Origin and Evolution of the Garo-Rajmahal Gap

The Garo-Rajmahal gap represents a physiographic gap in the outcrop continuity of Satpura strike due to alluvial cover between Garo and Rajmahal hills. The major part of this gap lies in Bangladesh. It is the junction of continental foredeep basin (Ganga valley) in the north and the Bengal basin in the south. A major drainage system of Ganga and Brahmaputra rivers flows through this narrow region from the Himalaya to the Bay of Bengal. Earlier, many differing views have been put forward regarding its origin. The present paper has brought out the origin and evolutionary stages of the gap on the basis of integrated analysis of geological and geophysical data of India and Bangladesh. A crustal model for the gap area is also presented. It has been concluded that the gap had its embryonic origin during Permo-Carboniferous (Lower Gondwana) period and evolved through the geological time to its present form.