The main geological Units
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The Moldanubian and Moravian Superunits are deep portions of an ancient mountain range, which extended from central Europe over the Iberian Peninsula to the Appalachian Mountains in North America. The southern end of these two units forms the Walviertel region. The mountain range developed during the so-called Variscan Orogeny before 360 to 300 million years ago on the southern margin of "Old Europe". The former high mountains were mostly eroded, flooded by seas and parts have only been uplifted again during Cenozoic time to form a low mountain range. The present-day, undulating highland landscape has been deeply incised by the Danube and its tributaries from the north. The range of rocks is varied and colourful and the prevailing rock types are granite, gneiss (paragneiss and orthogneiss) resulting from former sediments or igneous rocks, amphibolites attributable to volcanic activity, granulites, quartzites and marbles.
Helvetic Superunit and klippes of the Waschberg Zone: The rocks of the Helvetic Superunit are marine deposits and in the Vienna area occur as wedges within the flysch rocks in the form of red, green and grey, partly marly clays with thin layers of quartz sandstone. Like the rocks in the Bohemian Massif and the light-coloured, pure limestone klippes of the Weinviertel Waschberg Zone they belong to the depositional environment of "Old Europe". However, in contrast to the Moldanubian and Moravian Superunits they were included during the Cenozoic within the Alps.
The rocks of the Penninic Superunit are remnants of a past ocean, the so-called Penninic Ocean. The flysch rocks on the northern margin of the Calcareous Alps in Lower Austria and Vienna are composed of a characteristic, often repeating sequence of sandstones, silt- and claystone or marl. They formed from mudslides that flowed from the shelf edge into the deep sea. In southern Burgenland rocks associated to the Penninic Superunit are exposed in a tectonic window: these include greenschist that developed from the oceanfloor basalts, serpentinite, former mantle rocks, and altered ocean basin sediments such as calcareous schists, phyllites and quartzites.
The rocks of the Austroalpine Superunit were originally located on the northern edge of Africa, and later formed the northern margin of the Adriatic Plate. They form the Northern Calcareous Alps (Lower Austria and Vienna) and the Central Eastern Alps (Lower Austria, Burgenland, Styria). The sediments and volcanic rocks from which the oldest rocks of this unit are derived, are more than 540 million years old. These include paragneiss, mica schist and amphibolites. Later granite was intruded, being altered to so-called orthogneisses. In Palaeozoic time there followed deposition of sandy-clayey sediments with intercalated basalt lavas and tuffs, calcareous reefs, sands, gravels, and salt and gypsum deposits. Many of these rocks later underwent deformation and alteration to varying degrees and occur today as phyllites, mica schists, marbles, quartzites and amphibolites. Some were penetrated by molten rock from the Earth's interior which consolidated to form granite or pegmatite. The youngest and topmost sedimentary rocks of this unit are of Mesozoic age and were deposited in a shelf, which was located on the edge of the Tethys Ocean, and later lay between the Tethys and Penninic Oceans. The rock sequence begins with red shales and sandstones followed by bedded limestones, massive reef limestones, bedded dolomite, intercalations of sandstones and clayey sediments and, in turn, carbonate rocks which originated in reefs and lagoons. There are also siliceous limestones and radiolarites that formed in deeper marine areas. Starting with the tectonic movements at the end of the Mesozoic the rocks of the Gosau Group were deposited, consisting of sandstones, marls, conglomerates and marly limestones.
