INTEGRATED GEOPHYSICAL MAPPING OF SEDIMENT BELOW DECCAN TRAPS IN CHAMBAL VALLEY

Abstract

Vindhyan basin located in central India is one of the largest Proterozoic sedimentary basins of India. It is believed that the basin was formed due to collision of Bundelkhand craton with Deccan protocontinent in the south and Mewar craton in the west during early Mesoproterozoic period. The basin is divided into two sub-basins viz., Son valley in the east and Chambal valley towards west. Over the Mesozoic sediments several volcanic lava flows are deposited during Cretaceous period popularly known as Deccan traps or simply traps. They are exposed on the surface in most of the Chambal valley. Chambal valley is hardly explored except northern region, where trap is absent. A Number of gas seepages of thermogenic origin have been found over Chambal valley, which indicates the existence of favorable petroleum systems. As large part of the area is exposed with trap covered, seismic studies are not favorable. In such areas potential methods can be of immense help to explore and infer sub-surface structures in a better way. A maiden attempt has been made through this study to integrate all available geo-scientific data along with recently acquired high precision gravity data and bring out a reasonably reliable sub-surface structure and open this area for further exploration. High precision gravity data was acquired along four profiles (a total length 1100km) in logistically difficult terrain in Chambal valley to delineate the thickness of trap, sediment and depth to basement. As Northern part of the study area is devoid of trap and over which few seismic profiles of good quality are passing, they are integrated with other data sets of the study region, viz., vintage gravity, aeromagnetic, seismic, remote sensing, rock properties, topographical and geological data. Thickness maps of trap, sediment and depth to basement in Chambal valley have been inferred by our integrated approach, thereby leading to 3D models of subsurface in the study region. The study has shown a way forward to use an integrated geophysical approach for determining sediment thickness below trap and depth to basement in Chambal valley for hydrocarbon exploration. The designed methodology and achieved result could lead to better depth model along with acquisition of 2D and 3D seismic for targeting Mesozoic sand below the trap covered area of Chambal valley. The thesis could be a reference mark for further research for estimation of trap thickness and sediments below it in a localized pool as search for hydrocarbon prospects in sediments underlying basalt have given a new dimension to exploration activities now a days.