Palaeogeography, subsidence and thermal history of the Neogene Styrian Basin (Pannonian basin system, Austria)

The Neogene Styrian Basin represents an extensional structure on top of a crustal wedge, which was moving eastward during the final stages of the Alpine orogeny. Eastward extrusion was a consequence of continental escape and extensional collapse within the Eastern Alps. In a simple model the evolution of the Styrian Basin can be subdivided into an Early Miocene (Ottnangian to Karpatian) synrift and a subsequent postrift phase. Basement subsidence rates during the synrift phase reached 30 cm/100 yr and more than 2000 m of limnic to marine sediments were deposited. The coincidence of the synrift phase and the formation of pull apart structures along strike-slip zones bordering the eastward moving wedge is evidence for the close genetic relation between extrusion tectonics and basin formation. A Miocene magmatic phase is related to subduction along the Carpathian front. Magmatic activity started during the synrift stage and continued into the postrift stage. Heat flow in the vicinity of the Miocene volcanoes increased dramatically (> 300 mW/m2). A second volcanic phase producing basalts in Plio-Pleistocene times had only little influence on the heat flow pattern. Limnic to marine sediments of the synrift stage are separated by a major unconformity from Middle to Late Miocene (Badenian to Pontian) marine to limnic/fluvial postrift sediments. Sedimentation during the postrift phase was controlled by marine ingressions during Middle Miocene (early Badenian and Sarmatian) times from the south and a subsequent regression with a decline in salinity. Subsidence rates during the postrift stage were mostly below 2.5 cm/100 yr. In Pliocene times subsidence was replaced by uplift, which resulted in erosion of a few hundred metres of sediment. Present-day high heat flows are a consequence of thinned crust beneath the Styrian Basin.