facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

late cenozoic turbidite and contourite deposition in the southern brazil basin abstract piston and giant gravity cores together with 3 5 khz and seismic profiles reveal a complex pattern of dispersal of bioclastic calcareous turbidites in the southern brazil basin extensive canyons up to 500 m deep dissect the steep north flank of the rio grande rise and serve as conduits for turbidity currents which have eroded modern sediments as well as outcrops of tertiary and late cretaceous strata the resulting turbidites are up to several meters thick in channel axes and commonly several cm thick at distances up to hundreds of km from the canyon source region individual turbidity currents were apparently sufficiently strong to transport fine grained components several hundred meters upslope and several hundred km laterally across the brazil basin the lithology of both proximal and distal turbidites their presence well below the modern ccd and the lack of correspondence between their presence and that of displaced antarctic diatoms verifies that these calcareous deposits are not products of episodic antarctic bottom water flow but originated from a shallow water source area the late pleistocene and holocene witnessed major turbidity current episodes at intervals on the order of 50 000 yrs with at least two episodes coinciding approximately with interglacials following terminations i and ii sediments older than isotopic stage 8 275 000 yrs b p include thinly laminated contourites we interpret these units as intervals of normal pelagic sedimentation which were subsequently reworked under the influence of aabw pulses episodes of intensified aabw flow may have immediately preceded the onset of major glacial episodes extending corrosive eastward flowing aabw to relatively shallow depths 4200 4300 m along the north flank of the rio grande rise the undercutting of outcropping strata by chemical dissolution at the base of the faulted north flank has probably played a critical role in the initiation of canyon cutting episodic slumping due to oversteepening and the generation of debris flows progressively enlarged the canyons upslope in a dendritic pattern and gradually extended the canyons to shallower elevations on the rise vertical crustal displacements associated with the rio grande fracture zone have controlled the pathway of aabw in the southern brazil basin and accentuated the steep relief on the north flank of the rise these two processes have been essential conditions for the extensive canyon cutting and subsequent dispersal of carbonate turbidites over the brazil basin

cadmium isotopic evidence for increasing primary productivity during the late permian anoxic event abstract earth s most extreme extinction event near the end of the late permian decimated more than 90 of all extant marine species widespread and intensive oceanic anoxia almost certainly contributed to the catastrophe though the driving mechanisms that sustained such conditions are still debated of particular interest is whether water column anoxia was a consequence of a stagnant ocean or if it was controlled by increases in nutrient supply primary productivity and subsequent heterotrophic respiration testing these competing hypotheses requires deconvolving sedimentary bottom water redox conditions from changes in surface water productivity in marine sediments we address this issue by studying marine shales from east greenland and the mid norwegian shelf and combining sedimentary redox proxies with cadmium isotopic analyses sedimentary nitrogen isotopic data pyrite framboid analyses and organic and inorganic shale geochemistry reveal sulfidic conditions with vigorous upwelling and increasingly anoxic conditions with a strengthening upwelling in the greenland and norwegian sections respectively detailed analysis of sedimentary metal budgets illustrates that cd is primarily associated with organic carbon and records primary geochemical signatures thus enabling reconstruction of surface water nutrient utilization cadmium isotopic analyses of the authigenic shale fraction released by inverse aqua regia digestion yield an average cd 114 110 of 0 15 0 01 2 se n 12 rel nist srm 3108 indicative of incomplete surface water nutrient utilization up section the constant degree of nutrient utilization combined with strong upwelling requires increasing primary productivity and not oceanic stagnation to balance the larger nutrient fluxes to both study sites during the development of the late permian water column anoxia overall our data illustrate that if bottom water redox and upwelling can be adequately constrained cd isotopic analyses of organic rich sediments can be used to provide valuable information on nutrient utilization and therefore past productivity

bottom current controlled sand deposits a review of modern shallow to deep water environments abstract different examples of modern marine sand accumulations generated or strongly influenced by the action of bottom currents are here presented they are drawn from a variety of tectonic and morphological settings and grouped into three water depth zones deep water 2000 m mid water 300 2000 m and outer shelf upper slope 50 300 m deposits in the first two of these depth zones are normal contourites according to their original definition heezen and hollister 1971 being those sediments that have been transported and deposited by contour currents in deep water environments those deposited at shallower depths under the influence of surficial geostrophic currents combined with other hydrodynamic factors shelf currents induced by wind tide and waves gyres internal waves etc are more properly referred to as outer shelf upper slope bottom current sands or shallow water bottom current sands we have elaborated a facies model for each bathymetric zone deep water sandy contourites are relatively rare thin and very thin bedded highly bioturbated and mainly of bioclastic composition they are interbedded with muddy contourites and pelagites or in some areas with turbidites in the latter case thin bottom current reworked sandy tops of turbidites provide a different and distinct facies mid water sandy contourites are more common ranging up to a metre in thickness and may form extensive sandy sheets in a variety of slope bank and channel settings they are mainly of mixed siliciclastic bioclastic composition typically bioturbated and associated with muddy silty contourites in coarsening up fining up complete or truncated sequences shallow water bottom current sands occur in particular outer shelf upper slope settings where they may develop relatively thick 1 20 m laterally extensive sheets covered by fields of sandwaves megaripples and ribbons internal structures may be preserved along with much bioturbation their composition varies from mainly siliciclastic to bioclastic and they may be interbedded with both inner shelf facies and slope hemipelagites the principal factors that control the deposition of sandy contourites and shallow water bottom current sands are the hydrodynamic regime of the basin the availability of coarse grained sandy sediments and the physiographic context of the area swept by the currents the greater the depth the finer and rarer the bottom current or sandy contourite deposits global sea level and climatic changes and the time involved in the depositional history play an ultimate role in the development of important sand accumulations of this sort by controlling the ocean circulation pattern and its long term persistence from the present analysis we conclude that mid depth sandy contourites are the most commonly found in modern environments and that shallow water bottom current sands constitute the most significant potential oil reservoirs to be found in the geological record

isotopic fractionation of cadmium into calcite abstract cadmium mimics the distribution of the macronutrient phosphate in the oceans and has uses as a palaeoproxy of past ocean circulation and nutrient utilization isotopic analyses of dissolved cd in modern seawater show potential as a new tool for disentangling phytoplankton utilization of cd from abiotic processes such as ocean mixing extending this information into the past requires the cd isotope signal to be captured and faithfully preserved in a suitable sedimentary archive however the role that environmental factors such as temperature may play in controlling cd isotope fractionation into such archives has not been assessed to this end we have performed controlled inorganic caco3 precipitation experiments in artificial seawater solutions we grew calcite under different precipitation rates temperatures salinities and ambient mg2 before measuring cd isotopic compositions by double spike mc icpms we find that the isotopic fractionation factor for cd into calcite c a c o 3 c d aq in seawater is always less than one i e light isotopes of cd are preferred in calcite the fractionation factor has a value of 0 99955 0 00012 and shows no response to temperature mg2 or precipitation rate across the range studied the constancy of this fractionation in seawater suggests that marine calcites may provide a record of the local seawater composition without the need to correct for effects due to environmental variables we also performed caco3 growth in freshwater and in contrast to calcite precipitated from artificial seawater solutions no isotopic offset was recorded between the growth solution and calcite c a c o 3 c d aq 1 0000 0 0001 cadmium isotope fractionation during calcite growth can be explained by a kinetic isotope effect during the largely unidirectional incorporation of cd at the mineral surface further the rate of cd uptake and isotopic fractionation can be modulated by increased ion blocking of crystal surface sites at high salinity the fractionation of cd isotopes observed during precipitation of calcite has the same direction and similar magnitude to that implicated for cd removal from the surface ocean by seawater measurements however flux calculations show that caco3 precipitation is unlikely to play a significant role in setting the cd isotope composition in seawater compared to cd utilization in phytoplankton soft tissue marine carbonates therefore record seawater cd isotope chemistry with potential as a palaeoceanographic proxy rather than drive oceanic cd isotope compositions

