The biota and paleoecology of the upper Pennsylvanian (Missourian) Tinajas Locality, Socorro County, New Mexico
— Allan J. Lerner, Spencer G. Lucas, Justin A. Speilmann, Karl Krainer, William A. Dimichele, Dan S. Chaney, Joerg W. Schneider, W. John Nelson, and Alexander Ivanov

Upper Pennsylvanian (Missourian) strata of the Tinajas Member of the Atrasado Formation in the Cerros de Amado, Socorro County, include an unusual lacustrine deposit, the Tinajas locality. This locality yields a diverse fossil assemblage of plants, crustaceans, insects, a cnidarian, molluscs and fishes from laminar black shale that contains a prolific conchostracan assemblage. A lacustrine origin of the black shale is supported by the abundance of conchostracans; presence of darwinuloid (freshwater) ostracods, land plants and insect wings; lack of marine indicators; and the lithology and geometry of the deposit. Overlying gray shales are full of Dunbarella, which indicates the onset of nearshore, marginal marine conditions. Indeed, the stratigraphic succession at the Tinajas locality is analogous to a classical cyclothem. Thus, fluvial/deltaic deposits grade upward into a coastal lake that is then transgressively overlain by marginal marine and fully marine sediments. The preservation of the lacustrine sediments at the Tinajas locality was a local, unique event on the Late Pennsylvanian coastline in central New Mexico, as no other occurrence of a similar paleoenvironment is known.