Faulting and Jointing in and Near Surface Mines of Southwestern Indiana.

摘要

This project was directed towards the characterization of: (1) the known large faults in southern Indiana, i.e., the Georgetown Fault in Floyd County and the newly named Crandall Fault in Harrison County; and (2) the small scale fractures endemic to southwestern Indiana. The Georgetown and Crandall Faults are normal faults that have a maximum vertical displacement of about 65 feet. They are post-Valmeyeran and pre-Pleistocene in age and are probably the result of hinge-line deformation between the subsiding Illinois Basin and the Cincinnati Arch. In contrast, abundant small-scale faults and joints are related to regional compressive lithospheric stress or to sedimentologic processes that operated penecontemporaneously with deposition of the rocks in which they are found. Structures related to regional stress include small-scale thrust faults with displacements of a few inches to a few feet and joints that are widespread in mines and outcrops in rocks of Mississippian and Pennsylvanian age. The jointing and most of the small-scale thrust faulting indicate that southern Indiana is affected by the Midcontinent Stress Province in the northern part of the study area and by another stress field in the southern part. An east-west boundary can be defined between the two stress fields.