Trace elements and environmental significance of Messinian gypsum deposits, the Nijar Basin, southeastern Spain

Abstract

The Messinian evaporites in Nijar Basin, southeastern Spain are composed of coarse-crystalline Yesares selenites and Feos laminated fine-crystalline gypsum. These primary Yesares selenites, Feos gypsum, and secondary vein gypsum were analyzed for trace elements (Na, Mg, and Sr) in order to understand gypsum origin. Trace-element concentrations from the three types of gypsum differ significantly. The consistency of the Yesares data with natural marine and modeled marine results suggests that Yesares selenites were deposited from marine-dominated environments. Within the entire Yesares Formation or within one single-gypsum bed, Sr, Mg, and Na concentrations increase upward while crystal size decreases, probably indicating an increase of brine concentration as Yesares selenites were accumulating. The Sr, Na, and Mg concentrations from the Feos gypsum are partially overlapped with, but also significantly higher than those of the Yesares selenites. These Feos data are inconsistent with natural marine and modeled marine data. One interpretation for the inconsistency is that diagenetic alteration occurred to primary marine Feos gypsum. An alternative scenario is that the Feos gypsum was deposited from mixed nonmarine fluids with marine brine during the late Messinian. The latter interpretation is consistent with the stratigraphic, sedimentary, and O, S, and Sr isotopic data.