Palaeogene–Neogene Tectonics and Continental Aggradational Basins in North-Western India: Implications for Geological Evolution of Thar Desert

Abstract

Thar Desert is characterised by arid-semiarid ecologically fragile environment and occupies a unique tectonic-sedimentary domain in north-western (NW) India. It is confined essentially to West Rajasthan Shelf (WRS). The tectonic disposition and basement configuration of intra-cratonic basins and sedimentary formations here range from the Precambrian Delhi Supergroup in the east, Late Proterozoic to Early Palaeozoic Marwar Supergroup of sedimentary rocks in the middle, to Mesozoic and Cainozoic cover sedimentary formations on the western and north-western fringe areas in western parts of Thar desert in Rajasthan and Haryana in north-western India. It is remarkable that successive geological young age of sedimentary formations is mapped from the highly deformed Precambrian rock formations of the Aravalli Hill ranges on the east to the recent sand covered structurally undisturbed rocky plains on the west in the Thar Desert. Distinctive geomorphic expressions and relative lowering of relief are also deciphered and recorded across an east–west transect along northern parts of the Thar Desert. Geological mapping of Palaeogene–Neogene formations in NW India have helped reconstruction of the palaeo-geographic shore-line limits of the Tertiary sea. Such inferred basement disposition ostensibly had a bearing on the source of evaporate minerals and continuing salinity aspects of the present day inland lakes and playas in the region. Successive northward deepening of the Palaeogene–Neogene sedimentation basin is also inferred from the geological strata logs prepared during the drilling probes for the Potash Mineral Investigation by Geological Survey of India in NW India. It has been inferred that the NE–SW trending Aravalli hill ranges were rejuvenated as a horst bound by the Great Boundary Fault (GBF) in the east and well known Sardarshahar Fault (west of Churu) and a series of westerly down-thrown step faults (called Manpia Faults) on the west thus segmenting the Thar Desert in north-western Rajasthan into several Neogene depressions or the depocenters in-filled with Quaternary continental aggradational deposits of fluvio-lacustrine and aeolian origin. Based on geological field surveys, interpretation of sub-surface data and dug-well inventory, it has been feasible to delineate a series of linear stepped grabben structures hosting a succession of Quaternary deposits separated respectively by denudational relief features. Their stratigraphic succession is established and correlated to build-up a model for improved geological understanding. Present contribution attempts to elucidate role of Palaeogene–Neogene tectonics and its implications for the geological evolution of Thar Desert in NW India.