The biostratigraphy of the Bakken Formation: A review and new data

New paleontologic data from the Bakken Formation in the Williston Basin of North Dakota are described, with an updated synthesis of previous biostratigraphic studies done in the basin. By combining the new data with the previously published data, a revised biostratigraphic framework is established for the Bakken Formation. Conodont data suggests that the Lower Bakken Member is late Famennian in age, ranging from the Pseudopolygnathus granulosus Zone to the Bispathodus ultimus Zone, and possibly to the early Tournaisian Protognathodus kockeli Zone. Upper Bakken conodont data shows that the unit is entirely Tournaisian in age and may range from the Siphonodella duplicata Zone to the Siphonodella quadruplicata Zone. Although no conodont data was analyzed from the Middle Bakken, the age constraints provided by the Upper and Lower Bakken suggest that the earliest Tournaisian conodont Zones, and potentially the historical Devonian-Carboniferous Boundary interval are in this unit. Palynologic data from the Middle Bakken indicates that the historical Devonian-Carboniferous Boundary should be placed at the unconformable contact between the lower Middle Bakken (Middle Bakken 1) and the upper Middle Bakken (Middle Bakken 2) based on the highest stratigraphic occurrence of Retispora lepidophyta. Combining the biostratigraphic data with detailed core description and x-ray fluorescence (XRF) chemostratigraphy, several stratigraphic units can be identified within each member of the Bakken. These units can be mapped regionally throughout the Williston Basin, thus improving our understanding of the spatial distribution of the different source and reservoir rock intervals within the Williston Basin oil play.