Laminated sediments from the Vrica section (Calabria, S. Italy): evidence for plio-pleistocene climatic change in the Mediterranean region

Six laminated sedimentary units (laminites) from the Vrica section (Calabria, southern Italy) have been analyzed geochemically and micropaleontologically to assess paleoclimatic conditions in this region during the transition from the Pliocene to the Pleistocene. Two laminites formed during the early Pleistocene and one formed immediately below the Pliocene/Pleistocene boundary; all have a greater organic carbon content relative to the surrounding marls. By contrast, three late Pliocene laminites exhibit no significant increase in organic carbon, which indicates that the conditions associated with the formation of these three units were somewhat different than those associated with the formation of the three younger laminites. Stable isotope analyses of planktonic foraminifera from the laminites indicate that all of these units were formed during periods of decreased salinity concentrations in surface waters. The laminites were formed as a result of basin anoxia brought on by increased surface-water stratification during periods of high runoff. The Vrica planktonic foraminiferal census data indicates that the laminites contain a distinctive fauna which can be partially attributed to increased nutrient concentrations. By contrast, species assemblages within the marls seem to be primarily controlled by surface-water temperatures. Through the use of polytopic vector analysis, the foraminiferal census data can be simplified into five assemblages, each of which reflects temperature, salinity and/or nutrient concentrations. The nutrient-dependent assemblage indicates an intensification in surface water productivity during periods of laminite formation during the later Pliocene and early Pleistocene, while the temperature-dependent assemblages indicate an overall cooling of surface-water temperatures during the same period. The results of the planktonic foraminiferal analyses support the concept of a regional cooling across the Pliocene/Pleistocene boundary in the Mediterranean. In addition, the results of this study indicate that these climatic changes resulted in differences in the nature of the laminites. Cooler climatic conditions during the latest Pliocene and the early Pleistocene favored the formation of laminites slightly richer in organic carbon and nitrogen because of increased organic carbon input or enhanced organic matter preservation. The warmer climatic conditions of the late Pliocene produced laminites relatively poor in organic carbon and nitrogen as a result of either decreased runoff or decreased organic matter preservation. \ua9 1990