evidence for cavity dwelling microbial life in 3 22 ga tidal deposits cavities are considered plausible and favorable habitats for life on early earth in such microenvironments organisms may have found an adequate protection against the intense ultraviolet radiation that characterized the archean ozone free atmosphere however while there is clear evidence that benthic life existed in the paleoarchean the oldest traces of cavity dwelling microbes coelobionts have been found in neoarchean rocks here we present the results of a detailed investigation of early silicified cavities occurring in the oldest well preserved siliciclastic tidal deposits the 3 22 ga moodies group of the barberton greenstone belt south africa downward growing microstromatolitic columns composed of kerogenous laminae are commonly present in planar bedding parallel now silica filled cavities that formed in sediments of the peritidal zone in situ 13cpdb pdb peedee belemnite measurements of the kerogen range from 32 3 to 21 3 and are consistent with a biogenic origin scanning electron microscopy analysis of the silicified cavities shows well preserved chains of cell sized molds that are interpreted as fossil filamentous microorganisms the geological context the morphology of the microstromatolites the 13c composition of the kerogen and the presence of microfossils all suggest that a microbial community inhabited the cavities these results extend the geological record of coelobionts by 500 m y supporting the view that cavities were among the first ecological niches to have been occupied by early microorganisms

diversity of iron and silica precipitation by microbial mats in hydrothermal waters iceland implications for precambrian iron formations direct examination of microbial mats from icelandic hot springs with transmission electron microscopy and energy dispersive x ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters silica richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and insomecases intracellularlywhenpresumablythecell s hadlysed commonly these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and or replaced their cytoplasmic material however in other cells the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions atonelocality thebacteriaformedseveralepicellular iron minerals ranging from iron mineralized capsules tofine grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite the complete encrustation of bacterial cells by silica iron or a combination of both may greatly enhance their preservation potential such that these mineralized microorganisms may conceivably represent future microfossils thus we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past particularly with regard to the origin of some precambrian banded iron formations

paleoenvironmental implications of the guano phosphatic cementation on dongdao island in the south china sea abstract the phosphatic cement in the bioclastic sediment sequence on the northeastern shore of dongdao island in the south china sea was studied and its paleoenvironmental implications discussed petrological characteristics and major trace ree element data unequivocally supported the notion that phosphatization was closely associated with avian guano decomposition and leaching whereas carbon and oxygen isotope results further revealed that meteoric water were involved in these processes ams 14 c dates on the brown phosphate cements indicate that they were formed around 5700 5000 5100 and 2900 yr bp respectively the multi episodes of phosphatization very likely correspond to intermittent seabird occupation on this island possibly reflecting holocene sea level oscillation and or long term climate changes in the south china sea that have controlled seabird habitat the phosphate cementation which occurs widely in tropical islands may be another useful monitor for sea level and or paleoclimate changes

life associated with a 2 76 ga ephemeral pond evidence from mount roe 2 paleosol dark sericitic material at and near the top of the 2 765 0 01 ga mount roe 2 paleosol in western australia contains 0 05 0 10 wt organic carbon with delta 13c values between 33 and 51 pdb peedee belemnite such negative isotopic values strongly indicate that methanotrophs once inhabited this material the textures and the chemical composition of the dark sericitic material indicate that the methanotrophs lived in or at the edges of ephemeral ponds that these ponds became desiccated and that heavy rains transported the material to its present sites the discovery of methanotrophs associated with the mount roe 2 paleosol may extend their geologic record on land by at least 1 5 b y methanotrophy in this setting is consistent with the notion that atmospheric methane levels were or 20 mu atm during the late archean the radiative forcing due to such high atmospheric methane levels could have compensated for the faint younger sun and helped to prevent massive glaciation during the late archean

