interaction of magmatic fluids and silicate melt residues with saline groundwater in the footwall of the sudbury igneous complex ontario canada new evidence from bulk rock geochemistry fluid inclusions and stable isotopes abstract along the northern margin of the 1 85 ga sudbury igneous complex sic canada a volumetrically minor rock type known as the footwall granophyre fwgp preserves evidence of the interaction of magmatic fluid and groundwater the fwgp comprises veins dikes and irregular bodies of a quartz alkali feldspar plagioclase intergrowth that are most abundant near footwall style cu ni platinum group element mineralization textures and cross cutting relations show that the emplacement of the fwgp created favourable sites for the later deposition of sulfides geochemical and physical evidence show that the fwgp did not form by in situ partial melting of the archean country rocks in the footwall beneath the sic it represents a mobilized injected silicate residue from either the contact between partially melted country rocks and the sic or from the crystallizing sic itself its bulk composition can be modeled as the product of fractional crystallization of a liquid with an initial composition equivalent to granophyric matrix trapped liquid in the lowermost units of the sic norite and sublayer primary fluid saline h 2 o poor and melt silicate h 2 o rich inclusions hosted in quartz from the fwgp have bulk and trace element compositions consistent with those hosted in quartz from the granophyric matrix of the lower units of the sic norite sublayer fluid inclusions contain mixtures of a high salinity 44 70 wt nacl equivalent n 39 na fe rich aqueous magmatic fluid and a lower salinity ca and sr rich groundwater the magmatic end member is thought to be an sic derived volatile phase estimates of the mixing proportions show that primary and secondary inclusions in the fwgp contain 60 100 and 30 80 of the magmatic end member by mass respectively fluids responsible for the remobilization of ore metals represent mixtures containing a much higher proportion of the groundwater end member not less than 70 by mass compared to the fluids trapped in the fwgp at considerable distance 400 m from the sic the chlorine isotope composition of biotite in the fwgp is enriched in 37 cl 37 cl 0 98 to 1 61 scapolite from the high temperature veins and the interstices of rock types in the main mass of the sic shows similar enrichment in 37 cl up to 1 34 whereas biotite from the archean country rocks 37 cl 0 88 to 0 53 and associated groundwater are 37 cl depleted the results of this study lead to two important conclusions concerning genetic and exploration models for the footwall ore zones first magmatic end member fluid introduced into the footwall with the melt from which the fwgp crystallized contained very little cu rarely 100 ppm the main ore metal in the footwall ores this result questions hydrothermal models for footwall ore formation that hypothesize that cu and other ore metals were remobilized from sulfide deposits along the sic contact by magmatic hydrothermal fluids and redeposited in the footwall it is more likely that ore metals were only locally remobilized in the footwall ore zones when metal poor hybrid fluids interacted with pre existing sulfide veins of magmatic origin second inclusions containing the hybrid fluid occur in the fwgp rock type throughout the footwall in both mineralized and unmineralized areas therefore although the fwgp preserves stable cl isotope and fluid inclusion evidence that magmatic fluid was introduced into the footwall detection of this magmatic component alone will not serve as a useful exploration method in contrast mapping the distribution and abundance of fwgp may be ore predictive since fwgp emplacement and its higher abundance in mineralized areas appears to have been a structural and textural prerequisite for footwall ore emplacement

alpine crustal shear zones and pre alpine basement terranes in the romanian carpathians and apuseni mountains the carpathian orocline formed by complex suturing of small continental fragments to the east european and moesian plate remnants of continental fragments belong to three pre alpine lithotectonic assemblages a greenstone granite association and two gneissic assem blages during alpine collision pieces of crust were repeatedly fragmented and welded to accommodate heterogeneous strain along the irregular east european plate boundary shallow structural levels of alpine tectonic discontinuities in which the locus of most intense strain migrated over time are now exposed as wide retrograde greenschist grade belts repeated mainly transpressive deformation resulted in early ductile fabrics being overprinted by local brittle shear strain igneous intrusion accompanied different phases of tectonic activity the age of shearing initiation is probably late paleozoic and the configuration of the zones and their alpine internal structures are consistent with the geometry of the carpathian arc

a special issue devoted to the mineral deposits of the sudbury basin the magmatic ni cu platinum group element pge deposits in the sudbury area were discovered in 1883 giblin 1984 as ni has grown from a chemical curiosity through early use in armor plating to its present day pervasive role in modern industry resources have continued to be discovered around the periphery of the sudbury igneous complex and even richer ore zones have been identified in the footwall rocks making sudbury one of the world s largest and most productive mining camps the premining resource production current resource of the sudbury mining camp has been estimated to be 1 648 million metric tons at 1 2 percent ni and 1 0 percent cu naldrett and lightfoot 1993 as of 2000 the camp had produced 9 69 million metric tons of ni 9 59 million metric tons of cu 69 6 thousand metric tons of co 116 metric tons of au 319 metric tons of pt 335 metric tons of pd 37 6 metric tons of rh 23 3 metric tons of ru 11 5 metric tons of ir 3 710 metric tons of ag 3 002 metric tons of se and 256 metric tons of te from 781 million metric tons of ore ontario ministry of northern development and mines information and marketing services section 2002 sudbury remains one of the world s largest producers of ni with an annual production of 114 thousand metric tons plus 137 thousand metric tons of cu 1 8 metric tons of au and 11 4 metric tons of total platinum group minerals ontario ministry of northern development and mines information and marketing services section 2000 because of its great economic significance the sudbury basin has been studied intensively by local mining companies federal and provincial survey geologists and numerous university researchers landmark papers include the post war synthesis by stevenson 1963 the first recognition of the impact origin of the structure by dietz

