a low temperature transfer of alh84001 from mars to earth the ejection of material from mars is thought to be caused by large impacts that would heat much of the ejecta to high temperatures images of the magnetic field of martian meteorite alh84001 reveal a spatially heterogeneous pattern of magnetization associated with fractures and rock fragments heating the meteorite to 40 c reduces the intensity of some magnetic features indicating that the interior of the rock has not been above this temperature since before its ejection from the surface of mars because this temperature cannot sterilize most bacteria or eukarya these data support the hypothesis that meteorites could transfer life between planets in the solar system

model for the evolution of the avalonian cadomian belt the inception and termination of the ca 670 550 ma avalonian cadomian orogenic cycle are interpreted in terms of the amalgamation and breakup of a late precambrian supercontinent synorogenic arc related volcano sedimentary and granitoid rocks are attributed to oblique southward directed subduction along the margin of the supercontinent after its amalgamation breakup of the supercontinent and inception of the iapetus cycle led to termination of subduction and its replacement by transform activity the resulting closure of late precambrian arc related basins and the development of early cambrian platform successions with acado baltic fauna accompanied the formation of iapetus but took place on the active margin of a preexisting ocean and do not record the evolution of its rifted european flank

the role of hydrogeological base level in the formation of sub horizontal caves horizons example from the dead sea basin israel this paper deals with the hydrogeological relationship between base levels of saline lakes and the formation of sub horizontal caves the mechanism presented here suggests that many horizontal cave levels in carbonate sequences are created adjacent to the saline lakes shorelines because of the converging of the groundwater flow above the fresh saline water interface the main factors that control enhanced carbonate dissolution and cave formation are high groundwater flow velocities in the shallow phreatic zone during a relative long steady state of the water table high groundwater flow velocities are evident close to the dead sea due to the convergent fast flows above the shallow interface adjacent to the shoreline the same could prevail in the case of previous paleo lakes that existed in the basin the synergetic combination of the above preconditions for enhanced cave formation seems to be responsible for the formation of elevation controlled alignment of paleo near shore cave levels in the central and southern dead sea portion of the study area these are found on the western fault escarpment and basin margin in different stratigraphic horizons of carbonate lithology many of the cave levels can be linked to late quaternary holocene lake levels obtained from dated lake sediments within the basin the most common cave s elevation was found to be around 200 m below sea level which was the elevation of the lisan lake during part of its history on the other hand the hula basin in the northern part of the dead sea basin was not occupied by saline water bodies since its formation as a base level and thus the above preconditions for enhanced cave formation did not prevail indeed this is evident by the lack of horizontal cave levels on its western carbonate margins unlike the situation in the south

influence of grain fabric and lamination on the anisotropy of hydraulic conductivity in unconsolidated dune sands in local scale groundwater flow problems like for instance in contaminated groundwater studies it becomes increasingly important for proper prediction of contaminant migration to incorporate small scale geological and associated parameter heterogeneity in groundwater flow models of the micro scale geological heterogeneities the effect of grain fabric and lamination in unconsolidated sediments on the vertical anisotropy of effective hydraulic conductivity has received relatively little attention this is mainly due to the low conductivity contrast between laminae in combination with the friable nature of unconsolidated sediment which makes it sensitive to disturbances during experimental procedures as an alternative digital image analysis of sediment thin sections was applied to separate and quantify both causes of anisotropy the effective value of vertical anisotropy ratio of unconsolidated eolian dune sand as determined experimentally on distributed orientated core plugs ranges between 1 10 and 1 50 this wide range is partly caused by artificial noise introduced by distributed sampling in a heterogeneous medium and assuming thereby that the sampled material is homogeneous by applying digital image analysis of thin sections high resolution logs of hydraulic conductivity were generated simple upscaling of these values to effective conductivity parallel and perpendicular to sedimentary laminae provided quantitative estimates of the vertical anisotropy caused by lamination anisotropy values range between 1 0 and 1 075 the anisotropy ratio due to grain fabric ranges in value between 1 05 and 1 45 assuming that both anisotropy due to grain fabric and lamination are orientated identically if this is not the case the effective anisotropy is the weighted mean of anisotropies of the constituent layer types this study shows that for eolian sands the anisotropy owing to grain fabric dominates the effective value of anisotropy if conductivity contrast between laminae increases the contribution of anisotropy caused by grain fabric to the effective value of anisotropy decreases

spatial patterns of hyporheic exchange and biogeochemical cycling around cross vane restoration structures implications for stream restoration design 1 natural channel design restoration projects in streams often include the construction of cross vanes which are stone dam like structures that span the active channel vertical hyporheic exchange flux hef and redox sensitive solutes were measured in the streambed around four cross vanes with different morphologies observed patterns of hef and redox conditions are not dominated by a single downstream directed hyporheic flow cell beneath cross vanes instead spatial patterns of moderate 0 4 m d 1 upwelling and downwelling are distributed in smaller cells around pool and riffle bed forms upstream and downstream of structures patterns of biogeochemical cycling are controlled by dissolved oxygen concentrations and resulting redox conditions and are also oriented around secondary bed forms strong downwelling into the hyporheic zone 0 5 3 5 m d 1 was observed immediately upstream of structures but was limited to an area 1 2 m from the cross vane these hyporheic flow paths likely rejoin the stream at the base of cross vanes after residence times too short to alter nitrate concentrations or accumulate reaction products total hyporheic exchange volumes are 0 4 of stream discharge in restored reaches of 45 55 m results show that shallow hyporheic flow and associated biogeochemical cycling near cross vanes is primarily controlled by secondary bed forms created or augmented by the cross vane rather than by the cross vane itself this study suggests that cross vane restoration structures benefit the stream ecosystem by creating heterogeneous patches of varying hef and redox conditions in the hyporheic zone rather than by processing large amounts of nutrients to alter in stream water chemistry

groundwater transit time distribution and mean from streambed sampling in an agricultural coastal plain watershed north carolina usa we measured groundwater apparent age and seepage rate v in a sandy streambed using point scale sampling and seepage blankets a novel seepage meter we found very similar mtt estimates from streambed point sampling in a 58 m reach 29 years and a 2 5 km reach 31 years the ttd for groundwater discharging to the stream was best fit by a gamma distribution model and was very similar for streambed point sampling in both reaches between adjacent point scale and seepage blanket samples water from the seepage blankets was generally younger largely because blanket samples contained a fraction of young stream water correcting blanket data for the stream water fraction brought estimates for most blanket samples closer to those for adjacent point samples the mtt estimates from corrected blanket data were in good agreement with those from sampling streambed points adjacent to the blankets collectively agreement among age dating tracers general accord between tracer data and piston flow model curves and large groundwater age gradients in the streambed suggested that the piston flow apparent ages were reasonable estimates of the groundwater transit times for most samples overall our results from two field campaigns suggest that groundwater collected in the streambed can provide reasonable estimates of apparent age of groundwater discharge and that mtt can be determined from different age dating tracers and by sampling with different groundwater collection devices coupled streambed point measurements of groundwater age and groundwater seepage rate represent a novel reproducible and effective approach to estimating aquifer ttd and mtt

model for the precambrian evolution of the avalon terrane in southern new brunswick canada the tectonostratigraphic record of the avalon terrane in southern new brunswick is interpreted as that of a wilson cycle that followed the grenvillian and preceded the opening of lapetus development of a late precambrian continental shelf is attributed to the cadomian ocean whose initial subduction at 800 ma led to platform collapse regional metamorphism and minor mafic to ultramafic plutonism in response to back arc extension and crustal separation oblique subduction of the resulting back arc basin at 600 630 ma produced calcalkaline plutonism and cogenetic volcanism that ended in dextral transtension and the emplacement of a bimodal dike complex initial rifting of lapetus which isolated this record from cratonic north america is recorded in eocambrian redbeds and bimodal volcanics and produced a cambro ordovician overlap sequence bearing acado baltic fauna

three dimensional model of modern channel bend deposits 1 we present a three dimensional model of heterogeneous modern channel bend deposits developed through purely structure imitating interpolation kriging of hydraulic properties this model augmented with ground penetrating radar data and directional variograms agrees with detailed observations in similar modern environments and leads to a process based interpretation of the presented hydraulic conductivity structure integration of all available information permitted delineation and characterization of the modern streambed as a distinct hydrostratigraphic unit without coring or outcrop studies our results imply that the modern streambed is commonly oversimplified in available analytical and numerical models of groundwater surface water interactions where it is assumed to be homogeneous and isotropic and characterized by a constant width and thickness this three dimensional approach that integrates concepts and principles developed in sedimentology hydrogeology geophysics and geostatistics has potential implications on model development of stream aquifer systems

petrology age and tectonic setting of the white rock formation meguma terrane nova scotia evidence for silurian continental rifting the white rock formation in the yarmouth area of the meguma terrane of southern nova scotia consists mainly of mafic tuffaceous rocks with less abundant mafic flows epiclastic and clastic sedimentary rocks and minor intermediate and felsic crystal tuff it is divided into seven map units that appear to young from west to east inconsistent with a previously assumed synclinal structure the white rock formation is flanked on both northwest and southeast by mainly the cambrian to lower ordovician halifax formation the western contact is interpreted to be a sheared disconformity whereas the eastern contact appears to be a major brittle fault and shear zone that juxtaposes different crustal levels the granitic brenton pluton forms a faulted lens within the eastern shear zone a felsic tuff from the upper part of the white rock formation yielded a u pb zircon age of 438 3 2 ma identical within error to published ages for the brenton pluton and felsic volcanic rocks near the base of the white rock formati

