Lithologic Heterogeneity of the Wall Creek Member of the Frontier Formation in the Tisdale Anticline, Northeastern Wyoming

Abstract

The Powder River Basin is a prolific hydrocarbon province in NE Wyoming and SE Montana, USA. In the wake of advanced hydrocarbon recovery technologies, many previously tight rocks are becoming highly productive reservoirs, including the upper Cretaceous Frontier Formation. The Frontier Formation in the western Powder River Basin is separated into three members, the lower Belle Fourche member, the middle Emigrant Gap member, and the upper Wall Creek member. A 30 mile outcrop belt of the Wall Creek member rims the eastern flank of the Tisdale Anticline, southwest of Kaycee, Wyoming, and is the focus of this study. We present results from detailed facies analysis of 23 measured stratigraphic sections through the Wall Creek member in the Tisdale Anticline. In the study area the Wall Creek member is composed of a wide range of lithologies ranging from mudstone to sandstones and local conglomerates and bentonites. The basal unit of the Wall Creek member is generally composed of silty, bioturbated, mudstone with interbedded lenticular sandstones. Local ammonites, coal drapes, and septarian concretion horizons can be found in this facies. In some sections this facies is bioturbated, mainly exhibiting Planolites burrows. This lower interval is capped by a very-fine to fine grained sandstone along a sharp contact, which is present almost everywhere in the study area. Mud partings and rip-up clasts are abundant in this sandstone facies and bioturbation is common locally. Burrows include Skolithos, Diplocraterion, Thalassinoides, Palaeophycus and occasionally Ophiomorpha and Macaronichnus. Where not destroyed by bioturbation, sedimentary structures include planar lamination, hummocky cross stratification and planar cross beds with reactivation surfaces. The youngest sediments in the Wall Creek member are fine-grained sandstones with abundant trough cross beds and local lenses of medium-grained sandstone. Bioturbation in this facies is rare or completely absent. This complex facies assemblage observed in the Wall Creek member suggests deposition occurred in a tidally influenced, wave dominated delta in an overall low accommodation setting in the western Cretaceous Seaway. The results of our outcrop study provide new insights into the facies heterogeneity and stratigraphic architecture observed in the Wall Creek Member of the Frontier Formation in the western Powder River Basin.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015