irreversible change of the oceanic carbon cycle in the earliest cambrian high resolution organic and inorganic carbon chemostratigraphy in the three gorges area south china the terminal neoproterozoic and its transition into the cambrian witnessed major evolutionary and geochemical changes large fluctuations in the carbon isotope ratio for inorganic carbon 13ccarb across the precambrian cambrian boundary pc c boundary indicate a significant change in the oceanic carbon cycle at that time this work presents the first high resolution 13corg chemostratigraphy of drill core samples across the pc c boundary in the three gorges area south china and discusses carbon cycles based on the relation between 13corg and 13ccarb we found that changes of 13corg and 13ccarb values were decoupled during the significant negative excursion of 13ccarb across the pc c boundary suggesting the presence of a huge organic carbon pool ocp previously the large ocp was inferred to have been established in the terminal proterozoic and to have disappeared at the end of the mid ediacaran shuram excursion in contrast our study suggests that the large ocp lasted until the early nemakit daldynian stage on the other hand in the middle nemakit daldynian to atdabanian the 13ccarb and 13corg changed in parallel as observed normally in the phanerozoic in order to evaluate these scenarios quantitatively we performed numerical simulations and calculated the time evolution of the 13ccarb masses of the inorganic and organic carbon pools and the fluxes between them as a result we show that the observed negative 13ccarb excursion with steady 13corg can be produced by enhanced primary productivity and remineralization of the large ocp if the rate constant for removal of organic carbon was considerably lower than that of today the end of the decoupled negative 13ccarb excursion is attributable to an increase in the removal rates of inorganic and organic carbon from the ocean the enhanced flux of organic carbon burials eliminated the large ocp so that the modern style carbon cycle was established by the early nemakit daldynian stage the inferred rapid increases of both organic and inorganic carbon burial rates in the middle nemakit daldynian stage were likely caused by the appearance of planktonic metazoans with guts making fecal pellets and by the first skeletal animals the biological innovations may have changed the oceanic carbon cycle irreversibly just after the pc c boundary

the cycling of iron zinc and cadmium in the north east pacific ocean insights from stable isotopes abstract dissolved stable isotope ratios of the transition metals provide useful information both for understanding the cycling of these bioactive trace elements through the oceans and tracing their marine sources and sinks here we present seawater dissolved fe zn and cd concentration and stable isotope ratio 56fe 66zn and 114cd profiles from two stations in the pacific ocean the safe station 30 n 140 w in the subtropical north east pacific from the geotraces ic2 cruise and the marginal san pedro basin 33 8 n 118 4 w within the south california bight these data represent to our knowledge the first full water column profiles for 66zn and 56fe from the open ocean north pacific and the first observations of dissolved 66zn and 114cd in a low oxygen marginal basin at the safe station 56fe is isotopically lighter throughout the water column 0 6 to 0 1 relative to irrm 014 compared to the north atlantic suggesting significant differences in fe sources or fe cycling between these two ocean basins a broad minimum in 56fe associated with the north pacific oxygen minimum zone omz

fine scale spatial and interannual cadmium isotope variability in the subarctic northeast pacific abstract we present dissolved cadmium cd concentrations cd and stable isotope compositions e 112 110 cd in high resolution depth profiles from five stations along the line p transect in the subarctic northeast pacific ocean in addition to profiles collected in 2012 subsurface isopycnal samples and surface samples were collected in 2013 and 2014 respectively providing both temporal and spatial coverage surface waters are characterized by cd depletion relative to phosphate po 4 3 compared to deepwater cd po 4 3 and high inferred remineralization ratios in the nutricline 0 45 nmol mol 1 are observed consistent with cd enrichment relative to phosphorus p in surface derived biogenic particles the correlation between cd and po 4 3 weakens at depths where oxygen is highly depleted as shown by local minima in dissolved cd and the tracer cd the decoupling which is driven by a deficit of cd relative to po 4 3 appears consistent with the recent hypothesis of dissolved cd removal in oxygen depleted regions by insoluble metal sulfide formation dissolved e 112 110 cd indicates a biologically driven fractionation in surface waters with more positive heavy values in the upper water column and lower light values in deeper waters the highest e 112 110 cd observed in our sample set 5 19 0 23 is comparable to observations from the southern ocean but is significantly lighter than maximum reported surface values from the subtropical north pacific of e 112 110 cd 15 a global compilation of low cd surface water shows similar differences in maximum e 112 110 cd a surface water intercalibration should be prioritized to help determine if these differences at low cd reflect true physical or biological variability or are due to analytical artefacts surface samples from the 2012 sampling campaign fit a closed system rayleigh fractionation model however surface waters sampled in 2014 had much lower cd with relatively constant e 112 110 cd that cannot be explained by a closed system rayleigh model these results correspond with a warm water surface anomaly found along line p in 2014 and demonstrate that there is interannual variability in the biogeochemical cycling of cd and its isotopes in the subarctic north pacific in contrast to other ocean basins where vertical variability in e 112 110 cd is observed at depth deep and intermediate waters in the north pacific have a near uniform e 112 110 cd value mean of 1 14 0 37 n 43 2sd representative of nearly all samples at or below 1000 m depth imprinted upon this nearly homogeneous intermediate and deep north pacific e 112 110 cd signature are fine scale spatial trends with heavier values observed toward the coastal end of line p than the oceanic end at intermediate depths and with slightly heavier values in subtropical north pacific deep water compared to the subarctic north pacific the nearly constant cd isotopic composition of north pacific deep waters is consistent with the inflow of circumpolar deep water at depth in the pacific basin along with deep remineralization and supports the potential of e 112 110 cd as a tracer of global deepwater circulation

element accumulation rates in and growth histories of manganese nodules from the southwestern pacific basin abstract accretion rates and element accumulation rates of seven manganese nodules collected from the southwestern pacific basin during r v sonne cruise so 14 on a tahiti east pacific rise new zealand transect have been determined the accretion rates of the nodules lie in the range 3 5 6 0 mm 10 6 yr the highest rates correspond to areas with higher biogenic silica contents in the sediment suggesting a higher diagenetic contribution to the nodules in one nodule 143gb dated with 10 be nodule growth began at about 14 5 ma there is a change in structure of the nodule at 6 ma and concentric layers filled with detritus occur at 3 2 ma and 1 3 ma there is also a major change in the flux rates of the elements at the 6 ma time marker with the authigenic elements mn cu and ni showing greater accumulation rates in the outer zone and the detrital fraction al showing a greater accumulation rate in the inner zone the variations in the element accumulation rates probably reflect a change of abyssal circulation pattern at 6 2 ma however the precise nature of this change remains a matter for speculation

