Preliminary vertebrate biostratigraphy of the Silurian Avalanche Lake sections, Mackenzie Mountains, Canada

A preliminary vertebrate biostratigraphic scheme for the Avalanche Lake sections of the Delorme and Road River groups in the Selwyn Basin, southern Mackenzie Mountains, N.W.T., contains upper and lower heterostracan and thelodont faunal assemblages. Lower assemblages of both heterostracans and thelodonts are of Telychian-Sheinwoodian age while upper assemblages are late Sheinwoodian-Homerian. Constituent species, identified as precisely as currently possible, correlate with similar species at other vertebrate and invertebrate localities, and with zones both regional and generalized. The bases of the lower thelodont and heterostracan assemblages fall within the Ireviken Event. Possible chondrichthyan specimens of potential stratigraphic utility also occur at some horizons in the Avalanche Lake sections. Information on stratigraphy of Silurian vertebrates from other localities in the northwestern continental and Arctic island regions of Canada is compiled and reviewed with respect to recent changes in taxonomic and stratigraphic nomenclature.