trace metal distributions in seawater and anoxic brines in the eastern mediterranean sea abstract the vertical distribution of dissolved and particulate trace metals mn fe ni cu cd is reported for seawater and the anoxic brines of tyro and bannock basins in the eastern mediterranean in normal mediterranean seawater the distribution of dissolved trace metals is governed by water mass circulation as well as by local input sources for cd and possibly cu steady state behaviour is not a viable assumption probably as a result of anthropogenic sources in agreement with previous reports no correlation was observed between dissolved ni cu cd and the major nutrients at the seawater brine interface all trace metals show dramatic changes in concentration in the brines the concentrations of dissolved fe and mn are strongly elevated compared to overlying waters yet probably limited by formation of solid sulfide and or carbonate phases the distributions of dissolved fe and sulfide show a remarkable mirror image of those found previously in the orca brine gulf of mexico and the ionic concentration products are approximately the same in all three basins the difference in absolute fe and sulfide concentrations is thought to be caused by a high supply of fe to orca basin concentrations of dissolved ni cu and cd in the brines are at least one order of magnitude lower than in overlying waters most likely due to formation of solid sulfide phases we believe these data provide the first indication of substantial nickel sulfide co precipitation within an anoxic basin particulate metal concentrations are elevated at the seawater brine interface and are probably associated with the presence of solid sulfide phases in addition the extreme density gradient at the interface will slow the sinking rate of particles and lead to accumulation of particles at the interface due to accumulation

authigenic sulfide and carbonate mineral formation in holocene sediments of the baltic sea formation of authigenic sulfides and carbonates in holocene 14c dated sediments is interpreted based on analyses of cations fes s fes2 s corg and sulfur isotopes mineral distribution was studied in thin sections and mineral morphology with sem eds the sediments were deposited in the gotland deep baltic sea during freshwater and brackish stages calcium rich rhodochrosite mnco3 occurs in concentrations up to 17 dw in brackish water sediments and are mainly confined to 0 02 0 5 mm thick laminae the frequency with which these laminae occur suggests that they formed with a periodicity of one to a few years and their purity suggests that formation took place in a few weeks we propose that these carbonate laminae resulted from oxic water inflow to the euxinic basin mn ii dissolved in the water column was rapidly oxidized and large amounts of mn oxides reached the sediment reduction of these mn oxides in a high alkalinity environment facilitated rhodochrosite precipitation at the sediment surface pyrite in the brackish water sediments formed at or above the sediment water interface in an iron limited environment due to alternating oxic and euxinic conditions fes was oxidized resulting in a high fes2 sfes s ratio median 170 formation of iron sulfides in the freshwater sediments occurred below the sediment water interface in a sulfate limited environment as a result of the rapid exhaustion of reactive iron in the brackish water sediments excess h2s diffused downwards to pyritize the uppermost part of the underlying freshwater sediments

preliminary evaluation of trace hydrocarbon speciation and abundance as an exploration tool for footwall style sulfide ores associated with the sudbury igneous complex ontario canada deposits of cu ni platinum group elements pge rich sulfides occur along the north range footwall of the sudbury igneous complex ontario canada the deposits have been modified chemically mineralogically and texturally by multiple syn to postmagmatic hydrothermal events and are hosted mainly within sudbury breccia a contact metamorphosed and hydrothermally altered impact breccia the composition of c1 to c6 unsaturated and saturated hydrocarbons in bulk fluid inclusion volatiles in the matrix of the sudbury breccia was investigated using in line rock crushing gas chromatography gc in order to compare the hydrocarbon composition of this rock type in breccia zones containing economic footwall sulfide deposits at the morrison deposit levack mine north range sudbury ontario with barren breccia zones trace hydrocarbons possibly abiogenic in origin occur throughout the sudbury igneous complex footwall and country rocks investigated however there are differences in the composition and abundance of bulk hydrocarbons released from mineralized and barren sudbury breccia when fluid inclusions are opened volatiles released from samples of sudbury breccia from sulfide mineralized and sulfide barren environments showed the following 1 higher average abundances of light saturated hydrocarbons c1 c4 and an approximately 2 higher total abundance of hydrocarbons mol g of rock basis associated with samples from the mineralized study area and 2 comparable average unsaturated hydrocarbon abundances in both settings but a larger range in unsaturated hydrocarbon abundances in the mineralized study area differences in bulk hydrocarbon abundance and composition reflect differences in the abundance and hydrocarbon content of fluid inclusions trapped in the barren and mineralized sudbury breccia zones in addition the compositional modification of circulating fluids by processes and conditions unique to the mineralized sudbury breccia environment may have occurred prior to inclusion entrapment e g modification by mineral catalysts differences in temperature and oxygen fugacity preliminary spatial analysis of the hydrocarbon distribution within and surrounding the morrison deposit shows that the total hydrocarbon abundance in the sudbury breccia does not change with orebody proximity within a single host breccia zone however volatiles trapped in the sudbury breccia matrix near the top of the footwall deposit where it is physically connected to contact style ni cu pge ores have elevated unsaturated hydrocarbon abundances e g propene compared to other parts of the same breccia zone distal to this zone of physical connection samples of the pge enriched sudbury breccia and mineralized veins containing alteration assemblages characteristic of the footwall ore styles have higher unsaturated hydrocarbon abundances and unsaturated saturated ratios compared to sudbury breccia and vein samples that are pge poor localized enrichments in unsaturated hydrocarbons in sudbury breccia zones may be the result of specific ore minerals and metal complexes involving the pge and group viii metals that acted as catalytic agents modifying the composition of initially light saturated hydrocarbon species prior to entrapment in fluid inclusions to apply the analysis of hydrocarbon compositions in trapped fluid inclusions to discriminating mineralized from barren zones of sudbury breccia samples from targeted areas were compared to samples of barren sudbury breccia background although a large data set is presented here to establish these compositional fields analysis of smaller sample subsets from each environment yields a statistically significant separation between the two environments total hydrocarbon abundance c3 c1 ratios and unsaturated saturated hydrocarbon ratios are useful indicators of sulfide ore proximity and may help delineate regions enriched in pge

trace metal speciation in sea and pore water of the gotland deep baltic sea 1994 abstract studies on the speciation particulate colloidal anionic and cationic forms of trace metals cd co cu fe mn mo ni pb zn in the water column and in pore waters of the gotland deep following the 1993 94 salt water inflows showed dramatic changes in the total dissolved metal concentrations and in the ratios between different metal species in the freshly re oxygenated waters below 125 m changes in concentrations were greatest for those metals for which the solubility differs with the redox state fe mn co but were also noted for those metals which form insoluble sulphides cd pb cu zn and or stable complexes with natural ligands cu pore water data from segmented surface muds 0 200 mm indicated that significant redox and related metal speciation changes took place in the surface sediments only a few weeks after the inflow of the oxygenated sea water into the gotland deep

