in chronostratigraphy and
A system referred to in the geological a unit of Chronostratigraphy . In geochronology it corresponds to the unit period . A system or a period usually comprises time intervals of tens of millions of years.
In the hierarchy of ranks of the chronostratigraphic units, a system is the middle of a total of five units. In geochronology , this period corresponds to the unit period. The terms system and period are often - but not entirely correctly - used as synonyms in the literature . The boundaries of the chronostratigraphic unit system are limited by isochronous (simultaneous) stratigraphic areas that are defined by biostratigraphic markers or other events. The systems are relatively defined by the interfaces between two successive systems as well as by their sequence in time, i.e. the absolute age of the interfaces and the absolute amount of time of a system are not included in this definition, since the absolute ages of the interfaces are changed by others or newer age determination methods may still change. The definition of these limits takes place in real life at a specific location at a very specific point in the profile ( GSSP ). From the Ediacarium boundary back into geological history, the system boundaries are also defined absolutely geochronologically. From this limit onwards, the older systems below are identical with the respective equivalent geochronological units (periods). However, there are efforts to define these limits chronostratigraphically and to establish a GSSP. The absolute duration of a system or a period is mostly historical and varies considerably, from a few million years to several hundred million years in the Proterozoic .
In the hierarchy of chronostratigraphic units, a system is a subordinate unit of an arithmetic , that is, several systems are combined in an arationem. In geochronology , the corresponding periods are grouped into an era. A system can itself be divided into several subordinate series , a period into several epochs.
The names of the systems of chronostratigraphy or their equivalents in geochronology that are internationally valid today were all named in the 19th century. The naming was based on historical landscapes ( e.g. Cambrian ), ancient tribes ( e.g. Silurian ), peculiarities of rock formation (e.g. chalk ), mineral resources ( carbon ), development of the system in Central Europe ( e.g. Triassic = trinity) etc. However, for a long time there was often no consensus on the naming of individual systems ( e.g. Dyas vs. Perm ). Individual older systems were divided into two systems (for example the old Silurian into today's Silurian and Ordovician ), and the Tertiary even only recently into the Paleogene and Neogene systems .
- Felix Gradstein, Jim Ogg, Jim & Alan Smith: A Geologic timescale . Cambridge University Press 2005, ISBN 978-0-521-78673-7 .
- North American Commission on Stratigraphic Nomenclature (NACSN): North American stratigraphic code. American Association of Petroleum Geologists Bulletin, 89: 1547-1591, Tulsa, Oklahoma 1983 PDF; 1.04 MB
- FF Steininger & WE Piller: Recommendations (guidelines) for handling the stratigraphic nomenclature. Courier Forschungsinstitut Senckenberg, 209: 1–19, Frankfurt am Main 1999 .