Role of eustasy, climate and tectonics in late Quaternary evolution of Nal-Cambay region, NW India

During late Quaternary, global processes such as eustatic sea level change and climatic variations have influenced the evolution of a very large area lying in the semi-arid regions of north-west India. The effect of global pr ocesses has been superposed by the regional processes such as tectonism and erosion. A multidisciplinary study was undertaken to decipher the influenc e of these processes in shaping the present day landscape of the low lying tract, known as the Nal region, between the gulfs of Kachchh and Khambhat i n the state of Gujarat, India. Based on the results of various investigatio ns and their correlation with the adjoining Cambay basin to the east, a thr ee stage model for the late Quaternary evolution of the entire Nal-Cambay r egion has been developed. In STAGE 1 spanning the Marine Isotope Stage 5 (M IS-5; similar to 127-73 ka), a shallow sea linked the gulfs of Kachchh and Khambhat through the Nal-Cambay region. This study also indicated that the sea connection between the two gulfs broke up around the beginning of MIS-4 due to regression of the sea. Subsequently, only a land link has remained. In STAGE 2 (similar to 73-7 ka), alluvial fan deposits and reworked fluvia l sediments from east were episodically deposited in the Cambay and Nai reg ion in response to westward migration of depositional front of the eastern rivers, caused by a combination of marine regression and/or tectonic uplift in the region of Cambay Graben. At the beginning of STAGE 3, around simila r to 7 ka, the Nal region came to within few metres of its present elevatio n and a large shallow water lake known as the Nal Sarovar was formed.