Wc. Sweet, Conodonts and biostratigraphy of Upper Ordovician strata along a shelf to basin transect in central Nevada, J PALEONTOL, 74(6), 2000, pp. 1148-1160
Conodonts representing 38 species of 26 genera have been identified in samp
les from Upper Ordovician rocks at three central Nevada localities. Ranges
of these species and associated graptolites are used graphically to determi
ne correlation of the strata considered with an evolving composite standard
that includes information from Ordovician strata at mere than 100 localiti
es in North America. Results indicate that the Hanson Creek Formation at Lo
ne Mountain is latest Edenian through mid-Richmondian in age; that the Ordo
vician part of the Hanson Creek in the Monitor Range section spans an inter
val from Maysvillian through Richmondian; and that the upper 29 m of the Vi
nini Formation at the Vinini Creek locality is of mid-Maysvillian to late R
ichmondian age. Physical discontinuities in the Ordovician-Silurian boundar
y interval complicate correlations, but it is now clear that conodonts that
range upward into, and have long been considered distinctive of the Lower
Silurian, make their debut in central Nevada in an upper segment of the Upp
er Ordovician Normalograptus persculptus graptolite zone that may be latest
Richmondian in age.