SEISMIC STRATIGRAPHY OF PALMER-DEEP - A FAULT-BOUNDED LATE QUATERNARYSEDIMENT TRAP ON THE INNER CONTINENTAL-SHELF, ANTARCTIC PENINSULA PACIFIC MARGIN

The Palmer Deep is an enclosed bathymetric depression on the inner por tion of the Antarctic Peninsula continental shelf about 30 km southwes t of Anvers Island. Three sub-basins, separated by bathymetric sills, comprise the Palmer Deep: Basin I, Basin II, and Basin III. Deep-tow b oomer seismic reflection data reveal thick (>50 m) sediment sections i n each basin consisting of Holocene diatomaceous mud. The boomer recor ds proved fine-scale resolution of decimetre thick sediment layers wit hin the uppermost (Holocene) seismic unit. Deeper penetration GI and s mall airgun records obtained in 1997 provide insight into the structur al and depositional history of the basins which extends clearly back i n time before the Holocene (unit imaged by the boomer records). The Pa lmer Deep contains a sediment infill estimated at about 270 m thick ar ranged in a complex (five unit) internal stratigraphy unusual for the inner continental shelf of Antarctica. Combined use of the boomer and airgun sources allows complementary resolution of both deep and shallo w stratigraphy with some reflectors common in both records, such as th e Middle Basin Reflector at 45 ms twt below seafloor. The Middle Basin Reflector most likely is of latest Pleistocene age (isotopic Stage 2) and therefore 80% of the basin fill pre-dates the classic Last Glacia l Maximum. The Palmer Deep is bounded by active extensional faults as evidenced by offset and stratigraphic growth within Holocene sections. To accommodate shelf-wide glaciation on the Pacific margin of the Ant arctic Peninsula we suggest a subglacial and subaqueous origin for muc h of the Palmer Deep basin fill. Hence, the Palmer Deep basins were th e locus of subglacial 'lakes' beneath the ice sheet at times of glacia l maximum. (C) 1998 Elsevier Science B.V. All rights reserved.