The paleoenvironmental evolution of the Cambrian Miaolingian Epoch in South China

In contrast to the high-frequency, large-scale carbon isotope fluctuations of the Early Cambrian, the Miaolingian δ¹³C_carb record exhibits notably stable, disrupted only by a brief and minor negative excursion, known as the Drumian Carbon Isotope Excursion (DICE) event. Despite this apparent stability in the carbon cycle, limited research on the Miaolingian marine environment raises questions about whether the paleoceanographic conditions were similarly stable. This study addresses these uncertainties by analyzing carbon isotope and major and trace element data from carbonate fractions of samples from the Wangcun section in South China to reconstruct the evolution of the Miaolingian paleoenvironment. During the pre-DICE phase, continental weathering and primary productivity were relatively low, and redox conditions were relatively oxygenated. During the DICE event, concentrations of water-insoluble elements (Al, Ti, Zr, Sc, Th, and Hf) increased significantly, indicating intensified continental weathering. Concurrently, productivity-sensitive indicators (Ba/Al, Ni/Al, Cu/Al, and Zn/Al) suggest heightened primary productivity, driven by increased weathering. Redox-sensitive indicators (U/Al, V/Al, Mo/Al, and Mo/U) reveal that bottom waters became anoxic during the DICE event. Following the DICE, continental weathering and primary productivity returned to low levels with minor fluctuations. However, redox conditions transitioned back to stable oxygenated levels similar to those observed in the pre-DICE phase, exhibiting partial decoupling from productivity. This may reflect the overall stability of the Miaolingian marine environment. Notably, no mass extinctions were recorded during the DICE period, further underscoring the resilience of the ecosystem. This stability might be attributed to the co-evolution of life and the marine environment during the Cambrian explosion, fostering a relatively resilient and stable marine ecosystem throughout the Miaolingian Epoch.