HUSCAP logo Hokkaido Univ. logo

Hokkaido University Collection of Scholarly and Academic Papers >
Creative Research Institution >
Peer-reviewed Journal Articles, etc >

Magnetic polarity stratigraphy of Siwalik Group sediments of Karnali River section in western Nepal

Files in This Item:
Gautam_pub.pdf1.27 MBPDFView/Open
Please use this identifier to cite or link to this item:

Title: Magnetic polarity stratigraphy of Siwalik Group sediments of Karnali River section in western Nepal
Authors: Gautam, Pitambar Browse this author →KAKEN DB
Fujiwara, Yoshiki Browse this author
Keywords: Himalayas
foreland basin
Issue Date: Sep-2000
Publisher: For the Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft, and the European Geophysical Society by Blackwell Scientific Publications
Journal Title: Geophysical journal international
Volume: 142
Issue: 3
Start Page: 812
End Page: 824
Publisher DOI: 10.1046/j.1365-246x.2000.00185.x
Abstract: The remanent magnetization of siltstones and sandstones sampled at 476 levels/sites throughout a 3560 m thick molasse sequence belonging to the Siwalik Group (0-2015 m: Lower; 2015-3560 m: Middle) has been studied by stepwise thermal demagnetization. This section is exposed along the Karnali River in Nepal. The natural remanent magnetization (NRM) usually consists of two components: a viscous or thermoviscous component of recent field origin, and an ancient characteristic component (ChRM). The former component is of normal polarity and resides either in goethite (unblocking temperature < 150 ℃; resistant to AFD up to 150 mT) or in maghemite (unblocking temperature 150-400 ℃). Goethite contributes up to 90 per cent of the total intensity in the finer variegated muddy samples belonging to the lower half of the section. Maghemite content is significant in the grey mud-free lithologies from the upper half of the section. The main component, unblocked in the high-temperature range (commonly 610-680 ℃) and believed to reside in haematite, presumably of mostly detrital origin, represents a characteristic remanence (ChRM). The tilt-corrected ChRM directions at individual sites show antipodal clusters (ratio of normal- to reverse-polarity sites: 0.62), and yield mean inclinations recording significant inclination shallowing--a feature well recorded in the Siwaliks. This ChRM is interpreted to represent a largely primary detrital remanence. The ChRM data from 430 sites yield the Karnali River magnetic polarity sequence, whose correlation with the geomagnetic polarity timescale (Cande & Kent 1995) suggests a depositional age of 16 Ma (younger than chron C5Cn.1n) to 5.2 Ma (around the top of chron C3r) for the 3560 m section sampled. Hence, the Karnali River exposes the oldest part of the Siwalik Group in Nepal. Estimates of the sediment accumulation rate (SAR) average to 32.9 cm kyr^[-1] for the 10.8 Myr time span of deposition.
Rights: The definitive version is available at
Type: article
Appears in Collections:創成研究機構 (Creative Research Institution) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: Gautam Pitambar

Export metadata:

OAI-PMH ( junii2 , jpcoar_1.0 )

MathJax is now OFF:


 - Hokkaido University