the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

platinum in earth surface environments platinum pt is a rare precious metal that is a strategic commodity for industries in many countries the demand for pt has more than doubled in the last 30years due to its role in the catalytic conversion of co hydrocarbons and nox in modern automobiles to explore for new pt deposits process ores and deal with ecotoxicological effects of pt mining and usage the fundamental processes and pathways of pt dispersion and re concentration in surface environments need to be understood hence the aim of this review is to develop a synergistic model for the cycling of pt in earth surface environments this is achieved by integrating the geological biogeo chemical literature which focuses on naturally occurring pt mobility around ore deposits with the environmental ecotoxicological literature dealing with anthropogenic pt dispersion in pt deposits pt occurs as sulfide telluride and arsenide native metal and alloyed to other pges and iron fe increased mining and utilization of pt combined with the burning of fossil fuels have led to the dispersion of pt containing nano and micro particles hence soils and sediments in industrialized areas urban environments and along major roads are now commonly pt enriched platinum minerals nuggets and anthropogenic particles are transformed by physical and bio geochemical processes complexation of pt ions with chloride thiosulfate ammonium cyanide low and high molecular weight organic acids lmwoas and hmwoas and siderophores can facilitate pt mobilization iron oxides clays organic matter and micro biota are known to sequester pt complexes and particles microbes and plants are capable of bioaccumulating and reductively precipitating mobile pt complexes bioaccumulation can lead to toxic effects on plants and animals including humans bio mineralization in organic matter rich sediments can lead to the formation of secondary pt particles and grains ultimately pt is enriched in oceanic sediments where pt is commonly concentrated in manganese mn oxides when these sediments are subducted pt re enters the magmatic cycle in conclusion this review demonstrates that geological geochemical as well as biological and most recently anthropological processes are strongly interlinked in driving the cycling of pt in surface environments

platinum group elements in tulameen coal british columbia canada nickel sulfide fire assay neutron activation analysis and lead fire assay direct current plasma spectroscopy were used to determine platinum group elements pge and gold in 30 channel samples and 23 fault related samples from the blakeburn opencast mine south central british columbia canada in the majority of the channel samples concentrations of os ir ru rh pd and re were below detection pt in the coal ranged from below detection to 170 ppb and au from below detection to 38 ppb concentrations of all the pge with the exception of ru were on average higher in the coals than in the sediments in the deformed coal samples os ru rh and re were typically below detection anomalous values of pt up to 10 000 ppb were determined in three deformed coal samples and pd and ir were comparatively enriched in the majority of deformed coal samples up to 6 100 and 22 ppb respectively compared with channel samples on the basis of sem edx and comparisons with ash and organic matter contents it is likely that pt and au are present in the coal as discrete particles precipitated from circulating ground waters on contact with the organic rich reducing and low ph environment of the coal pt and au distributions appear to be related to sources of the elements in ground water i e interbedded volcanic units and the tulameen ultramafic complex for pt and interbedded clastic sedimentary units for au enhanced concentrations of pt and pd occur in coal samples associated with two faults

pt group metal anomalies in the lower mississippian of southern oklahoma four iridium pt group elements abundance anomalies have been found within a stratigraphic span of 3 m in the lower mississippian of oklahoma in ascending order the first anomalies occur at the top of the woodford shale ir 0 25 ppb pt 48 ppb os 7 5 ppb and au 18 ppb the anomalies occur just below a redox boundary and we suspect that the enriched elements were precipitated from sea water that contacted the organic and sulfide rick black shale two more anomalies occur in the welden limestone the lower one weak and the upper one strong ir 0 42 ppb pt 50 ppb os 0 075 ppb and au 0 14 ppb the excess ir and pt also co as and ni might have been enriched from sea water by bacteria at these two horizons a 70 cm thick interval of excess heavy siderophiles occurs in the overlying caney shale the interval contains the following peak concentrations ir 0 56 ppb pt 150 ppb os 0 51 ppb co 725 ppm and ni 1450 ppm these elements vary in proportion to the al clay content and we suspect that they were carried in with detrital material from erosion of ultramafic source rocks we found no evidence of microspherules or shocked mineral grains in any of these anomaly zones

early curvilinear fold structures and strain in the moine of the glen garry region inverness shire four regional deformation episodes d1 d4 are recognized in the moine rocks loch eil and glenfinnan divisions of the glen garry area inverness shire nw scotland these episodes fall into two groups early sub recumbent d1 d2 structures and later upright d3 d4 structures d2 structures occur on all scales and appear in a regional sense to be more important than the d1 structures the d1 d2 structures are only preserved in their original disposition where subsequent upright d3 reworking was minimal i e in the region to the e of the loch quoich line and in low strain augen developed in d3 hinge zones to the w of this structure the f2 folds are intensely curvilinear and at many localities f2 hinges lie approximately parallel to the n s trending extension lineation examination of these structures in three dimensions and application of the sanderson 1973 model provides information on the nature and orientation of the regional d2 strain ellipsoid in this part of the moine the d2 xy plane is sub horizontal with the x direction trending approximately n s this is markedly different in orientation from the d3 ellipsoid in this region which being of post glen dessary syenite 456 ma age is demonstrably caledonian the d2 linear fabrics suggest that the direction of tectonic transport was s to n or n to s markedly different from the generally accepted wnw directed movement attributed to caledonian orogenesis these findings are consistent with the proposal that the loch quoich line represents an eastern limit of intense caledonian d3 reworking and that the d1 d2 structures are of precambrian age

a baseline survey of the distribution and origin of platinum group elements in contemporary fluvial sediments of the kentish stour england the extensive anthropogenic use of the platinum group elements pge ru rh pd os ir and pt is the main factor responsible for the widespread dispersion of these elements throughout the environment significant quantities of the pge enter fluvial systems via road runoff storm drains and wastewater and sewage treatment systems and may accumulate in fluvial sediments by physical and chemical processes a baseline survey of contemporary fluvial sediments in the kentish stour river east kent england has been undertaken to document the sources and distribution of anthropogenic pge in an attempt to constrain some of the physical and chemical parameters that may influence the distribution of these elements the geology of the catchment of the kentish stour is dominated by carbonate and silicate sedimentary rocks and the river passes through urban and rural land and receives inputs of waste from sewage works nine sedimentary rocks 4 motorway runoff sediments and 22 river sediments were analysed for pge by nis fire assay preconcentration and icp ms the highest element abundances occur in the motorway runoff sediments maximum total pge content of 55 ng g whilst the lowest values were recorded in the sedimentary rocks where some samples contain pge at concentrations below the limit of detection the total pge content of the river sediments ranged from 0 4 to 10 8 ng g the distribution and variation in concentrations and ratios of the pge in the contemporary fluvial sediments of the kentish stour correspond strongly with land use changes urban versus rural and with points of discharge from sewage works the absence of a pure catalytic converter signature in the river sediments however indicates that source signatures may be mixed in sewage works or that pge may chemically fractionate in the fluvial environment

comparison between the distribution of pge in black shales from the bohemian massif csfr and other black shale occurrences selected metal rich and normal black shales of the bohemian massif have been analysed for pge and the results have been compared with other anoxic sediments of the world it has been discussed and partly proved that these rocks may represent an important and promising source of platinoids

decadal scale variation in dune erosion and accretion rates an investigation of the significance of changing storm tide frequency and magnitude on the sefton coast uk abstract monitoring of frontal dune erosion and accretion on the sefton coast in northwest england over the past 50 years has revealed significant spatial and temporal variations previous work has shown that the spatial variations primarily reflect longshore differences in beach and nearshore morphology energy regime and sediment budget but the causes of temporal variations have not previously been studied in detail this paper presents the results of work carried out to test the hypothesis that a major cause of temporal variation is changes in the frequency and magnitude of storms surges and resulting high tides dune toe erosion accretion records dating from 1958 have been compared with tide gauge records at liverpool and heysham relatively high dune erosion rates at formby point 1958 1968 were associated with a relatively large number of storm tides slower erosion at formby and relatively rapid accretion in areas to the north and south occurred during the 1970 s and 1980 s when there were relatively few major storm tides after 1990 rates of dune erosion at formby increased again and dunes to the north and south experienced slower accretion during this period high storm tides have been more frequent and the annual number of hours with water levels above the critical level for dune erosion has increased significantly an increase in the rate of mean sea level rise at both liverpool and heysham is evident since 1990 but we conclude that this factor is of less importance than the occurrence of extreme high tides and wave action associated with storms the incidence of extreme high tides shows an identifiable relationship with the lunar nodal tidal cycle but the evidence indicates that meteorological forcing has also had a significant effect storms and surges in the eastern irish sea are associated with atlantic depressions whose direction and rate of movement have a strong influence on wind speeds wave energy and the height of surge tides however preliminary analysis has indicated only a modest relationship between dune erosion accretion rates and the north atlantic oscillation index

beach and dune erosion during storm surges this paper presents the set up and results of an extensive research programme concerning the erosion of coastal dunes during storm surges a large number of two dimensional and three dimensional mobile bed model tests has been carried out to investigate the process of dune erosion the state of art after a series of small scale tests is summarized attention is focussed on large scale tests carried out in the delta flume with random waves up to 2 m significant height sediment concentration and orbital velocity measurements are discussed the large scale tests have confirmed the validity of a modelling technique based on the dimensionless fall velocity parameter h tw the model results are being applied to check the safety of existing coastal dunes as a water retaining structure that has to protect the major part of the netherlands from inundation during storm surges

quantifying thresholds for significant dune erosion along the sefton coast northwest england abstract field and model hindcast data are used to establish a critical dune erosion threshold for the sefton coast nw england events are classified as causing significant erosion if they result in a a mean dune retreat along the entire study area of 2 m b a dune retreat of 5 m along a coastal segment 2 km in length and c an eroded area 20 000 m2 for the period 1996 to 2008 individual storms were characterised using hindcast results from a polcoms wam model and measured data from the liverpool bay coastal observatory results show that combined extreme surge levels 1 5 m and wave heights 4 m or tidal water levels above 9 0 m chart datum cd do not always result in significant dune erosion evidence suggests that erosion is more likely to occur when wave heights are 2 6 m peak water level is 10 2 m cd at liverpool and when consecutive tidal cycles provide 10 h or more of water levels above 9 4 m cd however lower water levels and wave heights and shorter events of sustained water levels can cause significant erosion in the summer while the return period for events giving rise to the most severe erosion in the winter is 50 years significant erosion in the summer can be caused by events with return periods

