Moldanubian and Moravian Superunits
The Moldanubian and Moravian zones are deep sections of an ancient mountain range that began in central Europe, crossed the Iberian Peninsula and ended in the Appalachian Mountains in North America. The southern end of these two zones forms the Waldviertel region. The mountain range developed during the Variscan orogeny that took place on the southern edge of “Old Europe” some 360 to 300 million years ago. These former high-altitude mountains were once eroded almost completely and flooded by seas. It was only during the Cenozoic that sections rose up again to form a low mountain range. Today, the Danube and its tributaries from the north have cut deeply into the rolling, hilly landscape. There is a diverse and colourful range of rocks here, with a prevalence of granite, gneiss (paragneiss and orthogneiss) metamorphosed from former sediments or igneous rocks, amphibolite attributable to volcanic activity, granulite, quartzite and marble.
Helvetic Superunit and cliffs of the Waschberg Zone
The Helvetic zone and cliffs of the Waschberg zone: the rocks of the Helvetic zone are formed from sedimentary marine deposits. In the Wien wine-growing region, they appear as wedges within the flysch rocks in the form of red, green and grey clays (some of which are marly), interspersed with thin layers of quartz sandstone. These rocks belong to the depositional environment of “Old Europe”, similarly to the rocks in the Bohemian Massif and the light-coloured, pure limestone found in the cliffs in the Waschberg zone (Weinviertel). However, in contrast to the Moldanubian and Moravian zones, these rocks were integrated into the Alps during the Cenozoic.
The rocks of the Penninic zone are remnants of the former Penninic Ocean. The flysch rocks on the northern edge of the Calcareous Alps in Lower Austria and Vienna are composed of a distinctive, oft-repeated sequence of sandstone, siltstone and claystone (or marl). These were formed by mudslides that flowed from the shelf edge into the deep sea. In southern Burgenland, rocks from the Penninic zone crop out in a tectonic window. These include greenschist that developed from ocean-floor basalts, serpentinite and former mantle rock, as well as transformed ocean basin sediments such as calcareous schist, phyllite and quartzite.
Rocks of the Austroalpine Superunit
The rocks of the Austroalpine nappes were originally located on the northern edge of Africa, before forming the northern edge of the Adriatic plate. These rocks form the Northern Calcareous Alps (Lower Austria and Vienna) and the Central Eastern Alps (Lower Austria, Burgenland and Styria). The sediments and volcanic rocks, from which the oldest rocks in this unit developed, date back more than 540 million years. They include paragneiss, mica schist and amphibolite, as well as granite, which appeared at a later point in time and was transformed into orthogneiss. Sandy, clay sediments, intercalated with basalt lava and tuff followed during the Palaeozoic, as well as limestone reefs, sand, gravel, and salt and gypsum enclosures. Many of these rocks subsequently underwent various degrees of transformation, resulting in what we see here today: phyllite, mica schist, marble, quartzite and amphibolite. Some were penetrated by molten rock from the Earth’s interior, becoming consolidated as granite or pegmatite. The most recent and topmost sedimentary rocks in this unit date from the Mesozoic and were deposited in a shelf located at the time on the edge of the Tethys Ocean (later, located between the Tethys and Penninic oceans). The rock sequence begins with red claystone and sandstone, followed by bedded limestone, igneous reef limestone, bedded dolomite, intercalations of sandstone and clayey sediments, then more carbonate rocks, which originated in reefs and lagoons, as well as gravelly limestone and radiolarite, which formed in deeper marine areas. Tectonic movement at the end of the Mesozoic initiated the deposition of rocks from the Gosau Group, which consist of sandstone, marlite, conglomerates and marly limestones.
Molasse Zone and inner Alpine Basins
The Molasse zone in the Alpine foothills in Lower Austria contains gravel, sand and silty, clayey sediments, which formed in a basin in front of the approaching nappes of the Alps. The majority of the sediments developed during the Neogene, when the basin was occupied by the Paratethys Ocean. The sediments were deposited on the coasts and in deltas, in both deep and shallow waters. Once the sea had retreated, lakes and rivers were formed. The majority of the deposits originated from the heavily carbonaceous material from the Alps in the south as they rose, but some also came from the predominantly silicate rocks of the Bohemian Massif.
