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Overthrust Belts as Sites of Major Oil and Gas Fields

Johann-Christian Pratsch

Overthrust belts are linear areas of regional extent where older rocks are lying on younger rocks as a result of major tectonic transport and deformation. Overthrust belts have been formed throughout geologic history and are forming today. They exist inside crustal plates and at the contact zones between crustal plates. Major and minor oil and gas fields occur in overthrust belts across the world; however, industry has greatly overestimated the effects of traps, reservoirs, or geologic timing as explanations for such hydrocarbon occurrences. Most important for an understanding of past results and for predictions of future success of exploration in overthrust belts is knowledge of generative depocenters. They are parts of the tectonic thrust complex, or of the overthrust s ction. All presently known oil and gas fields in overthrust belts are explainable in terms of presence of mature source beds in a specific regional setting and of vertical and lateral hydrocarbon migration. Failure of past exploration in overthrust belts similarly is related to adverse geochemical parameters or to insufficient hydrocarbon migration. Examples from Wyoming, Colombia, Austria, Italy, and more locations serve as critical data. In addition, data from unsuccessful efforts in the United States, Germany, and Greece furnish equally important criteria for future overthrust belt hydrocarbon exploration.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.