Abstract Tectonic inheritance and structure reactivation have been of interest to geologists since it was noticed in the mid-nineteenth century that younger structures in an area tend to follow the direction of older structures. Three kinds of relationship may exist between these older and younger structures: younger structures may follow the older ones and repeat their function; younger structures may follow older ones, but function in the opposite sense to the older ones; and younger structures bear no relation to the older ones. These are named, respectively, resurrected, replacement and revolutionary structures. We present three examples, on three different scales, of tectonic inheritance and structure reactivation: Mesozoic and Cenozoic Europe on a continental scale; the US Rockies on a regional scale; and the Albula Pass in the Swiss Alps on an outcrop scale. We conclude that structure reactivation on a crustal scale occurs when the protective armour of the mantle lithosphere is removed and that, in such cases, resurrected and replacement structures form. In cratons with thick lithospheric roots, structure reactivation hardly ever occurs and when, in rare cases, it does occur, it commonly generates revolutionary structures. There can be no unique model for lithospheric strength.

Abstract In sedimetary basins not currently undergoing primary compaction (e.g., Rocky Mountain Basins), p-wave velocities noticeably vary with azimuth, yet the mechanism(s) controlling the anisotropy remain uncertain. Possible geologic causes for azimuthal anisotropy include but are not limited to sedimentary fabrics, steep bedding, changes in local in-situ or residual stress, and open or mineralized fractures. To test these hypotheses, P-wave velocity azimuths (Vfast) from a proprietary seismic survey of a NNW-trending Laramide Anticline on Casper Arch in central Wyoming were compared to image log data from the seismic coverage area and fracture orientations from nearby analog structures.

Abstract The Pennsylvanian-age Tensleep Formation in south-central Wyoming is comprised of repeated limestones, sandy limestones, and sandstones. Strata of these varied lithologic units are folded over Beer Mug Anticline and cut by numerous intersecting fractures. The anticline, with a near-vertical forelimb and backlimb dip up to 50 degrees, provides an ideal analog for fracture systems in tightly folded Paleozoic hydrocarbon reservoirs. Fracture type and degree of development vary systematically with lithology, structural position, and degree of folding. Fracturing is most intense towards the core of the anticline, which locally consists of folding. Fracturing is most intense towards the core of the anticline, which locally consists of brecciated, oil-stained rock with large-scale vuggy porosity. Most of these strata exhibit inherited (F0) fracture patterns that predate folding, as well as fold-related extension fractures that trend approximately normal (F1) and parallel (F2) to the axis of folding.