Abstract:
The redox chemistry of anoxic continental margin settings evolved from widespread sulfide-containing (euxinic) conditions to a global ferruginous (iron-containing) state in the early Neoproterozoic era (from ~1 to 0.8 billion years ago). Ocean redox chemistry exerts a strong control on the biogeochemical cycling of phosphorus, a limiting nutrient, and hence on primary production, but the response of the phosphorus cycle to this major ocean redox transition has not been investigated. I will present data generated by my PhD students and myself over the last 5 years from experimental work and natural environments, in order to understand the cycle of phosphorus during redox transitions. I will then focus on the phase partitioning of phosphorus in an open marine, early Neoproterozoic succession from the Huainan Basin, North China. We find that effective removal of bioavailable phosphorus in association with iron minerals in a globally ferruginous ocean resulted in oligotrophic (nutrient limited) conditions, and hence a probable global decrease in primary production, organic carbon burial and, subsequently, oxygen production.

Speaker: Romain Guilbaud, CNRS (French Scientific Research Centre) investigator at the ‘Geoscience Environment Toulouse’ laboratory, Toulouse, France

Speaker bio:
Geologist by training, Romain Guilbaud completed a PhD in experimental geochemistry in Edinburgh, where he discovered the world of Fe isotopes and pyrite. He then broadened his interests in the co-evolution of life and the planet, working on redox proxies (Leeds) and eukaryote evolution (Cambridge). He lectured at Lancaster University before starting his current position at CNRS, Toulouse.