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 .
22-586: The Santa Fe Group is a group of geologic formations in New Mexico and Colorado . It contains fossils characteristic of the Oligocene through Pleistocene epochs . The group consists of basin -filling sedimentary and volcanic rocks of the Rio Grande rift , and contains important regional aquifers . The Santa Fe Group is widely defined as basin -filling sedimentary and volcanic rocks of
44-860: A middle section transitional between the upper and lower sections. Formations of the Santa Fe Group are defined in each basin of the Rio Grande rift, though some formations extend across multiple basins. Upper Santa Fe Group: The lower Santa Fe Group is present only in the subsurface in the San Luis Basin and has not been divided into formations. Upper Santa Fe Group: Lower Santa Fe Group: Upper Santa Fe Group: Lower Santa Fe Group: Upper Santa Fe Group: Middle Santa Fe Group: Lower Santa Fe Group: Upper Santa Fe Group: Lower Santa Fe Group: Upper Santa Fe Group: Lower Santa Fe Group: G.K. Gilbert visited San Ildefonso Pueblo with
66-1239: Is an extinct family of proboscideans belonging to Elephantimorpha . It is best known for the mastodons (genus Mammut ), which inhabited North America from the Late Miocene until their extinction at beginning of the Holocene , around 11,000 years ago. The earliest fossils of the group are known from the Late Oligocene of Africa, around 24 million years ago, and fossils of the group have also been found across Eurasia. The name "mastodon" derives from Greek , μαστός "nipple" and ὀδούς "tooth", referring to their characteristic teeth. Mammutids are characterised by their zygodont molars, where pairs of parallel cusps are merged into sharp-sided riges, which are morphologically conservative and differ little between mammutid species. Like other members of Elephantimorpha , mammutids exhibited horizontal tooth replacement like modern elephants. Some authors have argued that horizontal tooth replacement evolved in parallel in mammutids and members of Elephantida (which includes gomphotheres and elephants), though this
88-432: Is uncertain. Compared to modern elephants, the bones of most mammutids were more robust, with the limb bones in particular being massive. Early members of the group like Eozygodon and Zygolophodon had elongate mandibular symphysis of the lower jaws with lower incisors/tusks, while in later representatives like Sinomammut and Mammut , the lower incisors/tusks were either lost or only vestigially present, and
110-586: 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
132-590: The Hayden Survey in 1873 and found fossil mammal bones characteristic of the Pliocene . Some of these were sent to Othniel Marsh . Marsh's bitter rival, Edward Drinker Cope , arrived at San Ildefonso the next year and collected a number of Miocene reptile, bird, and mammal fossils. Childs Frick sent an expedition into the Tesuque area in 1924, and immediately recognized the paleontological potential of
154-653: The Rio Grande rift . Galusha and Blick advocated a much narrower definition of the Santa Fe Group in 1971. They restricted it to the Tesuque Formation and Chamita Formation in the Espanola basin, and specifically excluded the older Abiquiu and Zia Formation and younger Ancha Formation . However, the broad 1956 definition by Baldwin has been widely accepted. Group (geology) Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying
176-439: The Rio Grande rift . These range in age from late Oligocene to Pleistocene. The oldest formations in the group correspond to the earliest structural deformation associated with rifting . Geologic uplift of the region around the rift has ended deposition, and erosion in the Rio Grande river system has exposed many of the beds deposited earlier, often spectacularly, as in the badlands north of Santa Fe . The formations in
198-866: 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
220-552: The Late Oligocene , with the oldest genus Losodokodon dating to around 27.5-24 million years ago. Mammutids belonging to the genus Zygolophodon (as well as possibly other mammutid genera) entered Eurasia across the " Gomphotherium land bridge " during the early Miocene, around 18 million years ago. Mammutid remains are generally rare in Eurasia in comparison to contemporary gomphotheres and deinotheres . During
242-612: The Santa Fe Formation had been traced from central New Mexico into southern Colorado. Two years later, Bryan recognized that it extended at least from the San Luis Basin to beyond El Paso and was extensively faulted and deformed. He interpreted the formation as being deposited in a series of basins along an ancestral Rio Grande. The formation was promoted to group rank in 1953 and defined by Baldwin three years later as basin-filling sedimentary and volcanic rocks of
