ABSTRACT: Yellowknife Geoheritage, emphasizing submarine volcanic eruptions, unique sedimentary deposits, and continental glaciation.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Several basic geological processes responsible for the evolution of Canadian Shield landscapes are exquisitely recorded along the shores of Great Slave Lake near Yellowknife. Of particular note is “The Giant Section”, a site visited for decades by numerous geologists seeking a better understanding of undersea volcanic processes and products. This locality provides a world-famous display of ancient pillow lavas. Not only can the tops of folded sequences be immediately recognized by morphology of the constituent “pillows” (actually sections through lava tubes), but lava flow directions also can be determined on the basis of asymmetric pillow sections and breached selvages (outer margins) of the pillows. Feeder dykes that provided pathways for release of molten lavas are abundant throughout the area. Some volcanic rocks display structures such as fiamme, which document deposition by gas-driven glowing avalanche flows (nuées ardentes) during violent eruptions. The volcanic history recorded in the Giant Section can be readily understood by those with little or no geological training. To draw public attention to some of the many marvelous geological features that can be recognized, a 1:10 scale map of the central part of the Giant Section has been prepared. Using this map, after a brief introduction to geological principles, the public can attain an appreciation of relative ages of different rock units based on their own observations of primary structures, unconformities and crosscutting relationships. The enormity of geological time, the dynamic nature of volcanism, recent glacial history, and sequential episodes of tectonism can all be readily assessed on the basis of features in the Giant Section and nearby exposures. Interbedded and overlying sedimentary strata provide additional clues to allow inferences about depositional environments as well as rates of recent and ancient sedimentary erosion, transport and deposition. Evidence of ice sheets that covered most of Canada during the last Ice Age is well displayed by glacial polish, scours, striae, and erratics plus distinctive landscape forms such as eskers, drumlins, crag-and-tail structures and roches moutonées. Given Yellowknife’s geology-related history, it is appropriate that such a fine example of Canadian geoheritage is so well preserved nearby

Bibliography of Canadian Geomorphology