vivianite formation and its role in phosphorus retention in lake orn denmark abstract vivianite fe 3 po 4 2 8h 2 o may precipitate in anoxic lake sediments affecting the porewater orthophosphate concentration and thereby the trophic status of lakes we have investigated changes in lake diagenesis of fe and p 1969 2009 with particular attention focused on vivianite formation with sediment depth 0 20 cm in an iron silica carbon rich lake sediment ornso denmark porewaters were supersaturated for vivianite by two to five orders of magnitude upper 10 cm with porewater phosphate concentrations ranging between 0 69 and 10 mol l 1 in winter and summer concentrations ranging between 9 8 and 40 mol l 1 significant formation of vivianite was confirmed by x ray diffraction while scanning electron microscopy and electron dispersive x ray spectroscopy indicated an increase in vivianite crystal size with depth 20 to 70 m across variations in elemental composition of vivianite crystals in relation to at p and fe were especially seen going from 9 5 cm to 24 5 cm the total sediment fe pool was very large 3000 mol g 1 and total p increased from 200 mol g 1 to 400 mol g 1 descending down the sediment profile differential extraction experiments of p release at ph 3 estimated that vivianite amounts to between 3 and 5 of the total fe pool the total p burial fluxes estimate that 38 mol cm 2 yr 1 or 26 of sedimentary p in the lower sediments is sequestered as vivianite there are seasonal variations in the porewater composition with lower fe orthophosphate and higher sulfate concentrations during winter 5 c than during summer 15 c this suggests that temperature modulates the rate of organic matter degradation which in turns affects the rate of fe iii phase reduction release of phosphate and thereby the porewater fe 2 and orthophosphate concentrations and hence vivianite formation this work highlights the role vivianite can play for p retention in a si fe c rich lake sediment

authigenic vivianite in potomac river sediments control by ferric oxy hydroxides abstract sand size particles of vivianite fe3 po4 2 8h2o have been identified by x ray diffraction and scanning electron microscopy in surficial sediments of the tidal potomac river near a major sewage treatment plant vivianitc particles are concentrated in a surface layer of coarse sand dredge spoil which overlies much finer sediment similar to that found in adjacent areas although saturation indices indicate that the pore waters of virtually all the sediments in the study area are supersaturated with respect to vivianite it is found only in association with dredge spoil pore water profiles of fe p and eh as well as the size and morphology of individual grains indicate that the vivianite is authigenic and was not introduced with he dredge spoil it is suggested that the major control on the occurrence of the mineral is the presence or absence of amorphous ferric oxy hydroxides which apparently react with pore water phosphorus to form stable ferric hydroxy phosphates preferentially to the formation of vivianite

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

zircon fission track ages from the gasherbrum diorite karakoram range northern pakistan the gasherbrum peaks in the himalaya of pakistan reach elevations of 8000 m the relief between the peaks and the adjacent valley baltoro glacier is in excess of 3000 m eight samples of the early cretaceous gasherbrum diorite at elevations between 4880 and 7165 m on gasherbrum iv were collected for fission track dating zircon fission track ages from the gasherbrum diorite vary from early cretaceous to middle tertiary in age there is no consistent pattern between age and elevation the cretaceous ages indicate that these rocks were never deeply buried i e heated to temperatures in excess of 175 c to reset the zircons during cenozoic time these results also indicate that the uplift of this part of the himalaya has been either very rapid and recent or very slow since early cretaceous time this latter possibility is not consistent with the high relief at gasherbrum and what is known about regional tectonics gasherbrum iv zircons currently at approximately 4880 m have never been at depths greater than 6 km and less than 3 km of material has been removed from the top of the range by erosion since the early cretaceous rapid uplift has occurred very recently and erosion rates have notmore been able to keep pace with this uplift less

