Evidence for low sulfate and anoxic deep waters in early Cambrian

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 648; p. 112281
• Main Authors: Gong, Yizhe, Li, Dandan, Li, Menghan, Sun, Lilin, Zhang, Xiaolin, Cui, Yawen, Fu, Yong, Xu, Yilun, Shen, Yanan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2024
• Subjects: anaerobic conditions; C-isotope; Cambrian period; China; Early Cambrian; Ediacaran period; extinction; Large animals; Multiple S-isotopes; organic matter; palaeogeography; paleoclimatology; paleoecology; pyrite; seawater; sulfates; Yangtze Block; China; Large animals; Early Cambrian; Yangtze Block; C-isotope; Multiple S-isotopes
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2024.112281

The role of environmental change as a significant force driving biological evolution during the Ediacaran–Cambrian transition remains a subject of extensive debate. In this study, we present high-resolution C-isotope data of organic matter (δ13Corg) and multiple S-isotope compositions of pyrite (δ34Spy and Δ33Spy) obtained from a continuous drill core (ZK1505) in South China, spanning the interval from the Ediacaran to Cambrian Stage 2. Our δ13Corg and δ34Spy data, combined with published data from four sections deposited across a shelf-to-basin transect, reveal substantial gradient from shallow to deep water in δ13Corg and sustained positive δ34Spy values in the early Cambrian. The vertical δ13Corg gradient suggests chemical stratification of the early Cambrian ocean, characterized by oxic shallow water and anoxic deep water. The sustained positive δ34Spy values in the same period suggest low seawater sulfate concentrations. Furthermore, we observed intermittent occurrences of negative Δ33Spy values coupled with positive δ34Spy, suggesting a dominant deep-water anoxia during early Cambrian in the Yangtze Block. We propose that protracted deep-water anoxia may have contributed to the extinction of the Ediacaran biota and played a significant role in the evolution of Cambrian animals. •Vertical δ13Corg gradient reveals chemical stratification of the early Cambrian ocean.•Positive δ34Spy may have resulted from low seawater sulfate concentrations in the early Cambrian ocean.•Negative Δ33Spy coupled with positive δ34Spy suggests a dominant deep-water anoxia.•Deep-water anoxia may have hindered the flourishing of early Cambrian animals on the seafloor.