seafloor alteration of basaltic glass textures geochemistry and endolithic microorganisms 1 the incipient low temperature alteration of glassy margins of recent seafloor lavas from the mohns ridge is characterized by scanning electron microscopy and bulk chemical analyses of major and trace elements these investigations are designed to evaluate the endolithic microbial biomass to identify relations between alteration textures and microorganisms and to identify the chemical processes that take place during alteration the basaltic glass along intersecting fractures and around vesicles is typically altered to concentrically zoned yellow brown amorphous gel palagonite in most fractures microorganisms are observed at the outer surfaces of palagonite rims within porous zones of the rims and frequently also at the glass palagonite interfaces the cells act as nucleation sites for precipitation and become encrusted and embedded in palagonite with time zones of porous palagonite containing numerous hollow fossilized cells alternate with zones of compact palagonite lacking distinct cell structures which together indicate that the microbial growth is discontinuous the palagonite has an average organic carbon content of 0 9 wt 13corg 22 which derive from both living and fossilized biomass the microbial growth and biomineralization are major controls on the porosity and texture of the palagonite and thus likely on the chemical exchange between glass and seawater pit marks in the glass in fractures both with and without microbes indicate that microbial as well as abiotic processes mediate pitting elemental and isotope data show that the transformation of glass to gel palagonite at seafloor conditions with high water rock ratios results in near complete loss of si and alkali elements to seawater formation of fe and al oxyhydroxides complete exchange of alkaline earth elements like sr with seawater retention of v cu y pb th u and trivalent rees accompanied by a strong gain of these and other elements from seawater higher fe ti ratios in the gel palagonite compared to the parental glass suggest that the palagonite represents a mixture of fe ti oxyhydroxides derived from both the glass and seawater

microbes play an important role in the alteration of oceanic crust microbes have been identified within altered parts of the glass rims of pillow lavas in the upper oceanic crust 237 m below the top of the volcanic basement of odp hole 896a at the costa rica rift their presence is verified by spherical and vermicular microbodies containing dna the elemental composition of the microbially processed areas differ from the parent glass further the microbially processed parts showing different morphological forms also show different elemental composition extreme k enrichment indicate that microbes are presently active in the alteration process the carbon isotopic composition of disseminated carbonates within the basaltic section of the hole 504b 1 km distance from hole 896a also give evidence for microbial activity during rock alteration the 13c values of most of these trace carbonates are very low reflecting metabolic control of the carbon cycle in these rocks microbial alteration of basaltic glass comprising a substantial volume and surface area of the upper oceanic crust may thus play an important role in the element exchange between oceanic crust and seawater

cenozoic and late mesozoic stratigraphy and subsidence history of the norwegian margin the stratigraphy of the passive continental margin off norway is mapped utilizing both deep sea drilling project dsdp data at five sites on the outer margin and multichannel seismic mcs data collected by lamont doherty geological observatory distinct units in the acoustic stratigraphy are tied to biostratigraphic and lithostratigraphic units in the drill data and mapped throughout most of the margin stratigraphy of the pre lower eocene section not encountered in drilling is inferred from depositional patterns and correlation with the continental shelf sequences the stratigraphy of which has been developed independently from detailed surveys the margin can be divided into three physiographic provinces two broad shelf and slope regions separated by the jan mayen fracture zone and the steep narrow shelf and slope off the lofoten islands each experienced a separate cenozoic subsidence history the voring plateau is partly underlain by oceanic crust it subsided nearly 1 000 m less than expected from thermal contraction but it did so following the development of a relatively deep water environment in the paleocene north of the voring plateau the margin may have subsided a few hundred metres more than thermal studies had predicted there is no evidence for a phase of extensional deformation associated with the inception of spreading the youngest faulted level occurs at the late jurassic level preceding sea floor spreading by nearly 100 ma and deformation in the cretaceous section is characterized by large uplift structures that may be of halokinetic origin the physiographic provinces as well as the cenozoic subsidence patterns along the margin appear to be related to the style and extent of mesozoic basin development and tectonics along the margin

biological mediation in ocean crust alteration how deep is the deep biosphere abstract biological mediation has been suggested as a control of the chemical exchange between the oceanic crust and seawater but very little is known about its distribution within the oceanic crust and the relative importance of biotic and abiotic processes alteration textures in glassy pillow lava margins record the proportions of biotic and abiotic alteration and the fraction of biotic alteration may be determined by point counting methods we used this method at dsdp odp sites 417d and 418a 110 ma crust south of bermuda rise and holes 504b and 896a 5 9 ma costa rica rift biotic alteration dominates glass alteration in the upper 250 m of the oceanic crust 60 85 of the total glass alteration and steadily declines in importance down to 10 20 at 500 m the consistency of data between two crustal sections of very different age and tectonic setting suggest that microbially mediated glass alteration may be largely confined to the upper oceanic crust however both sites studied are sealed by thick sedimentary layers and thus are typical for ocean crust underlying the oceanic basins rather than crust at mid ocean ridges with possibly deep and rapid hydrothermal circulation down hole temperature measurements at the costa rica rift suggest that glass altering microbes are hyperthermophilic and thrive at least up to temperatures of about 90 c microbial activity does occur at higher temperatures up to about 110 c but with reduced apparent abundance

evidence for microbial activity at the glass alteration interface in oceanic basalts a detailed microbiological and geochemical study related to the alteration of basaltic glass of pillow lavas from the oceanic crust recovered from hole 896a on the costa rica rift penetrating 290 m into the volcanic basement has been carried out a number of independent observations pointing to the influence of microbes may be summarized as follows 1 alteration textures are reminiscent of microbes in terms of form and shape 2 altered material contains appreciable amounts of c n and k and the n c ratios are comparable to those of nitrogen starved bacteria 3 samples stained with a dye dapi that binds specifically to nucleic acids show the presence of dna in the altered glass further staining with fluorescent labeled oligonucleotide probes that hybridize specifically to 16s ribosomal rna of bacteria and archaea demonstrate their presence in the altered part of the glass 4 disseminated carbonate in the glassy margin of the majority of pillows shows d 13 c values significantly lower than that of fresh basalt also suggests biological activity the majority of the samples have d 18 o values indicating temperatures of 20 100oc which is in the range of mesophilic and thermophilic micro organisms 1998 elsevier science b v all rights reserved

