columbia river hybrid modeling system a hybrid modeling method for predicting waterway sedimentation was developed and applied to the columbia river estuary the method uses physical hydraulic models two dimensional 2 d numerical models and analytical techniques in an integrated solution scheme the hybrid modeling system used to study the columbia consisted of a large physical model of the estuary rma 2v a depth integrated numerical model for sediment transport and a collection of analytical methods by using each method to address those phenomena that it is best able to describe an improved modeling technique is created

atmospheric oxygenation caused by a change in volcanic degassing pressure around two and a half billion years ago following the end of the archaean eon the atmosphere turned from anoxic to weakly oxic in what is known as the great oxidation event using a model of volcanic degassing gaillard et al demonstrate that a preceding period of continental crust formation may have been the trigger they propose that as continents emerged and volcanoes became increasingly subaerial rather than submarine magmatic volatiles were degassed at lower pressures leading to a progressive oxidation of the gases released this shift to a release of sulphur as sulphur dioxide rather than as hydrogen sulphide could then have fed marine sulphate reduction and the eventual oxygenation of earth s atmosphere the precambrian history of our planet is marked by two major events a pulse of continental crust formation at the end of the archaean eon and a weak oxygenation of the atmosphere the great oxidation event that followed at 2 45 billion years ago this oxygenation has been linked to the emergence of oxygenic cyanobacteria1 2 and to changes in the compositions of volcanic gases3 4 but not to the composition of erupting lavas geochemical constraints indicate that the oxidation state of basalts and their mantle sources has remained constant since 3 5 billion years ago5 6 here we propose that a decrease in the average pressure of volcanic degassing changed the oxidation state of sulphur in volcanic gases initiating the modern biogeochemical sulphur cycle and triggering atmospheric oxygenation using thermodynamic calculations simulating gas melt equilibria in erupting magmas we suggest that mostly submarine archaean volcanoes produced gases with so2 h2s 1 and low sulphur content emergence of the continents due to a global decrease in sea level and growth of the continental crust in the late archaean then led to widespread subaerial volcanism which in turn yielded gases much richer in sulphur and dominated by so2 dissolution of sulphur in sea water and the onset of sulphate reduction processes could then oxidize the atmosphere

variations in atmospheric sulphur chemistry on early earth linked to volcanic activity the nature of the atmospheric sulphur cycle on the early earth has been difficult to reconstruct an analysis of sulphur isotopes from 3 2 billion year old volcanic rocks suggests that episodic volcanism released pulses of sulphur dioxide that was then broken down by ultraviolet photodissociation

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

two coexisting sulfur metabolisms in a ca 3400 ma sandstone a sandstone from the ca 3400 ma strelley pool formation of western australia contains pristine micron sized pyrite intimately associated with organic material coating framework quartz grains a synsedimentary to early diagenetic origin for this pyrite is indicated by its occurrence in black bedded sandstone at the base of the formation and in reworked black clasts higher up in the formation high resolution multiple sulfur isotope analysis 32s 33s 34s using secondary ion mass spectrometry nanosims and large radius ion microprobe reveals 34svcdt vienna canyon diablo troilite values between 12 and 6 and 33s values between 1 65 and 1 43 from pyrite grains within a single thin section a large spread of 34s values over only 5 10 m together with the spatial association of pyrite with carbon and nitrogen indicates biological processing of sulfur the presence of both 33s and 33s signals overprinted by significant mass dependent 34s fractionation in this pyrite population indicates for the first time that both microbial sulfate reduction of aqueous sulfate 33s and microbial disproportionation of elemental sulfur 33s were co occurring in an open marine sedimentary hosted ecosystem in the paleoarchean

multiple sulfur isotopes and the evolution of earth s surface sulfur cycle abstract the distribution of sulfur isotopes in geological materials reveals information about earth history and biogeochemical processes research during the last several decades has used sulfur isotope geochemistry as a tool to better understand microbial processes harrison and thode 1958 kaplan 1975 monster et al 1979 peck 1959 peck 1962 rees 1973 and sediment diagenesis berner 1969 berner 1982 canfield et al 1993b earth historians also realized this potential as there exists a rich record of environmental change within the sedimentary records canfield and teske 1996 claypool et al 1980 goodwin et al 1976 habicht et al 2002 kah et al 2004 monster et al 1979 shen et al 2001 strauss 1993 thode and goodwin 1983 these applications have championed the use of the two most abundant sulfur isotopes 32s and 34s and provide a rich introduction to what the sulfur isotope record has to offer see canfield 2004 canfield and raiswell 1999 within the last decade this information has been supplemented by new data derived from the less abundant isotopes 33s and 36s the measurement of all four stable sulfur isotopes multiple sulfur isotope geochemistry has expanded our understanding of biological evolution and activity atmospheric chemistry and transport crustal recycling and many more fields related to earth surface processes see farquhar and wing 2003 here i present a review of recent works in multiple sulfur isotope geochemistry with a focus on results that inform our understanding of biogeochemical processes and earth surface evolution

cohesive sediment transport ii application typical engineering applications involving cohesive sediments in tidal water bodies including bays estuarial navigation channels small harbor basins piers and wharves have been cited reference has been made to problems in reservoirs and in the muddy coast environment techniques for prediction of estuarial sedimentation include field methods physical and numerical modeling and hybrid modeling which optimally combines physical and numerical modeling approaches in many cases simple zero dimensional modeling yields results of acceptable accuracy three dimensional numerical models have recently been developed for analyzing situations in which the complex structure of flows and associated sediment motion cannot be simplified further progress in improving the accuracy of prediction of sedimentation rates can be made by better understanding the basic laws governing cohesive sediment behavior and by developing new strategies and instrumentation for data collection

early archean hot springs above epithermal veins north pole western australia new insights from fluid inclusion microanalysis the world s most ancient biogenic structures are found in the north pole dome of western australia where 3 47 gyr old algal mats and stromatolites are closely associated with bedding conformable and discordant laminar quartz chalcedony and barite barite rich quartz hydrothermal veins with similar mineralogy occur throughout the stratigraphy below the conformable biogenic structures with the exception of the large volume of barite these bedding conformable and discordant laminar quartz veins exhibit textures and associated hydrothermal alteration quartz chalcedony chlorite illite calcite adularia pyrite typical of epithermal deposits formed from near neutral ph fluids we characterize the physical and chemical conditions of the ancient water responsible for depositing both the discordant and conformable quartz chalcedony barite as it passed through the upper parts of the archean crust field relationships combined with new fluid inclusion data suggest that the best documented stromatolites in the north pole dome occur adjacent to quartz chalcedony bands formed from cool 120 c low salinity 3 wt nacl equiv waters higher temperature up to 300 c more saline up to 10 wt nacl equiv and co2 h2s rich ch4 aqueous fluids occur in deeper level veins rare inclusions that are unusually rich in co2 containing liquid and gaseous co2 and liquid h2o support the existence of multiple batches of hydrothermal fluids with variable densities and gas contents oxygen isotope data 8 7 3 7 suggest that the causative fluids comprised admixtures of deeply circulated surface water with variable input of magmatic components our findings reveal that the earliest life known on earth lived in and around a hydrothermal system with temperatures from 300 c at depth to 120 c near the paleosurface in an environment closely analogous to modern hot springs developed above epithermal veins evidence exists for the introduction of different batches of hydrothermal fluids with variable densities and gas contents during the development of veins these findings support previous studies that demonstrate that the processes that form epithermal deposits have been active throughout geologic time and the present day distribution of epithermal deposits is dominantly a result of preservation not process

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

geological setting of earth s oldest fossils in the ca 3 5ga dresser formation pilbara craton western australia abstract detailed stratigraphic petrographic and zircon u pb geochronological data are provided for surface outcrops and newly obtained unweathered drillcore intersections of earth s oldest fossiliferous sedimentary rocks the lowermost chert barite unit of the ca 3 5 ga dresser formation warrawoona group pilbara craton results show that the 8 m thick unit at the drilling locality consists of thinly bedded originally micritic carbonates deposited under quiet water conditions that are interbedded with volcaniclastic conglomerates and coarse polymict conglomerates diamictites deposited during periods of tectonic instability the presence of rapid vertical and lateral facies changes tilted bedding in some members and internal erosional unconformities combined with analysis of fault offsets indicate that tectonically unstable periods were caused by growth faulting intense hydrothermal fluid flow accompanied episodes of growth faulting and resulted in pulsed repeated precipitation of silica barite sphalerite that alternated with precipitation of pyrite clasts of hydrothermal minerals in sandstone and coarse polymict conglomerate beds at several levels within the unit highlight the repeated nature of hydrothermal fluid circulation during sediment accumulation hydrothermal fluid circulation caused widespread acid sulfate alteration of the footwall extensive replacement of the newly deposited carbonate sediments by hydrothermal precipitates and crystallization of hydrothermal chert barite pyrite in veins perpendicular to bedding in the footwall and parallel to bedding in the sedimentary unit the combined evidence points to deposition of the chert barite unit within an active volcanic caldera a 10 cm thick bed of felsic volcaniclastic tuff within finely bedded carbonates near the top of the unit has yielded a maximum age of deposition of 3481 0 3 6 ma 2 uncertainty confirming earlier pb pb age data for the antiquity of these rocks putative signs of life are present as stratiform columnar domical and coniform stromatolitic laminates at various levels throughout the unit petrographic observations show that red and black weathering stromatolitic laminates on the surface consist of pyrite in unweathered drillcore material observation of local relics of carbonate between pyrite crystals in these laminates indicates a carbonate protolith prior to replacement by hydrothermal pyrite which provides support for a biological origin of stromatolitic laminates further support is provided by clasts of laminated carbonaceous material in thinly bedded primary micritic carbonates textural analysis of jaspilitic cherts near the top of the unit reveal haematite as tiny crystals within recrystallized siderite dolomite rhombs in carbonate beds affected by hydrothermal silica alteration the presence of unaltered diagenetic pyrite crystals in the haematite altered siderite indicates that alteration did not result from oxidizing fluids rather haematite alteration is interpreted as the result of an increase in ph during diagenetic alteration by mildly reducing silica rich fluids associated with eruption of overlying basalts possibly with the influence of microbial activity this has important implications for the origin of jaspilitic cherts throughout the early archean record and for atmospheric conditions of early earth

uncovering framboidal pyrite biogenicity using nano scale cnorg mapping framboidal pyrite has been used as a paleo redox proxy and a biomarker in ancient sediments but the interpretation of pyrite framboids can be controversial especially where later overgrowths have obscured primary textures here we show how nano scale chemical mapping of organic carbon and nitrogen cn org can detect relict framboids within precambrian pyrite grains and determine their formation mechanism pyrite grains associated with an ediacaran fossil lagerstatte from newfoundland ca 560 ma hold significance for our understanding of taphonomy and redox history of the earliest macrofossil assemblages they show distinct chemical zoning with respect to cn org relict framboids are revealed as spheroidal zones within larger pyrite grains whereby pure pyrite microcrystals are enclosed by a mesh like matrix of pyrite possessing elevated cn org replicating observations from framboids growing within modern biofilms subsequent pyrite overgrowths also incorporated cn org from biofilms with concentric cn org zoning showing that the availability of cn org progressively decreased during later pyrite growth multiple framboids are commonly cemented together by these overgrowths to form larger grains with relict framboids only detectable in cn org maps in situ sulfur isotope data 34 s 24 to 15 show that the source of sulfur for the pyrite was also biologically mediated most likely via a sulfate reducing microbial metabolism within the biofilms relict framboids have significantly smaller diameters than the pyrite grains that enclose them suggesting that the use of framboid diameters to infer water column paleo redox conditions should be approached with caution this work shows that pyrite framboids have formed within organic biofilms for at least 560 m y and provides a novel methodology that could readily be extended to search for such biomarkers in older rocks and potentially on other planets

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

quadruple sulfur isotope analysis of ca 3 5 ga dresser formation new evidence for microbial sulfate reduction in the early archean abstract multiple sulfur isotope system is a powerful new tracer for atmospheric volcanic and biological influences on sulfur cycles in the anoxic early earth here we report high precision quadruple sulfur isotope analyses 32s 33s 34s 36s of barite pyrite in barite and sulfides in related hydrothermal and igneous rocks occurring in the ca 3 5 ga dresser formation western australia our results indicate that observed isotopic variations are mainly controlled by mixing of mass dependently md and non mass dependently fractionated non md sulfur reservoirs based on the quadruple sulfur isotope systematics 34s 33s 36s for these minerals four end member sulfur reservoirs have been recognized 1 non md sulfate 34s 5 2 33s 3 1 2 md sulfate 34s 10 3 3 non md sulfur 34s 6 33s 4 and 4 igneous md sulfur 34s 33s 0 the first and third components show a clear non md signatures thus probably represent sulfate and sulfur aerosol inputs the md sulfate component 2 is enriched in 34s 10 3 and may have originated from microbial and or abiotic disproportionation of volcanic s or so2 our results reconfirm that the dresser barites contain small amounts of pyrite depleted in 34s by 15 22 relative to the host barite these barite pyrite pairs exhibit a mass dependent relationship of 33s 34s with slope less than 0 512 which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation 0 515 the barite pyrite pairs also show up to 1 difference in 36s values and steep 36s 33s slopes which deviate from the main archean array 36s 33s 0 9 and are comparable to isotope effects exhibited by sulfate reducing microbes 36s 33s 5 to 11 these new lines of evidence support the existence of sulfate reducers at ca 3 5 ga whereas microbial sulfur disproportionation may have been more limited than recently suggested

evidence from fluid inclusions for microbial methanogenesis in the early archaean era methanogenic microbes may be one of the most primitive organisms although it is uncertain when methanogens first appeared on earth during the archaean era before 2 5 gyr ago methanogens may have been important in regulating climate because they could have provided sufficient amounts of the greenhouse gas methane to mitigate a severely frozen condition that could have resulted from lower solar luminosity during these times nevertheless no direct geological evidence has hitherto been available in support of the existence of methanogens in the archaean period although circumstantial evidence is available in the form of approximately 2 8 gyr old carbon isotope depleted kerogen here we report crushing extraction and carbon isotope analysis of methane bearing fluid inclusions in approximately 3 5 gyr old hydrothermal precipitates from pilbara craton australia our results indicate that the extracted fluids contain microbial methane with carbon isotopic compositions of less than 56 per thousand included within original precipitates this provides the oldest evidence of methanogen 3 46 gyr ago pre dating previous geochemical evidence by about 700 million years

evaluating the role of microbial sulfate reduction in the early archean using quadruple isotope systematics abstract microscopic pyrites with low 34 s 32 s ratios in 3 47 gyr old sedimentary barites from north pole australia have been interpreted as evidence for microbial sulfate reduction and or sulfur disproportionation in the early archean we show that these microscopic sulfides have similar to slightly less negative 33 s and slightly more negative 36 s values compared to the enclosing sulfate crystals this finding is consistent with a primary mass independent signature overprinted by biological sulfate reduction as calibrated by previous experimental laboratory culture studies however it is inconsistent with an overprint by abiological sulfate reduction or sulfur disproportionation as predicted by isotope exchange theory and laboratory culture studies thus our multiple sulfur isotope measurements support the contention that sulfate reducing microbes had evolved by 3 47 billion years ago

