Normal Faults near the Top of Footwall of Ramgarh Thrust along Kosi River Valley, Kumaun Lesser Himalaya

Conjugate sets of normal faults formed in the Quaternary fan sediments lying near the top of footwall rocks of the Ramgarh Thrust are analysed. These faults are recognized on left hillslope of Kosi River valley, Kumaun Lesser Himalaya. The Ramgarh Thrust marks the mountain front of the uplifted Central Crystallines, which have been under thrust along the Ramgarh Thrust by its footwall of the Nagthat Formation belonging to the Lesser Himalayan Sequence. The existence of a regional-scale footwall anticlinal structure along the Kosi River suggests that the compressional stress regime is active in the subsurface region related to the Himalayan thrust tectonics. Analysis of structural data reveals that the normal faults have been formed by pure shear due to gravity. The WNW–ESE trending normal faults are recognized within the Quaternary fan deposit and also at the top of the country rocks just below and adjacent to the fan deposit. Therefore, it is interpreted that the deformation related to N–S extensional tectonics has taken place at the uppermost crustal level due to gravity, where influence of the Himalayan subsurface compressional tectonics is no more significant.

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