Size distribution and carbonate content of the sediments of the western shelf of India

Abstract

Sediment samples collected during the 25th cruise of I.N.S. KISTNA (Indian Programme of I.I.O.E.) were analysed for grain size and carbonate content. The shelf sediments show well defined zonation, except where river-borne sediments tend to mask this zonation, as off Bombay, and the zones have been classified into two categories. (1) The inner shelf, up to a depth of 20 fms is characterised by high rates of sedimentation and composed of recently deposited silts and clay with low carbonate values (20%). (2) The outer shelf (approximately 20 to 70 fms) is a zone of relict sediments, having relatively low rates of sedimentation and composed of fine to medium sands. Occasional patches of coarse iron stained sands and pebbles are also present. The carbonate content in this zone is high (30 to 80%) being contributed largely by molluscs with minor amounts due to foraminifera and other organisms. At slope depths (70fms), the outer shelf sands grade into foraminiferal sands