elemental abundance distributions in suboceanic basalt glass evidence of biogenic alteration 1 the alteration of subseafloor volcanic glass from three locations is qualitatively attributed to biological biotic or chemical abiotic reactions on the basis of microscopic morphology of the boundary between the unaltered and altered glass eleven element composition of fresh basalt glass sideromelane and its alteration products were determined by electron microprobe principal component analysis pca using these eleven elements as input na11 mg12 al13 si14 p15 cl17 k19 ca20 ti22 mn25 and fe26 extracts three factors accounting for 80 5 of the variance in the data these three factors can serve as inputs to a hierarchical cluster analysis hca algorithm for data driven discovery of three sample classes this autonomous classification agrees with the petrographic microscopic classification in 14 of 15 biotic clay analyses from a set of 34 analyses identified microscopically as abiotic clay the autonomous system identifies 4 with elemental abundance characteristics similar to the biotic clay and 4 similar to unaltered glass pca factors are then used as inputs to train an artificial neural network to produce a bayesian probability of correct classification using the classes discovered by hca mean bayesian probabilities of correct classification for abiotic clays biotic clays and glass were 76 1 8 5 64 9 9 0 and 77 0 7 2 respectively interestingly in the 9 of 74 cases where visual and elemental analysis disagree the bayesian probability estimate of correct classification using only elemental abundance data is low 60 0 11 7 compared to analyses where visual and elemental data agree 75 5 7 8 to our knowledge this is the first demonstration of a quantitative method for discrimination of biotic and abiotic alteration of subocean basalt glass as such the techniques make possible the systematic assessment of the impact of microbial life on subsurface basalts

sulfur 33 constraints on the origin of secondary pyrite in altered oceanic basement abstract low temperature alteration of oceanic basement rocks is characterized by net gain of sulfur which commonly yields low 34s values suggesting involvement of microbial sulfate reduction in order to test whether secondary sulfide minerals are consistent with a biogenic source we apply high precision multiple sulfur isotope analysis to bulk rock sulfide and pyrite isolates from two contrasting types of altered oceanic basement rocks namely serpentinized peridotites and altered basalts samples from two peridotite sites iberian margin and hess deep and from a basalt site on the eastern flank of the juan de fuca ridge yield overlapping 34s values ranging from 0 to 44 in contrast sulfides in the basalt site are characterized by relatively low 33s values ranging from 0 06 to 0 04 compared to those from peridotite sites 0 00 to 0 16 the observed 33s signal is significant considering the analytical precision of 0 014 2 we present a batch reaction model that uses observed 34s and 33s relationships to quantify the effect of closed system processes and constrain the isotope enrichment factor intrinsic to sulfate reduction the estimated enrichment factors as large as 61 and 53 for peridotite and basalt sites respectively suggest the involvement of microbial sulfate reduction the relatively high 33s values in the peridotite sites are due to sulfate reduction in a closed system environment whereas negative 33s values in the basalt site reflect open system sulfate reduction a larger extent of sulfate reduction during alteration of peridotite to serpentinite is consistent with its higher h2 production capacity compared to basalt alteration and further supports in situ microbial sulfate reduction coupled with h2 production during serpentinization reactions

pollen corrected leaf wax d h reconstructions of northeast african hydrological changes during the late miocene abstract plant leaf wax hydrogen isotope dwax reconstructions are increasingly being used to reconstruct hydrological change this approach is based upon the assumption that variations in hydroclimatic variables and in particular the isotopic composition of precipitation dp dominate dwax however modern calibration studies suggest that offsets between plant types may bias the dwax hydrological proxy at times of vegetation change in this study i pair leaf wax analyses with published pollen data to quantify this effect and construct the first vegetation corrected hydrogen isotopic evidence for precipitation dcorrp in marine sediments from deep sea drilling program site 231 in the gulf of aden spanning 11 4 3 8 ma late miocene and earliest pliocene i find 77 swings in dwax that correspond to pollen evidence for substantial vegetation change similarities between dp and dcorrp imply that the hydrological tracer is qualitatively robust to vegetation change however computed vegetation corrections can be as large as 31 indicating substantial quantitative uncertainty in the raw hydrological proxy the resulting dcorrp values quantify hydrological change and allow us to identify times considerably wetter than modern at 11 09 7 26 5 71 and 3 89 ma more generally this novel interpretative framework builds the foundations of improved quantitative paleohydrological reconstructions with the dwax proxy in contexts where vegetation change may bias the plant based proxy the vegetation corrected paleoprecipitation reconstruction dcorrp represents the best available estimate as proof of concept for an approach that i hope will be refined and more broadly applied

modern n alkane abundances and isotopic composition of vegetation in a gymnosperm dominated ecosystem of the southeastern u s coastal plain abstract prior analyses of n alkyl lipids in vegetation indicate low concentrations of n alkanes in gymnosperm leaves and significant offsets in lipid carbon isotope values of angiosperms and gymnosperms this finding has implications for paleoenvironmental studies utilizing n alkyl lipid proxies in gymnosperm dominated ecosystems such as the pine ecosystems of the u s southeastern coastal plain i provide here the n alkane abundances and distributions for 19 of the most dominant taxa in the longleaf pine ecosystem along with n c 29 alkane 13 c values 13 c n c29 additionally i assess modern relationships between stable hydrogen isotope values of n c 29 alkanes 2 h n c29 and mean annual precipitation to constrain apparent fractionations e 2 h n c29 map necessary to conduct regional paleoclimate reconstructions gymnosperms of the coastal plain have extremely low n alkane abundances relative to angiosperms and are unlikely to contribute significantly to sedimentary archives lake surface sediment n alkane distributions 2 h n c29 and 13 c n c29 values indicate that they are primarily sourced from less dominant angiosperms the e 2 h n c29 map values are 10 0 vsmow more positive for gymnosperms relative to angiosperms and e 13 c alkane leaf values are 1 5 vpdb more positive for gymnosperms relative to angiosperms but with overlap

