lithium saltworks of the salar de atacama a model for mgso 4 free ancient potash deposits abstract potash basins similar to those in the geological past no longer exist at present there are only hypersaline lakes such as those in the tibetan plateau where carnallite kcl mgcl2 6h2o precipitates given that the purpose of common saltworks is to obtain nacl the halitic stage is not exceeded by contrast saltworks extracting lithium by solar evaporation reach more advanced stages of brine evolution and saline precipitation in the salar de atacama saltworks with a relative humidity commonly below 30 monthly average salts precipitate following a sequence of halite nacl sylvite kcl carnallite and bischofite mgcl2 6h2o and display a useful model of evolution similar to that which gave rise to mgso4 free potash deposits in the past prismatic acicular gypsum caso4 2h2o the main accessory mineral is transformed into a less hydrated calcium sulfate probably anhydrite caso4 during carnallite precipitation mineral crystal size and annual sedimentary thickness of each paragenesis are compared with those in ancient potash deposits the behavior of sylvite and carnallite as cements is observed at the onset of their precipitation in ponds where both minerals coexist with previous halite millimeter cyclicity due to day night thermal variations is observed in these saltworks whereas cm and mm cyclicities have been interpreted in ancient sites as annual regular and intra annual irregular respectively conditions similar to those existing at the salar de atacama were necessary to preserve carnallite which is commonly the most evolved mineral in the ancient deposits the development of potash deposits in the south pyrenean foreland basin and the rhine graben near the eocene oligocene boundary is attributed to global aridity and cooling and to the basin restriction associated with a decrease in the ocean level caused by the spread of the antarctic ice cap

felsic magmatic phases and the role of late stage aplitic dykes in the formation of the world class cantung tungsten skarn deposit northwest territories canada abstract a field and petro chemical classification of felsic magmatic phases fmps at the world class cantung w skarn deposit was undertaken to document the evolution of magmatism and the relationships between different fmps metasomatism and mineralization early fmps include moderately differentiated zr hf 18 26 ti zr 14 15 biotite monzogranitic plutons and early biotite rich granitic dykes and compositionally similar quartz feldspar porphyry dykes late highly fractionated zr hf 8 17 ti zr 3 13 fmps sourced from a deeper monzogranitic intrusion include 1 leucocratic biotite or tourmaline bearing dykes derived from localized entrapments of residual magma and 2 sub vertical ne trending aplitic dykes derived from a larger segregation of residual fluid and incompatible element enriched magma the aplitic dykes have textures morphologies spatial associations and a pervasive calcic metasomatic mineral assemblage ca plagioclase quartz or clinozoisite indicative of syn mineralization emplacement very late stage overpressuring and initiation of sub vertical fractures into the overlying plutonic carapace and country rocks by supercritical magmatic fluid led to an interaction with calcareous country rocks that resulted in an increased aca2 in the fluid and the concurrent precipitation of w skarn residual magma also ascended with and quenched in equilibrium with the magmatic fluid to from the aplitic dykes then was metasomatized by the fluid as it interacted with calcareous country rocks overall highly fractionated and moderately to very highly undercooled fmps at cantung provide evidence for a large and evolving felsic magmatic system at depth that segregated and maintained a stable fluid and incompatible element enriched residual magma until the latest stages of crystallization the detailed study of fmps associated with magmatic hydrothermal mineral deposits allow us to refine our understanding of these mineralizing systems and better define metallogenic and exploration models for intrusion related mineralization

the initiation of sedimentary furrows by standing internal waves longitudinal helical vortices are generally considered to be the cause of longitudinal sedimentary bedforms in tidal oscillatory flows however it is not clear how a regular system of vortices will become fixed for long enough to establish the bedforms it is proposed that the presence of standing internal waves with axes parallel to the tidal current have provided the basic flow pattern on which longitudinal helical vortices develop in southampton water the observed furrows then developed in a pattern determined by the standing internal waves

environmental implications of salt facies in the dead sea thick sequences of salt halite have been recovered in a 456 m long core drilled at the deepest floor of the dead sea by the dead sea deep drilling project and extending 200 k y back in time the salt sequences were precipitated in the ancient lake that occupied the dead sea basin during the last three interglacials during intervals of extreme aridity in the lake s watershed the salt layers alternate with mud layers that indicate wetter periods in the watershed when floods transported fine detritus matter to the lake the salt sources include brine discharge and freshwater runoff that dissolved halite units dissolved salts accumulated in the lake during glacials and relatively wet periods when the lake expanded and precipitated during interglacials when the lake levels dropped this study establishes for the first time the evaporite facies and sedimentological features of the deep dead sea brine during interglacial periods by using the modern precipitation of halite in the dead sea as an analogue for past halite depositional periods as recorded in the drill core the halite intervals provide a record of facies characterizing a deep water evaporitic environment the halite layers consist mainly of two types of crystals small cumulate crystals containing halite rafts which indicate precipitation from the surface brine of the lake epilimnion and bottom growth usually large halite crystals that precipitated on the lake floor hypolimnion the layers of small halite crystals formed during drier periods as compared to the bottom growth crystals the bottom growth halite crystals contain variable quantities of detritus and show mild dissolution structures at the contact between the mud and the halite crystals these two main types of halite in combination with muds and gypsum comprise seven categories of salt facies that reflect the hydrological conditions dry to wet and that display a cyclic decadal to millennial pattern along the sampled core intervals frequent alternation of these two salt crystal types suggests seasonal changes whereby the small cumulate crystals were formed during the summer and the bottom growth crystals were formed during the winter when the surface temperatures of the lake were low and the surface water was less saline and less likely to be saturated with respect to halite comparison of the last interglacial halite with the modern halite facies together with the absence of significant dissolution features within the halite and the cyclic nature of the facies indicates that the lake was continuously deep 100 m during the last 200 k y

dissolution kinetics of plagioclase in the melt of the system diopside albite anorthite and origin of dusty plagioclase in andesites the textures and kinetics of reaction between plagioclase and melts have been investigated experimentally and origin of dusty plagioclase in andesites has been discussed in the experiments plagioclase of different compositions an96 an61 an54 an23 and an22 surrounded by glasses of six different compositions in the system diopside albite anorthite was heated at temperatures ranging from 1 200 to 1 410 c for 30 min to 88 h textures were closely related to temperature and chemical compositions a crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt glass and remained its original euhedral shape below the liquidus whatever the temperature the crystal melt interface became rough and often more complicated sieve like texture composed of plagioclase melt mixture in the scale of a few m was developed from the surface of the crystal inward formation of mantled plagioclase if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase from these results the following two types of dissolution have been recognized 1 a crystal simply dissolves in the melt which is undersaturated with respect to the phase simple dissolution and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt partial dissolution the amount of a crystal dissolved and reacted increased proportional to the square root of time this suggests that these processes are controlled by diffusion probably in the crystal mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so called resorbed plagioclase in igneous rocks chemical compositions and textures of plagioclase phenocrysts in island arc andesites of magma mixing origin have been examined cores of clear and dusty plagioclase were clacic about an90 and sodic about an50 respectively this result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing

large deformation analysis of suction caisson installation in clay large deformation finite element ldfe analyses were performed to study the installation of caissons by suction and jacking in normally consolidated clay the penetration of the caisson wall was m

undrained deep penetration i shear stresses the penetration of sampling tubes and various in situ testing devices and the installation of deep foundation elements disturb the surrounding soil this paper presents approximate solutions for predicting shearing distortions and stresses in soil due to steady undrained deep penetration of a closed ended simple pile in an isotropic soil modelled as an elastic perfectly plastic material predictions are used to illustrate fundamental mechanisms of deep penetration and to identify important soil and pile characteristics that affect disturbance such as non linear and inelastic aspects of soil behaviour and the effects of scale la penetration des tubes de carottage des appareils de mesure pour des essais in situ et l installation des elements d une fondation profonde perturbent le sol environnant cet article presente des solutions approchees pour predire les distorsions de cisaillement et les contraintes dans le sol provoquees par la penetration profonde continue et non drainee d un pieu simple a ext

chemistry of modern soils as a guide to interpreting precambrian paleosols precambrian paleosols are potentially one of our best sources of information about the composition of the atmosphere early in earth s history to be used this way however an alteration profile must be shown to be an in situ product of vadose processes data from modern soils show that the ratios of less mobile elements such as zr ti and al can be used as a preliminary screen to test for the in situ nature of a profile if the ti zr ratio departs from that of the host rock by more than 40 or the ti al ratio departs by more than 50 for moderate degrees of weathering then a significant allochthonous contribution to the profile is indicated this technique correctly separates in place from allochthonous horizons when applied to independent data from two modern profiles a review of published precambrian profiles identifies two often cited examples denison and pronto as suspect based on these criteria in the interpretation of paleoatmospheres it is also necessary to show that fe is controlled not b

molybdenum isotopes in late archean carbonate rocks implications for early earth oxygenation abstract we present carbonate mo isotope data of the 2 64 2 5 ga old ghaap group transvaal supergroup south africa to contribute to the debate on early earth oxygenation mo fractionation in carbonates has just recently been introduced as a potential new proxy for ocean redox chemistry and it was suggested that under favorable conditions non skeletal carbonates closely monitor the ambient seawater 98 95 mo composition the record presented here is characterized by three phases of moderately to strongly fractionated 98 95 mo with values of up to 1 6 interrupted by two shifts towards detrital levels this near continuous presence of heavy 98 95 mo suggests a quasi permanent availability of free atmospheric o 2 because fractionation relative to the continental background signature occurs exclusively when mo is present as dissolved molybdate ions moo 4 2 we compare our carbonate data to a previously published black shale mo record on samples from the same drill core the general interpretation of both records is identical a rise in o 2 preceded the commonly accepted transition to a consistently oxygenated atmosphere by 150 ma however in the ghaap group carbonates fractionated mo is found at a time when the coeval black shales still indicate detrital sedimentation a combination of detritus admixture and or redox controlled mo isotope fractionation during shale formation in suboxic to anoxic waters is suggested as cause for a period characterized by a persistent offset between lighter shale and heavier carbonate 98 95 mo the apparent offset can then be attributed to the different geochemical behavior of the two archives with respect to the local depositional conditions redox vs non redox dependent such changes in the sedimentary environment might also explain why the carbonates do not reproduce rapid fluctuations found throughout the shale record but show a continuous signature with scarce outliers thus by means of the combined archives the conspicuous 98 95 mo scatter found in the shale record could be attributed to variable depositional conditions during its formation rather than global oxic anoxic fluctuations simultaneously the carbonates provide a better approximation of the long term 98 95 mo seawater evolution this study introduces the mo isotopic composition of carbonates as a promising new tool for paleo redox studies in particular when combined with black shales

science and empiricism in pile foundation design scientific approaches to pile design have advanced enormously in recent decades and yet still the most fundamental aspect of pile design that of estimating the axial capacity relies heavily upon empirical correlations improvements have been made in identifying the processes that occur within the critical zone of soil immediately surrounding the pile but quantification of the changes in stress and fabric is not straightforward this paper addresses the degree of confidence we can now place a on the conceptual and analytical frameworks for estimating pile capacity and b on the quantitative parameters required to achieve a design the discussion is restricted to driven piles in clays and siliceous sands with particular attention given to extrapolating from design approaches derived for closed ended piles of relatively small diameter to the large diameter open ended piles that are used routinely in the offshore industry from a practical viewpoint we need design approaches that minimise sensitivity

mudflat runnels evidence and importance of very shallow flows in intertidal morphodynamics 1 mudflats are often dissected by nearly parallel runnels separated by ridges high resolution data of tidal velocity and sediment concentration measured in a mudflat runnel in willapa bay washington state usa indicate that very shallow flows draining the mudflat platform are concentrated in the runnels these flows with water depths of few tens of centimeters are characterized by velocities close to the flood and ebb maxima associated to the regional flow when the mudflat is submerged the corresponding shear stresses are higher than the critical stress for erosion thus suggesting possible remobilization of surface sediments moreover suspended sediment concentrations in the runnel are greater than those associated with the regional tidal flow and comparable to concentrations during energetic wave conditions all this evidence indicates that shallow flows in runnels are important morphodynamic agents producing noteworthy geomorphic work

use of state dependent strength in estimating end bearing capacity of piles in sand the pressure and density dependence of the shear strength of sand poses a tricky problem in pile foundation design in this study a correlation is suggested to link the effective friction angle of sand with its initial confining pressure and relative density and a simple approach incorporating this correlation is presented for predicting pile end bearing capacity assessment of the approach against pile load tests shows reasonably good agreement between predictions and measurements it is also shown that the effect of the state dependent strength is particularly important in cases where long piles are installed in dense sand deposits and the use of critical state friction angle will produce a conservative prediction in such cases

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

pile and penetrometer end bearing resistance in two layered soil profiles the paper examines the influence of soil strength and stiffness on the end resistance mobilised by a cone or displacement pile in a two layered soil profile i e strong soil overlying or underlying weak soil the investigation involved a series of numerical analyses that idealise pile cone penetration assuming the spherical cavity expansion analogue it is shown how the end resistance mobilised by a penetrometer in a dense sand i e strong soil varies with the number of penetrometer diameters d from a weak soil assumed here to be either a loose sand or soft clay and depends on the ratio of the steady state penetration resistances of the strong and weak layers the penetrometer resistance in the weak soil is not affected by an adjacent strong layer at penetrations greater than 2d a design procedure based on a numerical parametric study is proposed and this is subsequently shown to compare well with centrifuge test data and with previous numerical research

origin of polyhalite deposits in the zechstein upper permian zdrada platform northern poland polyhalite deposits in the zechstein upper permian of northern poland occur in the lower werra anhydrite in the zdrada sulphate platform the polyhalite appears to be a very early replacement of anhydrite the replacement was caused by the halite precipitating brines which contained potassium and magnesium ions the formation of polyhalite was preceded by the syndepositional anhydritization of the original gypsum deposit which has often preserved its primary textures this anhydritization on the platform and its slopes was a reaction of the precipitated gypsum in a hydrologically open evaporite basin with brines of salt basins adjacent to the sulphate platform these brines when nearly saturated with respect to halite and potassium and magnesium rich reacted with anhydrite to precipitate polyhalite along the slopes of the zdrada platform the oxygen and sulphur isotopic compositions of sulphate evaporites indicate that marine solutions were the only source of sulphate ions supplied to the zechstein basin and that anhydrite was transformed to polyhalite by reaction with marine brines more concentrated than those that precipitated precursor calcium sulphate minerals

numerical simulation of piezocone dissipation test in clays the piezocone is one of the most widely used in situ tools with which to characterise the soil profile distinguishing different types of sediment and to provide quantitative data on the soil strength and consolidation characteristics for fine grained soils where penetration occurs under nominally undrained conditions consolidation characteristics are obtained from dissipation tests conducted with the piezocone brought to rest dissipation testing is interpreted to yield a coefficient of consolidation by comparison of the excess pore pressure decay with theoretical solutions it is generally acknowledged that the coefficient of consolidation derived from in situ dissipation tests will be greater by a factor of perhaps 2 to 10 than values derived from oedometer tests on samples recovered from the corresponding depth apart from potential differences in horizontal and vertical permeability differences arise from the influence of the rigidity index on the initial excess pore pressure field and the mor

exponential decay of concentration variance during magma mixing robustness of a volcanic chronometer and implications for the homogenization of chemical heterogeneities in magmatic systems abstract the mixing of magmas is a fundamental process in the earth system causing extreme compositional variations in igneous rocks this process can develop with different intensities both in space and time making the interpretation of compositional patterns in igneous rocks a petrological challenge as a time dependent process magma mixing has been suggested to preserve information about the time elapsed between the injection of a new magma into sub volcanic magma chambers and eruptions this allowed the use of magma mixing as an additional volcanological tool to infer the mixing to eruption timescales in spite of the potential of magma mixing processes to provide information about the timing of volcanic eruptions its statistical robustness is not yet established this represents a prerequisite to apply reliably this conceptual model here new chaotic magma mixing experiments were performed at different times using natural melts the degree of reproducibility of experimental results was tested repeating one experiment at the same starting conditions and comparing the compositional variability we further tested the robustness of the statistical analysis by randomly removing from the analysed dataset a progressively increasing number of samples results highlight the robustness of the method to derive empirical relationships linking the efficiency of chemical exchanges and mixing time these empirical relationships remain valid by removing up to 80 of the analytical determinations experimental results were applied to constrain the homogenization time of chemical heterogeneities in natural magmatic system during mixing the calculations show that when the mixing dynamics generate millimetre thick filaments homogenization timescales of the order of a few minutes are to be expected

chemical and boron isotope compositions of non marine brines from the qaidam basin qinghai china the general chemistry and boron isotope composition were investigated in fresh waters and hypersaline brines from the qaidam basin northern qinghai xizang tibet plateau china this basin is a large tectonically active system isolated from the ocean and composed of thick clastic and evaporite sediments the modern playas are subject to intense evaporation and are characterized by hypersaline brines as well as potash and borate evaporites the chemical composition of the dissolved solutes in the modern brines and waters reveals three main sources 1 inflow of hot springs enriched in sodium sulphate and boron evaporation of these waters leads to a high na cl ratio 1 a na cl so4 brine and an evaporite mineral assemblage of halite mirabilite borate lakes daqaidam and xiaoqaidam 2 inflow surface river waters which are modified by preferential dissolution of halite and potassium and magnesium salts characterized by a na mg cl solute type with low na cl 1 brcl licl and bcl ratios and 3 ca chloridic subsurface brines which are controlled by both salt dissolution and dolomitization processes evaporation and salt crystallization of mixtures of the latter two types leads to a marine like brine e g na mg cl type nacl ratio 1 and mineral assemblages similar to that predicted for progressive evaporation of seawater e g qarhan playa halite sylvite carnallite bischofite the 11 b values of the input waters to the qaidam basin range of 0 7 to 10 9 vs nbs 951 and brines from salt lakes 0 5 to 15 0 are similar to those of associated granitic rocks 11b 2 3 to 3 7 n 3 and hence indicate the non marine origin of these fluids the highest 11b values are associated with fluids with low bli ratios indicating selective removal of elemental boron and 10b by adsorption onto clay minerals the magnitude of 11b enrichment due to adsorption is 15 20 and thus non marine brines are well distinguished from marine derived brines 11b of 39 to 59 preserving the large isotopic difference 40 of their source waters it is proposed to use this distinctive isotopic signature for tracing the origin of ancient evaporite environments

dusty and honeycomb plagioclase indicators of processes in the uchino stratified magma chamber izu peninsula japan abstract two types of melt inclusion bearing plagioclase coexist in the uchino basalt izu peninsula japan 1 dusty plagioclase with an ab rich core mantled by a dusty zone consisting of more an rich plagioclase and fine melt inclusions and 2 honeycomb plagioclase with a central core containing larger melt inclusions the dusty plagioclase probably forms through partial dissolution of ab rich plagioclase as dusty zones truncate the concentric zonal structure of the ab rich inner core the honeycomb plagioclase is formed by skeletal growth under supercooling conditions this is indicated by the euhedral geometry of the boundary between the inner inclusion free and the outer inclusion bearing zones of the honeycomb plagioclase which has a concentric inner core bimodal distribution of the chemical compositions of phenocryst cores and assemblages in crystal clots suggest that hybridization of basaltic and andesitic magmas took place before crystallization of phenocryst rims the core rim boundaries of phenocrysts derived from the andesitic magma and the basaltic magma have a rounded and a euhedral geometry respectively this suggests the andesitic magma was heated and the basaltic magma was cooled prior to hybridization these features are consistent with the development of a thermal diffusive interface between overlying andesitic magma and underlying basaltic magma in a stratified magma chamber

dolomitization of a carbonate platform during late burial lower to middle cambrian shady dolomite virginia appalachians abstract outer platform carbonates of the lower to middle cambrian shady dolomite virginia appalachians record a lengthy and complex diagenetic history ranging from marine cementation to burial diagenesis during late paleozoic overthrusting analysis of petrographically well preserved marine cements has provided an estimate of the isotopic composition of lower cambrian marine carbonate 18o 7 5 to 6 1 pdb 13c 0 2 to 0 8 pdb 87sr 86sr 0 70869 to 0 70975 establishing a base line with which to assess later diagenetic carbonate meteoric dissolution and early calcite cement postdate marine cementation and formed during subaerial exposure the platform margin carbonates were extensively dolomitized dolomitization postdates calcite cementation and the initial development of stylolites and tectonic fractures several episodes of dolomite replacement and cementation are evident zone 1 dolomite consists of rare relict dolomite cores which were replaced and overgrown by zone 2a dolomite the dominant replacement phase zone 2a dolomite is depleted in 18o 18o 10 2 to 7 0 and enriched in 13c 13c 1 0 to 1 6 relative to marine carbonate reflecting precipitation from warm formation fluids buffered by the host carbonate uniformly low sr contents 25 to 65 ppm and nonradiogenic 87sr 86sr 0 70900 to 0 70971 also attest to pore water equilibration with the host rock replacement dolomitization was followed by widespread carbonate dissolution which formed vuggy porosity and local solution breccias the host dolomite locally is encrusted by mississippi valley type mvt occurrences of ore mineralization consisting of sphalerite galena and pyrite this major generation of ore minerals is overgrown by three generations of dolomite cement the first dolomite cement zone 2b has similar 18o composition 13o 10 3 to 7 4 but slightly depleted 13c values 13c 0 4 to 1 1 relative to zone 2a dolomite and has similar sr contents 30 to 45 ppm and 87sr 86sr ratios 0 70933 to 0 70966 zone 2b dolomite cement exhibits petrographic isotopic and geochemical affinities with zone 2a replacement dolomite implying that the two dolomite types formed from fluids of similar composition and temperature primary fluid inclusions in zone 2b dolomite indicate precipitation from warm minimum 120 to 150 c brines 23 26 wt nacl equiv these temperatures imply that the dolomitizing fluid was enriched in 18o due to extensive water rock interaction with host carbonate which also buffered the fluid 13c sr and 87sr 86sr content zones 3 and 4 dolomite cement are depleted in 18o 13o 13 8 to 11 3 relative to the previous dolomites implying a temperature increase to 150 to 210 c the late dolomite cements have 13c compositions 13c 0 7 to 0 9 ranging from those similar to the earlier dolomites to more depleted values zones 3 and 4 dolomite cement are enriched in sr 60 to 135 ppm which is radiogenic 87sr 86sr 0 71025 to 0 71445 these later cements thus record fluids that were no longer buffered by the host carbonate dolomite cements locally were overgrown by sphalerite followed by authigenic quartz and calcite cement secondary three phase fluid inclusions in quartz and calcite indicate hot 175 to 225 c saline 30 to 33 wt nacl equiv fluids temperatures and pressures interpreted from the fluid inclusions are compatible with estimated burial depths in excess of 5 km the dolomites formed during deep burial coeval with late paleozoic alleghanian age thrusting the mg required for burial dolomitization was derived from pressure solution of structurally lower platform interior dolomites that were overridden by the shady dolomite thrust sheet tectonic uplift and deformation resulted in regional fluid flow which transported this mg to the shady dolomite outer platform during burial dolomitization

melting kinetics of a plagioclase feldspar partial melting experiments on plagioclase feldspar have been carried out to investigate textures and kinetics of the melting a labradorite single crystal was heated at one atmosphere pressure and temperatures within its melting interval as a function of time so called honeycomb fingerprint or sieve textures were produced except for the runs just below the liquidus the melting was initiated by heterogeneous nucleation of melt at the surface and or interior cracks and possively dislocations of the crystal the pattern of the melt is dendritic with a few m arm spacing after the melt develops throughout the crystal the volumes of melt and residual crystal become larger and smaller respectively without changing the arm spacings the melt is homogeneous and has the approximate temperature dependent liquidus composition irrespective of the time there are compositional gradients in the residual crystal after short periods of melting the an content of the crystals increases with increasing time until it finally reaches equilibrium with the melt after several thousands minutes of heating it is concluded that the enlargement of the melt the main process of the melting is controlled by diffusion in the crystal the fact that partial melts have the composition of the equilibrium liquidus even from the first several minutes strongly suggests that the local equilibrium at the crystal liquid interface is satisfied during the melting some of the honeycomb fingerprint and sieve textures found in xenoliths and phenocrysts of sodic plagioclase in volcanic rocks would be caused by heating events such as magma mixing during which temperatures of magmas were temporarily higher than the solidus of some of the minerals

shaft friction from instrumented displacement piles in an uncemented calcareous sand abstractthe behavior of displacement piles in uncemented calcareous sand is investigated using field piles instrumented with a sensor that simultaneously records the radial stress and shear stress at specific locations on the pile shafts these tests are interpreted with the assistance of data from adjacent self boring pressuremeter tests and from monotonic and cyclic direct shear interface tests performed on reconstituted samples the existence of extremely low radial stresses on the pile shafts is verified although dilation during shear is seen to compensate for such low radial stresses short term shaft capacities are much lower than capacities of equivalent piles in siliceous sands the development of a bonded or welded crust to the pile shaft was seen to be the primary contributor to the setup observed at the test site this crust forced failure to take place at a sand sand rather than a sand steel interface and also gave rise to higher levels of dilation during monotonic loading the welded sand cr

a paleoweathering profile from griqualand west south africa evidence for a dramatic rise in atmospheric oxygen between 2 2 and 1 9 bybp a core drilled near wolhaarkop in griqualand west south africa intersected highly oxidized kuruman iron formation below red beds of the gamagara formation the lateral equivalents of the kuruman iron formation in this drill hole consist largely of siderite ankerite magnetite greenalite and quartz the oxidation of the kuruman iron formation in wol 2 occurred almost certainly during weathering prior to the deposition of the gamagara formation the date of this weathering episode is bracketed between about 2 2 and 1 9 bybp by the age of the ongeluk lavas in the transvaal sequence below the unconformity and by the age of the hartley lavas in the olifantshoek group above the unconformity the ratio of iron to sio2 in the several facies of the weathered kuruman iron formation in wol 2 is nearly the same as that in their unweathered equivalents since sio2 loss during weathering was almost certainly minor the similarity of the fe sio2 ratio in the weathered and unweathered bif indicates that nearly all the feo in the kuruman iron formation was oxidized and retained as feo3 during weathering such a high degree of iron retention is best explained by an o2 content of the atmosphere or 0 03 atm at the time of weathering such an o2 pressure is very much greater than that suggested by the composition of paleosols developed on basalt or 2 2 bybp but is consistent with the highly oxidized nature of the 1 85 by flin flon paleosol the new data suggest that po2 rose dramatically from about 1 percent pal present atmospheric level to or 15 percent pal between 2 2 and 1 9 bybp

classification of sedimentary furrows and a model for furrow initiation and evolution sedimentary furrows are longitudinal bed forms which form in fine grained cohesive sediments of the deep sea floor as well as in similar sediments in estuaries and in large lakes deep sea furrows have been observed where bottom currents often flow in one direction at 5 to 20 cm sec currents are much stronger greater than 50 cm sec in furrowed estuarine environments but sediment accumulation rates are higher a review of furrows studied in a variety of locations and environments suggests that these bed forms fall into two broad morphological classes those developed in muddy cohesive sediments tend to have steep walls and flat floors while those developed in carbonate rich cohesive sediments are broad and have gently sloping walls at abyssal depths furrows can often be detected by their distinctive echo patterns on 3 5 khz echo sounders a series of similar evenly spaced hyperbolic echoes which often have their apices tangent to the sea floor however different furrow cross sections may generate distinctive hyperbolic echo patterns a model for furrow initiation and development in muddy cohesive sediments suggests that furrows develop in depositional environments swept by recurring directionally stable and episodically strong currents furrows are initiated when secondary circulations in the boundary layer align coarse generally light debris in sand ribbon like bed forms as the coarse light sediments move along the sea floor they abrade small longitudinal troughs into the muds the grooves may fill in during intervals between strong current events if sedimentation rates are too high once a furrow is established on the sea floor further development may be controlled by the balance between sediment deposition and erosion where deposition occurs continuously and erosion occurs only episodically during brief periods of increased current strength narrow furrows width 1 5 to 1 15 of spacing appear to develop where deposition exceeds erosion whereas wide furrows width 1 2 of spacing develop where erosion exceeds or equals deposition dissolution may play an important role in the formation and evolution of furrows in carbonate rich cohesive sediments secondary circulation patterns over established furrows may be strongly controlled by bed form topography

design of driven piles in sand estimation of the axial capacity of piles driven into sand involves considerable uncertainty and design rules are generally not consistent with the physical processes involved this paper reviews current understanding of the factors that determine the axial capacity of piles driven into sand and outlines a new framework for design which takes account of the physical processes is consistent with the existing database of load test results and is sufficiently flexible to permit refinement as new data become available it allows for the effects of confining stress on the frictional and compressibility characteristics of sand and hence on end bearing capacity in keeping with field observations shaft friction is assumed to degrade with driving of the pile past a particular location from an initial maximum value linked to the local end bearing capacity the resulting design approach is compared with field data and effects of factors such as the direction of loading are discussed l estimation de la resi

sediment and basalt hosted regoliths in the huronian supergroup role of parent lithology in middle precambrian weathering profiles weathering profiles developed side by side on sandstone and a mafic dike provide an unusual opportunity to examine the role of parent rock bulk composition in the chemical evolution of middle precambrian regoliths because the profiles are adjacent to one another differences in topography can be eliminated in accounting for differences in the chemical evolution of the two profiles both profiles show upward increases in al ti k and rb and decreases in mg ca and na in addition the mafic regolith increases upward in zr and nb and decreases in zn and ni total fe decreases upward in both profiles but the sandstone profile retains significantly more of its initial fe than does the mafic dike this difference in fe loss is consistent with weathering in a low oxygen atmosphere of rock types with very different initial fe contents and therefore different atmospheric requirements for complete oxidation of the fe present the fe in the sandstone was mostly oxidized and retained within the profile whereas

geology and geochemistry of paleosols developed on the hekpoort basalt pretoria group south africa the hekpoort paleosols comprise a regional paleoweathering horizon developed on 2 224 0 021 ga basaltic andesite lavas at the top of the hekpoort formation of the pretoria group transvaal supergroup south africa in five separate profiles from outcrops along road cuts near waterval onder and the daspoort tunnel and in three drill cores from the bank break area bb3 bb8 and bb14 the top of the paleosol is a sericite rich zone the sericite zone grades downward into a chlorite rich zone in core bb8 and in the road cut at the daspoort tunnel we sampled the underlying or parent basaltic andesite into which the chlorite zone grades we did not obtain samples of the parent material at waterval onder and in cores bb3 and bb14 but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core bb8 and at the daspoort tunnel the presence of apparent rip up clasts of the paleosol in the overlying ironstones of the strubenkop formation in the cores from bank break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at waterval onder point to a subaerial weathering origin very little if any al ti zr v or cr moved a discernible distance during weathering of any of the five profiles the vertical distribution of fe mg mn ni and co indicates that these elements were largely removed from the top of the soil during weathering the overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an fe 2 rich smectite the loss of fe from the top of the soil during weathering of the hekpoort paleosols indicates that atmospheric p o 2 was less than 8 x 10 4 atm about 2 22 ga fe 2 rich smectite should only precipitate during soil formation if atmospheric p co 2 is less than or equal to 2 x 10 2 atm rye kuo and holland 1995 ca and na were largely lost during weathering some na was apparently added to the sericite zone in cores bb3 bb8 and bb14 after weathering all five profiles are enriched in k and rb and most are enriched in ba the distribution of these elements indicates that they all were added during post weathering hydrothermal metasomatism rb sr analysis of the paleosol at the daspoort tunnel indicates that metasomatism last affected that profile 1 925 0 032 ga macfarlane and holland 1991

carbon and sulfur isotopic compositions of organic carbon and pyrite in sediments from the transvaal supergroup south africa abstract sedimentary organic matter and pyrite from parts of the lower transvaal supergroup and few samples from the olifantshoek group have been studied for their carbon and sulfur isotopic compositions respectively carbon isotopic compositions for minimally altered organic matter range from 43 to 31 sulfur isotope values for sedimentary pyrite display values between 1 3 to 23 6 results from this and previously published work are being interpreted with respect to past biochemical pathways carbon isotope data indicate autotrophic carbon fixation as the process of primary production in addition products of secondary biological reworking contributed to the total organic carbon content sulfur isotope data indicate bacterial sulfate reduction as the main process however changes in sulfate availability and or the rate of sulfate reduction may have caused the observed range in isotopic compositions

stable isotopic compositions of carbonates from the mesoproterozoic bangemall group northwestern australia marine carbonate rocks from the mesoproterozoic bangemall group of northwestern australia show little deviation 1 3 in whole rock delta 13c carb values about a mean of 0 5 this narrow range persists despite close sampling every 10 20 m through long sections up to 2500 m that are geographically widespread up to 250 km apart over many depositional environments supralittoral to outer shelf sediment sources stromatolitic bioherms to detrital calcilutites and rock types pure limestones to dolomitic shales the only major excursions from the norm seem related to unusual environmental or post depositional processes as they are correlated with large enrichments to 3 or depletions to 16 in 18o relatively heavy delta 13c values up to 2 5 occur in a single bed of brecciated ferruginous dolostone at a single locality these abnormal values may result from local evaporitic conditions limey and shaley nodular dolostones have delta 13c values as low as 4 3 probably caused by remineralization of organic matter during late and patchy dolomitization most notably sharp negative excursions in delta 13c up to 8 4 occur in bleached kerogen free rocks with mineral assemblages of dolomite quartz calcite tremolite talc reflecting isotopic re equilibration in thick metamorphic aureoles around dolerite intrusions general environmental variations are minor with delta 13c values of peritidal facies tending to be slightly positive whereas those of subtidal facies are slightly negative there are no strong secular trends but subtle fluctuations within the range 2 to l can be correlated along the northwestern margin of the basin this resembles the pattern seen in other mesoproterozoic successions but is markedly unlike the heavy background 5 and extreme variations up to l0 in delta 13c evident in neoproterozoic successions of similar thickness and environmental setting hence in contrast to the neoproterozoic the global rate of organic carbon burial was probably fairly constant during deposition of the bangemall group and perhaps generally during the mesoproterozoic as was the redox state of the atmosphere and hydrosphere

pile aging in cohesive soils abstractthis paper presents the results of a field investigation into pile aging in soft clay that was conducted over a period of 10 years static load tests were conducted after the excess pore pressure generated by the installation of 6 m long driven concrete piles were fully equalized these tests allowed the time capacity aging profile to be established a normalized capacity time trend established for the case history is seen to be consistent with the response observed from a wider database of pile tests in clay compiled from the literature a simple reliability based design example is provided to highlight the positive impact that pile aging could have for industrial practice

oxide sulphide relationships in sodalite bearing metasomatites of the epembe swartbooisdrif alkaline province north west namibia the south eastern part of kunene intrusive complex kic namibia angola is host to volumetrically significant and economically important concentrations of sodalite in the area around swartbooisdrif north west namibia the mineralisation was formed by metasomatic exchange with carbonatites of the epembe swartbooisdrif alkaline province this process led to the breakdown of ore minerals initially present in various rock types of the kic and caused the formation of new opaque phases in the sodalite bearing metasomatites a detailed investigation of textures and chemical compositions of the fe ti oxides and sulphides has allowed evaluation of the complex ore forming processes related to the polyphase magmatic and metasomatic history of the sodalite deposit the predominant opaque phases in the various rock types of the kic are ilmenite and titano magnetite which are highly concentrated in the so called magnetite plugs it is clear from the textural evidence that most of the ilmenite and titano magnetite although of orthomagmatic origin recrystallised under subsolidus conditions conformably their respective chemical compositions and phase relations represented in the system feo 1 2fe2o3 tio2 point to re equilibration at temperatures below 600 c ilmenite and titano magnetite were affected by later deformation and decomposed by various reactions related to or outlasting the metasomatic process oxidation of ilmenite led to the formation of symplectitic aggregates of rutile and secondary magnetite carbonatisation of the fe ti oxides produced rutile and the siderite and rhodochrosite components in ankerite pyrite in part together with rutile and secondary magnetite was formed by sulphidation of the fe ti oxides conspicuous aggregates of granular or lamellar intergrowths of pyrite with hematite and or magnetite are interpreted as products of contemporaneous sulphidation and oxidation of former igneous pyrrhotite rarely observed pyrrhotite with pentlandite lamellae is probably not an igneous relic but was formed during the metasomatic event smaller amounts of chalcopyrite bornite digenite chalcocite galena ferroan siegenite millerite and polydymite testify to different cooling stages during or after metasomatism applying the phase relations in the simplified system fe co ni s o we were able to reconstruct a semi quantitative t f s2 f o2 path for the ore forming processes

ree chemistry and sm nd systematics of late archean weathering profiles in the fortescue group western australia two weathering profiles each consisting of an upper sericite rich zone and a lower chlorite rich zone are preserved between flows of the mt roe basalt in the fortescue group hamersley basin western australia ree concentrations in samples from these two profiles which originally developed ca 2 760 ma show large variations depending on stratigraphic position lree abundances and la yb n are greatest at depths of 3 6 m below the paleosurface of the mt roe 1 profile and are somewhat lower in samples above this level the lrees reach concentrations 6 9 times greater than in the underlying basalt and thus appear to have been mobilized downward in the paleosol and concentrated in its middle part lree concentrations in the 2 profile show a similar distribution but with a sharp increase in all ree concentrations within 50 cm of the paleosurface the distinction between the ree profiles in the two paleosols may be related to the difference in the overlying material the 1 paleosol is overlain by a few meters of sediments and then by basalt whereas the 2 paleosol is directly overlain by basalt the lrees appear to have been mobilized both during chemical weathering of the parental basalt and during later lower greenschist facies metamorphism and metasomatism of the paleosols remobilization of the rees during the regional metamorphism of the fortescue group is confirmed by a whole rock sm nd reference isochron of mt roe 1 samples with an age of 2 151 360 ma variable initial 143nd 144nd values of unweathered basalt samples which may represent the paleosol protolith prevents a confident determination of the magnitude of lree mobility both the initial mobilization of the rees during weathering and the metasomatic remobilization appear to have taken place under redox conditions where ce was present dominantly as ce3 because ce anomalies are not developed within the sericite zone samples regardless of concentration europium anomalies in the paleoweathering profile are somewhat variable and were probably modified by mobilization of eu2 at metamorphic conditions in all samples the hrees appear to have been relatively immobile and correlate with al ti cr v zr and nb sm nd systematics and ree patterns of four unweathered basalt samples indicate derivation of the mt roe basalts from a heterogeneous and enriched source having epsilon nd between 4 0 and 7 4 initial 143nd 144nd values of these basalts are even lower than those reported by nelson et al 1992 for fortescue group basalts and indicate a substantial crustal component in the generation of mt roe basalts

geochemical and mineralogic effects of contact metamorphism on banded iron formation an example from the transvaal basin south africa intrusion of a diabase sill into the paleoproterozoic kuruman iron formation transvaal basin south africa makes it possible to distinguish between effects of contact and regional metamorphism on mineralogic elemental and isotopic compositions of banded iron formation bif lithofacies temperatures within the aureole of contact metamorphism likely did not significantly exceed 450 c as suggested by the presence of early diagenetic carbonates greenalite and stilpnomelane formed prior to intrusion in chert rich facies as close as 4 m from the sill in sediments 32 m away from the intrusion a temperature of 280 c is indicated by the magnitude of 18o fractionation between successive chert and siderite microbands in unmetamorphosed equivalents similar isotopic analyses on whole rock samples yield temperature estimates between 150 and 230 c in comparison with samples of similar lithofacies from the underlying campbellrand kuruman transition zone carbonates from within the metamorphic aureole are depleted in 13c and 18o the abundance and c isotopic composition of total organic c toc in whole rock samples is lower and more enriched in 13c than those in samples outside of the zone of contact metamorphism within 5 m of the diabase sill the abundance of fe increases dramatically and the oxidation state of the sediments fluctuates considerably more than in sediments outside of the metamorphic aureole isotopic and mineralogic systematics in the zone of contact metamorphism in the kuruman iron formation are similar to those in siliceous dolomites and limestones altered by similar thermal processes as the most distinct isotopic and elemental variations occur within 10 m of the diabase sill it is suggested that volatilization and fluid infiltration associated with the intrusion were the main processes of alteration consideration of the effects of metamorphism both contact and regional as well as early diagenesis on the mineralogy and isotopic chemistry of bif sediments may be a key to our understanding of primary mineralogies and oxidation state of these enigmatic deposits

origin of mantle rapakivi feldspars experimental evidence of a dissolution and diffusion controlled mechanism experiments designed to simulate the dissolution of alkali feldspar during magma mixing produced plagioclase mantles that are texturally and compositionally similar to those in some hybrid volcanic rocks in hydrous dacite melt 69 sio2 at 0 8 gpa 850 c orthoclase or93 and sanidine or30 partially dissolved and were mantled by sodic plagioclase an25 30 although plagioclase nucleated epitaxially as a thin shell on the alkali feldspar surface near the time of initial resorption plagioclase subsequently grew inward mostly in the form of parallel blades toaard the receding dissolution surface orthoclase dissolved at a rate approximately proportional to the square root of run duration indicating diffusional control plagioclase grew inward within a static boundary zone of melt that formed between the original crystal dacite interface and the dissolution surface during orthoclase dissolution this boundary zone rapidly and simultancously gained na by diffusion from dacite and lost k by diffusion into dacite ca diffused more slowly into this zone from which non feldspar species were mostly excluded plagioclase was stable where sufficient ca had diffused in that the boundary zone melt intersected the plagioclase saturation liquidus plagioclase subsequently grew toward the receding dissolution surface as the ca compositional gradient and hence the site of plagioclase saturation stepped inward crystallization of plagioclase in the form of parallel blades allowed continued diffusive exchange of melt components between the dissolution surface and the host melt bladed growth also served to maintain at blade tips proximity of plagioclase to the dissolution surface thereby apparently preserving locally a thin zone of low variance melt in natural systems mantling of alkali feldspar by plagioclase will occur in a similar manner when a p t or x are changed to induce alkali feldspar dissolution b sufficient ca is available in the host melt to drive by diffusion boundary zone melt compositions to plagioclase saturation and c temperatures are low enough to stabilize sodic plagioclase and to maintain a coherent boundary zone these reqjirements are satisfied in volcanic systems when alkali feldspar is juxtaposed during mixing with hybrid melts of dacitic composition mantled feldspars in some intrusive systems i e rapakivi granites may form by a similar dissolution and diffusion controlled mechanism textural evidence of a similar origin may be obscurred in intrusive rocks however by products of late stage magmatic and subsolidus processes

characterization of model uncertainty in predicting axial resistance of piles driven into clay this paper summarizes 239 static load tests to evaluate the performance of four static design methods for axial resistance of driven piles in clay the methods are iso 19901 4 2016 shansep icp 05

the antiquity of oxygenic photosynthesis evidence from stromatolites in sulphate deficient archaean lakes the tumbiana formation about 2700 million years old was largely deposited in ephemeral saline lakes as judged by the unusual evaporite paragenesis of carbonate and halite with no sulfate stromatolites of diverse morphology occur in the lacustrine sediments some with palimpsest fabrics after erect filaments these stromatolites were probably accreted by phototropic microbes that from their habitat in shallow isolated basins with negligible sulfate concentrations almost certainly metabolized by ozygenic photosynthesis

field studies of an instrumented model pile in clay an instrumented model pile was used to investigate the fundamental behaviour of driven cylindrical steel piles in clay soils data are described from two test bed sites one with heavily over consolidated clay and one with normally consoli dated clay these confirm that a residual shear surface is formed adjacent to the pile shaft during installation comparisons with other site investigation data and cavity expansion theoretical predic tions suggest that stress relief immediately behind the pile tip during installation gives rise to total radial stress and pore pressure measurements on the shaft which are lower than the simple cavity expansion model predicts however the data did indicate that the radial effective stress might be successfully predicted during reconsolidation the radial effective stress drops initially followed by a slow recovery which was insufticient in the two clays investigated for the final value to reach that during installation on undrained loading the clay adjacent to th

experimental study of uplift resistance of shallow skirted foundations in clay under transient and sustained concentric loading wind wave and current forces cause significant overturning loads to be transmitted to foundation systems of fixed bottom offshore structures while buoyancy forces in conjunction with environmental loading impart direct tensile loads to foundations of floating facilities shallow skirted foundations are a potentially attractive foundation solution when overturning or tension loading is significant as suctions mobilised within the soil plug provide tensile resistance while passive suctions are maintained undrained reverse end bearing will govern failure providing enhanced uplift resistance compared with vented pull out of the foundation unit with or without the soil plug governed by skirt soil friction currently uncertainty exists over the limiting ratio of skirt depth to foundation diameter to mobilise undrained reverse end bearing and the duration over which passive suctions can be sustained this paper reports results from beam centrifuge tests investigating the response of shallow skirted fou

tracking physicochemical conditions of evaporite deposition by stable magnesium isotopes a case study of late permian langbeinites magnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition we report mg isotopic values delta mg 26 dsm3 measured from an evaporite deposit of langbeinite k2mg2 so4 3 found in the permian salado formation we used these data to model mg isotope fractionation between langbeinite and its parent brine in addition both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment the salado langbeinite delta mg 26 values are relatively low and fall within a relatively narrow range 4 12 0 03 parts per thousand to 3 81 0 07 parts per thousand equilibrium fractionation factors between langbeinite and aqueous mg2 solutions were calculated using quantum chemical density functional theory all computations were performed at the b3lyp 6 31 g d p level solvation effects were addressed using a solvent model water droplet approach and mineral structures were investigated using volume variable cluster models vvcm the equilibrium mg isotopic fractionation factors a between langbeinite and model brine solution we obtained are 1 0005 1 0004 and 1 0003 delta mg 26 langb water approximate to 10 3 ln alpha 0 473 parts per thousand 0 390 parts per thousand and 0 322 parts per thousand at 10 degrees c 25 degrees c and 40 degrees c respectively these relatively large equilibrium fractionation factors indicate significant mg isotope fractionation between langbeinite and its parent brine during precipitation as langbeinite preferentially incorporates the heavier mg 26 and mg 25 isotopes rayleigh distillation modeling of the salado langbeinite s relatively light mg isotopic composition requires delta mg 26 dsm3 values of 4 parts per thousand for the parent brine models favor a precipitation temperature as high as 40 degrees c under equilibrium conditions potential disequilibrium precipitation conditions suggested by mg isotopic data also imply rapid deposition in a hot arid sedimentary environment prevailing in the southwestern u s during the late permian

field measurements of the stiffness of jacked piles and pile groups introduction this technical note presents a back analysis of the axial response of some field scale tubular displacement piles installed by jacking this study was motivated by the recent development of large pile jacking rigs these rigs are sufficiently strong to offer an alternative to bored piling in urban areas where conventional dynamic methods of displacement pile installation are not permitted white et al 2002 the most notable feature of the axial response was the very high stiffness some pile jacking machines walk along the pile wall under construction so all piles must necessarily be installed at close centres or indeed touching this geometry is in contrast to conventional design guidance which suggests that a separation of typically two or three diameters is required between piles to prevent harmful interaction effects bsi 1986 geo 1996 load test results from jacked piles installed closer than this recommended minimum spacing are presented the study comprised a series of field tests carried out in kochi japan full details are provided by yetginer et al 2003 and brief details are repeated below test piles were installed singly and in groups forming a cell foundation comprising jacked piles at close centres around an enclosed soil block in this technical note pile group efficiency is defined as the average performance per pile strength or stiffness when a group is loaded in unison divided by the performance of a single pile tested alone using this definition the behaviour of trial piles installed prior to the main group can be linked to the group response this definition is used by vesic 1969 and fleming et al 1992 and is shown in equation 1 for strength and stiffness group strength efficiency group is defined in equation 1a where qsingle and qgroup represent the capacity of a single isolated pile and the capacity of a group of n piles respectively group stiffness efficiency group is defined in equation 1b where ksingle and kgroup represent the stiffness of a single isolated pile and the stiffness of a group of n piles respectively

temperature seasonality control on modern halite layers in the dead sea in situ observations layered halite sequences are found in deep basins throughout the geological record however analogs for such sequences are commonly studied in shallow environments here we studied active precipitation of halite layers from the only modern analog for deep halite precipitating basins the hypersaline dead sea in situ observations in the dead sea link seasonal thermohaline stratification halite saturation and the characteristics of the actively forming halite layers the spatiotemporal evolution of halite precipitation in the dead sea was characterized by means of monthly observations of 1 lake thermohaline stratification temperature salinity and density 2 degree of halite saturation and 3 textural evolution of the active halite deposits we present the observed relationships between the textural characteristics of layered halite deposits i e grain size consolidation and roughness and the degree of saturation which in turn reflects the limnology and hydroclimatology the lake floor is divided into two principal environments a deep hypolimnetic lake floor and a shallow epilimnetic lake floor in the deeper hypolimnetic lake floor halite continuously precipitates with seasonal variations 1 during summer consolidated coarse halite crystals form rough surfaces under slight supersaturation 2 during winter unconsolidated fine halite crystals form smooth lake floor deposits under high supersaturation these observations support interpretations of the seasonal alternation of halite crystallization mechanisms the shallow epilimnetic lake floor is highly influenced by the seasonal temperature variations and by intensive summer dissolution of part of the previous year s halite deposit which results in thin sequences with annual unconformities this emphasizes the control of temperature seasonality on the characteristics of the precipitated halite layers in addition precipitation of halite on the hypolimnetic floor at the expense of the dissolution of the epilimnetic floor results in lateral focusing and thickening of halite deposits in the deeper part of the basin and thinning of the deposits in shallow marginal basins

crystallization processes of quartz in a granitic magma cathodoluminescence zonation pattern controlled by temperature and titanium diffusivity abstract quartz from a granitic pluton is found to have formed through sequential growth events under different mechanisms and crystallization temperatures which can provide new insights into magmatic processes of granitic magmas that were eventually consolidified into plutons the events were identified using 1 the description of crystal shape and occurrence 2 the study of the internal structure with cathodoluminescence cl and 3 derivation of the crystallization temperatures based on titaniq thermometry the magmatic quartz crystals from the toki granite central japan are characterized as having the following internal structures oscillatory zonation no oscillatory zonation with luminescence gradation gradational zonation and heterogeneous cl the quartz crystals with oscillatory zonation were formed in the temperature range of about 800 c to below 700 c which is referred to as oscillatory zoning temperature ozt conditions the cl zonation pattern was controlled by the temperature conditions and titanium diffusivity in the melt magma the crystallization process of quartz within the toki granite reveals the cooling processes of the granitic pluton the lithofacies with a high frequency of oscillatory zoned quartz underwent slower cooling under the ozt conditions than those in other lithofacies

geology and major and trace element chemistry of late archean weathering profiles in the fortescue group western australia implications for atmospheric po2 abstract we have identified two thick weathering profiles between flows of the mt roe basalt unit of the fortescue group in the pilbara area of western australia the age of weathering is constrained by u pb zircon dating to lie between 2765 and 2715 ma the profiles herein referred to as the mt roe 1 and 2 paleosols were mapped in detail for 1500 m and 760 m along strike respectively samples were collected along traverses across both profiles where they were well developed and well exposed the profiles which may be structurally offset parts of the same weathering horizon have well developed upper sericite zones 1 15 m thick these grade downward into chlorite rich zones which are chemically and physically heterogeneous the chlorite zones grade downward into unweathered basalts the mt roe 1 profile is overlain by 2 6 m of bedded probably lacustrine sediments these in turn are covered by succeeding lava flows evidence of a surficial origin for the paleosols includes mud cracks ripple marks and rip ups of the paleosol material in the post paleosol sediments soft sediment deformation and probable dewatering structures are present along the paleosol sediment contact the mt roe 2 profile is overlain directly by the succeeding lava flow with little or no intervening sediments some brecciation and pillowing is observed along the base of the overlying basalt flow in both cases probably due to emplacement of lava into a shallow lake or onto wet soil in the sericite zones of both profiles nearly all of the fe mn mg and zn and a substantial fraction of the ca pb na ni and si have been leached the chlorite zones have elevated fe pb ni and zn contents and appear to be repositories of elements lost from the sericite zone al ti zr and th were immobile in the mt roe 1 paleosol and are concentrated by factors of 2 5 2 6 over the unweathered basalt v u and cr were also nearly immobile major element and trace element data indicate that weathering took place under conditions of low atmospheric oxygen k is strongly enriched toward the upper contact of the sericite zone and was introduced during post weathering metasomatism together with rb and sr na and ca are also enriched near the top of each profile and small amounts of each may have been introduced during regional low grade metamorphism of the hamersley basin at 2168 10 ma

new experimental approach to understanding igneous texture thin sections containing a magma like mixture of three crystalline ammonium compounds and intercrystalline melt can be prepared and observed microscopically during crystallization melting and deformation the aim of such observations is to establish links between active processes in the crystal melt mixture and the textural signatures of the processes the hope is to improve the basis for process interpretation of textures in rocks although the value of the experimental system in this regard is still unknown three unexpected processes are seen creation of growth centers for later blocky grains by isothermal decomposition of early dendritic grains migration of grain boundaries early in the crystallization history and growth of porphyroblast like grains by phase boundary migration with abundant melt nearby textural metamorphism begins in this material well before its melt present history is complete

field investigation of ridge runnel dynamics on an intertidal mudflat flow parallel linear ridge runnel r r bedforms composed of mainly cohesive sediments have been investigated at an intertidal site located at hills flats in the severn estuary uk it is argued that the sequences of sand mud laminae in the ridge sediments indicate strongly that r r are depositional bedforms faint r r topography scoured in the underlying soft bedrock and parallel rows of coarser particle now found at the base of ridges are evidence of secondary vortices that may have provided a catalyst for mud ridge growth bed shear stress remains below the erosion threshold for all but the most recent and weak surficial mud deposits which are removed by evorsion mechanical erosion by turbulent flows that may also carry sand and or gravel during spring tidal flow ca 60 cm s differences in flow characteristics between ridges and runnel are minor corrasion to erode or be eroded by abrasion by sparse coarse sediment largely prevents net deposition in the runnels over time a slight imbalance between mud deposition and erosion rates allows slow growth of the ridges suggesting that these mudflats may be especially sensitive to slight changes in the local hydrodynamic regime and or sediment supply

displacement pile behaviour in a soft marine clay the paper presents the results of field experiments performed using the imperial college instrumented displacement pile in a soft sensitive marine clay at bothkennar scotland these results are compared with data from similar programmes of experiments performed in other clay types with this pile so that some of the major factors controlling displacement pile performance may be identified key words displacement pile instrumentation sensitive clay effective stress design

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

systematic retrograde metamorphism of sillimanite staurolite schists new salem area massachusetts the new salem retrograde metamorphic zone occupies an approximately triangular area covering 26 km 2 in sillimanite staurolite grade rocks largely pelitic schists of the devonian littleton formation acadian prograde metamorphism at 6 kbar and 600 c produced the common assemblage quartz muscovite biotite garnet staurolite iunenite albite graphite sillimanite pyrrhotite systematic hydration of the prograde assemblages by an influx of h 2 o produced the retrograde assemblages chlorite k feldspar celadonitic musco vite sphene anatase pyrite common and chlorite chloritoid musco vite anatase sphene rare retrograde sillimanite out staurolite out and garnet out isograds have been mapped representing the completion of important retrograde hydration reactions these isograds plus the thicknesses of chlorite rims on garnets 0 and 0 2 mm can be used to subdivide the area into six concentric retrograde metamorphic zones designated r1 to r6 during retrograde metamorphism the exchange reactions k na mn fe mg and fe mg proceeded while more or less consistent tie lines between the sheet silicates and ilmenite were maintained biotite and chlorite became more fe rich owing to staurolite garnet and ilmenite breakdown biotite chlorite and ilmenite became more mn rich owing to garnet breakdown coexisting biotite and muscovite became more k rich during biotite breakdown muscovite also became progressively more celadonite rich chlorite biotite and ilmenite are homogeneous in single thin sections muscovite is zoned with respect to m 2 m 2 al iv and k k na ratios which are higher in muscovite rims there is no evidence for re equilibration of staurolite garnet or albite during retrograde metamorphism temperature and pressure estimates for retrograde metamorphism are poorly constrained to 3 5 kbar and 280 c each kilometre of vertical extent of the retrograde zone required an influx of 0 26 km 3 of h 2 o at stp water may have been derived from a large volume of surrounding rock and concentrated in the study area by a pressure shadow effect around the north end of the prescott intrusive complex

settlement of piled foundations a numerical code for the prediction of the settlement of pile groups and piled rafts is presented the code is based on the interaction factors method the non linearity is simulated as suggested by caputo and viggiani that is concentrating it at the pile soil interface in the linear range the accuracy is checked against known benchmark solutions a standard procedure based on the results of load tests on single piles is suggested for the evaluation of soil properties and for the implementation of the analysis in real cases nineteen well documented case histories are then analysed calculating for each of them a linear elastic an equivalent linear elastic and a non linear solution five out of the 19 cases are illustrated in some detail to allow a deeper insight into the procedure in all but one of the analysed cases the predicted values of the average settlement are within 20 of the observed values the maximum differential settlement is predicted with slightly lesser accuracy for foundation

petrographic classification of crystal morphology the terms euhedral subhedral and anhedral have limited value as an expression of crystal morphology relating to conditions of crystal formation and rock forming processes the basis of this traditional nomenclature is the presence or absence of crystal faces implying that if a crystal has faces its overall shape is likely to reflect crystal structure experimental reproduction of growth dissolution and melting textures along with an ever increasing awareness of the importance of incomplete and malformed crystals in natural systems is the impetus for presentation here of a more detailed morphological classification of crystals at the petrographic scale the classification is binary based on the degree to which crystals are an expression of crystal structure and on the degree of completeness unlike the traditional scheme the proposed classification is sensitive to faceted crystals that do not have ideal shape and to incomplete crystals variously described as skeletal dendritic cellular

burial evolution of evaporites with implications for sublacustrine fan reservoir quality a case study from the eocene es4x interval dongying depression bohai bay basin china abstract eocene sublacustrine fan sandstones that developed in a rift basin are important tight gas reservoirs in the dongying depression bohai bay basin northeastern china two units of evaporites developed at the top and bottom of the lower unit of the es4 interval es4x consist predominantly of anhydrite with subordinate gypsum evaporite and related diagenetic processes greatly influenced reservoir quality 13 c values for micritic dolomite cements in es4x are depleted 7 45 to 2 57 due to microbial sulfate reduction msr under shallow burial conditions and this interpretation is supported by large 34 s fractionation between anhydrite and framboidal pyrite precipitation temperatures for micritic dolomite are calculated as 57 5 72 8 c anhydritization of gypsum probably occurred at 100 5 145 2 c during progressive burial as evidenced by homogenization temperatures of aqueous inclusions within anhydrite cements this process resulted in dehydration fractures within anhydrite cements that increased reservoir permeability by connecting isolated pores thermochemical sulfate reduction tsr probably resulted in dissolution of gypsum and anhydrite cements under relatively deep burial conditions ankerite cements are replaced by anhydrite cements and are enclosed by solid bitumen in es4x ankerite cements likely were derived from tsr as reflected in negative 13 c values 7 12 to 3 70 and high calculated temperatures 121 3 185 1 c dissolution by products e g saddle dolomite ankerite nodular pyrite related to tsr precipitated in adjacent pores a lack of significant 34 s fractionation between parent sulfate and nodular pyrite indicates that tsr occurred in a relatively closed system therefore dissolution of gypsum and anhydrite related to tsr contributed little to reservoir quality middle fan lithofacies with better sorting porosity and permeability than inner and outer fan lithofacies constitute high quality reservoirs in es4x

external radial stress changes and axial capacity for suction caissons in soft clay a series of centrifuge tests was performed on instrumented model caissons in normally consolidated lightly overconsolidated and sensitive clays to investigate the external radial stress changes around suction caissons during installation consolidation and pullout and axial capacity after consolidation total pressure transducers embedded at different elevations of the caisson wall showed external radial total stresses that varied almost linearly with depth during both penetration and extraction of the caisson with smaller gradients during post consolidation pullout only slight differences were found in the measured external radial total stress when pressure transducers entered the suction affected zone from the jacking affected zone comparisons are presented between measurements and two theoretical predictions for both the external radial total stress during caisson installation and the radial effective stress after consolidation a simple cavity expansion approach was found to give reasonable pr