THE STRATIGRAPHY OF THE UPPER PART OF THE SALESVILLE FORMATION (EARLY MISSOURIAN, PENNSYLVANIAN) NEAR MINERAL WELLS, TEXAS

Two well-exposed sections of the upper cycle of the Salesville Formation (Missourian) are present in two roadcuts near Mineral Wells, Texas. The first one is 3.65 m thick and located on the west side of Texas State Highway 337 about 1 mile north of U.S. Highway 180 west of Mineral Wells. At its base is a crinoidal siltstone with an abundant microfauna including the rare fusulinid Eowaeringella cf. E. joyitaensis, overlain by the 0.65 m thick Devil’s Hollow Sandstone. Above the Devil’s Hollow Sandstone is a 0.5 m thick black to dark gray shaley transgressive mudstone containing phosphate nodules, and a well-preserved microfossil assemblage containing ostracodes, foraminifers and conodonts. The next 2.5 m is a dark gray mudstone that transitions into a variegated mudstone with microfossils and decreasing fissility. The second exposure is a 4.7 m thick section on either side of Farm to Market Road 3027 about 3 miles north of U.S. 180 northwest of Mineral Wells. The base of the section is 0.75 m of loosely consolidated, brown, sandy mudstone overlain by the 2.0 m thick Devil’s Hollow Sandstone. One bed of the sandstone unit is highly bioturbated with abundant worm tubes. The uppermost bed of this unit is sparsely fossiliferous containing bryozoans, conulariids, brachiopods, and the rare crinoid Agassizocrinus. Directly above the Devil’s Hollow Sandstone is 1.7 m of black to dark gray shaley mudstone with a well-preserved microfossil assemblage containing ostracodes, foraminifers and conodonts. Above the black to dark gray shale is several meters of brown mudstone overlain by the Turkey Creek Sandstone. Weathering of the mudstone unit has exposed small pockets of fossiliferous more fissile gray mudstone at varying heights in the section. In both sections the strata below and including the Devil’s Hollow Sandstone, represent the end of a marine regression. The strata above the Devil’s Hollow Sandstone represent a partial marine transgression followed by a regression ending with the Turkey Creek Sandstone.