From diatom opal-A delta O-18 to chert delta O-18 in deep sea sediments

摘要

delta O-18 signature of marine deep-sea cherts was previously used to reconstruct past ocean temperature and oceanic bottom water delta O-18 through the Cenozoic and Mesozoic periods. Oxygen isotopes in deep-sea cherts which were never exposed to meteoric water exhibit a wide range of values indicating that the evolution and maturation of biogenic amorphous opal (opal-A) to opal-CT and microquartz chert is accompanied by isotopic changes. We measured delta O-18 of diatom opal-A, opal-CT, and microquartz chert in downcore profiles of sediment cores ODP 795 and 799 from the Sea of Japan. Diatom opal-A, opal-CT and microquartz chert were separated and purified from the bulk sediment. This was followed by XRD, SEM/EDS and XPS to identify and quantify the mineral phases, the qualitative elemental concentrations and the amounts of authigenic clays.