The oil fields of the Tertiary basins of Sumatra, Java, and Borneo have produced more than one billion barrels of oil to the end of 1940 from sands predominantly of Miocene and Pliocene age. Two major geosynclinal belts, the circum-Asiatic geosyncline and the Australo-Pacific geosyncline, meet in the East Indian archipelago. The Tertiary basins of Borneo are outside these two belts, lying near the edge of the Asiatic continent, constituting intra-continental geosynclines. An accompanying geotectonic map locates the oil-producing areas.

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