37. GEOCHEMICAL HISTORY OF POST-JURASSIC SEDIMENTATION IN THE CENTRAL

Analysis of the distribution of major components and heavy metals in a section of post-Jurassic deposits of southern Hess Rise (Deep Sea Drilling Project Site 465), the results of processing analytical data by factor analysis, in-terpretation of information on mineralogy and lithology of sediments, and evaluation of rates of component accumula-tion enable distinction of the main stages in the geochemical history: (1) Late Albian-early Cenomanian (early oceanic), in which the accumulation of mostly shallow-water carbonate sediments of turbiditic nature enriched in organic matter and volcanogenic materials was proceeding; the sediments are characterized by maximally high contents of Fe, Mn, SiO2, A12O3, and associated heavy metals, present in the form of basaltic volcaniclastic material and, to a lesser extent, hydrothermal and exhalation products and materials of their post-sedimentary transformation (smectite, hydromica, Mn-Fe-Mg-carbonates); extremely high rates of accumulation of components are representative of this given stage. (2) Late Cretaceous (middle Cenomanian-late Maastrichtian), in which the accumulating sediments were considerably eroded along some hiatuses (middle Cenomanian-middle Turonian; late Coniacian; early Campanian); during the Cenomanian-Coniacian, this region is assumed to have been in the subequatorial zone of high biological productivity, within the general northward movement of the Pacific Plate (Lancelot and Larson, 1975; Lancelot, 1978; van Andel, 1974). Considering geochemical features, the sediments of this stage are similar to biogenic carbonate pelagic oozes o