Structure and dynamics of deep-seated slope failures in the Magura Flysch Nappe, outer Western Carpathians (Czech Republic)

International audienceDeep-seated mass movements currently comprise one of the main morphogenetic processes in the Flysch Belt of the Western Carpathians of Central Europe. These mass movements result in a large spectrum of slope failures, depending on the type of movement and the nature of the bedrock. This paper presents the results of a detailed survey and reconstruction of three distinct deep-seated slope failures in the Raca Unit of the Magura Nappe, Flysch Belt of the Western Carpathians in the Czech Republic. An interdisciplinary approach has enabled a global view of the dynamics and development of these deep-seated slope failures. The three cases considered here have revealed a complex, poly-phase development of slope failure. They are deep-seated ones with depths to the failure surface ranging from 50 to 110m. They differ in mechanism of movement, failure structure, current activity, and total displacement. The main factors influencing their development have been flysch-bedrock structure, lithology, faulting by bedrock separation (which enabled further weakening through deep weathering), geomorphic setting, swelling of smectite-rich clays, and finally heavy rainfall. All of the slope failures considered here seem to have originated during humid phases of the Holocene or during the Late Glacial

Large scale deformation in a locked collisional boundary: Interplay between subsidence and uplift, intraplate stress and inherited lithospheric structure in the late stage of the SE Carpathians evolution.

The interplay between slab dynamics and intraplate stresses in postcollisional times creates large near-surface deformation, particularly in highly bent orogens with significant lateral variations in mechanical properties. This deformation is expressed through abnormal foredeep geometries and contrasting patterns of vertical movements. Intraplate folding is often the controlling mechanism, particularly when the orogenic belt is locked. The study of these tectonic processes in the SE Carpathians indicates a generalized subsidence period during latest Miocene-Pliocene times driven by the slab-pull and an intraplate folding due to an overall Quaternary inversion. The latter accommodates -5 km ESE-ward movement of this area with respect to the neighboring units, which creates complicated three-dimensional deformation patterns potentially driven at a larger scale by the interaction between the Adriatic indentor and the entire Carpathians system. The lithospheric anisotropy inherited from the subduction times concentrates strain and induces large-scale deformation far away from the active plate margins. This anisotropy is dynamic because of deep mantle processes related to the subducted slab during postcollisional times, such as thermal reequilibration or increase in slab dip. Copyright 2007 by the American Geophysical Union

THE NEED OF INTERDISCIPLINARITY APPROACH ON LANDSLIDES RESEARCH IN ROMANIA

According to the World Atlas of Natural Hazards (McGuire et al., 2004), the landslides are the most frequent and worldwide developed natural hazard. It can occur on any type of terrain where exist the proper conditions concerning the soil or bedrock, groundwater and slope. The landslides usually occur accompanying the other natural hazards like heavy rainfall, floods and earthquakes. In time, all subgroups of natural hazards (cosmic, geological, hydro-meteorological and biological) have been recorded in Romania. Types of natural hazard are very numerous (over 67). But five from the most important hazards, regarding the number of dead or affected persons, or economic damages, are the earthquakes, floods, droughts, excessive temperatures and landslides (Marinescu et al., 2010).Actually, the landslides affect strong many country’s regions. The high frequency of landslides on land have great importance in the evolution and shaping of the landscape. Large areas of agricultural land suffered from landslides which also damaged various buildings both in villages and cities, and destroyed roads, railways, etc. Damage in industrial areas is also important. Landslide terrains could seal some running rivers causing partial or total blocking of leakage. The landslide research involves considerable human and financial efforts. Being on very complex process, its survey implies the using of many scientific disciplines. The need for interdisciplinary approach within the landslides, who to conduct at better knowledge and, finally at more adequate stabilization solutions, is the main objective of this paper

A combined structural and sedimentological study of the Inner Carpathians at the northern rim of the Transylvanian basin (N. Romania)

