Oil and Gas Prospective Thrust Belts, West-Central North America: ABSTRACT

The prospective oil and gas producing thrust belt areas, now defined in west-central North America, should be expanded to include all shortened sequences of rocks where the overthrust (hanging wall) sequences have been emplaced over organic-rich rocks of all ages. The western part of the much-publicized Sevier thrust belt should be considered where any older sequence is emplaced over younger organic-rich rocks, if the younger rocks were not previously mature or if all hydrocarbons were not expelled from them before thrusting occurred. Where overthrusting has emplaced older rocks over younger organic-rich rocks, the added overburden can cause initial or additional hydrocarbon generation and expulsion into available traps. This thrust loading can cause hydrocarbon generation and expulsion on a selected basis where the depth of overburden is adequate with the temperature high as needed. The very deep organic-rich sediments can generate hydrocarbons by thrust loading, with the oil and gas migrating into the shallow immature sediment trap. Because of basin downwarping and sedimentation, the additional sediment load can cause initial or additional hydrocarbon generation. The COCORP seismic reflection data from western Utah indicate major regional detachment (decollement) horizontal planes for structural shortening in most of the Basin and Range province of western North America. End_of_Article - Last_Page 943------------