Formation of laminated and opal-rich sediments in the Mediterranean region during the late Neogene and Quaternary

The mechanisms for the formation of laminated and opal-rich facies from the Mediterranean region during the late Neogene have been investigated. Bannock Basin, a presently anoxic basin in the eastern Mediterranean has been studied to understand the roles of productivity and preservation in the formation of the most recent sapropel (9,000 YBP). Through the use of an organic carbon preservation factor, productivity during sapropel deposition 9,000 YBP is estimated to have been an order of magnitude higher than present. These results suggest that sapropel formation occurred primarily as a result of increased productivity, which along with changing hydrographic conditions resulted in enhanced organic matter preservation.;Opal-rich sediments known as diatomites from the Bianco section in southern Italy have also been examined geochemically. Biogenic silica and carbonate content, and the carbon isotopic composition of benthic foraminifera suggest that the Bianco diatomites represent periods of increased productivity. Stable isotope analyses of planktonic foraminifera suggests that the increased productivity was the result of basin eutrophication brought on by continental runoff.;Analyses of planktonic foraminifera from six Vrica laminites were made in order to assess what if any, paleoclimatic changes occurred during the transition from Pliocene to Pleistocene in this region. A distinctive low-salinity assemblage can be identified within the laminites, supporting earlier interpretations based on geochemical results. The temperature-dependent assemblages indicate that a significant climatic cooling occurred across the Plio/Pleistocene boundary. This boundary in the Mediterranean represents a climatic shift towards cooler temperatures, although this cooling cannot be always be recognized in Plio/Pleistocene sections outside this region.;Laminated sediments (known as laminites) also occur in uplifted marine sequences from southern Italy and Sicily. Selected laminites from Gela (Sicily) and from Vrica (southern Italy) were studied geochemically in order to reconstruct the sequence of events which led to the deposition of these sediments. The Vrica and Gela laminites were formed as a result of enhanced terrestrial organic carbon input and preservation, during periods of basin stratification.