Late Quaternary sediments from Nal Sarovar, Gujarat, India: Distribution and provenance

A 54-m long core was raised from the bed of the Nal Sarovar, a large shallo w lake located in the middle of the low-lying region linking the Gulfs of K achchh and Khambhat, in western India. A three-layer sequence comprising: Z one-1 (top 3m), predominantly silty-clay/clayey; Zone-2 (3-18 m), sandy; an d Zone-3 (18-54 m), dominated by sticky silty-clay/clsqyey-silt with occasi onal thin sand layers and basalt fragments was identified. Smectite and ill ite are the dominant clay minerals with minor amounts of kaolinite and chlo rite. Very high content of smectite (53-97%) in the clays of the lowermost zone (18-54 m) and the geomorphic features of the surrounding region sugges ted that the sediments were derived from the basaltic terrain of Saurashtra and/or via the Gulf of Khambhat. The clay content in the middle zone (3-18 m), dominantly sandy, is very low. Therefore, provenance for this zone was derived using heavy minerals in the sand fraction. The heavy mineral speci es in this zone suggested the mixed metamorphic and igneous terrain of Arav allis as the major source. The grain-size distribution of this zone closely matched with the sediments underlying the modern Sabarmati riverbed at Ahm edabad, suggesting fluvial depositional environment. Clays also dominate se diments of the topmost (0-3 m) zone with illite as the dominant (74-81%) sp ecie followed by smectite suggesting derivation from the mixed metamorphic and igneous terrain of Aravallis.