Abstract

The Piney Creek Thrust block is a prominent surface structural feature located on the east flank of the Bighorn Mountain, approximately 30 kilometers (18 miles) northwest of Buffalo, Wyoming.

Beginning in 1941, two years prior to the founding of the Wyoming Geological Society, the results of field investigations of Phanerozoic structure and stratigraphy associated with the thrust block led to the following conclusions: the Piney Creek thrust is a secondary structural feature formed distinctly later than the primary uplift and deformation of the mountain range and that both episodes of deformation are the result of horizontal compression. Later, detailed field work in Precambrian terrane substantiated both conclusions.

Within the past 15 years, considerable controversy has emerged concerning both the forces (vertical uplift us. horizontal compression) responsible for the Piney Creek thrust fault and the fundamental nature of the thrust itself (marginal structural feature or a deep-rooted thrust). Some of the controversy is based on concepts and structural models derived from other areas of the Wyoming foreland province. However, most of the controversy is generated by a partial or total disregard of critical structural relationships determined by surface geology, including: the structural style of the east-central Bighorn Mountains; the geometry of the bounding strike-slip faults of the Piney Creek thrust; the structural significance of Tertiary conglomerates; and critical information from the Precambrian rocks.

After critical review of each interpretation, it is concluded that: (1) the Piney Creek thrust is a secondary flank structure formed by stresses that result from continued horizontal compression and (2) below the thrust block, both the flank trap and the anticlinal structure represent worthwhile exploration objectives.