6. Imprints of Neo-tectonism in the Evolutionary Record Along the Course of Khari River in Damodar Fan Delta of Lower Ganga Basin

Neo-tectonism affected the evolution of landscape across the earth since post-Miocene. The Khari river in Lower Damodar fan delta in West Bengal similarly portrayed the imprints of neo-tectonism in the forms of rapidly changing meander geometry, deformation in long profiles, unpaired terraces, soft sediment structures (fluid escape structure and convolute), etc. The study of meander geometry considering 142 loops (upper—92, middle—38 and lower—12) for the years 1972 (Survey of India topo-sheet) and 2017 (Google Earth images) portrayed rapidity in channel evolution in the middle and the lower stretches of the river compared to its upper counterpart as shown by the changing sinuosity index during 1972 and 2017 (upper: 0.1, middle: −0.4 and lower: −0.42), radius–wavelength ratio (upper: 0.01, middle: −0.06 and lower: −0.04), meander shape index  (upper: −0.05, middle: −0.09 and lower: −0.01), and meander form index (upper: −0.02, middle: −0.17 and lower: −0.13). We found this kind of meander behaviour to be correlated with the negative Bouguer anomaly (−45 to −30 m Gal) in the middle reach. Similarly, based on SRTM DEM (30 m), we detected a break in the long profile at the middle reach underlain by a sub-surface fault. In addition, we observed unpaired terraces in the middle reach. Besides, our extensive field survey guided us to identify long continued fluid escape structure and convolute along the banks of the river and a typical sedimentary facies which proved to be tectonically controlled.