Structural and stratigraphic evolution of the offshore Adriatic

Abstract

The offshore Adriatic forms the foreland to two opposing fold-and-thrust belts, the Dinarides and Apennines which developed during the Cenozoic in response to Alpine tectonics. The region has been affected by multiple phases of deformation and hosts a number of contractional structures the genesis of which is still the subject of dispute in the literature. Proposed models utilise the limited existing seismic database and classify the same contractional structures as part of different and loosely defined tectonic domains (Apennines, Dinarides or intra-plate domain), which has led to uncertainty as to the controls on thrust system architecture. The interpretation of a new regional 2D seismic and well dataset led to a more detailed and complete understanding of the nature of deformation across the full foreland basin and its evolution through time, thus helping to resolve many of the existing challenges in structural interpretation. A new tectonic map with five domains, two of which completely new and unidentified in the literature, was produced and contractional structures were classified. The three known domains from the onshore geology (Dinaride, Apennines, Undeformed Foreland), which were loosely defined in the offshore Adriatic, now have clear boundaries and include a sub-domain of collision. In support of domain definition, a new tectonic restoration provides the spatial and temporal evolution of deformation. It can now be shown that the outer Dinaride structures initiated in the Oligocene-Miocene, whereas the outer Apennine structures initiated in the Pliocene and were re-folded by the evolving Dinaride thrust-belt. Accurate mapping of the pre-existing geological structure of the passive margin provided a new detailed stratigraphic unit map and helped determine the controlling factors on structural styles; a) the distribution of mechanical stratigraphy and (a) the extensional architecture. Rigid mechanical stratigraphy provided temporary or permanent buttresses to the propagating deformation fronts, while weaker stratigraphy (e.g Triassic evaporites) facilitated thrust propagation. Regarding extensional architecture, Permo-Triassic blocks localised thrusts detaching within overlying Triassic evaporites. Jurassic extensional architecture, affected by halokinesis, promoted footwall thrusting rather than inversion of dormant Jurassic normal faults. Messinian normal faults formed by salt collapse within the Ionian Basin and Cretaceous-Early Tertiary normal faults formed by minor extension on the Adriatic Platform were re-activated under compression post Eocene times.