Alluvial architecture and fluvial cycles in quaternary deposits in a continental interior Basin, E Hungary

Györgyi Juhász, Pál Müller, Ágnes Tóth-Makk

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Abstract

The thickness of the studied Quaternary alluvial complex, located in the eastern part of the Pannonian Basin System, can exceed 500 m. Based on subsurface facies analysis the following large-scale depositional elements were identified: channel-fill deposits, point bar deposits, alluvial fan (sandy sheet-flood) deposits, floodplain and floodbasin deposits, and thinner sandy-silty beds. They are classified into four types of facies associations, showing a characteristic stacking pattern on the logs. Facies zonation and basin-scale facies mapping of the overall Quaternary sedimentary succession shows that in several areas dominated by stacked, multistorey sandy channel fill sediments, pre-existing superimposed channel belts can be presumed. In the central and deepest part of the basin muddy flood basin (distal floodplain and wetland) sediments dominate. Between these the largest area represents the floodplain where single channel fill sands are interbedded in the alluvial plain muds. In the eastern part of the basin the well-logs highlight the distal part of an alluvial fan where sandy sheet-flood deposits alternate with floodplain sediments. The recognized facies associations show a vertical pattern, i.e. they form a 40-100 m thick fining-upward fluvial cycle. The most characteristic and even ideal cycle can be observed in the channel belts and in the proximal floodplain zone. Here the basal member of the cycle is made up of multistorey channel fill beds cut into the underlying floodplain deposits. This is overlain by an alternating sandy-muddy succession of channel fill and floodplain deposits forming the intermediate member. The upper member is composed of silty-clayey floodplain deposits with occasional very thin, discrete silty-sandy bodies. These three members form a fining upward sedimentary cycle interpreted as representing low-, increasing- and high-accumulation space deposits, respectively. As the basal multistorey channel fill sandstone facies association generally proved to lie above an extensive erosional surface which can be correlated regionally in the basin, allocyclic controls can be assumed. In some parts of the basin the cycle is not complete as the incised channels can be single, so the low-accumulation space deposits can be missing and the high accumulation space deposits, i.e. the aggrading floodplain sediments, can be truncated. On a regional scale, six regionally extensive cycles were differentiated above each other. Although these cycles were allocyclic the question of whether they were tectonically or climatically driven remains open. However, the fact that six of them have been identified, suggests that they represent the large-scale 400 ka Milankovitch cycles during the Quaternary. The tectonic overprint is apparent in the thickness and internal architecture of the individual cycles.

Original languageEnglish
Pages (from-to)171-190
Number of pages20
JournalGeologia Croatica
Volume57
Issue number2
Publication statusPublished - Jan 1 2004

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Keywords

  • Depositional cycles
  • Fluvial sedimentology
  • Hungary
  • Körös basin
  • Pannonian basin system
  • Quaternary
  • Sequence stratigraphy

ASJC Scopus subject areas

  • Geology
  • Earth and Planetary Sciences (miscellaneous)

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