Reinterpretation of the Upper Devonian-Lower Mississippian Bakken Formation of Subsurface Saskatchewan: Integrating Sedimentologic and Ichnologic Data Within a Sequence Stratigraphic Framework
Solange S. Angulo1, Luis Buatois1, and Steve Halabura2
1University of Saskatchewan, Department of Geological Sciences, Saskatoon, Canada; [email protected]; [email protected]
2North Rim Exploration Ltd., Suite 210, 3502 Taylor Street, Saskatoon, Canada; [email protected]
Important recent oil discoveries in North Dakota and Saskatchewan have focused attention on the Late Devonian to Early Mississippian Bakken Formation. The U.S. Geological Survey has reported that there is possibly 400 billion barrels of oil in the Bakken play. The area in southeastern Saskatchewan is estimated to hold up hold up to 25 billion barrels of oil. This unit is subdivided into three members: the lower and upper members (shelf black shale) and the sandy-silty middle member, which has been interpreted previously as open-marine deposits (offshore to shoreface). Based on core analysis, a new interpretation for the middle member is proposed. An open-marine progradational parasequence is interpreted from the lower member to the lower interval of the middle member, including, from base to top, shelf, lower- to upper-offshore, offshore-transition, and lower-shoreface deposits. With the exception of the anoxic to dysaerobic black shale, these open-marine deposits are intensely bioturbated, containing Phycosiphon incertum, Nereites missouriensis, Planolites montanus, Asterosoma isp., Chondrites isp., and Teichichnus rectus. Above this succession, an abrupt decrease in bioturbation index, the small size of trace fossils, low ichnodiversity, syneresis cracks, and mud drapes reveal tidal influence and brackish-water conditions in estuarine environments. Finally, a transgressive lag is recorded and open-marine conditions are re-established with deposition in upper offshore and shelf environments of the upper member. Integration of sedimentologic and ichnologic data within a sequence-stratigraphic framework is essential to provide a more robust depositional model for the Bakken Formation.
AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid