Some geochemical features of the Blackbird and Jackass zones of the Yellowjacket Formation (middle Proterozoic) in east-central Idaho

Abstract

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Revision of middle Proterozoic Yellowjacket Formation, central Idaho, and revision of Cretaceous Slim Sam Formation, Elkhorn Mountains area, Montana

“…1, 2). (3) North of the Iron Lake fault and east of the Quartzite Mountain fault, the lower subunit of the Yellowjacket, as used by Connor and Evans (1986), Connor (1990a), and Evans and Connor (1993), is correlatable with the Apple Creek Formation (named by Anderson, 1961) in the northern part of the Lemhi Range (Connor, 1990a(Connor, , 1991. Mapping in the Lemhi Range (Tysdal, 1996a(Tysdal, , 1996bTysdal and Moye, 1996) revealed that the Apple Creek lies depositionally above the Big Creek Formation (named by Ruppel, 1975) and that no "type" Yellowjacket, Hoodoo, or unnamed post-Hoodoo strata are present.…”

“…Strata directly above the Hoodoo remain unnamed. The most recent maps of the extensive area of the Salmon River Mountains directly north of the Iron Lake fault are those of Connor and Evans (1986), Connor (1990aConnor ( , 1991, and Evans and Connor (1993). These maps were completed prior to mapping and other studies in the northern part of the Lemhi Range (Tysdal, 1996a(Tysdal, , 1996b(Tysdal, , 1996c) that permit correlation and reconciliation of strata in the two mountain ranges.…”

“…The nomenclatural changes advocated here reflect this more recent work. Strata mapped and assigned to the lower subunit of the Yellowjacket by Connor and Evans on their maps here are reassigned to the Apple Creek Formation, with which they are contiguous (table 1), as Connor (1990aConnor ( , 1991 recognized. No correlation of the post-Apple Creek strata previously assigned to the Yellowjacket Formation is undertaken here, and the middle and upper units of the Yellowjacket, as the name is used by Connor and Evans in their papers, are not renamed.…”

“…Carter (1981) determined that the calcareous rocks form discrete lenses. The quartzite beds above Bennett (1977), Connor (1990a), Connor and Evans (1986), Ekren (1988), Evans and Connor (1993), Fisher and others (1992), Tysdal (1996aTysdal ( , 1996b, Tysdal and Moye (1996). the calcareous sequence are dark gray, dark bluish gray, or locally white and, in general, contain about 70 percent quartz, 15 percent biotite (or chlorite altered from biotite), with the remainder mainly feldspar (Ekren, 1988).…”

“…Subsequent mapping by Tysdal (1996aTysdal ( , 1996b and Tysdal and Moye (1996) showed that the Proterozoic strata in the northern part of the Lemhi Range are contiguous with strata in the central part, comprised of the Lemhi Group (in ascending order, Inyo Creek, West Fork, Big Creek, Apple Creek, and Gunsight Formations) and the overlying Swauger Formation (table 1). Connor (1990aConnor ( , 1991 previously had correlated some of these same strata in the northern part of the Lemhi Range with rocks in the Salmon River Mountains that he considered to be Yellowjacket Formation. This report discusses stratigraphic and structural data in the area in which the Yellowjacket was originally named by Ross (1934), bringing new geologic mapping and sedimentologic data into consideration to reinterpret application of the name Yellowjacket Formation and to refine stratigraphic correlations.…”