Basement Fault Configurations, Wyoming Province: ABSTRACT

Abstract

For many basement-cored folds and related mountain flank faults in the Wyoming province, locally balanced cross sections can be constructed using structural relief and line lengths in the sedimentary cover rocks. By conserving the length of the upper basement surface, possible basement fault movement can be inferred. This faulting includes: (1) motion along a reverse fault which yields a folded upper basement surface, and (2) displacement distributed along a series of parallel basement faults. The sedimentary cover rocks are force folded and may be cut by mountain flank faults which place Precambrian rocks overlying either Paleozoic or Mesozoic rocks. Previously recognized thrusts, blind thrusts, rootless anticlines, and buckle folds in the cover rocks in adjacent basins re reinterpreted to represent thin-skinned deformation related to basement faulting. Where there is relative translation of the cover rocks, cross sections need not balance locally and the fault dips and basement geometries previously determined are in error. The fault dips calculated from locally balanced cross sections have been overestimated, and/or the displacement on the basement fault(s) has been underestimated. The displacement observed on mountain flank faults may be far less than the total displacement on the basement fault. In the simplest case, it may be possible to project the mountain flank fault downdip to infer the orientation and location of the basement fault(s) at depth. End_of_Article - Last_Page 950------------