GEOMORPHIC EVOLUTION AND GENESIS OF LATERITES AROUND THE EAST-COAST OF MADRAS, TAMIL-NADU, INDIA

Laterites and lateritic soils (Red soils) of the east coast especially around Madras, Tamil Nadu have been formed in different geomorphic co nditions and on various geological deposits. They occur as caprocks ov er recent alluvium, Upper Gondwana sandstones and shales, and Precambr ian basement rocks. The laterite profiles studied around Madras are ge nerally 2 to 5 m thick and exposed 5 to 45 km inland from the present- day shoreline. Detailed analysis (micromorphological and chemical) and the bore hole lithe-log data reveal that lateritisation was not conti nuous but occurred in phases. Lateritisation could have taken place in humid to sub-humid conditions with a rich source of iron in the paren t rock and sediment and efficient internal drainage. Geoarchaeological investigations and Quaternary stratigraphical studies date the lateri tic crust surface to the early late Neogene. Neotectonics have played a vital role in shaping the present landscape.