By integrating detailed structural and sedimentological field-work with paleomagnetic data, this thesis provides constraints for the reconstruction of the Late Tertiary tectonic history of the nner Carpathians in Northern Romania. Central for the understanding of the formation of the Carpathians is the emplacement history of crustal blocks into the so-called ‘Carpathian embayment’. This large-scale bight in the European continental margin is situated between the Bohemian and Moesian promontories. Roll - back of the (partly?) oceanic crust formerly occupying the Carpathian embayment, combined with lateral escape due to indentation in the Eastern Alps are thought to be the driving forces for this emplacement. The irregular shape of the European continental margin ultimately led to the formation of a highly bent orogen, the Carpathians. The study area is a key area for the understanding of the tectonic processes during this emplacement, since it is situated at a triple point where three of the major continental bocks (ALCAPA, Tisza and Dacia) meet. During the time interval covered by this study, the Tisza and Dacia blocks are considered firmly attached to each other, representing one single block. A large fault zone between the ALCAPA block and the Tisza-Dacia block, termed Mid-Hungarian fault zone, accommodated most of the complex deformation caused by their contemporaneous invasion into the Carpathian embayment. During emplacement corner effects at the Bohemian and Moesian promontories resulted in large differential rotations of the invading blocks. The juxtaposition of the Tisza-Dacia block and the ALCAPA block along the MidHungarian fault zone resulted in the formation of a flexural basin on the northern part of Tisza-Dacia. The filling of this basin started in Oligocene times, developing from flysch units into Burdigalian-age molasse-type deposits. The last moment of thrusting of ALCAPA related units onto Tisza-Dacia is reflected by the Early Burdigalian SE - directed emplacement of unmetamorphic flysch nappes (Pienides) onto the autochthonous cover of Tisza-Dacia. Back-arc type extension leading to the formation of the Pannonian basin is in the study area only weakly documented as SW-NE extension. Roughly perpendicular ‘soft collision’ of Tisza-Dacia with the European margin leads to transpressional deformation in the study area after 16 Ma. Due to migration of slab retreat, the convergence direction of Tisza-Dacia becomes more oblique, initiating a deformation stage characterized by transtension (NW – SE extension). The northern rim of Tisza-Dacia is ‘fitted’ to the European continental margin by E-W trending, sinistral strike slip faults coupled to SW – NE trending normal faults. This process leads to a weak (~20°-30°) counterclockwise rotation as well as accelerated uplift of the northern part of Tisza-Dacia. After 16 Ma deformation in the study area is located within the Tisza-Dacia block, but most likely connected to the Mid-Hungarian fault zone

Selected aspects of modern seismic imaging and near-surface velocity model building in the area of Carpathian fold and thrust belt

Despite the increasing technological level of the reflection seismic method, the imaging of fold and thrust belts remains a demanding task, and usually leaves some questions regarding the dips, the shape of the subthrust structures or the most correct approach to velocity model building. There is no straightforward method that can provide structural representation of the near-surface geological boundaries and their velocities. The in-terpretation of refracted waves frequently remains the only available technique that may be used for this purpose, although one must be aware of its limitations which appear in the complex geological settings. In the presented study, the analysis of velocity values obtained in the shallow part of Carpathian orogenic wedge by means of various geophysical methods was carried out. It revealed the lack of consistency between the results of 3D refraction tomography and both the sonic log and uphole velocities. For that reason, instead of the indus-try-standard utilization of tomography, a novel, geologically-consistent method of velocity model building is pro-posed. In the near-surface part, the uphole velocities are assigned to the formations, documented by the surface geologic map. Interpreted time-domain horizons, supplemented by main thrusts, are used to make the velocity field fully-compatible with the litho-stratigraphic units of the Carpathians. The author demonstrates a retrospective overview of seismic data imaging in the area of the Polish Carpathian orogenic wedge and discusses the most recent global innovations in seismic methodology which are the key to successful hydrocarbon exploration in fold and thrust regions

THE NEED OF INTERDISCIPLINARITY APPROACH ON LANDSLIDES RESEARCH IN ROMANIA

According to the World Atlas of Natural Hazards (McGuire et al., 2004), the landslides are the most frequent and worldwide developed natural hazard. It can occur on any type of terrain where exist the proper conditions concerning the soil or bedrock, groundwater and slope. The landslides usually occur accompanying the other natural hazards like heavy rainfall, floods and earthquakes. In time, all subgroups of natural hazards (cosmic, geological, hydro-meteorological and biological) have been recorded in Romania. Types of natural hazard are very numerous (over 67). But five from the most important hazards, regarding the number of dead or affected persons, or economic damages, are the earthquakes, floods, droughts, excessive temperatures and landslides (Marinescu et al., 2010).Actually, the landslides affect strong many country’s regions. The high frequency of landslides on land have great importance in the evolution and shaping of the landscape. Large areas of agricultural land suffered from landslides which also damaged various buildings both in villages and cities, and destroyed roads, railways, etc. Damage in industrial areas is also important. Landslide terrains could seal some running rivers causing partial or total blocking of leakage. The landslide research involves considerable human and financial efforts. Being on very complex process, its survey implies the using of many scientific disciplines. The need for interdisciplinary approach within the landslides, who to conduct at better knowledge and, finally at more adequate stabilization solutions, is the main objective of this paper

