Determining middle Miocene through Pliocene changes in provenance and basal ice conditions through sedimentological analyses of subglacial diamictites in AND-2A, Ross Sea, Antarctica
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 a...
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Montclair State University Digital Commons
2011
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| Online Access: | https://digitalcommons.montclair.edu/etd/878 https://digitalcommons.montclair.edu/context/etd/article/1880/viewcontent/Hansen_Thesis_2011_Redacted.pdf |
| Summary: | 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 ... |
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