reply to the comments of d l pinti r mineau and v clement and of a o marshall and c p marshall on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 abstract the abundant and diverse assemblage of filamentous microbial fossils permineralized in the 3465 ma apex chert of northwestern australia among the oldest records of life are arguably the best studied by the most workers using the most advanced techniques in the history of science despite the extensive body of data establishing the biogenicity of the demonstrably cellular carbonaceous apex fossils pinti et al 2013 and marshall and marshall 2013 have raised issues regarding the interpretation of their studies of the apex chert presented in our recent review article schopf and kudryavtsev 2012 we agree with the assessment of both of the relevant papers by pinti et al 2009 2013 the observations they report do not apply to the bona fide microscopic fossils of the apex chert similarly like the minute objects reported by pinti et al 2009 2013 the quartz and haematite filled fractures discussed by marshall and marshall 2013 are mineralic pseudofossils that are not relevant to interpretation of the apex fossil microbes and their suggestion that multiple populations of carbonaceous material may be a wide spread issue through out the precambrian is without merit

thermal history of type 3 chondrites from the antarctic meteorite collection determined by raman spectroscopy of their polyaromatic carbonaceous matter abstract this paper is focused on the characterization of the thermal history of 151 cv co and unequilibrated ordinary chondrites uocs from the nasa antarctic meteorite collection using an approach based on the structure of the included polyaromatic carbonaceous matter determined by raman spectroscopy 114 out of these 151 chondrites provided raman spectra of carbonaceous matter and allowing to assign a petrologic type which mostly reflects the peak temperature experienced by the rock on the parent body a thorough review of literature shows however that it is not possible to deduce a peak temperature because accurate calibration is not available twenty three new weakly metamorphosed chondrites have been identified mil 07671 cv3 1 dom 08006 co3 0 dom 03238 mil 05024 mil 05104 mil 07193 co3 1 til 82408 lar 06279 ll3 05 3 1 eet 90628 l3 0 gro 06054 que 97008 l3 05 alha 77176 eet 90066 lar 04380 met 96515 mil 05050 l3 1 alha 78133 eet 87735 eet 90909 lew 87208 pre 95401 l3 05 3 1 mcy 05218 h3 05 3 1 and met 00506 h3 1 this study confirms that the width of the d band fwhmd and the ratio of the peak intensity of the d and g bands id ig are the most adapted tracers of the extent of thermal metamorphism in type 3 chondrites it also unambiguously shows thanks to the large number of samples that the width of the g band fwhmg does not correlate with the maturity of polyaromatic carbonaceous matter this parameter is nevertheless very valuable because it shows that raman spectra of cv chondrites preserve memory of either the metamorphic conditions possibly oxidation controlled by aqueous alteration or the nature of the organic precursor oxidation memory is our preferred interpretation however an extensive petrologic characterization of this cv series is required to get firm conclusions pre graphitic carbonaceous matter is reported in seven chondrites and is even the only carbonaceous material detected in the chondrites alha 78119 and dav 92302 this pre graphitic carbonaceous matter cannot be formed through radiogenic thermal metamorphism without metal catalysis shock metamorphism is another possible process for accounting its formation but it appears less plausible

evolution of the raman spectrum of carbonaceous material in low grade metasediments of the glarus alps switzerland terra nova 22 354 360 2010 abstract the raman spectrum of carbonaceous material cm from advanced diagenesis 200 c to low grade metamorphism 320 c is documented in the helvetic flysch of the glarus alps switzerland the spectrum is complex with several defect bands at 1200 d4 1350 d1 1500 d3 and 1620 d2 cm 1 we document the evolution of these bands relative to the graphite g band with increasing metamorphic grade and we show that this qualitative evolution may be used as a proxy for temperature in the glarus alps we develop a robust peak fitting method and propose quantitative parameters that may be used as proxies for thermal metamorphism in this region further work in other geological contexts is needed to assess whether the spectral evolution observed in the glarus alps may be generalized and to critically assess the potential for calibrating a general empirical and quantitative thermometer based on the raman spectrum of cm in low grade rocks

textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone alpine fault new zealand graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization we examine processes of graphitic carbon emplacement and deformation in the active alpine fault zone new zealand by analysing samples obtained from deep fault drilling project dfdp boreholes optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain raman spectroscopy allowed interpretation of the degree of graphite crystallinity which reflects both thermal and mechanical processes in the amphibolite facies alpine schist highly crystalline graphite indicating peak metamorphic temperatures up to 640 c occurs mainly on grain boundaries within quartzo feldspathic domains the subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions 500 600 c resulting in clustered in protomylonites and foliation aligned graphite in mylonites in cataclasites derived from the mylonitized schists graphite is most abundant 50 as opposed to 10 elsewhere and has two different habits inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon tectonic hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences the increasing abundance of graphite towards the fault zone core may be a significant source of strain localization allowing fault weakening

extending the applicability of the raman carbonaceous material geothermometer using data from contact metamorphic rocks the degree of graphitization of carbonaceous material cm has been widely used as an indicator of metamorphic grade previous work has demonstrated that peak metamorphic temperature t o f regional metamorphic rocks can be estimated by an area ratio r2 of peaks recognized in raman spectra of cm the applicability of this method to low pressure 50 that adequately reflects the range of sample heterogeneity using this procedure with 532 nm laser and adapting our new calibration the errors of the raman cm geothermometer for contact metamorphic rocks decrease to 30 c

comparative multi scale analysis of filamentous microfossils from the c 850 ma bitter springs group and filaments from the c 3460 ma apex chert filamentous microfossils belonging to cephalophytarion from the 850 ma bitter springs group have previously been used as key analogues in support of a biological interpretation for filamentous objects from the 3460 ma apex chert here we provide a new perspective on this interpretation by combining raman data with correlative electron microscopy data from both cephalophytarion and apex specimens we show that when analysed at high spatial resolution the apex filaments bear no morphological resemblance to the younger bitter springs microfossils cephalophytarion filaments are shown to be cylindrical comprising chains of box like cells of approximately constant dimensions with lateral kerogenous walls and transverse kerogenous septa they exhibit taphonomic shrinkage and folding possess fine cylindrical sheaths and are permineralized by sub micrometric quartz grains they fulfil all established biogenicity criteria for trichomic microfossils in contrast apex filaments do not possess lateral cell walls are not cylindrical in nature and vary considerably in diameter along their length their kerogenous carbon does not have a cell like distribution and their chemistry is consistent with an origin as exfoliated phyllosilicate grains this work demonstrates the importance of high resolution data when interpreting the microstructure and origins of putative precambrian microfossils

the problem of deep carbon an archean paradox black carbon rich chert dikes are common features of early archean terranes and are especially prominent on the pilbara craton of western australia the dikes cut across the local stratigraphy before truncating abruptly at specific stratigraphic horizons where they can be seen to interfinger with the stratigraphic succession these uniquely archean dike complexes are enigmatic and raise significant questions about the source of the carbon they contain is it biogenic and therefore indicative of the early biosphere or abiotic and perhaps indicative of prebiotic conditions that led to the appearance of the first life on earth the strelley pool chert which is exposed on the pilbara craton of western australia forms part of the warrawoona group and rests unconformably on older ultramafic volcanics the formation which is generally less than 30 m thick consists of a relatively consistent lithologic succession found over a wide area locally a basal transgressive sandstone is overlain by a sequence of carbonate barite black and white laminated chert and grey green chert which is locally stained blue green by weathered fuchsite the formation is intersected by normal faults about which the depositional successions thickens and thins the mineralogy and geochemistry including stable isotope data of the underlying dike complex closely parallels that of the lithologies preserved in the strelley pool chert similarly the depositional sequence of minerals in voids within the dike complex parallels that of the depositional sequence above this new data from the strelley pool chert and its associated dike complex show that the black chert dikes are an integral part of a hydrothermal mineralogical complex the complex accumulated around vents fed by growth fault controlled dikes that extended to a depth of more than 2 km below the archean paleo seafloor the mineralogy of the sedimentary succession reflects deposition during the declining temperature regime of an evolving hydrothermal system driven by an intruding granitoid complex below the fault system and associated hydrothermal complex evolved in the tensional environment developed during doming above the intermittently intruding granitoid complex that forms the framework of the pilbara protocontinent carbonaceous compounds contained within the black chert dikes could have been generated abiotically by a process similar to fischer tropsch synthesis at elevated temperatures 200 300 c and pressures 500 bar at a paleo depth of 2 km within the hydrothermal system the primordial medium in which life first evolved may thus have been a silica rich slurry with a low ph and a high co 2 content which contained basic abiotic organic building blocks fundamental to the origins of life the abiotic organic output from these hydrothermal systems may overwhelm any early biospheric geochemical signal and may therefore be the most difficult environment in which to recognise the early biospheric record 2005 elsevier b v all rights reserved

