Barley sand channel

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Barley sand: coarse sand and " barley "

The Graupensandrinne is a paleo river valley that existed in the higher Lower (18-17 mya ) or early Middle Miocene (14.5 mya) on the northern edge of the Alpine foreland depression . It got its name after the base conglomerate , the barley sand (contains small oils in the size of barley ), the erosion-discordant layers of the Upper Sea Molasse and Lower Freshwater Molasse , partly also directly Jura limestone. The channel runs from northeast to southwest almost along the southern edge of the Swabian- Franconian Jura .

History of exploration

The presence of a Miocene erosion channel on the northern edge of the Molasse trough was first recognized in 1925. The first publications of basic overall representations come from the geologists August Moos (1925) and Helmut Kiderlen (1931). Haus (1951) differentiated for the first time between an extended channel and the actual channel. The field research focused on outcrops on the north (west) edge of the channel in the Ulm area and in the Hegau / Lake Constance area , where the sands and gravels were or are being commercially mined. More recent knowledge has been gained from some scientific boreholes.

geology

General

Upper Danube and Swabian Alb today
Miocene barley sand channel on the northern edge of the Molasse basin .
Geological section through the Hegau with the barley sand channel.
Barley sands, covered by the OMM's Austernnagelfluh, neglected sand pit Riedern
Fossil teeth (sharks, mammals and? Crocodiles) from the barley sand of Riedern
Viviparus suevicus W ENZ 1919, diameter 1.9 cm, Miocene, sweet brackish water molasse, Unterkirchberg near Ulm

The barley sand channel is a predanubic drainage channel on the northern edge of the northern alpine molasse. It was refilled in the Miocene in the course of a last, weak transgression of the Molasse Sea ("Upper Brackish Water Molasse", OBM) and by fluvial sediments (Upper Freshwater Molasse, OSM) and is therefore no longer morphologically perceptible today. Its function as a drainage channel of the Alps, the Molasse Basin and the Frankish and Schwäbische finally took the evolving since about eight million years ancient Danube .

Due to the tectonic uplift of the Molasse Basin at the end of the Lower Miocene, the then flat sea, the western Paratethys , finally receded from what is now southern Germany, as far as eastern Bavaria and west into the Swiss plateau . In the course of this receding sea, an 8–13 km wide fluvial channel was cut on the northwestern edge of the Molasse basin, through which large parts of what is now southern Germany were drained. These regions included the western part of the Bohemian Massif (today Thuringian-Franconian-Vogtland Slate Mountains , Fichtel Mountains , Bavarian Forest ) as well as the then still flat areas of the Black Forest basement and the extensive Jura areas that still reached far into northern Württemberg . The corresponding river system is called the Ur-Naab / Ur-Main river system. Its main stream, which emerged from the union of Ur-Main and Ur-Naab and whose activity is primarily responsible for deepening the barley sand channel, is also known as the “barley sand river”. The drainage was to the southwest, in contrast to today's Danube, which drains to the east. The channel was at least 260 km (as the crow flies) long and extended from Manching near Ingolstadt over the Ulm area to at least Riedern am Sand , where the coast of the Molasse Sea was probably located at that time.

The uplift of the Alpine foothills took place in the form of a tilt, with stronger uplift amounts in the north and northwest and decreasing uplift amounts to the south and southeast. Correspondingly, the north and north-west edge of the channel is deepened 60–80 m, up to a maximum of 100 m, the south and south-east edge only up to 40 m deep into the underlying layers. This deepening of different depths is documented today in the form of erosion contacts between the Grimmelfinger layers and the Lower Freshwater Molasse (USM), sometimes even limestones from the White Jurassic (e.g. near Engen ), on the north and north-west edge of the channel. The general sequence of layers in the Molasse Basin shows a significant gap in the layers (a hiatus ).

Lithostratigraphy

The deposition conditions in the barley sand channel are complex. Its filling consists essentially of two formations: the predominantly gravelly barley sand , which is up to 20 m thick in the Ulm area, at the base and the overlying, mostly clayey silty Kirchberg layers .

In the barley sand there are fragments of lydite-like silica slate and an above-average number of heavy minerals , among other things. a. Zircon , rutile , thistle and tourmaline , and Buchner et al. (1998) mention "large amounts of rock fragments ( quartz , granite , gneiss , chert , vein quartz and feldspar ) of fine and medium grain size to an unusually large extent", which suggests that the material originates from the varisticum . The type locality of the barley sands is Grimmelfingen on the western edge of Ulm, which is why these deposits are also known as "Grimmelfinger barley sands", "Grimmelfinger layers" or Grimmelfingen formation. Fossils are generally rare in the Grimmelfinger Strata. Only in Klettgau are there numerous remains of marine animals and land vertebrates. The Grimmelfinger layers also interlock there with the so-called oyster nagelfluh , a marine conglomerate that is part of the OMM.

