The Early Ordovician was an important interval of marine biodiversification and environmental change. Widespread carbonate successions on the North China Block preserve rich fossil and sedimentary records, making the region a key area for investigating Lower Ordovician stratigraphic correlation, marine environments, and paleogeography. However, pronounced lateral facies variations have led to longstanding debates over the subdivision, correlation, and spatial and temporal distribution of Lower Ordovician lithostratigraphic units. Lithostratigraphic and chronostratigraphic boundaries have also sometimes been conflated. These issues have limited our understanding of Early Ordovician stratigraphy and biotic change in North China.
Recent studies by the researchers at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS), and their collaborators have integrated lithostratigraphy, conodont biostratigraphy, and carbon-isotope chemostratigraphy to refine the Lower Ordovician stratigraphic framework of the North China Block. Combining new observations with published records, these studies clarify correlations among different facies belts through detailed subdivision of the boundary interval and systematic regional lithostratigraphic comparison. The results have been published in Palaeoworld and Journal of Stratigraphy.
The biostratigraphic and chemostratigraphic study identified 30 conodont species belonging to 19 genera from the Yehli and Liangjiashan formations at the Jiguanshan and Wudingshan sections in Liaoning Province. Four successive biozones were recognized, in ascending order: the Colaptoconus quadraplicatus, Paltodus deltifer, Tropodus bifidus, and Serratognathus bilobatus zones. Recognition of the P. deltifer and T. bifidus zones refines the previous biostratigraphic subdivision and improves the resolution of stratigraphic correlation across the upper Tremadocian–lower Floian interval.
Carbon-isotope chemostratigraphy revealed the late Tremadocian carbon-isotope excursion (LTICE), extending from the upper C. quadraplicatus Zone to the lower S. bilobatus Zone. This excursion provides a chemostratigraphic marker for interregional correlation of strata around the stage boundary. Together with the conodont zonation, the isotope record further constrains the position of the base of the Floian within the Liangchiashan Formation in eastern North China, with the local first appearance of S. bilobatus serving as a regional marker. These results also strengthen correlations with coeval successions in South China, Argentina, Baltica, and North America.
The lithostratigraphic study reviews the lithological characteristics, ages, and spatial and temporal distribution of the Yehli, Liangchiashan, and Sanshanzi formations, clarifying the relationships among major lithostratigraphic units in the northern and southern facies belts of North China. It also examines the distribution and significance of Lower Ordovician depositional hiatuses. A regional hiatus within the Sanshanzi Formation in southern North China, spanning the uppermost Tremadocian–lowermost Floian interval, is associated with the Linxian Uplift. The disconformity separating the Liangchiashan or Sanshanzi Formation from the overlying Middle Ordovician Machiakou Formation records the influence of the first phase of the Huaiyuan Epeirogeny. By integrating the spatial and temporal changes in stratigraphy and sedimentary facies, the study reconstructs the distribution and evolution of open-platform, restricted-platform, evaporitic-platform, and tidal-flat environments, providing new insights into transgressive–regressive changes in the North China epicontinental sea.
These studies were supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, National Key Research and Development Program of China, and the National Natural Science Foundation of China.
Reference: Chi Xiangri, Yan Guanzhou, Calner Mikael, Gong Fangyi, Luan Xiaocong, Wu Rongchang. 2026. A refined stratigraphic framework for the Tremadocian–Floian stage boundary (Lower Ordovician) in the North China Block. Palaeoworld, 35, 201108. https://doi.org/10.1016/j.palwor.2026.201108
Chi Xiangri, Yan Guanzhou, Gong Fangyi, Wu Rongchang. 2026. Spatio-temporal distribution of the Lower Ordovician Yehli, Liangchiashan and Sansangtze formations in North China. Journal of Stratigraphy, https://doi.org/10.19839/j.cnki.dcxzz.2026.0002
Conodont biostratigraphic and stable carbon-isotope chemostratigraphic framework of the Jiguanshan section, Benxi, Liaoning Province
Conodonts from the Jiguanshan and Wudingshan sections, Benxi, Liaoning Province
Correlation of Early Ordovician lithostratigraphic units across the North China Block
Palaeogeographic map of the North China Block during the Early Ordovician
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