Reconstruction of a Pleistocene meandering river in East Hungary by VHR seismic images, and its climatic implications Ágnes Cserkész-Nagy a, ⁎, Edit Thamó-Bozsó b , Tamás Tóth c , Orsolya Sztanó a a Dept. Of Physical and Applied Geology, Eötvös Loránd University, Budapest, Hungary, H-1117, Pázmány P. s. 1/c b Geological Institute of Hungary, Budapest, Hungary, H-1442, Stefánia út 14 c Geomega Ltd., Budapest, Hungary, H-1095, Mester u. 4. I/2 abstract article info Article history: Received 2 August 2011 Received in revised form 25 February 2012 Accepted 27 February 2012 Available online 6 March 2012 Keywords: Point bar development VHR seismic Palaeo-hydrography Palaeoclimate Carpathian Basin Middle Pleniglacial The upper 20–30 m of the Pleistocene alluvial sequence on the Tisza River, Hungary is investigated by 200 km of VHR single-channel seismic sections. Frequent internal configurations, such as (1) bundles of inclined re- flections, (2) trough-shaped converging, and (3) horizontal, parallel reflections are interpreted, respectively, as lateral accretion of point bars, abandoned channel fills and floodplain deposits. The series of 5–8 m-thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43–47 ka in the Late Pleistocene according to OSL data. Newly recorded quasi-3D seismic profiles reveal that each 1–3 km-long inclined series correlates with an individual point bar continuously migrating in the same direction. Small deviations in the direction of migration are caused by natural wander- ing of the meander bend. Morphometric parameters of point bars are used to calculate ancient channel pa- rameters (width and depth of 200–500 m and 5–8 m, respectively). Values imply a channel-forming discharge of Q = 400–900 m 3 /s. These results imply a greater amount of runoff and supply in the basin during MIS3 compared to the present day. Long-lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in NW Europe. Our data support the thesis of the three-axis drainage system for the basin. New evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of Danube and Tisza Rivers, contrary to the present-day two-axis drainage pattern. © 2012 Elsevier B.V. All rights reserved. 1. Introduction In addition to the most highlighted questions of fluvial research, such as extreme events and their frequencies (e.g. Macklin et al., 2006) or the effects of climate and global changes on fluvial sedimen- tary processes (Vandenberghe, 2003 and references therein), there is a continuous demand on integration of phenomena as interpreted from the rock record (Herget et al., 2007). Knowledge of the past is necessary to understand present and possible future river processes and, therefore, necessary for effective river management. Continuously de- veloping methods of study and interdisciplinary approaches provide the means to meet these challenges. Recent studies of the Quaternary fluvial succession in Hungary integrate modern methodologies, such as aerial-photo or satellite image-based geomorphological mapping combined with drill core interpretation, magnetostratigraphy, pollen analysis, radiocarbon and OSL chronology, and provide new results about the climatic and tectonic factors involved in the development of the drainage system of the Carpathian Basin (Gábris et al., 2001; Timár et al., 2005; Gábris and Nádor, 2007; Nádor et al., 2007, 2011). Investigations of buried sedimentary architectures, especially those of Quaternary age, have advanced through the application of modern geophysical research methods, like ground penetrating radar (GPR) and high resolution (HR) or very high resolution (VHR) seismic surveys. The first geophysically aided studies of alluvial geometry are reported from GPR surveys (e.g. Huggenberger, 1993; Bridge et al., 1995; Vandenberghe and van Overmeeren, 1999). HR and VHR (or UHR – ultrahigh resolution) seismic surveys are more commonly used to study offshore marine environments (Billeaud et al., 2005; Fielding et al., 2005; Chaumillon et al., 2008). However, ancient alluvial deposits can also be visualized by VHR single- channel seismic surveys carried out in lacustrine or riverine environ- ments (Tóth et al., 1997; Sztanó et al., 2002). HR and VHR shallow water single-channel seismic profiling has been carried out in Hungary since the middle of 1990's by the Geo- mega Ltd. cooperating with Eötvös University (Budapest), with the first surveys being conducted on the Tisza River. Neotectonic results obtained by seismic surveys are summarized by Tóth and Horváth (1999), while internal architectures of alluvial Quaternary sediments below the recent channel of the river are introduced by Sztanó et al. Geomorphology 153–154 (2012) 205–218 ⁎ Corresponding author. Tel.: + 36 13812125; fax: + 36 13812128. E-mail addresses: agika_nagy@yahoo.com (Á. Cserkész-Nagy), sztano@ludens.elte.hu (O. Sztanó). 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2012.02.025 Contents lists available at SciVerse ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph