The Tres Hermanos Formation is a geologic

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 ...

in central and west-central

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 ...

.Hook ''et al.'' 1983 It contains fossils characteristic of the

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded ...

Age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming olde ...

of the

late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607.

Description

The formation is a

clastic wedge In geology, clastic wedge usually refers to a thick assemblage of sediments--often lens-shaped in profile--eroded and deposited landward of a mountain chain; they begin at the mountain front, thicken considerably landwards of it to a peak depth, an ...

Cobban and Hook 1989 directed to the northeast into the

Mancos Shale The Mancos Shale or Mancos Group is a Late Cretaceous (Upper Cretaceous) geologic formation of the Western United States. The Mancos Shale was first described by Cross and Purington in 1899 and was named for exposures near the town of Mancos ...

. This divides the Mancos Shale into the underlying Rio Salado Tongue and the overlying Pescado or D-Cross Tongue. The base of the wedge is approximately along a line from the

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 ...

-New Mexico border southwest of

Gallup, New Mexico Zuni: ''Kalabwaki'' , settlement_type = City , nickname = "Indian Capital of the World" , motto = , image_skyline = Gallup, New Mexico.jpg , imagesize = 250px , image_caption ...

to east of

Cookes Range The Cookes Range (Cooke's Range, Cooks Range or Cook's Range) is a small, 17-mi (27 km) long mountain range in northern Luna County, New Mexico, which extends slightly north into southeastern Grant County. The range is a southern continuati ...

, where the overlying Pescado or D-Cross Tongue of the Mancos Shale pinches out. The wedge itself pinches out along an arc that passes south of Gallup and just north of

Acoma Pueblo Acoma Pueblo (, kjq, Áakʼu) is a Native American pueblo approximately west of Albuquerque, New Mexico, in the United States. Four communities make up the village of Acoma Pueblo: Sky City (Old Acoma), Acomita, Anzac, and McCartys. These c ...

and west of

Capitan Capitan and Kapitan are equivalents of the English Captain in other European languages. Capitan, Capitano, and Kapitan may also refer to: Places in the United States *Capitan, Louisiana, an unincorporated community * Capitan, New Mexico, a villag ...

. Total thickness is . The formation itself is interpreted as a

regression Regression or regressions may refer to: Science * Marine regression, coastal advance due to falling sea level, the opposite of marine transgression * Regression (medicine), a characteristic of diseases to express lighter symptoms or less extent ( ...

transgression Transgression may refer to: Legal, religious and social *Sin, a violation of God's Ten Commandments or other elements of God's moral law *Crime, legal transgression, usually created by a violation of social or economic boundary **In civil law ju ...

sequence of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient se ...

. It is divided into three members: the lower Atarque Sandstone Member, which is regressive marine

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 Carthage Member, a sequence of marine and nonmarine

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

and

; and the upper Fite Ranch Member, a transgressive marine sandstone.

Fossils

The base of the formation contains the

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttle ...

'' Spathites coahuilaensis'' characteristic of the middle Turonian.Cobban 1988 The formation spans the ammonite zones of ''

Collignoniceras ''Collignociceras'' is a strongly ribbed and tuberculate, evolute ammonite from the Turonian of the western U.S. and Europe belonging to the ammonitid family Collignoniceratidae. The genus is named after the French paleontologist Maurice Colligno ...

woollgari'', '' Prionocyclus percarinatus'', ''P. hyatti'', and ''P. macombit'', indicating that the formation ranges from early middle Turonian to early late Turonian.

Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

History of investigation

The unit was first designated the Tres Hermanos Sandstone member of the Mancos Shale by C.L. Herrick in 1900.Herrick 1900 In 1983, Hook ''et al.'' raised the unit to formation rank and interpreted it as a clastic wedge directed to the northeast into the Mancos Shale. They also divided the formation into the Atarque Sandstone Member, the Carthage Member, and the Fite Ranch Member.

Footnotes

References

* * * * * Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. 861 pp. {{ISBN, 0-520-24209-2. Geologic formations of the United States Turonian Stage

Description

Fossils

History of investigation

See also

Footnotes

References