Unexpected latest Pleistocene W‐dipping reverse fault‐slip in the Maritimes Alps (SE France)—Insights from passage offset in Mescla Cave

We investigate the late Quaternary fault reactivation within Mescla Cave, offering the first dated offset in the southwestern Alps (SW France). While our dataset is limited to one outcrop, the observed W‐dipping reverse slip displacing cave passage represents an outlier among the scarce young Quaternary tectonic structures expected in this seismically active region. Using the 230 Th/U method, we dated fractured flowstones that predate the slip and stalagmite growth on the fault plane, bracketing the reactivation time frame from 51.6 ± 2.4 ka to 11.7 ± 1.3 ka. We interpret the detected displacement (23 cm) as secondary faulting associated with a larger, possibly distributed deformation along an unrecognised primary structure. Despite limited structural data containing only one strain, our findings highlight the geochronological value of caves in preserving deformation otherwise erased by erosion and provide new insights and questions into the active tectonics of the Maritimes Alps.