Abstract

Deep Sea Drilling Project Hole 148 was drilled on the Aves Ridge, eastern Caribbean Sea at a lower-bathyal depth (1232 m) beneath the eastern edge of the Orinoco plume. The drillhole penetrated ~124 m of Pleistocene sediment, but core recovery was poor (66%). From 62 samples taken at ~2-m intervals, 17,259 >105-μm benthonic foraminifera were picked and 212 species were identified. Only four species accounted for >5% of the total recovery: Sigmoilopsis schlumbergeri, Uvigerina peregrina, U. auberiana, and Bulimina aculeata. Species of Uvigerina and Bulimina, indicative of organic loading and low dissolved-oxygen content, respectively formed 22.6% and 14.3% of total recovery. Cibicidoides bradyi formed 4.4% of total recovery and Globocassidulina subglobosa 3.3%. This indicates that, although the Caribbean Sea is bordered to the north, east, and west by oligotrophic waters, the Pleistocene in DSDP Hole 148 was deposited under organic-rich, low-oxygen conditions. The organic material was derived from high surface productivity within the nutrient-rich Orinoco plume. Uvigerina and Bulimina show a long-term ecostratigraphic signal, beginning with U. hispida and B. alazanensis being common in the lower part of the section, then U. peregrina and B. aculeata in the middle and U. peregrina and U. dirupta in the upper part. This succession may reflect temporal changes in surface productivity, possibly resulting from plate tectonic movement of DSDP Hole 148 relative to the Orinoco plume, as surface productivity generally decreases from the center to the margins of the plume. The Stilostomella Extinction, in which uniserial foraminifera decreased through the section, occurred through a gradual loss of specimens.

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