ABSTRACT

During the initial southerly advance of the Lower Albian Clearwater Sea into the area of northeast Alberta, littoral sandstones were deposited along the flanks of Paleozoic ridges (Red Earth Highlands and Wainwright Ridge) while an extensive, shale-dominated succession was deposited basinward. These sediments make up the Wabiskaw Member, which averages 15 to 20 m in thickness. Regional correlations of the Wabiskaw, based on about 1300 well logs and 30 cores, are facilitated by a distinctive transgressive sand at the base and a widespread 2 to 3 m thick bentonite bed higher up. The Wabiskaw Member was deposited over an earlier, broad coastal plain incised by a major northward-flowing drainage system, controlled by salt dissolution along the Middle Devonian Prairie Evaporite salt scarp. Well beyond the ridges, out into the basin, a wedge-shaped sand was deposited in the Primrose area. Here, the sand may reach thicknesses of up to 39 m as it infills the underlying fluvial topography, although the basal transgressive sand is missing in these areas.

The Wabiskaw sand of the Primrose area may have been deposited in two stages. Following the initial flooding, the shoreline readvanced northward into the Primrose area while a deltaic system began to form in deeper embayments attributed to the drowned fluvial topography of the McMurray surface. Ensuing sea level rise led to the widespread deposition of marine shale and may have cut the delta system from its source. During the subsequent sea level fall, fluvial systems incised into the marine shales and reactivated deposition over the drowned Wabiskaw delta.

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