Municipalities

Municipality bold is capital	Department	Altitude of urban centre	Inhabitants 2015	Notes	Topography
Albania	La Guajira	320 m (1,050 ft)	26,606	[15]
Barrancas	La Guajira	40 m (130 ft)	34,619	[16]
Hatonuevo	La Guajira	50 m (160 ft)	24,916	[17]
Distracción	La Guajira	65 m (213 ft)	15,790	[18]
Fonseca	La Guajira	11.8 m (39 ft)	33,254	[19]
El Molino	La Guajira	240 m (790 ft)	8718	[20]
San Juan del Cesar	La Guajira	250 m (820 ft)	37,327	[21]
Villanueva	La Guajira	250 m (820 ft)	27,657	[22]
Urumita	La Guajira	255 m (837 ft)	17,910	[23]
La Jagua del Pilar	La Guajira	223 m (732 ft)	3213	[24]
Valledupar	Cesar	168 m (551 ft)	473,232	[25] [note 1]
Manaure Balcón del Cesar	Cesar	775 m (2,543 ft)	14,514	[26]
La Paz	Cesar	165 m (541 ft)	22,815	[27]
Pueblo Bello	Cesar	1,200 m (3,900 ft)	22,275	[28]
San Diego	Cesar	180 m (590 ft)	22,815	[29]
Agustín Codazzi	Cesar	131 m (430 ft)	50,829	[30]
Bosconia	Cesar	200 m (660 ft)	37,248	[31]
El Paso	Cesar	36 m (118 ft)	22,832	[32]
Becerril	Cesar	200 m (660 ft)	13,453	[33]
La Jagua de Ibirico	Cesar	150 m (490 ft)	22,283	[34]
Chiriguaná	Cesar	40 m (130 ft)	19,650	[35]
Curumaní	Cesar	112 m (367 ft)	24,367	[36]
Chimichagua	Cesar	49 m (161 ft)	30,658	[37]

Tectonic history

The tectonic history of the Cesar-Ranchería Basin at the North Andes Plate is influenced by the interaction of the Malpelo, South American and Caribbean Plates

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.^[38]

Compressive margin I

The Andean orogeny, active since the Cretaceous, has formed several volcanic arcs to the west of the Cesar-Ranchería Basin

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.^[39]

Back-arc basin

A back-arc basin is formed when a subducting plate creates accommodation space behind a volcanic arc

During the Cretaceous, the basins of northern South America were connected in a back-arc basin setting. The first phase of the Andean orogeny uplifted the Western Ranges and was characterised by magmatism in the Sierra de San Lucas in the northern Central Ranges, dated to the Albian to Cenomanian epochs. Sedimentation on the northern South American platform was of siliciclastic and carbonate character, the latter more dominant in the northern areas. In the Cesar-Ranchería Basin, this led to the deposition of the main source rock formations of the basin, most notably La Luna.^[40]

Compressive margin II

The uplift of the Serranía del Perijá made the Cesar-Ranchería Basin an intermontane basin

A second phase of compressive margin has been noted in the Cesar-Ranchería Basin by the strong differences between the sedimentary thicknesses of the Paleocene formations. During this stage in the basin development, the Cesar-Ranchería Basin was connected to the Middle Magdalena Valley to the west. The Paleocene Lisama Formation has a reduced thickness in the northern part of the Middle Magdalena Valley due to erosion, while the Paleocene section in the Cesar-Ranchería Basin is very thick. This has been explained by the tilt of the Sierra Nevada de Santa Marta and the formation of several thick-skinned thrust faults in the basin.^[40] The initiation of this compressive phase has been dated to the Maastrichtian, when tectonic uplift and deformation was active in the Central Ranges, to the west of the basin.^[41]

Stratigraphy

The stratigraphy of the Cesar-Ranchería Basin has been described by various authors. The coal producing area was mapped in 1961.^[42]

Paleontology

In the Cesar-Ranchería Basin several important fossils have been found, most notably in the Cerrejón Formation, together with the Lagerstãtte of the Honda Group at La Venta and the Paja Formation around Villa de Leyva, the most important fossiliferous stratigraphic unit of Colombia. The fossil flora and gigantic reptiles of the Cerrejón Formation provided abundant data on the paleo-ecology and climate of this first Neotropic environment of the Middle Paleocene.^[61]

