SEDIMENTOLOGY OF THE PERMIAN RADOK CONGLOMERATE IN THE BEAVER LAKE AREA OF MACROBERTSON LAND, EAST ANTARCTICA

The mid- to Upper Permian Radok Conglomerate, the lowermost formation of the Permo-Triassic Amery Group, crops out in the Beaver Lake area o f the northern Prince Charles Mountains, East Antarctica. Outcrop is c onfined to a north-south elongate, fault-bounded corridor interpreted as a remnant of a continental extensional basin formed during Late Pal aeozoic times. This basin forms a small part of the much larger Lamber t Graben, a major continental rift system. The Radok Conglomerate cons ists of interbedded conglomerates, argillaceous sandstones, siltstones , and minor, thin carbonaceous siltstones and coals. Textural, petrogr aphic, palaeocurrent and other data suggest local derivation from Prec ambrian massifs to the immediate west, during a period of fault activi ty. The unit is a minimum of 400 m thick, the base being unexposed, an d grossly fines upward. It is abruptly overlain by quartzo-feldspathic sandstone-dominated rocks of the Upper Permian Bainmedart Coal Measur es. Seven recurrent lithofacies have been recognized with the Radok Co nglomerate, and are interpreted as the products of poorly-confined str eam flow, sheet how and sediment gravity flow processes, suspension fa llout in shallow standing water, and organic sediment accumulation in peat-forming wetlands. The unit as a whole is interpreted as having ac cumulated as a coarse alluvial apron along the western margin of a ?gr aben extensional trough. Similar, though poorly exposed, facies are ex posed on the eastern margin of the basin and may reflect similar depos itional systems. Towards the top of the Radok Conglomerate, typical Ra dok lithologies are interbedded with quartzo-feldspathic sandstones de rived from the south, precursors of the overlying Bainmedart Coal Meas ures. Interference between transverse (Radok) and axial (Bainmedart) d rainage is possibly related to progressive infilling of extensional to pography, thereby allowing axially flowing rivers to avulse increasing ly into the Beaver Lake region from the main Lambert Graben.