Orbitoline layers
The orbital layers are marl-like sedimentary rocks in the Swiss Alps. They were first described on Lopperberg (Hellegg quarry 667.850 / 203.050) by Franz Joseph Kaufmann as the layers " between two Rudist limestone walls " (lower and upper Schrattenkalk ). The orbitoline layers were created in the time of the Aptium , which belongs to the Lower Cretaceous and belong to the Helvetic layer sequence . Today they are assigned as part of the Rawil members .
These are well-layered, brownish to blackish-gray limestone banks, alternating with marl layers and bulbous layers . A rhythmic sedimentation with several small regressions and transgressions is assumed to be the cause of this alternation . During the regression, the proportion of detritic sedimentation increased. So sometimes sandstone banks are embedded. The bulbous layers can be interpreted as deposits near the coast with greater flow energy of the water.
The orbitoline layers are very rich in fossils, including sea urchins , brachiopods , clams ( rudists ), oysters and, more rarely, corals . It is named after the numerous orbitolines ( foraminifera ). On the south side of Pilatus (locality: Chilchsteinen 1865 m. Above sea level) a fossil root soil, probably from a mangrove-like vegetation, could be proven. This is confirmed not only by the high proportion of detritus but also by the deposits near the bank.
Individual evidence
- ↑ Franz Joseph Kaufmann: Geological Description of Pilatus. Contributions to the geological map of Switzerland , 5 [text volume], Bern 1867, p. 78.
- ^ Lithostratigraphic Lexicon of Switzerland. Entry Rawil-Member (www.stratigraphie.ch)
- ↑ Viktor Steinhauser: Geology of the Eastern Pilatus Group . Diploma thesis ETHZ, 1981.