EARLY PLEISTOCENE AGE OF FLUVIAL SEDIMENT IN THE STARA GARDA CAVE REVEALED BY 26AL/10BE BURIAL DATING: IMPLICATIONS FOR GEOMORPHIC EVOLUTION OF THE MALE KARPATY MTS. (WESTERN CARPATHIANS)

Assessment of vertical movements of tectonically bounded blocks is crucial for determination of geohazards in densely inhabited zones, such as the border zone of western Slovakia and eastern Austria. The morphostructure of the Male Karpaty Mts. divides the Vienna and Danube basins in the Western Carpathian - Eastern Alpine junction, and its neotectonic activity is of high importance. This study was focused on Al-26/Be-10 burial dating of fluvial sediment in the Stara Garda Cave, located in the central part of the mountains. The structural research revealed predisposition of forming of horizontal passages in low angle to subhorizontal bedrock stratification together with low-grade metamorphic foliation. Fluvial origin of the passages was inferred from mezoscale erosional features on the bedrock as well as from facies character of the well preserved sedimentary profile. Cave sediment was according to petrographic analysis derived from a watershed comparable to recent one of the Stupavsky Potok Stream. Three analysed dating samples provided low values of isotopic concentrations, allowing us only to calculate the minimum burial age of the deposit of 1.72 Ma. Assuming the low position of the cave above recent surface streams, resulting maximum incision rate of 26 m/Ma indicates very low uplift of the mountains horst during the Quaternary. The slow incision of the river network is in good agreement with a widespread preservation of the planation surface called "Mid-mountain level". In contrast are relatively high values of palaeodenudation rates inferred from isotopic concentrations. Generally, our results indicate that the Male Karpaty Mts. horst underwent relatively intense but short uplift in the Early Pleistocene, followed by very moderate uplift up to the recent.