Master of Science (MS)
Geology and Geophysics
A sequence of three seismically-resolvable, back-stepping grounding zone wedges (GZWs) within the Glomar-Challenger Basin paleo-ice-stream trough is conventionally interpreted to have been deposited by the West Antarctic Ice Sheet (WAIS) since the end of the Last Glacial Maximum (LGM). For this to be true, there would have to have been voluminous GZW deposition via fast moving ice streams with high sediment flux during the short timeframe since the WAIS retreat began at 11 Ka 14C BP and when the WAIS moved south of Roosevelt Island at 3.2 Ka BP. In contrast to this interpretation of how the near-surface stratigraphy relates to post-LGM retreat of the WAIS, foraminiferal radiocarbon dates from Bart and Cone (2012) suggest that the youngest back-stepped GZW corresponds to the culmination of erosion and deposition during the LGM. If so, the older GZWs currently assigned to the post LGM time frame would need to be reassigned to pre-LGM glacial cycles. To test which of these interpretations is correct, the duration of the Brown Unit, the second of the three backstepped GZWs, was investigated in detail. Five seismic surveys from eastern Ross Sea were used to map the extent and thickness of the Brown Unit. Two end-member durations were deduced using 3D sediment flux values that would have existed were the WAIS in retreat mode versus advance mode. Utilizing the retreat-mode flux, a 5.12 ± 1 ky grounding event duration was calculated for the Brown Unit GZW. However, a 512.88 ± 100 ky grounding event duration was determined using the advance-mode sediment flux. Given the durations previously calculated for the Gray Unit (the youngest post-LGM GZW) from Bart and Owolana (2012) and the grounding event duration recently calculated for the Red Unit (the oldest post-LGM GZW) by Bowles (2013) suggests that the near surface stratigraphy must represent the amalgamation of erosion and deposition from many cycles of WAIS advance and retreat. In particular, the Brown Unit is tentatively assigned to time elapsed between MIS5 and MIS8.
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Kirst, Logan Gregory, "Evaluating quaternary glacial till sheet volume and duration of grounding events using sediment flux calculations in the Eastern basin paleotroughs, Ross Sea, Anarctica" (2013). LSU Master's Theses. 65.