New Mexico Geological Society Annual Spring Meeting — Abstracts

Carboniferous strata were first identified in the southern Sangre de Cristo Mountains in the 1870s, and, in 1928, Darton referred them to the Magdalena group overlain by the Abo sandstone capped by the Chupadera formation. In the 1940s, U. S. Geological Survey mappers brought the Pennsylvanian lithostratigraphic nomenclature used to the south into the Sangre de Cristo Mountains, and referred to the overlying red beds as Sangre de Cristo Formation. Thus, they assigned the lower part of the Pennsylvanian section to the Sandia Formation and most of the overlying Pennsylvanian strata to the Madera Limestone divided into a lower, gray limestone member and an upper, arkosic limestone member. In the 1960s-1970s, Sutherland proposed new lithostratigraphy, the La Pasada Formation (south) and equivalent Flechado Formation (north) correlated to the Sandia Formation and gray limestone member of the Madera Limestone, overlain by the Alamitos Formation, in part equivalent to and overlain by the Sangre de Cristo Formation. In the 1980s-1990s, Baltz and Myers proposed an alternative lithostratigraphic nomenclature that recognized the Sandia Formation overlain by the Madera Group composed of the Porvenir and Alamitos formations, unconformably overlain by the Sangre de Cristo Formation.

Sutherland stated that no consistent criteria could be identified by which to separate the Sandia from the Madera formations, but the Sandia-Madera contact south of the Sapello River is the same as it is to the south in the Sandia uplift. So, Sutherland’s La Pasada Formation is a composite unit made up of the Sandia and Gray Mesa formations, and it should be abandoned. The Porvenir Formation type section near Las Vegas is mostly limestone with a few thin quartzose sandstone interbeds and a shaley interval in its upper half. Baltz and Myers identified three facies of the Porvenir Formation: (1) in the south, a dominantly carbonate facies, including the formation type section; (2) in the north, a thicker more shaley facies; and (3) farther north, more arkosic sandstone. The carbonate facies is simply Gray Mesa Formation, so Porvenir is a synonym of Gray Mesa. Porvenir strata to the north can be assigned to the Flechado Formation.

Use of Sangre de Cristo Formation in the southern Sangre de Cristo Mountains was largely based on age, because, in Colorado, that unit encompasses Pennsylvanian and lower Permian strata, as it supposedly does in the southern Sangre de Cristos. Nevertheless, the Pennsylvanian-age Sangre de Cristo strata in New Mexico of earlier workers are mostly Alamitos Formation red beds. The Sangre de Cristo Formation in New Mexico lacks the marine interbeds characteristic of the Sangre de Cristo Formation in its type area, and was deposited in a basin separate from the basin in which Sangre de Cristo Formation strata were deposited in Colorado. In southern San Miguel County, the two Abo members recognized to the south (Scholle and Cañon de Espinoso members) can be recognized in the “Sangre de Cristo” strata. Thus, we abandon the name Sangre de Cristo Formation in northern New Mexico in favor of Abo Formation.