DEPOSITIONAL PROCESSES AND BASIN ANALYSIS OF MESSINIAN EVAPORITES IN CYPRUS

Messinian evaporites in Cyprus resulted from the interplay of Mediterr anean-wide and eustatic sea-level changes and local tectonics, in an i nferred above-subduction zone setting. Distinctive Tortonian-early Mes sinian pre-evaporitic facies include diatomaceous marls and microbial carbonates, overlain by a variety of gypsum facies and then by lagoona l-lacustrine deposits and local palaeosols. Facies analysis and compar isons allow construction of a simple model, in which evaporites formed in semi-isolated small basins not far below global eustatic sealevel. Coarsely crystalline gypsum formed in situ along the margins of small basins and within shallow-water lagoons (< 10 m deep); this comprised common banded-stacked (i.e. layered) selenite, swallowtail selenite, botryoidal selenite and sugary-bedded selenite. Fine-grained gypsum pr ecipitated widely and was reworked into basinal areas (< 70 m deep) by weak traction currents and low-density turbidity currents. Shallow-wa ter derived selenite was also reworked basinwards by high-density turb idity currents and debris flows. Slumps indicate tectonic instability. More detailed basin analysis can be achieved by study of individual s ub-basins. In the Polemi sub-basin in the west, a Lower Unit (up to 60 m thick) comprises basinal gypsum, interbedded with gypsum turbidites and mass flow deposits, with slumps. This is overlain by an extensive mega-rudite (up to 20 m thick) including up to metre-sized clasts of marginal gypsum facies. Above, the Upper Unit (up to 70 m thick) inclu des shallow-water gypsum (e.g. swallowtails), marl and minor microbial carbonates. The Pissouri sub-basin in the south-west exposes marginal facies of the Upper Unit, including deltaic clastics and palaeosols. The Maroni sub-basin in the south exhibits a basinal lower gypsum unit , with laterally equivalent marginal facies (up to 50 m thick), overla in by an extensive mega-rudite (up to 20 m thick). Finally, the Mesaor ia sub-basin in the north exposes relatively marginal gypsum facies in an unstable tectonic setting. Formation of the Polemi, Pissouri and M esaoria gypsum sub-basins relates to coeval extensional faulting and g raben development. Evaporites in south Cyprus (Maroni subbasin) formed in elongate basins between former compressional lineaments treated by localized Early Miocene thrusting. In the subbasins of west, south-we st and south Cyprus, large-scale stumping of marginal gypsum facies to ok place towards depocentres (to form mega-rudite debris flows), trigg ered by one or several phases of extensional faulting.