Bio-signatures in metabasaltic glass of a Caledonian ophiolite, West Norway

Abstract

Evidence of bioalteration of natural basaltic rocks, presently receiving much attention, has so far been restricted to in situ oceanic crust and ophiolites in which fresh glass is still present. Here we present evidence of preserved bio-signatures in the chilled margin of pillow lavas of an old (443 Ma) ophiolite that has suffered pervasive lower greenschist facies metamorphism and deformation. X-ray mapping of initial alteration zones shows the remains of organic carbon associated with highlyconcentrated Fe and S. Bioproduction of CO 2 is further reflected in the low δ 13 C values of calcite extracted from pillow rims, compatible with microbe-induced fractionation during oxidation of organic matter. We attribute these effects to growth of sulphate-reducing bacteria at the early stage of ophiolite formation. During energy metabolism these bacteria reduce sulphate to H 2 S and oxidize organic matter to CO 2 . Hydrogen sulphide will eventually react with iron and form pyrite, and carbon dioxide is precipitated as calcium carbonate. The results of this study may thus trigger the search for bio-signatures in glassy volcanic rocks of any age.

Tuff life: Bioalteration in volcaniclastic rocks from the Ontong Java Plateau

“…Similar textures to those described in this study have been attributed to microbial alteration of glassy pillow rims in modern oceanic crust and ophiolites [ Thorseth et al , 1992, 1995, 2001; Furnes et al , 1996, 1999, 2001a, 2001b, 2001c, 2002a, 2002b; Fisk et al , 1998; Torsvik et al , 1998; Furnes and Staudigel , 1999]. Furthermore, the sizes of both types of microbial textures are within the size range of common microbes and we have no sensible abiotic explanation for these features.…”

Tectonic control of bioalteration in modern and ancient oceanic crust as evidenced by carbon isotopes

“…In contrast, the crystalline interior of pillow lavas has isotope values bracketed between typical magmatic basalt values (inherited from mantle CO 2 ) and inorganically precipitated carbonate (in veins and amygdales). These contrasting C‐isotopic values from pillow rims and interiors are extremely important in investigating the activity of microbial life in the uppermost in situ oceanic crust and ancient ophiolites (Furnes et al . 2002, 2004, 2005; Banerjee et al .…”

“…Data sources: Mirdita ophiolite, N. R. Banerjee (unpubl. data, 2006); Solund–Stavfjord ophiolite, Furnes et al . (2002).…”

Septate‐tubular textures in 2.0‐Ga pillow lavas from the Pechenga Greenstone Belt: a nano‐spectroscopic approach to investigate their biogenicity

“…Along fractures and in the glassy rim tubular and granular textures are common and these features have been interpreted as trace fossils. These textures have been documented in recent oceanic crust (Torsvik et al, 1998;Furnes & Staudigel, 1999;Furnes et al, , 2001cBanerjee & Muehlenbachs, 2003;Benzerara et al, 2007), ophiolites of different age (Furnes et al, 2001b(Furnes et al, , 2002(Furnes et al, , 2005(Furnes et al, , 2006 and even in the Archean rock record (Furnes et al, 2004;Banerjee et al, 2007). The biogenicity of such structures has been discussed using various proxies.…”

“…, 1999, 2001c; Banerjee & Muehlenbachs, 2003; Benzerara et al. , 2007), ophiolites of different age (Furnes et al. , 2001b, 2002, 2005, 2006, 2007) and even in the Archean rock record (Furnes et al.…”