the formation of turbidity maximum zones by minor axis tidal straining in regions of freshwater influence abstractthis study investigates the influence of tidal straining in the generation of turbidity maximum zones tmz which are observed to extend for tens of kilometers along some shallow open coa

a climosequence of soils on late quaternary volcanic ash in highland papua new guinea abstract some chemical physical and mineralogical properties of three soils developed in volcanic ash at altitudes of 1040 m 1720 m and 2350 m in papua new guinea s enga province are presented silt fraction mineralogy and total chemical analyses show that fresh ash occurs in the upper approximately 30 cm of profile at each site this fresh ash is probably only a few thousand years old and overlies an older weathered ash tomba tephra more than 50000 years old at the lowest site the majority of the primary minerals predominantly amphiboles volcanic glass and felspar and some pyroxenes have been decomposed by weathering to produce a high clay content with increasing altitude greater proportions of silt sized unweathered and partially altered primary minerals are recognised and molar ratios of calcium magnesium sodium and potassium to aluminum increase accordingly in the clay fractions allophane with al si ratios of approximately 2 0 is dominant at the highest site whereas with decreasing altitude lower proportions of allophane occur al si ratios decline and halloysite becomes dominant gibbsite is found in all three profiles

wave mud interactions over the muddy atchafalaya subaqueous clinoform louisiana united states wave supported sediment transport 1 near bottom fluid mud layers were observed during two experiments conducted on the muddy atchafalaya inner shelf subaqueous clinoform louisiana united states on the face of the subaqueous delta 4 7 m water depth first experiment fluid mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages and supported by near bed wave induced turbulence the layers are episodic lifetime of 9 12 h form prior to significant postfrontal settling of sediment in the overlying water column and flow seaward downslope at about 5 cm s farther westward on the delta front finer grain size with negligible sand or coarse silt content second experiment similar wave supported fluid mud layers are observed to last longer 2 days show weaker alongshore westward flow of about 1 3 cm s the results suggest a sequence of near bed sediment transport processes triggered by frontal swell activity bed liquefaction resuspension and advection modulated by the bathymetric characteristics of the clinoform that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas

pedogenic weathering of upper quaternary tephras in new zealand abstract at ahuroa road 12 km east of te kuiti a sequence of weathered mantling tephra beds resting on a weathered pyroclastic flow represents progressive accretion of tephras for 250 000 yr using known dated tephras a time scale is constructed and rates of accumulation of andesitic tephras are calculated progressive accretion has meant that the length of time each tephra was exposed to soil forming processes at the surface was limited the lack of development of soil horizons is considered to be due to this short exposure time even so large cation losses have occurred when measured by the isovolumetric method namely base cations si fe ti and al field observations indicate that some beds are rhyolitic in origin others andesitic analysis shows that darker coloured chocolate beds of andesitic origin have higher fe and ti contents than lighter coloured ginger beds of rhyolitic origin pallid brown and yellow brown beds in the column are attributed either an andesitic or rhyolitic origin on the basis of their fe and ti contents generally lower cation losses occur in rhyolitic beds than in andesitic beds some beds show losses that depart from the general pattern and it is considered that such departures are due to a decrease in leaching intensity in two cases and to topography changes accompanying increasing tephra accumulation for the beds in the latter part of the time period

a numerical investigation of the dynamics and structure of hyperpycnal river plumes on sloping continental shelves 1 a 3 d hydrodynamic model regional ocean modeling system is used to investigate the dynamics and structure of hyperpycnal river plumes over sloping continental shelves the focus is on the plume s response to varying slopes and settling velocities ws the idealized model is configured to represent small mountainous river systems during a flood event a hyperpycnal sediment concentration of 60 g l is specified at the river mouth such that the sediment freshwater mixture is denser than the seawater causing the plumes to traverse the shelves as undercurrents a realistic range of shelf slope of 0 001 0 03 is chosen the settling velocity is varied based on river s carrying capacity the model derived velocity profiles and the entrainment rate compare favorably against prior laboratory experiments both cross shore and alongshore momentum balances are primarily between gravitational forcing and bottom friction but the coriolis deflection is significant at the plume core in the alongshore momentum budget i e ekman balance as the slope increases and settling velocity decreases hyperpycnal plumes transition from depositional to autosuspending regime an estimate of critical slope governed by a dimensionless parameter ws3 qb qb is buoyancy input reasonably captures the regime transition in the depositional regime the plume s runout cross shore penetration scales with advective distance increasing slopes and discharge enhance the gravitational forcing and plume velocity leading to an increase in runout in contrast increasing settling velocity shortens the vertical settling time thereby reducing the plume s horizontal footprint for the range of parameters considered the runout of depositional plumes is confined within 15 km from the mouth whereas the penetration of autosuspending plumes is essentially unlimited

fragile landscapes fragile civilizations how climate determined societies in the pre columbian south peruvian andes abstract this paper presents alternating periods of geo ecological fragility and stability in a highly sensitive environmental setting the desert margin area of southern peru 14 5 s there we have to state that fragility was dominantly triggered by climatic changes which induced several oscillations of the desert margin during the mid holocene the study area received the holocene maximum of precipitation soil formation occurred and the desert retreated as loess paleosoil formation documents in contrast the titicaca region further south east experienced extreme drought at that time this regional antagonism between humid and dry conditions was a result of meridional shifts in moisture transport across the andes and occurred also during pre columbian times considering a coincidence between environmental and cultural changes we state that success and decline of civilizations were dominated by hydrological oscillations triggering fertility as well as a critical loss of natural resources fragile periods i e periods of geomorphological activity occurred contemporaneous with cultural transitions in response to spatial changing resources cultural foci were shifted so the success of pre columbian civilizations was closely coupled to areas of geo ecological favorability which were directly controlled by distinct regional impacts of large scale circulation mechanisms including el nino southern oscillation enso this spatial view on non uniform environmental and cultural changes has not been thoroughly considered before therefore for the first time this paper offers geomorphological evidence for diachronous andean agri cultural development which was geographically determined

environmental arsenopyrite stability and dissolution theory experiment and field observations arsenopyrite has traditionally been considered to be chemically unstable in the surficial environment however field evidence demonstrates that arsenopyrite does not readily decompose under water saturated near surface conditions arsenopyrite occurs in the heavy mineral suite of a variety of thin sediments in southern new zealand with no evidence for chemical corrosion these sediments have been water saturated but within metres of the surface for 10 60 28000 and 2 million years these observations of long term arsenopyrite stability are in accord with geochemical predictions based on recent experimentally determined thermodynamic data for arsenopyrite calculations using the new thermodynamic data suggest that arsenopyrite has similar eh ph stability range to pyrite except under acid conditions ph 4 where arsenopyrite should transform to realgar or orpiment calculated as concentrations in equilibrium with the pyrite arsenopyrite assemblage in the surficial environment are 0 01 0 1 ppm similar to groundwater in arsenopyrite bearing rocks in this study 0 005 0 3 ppm and these waters may be in chemical equilibrium arsenopyrite decomposes in oxidised waters to yield up to 1100 ppm dissolved as in the laboratory and up to 400 ppm dissolved as in mine processing waters these concentrations of dissolved as are several orders of magnitude lower than equilibrium solubility of arsenopyrite because of kinetic effects and development of protective oxide coatings on arsenopyrite grains mine tailings containing arsenopyrite should be chemically stable during longterm storage provided they are kept water saturated and moderately reduced d 2003 elsevier science b v all rights reserved

acoustic inversions for measuring boundary layer suspended sediment processes although sound has been applied to the study of sediment transport processes for a number of years it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters in particular when the attenuation due to the suspension becomes significant the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension to study this attenuation propagation problem numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters the results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters which become increasingly erroneous with range as the sound propagates through the suspension to address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion this approach is not subject to the accumulation of errors and has an explicit solution here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion

spatial variability of arsenic in some iron rich deposits generated by acid mine drainage abstract potential contamination of rivers by trace elements can be controlled among others by the precipitation of oxyhydroxides the streambed of the studied area located in la ch taigneraie district lot river basin france is characterised by iron rich ochreous deposits acidic ph 2 7 4 8 and so 4 mg waters beyond the acid mine drainage the presence of as both in the dissolved fraction and in the deposits is also a problem upstream at the gallery outlet as concentrations are high as max 2 6 mol l and up to 5 wt locally respectively in the dissolved and in the solid fractions downstream as concentrations decrease below 0 1 mol l in the dissolved fraction and to 1327 mg kg in the solid fraction this natural attenuation is related to the as retention within ochreous precipitates amorphous to poorly crystalline fe oxyhydroxides schwertmannite and goethite which have great affinities for this metalloid upstream schwertmannite is dominant while downstream goethite becomes the main mineral the transformation of schwertmannite into goethite is observed in the upstream deposits as schwertmannite is unstable relative to goethite furthermore thermodynamic calculations indicate that the downstream goethite is not able to precipitate in situ according to the water chemistry goethite mainly results from the transformation of schwertmannite and its solid transport downstream moreover as highlighted by leaching experiments carried out on the ochreous precipitates this transformation does not seem to affect the as retention in solids as no release of as was observed in the solution arsenic may either be strongly trapped by co precipitation in the present minerals or it may be quickly released and re adsorbed on the precipitate surface

a lumped parameter model of groundwater influx to a mine adit in mountainous terrain 1 acidic and metal laden drainage from the portals of abandoned mines is a serious environmental problem in wet mountainous regions where steep hydraulic gradients ensure that fresh recharge waters are continuously flushed through the workings hydrogeological characterization of these sites is hampered by their geological complexity and their frequent inaccessibility this paper presents a material balance model for the groundwater capture zone associated with influx to a mountainside adit the model can be used to estimate bulk hydraulic properties of the rock surrounding an adit from hydrograph data commonly recorded at its portal this application is illustrated using data from the myra falls mining camp vancouver island british columbia by simultaneously fitting base flow recession slopes for hydrographs of discharge water table elevation and head in an underground borehole the model yields plausible and well constrained estimates of hydraulic conductivity porosity skin factor and hydraulic gradient

effects of ambient currents and waves on gravity driven sediment transport on continental shelves abstract observations from several shelf environments show that down slope gravity driven transport may constitute an important mode of suspended sediment dispersal across shelves and highlight the influence of ambient waves and currents on gravity induced sediment flux the phenomena discussed here involve high concentrations of suspended sediment mixed with seawater and thus differ in genesis from hyperpycnal plumes released directly from sediment laden rivers the field sites examined are the gulf of bohai off the mouth of the yellow river huanghe the northern california shelf off the mouth of the eel river and the louisiana shelf west of the mouths of the mississippi river off the yellow river rapid down slope transport over distances of a few km occurred when frictional resistance induced by strong along shelf currents was temporarily relaxed more prolonged down slope motion over longer distances occurred following floods of the eel river when wave and current agitation provided turbulence to sustain gravity driven transport of fluid mud on the louisiana inner shelf the down slope gravity force was much weaker but observations suggest that thin gravity flows may still have occurred in the presence of waves a simple analytical theory is developed that incorporates the influence of ambient shelf currents on gravity driven transport of suspended sediment this theory is quantitatively consistent with the observations from the three sites if the supply of easily suspended sediment is less than the capacity of ambient currents including waves to carry sediment then intense turbulence limits gravity induced sediment transport by increasing the drag at the base of the flow when ambient currents abruptly cease rapid down slope transport can then occur over short distances until the sediment settles such flows do not remain intensely turbulent because the slope of the continental shelf is too gentle to induce shear instability within the gravity flow the maximum sustained rate of gravity induced sediment transport occurs when ambient currents are strong but the supply of easily suspended sediment exceeds the resuspension capacity of the ambient currents feedback then leads to values of the gradient richardson number ri within the flow that are near the critical value of 1 4 this partially damps bottom drag but still allows the generation of sufficient turbulence to maintain sediment in suspension observations also indicate systematic relationships among ri the supply of easily suspended sediment and the bottom drag coefficient acting on the gravity flow

winter storms induced high suspended sediment concentration along the north offshore seabed of the changjiang estuary abstract fine grained sediments suspended in coastal waters play an important role in submarine topography evolution and associated environment changes the convergence of suspended sediments concentrated near the seabed results in high sediment concentration and contributes significantly to sediment transport in order to investigate the mechanism triggering high suspended sediment concentration ssc we deployed a tripod to the seabed to obtain in situ bottom boundary layer measurements of sediment dynamics and a buoy to the sea surface to collect meteorological and wave data at the northern changjiang river mouth from december 20 2015 to january 20 2016 the high ssc e g 3 g l events were observed together with fluid mud thicknesses of 4 16 cm near the seabed during neap tides when cold air intrusion generated winter storms and strong waves further we found that the high ssc event was mainly resulted from wind waves and sediment resuspension supported by local benthic fluid mud which was associated with three stages at the setting up stage the winter storm brought long duration of strong waves e g significant wave height 1 5 m more than 15 h resulting in a maximum wave current combined bottom shear stress of 3 2 pa and the increase of ssc to 1 g l at the reinforcement stage the strong waves and bottom shear stress lasted for several hours and further increased the ssc to 3 g l at the final decay stage wind waves and the maximum wave current shear stresses decreased significantly with the disappearance of high ssc thus there was no high ssc event observed even with strong wind waves during spring tides because strong wave duration was too short for the reinforcement process the sediment source for the high ssc events was mainly from bottom fluid mud resuspension as well as the advection transport from the adjacent subaqueous changjiang river delta

numerical modeling of gravity driven sediment transport and deposition on an energetic continental shelf eel river northern california 1 a two dimensional numerical model was applied to predict large scale deposition by wave supported sediment gravity flows on the eel river continental shelf for four consecutive flood seasons using measured bathymetry waves and river forcing the model assumes that sediment induced stratification maintains the near bed richardson number at its critical value which determines the sediment carrying capacity of the wave boundary layer deposition is predicted when the gravity driven flux of sediment exceeds the carrying capacity the model predicted 26 of fine sediment discharged by the eel river to be deposited on the midshelf with a magnitude and distribution largely consistent with field observations greatest deposition on the midshelf was predicted well north of the river mouth despite greater sediment input nearest the river mouth model results indicate that when the river delivers sufficient sediment to critically stratify the wave boundary layer wave intensity and the bathymetry of the eel shelf are the dominant factors controlling the observed pattern of deposition large wave energy caused the majority of fine sediment 65 to escape the shelf as gravity driven flows the greatest amount of sediment was predicted to leave the shelf from the region off shelf of the river mouth including 11 into the eel canyon where inshore sediment input was high and the concave downward bathymetry associated with the eel river subaqueous delta prevents significant midshelf gravity driven deposition

semidiurnal switching of stratification in the region of freshwater influence of the rhine observations in the rhine region of freshwater influence rofi system in the north sea show evidence of large semidiurnal oscillations in stability superimposed on a mean stratification occurring throughout the stratified region at times of reduced mixing the amplitude of this semidiurnal variation is of the same order as the mean stability and frequently results in conditions being mixed or nearly mixed once per tide it is deduced that this semidiurnal variation results primarily from cross shore tidal straining which interacts with the density gradient to induce stratification this conceptual picture of the contributing processes has been tested in a one dimensional point model forced by the observed slopes and the local density gradients the model exhibits the same qualitative behavior as the observations produces oscillations in stratification of the amplitude observed and confirms the critical role of cross shore tidal straining the large cross shore shear nder stratified conditions is identified with the changes in ellipse configuration which are observed between mixed and stratified conditions the occurrence of semidiurnal variations in stability in the rhine rofi is thus inferred to be a consequence of the development of mean stability whenever the horizontal density gradients relax in conditions of low stirring

in situ observations of wave supported fluid mud generation and deposition on an active continental margin wave supported fluid muds wsfm are a type of gravity flow that can rapidly transport sediment across continental margins they occur when wave induced bed stress maintains suspended sediment concentrations ssc 10 g l 1 and sediment induced stratification near the top of the wave boundary layer limits upward diffusion of sediment observations from near bed instrumentation are used to evaluate the conditions under which wsfms form on the continental shelf offshore of the waipaoa river nz an event in july 2010 featured 130 hours river of energetic ocean conditions and water discharge 1900 m3 s 1 a calibrated acoustic backscatter sensor at the mid shelf measured near bed ssc 50 g l 1 with a strong lutocline occurring 15 cm above the predicted wave current boundary layer resulting in 5 cm deposition a velocity anomaly occurred during this time with offshore directed currents faster at 1 meter above bed mab than at 3 5 mab using these observations we empirically solve a simple buoyancy drag force balance to estimate the gravity driven velocity of the wsfm which is always 0 03 m s 1 extending the force balance across a shelf transect suggests that wsfm carried sediment can reach the shelf edge in 50 240 hours spatial and temporal patterns of deposition predicted by the gradient of modeled sediment flux correlate well with seabed observations on the waipaoa shelf reported in walsh et al 2014 this study highlights the importance of wsfms for cross shelf sediment transport despite relatively slow gravity driven velocities and the infrequency with which they occur

use of soils and palaeosols on volcanic materials to establish the duration of soil formation at different chronological scales abstract in this paper we present an overview of the mexican volcanic palaeosol sequences as a valuable tool to establish the duration of soil formation at different chronological scales we have selected four study cases which cover time intervals from decennial centennial to millennial pedogenesis the first case corresponds to the soils in el chichon volcano where the short interval between the eruptions gives the opportunity to study the soil formation in periods less than 500 years in this interval the transformation from regosol to andosol is observable in el nevado de toluca pedogenesis of longer duration 4000 to 6000 y characterizes a vitric andosol stage in this area the transformation of andosol to luvisol is also shown in periods longer than 10 000 years the third study case corresponds to the tlaxcala palaeosol sequence where pedogenesis in intervals from 10 000 to 100 000 years is observable in this case no andosols are present and a complete set of luvisols showing different properties is found this differentiation is not only related to the duration of the pedogenesis but also to the climatic conditions which lead to changes in specific properties clay content weathering of the primary minerals fed content in this way these soils are valuable for palaeoenvironmental reconstruction the fourth case is related to faster pedogenesis in the volcanic regions of mexico where highly developed luvisols are found formed in intervals less than 15 000 y in this case the influence of a pre weathered volcanic material as a source of clay allows the rapid transformation

geochemistry of mineralizing fluids in the bralorne pioneer mesothermal gold vein deposit british columbia canada gold quartz veins at the bralorne mesothermal vein deposit have extensive quartz ankeritic carbonate muscovite hydrothermal alteration envelopes that grade outward to chlorite calcite albite minor pyrite with traces of sphalerite galena and tetrahedrite are found in the veins with native gold more abundant pyrite and arsenopyrite with lesser pyrrhotite and chalcopyrite occur in altered wall rock adjacent to the veins envelopes are characterized by addition of k 2 o co 2 s as and au with corresponding depletion of na 2 o feo total and mgo sio 2 and cao are locally depleted and reconcentrated fluid inclusions suggest that deposition of gold was from dilute aqueous solutions 2 ch 4 at 350 degrees c and 1 75 kbars progressive dilution of this fluid by cooler meteoric water led to fluids at 250 degrees c and 0 5 to 1 kbar with 1 wt percent or less nacl equivalent and no detectable carbonic component sulfur isotope ratios of sulfides associated with gold mineralization range from 7 to 9 per mil clustering about a magmatic signature of 0 per mil the ore fluid had a delta 18 o value of 13 or 1 and delta 13 c of 11 or 2 per mil based on measurements in coexisting vein quartz carbonate and muscovite temperature of the mineralizing fluids appears to have increased with depth at a normal geothermal gradient of approximately 30 degrees c km gold sulfides and the associated alteration assemblages are modeled using observed mineralogy and thermodynamic data for chloride complexes as having been deposited from a slightly acid solution ph 4 5 with an na k ratio of at least 8 1 and a high content of dissolved co 2 log fugacity 2 5 conditions were strongly reducing as suggested by the log fugacity of ch 4 0 5 with f sub o 2 about 10 super 30 bars and f sub s 2 about 10 super 7 bars precipitation of gold in the immediately adjacent highly quartz sericite ankerite pyrite altered wall rock was due to reaction with carbonation of the wall rock that caused the ph of the ore fluid to rise destabilizing aurous chloride complexes such a shift is in the direction of slightly increasing or constant stability of gold thiosulfide ions and at a relatively constant f sub o 2 the most significant result of this modeling is that in detail the actual precipitation of gold is by reduction of aurous ions by electrons donated through concurrent oxidation of s super 2 in h 2 s to s super in pyrite fes 2 this explains the empirically observed correlation between pyrite and gold in this type of deposit and in the model between consumption of fe super 2 and production of pyrite on the one hand with precipitation of gold on the other

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

geochemical fluxes and weathering of volcanic terrains on high standing islands taranaki and manawatu wanganui regions of new zealand abstract sediment fluxes from high standing oceanic islands hsis such as new zealand are some of the highest known milliman j d and syvitski j p m 1992 geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers j geol 100 525 544 recent geochemical work has suggested that along with their extremely high physical weathering yields many new zealand watersheds also have very high chemical weathering yields in new zealand the magnitude of both the physical and chemical weathering yields is related to the lithology of the watershed most of the previous work on this topic has been undertaken in southern alps watersheds of schist and greywacke and in east cape watersheds of semi consolidated marine sediments and greywacke we recently sampled north island watersheds in the taranaki and manawatu wanganui regions which have been subjected to volcanism since the miocene we sampled watersheds that contain both volcanic and sedimentary rocks a series of water and sediment samples was collected and analyzed for major minor and trace elements this was done to quantify the weathering intensities in the watersheds and to establish the relationship between physical and chemical weathering yields in volcanic lithologies our results reveal distinct chemical signatures for the different regions waters draining the taranaki region volcanics are significantly enriched in k and depleted in ca2 and sr2 compared to waters draining the manawatu wanganui region volcanics which also traverse expanses of sedimentary siltstones and mudstones the ca2 and sr2 depletions may reflect the relative absence of caco3 in the taranaki region watersheds in addition sediment samples from the taranaki region show significant enrichment in ti al ca fe mn mg ca and p and depletion in si and rb compared to those of the manawatu wanganui region from total dissolved solids concentrations and mean annual water discharge we calculate chemical weathering yields of 60 240 tons km 2 a 1 these weathering yields fall within the middle to upper range of those previously documented for the southern alps 93 480 tons km 2 a 1 and east cape 62 400 tons km 2 a 1 calculated silicate weathering yields of 12 33 6 tons km 2 a 1 and co2 consumption of 852 2390 103 mol km 2 a 1 for the rivers draining the taranaki volcanic region are higher than those previously reported for watersheds hosted in sedimentary and metamorphosed rock terrains on hsis co2 consumption is found to be within the range previously measured for the basaltic terrains of the deccan traps 580 2450 103 mol km 2 a 1 and reunion island 1300 4400 103 mol km 2 a 1 our calculated chemical weathering yields demonstrate the importance of hsis particularly those with volcanic terrains when considering global geochemical fluxes

structure of turbulence and sediment stratification in wave supported mud layers we present results from laboratory experiments in a wave flume with and without a sediment bed to investigate the turbulent structure and sediment dynamics of wave supported mud layers the presence of sediment on the bed significantly alters the structure of the wave boundary layer relative to that observed in the absence of sediment increasing the tke by more than a factor of 3 at low wave orbital velocities and suppressing it at the highest velocities the transition between the low and high velocity regimes occurs when re 450 where re is the stokes reynolds number in the low velocity regime re 450 the ripples are significantly smaller the near bed sediment concentrations are significantly higher and density stratification due to sediment becomes important in this regime the tke and reynolds stress are lower in the sediment bed runs than in comparable runs with no sediment the regime transition at re 450 appears to result from washout of the ripples and increased concentrations of fine sand suspended in the boundary layer which increases the settling flux and the stratification near the bed the increased stratification damps turbulence especially near the top of the high concentration layer reducing the layer thickness we anticipate that these effects will influence the transport capacity of wave supported gravity currents on the continental shelf

deposition by seasonal wave and current supported sediment gravity flows interacting with spatially varying bathymetry waiapu shelf new zealand abstract the waiapu river sedimentary system new zealand provides a prototype for investigating the relative importance of wave versus current supported gravity flows on continental shelf deposition a two dimensional model was used to represent gravity driven sediment transport and deposition on the waiapu shelf over an annual cycle of storm events and associated waiapu river floods model inputs of waves and wind driven currents were derived from wavewatch iii hindcasts and constrained by benthic tripod data the 12 month model run included a low energy period september 2003 to may 2004 with weak waves and currents and low river discharge and a high energy period may to august 2004 with stronger waves and wind driven currents and more frequent river floods model results suggested that during the low energy period riverine sediment was trapped between the 20 and 80 m isobaths during the high energy period sediment was deposited obliquely across the shelf between the 60 and 120 m isobaths the predicted deposit locations for the low and high energy periods respectively were consistent with short and long term observed accumulation patterns based on 7 be and 210 pb activity kniskern t a kuehl s a harris c k carter l 2010 sediment accumulation patterns and fine scale strata formation on the waiapu river shelf new zealand marine geology 270 188 201 gravity flows were mainly wave supported landward of the 60 m isobath but became increasingly current supported as wave orbital velocity attenuated in deeper water both analytical theory and numerical results indicated that wave supported gravity currents were sensitive to local water depth and favored deposition parallel to isobaths as depth increased in contrast current supported gravity currents were more sensitive to spatial variations in seabed slope with seaward decreases in slope and along shelf embayment of bathymetry favoring transport convergence and deposition we conclude that the longer term 100 yr shelf oblique mud deposit on the waiapu shelf mainly reflects current supported gravity flows responding to local variations in seabed slope and curvature of isobaths

high resolution numerical modeling of wave supported gravity driven mudflows 1 wave supported gravity driven mudflow has been identified as a major offshore fine sediment transport mechanism of terrestrial sediment into the coastal ocean this transport process essentially occurs within the wave boundary layer in this study wave supported gravity driven mudflow is investigated via a wave phase resolving high resolution numerical model for fluid mud transport the model results are verified with field observation of sediment concentration and near bed flow velocities at po prodelta the characteristics of wave supported gravity driven mudflows are diagnosed by varying the bed erodibility floc properties fractal dimension and rheological stresses in the numerical simulations model results for moderate concentration suggest that using an appropriately specified fractal dimension the dynamics of wave supported gravity driven mudflow can be predicted without explicitly incorporating rheological stress however incorporating rheological stress makes the results less sensitive to prescribed fractal dimension for high concentration conditions it is necessary to incorporate rheological stress in order to match observed intensity of downslope gravity driven current model results are further analyzed to evaluate and calibrate simple parameterizations analysis suggests that when neglecting rheological stress the drag coefficient decreases with increasing wave intensity and seems to follow a power law however when rheological stress is incorporated the resulting drag coefficient is more or less constant around 0 0013 for different wave intensities model results further suggest the bulk richardson number has a magnitude smaller than 0 25 and is essentially determined by the amount of available soft mud i e the erodibility suggesting a supply limited condition for unconsolidated mud

the assessment of chemical weathering rates within an upland catchment in north east scotland a study has been made of weathering in glendye an upland catchement of heather moorland underlain mainly by granite with some gneiss in north east scotland the concentrations of a range of elements and ions in precipitation and river water were measured over a twelve month period the total input and output of each element or ion was calculated the resulting balances show net outputs of all species except hydrogen ion large net outputs of silicon 38 5 kg ha 1 a 1 and bicarbonate 48 kg ha 1 a 1 indicate considerable chemical weathering a large net output of chloride 32 kg ha 1 a 1 indicates the importance of dry deposition of oceanic aerosols when this is allowed for the rate of output of elements due to weathering is si ca na mg k fe al these results were compared with the abundance of elements in bedrock and differential weathering ratios calculated these are compared with data from the hubbard brook study in new hampshire in both cases calcium is by far the most mobile element the relative importance of the atmosphere and of chemical weathering as sources of each element was calculated and the results compared with those of a study at wet sleddale in the lake district similar patterns emerge in both cases

structure and dynamics of fluid muds on the amazon continental shelf thick layers of fluid mud occur in strong tidal flows over the inner portion of the amazon continental shelf in regions of strong salinity fronts associated with the plume discharged from the amazon river detailed shipboard profile measurements obtained in this region during a multidisciplinary amazon shelf sediment study amasseds provide an unprecedented opportunity to examine the structure and dynamics of fluid muds under natural conditions the analysis focuses on flows in which the motion is fully turbulent and suspended sediment dominates the stratification under these conditions a comparison of measurements and one dimensional model calculations indicates that vertical transport is controlled by suppression of turbulent mixing at gradient richardson numbers near 1 4 this constraint produces a distinctive vertical structure and leads to an upper bound on the total amount of suspended sediment that may be carried in a turbulent suspension by a tidal flow

sediment sorting at the sand motor at storm and annual time scales bed sediment composition with a focus on the median grain size d50 was investigated at a large scale nourishment the sand motor at the dutch coast 21 5 million m3 sand considerable alongshore heterogeneity of the bed composition d50 was observed as the sand motor evolved over time with 1 coarsening of the exposed part of the sand motor 90 to 150 m and 2 a depositional area with relatively fine material 50 m finer just north and south of the sand motor the alongshore heterogeneity of the measured d50 values was most evident outside the surfzone i e seaward of msl 4 m coarsening of the bed after construction of the sand motor was attributed to hydrodynamic sorting processes because the alongshore heterogeneity of the d50 showed a similar spatial pattern as the mean bed shear stresses the observed alongshore heterogeneity of the d50 and correlation of d50 with modelled mean bed shear stresses suggest that preferential erosion of the finer sand fractions has taken place the selective transport of finer sand fractions results in a coarser top layer of the bed at the sand motor the preferential transport is most dominant during mild and moderate conditions when hydrodynamic forcing conditions are close to the critical bed shear stresses for transport the measurements also show the impact of a storm which consists of a 40 m finer d50 of the offshore bed composition in front of the sand motor i e where a considerably coarser bed was in place additionally storms may generate a temporary zone with fine bed material at the toe of the deposition profile this means that the coarsening of the bed is reduced by storms as a result of the mobilization of both coarse and fine sediment and mixing of the bed with the relatively finer substrate

cross shore transport of nearshore sediment by river plume frontal pumping we present a new mechanism for cross shore transport of fine sediment from the nearshore to the inner shelf resulting from the onshore propagation of river plume fronts onshore frontal propagation is observed in moorings and radar images which show that fronts penetrate onshore through the nearshore and surf zone almost to the waterline during frontal passage a two layer counterrotating velocity field characteristic of tidal straining is immediately set up generating a net offshore flow beneath the plume the seaward flow at depth carries with it high suspended sediment concentrations which appear to have been generated by wave resuspension in the nearshore region these observations describe a mechanism by which vertical density stratification can drive exchange of material between the nearshore region and the inner shelf to our knowledge these are the first observations of this frontal pumping mechanism which is expected to play an important role in sediment transport near river mouths

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

minerals formed and mineral formation from volcanic ash by weathering abstract weathering of volcanic ash and pumice is unique regarding minerals formed and mineral formation these minerals include allophane imogolite opaline silica and some halloysites and have distinctive structures and properties studies on the surface and subsurface weathering of various volcanic ashes in different settings are reviewed this review illustrates that relatively rapid weathering of finely comminuted volcanic ash well reflects the effects of climate vegetation and time and produces various combinations of weathering products the moisture regime the nature and amount of organic matter incorporated the deposition of volcanic ash as overburden and the chemical and mineralogical composition of parent ash are important in controlling the mineral formation in weathered volcanic ash

slow chemical weathering in a semiarid climate changes in the mineralogy and geochemistry of subaerial lava flows in the deschutes river basin central oregon abstract the progression of mineral alteration and chemical changes of thirteen pairs of fresh and weathered surficial lava samples from the deschutes river basin of central oregon were studied to understand incipient weathering in a semiarid climate samples range from basalt to dacite in composition and quaternary to late miocene in age only the tertiary samples showed significant chemical weathering based on element mobility and mineral alteration the slight climatic variations between tertiary outcrop locations map 38 74 cm yr and mat of 7 2 7 6 c did not correlate with degree of weathering the susceptibility sequence of phases was determined to be glass olivine plagioclase orthopyroxene clinopyroxene fe ti oxides the older weathered samples have experienced significant leaching of mobile cations e g ca mg sr resulting in a lower calculated weathering index the tertiary weathered samples are enriched in ree particularly lree which is attributed to a lree phosphate found in association with allophane clay mineralization in plagioclase these samples also have a negative ce anomaly likely due to its tetravalent state in oxidizing conditions and subsequent lack of mobility in weathering solutions although there is a clear petrographic and chemical distinction between fresh and weathered lavas 2 ma the distinction between fresh and weathered samples is not evident in the quaternary lavas significant element mobility between sample pairs is closely correlated to the breakdown of plagioclase and orthopyroxene and the subsequent secondary mineralization of clays and or lree rich phosphates with the exception of plagioclase all the mineral phases in the deschutes lavas have persistence times or stability of at least one and possibly several orders of magnitude greater than the same phases in soil chronosequences or weathering rinds in more temperate and humid climates as a result elemental release rates and silicate fluxes are much lower under semiarid conditions and their role in the global carbon cycle should be examined more closely

stratigraphy age and correlation of two widespread late holocene tephras preserved within lake kutubu southern highlands province papua new guinea sediment cores were retrieved from lake kutubu the largest upland lake in papua new guinea to assess palaeoenvironmental baselines two prominent tephra layers were encountered within the cores using a combination of core stratigraphy sediment properties and geochemical characterization electron microprobe and laser ablation inductively coupled plasma mass spectrometry techniques we were able to correlate these tephras with tibito and olgaboli tephras both previously described at adjacent distal localities glass shard compositional data of tibito tephra from lake kutubu kuk swamp and from proximal volcaniclastic successions from long island are indistinguishable and this similarity strongly supports long island as the eruptive source for olgaboli tephra the location of its eruptive source is less certain but the glass shard compositional data indicate a karkar island source the occurrence of tibito and olgaboli tephras in lake kubutu sediments extends their known distributions further south west into the southern highlands region and affirms their importance as inter regional stratigraphic markers of late holocene age that have considerable potential for use in future palaeoenvironmental archaeological and volcanic hazard and or impact studies

the impact of storms and stratification on sediment transport in the rhine region of freshwater influence we present measurements of along and across shore sediment transport in a region of the dutch coast 10 km north of the rhine river mouth this section of the coast is characterized by strong vertical density stratification because it is within the midfield region of the rhine region of freshwater influence where processes typical of the far field such as tidal straining are modified by the passage of distinct freshwater lenses at the surface the experiment captured two storms and a wide range of wind wave tidal and stratification conditions we focus primarily on the mechanisms leading to cross shore sediment flux at a mooring location in 12 m of water which are responsible for the exchange of sediment between the nearshore and the inner shelf net transport during storms was directed offshore and influenced by cross shelf winds while net transport during spring tides was determined by the mean state of stratification tidal straining dominated during neap tides however cross shore transport was negligible due to small sediment concentrations the passage of freshwater lenses manifested as strong pulses of offshore transport primarily during spring tides we observe that both barotropic and baroclinic processes are relevant for cross shore transport at depth and since transport rates due to these competing processes were similar the net transport direction will be determined by the frequency and sequencing of these modes of transport based on our observations we find that wind and wave driven transport during storms tends move fine sediment offshore while calmer more stratified conditions move it back onshore

erosional and chemical denudation rates in the southwestern idaho batholith annual erosional denudation ed and chemical denudation cd rates are determined on four forested watersheds located in the idaho batholith idaho u s a bedrock in the study area is a coarse grained quartz monzonite annual sediment yields are computed from sediment collected in settling ponds at the watershed mouths and corrected for trapping efficiency solution loads for denudation components na k ca mg sio2 a12o3 and feo are computed using equations relating concentration to flow and by integration of mean daily flow values eleven years of water chemistry data and 19 to 23 years of sediment yield data are used in the denudation estimates strong relationships exist between cd ed and annual water yield so probability distributions of annual water yield are used in monte carlo simulations to establish frequency distributions of annual cd and ed rates mean annual total denudation for the four watersheds cd ed equals 235 kg ha 1 yr 1 or 8 9 bubnoffs the 11 year mean ed rates exceed cd rates for three of the four watersheds although it is more probable in any given year that cd will exceed ed for three of the watersheds ed is temporally more variable than cd for all watersheds simulations of denudation over 1000 year periods indicate that the frequency of occurrence of ed is skewed toward higher denudation values and the modal ed rate is substantially lower than the mean value cd rates are less skewed with mean and mode in the same class ninety seven per cent of cd is composed of na ca and sio2 fluxes episodic high ed rates are related to high peak flows from snowmelt runoff associated with winters of large snow accumulation perturbations such as fire or road construction would be expected to accelerate ed more than cd

wave generation of gravity driven sediment flows on a predominantly sandy seabed wave supported gravity flows wsgfs generate rates of sediment flux far exceeding other cross shelf transport processes contributing disproportionately to shelf morphology and net cross shelf fluxes of sediment in many regions worldwide however the conditions deemed necessary for the formation of wsgf limit them to a narrow set of shelf conditions they have been observed exclusively in regions where the seabed consists of very fine grained sediment and typically co occur with nearby river flood events here we document the occurrence of a wsgf event on a predominantly sandy seabed and in the absence of a preceding river flood our measurements confirm that the dynamics are governed by the friction buoyancy balance observed in other wsgf and that wsgf can form in mixed grain size environments and transport high concentrations of sand the occurrence of wsgf on a predominantly sandy seabed suggests that they may occur under a much wider range of conditions and given the global prevalence of sandy shelves they may be a more frequent and more ubiquitous feature of shelf dynamics than previously thought

downstream changes in antimony and arsenic speciation in sediments at a mesothermal gold deposit in british columbia canada abstract this study investigates sb speciation in sediments along the drainage of the upper peter adit at the bralorne au mine in southern british columbia canada and compares the behavior of sb with that of as the upper peter mineralization consists of native au in quartz carbonate veins with 1 wt sulfides dominated by pyrite and arsenopyrite although stibnite the primary sb bearing sulfide mineral can be locally significant dissolved sb concentrations can reach up to 349 g l 1 in the mine pool sediments were collected for detailed geochemical and mineralogical characterization at locations along the 350 m flow path which includes a 100 m shallow channel within the adit a sediment settling pond about 45 m beyond the adit portal and an open wetland another 120 m farther downstream from the mine pool to the wetland outlet dissolved sb in the drainage drops from 199 g l 1 to below the detection limit due to the combined effect of dilution and removal from solution speciation analyses using x ray absorption near edge structure xanes spectroscopy indicate that sb iii s accounts for around 70 of total sb in the sediments in the main pool at the far end of the adit at a short distance 24 m downstream of the main adit pool however sb iii o and sb v o species represent 50 of total sb in the bulk sediments indicating significant oxidation of the primary sulfides inside the adit although sb appears largely oxidized in the bulk samples collected near the portal sb iii s species are nevertheless present in the

gravity driven sediment transport on the continental shelf implications for equilibrium profiles near river mouths an analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward convex upward portion of subaqueous deltas and clinoforms the model builds on recent field results demonstrating that gravity driven flux of suspended mud is important on shelves provided that wave induced suspension of sediment supports the requisite turbid hyperpycnal layer because the maximum sediment load is determined by the critical richardson number the results are independent of the properties of the suspended mud or the bed the model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave supported turbid near bed layers progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity the model is consistent with shelf profiles off the mouths of the eel california ganges brahmaputra bangladesh waiapu new zealand po italy and rhone france rivers the equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only with deeper and broader profiles associated with decreasing sediment supply increasing wave height and or increasing wave period

flood dispersal and deposition by near bed gravitational sediment flows and oceanographic transport a numerical modeling study of the eel river shelf northern california 1 a large flood of the eel river northern california created a thick sediment deposit between water depths of 50 and 70 m in january 1997 the freshwater plume however confined sediment delivery to water depths shallower than 30 m mechanisms proposed to explain the apparent cross shelf transport include dispersal by oceanographic currents resuspension by energetic waves and gravitationally forced transport of a thin layer of fluidized mud field observations indicate that these processes were all active but cannot determine their relative significance or whether these mechanisms alone explain the location size and timing of deposition approximately 30 of the sediment delivered by the eel river is accounted for in the midshelf mud bed and inner shelf but the fate of the remaining 70 is uncertain a three dimensional hydrodynamic model was used to examine potential mechanisms of sediment transport on the eel river shelf the model includes suspended sediment transport and was modified to account for a thin near bed layer of fluidized mud it was used to simulate flood dispersal on the eel river shelf to compare the relative importance of transport within the near bed fluid mud layer to suspended sediment transport and to evaluate sediment budgets for floods settling properties of fine grained sediment both within the flood plume and the fluid mud layer critically impact depositional patterns to a lesser degree wind driven ocean currents influence the volume of sediment that escapes the shelf and wave magnitude affects the cross shelf location of flood deposits though dilute suspension accounts for a large fraction of total flux cross shelf transport by gravitational forcing appears necessary to produce a midshelf mud deposit similar in volume location and timing to those seen offshore of the eel river

episodic holocene loess deposition in central nebraska abstract the mirdan canal section in central nebraska usa provides evidence for multiple episodes of holocene loess deposition in the central great plains this irrigation canal cut exposes more than 4 m of holocene sediment that overlies the late wisconsinan peoria loess the oldest holocene sediment is local slopewash that fills gullies but overlying beds are interpreted as holocene loess bignell loess three buried soil profiles occur within the holocene sediment and have yielded uncalibrated 14 c ages of 3010 yr bp uppermost buried soil and 8790 yr bp third buried soil from top a fourth buried soil yielded an age of 9330 yr bp and is correlated with the brady soil the bignell loess has a darker color slightly more organic matter more clay more coarse silt and sand less smectite and less volcanic glass than the underlying peoria loess the bignell loess is most plausibly interpreted as dust from local flood plains containing a mixture of reworked peoria loess and older silts with contrasting mineralogy episodes of loess deposition occurred in the early middle and late holocene probably during periods of dry climate but possibly also as a consequence of large erosive floods that made wind erodible sediment available on nearby flood plains

towards a weathering model of mount lamington ash papua new guinea abstract the mount lamington ash halo has been studied at six sites both close to and distant from the volcano negligible alumina occurs in the seepage waters from the ash and so alumina is assumed constant during weathering in andesitic ashes weathering to allophane an approximation to a first order reaction was found in 1968 and is confirmed here with given infiltration and silica concentration the weathering rate constant decreases with increasing content of weathering minerals and increasing thickness of ash being weathered the rate constant also increased with increasing infiltration and decreasing median size of the ash the total weathering rate is the product of the thickness percentage of ash being weathered and the weathering rate constant the total weathering rate is the same for thick less weathered proximal ashes as it is for the thin more weathered distal ashes first order kinetics imply a high rate of leaching decreasing with time but continual burial under new ash at a nearly constant rate leads to linear leaching of the upper part of the profile the leaching rate decreases exponentially with depth and appears to ignore buried topsoil barriers it is possible to construct weathering models exploring the rate constant and to link it with leaching rates two thirds of the loss on weathering is silica and there is a total leaching rate of 3 4 mg sio 2 cm 2 year 1 as on basalt in hawaii and on andesite in st vincent water analyses show silica concentrations in the ash of 17 35 ppm and in draining streamlets of 9 20 ppm measured concentrations agree with calculated concentrations from the weathering data silica concentrations are similar in other humid tropical rivers

some observations on the chemical weathering of the dartmoor granite the majority of geomorphological papers about dartmoor have been essentially speculative particularly when discussing weathering processes and the evolution of the dartmoor landscape in contrast this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of dartmoor granite through the systematic analysis of soil and water samples this involved the computation of a geochemical budget to determine the amount of erosion in the catchment as well as more detailed mineralogical investigations within a soil profile the annual output of solutes due to weathering was 116 kg ha 1 a 1 of which the majority was silica 93 kg ha 1 a 1 from an examination of the soil mineralogy it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha 1 a 1 plagioclase 90 kg ha 1 a 1 biotite and 40 kg ha 1 a 1 orthoclase as well as the weathering of granite there was also the production of kaolinite 150 kg ha 1 a 1 and gibbsite 0 02 kg ha 1 a 1 analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith although in areas where interflow was the dominant mode of water movement the solute composition was in equilibrium with both kaolinite and gibbsite examination of the clay mineralogy confirmed these results the microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil silica was found precipitated on all the grains examined but the maximum amount occurred in the bs horizon this evidence showed that firstly the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and secondly that models of granite weathering must take localized weathering in the soil profile into account the final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon particularly where there are high volumes of interflow at hill crest sites observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions

trace element zoning in dolomite proton microprobe data and thermodynamic constraints on fluid compositions abstract lower cretaceous euhedral dolomite crystals from the gargano peninsula italy have been analyzed by scanning proton microprobe spm for the trace elements sr zn fe mn cu ni y and rb intricate decoupled zoning patterns for fe mn and zn are a ubiquitous feature of the outer 55 microns of the dolomite crystals differences between peak and baseline concentrations are on the order of several hundred parts per million in contrast sr concentrations are nearly constant at 110 ppm the concentrations of the other cations are all low cu 20 ppm y 10 ppm and ni and rb 5 ppm in order to investigate the origin of the gargano dolomite we have used the method of tardy and garrels to estimate equilibrium partition coefficients for divalent cations between aqueous fluids and the dolomite structure 18o measurements on gargano dolomites show that they formed at a maximum temperature of 75 c 7 c estimated equilibrium constants for substitution of the cation m into dolomite calculated baseline molar cation ratios for fluids in equilibrium with gargano dolomite and measured cation ratios for seawater and marine sediment pore fluids at 75 c are as follows m n k eq log10 calculated ratio log10m n measured ratio in seawater log10m n measured ratio marine pore fluids mn mg 1 27 4 62 7 17 2 75 fe mg 12 66 4 77 6 57 3 81 zn mg 6 85 5 27 6 72 4 84 sr ca 0 17 2 94 1 92 1 83 cation ratios of fluids in equilibrium with the baseline concentrations of mn fe and zn in the gargano dolomite samples are bracketed by the cation ratios measured in seawater and in marine sediment pore fluids the factor often discrepancy for sr in the predicted fluid compared with seawater is probably due to nonideal mixing of sr on the ca site the decoupled fluctuations of the mn and fe concentrations in these samples can be explained by eh fluctuations in the reactant fluid zn fluctuations may be a product of ph dependent oxide surface reactions to test this hypothesis of origin unzoned tertiary dolomites from enewetak atoll and from the bahama bank have also been analyzed the homogeneous sr concentration in the gargano dolomite is similar to the sr concentrations measured in the enewetak atoll 175 ppm and bahama bank 150 ppm dolomites samples which in both cases almost certainly grew in equilibrium with seawater gargano baseline mn 20 ppm and fe 80 ppm concentrations are also much the same as the bahama bank dolomite mn 15 ppm and fe 140 ppm concentrations the lack of sr zoning in the gargano samples and the similarity of their sr mn and fe content to dolomite that formed in equilibrium with seawater indicates that the dolomitizing fluid was most likely seawater or a seawater type brine low sr concentrations 12 ppm in pore filling calcite from the gargano suggests that in contrast to the dolomite the calcite precipitated from meteoric fluids

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

geochemistry of mine waters draining a low sulfide gold quartz vein deposit bralorne british columbia abstract the bralorne and pioneer mines now inactive produced over 4 million ounces of au from an orogenic lode au deposit located on the eastern edge of the coastal mountains of sw british columbia between 2007 and 2009 drainage from a recently developed exploration adit was investigated in order to better understand and anticipate potential environmental management issues associated with the development of this type of deposit in the future portal discharge rate and specific conductance were monitored continuously over a 14 month period during which 36 water samples were collected additional samples were collected from flooded workings within the adit concentrations of as and sb at the portal range as high as 1738 and 316 g l respectively while those in the mine pool reach 3304 and 349 g l respectively effluent chemistry is mildly alkaline ph 8 7 and is dominated by na ca mg hco3 and so4 geochemical inverse modeling of effluent composition indicates weathering of albite 2515 kg a ferroan dolomite 718 kg a pyrite 456 kg a arsenopyrite 23 kg a and stibnite 2 kg a modeled sulfide reaction coefficients normalized by their corresponding host rock concentrations suggest that oxidation of arsenopyrite is 25 times slower than that of pyrite whereas oxidation of stibnite is 1 5 times faster oxidative dissolution of arsenopyrite and stibnite releases 10 6 kg a of as and 1 1 kg a of sb of which 57 and 46 respectively are sorbed to ferrihydrite and gibbsite on the bed of the shallow channel through which the mine pool drains to the portal although mass balance calculations predict the formation of sufficient ferrihydrite to sorb 100 of the as dissolved in the mine pool this attenuation process was ineffective possibly because the precipitated sorbents settled to the bottom of the water column or because of competition for sorption sites from ca and hco3 the dissolved sb as molar ratio in portal effluent 0 082 is much greater than the sb as ratio of the mineralization 0 002 because of slower arsenopyrite oxidation and somewhat lesser sorption of sb

field weathering rates of mt st helens tephra the initial stages of chemical weathering in tephra were examined under field conditions in a cool and humid forest ecosystem in the cascade mountains of washington unleached tephra from the 1980 eruption of mt st helens was applied in 5 cm and 15 cm depths to simulate natural tephra deposition leachate solutions from the tephra were then collected and analyzed over a 4 year period concentrations of dissolved elements were combined with the water fluxes to determine elemental fluxes from tephra and to estimate chemical weathering rates solutions leached from the tephra layer indicate incongruent dissolution resulting in formation of a cation depleted silica rich leached layer on glass and mineral surfaces measured weathering rates were 1 3 orders of magnitude less than comparable rates reported in the literature for laboratory dissolution studies but considerably greater than those measured for entire watersheds in field studies dissociation of carbonic acid originating primarily from upward transport of carbon dioxide from the buried soil was the dominant source of protons for weathering reactions weathering rates in the 5 cm treatment were approximately twice those of the 15 cm treatment a greater flux of co2 per unit volume of tephra in the 5 cm treatment is believed to be responsible for the differential weathering rates

wave enhanced sediment gravity flows and mud dispersal across continental shelves reappraising sediment transport processes operating in ancient mudstone successions recent studies of marine shelf sediment dispersal show that wave enhanced sediment gravity flows are widespread phenomena and can transport large volumes of fluid mud rapidly across low gradient shelves flow evolution is controlled by sediment supply seabed gradient and spatial distribution of wave energy at the seabed using existing flow models we predict that such flows in mud dominated sediments will develop a three part microstratigraphy produced by changing flow conditions beginning with wave induced turbulent resuspension then development of a wave enhanced sediment gravity flow prior to lutocline collapse and suspension settling petrographic examination of modern flow deposits collected from the eel shelf reveals that resultant beds possess a microstratigraphy consistent with our hypothesis a silt rich basal subunit with curved ripple laminae abruptly overlain by a subunit composed of continuous intercalated silt clay laminae and an upper clay rich drape analyses of beds from ancient mud rich outer shelf and basinal successions cleveland ironstone jurassic uk and mowry shale cretaceous united states show that they too contain beds with this three part organization suggesting that such flows were active in these ancient settings too recognition of these microstructures in these ancient mud dominated successions demonstrates that sediment in these settings was commonly reworked and transported advectively downslope by high energy events contrasting with previous interpretations of these units that deposition was dominated by quiescent suspension settling identification of these recognition criteria now allows the products of this newly recognized sediment dispersal mechanism to be identified in other shale dominated successions