Abstract

The Arbuckle Group (Upper Cambrian and Lower Ordovician) carbonates of the southern Midcontinent are an important petroleum reservoir and also are used to store petroleum waste-water. Additionally, the Arbuckle likely has been a major source and conduit for petroleum and metalliferous fluids that sourced large economic ore deposits in the Ozark region. The Arbuckle section is comprised of cyclic, cherty dolomites, interbedded, occasionally, with thin, quartzic sandstone. Depositional fabrics observed range from shallow subtidal to peritidal facies. Dolomites interpreted as early replacement, observed in all facies, exhibit a range of very fine to medium crystal size and planar textures. Carbon and oxygen isotope values of early diagenetic dolomite indicate equilibrium with evaporated early Ordovician seawater. Dolomite interpreted as late diagenetic replacement exhibits medium to coarse planar to nonplanar textures likely resulting from recrystallization of early diagenetic dolomites. Analysis of fluid inclusions in void filling rhombic and saddle dolomite cements indicate the presence of warm (90° to 155°C), saline (10 to 27 wt.% NaCl equivalent) basinal fluids. Late diagenetic replacive and void filling dolomite cements display more negative δ¹⁸O values compared with early diagenetic replacement dolomite. Reconstruction of the isotopic composition of these fluids indicate an evolved water that has interacted with continental basement or sediments derived from basement rocks. These fluids likely are sourced from the Arkoma and/or Anadarko basins and driven by a gravity fluid flow mechanism initiated during the Ouachita orogeny.