HR: 0830h
AN: PP31C-0271    [PDF]
TI: New seismic stratigraphic mapping suggests that the late Miocene/early Pliocene glacial regime did not include cross-shelf ice streams comparable with those existing during recent glacial maxima
AU: * Egan, D C
EM: degan@geol.lsu.edu
AF: Louisiana State University Department of Geology and Geophysics, E235 Howe-Russell, Baton Rouge, LA 70803 United States
AU: Bart, P J
EM: pbart@geol.lsu.edu
AF: Louisiana State University Department of Geology and Geophysics, E235 Howe-Russell, Baton Rouge, LA 70803 United States
AB: A grid containing several regional strike-oriented seismic profiles on the Pacific margin of the Antarctic Peninsula outer continental shelf were acquired in 2002 to evaluate the glacial unconformity interpretation of Package 3 strata (Bart and Anderson, 1995). These (NBP02) and previously acquired seismic data (PD88 and PD90) were used to create time-structure contour maps of the Package 3 stratal surfaces. Although ODP Leg 178 drill results demonstrate that the outer continental shelf probably experienced numerous episodes of ice-sheet advance and retreat during this timeframe, it is not clear whether the glacial conditions were similar to those in the Quaternary, during which large and robust, cross-shelf ice streams drained the mainland peninsula. Our mapping results show that there are indeed numerous cross-cutting relationships within Package 3 that result in an extremely patchy distribution of units and stratal surfaces. The patchy distribution of Package 3 surfaces seriously hampers our ability to make regional correlations and map large-scale features, but the largest patches have extents that exceed the dimension of modern banks and troughs. The surfaces show convex and concave topography similar to the bases of troughs and crests of banks of the modern seafloor. However, detailed comparison of the relief variations of Package 3 surfaces to that of the modern bathymetry shows that subsurface horizons do not exhibit dip-oriented deep troughs and high banks indicative of cross-shelf drainage. Although we favor a glacial-unconformity interpretation of Package-3 stratal surfaces, we propose that there were no large, cross-shelf ice streams separated by broad banks during this time (i.e. late Miocene/early Pliocene). We tentatively suggest that uplift on the middle shelf (associated with diachronous ridge-trench collision during this timeframe) may have created sub aerial exposure, precluding the existence of cross-shelf ice streams but providing a source of outer-shelf grounded ice of a much different scale.
DE: 1827 Glaciology (1863)
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting