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![Geological map of the North China Craton, and the Wutai Complex within the Trans-North China Orogen. Pillow lava sampling (shown by star) was undertaken within the greenschist facies tholeiites of the Middle Wutai Subgroup. Map is modified from Zhao et al., 2001 [31].](profile/Guochun-Zhao-zhaoguochun/publication/227129984/figure/fig2/AS:393859117928461@1470914739993/Geological-map-of-the-North-China-Craton-and-the-Wutai-Complex-within-the-Trans-North.png)
Geological map of the North China Craton, and the Wutai Complex within the Trans-North China Orogen. Pillow lava sampling (shown by star) was undertaken within the greenschist facies tholeiites of the Middle Wutai Subgroup. Map is modified from Zhao et al., 2001 [31].
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Microorganisms that inhabit sub-seafloor lavas are capable of etching volcanic glass and creating micron-sized tunnels and
pits. Mineralization of these bioalteration traces ensures that these textures survive deformation and transformation of the
host glass to metamorphic minerals. The fossil record of such bioalteration textures extends far beyon...
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... Aside from formation via dissolution [16], other potential abiotic causes include burial metamorphism of organic matter or un/misidentified ambient inclusion trails (AITs) formed as mineral inclusions forcibly migrate through a material with enough force and energy to erode a hollow tubular structure [31,47]. These can often be excluded where the diagnostic features (a terminal crystal and longitudinal striae) are missing [23,48]. None of these mechanisms are relevant to laboratory-dissolved crystal-free glasses. ...
... On the other hand, the trace element patterns of dolomite in the chlorite schist exhibit variation trends fairly similar to those of the experimentally constrained subduction zone fluids-especially the fluid with the presence of Cl anions (Figure 4b) [65,66]. (2) Plenty of rocks in the Wutai Group have protoliths typical of altered oceanic crustal materials-for instance, the garnet-orthoamphibole rock [35,120] and equivalent chlorite schist, the pillow basalt with microbial alteration textures [121], the volcanogenic massive sulfides (VMS) [122,123], and the epidosite with extremely low δ 18 O values (our unpublished data). (3) The metamorphic peak P-T conditions of the Wutai and Hengshan complexes lie along the oceanic slab-top P-T path representative of early warm subduction ( Figure 8) [117,118]-in particular, that of Hengshan, falling exactly on the ancient (2.7-0.8 ...
Greenschist facies metabasite (chlorite schist) and metasediments (banded iron formation (BIF)) in the Wutai Complex, North China Craton recorded extensive fluid activities during subduction-related metamorphism. The pervasive dolomitization in the chlorite schist and significant dolomite enrichment at the BIF–chlorite schist interface support the existence of highly channelized updip transportation of CO2-rich hydrothermal fluids. Xenotime from the chlorite schist has U concentrations of 39–254 ppm and Th concentrations of 121–2367 ppm, with U/Th ratios of 0.11–0.62, which is typical of xenotime precipitated from circulating hydrothermal fluids. SHRIMP U–Th–Pb dating of xenotime determines a fluid activity age of 1.85 ± 0.07 Ga. The metasomatic dolomite has δ13CV-PDB from −4.17‰ to −3.10‰, which is significantly lower than that of carbonates from greenschists, but similar to the fluid originated from Rayleigh fractionating decarbonation at amphibolite facies metamorphism along the regional geotherm (~15 °C/km) of the Wutai Complex. The δ18OV-SMOW values of the dolomite (12.08–13.85‰) can also correspond to this process, considering the contribution of dehydration. Based on phase equilibrium modelling, we ascertained that the hydrothermal fluid was rich in CO2, alkalis, and silica, with X(CO2) in the range of 0.24–0.28. All of these constraints suggest a channelized CO2-rich fluid activity along the sediment–basite interface in a warm Paleoproterozoic subduction zone, which allowed extensive migration and sequestration of volatiles (especially carbon species) beneath the forearc.
... Titanite (CaTiSiO 5 ) microtubes have been found in several occurrences of metamorphosed basaltic pillow-lava rims and basaltic hyaloclastite breccias spanning ~3.5 to ~2.5 Ga (Furnes et al., 2004;Banerjee et al., 2006Banerjee et al., , 2007Bridge et al., 2010;McLoughlin et al., 2010) as well as in Silurian metabasalts (Fliegel et al., 2011). They also occur in 2.72 Ga metamorphosed volcanoclastic rocks Lepot et al., 2011, Fig . ...
... This rules out the initial hypothesis that the titanite formed during seafloor hydrothermal alteration soon after biocorrosion (Furnes et al., 2004;Fliegel et al., 2010), because the regional metamorphism (that would have re-crystallized any remaining glass) is dated at 3.23 Ga, and rather supports the hypothesis that titanite formed in association with later contact metamorphism (Grosch and McLoughlin, 2014). Similarly, other Archean titanite microtubes display in situ U-Pb dates that correlate with regional metamorphism McLoughlin et al., 2010). ...
The Archean era (4 to 2.5 billion years ago, Ga) yielded rocks that include the oldest conclusive traces of life as well as many controversial occurrences. Carbonaceous matter is found in rocks as old as 3.95 Ga, but the oldest (graphitic) forms may be abiogenic. Due to the metamorphism that altered the molecular composition of all Archean organic matter, non-biological carbonaceous compounds such as those that could have formed in seafloor hydrothermal systems are difficult to rule out. Benthic microbial mats as old as 3.47 Ga are supported by the record of organic laminae in stromatolitic (layered) carbonates, in some stromatolitic siliceous sinters, and in some siliciclastic sediments. In these deposits, organic matter rarely preserved fossil cellular structures (e.g. cell walls) or ultrastructures (e.g. external sheaths) and its simple textures are difficult to attribute to either microfossils or coatings of cell-mimicking mineral templates. This distinction will require future nanoscale studies. Filamentous-sheath microfossils occur in 2.52 Ga rocks, and may have altered counterparts as old as 3.47 Ga. Surprisingly large spheres and complex organic lenses occur in rocks as old as 3.22 Ga and ~ 3.4 Ga, respectively, and represent the best candidates for the oldest microfossils. Titaniferous microtubes in volcanic or volcanoclastic rocks inferred as microbial trace fossils have been reevaluated as metamorphic or magmatic textures. Microbially-induced mineralization is supported by CaCO3 nanostructures in 2.72 Ga stromatolites. Sulfides 3.48 Ga and younger bear S-isotope ratios indicative of microbial sulfate reduction. Ferruginous conditions may have fueled primary production via anoxygenic photosynthesis–as suggested by Fe-isotope ratios–possibly as early as 3.77 Ga. Microbial methanogenesis and (likely anaerobic) methane oxidation are indicated by C-isotope ratios as early as 3.0 Ga and ~ 2.72 Ga, respectively. Photosynthetic production of O2 most likely started between 3.2 and 2.8 Ga, i.e. well before the Great Oxidation Event (2.45–2.31 Ga), as indicated by various inorganic tracers of oxidation reactions and consistent with morphology of benthic deposits and evidence for aerobic N metabolism in N-isotope ratios at ~ 2.7 Ga.
This picture of a wide diversification of the microbial biosphere during the Archean has largely been derived of bulk-rock geochemistry and petrography, supported by a recent increase in studied sample numbers and in constraints on their environments of deposition. Use of high-resolution microscopy and micro- to nanoscale analyses opens avenues to (re)assess and decipher the most ancient traces of life.
