Clay minerals in Southeast Indian Ocean sediments, transport mechanisms and depositional environments

Abstract

The clay mineralogy of the sediments of the Southeast Indian Ocean and Southwest Pacific Basin has been analysed by using chemical analyses and X-ray diffraction on 245 samples. The Wilkes Land sector of Antarctica supplies two different assemblages of clays to the South Indian Basin. The assemblage from western Wilkes Land is characterised by iron-bearing mica, amphibole and montmorillonite, while the eastern part is characterised by alkali felspar, quartz, muscovite and interstratified smectite. Both areas are the source of plagioclase, and the mineralogy is believed to reflect the change from a granitic to mafic shield from East to West Wilkes Land. The smectites are probably reworked from Tertiary strata on the continental shelf and rise. Minor kaolin is associated with the montmorillonite. Chlorite is derived from Victoria Land metasediments and transported by the west-flowing bottom waters to the Adélie continental rise. Abundant iron-bearing illite from western Wilkes Land must have been deposited on the continental shelf before the formation of the icecap. Eolian processes are believed to be the main supplier of kaolin, smectite and quartz to the South Australian basin. South Australia is the source area for abundant interstratified smectite. New Zealand supplies a dominantly mechanically weathered assemblage of muscovite, chlorite, amphibole and plagioclase to the surrounding basins. This assemblage is probably glacial eroded rock flour from South Island.