Seismic Stratigraphic Evidence From SE Ross Sea for Late Oligocene Glaciers and ice Streams Issuing From Marie Byrd Land
Abstract
The extent of the West Antarctic ice sheet during mid-Cenozoic time is controversial and important to climate models. High-resolution multichannel seismic reflection data were acquired using the RVIB Palmer along the edge of the Ross Ice Shelf across the Eastern Basin of Ross Sea, in an area where calving of the ice shelf has exposed seafloor that has not been accessible to marine geophysics in several decades. A sub-basin in the far southeast corner of Ross Sea contains a succession of sediment-filled troughs, each capped by an unconformity. These troughs range between 2 and 20 km across, are 100 to 150 m-deep, with the narrower ones bounded by flat-topped ridges interpreted as moraines. We interpret the troughs interval to slightly predate 25 Ma. Reflections just 100 m below the troughs interval can be directly correlated to near DSDP270 where they underlie strata dated at ~25 Ma. A deeper stack of prograding sequences associated with a flat- topped ridge are interpreted as pre-25 Ma, possibly early Oligocene, deltas formed adjacent to the grounding line of a glacier, and the flat-topped ridge to be a moraine. The shallowest of the stack of unconformities capping the broad troughs can be projected across a basement ridge on trend with Roosevelt Island to a regional angular unconformity ("Red"), present across 70 km to deep sedimentary Eastern Basin. This unconformity represents about 1 km of missing stratigraphic section, is smooth and level, and splits into several major sequence boundaries within deep Eastern Basin. The second shallowest of these boundaries is dated about 14 Ma at DSDP-270. We interpret this unconformity to be cut by regional thick, grounded ice at depths several hundred meters below sea level. Pre-25 Ma strata show evidence of narrow erosional troughs and reflective mounds or ridges on the west flank of the basement ridge, but such features are not present in southern deep Eastern Basin near the ice shelf edge. This is evidence that the troughs were carved by glaciers issuing from distant highlands of Marie Byrd Land and not from East Antarctica. Late Oligocene through mid Miocene and younger prograding and unconformities farther north in Eastern Basin indicate grounded ice there. One possible interpretation is that "Red" was cut by thick, grounded ice that affected all of the Eastern Ross Sea paleo-shelf, while the pre-25 Ma glaciers affected only the area proximal to Marie Byrd Land. Late Oligocene glaciation on the outer shelf above deep Eastern Basin may have been sourced from East Antarctica and/or Central High. Evidence for pre-25 Ma glaciation proximal to Marie Byrd Land, combined with evidence for Oligocene ice caps at widely-separated localities of West Antarctica, allow the interpretation that portions of the West Antarctic Ice Sheet developed during Oligocene time. The broad troughs and the stack of prograding sequences may be related to dynamic ice caps and sea level falls in mid Oligocene and earliest Oligocene time. The Middle Miocene Red unconformity may be related to development of polar (cold-base) ice sheets. Oligocene glaciation implies that Marie Byrd Land and eastern Ross Sea have subsided from higher elevation due to cooling after late Cretaceous crustal thinning.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMOS31D1659S
- Keywords:
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- 1621 Cryospheric change (0776);
- 4914 Continental climate records;
- 8177 Tectonics and climatic interactions;
- 9310 Antarctica (4207)