Permian Dollarhide Formation, Southern Smoky Mountains, South-Central Idaho: Depositional Environment and Petroleum Potential: ABSTRACT

Abstract

The Permian Dollarhide formation occurs as an allochthon west of the Big Wood River in the Smoky Mountains of south-central Idaho. It is part of the Idaho Black Shale belt described during pioneering studies by W.E. Hall. The formation contains carbonaceous limestones, fine-grained calcareous sandstones, and carbonaceous, siliceous, or calcareous siltites. The rocks contain high amounts of carbonaceous matter and local concentrations of syngenetic silver, zinc, and lead. The Dollarhide has been contact-metamorphosed by the Cretaceous Idaho batholith. The carbonaceous matter occurs as graphite. However, the possibility exists that unmetamorphosed Dollarhide with petroleum source rock potential occurs outside the Smoky Mountains. It is also possible that other allochthons within the Black Shale belt, if unmetamorphosed, could have petroleum source rock material. Near Willow Creek, SW 1/4 Buttercup Mountain Quadrangle, Blaine and Camas Counties, Idaho, the Dollarhide is 2100 m thick and was deposited in a submarine slope environment. Sandy graded beds with convolute bedding, cross-bedding, synsedimentary folds, and load casts are evidence of turbidite and debris flow deposition. Interbedded laminated and massive siltites, which are more abundant upward, represent pelagic deposition between times of turbidite activity. Stratigraphic marker horizons with anomalously high amounts of carbonaceous material and trace metals representmore » more euxinic conditions in the basin. These markers serve as valuable correlation lines in the dominantly unfossiliferous strata.« less