Wenlockian graptolite reference section, Clearwater Creek, Nahanni National Park, Northwest Territories, Canada

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Abstract
A sequence of 20 m of Wenlockian graptolite-bearing strata is described from southern Northwest Territories. The sequence is relatively rich in graptolites and represents the best Wenlockian graptolite interval known in the Canadian Cordilleria, even though the fauna is notably lacking in many of the typical Wenlockian species. The following Wenlockian biostratigraphic units are recognized (from oldest to youngest): Cyrtograptus centrifugus Zone, beds with C. cf. perneri, C. rigidus Zone, beds with Monograptus firmus nahanniensis ssp. nov., M. testis-C. lundgreni Zone, and beds with Pristiograptus etheringtoni sp. nov. Graptolites described in this study comprise M. antennularius, M. firmus nahanniensis, M. flemingii, P. sardous, P. etheringtoni, Monoclimacis flumendosae, C. centrifugus, C. cf. hamatus, C. cf. perneri and C. rigidus from Wenlockian strata, as well as the 1st report from outside China of the late Llandoverian genus Sinodiversograptus.