The Andean foreland basins or Sub-Andean basins are a group of

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithospher ...

s located in the western half of South America immediately east of the

Andes mountains The Andes, Andes Mountains or Andean Mountains (; ) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range i ...

. The Andean foreland basins in the Amazon River's

catchment area In human geography, a catchment area is the area from which a location, such as a city, service or institution, attracts a population that uses its services and economic opportunities. Catchment areas may be defined based on from where people are ...

are known as the Amazonian foreland basins. In part sediment accumulation, uplift and subsidence of the Andean foreland basins is controlled by transverse zones of "

structural A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such ...

accommodation", likely corresponding to ancient continent-wide faults. From the Bolivian Orocline (20° S, also known as Arica Deflection or Arica Elbow) north these zones of accommodation runs with a NEE-SWW orientation and south of the orocline they run with a NW-SE orientation. The Andean foreland basins in Bolivia have largely accumulated continental sediments, most of them of clastic nature. Beginning in 1920 the Ecuadorian and Peruvian basins were explored for

petroleum Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...

and in the 1970s their hydrocarbon production increased greatly.

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Further reading