Clay mineralogy and sedimentation in the western Indian ocean

The clay mineralogy of 235 surface sediment samples from the western Indian Ocean reveals many sedimentary sources and processes: (1) some areas, mainly in the central Indian Ocean, where very little sediment transport is involved, have smectite-rich clays derived from the alteration of in situ submarine basalts. (2) In many other areas, the mineralogy is significantly influenced by several modes of long-distance sediment transport, and the continental climate or the southern ocean volcanism. These areas consist of: (a) smectite-rich sediments in the Crozet and Madagascar basins and in the eastern Arabian Sea; (b) illite-rich sediments in the Indus Cone, the Agulhas Basin, and the ocean adjacent to Africa west of the Agulhas Plateau; (c) illite-palygorskite-rich sediments in the Carlsberg Ridge, Owen Ridge and in the westernmost Arabian Sea; (d) illite-kaolinite-rich sediments in the Mozambique Basin and in the regions between Madagascar and Africa; (e) kaolinite-rich sediments adjacent to central Africa and Madagascar. (3) A third category of areas has mixed type sediments with no specific mineral in characteristically high amounts. Mixing of sediments derived from the alteration of in situ submarine basalts and/or from other areas rich in different minerals resulted in this group.

The mineral distributions suggest that the Antarctic Bottom Water circulation is responsible for the sediment dispersal in the Crozet, Madagascar, Agulhas and Mozambique basins. Although the aeolian process could be effective throughout the Arabian Sea, it is dominant only in the western Arabian Sea.