GROSHONG, RICHARD H., Jr., The University of Alabama, Department of Geology, Tuscaloosa, AL

ABSTRACT: The Importance of Layer-Parallel Strain in Restoration of the Hangingwall of the Corsair Fault, Offshore Texas

The most successful practical approach to balancing and restoring cross sections of Gulf-of-Mexico style growth faults is the Chevron method, in which the shapes of the hangingwall rollover and the master fault are related by vertical or oblique simple shear. The shear angle is usually found by an iterative best fit between the shape of a key bed and the master fault. Shear oblique to bedding always results in bedding-parallel strain proportional to the shear angle and to the change in bedding dip. This strain, characteristically manifested as minor faults, provides an added control on the correct restoration of the cross section. When the Chevron method is iteratively applied to a depth section of the Corsair fault, the best-fit shear angle is synthetic, nearly parallel to the master fault. Although geometrically possible, this shear angle implies 18-30% layer-parallel shortening, whereas the observed strain is about 14% layer-parallel extension. The shear angle calculated from the actual extension dips 51-75 degrees antithetic to the master fault. Restoration of the cross section using antithetic oblique simple shear requires that the "regional", (the level to which beds are restored) had a depositional topography, rather than being planar, as commonly assumed. The resulting topography resembles the shelf-slope break with concomitant implications as to the stratigraphy and facies changes in the restored unit. The Chevron method is sensitive to vertical exaggeration and to topography on the "regional"; layer-parallel strain provides an independent constraint on the r construction.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.