mass occurrence of benthic coccoid cyanobacteria and their role in the production of neoarchean carbonates of south africa abstract the sparse archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post mortem silicification hitherto as an exception sedimentary carbonate rocks from the neoarchean nauga formation of south africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria chroococcales and pleurocapsales their remains visible under the scanning electron microscope sem after etching of polished rock samples comprise capsular envelopes mucilage sheaths and groups of cells mineralized by calcium carbonate with an admixture of al k mg fe silicates the capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the neoarchean microbiota described and their modern analogues the new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the neoarchean and offer a solution to the problem of the origin of archean carbonate platforms stromatolites and microbial reefs

origin of 3 45 ga coniform stromatolites in warrawoona group western australia a new occurrence of conical and branched pseudocolumnar stromatolites in archean dolostones in the pilbara region australia contributes significant new morphologic information on such structures these remains are interpreted as probably representing in part microbially mediated accretionary growth surfaces in an archean hypersaline depositional basin the structures comprise laterally linked pseudocolumns of centimeter width and decimeter height with first order conical laminae of as much as 15 cm of synoptic relief and apical angles of 30 80 the conical laminae are modified by a second order centimeter scale low amplitude primary corrugate lamination with crests and troughs occasionally stacked to form satellitic obliquely directed pseudocolumns bedding surfaces exhibit a preferred direction of elongation of the cones an orientation that is orthogonal and unrelated to the trend of younger folding the microstructure is secondary the stromatolites are better preserved than those previously known from chert in the warrawoona succession the remains exhibit certain distinct morphologic attributes corresponding to those in younger stromatolites such as displayed by thyssagetes and jacutophyton whose biogenicity is generally accepted although difficult to demonstrate conclusively the conical warrawoona forms may represent the oldest known precursor of these taxa

pattern of cell division in 3 4 ga old microbes from south africa abstract in cell division most microbes rely on binary fission some however show less common division patterns such as multiple fission or budding little is known about the nature of cell division in the earth s earliest fossil microbes largely because of their poor preservation but such details could be key in establishing the biogenicity of putative archean fossils and their relationships to modern microbes in this report we describe cellularly preserved microfossils from paleoarchean 3 4 ga old deposits of south africa kromberg formation their cellularity is revealed by well preserved reproduction patterns exemplified by binary symmetrical and asymmetrical and multiple coupled and or sequential cell fission although no clues concerning physiology or affinity of the studied cells can be drawn basing on their division mode the identified reproductive patterns link them particularly closely with coccoidal microbes classified within the cyanobacterial group pleurocapsales

nondestructive in situ cellular scale mapping of elemental abundances including organic carbon in permineralized fossils the electron microprobe allows elemental abundances to be mapped at the mm scale but until now high resolution mapping of light elements has been challenging modifications of electron microprobe procedure permit fine scale mapping of carbon when applied to permineralized fossils this technique allows simultaneous mapping of organic material major matrix forming elements and trace elements with mm scale resolution the resulting data make it possible to test taphonomic hypotheses for the formation of anatomically preserved silicified fossils including the role of trace elements in the initiation of silica precipitation and in the prevention of organic degradation the technique allows one to understand the localization of preserved organic matter before undertaking destructive chemical analyses and because it is nondestructive offers a potentially important tool for astrobiological investigations of samples returned from mars or other solar system bodies

controls of extreme isotopic enrichment in modern microbialites and associated abiogenic carbonates abstract microbialites and abiogenic carbonates of the closed basin hypersaline lake laguna negra catamarca province argentina are highly enriched in both 13c and 18o these carbonates precipitate in the zone of recharge where lake water mixes with groundwater we examined the processes controlling the isotopic evolution of input waters in order to better interpret the isotopic compositions of the carbonates large enrichments of 13c in dissolved inorganic carbon and 18o in water occur as input groundwater chemically evolves these enrichments can be explained through the abiotic processes of water equilibration evaporation degassing and carbonate precipitation the 13c and 18o contents of lake carbonates are consistent with equilibrium precipitation from lake water indicating that the currently ongoing processes can explain the isotopic patterns observed in carbonates isotopic compositions of these microbialites are largely unrelated to the biological processes controlling microbialite formation a pattern that may be generalizable to other settings however the isotopic compositions of these microbialites record information about their depositional environment

recognition genesis and evolution of manganese ore deposits in southeastern china abstract manganese ore deposits are common in the falang formation of ladinian age middle triassic southeastern yunan china the deposits containing manganese oxide and manganese carbonate ores are not metamorphic in origin and they commonly contain bioclasts concentric ring structures are clearly observed in oolitic and pisolitic manganese ores an integrated approach using sedimentology and paleoenvironment analysis provides new insight into the genesis of these ores systematic research has been conducted on typical deposits dounan yanzijiao laowu tujichong using cathodoluminescence and scanning electron microscope techniques which allow elucidation of changes in laminated microtextures at the mm m scale preliminary results show that manganese enrichment in triassic deposits of this region may be related to microbial activity and mineralization was a consequence of bacterially mediated diagenetic reactions in addition findings of biodetritus in the manganese ore indicate that manganese ore is close to the redox level the concentration of manganese in solution and in precipitates in triassic is controlled by bacterial oxidation and redox conditions corresponding to sea level changes during the ladinian

the influence of lake morphometry on sediment focusing sediment focusing is a process whereby water turbulence moves sedimented material from shallower to deeper zones of a lake sediment focusing occurs in lakes in both the erosional coarse grained sediments and the transportational zone with the latter characterized by discontinuous sedimentation and resuspension the zone of accumulation is diefined as the zone where sedimentation is final i e no resuspension and where there is no further sediment focusing a geochemical tracer pb was used to trace sediment focusing patterns in 12 lakes of different morphomctries the area occupied by the zone of accumulation is predicted from the mean basin slope a with 86 of the variance explained only in large exposed lakes in which turbulence from waves is more severe are the resulting sediment distributions more erratic this study is the first to provide a general model of sc diment focusing patterns among lakes the study of lake bottom dynamics has received attention in the contexts of sediment contaminant and eutrophication studies the fact that sediments are major depositories for contaminants and nutrients has made them a focus for research in limnology also because sediments provide a record of past events in lakes an understanding of the manner in whllch sediments accumulate is essential for hindcasting interpretations of the historical record in sediments will be confounded if the record has been obscured by sediment resuspension the term sediment focusing was coined by likens and davis 1975 to describe the resuspension of sediments in shallower zones by waves and water currents with subsequent transport to and settling in the deeper zones of lakes much of the work

subaerial freshwater phosphatic stromatolites in deer cave sarawak a unique geobiological cave formation abstract a suite of distinctive freshwater subaerial phosphatic stromatolites is developed close to the northeastern entrance of deer cave gunung mulu national park sarawak borneo in conditions of very low light but ample supply of nutrients from guano these stromatolites are not particulate they are composed of alternating layers of more porous and more dense amorphous hydroxylapatite this biomineralization occurs as moulds of coccoid the majority and filamentous less abundant cyanobacteria mineralization occurs at a ph of 7 0 in the extracellular sheaths and in micro domains of varying carbonate content in the surrounding mucus of the biofilm the most recent surfaces that are not yet strongly mineralized show still living filamentous coccoid and rod shaped forms trace element composition shows enrichment in metal ions especially mn and zn the stromatolites are present as horizontal shelves arranged in series on a steep rock face that is vertically under a guano laden shelf the rock face undergoes active dissolution from acidic guano drainage water e g ph of 2 43 and from aggressive rainwater from an overhead discharge however the rock surface under the stromatolite is protected while the rest of the cliff face is backcut creating a hoodoo like effect the stromatolites are 15 20 cm deep 4 7 cm thick and of variable width generally 50 cm eventually guano and biological detritus in the descending water film lodge in the lee of the stromatolite lip causing local acidification and erosion of stromatolite and rock on the underside of the ledge a dynamic equilibrium is established between upward accretion of the fresh surface and destruction at the base such that the base of the stromatolite does not reflect the date of its inception and the stromatolite climbs up the wall

cyanobacteria associated with hot spring travertines cyanobacteria are the major oxygenic photosynthetic microorganisms of hot spring travertines this review describes the known cyanobacterium flora of travertine depositing waters 37 c the communities develop either upon epilithon or within endolithon the travertine surface where they may influence the travertine fabric by providing nucleation sites for calcium carbonate mat photosynthesis locally increases the amount of travertine deposited but the importance of photosynthesis in travertine deposition is rarely significant because the main loss of co2 is by atmospheric evasion of the hot co2 rich waters the oscillatoriales are the most important group of cyanobacteria in terms of their biomass but the taxonomy of the order is in a state of chaos molecular methods will ultimately disclose the true affinities of the organisms but at present the use of form taxa based upon morphological characters provides a practical alternative identification of fossilized cyanobacteria is problematic sin

microfossils and possible microfossils from the early archean onverwacht group barberton mountain land south africa there is widespread textural evidence for microbial activity in the cherts of the early archean onverwacht group layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic hooggenoeg and kromberg formations in rare cases filamentous microfossils are associated with the laminae the morphologies of the fossils as well as the texture of the encompassing laminae suggest an affinity to modern mat dwelling cyanobacteria or bacteria a variety of spheroidal and ellipsoidal structures present in cherts of the hooggenoeg and kromberg formations resemble modern coccoidal bacteria and bacterial structures including spores the development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions including the effects of very large meteorite impacts on the young earth

reassessing the evidence for the earliest traces of life the isotopic composition of graphite is commonly used as a biomarker in the oldest 3 5 gyr ago highly metamorphosed terrestrial rocks earlier studies on isotopic characteristics of graphite occurring in rocks of the approximately 3 8 gyr old isua supracrustal belt isb in southern west greenland have suggested the presence of a vast microbial ecosystem in the early archean this interpretation however has to be approached with extreme care here we show that graphite occurs abundantly in secondary carbonate veins in the isb that are formed at depth in the crust by injection of hot fluids reacting with older crustal rocks metasomatism during these reactions graphite forms from the disproportionation of fe ii bearing carbonates at high temperature these metasomatic rocks which clearly lack biological relevance were earlier thought to be of sedimentary origin and their graphite association provided the basis for inferences about early life the new observations thus call for a reassessment of previously presented evidence for ancient traces of life in the highly metamorphosed early archaean rock record

zircon u pb ages and lu hf isotope systematics from late tectonic granites geita greenstone belt implications for crustal growth of the tanzania craton granite plutons that intruded south of lake victoria and north of the geita greenstone belt have geochemical characteristics similar to high k granites when compared to the late high k granites from the musoma mara region they have lower sio2 content and higher tio2 al2o3 cao na2o p2o5 mgo and feot they also show higher values for v sr zr ba and hf concentrations all samples display high total ree abundances ree 139 393 and weak to moderate eu depletion eu eu 0 25 0 77 their chondrite normalized pattern indicates that the light ree are moderately fractionated 3 03 lan smn 6 24 whereas the heavy ree are weakly fractionated 1 63 gdn ybn 2 80 the granite plutons are generally undeformed with 207pb 206pb ages between 2660 and 2620 ma and intruded after the main ductile deformation that affected the geita greenstone belt the 176hf 177hf ratios for zircons from all samples are identical within error suggesting evolution from an isotopically uniform reservoir the hf values plot along the chur evolution line indicating that the granite represents juvenile crustal melts derived from greenstone material available zircon ages from the tanzania craton suggest that crustal growth occurred in three distinct periods 2850 2800 ma 2770 2730 ma and 2700 2620 ma with the dominant period of crustal growth around 2700 ma zircon ages from the sukumaland and musoma mara greenstone belts indicate that the greenstone sequences formed during the same three periods of crustal growth

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

multifrequency acoustic profiling for water reservoir sedimentation studies abstract volume loss in water reservoirs due to sedimentation is conventionally estimated from the change in bathymetric surveys repeated five or more years apart despite many recent improvements in bathymetric surveying technology such estimates of volume loss still depend on older and less accurate bathymetric surveys we describe an alternative approach to reservoir surveying using a new multifrequency acoustic profiling system the new system includes a 200 khz precision fathometer and four subbottom profiling frequencies of 48 khz 24 khz 12 khz and 3 5 khz together with dgps navigation all data recording components are contained in one suitcase size instrument package specially designed software combines three or more signal frequencies into composite false color displays for interpretation of sediment thickness and type when calibrated by sparse coring or spud bar determinations of sediment thickness the method can produce accurate long term estimates of reservoir volume in one survey as an initial test of the new system we conducted a combined survey of water storage capacity and sediment volume of waco lake texas in november 1997 the water storage capacity of waco lake was previously determined by land surveying methods prior to the initial impoundment in 1965 and by bathymetric surveys in 1970 and 1995 our 1997 estimate of water storage capacity agrees with the 1995 bathymetric results to within 3 however we find 62 more sediment in the reservoir by direct acoustic measurement of the sediment thickness than indicated from the difference between the 1970 and 1995 bathymetric surveys

accumulation of transition metals and metalloids in sulfidized stromatolites of the 3 48 billion year old dresser formation pilbara craton abstract stromatolites of the 3 48 billion year old dresser formation pilbara craton western australia provide some of the oldest convincing evidence of life on earth here we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals cr mn co ni cu zn mo se ag sn au hg and pb and metalloids as sb and te in unweathered samples of strongly sulfidized stromatolites from drill cores high resolution elemental mapping and in situ compositional analysis of sulfides pyrite and sphalerite show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive nano porous pyrite enriched in autochthonous organic matter which forms the major petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites repeated cyclic alternations of various transition metals and metalloids most importantly ni and zn plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation because transition metals and metalloids generally have strong affinities for organic matter and can play active roles in biochemical processes we interpret these element accumulations in the dresser formation stromatolites to be the result of binding to organic matter of living microbial communities and or dead biomass and perhaps also microbial utilization collectively our results show that the precise characterization of transition metal metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity even in some of earth s oldest stromatolites

stromatolite reef from the early archaean era of australia the 3 430 million year old strelley pool chert spc pilbara craton australia is a sedimentary rock formation containing laminated structures of probable biological origin stromatolites determining the biogenicity of such ancient fossils is the subject of ongoing debate however many obstacles to interpretation of the fossils are overcome in the spc because of the broad extent excellent preservation and morphological variety of its stromatolitic outcrops which provide comprehensive palaeontological information on a scale exceeding other rocks of such age here we present a multi kilometre scale palaeontological and palaeoenvironmental study of the spc in which we identify seven stromatolite morphotypes many previously undiscovered in different parts of a peritidal carbonate platform we undertake the first morphotype specific analysis of the structures within their palaeoenvironment and refute contemporary abiogenic hypotheses for their formation finally we argue that the diversity complexity and environmental associations of the stromatolites describe patterns that in similar settings throughout earth s history reflect the presence of organisms

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

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

potential of epr imaging to detect traces of primitive life in sedimentary rocks abstract in the prospect of the search for traces of primitive life on earth and mars we investigated the possibility to detect and visualize the spatial distribution of minute amounts of organic matter in ancient rocks in a non destructive way by electron paramagnetic resonance imaging epri we studied a series of non or moderately metamorphosed siliceous rocks cherts of different ages ranging from 45 ma to 3490 ma and embedding fossile organic matter in the case of the oldest cherts containing only mature insoluble organic matter iom with iom radicals characterized by a single electron paramagnetic resonance epr line we could obtain three dimensional images with sub millimetric resolution of the organic matter distribution inside samples containing as low as 1014 1015 radicals per gram in the case of younger cherts containing less mature organic matter and thus several types of organic radicals we showed that selective imaging of each type of radical was possible provided that the epr spectra did not overlap selective imaging of either the organic radicals or of the oxygen vacancy e centres of the mineral matrix which are ubiquitous in siliceous rocks was possible selecting either one or the other paramagnetic species with high power in phase 1st harmonic detection or with 90 out of phase 2nd harmonic detection of the epr the influence of ferromagnetic inclusions in the mineral matrix on the epri of the organic matter was also addressed image artifacts due to the ferromagnetic resonance signal of these inclusions could be easily removed by background substraction from the epr spectra before image reconstruction we thus showed that selective imaging by epr of minute amounts of fossile organic matter in ancient rocks could be possible despite the magnetic complexity of such materials

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

filamentous microfossils in the early proterozoic transvaal supergroup their morphology significance and paleoenvironmental setting abstract well preserved filamentous microfossils siphonophycus transvaalensis n sp are described here from the carbonate campbellrand subgroup to iron formation kuruman iron formation transition of the transvaal supergroup south africa estimated to be 2 5 2 3 ga years old the microfossils occur in petrographic thin sections of a core sample of carbonate chert they are preserved by permineralization in both chert and in sparry ferroan dolomite stratigraphically the fossiliferous core sample occurs as part of an upward transition from a stromatolitic dolomite and limestone sequence campbellrand to the overlying iron rich sediments of the kuruman griquatown iron formations the average 13 c value of the kerogen in the sample is about 36 9 the microfossils are filamentous unbranched tubular to somewhat flattened 15 25 m in diameter and a few to many hundred microns in length they exhibit a coriaceous finely granular external surface texture resulting from the presence of adhering randomly distributed fine mineralic carbonate needles in salient morphological characteristics they are comparable to the tubular originally polysaccharide encompassing sheaths of extant oscillatoriacean cyanobacteria in comparison with previously described precambrian microfossils these fossil filaments are unusual because of their preservation in sparry carbonate in addition to chert their relatively large diameter and their coating by adhering precipitated carbonate needles they appear to be among the oldest assured microfossils now known from proterozoic age sediments the microfossils are interwoven occurring in subparallel aggregates that form a stromatolitic mat like fabric they are considered to be of an endogenetic in situ benthic origin occurring at the proximal margin of a deep shelf environment at the front distal margin of the campbellrand carbonate platform the water depth for this environment at the break in slope between deep shelf and euxinic basin is estimated to have been of the order of 40 45 m paleomagnetic data support our interpretation that the micro organisms inhabited a warm water marine environment probably at low latitudes

spatial distribution of major and trace elements in shallow reservoir sediments an example from lake waco texas sediment geochemistry of a shallow 6 m average reservoir lake waco was evaluated for the spatial distribution of major and trace elements sixty bottom and core samples along a 21 km transect within the reservoir 18 overbank sediment samples and 8 rock types in the drainage area were collected and analyzed for major al ca fe and trace elements as ba cr cu hg mn ni pb sr v zn elemental concentrations in the reservoir sediments closely correspond to concentrations in the regional rocks and represent a mixture of overbank sediment composition of the tributaries elemental concentrations were statistically regressed against al concentrations in order to establish regional baseline levels and thereby distinguish natural from anthropogenic sources spatial geochemical trends considered in terms of element to al ratio versus v to al ratio relate to the natural and anthropogenic sources contributing to the elemental concentrations the spatial elemental distribution in the reservoir which receive sediments from two mineralogically contrasting basins reflect textural and mineralogical transition within the reservoir and suggest a progressive mixing of sediment from the tributaries the spatial elemental distribution and sediment texture suggest that the sediment source which determines the sediment type has a greater influence on the major and trace element distributions in shallow reservoir sediments than bathymetry

the criteria for the biogeneicity of microbially induced sedimentary structures miss in archean and younger sandy deposits abstract the identification of fossils or biogenic sedimentary structures in rocks of archean age is difficult because similar lithological features could rise from purely physical or chemical processes alone therefore it is important to define criteria that serve the secure definition of a fossil or structure in question as of biological origin such criteria have been established for stromatolites and microfossils this contribution discusses the 6 criteria of biogeneicity of microbially induced sedimentary structures miss those structures are found in sandy deposits of early archean age to the present and rise from the interaction of benthic microbiota with physical sediment dynamics the six criteria for their biogeneicity are i miss occur in rocks of not more than lower greenschist facies ii in stratigraphic sections miss correlate with turning points of regression trangressions iii miss correlate with a characteristic depositional facies that enhances the development and the preservation of microbial mats iv the distribution of miss correlates with the ancient average hydraulic pattern v the geometries and dimensions of fossil miss correspond to that of the modern ones vi the miss include at least one of 9 specific microtextures

early biosphere magnifying ancient microstructures purported 3 465 million year old microfossils from australia have been the subject of considerable debate a method to distinguish between pristine fossils mineral artefacts and subsequent microbial contamination will aid the search for ancient biogenic material

olivine 100 normal to foliation lattice preferred orientation in prograde garnet peridotite formed at high h2o activity cima di gagnone central alps automated electron backscattered diffraction ebsd was applied using a scanning electron microscope to obtain lattice preferred orientation lpo data for olivine in garnet peridotites of the central alps as a reference frame the lpos of enstatite were also investigated in the garnet peridotite at cima di gagnone cdg a weak foliation carrying a distinct lineation is present the lineation is characterized by elongated enstatite olivine and poikiloblastic garnet olivine shows a very unusual lpo with 100 normal to foliation and 001 parallel to lineation achsenverteilungsanalyse ava maps demonstrate that 001 of olivine grains corresponds quite well to their maximum length axes which are preferentially parallel to the lineation numerous planar hydrous defects within 001 planes of olivine are marked by palisades of ilmenite rods and show a preferred orientation normal to lineation calculated p wave velocities for cdg are fastest 8 32 km s 1 normal to foliation with a relatively low anisotropy 2 9 compared to mantle peridotites with the usual 010 100 lpo where the fastest vp direction is towards the lineation the relationship between flow geometry and seismic anisotropy is significantly different at cdg several mechanisms for the formation of the lpo type at cdg are considered with glide possible on 100 001 of olivine on the basis of field data as well as petrographic and petrologic evidence it has been demonstrated that the cdg garnet peridotite formed by prograde metamorphism from a hydrous protolith at pressures and temperatures of about 3 0 gpa and 750 c respectively the cdg lpo is interpreted to have formed during hydrous subduction zone metamorphism the same interpretation may hold for the previously investigated olivine lpo at alpe arami which is similar to that at the nearby cdg the observed anomalous lpo is no proof for ultradeep 3 0 gpa conditions

carbon isotopes as biogeochemical recorders of life over 3 8 ga of earth history evolution of a concept ever since pioneering studies in the late 1930s had shown that the conversion of inorganic carbon into biogenic substances entails sizeable redistributions of the stable carbon isotopes biologically mediated 13c 12c fractionations have come to be recognized as a common corollary of biochemical reactions meanwhile it is firmly established that the universal bias in favour of 12c characterizing biological materials primarily derives from a kinetic isotope effect that is imposed on the first carbon fixing enzymatic carboxylation reaction in the primary metabolism of co2 fixing autotrophic organisms this preference for 12c has turned out to be one of the most enduring relics of the ordered state of the biological precursor substances that may be preserved in fossil organics over billions of years with the currently known sedimentary record at hand it can be stated with confidence that biological carbon isotope fractionations have persisted throughout 3 8 ga of recorded earth history indicating that microbial prokaryotic and archaeoprokaryotic ecosystems had been prolific already on the archean earth while for the time span 3 5 ga the isotopic evidence is unequivocal the information encoded in the preceding record is commonly blurred by a metamorphic overprint this holds particularly for the metasediments of the 3 8 ga old isua supracrustal belt of west greenland which apart from widespread metasomatism have suffered amphibolite grade metamorphism it is known that 13c 12c exchange occurs in organic kerogenous rock constituents during both amphibolite and granulite facies metamorphism if a second carbon partner is available as either fluids or carbonate with isotopic re equilibration often only partially achieved due to the sluggish kinetics of the exchange reaction thermodynamic equilibria predict however that 13c 12c ratios in kerogen and graphite increase during this process hence high t exchange equilibria are always bound to drive 13c values in positive direction the lowermost values encountered being consequently the least exchanged and most pristine with the lowest values of reduced graphitic carbon obtained in early isua studies falling into the range 22 to 28 pdb we had straightforward evidence since the late 1970s that carbon constituents with the isotopic composition of biogenic matter were indeed present in the pre metamorphic isua suite it was therefore by no means surprising that the results of recent isotope work performed on apatite hosted carbonaceous microdomains in isua banded iron formation utilizing advanced techniques of instrumental microanalysis had prompted similar conclusions hence the mainstream of the sedimentary carbon isotope record can be best interpreted as the geochemical manifestation of the isotope discriminating properties of the principal co2 fixing reactions s in biological carbon assimilation suggesting an extreme degree of evolutionary conservatism in the biochemistry of autotrophic carbon fixation as a consequence biological modulation of the geochemical carbon cycle had been established at least 3 8 ga ago having been fully operative by the time of formation of the earth s oldest sediments

environmental control on diverse stromatolite morphologies in the 3000 myr pongola supergroup south africa a unique outcrop of partly silicified dolomite in the white umfolozi section of the pongola supergroup south africa indicates that stromatolites were diverse and adapted to a range of shallow tidal depositional settings 3000 myr ago composite columnar stromatolitic bioherms 0 7 1 6m high and 0 4 1 0m in diameter formed along the margins of a tidal channel they were flanked away from the channel by flat stratiform and small domical stromatolites growing in low energy tidal flat environments conical stromatolites 0 05 0 30m high and 0 03 0 10m in diameter accreted in high energy coarse grained carbonate sand along the bottom of the tidal channel the stromatolites probably formed through the activities of filamentous oxygen producing photoautotrophic cyanobacteria

microbial pathways and palaeoenvironmental conditions involved in the formation of phosphorite grains safaga district egypt abstract phosphatic grains of the shallow marine phosphorite deposits of egypt are classified as either phosphatic bioclasts preserving biological structure e g skeletal fragments such as fish bones and teeth or phosphatic peloids and intraclasts this study describes the destructive and constructive microbial pathways represented by bioerosion of bones by endolithic cyanobacteria and accretion of phosphatic peloids by bacteria the palaeoenvironmental conditions and post depositional diagenetic history of these grains have also been considered scanning and transmission electron microscopy showed that the phosphatic peloids under transmitted light microscopy are composed mainly of microspheres 0 5 to 2 5 m similar in shape and size to coccoid like bacteria chemical mapping showed that these microspheres are composed of carbonate fluorapatite cfa and surrounded by degraded carbonaceous matrix these grains are suggested to be reworked from pre existing microbial mats during transgressive regressive cycles affecting the southern tethyan campanian maastrichtian shallow continental shelf the bioerosion of phosphatic bones is characterized by a network of meandering microborings that penetrated inward from the bone surface by endolithic cyanobacteria the bioerosion of bones resulted in a gradual centripetal digestion and conversion of bones into micritic phosphate peloids the bioerosion mechanism is probably started in the acidic sheath surrounding cyanobacteria followed by supersaturation of po 4 and reprecipitation of crystalline cfa as electron dense remineralized rims electron microprobe microanalyses showed that the remineralized microbored areas are higher in cao p 2 o 5 and f and depleted in cl relative to unaltered bones a gradual demineralization of remineralized rims followed by dissolution of cyanobacterial cells is probably occurred during diagenesis and meteoric water alteration leaving behind empty microborings bone exposed to meteoric water alteration is lower in cao and p 2 o 5 and higher in f and cl than the unaltered bones understanding bone bioerosion has significant implications for palaeoenvironmental and taphonomic reconstruction archaeological applications and a regional correlation of the late cretaceous to palaeogene phosphogenic province extending from middle east to north africa

fossil preservation through phosphatization and silicification in the ediacaran doushantuo formation south china a comparative synthesis phosphatized and silicified microfossils preserved through replication of organic templates by authigenic calcium phosphate and silica respectively form through mechanistically similar mineralization processes but under notably different conditions in order to characterize the environments and taphonomic processes associated with these preservational pathways we compare phosphatized and silicified fossil assemblages in the ediacaran doushantuo formation south china in terms of stratigraphic and paleogeographic distribution preservation and biodiversity several differences are recognized 1 phosphatization and silicification both occurred in sub tidal doushantuo sediments but phosphatized fossils generally occur in shallower sub tidal facies than silicified fossils 2 although both phosphatized and silicified fossils are preserved three dimensionally the latter are typically more compressed and 3 whereas phosphatized assemblages are numerically dominated by multicellular acritarchs putative metazoan eggs and embryos silicified assemblages are dominated by prokaryotes these differences can be explained by environmental and taphonomic distinctions phosphatized fossils occur in intraclastic phosphorites and phosphatic carbonates and were likely fossilized near the suboxic anoxic boundary in sediments under oxic bottom waters with redox and biogeochemical gradients conducive to p remineralization phosphate burial via iron pumping and calcium phosphate precipitation reworking and winnowing of phosphatized fossils preferentially concentrated certain taxa prior to final burial in contrast silicified fossils typically occur in chert nodules which formed deeper in the sediment column in ferruginous pore waters and perhaps under ferruginous bottom waters where bacterial sulfate reduction and pyrite formation created low ph conditions conducive to calcite dissolution and silica precipitation once formed chert nodules mostly remained in situ but some were reworked with turbidites and olistostromes developed in slope facies despite these distinctions phosphatized and silicified fossil assemblages in the doushantuo formation generally overlap in time and space and representatives of all major groups and many common genera of doushantuo organisms are present in both phosphorites and cherts consequently although both preservational pathways have paleoenvironmental and taphonomic biases their relative biases on taxonomic presence absence data are minimal given sufficient sampling efforts and paleobiologic and biostratigraphic information based on presence absence but not abundance data from the doushantuo formation appears to be robust

color encoding multifrequency acoustic data for near bottom studies in this paper we describe color encoding methods for combining acoustic data in widely separate spectral bands into composite displays these new display methods better image the near bottom is interval in fine grained depositional environments in fine grained depositional environments the water bottom is typically not a discrete surface but is a transition zone spanning 1 3 m this near bottom interval is not completely imaged by either fathometers or subbottom profilers alone multiple acoustic frequencies spanning both the fathometer and subbottom bands are needed for applications in which the details of the near bottom are critical such applications include surveys of water reservoirs scour around bridge piers and predredging surveys in harbors to make effective use of the multifrequency data we combine three or more signal frequencies into composite false color displays by adapting multispectral photography methods used in optical remote sensing one approach is to encode amplitudes of traces r

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

stromatolites from the 3 300 3 500 myr swaziland supergroup barberton mountain land south africa a morphologically variable assemblage of stromatolites has been discovered in thin chert layers within the fig tree group of the swaziland supergroup south africa they are commonly low relief nearly stratiform laterally linked domes rarer forms include pseudocolumns and crinkly stratiform stromatolites the stromatolites grew on a substrate of altered komatiitic lava and sediments deposited on the lava surface and in most places are covered by later komatiitic flows abundant fine grained tourmaline included within the stromatolite laminae suggests that stromatolites formed in an environment dominated by boron rich hot spring emissions and evaporitic brines

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

archean microbial mat communities much of the archean record of microbial communities consists of fossil mats and stromatolites critical physical emergent properties governing the evolution of large scale centimeters to meters topographic relief on the mat landscape are a mat surface roughness relative to the laminar sublayer and b cohesion these properties can be estimated for fossil samples under many circumstances a preliminary analysis of archean mat cohesion suggests that mats growing in shallow marine environments from throughout this time had cohesions similar to those of modern shallow marine mats there may have been a significant increase in mat strength at the end of the archean

steep rock lake sedimentology and geochemistry of an archean carbonate platform abstract the 2800 ma mosher carbonate formation at steep rock lake in south central canada is one of earth s oldest limestone deposits it is both thick up to 500 m and relatively well preserved and was one of the first precambrian successions to be noted for evidence of early life it continues to provide information on the antiquity of such processes as photosynthesis the carbonate contains a variety of fabrics and facies from apparently fine grained bedded limestones with domal and columnar stromatolites atikokania radial fans and sheet cracks to closely packed metric scale hybrid domes of originally aragonite seafloor crust interlayered with fenestral fabric here we review previous work provide new observations concerning these sediments and their geochemistry and discuss the inception overall development and ultimate demise of the steep rock platform we divide the mosher carbonate into the lower hogarth member and upper elbow point member these units constitute a shallow water carbonate platform succession the hogarth member overlies eroded 3000 ma tonalite and is at least 120 m thick thin horizons of domal pseudocolumnar columnar and fenestral stratiform stromatolites and occasional layers of atikokania radial crystal fans occur within relatively fine grained thin bedded limestone with iron carbonate horizons in the upper part meter scale domes occur locally with sheet cracks and stromatactis the irregular laminae that build the small domal and columnar stromatolites are interpreted to be lithified mats and biofilms presumably cyanobacteria dominated fine grained well bedded facies of the lower hogarth member and its varied association of small stromatolites is interpreted to have accumulated in a relatively protected inner platform environment numerous very thin horizons of iron carbonate in the lower and upper parts of the hogarth member suggest temporally limited influence of iron rich offshore waters vertical trends in fe mn ba sr ce and 13 c probably reflect progressive restriction of circulation with at least one abrupt but short lived change back to more open seawater conditions the upper hogarth member with large banded domes and fenestral crusts and stromatolites is interpreted as back margin facies the overlying elbow point member is at least 70 m thick and appears to be entirely composed of innumerable juxtaposed elongate smooth and thickly layered domes lacking intervening sediment each dome is typically several meters across and composed of centimetric alternations of cuspate fenestral fabric possibly microbial and crystal fan fabric that is probably abiotic seafloor aragonite precipitate adjacent cuspate fenestral and crystal fan fabric show significant differences in concentration of 13 c sr ba fe and mn this giant dome facies is interpreted as a platform margin deposit in which alternating calcite aragonite mineralogies within each dome reflect a laterally fluctuating offshore redox boundary negative ce anomalies positive gd anomalies and reduced positive eu anomalies relative to laterally correlative deep water iron formation occur in the majority of crystal fan samples and in some cuspate fenestral fabric samples ca carbonate precipitation at the margin of an anoxic iron rich sea would have been promoted by oxygenic removal of iron from seawater otherwise fe carbonate would have been favored over ca carbonate precipitation the mosher carbonate formation is interpreted as an early marine oxygen oasis a shallow platform that favored cyanobacterial productivity was sufficiently isolated from open marine circulation for the seawater to become relatively oxygenated and where carbonate sediment aggradation was a positive feedback that sustained these shallow water conditions limestone accumulation terminated as transgressive suboxic and anoxic seawater deposited first manganese oxide rich and then manganese oxide poor iron formation sediments

sedimentary phosphate and associated fossil bacteria in a paleoproterozoic tidal flat in the 1 85 ga michigamme formation michigan usa abstract phosphorus is a nutrient fundamental to life and when it precipitates in modern environments bacteria are intimately involved in its release concentration and mineralization preserved fossil bacteria in phosphate crusts and grains from the ca 1850 million year old bijiki iron formation member of the michigamme formation michigan provide insight into the longevity and nature of this relationship the michigamme formation accumulated near the end of the earth s initial phosphogenic episode ca 2 2 and 1 8 ga to produce one of the first granular phosphorites phosphatic lithofacies consist of fine to medium sand sized francolite peloids concentrated on bedding surfaces in peritidal facies granular beds are up to 2 cm thick and peloids are often partially to completely replaced by dolomite and chert the grains contain organic matter and pyrite framboids that suggest bacterial breakdown of organic matter and bacterial sulfate reduction the peritidal nature of phosphorite in the michigamme formation is in sharp contrast to phanerozoic phosphogenic environments in deeper coastal upwelling settings peritidal settings were well suited for phosphogenesis under the very low oxygen and low dissolved sulfate levels of the paleoproterozoic as cyanobacteria produced oxygen in shallow water and evaporation led to increased sulfate concentrations such concomitant processes helped establish focused redox interfaces in the sediment that chemosynthetic bacterial communities sulfur oxidizers reducers forms that concentrate p and possibly iron oxidizers could exploit phosphate released from organic matter by heterotrophic bacteria and fe redox pumping was further concentrated by these chemotrophs a process that forms late neoproterozoic to phanerozoic phosphorites but on a much larger scale this early example of a granular phosphorite demonstrates that like their phanerozoic counterparts paleoproterozoic phosphorites are the concentrated indirectly biomineralized products of bacterial communities but unlike younger analogs which accumulated across subtidal shelves and shelf margins these ancient deposits formed only in tidal flat settings where phosphogenic redox processes could be established in the sediment from this early beginning the zone of phosphogenesis likely migrated into deeper water settings as oxygen and sulfate levels rose expanding the zone of chemosynthetic bacterial and associated phosphogenesis across the shelf

sulfidization of 3 48 billion year old stromatolites of the dresser formation pilbara craton constraints from in situ sulfur isotope analysis of pyrite abstract this study reports in situ sulfur isotope analyses 32s 33s 34s and 36s of pyrite in strongly sulfidized stromatolites from the 3 48 billion year old dresser formation pilbara craton australia these data shed light on sulfur reservoirs and sulfide precipitation processes and provide clues for the contribution of sulfur cycling microbes to sulfidization sulfur isotope signatures derived from mass dependent fractionation mdf monitored by 34s and mass independent fractionation mif here 33s and 36s of pyrite in stromatolites and of microscopic pyrite within associated barite allow for the identification of distinctive sulfur sources i magmatic hydrothermal sulfide h2s with 34s and 33s 0 ii magmatic hydrothermal sulfate so42 with a mdf signature mdf so42 34s 10 and 33s 0 iii photochemically derived sulfate with a mif signature mif so4 34s 6 and 33s 3 0 iv photochemically derived elemental sulfur s0 with 34s 0 and 33s 0 the sulfur isotope data suggest that sulfidization was largely driven by reduction of intermixed mdf so42 and mif so42 bulk signature of 34s 5 and 33s 1 4 and dilution of produced h2s 34s 12 and 33s 1 4 by native h2s in magmatic hydrothermal fluids the 34s shifts up to 17 generated by sulfate reduction are consistent with both thermochemical reactions and influence of sulfate cycling microbes the latter which may have facilitated rapid pyrite precipitation and preservation of microbial remains that are entombed within the petrogenetically earliest pyrite generation of stromatolites collectively our data are consistent with ancient stromatolite growth in proximity to shallow marine hydrothermal vents where hydrothermal fluids contributed to sulfidization that may have been further influenced by sulfur cycling microbes

taphonomy of very ancient microfossils from the 3400ma strelley pool formation and 1900ma gunflint formation new insights using a focused ion beam abstract focused ion beam fib milling permits the accurate extraction of ultrathin c 100 nm cross sectional lamellae from microfossils found in geological thin sections subsequent tem analysis of these lamellae can provide unique insights into the ultrastructure chemistry and taphonomy of precambrian microfossils at the micrometer to nanometer scale combining serial fib milling with sem imaging extends this capability to three dimensional 3d tomographic reconstruction and visualization of precambrian microfossils revealing information not available in light microscopy here we apply these techniques to two iconic silicified microfossil assemblages from the 3400 ma strelley pool formation of western australia and the 1900 ma gunflint formation of canada all the examined microfossils have carbonaceous walls surrounded by pure silica impregnation of microfossil walls by nano grains of silica is common together with variable degrees of wall displacement and replacement by silica all microfossils are rigidly preserved in 3d and show little or no folding or compression however there are also notable differences in taphonomic preservation our examples of the spheroidal gunflint microfossil huroniospora showed the highest fidelity of preservation with a continuous carbonaceous wall fossilized by spheroidal nano silica grains that resemble those found on bacterial surfaces in modern silicifying hot spring environments the nucleation of these silica nano spheres on the microfossil walls has induced an artificial saw tooth like ridged wall texture that may subsequently hinder species level identification the strelley pool microfossils in comparison show a lower fidelity of preservation with small parts of the microfossil walls completely replaced by silica plus extensive recrystallization of spheroidal silica nano grains to angular micro quartz our examples of the sheath like filamentous gunflint microfossil siphonophycus showed the lowest fidelity of preservation with many gaps in the carbonaceous walls and significant redistribution of carbon by recrystallizing silica grains a model is presented to explain these observations criteria for distinguishing highly probable microfossils from non cellular carbonaceous microstructures e g botryoids and grain coatings using fib based imaging are put forward for the first time here using examples drawn from the strelley pool formation and comparisons with younger gunflint material the combined in situ techniques of fib tem and fib sem nano tomography potentially provide a wealth of new nano scale information regarding the biogenicity antiquity and taphonomy of precambrian microfossils however the destructive nature of both techniques makes their application to unique palaeontological specimens problematical

carbon isotopic composition of individual precambrian microfossils ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the approximately 850 ma bitter springs formation australia and the approximately 2100 ma gunflint formation canada the delta 13c pdb values from individual microfossils of the bitter springs formation ranged from 21 3 1 7 to 31 9 1 2 and the delta 13c pdb values from microfossils of the gunflint formation ranged from 32 4 0 7 to 45 4 1 2 with the exception of two highly 13c depleted gunflint microfossils the results generally yield values consistent with carbon fixation via either the calvin cycle or the acetyl coa pathway however the isotopic results are not consistent with the degree of fractionation expected from either the 3 hydroxypropionate cycle or the reductive tricarboxylic acid cycle suggesting that the microfossils studied did not use either of these pathways for carbon fixation the morphologies of the microfossils suggest an affinity to the cyanobacteria and our carbon isotopic data are consistent with this assignment

nanosims insights to biogenicity and syngeneity of archaean carbonaceous structures nanosims is a relatively new technology that is being applied to ancient carbonaceous structures to gain insight into their biogenicity and syngeneity nanosims studies of well preserved organic microfossils from the neoproterozoic similar to 0 8ga bitter springs formation have established elemental distributions in undisputedly biogenic structures results demonstrate that sub micron scale maps of metabolically important elements carbon c nitrogen measured as cn ion and sulfur s can be correlated with kerogenous structures identified by optical microscopy spatial distributions of c cn and s in individual microfossils are nearly identical and variations in concentrations of these elements parallel one another in elemental maps c cn and s appear as globules aligned to form remnant walls or sheaths of fossiliferous structures the aligned character and parallel variation of c and cn are the strongest indicators of biogenicity

confocal laser scanning microscopy and raman imagery of ancient microscopic fossils abstract among all problems confronting the study of ancient permineralized petrified microscopic fossils two stand out the need for 1 accurate documentation of their three dimensional morphology and 2 direct analysis of their chemical composition and that of their surrounding mineral matrices to address these problems we demonstrate the use of two techniques that we have recently introduced to precambrian paleobiology confocal laser scanning microscopy and raman imagery these techniques both of which are non intrusive and non destructive can provide data by which to characterize in situ and at micron scale resolution the cellular and organismal morphology of thin section embedded organic walled fossils in addition raman imagery provides direct analyses of the molecular structural composition of the kerogenous components of such fossils and of their surrounding matrices and a means to assess quantitatively the geochemical maturity of the preserved organics use of these techniques for studies of ancient microscopic fossils can provide information in three dimensions at high spatial resolution about their morphology and cellular anatomy taphonomy and fidelity of preservation composition and mode of preservation and their biogenicity and syngenetic origin with the rocks in which they occur

blanket peat erosion and sediment yield in an upland reservoir catchment in the southern pennines uk this paper investigates temporal variations in fluxes of peat and other sediment in the catchment of march haigh reservoir west yorkshire long term estimates of sediment yield were derived from a study of reservoir sediments magnetic properties were used to correlate ten cores to a master profile dated using 210pb and 137cs a 14c date suggests that most of the organic component of the sediment is allochthonous and derived from peat eroded from the catchment organic sediment yields suggest low catchment erosion rates between 1838 and 1963 blanket peat erosion increased significantly after 1963 and peaked between 1976 and 1984 estimates of total sediment yield range between 2 and 28 t km 2 a 1 these yields are significantly lower than those from some previous studies examining reservoir sedimentation in other blanket peat covered catchments the low yield estimates may be due to relatively low rates of erosion in the basin but may also be partly explained by maintenance of silt traps during the early life of the reservoir and removal of sediment by scouring sedimentation within the reservoir is spatially variable and bathymetry and sediment source appear to be the dominant controls on sedimentation patterns within the reservoir

the use of chromium reduction in the analysis of organic carbon and inorganic sulfur isotope compositions in archean rocks one of the most serious issues with deciphering the evolution of organisms and their biogeochemical environments from the ancient rock record is the difficulty in obtaining well preserved samples although not much can be done to avoid diagenetic and metamorphic alteration when they have occurred alteration due to weathering can be avoided by working on drill core samples this implies however that the amount of sample is limited which may in turn restrain the number of possible chemical and isotopic analyses that can be performed in order to save sample we show here that the chemical protocol used for the sulfur sulfide extraction for later sulfur isotope analyses is also suitable to decarbonate samples for later organic carbon isotope analyses in the case of carbonated rocks both sulfur sulfide extraction and decarbonation require high amounts of sample so that coupling them may save a significant amount of sample and time in addition it allows both organic carbon toc and 13c and sulfur isotope composition measurements to be performed on the exact same powder which is essential when trying to understand couplings between s and c cycles in heterogeneous samples we thus tested the efficiency of the acidic chromium solution commonly used to extract sulfur from sulfide for sample decarbonation on various archean rocks our results show that no significant carbon isotope fractionation is caused by this new decarbonation protocol even for the samples with low organic carbon content the chromium solution seems to be perfectly adapted for the analysis of organic matter in the ancient rock record at least when the rock samples have experienced low greenschist facies metamorphism further tests will be needed to verify if this protocol can also be used for less mature organic matter

natural radioactivity and formation of oxygen in earth s atmosphere decay of radioactive 40k and radiolysis of ocean water abstract the important role of radioactivity in the conversion of primary hydro and atmosphere is substantiated considering the decay of 40 k isotope in seawater by now the total energy resulting from the decay of 40 k in the ocean amounts to 6 3 1026 j the calculations show that the concentration of oxygen formed over the last 3 8 ga is approximately 8 1017 kg i e it is of the same order of magnitude as the content of oxygen in the modern atmosphere the ocean was an intermediate reservoir in which oxygen was formed and which was purified from toxic components the radiation provides the threshold concentrations of oxygen urey pasteur and berkner marshall points important for the development of oxygen breathing life the radical and ionic products of water radiolysis induced chemical transformations of the compounds dissolved in the ocean the calculations show that their total concentration over a period of 3 8 ga was approximately 0 3 mol l 1 seawater radiolysis resulted in water purification saturation with oxygen and formation of simple organic molecules

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

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

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

early earth microbes and the rise of oxygen reconstructions of atmospheric chemistry and microbial life early in the earth s history have been contentious observations increasingly point to the evolution of complex and variable environments earlier in time

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

can nanosims probe quantitatively the geochemical composition of ancient organic walled microfossils a case study from the early neoproterozoic liulaobei formation abstract assessing the biogenicity of precambrian putative remnants of life requires solid criteria among possible criteria searching for evidence of pristine biological signatures and identifying various biological organic matter om precursors in close association with microfossil morphology are of interest nano scale secondary ion mass spectrometry nanosims can provide a quantitative geochemical proxy at the scale of the individual microfossil but its use has remained limited because of potential analytical biases related to matrix effects and microtopography that may result in inaccurate nanosims derived measurement no study so far has assessed whether these potential analytical biases were strong enough to preclude any identification of pristine om degradation products and of organic precursors in ancient sediments in this study we characterized the geochemical composition of organic walled microfossils from the early neoproterozoic liulaobei formation in north china using nanosims the 12ch 12c2 ionic ratio allows us to distinguish filament from spheroid acritarchs revealing the co occurrence of two distinct pristine om signatures that differ by their h and or aliphatic contents in addition nanosims data show that morphological degradation was tightly linked to a loss of h and or hydrogenated organic compounds in spheroid acritarchs in contrast in situ n c atomic ratios are homogeneous across all organic walled microfossils studied although highly coherent with proterozoic n c atomic ratios from the literature such homogeneity may alternatively reflect i a similar n content for different organic precursors or ii an extensive homogenization related to early degradation overall these data obtained on microfossils from the proterozoic liulaobei formation are the first to demonstrate that the quantitative capability of nanosims can be used to track ancient om precursors and to probe the effects of degradation on pristine om these findings open up tremendous perspectives and put forward new criteria for assessing the biogenicity of the putative early traces of life found in archean metasediments

simulating transport and deposition of clastic sediments in an elongate basin using the simsafadim clastic program the camarasa artificial lake case study ne spain abstract predicting facies distribution and the stratigraphic architecture of sedimentary basins by process oriented numerical models is nowadays an essential tool in geologic studies they constitute a new approach to predict the geologic heterogeneity and the spatial distribution of the diverse facies generated in a depositional system jointly with the distribution of the physical chemical and petrophysical characteristics of the sedimentary deposits in a quantitative way simsafadim clastic is a 3d process based forward numerical model for the simulation of clastic sediment transport and sedimentation in aquatic systems it simulates the physical process of clastic transport using the advective diffusive and dispersive terms of the transport equation and clastic sediment deposition as a result of a variety of processes the capabilities of simsafadim clastic have been confirmed through the application of the program to a large deep elongated artificial lake the camarasa reservoir in the noguera pallaresa river ne of spain simulation results yield sedimentation rates ranging from 0 04 to 0 09 cm yr 1 close to the dam and from 1 73 to 1 63 cm yr 1 in the upper reservoir section the sample experiment results match well with the observed transport pattern linked to the flow system in camarasa s reservoir near bottom water layer which transports more than 50 of the sediment that is supplied to the reservoir opening and closure of turbine gates and the basin geometry are the main controlling factors on the fluid flow and depositional pattern in the reservoir with a more diversified pattern obtained when an open boundary is defined however the resulting model also shows some limitations of the program as it does consider a stratified water column that is consistently observed in the reservoir refined modeling exercises of the type described in this paper are of potential application to predict and quantify sedimentation patterns allowing the implementation of efficient preservation measures against reservoir siltation

microbiological processes in banded iron formation deposition banded iron formations have been studied for decades particularly regarding their potential as archives of the precambrian environment in spite of this effort the mechanism of their deposition and specifically the role that microbes played in the precipitation of banded iron formation minerals remains unresolved evidence of an anoxic earth with only localized oxic areas until the great oxidation event ca 2 45 to 2 32 ga makes the investigation of o2 independent mechanisms for banded iron formation deposition relevant recent studies have explored the long standing proposition that archean banded iron formations may have been formed and diagenetically modified by anaerobic microbial metabolisms these efforts encompass a wide array of approaches including isotope ecophysiological and phylogeny studies molecular and mineral marker analysis and sedimentological reconstructions herein the current theories of microbial processes in banded iron formation mineral deposition with particular regard to the mechanisms of chemical sedimentation and post depositional alteration are described the main findings of recent years are summarized and compared here and suggestions are made regarding cross disciplinary information still required to constrain the role of the biosphere in banded iron formation deposition

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

sediment type distribution in reservoirs sediment source versus morphometry bottom sediments were collected from seven texas reservoirs to assess the spatial distribution of sediment types in reservoirs the sediment samples were analyzed for water content organic content and grain size distributions the reservoirs are characterized by distinct water content patterns referred to in this paper as types i ii and iii that reflect the lithologic units comprising their drainage area the water content organic content and percent mud decreases from type i shale marl through type ii limestone marl sandstone to type iii granite gneiss schist sandstone reservoirs reported elemental concentrations in the reservoir sediments are consistent with concentrations in the dominant rocks within their drainage area while water depth accounts for part of the spatial distribution sediment source explains the overall distribution of sediment types coarse grained source rocks multiple source rocks and multiple tributaries which input sediment at different points contribute to an inconsistent sediment type distribution depending on the sediment source sand and gravel size sediments are present in the deeper regions of some reservoirs this disrupts the classical morphometry water depth slope controlled sediment distribution pattern coarser sediments in shallower regions and finer sediments in deeper regions of natural lakes thus the location of tributaries and the type of sediments they carry are the dominant factors that control the sediment type distribution in reservoirs

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

nanotextures of aragonite in stromatolites from the quasi marine satonda crater lake indonesia stromatolites have been extensively used as indicators of ancient life on earth although much work has been done on modern stromatolites the extent to which biological processes control their structure and the respective contributions of biological and abiotic processes in their formation are however still poorly constrained a better description of the mineralogical textures of these formations at the submicrometre scale may help improve our understanding of how carbonates nucleate and grow in stromatolites here we used a combination of microscopy and microspectroscopy techniques to study the chemical composition and the texture of aragonite in lacustrine stromatolites from the alkaline crator lake in satonda indonesia several textural features are described including morphological variations of aragonite from nanosized grains to micrometre sized fibres the presence of striations in the aragonite laminae showing a striking similarity with growth bands in corals and clusters of small aragonite crystals sharing a common crystallographic orientation these nanotextural features are compared with those observed in scleractinian corals and possible processes involved in their formation are discussed the geological society of london 2010

precambrian microbe like pseudofossils a promising solution to the problem of various problems that have hindered progress in documenting the precambrian history of life the difficulty in distinguishing between bona fide microbial fossils and nonbiological microscopic pseudofossils has been among the most serious though errors in the interpretation of putative precambrian fossil microbes have diminished greatly over recent years mistakes continue to be made we suggest that such errors can be avoided by the use of a multifaceted strategy based on a specified series of biologically definitive characteristics that document the presence of interrelated biological morphology and biologically derived chemistry to illustrate this promising approach we use optical microscopy confocal laser scanning microscopy and raman spectroscopy together to distinguish between authentic microbial fossils and microscopic look alikes both coccoidal and filamentous rock embedded in five proterozoic and two archean geological units bona fide fossils of the 800 ma bitter springs formation of central australia and 3050 ma farrel quartzite of northwestern australia and objects we regard to be pseudofossils from the 770 ma chanda limestone of southern india 800 ma myrtle springs formation of south australia 1020 ma lakhanda formation of southeastern siberia 1700 ma vempalle formation of central india and 2629 ma marra mamba iron formation of northwestern australia the results demonstrate that no single criterion by itself is sufficient to establish the biological origin of such objects instead as shown here this problem appears solvable by the use of an interdisciplinary approach that combines the data and techniques of geology biology and chemistry

filamentous microfossils from the 3 500 myr old onverwacht group barberton mountain land south africa the swaziland supergroup barberton mountain land south africa has long been regarded as a promising location for the earth s oldest fossils because it includes some of the most ancient well preserved sedimentary rocks many of which contain carbonaceous matter although there have been numerous reports of microfossils from swaziland group rocks1 7 the biogenicity of most of the structures has been questioned8 10 although some of the organic spheroids are probably biogenic10 11 the best early archaean simple spheroids are generally regarded as possible microfossils 10 because organic spheroids may form abiotically in several ways12 the discovery of less simple biological morphologies is therefore important in establishing the existence of early life forms in the early archaean uniformly sized curving filaments especially tubular ones are difficult to explain as anything other than the fossil remains of filamentous organisms here we report the discovery of numerous filaments from two different stratigraphical positions in the 3 500 myr old onverwacht group of the swaziland supergroup their morphologies and abundance provide convincing evidence for the existence of bacteria or cyanobacteria like organisms on the earth during the early archaean this supports recent reports of similar filamentous microfossils from 3 500 myr old rocks from western australia13