A SEISMO-STRATIGRAPHIC ANALYSIS OF GLACIOMARINE DEPOSITS IN THE EASTERN RIISER-LARSEN SEA (ANTARCTICA)

Abstract

Multichannel seismic data from the eastern parts of the Riiser-Larsen Sea have been analyzed with a sequence stratigraphic approach. The data set covers a wide bathymetric range from the lower continental slope to the abyssal plain. Four different sequences (termed RLS-A to RLS-D, from deepest to shallowest) are recognized within the sedimentary section. The RLS-A sequence encompasses the inferred pre-glacial part of the deposits. Initial phases of ice sheet arrival at the eastern Riiser-Larsen Sea margin resulted in the deposition of multiple debris flow units and/or slumps on the upper part of the continental rise (RLS-B). The nature and distribution of these deposits indicate sediment supply from a line or a multi-point source. The subsequent stage of downslope sediment transport activity was dominated by turbidity currents, depositing mainly as distal turbidite sheets on the lower rise/abyssal plain (RLS-C). We attribute this to margin progradation and/or a more focussed sediment delivery to the continental shelf edge. As the accommodation space on the lower rise/abyssal plain declined and the base level was raised, the turbidite channels started to backstep and develop large channel–levee complexes on the upper parts of the continental rise (RLS-D). The deposition of various drift deposits on the lower rise/abyssal plain and along the western margin of the Gunnerus Ridge indicates that the RLS-D sequence is also associated with increased activity of contour currents. The drift deposits overlie a distinct regional unconformity which is considered to reflect a major paleoceanographic event, probably related to a Middle Miocene intensification of the Antarctic Circumpolar Current.