vivianite is a key sink for phosphorus in sediments of the landsort deep an intermittently anoxic deep basin in the baltic sea phosphorus p is an essential nutrient for marine organisms its burial in hypoxic and anoxic marine basins is still incompletely understood recent studies suggest that p can be sequestered in sediments of such basins as reduced iron fe p but the exact phase and the underlying mechanisms that lead to its formation are unknown in this study we investigated sediments from the deepest basin in the baltic sea the landsort deep site m0063 that were retrieved during the integrated ocean drilling project iodp baltic sea paleoenvironment expedition 347 the record comprises the whole brackish marine littorina sea stage including past intervals of extensive hypoxia in the baltic sea that occurred during the holocene thermal maximum htmhi and the medieval climate anomaly mca1hi and mca2hi various redox proxies e g the presence of laminations and high mo contents suggest almost permanent bottom water hypoxia during the littorina sea stage in the landsort deep the bottom waters were likely even seasonally anoxic or sulfidic during the mca1hi and mca2hi and permanently sulfidic during the htmhi with the use of micro analysis of sieved minerals sem eds xrd and synchrotron based xas we show that mn and mg rich vivianite crystals are present at various depths in the littorina sea sediments we also have indications for vivianite in the mca1hi mca2hi and htmhi deposits the formation of vivianite thus likely explains the high fe bound p fraction throughout the whole littorina sea stage shuttling of fe and mn from the shelves into the basin and high inputs of p in settling organic matter are likely key drivers for vivianite formation our study shows that vivianite can likely form in near surface sediments under a broad range of bottom water redox conditions varying from hypoxic and anoxic to sulfidic

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

site dependent coda q at mono craters california abstract the coda q of the early coda of shear waves was determined from a network of seismic stations deployed in the mono craters area during the summer of 1982 coda amplitudes determined from a moving window analysis were fit to single scattering theory with an l1 norm for center frequencies from 1 5 to 12 0 hz we find that station to station variations in coda q observed for frequencies between 6 and 12 hz are well correlated with near site geology coda q for stations on crystalline rocks is larger and more frequency dependent than for stations sited on bishop tuff adjacent to mono craters coda q from sites on bishop tuff away from mono craters is still lower and less frequency dependent these observations suggest that site effects dominate the early coda in the mono craters region and that the single scattering model is inappropriate the mechanisms generating these site effects are inferred to be 1 multiple scattering from resonant structures such as sedimentary basins volcanic edifices variable basement topography and surface topography and 2 near site attenuation

microbial reduction of fe iii in illite smectite minerals by methanogen methanosarcina mazei abstract clay minerals are ubiquitous in soils sediments and sedimentary rocks and could coexist with methanogens in anoxic environments but whether or not methanogens can reduce structural fe iii in clay minerals other than smectite is not known the objective of this study was to understand the capability of a mesophilic methanogen methanosarcina mazei in reducing structural fe iii in illite smectite clay minerals and its potential role in inducing mineralogical changes bioreduction experiments were performed in batch systems where four different clay minerals nontronite nau 2 mixed layer illite smectite rar 1 and iscz 1 and illite imt 1 were exposed to m mazei in growth medium with and without anthraquinone 2 6 disulfonate aqds as electron shuttle the extent and rate of bioreduction were quantified via wet chemistry and mineralogical transformed by x ray diffraction and scanning and transmission electron microscopy our results demonstrated that m mazei was able to reduce structural fe iii in clay minerals with fe iii in smectite being the most reducible and illite the least aqds enhanced the reduction rate and extent the bioavailability of structural fe iii to m mazei was correlated to the smectite proportion in each clay mineral methanogenesis was inhibited by fe iii bioreduction possibly due to diversion of electrons from the methanogenesis pathway to structural fe iii in clay minerals bioreduction of fe iii in clay minerals induced formation of biogenic mixed layer illite smectite silica and vivianite these data collectively showed that mesophilic methanogen is capable of reducing structural fe iii in illite smectite minerals and of inducing a number of mineralogical changes

