Platform-Margin, Slope, and Basinal Carbonate Depositional Environments

Basinal Evaporite Depositional Environments

During drops in sea level, some basins can become barred from the open ocean (below). Under arid conditions, water within the basin begins to evaporate and becomes oversaturated with respect to gypsum or anhydrite. Small crystals of evaporites precipitate out of the water column and are deposited on the basin floor forming laminated evaporites. During periods of freshing, calcite laminae can form.

Diagram of a barred arid basin where water level in the restricted area is lower than that of the open sea. Water is slowly recharged to the restricted area through the barrier.

The Permian Castile Formation in West Texas is an excellent example of basinal evaporite produced in a barred basin.

Laminated Permian Castile evaporite from southeast New Mexico. The light laminae are anhydrite (deposited as gypsum). The darker laminae are calcite that precipitated as the basin freshened for short periods of time. Photograph courtesy of Peter Scholle.

Contorted Permian Castile evaporite from southeast New Mexico. The contortions are from gypsum converting to anhydrite. Photograph courtesy of Peter Scholle.

Thin sections of Castile laminated deep-water evaporites. (A) Darker layers are calcite, and lighter layers are gypsum.

(B) Same thin section but photograph taken with polarized light.

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