HR: 0830h
AN: PP31B-0262    [PDF]
TI: Formation of Bedrock Plateaus Within the Ross Sea Embayment, Antarctica, by Marine Erosion in Late Tertiary Time
AU: * Luyendyk, B P
EM: luyendyk@geol.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Cal 93106 United States
AU: Wilson, D S
EM: dwilson@geol.ucsb.edu
AF: Marine Science Institute, University of California, Santa Barbara, Cal 93106 United States
AU: Sorlien, C C
EM: chris@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, Cal 93106 United States
AB: Ice penetrating radar (mostly airborne) and marine seismic surveys have revealed plateaus and terraces beneath parts of the Ross Embayment including the West Antarctic ice sheet, the Ross Ice Shelf, and the eastern Ross Sea. These surfaces cover many thousands of square kilometers and are separated by bedrock troughs cut by the West Antarctic ice streams. Elevations of the plateaus vary from about 100-250 m below sea level (bsl) near the Edward VII Peninsula in the eastern Ross Sea to about 350 m bsl along the Siple Coast. Airborne geophysical surveys over a 350 by 450 kilometer area of western Marie Byrd Land (MBL) mapped one of the largest plateaus, a 300 km by 100 km level surface at about 250 meters bsl at the boundary between the Ross Embayment and MBL. We interpret these surfaces as remnants of a continental shelf formed by wave erosion when the coastal regions of Antarctica were relatively free of ice. The generally flat and level nature of the surfaces that are near the same depth over large distances supports an interpretation of an origin by marine rather than glacial erosion. Marine seismic reflection profiles over one of the plateau remnants in the Eastern Ross Sea west of Edward VII Peninsula show thin, flat-lying glacial marine sediments draped with angular unconformity over gently dipping RSS2 sediments of Early Miocene age. Combining this age constraint with ice sheet and global sea level histories suggests that the shallower plateaus were last eroded in the early Middle Miocene, about 15 Ma, prior to formation of the modern West Antarctic ice sheet, and when sea level was at least 30-50 m higher. The plateau surfaces might be correlated to Ross Sea unconformities including RSU5 and RSU4. One possible explanation of the present depths consistent with forming the plateaus near Miocene sea level is that a model for removal of extremely thick early Holocene ice, such as ICE-3G is approximately correct, and current bedrock depths are at least 200 m below isostatic equilibrium. Free Air gravity anomalies of about -30 milligals in the region are consistent with it being depressed below isostatic equilibrium by at least this amount. The plateaus along the Siple Coast, with depths around 350 m bsl, do not rebound to close to either present or Miocene sea level for simple models of removing the current and Holocene ice load. Another part of the explanation may be that the lithosphere was heated and at higher elevation in Oligocene time due to substantial extension or intense mantle plume activity. Subsequent cooling has caused a moderate amount of crustal subsidence since then so that rebound alone does not return the surfaces to sea level or above.
DE: 4267 Paleoceanography
DE: 8105 Continental margins and sedimentary basins
DE: 9310 Antarctica
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting