isotopic constraints on the origin of groundwater in the ordos basin of northern china despite its extreme aridity the ordos basin in northern china is rich in groundwater many artesian wells or springs with large fluxes are utilized for drinking irrigation and industrial production in a search for the origin of the groundwater a detailed investigation of the stable isotopes of oxygen and hydrogen in the local precipitation the river water the springs the well water as well as the soil water extracted from six soil profiles in the ordos basin was carried out the data show that d 18o and tds values of the river water are similar to those of groundwater while the tds values of the soil water are about ten times greater than those of groundwater furthermore the mean isotopic compositions of the local precipitation are significantly higher than those of river water and groundwater based on the chloride mass balance method the estimated recharge rates range from 5 2 to 17 2 mm year with a mean value of 10 5 mm year the results show that the main source of recharge of the groundwater in the ordos basin is not the local precipitation but must come from a region where the precipitation is characterized by much lower d and 18o values in addition the groundwater in the ordos basin contains a component of mantle derived 3he and crust derived 4he suggesting that the groundwater may partly derive from flows through basement faults beneath the ordos basin

coesite eclogites from the roberts victor kimberlite south africa abstract coesite or pseudomorphic quartz is more common than previously recognized in the eclogite xenolith suite from the roberts victor mine south africa all coesite eclogites in this study 18 samples are classified as group i and have mineral compositions that span virtually the entire compositional range of group i eclogites described from this locality most of the roberts victor group i eclogite suite may be in equilibrium with free silica thus weakening the case for these rocks representing residues of partial melting oxygen isotope compositions of garnets from 15 samples are in the range 5 32 6 95 similar to other roberts victor group i eclogites these observations are consistent with a model in which protoliths of these rocks were oceanic basalts and intrusive rocks that underwent exchange with seawater at relatively low temperatures to variable extents prior to subduction and metamorphism to eclogite facies without suffering significant partial melting during or following subduction

stable isotope compositions of waters in the great basin united states 3 comparison of groundwaters with modern precipitation 1 groundwater samples from wells and springs scattered over most of the great basin province were collected and analyzed for their isotopic makeup they were augmented by previously published isotopic data on groundwaters from southeast california and by several hundred unpublished isotopic analyses the ratio of 2h deuterium d to 1h in water samples from valleys in parts of california idaho nevada oregon and utah are here compared with the winter summer and annual isotopic compositions of precipitation falling in or near the sampled areas the main goal of this study was to identify basins where the groundwaters have isotopic compositions that are lighter depleted in the heavier isotope d relative to modern winter precipitation where these basins do not adjoin substantially higher terrain we consider those light groundwaters to be of pleistocene age and thus more than 10 000 years old where the groundwater is 10 to 19 lighter than local winter precipitation we consider it to be possibly an indication of pleistocene water where the d makeup is 20 lighter we consider it to be probably pleistocene water more than 80 sites underlain by waters of possible or probable pleistocene age were identified

intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

periodicities of caco3cycles in the pliocene of sicily discrepancies with the quasi periods of the earth s orbital cycles a high resolution caco3 record in combination with a detailed magnetostratigraphy is presented for the rhythmically bedded marly sequence of the pliocene trubi formation on sicily italy magnetostratigraphic age calibration and subsequent spectral analysis of the variatrions in caco3 content yield a remarkably consistent discrepancy between the resulting periodicities and the corresponding quasi periods of the earth s orbital cycles this discrepancy can only be explained by assuming that ages assigned to polarity reversal boundaries in the geomagnetic polarity time scale lack sufficient precision a new polarity time scale is presented for the major part of the gilbert and gauss chron using the radiometrically dated gilbert gauss chron boundary at 3 40 ma as an age reference point and extrapolating an average quasi period of 21 7 kyr of the precession cycle as the periodicity of small scale colour annex caco3 cycles

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

inferred glacio eustatic control for high frequency depositional sequences of the plio pleistocene kazusa group a forearc basin fill in boso peninsula japan abstract the plio pleistocene forearc basin fill of the kazusa group as much as 3000 m thick is represented by a series of marine environments ranging from deep sea basin plain to shallow sea it developed during about 2 4 to 0 45 ma and is well exposed in the boso peninsula japan chronostratigraphic resolution of the kazusa group is partly within about 0 05 m y based on the combination of fission track dating of volcanic ash layers and bio and magneto stratigraphy many volcanic ash layers are intercalated in the kazusa group and provide distinct chronostratigraphic surfaces within the heterogeneous lithologies detailed outcrop studies on depositional facies discontinuities and lateral terminations of volcanic ash layers allow high resolution sequence stratigraphic interpretation of the kazusa group seventeen depositional sequences were identified in the kazusa group each depositional sequence was tentatively correlated with the stable oxygen isotope sea level index integrated with the age framework of the kazusa group this correlation indicates that frequencies of the depositional sequences can be estimated to be in the range of 0 2 0 02 m y and are within fourth and fifth order stratigraphic cyclicities depositional sequences constitute third order transgressive and highstand sequence sets and the kazusa group is interpreted to represent a third order composite sequence with a duration of about 1 95 m y development of the third order composite sequence was also controlled by an overall rise and fall of glacio eustatic sea levels overprinted by tectonic events related to fluctuations in oceanic plate motion which occurred at about 2 6 ma and 0 5 ma respectively

characterization of water and solute transport in the unsaturated zone of a hypersaline environment we present a methodology for the analysis of chemical profiles from the unsaturated zone where ions from the sediment are extracted by two methods centrifugation and water addition the methodology enables one to 1 assess the ion amounts present in two different phases pore water and minerals 2 determine the depth in the unsaturated profile where the degree of saturation of each mineral is reached 3 establish the principal direction of water flow and 4 differentiate between upward transport of water either as vapor or as a saline solution the methodology was applied to the unsaturated zone of the dead sea coastal area where the original salinity of interstitial water in these sediments was 300 g l our analysis of the field data suggests that reduction of interstitial water salinity is the result of vertical upward transport of fresh water from a confined aquifer at a depth of 7 m flushing up to the potentiometric surface depth of 3 5 m is due to the positive pressure head of the aquifer above the potentiometric surface upward water transport is due to capillary forces and flow is maintained by evaporation at the soil surface evaporation leads to an increase in the salinity of the rising interstitial solution and to the sequential deposition of salts such as nacl and kmgcl3 6h2o

holocene vegetation and climate in the puerto blanco mountains southwestern arizona abstract plant macrofossils from 21 pack rat neotoma sp middens at 535 605 m from the puerto blanco mountains southwestern arizona provide and excellent history of vegetation and climate for the last 14 120 yr b p in the sonoran desert a late wisconsin juniper joshua tree woodland gave way to a transitional early holocene desertscrub with sparse juniperus californica california juniper by 10 540 yr b p important sonoran desert plants including carnegiea gigantea saguaro and encelia farinosa brittle bush were dominants riparian trees such as acacia greggii catclaw acacia prosopis velutina velvet mesquite and cerdicium floridum blue palo verde grew on dry south facing slopes in a middle holocene sonoran desertscrub in a warm wet summer climate with frequent winter freezes modern subtropical sonoran desertscrub formed about 4000 yr b p as summer rainfall and winter freezes declined cercidium microphyllum foothills palo verde sapium biloculare mexican jumping bean olneya tesota ironwood and stenocereus thurberi organ pipe cactus became dominant as riparian trees retreated to wash habitats the inferences of a latest wisconsin early holocene summer monsoonal maximum by j e kutzbach 1983 modeling of holocene climates in late quaternary environments of the united states vol 2 the holocene h e wright ed pp 271 277 univ of minnesota press minneapolis are not supported for the southwest apparently the persistence of late wisconsin circulation patterns offset any increases in insolation

timing of rifting in the alboran sea basin correlation of borehole odp leg 161 and andalucia a 1 to seismic reflection data implications for basin formation abstract to constrain the timing of rifting in the western eastern and northern parts of the alboran sea basin seismic reflectors corresponding to biostratigraphic boundaries and unconformities from the miocene to recent are correlated using synthetic seismograms regions of adjacent coeval compression and extension are found in the alboran sea basin normal faulting continues in parts of the eastern alboran sea basin later than in the western alboran sea basin seismic reflection data in the vicinity of odp site 976 western alboran sea basin suggest that rifting ended in the miocene near site 976 western alboran sea basin no compressional features affect miocene and younger sediments in the eastern alboran sea basin north of al mansour seamount odp site 977 normal faults are observed in miocene and early pliocene sediments later folds affect pleistocene recent sediments in the eastern alboran sea basin site 977 after the folding event there is evidence for normal faulting in pleistocene recent sediments close to site 977 south of al mansour seamount odp site 978 compressional features in the eastern alboran sea basin from miocene to recent are evidenced by reverse faulting followed by folding in the northern alboran sea basin andalucia a 1 well there is evidence for strike slip faulting in the late miocene that can be related to the serrata fault system we envision the development of the alboran sea basin through a southeasterly migration of the delaminating continental lithosphere to explain younger extension in the eastern alboran sea basin the rate of the migration of the delamination front is of the range of millimeters centimeters year we see evidence for the migration of the delamination front from miocene to recent as tectonic inversion occurs near site 977 in contradiction to an extensional collapse hypothesis for the formation of the alboran sea rifting did not end in the late miocene in the entire alboran sea basin we exclude retreating subduction in a westward direction or a westward continental delamination as a model for alboran sea basin development because it would predict younger extension in the western part of the basin

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

local and global effects on the early pliocene mediterranean stable isotope records abstract stable isotope analyses of the planktonic foraminifer globigerinoides obliquus from the monte singa section in south calabria italy yielded detailed early pliocene oxygen and carbon records which are directly calibrated to the numerical time scale two major local mediterranean signals are recognized 1 relatively rapid alternations of wet and dry climatic conditions with an average periodicity of 0 02 ma these are considered to reflect fluctuations in precipitation and run off volume 2 superimposed longer term alternations of relatively wetter and relatively drier intervals believed to reflect latitudinal shifts of precipitation zones or intensification of precipitation in an existing zone after an attempt had been made to reduce these local overprints to a minimum the isotope records for the mediterranean were compared with previously published ones from the pacific and atlantic oceans two approximately contemporaneous isotope events were found but in general there is little similarity between the mediterranean and extra mediterranean records therefore our records probably reflect the mediterranean paleoclimatologic and paleoceanographic development rather than global climatic signals

oxygen isotope evidence of climate change from pedogenic clay minerals in the himalayan molasse abstract in this study we examine the oxygen isotope ratios of smectite and kaolinite in a stratigraphic sequence of paleosols in the siwalik himalayan molasse on the potwar plateau northern pakistan there is a 3 4 o increase in the smectite 18 o values synchronous with a 3 5 o increase in 18 o values of pedogenic calcite at 8 5 6 5 ma previously observed by quade et al 1989 the covariation of the 18 o values of smectite with calcite gd 18 o values through time strongly suggests a pedogenic origin of smectite and that its 18 o values reflect the oxygen isotope ratio of the soil water present during pedogenesis these data show that the 18 o values of clay minerals in paleosols in aggrading sedimentary sequences are viable paleoclimate indicators kaolinite 18 o values are similar to smectite 18 o values as would be expected for pedogenic kaolinite but there is greater variation in these data which we attribute to incomplete mineral separation the measured permil oxygen isotope fractionation between calcite and smectite within individual paleosols is on average 3 o higher than the equilibrium fractionation this isotopic disequilibrium can be explained by the calcite forming predominantly during the dry winter season and the smectite forming predominantly during the wet summer season the synchronous 3 5 o increase in oxygen isotope ratios of smectite and calcite at 8 5 6 5 ma indicates that this 18 o 16 o increase is not due to diagenesis but rather results from a climate change the most likely causes of the 18 o 16 o increase in smectite and calcite are either increased aridity resulting in increased soil water evaporation thus 18 o enrichment and or a change from more continental to more marine sourced precipitation the tibetan plateau which is suggested to have undergone rapid uplift around 8 ma e g harrison et al 1992 may have acted as an effective orographic barrier to low 18 o precipitation originating from central asia causing higher 18 o values of the precipitation falling on the potwar plateau currently it is impossible to distinguish between these two potential causes of the 18 o 16 o increase at 8 5 6 5 ma but these clay mineral 18 o values support that there was a significant climate change in this region

the mid cretaceous water bearer isotope mass balance quantification of the albian hydrologic cycle a latitudinal gradient in meteoric n 18 o compositions compiled from paleosol sphaerosiderites throughout the cretaceous western interior basin kwib 34 75 n paleolatitude exhibits a steeper more depleted trend than modern predicted values 3 0x 34 n latitude to 9 7x 75 n lighter furthermore the sphaerosiderite meteoric n 18 o latitudinal gradient is significantly steeper and more depleted 5 8x 34 n to 13 8x 75 n lighter than a predicted gradient for the warm mid cretaceous using modern empirical temperature n 18 o precipitation relationships we have suggested that the steeper and more depleted relative to the modern theoretical gradient meteoric sphaerosiderite n 18 o latitudinal gradient resulted from increased air mass rainout effects in coastal areas of the kwib during the mid cretaceous the sphaerosiderite isotopic data have been used to constrain a mass balance model of the hydrologic cycle in the northern hemisphere and to quantify precipitation rates of the equable greenhouse albian stage in the kwib the mass balance model tracks the evolving isotopic composition of an air mass and its precipitation and is driven by latitudinal temperature gradients our simulations indicate that significant increases in albian precipitation 34 52 and evaporation fluxes 76 96 are required to reproduce the difference between modern and albian meteoric siderite n 18 o latitudinal gradients calculations of precipitation rates from model outputs suggest mid high latitude precipitation rates greatly exceeded modern rates 156 220 greater in mid latitudes 2600 3300 mm yr 99 greater at high latitudes 550 mm yr the calculated precipitation rates are significantly different from the precipitation rates predicted by some recent general circulation models gcms for the warm cretaceous particularly in the mid to high latitudes our mass balance model by no means replaces gcms however it is a simple and effective means of obtaining quantitative data regarding the mid cretaceous hydrologic cycle in the kwib our goal is to encourage the incorporation of isotopic tracers into gcm simulations of the midcretaceous and to show how our empirical data and mass balance model estimates help constrain the boundary conditions

stable isotope compositions and water contents of boninite series volcanic rocks from chichi jima bonin islands japan measurements of stable isotope compositions and water contents of boninite series volcanic rocks from the island of chichi jima bonin islands japan confirm that a large amount 1 6 2 4 wt of primary water was present in these unusual magmas an enrichment of 0 6 in18o during differentiation is explained by crystallization of18o depleted mafic phases silicic glasses have elevated 18o values and relatively low d values indicating that they were modified by low temperature alteration and hydration processes mafic glasses on the other hand have for the most part retained their primary isotopic signatures since eocene time primary d values of 53 for boninite glasses are higher than those of morb and suggest that the water was derived from subducted oceanic lithosphere

sonic and gamma ray astrochronology cycle to cycle calibration of atlantic climatic records to mediterranean sapropels and astronomical oscillations a high resolution analysis of cyclical patterns in gamma ray and sonic logs of the lower pliocene sediments from the gulf of cadiz southern spain was carried out results suggest that these cycles can be successfully used for a bed to bed correlation with the global reference section for the astronomical time scale in capo rossello sicily cycle patterns were used to tune the logs to the astronomical solutions of j laskar the gamma ray and sonic cyclicity was interpreted in terms of precession induced oscillations of annual rainfall in southern spain that were in part responsible for the increasing input of freshwater into the mediterranean at times of sapropel formation we demonstrate that gamma ray and sonic astrochronology can be successfully used for interregional correlation and astronomical dating with errors not higher than 20 k y

oxygen isotope systematics of eclogite mineral phases from south africa abstract eleven eclogite xenoliths from the bobbejaan and roberts victor mines south africa have been characterized by a variety of geochemical techniques the samples include nine bimineralic eclogites and two grospydites that span the range of mantle eclogite major element compositions primary phase end member compositions range from py 75 al 16 gr 09 jd 18 di 82 caes 0 to py 28 al 21 gr 51 jd 49 di 36 caes 15 oxygen isotope analyses of mineral separates were performed for clinopyroxene and garnet isotopic values 18 o range from 4 0 to 7 8 for clinopyroxene and 3 6 to 7 2 for garnet differences in isotopic values between the primary phases clinopyroxene minus garnet range in value from 0 6 to 0 6 although oxygen isotopes are not expected to fractionate at mantle temperatures the anion electrostatic site potential values determined by smyth 1989 are consistent with small degrees of fractionation in the mantle oxygen isotope fractionation between minerals may be calculated by the equation of smyth and clayton f a 10 6 t 2 where a 0 7911 ev fractionation values at 1300 k range from 0 6 jd pyr to 0 03 cats grs while at 1600 k these values are between 0 39 and 0 02 respectively the re equilibration temperatures of the studied eclogite suite are 1050 to 1250 c at 30 kbar therefore the obtained differences between the mineral phases are consistent with the calculated isotope fractionation values the data obtained for eclogite oxygen isotopes suggest that 18 o may fractionate to a small extent at mantle pt conditions

late pliocene to early pleistocene astronomically forced sea surface productivity and temperature variations in the mediterranean abstract principal component analysis of late pliocene to early pleistocene planktonic foraminiferal abundances from the mediterranean yielded two significant components which represent first order approximations for sea surface productivity and temperature this interpretation is confirmed by the good fit between the score plots and sea surface productivity and sea surface temperature proxy records based on selected eutrophic and temperature sensitive species using present day habitat characteristics spectral analysis revealed significant peaks in the orbital frequency bands of the spectrum suggesting that variations in sea surface productivity and temperature are controlled by the quasi periodic variations in the earth s orbit precession forced variations are reflected primarily in sea surface productivity and to a lesser degree in sea surface temperature maxima in sea surface productivity and temperature in this frequency band occurred at times of sapropel formation the sea surface productivity maxima can be explained by an increased input of river borne nutrients and by the shoaling of the pycnocline and the associated intensification of the deep chlorophyll maximum dcm layer precession forced variations in sea surface temperature are not related to glacial cycles since this frequency component is almost completely absent in ice volume proxy records for this time interval sapropel bound sea surface temperature maxima presumably reflect periods of maximum insolation during the northern hemisphere summer the contrasting winter signal corresponds to minimum insolation values which may be reflected by peak abundances ofgloborotalia inflata obliquity forced variations are reflected primarily in sea surface temperature and not in sea surface productivity these temperature fluctuations correspond with ice volume changes registered in the oxygen isotope record at the north atlantic dsdp site 607 this shows that obliquity forced sea surface temperature variations in the mediterranean are primarily driven by glacial cycles

palaeoclimatic cyclicity in central mediterranean pliocene sediments the mineralogical signal abstract a high resolution x ray mineralogical study of four pliocene sediment sections from the central mediterranean punta piccola sicily monte singa and vrica calabria odp hole 964 a ionian sea shows cyclic opposite abundance variations of two groups of clay minerals the first is dominated by palygorskite and kaolinite whose abundance maxima can be interpreted as resulting from periods of aridity on the african continent allowing their transport as wind blown dust the second is dominated by smectite whose abundance maxima can be interpreted as indicative of periods of abundant rainfall on the mediterranean borderlands these variations in abundance show a 22 ky cyclicity implying a control by the precession of the earth s orbit sapropels and sapropelic layers always occur in the smectite rich beds and therefore appear to have been deposited during the wet periods

morphology and stable and radiogenic isotope composition of pedogenic carbonates in late quaternary relict soils new mexico u s a an integrated record of pedogenic overprinting abstract this petrographic and stable 13c and 18o and radiogenic 14c isotope study of pedogenic carbonates from late quaternary soils in the rio grande rift region of new mexico documents that carbonate formation in semiarid to arid soils aridisols occurs principally by overprinting and can result in a complex petrographic and isotopic record with increasing duration of exposure 7 to 900 ky of the four studied profiles pedogenic carbonates exhibit 1 an increase in the degree of intraprofile 13c and 18o heterogeneity 2 increased development of down profile 13c and 18o trends 3 an increase in the degree of intermorphologic and intramorphologic stable isotope variation commonly in samples distributed laterally within narrow depth intervals and 4 development of covariation between 13c and 18o values radiocarbon ages of the carbonates permit assessment of the degree of isotope heterogeneity in contemporaneous carbonates and recognition of temporal isotopic trends the range of exposure times recorded by the studied soils are analogous to those associated with the formation of fossil soils this makes the studied soils ideal for evaluating the origin of stable isotope heterogeneity in paleosol carbonates and the implications of those heterogeneities for the use of stable isotopes as paleoenvironmental proxies specific implications of this study include the following 1 pedogenic carbonates that form by overprinting are a cumulative record of the soil conditions present during their accumulation thus isotope analysis of overprinted carbonates can result in time averaging of changing climatic paleoenvironmental and paleoecologic conditions 2 carbonates may record only a fraction of the duration of development of their host profile 3 there is a high level of uncertainty associated with using the sequence of morphologic development of carbonate as a function of time or maturity in paleosols 4 an exponential decrease in carbonate 13c values with depth in a paleosol does not imply that the carbonates are contemporaneous or accumulated under invariant soil conditions 5 shifts in soil and paleoclimatic conditions may be recorded by the 13c and 18o values of carbonates distributed within narrow depth intervals of a given soil in addition to those distributed down profile or even from within individual carbonate samples

graphite and diamond bearing eclogite xenoliths from the bellsbank kimberlites northern cape south africa one diamond bearing and eight graphite bearing eclogite xenoliths are described from the bellsbank kimberlites cape province south africa graphite mostly occurs as discrete grains which are commonly in the form of tabular prisms diamond is octahedral both group i and group ii eclogite varieties are represented by the graphite bearing specimens while the single diamond bearing eclogite is of the group i variety the carbon isotopic composition of the graphite varies from 13c 7 to 13c 2 8 this is within the range of carbon isotopic compositions for inclusion free diamonds in kimberlite from this locality suggesting that the carbon for the eclogites as well as some of the kimberlite diamonds are derived from the same source the present day nd isotopic compositions of clinopyroxene from three graphite bearing xenoliths are slightly higher than the bulk earth estimate sr isotopic compositions of the clinopyroxene in these xenoliths vary from 87sr 86sr 0 703 to 87sr 86sr 0 706 this could be due to derivation of the xenoliths from a protolith with variable 87sr 86sr isotopic composition or could be the result of mixing between a low sr high 87sr 86sr component and a high sr low 87sr 86sr component

salt crust development in paddy fields owing to soil evaporation and drainage contribution of chloride and deuterium profile analysis summary in northeast thailand lowlands with shallow saline watertable rainfed paddy fields often present high salt concentration in the dry season forming patches or spots of salt crusts on the soil surface in this context the mechanisms implied in salt concentration during dry season were studied by establishing salt budget with evaporation and drainage estimates inside and outside a saline patch drainage was estimated by hydrus 1d modelling constrained by an hydrodynamic characterization and the profile of water contents at the end of dry season evaporation rates at the end of the dry season were computed by interpreting natural detailed profiles of deuterium d and chloride cl contents because of the drastic diminution of hydraulic conductivity at saturation with depth and the decrease of groundwater level at the end of the cropping season simulated hydrological balance with hydrus 1d pointed out zero cumulated fluxes for depths of 39 5 cm outside the saline patch and 37 5 cm inside the saline patch therefore all the chloride accumulated in the very upper layers during dry season comes from the chloride that was present in the 0 39 5 cm layers before the beginning of the drying inside the saline patch the tentative cl budget is coherent with the hypothesis of saturation of the profile by aquifer saline water during the flooding evaporation rates computed from the diffusion of chloride and deuterium at the end of the drying season when the aquifer level was 1 4 m deep range between 0 121 and 0 378 mm d 1 this does not sustain the assumption of a considerable salinity contribution from the aquifer during the dry season moreover evaporation estimates based on cl and d diffusion equilibrium showed depleted rates 38 63 inside the saline patch due to salt accumulation in the first 12 cm of the soil in the vapour transfer layer estimated evaporation rate based on the vapour movement of d was in the same order of magnitude than computed rate assuming liquid cl diffusion this coincidence is attributed to the liquid fluxes that occurred during the expansion of the vapour transfer layer during the progression of the evaporation front

in situ oxygen isotope major and trace element constraints on the metasomatic modification and crustal origin of a diamondiferous eclogite from roberts victor kaapvaal craton a subducted oceanic crustal origin for most eclogite xenoliths in kimberlites has long been a cornerstone of tectonic models for craton development however eclogite xenoliths often have protracted and complex histories involving multiple metasomatic events that could overprint some of the key geochemical indicators typically taken as evidence of a subducted origin e g garnet 18o values and mineral 87sr 86sr compositions to assess the potential for disturbance of oxygen isotopic compositions in mantle eclogites via diamond forming and other possible metasomatic fluids we have conducted a multi technique in situ study of a diamondiferous eclogite xenolith from the roberts victor kimberlite s africa using sims we provide the first texturally controlled in situ measurements of 18o values in eclogitic garnet in close proximity to diamond garnet and clinopyroxene modal proportions are heterogeneous in the xenolith and garnet compositions vary from mg 75 8 79 2 grossular proportions 8 05 10 14 mol and omphacitic pyroxene has jd13 24 and mg 86 6 90 0 rare earth element patterns of minerals across the xenolith including grains close to diamond are typical lree depleted garnets and markedly lree enriched pyroxenes these silicate minerals also record detectable intra and inter grain lree abundance variations clinopyroxenes of the studied xenoliths show hfse and sr abundance variations that are decoupled from lree contents and major element variations mineralogical constraints and bulk rock reconstructions indicate that the studied sample likely experienced selective incompatible element enrichment during small volume 0 03 wt infiltration of metasomatic fluid s potentially linked to ancient diamond evolution intra grain major element lree and hfse variations in clinopyroxene resulted from late stage metasomatism oxygen isotope compositions in garnet are decoupled from all major and trace element variations with garnet 18o values being uniform across the xenolith in a wide variety of textural settings garnet 18o values of 6 5 0 2 are higher than the mean 5 19 0 26 of the mantle garnet range 4 8 5 5 modelling of the buffering effect of mantle peridotite on co2 rich and h2o rich metasomatic fluids at temperatures within the diamond stability field indicates that the likelihood of a metasomatic fluid with exotic oxygen isotopic composition arriving at a mantle eclogite body with its isotopic composition unmodified after percolative flow through dominantly peridotitic mantle at great depth is very low as we find no evidence of metasomatically induced garnet oxygen isotope variations in the studied diamondiferous eclogite xenolith we conclude that the most likely origin for the elevated garnet 18o values is via inheritance from a crustal protolith altered at relatively low temperatures these results have broader relevance and support the hypothesis of a low pressure protolith for mantle eclogite xenoliths demonstrating the robust nature of garnet oxygen isotope compositions even in diamond bearing eclogites

