Paleogene to Neogene deep-sea paleoceanography in the eastern Indian Ocean: benthic foraminifera from ODP Sites 747,757 and 758

摘要

Deep sea Cenozoic paleoceanographic evolution was studied using quantitative analysis of benthic foraminifera from ODP Sites 757 and 758 (Ninetyeast Ridge) and Site 747 (Kerguelen Plateau), on the south-north transect of the Indian Ocean. Bathyal Site 747 records high latitude paleoceanography and Sites 757 and 758 record mid- to low- latitude bathyal and abyssal paleoceanography respectively. Benthic foraminiferal assemblages reflect global paleoceanographic changes, but the faunal changes are not all coeval, due to the different paleodepths and paleolatitudes. At Site 747, Southern Component Water (SCW) developed in the Oligocene and middle Miocene; Northern Component Water (NCW) and SCW developed in the Oligocene and the late Miocene. At bathyal Site 757, the following periods of paleoceanographic change were recognized: early to middle Eocene (～52 Ma), late middle Eocene (～42 Ma), latest Eocene (～38 Ma), early Oligocene (～32 Ma), middle Miocene (～12 Ma), and late Miocene (～8 Ma). At abyssal Site 758, the paleoceanographic changes are complex, with both NCW- and SCW-allied assemblages occurring in the Oligocene and the middle Miocene to Pliocene (～33-29, ～26-24, ～9, ～6-4, ～3 Ma). Comparison of the benthic foraminiferal assemblages with the modern distribution of foraminiferal species and with oxygen and carbon isotopic data suggests the following paleoecological conditions at Sites 757 and 758: Cold water and high organic matter-exploiting assemblages appeared from the late Miocene to Pleistocene; warm water and lower organic matter-exploiting assemblages occurred from the early Eocene to middle Miocene. Resistant to high carbonate corrosion-type assemblages developed during the Oligocene and from the late Miocene to Pliocene at Site 747. Temperature decrease and changes in the food resource (phytodetritus) level of deep water are important factors for the benthic faunal changes throughout the Cenozoic. Faunal changes at bathyal depths before the middle Miocene occurred during a lower food resource level and those from the middle Miocene onward occurred in an enriched phytodetritus flux in deep water. The modern deep water is formed at ～2 Ma in the Indian Ocean at Sites 757 and 758. The cold-water and carbonate corrosion-type assemblages are more dominant at Subantarctic Site 747.