Bioalteration of basaltic glass in the oceanic crust

Abstract

[1] Abstract: Bioalteration of Quaternary to Early Cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ ODP) samples from shallow to deep drill holes from the north to central Atlantic Ocean, Lau Basin, and Costa Rica Rift, a wide range of marine settings. Biogenerated textures are rooted in fractures and occur as two main types, a granular type and a tubular type. The granular type, common at all depths within the volcanic pile, appears as solid bands, semicircles or irregular patches of individual and/or coalesced spherical bodies, mostly 0.2-0.6 mm in diameter, with irregular protrusions into the fresh glass. The tubular type is more common at deeper levels in the crust and consists of thin tubes, sometime branching bodies, mostly 20 -30 mm long and are more common at deeper levels. The upper crust displays a large variability in the relative importance of biotic to abiotic alteration, and the degree of bioalteration appears to decrease with depth. Thus the fraction of bioalteration of the total alteration of the glass ranges from 20 -90% in the upper 300 m down to a maximum of 10% at about 500 m depth. This might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust. The proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust. Thus bioalteration lasts as long as abiotic alteration, i.e., for as long as water is available to the hydration of the oceanic crust. Evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least 70 Ma, and thus the deep biosphere is likely to expand at least into crust of this age.

Microbial Ecology of the Dark Ocean above, at, and below the Seafloor

“…Additional studies have confirmed colonization of fresh mineral surfaces by microorganisms (133,425,517,540). Further support for microbial activity in crustal materials derives from the observation of conspicuous "tubes" that are observed in basalt glasses, which are hypothesized to be generated by microorganisms growing into the surfaces of minerals (162,163,178,179,188).…”

Paleoarchean trace fossils in altered volcanic glass

“…We suggest here that this is due to its original scarcity as precursor fossils and its low probability of preservation. Quantitative studies of bioalteration texture abundance in Cenozoic glasses have shown that by far the most abundant bioalteration features are granular textures, making up more than 90% of all textures observed (1,18). The remaining 10% (or less) are made by tubular or tunnel-like cavities, whereby the most distinctive "signature" types of tunnels, spirals, annulated, or decorated tubes, or bifurcating tubes, are only a miniscule fraction of that 10%.…”

“…1C). Varioles commonly occur in the outermost 1-5 mm of pillow margins, where they range in size from ∼5-50 microns, and occur as isolated occurrences, in bands, or they may coalesce into opaque glass or tachylite (13,(18)(19)(20)(21). Bioalteration textures may show an intimate textural relationship with such varioles (Fig.…”

Prokaryotic diversity, distribution, and insights into their role in biogeochemical cycling in marine basalts

“…These observations raise intriguing questions about the role that microorganisms play in biogeochemical cycling in basalts. Biological alteration of basalt by microorganisms has been the focus of numerous studies, with compelling evidence suggesting that they do play a part in this process (Thorseth et al, 1995;Giovannoni et al, 1996;Fisk et al, 1998Fisk et al, , 2003Torsvik et al, 1998;Furnes and Staudigel, 1999;Furnes et al, 2001Furnes et al, , 2004Banerjee and Muehlenbachs, 2003).…”