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 .
6-733: The Eycott Volcanic Group is a group of volcanic rock formations of Ordovician age ( Llandeilo to Caradoc epochs ) named after the locality of Eycott Hill in the English Lake District . The group overlies the Skiddaw Group and is unconformably overlain by a variety of different Devonian and Carboniferous age rocks. This rock sequence has previously been known as the Eycott Group . It consists largely of andesitic lavas and sills with tuffs , breccias and volcaniclastic sandstones . Its main outcrop
12-692: 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
18-471: Is in an east-west oriented band of country in the northern part of the Skiddaw range in the northern Lake District stretching from the village of Bothel east to form the hill of Binsey and further east, the more extensive Caldbeck Fells . A smaller outcrop underlies Greystoke Park just to the east of this area and forms Eycott Hill east of Mungrisdale . There is a further inlier at Melmerby Fell in
24-713: 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
30-545: The North Pennines . The outcrops are intensely faulted and in the Caldbeck area are crossed by numerous mineral veins yielding arsenic , barium , copper and lead which have been worked in the past. Group (stratigraphy) 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
36-459: 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
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