The Raton Formation is a geological formation of

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cret ...

and

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

age which outcrops in the

Raton Basin The Raton Basin is a geologic structural basin in southern Colorado and northern New Mexico. It takes its name from Raton Pass and the town of Raton, New Mexico. In extent, the basin is approximately east-west, and north-south, in Huerfano an ...

of northeast

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 ...

and southeast

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 ...

Description

The formation consists of

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal i ...

with carbonaceous

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

, brown to buff

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 ...

, and conglomerate (usually at the base). It is about thick at the type locality. The formation unconformably overlies the Vermejo Formation, and unconformably (?) underlies the Poison Canyon Formation. It is of

late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

age. The formation can be divided into three informal members. The lowest member is a basal sandstone and conglomerate of

quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

and

gneiss Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...

pebbles and cobbles in a coarse-grained quartzose to arkosic sandstone matrix. The middle member is fine to coarse grained sandstone, with some

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

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, ...

, and coal. The upper member is coal-bearing and contains sandstone, siltstone, mudstone, shale, and mineable coal. Numerous

igneous intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s, ranging in age from 6.7 to 29.5 million years old, are found in the formation. These range from

dikes Dyke or dike may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), formations of magma or sediment that cut through and across the layering of adjacent rocks * Dike (mythology), ''Dikē'', the Greek goddess ...

and that have locally altered the coal to sills that preferentially penetrated along coal beds and destroyed the coal. It is likely that hundreds of millions of tons of the original coal deposits were destroyed this way.

Cretaceous-Paleogene boundary

Because the Raton Formation is a well-preserved sequence of rocks spanning the Cretaceous-Paleogene boundary, it has been studied for evidence of a large meteor impact at the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

that is thought to have caused the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...

. The boundary is represented by a 1-cm thick tonstein clay layer which has been found to contain anomalously high concentrations of

iridium Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density ...

. The boundary clay layer is accessible to the public at

Trinidad Lake State Park Trinidad Lake State Park is a state park west of Trinidad, Colorado, United States. The park protects Trinidad Lake, a dammed reservoir. There are hiking trails, and camping and boating opportunities. The park features historical attractions su ...

, among other places in the Raton Basin.

Fossils

The formation contains fossils of the

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

Pediastrum ''Pediastrum'' is a genus of green algae, in the family Hydrodictyaceae. It is a photoautotrophic, nonmotile coenobial green alga that inhabits freshwater environments. The name ''Pediastrum'' comes from the Greek root words ''pedion'', meaning ...

'' and ''

Scenedesmus ''Scenedesmus'' is a genus of green algae, in the class Chlorophyceae. They are colonial and non-motile. They are one of the most common components of phytoplankton in freshwater habitats worldwide. Taxonomy The starting point of ''Scenedesmus'' ...

'' characteristic of a freshwater lake or pond environment. Plant fossils suggest the formation was deposited in a tropical rain forest environment, with the presence of '' Icacinicaryites corruga'' and the

understory In forestry and ecology, understory (American English), or understorey (English in the Commonwealth of Nations, Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the Canopy (biology), forest ca ...

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

Cyclosorus ''Cyclosorus'' is a genus of ferns in the family Thelypteridaceae, subfamily Thelypteridoideae, in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Other sources sink ''Cyclosorus'' into a very broadly defined genus ''Thelypteri ...

'' indicating a very warm environment.

Economic resources

The Raton Formation contains economically important deposits of

. These were first discovered in 1841 and mining began in 1873. Mining declined precipitously in the mid-20th century with the decline of the

steel industry Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high elastic modulus, yield strength, fracture strength and low raw material cost, steel is one of the ...

using the coal, but the formation is now being developed for

coalbed methane ''Coalbed methane'' (CBM or coal-bed methane), coalbed gas, or coal seam gas (CSG) is a form of natural gas extracted from coal beds. In recent decades it has become an important source of energy in United States, Canada, Australia, and other co ...

. Reserves in 1999 were estimated at 18.4 trillion cubic feet (520 billion cubic meters). Production at that time was 17.5 million cubic feet per day (500,000 cubic meters per day) from 85 wells.

History of investigation

The Raton Formation was originally named "Raton Hills Group" by

Ferdinand Vandeveer Hayden Ferdinand Vandeveer Hayden (September 7, 1829 – December 22, 1887) was an American geologist noted for his pioneering surveying expeditions of the Rocky Mountains in the late 19th century. He was also a physician who served with the Union A ...

in 1869 for coal beds in the Raton Hills in

Colfax County, New Mexico Colfax County is a county in the U.S. state of New Mexico. As of the 2020 census, the population was 12,387. Its county seat is Raton. It is south from the Colorado state line. This county was named for Schuyler Colfax (18231885), seventee ...

. In 1913, W.T. Lee changed the name to Raton Formation.

References

{{Reflist Maastrichtian Stage of North America Paleogene Colorado Cretaceous formations of New Mexico Paleogene formations of New Mexico Geologic formations of Colorado Sandstone formations of the United States Conglomerate formations of the United States Coal formations Shale formations of the United States