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

marine cobalt resources ferromanganese oxides in the open oceans are more enriched in cobalt than any other widely distributed sediments or rocks concentrations of cobalt exceed 1 percent in ferromanganese crusts on seamounts ocean ridges and other raised areas of the ocean the cobaltrich crusts may be the slowest growing of any earth material accumulating one molecular layer every 1 to 3 months attention has been drawn to crusts as potential resources because they contain cobalt manganese and platinum three of the four priority strategic metals for the united states moreover unlike abyssal nodules whose recovery is complicated by their dominant location in international waters some of the most cobalt rich crusts occur within the exclusive economic zone of the united states and other nations environmental impact statements for crust exploitation are under current development by the department of the interior

the geology and structural evolution of a caledonian fold and ductile thrust zone kyle of tongue region sutherland northern scotland the middle to upper proterozoic metasedimentary rocks of the northern highland moine in sutherland are disposed in a series of major caledonian c 470 430 ma metamorphic thrust nappes produced by nw wnw directed shortening and reworking of parts of a pre existing precambrian c 1000 ma orogen lewisian inliers occur throughout sutherland and represent tectonically interleaved units of the original basement gneisses upon which the moine cover sequence was deposited in the western moine nappe of the kyle of tongue region the rocks are deformed by two main episodes d1 and d2 which are thought to represent the effects of precambrian and caledonian orogenesis respectively little basement cover interleaving or large scale folding occurred during the d1 event in the moine nappe but the associated metamorphism to ut leust garnet grade produced peak metamorphic mineral assemblages subsequent caledonian reworking d2 produced a foreland propagating system of wnw directed ductile thrusts and related major f2 sheath folds both of which resulted in much of the observed moine lewisian interleaving metamorphism associated with d2 decreases in grade westwards occurring at similar or slightly lower grades than the earlier d1 event this retrogressive overprint is most obvious at the w margin of the moine nappe the d2 folds and ductile thrusts are geometrically and kinematically similar to the caledonian structures recognized within the moine thrust zone to the west the very low 5 ramp angles suggesting that the thrusts must have very shallow dipping trajectories through the crust f2 fold formation is attributed to an early phase of wnw directed overthrusting compression which was then progressively superseded by a regional ductile extensional strain contemporaneous with continued wnw directed thrusting the occurrence of internal extension in the orogenic wedge during active thrust related foreshortening implies that the shear strength of the material close to the basal detatchment s was continuously reduced i e wedge motion became supercritical in this context strain softening processes within the ductile thrust mylonites were probably of major significance

the geometry and kinematics of flow perturbation folds abstract minor folds formed synchronous with ductile deformation in high strain zones can preserve a record of the scale and kinematics of heterogeneous flow using structures associated with wnw directed caledonian thrusting in n scotland we show that localised perturbations in flow resulted in the generation of predominantly cylindrical minor folds with hinges lying at low angles to the transport direction these define a series of larger scale fold culminations reflecting surging flow or depressions reflecting slackening flow that are bisected by transport parallel culmination and depression surfaces the fold patterns suggest a dominance of layer normal differential shearing due to gradients in shear strain normal to transport culmination surfaces are marked by along strike reversals in the polarity of structural facing and vergence of minor folds which contrary to classic fold patterns define reverse asymmetric relationships culmination surfaces separate folding in to clockwise z folds and anticlockwise s folds domains relative to the transport lineation the dip of fold axial planes systematically increases as their strike becomes sub parallel to transport resulting in a 3d statistical fanning arrangement centred about the transport direction thus mean s and z fold axial planes intersect precisely parallel to the transport lineation and potentially provide a means of determining transport directions in cases where lineations are poorly preserved culminations display convergent fold patterns with fold hinges becoming sub parallel to transport towards the culmination surface and underlying detachment whilst axial planes define overall concave up listric geometries which are bisected by the culmination surface thus around culminations and depressions there are ordered scale independent relationships between transport direction shear sense fold facing vergence and hinge axial plane orientations the techniques described here can be applied and used predictively within any kinematically coherent system of ductile flow

highly siderophile elements re os ir ru rh pd au in impact melts from three european impact craters saaksjarvi mien and dellen clues to the nature of the impacting bodies twenty two large 10 g impact melt samples from three scandinavian craters i e saaksjarvi finland and mien and dellen sweden were analyzed for highly siderophile elements hse platinum group elements rh and au by the nickel sulfide technique in combination with neutron activation the ten impact melt samples from saaksjarvi are enriched in ir and other highly siderophile elements ir 2 48 0 73 ng g relative to average upper crust concentrations 0 03 0 02 ng g ir the twelve dellen and mien samples are marginally enriched in ir 0 48 0 23 ng g for dellen and 0 37 0 23 ng g for mien the amount of meteoritic component corresponds to 0 5 of a nominal ci component for saaksjarvi and about 0 1 for mien and dellen the saaksjarvi pattern is fractionated relative to ci chondrites normalized abundances increase from the refractory to the more volatile siderophile elements ir ni the trend is qualitatively similar to magmatic iron meteorites and corresponds to 0 4 of a nominal magmatic iron meteorite component tamarugal iiiab for mien and dellen no projectile assignment can be made all samples from the three impact craters have low osir ratios compared to chondritic ratios either the projectile had low osir ratios or os was lost during the impact as volatile oso4 based on the results of this study and on a compilation of literature data average upper crustal abundances of the highly siderophile elements in the target area baltic shield are estimated as 0 03 ng g for ir and os 1 1 ng g for ru 0 38 ng g for rh 2 0 ng g for pd 8 g g for co and 37 g g for cr these data are representative of the upper crust they allow for the first time reliable estimates of crustal abundances for rh and ru upper crustal abundances also show that ir and os are the most favourable elements for the identification of meteoritic signatures fractionated osir ratios in magmatic iron meteorites or potential losses of os during the impact leaves ir as the best indicator element for meteoritic contamination with ir extraterrestrial components as low as 2 104 ci may be identified

quantification and implications of change in organic carbon bearing coastal dune cliffs a multiscale analysis from the northumberland coast uk eroding coastlines composed of sequences of till carbon rich peat and sand layers are characteristic of many formerly glaciated coastlines due to the interplay of relative land and sea levels dune cliffs cut into these materials represent one of the most sensitive systems to the processes of coastal change establishing appropriate scales for the quantification and analysis of change in coastal dune cliffs remains limited by the speed and nature of change the intensity of environmental processes and the challenges of achieving adequate survey control this paper presents the results from multi scale analyses into the behaviour of dune cliffs on the northeast coast uk over a 118 year period repeat unmanned aerial vehicle uav survey differences have been used to identify and quantify system behaviour set in context with historic map comparisons at the landform scale monthly dune cliff dynamics have been analysed over the course of a year with terrestrial laser scanning tls in order to gain insights into the drivers of contemporary dune cliff behaviour finally pseudo three dimensional ground penetrating radar gpr data are used to trace subsurface stratigraphy from which the potential extent of stored carbon in excess of 100 t over 50 m of monitored dune cliff at risk of release by coastal erosion over the next 50 years can be calculated the consideration of multi scale changes over time periods relevant to well constrained sea level change has revealed a complex combination of failure mechanisms that have resulted in an acceleration in dune cliff recession particularly over the last decade and a form change to shallower divergent profiles this potential acceleration in contemporary dune cliff response holds significant implications for both coastal management and the contribution of this poorly quantified input to the coastal carbon flux

soft sediment deformation within seismogenic slumps of the dead sea basin abstract the late pleistocene lisan formation preserved next to the dead sea provides exceptional 3 d exposures of folds and faults generated during soft sediment slumping and deformation it is possible to generate a range of four different scenarios associated with overprinting in a single slump event the progressive evolution of slump systems may be broadly categorised into initiation translation cessation relaxation and compaction phases thrust packages typically define piggyback sequences during slump translation with back steepening of imbricate faults leading to collapse of folds back up the regional palaeoslope detailed evaluation of slumped horizons may also permit structures to be traced across apparently separate and distinct slumped units the recognition that slumps may be reworked by younger seismically triggered events suggests that in some cases the seismic recurrence interval may be shorter than previously anticipated

the facing of faults it is proposed that the usage of the term structural facing be extended to include fault structures fault facing is defined as the direction in a fault plane which is at right angles to the trace of the bedding and is directed towards the younger beds certain types of faulted structures are found to have diagnostic patterns of facing variation

progressive deformation structures associated with ductile thrusts in the moine nappe sutherland n scotland in the deeper parts of mountain belts polyphase structural sequences observed at outcrop scale can arise due either to overprinting of regionally distinct deformation phases e g reworking changes in orogenic boundary conditions or to localized controls that bring about transient changes in the patterns of ductile flow these are unlikely to be mutually exclusive processes and examples from scotland demonstrate that once regionally separate events are delimited using radiometric evidence it is possible to isolate complex deformation sequences arising due to local controls in the western moine nappe of sutherland the dominant structures were formed during caledonian ductile thrusting towards the wnw whilst earlier precambrian phases are relatively minor in importance two groups of caledonian folds and fabrics are recognized in many exposures main phase d2 structures which are broadly contemporaneous with ductile thrust fabrics and later secondary phase f3 folds the latter can be divided into two geometric groups sheath fold types which formed initially as wnw overturned buckles subsequently modified by ductile shearing and asymmetric types which are commonly open folds apparently formed with axes close or sub parallel to the thrust transport direction secondary structures show a close spatial association with high strain zones along ductile thrusts and can be shown to have formed during the later stages of thrusting in certain critical exposures i propose that they may form due to strain perturbations resulting from variations in the relative rates of ductile flow within the mylonites where differential shearing occurs due to flow normal perturbations wrench related asymmetric fold types may form in contrast secondary sheath fold structures may result from localized compression phases caused by flow parallel perturbations local flow perturbation models may be appropriate in situations where the distribution of later structures is apparently related to spatial variations in strain intensity and or there is a strong geometric and kinematic similarity between sets of folds and fabrics if such features are not observed a regional polyphase sequence is more likely and it is therefore necessary to obtain radiometric dates or some other independent source of data to demonstrate a time separation

the distribution geometry and kinematic significance of caledonian buckle folds in the western moine nappe northwestern scotland within internal regions of orogenic belts systems of ductile thrusts and folds may form which are geometrically and kinematically analogous to those observed in foreland thrust belts the moine nappe of sutherland northwestern scotland developed during wnw directed caledonian displacements under amphibolite facies conditions broad zones of mylonite associated with the ductile ben hope and moine thrusts both contain numerous small scale folds which can be attributed to transient flow perturbations it is possible to isolate and differentiate generations of such folds basedon their association with particular major thrust zones and or their geometry in regions of lower strain between these thrusts there are a series ofkilometre scale buckle folds the axial traces of which define arcuate trends those with hinges orthogonal to transport are northwestvergent whilst those plunging subparallel to the mineral lineation display variable vergence the spatial distribution of these geometries suggests a causal relationship with displacements on specific underlying thrusts we propose that they reflect larger kilometre scale and possibly longer lived flow perturbations the transport parallel folds are persistent features that often centre on earlier structural culminations and are thought to reflect components of differential shear the most prominent set of regional buckle folds root downwards into the ductile moine thrust and openly refold the structurally overlying ben hope thrust and its associated buckle folds thus supporting a foreland propagating sequence of ductile displacements

sedimentary and structural controls on seismogenic slumping within mass transport deposits from the dead sea basin abstract comparatively little work has been undertaken on how sedimentary environments and facies changes can influence detailed structural development in slump sheets associated with mass transport deposits mtds the nature of downslope deformation at the leading edge of mtds is currently debated in terms of frontally emergent frontally confined and open toed models an opportunity to study and address these issues occurs within the dead sea basin where six individual slump sheets s1 s6 form mtds in the late pleistocene lisan formation all six slumps which are separated from one another by undeformed beds are traced towards the ne for up to 1 km and each shows a change in sedimentary facies from detrital rich in the sw to more aragonite rich in the ne the detrital rich facies is sourced predominantly from the rift margin 1 5 km further sw while the aragonite rich facies represents evaporitic precipitation in the hyper saline lake lisan the stacked system of mtds translates downslope towards the ne and follows a pre determined sequence controlled by the sedimentary facies each individual slump roots downwards into underlying detrital rich layers and displays a greater detrital content towards the sw which is marked by increasing folding while increasing aragonite content towards the ne is associated with more discrete thrusts the mtds thin downslope towards the ne until they pass laterally into undeformed beds at the toe the amount of contraction also reduces downslope from a maximum of 50 to

platinum and the platinum anomaly in the marine environment abstract platinum is markedly enriched over palladium in ferromanganese minerals compared to seawater concentrations of these two elements this anomalous behavior similar to that of cerium in the rare earth series is attributed to the oxidation of platinum from the dissolved divalent state in seawater to the tetravalent state during mineral formation the platinum to palladium weight ratio in seawaters is around 4 5 in marine sediments around 1 and in ferromanganese nodules between 50 and 1000 platinum similar to palladium shows a nutrient type profile in seawater

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

late brittle deformation in a caledonian ductile thrust wedge new evidence for gravitational collapse in the moine thrust sheet sutherland scotland abstract in the ductile regions of orogenic wedges late brittle structures formed at shallow crustal depths have received little attention however they are important as they of ten record the final stages in deformational history during uplift and erosion of the orogen in the moine rocks of sutherland late caledonian brittle folds and low angle faults post date ductile structures formed during wnw nw directed thrust movements earlier in the same orogenic event in the western moine nappe the late structures display geometries which indicate that they formed during regionally ese directed extensional movements down the dip of the pre existing regional foliation these late structures are correlated with similar wnw directed extensional low angle faults recognised in the moine thrust zone south of the assynt culmination both are thought to have formed in response to late caledonian gravity induced thinning of the moine thrust wedge and both pre date devonian extension associated with the formation of the west orkney basin along strike changes in the location and sense of extensional movements north and south of the assynt culmination are explained by changes in the pre existing structural geometry of the caledonian ductile thrust nappes within the moine hence earlier deformation patterns are thought to exert important controls over later events in an evolving orogenic wedge

osmium isotopes and silver as tracers of anthropogenic metals in sediments from massachusetts and cape cod bays high concentrations of osmium os and silver ag and low 187os 186os ratios in boston sewage make these elements sensitive tracers of the influence of sewage on marine sediments in massachusetts and cape cod bays pristine marine sediments have ag concentrations more than 200 times lower than sewage sludge os concentrations 10 40 times lower and 187os 186os ratios six times higher surface sediments from both massachusetts and cape cod bays exhibit both high ag concentrations and low 187os 186os ratios indicating the influence of sewage particles on marine sediments in this region extends some 70 km from the point of sewage release in detail the distribution of os and ag do not support a model of simple physical mixing of sewage particles with normal marine sediments deviations from the mixing model may be the result of fractionation of os and ag in the marine environment and or independent temporal variations in the os and ag content of the waste stream the results of this investigation suggest that osmium isotopes may be widely applicable as tracers of the influence of sewage on sediments in estuarine environments and that subtle variations in the isotopic composition of os in the waste stream may help constrain the sources of os and other metals delivered to the environment

developing the scientific framework for urban geochemistry abstract urban geochemistry is a unique discipline that is distinguished from general geochemistry by the complex infrastructure and intense human activities associated with concentrated population centers as stated by thornton 1991 this subject is concerned with the complex interactions and relationships between chemical elements and their compounds in the urban environment the influence of past and present human and industrial activities on these and the impacts or effects of geochemical parameters in urban areas on plant animal and human health urban areas present special challenges to geochemists attempting to understand geochemical states and fluxes on the 5 6 of august 2014 the first meeting of the reorganized urban geochemistry working group of the international association of geochemistry iagc was held in columbus ohio united states two goals of the meeting were to develop the overall scope and a general definition of urban geochemistry five grand themes were developed 1 recognizing the urban geochemical signature 2 recognizing the legacy of altered hydrologic and geochemical cycles in urban environments 3 measuring the urban geochemical signature 4 understanding the urban influence on geochemical cycles from the continuous development and erosion of physical infrastructure and episodic perturbations and 5 relating urban geochemistry to human and environmental health and policy after synthesizing the discussion of these themes we offer the following perspective on the science of urban geochemistry building on the work of thornton 1991 urban geochemistry as a scienti c discipline provides valuable information on the chemical composition of environments that support large populations and are critical to human health and well being research into urban geochemistry seeks to 1 elucidate and quantify the sources transport transformations and fate of chemicals in the urban environment 2 recognize the spatial and temporal including legacies variability in these processes and 3 integrate urban studies into global perspectives on climate change biogeochemical cycles and human and ecosystem health we hope that this discussion will encourage other geochemists to engage in challenges unique to urban systems as well as provide a framework for the future of urban geochemistry research

