Geomorphology and surficial geology of the Western continental shelf and upper slope of India: a review

Abstract

The geomorphology and geology of the western con­tinental margin of India have become better known only after the International Indian Ocean Expedition (1962-1965). The continental shelf of western India is wide off the river mouths, becoming narrower south-eastwards and narrowest on the SW margin. Shelf break occurs at depths between 60 and 150 m. The Fifty Fathom Flat is a prominent feature on the outer shelf. Submarine terraces at depths between 35 and 170 m and shelf edge reefs are also present along the margin. Coastal geology and geomorphology of the area and nearshore currents played a significant role in the distribution of placer minerals off Kerala and Maharashtra. Transport and sedimentation of fine­ grained materials at places on the shelf are influ­enced by high-energy conditions. Clay minerals de­ rived from the Indus, Deccan Trap basalt and Gneissic provinces are distinct along the inner shelf, but bypassed the outer shelf and got deposited on the continental slope. Relict biogenic carbonates com­ prising Halimeda litho-facies, rhodalgal-coral facies and molechfer facies, occur in the northern, central and southwestern shelf, respectively. Terrestrial limestones described as palaeo-shoreline indicators occur at mid-shelf. Several evidences exist in favour of Late Quaternary neotectonic activity and subsidence. Phosphorites and phosphatized limestones occur on the shelf and slope and phosphatization seems to be a short event in the Early Holocene. Verdine and Glau­cony facies occur on the shelf and slope of the central and southwestern margin of India. Systematic sampling/radiocarbon dating is lacking on many geomorphic features. Some coastal bays in Maharashtra are least explored for heavy minerals. Phosphorites at places could prove economic, if de­tailed exploration is done. Several gaps exist in the data on sea level changes during the Late Quater­nary. Shelf edge exchange processes are to be studied in understanding the organic carbon distribution. Attention should be directed in solving the problems highlighted.