Geological Development

The territory of Podyjí NP lies on the south-eastern slopes of the Bohemian Massif, where it gradually subsides into the younger sediments of the Carpathian Foredeep.

  

The oldest and most extensive mineral complex are metamorphites of the Moravicum and the Dyje. These are represented by three units: from the west to the east they are the Vranov Unit (which only forms the basement on the NP territory in a narrow belt on the west and north-western edge), the Bíteš orthogneiss and the Lukov Unit. These units are separated from each other by faults striking NE – SW and dipping to the NW.

  

The Vranov Unit is predominantly built of massive or schistose biotite paragneisses but also contains minor bodies of garnet-bearing two-mica mica schists and numerous bodies of garnet amphibolites where the mineral types are interlaid in centimetres to metre thick layers. Within the paragneiss we can also find bodies of crystalline limestones, calc-silicate rocks and quartzites (Jenček 1984).

 

The south-eastern edge of the Vranov Unit is in contact with the Bíteš orthogneiss. This was probably formed by the metamorphosis of deposited volcanic material. The Bíteš orthogneiss is predominantly in the form of massive leucocratic two-mica orthogneiss with augen texture, and is light grey in colour. At the contact with the Vranov Unit the orthogneiss is interlayered with biotite amphibolites of millimetres to decimetres in thickness or muscovite-biotite paragneisses (marginal type) (Jenček 1984).

  

The Lukov Unit is built of two-mica paragneisses, which are interlayered with biotite-chlorite phyllites. In the middle of this unit there is a body of Weitersfeld (Pleissing) orthogneiss, which has a granodiorite to tonalite composition. The paragneiss also contains bodies of crystalline limestones, quartzitic phyllites and quartzites. A horizon of calc-silicate rock is developed at the contact with the Bíteš orthogneiss (Mísař 1983).

  

Dyje Alluvial PlainDyje Alluvial Plain

   

 

Effusive rocks in the Thaya Dome of the Moravicum are only represented by scattered small quartz veins, dykes of lamprophyre, aplite and aplopegmatite. These are probably of Paleozoic age, and are connected to the final phases of the Variscan Orogeny.

  

The Dyje Massif, which forms approximately 1/3 of the basement in the south-eastern part of the NP territory, penetrated into the Lukov Unit and triggered the process of contact metamorphism here. The majority of this massif is overlain with Tertiary and Quaternary sediments. The biotite granite which is most represented in its western part passes into biotite granodiorite. The degree of preferred mineral alignment in the rock also decreases to the south-east. A body of biotite-amphibolite diorite to tonalite is exposed in the central part of the massif. The eastern part of the massif is built of fine-grained granodiorite with pink feldspar crystals (Tasovice type) (Batík et al., 1982).

   

Rock pillars in the Western part of NPRock pillars in the Western part of NP

   

 

The age of the units of the Moravicum has not been clearly defined but most authors consider them to be Precambrian, probably Proterozoic. The age of the Bíteš orthogneiss was determined by Scharbertová in 1977 using the Rb/Sr method at 795 million years. The Dyje Massif is probably also of Proterozoic age (630 million years old using the K/Ar method). The metamorphism of the Moravicum is of a lower grade than that of the neighbouring Moldanubicum to the west. Moving from the south and the north towards the centre of the dome we can observe metamorphic zones of the following minerals: chlorite, biotite, garnet, staurolite, and sometimes even kyanite to sillimanite (Mísař, 1983).

   

From the Lower Paleozoic the territory was gradually denuded and flattened into a peneplain. At the same time the process of kaolinitic weathering took place to a depth of up to 25 metres in the tropical climate of the time.

   

We have no definitive proof of the geological development of the area during the Mesozoic period. In the late Tertiary the region was flooded by a sea which spread from the Alpine-Carpathian region in the south-east. This sea left behind sediments of quartzose sands and gravels, sands and sandy clays. At the end of the Eggenburg the area was covered with falling volcanic ash, which led to the formation of rhyolite tuffs and montmorillionite clays. In this period the sedimentary areas became smaller and isolated basins formed and were isolated from the sea. During the Ottnangian the basins were gradually uplifted as a result of orogenic pressures and basal sediments were formed directly on the crystalline complex. New subsidence in the Carpathian period and at the beginning of the Lower Badenian caused further, but less extensive flooding by the sea, but the resulting sediments were mostly carried away in later periods. Small remnants of these sediments can be seen around Šatov (Čtyřoký et al., 1983).

 

We have no direct evidence of the geological development of the area in the late Tertiary period (Upper Miocene and Pliocene). During the Quaternary period the area was uplifted and sediments were carried away from the whole region, which exposed the older pre-Tertiary surface. During the Quaternary period erosional activities predominated over the deposition of sediments and therefore the Quaternary cover is not very thick and is non-contiguous. Only in the south-eastern part of the NP, on the edge of the Dyje-Svratka Graben, can we find greater thicknesses of Pleistocene fluvial, lacustrine and wind-blown sediments.

   

The loess accumulations of Würm age are of special interest and these deposits can be found on the fringes of the rocks of the Moravicum and the Dyje Massif along the northern and eastern borders of the NP and also occur irregularly on nearly all of the NP territory. The soils which formed on loess are relatively nutrient-rich and together with the belts of crystalline limestone and calc-silicate rocks of the Lukov Unit this contributes to the changing character of the vegetation and increases the overall variety of the nature in Podyjí NP.