Abstract

The peripheral evaporite platform of the Zechstein (Upper Permian) Werra Anhydrite of western Poland comprises a series of shoals (with thick sulfate deposits) and lows (with thin sulfate and thick halite deposits). Three cores were selected to examine facies variations from a sulfate platform, slope, and basin. The basal unit of the Lower Werra Anhydrite is represented by different varieties of nodular, bedded-nodular, fluidal-nodular, and brecciated facies. Some nodular fabrics probably originated within sabkha and/or gypsumpond environments, and the deposit was then mechanically redistributed. The absence of nodular structures in units other than the lower one in two of the wells suggests that the origin of these structures cannot be related to deep burial. Other units of the Lower Werra Anhydrite represent subaqueous deposits. The facies in the middle and upper units have no recent analog in coastal salina environments. Turbidity currents displaced sulfates from the platform to the adjacent basin. The origin of lenticular-bedded anhydrite may be related to deformation by compaction or by gravitational instability and slumping, which may have initiated crystallization or recrystallization of anhydrite. The vertical sequence of facies shows a distinct deepening-upward trend starting from the top of the basal nodular units. Deposition in shallow (salina) environments dominated the early history of the Lower Werra Anhydrite basin, although it was probably preceded by transgressive sabkha deposits. Relatively thick nodular anhydrites probably formed by syndepositional diagenesis of probable salina deposits and minor sabkha sediments. Gypsum was the original sedimentary mineral; it was later transformed into anhydrite, during either early or late (burial) diagenesis. We show that in deeply buried evaporites not only some macroscopic primary textures remain but also even microscopic details, which allow reconstruction of depositional environments and primary mineralogy of ancient anhydrites.

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