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

volcanic degassing hydrothermal circulation and the flourishing of early life on earth a review of the evidence from c 3490 3240 ma rocks of the pilbara supergroup pilbara craton western australia abstract new data gathered during mapping of c 3490 3240 ma rocks of the pilbara supergroup in the pilbara craton show that most bedded chert units originated as epiclastic and evaporative sedimentary rocks that were silicified by repeated pulses of hydrothermal fluids that circulated through the footwall basalts during hiatuses in volcanism for most cherts fossil hydrothermal fluid pathways are preserved as silica barite fe bearing veins that cut through the footwall and up to the level of individual bedded chert units but not above indicating the contemporaneity of hydrothermal silica veining and bedded chert deposition at the end of volcanic eruptive events silica barite fe bearing vein swarms are accompanied by extensive hydrothermal alteration of the footwall to the bedded chert units and occurred under alternating high sulphidation and low sulphidation conditions these veins provided pathways to the surface for elements leached from the footwall e g si ba fe and volcanogenic emissions from underlying felsic magma chambers e g co 2 h 2 s hs so 2 stratigraphic evidence of shallowing upward and subsequent deepening associated with the deposition of warrawoona group cherts is interpreted to relate to the emplacement of subvolcanic laccoliths and subsequent eruption and or degassing of these magmas heat from these intrusions drove episodes of hydrothermal circulation listric normal faulting during caldera collapse produced basins with restricted circulation of seawater eruption of volcanogenic emissions into these restricted basins formed brine pools with concentration of the volcanogenic components thereby providing habitats suitable for early life forms fossil stromatolites from two distinct stratigraphic units in the north pole dome grew in shallow water conditions but in two very different geological settings with different morphologies stratiform and domical stromatolites in the stratigraphically lower c 3490 ma dresser formation of the warrawoona group are intimately associated with barite and chert precipitates from hydrothermal vents suggesting that component microbes may have been chemoautotrophic hyperthermophiles evidence of shallow water to periodically exposed conditions active growth faulting and soft sediment deformation indicates that the volcanogenic emissions were erupted into a shallow water tectonically active caldera and concentrated therein to produce an extreme habitat for early life widespread conical and pseudocolumnar stromatolites in the c 3400 ma strelley pool chert at the base of the unconformably overlying kelly group occur in shallow marine platform carbonates silicification was the result of later hydrothermal circulation driven by heat from the overlying newly erupted euro basalt the markedly different morphology and geological setting of these only slightly younger stromatolites compared with the dresser formation suggests a diversity of microbial life on early earth the biogenicity of putative microfossils from this and younger hydrothermal silica veins in the warrawoona group remains controversial and requires further detailed study

biogenic origin for earth s oldest putative microfossils carbonaceous microbe like features preserved within a local chert unit of the 3 5 ga old apex basalt in western australia may represent some of the oldest evidence of life on earth however the biogenicity of these putative microfossils has been called into question primarily because the sample collection locality is a black carbon rich brecciated chert dike representing an archean submarine hydrothermal spring suggesting a formation via an abiotic organic synthesis mechanism here we describe the macromolecular hydrocarbon structure carbon bonding functional group chemistry and biotic element abundance of carbonaceous matter associated with these filamentous features these characteristics are similar to those of biogenic kerogen from the ca 1 9 ga old gunflint formation although an abiotic origin cannot be entirely ruled out it is unlikely that known abiotic synthesis mechanisms could recreate both the structural and compositional complexity of this ancient carbonaceous matter thus we find that a biogenic origin for this material is more likely implying that the apex microbe like features represent authentic biogenic organic matter

characterization of kerogenous films and taphonomic modes of the sirius passet lagerstatte greenland the sirius passet lagerstatte northern greenland is an exceptionally well preserved early cambrian faunal community containing a diverse array of stem group euarthropods lobopodians worms sponges and the iconic halkieria material collected in situ during recent expeditions has yielded a range of fossil specimens that are preserved as two dimensional reflective films here we document in detail for the first time from the sirius passet compressed kerogenous fossil films characteristic of burgess shale type bst preservation the carbon structure and the taphonomic mode associated with these films were investigated using raman spectroscopy our analysis confirms that these reflective films are kerogenous showing a higher d1 disordered band and g graphite band intensity and area indicating a greater concentration of disordered carbon compared to the surrounding matrix the spectral characteristics of the fossils denote moderately ordered kerogenous matter indicating that the transitional buen formation that hosts the sirius passet was thermally altered at a peak temperature of 409 50 c phyllosilicate minerals are associated with the films but they are not anatomical or taxon specific suggesting that the higher thermal maturation of the kerogen in the sirius passet produced a uniform distribution of minerals this is unlike the kerogenous films in the burgess shale lagerstatte british columbia canada that have been metamorphosed at a lower temperature of 335 50 c and typically show an anatomically specific phyllosilicate distribution preservation as kerogenous films however is not continuous and the presence of other taphonomic modes not indicative of bst preservation suggests that the sirius passet represents a unique and complex deposit

carbon isotopes and petrography of kerogens in 3 5 ga hydrothermal silica dikes in the north pole area western australia more than 600 specimens of 3 5 ga old hydrothermal silica dikes from the north pole area pilbara craton western australia have been studied petrographically the kerogens in 44 samples have been analyzed isotopically c and n and chemically c n and h the silica dikes are composed mainly of fine grained silica modal abundance 97 and are classified into two types by minor mineral assemblages b black type and g gray type the b type silica dikes contain kerogen 0 37 to 6 72 mgc g average 2 44 mgc g n 21 and disseminated sulfides dominantly pyrite and fe poor sphalerite in some cases carbonate and apatite are also present their silica dominated and sulfide poor mineral assemblages suggest precipitation from low temperature reducing hydrothermal fluid likely 100 200 c on the other hand the g type silica dikes are sulfide free and concentrations of kerogen are relatively low 0 05 to 0 41 mgc g average 0 17 mgc g n 13 they typically contain fe oxide mainly hematite which commonly replaces cubic pyrite and rhombic carbonate some g types occur along secondary quartz veins these textures indicate that the g type silica dikes were formed by postdepositional metasomatism oxidation of the b types and that the b types probably possess premetasomatic signatures the 13c values of kerogen in the b types are 38 1 to 33 1 average 35 9 n 21 which are 4 lower than those of the g types 34 5 to 30 0 average 32 2 n 19 and 6 lower than bedded chert 31 2 to 29 4 average 30 5 n 4 this indicates the preferential loss of 12c during the metasomatism estimated fractionation factor 0 9985 considering the metasomatic effect on carbon isotopes with probably minor diagenetic and metamorphic overprints we conclude that the original 13c values of the kerogen in the silica dikes would have been heterogeneous 5 and at least some material had initial 13c values of 38 the inferred 13c depletions of organic carbon could have been produced by anaerobic chemoautotrophs such as methanogen but not by aerobic photoautotrophs this is consistent with the estimated physical and chemical condition of the hydrothermal fluid which was probably habitable for anaerobic and thermophilic hyperthermophilic chemoautotrophs alternatively the organic matter may have been possibly produced by abiological reaction such as fischer tropsch type ftt synthesis under the hydrothermal condition however the estimated condition is inconsistent with the presence of the effective catalysts for the ftt reaction i e fe ni alloy magnetite and hematite these lines of evidence suggest the possible existence of biosphere in the 3 5 ga sub seafloor hydrothermal system