the meaning of stromatolites stromatolites document microbial interactions with sediments and flowing water throughout recorded earth history and have the potential to illuminate the long term history of life and environments modern stromatolites however provide analogs to only a small subset of the structures preserved in archean and proterozoic carbonates thus interpretations of secular trends in the shapes and textures of ancient columnar stromatolites require nonuniformitarian scale dependent models of microbial responses to nutrient availability seawater chemistry influx of sediment grains shear and burial models that integrate stromatolite scales macroscopic organization and shapes could also help test the biogenicity of the oldest stromatolites and other structures whose petrographic fabrics do not preserve direct evidence of microbial activity an improved understanding of stromatolite morphogenesis in the presence of oxygenic and anoxygenic microbial mats may illuminate the diversity of microbial metabolisms tha

geochemistry and petrogenesis of the basal aravalli volcanics near nathdwara rajasthan india the early proterozoic aravalli supergroup of rajasthan near nathdwara includes a thick basal unit of mafic volcanics with intercalated quartzites the volcanics have been metamorphosed from greenschist to amphibolite facies which together with intense deformation obliterated original mineralogy and textures based on geochemical criteria we infer that the volcanics consist predominantly of tholeiitic rocks with minor amounts of komatiitic rocks which are referred to here as picritic because of the absence of textural criteria modelling of both major and trace element data suggests that the picritic magmas were generated by different extents of adiabatic melting of mantle sources over a range of p t conditions at pressures as high as 50 kbar their sources were enriched in light ree elements the tholeiite series could not be related to the picrites either by fractional crystallization processes or by considering that the former represent lower extents of melting of sources similar to those for the latter under any physical conditions the tholeiites require shallow lithospheric sources with enrichment in light ree and fe me ratios which are significantly higher than those of a pyrolite addition of melts from deeper levels to the shallow source regions of the tholeite is considered a possible mechanism for the generation of tholeiitic magmas source characteristics and physical conditions of magma generation indicate that the basal aravalli volcanism could be related to deep mantle plumes

two dimensional horizontal modeling of fine sediment transport at the south channel north passage of the partially mixed changjiang river estuary china tidal flow and fine sediment transport at the south channel north passage of the partially mixed changjiang river estuary were studied using a two dimensional horizontal 2dh numerical model this 2dh model was achieved by depth integrating the momentum and convection diffusion equations the alternating direction implicit scheme was used to solve the governing equations the iterative method was adopted for the calculation of convection and diffusion terms of momentum equation comparisons between calculated and measured results tidal elevations and depth averaged velocities have shown reasonable agreement horizontal distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal variations in fine sediment transport processes

extending the upper temperature limit for life the upper temperature limit for life is a key parameter for delimiting when and where life might have evolved on a hot early earth the depth to which life exists in the earth s subsurface and the potential for life in hot extraterrestrial environments a combination of geological and

archean ocean floor metamorphism in the north pole area pilbara craton western australia abstract archean greenstones ca 3 49 3 46 ga in the north pole dome pilbara craton western australia have undergone prograde metamorphism from prehnite pumpellyite facies to greenschist amphibolite facies observations of 3000 thin sections shows that a metamorphic aureole was restricted to within a few kilometers of the contact with the 3459 ma north pole monzogranite three types of alteration were observed carbonate silicic and chlorite types the distribution of the three types of alteration suggests that secondary chemical migration of elements occurred in the whole area but that some samples were unaffected by this alteration the southern north pole area is outside of the contact metamorphic aureole and is composed of five units from north unit i to south unit v dipping south about 30 70 metamorphism of the north pole greenstones corresponds to the low pressure type which is broadly comparable to that inferred for ocean floor metamorphism prehnite pumpellyite pp transitional tr and greenschist gs facies prograde metamorphic zones occur from structural top to bottom within each of units metamorphic grade increases downward through the units and metamorphic isograds never cut unit boundaries