biogenic origin of intergrown mo sulphide and carbonaceous matter in lower cambrian black shales zunyi formation southern china abstract the lower cambrian zunyi formation in southern china hosts complex intergrown phases of mo sulphides and anthracite like carbonaceous matter and graphite mosc pyrite and ni sulphides these sulphides occur in a few centimeters thick polymetallic stratiform layer in black shales above phosphorites cherts dolomites and barite the ore horizon contains 7 wt mo 2 wt ni 19 wt s and 13 wt c org and c tot co 2 58 wt 14 wt cao 1 2 wt as 2000 ppm se 5400 ppm zn 450 ppm u and v and up to 1 ppm platinum group elements three types of mosc phases always including framboidal pyrite are distinguished 1 rounded structures few hundred microns large 2 relict inclusions in diagenetic pyrite 3 grains interstitial to sulphurised and phosphatised organic matter at the nanoscale mosc is represented by nanometric porous rounded structures of mos 2 finely intergrown with carbonaceous matter of typical nano onion structures mosc also contains nanocrysts of quartz clays ca sulphate carbonate and ni sulphides micro raman spectroscopy shows that the carbon phase has a maturation grade of anthracite indicating temperatures below 300 c mosc is mainly composed of 25 wt mo 23 wt s 5 6 wt fe 2 5 wt ni 33 wt c 1 5 wt o 0 6 wt n and several hundreds of ppm of cu as se sb pd zn co and sn electron energy loss spectra show that n is related to nanosized carbonaceous matter the mean c n ratio 57 of mosc is similar to those observed in marine organic matter and those reported from zooplankton at hydrothermal vents the mineralized shales are crosscut by hydrothermal veins composed of carbonate or barite always associated with quartz apatite and fe and zn sulphides a paragenesis also observed as nanocrysts in mosc although mo originated from seawater its extreme concentration is due to an enhanced growth of bacterial consortia in a diffuse hydrothermal vent system these consortia may be dominated by nitrogen fixing and mo dependant hyperthermophilic or mesophilic species containing nitrogenase composed also of mo s fe organic matter decay led thus to the formation of mosc and the included framboidal pyrite

cadmium isotopic evidence for the evolution of marine primary productivity and the biological extinction event during the permian triassic crisis from the meishan section south china abstract cadmium cd isotopic compositions in seawater are important parameters for tracing the biogeochemical cycling of cd in modern oceans and may be used as a direct proxy for nutrient utilization by phytoplankton and an indirect proxy for primary productivity in this study we measured the stable cd isotope ratios 114cd of marine sedimentary carbonates from the meishan section in changxing county of zhejiang province south china the global stratotype section and point gssp of the permian triassic boundary ptb the results suggest that the inferred marine primary productivity recorded in the marine carbonates from the late permian i e before the mass extinction was high and relatively stable the 114 110cd values of carbonates range from 0 31 to 0 60 after correction for salinity controlled fractionation into inorganic calcite the 114 110cd values of palaeo seawater range from 0 47 to 0 79 during the mass extinctions the 114 110cd values of carbonates abruptly decreased at the beginning of each episode of mass extinction suggesting that the primary productivity of the palaeo ocean declined before each episode of extinction events at the ptb we suggest that the mass extinction events at the ptb in the meishan section could be a ripple effect due to the destruction of primary producers at the base of the food chain in the palaeo ocean ecosystem

biogeochemical cycling of cadmium isotopes along a high resolution section through the north atlantic ocean abstract cadmium cd is a bioactive trace element in the oceans with a nutrient like distribution that closely matches dissolved phosphate seawater dissolved stable cd isotope ratios 114cd are a relatively new parameter which show much promise for furthering our understanding of the biogeochemical cycling of cd in the oceans here we present a high resolution paired section of dissolved cd concentrations and dissolved 114cd from 21 open ocean stations along the us geotraces ga03 transect through the north atlantic ocean dissolved cd concentrations along the section are strongly influenced by water mass distribution and the cycling of cd the highest dissolved cd concentrations 400 540 pmol kg 1 are associated with antarctic sourced water masses whilst biological uptake in the surface ocean results in a strong vertical gradient in dissolved cd towards the surface reaching as low as 0 03 pmol kg 1 in western surface waters dissolved 114cd is also characterized by a vertical gradient from 0 2 in the deep ocean to 2 to 5 in the cd depleted surface ocean relative to nist srm 3108 this variability in 114cd can be ascribed to mixing of antarctic and north atlantic water masses together with fractionation due to in situ biological uptake of light cd in the very surface ocean subtle deviations from this overall pattern of dissolved cd concentration and dissolved 114cd are observed within low oxygen waters off north africa where a dissolved cd deficit relative to phosphate is associated with higher dissolved 114cd values together with elevated particulate cd and ba this suggests that cd sulfide precipitation is occurring within the water column of the north atlantic constituting a potentially important sink for isotopically light cd additionally the first measurements of dissolved 114cd within a hydrothermal plume at the mid atlantic ridge show that cd is scavenged from the dissolved phase leaving the remnant dissolved cd isotopically heavier constraining the significance of these marine sinks for dissolved cd is important not only for our understanding of the marine biogeochemical cycling of cd in the modern oceans but also for the successful application of the microfossil cd ca proxy and the development of 114cd as a tracer for past ocean biogeochemical cycling

a deep sea thermohaline flow path in the northwest pacific abstract a recent reevaluation of the bathymetry of the northwest pacific accompanied by an analysis of reflection profiler records and deep sea drilling sites provide geological evidence for a 2000 km long north south flow path east of the emperor seamounts the geological evidence is similar to that associated elsewhere with thermohaline currents as there are no present day physical oceanographic observations of a north south flowing thermohaline current i conclude that the inferred bottom current is either presently inactive or has not been observed by the methods of investigation used to determine its presence

the link between metazoan diversity and paleo oxygenation in the early cambrian an integrated palaeontological and geochemical record from the eastern three gorges region of south china abstract the link between environmental perturbations especially oceanic redox conditions and evolution during the cambrian biodiversification event is still highly controversial although this issue has attracted considerable attention for decades we here report on the fossil record of the early cambrian biota discovered in the uppermost yanjiahe and shuijingtuo formations that crop out in the luojiacun and qiaojiaping sections eastern three gorges area south china the uppermost member of the yanjiahe formation contains abundant benthic algae based on the fossil record four distinct intervals were recognized in the shuijingtuo formation i few sessile suspension feeders such as sponges were recovered from interval i ii interval ii is dominated by bivalved arthropods living in the water column in this interval are also found a few sponges and eodiscoid trilobites iii no fossils other than few sponge spicules were recovered from interval iii iv diverse benthic communities composed of sponges cnidarians brachiopods as well as bradoriids dominate interval iv comprehensive research on framboidal pyrite morphology whole rock geochemistry as well as in situ la icp ms analyses were carried out on samples from the luojiacun section in order to assess paleo redox conditions the results show that the overall evolution of the paleo redox conditions was characterized by a double episode of sharp anoxic events ae observed at the base of intervals i and iii followed by a gradual oxygenation event oe evidence of oxygenation fluctuations were detected especially within interval iv a case study is presented herein which brings together early cambrian changes in metazoan diversity and changes in environmental conditions it is suggested that periodical oxygenation of the water column increased the biological diversity in the restricted basins of the eastern three gorges thus four intervals of habitat succession can be tentatively reconstructed in the studied area for the cambrian age 2 age 3 interval indicating a transition from uninhabited sediments to well populated habitats finally both the temporal and spatial characteristics of the cambrian aes oes and the fossil record in south china are compared and links between them are discussed in the context of their specific paleo geographical setting

a comparative analysis of compositional variations in and between marine ferromanganese nodules and crusts in the south pacific and their environmental controls abstract regional variation of mn fe co ni and cu in ferromanganese oxides nodules and crusts in the central south pacific is related to primary productivity oxygen minimum layer and calcium carbonate compensation depth the largely latitudinal influence of these environmental parameters on nodule and crust composition reflects their predominantly latitudinal variation primary productivity is the principal regional environmental control influencing diagenetic enrichment of these elements in nodules through its effect mediated by the ccd on supply and concentration of labile organic matter vs carbonate remains to the sediments it influences hydrogenetic enrichment of these elements in nodules and crusts through its effect mediated by the oxygen minimum layer mainly in the case of crusts on their export from surface waters the elements varying susceptibility to being scavenged or organically bound influences the contrasting composition of diagenetic vs hydrogenetic ferromanganese oxides which is further influenced by depth hydrogenesis is the fundamental process governing nodule and crust formation superimposed on which is diagenesis under specific circumstances both are subject to intermittent interruption diminution and augmentation by changes in environmental parameters application of regionally operative environmental controls locally explains local compositional variations and helps refine exploration criteria for economically viable nodules and crusts