The Kirchberg strata, whose type locality is near Illerkirchberg , south of Ulm, are clayey-marl-like in the Ulm area, about 10 m thick and contain a characteristic brackish water micro and macro fauna, occasionally also mammal remains. They are interpreted as the result of a last transgressive pulse of the Molasse Sea. In the Klettgau, the Kirchberg layers are directly overlaid by erosive deposits of the OMM. This indicates that when the Kirchberg strata were deposited, the actual valley of the “Graupensandflusses” in this area was already flooded by the sea. In connection with this stratigraphic constellation, one speaks of the "extended barley sand channel". The contact of the Kirchberg strata to the overlying OSM is fuzzy and can often only be determined by exposing marine fossils.

In the Ulm area, an up to 13.5 m thick, fine-sand-silty transition horizon, the so-called "Suevicus layers" (named after a sometimes massive occurrence of the brackish water snail Viviparus suevicus ) is stored between the two units .

All three units, Grimmelfinger layers, Suevicus layers and Kirchberg layers, are also referred to as the "Upper Brackish Water Molasse" (OBM). In southern Germany they are stratigraphically between the OMM and the OSM, but are probably lateral equivalents of the OMM.

Biostratigraphy

Fossils, especially mammalian fossils, are rarely found in the channel filling, but often enough to be able to make a detailed and well-secured temporal classification based on the biostratigraphy of neogene land mammals . According to the results of corresponding investigations, the upper brackish water molasses is placed in the mammalian biozone MN 4, which corresponds to an absolute age of 18-17 million years and thus Ottnangium (upper lower Miocene).

Interpretation of the gutter filling

The designation of the channel filling as "Upper Brackish Water Molasse" already includes the interpretation of the corresponding sediments as brackish formations. Almost all relevant authors see in the contained marine and brackish faunas the influence of a molasse residual sea that was presumably still present in Switzerland at that time. Whether the character of the Grimmelfinger strata was estuarine with tidal influences or purely fluvial is, however, a matter of dispute.

Controversy about the age of barley sand gutter filling

On a biostratigraphic basis, the filling of the barley sand channel is dated to 18-17 million years (see above ).

With discoveries of “shocked quartz” in the Grimmelfinger layers, Buchner et al. (1996) noted a lively controversy among geologists engaged in the study of the barley sand channel. The finds did not question the models for the formation and development of the barley sand channel, but did question the chronological classification of their sediments. The shocked crystals were described by Buchner et al. regarded as the ejection material of the Ries event (14.5 million years ago, Badenian , Middle Miocene) and the basal channel filling as the same old and thus at least 2.5 million years younger than previously thought. The ensuing debate led to a number of new studies and fieldwork, including petrographic analyzes using the most modern methods. The demand for a precise determination of time of the alleged stoßwellenmetamorphen quartz pebbles by highly accurate 40Ar / 39Ar - isotope dating came Buchner et al. (2003), with the result that their hypothesis on the age of the Grimmelfinger layers was confirmed. As early as 1998, Buchner et al. claims that the Grimmelfinger strata are younger than the Kirchberg strata. This is vehemently rejected by other processors based on their own findings in the field.

The biostratigraphs maintained that the formation and main pouring time of the barley sand channel should be set at 18-17 million years.

The controversy continues and has been summarized as follows: "Both views are very well established".

Individual evidence

  1. ↑ The former presence of the Molasse Sea expresses itself today u. a. through a partially preserved and exposed cliff line up to 50 m high on the southern flank of the Swabian Alb.
  2. ^ Sach & Heizmann (2001)
  3. ↑ Sach & Heizmann (2001), p. 5
  4. ↑ Reichenbacher et al. (1998) p. 133
  5. ^ Sach & Heizmann (2001)
  6. ↑ Buchner (1998), p. 405
  7. ^ Sach & Heizmann (2001)
  8. ↑ Reichenbacher et al. (1998), p. 127
  9. ↑ estuarine a. a. according to Luterbacher (2000) and this also in the Ulm area, Reichenbacher et al. (1998) p. 132. Contrary to Zöbelein (1995): According to him, the marine finds from the OMM have been relocated and the channel led into a Urrhône , pp. 85, 90f
  10. ↑ cf. Reichenbacher et al. (1998), Buchner (2001), Sach & Heizmann (2001), Then et al. (2002), Baier et al. (2002), Buchner et al. (2003), Baier (2005), Megerle (2008)
  11. ↑ Sach & Heizmann (2001), Baier et al. (2002), Baier & Hofmann (2003)
  12. ↑ "The faunas from the brackish water molasses of the Ulm area clearly belong to the mammalian zone MN 4. [...] The stratigraphic situation shown cannot be reconciled with the argumentation of Buchner, Seyfried & Hirsche (1996)", Reichenbacher et al. (1998), p. 127.
  13. ↑ Schweigert in Buchner (2001), p. 305.