incremental subglacial meltwater sediment deposition and deformation associated with repeated ice bed decoupling a case study from the island of funen denmark abstract on the island of funen denmark sediments that are 4 7 m below the land surface consist of a 2 4 m thick sequence of stacked and folded glaciofluvial sediments overlain by a 2 3 m thick basal till the glaciofluvial sediments consist of tabular beds of planar stratified massive and cross stratified sand and gravel with localized channel fills of open framework gravel sand and gravel beds exhibit curvilinear sheath folding often leading to eye folds this folding is attributed to repeated glacier bed decoupling and recoupling with subglacial deposition of sand and gravel by meltwater occurring during the decoupling phase and deformation occurring during recoupling sand and gravel beds are typically separated by silty clay beds and laminations recording slackwater deposition within subglacial cavities folds frequently display attenuated upper limbs reflecting shearing associated with overlying ice movement on lower fold limbs only localized thrusting is observed suggesting water saturation of sands and gravels during deformation and relatively low strain rates folds are frequently truncated by overlying sand and gravel beds no evidence of shearing is found along these contacts which are interpreted as erosional surfaces thus we propose that the glaciofluvial sediment sequence records incremental step wise subglacial deposition and deformation rather than wholesale deformation following emplacement of the entire glaciofluvial sequence specifically we envisage that individual beds were deposited and folded subglacially with ice bed decoupling occurring during sediment deposition followed by recoupling and shearing of the upper bed surface by the ice base to produce folds with attenuated upper limbs incremental deformation and folding were facilitated by elevated porewater pressure within the sediments silty clay beds helped to maintain elevated porewater pressure by acting as local aquitards a general absence of till from the glaciofluvial sequence save for localized cm scale blocks suggests either non deposition or reworking into the glaciofluvial sediments deposition of tabular sand and gravel beds and open framework gravel filling scours within single beds suggest broad sheet like subglacial flows 10 100 m wide that become increasingly channelized we propose that the sedimentary sequence records a highly dynamic glaciohydraulic system characterized by repeated localized subglacial cavity development and storage and release of meltwater leading to glacier decoupling that may have facilitated fast flow of the baltic ice stream

geochemistry of platinum group elements in marine oil shale from the changshe mountain area china implications for modes of occurrence and origins abstract the shengli river changshe mountain oil shale zone located in the north qiangtang depression northern tibet plateau represents a potentially largest marine oil shale resource in china eighteen samples including oil shale and micritic limestone were collected from the changshe mountain oil shale to determine the concentrations the modes of occurrence and origins of platinum group elements pges in marine oil shale the oil shale samples from the changshe mountain area exhibit low total pge contents ranging from 3 196 to 8 071 ng g with a weighted mean value of 5 383 ng g while the micritic limestone samples from the changshe mountain area exhibit a little lower ranging from 0 471 to 5 669 ng g pges in oil shale samples are characterized by high contents in pd 3 23 ng g pt 1 60 ng g and os 0 32 ng g as compared to rh 0 083 ng g ru 0 112 ng g and ir 0 043 ng g the individual pges of oil shale samples from the changshe mountain area exhibit various modes of occurrence ru and ir are mainly controlled by clay minerals and partly present as sulfide rh is mainly associated with sulfide and possibly present as clay minerals pt is associated with clay minerals and sulfide and pd is controlled by organic matter and pyrite while os is mainly present in organic matter three possible sources of pges were identified in oil shale seams in the changshe mountain area ru and ir are mainly terrigenous inputs rh and pt are derived from mixed sources seawater and terrigemnous supply while pd and os are mainly derived from seawater the terrestrial source of the oil shale seams in the changshe mountain oil shale was the suowa formation limestone and the nadi kangri felsic volcanic rocks

genesis of kupferschiefer cu ag deposits by convective flow of rotliegendes brines during triassic rifting extensive and rich cu ag sulfide mineralization occurs in poland across the contact between the upper permian zechstein restricted marine sequence and the lower permian rotliegende continental volcanic and clastic sequence geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the rotliegende leaching metals from the volcanic detritus and up the flanks of basement highs possibly along fracture porosity to the pyritic kupferschiefer and zechstein limestone above thick evaporites in the lower zechstein preclude a vertical flow through model but metal zoning attitudes suggest that the brines overturned where the rotliegende pinched out against the highs and moved laterally along the base of the zechstein toward the basin centers presumably to sink back down into the rotliegende completing a convection cell a middle triassic paleomagnetic age for the metal zoning and kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the tethys ocean slow unicellular convection may be commonplace in sandstone basins where small lateral temperature gradients delta t exist but greater velocities are necessary to form large orebodies an anomalous tensional and thermal event such as rifting can increase velocities by increasing permeability slope angle or delta t the paleothermal structure of southwestern poland was determined by modeling the conductive heat flow in 14 one dimensional geologic sections which described the evolution of the basin architecture for 10 m y in the early triassic rifting was simulated by increasing the lower boundary condition from 500 degrees to 1 000 degrees c at 25 km this thermal pulse produced a surprisingly high delta t of 25 degrees c across the lubin ore district solely from differences in thermal conductivities between the basement high 4 2 w m degrees c the sandstone 2 5 w m degrees c and the shale basin center 1 25 w m degrees c unicellular convection patterns would be induced by the lateral boundary conditions of warm basement highs and cold shale centers and by the greater horizontal permeability these cells were 15 to 20 km long 400 m high and subhorizontal a slope angle of 2 degrees and a permeability of 1 d produces a convection velocity of 13 cm yr which with a copper solubility of 1 000 mg kg in 20 to 30 percent ca na cl brines in equilibrium with hematite can form the lubin deposit in less than 6 m y using a fracture permeability of 2 d and a solubility of 300 mg kg the time needed is less than 10 m y the konrad mine can be formed in similar time periods without the continuous recycling of the brine inherent in convective flow 20 times or more the metal solubilities needed to form the lubin deposits by a flow through model would be unreasonably high natural gases likely migrated along with the metalliferous brines and helped convection by creating secondary porosity and increasing the buoyancy of the fluids because the fluids are recirculated and not expelled convection provides a way in which secondary migration of methane and petroleum can occur effectively in solution as well as in separate phases

vergence an evaluation abstract fold asymmetry is an independent concept distinct from facing fold vergence is a direction relating to the sense of asymmetry of folds the complementary concept of cleavage vergence is defined allowing asymmetry to be used to locate major fold traces where no minor folds exist cleavage vergence is a valuable tool in complex structural terrains both concepts can be used singly or in combination to identify refolding vergence can define structural way up where sedimentological or stratigraphic way up cannot be recognised

base metal rich metamorphosed black shales associated with proterozoic ophiolites in the kainuu schist belt finland a genetic link with the outokumpu rock assemblage metamorphosed black shale is an essential component of the early proterozoic outokumpu rock assemblage together with serpentinite calc silicate rock and quartz rock this rock assemblage hosting the major cu co zn deposits of outokumpu and considered ophiolitic in origin has also been encountered to the northwest in the kainuu schist belt the rift basin encompassing the two areas was intruded by ophiolite complexes 1 96 1 97 billion years ago remnants of ultramafites are met as serpentinite and talc carbonate rock lenses bounded by faults along the western margin of the kainuu schist belt the black schist formations range in thickness from tens of metres to 400 m metal rich layers occur close to the serpentinite bodies the most extensive formations of metal rich black schist 300 mt 0 26 ni 0 14 cu 0 53 zn have been encountered at talvivaara the lithological mineralogical and geochemical results indicate a genetic link between the jormua talvivaara alanen and pappilanmaki prospects in the kainuu schist belt and the outokumpu rock assemblage

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

the anatomy and evolution of a transpressional imbricate zone southern uplands scotland this paper describes in detail a spectacularly exposed transpressional imbricate zone from the southern uplands of se scotland a highly heterogeneous assemblage of contemporaneous structures is preserved and is interpreted to have formed during bulk inclined triclinic sinistral transpression in an obliquely convergent thrust wedge the resulting structures include a piggy back imbricate system of closely related strike slip detachments highly curvilinear folds oblique thrust faults and a clockwise transecting cleavage a series of sub domains are recognised which are interpreted to result from imperfect kinematic partitioning of the bulk transpression into either contraction or wrench dominated strains in this case the partitioning appears to be controlled by pre existing lithological anisotropy and how this was subsequently modified by processes such as folding once deformation began our findings demonstrate that transpressional deformation zones can develop structural patterns geometrically very similar to those found in dip slip fold and thrust belts such geometries are likely to occur in many other obliquely convergent wedges because deformation zone boundaries are very often inclined and lie at low angles or subparallel to regional bedding imbricate systems inevitably form because the sedimentary anisotropy is a key mechanical control in their development our observations illustrate therefore the fundamental importance of measuring fault movement directions in the field using fault slickenline lineations in imbricate systems it is possible that a number of imbricate zones identified in other thrust wedges may turn out to be transpressional features q 2004 elsevier ltd all rights reserved

