The Overthrust-hinge line belt of central Utah is part of the Rocky Mountain orogenic complex. When viewed in its entirety, the hinge line extends many miles to the north and south, representing the western margin of the North American continent during Paleozoic time. Except for occasional eastward transgressions of the seas onto the continental shelf, the position of this transition zone remained closely confined through Triassic time.

An ancient continental margin with superimposed overthrusting and the ability to successfully explore such a setting have excited the petroleum industry.

The Overthrust-hinge line play has now been extended from southwest Utah-northwest Arizona to southeast Arizona and into Mexico. Recent geologic and geophysical work in Arizona indicates the presence of deep troughs and large anticlines that are locally covered by multiple thrust plates.

Much of southwest Arizona has previously been defined as part of the Basin and Range province. Many Tertiary-filled basins are bounded by mountain ranges (horsts) made up of allochthonous Mesozoic, Paleozoic, and Precambrian strata.

Some of the most favorable areas to explore for oil and gas have been defined within and below the allochthonous sequences. Deep regional grabens and rifts were probably filled with mostly marine sediments and some salt deposits. We believe that some of these salt sequences will be documented within the Jurassic system.

The marine sediments in the Sonora trough, just south of Arizona in Mexico, are more than 45,000 ft

End_Page 717------------------------------

(13,716 m) thick. It is believed that these sediments range from Pennsylvanian through middle Cretaceous. We project these Sonora trough marine sedimentary rocks to the northwest under the thrust plates exposed in southwestern Arizona.

End_of_Article - Last_Page 718------------