Clay mineralogy of innershelf sediments off Cochin, west coast of India

Abstract

Kaolinite, montmorillonite and illite are the clay minerals occurring in decreasing order of abundance in the Holocene sediments of inner shelf and adjacent coastal environments of Cochin Region. Southern part of Vembanad Lake, estuarine part of Periyar River and outer parts of inner shelf have relatively more kaolinite (greater than 60%) than in sediments of northern part of lake and near inner shelf. In Vembanad Lake, kaolinite concentration shows a gradual decrease with concomitant increase in smectite from south to north. Such a variation from the source indicates size sorting of clay minerals with coarser kaolinite depositing closer to the source than finer montmorillonite. In the inner shelf, sediments from outer parts have significantly more kaolinite than nearshore sediments. Higher proportion of kaolinite in sediments of outer parts of inner shelf are considered to have been deposited during a lowered sea level in Holocene