biogenicity of earth s earliest fossils a resolution of the controversy abstract the abundant and diverse assemblage of filamentous microbial fossils and associated organic matter permineralized in the 3465 ma apex chert of northwestern australia widely regarded as among the oldest records of life have been investigated intensively first reported in 1987 and formally described in 1992 and 1993 the biogenicity of the apex fossils was questioned in 2002 and in three subsequent reports however as is shown here by use of analytical techniques unavailable twenty years ago the apex filaments are now established to be bona fide fossil microbes composed of three dimensionally cylindrical organic kerogenous walled cells backed by a large body of supporting evidence of similar age other microfossils stromatolites and carbon isotopic data it seems clear that microbial life was present and flourishing on the early earth 3500 ma ago

mineralogical and isotopic characterization of graphite deposits in the western part of the north qaidam orogen and east kunlun orogen northeast tibetan plateau china abstract medium to high grade metamorphic rocks comprising numerous graphite deposits are widely distributed in the periphery of the qaidam basin northern tibetan plateau china we present textural xrd and raman spectroscopy characteristics of graphite 13c results of graphite and cogenetic calcite and 18o results of calcite in three graphite occurrences located at the periphery of qaidam basin graphite displays hexagonal platy flaky irregular polygonal ovate morphologies with occasional spherulitic textures graphite morphologies combined with xrd and raman spectroscopy indicate that graphite has relatively high crystallinity raman microspectroscopy of graphite shows that peak metamorphic temperatures vary between 690 and 801 c graphite 13cv pdb values range between 26 3 and 21 6 indicating organic carbon as the major carbon source for graphite calcite 13cv pdb and calcite 18ov smow values range between 10 8 and 3 9 and between 6 6 and 29 5 respectively calcite 13cv pdb results show that organic carbon was mixed with inorganic carbon which resulted in an increase of 13cv pdb calcite 18ov smow values indicate that the graphite deposits experienced late stage water rock interaction the positive and negative anomalies of calcite 13cv pdb indicate that organic matter oxidation and recycling locally occurred during the final stage of the great oxidation event the wide distribution of regional metamorphic organogenic graphite deposits provides evidence for large scale paleoproterozoic biological activity in the periphery of the qaidam basin

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

raman microspectroscopy bitumen reflectance and illite crystallinity scale comparison of different geothermometry methods on fossiliferous proterozoic sedimentary basins dr congo mauritania and australia abstract sedimentary rocks containing microfossils are crucial archives to reconstitute early life evolution on earth however the preservation of microfossils within rocks depends on several physico chemical factors among these factors the thermal evolution of the host rocks can be decisive here we investigated carbonaceous shale samples containing exquisitely preserved organic walled microfossils assemblages from three proterozoic shallow marine sedimentary sequences the mbuji mayi supergroup democratic republic of congo congo basin the atar el mreiti group mauritania taoudeni basin and the kanpa formation australia officer basin thermal maturity of these rock samples is evaluated with raman geothermometry raman reflectance solid bitumen reflectance illite crystallinity and thermal alteration index the comparison of results coming from these different techniques validates the use of raman reflectance on proterozoic carbonaceous material and especially for poorly ordered carbonaceous material we show that extracted kerogen microfossils and amorphous organic material is more accurate to estimate the thermal maturity of low grade temperature proterozoic sequences than kerogen in thin section all techniques provide consistent range of temperatures except for raman geothermometry giving slightly higher estimates raman reflectance appears to be a fast robust and non destructive tool to evaluate the thermal maturity of poorly organized carbonaceous material from proterozoic rocks

pre and post drill comparison of the mount elbert gas hydrate prospect alaska north slope abstract in 2006 the united states geological survey usgs completed a detailed analysis and interpretation of available 2 d and 3 d seismic data along with seismic modeling and correlation with specially processed downhole well log data for identifying potential gas hydrate accumulations on the north slope of alaska a methodology was developed for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area the study revealed a total of 14 gas hydrate prospects in this area in order to validate the gas hydrate prospecting protocol of the usgs and to acquire critical reservoir data needed to develop a longer term production testing program a stratigraphic test well was drilled at the mount elbert prospect in the milne point area in early 2007 the drilling confirmed the presence of two prominent gas hydrate bearing units in the mount elbert prospect and high quality well logs and core data were acquired the post drill results indicate pre drill predictions of the reservoir thickness and the gas hydrate saturations based on seismic and existing well data were 90 accurate for the upper unit hydrate unit d and 70 accurate for the lower unit hydrate unit c confirming the validity of the usgs approach to gas hydrate prospecting the mount elbert prospect is the first gas hydrate accumulation on the north slope of alaska identified primarily on the basis of seismic attribute analysis and specially processed downhole log data post drill well log data enabled a better constraint of the elastic model and the development of an improved approach to the gas hydrate prospecting using seismic attributes

multiple generations of carbonaceous material deposited in apex chert by basin scale pervasive hydrothermal fluid flow abstract the pilbara craton in western australia contains the best preserved and most complete record of archean rocks in the world as such they are some of the most studied rocks in the world paleontologists isotopic geochemists geologists and geobiologists have all investigated these rocks for clues about the early biosphere and atmosphere here we show using high resolution transmission electron microscopy that the carbonaceous material found in the apex chert and potentially in other associated units was formed by multiple processes such as abiotic catalytic synthesis and or biological synthesis we use these data as well as the geological history of the craton to demonstrate that when the rocks of the pilbara craton experienced a high degree of post depositional hydrothermal alteration carbonaceous material could have been remobilized and redeposited as the carbonaceous material within the apex chert samples was formed over nearly a billion years bulk chemistry even at the micron level will be unable to unambiguously delineate the presence of life in these ancient rocks although nanoscale observations may provide a way forward in the search for ancient life

changing the picture of earth s earliest fossils 3 5 1 9 ga with new approaches and new discoveries new analytical approaches and discoveries are demanding fresh thinking about the early fossil record the 1 88 ga gunflint chert provides an important benchmark for the analysis of early fossil preservation high resolution analysis of gunflintia shows that microtaphonomy can help to resolve long standing paleobiological questions novel 3d nanoscale reconstructions of the most ancient complex fossil eosphaera reveal features hitherto unmatched in any crown group microbe while eosphaera may preserve a symbiotic consortium a stronger conclusion is that multicellular morphospace was differently occupied in the paleoproterozoic the 3 46 ga apex chert provides a test bed for claims of biogenicity of cell like structures mapping plus focused ion beam milling combined with transmission electron microscopy data demonstrate that microfossil like taxa including species of archaeoscillatoriopsis and primaevifilum are pseudofossils formed from vermiform phyllosilicate grains during hydrothermal alteration events the 3 43 ga strelley pool formation shows that plausible early fossil candidates are turning up in unexpected environmental settings our data reveal how cellular clusters of unexpectedly large coccoids and tubular sheath like envelopes were trapped between sand grains and entombed within coatings of dripstone beach rock silica cement these fossils come from earth s earliest known intertidal to supratidal shoreline deposit accumulated under aerated but oxygen poor conditions

