Sediments containing fossils and organic material occur within Pleistocene deposits underlying multiple tills in the Duck Mountain and Riding Mountain Uplands of southwestern Manitoba. Pollen, ostracods, and mollusks within the sediments on Duck Mountain indicate a cool–warm–cool climatic sequence, which began more than 37 760 years B.P. Bones of a ground squirrel (Citellus) and vole (Microtus) were recovered from an intertill silt on Riding Mountain. Grass associated with the bones was dated as more than 31 300 radiocarbon years B.P.The sediments may be correlative with some of the beds of the recently redefined Port Talbot interstade in the Lake Erie region, though it is inferred they are older and correlative either with an early Wisconsin interstade or with the Sangamon interglacial in the mid-western United States.

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