Abstract

Abstract: Recent disintegration of a number of Antarctic Peninsula ice shelves has given us a unique opportunity to investigate sub-ice-shelf sediments. We characterize three sediment facies associations of two Antarctic Peninsula ice shelves (Larsen-A and Larsen Inlet). Subglacial facies consist mainly of basal till (diamicton) with high shear strengths deposited under a grounded ice sheet. Progressive upward decrease in shear strength reflects a gradual decrease in the confining vertical effective pressure of grounded ice during till deposition. Proximal ice-shelf glacimarine facies (diamicton, gravel-rich and sand-rich facies, gravelly mud, dropstone mud and sandy muds) were deposited by sub-ice-shelf rain out, bottom current activity and sediment gravity flows following decoupling of grounded ice from the sea-floor. Distal, ice-shelf glacimarine and/or open marinefacies comprise terrigenous and diatom-bearing bioturbated muds and gravelly muds that contain limited ice-rafted debris; these accumulated after recession of the grounding line to the coast, with coarse-grained surface sediments possibly documenting most recent ice-shelf break-up. Antarctic Peninsula ice-shelf sediments are more heterogeneous than ice-shelf facies deposited elsewhere in Antarctica. Cold, polar Antarctic ice shelves can be differentiated from temperate and sub-polar marine-terminated glacial sedimentary systems by the dominance of coarse-grained proximal, ice-shelf glacimarine facies and an absence of subaqueous outwash/meltwater sediment facies.

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