structural characterization of kerogen in 3 4 ga archaean cherts from the pilbara craton western australia hydrogen lean kerogen atomic h c 0 46 isolated from the 3 4 ga strelley pool chert in the north pole area pilbara craton western australia were studied by vibrational spectroscopy fourier transform infrared ftir spectroscopy and raman spectroscopy nuclear magnetic resonance spectroscopy solid state 13 c nmr spectroscopy catalytic hydropyrolysis followed by gas chromatography mass spectrometry hypy gc ms and isotope ratio mass spectrometry irms the kerogen occurs in sedimentary rocks as clasts and clots deposited together with other detrital materials that are finely disseminated throughout a chert matrix the bulk kerogen 13 c values range from 28 3 to 35 8 solid state 13 c nmr spectroscopy and ftir spectroscopy reveals that the kerogen is highly aromatic fa varying from 0 90 to 0 92 and contains only minor aliphatic carbon or carbon oxygenated c o functionalities the raman carbon first order spectra for the isolated kerogens are typical of spectra obtained from disordered sp 2 carbons with low 2 d ordering biperiodic structure the implications of the raman results show low 2 d ordering throughout the carbonaceous network indicate the incorrect usage of the term graphite in the literature to describe the kerogen or carbonaceous material in the warrawoona cherts hydropyrolysates contain aromatic compounds consisting of 1 ring to 7 ring polycyclic aromatic hydrocarbons which were covalently bound into the kerogen as well as alkanes linear branched and cyclic which were most probably trapped in the microporous network of the kerogen these pahs have mainly c1 and c2 alkylation while c3 substitued aromatics are low in abundance and do not show a high degree of branched alkylation for the first time we have shown a correlation between elemental analysis h c atomic ratios raman spectroscopic parameters id1 ig id1 id1 ig and la and the degree of alkylation of bound polyaromatic molecular constituents generated from hypy for archaean kerogens similarities in molecular

organic composition and diagenetic mineralization of microfossils in the ediacaran doushantuo chert nodule by raman and petrographic analyses abstract we studied microfossils and their embedding matrix minerals from chert nodules in the ediacaran doushantuo formation of the yangtze gorges area in south china using raman spectroscopy as well as transmitted and polarized light microscopy the microfossils are composed of organic carbonaceous material with weak structural organization ordering which indicates a low degree of thermal maturation and alteration raman spectral disparity of carbonaceous material among different portions vesicle inclusion of microfossils reveals some differences in organic composition and structure of their precursor biological matters the mineral phases of silica matrix that entombs the microfossils are recognized as opal ct cryptocrystalline quartz and their transitional phases overall raman spectral analyses and petrographic observations document a complete and continuous sequence of silica phase transformation from opal ct to quartz when reconstructing the diagenetic history of sediments and mineralization process of microfossils in a localized microenvironment the silica in pore waters precipitated preferentially at the periphery of microorganisms in the form of opal gradually decreasing in abundance as it transformed into more stable cryptocrystalline quartz the recrystallization took place in cryptocrystalline quartz to form grains authigenic fluorapatite readily precipitated in the vicinity of some microfossils and within their degraded organic fragments while apatite was crystallizing around organisms and their biostructures silica precipitated in the surrounding voids inhibiting the space of potential apatite crystallization the silicification and phosphatization of microfossils occurred in the microbial sulfate reduction msr zone of the sediment column and both were driven by the localized ph change resulting from msr and pyrite precipitation in the microenvironment thus facilitating the exceptional fossil preservation in the doushantuo chert nodules

critical testing of earth s oldest putative fossil assemblage from the 3 5ga apex chert chinaman creek western australia abstract structures resembling cyanobacterial microfossils from the ca 3465 ma old apex chert of the warrawoona group in western australia have until recently been accepted as providing the oldest morphological evidence for life on earth and have been taken to support an early beginning for oxygen releasing photosynthesis eleven species of filamentous prokaryote principally distinguished by shape and geometry have been put forward as meeting the criteria required of authentic archaean microfossils they were contrasted with other microfossils that were dismissed as either unreliable or irreproducible the aim of this paper is to provide a detailed account of research recently reported by us on the type and recollected material involving optical and electron microscopy digital image analysis and other techniques all previously figured holotype materials are illustrated here and the context for all the published materials is re evaluated the apex chert microfossils occur near the top of a 1 5 km long chert dyke complex associated with major synsedimentary growth faults highly localised glassy felsic tuffs erupted explosively from this and other fissures during the early stages of volcanism and were followed by the deposition of essentially hydrothermal black and white baso4 rich cherts that infiltrated the feeder dykes underplating and dilating adjacent stratiform cherts before the start of the next volcanic cycle the apex chert microfossils occur within multiple generations of these metalliferous hydrothermal vein cherts some 100 m down the dyke system comparable structures occur in associated volcanic vent glass and in hydrothermal cherts at least 1 km deep we find no supporting evidence for a primary biological origin we reinterpret the purported microfossil like structures as pseudofossils that formed from the reorganization of carbonaceous matter mainly during recrystallization from amorphous to spherulitic silica

evidence of archean life stromatolites and microfossils abstract fossil evidence of the existence of life during the archean eon of earth history 2500 ma is summarized data are outlined for 48 archean deposits reported to contain biogenic stromatolites and for 14 such units that contain a total of 40 morphotypes of described microfossils among the oldest of these putatively microfossiliferous units is a brecciated chert of the 3465 ma apex basalt of western australia the paleoenvironment carbonaceous composition mode of preservation and morphology of the apex microbe like filaments backed by new evidence of their cellular structure provided by two and three dimensional raman imagery support their biogenic interpretation such data together with the presence of stromatolites microfossils and carbon isotopic evidence of biological activity in similarly aged deposits indicate that the antiquity of life on earth extends to at least 3500 ma

depth dependent δ 13 c trends in platform and slope settings of the campbellrand malmani carbonate platform and possible implications for early earth oxygenation highlights carbon cycle of neoarchean carbonate platform and potential oxygen oasis carbon isotopes reveal a shift to aerobic biosphere and increasing oxidation state rare earth element patterns reveal decrease in open ocean water influx rimmed margin architecture was crucial for evolution of aerobic ecosystems abstract the evolution of oxygenic photosynthesis is widely seen as the major biological factor for the profound shift from reducing to slightly oxidizing conditions in earth s atmosphere during the archean proterozoic transition period the delay from the first biogenic production of oxygen and the permanent oxidation of earth s atmosphere during the early paleoproteorozoic great oxidation event goe indicates that significant environmental modifications were necessary for an effective accumulation of metabolically produced oxygen here we report a distinct temporal shift to heavier carbon isotope signatures in lagoonal and intertidal carbonates 13ccarb from 1 6 to 0 2 relative to vpdb and organic matter 13corg from about 40 to 25 relative to vpdb from the 2 58 2 50 gy old shallow marine campbellrand malmani carbonate platform south africa this indicates an increase in the burial rate of organic matter caused by enhanced primary production as well as a change from an anaerobic to an aerobic ecosystem trace element data indicate limited influx of reducing species from deep open ocean water into the platform and an increased supply of nutrients from the continent both supporting primary production and an increasing oxidation state of the platform interior these restricted conditions allowed that the dissolved inorganic carbon dic pool in the platform interior developed differently than the open ocean this is supported by coeval carbonates from the marginal slope setting which had a higher interaction with open ocean water and do not record a comparable shift in 13ccarb throughout the sequence we propose that the emergence of stable shallow water carbonate platforms in the neoarchean provided ideal conditions for the evolution of early aerobic ecosystems which finally led to the full oxidation of earth s atmosphere during the goe

earliest microbially mediated pyrite oxidation in 3 4 billion year old sediments abstract pyrite fes2 oxidation in modern sedimentary environments is neither a purely chemical nor purely microbial process but it is significantly enhanced by the activity of microorganisms that use reduced forms of iron and sulphur in their metabolisms on the early earth where oxygen levels were thought to be

characteristics and interpretation of fracture filled gas hydrate an example from the ulleung basin east sea of korea abstract through the use of 2 d and 3 d seismic data a total of thirteen sites were selected and drilled in the east sea of korea in 2010 a suite of logging while drilling lwd logs was acquired at each site lwd logs from the ubgh2 3a well indicate significant gas hydrate in clay bearing sediments including several zones with massive gas hydrate with a bulk density less than 1 0 g m 3 for depths between 5 and 103 m below the sea floor the ubgh2 3a well was drilled on a seismically identified chimney structure with a mound feature at the sea floor average gas hydrate saturations estimated from the isotropic analysis of ring resistivity and p wave velocity logs are 80 13 and 47 16 respectively whereas they are 46 17 and 45 16 respectively from the anisotropic analysis modeling indicates that the upper part of chimney between 5 and 45 m below sea floor mbsf is characterized by gas hydrate filling near horizontal fractures 7 dip and the lower part of chimney between 45 and 103 mbsf is characterized by gas hydrate filling high angle fractures on the basis of ring resistivity and p wave velocity the anisotropic analysis using p40h resistivity phase shift resistivity at 32 mhz with 40 inch spacing and the p wave velocity yields a gas hydrate saturation of 46 15 and 46 15 respectively similar to those estimated using ring resistivity and p wave velocity but with quite different fracture dip angles differences in vertical resolution depth of investigation and a finite fracture dimension relative to the tool separation appear to contribute to this discrepancy forward modeling of anisotropic resistivity and velocity are essential to identify gas hydrate in fractures and to estimate accurate gas hydrate amounts

