--> A new structural model for the Europe-derived Jurassic Para-autochthonous of Lower Austria

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A new structural model for the Europe-derived Jurassic Para-autochthonous of Lower Austria


The Lower Austria province of the Alpine-Carpathian junction, which includes the Höflein gas-condensate field, contains large reserves of hydrocarbons. This contribution presents a new model for the structural development of the area based on the re-appraisal of vintage seismic and well data. In Lower Austria, the Alpine-Carpathian Miocene fold and thrust belt developed from the N to NW telescoping of continental margin sequences. The imbricated units were emplaced onto the previously stretched European continental margin. Underneath the thrust stack and the deformation front, the Jurassic (Doggerian to Malmian) petroleum system consists of syn-rift and post-rift megasequences which remain preserved in at least 4 half-graben structures. These structures are known as the Mailberg, Altenmarkt, Haselbach and Höflein half-grabens. Data re-appraisal has shown that these Jurassic half-graben structures underwent several episodes of fault reactivation and inversion, in contrast with the previous, purely extensional interpretations.

The tectonic evolution of the area is supported by seismic evidence and biostratigraphically constrained well data. In broad terms, the rift faults first underwent extensional reactivation upon the flexural bending of the foreland plate. Such bending is explained by the foreland-ward moving load of the advancing thrust sheets. This migration of deformation occurred in space and time from the hinterland-most half-graben in Oligocene times to the external-most structures in late Early Miocene times. Afterwards, positive tectonic inversion of the rift basin took place. This inversion is represented by a suite of structures that include footwall shortcuts, hanging-wall back-thrusts and forced folds. The resulting structures were controlled by the configuration of the rift basin as well as the mechanical stratigraphy of the Jurassic rift to continental margin sequences. The observed reactivation of the rift fault system has interacted with the development of thin-skinned thrust system at the thrust front and has locally folded the overlying thrust stack. The end of this positive inversion is constrained by the onset of the Middle to Late Miocene regional extension.

The model presented here is supported by a recently drilled prospect in a sub-thrust play and is crucial for future exploration efforts and new hydrocarbon discoveries in an already mature basin.