ABSTRACT

Fort Peck Reservation is located on the western margin of the Williston Basin in northeastern Montana. It is made up of a mosaic of lithosphere blocks that have expression on maps made from wireline logs, observations on Landsat images, and seismic data. In general, the blocks bounded by lineament zones step up and out of the Williston Basin westward across the Reservation to Bowdoin dome. An understanding of the tectonic setting and paleotectonic history is important because of possible influences on hydrocarbon exploration and production.

The tectonic setting of Fort Peck Reservation is a hierarchical arrangement of geologic structures. Williston Basin and Bowdoin dome are the largest elements; Poplar dome and Smoke Creek syncline are of intermediate size; and Wolf Creek nose and Wolf Point syncline are the smallest elements. The paleotectonic history of the Reservation also reflects this tectonic hierarchy. The large elements have maintained their structural configuration throughout the Phanerozoic, but the small elements have undergone tectonic reversals. Poplar dome has been long-lived, but Smoke Creek syncline has experienced a reversal.