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Stable Eocene Magnetization Carried by Magnetite and Iron Sulphides in Marine Marls (Pamplona-Arguis Formation, Southern Pyrenees, Northern Spain)

Record type: Article

In order to establish the magnetic carriers and assess the reliability of previous paleomagnetic results obtained for Eocene marine marls from the south Pyrenean basin, we carried out a combined paleo- and rock-magnetic study of the Pamplona-Arguis Formation, which crops out in the western sector of the southern Pyrenees (N Spain). The unblocking temperatures suggest that the characteristic remanent magnetization (ChRM) is carried by magnetite and iron sulphides. The ChRM has both normal and reversed polarities regardless of whether it resides in magnetite or iron sulphides, and represents a primary Eocene magnetization acquired before folding. Rock magnetic results confirm the presence of magnetite and smaller amounts of magnetic iron sulphides, most likely pyrrhotite, in all the studied samples. Framboidal pyrite is ubiquitous in the marls and suggests that iron sulphides formed during early diagenesis under sulphate-reducing conditions. ChRM directions carried by magnetic iron sulphides are consistent with those recorded by magnetite. These observations suggest that magnetic iron sulphides carry a chemical remanent magnetization that coexists with a remanence residing in detrital magnetite. We suggest that the south Pyrenean Eocene marls are suitable for magnetostratigraphic and tectonic purposes but not for studies of polarity transitions, secular variations and geomagnetic excursions, because it is difficult to test for short time differences in remanence lock-in time for the two minerals. The presence of iron sulphide minerals contributing to the primary magnetization in Eocene marine marls reinforces the idea that these minerals can persist over long periods of time in the geological record.

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Citation

Larrasoaña, J.C., Parés, J.M. and Pueyo, E.L. (2003) Stable Eocene Magnetization Carried by Magnetite and Iron Sulphides in Marine Marls (Pamplona-Arguis Formation, Southern Pyrenees, Northern Spain) Studia Geophysica et Geodaetica, 47, (2), pp. 237-254. (doi:10.1023/A:1023770106613).

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Published date: April 2003

Identifiers

Local EPrints ID: 58946
URI: http://eprints.soton.ac.uk/id/eprint/58946
ISSN: 0039-3169
PURE UUID: 7b7aac6d-75ae-4616-af68-e44643252990

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Date deposited: 19 Aug 2008
Last modified: 17 Jul 2017 14:25

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Contributors

Author: J.C. Larrasoaña
Author: J.M. Parés
Author: E.L. Pueyo

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