South Fork and Heart Mountain Faults: Examples of Catastrophic, Gravity-Drive "Overthrusts," Northwest Wyoming, USA
by Tim Clarey, Ph.D.
In M. Horstemeyer, ed., 2013, Proceedings of the Seventh International Conference on Creationism, Pittsburgh, PA: Creation Science Fellowship. Visit the ICC at www.creationicc.org.
Overthrust faults have been a source of debate and discussion in creation literature for many years. Their interpretation demands a better explanation in a Flood context. Two fault systems are examined as analogies for an “overthrust” model. The South Fork Fault System (SFFS) and the Heart Mountain Fault System (HMFS) exhibit folding and faulting consistent with thin-skinned overthrust systems. Both systems moved catastrophically under the influence of gravity. The South Fork Fault system (SFFS, southwest of Cody, Wyoming, exhibits tear faults, tight folds, a triangle zone, and flat-ramp geometries along the leading edge of the system. Transport was southeast, down a gentle slope during early to middle Eocene time (Late Flood), approximately coeval with the Heart Mountain Fault system (HMFS). The SFFS detaches in lower Jurassic strata, rich in gypsum-anhydrite, overlain by about 1250 m of Jurassic through Tertiary sedimentary and volcanic rocks. Movement between 5 km and 10 km to the southeast spread the allochthonous mass over an area exceeding 1400 km2. A break-away fault and an area of tectonic denudation mark the upper northwest part of the system. The exposed denuded surface was buried by additional Eocene-age volcanic rocks soon after slip. Catastrophic rear-loading during emplacement of HMFS may have initiated subsequent movement on the SFFS, with dehydration processes trapping water in a near frictionless anhydrite-water slurry. Rapid development of near-surface folds, as observed in the toe of the SFFS, could only have developed while the sediments were still unlithified.
Break-away fault, denudation, detachment, gravity slide, gypsum dehydration, overthrust
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