New Mexico Geological Society Annual Spring Meeting — Abstracts

The Bursum Formation (Lower Permian Wolfcampian) in Socorro County represents transitional strata between the underlying marine Madera Formation and the overlying terrestrial Abo Formation. The Bursum includes rocks deposited in both marine and nonmarine environments, and both environments preserve fossil vertebrates. Preliminary collecting indicates that the Bursum has a diverse vertebrate fauna that is locally abundant.

Altares (1990 NMIMT MS thesis) divided the Bursum into three intervals, a lower clastic zone, a middle carbonate zone and an upper mixed zone. Vertebrate fossils occur in the middle and upper zones. Isolated teeth pertain to the petalodontid elasmobranch Petalodus and the cochliodrintid chimaerine Deltodus. The largest vertebrate fauna derives from a fluvial conglomerate dominantly composed of intraformational limestone (calcrete) clasts. The xenacanthid elasmobranch Orthacanthus is represented by a well-preserved occipital spine that is about 5 cm long with posterolateral denticle rows. Tetrapod specimens include isolated teeth and bones which indicate the presence of a temnospondyl and one or more probable pelycosaurian reptiles.

The overlying Abo Formation contains a limited vertebrate body fossil fauna in Socorro County and a large, unstudied vertebrate ichnofauna that includes Dimetropus and Dromopus.

The Bursum vertebrate fauna is important for several reasons: (1) it occurs in a sequence that contains fusulinids and can be therefore better dated than most Permian vertebrates from New Mexico; (2) it is older, by superposition, than the Abo fauna in Socorro County and may aid in elucidating the biostratigraphy of the sequence of Early Permian faunas that are known from north-central New Mexico; and (3) it represents a more coastal ecosystem than most Abo redbed faunas and probably includes many of the trackmakers which made the extremely diverse ichnofaunas of the Abo Tongue of the Hueco Formation in southern New Mexico which occur in tidalfl at deposits.