Fossil content

Formation	Group	Species	Image	Notes
Cerrejón Fm.	Snakes	Titanoboa cerrejonensis		[62][63]
	Crocodylians	Acherontisuchus guajiraensis		[64][65]
		Anthracosuchus balrogus		[66][67]
		Cerrejonisuchus improcerus		[68][69]
	Turtles	Carbonemys cofrinii		[70][71]
		Cerrejonemys wayuunaiki		[72][73]
		Puentemys mushaisaensis		[74][75]
	Macroflora	Aerofructus dillhoffi, Menispermites cerrejonensis, M. guajiraensis, Montrichardia aquatica, Petrocardium cerrejonense, P. wayuuorum, Stephania palaeosudamericana, Ulmoidicarpum tupperi, Acrostichum sp., Amaryllidaceae sp., Anacardiaceae sp., Annonaceae sp., Apocynaceae sp., Araceae sp., Arecaceae sp., Dicotyledonae sp., Elaeocarpaceae sp., Euphorbiaceae sp., Fabaceae sp., Lauraceae sp., Malvaceae sp., Malvoideae sp., Meliaceae sp., Monocotyledoneae sp., Moraceae sp., Pinales sp., Pteridophyta sp., Salicaceae sp., Salvinia sp., Sapotaceae sp., Stenochlaena sp., Sterculioideae sp., Violaceae sp., Zingiberales sp.		[76][77] [78][79] [80][81] [82][83] [84][85] [86][87] [88][89] [90][91]
	Pollen	Proxapertites operculatus, Gemmatus phanocolpites gemmatus, Mauritidlites franciscoi, M. franciscoi var. pachyexinatus, Ctenolophonidites lisamae, Psilatriatriletes guaduensis, Foveotriletes cf. margaritae, Psilamonocolpites sp., Longapertites vaneenderburgi, Retidiporites magdalenensis		[92]
Manantial Fm. Hato Nuevo Fm.	Foraminifera	Rzehakina epigona, Globorotalia conicotruncana, Globigerina eugubina		[92]
	Pollen	Fovetriletes margaritae, Psilatriletes guaduensis, P. martinensis, Zonotricolpites cf. variabilis, Proxapertites opercutatus, P. maracaiboensis, P. humbertoides, Psilabrevitricolpites marginatus, Ctenolophonidites sp.		[92]
Molino Fm.	Foraminifera	Globotruncana fornicata, G. caniculata ventricosa, Globigerina cretacea, Gumbelina globulosa, G. excolta, Siphogenerinoides cretacea, S. bramlettei, Abathomphalus mayorensis, Guembelitria cretacea, Globorotruncanita conica, Gansserina gansseri, Racemiguembelina fructicosa, Heferohelix striata, H. navarroensis, Pseudoguembelina excolata, P. palpebra, Globotruncana aegyptiaca		[93]
	Pollen	Echitriporites suescae, Echimonocolpites ruedae, Foveotriletes margaritae, Mauritildites protofranciscoi, Psilatriletes guaduensis, Araucariacites sp., Rugutriletes sp., Proxapertites operculatus, P. psilatus, Spiniferites cf. ramosus, Achomosphaera sp., Dinogymnium sp.		[94]
La Luna Fm.	Molluscs, & foraminifera	Neoptychites sp., Holitoides sp., Fagesia sp., Prothocantoceras sp., Eucalycoceras sp., Cloleopoceras sp., Baroisiceras sp., Baculites sp., Tissotis sp., Perinoceras aff. moureti, Whiteinella archeocretacea		[94][95]
Aguas Blancas Fm.	Molluscs & foraminifera	Ostrea scyfax, Exogyra toxaster, Choffatella decipiens, Cheloniceras sp., Pseudosaynella sp., Dufrenoya sp., Turrulitas sp., Acanthoceras sp., ?Montelliceras sp., ?Calvoceras sp., Orbitolina conica texana, Heterohelix reussi, Marginotruncana sinuosa		[94][95]
Río Cachirí Gp.	Molluscs	Acrospirifer olssoni; Spirifer kingi, Leptaena boyaca, Fenestella venezuelansis, Neospirifer latus, Composita subtilita, Phricodrotis planoconvexa, Pecten sp.		[96]

Paleozoic to Early Mesozoic

During deposition of the Río Cachirí Group around 380 Ma, the Cesar-Ranchería Basin was located at the edge of the Paleo-Tethys Ocean, by Stampfli & Borel

