engleski

Korelacija kvartarnih i tercijarnih sedimenata doline Drave sa lista Sellye–Slatina, M 1: 100 000

This article shows first results of common geological mapping begun in 2007 in Drava-valley made by Croatian Geological Survey and Geological Institute of Hungary. It shows surface formations and its correlation on the territory, the basement formations, and types and thickness of Miocene sediments. We can correlate Pannonian (Pontian) sediments in detail along the Drava River from Barcs to the end of common Drava-section due to log data of hydrocarbon prospect holes. The boreholes data near Sellye and Okorág show that the upper part of Újfalu Formation (Pontian) consist of 150-200 m thick brown coal and overlaying 200 m thick coarse grained gravel instead of typical section of alternate sandstone, siltstone and clayey marl. Regional facies of Pannonian (Pontian) formations is featured by stepped filling up of Miocene part-basins with smaller oscillation and by compensation of ground surface. There is a basement of Pannonian sediments on this territory, which is deeper than 3300 m and the centre of this basin is at Felsőszentmárton–Gačište area. The basement of this basin ascends from Felsőszentmárton–Gačište to Drávaszabolcs to 1500 m and to Donji Miholjac at 1000 m deep. During the Pannonian sedimentation, both regional alleviation and ground surface compensation took place. As a result, the level of beds overlying the youngest Pannonian sediments is at -100 m (±50 m) in the whole area. A lot of data about post-Pannonian formations are obtained from the sections of water-wells, and from field work. One of the most important post-Pannonian formations is the Marcali Formation (Pliocene–Pleistocene) which is the underlying formation of Drava sediments. This formation consists of alternating fluvial fine grained sand and silt, and it is few hundred meters thick. This formation is well known on the Hungarian side in Belső-(Inner-) Somogy, and we could verify it in Drava-basin too, and separate from underlying Upper Pannonian and overlying flood plain sediments (FPS) of Drava. The Drava sediments are discordant on Marcali Formation (Pliocene–Pleistocene) and coarser grained as underlying beds. This FPS is about 100 m thick on the Sellye territory and over 200 m thick at Slatina. This sequence can be distributed to two or three fluvial sedimentary cycles which have upwards finer grain size and consist of pebbly, medium-grained channel sand. Twenty three Quaternary formations are separated on the Sellye-Slatina sheet and correlated them on the Croatian and Hungarian side of the sheet. Territory can be distributed in different part, on the grounds of its geological and geomorphologic features. Drava sediments are found on the Drava alluvial plane, on the Ormánság-terrace, on the Podravina terrace and under the eolian sand of flood plain. The border of surface and subsurface Drava sediments are in south, the foreland of Bilogora Hill and Papuk Mts., on north the plain of Fekete-víz and the foreland of Dunántúl Hill. Holocene alluvial sediments distributed by point bars and dead channels, are typical on the Drava floodplain. Zone of fractured terrace relicts consisting of mainly fluvial sand, runs along north from young alluvial plain in Ormánság, emerged from high alluvial level of Drava. The overlaying well developed loess-like gleyey podzol-type soil shows, the relative age of these terrace relicts. This soil is a relict from Upper Pleistocene representing warm/cold and wet/arid climate changes. It is typical of the high floodplain level that some of the Lower Holocene alluvial formations of Drava were inherited by the influent creeks coming from the north during the Upper Holocene. Podravina terrace consists of Pleistocene fluvial sands, which are overlyed by Holocene-Pleistocene fluvial-marsh sediments and Holocene eolian sands. The morphology of this area with equated surface, which is barely, reflects fluvial activity is very different from braided alluvial plain of Drava. A series of formations developing from marshy sedimentation to loess-formation is typical on the south border of Drava-valley at the Bilogora Hill foreland. Colluvial sediments and loess originated from this series cover huge areas as well. Multigenerational eolian sand bodies lay out the NW boundary of Drava-valley. The oldest of these is covered by Pleistocene podzol-type relict soils at Barcs and Darány. The loess-sediments of Baranya region (HUN) and the resedimented, 10-20 m thick formations of this loess reclined against Drava FPS, border the valley on the NE side. Terrain affected by fluvial sedimentation, on the mapped area of Drava-valley, is asymmetric. One of the most interesting differences between north and south part is that the terrace sediments and relict soils of north side are missing on the Croatian side. Also it is conspicuous that Podravina terrace featured by Pleistocene-Holocene sediments had an occlusion, from the territory of young alluvial plain of Drava, which is laying on the same morphological level and which is characterized by intensive fluvial meanders of the river. It is very probable that these differences are correlated with young structural development of territory. Acknowledgements This project was established by the support of the National Office for Research and Technology (Hungary) and was supported by the K 75 801 National Research Foundation (OTKA), the HR-15/2008 and HR-16/2008 projects of S&T Foundation of Hungary and Croatian Ministry of Science, Education and Sports.

geološka karta; Drava; pleistocen; holocen; pijesak; les

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