FAULTS IN CENTRAL POTTAWATOMIE COUNTY, KANSAS: FIELD RELATIONSHIPS, KINEMATICS, AND BASEMENT RELATIONSHIPS

A dome and several high-angle faults were mapped in Pottawatomie County, Kansas approximately 16 kilometers north of Wamego. These structures affect rocks on top of the Pennsylvanian Nemaha Anticline and overlie a complexly faulted basement terrain east of the central part of the Precambrian Midcontinent Rift.

A north-trending fault was first recognized on aerial photography by an offset in limestone layers. This high-angle reverse fault strikes N 5º W and dips southwest. The north portion of the fault is relatively straight with a vertical displacement of approximately 2 meters. To the south the fault trace curves to the southwest and the vertical displacement increases to approximately 7 meters. The fault trace continues to the southwest with the up side to the northwest. A second fault is located to the north and west of the first fault and trends to the northeast. The up side of second fault is to the southeast. The area bounded by these faults is uplifted to form a small dome measuring slightly more than 2.6 square kilometers. The dome has a structural relief of about 14 meters.

The proposed kinematic model involves a contractional stepover or push-up ridge. In this model the northeast-trending faults are right-lateral faults that step to the left to generate a contractional area. The dome and the high-angle reverse fault form in response to the contraction between the two northeast-trending faults.

These faults are mapped in Pennsylvanian units and the age of faulting has not been determined. Additionally, these faults occur above an interpreted northeast-trending basement fault. The basement fault is based on changes in elevation of the basement surface observed in drill holes. The surface faulting may indicate a reactivation of the basement fault sometime during or after the Pennsylvanian.