Abstract

A refined conodont biochronology is presented for the Triassic of Western Canada Sedimentary Basin (WCSB). This is supplemented with additional conodont data from Arctic and western Canada and from the western U.S.A. The conodont scale is intercalibrated with ammonoid zones and standard Triassic stages to produce a continental conodont standard with good potential for global application. Griesbachian conodont faunas from the Canadian Arctic are regarded as wholly Triassic rather than as partly Permian. Above the base of the Triassic, a significant change in the conodont fauna is recognized within the upper Griesbachian Strigatus Zone. Neospathodus species and divergent lineages of "Neogondolella" provide indices through Dienerian, Smithian and Spathian strata. Neogondolella regale characterizes strata of late Spathian through middle Anisian age and therefore did not develop from early Anisian Chiosella timorensis, which is reported for the first time from the WCSB. In the Late Anisian, the Neogondolella constricta group completely replaces the Neogondolella regale group. Ladinian conodont fauna changes significantly within the Meginae Zone, with Neogondolella ex. gr. constricta (N. aldae) characterizing the early part and Paragondolella ex gr. foliata dominating the later part. Budurovignathus spp. are important but occur sporadically through the Ladinian. The base of the Carnian is identified by the first appearance of Metapolygnathus. The Ladinian holdovers Paragondolella and Mosherella disappear within the Lower Carnian. In the Upper Carnian, rapid evolution of the Metapolygnathus nodosus group is represented by the M. samueli lineage and leads ultimately to M. primitius, the precursor of Norian Epigondolella. The latest Triassic conodont zonation is highly resolved on the basis of this genus, which ends with Rhaetian Epigondolella mosheri in WCSB. Biostratigraphic constraints are summarized for each of the formations for which conodont and molluscan data are available. Most of this data is from the outcrop belt of northeastern British Columbia where virtually all the present stratigraphic units have diachronous contacts. The Grayling Formation is Griesbachian-Smithian in age, the Toad Formation is Smithian-Ladinian, the Liard Formation is Ladinian, the Ludington Formation is late Ladinian-late Carnian, the Baldonnel Formation is Carnian, the Pardonet Formation is late Carnian-Rhaetian and the Bocock Limestone is Rhaetian. The Grayling-Toad formational boundary is younger in the south than in the north, the Toad-Liard formational boundary is younger in the west, and the base of the Pardonet Formation is younger in the east. On Williston Lake, a remarkable record of Smithian through Carnian conodonts occurs in the Toad and Ludington formations at Ursula Creek. The top of the Ludington at this locality is the same age as the base of the Pardonet Formation at Black Bear Ridge to the east, which itself is age-equivalent to the top of the Baldonnel Formation farther east at Carbon Creek. At the top of the Triassic succession, the Pardonet Formation is locally equivalent to the Rhaetian Bocock Limestone.

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