Cesar-Ranchería Basin
The Cesar-Ranchería Basin is a sedimentary basin in northeastern Colombia. It is located in the southern part of the department of La Guajira and northeastern portion of Cesar. The basin is bound by the Oca Fault in the northeast and the Bucaramanga-Santa Marta Fault in the west. The mountain ranges Sierra Nevada de Santa Marta and the Serranía del Perijá enclose the narrow triangular intermontane basin, that covers an area of. The Cesar and Ranchería Rivers flow through the basin, bearing their names.
The basin is of importance for hosting the worldwide tenth biggest and largest coal mine of Latin America, Cerrejón. The coals are mined from the Paleocene Cerrejón Formation, that also has provided several important paleontological finds, among others Titanoboa cerrejonensis, with an estimated length of and a weight of, the biggest snake discovered to date, the giant crocodylians Cerrejonisuchus improcerus, Anthracosuchus balrogus and Acherontisuchus guajiraensis, and the large turtles Carbonemys cofrinii, Puentemys mushaisaensis and Cerrejonemys wayuunaiki. Various genera of flora, as Aerofructus dillhoffi, Menispermites cerrejonensis, M. guajiraensis, Montrichardia aquatica, Petrocardium cerrejonense and P. wayuuorum, Stephania palaeosudamericana and Ulmoidicarpum tupperi among others, have been found in the Cerrejón Formation, the sediments of which are interpreted as representing the first Neotropic forest in the world. Mean annual temperature has been estimated to have been between and yearly precipitation ranging from per year.
The Cesar-Ranchería Basin is relatively underexplored for hydrocarbons, compared to neighbouring hydrocarbon-rich provinces as the Maracaibo Basin and Middle Magdalena Valley. The first oil exploration was conducted in 1916 and several wells have been drilled since then. The basin is estimated to host the second-largest reserves of coal bed methane of Colombia, with 25% of the country's total resources. The coal of the basin is mined in several quarries, most notably Cerrejón and La Francia. The total production of coal from the Cesar-Ranchería Basin in 2016 was almost 81 Megatons.
Etymology
The name of the basin is taken from the Cesar and Ranchería Rivers.Description
The Cesar-Ranchería Basin is an intermontane foreland basin enclosed by two main mountain ranges; the northernmost Andean Serranía del Perijá in the southeast of the basin and the triangular Sierra Nevada de Santa Marta to the northwest. The northeastern limit is sharply formed by the dextral strike-slip Oca Fault, while the Bucaramanga-Santa Marta Fault forms the boundary to the west. The faults form the border with the Guajira Basin and Middle Magdalena Valley respectively. The basin has a general orientation of 30 degrees from north. The Cesar-Ranchería Basin is subdivided into the Cesar Basin in the west, named after and hydrographically dominated by the Cesar River in the Magdalena River watershed, and the Ranchería Basin in the east. The latter is named after the Ranchería River flowing towards the Caribbean Sea and separated from the Cesar River by the intrabasinal Valledupar High, an extension of the Verdesia High. The southeastern edge of the basin is formed by the border with Venezuela. In total, the basin covers an area of.The sedimentary sequence inside the basin comprises Jurassic to Quaternary rocks, underlain by Paleozoic basement. An important unit is the Paleocene Cerrejón Formation, hosting major coal reserves, excavated in several open-pit mines of which Cerrejón in the northeast of the basin is the most striking. Cerrejón is the tenth biggest coal mine worldwide and the largest of Latin America. The formation provides low-ash, low-sulphur bituminous coal with a total production in 2016 of almost 33 Megatons. Other coal mines include La Francia, in the western Cesar portion of the basin. The total coal production of the Cesar-Ranchería Basin in 2016 was nearly 81 Megatons.
The Cesar-Ranchería Basin is located at the northern edge of the South American Plate, close to the Caribbean Plate. During the Mesozoic and early Cenozoic eras, the basin was connected to the Magdalena River basins and the Sinú-Jacinto Basin in the west and the Maracaibo Basin, of which the Catatumbo Basin forms the Colombian part, in the east. Compressional tectonic movement commenced in the Late Paleogene, creating an intermontane foreland basin enclosed by the Serranía del Perijá and the Sierra Nevada de Santa Marta. The east-west oriented dextral strike-slip Oca Fault in the north is estimated to have been active since the Early Eocene with a total displacement of. The Bucaramanga-Santa Marta Fault was a Jurassic extensional rift fault, reactivated as oblique reverse fault in the Oligocene.
Petroleum exploration in the Cesar-Ranchería Basin commenced in 1916. The first exploitation of hydrocarbons was performed in 1921 and 1922 at Infantas in the Ranchería Basin and in 1938 the first well was drilled in the Cesar Basin. The basin is relatively underexplored. The first 2D seismic lines were shot in the late 1970s and 1980s. The deepest well, El Paso-3, drilled to a total depth of into the Cretaceous Aguas Blancas Formation. Oil extracted from the La Luna and Lagunitas Formations in the Papayal-1 well provided API gravities between 27 and 42. Gas is produced from the Colón and La Luna Formations at the Maracas Field in the extreme southwest of the basin. A 2012 study of the yet-to-find potential of the Colombian sedimentary basins provided estimates of total generated oil in the Cesar-Ranchería Basin. The basin is considered to be the second-most prospective of Colombia in coal bed methane with 25% of the country's total resources. Total probable gas reserves from this unconventional source have been estimated in 2014 at between, up from an estimate ten years before of.
Municipalities
Tectonic history
The tectonic history of the Cesar-Ranchería Basin has been subdivided into six phases. The basin started as a passive margin in the Paleozoic, followed by a compressive margin in the Late Permian to Triassic, a phase of rifting in the Jurassic. Subsequently, the basin experienced a back-arc basin setting in the Cretaceous, a second compressive margin during the Late Cretaceous to Eocene and a final intramontane phase since the Eocene.Passive margin
The passive margin phase was characterised by the deposition of shallow marine sediments in three periods, divided by unconformities. The unconformities have been dated to the Ordovician-Silurian, Early Carboniferous and Early Permian respectively. The events were accompanied by acidic plutons found all across northern South America.Compressive margin I
Sediments from the Late Permian to Triassic periods are absent in the Cesar-Ranchería Basin, but evidenced in the surrounding orogens. Intense magmatism and metamorphism affected the Sierra Nevada de Santa Marta and the Central Ranges of the Colombian Andes. The compressive phase is associated with the Hercynian orogeny, leading to the formation of Pangea.Rift basin
The break-up of Pangea in the Early Jurassic generated a sequence of rift basins in northern South America, surrounding the proto-Caribbean. The area of the present-day Serranía del Perijá was a continental rift, while basins to the west were marine in origin. Regional fault lineaments formed during this phase, that during the compression of the Andean orogenic stage were reactivated as thrust faults. The current compressional faults of the Cesar-Ranchería Basin are high-angle.The rift basin setting spanned the Jurassic period and was followed by post-rift sedimentation in the Early Cretaceous, evidenced by the Río Negro and Lagunitas Formations.