geochronology of mid cretaceous to eocene magmatism babine porphyry copper district central british columbia new u pb and 40 ar 39 ar isotopic dating in the babine porphyry copper district of central british columbia documents three distinct magmatic events at 107 104 85 78 and 54 50 ma the earliest event involved emplacement of rhyolite domes into submarine volcanic rocks of the rocky ridge formation the rhyolite domes and related dacitic to basaltic volcanic rocks gave a u pb age of 107 9 0 2 ma and an 40 ar 39 ar age of 104 8 1 2 ma the rhyolites which were previously mapped as eocene are reinterpreted to be part of a previously unrecognized mid cretaceous cauldron subsidence complex the regionally extensive late cretaceous magmatic event is also recognized in the babine district and is represented by 40 ar 39 ar ages of 85 2 2 8 and 78 3 0 8 ma on two bulkley intrusions one of which has associated porphyry copper mineralization the final magmatic event is the most widespread and involved emplacement of the babine intrusions and formation of numerous porphyry copper deposits including the bell and granisle past producers twenty one new 40 ar 39 ar isotopic ages for these intrusions and coeval andesites of the newman formation have a narrow range from 53 6 0 9 to 49 9 0 6 ma whereas previous k ar isotopic dating had a possible range of 15 ma the mid cretaceous late cretaceous and eocene magmatic suites in the babine dis trict are interpreted to be part of a long lived volcano plutonic complex that was the site of periodic magmatism and porphyry copper mineralization over a 60 ma time period this complex may have evolved within a zone of extension pull apart basins situated between dextral strike slip faults that were active during periods of rapid oblique plate con vergence

raman spectroscopic carbonaceous material thermometry of low grade metamorphic rocks calibration and application to tectonic exhumation in crete greece we present new raman spectra data of carbonaceous material cm to extend the range of the raman spectra of cm thermometer rscm to temperatures as low as 100 8c previous work has demonstrated that raman spectroscopy is an excellent tool to describe the degree of graphitization of cm a process that is independent of pressure but strongly dependent on metamorphic temperature a linear relationship between temperature and the raman parameter r2 derived from the area of the defect band relative to the ordered graphite band forms the basis of a previous thermometer because r2 shows little variability in low temperature samples 330 8c serves as a lower limit on the existing thermometer herein we present raman spectra from a suite of low temperature 100 to 300 8c samples from the olympics mountains and describe other aspects of the raman spectra of cm that vary over this range in particular the raman parameter r1 the ratio of heights of the disordered peak to ordered peak varies regularly between 100 and 350 8c these data together with published results from higher temperature rocks are used to calibrate a modified rscm thermometer applicable from 100 to 700 8c application to low grade metasediments in the otago region in the south island of new zealand gives temperatures consistent with previous estimates demonstrating the reliability of the modified rscm thermometer we apply the modified rscm thermometer to 53 samples from crete to evaluate the role of the cretan detachment fault in exhuming miocene high pressure low temperature metamorphic rocks exposed there the metamorphic rocks below the detachment the plattenkalk and phyllite quartzite units give metamorphic temperatures that range from 250 to 400 8c consistent with previous petrologic estimates we also demonstrate that the tripolitza unit which lies directly above the detachment gives an average metamorphic temperature of about 260 8c the modest break in metamorphic temperature in central crete indicates that the cretan detachment accounts for only 5 to 7 km of exhumation of the underlying hp lt metamorphic rocks which were initially accreted at 35 km we argue that the bulk of the exhumation 28 km out of 35 km total occurred by pervasive brittle stretching and erosion of structural units above the detachment d 2005 elsevier b v all rights reserved

carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the ediacaran doushantuo formation the ediacaran doushantuo formation dst is renowned for exceptionally preserved precambrian fossils including metazoans some of these fossils particularly microfossils such as multicellular algae and acanthomorphic acritarchs are preserved in dst chert nodules to better understand the geomicrobiological processes that contributed to the authigenic formation of dst chert nodules and facilitated exceptional fossil preservation we analyzed organic matter in these chert nodules and the surrounding matrix calcareous mudstone using multiple in situ techniques confocal laser raman spectroscopy micro fourier transform infrared spectroscopy ftir and secondary ion mass spectroscopy sims we found strong ultrastructural chemical and isotopic heterogeneities in the organic matter as indicated by the raman spectral parameter i 1350 1600 ranging from 0 49 to 0 88 the infrared spectral index r3 2 from 0 12 to 0 90 and an estimated 13corg sims range of 44 v pdb these micron scale heterogeneities imply that the organic matter preserved in the dst chert nodules is derived from different carbonaceous sources in a diverse microbial ecosystem including eukaryotic and or prokaryotic photoautotrophs as well as chemotrophs involved in the fermentation and probably anaerobic oxidation of organic remains thus the microbial ecosystems in ediacaran ocean waters and sediments were more complex than previously thought and these microbial processes controlled dynamic micro environments in dst sediments where chert nodules were formed and fossils were mineralized the results also show that variations in the relative abundances activities and interactions of co existing microorganisms in dst sediments may have modulated 13corg shifts causing local decoupling between 13corg and 13ccarb as measured in bulk samples

application of raman microspectrometry in the study of structural changes in precambrian kerogens during regional metamorphism abstract a series of kerogens isolated from upper proterozoic shales and schists from a regionally metamorphosed complex barrandian region czechoslovakia were examined by raman microspectrometry changes in the spectra indicate evolution in the chemical structure of the kerogen in the direction of the metamorphic gradient

ore forming processes of the daqiao epizonal orogenic gold deposit west qinling orogen china constraints from textures trace elements and sulfur isotopes of pyrite and marcasite and raman spectroscopy of carbonaceous material

elastic properties of hydrate bearing sediments using effective medium theory accurate and detailed models of the seismic velocity structure of gas hydrate bearing sediments may be determined by careful analysis of controlled source seismic data however interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and or simple effective medium theory we develop a rigorous theoretical scheme to relate the seismic properties of a clay rich hydrate bearing sediment to its porosity mineralogy microstructural features and hydrate saturation we consider separately the two possible end members for the distribution of hydrate in the pore space 1 hydrates are unconnected and located in the pore voids without appreciable grain contact and 2 connected hydrates are forming cement binding around the grains the scheme is transversely isotropic to allow for anisotropy due to alignment of clay platelets and is based on a combination of a self consistent approximation a differential effective medium theory and a method of smoothing for crystalline aggregates we have applied the scheme to lithological and seismic velocity data from ocean drilling program site 995 on the blake ridge southeastern u s continental margin to make estimates of the hydrate saturation it was found that the hydrates are probably unconnected and their volume concentration varies between approx 0 at 100 m below the seabed and approx 9 at 400 m depth just above the bottom simulating reflector if the clay platelet orientation distribution resembles the function we have used