literature

  • Baier, J. (2005): On the “biogenic base location” of the Hochsträß (Middle Swabian Alb, SW Germany): Discussion of inorganic-geochemical investigations. Annual reports and communications from the Upper Rhine Geological Association, Neue Reihe, 87, Stuttgart 2005, pp. 361–370.
  • Baier, J. & Hofmann, F. (2003): Goethite pseudomorphoses from the Kirchberg strata of the Hochstrasse (Middle Alb, SW Germany). Annual reports and communications from the Upper Rhine Geological Association, Neue Reihe, 85, Stuttgart 2002, pp. 485–492.
  • Baier, J., Then, R. & Hofmann, F. (2002): Chemical-petrographic investigations of a "carbonaceous" intermediate layer in the Kirchberg strata of the Hochstrasse (Swabian Alb, SW Germany). New Yearbook for Geology and Palaeontology Abhandlungen, 226 (1), Stuttgart 2002, pp. 131–143
  • Buchner, E., Seyfried, H. & Hische, R. (1996): The barley sands of the southern German brackish water molasses: an incised valley fill as a result of the Ries impact. Journal of the German Geological Society, 147, Stuttgart 1996, pp. 169–181
  • Buchner, E., Schweigert, G., Seyfried, H. (1998): Revision of the stratigraphy of the southern German brackish water molasses. Journal of the German Geological Society, 149, H 2, Stuttgart 1998, pp. 305-320
  • Buchner, E. (1998): The South German brackish water molasse in the Graupensandrinne and its relationship to the Ries impact. Annual reports and communications from the Upper Rhine Geological Association, Neue Reihe, 80, Stuttgart 1998, pp. 399–459
  • Buchner, E .; Seyfried, H; Bogaard, PVD (2003): 40Ar / 39Ar laser probe age determination confirms the Ries impact crater as the source of the glass particles in Graupensand sediments (Grimmelfingen Formation, North Alpine Foreland Basin). International Journal of Earth Sciences (Geologische Rundschau), 92, Heidelberg 2003, pp. 1–6
  • Eberle, J., Eitel, B., Blümel, WD, Wittmann, P. (2007): Germany's South from the Middle Ages to the Present, Heidelberg 2007
  • Geyer, OF & Gwinner, MP (1986): Geology of Baden-Württemberg, Stuttgart 1986, 3rd edition
  • Geyer, OF, Gwinner, MP, Geyer, M., Nitsch, E., Simon, Th. (Ed., 2011), Geologie von Baden-Württemberg, 5th completely revised edition, Stuttgart 2011
  • Geological overview map, 1: 50000, sheet Hegau and western Lake Constance, Geological State Office Baden-Württemberg, Freiburg 1992
  • Haus, HA (1951): On the paleogeographical development of the molasse trough in the Lake Constance area during the Middle Miocene. Middle leaf bath. geol. Landesanst, Freiburg 1950, pp. 48-66
  • Kiderlen, H. (1931): Contributions to the stratigraphy and paleogeography of the southern German tertiary. N. Jb. Min. Geol. Pal., B66, Stuttgart 1931, pp. 215-384
  • Megerle, A., Vogt, J. (2008): Sand, gravel and lime, re-experienced mining sites. In: Rosendahl, W., et al., (Ed.): Migrations in der Erdgeschichte (18), Schwäbische Alb, Munich 2008, p. 24ff
  • Moos, A. (1925): Contributions to the geology of the tertiary in the area between Ulm a. d. D. and Donauwörth. Geogr. Jahrhundert, 37, Munich 1924, pp. 167–252
  • Reichenbacher, B. et al. (16 co-authors, 1998): Graupensandrinne Ries impact: on the stratigraphy of the Grimmelfinger layers, Kirchberg layers and upper freshwater molasses (northern foreland molasses, southern Germany). Journal of the German Geological Society, 149, Stuttgart 1998, pp. 127–161
  • Reichenbacher, B., et al. (1998): Storage conditions of Grimmelfinger layers and Kirchberg layers: Commentary on the “revision of the stratigraphy of the southern German brackish water molasses”. Journal of the German Geological Society, 149, Stuttgart 1998, pp. 321–326
  • Sach, VJ & Heizmann, EPJ (2001): Stratigraphy and mammalian faunas of the brackish water molasses in the vicinity of Ulm (southern Germany), Stuttgart contributions to natural history, Series B, SMNS, Stuttgart 2001
  • Schreiner, A. (1992): Explanations of the geological overview map, 1: 50000, sheet Hegau and western Lake Constance, Geological State Office Baden-Württemberg, Freiburg 1992
  • Then, R., Baier, J. & Welsch, T. (2002): Analytical studies on the origin of the “biogenic base layer” at the base of the barley sand channel of the Hochstäß (Middle Alb, SW Germany). Annual reports and communications from the Upper Rhine Geological Association, Neue Reihe, 84, Stuttgart 2002, pp. 355–377
  • Zöbelein, HK (1995): The young tertiary barley sand channel in the foreland molasse of southwest Germany. Documenta naturae, 91, Munich 1995

Web links

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Coordinates: 48 ° 22 '  N , 9 ° 59'  E