Sequence Stratigraphy, Depositional Environments, and Regional Mapping of the Late Devonian Interval, Upper Three Forks Formation, Sanish Member, and Lower Bakken Shale, U.S. Portion of the Williston Basin
Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
Timothy R. Carr
Cores of the Late Devonian upper Three Forks, Sanish, and lower Bakken units from eight wells were examined and described at the North Dakota core depository. Core descriptions, wireline log correlation and mapping, and X-ray diffraction (XRD) data were integrated to recognize seven facies: The Three Forks D and the (600-900API) lower Bakken Shale, four facies belonging to the Sanish, and a basal siltstone facies assigned to the Lower Bakken. Facies identified were then grouped into separate systems tracts based on the identification of several significant sequence stratigraphic surfaces.;The four facies identified in the Sanish include: Facies A, a dolomitic and Skolithos burrowed sandstone with a hard-ground at the base as originally defined in the Antelope Field; the widely distributed Facies B, a dolomitic siltstone characterized by burrows of the Cruziana ichnofacies with periodic silty dolostone event beds (interpreted as of storm origin); Facies C, an argillaceous siltstone containing Planolites burrows; and Facies D, a fossiliferous wackestone to packstone resting above an interpreted maximum flooding surface (MFS) characterized by Glossifungities. A silty shale to siltstone assigned to the Bakken Formation with a total organic carbon (TOC) averaging 8.2% and a gamma ray reading of approximately 130 to 170 API was identified in cores and logs and was interpreted as the first phase of a transgression, showing the progression toward a stratified water column and accumulation of the Lower Bakken organicrich shale.;The Sanish Facies A,B, and C are grouped into the transgressive systems tract (TST) of the Sanish, Facies C&D overlying the maximum flooding surface (MFS) composes the highstand systems tract (HST) with a depositional hiatus resulting in a corrosion surface (phosphatic pebble lag) capping off the sequence. The lower Bakken is considered its own depositional sequence with the Basal Bakken as the LST, the bottom half of the lower Bakken Shale (up to the highest gamma ray) as the TST, and from the highest gamma ray to the sequence boundary between the lower and middle Bakken as the HST.
Sesack, Steven A., "Sequence Stratigraphy, Depositional Environments, and Regional Mapping of the Late Devonian Interval, Upper Three Forks Formation, Sanish Member, and Lower Bakken Shale, U.S. Portion of the Williston Basin" (2011). Graduate Theses, Dissertations, and Problem Reports. 632.