Application of geological mapping and teledetection techniques for identification of olistostromes and olistoliths in the Outer Carpathians

Olistostromes formed in the Outer North Carpathians during different stages of the development of flysch basins are quite frequent. They are known from the Cretaceous, Paleogene and Miocene flysch deposits of the main tectonic units (the Pieniny Klippen Belt, the Magura, Dukla, Fore-Magura, Silesian, Subsilesian and Skole nappes and from the Miocene molasse of the Carpathian Foredeep). Detailed field mapping enabled the identification of new localities with olistostromes and large olistoliths. In the inner zones of the Silesian Nappe they were found within the Lower Cretaceous deposits of the Hradište Formation in Żywiec, the Upper Cretaceous Godula Formation in the Silesian Beskid Mts., Late Cretaceous and Middle Eocene in Rożnów Lake surroundings. Olistostromes with large olistoliths, or occasionally olistoplaques, within and above the Oligocene-Early Miocene Krosno Beds occur near Gorlice and Skrzydlna. The Paleogene and Early Miocene olistostromes have been found in the Subsilesian Nappe and olistostromes composed of Upper Cretaceous, Palaeocene, as well as Oligocene and Miocene strata, were identified in the Skole Nappe. In the Bystrica Subunit of the Magura Nappe olistostromes of Middle Eocene and probably Late Oligocene–Early Miocene age were mapped. In the course of a recently conducted detailed field mapping it was found that large portions of the Pieniny Klippen Belt consist of huge olistostrome bodies.
   In some cases, studies of the geological maps also helped to identify olistoliths and olistostromes. The presence of single olistoliths is manifested by single “spots” that remain in lithological and/or stratigraphical contrast with the surrounding strata. Olistostromes create a random (spotty) texture remaining in contrast with ordered linear texture of the surrounding flysch strata. Revision of geological maps revealed that, e.g. the so-called Fore-Magura thrust-sheet between Koniaków and Żywiec is not a separate tectonic unit but a sequence of the Krosno Beds of the Silesian Nappe containing two or three levels of olistostromes as well as solitary olistoliths. East of this area, between Andrychów and Myślenice, numerous
individual olistoliths have been recorded within the Krosno Beds. Field observations reveal that these olistoliths are usually associated with debris-flows.
   The teledetection techniques (geological interpretation of aerial photographs, satellite images, radar images, condensed contour maps and DEM - Digital Elevation Models) were used by the present authors to identify olistostromes and olistoliths. At first, images of known olistostromes and olistoliths were studied to find the remotely-sensed geomorphological features that would be helpful in the identification of olistostromes at other localities. Subsequently, on the basis of these experiences and relations between morphology of the terrain and the geological structure the authors attempted to identify previously unknown occurrences of olistostromes and olistoliths. The results are satisfactory if olistoliths consisting of rocks more resistant to weathering than the matrix of the surrounding olistostrome body. Such features are clearly observed on DEM and satellite images as random morphological patterns (mound-like texture). On the condensed contour maps olistoliths often appear as small closed ovals of contour lines, marking separate klippen which form hills or mounds. Especially pronounced appear megablocks of the Pieniny Klippen Belt in Poland and Slovakia which are huge olistoliths of the Middle Triassic-Lower Cretaceous carbonate and siliceous rocks embedded within the Cretaceous-Palaeogene flysch of the Złatne Successions in the vicinity of Haligovce village (eastern Slovakia) and the Middle Jurassic-Early Cretaceous limestone olistoliths in the vicinity of Maruszyna (Poland). Spectacular are large olistoliths of the Upper Jurassic limestones of Štramberg and Pavlovské Kopce (Czech Republic) clearly seen on DEM and satellite images. E.g. an irregular mound-like structure marks the occurrence of the Middle Eocene olistostrome in the Bystrica Subunit of the Magura Nappe in north-east part of the Orava region.
   Acknowledgements: This research has been financed by the Ministry of Science and Higher Eeducation in Poland, grant no N N307 249733.