ABSTRACT

A major paleokarst erosion surface is developed within the middle Proterozoic Elu Basin, northwestern Canada. This paleokarst is named the sub-Kanuyak unconformity and truncates the Parry Bay Formation, a sequence of shallow-marine dolostones that were deposited within a northfacing carbonate platform in a semiarid climate.

The sub-Kanuyak unconformity exhibits up to 90 m of local relief, and also formed under semiarid conditions, when Parry Bay dolostones were subaerially exposed during a relative sea level drop of about 180 m. Caves and various karren developed within the meteoric vadose and phreatic zones. Their geometry, size and orientation were largely controlled by northwest- and northeast-trending antecedent joints, bedding, and lithology. Near-surface caves later collapsed, forming valleys and intervening towers or walls, and plains. Minor terra rossa formed on top of highs. Karstification was most pronounced in southern parts of Bathurst Inlet decreasing northward, probably reflecting varying lengths of exposure time along a north-dipping slope.

The Kanuyak Formation is up to 65 m thick, and partially covers the underlying paleokarst. It consists of six lithofacies: 1) breccia, formed during collapse of caves, as reworked collpase breccia and regolith; 2) conglomerate, representing gravel-dominated braided-fluvial deposits; 3) sandstone, deposited as braided-fluvial, and storm-dominated lacustrine deposits; (4) interbedded sandstone, siltstone and mudstone representing sheet flood deposits; 5) dolostones, comprising calcretes, and quiet-water lacustrine deposits; and 6) red-beds, representing intertidal-marine mud flat deposits. Rivers flowed toward the northwest and northeast within karst valleys and caves; lakes were also situated within valleys; and marine mud flat sediments completely cover the paleokarst to the north.

A regional correlation of the sub-Kanuyak unconformity with the intra-Greenhorn Lakes disconformity within the Coppermine homocline suggests that similar styles of karstification occurred over an extensive region. The Elu Basin paleokarst, however, developed more landward, and was exposed longer than the Coppermine homocline paleokarst.

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