Kraichgau basin

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The Kraichgau basin is an intramontane molasse basin , approx. 70 km by 150 km , which was created at the end of the Variski mountain formation in northern Baden-Württemberg . The maximum thickness of the permocarbonic sediments and volcanic rocks , as confirmed by drilling and seismic studies, is more than 1500 meters in some places. The sediments and volcanic rocks of the Kraichgau basin, the largest permocarbon basin in Baden-Württemberg, are now largely covered by younger deposits.

Location and limitation

The Kraichgau basin is located with its center in the eponymous Kraichgau , a landscape in northern Baden-Württemberg. However, in the course of its development in the Upper Carboniferous and then in the Permian it expanded far beyond this region and also extended to parts of the neighboring federal states of Rhineland-Palatinate, Hesse and in the east to western Bavaria and the northern Vosges (France).

In the north the Kraichgau Basin was separated from the Saar-Nahe Basin by the Odenwald-Spessart-Schwelle , which was a delivery area for sediments until the end of the Permian. The Kraichgau basin had a connection in the northeast in the Main-Tauber area to the Rotliegend of the Saale and Mühlhausen basins , and in the southwest to the Rotliegend of the Haardt and the northern Vosges . The Odenwald-Spessart-Schwelle no longer has a relief effect there and the Kraichgau Basin merges there with the permocarbonic sequences of the Saar-Nahe Basin. To the south it is separated from the Schramberg Basin and Offenburg Basin by the Northern Black Forest threshold . To the east it ends at the Ries-Tauber threshold . The sediments of the Kraichgau basin i. w. S. are only open on its southern edge in the Baden-Baden and Gaggenau area and on the northern edge in the southern Odenwald .

Origin and history of sedimentation

The Kraichgau Basin probably originated in the upper Pennsylvania (Upper Carboniferous) as a small, tectonically delimited single basin about 50 km long and less than 20 km wide between mountainous basement clods in today's Kraichgau. In the few outcrops of the Kraichgau Basin, however, there are no Upper Carboniferous sedimentary rocks, but older Upper Carboniferous deposits are suspected in the center of the basin. Coarse rubble was delivered into the basin from the high clods. The sediment sequence begins in the Odenwald with Rotliegend above a pedogenic weathering horizon of the crystalline basement. This former land surface with weathered crystalline is also known as the base paleosolite. In the actual Kraichgau basin, the Rotliegend begins with rhyolithic tuffs and ignimbrites. The ash and lapilli tuffs are unwelded and are excreted as a separate subformation (Altenbach subformation). Above this are the welded, over 100 m thick ignimbrites of the Dossenheim quartz porphyry. The Wachenberg near Weinheim is a mining slot for these volcanic rocks. It is lithostratigraphically referred to as the Wachenberg quartz porphyry. The Magmatites of the Rotliegend are overlaid by the Michelbach Formation, which also extends to the Baden-Baden Basin.

The Kraichgau basin expanded in the course of the Permian and at the end of its development was connected to the Saar-Nahe basin, the Saale basin and also through a narrow depression in the northern Black Forest threshold with the Schramberg basin. The Baden-Baden basin , initially isolated in the Upper Carboniferous and separated from the Kraichgau basin by the Battert sill, became the edge basin of the Kraichgau basin in the course of the Rotliegend. The independent development of the Kraichgau basin ends with the Zechstein , which covers southern Germany up to about Schramberg . it is largely included in the Franconian Valley . The lithostratigraphic sequence at a glance:

literature

  • Matthias Geyer, Edgar Nitsch and Theo Simon: Geology of Baden-Württemberg. 5th completely revised edition, 627 pages, Schweizerbart, Stuttgart 2011 ISBN 978-3-510-65267-9
  • Edgar Nitsch and Hubert Zedler: Upper Carboniferous and Permian in Baden-Württemberg. State Office for Geology, Raw Materials and Mining, Information, 22: 7-102, Freiburg 2009.