Stratigraphic Architecture of the Frontier Formation, Powder River Basin, Wyoming

Abstract

The Cretaceous Frontier Formation in the Powder River Basin of Wyoming, USA contains actively produced unconventional hydrocarbon reservoirs. One facies of interest within the Wall Creek Member of the Frontier Formation consists of thinly interbedded sandstones and shales with varying degrees of bioturbation. Determining potential for new plays is partly dependent on understanding this facies’ sedimentology and architecture. Ten cores have been documented in addition to four full stratigraphic sections and two partial stratigraphic sections measured along a north-south traverse at the western margin of the basin. Comparisons of measured stratigraphic sections reveal that all sections exhibit sequences that grade up from shales, to non-bioturbated thinly interbedded facies, to bioturbated thinly interbedded facies, to a unidirectional cross stratified sandstone facies. Sandstone bodies range in thickness from 20 cm to 26 meters and almost ubiquitously contain cross stratification indicative of unidirectional or channelized flow, implying a southerly paleo-transport direction. Bioturbation via vertical and horizontal burrows of the thinly interbedded facies is common. These preliminary data support the hypothesis that the sequences shown are deltaic in nature. The primary evidence includes the great abundance of unidirectional cross stratification, the amount and nature of the bioturbation, and the ordering of the facies.

AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014