The Llanos Basin () or Eastern Llanos Basin () is a major sedimentary basin of in northeastern Colombia. The onshore foreland on Mesozoic rift basin covers the departments of Arauca, Casanare and Meta and parts of eastern Boyacá and Cundinamarca, western Guainía, northern Guaviare and southeasternmost Norte de Santander. The northern boundary is formed by the border with Venezuela, where the basin grades into the Barinas-Apure Basin.
Description
The northeastern part of Colombia is characterized by its wavy plains, called Llanos Orientales, as part of the bigger Llanos that extend into Venezuela. The landscape is similar to a savanna and is poor in trees. It is located between the Eastern Ranges of the Colombian Andes in the west, the Vaupés Arch in the south and the Guiana Shield in the east.
Geologically, the Llanos Basin underlies this typical landscape of the Llanos. An area where transport occurs mostly by small boats along the many rivers and the "buses of the Llanos", the Douglas DC-3 planes. The basin covers an area of and contains a stratigraphic column from the Paleozoic to recent. Several of the formations in the basins are source rocks (Gachetá, Los Cuervos, Carbonera C8), reservoir rocks (Mirador, Barco, Guadalupe and the uneven numbered members of Carbonera). Seals are formed by the shaly intervals (even numbered) of the Carbonera Formation, Los Cuervos, and León.
The basin is the main petroleum producing basin of Colombia, with four of the nations biggest oil fields located in the Llanos Basin. Major fields are Rubiales, Colombia's biggest and most recent giant discovery sealed by a complex of hydrodynamic processes, and Caño Limón, at the border with Venezuela.
Major concerns in the basin for the production of petroleum are biodegradation, hydrocarbon migration, fault seal capacity and water flow.
Hydrography
The Llanos Basin is crossed by numerous rivers, all belonging to the Orinoco watershed. From north to south:
Arauca River
Bojabá
Margua
Orinoco River
Capanaparo
Cinaruco
Tomo
Elvita
Bita
Meta River
Casanare
Cravo Norte
Ele
Tame
Ariporo
La Fortaleza
Guachiría
Pauto
Cravo Sur
Cusiana
Upía
Guavio
Lengupá
Guatiquía
Manacacías
Metica
Guayuriba
Guaviare River
Ariarí
Güejar
Guayabero
Duda
Losada
Uvá
Siare
Vichada River
Muco
Tillava
Flora and fauna
Fauna
Among other species, Lynch's swamp frog (Pseudopaludicola llanera) is endemic to the Llanos, with the species epithet referring to the plains. Also the whip scorpion Mastigoproctus colombianus is reported from the Llanos Basin.
Geodynamic situation
The country of Colombia spreads out over six tectonic plates, clockwise from north: Caribbean Plate North Andes Plate South American Plate Malpelo Plate Coiba Plate Panama Plate
The Llanos Basin is situated entirely on the South American Plate, bordering the North Andean Block or North Andean microplate in the west. The basin is one of three Colombian basins on the South American Plate, to the south the Caguán-Putumayo Basin and to the southeast the Vaupés-Amazonas Basin. The northern boundary of the Llanos Basin is formed by the Colombia-Venezuela border where the basin grades into the Barinas-Apure Basin on the Venezuelan side. The Catatumbo Basin, representing the Colombian portion of the larger Maracaibo Basin borders the Llanos Basin in the northwest and the western boundary is formed by the foothills (Piedemonte) of the Eastern Cordillera Basin, the sedimentary basin covering the Eastern Ranges of the Colombian Andes.
Tectonics
The basin is bound to the west by the Eastern Frontal Fault System, a long fault system connecting the North Andes and South American Plates and thus the Eastern Cordillera Basin and the Llanos Basin. The fault system has an average strike of 042.1±19, but this orientation varies greatly along its course. The 1827, 1834, 1917, 1967, 1995, and 2008 earthquakes were all caused by fault movement as part of the system.
Basin history
The tectonic history of the Llanos Basin, a foreland basin formed on top of Mesozoic rift basins, Paleozoic metasediments and Precambrian basement underlain by continental crust, goes back to the Early Jurassic.