Date of Award

5-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Sandra Passchier

Committee Member

Stefanie A. Brachfeld

Committee Member

Matthew L. Gorring

Abstract

Prior to the mid-Miocene the Antarctic ice sheet is believed to have been very dynamic with periods of expansion and contraction (Naish et ah, 2001). Previous studies have suggested that the ice sheet changed from a wet-based temperate ice-sheet to a drybased polar ice sheet at ca. 14 Ma (Lewis et al., 2007). Utilizing a sediment core obtained through the Antarctic Geological Drilling (ANDRILL) program, changes in the flow configurations and conditions in the basal ice were documented across the middle Miocene climate transition. Glaciers eroded bedrock from the Transantarctic Mountains and deposited sediments into the embayment mixing with materials transported from further south. The basal melt out deposited diamictites, ranging from coarse angular fragments to well-rounded, sedimentary clastic fragments that are supported by a finegrained matrix.

The bulk chemistry of the matrix was determined and used to obtain the provenance of the materials. Through particle size analysis, the type of ice sheet (temperate wet-based vs. polar dry-based) that transported the sediment was traced as well as providing evidence of the conditions of the original depositional environment (i.e. subglacial or glaciomarine). Surface microtextural analysis of sand grains, using the Scanning Electron Microscope (SEM) yielded evidence of glacial crushing or abrasion intensity during basal ice transport. Combining the results from the particle size analysis and the geochemistry provided a better understanding of the changes in ice-flow configuration and basal ice conditions during this time. Principal component analysis determined which variables account for the most variability in the geochemistry, particle size, and microtextural results while discriminant analysis was used to test the hypothesis of differences in composition of diamictites before and after the middle Miocene climate transition.

Geochemical analysis determined that prior to the middle Miocene, the Ferrar dolerite was the main source of input while basement granitoid was eroded subsequently. Particle size distributions yielded evidence for a dynamic wet-based temperate ice sheet before and after the middle Miocene climate transition (14 Ma). High fractal values for the particle size distribution >2.9 according to Hooke and Iverson (1995) indicate an excess of fines and grain abrasion and such values are found throughout all the intervals. A higher content of fines as a result of grain abrasion rather than grain fracture is indicative of a wet-based ice sheet. Microtextural analysis supports particle size and fractal results with a mix of mechanical and chemical textures; mechanical textures are characteristic of glacial crushing while chemical textures indicate the presence of basal melt waters. With a mix of both textures present, it can be concluded that some grain crushing as well as abrasion occurred during transport under a wet-based ice sheet.

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