Bench (stratigraphy)

from Wikipedia, the free encyclopedia

The bank or layer (abbreviated Bk. Or Lg., English bed , layer ; Latin stratum ) is the smallest unit of lithostratigraphy and comprises a structure , color or material that is particularly striking and spatially widespread ( laterally wide) layer. Thus, the meaning of the lithostratigraphic bank term is significantly more exclusive than the term with the same name, which is generally used in geology to describe stratification patterns and thus has petrological connotations .

Requirements for a bank as a lithostratigraphic unit

The thickness of a bank can range from a few centimeters to several meters, and U. also about it. Like other lithostratigraphic units, it should be defined by a type profile and a type region . The precipitation of a single layer as a lithostratigraphic unit should be limited to very distinctive banks with a high recognition value, which can be followed geographically over long distances both in daily outcrops and in boreholes. In classical geology, such benches were often called guide benches . They are distinguished by their special fossil or mineral content, special lithology , extraordinary thickness, or special sedimentary structures, among others.

definition

In the hierarchical level of the units of lithostratigraphy , the bank (or location) is the smallest or lowest unit. Earlier (and partly still) the older term “ layer ” was used as a synonym for a bank (in the sense of a lithostratigraphic unit). However, the term “layer” is so ambiguous in geological literature that it should no longer be used for a bank (in the sense of the smallest unit of lithostratigraphy). In sedimentology , however, this term is often (and correctly) used as a synonym for bank.

structure

The bank is not further subdivided in lithostratigraphy (in contrast to the bank in sedimentology ). Internal structures or intervals (e.g. in the case of turbidites ) are only regarded as particularly distinctive properties of a bank. Several layers or banks including rock units that are not further lithostratigraphically subdivided form a subformation or formation , whereby a formation does not have to be subdivided into subformations. Often the upper and / or lower limits of a formation are placed at the top or at the base of a bank in the sense of lithostratigraphy. Furthermore, such banks can also function as separating elements in the subdivision of a formation or subformation.

literature

  • Fritz F. Steininger , Werner E. Piller: Recommendations (guidelines) for handling the stratigraphic nomenclature. In: Courier Research Institute Senckenberg 209, 1999, ZDB -ID 530500-7 , pp. 1-19.
  • North American Commission on Stratigraphic Nomenclature (NACSN): North American stratigraphic code. In: American Association of Petroleum Geologists Bulletin. Vol. 89, 2005, ISSN  0149-1423 , pp. 1547–1591, (PDF; 1.4 MB) .