Kellwasserkalk (Kellwassertal)
The Kellwasserkalk in the Kellwassertal is a geologically significant outcrop with rock units from the Upper Devonian . It contains the well-known Kellwasser horizons , which represent the two Kellwasser events , including one of the five major extinction events in the history of the earth.
location
The outcrop of the Kellwasserkalk in the Kellwassertal is about two kilometers north of Altenau at the Oker dam . The access can be reached via Landstrasse 498 from Altenau and the dam wall of the Oker dam. It is located on the southern slope of the Kellwassertal.
Rock description
The rock of the Kellwasserkalk shows a clear alternation between claystone and limestone . The limestone layers have a thickness between 5 and 15 cm and are solidly banked, while the clay layers are only a few centimeters thick and have a softer consistency. Numerous ostracodes were microscopically detected in the massive limestone layers .
Also striking are the two cellar water horizons, which are characterized by black slate that is very rich in biomass. They suggest anoxic conditions during deposition.
Geological importance
The basement limestone was first described by Friedrich Adolph Roemer in 1850 and received its current name after the series of rocks was found elsewhere. He is the type locality for this sequence and the namesake of the cellar water event. At the border between Frasnium and Famennium in the late Devonian, about 75% of the species on earth became extinct due to factors that are not yet fully understood. The only fact is that it was not a prominent event that led to the extinction of many species, but rather complex systems were responsible.
The exact boundary between the lower grades frasnium and famennium is defined by biostratigraphy with the help of conodonts . The rocks, which are around 372 million years old, were exposed by the uplift of the Harz Mountains.
literature
- Riquier, L. et al: The Late Frasnian Kellwasser horizons of the Harz Mountains (Germany): Two oxygen-deficient periods resulting from different mechanisms; Chemical Geology, Volume 233, Issues 1-2, Sep 30, 2006, Pages 137-155.
- Girard & Renaud: Quantitative conodont-based approaches for correlation of the Late Devonian Kellwasser anoxic events; Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 250, Issues 1-4, June 25, 2007, Pages 114-125.
Web links
- The great mass extinction. Information board of the Harz Geopark, Braunschweiger Land, Ostfalen. Retrieved August 22, 2017.
Coordinates: 51 ° 49 ′ 10 ″ N , 10 ° 26 ′ 55 ″ E