New Mexico Geological Society Annual Spring Meeting — Abstracts

The marine macroinvertebrate assemblage of the Hueco Group in the Dona Ana Mountains have yet to receive thorough study, although extensive assemblages have been well described from the neighboring Robledo Mountains. We report and illustrate a diverse macroinvertebrate assemblage recently discovered on the Dona Ana Mountains in a shale bed ~ 15 m below the top of the Shalem Colony Formation and only a few meters below fusulinacean packstones of the Pseudoschwagerina zone. This assemblage occurs in the upper part of a 2.7 m thick shale interval, which is overlain by a 0.4 m thick, fossiliferous limestone bed containing brachiopods and gastropods. This assemblage consists of brachiopods (Squamariamoorei? Muir-Wood & Cooper, Derbyia sp., Compositecracens Cooper & Grant, Crurithyristumibilis Cooper & Grant), bivalves (Septimyalinaburmai Newell), nautiloids (Pseudorthoceratidae), gastropods (Tychoniainexpectata Kues, Euphemites sp.) and bryozoans (Protoretepora sp.). The fauna is dominated by S. moorei? and bryozoans. The S. moorei? are in various states of preservation, including specimens more complete that previously reported from the Robledo Mountains. The Shalem Colony Formation assemblage is indicative of shallow marine, shelf waters with enough energy to move large brachiopod shells. The macroinvertebrate assemblage from the Shalem Colony Formation is less diverse than, but similar in composition and relative abundances to, the more extensive assemblages known from the stratigraphically higher Robledo Mountain Formation in the Robledo Mountains. This suggests chronofaunal stability of the invertebrate macrofauna during much of Hueco Group deposition on the Early Permian Robledo shelf of southern New Mexico.