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 display a spatial organization that suggests that large fault belts, often coincident with exposed Jurassic extensional structures, transected large parts of the platform. The network 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