Seismic morphology and distribution of inferred glaciomarine deposits along the East Antarctic continental margin, 20°E–60°E

Abstract

Seismic-reflection profiles from the continental rise and abyssal plain along a nearly 2000-km long stretch of the East Antarctic margin have been studied, including the Cosmonaut Sea basin and adjacent parts of the Riiser-Larsen Sea to the west and the Cooperation Sea to the east. The recognition of glaciomarine deposits is based on their correlative basal reflector and acoustic characteristics. The lateral distribution of seismostratigraphic sediment thickness, internal architecture of reflectors and seafloor morphology reveal a number of deep-water depocentres with large paleo-channels. These main depocentres correspond to the coastal outlets of present-day ice streams and hence indicate longer-term stabilities in the ice-stream positions during the Neogene advance and retreat phases of the Antarctic Ice Sheet. Scattered paleo-channels and subordinate depocentres in the Cosmonaut Sea suggest that some of the ice streams might occasionally change their position or that also other ice streams were episodically involved during earlier glacial maxima. Several paleo-channels are > 30 km wide and > 500 m deep, the largest one being approximately 40 km wide and 1000 m deep. These channels show evidence of multiple incisions and have prominent, multi-storey levees. The giant conduits are considered to be formed through several extensive phases of mass wasting from the shelf edge and upper slope to the continental rise and adjoining abyssal plain. Downslope transport by sediment gravity flows predominates with a subordinate role of along-slope sediment drift by circumpolar contour current. The repetitive advances and retreats of the ice sheet and recharging of ice streams with terrigenous detritus allowed enormous amounts of glacigenic sediment to be transferred from the Antarctic interior to the shelf margin during glacial phases. It was probably a high rate of localized sediment supply by ice streams and a wide range of sediment grain sizes that promoted the long series of large and highly efficient turbidity currents. The study demonstrates that a seismostratigraphic mapping of deep-water depocentres and recognition of paleo-channels along a glaciated continental margin may provide important information on the long-term ice-sheet dynamics, particularly on the pattern of ice drainage represented by coastal ice streams.