HOME
TheInfoList



A group is a lithostratigraphic
unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * Unit (album), ' ...
, a part of the geologic record preserved in
rock strata (Argentina Argentina (), officially the Argentine Republic ( es, link=no, Rep├║blica Argentina), is a country located mostly in the southern half of South America. Sharing the bulk of the Southern Cone with Chile to the west, the country is ...
. Groups are generally divided into individual formations. Groups may sometimes be combined into supergroups. Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying the stratigraphy of large regions. Geologists exploring a new area have sometimes defined groups when they believe the strata within the groups can be divided into formations during subsequent investigations of the area. It is possible for only some of the strata making up a group to be divided into formations. An example of a group is the Glen Canyon Group, which includes (in ascending order) the Wingate Sandstone, the Moenave Formation, the Kayenta Formation, and the Navajo Sandstone. Each of the formations can be distinguished from its neighbor by its lithology, but all were deposited in the same vast erg. Not all these formations are present in all areas where the Glen Canyon Group is present. Another example of a group is the Vadito Group of northern New Mexico. Although many of its strata have been divided into formations, such as the Glenwoody Formation, other strata (particularly in the lower part of the group) remain undivided into formations. Some well known groups of northwestern Europe have in the past also been used as units for chronostratigraphy and geochronology. These are the Rotliegend and Zechstein (both of Permian age); Buntsandstein, Muschelkalk, and Keuper (Triassic in age); Lias Group, Lias, Middle Jurassic, Dogger, and Malm (geology), Malm (Jurassic in age) groups. Because of the confusion this causes, the official geologic timescale of the International Commission on Stratigraphy, ICS does not contain any of these names. As with other lithostratigraphic ranks, a group cannot be defined by fossil taxonomy.


See also

* Stratigraphic unit


Footnotes


References

* * * * * * Stratigraphy Geological units {{geology-stub