Depositional patterns of the upper Devonian Waterways Formation, Swan Hills area, Alberta

Abstract

ABSTRACT The Waterways Formation is comprised of deeper-water sediments which envelop the Swan Hills Formation, an early Upper Devonian reef complex, in west-central Alberta. The interbedded shales and limestones of the formation range in thickness from less than 20 ft in the area of maximum reef development in the Swan Hills fields to more than 750 ft in the central portion of the basin eastward from the area of study. On the basis of electric-log correlations, the Waterways Formation was divided into eight major units (Units I-VIII). Isopach maps constructed from an overlying datum to the upper surface of each unit illustrate the depositional topography on which each subsequent unit was deposited. Stratigraphic cross-sections constructed perpendicular to regional strike illustrate a prograding type of basinfill process compatible with the Rich (1951) model. Sediments of the Waterways Formation in the Swan Hills area appear: (1) to have been transported from an eastern source area; (2) to have been deposited below wave base in an intermediate- to deep-water environment; and (3) to be significantly younger than the reef complex comprising the Swan Hills Formation. The lack of apparent shallow-water sediments or erosional surfaces suggests "starved basin" conditions in the area at the time of reef development, and supports the suggestion that the cessation of reef growth was due to "drowning" rather than subaerial erosion.