biogenic versus metamorphic origins of diverse microtubes in 2 7 gyr old volcanic ashes multi scale investigations abstract titanite bearing microtubes in metabasalts have been interpreted as evidence for early microbial life thriving in the oceanic crust up to 3 5 ga ago based on similarities with microtubular pitting occurring in modern volcanic glass an alternative abiogenic origin as ambient inclusions trails aits has been debated but textural evidence such as the absence of diagnostic terminal inclusions was used to discard this possibility here we describe a variety of microtubes occurring in pyroclastic tuff of the 2 72 ga tumbiana formation western australia some of which resemble titanite filled microtubes reported in metamorphosed archean pillow basalts to assess the origin of the tumbiana microtubes we investigated their structure and chemistry and their root zone down to the sub micrometer scale using a combination of raman microspectroscopy scanning electron microscopy sem focused ion beam fib milling and scanning transmission electron microscopy stem coupled with energy dispersive x ray spectrometry edxs we report four types of microtubes type 1 comprises calcite microtubes type 2 comprises aits showing terminal pyrite and trails with negative crystal shapes type 3 comprises titanite microtubes in chlorite displaying morphologies similar to those reported in 3 5 ga old archean lavas at the sub micrometer scale they display a dendritic structure depending on their localization type 3 microtubes have been divided in three main sub types i type 3a extends in pores filled by chloritized cement ii type 3b occurs in pyroclasts and iii type 3c overgrows and thus post dates type 2 aits type 4 comprises titanite microtubes confined to quartz and calcite rims types 3 and 4 microtubes are terminated by sub micrometric carbonaceous and or mineral inclusions altogether these features suggest that the tumbiana titanite microtubes have formed as dendritic aits associated with displacement of mineral and or organic inclusions in pyroclasts and in surrounding void filling cements during recrystallization they are therefore unlikely to represent relics of the activity of early microbial life rather abiotic features formed in the presence of organic matter during burial metamorphism in that sense they may represent some sort of indirect evidence for life

extent of the microbial biosphere in the oceanic crust we estimate the depth of the 120 c isotherm by constructing crustal thermal gradients based on theoretical and observed conductive heat flux as a function of lithospheric age we chose the 120 c isotherm because it is close to the upper limit for prokaryotic life and therefore the isotherm approximates the maximum depth at which life can persist in the ocean crust the depth of the potential microbial biosphere increases with lithospheric age from approximately 0 5 to 1 km for 1 ma lithosphere to as much as 5 km at a subduction age of 180 ma we use global models of oceanic plate creation to estimate the volume of crust occupied by the biosphere today and throughout geologic time presently the volume of the ocean crust that is capable of containing life is similar to the volume of the oceans 1018 m3 depending on the model used for the growth of continental crust the volume of rock available to house the subsurface biosphere may have remained constant or doubled since the archean although the thermal models presented here provide estimates for the potential depth and volume of rock in which microbes may live the biomass in this volume is not well constrained using a previously published model the prokaryotic biomass in the igneous ocean crust is estimated to exceed that in all aquatic and soil environments and is similar to that in the continental subsurface and in marine sediment most of the crustal biomass beneath the sediments is likely contained within the extrusive layer and this has probably been the case since microbes first colonized the oceanic crust in the archean

alteration of oceanic volcanic glass textural evidence of microbial activity the subsurface biosphere may constitute as much as 50 percent of earth9s biomass direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor this survey of basalts of the atlantic pacific and indian oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust which has a volume estimated at 1018 cubic meters although this is the largest habitat on earth its low abundance of bacteria constitutes much less than 1 percent of earth9s biomass

characterization of alteration textures in cretaceous oceanic crust pillow lava from the n atlantic dsdp hole 418a by spatially resolved spectroscopy abstract the habit mineralogy crystallography and fe speciation of tubular and granular alteration textures in basaltic glass recovered from dsdp hole 418a which have previously been associated with biologically mediated alteration were investigated using an integrated suite of microscopic and spectroscopic approaches in order to shine light on their formation and mineralization history two different analytical approaches were used 1 micro scale investigations with conventional petrographic optical microcopy and microscale x ray fluorescence mapping and x ray absorption spectroscopy and 2 nano scale analyses with fib focused ion beam milling to prepare cross sections for tem transmission electron microscopy eels electron energy loss spectroscopy and stxm scanning transmission electron microscopy analyses the integrated data show that tubular and granular textures are similar in chemical mineralogical and structural habit both granular and tubular alteration textures show a marked transition from ferrous iron in the glass matrix to ferric iron in the textures granular and tubular textures are filled with sheet silicates of similar chemistry and both exhibit thin amorphous alteration rims 10 20 nm wide the alteration rims are typically depleted in ca and fe ca is enriched at the contact between the secondary mineralization and the alteration rims whereas fe is enriched throughout the alteration features and is mainly present as fe iii in contrast to fe ii in the host glass carbon is enriched only in a few areas and could possibly be of organic origin but is not bound in carbonate the mineralization of the features follows the sequence dissolution of the glass formation of a leached amorphous rim mineralizing the cavities by smectide type clays and subsequently congruent growing of the texture diameter by diffusing of the elements through the alteration layer none of the features could be linked solely to a biogenic origin and hence the biogenicity of the textures can neither be refuted nor supported by this micro and nano scale data set

experimental study on weathering of seafloor volcanic glass by bacteria pseudomonas fluorescens implications for the contribution of bacteria to the water rock reaction at the mid oceanic ridge setting the biologically mediated weathering of the ocean crust has received increasing attention in recent decades but the rates and the possible mechanism of elemental release during microbe basalt interactions occurring below the seafloor have not been studied in detail in this study we established an experimental weathering study of seafloor natural basaltic glass comparing the effect of microbial activity pseudomonas fluorescens in p rich and p poor media with parallel controls containing either nonviable cells or organic acid the changes in the chemical parameters including ph bacterial densities and ion concentrations ca mg si mn al fe and p in the solution were examined during the different batch experiments the results showed that the ph decreased from 7 0 to 3 5 and the bacterial density increased from 10 5 to 10 8 cells ml during the first 120 h and the cell numbers remained constant at 10 8 cells ml and the ph increased from 3 5 to 6 between 120 h and 864 h in the p bearing reactors containing bacteria in contrast during all the experimental time the ph remained close to neutral condition in the abiotic control systems and the dissolution rates increased markedly with a decrease in ph and became minimal at near neutral ph in p bearing reactors containing bacteria where ca si and mg release rates were 2 to 4 fold higher than those obtained in chemical systems and biotic p limited systems furthermore the surfaces of the natural volcanic glass from the biotic systems were colonized by bacteria simultaneously the etch pits were observed by scanning electron microscope which further indicate that the bacteria may promote the mineral dissolution for energy gain some elements e g fe mn and al releasing from natural volcanic glass are likely an important source of the elemental budget in the ocean and thus the element release and its possible mechanism conducted in this experimental study have potential implications on the biogeochemical cycling process in the mid oceanic ridge setting c 2014 elsevier ltd all rights reserved

