Biogeochemical changes across the Ediacaran–Cambrian transition in South China

The late Neoproterozoic successions of South China comprise some of the most complete and well-preserved records of the Ediacaran–Cambrian transition. The articles in this special issue provide a snapshot of ongoing research that is helping us to understand early stages in the development of the modern Earth system. These studies illustrate the transitional character of the Ediacaran–Cambrian interval from the evolution and early extinctions of the first bilaterian metazoans during the Ediacaran Period to their dominance of pelagic and benthic realms by the end of the early Cambrian. Geochemical data reveal a noisy transition of increasing baseline δ13C values punctuated by extreme isotopic oscillations. It is evident that highly negative δ13C values and large amplitude δ13C swings ceased once modern marine ecosystems had become firmly established by ∼520 Ma. We postulate that sub-surface bioturbation helped to strengthen the relationship between benthic oxidation state and P-retention, thus tightening an important negative feedback that helps to stabilize productivity, climate and oxygen levels in the modern Earth system. The disappearance of negative excursions after ∼520 Ma might also suggest a key role for methanogenesis which would have declined following the rise of in-sediment sulphur cycling due to bioturbation. Further insight into this fascinating interval is needed before we can disentangle the complex interactions between biological evolution and biogeochemical cycling during the emergence of the modern Earth system.

► Low δ13C excursions and extreme oscillations ceased once modern marine ecosystems became established by ∼520 Ma.
► Sub-surface bioturbation tightened key negative feedbacks of the modern Earth system.
► Importance of methanogenesis declined after early Cambrian.