geochemistry and petrology of witwatersrand and dwyka diamictites from south africa search for an extraterrestrial component abstract diamictites are poorly sorted sediments characteristically carrying coarse grained clasts in a fine grained matrix they have generally been considered of glaciogenic or glaciomarine origin recently however it has been suggested that some massive tillite diamictite layers could represent impact breccias an earlier petrographic study of rock and mineral clasts from dwyka group diamictites revealed no evidence for shock metamorphism such as planar deformation features detailed geochemical studies of diamictite samples from the archean witwatersrand supergroup and the dwyka group of the mesozoic karoo supergroup from south africa are reported we studied the contents of the siderophile elements in these breccias as elevated abundances of such elements especially iridium could be indicative for an impact origin by use of coincidence spectrometry and other trace element analysis geochemical tracers of extraterrestrial components were sought however no enrichments of indicator elements for extraterrestrial components compared with ordinary continental crust were found thus neither geochemical nor petrographic evidence supports an impact origin of the diamictites from the dwyka group and the witwatersrand supergroup in south africa

anoxic sediments an important environment for pge an overview anoxic sediments and metasediments have been recently recognized as important host environments for the platinum group elements pge economically significant pge concentrations have been reported from marine metal rich black shales in china yukon canada and poland these ore bearing horizons are characterized by extremely restricted vertical and sometimes larger horizontal extents they are associated with the evolution of intracontinental rifting structures without any magmatic activity suggesting a possible driving mechanism for mineralization processes complex pge associations including a significant relationship of pd and pt with ni bi se y and also with sb cu co au u and f are suggested using the results of a new statistical evaluation of available geochemical data these occurrences show more common features with other hydrothermal pge deposits the rift volcanic related marine metal rich black shales of the czech republic and finland however display lower pge values the mineralized layers are much thicker with a typically limited horizontal extent showing a close association with volcanic centres pd reveals a strong correlation with ni zn au and v pt exhibits a highly significant link with the cu and mo phases low average nicu ratios and pge au chondrite normalized patterns are similar to those of some magmatic pge deposits hosted in mafic and ultramafic rocks it is very likely that organic matter played an important role in the genesis of pge accumulations in metal rich black shales in both rift and rift volcanic related environments

geochemistry of 2 63 2 49 ga impact spherule layers and implications for stratigraphic correlations and impact processes thin layers rich in spherules formed during impacts by large extraterrestrial objects have the potential to shed new light on impact processes and aid in the long distance stratigraphic correlation of precambrian successions seven formations in western australia and south africa clustered around the archean proterozoic boundary each contain a single spherule layer all of which were deposited between ca 2 49 and 2 63 ga analyses of 25 samples from 6 of the 7 spherule layers and 23 samples from closely associated strata free of spherules revealed an extraterrestrial component etc in all six layers based on pge ratios and or cr isotopic composition the amount of etc varies from marginally detectable to clear and obvious it generally amounts to ca a few percent both pge ratios and cr isotopic anomalies indicate most if not all of the impactors were ordinary chondritic in composition in contrast all spherule layers older than ca 3 0 ga that have been analyzed were produced by carbonaceous chondritic impactors normalized rare earth element patterns suggest most target rocks were basaltic in composition and variability in pge ratios favors ballistic emplacement of melt droplets rather than spherule formation via vapor condensation the geochemical data also provide a means to test proposed intra and intercontinental stratigraphic correlations cr isotopic compositions are consistent with the formation of the oldest layers on both continents by a single impact event about 2 63 ga in contrast clear geochemical differences between the middle layers both deposited ca 2 54 ga suggest they were not produced by the same impact event the youngest banded iron formation hosted layers on both continents have also been correlated but no geochemical data are available on the african layer to test this at present

the caledonian evolution of the laurentian margin in western ireland the highland border clew bay fair head baie verte brompton line which probably marks the laurentian margin passes through achill island in western ireland as a zone of ductile transpression within which the clew bay complex and dalradian supergroup are juxtaposed dextral greenschist facies transpression fabrics in the clew bay complex record the northwest directed emplacement of terranes bearing high p low t mineral assemblages against laurentia causing the dalradian continental margin sediments to be thrust westward there are significant differences in timing structural geometry and regional facing between w ireland and the scottish highland border zone

potential cretaceous paleogene boundary tsunami deposit in the intra tethyan adriatic carbonate platform section of hvar croatia an exceptional 47 m thick succession of maastrichtian to paleocene inner platform carbonates is exposed on the dalmatian island of hvar adriatic sea croatia in a seaside locality called majerovica the middle part of this succession is an 5 m thick intraformational massive deposit which is underlain by well bedded peritidal inner platform limestones containing latest maastrichtian rudists and shallow water benthic foraminifera this deposit includes a polygenic matrix supported carbonate breccia characterized by ripped up platform limestone lithoclasts up to boulder sized and polygenic microbreccia in a muddy matrix the microbreccia contains rare small intraclasts of pelagic mudstone containing terminal maastrichtian planktonic foraminifera the deposit is overlain in turn by mudstone containing a planktonic foraminiferal association belonging to the p0 and p zones of the basal paleogene and by shallow water muddy limestones containing planktonic foraminifera belonging to the p1 zone while facies suggest that the deposit was emplaced over the inner platform by a single large tsunami the biostratigraphic assessment of this section and the presence of enhanced concentrations of platinum group elements such as iridium in the topmost part of the massive deposit lend support to the hypothesis that this tsunamite is related to the chicxulub impact in yucatan this is potentially the first case of a tropical carbonate platform sedimentary succession recording the cretaceous paleogene boundary event which provides a new constraint for modeling both the western tethyan paleogeography and the catastrophic aftermaths of the chicxulub impact at the end of the mesozoic era

gold and platinum in shales with evidence against extraterrestrial sources of metals abstract few black shales contain concentrations of precious metals higher than average continental crust i e 5 ppb au yet au and pt alloys have been reported from the kupferschiefer in poland moreover thin sulfide beds in certain chinese and canadian shales contain several hundred ppb au pd and pt and average 4 mo and 2 5 ni in an association that is difficult to explain volcanic and non volcanic exhalations hydrothermal epigenesis involving either igneous or sedex fluids biogenic processes and low temperature secondary enrichment are among the possible factors involved in deriving ni pge and au for black shales and sulfide beds in black shales extraterrestrial sources have been invoked in some cases e g the cambrian of china however available data on abundances of pge indicate relatively low values for ir

the stereographic analysis of facing abstract facing directions represent an accurate means by which tectonic structure and sedimentary way up may be related a simple method is presented for determining facing directions accurately using a stereonet once determined larger amounts of facing data can be quickly collated and analysed using similar techniques to those employed for other lineations an example is given for some sheath fold structures in the moine rocks of sutherland n scotland

regional trends in the platinum group mineralogy of the critical zone of the bushveld complex south africa a wealth of quantitative data on the types volume distribution and mode of occurrence of the platinum group minerals residing in the merensky reef the ug 2 chromitite layer and platreef has been obtained over a twelve year period with the result that general platinum group mineral types for unexplored areas can perhaps now be predicted the platinum group minerals of the ug 2 and overlying merensky layers although locally different in composition mode of occurrence and size show close ties when viewed on a regional scale especially with regard to their pt pd sulfide and pt fe alloy contents thus if in one particular area the merensky reef contains pt pd sulfides as the predominant platinum group minerals then it can be safely inferred that pt pd sulfides will be a significant component of the ug 2 layer in that area the occurrence of pt fe alloy also follows this principle the distribution of pt fe alloy is in fact a major factor in differentiating the ores in the vicinity north and south of the pilansberg alkaline complex from those of the same layers farther along the arcuate strike northeastern and southeastern horns of the western bushveld and has led to an overall concept relating platinum group mineral types to postulated centers of increased volatile activity or perhaps feeder sites of the complex the mineralogy of reef disturbances such as potholes is discussed the mode of occurrence of the platinum group minerals varies between base metal sulfide silicate and chromite associations and the size of platinum group minerals in the various reefs is given solid solution or lattice substitutions of platinum group elements in the base metal sulfides account for the very important latent fraction of the total platinum group elements as distinct from platinum group minerals of the bushveld complex rhodium in the merensky reef occurs almost wholly in solid solution within pentlandite whereas rh minerals occur in the ug 2 layer chromite tends to host microscopic to submicroscopic inclusions of laurite and does not appear to take ru into the crystal lattice the probability of solid solution of platinum group elements in silicate and other oxide phases is discussed

basement cover relationships and structure within the moine rocks of central and southeast sutherland inliers of archaean to early proterozoic lewisian basement crop out within the proterozoic moine succession of central and se sutherland both the lewisian basement and the moine cover have been affected by two major tectonic events the earliest event probably occurred during the late proterozoic and involved minor folding and upper greenschist to upper amphibolite facies metamorphism intense deformation largely obliterated the unconformable relationship between the lewisian and moine rocks and imposed a planar banding on the basement lithologies subsequent reworking during the caledonian orogeny 500 400 ma resulted in ductile thrusting and folding and was associated with a widespread low to mid amphibolite facies metamorphic overprint within this context the lewisian inliers of central and se sutherland occur in two distinct structural settings i as allochthonous sheets which rest on major caledonian ductile thrusts ii in the cores of nw verging intensely curvilinear sheath folds of caledonian age

