A new study proposes a refined stratigraphic scheme for the Sanqushan Group, clarifying the Katian Zhe-Gan platform stratigraphy in South China. By integrating sedimentologic and paleontologic data, this work provides a high-resolution framework for understanding biotic evolution immediately preceding the Late Ordovician Mass Extinction (LOME) in the region.
The late Katian carbonate deposits in the Jiangshan–Changshan–Yushan (JCY) area of East China are virtually the only strata in South China preserving diverse shallow marine biotas, but the lithostratigraphic framework and age constraints of these fossiliferous rocks remain debated. In a study published this week in Continent and Life Evolution, Guang-Xu Wang and Ren-Bin Zhan of Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences establishes a revised stratigraphic framework of this interval in this area, therefore necessitating a reinterpretation of the processes and consequences of these major biotic events in the region.
Exceptionally preserved Late Ordovician successions in South China offer a globally significant archive for investigating both the Great Ordovician Biodiversification Event (GOBE) and the Late Ordovician Mass Extinction (LOME). In contrast to the graptolitic facies that dominate much of the region, the late Katian carbonate deposits in the JCY area of East China (South China paleoplate), formerly referred to as the Sanqushan Formation (or its equivalents), produce diverse shallow marine biotas. This exceptional fossil record constitutes virtually the only evidence of shallow-marine ecosystems in South China, therefore offering crucial insights into the process and dynamics of these biotic events.
"Despite their importance, the lithostratigraphic framework and age constraints of these fossiliferous rocks remain debated. The prevailing view interprets the Xiazhen Formation as a nearshore equivalent of the Sanqushan Formation, with both units broadly assigned to a generalized late Katian age." says Dr. Wang.
To address these long-standing uncertainties, the study integrated sedimentologic and biostratigraphic evidence with new field observations to undertake a systematic revision.
Key findings include:
(1) The 'Sanqushan Formation' is elevated to group rank, comprising, in ascending order, the Yaojiakeng, Jitoushan, and Xiazhen formations;
(2) The Yaojiakeng and Jitoushan formations correlate with the Dicellograptus complexus Biozone, while the Xiazhen Formation aligns with the Paraorthograptus pacificus Biozone.
(3) The evolution of the regional shallow marine ecosystem with high resolution is constructed within a refined stratigraphic framework.
"These findings demonstrate that the evolution of marine ecosystems prior to the LOME was significantly more complex than previously understood" explains Dr. Zhan.
This paper "Stratigraphic refinement unveils high-resolution shallow marine biotic dynamics immediately preceding the Late Ordovician Mass Extinction in South China" was published in Continent and Life Evolution.
Citation:
Wang G, Zhan R. Stratigraphic refinement unveils high-resolution shallow marine biotic dynamics immediately preceding the Late Ordovician Mass Extinction in South China. Cont. Life Evol. 2026(1):0002, https://doi.org/10.55092/cle20260002.