redox condition in the nanhua basin during the waning of the sturtian glaciation a chromium isotope perspective abstract the neoproterozoic oxygenation event noe is often considered to be synchronously and possibly causally associated with the cryogenian glaciations reconstructing early cryogenian redox conditions is therefore essential for understanding the onset of the noe we analyzed cr isotope compositions 53cr as well as major and rare earth element ree concentrations of the banded iron formations bifs in the basal fulu formation of the xiajiajiang section nanhua basin which are thought to have been deposited during the waning stage of the sturtian glaciation strongly positively fractionated authigenic 53cr values were obtained after detrital correction ranging from 0 64 to 1 22 and averaging at 0 91 0 40 2 n 10 or after detrital evaluation 0 71 this suggests extensive oxidative cr cycling occurred at the earth s surface and implies that the po2 was probably higher than 1 pal during this period the lack of ce anomalies 0 90

global variability of chromium isotopes in seawater demonstrated by pacific atlantic and arctic ocean samples abstract seawater chromium cr isotope and concentration data are presented from multiple sites in the arctic ocean and three locations in the atlantic and pacific oceans a 2400 m profile illustrates the heterogeneity of 53cr in the arctic ocean with depth and water mass source pacific vs atlantic the highest 53cr values occur in pacific sourced waters which also have the lowest cr concentration chromium concentration and 53cr data from these locations in conjunction with published data for the south atlantic ocean yield a simple logarithmic function as predicted by rayleigh fractionation in a closed system the observed cr isotope signature is hypothesized to arise from fractionation during the reduction of cr vi in surface waters and oxygen minimum zones scavenging of isotopically light cr iii to deeper water and sediment and subsequent release of this seawater derived cr iii back into seawater either as organic complexes with cr iii or after oxidation to cr vi the isotopic fractionation factor e associated with cr cycling in seawater is estimated to be 0 80 0 03 2 samples from the sea ice affected surface mixed layer of the arctic ocean 10 m depth deviate from the general trend and samples proximal to rivers illustrate geographic variation in 53cr values for continental runoff but prompt loss of this signature away from the source

new carbon isotope stratigraphy of the ediacaran cambrian boundary interval from sw china implications for global correlation the yangtze platform preserves relatively thick carbonate successions and excellent fossil records across the ediacaran cambrian boundary interval the intensely studied meishucun section in east yunnan was one of the global stratotype section candidates for the precambrian cambrian boundary however depositional breaks were suspected in the section and the first appearance of small shelly fossils could not be verified the laolin section located in ne yunnan is more continuous and shows great potential for global correlation of carbon isotope features across the precambrian cambrian boundary however the stratigraphic framework and correlations were controversial we studied and systematically sampled the laolin section and present here new carbon isotope data for this section the laolin section consists of in ascending order the baiyanshao dolostone of the dengying formation the daibu siliceous dolostone zhongyicun dolomitic phosphorite lower dahai dolostone and upper dahai limestone of the zhujiaqing formation and the black siltstone of the shiyantou formation our data reveal a large negative 13 c excursion 7 2 l1 in the daibu member which matches the previously published data for the laolin section and a large positive excursion 3 5 l4 in the dahai member which was not shown in the published data the excursion l1 correlates well with the similarly large negative excursion near the first appearance of small shelly fossils in siberia and mongolia similar magnitude excursions are also known from morocco and oman for which there are no robust fossil constraints but from where volcanic ash beds have been dated precisely at 542 ma thus confirming a global biogeochemical event near the ediacaran cambrian boundary our data also indicate that deposition was more continuous at the laolin section compared with the meishucun section where there are no records of a comparable negative excursion near the ediacaran cambrian boundary nor any comparable positive excursion in the dahai member therefore the laolin section has proven potential to be a supplementary global stratotype section for the ediacaran cambrian boundary on the yangtze platform

the chromium isotopic composition of seawater and marine carbonates article history chromium isotopes are fractionated during redox reactions and have the potential to provide a record of changes in the oxygenation levels of the oceans in the geological past however cr is a trace metal in seawater and its low concentrations make isotopic measurements challenging here we report the first determinations of 53 cr for seawater from open ocean argentine basin and coastal southampton water settings using a double spike technique the total chromium concentration in seawater from southampton water is 1 85 nm whereas the cr content of argentine basin samples is 5 8 6 6 nm the 53cr value of seawater from the argentine basin is 0 491 0 556 in intermediate and deep waters and varies between 0 412 and 0 664 in surface waters 150 m the 53

zinc and cadmium stable isotopes in the geological record a case study from the post snowball earth nuccaleena cap dolostone abstract zinc and cadmium are important biologically cycled nutrients in the modern ocean recent analytical advances and sampling efforts such as geotraces have led to measurements of the global distribution of zn and cd and their stable isotope ratios 66zn and 114cd providing an understanding of how biological processes cycle these elements and their isotopes in the modern ocean this opens the door to better application of 66zn and 114cd as tracers of biogeochemical processes archived in the geological record here we present new measurements of cd and 114cd on samples from the nuccaleena cap dolostone in south australia which was deposited during deglaciation of the ca 635 ma old marinoan snowball earth our new data are combined with previously measured 66zn data from the same samples the combined record of 114cd and 66zn is used to explore various hypotheses about the sources and sinks of cd and zn in the post marinoan ocean key features of this record are that zn and cd remain relatively similar throughout that 66zn and 114cd change at the same stratigraphic level and in the same direction and that 66zn changes are about four times larger than 114cd changes even though both quantities reflect a similar fractional mass difference we suggest that both zn and cd concentration and isotopic data are consistent with a change in the sink by which zn and cd are removed from the oceans we propose that no isotope fractionation is expressed during removal of zn and cd as sulfides while zn and cd removed with biological material are about 0 6 and 0 2 lighter than deep ocean 66zn and 114cd respectively many previous studies attribute the burial of isotopically light biological zn to preferential assimilation of isotopically lighter zn by phytoplankton in contrast we propose that lighter biological 66zn occurs mostly because isotopically heavy zn was scavenged by organic matter which causes dissolved 66zn in the surface ocean to be lighter than deep ocean 66zn the organic matter originated from primary producers that thrived in the surface ocean during deglaciation for cd whose isotope cycling in the modern ocean is dominated by preferential assimilation of isotopically lighter cd by phytoplankton much less biological fractionation is expressed the combined analyses of 66zn and 114cd provide insight into the biogeochemical processes which occurred after the marinoan snowball earth glaciation and may be a useful new tool to explore the history of life on earth in other geological records as well

an assessment of bottom current controlled sedimentation in pacific ocean abyssal environments the effect of the circulation of polar sourced dense waters on the deep seafloor is still largely unknown this paper presents multibeam bathymetric evidence for the existence of present day contourite drifts on the central pacific ocean at depths ranging between 4000 and 5000 m based on the identification of their diagnostic erosive moats linear moats furrows and abyssal sinuous channels and depositional plastered elongated separated and abyssal contourite fan drifts contourite morphological features these contourite drifts display a patchy distribution sculpted by the secondary flows of the lower circumpolar water lcpw and the north pacific deep waters npdw as well as local dynamics of the flow in the form of internal waves and bottom currents modulated by tides which are capable of accelerating the typically sluggish bottom currents and contribute to the erosion transport and deposition of sediments the formation of contourites is also predominantly controlled by the presence of large scale tectonic and volcanic features ridges seamounts and deep elongated valleys which affect the morphology and distribution of the basins and induce the acceleration of bottom currents overall this study allows to re assess the effects distribution and significance of bottom current controlled sedimentation in abyssal environments where examples of contourite features are still rather scarce in part because of the technical challenges and their remote location but also because the effect of bottom currents is not well known in the central oceanic basins and only capable of marginally affecting their sedimentological record

