School of Earth Sciences, The University of Western Australia, Perth, Australia.
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA.
Astrobiology. 2021 Jun;21(6):655-672. doi: 10.1089/ast.2020.2376. Epub 2021 Mar 8.
The 1.88-billion-year-old Gunflint carbonaceous microfossils are renowned for their exceptional morphological and chemical preservation, attributed to early and rapid entombment in amorphous silica. The carbonaceous matter lining and partly filling filamentous and spherical structures is interpreted to be indigenous, representing thermally altered relicts of cellular material ( kerogen). Here we show that stromatolitic black cherts from the Gunflint Formation, Schreiber Beach, Ontario, Canada, were saturated in syn-sedimentary oil. The thermally altered oil (pyrobitumen), which occurs in the stromatolites and intercolumn sediments, fills pores and fractures, and coats detrital and diagenetic grain surfaces. The occurrence of detrital bitumen grains in the stromatolites points to the proximity of shallow seafloor oil seeps and hence the possible existence of chemosynthetic microbes degrading hydrocarbons. We suggest that hydrocarbons that migrated through the silicifying stromatolites infiltrated semi-hollow microbial molds that formed following silica nucleation on the walls or sheaths of decayed cells. Upon heating, the hydrocarbons were transformed to nanoporous pyrobitumen, retarding silica recrystallization and enhancing detailed preservation of the carbon-rich microfossils. Hydrocarbon infiltration of silicified microbes offers a new explanation for the preservation of the Gunflint microfossils and may have played a role in the formation of some of Earth's oldest microfossils.
1.88 亿年前的 Gunflint 碳质微化石以其出色的形态和化学保存而闻名，这归因于它们早期和快速被无定形二氧化硅埋葬。线状和球状结构内部和部分填充的碳质物质被解释为原地的，代表着细胞物质（干酪根）的热改造残余物。在这里，我们表明，来自加拿大安大略省 Schreiber 海滩的 Gunflint 组的层状燧石黑色燧石充满了同沉积期的石油。热变质油（热沥青）存在于层状石和柱间沉积物中，填充孔隙和裂缝，并覆盖碎屑和成岩颗粒表面。层状石中存在碎屑沥青颗粒表明，浅海底石油渗漏的存在，以及可能存在降解碳氢化合物的化能合成微生物。我们认为，通过硅化层状石迁移的碳氢化合物渗透到半空心微生物模具中，这些模具是在细胞壁或腐烂细胞的鞘上形成的二氧化硅核后形成的。加热时，碳氢化合物转化为纳米多孔热沥青，减缓了二氧化硅的重结晶，并增强了富含碳的微化石的详细保存。碳化硅微生物的碳氢化合物渗透为 Gunflint 微化石的保存提供了一个新的解释，并且可能在一些地球上最古老的微化石的形成中发挥了作用。
