Pennsylvanian stratigraphy in the Sierra Ladrones, Socorro County, New Mexico
— Spencer G. Lucas, Karl Krainer, and Bruce D. Allen


The Pennsylvanian stratigraphic section in the Sierra Ladrones of northern Socorro County can be assigned to the (ascending) Sandia, Gray Mesa, and Atrasado formations. The Sandia Formation is 105 m thick and consists of a lower part that is mostly conglomerate, conglomeratic sandstone, sandstone, limestone, and covered intervals, and an upper part that is covered intervals, shale/siltstone, and intercalated thin beds of sandstone and limestone. The Gray Mesa Formation is 234 m thick and of fairly uniform lithology throughout, so subdivision into three members, as can be done at some other outcrop areas, is not possible. The Gray Mesa Formation is covered intervals (likely shale or nodular limestone), shale, and mostly limestone of diverse lithologies; most limestone beds have chert nodules or layers. The Atrasado Formation is 261 m thick and can be divided into the eight members present in other outcrop belts (ascending): Bartolo, Amado, Tinajas, Council Spring, Burrego, Story, Del Cuerto, and Moya members. The overlying Bursum Formation is considered by some to be of Pennsylvanian age, but we regard it as early Permian. It is up to 92 m thick, a mixture of siliciclastic red beds and marine limestones, and is overlain by the lower Permian Abo Formation. Fusulinids indicate the Sandia Formation is of late Atokan age, and the Gray Mesa Formation is of early Desmoinesian age. Missourian and Virgilian fusulinids are present in the Atrasado Formation, and it is likely that the Bartolo Member and part of the Amado Member are Desmoinesian, as they are to the southeast and east. Some previous workers overstated the thickness of the Pennsylvanian section in the Sierra Ladrones as 820–840 m thick, but it is about 550 m thick in the Navajo Gap area. The overstated thicknesses were the basis for identifying a Pennsylvanian Lucero basin that did not exist.

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Recommended Citation:

  1. Lucas, Spencer G.; Krainer, Karl; Allen, Bruce D., 2022, Pennsylvanian stratigraphy in the Sierra Ladrones, Socorro County, New Mexico, in: New Mexico Geological Society, 72nd Fall Field Conference, Sept. 2022, Socorro, New Mexico, Koning, Daniel J.; Hobbs, Kevin J.; Phillips, Fred M.; Nelson, W. John; Cather, Steven M.; Jakle, Anne C.; Van Der Werff, Brittney, New Mexico Geological Society, Field Conference, pp. 171-185.

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