The Summerville Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

, and

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

of the

Southwestern United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural region of the United States that generally includes Arizona, New Mexico, and adjacent portions of California, Colorado, N ...

. It dates back to the Oxfordian stage of the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the ...

.Wilcox 2007

Description

The formation consists of up to of red mudstone, with thin interbeds of green and red

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

. The lower portion of the formation shows polygonal desiccation cracks and localized salt-hopper casts while the upper portion contains considerable

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and dr ...

, consistent with deposition in a

sabkha A sabkha ( ar, سبخة) is a coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coastal p ...

on the margin of the Sundance Sea.It is exposed in the San Rafael Reef, the Waterpocket Fold, in the

Henry Mountains The Henry Mountains is a mountain range located in the southeastern portion of the U.S. state of Utah that runs in a generally north-south direction, extending over a distance of about . They were named by Almon Thompson in honor of Joseph Henry, ...

, with additional exposures scattered across the region from the San Rafael Reef to the

Paradox Basin The Paradox Basin is an asymmetric foreland basin located mostly in southeast Utah and southwest Colorado, but extending into northeast Arizona and northwest New Mexico. The basin is a large elongate northwest to southeast oriented depression ...

, and in north-central New Mexico. The thin bedding is characteristic throughout the formation, but gypsum is not found in the

San Juan Basin The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah ...

and some conglomerate is found on the south and southwestern margins of the formation.Lucas and Anderson 1992, p.81 The correlation of late Jurassic beds in northwestern New Mexico with the Summerville Formation in Utah has been questioned, and it has been suggested that they be assigned to the

Beclabito Formation The Beclabito Formation is a late Jurassic sedimentary geologic formation, found in northwestern New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerq ...

instead. The Summerville Formation rests conformably on the underlying Curtis Formation (Utah and western Colorado) or

Todilto Formation The Todilto Formation is a geologic formation in northern New Mexico and southeastern Colorado. It preserves fossils dating back to the Callovian stage of the middle Jurassic period. Description The formation consists of evaporites. It is di ...

(southwest Colorado and New Mexico) but is separated from the overlying

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, ...

by the regional J5

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

. It thins significantly in the Moab- La Sal area, the likely area of the divide between the marine Curtis basin to the northwest and the salina lake Todilto basin to the southeast. Here the formation is just thick and rests directly on

Entrada Sandstone The Entrada Sandstone is a formation in the San Rafael Group found in the U.S. states of Wyoming, Colorado, northwest New Mexico, northeast Arizona, and southeast Utah. Part of the Colorado Plateau, this formation was deposited during the Jurass ...

. In many locations the Summerville is separated from the Morrison by eolian sandstones, such as the Bluff Sandstone, variously assigned to the Morrison Formation or the San Rafael Group. The Morrison Formation represents a return to more humid conditions with increased clastic input.Lucas and Anderson 1992, p.80 The

Bell Ranch Formation The Bell Ranch Formation is a Late Jurassic ( Kimmeridgian) geologic formation in eastern and northeastern New Mexico and the western Oklahoma panhandle. Fossil theropod tracks have been reported from the formation. Description At the type ...

of northeastern New Mexico is correlative with the Summerville Formation.Lucas and Anderson 1992 The Summerville Formation is interpreted as recording a regression of the Sundance Sea to the north, with simultaneous infilling of both the Curtis and Todilto basins. This produced a depositional environment of very low relief, in which occasional encroachments of eolian sand during times of drought were subsequently worked into thin strata by wave action in ephemeral saline lakes. File:Summerville Formation west of Hanksville.jpg, Evenly bedded Summerville Formation exposed along Utah Highway 24, 2.4 miles west of Hanksville, Utah File:Closeup of Summerville Formation.jpg, Closeup of the Summerville Formation showing even bedding, 2.4 miles west of Hanksville, Utah. File:Summerville Formation gypsum cracks.jpg, Summerville Formation with gypsum-filled cracks. U.S. quarter dollar (24 mm) for scale

Fossil content

The formation is almost completely lacking in body fossils.Lucas and Anderson 1992, p.84 However, theropod tracks were found in the formation in Utah, New Mexico, and Colorado.Weishampel 2004

Avemetatarsalians

History of investigation

The formation was first defined in 1928 for exposures in the San Rafael Reef.Gilluly and Reeside, 1927 Similar beds in northeastern

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14 ...

and the

are assigned to the Wanakah Formation,Condon ''et al.'' 1988 but continue to be assigned to the Summerville Formation in north-central New Mexico.Koning and Read 2010

Footnotes

References

* * * * Lockley, M.; Harris, J.D.; and Mitchell, L. 2008. "A global overview of pterosaur ichnology: tracksite distribution in space and time." ''Zitteliana''. B28. p. 187-198. . * * * Weishampel, David B; et al. (2004). "Dinosaur distribution (Middle Jurassic, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 537–538. {{ISBN, 0-520-24209-2. Geologic formations of Arizona Geologic formations of Oklahoma Geologic formations of Colorado Geologic formations of Utah Oxfordian Stage Jurassic Arizona Jurassic formations of New Mexico Jurassic geology of Oklahoma Jurassic Colorado Jurassic geology of Utah Mudstone formations Sandstone formations of the United States Ichnofossiliferous formations Paleontology in Arizona Paleontology in New Mexico Jurassic System of North America

Description

Fossil content

Avemetatarsalians

History of investigation

See also

Footnotes

References