The supermature Middle-Late Ordovician Swan Peak quartz arenite was deposited on the western Laurentia passive margin and is very fine to fine grained, well-rounded, well-sorted, and silica-cemented. Laurentia was positioned over the equator during the Middle-Late Ordovician, suggesting that basement rock along the Transcontinental Arch was intensely eroded in a humid climate to produce this and other coeval quartz arenites. To determine provenance for the Swan Peak Quartzite, zircon grains were analyzed using LA-ICP-MS and the results were constrained within a sequence stratigraphic framework. Depositional environments of the Swan Peak Quartzite record an offshore-to-onshore transition with five facies (A-E). Facies A only occurs at the base of the Bear Lake section and may record an incised valley or localized embayment. It is the deepest water facies in the succession containing shale and quartz arenite interbeds. Facies B through E are interpreted as lower, middle, upper shoreface/foreshore depositional environments, respectively, based on primary sedimentary structures and bioturbation. Detrital zircon age spectra of the Swan Peak Quartzite have four distinct populations: the two main populations are at 1.8 - 2.0 Ga (Paleoproterozoic) and between 2.5 - 3.0 Ga (Archean), with a smaller, but persistent, population at 2.0 - 2.1 Ga, and a very minor 0.8 - 1.2 Ga (Mesoproterozoic) population occurring mainly in the tops of the measured sections. The base of each section has a larger Archean peak whereas the top of each section is predominantly Paleoproterozoic grains. Zircon data have overlap and similarity values ranging between 0.531 - 0.771 and 0.506 - 0.881, respectively, which indicates zircon age spectra of the Swan Peak Quartzite is similar to other Cordilleran Ordovician quartzites and that recycling of heterogeneous underlying sedimentary rocks was minimal. The Wyoming Craton (2.5 - 2.8 Ga) and the Trans-Hudson Orogen (1.8 - 2.0 Ga) provinces near the paleoequator likely provided the majority of zircons in the Swan Peak Quartzite. The source for the 2.0 - 2.1 Ga grains is currently unknown and the 0.8 - 1.2 Ga grains are interpreted to reflect Mesoproterozoic Laurentian tectonism. Sediment input varied in response to sea level fluctuations. Longshore transport was likely an important process in redistributing grains along the coastline during later deposition of the Swan Peak Quartzite.

The Swan Peak Formation in southeastern Idaho and north-central Utah is a sedimentary unit consisting of orthoquartzite, sandstone, siltite, shale, and limestone. The formation is divisible into three members, and the lower two members each are divisible into two informal lithologic subunits. The lower member consists of a lower subunit of gray, calcareous sandy siltite composed of subangular to subrounded quartz grains cemented by quartz overgrowths, calcite, or iron oxide, and an upper subunit of black shale with minor interbedded silty quartzose sandstone and biomicrite (limestone). The middle member consists of a lower subunit of interbedded pale green shale and yellowish brown silty orthoquartzite and an upper subunit of purple orthoquartzite. The brown orthoquartzite consists of well-sorted, well-rounded very fine sand- to silt-sized quartz grains cemented by quartz overgrowths which are in optical continuity with the grains they surround. The purple orthoquartzite consists of wellsorted, well-rounded, very fine to medium sand-sized quartz grains cemented by quartz overgrowths and hematite. Hematite gives the rock its purple color. gydroxylapatite is locally abundant. The upper member is an orthoquartzite consisting of very fine to medium sand-sized, well-sorted, well-rounded quartz grains cemented by quartz overgrowths. The gastropod Murchisonia (Hormotoma) sp., the first body fossil found in the upper member, is reported. Previous work has shown that the upper member of the Swan Peak Formation and the Eureka Quartzite are similar in lithology, stratigraphy, and trace fossils. The Eureka Quartzite in the Newfoundland Range is a very fine to medium sand-sized, well-sorted, well-rounded orthoquartzite cemented predominantly by quartz overgrowths, locally by dolomite. The petrographic similarities of the two units, shown in the present study, strengthens their proposed correlation. High percentages of well rounded, polycrystalline and undulatory extinction quartz show that source areas for the Eureka Quartzite and Swan Peak Formation probably were immature sandstones or quartzites of Cambrian or Precambrian age, and./or exposed igneous or metamorphic rocks. The source for most of the sand probably was the Northwest Montana Uplift, although local sources along the Uinta Uplift undoubtedly played a minor role in supplying hydroxylapatite to the middle member and fine-grained elastics to the lower member.

The Swan Peak Formation in north-central Utah thickens westward, from zero feet near Logan to 687 feet in the Promontory Range. The unit is subdivided into three distinct members: 1) A lower member of interbedded shales, limestones, and quartzites; 2) A middle member of interbedded shales and brown quartzites; and 3) An upper member of white quartzites. The Swan Peak thins southward toward the east-west-trending Tooele Arch in the area of study; this thinning probably reflects both lesser deposition and greater subsequent erosion there than elsewhere. The lower member in northern Utah probably was deposited in shallow-shelf and/or transitional shorefaceshelf environments. The middle member represents shoreface to intertidal environments. Western miogeosynclinal equivalents of the lower and middle members are more carbonate-rich, the results of their more basinward position and thus greater distance from terrigenous sediment sources. The upper member was deposited in a shallow-shelf to intertidal environment by strong, predominantly south-flowing currents.