Early, far-field and diffuse tectonics records in the North Aquitaine Basin (France)

Abstract

During the Mesozoic and the Cenozoic periods, Europe recorded several tectonic events that have been interpreted as far-field tectonics. This may be diffuse tectonics that occur at the onset of a major tectonic event or propagation of the deformation away from orogenic fronts. In Western Europe, the deformations related to the opening of the Bay of Biscay and the formation of the Pyrenean belt are well described in the southern part of the Aquitaine basin, but little is known about the “Northern Aquitaine Platform”. We combine field observation with Unmanned Aerial Vehicle (UAV) imagery and U-Pb laser dating on calcite to determine the tectonic evolution in the Vendée Coastal domain. Our results highlight the occurrence of two main tectonic events since the early Jurassic: (1) At the transition from the Late Jurassic to Early Cretaceous, WNW-ESE striking normal faults exhibit a horst and graben pattern that emplaced at the onset of the opening of the Bay of Biscay. Their association with reactivated Variscan strike-slip faults is consistent with oblique extension processes. Such a tectonic event was accompanied by fluid flow coming from depth. (2) During the Late Cretaceous, fractures, wide-open folds, veins, and joints are consistent with the N-S shortening direction that occurs during the earliest stages of the N-S Pyrenenan compression. In both cases, the early stages of the main regional deformation stages are recorded in the “Northern Aquitaine Platform” in a far-field position and before the focus of strain in rifts or orogenic belts. In the Aquitaine basin as in many other places in Europe, the tectonic study of sedimentary platforms located far from the main plate-scale deformation zone provides new constraints on the early diffuse deformation process that predate the main tectonic phases.