North American Devonian Conodont Biostratigraphy

The Lower Devonian of Nevada provides a reference sequence of nine conodont faunas, five of which are also at Royal Creek, Yukon Territory. The first appearance of Icriodus woschmidtiis comparable to that in the lower Gedinnian in Europe; the Polygnathus dehiscens-P. foveolatuslineage correlates with the Emsian. Directly associated graptolite and brachiopod zones in Nevada date the intervening conodont succession as upper Gedinnian and Siegenian. Five faunas characterize the lower Middle Devonian (Eifelian) in New York ; at least two of the lower three are present in the Illinois Basin. Illinois Basin faunas correlative to the upper two New York faunas (Seneca and Cherry Valley) have Icriodus angustus,which is absent in New York, but lack Polygnathus kockelianus,which marks the top of the New York Eifelian. Three faunas subdivide the upper Middle Devonian (Givetian) in the Illinois Basin; the lower two occur in New York and Michigan. The Middle Devonian-Upper Devonian boundary possibly falls at the base of or within beds carrying the Spathognathodus insitusfauna. Alberta and Iowa sequences from the Lower Polygnathus asymmetricusthrough Upper Palmatolepis gigasZones closely correspond to the lower Upper Devonian in Germany. An Iowa section yields the standard lower Famennian zonal succession (Middle Palma-tolepis triangularisthrough Upper Palmatolepis quadrantinodosaZones). Higher Devonian faunas, in the western and central United States, are assigned with difficulty to the Scaphignathus velifer,Upper Polygnathus styriacus,and Spathognathodus costatusZones. The faunal sequence of the S. costatusZone differs significantly from that in Germany.