DIAGENESIS OF THE CARRIZO SANDSTONE AT BUTLER SALT DOME, EAST TEXAS BASIN, U.S.A.: EVIDENCE FOR FLUID–SEDIMENT INTERACTION NEAR HALOKINETIC STRUCTURES

ABSTRACT: The Eocene Carrizo Sandstone adjacent to the Butler salt dome in the East Texas basin was cemented locally as the result of processes similar to those that have created salt dome calcite cap rocks throughout the Gulf Coast. The geometry of this anomalous cemented zone was established using Carrizo exposures in a large quarry and cores in the contiguous area. The cemented zone is delimited by a steeply dipping normal fault that is radial to the dome; the cements extend southeast of the fault for about 750 m. The Carrizo is a fine-to medium-grained quartzarenite to sublitharenite with 42 to 50 % ce-ment, principally poikilotopic calcite with local pyrite. Pyrite concre-tions are found on both northwest and southeast sides of the fault, as well as along the fault plane, whereas the calcite cement is present only to the southeast. d13C data for calcite (219 to 237‰) suggest that bicarbonate was supplied mainly by bacterial oxidation of methane, whereas d18O dat