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Abstract

Exploration in many nonmarine sequences requires an understanding of what conditions permit the development of lacustrine hydrocarbon source rocks. Although quantitative predictions are not yet possible, qualitative assessments of the probability of source presence may be made.

To establish the presence of a lacustrine water body requires an understanding of the distribution of topographic depressions and paleoclimatic conditions. The lacustrine water body needs to be areally significant and long-lived to permit the development of substantial volumes of organic-rich rocks. This typically means that “commercial” volumes of lacustrine source rocks can only develop in lakes of tectonic origin.

Paleoclimate and paleogeography not only play major roles in controlling distribution of lake bodies but also influence water chemistry. Saline lakes develop when evaporation exceeds precipitation and during geologic episodes of maximum continentality. Fresh-water lakes develop when precipitation exceeds evaporation and along continental margins, even during times of high continentality. Water chemistry controls the nature and level of organic productivity and influences preservation by altering water density and oxygen solubility and determining availability of other chemical oxidizing agents (e.g., sulfates and nitrates).

The most favorable conditions for development of hydrocarbon sources occur in lakes of moderate water depth (50-400 m) at low latitudes and altitudes. Such lakes typically exhibit elevated levels of organic productivity and preservation.

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