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Relationship between
Midland and Delaware Basin Units

The exact equivalence between the Delaware Basin units and the Central Basin Platform-Midland Basin units remains somewhat problematic. Time and facies relationships require that the units equivalent to the Castile on the shelf equivalent are thin or missing. The Castile evaporite in the basin was deposited very rapidly because of relatively high CaSO4 concentrations in evaporite brine and accommodation in the deep basin.

I interpret that the most likely platform equivalent to the Castile Formation are the stacked high-frequency anhydrite cycles in the lower anhydritic part of the Tansill Formation. This interval (commonly called the Fletcher Anhydrite) in the Gulf PDB-04 core from the Capitan Reef in New Mexico is composed of anhydrite, minor carbonate, and red mudstone (Garber and others, 1989). I interpret the textures in this core as the product of repeated episodes of brine-pool deposition followed by diagenetic modification of brine-pool gypsum in a vadose-to-hypersaline ground-water environment. Bottom-grown textures have been intensely modified, red mud introduced during exposure episodes, and displacive gypsum sand crystals formed in a shallow ground-water environment. This correlation fits an interpretation of an alternately flooded and exposed shelf that accumulated condensed cycles at the same time the basin was rapidly filling with gypsum and halite.

If this correlation is accepted, then the shallow-water halite of the Salado Formation above MB134 in the Delaware Basin is then approximately correlated with the halite-siliciclastic cycles at the top of the Tansill and base of the Salado Formations of the Central Basin Platform and Midland Basin. Tentative correlations of groups of Salado polyhalite beds and individual anhydrite beds can then be made from the Delaware Basin into the Salado Formation on the Central Basin Platform.

Stratigraphic Units and Type Logs
North–South Stratigraphic Cross Section