Magnetic Polarity Stratigraphy of the Siwalik Sequence of Haripur area (H.P), NW Himalaya

A 2375 m thick sequence consisting of sandstone-mudstone alterations was sampled for magnetic polarity stratigraphy in Somb Nadi and its tributary, Jamni-Khol in the Haripur area of Himachal Pradesh. 200 palaeomagnetic sampling sites were selected from 45 overbank intervals of fluvial cycles. Only fine-grained sediments were sampled to get the ideal results from stable single domain grains. Progressive thermal demagnetization was carried out at intervals of 25, 50 and/or 100°C. A considerably stable secondary remanant magnetization was removed above 450°C with the isolation of characteristic remnant magnetization component at 600°C. Corrected mean directions for the normal and the reversed sites are D = 349°, I= 28° and D = 168°, I= -28°, respectively. The Tatrot/Pinjor faunal event is recognised on the local magnetic polarity time scale at 2.6 Ma (1685 m level) and the Middle to Upper Siwalik transition (Dhok Pathan/Tatrot boundry) at 5.26 Ma (500 m level), approximately. Predominance of piedmont depositional system at around 3.2 Ma (1450 m level) suggests uplift and denudation of the Outer Leesser Himalaya during this period. First record of the Pre-Tertiary clast-dominated conglomerate is observed at 2.6 Ma and that of Tertiary clast-dominated conglomerate at 1.76 Ma. An average rate of sedimentation of 45 cm/1000 years was observed till 2.6 Ma. Further, it shows increasing and decreasing trend after 2.6 Ma with a maximum value of 54 cm/1000 years and a minimum of 8 cm/1000 years sediment accumulation.