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 Mountain Range (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long and wide (widest between 18°S ...

. The Andean foreland basins in the Amazon River's

catchment area A catchment area in human geography, 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 as ...

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 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 rocks by ...

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 chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...

and in the 1970s their hydrocarbon production increased greatly. A 2018 synthesis of previous research looked at the sedimentary record of eight foreland basins and 5 hinterland basins to reconstruct a composite model for their development as a single Andean foreland basin system. During the Mesozoic, rapid accumulation of sediment occurred at the onset of back arc extension between 250 and 140 Ma. A dramatic pulse of sediment accumulation occurred during the late Cretaceous linked to the inception of large scale shortening, occurring from 70 to 60 Mya in the northern basins and 100-600 Mya in the southern basins. The Paleogene saw a phase of limited accumulation due to a lull of Andean shortening, 60-20 Mya in the south, 50-30 Mya in the north. From 20 to 30 Ma, rapid accumulation occurred with the highest sedimentation rate recorded in the central Andes, between 3–8 km of sediment was accumulated. Detrital Zircon data aided in identifying sediment source reversals from cratonic sediment sources to magmatic orogenic sources. This inflection occurred in the northern Andes from 70 to 30 Ma, depending on the basin, central Andes around 50 Ma, and in the southern Andes around 100 Ma. Interplay of local climate, uplift histories, shortening and subducting slab geometries influenced the development of individual foreland basins and shaped continent scale drainage patterns, offshore sediment dispersal and ecological development on the South American continent.

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Further reading