dolomite compositions as a guide to epigenetic copper mineralization mount isa inlier nw queensland dolomites associated with copper mineralization have higher fe contents and lower mn fe ratios than their unmineralized equivalents over a wide stratigraphic interval and range of original depositional environments copper associated dolomite in the proterozoic mount isa inlier of nw queensland has mn fe 0 11 vein dolomite has a higher fe content than its corresponding matrix nevertheless the mn fe ratio of the matrix is a good guide to the maximum mn fe ratio for a dolomitic vein thus the simple determination of the fe and mn component in the dolomite of a rock gives information about the possible association with copper mineralization even when the rock itself is completely barren

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

contributions of the siberian shelf polynyas to the arctic ocean intermediate and deep water the role of the open water regions or polynyas in the winter ice pack over the siberian continental shelves in the production of arctic ocean intermediate and deep water is examined through use of a combination of passive microwave satellite data coastal weather station data and oceanographic data the satellite data allow us to derive a time series of the open water areas of selected polynyas for the 1978 1982 winters the polynyas which occur north of svalbard around franz josef land along the west coast and north end of novaya zemlya and to the east of severnaya zemlya and the taymyr peninsula are the primary oceanographic contributors the open water time series for these polynyas are used in combination with coastal weather station data to estimate the heat loss from each polynya for the region north of svalbard which is historically known as whalers bay the study shows that the heat loss is sufficient to provide the observed cooling of the west spitsbergen current for the other polynyas the heat loss is used to compute the ice production rates and the oceanic salt flux we then use the historic oceanographic salinities with the salt fluxes to estimate the contribution of each polynya to the arctic ocean water masses if we assume that the salt contributes only to the arctic intermediate water our results show that the shelves are capable of producing about 20 60 of this water alternatively if the salt contributes only to the deep water of the eurasian basin then without consideration of the mixing of the bottom water with the greenland and norwegian sea water the contribution from the shelves yields a renewal time of about 100 years our results imply that there is insufficient water produced in the shelf polynyas to perform all of the roles that have been historically assigned to it

characteristics of colored dissolved organic matter cdom in the arctic outflow in the fram strait assessing the changes and fate of terrigenous cdom in the arctic ocean absorption coefficients of colored dissolved organic matter cdom were measured together with salinity delta o 18 and inorganic nutrients across the fram strait a pronounced cdom absorption maximum between 30 and 120 m depth was associated with river and sea ice brine enriched water characteristic of the arctic mixed layer and upper halocline waters in the east greenland current egc the lowest cdom concentrations were found in the atlantic inflow we show that the salinity cdom relationship is not suitable for evaluating conservative mixing of cdom the strong correlation between meteoric water and cdom is indicative of the riverine terrigenous origin of cdom in the egc based on cdom absorption in polar water and comparison with an arctic river discharge weighted mean we estimate that a 49 59 integrated loss of cdom absorption across 250 600 nm has occurred a preferential removal of absorption at longer wavelengths reflects the loss of high molecular weight material in contrast cdom fluxes through the fram strait using september velocity fields from a high resolution ocean sea ice model indicate that the net southward transport of terrigenous cdom through the fram strait equals up to 50 of the total riverine cdom input this suggests that the fram strait export is a major sink of cdom these contrasting results indicate that we have to constrain the c dom budgets for the arctic ocean much better and examine uncertainties related to using tracers to assess conservative mixing in polar waters citation granskog m a c a stedmon p a dodd r m w amon a k pavlov l de steur and e hansen 2012 characteristics of colored dissolved organic matter cdom in the arctic outflow in the fram strait assessing the changes and fate of terrigenous cdom in the arctic ocean j geophys res 117 c12021 doi 10 1029 2012jc008075

the uranium mineralization potential of the paleoproterozoic sioux basin and its relationship to other basins in the southern lake superior region abstract the paleoproterozoic sioux basin and the baraboo barron flambeau mccaslin and waterloo quartzites in northcentral usa are all supermature quartz arenites that are among the world s oldest redbeds these quartzites were deposited on a stable craton at ca 1750 ma following exhumation and uplift of penokean crust and major orogenic activity related to the amalgamation of archean microcontinents at ca 2 0 1 8 ga to form laurentia 40ar 39ar ages of 1615 1543 ma from diagenetic muscovite in the sioux basin provide the first geochronological evidence for mazatzal related deformation and low grade metamorphism of the quartzites during subsequent convergence on the southern margin of laurentia one muscovite sample from the sioux basin has a 40ar 39ar age of 1465 ma that likely corresponds with fluid and thermal resetting due to felsic magmatism in the region and is similar to 40ar 39ar ages for muscovite from the baraboo and waterloo quartzites thus the sioux basin and other quartzites in the region have experienced a similar tectonic and fluid history the sioux basin has similar sedimentologic characteristics as other paleoproterozoic basins in north america including the uranium rich athabasca basin canada that is host to some of the world s largest and highest grade unconformity type uranium deposits we compared key characteristics such as the stratigraphy character of diagenetic fluids paleoaquifer characteristics and composition of leachable pb in the sandstones from the sioux basin with the athabasca basin in order to evaluate the fluid history of the basin and the potential of the sioux basin to host unconformity type uranium mineralization based on the hydrogen and oxygen isotopic composition of muscovite m1 that formed during diagenesis at 150 200 c the pore fluids that were present during peak diagenesis in the sioux basin had 18o and d values of 0 5 to 5 2 and 32 to 46 respectively similar to those of the fluids associated with uranium mineralization and alteration in the athabasca basin however fluid flow in the sioux basin was likely restricted to relatively thin and discontinous proximal fluvial facies that could have been diagenetic paleoaquifers in contrast to the extensive paleoaquifers in the athabasca basin that promoted large scale diagenetic reactions and alteration that led to the formation of unconformity type uranium mineralization in addition the non radiogenic isotopic composition of leachable pb in the sioux basin sandstones indicates that the majority of the pb is from a normal crustal source inconsistent with mobilization of radiogenic pb from a uranium rich source such as a uranium deposit although the sioux basin shares similar general characteristics to the athabasca basin the results of this study suggest that it has a lower potential than the athabasca basin to host significant high grade unconformity type deposits

correlation of river water and local sea ice melting on the laptev sea shelf siberian arctic hydrographic and stable isotope 18o data from 4 summer surveys in the laptev sea are used to derive fractions of sea ice meltwater and river water sea ice meltwater fractions are found to be correlated to river water fractions while initial heat of river discharge is too small to melt the observed 0 158 km3 of sea ice meltwater arctic rivers contain suspended particles spm and colored dissolved organic material cdom that preferentially absorb solar radiation accordingly heat content in surface waters is correlated to river water fractions but in years when river water is largely absent within the surface layer absolute heat content values increase to considerably higher values with extended exposure time to solar radiation and sensible heat nevertheless no net sea ice melting is observed on the shelf in years when river water is largely absent within the surface layer the total freshwater volume of the central eastern laptev sea 72 76 n 122 140 e varies between 1000 1500 km3 34 92 reference salinity it is dominated by varying river water volumes 1300 1800 km3 reduced by an about constant freshwater deficit 350 400 km3 related to sea ice formation net sea ice melt 109 158 km3 is only present in years with high river water budgets intermediate to bottom layer 25 salinities contain 60 and 30 of the river budget in years with low and high river budgets respectively the average mean residence time of shelf waters was 2 3 years during 2007 2009

lead isotope studies bearing on the genesis of copper orebodies at mount isa queensland significant differences between the lead zinc silver and copper ore bodies unlike the lead zinc silver deposits the copper orebodies appear epigenetic two texturally distinct generations of iron sulfides later relative to the lead zinc mineralization origin of the main copper ore bodies from the basement metamorphic and granitic complexes direct relationship between the regional metamorphism generation of hypersaline fluids and metal extraction modified journal abstract

the freshwater budget and under ice spreading of mackenzie river water in the canadian beaufort sea based on salinity and 18o 16o measurements in water and ice observations of salinity and oxygen isotope composition 18o were made for the beaufort shelf mackenzie estuary waters in september 1990 just prior to ice formation and for both the water column and ice in april may 1991 at the end of winter these measurements are used to determine the apportioning of fresh water in the estuary between its two main sources runoff and sea ice melt changes in disposition of water between seasons and amounts frozen into the growing ice sheet are also derived two domains are considered in order to construct a freshwater budget for the mackenzie shelf the nearshore within which landfast ice grows in winter and the outer shelf most of the winter inflow from the mackenzie river appears to remain impounded as liquid under the ice within the landfast zone at the end of winter and about 15 of it is incorporated into the landfast ice oxygen isotopes 18o in ice cores collected from across the shelf record the progress beneath the ice of new mackenzie inflow as it invades the nearshore throughout winter rates of spreading are about 0 2 cm s 1 away from the coast and 1 3 cm s 1 along the coast as this inflow spreads across the shelf it progressively shuts off convection driven by brine production at locations within the landfast ice salinity and 18o in the offshore water column suggest that about 3 m of sea ice was formed in the outer shelf domain since both brine and newly formed sea ice can be advected off the shelf a complete budget for brine or sea ice production cannot be established without first measuring the advection of one of these two components

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

a stable isotope study of magnesites from the rum jungle uranium field australia implications for the origin of strata bound massive magnesites the contrast between the scanty magnesite deposition in modern sedimentary environments and the large strata bound magnesites of the past constitutes a magnesite problem which unlike the dolomite problem has so far attracted little attention from the geologists magnesite beds up to 700 m thick from the lower proterozoic rocks of the rum jungle uranium field northern territory of australia offer attractive circumstances for studying the isotope systematics of coarse crystalline magnesite and coexisting dolomite magnesites yield 18o and 13c compositions of 11 2 to 14 6 smow and 1 0 to 5 8 pdb respectively dolomites yield 18o and 13c values of 11 7 to 21 9 and 4 0 to 2 9 respectively and show an 18o enrichment gradient away from the magnesite fluid inclusion homogenization temperatures used in conjunction with the isotope determinations and an approximate magnesite water equation indicate that magnesites were formed in the temperature range of 100 200 c from fluids that became progressively enriched in 18o the results support an epigenetic metasomatic replacement model of dolomite by magnesite under the influence of invasive hot mg rich basinal fluids strata bound massive magnesites which abound particularly in archean proterozoic rock sequences generally preserve the sedimentary structures but do not retain primary isotopic compositions and are therefore unsatisfactory indicators of oceanic isotope evolution and ocean paleotemperatures

proterozoic copper deposits in nw queensland australia sulfur isotopic data sulfur isotopic disequilibrium is commonly observed between associated pyrite and copper sulfides in nw queensland a sulfur isotopic study of copper mineralization in dolomites at paradise valley and arenites at mammoth has allowed the significance of such disequilibrium to be evaluated copper mineralization at paradise valley is characterized by a greater enrichment in 34s with 34s values often greater than 30 for both copper sulfides and associated syngenetic diagneetic pyrite at mammoth copper sulfides have isotopic compositions 34s 15 9 to 0 3 transitional between disseminated syngenetic diagenetic pyrite 34s 5 7 to 1 7 and epigenetic vein pyrite 34s 17 9 to 7 1 suggesting progressive reaction and replacement of syngenetic diagenetic pyrite by a copper bearing mineralizing fluid under oxidizing conditions the isotopic data within the constraints imposed by geological and geochemical factors support a model of reaction between copper bearing mineralizing fluids and pre existing syngenetic diagenetic pyrite for both the carbonate and arenite hosted deposits

genesis of copper mineralisation myall creek prospect south australia the myall creek copper prospect is in unmetamorphosed carbonaceous dolosiltstone and sandstone at the base of the late proterozoic adelaidean tapley hill formation it contains disseminated fine grained chalcopyrite zincian tennanite bornite chalcocite pyrite sphalerite and galena and irregular to straight chalcopyrite rich veinlets some ore minerals rim and or partially replace pyrite or clastic grains there is no evidence of hydrothermal activity the 34scdt values of pyrite and the other sulfides fall in the wide range 3 6 to 44 2 dolomite in both mineralised and unmineralised samples has 13cpdb values concentrated around 3 and 18osmow values around 25 it is concluded that the mineralising fluids were near neutral brines which leached metals from the basement and early adelaidean rocks they entered the tapley hill sediments at moderately low temperatures via permeable strata and faults the metals were precipitated by biogenic h2s and also fixed by reaction with iron sulfides and possibly organic matter continuing ascent of brines into the mineralised strata caused breakdown of detrital feldspars and fe ti oxides and some solution remobilisation of early formed sulfides

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

2000 ma sulphide concretions from the productive formation of the pechenga greenstone belt nw russia genetic history based on morphological and isotopic evidence abstract two hundred and fifty nine sulphide samples from black shales of the productive formation belonging to the palaeoproterozoic 2000 ma petsamo supergroup in the kola region nw russia have been analysed for their sulphur isotope ratio the sulphide bearing black shales were formed in a non euxinic basin within an oceanic rift environment the rocks have undergone greenschist facies metamorphism the black shales are marked by very high s corg ratios and a strong positive correlation between corg and s r 0 70 with zero intercept on the sulphur axis different generations of sulphide concretions have been distinguished by means of concretional analysis individual isotope study of synsedimentary sulphide layers and sulphides from early middle and late diagenetic catagenetic sulphide concretions yields trends which suggest bacterial sulphate reduction as the concretion forming process the overall spread of 34 s from 8 3 to 24 9 indicates 34 s sulphate sulphide between 29 and 4 given a seawater sulphate at around 21 the first order trend is a progressive enrichment in 34 s with increase of burial two major populations of sulphides have been distinguished the first concretions and perhaps thin layers formed in an open system with respect to seawater sulphate and has a limited 34 s range of 2 7 to 3 8 this is coupled with extensive formation of diagenetic carbonate beds marked by 13 c of 8 7 to 12 5 the second population lenses thin layers concretions and microconcretions in carbonate nodules formed in a closed system and is characterized by a high fe2 s2 ratio and progressive development of a rayleigh distillation process which drove 34 s from 8 3 up to 24 9 the high fe2 s2 and possibly change in ph parameter resulted in pyrrhotite rather than in pyrite associated abundant carbonate nodules have 13 c in the range 8 2 to 14 1 overall low 34 s sulphate sulphide and the high s corg ratio are consistent with one stage bacterial sulphate reduction in a non euxinic basin the observed 34 s sulphate sulphide of 29 as maximum is within the pure sulphate reducing bacteria range of 4 46 advanced isotopic modification involving the oxidative part of the sulphur cycle has not been detected based on the data available one can not exclude the presence of a third population of sulphides thin massive layers with 34 s from 2 5 to 0 3 which might have inorganic origin and formed from an exhalative source

criteria for the retention of original seawater 87sr86sr in ancient shelf limestones abstract a suite of 40 pennsylvanian and permian shelf limestones from kansas and oklahoma has been analyzed for major and trace elements and for c o and sr isotopes the chemistry and c and o isotope ratios were compared to the difference between the measured 87 sr 86 sr and original seawater ratio concentrations of mn sr and fe varied most systematically with the change in the seawater sr ratio all samples containing 700 ppm mn yielded altered ratios fe and sr contents were also found to have a less well defined correlation with the retention of the original sr ratio all limestones with 900 ppm sr and 20 of 22 samples with a sr mn 2 0 yielded correct ratios the geochemical guidelines were applied to the chemical and isotopic results from 76 shelf limestones mostly of pennsylvanian age from texas and oklahoma more than 92 of the samples that contain sr mn 2 0 yielded correct seawater ratios every sample with sr mn 2 0 retained the original seawater ratio

primary and diagenetic controls of isotopic compositions of iron formation carbonates mineralogic chemical and isotopic compositions have been determined for 97 carbonate microbands in five core segments from the early proterozoic 2 5 ga dales gorge member of the brockman iron formation hamersley basin western australia samples were obtained both from banded iron formation bif macrobands 9 12 at paraburdoo on the southern margin of the basin and from bif macroband 13 at wittenoom 130 km nw at paraburdoo oxygen isotopic compositions of coexisting chert and magnetite microbands were measured and indicated final equilibration temperatures ranging from 60 160 degrees c this range is consistent with observed mineral assemblages and indicates a considerable temperature gradient across the basin cf t approximately 300 degrees c at wittenoom becker and clayton 1976 carbon isotopic compositions of carbonates are near 7 vs pdb at paraburdoo and 10 5 at wittenoom but the greater isotopic depletion at wittenoom appears related to primary or diagenetic processes not metamorphism contents of organic carbon are consistently low isotopic depletion is roughly correlated with iron abundance and together with petrographic observations and chemical balances is consistent with the model of bif deposition introduced by beukes et al 1990 primary siderite delta approximately 5 precipitated from an anoxic water column depleted in 13c additional depletion of 13c is associated with coprecipitation of iron oxides and organic carbon oxygen isotopic abundances of microbanded carbonates are similar to those under and overlying massive marine carbonates ranging from 17 6 to 21 0 vs smow 9 6 to 12 9 vs pdb millimeter scale variations in abundances of 13c and 18o are associated with diagenetic replacement of primary siderite by secondary ankerite and or magnetite it is shown that these isotopic variations cannot result from mineral dependent fractionations metamorphism or the influence of large volumes of water in an open system

