Lithostratigraphy, biostratigraphy and sedimentology of the Upper Paleozoic Sangre De Cristo Formation, southwestern San Miguel County, New Mexico
— S. G. Lucas, K. Krainer, W. A Dimichele, S. Voigt, D. S. Berman, A. C. Henrici, L. H. Tanner, D. S. Chaney, S. D. elrick, W. J. Nelson, and L. F. Rinehart

In southwestern San Miguel County, New Mexico, the upper Paleozoic Sangre de Cristo Formation is ~300 m thick. Most of the lower-middle parts of the formation are poorly exposed, but the base of the formation crops out as extrabasinal conglomerate resting with evident disconformity on the Middle Pennsylvanian Porvenir Formation. The upper 160 m of the Sangre de Cristo Formation are continuously exposed, and are mostly red-bed, non-fissile mudstone, and less common sandstone, conglomerate and calcrete. The contact of Yeso Group strata on Sangre de Cristo Formation strata is very similar to the conformable Abo-Yeso contact to the south. Most of the sandstones of the Sangre de Cristo Formation are subarkose to arkose, and a few sandstones and pebbly sandstones containing abundant reworked carbonate grains are classified as lithic arenites. Trace fossils of invertebrates and vertebrates (mostly arthropod and tetrapod walking traces) are locally common in the upper part of the Sangre de Cristo Formation. The tetrapod ichnofauna is quite similar to vertebrate trace fossil assemblages described from the Abo Formation of central New Mexico. Plant fossils are sparse in the Sangre de Cristo Formation and are mostly macrofossil foliar remains preserved as impressions. The flora of the Sangre de Cristo Formation red beds appears to be much the same as that of the finer grained units (Abo and Robledo Mountains Faormations) to the south, and likely indicates seasonally dry climates and that much of Early Permian New Mexico was covered with conifer forests of great extent and low biodiversity. The fossil vertebrate assemblage from the upper Sangre de Cristo Formation encompasses xenacanth sharks, lungfishes, lepospondyl and temnospondyl amphibians, diadectomorphs and eupelycosaurs and represents a mixture of aquatic, semi-aquatic, semi-terrestrial and terrestrial fauna. The tetrapod footprints and vertebrate body fossils indicate a late Wolfcampian age. The Sangre de Cristo Formation comprises sediments that were deposited on a broad alluvial fan in response to tectonic movements of the Ancestral Rocky Mountain deformation. These sediments are nonmarine red beds dominated by fine-grained deposits of the overbank environment and subordinately composed of coarser deposits of sandstone sheets that represent isolated broad, shallow channels of low gradient and low stream power.