authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

a model of long term oxidation and leaching processes in pyritic coal cleaning wastes this study presents a numerical model to simulate a long term pyrite oxidation process and subsequent multi component reactive transportation of the oxidation productions in an abandoned coal waste pile in northeast of iran for this purpose 240 solid samples of wastes were obtained from different depths of 10 vertical trenches excavated in the pile then geochemical analyses including determination of pyrite content remaining in the waste particles paste ph tests sulfate concentration were conducted on the collected samples in addition oxygen concentration profile associated with each trench was determined the results show that the oxidation zone is limited to the shallower depths of the pile where oxygen was readily available furthermore governing mathematical equations describing oxygen transport pyrite oxidation and transport of oxidation products were formulated based on the fact that the oxidation process follows a shrinking core concept and gaseous diffusion is the main process for oxygen supply within the waste materials the transport equation incorporates physical processes of advection and dispersion eventually an existing one dimensional numerical finite volume model was slightly modified and the governing equations were simultaneously solved using a commercial computational fluid dynamics software called phoenics by providing extra codes for those terms of equations which are not included in phoenics governing equation the results of simulation for 15 years of abandoned of the pile showed close agreement with the geochemical data the simulations were further performed to predict the pyrite oxidation and subsequent transportation processes for years 5 10 and 20 from now the results revealed that more load of the oxidation products would be expected than those are generated now and the products would reach the pile base it will result in environmental problems for soil surface and groundwater of the study area and nearby lands in future

paired carbon isotopic analysis of ordovician bulk carbonate δ 13 c carb and organic matter δ 13 c org spanning the great ordovician biodiversification event abstract paired measurements of bulk carbonate 13ccarb organic matter 13corg and their difference 13c can be used to estimate changes in isotopic fractionation through time as a function of o2 co2 in the atmosphere however because local scale processes can also affect 13c it is essential to compare sections from widely separated water masses here we present new 13corg data from ordovician carbonate rocks from the great basin oklahoma and appalachian basin and compare with published 13ccarb records from these sections and paired 13c values from other carbonate successions around north america these new data complement previous studies that focused on upper ordovician 13ccarb excursions and now provide a composite ordovician 13corg record new lower ordovician tremadocian stage 13corg data range from ca 26 to 28 decreasing throughout the lower middle ordovician floian dapingian stages to ca 29 to 31 13corg values remain at their lowest throughout the sandbian and are similar to other published upper ordovician sandbian katian 13corg data from north america 13c values from well preserved intervals generally vary between 26 to 28 throughout the lower to middle ordovician tremadocian to early darriwilian but increase to 31 during the mid late darriwilian and mid sandbian similar to published data from younger late ordovician positive 13c excursions known as the guttenberg gice and hirnantian hice events the overall 13c trend shows a 3 increase throughout the early middle ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms modeling studies predict that pco2 decreased during this time suggesting that the effect of pco2 on 13c may have been overwhelmed by other controls such as an in increase in po2 or a higher o2 co2 ratio during this biodiversification event

the road river group of northern yukon canada early paleozoic deep water sedimentation within the great american carbonate bank cambrian devonian sedimentary rocks of the northern canadian cordillera record both the establishment and demise of the great american carbonate bank a widespread carbonate platform system that fr

perspectives on proterozoic surface ocean redox from iodine contents in ancient and recent carbonate abstract the proterozoic eon hosted the emergence and initial recorded diversification of eukaryotes oxygen levels in the shallow marine settings critical to these events were lower than today s although how much lower is debated here we use concentrations of iodate the oxidized iodine species in shallow marine limestones and dolostones to generate the first comprehensive record of proterozoic near surface marine redox conditions the iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters to assess the validity of our approach neogene quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate iodine contents despite the potential for diagenetic loss maximum proterozoic carbonate iodine levels are elevated relative to those of the archean particularly during the lomagundi and shuram carbon isotope excursions of the paleo and neoproterozoic respectively for the shuram anomaly comparisons to neogene quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends the baseline low iodine levels in proterozoic carbonates relative to the phanerozoic are linked to a shallow oxic anoxic interface oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes however the diagnostically low iodine data from mid proterozoic shallow water carbonates relative to those of the bracketing time intervals are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans this redox instability may have challenged early eukaryotic diversification and expansion creating an evolutionary landscape unfavorable for the emergence of animals

geochemical evidence for widespread euxinia in the later cambrian ocean it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking gill et al present sulphur isotope data from cambrian rocks at six different locations around the world and find a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time a prolonged period of anoxia during the cambrian may explain the previously enigmatic peculiarities seen in the fossil record it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking now sulphur isotope data from cambrian rocks at six different locations around the world is presented with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time with the help of a box model these isotope shifts support the idea of large scale anoxic and sulphidic conditions in the later cambrian ocean widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long term inhibitor of evolutionary radiation on early earth in recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later cambrian oceans1 2 possibly influencing evolutionary events during this time1 2 3 physical evidence of widespread anoxia in cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored here we present sulphur isotope records from six globally distributed stratigraphic sections of later cambrian marine rocks about 499 million years old we find a positive sulphur isotope excursion in phase with the steptoean positive carbon isotope excursion spice a large and rapid excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation4 5 numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large scale anoxic and sulphidic euxinic conditions independently molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia these results identify the spice interval as the best characterized ocean anoxic event in the pre mesozoic ocean and an extreme example of oxygen deficiency in the later cambrian ocean thus a redox structure similar to those in proterozoic oceans6 7 8 may have persisted or returned in the oceans of the early phanerozoic eon indeed the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in cambrian oceans

paleosecular variations since 9000 yr bp as recorded by sediments from maar lake shuangchiling hainan south china abstract high resolution paleosecular variation psv can play an important role in sediment dating and for understanding the temporal characteristics of the geodynamo of the earth s magnetic field in this article based on magnetic susceptibility correlation a composite sediment profile has been compiled from a 16 m long core hn 2 and a 8 m deep well hn 3 in shuangchiling maar lake a crater basin located on hainan island southern china fine and homogeneous silty clay corroborates with a stable continuous and undisturbed deposition a u channel based paleomagnetic study constrained by ams14c chronology derived from leaves plant debris and woods and supported by rock magnetic data indicates that the lake sediments document a reliable paleosecular variation psv record since 9000 cal year bp comparison of our psv features with other records from lakes biwa japan erhai china baikal russia as well as archaeomagnetic records demonstrate that the inclination pattern is generally synchronous within chronological uncertainties suggesting further psv dating may be valuable for stratigraphic correlation on a regional scale

variability in sulfur isotope records of phanerozoic seawater sulfate the s of seawater sulfate reflects processes operating at the nexus of sulfur carbon and oxygen cycles however knowledge of past seawater sulfate s values must be derived from proxy materials that are impacted differently by depositional and post depositional processes we produced new timeseries estimates for the s value of seawater sulfate by combining 6710 published data from three sedimentary archives marine barite evaporites and carbonate associated sulfate with updated age constraints on the deposits robust features in multiple records capture temporal trends in the s value of seawater and its interplay with other phanerozoic geochemical and stratigraphic trends however high frequency discordances indicate that each record is differentially prone to depositional biases and diagenetic overprints the amount of noise quantified from the variograms of each record increases with age for all s proxies indicating that post depositional processes obscure detailed knowledge of seawater sulfate s s value deeper in time

an iodine record of paleoproterozoic surface ocean oxygenation constraining oxygen levels in the early precambrian surface ocean has been a longstanding goal but efforts have been challenged by the availability of suitable proxies here we present a novel approach iodine geochemistry which broadens our perspective by providing constraints on shallow carbonate dominated marine settings iodate io 3 persists exclusively in oxic waters and is the sole iodine species incorporated into carbonate minerals allowing iodine to calcium ratios i ca in shallow carbonates to be used as a paleoredox indicator our data from a series of mesoarchean through paleoproterozoic carbonates deposited under shallow marine conditions reveal a progressive surface ocean oxygenation in the early paleoproterozoic these data seem to indicate that a largely anoxic surface ocean extended throughout the archean until the great oxidation event goe at ca 2 4 ga implying that previous inferences of pre goe oxygen production may reflect oxygen oases transient oxidation events or oxygen levels below those required for io 3 accumulation the data suggest formation and persistence of io 3 and consequently surface ocean oxygen concentrations of at least 1 m during the goe following the initial rise of oxygen carbonate associated iodine in globally extensive carbonate units deposited during the lomagundi positive carbon isotope excursion at ca 2 22 2 1 ga suggests a widespread aerobic iodine cycle beyond that operating prior to the event synchronous with high relative rates of organic carbon burial and apparent expansion of oxidative conditions

upper ocean oxygenation dynamics from i ca ratios during the cenomanian turonian oae 2 global warming lowers the solubility of gases in the ocean and drives an enhanced hydrological cycle with increased nutrient loads delivered to the oceans leading to increases in organic production the degradation of which causes a further decrease in dissolved oxygen in extreme cases in the geological past this trajectory has led to catastrophic marine oxygen depletion during the so called oceanic anoxic events oaes how the water column oscillated between generally oxic conditions and local global anoxia remains a challenging question exacerbated by a lack of sensitive redox proxies especially for the suboxic window to address this problem we use bulk carbonate i ca to reconstruct subtle redox changes in the upper ocean water column at seven sites recording the cretaceous oae 2 in general i ca ratios were relatively low preceding and during the oae interval indicating deep suboxic or anoxic waters exchanging directly with near surface waters however individual sites display a wide range of initial values and excursions in i ca through the oae interval reflecting the importance of local controls and suggesting a high spatial variability in redox state both i ca and an earth system model suggest that the northeast proto atlantic had notably higher oxygen levels in the upper water column than the rest of the north atlantic indicating that anoxia was not global during oae 2 and that important regional differences in redox conditions existed a lack of correlation with calcium lithium and carbon isotope records suggests that neither enhanced global weathering nor carbon burial was a dominant control on the i ca proxy during oae 2

carbon isotope δ13ccarb stratigraphy of the lower middle ordovician tremadocian darriwilian in the great basin western united states implications for global correlation abstract new stable carbon isotope data 13ccarb from lower middle ordovician tremadocian to darriwilian carbonate mudstone and wackestone rocks of the pogonip group are presented from two sections in the great basin region usa shingle pass east central nevada and the ibex area western utah the pogonip group is a succession of mixed carbonate and siliciclastic rocks that accumulated on a carbonate ramp under normal marine conditions during the late cambrian furongian to middle ordovician darriwilian the shingle pass and ibex area sections have been previously studied for their conodont biostratigraphy and contain a north american midcontinent conodont fauna that range from the cordylodus intermedius zone uppermost cambrian to the phragmodus polonicus zone darriwilian the 13c trend has four distinct characteristics recognized in both great basin sections 1 a drop in 13c from 1 at the base of the ordovician tremadocian to 0 7 2 a 1 to 2 positive 13c shift in the uppermost rossodus manitouensis zone during the late tremadocian 3 a gradual 13c increase from 2 to ca 0 during the end of the early ordovician floian and 4 a steady 13c decrease from 0 to 4 to 5 during middle ordovician dapingian darriwilian in the lower ordovician 13c trends reported here from the great basin are not consistent with a causal mechanism involving sea level change and the migration of isotopically distinct water bodies instead these lower ordovician isotope data most likely reflect primary seawater chemistry and changes in 13c on a global scale this interpretation is supported by the excellent correlation of 13c in the lower ordovician to other 13c trends reported from the sections in the argentine precordillera la silla and san juan formations and in western newfoundland st george and table head groups these correlations using 13c are consistent with published biostratigraphic data and provide an integrated and high resolution chemo biostratigraphic framework for the lower ordovician sedimentary record of the laurentian margin the middle ordovician portion of the 13c curves in the great basin represented by the kanosh and lehman formations shows significant isotopic depletion relative to the section in argentina thus although there is some indication that minima and maxima in the middle ordovician curves can be correlated the great basin sections show clear evidence of overprinting by local variables related to both diagenesis dolomitization and platform restriction

sulfur isotopes track the global extent and dynamics of euxinia during cretaceous oceanic anoxic event 2 the mesozoic era is characterized by numerous oceanic anoxic events oaes that are diagnostically expressed by widespread marine organic carbon burial and coeval carbon isotope excursions here we present coupled high resolution carbon and sulfur isotope data from four european oae 2 sections spanning the cenomanian turonian boundary that show roughly parallel positive excursions significantly however the interval of peak magnitude for carbon isotopes precedes that of sulfur isotopes with an estimated offset of a few hundred thousand years based on geochemical box modeling of organic carbon and pyrite burial the sulfur isotope excursion can be generated by transiently increasing the marine burial rate of pyrite precipitated under euxinic i e anoxic and sulfidic water column conditions to replicate the observed isotopic offset the model requires that enhanced levels of organic carbon and pyrite burial continued a few hundred thousand years after peak organic carbon burial but that their isotope records responded differently due to dramatically different residence times for dissolved inorganic carbon and sulfate in seawater the significant inference is that euxinia persisted post oae but with its global extent dwindling over this time period the model further suggests that only 5 of the global seafloor area was overlain by euxinic bottom waters during oae 2 although this figure is 30 greater than the small euxinic fraction present today 0 15 the result challenges previous suggestions that one of the best documented oaes was defined by globally pervasive euxinic deep waters our results place important controls instead on local conditions and point to the difficulty in sustaining whole ocean euxinia

holocene secular variation in western north america paleomagnetic record from fish lake harney county oregon an 8 9 m composite section of lake sediment from fish lake steens mountain southeastern oregon has provided a high resolution record of holocene geomagnetic secular variation in western north america the section is composed of overlapping core segments with stratigraphic control based on six tephra layers and other thin distinct bands and with age control from 37 radiocarbon dates the 455 paleomagnetic samples possess a strong and stable magnetic remanence which is carried by pseudo single domain magnetite paleomagnetic records for individual core segments show low scatter and high serial correlation and where the segments overlap there is excellent agreement between records the azimuthal orientation of the composite section was recovered from the known direction of the geomagnetic field at the time of the climactic eruption of mount mazama tephra which is present in fish lake both internal and external evidence including the correspondence with an archaeomagnetic record from the southwestern united states support the conclusion that the fish lake record represents the history of geomagnetic field behavior during at least the last 10 000 years b p analysis of that record reveals that the average geomagnetic direction can not be distinguished from that of a geocentric axial dipole field and that the overall circularity of the field was clockwise but the detailed behavior was quite complex angular standard deviations of both field directions and virtual geomagnetic poles differ significantly from the values predicted from theoretical models of secular variation but are consistent with those of other holocene records when the record from fish lake is compared to the proposed type curve for east central north america there is excellent agreement for the past 6000 years provided the curves are offset by about 400 years this offset corresponds to a rate of westward drift of about 0 062 yr beyond about 6000 radiocarbon years ago good agreement between the two curves occurs when there is no offset suggesting that the field was standing rather than drifting during this time

diagenesis in anoxic sediments from the california continental borderland and its influence on iron sulfur and magnetite behavior solid phase and pore water profiles of compounds containing iron and sulfur have been determined by wet chemical magnetic and x ray diffraction techniques in three california continental borderland basins the observed profiles have been fit by simple reaction diffusion models in order to determine reaction rates and constrain budgets for iron and sulfur more than 95 of the solid phase reduced sulfur is pyrite and down core profiles are well fit by a model in which net sulfate reduction rates decrease exponentially with depth net sulfate reduction rates determined from models fit to solid phase reduced sulfur measurements and pore water sulfate profiles yield results that are consistent depth integrated sulfate reduction rates for modern sediments in san pedro santa catalina and san nicolas basins are 11 4 6 3 and 6 3 8 8 mol cm 2yr 1 respectively measurements of solid phase iron species indicate that surficial sediments are enriched in easily reducible ferric oxyhydroxides the enrichment is maintained by a combination of oxidation of fe2 diffusing upward from underlying anoxic sediments as well as input of fresh sediment enriched in ferric oxyhydroxides the three primary sources for iron converted to pyrite and the sequence in which they are utilized are ferric oxyhydroxides magnetite and other crystalline oxides and exchangeable iron in phyllosilicates the majority 50 80 of the iron converted to pyrite is from the silicates and budgetary calculations indicate the amount of iron released from san pedro basin silicates agrees within 35 with the amount of magnesium removed from pore water to solid phases fe2 is enriched in near surface pore waters because rates of dissolved iron production by oxyhydroxide reduction exceed rates of sulfate reduction and pyrite formation at depth pore waters are sulfidic because rates of sulfate reduction exceed rates of iron release from silicates sulfide produced at depth diffuses upward until it reaches sediments with available iron causing a step like increase in solid phase sulfur concentration over 90 of the magnetite present in surficial sediments is dissolved at depth due to reaction with h2s a model is developed to predict the depth at which magnetite dissolution should occur based on sulfate reduction rates and the flux of ferric oxyhydroxides the results of this model predict the onset of dissolution at depths of 5 40 cm in different basins and agree well with the observed depths of magnetite dissolution

paleomagnetism of late quaternary marine sediments from santa catalina basin california continental borderland paleomagnetic secular variation psv records have been recovered from three marine sediment cores from santa catalina basin california continental borderland in order to more accurately date these late quaternary sediments the psv records are not high in resolution due to low sedimentation rates coupled with a 3 cm sampling interval and some inherent smoothing of the psv signal during remanence lock in however the psv waveforms are sufficiently clear to permit their correlation among the three separate cores these psv records can also be correlated with four independent psv calibration curves from western north america that have detailed radiocarbon age control the four calibration curves are developed in this paper to improve the dating and regional comparison of psv records from western north america the psv correlations establish time depth curves for the three cores which indicate that the sediments are all younger than about 11 000 years b p the relative accuracy of the time depth curves is approximately 200 years which represents an order of magnitude improvement in the chronology of these sediments sedimentation rates derived from the three time depth curves indicate a constant rate of 20 25 cm kyr for the last 6700 years throughout santa catalina basin and more variable rates but constant within each core of 13 86 cm kyr prior to 6700 years b p in all three cores the change in sedimentation rate corresponds to a subtle but distinct change in lithology these changes probably indicate a major shift in paleoceanographic processes within santa catalina basin 6700 years b p

late quaternary paleomagnetic field secular variation from two minnesota lakes detailed paleomagnetic records from the wet sediments of two minnesota lakes are the basis for estimating the local secular variation of the earth s magnetic field during late quaternary time results from lake st croix cover the interval 0 9500 years b p and results from kylen lake cover the interval 4000 14 000 years b p paleomagnetic data were recovered from two replicate cores in each lake by sampling the sediments at 3 to 10 cm intervals analysis of the potential errors in the results indicates that all cores were correctly oriented in the vertical plane but that some azimuthal offsets of individual core segments did occur various methods for correcting the occasional azimuthal offsets are described the final paleomagnetic data sets from each lake show a high degree of internal consistency these results also show close correspondence 1 between the two lakes 2 with the known historic magnetic field variation and 3 with paleomagnetic results from dated archeological material and lava flows from the western united states rock magnetic analysis of the lake sediments indicates that the natural remanent magnetization is the result of a physical remanence acquisition process detrital remanent magnetization active at or near the sediment water interface there is no evidence for a systematic inclination error in the results statistical analysis of vector time series determined from the paleomagnetic data indicates that both the field vector and virtual geomagnetic pole vgp distributions are non fisherian and essentially axial dipolar when averaged over 10 000 years spectral analysis of the scalar inclination and declination suggests that the field behavior is separable into a dominant low frequency dipolelike waveform period of 9500 years and a higher frequency band irregular waveform fundamental period of 2400 years with multiples at 1200 800 and 600 years that may represent the nondipole field this irregular waveform is interpreted as resulting from zonal drift of the nondipole field past minnesota on the basis of waveform morphology and vgp circularity zonal drift of the nondipole field plus a low frequency dipole variation can account for almost all of the observed paleomagnetic field variation

paleosecular variations 0 19 000 years recorded by sediments from escondido lake argentina abstract paleomagnetic and sedimentological studies carried out on four cores about 11 m long from the bottom sediments of escondido lake southwestern argentina are described this lake is geologically related to the set of lakes of glacial origin located in western patagonia using several magnetic studies the predominance of pseudo single single domain magnetite as main carrier as well as an increase of concentration and grain size with depth was determined the pairs of magnetic susceptibility and intensity of remanent magnetization profiles show a good correlation with the sedimentological macroscopic descriptions and also with those of shorter cores previously studied the stability of the natural remanent magnetization was investigated by alternating field demagnetization within lake correlation was based on lithology magnetic susceptibility and intensity of remanent magnetization because the patterns of these parameters showed similarity for every core radiocarbon dating suggests higher deposition rates during the early stage of the lacustrine basin late pleistocene the transfer function depth age also allowed constructing a secular variation record from south argentina for the past 19 000 years the declination and inclination logs show some anomalous directions at about 18 000 calibrated years

marine redox variability from baltica during extinction events in the latest ordovician early silurian abstract it is well documented that upper ordovician and silurian successions record multiple marine turnover events including the second largest mass extinction in the phanerozoic widespread glaciation and multiple global carbon cycle perturbations whereas causal mechanisms for the late ordovician major mass extinction event involving climate paleoceanographic variation and 13c records have been published similar records remain poorly constrained for subsequent extinction events in the early silurian here we present new organic matter carbon isotope 13corg chemostratigraphy and corresponding paleoredox proxies fe speciation mn v mo and pyrite sulfur isotopes from two organic rich drill core sections in sweden and latvia that span the upper katian through lower wenlock stages 446 431 ma pyritized fe and bulk sedimentary mn concentrations from upper ordovician strata in southern sweden suggest a local redox shift to more reducing conditions in the late hirnantian possibly including euxinic anoxic and sulfidic water column conditions that coincide with the second mass extinction pulse the new high resolution 13corg and 34spyr datasets from the late aeronian early silurian interval within both drill cores show positive excursions that are broadly coincident with the associated sandvika and sedgwickii extinction events independently fe speciation and bulk sedimentary trace metal data from this late aeronian interval record locally euxinic conditions in both the deep basinal sweden and distal shelf latvia settings before and during the late aeronian positive 13c excursion this multiproxy paleoredox dataset provides the first direct evidence for local to regional expansion of reducing marine conditions coincident with this early silurian late aeronian biotic event and positive 13c excursion additionally new 34spyr values spanning the llandovery wenlock boundary interval in the latvia core show a positive excursion coincident with fe speciation and trace metal enrichments that imply a local redox perturbation with intermittently euxinic bottom waters during the rising limb of the ireviken positive 13c excursion the combination of these geochemical data for local to regional scale more data required for global interpretations changes in marine redox conditions with paleobiological records and evidence for eustatic sea level rise indicate that environmental stresses related to an expansion of anoxic to euxinic conditions were a probable driver for several extinction events during the latest ordovician early silurian

sulfide mineral oxidation and subsequent reactive transport of oxidation products in mine tailings impoundments a numerical model a versatile numerical model that couples oxygen diffusion and sulfide mineral oxidation pyrox has been developed to simulate the oxidation of pyrite in the vadose zone of mine tailings a shrinking core oxidation model and a finite element numerical scheme are used to simulate the transport of oxygen and oxidation of pyrite grains the rate of pyrite oxidation is assumed to be limited by the transport of oxygen to the reaction site the model determines the spatially variable bulk diffusion coefficient for oxygen on the basis of moisture content porosity and temperature all of which are variable input parameters the model pyrox has been coupled to an existing reactive transport model mintran which uses a finite element scheme for transport of contaminants and minteqa2 to solve for the equilibrium geochemistry the reactions described by mintran are subject to the local equilibrium assumption the resulting model mintox is capable of simulating tailings impoundments where the oxidation of pyrite or pyrrhotite is causing acidic drainage and where acid neutralization and attenuation of dissolved metals can be attributed to equilibrium reactions because mintox uses realistic boundary conditions and hydrogeological properties the potential benefits of various remediation schemes such as moisture retaining covers can be quantitatively evaluated

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

proterozoic ocean redox and biogeochemical stasis the partial pressure of oxygen in earth s atmosphere has increased dramatically through time and this increase is thought to have occurred in two rapid steps at both ends of the proterozoic eon 2 5 0 543 ga however the trajectory and mechanisms of earth s oxygenation are still poorly constrained and little is known regarding attendant changes in ocean ventilation and seafloor redox we have a particularly poor understanding of ocean chemistry during the mid proterozoic 1 8 0 8 ga given the coupling between redox sensitive trace element cycles and planktonic productivity various models for mid proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients with potential ecological constraints on emerging eukaryotic life here we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates we find that the metal enrichment record implies a proterozoic deep ocean characterized by pervasive anoxia relative to the phanerozoic at least 30 40 of modern seafloor area but a relatively small extent of euxinic anoxic and sulfidic seafloor less than 1 10 of modern seafloor area our model suggests that the oceanic mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of mo and chromium enrichments through time is consistent with the possibility of a mo n colimited marine biosphere during many periods of earth s history

organically bound iodine as a bottom water redox proxy preliminary validation and application abstract carbonate associated iodine i ca has been used as a proxy of local upper ocean redox conditions and has successfully demonstrated highly dynamic spatial and temporal patterns across different time scales of earth history to further explore the utility of iodine as a paleo environmental proxy we present here a new method of extracting organically bound iodine iorg from shale using volumes of samples on the order of tens of milligrams thus offering the potential for high resolution work across thin shale beds the ratio of iorg to total organic carbon i toc in modern surface and subsurface sediments decreases with decreasing bottom water oxygen which may be used to reconstruct paleo redox changes as a proof of concept we evaluate the i toc proxy in holocene sediments from the baltic sea landsort deep iodp 347 and discuss those data within a framework of additional independent redox proxies e g iron speciation and mo the results imply that i toc may be sensitive to hypoxic suboxic conditions complementary to proxies sensitive to more reducing anoxic euxinic conditions then we test the usage of i toc in sediments deposited during late cretaceous cenomanian turonian oceanic anoxic event oae 2 from 94 million years ago ma we generated i toc and iorg records from six oae 2 sections tarfaya morocco furlo central italy demerara rise western equatorial atlantic cape verde basin eastern equatorial atlantic south ferriby uk and kerguelen plateau southern indian ocean which provide a broad spatial coverage generally i toc decreases over the interval recorded by the positive carbon isotope excursion the global signature of oae 2 suggesting an expansion of more reducing bottom water conditions and consistent with independent constraints from iron speciation and redox sensitive trace metals e g mo relatively higher i toc values thus more oxic conditions are recorded at two high latitude sites for oae 2 supporting previous model simulations cgenie that indicated higher bottom water oxygen concentrations in these regions our results also indicate that organic rich and oxygenated seafloors are likely a major sink of iodine and correspondingly influence its global seawater inventory

empirical links between trace metal cycling and marine microbial ecology during a large perturbation to earth s carbon cycle abstract understanding the global redox state of the oceans and its cause and effect relationship with periods of widespread organic carbon deposition is vital to interpretations of earth s climatic and biotic feedbacks during periods of expanded oceanic oxygen deficiency here we present a compilation of new and published data from an organic rich locality within the proto north atlantic ocean during the cenomanian turonian boundary event that shows a dramatic drawdown of redox sensitive trace elements iron geochemistry independently suggests euxinic deposition i e anoxic and sulfidic bottom waters for the entire section thus confirming its potential as an archive of global marine metal inventories in particular depleted molybdenum mo and vanadium v concentrations effectively record the global expansion of euxinic and oxygen deficient but non sulfidic waters respectively the v drawdown precedes the oae fingerprinting an expansion of oxygen deficiency prior to an expansion of euxinia molybdenum drawdown in contrast is delayed with respect to v and coincides with the onset of oae2 parallel lipid biomarker analyses provide evidence for significant and progressive reorganization of marine microbial ecology during the oae in this region of the proto north atlantic with the smallest relative eukaryotic contributions to total primary production occurring during metal depleted intervals this relationship may be related to decreasing supplies of enzymatically important trace elements similarly box modeling suggests that oceanic drawdown of mo may have approached levels capable of affecting marine nitrogen fixation predictions of possible nitrogen stress on eukaryotic production locally and globally are consistent with the low observed levels of mo and a rise in 2 methylhopane index values during the peak of the oae at the same time the environmental challenge presented by low dissolved oxygen and euxinia coincides with increased turnover rates of radiolarian clades calcareous nanofossils and foraminifera suggesting that the temporal patterns of anoxia euxinia and associated nutrient limitation may have contributed to the fabric of oae2 related turnover

iodine content of the carbonates from the doushantuo formation and shallow ocean redox change on the ediacaran yangtze platform south china abstract the ediacaran period 635 541 ma is characterized by remarkable carbon isotope 13c excursions significant ocean redox changes and rapid diversification of eukaryotes including early animals these biological and geochemical events are commonly thought to be linked but their causal relationships remain controversial a particular point relates to the shallow ocean redox change across the negative 13c excursions most existing geochemical proxy data focused on tracking the redox conditions of deep or bottom water columns and provided limited information about the surface ocean ratios of iodine to calcium magnesium i ca mg from carbonates represent one of the few redox proxies that track the oxidation state of the shallow oceans here we report paired carbonate carbon isotopes 13ccarb and i ca mg ratios of the doushantuo formation from a drillcore section at daotuo paleogeographically located at the slope of the ediacaran yangtze platform south china in addition we compare the i ca mg ratios across the shuram upper doushantuo 13ccarb excursion in four sections of a shelf to slope transect in the slope section at daotuo the 13ccarb of the doushantuo formation shows three negative anomalies that are correlatable with those documented from the yangtze gorges area shelf and the siduping section slope the i ca mg ratios of the doushantuo formation from the drillcore are dominated by low but non zero

halogens cl br and i geochemistry in middle triassic carbonates implications for salinity and diagenetic alteration of i ca mg ratios abstract as an important family of elements halogens cl br and i have been widely used to study geological processes particularly in high temperature environments showing great prospects either in fundamental or in applied studies however little work has been conducted for sedimentary and low temperature diagenetic environments re construction although these elements have the potential in theory here we perform a pilot study on this issue using a case study of middle triassic marine dolomitization in south china our results show that the average cl concentrations in limestone dolomitic limestone calcitic dolomite and dolomite are 88 3 ppm 114 7 ppm 121 3 ppm and 142 9 ppm respectively and the corresponding br concentrations are 1 15 ppm 1 42 ppm 1 59 ppm and 2 13 ppm respectively both the concentrations of cl and br increased with the increasing dolomitization degree the increasing tendency of cl and br is similar to the seawater evaporation trajectory before halite precipitation indicating that dolomitization occurs in fluids with elevated salinity meanwhile the difference of cl br ratios between our carbonate samples and seawater may be ascribed to the input of terrestrial water which has variable cl br ratios as for the concentration of i the mean values sharply decreased from 0 36 ppm in limestone to 0 13 ppm in dolomitic limestone samples and it further lowered to 0 09 ppm and 0 08 ppm in calcitic dolomite and dolomite samples respectively the calculated i ca mg ratios in limestones vary between 0 05 and 0 58 mol mol with an average value of 0 29 mol mol indicating that limestone formed in open ocean oxygen minimum zone omzs or anoxic basin environment the average i ca mg ratio decreases from 0 29 mol mol in limestone to 0 06 mol mol in dolomite serving as an important case that dolomitization decreases i ca mg ratios of carbonates rocks halogens in carbonates therefore have promising potential for investigating the sedimentary and diagenetic environments of carbonate rocks

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

a statistical model to relate pyrite oxidation and oxygen transport within a coal waste pile case study alborz sharghi northeast of iran this paper presents a statistical model for predicting pyrite fraction remaining in a coal waste pile at the alborz sharghi coal mine located at northeast of iran this model calculates the fraction of pyrite remaining using mole fraction of oxygen diffused into the pore spaces of the pile and the pile depth comparison of the statistical outputs revealed that a second order polynomial expression with respect to oxygen mole fraction and depth provides a better correspondence to the field measurements for the fraction of pyrite remaining with a rmse of 0 089231 besides two statistical relationships have been proposed for the remaining pyrite fraction and the mole fraction of oxygen versus the pile depth a quadratic polynomial shows the best correlation of the field measured data the suggested models were successfully validated with the acceptable confidence levels of 92 and 90 for remaining pyrite and oxygen using a new data set which revealed the fact that they can be applied in similar situations both statistical analysis and field data indicate that the pyrite oxidation process is limited to the shallower depths of the waste pile where the mole fraction of oxygen decreased rapidly

iodine to calcium ratios in marine carbonate as a paleo redox proxy during oceanic anoxic events periods of globally distributed extreme oxygen depletion so called oceanic anoxic events oaes have been recognized in the mesozoic geological record and appear to be characteristic of episodes of extreme warmth here we explore the application of iodine calcium ratios i ca in marine carbonate as a new geochemical proxy to constrain seawater redox change and provide additional insights into the response of ocean chemistry to ancient climatic warming iodine has long been known as a redox sensitive and biophilic element mainly present as iodate and iodide in seawater iodate converting to iodide under anoxic conditions laboratory experiments growing calcite crystals from solutions spiked with iodate show that this is the ionic species incorporated into the carbonate structure likely substituting for the co 3 2 ion a fall in the i ca ratio measured in carbonates formed in shallow water by marine calcifiers during the early toarcian and cenomanian turonian oaes is interpreted both as a response to a decrease in the iodate iodide ratio in ocean waters and the drawdown of the global iodine inventory under conditions of accelerated organic matter burial the results suggest that i ca ratios in carbonates may be used to monitor seawater oxidation levels throughout earth history

evidence for local and global redox conditions at an early ordovician tremadocian mass extinction abstract profound changes in environmental conditions particularly atmospheric oxygen levels are thought to be important drivers of several major biotic events e g mass extinctions and diversifications the early paleozoic represents a key interval in the oxygenation of the ocean atmosphere system and evolution of the biosphere global proxies e g carbon 13c and sulfur 34s isotopes are used to diagnose potential changes in oxygenation and infer causes of environmental change and biotic turnover the cambrian ordovician contains several trilobite extinctions some are apparently local but others are globally correlative that are attributed to anoxia based on coeval positive 13c and 34s excursions these extinction and excursion events have yet to be coupled with more recently developed proxies thought to be more reflective of local redox conditions in the water column e g i ca to confirm whether these extinctions were associated with oxygen crises over a regional or global scale here we examine an early ordovician tremadocian stage extinction event previously interpreted to reflect a continuation of recurrent early paleozoic anoxic events that expanded into nearshore environments 13c 34s and i ca trends were measured from three sections in the great basin region to test whether i ca trends support the notion that anoxia was locally present in the water column along the laurentian margin evidence for anoxia is based on coincident but not always synchronous positive 13c and 34s excursions mainly from carbonate associated sulfate and less so from pyrite data a 30 extinction of standing generic diversity and near zero i ca values although evidence for local water column anoxia from the i ca proxy broadly agrees with intervals of global anoxia inferred from 13c and 34s trends a more complex picture is evident where spatially and temporally variable local trends are superimposed on time averaged global trends stratigraphic sections from the distal and deeper part of the basin shingle pass and meiklejohn peak preserve synchronous global 13c and 34s and water column i ca evidence for anoxia but not at the more proximal section ibex ut although geochemical and paleontological evidence point toward anoxia as the driver of this early ordovician extinction event differences between i ca and 13c 34s signals suggest regional variation in the timing extent and persistence of anoxia

lower cretaceous magnetic stratigraphy in umbrian pelagic limestone sections abstract the magnetic stratigraphy of the lower cretaceous pelagic maiolica limestone has been investigated in three partially correlative sections at gorgo a cerbara presale and frontale in the northern umbrian apennines of central italy the white well bedded limestone has a magnetic mineralogy dominated by magnetite stable magnetic directions isolated by thermal demagnetization define alternating polarity zones in each section the magnetozone patterns are distinctive and can be correlated with the geomagnetic reversal history derived from the m sequence marine magnetic anomalies the three new sections confirm the polarity sequence for anomalies m0 to m10n although the maiolica is inadequately dated the correlated anomalies together with the results of other investigations allow tentative associations of anomalies m0 m19 with individual stages in the lower cretaceous and upper tithonian the investigations also demonstrate the usefulness of magnetic stratigraphy in basin analysis they yield mean sedimentation rates confirm that there is a hiatus between the base of the presale section and the underlying jurassic formations and show that a large part of the frontale section has been cut out by faulting

dynamic sulfur and carbon cycling through the end ordovician extinction revealed by paired sulfate pyrite δ34s geochemical records of the end ordovician hirnantian stage show parallel positive excursions in the stable isotope compositions of sedimentary pyrite sulfur 34spyr organic carbon 13corg and carbonate carbon 13ccarb these isotope excursions coincide with the end ordovician glaciation and mass extinction a relative increase in pyrite burial fpyr attributed to marine anoxia has been invoked to explain the sulfur isotope excursion and link oceanic redox conditions to the extinction of marine fauna an increase in fpyr would necessarily generate a parallel excursion of equal magnitude in the isotopic composition of coeval marine sulfate 34sso4 34sso4 here we present new high resolution paired sulfur isotope data from carbonate associated sulfate 34scas and pyrite from the hirnantian stage of western anticosti island quebec canada these data document a positive 20 enrichment in 34spyr comparable in magnitude to previous reports but no parallel excursion in 34scas this pattern provides new constraints on the origin of the 34spyr excursion and the nature of carbon sulfur coupling through hirnantian time specifically these observations preclude enhanced pyrite burial as the cause of the hirnantian 34spyr excursion and suggest the possible role of anoxia in the mass extinction may need to be reevaluated rather the global 34spyr excursion is best explained by a transient reduction in the isotopic fractionations expressed during microbial sulfur cycling epyr the epyr record shows a strong inverse correlation with 13c suggesting a mechanistic link between carbon cycling and processes controlling epyr during the hirnantian changes in sea level or marine redox state associated with glaciation could further impact the expression of the biological fractionation e g through syndepositional sediment reworking and or chemocline migration and resultant restricted exchange of porewater sulfate the magnitude of isotopic fractionation during microbial sulfate reduction is partially controlled by metabolic rates which are sensitive to the abundance type and lability of metabolically relevant substrates environmental change associated with the end ordovician glaciation may have elevated the flux of organic material to marine sediments or caused an increase in physical reworking of sediments leading to increased microbial sulfate reduction rates and reduced epyr as such the hirnantian 34spyr excursion may be viewed as a dynamic biological response to global climate change highlighting the connections between the carbon and sulfur biogeochemical cycles

persistent oceanic anoxia and elevated extinction rates separate the cambrian and ordovician radiations recurrent mass extinction events at biomere a biostratigraphic unit boundaries characterize the middle cambrian to early ordovician tremadocian time interval that is between the major cambrian and ordovician radiations of animal life a role for anoxia in maintaining elevated extinction rates in the late cambrian has been proposed based on coincidence of an extinction with positive excursions in 13ccarb and 34scas cas carbonate associated sulfate here we examine an early ordovician extinction event at the base of the north american stairsian stage upper tremadocian and demonstrate concurrent onset of positive excursions in 13c and 34s inferred to reflect enhanced organic matter burial under anoxic waters sea level rise may have brought anoxic waters onto the shelf to initiate extinctions the evidence for 13c excursions and elevated extinction rates appears to wane in the tremadocian consistent with progressive oxygenation of the oceans reaching a threshold that helped facilitate initial stages of the great ordovician biodiversification event

investigation of pyrite oxidation and acid mine drainage characterization associated with razi active coal mine and coal washing waste dumps in the azad shahr ramian region northeast iran acid mine drainage amd pollution is considered to be the most serious water pollution problem in mining areas amd containing iron sulfates and other components can affect the receiving water bodies pyrite oxidation and amd generation can be considered as important processes that may take place in the wastes produced by coal mining and coal washing operations in the golestan province northeast iran the study area is characterized by appropriate atmospheric conditions that favor pyrite oxidation and the presence of a large amount of water bodies this study attempts to consider pyrite oxidation and amd generation in the azad shahr ramian region the impact of amd on the quality of the surface water bodies was investigated by taking samples and analyzing them for hydro geochemical parameters stiff and piper diagrams were used to represent chemical analyses of water samples the coal samples taken from different depths at four points on two different coal waste dumps were analyzed to find the fraction of pyrite that remained in the waste particles to investigate the pyrite oxidation process a computational fluid dynamic package called phoenics was used to model pyrite oxidation process numerically the results obtained from the geochemical analyses of water and coal samples and numerical simulation show pyrite oxidation and acid generation in the region however the presence of carbonate rocks raised the ph of the water samples the drainages of the razi mine may be recognized as natural alkaline mine drainages

i ca evidence for upper ocean deoxygenation during the petm anthropogenic global warming affects marine ecosystems in complex ways and declining ocean oxygenation is a growing concern forecasting the geographical and bathymetric extent rate and intensity of future deoxygenation and its effects on oceanic biota however remains highly challenging because of the complex feedbacks in the earth ocean biota system information on past global warming events such as the paleocene eocene thermal maximum petm 55 5 ma a potential analog for present and future global warming may help in such forecasting documenting past ocean deoxygenation however is hampered by the lack of sensitive proxies for past oceanic oxygen levels throughout the water column as yet no evidence has been presented for pervasive deoxygenation in the upper water column through expansion of oxygen minimum zones omzs we apply a novel proxy for paleoredox conditions the iodine to calcium ratio i ca in bulk coarse fraction sediment and planktonic foraminiferal tests from pelagic sites in different oceans and compared our reconstruction with modeled oxygen levels the reconstructed iodate gradients indicate that deoxygenation occurred in the upper water column in the atlantic indian oceans and possibly the pacific ocean as well during the petm due to vertical and potentially lateral expansion of omzs

patterns of local and global redox variability during the cenomanian turonian boundary event oceanic anoxic event 2 recorded in carbonates and shales from central italy careful evaluation of the local geochemical conditions in past marine settings can provide a window to the average redox state of the global ocean during episodes of extensive organic carbon deposition these comparisons aid in identifying the interplay between climate and biotic feedbacks contributing to and resulting from these events well documented examples are known from the mesozoic era which is characterized by episodes of widespread organic carbon deposition known as oceanic anoxic events this organic carbon burial typically leads to coeval positive carbon isotope excursions geochemical data are presented here for several palaeoredox proxies cr ti v mo zn mn fe speciation i ca and sulphur isotopes from a section exposed at furlo in the marche umbrian apennines of italy that spans the cenomanian turonian boundary here oceanic anoxic event 2 is represented by a ca 1 m thick radiolarian rich millimetre laminated organic rich shale known locally as the bonarelli level iron speciation data for thin organic rich intervals observed below the bonarelli level imply a local redox shift going into the oceanic anoxic event with ferruginous conditions i e anoxic with dissolved ferrous iron transiently developed prior to the event and euxinia i e anoxic and sulphidic bottom waters throughout the event itself pre oceanic anoxic event enrichments of elements sensitive to anoxic water columns were due to initial development of locally ferruginous bottom waters as a precursor to the event however the greater global expanse of dysoxic to euxinic conditions during the oceanic anoxic event greatly reduced redox sensitive trace metal concentrations in seawater pyrite sulfur isotopes document a positive shift leading into the oae carbonate i ca ratios were generally low suggesting locally reduced bottom water oxygen conditions preceding the event and relatively increased o2 concentrations post event combined the furlo geochemical data suggest a redox stratified water column with oxic surface waters and a shallow chemocline overlying locally ferruginous bottom waters preceding the event globally widespread euxinic bottom waters during the oceanic anoxic event followed by chemocline shallowing but sustained local redox stratification following the event this article is protected by copyright all rights reserved

mapping the flow pathways and contaminants transportation around a coal washing plant using the vlf em geo electrical and ip techniques a case study ne iran coal washing operation is now being carried out in the alborz sharghi plant located in northeast of iran this can in effect create a number of environmental problems in this research different geophysical surveys were conducted to investigate the leachate flow pathways and time dependent transportation of contaminants in downstream of the plant which is situated between a coal waste pile and tailings impoundments the very low frequency survey identified the most likely contamination zones and flow pathways furthermore two dimensional resistivity models obtained by the inversion of geoelectrical data measured with the use of a dipole dipole array incorporating a time laps technique showed the contaminated plumes with low resistivity values 1 m to carry out a time laps technique 2 d geoelectrical surveys were repeated at same profiles by a time interval of 6 months the results distinguished a time dependent movement of the plume in a lateral and longitudinal form as well as its further extension to the deeper layers towards the groundwater table this was also verified by the results obtained by the induced polarization measurements

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

paleomagnetic secular variation records from holocene sediments of lake victoria 0 5 s 33 3 e we have conducted a paleomagnetic study of holocene sediments from lake victoria in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv

expanded oxygen minimum zones during the late paleocene early eocene hints from multiproxy comparison and ocean modeling anthropogenic warming could well drive depletion of oceanic oxygen in the future important insight into the relationship between deoxygenation and warming can be gleaned from the geological record but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions we use i ca in benthic foraminifera to reconstruct late paleocene through early eocene bottom and pore water redox conditions in the south atlantic and southern indian oceans and compare our results with those derived from mn speciation and the ce anomaly in fish teeth we conclude that waters with lower oxygen concentrations were widespread at intermediate depths 1 5 2 km whereas bottom waters were more oxygenated at the deepest site in the southeast atlantic ocean 3 km epifaunal benthic foraminiferal i ca values were higher in the late paleocene especially at low oxygen sites than at well oxygenated modern sites indicating higher seawater total iodine concentrations in the late paleocene than today the proxy based bottom water oxygenation pattern agrees with the site to site o2 gradient as simulated in a comprehensive climate model community climate system model version 3 but the simulated absolute dissolved o2 values are low 35 mol kg while higher o2 values 60 100 mol kg were obtained in an earth system model grid enabled integrated earth system model multiproxy data together with improvements in boundary conditions and model parameterization are necessary if the details of past oceanographic oxygenation are to be resolved

rock magnetic evidence for the dissolution and authigenic growth of magnetic minerals within anoxic marine sediments of the california continental borderland the rock magnetic properties of marine sediments from the california continental borderland san pedro santa catalina and san nicolas basins have been studied in order to quantitatively assess the effects of sediment diagenesis on magnetic minerals previous studies have noted that the natural remanent magnetization in these sediments primarily carried by detrital magnetite decays to 10 or less of its surface value soon after deposition this decrease is caused by magnetite dissolution related to sediment diagenesis and is unrelated to paleoclimatic variations or changes in the regional influx of detrital magnetic material detailed rock magnetic measurements show that shifts to softer remanent coercivity and differences in the rate and degree of magnetic intensity loss with depth can be related to the dissolution process the shift to softer remanent coercivity is related to a coarsening of the magnetic mineral grain sizes with depth due to preferential dissolution of the finest grained magnetic material the intensity decreases which are linearly proportional to magnetite concentration decreases indicate that dissolution occurs with rate constants ranging from 0 3 to 1 6 kyr 1 the rate constants sulfide concentrations and magnetite grain size estimates from the borderland are consistant with previous studies of magnetite dissolution our results demonstrate the importance of both sulfide and magnetite surface area in the dissolution process anomalous peaks in viscous remanence within the sediments suggest the authigenic growth of greigite and its subsequent transformation to pyrite

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

rock magnetic characteristics of surficial marine sediments from the california continental borderland abstract the rock magnetic variability of surficial marine sediments from the california continental borderland adjacent to southern california is described the data were derived from measurement of the natural nrm anhysteretic arm and isothermal irm remanent magnetization and magnetic susceptibility of 385 samples from 230 cores magnetic mineralogy studies carried out on selected samples indicate that detrital magnetite predominates throughout the borderland but there are also locally important contributions from detrital and authigenic hematite altered glauconite and biogenic magnetite maps of the distributions of various rock magnetic parameters show that 1 the proportion of magnetic material decreases outward from the coastline through dilution by organic material and carbonate 2 the magnetic grain size distribution shifts to finer average grain size outward from the coastline 3 important local contributions to the sediment magnetic material can come from erosion of submerged bank tops or ridges 4 glauconite rich zones on bank tops can be altered to remanent magnetic material that is anomalously strong in intensity and coercivity and 5 that diagenetic processes occur ubiquitously within the deep basins causing large scale dissolution of the magnetic material comparisons of arm and sirm saturation irm indicate that arm is very sensitive to grain size changes and that both the quantity arm 2 2 0 5 and sirm are good indicators of volume of remanent magnetic material in the borderland

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

construction of type curves of geomagnetic secular variation for dating lake sediments from east central north america type curves of palaeomagnetic secular variations of declination and inclination through the last 12 000 radiocarbon years have been constructed by combining data from the minnesota lakes with paral

behavior of carbonate associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy abstract although carbonate associated sulfate cas is used widely as a proxy for the sulfur isotope composition of ancient seawater little is known about the effects of diagenesis on retention of primary 34 s signals our case study of the key largo limestone pleistocene florida is the first systematic assessment of the impact of meteoric diagenesis on cas properties geochemical and petrographic data show that meteoric diagenesis has affected the exposed coralline facies to varying degrees yielding differences now expressed as sharp reaction fronts between primary and secondary carbonate minerals within individual coral heads specifically analyses across high resolution transects in the key largo limestone show that concentrations of strontium and sodium decrease across the recrystallization front from original aragonite to meteoric low magnesium calcite by factors of roughly 5 and 10 respectively predictably 18 o values decrease across these same fronts the 13 c relationships are more complex with the most depleted values observed in the latest formed calcite such trends likely reflect carbon isotope buffering capacity that decreased as reaction progressed as well as protracted development of soil profiles and the associated terrestrial biomass and thus depleted 13 c during sea level lowstand conversely 34 s values of cas vary within a narrow buffered range from 20 6 to 22 6 compared to 20 8 22 0 of coeval pleistocene seawater across the same mineralogical transition despite sulfate concentrations that drop in the diagenetic calcite by an average factor of 12 collectively these data point to robust preservation of primary 34 s for carbonates that have experienced intense meteoric diagenesis which is encouraging news for those using the isotopic composition of cas as a paleoceanographic proxy at the same time the vulnerability of cas concentrations to diagenetic resetting is clear

immobilization of copper under an acid leach of colloidal pyrite waste rocks by a fixed bed column colloidal pyrite waste rocks cpwr which are mainly composed of colloidal pyrite and siderite widely deposit in sulfide mines in the middle and lower reaches of the yangtze river belt china especially in tongling city anhui province china in this paper a fixed bed column was used to investigate the weathering and oxidation of cpwr and its role in immobilizing low concentration cu 10 mg l 1 under weakly acidic leach ph 5 0 the experimental results indicated that the breakthrough capacity was around 14 0 mg cu g 1 cpwr when cu2 breakthrough concentration was 0 5 mg l 1 sequential extraction of cu and dithionite citrate bicarbonate extraction of free iron in the used cpwr after the column breakthrough indicated that cu removal by cpwr consisted of the following processes oxidation of pyrite and dissolution of siderite in cpwr ferrous oxidation and adsorption of cu on ferric hydr oxides this study shows the potential application of cpwr as an effective sorbent for the removal of low concentration cu from acid mine drainage