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Geologic Significance of Rising Fawn Cross-Strike Structural Discontinuity, Northwest Georgia Appalachians

J. L. Coleman, Jr.

Cross-strike structural discontinuities (CSDs) are defined by R. L. Wheeler as "broad, diffuse, transverse zones of structural disruption in ... overthrust belts." Fracturing along them has been inferred to enhance hydrocarbon production, especially in low permeability reservoirs. A detailed study of the Rising Fawn CSD, northwest Georgia, illustrates the long-term effects of these features.

The Rising Fawn CSD is a long-lasting, Precambrian to Tertiary, structural zone that controlled depositional facies, economic deposits, decollement development, and Tertiary erosion patterns. Beginning with the Cambrian-Ordovician Knox Group, Paleozoic carbonate facies were deflected by the CSD, which acted as the axis of a southeast-plunging anticline throughout most of geologic time. Clastic depocenters were also affected.

Precambrian continental rifting and Pennsylvanian-Permian decollement thrusting were controlled to varying extents by the zone. Even ductile folding in the crystalline belt was affected. The present-day outcrop pattern of the metamorphic front is deflected around the CSD, suggesting Tertiary uplift of the area. This is confirmed by the cross-cutting nature of the aeromagnetic trends and conodont isograds across outcrop trends. Recent earthquake epicenters, concentrated along the CSD, illustrate its enduring structural influence.

Since hydrocarbon production has not been established in the Georgia Appalachians, the effect of the CSD on reservoir deliverability cannot be determined. However, other economic deposits appear to be concentrated along the zone.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.