High salinity variability during the early Messinian revealed by stable isotope signatures from vermetid and Halimeda reefs of the Mediterranean region.

The early Messinian deep-water record of the Mediterranean region reveals increasing evidenceof significant salinity stress prior to the Messinian Salinity Crisis (MSC). In shallow reef environments such apattern has not yet been documented, however, the paleoecological interpretation of some sedimentarycomponents, such as stromatolites in coral reef frameworks, has remained ambiguous. We present data from openand semi-restricted reef settings of southern Italy and Greece (Crete), where stable isotope analyses have beenmade on early marine carbonate cements from vermetid reefs and Halimeda bioherms. d18O compositions ofmarine cements translate into sea surface salinity (SSS) peaking at 50 to 60‰, certainly too high for most shallowwater biota (i.e. zooxanthellate corals). It seems, therefore, that recurrent events of high salinity have occurredcausing events of community replacement eventually ending up in “abiotic” episodes. These events, however, weretoo short to be recorded as discrete beds in 4th order depositional sequences. Because the cements reflecting highsalinity occur equally in the platform margin and reefal slope facies, salinity build-up was not linked to evaporativedraw-downs of sea level. Such a scenario fits concepts of the MSC starting synchronously over great part of theMediterranean as a deep brine pool.