AbstractThe 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 theIdiognathodus luodianensisgroup and cosmopolitan species of theI. simulatorgroup. TheI. luodianensisgroup includes the new speciesI. fengtingensis,I. luodianensis,I. naqingensisandI. naraoensis. On platform landmark analysis the species of theI. luodianensisgroup differ in morphological features from co‐occurring species of theI. simulatorgroup. Both groups display similar increasing asymmetry in P1element pairs across the Kasimovian–Gzhelian boundary, as recognized on the basis of the first occurrence ofI. simulator. Many KasimovianIdiognathodusspecies disappear and several Gzhelian species first appear withI. simulator, including two new species ofStreptognathodus:S. nemyrovskaeandS. zhihaoi. Just below the base of the Gzhelian, carbonate δ13C falls from 4‰ to 2‰ in both sections. The combination of an abrupt faunal turnover immediately above the prominent negative δ13C 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 theGSSPfor the base of the Gzhelian Stage.