Common Biogenicity Markers in Barberton (South Africa) and Warrawoona (Australia) Archean Cherts
Résumé
Cherts are amongst the oldest sedimentary rocks on Earth and Archean cherts contain traces of organic matter the origin of which is highly debated: abiotic formation under hydrothermal conditions or organic microfossils? (Schopf et al. 2002; Brasier et al. 2002). In order to cut short that controversy, biogenicity markers were found, notably in a sample of chert from Warrawoona, Australia (Derenne et al. 2008). The occurence of organic biomarkers in the soluble fraction of the organic matter is often disputable, as this fraction may be easily contaminated through migration of more recent organic matter. Therefore, it is of greater interest to focus on the insoluble fraction (kerogen) of the organic matter that is in all likelihood of the same age as the host rock, since its structure is characterized by covalent bonds. In the Warrawoona chert, the pyrolysis of the kerogen revealed the presence of long aliphatic chains with a predominance of odd-over-even carbon numbers. The same analysis was run on a sample of Josefsdal chert from the Barberton Greenstone Belt, South Africa, coupled to 13C NMR and FTIR spectroscopies, and microscopy. Again an odd-over-even carbon number predominance was found, showing that the Warrawoona distribution was not an isolated feature and confirming the potential use of the aforementioned biogenicity marker. Such biogenicity markers will be powerful tools in further exobiology studies. [abstract only]