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#1732802260719264-589: The Santa Fe Group include the canids Hemicyon and Carpocyon webbi , the antilocaprids Cosoryx , Merycodus , and Ramoceros , chiroptera from the Vespertilionidae and Antrozoinae , the turtle Glyptemys valentinensis , and mastodonts . The groundwater potential of the Santa Fe Group was recognized by Bryan Kirk in 1938, and the Alamosa subbasin of the San Luis Valley,
286-897: The Santa Fe beds. The Fricks Laboratory (merged with the Department of Vertebrate Paleontology of the American Museum of Natural History in 1968) carried out field work through 1972. Work prior to 1940 was careless about identifying exact source strata, though greater care was taken thereafter. Most of the fossils came from the Pojoaque Member of the Tesuque Formation and were almost entire found within thin (0.5–3 m) maroon-red to pale green claystone to fine-grained siltstone beds of lithosome B. These are interpreted as small lacustrine deposits. Fossils found in
308-550: The aquifer. Hayden gave the name "Santa Fe Marls" to the extensive sedimentary beds in the valley of the Rio Grande near Santa Fe during his 1869 survey of New Mexico and Colorado. He likened these to the badlands of South Dakota and correctly determined that they were upper Tertiary in age and were much younger than the Galisteo Formation beds which they overlie. He noted their great thickness, which he observed to be at least 1,500 feet (460 m). By 1936,
330-600: The central part of the Albuquerque Basin , and the southern Mesilla basin from Las Cruces to El Paso are now among the most productive groundwater reservoirs in the western United States. In the Albuquerque area, this has produced significant drawdown of the water table , in some places exceeding 100 feet (30 m). The aquifer continues to be studied to characterize the effects of new development, and resulting shifts in groundwater flow, on pollutants in
352-541: 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. Mastodont † Eozygodon Tassy and Pickford, 1983 † Losodokodon Rasmussen & Gutiérrez, 2009 † Mammut Blumenbach, 1799 † Miomastodon ? Osborn, 1922 † Sinomammut Mothé et al. , 2016 † Zygolophodon Vacek, 1877 Mammutidae
374-439: The group are divided into lower and upper sections. The lower Santa Fe Group was deposited in bolsons (closed arid basins) where streams drained into intermittent playa lakes surrounded by piedmont deposits eroded from basin-margin uplifts. The upper Santa Fe Group was deposited after integration of these basins into the ancestral Rio Grande, so that their drainage flowed toward southern New Mexico. Some geologists also define
396-739: The late early Miocene, around 16.5 million years ago, a population of Zygolophodon entered North America, giving rise to Mammut. The youngest confirmed records of mammutids in Africa date to around 13 million years ago, though possible Late Miocene fossils have been reported from North Africa. At the beginning of the Pleistocene , around 2 to 2.5 million years ago, the last of the Eurasian mammutids, "Mammut" borsoni became extinct, with members of Mammut persisting in North America until
418-566: The longest known of any animal, reaching over 5 metres (16 ft) in length. Members of Mammutidae are thought to have been primarily browsers on the foliage and twigs of trees and shrubs. Analysis of American mastodon ( Mammut americanum ) remains suggests that mammutids had a similar social structure to modern elephants, with herds of adult females and juveniles, with adult males living solitarily or in bonding groups with other males, with adult males periodically engaging in musth -like fighting behaviour against other males. Mammutids are
440-426: The lower jaws shortened (brevirostrine). This process happened convergently amongst other elephantimorph proboscideans, including gomphotheres , stegodontids , and elephantids . The mammutid "Mammut" borsoni is one of the largest of all proboscideans with an estimated average male body weight of 16 tonnes (35,000 lb) making it one of the largest land mammals of all time, with the tusks of this species being
462-525: The most basal group within Elephantimorpha , with gomphotheres and other members of Elephantida like amebelodonts being more closely related to elephants. Cladogram after Li et al. (2024). Phiomia Losodokodon Eozygodon Zygolophodon (ancestral to Mammut ) Choerolophodontidae Amebelodontidae (shovel tuskers) " Gomphotheriidae " (paraphyletic, ancestral to Elephantidae ) Mammutids originated in Africa during
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#1732802260719484-468: 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)
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