Structural organization of the Lorraine coal basin and formation of the Alsting thrust fold

The Lorraine Coal Basin (LCB), filled with continental clastic formations of the Upper Carboniferous-Permian age, developed along the Metz-Hunsrück-Fault-Zone (MHFZ). Despite the structural studies, the structure of the basement which control the total sedimentary thickness variations, and the Alsting fold structure and formation remains poorly constrained. In this study, the analysis of gravity data has allowed to map the MHFZ and more regionally the top basement structures beneath the basin. The analysis of 2D seismic lines and well data analysis has allowed to constrain the structure and formation of the Alsting fold. The top basement map highlights the presence of highs (−1, 5 km) and deeps (−6, 5 km) trending NE-SW, NNE-SSW to N-S and NW-SE. This structuration explains the global sedimentary thickness variation of the sedimentary series in place. The first vertical derivative of the Bouger anomaly suggests that the MHFZ is continuous throughout the LCB and the SNCB. Furthermore, seismic interpretations show that the Alsting fold is a thrust fold whose formation and post-compression erosion occurred during the Stephanian. After this deformation phase, subsidence and deposition restarted during the late Stephanian. This study highlights a different Stephanian geological history of the BHL compared with other basins of the same age due to its structural position.