Cerrejón Formation
Encyclopedia
The Cerrejón Formation is a geologic formation in Colombia
dating back to the Middle-Late Paleocene
. It is found in the El Cerrejón subbasin of the Racheria basin of La Guajira. The formation consists of bituminous coal
fields that are an important economic resource. Coal from the Cerrejón Formation is mined extensively from the Cerrejón
open-pit
coal mine, one of the largest in the world. The formation also bears fossils that are the earliest record of Neotropical rainforest
s.
Based on lithofacies
associations and paleofloral
composition, the depositional environment fluctuated from an estuarine-influenced coastal plain
at the base of the formation to a fluvial
-influenced coastal plain at the top.
In the geologically recent past, some coal in the formation has spontaneously and naturally combusted to form clinker, red and brick-looking burnt coal. These rocks outcrop irregularly and are up to 100 metres (328.1 ft) thick. Clinker is found near deformed zones such as faults or tight folds, and is older than the deformities themselves. They are thought to have combusted after the development of the Cerrejón thrust fault
and alluvial fan
.
s found from the Cerrejón Formation are the earliest record of Neotropical rainforests, with an abundance of plant macrofossils and palynomorph
s. The Cerrejón Formation also records a riverine vertebrate fauna that includes lungfish
, turtle
s, snake
s, and crocodyliforms. Based on these fossils and the stratigraphy of the formation, the Cerrejón Formation was likely formed on a coastal plain covered in a wet tropical rainforest and incised by a large river system.
The rainforest is estimated to have been around 5°N paleolatitude. During the Paleocene, equatorial temperatures were much higher than they are today. Based on the size of the giant boid Titanoboa
(specimens of which have been found from the Cerrejón Formation), the mean annual temperature of Paleocene equatorial South America was between 30 °C (86 °F) and 34 °C (93.2 °F). This is the minimum annual temperature range that a poikilotherm
as large as Titanoboa could live. It is consistent with Paleocene climate models which predict greenhouse temperatures and an atmospheric pCO2
concentration of 2,000 parts per million. Paleotemperature estimates based on fossil leaf assemblages from the Cerrejón Formation predict the mean annual temperature to be 6 to 8 °C (42.8 to 46.4 F) lower than other estimates. However, such temperature estimates based on riparian and wetland
rainforest paleoflora have been considered underestimates.
Mean annual temperatures of 30 to 34 °C are considered to be too high for modern tropical forests, but the Cerrejón rainforest could have been maintained by increased atmospheric pCO2 levels and the high regional rainfall, which is estimated to have been around 4 metres (13.1 ft) per year.
Many plants from the Cerrejón Formation belong to families
that are still common today in modern Neotropical rainforests. There is a diverse variety of palms
and legumes in the formation. In addition to palms and legumes, much of the biomass of the Paleocene forest consisted of laurales
, malvales
, menisperms
, aroids
, and zingiberaleans
. Studies of fossil plants from Cretaceous
-age sites indicate that the floral composition below the K–T boundary
was very different from that of the Paleocene. Legumes are absent from Cretaceous strata, and likely appeared or diversified during the Paleocene.
The presence of these types of flora in Paleocene strata shows that plants characteristic of modern Neotropical rainforests have existed for geologically long periods of time, being able to withstand climactic and geographic changes in South America. It has been suggested that today's Neotropical rainforests are the result of environmental changes brought about by Quaternary glacial cycles
(i.e. the recent ice age). These cycles would have caused fluctuation in the diversity and extent of rainforests. If this was the case, the current diversity of the Amazon rainforest
would be a recent speciation in a changing environment. However, the floral record from the Cerrejón Formation shows that the current diversity of the Amazon Rainforest can be traced back into the early Cenozoic.
feeders, unlike modern Neotropical insects that are mainly specialist
herbivores. There is no evidence of the elevated insect-feeding diversity or host
-specialized feeding associations that are seen in later Neotropical forests. The insect diversity in the Cerrejón Formation is low in comparison to the diversity of insects in Neotropical rainforests today, and it is likely that leaf damage was made by relatively few species.
