Palynological interpretation of frontier environments in central Wyoming

Abstract

Correlation of 15 Frontier Formation surface sections and 3 wells extending from central Wyoming to southern Montana is shown on four cross sections. The basis for correlation is the first occurrence of Deflandrea (Rigaudia) sp. cf. D. acuminata, along with four dinoflagellate cyst species present in the Lower Cretaceous, but which became extinct in the lower part of the Frontier. These four species are Diconodinium caulleryi, Ascodinium, cf. A. verrucosoum, Dinoflagellate A, and Coniferatium frontierensis gen. et sp. nov. The first occurrence of Dinogymnium heterocostatum near the base of the overlying Cody Formation parallels the Deflandrea datum and enforces postulated time‐stratigraphic relationships. The mean Frontier shoreline during any 100‐foot time rock interval is located by constructing six 100‐foot slice maps, and identifying the aggregate continental thickness based on palynomorph or micro‐plankton recovery. Interpretation of each 100‐foot interval reveals areas of maximum and minimum sedimentation suggesting delta building and subsequent destruction.