the significance of partial melting processes in hydrothermal low sulfide cu ni pge mineralization within the footwall of the sudbury igneous complex ontario canada we present new results and review existing data highlighting different aspects of the genetic relationship between partial melting and hydrothermal mineralizing processes in the contact aureole of the sudbury igneous complex at the basal contact of the igneous complex in the footwall breccia crystallized partial melt pods and veins referred to as footwall granophyres are abundant and intrude all rock types including the breccia matrix as well as massive ni cu sulfide ore the final crystallization of these melts was accompanied by the segregation of high salinity fluids dominantly in the temperature range of 450 to 550 c as revealed by ti inquartz thermometry and studies on primary fluid inclusions in mineralized parts of the footwall breccia there is clear evidence that interaction of partial melts exsolved fluids and preexisting magmatic sulfides occurred in the deeper footwall of the sudbury igneous complex similar footwall granophyres occur as networks of veins intruding impact brecciated sudbury breccia country rocks and have an intimate spatial association with hydrothermal low sulfide assemblages highly enriched in pt pd and au with a unique assemblage of pgm including malyshevite and lisiguangite it is suggested that partial melting processes were widespread in the contact and proximal footwall environment of the igneous complex and they were important in providing high salinity magmatic fluids to a hydrothermal system responsible for redistribution of base and precious metals we describe observations which may evidence the migration of partial melts from the contact into the deeper footwall furthermore we suggest a cogenetic model for the precipitation of sulfide hydrous silicate assemblages in close spatial association to footwall granophyres we emphasize that the use of footwall granophyres in mineral exploration for cu ni pge ores in the footwall of the sudbury igneous complex is clearly justified mapping of footwall granophyre vein networks highlights areas that were proximal to the contact environment and point out structural pathways that may have been used by syn or postgenetic mineralizing fluids in a given area widespread partial melting appears to have occurred in the footwall of other large mafic ultramafic complexes such as bushveld and duluth and similar genetic relationships of partial melting and ore forming hydrothermal processes may have possibly existed also in these systems

regional gravity setting of the sudbury structure in the vicinity of sudbury ontario canada the boundary between the southern and superior tectonic provinces is overlain by the elliptical sudbury structure on the basis of gravity modeling genesis of the sudbury structure has been attributed to either a magmatic origin having a dense hidden differentiate zone or a meteorite impact origin there being no dense hidden mass the difference between the two gravity models centers on the problem of regional residual separation as shown by numerous previous studies any such separation of components is nonunique this becomes especially problematic when as in sudbury a portion of the near surface geology has a similar orientation and dimension to more deep seated sources in this paper several numerical methods upward continuation downward continuation wavelength filtering trend surface analysis for determining the regional component of the gravity field associated with the sudbury structure have been applied and evaluated of the numerical methods used the upward and downward continuation operators provided the most insight into the deep structural controls of the sudbury basin our preferred interpretation of the regional gravity field invokes a two component structure underlying the southern half of the sudbury structure is a laterally continuous gravity anomaly that is probably associated with a zone of uplifted huronian volcanics the gravity anomaly under the northern portion of the sudbury structure has a more restricted spatial extent the close association between the northern limit of the gravity anomaly and the surface outcrop of the levack gneiss suggests the source of this anomaly is probably a slab of dense levack gneiss this interpretation favors a meteorite impact origin for the sudbury structure

a model for late quaternary methane ice core signals wetlands versus a shallow marine source 1 a three reservoir model with first order kinetics for methane records in the vostok antarctica and gisp2 greenland ice cores reproduces the sawtooth pattern and the maximum and minimum concentrations the model also returns an atmospheric methane relaxation time of 10 years for both cores which is the same as current estimates the characteristics of the source reservoirs are long relaxation times 33 3 and 100 ky and high initial methane concentrations 2500 and 7000 ppm for gisp2 and vostok respectively these characteristics are consistent with gas hydrate sources in shallow marine sediments but not with wetland sources which have insufficient storage capacity and low source strength

a textural mineralogical and statistical study of the footwall breccia within the strathcona embayment of the sudbury structure the footwall breccia is one of the main ni cu pge ore hosting units of the sudbury camp this polymict matrix supported contact metamorphosed breccia occurs between the sudbury igneous complex and the footwall rocks along the west north and east margins of the sudbury structure in areas where there are depressions or embayments in the footwall the footwall breccia and basal units of the sudbury igneous complex are thickened and the footwall breccia is variably mineralized mineralogical and textural variations of footwall breccia samples from the strathcona embayment in proximity to the fraser mine suggest that the mineralogy and texture of this unit vary as a function of proximity to the sudbury igneous complex proximity to ore and location within the embayment the most mafic footwall breccia mineralogy is present proximal to the base of the sudbury igneous complex within a transition zone the presence of relatively mafic hydrous and cl rich silicate minerals e g biotite and amphibole characterize the footwall breccia matrix around ore zones and form an alteration halo of up to 5 m thick textural variations include a coarsening of quartz and feldspar grains with increasing proximity to the sudbury igneous complex contact textural coarsening also occurs from the margins of the strathcona embayment to the center together these mineralogical and textural variations influence the color of the footwall breccia matrix and can explain some of the gray colors that are typical of mineralized footwall breccia these variations also constrain the timing of formation of this unit and suggest that at least three phases of footwall breccia exist

atmospheric impacts and ice core imprints of a methane pulse from clathrates in relation to arctic warming the possible occurrence of methane hydrate degassing events has attracted an increasing interest in recent years we evaluate the atmospheric impact of rapid and massive emissions of methane and how they are imprinted in ice core records by combining for the first time models of atmospheric chemistry and trace gas transport in firn different emission characteristics as well as climatic conditions present pre industrial glacial are considered the d isotopic signatures characterizing stable isotopologues of methane dch3 and 13 ch4 are also analysed our results suggest little effect of clathrate degassing on the main methane oxidant oh radicals due to the relatively short atmospheric lifetime of methane the simulated clathrate induced perturbations last for less than a century this time scale is comparable to or shorter than the duration of air bubble closure in polar ice sheets as a consequence rapid methane perturbations in the atmosphere are strongly smoothed in ice core records this smoothing mostly depends on the snow accumulation rate at the site of ice core drilling we propose a methodology to identify a potential clathrate degassing event in ice core records continuous ch4 records from high accumulation rate sites could allow to decipher short time scale events d do f ch 4 should reveal a typical lying s shape at high accumulation rate sites reflecting the combined effects of the clathrate source signature negative excursion and subsequent oh fractionation in the atmosphere positive excursion the amplitude ratio of the negative and positive dd swings recorded in greenland and antarctica under similar accumulation rate conditions could also indicate the latitude of a clathrate degassing event

