Pennsylvanian and Permian Paleogeography of South-Central Idaho: the Wood River Basin

MAHONEY, J. BRIAN, University of British Columbia, Vancouver, British Columbia, BRADFORD R. BURTON, Norcen Energy Resources Ltd., Calgary, Alberta, and JAMES P. O'BRIEN and PAUL KARL LINK, Idaho State University, Pocatello, ID

The Sun Valley Assemblage (Wood River, Dollarhide, and Grand Prize formations) was deposited in the Wood River basin in what is now south-central Idaho, north of the Snake River Plain, from the Atokan to Wolfcampian and Leonardian(?). Atokan and Des Moinesian deposition occurred in braided deltas and overlying clear water carbonate shoals. The rocks of this depositional system vary in thickness from tens to several hundreds of meters reflecting irregularities in the erosional surface on the underlying foundered Antler highland. This basal unconformity has been sheared during Mesozoic and Paleogene deformation.

Significant regional subsidence of the Wood River basin began in the Des Moinesian, was most rapid in the Virgilian, and slowed in the Wolfcampian, resulting in total thickness of over 2000 m for each of the three formations. In the central part of the basin (Wood River Formation) a sub-wave-base ramp system with southeastern paleoslope was fed by turbidite flows of mixed carbonate-siliciclastic fine-grained sediment that had been thoroughly mixed on a shelf area to the north and east. The carbonate fraction may have been derived from the Snaky Canyon Formation carbonate platform to the east, whereas siliciclastic fraction is cratonal. The distal part of the southward-sloping ramp system is present in the Dollarhide Formation, which represents a lower and middle slope depositional sys em that accumulated fine-grained carbonaceous mixed sediment. To the north, a siliciclastic fan or ramp system (Grand Prize Formation) was present. Virgilian and Wolfcampian strata represent highstand systems tracts and a lowstand tract is present in strata deposited near the Virgilian-Wolfcampian boundary.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)