hydrothermal circulation and oil migration at the root of the heterogeneous micro structure of carbonaceous material in the 2 0 ga zaonega formation onega basin russia abstract organic rich rocks of the 2 0 ga zaonega formation karelia russia have been studied extensively to gain understanding of the global carbon cycle and reconstruction of paleo environments directly after the great oxidation event goe this formation has a complex history of alteration involving pervasive hydrothermal circulation hydrocarbon generation migration and mineral authigenesis several previous studies have focused on the description of these secondary effects and the identification of primary geochemical signals in the carbonaceous phases migration and infiltration of organic rich fluids appear to have had only limited effect on the primary carbon isotope record 13corg however the structural variability of carbonaceous material cm appears to have been strongly affected with a range of reported structures including carbon onion shaped nanostructures and mineral templated graphite films here we present a systematic raman spectroscopy based study of the structural variability of cm in a drill core representing the middle and upper strata of the zaonega formation the raman spectra of cm show a systematic difference in structural order between the bulk carbonaceous matrix matrix cm and the cm occurring near mineral contacts contact cm indicating that mineral templating was an important process affecting structural order in the formation the templating effect was observed on the surface of a wide range of minerals the difference in structural order between matrix cm and contact cm can be traced throughout the ca 400 m stratigraphy the structural order varied with the degree of alteration and hydrothermal circulation from highly ordered structures directly above a large gabbro intrusion at the bottom of the stratigraphy to less ordered structures higher up in the sequence this trend directly correlates with the 18o trend of secondary calcite and can be attributed to the decreasing influence and temperature regime of hydrothermal circulation upward in the stratigraphy the results presented here suggest that organic rich hydrothermal fluids can locally strongly enhance graphitization of carbonaceous materials and cause sample scale heterogeneities in the structural order of organic materials this has implications for the interpretation of carbonaceous materials in other ancient rocks experiencing circulation of organic rich hydrothermal fluids

raman characterization of carbonaceous material in the macraes orogenic gold deposit and metasedimentary host rocks new zealand abstract raman spectroscopic and petrographic analyses were performed on samples collected from zones distal and proximal to the macraes gold deposit in the otago schist of new zealand to characterize the features and possible origins of carbonaceous material cm and to assess the potential role of cm in the formation of gold deposits cm is a common component in meta sedimentary orogenic gold deposits and it has been proposed that cm contributes to gold mineralization processes but the details of the mechanisms responsible are not fully understood documentation of the origins of the otago schist cm will improve our understanding of the role of cm in gold deposits this work has identified four types of cm of varying thermal maturity and origins from prehnite pumpellyite grade to lower greenschist grade samples in prehnite pumpellyite and pumpellyite actinolite grade rocks low maturity cm 1 coexists with framboidal pyrite indicating an in situ sedimentary origin with a potential association with the source of gold low crystallinity cm 2 is also found in low grade samples and is likely to have been deposited from fluids unrelated to gold mobilization cm 3 is the highest maturity cm recognized cm 3 is found in samples from the highest metamorphic grades studied lower greenschist facies where bands of cm 3 cross cut the foliation cm 3 is therefore thought to have been transported by fluids though possibly only at short length scales cm 4 is less mature than cm 3 and is found in mineralized rocks in association with sulfide minerals and gold cm 4 is likely to have a depositional origin but its precise role with respect to gold mineralization has not been identified

determination of the petrologic type of cv3 chondrites by raman spectroscopy of included organic matter abstract this paper reports the first reliable quantitative determination of the thermal metamorphism grade of a series of nine cv3 chondrites allende axtell bali mokoia grosnaja efremovka vigarano leoville and kaba the maturity of the organic matter in matrix determined by raman spectroscopy has been used as a powerful metamorphic tracer independent of the mineralogical context and extent of aqueous alteration this tracer has been used along with other metamorphic tracers such as fe zoning in type i chondrules of olivine phenocrysts presolar grain abundance and noble gas abundance bulk and p3 component the study shows that the petrologic types determined earlier by induced thermoluminescence were underestimated and suggests the following values pt allende axtell 3 6 pt bali mokoia grosnaja 3 6 pt efremovka leoville vigarano 3 1 3 4 pt kaba 3 1 the most commonly studied cv3 allende is also the most metamorphosed bali is a breccia containing clasts of different petrologic types the attribution suggested by this study is that of clasts of the highest petrologic types as pointed out by iom maturity and noble gas bulk abundance cv3 chondrites have complex asteroidal backgrounds with various degrees of aqueous alteration and or thermal metamorphism leading to complex mineralogical and petrologic patterns fe mg chemical zoning in olivine phenocrysts on the borders of type i chondrules of porphyritic olivine and pyroxene rich textural types has been found to correlate with the metamorphism grade this suggests that chemical zoning in some chondrules often interpreted as exchanges between chondrules and nebular gas may well have an asteroidal origin furthermore the compositional range of olivine matrix is controlled both by thermal metamorphism and aqueous alteration this does not support evidence of a nebular origin and does not necessarily mirror the metamorphism grade through fe mg equilibration on the other hand it may provide clues on the degree of aqueous alteration vs thermal metamorphism and on the timing of both processes in particular mokoia experienced significant aqueous alteration after the metamorphism peak whereas grosnaja which has similar metamorphism grade did not

archean gravity driven tectonics on hot and flooded continents controls on long lived mineralised hydrothermal systems away from continental margins abstract we present the results of two dimensional numerical modelling experiments on the thermal evolution of archean greenstones as they sink into a less dense hot and weak felsic crust we compare this thermal evolution to that obtained via the analysis of isotopic data and fluid inclusion microthermometry data obtained in the paleoarchean to mesoarchean warrawoona synform eastern pilbara craton western australia our numerical experiments reveal a two stage evolution in the first stage cooling affects zones of downwelling as greenstone belts are advected downward whereas adjacent domes become warmer as deep and hot material is advected upward we show that this is consistent with stable isotopes data from the warrawoona synform which reveal an early episode of seafloor like alteration 90 160 c strongly focused along steeply dipping shear zones in a second long lived stage lateral heat exchanges between domes and basins dominate the system as domes cool down while downwelling zones become increasingly warmer in the warrawoona greenstone belt stable isotopes in gold bearing quartz veins post dating the sagduction related vertical fabrics reveal that rock fluid interaction occurred at much higher temperatures 234 372 c than seafloor like alteration we propose that emplacement of thick and dense continental flood basalts on flooded hot and weak continental plates led to conditions particularly favourable to hydrothermal processes and the formation of mineral deposits we further argue that sagduction was able to drive crustal scale deformation in the interior of continents away from plate margins on largely flooded continents sagduction related shear zones acted as fluid pathways promoting gold mineralisation far away from active plate boundaries continental rift zones or collisional mountain belts

sediments with gas hydrates internal structure from seismic avo we interpret amplitude variation with offset avo data from a bottom simulating reflector bsr offshore florida by using rock physics based synthetic seismic models a previously conducted velocity and avo analysis of the in situ seismic data showed that the bsr separates hydrate bearing sediments from sediments containing free methane the amplitudes at the bsr are increasingly negative with increasing offset this behavior was explained by p wave velocity above the bsr being larger than that below the bsr and s wave velocity above the bsr being smaller than that below the bsr we use these avo and velocity results to infer the internal structure of the hydrated sediment to do so we examine two micromechanical models that correspond to the two extreme cases of hydrate deposition in the pore space 1 the hydrate cements grain contacts and strongly reinforces the sediment and 2 the hydrate is located away from grain contacts and does not affect the stiffness of the sediment frame only the second model can qualitatively reproduce the observed avo response thus inferred internal structure of the hydrate bearing sediment means that 1 the sediment above the bsr is uncemented and thereby mechanically weak and 2 its permeability is very low because the hydrate clogs large pore space conduits the latter explains why free gas is trapped underneath the bsr the seismic data also indicate the absence of strong reflections at the top of the hydrate layer this fact suggests that the high concentration of hydrates in the sediment just above the bsr gradually decreases with decreasing depth this effect is consistent with the fact that the low permeability hydrated sediments above the bsr prevent free methane from migrating upwards

