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RAEDEKE, LINDA D., Chevron Overseas Petroleum Inc., San Ramon, CA

ABSTRACT: Source Rocks of the Sub-Andean Basins

Seven source rock systems were mapped using a consistent methodology to allow basin comparison from Trinidad to southern Chile.

Silurian and Devonian systems, deposited in passive margin and intracratonic settings, have fair-good original oil/gas potential from central and northern Bolivia to southern Peru. Kerogens range from mature in the foreland to overmature in the thrust belt.

Permian to Carboniferous deposition in local restricted basins formed organic-rich shales and carbonates with very good original oil/gas potential, principally in northern Bolivia and southern Peru.

Late Triassic to early Jurassic marine shales and limestones, deposited in deep, narrow, basins from Ecuador to north-central Peru, have very good original oil potential, now at wet-dry gas maturity. Locally, in the Cuyo rift basin of northern Argentina, a Triassic lacustrine unit is a very good, mature oil source.

Early Cretaceous to Jurassic marine incursions into the back-arc basins of Chile-Argentina deposited shales and limestones. Although time transgressive (younging to the south), this system is the principal source in southern back-arc basins, with best potential in Neuquen, where three intervals are stacked!

A late Cretaceous marine transgressive shale is the most important source in northern South America. The unit includes the La Luna and equivalents extending from Trinidad through Venezuela, Colombia, Ecuador, and into northern Peru. Elsewhere in South America upper Cretaceous marine-lacustrine rocks are a possible source in the Altiplano and Northwest basins of Bolivia and Argentina.

Middle Miocene to Oligocene source system includes shallow marine, deltaic, and lacustrine sediments from Trinidad to northern Peru.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.