Sedimentology and geochemistry of late Miocene carbonates and evaporites in Nijar area, southeastern Spain

Late Miocene stratigraphy in Nijar area, Spain consists of platform carbonates and basinal evaporites. The Nijar Miocene platform carbonates composed of skeletal carbonates, reef rocks and post-reef oolites, have been extensively dolomitized. Limestones are present in the most landward parts of the platform, in stratigraphically lower units and topographically highest outcrops, suggesting that dolomitizing fluids were derived from the adjacent Nijar Basin. The dolomite crystals range from <10 to ∼100 mum existing as both replacements and cements. Tertiary and modern brine dolomite values, and also overlapping values from mixing-zone dolomites. Sr concentrations range between 50 to 300 ppm, and the molar Sr/Ca ratios of dolomitizing fluids are estimated to range between 7x seawater brine to freshwater ratios. The delta18O and delta13C of the dolomite range from -1.0 to +4.2‰ PDB, and -4.0 to +2.0‰ PDB, respectively.; Minor and trace element (Na, Cl, Mg, K, Sr) abundances in gypsum and anhydrite can be used to help elucidate paleosalinity and depositional environments. However, gypsum may contain abundant fluid and solid inclusions which can contribute considerable amounts of elements to bulk-analyses. Results show that Mg and Sr are less sensitive (usually <30%) to the inclusion stripping procedures than Na and Cl. Up to 98% of the Cl was removed from bulk gypsum and anhydrite by the grinding, heating and rinsing procedures. Cl contents in treated samples and inclusion-free samples are very low (usually a few ppm). The procedures also removed Na up to 80% from the bulk-samples.; Messinian Nijar basinal strata consist of three formations, the marine Abad marls, Yesares marine evaporites, and nonmarine Feos rocks in an ascending order. Six gypsum lithofacies characterized by crystal size, fabrics, and carbonate content were identified from the Nijar Messinian gypsums: coarse twinned selenite, grass-like selenite, hemiradial to radial selenites, reworked/turbidite selenites in the Yesares Formation, and conglomerate gypsum and laminated gypsum in the Feos Formation. Each represents a different depositional environment.; The Yesares selenites, Feos laminated gypsum, and vein gypsum from the Nijar Basin, were analyzed for Na, Mg, Sr, Mn, and Fe abundances in order to understand their depositional environments and diagenesis.; The similarity of 87Sr/86Sr values of Yesares gypsum to the Messinian seawater suggests a marine origin.; The modeled results suggest that the Yesares selenites were deposited from marine brines in which significant redox reaction took place between sulfate and sulfide. The modeled results also could provide important geological implications for isotope and environment interpretations of other ancient evaporites. (Abstract shortened by UMI.)...