Molasse Zone and Inner Alpine Basins: the Molasse Zone of the Alpine Foreland in Lower Austria includes gravels, sands and silty-clayey sediments, which formed in a basin in front of the approaching nappes of the Alps. The majority of the sediments developed as the basin was filled by the so-called Paratethys Sea during Neogene time. They were deposited in deep and shallow waters, on the coasts and in deltas. After the sea had retreated lakes and rivers were formed. The deposited material came largely from the uplifting, mainly calcareous rocks of the Alps in the south and to a lesser extent from the dominantly silicate rocks of the Bohemian Massif. The history of the Inner Alpine Basins in eastern Austria (Weinviertel region, Vienna, Burgenland, Styria) begins somewhat later. They formed due to a plate tectonic related, easterly directed extension. However, a similar development of marine (Paratethys) to freshwater deposits is found. Under brackish and freshwater conditions (Lake Pannon) these basins finally became silted up and alluvial deposition became dominant. The sediments include rock debris, gravels, sands, silts and clays with varying amounts of carbonate content, which were supplied from the adjacent uplifting mountains. In quiet shallow marine areas, limestone developed, such as the Leitha Limestone, composed of skeletal fragments of lime-precipitating red algae. Where rivers flowed into the sea, we now find gravels and conglomerates, and in the basins silts, clays and clay marls also referred to locally as schlier. The most recent marine sediments are about 12 million years old. In the Styrian Basin deposition was accompanied by an intense volcanic activity about 15 million years ago, remnants of which can be found near Bad Gleichenberg and Weitendorf.
The geological development of the Quaternary, the most recent geological time period, started about 2.6 million years ago and is still ongoing today. It is of great importance for all the wine regions of Austria. The essential characteristic of this geological period is the repeated alternation of cold phases (glacials) and warm intervals (interglacials): the last Ice Age ended in the Pleistocene about 10,000 years ago. These climate fluctuations are responsible for the shaping of the landscape with its valleys, terraces, hills and mountains, as we know them today, and also for the types of the most recent deposits. In Styria, about 2 million years ago, there was a second volcanic phase, to which the rocks of the areas of Klöch, Kapfenstein and Riegersburg are attributed.
The wine regions of Austria were not glaciated during the cold phases but were located in the vicinity of the glaciers, in the so-called periglacial areas. The latter were marked by intense freezing, frost and reduced vegetation cover. The glaciers planed large amounts of rock from the mountain ranges, which were transported as boulders by the meltwaters into the foreland areas and deposited there under decreasing rates of drag force and transport capacity. They form the terrace landforms into which the rivers cut when subject to renewed swelling. Thus, giving rise to a staircase of old valley floors with younger terraces occurring in a downward direction, ending with the present-day flood plain. Loess also developed in the same time as the terrace gravels during the cold phases of the Quaternary. It consists of rock dust blown by the wind from the vegetation-free, dry plains in front of the glaciers which was re-deposited in the foreland areas, in particular on the east and southeast-facing slopes. Loess shows a characteristic flour-like consistency and is yellow in colour. It is always calcareous, but with a varying content ranging from magnesium-free calcite to magnesium-bearing dolomite. Typical features also include its porosity and high degree of stability in the dry state: for example, the walls of narrow gorges remain standing while the non-compacted floor subjected to severe wetting is eroded deeper and deeper. Not all loess is preserved in the classical form: the ground became frozen at depth during the cold periods, thus only the slightest dip in slope was required to cause superficially thawed, water-saturated material to slide. Consequently, due to its altered structure, weathering and multiple freeze-thaw cycles caused further changes. Through these processes loam was formed, which is decalcified loess with increased clay content. In the terrain where deposits are exposed both horizontal and vertical gradation of loess and loam can be seen: such occurrences make it extremely difficult to delimit these areas on geological maps.
Extremely young in age geological processes such as weathering as well as extensive erosion and re-accumulation of deposits in linear streams and on slopes are of great importance for wine growing. Products of these processes include loosening and disintegration of consolidated rocks, loamification of clay and mica-rich rocks, talus and alluvium, alluvial fans, muds, slope wash and colluvium as well as overbank loam and ultimately the soil-formation above all parent-rocks; the soil that supports and anchors the vines and serves as a water and nutrient reservoir.
Soil is a mixture of weathered rock and organic matter, in addition to its content of water and air. The formation of a soil usually starts at the surface of the rock, which can be either unconsolidated or consolidated, and progressively increases in depth over time. Soil formation and its further development takes place over long periods of time under the influence of various factors such as climate, groundwater, surface relief, vegetation, soil organisms and human use.