PLIOCENE-QUATERNARY LANDFORM EVOLUTION OF THE GODOLLO HILLS, CENTRAL HUNGARY: COMPETING AEOLIAN TO FLUVIAL DENUDATION, SEDIMENTATION AND TECTONIC FORCES

The Gödöllö Hills are located east of Budapest, in the central part of the Pannonian Basin, Hungary. The upper 1 km is consisted of Upper Miocene to Pliocene, poorly lithified sand(stone), siltstone and claystone of lacustrine, delta or fluvial origin. These sediments are covered by Quaternary loess units with intercalated paleosols, dune and fluvial sand, silt and peat. We aimed to determine the geomorphologic evolution of the area and the role of tectonic control on landscape evolution, using geomorphic-geological mapping, digital elevation model, analysis of seismic reflection profiles. To establish chronostratigraphy, thermoluminescence dating, molluscs and rare vertebrate fossils were combined with paleosol stratigraphy. Morphology is characterised by a simple, parallel set of NW-SE trending, southeast flowing valleys and intervening flat-toped plateaus. Two effects may control this uniform direction. It can be due to a regional tilt of a Pliocene denudation surface, but wind erosion played an important role in valley formation. It is demonstrated by linear, broad valleys, by the occurrence of ventifacts and distribution of wind-blown sands. Moderately dipping, truncated intra-loess paleosol units, redeposited older Quaternary fragments, sliding surfaces show that the actual slope are close to older, gently dipping morphological surfaces. This suggest a relative longevity of the morphological elements; valleys, slopes and plateaus existed already at the time of earliest paleosol formations, before 400 ky. Seismic sections demonstrate that most valleys do not correspond to seismically resolvable faults. Morphology is rather controlled by the denudation processes or by lithological differences. However, some important disturbances in drainage correspond to strike-slip faulting or folding of underlying Upper Miocene rocks. Historical earthquakes might suggest ongoing activity of some structures. Crustal deformation could divert original fluvial network, but wind erosion, surface wash significantly lowered tectonic topography. Supported by the ISES Group, the Netherlands, by the grant OTKA 29798 of Hungary and the Bolyai scholarship of the Hungarian Academy of Sciences for L. Fodor.