CRUSTAL DENSITY MODEL ACROSS WEST-BENGAL BASIN, INDIA - AN INTEGRATEDINTERPRETATION OF SEISMIC AND GRAVITY-DATA

An integrated interpretation of the seismic refraction and wide-angle reflection data, geological and structural details, bore-hole litholog information and gravity particulars along Beliator-Burdwan-Bangaon de ep seismic sounding (DSS) profile in West Bengal basin has helped in g etting a crustal density model. This model is consistent with all avai lable surface and bore-hole geophysical data that can realistically ex plain the trend, shape and magnitude of gravity data across the West B engal basin. The present exercise pointed out that the thick sedimenta ry column (with thickening trend towards east), conspicuous lateral va riations in the Moho configuration (with a prominent 40 km wide domal feature covering the eastern part of the stable shelf and the western segment of the deep basinal part) coupled with the structural trends i n the basement, mid and lower crustal columns have combinedly contribu ted to the gravity effect and as such the prominent lateral variations in the Bouguer gravity anomalies could be mainly attributed to region ally extending causative factors. The synthesis clearly points out the need to take proper care in selecting the density values as direct co nversion of velocities into densities, adapting well-known conversion formulae, does not always hold good specially in the eastern part of t he West Bengal basin where a huge thickness of sediments (velocities r anging between 4 to 5 km/sec) of high density 2.6 to 2-8 g/cm3 are san dwiched between younger sediments and the crystalline basement.