Role of the olistostromes and olistoliths in tectonostratigraphic evolution of the Outer West Carpathians

The oldest olistostromes in the Outer West Carpathians are related to the Late Jurassic-Early Cretaceous rifting and post-rifting stage in which the Outer Carpathian deep sea sedimentary basins were opening. Then forming the proto-Silesian Basin later was split into separate tectonic units – Silesian and Subsilesian nappes. In the Silesian Nappe the oldest deposits are represented by the Vendryně Formation (Late Jurassic) that consists in many places of clasts and olistolithes of shales and marls. The Hradište Formation (Early Cretaceous) often bears debris-flow deposits rich of exotic-rock pebbles, but also olistostromes with olistoliths or olistoplaques of the Cieszyn and Vendryně formations.
   In the Late Cretaceous – Paleocene took place a contraction. It was a formation time of subduction zones along the active margins and development of deep-marine flysch basins. The Magura, Dukla, Silesian and Skole basins have been formed then. Ridges separated them supplying the basins with huge amounts of coarse-clastic material marked by numerous debris-flow sediments and occasionally olistostromes and levels with huge olistoliths. They occur in the Upper Cretaceous, Paleocene and Eocene strata of the Silesian, Subsilesian and Skole nappes. Specially known are large olistholits of the Węgierka from the Upper Cretaceous deposits of the Skole Nappe Marls and the Frydek Marls with huge blocks of andesites and pebbles of other exotic rocks from the Subsilesian. In the Silesian Nappe the debris-flow with flysch olistolites and exotics are frequent within the Godula and Istebna Beds (Late Cretaceous –Paleocene), the Ciężkowice Sandstones (Early – Middle Eocene) and occasionally within the Hieroglyphic Beds (Middle – Late Eocene). The Middle Eocene olistostromes are known also from the Bystrica and Rača subunits of the Magura Nappe.
   A collision of the European Platform with the Inner Carpathian terrain took place in the Oligocene and Early Miocene stage causing a development of the Outer Carpathian accretionary prisms. Evolving prism supported olistolithes and olistostromes to the basins until their structural closure. Especially in the inner part of the Silesian Nappe the Krosno Beds (Oligocene – Early Miocene) are rich of olistoliths and in some places olistostomes with large olistoplaques occur. Olistostroms at the top of the section of the Krosno Beds has finished sedimentation in the Silesian Beds. In the western part of the Subsilesian Nappe section of the Krosno Beds is ended with olistostrome rich of huge olistoliths of the Jurassic,Cretaceous and Palaeogene rocks as well as older crystalline. There occur spectacular blocks of Jurassic limestones forming the klippes of Andrychów, Pavlovske Kopce and Štramberg.
   During the Miocene tectonic movements caused final folding of the basins’ fill and created several imbricated nappes. The nappes are thrusted one upon another and all together overthusted the marine molasses of the Carpathian Foredeep developed on the North European Platform. From thrusting nappes large olistoliths glided down into the foredeep. Recently they are known from deep boreholes from bellow of the nappes. In front of the thrusting Outer Carpathian the molasses of fordeep were partly folded. It occasionally caused the formation of olistostromes, e.g. the Badenian evaporites known from the salt mines of the Wieliczka and Bochnia.
   Acknowledgments: This research has been financed by Ministry of Science and Higher Eeducation in Poland, grant no N N307 249733.