Remains of the giant boid Titanoboa cerrejonensis have been found from a gray claystone
layer underlying Coal Seam 90 in the Cerrejón mine. Titanoboa is the largest known snake to have ever existed, reaching an estimated length of 13 metres (42.7 ft). Eunectes, the anaconda
, is likely to be a close living analogue of Titanoboa.
A dyrosaurid crocodylomorph called Cerrejonisuchus improcerus
was described in 2010 from the Cerrejón Formation in the same layer as Titanoboa. It was a small dyrosaurid, and had the shortest snout length relative to its skull length of any dyrosaurid. Most dyrosaurids were marine, with long snouts adapted for catching fish. The short snout of Cerrejonisuchus is likely to have been an adaptation for a more generalized diet in a transitional aquatic environment. It is possible that Cerrejonisuchus was a food source for Titanoboa, as the two inhabited the same riverine environment. The anaconda has been documented consuming caiman
s, a feeding habit that is similar to the inferred habit of Titanoboa. A second dyrosaurid, Acherontisuchus
, was named in 2011 from the formation. With a large body and long snout, it resembles most other dyrosaurids.
The Cerrejón Formation contains extensive coal seams that are mined primarily at the Cerrejón mine. The coal is desirable for its low ash and sulfur
content and for its resistance to caking. Cerrejón is Colombia's largest coal producing mine, with most of the production exported to Europe
. It is the largest coal mining operation in Latin America
, with an estimated 28.4 million tons mined in 2006.
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
dating back to the Middle-Late Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
. It is found in the El Cerrejón subbasin of the Racheria basin of La Guajira. The formation consists of bituminous coal
Bituminous coal
Bituminous coal or black coal is a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than Anthracite...
fields that are an important economic resource. Coal from the Cerrejón Formation is mined extensively from the Cerrejón
Cerrejón
Cerrejón is a coal mine located in the Guajira department in the north of Colombia. It is the largest mining operation in Colombia and among the largest open-pit coal mines in the world. The legal entity managing the Cerrejón operation is known as Carbones del Cerrejón Ltd...
open-pit
Open-pit mining
Open-pit mining or opencast mining refers to a method of extracting rock or minerals from the earth by their removal from an open pit or borrow....
coal mine, one of the largest in the world. The formation also bears fossils that are the earliest record of Neotropical rainforest
Rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
s.
Geology
The Cerrejón Formation is subdivided into lower, middle, and upper groups based on the thickness and distribution of coal beds. On average the coal beds are 3 metres (9.8 ft) thick, and range from 0.7 metres (2.3 ft) to 10 metres (32.8 ft) in thickness. The thickest beds are in the upper part of the formation.Based on lithofacies
Facies
In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
associations and paleofloral
Paleobotany
Paleobotany, also spelled as palaeobotany , is the branch of paleontology or paleobiology dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments , and both the evolutionary history of plants, with a...
composition, the depositional environment fluctuated from an estuarine-influenced coastal plain
Coastal plain
A coastal plain is an area of flat, low-lying land adjacent to a seacoast and separated from the interior by other features. One of the world's longest coastal plains is located in eastern South America. The southwestern coastal plain of North America is notable for its species diversity...
at the base of the formation to a fluvial
Fluvial
Fluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
-influenced coastal plain at the top.
In the geologically recent past, some coal in the formation has spontaneously and naturally combusted to form clinker, red and brick-looking burnt coal. These rocks outcrop irregularly and are up to 100 metres (328.1 ft) thick. Clinker is found near deformed zones such as faults or tight folds, and is older than the deformities themselves. They are thought to have combusted after the development of the Cerrejón thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
and alluvial fan
Alluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...
.
Paleoenvironment
FossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s found from the Cerrejón Formation are the earliest record of Neotropical rainforests, with an abundance of plant macrofossils and palynomorph
Palynomorph
Palynomorph is the geological term used to describe a particle of a size between five and 500 micrometres, found in rock deposits and composed of organic material such as chitin, pseudochitin and sporopollenin...
s. The Cerrejón Formation also records a riverine vertebrate fauna that includes lungfish
Lungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...
, turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, and crocodyliforms. Based on these fossils and the stratigraphy of the formation, the Cerrejón Formation was likely formed on a coastal plain covered in a wet tropical rainforest and incised by a large river system.
