Diagenetic gypsum related to sulfur deposits in evaporites (Libros Gypsum, Miocene, NE Spain)

In the diagenetic gypsum, the δ34S values are in agreement with a native sulfur and H2S provenance. The δ18Osulfate values, however, enable us to differentiate two main groups of values: one with positive values and the other with negative values. In the group of positive values, interstitial (evaporated) solutions participated in the sulfur oxidation; this process presumably occurred in a first oxidation stage during shallow-to-deeper burial of the Libros Gypsum unit. In the group of negative values, however, only meteoric waters participated in the oxidation, which presumably occurred in a second oxidation stage during the final exhumation of the unit. A third group of values is characterized by very high sulfur and oxygen values, suggesting that BSR residual solutions also participated in the oxidation processes locally. During the two oxidation stages, both the textural characteristics and the isotopic composition of the diagenetic gypsum indicate that gypsification operated as a multistadic process.