Geologica Belgica

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Christian J. NYHUIS, Daniel RIPPEN & Julien DENAYER

Facies characterization of organic-rich mudstones from the Chokier Formation (lower Namurian), south Belgium

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Abstract

In a case study of two wells from the Namur Synclinorium, theblack shale-dominated Chokier Formation was analyzed for petrography, mineralogy and organic geochemistry. Thin section petrography revealed a different facies assemblage for each well and a total of six microfacies types. Whole rock mineralogical data largely confirms a facies-dependent mineral composition. All different microfacies types of locality 1 (MFT-1, laminated silty mudstone; MFT-2, laminated mud-clast-rich mudstone; MFT-3, calcareous bioclast-rich mudstone) and locality 2 (MFT-4, lenticular mudstone; MFT-5, burrow-mottled mudstone; MFT-6, burrowed silty laminated mudstone) show ample evidence of a distal shelf environment that is sourced by currents, which may be linked to seasonal (monsoonal) transport of sediment from land to sea. Erosive bedload transport is an important mechanism of sedimentation whereas accumulation by settling from the water column can be excluded for the majority of investigated strata. Frequently, endobenthic activity and other processes after deposition, e.g. winnowing and reworking, caused strong fabric modifications. Various, but simple ichnofabrics prove at least temporary dysoxic conditions as confirmed by relatively low TS/TOC ratios. With regard to sedimentary features, organic geochemistry data hints to organic matter preservation due to rapid burial rather than intense anoxity. Silicification is a widespread diagenetic feature independent from facies and locality. It is most likely linked to a high supply rate of terrestrially dissolved silica as indicated by SEM observations, paleogeographic constraints and sedimentary features.

Keywords : Carboniferous, Namur Synclinorium, drill core, black shale, petrography, TOC, XRD

To cite this article

Christian J. NYHUIS, Daniel RIPPEN & Julien DENAYER, «Facies characterization of organic-rich mudstones from the Chokier Formation (lower Namurian), south Belgium», Geologica Belgica [En ligne], volume 17 (2014), number 3-4, 311-322 URL : http://popups.ulg.ac.be/1374-8505/index.php?id=4671.

About: Christian J. NYHUIS

Institute of Geology and Mineralogy, University of Cologne, Zülpicher Straße 49a, D-50674 Cologne, Germany. E-mail: chr.nyhuis@googlemail.com

About: Daniel RIPPEN

Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Lochnerstraße 4-20, D-52056 Aachen, Germany

About: Julien DENAYER

Service de Paléontologie animale et Humaine, Département de Géologie, Université de Liège, Allée du Six Août, Bat. B18, Sart Tilman, B-4000 Liège, Belgium; School of Earth Sciences, The University of Queensland, Saint Lucia, Queensland 4072, Brisbane, Australia