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21-657: The Montoya Group is a group of geologic formations in westernmost Texas and southern New Mexico . It preserves fossils dating back to the late Ordovician period . The group consists mostly of dolomite but with some limestone and a basal sandstone . The total thickness is about 180 meters (590 ft). The group overlies the El Paso Formation and is overlain by the Fusselman Formation or Percha Formation , with both contacts difficult to define in some exposure areas. Biostratigraphy of

42-584: 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 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

63-713: 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 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

84-437: Is interpreted as having been deposited within 30 degrees of the equator on the subtidal zone of a passive continental margin during the transition to late Ordovician glaciation . The presence of abundant chert and phosphate minerals in the group is attributed to upwelling along the continental margin, possibly triggered by glaciation . The Cable Canyon Sandstone contains trace fossils ( Skolithos ). The Upham Formation

105-436: Is rich in fossils, including brachiopods , bryozoans , corals , crinoids , gastropods , nautiloids , and receptaculids . The gastropod Maclurites is particularly prominent. The Aleman Formation is dominated by brachiopods, with some gastropods and tentaculites but few crinoids or bryozoans. The Cutter Formation contains abundant thin packstone beds with numerous brachiopods, bryozoans, and crinoids. The formation has

126-728: 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 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

147-550: 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 is likewise separated from the overlying San Rafael Group by the regional J-2 conformity, representing

168-539: 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 the unflooded portions of Glen Canyon . Deposition of the Glen Canyon Group ceased in the Middle Jurassic with the transgression of

189-878: 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 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

210-826: The El Paso Formation. In the southern exposures, the Cable Canyon Sandstone is not present and the Upham Dolomite has a thin basal quartz sandstone. The bulk of the Upham Dolomite is skeletal packstone and grainstone arising from dolomitization of a crinoidal calcarenite . Hardgrounds are found throughout the unit. The Aleman Formation has up to 70% chert , in the form of thin continuous beds of sponge spicules within calcisiltite beds or of diagenetic lenses of chert nodules within skeletal wackestone or packstone. The continuous chert beds appear to have been laid down in cool water, while

231-555: The Franklin Mountains, but the Montoya remains a formation in southern New Mexico, where its subunits are too thin to be mappable at the usual 1:24,000 scale. Group (geology) 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 a new area have sometimes defined groups when they believe

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252-748: 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, 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

273-594: 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 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

294-551: The group is consistent with deposition in the Cincinnatian . The group is divided into the Cable Canyon Sandstone , Upham Dolomite , Aleman Formation , and Cutter Formation These are treated as members in most of southern New Mexico, where the Montoya is relatively thin and remains at formation rank. The Cable Canyon Sandstone is present in the northern exposures of the group and lies unconformably on

315-478: The packstone was deposited in warmer water. The Cutter Formation is mostly bioturbated tidal flat carbonate mudstone or dolomite. The contact with the underlying El Paso Formation is an unconformity corresponding to a hiatus of about 30 million years. In the Franklin Mountains , the upper El Paso Formation shows pronounced karst weathering. In other locations, the contact is sharp. The group

336-540: 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 the confusion this causes, the official geologic timescale of the ICS does not contain any of these names. As with other lithostratigraphic ranks,

357-543: The potential to be an important natural gas reservoir in southern New Mexico, using horizontal drilling with hydrofacturing , with successful drilling reported by 2004. The name was first used by G.B. Richardson in 2008, who did not explain the origin of the name or designate a type section. The formation was promoted to group rank by Kelley and Silver in 1952, who divided the group into the Cable Canyon sandstone, Upham dolomite, Aleman formation, and Cutter formation in

378-567: 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 the lower part of the group) remain undivided into formations. Some well known groups of northwestern Europe have in

399-697: 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 the Navajo Sandstone . Each of the formations can be distinguished from its neighbor by its lithology , but all were deposited in

420-478: 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 a diverse skeletal fauna including the theropods "Syntarsus" kayentakatae and Dilophosaurus , the prosauropod Sarahsaurus , an unnamed heterodontosaurid , and

441-505: 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 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

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