Geophysical, structural, and kinematic analysis of the Weaubleau structure: Implications for an oblique impact
The central uplift is a ring-like topographic low in SRTM and DEM imagery, and is coincident with the distribution of a fine-grain carbonate resurge breccia. A Bouguer gravity low is present in the center of the central uplift, where drill core indicates filling with sediment-gravity-flow breccias. A ridge-like gravity high to the northeast appears to be related to the emplacement of crystalline basement breccia at depth on the interior periphery of the central uplift.
Target rocks include a succession (<50 m thick) of middle Mississippian limestone that overlies 3 m of incompetent shale and siltstone. The latter facilitated strain transfer and slip to the northwest. In quarry-wall exposures 3 km northeast of the central uplift (downrange), structural deformation can be divided into two domains: (1) a brittle, upper domain with fracture and injection breccia between megabreccia blocks, and (2) a ductile to brittle lower domain with tight to isoclinal folds, normal and thrust faults, and injection and dilation breccias. L-tectonites indicate subvertical and radial movement away from the central uplift.
In contrast, proximal target rocks 3 km northwest of the central uplift are gently folded. To the southeast, strata are modestly deformed, and to the southwest, Mississippian rocks have been eroded below the sub-Pennsylvanian unconformity on an upthrown block of undeformed Lower Ordovician strata.