The Cesar-Ranchería Basin is underlain by Neoproterozoic basement. The Sierra Nevada Metamorphic Belt was formed during the Grenville orogeny, when the supercontinent Rodinia was formed due to the collision of Amazonia, Baltica and Laurentia. The granulites and gneisses of the complex metamorphosed 1.5 to 1.0 billion years ago.^[97] The phyllites and quartzites of the Perijá Formation were formed during the Early Paleozoic and are related to the Caledonian orogeny.^[60] The shales of the Río Cachirí Group were deposited in the Devonian and contain abundant fossils of brachiopods, bryozoa, corals and crinoids. The formation is time-equivalent with the fossiliferous Floresta and Cuche Formations of the Altiplano Cundiboyacense. The sediments were deposited in an epicontinental sea at the edge of the Paleo-Tethys Ocean, the last remnant of the Rheic Ocean.^[59][98]

During the Early Carboniferous (Pennsylvanian), the Cesar-Ranchería Basin experienced a regressional phase with the deposition of sandstones and limestones.^[99] The Early Permian is represented by the Manaure Formation, a sequence of sandstones and conglomerates. The formation of Pangea in the Late Permian to Early Triassic led to the formation of a metamorphic complex, named Sevilla. The gneisses, amphibolites, greenschists and marbles are dated to 280 to 250 Ma.^[57] The basin was intruded by granites during the Early to Middle Jurassic being accompanied by volcanics and volcanoclastic sediments such as the basalts, tuffs, sandstones and breccias found in the Sierra Nevada de Santa Marta. This magmatic phase correlated with the sedimentary sequence of the La Ge Group, subdivided into the Tinacoa and Macoíta Formations, a series of tuffaceous sandstones, limestones, shales and siltstones.^[56]

Paleogeography of Colombia
	170 Ma
	150 Ma
	120 Ma
	105 Ma
	90 Ma
	65 Ma
	50 Ma
	35 Ma
	20 Ma
	Present

Early to Late Mesozoic

The sedimentary sequence drilled in the basin starts with the La Quinta Formation, that is found in a widespread area across northern Colombia and Venezuela. The formation of sandstones, basalts, conglomerates and volcanic ash was deposited in a lacustrine depositional environment in a rift basin setting related to the break-up of Pangea and has been dated to the Late Jurassic and earliest Cretaceous, 160 to 140 Ma. The formation is time-equivalent with the Girón Formation of the Eastern Ranges.^[55] The Early Cretaceous Río Negro Formation, a unit composed of sandstones, conglomerates and siltstones, is very variable in thickness in the basin and associated with continental sedimentation on rift shoulders to a post-rift setting. The formation is time-equivalent with the Tibasosa Formation of the Eastern Ranges and the Tambor Formation of the Middle Magdalena Valley.^[100] The fossiliferous limestones and shales of the Lagunitas Formation, lower member of the Cogollo Group, contain beds of dolomite and are indicative of a shallow, saline environment. The formation is correlated with the Rosablanca Formation of the Middle Magdalena Valley and western Eastern Ranges and the Tibú Formation of the Maracaibo Basin. The unit is the deepest source rock for the oils in the Cesar-Ranchería Basin.^[53] The upper member of the Cogollo Group, the Aguas Blancas Formation, presents a large lateral variability in lithologies. Black biomicrites and fossiliferous limestones are indicative of a middle to outer platform environment, while sandy shales and glauconitic sandstones indicate a shallow marine environment. The variation in lithologies and organic content of this source rock formation is associated with basinal relative sea level changes and the organic-rich strata to the Aptian anoxic event, dated to approximately 120 million years ago.^[52][101]

The Lower Cretaceous series is followed by the deposition of the regional main source rock of northern Colombia and northwestern Venezuela, La Luna. The world class source rock contains high levels of Total Organic Carbon, comparable to the Kimmeridge Clay Formation of the basins of the North Sea.^[52] The ammonite-rich shales and biomicrites of La Luna were deposited during the global anoxic event of the Cenomanian-Turonian (around 90 Ma) characterised by a maximum flooding surface sequence.^[102] The highly organic formation is time-equivalent with the Querecual Formation of eastern Venezuela, the Chipaque and Gachetá Formations of the Colombian Eastern Ranges and Llanos Basin respectively and the Celendín Formation of northeastern Peru.^[51] The Late Cretaceous Molino Formation, laterally equivalent with the Colón and Mito Juan Formations of the Maracaibo and Catatumbo Basins, and the Umir Formation of the Middle Magdalena Valley, consists of calcareous shales intercalated by sandstones. The widespread correlation of this unit with the neighbouring formations indicates an open marine environment all across northwestern South America.^[48]

