Formation (stratigraphy)

The term formation is used in geology for the site easily recognizable and well representable in a geological map lithostratigraphical rock unit that is used for a more detailed description and breakdown of the rock sequence in a region. The formation is the fundamental unit in the Lithostratigrafie, which can be further subdivided or grouped with other formations into larger units. Their definition is independent of the chronostratigraphy, biostratigraphy and geochronology of.

Requirements for formation

A formation should lithological differ significantly from adjacent space or time lithostratigrafischen units. Next a formation in a geological map must be represented in a scale of 1:10,000 as an independent body of rock or mapping unit.

Definition

A formation is defined by a type profile at a specific locality (type locality). The limits are set only by changes in lithology, not geochronological or chrono- or biostratigrafisch. To define a formation morphological, sedimentological, petrological, mineralogical, palaeontological and chemical or physical characteristics can be used. Fossils are first of all considered as lithological feature. The name of a formation is in two parts and is mostly of the name of the type locality or a historical concept with the addition of the term " formation " is formed (separated by dash) (eg Mergelstetten lineup after Mergelstetten or Opalinus Clay formation = old historical term; both examples from the South Jura).

The telling of a formation name must be unique, wherefore, a locality name (or historical name ) can be used only once. Formations are taken as all other lithostratigraphic units in gazetteers, which are guided by the geological surveys of the respective states.

In Austria, new lithostratigraphic units of the Geological Survey in Vienna and will be published in the database " Lithstrat " of the Austrian Academy of Sciences, received the Working Group " stratigraphy " of the Austrian Geological Society and the Geological Survey. In Germany, the Federal Institute for Geosciences and Natural Resources ( BGR) in Hannover maintains an online database of the lithostratigraphic units of Germany ( LithoLex ).

Structure

A formation may (but need not ) be divided into Subformationen, in turn, consists of individual banks ( or layers ) can be constructed. Several formations can be summarized into groups.

Historic designations

In the older literature, sometimes even in today's popular scientific literature, lithostratigraphically specific term " formation " is often blurred and / or used for completely different units in geology. Thus formation has often been synonymous with the chronostratigraphic terms system, series, or in some cases also stage used ( " Jura - formation ", " Lias Formation" or " Tithonian formation "). The term " formation" was also used to designate major lithostratigraphic units (eg " Subapenninen lineup "), which are now referred to in the hierarchy of lithostratigraphic units significantly higher echelons.

Conversely, earlier lithostratigraphic units, which are now referred to as formation or Subformation, often referred to as " series " or " layer". In particular, the term " series" should no longer be used for the purposes of the current importance of formation ( or Subformation ), because it is reserved for a chronostratigraphic unit.