The Carboniferous Bragdon Formation comprises sandstone, argillite, and conglomerate, which were deposited in a hybrid submarine-fan setting. The Bragdon Formation contains a crudely progradational succession of sand-rich turbidites and intercalated channel fill and debris flows. Apparent paucity of fine-grained rocks and relatively high sedimentation rates may suggest deposition within a small, rapidly subsiding, ponded basin. Three end-member petrologic sandstone types include (i) quartz-rich, chert-rich, and sedimentary-lithic-rich sandstone, (ii) volcanic-lithic- and feldspar-rich sandstone, and (iii) crystal-rich sandstone and tuffaceous argillite. The compositions reflect basement uplift, arc dissection, and the persistence of volcanism, respectively. Interbedded strata of differing provenance, together with little or no provenance mixing within beds, indicate multicomponent source terranes, line-source sediment dispersal pattern, and limited transport distances.Facies associations and provenance together suggest extension or transtension within an arc-related basinal setting during the Late Devonian and Early Carboniferous, resulting in deposition of epiclastic sediments that were rich in sedimentary rock fragments in a Paleozoic succession otherwise dominated by volcaniclastic rocks or fringing carbonates. Mid-Paleozoic chert-rich epiclastic strata are widespread within the western Cordillera in a variety of tectonic regimes that may be broadly related to the same oblique plate margin.
