Upper Ordovician conodont biostratigraphy and biofacies from the Sigang section, Neixiang, Henan, central China

Abstract

The 186-m-thick Shiyanhe Formation exposed at the Sigang section, Neixiang area, Henan Province, central China has been investigated for conodonts. The collected 33 samples yielded 8858 conodont specimens. The conodonts are referred to 15 genera and 34 species, but four species cannot be positively identified and one taxon is kept in open nomenclature. The Oulodus ulrichi, the Oulodus robustus, the Aphelognathus grandis and the Aphelognathus divergens conodont biozones are introduced and the conodont fauna and biozones of the Shiyanhe Formation are referred to the Katian Stage (Stage slices Ka2–Ka4) of the Upper Ordovician. The presence of biostratigraphically important species of the genera Aphelognathus, Oulodus and Yaoxianognathus allows for the recognition of the previously defined local conodont biozones that were established from the studied section. Regionally, the Shiyanhe Formation fauna is relatively similar to the contemporaneous faunas from the Tarim terrane in western China and from the southwestern margin of the North China Platform. However, the faunal composition also shows a close affinity to the North American Midcontinent Province and correlation to North America is clear. The conodont fauna is dominated by the species of Aphelognathus, Belodina, Drepanoistodus, Oulodus, Panderodus, Phragmodus, “Plectodina” and Yaoxianognathus. The Aphelognathus–Oulodus biofacies, the “Plectodina” biofacies, the Panderodus biofacies, the Drepanoistodus biofacies and the Phragmodus biofacies have been established using multivariate statistical techniques on the conodont assemblage. As their turnovers were related to sea-level changes, the conodont biofacies are used to demonstrate the transgressive-regressive pattern in the studied section.