Stratigraphic expression and numerical modeling of meteoric diagenesis in carbonate platforms during the Late Paleozoic Ice Age

Abstract

The history of life on Earth is intricately tied to the coevolution of the biosphere, atmosphere, and lithosphere over billions of years. Ancient sediments are the fragmented historical record of the interactions among these systems. The Late Paleozoic Ice Age (LPIA) is an interval of extreme climate change and variability that is expressed in the physical and chemical stratigraphy of tropical sediments. The focus of this thesis is refining strategies to extract information about global and local sea level from carbonate-rich sedimentary basins.

The second chapter explores the impact sea level had on the stratigraphic expression of carbonate cycles from the late Pennsylvanian. These carbonate cycles classically are interpreted as the sedimentary response to Milankovitch-style orbital forcing of climate in the Late Paleozoic, but the lateral synthesis of sedimentary facies and their carbon isotopic values suggests that sea level change was a minor component to sedimentary expression in the basin. Therefore, late Pennsylvanian ice sheets were relatively stable and not responding rapidly to changes in orbital forcings.

The third chapter investigates a globally expressed sedimentary unconformity near the middle Carboniferous boundary. Glacial expansion and subsequent sea level fall results in sedimentary hiatus and meteoric diagenesis of the carbon isotopes in the exposed carbonates. The observations of negative carbon isotopes in the carbonate platforms motivates the exploration of the impact on the global carbon cycle, and suggests that the δ13C of the ocean may be elevated during glacioeustasy of the LPIA. This result offers a much needed improvement on global biogeochemical models that have struggled to provide a congruent solution to the high δ13C of the LPIA. The final chapter provides numerical methods to interpret superimposed seawater and meteoric diagenetic isotopic signals in the stratigraphy. The merger of these numerical methods and the carbon and calcium isotopic excursions beneath the middle Carboniferous unconformity offers insight into the processes by which sea water chemistry, carbonate weathering, meteoric diagenesis, and local platform hydrology contribute to the composite stratigraphic record.