Named oldest of 5 formations in Phantom Lake Metamorphic Suite in Medicine Bow Mountains for Stud Creek, T18N, R79W, Carbon Co, WY, Northern Rocky Mountain region. Type area designated as its southern exposures (500 m thick) in sec 15, T18N, R79W. Also occurs near Rock Mountain, its northern outcrop area (330 m thick), in sec 1, T18N, R79W. These two localities form core of large overturned doubly plunging anticlinorium. Consists of heterogeneous assemblage of metavolcanic and metasedimentary rocks. Divisible: pelitic schists (50%), amphibolitic schists (30%), quartzites and conglomerates (20%), calcareous rocks (local). Pelitic schists are predominately biotite- and muscovite-rich quartz schists; were probably tuffs, graywackes, and volcanogenic shales. Amphibolitic rocks were probably basalts and mafic tuffs. Quartzites may be fine-grained micaceous, fuchsitic, granule conglomerates, or quartz-rich schistose paraconglomerates. Calcareous rocks range impure marble to calcareous pelitic schist. Bedding only locally recognizable. Represent fluvial to shallow marine environments; variable rock types; rapid facies changes; lack of thick, continuous layered graywackes and pillow basalts suggest subaerial deposition, volcanism. Overlies Overland Creek Gneiss (named); gradationally underlies Rock Mountain Conglomerate (named) of Phantom Lake Suite. Late Archean age. Stratigraphic chart; geologic map; chemical analyses; petrographic data.

Source: GNU records (USGS DDS-6; Denver GNULEX).