hafnium and neodymium isotopes in seawater and in ferromanganese crusts the element perspective abstract hafnium and nd isotopes are increasingly used as paleoceanographic proxies comparing the mantle crust array and the seawater array in plots of e hf vs e nd it has been observed that for a given e nd value the corresponding e hf value is higher for seawater than it is for terrestrial rocks while this difference had initially been explained by significant hydrothermal input of mantle hf into seawater the currently favoured explanation is incongruent weathering of continental rocks producing radiogenic riverine hf input we here address this topic from the perspective of the behaviour of these two elements in seawater and in ferromanganese fe mn crusts we distinguish between a truly dissolved and a dissolved hf and nd pool the latter being comprised of truly dissolved and colloid bound colloidal hf and nd while there exists a hydrothermal pathway for colloid bound dissolved mantle hf into the oceans there is in marked contrast to nd no important riverine pathway for colloidal or truly dissolved continental hf owing to their respective chemical speciation in seawater there exists truly dissolved nd in the ocean while the amount of truly dissolved hf is insignificant neodymium is in exchange equilibrium between local seawater and both the hydrous fe and mn oxides hydrogenetic fe mn crusts are composed of due to continuous ad and desorption there is continuous isotopic re equilibration and the isotopic composition of nd in a fe mn crust reflects that of truly dissolved nd in local ambient seawater in contrast hf is only associated with the hydrous fe oxides on which it forms surface precipitates that do not exchange with seawater due to this lack of isotopic re equilibration the isotopic composition of hf in a fe mn crust is the average of that of all the hf scavenged during the lifetime of the hydrous fe oxide particles since the hf bearing hydrous fe oxides in a fe mn crust do not form from local ambient seawater at the crust s growth site but are advected as colloids or fine particles their hf isotopic composition depends on the origin and migration pathway of these colloids hence while nd isotopes in fe mn crusts provide reliable information on truly dissolved nd in local ambient seawater hf isotopes rather indicate the origin and pathway of hydrous fe oxide colloids and might differ from truly dissolved hf in local ambient seawater this may explain the occasional decoupling of nd and hf isotopes in fe mn crusts and supports the notion of a significant hydrothermal mantle signal of hf in seawater

osmium isotope variations in the oceans recorded by fe mn crusts this study presents osmium os isotope data for recent growth surfaces of hydrogenetic ferromanganese fe mn crusts from the pacific atlantic and indian oceans in general these data indicate a relatively uniform os isotopic composition for modern seawater but suggest that north atlantic seawater is slightly more radiogenic than that of the pacific and indian oceans the systematic difference in the os isotopic composition between the major oceans probably reflects a greater input of old continental material with a high re os ratio in the north atlantic ocean consistent with the distribution of nd and pb isotopes this spatial variation in the os isotope composition in seawater is consistent with a residence time for os of between 2 and 60 kyr indian ocean samples show no evidence of a local source of radiogenic os which suggests that the present day riverine input from the himalaya tibet region is not a major source for os recently formed fe mn crusts from the tag hydrothermal field in the north atlantic yield an os isotopic composition close to that of modern seawater which indicates that in this area the input of unradiogenic os from the hydrothermal alteration of oceanic crust is small however some samples from the deep pacific 4 km possess a remarkably unradiogenic os isotope composition 187 os 186 os ratios as low as 4 3 the compositional control of os incorporation into the crusts and mixing relationships suggest that this unradiogenic composition is most likely due to the direct incorporation of micrometeoritic or abyssal peridotite particles rather than indicating the presence of an unradiogenic deep water mass moreover this unradiogenic signal appears to be temporary and local and has had little apparent effect on the overall evolution of seawater these results confirm that input of continental material through erosion is the dominant source of os in seawater but it is not clear whether global os variations are due to the input of mantle or meteoritic material or simply indicate that the continental source itself is not uniform 1999 elsevier science b v all rights reserved

mapping magnetic sources at the millimeter to micrometer scale in dunite and serpentinite by high resolution magnetic microscopy abstract rock samples can have wide range of magnetic properties depending on composition amount of ferromagnetic minerals grain sizes and microstructures here we used scanning magnetic microscopy a highly sensitive and high resolution magnetometric technique to map remanent magnetic fields over a planar surface of a rock sample the technique allows for the investigation of discrete magnetic mineral grains or magnetic textures and structures with submillimeter scale resolution here we present a case study of magnetic scans of pristine and serpentinized dunite thin sections from the reinfjord ultramafic complex in northern norway the magnetic mineralogy is characterized by electron microprobe scanning electron and optical microscopy and with rock magnetic methods in serpentinized samples the magnetic carrier is end member magnetite occurring as large discrete grains and small grains in micron scale veins by contrast the pristine dunite sample contains large cr spinel grains with very fine equant exsolutions ranging in composition from ferrichromite to end member magnetite forward and inverse modeling of the magnetic anomalies is used to determine the remanent magnetization directions and intensities of discrete magnetic sources observed in the scanning magnetic microscopy the fine scale magnetization of the rock sample is used to investigate the magnetic carriers and the effect of serpentinization on the magnetic properties of the dunite modeling shows that the dipolar magnetic anomalies that are mapped by scanning magnetic microscopy are caused by grains with heterogeneous magnetic sources the intensity of the magnetization and the amount of magnetic minerals are higher in the serpentinized sample than the pristine dunite sample consistent with the measured bulk magnetic properties furthermore the serpentinized samples show a larger variability in the direction of the magnetization and a stronger heterogeneity with respect to the pristine sample the ability to rigorously associate components of the bulk magnetic properties to individual mineral phases creates new possibilities for rock magnetic paleomagnetic and exploration applications

u pb geochronological constraints on the evolution of the aspy terrane cape breton island implications for relationships between aspy and bras d or terranes and ganderia in the canadian appalachians new u pb zircon ages from nine samples of igneous and sedimentary rocks in the aspy terrane cape breton island show that neoproterozoic rocks form a major part of the terrane and confirm that the terrane was affected by a major silurian devonian tectonothermal event a rhyolitic crystal tuff a leucotonalite pluton and a felsic sheet yield ages of 618 8 0 6 ma 619 7 0 9 ma and 573 5 2 7 ma respectively a metasedimentary unit contains zircon ranging in age from ca 546 to ca 1520 ma a diorite has an age of 428 6 1 9 ma and another diorite unit and a quartz porphyry also have probable late silurian ages a third diorite yields an age of 373 0 0 5 ma part of a widespread bimodal igneous event represented by both volcanic and plutonic rocks throughout the aspy region geochronological results and field relationships indicate that the neoproterozoic rocks are similar to those in the bras d9or terrane and form the basement to the ordovician silurian rocks in the aspy terrane and that the aspy terrane is probably correlative with rocks in the hermitage flexure of southern newfoundland where silurian metasedimentary and metavolcanic rocks lie unconformably on similar neoproterozoic rocks likely correlative rocks also occur in the kingston terrane of southern new brunswick the results of this study support the idea that the aspy kingston terrane is part of ganderia and that neoproterozoic rocks in the bras d9or terrane and correlative rocks in southwestern newfoundland and elsewhere represent exposed basement to ganderia in the canadian appalachians

silurian tectonics of western avalonia strain corrected subsidence history of the arisaig group nova scotia the arisaig group is a silurian succession of predominantly shallow marine clastic sediments overlying volcanics exposed in northern mainland nova scotia sediment accumulation provides a record of the subsidence of western avalonia during the interval when terranes were being accreted within the canadian appalachians to calculate the amount of subsidence one must correct the measured thicknesses for the effects of tectonic strain deformed fossils on bedding surfaces indicate strain ratios mainly between 1 2 and 1 6 an empirical porosity depth relationship is used to correct for compaction the subsidence curves are then adjusted to allow for variations in water depth and eustatic sea level the resulting curves show significant variations in subsidence rate regardless of which version of the silurian time scale is used an initial episode of rapid subsidence followed eruption of llandoverian volcanics slower subsidence took place in wenlockian and ludlovian time with deeper water sedimentation dur

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

influence of the central american seaway and drake passage on ocean circulation and neodymium isotopes a model study the sensitivity of the neodymium isotopic composition nd to tectonic rearrangements of seaways is investigated using an earth system model of intermediate complexity the shoaling and closure of the central american seaway cas is simulated as well as the opening and deepening of drake passage dp multiple series of equilibrium simulations with various intermediate depths are performed for both seaways providing insight into nd and circulation responses to progressive throughflow evolutions furthermore the sensitivity of these responses to the atlantic meridional overturning circulation amoc and the neodymium boundary source is examined modeled nd changes are compared to sediment core and ferromanganese fe mn crust data the model results indicate that the north atlantic nd response to the cas shoaling is highly dependent on the amoc state i e on the amoc strength before the shoaling to shallow depths preclosure three scenarios based on different amoc forcings are discussed of which the model data agreement favors a shallow preclosure miocene amoc 6 sv the dp opening causes a rather complex circulation response resulting in an initial south atlantic nd decrease preceding a larger increase this feature may be specific to our model setup which induces a vigorous cas throughflow that is strongly anticorrelated to the dp throughflow in freshwater experiments following the dp deepening odp site 1090 is mainly influenced by amoc and dp throughflow changes while odp site 689 is more strongly influenced by southern ocean meridional overturning circulation and cas throughflow changes the boundary source uncertainty is largest for shallow seaways and at shallow sites

denitrification in the recharge area and discharge area of a transient agricultural nitrate plume in a glacial outwash sand aquifer minnesota 1 recharge rates of nitrate no3 to groundwater beneath agricultural land commonly are greater than discharge rates of no3 in nearby streams but local controls of no3 distribution in the subsurface generally are poorly known groundwater dating cfc 3h was combined with chemical ions and gases and stable isotope n s and c analyses to resolve the effects of land use changes flow patterns and water aquifer reactions on the distributions of o2 no3 so4 and other constituents in a two dimensional vertical section leading from upland cultivated fields to a riparian wetland and stream in a glacial outwash sand aquifer near princeton minnesota within this section a plume of oxic no3 rich groundwater was present at shallow depths beneath the fields and part of the wetland but terminated before reaching the stream or the wetland surface groundwater dating and hydraulic measurements indicate travel times in the local flow system of 0 to 40 years with stratified recharge beneath the fields downward diversion of the shallow no3 bearing plume by semiconfining organic rich valley filling sediments under the wetland and upward discharge across the valley and stream bottom the concentrations and 15n values of no3 and n2 indicate that the no3 plume section was bounded in three directions by a curvilinear zone of active denitrification that limited its progress however when recalculated to remove the effects of denitrification the data also indicate changes in both the concentrations and 15n values of no3 that was recharged in the past isotope data and mass balance calculations indicate that fes2 and other ferrous fe phases were the major electron donors for denitrification in at least two settings 1 within the glacial fluvial aquifer sediments beneath the recharge and discharge areas and 2 along the bottom of the valley filling sediments in the discharge area combined results indicate that the shape and progress of the oxic no3 plume termination were controlled by a combination of 1 historical and spatial variations in land use practices 2 contrast in groundwater flow patterns between the agricultural recharge area and riparian wetland discharge area and 3 distribution and abundance of electron donors in both the sand aquifer and valley filling sediments the data are consistent with slow migration of redox zones through the aquifer in response to recharging oxic groundwater during holocene time then an order of magnitude increase in the flux of electron acceptors as a result of agricultural no3 contamination in the late twentieth century to which the redox zone configuration still may be adjusting the importance of denitrification for no3 movement through formerly glaciated terrains should depend on the source areas and depositional environments of the glacial sediments as well as geomorphology and recent stream valley sediment history

