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

Source of sediment components and processes with time in middle regions of tropical estuaries along west coast of India

114-126To understand the source of materials and processes operating, the sediment cores collected from mudflats representing middle region of Sharavathi and Gurupur estuaries were analysed for grain size, organic carbon, clay mineralogy, bulk metals and clay chemistry. Relatively higher concentration of sand in the Sharavathi and higher clay and organic carbon content in the Gurupur estuary indicated variations in the depositional environment between the two estuaries. Further, higher sand in middle section and silt in the upper section in Sharavathi and Gurupur estuaries respectively indicated variations in the depositional conditions with time in both the estuaries. The kaolinite was the most abundant clay mineral, and the abundance and distribution of clay minerals in the two estuaries revealed the role of catchment area geology and river-sea water mixing conditions as major factors in sediment deposition. All the metals showed similar distribution pattern to finer sediments and organic carbon in the Sharavathi estuary, indicating their role in distribution of metals. Also, significant association of metals with Al suggested their natural source in this estuary. Similar distribution pattern of metals with Al in the clay fraction also supported lithogenic source of metals in the Sharavathi estuary. In the Gurupur estuary, role of sediment components was limited in the distribution of metals and insignificant association of metals with Al suggested their non-natural source. Non-similar distribution pattern of metals to that of Al in the clay fraction of the Gurupur estuary and their insignificant association with Al indicated metals source as anthropogenic.