CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China.
Key Laboratory of Submarine Geosciences and Prospecting Techniques, Ministry of Education, Institute for Advanced Ocean Study, College of Marine Geosciences, Ocean University of China, Qingdao, 266100, China.
Sci Rep. 2019 Jul 23;9(1):10630. doi: 10.1038/s41598-019-47142-3.
A shift toward a higher oxygen level in both ocean and atmosphere systems during the late Ediacaran to the early Cambrian has been suggested from multiple indirect proxies. However, the mechanism and magnitude of this oxidation remain unclear. To solve this issue, we measured carbon isotopes in both carbonate and organic matter as well as their trace element compositions for an Ediacaran-Cambrian sequence in the Lower Yangtze basin, South China. The δC and δC excursions of this sequence are coupled and can be compared with contemporaneous global carbon isotope curves. A 2‰ rise in ΔC occurred from the late Ediacaran to the early Cambrian, suggesting a substantial increase in atmospheric oxygen level from 16% to 30% of the present atmospheric level (PAL). Furthermore, the distribution pattern of rare earth elements and the concentrations of water-insoluble elements in the carbonates indicate a sudden enhancement in chemical weathering of the continental crust during the early Cambrian, which may be a trigger for the rise of atmospheric O level. Both the supply of a large amount of nutrients due to the enhanced continental weathering and the contemporary increase of atmospheric oxygen concentrations may have promoted the appearance of large metazoans in the early Cambrian.
已有多项间接指标表明，晚埃迪卡拉纪到早寒武纪期间，海洋和大气系统中的氧含量呈上升趋势。然而，这种氧化的机制和幅度仍不清楚。为了解决这个问题，我们对华南扬子地块埃迪卡拉纪-寒武纪地层中的碳酸盐和有机质进行了碳同位素及其微量元素组成的测量。该序列的δC 和 δC 偏移是耦合的，可以与同期的全球碳同位素曲线进行比较。从晚埃迪卡拉纪到早寒武纪，ΔC 上升了 2‰，表明大气氧气水平从目前大气水平（PAL）的 16%上升到 30%。此外，碳酸盐中稀土元素的分布模式和不溶性元素的浓度表明，早寒武纪大陆地壳的化学风化突然增强，这可能是大气 O 水平上升的一个触发因素。由于增强的大陆风化而导致的大量营养物质的供应，以及同期大气氧气浓度的增加，可能都促进了早寒武纪大型后生动物的出现。
