Chemostratigraphy, Mineralogy, and Depositional Environment of the Wolfcamp Formation, Midland Basin, Reagan County, Texas

Increased interest in petroleum exploration of late Paleozoic strata in the Midland Basin, Texas, has spurred fundamental research into the mineralogical and geochemical signatures preserved in the strata and their linkages to depositional environments and well log interpretation. We demonstrate using geochemical methods that much of the mineralogical shifts in the two cores represents a dilution of siliciclastics by calcium carbonate. We present chemostratigraphic results from two drill cores recovered from Reagan County, Texas, that we interpret in terms of changes in mineralogy, organic deposition, and basinal hydrography. Geochemical and sedimentological interpretations are integrated to develop a multi-proxy model of depositional history for the late Pennsylvanian Wolfcamp Formation. Preliminary investigation of the trace-metal chemistry of carbonate phases may provide useful chemostratigraphic information. Specifically, cross-plots of calcium versus magnesium, iron, manganese, and strontium indicate the occurrence of impure carbonate mineralogies (in addition to the pure carbonate shed off the platform--presumed to be calcite) that may represent signatures from changing depositional conditions in the deep basin or diagenetic history. Steady deposition of mixed siliciclastic and carbonate sources are punctuated by abrupt, co-varying changes in Si/Al, Si/Al, and Ti/Al, suggesting a dynamic system with two very different modes of deposition.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California