preservation of biosignatures in metaglassy volcanic rocks from the jormua ophiolite complex finland evidence of microbially mediated alteration of basaltic glass is preserved in originally glassy basalts rims of pillow lavas hyaloclastite breccias and chilled margins of dykes from the well preserved 1 95ga jormua ophiolite complex joc of northeastern finland although textural evidence of microbial alteration is commonly observed in relic glass from recent oceanic crust and some ophiolites these textures have been destroyed during greenschist to lower amphibolite facies regional metamorphism and deformation of the joc however another robust biosignature is found in the generally depleted d 13 c values of disseminated carbonate extracted from originally glassy basalts relative to crystalline samples the same distribution of d 13 c values is well documented in samples from recent oceanic crust as well as ophiolites of phanerozoic age this characteristic contrastinthe d 13 cvaluesofdisseminatedcarbonateisinterpretedtoresultfrommicrobe inducedfractionationduringoxidation of organic matter x ray mapping of initial alteration zones has identified residual carbon associated with highly concentrated s that is unrelated to carbonate we attribute these biosignatures to microbially mediated alteration of originally glassy material prior to ophiolite emplacement 2004 elsevier b v all rights reserved

on the role of microbes in the alteration of submarine basaltic glass a tem study abstract the alteration of submarine basaltic glass that has been attributed to microbial activity was investigated via transmission electron microscopy in order to document glass alteration and to understand the chemical reactions that bacteria could utilize the features that were examined occur within fresh glass at the alteration front and consist of 0 1 2 3 m patches or tubes of phyllosilicates rimmed by 0 1 0 3 m wide zones of altered glass the altered glass has lost significant mg fe ca and na slight amounts of al and mn and exhibits an order of magnitude increase of k this incongruent dissolution occurred at neutral to acid ph and temperatures 100 fracture volumes which may be important for the supply of nutrients for microbial activity

microbial mediation of authigenic clays during hydrothermal alteration of basaltic tephra kilauea volcano 1 highly altered glassy tephras within the active steam vents at kilauea volcano hawaii contain subsurface bacteria characterized by small 500 nm in diameter epicellular grains attached directly to the cell walls compositionally the grains were dominated by si al fe and k in a stoichiometry similar to a dioctahedral smectite the initial dissolution of glass which may in part have been microbiologically mediated served as the source for many of the elements sequestered into the biomineralized clays overlying the tephras are white crusts silica and calcite and green colored biofilms the biofilms comprise a filamentous likely cyanobacterial community coated with spherical 100 nm in diameter grains of amorphous silica directly attached to the sheaths individual precipitates can easily be resolved but quite often they coalesce forming a dense mineral matrix of amorphous silica for both the clays and silica the microbial surfaces are clearly sites for mineral nucleation and growth these observations imply that microbial biomineralization may be a significant process in the overall alteration of primary basaltic glass in active steam vent systems

biologically mediated dissolution of volcanic glass in seawater we studied the effects of biological mediation on the dissolution of basaltic glass in seawater experiments with typical seawater microbial populations were contrasted with a sterile control and reactions were monitored chemically and isotopically biologically mediated experiments produce twice the mass of authigenic phases than abiotic experiments and the phases are different abiotic alteration of glass dissolves basaltic si and ca and scavenges seawater mg while biotic alteration removes ca from seawater such opposing behavior of ca and mg in biotic and abiotic alteration of basaltic glass may have important implications for the carbon cycle and the exchange processes between ocean crust and seawater 87sr 86sr data of glass and alteration products suggest that biological mediation enhances both the diffusion of seawater sr into glass by a factor of 3 4 and the dissolution of basaltic sr into seawater by a factor of 20 40 the dependence of chemical exchange processes between seawater and glass on biological activity implies that chemical fluxes from water rock interaction at low temperatures may change as life on earth evolves

early life recorded in archean pillow lavas pillow lava rims from the mesoarchean barberton greenstone belt in south africa contain micrometer scale mineralized tubes that provide evidence of submarine microbial activity during the early history of earth the tubes formed during microbial etching of glass along fractures as seen in pillow lavas from recent oceanic crust the margins of the tubes contain organic carbon and many of the pillow rims exhibit isotopically light bulk rock carbonate 13 c values supporting their biogenic origin overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3 5 billion years ago

tem study of the alteration of interstitial glass in morb by inorganic processes abstract scanning electron microscopy sem and transmission electron microscopy tem observations on a suite of mid ocean ridge basalts morb reveal abundant interstitial glass which differs in occurrence and composition from basaltic glass at pillow rims interstitial glass consists dominantly of sio2 and al2o3 and is depleted in other cations representing a highly differentiated residual material low temperature alteration by seawater solutions results in the formation of saponite mg rich variety of smectite replacing the interstitial glass the si al ratio of this saponite reflects that of the source glass chemical changes during this transition differ from those resulting from alteration of basaltic or rhyolitic glass alteration of interstitial glass results in uptake of mg and fe and loss of si and al but there is little or no leaching of alkalis this reflects a strong control on chemical reactions by solution composition high na and mg concentrations of seawater fluids in contrast to basaltic glass at pillow rims our observations do not reveal microbial activities in the alteration of interstitial glass

biogenicity of silicified microbes from a hydrothermal system relevance to the search for evidence of life on earth and other planets biogenicity of silicified microbes from a hydrothermal system relevance to the search for life on earth and other planets

biogenic alteration of volcanic glass from the troodos ophiolite cyprus alteration of basaltic glass through the entire volcanic sequence of the troodos ophiolite is partly bio mediated the following observations support this conclusion alteration textures resembling microbes in form and size altered glass locally shows high carbon concentrations at the alteration front and organic remains the absence of dna suggests that the bio alteration is a fossil process temperatures calculated from 18 o of carbonate assumed to have been in equilibrium with seawater yield 27 65 c and 18 o silicate versus h 2 o relationships indicate seawater alteration these data are consistent with biogenic alteration during an early stage of ocean floor alteration of the troodos oceanic crust some 70 90 ma ago

