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Rift basins contain only 5% of the earth's sedimentary volume yet yield 10% of the world's hydrocarbon production. They consist of graben, half-graben, tilted fault blocks, and synclinal downwarps and are commonly preserved along continental margins. The Newark rift system represents the sediments preserved
along the eastern seaboard which were deposited during the Triassic-Jurassic rifting of Pangea.
Continental rifting creates a linear series of tectonic depressions which form rift valleys. Commonly, these valleys are ponded, yielding long, narrow, deep lakes. The best modern example of this geologic setting is the East Africa rift system. Lake Tanganyika is 300 mi (483 km) long, 40 mi (64 km) wide and as deep as 4,000 ft (1,220 m). A fluviolacustrine depositional system is developed here where deltaic, littoral, shallow lake, and deep lake facies are well defined. Drastically fluctuating lake levels cause cyclic onlap and offlap resulting in a finely bedded stratigraphic section. The interfingering of these facies conveniently create a favorable source (deep lake) and reservoir (littoral, deltaic) relationship.
The lakes in rift valleys support prolific biologic ecosystems. The equatorial lakes are thermally stratified inducing anoxic conditions which preserve the organic material raining down from the surface. East African lake-bottom sediments often exceed 10% TOC. Some organic rift lake shales from the Cabinda basin contain more than 20% TOC. The Green River formation lake shales contain as much as 40% TOC. The Newark shales contain between 2 and 35% TOC and are up to 4,000 ft (1,220 m) thick. The shales from these basins often qualify as oil shales. The quantities cited are well above the general requirements for legitimate hydrocarbon source rocks.
There are other rift systems, analogous to the Newark rift system, that produce significant quantities of hydrocarbons. The Cabinda, Angola, and the Reconcavo (Brazil) basins of the southern hemisphere combined produce nearly 200,000 BOPD and have total recoverable reserves in excess of 2 billion bbl. There is notable production from rift basins in Australia, the southern North Sea, the Rhine graben, and China. Reservoir rocks are fluviolacustrine, deltaic, and alluvial siliciclastics, fractured shales, freshwater carbonates, intrusives, and turbidites. Attractive reservoir sandstones with up to 25% porosity are documented in the Newark basins.
The Newark rift system remains essentially unexplored. The archaic theory that "oil does not occur in continental settings" has stifled exploration. There have been encouraging signs. Oil has been recovered from the Richmond basin, a major discovery was made in the Triassic rift sediments of western Morocco in 1981, and significant oil and gas shows were found in the buried Georgia rift basin. Obviously the Newark rift system needs to be reevaluated. The current state of knowledge indicates that all of the necessary criteria of oil and gas generation and accumulation have been met. These basins warrant a thorough investigation.
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