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

thermal and structural evolution of the intracratonic arltunga nappe complex central australia the thermal and structural evolution of a paleozoic thrust system in central australia the arltunga nappe complex has been examined through field mapping petrographic microstructural and chemical analyses k ar and 40ar 39ar thermochronology and multi diffusion domain time temperature modeling of k feldspar 40ar 39ar data the arltunga nappe complex contains three distinct tectonic units bounded by regional faults and shear zones that have undergone contrasting deformational and metamorphic histories the cooling history of the three tectonic units has been constrained by k ar and 40ar 39ar isotopic age data from k feldspars micas and amphiboles results are consistent with a piggyback history of crustal imbrication spanning over 100 m y with the hottest rocks uplifted and cooled first and with imbrication acting progressively toward the foreland implications for the intracratonic paleozoic tectonics of central australia are 1 uplift within the structurally highest tectonic unit was initiated before 400 ma 2 continued piggyback imbrication footwall failure and uplift and exhumation of the crust resulted in duplexing in the lowest structural unit at approximately 325 300 ma 3 the contrast in thermal history between the tectonic units indicates that once widely separated crustal segments were juxtaposed during thrusting above a hinterland dipping megathrust resulting in 85 km of crustal shortening

geochemical cycling of phosphorus in rivers abstract concentrations of contaminants in fresh waters are controlled not only by point and diffuse sources within the catchment but by a multitude of biogeochemical reactions riverine processes that may occur in the water column during transport as an example the results of mass balance studies using snapshot field sampling techniques for p transport in a large river in northern england r swale are summarised to identify the processes that contribute to internal cycling within the river and their relative size compared with the total export of p the interaction of p with sediments is an important factor controlling concentrations of soluble p in the water column during both low and high river flows with in river storage in some instances amounting to 30 of the load throughput antecedent weather conditions are identified as important in controlling the pool of fine sediment and associated p available for remobilisation during storm pulses examples of p reactions with sediments that have been identified from field studies are briefly reviewed firstly a mass balance approach to elucidate the net interaction of p with river bed sediments is presented and then two specific interactions of p with sediments are discussed a the coprecipitation of phosphate with calcite in lakes during phytoplankton blooms and in benthic algal biofilms on river sediments and b the formation of vivianite in the anoxic zone of bed sediment in eutrophic lakes and rivers phosphate coprecipitation with calcite is an important mechanism controlling p concentrations in some hardwater lakes and has been found to contribute as much as 30 of the dry mass associated with the colonisation and development of algal biofilms on hardwater river beds vivianite has been detected in anoxic river sediments up to 20 by mass receiving treated sewage although little is known about the conditions of formation and how widespread the occurrence of vivianite is in sediments

u pb age of the baltoro granite northwest himalaya and implications for monazite u pb systematics the baltoro granite is a major late to post tectonic plutonic phase of the karakoram batholith of the northwest himalaya in northern pakistan u pb zircon analyses indicate both emplacement at 21 0 0 5 ma and significant precambrian zircon inheritance dates on monazite are 17 19 ma and are interpreted to have remained near their closure temperature of about 700 c for several million years after emplacement resulting in pb loss by diffusion we suggest that the granite was emplaced into rocks which were at high temperature and that they remained so until late miocene northeast tilting rapid uplift and or tectonic denudation and cooling

kongur shan normal fault type example of mountain building assisted by extension karakoram fault eastern pamir the northernmost segment of the karakoram fault is an active normal dextral wrench fault that bounds the muji tashgurgan pliocene quaternary basin eastern pamir the kongurshan 7719 m and mustaghata 7546 m mountains are interpreted as twin crustal ramp anticlines formed en echelon on the eastern side of the karakoram fault by subduction of the tarim lithosphere under the pamir west dipping s c mylonitic gneisses that have downdip stretching lineations form the western flank of kongur mountain kinematic criteria consistently indicate a top to the west sense of shear the mylonitic foliation is cut by a steeper active normal fault which is marked by prominent triangular facets on west facing spurs the ductile normal shearing deformation occurred during the interval 5 1 ma therefore like the himalayas the pamir mountain range shows the coeval development of frontal thrusting and rear normal faulting the kongur fault thus appears to be an excellent example of synorogenic extension where normal faulting contributes to relief

biomineralization of iron phosphates in the water column of lake pavin massif central france the availabilities of iron and phosphorus have considerably impacted biological productivity in past and present natural aquatic environments and therefore have been key regulators of climate changes over geological time scales microbial organisms are known to play important roles in reactions that drive fe and p cycling at redox interfaces in earth s surface environments here we study the depth variations of fe and p speciation in lake pavin massif central france a deep bottom depth 92 m and permanently stratified lake with anoxic and ferruginous conditions in the water column below 60 m depth we particularly focus on the potential roles of microbes on fe and p transformations and traces left by these processes in the sedimenting particular matter bulk chemical analyses powder x ray diffraction and x ray absorption spectroscopy xas at the fe k edge were performed to characterize the mineralogy and fe oxidation state of solid particles at different depths in the water column and in sediments deposited at the bottom of the lake fe is mainly hosted by fe iii oxyhydr oxides and phyllosilicates in the shallower oxygenated water column of the lake 25 m the amount of fe in suspended matter increases with depth and an additional amorphous fe ii fe iii phosphate phase is detected close to the chemocline at 56 m depth while vivianite an fe ii phosphate with a formula of fe ii 3 po4 2 8 h2o becomes dominant in the deeper anoxic water 67 m and 86 m depths fe oxyhydr oxides are preserved down to these depths in the water column suggesting that fe reduction has little impact on the particulate fe budget over the monimolimnion these fe oxyhydr oxides undergo reductive dissolution at the surface of the sediments where vivianite is the main fe bearing phase these results are confirmed by imaging at the micrometer and nano scales using scanning electron microscopy sem transmission electron microscopy tem and synchrotron based scanning transmission x ray microscopy stxm as well as high spatial and energy resolution xanes spectra at the fe l2 3 edges and the c k edge moreover polyphosphate accumulating microorganisms were observed by microscopy and chemical imaging at all depths except in the deeper part of the lake 86 m and some fe was associated with these polyphosphate inclusions below 56 m finally the fe phosphates encrust microbial bodies suggesting that microbial activities might be involved in the formation of these phases based on comparisons with laboratory experiments we propose that fe oxidation in contrast to fe reduction may play a role in the precipitation of fe phosphates in the water column of lake pavin polyphosphate accumulating microorganisms could also be involved in fe phosphate formation in the lake for instance by increasing dissolved phosphate concentrations in the monimolimnion

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

diagenetic changes of magnetic and geochemical signals by anaerobic methane oxidation in sediments of the zambezi deep sea fan sw indian ocean abstract the zambezi deep sea fan the largest of its kind along the east african continental margin is poorly studied to date despite its potential to record marine and terrestrial climate signals in the southwest indian ocean therefore gravity core geob 9309 1 retrieved from 1219 m water depth was investigated for various geophysical magnetic susceptibility porosity colour reflectance and geochemical pore water and sediment geochemistry fe and p speciation properties onboard and onshore data documented a sulphate methane transition smt zone at 450 530 cm sediment depth where the simultaneous consumption of pore water sulphate and methane liberates hydrogen sulphide and bi carbonate into the pore space this leads to characteristic changes in the sediment and pore water chemistry as the reduction of primary fe oxyhydr oxides the precipitation of fe sulphides and the mobilization of fe oxyhydr oxide bound p these chemical processes also lead to a marked decrease in magnetic susceptibility below the smt we find a reduction of porosity possibly due to pore space cementation by authigenic minerals formation of the observed geochemical magnetic and mineralogical patterns requires a fixation of the smt at this distinct sediment depth for a considerable time which we calculated to be 10 000 years assuming steady state conditions following a period of rapid upward migration towards this interval we postulate that the worldwide sea level rise at the last glacial interglacial transition 10 000 years b p most probably caused the fixation of the smt at its present position through drastically reduced sediment delivery to the deep sea fan in addition we report an internal redistribution of p occurring around the smt closely linked to the de coupling of sedimentary fe and p and leaving a characteristic pattern in the solid p record by phosphate re adsorption onto fe oxyhydr oxides above and formation of authigenic p minerals e g vivianite below the smt deep sea fan deposits may potentially act as long term sinks for p

