The Galisteo Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

. It contains

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s characteristic of the

Bartonian The Bartonian is, in the ICS's geologic time scale, a stage or age in the middle Eocene Epoch or Series. The Bartonian Age spans the time between . It is preceded by the Lutetian and is followed by the Priabonian Age. Stratigraphic definitio ...

stage of the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

Duchesnean The Duchesnean North American Stage on the geologic timescale is a North American Land Mammal Age (NALMA), with an age from 42 to 38 million years BP, representing . It falls within the Eocene epoch. The Duchesnean is preceded by the Uintan and ...

in the NALMA classification.Galisteo Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org

Description

The Galisteo Formation is primarily

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

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) ...

and

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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

, with small amounts of conglomerate, freshwater

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, and sedimentary

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

. It crops out over a limited area between

Sandia Crest Sandia Crest, also known locally as Sandia Peak or simply as the Crest, is a mountain ridge that, at , is the highpoint of the Sandia–Manzano Mountains, and is located in the Sandia Mountains of Bernalillo County, New Mexico, United States. ...

and the southern

Sangre de Cristo Mountains ) , country= United States , subdivision1_type= States , subdivision1= , parent= Rocky Mountains , geology= , orogeny= , area_mi2= 17193 , range_coordinates= , length_mi= 242 , length_orientation= north-south , width_mi= 120 , w ...

, with an outlier at the eastern feet of the San Miguel subrange of the

Jemez Mountains The Jemez Mountains are a group of mountains in Rio Arriba, Sandoval, and Los Alamos counties, New Mexico, United States. Numerous Puebloan Indian tribes have lived in the Jemez Mountains region since before the Spanish arrived in New Mexico. T ...

. Its contact with the overlying

Espinaso Formation The Espinaso Formation is a geologic formation in New Mexico. It has a radiometric age of 34.6 to 26.9 million years, corresponding to the late Eocene through Oligocene epochs. Description The Espinaso Formation is principally debris flows a ...

is gradational. The formation rests on the Diamond Tail Formation in most locations where its base is exposed, but the Diamond Tail is not present in the exposures south of

San Ysidro San Ysidro (Spanish for " St. Isidore", ) is a district of the City of San Diego, immediately north of the Mexico–United States border. It neighbors Otay Mesa West to the north, Otay Mesa to the east, and Nestor and the Tijuana River Valley t ...

. The presence of

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

and

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

clasts at the base of the Galisteo Formation suggests that the discontinuity separating it from the Diamond Tail is

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...

in origin. There are indications the formation itself experienced penecontemporaneous deformation, possibly due to renewed uplift of the southern

. The maximum thickness of the formation is .

Paleocurrent A paleocurrent or paleocurrent indicator is a geological feature (typically a sedimentary structure) that helps one determine the direction of flowing water in the geologic past. This is an invaluable tool in the reconstruction of ancient depositio ...

directions indicate the

sources Source may refer to: Research * Historical document * Historical source * Source (intelligence) or sub source, typically a confidential provider of non open-source intelligence * Source (journalism), a person, publication, publishing institute o ...

of the

sediments Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand a ...

deposited in the formation came from the Brazos- Sangre de Cristo Geanticline to the northeast and the

Nacimiento Mountains The Sierra Nacimiento (official name), or Nacimiento Mountains, are a mountain range in the northwestern part of the U.S. state of New Mexico. They are just west of the more prominent Jemez Mountains near the town of Cuba, and are separated from ...

to the northwest. There are no indications of sediments from Sandia Crest to the south, suggesting that Sandia Crest was not uplifted until after the Eocene. The presence of Precambrian clasts in the upper part of the formation in the San Miguel Mountains was some of the first evidence for the existence of the Pajarito Uplift, a

Laramide The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the o ...

structure occupying what is now the southern

Espanola Basin The Espanola basin is a structural basin in northern New Mexico. It is located in the Rio Grande watershed and is part of the Rio Grande rift. The definition of its boundaries is not fully settled, but the basin is usually defined such that it i ...

between the current locations of Los Alamos and Santa Fe that later foundered into the

Rio Grande Rift The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihua ...

. The Galisteo Formation likely correlates with the

El Rito Formation The El Rito Formation is a geologic formation in New Mexico dating to the Eocene epoch. It records a time when sediments were trapped in deep basins in western North America rather than being carried downstream to the Gulf of Mexico, so that sed ...

to the north of the

. It may also correlate with the Tapicito Member of the San Jose Formation.

Paleontology

The most important fossil site in the Galisteo Formation, the Stearns quarry at Arroyo del Tuerto, contains numerous fossil remains of

titanotheres Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like rhinos, although they were actually more closely related to ...

dating to the

Stage, about 42 to 38 million years ago.

Petrified wood Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial vegetation. ''P ...

is also found in this area. The formation is otherwise largely barren of fossils.

Fossil content

The following fossils have been reported from the formation:

Mammals

;Carnivora * '' Angelarctocyon cf. australis'' ;Glires * Paramyidae indet. ;Pantodonta * '' Coryphodon sp.'' ;Perissodactyls * '' cf. Homogalax protapirinus'' * Brontotheriidae indet. * Equidae indet. ;Placentalia * '' Hyopsodus powellianus'' ;Primates * Microsyopidae indet. ;Theriiformes * '' Ectoganus sp.''

History of investigation

The formation was first described by F.V. Hayden during the 1869 expedition to New Mexico and

Colorado Colorado (, other variants) is a state in the 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 western edge of t ...

. He named the formation the Galisteo sand group and noted that its sandstone beds dipped from 5 to 50 degrees and varied in color from off-white to brick red. He could find no fossils other than petrified logs, some of which were enormous. The formation originally included older beds separated from the rest of the formation by a significant

disconformity 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 ...

. These were split off into the Diamond Tail Formation in 1997.

References

Bibliography

* * * * * * * * {{cite journal , last1=Tomiya , first1=S. , first2=Z. S. , last2=Morris , year=2020 , title=Reidentification of late middle Eocene "''Uintacyon''" from the Galisteo Formation (New Mexico, U.S.A.) as an early beardog (Mammalia, Carnivora, Amphicyonidae) , url=https://bioone.org/journals/breviora/volume-567/issue-1/0006-9698-567.1.1/REIDENTIFICATION-OF-LATE-MIDDLE-EOCENE-UINTACYON-FROM-THE-GALISTEO-FORMATION/10.3099/0006-9698-567.1.1.full , journal= Breviora , volume=567 , pages=1–12, doi=10.3099/0006-9698-567.1.1 , s2cid=218643803 , doi-access=free Paleogene formations of New Mexico Eocene Series of North America Bartonian Stage Duchesnean Sandstone formations of the United States Tuff formations Fluvial deposits Paleontology in New Mexico