isotopic dating of the migration of a low grade metamorphic front during orogenesis the southern margin of the pilbara craton in northwestern australia underwent regional heating folding and thrusting as well as extensive fluid flow during collision in the paleoproterozoic however the precise timing of this event is uncertain previous geochronologic studies of archean basement rocks have yielded a wide range of younger radiometric dates from ca 2 4 ga to ca 2 0 ga interpreted to record multiple hydrothermal alteration events in situ u pb geochronology of authigenic monazite and xenotime in very low grade archean metasedimentary rocks from across the craton suggests that the pilbara was affected by at least two cryptic thermotectonic events the first between ca 2430 ma and ca 2400 ma and the second between ca 2215 ma and ca 2145 ma the older event is restricted to three localities in the west and its cause is unknown the younger event affected most of the craton 100 000 km 2 spanning a 70 m y period from ca 2215 ma nearest the collisional margin in the south to ca 2145 ma toward the craton interior in the north the widespread geographic and stratigraphic distribution of ca 2 2 ga phosphates suggests that fluid flow was pervasive this event was probably driven by the northward advancing ophthalmian fold and thrust belt that developed during protracted collision the associated low grade metamorphic front migrated over 350 km at an average rate of 5 0 mm yr placing important constraints on the rate and duration of deformation and metamorphism in orogenic settings

paleoecology of seabirds at nandao xisha islands south china sea sub fossil evidence for ashmole s halo during the little ice age abstract tropical seabirds play a key role in coral island ecosystems but there are still many uncertainties regarding their paleoecology seabird paleoecology was investigated on nandao island xisha islands south china sea from sub fossil remains spanning the past 800 years ornithogenic sediments were collected beneath seabird inhabited shrubs where a large number of seabird fish sub fossils were recovered we used reflectance spectroscopy to show that seabird population size was overall higher during the little ice age lia compared to periods before and after this event nonetheless the number of seabirds also fluctuated during the lia seabird populations on nandao reached their highest points at 1480 1550 and 1650 1800 ce respectively but the population remained low from 1550 to 1650 ce a large migration of seabirds from nandao island to the adjacent beidao island where the population size surged at that time is hypothesized to explain the corresponding decrease in the seabirds at nandao stable isotope 15n and 13c analyses also suggest a change in foraging behavior by seabirds at nandao during the period 1550 1650 ce seabirds at low population size foraged near the island and preyed upon smaller flying fish as inferred from low 15n and high 13c values in fish scales but fed upon larger flying fish farther from the island during times of high population this shift in foraging behavior is in accordance with predictions for ashmole s halo in that islands with high densities of birds will cause a depletion of resources near the colonies and force more distant foraging away from the colony

eco environmental implications of elemental and carbon isotope distributions in ornithogenic sediments from the ross sea region antarctica abstract seabirds have substantial influence on geochemical circulation of elements serving as a link for substance exchange between their foraging area and colonies in this study we investigated the elemental and carbon isotopic composition of five penguin affected sediment profiles excavated from ross island and beaufort island in the ross sea region antarctica among the three main constituents of the sediments including weathered bedrock guano and algae guano was the main source of organic matter and nutrients causing selective enrichment of several elements in each of the sediment profiles in the 22 measured elements as cd cu p s se and zn were identified as penguin bio elements in the ross sea region through statistical analysis and comparison with local end member environmental media such as weathered bedrock fresh guano and fresh algae carbon isotopic composition in the ornithogenic sediments showed a mixing feature of guano and algae using a two member isotope mixing equation we were able to reconstruct the historical change of guano input and algal bio mass compared with research in other parts of antarctic arctic and south china sea we found apparent overlap of avian bio elements including as cd cu p se and zn information on the composition and behavior of bio elements in seabird guano on a global scale and the role that bio vectors play in the geochemical circulation between land and sea will facilitate future research on avian ecology and paleoclimatic reconstruction

preliminary geochemical evidence of groundwater contamination in coral islands of xi sha south china sea geochemical data on dissolved major minor and trace constituents in groundwater samples from xi sha coral islands paratas islands reveal the main processes responsible for their geochemical evolution multivariate statistical analysis indicates four sources of solutes 1 seawater intrusion due to limited groundwater recharge 2 leaching of heavy metals from imported granite soil 3 leaching of toxic elements such as as due to guano soil erosion and historical phosphatic guano mining and 4 local and regional contamination characterized by high loadings of cu ag and hg although process 1 dominates the geochemical characteristics of the groundwater process 4 indicates the significant role of anthropogenic impact by local e g cu and regional e g hg sources such contamination in groundwater will potentially impose adverse effects on the fragile ecosystem of the coral islands it is necessary to monitor microorganisms associated with human feces in the nearshore water column as well as nutrient levels in coastal waters in order to further assess the impact of human activities on the ecosystem of these islands

