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

Abstract

Fe-(oxyhydr)oxide-encrusted filamentous microstructures produced by microorganisms have been widely reported in various modern and ancient extreme environments; however, the iron-dependent microorganisms preserved in hydrothermal quartz veins have not been explored in detail because of limited materials available. In this study, abundant well-preserved filamentous microstructures were observed in the hydrothermal quartz veins of the uppermost dolostones of the terminal-Ediacaran Qigebulake Formation in the Aksu area, northwestern Tarim Basin, China. These filamentous microstructures were permineralized by goethite and hematite as revealed by Raman spectroscopy and completely entombed in chalcedony and quartz cements. Microscopically, they are characterized by biogenic filamentous morphologies (commonly 20-200 μm in length and 1-5 μm in diameter) and structures (curved, tubular sheath-like, segmented, and mat-like filaments), similar to the Fe-oxidizing bacteria (FeOB) living in modern and ancient hydrothermal vent fields. A previous study revealed that quartz-barite vein swarms were subseafloor channels of low-temperature, silica-rich, diffusive hydrothermal vents in the earliest Cambrian, which contributed silica to the deposition of the overlying bedded chert of the Yurtus Formation. In this context, this study suggests that the putative filamentous FeOB preserved in the quartz veins might have thrived in the low-temperature, silica- and Fe(II)-rich hydrothermal vent channels in subseafloor mixing zones and were rapidly fossilized by subsequent higher-temperature, silica-rich hydrothermal fluids in response to waning and waxing fluctuations of diffuse hydrothermal venting. In view of the occurrence in a relatively stable passive continental margin shelf environment in Tarim Block, the silica-rich submarine hydrothermal vent system may represent a new and important geological niche favorable for FeOB colonization, which is different from their traditional habitats reported in hydrothermal vent systems at oceanic spreading centers or volcanic seamounts. Thus, these newly recognized microfossils offer a new clue to explore the biological signatures and habitat diversity of microorganisms on Earth and beyond.

Earth's earliest and deepest purported fossils may be iron-mineralized chemical gardens

“…[1,2,7,8,11,15]), iron oxyhydroxides such as goethite and ferrihydrite (e.g. [2,5,7,8,[10][11][12]28]), and ironrich aluminosilicate clay minerals [6][7][8]10,25]. In line with previous studies of tubular chemical gardens using iron salts [30,32,33], the Raman, EDX, and XRD analyses in the present study suggest that biomorphs produced by reacting ferrous sulfate with either sodium carbonate or sodium silicate solutions were composed largely of iron oxyhydroxides.…”

“…Filaments and tubes composed predominantly of nano-and microcrystalline iron (oxyhydr)oxides and iron (alumino)silicates occur as dense assemblages in diverse rocks of all ages, including submarine hydrothermal chert ( jasper) beds and veins [1][2][3][4][5]; fractures, veins, vesicles, and amygdales in numerous marine and terrestrial basalts [6][7][8][9][10]; mineralized cavities in limestones [8,11,12]; and the porous oxidation zones of metal ore bodies [7,8]. These microstructures range from 1 to approximately 50 µm in diameter and up to several millimetres in length, and show complex morphological features taken to indicate a high probability that they are mineral-encrusted microorganisms, including strongly curved growth trajectories, circular cross-sections, discrete spore-like swellings, true bifurcate branching and anastomosis (cross-linking or convergence of adjacent branches), hollowness, and nestedness [1,2,4,[6][7][8][9][10][11][12][13][14][15].…”

Mineral‐Filled Fractures as Indicators of Multigenerational Fluid Flow in the Pahrump Hills Member of the Murray Formation, Gale Crater, Mars

“…The growth of primary sulfate phases in such evaporitic environments has been observed to encounter, invade, and potentially incorporate material from microbial mat communities (James & Dalrymple, 2010). In recent studies, several authors report on the preservation of microfossils that were transported and trapped in vein-forming fluids (Bons et al, 2007;Bons & Montenari, 2005;Elburg et al, 2002;Hofmann & Farmer, 2000;Kirkland et al, 1999;Pederson et al, 1997;Schopf & Kudryavstev, 2012;Trewin & Knoll, 1999;Zhou et al, 2015).…”

A New Frontier for Palaeobiology: Earth's Vast Deep Biosphere

“…However, nonbiological origins for the (more common) purely inorganic filaments cannot be excluded so easily. Common fibrous and asbestiform minerals such as Mn oxides, illite, serpentine, and palygorskite can produce straight or curved crystals that might superficially resemble these filaments, perhaps especially if coated by mineral overgrowths; such crystals would not form true branches, anastomoses, or hollow tubes, but these morphologies are not always seen in the candidate fossil assemblages either . The propulsion of mineral or organic grains through a solidifying gel can also leave behind curving, irregular tubular cavities of “ambient inclusion trails” that might become filled over time; this process could produce filament‐like structures of constant thickness, but could not produce complex branching or anastomosis, and would leave behind tell‐tale terminal inclusions .…”

“…Although the mineral filaments tend to exceed bacteria in apparent diameter, this could result from simple mineral encrustation of the original cells or sheaths. Thus, early reports assumed that the mineralized filaments in rocks were autofossilized iron‐oxidizing bacteria; more recent work has tended to reserve this interpretation for unbranched examples . Branching/anastomosing morphologies and the presence of terminal swellings resembling fruiting bodies (sporophores) have led recent studies to favor a fungal origin of the filaments .…”