HR: 0800h
AN: T11A-1238    [Abstracts]
TI: Evidence That Early to Middle Miocene ice Streams From West Antarctica cut Into Southeastern Ross Sea Continental Shelf
AU: * Sorlien, C C
EM: chris@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Luyendyk, B P
EM: luyendyk@geol.ucsb.edu
AF: Dept. Geological Sciences, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Wilson, D S
EM: dwilson@geol.ucsb.edu
AF: Dept. Geological Sciences, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Decesari, R C
EM: rdecesari@umail.ucsb.edu
AF: Dept. Geological Sciences, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Bartek, L R
EM: bartek@umail.unc.edu
AF: Dept. of Geological Sciences, CB# 3315 University of North Carolina, Chapel Hill, Chapel Hill, NC 27599 United States
AU: Diebold, J B
EM: johnd@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory-Columbia U., 61 Route 9W, Palisades, NY 10964 United States
AB: 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 5 and 20 km across, and are 100 to 150 m-deep. They are cut into a sequence correlated to slightly predate ~24 Ma. The shallowest of these unconformities (named "Red" here) can be tentatively projected across the northern plunge of a basement ridge located north of Roosevelt Island (named "Roosevelt Ridge" here), and is a regional unconformity in the Eastern Basin. Reflections just below Red can be correlated to DSDP 272, where they are dated at ~14 Ma. Red is flat and level in the south, adjacent to the ice shelf edge. Older sequence boundaries beneath Red merge with it across a 70 km extent between the deep Eastern Basin and Roosevelt Ridge. Much of the late-Early Miocene and early-Middle Miocene section is missing and appears to be removed by erosion associated with the Red unconformity. There is no evidence for broad glacial troughs that predate Red west of Roosevelt Ridge. If our correlations are correct, the succession of glacial troughs must be Middle Miocene and older, and we cannot rule out the oldest being Late Oligocene without additional data. Because we do not believe that a glacier or grounded ice sheet could erode a thick interval of sedimentary rocks and still produce a smooth and level unconformity, our preferred hypothesis is that Red is a wavecut surface that has since subsided to its present 700 m depth. The fill of one 20 km-wide trough is exposed at the seafloor and accessible to Shaldrill coring to test our hypothesis. The Ross Ice Shelf is advancing over the surveyed troughs and future drilling from the ice shelf will also be possible. Finally, it may be possible to correlate the fill of the troughs to DSDP stratigraphy with acquisition of carefully-positioned seismic reflection profiles. These troughs are consistent with erosion by ice streams or glaciers fed from an ice cap over at least part of western Marie Byrd Land. An Early Miocene ice cap contrasts with the Late Miocene age for the earliest widely accepted time for grounded ice in West Antarctica.
DE: 9310 Antarctica
DE: 8105 Continental margins and sedimentary basins
DE: 3344 Paleoclimatology
DE: 3025 Marine seismics (0935)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting