Inherited geochemical diversity of 3.4 Ga organic films from the Buck Reef Chert, South Africa

Abstract

Archean rocks contain crucial information about the earliest life forms on Earth, but documenting these early stages of biological evolution remains challenging. The main issue lies in the geochemical transformations experienced by Archean organic matter through its multi-billion-year geological history. Here we present spatially resolved chemical investigations conducted on 3.4 Ga organic films from the Buck Reef Chert, South Africa which indicate that they possess significantly different chemical compositions. Since these organic films all underwent the same post-depositional geological history, this geochemical diversity is most likely inherited, reflecting original chemical differences which were not completely obliterated by subsequent burial-induced degradation processes. These results demonstrate that early Archean organic films carry chemical information directly related to their original molecular compositions. This paves the way for the reconstruction of the initial chemical nature of organic microfossils found in ancient rocks, provided that the geologically-induced chemical transformations they underwent are properly constrained.

Formation of Pyrite Spherules From Mixtures of Biogenic FeS and Organic Compounds During Experimental Diagenesis

“…Besides lipids, all these compounds are poorly resistant to thermal diagenesis (Alleon et al, 2017;Bernard et al, 2015;Criouet et al, 2021;Viennet et al, 2019). Yet, amide-rich organic compounds, possibly derived from proteins, have been detected in ancient cherts as old as 3.5 Ga old (Alleon, Bernard, Le Guillou, Marin-Carbonne, et al, 2016;Alleon et al, 2018Alleon et al, , 2021, likely thanks to their early entombment within silica (Alleon, Bernard, Le Guillou, Daval, et al, 2016). The diagenetic chemical degradation of biogenic organic compounds is also limited when encrusted in calcium phosphates (Li et al, 2014) or iron oxides (Picard et al, 2015(Picard et al, , 2016, but this is the opposite with iron phosphates (Miot et al, 2017) or clay minerals (Jacquemot et al, 2019;Viennet et al, 2019Viennet et al, , 2020.…”

Early precipitated micropyrite in microbialites: A time capsule of microbial sulfur cycling

“…Interestingly, determining the precise nature of the fossil microbial community is challenging because these organosedimentary rocks resulted from a complex balance between microbial activities, sedimentation and intermittent lithification (Reid et al, 2000). In addition, the biosignatures preserved in fossil biofilms are ambiguous, especially after diagenesis and post-depositional history (Javaux, 2019;Alleon et al, 2021). The oldest evidence for MSR in the Archaean geological record are sulfur isotopic signatures from deep marine sediments (Kamber and Whitehouse, 2007;Shen et al, 2009) and stromatolites (Shen and Buick, 2004).…”

Multiple sulphur isotope record of Paleoarchean sedimentary rocks across the Onverwacht Group, Barberton Greenstone Belt, South Africa

“…an estimate of 312 ± 50°C from the Buck Ridge chert at the top of the Hoogenoeg Formation (Alleon et al, 2021). Metamorphic temperature constraints obtained using chlorite thermodynamic modelling of pillow lavas from the lowermost Kromberg Formation have yielded sub-greenschist facies metamorphic temperatures of T = 140 ± 30°C (Grosch, 2019;Grosch et al, 2012).…”