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

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 Received 14 January 1982, accepted 16 September 1982 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.

Sonar Studies of Submarine Mass Wasting and Volcanic structures off Savaii Island, Samoa

“…Blocks within debris avalanche deposits of several hundred meters to 1 kilometer in size are observed at abyssal depths. A regional sedimentological study of the southwestern Pacific reports that the western Samoan Basin is characterized by gray-colored, siliceous microfossil hash (mostly radiolarian) and ooze that is ash rich (MEYLAN et al, 1982). EXON (1982) reports that the shallow flanks of the island (0 to −4000 m) are characterized by outcrops of basalt and limestone, biogenic and volcanic silt, sand and gravel, calcareous pavements and calcareous ooze.…”

Metal accumulation rates in sediments from the Southwestern Pacific Basin.

“…This suggests that the chemical characteristics of red clays at particular locations in the Southwestern Pacific Basin have remained relatively constant over this time period and that diagenetic effects have not led to large scale post-depositional remobilization of elements within the sediment column such as observed, for instance, in sediments from the Eastern Pacific (Graybill and Heath, 1984;Finney et al, 1988). Factors controlling regional variations in the composition of the surface sediments in the Southwestern Pacific Basin have already received attention (Meylan et al, 1982;Stoffers et al, 1985) and these will not be considered further here.…”

“…From a knowledge of the sediment accumula tion rate and density (Schmitz et al, 1986) and the average element content of the sediment (Meylan et al, 1982;Stoffers et al, 1985), it is possible to compute the element accumulation rate for the sediment by simple multiplication (McMurtry et al, 1981;Thomson et al, 1984). Table 2 repre sents the first compilation of such rates for the Southwestern Pacific Basin.…”

“…In previous papers, we have shown that the colour, grain size, mineralogy, chemical compo sition, oxidation state of iron and manganese micronodule abundance in surface sediments of the Southwestern Pacific Basin vary with increas ing distance from New Zealand and that this variation is probably related to the decreasing sedimentation rate in the basin with increasing distance from New Zealand (Meylan et al, 1982;Stoffers et al, 1985;Glasby, 1991;Graham et al, 1997). There also seemed to be a threshold sedi ment accumulation rate below which manganese nodules form in abundance.…”

“…This has enabled palaeoceanographic changes in the basin over the last 13 Ma to be established. We types are given by Meylan et al (1982) and Stoffers et al (1985). Accounts of the analytical and dating methods have previously been reported by Stoffers et al (1985) and Schmitz et al (1986).…”