Frontal accretion vs. foreland plate deformation: discriminating the style of post-collisional shortening in the Apennines

Interpretation of confidential and public data was carried out in this study focusing on the structural setting and seismic stratigraphy of both foreland basin deposits and underlying shallow water carbonates of the foreland plate. Our structural interpretation, supported by accurate depth conversion of the seismic data and 2D restoration, reveals how the style of deformation of the foreland carbonate platform is dominated by positive inversion involving the oblique-slip reactivation of high-angle, inherited extensional faults rooted below the base of the carbonate succession. Rather than thrust accretion involving the foreland carbonate platform postulated by thin-skinned thrusting models, the observed structures record post-collisional foreland plate deformation associated with the far-field transmission of compressive stresses. Plio-Pleistocene foreland shortening resulted in the formation of segmented positive flower structures arranged in a right-stepping en-échelon pattern and in the coeval development of bending-moment faults accommodating arc-parallel extension in the growing anticlines. Our results emphasize the importance of Permo-Triassic extensional faults during later shortening, reducing on the other hand the role locally played by forebulge-and foreland plate flexuring-related normal faults in inversion structures involving the foreland carbonate platform. Oblique-slip faulting with substantial strike-slip components of motion and associated positive structures exerted a significant control in the development of structural traps and related hydrocarbon accumulation in the deformed foreland plate.