TECTONICALLY-INDUCED PRESSURE SOLUTION IN THE PENNSYLVANIAN COLLINGS RANCH CONGLOMERATE IN THE ARBUCKLE MOUNTAINS OF SOUTHERN OKLAHOMA

The Collings Ranch Conglomerate was deposited in a small (~6.5 X 1 Km) pull-apart basin, trending WNW-ESE, that developed at a releasing bend on the Washita Valley fault, a major oblique (left lateral reverse) structure that formed the northwestern margin of the Southern Oklahoma aulacogen during intense Pennsylvanian-age deformation. The Conglomerate consists of meter-scale beds of pebble and boulder breccio-conglomerate separated by thin (mm scale) red shales. Nearly all clasts are derived from Lower Paleozoic carbonate units that border the basin. Texturally the Conglomerate is an open-framework deposit, lightly cemented by both vadose and phreatic calcsparite. The Conglomerate was tectonically deformed by a later Pennsylvanian transpressive stress event that resulted in further faulting and open flexural slip folding (utilizing the red shales as slip horizons). Carbonate pebbles show the effects intense pressure solution in the form of marginal stylolitization; the orientation of this pressure solution was examined quantitatively to determine its relationship to both folding and confining stress. It appears that the pressure solution is of tectonic origin and likely accompanied folding. Calcite cementation both preceded and postdated pressure solution to which it may have been causally related. The ubiquitous pebble dissolution is an unusual accommodation of strain during folding of a near surface partially consolidated deposit of alluvium.