On the Triassic Chronostratigraphy of China

The chronostratigraphic scheme of Chinese Stages, proposed by the National Stratigraphic Commission of China at the Third National Stratigraphic Conference in 2000, has been widely adopted in regional geological surveys, as well as in related scientific research and practical application in China. Notably, it has been comprehensively applied in the recently published series of monographs titled “Regional Geology of China”. Over the past two decades, extensive scientific exploration and practical application on this Chinese chronostratigraphic scheme have accumulated rich experience, also raising several challenging scientific questions that merit in-depth review and discussion. Herein I would like to share some personal insights and suggestions regarding the Triassic chronostratigraphy of China. The Triassic Period represents a highly distinctive interval in Earth's history, characterized by exceptional biological evolutionary events and unique global paleotectonic and paleoclimatic backgrounds, resulting in an extraordinary stratigraphic record. Dominated by continental regions with scattered marine sedimentary basins, the Triassic chronostratigraphic framework is notably irregular, for instance, the combined duration of the Early and Middle Triassic is less than half that of the Late Triassic. Consequently, the designation of Global Stratotype Section and Point (GSSP) for the Triassic has been significantly delayed. In China, the Triassic System constitutes a unique geological entity, representing the only system within the Chinese chronostratigraphic system for which both marine and terrestrial schemes have been proposed. Among the three currently established GSSPs for the Triassic, while the GSSP defining the base of Triassic, established in China, serves as a global model, the other two are difficult to apply with precision in China. Furthermore, regarding the four GSSPs currently under selection, if the Chinese proposals are not adopted, their application in China is likely to be challenging. Consequently, there is an urgent need to develop innovative approaches based on China's specific geological context and to explore the establishment and improvement of China's own chronostratigraphic system and Stage-division schemes. From a practical perspective, the establishment of the Chinese Triassic Stages should be based on 1:200,000 regional geological survey works, particularly focusing on the classic stratigraphic units with extensive distribution located in stable marine and continental sedimentary regions, such as shallow marine shelves and large lacustrine basins, because the stratigraphic units established or redefined during these surveys generally possess dual significance in terms of lithology (environment) and age (biology), and the majority are correlate with the temporal attributes of the international chronostratigraphic scale (Stages). This is especially true for those classic stratigraphic units and their constructed regional sequences that were extensively discussed during the First and Second National Stratigraphic Conferences. These stratigraphic units serve as the foundation for the establishment of the Chinese Triassic Stages and are also the key reason why they have been effectively applied in China's geological survey works over the past two decades. The precise definition of the upper and lower boundaries of each Stage is a meticulous scientific endeavor; strictly speaking, its scientific significance outweighs its practical application, much like the work involved in establishing GSSPs. However, the objectives and priorities of establishing the Chinese Stages should differ from those of the International Stages. The Chinese Stages should focus on their application within China, with the emphasis of their establishment and definition placed on distinctive connotations, i.e., unit stratotypes, and clearly identifiable upper and lower boundaries, i.e., boundary stratotypes. The connotation refers to the biological (evolutionary stage) and environmental (regionally stable sedimentary facies) markers identifying the certain Stage (Age), while the boundaries are marked by significant biological and environmental turning events that are easily recognizable. Any innovative scientific ideas and technical methods should conductive to promoting and refining the definition of the connotation and boundaries of the Stage.