geochemistry of vanadium in an epigenetic sandstone hosted vanadium uranium deposit henry basin utah the epigenetic tony m vanadium uranium orebody in south central utah is hosted in fluvial sandstones of the morrison formation upper jurassic although the deposit is mined for uranium vanadium has a higher average abundance in the ore thus the geochemistry of vanadium in the orebody was studied to characterize ore forming processes within the inferred ground water flow regime measurements of the relative amounts of v super 3 and v super 4 in ore minerals show that v super 3 is more abundant thermodynamic calculations show that vanadium was more likely transported to the site of mineralization as v super 4 the ore formed as v super 4 was reduced by hydrogen sulfide followed by hydrolysis and precipitation of v super 3 in oxide minerals e g montroseitc or paramontroseite or chlorite uranium was transported as uranyl ion u super 6 or some complex thereof and reduced by hydrogen sulfide forming coffinite detrital organic matter in the rocks served as the carbon source for sulfate reducing bacteria it was this bacteriogenic h 2 s that reduced the metals in the mineralization process possible sources for the v and u in this deposit have been identified previously vanadium most likely was derived from the dissolution of iron titanium oxides which liberated fe as well as v a zone of titanium rich remnants is observed updip and up the hydrologic gradient from the deposit m goldhaber and r l reynolds unpub data uranium probably was derived from the overlying brushy basin member of the morrison formation northrop 1982 a preliminary age date for the deposit of 115 ma k ludwig 1986 pers commun indicates that the ore formed after deposition of the brushy basin member previous studies have shown that the ore formed at the density stratified interface between a basinal brine and dilute meteoric water the mineralization processes described above occurred within the mixing zone between these two fluids stable isotope analyses of ore stage dolomite show a progressively heavier carbon and oxygen isotope signature with increasing depth through an ore horizon consistent with the two solution interface model

the changes in isotope composition and accumulation of snow at vostok station east antarctica over the past 200 years high resolution records of isotope composition dd and accumulation of snow have been obtained from 10 12 m deep snow pits dug in the vicinity of vostok station during the 1979 80 and 1999 2000 antarctic field seasons we employ meteorological balloon sounding and snow stake data to interpret the isotope record in terms of past temperature changes our reconstruction suggests that snow accumulation rate and the near surface air temperature at vostok have varied during the past 200 years between 15 and 30 kg m 2 a 1 and between 56 and 558c respectively with a slight general tendency to increase from the past to the present both parameters reveal a 50 year periodicity that correlates with the pacific decadal oscillation index implying a climatic teleconnection between central antarctica and the tropical pacific

spatial and temporal variability in isotope composition of recent snow in the vicinity of vostok station antarctica implications for ice core record interpretation continuous detailedisotope ddandd 18 o profileswereobtainedfrom eight snow pits dug in the vicinity of vostok station antarctica during the period1984 2000 in addition snow samples taken along the 1km long accumulation stake profile were measured to determine spatial variability in isotope composition of recent snow the stacked dd time series spanning the last 55years shows only weak correlation with the mean annual air temperature recorded at vostok station significant oscillations of both snow accumulation and snow isotope composition with the periods 2 5 5 20 and possibly 10 2 years observed at single points are interpreted in terms of drift of snow accumulationwaves of various scales onthe surface of the ice sheet

early diagenesis and accumulation of redox sensitive elements in east siberian arctic shelves abstract the arctic shelf makes up half of the area within the arctic ocean it plays an important role in the global carbon cycle whilst its part in the recycling process of redox sensitive elements rses is still not clear this study has selected nine sediment cores 30 to 40 cm in length covering a wide area over the east siberian arctic shelves esas and analyzed a suite of rses s mn mo u v cd in the sediments along with al fe total organic carbon toc grain size and sedimentation rate the redox environment in surface sediments was clearly divided based on the s and mn contents of the cores ranging from being more oxidized on the western east siberian sea shelf to more reduced on the chukchi sea shelf toc also showed an increasing trend eastward in the study region statistically significant correlations were found between cd and s v and fe mo and mn and u and toc implying their close relationships during early diagenetic processes at the sediment water interface across the study area authigenic accumulation occurred for all rses except mn the estimated authigenic accumulation fluxes for mo u v and cd over the entire esas are 0 21 0 09 0 086 0 043 11 0 9 2 and 0 019 0 014 108 mol y 1 respectively which are comparable to values reported in suboxic marginal sediments for mo u and cd but exceptionally high for v although the sampling resolution was coarse and there are uncertainties in the sedimentation rates and detrital background values of v we propose the authigenic accumulation flux for v on the broad and shallow esas may be a significant but missing sink term for the global v cycle

