Detailed sedimentological study of a non-classical succession for Trois-Fontaines and Terres d'Haurs formations (Lower Givetian, Marenne, Belgium)- Introduction of the Marenne Member

This work details for the first time the sedimentology of the Marenne quarry. It exposes a remarkable succession of strata from the Trois-Fontaines Formation and the base of the Terres d’Haurs Formation. Two sections (Marenne East and Marenne Centre) are investigated within the quarry. The first one (115 metres) covers both formations and is characterized by a mixed carbonate-siliciclastic succession replacing the classical base of the Trois-Fontaines Formation. We propose here to include these particular facies into a new member of the Trois-Fontaines Formation, the Marenne Member. The second one (48 metres) exposes a reefal lens also attributed to this new Marenne Member. Magnetic susceptibility was used to confirm geometric correlations previously obtained between these two sections. Petrographic study leads to the definition of 14 microfacies which are integrated into three palaeoenvironmental models. The first model (six microfacies) is proposed for the Marenne Member. In this ramp model, terrigenous inputs are particularly important. The mid-ramp is composed of four microfacies more or less influenced by storm events. The inner ramp (limited to the FWWB vicinity) is characterized by the development of the reefal lens and by peloidal microfacies. The upper part of Trois-Fontaines Formation is depicted by a back-reef model (three microfacies) which is mainly dominated by lagoons. However, intermittent agitation and non-restricted settings allow the local development and the reworking of branching organisms. The last model proposed (five microfacies) concerns the Terres d’Haurs Formation and corresponds to a ramp profile with the development of shoals. Those shoals locally protect semi-restricted lagoons. Algal mats are also observed. The last part of the work concerns the sedimentary dynamics and proposes sea level variations as the key parameter probably responsible for the succession of these three depositional settings