Morphogenetic controls on the distribution of the littoral placers along central west coast of India

Abstract

The total heavy mineral concentration along the central west coast of India varies from 0.17 to 98.54 percent. A zone of higher concentration is confined to the central protion of the coastal segment between 17 degrees 59' and 16 degrees 30'N latitude. The coastline in this zone is of submergent type and bounded by plunging steep cliffs, arcuate to semi-arcuate bays with low gradients. The rivers are of moderate length with steep thalweg. These rivers are regulated by topography resulting in more fluvial erosion, however, overall sediment input is low due to the lithological variations along their courses. Headlands and plunging cliffs favour the sediment deposition by impeding the long shore drift and the sediments passing headlands enter the low energy zone leeward side and gets deposited in pocket beaches. The area north of 17 degrees 59' and south of 16 degrees 30'N latitude shows poor concentrations of placer which may be attributed to contrasting physiography, drainage and variable sediment inputs. The northern areas has irregular emergent type of coastline with extensive mudflats and creeks. The rivers have long graded profiles showing control of tectonic lineanents and the total sediment input is high. Similarly, the southernmost area also has irregular narrow coastline. The drainage is shallow thereby causing decreasing erosion resulting in low sediment input. In view of the above it is envisaged that the morphogenetic control exists over the placer distribution in the littoral zone.