greater role for atlantic inflows on sea ice loss in the eurasian basin of the arctic ocean arctic sea ice loss is a leading indicator of climate change and can be attributed in large part to atmospheric forcing here we show that recent ice reductions weakening of the halocline and shoaling of the intermediate depth atlantic water layer in the eastern eurasian basin have increased winter ventilation in the ocean interior making this region structurally similar to that of the western eurasian basin the associated enhanced release of oceanic heat has reduced winter sea ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing thus explaining the recent reduction in sea ice cover in the eastern eurasian basin this encroaching atlantification of the eurasian basin represents an essential step toward a new arctic climate state with a substantially greater role for atlantic inflows

genesis of late proterozoic copper mineralization copper claim south australia bedded disseminations no evidence for hydrothermal alteration the disseminated sulfides have a delta 34 s range of 17 3 to 15 8 per mil consistent with bacterial reduction of sulfate veinlet sulfides have a similar but smaller delta 34 s range in accord with formation by remobilization of the disseminated sulfides no significant delta 13 c differences between bedded and veinlet carbonates marked variations in delta 18 o values with magnesite values being generally higher than dolomite and the median value for bedded carbonates being around 23 per mil some 3 per mil higher than the median value for veinlet carbonates low temperature oxygen isotope equilibration during early diagenetic carbonate reactions low grade regional metamorphism caused minor recrystallization and formation of additional veinlets but did not extensively overprint the diagenetic isotopic trends isotopic similarities between the cupriferous and the unmineralized lithologies support introduction of the copper during sedimentation and or early diagenesis veinlet carbonates contain small nacl rich fluid inclusions formed at around 300 degrees c and 4 km depth during the metamorphism general trend of increasing mean delta 34 s values with decreasing age of the late proterozoic strata in the adelaide geosyncline and stuart shelf this trend may be the product of local environmental conditions which resulted in sulfate reduction outweighing sulfate replenishment alternatively it could be reflecting global processes which caused major 34 s enrichment of seawater sulfate modified journal abstract

sulphur isotope composition of silurian shale hosted pge ag au zn cu mineralisations of the prades mountains catalonia spain several silurian metamorphosed shale hosted sulphide occurrences have been studied in the prades mountains southern part of the coastal catalonian ranges most of the sulphides are found as stratiform or shale disseminated occurrences pyrrhotite is the most abundant sulphide mineral chalcopyrite and arsenopyrite are less common gold pd bearing lollingite partly replaced by arsenopyrite sperrylite hessite clausthalite altaite galena sphalerite molybdenite scheelite and v cr oxides and silicates are minor components sulphur isotopic analyses were made on three outcrops roca de ponent coma fosca and sant miquel and in the silurian black shales of the sant bernat series in order to determine the origin of the sulphur which formed these deposits the coma fosca and sant miquel outcrops yield a narrow range of 34s values 11 3 to 4 6 whereas the roca de ponent and sant bernat series have a wider range 19 9 to 7 6 in pyrrhotite and up to 36 in pyrite from the top of the sant bernat series in the roca de ponent outcrop the 34s values decrease with increasing stratigraphic height all the deposits have a mean 34s composition close to 9 annealing of pyrrhotite took place during the hercynian metamorphism later during the retrograde metamorphism pyrite replaced pyrrhotite and arsenopyrite replaced lollingite large scale compositional inhomogeneities survived metamorphism from pyroxene to amphibolite facies a hydrothermal source of s has been postulated for the coma fosca and sant miquel outcrops sulphur in these deposits is from leaching of sulphides from the underlying rocks in the roca de ponent outcrop and in the sant bernat series sulphur was derived from a hydrothermal source and from biogenic reduction of seawater sulphate the contribution of the latter source increased with time biogenic reduction of seawater sulphide in a closed or semi closed system for sulphate is considered responsible of the high 34s values of pyrite from the uppermost part of the sant bernat series based on textural and isotopic evidence we propose an exhalative origin for the precious metals cogenetic with the stratiform sulphides

spectral properties of ca sulfates gypsum bassanite and anhydrite this study of the spectral properties of ca sulfates was initiated to support remote detection of these minerals on mars gypsum bassanite and anhydrite are the currently known forms of ca sulfates they are typically found in sedimentary evaporites on earth but can also form via reaction of acidic fluids associated with volcanic activity reflectance emission transmittance and raman spectra are discussed here for various sample forms gypsum and bassanite spectra exhibit characteristic and distinct triplet bands near 1 4 1 5 m a strong band near 1 93 1 94 m and multiple features near 2 1 2 3 m attributed to h2o anhydrite bassanite and gypsum all have so4 combination and overtone features from 4 2 5 m that are present in reflectance spectra the mid ir region spectra exhibit strong so4 3 and 4 vibrational bands near 1150 1200 and 600 680 cm 1 8 5 and 16 m respectively additional weaker features are observed near 1005 1015 cm 1 10 m for 1 and near 470 510 cm 1 20 m for 2 the mid ir h2o bending vibration occurs near 1623 1630 cm 1 6 2 m the visible near infrared region spectra are brighter for the finer grained samples in reflectance and emission spectra of the mid ir region the 4 bands begin to invert for the finer grained samples and the 1 vibration occurs as a band instead of a peak and has the strongest intensity for the finer grained samples the 2 vibration is a sharp band for anhydrite and a broad peak for gypsum the band center of the 1 vibration follows a trend of decreasing frequency increasing wavelength with increasing hydration of the sample in the transmittance raman and reflectance spectra anhydrite forms at elevated temperatures compared to gypsum and at lower temperature salt concentration and ph than bassanite the relative humidity controls whether bassanite or gypsum is stable thus distinguishing among gypsum bassanite and anhydrite via remote sensing can provide constraints on the geochemical environment

the impact of climatic and atmospheric teleconnections on the brine inventory over the laptev sea shelf between 2007 and 2011 export of brine enriched water from siberian shelves is thought to be a key parameter in maintaining the arctic halocline which isolates the fresh and cold surface water from the warm atlantic water and thus prevent dramatic change in the arctic sea ice thermodynamic in this study we used five years of oxygen isotope and hydrological summer surveys to better understand the factors controlling the brine inventory and distribution over the laptev sea shelf the inventory was maximal in 2011 and 2007 and minimal in 2010 the brine inventory interannual variations are coherent with the winter arctic oscillation index that was maximal in 2011 and 2007 and minimal in 2010 which is known to modulate arctic winds and sea ice export pattern while we should remain cautious since our record is limited to 5 years our results suggest that the combined effect of the arctic oscillation and of the arctic dipole is the main factor controlling the annual variations in the inventory of brine enriched waters from the laptev sea shelf between 2007 and 2011 especially during extreme negative arctic oscillation and arctic dipole conditions as in 2010

metamorphosed proterozoic zn pb ag mineralization in the foster river area northern saskatchewan canada metamorphosed zn pb occurrences fable lake george sito south sito southwest sito west sito east robyn lake and mackie lake with high zn pb ratios occur in the foster river area northern saskatchewan on the southeast margin of the paleoproterozoic wollaston domain the sito east prospect the largest of these occurrences contains 50 000 tonnes of 4 5 zn with one drill intercept containing 11 m of 4 2 zn and 0 6 pb most prospects are hosted in a thin areally extensive metaquartzite within a thick sequence of metasiltstones and metaquartzites in the middle of the paleoproterozoic wollaston group occurrences in metaquartzites and metaarkoses which locally contain gahnite spessartine and or graphite are spatially associated with metaexhalites iron formation and quartz garnetite and strata bound metamorphosed hydrothermal alteration zones nodular sillimanite rock post archean australian shale normalized rare earth element ree patterns of all three rock types are characterized by light ree enrichment positive ce anomalies neutral to strongly negative eu anomalies and heavy ree depletion consistent with an environment of deposition distinguished by a high 30 wt continental detrital component and formation from or interaction with low temperature 250 c near neutral ph and high fo2 fluids sulfur isotope compositions of sulfides at foster river are highly enriched in 34s 34s 26 2 38 1 n 20 and resulted from microbial reduction of partially reduced seawater sulfate in a restricted basin the spatial association of spessartine and gahnite bearing lithologies and silicate facies iron formation with paleoproterozoic base metal sulfides in a psammopelitic host sequence implies similarities between sulfide mineralization in the foster river area and broken hill type pb zn ag deposits however the markedly enriched 34ssulfide compositions low pb pb zn and ag pb zn ag ratios low ag contents and apparent absence of metavolcanic and metavolcaniclastic rocks in the dominantly clastic rock sequence hosting the sulfides in the foster river area suggest that these occurrences are part of a metamorphosed sedimentary exhalative system with broken hill type affinities similar to that associated with the formation of the gamsberg zn south africa kanmantoo group pb zn south australia and sullivan pb zn canada deposits

stable isotope geochemistry of cherts and carbonates from the 2 0 ga gunflint iron formation implications for the depositional setting and the effects of diagenesis and metamorphism abstract 18 o values for all but three of 97 samples of chert along a 220 km transect through the 2 0 ga gunflint iron formation of the animikie basin north america range from 21 3 to 24 7 o there is no correlation between 18 o and the type of chert i e deeper water lutitic chert shallower water arenitic chert and peritidal algal chert the fact that the gunflint iron formation has been exposed to thermal conditions only slightly above burial diagenesis suggests that the values of the chert have not been significantly affected by metamorphism field and petrographic observations and the small 18 o range of all the chert types suggests that silicification lithification and any conversion to quartz chert from a hydrous silica precursor occurred close to the sediment water interface the uniform 18 o values of all the different chert types suggest that all cherts precipitated over a relatively common temperature interval 20 c from a common parent water having a relatively uniform 18 o the isotopic data suggest silica saturation and precipitation was not the result of the mixing of seawater and meteoric water or the result of evaporative processes siderite in the deep water banded facies of the gunflint displays a 18 o range of 6 0 to 2 6 o whereas siderite in the more shoreward organic rich shale facies is significantly enriched in 13 c 13 c 2 5 to 0 5 o 18 c of siderite does not appear to have been altered as a result of neomorphic recrystallization and authigenic microsparitic siderite along stylolites displays the same 13 c range as primary and neomorphosed siderite however neomorphic and authigenic siderite are depleted in 18 o by up to 7 o relative to primary unaltered microspheroidal siderite the lower 13 c of banded facies siderite relative to the shale facies siderite does not seem to be the result of thermal decarboxylation or anaerobic oxidation abiotic or bacterial of organic matter but rather is better explained by primary precipitation in an ocean system that was layered with respect to carbon isotopes the more basinward banded facies siderite precipitated from a 13 c depleted fe 2 rich hydrothermal water mass that was moved by advective upwelling from submarine regions of magmatic volcanic hydrothermal activity onto the continental shelf the siderite of the shale facies precipitated from a more near shore shallow seawater mass that was comparatively enriched in 13 c 13 c 0 2 o ankerite in the gunflint iron formation occurs as a replacement of primary siderite in the banded facies and as a replacement of greenalite and chert in the arenite facies many ankerite samples have 13 c values that are similar to those of the shale facies siderite which suggests that shallow seawater was a major component of the diagenetic fluid later neomorphism of the replacement ankerite at higher burial temperatures and probably in the presence of 18 o depleted waters resulted in a wide range of 18 o values 13 8 22 5 o the unique mineralogy of the upper most gunflint iron formation calcite serpentine and magnetite compared to the majority of the formation the very low values and overlying diabase sills suggest that the non ferroan nature of the carbonate in the upper gunflint is the result of contact metamorphism

stratigraphic variations in carbon and oxygen isotopes in the dolostone of the carswell formation proterozoic of northern saskatchewan petrographic and stable isotopic analyses of stromatolitic sediments deposited in nearshore environments provides us with some of the best information available on ancient environments diamond dri

post glacial variability of sea ice cover river run off and biological production in the western laptev sea arctic ocean a high resolution biomarker study abstract multi proxy biomarker measurements were applied on two sediment cores ps51 154 ps51 159 to reconstruct sea ice cover ip25 biological production brassicasterol dinosterol and river run off campesterol sitosterol in the western laptev sea over the last 17 ka with unprecedented temporal resolution the absence of ip25 from 17 2 to 15 5 ka in combination with minimum concentration of phytoplankton biomarkers suggests that the western laptev sea shelf was mostly covered with permanent sea ice very minor river run off and restricted biological production occurred during this cold interval from 16 ka until 7 5 ka a long term decrease of terrigenous riverine organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western laptev sea caused by the onset of the post glacial transgression intensified river run off and reduced sea ice cover characterized the time interval between 15 2 and 12 9 ka including the bolling allerod warm period 14 7 12 9 ka prominent peaks of the dip25 index coinciding with maximum abundances of subpolar foraminifers are interpreted as pulses of atlantic water inflow on the western laptev sea shelf after the warm period a sudden return to severe sea ice conditions with strongest ice coverage between 11 9 and 11 ka coincided with the younger dryas 12 9 11 6 ka at the onset of the younger dryas a distinct alteration of the ecosystem reflected in a distinct drop in terrigenous and phytoplankton biomarkers was detected during the last 7 ka the sea ice proxies reflect a cooling of the laptev sea spring summer season this cooling trend was superimposed by a short term variability in sea ice coverage probably representing bond cycles 1500 500 ka that are related to solar activity changes hence atmospheric circulation changes were apparently able to affect the sea ice conditions on the laptev sea shelf under modern sea level conditions

neoproterozoic sulfur isotope variation in australia and global implications abstract seven sulfur isotope stages are apparent in australian neoproterozoic sections 1 from 840 ma to the sturtian glaciation 700 ma 34ssulfate varied little 19 to 17 5 and 34ssulfide ranged from 20 to 23 2 the sturtian glaciation was followed by 3 a rise in 34ssulfide to an average of 30 seen also in china namibia and canada and in 34ssulfate at least to 26 and possibly to 45 the sharp rise in 34s of all sulfur fractions sulfate sulfide and organic leads us to speculate that sulfide depleted in 34s was deposited on the abyssal plain and that residual sulfate enriched in 34s remained beneath a stagnant ice covered ocean during the sturtian glaciation and was brought to the shallow continental margin during the post glacial transgression 4 34ssulfide and 34ssulfate fall from 640 to 607 ma 34ssulfate down to 17 probably from oxygen excess through massive organic carbon burial which causes weathering of sulfide depleted in 34s continental sulfide and previously deposited sulfide on the abyssal plain 5 the oxic environment of the marinoan 605 595 ma glaciation minimises sulfate reduction unlike the sturtian so that 34ssulfate is unvarying 6 the post glacial environment has sulfide depleted in 34s average 34ssulfide

stable oxygen and carbon isotopes in planktonic foraminifera neogloboquadrina pachyderma in the arctic ocean an overview of published and new surface sediment data abstract a summary study on oxygen and carbon stable isotopes in planktonic foraminifera from arctic ocean floor appeared in marine geology 20 years ago spielhagen and erlenkeuser 1994 we revisit this topic with a wealth of new data focused on the western amerasian arctic a spotlight in the current climatic and oceanic change neogloboquadrina pachyderma the most abundant polar planktonic foraminiferal species is an important tool for reconstructing surface subsurface water changes in the arctic our new data on n pachyderma 150 250 m from the surface sediments show 18 o and 13 c values of 18 o and 13 c are both influenced by complex water sources water column structure and foraminiferal depth habitat the observed distribution of n pachyderma stable isotopes confirms a shallow habitat of this species in the sea ice covered central arctic especially in the canada basin probably in relation to the shallow chlorophyll maximum the associated light n pachyderma 18 o reflects the long term storage of fresh water at the shelf break a deeper dwelling of n pachyderma with heavier 18 o is supported by a more extensive photic zone and nutrient availability air sea exchange plays an important role in 13 c distribution and is consistent with heavy n pachyderma 13 c in the perennially ice covered central arctic ocean light 13 c composition at the shelf break is additionally influenced by shelf bottom waters enriched in isotopically light remineralized terrestrial carbon distribution of foraminiferal 13 c on the chukchi shelf reflects primary production patterns in the area

the laptev sea as a source for recent arctic ocean salinity changes this study was motivated by observations of significant salinification of the upper eurasian basin that began around 1989 observational data and modeling results provide evidence that increased arctic atmospheric cyclonicity in the 1990s resulted in a dramatic increase of the salinity in the eurasian basin two mechanisms account for the laptev sea salinization eastward diversion of russian rivers and increased brine formation due to enhanced ice production in numerous leads in the laptev sea ice cover both these mechanisms are linked to changes in wind patterns and were essential to the formation of salinity anomalies the resulting laptev sea salinity anomaly was advected to the central eurasian basin the strong salinization over the eurasian basin altered the formation of cold halocline waters weakened vertical stratification and released heat upward from below the cold halocline layer our analysis suggests that local processes in the laptev sea may have a basin wide impact on the thermohaline structure of the arctic ocean

impact of the arctic ocean atlantic water layer on siberian shelf hydrography this paper examines the role of the arctic ocean atlantic water aw in modifying the laptev sea shelf bottom hydrography on the basis of historical records from 1932 to 2008 field observations carried out in april may 2008 and 2002 2009 cross slope measurements a climatology of bottom hydrography demonstrates warming that extends offshore from the 30 50 m depth contour bottom layer temperature time series constructed from historical records links the laptev sea outer shelf to the aw boundary current transporting warm and saline water from the north atlantic the aw warming of the mid 1990s and the mid 2000s is consistent with outer shelf bottom temperature variability for april may 2008 we observed on shelf near bottom warm and saline water intrusions up to the 20 m isobath these intrusions are typically about 0 2 c warmer and 1 1 5 practical salinity units saltier than ambient water the 2002 2009 cross slope observations are suggestive for the continental slope upward heat flux from the aw to the overlying low halocline water lhw the lateral on shelf wind driven transport of the lhw then results in the bottom layer thermohaline anomalies recorded over the laptev sea shelf we also found that polynya induced vertical mixing may act as a drainage of the bottom layer permitting a relatively small portion of the aw heat to be directly released to the atmosphere finally we see no significant warming up until now over the laptev sea shelf deeper than 10 15 m in the historical record future climate change however may bring more intrusions of atlantic modified waters with potentially warmer temperature onto the shelf which could have a critical impact on the stability of offshore submarine permafrost

two sulphur isotope provinces deduced from ores in the mount isa eastern succession australia the sulphur isotopic characteristics of ore deposits in the australian mount isa eastern succession are not well known unlike those of the western succession in this study new detailed analyses are provided for recently discovered eastern succession mineralisation such as the starra and osborne bif hosted cu au ores the dugald river sediment hosted pb zn prospect and four vein hosted cloncurry style cu au deposits hampden mt elliot swan mt cobalt and the answer mine all of the deposits of the eastern succession have 34ssulphide between 8 and 9 regardless of their genesis empirically a moderate 34s range averaging close to 0 characterises starra style cu au and pegmont pb zn bif ores whereas shear and vein style cu mineralisation populations are tighter and do not average close to 0 this is a particularly surprising result for dugald river where a larger isotopic variation more typical of stratiform sediment hosted pb zn ores in the region might have been expected by comparison western succession stratiform pb zn and vein style cu deposits span a huge range of 15 to 51 large sulphur isotope ranges typify sulphate evaporite or organic sulphur rich sedimentary successions the lack of such variation in the eastern succession in turn suggests that primary evaporite sequences there were halite dominated but sulphate poor and or contained only limited volumes of organic sulphur rich sediment eastern succession sequences were therefore less likely hosts for giant stratiform pb zn deposits because of their paucity of sulphur although local sulphur sources permitted small deposits such as dugald river to develop sedimentary conditions were more favourable for the development of sulphur poor synsedimentary hydrothermal systems such as starra osborne and pegmont although sulphur isotope evidence is equivocal about the origin of these epigenetic deposits close to the williams batholith mt dore hampden owe their clustering around 0 to their granitic fluid source

a paleoweathering profile from griqualand west south africa evidence for a dramatic rise in atmospheric oxygen between 2 2 and 1 9 bybp a core drilled near wolhaarkop in griqualand west south africa intersected highly oxidized kuruman iron formation below red beds of the gamagara formation the lateral equivalents of the kuruman iron formation in this drill hole consist largely of siderite ankerite magnetite greenalite and quartz the oxidation of the kuruman iron formation in wol 2 occurred almost certainly during weathering prior to the deposition of the gamagara formation the date of this weathering episode is bracketed between about 2 2 and 1 9 bybp by the age of the ongeluk lavas in the transvaal sequence below the unconformity and by the age of the hartley lavas in the olifantshoek group above the unconformity the ratio of iron to sio2 in the several facies of the weathered kuruman iron formation in wol 2 is nearly the same as that in their unweathered equivalents since sio2 loss during weathering was almost certainly minor the similarity of the fe sio2 ratio in the weathered and unweathered bif indicates that nearly all the feo in the kuruman iron formation was oxidized and retained as feo3 during weathering such a high degree of iron retention is best explained by an o2 content of the atmosphere or 0 03 atm at the time of weathering such an o2 pressure is very much greater than that suggested by the composition of paleosols developed on basalt or 2 2 bybp but is consistent with the highly oxidized nature of the 1 85 by flin flon paleosol the new data suggest that po2 rose dramatically from about 1 percent pal present atmospheric level to or 15 percent pal between 2 2 and 1 9 bybp

river runoff sea ice meltwater and pacific water distribution and mean residence times in the arctic ocean hydrographic and tracer data collected during ark iv 3 fs polarstern in 1987 arctic91 ib oden and aos94 ccgs louis s st laurent expeditions reveal the evolution of the near surface waters in the arctic ocean during the late 1980s and early 1990s salinity nutrients dissolved oxygen and 18 o data are used to quantify the components of arctic freshwater river runoff sea ice meltwater and pacific water the calculated river runoff fractions suggest that in 1994 a large portion of water from the pechora ob yenisey kotuy and lena rivers did not flow off the shelf closest to their river deltas but remained on the shelf and traveled via cyclonic circulation into the laptev and east siberian seas river runoff flowed off the shelf at the lomonosov ridge and most left the shelf at the mendeleyev ridge arctic91 and aos94 pacific water fraction estimates of upper halocline water the traditionally defined core of the pacific water mass document a decrease in extent compared to historical data the front between atlantic water and pacific water shifted from the lomonosov ridge location in 1991 to the mendeleyev ridge in 1994 the relative age structure of the upper waters is described by using the 3 h 3 he age the mean 3 h 3 he age measured in the halocline within the salinity surface of 33 1 0 3 is 4 3 1 7 years and that for the 34 2 0 2 salinity surface is 9 6 4 6 years lateral variations in the relative age structure within the halocline and atlantic water support the well known cyclonic boundary current circulation

stable isotopic compositions of carbonates from the mesoproterozoic bangemall group northwestern australia marine carbonate rocks from the mesoproterozoic bangemall group of northwestern australia show little deviation 1 3 in whole rock delta 13c carb values about a mean of 0 5 this narrow range persists despite close sampling every 10 20 m through long sections up to 2500 m that are geographically widespread up to 250 km apart over many depositional environments supralittoral to outer shelf sediment sources stromatolitic bioherms to detrital calcilutites and rock types pure limestones to dolomitic shales the only major excursions from the norm seem related to unusual environmental or post depositional processes as they are correlated with large enrichments to 3 or depletions to 16 in 18o relatively heavy delta 13c values up to 2 5 occur in a single bed of brecciated ferruginous dolostone at a single locality these abnormal values may result from local evaporitic conditions limey and shaley nodular dolostones have delta 13c values as low as 4 3 probably caused by remineralization of organic matter during late and patchy dolomitization most notably sharp negative excursions in delta 13c up to 8 4 occur in bleached kerogen free rocks with mineral assemblages of dolomite quartz calcite tremolite talc reflecting isotopic re equilibration in thick metamorphic aureoles around dolerite intrusions general environmental variations are minor with delta 13c values of peritidal facies tending to be slightly positive whereas those of subtidal facies are slightly negative there are no strong secular trends but subtle fluctuations within the range 2 to l can be correlated along the northwestern margin of the basin this resembles the pattern seen in other mesoproterozoic successions but is markedly unlike the heavy background 5 and extreme variations up to l0 in delta 13c evident in neoproterozoic successions of similar thickness and environmental setting hence in contrast to the neoproterozoic the global rate of organic carbon burial was probably fairly constant during deposition of the bangemall group and perhaps generally during the mesoproterozoic as was the redox state of the atmosphere and hydrosphere

a meteoric water budget for the arctic ocean a budget of meteoric water mw river runoff net precipitation minus evaporation and glacial meltwater over four regions of the arctic ocean is constructed using a simple box model regional precipitation evaporation estimates from reanalysis data sets and estimates of import and export fluxes derived from the literature with a focus on the 2003 2008 period the budget indicates an approximate slightly positive balance between mw imports and exports i e no change in storage thus the observed total freshwater increase observed during this time period likely resulted primarily from changes in non mw freshwater components i e increases in sea ice melt or pacific water and or a decrease in ice export further our analysis indicates that the mw increase observed in the canada basin resulted from a spatial redistribution of mw over the arctic ocean mean residence times for mw were estimated for the western arctic 5 7 years eastern arctic 3 4 years and lincoln sea 1 2 years the mw content over the siberian shelves was estimated 14 000 km3 based on a residence time of 3 5 years the mw content over the entire arctic ocean was estimated to be 44 000 km3 the mw export through fram strait consisted mostly of water from the eastern arctic 3 237 1 370 km3 yr 1 whereas the export through the canadian archipelago was nearly equally derived from both the western arctic 1 182 534 km3 yr 1 and lincoln sea 972 391 km3 yr 1

the fate of terrigenous dissolved organic carbon on the eurasian shelves and export to the north atlantic dissolved lignin phenols chromophoric dissolved organic matter cdom absorption and fluorescence were analyzed along cross slope mooring locations in the barents laptev and east siberian seas to gain a better understanding of terrigenous dissolved organic carbon tdoc dynamics in arctic shelf seas and the arctic ocean a gradient of river water and tdoc was observed along the continental shelf eastward into the east siberian sea correlations of carbon normalized yields of lignin derived phenols supplied by siberian rivers with river water fractions and known water residence times yielded in situ decay constants of 0 18 0 58 yr 1 calculations showed 50 of annual tdoc discharged by siberian rivers was mineralized in estuaries and on eurasian shelves per year indicating extensive removal of tdoc bioassay experiments and in situ decay constants indicated a reactivity continuum for tdoc cdom parameters and acid aldehyde ratios of vanillyl v and syringyl s lignin phenols showed biomineralization was the dominant mechanism for the removal of tdoc characteristic ratios of p hydroxy p s and v phenols p v s v also identified shelf regions in the kara sea and regions along the western laptev sea shelf where formation of low salinity halocline waters lshw and lower halocline water lhw occurred the efficient removal of tdoc demonstrates the importance of eurasian margins as sinks of tdoc derived from the large siberian rivers and confirms tdoc mineralization has a major impact on nutrients budgets air sea co2 exchange and acidification in the siberian shelf seas

impact of siberian coastal polynyas on shelf derived arctic ocean halocline waters hydrographic and stable oxygen isotope h218o h216o sampling was carried out within the west new siberian wns coastal polynyas in the southern laptev sea in late winters 2008 and 2009 the impact of sea ice formation on the water column was quantified by a salinity lower case delta 18o mass balance several stations had vertically homogeneous physical properties in april may 2008 and featured polynya formed local bottom water with elevated signals of brine released during sea ice formation and elevated fractions of river water the polynya formed bottom water was fresher than surrounding bottom waters at other stations salinity lower case delta 18o correlation showed well defined mixing lines for bottom and surface layers in march april 2009 surface waters were strongly influenced by lena river water and local polynya activity with elevated brine signals reached to intermediate depth but did not penetrate the bottom layer in the highly stratified water column inventory values of sea ice formation were comparable in both years but freshwater distributions from the preceding summers were different therefore the observed difference in the impact of polynya activity on the water column is not primarily controlled by the amount of sea ice formed during winter but by preconditioning from the preceding summer only in years when the river plume is mostly absent in the polynya region stratification is weak and allows winter sea ice formation to reach the bottom layer thus summer stratification controls the influence of local polynya water on the shelf s bottom hydrography and as bottom water is exported impacts on the source water of shelf derived halocline waters

latest proterozoic stratigraphy and earth history the end of the proterozoic eon was a time of pronounced biological biogeochemical climatic and tectonic change new bio and chemostratigraphic data provide an improved framework for stratigraphic correlation making possible a deeper understanding of latest proterozoic earth history and providing tools for a chronostratigraphic division of late proterozoic time

exchange of laptev sea and arctic ocean halocline waters in response to atmospheric forcing combined delta o18 salinity data reveal a distinctive water mass generated during winter sea ice formation which is found predominantly in the coastal polynya region of the southern laptev sea export of the brine enriched bottom water shows interannual variability in correlation with atmospheric conditions summer anticyclonic circulation is favoring an offshore transport of river water at the surface as well as a pronounced signal of brine enriched waters at about 50 m water depth at the shelf break summer cyclonic atmospheric circulation favors onshore or an eastward alongshore water transport and at the shelf break the river water fraction is reduced and the pronounced brine signal is missing while on the middle laptev sea shelf brine enriched waters are found in high proportions residence times of bottom and subsurface waters on the shelf may thereby vary considerably an export of shelf waters to the arctic ocean halocline might be shut down or strongly reduced during onshore cyclonic atmospheric circulation while with offshore anticyclonic atmospheric circulation brine waters are exported and residence times may be as short as 1 year only

aspects of proterozoic stromatolite biostratigraphy in western australia abstract stromatolites are abundant at many horizons in the proterozoic of western australia recent advances in knowledge of proterozoic stratigraphy of the state have provided a more detailed framework for interpreting the stromatolite data than has been available previously in the 1 7 ga earaheedy group of the nabberu basin a characteristic stromatolite assemblage occurs and within the basin a biostratigraphic succession can be recognized the assemblage contains several new forms which belong to new groups the need to erect new groups for these early proterozoic stromatolites is in agreement with recent studies in canada northern europe and south africa and suggests that the problem of younger or late proterozoic stromatolite groups in early proterozoic rocks mentioned by previous workers is a result of a lack of rigour in defining taxa examination of type material is necessary to determine how closely the earaheedy forms resemble those described from these other regions in western australia some stromatolite forms have a restricted vertical range and similar taxa occur in beds of approximately the same age in widely separated areas e g kimberley group and earaheedy group scorpion group and limbunya birrindudu mcarthur mt rigg and mt albert groups and bungle bungle dolomite tolmer and bullita groups moora and bangemall groups kai ki beds louisa downs mount house and albert edward groups stromatolite diversity shows a decline in the number of taxa at about 1 1 ga in the bangemall group more data are required to determine whether this decline is universal or specific to the bangemall group this study indicates that a stromatolite biostratigraphy for western australia is feasible and is consistent with data from other parts of australia thus emphasis on correlation should be placed on the stromatolite form rather than the group and intercontinental correlations should be attempted only when local biostratigraphic schemes have been firmly established

wind driven transport pathways for eurasian arctic river discharge distributions of temperature salinity and barium in near surface waters depth 50 m of the laptev sea and adjacent areas of the arctic ocean are presented for the summers of 1993 1995 and 1996 the tracer data indicate that while fluvial discharge was largely confined to the shelf region of the laptev sea in the summer of 1993 surface waters containing a significant fluvial component extended beyond the shelf break and over the slope and basin areas north of the laptev sea in the summers of 1995 and 1996 these distributions of fluvial discharge are consistent with local winds and suggest two principal pathways by which river waters can enter the central arctic basins from the laptev sea when southerly to southeasterly wind conditions prevail river waters are transported northward beyond the shelf break and over the slope and adjacent basin areas these waters can then enter the interior arctic ocean via upper layer flow in the vicinity of the lomonosov ridge under other wind conditions river waters are steered primarily along the inner laptev shelf and into the east siberian sea as part of the predominantly eastward coastal current system these waters then appear to cross the shelf and enter the interior arctic ocean via upper layer flow aligned roughly along the mendeleyev ridge the extent to which either pathway is favored in a given year is largely determined by local wind patterns during the summer months when fluvial discharge is greatest and shelf waters are at the lowest salinity of their annual cycle

canadian basin freshwater sources and changes results from the 2005 arctic ocean section 1 we present measurements of oxygen isotope ratios and nutrient concentrations along the 2005 arctic ocean section aboard the icebreaker oden the data are used to estimate freshwater contributions from meteoric water mainly river runoff sea ice meltwater and chukchi sea shelf water itself a combination of pacific and indigenous arctic water types nutrients ratios are combined to form quasi conservative water mass tracers phosphate star n star and the empirical arctic n p relationship and used along with salinity and 18o which are conservative in the ocean interior disagreements between two different freshwater analyses in the western arctic are largely resolved using a salinity dependent redfield ratio a new estimate of the pacific end member and an analysis of the bering strait inflow contribution to detraining shelf waters freshwater components from 2005 are placed into the context of the overlapping 1994 arctic ocean section aboard the louis st laurent and a time series of hydrographic tracer casts between 1987 and 1992 in the canada basin compared to 1987 1994 the 2005 transect exhibits increased meteoric water concentrations in the northern part of the canadian basin and a decrease in the southern part this pattern is related to changes in the distribution of wind stress curl during the several years prior to each sampling campaign in addition a previously observed correlation between sea ice formation and river runoff disappears over the central arctic in 2005 a change that we attribute to a northward shift of sea ice formation resampling approximately every 3 years should resolve the dynamics driving changes in freshwater and nutrient distributions

carbonate petrography kerogen distribution and carbon and oxygen isotope variations in an early proterozoic transition from limestone to iron formation deposition transvaal supergroup south africa the transition zone comprises campbellrand microbialaminated replacing cryptalgalaminate limestone and shale with minor dolomite conformably overlain by the kuruman iron formation of which the basal part is characterized by siderite rich microbanded iron formation with minor magnetite and some hematite containing units the iron formation contains subordinate intraclastic and microbialaminated siderite mesobands and was deposited in deeper water than the limestones the sequence is virtually unaltered with diagenetic mineral assemblages reflecting a temperature interval of about 110 degrees to 170 degrees c and pressures of 2 kbars carbonate minerals in the different rock types are represented by primary micritic precipitates now recrystallized to microsparite early precompactional sparry cements and concretions deep burial limpid euhedral sparites and spar cements precipitated from metamorphic fluids in close contact with diabase sills paragenetic pathways of the carbonate minerals are broadly similar in all lithofacies with kerogen intimately associated with them kerogen occurs as pigmentation in carbonate crystals as reworked organic detritus in clastic textured carbonate units and as segregations of kerogen pigment around late diagenetic carbonate crystals locally kerogen may also be replaced by carbonate spar carbon isotope compositions of the carbonate minerals and kerogen are dependent on their mode of occurrence and on the composition of the dominant carbonate species in a specific lithofacies integration of sedimentary petrographic geochemical and isotopic results makes it possible to distinguish between depositional early diagenetic deep burial and metamorphic effects on the isotopic compositions of the carbonate minerals and the kerogen in the sequence major conclusions are that deep burial thermal decarboxylation led to 13c depletion in euhedral ferroan sparites and 13c enrichment in kerogen organic carbon metamorphic sparites are most depleted in 13c carbonates in oxide rich iron formations are more depleted in 13c than those in siderite rich iron formation whereas the kerogens in oxide banded iron formations bif are more enriched this implies that the siderite rich iron formations were not derived from oxide rich iron formation through reduction of ferric iron by organic matter organic matter oxidation by ferric iron did however decrease the abundance of kerogen in oxide rich iron formation and led to the formation of isotopically very light sparry carbonates siderite and calcmicrosparite both represent recrystallized primary micritic precipitates but differ in their 13c composition with the siderites depleted in 13c by 4 6 per mil on average relative to calcmicrosparite this means that the siderites were precipitated from water with dissolved inorganic carbon depleted in 13c by about 9 per mil relative to that from which the limestones precipitated this implies an ocean system stratified with regard to total carbonate with the deeper water from which siderite rich iron formation formed depleted in 13c iron formations were deposited in areas of very low organic matter supply depletion of 13c may therefore derive not from degradation of organic matter but from hydrothermal activity a conclusion which is supported by 18o composition of the carbonate minerals and trace element and rare earth element ree compositions of the iron formations

tide induced vertical mixing in the laptev sea coastal polynya enhanced semidiurnal band velocity shear across the shelf halocline layer shl was found during land fast ice edge mooring based acoustic doppler current profiler adcp and conductivity temperature depth ctd observations over the eastern laptev sea shelf 74 n 128 e in april may 2008 and april 2009 in 2008 the major axis amplitude for the lunar semidiurnal m2tidal ellipses demonstrated intermediate maximum in the shl at 11 13 m 15 3 cm s gradually decreasing to subice and near bottom layers to 9 3 cm s at 7 m and 7 2 cm s at 19 m respectively in 2009 the semidiurnal tidal flow exhibited similar patterns but velocities were reduced by about factor of 2 our estimates of gradient richardson numbers suggest that the velocity shear associated with semidiurnal baroclinic tidal flow may be strong enough to play a role in water mass modification promoting shear instabilities turbulence and vertical mixing of seawater properties across the shl this suggestion is consistent with near homogeneous water layers episodically occurring in the shl differences in the background stratification and local tidal dynamics between 2008 and 2009 together with rapid responses of the semidiurnal motion to polynya openings suggest that the baroclinic tide is locally generated

palaeoenvironment and carbon isotope stratigraphy of upper proterozoic carbonates of the yangtze platform the 13c values for phanerozoic marine carbonates display secular trends mainly in the range 1 to 2 1 these have been interpreted as primary features reflecting changes in the carbon isotope composition of dissolved bicarbonate in seawater brought about largely by variations in the proportions of carbon being sequestered in the oxidized and reduced carbon reservoirs1 2 carbon isotope trends are not as well established for the precambrian but there are indications that upper proterozoic sequences contain carbonates with unusually high 13c values3 9 here we present the results of the first carbon isotopic study of the upper proterozoic carbonate strata from the type locality of the sinian system in the yangtze gorges sections near yichang south china and discuss their implications for accumulation of organic matter we also compare the results for these chinese strata with 13c trends in other upper proterozoic cambrian sequences and assess the extent to which such isotopic data can be used to make stratigraphic correlations between widely spaced sequences

geochemistry of precambrian carbonates vi aphebian albanel formations quebec canada abstract the 1 85 0 15 ga old albanel formations of northern quebec canada an example of paleoproterozoic carbonate buildups are lithologically composed of cherty dolostones subordinate limestones are encountered only near the base of the sequence coincident with maximal transgression the chemistry of the bulk rocks is almost entirely controlled by noncarbonate phases such as chert quartz plagioclase illite k spar pyrite and fe mn oxides all abundant particularly in the basal part of the section the chemistry of the carbonate portion of limestones is strongly reset by post depositional phenomena but the relict high sr contents suggest that aragonite may have been an original precursor phase geochemically the carbonate portion of dolostones can be subdivided into two populations reflecting the stratigraphie bottom and top of the sequence trace element and oxygen isotope criteria suggest that the entire sequence was subjected to meteoric and subsequent burial diagenesis with the less deeply buried top portion of the sequence having recrystallized and stabilized at lower temperatures but in a more open system the latter reflects the greater lithological variability and permeability of the younger strata the 13c varies up section from about 3 to 1 perhaps a reflection of progressively more open marine circulation the associated four generations of post depositional pyrites have overlapping 34s from 7 1 to 54 with a mean of 24 a reflection of dissimilatory bacterial sulfate reduction in a relatively closed diagenetic system with perhaps a limited sulfate availability and or replenishment the best measured 87 sr 86 sr of 0 70600 although possibly not a direct reflection of the coeval seawater may still be a near original value as indicated by its coherency with the roughly co stratigraphic paleo proterozoic sequences evaluation of the existing data indicates that strontium isotopic composition of the precambrian seawater was characterized by oscillations similar to those of the phanerozoic the interval of 0 8 1 5 ga ago being dominated by relatively nonradiogenic values followed by a radiogenic period at 1 6 2 2 ga ago near mantle values during the late archean and possibly another radiogenic peak at 3 5 ga ago

