Overthrusts Are Real

Timothy L. Clarey  tclarey@icr.org

Clarey, T.L. 2013. South Fork and Heart Mountain Faults: Examples of catastrophic, gravity-driven “overthrusts,” northwest Wyoming, USA. In M. Horstemeyer (editor), Proceedings of the Seventh International Conference on Creationism, [no page numbers]. Pittsburgh, Pennsylvania: Creation Science Fellowship.

Creationists in the past have been openly critical of secular explanations of overthrust faults. Some have denied their existence altogether, claiming that “overthrusts” were merely strata containing out-of-order fossils, and that no real faulting had occurred. To their credit, the mechanical difficulty of moving large, coherent sheets of strata great distances down fairly flat slopes has never been adequately explained. Today, however, creationists must accept the results of 1000s of drill-hole penetrations and 1000s of kilometers of seismic reflection data, collected since the 1970s, proving the existence overthrusts. Yet, the question remains, just how could overthrusts have formed?

The “rules” of overthrusting, established by the oil industry in the 1970s, suggest consistent movement directions away from uplifted regions. Overthrusts generally get younger in the direction of transport, often folding and deforming earlier-emplaced thrust sheets in the process. The apparent “uphill” movement of many overthrusts can usually be explained as a consequence of later folding by subsequent thrusts or by ramping uphill as the thrusting ceased. Overthrusts, generally, have a basal detachment from which all younger thrusts originate. High fluid pressures, developing during dewatering reactions and sediment loading, have the ability to create temporary overpressured zones and “float” large thrust sheets down slope.

This paper examines two fault systems as analogies for an “overthrust” Flood model. The famous Heart Mountain Fault near Cody, Wyoming and the lesser-known South Fork Fault in the same locale. Both faults moved catastrophically under the influence of gravity on a horizon of overpressured fluid and/or gasses. Transport was east-southeast. Both have a break-away fault which marks the origin site of the fault systems. Rapid development of near-surface folds in the detached sheets could only have developed while the sediments were still unlithified.

 Late Flood loading by sediment probably created overpressured horizons and rapid uplift and volcanism initiated sliding of the Heart Mountain and South Fork Faults. Similar processes undoubtedly occurred in many mountain belts globally. However, secular explanations of overthrusts, using slow movement and maintenance of overpressured horizons over great distances and long timeframes, still cannot resolve the glaring mechanical paradox. In contrast, a catastrophic model involving rapid downhill movement of unlithified sediments on overpressured detachments, provides both a cause and a mechanism for the development of large and tightly folded thrust sheets.

Creationists who are critical of the geologic column should no longer use the denial of overthrusts as part of their argument. They are, in fact, real features found in many mountain belts across the globe. Instead, creationists should recognize that overthrusts can only be explained in the context of the global Flood.

Heart Mountain near Cody Wyoming, USA. Ordovician and Mississippian strata are emplaced on top of Eocene strata in the northwestern Bighorn Basin.


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