Magnetostratigraphic study on post-Miocene transitions in the uplift-erosion processes, climate and biota in Nepal Himalaya

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New magnetic and sedimentological data from Nepalese Subhimalayan and Kathmandu Valley sediments obtained in this project provide following valuable geoscientific/environmental information:1. Magnetic polarity data for 8 up to 5km thick Siwalik sediment sections, including Tinau Khola North studied anew, over 600 km length of the Sub Himalaya firmly bracket the sediment deposition age from >16 to 1 myr ago. Sediment accumulation rate ranged from 25 to 65 cm/kyr with two peaks during 10.9-9.7 and 5.2-3.6 myr ago; the former likey to be a combined response of multiple causal phenomena such as uplift of Higher Himalayan Crystallines, elevated mountain erosion/denudation, and effects marked by initiation of flood-flow dominated meandering system in the foreland basin, basin subsidence, etc. triggered by advent of summer monsoon. A consistent W-E to NW-SE magnetic lineation in fine-grained sediments records weak deformation induced by mild N-S or NNE-SSW directed compression and serves as a … More paleostress proxy.2. In Kathmandu Valley, reversal stratigraphy in Lukundol section reveals sediment deposition during 1.1-0.7 myr ago and gives evidence for massive deposition of gravel at ca. 0.96 myr ago coinciding with uplift of Mahabharat range that now forms the southern valley wall. New data from the basin's north bracket the age of Gokarna Formation at Dhapasi to ca. 45-34 kyr ago supported by Laschamp reversal event near the base of Dhapasi section. Laser granulometry of fine-grained prodelta deposits-indicators of calm subaqueous deposition suggests bi- to trimodal distribution for the silt to silty sand deposits indicative of a mixed sediment provenance or post-depositional sediment mixing.3. Magnetic susceptibility serves as a practical tool for mapping the Lesser Himalayan formations, rapid lithological correlation of the adjacent sections and deciphering the cyclic deposition in Kathmandu basin, and also quantification of paleo- and present- day environmental pollution (e.g. due to vehicular traffic). Less