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The Churchill-Reindeer Rivers Area:
Evolution of its Landscape

by Walter Kupsch

More than ninety percent of the canoeing within Saskatchewan traverses the Churchill River and its environs. It is with this in mind that Professor Walter Kupsch's Churchill River Study, originally printed in "The Muskox" published by the Institute for Northern Studies, is presented.


Summary

The landscape of the Churchill-Reindeer Rivers area has had an ancient and complex history which dates back to early Precambrian times, some 2 billion years ago or more. At that time an ocean existed, with island arcs of volcanoes rising above the waters. The exposed lavas were subjected to weathering and erosion by the interaction between rocks and an oxygen-free atmosphere. Only the most primitive of uni-cellular life existed in these waters. There was no life on land.

Although the evidence for the ocean and its volcanoes can now be seen in the study area, in early Precambrian time that area was likely in another location on the earth's surface. Moreover, Earth was then a planet quite different from what it is today. It revolved around its axis in some 4 rather than 24 hours. Possibly it was of smaller diameter.

For several millions of years internal forces of the Earth, culminating in intensity about 1,735 million years ago, folded, twisted, and broke the volcanic and sedimentary rocks. High pressures and elevated temperatures deep in the Earth's crust changed or metamorphosed these rocks. Intrusive masses, mainly of granitic magma, invaded the folded rocks. When the rock masses gradually rose as mountains above the retreating sea, they were weathered and eroded into a landscape similar to that of the Rocky Mountains today. As levelling proceeded the mountains were worn down to a plain resembling the present surface of low relief that characterizes the peneplain of the Canadian Shield.

On those parts of the plain that slowly subsided, large quantities of sand and gravel were deposited by regionally eastward-flowing streams, which shifted their courses through hundreds of million years of time. Regional uplift then initiated a long period of erosion during which much of the Athabasca Sandstone was removed and the underlying older Precambrian rocks were once more exposed.

When the sea encroached upon this land, in early Paleozoic time, a thin body of sand was first laid down over the Precambrian crystalline rocks. As the sea deepened somewhat, lime and clay muds were deposited. In these seas sponge-like organisms, corals, and other invertebrate animals thrived and the first vertebrates, the fishes, made their appearance. Only toward the end of this time of ocean coverage did plants and animals appear on adjacent lands.

Possibly some time late in the Devonian Period, the northern part of Saskatchewan once again became land and remained so for hundreds of millions of years. Continuing erosion constantly removed any evidence of land deposits along with the fossil plants and animals which they may have contained. A large meteorite, which formed the Deep Bay crater [in Reindeer Lake], is believed to have struck the area some 150 million years ago.

During the Cretaceous almost the whole of Saskatchewan was covered by an ocean which stretched across the province from the south to Hudson Bay and beyond. The sediments then laid down were stripped off the Precambrian basement during the Tertiary Period. The products of weathering and erosion were removed by a north-easterly trending drainage system, of which the ancestral Churchill River was an important part. When the rivers flowed on a surface of Cretaceous rocks of rather homogeneous lithology throughout and without pronounced or abundant structural weaknesses, they occupied normal stream valleys. As the Churchill eroded its way into the underlying Precambrian rocks its stream channel became locally adjusted to the lithology and structure of the varying rock types, although its general course remained transverse to the "grain" of the country.

The Manitoba Escarpment was formed by erosion during the Tertiary and the major streams created large water gaps in the escarpment. Thus before Pleistocene glaciation set in, the Churchill had already acquired its characteristic tripartite division:

  1. a normal stream valley in its upper reaches lying on Cretaceous and Paleozoic rocks that were not stripped by erosion,
  2. a bedrock adjusted middle reach cutting across major structural trends,
  3. and a normal lower reach with minimal local bedrock control in the Paleozoic rocks near Hudson Bay.

The glaciers of Pleistocene time emphasized the "grain" of the country as they flowed over the rocks parallel to the major south-westerly-trending Precambrian structures. They converted the valley of the Churchill on the Shield to a string of lakes connected by short channels by removing the softer, more easily eroded rocks in preference to those more resistant to their erosion.

As the ice retreated northward about 10,000 years ago, water became ponded in front of the glacier, and large lakes formed in which clays were deposited. Following the draining of these lakes, plants invaded the area, permafrost developed, and soils began to form. Man reached the Churchill-Reindeer Rivers area possibly some 8,000 years ago.


Full article- the physiographic divisions, glacial erosion and deposits, and post-glacial events. (80K)
Geological History | Geological Domains | Churchill River Study | Geological Definitions | Gold in the Rocks | Reading list
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