The Cordilleran hinge line of Utah has been one of the most persistent geologic features in western North America. Its influence on sedimentation patterns and tectonic events continues from the Precambrian. What the hinge line is or what is its cause remains unresolved; however, gross sedimentation patterns indicate the existence of an enduring western geosyncline that received tens of thousands of feet of sediment from the Precambrian to Late Permian. Subsequently, rocks of the geosyncline began to rise, and a general reversal of sedimentation patterns occurred. This tectonism not only elevated the western region but had at least three phases of igneous activity in parts of it.

These igneous phases range in age from Jurassic to Tertiary, and with accompanying faulting, they greatly modified the area adjacent to the hinge line. The main cause of this tectonism is considered to be related to divergent plate motions. Subsequent to the Oligocene phase of igneous activity, the area east of the hinge line gradually rose. The net effect put Cretaceous marine rocks higher than their one-time source areas.

Despite being the depositional site of many favorable marine rock units and having experienced some conducive tectonism, oil and gas finds along the hinge line have not only been few but also relatively small. Factors such as adequate source rocks and traps along the hinge line, the net effect of the igneous activity, as well as high cost for seismic exploration and drilling have prevented adequate testing of the region. In addition, exploration philosophies have been tied too closely to a Wyoming thrust belt model. Several relatively unexplored areas, some over 1,000 mi² (2,600 km²), still have potential. Devonian through Tertiary rocks all have reasonable qualities to expect generation of hydrocarbons. Potential stratigraphic and structural traps are both prese t. If hydrocarbons are to be found in the area, an innovative and geologically intricate exploration scheme will be required.

End_of_Article - Last_Page 931------------