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 .
17-459: The Ribband Group is a geologic group in south-eastern Ireland . It is the most extensive stratigraphic unit in this part of Ireland. It underlies much of County Wexford . It overlies the Bray Group and Cahore Group. It is made up of medium to dark grey laminated greywacke siltstones and mudstones with occasional green beds . Turbidite structures are locally prominent and the unit
34-677: Is a classification by Brück & Molyneux (2011). The Ballymadder Shear Zone (just east of Hook Head on the coast of south County Wexford ), separates a to some extent different Cambrian succession immediately to the east to the one to its west. To its west the Clammers Point Unit (in the Bannow area) exposes a coastal section comprising Cahore Group and Ribband Group sediments. Group (stratigraphy) Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
51-697: Is basically a continuation of the same unit. In Germany the Buntsandstein is subdivided into three subgroups with seven formations (from top to base): Upper Buntsandstein Middle Buntsandstein Lower Buntsandstein All of these are reasonably good reservoir rocks for oil and gas. In the Dutch subdivision, the upper two formations are part of the Upper Germanic Trias and the others part of
68-784: Is conformably overlain by the Ribband Group; the Duncannon Group (a highly faulted, predominantly volcanic, platform sequence) which unconformably overlies the Ribband Group except in the west; the Kilcullen Group in the Comeragh Mountains , which is composed of sand-dominant turbidites (lower Ordovician to at least the Llandovery Epoch of the Silurian ) which are conformably underlain by
85-625: Is dominantly a distal turbidite succession. Intercalated volcanic rocks are locally abundant. The ages of the rocks of the group range from the Cambrian to the Ordovician, Middle Cambrian - Llanvirn (Middle Ordovician). The Ribband group is one of the four Early Palaeozoic stratigraphic groups in SE Ireland. The others are: the Bray group (made up of laterally-derived flysch ) which
102-708: Is normally lying on top of the Permian Zechstein and below the Muschelkalk. In the past the name Buntsandstein was in Europe also used in a chronostratigraphic sense, as a subdivision of the Triassic system. Among reasons to abandon this use was the discovery that its base lies actually in the latest Permian. The Buntsandstein was deposited in the Germanic Basin , a large sedimentary basin that
119-590: The Changhsingian to Anisian stages , meaning it is between 252 and 246 million years old. In German lithostratigraphy, it is seen as a group, in the Netherlands and North Sea the name has no official status (though that does not keep geologists from using it). In the official Dutch lithostratigraphy, the Buntsandstein is divided into the Lower and Upper Germanic Trias Groups . The British Bunter Formation
136-586: 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
153-866: 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
170-719: The subsurface of large parts of west and central Europe. The Buntsandstein predominantly consists of sandstone layers of the Lower Triassic series and is one of three characteristic Triassic units, together with the Muschelkalk and Keuper that form the Germanic Trias Supergroup . The Buntsandstein is similar in age, facies and lithology with the Bunter of the British Isles . It
187-603: The Lower Germanic Trias. Bunter sandstone often forms spectacular rock formations as a result of weathering: including isolated rocks several tens of metres high. Most of them are designated natural monuments , for example, the Devil's Table near Hinterweidenthal . In the Palatinate, near Eppenbrunn , are the so-called Altschlossfelsen ("Old Castle Rocks"). The massif has a length of around 1.5 km and
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#1732775257728204-719: The Ribband and Duncannon Groups. The sediments of the Ribband group pass upward into the Kilcullen Group turbidites. This reflects a continuous period of flysch sedimentation . Although most of the Group is unfossiliferous (without fossils), locally sparse graptolite faunas and acritarchs have been found. Their dating range from the Drumian stage of the Cambrian to the Early-Mid Ordovician. The following
221-520: The confusion this causes, the official geologic timescale of the ICS does not contain any of these names. As with other lithostratigraphic ranks, a group must not be defined by fossil taxonomy. Buntsandstein The Buntsandstein (German for coloured or colourful sandstone ) or Bunter sandstone is a lithostratigraphic and allostratigraphic unit (a sequence of rock strata ) in
238-492: The south was formed in present-day southeast Poland, causing sea water to flow in periodically. This caused the inflow of more clastic material, which was deposited in the form of large alluvial fans . The same process happened in the Triassic for the Basque-Cantabrian Basin , in the axis of the future Pyrenees . Deposition took place in an arid, continental environment ( playa facies), so that there
255-468: 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)
272-480: Was little chemical weathering . Therefore, the Buntsandstein deposits are typical red beds , mainly sandstones and conglomerates with little clay . The late Anisian saw a major rise of the global ( eustatic ) sea level. A tropical sea filled the Germanic Basin then, stopping the deposition of the Buntsandstein and marking the beginning of the deposition of the Muschelkalk. The Buntsandstein belongs to
289-702: Was the successor of the smaller Permian Basin and spread across present day Poland , Germany, Denmark , the southern regions of the North Sea and Baltic Sea , the Netherlands and south England. In the late Permian this region had an arid climate and it was covered by inland seas which deposited the Zechstein evaporites . At the end of the Permian a connection with the Paleo-Tethys Ocean to
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