River history of the bear

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The river history of Bara Like the other recent Albflüsse a geologically very long, eventful development behind it. Only a few, very old, formerly very large bodies of water in the Swabian Alb still transport their water and sediment loads above ground to their confluence with the Danube.

The Bära is the main body of water in the sub-natural area Hohe Schwabenalb of the Swabian Alb. It's a very old river. Its forerunner, the Ur-Baer, ​​is probably older than the Ur-Danube . River pebbles from the prehistoric era were found on extensive areas of the upper soils near Buchheim in the Tuttlingen district and Altheim in the Sigmaringen district, i.e. south of today's Danube. The varied development of the Bära can be described with the help of numerous findings on the Bära, other important rivers and geological phenomena in the same region, the “Western Swabian Alb” and the Northern Alb foreland for several geological epochs.

The primal bear in the Miocene

Ur-Danube and development since the Miocene
Miocene Juranagelfluh, poorly sorted, well rounded, here in the Tengener Rinne

A considerable amount of river gravel from the so-called “Younger Juranagelfluh ” lies in several scree fields on an area of ​​around 6.5 km in length, near Buchheim and Altheim in the Tuttlingen district, around three kilometers south of today's Danube. These rubble finds, recorded in current geological maps with the designation "tJN2", are veritable evidence of a primeval bear that flowed into the barley sand channel . This large channel was the main drainage channel in southwest Germany in the Middle Miocene

Further evidence for the primal bears of this Miocene period is not known. However, comparisons can be drawn from numerous geological publications on the original Danube . Numerous gravel pebbles from different stages of development of the Danube were found and petrographically analyzed for age, size, composition, area of ​​origin, find height and place of discovery, so that reliable information is now made about the courses of different earlier phases of the original Danube and the Danube from Switzerland to today's Ulm could become:

The prehistoric era was an interwoven river that spread out high above today's land surface on a bas-relief . Its upper course will have extended further north than it does today. The Juranagelfluh pebbles found at the mouth of the Ur-Bära contain only white Jurassic rocks, but no deeper rock formations of the former south-west German layered plain . The upper course did not extend far beyond today's Albtrauf .

Tectonics in the Miocene / Pliocene

The all-changing events for all of southwest Germany on the Miocene / Pliocene border were the further lowering of the Upper Rhine Rift - and congruent - the uplift and tilting of the limestone table of the Alb. The Alb was inclined from north to south and tilted to the east. The tectonic events made the river system of the Rhine and Neckar (called the "Tübinger Urlone" in the early days) aggressively penetrating. The areally acting removal rate and the erosion were enormous, the escarpment at the end of the Swabian Alb, as Albtrauf better known, have been steadily moved southeast. The catchment area of ​​the primeval bears in the north was thereby reduced. The uplift slightly increased the gradient of all channels facing the Danube and gradually led to increased relief formation due to the disruption and karstification of the Alb table. Finally, in the Pliocene, the Upper Bära were tapped by the rapidly advancing Rhenish sneak in the Tieringer Sattel (780 m). The Lower Bära was beheaded near Gosheim (835 m), as was its branch, the " Deilinger Mühlbach" on the Deilinger Strunkpass (835 m).

Karst events from the Middle Pliocene

With the deepening of the Danube and therefore also the Baer from the Middle Pliocene, the karstification of the Swabian Alb was able to penetrate deeper rock layers. Solution processes widened gaps and even created larger karst waterways. The water supply, fed by numerous streams in the side valleys, made the Bäratal deeper and wider. The karst water level followed the deeper cutting valleys of the Danube and the Bära. From the Middle Pleistocene , less and less water flowed off above ground. The aboveground Bära waters in their large valleys became smaller, most of the side valleys became dry valleys in which wash-off masses and debris accumulated.

Development in the Quaternary until today

Deep valley of Bara in the high plateau of the High Schwabenalb deepened
There are natural valley, visible, hard mass limestone cliffs at various points in the Bäratal

The valleys of the Bära are completely natural, the slopes are overgrown by dense bushes or forest - a jewel of calm and aesthetics. Valley floors, slopes and parts of the high plateau are extensively protected as a landscape protection area and also protected by the EU Habitat Directive (" FFH "). The valley floors at the confluence of the Unterer and Oberer Bära rivers are specially protected as a nature reserve (" Galgenwiesen "), especially since the two Bära brooks branch off here into several natural rivers and backwaters. The valleys of the Upper and Lower Bära are wide today (approx. 100–300 m), but only slightly deepened. the river Bära is today a pathetic brook along its entire length (except during high water) (see the photo of the Upper Bära near Oberdigisheim).

