REVISED UPPER PALEOZOIC LITHOSTRATIGRAPHIC NOMENCLATURE IN THE TAOS TROUGH, NEW MEXICO

In 1928, Darton termed upper Paleozoic strata in the Taos trough the Magdalena group, Abo sandstone and Chupadera formation. In the 1940s, USGS mappers brought Pennsylvanian nomenclature used to the south into the Taos trough, and referred to the overlying red beds as Sangre de Cristo Formation. They assigned the lower part of the 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), overlain by the Alamitos Formation, in part equivalent to and overlain by the Sangre de Cristo Formation. In the 1980s-1990s, Baltz and Myers recognized the Sandia Formation overlain by Madera Group (Porvenir and Alamitos formations), unconformably overlain by Sangre de Cristo Formation.

Sutherland stated that no consistent criteria 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 should be abandoned. 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 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 Taos trough was largely based on age, but the Pennsylvanian-age Sangre de Cristo strata of earlier workers are mostly Alamitos Formation red beds. The “Sangre de Cristo Formation” in the Taos trough was deposited in a basin separate from that 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.