Late Jurassic-Early Cretaceous faulting in the Southeastern French basin: does it reflect a tectonic reorganization?
Résumé
We present new data constraining the Late Jurassic to Early Cretaceous evolution of the Southeastern French basin (SFB). Meso-scale faults with displacement of several decimeters to 1–2 meters were sampled for geometric and kinematic data analysis and the faulted and un-faulted sedimentary units were examined for sedimentologic and bio-stratigraphic purposes. Small-scale faults were also extensively collected to determine the local stress states during this period. Meso-scale normal faults formed during sediment deposition or before its complete lithification attest of a recurrent activity in the Late Jurassic to Early Cretaceous period in an overall extensional context. The fault network cutting the Oxfordian to Aptian sequences included normal faults of various trends, ranging between WSW-ENE and NNW-SSE. We show that the deformation mechanism in the SFB drastically changed in the Jurassic-Cretaceous transition (latermost Tithonian?), with the direction of extension rotating from a WNW-ESE to a NNE-SSW direction. Lateral thickness variation of the sequences, redistribution of sediments, faulting at various scales concur that the Early Cretaceous period marks a tectono-stratigraphic reorganization of the basin. We suggest that it traduces the rifting and later opening of the North Atlantic (main branch and bay of Biscay branch).