Tectonic implication in the development of fluvial landforms, morphotectonic features, and surface processes in the main boundary thrust zone of Dehradun

The development of varied landforms in the Dehradun valley is the result of tectonic activity and sculptured climatically driven surface processes. Stretching for about 35 km between the Tons and Song river valleys, the Main Boundary Thrust (MBT) in the Dehradun valley is defined by geomorphological attributes that suggest neotectonics along this active geological structure. The MBT and its splay thrusts are arcuate in nature as evident from deformation on the landforms, where north dipping discontinuous fault scarps are developed along the MBT. The conglomerates of the Upper Siwalik rocks in the immediate footwall of the MBT are highly sheared, having dips ranging from steeply dipping to vertical. Three fault traces in the hanging wall of the MBT are observed that stretch for about 1.5 km and are aligned in parallel. The fault traces are represented by linearly arranged paleo-sag ponds, and the fault zones are marked by highly sheared bedrock. Fault traces are also observed along the Main Boundary Fault in the Kalawa-Kalsi area, where the fault plane dips north. Structurally controlled drainages are observed along the trace of the MBT, Santaurgarh Thrust, Santaurgarh Anticline, and Nagsidh Anticline; where numerous paleochannels, incised channels, and radial drainage are observed. Wide wind gaps are formed, some measuring more than 1.5 km in width. Present findings address the adjustment of the fluvial system with the ongoing tectonic activity.