Neo-Archaean Palaeo-Environmental Changes Determined by Microbial Activities Using Stable Isotopic Compositions

Nathalie Grassineau, Jie Yang, Aubrey Zerkle, Euan Nisbet

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


Reconstitution of Archaean environments can be challenging due to the lack of complete rock records and thermal overprinting and information is then lost. Many past studies have been based on scattered results because of limited material available. They relate to very specific time “capsules” and it is not always appropriate to generalize the findings at a global scale. As now in the Phanerozoic, environmental variations existed in the Archaean and one model-fits-all can be misleading. Recent studies have uncovered how remarkably similar some of the conditions in Archaean are to more recent periods. Each new Archaean locality adds to the general database to help to create a more complete picture, however a continuous record on one locality can bring more information because of its temporal and spatial context.

Studying metabolisms of early life in Archaean is a very good approach to determine environmental conditions, and Archaean Greenstone belts are the preferred formations to look for traces of life. Carbon and sulphur isotopes are important tools to study them, as metabolic processes leave isotopic fingerprints, which are often the only remaining evidence of biological activity.

The study of carbon- and sulphur-rich cherts and dark shales of 2.7 to 2.65 Ga deposited in a sedimentary basin, from three well-preserved cores and coexisting stromatolites Belingwe Greenstone Belt (Zimbabwe) allows reconstitution of contemporary Archaean environments by determining how life responded to changes in its ecosystem. Overall ranges of 39‰ for δ13Cred and 40‰ for δ34S suggest a wide spectrum of bacterial activities. There is evidence of a change from aerobic to more anaerobic activity. And this is most likely due to modification of the environmental conditions. New major and trace element data also confirm changes in the basin deposition with decrease in Al, K, Ba and Rb concentrations towards the top sediments. These parameters indicate a deepening of the basin. The reducing environment corresponds to a lower sedimentation rate.

Stable isotopic study of microbial activities in 3 cores determines spatial and temporal variation within the basin at different depths. Even in the Neo-Archaean, well established sulphur and carbon biological cycles allowed interactive bacterial communities to adapt to the changing environment.
Original languageEnglish
Title of host publicationAmerican Geophysical Union Fall Annual Meeting
Place of PublicationNew Orleans
Number of pages1
Publication statusPublished - 12 Dec 2017

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