The rainforest is estimated to have been around 5°N paleolatitude. During the Paleocene, equatorial temperatures were much higher than they are today. Based on the size of the giant boid Titanoboa
Titanoboa
Titanoboa, , meaning "titanic boa," is a genus of snake that lived approximately 58 to 60 million years ago, in the Paleocene epoch, a 10-million-year period immediately following the dinosaur extinction event...
(specimens of which have been found from the Cerrejón Formation), the mean annual temperature of Paleocene equatorial South America was between 30 °C (86 °F) and 34 °C (93.2 °F). This is the minimum annual temperature range that a poikilotherm
Poikilotherm
A poikilotherm is an organism whose internal temperature varies considerably. It is the opposite of a homeotherm, an organism which maintains thermal homeostasis. Usually the variation is a consequence of variation in the ambient environmental temperature...
as large as Titanoboa could live. It is consistent with Paleocene climate models which predict greenhouse temperatures and an atmospheric pCO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
concentration of 2,000 parts per million. Paleotemperature estimates based on fossil leaf assemblages from the Cerrejón Formation predict the mean annual temperature to be 6 to 8 °C (42.8 to 46.4 F) lower than other estimates. However, such temperature estimates based on riparian and wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
rainforest paleoflora have been considered underestimates.
Mean annual temperatures of 30 to 34 °C are considered to be too high for modern tropical forests, but the Cerrejón rainforest could have been maintained by increased atmospheric pCO2 levels and the high regional rainfall, which is estimated to have been around 4 metres (13.1 ft) per year.
Flora
The floral record of the Cerrejón Formation is well known, with many identifiable and well preserved plant microfossils having been found from the Cerrejón mine. The fossils are well preserved, and in some cases their cell structure is intact. In comparison to modern Neotropical rainforests, the diversity of plants is quite low. This may be an indication of the early stage of Neotropical diversification, or a delayed recovery period following the Cretaceous–Tertiary extinction event.Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
that are still common today in modern Neotropical rainforests. There is a diverse variety of palms
Arecaceae
Arecaceae or Palmae , are a family of flowering plants, the only family in the monocot order Arecales. There are roughly 202 currently known genera with around 2600 species, most of which are restricted to tropical, subtropical, and warm temperate climates...
and legumes in the formation. In addition to palms and legumes, much of the biomass of the Paleocene forest consisted of laurales
Laurales
The Laurales are an order of flowering plants. They are magnoliids, related to the Magnoliales.The order includes about 2500-2800 species from 85-90 genera, which comprise seven families of trees and shrubs. Most of the species are tropical and subtropical, though a few genera reach the temperate...
, malvales
Malvales
Malvales are an order of flowering plants. As circumscribed by APG II-system, it includes about 6000 species within nine families. The order is placed in the eurosids II, which are part of the eudicots....
, menisperms
Menispermaceae
Menispermaceae, the botanical name for a family of flowering plants, has been universally recognized by taxonomists. Tubocurare, a neuromuscular blocker and active ingredient in curare, is derived from plants of this family....
, aroids
Araceae
Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe or leaf-like bract. Also known as the Arum family, members are often colloquially...
, and zingiberaleans
Zingiberales
Zingiberales is an order of flowering plants. The order has been widely recognised by the taxonomists, at least for the past few decades. This order includes many familiar plants like ginger, cardamom, turmeric, galangal and myoga of the Zingiberaceae or ginger family, and bananas and plantains...
. Studies of fossil plants from Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
-age sites indicate that the floral composition below the K–T boundary
K–T boundary
The K–T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 Ma ago. K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period...
was very different from that of the Paleocene. Legumes are absent from Cretaceous strata, and likely appeared or diversified during the Paleocene.
The presence of these types of flora in Paleocene strata shows that plants characteristic of modern Neotropical rainforests have existed for geologically long periods of time, being able to withstand climactic and geographic changes in South America. It has been suggested that today's Neotropical rainforests are the result of environmental changes brought about by Quaternary glacial cycles
Quaternary glaciation
Quaternary glaciation, also known as the Pleistocene glaciation, the current ice age or simply the ice age, refers to the period of the last few million years in which permanent ice sheets were established in Antarctica and perhaps Greenland, and fluctuating ice sheets have occurred elsewhere...
