Clay Mineralogy of the Pelagic Sediments: Along a West-East Transect in the Indian Ocean

The clay fraction of the sediments contain illite, chlorite, kaolinite, montmorillonite and iron-smectite with minor amounts of goethite. The siliceous sediments contain both montmorillonite and iron-smectite, while the calcareous sediments show only montmorillonite. This suggests that montmorillonite is formed by the alterations of ridge basalts, palagonite and volcanic glass. Iron-smectite is probably formed during low temperature diagenesis by the chemical combination of iron and silicon. High biogenic sedimentation in the calcareous sediments inhibited the formation of iron-smectite.