Petroleum Exploration in Western United States in Light of Principles of Comparative Tectonics
Lee A. Woodward
Worldwide comparison of tectonic elements shows some elements to be abundantly petroliferous, some to be only partly petroliferous, and others to be nonpetroliferous. Thus, an understanding of comparative tectonics is, or should be, the basis for petroleum exploration.
In the western United States, some of the major tectonic elements may be classified as craton, shelf or foreland, miogeosyncline, eugeosyncline, and postorogenic basins. These features are temporal as well as spatial. Their character and distribution principally control the accumulation of petroleum.
The formation of the Cordilleran eugeosyncline was characterized by intense folding, thrusting, regional metamorphism, and emplacement of ultrabasic to granitic bodies; the eugeosyncline is essentially barren of petroleum.
The Cordilleran miogeosyncline typically has flat thrusts of many miles of displacement, pronounced folds, and rocks of regional metamorphic tones near the base of the sedimentary section. Intrusives are common, but most are small. This region is not presently favorable for petroleum exploration because of extreme disharmony of structures above and below the thrusts.
The Rocky Mountain shelf or foreland is characterized principally by vertical tectonics with horizontal adjustments. Some complex structural and stratigraphic problems occur, but this region generally has been favorable for exploration.
Postorogenic basins developed on the deformed geosyncline and shelf commonly are petroliferous, especially those along the Pacific Coast. Thorough knowledge of the time of orogeny is essential in exploring these basins. Comparative tectonics should be fundamental in the thinking of exploration petroleum geologists.
AAPG Search and Discovery Article #91051©2012 AAPG Rocky Mountain Section Meeting, Albuquerque, New Mexico, 23-26 February 1969