The distribution of dolomite in the Laney Shale Member of the Green River Formation in the western Green River Basin provides further documentation regarding the suitability of the playa-lake model for the Green River Formation in Wyoming. Four alternate mechanisms were considered in evaluating the origin of the dolomite: (1) detrital, (2) late diagenetic, (3) primary, and (4) penecontemporaneous. It is concluded that dolomite in the Laney Shale Member is the product of penecontemporaneous dolomite formation that results from the evaporative concentration of subsurface Mg-rich brines in the mud flats. Qualitative thermodynamic diagrams are constructed that depict carbonate equilibrium relations in the mud flats and adjacent environments.

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