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International audience; The region of northeastern France is affected by low-magnitude background seismicity, with the rare occurrence of moderate earthquakes, which gives this region a non-negligible seismic risk. We provide an overview of the seismicity and seismotectonics of this intraplate domain and of its subregions: the Upper-Rhine Graben (URG), the external range and foreland of Jura, the Vosges, northern France and southern Belgium. Previously published catalogues over historical and instrumental times are used, and the epicentral distribution of earthquakes is compared to known tectonic structures, and the recently computed deformation field. Although no large earthquakes with M w > 6.0 occurred since the 1356 Basel seismic event (Io IX, MKS), the recent identification of active faults suggests periods of high seismic strain rates in the past. The origin of the seismic activity in each of these sub-regions, characterized by low to very-low strain rates, is attributed to pre-existing faults reactivated under specific natural or anthropogenic conditions.

We compared different potential indicators of nitrogen (N) availability across 50 beech forests growing on a wide range of soils in northeastern France. Among the 50 sites measured, high elevation acidic soils had the highest potential net N mineralization in the A horizon (PNM 0–5 cm ), while low elevation neutral and calcareous soils had the lowest (PNM 0–5 cm ). We found that (PNM 0–5 cm ) was negatively correlated with soil pH ( R 2 = 0.47***) and positively correlated with microbial C/N ( R 2 = 0.34***). However, when high elevation sites were excluded from analyses, the relationship between PNM 0–5 cm and soil pH as well as microbial C/N became weaker ( R 2 = 0.23*** for both variables). We found no relationship between PNM 0–5 cm and organic N concentration, soil C/N, or vegetation-based indices for N availability (Ellenberg N and Ecoplant C/N). Bivariate linear regression analyses showed that 69% of the variability in percent nitrification (%Nitrif) was explained by both soil pH (0–5 cm) and soil C/N. Percent nitrification was strongly correlated with vegetation-based indices for N availability. The Ellenberg N and R (pH index) values together explained 74% of the variation in %Nitrif. No relationship was found between %Nitrif and soil δ 15 N (natural abundance in 15 N). Of the 76 plant species evaluated, the probability of presence of 61 plant species was significantly correlated with %Nitrif while the probability of presence of 27 plant species only was correlated with PNM 0–5 cm . From these results, we believe that the use of plant community composition or the combination of soil pH and C/N are robust indicators of N availability.

International audience; Middle to Upper Oxfordian reefs of a shallow marine carbonate platform located in northeastern France show important facies changes in conjunction with terri-geneous contents. The Pagny-sur-Meuse section shows coral-microbialite reefs that developed both in pure car-bonate limestones and in mixed carbonate-siliciclastic deposits. Phototrophic coral associations dominated in pure carbonate environments, whereas a mixed photo-trophic/heterotrophic coral fauna occurred in more sili-ciclastic settings. Microbialites occur in pure carbonate facies but are more abundant in mixed carbonate-silici-clastic settings. Reefs seem to have lived through periods favourable for intense coral growth that was contempo-raneous with a first microbialitic layer and periods more favourable for large microbialitic development (second microbialitic layer). The first microbialitic crust probably developed within the reef body and thus appears to be controlled by autogenic factors. The second generation of microbialites tended to develop over the entire reef surface and was probably mainly controlled by allogenic factors. Variations in terrigeneous input and nutrient content, rather related to climatic conditions than to water depth and accumulation rate, were major factors controlling development of reefs and their taxonomic composition .