Flow dynamics and till genesis associated with a marine-based Antarctic palaeo-ice stream

Geophysical and geological data indicate that during the last glacial cycle a palaeo-ice stream drained the Antarctic Peninsula Ice Sheet (APIS) through Marguerite Bay to the edge of the continental shelf via a bathymetric trough (Marguerite Trough). Mega-scale glacial lineations (MSGL) in outer Marguerite Trough are formed in an acoustically transparent sediment unit, consisting of a soft deformation till. The association of MSGL with deformation till indicates that bed deformation occurred beneath the ice stream, and the thickness of the subglacial deforming layer was on the order of several metres. MSGL within outer Marguerite Trough are related to a pre-existing thick sequence of soft sediments on the outer shelf and are inferred to have formed by a combination of subglacial sediment deformation by attenuation from a point source and groove-ploughing. Morphologically, the MSGL differ in several respects from those documented elsewhere and this variation suggests a polygenetic origin for this subglacial landform. An initial advance of the APIS across the Marguerite Bay continental shelf at the LGM deposited a stiff subglacial till. Following this advance, the ice margin within Marguerite Trough retreated 70–100 km before stabilising and depositing a grounding zone wedge. An ice stream then developed in the trough and extended to the shelf edge forming a soft deformation till. Development of the ice stream may have been a glacio-dynamic response to regional deglaciation. Subsequent retreat of the Marguerite Trough ice stream was underway by 13,490 (uncorrected) 14C years before present. Based on the geophysical and core data, ice-stream retreat appears to have been rapid and it contrasts with reconstructions of palaeo-ice streams from other locations in Antarctica. This implies marked regional variations in Antarctic ice-stream dynamics during Late Quaternary deglaciation.

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