MORPHOLOGICAL GROUPING OF FOSSIL FLOODPLAIN FORMS IN THE NORTHEASTERN PART OF THE PANNONIAN PLAIN
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Kiadó
University of Debrecen, Institute of Earth Sciences
Absztrakt
Leírás
The Bereg Plain is located in the northeastern part of the Pannonian Plain, close to the CarpathianMountains. Clarification of the evolution of its topography is essential for the development of the wholearea. The former single alluvial cone has been fragmented, some parts of it subsiding and others rising.The displacements of the subsided parts of the area were dominated by erosion processes, as in the BeregPlain. As a consequence, a significant part of the sand in the area has been degraded and only traces of itremain in the Bereg Plain. The existing sand patches have been identified and classified using DEM. In thearea identified 10 floodplain islands not yet mentioned in the scientific literature. The investigation ofthe numerous islands – hitherto unknown and be-longing to different morphological types – enabled us areconstruction of the surface development of the Bereg Plain that is more differentiated and precise thanever before. Based on their morphogenetic properties, these floodplain islands can be divided into threemain types: (1) erosion islands, (2) point-bars, (3) coastal dunes. In the area, I could recognize no patternor re-gularity in the position of the individual forms of any type. In many cases, the direction of thelongitudinal trends is perpendicular to one another, which excludes their Aeolian origin. The sedimentof the floodplain islands mainly consists of medium-, small- and fine-sized sand, but the settlement ofloess-mantled and loess-like layers among the sandy sediment of certain forms can also be observed. Thelayer with 15 % lime content and 53–60 % loess fraction (0.05–0.01 mm) – found in the 110–50 cm highsection of the erosion island called the Homok-tanya in Mátyus – can be considered a typical loess, basedon the detailed parameters. Its formation in all probability took place at the same time and under similarconditions than that of the more than 2 m thick aeolian loess mantle found in the Nyírség area, some 10km west from there, which had accumulated before the Bölling period. In case of an erosion island 2.5km to the south and lying some 2 m lower, such a loess mantle cannot be found anymore, despite the factthat the sandy layers of the two sediment series are almost completely identical. The background of thisphenomenon is the more active and frequent, mainly erosional fluvial processes – because of the lowerposition –, which eroded the loess mantle.The composition of the surface sediments is de-termined by the absolute altitude as well. The coversediment of the lower-lying islands is identical to the finishing silt-clay deposits found at the alluvialparts of the Bereg Plain, whereas the surface of higher-lying forms that have not seen flood for ages, iscovered by sand or loessy sand.
Kulcsszavak
alluvial fun, DEM, erosin island, point-bar, coastal dune