structural analysis of the central and southwestern sudbury structure southern province canadian shield the sudbury structure ss is an unusual crater structure which acquired its present oval surface shape during northwest directed ductile thrusting lower amphibolite facies metamorphism accompanied the thrusting which generated a major reverse shear zone at least 50 km long the south range shear zone srsz transects the south range of the sudbury structure and exhumes a low level of the sudbury igneous complex sic assuming heterogeneous simple shear in the northwest southeast vertical plane on northeasterly striking glide surfaces minimal estimates of net displacement across the srsz exceed 8 km this displacement magnitude and the map pattern of the sic require the southwest closure of the ss to be steeply plunging in accord with a hypothetical funnel shape of the sic the rocks of the metasedimentary core of the ss are deformed into a family of second order buckle folds the tangent surface of which forms an upright open flexure within the first order structure of the sudbury synclinorium the

multiple fluid generations in the sudbury igneous complex fluid inclusion ar o h rb and sr evidence abstract the elliptically zoned sudbury structure in northern ontario is host to world class nickel copper pge deposits which are generally regarded as the products of a single magmatic event however there is increasing evidence of multi episodic fluid rock including ni cu sulphide interactions in the sudbury structure that range from early remobilization of the cooling ores ca 1850 ma through metamorphism and deformation related to the penokean orogeny to neotectonic fracturing ca 5 13 ma previous fluid inclusion studies have identified an h2o nacl co2 kcl fluid of highly variable phase ratios intimately associated with the ores and a distinct population of primary two phase fluid inclusions associated with post intrusion metasomatic alteration this study introduces two new distinct populations of fluid inclusions 1 a population represented by two phase co2 bearing fluid inclusions hosted along healed fracture planes in quartz that offset ore minerals that was trapped between 280 340 c and 1750 to 3500 bars pressure as the fluid inclusion trails offset and therefore post date the ore their genesis is consistent with a late penokean 1 83 1 89 ga or later ca 1450 contractional event 2 a two phase highly saline 16 wt nacl equivalent fluid hosted within neotectonic 5 13 ma rb sr galena sphalerite calcite quartz chlorite veins inclusions of this fluid were trapped at temperatures ranging from 60 to 135 c and maximum confining pressures of 950 bars stable isotope data o d from biotite amphibole and epidote from the alteration assemblages of remobilized veins within the sudbury structure show distinct evidence of a mixing trend of fluids originating within or near the magmatic water box and trending towards a metamorphic fluid of isotopic composition similar to an evolved sudbury structure groundwater ar ar data from the amphiboles within sudbury intrusive complex sic footwall breccia from the craig mine are consistent with a mixed ar ar spectrum the step heating ar release spectrum yields ages ranging from ca 1800 ma at the low temperature end to approximately 2640 ma for high temperature steps these dates are in agreement with the ca 1850 and 2647 ma ages for the sic and levack gneisses respectively and are interpreted as the reinjection of country rocks partially melted by the sic back into the sudbury structure the isotopic evidence for mixed fluids derived from a combination of a magmatic fluid and a regional groundwater metamorphic fluid suggests that the highly variable phase ratio fluid inclusions associated with the ore may be divided into two end member fluids represented by an exsolved sic fluid and a regional groundwater metamorphic fluid this is consistent with at least five distinct fluids being present during the evolution of the sudbury structure

natural flux of greenhouse methane from the timor sea to the atmosphere 1 methane gas bubbles from the cornea seep were sampled at the sea surface in the timor sea continental shelf area in june 2005 total bubble gas flux was 0 076 to 0 76 l m 2 h 1 during the 6 h d 1 periods of low neap tides in june 2005 this bubble gas contained an average of 26 mmol ch4 l 1 and about 0 16 and 0 006 mmol l 1 of ethane and propane we estimate the daily flux from the sea surface to the atmosphere to be 0 012 to 0 12 mol ch4 m 2 d 1 or 0 13 to 1 3 t ch4 d 1 from an area of about 0 7 km2 this methane flux came from a 500 1400 m carbonate pavement dome on the seafloor at 84 m water depth the seep hard ground was swath mapped and 3 5 khz subbottom profile data indicate that the seep dome was strongly reflective with poor penetration into the subsurface consistent with the presence of a carbonate hard ground carbon and deuterium isotope ratios 13c 41 to 42 d 157 to 158 of the seep bubble gas indicate that this methane had a thermogenic origin and was in the same isotopic range as gas within the late cretaceous cornea oil and gas field we could not detect inputs of fluids containing nutrients or short lived radium isotopes at this site commonly associated with other cold seeps tens to a hundred of kilometers seaward from the cornea seep site water column dissolved methane concentrations in this sector of the timor sea shelf and slope were 100 500 times supersaturated with respect to the atmosphere and thus the water column is expected to be degassing additional methane to the atmosphere perhaps there are thousands of other methane seeps of similar magnitude to the cornea seep on this shelf and slope to account for all the excess dissolved methane 86 000 t measured in the water column these measured and calculated fluxes provide evidence for the hypothesis that shallow sea seeps may be a significant source of atmospheric methane in contrast to deep sea vents where most of the methane is dissolved and oxidized in seawater and does not reach the atmosphere

the recent salt inflow into the baltic sea abstract major inflows of highly saline and oxygenated water into the baltic sea are rare events and many of the basic processes underlying them are unknown in january 1993 strong gales led to an intensive inflow that interrupted the 16 year stagnation of the central baltic deep water the different stages of the overflow across the sill area between the north sea and the baltic are discussed in connection with the forcing conditions and the propagation of the water that flowed into the central baltic is briefly described moreover the potential effects of the recent inflow are estimated