... nov., a granular species. (Thorseth et al., 1995a;Furnes et al., 2001bFurnes et al., , 2006Furnes et al., , 2008 et al., 1996;Furnes et al., 2008), 这与一些细菌或古菌 新陈代谢所引起的 δ 13 C 变化非常相似 (Kelts and McKenzie, 1982) (Preston et al., 2011;Türke et al., 2018)。荧 光染色(DAPI)的方法, 也成功在玄武岩玻璃中提 取到细菌和古菌 DNA 残留 (Torsvik et al., 1998;Fisk et al., 2000Fisk et al., , 2003Furnes et al., 2001b)。这些 (Thorseth et al., 1995b;Staudigel et al., 1998;Chen et al., 2014) (Veksler et al., 2007;Mauro et al., 2013); 3)海水 或热液流体与玻璃的化学扩散和化学交换作用 形成橙玄玻璃中伴随的蚀变微结构 (Thorseth et al., 1991;Stroncik et al., 2001;Walton et al., 2003Walton et al., , 2005 (Thorseth et al., 1992;Staudigel et al., 2006Staudigel et al., , 2014Furnes et al., 2008)和质子梯度模型 (Fisk et al., 表 2)。在时间尺度上, 微结构在现代海水覆盖的 洋壳和古老洋壳残片(如蛇绿岩和绿岩带中的玄 武岩)中都有广泛发育 (Furnes et al., 2005;Banerjee et al., 2008;Fliegel et al., 2010a;Staudigel et al., 2014;Wacey et al., 2014), 这一时间跨度从第 四纪到太古代(图 7-B)。其中, 最早微结构可追溯 到 35 亿年以前的玄武岩玻璃中 (Furnes et al., 2004;, 这表明在地球演化早期微 生物很可能已出现, 并能利用玄武岩这一基质进 行新陈代谢。在古老洋壳残片中微结构分布零星, Furnes et al., 2008;Fliegel et al., 2010b;McLoughlin et al., 2010b Furnes et al., 2004;Fliegel et al., 2010a;Staudigel et al., 2015 注: "-"该文献未报道或数据缺失。 Note: "-" not reported or data missing. Staudigel, 1999;Furnes et al., 2007)。 With the increase of depth, the permeability and porosity of oceanic crust rock will decrease, and the temperature will increase. ...
Bioalteration microstructures in basaltic glasses are those pits and grooves formed by microbial metabolisms. Microbes produce organic acid while absorbing nutrients within basaltic glasses, dissolving the basaltic glasses and forming bioalteration microstructures. Bioalteration microstructures within basalts not only occur in modern oceanic crusts, but have been discovered in ophiolites and greenstone belts representing ancient oceanic crusts. Studying the morphological characteristics, formation mechanisms and spatio-temporal distributions of bioalterated microstructures within basaltic glasses is thus pivotal to exploring the origin and evolution of early lives on Earth, and provide new materials to understand the composition of microbial organisms in the sub-seafloor deep biosphere and their spatio-temporal distribution characteristics. Morphologically, bioalterated microstructures within basaltic glasses can be divided into granular and tubular microstructures. However, abiotic microstructures can also occur in basalt glasses mimicking those bio-alterted microstructures. Thus, multi-disciplinary studies combining morphologies, elemental and isotopic geochemistry, organic and DNA detection are all significant in distinguishing bioalterated microstructures from abiotic ones. A summary of occurrences of bioalteration microstructures from geological records show that they occur more common than previously thought, and the vertical distribution of these microstructures within oceanic crusts may be closely related to the porosity and permeability of basaltic rocks. In addition, different seafloor environmental conditions, such as redox, pH, water depth, temperature, and porosity, can all greatly affect the composition of microbial community and their subsequently formed bioalteration microstructures. It remains to be answered, however, that which of these factors play a major control.
Key words: basaltic glass, bioalteration microstructure, ichnofossil, subseafloor deep biosphere
... Indirect evidence of microbial, including fungal, activities appears early in the history of the earth (Furnes et al. 2004;McLoughlin et al. 2009McLoughlin et al. , 2010 in the form of what are referred to as ichnofossils (trace fossils), a term used to describe morphologically recurrent structures resulting from the activities of an organism that modi es the substrate (Bertling et al. 2006;Knaust and Bromley 2012). Ichnofossils, suggestive of early microbial activity, are found in a variety of the Precambrian rocks, some of which are 4.0-2.5 Ga (Fisk et al. 1998;Staudigel et al. 2008;McLoughlin et al. 2010;Knoll 2014). ...
... Indirect evidence of microbial, including fungal, activities appears early in the history of the earth (Furnes et al. 2004;McLoughlin et al. 2009McLoughlin et al. , 2010 in the form of what are referred to as ichnofossils (trace fossils), a term used to describe morphologically recurrent structures resulting from the activities of an organism that modi es the substrate (Bertling et al. 2006;Knaust and Bromley 2012). Ichnofossils, suggestive of early microbial activity, are found in a variety of the Precambrian rocks, some of which are 4.0-2.5 Ga (Fisk et al. 1998;Staudigel et al. 2008;McLoughlin et al. 2010;Knoll 2014). For example, one type of evidence takes the form of 1.3-1.93 ...