opaque minerals as keys for distinguishing oxidising and reducing diagenetic conditions in the lower triassic bunter sandstone north german basin abstract the diagenetic evolution in red and white drab parts of the bunter sandstone from outcrops and wells in the north german basin was unraveled by a detailed petrographical mineralogical and chemical study the diagenetic sequences for the red and white drab parts differ in the degree of alteration of iron bearing detrital minerals and in the authigenic opaque minerals in the white drab parts one typically sees reduction of red mica dissolution of hematite and magnetite and alteration of ilmenite and titanomagnetite to leucoxene in contrast the red parts commonly display oxidation of glauconite red zonation in ooids hematisation of magnetite biotite and magnetite host in titanomagnetite and leucoxene replacement of the ilmenite lamellae in titanomagnetite the red colour of the red bed host is due to red coatings of goethite needles and or hematite needles goethite needles precipitated in the prevailing oxidising conditions present shortly after deposition whereas pseudomorphous replacement by hematite occurred during the burial process the white drab colour of the reduced areas is the original colour of the sediment the black core in reduction spots is due to mineralization uranium and vanadium minerals coffinite montroseite and v illite in reduction spots are located close to carbonate fragments which probably contained organic matter isolated reduction spots may have formed immediately after deposition inside these were clasts eroded from algal mats formed in the sabkha environment the copper minerals typically occur in areas with high porosity reflecting the importance of access to chloride rich brines which transported dissolved copper when these brines reached reducing environments chalcocite and chalcopyrite were precipitated possibly by replacement of pyrite in the red areas these saline brines may also have promoted the second stage alteration of ilmenite in which leucoxene the first stage alteration product was impregnated with iron oxide hydroxide needles this study emphasises the importance of opaque minerals especially fe ti oxides and authigenic opaques as diagnostic for the diagenetic environment of the bunter sandstone which can thus be divided into primary reduced primary oxidised secondary reduced and secondary oxidised diagenetic environments furthermore the influence of saline brines can be detected using the opaque mineral assemblage

the little ice age climate of new zealand reconstructed from southern alps cirque glaciers a synoptic type approach little ice age lia austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the southern alps of new zealand modern analog seasons with temperature anomalies akin to the lia reconstructions were selected and then applied in a sampling of high resolution gridded new zealand climate data and global reanalysis data to generate lia climate composites at local regional and hemispheric scales the composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the lia climate state allow an interrogation of synoptic type frequency changes for the lia relative to present and provide a hemispheric context of the past conditions in new zealand an lia summer temperature anomaly of 0 56 c 0 29 c for the southern alps based on palaeo equilibrium lines compares well with local tree ring reconstructions of austral summer temperature reconstructed geopotential height at 1 000 hpa z1000 suggests enhanced southwesterly flow across new zealand occurred during the lia to generate the terrestrial temperature anomalies the mean atmospheric circulation pattern for summer resulted from a crucial reduction of the hse blocking synoptic type highs over and to the west of nz largely settled conditions and increases in both the t and sw trough synoptic types lows passing over nz enhanced southerly and southwesterly flow relative to normal associated land based temperature and precipitation anomalies suggest both colder and wetter than normal conditions were a pervasive component of the base climate state across new zealand during the lia as were colder than normal tasman sea surface temperatures proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous southern hemisphere composite z1000 and sea surface temperature patterns generated in this study a comparison of the composites to climate mode archetypes suggests lia summer climate and atmospheric circulation over new zealand was driven by increased frequency of weak el nino modoki in the tropical pacific and negative southern annular mode activity

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

diagenesis of oxyanions v u re and mo in pore waters and sediments from a continental margin this research tests the hypothesis that trace metals respond to the extent of reducing conditions in a predictable way we describe pore water and sediment measurements of iron fe manganese mn vanadium v uranium u rhenium re and molybdenum mo along a transect off washington state usa sediments become less reducing away from the continent and the stations have a range of oxygen penetration depths depth to unmeasurable o2 concentration varying from a few millimeters to five centi meters when oxygen penetrates 1 cm or less fe is reduced in the pore waters but reoxidized near the sediment water interface preventing a flux of fe 2 to overlying waters whereas mn oxides are reduced and mn 2 diffuses to overlying waters both re and u authigenically accumulate in sediments only at the most reducing location where the oxygen penetrates 0 3 cm below the sediment water interface does the surface 30 cm of sediments become reducing enough to authigenically accumulate mo stations in close proximity to the juan de fuca ridge crest are enriched in mn and fe from hydrothermal plume processes both v and mo clearly associate with mn cycling whereas u may be associating with either mn oxides and or fe oxyhydroxides rhenium is uncomplicated by adsorption to mn oxides and or fe oxyhydroxides and re accumulation in sediments appears to be due solely to the extent of reducing conditions therefore authigenic sediment re enrichment appears to be the best indicator for intermediate reducing conditions where oxygen penetrates less than 1 cm below the sediment water interface when coupled with negligible authigenic mo enrichment copyright 2005 elsevier ltd 1 introduction oceanic and atmospheric carbon cycles are strongly coupled with the ocean reservoir of dissolved inorganic carbon being 60 times larger than that of the atmosphere broecker and peng 1987 models that couple both ocean and atmosphere have been used to investigate why atmospheric carbon dioxide pco2 atm was reduced during the last glacial age and thus may be useful in predicting the environmental impact of future changes in pco2 atm some of these models require a large increase in organic carbon export through the more efficient use of nutrients to predict the lower pco2 atm observed during

insights into hydrological regime of lake vostok from differential behavior of deuterium and oxygen 18 in accreted ice 1 we use isotopic data deuterium and oxygen 18 of the recently recovered deepest vostok ice core section down to 3650 m depth to study processes leading to the formation of lake ice and the hydrological regime of subglacial lake vostok the significant variability of the lake ice isotopic content implies fluctuations in physical conditions of ice formation mainly volume and or growth rate of frazil ice crystals as well as variations of the isotope composition of the freezing water the latter implies a poor mixing of the source waters glacier melt and hydrothermal water with the water of the main lake body poor mixing within the lake may have important consequences for the lake s chemical and gas balance and particularly for its microbiological content a poorly mixed lake may provide ecological niches where microbial life can hide from high oxygen concentrations likely typical for the lake we also show that the isotopic content of the main lake s input meltwater significantly differs from that of the output lake ice which can be explained by the contribution of an additional hydrothermal source this latter conclusion is supported by the observed noncovariant behavior of deuterium and oxygen 18 isotopes in the lake ice

the international trans antarctic scientific expedition itase an overview from its original formulation in 1990 the international trans antarctic scientific expedition itase has had as its primary aim the collection and interpretation of a continent wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations itase offers the ground based opportunities of traditional style traverse travel coupled with the modern technology of gps crevasse detecting radar satellite communications and multidisciplinary research by operating predominantly in the mode of an oversnow traverse itase offers scientists the opportunity to experience the dynamic range of the antarctic environment itase also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps without the cost of the former or the lack of mobility of the latter more importantly the combination of disciplines represented by itase provides a unique multidimensional space and time view of the ice sheet and its history itase has now collected 20 000 km of snow radar recovered more than 240 firn ice cores total length 7000 m remotely penetrated to 4000 m into the ice sheet and sampled the atmosphere to heights of 20 km

height changes over subglacial lake vostok east antarctica insights from gnss observations height changes of the ice surface above subglacial lake vostok east antarctica reflect the integral effect of different processes within the subglacial environment and the ice sheet repeated gnss global navigation satellite systems observations on 56 surface markers in the lake vostok region spanning 11 years and continuous gnss observations at vostok station over 5 years are used to determine the vertical firn particle movement vertical marker velocities are derived with an accuracy of 1 cm yr or better repeated measurements of surface height profiles around vostok station using kinematic gnss observations on a snowmobile allow the quantification of surface height changes at 308 crossover points the height change rate was determined at 1 5 mm yr thus indicating a stable ice surface height over the last decade it is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period the continuous gnss observations demonstrate that the particle heights vary linearly with time nonlinear height changes do not exceed 1 cm at vostok station and constrain the magnitude of spatiotemporal lake level variations icesat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters assuming the ice sheet to be in steady state over the entire lake estimates for the surface accumulation on basal accretion melt rates and on flux divergence are derived

observational evidence on the stability of the hydro glaciological regime of subglacial lake vostok 1 combined geodetic geophysical and glaciological in situ measurements are interpreted regarding surface height changes over subglacial lake vostok and the local mass balance of the ice sheet at vostok station repeated gps observations spanning 5 years and long term surface accumulation data show that the height of the lake surface has not changed over the observation period the application of the mass conservation equation to purely observational data yields an ice mass balance for vostok station close to equilibrium

record of δ18o and 17o excess in ice from vostok antarctica during the last 150 000 years 1 we measured 17 o and 18 o in recent antarctic snow and down the vostok ice core and calculated the excess of 17 o with respect to vsmow the magnitude of the 17 o excess in the holocene and the last interglacial is 45 per meg and it remains constant in a transect from the coast to the continental interior analysis of the transect data shows that the 17 o excess is not sensitive to temperature variations over the continent there are significant shifts in 70 excess from low values in glacial to high values in interglacial times the observed shifts suggest higher normalized relative humidity and or wind speeds over the source oceanic regions in glacial times

tracing acidification induced by deccan phase 2 volcanism abstract the deccan volcanic province dvp was built up by three major phases of eruptions the most voluminous of which the deccan phase 2 encompassed the cretaceous palaeogene kt boundary deccan eruptions have been implicated as a contributor to the end cretaceous mass extinction however mechanism by which volcanic activity affected biota remains poorly understood we applied a combination of rock magnetic techniques scanning electron microscopy to characterize mineral assemblages of three sections of intertrappean lacustrine sediments from the north western maharashtra deccan volcanic provinces our results indicate that in sediments deposited during the early stages of the deccan phase 2 the daiwal river and dhapewada sequences iron bearing mineral association is dominated by detrital iron oxides magnetite and hematite sourced from the weathering of the surrounding basaltic bedrocks with minor contribution form authigenic iron sulphides framboidal pyrite pyrrhotite and or greigite the sediments deposited during the final stages of phase 2 the podgawan sequence differ significantly in their characteristics in particular the podgawan sediments have 1 very low magnetic susceptibility values but higher terrigenous fraction clays and shales content 2 more complex assemblage of magnetic minerals 3 ubiquitous presence of fe ca ce vanadates and 4 unusual lithological variations in the middle part of the section represented by a charcoal rich level that is capped by a red clay layer containing fossilized bacterial colonies we suggest that these unusual characteristics reflect increased acidity in the region during the deposition of the podgawan sequence likely due to cumulative effects of volcanic aerosols released during the deccan phase 2 eruptions the combination of these features may be used to recognize episodes of increased acidity in the geological record our results also contribute to understanding of local vs global effects of the deccan volcanism

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

hydrothermal mineralization in the sandstone hosted hangjinqi uranium deposit north ordos basin china abstract tabular type uranium ore deposits the hangjinqi and daying deposits have recently been found in the middle jurassic zhiluo formation north of the ordos basin china petrographic observations the chemical composition of u minerals determined by empa and fs la icp ms whole rock geochemistry and the microthermometric study of fluid inclusions have been integrated to characterize the genetic conditions of the u mineralization in the hangjinqi sandstone hosted deposit two different groups of u minerals have been identified one group includes coffinite i associated with vanadium rich micas coffinite i is enriched in vanadium v and devoid of iron fe and yttrium y and has a lree enriched chondrite normalized ree pattern the u minerals of this group are similar to meteoric fluid infiltration related deposits the second group has coeval coffinite ii and coarsely crystalline calcite cement coffinite ii is enriched in y and fe and depleted in v and is marked by a flat chondrite normalized ree pattern which is compatible with typical hydrothermal genetic deposits with high salinity mineralizing fluids the temperature and salinity of the primary aqueous inclusions in the ore stage calcite are 120 180 c and 8 00 16 34 eq wt nacl respectively these mineral assemblages temperatures and salinities indicate that the hangjinqi deposit was affected by two distinct types of ore bearing fluids low salinity meteoric waters and high salinity hydrothermal fluids the meteoric fluids event began at 97 5 ma with the titling of the northern ordos basin and the uplift of the hetao region to the north hydrothermal u mineralization occurred since 39 2 ma with the rifting of the hetao graben thus the previous biogenic model for the u mineralization should be modified in the uraniferous region of the north ordos basin

identification of antarctic ablation areas using a regional atmospheric climate model the occurrence of antarctic ablation areas in dronning maud land the lambert glacier basin victoria land the transantarctic mountains and the antarctic peninsula is realistically predicted by the regional atmospheric climate model racmo2 ant with snowdrift related processes calculated offline antarctic ablation areas are characterized by a low solid precipitation flux in combination with strong sublimation snowdrift erosion and or melt the strong interaction between atmospheric circulation and topography plays a decisive role in the precipitation distribution and hence that of ablation areas three types of antarctic ablation areas can be distinguished all occurring in dry regions type 1 is the erosion driven ablation area caused by 1 d and or 2 d divergence in the katabatic wind field at high elevations 2000 3200 m asl type 2 is the sublimation driven ablation area this type occurs at lower elevations

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

multiple climate shifts in the southern hemisphere over the past three centuries based on central antarctic snow pits and core studies based on the results of geochemical and glaciological investigations in snow pits and shallow cores regional stack series of air temperature in central antarctica in the southern part of vostok subglacial lake were obtained covering the last 350 years it is shown that this parameter varied quasi periodically with a wavelength of 30 50 years the correlation of the newly obtained record with the circulation indices of the southern hemisphere sh shows that the central antarctic climate is mainly governed by the type of circulation in the sh under conditions of zonal circulation negative anomalies of temperature and precipitation rate are observed whereas the sign of the anomalies is positive during meridional circulation in the 1970s the sign of the relationship between many climatic parameters changed which is likely related to the rearrangement of the climatic system of the sh the data suggest that during the past 350 years such events have taken place at least five times the stable water isotope content of the central antarctic snow is governed by the summer temperature rather than the mean annual temperature which is interpreted as the influence of post depositional effects

influence of summer sublimation on δd δ18o and δ17o in precipitation east antarctica and implications for climate reconstruction from ice cores