New Mexico Geological Society Annual Spring Meeting — Abstracts

The Red Tanks Formation, of latest Pennsylvanian to earliest Permian age (or entirely latest Pennsylvanian by a recent proposal to raise the boundary), is about 100 m thick at its type section in Carrizo Arroyo, and is coeval with the Bursum and Laborcita Formations elsewhere in central and south-central New Mexico. The Red Tanks consists mainly of red or green nonmarine shales, with a few thin limestone and shale beds containing marginal marine mollusc faunas. The only thick marine interval with welldeveloped, stenohaline, invertebrate faunas is a 5-m-thick sequence of limestones and calcareous shales about in the middle of the formation, and this interval contains diverse brachiopods comprising about 25 species. The most abundant taxa are the productoids Juresania n. sp. aff. nebrascensis, and Linoproductus (represented by three species, L. magnispinus, L. aff. prattenianus, and L. aff. platyumbonus), and the small spiriferid Crurithyris planoconvexa. Neochonetes granulifer (including the form N. "transversalis"), Composita subtilita, Neospirifer alatus, Meekella mexicana, Reticulatia americana, Hystriculina aff. wabashensis, and Wellerella aff. osagensis, are moderately common in some beds, and such species as Phricodothyris perplexa, Punctospirifer kentud.-yensis, Echinaria aff. semipunctatus, Derbyia sp. and Orbiculoidea missouriensis are rare. Above these middle Red Tanks marine units brachiopods are completely absent, with the exception of Lingula carbonaria, which occurs in a thin bed about 20 m below the top of the formation that contains a low-diversity, predominantly molluscan fauna. A bed of dark gray shale at the boundary between the Red Tanks and the underlying Atrasado Formation also contains L. carbonaria in abundance. Nearly all of these brachiopod species are also known from earlier Virgilian strata in central New Mexico, and many also occur in the Bursum Formation, although the Red Tanks brachiopod fauna appears to be taxonomically more diverse. In contrast, there is little evidence in the Red Tanks Formation of brachiopod taxa that characterize early Wolfcampian strata in the west Texas region.