Geologic stratification (see Fig. 2.5) of the Upper Danube Basin can be classified into four units (GLA, 1996):
(a) The Variscan North-Bavarian basement rock consists predominantly of granite and meta- morphic rock, representing the fundament of the considerably younger overlying rock. Due to tectonic lift and erosion since the Cretaceous the bedrock appears at the surface in the northeastern parts of the catchment Fig. 2.6.
(b) The overlying rock north of the River Danube lies over the basement. The sedimentary
rock originated during late Palaeozoic and Mesozoic ranges with a thickness of 300mto
1500mfrom theSpessartin the north down to the Danube into the molasse basin. South
of the Danube the basement rock and the overlying cap-rock decline some thousand metres and are covered by molasse sediments.
(c) The Alpine orogeny began in early Mesozoic with deposition of sediments from the Tethys Ocean. Beginning convergent movement of the European and African plates in the Cre- taceous led to folding and faulting of the sediment layers. The upper crust of the Apulian plate was thrusted over the European crust. When in early Tertiary the subducting slab
broke off, isostatic lift and further collision of the plates let the Alps rise with up to 5mmper
year.
(d) The molasse basin between the Danube and the forelands of the Alps is filled with a
stratified sediment layer of up to 5000m, which was eroded during the Alpine orogeny
in Tertiary and deposited in the basin. It consists of limnic and fluviatile sediments of various grain sizes and was influenced temporarily either by salt water or fresh water. These four geological units are characterised by different hydrogeological properties (Barthel et al., 2005):
(a) Paleozoic basement: the gneiss and granite parent material of the Bavarian Forest, the Upper Palatinate Forest and the Black Forest shows basically low permeability. Merely a few granite deposits are weathered at their top layer, forming aquifers of only local relevance.
Fig. 2.5: Schematic cross section of the geological layers in the Upper Danube Basin (Barthel et al., 2005)
(b) Jurassic karst: The low mountain ranges in the north of the Upper Danube Basin evolved
during the Mesozoic. Vast parts of the Swabian and Franconian Alb are made up ofMalm
karst with very high permeabilities, contributing great amounts of water to the aquifer in the Danube valley. Some small areas are covered with non-alpine Cretaceous and
Jurassic rock showing lower permeabilities. The breccies of theNördlinger Ries, emerged
from a meteorite impact, are also fairly impermeable.
(c) The Alps: the Central Alps are consisting of alpine magmatic and metamorphic rocks from Triassic and Jurassic periods, representing an aquiclude. Sediments of the northern limestone Alps are mainly limestone, dolomite and marl, thus they are karstified resulting in medium to high permeabilities.
(d) The molasse basin: The lowermost layer consists of tertiary marine and freshwater mo- lasse sediments, acting altogether rather as an aquiclude. But in the regions surrounding the Pleistocene and Holocene drainage areas, quaternary alluvial sand and gravel de- posits form the most important aquifer for the Upper Danube Basin. Unsorted moraine sediments, which can be found in areas near the foothills of the Alps, are very imperme- able.
During the last period of the Quaternary, the Pleistocene, vast parts of Northern and Central Europe were glaciated. The glaciers spread from the Alps into the forelands, and some peaks of the low mountain ranges were marginally covered by ice. The last four glacial periods,
calledGünz,Mindel,RißandWürm, reshaped the tertiary forms. Changes between glacials
and interglacials led to advances and retreats of the glacier tongues, which formed moraines and cut in stream terraces by their drainage. The areas of Pleistocene glaciation have an above-average coverage with lakes and moor, compared to the ice free regions. Abrasion and plucking by the glacier tongue left depressions which were sealed with fine sediments and filled with water. This led to development of lakes and frequently through subsequent
9°E 10°E 11°E 12°E 13°E 47°N N 48°N 49°N 50°N 0 15 30 60 90 120 Kilometer Quaternary alluvial deposits
Impact breccia
Quaternary moraine sediments Tertiary molasse sediments Non-alpine Cretaceous rock Malm limestone
Jurassic and Triassic clay- and marlstone Alpine limestone and flysch Alpine magmatic und metamorphic rock Gneiss and granite rock
Water bodies and glaciers
Fig. 2.6: Geology of the Upper Danube Basin, modified afterBarthel et al.(2006). Red: Alps (a),
blue: molasse basin (b), green: Jurassic karst (c), black: Palaeozoic basement (c), see text for detailed description.
Schotterebene), which forms the aquifer for the region. Transported rock is mainly composed of calcium carbonate, but also crystalline fractions can be found, which were transported via ice stream networks over transfluence passes from the Central Alps. To the north adjoins the Tertiärhügelland, which was formed during the Tertiary and remained free of ice in the Pleistocene. Aeolian transport from the glaciated areas deposited Loess sediments in the hilly terrain.
Due to the regional differences of bedrock, terrain, climate, vegetation and time of pedo- genesis, the Upper Danube Basin is characterised by a variety of soil textures and soil types, which resemble the spatial pattern of the surface geology and geomorphology.
The Alps show distinct influences of the climatic altitudinal belt and parent material. The nival zone consists of very shallow, unconsolidated, extremely gravelly and stony material,
designated by the World Reference Base for Soil Resources (WRB) (FAO, 2006) as Lithic Lep-
tosols. These are followed further downhill – depending on the content of calcium carbonate in the parent material – by Dystric Leptosols in the northern Limestone Alps or by Rendzic Leptosols in the crystalline Central Alps.
The foothills of the Alps, made up of mainly unsorted moraine material, are dominated by
Luvisols in the plain areas (e.g. theMünchner Schotterebene), with clay loam and sandy loam
influences. In the depressions accumulation of fine colluvial material induces frequent back- water conditions which explains development of gleyic Cambisols. High groundwater levels in river valleys form gleyic Fluvisols or Gleysols in hollows. Occasionally a transformation of Gleysols into eutric and distric Histosols can be found in depressions of various size. On the
thick Loess sediments of theTertiärhügellandfertile Cambisols with fine soil textures, ranging
from silty loam to clay silt, developed.
In the Swabian and Franconian Alb loamy-clay soil textures prevail. As here the older bedrock was not covered by quaternary deposits, weathering is much more advanced as in the forelands of the Alps, and soil is more deficient in lime. On areas covered with upper
Jurassic (Malm) limestone chromic Cambisols and rendzinic Leptosols can be found. In the
older layers of the Jurassic (Dogger and Lias) Vertisols can be discovered, which partially
merge into stagnic or gleyic Luvisols. The Upper Triassic sandstones naturally exhibit sandy soil textures, with dystric Leptosols, leptic Cambisols and Podzols.
The crystalline low mountain ranges of the Black Forest, Bavarian Forest, Bohemian Forest and Upper Palatinate Forest are dominated by dystric Leptosols and (leptic) Cambisols on granite bedrock, but tend to acidification and thus to podzolisation on gneissic parent material. (Ludwig & Muerth, 2006)