaceous. Application of spectral techniques to depositional rhythms demonstrates Milankovitch cyclicity and provides an orbital timescale for calculation of high-resolution accumulation rates. The third study evaluates chalk and marl facies changes and the potential linkage to sea level change in the Upper Cretaceous. The results suggest the need for revising reconstructions of sea level history based on hemipelagic facies. The fourth study attempts to discriminate between paleoceanographic hypotheses responsible for orbital-scale depositional rhythmicity in the Late Cretaceous. Stratigraphic, geochemical, and modeling evidence indicate oscillations in siliciclastic flux to offshore settings. The fifth study incorporates a geochemical model to evaluate the potential effect of widespread chalk deposition on the global carbon isotopic composition of marine waters in the Late Cretaceous. Changes in the global proportion of carbonate production may have significantly influenced the carbon isotopic signature of dissolved inorganic carbon and dampened positive carbon isotopic excursions associated with times of elevated organic carbon flux in the Upper Cretaceous. The final study examines the role of siliciclastic flux on organic carbon enrichment in the Late Permian. Organic enrichment is interpreted to reflect depositional condensation.