DEPOSITIONAL MODELS FOR MORAINE FORMATION IN EAST ANTARCTIC COASTAL OASES

This paper examines the origin of moraine ridges in East Antarctic coa stal eases and derives depositional models appropriate for the reconst ruction of Quaternary history. On the basis of morphology, structure a nd sedimentology, four principal types of ridge may be identified: (1) type,A moraines form when the basal debris zone crops out near an ice margin; (2) type B moraines form when large recumbent folds develop i n the basal debris zone; (3) type C moraines are ice-contact screes an d fans which form when debris accumulates at steep or cliffed ice marg ins; and (4) type D moraines are thrust-block moraines that form when unconsolidated sediment is entrained by freezing, shearing and thrusti ng of sediment blocks at the base of the glacier. Simple calculations of the rate of debris accumulation at ice margins suggest that type A, B and C moraines take thousands of years to form and record stable ic e margins. Type D moraines are structural features that may form relat ively quickly when ice margins override unconsolidated sediment. Const ructing models to explain the origin of the moraines is an important p art of reconstructing the Quaternary history of Antarctic coastal ease s, because the models provide a basis for reconstructing the position and behaviour of the ice sheet during advance and retreat.