Progresses and Challenges in the Study of a Candidate GSSP for the Base of the Serpukhovian Stage (mississippian) in South China

The Global Stratotype Sections and Points (GSSPs) provide a unified temporal framework for studying Earth history. Establishing a new GSSP requires not only detailed biostratigraphic data and robust correlations but also an integrated dataset including high-precision geochronology, isotopic chemostratigraphy, magnetostratigraphy, astronomical cyclostratigraphy, and other complementary proxies. Various facies of marine sediments are well preserved in South China from the late Visean to early Serpukhovian (Middle-Late Mississippian), enabling South China an ideal area for the GSSP research on this boundary. The First Appearance Datum (FAD) of the conodont Lochrieaziegleri in the L. nodosa- L. ziegleri lineage has been tested for the index criteria, including the cosmopolitan distribution, the undisputed evolutionary lineage, the distinct morphological features, and the applicability on correlation. This makes it the most promising index among all proxies. In South China, abundant conodonts and foraminifers have been found in slope-facies sections such as the Naqing, Narao, Lianhua and Danlu sections. The first occurrences of L. ziegleri are often accompanied by some index foraminifers such as Janischewskinadelicata or/and “Millerella” tortula in adjacent levels in different sections, demonstrating a robust biostratigraphic correlation scheme for this boundary. In terms of ecological research, comprehensive studies exhibit a significant change in the marine environment coincides with a marked decrease in the biodiversity of corals, brachiopods, crinoids, gastropods, etc. across the Visean-Serpukhovian (V-S) transition. The carbon isotope stratigraphy is recently studied at several shallow- and deep-water sections in South China, and is referred to as a useful auxiliary marker. The cyclostratigraphic studies have also been conducted at the Naqing and Narao sections, providing astronomically-calibrated and high-resolution stratigraphic frameworks. However, our current research still faces several challenges. Arguments arose on the taxonomy of Lochrieanodosa and L. costata, leading to uncertainty about the ancestor of L. ziegleri. Meanwhile, the precise correlation between conodonts and foraminifers across the V-S boundary needs more work to provide additional well preserved index foraminifers. The carbon isotope trajectories across the V-S boundary require further clarification, especially for a systematic comparison between the organic and inorganic carbon isotope stratigraphy worldwide. Other insufficient but ongoing work in South China focuses on high-precision geochronology and magnetostratigraphy.