thermal history of the 3 5 3 2 ga onverwacht and fig tree groups barberton greenstone belt south africa inferred by raman microspectroscopy of carbonaceous material raman spectra of carbonaceous material were collected in situ from samples of cherts of the onverwacht and fig tree groups in the central barberton greenstone belt the spectra feature two dominant peaks characteristic of disordered carbon the d peak at 1310 cm 21 and the o peak at 1580 1600 cm 21 d peak positions and relative peak intensities and areas indicate that all samples have been altered to lower greenschist facies or above no correlation was observed between maximum temperature and stratigraphic position or degree of hydrothermal alteration implying that metamorphism in the central barberton greenstone belt was regional and unaccompanied by the flow of large quantities of hydrothermal fluids samples from the marble bar chert of the pilbara block western australia have been heated to the same extent as samples from barberton this study demonstrates the use of raman spectra of carbonaceous material as a sensitive geother mometer for low temperature metamorphic facies this application could also be used to establish the antiquity of putative microfossils from metamorphic terranes

mineral templated growth of natural graphite films abstract organic material in sediments is progressively altered during diagenesis and metamorphism leading to the formation of kerogen and ultimately crystalline graphite bulk carbonaceous material in metamorphic terrains typically has attained an overall degree of structural order that is in line with peak metamorphic temperature on a micron to nano scale however carbonaceous material can display strong structural variation the main factor that drives this variation is the chemical and molecular heterogeneity of the precursor biologic material specific conditions during metamorphism however can also play a role in shaping the microstructure of carbonaceous material here we describe the structural variation of carbonaceous material in rocks of the 2 0 ga zaonega formation karelia russia raman spectroscopy indicates that bulk carbonaceous matter in these rocks has experienced peak temperatures between 350 and 400 c consistent with greenschist facies metamorphism on a nano scale however a strong structural heterogeneity is observed transmission electron microscopy tem reveals the occurrence of thin films of highly ordered graphitic carbon at mineral surfaces these graphite films consisting of 20 100 individual layers completely envelop quartz crystals and occur on specific crystal surfaces of chlorite it is proposed that minerals can act as templates for the parallel ordering of carbon crystallites causing enhanced graphitization within narrow zones at mineral surfaces alternatively oriented organic precursor molecules could have been adsorbed onto charged mineral surfaces leading to thin graphitic films during later metamorphic heating episodes overall the presented observations demonstrate that mineral surfaces can initiate and accelerate localized graphitization of sedimentary organic material during metamorphism and therefore cause distinct nano scale variation in structural order

the structure and distribution of carbon in 3 5 ga apex chert implications for the biogenicity of earth s oldest putative microfossils the oldest putative microfossils on earth occur in the 3 5 ga apex chert of the warrawoona group western australia we have analyzed disseminated interstitial carbon found within apex chert using transmission electron microscopy tem and electron energy loss spectroscopy eels to address the controversy regarding its state of structural disorder we found that the carbonaceous material is structurally amorphous with no evidence of graphitization and contains aromatic domains most likely as polyaromatic ring structures similar to preserved kerogen in bona fide microfossils in addition amorphous carbonaceous material occurs as a grain boundary phase between quartz crystals and within fluid inclusions in quartz crystals indicating that hydrocarbons moved through the chert during crystallization and hydrothermal alteration the results suggest that the carbonaceous material is similar in structure to microfossil kerogen implying the microbe like features within apex chert are also microfossils however this kerogen like material may also be produced abiotically via fischer tropsch type ftt synthesis reactions in an ancient hydrothermal vent

microbial life and biogeochemical cycling on land 3 220 million years ago the colonization of emergent continental landmass by microbial life was an evolutionary step of paramount importance in earth history here we report direct fossil evidence for life on land 3 220 million years ago ma in the form of terrestrial microbial mats draping fluvial conglomerates and gravelly sandstones of the moodies group south africa combined field petrographic carbon isotope and raman spectroscopic analyses confirm the synsedimentary origin and biogenicity of these unique fossil mats as well as their fluvial habitat the carbon isotope compositions of organic matter 13corg from these mats define a narrow range centred on 21 in contrast to fossil mats of marine origin from nearby tidal deposits that show 13corg values as low as 34 bulk nitrogen isotope compositions 2 15n 5 are also significantly different from their marine counterparts 0 15n 3 which we interpret as reflecting denitrification in the terrestrial habitat possibly of an atmospheric source of nitrate our results support the antiquity of a thriving terrestrial biosphere during the palaeoarchaean and suggest that a complex and microbially driven redox landscape existed during the deposition of the moodies group with distinct biogeochemical cycling occurring on land by 3 220 ma microbial life colonized the land surface by 3 2 billion years ago forming complex communities distinct from those in nearby marine environments according to analyses of fossilized microbial mats in the moodies group south africa

comment on biogenicity of earth s earliest fossils a resolution of the controversy by j william schopf and anatoliy b kudryavtsev gondwana research 22 2012 761 771 recently schopf and kudryavtsev 2012 have published an exhaustive review on the biogenicity of the most controversial evidence of ancient life on earth to date an assemblage of carbonaceous filaments found in the 3465 ma apex chert of northwestern australia schopf and packer 1987 schopf 1993 the morphology of the filaments their carbon isotopic composition and the sedimentary environment interpreted as shallow marine suggested to schopf 1993 that these filaments were fossilized cyanobacteria this discovery sparkled a large controversy among the scientific community that lasted for more than 25 years see pinti and altermann 2011 for a review on the subject in the synopsis of the controversy page 762 schopf andkudryavtsev 2012 wrote the apex fossils have subsequently been suggested to be inorganic silica or clay mineral needle like crystals pinti et al 2009 again at page 769 the authors reported that needles composed of halloysite al2si2o5 oh 4 a clay mineral and of quartz sio2 have been compared with the apex fossils pinti et al 2009 these are two serious misstatements because we never compared any of the pseudofossils that we observed in apex chert to the microfossils of schopf 1993 schopf and kudryavtsev 2012 themselves report at

carbonaceous microstructures from sedimentary laminated chert within the 3 46 ga apex basalt chinaman creek locality pilbara western australia abstract hydrothermal black chert veins intruding the 3 46 ga apex basalt contain some of earth s oldest microfossil like objects whose biogenicity has been questioned whilst these black chert veins have been studied in great detail relatively little is known about the stratiform seafloor sedimentary cherts that are conformably interbedded with volcanic rocks of the apex basalt herein we document and assess the biogenicity of carbonaceous microstructures present in the lowermost of the stratiform chert units informally known as the apex chert at the chinaman creek locality in the marble bar greenstone belt pilbara craton western australia carbonaceous material mostly occurs within clotted grey black cherts and microgranular grainstone like cherts within the stratiform unit the latter being the major focus of this study in the clotted cherts carbon occurs as lobate fluffy grains rare compressed flakes and as a grain boundary phase around spherulitic silica there is no morphological evidence to support the biogenicity of these microstructures in contrast the microgranular chert contains fluffy and flaky carbonaceous grains plus laminated grains comprising multiple non isopachous wrinkled carbonaceous laminae with noted thickening towards some ridge crests as determined by confocal laser scanning microscopy roll up structures provide evidence of an initial plasticity interpreted to have formed via the tearing up and current induced plastic deformation of microbial mat fragments geochemical mapping using laser raman micro spectroscopy and nanosims respectively demonstrates the antiquity of the carbon and reveals a close correlation between carbon nitrogen and sometimes sulphur concentrated within dark brown to black laminae adjacent to microgranular zones are zones of more persistent carbonaceous undulose filament like laminae that entrain relict sediment grains these microstructures are directly comparable to a sub type of microbially induced sedimentary structure miss widely reported from younger siliciclastic sediments colonised by microbial biofilms the morphology and chemical composition of both the non isopachous laminated grains and the filament like laminae are consistent with a biological interpretation suggesting microscopic miss were present in the microgranular stratiform apex chert however the fact that neither macroscopic miss nor bona fide microfossils have yet been reported from this unit coupled with the proximity of these structures to active hydrothermal vents potentially discharging hot carbon rich fluids urges caution in such an interpretation the chinaman creek apex chert investigated here is one of at least five sedimentary laminated cherts within the apex basalt these horizons are promising targets in the search for biological activity within a dominantly volcanic archaean environment

elastic wave velocity in marine sediments with gas hydrates effective medium modeling we offer a first principle based effective medium model for elastic wave velocity in unconsolidated high porosity ocean bottom sediments containing gas hydrate the dry sediment frame elastic constants depend on porosity elastic moduli of the solid phase and effective pressure elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation to model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions a hydrate modifies the pore fluid elastic properties without affecting the frame b hydrate becomes a component of the solid phase modifying the elasticity of the frame the goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data we apply the model to sonic and vsp data from odp hole 995 and obtain hydrate concentration estimates from assumption b consistent with estimates obtained from resistivity chlorinity and evolved gas data

cellular taphonomy of well preserved gaoyuzhuang microfossils a window into the preservation of ancient cyanobacteria abstract the 1500 ma gaoyuzhuang microfossils a representative mesoproterozoic cyanobacteria assemblage are crucial for understanding and searching for early precambrian life on earth the cellular taphonomy of fossils in this assemblage is poorly known however here we combined in situ microscopic and microanalytical techniques to study the detailed taphonomy of these microfossils light microscopy lm scanning electron microscopy sem and transmission electron microscopy tem observations show that gaoyuzhuang microfossils are mainly preserved in black chert layers and that silica particles can be found within fossilized cell walls and sheaths raman spectra show the characteristic first order bands at 1350 and 1605 cm 1 of carbonaceous material comprising microfossils indicating that they have experienced peak temperatures of 215 to 308 c raman maps show the spatial distribution of the carbonaceous matter as well as that of the silica matrix consistent with nano scale secondary ion mass spectrometry nanosims analyses variations in 13c versus 12c and 34s versus 32s within individual microfossils are likely the result of original differences in the isotopic compositions of cellular components confocal laser scanning microscopy clsm analyses provide fluorescence based 2 d and 3 d images of the cellular components of such microfossils at high spatial resolution the micro scale chemical isotopic and structural heterogeneities together with the subcellular morphological features support the preferential preservation of cyanobacterial cell walls and sheaths over cell contents in precambrian chert we proposed a potential taphonomic model perhaps responsible for the high fidelity of preservation for such microfossils permineralized in precambrian rocks the integrated approach has potential for deciphering the enigmatic nature of mesoproterozoic microorganisms preserved in stromatolitic cherts with significant implications for microbial preservation in the geological record

sulfur isotope mass independent fractionation in impact deposits of the 3 2 billion year old mapepe formation barberton greenstone belt south africa abstract theoretical and experimental studies have shown that atmospheric so 2 isotopologue self shielding effects in the 190 220 nm region of the solar spectrum are the likely cause for mass independent fractionation of sulfur isotopes s mif the main products of this photochemical reaction so 3 and s 0 typically define a compositional array of ca 33 s 34 s 0 06 0 14 this is at odds with the generally observed trend in archean sulfides which broadly defines an array of ca 33 s 34 s 0 9 various explanations have been proposed including a diminution of 34 s caused by chemical and biogenic mass dependent fractionation of sulfur isotopes s mdf mixing with photolytic products produced during felsic volcanic events or partial blocking of the low wavelength part of the spectrum due to the presence of reduced atmospheric gases or an organic haze early in earth history large meteorite impacts would have ejected dust and gas clouds into the atmosphere that shielded solar radiation and affected global climate it is thus likely that at certain time intervals of high meteorite flux the atmosphere was significantly perturbed having an effect on atmospheric photochemistry and possibly leaving anomalous sulfur isotopic signatures in the rock record here we describe the sulfur isotopic signatures in sulfides of spherule beds s2 s3 and s4 of the barberton greenstone belt south africa in particular in spherule bed s3 and to a lesser extent s4 a trend of ca 33 s 34 s 0 23 is observed that closely follows the expected trend for so 2 photolysis in the 190 220 nm spectral range this suggests that an impact dust cloud deposited as spherule beds which sampled the higher region of the atmosphere specifically incorporated products of so 2 photolysis in the 190 220 nm range and blocked photochemical reactions at higher wavelengths 250 330 nm band by implication the generally observed archean trend appears to be the result of mixing of different mif s sources arising from a variety of photochemical reactions that took place in the lower part of the atmosphere

haematite pseudomicrofossils present in the 3 5 billion year old apex chert microstructures from the 3 5 billion year old apex chert have been interpreted as the remains of ancient cyanobacteria geochemical analyses suggest similar structures at the same location are instead haematite filled fractures although carbonaceous material in the surrounding matrix is consistent with the presence of microbes at this time

structural characterization by raman hyperspectral mapping of organic carbon in the 3 46 billion year old apex chert western australia abstract the 3 46 billion years old apex chert pilbara craton western australia is well known for hosting the oldest highly disputed microfossils on earth this rock has a complex history of thermal alteration that includes circulation of hydrothermal fluids lower greenschist facies regional metamorphism and post metamorphic weathering by meteoric fluids carbonaceous material occurs in the sedimentary stratiform part of the chert as well as the underlying intruding hydrothermal black chert veins in order to identify a least altered remnant of early life it is necessary to develop a method that enables rapid evaluation of cm structural order on a small spatial scale here we present the detailed characterization of cm in the apex chert by raman hyperspectral mapping it is shown that this approach gives better estimates of average raman band ratios than individual point analyses and it is demonstrated that significant differences in structure exist between cm in the stratiform part of the apex chert and cm in an underlying black chert vein the large raman map based datasets also reveal that significant mixing took place between these two end members cm s indicating that the apex chert has been thoroughly altered by hydrothermal fluid circulation at the brecciated intersection between the stratiform chert and the intrusive hydrothermal chert vein very poorly ordered cm was found that is not in line with lower greenschist facies regional metamorphism it is speculated here that this cm represents an organic fraction that was introduced or thoroughly altered by late stage meteoric fluids alternatively the ubiquitous presence of hematite in this sample caused a perturbation in the raman spectra of the cm leading to an artifact in the calculated raman based band ratios overall it can be concluded that the best preserved cm occurs in the stratiform parts of the apex chert while earlier discussions on organic microfossils in this rock often focused on parts of the chert that either represented the hydrothermal veins or the brecciated intersection between the veins and the stratiform part

organic rich microfossils produced by oil infiltration of hollow silicified bacteria evidence from the ca 340 ma red dog zn pb deposit alaska

raman spectroscopy and structural heterogeneity of carbonaceous material in proterozoic organic walled microfossils in the north china craton abstract raman spectroscopy is a minimally intrusive and minimally destructive technique that has played an important role in analyzing precambrian carbonaceous microfossils and microstructures previous studies have shown that heterogeneities in structural order of carbonaceous material cm as revealed by raman spectroscopy can be preserved in proterozoic silicified cyanobacterial fossils however such heterogeneities have not been documented in proterozoic eukaryotic microfossils preserved as carbonaceous compressions in this study we used raman spectroscopy to investigate the structural characteristics of organic walled microfossils including eukaryotes preserved as carbonaceous compressions from the late paleoproterozoic ruyang group and the early neoproterozoic tonian liulaobei formation in the north china craton raman geothermometers indicate that cm experienced low grade metamorphism with apparent peak metamorphic temperatures of 200 c for both the ruyang and liulaobei microfossils heterogeneities in structural characteristics of cm in eukaryotic microfossils were found among different subcellular structures of shuiyousphaeridium macroreticulatum and among different taxa from the same stratigraphic horizon we suggest that these heterogeneities can be attributed to differences in precursor organic compounds thus the importance of organic precursors should be considered in cm raman geothermometry studies especially in environments where heating events occurred quickly the raman data presented here are also consistent with hypotheses that the ruyang microfossils dictyosphaera delicata and s macroreticulatum are biologically conspecific taxa with their vesicle walls having similar cm raman features and that the liulaobei microfossils leiosphaeridia jacutica and l tenuissima are distinct taxa despite their similarities in morphologies other than vesicle wall thickness although more data are needed to verify the consistency of interspecies intraspecies and intraspecimen variability this study indicates that raman spectroscopy may have the potential to provide an independent test of early eukaryote taxonomy which has been traditionally based only on morphological features and to reveal heterogeneities of cm of early eukaryotic organisms