Magnetic susceptibility, corellations and palaeozoic environments
[en] Emsian ; Luxembourg ; magnetic susceptibilitty ; tide-dominated environment
[en] 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.
Laboratoire de Pétrologie Sédimentaire ULg ; Musée Nationale d'Histoire Naturelle du Luxembourg (MNHNL)
Fondation Nationale de la Recherche Luxembourgeoise
Etude sédimentologique et séquentielle du Quartzite de Berlé (Grand-Duché de Luxembourg).