The University of Southampton
University of Southampton Institutional Repository
Warning ePrints Soton is experiencing an issue with some file downloads not being available. We are working hard to fix this. Please bear with us.

A late diagenetic (syn-folding) magnetization carried by pyrrhotite: implications for paleomagnetic studies from magnetic iron sulphide-bearing sediments

A late diagenetic (syn-folding) magnetization carried by pyrrhotite: implications for paleomagnetic studies from magnetic iron sulphide-bearing sediments
A late diagenetic (syn-folding) magnetization carried by pyrrhotite: implications for paleomagnetic studies from magnetic iron sulphide-bearing sediments
Paleomagnetic, rock magnetic, and sedimentary micro-textural data from an early Miocene mudstone sequence exposed in Okhta River, Sakhalin, Russia, indicate the presence of pyrrhotite and magnetite at different stratigraphic levels. Sites that contain only magnetite have a reversed polarity characteristic remanent magnetization (ChRM) with a low-coercivity overprint, which coincides with the present-day geomagnetic field direction. Pyrrhotite-bearing sites have stable normal polarity ChRMs that are significantly different from the present-day field direction. After correction for bedding tilt, the ChRM data fail a reversals test. However, the normal polarity pyrrhotite ChRM directions become antipodal to the tilt-corrected magnetite ChRM directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40% partial unfolding. These data suggest that the pyrrhotite magnetization was acquired during folding and after lock-in of the magnetite remanences. Electron microscope observations of polished sections indicate that fluid-associated halos surround iron sulphide nodules. Pyrrhotite is present in randomly oriented laths in and around the nodules, and the nodules do not appear to have been deformed by sediment compaction. This observation is consistent with a late diagenetic origin of pyrrhotite. Documentation of a late diagenetic magnetization in pyrrhotite-bearing sediments here, and in recent studies of greigite-bearing sediments, suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn-depositional magnetization.
diagenesis, greigite, magnetite, pyrrhotite, sakhalin russian federation, magnetization
0012-821X
371-386
Weaver, R.
f4c9143b-6c82-4683-960b-a9614edd5244
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Barker, A.J.
b7a9d943-e954-44a2-b070-4e9f3f5e5d4f
Weaver, R.
f4c9143b-6c82-4683-960b-a9614edd5244
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Barker, A.J.
b7a9d943-e954-44a2-b070-4e9f3f5e5d4f

Weaver, R., Roberts, A.P. and Barker, A.J. (2002) A late diagenetic (syn-folding) magnetization carried by pyrrhotite: implications for paleomagnetic studies from magnetic iron sulphide-bearing sediments. Earth and Planetary Science Letters, 200 (3-4), 371-386. (doi:10.1016/S0012-821X(02)00652-0).

Record type: Article

Abstract

Paleomagnetic, rock magnetic, and sedimentary micro-textural data from an early Miocene mudstone sequence exposed in Okhta River, Sakhalin, Russia, indicate the presence of pyrrhotite and magnetite at different stratigraphic levels. Sites that contain only magnetite have a reversed polarity characteristic remanent magnetization (ChRM) with a low-coercivity overprint, which coincides with the present-day geomagnetic field direction. Pyrrhotite-bearing sites have stable normal polarity ChRMs that are significantly different from the present-day field direction. After correction for bedding tilt, the ChRM data fail a reversals test. However, the normal polarity pyrrhotite ChRM directions become antipodal to the tilt-corrected magnetite ChRM directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40% partial unfolding. These data suggest that the pyrrhotite magnetization was acquired during folding and after lock-in of the magnetite remanences. Electron microscope observations of polished sections indicate that fluid-associated halos surround iron sulphide nodules. Pyrrhotite is present in randomly oriented laths in and around the nodules, and the nodules do not appear to have been deformed by sediment compaction. This observation is consistent with a late diagenetic origin of pyrrhotite. Documentation of a late diagenetic magnetization in pyrrhotite-bearing sediments here, and in recent studies of greigite-bearing sediments, suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn-depositional magnetization.

This record has no associated files available for download.

More information

Published date: 30 June 2002
Keywords: diagenesis, greigite, magnetite, pyrrhotite, sakhalin russian federation, magnetization

Identifiers

Local EPrints ID: 2157
URI: http://eprints.soton.ac.uk/id/eprint/2157
ISSN: 0012-821X
PURE UUID: c5cabaf0-55c6-4cee-b0d3-412f253ad8a6

Catalogue record

Date deposited: 14 May 2004
Last modified: 09 Nov 2021 06:05

Export record

Altmetrics

Contributors

Author: R. Weaver
Author: A.P. Roberts
Author: A.J. Barker

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×