Late Quaternary Deflections of the Beas-Satluj rivers at the Himalayan mountain front, Kangra re-entrant, India: Response to fold growth and climate

Abstract

Late Quaternary fluvial deposits along the Janauri (JA; comprises Siwalik rocks) and Bhaddi (BA; dominantly of Quaternary deposits) anticlines over independent fault segments of the Himalayan Frontal Thrust (HFT), Kangra re-entrant, were studied to deduce the timing and causes of the Beas-Satluj rivers deflections. The deposits, 4–60 m thick, were documented from the northwestern fringe of the JA (Site-1), between JA and BA (Site-2) and entire BA (Site-3), and along the present course of the Satluj River (Site-4) in the piggyback Soan Dun. They comprise quartzite-bearing gravels and multistorey sheet sand bodies with large-scale trough cross-stratification and are deposited by the Beas (Site-1) and Satluj (Sites 2–4) rivers. The deposits at Sites 1–3 are uplifted, tilted or folded, whereas, horizontally bedded at Site-4. Based on quartz Optically Stimulated Luminescence chrono-stratigraphy, the aggradation phase is bracketed between >46.4 ± 2.9 and 37.4 ± 2.3 ka (Site-1), >69.9 ± 4.5 and 26.1 ± 2.6 ka (Site-2) and >55.2 ± 1.7 and 50.3 ± 3.5 ka (Site-3). The terrace deposits at Site-4 were formed around 26, 11 and 6 ka. The sedimentation (9.9 to 2.7 mm yr−1 between 61.8 and 26 ka) and uplift (3.4 ± 0.3 mm yr−1 over a period of 44 ka) rates along HFT show that the latter exceeds the aggradation rate with time. It is envisaged that time variable tectonic movements along independent fault segments of the HFT forced river deflection and termination of deposition at Sites 1–3, however, the absence of any forced aggradation at the Site-4 concomitant with Site-2 termination suggests it is also governed by climate.