ENHANCED CONTINENTAL WEATHERING INTENSITY IN THE EARLY CAMBRIAN AND ITS EFFECTS ON MARINE OXYGENATION AND PRODUCTION

The early Cambrian (541 – 509 Ma) is a crucial period in the Earth early history, which witnessed a rise surface oxygen levels and explosion of metazoan diversity. Increasing atmospheric and oceanic oxygen during this period surplushas been suggested as the potential factor resulting in the rapid diversification of the animals, although there is still debate about the evolution of the marine redox landscape. The drivers of increasing oceanic oxygenation and the links between metazoan evolution and environmental oxygenation are also debated. Some studies have suggested the enhanced weathering was a trigger for ‘Cambrian explosion’ (Horita et al., 2002; Peters and Gaines, 2012), consistent with suggestions of high rates of volcanogenic outgassing (McKenzie et al., 2016). However, there is no direct evidence of the enhanced continental weathering provided. In this study, we use lithium isotope combined with chemical index of alteration (CIA) of black shales from South China to track the continental weathering in the early Cambrian. Progressively increasing lithium isotopic and CIA values of our samples significantly indicates the enhanced continental weathering during the early Cambrian. The intense continental weathering would have provided nutrient surplus that would have been likely to have driven oxygenation and biological innovation.

Reference:

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Peters, S. E. and Gaines, R. R. 2012. Formation of the ‘Great Unconformity’ as a trigger for the Cambrian explosion. Nature 484, 363-366.

Mckenzie, N. R., Horton, B. K., Loomis, S. E., Stockli, D. F., Planavsky, N.J. and Lee, C. T. 2016. Continental arc volcanism as the principal driver of icehouse-greenhouse variability. Science 352, 444-447.