102 / 2025-03-31 20:58:18

The comprehensive application of microscopic techniques in the study of early microbial fossils

Keywords: microfossils; Microscopy; biomineralization

Theme 1: Novel Tools and Techniques in Geobiology > Session 1g: Novel Tools and Techniques in Geobiology

Microfossils are interpreted as signs of life in the geological record, containing rich information about the origin of life and early Earth environments, and have played a critical role in the search for life on Earth and beyond. However, fossilized remains of microbial algae in ancient rocks are typically small, ranging between micrometer and nanometer scales. The coexistence of different types of microbial fossils and their abiotic analogs at microscopic scales, coupled with the susceptibility of molecular biomarkers produced by microbial algae to post-depositional alteration and destruction through diagenesis and other abiotic processes, makes the identification and taphonomic analysis of microfossils a persistently challenging task.

Through the study of microbialite microfossils from various geological ages, preservation environments, and microbial communities, we have gradually established a comprehensive suite of electron microscopy methods. By advancing electron microscopy (including scanning electron microscopy and transmission e-lectron microscopy), microspectroscopy (such as laser Raman spectroscopy), and synchrotron radiation STXM, among other micro-scale, in-situ elemental and isotopic analysis techniques, we integrate multiple microscopy and microspectroscopy approaches to leverage their respective strengths in structural and compositional analysis. This enables the observation of fossilized microstructures—ranging from micrometer to nanometer scales and even down to atomic levels—in ancient rock samples, determining their formation s-equences and chemical compositions.

(i) Extensive microscopic structural observations and chemical composition analyses were conducted on o-n siliceous nodules and their preserved microfossils from the Ediacaran Doushantuo Formation in the Three Gorges area of South China. These revealed the initial precipitation process of silicification within cell walls or extracellular sheaths, which plays a crucial role in preserving microbial subcellular structures. (ii) For samples from the Mesoproterozoic Wumishan Formation in North China, featuring alternating siliceous bands and dolomite layers, a multi-scale analytical approach from macro to micro to nano was primarily adopted. Combining SEM-EDS morphological and elemental analysis, TEM-SAED crystal structure analysis, XRF elemental distribution, and Raman spectroscopy for organic matter maturity assessment, a detailed comparison of microfossil microstructures within siliceous bands elucidated the influence of organic-mineral coupled silicification mechanisms on microfossil preservation. (iii) Morphological, structural, and compositional characterizations were performed on acritarch-like spherical microfossils preserved in siliceous rocks from the Mesoproterozoic Gaoyuzhuang Formation in northern China, with comprehensive analyses of organic-bearing microfossils and their internal minerals.

The aforementioned studies unveiled the silicification preservation characteristics of microbial fossils from three distinct geological periods. Microscopic comprehensive analyses were conducted on the preservation of subcellular structures in microfossils, organic-mineral coupled silicification mechanisms, and organic microfossils along with their internal minerals. These efforts enabled the precise identification of fossilized remains left by microbial algae in ancient rocks and the interpretation of their paleobiological and paleoenvironmental information. By examining the fine structures and chemical compositions of the fossils themselves and their surrounding rocks, biological and environmental insights into the formation and preservation of these microfossils were obtained. This work provides a methodological reference for the integrated use of microscopy techniques in the study of early microbial fossils.