actively heated high resolution fiber optic distributed temperature sensing to quantify streambed flow dynamics in zones of strong groundwater upwelling zones of strong groundwater upwelling to streams enhance thermal stability and moderate thermal extremes which is particularly important to aquatic ecosystems in a warming climate passive thermal tracer methods used to quantify vertical upwelling rates rely on downward conduction of surface temperature signals however moderate to high groundwater flux rates 1 5 m d 1 restrict downward propagation of diurnal temperature signals and therefore the applicability of several passive thermal methods active streambed heating from within high resolution fiber optic temperature sensors a hrts has the potential to define multidimensional fluid flux patterns below the extinction depth of surface thermal signals allowing better quantification and separation of local and regional groundwater discharge to demonstrate this concept nine a hrts were emplaced vertically into the streambed in a grid with 0 40 m lateral spacing at a stream with strong upward vertical flux in mashpee massachusetts usa long term 8 9 h heating events were performed to confirm the dominance of vertical flow to the 0 6 m depth well below the extinction of ambient diurnal signals to quantify vertical flux short term heating events 28 min were performed at each a hrts and heat pulse decay over vertical profiles was numerically modeled in radial two dimension 2 d using sutra modeled flux values are similar to those obtained with seepage meters darcy methods and analytical modeling of shallow diurnal signals we also observed repeatable differential heating patterns along the length of vertically oriented sensors that may indicate sediment layering and hyporheic exchange superimposed on regional groundwater discharge

nitrogen transport and transformations in a coastal plain watershed influence of geomorphology on flow paths and residence times 1 nitrogen transport and groundwater surface water interactions were examined in a coastal plain watershed in the southeastern united states groundwater age dates calculated using chlorofluorocarbon and tritium concentrations along with concentrations of nitrogen species and other redox active constituents were used to evaluate the fate and transport of nitrate nitrate is stable only in recently recharged 10 years water found in the upper few meters of saturated thickness in the upland portion of a surficial aquifer groundwater with a residence time between 10 and 30 years typically has low nitrate and elevated excess n2 concentrations indications that denitrification has reduced nitrate concentrations groundwater older than 30 years also has low nitrate concentrations but contains little or no excess n2 suggesting that this water did not contain elevated concentrations of nitrate along its flow path nitrate transport to streams varies between first and third order streams hydrologic lithologic and chemical data suggest that the surficial aquifer is the dominant source of flow and nitrate to a first order stream iron reducing conditions occur in groundwater samples from the bed and banks of the first order stream suggesting that direct groundwater discharge is denitrified prior to entering the stream however nitrogen from the surficial aquifer is transported directly to the stream via a tile drain that bypasses these reduced zones in the alluvial valley of a third order stream the erosion of a confining layer creates a much thicker unconfined alluvial aquifer with larger zones of nitrate stability age dating and chemical information sio2 na k ratios suggest that water in the alluvial aquifer is derived from short flow paths through the riparian zone and or from adjacent streams during high discharge periods

the potential of marine ferromanganese nodules from eastern pacific as recorders of earth s magnetic field changes during the past 4 7 myr a geochronological study by magnetic scanning and authigenic 10be 9be dating

paleoceanographic conditions on the sao paulo ridge sw atlantic ocean for the past 30 million years inferred from os and pb isotopes of a hydrogenous ferromanganese crust abstract hydrogenous ferromanganese fe mn crusts can provide records of long term environmental changes during the cenozoic to understand the paleoceanographic conditions in the southwestern atlantic ocean we investigated depth profiles of major and trace element concentrations as well as os and pb isotopic compositions in a fe mn crust collected from the southern flank of the sao paulo ridge in the southwestern atlantic major and trace element data plotted on ternary mn fe 10 ni co cu and rare earth element plus yttrium rey discrimination diagrams indicate that the analyzed sample is a typical hydrogenous fe mn crust the obtained 187 os 188 os data were matched to the cenozoic seawater os isotope evolution curve reconstructed from pelagic sediments the result suggests that the fe mn crust has accreted over 30 myr with growth rates of 0 5 3 mm myr although the sample likely grew in two directions during the early stage of its growth we found no evidence of growth hiatus in the sample which may contrast with the growth histories of many pacific fe mn crusts hence the conditions favorable for the accretion of hydrogenous fe mn crusts were likely to have developed on the sao paulo ridge over the past 30 myr the pb isotopic compositions show very limited ranges e g 206 pb 204 pb 18 80 18 85 and are similar to those of pre anthropogenic seawater in the southern ocean as the sao paulo ridge is located near the vema channel which is presently a major path of antarctic bottom water we suggest that a strong northward bottom current has continuously swept detrital and biogenic sediments from the ridge and played a vital role in the fe mn crust formation since 30 ma

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

practical limitations on the use of diurnal temperature signals to quantify groundwater upwelling groundwater upwelling to streams creates unique habitat by influencing stream water quality and temperature upwelling zones also serve as vectors for contamination when groundwater is degraded temperature time series data acquired along vertical profiles in the streambed have been applied to simple analytical models to determine rates of vertical fluid flux these models are based on the downward propagation characteristics amplitude attenuation and phase lag of the surface diurnal signal despite the popularity of these models there are few published characterizations of moderate to strong upwelling we attribute this limitation to the thermodynamics of upwelling under which the downward conductive signal transport from the streambed interface occurs opposite the upward advective fluid flux governing equations describing the advection diffusion of heat within the streambed predict that under upwelling conditions signal amplitude attenuation will increase but counterintuitively phase lag will decrease therefore the extinction measurable depth of the diurnal signal is very shallow but phase lag is also short yielding low signal to noise ratio and poor model sensitivity conversely amplitude attenuation over similar sensor spacing is strong yielding greater potential model sensitivity here we present streambed thermal time series over a range of moderate to strong upwelling sites in the quashnet river cape cod massachusetts the predicted inverse relationship between phase lag and rate of upwelling was observed in the field data over a range of conditions but the observed phase lags were consistently shorter than predicted analytical solutions for fluid flux based on signal amplitude attenuation return results consistent with numerical models and physical seepage meters but the phase lag analytical model results are generally unreasonable through numerical modeling we explore reasons why phase lag may have been over predicted by the analytical models and develop guiding relations of diurnal temperature signal extinction depth based on stream diurnal signal amplitude upwelling magnitude and streambed thermal properties that will be useful in designing future experiments

a cenozoic seawater redox record derived from 238u 235u in ferromanganese crusts oceanic oxygen levels are projected to drop in certain areas due to warming climate but the net effect to the overall ocean redox state is difficult to predict here we measured the stable uranium isotope composition 238u 235u in globally representative hydrogenous ferromanganese crusts in order to reconstruct the redox evolution of the global ocean throughout the cenozoic samples averaging 3 myr intervals have analytically indistinguishable 238u 235u throughout the cenozoic combined with a u isotope mass balance model we suggest that the overall ocean redox state has remained remarkably stable on million year time scales throughout the cenozoic despite large surface temperature fluctuations during this time this suggests that stabilizing feedbacks for example nutrient limitation in low oxygen zones may have prevented dramatic large scale shifts in oxygen levels in the ocean however the fe mn crust record will be unlikely to reflect rapid perturbations in ocean redox state to investigate these events sediment archives with faster accumulation rates and redox proxies with faster response time must be explored

formation age of the dual structure and environmental change recorded in hydrogenetic ferromanganese crusts from northwest and central pacific seamounts abstract thick hydrogenetic ferromanganese fe mn crusts from the northwest and central pacific seamounts often show a distinct dual structure composed of a typical hydrogenetic porous friable upper part of fe mn oxides layer 1 and the underlying dense hard phosphatized growth generation of fe mn oxides layer 2 in this study layer 2 always appears above the substrate rock and composes the lower part of the crust it is never found as the upper crust layer in contact with seawater the chemical composition of layer 2 clearly differs from the younger layer 1 hydrogenetic fe mn oxides and is depleted in fe al ti and co and enriched in ni cu and zn relative to layer 1 the be isotope age models of the crusts were refined with paleomagnetic and paleontological information and applied to selected crust samples the age model indicates fairly continuous growth from the substrate to the surface and fairly constant growth rates during the past 17 ma the growth rate from the miocene to the present has varied by a factor of two about 2 4 mm myr in layer 1 while layer 2 has similar but more variable growth rates than layer 1 the calculated age for the base of layer 1 and possibly the age of termination of phosphatization is never younger than the late miocene the age seems to vary with water depth shallower water crusts between 991 and 1575 m showing a younger age of about 10 ma whereas the deeper water 2262 m crusts have extrapolated ages for the base of layer 1 of be 17 1 2 5 ma this trend indicates that phosphatization took place in a less oxidizing environment during growth of layer 2 followed by a weakened oxygen minimum zone or intensified aabw during growth of layer 1

