Architecture and Structure of a Fold-and-Thrust Belt During Initial Inversion of a Salt-Bearing Passive Margin (Jurassic of the Eastern Alps, Austria)

Inversion of the Austroalpine Triassic salt-bearing passive margin, represented by the Northern Calcareous Alps (Eastern Alps), started in the Late Jurassic. Subsequent deformation during the Cretaceous and Cenozoic mostly preserved the Late Jurassic deformation fabric in the central Northern Calcareous Alps, making it an outstanding location to understand the early history of inversion of salt-bearing margins. Thrusting and folding in the central NCA during the Late Jurassic were strongly conditioned by the distribution of Triassic salt structures, the thickness of supra-salt stratigraphy, the lateral propagation of deformation, and the possible influence of sub-salt basement faults. Syn-orogenic sediments make it possible to reliably reconstruct the timing of structural inversion. The description of Late Jurassic structures presented here indicates that initial inversion of the Northern Calcareous Alps led to the development of coherent deformation systems that accumulated limited amounts of shortening, totaling few tens of kilometers. This differs from previous interpretations of Late Jurassic deformation of the area, that involve major amounts of allochthony (many tens of kilometers). As a specific example of coherent structural development, we present here an 80 km long linked system of thrusts and folds (the Totengebirge–Trattberg contractional system), whose outstanding continuity has gone previously unrecognized. The anatomy of this system and its temporal evolution are described in detail and discussed in the framework of the Jurassic to recent evolution of the Eastern Alps.