Microorganisms in extreme environments help to understand the evolution of life on the early days. During the geological history, a variety of filamentous microstructures with unique shapes and easy identification have been reported. These filaments are generally considered to be genetically linked to microorganisms such as iron-oxidizing bacteria, archaea, fungi, or other unknown organisms. To date, there are few reports on the production of microorganisms in the form of hydrothermal veins, so little is known about their living conditions and mineralization processes.
Zhou Xiqiang, a postdoctoral fellow in the Institute of Geology and Geophysics, Chinese Academy of Sciences's Institute of Geology and Geophysics, under the guidance of his coordinator, Chen Daixuan, discovered the development of subsea low temperature and silicon-rich hydrothermal systems in the Early Cambrian in the Aksu area of ​​the Tarim Basin. The hydrothermal system consists of a silicon-rich hydrothermal channel (silicon veins in the karst dolomite of the Upper Edikatara Tsigebrak Formation) (Fig. 1) and siliceous deposits above the bottom of the sea (on top) Overlays the layered siliceous rocks of the Yurtus Formation of the Cambrian. Silica veins are mainly filled with various types of siliceous minerals (amorphous silicon, chalcedony, siliceous spherulites, microcrystalline to coarse-crystalline quartz) and a small amount of amorphous Fe-(hydrogen) oxides, pyrite, and heavy crystals. Stones, etc., are similar to the ancient and modern seafloor low-temperature and silicon-rich hydrothermal spray systems.
In addition, they discovered a large number of iron filamentous microstructures in the silicon veins of the Chigburak group (Figure 2), providing valuable opportunities for the study of microorganisms in extreme environments. These filaments are mineralized by goethite and hematite (Figure 3) and embedded in various siliceous fillers. Under the microscope, they have the typical morphology and structure (bending, sheath-like, chain-like, and mat-like) characteristics of the biogenic filaments, which can be compared with the micro-aerobic iron-oxidizing bacteria (FeOB) associated with the ancient and modern submarine hydrothermal jet system. . In this regard, they reconstructed their survival process (Figure 4): the low-temperature hydrothermal fluids in the fluid channels under the seabed are mixed with seawater to form a rich Fe (II) and micro-oxygen fluid environment, which creates the conditions for the survival of FeOB, followed by The silicon-rich hydrothermal activity was rapidly silicified, embedded and preserved during the period of activity.
It is worth noting that FeOB in siliceous veins of the Chigbulak Formation develops in the seafloor hydrothermal system in the continental shelf environment, which is different from that in the traditional submarine hydrothermal stream area (such as the ridge expansion center) and may represent An important geological habitat. The study can provide useful references for exploring the biomarkers, habitat diversity, and early biosphere evolution of the Earth and other planets' extremophiles.
The above research results have recently been published in the international SCI journal Astrobiology (Zhou et al. Biogenic Iron-Rich Filaments in the Quartz Veins in the Uppermost Ediacaran Qigebulake Formation, Aksu Area, Northwestern Tarim Basin, China: Implications for Iron Oxidizers in Subseafloor Hydrothermal Systems. Astrobiology, 2015, 15(7): 523-537).
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