Paired lithium and barium isotopes uncover weathering and productivity controls on the late cambrian SPICE event

The late Cambrian SPICE (Steptoean Positive Carbon Isotope Excursion) event (ca. 497–494 Ma) represents one of the largest positive carbonate carbon isotope excursions in the Phanerozoic era, coinciding with rapid trilobite turnover events. It has been proposed that the SPICE event was driven by an increase in organic carbon burial, potentially triggered by enhanced marine productivity, expanded marine anoxia, and/or intensified continental chemical weathering. In this study, we present high-resolution paired lithium (δ 7 Li) and barium (δ 138 Ba) isotope analyses of carbonates from the Jiulongshan section of the North China Craton to reconstruct variations in continental weathering and marine productivity during the SPICE event. Barium isotopes show a ∼0.8 ‰ positive excursion immediately before the onset of SPICE, followed by a rapid decline to values as low as 0.2 ‰ during the rising limb of the SPICE. This suggests an increase in regional marine productivity preceding the SPICE event, followed by productivity-driven marine anoxia during the rising limb of SPICE. Lithium isotopes reveal a ∼4 ‰ negative excursion coinciding with the onset of SPICE, followed by a positive excursion of ∼5.5 ‰ during the falling limb of the SPICE. These lithium isotope trends suggest an episode of enhanced continental weathering during the rising limb of SPICE, which likely contributed to a further increase in marine productivity. This led to enhanced organic carbon burial, the expansion of ocean anoxia, and widespread positive carbon isotope excursions recorded globally. Our paired δ 7 Li and δ 138 Ba data thus provide new insights into the detailed mechanisms underlying the SPICE event and its potential relationship to the concurrent biotic changes.