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See detailLithostratigraphie, sédimentologie et analyse séquentielle du Quartzite de Berlé (Emsien supérieur, Grand-Duché de Luxembourg)
Michel, Jonathan ULg

Doctoral thesis (2012)

The Lower Devonian is a period of interest because it is characterized by the first transgression of the Rheic Ocean, after the Caledonian orogeny, over the coasts of the Old Red Sandstones Continent. In ... [more ▼]

The Lower Devonian is a period of interest because it is characterized by the first transgression of the Rheic Ocean, after the Caledonian orogeny, over the coasts of the Old Red Sandstones Continent. In the Ardenne Basin, during this transgression, widespread siliciclastic deposits were deposited. From the Lochkovian to the Upper Emsian, the basin underwent various stages of development. The main object of this PhD thesis was to focus on one of these episodes recorded in the Neufchâteau-Wiltz-Eifel Basin. This work is the result of the integration of different techniques, such as field work, microscopic analyses, biostratigraphy, sequence stratigraphy, magnetic susceptibility and diagenesis. The analysis of the microfossil content of four sections in Luxembourg led to the identification of 23 species of spores and 11 species of acritarchs. Biostratigraphically, these spores confirmed the Emsian age of the different lithological units (“Couches de Clervaux”, “Quartzite de Berlé” and “Schistes de Wiltz”). The sedimentological analysis of the Neufchâteau-Wiltz-Eifel Basin is based on the study of more than 600 thin sections from 11 sections covering the entire basin. This study allowed to identify an estuary setting divided into three types of environments: an alluvial, a tidal and finally a marine distal environment. Detailed sedimentology associated with sequence stratigraphy of the whole Neufchâteau-Wiltz-Eifel Basin allowed to propose a vertical and lateral succession model of this estuarine setting. In this model, the “Quartzite de Berlé” corresponds to tidal sand ridges and changes laterally to the flaser bedded sandstones of the top of the “Couches de Clervaux”. This lateral facies transition tends to proof that the “Quartzite de Berlé” is a lenticular deposit. The “Quartzite de Berlé” is a prominent feature in the landscapes and a very resistant rock appreciated as a building material. Diagenesis study allows a better understanding of the mechanisms responsible for these characteristics, trough the identification of different cements and authigenic minerals. Temporal relationships between these different components are integrated in a paragenetic modelisation that includes four distinct phases: an eogenetic, a mesogenetic, a metamorphic and a telogenetic phase. The clay mineralogy (illite cristallinity) shows that the “Quartzite de Berlé” underwent variable conditions of burial, depending of the area considered. Our results point out that this variability is related to the pre-orogenetic rifting stage of the Rhenohercynian Basin. Finally, the use of magnetic susceptibility, suggested that in proximal setting, the magnetic susceptibility signal is mainly controlled by environmental parameters (water agitation, sedimentation rates) and diagenesis. [less ▲]

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See detailPalaeoenvironmental study and small scale correlations using facies analysis and magnetic susceptibility of the Mid-Emsian (Himmelbaach quarry, Luxembourg).
Michel, Jonathan ULg; Boulvain, Frédéric ULg; Philippo, Simon et al

in Geologica Belgica (2010), 13(4), 447-458

The Himmelbaach quarry is located in the Wiltz Synclinorium in Luxembourg. The rocks outcropping in this quarry correspond to the mid-Emsian Clervaux Shales Formation. Three different facies have been ... [more ▼]

The Himmelbaach quarry is located in the Wiltz Synclinorium in Luxembourg. The rocks outcropping in this quarry correspond to the mid-Emsian Clervaux Shales Formation. Three different facies have been identified in the quarry. An argillaceous sandstone facies with oblique stratifications, cross-stratifications, herring-bones and erosive bases represent the first facies; the second facies is characterized by lenticular- (with connected lenses) to wavy-bedded sandy argillites, argillaceous sandstones and quartz arenites. The last facies corresponds to a quartz arenite with oblique stratification, planar laminations and mud drapes. The base of this facies shows flaser bedding and sigmoidally curved bed surfaces. The palaeoenvironmental study of this area is rather difficult because of the structural deformation and lateral variation of the facies. Due to this deformation, six partial sections (4a to 4f) were sampled here. In order to reconstruct a reliable vertical and lateral succession of the depositional setting, facies analysis and magnetic susceptibility were used. Magnetic susceptibility (MS) is generally applied as a tool for correlation in a deepwater carbonated environment. In this paper we used the MS technique successfully in a siliciclastic proximal setting. Analysis of MS curves as well as the recognition of three marker beds ((1) the last bed of argillaceous sandstones in Facies 1; (2) a thin horizon of carbonated sandstone within Facies 2; (3) the first appearance of the characteristics massive quartzitic beds in Facies 3) allowed the correlation of sections 4a, 4b and 4c. These correlations helped us to reconstruct a vertical and lateral succession of facies, which ultimately led to the recognition of a tide-dominated marginal-marine depositional model composed respectively of tidal channels (Facies 1), a tidal flat (Facies 2) and a tidal sand ridge (Facies 3). This example also shows the usefulness of magnetic susceptibility for small scale correlation, even in a proximal environment such as a marginal-marine setting. [less ▲]

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