The Sheep Pen Sandstone is a
late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...
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 ...
exposed in northeastern
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 ...
.
Fossil
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ...
tracks have been reported from the formation.
Description
The formation consists of up to of thinly bedded light brown
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 ...
. It with a slight
angular 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 ...
on the
Sloan Canyon Formation and is overlain
unconformably
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 ...
by the
Exeter Sandstone.
The formation is usually assigned to the
Dockum Group
The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Color ...
.
The proposal of
Spencer G. Lucas
Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fo ...
and his collaborators to abandon the Dockum Group, possibly in favor of the
Chinle Group
The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...
, is highly controversial.
Fossils
Ichnofossil
A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...
s (track fossils) have been found in thee different locations north of
Kenton, Oklahoma
Kenton is a town in Cimarron County, Oklahoma, United States. Kenton is the westernmost town in Oklahoma. From Kenton, it is approximately south to Amarillo, Texas, northwest to Colorado Springs, Colorado, northwest to Denver, Colorado, sout ...
. The lower site includes the invertebrates ''
Scoyenia
''Scoyenia'' is an ichnogenus found in paleozoic-mesozoic strata
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjac ...
'' and the dinosauroid ''
Grallator
''Grallator'' GRA-luh-tor"is an ichnogenus (form taxon based on footprints) which covers a common type of small, three-toed print made by a variety of bipedal theropod dinosaurs. ''Grallator''-type footprints have been found in formations dating ...
'' on a scour surface. The traces are numerous but of low diversity. The middle site has at least ten distinct trackways, eight of ''Grallator'' and two of ''
Brachychirotherium''. The upper site has well-preserved tracks of ''Grallator'' and some poorly preserved tracks, possibly of ''Brachychirotherium''. The tracks suggest a stable
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
with low diversity, which may be typical of the middle
Norian
The Norian is a division of the Triassic Period. It has the rank of an age ( geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.
Stratigraphic ...
.
Economic geology
The formation has some
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish ...
mineralization around the western Oklahoma panhandle. Some 200 mines were in operation from 1884 to 1925. but these likely produced less than 10,000 tons of ore. The ore took the form of
chalcocite
Chalcocite (), copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark gray to black, with a metallic luster. It has a hardness of 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system.
...
,
malachite
Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fracture ...
, and
azurite
Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits. During the early 19th century, it was also known as chessylite, after the type locality at Chessy-les-Mines near Lyon, France. The mineral, a basic car ...
, deposited both in lenticular beds and in
clastic plugs.
History of investigation
The formation was first named by B.H. Parker in 1930.
See also
*
List of fossiliferous stratigraphic units in Colorado
This article contains a list of fossil-bearing stratigraphic units in the state of Colorado, U.S.
Sites
See also
* Paleontology in Colorado
References
*
{{DEFAULTSORT:Fossiliferous stratigraphic units in Colorado
Colorado
Co ...
*
Paleontology in Colorado
The location of the state of Colorado
Paleontology in Colorado refers to paleontological research occurring within or conducted by people from the U.S. state of Colorado.
The geologic column of Colorado spans about one third of Earth's history. ...
References
{{Reflist
Sandstone formations of the United States
Triassic formations of New Mexico