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Upper Permian and Triassic conodont biostratigraphy of the Cache Creek Group, Marble Range, south-central British Columbia Beyers, Joanna Maria


Two Upper Permian and seven Triassic conodont faunas occur in the limestones, cherts and argillites of the Cache Creek Group, which underlies the Marble Range in south-central British Columbia. The oldest fauna is Guadalupian in age with species of Sweetognathus at Hat Creek-Marble Canyon, and Neogondolella phosphoriensis west of Clinton. The youngest Permian fauna, from the Jesmond area, includes three morphotypes of Iranognathus ex gr. nudus that are distinguished on the basis of carina morphology, a new species of Iranognathus, subspecies of Neogondolella subcarinata, N. orientalis and N. n.sp. A. The fauna is probably early to middle Dorashamian/Changxingian in age, but may be as old as late Dzhulfian. Adenticulate elements of Isarcicella isarcica constitute Fauna 3 in upper Griesbachian strata along Porcupine Creek. Fauna 4A from Marble Canyon, characterized by 'Neogondolella' carinata, Neospathodus dieneri and N. peculiaris, is middle Dienerian in age, . and Fauna 4B, from Cornwall Hills, recognized by the presence of Neospathodus sp. cf. N. peculiaris and N. sp. cf. N. pakistanensis, appears to straddle the Dienerian-Smithian boundary. Elements of Smithian Fauna 5 occur on Pavilion Mountain, near Jesmond and on Cornwall Hills. Key taxa include Neospathodus novaehollandiae, Lonchodina nevadensis and Pachycladina obliqua. Neogondolella milleri and Platyvillosus costatus allow recognition of a late Smithian subfauna 5B on Cornwall Hills. The youngest of the Scythian faunas is Spathian Fauna 6, known from the Jesmond fire lookout area. It consists of elements of Neospathodus homeri and N. triangularis. Undifferentiated Middle Triassic Fauna 7 is represented by poorly preserved species of Neogondolella found in cherts on the Cornwall Hills fire lookout road. Faunas 8 and 9 are Late Triassic in age. The former, from Cornwall Hills, is thought to be Carnian in age, with species of Metapolygnathus and ?Neocavitella. Early Norian Fauna 9, best represented in a sample from Oregon Jack Creek valley but with some elements found in the central area of the Marble Range, consists of Epigondolella primitia, Neogondolella navicula, Metapolygnathus nodosus and M. echinatus. Conodont biostratigraphy shows that several interruptions in sedimentation or episodes of erosion occurred in the Marble Range during the Upper Permian-Triassic interval. At Jesmond, where the Permian-Triassic boundary is now well documented, an unconformity represents part of Dorashamian/Changxingian to ?early Smithian time. This hiatus may be narrower elsewhere in the Marble Range as Griesbachian strata have also been found. The second significant break in sedimentation appears to have taken place during the Middle Triassic, since strata of this age are known only from Cornwall Hills and Hat Creek junction, and on Pavilion Mountain Early Triassic limestone clasts occur in Late Triassic argillites. While carbonate sedimentation was dominant during the Late Permian and Early Triassic, Upper Triassic outcrop in the central and southern parts of the study area is primarily deeper water argillite with an admixture of volcaniclastic material, suggesting that the region underwent a change in environment or tectonic conditions. By the end of the Triassic, Cache Creek terrane ceased to be an oceanic carbonate platform.

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