The Ordovician–Silurian boundary, northern Canadian Cordillera: graptolite and conodont correlation

Abstract

The Upper Ordovician graptolite faceis of the northern Canadian Cordillera is divided into 2 biostratigraphic units, the Dicellograptus ornatus Zone and the Pacificograptus pacificus Zone. Interbedded limestone yielded conodont Fauna 12. The uppermost Ordovician equivalents to the graptolite Climacograptus extraordinarius Zone and conondont Fauna 13 are absent, signifying a widespread stratigraphic hiatus probably attributable to the effects of glacially induced regression. The lowest Silurian graptolite fauna, of the Glyptograptus persculptus Zone, is tentatively identified in some sections, although it is absent in others. Conodonts from the zone, although present, are not diagnostic. Thicknesses of the lowest Silurian G. persculptus Zone sediments are anomalously high in comparison with average thicknesses of the zone elsewhere in the world.