Nature Conservation Act Galgenwiesen at the confluence of the Upper and Lower Danube
Upper bear, wide valley, slender brook

From the confluence of the upper courses, the valley floor finally reaches a mighty depth of 180-200 m compared to the high plateau. To reach the confluence with the Danube, the gradient of the Bära had to increase considerably over the last five kilometers of the lower reaches; the valley becomes even deeper, but also narrower. This great breadth and depth cannot be explained with the current state of the small channel.

In the warm and humid times of the Holocene ( Atlantic , approx. 8000–4000) the amount of water must have been considerably larger than today - there will therefore have been numerous karst springs that poured heavily. Seven “ sinter ” sediment deposits of lime chemically precipitated from karst spring water, which have been preserved on the slopes of the valley, are evidence of this . In two quarries, large remains of these remarkable tufa limestone bars are still clearly visible (see also the photographs in Bärenthal ).

Large tufa-lime bar in the abandoned Ensisheim quarry (municipality of Bärenthal )

literature

  • LGRB Geological Map GK50 sheet 7919 and sheet 8020, State Office for Geology, Raw Materials and Mining, Freiburg i. Br.
  • Dongus, Hansjörg. The surface forms of the Swabian Alb and its foreland, Marburg / Lahn 1977
  • Geyer, OF, Gwinner, MS, Geology of Baden-Württemberg, 3rd edition, Stuttgart, 1986
  • Dongus, Hansörg. The surface forms of southwest Germany, Berlin, Stuttgart 2000
  • Tillmanns, W., History of the River Upper Danube, Jh geol. State Office, Baden-Württemberg, 26, 1984, Freiburg
  • Eberle, J .; Eitel, B .; Blümel, WD; Wittmann, S. Germany's South from the Middle Ages to the Present, Heidelberg, 2007
  • Schreiner, Alfred, The Juranagelfluh im Hegau, annual journal of the Geological State Office, 7, 1965, Freiburg
  • Ford, D., Williams, P., Karst Hydrogeology and Geomorphology, Revised edition, Chichester, 2007 in English
  • Villinger, E., The Swabian Alb - a geological picture book landscape, in: Rosendahl W., et al.
  • Rosendahl, W., Junker, B., Megerle, A. Vogt, J., (Eds), Walks in die Erdgeschichte, 18, Swabian Alb, 2nd edition, Munich 2008

Individual evidence

  1. ↑ Rubble, probably the alluvial fan of the primeval bears. Surface forms of southwest Germany ... p. 149. See literature
  2. ↑ Schreiner, Juranagelfluh im Hegau… p. 335. See literature
  3. ↑ Villinger, Schwäbische Alb… p. 15. See literature
  4. ↑ Tillmanns, river history of the upper Danube ... See literature
  5. ^ Surface forms of Southwest Germany ... p. 29 and p. 138. See literature
  6. ↑ Proof of this is the cliff line of the Miocene Molasse Sea , which today falls from 900 to 500 m. Germany's south ... p. 48 and 60. See literature
  7. ↑ Since "Rhenish" channels typically have steeper slopes, they penetrate quickly through "receding erosion "
  8. ↑ Germany's south ... p. 76. See literature
  9. ↑ The broad valley floor of the Bära valley, which is "beheaded" here, "strikes out in the air". Geology of Baden-Württemberg… p. 317. See literature
  10. ↑ Germany's south ... p. 74. See literature
  11. ↑ Germany's south ... p. 74. See literature
  12. ↑ The sediments are shown on the current geological maps of the LGRB
  13. ↑ In the amount of the community Bärenthal z. B. around 190 m deep and around 110 m wide
  14. ^ Surface forms of Southwest Germany ... p. 152. See literature
  15. ↑ Geology of Baden-Württemberg ... p. 317. See literature

Web links

Commons : Bära  - collection of images, videos and audio files