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 lithosphere ...

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

Andes mountains The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S l ...

. 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 ar ...

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 as ...

accommodation", likely corresponding to ancient continent-wide faults. From the

Bolivian Orocline An orocline — from the Greek words for "mountain" and "to bend" — is a bend or curvature of an orogenic (mountain building) belt imposed after it was formed. The term was introduced by S. Warren Carey in 1955 in a paper setting forth how comp ...

(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 Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rock ...

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 crude ...

and in the 1970s their hydrocarbon production increased greatly.

References

Further reading