The Trujillo 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 ...
in
Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
and
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 preserves
fossils
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 in ...
dating back to the
upper Triassic period.
It is also known as the Trujillo Sandstone.
Description
The formation consists mostly of gray to brown or 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) ...
, but with some
conglomerate
Conglomerate or conglomeration may refer to:
* Conglomerate (company)
* Conglomerate (geology)
* Conglomerate (mathematics)
In popular culture:
* The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes
** Co ...
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. ...
. Conglomerate is more common in the middle beds while mudstone is more common in the middle and upper beds. The sandstone is typically
crossbedded
In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The original ...
and is fine-grained in the lower beds and more coarse in the middle and upper beds. The lower sandstone beds tend to form a prominent cliff. The total thickness varies from . The formation overlies the
Tecovas Formation.
The Cuervo Sandstone Member is preempted by the Trujillo Formation.
The formation crops out along
Palo Duro Canyon
Palo Duro Canyon is a canyon system of the Caprock Escarpment located in the Texas Panhandle near the cities of Amarillo, Texas, Amarillo and Canyon, Texas, Canyon. As the second-largest canyon in the United States, it is roughly long and has an ...
and the
Canadian River and their tributaries.
It is also widespread in the
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 ...
.
[
]
The formation is interpreted as
deposition in a
braided stream
A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''.
Braided streams tend to occur in rivers with high sediment lo ...
system.
The lower beds at Palo Duro Canyon contain unusual cone-shaped iron
concretions that likely formed in the
vadose zone.
Fossils
The formation contains ''
Typothorax
''Typothorax'' is an extinct genus of typothoracine aetosaur that lived in the Late Triassic. Its remains have been found in North America. Two species are known: ''T. coccinarum'', the type species, and ''T. antiquum''.
Description
''Typothor ...
'' scutes
and the unusual
cycad
Cycads are seed plants that typically have a stout and woody (ligneous) trunk (botany), trunk with a crown (botany), crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants o ...
''
Sanmiguelia
''Sanmiguelia lewisi'' is an extinct plant genus, possibly of flowering plants. The fossil was first described from Late Triassic Chinle Formation in Colorado, and later in Lower Jurassic Moenave Formation in Utah
Utah ( , ) is a state ...
''.
History of investigation
The formation was first named as the upper formation of the
Dockum Group in 1907 by C.N. Gould.
See also
*
List of fossiliferous stratigraphic units in Texas
*
Paleontology in Texas
References
Triassic geology of Texas
Triassic formations of New Mexico
{{Triassic-stub