Slope deviatory alignment, stream network and lineament orientation of the Sabarmati river system- neotectonic activity in the Mid -to Late Quaternary

Abstract

The Gujarat alluvial plain located in the semi-arid zone is bounded by the arid Thar region in the north and the coastal/estuarine zone fringing the Arabian Sea in the south. It has been built by the rivers originating in the Aravalli Hills in the northeast. The drainages, with an average length of about 300 km, generally follow the NE-SW regional slope. However, the Sabannati River shows a flow deviating from the regional slope and follows a N-S to NNE-SSW trend in the alluvial area. The slope-deviatory trend of the Sabarmati has been investigated with regard to Late Quaternary neotectonics, fluvial-aeolian interaction and sea-level change. Lineament analysis indicates an E-W to WNW-ESE trajectory of maximum principal stress, and that drainage is primarily controlled by geodynamic processes. This is obvious from the correspondence in stress trajectories obtained from the lineament and drainage orientations, respectively. Sub-surface data indicate pre-Neogene faulting in the basin. It is inferred that these faults have been reactivated in the Mid- to Late Quaternary times. The slope-deviatory drainage of the Sabarmati River is, to a large extent, the result of fluvial adjustment to neotectonic reactivation in the region.