depositional setting of gypsum deposits southwestern ontario the domtar mine the depositional environment of the a and b units of the upper silurian salina formation in the appalachian and michigan basins has been a contentious issue for the past century in large measure this is due to the fact that exposures of the salina formation are rare and that many published models are based only on data obtained from drill cores also most studies have concentrated on the basins themselves and have largely ignored the intervening area across the positive high of the algonquin arch the domtar construction materials gypsum deposit is situated in the niagara peninsula on the eastern flank of the algonquin arch stratigraphic correlation from drill cores and underground mapping indicates that the mined gypsum bed is the salina formation b anhydrite unit this is overlain by shales and gypsiferous rocks of the salina formation b unit and underlain by shales dolomite dolomitic shales and gypsum of the salina a 2 unit dolomitic shales of the salina a 1 unit and dolomite of the guelph formation at the domtar deposit the salina a and b units comprise five distinct dolomitic shale to gypsum cycles that increase progressively upward in gypsum content underground mapping at mines 2 and 3 reveals that a wide range of facies and textures are present in the mined gypsum bed and that the enclosing sediments were deposited in a relatively anoxic subaqueous environment although primary evaporite textures have been modified by both dehydration of gypsum to anhydrite on burial and later rehydration of anhydrite to gypsum on post pleistocene uplift they are consistent with subaqueous deposition in a coastal salina or lagoon it is suggested that the salina a and b units of the niagara peninsula were deposited in a sedimentary setting similar to the modern evaporitic environment of the northern sinai here gypsum is precipitating in coastal lagoons and salinas adjacent to the nile estuary in the same area evaporites are also present in sabkhas and continental playas thus comparison of the salina formation with the modern environment of northeastern egypt may also explain the apparently contradictory evidence from other studies of adjacent subaqueous supratidal and subaerial evaporitic environments in the salina a unit of the michigan and appalachian basins

wind driven summer surface hydrography of the eastern siberian shelf 1 high interannual variability of summer surface salinity over the laptev and east siberian sea shelves derived from historical records of the 1950s 2000s is attributed to atmospheric vorticity variations in the cyclonic regime positive vorticity the eastward diversion of the laptev sea riverine water results in a negative salinity anomaly to the east of the lena delta and farther to the east siberian sea and a positive anomaly to the north of the lena delta anticyclonic negative vorticity results in negative salinity anomalies northward from the lena delta due to freshwater advection toward the north and a corresponding salinity increase eastward

problematic bedding plane markings from the middle proterozoic manganese subgroup bangemall basin western australia abstract enigmatic bedding plane markings impressions resembling isolated strings of beads occur in sandy and argillaceous strata of the stag arrow formation in the middle proterozoic manganese subgroup bangemall group of the bangemall basin east of newman western australia markings are abundant at two localities and traces are found at a third structures similar in both morphology and dimension have previously been reported from the appekunny formation in the middle proterozoic belt supergroup of u s a the manganese subgroup structures provide further details of morphology enabling comparison with a variety of biogenic and non biogenic structures a source for the markings still cannot be determined with certainty but a biogenic origin is favoured and affinities with the green or brown algae suggested such an origin is consistent with records of megascopic algae from rocks of similar age

dissolved iron in the arctic shelf seas and surface waters of the central arctic ocean impact of arctic river water and ice melt key points dfe in the arctic shelves and surface is linked to freshwater and alkalinity fluvial input main contributor to high dfe low alkalinity in central arctic remineralisation and biological depletion determine dfe in the arctic shelf seas abstract concentrations of dissolved 10 nm in the bottom waters of the laptev sea shelf may be attributed to either sediment resuspension sinking of brine or regeneration of dfe in the lower layers a significant correlation r2 0 60 between salinity and dfe is observed using 18o salinity nutrients and total alkalinity data the main source for the high 2 nm dfe concentrations in the amundsen and makarov basins is identified as eurasian river water transported with the transpolar drift tpd on the north american side of the tpd the dfe concentrations are low 4 above the shelf and low 4 off the shelf

changes in distribution of brine waters on the laptev sea shelf in 2007 combined salinity and 18o data from summer 2007 reveal a significant change in brine production in the laptev sea relative to summer 1994 the distribution of river water and brine enriched waters on the laptev sea shelf is derived based on mass balance calculations using salinity and 18o data while in 1994 maximal influence of brines is seen within bottom waters bauch et al 2009a in 2007 the influence of brines is highest within the surface layer and only a moderate influence of brines is observed in the bottom layer in contrast to 2007 salinity and 18o data from summer 1994 clearly identify a locally formed brine enriched bottom water mass as mixing endmember between surface layer and inner shelf waters on one side and with higher salinity water from the outer laptev sea on the other side in 2007 the brine enriched waters are predominantly part of the surface regime and the mixing endmember between surface layer and outer shelf waters is replaced by a relatively salty bottom water mass this relatively salty bottom water probably originates from the western laptev sea the inverted distribution of brines in the water column in 2007 relative to 1994 suggests a less effective winter sea ice formation in winter 2006 2007 combined with advection of more saline waters from the western laptev sea or the outer shelf precedent to 1 the climatically extreme summer 2007 the observed changes result in an altered export of waters from the laptev sea to the arctic ocean halocline

palaeoproterozoic magnesite lithological and isotopic evidence for playa sabkha environments magnesite forms a series of 1 to 15 m thick beds within the 2ae 0g a palaeoproterozoic tulomozerskaya formation nw fennoscandian shield russia drillcore material together with natural exposures reveal that the 680m thick formation is composed of a stromatolite dolomite red bed sequence formed in a complex combination of shallow marine and non marine evaporitic environments dolomite collapse breccia stromatolitic and micritic dolostones and sparry allochemical dolostones are the principal rocks hosting the magnesite beds all dolomite lithologies are marked by d 13 c values from 7ae1 to 11ae6 v pdb and d 18 o ranging from 17ae4 to 26ae3 v smow magnesite occurs in different forms finely laminated micritic stromatolitic magnesite and structureless micritic crystalline and coarsely crystalline magnesite all varieties exhibit anomalously high d 13 c values ranging from 9ae0 to 11ae6 and d 18 o values of 20ae0 25ae7 laminated and structureless micritic magnesite forms as a secondary phase replacing dolomite during early diagenesis and replaced dolomite before the major phase of burial crystalline and coarsely crystalline magnesite replacing micritic magnesite formed late in the diagenetic metamorphic history magnesite apparently precipitated from sea water derived brine diluted by meteoric fluids magnesitization was accomplished under evaporitic conditions sabkha to playa lake environment proposed to be similar to the coorong or lake walyungup coastal playa magnesite magnesite and host dolostones formed in evaporative and partly restricted environments consequently extremely high d 13 c values reflect a combined contribution from both global and local carbon reservoirs a 13 c rich global carbon reservoir d 13 c at around 5 is related to the perturbation of the carbon cycle at 2ae0 ga whereas the local enhancement in 13 c up to 12 is associated with evaporative and restricted environments

a sulfur isotope study of pyrite genesis the mid proterozoic newland formation belt supergroup montana abstract different generations of sedimentary pyrite from the mid proterozoic newland formation usa have been analysed for their sulfur isotopic compositions the results indicate bacterial sulfate reduction as the pyrite forming process the 34 s values for early diagenetic pyrite around 14 are in contrast to dominantly more positive values for many other middle proterozoic units a progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34 s content rayleigh distillation as well as through detailed petrographic observations contemporaneous seawater had a sulfur isotopic ratio between 14 and 18 as measured from sedimentary barite within the unit

diagenesis and copper mineralization in carbonates in the spokane formation belt supergroup at wolf creek montana strata bound silver bearing copper sulfides occur in two thin green siltstone units a thin phosphatic green siltstone bed and a stromatolitic oolitic carbonate bed of the spokane formation near wolf creek montana red mudstone and fine grained sandstone sequences containing sedimentary structures indicative of shallow water deposition with periodic emergence surround these mineralized zones the 10 to 30 cm thick carbonate bed the lowest and most intensely mineralized unit crops out discontinuously over 7 5 km it varies from an ooid peloid packstone to an ooid peloid bearing calcareous siltstone chalcocite family minerals covellite and bornite or chalcopyrite pyrite and galena occur in the eastern part of the area chalcopyrite and pyrite or chalcocite family minerals covellite and galena occur in the western part sulfur isotope values of the sulfides are compatible with bacterial production from seawater sulfate oxygen and carbon isotope values of the oolitic limestone are slightly lighter than those obtained for 1 b y old marine limestone elsewhere but are within the range of ravalli group and middle belt carbonate rocks of the belt supergroup element analyses show that cu ag mo pb and cd in the mineralized units are enriched over average country rock values from the enclosing section ni and fe are more abundant in the country rock and co values are similar in both rock types elemental values of the wall rock samples are very similar regardless of stratigraphic position color or grain size textures in the oolitic limestone indicate mineralization occurred during diagenesis following deposition of calcareous clastics dolomite gypsum and halite formed in evaporitic early diagenesis pseudomorphic replacement of these minerals by quartz and albite followed pyrite formed prior to silicification and was partially to totally replaced by copper sulfides and galena as waters containing copper and lead apparently moved upward through the sequence radial calcite and microspar formed both during and after mineralization finally greenschist facies metamorphism altered the rocks causing partial to almost complete destruction of the original fabrics and recrystallization of the sulfides in some areas