ABSTRACT: Kinematics of the Eastern Flank of the Beartooth Mountains, Montana and Wyoming

O'CONNELL, PATRICK, Conoco Inc., Casper, WY, and Baylor University, Waco, TX

Three miles west of Red Lodge Montana, well data, gravity data, and surface data indicate the Beartooth fault is dipping at 25-30 degrees southwest and is trending northwest-southeast. A minimum of 16,500 ft of basement overhang is estimated along this segment of the uplift. South of the Maurice tear fault, the Beartooth fault changes to a north-south trend. With the northeast vergence of the Beartooth fault, the eastern flank of the mountains present an interpretational dilemma between horizontal compression and vertical uplift models. The interpretation of reverse right oblique slip has been applied to the north-south trending segment of the Beartooth fault.

As the Beartooth fault is traced southward, the dip angle of faulting begins to gradually steepen, decreasing the magnitude of overhang. A recent well that penetrates the Precambrian overhang at Ruby Creek established 8000 ft of basement overhang.

The Bennett Creek flatiron represents an asymmetric syncline created as part of a backlimb fold by early stages of northeast movement. As northeast vergence continued, the north-south segment of the Beartooth fault cut this structure leaving the southeast continuation of the structure buried in the basin or under the basement overhang. These potential hydrocarbon traps are targets for future exploration.

As the Beartooth fault is traced further southward, displacement begins to die out as it nears Clarks Fork Canyon. The Beartooth fault appears to propagate into the Canyon Mount anticline as fault displacement diminishes toward the Bighorn basin.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)