Schriesheim formation
The Schriesheim Formation is a lithostratigraphic rock unit in the history of the earth in the Rotliegend ( Unterperm ) of the southern Odenwald ( Baden-Württemberg ). It is a small, almost 100 km² large volcanic area and its deposits, including chimney fillings, which are now largely eroded or covered by younger deposits. The formation shapes the geomorphology in the distribution area to a large extent.
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Naming and type locality
The name was proposed by Edgar Nitsch and Hubert Zedler in 2009. Older informal names in geological maps and publications are: Middle Rotliegend and porphyries of Middle Rotliegend or Rotliegend volcanic rocks. The type locality is on the Ölberg near Schriesheim ( Rhein-Neckar-Kreis ) (TK 25-Nr.6518: R 34 76 500, H 54 81 700).
Definition, Correlation and Age
The lower limit of the Schriesheim Formation is formed by the first volcanic rocks above crystalline basement rock. The upper limit is the Rotliegend (without volcanic rocks) or the Zechstein , i.e. H. the Michelbach Formation or the Zechsteindolomit Formation . The rock unit consists of ash - tuffs , lapilli tuffs- , Lapillisteinen , ignimbrites and lavas rhyolitic composition and vent fillings. The result is hydrothermally changed to varying degrees. At the base, directly above the basement, there are often pebble crusts, the so-called base paleosolite, or thin arkose and breccia layers. The thickness of the formation is up to about 120 m. According to Ar-Ar dating, it is most likely 290 million years old. This age corresponds to the chronostratigraphic Asselium level of the Unterperm (Cisuralium).
Storage room
The Schriesheim Formation consists mainly of pyroclastic flow and pyroclastic fall deposits , a consequence of Plinian eruptions , and in the southern Odenwald it leads to the Rotliegend above the basement. The basement was loosened and weathered on the surface. The basic paleosolite is mostly formed as a pebble crust (Durisol or Silcrete ) in loosened saprolite or regolith in hardly transported litter. This indicates an arid climate. The pyroclastic flow deposits have mostly been deposited as welded or unwelded ignimbrites. There are no known fossils.
Breakdown
The Schriesheim Formation is currently divided into three sub-formations according to the rock stock:
- Schriesheim formation
- Altenbach subformation (rTA), unwelded to slightly welded ignimbrites
- Dossenheim quartz porphyry (subformation) (DQ), strongly welded ignimbrite
- Wachenberg quartz porphyry (subformation) (WQ), stick-shaped lavas as chimney filling
Economical meaning
The ignimbrites of the Dossenheim quartz porphyry were already mined in the 18th century and then until 2002 in several quarries near Dossenheim . Up to 400 people found work in the quarries. These were also extracted in a quarry near Schriesheim . Today, 9 geopoint display boards in the Leferenz quarry (Dossenheim) remind of this time. The solidified lava of a chimney was mined on the Wachenberg near Weinheim. During the eruption, chunks of granite from the surrounding granite also fell into the melt and are now preserved as xenolites in the quartz porphyry .
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.