Brachiopod sclerochemistry and climate change: a case study from the Wuchiapingian of Iran

The Lopingian (Late Permian) time interval is represented by several brachiopod-bearing sedimentary successions across Iran. As brachiopods are considered one of the best tools for investigating past conditions (e.g. Brand et al., 2011), a sclerochemical analysis has been performed on brachiopod shells from the Julfa and Abadeh sections (Ghaderi et al., 2014; Viaretti et al., 2022) to unravel the still debated Wuchiapingian (early Lopingian) climate change. All the analysed shells belong to the species Araxilevis intermedius (Abich, 1878), coming from correlatable beds in the two sections. Shells were sampled for sclerochemistry (δ18O and δ13C), with calcite powder collected at a high resolution along the axis of maximum growth, obtaining a seasonal record. Comparing our results to modern seasonal variations at similar palaeolatitudes and environmental settings, a higher temperature seasonality is recorded at the base of both sections; seasonality then decreases upward, returning to the expected variation. Since stronger seasonal variations can be associated with cooler climates, our data suggest the occurrence of a cooling phase at the start of the Lopingian, adding a new piece of evidence to the collection of different archives and proxies supporting a cooling phase linked to the emplacement and weathering of the Emeishan LIP in South China. Our study highlights the robustness of the brachiopod archive for studying past climate and improves the constraints on the debated duration of the cooling phase, which should have lasted slightly more than one million years. Interestingly, the analysis of other proxies (shell size, microstructural elements and biodiversity indices) indicates that brachiopods were quite resilient to the observed climatic change.