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

O'CONNELL, PATRICK, 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 degrees to 30 degrees southwest and is trending northwest-southeast. South of the Maurice tear fault, the Beartooth fault changes to a north-south trend. The intersection of these two trends forms the Red Lodge "corner." With the northeast vergence of the Beartooth fault, the eastern flank of the mountains presents 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. This necessitates a reinterpretation of the left-lateral strike-slip motion of the Maurice tear fault to include a component of reverse o lique motion.

The Bennett Creek flatiron represents an asymmetric syncline created as part of a back-limb 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 Mouth Anticline as fault displacement diminishes toward the Bighorn basin. Compressional features seen at the crest of the Canyon Mouth Anticline seem to negate a vertical component of movement previously suggested at this southeast corner of the Beartooth Block.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)