geochemical evidence for the hydrothermal origin of sulphur base metals and gold in proterozoic metamorphosed black shales kainuu and outokumpu areas finland metamorphosed black shale formations 120 150 m thick with median concentrations of 7 non carbonate carbon and 6 8 sulphur are abundantly met in drill cores in the kainuu and outokumpu areas carbon isotope 3c values are comparable to the average isotopic composition of non carbonate carbon in sedimentary rocks the rare earth element patterns show cerium depletion indicating a marine origin base metal concentrations in black shales are high in the talvivaara mineralization ore estimate 300 mt with 0 26 ni 0 14 cu and 0 53 zn and in the vicinity of ophiolite complexes in the kainuu schist belt the median value for gold is 35 ppb max 170 ppb in the western part and 16 ppb max 180 ppb in the east highest platinum and palladium concentrations encountered are 60 70 ppb it is shown that in the kainuu black shales concentrations of sulphur base metals and precious metals have been increased by hydrothermal processes as indicated by positive europium anomalies elevated mercury concentrations max 7 5 ppm high sulphur isotope 34s values and the enrichment of sulphur and base metals relative to carbon the processes operative during the deposition of these shales find an analogy in recent processes in ocean ridge spreading axes

the calculated solubility of platinum and gold in oxygen saturated fluids and the genesis of platinum palladium and gold mineralization in the unconformity related uranium deposits thermodynamic calculations on the solubility of platinum and gold indicate that saline 1 m nacl fluids saturated with atmospheric oxygen can transport geologically realistic concentrations of platinum group elements pge gold and uranium as chloro complexes a number of calculations involving fluid rock interaction suggest that the oxygen saturated fluids flowing through rocks containing quartz muscovite kaolinite magnetite and hematite initially oxidize any magnetite to hematite allowing subsequent batches of ore fluids to retain their high oxidation state during their migration through the aquifer the oxidizing fluids would move the oxidation reduction interface deeper into the aquifer leaching and redepositing platinum and gold the redissolution of earlier precipitated platinum and gold depends on the fluid rock ratio and the associated increase in the oxidation state therefore lowering of fluid rock ratios and or mixing of the oxidized fluids with a large amount of reduced fluid will precipitate uranium pge and gold it is suggested that this model can explain the genesis of gold and pge mineralization in the unconformity related uranium deposits of the alligator rivers uranium field in the northern territory australia

vergence and facing patterns in large scale sheath folds the careful geometric analysis of minor structural detail elucidates the relationships and evolution of associated large scale curvilinear hinge geometries developed during wnw directed caledonian thrusting exposed in neoproterozoic moine psammites of the moine nappe reversals in the polarity of structural facing associated with minor folding mark the position of major sheath folds which parallel transport upwardly convex sheaths closing in the direction of thrust transport cored by older gneissose basement inliers are termed culminations whilst those opening in the transport direction and cored by moine psammites are termed depressions sheath folds are bisected by transport parallel and foliation normal culmination depression surfaces which separate not only the reversals in facing but also delineate zones of minor fold hinge obliquity into clockwise and anticlockwise domains relative to the transport direction the sense of obliquity of minor z and s folds is thus dependent on position with respect to the surfaces of culmination and depression and not the fold axial surfaces surfaces of culmination and depression may be superimposed on original overturned antiformal and synformal folds to produce a variety of dome culmination on antiform saddle depression on antiform inverted saddle culmination on synform and basin depression on synform configurations the curvilinear hinges of minor folds may also be asymmetrical about the transport direction and within the plane of the regional foliation to define patterns of fold hinge line vergence classical concepts of fold limb vergence may thus relate to larger antiformal and synformal hinges whilst the fold hinge line vergence defines major curvilinear hinges associated with culminations and depressions major sheath folds may therefore be interpreted in terms of both minor fold hinge line and limb vergence coupled with fold axis obliquity and reversals in the polarity of structural facing the ability to recognise consistent and reliable structural relationships between facing and hinge obliquity at small scales indicates that the regional deformation process forms a linked and coherent system through several orders of magnitude 1999 elsevier science ltd all rights reserved

platinum group element mineralization in a hydrothermal cu ni sulfide occurrence rathbun lake northeastern ontario pt pd and au are concentrated in a hydrothermal cu ni sulfide occurrence near rathbun lake northeastern ontario the mineralization is associated with a sheared zone of the wanapitei intrusion where hydrothermal fluids have altered relatively pristine gabbronorite to chlorite sericite quartz epidote and biotite chalcopyrite and pyrite the principal sulfide minerals occur as massive and disseminated mineralization bismuthian merenskyite and to a lesser extent kotulskite michenerite and temagamite are the pd bearing minerals whereas pt occurs primarily in sperrylite 64 percent of the pd mineral grains are associated with altered silicates rather than sulfides although grains within sulfides may have been exsolved the size and number associated with silicates suggest many were precipitated independently grab samples average 9 percent cu 0 2 percent ni 20 829 ppb pd 9 736 ppb pt and 3 053 ppb au values for the other platinum group elements are near background levels no correlation is evident between cu and the platinum group elements or au the ratio of pt pd os ir ru is much larger than for tholeiitic hosted deposits of magmatic origin and probably reflects the relative solubilities of the platinum group elements

the three dimensional shape and localisation of deformation within multilayer sheath folds abstract sheath folds are widely believed to develop by the passive geometric amplification of folds in which layering has no mechanical influence during non coaxial deformation where layering becomes rheologically significant then active sheath folds may form in which the inner nose of the sheath decouples along detachments and undergoes a translation relative to the outer folded layers that surround and envelope the nose we present a systematic 3 d analysis of multiple folded layer geometries in a serially sectioned natural sheath fold weak layers which are reactivated as detachments define different shaped sheath folds relative to other layers with the sense of cut off along detachments reversing across the axial surface as the inner fold nose has protruded into the surrounding sheath envelope detachment layers are more tightly folded meaning that such active sheath folds are non similar shapes the obliquely oriented bifurcating en echelon nature of the fold hinges developed in adjacent layers suggest that pre cursor folds formed with pronounced 3 d obliquity relative to the subsequent shear plane mineral lineations folded around sheath closures display asymmetric star burst patterns consistent with recrystallisation during active folding and hinge rotation we show that the eye fold shapes exposed in any 2 d y z slice can be used to predict the geometry of marker horizons back along the x axis in the third dimension this self similarity may be of value when tracing stratiform mineralised horizons in large scale sheath folds

the influence of country rock structural architecture during pluton emplacement the loch loyal syenites scotland the late caledonian loch loyal syenites comprise three related but geographically separate composite intrusions the ben loyal ben stumanadh and cnoc nan cuilean bodies they were emplaced c 426 ma into moine and lewisian rocks of the moine and naver thrust sheets previously deformed by caledonian nw directed folding and thrusting at amphibolite facies metamorphic conditions the intrusions lie mainly within a zone of large scale cross folds in which the regional foliation trends nw se at high angles to regional orogenic strike nne ssw the cross folds are underlain by a broad ese dipping zone of high strain known as the ben blandy shear zone the nw basal contact of the ben loyal body dips generally se and strikes sub parallel to the foliation in the underlying ben blandy shear zone the higher parts of this syenite together with those of the ben stumanadh and cnoc nan cuilean intrusions form a series of variably coalesced dykes trending nw se sub parallel to the foliation in the pre existing zone of cross folds there is little evidence for significant country rock deformation during emplacement of the syenites minor components of top to the se extension occurred along the nw boundary of the ben loyal body whilst minor dextral shearing is associated with the emplacement of the nw se vertical sheet like units that are thought to form the se part of this intrusion and the other loch loyal syenites generally contact parallel magma tic state deformation fabrics are dominant in most of the intrusions and are thought to reflect limited magma pressure driven internal deformation of the igneous bodies during and immediately after emplacement the geometry of these fabrics and the loch loyal syenites as a whole has been directly controlled by the pre existing structural architecture of the surrounding country rocks this appears to be a previously overlooked feature of many plutons emplaced at mid to upper crustal depths below the region influenced by the free surface the siting and emplacement of the loch loyal syenites may have been initially facilitated by late caledonian gravity driven extension of the moine thrust sheets following the initial phase of intrusion it is also possible that the presence of magma actually promoted further nappe collapse in the adjacent country rocks there is no compelling reason to link the upper crustal extension observed during emplacement to the genesis of the alkaline magmas in the underlying mantle the siting and ascent of the syenites at depth may be linked to the presence of steeply dipping structures in the lewisian autochthon buried beneath the moine nappe