the isotopic composition of authigenic chromium in anoxic marine sediments a case study from the cariaco basin chromium cr isotopes are an emerging proxy for tracking redox processes at the earth s surface however there has been limited exploration of the cr isotope record of modern and recent marine sediments the basic inorganic chemistry of cr suggests that anoxic marine basins should factor prominently in the global cr cycle and that sediments deposited within anoxic basins may offer a valuable cr isotope archive throughout earth s history here we present 53 cr data from sediments of the cariaco basin venezuela a type environment for large perennially anoxic basins with a relatively strong hydrological connection to the global oceans we document a marked positive shift in bulk 53 cr values following the termination of the last glacial maximum followed by relative stasis based on a suite of independent redox proxies this transition marks a switch from oxic to persistently anoxic and sulfidic euxinic depositional conditions within the basin we find good agreement between two independent approaches toward estimating the 53 cr composition of authigenic cr in euxinic cariaco basin sediments and that these estimates are very similar to the 53 cr composition of modern open atlantic ocean seawater these data together with considerations of reaction kinetics and mass balance within the cariaco basin are consistent with the hypothesis that anoxic marine settings can serve as a chemical archive of first order trends in seawater 53 cr composition additionally the cariaco basin data suggest that there has been secular stability in the average 53 cr value of atlantic seawater over the last 15 kyr

uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late ediacaran period abstract to improve estimates of the extent of ocean oxygenation during the late ediacaran period we measured the u and mo isotope compositions of euxinic anoxic and sulfidic organic rich mudrocks orm of member iv upper doushantuo formation south china the average 238 u of most samples is 0 24 0 16 2sd relative to standard crm145 which is slightly higher than the average 238 u of 0 02 0 12 for restricted black sea deep water unit i euxinic sediments and is similar to a modeled 238 u value of 0 2 for open ocean euxinic sediments in the modern well oxygenated oceans because 238 u is preferentially removed to euxinic sediments compared to 235 u expanded ocean anoxia will deplete seawater of 238 u relative to 235 u ultimately leading to deposition of orm with low 238 u hence the high 238 u of member iv orm points to a common occurrence of extensive ocean oxygenation ca 560 to 551 myr ago the mo isotope composition of sediments deposited from strongly euxinic bottom waters h 2 s aq 11 m either directly records the global seawater mo isotope composition if mo removal from deep waters is quantitative or represents a minimum value for seawater if mo removal is not quantitative near the top of member iv 98 mo approaches the modern seawater value of 2 34 0 10 high 98 mo points to widespread ocean oxygenation because the preferential removal of isotopically light mo to sediments occurs to a greater extent in o 2 rich compared to o 2 deficient marine environments however the 98 mo value for most member iv orm is near 0 relative to standard nist srm 3134 0 25 suggesting extensive anoxia the low 98 mo is at odds with the high mo concentrations of member iv orm which suggest a large seawater mo inventory in well oxygenated oceans and the high 238 u hence we propose that the low 98 mo of most member iv orm was fractionated from contemporaneous seawater possible mechanisms driving this isotope fractionation include 1 inadequate dissolved sulfide for quantitative thiomolybdate formation and capture of a seawater like 98 mo signature in sediments or 2 delivery of isotopically light mo to sediments via a particulate fe mn oxyhydroxide shuttle a compilation of mo isotope data from euxinic orm suggests that there were transient episodes of extensive ocean oxygenation that break up intervals of less oxygenated oceans during late neoproterozoic and early paleozoic time hence member iv does not capture irreversible deep ocean oxygenation instead complex ocean redox variations likely marked the transition from o 2 deficient proterozoic oceans to widely oxygenated later phanerozoic oceans

the cr isotope signature of surface seawater a global perspective abstract this study presents chromium isotope data expressed as 53 cr and chromium concentrations cr of surface seawater 0 2 m depth from a variety of locations worldwide in addition to samples from the open ocean arctic southern pacific and atlantic oceans samples were analysed from areas with more restricted water exchange rates the mediterranean sea oresund and baltic sea the data indicate a heterogeneous distribution of 53 cr in seawater with a total range from 0 13 to 1 24 the data are in agreement with a previous study which focused on depth profiles suggesting that seawater heterogeneity in 53 cr and cr concentration can be explained using a single fractionation factor for cr reduction e 0 79 0 06 2sd in basins with limited water exchange with the open ocean however local factors seem to control the cr isotope composition

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

cadmium isotope variations in the southern ocean abstract cadmium concentrations and isotope compositions were determined for 47 seawater samples from the high nutrient low chlorophyll hnlc zone of the atlantic sector of the southern ocean the samples include 13 surface waters from a transect of the weddell gyre and 3 depth profiles from the weddell sea and drake passage the southern ocean mixed layer samples from this study and abouchami et al 2011 define a clear but broad hnlc trend in a plot of e cd 114 110 versus cd which is primarily a consequence of isotopic fractionation associated with biological uptake e cd 114 110 is the deviation of the 114cd 110cd ratio of a sample from nist srm 3108 cd in parts per 10 000 the trend is especially apparent in comparison to the large range of values shown by a global set of seawater cd data for shallow depths the southern ocean samples are also distinguished by their relatively high cd concentrations typically 0 2 to 0 6 nmol kg and moderately fractionated e cd 114 110 generally between 4 and 8 that reflect the limited biological productivity of this region detailed assessment reveals fine structure within the hnlc trend which may record differences in the biological fractionation factor different scenarios of closed and open system isotope fractionation and or distinct source water compositions southern ocean seawater from depths 1000 m has an average e cd 114 110 of 2 5 0 2 2se n 16 and together with previous results this establishes a relatively constant e cd 114 110 value of 3 0 0 3 2se n 27 for global deep waters significant isotopic variability was observed at intermediate depths in the southern ocean seawater from 200 m to 400 m in weddell sea has high cd concentrations and e cd 114 110 as low as 1 presumably due to remineralization of cd from biomass that records incomplete nutrient utilization antarctic intermediate water which was sampled at 150 to 750 m depth in the drake passage features a distinct cd isotope signature of e cd 114 110 4 which reflects biological isotope fractionation at the surface and subsequent mixing into the ocean interior taken together our results demonstrate that coupled cd isotope and concentration data provide valuable insights into the distribution and biological cycling of cd in the water column the highly systematic nature of cd isotope signatures may furthermore prove to be of utility for future research in marine geochemistry and paleoceanography

modulation of the southern ocean cadmium isotope signature by ocean circulation and primary productivity article i nfo article history the high nutrient low chlorophyll hnlc southern ocean plays a key role in regulating the biological pump and the global carbon cycle here we examine the efficacy of stable cadmium cd isotope fractionation for detecting differences in biological productivity between regions our results show strong meridional cd isotope and concentration gradients modulated by the antarctic fronts with a clear biogeochemical divide located near 56 s the coincidence of the cd isotope divide with the southern boundary of the antarctic circumpolar current acc together with evidence for northward advection of the cd signal in the acc demonstrate that cd isotopes trace surface ocean circulation regimes the relationships between cd isotope ratios and concentrations display two negative correlations separating the acc and weddell gyre into two distinct cd isoscapes these arrays are consistent with rayleigh fractionation and imply a doubling of the isotope effect due to biological consumption of cd during water transport from the weddell gyre into the acc the increase in magnitude of cd isotope fractionation can be accounted for by differences in the phytoplankton biomass community composition and their physiological uptake mechanisms in the weddell gyre and acc thus linking cd isotope fractionation to primary production and the global carbon cycle 2011 elsevier b v all rights reserved

