Late Quaternary glacial marine to marine sedimentation in the Pennell Trough (Ross Sea, Antarctica)

Abstract

Late Pleistocene and Holocene palaeoenvironmental changes were studied in four gravity cores up to 7.8 m long from the Pennell Trough, a NW–SE-trending basin 160 km long and 60 km wide in the central Ross Sea, Antarctica, with depths occasionally greater than 600 m. Differences in environments and depositional processes during the last glacial and postglacial epochs were investigated using X-rays and volume magnetic susceptibility (VMS). Further analyses included bulk and clay mineral composition, micropalaeontological studies (both benthic and planktic foraminifera) and radiometric dating. We compare our sedimentological, geochemical (organic carbon and nitrogen content), and geotechnical (shear strength and water content) results to those on cores previously taken from the region. These analyses suggest that prior to the Last Glacial Maximum (LGM), a glacial marine diamicton (< 37,000 yr BP uncorrected age) was deposited across the basin from beneath an expanded Ross ice shelf that was grounded on the basin flanks. Sediment gravity flow deposits (27,000–21,000 yr BP uncorrected ages) that overlie the diamicton in the deepest part of the southernmost area of the basin are interpreted to have been deposited during the Last Glacial Maximum (∼18,000 yr BP) as remobilized subglacial diamicton from the flanks of the basin, initiated by the movement of grounded ice. These sediments are followed by a period of non-deposition caused by basin starvation after retreat of the grounding line of Ross Sea ice far to the south. As a consequence, terrigenous supply was limited, and the persistence of floating shelf ice followed by multi-year sea-ice coverage inhibited the biogenic activity. During the Holocene, as climate became warmer, summer open-sea conditions began to dominate, leading to the deposition of a thin diatomaceous mud/ooze draping the basin.