Lower Triassic conodonts from the Canadian Arctic, their intercalibration with ammonoid-based stages and a comparison with other North American Olenekian faunas

Abstract

Conodont faunas are described from the type sections of Lower Triassic stages in the Canadian Arctic. The collections come largely from ammonoid-bearing strata of the Strigatus (upper Griesbachian), Candidus (lower Dienerian), Romunduri and Tardus (lower and upper Smithian), and Subrobustus (upper Spathian) zones. These demonstrate that diverse late Griesbachian conodont faunas included the first species of Borinella, Neospathodus and Scythogondolella, accompanied by several species of Neogondolella. Dienerian faunas are dominated by Neospathodus, but explosive radiation led to several Smithian Scythogondolella species and diverse cosmopolitan “neospathodid” species of Conservatella, Discretella and Neospathodus. Smithian Paullella (nomen novum) and Wapitiodus are recorded here for the first time in the Arctic collections, and emphasize the correlation with successions in the Western Canada Sedimentary Basin (WCSB) and in the western USA. Conodonts from the Romunduri Zone differ in the three regions: Conservatella, Discretella and Paullella are rare in the Arctic, are more common in WCSB and are most common in the USA; Scythogondolella species are common in the Arctic, less so in WCSB and are virtually absent in the USA. Conodonts from the Tardus Zone, both in the Arctic and elsewhere, contain cosmopolitan Borinella buurensis, Neospathodus waageni, Scythogondolella mosheri and Scythogondolella milleri. Spathian conodont faunas from the Subrobustus Zone are dominated by Neogondolella species, which also occur in the WCSB associated with Triassospathodus. These two genera have an inverse relationship: Triassospathodus dominates the USA successions, and is virtually absent in the Arctic. Scythogondolella ellesmerensis sp. nov. and Scythogondolella lachrymiformis sp. nov. are described.