contourites associated with pelagic mudrocks and distal delta fed turbidites in the lower proterozoic timeball hill formation epeiric basin transvaal supergroup south africa abstract five genetic facies associations architectural elements are recognised for the epeiric sea deposits preserved in the early proterozoic timeball hill formation south africa basal carbonaceous mudrocks interpreted as anoxic suspension deposits grade up into sheet like laminated graded mudrocks and succeeding sheets of laminated and cross laminated siltstones and fine grained sandstones the latter two architectural elements are compatible with the te td and tc subdivisions of low density turbidity current systems thin interbeds of stromatolitic carbonate within these first three facies associations support photic water depths up to about 100 m laterally extensive sheets of mature cross bedded sandstone disconformably overlie the turbidite deposits and are ascribed to lower tidal flat processes interbedded lenticular immature sandstones and mudrocks comprise the fifth architectural element and are interpreted as medial to upper tidal flat sediments small lenses of coarse siltstone very fine grained sandstone analogous to modern continental rise contourite deposits occur within the suspension and distal turbidite sediments and also form local wedges of inferred contourites at the transition from suspension to lowermost turbidite deposits blanketing and progressive shallowing of the floor of the timeball hill basin by basal suspension deposits greatly reduced wave action thereby promoting preservation of low density turbidity current deposits across the basin under stillstand or highstand conditions a lowstand tidal flat facies tract laid down widespread sandy deposits of the medial klapperkop member within the formation salinity gradients and contemporaneous cold periglacial water masses were probably responsible for formation of the inferred contourites the combination of the depositional systems interpreted for the timeball hill formation may provide a provisional model for early proterozoic epeiric basin settings

a c mos2 mixed layer phase mosc occurring in metalliferous black shales from southern china and new data on jordisite a new phase composed mainly of mo s and c and referred to herein as mosc occurs widely in organic rich metalliferous cambrian black shales in south china mosc which has previously been referred to as jordisite has been studied by scanning electron microscopy sem electron microprobe analysis empa transmission electron microscopy tem powder x ray diffraction xrd extended x ray absorption fine structure exafs and catalytic activity tem data show mosc to have a layered structure with packets resembling molybdenite and graphite like carbon that average five layers in thickness analytical data are consistent with an idealized formula of mo3s6c10 but it commonly contains 1 3 wt each of fe ni and as so that its composition may be better approximated by the formula mo fe ni 3 s as 6c10 selected area electron diffraction saed patterns show a small number of broad inhomogeneous rings corresponding to randomly oriented layers arranged in subspherical cells a single broad weak peak corresponds to a 10 11 a layer spacing in powder xrd diffraction patterns pseudomorphism after fossil bacteria implies an origin by replacement of sedimentary organic material in its chemical properties and structure mosc resembles synthetic compounds used as catalysts for hydrodesulfurization hds in the petrochemical industry the large surface to volume ratio for mosc may be an important factor in its relatively strong hds catalytic activity cotype samples of jordisite from germany previously thought to be amorphous mos2 were also studied by sem and tem jordisite occurs as sequences of a few curved layers that form sub spherical units with an appearance remarkably like that of mosc however the layer spacing is 6 a like that of molybdenite the ratio of mo s is 1 2 and no carbon was detected although it coexists with kerogen jordisite is thus confirmed to be a form of mos2 but because powder diffraction like saed patterns were obtained it is not amorphous

transient deep water oxygenation in the early cambrian nanhua basin south china abstract many late neoproterozoic to early cambrian fossils of multicellular eukaryotes including those of benthic animals are found preserved under anoxic and even euxinic bottom water conditions which is contradictory to the consensus that oxygen is essential to eukaryotes to investigate this conundrum we conducted an integrated study of iron speciation redox sensitive trace elements and mo isotopes 98 mo on the black shale interval of the lower cambrian hetang formation 535 521 ma at lantian south china in which benthic sponge fossils are abundant in the lower member lm but absent in the upper member um iron speciation data point to uniformly anoxic ferruginous conditions in the lm and euxinic conditions in the um whereas the trace element and 98 mo data show greater secular variation in redox conditions the lm shows higher mean trace element concentrations mo 108 ppm u 36 ppm v 791 ppm and lower and more variable 98 mo 0 13 to 1 76 relative to the um mo 45 ppm u 18 ppm v 265 ppm 98 mo 1 59 to 1 67 and ratios of redox sensitive trace element concentrations to total organic carbon are significantly more variable and higher on average in the lm relative to the um the appearance of sponge fossils and lower 98 mo values correlate strongly with gray i e lighter colored layers in the lm these patterns can best be interpreted as recording mainly euxinic conditions throughout deposition of the study units with more intense background euxinia in the lm relative to the um but also with frequent transient oxygenation events in the lm that do not appear in the um the transient oxygenation events of the lm led to the initial colonization of the deep nanhua basin by sponges and the termination of these events in the um caused sponge faunas to disappear until a general rise in o 2 levels later in the cambrian permitted their return to deeper water habitats our study also illustrates that multiple geochemical and paleobiological proxies exhibit different responses in poikiloredox environments i e characterized by small scale spatial and high frequency temporal variations which can lead to apparent contradictions between metazoan fossil occurrences and their inferred watermass redox conditions

surface water oxygenation and bioproductivity a link provided by combined chromium and cadmium isotopes in early cambrian metalliferous black shales nanhua basin south china abstract the intrinsic link between atmospheric oxygenation surface seawater redox and bioproductivity in the upper water column of oceans offers to combine cadmium with chromium isotopes in marine archives to deduce information on past controls of biological metal and nutrient cycling we here use a novel approach in combining chromium and cadmium isotope signatures in metalliferous and organic matter om rich shales from the early cambrian niutitang formation south china to reconstruct the surface water redox and cycling of bioessential metals in a period directly following the cambrian animal evolution the inventory of authigenic cd in the black shales is controlled by their sulfide abundance whereas authigenic cr is dominantly controlled by iron oxy hydroxides and om cadmium isotopes measured on bulk sediments and 3 n hno3 leachates exhibit e114cd values from 1 5 to 4 5 with mo ni rich sulfidic shales revealing elevated values 2 5 chromium isotopes define 53cr values from 0 4 to 1 7 with v rich non sulfidic shales yielding more positively fractionated signatures than mo ni rich sulfidic shales the negative 53cr e114cd correlation trend recorded in the black shales suggests a high e114cd sulfide endmember of authigenic cd preserved in anoxic bottom conditions the other endmember is constituted by om with the isotopically heavy cr and light cd signals reflecting efficient phytoplankton uptake in the photic zone the endmembers constrain the cd and cr isotope signatures of surface waters in the early cambrian nanhua basin to e114cd of 7 to 17 and to 53cr of 0 7 to 1 9 these values are compatible with those of modern ocean surface waters and attest to a cambrian surface ocean water sustaining elevated primary bioproductivity in the aftermath of late ediacaran snowball earth glaciations our study emphasizes the potential of the cr cd double tracer in studies aimed at the reconstruction of paleoproductivity and bio geochemical metal cycling in marine paleo basins

late holocene mobilisation of loess like sediments in hohuan shan high mountains of taiwan abstract silty cover soils are found in lower slope positions in the highest massifs of the high mountains of taiwan they are not formed under present day conditions and remain well preserved in locations not affected by fluvial morphodynamics this study focuses on an outcrop in the hohuan mountain summit area the sediment infill of a gully is described and sediment properties are analysed size frequency distributions of the sediment grains suggest that they are partly aeolian deposits the loess like sediments yielded osl ages between 3 65 0 62 ka and 1 72 0 48 ka results from radiocarbon dating of organic rich bulk sediments support the age estimates from osl the timing of gully infilling coincides with a cool and dry phase reported by palynological studies from toushe basin and chitsai lake the sediment record reflects a large scale climatic change to cooler and less humid conditions in the hohuan mountain area

