Tectonic Evaluation of Big Horn Basin Using Landsat Imagery--Implications of Structural Style and Hydrocarbon Exploration

Ira S. Merin, John R. Everett

Landsat imagery reveals that the Big Horn basin can be divided into three regions. This aids understanding the kinematic history and defining exploration fairways and leads. Linear northwest-trending folds southwest of the Bighorn Mountains characterize the northeast portion of the basin. South of the Tensleep fault, the basin is characterized by west-northwest-trending curved folds that become more curved to the west. West of Elk Basin thrust, north-northwest-trending curved folds characterize the basin. North of the Pat O'Hara thrust, these folds bend west into the Nye-Bowler structure. To the south they bend east and merge with the southern portion of the basin.

These differences probably reflect reorientation of principal horizontal stress from east-northeast during the early phase to northeast during the late phase of the Laramide orogeny. The linearity of structures comprising the northeast portion of the basin suggests they were subjected to predominantly direct compression throughout the orogeny. The strong curvature of structures elsewhere suggests that late Laramide compression overprinted early Laramide deformation. West-northwest-trending structures in the south were initially left-slip faults and subsequently became thrusts. North-northwest-trending structures in the west were originally thrusts and subsequently became right-slip compressional faults. In the western and southern portions of the basin there are several features, prev ously unrecognized as overprinted structures, consisting of curved folds riding on thrusts that crosscut one another, revealing the sequence of overprinting.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.