A group in stratigraphy

Stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

 is a lithostratigraphic

Lithostratigraphy

Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology...

 unit, a part of the geologic record or rock column

Geologic record

The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata — deposits laid down in volcanism or by sediment deposition of weathering detritus including all its fossil content and the information it yields about the history...

 that consists of defined rock strata

Stratum

In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...

. Groups are divided into formations (and sometimes into "subgroups") and are sometimes themselves grouped into "supergroups".

Some wellknown groups of northwestern Europe have in the past also been used as units for chronostratigraphy

Chronostratigraphy

Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time.The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of...

 and geochronology

Geochronology

Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...

. These are the Rotliegend

Rotliegend

The Rotliegend or Rotliegendes is a lithostratigraphic unit of Cisuralian age that is found in the subsurface of large areas in western and central Europe. The Rotliegend mainly consists of sandstone layers...

, Zechstein

Zechstein

The Zechstein is a unit of sedimentary rock layers of Middle to Late Permian age located in the European Permian Basin which stretches from the east coast of England to northern Poland...

 (both of Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 age), Buntsandstein

Buntsandstein

The Buntsandstein or Bunter sandstone is a lithostratigraphic and allostratigraphic unit in the subsurface of large parts of west and central Europe...

, Muschelkalk

Muschelkalk

The Muschelkalk is a sequence of sedimentary rock strata in the geology of central and western Europe. It has a Middle Triassic age and forms the middle part of the Germanic Trias, that further consists of the Buntsandstein and Keuper...

, Keuper

Keuper

The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolostone, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs...

 (Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 in age), Lias

Lias Group

The Lias Group or Lias is a lithostratigraphic unit found in a large area of western Europe, including the British Isles, the North Sea, the low countries and the north of Germany...

, Dogger

Dogger

Dogger can mean:-*A sea area in the North Sea, noted in shipping forecasts, named after:**The Dogger Bank, a large shallow area in the North Sea between Britain and Denmark...

 and Malm

Malm

is a former municipality, a village, and the administrative centre of the municipality of Verran in Nord-Trøndelag county, Norway. Malm is located along the Trondheimsfjord, about a drive west from the town of Steinkjer. The village of Malm has a population of 1,572. The population density of...

 (Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 in age) groups. Because of the confusion this causes, the official geologic timescale of the ICS

International Commission on Stratigraphy

The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...

does not contain any of these names any longer.