multi stage hydrothermal processes involved in low sulfide cu ni pge mineralization in the footwall of the sudbury igneous complex canada amy lake pge zone east range the amy lake pge zone is a low sulfide type cu ni pge mineralization in the east range footwall of the 1 85 ga sudbury igneous complex occurring in a 100 m wide sudbury breccia belt that coincides with an impact related major fracture zone bay fault zone detailed hydrothermal alteration mapping fluid inclusion trace element and stable isotope studies revealed a complex alteration and mineralization history in a multi source multi stage sudbury related hydrothermal system the two major stages of syn sudbury hydrothermal activity are characterized by similarly high salinity high temperature fluids that are 1 locally derived from footwall granophyre bodies and typified with high ni cu and pge s ratios and high ree contents magmatic hydrothermal stage and 2 a more voluminous cu ni pge rich fluid flux probably originated from the sudbury igneous complex footwall contact hydrothermal stage the second hydrothermal flux was introduced by brittle fractures in the area and resulted in a complex zonation of alteration assemblages and mineralization governed by local footwall composition the sudbury related hydrothermal event was overprinted by shear related epidote veining and calcite chlorite replacement both regionally present in the sudbury structure based on analogies the most important factors involved in the formation of hydrothermal low sulfide mineralization are proposed to be 1 accumulation of pge enriched fluids 2 large scale brittle structures as conduits to these fluids and 3 adequate host rock composition as a chemical trap resulting in sulfide and pgm precipitation in environments meeting these criteria hydrothermal pge mineralization is known to have formed not only in the sudbury footwall but also from mafic ultramafic intrusions associated with primary magmatic pge from several locations around the world

recycling of manganese from anoxic sediments in stagnant basins by seawater inflow a study of surface sediments from the gotland basin baltic sea abstract the occurrence of mn carbonates in sapropelic sediments has been proposed to indicate that the host sediment originally accumulated under oxygenated bottomwaters in the central baltic sea ca rich rhodochrosite layers in sapropelic sediments have been related to inflows of oxic seawater from the north sea into the brackish predominantly anoxic deeps of the central baltic this study attempts to verify the model of authigenic mn carbonate formation by comparing oceanographic records directly with the composition of surficial sediments of the gotland basin surface sediments of the gotland deep sampled in 1997 displayed significant ca rich rhodochrosite enrichments at 6 5 11 and 15 cm sediment depth which reflect periods of intense seawater inflows in 1969 76 1948 56 and 1931 39 respectively however the latest major seawater inflow detected in 1993 was not reflected in the surface sediment the topmost 6 cm of the sediment was totally depleted in mn and 210pb data implied a disturbed top layer down to 5 cm calculations of saturation indices indicate that the porewaters were undersaturated with respect to mn and ca carbonate phases in the uppermost 8 cm in 1997 at greater depths the porewaters were close to equilibrium with respect to calcite and rhodochrosite the ca rhodochrosite layers corresponded well to a sediment core sampled at the same location in 1994 but that core displayed a further enrichment of ca rich rhodochrosite close to the sediment surface which can be related to a major inflow of north sea water in 1993 the significant decrease of about 2 3 mol m2 mn in the uppermost 6 cm of a disturbed sediment surface from 1994 to 1997 corresponds to an enrichment of about 20 mol l of dissolved mn within the 90 m thick anoxic water column in 1997 we conclude that several inflows of dense seawater into the gotland deep monitored between 1994 and 1997 led to a resuspension of the unstable fluffy surface sediment layer authigenic ca rich rhodochrosite which had formed immediately after the major inflow of oxic seawater in 1993 was therefore redissolved in undersaturated bottomwaters and mn was recycled from surficial sediments into the water column this in turn means that in contrast to the established model of ca rhodochrosite formation as a result of seawater inflow the occurrence of mixed mn depleted layers does not prove that seawater inflow has not occurred during the deposition of these sediments

deformation of the sudbury structure paleomagnetic evidence from the sudbury breccia abstract paleomagnetic results from fine grained samples of sudbury breccia collected from 28 sites around the northern half of the 1 85 ga sudbury igneous complex sic reveal the existence of two major components of magnetization a and b a carried by magnetite was formed close to the time of the sic and has a direction that is related to the dip of the norite unit within the different ranges of the sic component b mainly carried by pyrrhotite is a younger secondary magnetization of more problematical origin in part related to heating during the 1 24 ga sudbury magmatic event in the northwest part of the sic a is found in breccia clasts intermediate norite sublayer levack gneiss and matachewan diabase indicating that it is due to baking by the sic tilt correcting the west range by 36 the north range by 22 and the northern east range by 36 about axes parallel to local strike of the norite minimises the dispersion of the paleomagnetic data to give a pre folding direction of 199 4 78 8 the paleomagnetic data are similar to those obtained by morris morris w a 1984 paleomagnetic constraints on the magmatic tectonic and metamorphic history of the sudbury basin region in pye e g naldrett a j giblin p e eds the geology and ore deposits of the sudbury structure special vol 1 ontario geological survey pp 411 427 on the sic suggesting for the first time that the sic and the surrounding basement were deformed probably during the 1 9 1 7 ga penokean orogen as a single unit the un folding of the paleomagnetic directions indicates that sic limbs were already inclined a result of the original intrusion configuration or a syn folding remanence it is possible that the sic was originally flatter if the distribution of paleomagnetic directions is the result of flexural flow folding this explanation could also produce a similar distribution of paleomagnetic directions across the basin but cannot be quantified due to the lack of measurable fold related strain in breccia and sic units around the northern half of the basin

strontium and neodymium isotopic characteristics of a heterolithic breccia in the basement of the sudbury impact structure canada abstract rb sr and sm nd measurements were undertaken on footwall breccia samples originating from levack township in the north range of the sudbury structure the granitic to quartzdioritic matrix of this heterolithic breccia which contains shocked rock and mineral fragments yields a rb sr isochron age of 1 825 0 021 ga isr 0 70356 0 00005 2 errors based on the analysis of 3 6 mm thick adjacent whole rock slabs from a large hand specimen this age is interpreted as a cooling age after the thermal metamorphism of the footwall breccia by the 1 85 ga old sudbury igneous complex which had caused temperatures in excess of 1000 c in the matrix near the contact mafic rock fragments in this breccia were excluded from the sr isotope exchange at that time the sm nd system of the identical small whole rock samples was only partly disturbed by the sudbury igneous complex the data points scatter around a 2 05 0 49 ga regression line without age significance plagioclase k feldspar and mafic mineral phases of the breccia matrix combined with the corresponding whole rocks display a range in rb sr ages from 1 67 0 08 ga to 1 430 0 015 ga obviously associated with metasomatic processes in the footwall breccia during the declining penokean metamorphism strontium and neodymium model parameters of the footwall breccia matrix near levack show little variation esrt 16 33 to 18 07 endt 10 69 to 11 79 t 1 86 ga and mean tnddm 2 74 0 04 ga based on these results bedrocks exposed in the south range and rocks now forming the sedimentary filling of the sudbury basin can be excluded as major components in the matrix of the analyzed footwall breccia the convergence of neodymium model ages with u pb ages on zircons from the levack gneiss which forms the crystalline basement adjacent to the footwall breccia in the levack area support an exclusively local origin for matrix and fragments of this breccia it is proposed that the footwall breccia is part of the uplifted floor of the sudbury crater