... It then follows that "older" examples of titanitemineralized tubular textures attributed to microbial activity that are preserved along healed fractures in the metamorphosed margins of pillow lavas in Archean greenstone belts [25,35,37,91,94] might also simply represent the preserved (titanite-mineralized) relicts of preferential corrosion of radiation damage and/or pressure solution etch-tunnelling (i.e., "abiotic" microtextures) that formed during the encroachment of seawater into these basaltic glass pillow margins in Archean times. ...
Over the last two decades, conspicuously “biogenic-looking” corrosion microtextures have been found to occur globally within volcanic glass of the
in situ
oceanic crust, ophiolites, and greenstone belts dating back to ~3.5 Ga. These so-called “tubular” and “granular” microtextures are widely interpreted to represent
bona fide
microbial trace fossils; however, possible nonbiological origins for these complex alteration microtextures have yet to be explored. Here, we reevaluate the origin of these enigmatic microtextures from a strictly nonbiological standpoint, using a case study on submarine glasses from the western North Atlantic Ocean (DSDP 418A). By combining petrographic and SEM observations of corrosion microtextures at the glass-palagonite interface, considerations of the tectonic setting, measurement of U and Th concentrations of fresh basaltic glass by ICP-MS, and theoretical modelling of the present-day distribution of radiation damage in basaltic glass caused by radioactive decay of U and Th, we reinterpret these enigmatic microtextures as the end product of the preferential corrosion/dissolution of radiation damage (alpha-recoil tracks and fission tracks) in the glass by seawater, possibly combined with pressure solution etch-tunnelling. Our findings have important implications for geomicrobiology, astrobiological exploration of Mars, and understanding of the long-term breakdown of nuclear waste glass.
... Unlike bioalteration textures previously dated from the Hooeggenoeg Complex of the Barberton Greenstone Belt, the Euro basalt of the Pilbara Craton ( Banerjee et al., 2007), and the Wutai belt of north-China ( McLoughlin et al., 2010a,b), the textures investigated here are not mineralized by titanite and hence direct in situ dating of the textures themselves is not possible. However, the samples record a prograde metamorphic assemblage from subgreenschist to lower greenschist facies. ...
Pillow lava rims and interpillow hyaloclastites from the upper part of the Pechenga Greenstone Belt, Kola Peninsula, N-Russia contain rare tubular textures 15-20 μm in diameter and up to several hundred μm long in prehnite-pumpellyite to lower greenschist facies meta-volcanic glass. The textures are septate with regular compartments 5-20 μm across and exhibit branching, stopping and no intersecting features. Synchrotron micro-energy dispersive X-ray was used to image elemental distributions; scanning transmission X-ray microscopy, Fe L-edge and C K-edge were used to identify iron and carbon speciation at interfaces between the tubular textures and the host rock. In situ U-Pb radiometric dating by LA-MC-ICP-MS (laser ablation multicollector inductively coupled plasma mass spectrometry) of titanite from pillow lavas yielded a metamorphic age of 1790 ± 89 Ma. Focused ion-beam milling combined with transmission electron microscopy was used to analyze the textures in three dimensions. Electron diffraction showed that the textures are mineralized by orientated pumpellyite. On the margins of the tubes, an interface between mica or chlorite and the pumpellyite shows evidence of dissolution reactions where the pumpellyite is replaced by mica/chlorite. A thin poorly crystalline Fe-phase, probably precipitated out of solution, occurs at the interface between pumpellyite and mica/chlorite. This sequence of phases leads to the hypothesis that the tubes were initially hollow, compartmentalized structures in volcanic glass that were mineralized by pumpellyite during low-grade metamorphism. Later, a Fe-bearing fluid mineralized the compartments between the pumpellyite and lastly the pumpellyite was partially dissolved and replaced by chlorite during greenschist metamorphism. The most plausible origin for a septate-tubular texture is a progressive etching of the host matrix by several generations of microbes and subsequently these tubes were filled by authigenic mineral precipitates. This preserves the textures in the rock record over geological time. The micro textures reported here thus represent a pumpellyite-mineralized trace fossil that records a Paleoproterozoic sub-seafloor biosphere.
