2024 Theses Doctoral

Sediment Histories: Early Mesozoic Ice and North American Pleistocene-Holocene Deglaciation

Chang, Clara Yunn

We use sedimentary structures, fossil evidence, sediment petrophysical properties, and geochemistry to investigate past climate.

In the first two chapters, we outline a toolkit to identify the presence of ice rafted debris in lake sediments using a combination of grain size analysis, computed tomography and image analysis. We apply this toolkit to sediments from the early Mesozoic, paleo-Arctic Junggar Basin, and describe the first evidence of continental freezing from this time period. We also discuss characteristics of algae rafted debris; clusters of coarse sediment suspended in a fine sediment matrix can be deposited without freezing conditions and may be a confounding factor in the geological record.

In chapters three and four, we examine sediment cores from the coast of New York and the effects of sea level rise after the last deglaciation. New AMS radiocarbon dates from submerged terrestrial sediments on the US Atlantic continental shelf provide key constraints on the timing of marine transgression following the retreat of the Laurentide Ice Sheet. We use sediment elevation tables (SETs) and sediment cores to measure the accretion rate in a Hudson River tidal wetland to determine its vulnerability to sea level rise. We find that SETs overestimate accretion and underestimate vulnerability on timescales relevant to coastal flooding risk. Together, these chapters outline novel tools and approaches in imaging, geochemistry, and micro-stratigraphy broadly applicable for investigations on paleoclimate research through time and space.