are slump folds reliable indicators of downslope flow in recent mass transport deposits abstract despite the widespread use of slump folds as indicators of palaeoslope orientation there is a lack of detailed analysis of variations in fold geometries and orientations down the length of individual slump profiles within mass transport deposits mtds to address this gap in knowledge we have systematically recorded more than 500 structural measurements of fold hinges and axial planes along a 25 m section through a mesoscopic slump profile our case study is performed in wet unconsolidated late holocene sediments which are only recently exposed due to falling water levels in the dead sea in this situation the modern slope is exposed and directly visible slumping having occurred in the past few centuries fold hinges define broad arcs at high angles to flow in the downslope toe of the slump and progressively swing to become sub parallel to flow in the upslope region greatest amounts of shortening 35 are recorded at the toe suggesting that the swing in trends of fold hinges and axial planes is a consequence of differential layer normal shear rather than downslope strain gradients significant variations of 90 occur in the orientation and vergence of slump folds on either side of a 10 m wide gully which cuts the slump sheet in some instances folds have nucleated around longer 10 cm wooden sticks that were incorporated into the slump whereas shorter wooden fragments align parallel to the flow direction the differences in orientations of wooden sticks and wooden fragments are consistent with differential layer normal shear on each side of a flow cell evaporite concretions grew within the sediments during slumping and influenced the geometry and kinematics of slump folds suggesting that slope failure may have been a slow creep event generated by slope instability rather than a result of catastrophic failure associated with large earthquakes our work illustrates the problems associated with using partial datasets where classical structural analysis of transects

geochemical investigation of the lower cambrian mineralised black shales of south china and the late devonian nick deposit canada abstract lower cambrian tommotian black shales of the niutitang formation south china host a thin accumulation 5 20 cm of ni mo platinum group elements pge au ni as zn cu v and rare earth elements ree of all known deposits the late devonian ni mo pge sulphide horizon in black shales of the nick deposit selwyn basin in canadian yukon presents the strongest similarity with the niutitang formation polymetallic layer in the present study samples of the mineralised layer and host shales in south china from two mine sites zunyi and sancha were investigated in order to further characterise the prevailing redox conditions and mechanisms involved in the metal concentration process at both sites additional comparison with the nick deposit mineralised layer was also undertaken bulk geochemical analysis including pge analysis were conducted on all samples along with m scale investigation of metal distributions and associations by x ray fluorescence xrf mapping and synchrotron xrf mapping the comparison of the two sites from south china highlights strong similarities in metal enrichment factors pge and ree distribution patterns are also highly similar and suggest a source from seawater strong variations in elemental distributions at m scale were observed at both sites most likely related to intense variations in redox conditions in the sediment the comparison with the nick deposit highlights a stronger enrichment in ni and zn in the nick deposit and a greater variety of minerals in the niutitang shales the pge and ree distributions of both the nick deposit and the niutitang shales however present highly similar patterns and support an origin from seawater the present study provides further insight into mineralisation style and processes in these mineralised black shales highlighting the importance of redox conditions and re emphasizing the role of organic matter in the formation of these mineralised layers

osmium in marine sediments osmium is enriched in ferromanganese minerals and its concentrations follow those of other pt group metals except pd oxidative capture during solid formation is the probable mechanism for uptake in some sediments forming under reducing conditions phosphorites and anoxic coastal deposits there is also an enrichment this may relate to reductive capture although deposits also formed under reducing conditions from hydrothermal areas are depleted in osmium

tectonic history of the ellsworth mountains west antarctica reconciling a gondwana enigma early paleozoic orogenesis has been recognized along the southern african saldanian orogeny and east antarctic ross orogeny sectors of the gondwana paleo pacific margin however the absence of a contemporaneous orogenic event in the ellsworth mountains of west antarctica once a contiguous part of this margin has resulted in their geology being considered enigmatic in this contribution widespread detailed structural studies from all stratigraphic levels of the ellsworth mountains allow their tectonic evolution to be reassessed geochemical stratigraphic and structural data indicate that the middle to upper cambrian heritage group developed in a continental rift basin multiple observations of the crucial end cambrian contact between this rift sequence and the overlying crashsite group reveal the contact to be regionally conformable there are localized outcrop scale unconformities furthermore structural continuity can be demonstrated across this key boundary thus precluding the possibility of an end cambrian orogenic event the entire stratigraphic succession was affected by two post permian phases of deformation d1 structures are locally developed and superimposed by the main dextral transpressive d2 permian triassic gondwanian deformation event d2 is succeeded by an episode of extension orthogonal to orogenic strike recent geochronological data on the early paleozoic evolution of the cape fold belt reveal a strong tectonostratigraphic correlation with the ellsworth mountains indicating that this sector of the gondwana paleo pacific margin was affected by middle to late cambrian rifting a new tectonic model is proposed for the southwestern paleo pacific margin of gondwana that accounts for the presence of rifting along a margin otherwise dominated by active subduction

speciation and solubility of palladium in aqueous magmatic hydrothermal solutions combining thermodynamic data at 25c and 1 bar with correlation algorithms enables prediction of equilibrium dissociation constants for aqueous platinum group element pge complexes at high pressures and temperatures we used these data 1 to calculate the speciation of pd ii in nacl solutions at temperatures to 750c pressures to 2 kbar and values from 3 to 8 and 2 to predict the solubility of palladium at 2 kbar as a function of temperature oxygen fugacity f sub o2 ph and total chloride concentration m sub t cl sup minus calculations indicate that as ph increases there is a sharp transition from chloride to hydroxide complex dominance at all chloride concentrations this shift occurs at or below neutral ph in dilute solution but at m sub t cl sup minus ge 1 0 pd ii chloride complexes account for the majority of dissolved pd ii well into alkaline conditions solubility of palladium increases with increasing temperature m sub t cl sup minus and f sub o2 at 700c 2 kbar and the f sub o2 set by the fmq buffer palladium solubility in a 3 0 m nacl solution is approximately 0 3 ppm at a ph of 4 and one unit ph variation can change palladium solubility by two orders of magnitude these results suggest that pge can be transported as chloridemore complexes in cl rich magmatic hydrothermal solutions like those inferred from petrologic studies of the stillwater and bushveld complexes less

critical storm thresholds for the generation of significant dune erosion at dziwnow spit poland abstract storm influence on the southern baltic coast was examined for a 14 km long section of the polish coast along the dziwnow spit based on 30 years of post storm dune erosion observations in this study we assumed that a significant storm causes noticeable sand dune erosion significant changes of the coast after each major storm were analysed based on reports from 1978 to 2008 provided by the maritime office szczecin thirty two storms that caused dune losses were chosen for analysis correlation and hierarchical cluster analysis allowed us to distinguish three groups of storms that caused varying amounts of dune erosion g1 small g2 medium and g3 large sea level is the main parameter that influences the amount of dune erosion caused by storms on the southern baltic coast factors such as maximum significant wave height mean wave direction storm energy and duration can also but less significantly influence dune erosion the study area was divided into two sections dziwnow where there are many protection measures in place and miedzywodzie which has no protection measures in place in both areas we observed differences in the impact of sea level and significant wave height and storm groupings approximate minimum sea level and significant wave height thresholds were defined for particular storm groups

tsunami and seiche triggered deformation within offshore sediments abstract most studies of tsunami and seiche related deposits have focussed on coastal and near coastal zones which are most readily accessible with few investigations of deeper water settings and the potential soft sediment deformation effects of such waves the late pleistocene lisan formation outcropping to the west of the dead sea contains superb examples of sedimentary slump folds formed in water depths of

iridium content of basaltic tuffs and enclosing black shales of the balder formation north sea abstract the anomalous levels of ir and the presence of shocked metamorphosed quartz deposited at the cretaceous tertiary k t boundary worldwide is strong evidence that a meteorite impact took place during the k t boundary interval however because of observed high ir contents at kilauea vents it is still a major point of contention that the ir anomaly could have been produced by flood basaltic volcanism this might especially be true at stevns klint denmark where the k t boundary marl contains pyroclastic labradorite and mg smectite thought to have been produced by basaltic volcanism however up to now no study has determined whether or not a depositional ir anomaly has formed in association with a known major basaltic eruption herein we report the concentrations of ir pt au and ag in basaltic tuffs and enclosing marine black shales of the widespread paleocene eocene balder formation the tuffs in the balder formation represent explosive basaltic volcanism associated with the major volcano tectonic activity of the opening of the northern north atlantic ocean as such they are the kind of eruption that could have possibly created a global k t boundary type ir anomaly our results show that the tuffs and the shales on a per weight basis both contain concentrations of ir 0 1 0 25 ppb that are higher than the ir levels recently measured from terrestrial rocks including the deccan trap and columbia river flood basalts but are comparable to hawaiian and reunion island basalts because of its thickness the absolute amount of ir expelled during the eruption of the main tuff sequence of the balder tuff is sizable yet for such an eruption to have produced a global ir anomaly would mandate it having been one of an extremely high volatile content and it would have to have been erupted over a very short interval of time furthermore such a high proportion of the volatilized ir would have to have been injected into the stratosphere so that only small enrichments of ir were formed in the proximal tuffs on a per gram basis

caledonian transpressional terrane accretion along the laurentian margin in co mayo ireland the highland border fair head clew bay baie verte brompton suture clew bay suture on achill island western ireland is an e w trending zone of vertical ductile dextral transpression bounding the southern edge of the dalradian terrane the achill dalradian a sequence of coarse grained psammite overlain by conglomerate quartzite schist and limestone disposed in recumbent curvilinear folds represents laurentian continental margin deposits which were translated westward during deformation parallel to the suture trace studies of fabric development and albite porphyroblast growth indicate that e w dextral transpression and west directed recumbent folding were synchronous and are interpreted as separate expressions of the same nw directed terrane impingement event this process of terrane docking was marked by a c 4kbar phase of decompression within the suture four separate terrane slivers are recognized the presence of pyrope garnet and crossite amphibole within two imply the clew bay zone experienced sufficient displacement to exhume rocks from deep lithospheric levels in addition the extensive retrogression and destruction suffered by these remnant high pressure mineral assemblages during the albite generating transpressional phase implies that ductile deformation was enhanced by the introduction of fluid into and along the suture zone during impingement

