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 .
20-611: The Corallian Group or Corallian Limestone is a geologic group in England . It is predominantly a coralliferous sedimentary rock, laid down in the Oxfordian stage of the Jurassic . It is a hard variety of " coral rag ". Building stones from this geological structure tend to be irregular in shape. It is often found close to seams of Portland Limestone (e.g. Abbotsbury in Dorset , England ). It
40-428: A diverse skeletal fauna including the theropods "Syntarsus" kayentakatae and Dilophosaurus , the prosauropod Sarahsaurus , an unnamed heterodontosaurid , and the armored dinosaurs Scelidosaurus and Scutellosaurus . The Navajo Sandstone has body fossils of the theropod Segisaurus and an Ammosaurus -like prosauropod, and tracks. The following summarizes vertebrate fossils and tracks reported in
60-718: Is a younger limestone than its near-neighbour, the Oolitic , as found in the Cotswolds , in Gloucestershire . It is laterally equivalent to and interfingers with units of the Ancholme Group . A ridge of Corallian Limestone rises above the Vale of Avon and the Thames Valley in its Oxfordshire stretch. The Oxfordshire Corallian ridge is an escarpment holding back the hanging valley that
80-754: Is called the Glen Canyon Sandstone in the Green River Basin of Colorado and Utah. There are four formations within the group. From oldest to youngest, these are the Wingate Sandstone , Moenave Formation , Kayenta Formation , and Navajo Sandstone . Part of the Colorado Plateau and the Basin and Range , this group of formations was laid down during the Late Triassic and Early Jurassic , with
100-459: Is likewise separated from the overlying San Rafael Group by the regional J-2 conformity, representing a renewal of widespread erosion. The Glen Canyon Group was deposited in a foreland basin created by the uplift of the Sevier Mountains in what is now Nevada and eastern Utah. As a result, the formations of the group thicken to the west. The Kayenta Formation pinches out and disappears to
120-613: Is the Vale of White Horse and its hardness forced the River Thames to take a wide northern detour, to cut through the low ridge at Oxford . High points along the ridge are Cumnor Hurst and Wytham Hill. The outcrop known as Headington stone was quarried at Headington Quarry on the outskirts of Oxford and used for many of the historic University buildings there. Hilly outcrops above this corallian ridge, composed of Lower Greensand , occur at Badbury Hill , Faringdon (Folly Hill) and Boars Hill . Softer sandy deposits occur within
140-577: Is typically well jointed and gives rise to numerous springs. Here it yields up to 15 L/sec. In the Cotswolds the aquifer is up to 40 m thick, give yields of 5 to 10 L/sec, with water quality becoming increasingly saline down dip as the aquifer becomes confined in the Wessex Basin . In England, Corallian Limestone is to be found in Dorset , Wiltshire , Oxfordshire , Buckinghamshire , Cambridgeshire , Lincolnshire and Yorkshire . The most noted scholar of
160-571: 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
180-761: 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
200-680: The Corallian strata of England was the geologist W.J. Arkell (1904–1958). This article about a specific stratigraphic formation in the United Kingdom is a stub . You can help Misplaced Pages by expanding it . This article related to the Jurassic period is a stub . You can help Misplaced Pages by expanding it . This England -related article is a stub . You can help Misplaced Pages by expanding it . Group (geology) Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
220-540: The Corallian, found for example at Faringdon , Shellingford and Hatford in Oxfordshire , where the sands and gravels are extensively quarried. The Corallian Limestone aquifer is present at outcrop in Yorkshire and in the Cotswolds . In Yorkshire it consists of limestones and grits up to about 110 m thick, thinning to about 20 m towards the south of the region, where the limestones are progressively replaced by clay. It
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#1732859052750240-760: The Triassic-Jurassic boundary within the Wingate Sandstone. The top of the Glen Canyon Group is thought to date to the Toarcian stage of the Early Jurassic. Asterisks (*) below indicate usage by the U.S. Geological Survey . The Glen Canyon Group consists of extensive eolian deposits of latest Triassic to Early Jurassic age on the Colorado Plateau. These form the spectacular orange canyon walls of Canyonlands National Park and Paria Canyon as well as
260-472: 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. Glen Canyon Group The Glen Canyon Group is a geologic group of formations that is spread across the U.S. states of Nevada , Utah , northern Arizona , north west New Mexico and western Colorado . It
280-602: The north, in the Uintah Basin , and the Wingate Sandstone and Navajo Sandstone become indistinguishable. These remaining eolian beds have sometimes been mapped as simply Glen Canyon Formation, but they correlate with the Nugget Sandstone further north, and it has been recommended that they be assigned to the Nugget Sandstone. Group rank (stratigraphic order): There is no designated type locality for this group. It
300-460: 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)
320-567: The unflooded portions of Glen Canyon . Deposition of the Glen Canyon Group ceased in the Middle Jurassic with the transgression of the Sundance Sea , which separated deposition of the Glen Canyon Group from deposition of the overlying San Rafael Group . The Glen Canyon Group is separated from the underlying Chinle Formation by the regional J-0 unconformity, which represents a time of widespread erosion across western North America. The group
340-518: The upper contact and created an overview in 1979. In 1989 the age of the group was reexamined by Padian and separately by Dubiel (who also revised the lower contact). Geologic Province: Prehistoric animals from the various formations of the Glen Canyon Group include several types of dinosaurs , known from both skeletal remains and tracks. Dinosaur finds in the Wingate and Moenave formations are presently almost entirely tracks. The Kayenta Formation has
360-722: The upper contact was revised by Phoenix, who moved the uppermost silstone beds of the Navajo Sandstone into the Judd Hollow Tongue of the Carmel Formation. Poole and Stewart mapped the group into the Green River Basin in 1964, treating it here as a single formation. Areal extent limits were revised by Wilson and Stewart in 1967 and again by Green in 1974, who added the Iyanbito Member. Peterson and Pipiringos revised
380-580: Was named by Gregory and Moore prior to 1928 for exposures in walls that form the Glen Canyon of the Colorado River in Coconino County, Arizona and San Juan County, Utah , though their report was not published until 1931. The name had by then been published by Gilluly and Reeside, who gave an overview of the group. In 1936, A.A. Baker reexamined the group and named the Kayenta Formation . The work
400-567: Was revised again in 1955 by Averitt and others. They assigned the Shurtz Sandstone Tongue (new) and Lamb Point Tongue (new) to the Navajo Sandstone , and Cedar City Tongue (new) and Tenney Canyon Tongue (new) to the Kayenta Formation. In 1957 Harshbarger and others created an overview and revision that assigned the Moenave Formation and divided the Wingate Sandstone into the newly named Rock Point and Lukachukai members. In 1963,
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