Abstract The Lorca and Fortuna basins are two intramontane Neogene basins located in the eastern Betic Cordillera (SE Spain). During the Late Tortonian—Early Messinian, marine and continental evaporites precipitated in these basins as a consequence of increased marine restriction and isolation. Here we show a stratigraphic correlation between the evaporite records of these basins based on geochemical indicators. We use SO 4 isotope compositions and Sr isotopic ratios in gypsum, and halite Br contents to characterize these units and to identify the marine or continental source of the waters feeding the evaporite basins. In addition, we review the available chronological information used to date these evaporites in Lorca (La Serrata Fm), including a thick saline deposit, that we correlate with the First Evaporitic Group in Fortuna (Los Baños Fm). This correlation is also supported by micropalaeontological data, giving a Late Tortonian age for this sequence. The Second Evaporitic Group, (Chicamo Fm), and the Third Evaporitic Group (Rambla Salada Fm) developed only in Fortuna during the Messinian. According to the palaeogeographical scheme presented here, the evaporites of the Lorca and Fortuna basins were formed during the Late Tortonian—Early Messinian, close to the Betic Seaway closure. Sulphate isotope compositions and Sr isotopic ratios of the Ribera Gypsum Mb, at the base of the Rambla Salada Fm (Fortuna basin), match those of the Late Messinian selenite gypsum beds in San Miguel de Salinas, in the near Bajo Segura basin (40 km to the East), and other Messinian Salinity Crisis gypsum deposits in the Mediterranean. According to these geochemical indicators and the uncertainty of the chronology of this unit, the assignment of the Rambla Salada Fm to the MSC cannot be ruled out.
Gypsiferous units occur along the margins of some Paleogene and Neogene basins in Spain. These units accumulated in shallow saline lakes of low ionic concentration. Other gypsiferous facies constitute outer rings of the thick, highly-saline evaporite formations that occupy the central parts of the basins. In some of these gypsum units and rings, large nodules (from 0.5 m to several metres across) of secondary gypsum that originated as replacive or displacive nodular anhydrite are present. Although these occurrences usually show a stratiform arrangement, vertical geometries are observed locally, suggesting ascending circulation of anhydritizing flows. The common characteristics of the large gypsum nodules in the various occurrences indicate that the precursor anhydrite formed in burial conditions from shallow to moderate depths. A few occurrences of large, secondary gypsum nodules in the gypsum units are linked to deep faults or diapiric structures.
Large volume of evaporites were deposited during the Messinian Salinity Crisis (MSC) across the Mediterranean. These evaporites are currently outcropping on land and are interpreted by seismic profiles beneath the Mediterranean floor. Biostratigraphic, magnetostratigraphic and astrochronologic data recovered from sediments below and above outcropping evaporites, together with gypsum facies associations and stratigraphic cyclicity, are the cornerstone of what is known as the MSC 'three-stage' model: Primary Lower Gypsum (PLG) – MSC stage 1, Resedimented Lower Gypsum (RLG) - MSC stage 2, and Upper Gypsum (UG) – MSC stage 3. Although this litho- and chronostratigraphic model is mainly based on the gypsum succession in Sicily, it is being currently applied by many investigators across the Mediterranean. The Mesaoria basin, in North Cyprus, hosts well exposed MSC gypsum deposits of the Kalavasos Fm. Two informal units are distinguished in the gypsum succession. The lower unit, largely consisting of clastic gypsum deposits, is conformably overlaid by the upper unit, mostly consisting of 'in situ' vertically-oriented selenite deposits. Based on the lithostratigraphic gypsum succession, the lower unit could be tentatively assigned to RLG - MSC stage 2, while the upper unit could correspond to UG - MSC stage 3. However, our lithologic and geochemical (δ34Ssulfate δ18Osulfate, 87Sr/86Sr) data in gypsum points that the upper unit fits with those of the PLG – MSC stage 1. For the first time, thick vertically-oriented selenite beds with lithofacies and geochemical signatures diagnostic of PLG deposits lay conformably over clastic gypsum successions diagnostic of RLG deposits in the currently accepted 'three-stage' model. In North Cyprus, 'in situ' selenite platforms and 'clastic' gravity-flow gypsum deposits are coeval involving erosion and redeposition during the same evolutive stage. The complete gypsum succession in North Cyprus must be considered as MSC Lower Evaporites in the 'two-step' model (Lower Evaporites and Upper Evaporites) classically proposed prior to the 'three-stage' model. We show how nearby Messinian evaporite basins in the same island (North and South Cyprus) can produce different sedimentary records. Our data cast doubts on the systematic application of the 'three-stage' litho- and chronostratigraphic model to North Cyprus and other MSC Mediterranean evaporite successions. This work highlights the importance of local processes in the sedimentation and distribution of MSC evaporites in active tectonic settings, and alerts against extrabasinal MSC correlations based on gypsum facies distribution.
Sedimentological evidence for an abrupt dry spell in south-eastern Spain during the middle Holocene, from c. 4906 to 4384 cal. yr BP, is presented. This phase was determined primarily from halite beds deposited between muddy slimes in a lagoon system of Puerto de Mazarrón (Murcia province) with a peak phase from c. 4550 to 4400 cal. yr BP. A multi-core, multi-proxy study of 20 geotechnical drills was made in the lagoon basin to identify the main sedimentary episodes and depositional environments. The results suggest that this halite bed, more than 80 cm thick, was conditioned by climate change and was accompanied by a generalized drying-out of the basin. Halite precipitation was linked with palaeoecological changes, including forest and mesophyte depletions and increasing cover and diversity of xerophytic plant species. Archaeological evidence indicates a demise of the population at this period probably due to resource exhaustion. An overall picture of the biostratigraphy and palaeoclimates of the region is given in a broader geographical context.