Why Earthquakes Threaten Two Major European Cities: Istanbul and Bucharest

Istanbul and Bucharest are major European cities that face a continuing threat of large earthquakes. The geological contexts for these two case studies enable us to understand the nature of the threat and to predict more precisely the consequences of future earthquakes, although we remain unable to predict the time of those events with any precision better than multi-decadal. These two cities face contrasting threats: Istanbul is located on a major geological boundary, the North Anatolian Fault, which separates a westward moving Anatolia from the stable European landmass. Bucharest is located within the stable European continent, but large-scale mass movements in the upper mantle beneath the lithosphere cause relatively frequent large earthquakes that represent a serious threat to the city and surrounding regions

Early Pleistocene age of fluvial sediment in the Stará Garda Cave revealed by 26Al/10Be burial dating: implications for geomorphic evolution of the Malé Karpaty Mts. (Western Carpathians)

Assessment of vertical movements of tectonically boundedblocks is crucial for determination of geohazards in denselyinhabited zones, such as the border zone of western Slovakiaand eastern Austria. The morphostructure of the Malé KarpatyMts. divides the Vienna and Danube basins in the WesternCarpathian – Eastern Alpine junction, and its neotectonicactivity is of high importance. This study was focused on26Al/10Be burial dating of fluvial sediment in the Stará GardaCave, located in the central part of the mountains. The structuralresearch revealed predisposition of forming of horizontalpassages in low angle to subhorizontal bedrock stratificationtogether with low-grade metamorphic foliation. Fluvial originof the passages was inferred from mezoscale erosional featureson the bedrock as well as from facies character of the well preservedsedimentary profile. Cave sediment was according topetrographic analysis derived from a watershed comparableto recent one of the Stupavský Potok Stream. Three analyseddating samples provided low values of isotopic concentrations,allowing us only to calculate the minimum burial age of thedeposit of 1.72 Ma. Assuming the low position of the caveabove recent surface streams, resulting maximum incision rateof 26 m/Ma indicates very low uplift of the mountains horstduring the Quaternary. The slow incision of the river network is in good agreement with a widespread preservation of theplanation surface called "Mid-mountain level". In contrast arerelatively high values of palaeodenudation rates inferred fromisotopic concentrations. Generally, our results indicate that theMalé Karpaty Mts. horst underwent relatively intense but shortuplift in the Early Pleistocene, followed by very moderate upliftup to the recent.Key words: Western Carpathians, Malé Karpaty Mts., fluvialcave sediment, burial dating, Early Pleistocene, neotectonics.Zgodnja pleistocenska starost fluvialnihsedimentov v jami Stará Garda, ki jo je dala 26Al/10Be datacija:uporabnost za geomorfni razvoj Nizkih Karpatov (ZahodniKarpati)Ocena vertikalnih premikov tektonsko omejenih blokov jeključna za določitev geohazardov v gosto naseljenih območjih.Morfostruktura Malih Karpatov deli Dunajski in Donavski bazenna stičišču Zahodnih Karpatov – Vzhodnih Alp in njegovaneotektonska aktivnost je zelo pomembna. Študija se je posvetila26Al/10Be dataciji fluvialnih sedimentov v jami Stará Gardav osrednjem delu gorovja. Strukturna raziskava je razkrilapredispozicijooblikovanja vodoravnih jamskih rovov pod nizkimkotom v odvisnosti od subhorozontalne stratifikacije kamnineter tudi z nizko stopnjo metamorfne foliacije. Na fluvialnoporeklo rovov smo sklepali iz srednje velikih erozijskih oblik nanjihovih stenah kot tudi iz lastnosti faciesov dobro ohranjenegasedimentnega profila. Glede na petrografske analizejamskisediment izhaja iz povodja, ki je primerljiv z recentnim povodjempotoka Stupavský. Trije analizirani vzorci so nam dalinizke vrednosti koncentracij izotopov, ki so nam omogočilele izračun najnižje pokopne starosti sedimenta, ki je znašala1,72 Ma. Če upoštevamo, da leži jama nizko nad recentnimivodnimi tokovi, dobimo maksimalno hitrost vrezovanja dolinsamo 26 m/Ma, kar kaže na zelo majhen tektonski dvig v časukvartarja. Počasno vrezovanje rečne mreže se dobro ujema sširoko ohranjenim uravnanim površjem, imenovanim »Srednjegorskauravnava«. V nasprotju pa so sorazmerno visoke vrednosti hitrosti paleodenudacije, ki izhajajo iz koncentracijizotopov. Na splošno naši rezultati kažejo, da je bil horst NizkihKarpatov podvržen relativno močnemu, toda kratkemu dvigovanjuv spodnjem pleistocenu, ki mu je sledil zmeren dvig dosedanjosti.Ključne besede: Zahodni Karpati, Nizki Karpati, fluvialnijamski sedimenti, pokopna datacija, starejši pleistocen, neotektonika.

TECTONOTHERMAL EVOLUTION OF THE CENTRAL-WESTERN CARPATHIANS AND THEIR FORELAND

The tectonic and thermal evolution of the Carpathian thrust and fold belt-foreland system is a topic of great interest both for the occurrence of potential oil and gas fields and for the presence of any enigmatic features that needs an alternative interpretation to the commonly accepted models proposed so far. This study is focussed on the area including the southern Poland, the western Ukraine and the crystalline complex and its sedimentary cover cropping out in the Western Slovakia. The analysis of such a complex tectonic scenario is carried out by the construction of new balanced and sequentially restored cross-sections integrated with low-Temperature (low-T) thermochronometry. Coupling these data it is possible to provide a thermo-kinematic model honouring both the presented structural model and the thermochronometric data and, at the same time, validate the proposed tectonic scenario. Five balanced cross-sections were constructed from the foreland to the Inner Carpathian domain. Cross-section building and balancing are performed using Move, software dedicated to the kinematic restoration. These sections were then integrated with new apatite fission track and apatite (U-Th)/He data to constrain the last cooling event. Although the cooling of the Inner and the Outer Carpathians are well documented in literature, no low-T thermochronometric data are present from the Pieniny Klippen Belt located between them. Apatite fission track and apatite (U-Th)/He analysis were performed on five samples made of siliciclastic sandstones coming from this narrow belt .Both the balanced sections and low-T thermochronometric data were processed with FETKIN, software developed at The University of Texas in Austin in collaboration with Ecopetrol and dedicated to low-T thermochronometric age prediction and forward modelling. This processing allows to define the evolution of the thermal field through time. Basing on a review of the sedimentological and stratigraphic works, the Outer and the Inner Carpathian successions are interpreted as deposited in the same sedimentary domain and the Pieniny Klippen Belt as a sedimentary unit deposited in the proximal part of the Inner Carpathian foreland basin, overthrusted on the Outer Carpathian deposits during the Late Eocene. The Mesozoic olistoliths and olistostromes forming the Pieniny wildflysh are here interpreted as coming from the eroded Mesozoic cover of the IC range. New apatite fission track and apatite (U-Th)/He data coming from the Pieniny Klippen Belt constrained its last cooling event to the Middle-Late Miocene, coeval with the cooling of the Inner Carpathian region. The balanced cross-sections show a progressive increasing of the Outer Carpathian shortening moving to the east (from 60% in the Polish region to 64% in the Ukrainian Carpathians). Furthermore, the cross-sections constructed in the central part of our study area highlight the relevant role of the post-thrusting low-angle normal faults in the exhumation process of this area. On the other side, no evidences of post thrusting normal faults occur in the Ukrainian region, where published low-T thermochronometric data suggest an exhumation triggered mainly by regional uplift. In this work the suggested tectonic scenario is successfully tested with FETKIN, to demonstrate that thrusting is the principal mechanism controlling the exhumation ages of the Western Polish Carpathians and to evaluate the effects of subsidence, topography and tectonics on the thermochronometric age prediction.

Architecture, 3D geometry and tectonic evolution of the Carpathians foreland basin

Cloetingh, S.A.P.L. [Promotor]Dinu, C. [Promotor]Bertotti, G. [Copromotor]Matenco, L. [Copromotor