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 .
5-724: The Rolling Downs Group is a stratigraphic group present in the Eromanga and Surat Basins in eastern Australia , which was deposited between the mid Barremian to early Turonian of the Cretaceous period. It primarily consists of nearshore shallow marine sediments deposited in the Eromanga Sea , though the uppermost and terminal members, the Winton Formation and the Griman Creek Formation represents freshwater deposits. It
10-434: Is notable for its fossil content including many dinosaurs and mammals , as well as opal. A relict species of dicynodont was suggested to have been found in these rocks, but is more likely to be misidentified pieces of a Cenozoic marsupial from younger sediments. Group (stratigraphy) Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
15-571: 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
20-820: 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
25-460: 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)
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