Where are the limits of Mesozoic intracontinental sedimentary basins of southern France?

• Published in: Marine and petroleum geology Vol. 121; p. 104589
• Main Authors: Barbarand, J., Préhaud, P., Baudin, F., Missenard, Y., Matray, J.M., François, T., Blaise, T., Pinna-Jamme, R., Gautheron, C.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2020; Elsevier
• Subjects: Aquitaine Basin; Causses Basin; Earth Sciences; Erosion in sedimentary basins; Paleogeography of western Europe during Jurassic and Early Cretaceous; Sciences of the Universe; South-East Basin; Thermal history reconstruction; South-East Basin; Aquitaine Basin; Thermal history reconstruction; Erosion in sedimentary basins; Causses Basin; Paleogeography of western Europe during Jurassic and Early Cretaceous
• DOI: 10.1016/j.marpetgeo.2020.104589
• ISSN: 0264-8172

Reconstitution of the geometry of sedimentary basins is fundamental to understand the nature of present sedimentary rocks and the economic potential in hydrocarbon and mineral resources. Present-day topography of southern France shows elevations growing between the Meso-Cenozoic Aquitaine Basin to the South-East Basin across the Variscan domain and the Jurassic Causses small basin with maximum relief in the Cévennes area. Present-day elevation offset is of approximately 1000 m. This geometry questions the paleogeography and dynamics of these various domains and the relative elevation of the Variscan domain during the subsidence of adjacent Aquitaine and South-East Basins. In this study, we investigate the geological history of the Variscan basement high and the Causses small basin using paleotemperatures deduced from organic matter analysis, low temperature thermochronology and regional geological constraints. Lower Jurassic (upper Pliensbachian and Toarcian) marls sampled across the area from the Aquitaine Basin to the South-East Basin have similar depositional environments containing mainly type III oganic matter, and close Tmax values ranging between 430 and 440 ± 2 °C. These data show that the entire south Massif Central has undergone a similar burial history. considering that these values are explained by burial. Low temperature thermochronology data have been acquired on basement rocks outcropping on the borders of sedimentary basins (Rouergue, Cévennes and Margeride). Fission-track ages are ranging between 74 ± 5 and 187 ± 6 Ma and track lengths between 11.5 ± 0.3 and 13.6 ± 0.1 μm; apatite (U–Th)/He corrected ages are ranging between 65 ± 5 and 184 ± 15 Ma. Data inversion with the software QTQt indicates a cooling episode starting at the end of Early Cretaceous or beginning of Late Cretaceous from maximum temperature of 100 ± 10 °C in the Rouergue and Cévennes area and from 80 ± 10 °C in most of the Margeride area. Thermal indicators are compatible with the erosion of a Middle/Upper Jurassic and Cretaceous sedimentary cover of 1400 ± 400 m assuming a thermal paleogradient of 35 °C/km. The preserved sedimentary cover attests of a Middle and Upper Jurassic – Lower Cretaceous sedimentary cover of 1000–2000m in the Aquitaine and South-East basins. This erosion phase occurred during mid-Cretaceous and is associated to a major geodynamical event characterized by large amplitude (from the Aquitaine Basin to Durancian doming in the South-East Basin) and by kilometric offset. We interpret also these data to show that marine connections have existed between the Aquitaine Basin and the South-East Basin during the Jurassic and likely Early Cretaceous. The present-day morphology of the area has then been acquired after Cretaceous times and may result from the Pyrenean orogenic event during Eocene times. •Organic matter evolution and low temperature thermochronology show high paleotemperatures for samples from southern France.•Present-day borders of the Aquitaine and South-East basins correspond to erosion limit.•A former Jurassic and Lower Cretaceous sedimentary cover has to be considered for a large area of southern France.•Erosion occurred at the end of Early Cretaceous during a major intracontinental reorganization.