Cretaceous Stratigraphy of Vermilion Area, Alberta, Canada

Abstract

Cretaceous sediments are penetrated in wells in the Vermilion area of east-central Alberta to depths of 2,000 to 2,500 feet; they rest unconformably either on Devonian dolomites or on a few feet of green shale possibly Jurassic in age. Only one formation, previously unnamed, is Lower Cretaceous in age. It consists of deltaic and associated sediments which are subdivided for the first time into six local members largely on the basis of presence or absence of dark minerals in the sands, microfossils in the marine shale tongue, and occurrence of coal seams. This association of sediments is comparable with the Recent deposits of the Mississippi Delta region. The lower part of the Upper Cretaceous consists of two rather widespread marine shale formations, together about 1,600 feet thick, the older one with white calcareous specks, the younger one without them. These formations are overlain by fresh- and brackish-water sandy sediments, which thin toward the east and are replaced by interfingering marine shales. The interfingering marine shales and near-shore deposits are exposed in the Vermilion area. Their rapid lateral variations make detailed correlations and surface geology difficult.