Nitrogen cycling in ~2.7 Ga oceans. / Yang, Jie; Zerkle, Aubrey; Grassineau, Nathalie; Nisbet, Euan; Mettam, C; Hunter, Morag; Martin, Anthony; Newton, J; Boyce, A.

American Geophysical Union Fall Annual Meeting. San Francisco, 2016. p. PP21D-04.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Abstract

A growing body of geochemical evidence suggests that localized oxygenation of the surface earth must have begun much earlier than the GOE (~2.4 Ga). This could have triggered the emergence of the aerobic biogeochemical cycle of nitrogen (N), an essential nutrient for all organisms. However, the timing of this revolutionary transition is poorly known. Some sediments from ~2.7 Ga possess
exceptionally high enrichment of 15N. Whether these values are linked to the onset of the aerobic N cycle[1], or reflective of alkaline lakes on land[2], has been in dispute. To explore this, we are investigating one of the best-preserved unambiguously marine Achaean successions from the Belingwe Greenstone Belt, in Zimbabwe. We are focusing on nearly pristine sediments from the ~2.7 Ga Manjeri Formation, which span both shallow and deep-water environments, preserving organic-rich shales and some of the oldest and most well-preserved stromatolites. The depositional conditions for this succession are further constrained by iron speciation data and sulfur isotopes, which show a redox transition from ferruginous to oxic environments from older to younger sediments. Nitrogen
isotopes in these sediments will constrain the global nature of the extremely 15N-enriched values, and test hypotheses for the Neoarchean nitrogen cycle in a non-disputed marine setting.
[1] Thomazo et al. (2011) Geobiology; [2] Stüeken et al. (2015) EPSL.
Original languageEnglish
Title of host publicationAmerican Geophysical Union Fall Annual Meeting
Place of PublicationSan Francisco
PagesPP21D-04
Publication statusPublished - 13 Dec 2016

ID: 27713010