Abstract

The Laurentide Ice Sheet deposited three tills on Anticosti Island. The oldest, the Rivière à la Patate Till, was formed by southeastward-flowing ice as determined from till fabrics. The till has an estimated age of 85 000 years BP based on the aminoacid racemization of shell fragments in overlying marine sediments. Thus it is probably Early Wisconsinan in age. The Middle Wisconsinan Rivière Jupiter Till and the Late Wisconsinan Île d'Anticosti Till are the result of the southwest-flowing Laurentide ice. The ice flowed without restriction though without accomplishing deep erosion of the bedrock, as indicated by glaciotectonic structures and till fabrics. However, striated blocks and pebbles in the tills reveal that basal shearing occurred. The ice limit in the Gulf of St. Lawrence from about 36 000 years BP onwards was located along the south coast of the island. This was the result of active calving at the margin of the relatively slow moving ice sheet. During retreat of the ice sheet, an ice cap became isolated on the island. It appears to have remained active in the western part of the island, where it formed the Sainte-Marie Moraine on the south, west, and north coasts, but was less active in the eastern part of the island, where a loose, sandy, but rare till (the Sainte-Marie Till) is the only proof of its activity. Deeper water in the eastern end of the Jacques-Cartier Strait, north of the island, accelerated ice calving and thus probably reduced the ice dynamic in the eastern part of the island. The names of tills used here are proposed as formal nomenclature.

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