Geophysical studies of the major sedimentary basins of the indian craton, their deep structural features and evolution

The peninsular shield of India is characterized by a number of intra-cratonic sedimentary basins of which the Cuddapah and Vindhyan Basins are conspicuous.The crescent-shaped Cuddapah Basin (~1400 m.y.) covering roughly 35,000 square kilometers in the southern peninsula and enclosing the Cuddapah formations (Precambrian) includes shallow marine shales, limestones, sandstones and quartzites. These sediments are overlain by the younger Kurnool formations of Vindhyan (Upper Precambrian) age in the western and northern marginal portions of the basin and are intruded by basaltic sils and dykes. The eastern margin of the basin is characterized by an overthrust with steeply folded beds, while in the remaining parts, the formations show a gentle eastward dip. Evidence for Recent epeirogenic movements is provided by geomorphic features and current seismicity.The Great Vindhyan Basin of north-central India covering more than 100,000 square kilometers encloses Vindhyan sediments including some marine shales and limestones in the lower parts and shallow-water deposits of red sandstones and shales in the upper parts. The beds are generally horizontal, but are strongly disturbed along the southern margin. There are intrusions of basaltic dykes and kimberlite pipes.The Gondwana basins (Upper Carboniferous to Jurassic) are relatively smaller cratonic units in Archaean faulted troughs.Gravity and magnetic investigations, both regional and detailed, supplemented by deep seismic sounding profiles in the Cuddapah Basin have brought out the deep structural features of the basin, including the Moho, indicating a total thickness of generally 5–8 km with a maximum thickness of sediments of nearly 12 km in the eastern part. The beds show both a layered structure in the horizontal and block structure in the vertical, disturbed by a low-angle thrust fault on the eastern margin. In the Vindhyan Basin, the gravity and magnetic data indicate about 5000 m of sediments in the central portions, with major, roughly faults over the western and southern margins.The deep structural features of these intra-cratonic basins, as indicated by the geophysical results, are discussed in relation to the geological theories proposed for their genesis and development.