hydrothermal alteration and microbial sulfate reduction in peridotite and gabbro exposed by detachment faulting at the mid atlantic ridge 15 20 n odp leg 209 a sulfur and oxygen isotope study whole rock sulfur and oxygen isotope compositions of altered peridotites and gabbros from near the 15 20 n fracture zone on the mid atlantic ridge were analyzed to investigate hydrothermal alteration processes and test for a subsurface biosphere in oceanic basement three processes are identified 1 high temperature hydrothermal alteration 250 350 c at sites 1268 and 1271 is characterized by 18o depletion 2 6 4 4 elevated sulfide s and high 34s up to 2 wt and 4 4 10 8 fluids were derived from high temperature 350 c reaction of seawater with gabbro at depth these cores contain gabbroic rocks suggesting that associated heat may influence serpentinization 2 low temperature 150 c serpentinization at sites 1272 and 1274 is characterized by elevated 18o up to 8 1 high sulfide s up to 3000 ppm and negative 34s to 32 1 that reflect microbial reduction of seawater sulfate these holes penetrate faults at depth suggesting links between faulting and temperatures of serpentinization 3 late low temperature oxidation of sulfide minerals caused loss of sulfur from rocks close to the seafloor sulfate at all sites contains a component of oxidized sulfide minerals low 34s of sulfate may result from kinetic isotope fractionation during oxidation or may indicate readily oxidized low 34s sulfide derived from microbial sulfate reduction results show that peridotite alteration may be commonly affected by fluids heat derived from mafic intrusions and that microbial sulfate reduction is widespread in mantle exposed at the seafloor

3 5 billion years of glass bioalteration volcanic rocks as a basis for microbial life abstract alteration textures in volcanic glass from the seafloor fall into two classes one suggestive of abiotic diffusive hydration and chemical exchange and another likely to be caused by microbial cavity forming congruent dissolution glass bioalteration is common in submarine lavas throughout the world s ocean dominant in the upper 300 m of the oceanic crust and found in all well preserved ophiolites and greenstone belts dating back to 3 5 ga it may yield a significant fraction of the global biomass and geochemical fluxes and is relevant to the development of the earliest life on earth we present a critical review concerning these glass bioalteration textures and present new data on their microchemical environment we explore arguments for their biogenicity and further develop the prevalent model for their formation by relating corrosion morphology to the mechanism of microbial dissolution biological alteration produces conspicuous micron scale granular and tubular textures granular glass alteration is well explained by colonizing microbes that selectively dissolve the glass in their contact area forming a sponge like interconnected network of micron sized cavities along glass surfaces tubular alteration meanwhile is more likely to be caused by filamentous cell extensions in a process similar to fungal tunneling of soil feldspars and marine carbonates while we see clear functional similarities to fungal dissolution behavior we do not know whether fungal or prokaryotic organisms are involved however this functional constraint may eventually help to identify potential microbes responsible for these features potentially including eukaryotic or prokaryotic organisms yet we caution that these organisms may be difficult to identify and to study because they are likely to be sparsely distributed slow growing and difficult to cultivate

depth of active bio alteration in the ocean crust costa rica rift hole 504b bio alteration of basaltic glass in the oceanic crust has lately attained much attention one of the many questions related to this topic is the depth at which bio alteration presently takes place in the oceanic crust for this purpose we have investigated samples from the deepest drill hole i e hole 540b at the costa rica rift in the eastern equatorial pacific the glassy rim of pillow lava samples show alteration textures and 13c values compatible with microbial activity throughout the upper 500 m part of the volcanic succession the concentration and distribution patterns of carbon and potassium within the microbially altered parts however indicate that microbes presently interact with the fresh glass to depths of about 380 m into the volcanic basement at temperatures up to 100 c

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

comparing petrographic signatures of bioalteration in recent to mesoarchean pillow lavas tracing subsurface life in oceanic igneous rocks abstract bioalteration of basaltic glass in pillow lava rims and glassy volcanic breccias hyaloclastites produces several distinctive traces including conspicuous petrographic textures these biologically generated textures include granular and tubular morphologies that form during glass dissolution by microbes and subsequent precipitation of amorphous material such bioalteration textures have been described from upper in situ oceanic crust spanning the youngest to the oldest oceanic basins 0 170 ma the granular type consists of individual and or coalescing spherical bodies with diameters typically around 0 4 m these are by far the most abundant having been traced up to 550 m depths in the oceanic crust the tubular type is defined by distinct straight to irregular tubes with diameters most commonly around 1 2 m and lengths exceeding 100 m the tubes are most abundant between 50 m and 250 m into the volcanic basement we advance a model for the production of these bioalteration textures and propose criteria for testing the biogenicity and antiquity of ancient examples similar bioalteration textures have also been found in hyaloclastites and well preserved pillow lava margins of phanerozoic to proterozoic ophiolites and archean greenstone belts the latter include pillow lavas and hyaloclastites from the mesoarchean barberton greenstone belt of south africa and the east pilbara terrane of the pilbara craton western australia where conspicuous titanite mineralized tubes have been found petrographic relationships and age data confirm that these structures developed in the archean thus these biologically generated textures may provide an important tool for mapping the deep oceanic biosphere and for tracing some of the earliest biological processes on earth and perhaps other planetary surfaces

sulfur geochemistry and microbial sulfate reduction during low temperature alteration of uplifted lower oceanic crust insights from odp hole 735b abstract sulfide petrography plus whole rock contents and isotope ratios of sulfur were measured in a 1 5 km section of oceanic gabbros in order to understand the geochemistry of sulfur cycling during low temperature seawater alteration of the lower oceanic crust and to test whether microbial effects may be present most samples have low so4 s values 0 15 have retained igneous globules of pyrrhotite chalcopyrite pentlandite and host secondary aggregates of pyrrhotite and pyrite laths in smectite iron oxyhydroxide magnetite calcite pseudomorphs of olivine and clinopyroxene compared to fresh gabbro containing 100 1800 ppm sulfur our data indicate an overall addition of sulfide to the lower crust selection of samples altered only at temperatures 110 c constrains microbial sulfate reduction as the only viable mechanism for the observed sulfide addition which may have been enabled by the production of h2 from oxidation of associated olivine and pyroxene the wide range in 34ssulfide values 1 5 to 16 3 and variable additions of sulfide are explained by variable esulfate sulfide under open system pathways with a possible progression into closed system pathways some samples underwent oxidation related to seawater penetration along permeable fault horizons and have lost sulfur have high so4 s 0 46 and variable 34ssulfide 0 7 to 16 9 negative 34ssulfate 34ssulfide values for the majority of samples indicate kinetic isotope fractionation during oxidation of sulfide minerals depth trends in sulfide sulfur contents and sulfide mineral assemblages indicate a late stage downward penetration of seawater into the lower 1 km of hole 735b our results show that under appropriate temperature conditions a subsurface biosphere can persist in the lower oceanic crust and alter its geochemistry