new u pb age from the basal niutitang formation in south china implications for diachronous development and condensation of stratigraphic units across the yangtze platform at the ediacaran cambrian transition abstract the black shale dominated niutitang formation covers a large portion of the early cambrian yangtze platform in south china the base of this unit has been traditionally taken as the ediacaran cambrian boundary ca 542 ma recent radiometric ages from the basal niutitang formation and its correlative units however are significantly younger than 542 ma and raise questions about the diachrony of stratigraphic units across the yangtze platform at the ediacaran cambrian transition here we report a new u pb sensitive high resolution ion microprobe shrimp age of 522 7 4 9 ma from a tuffaceous bed of the basal niutitang formation in a deep water section in taoying guizhou province of south china this age in combination with existing ages and biostratigraphic data suggests that the base of the niutitang formation is of tommotian or upper meishucunian age and the ediacaran cambrian boundary is most likely within the liuchapo formation the depositional age of the unusual metal enriched ni mo pge sulfide deposits which are approximately 1 m above the ca 523 ma tuffaceous bed should be early tommotian upper meishucunian rather than early nemakit daldynian lower meishucunian regional correlation confirms the diachronous development and condensation of stratigraphic units across the early cambrian yangtze platform and provides important information for understanding the paleogeography and paleoceanographic events at the ediacaran cambrian transition in south china

extensive oxidative weathering in the aftermath of a late neoproterozoic glaciation evidence from trace element and chromium isotope records in the urucum district jacadigo group and puga iron formations mato grosso do sul brazil abstract the massive fe and mn deposits of the urucum district banda alta formation and the iron formations from fazenda sao manoel puga formation in mato grosso do sul brazil are associated with glacigenic deposits and represent the youngest and largest sedimentary fe and associated mn formation if mnf deposits of cryogenian age in the world the urucum district ifs studied are predominantly composed of pure classical plane parallel and stratified hematite chert iron and intercalated manganese cryptomelane micro and mesobands whereas the ifs at fazenda sao manoel are closely associated with diamictites and shales although the precise depositional age is unknown maximum age constraints for the puga ifs are defined by the youngest detrital zircon with an u pb age of 706 9 ma babinski et al 2013 a result which we here confirm by a u pb age of the youngest zircon of 695 17 ma from within shaly beds in the urucum district if succession redox sensitive trace element signatures and tendency to hump shaped rare earth element yttrium rey patterns with negative ce but without eu anomalies support the presence of an oxic surface water layer fertilized by low temperature hydrothermal fluids injected from submarine thermal springs and or alternatively by significant fresh water input directly derived from glacial meltdown strongly positively fractionated authigenic chromium isotope signatures average 53 cr 1 10 0 4 n 16 2 prevailing throughout the entire stratigraphic section indicate that riverine supply of continentally derived cr remained more or less constant throughout the glacier meltdown and if depositional period cycling across a redoxcline and predominant deposition of the if in anoxic deeper seawater of the jacadigo basin is supported by the peculiar presence of subchondritic y ho ratios by decreased negative ce anomalies and by shifts of lree patterns towards higher values in the urucum district ifs that are independent of detrital contamination the strongly positively fractionated cr isotope signatures measured in these iron formations are compatible with those from other iron formations and black shales deposited during the late neoproterozoic and precambrian cambrian transition worldwide and are in support of prevailing high atmospheric o 2 levels following the late neoproterozoic glaciations that accompanied the evolution of macroscopic multicellular organisms

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

cadmium isotope fractionation in seawater a signature of biological activity investigations of cadmium isotope variations in the oceans may provide new insights into the factors that control the marine distribution and cycling of this element here we present the results of cd isotope and concentration analyses for 22 seawater samples from the atlantic southern pacific and arctic oceans the results reveal for the first time large and well resolved cd isotope fractionations in the marine environment the majority of the seawater samples display an inverse relationship between dissolved cd contents and isotope compositions which range from e114 110cd 3 0 5 for cd rich waters 0 8 1 0 nmol kg to e114 110cd 38 6 for surface water with a cd concentration of only 0 003 nmol kg all e114 110cd data are reported relative to the jmc cd munster standard this suggests that the cd isotope variations reflect kinetic isotope effects that are generated during closed system uptake of dissolved seawater cd by phytoplankton a few samples do not follow this trend as they exhibit extremely low cd contents 0 008 nmol kg and nearly un fractionated cd isotope compositions such complexities which are not revealed by concentration data alone require that the cd distribution at the respective sites was affected by additional processes such as water mass mixing atmospheric inputs of cd and or adsorption uniform isotope compositions of e114 110cd 3 3 0 5 1 s d were determined for seawater from 900 m depth despite of cd concentrations that display the expected increase along the global deep water pathway from the atlantic 0 3 nmol kg to the pacific ocean 0 9 nmol kg this indicates that the biomass which is remineralized in the deeper ocean is also characterized by a very constant cd isotope composition this observation is in accord with the interpretation that the cd distribution in surface waters is primarily governed by rayleigh fractionation during near quantitative uptake of dissolved seawater cd

non rayleigh control of upper ocean cd isotope fractionation in the western south atlantic abstract we present seawater cd isotopic compositions in five depth profiles and a continuous surface water transect from 50 s to the equator in the western south atlantic sampled during geotraces cruise 74jc057 ga02 section leg 3 and investigate the mechanisms governing cd isotope cycling in the upper and deep ocean the depth profiles generally display high e 112 110 cd at the surface and decrease with increasing depth toward values typical of antarctic bottom water aabw however at stations north of the subantarctic front the decrease in e 112 110 cd is interrupted by a shift to values intermediate between those of surface and bottom waters which occurs at depths occupied by north atlantic deep water nadw this pattern is associated with variations in cd concentration from low surface values to a maximum at mid depths and is attributed to preferential utilization of light cd by phytoplankton in the surface ocean our new results show that in this region cd deficient waters do not display the extreme highly fractionated e 112 110 cd reported in some earlier studies from other oceanic regions instead in the surface and subsurface southwest sw atlantic when cd drops below 0 1 nmol kg 1 e 112 110 cd are relatively homogeneous and cluster around a value of 3 7 in agreement with the mean value of 3 8 3 3 2sd n 164 obtained from a statistical evaluation of the global ocean cd isotope dataset we suggest that cd deficient surface waters may acquire their cd isotope signature via sorption of cd onto organic ligands colloids or bacterial picoplankton extracellular functional groups alternatively we show that an open system steady state model is in good accord with the observed cd isotope systematics in the upper ocean north of the southern ocean the distribution of e 112 110 cd in intermediate and deep waters is consistent with the water mass distribution with the north south variations reflecting changes in the mixing proportion of nadw and either aabw or aaiw depending on the depth overall the sw atlantic cd isotope dataset demonstrates that the large scale ocean circulation exerts the primary control on e 112 110 cd cycling in the global deep ocean

drifts and ponds of reworked pelagic sediment in part of the southwest pacific abstract since the late oligocene a bottom current that decelerates as it leaves the constricted samoan passage has deposited patches of reworked sediment on a blanket of paleogene clay and on a scoured terrain of mesozoic outcrops the sediments preserve a record of fluctuations in the geological effect and by inference the velocity of the pacific s western boundary current an area of 750 km 2 sediment drift was studied in detail with 18 cores and observations from a near bottom instrument it has rapid vertical and lateral facies changes from nodule covered zeolitic clay to radiolarian clay and ooze related to temporal and spatial changes in rate of deposition of current transported particles the source of most of the radiolaria is erosion of older outcrops upstream or current trimming of the drift margins so the siliceous ooze may be considered a variety of muddy contourite small ferromanganese concretions on the surface of a slowly accumulating part of the drift are arranged in long narrow stripes resembling abyssal furrows similar patterns believed to be caused by erosional bedforms were mapped by side scan sonars on the corrugated surfaces of ponds of calcareous turbidites other pelagic carbonate beds within the drifts were rapidly deposited from thermohaline currents it may be difficult to distinguish some calcareous contourites from turbidites after textures have been altered by early diagenesis but identifications based on field relations and topographic situation can be supported by detailed lithologic study the times of most rapid drift deposition from the bottom current were late oligocene early miocene probably caused by initiation of this western boundary flow from antarctica and late miocene early pliocene probably caused by intensified bottom circulation following glacial expansion

