Isotope Composition of Messinian Sediments from the Mediterranean Sea as Indicators of Paleoenvironments and Diagensis

Abstract

Selected samples of Messinian sediments from four Leg 42A sites (Site 372 in the western Mediterranean; Sites 374, 375, and 376 in the eastern Mediterranean) were analyzed for their isotope content. Analyses were performed on carbonates (calcite, dolomite, and magnesite) for 18 O and 13 C, on sulfates (gypsum and anhy-drite) for 18 O and 34 S, and on the crystallization water of the gypsums for 18 O and 2 H. The large fluctuations of the isotopic contents of carbonates and sulfates correspond to significant changes in the sedimentary environment as follows: 1) Change from normal marine salinity to hypersaline condition. 2) Occasional influxes of large masses of continental waters and influence of groundwater circulation. 3) Variations of the redox potential which reflect changes in the hydraulic regime in the basin. These are general conditions that pertain to all the sites studied, although specific environmental conditions, as a result of local physiographic features, were noted for each site. The concept that a unique basin existed during the Messinian must be abandoned in favor of a system of minor basins which were partially and intermittently connected allowing sporadic influxes of surficial, underground, and Atlantic waters.