ENTRAINMENT OF GLACIOMARINE SEDIMENTS AND FORMATION OF THRUST-BLOCK MORAINES AT THE MARGIN OF SORSDALE GLACIER, EAST ANTARCTICA

The morphology, sedimentology and structure of moraines at the margin of an outlet glacier in east Antarctica are described, and contemporar y depositional processes in a marine inlet adjacent to the ice margin are examined. Results indicate that the principal moraines are thrust- block moraines produced by basal freezing and deformation of glaciomar ine sediment as the outlet glacier expands into a marine inlet. Preser vation of detailed glaciomarine sedimentary structures and beds of mar ine shells suggests that the sediment was frozen during entrainment, t ransportation and deposition. The presence of low-angle faults in the moraines show that the moraines consist of an en echelon arrangement o f thrust plates. The sedimentology, structure, thickness of the thrust plates, and inferred entrainment processes are consistent with Weertm an's ice-debris accretion hypothesis for debris entrainment at the edg e of cold ice sheets. A model of thrust-block moraine development prod uced by this study provides a framework for the interpretation of radi ocarbon dates from marine macrofossils in the moraines. The model may also be useful in the interpretation of similar moraines in coastal ea st Antarctic eases and other polar marginal marine environments. (C) 1 997 by John Wiley & Sons, Ltd.