Control of sedimentation by active tectonics, glaciation and contourite-depositing currents in Endurance Basin, South Georgia

Abstract

Endurance Basin is an elongate broadly WNW–ESE trending basin located on the northern margin of the Scotia Sea, adjacent to the southern margin of the South Georgia micro-continent. Bathymetric and TOPAS sub-bottom profile data acquired in 2010 by the British research ship RRS James Clark Ross map this basin and its sedimentology for the first time. Endurance Basin contains a number of sub-basins and a substantial glaciogenic fan. The northern margin of Endurance Basin is formed by a series of steep slopes and intervening troughs. These are interpreted as a left-stepping en echelon array of oblique, strike–slip faults whilst the sub-basins are separated by compressional dip–slip faults. It appears that South Georgia is moving NW with respect to the basin. We interpret five seismic facies from TOPAS data, which are associated with distinct sedimentologies. The most striking units in the basin fill are: substantial contourite drifts located in the NW of the basin and on its southern margin; and two distinct mass transport deposits that pond in the centre of the basin. Combined with the known regional oceanographic setting, the contourites provide evidence of broadly eastward flowing bottom currents, entering the basin from at least two locations. Although landslide scars are present on the steep northern basin margin, the imaged mass transport deposits are interpreted to have been sourced from the glaciogenic fan, located in the SE of the basin, and from a contourite unit located on the basin's southern margin. Sediments from these events are transported at least 40km. The contourite drift sequence is at least 100m thick in the west of the basin and may contain a palaeoenvironmental archive of Antarctic Circumpolar Current (ACC) flow and the climate of South Georgia extending to the Pliocene. Such an archive would allow the reconstruction of ACC flow through the Pleistocene glaciations and provide a means of linking ocean circulation and climate records in the sub-Antarctic Polar Front region.