precious metal enrichment at low redox in terrestrial native fe bearing basalts investigated using laser ablation icp ms primary native fe is a rare crystallizing phase from terrestrial basaltic magmas requiring highly reducing conditions fo2 iron wustite buffer in order to form reducing conditions in basaltic magmas can be achieved through assimilation of carbonaceous crustal material which leads to formation of an immiscible molten c rich native fe alloy liquid if this liquid also contains sufficient sulfur it can undergo further division into conjugate fe c rich and a fe s rich immiscible melts that can effectively scavenge the highly siderophile elements hse re au and the platinum group elements pge pd pt rh ru ir os as well as ni and cu to economic abundances three localities are known globally where native fe bearing mafic rocks occur 1 paleocene basalts of disko island west greenland 2 a miocene lava of the buhl basalts germany and 3 mafic intrusions associated with the late permian siberian flood basalts in this contribution we report major and minor element compositions and hse concentrations for the main alloy phases feni metal and cohenite and sulfide for all three known global occurrences of native fe bearing basalt total hse abundances in metal grains obtained by laser ablation inductively coupled plasma mass spectrometry la icp ms are lowest in the buhl basalt 0 05 ppm intermediate in the disko island basalts 4 8 ppm and highest the siberian khungtukun and dzhaltul intrusions 10 30 ppm these differences demonstrate that while native fe formation is the result of carbonaceous crustal assimilation hse enrichment is not ubiquitous during this process the siberian occurrences are characterized by pt pge ppge pt pd enrichment relative to the ir pge ipge rh ru ir os consistent with models of early stage fractionation of olivine chromite and metallic ipge in staging magma reservoirs prior to the addition of c rich crustal materials in the shallow crust relative to noril sk ni cu pge sulfide ores the siberian native fe basalts are enriched in the ppge relative to the ipge but exhibit ru enrichments in contrast disko island native fe rocks do not show significant fractionation of the ppge from the ipge but have positive re and ru anomalies and high os ir ratios to reconcile these observations we present a general model where some parental melts experienced early stage crustal assimilation in staging magma reservoirs prior to reduction by carbon rich materials e g khungtukun dzhaltul whereas basaltic parental melts to disko island and buhl solely experienced interaction with carbonaceous material resulting in extensive devolatilization native fe segregation and native fe formation

a review of the origins of metal rich pennsylvanian black shales central u s a with an inferred role for basinal brines abstract compared to most shales even most black shales numerous thin pennsylvanian marine black shales of the u s midwest are very enriched in organic c 5 40wt and heavy elements for example instrumental neutron activation analysis of 74 samples of mostly black and dark gray pennsylvanian shales of the u s midwest average 1300 ppm zn 85 ppm u 655 ppm mo 130 ppm se and 55 ppm cd amounts sufficient to raise concerns about heavy element pollution direct precipitation of sulfides and fixation by abundant organic matter during sedimentation and early diagenesis may account for heavy metals contained by shales in most cases metal supply calculations however indicate that a special source would be needed to supply metals for a strictly syngenetic origin possible sources for such metals include submarine hot springs and pennsylvanian seas that may have been more enriched in metals than modern ocean water at least at some localities additional metal values may have been added later from basinal brines e g zn or from modern groundwaters e g mo se u the actions of modern supergene processes may fix metals mitigating detrimental effects from black shales

sulfide and platinum mineralization in the merensky reef evidence from hydrous silicates and fluid inclusions the base metal sulfides of the merensky reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates biotite and phlogopite crystallized in the vicinity of sulfides from a volatile enriched highly fractionated intercumulus melt amphibole chlorite and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase biotite is often accompanied by zircon rutile and quartz accessory quartz hosts a complex suite of h2o nacl cacl2 co2 ch4 fluid inclusions which have thus far not been described from the merensky reef the earliest fluid inclusion compositions are nacl h2o with less than 10 vol water co2 coexisting with a halite daughter crystal and brine and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations the maximum trapping temperature is around 730 c at 4 to 5 kb pressure later inclusion generations are h2o nacl co2 h2o and pure co2 and ch4 the presence of cl rich fluids during the intercumulus stage of the crystallizing merensky reef is directly related to the mode of sulfide precipitation prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as h2s sulfur saturation causes reaction of h2s with oxides of the silicate melt to form a sulfide melt plus water during reaction the magma is enriched in water until a separate fluid unmixes it carries all compounds with high fluid melt partition coefficients as well as metals capable of forming oh and cl complexes precious metals are assumed to have fractionated into the cl rich fluid as cl complexes rather than being dissolved in the sulfide melt during the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets the model proposed explains the distribution pattern of platinum group minerals in the merensky reef better than any orthomagmatic mineralization concept offered so far

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

geochemistry of the la erma and qiongmo au se deposits in the western qinling mountains china abstract the microdisseminated gold deposits at la erma and qiongmo are typically hosted in cambrian chert formation in western qinling mountains china both in the host rocks and the gold ores selenium is present in high abundance as selenide minerals or isomorphous admixtures in sulfides with independent selenium orebodies can be delineated in some localities intergrowth of selenides and native gold is commonly observed selenium is also noticed in considerably high content in fluid inclusions in quartz and barite which are closely related to gold mineralization studies show that gold and selenium may have been transported together in ore solutions as au s se complex in view of the wide difference in electrode potential between selenium and sulfur the two elements would be separated under oxidizing conditions selenium would mostly occur as isomorphic mixtures in sulfides during the early stage of mineralization when the environment is more reducing but would precipitate as selenides during the late oxidizing stage simultaneous enrichment of gold and selenium would be favored by boiling of the ore solution or mixing of ore solution with oxygen rich water at shallow depths

thrust sequences and the significance of low angle out of sequence faults in the northernmost moine nappe and moine thrust zone nw scotland in common with most thrust belts the moine thrust zone scotland preserves a foreland propagating sequence of thrusting however significant examples of local to regional overstep sequences are also recognized and their interpretation remains controversial remapping of the northernmost moine thrust zone has defined a thick belt of mylonites in the centre of which lies the ductile wnw directed moine thrust the base of the mylonite belt however is marked by a regionally significant low angle west directed brittle fault here termed the lochan riabhach thrust that truncates thrust related structures in its footwall comparison of the tectonic stratigraphy of the mylonite belt with that preserved in a downfaulted outlier to the west at durness indicates that the lochan riabhach thrust cuts down section in its footwall and therefore appears to be extensional locally it is unequivocally breached by underlying imbricate thrusts we prefer to interpret the lochan riabhach thrust as an extensional fault that formed during a hiatus in thrust stacking we relate this faulting episode to the changes in the stability of the evolving orogenic wedge and reiterate that such extensional faults may be common although possibly unrecognized features in many other thrust belts

the geometry and topology of natural sheath folds a new tool for structural analysis abstract curvilinear sheath folds are classically depicted as displaying symmetrical geometries about two orthogonal mirror planes centred along the x y axial surface and the x z medial culmination depression surface which bisects the fold nose however 10 000 geometric analyses of minor folds and fabrics formed during ductile thrusting in the caledonides of northern scotland reveals that major dome and basin sheath folds can display distinct and predictable asymmetries across both axial and medial surfaces the strain is typically heterogeneous so that structural fabrics and younging evidence are preserved within sheath folds at varying stages of development this allows an analysis of the evolution of such structures from tongue folds to more extreme tubular forms geometric relationships between measured orientations of fold hinges axial planes extension lineations and foliations are compared on fabric topology plots ftps which provide an effective tool for monitoring planar and linear fabric rotations with increasing progressive non coaxial deformation they consistently display systematic variation from regions of lower to higher strain on passing from upper to lower fold limbs across major axial surfaces and on crossing medial surfaces from short to long hinge line segments axial and medial surfaces effectively therefore divide major sheath folds into quadrants with different amounts senses and combinations of planar and linear fabric rotation within each domain such heterogeneous deformation implies that models of intense non coaxial deformation uniformly affecting pre existing folds may overestimate bulk displacement and shear strain variable fold hinge line rotation about medial surfaces also provides an effective mechanism for the closure of major sheaths which may otherwise project for unfeasible distances in the x direction bedding cleavage intersections are developed at greater angles to the transport direction than fold hinges which they transect in a consistent and predictable sense thereby confirming the direction of fold rotation even in areas which lack information on fold facing in cross section asymmetric tear drop eyes indicate the sense of fold hinge line vergence whilst fold limb and hinge line asymmetry may be combined on 3 d vergence ranking and rotation grids which allow location and relative strain states of minor structures to be accurately predicted within the overall sheath framework systematic fabric analysis on ftps may be applied to the investigation of ductile deformation across a broad range of scenarios