Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C

Papineau D, De Gregorio BT, Sagar J, Thorogate R, Wang J, Nittler L, Kilcoyne DA, Marbach H, Drost M, Thornton G (2019)

Publication Type: Journal article

Publication year: 2019

Journal

Journal of the Geological Society Geological Society

Book Volume: 176

Pages Range: 651-668

Journal Issue: 4

DOI: 10.1144/jgs2018-097

Abstract

Metamorphism is thought to destroy microfossils, partly through devolatilization and graphitization of biogenic organic matter. However, the extent to which there is a loss of molecular, elemental and isotope signatures from biomass during high-temperature metamorphism is not clearly established. We report on graphitic structures inside and coating apatite grains from the c. 1850 Ma Michigamme silicate banded iron formation from Michigan, metamorphosed above 550°C. Traces of N, S, O, H, Ca and Fe are preserved in this graphitic carbon and X-ray spectra show traces of aliphatic groups. Graphitic carbon has an expanded lattice around 3.6 Å, forms microscopic concentrically-layered and radiating polygonal flakes and has homogeneous δ13C values around −22‰, identical to bulk analyses. Graphitic carbon inside apatite is associated with nanometre-size ammoniated phyllosilicate. Precursors of these metamorphic minerals and graphitic carbon originated from ferruginous clayrich sediments with biomass. We conclude that graphite coatings and inclusions in apatite grains indicate fluid remobilization during amphibolite-facies metamorphism of precursor biomass. This new evidence fills in observational gaps of metamorphosed biomass into graphite and supports the existence of biosignatures in the highly metamorphosed iron formation from the Eoarchean Akilia Association, which dates from the beginning of the sedimentary rock record.

Authors with CRIS profile

Hubertus Marbach Lehrstuhl für Physikalische Chemie II Martin Drost Lehrstuhl für Physikalische Chemie II

Involved external institutions

University College London (UCL) GB United Kingdom (GB) Lawrence Berkeley National Laboratory (LBNL) US United States (USA) (US) U.S. Naval Research Laboratory US United States (USA) (US) Carnegie Institution for Science US United States (USA) (US)

How to cite

APA:

Papineau, D., De Gregorio, B.T., Sagar, J., Thorogate, R., Wang, J., Nittler, L.,... Thornton, G. (2019). Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C. Journal of the Geological Society, 176(4), 651-668. https://dx.doi.org/10.1144/jgs2018-097

MLA:

Papineau, Dominic, et al. "Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C." Journal of the Geological Society 176.4 (2019): 651-668.

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