NEW SEDIMENTOLOGICAL DATA FROM TRIASSIC TO JURASSIC BOREHOLES (BONNERT, HAEBICHT, GROUFT, GRUND, CONSDORF) AND SECTIONS (TONTELANGE, DIFFERDANGE, RUMELANGE) FROM SOUTHERN BELGIUM AND LUXEMBOURG

Abstract

This study offers a detailed description of a series of Triassic to Jurassic representative boreholes (Bonnert, Haebicht, Grouft, Grund, Consdorf) and sections (Tontelange, Differdange, Rumelange) from southern Belgium and the Grand-Duchy of Luxembourg. Investigations provide information about microfacies, paleoenvironments and magnetic susceptibility (MS). Three sets of microfacies, corresponding to three different sedimentary systems were needed in order to address the complexity of the paleoenvironments: a transgressive mixed siliciclastic-carbonate ramp system for the Triassic to Lower Jurassic (Toarcian) interval (microfacies TT1-8), and, for the Middle Jurassic, an early transgressive low productivity mixed ramp system for the Aalenian (microfacies A1-2) and a transgressive carbonate ramp for the Lower Bajocian (microfacies B1-3). A comparison of the MS and microfacies curves shows a clear correlation between the two, suggesting that the MS signal is primary. Moreover, the MS values regularly decrease from the marine distal (TT1) to the marine proximal microfacies (TT5), with relatively weak mean MS values for sandstones and limestones, and high mean MS values for marls, argillites and ironstone. This relationship is interpreted as the consequence of local water agitation in the shallower parts of a ramp, preventing the detrital particles from settling down and to the higher sedimentation rate that dilutes the magnetic and/or paramagnetic minerals