... Titanite is a common mineralizing phase and micro-textures with comparable morphologies to those found in the in-situ oceanic crust have now been reported from Phanerozoic ophiolites and Archean greenstone belts (reviewed by Furnes et al., 2007). The sequence of events is: microbial alteration, authigenic mineralization and subsequent metamorphism; this is summarized in Fig. 7 of McLoughlin et al. (2010b). The mineralization process appears to obscure some of the fine morphological detail seen in recent bioalteration textures, such as spirals and annulations, and on average results in filaments with larger diameters than that of the original hollow tubes (Fig. 2 and Furnes et al., 2007). ...
... Morphologically comparable textures, have also been described from the 3.35-3.31 Ga pillow lavas of the Euro Basalt in Western Australia and 2.52 Ga pillow lavas of the Wutai Group of North West China (McLoughlin et al., 2010b). The evidence for the biogenicity of these trace fossils has been extensively explained elsewhere (see Banerjee et al., 2006;Furnes et al., 2004;Furnes et al., 2008) and rather here, we summarise the major features that support the biogenicity and especially antiquity of the Barberton trace fossils. ...
... Bioalteration textures can remain hollow for long periods of time, as for example, micro-textures from the little deformed 0.092 Ga Troodos ophiolite (Furnes et al., 2001c) and the 0.122 Ga Ontong Java Plateau (Banerjee and Muehlenbachs, 2003) are largely unmineralized. A summary of this sequence of events is shown in Fig. 7 of McLoughlin et al. (2010b). ...
... This may, in part, be due to the enhancement and masking of titanite grains. The early precipitation of titanite within the larger microtubular textures is suggested to enhance microtube preservation by means of limiting those morphological changes that would otherwise be caused by re-crystallization of the host rock (see Fig 7 in McLoughlin et al. (2010a)). It is also possible, of course, that the smaller granular textures have been obscured by recrystallization of the glass. ...
There is an apparent preservational paradox in the early rock record. Cellularly preserved and ensheathed microfossils which are remarkably preserved from the late Archaean (c.2700 Ma) onward, have rarely been found in the earlier rock record and when they are their biogenicity is debated. Likewise, the abundance and morphological complexity of stromatolites appears much reduced in the early Archaean and even these lack compelling associations with organic remains of microbial mats. This ‘preservational dark age’ may have arisen because microfossils and microbial mats were absent, because conditions for their preservation were rare or, as we suggest here, because scientists have largely been looking in the wrong places.
To illustrate the potential of looking far beyond ‘chertified Bahamian lagoons’, we make a traverse across the key potential habitats for early life on Earth and identify some exciting and new taphonomic windows, in the search for Earth’s earliest microfossils, trace fossils and stromatolites. Such habitats include hitherto little explored pillow lavas, hydrothermal vents and beach sandstones. These new windows are already starting to provide surprising insights into the nature of the earliest vital processes.
... The biogenicity of such textures has been discussed using various approaches such as morphology [McLoughlin et al., 2009b], elemental distributions (C, N, S and P) [Banerjee et al., 2007; Banerjee and Muehlenbachs, 2003], DNA staining [Banerjee and Muehlenbachs, 2003], organic carbon analysis [Benzerara et al., 2007], and stable isotope signatures [Furnes et al., 2002; Torsvik et al., 1998]. Such textures have been described within glassy pillow lava rims from in situ oceanic crust [Banerjee and Muehlenbachs, 2003], ophiolites [Furnes et al., 2002, 2008], and even from Archean greenstone belts [Banerjee et al., 2004, 2007; Furnes et al., 2004; McLoughlin et al., 2009a; Staudigel et al., 2008] that represent some of the oldest oceanic crustal fragments on Earth [Staudigel et al., 2008]. [3] In the older crustal fragments and ancient oceanic crust preserved in greenstones belts, the tubular textures are infilled with secondary minerals (commonly titanite) and preserved over billions of years in the rock record. ...
