Triassic stratigraphy in the Sangre de Cristo Mountains, New Mexico
— Spencer G. Lucas, Adrian P. Hunt, and Phillip Huber
Triassic strata exposed in the Sangre de Cristo Mountains of Colfax, Taos, Mora and San Miguel Counties, New Mexico, pertain to eight formations: Moenkopi, Santa Rosa, Baldy Hill, Garita Creek, Trujillo, Bull Canyon, Redonda and Johnson Gap. The Middle Triassic Anton Chico Member of the Moenkopi Formation disconformably overlies the Permian Bernal or Glorieta Formations from Montezuma Gap to Rayado Creek and is as much as 47.0 m thick and dominated by grayish-red, trough-crossbedded litharenite and lithic wacke. We apply the informal term mottled strata to the paleosol(s) developed in the top of the Moenkopi and the Pennsylvanian-Permian Sangre de Cristo Formation. The Upper Triassic Santa Rosa Formation disconformably overlies the Moenkopi Formation or, north of Rayado Creek, the Pennsylvanian-Permian Sangre de Cristo Formation. The Santa Rosa is as much as 38.5 m thick and is dominated by yellowish gray, trough crossbedded quartzarenite. South of La Cueva three members of the Santa Rosa Formation (Tecolotito, Los Esteros and Tres Lagunas) are present, but to the north only the Tecolotito Member is present. The Baldy Hill Formation is 13.0 m of mottled siltstone at Ricardo Creek that overlies the Santa Rosa Formation. To the south, as much as 26.0 m of dominantly red mudstone of the Garita Creek Formation overlie the Santa Rosa Formation. The Trujillo Formation disconformably overlies the Baldy Hill and Garita Creek Formations and is the most pervasive Triassic stratigraphic unit in the Sangre de Cristo Mountains. It is as much as 58.0 m thick and is dominated by olive, yellow, and/or gray trough crossbedded and laminar quartzose sandstone and limestone- and siltstonepebble conglomerate. Reddish, bentonitic mudstones of the Bull Canyon Formation overlie the Trujillo Formation at Naranjos and to the south. The Redonda Formation ( = Naranjos Formation), 60-65 m thick and dominated by reddish siltstone, disconformably overlies the Bull Canyon Formation in this area. North of Naranjos, we assign the post-Trujillo Triassic strata to the Johnson Gap Formation. We thus redefine the Johnson Gap Formation by eliminating the Trujillo-equivalent strata from its type section and recognize it as 15.4-84.9 m of variegated siltstone, litharenite and intraformational conglomerate that crops out from Rayado Creek, New Mexico to Stonewall, Colorado. The Entrada Sandstone disconformably overlies the Johnson Gap and Redonda Formations in the Sangre de Cristo Mountains.
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- Lucas, Spencer G.; Hunt, Adrian P.; Huber, Phillip, 1990, Triassic stratigraphy in the Sangre de Cristo Mountains, New Mexico, in: Tectonic development of the southern Sangre de Cristo Mountains, New Mexico, Bauer, Paul W.; Lucas, Spencer G.; Mawer, Christopher K.; McIntosh, William C., New Mexico Geological Society, Guidebook, 41st Field Conference, pp. 305-318. https://doi.org/10.56577/FFC-41.305