PALEOECOLOGY OF THE BEARPAW AND CONTIGUOUS UPPER CRETACEOUS FORMATIONS IN THE C.P.O.G. STRATHMORE WELL, SOUTHERN ALBERTA

Abstract

ABSTRACT Foraminifera and megaspores are present through a cored section 1350 to 1760 ft in the C.P.O.G. Strathmore EV Well, which includes in descending order beds from the lower part of the Horseshoe Canyon Formation, a transitional interval, the Bearpaw Formation, and the uppermost part of the Belly River Group. Three distinct types of microfossil assemblages are recognizable: (1) inner-neritic shallow marine, (2) salt-marsh brackish marine, (3) continental. The inner-neritic assemblage, consisting of a mixed agglutinated-calcareous foraminiferal fauna, is characteristic of much of the Bearpaw Formation, but recurs in the overlying Bearpaw - Horseshoe Canyon Formation transitional interval. The salt-marsh assemblage, consisting mainly of thin-walled representatives of the agglutinated foraminiferal genera Miliammina, Ammomarginulina, Trochammina and Verneuilinoides, is recognized at the contact of the Bearpaw and the transitional interval and from two higher levels in the transition. The continental assemblage, characterized in relative abundances of Azolla, Balmeisporites, Molaspora, Costatheca and Spermatites, is prominent in parts of the Belly River Group, transitional interval, and Horseshoe Canyon Formation. All these genera are markedly reduced in the salt-marsh brackish-marine and inner-neritic shallow-marine intervals. Relative abundances of foraminifera and megaspores serve to reveal transgressive and regressive cycles near the western margin of the last widespread marine transgression in the Canadian western interior.