New Mexico Geological Society Annual Spring Meeting — Abstracts

Strata of the Hueco Group exposed in the Dona Ana Mountain (T21S, R1E) were previously assigned to the Bursum (?), Lower Hueco, Middle Hueco, Gastropod-bearing member and Abo Tongue of a “shelf facies,” and to a supposedly equivalent “basin facies” exposed to the east of the shelf facies. This lithostratigraphy was used to identify a downwrap across the northwestern margin of the Orogrande basin that divided the Robledo shelf into western and eastern segments. However, a careful re-examination of Hueco group stratigraphy in the Dona Ana Mountains does not support previously proposed lithostratigraphic relationships or the paleogeographic interpretations based on them. No Bursum Formation strata are present in the Dona Ana Mountains, and the Hueco Group strata can be assigned to the: (1) Shalem Colony Formation, ~63 m thick, consisting mostly of dark gray, bioclastic wackestone-mudstone and shale, and containing fusulinaceans of the Pseudoschwagernia zone; (2) Community Pit Formation, at least 108 m thick and mostly shale and brownish-weathered lime mudstones; and (3) Robledo Mountain Formation, at least 156 m thick and characterized by red0bed siltstones and fine sandstones (with tetrapod tracks and plants), shale and marine limestones. These are the “self facies” strata of previous workers. Their “basin facies” strata are either faulted strata of the Community Pit Formation or strata of the Panther Seep Formation, which underlies the Shalem Colony Formation in the Dona Ana Mountains. These Panther Seep strata are at least 64 m thick and consist of thick shale slopes interbedded with thin-bedded limestones, sandy limestones and thin intraformational conglomerates. These facies (especially the peritidal limestones) closely resemble Panther Seep strata in the San Andres and Jarilla Mountains. The absence of a Hueco “basin facies” in the Dona Ana Mountains indicates general continuity of the Robledo shelf from the Robledo Mountains on the southwest to the San Andres Mountains in the northeast. Indeed, the lithostratigraphy of the Hueco Group across this transect is remarkably uniform.