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Synthesis of seismic data, geologic mapping, and satellite imagery suggests a general 3-stage model of thrust and fold development in the Southern Appalachian belt. Essential to the model is the contrast in gross physical properties of the 2 basic rock packages present: (1) lower Paleozoic carbonates and chert, which behave competently, and (2) upper Paleozoic sandstones and shales, which behave incompetently. The individual structural development of each of the 2 rock packages differs but both are directly related to the development of a thrust structure.
Initial displacement (0-3 mi) creates a large hanging-wall anticline (drag fold) in the lower Paleozoic.
With greater displacement (2-5 mi), a J. L. Rich model anticline develops in the lower Paleozoic hanging wall. In the process, the upper Paleozoic was bulldozed by the lower Paleozoic, creating more internal folding and faulting.
With further displacement (> 5 mi), the thrust will probably become a major overthrust. It develops by ramping of the lower Paleozoic through the highly deformed upper Paleozoic with intense penetrative deformation developing in areas of significant overthrusting.
From this 3-stage model, it may be possible to infer source rock and reservoir juxtapositions, relative timing of hydrocarbon generation, and fracture development. The regional distribution of structural types suggests that initiation of thrusting progressed westward with time. The model may have application in other orogenic belts (e.g., the Idaho and Wyoming Overthrust belt.
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