In geology, a group is a lithostratigraphic unit consisting of a series of related formations that have been classified together to form a group. Formations are the fundamental unit of stratigraphy. Groups may sometimes be combined into supergroups .
5-553: The Marree Subgroup , previously described as Maree Formation and Marree Formation , is a geological subgroup in the Eromanga Basin of South Australia whose strata date back to the Aptian . The subgroup was first described as a formation by Forbes in 1966. Dinosaur remains are among the fossils that have been recovered from the formation. An opalised plesiosaur specimen of the genus Umoonasaurus has been nicknamed 'Eric' and
10-571: 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 , Dogger , and Malm ( Jurassic in age) groups. Because of
15-820: 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
20-460: 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)
25-724: Was described in 1998 by Schroeder. The decapod crab Dioratiopus salebrosus was described in 1980. Indeterminate theropod remains present in Western Australia. Dinosaurs Kakuru K. kujani Geographically present in Western Australia , Australia. "Hindlimb." Sauropterygians Umoonasaurus U. demoscyllus Bulldog Shale of northern South Australia. Known from an opalized skeleton nicknamed 'Eric'. Group (stratigraphy) Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
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