mobilization of arsenic and iron from red river floodplain sediments vietnam abstract sediments from the red river and from an adjacent floodplain aquifer were investigated with respect to the speciation of fe and as in the solid phase to trace the diagenetic changes in the river sediment upon burial into young aquifers and the related mechanisms of arsenic release to the groundwater goethite with subordinate amounts of hematite were using mossbauer spectroscopy identified as the iron oxide minerals present in both types of sediment the release kinetics of fe as mn and po 4 from the sediment were investigated in leaching experiments with hcl and 10 mm ascorbic acid both at ph 3 from the river sediments most of the fe and as was mobilized by reductive dissolution with ascorbic acid while hcl released very little fe and as this suggests as to be associated with an fe oxide phase for oxidized aquifer sediment most fe was mobilized by ascorbic acid but here not much as was released however the reduced aquifer sediments contained a large pool of fe ii and as that is readily leached by hcl probably derived from an unidentified authigenic fe ii containing mineral which incorporates as as well extraction with ascorbic acid indicates that the river sediments contain both as v and as iii while the reduced aquifer sediment almost exclusively releases as iii the difference in the amount of fe ii leached from river and oxidized aquifer sediments by ascorbic acid and hcl was attributed to reductive dissolution of fe iii the reactivity of this pool of fe iii was quantified by a rate law and compared to that of synthetic iron oxides in the river mud fe iii had a reactivity close to that of ferrihydrite while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic fe oxides as a reference sediments were incubated both unamended and with acetate added and monitored for up to 2 months the river mud showed the fastest release of both fe and as while the effect of acetate addition was minor this suggests that the presence of reactive organic carbon is not rate limiting in the case of the river and aquifer sediments the release of fe and as was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor the reduced aquifer sediment apparently can sustain slower but prolonged microbially driven release of as the highly reactive pools of fe iii and as in the river mud could be due to reoxidation of as and fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of as onto the floodplain and into the underlying aquifers

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

the role of grain dissolution and diagenetic mineral precipitation in the cycling of metals and phosphorus a study of a contaminated urban freshwater sediment this paper describes the detrital mineralogy early diagenetic reactions and authigenic mineral precipitates for freshwater contaminated sediments deposited in an urban water body the salford quays of the manchester ship canal greater manchester uk these sediments contain a mix of natural and anthropogenic detrital grains detrital grains are dominated by quartz and clay grains whilst anthropogenic grains are dominated by metal rich glass grains concentrated at a depth of 12 17 cm in the sediment as a result of historical inputs sediment porewaters contain significant concentrations of fe mn zn and phosphate bacterial fe iii and mn iv reduction are hypothesised to supply fe2 and mn2 to porewaters with phosphate released from fe oxide reduction or organic matter oxidation petrographic observations indicate that the metal rich glass grains are undergoing chemical dissolution during early diagenesis supplying fe and zn to porewaters the most abundant authigenic mineral in the sediments is vivianite fe3 po4 2 8h2o containing a significant level of redlingite with minor framboidal pyrite fes2 electron microprobe analysis shows the vivianite to contain zn cu and pb suggesting that vivianite acts as a long term sink for these metals in this sediment this implies that authigenic vivianite in freshwater sediments may act as a long term sink for metals in a similar manner to sulphides in marine sediments this study highlights that the nature of detrital and diagenetic mineralogy in addition to porewater and sediment chemistry needs to be considered in assessing contaminated sediments

