A comprehensive analysis of the Cambrian Drumian carbon isotope excursion (DICE): Insights from paleoclimate, paleoenvironment and global correlations

The Drumian Carbon Isotope Excursion (DICE) has been proposed as a potential marker for the Global Boundary Stratum Section and Point (GSSP) at the base of the Drumian. However, the characteristics of δ¹³C excursions (i.e., strength, number of subpeaks, and range of the excursion) show significant regional variability, necessitating further verification. Additionally, the paleoenvironmental conditions during the DICE event require deeper investigation to better understand their nature and mechanism. The current study examines carbon-isotope variations across the Qinglongshan section, a representative site within the Miaolingian–Furongian carbonate platform of the Ordos Basin, which spans the DICE event. The δ¹³C profile of the section documents several key carbon-isotope excursion events: the global Steptoean Positive Isotopic Carbon Excursion (SPICE, ∼2.5 ‰ positive excursion), DICE (∼4.0 ‰ negative excursion 1), and a potential globally negative excursion 2 (NE2, ∼3.5 ‰) which may correlate with the Drumian–Guzhangian boundary. These excursions are linked to major fluctuations in the carbon cycle and significant environmental changes. Sedimentological and geochemical analyses suggest that the DICE event coincided with marine transgression and a shift from warm and arid to more humid climate. The climate transition likely enhanced chemical weathering and increased terrestrial detrital input, leading to reduced salinity and intermittent anoxic conditions. Variations in seawater chemistry driven by sealevel and terrestrial input fluctuations likely contributed to the deposition of alternating red beds and negative excursion of DICE. Minor discrepancies in the stratigraphic position of the global δ¹³C peak may reflect uncertainties in biostratigraphy or limitations in data resolution. Moreover, terrestrial input is thought to have influenced both the amplitude of the peak negative δ¹³C values and the overall duration of the DICE event.