Geochemistry and mineralogy of marine sediments from the Yasawa Trough and Braemar Ridge, northwest of Viti Levu, Fiji

Abstract

Mineralogical and geochemical studies of 11 sediment cores from the Yasawa Trough and Braemar Ridge area, northwest of Viti Levu, reveal 2 sediment groupings. Sediments in the vicinity of the Braemar Ridge have high carbonate contents (> 60% CaC0₃), reflecting the shallower water depths, whereas sediments within the trough have a high terrigenous component derived from the adjacent Fiji Islands. The lower terrigenous component of the sediments more distant from Fiji is accompanied by a lower chlorite:mont-morillonite ratio. The Fe³⁺:Fe²⁺ ratio of the sediments is higher with greater distance from Fiji, reflecting the change in character of the iron from predominantly detrital minerals containing both ^Fe3+ and Fe²⁺ near Fiji to predominantly autogenic Fe³⁺-containing minerals further to the northwest. Sediments from this area of the North Fiji Basin are not metalliferous as previously suspected.

Keywords:

• geochemistry
• mineralogy
• Mössbauer spectroscopy
• iron
• sediments
• Yasawa Trough
• Fiji