Abstract

Three stages of paradiagenetic transformation of primary anhydrite are considered responsible for formation of selenitic secondary gypsum which is abundantly developed in one of the two facies distinguished in the gypsum member of the upper Miocene sulfur series of Sicily (Italy). An initial stage of relatively free growth of large clear selenite crystals was followed by ruptural deformation in border zones as a result of volume increase, and finally by development of a fine-grained aggregate of mylonitic character. The sequence is the reverse of the integration process postulated by Goldman for the growth of large gypsum crystals from aggregates of smaller ones. The saliferous facies of the gypsum formation is characterized by the presence of alabastrine secondary gypsum, formed under considerable load and probably in a later stage of diagenesis.

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