Duration and intensity of the Late Permian (early Wuchiapingian) cool climate episode: Sclerochemical evidence from brachiopod assemblages in Iran

The Permian period witnessed some of the most dramatic environmental and climate changes in Earth's history. In this paper, we focused on the cool climate episode that occurred during the early Wuchiapingian (Lopingian), which was possibly triggered by CO2 drawdown linked to weathering of the Emeishan LIP in South China. To unravel the duration and magnitude of this climate episode, we analysed brachiopod shells of Araxilevis intermedius (Abich, 1878) from correlatable Upper Permian beds in the Julfa and Abadeh sections of North and Central Iran, deposited near to the palaeoequator. After a multidisciplinary diagenetic screening involving petrography, CL, SEM, EBSD, elemental and isotopic analyses, the stable isotope sclerochemistry was studied in well-preserved shells, to investigate seasonal variations in δ18O and δ13C. At the base of both sections (Clarkina asymmetrica Zone), shells of A. intermedius recorded a high amplitude of temperature seasonality (∼6 °C) indicating the onset of the early Wuchiapingian cooling episode. Temperature seasonality decreased upwards (∼3.2 °C) and returned close to the seasonal temperature variation observed at comparable modern latitudes. The inferred seasonality pattern allowed us to constrain the end of the Wuchiapingian cooling phase to ∼257 Ma, at the top of the Clarkina guangyuanensis Zone. We found that the early Wuchiapingian cooling episode was short-lived, lasting about 2 Myr, supporting previous reports from South China. Based on δ13C results and biodiversity curves, we concluded that, despite witnessing variations in productivity and food supply, brachiopod assemblages showed high ecological resilience and did not undergo a major change in biodiversity.