Recent Evaporites from The Abu Dhabi Coastal Flats
G. P. Butler, P. M. Harris, C. G. St. C. Kendall, 1982. "Recent Evaporites from The Abu Dhabi Coastal Flats", Depositional and Diagenetic Spectra of Evaporites - A Core Workshop, C. Robertson Handford, Robert G. Loucks, Graham R. Davies
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Recent sediments from the Abu Dhabi coast provide one of the best Holocene analogs for many ancient carbonate and evaporite sequences. These Recent deposits (locally up to 10 m thick) occur as a seaward-prograding, shoaling-upward veneer, several hundred miles long and up to 25 mi wide, over Pleistocene and Tertiary rocks. Shallow-water carbonates associated with the coastal flats include bioclastic, grapestone, and oolitic sands, pelleted aragonitic muds, and algal stromatolites. Tidal and supratidal evaporites include gypsum, anhydrite, halite, and dolomite. Landward the sediments grade into windblown clastics.
Sediment cores and trenches show that changes in evaporite mineralogy and texture occur landward across the coastal flats. The most significant changes include: 1) A bedded mush of gypsum crystals becomes more contorted and diapiric in a landward direction as it is progressively replaced by chicken-wire anhydrite. 2) Simultaneously this bed is overlain by storm washover sediments in which anhydrite occurs as nodules and blebs. 3) Further landward the anhydrite nodules coalesce to create contorted thin layers, ptygmatic in structure, that form polygonal saucers at the sediment surface. 4) At the landward margin of the coastal flats the diagenetic sequence is reversed and anhydrite is totally replaced by gypsum. These occurrences of evaporites have structures common to shoaling-upward cycles that typify many ancient sequences of carbonate and evaporite.
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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.