PETROLEUM POTENTIAL OF OROGENIC BELTS

Orogeny denotes tectonic deformation resulting in distinct folding and thrusting, while epeirogeny produces and maintains the continental plateaus and the broad depressions which are covered by the sea. The sequence of events in part of an orogenic belt in Idaho provides positive pointers for petroleum exploration. The structural and stratigraphic patterns of deposition during the tectonic evolution in Paleozoic and Early Mesozoic time show that the most favorable areas for petroleum occurrence are the South Central Idaho block of miogeosynclinal sediments and East-Eastern Idaho block, or shelf zone, of the Cordilleran geosyncline. The Northern Idaho block is bounded on the south by the Osburn fault zone which has been cyclically active from Precambrian to Recent. Idaho's most promising gas show occurs in nonmarine Tertiary (Payette) sediments near Boise. Drilling and logistic costs should be comparable to other areas in the Rocky Mountains.