STRONTIUM GEOCHEMISTRY OF MIOCENE PRIMARY GYPSUM - MESSINIAN OF SOUTHEASTERN SPAIN AND SICILY AND BADENIAN OF POLAND

The strontium contents of primary marine gypsum facies were studied in Messinian (Upper Miocene) basins of SE Spain and Sicily, and in the B adenian (Middle Miocene) Carpathian foreland basin of Poland, The resu lts obtained were interpreted on the basis of the findings reported fo r the gypsum facies of recent salinas in the western Mediterranean coa st, The strontium profile obtained from the lower part of the gypsum d eposit of the Sorbas basin (SE Spain) has homogeneous strontium conten ts, reflecting deposition under conditions of hydrological stability a nd relatively deep waters, but the upper part has a more variable stro ntium content related, in accordance with other sedimentological crite ria, to a shallowing of the basin, This is consistent with data report ed from other Messinian basins of SE Spain (San Miguel de Salinas and Palma de Mallorca), In the Caltanissetta basin (Sicily), the section s tudied in Eraclea Minoa (Upper Evaporite) is made up of 6-8 gypsum cyc les that have a facies evolution from fine-grained laminar gypsum at t he base of each cycle to selenites at the top, accompanied by increasi ng strontium values, This evolution is attributed to increasing salini ty conditions and is consistent with geochemical data reported in the Literature, In the Badenian basin the six gypsum sections studied are from different subbasins, The gypsum deposits comprise two members, In the lower member, which is mainly selenitic, two parts can be differe ntiated and a significant strontium increase (attributed to a rise in salinity) was recorded in the transition from the lower to the upper p art, In the upper member, which is mainly elastic gypsum, a general st rontium decrease indicates a fall in salinity linked to a deepening or freshening of the platform, In the Badenian selenitic layers a latera l variation in the strontium contents exists: higher and less homogene ous strontium contents were recorded in the marginal zones, suggesting variable salinity conditions, whereas in the deeper areas the gypsum layers show more homogeneous strontium values, expected from more stab le and less concentrated brines, This distribution is in agreement wit h data reported from the Messinian basin of San Miguel de Salinas (SE Spain), The strontium contents in both the Messinian and Badenian sele nitic samples are lower than those in the selenitic crusts of the rece nt salinas, These lower contents may be a result of a lower salinity o f the mother brines at the steady state achieved during the precipitat ion of the thick selenitic sequences, with respect to the highly conce ntrated (with no reflux) brines of the recent salinas, Our findings hi ghlight the relevance of studying strontium contents in primary gypsum facies of marine formations as a tool for interpreting the paleogeogr aphy and the paleosalinity of the evaporitic environments and for corr elating cyclic selenite formations, This method could be especially he lpful when combined with other geochemical indicators (i.e., isotopic and/or fluid inclusions composition).