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Petroleum Geoscience

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The influence of intraplate structural accommodation zones on delineating petroleum provinces of the Sub-Andean foreland basins

Tellus Division, Robertson Research International Limited, Llandudno, North Wales LL30 1SA, UK(e-mail: jmj@robresint.co.uk)

The Sub-Andean foreland region is summarized in a series of palaeogeographical maps. Various time-slices show important basin-forming processes and the extent and evolution of principal depositional elements. Based on spatial and temporal changes in palaeodepositional setting, the Sub-Andean region can be subdivided longitudinally into a number of tectonostratigraphic domains. The differential amount of subsidence between two adjacent tectonostratigraphic provinces or sub-provinces has been taken up across, complex, broad, transverse, transcontinental accommodation zones, which probably represent the multiphase reactivation of pre-existing fault systems in the underlying basement. Two predominant sets of basement lineaments are recognized: ENE–WSW and NW–SE. Both sets of lineaments occur as major structural anisotropies throughout the basement rocks of South America, providing zones of weakness, which were repeatedly reactivated and, at least in part, controlled: (a) the geometry of inter- and intra-cratonic rifting; (b) rates of subsidence and uplift along the Andean depositional axis; (c) the position of basin-bounding and intra-basinal highs/arches; (d) the structural geometry of the Andean Deformation Zone, correlating with changes in deformational style and major deflections; and (e) the location of magmatism.

Based primarily on source rock age, it is suggested that these transverse, structural accommodation zones had a profound effect on source rock distribution and hydrocarbon occurrence; subdividing the Sub-Andean region into five petroleum provinces/megasystems: a ‘Northern’ Late Cretaceous (La Luna Formation and equivalents); a ‘Western’ Late Palaeozoic–Early Mesozoic (Permian and Upper Triassic to Lower Jurassic source rocks); a ‘Central’ Palaeozoic (Late Devonian and Silurian); an ‘Eastern’ Tertiary; and a ‘Southern’ Mesozoic.

KEYWORDS: Sub-Andean, megasequences, petroleum provinces, crustal lineaments