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The Vienna basin is an area of middle Miocene (Karpatian-Badenian, 17.5-13.0 Ma) extension and contains up to 6 km (20,000 ft) of Miocene to Quaternary sedimentary rocks. This basin is partly superimposed on the north-vergent flysch belt of the outer West Carpathians and partly on more internal Carpathian nappes. The obvious rhombohedral shape of the Vienna basin, the left-stepping pattern of en echelon faults within the basin, and the southward migration of basin extension through time strongly suggest that this basin is a pull-apart feature formed during middle Miocene sinistral strike-slip faulting along a northeast-trending fault (or fault system). This interpretation is supported by geologic mapping in the Carpathians indicating several tens of kilometers of Tertiary sinistral displacement along a fault that trends northeast from the Vienna basin.
This fault appears to have functioned mainly as a middle Miocene tear fault within the Carpathian nappes, separating the areas of active north-vergent thrusting east of the Vienna basin from areas west of the basin where thrusting had already been completed. Reflection seismic lines show that the autochthonous European plate basement continues beneath the allochthonous Carpathian nappes and beneath the Vienna basin, and that the European plate is not significantly disrupted by the normal faults that bound the basin. Thus both the normal faults that bound the basin and the associated strike-slip faults appear to merge into a gently southeast-dipping detachment horizon at depth. In this way extension of the Vienna basin appears to have been restricted mainly to shallow crustal levels ab ve that detachment horizon (i.e., restricted mainly to the allochthonous nappes of the Carpathians). Detailed analyses of subsidence and heat-flow data indicate that little or no heating of the lithosphere occurred during extension of the Vienna basin, and support the interpretation that extension was confined to shallow crustal levels.
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