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29-676: The Keres Group is a group of geologic formations exposed in and around the Jemez Mountains of northern New Mexico . Radiometric dating gives it an age of 13 to 6 million years, corresponding to the Miocene epoch . The Jemez Mountains lie on the intersection of the western margin of the Rio Grande Rift and the Jemez Lineament . Here magma produced from the fertile rock of an ancient subduction zone has repeatedly found its way to

58-599: A maximum exposed thickness of 300 meters (980 feet) and extends to Borrego Mesa to the southwest. Isolated exposures are found further to the east as far as the San Miguel Mountains. The formation is generally overlain and interbedded with flows of the Paliza Canyon Formation. It overlies beds of the Santa Fe Group . Radimetric ages for this formation range from 12 to 8 million years. The Bearhead Rhyolite

87-523: A name first used by Kirk Bryan and J. E. Upson. The member is named for its exposures in Peralta Canyon. It consists mainly of bedded air-fall tuffs but includes pyroclastic flows and reworked tuffs. Gold has been mined from the Bland district, from beds identified as the exhumed interior of a Keres Group volcano. The group was first defined by Bailey, Smith, and Ross in 1969 as part of their work establishing

116-603: Is a sequence of basalt , andesite , dacite , and rhyolite flows that underlie the southern Jemez Mountains. It overlaps the Polvadera Group to the north and has a maximum thickness of about 900 meters (3,000 feet). It overlies the Santa Fe Group to the south and is overlain by the Tewa Group. Keres volcanism began about 12 million years ago and continued to 6 million years ago. Volcanic activity generally shifted eastward over time during this interval. From oldest to youngest,

145-457: Is a thick stack of rhyolite tuffs, flows, domes, and associated shallow intrusions exposed from the northeastern Valles caldera rim to north of Cochiti Pueblo . It is named for exposures on Bearhead Peak ( 35°43′30″N 106°28′59″W  /  35.725°N 106.483°W  / 35.725; -106.483 ), one of the major source vents of the formation. The formation ranges in age from 7.1 to 6.5 million years. High-silica volcanism shifted to

174-473: 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

203-571: 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

232-574: 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

261-487: 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 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

290-438: The Rio Grande rift , and contains important regional aquifers . The Santa Fe Group is widely defined as basin -filling sedimentary and volcanic rocks of 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

319-820: 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

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348-730: The stratigraphy of the Jemez Mountains. The group was named for the Keresean Range, an older name for the southern Jemez Mountains. They included in the group the Basalt of Chamisa Mesa, the Canovas Canyon Rhyolite, the Paliza Canyon Formation, and the Bearhead Rhyolite. The Basalt of Chamisa Mesa has since been abandoned as a formation name, since it is similar in age and composition to the Paliza Canyon Formation. The division of

377-485: The Bearhead Rhyolite seems to have been erupted effusively. This has been attributed to rapid crustal extension associated with the Rio Grande rift , whose faulting opened numerous paths to the surface for the magma before it could build up to a catastrophic caldera eruption. Tuffs of the Bearhead Rhyolite, extensively exposed at Kasha-Katuwe Tent Rocks National Monument , are assigned to the Peralta Tuff Member ,

406-534: The Paliza Canyon Formation. The Canovas Canyon Formation is a sequence of rhyolite flows, tuffs , domes , and associated shallow intrusions exposed primarily around Bear Springs Peak ( 35°40′08″N 106°33′32″W  /  35.669°N 106.559°W  / 35.669; -106.559 ). The formation is named for exposures in Canovas Canyon ( 35°36′25″N 106°34′23″W  /  35.607°N 106.573°W  / 35.607; -106.573 ). It has

435-600: 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

464-629: 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,

493-866: 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

522-613: The alteration of the Paliza Canyon beds in contrast with the fresh appearance of the Tschicoma beds suggests a disconformity between the formations. The Paliza Canyon Formation is also locally overlain unconformably by the Bandelier Tuff . Beds assigned to the Basalt of Chamisa Mesa, once thought to be the earliest volcanic rock of the Jemez Mountains, have since been found to be unremarkable in age and composition and are now assigned to

551-544: 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,

580-588: 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

609-644: 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. Santa Fe Group (geology) 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

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638-605: The formation is not exposed along this axis, so its total thickness is unknown, but it is estimated from exposures to the west to be about 900 meters (3,000 feet). The formation rests on rocks dating from the Permian to the Miocene . These include red beds of the Abo Formation in the valley of the Rio Guadalupe in the western Jemez and in upper Canon de San Diego; Chinle Formation beds in lower Paliza Canyon; Abiquiu Formation on

667-707: The formations recognized within the Keres Group are the Paliza Canyon Formation, the Canovas Canyon Rhyolite, and the Bearhead Rhyolite. The Paliza Canyon Formation is a sequence of mostly andesite flows that is widely exposed in the southern Jemez Mountains. The formation was erupted by numerous coalesced composite volcanoes centered on an axis from the northern Valles Caldera wall south through Paliza and Peralta Canyons to Ruiz Peak ( 35°43′01″N 106°32′38″W  /  35.717°N 106.544°W  / 35.717; -106.544 ). Exposures along this axis generally exceed 500 meters (1,600 feet) in thickness. The base of

696-478: The north around 7.5 million years ago, producing the separation between the Canovas Canyon Rhyolite and the Bearhead Rhyolite. The Bearhead Rhyolite is similar to the Canovas Canyon Rhyolite, but is distinguished by field relationships: It rests on an erosional surface cut mostly on flows of the Paliza Canyon Formation. Its uppermost beds interfinger with the Cochiti Formation . Unlike most felsic volcanism,

725-567: The precaldera formations of the Jemez Mountains into the Keres and Polvadera Groups , based largely on geography, has been criticized as artificial. Fraser Goff and coinvestigators abandoned the Polvadera Group in their 2011 mapping of the Valles Caldera and included its formations in the Keres Group. Group (geology) Groups are useful for showing relationships between formations, and they are also useful for small-scale mapping or for studying

754-460: 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)

783-452: The surface along faults produced by rifting. This has produced a long-lived volcanic field , with the earliest eruptions beginning at least 13 million years ago in both the northern ( Polvadera Group ) and southern (Keres Group) portions of the volcanic field. High-silica eruptions of the Tewa Group began about 1.85 million years ago and continued almost to the present day. The Keres Group

812-539: The west wall of the Valles caldera and in upper San Juan Canyon; and Santa Fe Group at the east foot of St. Peter's Dome to the east. The Paliza Canyon Formation is intruded and locally overlain by Bearhead Rhyolite. In the north and northeast wall of the Valles caldera, the Paliza Canyon Formation appears to be conformably overlain with dacite and quartz latite flows of the Tschicoma Formation (Polvadera Group). However,

841-478: 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 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

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