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Tracking the Ice Age: Applying Facies Changes and Grain Size Variability to Trace Environmental Shifts Linked to the Laurentide Ice Sheet in the Cincinnati, Ohio Area

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Laura Comstock

Authors:

Comstock, Laura K.¹, Mandick, Abigail², Ward, Dylan J.³, Clements, Alexa⁴

(1) Earth and Environmental Sciences, University of Northern Iowa, Cedar Falls, IA, USA, (2) Earth and Environmental Sciences, University of Northern Iowa, Cedar Falls, Iowa, USA, (3) Geosciences, University of Cincinnati, Cincinnati, OH, USA, (4) Earth and Environmental Sciences, University of Northern Iowa, Cedar Falls, IA, USA,

Abstract:

Reconstructing the history of ice sheet dynamics is essential for understanding how past climate change has shaped modern landscapes. The Laurentide Ice Sheet advanced and retreated multiple times over North America during the Pleistocene Epoch. Although there is widespread sedimentary evidence for the most recent glacial episode, much of the evidence of older glaciations has been overwritten by more recent glacial advances. This study focuses on Paddison Run, an exposed Pleistocene sequence near Cincinnati, Ohio, that previously has been interpreted as Illinoian in age. We identify 5 distinct units within the exposure, based on centimeter logging of this section, high resolution sampling, and grain size and geochemical analyses. Individual samples were processed using sediment sieves to assess grain size distribution within and between units. Individual representative sample splits were then analyzed for elemental composition using a handheld XRF. Sediments within this succession fine upwards, with grain sizes between 500-250 μm in the lowest unit and fining upward to between 125-63 μm. Initial results also indicate that iron concentrations are highest in the lower most units. Our results indicate that the basal units were deposited in higher energy, shallow water environments. The overlying unit is composed of finer sediments and has lower iron concentrations. In addition, fine laminations at the base of this unit and several large dimictite clasts are consistent with the formation of a glacial lake with occasional ice rafted debris deposition. These features are consistent with previous work documenting the formation of ice-dammed lakes in the region. A sharp contact between the lake sediments and a distinct diamictic bed may represent a later advance of the ice sheet, erosion, and subsequent deposition of glacial till. Our findings provide a high-resolution record demonstrating the complex environmental responses to changes in the position of the ice sheet margin.