Paleogene Larger Foraminifer Biostratigraphy from Limalok Guyot, Site 871

Abstract

About 290 m of shallow-water carbonate limestone, mainly of early to middle Eocene age, was drilled at Site 871, which is in the center of Limalok Guyot. The limestone was below more than 130 m of pelagic sediment and a thin manganese-rich crust. Despite the poor recovery, recovered sediments were rich in age-diagnostic larger benthic foraminifers, primarily belonging to the genera Alveolina and Nummulites. Flooding of the volcanic island occurred during the early late Paleocene as indicated by sparse, depauperate calcareous nannofossil assemblages preserved in association with dark gray aragonitic grainstones. This implies that open-marine conditions existed during the initial stages of inundation. A substantial carbonate platform became established, possibly during the latest Paleocene. This platform complex persisted throughout the early Eocene into the early middle Eocene. Faunal and floral assemblages indicate that the evolution of Limalok platform was complex, with several fluctuations of water depth. Three distinct paleoecological assemblages, with some subassemblages, developed during the course of the platform's evolution; larger foraminifers and red algae often played a major role in the paleocommunity. Paleoenvironmental conditions in the central lagoon varied from deeper water and well oxygenated, to restricted and poorly oxygenated. There was at least one period of open-marine influx. More open-marine conditions resumed at Site 871 in the early middle Eocene, just before the drowning of the platform in the middle middle Eocene. The hiatus between the youngest shallow-water carbonates and the oldest calcareous plankton preserved in the overlying Mn-crust is estimated to not exceed 3-4 m.y.