REGIONAL STRESS REGIME STUDY OF EAST TEXAS BASED ON ORIENTATION OF FRACTURES IN THE WECHES FORMATION
Fractures in the Weches Formation in a roughly 50 mile radius around Nacogdoches, Texas were documented and analyzed using data obtained at various outcrops. This data was used to infer information about the regional stress regime based on the direction of maximum/minimum horizontal stresses (SHmax / SHmin) that formed the fractures. This is based on the principle that systematic, steeply dipping, mode I joints propagate in the direction of SHmax and normal to the direction of SHmin. Joints in the Weches Formation are typically iron filled and are predominantly opening mode, indicated by crack-seal formation, steep dip (700 – 900) and a lack of shear movement. Slickenlines are visible on some fracture planes; however, their bearings show random orientation indicating unloading movement during erosion. Crosscutting relationships with ironstone layers, a late diagenetic feature in the Weches Formation, indicate joints formed close to the surface during exhumation. Orientation data of 540 fractures from 14 different outcrops show three main joint sets: N75-85W, N75-85E, and N40E. These sets persist over distances of up to 90 miles. The orientations are believed to be the result of Neogene to very recent tectonic stress states related to large scale deformational events including gulfward extension, salt movement in the East Texas Basin and possibly the Sabine Arch or basement faulting.
joints, stress regime, neotectonic joints, stress from jointing, inferring stress, contemporary stress regime, Geology, Geomorphology, Geophysics and Seismology, Sedimentology, Tectonics and Structure
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