--> ABSTRACT: South American Subandean Basins: Tectostratigraphic Evolution and Petroleum Habitats, by Carlos M. Urien and Timothy P. Garvey; #91022 (1989)

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South American Subandean Basins: Tectostratigraphic Evolution and Petroleum Habitats

Carlos M. Urien, Timothy P. Garvey

In South America a roughly south-trending tectogenic belt extends more than 5,000 km areally and contains 20 Mesozoic sedimentary basins that lie west of the South American cratogenes and east of the Andean orogenic belt. These Subandean basins have evolved through three main northward-migrating tectonic regimes since Paleozoic time; each respective phase influenced basin geometry, styles of sedimentation, and, in turn, resultant areas of hydrocarbon accumulation.

The first two of these three tectonic phases were associated with the evolution of a migratory arc trench system that developed in response to nascent subduction of oceanic crust beneath South America. In an early to middle Mesozoic phase, a series of locally rifted grabenlike basins developed and were filled with volcaniclastic detritus of primarily nonmarine origin. A second phase occurred during the late middle and late Mesozoic in the south and through the early Tertiary in the north as back-arc flexural subsidence and perhaps crustal divergence led to the development of a complex network of partially interconnected marginal basins between the arc and cratonic realms. Marine and nonmarine sedimentation occurred in all of the basins. Several system-wide depositional cycles are reco nized and are commonly marked by onlapping basal transgressive clastic units which were deposited at times coincident with postulated eustatic rises in sea level. Sedimentary provenances existed within both the arc and craton.

A final compressional phase during Tertiary time has incorporated the Subandean basins into retroarc foreland and intra-arc settings within the Andean contractional continental margin arc trench system. The Mesozoic and early Tertiary sedimentary basins along with older Paleozoic sedimentary suites, which contain the major hydrocarbon source, reservoir, and seal rocks, have been structurally deformed by east-west compression and, in most places, covered by the Tertiary east Andean clastic/volcaniclastic prism.

Commercial hydrocarbon accumulations have traditionally been found in the mildly deformed hinge areas on the eastern cratonic flanks of the Subandean basins. Recently, new structural models along with several significant discoveries have focused attention on the retroarc fold and thrust regions where numerous additional large fields are bound to exist.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.