Conodont faunas across the Kasimovian–Gzhelian boundary (Late Pennsylvanian) in South China and implications for the selection of the stratotype for the base of the global Gzhelian Stage

Abstract

The upper Pennsylvanian Naqing and Narao carbonate successions were deposited in intra-platform slope-to-basinal settings across the Kasimovian-Gzhelian boundary in Guizhou, South China. Conodont faunas consist of a mixture of the endemic taxa of the Idiognathodus luodianensis group and cosmopolitan species of the I. simulator group. The I. luodianensis group includes the new species I. fengtingensis, I. luodianensis, I. naqingensis and I. naraoensis. On platform landmark analysis the species of the I. luodianensis group differ in morphological features from co-occurring species of the I. simulator group. Both groups display similar increasing asymmetry in P 1 element pairs across the Kasimovian-Gzhelian boundary, as recognized on the basis of the first occurrence of I. simulator. Many Kasimovian Idiognathodus species disappear and several Gzhelian species first appear with I. simulator, including two new species of Streptognathodus: S. nemyrovskae and S. zhihaoi. Just below the base of the Gzhelian, carbonate d 13 C falls from 4& to 2& in both sections. The combination of an abrupt faunal turnover immediately above the prominent negative d 13 C excursion might represent an oceanic event in South China, perhaps recognizable on a global scale. One of these two South China sections may be the best location to place the GSSP for the base of the Gzhelian Stage.

Marine anoxia linked to abrupt global warming during Earth’s penultimate icehouse

“… 25 and marine bulk carbonates (circles) from refs. 27 and 28 with a LOESS trendline (dark gray; 20% smoothing) and bootstrapped errors (shaded; 2 SD). ( C ) Oxygen isotopes (δ 18 O) of calcitic brachiopods (gray) from ref.…”

“…Our records were developed from two open-water slope carbonate successions—the Naqing and Narao sections ( SI Appendix , Fig. S1 )—both which were the targets of previous high-resolution δ 13 C carb studies ( 27 , 28 ). The Naqing (N 25° 14′ 40″, E 106° 29′ 26″) and Narao (N 25° 24′ 39″, E 106° 36′ 25″) successions (∼22 km apart) were deposited on carbonate slopes of the Qian-Gui Basin, now located in the Luodian region, Guizhou Province, in southern China ( SI Appendix , Fig.…”

“…( C and F ) Bulk δ 13 C carb (blue) from refs. 27 and 28 with a LOESS trendline (gray; 10% smoothing) and bulk rock organic matter δ 13 C (orange). For all panels, the bootstrapped errors are indicated by the shaded region (95% CI).…”

A new species Idiognathodus praeguizhouensis n. sp. (Conodonta, Pennsylvanian) from South China

“…The first was later reassigned to Idiognathodus because its transverse ridges are mostly uninterrupted (Barrick et al, 2010). The last was later reassigned to Idiognathodus mainly because of its eccentric groove (Qi et al, 2020). Idiognathodus guizhouensis has a slightly concave platform with an extremely short carina, partially interrupted transverse ridges, and noticeably short rostral ridges that are distinct from those of coeval Idiognathodus spp., i.e., I. magnificus Stauffer and Plummer, 1932 and related forms.…”

“…It was previously believed that this species appeared suddenly and then disappeared in the Kasimovian. Recently, Qi et al (2020) named several species from the Kasimovian-Gzhelian boundary of the Naqing section, namely I. fengtingensis Qi, Barrick, and Hogancamp in Qi et al, 2020, I. luodianensis Qi, Barrick, and Hogancamp in Qi et al, 2020, I. naqingensis Qi, Barrick, and Hogancamp in Qi et al, 2020, and I. naraoensis Qi, Barrick, and Hogancamp in Qi et al, 2020, which are related to I. guizhouensis, I. luosuensis, and I. nashuiensis. Here, I. praeguizhouensis n.…”