Open Access

Magnetic minerals and magnetic properties of the Siwalik Group sediments of the Karnali river section in Nepal

  • Pitambar Gautam1, 2Email author,
  • Azumi Hosoi1,
  • Kamal Raj Regmi1, 2,
  • Dharma Raj Khadka2 and
  • Yoshiki Fujiwara1
Earth, Planets and Space201452:BF03351645

DOI: 10.1186/BF03351645

Received: 5 July 1999

Accepted: 10 April 2000

Published: 20 June 2014

Abstract

Sandstones and siltstones collected from the Siwalik molasse sequence (~ 16 to 5 Ma) of the Karnali river section have been studied for their magnetic properties. Behavior of the specimens during demagnetization (of the NRM and IRM) and magnetic susceptibility vs. temperature data suggest that goethite, maghemite/magnetite, and hematite are the main magnetic minerals in the section. Goethite, carrying a recent component, is the dominant magnetic mineral in the fine-grained lithologies from the lower part. Maghemite and magnetite, which also carry a secondary remanence, occur in the sandstones from the upper part. Hematite, mainly of detrital origin, is present in the whole sequence. The magnetic fabric is defined by mainly oblate AMS ellipsoids and a low degree of anisotropy (P′ < 1.20). The magnetic lineations (declinations: 75°–130° or 245°–310°; peak orientation: 290°/2.8°) are subparallel to the fold axes/bedding strikes/thrust fronts (WNW-ESE). The initial sedimentary-compactional fabric has been overprinted by a secondary tectonic fabric, which was probably induced by mild deformation active in the compressive tectonic setting.