New Mexico Geological Society Annual Spring Meeting — Abstracts

Along the Sangre de Cristo front range in Colfax and Mora Counties, Triassic strata are generally poorly exposed along steeply dipping hogbacks, disconformably overlie Permian strata and are disconformably overlain by the Middle Jurassic Entrada Sandstone. The oldest Triassic strata are grayish red, crossbedded litharenites and lithic wackestones of the Middle Triassic Anton Chico Member of the Moenkopi Formation exposed as far north as Naranjos (T22N, R19E). Baltz and O'Neill (1984, USGS Map I-1456) identified the 47 m of Anton Chico Member at La Cueva (T20N, R16E) as Permian Bernal Formation. Crossbedded quartzarenites, extraformational conglomerates and mudstones of the Upper Triassic Santa Rosa Formation rest disconformably on the Anton Chico in Mora county, but north of Naranjos the Santa Rosa rests on "mottled strata" (e.g., Ricardo Creek, T32N, R17E) or on Permian rocks. The Santa Rosa is as much as 43 m thick, and, at La Cueva, its three members (Tecolotito, Los Esteros, Tres Lagunas) can be recognized. Baltz and O'Neill's Santa Rosa Formation includes the Santa Rosa, Garita Creek and Trujillo Formations of our usage. The Garita Creek Formation above the Santa Rosa is as much as 26 m (at La Cueva) dominated by reddish brown mudstone. The crossbedded quartzarenites and intraformational conglomerates of the Trujillo Formation rest disconformably on the Garita Creek and thin northward from 42 m at La Cueva to 12 m at Ricardo Creek. Triassic strata above the Trujillo are equivalent to the Bull Canyon and Redonda Formations of the Tucumcari basin and represent the Johnson Gap Formation north of Naranjos where the Bull Canyon is overlain by the Redonda (=Naranjo Formation of Bachman, 1953, USGS Map OM-137). The Johnson Gap is as much as 85 m (at Urraca Creek, T25N, RI8E) dominated by moderate reddish brown, laminar sandstone and siltstone and thins to 17.3 m at Ricardo Creek near its type section in southern Colorado.