Abstract

The Molasse deposits of the Central Eastern Alps are partly incorporated into a fold and thrust belt that recently has come into exploration focus. The structural style and timing of deformation varies significantly alongstrike. Regional three-dimensional seismic and well data interpretation indicate three different structural segments from east to west: (1) The Sierning imbricates have a decollement close to the base of the Molasse sequence and consist of varying numbers of thrust sheets alongstrike. Early Miocene shortening of the Molasse is at least 6.2 km (3.9 mi). Overthrusting of the internal Penninic and Helvetic wedge since the Oligocene accommodated at least 25 km (15.5 mi) of additional shortening. (2) The Regau segment is dominated by one to two small thrust sheets above a shallow detachment. This segment is dominated by overthrusting of the Alpine wedge. (3) The Perwang imbricates consist of an Oligocene wedge with complex deformed thrust sheets above a detachment horizon in Upper Cretaceous marls. Minimum shortening in the imbricates is 18.5 km (11.5 mi) with overthrusting 33.3 km (20.7 mi). All shortening estimates have an uncertainty of approximately 20% to 35%. The laterally varying thrust-belt architecture results from predeformational conditions (e.g., sediment thickness, mechanical stratigraphy, and basement dip). In the Sierning imbricates, hydrocarbon trap definition and charge issues are exploration risks. In the Regau segment, exploration is focused on the subthrust play. The Perwang imbricates have hydrocarbon shows but no economic discoveries. Charge and seal issues are the main risks. The petroleum systems in the context of the structural evolution are not yet fully understood.

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