Himalayan Geology, Vol. 21 (1& 2), 2000, pp. 133-144, Printed in India
Influence of Delhi-Hardwar-Harsil Ridge (DHHR) on Basin Configuration in Himalayan Foothills Belt during Tertiary
DEVENDRA PAL, R.A.K. SRIVASTAVA AND N.S. MATHUR Wadia Institute of Himalayan Geology, Dehra Dun 248 001, India
The lower Tertiary successions extend from northwest to southeast along the Sub Himalaya, the Lesser Himalaya and the Zanskar and Indus belts. However, in the Sub Himalaya these successions are not exposed east of the Delhi –Hardwar-Harsil Ridge (DHHR), which is a NNE-SSW trending basement ridge of the Aravallis and Delhis. In the Sub Himalaya, the lower Tertiary successions were deposited in a linear foredeep that was formed to the south of the Himalaya during the late Mesozoic Orogeny and was restricted by the DHHR to its west.
Taking all the facts and field relations into account the authors have interpreted that: (a) the Main Boundry Thrust (MBT) of the western Sub Himalaya cannot be equated with the MBT of central parts, (b) the DHHR controlled the Maastrichtian – lower Tertiary sedimentation and restricted it to the west of the DHHR in the Sub Himalaya, (c) the lower horizons of the Siwalik succession (the Kamlial) are not exposed east of Nahan, and (d) the Palaeocene-Eocene successions of Rajpur (the Tethyan sequence towards north of the Pir Panjal Range) and Garhwal (the Lesser Himalaya sequence ) are part of totally different setups, which are neither in continuity of the Sub Himalaya, nor are parts of these setups. In fact, these are only time equivalents.
Palaeogeographic reconstruction, based on faunal and sedimentological studies and geomorphic controls besides the tectonic setup, has led the authors to redefine the existing model pertaining to basin development of the Sub Himalaya. In the first part only basement rocks of the Vaishnodevi Limestone and the Aravalli of the DHHR existed. Marine transgression from west to east took place immediately after the late Mesozoic Orogeny. The sea was nearly 80-100 km wide in the western part and 10-15 km in the Sataun-Nahan peripheral area, where the Kakara-Subathu succession was deposited. The Lower Murree (=Dagshai/Lower Dharamsala) was deposited when the Subathu Sea regressed. Monsoon conditions commenced with deposition of the Kasauli (= Upper Murree/Upper Dharamsala). At this stage another basin came into existence south of Vaishnodevi and Bilaspur where fluvial conditions led to deposition of the Lower Siwalik to north of Ramnagar and Jogindernagar. Next stage was marked by deposition of the Middle and Uppper Siwalik not only to the west of the DHHR (the Delhi-Aravalli and Vindhyan) but also to the east in the central part of the Himalaya. The Middle and Upper Siwalik successions are much richer in mammalian fossils in the western part than in the east
