Lower Cretaceous Ferry Lake Anhydrite, Fairway Field, East Texas: Product of Shallow-Subtidal Deposition
R. G. Loucks, M. W. Longman, 1982. "Lower Cretaceous Ferry Lake Anhydrite, Fairway Field, East Texas: Product of Shallow-Subtidal Deposition", Depositional and Diagenetic Spectra of Evaporites - A Core Workshop, C. Robertson Handford, Robert G. Loucks, Graham R. Davies
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The Lower Cretaceous Ferry Lake Anhydrite, as indicated by a core study of the Cities Service Co. No. 1 J. B. Kitchens well in Henderson County, East Texas, is composed of alternating carbonate and eva-porite units that were deposited in a broad, shallow-subtidal hypersa-line, lagoonal environment. The evaporitic lagoon was up to 260 km (160 mi) wide in East Texas and was barred from the sea by shelf-margin rudist bank buildups and possibly by a tectonic sill.
Vertically to randomly aligned (elongated) mosaic anhydrite was deposited as subaqueous gypsum palmate structures that were transformed to anhydrite during diagenesis. Some bedded gypsum was also deposited subaqueously in the lagoon. The thick [up to 6.7 m (22 ft)] evaporite units contain thin carbonate mudstone layers with anhydrite rip-up clasts which represent either exposure or storm flooding of the lagoon.
Most of the carbonates, predominantly mudstones and wackestones, also were deposited in a restricted, shallow-subtidal to low-intertidal environment. The fauna consists primarily of ostracods and mollusks. Several units contain Orbitolina, and/or echinoids indicating near normal salinity prevailed periodically. Evaporites and carbonates deposited in a sabkha environment are rare.
Evaporites deposited subaqueously in a broad-shelf lagoonal setting have good lateral continuity and form excellent seals for interbedded carbonate reservoirs, and for reservoirs in the underlying stratigraphic section.
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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.