Various shallow-water marine facies are recognized in four exposures of upper Neocomian to lower Aptian strata on the eastern side of the Chihuahua trough. These facies display characteristics of a fluctuating carbonate-clastic shoreline with hypersaline, normal marine, and brackish water in nearshore, subtidal, supratidal, and lagoonal environments.

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The stratigraphic sequence between the Paleozoic-Cretaceous unconformity and the first occurrence of the Foraminifera Orbitolina was studied in the areas of the Solitario, Shafter, Pinto Canyon, and the Van Horn Mountains of southwest Texas. Due to the scarcity of environmentally indicative fossils in these sections, most environmental interpretations are based on physical structures such as cross-bedding and ripple marks, geochemistry, and the petrology of the sandstones and carbonates.

As the sea transgressed into the area during the late Neocomian, it eroded a topographically high Paleozoic terrane into a gently sloping surface. A basal conglomerate, the initial deposit in the sequence, is gradational upward into lagoonal, tidal flat, and beach facies, characteristic of a low-relief shoreline. During deposition, terrigenous clastic input was influential in sedimentation, and perhaps created turbid water, prohibiting development of a filter-feeding community. The stratigraphic sequence grades into the sequential development of milliolid biosparite and oosparite facies, followed by Exogyra banks and intrasparites, and finally a rudistid-bearing biosparite facies, indicating a gradual increase in water depth.

These facies patterns are recognizable in all four study localities, but were probably not synchronously deposited. The absence of correlatable biostratigraphic units makes time equivalency extremely speculative for this part of the Cretaceous section.

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