Clay mineralogy and chemistry of mudflat core sediments from Sharavathi and Gurupur estuaries: Source and processes

379-388Clay minerals were investigated in mudflat core sediments representing lower and middle regions of the tropical estuaries, viz., Sharavathi and Gurupur, west coast of India to understand the source and the role of estuarine processes in clay mineral distribution. Clay chemistry of the sediments was also determined to understand the interaction of metals with clay minerals. Among the clay minerals, kaolinite was abundant in both the estuaries which reflected chemical weathering of source rocks, granites and granitic gneisses. Smectite was present in slightly higher concentration in the lower Sharavathi estuary than the middle region, while kaolinite was higher in the middle region of both the estuaries. Illite and chlorite were relatively higher in the lower region than the middle region of both the estuaries. Thus, the distribution of clay minerals within estuaries was regulated by salinity. Further, study of metals in the clay fraction from both the estuaries revealed higher concentration of metals in the middle region than the lower, which was attributed to mixing processes facilitating enhanced adsorption of metals onto suspended clay particles. The distribution of major elements, viz., Al, Fe and Mn in the lower Sharavathi estuary, and of all the metals in the lower Gurupur estuary indicated their association with kaolinite. On the other hand, distribution of Al, Fe, Ni, Co, Cu, Zn and Cr in the middle Sharavathi estuary and Al, Fe and Zn in the middle Gurupur estuary suggested their association with smectite and illite