Identification of the Cretaceous Oceanic Anoxic Event 2 on Land: A Case from Xingguo of Jiangxi, South China

Oceanic Anoxic Event 2 (OAE 2), an extreme paleoceanographic and paleoclimatic perturbation spanning the Cenomanian–Turonian boundary in the mid-Cretaceous, is well documented in marine organic-rich shales and is characterized by a widespread positive carbon isotope excursion (CIE). To date, carbon isotope records of OAE 2 have been derived predominantly from marine sediments and marine organic matter. In contrast, an equivalent terrestrial carbon isotope expression has not yet been clearly identified, limiting a comprehensive understanding of the coupling and decoupling between the global carbon cycle and climate system. To address this gap, we conducted a systematic study of geochronology, paleosols, and terrestrial carbon isotopes in Xingguo, Jiangxi Province, South China. Palynological evidence indicates that the lower part of the Maodian Formation of the Ganzhou Group is Cenomanian in age. The youngest detrital zircon age cluster of ~100–95 Ma, together with a high-precision ID-TIMS age of 97.211 ± 0.093 Ma obtained from a volcanic ash layer in the fourth bed of the section, suggests that the target paleosol-bearing horizons are no older than ~96–95 Ma. In addition, the U–Pb age of 93.8 ± 6.1 Ma from crystalline calcite infilling shrinkage fractures within calcretes further constrains the depositional age of the paleosol horizons to the latest Cenomanian to early Turonian. Carbon isotope (δ¹³C) records from pedogenic carbonates and organic matter define three evolutionary stages. Of them, Stage II (169.65–243.27 m) is characterized by a pronounced high-value plateau in both inorganic and organic carbon isotope compositions, representing a significant positive excursion. The overall pattern and temporal evolution closely parallel those of coeval marine carbon isotope records. Combined with the geochronological constraints, these results indicate that the terrestrial paleosol succession preserves a land-based record of OAE 2 in carbon cycle. The identification of OAE 2 in terrestrial paleosols provides an important basis for marine–terrestrial correlation of the global carbon cycle and promotes our understanding of the links between carbon cycle perturbations and global climate change.