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

high chlorine alteration minerals and calcium rich brines in fluid inclusions from the strathcona deep copper zone sudbury ontario the strathcona deep copper zone consists of a complex suite of massive sulfide veins that occupy a series of fractures in the footwall gneisses and sudbury breccia it is characterized by the occurrence of branching quartz veinlets and hydrothermal alteration selvages along the margins of massive sulfide veins hornblende or actinolite epidote calcite and ferropyrosmalite fe mn 8 si 6 o 15 oh c1 10 occur in the inner zones of the alteration selvages adjacent to the massive sulfide veins annite chlorite and albite are developed in the outer zones fe rich silicates of the alteration assemblages contain significant amounts of chlorine ferropyrosmalite contains 5 79 to 6 54 wt percent cl hornblende contains up to 2 99 wt percent cl annite contains up to 2 13 wt percent cl primary fluid inclusions in the quartz from the branching veinlets are mutiphase consisting of vapor liquid and more than four solids the solid crystals of opened inclusions identified by scanning electron microscope are na ca k k pb k fe and fe mn chlorides the sequence of melting events and the nature of the solid phases suggest that the trapped fluids are nacl cacl 2 h 2 o solutions with minor k fe mn and pb these fluid inclusions are highly saline avg 60 wt nacl cacl 2 calcium rich ca na 1 by weight and homogenize to liquid at temperatures 260 degrees to 420 degrees c 342 degrees or 35 degrees c mean or std dev two options are proposed for the origin of the fluids melt fluid phase separation during sulfide liquid crystallization and convection of ambient fluids across the contact of the sulfide veins the cl rich fluids may have participated in the precipitation of pd and probably other platinum group elements pge at a later stage but they did not transport the pge very far from the magmatic sulfide veins

geologic transect across the grenville orogen of ontario and new york revised cross sections of the western grenville province incorporate new geologic results and reprocessed seismic reflection data the geology is presented in terms of three tectonic elements 1 pre grenvillian laurentia and its margin with ca 1740 and 1450 ma continental arc plutons and associated supracrustal rocks 2 composite arc belt of allochthonous 1300 1250 ma volcanic arcs and sedimentary rocks and 3 frontenac adirondack belt characterized by supracrustal and granitoid rocks and anorthosites of uncertain affinity that may represent a distinctive part of the composite arc belt or an offshore micro continent rocks of the composite arc and frontenac adirondack belts were amalgamated with each other by ca 1160 ma were then thrust over laurentia during ca 1080 1035 ma and ca 1010 980 ma phases of convergence and were dissected and exhumed by 1040 ma normal faults penetrative deformation was restricted to that part of the pre grenvillian laurentian margin that lies to the southeast of the grenville front and parts of the accreted composite arc and frontenac adirondack belts the laurentian rocks in the grenville province are bounded to the northwest and southeast by southeast dipping ductile thrust and or normal shear zones the composite arc and frontenac adirondack belts to the southeast are bounded by ductile and brittle ductile thrust and or normal faults that separate domains with contrasting cooling histories despite a long pre grenvillian tectonic and plutonic history the present crustal architecture and much of the seismic reflectivity were acquired during 1080 980 ma phases of compression and extension

dynamic response of oceanic hydrate deposits to ocean temperature change the dynamic response of oceanic hydrate deposits to ocean temperature change matthew t reagan and george j moridis earth sciences division lawrence berkeley national laboratory 1 cyclotron rd berkeley ca 94720 usa

magnetic interpretation along the sudbury structure lithoprobe transect magnetic modelling of the sudbury structure ss has been undertaken using the geometrical and lithological framework provided by high resolution seismic reflection data this initial constraint was required because of the complex magnetic properties exhibited by rock units of the ss locally remanent magnetisation nrm dominates over induced magnetisation and the orientation and amplitude of the nrm vector varies both between and within individual rock units the use of measured magnetic susceptibility and nrm values afforded an important constraint in the modelling process and provided a valuable insight into the genesis of the various magnetic anomalies the magnetic anomaly profile along the lithoprobe transect across the ss appears to arise from three main sources a a broad regional magnetic anomaly ascribed to a more magnetic layer of the levack gneiss complex subjacent to the base of the sudbury igneous complex sic b a prominent magnetic high associated with the southern contact between the onwatin and onaping formations believed to reflect a zone of hydrothermal mineralisation and c a magnetic high associated with the southern contact between the sic and the huronian mafics is related to the juxtaposition of rock units produced by northward directed thrusting and an enhanced nrm signature in the basal unit of the south range norite

the end of the ice age methane gas hydrates may have contributed to the rapid rise in atmospheric ch4 co2 and global temperatures at the end of the last major glaciation about 13 500 years ago given suitable orbital conditions and insolation at high latitude a small triggering event such as the release of one or more arctic gas pools may have initiated massive release of methane from hydrate under ice and in permafrost the consequent greenhouse warming would have provided strong positive feedback amplifying emission this warming driven by ch4 may have induced the release of co2 from the oceans to the biosphere stabilizing the interglacial carbon cycle

