Middle shell limestone
The Middle Muschelkalk is a lithostratigraphic subgroup of the Muschelkalk of the Germanic Triassic . The lithostratigraphic unit is underlain by the Lower Muschelkalk subgroup and overlaid by the subgroup of the Upper Muschelkalk . After the marine deposits of the Lower Muschelkalk, the connection to the open sea was interrupted during the Middle Muschelkalk and evaporation rocks ( evaporite ) were deposited . Limestone-rich sandstones were sedimented in the eastern edge areas.
definition
The lower limit of the Middle Muschelkalk forms the onset of the clay marl and clay stones of the Karlstadt Formation . Regionally, these are the so-called "orbicularis layers". The upper limit is defined by the base of the Upper Muschelkalk. The basis of the Middle Muschelkalk lies biostratigraphically in the lower anisium , the upper limit lies in the middle anisium. In geochronology, this correlates with the period from 240 to 238.5 million years.
structure
The Middle Muschelkalk is divided into five lithostratigraphic formations in Germany . However, the five formations are usually not on top of each other, but represent each other regionally:
- Karlstadt formation , it is developed all over the basin except for the edge areas.
- Heilbronn Formation , in the central parts of the basin rock salt was deposited in the more peripheral areas of anhydrite and gypsum .
- Diemel formation , dolomites and dolomitic limestone marls and marl stones, occasionally also ooid-bearing.
- Ralingen formation , sandstones , colorful, fine-sand clay marl stones as well as gypsum, anhydrite and dolomite rocks on the western edge of the basin
- Grafenwoehr formation , pebbly, feldspar-rich or carbonate quartz sandstones on the eastern edge of the basin. It extends into the upper Muschelkalk and Unterseuper.
Storage room
The rocks of the Middle Muschelkalk contain in the lower part an euryhaline fauna that is rich in individuals but poor in species . H. Species that were very tolerant of fluctuations in salinity. The Heilbronn Formation contains evaporites (rock salt and anhydrite / gypsum), which indicate a marine marginal basin with severely restricted water circulation. In the higher parts of the Middle Muschelkalk the fauna again indicates strongly fluctuating salinity.
geomorphology
Compared to the Lower and Upper Muschelkalk, the Middle Muschelkalk contains rocks that weather relatively easily, as well as salts that are leached relatively quickly on the surface and in the groundwater area. In the slopes of the slopes, Lower and Upper Muschelkalk form steep steps, while the Middle Muschelkalk, on the other hand, is a leveling surface with deep soils. Outcrops in the Middle Muschelkalk are therefore rare. In areas where the salts of the Middle Muschelkalk are depleted, the Upper Muschelkalk rocks have collapsed, very often on valley slopes where a river has cut into the Middle Muschelkalk (e.g. on the Upper Neckar between Rottweil and Oberndorf am Neckar or in the Wutach Gorge ). A typical residual rock of the middle shell limestone is the so-called cell endolomite or cell limestone .
Individual evidence
- ↑ According to the latest dating from Menning et al. (2005) this period has to be corrected to 244.6 to 243.4 million years and thus to a period of 1.2 million. However, the authors recommend using the numbers in the Stratigraphic Table of Germany until the new dates can be further confirmed.
- ↑ Hans Hagdorn, Theo Simon: Der Muschelkalk in the Stratigraphic Table of Germany 2002 . In: Newsletters on Stratigraphy . tape 41 . Borntraeger brothers, Berlin, Stuttgart 2005, p. 143-158 .
literature
- 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
- Hans Hagdorn and Theo Simon: The Muschelkalk in the Stratigraphic Table of Germany 2002. Newsletters on Stratigraphy, 41 (1-3): 129-142, Stuttgart 2005 ISSN 0078-0421
- Norbert Hauschke & Volker Wilde (eds.): Trias A whole different world from Central Europe in the early Middle Ages. 647 pp., Verlag Dr. Friedrich Pfeil, Munich 1999 ISBN 3-931516-55-5