Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XXII, No.3


Magnetic Properties of some late Paleozoic to Tertiary Sedimentary Rocks of Tansen Area, Lesser Himalaya, Nepal

Gautam, Pitambar

Permalink :


Magnetic properties of a total number of 117 samples collected with an aim of preliminary paleomagnetic study from 26 sites in the Tansen area were investigated. Measurements of natural remanent magnetization (NRM) showed that only 11 sites (61 samples), which are represented by olive green sandstones and siltstones and redbeds (red-colored shale, sandstone and iron-rich rocks) possess magnetizations strong enough to be analyzed for stability of the remanence by alternating field (AF) and thermal (TH) demagnetization techniques. Demagnetization behavior, isothermal remanent magnetization (IRM) characteristics, X-ray diffraction patterns and variation of saturation magnetization with temperature have been studied. Chemical changes of siderite to magnetite during laboratory heating and instability of siderite-containing specimens was established. Analysis of magnetic directions obtained in the present study when combined with the paleomagnetic results on Aulis volcanics from the Tansen Group leads to recognize characteristic (probably primary), and secondary magnetizations of various ages: recent, Early Miocene. Late Eocene, Early Eocene and older.