Cenozoic nannofossils from the Exmouth Plateau, eastern Indian Ocean

Six sites (759-764) were drilled on the Exmouth Plateau during Ocean Drilling Program Leg 122. Nannofossilrich Cenozoic sediments were recovered at all six sites, reflecting the open-ocean conditions that prevailed over the Exmouth Plateau during the Cenozoic. Calcareous nannofossils are abundant, diverse (250 different species identified), and generally well preserved throughout the composite lower Paleocene to Quaternary section. The diversity and preservation of nannofossils permits a high degree of stratigraphic resolution at each site. Site 762 on the central part of the Exmouth Plateau contains an almost unbroken Cenozoic record (only Miocene Zones NN3, NN8, and NN10 are missing). This site may prove to be a useful Cenozoic biostratigraphic and biomagnetochronologic reference section for the eastern Indian Ocean.

(Table 1) Chemical composition of ethmodiscus oozes from the Indian Ocean

This paper synthesizes all known finds of Ethmodiscus ooze in the Eastern Indian Ocean and indicates areas of its occurrence. Accumulation of Ethmodiscus ooze is controlled by water circulation and relief of the ocean floor. Bedding of Ethmodiscus ooze has gradational layering and cyclicity caused by multiple redeposition of diatom tests. The maximum occurrence of Ethmodiscus rex in sediments corresponds to Late Pleistocene.

Heavy metal contents in Fe-Mn nodules and crusts from R/V Vityaz polygons and stations in the East Indian Ocean

Regional variations in abundance, morphology, and chemical composition of Fe-Mn nodules have a zonal character. Due to circumcontinental zonality of terrigenous sedimentation the main mass of the nodules occurs in the pelagic part of the ocean, in areas of minimal sedimentation rates. In spatial variations in morphology and chemical composition of the nodules the latitudinal zonality is very clear and associated with latitudinal changes in facial conditions of sedimentation. Elevated contents of Mn, Ni, and Cu and of Mn/Fe ratio occur in nodules from the radiolarian belt. Changes of chemical composition of the nodules with depth (vertical zonality of mineralization) are confirmed. Local variations in abundance, morphology and chemical composition of the nodules are caused by ruggedness of relief and depth variations, variations in sedimentation rate, age of ore formation, intensity of diagenetic redistribution of metals.