Paleogene to recent

At the end of the Cretaceous, the tectonic regime changed to a compressive phase, due to the movement of the Caribbean Plate.^[103] The Early Paleocene deposits of the Hato Nuevo and Manantial Formations show a more calcareous character in the north, while the Cesar Sub-basin contained more siliclastic sedimentation, represented in the Barco Formation, consisting of more lithic fragments than the equivalent of the Llanos Basin. Compression continued during the Paleocene, with uplifted areas to the northwest and southeast and volcanism in the proto-Caribbean.^[104] The global climate was very hot in this period and in the restricted basin between the two forming mountain ranges, a unique ecosystem developed; the first Neotropic forest. In this hot and humid environment, the largest species of reptiles since the extinction of the dinosaurs evolved, of which Titanoboa was the main predator. It has been estimated on the basis of the fossil flora, pollen and large reptiles that the mean annual temperature was between 28.5 and 33 °C (83.3 and 91.4 °F) and yearly precipitation ranging from 2,260 to 4,640 millimetres (89 to 183 in) per year.^[105] Provenance analysis of the sediments of the Los Cuervos and Cerrejón Formations show a predominant west to east paleocurrent, followed by a more southeastern flow.^[106] A secondary source of sediments was the growing Serranía del Perijá.^[107]

During the Eocene and Early Oligocene, the western part of the basin was exposed and modest deposition concentrated in the Ranchería Sub-basin. The previously humid ecosystem changed to an arid plain environment.^[108] In contrast, the Neogene conglomerates of the Cuesta Formation show a larger thickness in the southwestern part of the basin, close to the connected Middle Magdalena Valley.^[109] During this period, especially in the Late Miocene to Pliocene, the Oca and Bucaramanga-Santa Marta Faults were tectonically active,^[110] which is still observed in the present day.^[111] Ongoing uplift and reverse faulting created the intermontane fluvial-dominated basin architecture of today.^[109]

Petroleum geology

Despite various detailed studies and the similarities with neighbouring hydrocarbon rich provinces as the Maracaibo, Catatumbo and Middle Magdalena Basins, the Cesar-Ranchería Basin is relatively underexplored.^[112] Minor gas production is centered in the south of the Cesar Sub-basin, but most exploration wells were drilled before the 1950s. As of 2007, 14 wells were drilled in the basin.^[113] A major project to reprocess and interpret 2D seismic lines has been conducted in 2006.^[114] The basin is considered a major target for coal bed methane (CBM), due to the major coal deposits of the Los Cuervos and Cerrejón Formations. Total probable gas reserves for CBM are estimated at between 12.8 and 25.1 trillion cubic feet (360×10^⁹ and 710×10^⁹ m³),^[13]

Vitrinite reflectance data from several source rocks of the Cesar-Ranchería Basin show present-day mature to overmature Cretaceous formations (La Luna, Aguas Blancas and Lagunitas Formations) and (marginally) mature Paleocene source rocks, mainly Los Cuervos.^[4] Apatite fission track analysis and modeling combined with vitrinite reflectance data, showed the Cretaceous units have a significant potential for hydrocarbon generation.^[115] The Lagunitas and Aguas Blancas Formations are heavily fractured and considered a good potential fractured reservoir, while the Río Negro Formation has been analysed to be cemented and bearing low porosities.^[116]

Mining

Mining in Cerrejón

Coal mining in the Cesar-Ranchería Basin is concentrated in the northeast, with Cerrejón spanning the municipalities Albania, Barrancas and Hatonuevo, and in the southwest, with La Francia in the municipalities Becerril and El Paso. At Cerrejón, the coal is excavated from the Cerrejón Formation and in La Francia from the time-equivalent Los Cuervos Formation. Coal is also mined in Agustín Codazzi, Chiriguaná and La Jagua de Ibirico. The total coal production of the Cesar-Ranchería Basin in 2016 was nearly 81 Megatons.^[7] Minor gold mining was active in Valledupar in 2008.^[117]

A study published in 2015 on the La Quinta Formation, shows the presence of 1.45% of copper, present mainly in malachite mineralisations in the volcanoclastic beds of the formation.^[118]

Notes

References

Bibliography