The history of the inner Alpine Basins in eastern Austria (Weinviertel, Vienna, Burgenland and Styria) begins somewhat later. These basins can be traced back to tectonic movement that caused a lateral spreading towards the east. However, they developed similarly to the Molasse zone, with a build-up of marine deposits from the Paratethys Ocean, deposits from the brackish, freshwater Lake Pannon and alluvial deposits until the basins finally became silted up. The deposits include rock debris, gravel, sand, silt and clay containing varying levels of carbonate, which was supplied by the adjacent mountains as these rose. The calm, shallow marine areas were conducive to the development of limestone, referred to as Leitha limestone, which is composed of skeletal fragments of lime-secreting red algae. Today, gravel and conglomerate mark the former places where rivers used to flow into the sea, while the basins contain silt, clay and clay marls (referred to locally as “Schlier” and “Tegel”). The most recent marine sediments are around 12 million years old.
The sedimentary deposits in the Styrian Basin settled around 15 million years ago, at a time of intense volcanic activity, testimony to which can be found near Bad Gleichenberg and Weitendorf. The Earth’s development during the Quaternary, the most recent geological time period, began around 2.6 million years ago and is still continuing today. This period, which is of great significance for all Austrian wine-growing regions, is characterised by the repeated cycle of cold, glacial periods and warm, interglacial periods. The last ice age ended in the Pleistocene about 10,000 years ago. These climate fluctuations are not only responsible for shaping the landscape – resulting in the valleys, terraces, hills and mountains that we see today – but also for influencing the most recent types of sedimentary deposits. There was a second volcanic phase in Styria about 2 million years ago, to which the rocks in Klöch, Kapfenstein and Riegersburg are attributed.
Although Austria’s wine-growing regions were not glaciated during the cold phases, they lay close to the glaciers, in areas described as periglacial. These areas were characterised by permafrost, frost and sparse vegetation. The glaciers eroded large amounts of rock from the mountains, which the glacial meltwaters transported – in the form of pebbles – to the foothills, where they were gradually deposited as the waters slowed down and lost their power. These rocks form the terrace material into which the rivers repeatedly cut when they rose, resulting in the creation of stepped layers of former valley floors – the oldest at the top and the most recent at the bottom, with today’s flood plain at the very base. Similarly to the terrace gravels, loess also developed during the cold phases of the Quaternary period. Loess is composed of rock dust that was blown off the dry, barren glacial forelands and came to rest on the floodplains, settling particularly heavily on eastward and south-eastward facing hillsides. It has a characteristic powdery consistency and is yellow in colour. It is always carbonaceous and contains varying proportions of magnesium-free calcite and magnesium-bearing dolomite. Other typical characteristics include its high porosity, as well as a high degree of stability in a dry state. This explains why the walls of the sunken pathways that are cut into loess remain intact, while the unconsolidated path floors sink increasingly deeper due to erosion when they become heavily saturated. Not all loess exists in this classic form, however. During the glacial periods, the substratum became so deeply frozen that material immediately slid down even the smallest incline as soon as the surface thawed and became saturated with water. This upset the fabric of the rock, which underwent further transformation as a result of weathering and multiple freeze/thaw cycles. These processes resulted in the formation of a mixture of loess and loam, which is decalcified loess with a higher clay content. In the field, we can find both horizontal and vertical transitions between pure loess and loess loam, which makes it extremely difficult to mark the boundaries of these areas on geological maps.
Very recent geological processes that are significant for viticulture include weathering and linear and surface erosion (in rivers and on hillsides, respectively), as well as the accumulation of the resulting deposits. These processes cause the loosening and granular disintegration of consolidated rocks, the loamification of schistous rocks, and the formation of scree, river gravel, alluvial fans, solifluction, slope run-off and colluvium, as well as alluvial loam and ultimately the soil itself, which forms on top of all parent rocks. This is the soil in which the vines are rooted and which serves as their supply of water and nutrients. Soil is a mixture of weathered rock and organic matter, as well as a certain amount of water and air. Formation of soil usually begins on the surface of the rock, which is either consolidated or unconsolidated, and becomes progressively deeper over time. The soil continues to develop over a long period, influenced by factors such as climate, groundwater, topographical relief, vegetation, soil organisms and human intervention.