Atrasado Formation

The formation consists primarily of marine limestone with some sandstone and shale. It is exposed in the Sandia Mountains,^[1] the Lucero Uplift (34°37′16″N 107°17′56″W / 34.621°N 107.299°W / 34.621; -107.299),^[2] the western Jemez Mountains,^[3] and in the Manzano Mountains.^[1]

The formation has been mapped as the Wild Cow Formation in the Manzano Mountains^[4] and as the Guadelupe Box Formation in the Jemez Mountains.^[5] However, Spencer G. Lucas and coinvestigators have recommended abandoning the name Wild Cow Formation and using Atrasado Formation throughout the Madera Group.^[1] The formation is likely correlative with the Alamitos Formation in the Sangre de Cristo Mountains.^[3]

The formation is underlain by the Gray Mesa Formation, with its base defined by a sandstone interval atop an eroded limestone surface of the Gray Mesa Formation.^[3] It is further distinguished from the Gray Mesa Formation in having frequent intervals of slope-forming sandstone or shale beds between cliff-forming limestone intervals, whereas the Gray Mesa Formation is mostly massive limestone.^[6] The Atrasado Formation is overlain by the Bursum Formation or by the Abo Formation where the Bursum Formation is not present.^[3]

The formation is divided into eight members. In ascending stratigraphic order, these are the Bartolo Member, which is 66 meters (217 feet) of slope-forming shale with thin sandstone, limestone and conglomerate beds; the Amado Member, which is 9 meters (30 feet) of bedded, cherty limestone; the Tinajas Member, which is 115 meters (377 feet) of shale with interbedded limestone and sandstone; the Council Spring Member which is 23 meters (75 feet) of mostly algal limestone without chert; the Burrego Member, which is 26 meters (85 feet) of arkosic red beds and limestone; the Story Member, which is 6 meters (20 feet) of limestone; the Del Cuerto Member, which is 16 meters (52 feet) of arkosic red beds and limestone; and the Moya Member, which is 11 meters (36 feet) of bedded limestone and shale.^[1]

The lowest few meters of the Bartolo Member is often a distinctive pebbly sandstone, the Coyote Sandstone Bed.^[6]

The formation was laid down during the Ancestral Rocky Mountains orogeny, when most of New Mexico consisted of high islands surrounded by marine basins. The Burrego Member, in particular, contains both marine and continental beds, and the continental beds include paleosols (fossil soils) typical of a monsoon climate. New Mexico was then located at the western end of the Pangean tropical belt. Analysis of the paleosols suggests a carbon dioxide concentration in the atmosphere of around 400 ppm by volume at the time of deposition.^[7]

The exposures near Jemez Springs include some of the richest brachiopod fossil beds in North America. Crinoid stems and bryozoans are also part of the fossil assemblage. The Amado Member is particularly rich in brachiopods in the Manzano Mountains.^[1]

The lower part of the Atrasado Formation (Tinajas Member) contains the index fusulinid Eowaeringella indicating the beds were laid down in the lower Missourian Age. These are overlain by beds containing abundant early Triticites.^[6]

The unit was first described as the Atrasado Member of the Madera Formation by Kelley and Wood in 1946.^[2]

The Pennsylvanian stratigraphy of New Mexico has historically been unusually complex and inconsistent, with dozens of names for groups, formations, and members.^[8][1] Barry Kues and Katherine Giles recommended that the name Madera Group be applied to similar exposures of shelf and marginal basin beds of Desmoinean (upper Moscovian) to early Virgilian age found from north-central and central New Mexico south along the west side of the Orogrande Basin as far as the Caballo and Robledo Mountains.^[9] Lucas and coinvestigators recommended abandoning the name Wild Cow Formation and using Atrasado Formation throughout the Madera Group.^[1]

• List of fossiliferous stratigraphic units in New Mexico
• Paleontology in New Mexico

• Allen, Bruce D.; Lucas, Spencer G. (Fall 2018). "The Late Pennsylvanian (Missourian) index fusulinid Eowaeringella in the Manzanita Mountains of central New Mexico" (PDF). New Mexico Geology. 40 (2): 35–44. Retrieved 25 February 2021.
• Kelley, V.C.; Wood, G.H. Jr. (1946). "Geology of the Lucero uplift, Valencia, Socorro, and Bernalillo Counties, New Mexico". U.S. Geological Survey Oil and Gas Investigations. Preliminary Map OM-47. Retrieved 22 May 2019.
• Krainer, Karl; Vachard, Daniel; Lucas, Spencer G. (2005). "Lithostratigraphy and biostratigraphy of the Pennsylvanian-Permian transition in the Jemez Mountains, north-central New Mexico". In Lucas, S.G.; Zeigler, K.E.; Spielman, J.A. (eds.). The Permian of Central New Mexico. Vol. 31. New Mexico Museum of Natural History and Science Bulletin. Retrieved 24 February 2021.
• Kues, B.S.; Giles, K.A. (2004). "The late Paleozoic Ancestral Rocky Mountain system in New Mexico". In Mack, G.H.; Giles, K.A. (eds.). The geology of New Mexico. A geologic history: New Mexico Geological Society Special Volume 11. ISBN 9781585460106.
• Lucas, Spencer G.; Krainer, Karl; Vachard, Daniel (2016). "The Pennsylvanian section at Priest Canyon, southern Manzano Mountains, New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 67. Retrieved 11 June 2020.
• Lucas, Spencer G.; Tanner, Lawrence H. (2021). "Late Pennsylvanian Calcareous Paleosols from Central New Mexico: Implications for Paleoclimate" (PDF). New Mexico Geology. 43 (1): 3–9. Retrieved 1 June 2021.
• Myers, D.A. (1973). "The Upper Paleozoic Madera Group in the Manzano Mountains, New Mexico". Contributions to Stratigraphy. Bulletin 1372-F. doi:10.3133/b1372F.