Norian (late Triassic) Foraminifera in the Baoshan Block, China: Implications for Late Triassic Palaeoenvironmental Changes

Establishing a high-resolution integrated stratigraphic framework is essential for understanding the palaeoenvironmental perturbations that preceded the end-Triassic mass extinction. This study investigates the Norian (Late Triassic) foraminiferal assemblages from the Potou section (Baoshan Block, Yunnan, China) and explores biotic responses to palaeoenvironmental changes in the eastern Tethys. A total of 37 taxa are identified. The dominant genera are genera Aulotortus, Miliolipora, Galeanella, Parvalamella, Decapoalina and Triasina. Two Norian (Sevatian age) foraminiferal biozones are distinguished in the Potou section, namely the Aulosina oberhauseri Zone and the Triasina hantkeni Zone. Ten foraminiferal morphogroups (B, C, D, E, F, G, H, I, J and K) are categorized based on their chamber growth patterns and inferred lifestyles (refer to the habits of modern foraminifera). In the lower part of the Potou section (Aulosina oberhauseri Zone), the assemblages are dominated by morphogroup I taxa (Decapoalina, Galeanella, Miliolipora, Milioliporidae, Ophthalmidium and Paraophthalmidium) whilst in the upper part of the section (Triasina hantkeni Zone), there was a gradual increase in the relative abundance of morphogroup H taxa (Aulosina, Aulotortus, Lamelliconus, Parvalamella, Prorakusia and Triasina). Microfacies analysis indicate that the Potou section was deposited in inner to middle carbonate platform environments, and shows a gradual up-section increase in the relative abundance of bioclastic components, such as dasycladaceans and sponges. The integrated data suggest that the foraminiferal community turnover was primarily controlled by shifts in platform ecology, likely related to fluctuations in hydrodynamics or nutrient availability. This study highlights the utility of integrating biostratigraphy, morphogroup analysis, and microfacies to in reconstructing a holistic record of Late Triassic palaeoenvironmental Changes.