Lithology, colour, mineralogy, and geochemistry of marine sediments from the Southwestern Pacific and Samoan Basins

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Abstract
The principal facies of the surface sediments of the Southwestern Pacific and Samoan Basins have been characterised by differences in colour, grain size, lithology, mineralogy, and chemical composition, based on 77 dredge and grab samples collected during 2 cruises of the NZOI research vessel RV Tangaroa. Light-coloured foram/nannofossil oozes mixed with coarse volcaniclastics (pumice, ash) occupy the relatively shallow seafloor areas near volcanoes of New Zealand, the Tonga-Kermadec island are, Samoan chain, and Cook Islands. Up to several hundred kilometres east of the North Island of New Zealand and the Tonga-Kermadec volcanoes, volcaniclastics are the dominant sediment component, being mixed with increasing amounts of clay minerals eastward. In the western part of the Samoan Basin, and the area immediately to the south, a siliceous microfossil (mostly radiolarian) hash ooze is found, probably containing volcanic ash. The siliceous ooze and ash-rich sediments are mostly grey coloured. The sediment changes gradationally in character eastward as microfossil and/or ash content decreases. It becomes darker in colour, finer grained, and contains higher concentrations of Mn, Ni, Cu, and Co. The dominant sediment of the eastern sector of the study area is a brown to dark brown detrital silt-bearing, RSObearing to RSO-rich clay. Manganese nodules are principally associated with this sediment facies. The eastward changes in sediment character are interpreted as the result of a decreasing sedimentation rate.