evidence for microbial life in synsedimentary cavities from 2 75 ga terrestrial environments fluviolacustrine sediments of the 2 75 ga hardey formation fortescue group australia preserve pendant columnar structures with stromatolitic lamination within synsedimentary cavities the millimeter sized finger like columns strongly resemble microbialites from modern basaltic caves and indicate the likely presence of microbial biofilms the ancient microbial columns are preserved by chert and locally occur as reworked clasts indicating a near depositional age for the structures sulfur isotopic analysis of pyrite in the columns and adjacent carbonaceous matrix yields 34scdt cdt canyon diablo troilite values between 8 5 and 19 showing significant fractionation characteristic of biological cycling of sulfur organic matter in cavity ceilings and shale matrix has 13cpdb pdb peedee belemnite values between 55 and 43 suggesting the presence of methanotrophs our results suggest that 2 75 ga terrestrial environments supported a microbial ecosystem including microbes that inhabited synsedimentary hollows extending the fossil record of coelobionts by 1 5 b y subsurface cavities represent a new habitable microenvironment for early life on earth and an analogue for ancient life on mars

evidence for pervasive petroleum generation and migration in 3 2 and 2 63 ga shales petroleum generation largely occurs through the thermal decomposition of organic matter the presence of oil bearing fluid inclusions and pyrobitumen in archean rocks suggests that similar processes operated as early as ca 3 25 ga however direct evidence of petroleum generation from potential source rocks is lacking and an abiogenic origin has been proposed for some archean carbonaceous residues pilbara craton ca 3 2 ga and ca 2 63 ga black shales were found to contain abundant kerogenous streaks and laminae as well as bitumen nodules comprising a radioactive mineral core surrounded by a carbonaceous rim and pyrobitumen formerly petroleum globules films and aggregates the bitumen nodules formed around detrital radioactive grains via polymerization of fluid hydrocarbons generated within the shale and represent diagnostic indicators of oil generation in ancient shales the bitumen globules films and masses are preserved within authigenic pyrite and demonstrate that a separate hydrocarbon phase had developed in the shale matrix during burial providing compelling evidence for in situ petroleum generation and expulsion the abundance of bitumen nodules and residual pyrobitumen in black shales across the pilbara craton suggests that hydrocarbon generation from kerogenous shales was a common phenomenon during the middle to late archean the petroleum was generated from organic matter that accumulated in marine environments most probably comprising the remains of photosynthetic and chemosynthetic organisms pointing to a sizeable biomass as early as 3 2 ga

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

archean oil evidence for extensive hydrocarbon generation and migration 2 5 3 5 ga archean sedimentary rocks from the pilbara craton australia contain evidence for petroleum generation and migration in the form of bitumen nodules produced by radiogenic immobilization of fluid hydrocarbons around detrital uraninite thorite and monazite grains the nodules are preserved in sandstones at several stratigraphic levels in the fortescue group 2 75 ga and lalla rookh formation 3 0 ga both nonmarine successions and in deltaic sediments of the mosquito creek formation 3 25 ga the most ancient evidence comes from the warrawoona group 3 46 ga where hydrocarbon droplets were apparently formed in situ from kerogenous sediments by flash maturation during early hydrothermal silicification bituminous relics of petroleum are also commonly preserved in shallow marine sandstones of the black reef formation 2 59 ga and the witwatersrand supergroup 2 85 ga from the kaapvaal craton south africa along with subeconomic methane accumulations in all cases the petroleum was apparently sourced from archean shales generated during the archean and migrated before the late archean or early early proterozoic metamorphism occluded fluid pathways given this widespread and abundant evidence for hydrocarbon generation and migration in archean depositional basins it seems that primordial bacterial biomass producing labile type i kerogen was often buried in sufficient quantities to successfully generate and expel petroleum depositional basins on ancient cratons clearly contained permeable rocks amenable to the migration and probably to the accumulation of petroleum thus the main factors precluding the discovery of economically exploitable hydrocarbon accumulations in archean basins are the subsequent destructive effects of deformation and metamorphism which causes trap breaching imperfect sealing or thermal obliteration however there are ancient stable cratons where such disruption may not have occurred and so petroleum explorers may wish to reassess the possibility of finding valuable hydrocarbon resources in archean rocks

the mineral springs of the scrajo spa sorrento peninsula italy a case of natural seawater intrusion this paper deals with the mineral springs feeding the scrajo spa in the sorrento peninsula southeast of naples approximately 6 km from castellammare di stabia another spa location the scrajo mineral water is sulphureous salt bromine iodic and co2 rich the two hydromineral areas fall within the groundwater basin of mt faito formed chiefly by limestones due to the high permeability of the limestones there is considerable rainwater infiltration which recharges a basal fresh groundwater resting on denser seawater this groundwater body feeds the mineral springs of the scrajo spa the springs of castellammare di stabia and some submarine springs all the data gathered for the scrajo springs led to propose the following mineralisation scheme 1 the basal fresh groundwater of mt faito on underlying seawater receives endogenous contributions of co2 and h2s which cause a natural seawater intrusion within the fresh groundwater 2 the upwelling of gases would appear to occur via the major faults which bound sorrento peninsula to the nw 3 during the year the chemistry of the springs changes according to different degrees of seawater intrusion the minimum occurs in june and the maximum in november the close interaction between the sea and the scrajo s mineral waters but also those of castellammare di stabia highlights their particular vulnerability not only to over extraction of groundwater but also to climate change finally a hypothesis is presented to explain the connection between the mineral waters rich in co2 and h2s and the concentration of karst phenomena observed in the scrajo area

ubiquitous occurrence of basaltic derived paleosols in the late archean fortescue group western australia abstract the 2 76 ga old mount roe basalt paleosols mr 1 and mr 2 recognized near the base of the 2 76 2 69 ga fortescue group in western australia represent some of the oldest definite examples of archean paleoweathering profiles the loss of fe and the absence of pedogenic carbonates in these reference paleosols have been considered as strong evidence for low oxygen and moderate carbon dioxide in the late archean atmosphere respectively however the robustness of such interpretations suffers both from the scarcity of paleosol exposures and the superposition of post weathering alteration over primary soil profiles here we report new exposures of the mr 1 paleosol as well as a number of new basalt derived paleosol occurrences distributed in the mount roe basalt and the 2 73 ga old kylena formations of the fortescue group we show that all these paleosols including mr 1 and mr 2 were strongly affected by post weathering reductive alteration nevertheless we discovered early lithologic units locally preserved within the hydrothermally altered paleosols which feature distinct chemical and mineralogic compositions these include i 13c depleted carbonaceous rich diaspore pyrophyllite boudins likely inherited from the hydrolysis and bauxitization of the parent basalt and ii green hard core material mostly composed of fe sericite associated with authigenic sphene and containing early relics of sulfate bearing iron rich smectite or berthierine we argue that smectite relics may constitute a part of the primary pedogenic mineral assemblage while berthierine and sphene formed during diagenesis through the circulation of reductive fluids because the depletion of iron observed in the fortescue paleosols is not solely due to pedogenesis but also to post weathering alteration particular care has to be taken when bulk chemical profiles of iron in such paleosols are used as atmospheric paleobarometer recognition of the regional scale syn depositional alteration of the fortescue subaerial basalts over the north pilbara suggests the onset of intense continental weathering associated with the uplift and emergence of the pilbara craton during continental break up and rifting such a regional onset of continental weathering may have provided large amounts of nutrients to nearby marine and or lacustrine systems favoring the development of microbial life in shallow waters

microbial fixation of methane carbon at 2 7 ga was an anaerobic mechanism possible 1 in earth s history the most extreme episode of 13c depletion in sedimentary organic matter occurred about 2 7 billion years ago this isotopic excursion is widely interpreted as resulting from increased burial of organic carbon derived from microbial fixation of 13c depleted methane modern microbial physiologies involve either oxygen or sulfate as electron acceptors in such processes until now the isotopic signal has been exclusively assigned to growth of aerobic methanotrophic bacteria and consequently interpreted as an indication for the presence of molecular oxygen in late archaean surface environments the alternative anaerobic pathway involving sulfate as the electron acceptor was dismissed because this process has been considered inefficient in producing biomass sufficient to account for significant fractions of 13c depleted carbon in some archaean rocks calculations based on recent findings at two modern sites now show however that anaerobic processes could account for the archaean signal

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

the antiquity of oxygenic photosynthesis evidence from stromatolites in sulphate deficient archaean lakes the tumbiana formation about 2700 million years old was largely deposited in ephemeral saline lakes as judged by the unusual evaporite paragenesis of carbonate and halite with no sulfate stromatolites of diverse morphology occur in the lacustrine sediments some with palimpsest fabrics after erect filaments these stromatolites were probably accreted by phototropic microbes that from their habitat in shallow isolated basins with negligible sulfate concentrations almost certainly metabolized by ozygenic photosynthesis

negligible microbial matground influence on pre vegetation river functioning evidence from the ediacaran lower cambrian series rouge france supported by shell international exploration and production b v under research framework agreement pt38181

stromatolitic fabric of authigenic carbonate crusts result of anaerobic methane oxidation at cold seeps in 4 850 m water depth methane seepage leads to mg calcite and aragonite precipitation at a depth of 4 850 m on the aleutian accretionary margin stromatolitic and oncoid growth structures imply encrustation of microorganisms microbial mats in the host sediment with a unique growth direction downward into the sediment forming crust shaped lithologies biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol which contain extremely low 13c values this indicates the presence of methane consuming archaea and 13c values of 42 to 51 pdb indicate that methane is the carbon source for the carbonate crusts thus it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate reducing bacteria and that carbonate precipitation proceeds downward into the sediment where ascending cold fluids provide a methane source strontium and oxygen isotope analyses as well as 14c ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3 000 years ago

origin of recent insular phosphate rock on a coral cay raine island northern great barrier reef australia abstract raine island is a small vegetated coral cay that is capped by recent insular phosphate rock on the northeastern shore phosphate rock also extends into the intertidal zone where it is juxtaposed against calcareous beachrock a petrological and isotopic study was carried out on the phosphate rock in order to clarify some of the uncertainties concerning the genesis of insular phosphate rocks in general and on raine island in particular the main phosphate mineral is dahllite carbonate hydroxyapatite which occurs as microlaminated grain coatings and as a bioclast replacement minor pore filling whitlockite tricalcium phosphate was recorded in one sample organic carbon is intimately associated with phosphate cement and accounts for color variations between microlaminae phosphate 18op smow values range from 14 4 to 16 6o oo indicating that phosphatic porewaters were entirely fresh and had not undergone evaporative 18o enrichment phosphate cement records the passage of both downward percolating near surface porewater and seaward moving groundwater at or close to the freshwater saltwater interface intertidal phosphatic rock on the northeastern shore is a rare example of a lithified intertidal tropical beach sand deposit with a definite fresh water origin

biofilm architecture of phanerozoic cryptic carbonate marine veneers thin 150 m micritic veneers lining crypts in paleozoic and mesozoic reef microbial and bioclastic carbonates have the dimensions and architecture of modern uncalcified bacterial biofilm morphologic attributes include rounded aggregate nanofabric internal channels external towers mushrooms and plumes all can be interpreted as characteristics of attached bacterial communities i e aggregates as microcolonies originally embedded in a matrix of extracellular polymeric substances channels as water conduits and or uncolonized nutrient poor spaces external protuberances as localized growths and plumes as surface streamers cryptic habitat favored pristine biofilm preservation by precluding disturbance and overgrowth and suggests aphotic and anoxic conditions these examples provide diagnostic morphologic criteria for wider recognition of biofilm in phanerozoic and older carbonates

geochemical evidence for the development of coral island ecosystem in the xisha archipelago of south china sea from four ornithogenic sediment profiles abstract geochemical characteristics of four ornithogenic sediment profiles gq gj3 jq and jy2 from ganquan gq guangjin gj3 jinqing jq and jinyin jy2 coral islands in the south china sea were analyzed we noted clear differences in the distribution of organic matter om and elements above and below the respective critical depths of 11 cm gq 16 cm gj3 9 cm jq and 12 cm jy2 in the four profiles revealing an apparent change in sediment source materials for all the sediment profiles there were statistically significant positive correlations between toc and p in the sediments below these critical depths indicating that the composition of organic matter was predominantly derived from guano however these positive correlations were significantly weakened above the critical depths probably due to the increased contribution of plant humus to the organic matter our results suggest that the source materials of ornithogenic sediments have changed gradually from a two component coral sand guano mixture to a three component coral sand guano and humus mixture likely indicating the slow development of vegetation following seabird occupation cu cd zn p as se and ba whose controlling factors are guano input were identified as a group of avian bio elements in the xisha archipelago the distributions of other mineral elements such as fe al ti mn and k were mainly controlled by organic matter based on this integrated analysis of the geochemical characteristics of inorganic elements we inferred that the compositional materials coral sands guano and plant residues were the key factors controlling the geochemical behavior of elements in the ornithogenic sediment profiles on the coral islands of the south china sea seabird activities and vegetation development have significantly changed the original sediment structure and have exerted a positive impact on terrestrial production and soil development on the islands

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

earliest life on earth evidence from the barberton greenstone belt south africa abstract studies investigating the structure and diversity of earth s record of life older than 3 2 ga are restricted to two locations worldwide in which sedimentary rocks have escaped regional high grade metamorphism and penetrative deformation the pilbara craton of western australia and the barberton greenstone belt in the kaapvaal craton of south africa this paper provides a south african perspective on the evidence of paleoarchean life a record that is often overlooked in the literature it aims to summarize and critically review previously reported claims of early life in the bgb gives an overview of the latest findings and provides an outlook on potential future discoveries the 15 km thick volcanic sedimentary succession making up the barberton supergroup was deposited between 3 55 to ca 3 20 ga and can be subdivided in three stratigraphic units that provide a unique window into a diverse and widespread paleoarchean microbial ecosystem landscape putative biosignatures occur almost throughout the entire bgb stratigraphy and range from carbonaceous cherts containing filamentous spheroidal and lenticular microstructures traces of hydrothermal biofilms photosynthetic microbial mats remnants of pseudocolumnar stromatolites and large organic walled spheroidal microfossils of currently unknown affinity the bgb also contains one of the world s oldest known record of tufted microbial mats which extensively colonized tidally influenced siliciclastic shorelines and were most likely formed by filamentous photosynthesizers other mat associated biosignatures include silicified gas bubbles domes and lenses that likely formed due to metabolic activity or the decay of buried organic matter some of these subsurface voids beneath the cohesive mats were inhabited by the earliest known forms of cavity dwelling microbial communities that were probably dominated by chemotrophic or photosynthetic microbes recently discovered terrestrial microbial mats once thriving in a fluvial dominated setting represent the oldest macroscopically visible fossil traces of life on land which is also supported by the occurrence of nearby paleosols that carry signals of biogenic sulfur fractionation the wealth of preserved microbial biosignatures from marine fluvial hydrothermal and possibly planktonic settings combined with the high spatial and temporal resolution of the barberton greenstone belt deposits is truly exceptional consequently the bgb deserves an equal level of attention and protection for future generations like its australian counterpart

geochronology of a late archaean flood basalt province in the pilbara craton australia constraints on basin evolution volcanic and sedimentary accumulation and continental drift rates abstract eleven high precision 2 5 million years shrimp zircon u pb ages have been obtained from felsic rocks within a single stratigraphic section of late archaean volcanic and sedimentary rocks in the east pilbara of western australia the stratigraphic succession nullagine and mount jope supersequences in sequence stratigraphic terminology fortescue group in lithostratigraphic terminology is interpreted to be the rock record of three major geotectonic cycles that formed in an extensional rift related environment between about 2772 and 2715 ma the geochronology is constrained by a detailed stratigraphic framework based on unconformities and supported by a preliminary magnetostratigraphy field mapping geochemical and petrographic studies have shown that previously unrecognised thin felsic tuff bands are interbedded in subaerial flood basalt piles and mafic tuffs while flood basalts and proximal felsic volcanic rocks comprise by volume most of the volcanogenic components of the succession felsic volcanism is now known to have been active periodically through each geotectonic cycle the succession covers a time period of about 57 million years the lower 1400 m of a thick 1700 m clastic sedimentary succession from the oldest geotectonic cycle was deposited at a rate of about 100 m per million years over a mean time period of 14 million years in contrast a younger 150 m thick cogenetic tuff basalt unit accumulated in less than 3 million years and others probably accumulated at similar rates comparable to those of phanerozoic flood basalts unconformities in the succession are shown to be of variable duration and one unconformity marking the boundary between the first and second geotectonic cycles may represent a time gap of more than 10 million years the unconformity based stratigraphic framework the new geochronology and palaeomagnetic studies j geophys res 108 2003 b12 2551 emp 2 1 to 2 21 have been combined to determine a possible late archaean continental drift rate for one part of the succession implying a period of motion as fast as or up to five times faster than any known from the phanerozoic

paleosecular variation of brunhes age lava flows from british columbia canada 1 brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern british columbia silverthrone garibaldi lake mt meager clearwater wells gray park and kelowna area a total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site previous radiometric studies indicate that the ages of these lava flows range from 2 3 to 760 ka stepwise thermal demagnetization 14 to 21 steps was carried out for all the samples in each site and af demagnetization was performed on one sample per site forty five sites were selected based on rigorous criteria 95 5 to calculate a mean direction d 356 9 i 70 2 95 2 8 that is statistically indistinguishable from the direction of the dipole field at the area i 68 3 virtual geomagnetic poles vgps do not show the far sided effect and the angular standard deviation is 17 5 a value in agreement with the paleomagnetic field dispersion for that latitude these high quality results are expected to improve the time averaged field taf and secular variation models

late archaean crustal extension sedimentary basin formation flood basalt volcanism and continental rifting the nullagine and mount jope supersequences western australia abstract the mount bruce megasequence set formerly the mount bruce supergroup is a succession of volcanic and sedimentary rocks that was deposited on the pilbara craton of western australia in the late archaean to early proterozoic its history can be described and explained in terms of modern style sequence stratigraphy and of phanerozoic style plate tectonics the megasequence set comprises the chichester range megasequence that was deposited on a rifted to divergent continental margin and the overlying hamersley range megasequence that was deposited on a convergent continental margin the chichester range megasequence comprises in order of superposition the nullagine and mount jope supersequences and the marra mamba supersequence package the nullagine and mount jope supersequences are each the rock record of one phase of a protracted two phase late archaean 2770 2700 ma continental break up the nullagine supersequence consists of the mount roe sequence which comprises mostly subaerial basalt and the overlying hardey sequence package which comprises mostly terrigenous sedimentary rocks that were deposited in extensional sedimentary basins the mount jope supersequence consists of in order of superposition the kylena sequence which comprises mostly basalt the tumbiana sequence which comprises mostly tuff and tuffaceous rocks and the maddina sequence package which comprises mostly basalt the nullagine supersequence was deposited during an episode of wnw ese directed crustal extension that possibly led to the development of a rift to the west of the present pilbara craton the mount jope supersequence was deposited during the subsequent development of a wnw ese trending rift the position of which approximates the present southern craton margin regional scale uplift was associated with the development of both supersequences particularly with the nullagine supersequence basement strike slip faults were reactivated as dip slip structures during crustal extension and controlled the locations of some hardey sequence package extensional sedimentary basins nullagine supersequence and mount jope supersequence rifting led to a divergent continental margin bordering an ocean along the south and probably the far west of the craton post rift thermal subsidence was accompanied by the accumulation of mudrock carbonate sedimentary rock and iron formation of the marra mamba supersequence package in a shelf setting the implications of these interpretations are that at 2800 ma the pilbara craton was significantly larger than at present and that it had a sufficiently thick subcontinental lithosphere that divided it in a manner analogous to the break up of phanerozoic continents the nullagine and mount jope supersequences contain three stacked flood basalt successions which were erupted over a time period of between of 55 and 80 m y stacked flood basalt successions covering such a long time period are not known in the phanerozoic and are tangible evidence of a hotter late archaean mantle

morphological characterization of coral reefs by combining lidar and mbes data a case study from yuanzhi island south china sea the correlation between seafloor morphological features and biological complexity has been identified in numerous recent studies this research focused on the potential for accurate characterization of coral reefs based on high resolution bathymetry from multiple sources a standard deviation std based method for quantitatively characterizing terrain complexity was developed that includes robust estimation to correct for irregular bathymetry and a calibration for the depth dependent variablity of measurement noise airborne lidar and shipborne sonar bathymetry measurements from yuanzhi island south china sea were merged to generate seamless high resolution coverage of coral bathymetry from the shoreline to deep water the new algorithm was applied to the yuanzhi island surveys to generate maps of quantitive terrain complexity which were then compared to in situ video observations of coral abundance the terrain complexity parameter is significantly correlated with seafloor coral abundance demonstrating the potential for accurately and efficiently mapping coral abundance through seafloor surveys including combinations of surveys using different sensors

geomicrobiology of carbonate silicate microbialites from hawaiian basaltic sea caves abstract modern microbial mats and microbialites are described from basaltic sea caves on the island of kauai hi the mats grow on the ceilings and walls in the photic zone of several open caves where fresh water seeps out of the rock scanning sem and transmission electron microscopy tem showed that the active mats are dominated by filamentous and nonfilamentous cyanobacteria in the surface layers and heterotrophic bacteria in deeper layers energy dispersive x ray analysis revealed that copious amounts of extracellular polymeric substances eps are rich in mg si o and ca likely concentrated from solution petrographic microscopy and electron microprobe analysis of the mineralized microbialites showed textures reminiscent of stromatolitic laminations consisting mainly of alternating calcium carbonate calcite and aragonite and magnesium rich silicate kerolite thin coatings rich in magnesite hydromagnesite and monohydrocalcite surround the microbialites on the rock surfaces and are likely inorganic in origin within the mats minerals tend to form and concentrate within or around dense matrices of eps microenvironments with geochemical conditions favorable for mineral crystallization likely develop in the mats as a result of the mucilaginous extracellular material and the development of bacterial microcolonies in addition copious amounts of extracellular polymers bind ions from solution and provide nucleation sites for mineral crystallization and growth this combination of biological and inorganic processes can explain the occurrence of the secondary minerals in these caves as well as the stromatolitic textures of the microbialites

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes

benthic perspective on earth s oldest evidence for oxygenic photosynthesis the great oxidation event goe is currently viewed as a protracted process during which atmospheric oxygen increased above 10 5 times the present atmospheric level pal this threshold represents an estimated upper limit for sulfur isotope mass independent fractionation s mif an archean signature of atmospheric anoxia that begins to disappear from the rock record at 2 45 ga however an increasing number of papers have suggested that the timing for oxidative continental weathering and by conventional thinking the onset of atmospheric oxygenation was hundreds of million years earlier than previously thought despite the presence of s mif we suggest that this apparent discrepancy can be resolved by the earliest oxidative weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere such as biological soil crusts and freshwater microbial mats covering riverbed lacustrine and estuarine sediments we calculate that oxygenic photosynthesis in these millimeter thick ecosystems provides sufficient oxidizing equivalents to mobilize sulfate and redox sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant s mif signature as continental freeboard increased significantly between 3 0 and 2 5 ga the chemical and isotopic signatures of benthic oxidative weathering would have become more globally significant from a mass balance perspective these observations help reconcile evidence for pre goe oxidative weathering with the history of atmospheric chemistry and support the plausible antiquity of a terrestrial biosphere populated by cyanobacteria well before the goe

microbially influenced formation of 2 724 million year old stromatolites nanoscale evidence suggests that the tumbiana formation stromatolites in australia were influenced by microbial activity in the stromatolites clusters of organic globules are closely associated with 2 724 million year old aragonite crystals