the connection between iron ore formations and mud shrimp colonizations around sunken wood debris and hydrothermal sediments in a lower cretaceous continental rift basin mecsek mts hungary in the early cretaceous the continental rift basin of the mecsek mts hungary was situated on the southern edge of the european plate the opening of the north atlantic ocean created a dilatational regime that expanded to the southern edge of the european plate where several extensional basins and submarine volcanoes were formed during the early cretaceous epoch permanent seaquake activity caused high swell events during which a large amount of terrestrial wood fragments entered into submarine canyons from rivers or suspended woods which had sunk into the deep seafloor these fragments created extended wood fall deposits which contributed large scale flourishing of numerous burrowing thalassinid crustaceans twelve different thalassinid coprolite ichnospecies can be found in the berriasian hauterivian volcano sedimentary formations

ichnotaxonomy of microbial trace fossils in volcanic glass abstract ancient microbial activity in volcanic glass creates micron sized cavities that can be regarded as trace fossils these are common in glassy rims of oceanic pillow lavas and volcanic breccias morphologically comparable mineralized traces are also found in meta volcanic glasses from ophiolites and precambrian greenstone belts multiple lines of evidence indicate microbial formation of these borings although the affinity of the trace maker s is poorly constrained two broad morphological types have been previously recognized and termed granular9 and tubular9 bioalteration textures here optical microscopy and sem observations are used to erect two new ichnogenera granulohyalichnus igen nov and tubulohyalichnus igen nov five ichnospecies are also defined granulohyalichnus vulgaris isp nov a granular species tubulohyalichnus simplus isp nov an unornamented tubular species tubulohyalichnus annularis isp nov an annulated tubular species tubulohyalichnus spiralis isp nov a helicoidal tubular species tubulohyalichnus stipes isp nov a branched tubular species this systematic taxonomy is advanced to allow reliable comparisons to be made between new and existing reports of these microbial borings moreover the adoption of a taxonomic framework will aid the development of these ichnofossils as palaeoenvironmental indicators and tracers of microbial evolution

evidence for cryptoendolithic life in devonian pillow basalts of variscan orogens germany abstract late devonian frasnian pillow basalts from the frankenwald and thuringer wald within the saxothuringian zone in germany were found to contain abundant putative biogenic filaments indicating that the volcanic rocks once harbored microbial life the mineralized filaments are found in calcite filled amygdules former vesicles where they started to form on internal surfaces of vesicles after seawater ingress the filaments postdate an early fibrous carbonate cement but predate later equant calcite spar revealing syngenetic formation a biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms their independence of crystal faces and cleavage plans complex branching patterns and internal segmentation the filamentous microorganisms represent cryptoendoliths that lived in structural cavities of the basalt they became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron rich environments filaments consist of clay minerals with the endmember composition berthierine chamosite and illite glauconite based on the discovery of fossilized filamentous microorganisms in late devonian pillow basalts of the saxothurigian zone that are similar to filaments previously found in middle devonian pillow basalts of the rhenohercynian zone it is apparent that cryptoendolithic life was more widespread than previously recognized structural cavities within seafloor basalt may thus represent a common perhaps universal niche for life in the oceanic crust

microbial proliferation coinciding with volcanism during the permian triassic transition new direct evidence from volcanic ashes south china abstract coupling with major biotic extinction both widespread microbially mediated deposits and ash beds characterize the permian triassic boundary ptb successions worldwide thus active volcanism through the ptb interval has been proposed to account for contemporary microbial bloom direct evidence however has long been scarce here we present several lines of evidence for microbial proliferation in the ptb ashes from south china petrographic analysis reveals annular granular and tubular bioalteration textures that formed during microbial dissolution of glass and subsequent precipitation annular textures appear as fresh glass shards connected with bands in different thicknesses showing rough and sharp interfaces and are bordered with fibrous textures granular textures are composed of clusters of near spherical bodies ranging in size from 0 05 to 2 m tubular textures occur as straight curved or spiral tunnels excavating into fresh glass their distinctive morphologies microbe analogous sizes and log normal size distributions all indicate a biogenic origin element mapping along alteration fronts shows enrichment of organic carbon and depletion in metabolically significant elements providing further support for their biogenicity besides textural relationships low n k and high c contents as well as pronounced microstructure density variations between different ash beds in same section all suggest that the bioalteration textures are syngenetic with volcanic glass relevant to microfossils rather than recent microbes we interpret the fossilized organic remains e g small coccoid like spheroids rods filaments and thin films as extracellular polymeric substances eps probably produced by microorganisms which might have served as templates for nucleation and played a crucial role in bio mineralization process the diversity of microstructure sizes shapes and organic remains may reflect a complex community of microbes in the ptb ashes we infer that microbial proliferation may contribute to negative c isotope excursions in the ptb ashes microbial blooms in ash beds directly triggered by large scale volcanism may reveal that extreme environmental stresses prevailed during the ptb crisis

bio signatures in metabasaltic glass of a caledonian ophiolite west norway 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 highly concentrated fe and s bioproduction of co 2 is further reflected in the low 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

microbial alteration of 0 30 ma seafloor and sub seafloor basaltic glasses from the australian antarctic discordance scanning electron microscopic observations of alteration rims in basaltic glasses dredged from 0 2 5 ma seafloor and drilled from 18 28 ma ocean crust ocean drilling program odp leg 187 in the australian antarctic discordance aad document the presence of endolithic microbes in altered basalt glass in very young aad lavas 10 m thick alteration rims are developed along intersecting fractures and cracks and the altered glass contains numerous spherical rod and star shaped partially fossilised microbial cells similar to those from the arctic ridges 1 2 in 2 5 ma basalt glasses altered rims are up to 250 m thick and zeolite phillipsite is present within many fractures spherical cells occur in porous outer zones of alteration rims and on zeolite crystal surfaces within fractures indicating that microbial activity persists in the region for at least 2 5 ma mn rich microbial cell encrustations associated with zeolite suggest that mn is used in an energy yielding metabolic process combined with recent results from the arctic ridges the results from this study demonstrate that endolithic microbial growth is a persistent feature of mid ocean spreading ridges in glasses from odp cores 1 mm thick alteration rims are developed along the widest fractures lined with mn fe oxyhydroxides and or clay and filled by zeolite and calcite most common however are 10 200 m thick rims developed along zeolite filled more narrow fractures and cracks zeolite filled fractures with only minor to no alteration indicate several episodes of fracturing followed by relatively fast sealing there is no age progression in alteration thickness along fractures or other characteristics suggesting that alteration is essentially completed between 2 5 and 18 ma a comparison of alteration in the 2 5 ma glass with that in the odp samples indicates that a significant proportion of the glass alteration in the drilled samples developed prior to burial although one type of diffuse highly irregular front that is only observed in the odp samples most likely developed after burial these diffuse alteration fronts are caused by dissolution and alteration of the glass into minute globules 0 05 0 2 m in diameter with no associated microbial morphologies fossilised mn rich cells do occur within zeolite filled fractures possibly indicating that microbial activity continued in the fractures for as long as circulation continued the apparent non biological origin of diffuse irregular alteration fronts in buried aad glasses indicates that these textural features are not reliable as diagnostic criteria for the existence of a deep biosphere in the volcanic ocean crust