vivianite is a major sink for phosphorus in methanogenic coastal surface sediments abstract studies of authigenic phosphorus p minerals in marine sediments typically focus on authigenic carbonate fluorapatite which is considered to be the major sink for p in marine sediments and can easily be semi quantitatively extracted with the sedex sequential extraction method the role of other potentially important authigenic p phases such as the reduced iron fe phosphate mineral vivianite fe ii 3 po4 8h2o has so far largely been ignored in marine systems this is in part likely due to the fact that the sedex method does not distinguish between vivianite and p associated with fe oxides here we show that vivianite can be quantified in marine sediments by combining the sedex method with microscopic and spectroscopic techniques such as micro x ray fluorescence xrf elemental mapping of resin embedded sediments as well as scanning electron microscope energy dispersive spectroscopy sem eds and powder x ray diffraction xrd we further demonstrate that resin embedding of vertically intact sediment sub cores enables the use of synchrotron based microanalysis x ray absorption near edge structure xanes spectroscopy to differentiate between different p burial phases in aquatic sediments our results reveal that vivianite represents a major burial sink for p below a shallow sulfate methane transition zone in bothnian sea sediments accounting for 40 50 of total p burial we further show that anaerobic oxidation of methane aom drives a sink switching from fe oxide bound p to vivianite by driving the release of both phosphate aom with sulfate and fe oxides and ferrous fe aom with fe oxides to the pore water allowing supersaturation with respect to vivianite to be reached the vivianite in the sediment contains significant amounts of manganese 4 8 wt similar to vivianite obtained from freshwater sediments our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments we suggest that vivianite may act as an important burial sink for p in brackish coastal environments worldwide

nyainqentanglha shear zone a late miocene extensional detachment in the southern tibetan plateau a major low angle ductile shear zone containing s c mylonites involves metamorphosed granitic rocks at the southeastern edge of the nyainqentanglha mountain range southern tibet prominent triangular facet geomorphology is developed by valley erosion of the detachment surface defined by the top of the southeast dipping mylonitec shear zone kinematic criteria consistently indicate a top to southeast sense of shear the ductile shearing deformation is inferred from isotopic cooling ages to have occurred during the interval 11 5 ma late miocene we interpret the shear zone as a regional extensional detachment its development indicates when the extensional tectonics in this area started which in turn may mark the time when the maximum sustainable surface elevation and perhaps crustal thickness was reached in southern tibet

the occurrence identification and environmental relevance of vivianite in waterlogged soils and aquatic sediments abstract in this article we review the nature occurrence and environmental relevance of the authigenic ferrous iron phosphate mineral vivianite fe 3 po 4 2 8h 2 o in waterlogged soils and aquatic sediments we critically discuss existing work from freshwater and marine systems laboratory studies and microbial batch culture experiments aiming to deduce common characteristics of the mineral s occurrence and the processes governing its formation vivianite regularly occurs in close association with organic remains in iron rich sediments simultaneously it is a biogenic mineral product of metal reducing bacteria these findings suggest that vivianite nucleation in natural systems is directed by the activity of such bacteria and crystal growth is particularly favoured within protected microzones taking into account recent findings from coastal marine sediments where vivianite authigenesis has been shown to be coupled to the anaerobic oxidation of methane small scale microbially mediated reactions appear to be crucial for the formation of vivianite small scale heterogeneity within the sediment matrix may also explain why saturation calculations based upon bulk pore water constitutions often fail to accurately predict the occurrence of the mineral vivianite is not restricted to a specific trophic state of a system the mineral forms in oligotrophic as well as in eutrophic waters however depending on the iron inventory the production supply and degradation of organic matter determine the relative contribution of iron sulphide formation to the iron pool and the concentration of inorganic phosphate and fe 2 in pore waters thus vivianite authigenesis is also governed by bulk chemical conditions such as the rate of sulphide formation relative to that of fe 2 production this situation allows stimulation of vivianite formation by iron supplementation aimed at restoring eutrophic lakes recent results from coastal marine sediments suggest that vivianite authigenesis is of significance for p burial in the marine realm vivianite authigenesis is likely important at the global scale but has so far largely been ignored

