Geologica BelgicaISSN 1374-8505
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Xavier DEVLEESCHOUWER, Estelle PETITCLERC, Simo SPASSOV, Alain PREAT
The Givetian-Frasnian boundary at Nismes parastratotype (Belgium): the magnetic susceptibility signal controlled by ferromagnetic mineralsAbstract
A comparison between microfacies and magnetic susceptibility (MS) curves has been performed at the Givetian-Frasnian transition in southern Belgium. The MS curve is subdivided in four magnetic sequences. Most of the section has MS and MF curves anti-correlated. Hysteresis parameters reveal a low coercivity mineral of magnetite type phase and a high coercivity mineral (i.e. hematite) in all samples. Strong correlation between ferromagnetic and low-field magnetic susceptibilities suggests that ferromagnetic minerals control almost totally the MS signal with an increasing upsection abundance of paramagnetic grains (iron-bearing clay minerals and pyrite). A decreased proportion of superparamagnetic grains, probably of diagenetic origin, is observed upsection. The hematite grains increases in the Frasnian as attested by the higher hematite contribution to the IRM500mT. The anti-correlation between the magnetic viscosity coefficient and the hematite contribution to the IRM500mT suggest that hematite are not associated to the superparamagnetic fraction and has a detrital origin. The opposite evolutions could be partly explained by sedimentological parameters and by an increased amount of primary detrital magnetite and hematite upsection. This detrital influx highlights the drowning of the carbonate platform at the end of the Givetian illustrating the progressive change from a Givetian rimmed platform towards a Frasnian ramp setting. Documents annexes
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Pour citer cet article :
Xavier DEVLEESCHOUWER, Estelle PETITCLERC, Simo SPASSOV & Alain PREAT. «The Givetian-Frasnian boundary at Nismes parastratotype (Belgium): the magnetic susceptibility signal controlled by ferromagnetic minerals». Geologica Belgica,
volume 13 (2010)
number 4 Magnetic susceptibility, correlations and Palaeozoic environments : 351-366
http://popups.ulg.ac.be/Geol/document.php?id=3072
Les auteurs :
Xavier
DEVLEESCHOUWER
Royal Belgian Institute of Natural Sciences, Geological Survey of Belgium, 13 Rue Jenner, B-1000 Brussels, Belgium. E-mail : Xavier.Devleeschouwer@naturalsciences.be
Estelle
PETITCLERC
Royal Belgian Institute of Natural Sciences, Geological Survey of Belgium, 13 Rue Jenner, B-1000 Brussels, Belgium. E-mail: Estelle.Petitclerc@naturalsciences.be
Simo
SPASSOV
Royal Meteorological Institute of Belgium, Centre de Physique du Globe, Section du Magnétisme Environnemental, B-5670 Dourbes (Viroinval), Belgium. E-mail: simo.spassov@oma.be
Alain
PREAT
Department of Earth and Environmental Sciences, Sedimentology and Basin Analysis, Université Libre de Bruxelles CP 160/02, 50 av F.D Roosevelt, B-1050 Brussels, Belgium. E-mail : apreat@ulb.ac.be
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