The Messinian marine to nonmarine gypsums of Jumilla (Northern Betic Cordillera, SE Spain): Isotopic and Sr concentration constraints on the origin of parent brines Carlos Rossi a, ⁎, Lorenzo Vilas b , Consuelo Arias b a Dept. Petrología y Geoquímica, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain b Dept. Estratigrafía (CSIC-UCM), Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain abstract article info Article history: Received 17 July 2015 Received in revised form 24 August 2015 Accepted 25 August 2015 Available online 2 September 2015 Editor: B. Jones Keywords: Evaporites Gypsum Sulfur isotopes Strontium isotopes Messinian Salinity Crisis Betic Cordillera The origin of the Messinian Hoya de la Sima (HS) gypsum (Betic foreland) is constrained using 87 Sr/ 86 Sr, δ 34 S, Sr concentration, and petrographic data. The Lower and Middle HS units consist of subaqueous vertically-aligned and stromatolitic selenites, the latter containing unusual microbial depositional textures. The Upper Unit consists of very-shallow-water bioturbated lenticular gypsum with Paracamelus ichnites. 87 Sr/ 86 Sr and δ 34 S indicate pre- cipitation from predominantly marine waters, with upward increasing continental influence. Mixing models be- tween Messinian seawater and continental water that dissolved Triassic evaporites show that the percentages of seawater required to explain the measured 87 Sr/ 86 Sr are analogous to the percentages obtained using δ 34 S, supporting precipitation from such mixtures. 87 Sr/ 86 Sr and δ 34 S of Lower HS selenites resemble those of the Primary Lower Gypsum (PLG) of the Messinian Salinity Crisis (MSC), in both cases indicating precipitation from seawater–continental water mixtures in which most Sr and SO 4 were supplied by Messinian seawater. In the Lower HS selenites, Sr concentrations indicate contributing continental waters with Sr/Ca ratios similar to seawater. However, Sr concentrations of PLG selenites from other Betic basins (Bajo Segura, Sorbas indicate par- ent waters with Sr/Ca ratios lower than seawater. If the Sr contents of the betic PLG selenites are representative, it is unlikely that the Lower HS selenites represent the PLG. However, we cannot completely discard that option since different LPG subbasins could have had variable Sr/Ca. The HS gypsums formed coevally to diapirism of Tri- assic evaporites, in a restricted lagoonal basin developed during or slightly after a phase of strike-slip faulting in the Betic Cordillera. More general implications of this work are that Sr concentrations, combined with 87 Sr/ 86 Sr and δ 34 S data, provide key constraints on the origin of parent brines, and using Sr concentrations as paleosalinity proxy in gypsum precipitated from seawater–continental water mixtures is inconclusive because they largely de- pend on the initial Sr/Ca ratio of the brine. This study also illustrates that the electron microprobe is ideal to obtain reliable, spatially-resolved, Sr concentration data in selenitic gypsum. These data, in combination with fluores- cence petrography, provide valuable criteria to discriminate primary depositional from diagenetic gypsum, a crit- ical step in the interpretation of geochemical data. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Gypsum/anhydrite formations typically lack diagnostic fossils; therefore their precise age and origin (marine vs. continental) are com- monly uncertain. Since the evaporative precipitation of CaSO 4 requires Ca 2+ not to be consumed during the CaCO 3 precipitation phase, parent waters must have a relatively high Ca 2+ to HCO 3 - ratio, i.e. they must have significant concentrations of other anions apart from bicarbonate (such as SO 4 2 - and Cl - ). Consequently, CaSO 4 easily forms by evaporation of seawater, given its relatively high Ca 2+ /HCO 3 - and SO 4 / HCO 3 - ratios. By contrast, the evaporative concentration of typical conti- nental waters does not produce CaSO 4 . This is because the anionic con- tent of those waters is largely dominated by bicarbonate, causing Ca 2+ to be eliminated from the brine during the phase of evaporative CaCO 3 precipitation, impeding further precipitation of Ca-bearing evaporites such as gypsum (Hardie and Eugster, 1970). Therefore, the precipitation of CaSO 4 evaporites from continental waters normally requires these waters to be enriched in sulfate, via mixing with seawater or by interac- tion with sulfate-bearing rocks such as marine-derived evaporites. The isotopic composition of CaSO 4 evaporites constrains the origin of the parent brines. The fractionation of sulfur isotopes during gypsum precipitation is very small: δ 34 S of evaporitic sulfate is only slightly higher (less than ~ 1‰) than in the brine (Raab and Spiro, 1991). Taking Sedimentary Geology 328 (2015) 96–114 ⁎ Corresponding author. E-mail address: crossi@geo.ucm.es (C. Rossi). http://dx.doi.org/10.1016/j.sedgeo.2015.08.007 0037-0738/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo