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.

Structural evolution of the Turňa Unit constrained by fold and cleavage analyses and its consequences for the regional tectonic models of the Western Carpathians

The Turňa Unit (Turnaicum, Tornaicum) is one of the three nappe systems involved in the geological structure of the inner zones of the Western Carpathians. The unit is formed by a system of partial nappes and duplexes, which overlie the Meliata Unit s.l. and are overridden by the Silica Nappe. The Slovenská skala partial nappe in the investigated area includes clastic sediments of the mid-Carboniferous, Permian and Early Triassic age, followed by mostly deep-water Middle-Upper Triassic succession predominantly composed of carbonates. Structural analysis of cleavage planes and folds was carried out predominantly in the Lower Triassic Werfen Formation. The measured deformational structures are polygenetic and were principally formed in three successive deformation stages. The first deformation stage is represented by bedding-parallel, very low-grade metamorphic foliation that was related to nappe stacking and formation of the Mesozoic accretionary wedge during the latest Jurassic and earliest Cretaceous. The second deformation stage is represented by systems of open to closed, partly asymmetric folds with SW-NE oriented, steeply NW- or SE-dipping axial-plane cleavage. Regionally, the folded bedding planes are usually moderately SE-ward dipping, the NW-ward and subvertical dips are less common. The mesoscopic fold structures predominantly occur in the SW-NE trending anticlinal and synclinal hinge zones of large-scale folds. These structures evolved in a compressional tectonic regime with the NW-SE to N-S orientation of the maximum compressional axis. The third observed deformation stage was activated during ENE-WSW oriented shortening. This stage is chiefly represented by open, kink-type folds. Some inferences for regional structures and tectonic evolution of the area are discussed as well