Fluvial Sedimentary Response to Late Quaternary Climate and Tectonics at the Himalayan Frontal Thrust, Central Nepal

To investigate the subsurface structure surrounding Main Frontal Thrust (MFT) in central Nepal, we drilled and cored sediments to depths of 45–100 m at 10 sites. Our boreholes were located along previously acquired high-resolution seismic profiles across MFT imaging upper 1–2 km subsurface, which revealed a beveled erosional surface hanging wall above broad, gentle anticline, as well growth strata footwall. The exhibit interlayered clays, silts, sands, gravels, dated with optically stimulated luminescence radiocarbon <72.5 ± 4.3 ka, transition from finer coarser ∼13.5 0.1 ka. Near fault tip, deposits steeper dips deformation bands. A 25-m-thick section silt clay south end buried anticline is interpreted temporary lacustrine depocenter formed due uplift near tip. Based on distribution marker beds sediment ages, interpret shortening rate 3.1–12.1 m/ka MFT. Three major transitions between fluvial-lacustrine coarse fluvial channel facies are inferred boreholes, timings these correlate Indian monsoonal intensity variations linked Earth's precession. We infer that strengthened monsoon led increased river discharge advance bedload-dominant braided channels, whereas weak finer-grained environment. These climate have affected depositional environment base levels this region, influencing formation apparent relative nearby terraces.