Global Stratotype Section and Point (gssp) for the Gzhelian Stage (upper Pennsylvanian/carboniferous)

The GSSP for the Gzhelian Stage is proposed at the Naqing section (25°15′03.9″N, 106°29′06.9″E), Guizhou Province, South China. The section is easily accessible via Highway S312 and travel time by car is about 2.5 hours from Guiyang, the provincial capital. The Naqing section is fully exposed in a roadcut and consists of continuous carbonate deposition in an open-marine deeper-water setting with no significant vertical facies changes. It yields abundant and diverse conodont faunas. The first appearance of the conodont species Heckelina simulator (Ellison, 1941) within the evolutionary lineage H. abdivitus→H. simulator is selected as the primary marker for the base of the Gzhelian Stage at 220.45 m above the base of the measured section. Slightly higher, the fusuline foraminifer Rauserites stuckenbergi occurs at a slightly higher horizon (226.0 m) and serves as a valuable auxiliary marker for correlation, particularly with shallower-water marine successions. Supporting chemostratigraphic evidence includes pronounced negative excursions in δ¹³C, δ¹⁸Oapatite, and δ²³⁸U across the Kasimovian–Gzhelian boundary, while the ⁸⁷Sr/⁸⁶Sr curve displays a clear inflection from a prolonged high plateau to a rapid decline across the boundary. The combination of well-documented conodont and fusuline index taxa with distinctive chemostratigraphic signals confers exceptional potential for precise and reliable global correlation on the Naqing GSSP. The nearby Narao section (25°24′52.69″N, 106°36′12.78″E), approximately 22 km northeast of Naqing, is proposed as an auxiliary stratotype. It contains the same H. abdivitus →H. simulator lineage, with the appearance of H. simulator at 229.61 m. The horizon with first appearance of H. simulator can be well correlated to that from Moscow Basin, Ural, Donets Basin, and North American Mid-continent Basin. The H. simulator Zone corresponds to the middle part of the Xiaodushanian Stage of South China, the lower Dobryatinian Substage of Russia, and the lower part of the Virgilian Stage of the USA.