Seismic stratigraphy of Palmer Deep: a fault-bounded late Quaternary sediment trap on the inner continental shelf, Antarctic Peninsula Pacific margin

Abstract

The Palmer Deep is an enclosed bathymetric depression on the inner portion of the Antarctic Peninsula continental shelf about 30 km southwest of Anvers Island. Three sub-basins, separated by bathymetric sills, comprise the Palmer Deep: Basin I, Basin II, and Basin III. Deep-tow boomer seismic reflection data reveal thick (>50 m) sediment sections in each basin consisting of Holocene diatomaceous mud. The boomer records proved fine-scale resolution of decimetre thick sediment layers within the uppermost (Holocene) seismic unit. Deeper penetration GI and small airgun records obtained in 1997 provide insight into the structural and depositional history of the basins which extends clearly back in time before the Holocene (unit imaged by the boomer records). The Palmer Deep contains a sediment infill estimated at about 270 m thick arranged 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 shallow stratigraphy with some reflectors common in both records, such as the 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 Glacial 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 Antarctic Peninsula we suggest a subglacial and subaqueous origin for much of the Palmer Deep basin fill. Hence, the Palmer Deep basins were the locus of subglacial `lakes' beneath the ice sheet at times of glacial maximum.