deformational history of an archean fold belt eastern point lake area slave structural province n w t archean metasedimentary rocks in the eastern point lake area of the slave structural province preserve a sequence of archean structures consisting of two generations of folds f1 and f2 with littl

k feldspar megacrysts in granites phenocrysts not porphyroblasts abstract k feldspar megacrysts in granitoid plutons have been interpreted as either phenocrysts or porphyroblasts most of the microstructural mineralogical and chemical evidence e g shape alignment concentration ba content zoning inclusions and twinning favours a phenocryst origin the main features that have been used to support a porphyroblast origin are occurrence of megacrysts 1 across aplite vein boundaries 2 in country rocks and 3 in or across boundaries of microgranitoid enclaves mafic inclusions however these features can be explained by the phenocryst hypothesis in particular megacrysts in microgranitoid enclaves can be explained by growth or mixing in magma before a globule of that magma or a fragment of the resulting igneous rock was incorporated as an enclave all available evidence favours or is consistent with a phenocryst origin for k feldspar megacrysts in granitoid rocks and their enclaves the large size of the megacrysts is evidently due to nucleation difficulties for k feldspar in granitic melts though k feldspar is commonly the last mineral to begin crystallizing in granitic magmas abundant melt is still present at that stage allowing sufficient space for the megacrysts to grow the reason for the common lack of megacrysts in volcanic rocks may be that the phenocrysts do not grow large enough to be called megacrysts until the magma contains such a high proportion of crystals that it cannot erupt

two dimensional soil moisture flow in a sloping rectangular region experimental and numerical studies results from experiments with a 3 66 by 0 58 by 0 108 m flume filled with sand are used to study the two dimensional flow of soil moisture under the condition of rainfall infiltration the experimental results are compared to results obtained by a numerical solution via a finite element finite difference transformation of the two dimensional richards equation the results are presented in the form of flow field conditions hydraulic head distribution and position of the phreatic surface and the rising limb of the runoff hydrograph the experimental and the numerical results are in satisfactory agreement when the effect of capillary hysteresis is incorporated into the numerical solution when capillary hysteresis is ignored the numerically simulated hydrograph lags far behind the experimentally derived hydrograph

dolomite formation and biogeochemical cycles in the phanerozoic summary based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation the abundance and distribution of dolomite throughout the phanerozoic remains an enigma sometimes referred to as the dolomite problem comparing dolomite abundance to secular variation in seawater chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have caused it the recently formulated microbial dolomite model provides the opportunity to view the geological history of dolomite formation from a new perspective a biogeochemical approach to the dolomite problem reveals a plausible connection between phanerozoic geochemical cycles and dolomite formation in particular periods of more extensive dolomitization broadly correlate with diverse indicators of decreased oxygen levels in the atmosphere and oceans lowered oxygen levels would have fostered a more active community of anaerobic microbes including sulphate reducing bacteria which in turn could have led to more extensive dolomitization of marine carbonates

surface hydrology iv flow in sloping layered soil in a nonuniform soil with rotational symmetry the properties change along a coordinate n that forms an angle ia n with the vertical during infiltration there will be a flow component in the parallel direction s downstream which is proportional to the rain itself and the slope the horizontal flow is proportional to the vertical flow the slope and the coefficient of anisotropy the last has been calculated for a soil made up distinct layers in the limiting case of very thin layers or near the saturation point the vertical and horizontal conductivities are respectively the expected arithmetic and harmonic means familiar from saturated flow the coefficient of anisotropy increases with the rate of vertical flow to a power greater than unity the horizontal flow component can be many times the vertical one it finds application in pollution problems and in the study of the underground water regime

the diversion capacity of capillary barriers an arrangement of unsaturated fine grained soil overlying unsaturated coarse grained soil along a sloping contact can under appropriate circumstances divert infiltrating water away from the coarser material such an arrangement is called a capillary barrier the water diverted by a capillary barrier flows downdip above the contact the volume of water moving laterally increases in the downdip direction as additional infiltration is diverted by the barrier sufficiently far downdip the laterally moving water wets the contact to the point that an amount of water equal to the infiltration flows downward through the coarse soil the lateral flow at such a point represents the diversion capacity of the capillary barrier because this flow will not increase farther downdip if the width measured in the direction of dip of the system is large enough that total infiltration exceeds the diversion capacity the downdip portion of the barrier will not be effective the diversion capacity can be calculated exactly in the quasi linear approximation where the relationship between relative permeability krel and pressure potential takes the form krel e this calculation shows that an upper bound on the width of capillary barriers is ks tan o q where ks is the saturated hydraulic conductivity of the fine soil o is the dip angle of the contact and q is the infiltration rate

surface hydrology iii causes of lateral flow streamlines bend after they enter a nonuniform sloping soil on penetrating to a more permeable soil layer they bend downstream this can occur in unsaturated soil above a sloping water table or in a layer in which water accumulates because of the presence of less permeable underlying layer we considered the general case of a nonuniform soil with rotational symmetry at an angle to the vertical i e a sloping soil general proof is provided that the soil generally behaves as a anisotropic medium so that infiltration also invloves a horizontal net flow component this net flow component is proportional to the slope the vertical flow and the coefficient of anisotropy the existence of such a mechanism can account for the concentration of water in concave spots possible seepage and runoff and erosion phenomena at low rates of rainfall it can also explain how a previous rainfall leads to earlier onset of runoff during the next rain etc

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

lateral moisture flow beneath a sandy hillslope without an apparent impeding layer part of a small drainage basin on the sevilleta national wildlife refuge about 25 km north of socorro nm was intensively instrumented with soil monitoring equipment to estimate natural ground water recharge soil moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand moisture content data were obtained by the neutron scattering technique and hydraulic head data were obtained using tensiometers in addition tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water the results indicate that there is a strong lateral component to unsaturated flow on a hillslope even in the absence of apparent sublayers of much lower permeability darcian calculations estimate the long term steady deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm the deep soil water flux downward varied by several orders of magnitude during the 17 month period of record

reactive transport modelling of the hydro geochemical behaviour of partially oxidized acid generating mine tailings with a monolayer cover abstract the efficiency of a monolayer cover to prevent acid mine drainage amd generation from two pre oxidized tailings impoundments was assessed using the min3p code a finite volume model for coupled groundwater flow oxygen diffusion and multi component reactive transport numerical simulations were validated using large column tests set up in the laboratory and monitored during 19 wetting and drying cycles over approximately two years results indicate that a monolayer cover made of either non acid generating tailings or a till was not able to prevent sulfide oxidation in the underlying reactive tailings both for the conditions applied in the laboratory and under conditions more representative of field observations the efficiency of the simulated monolayer cover was highly dependent on the position of the water table despite improved water quality the reactive tailings nonetheless continued to oxidize and generate amd even when the water table was close to the surface of the tailings 1 m depth the results from this study indicate that the efficiency criteria for cover systems on fresh unoxidized tailings may not be directly applicable for pre oxidized tailings the paper also presents a few modifications to the min3p code that were successfully applied to simulate the hydrogeological and geochemical response of pre oxidized already acidic and highly contaminated tailings

multiphase deformation and displacement within a basement complex on a continental margin the wudang complex in the qinling orogen china abstract the structural evolution of the wudang complex in the foreland of the southern qinling has been resolved through detailed field mapping and microstructural analysis four major deformational episodes were developed within the complex these involved 1 1 accretion of preliminary continental nuclei to form the basement of the south china block in the late mesoproterozoic early neoproterozoic 2 2 extension and subsidence of the continental margin associated with accumulation of thick sediments from the end of the neoproterozoic to the mid triassic 3 3 thrust stacking of basement and cover during collision detachment orogenesis in the late triassic to early cretaceous and 4 4 development of intermontane basins since the late cretaceous the wudang complex including the wudang and yaolinghe groups is considered mesoproterozoic in age based on 1 recent isotopic data such as a 1304 ma zircon age and 2 recognition of new stratigraphie and structural relationships such as the supposed discontinuous sedimentary contact between the yaolinghe group and sinian rocks which actually is a detachment zone wide ranging isotopic ages in the wudang complex could be due to 1 emplacement of new material associated with magma during extension of the continental margin and 2 reworking and overprinting of early fabrics during basement subsidence and burial the mesozoic orogeny resulted in renewed intense deformation of the basement complex but preservation of early fabrics in these rocks allowed analysis of the kinematics of proterozoic accretion on the northern margin of the preliminary continental nuclei the foliation intersection axes fia preserved in porphyroblasts within the wudang complex display a consistent 115 trend independent of the strike of bedding and late foliations this suggests that the bulk orientation of material movement may have been about n25 e to s25 w during that accretion event

laboratory and numerical modeling of water balance in a layered sloped soil cover with channel flow pathway over mine waste rock macropores developed in barrier layers in soil covers overlying acid generating waste rock may produce preferential flow through the barrier layers and compromise cover performance however little has been published on the effects of preferential flow on water balance in soil covers in the current study an inclined layered soil cover with a 10 cm wide sand filled channel pathway in a silty clay barrier layer was built over reactive waste rock in the laboratory the channel or preferential flow pathway represented the aggregate of cracks or fissures that may occur in the barrier during compaction and or climate induced deterioration precipitation runoff interflow percolation and water content were recorded during the test a commercial software vadose w was used to simulate the measured water balance and to conduct further sensitivity analysis on the effects of the location of the channel and the saturated hydraulic conductivity of the channel material on water balance the maximum percolation 80 1 of the total precipitation was obtained when the distance between the mid point of the channel pathway and the highest point on the slope accounted for 71 of the total horizontal length of the soil cover the modeled percolation increased steadily with an increase in the hydraulic conductivity of the channel material percolation was found to be sensitive to the location of the channel and the saturated hydraulic conductivity of the channel material confirming that proper cover design and construction should aim at minimizing the development of vertical preferential flow in barrier layers the sum of percolation and interflow was relatively constant when the location of the channel changed along the slope which may be helpful in locating preferential flow pathways and repairing the barrier

oxygen influx and geochemistry of percolate water from reactive mine waste rock underlying a sloping channelled soil cover an ideal engineered soil cover can mitigate acid rock drainage ard by limiting water and gaseous o2 ingress into an underlying waste rock pile however the barrier layer in the soil cover almost invariably tends to develop cracks or fractures after placement these cracks may change water flow and o2 transport in the soil cover and decrease performance in the long run the present study employed a 10 cmwide sand filled channel installed in a soil barrier layer silty clay to model the aggregate of cracks or fractures that may be present in the cover the soil cover had a slope of 20 oxygen transport through the soil cover and oxidation of the underlying waste rock were investigated and compared to a controlled column test with bare waste rock without soil cover moreover gaseous o2 transport in the soil cover with channel and its sensitivity to channel location as well as the influence of the saturated hydraulic conductivity of the channel material were modeled using the commercial software vadose w the results indicted that the waste rock underlying the soil cover with channel had a lower oxidation rate than the waste rock without cover because of reduced o2 ingress and water flushing in the soil cover with channel which meant a partial soil cover might still be effective to some extent in reducing ard generation gaseous o2 ingress into the covered waste rock was more sensitive to the channel location than to the saturated hydraulic conductivity of the material filling the channel aqueous equilibrium speciation modeling and scanning electron microscopy with energy dispersive x ray analysis indicated that secondary minerals formed as a result of the oxidation of the waste rock included gypsum and goethite in the covered waste rock and schwertmannite and other fe oxides in the uncovered waste rock the findings of the study provided insight into the effect of channel flow on o2 transport and oxidation of the covered waste rock which may help to improve soil cover design and construction to minimise the generation of preferential flow in the barrier layer

the behavior of inclined covers used as oxygen barriers covers with capillary barrier effects ccbe have been recently proposed as a viable option for gas migration barriers however the effect of geometry on ccbe performance has not been clearly demonstrated in this paper the results of a laboratory study performed with an original apparatus called the inclined box are presented the results obtained show that the hydraulic behavior of layered covers is influenced by the inclination of the slope generally the upper part of the slope contains less water than the lower part this means that the upper part is less efficient than the lower part for limiting gas migration the authors have also studied an existing site where a ccbe was built on a sloping surface after validation of the numerical model with in situ measured data the model was used to perform a parametric study to quantify the influence of the main ccbe parameters on its performance the results obtained confirm those measured in the lab and clearly show how geometry influences the performan

modelling and field measurements of water percolation through an experimental soil cover on mine tailings a composite soil cover constructed on acid producing tailings was evaluated for its ability to retain a high degree of water saturation and low hydraulic conductivity the cover consisted of a 60 c

design and laboratory verification of a physical model of sloping capillary barrier a physical model was designed and constructed to study the mechanisms associated with capillary barriers for slope stabilization purposes prior to construction of the model various numerical anal

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

lateral flow in a layered profile of an infinite uniform slope a numerical solution was used to calculate vertical infiltration of rainfall into a periodic layered profile of an infinite uniform slope the calculated pressure head distribution within the profile was then used to evaluate transient un saturated lateral flow in the slope which is not limited to the existence of an impervious barrier because of the pressure line distribution within the layers the horizontal component of the lateral flow changes direction from one layer to another as a result the net discharge across the profile can be directed upstream during the initial stages of infiltration into a relatively dry profile over longer times it is always directed downstream and its value is proportional to the slope this indicates that the layered soil profile behaves as an anisotropy media on the point scales and on the average for a two periodic layered profile the total volume that passes in the direction parallel to the slope is very nearly proportional to the square of the total rainfall and it is represented versus the accumulated rainwater by one curve for all rainfall intensities thus the total rainfall is controlling the rate of lateral flow rather than the rainfall intensity the thickness of the soil layers has only a secondary effect on lateral flow the net volume that moves horizontally is a potential source for water accumulation at concave parts of a regular slope this water accumulation can form saturated or near saturated wedges that may contribute to surface runoff generation at these partial areas for cases of low rainfall intensities and short ponding times these wet zones of the hillslope may also contribute massive recharge of water and chemicals if exist to groundwater in narrow columns

on the secular variations in the composition of phanerozoic marine potash evaporites in a recent paper l a hardie proposed that the secular changes in the mineralogy of marine nonskeletal limestones and in the mineralogy of marine potash evaporites during the phanerozoic are the result of changes in the composition of seawater caused primarily by fluctuations in the flux of seawater through mid ocean ridges he suggested that even quite small variations 25 in this flux have a profound effect on the composition of seawater we show that the effects of changes in the hydrothermal flux are much smaller than he proposed nevertheless a doubling of the hydrothermal flux could probably alter the composition of seawater sufficiently to affect the mineralogy of marine potash evaporites an alternative explanation for the variations in the mineralogy of these deposits invokes differences in the degree of dolomitization during the evaporation of seawater the apparent near constancy of the k sup content of seawater during the phanerozoic supports this hypothesis it seems likely that during periods of rapid seafloor spreading the rate of seawater cycling is greater than today that sea level is higher that very large carbonate platforms are more abundant and that changes in seawater chemistry together with increases in dolomitization during the evaporation of seawatermore lead to mgso sub 4 free potash deposits the relative importance of these several effects can probably be determined with certainty only when we have analyses of relatively unaltered seawater from the several phanerozoic periods 27 refs 1 fig 1 tab less

water flow in unsaturated soil in layered slopes abstract the water flow in unsaturated soil in layered slopes sandwiching coarse materials was measured using inclined soil containers placed under a rain simulator the refraction law of water flow in saturated soils was extended to the flow in unsaturated soils the extended refraction law of water flow in saturated and unsaturated soils was applied to the flow at the interface between the masa sandy loam and either the plant or gravel layer using a jump condition and particular assumptions of hydraulic conductivity of materials the data obtained on infiltration steady percolation and drainage in the soil containers could be well explained by the proposed new concept of saturated and unsaturated refraction flow so far as we know the work reported here is the first specifically designed to elucidate the effects of abrupt change of hydraulic conductivity on the flow of water in unsaturated soil slopes

field determination of sulphide oxidation rates in mine tailings a field study was conducted to assess the rates of oxygen consumption in the vadose zone of sulphide mine tailings oxygen uptake rates were measured directly at the ground surface and were compared to rates of sulphate production in the tailings profile a nonreactive tracer gas was also used to assess effective diffusion coefficients in the shallow subsurface the 26 measurement sites were located within a 0 1 km2 area in tailings with a water table depth ranging from 0 6 m to ponding at the surface ambient oxygen consumption rates in the 8 year old tailings were compared to measurements through 0 2 m thick covers of fine sand and 0 2 m layers of fresh tailings replacing oxidized tailings at ground surface the oxygen flux across the tailings surface ranged from 0 1 to 250 mol o2 m 2 yr 1 for ambient oxidation conditions fresh tailings at the surface produced rates that were as much as twice the ambient rates the 0 2 m fine sand cover lowered rates by a factor of 100 below ambient rates sulphate production rates agreed well with oxygen consumption measurements independent diffusion flux measurements with a nonreactive gas exhibited an excellent correlation with oxygen uptake fluxes indicating the dominance of oxygen diffusion in the control of oxidation rates in the tailings spatial trends in oxidation rates were consistent with depth to the water table and temporal changes by as much as a factor of 2 were attributed to a 0 16 m variation in the depth to the water table over a 2 week period the results of this study support the use of simple fickian models to evaluate oxygen diffusion and oxidation rates in sulphide tailings

deformed conglomerates and textural zones in the otago schists south island new zealand abstract the prehnite pumpellyite to greenschist facies rocks of the classic low grade otago schist terrane are subdivided into a number of textural zones based on the development of slaty cleavage and the appearance of segregation lamination in metagreywackes in this study conglomerates from fifteen localities have been studied in order to investigate the relationship between ductile strain and the sequence of textural zones strain measurements on lithic pebbles show a clear correlation between strain and textural zone ranging from around 40 shortening in tz iia with the development of slaty cleavage to more than 70 in tz iiia corresponding to the appearence of segregation lamination the much lower and more prolate strains of the quartzose pebbles compared to the corresponding lithic clasts may be explained by differential strain partitioning between clast and matrix microstructural evidence including well developed strain shadows and solution seams indicates that solution transfer was the dominant deformation mechanism the development of quartz segregation laminae in tz iii is due to three related processes the development of mica rich solution seams demarcating quartzo feldspathic microlithons the development of amalgamated and recrystallised strain shadow overgrowths on clastic grains and the formation rotation and disruption of early formed veins the large increase in strain from tz ii to tz iii is responsible both for increased segregation and for the rotation and flattening of segregation features into the foliation thus producing a segregation lamination large strains developed by solution transfer during the low grade metamorphism of greywackes will lead inevitably to segregated schists

rheological implications of heterogeneous deformation at multiple scales in the late cretaceous sierra nevada california late cretaceous deformation in the east central sierra nevada arc of california was heterogeneous at multiple scales we quantify this heterogeneous deformation at centimeter meter and kilometer scales in the vicinity of the gem lake shear zone and infer variations in effective viscosity from our data at the centimeter scale variations in strain of different clast types in conglomerate suggest that effective viscosities varied by less than an order of magnitude lithology controlled the magnitude and nature of deformation recorded by clasts at the meter scale cleavage refraction between stratigraphic layers records variations in finite strain comparison of our observations with cleavage refraction models suggests a maximum effective viscosity contrast of 10 between layers bulk composition controls variations in deformation of the different layers at the kilometer scale variation in finite strain magnitude and orientation in similar rock types both within and outside the shear zone demonstrates that deformation inside the zone was relatively intense comparing these results to numerical models of heterogeneous regional deformation we estimate that the angle of oblique convergence inside the zone was 15 10 while outside it was greater than 60 these kilometer scale results imply regional deformation was moderately strike slip partitioned during the late cretaceous and suggest regional effective viscosity varied by a factor between 6 and 17 at each scale of observation the apparent range of effective viscosity varies by an order of magnitude or less consequently we infer that relatively modest strength variations produced the structures observed at hand sample to tectonic scales

performance of an instrumented slope covered by a capillary barrier system abstracta capillary barrier as a cover system is a two layer system of distinct hydraulic properties to prevent water infiltration into the underlying soil by utilizing unsaturated soil mechanics principles this paper illustrates the application of the capillary barrier system on a slope that experienced shallow slip failures to prevent future rainfall induced slope failures in this study the capillary barrier system was designed as a cover system for residual soil slopes with a steep slope angle under heavy rainfall conditions of the tropics the capillary barrier system was constructed using fine sand as the fine grained layer and granite chips as the coarse grained layer both layers were contained in a cellular confinement system the slope was instrumented with tensiometers and piezometers the tensiometers were installed at different depths from about 0 5 m to 2 0 m below the slope surface an adjacent original slope without the capillary barrier system was also instrumented using tensiometers to

the long term impact of magnesium in seawater on foraminiferal mineralogy mechanism and consequences foraminifera are unicellular protists primarily known for their calcium carbonate shells that provide an extensive fossil record this record ranging from cambrian to present shows both major shifts and gradual changes in the relative occurrence of taxa producing different polymorphs of carbonate here we present evidence for coupling between shifts in calcite versus aragonite producing species and periods with respectively low and high seawater mg ca throughout the phanerozoic during periods when seawater mg ca is 2 mol mol low mg calcite producing species dominate the foraminiferal community vice versa high mg calcite and aragonite producing species are more abundant during periods with relatively high seawater mg ca this alteration in dominance of the phase precipitated is due to selective recovery of groups producing the favorable polymorph after shifts from calcite to aragonite seas in addition relatively high extinction rates of species producing the mineral phase not favored by the seawater mg ca of that time may be responsible for this alteration these results imply that the current high seawater mg ca will in the long term favor prevalence of high mg and aragonite producing foraminifera over calcite producing taxa possibly shifting the balance toward a community in which calcite production is less dominant

echinoderm skeletal preservation calcite aragonite seas and the mg ca ratio of phanerozoic oceans abstract the alternation between abiotic calcite and aragonite precipitation in shallow seawater and the oscillation of seawater mg ca ratio throughout the phanerozoic are both popular hypotheses echinoderms with well preserved stereom provide new empirical evidence that supports both these hypotheses analyses are reported from 29 specimens cambrian to eocene age containing ossicles preserved either as mg calcite 3 3 to 8 mole mgco3 or as mixed calcite and dolomite 5 to 12 5 mole mgco3 echinoderms with high mole mgco3 occur in the early cambrian and late carboniferous to triassic low values come from the silurian and jurassic to cretaceous the average composition of echinoderms with preserved stereom does not fall below 3 5 mol mgco3 during the phanerozoic and reaches its highest mean value of 16 0 mol mgco3 today an empirical partition coefficient of 0 03182 for modern tropical echinoids is used to indicate the mg ca ratio of ancient seawater from the mg ca ratio of fossil stereom some assumptions are involved and a likely error is calculated from the mg2 variation of modern echinoids high mean seawater mg ca ratios are calculated for early cambrian 3 3 and the late carboniferous to triassic 2 3 but never reached today s value of 5 2 low mg ca ratios 1 1 are indicated from jurassic to cretaceous echinoderms the 29 echinoderm samples plot close to first order mg ca seawater oscillations derived from geochemical models and mg ca ratios determined from fluid inclusions but considerable discrepancies exist when shorter 106 myr time intervals are considered further data and improved understanding of mg partitioning is required before accurate secular variation in the mg ca of seawater can be determined from echinoderms however they are an underused resource in this context and provide an excellent seawater archive

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

the role of bacterial sulfate reduction during dolomite precipitation implications from upper jurassic platform carbonates the early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine anoxic organic rich sediments dominated by bacterial sulfate reduction bsr in such environments bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non stoichiometric highly disordered and metastable proto dolomite although the boundary conditions for the formation of modern proto dolomites are considered to be generally understood the role of bsr during limestone dolomitization in ancient marine environments remains questionable herein we present a study about the physicochemical conditions and processes which led to the formation of partly dolomitized limestone and dolostone in the presence of bsr on a stable carbonate platform during the upper jurassic at oker northern german basin the dolomite textures the spatial trace elemental patterns of the dolomite and of the surrounding limestone and the results of 18o and 13c isotope analyses reveal that the oker dolomite has been formed by the early diagenetic replacement of magnesian calcite precursors at temperatures between 26 c and 37 c we interpret the mineralizing fluids responsible for dolomitization as pristine marine to slightly evaporitic and reducing seawater being modified during shallow seepage reflux and or evaporitic tidal pumping the elevated 34scas values 17 9 to 19 7 v cdt of the oker dolomite compared to ambient upper jurassic seawater indicate that bsr facilitated dolomite formation for the first time we show that a linear anti correlation exists between decreasing carbonate associated sulfate cas contents in dolomite and increasing ordering ratio of the dolomite lattice structure with the degree of cation order in dolomite to be given by degree of cation order dol 0 018 cas dol 68 3 r2 0 98 this correlation implies that the cas content of sedimentary dolomite can be used as a measure for dolomite maturity the relationships between the ambient paleo environmental controls the resultant dolomitization pathways and subsequently the structure and the composition of the precipitating dolomite are presented and discussed in relation to the stability of modern and ancient proto dolomites throughout burial diagenesis

discussion of variations in moisture content for a soil cover over a 10 year period the authors have presented a very interesting paper on the in situ behaviour of a soil cover constructed on a large waste rock pile as this type of cover is relatively new at least in the mining industry few investigations with such extensive field data have been reported in the literature this type of information is quite useful to those who must design cover systems as it brings an improved understanding of how such a complex system responds to actual field conditions the discussers and their collaborators have also been involved in somewhat similar projects e g ricard et al 1997 1999 bussiere et al 2003c dagenais et al 2005 and the results obtained from the corresponding monitoring and modelling programs have revealed similar trends many of the main findings presented by the authors are in close agreement with those gathered by the discussers the results confirm that under actual field conditions cover system behaviour is intrinsically dynamic and rarely if ever reaches a steady state under a relatively humid climate common in many parts of canada this means that the monitoring program and modelling work should focus on the transient conditions that dominate the cover response aubertin and bussiere 2001 aubertin et al 106 the authors results also show that a cover with capillary barrier effects ccbe can induce the favourable conditions required to control the production of acid rock or mine drainage ard or amd the authors should also be complimented for reporting on a diversity of performance indicators and for pointing out some of the challenges and difficulties encountered when monitoring the in situ behaviour of a ccbe on a large scale and in the interpretation of the data in the following paragraphs the discussers would like to draw attention to some complementary issues that may be of interest but were not addressed in detail in the authors paper however the authors have probably considered these issues elsewhere as mentioned by the authors in their paper and also pointed out in a recently published companion article fredlund and wilson 2006 soil covers seldom behave as a one dimensional system except for the relatively flat surfaces encountered on some tailing stacks the actual flow of water in a layered cover usually involves both vertical and lateral movements within and between the different soil layers in this regard previous work by aubertin et al 1997 and bussiere et al 2000 2003b has shown using numerical simulations and in situ observations that the difference in elevation between the bottom and top portions of an inclined cover can induce a significant suction gradient this in turn can create a variation in the moisture distribution in the cover along the slope in many instances there is a tendency for water to accumulate at lower elevations with increasing desaturation towards the top of the cover aubertin et al 1997 bussiere et al 2000 this is an important aspect of the behaviour of ccbes that may not have received enough attention in the past for inclined cover systems the local degree of saturation along the slope depends on many factors including the water retention curve of the materials particularly the air entry value aev of the moisture retaining layer the thickness of the layer s the water budget components and sequence the slope angle length and other geometric features such as benches bussiere et al 2003b it would thus be interesting if the authors could use available field data or new data gathered in the future to investigate how the slopes may influence the cover behaviour at the equity silver mine site in houston british columbia this aspect is important because as the authors pointed out a ccbe that aims to control the production of ard by reducing the oxygen flux must rely on a highly saturated layer to act as an oxygen barrier limiting oxygen penetration into reactive mine wastes has in fact been shown to be an effective control method that is well suited to relatively humid climates particularly on flat areas bussiere et al 2003b 2003c dagenais et al 2005 the cover geometry may however create additional difficulties in maintaining an effective oxygen barrier along the entire sloping area because the suction that develops at higher elevation can in some cases exceed the aev of the material used for the moisture retaining layer the conditions at the site described by the authors do not seem to have created such situations based on the properties given in the paper but it is not clear from the presented data if and how the

model of seawater composition for the phanerozoic we present an inverse model of phanerozoic seawater com position calibrated against updated paleoseawater compositions from fluid inclusions in marine halites the model considers step wise alteration of seawater composition via 1 variable input of river water 2 variable rates of alteration of seawater through reactions at mid ocean ridges and 3 variable rates of alteration of seawater through reactions on ridge flanks and across the ocean floor in general the model achieves agreement with paleoseawater fluid inclusion data for na 1 c a 2 1 s o 4 2 2 and k 1 particularly when variable runoff is considered variable rates of basalt seawater interactions at both ridges and ridge flanks are required to understand the evolution of seawater particularly the observed near constant concentration of k 1 through time

hillslope infiltration and lateral downslope unsaturated flow lateral downslope vadose flow occurs in hillslopes with deep homogeneous soils when and why this happens has been partially answered by past experimental numerical and quasi analytical studies what has been overlooked however is that lateral downslope flow in unlayered soils is largely a drainage phenomenon driven by the changing character of the boundary condition at the soil surface numerical simulations show that when rainfall ceases the near surface head gradient in a hillslope becomes nearly parallel to the slope as a simple consequence of the surfaces becoming a no flow boundary neglecting evaporation during rainfall infiltration is nearly vertical for most soils except those with high constant anisotropy

influence of clod size and water content on gas permeability of a compacted loess1 the northwestern region of china is mainly semi arid to arid and loess is ubiquitous this natural resource has considerable potential to be transformed into earthen final covers for local landfills but first its suitability must be ascertained through extensive tests in this study a device was developed to measure the gas permeability of unsaturated compacted loess specimens experiments were carried out to investigate the influence of clod size compaction water content and post compaction water content on the gas permeability of the compacted loess to maintain an identical soil structure the post compaction water content was changed using the osmotic technique it was found that the compaction water content and resultant soil clod size exerted a combined effect on the gas permeability such that at low water contents the gas permeability remained fairly constant but at high water contents the clods became relatively large and the effect of the clod size dominated the water blockage effect from

quartz c axis fabric differences between porphyroclasts and recrystallized grains abstract observed differences in c axis fabrics between quartz porphyroclasts and recrystallized quartz from the same quartzite samples suggest some changes in the fabric forming parameters during deformation the fabric patterns are consistent with a change in the incremental strain history from flattening to constriction during duplex development which is supported by the observed overprinting of structures in the field

design of a composite soil cover for an experimental waste rock pile near newcastle new brunswick canada the heath steele waste rock project was initiated in 1989 under canada s mine environment neutral drainage mend program to develop and test strategies for managing acid generating waste rock the

waste rock hydrogeology and geochemistry abstract the oxidation of sulfide minerals in waste rock has the potential to generate low quality drainage that can present a significant challenge to mine owners regulators and other stakeholders challenges involved in managing waste rock include the large volume of waste rock produced and the difficulty in predicting the quality and quantity of leach water due to the chemical and physical heterogeneities in the waste rock and the highly non linear coupling of geochemical and physical processes many important studies have been conducted over the past decade particularly at the field scale that have investigated the geochemical hydrological microbiological and gas and heat transport aspects of waste rock these studies show that although the parameters and processes that influence amd generation and solute release are fundamentally similar between different waste rock piles major differences in the dominant mechanisms of water gas and heat transport result from differences in the physical and mineralogical properties of the rock piles and the climatic conditions including the amount of precipitation and prevailing temperatures accurate prediction of the leach water quality from waste rock requires a detailed characterization of the properties of the rock piles and the coupling of processes specific to the particular conditions this paper provides a review of the physical and mineralogical characteristics of waste rock piles followed by a discussion of the principal processes related to sulfide oxidation and solute loading and concluding with a discussion on acid mine drainage prediction and prevention techniques

reactive transport modelling of mine tailings columns with capillarity induced high water saturation for preventing sulfide oxidation abstract a series of laboratory column tests on reactive mine tailings was numerically simulated to study the effect of high water saturation on preventing sulfide mineral oxidation and acid mine drainage amd the approach also known as an elevated water table ewt is a promising alternative to full water covers for the management and closure of sulfidic tailings impoundments and for the long term control of acid mine drainage the instrumented columns contained reactive tailings from the louvicourt mine quebec and were overlain by a protective sand cover over a 13 19 month period the columns were exposed to atmospheric o 2 and flushed approximately every month with demineralized water a free draining control column with no sand cover was also used during each cycle water table elevations were controlled by fixing the pressure at the column base and drainage water was collected and analyzed for ph and eh major ions and dissolved metals fe zn cu pb and mg the columns were simulated using the multi component reactive transport model min3p which solves the coupled nonlinear equations for transient water flow o 2 diffusion advective dispersive transport and kinetic geochemical reactions physical properties and mineralogical compositions for the material layers were obtained from independent laboratory data the simulated and observed data showed that as the water table elevation increased the effluent ph became more neutral and so 4 and dissolved metal concentrations decreased by factors on the order of 10 2 10 3 it is concluded that water table depths less than or equal to one half of the air entry value aev can keep mine tailings sufficiently saturated over the long term thus reducing sulfide oxidation and amd production

a predictive model for the water retention curve application to tailings from hard rock mines it is now commonly recognized that many geotechnical problems are related to the unsaturated behavior of soils such is the case for phenomena occurring at shallow depths in the so called vadose zone unsaturated flow is also very important for the management of milling wastes especially for seepage in and around tailings ponds suction properties constitute a key element for the functional representation of unsaturated flow conditions these are usually shown by the water retention curve which gives the relationship between volumetric water content theta and matric suction psi laboratory measurements have been performed on three different tailings from hard rock mines in the abitibi region to study the effect of various factors including grain size and porosity on the theta psi relationship the main results are presented in this paper the data are first analyzed using a well known descriptive model the experimental results are also used to estimate the air entry value according to vario

history of carbonate ion concentration over the last 100 million years abstract instead of having been more or less constant as once assumed it is now apparent that the major ion chemistry of the oceans has varied substantially over time for instance independent lines of evidence suggest that calcium concentration ca2 has approximately halved and magnesium concentration mg2 approximately doubled over the last 100 million years on the other hand the calcite compensation depth and hence the caco3 saturation has varied little over the last 100 my as documented in deep sea sediments we combine these pieces of evidence to develop a proxy for seawater carbonate ion concentration co32 over this period of time from the calcite saturation state which is proportional to the product of ca2 times co32 but also affected by mg2 we can calculate seawater co32 our results show that co32 has nearly quadrupled since the cretaceous furthermore by combining our co32 proxy with other carbonate system proxies we provide calculations of the entire seawater carbonate system and atmospheric co2 based on this reconstructed atmospheric co2 is relatively low in the miocene but high in the eocene finally we make a strong case that seawater ph has increased over the last 100 my

plate tectonic control on the evolution of cretaceous platform carbonate production carbonate producing biota on cretaceous carbonate platforms changed from early cretaceous aragonitic coral algal and coral rudist associations to turonian maastrichtian calcite dominated rudist associations abundance patterns of rudist bivalves examined from a large database show a shift from barremian cenomanian aragonite dominated to post cenomanian calcite dominated shells these skeletal mineral changes agree with a decrease in the mg ca ratio of seawater owing to high rates of production of oceanic crust during the barremian early turonian and its effect on seawater saturation with respect to aragonite and calcite increasing sr concentrations in biotic calcite from the barremian to the maastrichtian reflect the shift from aragonite dominated to calcite dominated platform sedimentation because aragonite precipitation is a major sink for seawater sr it is speculated that a particularly low mg ca ratio and the corresponding low supersaturation of seawater with respect to aragonite during the middle cretaceous was a major cue for the radiation of calcite dominated rudist bivalves which became important carbonate producers on turonian maastrichtian carbonate platforms changing mg ca ratios of seawater are not considered to have caused middle cretaceous crises in the evolution of carbonate platforms but seawater composition could have selected for calcite dominated biota when carbonate production resumed

k uptake by modern estuarine sediments during early marine diagenesis mississippi delta plain louisiana u s a abstract marine sediment porewaters are commonly depleted in k relative to conservative mixing trends but the mineralogical sink for k in the sediment has not been well characterized results are presented from a geochemical study of surface waters and porewaters and associated muddy sediments in the mississippi delta plain estuary spanning the salinity gradient from 0 12 evidence of k depletion in sediment porewaters is integrated with scanning transmission and analytical electron microscopy stem aem analyses of clay components to determine possible mineralogical sinks for k in the sediments conservative mixing between the freshwater influx from the atchafalaya mississippi river systems and gulf of mexico seawater controls the surface water major element composition porewaters from the most saline site however are depleted in k by up to 33 relative to overlying water implying uptake of k by the sediment textural characterization of the sediment at the same location by tem indicates that it is dominated by aggregates of highly disordered smectite rich clay material which is mixed with a small component of more ordered illite rich material aem compositions obtained on the most smectite like component in these aggregates indicates that the average k contents increase by up to 1 0 wt k2o relative to similar smectite rich clay in freshwater sediments ca2 concentrations in smectite rich clay decrease concomitantly whereas na concentrations are similar between the sites x ray diffraction xrd analyses confirm that smectite rich clay from the freshwater site has a larger interlayer spacing than smectite rich clay from the brackish water site consistent with exchange of smaller hydrated interlayer k na for larger ca2 mg2 aem data indicate that the discrete illite rich component also takes up k the integrated porewater and sediment analytical data imply that uptake of k by smectite rich clay is a rapid process decadal occurring at the earliest stages of diagenesis in estuarine environments upon exposure to brackish water our study shows that k uptake in marine sediments may not require the formation of authigenic minerals instead exchange of k for other interlayer cations in smectite rich clay and weathered illite may provide a substantial sink for k in the marine environment

colloquium 2004 hydrogeotechnical properties of hard rock tailings from metal mines and emerging geoenvironmental disposal approaches tailings are ground rock particles from which the valuable minerals or metals have been extracted an historical overview on hard rock mines shows that since the 1930s it has become current practice to pump the tailings into storage areas circumscribed by dykes made of the tailings themselves however numerous physical and chemical stability problems were observed mainly owing to the particular hydrogeotechnical and mineralogical properties of the tailings therefore modifications to the conventional methods were proposed but these were relatively costly not always efficient and sometimes difficult to implement new management methods that improve the physical and or chemical stability have hence been developed to reduce environmental risks associated with tailings storage namely densified tailings environmental desulphurization covers built with tailings and co disposal of tailings and waste rock even if many aspects need to be optimized these approaches can be considered today as interest

oxygen isotope and mg ca composition of late visean mississippian brachiopod shells from sw iberia palaeoclimatic and palaeogeographic implications in northern gondwana abstract latest visean brachiopod shells gigantoproductus sp from the pedroches basin of sw spain were sampled in order to obtain chemical and isotopic evidence that may help first to assess if primary geochemical and isotopical signals are preserved in these shells and second to reconstruct temporal variations in palaeoceanographic and palaeoclimatic conditions in northern gondwana during this time span microtexture cathodoluminescence cl and ultrastructure under sem of the brachiopods were examined to avoid sampling of shell portions altered after deposition shell portions classified as non luminescent nl and non luminescent to slightly luminescent nl sl present geochemical signatures within the ranges considered normal for recent brachiopods that have not undergone significant diagenetic modification these include low to undetectable fe and mn contents high sr values and 18o values similar to those of carbonates in equilibrium with seawater on the other hand valve areas that are luminescent l or moderately luminescent with luminescent portions ml l present higher fe and mn contents lower sr concentrations and lower 18o values than those corresponding to nl and nl sl shells this suggests a greater diagenetic alteration of these portions and that they acted as microzones of reaction with the diagenetic fluids temporal trends through the studied interval show a spread in 13c values much lower than that observed for contemporaneous samples up to 1 6 thus obscuring the 13c global signal at the time scale resolution of this study in contrast the 18o record of brachiopod calcite 18oc shows an overall increase of 1 relative to v pdb from the oldest to the youngest samples this is accompanied by a 30 decrease in mg ca ratios of the brachiopod calcites confirming that at least part of this shift in 18oc was related to cooling combination of mg ca and 18oc proxies established in this paper although not full proof for brachiopods yet allowed for the calculation of a temperature drop of 3 3 c and a change in seawater 18ow that becomes 0 4 more positive during this interval the data are consistent with regional seawater cooling that accompanied an increase in continental ice volume over a relatively short time period of

a deformed polymictic conglomerate the influence of grain size and composition on the mechanism and rate of deformation abstract in a deformed polymictic conglomerate from the hill end area new south wales australia almost all the strain is confined to fine grained quartz rich rock fragments coarse quartz and feldspar clasts generally show little evidence of intracrystalline plasticity the most strongly elongated rock fragments are finer grained and richer in layer silicates relative to quartz and feldspar indicating that both grain size and composition have influenced finite strain and thus strain rate the relationship between grain size and strain rate is broadly consistent with a dominance of grain boundary deformation mechanisms over intracrystalline dislocation mechanisms at finer grain sizes however strong quartz c axis preferred orientations have been measured in the most highly strained clasts implying a significant component of dislocation glide close examination of the microfabric mineralogy and petrology of the fine grained clasts shows that other factors are likely to have influenced their mechanical behaviour and led to enhancement of strain rate these factors include the trace element chemistry of the phases especially quartz the role of a mobile fluid phase the presence of poorly bonded mica 001 interfaces and the evolutionary nature of microfabric and mineralogy all of which are relevant to the bulk of crustal metamorphic rocks and should be taken into account in developing mechanical models of metamorphic belts

metamorphism and deformation mechanisms in the sierras australes fold and thrust belt buenos aires province argentina abstract the sierras australes fold and thrust belt is affected by an easternmost anchizonal metamorphism which grades into a western area of greenschist facies metamorphism both areas and their inferred boundary are distinguished on the basis of quartz recrystallization and illite crystallinity data during the first deformation pressure solution and grain boundary diffusion accompanied rigid body rotation and grain boundary gliding processes these mechanisms together with intracrystalline quartz deformation and recrystallization contributed to increasing rock ductility in the area of greenschist facies metamorphism two deformational events expressed by folding cleavage formation and thrusting were followed by static annealing of quartz which affects the southwestern part of the mountain range evidence for fluid and mass transfer also suggests convective fluid driven heat transport as an important mechanism for the final metamorphic overprint under static conditions

a master of the earth h d holland and his contributions to geochemistry abstract h d holland was one of the great geochemists of modern times as a professor at princeton university for 22 years and at harvard for 33 he mentored 24 graduate students and 24 postdoctoral researchers he was a member of the u s national academy of sciences and a president of the geochemical society he co authored 179 publications in 64 years from 1949 to 2012 including four books he edited one other book and with karl turekian co edited the ten volume treatise on geochemistry his contributions to geochemistry were mainly in economic geology hydrothermal processes and especially the chemistry and evolution of the earth s atmosphere and oceans a topic to which he devoted nearly half of his publications his most significant contributions documented changes in the composition of seawater through geologic time and the rise of oxygen in earth s atmosphere he pioneered the use of mineral sequences in marine evaporite deposits and fluid inclusions in evaporite minerals to determine the composition of ancient seawater he collected extensive data on paleosols and used them to calibrate the oxygen content of the ancient atmosphere documenting its rise in the great oxidation event that peaked between 2 41 and 2 32 ga and writing extensively about the causes of this event one of the most significant in earth history

preservation and evolution of quartz phenocrysts in deformed rhyolites from the proterozoic of southwestern north america abstract euhedral quartz phenocrysts quartz eyes are well preserved in ductilely deformed proterozoic metarhyolites in southwestern north america in a single sample the phenocrysts can range from undeformed to highly deformed and recrystallized matrix fabrics are extremely similar to those in undeformed ash flow tuffs the preservation of the phenocrysts reflects an efficient partitioning of strain from the phenocrysts into the finegrained wet and possibly glassy matrix variations in the degree of phenocryst deformation involve 1 the chemical and mechanical character of the original phenocryst 2 the degree to which matrix water has access to the quartz crystal and 3 crystallographic orientation phenocryst bearing metarhyolites are relatively strain insensitive but they contain important kinematic information even in recrystallized rocks where constraints on early structural events are rare most phenocrysts have asymmetrical tails shadows or deflected matrix foliations that indicate a consistent sense of shear throughout a sample or outcrop these deformation induced fabrics are readily distinguishable from primary fabrics in all but the lowest grade samples in the tusas mountains of northern new mexico and in the shylock fault zone of central arizona quartz eye metarhyolites have been useful in differentiating early thrusting and shortening events from later syn metamorphic events that dominate the microstructures and obscure the early tectonic history

numerical parametric study of an alternative three layer capillary barrier cover system a common practice for disposing of municipal waste is to dump it in landfills where it is then protected by a cover system the main purpose of this cover system is to minimise the amount of water percolating into the waste and hence to reduce the excessive formation of leachate to achieve this objective conventional landfill covers employ low permeability materials such as composite liners to meet the permeability design criterion however their long term hydraulic behaviour cost and shear resistance are not entirely satisfactory increasingly covers with capillary barrier effects ccbes have been considered as an alternative cover system in semi arid and arid regions it is questionable however whether ccbes can be successfully applied in humid climate conditions where the annual rainfall often exceeds 2000 mm in this paper an alternative three layer capillary barrier cover system for use in humid climates is proposed and its feasibility is investigated by a numerical parametric study this alternative system consists of a fine grained soil layer overlaying a coarse grained layer which in turn overlies a fine grained soil such as clay to minimise water percolation in humid climates this bottom clay layer is protected by the upper two coarser soil layers the factors considered in the numerical parametric finite element analyses include the thickness of this additional clay layer rainfall conditions and degrees of saturation of the municipal waste it was verified that the middle sand layer serves as a capillary break when the rainfall intensity is light or the duration is short after the upper two layers are permeated the bottom clay layer serves as an impeding layer whereas the sand layer shifts to serve as a lateral drainage layer it was also found that the amount of percolation increases with an increase in rainfall duration but decreases with saturation of the waste based on the six simulated durations of rainfall the most severe rainfall duration is 1 day irrespective of the return period

geological evolution of seawater boron isotopic composition recorded in evaporites the abundance of boron isotopes in ancient marine carbonates can be used to estimate oceanic ph that reflects atmospheric co 2 levels this proxy requires that the boron isotopic composition of seawater at the time the carbonate has formed is known and thus the past changes in seawater chemistry here we report the boron isotopic composition of selected ancient marine halites and modern sea salts the signal interpreted as marine reveals a clear evolution of the boron isotopic composition of seawater to 8 variations over the cenozoic comparison between this reconstructed curve and the mg ca ratio reveals a high level of consistency that will help to better define oceanic geochemical cycles

deev jahi model of the permian triassic boundary mass extinction a case for gas hydrates as the main cause of biological crisis on earth the smoking gun revealing the secrets of the end permian mass mortality is a unique 1 2 m thick layer consisting of 5 20 cm long crystals of calcite that occurs precisely at the permian triassic boundary ptb in iran armenia turkey and china this layer is interpreted as synsedimentary abiotic seafloor cement indicative of precipitation from a highly carbonate supersaturated seawater its 13 c composition 13 c 0 pdb is 4 to 5 pdb lower than the typical upper permian values 4 to 5 pdb suggesting the involvement of massive amounts of gas hydrate ch 4 13 c 60 pdb the temporal coincidence of the cement layer with the ptb suggests that the process that promoted seafloor cementation was also responsible for the biological crisis a cementation model is developed based on accumulation dissociation cycle of gas hydrates which also explains the mass extinction at the ptb the upper permian accumulation period of gas hydrates ended abruptly adjacent to the ptb and the dissociation event began releasing 3 2 to 4 7 10 18 g ch 4 into the ocean oxidation of ch 4 in the water column created a seawater that was charged with co 2 an oceanic acid bath and had lower than normal o 2 content but not anoxic this oceanic acid bath first dissolved suspended fine grained carbonate particles and small calcareous organisms followed by extensive dissolution of platform carbonates raising ca 2 and hco 3 concentrations of seawater when the release of ch 4 declined the acid bath ocean became a soda ocean precipitating massive amount of seafloor cements observed globally at the ptb the study suggests that prior to cement precipitation the ptb ocean was charged with co 2 warm had low oxygen high ca 2 and high hco 3 concentrations these conditions collectively created stressful conditions causing the marine mass mortality the leakage of ch 4 to the atmosphere produced a super hot climate resulting in the biological devastation on land the proposed kill mechanism is developed on the basis of the physical clue the cement layer left behind by the killing process the change in ocean chemistry the accumulation dissociation cycles of gas hydrates also explain the 13 c pattern of marine carbonates and the periodicity of mass extinction events during the phanerozoic accumulation periods were long 5 to 20 my providing favorable conditions for ecosystem development pardeess phase the dissociation events were short and catastrophic 10 to 500 ky causing low oxygenation super hot climate and biological devastation doozakh phase it appears that most mass extinctions of the phanerozoic have been related to the internal working of the earth system during the phanerozoic methane has played the role of the deev jahi a female demon in persian mythology whose task is to attack the earth every so often to kill life on land and in sea

testing models for obliquely plunging lineations in transpression a natural example and theoretical discussion theory predicts that stretching lineations in an ideal vertical transpressional zone should be either vertical or horizontal many field descriptions of transpressional zones however indicate a range of lineation orientations between these extremes several theoretical models have been developed to explain such departures from expected lineation orientation and we discuss these in the context of a field example from the archean superior province in the north american craton existing models are insufficient to explain obliquely plunging lineations in this example because 1 obliquely plunging lineations cannot be accounted for by shear zone boundary effects imposed by a no slip condition 2 foliations and lineations vary independently 3 the vorticity normal section is subhorizontal limiting possibilities for inclined simple shear 4 high vorticity is needed for finite strains and lineations to match previously proposed triclinic models but vorticity is relatively low and 5 juxtaposed east and west plunging lineations are unlikely in the previously proposed triclinic models because existing theoretical models are not applicable to our field example we contemplate a new model to explain obliquely plunging lineations within quasi homogeneous transpression

drainage from a uniform soil layer on a hillslope note 22 631 634 reference eflum article 1986 001 record created on 2005 09 08 modified on 2017 02 23

geochemical transport modelling of drainage from experimental mine tailings cells covered by capillary barriers the use of covers with capillary barrier effects ccbes for reducing acid mine drainage amd from sulphidic mine tailings is simulated using the min3p finite volume model for coupled groundwater flow o2 diffusion and multi component reactive transport the model is applied to simulate five pilot scale in situ test cells containing reactive tailings from the manitou mine site val d or que canada four of the cells were constructed with ccbes over the tailings while the fifth tailings cell was left uncovered observed and simulated discharge from the base of each cell showed that the capillary barrier covers significantly reduced sulphide oxidation and amd compared to acidic discharge from the uncovered cell discharge from the four ccbe covered cells had neutral ph levels and 1 7 orders of magnitude lower concentrations of so4 fe zn cu and al the simulations showed that the moisture retaining layer of the ccbes reduced amd by inhibiting o2 diffusion into the underlying reactive wastes provided the moisture retention layer of the ccbe remains close to saturation its thickness had a relatively minor effect under such near saturated conditions o2 availability is limited by its diffusion rate through the bulk porous medium and not by the diffusion rate through the oxidized grain shells the model is providing important new insights for comparing design alternatives for reducing or controlling amd

the origins of the mengye potash deposit in the lanping simao basin yunnan province western china abstract the lanping simao basin lsb is a mesozoic cenozoic continental margin rift basin in western china it formed during the opening and closing of the tethys ocean this basin is also known as a metal belt as it hosts several metal deposits besides the mengye potash deposit however the exact dates of the formation either in the paleocene or the cretaceous and thus the origins of the marine continental or mixed origins of the mengye deposits remain disputed based on the basin s evolution materials of marine origin and or remnant seawater should be present but instead the salt layers of the mengye potash deposit present typically continental lithological features this study examines and reviews evaporative minerals br cl and i cl molar ratios and isotopes of s b and sr i and i cl data for this area has not been previously reported the basin s evaporative minerals are dominated by halite and sylvite the amounts of anhydrite chlorocalcite langbeinite glaserite tachyhydrite and glauberite are small all of these form in both marine and continental environments the values of i and the i cl molar ratios of halite and sylvite are from 0 07 to 0 27 ppm and from 0 03 to 0 11 10 6 respectively dependent on organic substances br and molar br cl values are from 89 08 to 555 45 ppm and from 0 06 10 3 to 0 38 10 3 respectively all of the br cl molar ratios are lower than those of seawater and most of them are 34 s 11 b and 87 sr 86 sr values for evaporative minerals indicate a continental origin for the mengye potash deposit however materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit thus the mengye potash deposit could be of continental origin with a remnant seawater trace