UMR 7285 CNRS IC2MP, University of Poitiers, Poitiers, 86073, France.
Department of Earth and Planetary Sciences, University of California, Riverside, CA, 92521, USA.
Nat Commun. 2019 Jun 17;10(1):2670. doi: 10.1038/s41467-019-10620-3.
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.
伊利石化需要钾离子掺入到蒙脱石前驱体中，这一过程类似于反向风化。然而，目前尚不清楚微生物是否有助于沉积物对钾的吸收，以及伊利石化在地质历史上是否重要。加蓬的 21 亿年前的弗朗斯维尔系列地层被证明存在与基质相关的结构（MRS），在这方面，这些岩石为测试古代微生物是否诱导伊利石化提供了独特的机会。在这里，我们发现高钾含量局限于伊利石颗粒中，这些伊利石颗粒在含有 MRS 的相带中丰富，但在母体砂岩和黑色页岩中却没有。这一观察结果表明，微生物生物膜从海水中捕获钾，并在呼吸过程中将其释放到孔隙水中，从而导致伊利石化。富钾伊利石仅在化石化的 MRS 中发育，因此为源自钾长石贫化岩石的变质沉积物提供了一个新的生物特征，这些岩石是古代地球上丰富的地壳成分。
