The Nastapoka drift belt, eastern Hudson Bay: implications of a stillstand of the Quebec–Labrador ice margin in the Tyrrell Sea at 8 ka BP

Abstract

During deglaciation of eastern Hudson Bay, the western margin of the Québec–Labrador sector of the Laurentide Ice Sheet came to a stillstand about 8 14C ka BP along the Nastapoka Hills, a series of topographic highs along the bay. These hills are the northward continuation of the eastern Hudson Bay cuesta system. It left a drift belt consisting of ice-contact submarine fans along the western slopes of the hills, small frontal moraines on hilltops, and grounding-line deposits on sills between the hills. Geomorphological, sedimentary, and radiometric evidence suggest that the stillstand responsible for deposition of the Nastapoka drift belt was either entirely or partly synchronous with the deposition of the Sakami moraine farther south. There was a period when these two morainic systems marked a continuous ice margin. These stillstands occurred due to reduction of ablation at the ice margin. In the Nastapoka Hills, ablation slowed down when the ice margin was anchored on higher relief and stood at a regional break of slope that grounded the ice margin and reduced water depth at the ice terminus, therefore, putting an end to intensive calving. In eastern James Bay and southeastern Hudson Bay, stabilization of the ice margin was caused by a reequilibrium of the ice terminus after a rapid drop of water level due to the drainage of Glacial Lake Ojibway. The new data improves the resolution of the position ice margin in eastern Hudson Bay at 8 ka BP.