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Sabkhas, Ancient and Modern

By

LOCK, BRIAN E.

University of Louisiana, Lafayette, LA

 

Sabkhas are common sedimentary environments and in many cases have associated hydrocarbon traps. The Gulf Coast Jurassic and Cretaceous includes several subsurface examples (Smackover, Buckner, Norphlet Formations) as do older formations in the Upper Paleozoic of Texas and neighboring states.

This study concentrates on Recent sediments neighboring the Gulf of California, together with Cretaceous outcrops in southern Arkansas and central Texas and Permian strata in southeastern Utah.

The Mexican sabkhas are dominated by trona and other sodium carbonate minerals, derived from volcanics in the interior of the Gran Desierto. A hydrologic system similar to that recognized from the Abu Dhabi sabkhas is confirmed, since most of the Sonoran evaporites are derived by evaporative pumping of continental groundwaters. Near the coast, groundwater chemistry becomes marine in character, although of exceptionally high salinity.

The Cedar Mesa Formation (Permian) of Utah is primarily composed of eolian dunes. To the southeast, these dune sands include gypsum eolianites deflated from neighboring sabkhas. Interdunes in this area include thin limestones, some of which contain marine fossils. The sabkha sediments display many of the textures and structures described from Abu Dhabi, including enterolithic anhydrite and “desert rose” gypsum nodules.

The Cretaceous (De Queen Formation) sabkhas of Arkansas illustrate very well the dual source of detrital sediment in this environment. Siliciclastic muds (containing Chara) are washed in from the landward side during floods, and ooliths from the seaward side during storms. Changing patterns of salinity are documented by the foraminiferal abundance and diversity in fine grained sediments. Sedimentary structures include desert roses and lenticular (discoidal) gypsum and related anhydrite nodules, and palmate gypsum in supratidal ponds.

This variety of examples provides additional templates for recognizing and understanding subsurface sabkhas.