the kingston terrane southern new brunswick canada evidence for an early silurian volcanic arc the fault bounded kingston terrane of southern new brunswick consists of felsic and less abundant mafic volcaniclastic rocks and flows and minor interbedded sedimentary rocks of the kingston group intruded by mainly granitic plutons and abundant younger mafic sheets the granitic plutons form about half of the terrane and are characterized by fine grain size and typically granophyric and porphyritic textures indicative of high level emplacement mafic sheets were emplaced in the granitic plutons and parallel to primary layering in the kingston group which is typically steeply dipping and trends northeast to north northeast hence in contrast to some earlier interpretations the kingston terrane does not consist of a bimodal dike complex the kingston group granitic rocks and mafic sheets contain mineral assemblages consistent with metamorphism to upper greenschist lower amphibolite facies new u pb zircon ages of 442 6 ma from a dacitic tuff unit and 437 10 ma from a granitic pluton corroborate previous u pb dates that had suggested that the volcanic and granitic rocks in the kingston terrane are early silurian rather than precambrian as had been earlier assumed the felsic volcanic and granitic rocks are interpreted to be comagmatic on the basis of their field relationships and similar u pb ages and chemical character compositions of both the felsic rocks and less abundant mafic and intermediate and mafic rocks are consistent with calc alkalic affinity and emplacement in a continental margin volcanic arc herein termed the kingston arc a u pb date of 435 5 ma was also obtained from compositionally similar granite that forms a dike in an adjacent fault bounded amphibolite facies metasedimentary unit the similarity in age and composition of the granite dike suggests a link between these metasedimentary rocks and the kingston terrane possibly as part of an accretionary complex if so its location southeast of the kingston terrane indicates that subduction was to the present northwest mafic sheets in the kingston terrane are tholeiitic but have some arc like characteristics consistent with their origin in a former arc setting but the sheets were likely emplaced in a subsequent extensional setting the compositional similarity of the mafic sheets to late silurian mafic volcanic rocks and plutons of the coastal maine magmatic province suggests that they may be related a possible model for evolution of the kingston terrane is proposed wherein the kingston group and related granite formed in an early silurian arc on the margin of ganderia as represented by the new river terrane of late precambrian and early paleozoic age northwestward subduction culminated in collision between the kingston arc and a continental block now represented by the brookville terrane to the southeast subsequent transpressive mo tions in the late silurian may have been responsible for the crustal scale extensional environment in which the coastal maine magmatic province was formed including emplacement of mafic dikes into the deformed former kingston arc transpressive motions related to juxtaposition of the avalon and meguma terranes with the previously accreted more inboard terranes continued through the devonian and into the carboniferous

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

chemical and isotopic signature of old groundwater and magmatic solutes in a costa rican rain forest evidence from carbon helium and chlorine 1 c he and cl concentrations and isotopes in groundwater and surface water in a lowland costa rican rain forest are consistent with the mixing of two distinct groundwaters 1 high solute bedrock groundwater representing interbasin groundwater flow igf into the rain forest and 2 low solute local groundwater recharged in the lowlands in bedrock groundwater high 13c 4 89 low 14c 7 98 pm high r ra for he 6 88 and low 36cl cl 17 10 15 suggest that elevated tracer concentrations are derived from magmatic outgassing and or weathering of volcanic rock beneath nearby volcan barva in local groundwater the magmatic signature is absent and data suggest atmospheric sources for he and cl and a biogenic soil gas co2 source for dissolved inorganic carbon dating of 14c suggests that the age of bedrock groundwater is 2400 4000 years most likely at the lower end of the range local groundwater has 14c 100 pm indicating the presence of bomb carbon and thus ages less than 55 years overall data are consistent with a conceptual hydrologic model originally proposed on the basis of water budget and major ion data 1 large variation in solute concentrations can be explained by mixing of the two distinct groundwaters 2 bedrock groundwater is much older than local groundwater 3 elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and or rock and 4 local groundwater has not interacted with volcanic rock tracers with different capabilities converge on the same hydrologic interpretation also transport of magmatic co2 into the lowland rain forest via igf seems to be significant relative to other large ecosystem level carbon fluxes

heat as a groundwater tracer in shallow and deep heterogeneous media analytical solution spreadsheet tool and field applications groundwater flow advects heat and thus the deviation of subsurface temperatures from an expected conduction dominated regime can be analysed to estimate vertical water fluxes a number of analytical approaches have been proposed for using heat as a groundwater tracer and these have typically assumed a homogeneous medium however heterogeneous thermal properties are ubiquitous in subsurface environments both at the scale of geologic strata and at finer scales in streambeds herein we apply the analytical solution of shan and bodvarsson 2004 developed for estimating vertical water fluxes in layered systems in 2 new environments distinct from previous vadose zone applications the utility of the solution for studying groundwater surface water exchange is demonstrated using temperature data collected from an upwelling streambed with sediment layers and a simple sensitivity analysis using these data indicates the solution is relatively robust also a deeper temperature profile recorded in a borehole in south australia is analysed to estimate deeper water fluxes the analytical solution is able to match observed thermal gradients including the change in slope at sediment interfaces results indicate that not accounting for layering can yield errors in the magnitude and even direction of the inferred darcy fluxes a simple automated spreadsheet tool flux lm is presented to allow users to input temperature and layer data and solve the inverse problem to estimate groundwater flux rates from shallow e g 1 m or deep e g up to 100 m profiles the solution is not transient and thus it should be cautiously applied where diel signals propagate or in deeper zones where multi decadal surface signals have disturbed subsurface thermal regimes

horizontal hydraulic conductivity of shallow streambed sediments and comparison with the grain size analysis results streambed horizontal hydraulic conductivity kh has a substantial role in controlling exchanges between stream water and groundwater we propose a new approach for determining kh of the shallow streambed sediments undisturbed sediment samples were collected using tubes that were horizontally driven into streambeds the sediment columns were analysed using a permeameter test pt on site this new test approach minimizes uncertainties due to vertical flow in the vicinity of test tube and stream stage fluctuations in the computation of the kh values ninety eight pts using the new approach were conducted at eight sites in four tributaries of the platte river east central nebraska usa the kh values were compared with the nondirectional hydraulic conductivity values kg determined from 12 empirical grain size analysis methods the grain size analysis methods used the same sediment samples as kh tests only two methods the terzaghi and shepherd methods yielded kg values close to the kh values although the sauerbrei method produced a value relatively closer to kh than other nine grain size analysis methods the values from this method were not as reliable as the methods of terzaghi and shepherd due to the inconsistent fluctuation of the average estimates at each of the test sites the zunker zamarin hazen beyer and kozeny methods overestimated kh while the slichter us bureau of reclamation usbr harleman and alyamani and sen methods underestimated kh any of these specific grain size methods might yield good estimates of streambed kh at some sites but give poor estimates at other sites indicating that the relationship between kg and kh is significantly site dependent in our study copyright 2011 john wiley sons ltd

the position and nature of the gander avalon boundary southern new brunswick based on geochemical and isotopic data from granitoid rocks in southern new brunswick the gander avalon boundary is obscured by boundary parallel faults and various cover sequences siluro devonian granites which intrude unequivocal gander or avalon rocks display exclusively negative 1 9 1 0 and positive 1 9 0 7 end t signatures respectively such contrasting nd isotopic signatures combined with other geochemical differences between plutons are potentially valuable tools for terrane analysis nine small devonian plutons intruding the boundary zone fall into contrasting geochemical groups with la lu n 4 the former are topaz bearing granites while the latter are volcanic arc type granites except for one pluton with an end t signature of 2 0 end t values range from 0 4 to 0 7 spanning the gap between type avalon and type gander plutons these results suggest the plutons sampled either i stratigraphically overlapping or tectonically interleaved gander and avalon basement rocks or ii a distinct basement source beneath the b

tectonics of the acadian orogeny in new england and adjacent canada paleogeographic analysis of post taconian rocks in new england and adjacent parts of canada has revealed the existence of two volcanic arcs which shut off at the time of the acadian orogeny one was built on arc basement previously accreted to north america during the taconic orogeny the other on precambrian continental basement of avalonia in the intervening merrimack fredericton trough metamorphosed and poly deformed turbidites and black shales record deep water conditions in silurian following mckerrow and ziegler 1971 this tract is interpreted as the site of an ocean which closed in siluro devonian by simultaneous subduction beneath both continental margins in the molucca sea in indonesia a comparable arc arc collision is in an early stage of development moore et al 1982 suggested that an accretionary prism built against one arc is overthrusting its counterpart which developed on the other side of the ocean an identical geometry with an avalonian accretionary prism overriding the conve

ultrafine scale magnetostratigraphy of marine ferromanganese crust hydrogenetic ferromanganese crusts are iron manganese oxide chemical precipitates on the seafloor that grow over periods of tens of millions of years their secular records of chemical mineralogical and textural variations are archives of deep sea environmental changes however environmental reconstruction requires reliable high resolution age dating earlier chronological methods using radiochemical and stable isotopes provided age models for ferromanganese crusts but have limitations on the millimeter scale for example the reliability of 10 be 9 be chronometry commonly considered the most reliable technique depends on the assumption that the production and preservation of 10 be are constant and requires accurate knowledge of the 10 be half life to overcome these limitations we applied an alternative chronometric technique magnetostratigraphy to a 50 mm thick hydrogenetic ferromanganese crust d96 m4 from the northwest pacific submillimeter scale magnetic stripes originating from approximately oppositely magnetized regions oriented parallel to bedding were clearly recognized on thin sections of the crust using a high resolution magnetometry technique called scanning squid superconducting quantum interference device microscopy by correlating the boundaries of the magnetic stripes with known geomagnetic reversals we determined an average growth rate of 5 1 0 2 mm m y which is within 16 of that deduced from the 10 be 9 be method 6 0 0 2 mm m y this is the finest scale magnetostratigraphic study of a geologic sample to date ultrafine scale magnetostratigraphy using squid microscopy is a powerful new chronological tool for estimating ages and growth rates for hydrogenetic ferromanganese crusts it provides chronological constraints with the accuracy promised by the astronomically calibrated magnetostratigraphic time scale 1 40 k y

new age for ferromanganese crust 109d c and implications for isotopic records of lead neodymium hafnium and thallium in the pliocene indian ocean 1 this study presents a high resolution record of osmium and thallium isotopes in a ferro manganese fe mn crust from the indian ocean antipode 109d c these results when combined with additional new os isotope data from odp hole 756b in the southeast indian ocean define a new best estimate for the age at the base of this crust of 6 5 ma which is significantly different from a previous estimate of 15 ma based on co flux modeling the tl isotope record obtained for the indian ocean resembles that for the pacific ocean with a small but well defined increase occurring over the last 5 myr this contrasts with two records from the atlantic ocean which do not have resolvable variations ocean basin scale tl isotope variation may be inconsistent with the inferred modern marine residence time for tl of 20 kyr but could be explained by an increase in ocean crust production rates in the pacific and indian oceans since 10 ma the improved age model for 109d c reveals that the hf isotope composition of indian ocean bottom waters has remained homogenous over the last 6 myr thus this isotope system does not bear any evidence that the influence of north atlantic deep water in the formation of indian ocean bottom waters has changed during that time however because of the lack of knowledge about hf isotopes as a tracer of ocean circulation we cannot conclude that export of nadw decreased over the last 6 myr

mechanism and rate of denitrification in an agricultural watershed electron and mass balance along groundwater flow paths the rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards both the extent and rate of denitrification varied depending on the groundwater flow path while little or no denitrification occurred in much of the upland portions of the aquifer a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer in contrast a sharp shallow redox gradient is observed adjacent to a third order stream as aerobic groundwater enters reduced sediments an essentially complete loss of nitrate concurrent with increases in excess n2 provide evidence that denitrification occurs as groundwater enters this zone electron and mass balance calculations suggest that iron sulfide e g pyrite oxidation is the primary source of electrons for denitrification denitrification rate estimates were based on mass balance calculations using nitrate and excess n2 coupled with groundwater travel times travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon based age dates denitrification rates were found to vary considerably between the two areas where denitrification occurs denitrification rates in the deep upland portions of the aquifer were found to range from 0 01 to 0 14 mm of n per year rates at the redoxcline along the shallow flow path range from 1 0 to 2 7 mm of n per year potential denitrification rates in groundwater adjacent to the stream may be much faster with rates up to 140 mm per year based on an in situ experiment conducted in this zone

thermal skin effect of pipes in streambeds and its implications on groundwater flux estimation using diurnal temperature signals 1 heat tracing is widely used for quantifying groundwater flux across the river streambed interface this study investigates the potential for a thermal skin effect tse whereby temperature measured inside a pipe buried in sediment is lagged and damped compared to temperature outside of the pipe violating the assumption that monitored temperatures are representative of the saturated sediment numerical simulations show that 1 3 inch diameter pipes lead to an additional lag of tens of minutes to almost 1 5 h when diurnal temperature signals originating from the river and propagating into the sediment are monitored the lag increases with pipe diameter and diminishes when steel is used instead of pvc the temperatures taken from inside the pipe lead to substantial errors when they are used as targets for fitting with a forward heat transport model the errors are large when the fit is made to the timing of the temperature signals but is small when the fit is made to the amplitude of the signal while ignoring the timing this is because the tse leads to little damping of the amplitude of the temperature fluctuations and mostly exhibits as extra lag therefore methods that take advantage of the amplitude of the signal such as time series analysis using amplitude ratios are not sensitive to the tse time series data can be corrected by subtracting the response time of the water filled pipe or by adding the response time as a phase shift to analytical models

heat tracing of heterogeneous hyporheic exchange adjacent to in stream geomorphic features there are many field techniques used to quantify rates of hyporheic exchange which can vary in magnitude and direction spatially over distances of only a few metres both within and between morphological features we used in stream mini piezometers and heat transport modelling of stream and streambed temperatures to quantify the rates and directions of water flux across the streambed interface upstream and downstream of three types of in stream geomorphic features a permanent dam a beaver dam remnant and a stream meander we derived hyporheic flux estimates at three different depths at six different sites for a month and then paired those flux rates with measurements of gradient to derive hydraulic conductivity k of the streambed sediments heat transport modelling provided consistent daily flux estimates that were in agreement directionally with hydraulic gradient measurements and also identified vertical heterogeneities in hydraulic conductivity that led to variable hyporheic exchange streambed k varied over an order of magnitude 1 9 10 6 to 5 7 10 5 m s average rates of hyporheic flux ranged from static q 0 02 m day to 0 42 m day heat transport modelling results suggest three kinds of flow around the dams and the meander copyright 2010 john wiley sons ltd

deducing the distribution of terminal electron accepting processes in hydrologically diverse groundwater systems the distribution of microbially mediated terminal electron accepting processes teaps was investigated in four hydrologically diverse groundwater systems by considering patterns of electron acceptor nitrate sulfate consumption intermediate product hydrogen h sub 2 concentrations and final product ferrous ion sulfide and methane production in each hydrologic system a determination of predominant teaps could be arrived at but the level of confidence appropriate for each determination differed in a portion of the lacustrine aquifer of the san joaquin valley for example all three indicators sulfate concentrations decreasing h sub 2 concentrations in the 1 2 nmol range and sulfide concentrations increasing along flow paths identified sulfate reduction as the predominant teap leading to a high degree of confidence in the determination in portions of the floridan aquifer and a petroleum hydrocarbon contaminated aquifer sulfate reduction and methanogenesis are indicated by production of sulfide and methane and hydrogen concentrations in the 1 4 nmol and 5 14 nmol range respectively however because electron acceptor consumption could not be documented in these systems less confidence is warranted in the teap determination in the black creek aquifer no pattern of sulfate consumption and sulfide production were observed but h sub 2 concentrations indicated sulfate reduction as the predominant teap in this case more where just a single line of evidence is available the least confidence in the teap diagnosis is justified because this methodology is based on measurable water chemistry parameters and upon the physiology of microbial electron transfer processes it provides a better description of predominant redox processes in groundwater systems than more traditional eh based methods less

scanning squid microscopy of a ferromanganese crust from the northwestern pacific submillimeter scale magnetostratigraphy as a new tool for age determination and mapping of environmental magnetic parameters ferromanganese crusts record long term deep sea environmental changes thus providing their reliable high resolution age models is important we applied a magnetostratigraphic technique to estimate the growth rate of a ferromanganese crust using scanning squid superconducting quantum interference device microscope ssm ssm is designed to map the magnetic field across thins sections with sub millimeter resolution the crust sample was taken from the takuyo daigo seamount northwestern pacific and recorded a limited supply of dust and sediment from continents after drift correction and removal of spike noises the magnetic field values were stacked within the areas of high signal to noise ratios by correlating the obtained profiles with a standard geomagnetic polarity timescale we obtained an average growth rate of 3 37 0 06 mm m y which is consistent with that obtained by 10be 9be geochronology 2 93 0 15 mm m y s ratio mapping shows low values after 3 ma associated with voids between columnar structures

40 ar 39 ar amphibole ages from the kingston complex new brunswick evidence for silurian devonian tectonothermal activity and implications for the accretion of the avalon composite terrane the kingston complex of southern new brunswick canada is a regional ne trending belt of mafic and felsic dikes bordered by dextral ductile shear zones the complex separates two contrasting late precambrian early paleozoic tectonostratigraphic assemblages near the nw margin of the avalon composite terrane rhyolitic dikes within the complex record an early silurian crystallization age dike orientations suggest that emplacement of the complex accompanied sinistral movement interpreted to reflect accretion of the avalon composite terrane to cratonic north america mafic dikes within the complex display greenschist to epidote amphibolite facies metamorphic assemblages that developed during dextral transpression amphibole concentrates from seven metamorphosed mafic dikes record late silurian to early devonian ca 416 390 ma 36 ar 40 ar vs 39 ar 40 ar isotope correlation ages interpreted to date closely the dextral transpressive deformation together with other recent age data the 40 a

a tectonomagmatic model for the genesis and emplacement of caledonian calc alkaline lamprophyres petrogenetically related caledonian calc alkaline lamprophyric and shoshonitic dykes in eastern ireland appear coeval with sinistral transtension these dykes are exposed in a 10 km wide zone trending sw from clogher head that strikes anticlockwise of the surface trace of the iapetus suture lamprophyre dykes intruded sinistral riedel shears with a mean strike trend at 040 riedel shears that host lamprophyre dykes strike anticlockwise of primary sinistral shears by 35 consistent with sinistral transtension primary shears strike 070 parallel to the mean strike trend of shoshonitic dykes sinistral primary shears may have controlled the emplacement of caledonian shoshonitic intrusive rocks using lamprophyres from clogher head as examples a new model is proposed for lamprophyre genesis and emplacement related to simple shear in this model transient decompression of metasomatized mantle during simple shear triggers release of volatile rich potassic magma which ascends to crustal levels along steep strike slip faults an association between lamprophyre magmatism and deep faulting suggests that relatively deep 60km seismicity may precede magma ascent this model can account for several paradoxes of caledonian magmatism

tectonic setting of avalonian volcanic and plutonic rocks in the caledonian highlands southern new brunswick canada the caledonian highlands of southern new brunswick consist of late proterozoic to cambrian rocks generally considered typical of the avalon terrane of the northern appalachian orogen mainly tuffaceous volcanic and sedimentary rocks of the broad river group and cogenetic dioritic to granitic plutons with ages ca 620 ma form most of the eastern caledonian highlands they have petrological features indicative of origin in a continental margin subduction zone significantly younger ca 560 550 ma dacitic to rhyolitic lapilli tuffs and flows laminated tuffaceous siltstone basaltic and rhyolitic flows and clastic sedimentary rocks of the coldbrook group form most of the western highlands and occur locally throughout the highlands the mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group this voluminous subaerial magmatism may have formed during postorogenic ex

factors affecting the movement and persistence of nitrate and pesticides in the surficial and upper floridan aquifers in two agricultural areas in the southeastern united states differences in the degree of confinement redox conditions and dissolved organic carbon doc are the main factors that control the persistence of nitrate and pesticides in the upper floridan aquifer ufa and overlying surficial aquifer beneath two agricultural areas in the southeastern us groundwater samples were collected multiple times from 66 wells during 1993 2007 in a study area in southwestern georgia acfb and from 48 wells in 1997 98 and 2007 08 in a study area in south carolina sant as part of the us geological survey national water quality assessment program in the acfb study area where karst features are prevalent elevated nitrate n concentrations in the oxic unconfined ufa median 2 5 mg l were significantly p 0 03 higher than those in the overlying oxic surficial aquifer median 1 5 mg l concentrations of atrazine and deethylatrazine dea the most frequently detected pesticide and degradate were higher in more recent groundwater samples from the acfb study area than in samples collected prior to 2000 conversely in the sant study area nitrate n concentrations in the ufa were mostly 0 06 mg l resulting from anoxic conditions and elevated doc concentrations that favored denitrification although most parts of the partially confined ufa in the sant study area were anoxic or had mixed redox conditions water from 28 of the sampled wells was oxic and had low doc concentrations based on the groundwater age information nitrate concentrations reflect historic fertilizer n usage in both the study areas but with a lag time of about 15 20 years simulated responses to future management scenarios of fertilizer n inputs indicated that elevated nitrate n concentrations would likely persist in oxic parts of the surficial aquifer and ufa for decades even with substantial decreases in fertilizer n inputs over the next 40 years

assessing the importance of seepage and springs to nitrate flux in a stream network in the wisconsin sand plains evaluating the flow paths that contribute to solute flux in stream networks can lead to greater understanding of the linkages between biogeochemistry and hydrology we compared the contributions of groundwater in spring brooks and in seepage through the streambed to nitrate flux in the emmons creek network in the wisconsin sand plains we predicted that spring brooks would contribute disproportionately to nitrate flux due to the presumed higher advection rates in springs and less opportunity for nitrate removal relative to seeps nitrate flux was measured in 15 spring brooks that entered emmons creek nitrate flux from seepage was measured at the locations of 30 piezometers based on darcy s law and by a reach scale injection of rhodamine water tracing rwt when seepage discharge was estimated from the rwt release groundwater inputs from seepage and springs accounted for the discharge gain in the emmons creek channel springs brooks and seepage based on the rwt release contributed 37 and 63 respectively to nitrate flux inputs in the study reach contrary to our prediction seeps contributed disproportionately to nitrate flux relative to their discharge relatively high rates of seepage discharge and higher than anticipated nitrate concentrations in the shallow pore water at seepage locations contributed to the unanticipated result

geochemistry of siluro devonian tobique volcanic belt in northern and central new brunswick canada tectonic implications siluro devonian volcanic rocks of the northwestern mainland appalachians are found mainly in the tobique belt of new brunswick where they consist predominantly of bimodal mafic felsic suites erupted in a continental rift environment the axis of the tobique rift trends north northeast south southwest obliquely to the regional northeast southwest trend of the appalachians these geometric relationships are interpreted as being the result of rifting in a sinistral shear regime produced during emplacement of the avalon terrene the basaltic rocks are continental tholeiites and transitional basalts derived from a heterogeneous upper mantle source that was enriched in incompatible elements relative to the primordial mantle the mantle source was probably affected by the subduction processes

continuous growth of hydrogenetic ferromanganese crusts since 17 myr ago on takuyo daigo seamount nw pacific at water depths of 800 5500 m ferromanganese crusts cover all outcrops on takuyo daigo seamount traversed during remotely operated underwater vehicle rov dives except in places covered by foraminifera sand takuyo daigo is a cretaceous seamount located in the northwest pacific ocean geological and bathymetric mapping provide the framework for this study chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths even through the modern oxygen minimum zone omz contrary to some earlier models for deposition growth rates vary from 2 3 to 3 5 mm myr with fe or mn fluxes of 0 07 0 11 g cm2 myr since the early middle miocene co mn ratios decrease with water depth while fe mn and other metallic elements increase or show no change based on the analysis of the uppermost crust surface this is probably because co is the most abundant redox sensitive element derived from seawater that occurs in crusts

paleomagnetic study of ferromanganese crusts recovered from the northwest pacific testing the applicability of the magnetostratigraphic method to estimate growth rate abstract previous studies have shown that ferromanganese crusts in the pacific ocean commonly record paleomagnetic reversals and that the reversal patterns can be used to estimate growth rates in order to investigate the applicability of the magnetostratigraphic method we conducted paleomagnetic measurements of crust samples recovered from five locations in the northwest pacific a series of thin slices with thicknesses of 0 5 1 0 mm was prepared for each sample and a paleomagnetic polarity was determined for each slice in all five samples we found a consistent reversal pattern of n1 r1 n2 r2 n3 from the surface to the inner part of the crust in three samples another polarity interval r3 was recognized below the n3 section of the crust these data suggest that ferromanganese crusts in the northwest pacific recorded paleomagnetic reversals and that reversal patterns can be used for ocean scale correlations the magnetostratigraphic method suggests constant growth rates of 1 49 2 54 3 56 and 3 67 mm ma for four samples three of which are consistent with those estimated using 10 be 9 be dating at the 2 standard deviation level

resolving hyporheic and groundwater components of streambed water flux using heat as a tracer 1 hyporheic and groundwater fluxes typically occur together in permeable sediments beneath flowing stream water however streambed water fluxes quantified using the thermal method are usually interpreted as representing either groundwater or hyporheic fluxes our purpose was to improve understanding of co occurring groundwater and hyporheic fluxes using streambed temperature measurements and analysis of one dimensional heat transport in shallow streambeds first we examined how changes in hyporheic and groundwater fluxes affect their relative magnitudes by reevaluating previously published simulations these indicated that flux magnitudes are largely independent until a threshold is crossed past which hyporheic fluxes are diminished by much larger 1000 fold groundwater fluxes we tested accurate quantification of co occurring fluxes using one dimensional approaches that are appropriate for analyzing streambed temperature data collected at field sites the thermal analytical method which uses an analytical solution to the one dimensional heat transport equation was used to analyze results from a numerical heat transport model in which hyporheic flow was represented as increased thermal dispersion at shallow depths we found that co occurring groundwater and hyporheic fluxes can be quantified in streambeds although not always accurately for example using a temperature time series collected in a sandy streambed we found that hyporheic and groundwater flow could both be detected when thermal dispersion due to hyporheic flow was significant compared to thermal conduction we provide guidance for when thermal data can be used to quantify both hyporheic and groundwater fluxes and we show that neglecting thermal dispersion may affect accuracy and interpretation of estimated streambed water fluxes

structural and tectonic evolution of the acatlan complex southern mexico its role in the collisional history of laurentia and gondwana 1 correlation of deformational phases and thermal events in the acatlan complex permits definition of nine major tectonic events seven events are related to the evolution of the iapetus and rheic oceans by the early ordovician the xayacatlan suite of laurentian affinity was metamorphosed to eclogite facies and exhumed before colliding with the el rodeo suite from the late ordovician to silurian the upper ordovician ixcamilpa suite with peri gondwanan affinity was metamorphosed to blueschist facies exhumed and subsequently was overthrust by the xayacatlan el rodeo block part of the esperanza suite is an early silurian intra iapetian continental arc that collided with and subducted beneath continental crust generating a silurian eclogitic event by the late devonian collision of the three high p t suites closed the iapetus ocean the resulting composite terrain was thrust over the gondwana bordering cosoltepec suite to close the rheic ocean during the earliest mississippian the collision of the acatlan complex and the oaxaca terrane uplifted and deformed the composite terrane by the early permian deposition of the chazumba suite occurred in a pull apart basin a latest early permian event produced thrust shear zones with n s directed shortening during the middle jurassic plume rise caused regional doming magmatism and amphibolite facies metamorphism during the late cretaceous paleogene folds and thrust faults overprint the acatlan complex most events in the acatlan complex correlate with events in the appalachian chain suggesting that the acatlan complex was located near the appalachians until the jurassic when it was displaced by the gulf of mexico opening

geochemistry of silurian devonian volcanic rocks in the coastal volcanic belt machias eastport area maine evidence for a pre acadian arc the coastal volcanic belt in easternmost maine consists of silurian devonian volcanic rocks related to the convergence of avalonia with the leading edge of composite laurentia just before and during early stages of the acadian orogeny new major and trace element analyses from the machias eastport area indicate that the early to late silurian volcanic rocks in the dennys edmunds and leighton formations formed in a continental arc environment in contrast to some earlier interpretations these rocks have a continuous compositional range from basalt through andesite to rhyolite the mafic rocks in these formations are calc alkaline and show subduction related geochemical signatures on various discrimination diagrams whereas the felsic rocks have geochemical characteristics of volcanic arc granites in contrast the thick volcanic deposits of the younger late silurian eastport formation are bimodal and tholeiitic and have transitional to within plate geochemical signatures thus the transition over time as the acadian seaway closed from subduction and arc settings to continental extension can been seen in this rock sequence and it constrains the time of avalonia s docking regionally volcanic rocks in the kingston terrane of southern new brunswick are likely correlatives of the earlier arc volcanic rocks dennys edmunds and leighton formations while eastport formation analogues are found in the coastal maine magmatic province cranberry island series and probably the passamaquoddy bay volcanic series which similarly appear to have formed after the transition to an extensional environment occurred although other extensional settings cannot be entirely ruled out basalts in the post acadian perry formation indicate continental extension was also active in the late devonian

palaeozoic palaeogeography of laurentia and its margins a reassessment of palaeomagnetic data summary the recognition of wide spread remagnetization events during the palaeozoic has greatly added to the problems of reconstructing the palaeozoic drift history of laurentia and in recent years increasing emphasis has been placed on evaluating the relative reliability of palaeomagnetic data in an attempt to overcome some of these difficulties in the light of these developments a revised apparent polar wander apw path has been constructed following a rigorous evaluation of all published palaeozoic palaeomagnetic data from laurentia and its palaeozoic margins i e north america northern britain northern ireland and greenland the use of data from the laurentian margins when corrected for the opening of the north atlantic has resulted in a revision of previously published palaeozoic palaeogeographic reconstructions and these new palaeogeographic reconstructions for laurentia are in good agreement with faunal and lithological data a comparison of this new apw path with other apw paths from avalonia and baltica reveals a very close agreement between all three paths from mid silurian times onwards indicating that the closure of the iapetus ocean and the tornquist sea was essentially complete by this time laurentia occupied equatorial latitudes from cambrian to early silurian times and its drift history was dominated by anti clockwise rotation up to 0 7 ma 1 and low latitudinal drift rates up to 3 cm yr 1 late silurian and early devonian times were characterized by increased rates of anti clockwise rotation up to 1 3 ma 1 and southerly directed latitudinal drift rates up to 13 cm yr 1 of the continent which place laurentia in moderate southerly latitudes 30 40 s by the early devonian these palaeolatitudes are comparable with those from avalonia and baltica for this time indicating that the amalgamation of eurmerica had already taken place by late devonian time laurentia had begun to drift north rates up to 5 cm yr 1 towards equatorial latitudes by mid carboniferous time

paleomagnetic analysis using squid microscopy 1 superconducting quantum interference device squid microscopes are a new generation of instruments that map magnetic fields with unprecedented spatial resolution and moment sensitivity unlike standard rock magnetometers squid microscopes map magnetic fields rather than measuring magnetic moments such that the sample magnetization pattern must be retrieved from source model fits to the measured field data here we present the first direct comparison between paleomagnetic analyses on natural samples using joint measurements from squid microscopy and moment magnetometry we demonstrate that in combination with a priori geologic and petrographic data squid microscopy can accurately characterize the magnetization of lunar glass spherules and hawaiian basalt the bulk moment magnitude and direction of these samples inferred from inversions of squid microscopy data match direct measurements on the same samples using moment magnetometry in addition these inversions provide unique constraints on the magnetization distribution within the sample these measurements are among the most sensitive and highest resolution quantitative paleomagnetic studies of natural remanent magnetization to date we expect that this technique will be able to extend many other standard paleomagnetic techniques to previously inaccessible microscale samples

petrology of upper ordovician lower silurian rocks of the antigonish highlands nova scotia upper ordovician to lower silurian rocks in the antigonish highlands consist of interlayered basalts rhyodacites arkoses and conglomerates overlain by a thick sequence of marine clastic rocks and minor rhyolites the stratigraphy documents a marine transgression the volcanic rocks were deposited in a within plate continental extensional environment the basalts display alkalic and tholeiitic affinities and the rhyodacites were formed by anatexis of the crust the origin of the younger rhyolites is not clear they are compositionally distinct from the rhyodacites but may be related to them as late stage differentiates at present it is not possible to evaluate whether the tectonic setting and magmatic affinities are regionally or locally controlled the geological history is very similar to that of lower silurian rocks immediately north of the antigonish highlands at arisaig in the simplest sense this indicates these areas may have been juxtaposed prior to the late ordovician and limits cumulative

using chemical hydrologic and age dating analysis to delineate redox processes and flow paths in the riparian zone of a glacial outwash aquifer stream system 1 a combination of chemical and dissolved gas analyses chlorofluorocarbon age dating and hydrologic measurements were used to determine the degree to which biogeochemical processes in a riparian wetland were responsible for removing no3 from groundwaters discharging to the otter tail river in west central minnesota an analysis of river chemistry and flow data revealed that no3 concentrations in the river increased in the lower half of the 8 3 km study reach as the result of groundwater discharge to the river groundwater head measurements along a study transect through the riparian wetland revealed a zone of groundwater discharge extending out under the river on the basis of combined chemical dissolved gas age date and hydrologic results it was determined that water chemistry under the riparian wetland was controlled largely by upgradient groundwaters that followed flow paths up to 16 m deep and discharged under the wetland creating a pattern of progressively older more chemically reduced low no3 water the farther one progressed from the edge of the wetland toward the river these findings pose challenges for researchers investigating biogeochemical processes in riparian buffer zones because the progressively older groundwaters entered the aquifer in earlier years when less no3 fertilizer was being used no3 concentrations originally present in the groundwater had also decreased in the upgradient aquifer as a result of denitrification and progressively stronger reducing conditions there the resulting pattern of decreasing no3 concentrations across the riparian zone may be incorrectly interpreted as evidence of denitrification losses there instead of in the upgradient aquifer consequently it is important to understand the hydrogeologic setting and age structure of the groundwaters being sampled in order to avoid misinterpreting biogeochemical processes in riparian zones

evidence for silurian sinistral accretion of avalon composite terrane in canada the kingston dyke complex forms a regionally developed belt of sheeted bimodal dykes within the avalon composite terrane of southern new brunswick canada dyke orientation relative to the belt suggests their injection accompanied sinistral movement and the belt has previously been attributed to transform activity within the late precambrian magmatic arc regime typical of the avalon composite terrane in the northern appalachians however rhyolite dykes of the sheeted complex yield a u pb age of 435 5 1 5 ma that is interpreted to date their emplacement the complex therefore provides evidence of early silurian sinistral displacement in the northern appalachians such movement is suggested by palaeomagnetic data and may record the accretion of the avalon composite terrane to cratonic north america

a new silurian palaeolatitude for eastern avalonia and evidence for crustal rotations in the avalonian margin of southwestern ireland summary palaeomagnetic data are presented from mid silurian homerian upper wenlock 425 ma sediments from the dingle peninsula sw ireland which forms part of thenorthern margin of the palaeozoic microcontinent of avalonia three remanencecomponents were recognized after removal of a low temperature component l oriented parallel to the present earth eld at the sampling area two higher stabilitycomponents were isolated an intermediate unblocking temperature component i with mean in situ d 196 9 i 11 0 a95 10 8 with a corresponding palaeopole at330 0 e 30 6 s dp 5 6 dm 11 0 and a high unblocking temperature component h with mean tilt corrected d 218 6 i 22 1 a95 7 9 with a correspondingpalaeopole at 309 5 e 18 3 s dp 4 4 dm 8 4 a primary wenlock age is indicatedfor the h component by a positive intraformational conglomerate test whereas the i component is thought to be a secondary mid carboniferous partial remagnetization these data con rm that the sector of the iapetus ocean between avalonia andlaurentia was essentially closed within the limits of palaeomagnetic resolution by thewenlock there is still however a discrepancy between the declinations recorded bysimilar aged sequences to the north and south of the iapetus suture these point toeither an approximately 30 clockwise rotation of the entire avalonian microcontinentrelative to laurentia during closure or local vertical axis rotations of the samplingsites in southern britain

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

nutrient inputs to the coastal ocean from submarine groundwater discharge in a groundwater dominated system relation to land use kona coast hawaii u s a we evaluated the magnitude and composition in terms of salinity 223ra and 224ra activity and nutrient concentrations of submarine groundwater discharge sgd fluxes at 11 sites on the kona coast of hawaii discharging groundwater was typically brackish to saline and had high ra activity relative to ocean water and fresher inland groundwater brackish sgd fluxes estimated using a mass balance approach based on excess coastal ocean 224ra activity ranged from 3 to 1300 l m21 of coastline min21 fluxes of the freshwater component of sgd calculated based on salinity ranged from 2 to 310 l m21 min21 nutrient fluxes into coastal waters from sgd varied by up to three orders of magnitude among sites nitrate nitrite n n phosphate and silica concentrations showed strong inverse linear correlations with salinity in coastal seawater and groundwater these correlations were consistent with previous work that documented conservative mixing between fresh highnutrient groundwater and saline low nutrient seawater at a few coastal ocean sites we extend this conservative relationship to more coastal ocean sites and to groundwater in the coastal aquifer n n concentrations in the fresh component of discharging groundwater were higher at sites near golf courses and those with a greater percentage of bare land within a 5 km radius and silica concentrations in the fresh component of discharging groundwater were higher at sites with more bare land and lower population densities however neither urbanization nor agriculture was significantly correlated with groundwater nutrient concentrations on this relatively undeveloped coast

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

comparative geochemistry of four ferromanganese crusts from the pacific ocean and significance for the use of ni isotopes as paleoceanographic tracers abstract ferromanganese fe mn crusts are potential archive of the ni isotope composition of seawater through time in this study we aim at 1 understanding ni isotope fractionation mechanisms and metal enrichment processes in fe mn deposits 2 addressing global vs local control of ni isotope composition of these deposits two fe mn crusts from the north pacific ocean apuupuu seamount hawaii and two fe mn crusts from the south pacific ocean near rurutu island austral archipelago of french polynesia were characterized for their elemental geochemistry and ni isotope composition geochemical analyses were performed at millimeter intervals in order to provide time resolved record of ni isotopes chronology and growth rates were determined using cosmogenic 10be isotope abundances the results show that despite different growth rates textures and geochemical patterns fe mn crusts from both north and south pacific oceans have fairly homogenous ni isotope compositions over the last 17 ma yielding average 60 58ni values of 1 79 0 21 2sd n 31 and 1 73 0 21 2sd n 21 respectively in one crust sample however layers directly in contact with the altered substrate show anomalously light 60 58ni values down to 0 25 0 05 2se together with rejuvenated 10be 9be ratios correlating with elevated ni mn ratios such patterns are best explained by protracted fluid rock interactions leading to alteration of mn phases after crust formation isotopically light ni would be the result of ni isotope fractionation during adsorption rather than the contribution of external ni sources e g hydrothermal sources having light ni isotope compositions the combination of our results with previously published data on fe mn crusts indicates that the average ni isotope composition in deep waters has not changed through the cenozoic 70 ma we propose that ni isotope variations in fe mn crusts may not only record variations of ni sources to the oceans but also post depositional processes depending on the growth history and geological settings of fe mn crusts

rethinking the use of seabed sediment temperature profiles to trace submarine groundwater flow submarine groundwater fluxes across the seafloor facilitate important hydrological and biogeochemical exchanges between oceans and seabed sediment yet few studies have investigated spatially distributed groundwater fluxes in deep ocean environments such as continental slopes heat has been previously applied as a submarine groundwater tracer using an analytical solution to a heat flow equation assuming steady state conditions and homogeneous thermal conductivity these assumptions are often violated in shallow seabeds due to ocean bottom temperature changes or sediment property variations here heat tracing analysis techniques recently developed for terrestrial settings are applied in concert to examine the influences of groundwater flow ocean temperature changes and seabed thermal conductivity variations on deep ocean sediment temperature profiles temperature observations from the sediment and bottom ocean water on the scotian slope off eastern canada are used to demonstrate how simple thermal methods for tracing groundwater can be employed if more comprehensive techniques indicate that the simplifying assumptions are valid the spatial distribution of the inferred groundwater fluxes on the slope suggests a downward groundwater flow system with recharge occurring over the upper middle slope and discharge on the lower slope we speculate that the downward groundwater flow inferred on the scotian slope is due to density driven processes arising from underlying salt domes in contrast with upward slope systems driven by geothermal convection improvements in the design of future submarine hydrogeological studies are proposed for thermal data collection and groundwater flow analysis including new equations that quantify the minimum detectable flux magnitude for a given sensor accuracy and profile length

age and tectonic setting of granitoid plutons in the cheticamp belt western cape breton island nova scotia canada geological mapping in the cheticamp granitoid belt in combination with petrographic and geochemical studies and u pb zircon dating by laser ablation inductively coupled plasma mass spectrometry have resulted in major reinterpretation of the geology in the western part of the ganderian aspy terrane of cape breton island nine new u pb zircon ages show that the former cheticamp pluton consists of 10 separate plutons of five different ages late neoproterozoic ca 567 ma cambrian ordovician 490 482 ma ordovician silurian 442 440 ma mid silurian ca 428 ma and late devonian 366 ma the three late neoproterozoic granodioritic to monzogranitic plutons are older than the adjacent metavolcanic and metasedimentary rocks of the jumping brook metamorphic suite whereas the tonalitic to quartz dioritic cambrian ordovician plutons intruded those metamorphic rocks petrographic characteristics and approximately 100 whole rock chemical analyses show that with the exception of the mid silurian grand falaise alkali feldspar granite which has a type within plate characteristics the plutonic units have calc alkaline affinity and were emplaced in a volcanic arc tectonic setting these results are evidence that fragments of a long history of episodic subduction related magmatism and terrane collision are preserved in this small part of ganderia eight new sm nd isotopic analyses are consistent with the ganderian affinity of the cheticamp plutonic belt the ca 490 482 ma plutons are the first direct evidence in cape breton island for the penobscottian event recognized in the exploits subzone of central newfoundland and in new brunswick however the structural relationship of the cheticamp plutonic belt to the rest of the aspy and bras d or terranes remains enigmatic as is the apparent absence of effects of devonian deformation and metamorphism in the older plutonic units

abrupt intensification of north atlantic deep water formation at the nordic seas during the late pliocene climate transition knowledge of the evolution of north atlantic deep water nadw is key to understanding the past evolution of the climatic system here we developed a new rock magnetic method to determine the constituent magnetic minerals of sediments and report on the evolution of nadw during 2 2 2 9 ma we measured isothermal remanence acquisition curves of north atlantic deep sea sediments drilled at the gardar drift and decomposed the first derivatives of these curves into high coercivity and low coercivity components residuals of the decomposition were sufficiently small throughout the study interval confirming that the gardar drift sediments represent a mixing of the two end members fractional changes of the high coercivity component represent variation of the iceland scotland overflow water a branch of nadw formed at the nordic seas the high coercivity component increased significantly during an interglacial period just after 2 68 ma which suggests that nadw formation in the nordic seas abruptly intensified at this time

streambed nitrogen cycling beyond the hyporheic zone flow controls on horizontal patterns and depth distribution of nitrate and dissolved oxygen in the upwelling groundwater of a lowland river 1 biogeochemical turnover in hyporheic zones is known to have the potential to affect the chemical signature of surface water cycling through shallow streambed sediments this study investigates the impact of streambed physical properties on the fate of nitrate and dissolved oxygen in groundwater upwelling through the streambed of a lowland river for analyzing depth dependent patterns and zonation of nitrogen concentrations diffuse gel probes in shallow top 15 cm streambed sediments have been deployed in a nested setup together with multilevel minipiezometers for streambed sediments of 15 150 cm spatial heterogeneity of groundwater upwelling was controlled by patterns of low conductivity peat and clay strata that caused locally confined conditions suggesting increased streambed residence times nitrate concentrations in the upwelling groundwater changed by up to 68 06 mg l 1 within the top 15 cm of streambed sediments and by up to 107 47 mg l 1 at depths of 15 150 cm indicating that significant nitrogen turnover was not restricted to shallow streambed sediments intensive reduction of nitrate concentrations was found in particular in vicinity of low conductivity streambed strata the coincidence of confined groundwater upwelling and reduced oxygen concentrations at these locations suggests that increased residence times and associated depletion of dissolved oxygen create conditions favorable for nitrate reduction our results highlight that increased nitrogen turnover at aquifer river interfaces is not necessarily limited to shallow streambed zones where surface water is mixing with groundwater but can affect upwelling groundwater in reactive hot spots that extend to greater streambed depths and beyond hyporheic mixing zones

use of heat as tracer to quantify vertical streambed flow in a two dimensional flow field 1 analytical solutions to the heat transport equation in porous media have been developed in the past to estimate surface water groundwater interactions these solutions however are based upon simplifying assumptions that are frequently violated in natural systems a nonvertical flow field inherent to most field settings can violate the one dimensional 1 d flow assumption and lead to erroneous velocity estimates in this study we have developed a 2 d heat and mass transport finite element based numerical model for a stream aquifer cross section experiencing flow through synthetic multilevel streambed temperature time series were generated with the model using a sinusoidal temperature boundary the temperature data was used to quantify the vertical flow velocity with a 1 d analytical solution based on the amplitude decay and phase shift of temperature with depth results demonstrate that erroneous vertical components of fluid velocity can be obtained by the 1 d analytical solution when the true vertical velocity approaches zero and the flow regime becomes almost horizontal the results also illustrate that the amplitude ratio method performs quite poorly on the gaining side of the stream where the only reliable method is phase shift on the losing side of the stream both methods can be employed but a better estimation is obtained from the amplitude ratio method in general amplitude ratio and phase shift data should be used in conjunction to maximize the information of the system

magnetostratigraphy of hydrogenetic manganese crusts from northwestern pacific seamounts abstract fine scale dating is crucial to understanding the growth and environments of formation of marine manganese deposits the paleomagnetic method of dating of manganese nodules and crusts has been attempted but with no success so far we measured remanent magnetization rm on up to 75 mm thick hydrogenetic crusts at intervals of 2 5 mm after mineralogical and chemical examination careful separation and alternative field demagnetization stable sharp rm and well correlated polarity change patterns between four samples made it possible to identify the pliocene quaternary magnetic chrons in them these data show that the three crusts have grown continuously at rates of 14 17 mm m y since the early pliocene this is three or four times faster than those for central pacific seamount hydrogenetic crusts estimates of growth rate based on determination of co flux are within this range magnetostratigraphy therefore appears to be a powerful method for dating hydrogenetic manganese crusts when supported by conventional dating methods these results encourage finer scale investigations which promise more detailed paleoceanographic reconstruction

the burnsville fault evidence for the timing and kinematics of southern appalachian acadian dextral transform tectonics there has been a conspicuous absence of documented acadian structures in the blue ridge province of the southern appalachians even though a growing body of evidence suggests that the middle paleozoic acadian orogeny affected the rocks of this region new mapping along with structural petrologic and geochronologic data from western north carolina show that the contact between the metasedimentary and metavolcanic rocks of the ashe metamorphic suite and the grenville basement rocks of the western blue ridge corresponds to a devonian high grade dextral strike slip fault zone the burnsville fault timing of motion on the burnsville fault is constrained by field relationships metamorphic fabrics and assemblages and radiometric ages a u pb zircon crystallization age for a pegmatite sheared by the burnsville fault shows that the last movement on the fault must he younger than 377 ma previously published 4 0 ar 3 9 ar cooling ages show that the burnsville fault must be older than ca 360 ma we have mapped the burnsville fault for 100 km in northwest ern north carolina the gossan lead fault of northwesternmost north carolina and southwestern virginia is the likely continuation of the burnsville fault to the north east southwest of asheville north carolina the burnsville fault may connect to the devonian dahlonega shear zone or may be cut by post devonian thrust faults associated with the alleghanian orogeny diachroneity of acadian elastic wedge the presence of silurian devonian pull apart basins the presence of devonian high grade dextral shearing in the inner piedmont and recent plate reconstructions for the middle paleozoic support the interpretation that the late phase of the acadian orogeny in the southern appalachians was primarily a dextral transpressional event the burnsville fault and the inner piedmont formed the boundaries of a dextral transform margin that may have extended the length of the appalachian orogen this interpretation requires that models for the paleozoic tectonics of the appalachians incorporate major pre alleghanian dextral displacement

magnetic stratigraphy observed in ferromanganese crust summary a sample of ferromanganese crust deposit schw 1d was cut into two sets of 1 mm slices for palaeomagnetic study alternating field and thermal demagnetization and isothermal remanent magnetization analyses were performed on each thin slice the results reveal the presence of a stable magnetism and both normal and reversed polarity intervals in the specimens the observed polarity intervals cannot be confidently correlated with the geomagnetic polarity time scale of the last 10 myr due to the polarity overlap inherent in the sampling technique but the results confirm the slow accretion rate of ferromanganese deposit determined by 10be method and suggest potential use of ferromanganese deposits in palaeomagnetic and tectonic studies

nd isotopic characteristics of terranes within the avalon zone southern new brunswick nd isotopic data are presented for rock units in four terranes within the traditional avalon zone of southern new brunswick initial end values for igneous rocks within the caledonia terrane range from 1 6 to 4 6 whereas values for sedimentary rocks range from 8 4 to 3 6 a granite within the kingston terrane has end 438 ma 4 0 nd isotopic compositions for the kingston and caledonia terranes are similar to those of the mira terrane in cape breton island the antigonish highlands of nova scotia and plutonic rocks of eastern newfoundland each of these regions may be a dismembered part of a single terrane the avalon terrane sensu stricto initial end values for rocks from the brookville terrane range from 1 3 to 2 8 the coverdale anorthosite within the brookville terrane has a present day end value of 12 1 and a depleted mantle model age of 1 3 ga similar to mesoproterozoic anorthosites in laurentia clastic sedimentary rocks in the green head group have end 750 ma values of 2 0 and 10 9