candidate microbial ichnofossils in continental basaltic tuffs of central oregon usa expanding the record of endolithic microborings the presence of potential microbial trace fossils endolithic microborings has been well documented in oceanic basaltic pillow lavas hyaloclastites tuffs and transitional subglacial marine lavas in the past 30 yr despite their evident abundance in oceanic to subglacial environments they have not been observed in continental basalts that were not erupted in marine or subglacial settings to expand the record of putative endolithic microborings in volcanic rocks to nonmarine continental lacustrine environments we examined hydrovolcanic pyroclastic deposits in the fort rock volcanic field central oregon this study presents the textures mineralogy and geochemistry of basaltic tuffs containing possible endolithic microborings comparable in morphology size and distribution to those described in earlier oceanic and subglacial basalt studies we observed a variety of tubular and granular textures that show evidence of biogenic morphologies and behavior and a primary geological context that expresses their age and syngenicity petrographic relationships with secondary phases chabazite nontronite calcite indicate that the construction of microtunnels occurred in saline alkaline fluids at temperatures of 25 80 c in addition positive correlations were observed between the extent of aqueous abiotic alteration and both the abundance of microtunnels and morphological type these correlations suggest that microtunnels were more readily formed where there was greater abiotic alteration fluid flux and that the resulting change in chemical composition of those fluids may have had a direct influence on the formation process or possibly the type of constructing microbe this work adds to understanding of factors controlling microtunnel formation and is the first account of putative endolithic microborings in a continental lacustrine setting this new information may also have implications in the search for habitable extraterrestrial environments such as on mars

preservation of 3 4 3 5 ga microbial biomarkers in pillow lavas and hyaloclastites from the barberton greenstone belt south africa exceptionally well preserved pillow lavas and inter pillow hyaloclastites from the barberton greenstone belt in south africa contain textural geochemical and isotopic biomarkers indicative of microbially mediated alteration of basaltic glass in the archean the textures are micrometer scale tubular structures interpreted to have originally formed during microbial etching of glass along fractures textures of similar size morphology and distribution have been attributed to microbial activity and are commonly observed in the glassy margins of pillow lavas from in situ oceanic crust and young ophiolites the tubes from the barberton greenstone belt were preserved by precipitation of fine grained titanite during greenschist facies metamorphism associated with seafloor hydrothermal alteration the presence of organic carbon along the margins of the tubes and low d 13 c values of bulk rock carbonate in formerly glassy samples support a biogenic origin for the tubes overprinting relationships of secondary minerals observed in thin section indicate the tubular structures are pre metamorphic overlapping metamorphic and igneous crystallization ages thus imply the microbes colonized these rocks 3 4 3 5 ga although the search for traces of early life on earth has recently intensified research has largely been confined to sedimentary rocks subaqueous volcanic rocks represent a new geological setting in the search for early life that may preserve a largely unexplored archean biomass d 2005 elsevier b v all rights reserved

microbial endolithic colonization and the geochemical environment in young seafloor basalts the colonization and weathering of young seafloor basaltic glass from the mid atlantic ridge was examined microorganisms were localised to fractures in the surface of the basalt and grew on the surfaces of material in the fractures xas raman spectroscopy and nanosims analysis of the fracture filling material shows that it contains non crystallised iron enriched altered glass and poorly ordered iron oxides organisms which in places develop into contiguous biofilms develop on the surface of the material no putative biogenic alteration textures were observed in the basaltic glass at the fracture boundaries suggesting that the microbial community is restricted to the secondary alteration products microbial culturing shows the presence of heterotrophic bacteria including sufitobacter and halomonas consistent with observations of photic zone detritus associated with fracture filling material these data show that the interior of fresh basaltic glass is an endolithic habitat for microorganisms but that the glass itself is not a primary source of cations or energy for the developing communities

abiotic and candidate biotic micro alteration textures in subseafloor basaltic glass a high resolution in situ textural and geochemical investigation abstract the oceanic crust provides one of the largest habitats for subsurface microbial life on earth where lithoautotrophs utilize redox gradients between reduced elements in volcanic rocks and oxygenated seawater to form the basis of a deep microbial biosphere progressive alteration of the oceanic crust is argued to be in part microbially mediated but identifying robust textural and geochemical biosignatures with good fossilization potential is challenging this study investigates pillow basalts from the antarctic australian discordance aad at the south east indian ridge seir containing candidate textural biosignatures in alteration products of the glassy margins thorseth et al 2003 samples include 2 5 ma dredged seafloor basalts and 18 28 ma drill core samples from the ocean drilling program odp leg 187 the focused ion beam fib technique was used to prepare electron transparent foils across spherical microtextures in zeolite filled fractures and altered glass palagonite and across microtunnels at the interface of fresh and altered glass transmission electron microscopy tem was used to map chemical and ultrastructural variations and to evaluate both biotic and abiotic origins of the candidate textural biosignatures in the fib prepared foils three foils were cut from zeolite hosted hollow microspheres which comprise purely fe oxyhydroxides or mixed mn mg and fe mn oxyhydroxides the microspheres are 1 to 4 m across with a radiating ultrastructure and have a denser inner surface and a more porous outer surface suggesting outwards growth from a spherical initial surface amorphous organic carbon is associated with some of the microtextures both on the inner and outer walls these microtextures are interpreted as mineral encrusted microbial cells a fib foil was also cut from palagonite hosted microspheres which are more irregular in shape and partially infilled by palagonite amorphous organic carbon is abundant in the vicinity of the microtextures but is spatially unrelated and may be derived from several sources the results indicate that maturation of the palagonite involving dehydration and recrystallization overprints and destroys potential biosignatures in this alteration phase in contrast the zeolite hosted microtextures appear to have a higher preservation potential tubular microtextures in the glass at the alteration front comparable to argued bioalteration textures are also abundant in the aad basalts however their angular cross sectional shape and lack of bio elements in the palagonite infill mean that an abiotic origin cannot be excluded in summary fib tem provides multiple high resolution lines of information to characterize alteration textures in ocean floor basalts comparing the evidence obtained from glass hosted microtunnels zeolite and palagonite hosted microspheres we conclude that the zeolite hosted microtextures are the strongest candidate biosignature the combination of the size rim ultrastructure and elemental composition is consistent with an origin as cell encrustations resulting from the biologically induced mineralization of microbial cells that inhabited fractures in pillow lavas both at the seafloor and the subseafloor stage

