REE and trace element patterns from organic-rich rocks of the Ediacaran–Cambrian transitional interval

• Concentrations of REE and trace elements in kerogen.
• Ocean oxygenation across the Ediacaran–Cambrian transition.
• A trigger for the “Cambrian explosion.”

It has been established that important changes in the marine environment and the biosphere occurred during the Cambrian. However, the relationships between the so-called “Cambrian Explosion” and the concomitant environmental changes are not yet fully understood. This study presents new geochemical data from the black shale successions from different facies belts of the Yangtze Platform in South China. Variations in the concentrations of REE and trace elements (varying Ce/Ce*, Th/U, V/Sc, and V/Cr ratios) in kerogen as well as in bulk rocks from different depositional environments along a transect from platform to basin indicate two oxidation events, which led to the oxygenation of the water column in shallow-marine environments and euxinic conditions (weak correlation between TOC, V, U, and Mo) in the deeper sea. During the first oxidation event in the late Terreneuvian, anoxic conditions in bottom waters rapidly changed to euxinic conditions. Subsequently, the second oxidation event during the early Epoch 2 of the Cambrian led to oxic–suboxic conditions in deeper seawater.

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