Sabkha Anhydrite: The Supratidal Facies Of Cyclic Deposition In The Upper Minnelusa Formation (Permian) Rozet Fields Area, Powder River Basin, Wyoming
C. W. Achauer, 1982. "Sabkha Anhydrite: The Supratidal Facies Of Cyclic Deposition In The Upper Minnelusa Formation (Permian) Rozet Fields Area, Powder River Basin, Wyoming", Depositional and Diagenetic Spectra of Evaporites - A Core Workshop, C. Robertson Handford, Robert G. Loucks, Graham R. Davies
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Marine cyclic deposition is very apparent in cores of the Upper Minnelusa Formation in the Rozet Fields area, Powder River Basin, Wyoming. A complete cycle from bottom to top is comprised of 1) subtidal facies of dolomicrite or dolomitized packstone that may contain fusulinids or crinoid fragments, 2) intertidal facies of algal-laminated or layered dolomicrite which may be desiccated and slightly brecciated, and 3) supratidal facies of anhydrite marked by “chicken wire” structure. However, complete cycles are interrupted by exceptionally clean, well sorted quartz sandstone units that may have been deposited in a variety of closely-related, coastal environments including very shallow subtidal (foreshore), beach, and eolian.
A Minnelusa cycle and its facies have close counterparts in the Recent sabkhas near Abu Dhabi on the Trucial Coast, Persian Gulf. In addition, mapping of Minnelusa sabkha facies reveals 1) sabkhas were very narrow, 2) trend in the same direction, and 3) are separated by quartz sandstones that make up linear dune trends of possible eolian origin. A Recent analog of the Minnelusa sabkha-eolian dune complex is seen in the area southeast of Abu Dhabi where narrow sabkhas are separated by longitudinal, eolian dunes. Thus, it appears that Minnelusa anhydrites formed in a sabkha setting very similar to the modern sabkha-eolian dune complex southeast of Abu Dhabi.
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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.