Geologica Belgica

1374-8505 2034-1954

 

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Ondřej BÁBEK, Jiří KALVODA, Markus ARETZ, Patrick J. COSSEY, François-Xavier Devuyst, Hans-Georg HERBIG & George SEVASTOPULO

The correlation potential of magnetic susceptibility and outcrop gamma-ray logs at Tournaisian-Viséan boundary sections in western Europe

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Mots-clés : Carboniferous, Outcrop logging techniques, foraminifer biostratigraphy, deep-marine sediments, sea-level changes

Abstract

We have measured five deep-water carbonate and carbonate-siliciclastic sections at the Tournaisian-Viséan (Tn/V) boundary in western Europe, using petrophysical outcrop logging techniques (gamma-ray spectrometry /GRS/ and magnetic susceptibility /MS/). The aim was to trace correlatable log patterns across the flanks of the London-Brabant Massif from eastern Ireland to western Germany. Both GRS and MS logging proved useful for long-distance (up to ~1000 km) correlation. The log patterns can be interpreted in terms of sea-level fluctuations. A late Tournaisian regression, a sequence boundary at the Tn/V boundary, early Viséan lowstand systems tract and an overlying transgressive to regressive succession can be identified from the GRS and MS logs. The Tn/V sequence boundary can be correlated with exposure features and karstic surfaces in the up-dip shallow-water settings at the boundary between sequence 4 and 5 of Hance et al. (2001, 2002). This indicates that sea-level fluctuations around the Tn/V boundary were synchronous and traceable on the flanks of the London-Brabant Massif. The GRS-based logging has a greater correlation potential than MS as it can be applied in a broad spectrum of facies and depositional settings. In certain sections, the MS signal shows an increasing trend during transgression and a decreasing during regression, which is opposite to the MS paradigm from shallow-water carbonate platform settings. These trends are assumed to result from landward/basinward facies shifts of a low-productivity carbonate ramp system. Lowstand shedding of carbonate tempestites and turbidites results in low MS values while during sea-level rise the ramp systems backstep, developing a retrograding facies succession in its distal parts, which is associated with upward-increasing MS values.

To cite this article

Ondřej BÁBEK, Jiří KALVODA, Markus ARETZ, Patrick J. COSSEY, François-Xavier Devuyst, Hans-Georg HERBIG & George SEVASTOPULO, «The correlation potential of magnetic susceptibility and outcrop gamma-ray logs at Tournaisian-Viséan boundary sections in western Europe», Geologica Belgica [En ligne], number 4 - Magnetic susceptibility, correlations and Palaeozoic environments, volume 13 (2010), 291-308 URL : http://popups.ulg.ac.be/1374-8505/index.php?id=3148.

About: Ondřej BÁBEK

Department of Geology, Palacky University, Tř. 17. listopadu 12, 77200 Olomouc, Czech Republic. E-mail: babek@sci.muni.cz

About: Jiří KALVODA

Department of Geological Sciences, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic

About: Markus ARETZ

Université de Toulouse (UPS), LMTG (OMP), CNRS, IRD, 14 avenue Edouard Belin, 31400 Toulouse, France

About: Patrick J. COSSEY

Faculty of Science, Staffordshire University, College Road, Stoke-on-Trent, Staffordshire, ST4 2DE, United Kingdom

About: François-Xavier Devuyst

Carmeuse Coordination Center, bd. de Lauzelles, 65, B-1348 Louvain-la-Neuve, Belgium

About: Hans-Georg HERBIG

Institut of Geology and Mineralogy, University of Cologne, Zuelpicher Str. 49a, 50674 Cologne, Germany

About: George SEVASTOPULO

Department of Geology, Trinity College Dublin, Dublin 2, Ireland