Environmental and trilobite diversity changes during the middle-late Cambrian SPICE event

The Steptoean Positive Carbon Isotope Excursion (SPICE) event at ca. 497−494 Ma was a major carbon-cycle perturbation of the late Cambrian that coincided with rapid diversity changes among trilobites. Several scenarios (e.g., climatic/oceanic cooling and seawater anoxia) have been proposed to account for an extinction trilobites onset SPICE, but exact mechanism remains unclear. Here, we present chemostratigraphic study carbonate carbon carbonate-associated sulfate sulfur isotopes (δ13Ccarb δ34SCAS) elemental redox proxies (UEF, MoEF, Corg/P), augmented by secular trilobite data, from both upper slope (Wangcun) lower (Duibian) successions Jiangnan Slope, South China, spanning Drumian Jiangshanian. Redox data indicate locally/regionally well-oxygenated conditions throughout SPICE in sections except low-oxygen (hypoxic) within rising limb (early-middle Paibian) Duibian. As coeval globally, reported δ13Ccarb δ34SCAS profiles exhibit first-order coupling event, reflecting co-burial organic matter pyrite controlled globally integrated marine productivity, preservation rates, shelf hypoxia. Increasing “Early SPICE” interval (late Guzhangian) suggests significant environmental change global-oceanic hypoxia) under way before global cycle markedly affected. Assessment range high-resolution biostratigraphic framework middle-late facilitated re-evaluation relationship contemporaneous biodiversity changes. Trilobite China declined during Early (corresponding End-Marjuman Biomere Extinction, or EMBE, Laurentia) termination End-Steptoean ESBE, Laurentia), consistent biotic patterns other cratons. We infer oxygen minimum zone and/or hypoxia expanded as result locally enhanced productivity due intensified upwelling following climatic cooling, played role EMBE SPICE. During global-ocean ventilation promoted recovery, SPICE-related Paibian may reduced circulation, triggering further precipitated ESBE. Major Guzhangian demonstrate began earlier than Guzhangian-Paibian boundary, previously proposed.