Abstract: Stratigraphic and Geochemical Investigation of Middle to Upper Devonian "Aquitards" in west-central Alberta, Canada

SKILLITER, CATHERINE C., University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, Alberta

The major objective of this study is to provide a regional investigation of the stratigraphy of Devonian shales, marls, and evaporites in the subsurface of west-central Alberta, to determine whether they have been effective aquitards relative to the interbedded carbonate aquifers. Geochemical analyses (⁸⁷Sr/⁸⁶Sr, d¹⁸O, d¹³C) of the aquitards will be used to distinguish "primary" from diagenetically altered lithologies.

The context for this research is based on elevated ⁸⁷Sr/⁸⁶Sr-ratios of late diagenetic, coarse-crystalline calcite and dolomite cements within Devonian carbonates in west-central Alberta. It has been a commonly accepted theory that elevated ⁸⁷Sr/⁸⁶Sr ratios are derived from adjacent shales during diagenesis. However, this theory was based on a very limited database and more recent evidence indicates an exotic source for late diagenetic fluids. A regional analysis of ⁸⁷Sr/⁸⁶Sr ratios of shales will allow an evaluation of their potential influence during diagenesis and regional fluid flow.

Methods involve drill core description, sampling, geochemical analyses, and well log correlation. This study is the first to undertake a regional investigation of the aquitards with respect to diagenetic alteration. The data can be used to predict potential pathways of aqueous fluid migration, which will further the understanding of the extent of hydrocarbon migration in the west-central Alberta Basin, for it is commonly accepted that hydrocarbons tend to follow the same pathways as aqueous fluids.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid