an updated holocene sea level curve for the delaware coast abstract we present an updated holocene sea level curve for the delaware coast based on new calibrations of 16 previously published radiocarbon dates kraft 1976 belknap and kraft 1977 and 22 new radiocarbon dates of basal peat deposits a review of published and unpublished 137 cs and 210 pb analyses and tide gauge data provide the basis for evaluating shorter term 10 2 yr sea level trends paleosea level elevations for the new basal peat samples were determined from the present vertical zonation of marsh plants relative to mean high water along the delaware coast and the composition of plant fossils and foraminifera current trends in tidal range along the delaware coast were used to reduce elevations from different locations to a common vertical datum of mean high water at breakwater harbor delaware the updated curve is similar to belknap and kraft s j sediment petrol 47 1977 610 629 original sea level curve from 12 000 to about 2000 yr bp the updated curve documents a rate of sea level rise of 0 9 mm yr from 1250 yr bp to present based on 11 dates in good agreement with other recent sea level curves from the northern and central u s atlantic coast while the previous curve documents rates of about 1 3 mm yr based on 4 dates the precision of both estimates however is very low so the significance of these differences is uncertain a review of 210 pb and 137 cs analyses from salt marshes of delaware indicates average marsh accretion rates of 3 mm yr for the last 100 yr in good agreement with shorter term estimates of sea level rise from tide gauge records

genesis of the huangshannan high ni tenor magmatic sulfide deposit in the eastern tianshan northwest china constraints from pge geochemistry and os s isotopes abstract the huangshannan magmatic ni cu sulfide deposit is one of a group of permian magmatic ni cu deposits located in the southern central asian orogenic belt in the eastern tianshan northwest china it is characterized by elevated ni tenor concentrations in recalculated 100 sulfide in sulfide within ultramafic rocks 9 19 wt with values much higher than other deposits in the region sulfides of the huangshannan deposit are composed of pentlandite chalcopyrite and pyrrhotite and the host rock is relatively fresh indicating that the high ni tenor is a primary magmatic feature rather than formed by alteration processes it is shown that sulfides with high ni tenor can be generated by sulfide olivine equilibrium at an oxygen fugacity of qfm 0 5 for magmas containing 450 ppm ni and 20 olivine ores with 10 wt sulfur have relatively low pge and ni tenors compared to other ores r factor mass ratio of silicate to sulfide liquid modeling of ni indicates that they formed at moderate r values 150 600 based on this constraint on r values ores with 4 5 wt as sulfide rich samples are also depleted in cu and as interstitial sulfides in those samples are physically interconnected at a scale of several cms the low pt and pd anomalies are attributed to solid pt and pd phases crystallization and retention with the monosulfide solid solution mss and cu rich sulfide liquid percolation during mss fractionation this finding indicates that pt anomalies in sulfide rich rocks from magmatic ni cu deposits in the eastern tianshan are the result of sulfide fractionation rather than a hydrothermal effect 187 os 188 os 278ma values of the lherzolite samples vary from 0 27 to 0 37 and os 278ma values vary from 110 to 189 indicating significant magma interaction with crustal sulfides rich in radiogenic os well constrained os values and 34 s values 0 4 to 0 8 indicate that crustal contamination occurred at depth before the arrival of the magma in the huangshannan chamber regionally deposits with high ni tenor have not been reported other than the huangshannan deposit however many intrusions with high ni contents in olivine are present in nw china such as the erhongwa poyi and poshi intrusions those intrusions are capable of forming high ni tenor sulfides due to olivine sulfide silicate equilibrium and relative high ni content in parent magma making them attractive exploration targets

effects of magmatic processes serpentinization and talc carbonate alteration on sulfide mineralogy and ore textures in the black swan disseminated nickel sulfide deposit yilgarn craton the black swan disseminated orebody occurs predominantly within the partially carbonated serpentinite core of a zoned serpentinite talc carbonate ultramafic cumulate body of komatiitic parentage the black swan disseminated sulfides depart significantly from the characteristic pattern observed in otherwise similar deposits in western australia and canada which display magnetite bearing pentlandite rich sulfide aggregates blebs in serpentinites and s rich millerite bearing assemblages in talc carbonates the black swan disseminated ores in contrast are dominated by millerite pyrite polydymite assemblages in both serpentinites and talc carbonates with no evident relationship to the progression of carbonation sulfides show three types of intergrowth with gangue minerals which can occur separately or all together intergrowth with magnetite at least some of which appear to be primary magmatic in origin fine intergrowth with interlocking lath textured antigorite and intergrowth with carbonate minerals carbonate commonly replaces the core of sulfide blebs while retaining the primary magmatic outline carbonate replacement of sulfide roughly parallels the overall progression of carbonation of the whole rock but no systematic relationship of the other intergrowth types to carbonate content is observed in the serpentinites serpentine mineralogy determined by microbeam raman spectroscopy comprises lizardite which occurs in pseudomorphic mesh textures after olivine and antigorite formed by variable degrees of overprinting of original lizardite mesh textures ranging to a completely overprinting interlocking texture with no relic igneous texture this progression is interpreted as the result of mild thermal metamorphism of original lizardite serpentinite this progression is completely independent of carbonate content and is also apparently independent of extent of sulfide antigorite intergrowth which is interpreted as being early and related to volume expansion during initial sea floor serpentinization talc is almost completely absent from serpentinites while carbonate content varies widely whole rock ni and s data are very strongly correlated in millerite poor pentlandite rich samples and poorly correlated in samples where millerite is the dominant ni bearing sulfide on this basis we conclude that the pentlandite assemblages are slightly modified survivors of the original magmatic event while the millerite pyrite assemblages formed during the earliest stages of serpentinization overprinting of the early serpentinization event by talc carbonate had essentially no effect on sulfide mineralogy other than inducing intergrowth with carbonate a number of distinctive features such as magnetite rich bleb cores the association of sulfides with segregation vesicles and chromite shells the subspherical morphology of the blebs and preferential replacement of bleb cores are considered to be inherited from the magmatic phase and are attributed to an original high but variable oxygen and halogen content of the sulfide melt component exsolution of this component during solidification of the blebs in some cases produced sulfide centered bubbles now preserved as segregation vesicles while in other cases oxygen was retained within the bleb forming magnetite sulfide intergrowths chromite shells formed as a result of exsolved oxygen interacting with komatiite magma volatile rich blebs solidified in some cases with hollow or porous cores which were subsequently exploited by carbonate replacement

sea level rise a review of recent past and near future trends global mean sea level is a potentially sensitive indicator of climate change global warming will contribute to worldwide sea level rise slr from thermal expansion of ocean water melting of mountain glaciers and polar ice sheets a number of studies mostly using tide gauge data from the permanent service for mean sea level bidston observatory england have obtained rates of global slr within the last 100 years that range between 0 3 and 3 mm yr 1 with most values concentrated between 1 and 2 mm yr 1 however the reliability of these results has been questioned because of problems with data quality and physical processes that introduce a high level of spatial and temporal variability sources of uncertainty in the sea level data include variations in winds ocean currents river runoff vertical earth movements and geographically uneven distribution of long term records crustal motions introduce a major source of error to a large extent these can be filtered by employing palaeo sea level proxies and geophysical modelling to remove glacio isostatic changes ultimately satellite geodesy will help resolve the inherent ambiguity between the land and ocean level changes recorded by tide gauges future sea level is expected to rise by 1 m with a best guess value of 48 cm by the year 2100 such rates represent an acceleration of four to seven times over present rates local land subsidence could substantially increase the apparent slr for example louisiana is currently experiencing slr trends nearly 10 times the global mean rate these recently reduced slr estimates are based on climate models that predict a zero to negative contribution to slr from antarctica most global climate models gcms indicate an ice accumulation over antarctica because in a warmer world precipitation will exceed ablation snow melt however the impacts of attritional processes such as thinning of the ice shelves have been downplayed according to some experts furthermore not all climate models are in agreement opposite conclusions may be drawn from the results of other gcms in addition the west antarctic ice sheet is potentially subject to dynamic and volcanic instabilities that are difficult to predict because of the great uncertainty in slr projections careful monitoring of future sea level trends by upgraded tide gauge networks and satellite geodesy will become essential finally because of the high spatial variability in crustal subsidence rates wave climates and tidal regimes it will be the set of local conditions especially the relative sea level rise rather than a single global mean sea level trend that will determine each locality s vulnerability to future slr

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

redistribution of ore elements during serpentinization and talc carbonate alteration of some archean dunites western australia serpentinization of barren and weakly mineralized archean dunites in the yilgarn block western australia occurred without any apparent loss of major components including the important ore elements ni and fe sulfur addition during initial serpentinization resulted in about 30 percent of original silicate ni being redistributed to newly formed sulfide by reactions similar to olivine water lizardite brucite and lizardite brucite s lizardite brucite magnetite heazlewoodite water h 2 serpentinization at a higher temperature or metamorphism of the lizardite bearing assemblage formed antigorite serpentinite in which up to 60 percent of bulk rock ni is incorporated in sulfide form lizardite brucite magnetite heazlewoodite co 2 s antigorite magnesite magnetite ni sulfide water h 2 complete co 2 metasomatism resulted in talc carbonate rocks with still more ni redistributed to sulfides and the formation of some fe sulfide antigorite magnesite magnetite ni sulfide co 2 s talc magnesite pentlanditc fe sulfide or magnetite water o 2 in areas where low s activity precluded sulfide formation ni was strongly enriched in magnetite in serpentinites or talc in talc carbonate rocks preexisting disseminated ni sulfides of magmatic origin were significantly upgraded by serpentinization up to 30 percent of sulfide ni in ores averaging about 0 7 percent ni is of metamorphic origin and this proportion may be higher in talc carbonate ores fe sulfides of metamorphic origin form up to 20 percent of the total sulfide fraction in talc carbonate altered disseminated ni ores so that about half the sulfide content of these ores may be metamorphically derived by redistribution of elements originally held in olivine

crustal and uppermost mantle s velocity structure under hi climb seismic array in central tibetan plateau from joint inversion of surface wave dispersion and receiver function data abstract trade off between the depth of an interface and the average velocity above the interface is well known in receiver function inversion to resolve model ambiguity surface wave dispersion data which are sensitive to vertical shear velocity average are commonly combined with p receiver functions in the inversion in this paper we design a joint inversion scheme using the neighborhood searching algorithm to solve shear velocity structure of the crust and uppermost mantle with receiver function and surface wave dispersion data two sets of stretched splines are implemented in the inversion to obtain smooth velocity profiles separated by a specifically defined moho discontinuity we apply this method to the dense hi climb seismic array in the central tibetan plateau tp the indian crust is observed to subduct and underplate the tibetan crust between the yarlung zangbo suture and the bangong nujiang suture at the latitude of about 31 5 n the crust thickens from about 50 km below the indian foreland to over 75 km south of bangong nujiang suture and turns shallower at around 65 km under the qiangtang block we identify two zones with complicated moho structure beneath the northern lhasa block and southern qiangtang block indicating highly deformed moho morphology and beneath the himalaya block associated with the underthrusting of the indian plate respectively a low velocity zone is present in the mid crust in most parts of the profile under the tp with up to more than 10 velocity reduction the low velocity structure is not continuous forming discontinuous patches rather than channels calling for a revision of the channel flow model

magnitude of hurricane ike storm surge sedimentation implications for coastal marsh aggradation there is a paucity of information on the regional distribution and magnitude of hurricane storm surge sedimentation this study assesses the spatial extent and magnitude of hurricane ike s 2008 storm surge sedimentation and discusses implications for the role of hurricanes in marsh aggradation the characteristics of the storm surge deposit including thickness inland penetration volume and mass were determined for 15 transects across marshes bordering the gulf of mexico in south eastern texas and south western louisiana the deposit is up to 0 85 m thick extends up to 3 6 km inland and has an estimated volume of about 13 7 million m3 and an estimated mass of about 16 2 million metric tons this level of sedimentation is one to two orders of magnitude larger than other potential sources of marsh sedimentation including annual riverine inputs and inputs from alongshore sediment transport the study findings add support to a growing body of evidence that hurricanes may be the predominant sediment source for long term aggradation of many coastal marshes bordering the gulf of mexico copyright 2012 john wiley sons ltd

geologic and human factors in the decline of the tidal salt marsh lithosome the delaware estuary and atlantic coastal zone abstract two to three thousand years ago the fringing tidal salt marsh wetlands including brackish and freshwater marsh of the delaware coastal zone were three to four times wider than at present observed variations in rates of marsh surface aggradation suggest that some areas are undergoing inundation whereas many other areas are undergoing aggradation at rates greater than sea level rise as measured by a local tidal gauge average 33 cm century based on a 70 year record and may be undergoing floral succession accompanying these sedimentary processes are coastal erosion rates up to 6 9 m yr along the delaware estuary up to 2 8 m yr along the delaware atlantic coast and ranging from 0 1 m yr to 0 6 m yr along the delaware atlantic coastal lagoons human development has destroyed nearly 9 of delaware s fringing salt marshes between 1938 and 1975 the rapidly growing trend toward hardening the edge of the adjacent landward uplands leads us to the conclusion that much of the fringing salt marsh of delaware will disappear over the next two to three centuries with only small remnants declining to extinction ca 1500 1700 years into the future impacts on the state of delaware comprised of 13 fringing salt marshes 1 4 century ago will be profound in terms of destruction of a large segment of the atlantic coastal or eastern north american migratory bird flyway and an eventual forced accommodation of the inhabitants of delaware to these naturally ongoing geological processes

biophysical controls on accretion and elevation change in caribbean mangrove ecosystems abstract habitat stability of coastal ecosystems such as marshes and mangroves depends on maintenance of soil elevations relative to sea level many such systems are characterized by limited mineral sedimentation and or rapid subsidence and are consequently dependent upon accumulation of organic matter to maintain elevations however little field information exists regarding the contribution of specific biological processes to vertical accretion and elevation change this study used biogenic mangrove systems in carbonate settings in belize bz and southwest florida fl to examine biophysical controls on elevation change rates of elevation change vertical accretion benthic mat formation and belowground root accumulation were measured in fringe basin scrub and dwarf forest types plus a restored forest elevation change rates mm yr 1 measured with surface elevation tables varied widely bz dwarf 3 7 bz scrub 1 1 fl fringe 0 6 fl basin 2 1 bz fringe 4 1 and fl restored 9 9 root mass accumulation varied across sites 82 739 g m 2 yr 1 and was positively correlated with elevation change root volumetric contribution to vertical change mm yr 1 was lowest in bz dwarf 1 2 and fl fringe 2 4 intermediate in fl basin 4 1 and bz scrub 4 3 and highest in bz fringe 8 8 and fl restored 11 8 sites surface growth of turf forming algae microbial mats or accumulation of leaf litter and detritus also made significant contributions to vertical accretion turf algal mats in fringe and scrub forests accreted faster 2 7 mm yr 1 than leaf litter mats in basin forests 1 9 mm yr 1 but similarly to microbial mats in dwarf forests 2 1 mm yr 1 surface accretion of mineral material accounted for only 0 2 3 3 of total vertical change those sites with high root contributions and or rapid growth of living mats exhibited an elevation surplus 2 to 8 mm yr 1 whereas those with low root inputs and low or non living mat accumulation showed an elevation deficit 1 to 5 7 mm yr 1 this study indicates that biotic processes of root production and benthic mat formation are important controls on accretion and elevation change in mangrove ecosystems common to the caribbean region quantification of specific biological controls on elevation provides better insight into how sustainability of such systems might be influenced by global e g climate atmospheric co2 and local e g nutrients disturbance factors affecting organic matter accumulation in addition to relative sea level rise

a re appraisal of the epoch nickel sulphide deposit filabusi greenstone belt zimbabwe a hydrothermal nickel mineral system abstract the neoarchaean epoch nickel sulphide nis deposit discovered in 1970 and subsequently mined from 1972 to 1998 has been previously interpreted to be a magmatic ore system however on the basis of field petrographic and analytical data obtained during the initial exploration and evaluation stages integrated with limited new analytical data sem and ore microscopy we propose that the epoch nis may be of hydrothermal origin key features that have prompted a re appraisal of the genesis of the epoch mineralisation include a ore lenses are irregularly distributed along foliation fabrics of the host talc carbonate rocks and as such no relationship to basal ultramafic mafic units b the thickness of the ore lenses are highly variable from tens of centimetres to several metres c ore mineralogy is characterised by dominant millerite pyrite chalcopyrite assemblages and d high pd pt ratios although our hydrothermal model is somewhat speculative we suggest that on present evidence there is little doubt that the epoch nis lacks the features of typical magmatic sulphide deposits more geochemical and isotopic data are needed to test our model

komatiites and nickel sulfide ores of the black swan area yilgarn craton western australia 2 geology and genesis of the orebodies the black swan ultramafic succession hosts a number of magmatic fe ni cu pge sulfide ore shoots ranging from high grade massive ore to low grade disseminated sulfides of these the most economically significant is the silver swan massive sulfide orebody associated with the basal contact of the succession the deposit varies in thickness between 5 and 20 m reaches a n s strike length of 75 m extends for at least 1 2 km of vertical plunge and is open at depth overlying matrix net textured ore is rare inclusions of dacite are abundant within the lower 5 m of the massive sulfide they range from angular fragments through smooth sinuous and plumose morphologies to fine lace like intergrowths with the sulfide matrix and comprise variable proportions of cores of porphyritic dacite and carapaces with skeletal plagioclase phenocrysts dynamic crystallisation and kinetic melting textures in the carapaces indicate that the inclusions have been heated to various temperatures some well above their liquidus temperature the composition of the inclusions ranges from a perfect match with the immediate footwall dacites to mixtures of dacite with up to 30 komatiite the consistent thickness of the inclusion bearing basal layer within the massive sulphide is interpreted as the extent of 3 d physical connectivity between the inclusions and a partially molten underlying hybrid layer primary contacts between the silver swan massive sulfide orebody and overlying ultramafic rocks are marked by thin rinds containing coarse grained chevron textured chromites with skeletal textures compositions of these chromites match those from kambalda perseverance and other localities and are inconsistent with a metamorphic origin they are interpreted as markers of primary magmatic contacts the combination of this feature with the general paucity of matrix ore implies that the massive ore accumulated and solidified before the accumulation of the overlying thick sequence of olivine cumulates taken together with observations on the internal fractionation of platinum group elements within the massive ores these observations are consistent with a model where the massive ore were emplaced at the floor of a small partially drained lava tube the floor of the tube had been previously heated by passage of large volumes of lava such that it had reached its melting range the felsic inclusions within the ore are the result of buoyant ascent of partially molten substrate into the ore magma this constitutes strong evidence for the operation of thermo mechanical erosion during ore emplacement the disseminated cygnet and black swan orebodies show a number of distinctive features cygnet contains a assemblage of clasts and inclusions which are interpreted as the result of rip up transport and redeposition of sulfides from a pre existing massive sulfide orebody of which black duck may be a remnant the black swan orebody by contrast does not show xenolithic features but is characterised by an association of sulfide blebs with segregation vesicles and by unusually coarse grained olivine the black swan orebody is interpreted as the result of transport of sulfide droplets within a lava charged with a suspended load of coarse olivine crystals

a sea level rise curve from guilford connecticut usa abstract high resolution stratigraphic studies based on sediment chemistry lithology macroflora and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at guilford connecticut show that coastal marshes are ephemeral environments marsh wide environmental variations were common and century long episodes of relative submergence alternated with emergence despite about 2 m of relative sea level rise rslr in connecticut over the last 1500 years the marshes have expanded both landwards and seawards and marsh accretion has been outpaced only marginally by rslr we used radiocarbon dating and the level of anthropogenic markers metal pollution as dated with 210 pb in the cores for age control for most of the last 1000 years the rate of rslr was between 1 3 and 1 8 mm yr but over the last 300 400 years it increased to 2 9 3 3 mm yr and has been faster than the accretion rate especially in the middle marsh the net submergence rate or submergence index ratio of the rate of rslr and marsh accretion rate averaged about 1 15 over the last 1000 years and increased to about 1 5 over the last 200 years the rate of rslr was very sluggish during the early part of the little ice age but we found a slightly higher rate during the little climate optimum this excursion is close to the noise level however the most significant observation is that rslr increased strongly around a d 1650 the onset of this acceleration falls in the middle to end of the little ice age and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases

native metals and intermetallic compounds in subduction related ultramafic rocks from the stanovoy mobile belt russian far east implications for redox heterogeneity in subduction zones abstract plutonic associations in orogenic belts are potent indicators of multi stage fractionation of primitive arc magmas and growth of island arc crust under evolving redox conditions in ancient subduction zones ildeus lucha ultramafic mafic complex ilc was emplaced at 232 233 ma within the mesozoic stanovoy convergent margin and subsequently underwent multi stage hydrothermal alteration and greenschist to amphibolite facies metamorphism 140 ma followed by adakite and k lamprophyre magmatism 114 117 ma dunite wehrlite pyroxenite and gabbro in the ilc are composed of olivine clinopyroxene orthopyroxene plagioclase and late magmatic amphibole mineral compositions in the ilc are typical of island arc plutonic complexes characterized by early crystallization of orthopyroxene plagioclase intercumulus and presence of magmatic amphibole ultramafic mafic rocks display high field strength hfs element depletions coupled with large ion lithophile lil element enrichments indicating formation via crystal fractionation of mafic primary magma derived from a subduction related mantle source some ultramafic rocks from the ilc contain native metals w pt au ag zn bi and intermetallic compounds cu au ag pt rh pd cu sn zn etc included in silicate minerals or observed as discrete phases in the finer grained silicate oxide sulfide matrix textural evidence and association with either primary magmatic or secondary metasomatic or metamorphic mineral phases suggest either magmatic high temperature or metasomatic low temperature origin of metals and metallic compounds the following models of their formation can be proposed on the basis of the presented data a crystallization w and possibly pt from metal rich arc magmas under unusually reduced conditions in subduction related lithosphere b formation from magmatic sulfides during pervasive serpentinization and release of abiogenic hydrocarbons and c precipitation from chlorine rich saline aqueous fluids associated with collision related metasomatism of the stanovoy island arc crust

comparison of archean dunites and komatiites associated with nickel mineralisation in western australia implications for dunite genesis the two important classes of archean fe ni cu sulphide deposits in western australia are those hosted by 1 coarse grained adcumulate dunites e g agnew mount keith and 2 komatiitic lavas e g kambalda close similarities in compositions of relict olivine pyroxene and chromite from dunitic and komatiitic host rocks and compositional and textural similarities between chilled margins of some dunites and some komatiites indicate origins from similar komatiitic liquids which contained 20 32 mgo as field relations suggest that the dunites are probably lateral stratigraphic equivalents of spinifextextured komatiites they are interpreted as the slowcooled end member of a continuum from spinifex textured komatiites former liquids through cumulate komatiites 40 90 olivine to adcumulate komatiitic dunite 90 olivine previous classification of these ni deposits as intrusive and volcanic related deposits now appears unwarranted and the terms komatiitic dunite hosted and komatiite hosted deposits are preferred

historical rates of salt marsh accretion on the outer bay of fundy we examine rates of salt marsh accumulation in three marshes of the outer bay of fundy at each marsh we selected a site in the high marsh with similar vegetation and thus similar elevation accretion rates were estimated by 137 cs 210 pb and pollen stratigraphy to estimate rates of change over periods of 30 100 and 170 years respectively these rates are compared with records from the two closest tide gauges saint john new brunswick and eastport maine to assess the balance of recent marsh accretion and sea level change averaged marsh accretion rates have ranged from 1 3 0 4 to 4 4 1 6 mm year 1 over the last two centuries recent rates are similar to the rate of sea level change recorded at eastport maine suggesting that they are in step with recent sea level change but very sensi tive to short term variation in relative sea level based on the pollen stratigraphy in the marsh sediments the marsh ac cretion rate was higher during the late 18th to early 19th century higher rates probably were due to local increases in relative sea level as a result of neotectonic activity and may have been enhanced by increased sediment deposition through ice rafting

shoreline erosion and decadal sediment accumulation in the tar pamlico estuary north carolina usa a source to sink analysis abstract estuaries contain vital habitats and it is important to understand how these areas respond to human activities and natural processes such as sea level rise and wave attack as estuarine shorelines erode or become modified with hard structures there is potential for significantly altering the availability of sediment and the filling of coastal systems this study used a source to sink approach and quantified rates of shoreline erosion in the tar pamlico sub estuary a tributary of the larger albemarle pamlico estuarine system apes the average shoreline change rate scr determined using an end point method was 0 5 0 9 m yr 1 for the tar pamlico incorporating bulk density estimates this contributes 0 6 105 tons of fine sediment to the system annually or after accounting for fluvial input about 40 of the total sediment supply to the sub estuary the role of the tar pamlico as a sink for these sediments was addressed using the radionuclide tracers 210pb and 137cs radionuclide activities and sediment accumulation rates identified several depositional regions in particular in the middle of the estuary linear sediment accumulation rates ranged from 0 10 0 02 to 0 38 0 02 g cm 2 yr 1 and total storage of fine sediment in the system was 1 6 105 t yr 1 it was not possible to confidently discern a change in the rate of shoreline erosion or seabed accumulation a preliminary budget for fine sediments grain size

geological impacts on coastal wetland landscapes some general effects of sediment autocompaction in the holocene of northwest europe a simulation model is described providing general insights into autocompaction effects in stratigraphic sequences formed on coastal mudflats and marshes over uneven basements lithological units and buried landscapes are progressively displaced and distorted the synthetic sequences resembling bedding geometries described from the northwest european holocene autocompaction also promotes local deposition rates that may greatly exceed the rates at which accommodation space is created transgressive silts are associated with especially large deposition rates because of the high compressibility of underlying peats the experimental relationships between apparent rates of sea level rise and bed thickness resemble empirical trends for the holocene the latter are however reinforced by an intrinsic lithology related effect not included in the model

recent volumetric changes in salt marsh soils salt marsh sediment volume decreases from organic decomposition compaction of solids and de watering and each of these processes may change with age variability in the vertical accretion rate within the upper 2 m was determined by assembling results from concurrent application of the 137 cs and 210 pb dating techniques used to estimate sediment age since 1963 1964 and 0 to ca 100 years before present ybp respectively the relationship between 210 pb and the 137 cs dated accretion rates sed 210 and sed 137 respectively was linear for 45 salt marsh and mangrove environments sed 210 averaged 75 of sed 137 suggesting that vertical accretion over the last 100 years is driven by soil organic matter accumulation as shown for the pre 137 cs dated horizon the ratio of sed 210 sed 137 declines with increasing mineral content a linear multiple regression equation that includes bulk density and sed 137 to predict sed 210 described 97 of the variance in sed 210 sediments from connecticut delaware and louisiana coastal environments dated with 14 c indicate a relatively constant sediment accretion rate of 0 13 cm year 1 for 1000 7000 ybp which occurs within 2 m of today s marsh surface and equals modern sea level rise rates soil subsidence is not shown to be distinctly different in these vastly different coastal settings the major reason why the sed 137 measurements indicate higher accretion rates than do the sed 210 measurements is because the former apply to younger sediments where the effects of root growth and decomposition are greater than in the latter the most intense rates of change in soil volume in organic rich salt marshes sediments is therefore neither in deep or old sediments 4 m 1000 years but within the first several hundreds of years after accumulation the average changes in organic and inorganic constituents downcore are nearly equal for 58 dated sediment cores from the northern gulf of mexico these parallel changes downcore are best described as resulting from compaction rather than from organic matter decomposition thus most of the volumetric changes in these salt marsh sediments occurs in the upper 2 m and declines quickly with depth extrapolation forwards or backwards using results from the 210 pb and the 137 cs dating technique appear to be warranted for the types of samples from the environments described here

partitioning the relative contributions of organic matter and mineral sediment to accretion rates in carbonate platform mangrove soils abstract in coming decades the global rate of sea level rise slr is projected to accelerate beyond rates observed over the past several millennia when mangrove wetlands have expanded in tropical sub tropical and temperate regions there is substantial uncertainty about how distinct mangrove ecotypes inhabiting a wide range of geomorphic settings will respond to slr acceleration including the thresholds at which they will submerge permanently in this study the relative contributions of soil organic and inorganic matter som and sim to 210 pb derived accretion rates were examined at 23 mangrove sites in southwest florida usa and the yucatan peninsula in mexico these sites are situated atop carbonate platforms where there is wide variation in the availability of sim generally marine marl to account for this variability research sites were classified by sim presence based on the som content estimated using loss on ignition organic sites som 70 intermediate sites som 40 70 and mineral sites som som accumulation rates were largely the same in the three soil classes during the past century p p overall accretion rates in the fl sites and a yucatan site on the caribbean sea are maintaining pace with regional rates of slr over the past 100 year and 50 year timespans whereas the sites in celestun lagoon mx located on the gulf of mexico exhibit an accretion deficit estimates of regional slr rates range from 4 6 to 12 2 mm yr 1 by the year 2060 based on accretion rates observed in the past century some of these sites may be able to keep pace with the lower slr estimate but there is no evidence that any of these sites can match the higher rate

contributions of mineral and organic components to tidal freshwater marsh accretion abstract vertical accretion in tidal marshes is necessary to prevent submergence due to rising sea levels mineral materials may be more important in driving vertical accretion in tidal freshwater marshes which are found near the heads of estuaries than has been reported for salt marshes accretion rates for tidal freshwater marshes in north america and europe n 76 data points were compiled from the literature simple and multiple linear regression analyses revealed that both organic and mineral accumulations played a role in driving tidal freshwater marsh vertical accretion rates although a unit mass of organic material contributed 4 times more to marsh volume than the same mass input of mineral material despite the higher mineral content of tidal freshwater marsh soils this ability of organic matter to effectively hold water and air in interstitial spaces suggests that organic matter is responsible for 62 of marsh accretion with the remaining 38 from mineral contributions the organic material that helps to build marsh elevation is likely a combination of in situ production and organic materials that are deposited in association with mineral sediment particles regional differences between tidal freshwater marshes in the importance of organic vs mineral contributions may reflect differences in sediment availability climate tidal range rates of sea level rise and local scale factors such as site elevation and distance to tidal creeks differences in the importance of organic and mineral accumulations between tidal freshwater and salt marshes are likely due to a combination of factors including sediment availability e g proximity to upland sources and estuarine turbidity maxima and the lability of freshwater vs salt marsh plant production

interpreting sea level rise and rates of vertical marsh accretion in a southern new england tidal salt marsh an investigation of marsh accretion rates on a new england type high marsh barn island wildlife management area stonington connecticut reveals that this system is sensitive to changes in sea level and storm activity and the peat can accurately record rates of relative submergence as determined by tide gauge records over intervals of 2 5 decades the results also suggest that the relationship between the accretion deficit and plant community structure is important when utilizing peat records to reconstruct historic sea level curves within stablespartina patenshigh marsh communities in systems where major vegetation changes are prominent over short periods of time 50 years interpretations of sea level rise should be limited to the system in which they are developed unless careful vertical controls can be maintained on the data and multiple datable horizons can be identified within the substrate the results of this investigation further show that in a stablespartina patenscommunity within this particular system there is little vertical translocation of137cs making this isotope a powerful tool for assessing rates of vertical marsh development since 1954

hydrothermal remobilisation around a deformed and remobilised komatiite hosted ni cu pge deposit sarah s find agnew wiluna greenstone belt yilgarn craton western australia the sarah s find nickel deposit located 4 5 km north of the mount keith nickel mine western australia was chosen as a case study to investigate the nature and three dimensional geometry of a geochemical halo created by the hydrothermal remobilisation of base metals and platinum group elements into the country rock surrounding a small massive ni sulphide orebody portable and laboratory based xrf analyses were carried out on samples from a shear zone localised along the basal komatiite dacite contact that hosts the orebody a geochemical halo was identified that extends along the shear zone up to 1780 m away from the massive sulphides parallel to a prominent stretching lineation elevated ni and pd are associated with high as co cu and s palladium and pt concentrations increase with proximity to massive sulphides from 6 to 1190 ppb pd these anomalous concentrations reflect the presence of sulfarsenides and sulphides either physically remobilised and forming veinlets close to the massive sulphides or hydrothermally transported and redeposited within the foliation in situ laser ablation icp ms indicates that pd and pt are hosted within these nickel sulfarsenides this ni co as pd geochemical halo observed around the sarah s find ore body is interpreted as forming syn deformation by the circulation of as rich hydrothermal fluids dissolving base metals pd and pt from the orebody and redepositing them along the sheared footwall contact similar ni co pd pt as geochemical haloes could potentially exist around any magmatic nickel sulphide mineral system that has undergone a phase of arsenic metasomatism and may be a generally applicable proximity indicator for nickel sulphides in hydrothermally altered terranes

stratigraphy pollen history and geochronology of tidal marshes in a gulf of maine estuarine system climatic and relative sea level impacts abstract sedimentologic and stratigraphic characteristics of five tidal marshes in great bay estuary new hampshire which is located on the western boundary of the gulf of maine were assessed from 20 vibracores detailed descriptions of surficial environments pollen analyses and radiocarbon dating modern marsh sequences in great bay estuary initiated with a time transgressive basal peat that formed at the upland brackish marsh boundary the oldest basal peat deposit sampled during this study was dated at 4560 cal yr b p based on an age of 4060 40 14 c yr b p the original tidal marshes that formed in great bay estuary apparently were unable to accrete at a high enough rate to allow seaward expansion resulting in a transgressive sequence of low marsh or mudflat sediments overlying the basal peat the transgressive tidal marsh sequence is capped by high marsh sediments that corresponded to a slowing of relative sea level rsl rise in the region and regressive seaward expansion of the tidal marshes however significant variations from these transgressive regressive sequences occur in the great bay tidal marshes as a result of more recent marsh expansion and tidal channel migrations detailed pollen analyses of a vibracore taken in a tidal marsh along squamscott river with a sedimentary record spanning the last 3900 cal yr b p exhibit five well documented marker horizons including 1 an increase of tsuga hemlock 2 the appearance of picea spruce 3 tsuga and fagus beech declines 4 an increase in ambrosia ragweed coupled with a sudden decrease in quercus oak and 5 the castanea chestnut decline using published ages for these pollen horizons and a calibrated 14 c age obtained during this study for a basal peat accretion rates for this marsh system over five time intervals were calculated 1 0 4 to 0 5 mm yr 1 from 3900 to 2850 cal yr b p 2 0 6 mm yr 1 from 2850 to 1960 cal yr b p 3 0 8 mm yr 1 from 1960 to 580 cal yr b p 4 0 7 to 0 8 mm yr 1 from 580 to 210 cal yr b p and 5 0 8 to 0 9 mm yr 1 over the last 210 years the long term accretion rate for the entire sequence based on the calibrated 14 c age of the basal peat was 0 6 to 0 7 mm yr 1 this result agrees with accretion rates determined from calibrated 14 c ages from two other tidal marsh systems in great bay estuary with accretion rates between 0 6 to 0 8 mm yr 1 higher accretion rates were obtained at a nearby tidal marsh with 1 2 mm yr 1 for just the marsh and 1 3 mm yr 1 for the marsh and underlying subtidal sediment the results of this study indicate that the sedimentology and stratigraphy of moderate size tidal marshes in rocky glaciated coasts are highly variable and are strongly influenced by complex interactions among rsl climatic variations and anthropogenic influences for instance the early development of many of the marshes in the great bay estuary area were likely driven by changes in rates of rsl resulting in transgressive onlap boundaries subsequently overlain by regressive intertidal marsh sequences however more recent changes in tidal marsh sediment composition deposited during a relatively slow steady rsl rise likely result from other forcings such as changes in minerogenic and orogenic sediment inputs due to anthropogenic effects tidal channel migrations major storms causing erosion of the marsh or climatic changes causing shifts in sediment delivery or vegetation

geochemistry of komatiites from forrestania southern cross province western australia evidence for crustal contamination the 2 9 ga old forrestania greenstone belt is intermediate in character between typical 3 0 ga and 2 7 ga belts in containing both al depleted and al undepleted komatiites the extensive nickel exploration database on the belt provides a unique opportunity to examine geochemical variations in the context of volcanological evolution within each of the six komatiitic units in the greenstone belt there is a transition from komatiites 18 28 wt mgo in the liquid to high and low magnesium komatiitic basalts 5 18 wt mgo with stratigraphic height and much of the chemical variance within the komatiitic suite can be explained in terms of the addition or fractionation of olivine there are however aspects of the incompatible element signatures which must be attributed to other factors the more primitive komatiites from the lower ultramafic units are al depleted al2o3 tio2 10 5 13 0 and depleted in both light and heavy ree lasmn 0 5 gdybn 1 5 komatiites from the uppermost ultramafic units are variably less depleted in al al2o3tio2 16 5 20 5 this is interpreted to reflect decreasing retention of garnet in the source region of the forrestania komatiites over time and possibly a decrease in the depth of melting within the al depleted suite there are also anomalous enrichments in sio2 feo tio2 and zr which correlate with regional variations in the composition of substrate metasedimentary rocks banded iron formation versus felsic tuff coupled with field evidence for trough structures at the base of lava channel sequences these chemical anomalies provide strong evidence for supracrustal thermal erosion by komatiite lavas the forrestania data indicate that 2 9 ga old komatiites were generated over a range of melting conditions spanning those typical of older and younger archaean sequences and that contamination by supracrustal thermal erosion can influence komatiite chemistry on a regional scale

geology mineralogy and geochemistry of magnetite associated au mineralization of the ultramafic basalt greenstone hosted crusader complex agnew gold camp eastern yilgarn craton western australia a late archean intrusion related au deposit abstract the crusader complex part of the agnew gold camp of the lawlers anticline of the yilgarn craton western australia is located close to or along the contact between the lawlers basalt and agnew ultramafics units au mineralization within the four orebodies that form the crusader complex is dominated by very pure au containing less than 1 wt ag with au variably associated with scheelite bi tellurides and minor chalcopyrite within a magnetite and titanite gangue assemblage hydrothermal alteration associated with this style of mineralization is characterized by increasing concentrations of mo be li sn and fe and depletions in na cu ba pb mn zn si and k relative to protolith concentrations these enrichments are more typical in orebodies associated with felsic intrusive related mineralizing systems rather than the more well known orogenic au deposits found elsewhere within the lawlers anticline e g at waroonga and within the greater yilgarn craton we propose that flexures of the contact between the lawlers basalt and agnew ultramafic units acted as conduits for au bearing felsic intrusive derived fluids and generated structural traps that enhanced fluid flow the mineralizing fluids that formed the crusader deposits were derived from the lawlers granitoid pluton that intruded into the study area enhanced fluid flow promoted interaction between hydrothermal fluids and the reactive mafic ultramafic rock sequence augmenting the amount of au that was precipitated during formation of the orebodies at crusader the magnetite dominated quartz and sulfide poor intrusion related mineralization at crusader contrasts sharply with other late archean intrusion related deposits of the yilgarn craton that are usually sulfide and or quartz rich this may in turn suggest that the crusader deposit represents a new class of under explored intrusion derived deposits possibly opening new mineral exploration opportunities for the agnew region and potentially the wider eastern goldfields superterrane enrichments in mo and sn and significant depletions in cu suggest that other parts of the lawlers batholith may also be prospective for base metal mineralization integration of stratigraphic interpretation with the identification of key structural fluid pathways and the presence of felsic intrusive bodies as presented in this study enables the delineation of the key elements that underlie mineralization at the crusader complex we propose that these key elements provide vital information for future gold exploration models that can be used within other archean terranes and within the eastern yilgarn craton in particular