Magnetic Polarity Stratigraphy of Siwalik Sediments from Kotla Section, Himachal Pradesh, NW Himalaya

Magnetic polarity stratigraphy studies of the Brahl Khad section from Kotla area (32°14 N, 76°05 E) in Kangra district, Himachal Pradesh are carried out. This section exposes 3640 m thick continuous sequence of sediments consisting of Sandstone-Mudstone alternations. Total 1000 oriented block samples of fine grained sediments from 256 sites were collected at close intervals. Samples from 65 sites were selected randomly and subjected to progressive thermal demagnetization at 15 different temperatures (100°-700°C) in order to isolate the Characteristic Remanent Magnetization (ChRM). The corrected mean directions obtained from normal and reverse magnetized sites are D = 9° and I = 29° and D = 185° and I = -27° respectively. Virtual Geomagnetic Pole (VGP) positions were calculated for individual sites followed by reconstruction of local Magnetic Polarity Stratigraphy (MPS). This MPS can be matched very well with the Global Polarity Time Scale (GPTS) from Chron 5An to Chron 3n 4 based on iterative matching. It is inferred here that the entire section falls in the age range from 12401 Ma to 4890 Ma (Lower Siwaliks from 12401 Ma to 10749 Ma and Middle Siwaliks from 10 749 Ma to 4 890 Ma). An average sedimentation rate of 49 cm/Kyr for the Lower and Middle Siwaliks combined is estimated through this Magnetostratigraphic study.