TRANS-PACIFIC GRAPTOLITE FAUNAL RELATIONS - THE BIOSTRATIGRAPHIC POSITION OF THE BASE OF THE CINCINNATIAN SERIES (UPPER ORDOVICIAN) IN THE STANDARD AUSTRALIAN GRAPTOLITE ZONE SUCCESSION

Recent studies of drill-cores and outcrops have resulted in the discovery of previously unknown, taxonomically diverse, graptolite faunas in the late Middle (Mohawkian) and early Late Ordovician (Cincinnatian) strata in the Cincinnati region, the type area of the Cincinnatian Series. These faunas contain several zonal indices and other biostratigraphically important species that are used for close correlation with the standard graptolite zone succession in New York and Quebec. The new data show that the base of the Cincinnatian Series in its type area is near the middle of the Climacograptus (Diplacanthograptus) spiniferus Zone. Significantly, about a dozen Cincinnati region graptolite species are shared with apparently coeval strata in the standard Australian graptolite zone succession in Victoria, and this key faunal evidence indicates that the base of the typical Cincinnatian corresponds to a level near the middle of the Climacograptus (Climacograptus) baragwanathi Zone (Ea2) of the Eastonian Stage. This represents a considerable revision of some recently published correlations of the basal Cincinnatian in terms of the Australian graptolite zone succession.