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

Earth, Planets and Space volume 52, pages 337–345 (2000)Cite this article

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.

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Authors and Affiliations

  1. Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, N10 W8, Sapporo, 060-0810, Japan

    Pitambar Gautam, Azumi Hosoi, Kamal Raj Regmi & Yoshiki Fujiwara

  2. Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal

    Pitambar Gautam, Kamal Raj Regmi & Dharma Raj Khadka

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  1. Pitambar Gautam
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  2. Azumi Hosoi
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  3. Kamal Raj Regmi
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  4. Dharma Raj Khadka
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  5. Yoshiki Fujiwara
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Correspondence to Pitambar Gautam.

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Gautam, P., Hosoi, A., Regmi, K.R. et al. Magnetic minerals and magnetic properties of the Siwalik Group sediments of the Karnali river section in Nepal. Earth Planet Sp 52, 337–345 (2000). https://doi.org/10.1186/BF03351645

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