Depositional facies and detrital composition of the Paleoproterozoic Et-Then Group, N.W.T., Canada: sedimentary response to intracratonic indentation

Abstract

Paleoproterozoic intracratonic compression across the Slave Province resulted in eastward indentation of the wedge-shaped Slave craton into the Thelon orogen. Indentation was accommodated by shortening and crustal thickening at the apex of the Slave wedge, bounded to the south by the right-lateral McDonald fault and to the north by the left-lateral Bathurst fault. The Paleoproterozoic, nonmarine Et-Then Group in the East Arm of Great Slave Lake records the history of this indentation. The Et-Then Group consists of two formations. The older Murky Formation is an alluvial-fan conglomerate deposited unconformably over older Paleoproterozoic sedimentary and igneous rocks and Archean metamorphic and igneous rocks. Clast composition indicates that the Murky Formation was derived from these older rocks, eroded during initial translation and uplift on the McDonald fault system. The younger Preble Formation conformably overlies the Murky Formation and is a braided fluvial sandstone. The modal framework composition indicates a granitoid source. On the basis of west-southwest paleocurrrents, modal composition, and depositional style, the Preble Formation is interpreted to be derived from the apex of the Slave wedge. Isostatic uplift at the apex of the Slave craton, due to crustal thickening, provided sufficient amounts of sediment to effectively bury local relief in the East Arm and change the depositional style from one of locally derived alluvial fans (Murky style) to a westward-sloping, regionally extensive braid plain (Preble style).