Lithostratigraphy

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Column profile of the sedimentary sequence of Monte San Giorgio with u. a. the naming of the lithostratigraphic units (Italian)
Sequence of layers of terrestrial silicicoplastics on the west side of Capitol Reef (Colorado Plateau, USA). The various lithologies comment here on the one hand in color and the other in weathering behavior or the erosion resistance that comes in the slope expressed. In the foreground and on the lower slope in orange-brown tones the Moenkopi Formation (lower Triassic ) The extremely steep upper slope is built up by the Wingate Formation ( Lower Jurassic ). Between the Moenkopi and Wingate Formations lies the “colorful” sequence of the Chinle Formation (higher Triassic).

The Lithostratigraphy is the spatial and structural breakdown of rock units exclusively according to their lithological properties. It is one of the basic methods of stratigraphy , which was principally developed and used in the early days of geosciences. The lithostratigraphy and the definition of the lithostratigraphic units and their lower and upper limits are in principle independent of the chronostratigraphic units and the geological age of the corresponding rocks.

Lithostratigraphic units and their definition

A lithostratigraphic unit is defined exclusively by lithological features, which can be sedimentological , petrological , mineralogical , chemical, paleontological , physical and morphological characteristics. The fossils occurring in a lithostratigraphic unit are assessed as a lithological feature from the perspective of lithostratigraphy. The relative or absolute geological age is not part of the definition of a lithostratigraphic unit.

Each lithostratigraphic unit is also relatively defined by its lower limit ( lying limit) and also by its geographical distribution. The upper limit ( hanging limit) is defined by the horizontal limit of the subsequent (overlying) unit. The relative position of a lithostratigraphic unit within its parent unit is described by a top-to-bottom and a spatial relationship; That is, it is described by the location between the unit of equal rank below and above it, as well as the geographical distribution within the distribution area of ​​the higher-level unit. The extent and structure of lithostratigraphic units can vary between hundreds of meters thick and homogeneous rock sequences formed over millions of years and layers in the centimeter range that are only a few meters wide and vary greatly in their lithological properties.

Units of lithostratigraphy

The bank or the location ( Latin stratum ) is the smallest lithostratigraphic unit that can be clearly distinguished lithologically in a sequence of rocks. The older term layer should no longer be used as it is ambiguous. Several layers or banks form a subformation or formation, whereby a formation does not necessarily have to be divided into subformations. Several formations are combined into a subgroup or group, whereby the subgroup rank does not have to be used here either. Several groups form a super group. The South German Jura is viewed as a supergroup in the lithostratigraphic classification. Black Jura , Brown Jura, and White Jura are considered groups. These units each contain more than ten formations (e.g. the Brown Jura Opalinus Clay Formation , Wedelsandstone Formation or Ostreenkalk Formation, etc.). The lithostratigraphic hierarchy levels at a glance:

An informal term outside of this hierarchy is complex. It is a rock unit that can be separated from the neighboring lithostratigraphic units, but whose complicated internal structure cannot be further subdivided lithostratigraphically. The term complex should only be used for larger units and higher hierarchical levels (from formation).

Historical names

The term series was often used in the older literature in the sense of formation (or subformation, group, complex). Today it is reserved for a chronostratigraphic unit and should therefore no longer be used for lithostratigraphic units.

The term layer (s) is very ambiguous and should no longer be used to name lithostratigraphic units.

Furthermore, lithostratigraphic units may no longer be provided with the addition level (as in Lias level ) or the Latinized ending -ium (as in Erdbachium ), as this could lead to confusion with the chronostratigraphic unit level or it gave the impression that it if it were a chronostratigraphic unit.

The requirement to not use the historical names mentioned above applies primarily to the renaming of lithostratigraphic units. Traditionally used names that do not correspond to today's nomenclature requirements should only be replaced by names that meet these requirements after a revision of the lithostratigraphy of their area of ​​distribution. That is why traditional names can still be found in current geological literature.

In addition, mainly in literature from the 19th century, the term mountains, taken from the miner's language , is found as part of the name of partly higher-ranking quasi-lithostratigraphic, partly regional geological units, for example in "Ruhrkohlengebirge" and "Saxon-Bohemian Chalk Mountains", their approximate equivalents according to modern Nomenclature are the Ruhr group or (only in the German part) the Elbtal group . In the Upper Permian of the Northern Limestone Alps , the Hasel Mountains are still preserved today as a lithostratigraphic unit, whereas Hasel Mountains outside the Alps are only a facies term.

Dating problem

In the early days of geology, lithostratigraphy was also used to date rock units. But that very quickly turned out to be unreliable. The lithostratigraphic rock units can usually not be correlated over long distances . In addition, lithologically quite similar lithostratigraphic units often occur in different regions and with different ages. Lithostratigraphic units may therefore only ever be viewed in the context of the other formations of a certain region in order to be able to make age statements to a limited extent. With this lithostratigraphic method a relative dating is then possible, i. This means that the formations of a certain area can be dated relative to one another (e.g. the x-formation is older than the y-formation, this interlocks with the z-formation and is therefore the same age as the y-formation). This topic is dealt with in detail in the article on stratigraphy , the general layerology.

Web links

Commons : Lithostratigraphy  - collection of images, videos and audio files

literature

  • Amos Salvador: International Stratigraphic Guide. A Guide to Stratigraphic Classification, Terminology and Procedures. 2nd Edition. The International Union of Geological Sciences et al., Boulder CO 1994, ISBN 0-8137-7401-2 , pp. 31-43.
  • Michael A. Murphy, Amos Salvador, International Subcommission on Stratigraphic Classification of IUGS, International Commission on Stratigraphy: International Stratigraphic Guide - An abridged version. Episodes. Vol. 22, No. 4, 1999, pp. 255–271 ( PDF 190 kB), pp. 259–261 (Chapter 5, HTML version on stratigraphy.org)
  • 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.

Individual evidence

  1. ↑ Ruhr coal mountains. Meyers Großes Konversations-Lexikon, Volume 17. Leipzig 1909, p. 245 f.
  2. ↑ Hans Bruno Geinitz: Characteristics of the layers and petrefacts of the Saxon chalk mountains. First issue: The tunnel near Oberau. Arnoldische Buchhandlung, Dresden 1839 ( MDZ-Reader )
  3. ↑ cf. German Stratigraphic Commission (Ed .; coordination and design: Manfred Menning, Andreas Hendrich): Stratigraphic Table of Germany 2016. Deutsches GeoForschungsZentrum, Potsdam 2016, ISBN 978-3-9816597-7-1 ( online )