Late Jurassic Initial Development of a Salt‐Dominated Fold‐And‐Thrust Belt: The Inverted Passive Margin of the Eastern Alps (Austria)

The Northern Calcareous Alps (Eastern Alps, Austria) represent a well‐preserved example of the early stages of inversion of a salt‐bearing passive margin, which occurred in a fully submarine setting. Late Jurassic shortening led to widespread thrusting and folding that nucleated preferentially, although not exclusively, along salt structures developed during the Triassic passive‐margin stage. The presence of a highly effective basal décollement permitted the propagation of deformation without generalized uplift in the area, which was limited to thrusts, folds and squeezed salt structures. The development of individual structures was controlled by the orientation of pre‐existing salt structures, the thickness of supra‐salt stratigraphy, the lateral propagation of deformation, and, possibly, the redistribution of salt within salt structures prior to contraction and the influence of sub‐salt basement faults. Syn‐tectonic sediments make it possible to reliably reconstruct the timing of structural inversion. These same sediments were in turn controlled by structural evolution, with depocenters developing roughly parallel to the inverting structures. The structures documented here are evidence for Late Jurassic shortening across the central Eastern Alps, totaling a few to few tens of kilometers. This is the first systematic description of structures of Late Jurassic age in the Eastern Alps and provides a framework within which to understand the abundance of syn‐tectonic deposits of this age in the area. Particular attention is paid to the Totengebirge–Trattberg contractional system, an outstandingly long set of structures, whose continuity and significance has gone previously unrecognized.