Abstract: Environments of Evaporitic Sedimentation: Shallows, Sabkhas, Shelves, and Sumps

Robert Evans

For too long, many geologists have accepted the simplistic explanation that evaporites are formed in shallow-barred basins. In recent years, an understanding of supratidal environments led to widespread acceptance of the sabkha as another model for some ancient deposits of anhydrite. An appreciation of the subtlety of evaporitic rocks is dependent, however, upon the realization that they can form in a variety of environments: shallow lagoons, supratidal flats, deep-water basins, and broad shelves.

Kara-Bogaz-Gol, on the east side of the Caspian Sea, still serves as the classic model of a shallow-barred lagoon. The Castile Formation of the Delaware basin is a familiar example of a thick evaporite formed in deep water. Sabkhas along the Persian Gulf have been described in such detail that there is no difficulty in applying a supratidal model to explain some ancient anhydrite or gypsum units. The little known Cambrian evaporites of Siberia formed from marine waters which became hypersaline as they moved across a broad shelf.

Several large evaporite deposits can be understood only when several of these models are applied to the same rocks. The Silurian deposits of Michigan, Ohio, and New York display features of deep-water deposition in basin centers, shallow-water features near margins, and sabkha-like characteristics at the basin edge. Deep-water deposition which produced the Castile Formation changed to shallow-water and supratidal sedimentation after the original basin filled, and the Salado Formation therefore is markedly different in sedimentologic features from the Castile, even though the two deposits are stratigraphically adjacent, and superficially similar.

Evaporites can provide us with much environmental information if we recognize that they result not from simple shallow-water or sabkha sedimentation, but from an interplay of several sedimentary regimes.

AAPG Search and Discovery Article #90970©1977 AAPG Southwest Section Meeting, Abilene, Texas