Drainage migration and out of sequence thrusting in Bhalukpong, Western Arunachal Himalaya, India

In the foreland regions of the Western Arunachal Himalaya (WAH), geological studies along the Kameng river (between Tipi village and the Himalayan Frontal Thrust (HFT)) reveal four levels of unpaired terraces and a paired terrace. In WAH, wrench deformation of HFT zone resulted in a SE propagation of the Balipara anticline and it is suggested that the Mikir high basement controls its orientation. Ages of terrace surfaces from Siwaliks suggest that since the Late Pleistocene, Kameng River migrated at a rate varying between similar to 7.5 cm/yr in upper reaches and similar to 13.5 cm/yr towards northeast due to HFT related uplift. In the Brahmaputra plains, luminescence ages of abandoned paleochannel deposits suggest eastward shifting of the Kameng river at an average rate of similar to 1 m/yr. Field evidences between Bhalukpong and Tipi villages show Pliocene strath and Quaternary terrace surfaces, displaced by faults that do not correspond to the mapped faults in the foreland region. We interpret them as out-of-sequence thrusts (00STs). This is the first such report of OOST in the NE Himalaya. Presence of active COST is inferred by similar age (similar to 1 ka) and differing incision rates of the surface of same terrace (T-2b) in adjacent locations. This suggests that OOSTs in the western Arunachal Siwalik are