Model późnojurajsko-wczesnomioceńskiej ewolucji tektonicznej zachodnich Karpat zewnętrznych
Abstract
Model of late Jurassic to early Miocene tectonic evolution of the Western Outer Carpathians.
S u m m a r y. At the end of the Jurassic and beginning of the Cretaceous in the Western Outer Carpathians (WOC) rift-related extension led to development of: the deep marine grabens with flysch and pelagic sedimentation, the zones of shallow marine carbonate sedimentation, and the elevated horsts, supplying the basins with sediments. Transition to the Early Cretaceous and Cenomanian post-rift thermal sag stage was responsible for a general ceasing of tectonic activity in the source areas and unification of the previous sub basins. In Barremian–Albian time, the northern, external sources for sediments were uplifted due to compression, presumably caused by the orogenic collision in the Middle and Outer Dacides and/or collision related to subduction of the Penninic Ocean. The Silesian Ridge, rapidly elevated and eroded during Late Cretaceous and Paleocene, is interpreted here as an active thick-skinned thrust belt. Nappe stacking in that area and stress transmission towards foreland caused flexural subsidence of the proximal zone (the inner Silesian Basin) and uplift in the distal zone (including: the outer Silesian Basin, the Subsilesian facies zone, the Skole Basin and the northern sediment source areas). The Eocene alternating shallow marine deposition in the Silesian Ridge and its exposition for erosion is interpreted as controlled by both eustatic sea level changes and episodic tectonic activity. At this time new thick-skinned thrust belt developed south of the Magura Basin, which supplied vast amount of detritus for the Magura Beds. The Eocene tectonic shortening and deformations in the Southern Magura Ridge and development of the accretionary prism caused flexural bending of its broad foreland, subsidence and relative facies unification of the basins and decrease of activity of the source areas located north of the Magura Basin. The Oligocene progress of plates/microplates convergence and relocation of the zone of tectonic shortening towards the north led to compressional uplift of the source areas located both to the north of the WOC basins and to the south of the Silesian facies zone, the later composed of crystalline basement, as well as sediments of the Magura Unit. That sources supplied with detritus the Upper Oligocene–Llower Miocene Krosno Beds, being a diachronic continuation of synorogenic deposition of the Magura Beds. During the Late Cretaceous–Paleogene–Early Miocene, an important tectonic shortening across the WOC took place, accommodated mainly in the source areas. This indicates that the palaeogeographic relationships between the Silesian Basin, the Magura Basin and the Central Carpathian Paleogene Basin were changing during the Cretaceous and Cainozoic. In the time span of Albian to Oligocene in the zone palaeogeographically located between the Magura Basin and the Central Carpathians three separate source areas were active, each characterized by a different geological setting. These sources were replacing each other in time, suggesting significant collisional and/or strike slip reorganisation of the zone during that period. The collision of the WOC evolved in time from thick-skinned mode during the Late Cretaceous–Paleogene to thin-skinned one during the Middle Miocene.
S u m m a r y. At the end of the Jurassic and beginning of the Cretaceous in the Western Outer Carpathians (WOC) rift-related extension led to development of: the deep marine grabens with flysch and pelagic sedimentation, the zones of shallow marine carbonate sedimentation, and the elevated horsts, supplying the basins with sediments. Transition to the Early Cretaceous and Cenomanian post-rift thermal sag stage was responsible for a general ceasing of tectonic activity in the source areas and unification of the previous sub basins. In Barremian–Albian time, the northern, external sources for sediments were uplifted due to compression, presumably caused by the orogenic collision in the Middle and Outer Dacides and/or collision related to subduction of the Penninic Ocean. The Silesian Ridge, rapidly elevated and eroded during Late Cretaceous and Paleocene, is interpreted here as an active thick-skinned thrust belt. Nappe stacking in that area and stress transmission towards foreland caused flexural subsidence of the proximal zone (the inner Silesian Basin) and uplift in the distal zone (including: the outer Silesian Basin, the Subsilesian facies zone, the Skole Basin and the northern sediment source areas). The Eocene alternating shallow marine deposition in the Silesian Ridge and its exposition for erosion is interpreted as controlled by both eustatic sea level changes and episodic tectonic activity. At this time new thick-skinned thrust belt developed south of the Magura Basin, which supplied vast amount of detritus for the Magura Beds. The Eocene tectonic shortening and deformations in the Southern Magura Ridge and development of the accretionary prism caused flexural bending of its broad foreland, subsidence and relative facies unification of the basins and decrease of activity of the source areas located north of the Magura Basin. The Oligocene progress of plates/microplates convergence and relocation of the zone of tectonic shortening towards the north led to compressional uplift of the source areas located both to the north of the WOC basins and to the south of the Silesian facies zone, the later composed of crystalline basement, as well as sediments of the Magura Unit. That sources supplied with detritus the Upper Oligocene–Llower Miocene Krosno Beds, being a diachronic continuation of synorogenic deposition of the Magura Beds. During the Late Cretaceous–Paleogene–Early Miocene, an important tectonic shortening across the WOC took place, accommodated mainly in the source areas. This indicates that the palaeogeographic relationships between the Silesian Basin, the Magura Basin and the Central Carpathian Paleogene Basin were changing during the Cretaceous and Cainozoic. In the time span of Albian to Oligocene in the zone palaeogeographically located between the Magura Basin and the Central Carpathians three separate source areas were active, each characterized by a different geological setting. These sources were replacing each other in time, suggesting significant collisional and/or strike slip reorganisation of the zone during that period. The collision of the WOC evolved in time from thick-skinned mode during the Late Cretaceous–Paleogene to thin-skinned one during the Middle Miocene.