influence of terrestrial vegetation on leaf wax δd of holocene lake sediments abstract the hydrogen isotope composition of terrestrial plant leaf wax in sediments is increasingly used as a paleoclimatic indicator modern calibration studies suggest that paleoclimatic interpretation of leaf wax d values requires consideration of the differences in the apparent fractionation of hydrogen isotopes among different groups of plants however it is not common that paleoecological data are used to help interpret leaf wax d profiles here we assess the relative importance of factors influencing millennial scale shifts in d values of n alkanoic acids at steel lake minnesota usa an extensively studied site with independent records of vegetation composition d of input water to the lake and evaporation the d values of the n c 28 alkanoic acid d c28 vary between 190 and 168 and do not correlate with d of input water or the extent of evaporation however d c28 is negatively correlated with the 13 c values of the n c 28 alkanoic acid 13 c c28 the correlation along with pollen assemblage and carbonate 13 c records suggests that holocene shifts between forest and grassland and or in the water use efficiency of c 3 plants influenced the stratigraphic variation in leaf wax d thus paleoecological information such as that inferred from pollen assemblages and carbon isotopes of plant derived compounds may aid paleoclimatic interpretation of leaf wax d profiles from lake sediments

native cu from the oceanic crust isotopic insights into native metal origin abstract ocean drilling has revealed that although a minor mineral phase native cu ubiquitously occurs in the oceanic crust cu isotope systematics for native cu from a set of occurrences from volcanic basement and sediment cover of the oceanic crust drilled at several sites in the pacific atlantic and indian oceans constrains the sources of cu and processes that produced cu0 we propose that both hydrothermally released cu and seawater were the sources of cu at these sites phase stability diagrams suggest that cu0 precipitation is favored only under strictly anoxic but not sulfidic conditions at circum neutral ph even at low temperature in the basaltic basement dissolution of primary igneous and potentially hydrothermal cu sulfides leads to cu0 precipitation along veins the restricted cu isotope variations 65cu 0 02 0 19 similar to host volcanic rocks suggest that cu0 precipitation occurred under conditions where cu species were dominant precluding cu redox fractionation in contrast the cu isotope variations observed in the cu0 from sedimentary layers yield larger cu isotope fractionation 65cu 0 41 0 95 suggesting that cu0 precipitation involved redox processes during the diagenesis with potentially seawater as the primary cu source we interpret that native cu precipitation in the basaltic basement is a result of low temperature 20 65 c hydrothermal processes under anoxic but not h2s rich conditions consistent with positive 65cu signatures the sediment cover receives major cu contribution from hydrogenous i e seawater sources although hydrothermal contribution from plume fallout cannot be entirely discarded in this case disseminated hydrogenous and or hydrothermal cu might be diagenetically remobilized and reprecipitated as cu0 in reducing microenvironment

paleoarchean trace fossils in altered volcanic glass microbial corrosion textures in volcanic glass from cenozoic seafloor basalts and the corresponding titanite replacement microtextures in metamorphosed paleoarchean pillow lavas have been interpreted as evidence for a deep biosphere dating back in time through the earliest periods of preserved life on earth this interpretation has been recently challenged for paleoarchean titanite replacement textures based on textural and geochronological data from pillow lavas in the hooggenoeg complex of the barberton greenstone belt in south africa we use this controversy to explore the strengths and weaknesses of arguments made in support or rejection of the biogenicity interpretation of bioalteration trace fossils in cenozoic basalt glasses and their putative equivalents in paleoarchean greenstones our analysis suggests that biogenicity cannot be taken for granted for all titanite based textures in metamorphosed basalt glass but a cautious and critical evaluation of evidence suggests that biogenicity remains the most likely interpretation for previously described titanite microtextures in paleoarchean pillow lavas

bioalteration of basaltic glass in the oceanic crust 1 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 m 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 m 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

dissolved hydrogen and methane in the oceanic basaltic biosphere abstract the oceanic basaltic crust is the largest aquifer on earth and has the potential to harbor substantial subsurface microbial ecosystems which hitherto remains largely uncharacterized and is analogous to extraterrestrial subsurface habitats within the sediment buried 3 5 myr old basaltic crust of the eastern juan de fuca ridge flank the circulating basement fluids have moderate temperature 65 c and low to undetectable dissolved oxygen and nitrate concentrations sulfate present in high concentrations is therefore expected to serve as the major electron acceptor in this subsurface environment this study focused on the availability and potential sources of two important electron donors methane ch4 and hydrogen h2 for the subseafloor biosphere high integrity basement fluids were collected via fluid delivery lines associated with integrated ocean drilling program iodp circulation obviation retrofit kits corks that extend from basement depths to outlet ports at the seafloor two new corks installed during iodp 327 in 2010 1362a and 1362b were sampled in 2011 and 2013 the two corks are superior than earlier style corks in that they are equipped with coated casing and polytetrafluoroethylene fluid delivery lines reducing the interaction between casing materials with the environment additional samples were collected from an earlier style cork at borehole 1301a the basement fluids are enriched in h2 0 05 1 8 mol kg suggesting that the ocean basaltic aquifer can support h2 driven metabolism the basement fluids also contain significant amount of ch4 5 32 mol kg revealing ch4 as an available substrate for subseafloor basaltic habitats the 13c values of ch4 from the three boreholes ranged from 22 5 to 58 while the 2h values ranged from 316 to 57 the isotopic compositions of ch4 and the molecular compositions of hydrocarbons suggest that ch4 in the basement fluids is of both biogenic and abiotic origins varying among sites and sampling times the 2h values of ch4 in cork 1301a fluid samples are much more positive than found in all other marine environments investigated to date and are best explained by the partial microbial oxidation of biogenic ch4 in conclusion our study shows that ch4 and h2 are persistently available to fuel the deep biosphere and that ch4 is both produced and potentially consumed by microorganisms in the oceanic basement