NEW DATA SUGGESTS AN EARLY ONSET AND DYNAMIC HISTORY OF OUTER-SHELF GLACIAL GROUNDING ON THE PACIFIC MARGIN OF THE ANTARCTIC PENINSULA

On the basis of detailed seismic analyses, Bart and Anderson (1995) suggest a dynamic glacial history for the Pacific margin of the Antarctic Peninsula, with ice grounding at the shelf edge ~3 times since the middle Miocene. In contrast, Larter et al. (1997) argued that grounding events were less frequent (i.e. 6), beginning in the late Miocene. The primary difference between the two age models concerns the glacial vs. non-glacial origin of the lower-most stratal package of Bart and Anderson (1995) and its overall age. Drilling of ODP site 1097 on the Antarctic Peninsula outer continental shelf shows that both of the existing age models are in error. The deepest sediments drilled at that site were older than Larter et al. (1997) suggest but not as old as Bart and Anderson (1995) argue, and are interpreted to be ‘glacially influenced,’ but may or may not involve outer shelf grounding. These findings require that the existing glacial models be re-evaluated. During the 2002 field season, ~3300 km of single-channel seismic data were collected from the Pacific margin of the Antarctic Peninsula aboard the RVIB Nathaniel B. Palmer. This grid contains 4 regional strike-oriented profiles on the outer continental shelf and complements 2 existing seismic grids (i.e. PD90 and PD88). In this study, we correlated these 3 grids to age and lithologic control at ODP Site 1097. If the system is as dynamic as Bart and Anderson (1995) suggests, then the seismic reflectors interpreted as glacial unconformities should show trough and bank morphology and a pattern of truncation of underlying layers. Otherwise those reflections may represent either pre-glacial or interglacial periods, or multiple reflectors within a single grounding event (e.g. prograding foresets.) Our preliminary examination of the data shows that the lower-most stratal package has a similar seismic facies in strike section to the upper stratal packages. This seismic facies, which consists of sub-parallel reflectors, is interpreted by both studies to be of glacial origin. This observation supports the Bart and Anderson (1995) view of early onset of glacial advances to the outer continental shelf.