The Summerville Formation is a geological formation in

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

, and

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

of the

Southwestern United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural list of regions of the United States, region of the United States that includes Arizona and New Mexico, along with adjacen ...

. It dates back to the Oxfordian

stage Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

.Wilcox 2007

Description

The formation consists of up to of red

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

, with thin interbeds of green and red

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

. 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 Hydrate, 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, drywall and blackboard or sidewalk ...

, consistent with deposition in a

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

on the margin of the

Sundance Sea The Sundance Sea was an epeiric sea that existed in North America during the mid-to-late Jurassic Period of the Mesozoic Era. It was an arm of what is now the Arctic Ocean, and extended through what is now western Canada into the central western ...

.It is exposed in the

San Rafael Reef The San Rafael Reef is a geologic feature located in Emery County in central Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a ...

, 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 Henr ...

, with additional exposures scattered across the region from the San Rafael Reef to the Paradox Basin, 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 a ...

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 and northeastern Arizona. Description The formation is composed mostly of thinly bedded sandstone, siltstone, and mudstone which is reddi ...

instead. The Summerville Formation rests conformably on the underlying

Curtis Formation The Curtis Formation is a geologic formation in Utah. It preserves fossils dating back to the Callovian age of the Jurassic period. Description The Curtis Formation is composed of shallow marine sandstone, with thin beds of mudstone and mino ...

(Utah and western Colorado) or Todilto Formation (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, siltston ...

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 ...

. It thins significantly in the

Moab Moab () was an ancient Levant, Levantine kingdom whose territory is today located in southern Jordan. The land is mountainous and lies alongside much of the eastern shore of the Dead Sea. The existence of the Kingdom of Moab is attested to by ...

- La Sal area, the likely area of the divide between the marine

Curtis Curtis or Curtiss is a common English given name and surname of Anglo-Norman origin, deriving from the Old French ''curteis'' (Modern French">-4; we might wonder whether there's a point at which it's appropriate to talk of the beginnings of Fren ...

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 (geology), 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 deposi ...

. 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 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

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 is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

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 of the United States 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