A Textural Analysis of Trona and Associated Lithologies, Wilkins Peak Member, Eocene Green River Formation, Southwestern Wyoming
Stuart J. Birnbaum, Thomas M. Radlick, 1982. "A Textural Analysis of Trona and Associated Lithologies, Wilkins Peak Member, Eocene Green River Formation, Southwestern Wyoming", Depositional and Diagenetic Spectra of Evaporites - A Core Workshop, C. Robertson Handford, Robert G. Loucks, Graham R. Davies
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A TexasGulf composite core representing deposition during Wilkins Peak time of the Green River Formation (Eocene) is described. Two major facies, a mudstone facies and a trona facies, represent deposition within ephemeral alkaline saline Lake Gosiute. A laminated mud-stone subfacies indicates a distal saline mudflat subenvironment, whereas a crumbly, homogeneous mudstone formed within a proximal saline mudflat subenvironment. Oil shale signifies flooding and expansion of the lake with associated organic blooms. Drying of the lake permitted precipitation of trona in two forms; a) a displacive nodular type consisting of radiating crystals, and b) a granular or sugary type of detrital origin. A third, postdepositional trona type is described as a columnar crystalline vein type associated with hydraulic fracturing.
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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.