Depositional models for moraine formation in East Antarctic coastal oases

Abstract

AbstractThis paper examines the origin of moraine ridges in East Antarctic coastal oases and derives depositional models appropriate for the reconstruction of Quaternary history. On the basis of morphology, structure and sedimentology, four principal types of ridge may be identified: (1) type A moraines from when the basal debris zone crops out near an ice margin; (2) type B moraines form when large recumbent folds develop in the basal debris zone; (3) type C moraines are ice-contact screes and fans which form when debris accumulates at steep or cliffed ice margins; and (4) type D moraines are thrust-block moraines that form when unconsolidated sediment is entrained by freezing, shearing and thrusting 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 ice margins. Type D moraines are structural features that may form relatively quickly when ice margins override unconsolidated sediment. Constructing models to explain the origin of the moraines is an important part of reconstructing the Quaternary history of Antarctic coastal oases, because the models provide a basis for reconstructing the position and behaviour of the ice sheet during advance and retreat