fluid inclusion evidence for hydrothermal enrichment of magmatic ore at the contact zone of the ni cu platinum group element 4b deposit lindsley mine sudbury canada most ni cu platinum group element pge deposits of the sudbury igneous complex 1 85 ga have massive or disseminated magmatic segregational characteristics however stringers and disseminations of chalcopyrite rich platinum group mineral pgm bearing fe ni cu sulfides at the contact of the lindsley 4b orebody with the enclosing murray granite 2 4 ga contain quartz k feldspar biotite epidote stilpnomelane amphibole garnet and other hydrous silicates associated with pgm sphalerite galena native au pyrite and mackinawite these assemblages in fracture controlled veins and disseminations are compatible with hydrothermal processes being responsible for the enriched grade near the contact fluid inclusion petrography and microthermometry reveal that hydrothermal activity took place in five stages early nacl cacl 2 h 2 o type fluids were trapped in k feldspar of the metasomatically altered murray granite at temperatures of about 370 degrees to 410 degrees c and 270 degrees c later quartz intergrown with sulfides contains fluid inclusions with nacl kcl cacl 2 h 2 o type solutions trapped between 200 degrees to 380 degrees c and 130 degrees to 230 degrees c sem eds analyses of chlorides in inclusions reveal that these fluids were also enriched in ba pb fe and mn later fluids trapped in secondary inclusions 200 degrees 240 degrees c were cacl 2 nacl h 2 o type temperature calculations assume 2 kbars lithostatic pressure all aqueous inclusions are characterized by high salinity 23 43 wt low temperature secondary inclusions contain co 2 ch 4 fluids carbonic fluids are related to metamorphism accompanying deformation during the penokean orogeny the higher temperature fluids were heated by the sudbury igneous complex the observations support the hypothesis that very saline hot fluids interacted with igneous minerals and primary magmatic ores and remobilized base and precious metals and precipitated them along permeable fractured and brecciated zones to produce cu pge au concentration disseminated sulfides and veins

formation and solid solution behavior of ca rhodochrosites in marine muds of the baltic deeps authigenic ca rhodochrosites are found in organic rich sediments in the deep anoxic basins of the baltic sea rhodochrosite formation is apparently the result of organic matter degradation the rhodochrosite contains 10 to 40 mol caco3 and 2 to 5 mol mgco3 as determined by microprobe the composition of the carbonates at a given depth varies by about 5 mol mnco3 sem revealed the rhodochrosite to be present as globular aggregates consisting of microcrystallites dissolution features such as cavities within the aggregates are frequently observed and indicate that extensive recrystallization takes place pore waters are greatly supersaturated with respect to both rhodochrosite and calcite rhodochrosite is only found in sediments where pore waters show the highest degree of supersaturation due to ion exchange ca2 diffuses from the underlying freshwater clays this results in increasing aca2 amn2 ratios in the pore waters from the sediment surface downward in response to this the maximum caco3mnco3 ratio also increases with depth the composition of rhodochrosite which forms under these conditions may be determined by both the porewater aca2 amn2 and precipitation kinetics however if their composition is controlled solely by the aca2 amn2 in solution their behavior can be described by a regular solid solution model

chlorine and alkali geochemical halos in the footwall breccia and sublayer norite at the margin of the strathcona embayment sudbury structure ontario the ni cu platinum group element ores in the sublayer and footwall breccia of the sudbury structure have distinctive geochemical halos in the fraser mine f cl ratios of the sublayer rocks appear to decrease na2o k2o ratios of the footwall breccia samples decrease and cl in both units increases with proximity to mineralization these halos are interpreted to result from interaction of residual magmatic fluids with host rocks which altered the host rock mineralogy and precipitated cl bearing minerals the results of this study together with the results of previous studies suggest that most ores at sudbury including sublayer and footwall breccia hosted contact ores and sudbury breccia hosted footwall ores are surrounded by cl and possibly alkali halos and that these geochemical signatures may be used to identify rocks that are proximal to mineralization

heavy metal pollution of sediments from the polish exclusive economic zone southern baltic sea analysis of 59 surface sediment samples from the polish exclusive economic zone eez shows that szczecin lagoon sediments are the most polluted by heavy metals and that the degree of heavy metal pollution decreases substantially on passing from the szczecin lagoon to the pomeranian bay and the inner shelf area and then on passing to the bornholm deep and slupsk furrow heavy metal pollution in the sediments of the western part of the polish eez therefore appears to follow the dispersion of the oder river fluffy material from the oder estuary appears to be the main source of heavy metals in the muddy sediments of the bornholm deep the formation of sulphides is therefore not the principal factor controlling the enrichment of heavy metals in the sediments of this anoxic basin although it may be responsible for the uptake of mo sb and as two main factors control the distribution of the rare earth elements ree in sediments of the polish eez the input of fe organic colloids from rivers and the presence of detrital material in the sediments

combined organic and inorganic geochemical reconstruction of paleodepositional conditions of a pliocene sapropel from the eastern mediterranean sea layers of organic carbon rich sapropels in the sediment record of the mediterranean sea give evidence of repetitive changes in regional plio pleistocene climate results from biomarker molecule and major and trace element analyses of closely spaced samples are used to reconstruct the conditions leading to deposition of a pliocene sapropel at ocean drilling program odp site 969 on the mediterranean ridge organic carbon concentrations increase from 0 2 outside the sapropel and peak to more than 30 within it major and trace elemental composition and biomarker derived parameters indicate elevated productivity depletion of water column dissolved oxygen content and changes in sediment provenance in response to climatic changes budgets of rhenium thallium and other trace metals indicate that deep water exchange between the mediterranean subbasins and the atlantic ocean was not completely interrupted during sapropel formation enrichment factors of redox sensitive and sulfide forming trace metals as well as the presence of isorenieratene derivatives and high stanol sterol ratios point to an extended zone of anoxic water masses depth profiles of biomarker compositions sterols long chain alkenones alkandiols and ketols fatty acids indicate great floral diversity during deposition of a single sapropel and highlight the sensitive response of the marine community to variable environmental conditions changes in water mass circulation and eolian transport can be reconstructed by use of both lithogenic elements and average chain lengths of n alkanes acl index

dynamic treatment of geochemical cycles global kinetics some of the key concepts needed to understand global kinetics of geochemical cycles are discussed residence times are related in a simple way to the kinetics of a cycle with one reservoir because geochemical cycles may sometimes require non linear global kinetics and because non linear systems can behave quite differentialy from their linear counterparts two particularly important aspects of non linear global kinetics are discussed first non linearity may lead to the existence of multiple steady state and under some circumstances systems may incur sudden changes from one steady state to another the second aspect of non linearity deals with the effects of coupling feedback between the cycles of different elements coupling between elements occurs within a local environment or in a true global sense and the kinetics analyzed show that coupling can have dramatic effects of the stability of the cycles hence the relative constancy of the amounts of some elements in various global reservoirs can be understood from the point of view of coupling of the global kinetics jmt

