ABSTRACT: Surficial geology of the Drumheller area, Alberta, Canada

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Abstract

The Drumheller area lies in south-central Alberta about 80 miles northeast of Calgary. The field study was carried out as part of the mapping program of the Geological Survey of Canada. Shales and sandstone ofupper Cretaceous and Paleocene age underlie the area. Elevated plateaux, capped with Late Tertiary gravel derived from the Rocky Mountains, remain from a former Tertiary erosion surface. The gravel is thinner but more extensive than previously supposed. Comparison of this gravel with similar gravel elsewhere on the prairies indicates that it is correlative with the early Pliocene Flaxville gravel. The Pleistocene deposits are divided on the basis of environment of deposition into four major groups that consist of glacial deposits, ice- contact deposits, lacustrine deposits, and fluvial deposits. The glacial deposits are composed of clay till deposited direct1y from glacial ice. The end moraine was formed over widespread areas by processes of ablation and does not represent accumulation of debris at the ice front. Deposition of end moraine was confined to certain elevations by early stagnation at high altitudes within the area. Stagnant ice features composed of tiIl, lacustrine sediments, and gravel occur as flat elevated areas within the end moraine, They were formed in part by deposition of water-transported material in small ice-bound lakes. Ground moraine composed of clay till covers much of the area, but on the Hand Hills the till in the ground moraine contains much Tertiary gravel. Some areas of ground moraine have been reworked by water. The ice-contact deposits are composed of material that was deposited by meltwater in juxtaposition with glacial ice. They consist of outwash, eskers, and kames, and are not extensive. Lacustrine deposits, which consist of sand, silt, and clay, were deposited in glacial-lake basins. Clay and sand are most extensive although some silt is found in the vicinity of Drumheller. The fluvial deposits consist of alluvium deposited in meltwater channels that served to drain both the melting ice and the glacial lakes. The location and shape of these channels is important in the interpretation of the glacial history. A blue till, older than and easily distinguishable from the common clay till, occurs in a few sections along the Red Deer and Rosebud Rivers. It is overlain locally by interglacial sand and clay till, and elsewhere has been contorted by a subsequent glacier. The Pleistocene glaciers did not modify the preglacial topography to any great extent. Flutings and drumlinoid ridges indicate that the last glacier moved southerly to southeasterly.This glacier overrode the whole area. It retreated by northeastward melting of its margin and by local stagnation and melting on high land. The retreating margin blocked norma1 eastward drainage and successively lower lakes were formed as it melted back downslope and lower outlets were opened.

Bibliography of Canadian Geomorphology