Spatial analysis of thickness variability applied to an Early Jurassic carbonate platform in the central Southern Alps (Italy): a tool to unravel syn-sedimentary faulting

Early Jurassic syn-sedimentary extensional tectonics in the central Southern Alps controlled patterns of deposition within the Calcari Grigi carbonate platform. We used variogram maps to gather model-independent information on the spatial distribution of thicknesses of selected platform units and investigated whether major syn-sedimentary faults outlined subsiding domains during platform growth. Thicknesses dis- play a spatial organization that suggests that large fault belts, often coincident with exposed Jurassic extensional structures, transected large parts of the platform. The net- work of four fault systems (trending NNW–SSE and NE–SW) displays orthorhombic symmetry, suggesting non-Andersonian faulting and a true triaxial strain field with N100°E maximum extension or transfer shear zones connecting major NNW–SSE- trending extensional faults. In both cases, inherited structures of Permian to Triassic age may have played a primary role in Jurassic faulting. If confirmed throughout the South-Alpine domain, this arrangement could shed new light on Early Jurassic rifting mechanisms in the Southern Alps.