Lower Paleogene denudation of Upper Cretaceous cover of the Morvan Massif and southeastern Paris Basin (France) revealed by AFT thermochronology and constrained by stratigraphy and paleosurfaces
Résumé
Low-temperature thermochronology data have been acquired from outcrop samples from the southeastern edge of the Paris Basin (Morvan). They provide indications about the former sedimentary cover, its denudation and about inversion tectonics in the Paris Basin. Apatite fission-track data acquired on Variscan granites and Triassic sandstones reveal that the basement was subjected to temperatures of about 70 ± 10 °C during the Late Cretaceous. We suggest that the peak temperature was generated by an Upper Cretaceous sedimentary cover of low thermal-conductivity chalk. Additional stratigraphic, sedimentological, paleogeographic, paleoweathering, and continental paleosurface data support the reconstruction of this chalk paleocover and of its erosion. This former blanketing sequence was removed during the Early Paleogene regional inversion episode which affected the southern edge of the Basin intensively and was related to far-field compression between Europe and Africa. This study shows that (i) for the SE border of the intracontinental Paris Basin, kilometer-scale vertical deformation occurred, (ii) the sedimentary sequences of the Paris Basin covered considerably larger areas than the present contours of the sediment fill, (iii) paleoweathering and erosion processes later removed the sedimentary cover rather quickly (< 10 My) due to inversion tectonics.