The Messinian evaporites of the Mesaoria basin (North Cyprus): A discrepancy with the current chronostratigraphic understanding

Abstract

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 (δ 34 S sulfate δ 18 O sulfate , 87 Sr/ 86 Sr) 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. • North Cyprus hosts important Messinian Salinity Crisis (MSC) evaporite deposits • MSC gypsum successions in North and South Cyprus are different • Geochemical data assigns North Cyprus evaporites to the MSC Lower Evaporites • The MSC gypsum succession in North Cyprus differs from the three-stage model • Extension of the Sicily based three-stage model to other basins is questionable