New Mexico Geological Society Annual Spring Meeting — Abstracts

The Triassic stratigraphy around Lamy, Santa Fe County, New Mexico, has been relatively understudied compared to contemporaneous sections in north-central (Rio Arriba County) and east-central New Mexico (Quay County). A composite section is ~507 m thick and consists of Permian (Artesia Group), Middle Triassic (Moenkopi Group) and Upper Triassic strata (Santa Rosa, Garita Creek, Trujillo, Petrified Forest and Rock Point formations). The Artesia Group (18-25 m) overlies limestones of the San Andres Formation and consists of interbedded sandy mudstones and crossbedded sandstones with rare gypsiferous beds. A thick (~6 m), crossbedded sandstone marks the onset of Moenkopi Group deposition. Overall, the Moenkopi Group is 27-30 m thick. Crossbedded sandstones predominate in the Moenkopi Group strata, with lesser lithologies, including cherty sandstones and mudstones. The Santa Rosa Formation unconformably overlies the Moenkopi Group and all three of its members (ascending order), Tecolotito, Los Esteros and Tres Lagunas, are present. The Tecolotito Member (12 m thick) consists of crossbedded sandstones, some with chert, and sandy mudstone. The Los Esteros Member (54 m thick) has a lower third that is mudstone-dominated, a medial third that has crossbedded sandstones and sandy mudstones and an upper third that is also mudstonedominated. Crossbedded sandstones are the dominant lithology of the Tres Lagunas Member (14 m thick). The mudstone-dominated Garita Creek Formation overlies the Tres Lagunas Member. This unit is at least 94 m thick, though regional topography made it impossible to find a single section of the entire unit. The Trujillo Formation (26 m thick) is sandstone dominated with some mudstones. The Petrified Forest Formation (196 m thick) is almost entirely composed of mudstone, the exception being the cherty, crossbedded sandstone Correo bed that occurs in the upper third of the formation. The Rock Point Formation (56 m thick) is present as a series of sandy mudstones with occasional sandstone beds. The Lamy collecting area yields the type assemblage of the Lamyan sub-land vertebrate faunachron, including the famous Late Triassic Lamy amphibian quarry that has produced dozens of individuals of the metoposaurid amphibian Buettneria perfecta.