Lower red sandstone

The lower limit of the Lower Buntsandstein (and thus the limit of the Buntsandstein and the Germanic Triassic supergroup) is determined in the basin center with the onset of the Calvörde formation . In the Spessart and Odenwald the border is drawn with the lower limit of the Heigenbrücken sandstone . In the Black Forest, the lower limit is placed at the base of the so-called (lower) Eck conglomerate . In the center of the basin, mostly fine-sand, silty to clayey sediments were deposited. These are rhythmic deposits that are coarser at the base and finer towards the top (“fining upward” cycles). Around 20 such cycles have been distinguished so far. They can be followed over a wide area in the pelvic center. Layers with large ooids (so-called " roe stones ") and stromatolites are particularly characteristic . The thickness in the center of the pelvis is between 135 m and 190 m, it continuously decreases towards the respective edges of the pelvis. Mostly coarse-grained sandstones with rubble were deposited there.

The lower limit of the Lower Buntsandstein (and thus of the Buntsandstein and the Germanic Trias in general) is biostratigraphically dated to the highest Changhsingian , the upper chronostratigraphic level of the Upper Permian (or Lopingian). According to the latest work, the upper limit or the lower / middle red sandstone limit is placed in the Lower Olenekian . According to the stratigraphic table of Germany, this corresponds geochronologically to a period of 251 to 249 million years and a duration of 2 million years.

structure

The lower red sandstone is divided into two lithostratigraphic formations or two allostratigraphic sequences, which in this case are identical. That is why the terms formation or sequence are often used alternately in red sandstone. The two formations / sequences are from top to bottom:

Bernburg formation
Calvörde formation

Storage room

At the time the Lower Buntsandstein was deposited, Central Europe was located at around 25 ° north latitude and thus in the then dry belt of the earth. The lower red sandstone was deposited in a flat and wide basin that was flooded again and again and largely dried out again (frequent dry cracks ). In the center of the basin there are several oolite limestone banks up to a maximum of 7 m thick, the formation of which is only conceivable under constant water cover. The ooids formed underwater dunes with sloping layers and ripples , which indicate a high-energy milieu under shallow water cover. In a small area north of the Harz there are stromatolites at the top of the oolite banks. The terms ooid and stromatolite were coined by Ernst Kalkowsky in 1908 for these structures of the Lower Buntsandstein, they are used worldwide today. The storage area is to be imagined as a large inland lake with no outflow (technical term Playa or salt plains ), the water level of which fluctuated strongly depending on the season or cyclically. In the dry seasons or in times with lower inflows, the lake dried up except for the center of the lake or a few remaining lakes. The water in these residual lakes was oversalted. In this milieu the ooids and stromatolites formed. The deposit environment is thus comparable to that of the large salt lakes in North America or Australia.

Individual evidence

↑ According to the more recent dating from Menning et al. (2005) the Permian Triassic boundary shifts to about 252.5 million years; For the Lower Buntsandstein there is geochronologically a period of 252.6 to 250.6 million years. Menning et al. (2005) recommend the continued use of the numbers used in the Stratigraphic Table of Germany until the new dates can be confirmed.
↑ Paul 1999, p. 269

literature

Peter Brack, Hans Rieber, Alda Nicora and Roland Mundil: The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale. Episodes, 28 (4), pp. 233-244, Beijing 2005, ISSN 0705-3797 .
Felix Gradstein, Jim Ogg, Jim & Alan Smith: A Geologic timescale. Cambridge University Press 2004, ISBN 9780521786737
Manfred Menning, Reinhard Gast, Hans Hagdorn, Karl-Christian Käding, Theo Simon, Michael Szurlies and Edgar Nitsch: time scale for Permian and Triassic in the Stratigraphic Table of Germany 2002, cyclostratigraphic calibration of the higher Dyas and Germanic Trias and the age of the Roadium stages to Rhaetium 2005. Newsletters on Stratigraphy, 41 (1-3): 173-210, Stuttgart 2005, ISSN 0078-0421
Ernst Kalkowsky : Oolite and stromatolite in the north German red sandstone. Journal of the German Geological Society, 60, pp. 68–125, Berlin 1908, ISSN 0012-0189
Josef Paul: Oolites and stromatolites in the Lower Buntsandstein. In: Norbert Hauschke and Volker Wilde (eds.): Trias. A whole different world from Central Europe in the early Middle Ages. P. 263–270, Verlag Dr. Friedrich Pfeil, Munich 1999, ISBN 3-931516-55-5
Jochen Lepper, Dietrich Rambow and Heinz-Gerd Röhling: The red sandstone in the Stratigraphic Table of Germany 2002. Newsletters on Stratigraphy, 41 (1-3), pp. 129-142, Stuttgart 2005, ISSN 0078-0421

[1] According to the more recent dating from Menning et al. (2005) the Permian Triassic boundary shifts to about 252.5 million years; For the Lower Buntsandstein there is geochronologically a period of 252.6 to 250.6 million years. Menning et al. (2005) recommend the continued use of the numbers used in the Stratigraphic Table of Germany until the new dates can be confirmed.

[2] Paul 1999, p. 269