Ultrastructural Perspectives on the Biology and Taphonomy of Tonian Microfossils From the Draken Formation, Spitsbergen

IF 2.7 2区 地球科学 Q2 BIOLOGY
Geobiology Pub Date : 2024-10-30 DOI:10.1111/gbi.70000
Alexandre Fadel, Kevin Lepot, Sylvain Bernard, Ahmed Addad, Armelle Riboulleau, Andrew H. Knoll
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引用次数: 0

Abstract

Silicified peritidal carbonates of the Tonian Draken Formation, Spitsbergen, contain highly diverse and well-preserved microfossil assemblages dominated by filamentous microbial mats, but also including diverse benthic and/or allochthonous (possibly planktonic) microorganisms. Here, we characterize eight morphospecies in focused ion beam (FIB) ultrathin sections using transmission electron microscopy (TEM) and X-ray absorption near-edge structure (XANES) spectromicroscopy. Raman and XANES spectroscopies show the highly aromatic molecular structure of preserved organic matter. Despite this apparently poor molecular preservation, nano-quartz crystallization allowed for the preservation of various ultrastructures distinguished in TEM. In some filamentous microfossils (Siphonophycus) as well as in all cyanobacterial coccoids, extracellular polysaccharide sheaths appear as bands of dispersed organic nanoparticles. Synodophycus microfossils, made up of pluricellular colonies of coccoids, contain organic walls similar to the F-layers of pleurocapsalean cyanobacteria. In some fossils, internal content occurs as particulate organic matter, forming dense networks throughout ghosts of the intracellular space (e.g., in Salome svalbardensis filaments), or scarce granules (in some Chroococcales). In some chroococcalean microfossils (Gloeodiniopsis mikros, and also possibly Polybessurus), we find layered internal contents that are more continuous than nanoparticulate bands defining the sheaths, and with a shape that can be contracted, folded, or invaginated. We interpret these internal layers as the remains of cell envelope substructures and/or photosynthetic membranes thickened by additional cellular material. Some Myxococccoides show a thick (up to ~ 0.9 μm) wall ultrastructure displaying organic pillars that is best reconciled with a eukaryotic affinity. Finally, a large spheroid with ruptured wall, of uncertain affinity, displays a bi-layered envelope. Altogether, our nanoscale investigations provide unprecedented insights into the taphonomy and taxonomy of this well-preserved assemblage, which can help to assess the nature of organic microstructures in older rocks.

Abstract Image

从超微结构角度看斯匹次卑尔根德拉肯地层托尼微化石的生物学和岩石学。
斯匹次卑尔根岛托尼安德拉肯地层的硅化潮间带碳酸盐岩含有种类繁多、保存完好的微化石群,其中以丝状微生物垫为主,也包括多种底栖和/或同栖(可能是浮游)微生物。在此,我们利用透射电子显微镜(TEM)和 X 射线吸收近边结构(XANES)光谱分析了聚焦离子束(FIB)超薄切片中的八个形态物种。拉曼光谱和 XANES 光谱显示了所保存有机物的高度芳香分子结构。尽管分子结构明显保存不佳,但纳米石英结晶却保存了 TEM 所显示的各种超微结构。在一些丝状微化石(Siphonophycus)和所有蓝藻茧菌中,胞外多糖鞘以分散的有机纳米颗粒带的形式出现。Synodophycus 微化石由多细胞茧状菌落组成,含有类似于胸囊蓝藻 F 层的有机壁。在一些化石中,内部内容物以颗粒状有机物的形式出现,在整个细胞内空间的幽灵中形成致密的网络(如 Salome svalbardensis 细丝),或稀少的颗粒(在一些绿球藻中)。在一些绿球藻微化石(Gloeodiniopsis mikros,也可能是 Polybessurus)中,我们发现了分层的内部内容物,它们比定义鞘的纳米颗粒带更加连续,形状可以收缩、折叠或内陷。我们将这些内层解释为细胞包膜下层结构和/或光合膜的残余物,并由额外的细胞材料加厚。一些 Myxococccoides 的壁超微结构很厚(达约 0.9 μm),显示出有机柱,这与真核生物的亲缘关系最为吻合。最后,一个壁破裂的大球体显示出双层包膜,其亲缘关系尚不确定。总之,我们的纳米级研究为这一保存完好的集合体的岩相学和分类学提供了前所未有的见解,有助于评估较古老岩石中有机微结构的性质。
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来源期刊
Geobiology
Geobiology 生物-地球科学综合
CiteScore
6.80
自引率
5.40%
发文量
56
审稿时长
3 months
期刊介绍: The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time. Geobiology invites submission of high-quality articles in the following areas: Origins and evolution of life Co-evolution of the atmosphere, hydrosphere and biosphere The sedimentary rock record and geobiology of critical intervals Paleobiology and evolutionary ecology Biogeochemistry and global elemental cycles Microbe-mineral interactions Biomarkers Molecular ecology and phylogenetics.
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