incipient india eurasia collision and plutonism the lower cenozoic batura granites hunza karakorum north pakistan plutonism of the karakorum north of the india eurasia suture zone comprises two major intrusive stages the oldest mid cretaceous predates the collision the youngest miocene is post suturing in between lower cenozoic plutonism roughly syn suturing and represented by the batura complex is made up of a few small and usually undeformed plutons the complex has a subalkaline i e intermediate between alkaline and calc alkaline and ferriferous association dominated by light coloured metaluminous and slightly peraluminous granites and adamellites with biotite amphibole titanite whole rock rb sr isochron ages of 63 ma this study and 43 ma debon et al 1987b have been obtained for two plutons with rather low initial 87 sr 86 sr ratios 0 7050 0 7056 a comparison with granitoids of similar age from kohistan suggests that the complex relates to the subduction of the tethys ocean and originates from a mantle source with but small crustal contribution through a two stage melting process the apparently limited extent of lower cenozoic plutonism in the karakorum contrasts with its wider development in the transhimalaya and kohistan this contrast could be partly accounted for by changes in tectonic and magmatic suduction related processes after the initial contact between india and eurasia was established in the nw himalaya

field relationships and geochemistry of pre collisional india asia granitoid magmatism in the central karakoram northern pakistan in the central karakoram range northern pakistan seven major granitic units which were emplaced prior to the eocene ca 50 ma india asia collision have been mapped and analysed geochemically the mid cretaceous hunza plutonic complex dominates the karakoram batholith in the west and is composed of quartz diorite granodiorite plutons which have been deformed in the south by later collision related thrusting the sost and khunjerab plutons intrude the palaeozoic early mesozoic sediments north of the batholith in the east pre collision magmatic units occur both north of k2 gneiss broad peak quartz diorite muztagh tower unit and south of hushe gneiss the batholith which is dominated by a miocene monzogranite leucogranite pluton baltoro unit the plutonic units to the north of the batholith are mid to late cretaceous with an age range of ca 115 80 ma whereas the hushe gneiss to the south is dominantly jurassic spanning the age range 200 145 ma all the pre collision magmatic units display similar chemical and isotopic characteristics major trace and ree variations in the hunza plutonic complex are controlled by high level fractionation of clinopyroxene hornblende plagioclase biotite ilmenite and allanite high lile hfse and lree hree ratios together with negative nb p and ti anomalies suggest an ultimate source in the mantle wedge above the subducting slab 87sr 86sr initial ratios 0 7055 0 7157 in the hunza plutonic complex can best be explained by contamination of a mantle derived magma by a crustal component with highly radiogenic sr all the units except the hushe gneiss are probably related to subduction during closure of a back arc basin between the karakoram to the north and the kohistan dras arc to the south during the mid to late cretaceous and correlate with widespread plutonism from the same period in kohistan ladakh and southern tibet along the southern margin of asia the hushe gneiss is probably related to an earlier northward directed subduction phase during the jurassic

why the phosphorus retention of lakes does not necessarily depend on the oxygen supply to their sediment surface in order to improve the trophic state of lake sempach a eutrophied lake in central switzerland its external phosphorus p load has been decreased and its hypolimnion has been artificially oxygenated to lower the lake internal p recycling based on more than 15 yr of experience we conclude that the reduction of the external p load resulted in a corresponding decrease of the lake s p concentration however contrary to initial expectations increased hypolimnetic dissolved oxygen concentrations neither 1 reduced the p release from sediments during summer nor 2 resulted in an increased permanent p retention these observations warrant a reevaluation of the well accepted management strategy of decreasing the lake internal p cycling by maintaining an aerobic hypolimnion and sediment surface we hypothesize that oxygenation only results in an increased permanent benthic p burial if because of the depressed sulfide production more ferrous phosphate e g vivianite and less fes is deposited in the anoxic sediment hence it is not the oxic sediment surface that directly affects the permanent redox dependent sediment p retention but the molar ratio of the available reactive fe ii s 2 po 4 in the anoxic sediment this ratio is driven by the settling rate and the nature of organic matter and particulate iron as well as the supply of oxygen nitrate and sulfate to the sediment