Deepwater Evaporites in The Bell Canyon Formation, Delaware Basin, West Texas
Wayne M. Ahr, R. R. Berg, 1982. "Deepwater Evaporites in The Bell Canyon Formation, Delaware Basin, West Texas", Depositional and Diagenetic Spectra of Evaporites - A Core Workshop, C. Robertson Handford, Robert G. Loucks, Graham R. Davies
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Thin beds of sandy, anhydritic dolomite are present in the dominantly sandy Bell Canyon Formation. Since Adams’ (1936) work, the Delaware Mountain Group has been known to be basinal in origin. Recently, Bell Canyon sandstones have been considered to represent several different processes of transportation. Various mechanisms of sedimentation notwithstanding, the Bell Canyon dolomites occur in a basinal stratigraphic setting. They contain texturally graded sands, they occur in repetitive bedsets, and they are biologically depauperate.
The dolomite consists of two distinct categories: 1) murky-brown, anhedral, subequant groundmass crystals and 2) limpid, euhedral pore filling crystals.
The anhedral, murky dolomite occurs as grains about 0.02 mm in diameter, which do not vary in size even though the included clastic fractions are graded. The limpid crystals occur only in permeability avenues in the groundmass, in burrows or as replacements in skeletal voids.
Anhydrite is present as nodules, pore-fillings and as groundmass replacements. The nodules do not exhibit fabric-penetrating crystal growth as do the pore-filling and replacement varieties, suggesting that the nodules had an early, depositional origin as gypsum spherulites.
The anhedral dolomite and the anhydrite nodules are interpreted to be early (sediment-water interface) diagenetic products which replaced gypsiferous calcilutite or calcisiltite in the deep, hypersaline stratified Delaware Basin at Bell Canyon time. The limpid dolomite, pore-filling and replacement anhydrite are interpreted to be products of early burial diagenesis. The pre-dolomitization Bell Canyon carbonates are interpreted to have been part of a cyclical-reciprocal system of sedimentation in which clastics and carbonates alternately dominated the shelf depending on variations in climate and supply of clastics. The virgin carbonates were probably soft, peloidal, gypsiferous, aragonitic muds that were entrained in density flows off the shallow Permian shelf.
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Geologists do not often have an opportunity to examine evaporites, whether in outcrops as badly weathered exposures, or in the subsurface, where evaporites are not as frequently cored as other rock types. Nevertheless, evaporites are important economically (mineral resource, seals for hydrocarbons, disposal sites for radioactive wastes, etc.) and geologists are, by necessity, becoming more aware of their origins. This workshop is intended to increase awareness and provide useful information for comparison to other evaporites, all of which should eventually benefit geologists in their efforts to understand the depositional and diagenetic spectra of evaporites.