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Structural Cross Section and Petroleum Potential of the Central Idaho Thrust Belt

LINK, P. K., and D. W. RODGERS, Idaho State University, Pocatello, ID, and B. R. BURTON, Norcen Energy Resources, Calgary, Alberta, Canada

The central Idaho thrust belt comprises several major thrust plates, including, from west to east, the Pioneer, Glide Mountain, Copper Basin, Hawley Creek, Fritz Creek, and Cabin-Medicine Lodge plates. The Pioneer plate of the Smoky, Boulder, White Cloud, and western Pioneer Mountains includes carbonaceous Devonian Milligen Formation and older Paleozoic eugeoclinal strata, overlain along a sheared unconformity by mixed carbonate-siliciclastic rocks of the Pennsylvanian-Permian Sun Valley Group, including the carbonaceous Dollarhide Formation. The Glide Mountain plate in the central Pioneer Mountains contains the western facies of the Mississippian Copper Basin Formation (quartzose flysch). The Copper Basin plate in the eastern Pioneer Mountains contains the eastern, more carbonaceous acies of the Copper Basin Formation and underlying Paleozoic platform carbonate rocks. The Hawley Creek plate comprises the rocks of the White Knob, Lost River, and Lemhi Ranges and has been mapped previously as several thrust plates with different internal stratigraphy. It includes middle Proterozoic Lemhi Group, late Proterozoic and Cambrian Wilbert Formation, Ordovician coarse-grained sandstones, and overlying lower Paleozoic platform carbonates including the carbonaceous Devonian Jefferson Dolomite. Carbonaceous shales of the distal eastern side of the Mississippian flysch trough (McGowan Creek Formation) are overlain by Mississippian and younger Paleozoic platform carbonates which contain algal buildups. The Beaverhead Mountains on the eastern side of the thrust belt (mapped most re ently by B. Skipp, U.S. Geological Survey) contain the western Fritz Creek and eastern Cabin-Medicine Lodge plates.

Petroleum source rocks exist in several stratigraphic and geographic settings, though in many cases they are overmature. The Atlanta lobe of the Cretaceous Idaho batholith intrudes the western Pioneer plate, and hypabyssal dikes and stocks associated with the Eocene Challis magmatic episode locally intrude the Pioneer, Glide Mountain, Copper Basin, and western Hawley Creek plates. The Devonian Jefferson Formation, Mississippian McGowan Creek Formation, and overlying carbonate platform strata of the Hawley Creek plate are the most prospective for petroleum resources. Neogene extension has produced the present-day topography of Basin and Range and formed deep Tertiary basins which contain coal deposits and possibly natural gas resources.

 

AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)