(i.e. the recent ice age). These cycles would have caused fluctuation in the diversity and extent of rainforests. If this was the case, the current diversity of the Amazon rainforest
Amazon Rainforest
The Amazon Rainforest , also known in English as Amazonia or the Amazon Jungle, is a moist broadleaf forest that covers most of the Amazon Basin of South America...
would be a recent speciation in a changing environment. However, the floral record from the Cerrejón Formation shows that the current diversity of the Amazon Rainforest can be traced back into the early Cenozoic.
Fauna
Feeding damage from insects is evident on some of the plant macrofossils from the Cerrejón Formation. One survey of plant macrofossils showed that around half of the studied specimens had been attacked by herbivorous insects. The insects that damaged the leaves were predominantly generalistGeneralist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
feeders, unlike modern Neotropical insects that are mainly specialist
Generalist and specialist species
A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources . A specialist species can only thrive in a narrow range of environmental conditions or has a limited diet. Most organisms do not all fit neatly into either...
herbivores. There is no evidence of the elevated insect-feeding diversity or host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
-specialized feeding associations that are seen in later Neotropical forests. The insect diversity in the Cerrejón Formation is low in comparison to the diversity of insects in Neotropical rainforests today, and it is likely that leaf damage was made by relatively few species.
Remains of the giant boid Titanoboa cerrejonensis have been found from a gray claystone
Claystone
Claystone is a geological term used to describe a clastic sedimentary rock that is composed primarily of clay-sized particles ....
layer underlying Coal Seam 90 in the Cerrejón mine. Titanoboa is the largest known snake to have ever existed, reaching an estimated length of 13 metres (42.7 ft). Eunectes, the anaconda
Anaconda
An anaconda is a large, non-venomous snake found in tropical South America. Although the name actually applies to a group of snakes, it is often used to refer only to one species in particular, the common or green anaconda, Eunectes murinus, which is one of the largest snakes in the world.Anaconda...
, is likely to be a close living analogue of Titanoboa.
A dyrosaurid crocodylomorph called Cerrejonisuchus improcerus
Cerrejonisuchus
Cerrejonisuchus is an extinct genus of dyrosaurid crocodylomorph. It is known from a complete skull and mandible from the Cerrejón Formation in northeastern Colombia, which is Paleocene in age. Specimens belonging to Cerrejonisuchus and to several other dyrosaurids have been found from the Cerrejón...
was described in 2010 from the Cerrejón Formation in the same layer as Titanoboa. It was a small dyrosaurid, and had the shortest snout length relative to its skull length of any dyrosaurid. Most dyrosaurids were marine, with long snouts adapted for catching fish. The short snout of Cerrejonisuchus is likely to have been an adaptation for a more generalized diet in a transitional aquatic environment. It is possible that Cerrejonisuchus was a food source for Titanoboa, as the two inhabited the same riverine environment. The anaconda has been documented consuming caiman
Caiman
Caimans are alligatorid crocodylians within the subfamily Caimaninae. The group is one of two subfamilies of the family Alligatoridae, the other being alligators. Caimans inhabit Central and South America. They are relatively small crocodilians, with most species reaching lengths of only a few...
s, a feeding habit that is similar to the inferred habit of Titanoboa. A second dyrosaurid, Acherontisuchus
Acherontisuchus
Acherontisuchus is an extinct genus of dyrosaurid neosuchian from Middle to Late Paleocene deposits of Colombia. The only known species is A. guajiraensis, whose name means "Acheron crocodile of the Guajira Peninsula".-Description:...
, was named in 2011 from the formation. With a large body and long snout, it resembles most other dyrosaurids.
Coal resources
The Cerrejón Formation contains extensive coal seams that are mined primarily at the Cerrejón mine. The coal is desirable for its low ash and sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
content and for its resistance to caking. Cerrejón is Colombia's largest coal producing mine, with most of the production exported to Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. It is the largest coal mining operation in Latin America
Latin America
Latin America is a region of the Americas where Romance languages – particularly Spanish and Portuguese, and variably French – are primarily spoken. Latin America has an area of approximately 21,069,500 km² , almost 3.9% of the Earth's surface or 14.1% of its land surface area...
, with an estimated 28.4 million tons mined in 2006.