Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name


Department or School/College

Department of Geosciences

Committee Chair

Marc Hendrix

Commitee Members

Michael Hofmann, Christopher Palmer


Sappington, Diagenesis, Bakken, Reservoir Quality


University of Montana


The Late Devonian to Early Mississippian Sappington Formation in southwestern Montana documents the eustatic and tectonic control southern hemisphere glaciation and the emergence of the Antler Orogeny had on sedimentation across western North America. Deposition was limited to a series of basins separated by structural highs where sedimentation was driven by transgressive- regressive cycles. The Sappington Formation was deposited in a portion of the Central Montana Trough, with resulting marine stratigraphy represented by a basal organic rich-shale, a middle dolomitic to calcareous siltstone, and an upper organic-rich shale. Strikingly similar stratigraphy is found across in other basins across western North America, representing deposition influenced by similar tectonic and eustatic forces. This study focuses on understanding the diagenetic history of the Sappington Formation within a sequence stratigraphic and depositional framework to improve the understanding of petroleum reservoir potential and quality of time-equivalent strata regionally.

The diagenetic history of the Sappington Formation depicts a complex sequence of cement formation and mineral dissolution stages. The overall diagenetic sequence is characterized by zoned, planar dolomite rhombs, with variations in magnesium to iron ratios. Other diagenetic stages include quartz, calcite, and clay cement, feldspar and carbonate dissolution, and pyrite formation. Particular focus was placed on the formation of dolomite, as ferroan stages are preferentially dissolved over magnesium stages, creating secondary dissolution porosity.

Timing, presence, and extent of diagenetic events is controlled by the distribution of primary grains, depositional facies, sequence stratigraphic surfaces, and structural lineaments. Integrating the diagenetic history with the primary depositional fabric indicates significant complexity in the distribution of diagenetic minerals throughout the Sappington Formation in the Bridger Range. Utilizing this diagenetic framework in the time-equivalent Bakken Formation may aid in understanding of the diagenetic history of the unit, potentially resulting in development of new exploration and development strategies within the Williston Basin.


© Copyright 2016 Clayton Schultz