The Cambrian ROECE and DICE carbon isotope excursions in western Gondwana (Montagne Noire, southern France): Implications for regional and global correlations of the Miaolingian Series

The Stage 4 – lower Guzhangian interval, which includes the Drumian and Wuliuan stages is critical for understanding biogeochemical and evolutionary events of the Cambrian. It coincides with the first widespread extinction event of the Phanerozoic associated with the negative Redlichiid – Olenellid Extinction Carbon Isotope Excursion (ROECE). It marks a shift from a lower Cambrian endemic-dominated fauna to a Paleozoic-type cosmopolitan-dominated fauna, and finally, the interval includes the negative Drumian Carbon Isotope Excursion (DICE). The precise identification of the ROECE to DICE interval beyond the tropical belts has been hindered by global regression events and the limited number of geochemical studies. However, rifting in the Mediterranean subprovince of western Gondwana during this transition provides a key sedimentary record of this interval in the southern hemisphere. The Ferrals-les-Montagnes section (Montagne Noire, southern France) offers crucial stratigraphic data for defining ROECE and DICE in western Gondwana. Although significant advances have been made in biostratigraphy, the geochemical characterization of ROECE – DICE carbon isotope excursions remain insufficiently explored, posing challenges for the precise delineation of the Series 2 – Miaolingian and Wuliuan – Drumian boundaries in Montagne Noire, where diagenetic alteration has further compromised fossil preservation. This study presents new paleontological (trilobites, echinoderms), carbon stable isotope (δ¹³C_carb, δ¹³C_org), and total organic carbon (TOC) datasets from the lower to middle Cambrian Ferrals-les-Montagnes succession. These data provide the first reliable ROECE and DICE records in western Gondwana, refining the Series 2 – Miaolingian and Wuliuan – Drumian boundaries in the region, and allow refining regional and global correlations of the Miaolingian Series.