anomalous mercury enrichment in early cambrian black shales of south china mercury isotopes indicate a seawater source abstract extremely elevated hg levels up to the g g 1 range were found in sulfide rich black shale and phosphorite in the lowermost part of the early cambrian black shale sequences on the yangtze platform in south china in this study mercury isotopes were used to help resolve the origin of this anomalous hg enrichment mass independent fractionation signatures of hg isotopes with positive 199 hg values of 0 13 to 0 24 and positive 200 hg values of 0 05 to 0 10 were observed indicating seawater is an important source of hg we hypothesize that upwelling of nutrient rich waters from the open ocean resulted in high bioproductivity in the photic zone with concomitant scavenging of hg from seawater advanced decay of biomass and remineralization under anoxic to euxinic conditions combined with very low clastic input led to enrichment of hg and a broad spectrum of other redox sensitive and biogenic metals up to 10 7 compared to modern seawater such spectacular hydrogenous metal enrichment has previously been observed in the oxic deep sea environment only i e manganese crusts nodules

the stable cr isotope inventory of solid earth reservoirs determined by double spike mc icp ms abstract we present the first comprehensive set of stable cr isotope data for the major igneous silicate earth reservoirs cr iii rich ores and minerals and hydrothermal chromates these were determined by mc icp ms using a double spike technique mantle xenoliths ultramafic rocks cumulates as well as oceanic and continental basalts share a common cr isotope composition with an average 53 52 cr value of 0 124 0 101 2 sd relative to the isotopically certified chromium standard nist srm 979 an isotopic difference between mantle xenoliths and basalts as was reported for iron was not observed for chromium thus the change in oxidation state that is observed when solid mantle rocks containing only trivalent chromium partially melt to form basaltic melts which predominantly contain bivalent chromium does not cause any measurable cr isotope fractionation chromite separates from major chromitite seams of the bushveld and great dyke layered igneous complexes are invariable in their cr isotope compositions and reproduce within uncertainties the average 53 52 cr srm 979 value of igneous silicate earth reservoirs this is important for environmental stable cr isotope studies because it labels the approximate isotope composition of industrial cr vi pollutants the cr isotope compositions of hydrothermal lead chromates crocoites pbcr vi o 4 from various localities yield 53 52 cr srm 979 values between 0 640 and 1 037 these cr isotope compositions are substantially heavier than those of igneous silicate rocks from which the chromium was leached precipitation experiments revealed an isotope fractionation of 53 52 cr crocoite cr vi aq of only ca 0 10 0 05 at a temperature of 20 c thus the heavy cr isotope signature of crocoites is most likely the result of repeated redox cycling of chromium in hydrothermal processes

trace and rare earth element geochemistry of black shale and kerogen in the early cambrian niutitang formation in guizhou province south china constraints for redox environments and origin of metal enrichments abstract early cambrian black shales of south china not only host important sponge arthropod and other soft bodied fossils that have helped to trace early metazoan diversification but also show extreme enrichments of a number of trace metals in particular ni mo and v in this study we use a new approach by analyzing rare earth elements in kerogen extracted from the black shales together with a number of redox sensitive trace element compositions and total organic carbon toc concentrations in an early cambrian black shale sequence in zunyi guizhou province south china to place better constraints on the oceanic redox conditions and the origin of the extreme metal enrichment our data show significant negative ce anomalies ce ce as low as 0 4 occurring in kerogen which indicate an oxygenated surface environment of primary productivity in consistent with the concept that the organic matter is mainly derived from organisms in the euphotic zone mass balance calculation suggests that the kerogen associated ree can dominate the measured black shale ree budget while similarity between our measured ree patterns and those of similarly aged phosphorites indicates that the ree content of ancient phosphorites may have also derived initially from organic matter the redox sensitive trace elements such as u v mo and their ratios of u al v al and mo al in black shales show different correlation patterns with toc contents the upper black shales show a good metal toc correlation but such a correlation is absent in the lower part the lower black shales exhibit much higher metal enrichments compared to black sea sulphidic euxinic sediment this is taken to indicate the presence of sulphidic bottom waters during the deposition of the lower black shales including the ni mo ore layer in contrast anoxic non sulphidic conditions occurred during the deposition of the upper black shales taking all these geochemical data together we suggest that the early cambrian south china seaway was strongly stratified and stagnant and that euxinic bottom water conditions may have led to enrichment of the redox sensitive metals such as u v and mo in the lower black shales and in one case the occurrence of a polymetallic ni mo sulphide ore bed bearing an extraordinarily extreme metal enrichment which according to the mo toc and ni toc ratios and much other geochemical evidence may have been additionally influenced by hydrothermal input of metals within the rift basin as suggested by a number of previous studies

mass dependent cadmium isotopic variations in nature with emphasis on the marine environment abstract we report a survey of natural mass dependent cadmium isotope fractionation measured by thermal ionization mass spectrometry using a double spike technique ds tims over sixty samples of natural terrestrial cd from diverse environments including morb oib continental loess hydrogenic and hydrothermal ferromanganese deposits and sphalerites both oceanic and from major continental ore deposits were analysed our results are expressed in terms of e 112 110 cd which are deviations in 112 cd 110 cd from our in house jmc cd standard in parts per 10 4 the total e 112 110 cd variation is relatively small with a range of only 5 e units and is one to two orders of magnitude smaller than that previously found in meteorites the morb oib and loess e 112 110 cd values are similar and provide a good estimate for the bulk silicate earth bse value which is 0 95 0 12 relative to our cd standard e 112 110 cd 0 16 relative to munster jmc cd taken together these data suggest little cd isotope fractionation takes place during crust mantle segregation cd isotopic compositions of continental sphalerite zns deposits worldwide and high temperature oceanic hydrothermal sulphides show remarkably similar e 112 110 cd values consistent with our estimate for the bse in contrast mid temperature oceanic sulphides from a single extinct hydrothermal chimney display over 4 e units variation along with the most negative values these variations are most probably caused by precipitation redissolution of sulphide phases en route within the hydrothermal system the e 112 110 cd variability found in worldwide marine fe mn deposits reflects the seawater cd isotope signal upon precipitation from ambient seawater a decrease in e 112 110 cd is observed in passing from shallow water fe mn deposits to those from deeper waters 2000 m depth this shift is explained by biological fractionation related to the uptake of dissolved seawater cd by phytoplankton in the upper water column the relatively uniform e 112 110 cd values close to zero at great depths are consistent with regeneration and remineralization of cd at depth our data suggest that cd isotopes much like the cd ca ratio in foraminifera could potentially serve as a proxy for past changes in biological productivity the temporal cd isotope record in a fe mn crust archive at 2000 m depth from the ne atlantic suggests no gross long term changes in cd cycling took place over the past 8 ma

bottom current controlled sedimentation a synthesis of the contourite problem abstract an overview of the main items concerning deep bottom current controlled deposits is presented these include the definition of contourites their processes of deposition and facies characteristics contourite drift types and seismic patterns the interplay of turbidity and bottom current processes and the correlation between bottom current processes and global changes in climate sea level from this discussion several of the more significant problems are highlighted which we believe should be priority targets for future research 1 identification of contourites especially in ancient series where they are interbedded with turbidites and other facies 2 refinement of the numerous parameters used as tracers of palaeocirculation patterns 3 understanding the interaction between the different types of bottom currents and also between bottom current and other deep water processes 4 distinction in the sedimentary record between the effects of short time scale bottom current variations due to regional causes like benthic storms and geological scale current fluctuations related to climatic or astronomic control 5 understanding the control of glacial interglacial climatic cycles on the nature and rate of contourite deposition