Mid- Cretaceous calcareous nannoplankton from the central Pacific: implications for paleoceanography.

Abstract

Moderately well-preserved calcareous-nannoplankton assemblages from the western Mid-Pacific Mountains and Hess Rise reflect paleoceanographic conditions during the middle Cretaceous. Sediments enriched in detrital organic carbon from the Barremian (NC6) at DSDP Site 464 contain impoverished assemblages indicative of strong dissolution and adverse water conditions. A steady increase in the nannolith genera Zygodiscus and Biscutum and in overall diversity throughout the middle Cretaceous at Site 463 is indicative of a change to more favorable surface-water conditions.Assemblages with a high relative abundance of cocolith species indicative of high nutrient concentrations occur on southern Hess ?Rise (Sites 465 and 466). High productivity in conjunction with warm deep waters of low oxygen content seems sufficient to explain the occurrence of 'black shales' in the Pacific. -from Author Mid Pacific Mountains Hess Rise productivity