Stratigraphy, paleoecology, and glacial history of the Gillam area, Manitoba

Abstract

Sections along the Nelson River in northern Manitoba, outcropping upstream and downstream from Limestone Dam, record a long succession of late Quaternary events. The oldest sediment exposed consists of sandy, nonfossiliferous Sundance till of northwestern provenance and related to a Kansan or Illinoian glaciation. The paleosol developed in the Sundance till is assigned to the Yarmouthian or Sangamon interglacial on its stratigraphic position and depth of weathering. Fossiliferous, clayey Amery till of eastern provenance overlies the Sundance till and underlies the nonglacial Nelson River sediments. Aspartic acid D/L ratios of wood fragments from the Nelson River sediments correlate with an aspartic acid D/L ratio of similar wood from the Missinaibi Formation in Ontario. Beetle analysis indicates the Nelson River sediments were deposited north of the tree line under conditions more severe than those found in the area today. The deposits are believed to be of latest Sangamon or possibly Mid-Wisconsinan age. The Wisconsinan Stage is represented by the Long Spruce and Sky Pilot tills deposited by ice from the east. These tills are texturally and compositionally similar but are different colours. The overlying Henday sediments record glaciofiuvial deposition and mass wasting along the eastward retreating ice margin. Varves indicate the area was covered by glacial Lake Agassiz for less than 100 years after the ice retreated. The breakup of the Laurentide Ice Sheet in Hudson Bay and the final drainage of Lake Agassiz took place 7800–8000 years ago when the Hudson Bay Lowland was inundated by the marine water of the Tyrrell Sea. The area emerged from the Tyrrell Sea about 6500 years BP.