Botryoidal quartz as an abiotic signature in Palaeoarchean cherts of the Pilbara Supergroup, Western Australia

• Main Authors: Varkouhi, Shahab, Papineau, Dominic, Guo, Zixiao
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2022
• Subjects: Palaeoarchean; quartz botryoid; Pilbara Supergroup; chemically oscillating reactions; Belousov-Zhabotinsky reaction; organic matter; Carbonic acid
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10160352/1/Varkouhi_et_al_2022_PrecRes_Accepted_Manuscript.pdf; https://discovery.ucl.ac.uk/id/eprint/10160352/

Chemically oscillating reactions (COR) are abiotic processes that generate self-repeating circularly concentric morphologies during decarboxylation of organic acids. The geometry and millimetre to centimetre size dimensions of laminated quartz botryoids recorded in the Palaeoarchean Apex and Strelley Pool chert horizons in Western Australia simulate the self-similar fractal patterns arising in vitro from COR using classical and modified reactants of the Belousov-Zhabotinsky (B-Z) reaction. The botryoidal patterns akin to those developed by the COR include circular concentric laminae, open-book features, microbialite- and stromatolite-like laminations, wavy and domal structures, and rosettes. The mineral composition and organic matter (OM) distribution of these objects indicates an origin from the early diagenetic decarboxylation of carboxylic acids. Pore-water alkalinity decrease is likely due to the decomposition of OM, the generation of carbonic acid, and the cessation of chemical wave diffusion. The chemical waves developed from primary circular oxidation spots, under solubility equilibrium with respect to silica could trigger diagenetic precipitation of quartz. The presence of Fe2+-bearing hematite in various botryoidal geometries in the Apex chert is an analogue of ferroin-derived Fe in B-Z solutions, whereas the presence of Fe and Zn sulphides in the Strelley Pool quartz botryoids is akin to sulphur redox intermediates in B-Z experiments. Correlated microscopy and Raman spectral analysis corroborate that the metamorphosed OM associated with these Palaeoarchean botryoids is indigenous and syngenetic with the host chert. OM in botryoidal quartz displays circular concentric laminations as well as gradients of its density. Accordingly, an abiotic model of COR for the diagenetic growth of the studied Apex and Strelley Pool quartz botryoids is proposed. Comparisons with the chemical compositions, geometric morphology and range of size dimensions of self-similar patterns have been the criteria for development of ...