Namurian
The Namurium, also shortened to Namur, is in the Earth's history, a time interval of the Carboniferous ( Paleozoic ). It is the lower regional and national level of Silesium or the former Upper Carboniferous in Central and Western Europe. The boundaries of the European Upper Carboniferous or the Silesium do not agree with the boundaries of the global Pennsylvanian subsystem, which is the equivalent of the Upper Carboniferous in about. In absolute terms, expressed ( geochronological ) reaches the Namurium of about 326.5 million to 316.5 million years ago. It follows the Viseum stage and is peeled from the Westfalium stage.
History and naming
The stage is named after the Belgian city of Namur. J.-C. Purves retired in 1881 from a level that was between the layers of the coal seams and the Carboniferous. In 1883 he called this stage Namurium ( " Namurien "). The Namurium stage was ratified by the first Carboniferous Congress in Heerlen in 1927, the stratigraphic extent but was extended upwards and now encompassed all Upper Carboniferous strata that did not belong to the productive Upper Carboniferous. The Namurium was not adopted by the International Commission on Stratigraphy as a global level. However, it is still available as a regional and national level in Central and Western Europe.
Definition and correlation
The lower limit of Namurium and also the Silesium defined by the Ersteinsetzen the ammonite species " Cravenoceras " Leion ( = Emstites Leion ). The ceiling was originally marked by the onset of the first coal seams. Meanwhile, the Namurium / Westfalium border with the Ersteinsetzen the ammonite species Gastrioceras subcrenatum ( Schlotheim ) is defined. In the global stage structure corresponding to the median Bashkirian. In absolute numbers that enough Namurium depending on your choice of stratigraphic table of 328.3 to about 315 million years, or 326.5 to 316.5 million years.
Subdivision
Traditionally Namurium is divided into three sub-stages, which are denoted by the capital letters A, B and C. However, it turned out that these three levels represent very different long periods of time, with Namurium A occupies the vast majority of the time, more than Namurium B and C together. In England, a different sub-stages structure established. Biostratigraphically the Namurium was also divided into E1, 2, H1, 2, R1, 2 and G1. This means E = Eumorphoceras, H = Homoceras, R = G = Reticuloceras and Gastrioceras; All four genera are ammonoids.
- Namurium C corresponds to the Yeadonium (or G1)
- Namurium B and R2 corresponds to the Kinderscoutium (or R1) and Marsdenium ( or R2)
- Namurium A, corresponds to the Pendleium (or E1), Arnsbergium (or E2), Chokierium (or H1) and Alportium (or H2)