deep geometry of the sudbury structure from seismic reflection profiling seismic reflection data show the deep geometry of the sudbury structure to be markedly asymmetric the sudbury north range comprises shallowly south dipping sedimentary strata overlying a thick unit of heterolithic breccia and melt bodies layered rocks of the sudbury igneous complex and footwall gneiss reflections from the upper layers are interrupted by faults near the center of the sudbury basin whereas the basal mafic units and footwall gneiss continue dipping southward and appear to be tightly folded or truncated near the creighton fault in contrast the seismic image of the south range is dominated by a distinctive series of moderately south dipping reflections interpreted as thrust faults or shear zones on which severe telescoping and imbrication of lithological units and considerable northwest southeast shortening of the sudbury structure have occurred such shortening explains the noncircular shape of the structure and thus removes a critical objection to the sudbury impact crater hypothesis the new structural model is shown to be consistent with regional magnetic and gravity fields a large hidden ultramfic mafic mass is no longer required to explain the potential field data

dating of a regional hydrothermal system induced by the 1850 ma sudbury impact event new u pb geochronologic data from the sudbury structure directly link extensive hydrothermal activity in crater fill breccias with the 1850 ma impact event and constrain complex impact induced processes to 4 m y semiconformable alteration of breccias in the onaping formation includes silicification albitization chloritization calcitization and complex feldspathization which directly underlies zn cu pb ore deposits geochronologic data demonstrate a middle to lower crustal source for the crater fill deposit that was subsequently affected by the hydrothermal event at 1848 4 3 8 1 8 ma these and other data confirm that the crater fill breccia hydrothermal system sudbury igneous complex and its sublayer ni ore bearing units were emplaced as a result of impact the ages of events associated with the sudbury structure are now more closely constrained than in any other meteorite impact structure

petrology and crystallization history of multiphase sulfide droplets in a mafic dike from uruguay implications for the origin of cu ni pge sulfide deposits sulfide blebs in a mafic dike belonging to the uruguayan dike swarm replicate at a small scale many features observed in larger platinum group element enriched nickel copper sulfide deposits such as in sudbury and noril sk these blebs formed by the crystallization of droplets of immiscible sulfide liquid form 1 cm sized ovoid geopetal structures with pyrrhotite and pentlandite at the base chalcopyrite and cubanite at the top and titaniferous magnetite at the margins magnetite crystallized first followed by nickel and iron rich monosulfide solid solution which sank to the bottom of the droplets and from which pyrrhotite and pentlandite subsequently exsolved the remaining copper rich liquid in the upper part of the droplets crystallized to form an intermediate solid solution from which chalcopyrite and cubanite subsequently exsolved the final extremely evolved cu fe s rich pd sn pb mo ag bi te and sb bearing liquid crystallized as 10 to 20 sized veinlets filling fractures in the magnetite and adjacent silicate minerals the veinlets crossing the magnetite often terminate in 100 m sized subrounded globules at the contact of the magnetite and the surrounding silicate minerals indicating a direction of veinlet filling away from the center of the blebs textural evidence in the blebs illustrates that as crystallization proceeded and the immiscible sulfide liquid droplets within the dike sank a distance of less than 1 mm relative to the adjacent silicate onto already partially crystallized silicate minerals the sulfide liquid surrounded and resorbed the already solid magnetite grains at the top of the blebs magnetite grains were isolated above the sulfide liquid and partially surrounded by quartz plagioclase and amphibole an assemblage representing a late stage magma that had been drawn into the space created above the droplets as they sank and which is more evolved than that of the surrounding host dike the location of the blebs within the dike isolated from influences external to the dike indicates both that the fracture filling by evolved immiscible cu rich sulfide liquid is related to crystallization processes rather than later tectonic events and that the bismuth tellurium and antimony have a late magmatic origin associated with crystallization of the immiscible sulfide liquid

hydrous sulfide melting experimental evidence for the solubility of h2oin sulfide melts the effect of h 2 o on sulfide melting temperatures has been investigated in the fes pbs zns system at 1 5 gpa revealing that the addition of h 2 o results in a 35 c drop in melting temperature from 900 to 865 c in addition to the melting point depression the solubility of h 2 o is confirmed by the presence of vesicles in the quenched melt no oxide phases were present in any of the run products ruling out oxidation as a cause of the melting point depression confirmation of the solubility of h 2 o in sulfide melts is consistent with the recent suggestion by mungall and brenan 2003 of a magmatic origin for halogen rich alteration associated with magmatic sulfide ore deposits as the hydrous component of the alteration may similarly originate in the fractionating sulfide melt anatectic sulfide melts could be expected to contain more h 2 o than magmatic sulfide melts owing to the lack of a parental silicate melt that buffers the h 2 o content of magmatic sulfide melts fluids expelled from the cooling anatectic melts such as that present during granulite facies metamorphism of sulfide deposits at broken hill australia may have been responsible for associated retrograde hydrothermal alteration

early diagenesis of trace metals used as an indicator of past productivity changes in coastal sediments in sediments of kiel bight which differ significantly in their redox states and the rates of corg degradation depth profiles of both dissolved and solid phase fe mn cd cu ni and co were measured porewater fluxes of cd cu and ni were significantly higher at shallower more oxic stations as compared to highly reducing deeper subthermocline sediments while mn fluxes behaved the opposite way when normalized to fe for grain size correction the measured solid phase metal contents revealed that the high porewater flux has led to a near surface depletion of mn from more anoxic sediments and to a reduced rate of accumulation of anthropogenic cd in more oxic sediments this difference in early diagenetic behaviour suggests the use of these metals as a proxy for the redox state and the intensity of carbon recycling contrary to the recent sediment layers the normalized metal contents of preindustrially deposited sediment layers were similar for both metals at all stations thus at stations having highly anoxic sediments today the preindustrial benthic flux must have been lower for mn and higher for cd reflecting a shift from more oxic to more reducing conditions in subthermocline sediments during the last 100 years this change of the redox state in subthermocline sediments reflects an increase of primary production and of subsequent corg input to the sediment due to eutrophication which accompanied industrialization