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Lacustrine rocks are a significant component of many rift-valley sequences. Comparisons of both active and ancient rift valleys indicate that the lacustrine facies are commonly rich in organic matter and may be important sources for oil. For example, Holocene sediments in Lake Tanganyika and Cretaceous lacustrine rocks in west Africa contain as much as 12% and 20% TOC, respectively.
The Newark Supergroup contains abundant lacustrine rocks. The widespread occurrence of "black shales," the general similarity to known organically rich rift systems, and a few isolated geochemical analyses have caused some speculation about the potential of the Newark Supergroup to be an effective source of oil and gas.
Sufficient geochemical analyses are available from lacustrine rocks in the Newark, Connecticut, and Deep River basins to evaluate their potential as hydrocarbon sources. In general, both the quantity and quality of organic matter in these rocks are less than that required for potential source rocks. Some samples do qualify as potential sources, but the total generative capacity of lacustrine rocks within these basins is relatively small.
Despite these results, the numerous unexplored buried Newark rift basins retain some potential for containing significant hydrocarbon source rocks. Analyses of the lacustrine rocks from the Newark basin indicate that the original sediments were rich in oil-prone organic matter. However, the unusual water chemistry of this lake resulted in the almost complete destruction of the organic matter by sulfate-reducing bacteria. Slight changes in water chemistry in other Newark lakes could have resulted in large volumes of organically rich sediment being preserved in these unexplored basins.
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