Pyrite Responses and Sulphur Isotope Signatures of Hydrothermal, Biological and Sedimentary Processes in Palaeolacustrine Systems: A Case Study from the Early Cretaceous Bayingebi Formation, Yin'e Basin

ABSTRACT

As one of the most common minerals in sedimentary environments, pyrite's sensitivity to depositional conditions makes it a valuable proxy for reconstructing palaeoenvironmental parameters. The diversity of pyrite types in the Yin'e Basin – including pyrite framboids, lumpy pyrites and radial pyrites – reflects the intricate interactions between sedimentary, hydrothermal and biological systems. Pyrite framboids, found mainly in oil shales, are ortho‐octahedral and penta‐dodecahedral. Their small size and low δ ³⁴ S values suggest a moderate hydrothermal environment with dysoxic–suboxic conditions, linked to organic matter and microbial sulphate reduction. Lumpy pyrites, observed in both oil shale and dolomite, show hydrothermal dissolution features and intermediate δ ³⁴ S values, indicating both sedimentary and hydrothermal diagenesis. Radial pyrites, prevalent in dolomite, form network‐like structures composed of layered thin plates. Redox indicators ( δ U, U _EF and Mo _EF ) point to anoxic conditions, while hydrothermal element enrichment (Fe, Ba and U) and high δ ³⁴ S values suggest an intense hydrothermal background. Their unique morphology and association with carbonates suggest a link to microbial activities in extreme environments.