Master of Science (MS)
Geology and Geophysics
Previously acquired seismic surveys provide strong evidence that the post-Last Glacial Maximum (LGM) retreat of the West Antarctic Ice Sheet (WAIS) deposited a back-stepping succession of seismically-resolved grounding zone wedges (GZWs) in eastern Ross Sea. However, the chronology of WAIS retreat is debated. The conventional view is that three GZWs (Red, Brown, and Gray Units) were deposited since the LGM. An alternative view, based on recent radiocarbon dates, is that the youngest GZW (the Gray Unit) was deposited during the LGM. If correct, then the older GZWs (Red and Brown Units) were deposited prior to LGM. A recent study (Bart and Owolana, 2012) evaluated these interpretations with respect to the Gray GZW. They concluded that both interpretations are feasible working hypotheses for how the Gray Unit relates to grounding-line translations during the last glacial cycle. They proposed that the volume of the Red and Brown GZWs may be too large to have been deposited in the post-LGM timeframe. However, neither the Red or Brown unit have been mapped in detail. The purpose of this study is to use the framework defined by Bart and Owolana (2012) to evaluate how much time would be required to deposit the Red Unit. Mapping showed that the Red Unit is extensive across eastern Ross Sea and is best described as a till sheet. Isopach mapping shows that the volume of the Red Unit is far less than predicted by Bart and Owolana (2012) and is estimated to be 2.12 ± 0.06 x 1012 m3. Using a retreat-mode flux, the Red Unit grounding event duration is calculated to have been 7.5 ± 1.5 ky. Using the advance-mode flux, the Red Unit grounding event duration is calculated to have been 750.69 ± 159.70 ky. When combined with the estimated durations for the Gray GZW (Bart and Owolana, 2012) and Brown GZW (Kirst, in prep), both the advance and retreat-mode durations exceed the maximum time of the post-LGM timeframe. Within this context, the data strongly suggests that the Red Unit represents an amalgamation of erosion and deposition during several glacial-interglacial cycles prior to the LGM.
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Bowles, Sydney Grace, "On the long duration of Till sheet construction : a reassessment of how quaternary grounding line translations relate to near-surface seismic-stratigraphy of eastern Ross Sea, Antarctica" (2013). LSU Master's Theses. 1173.