Abstract:
Prydz Bay, located at the mouth of the Lambert Glacier-Amery Ice shelf system that now drains nearly 20% of the East Antarctic Ice Sheet, contains a sediment record of earliest Cenozoic Antarctic glaciation. We present a new seismic reflection profile that crosses two of five shelf sites, drilled by Ocean Drilling Program Legs 119 and 188. Together Site 742 (Leg 119) and Site 1166 (Leg 188) record the pre-glacial to glacial transition during the early Cenozoic. Downhole logs and geologic core data are integrated with seismic data to illustrate the character of the transition from pre-glacial, predominantly non-marine lacustrine and alluvial fan deposits, to early glacial shallow marine sections (late Eocene to early Oligocene age) that were buried in late Neogene time by subglacial and proximal glaciomarine diamictons. Pre-glacial sections have layered reflections overlain by a discontinuous and chaotic unit that we infer to be fan and channel/bank deposits with massive sands. Early glacial marine strata have strong layered reflections that fill channels and cover banks. Above these strata, a regional unconformity (Oligocene/Pliocene age) is marked by a strong continuous reflection, abrupt shifts in downhole log values, and lithologic change to massive diamictites with chaotic internal reflections. This regional unconformity is overlain by discontinuously layered sections of marine diamictons. Thin diatom bearing units with similar biostratigraphy (Pliocene age) and downhole log signatures are observed at Sites 742 and 1166. Our new seismic data show that these units are not continuous between the sites, as previously believed. Seismic data presented here provide a new regional subsurface image of earliest (and latest) Cenozoic glaciation in Prydz Bay.