Abstract
To investigate the subsurface structure surrounding the 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 the MFT imaging the upper 1–2 km of the subsurface, which revealed a beveled erosional surface in the hanging wall above a broad, gentle anticline, as well as growth strata in the footwall. The boreholes exhibit interlayered clays, silts, sands, and gravels, dated with optically stimulated luminescence and radiocarbon to <72.5 ± 4.3 ka,="" with="" a="" transition="" from="" finer="" to="" coarser="" sediments="" at="" ∼13.5 ± 0.1="" ka.="" near="" the="" fault="" tip,="" the="" deposits="" exhibit="" steeper="" dips="" and="" deformation="" bands.="" a="" 25-m-thick="" section="" of="" silt="" and="" clay="" above="" the="" south="" end="" of="" the="" buried="" anticline="" is="" interpreted="" as="" a="" temporary="" lacustrine="" depocenter="" formed="" due="" to="" uplift="" near="" the="" fault="" tip.="" based="" on="" the="" distribution="" of="" marker="" beds="" and="" sediment="" ages,="" we="" interpret="" a="" shortening="" rate="" of="" 3.1–12.1 m/ka="" on="" the="" mft.="" three="" major="" transitions="" between="" fluvial-lacustrine="" and="" coarse="" fluvial="" channel="" facies="" are="" inferred="" from="" the="" boreholes,="" and="" the="" timings="" of="" these="" transitions="" correlate="" with="" indian="" monsoonal="" intensity="" variations="" linked="" to="" earth's="" precession.="" we="" infer="" that="" a="" strengthened="" monsoon="" led="" to="" increased="" river="" discharge="" and="" advance="" of="" coarse="" bedload-dominant="" braided="" channels,="" whereas="" a="" weak="" monsoon="" formed="" a="" finer-grained="" channel="" environment.="" these="" monsoonal="" climate="" variations="" have="" affected="" the="" depositional="" environment="" and="" river="" base="" levels="" in="" this="" region,="" influencing="" the="" formation="" and="" apparent="" relative="" uplift="" of="" nearby="" river="">