Considerations of vertical tectonics for Big Horn Basin

Referring to the tectonic style of the Big Horn Basin as either horizontal or vertical is an oversimplification. However, these terms have come into vogue and the author supports vertical tectonics. This term implies that on most structures the vertical component of displacement is larger than the horizontal component of displacement. It does not imply that all faults are absolutely vertical, nor does it preclude crustal shortening. If high-angle reverse faults (dips steeper than 45/sup 0/) dominate in a basin, a net shortening will result even in a vertical tectonic domain. Furthermore, when applied to the Big Horn Basin, the expression vertical tectonic style only characterizes behavior 10 to 15 km (6 to 9 mi) into the basement. It implies nothing concerning causative conditions in the lower crust or upper mantle. A given mantle stress condition can produce several different displacement fields in the upper crust depending upon the behavior of the crust. In accepting either horizontal or vertical as the tectonic style of a region, all of the structures produced during the deformation episode should be considered together as opposed to examining one feature at a time. It is also important to separate second and third order features frommore » primary features. Finally, if there is a governing style, it should be consistent with three-dimensional movements, not just individual cross sections.« less