RESUMO
Illitisation requires potassium incorporation into a smectite precursor, a process akin to reverse weathering. However, it remains unclear whether microbes facilitate K+ uptake to the sediments and whether illitisation was important in the geological past. The 2.1 billion-year-old Francevillian Series of Gabon has been shown to host mat-related structures (MRS) and, in this regard, these rocks offer a unique opportunity to test whether ancient microbes induced illitisation. Here, we show high K content confined to illite particles that are abundant in the facies bearing MRS, but not in the host sandstone and black shale. This observation suggests that microbial biofilms trapped K+ from the seawater and released it into the pore-waters during respiration, resulting in illitisation. The K-rich illite developed exclusively in the fossilized MRS thus provides a new biosignature for metasediments derived from K-feldspar-depleted rocks that were abundant crustal components on ancient Earth.
Assuntos
Bactérias/metabolismo , Sedimentos Geológicos/química , Potássio/metabolismo , Água do Mar/química , Tempo (Meteorologia) , Biofilmes , Planeta Terra , Fósseis , Gabão , Sedimentos Geológicos/análise , Minerais/análise , Minerais/química , Potássio/análise , Silicatos/químicaRESUMO
An amendment to this paper has been published and can be accessed via a link at the top of the paper.