stable carbon and oxygen isotopes in quaternary soil carbonates as indicators of ecogeomorphic changes in the northern chihuahuan desert usa stable carbon and oxygen isotopes in soil carbonates provide an additional technique for investigating quaternary ecogeomorphic changes in arid and semiarid regions this study presents 13c and 18o values in surface and buried soils in a basin and range region of southern new mexico and west texas three landform categories were investigated for their isotopic content 1 middle piedmont slopes 2 a lower piedmont slope and adjacent playa depressions and 3 an intermontane basin floor soils of the middle piedmont slopes had greatest 13c variability ranging from 0 6 in buried soils to 11 1 pdb in surface soils soils of the basin floor had greatest variability in 18o values ranging from 0 6 to 7 6 pdb fossil pollen patterns roughly paralleled 13c shifts with cheno am pollen exhibiting greatest changes both isotope and pollen data across stratigraphic discontinuities suggest that a conversion from c4 grasses to c3 desert shrubs accompanied holocene erosion

magnetic stratigraphy and biostratigraphy of pliocene argille azzurre northern apennines italy abstract an integrated biomanetostratigraphic chronology for the mediterranean pliocene has been developed in the last five years mainly from land sections in southern italy calabria and sicily and odp leg 107 tyrrhenian sea cores in this paper the chronology is applied to terrigenous sediments from the northern apennine foredeep where reworking as well as sedimentation rate and facies variations limit the resolution of biostratigraphy and physical stratigraphy the integrated chronology gives improved stratigraphic control for a messinian to upper pliocene section exposed on the banks of the stirone near parma northern italy and for a short lower pliocene section located nearby at sant andrea bagni the sections are in the vicinity of stratotype sections for the tabianian lower pliocene and piacenzian upper pliocene and the chronology gives new insights into the complex pliocene sedimentation history in the northern apennine foredeep at this time at the stirone section the base of the pliocene record is in a normal polarity chronm correlated to the thvera subchron indicating a hiatus at the miocene pliocene boundary and the absence of the mpl1 foraminiferal zone at sant andrea bagni mpl1 is also missing in contrast to previous reports we conclude that this biozone is probably absent throughout the northern apennines where post messinian flooding appears to have occurred at the onset of mpl2 time during the gilbert chron sedimentation rates at stirone reached 104 cm kyr as nearly 300 m of argille azzurre blue clay were deposited in less than 0 5 myr very sporadic sedimentation is apparent from the late nunivak to the top of the section late gauss chron with a number of hiatuses being recognized within chron 2ar late gilbert and in the early gauss this interruption of sedimentation at about 4 1 ma is associated with a widely recognized early pliocene tectonic event involving thrusting and migration of the depocenter of the northern apennine foredeep

estimating paleorecharge and paleoclimate from unsaturated zone profiles unsaturated zone solute and isotope profiles may be interpreted in terms of past changes in recharge rate in cases where water movement can be approximated by piston flow a model is presented which describes water movement in terms of piston flow below a surface mixing layer below the mixing layer diffusion and dispersion occur in the liquid phase in the case of solutes and in both the liquid and gas phases in the case of isotopically labeled water climatic events of 4 5 years duration may be preserved in the unsaturated zone for more than 50 years if the recharge rate is greater than approximately 20 mm yr 1 longer term fluctuations in climatic conditions century scale might be preserved for over 1000 years provided the recharge rate is greater than approximately 2 mm yr 1 and the unsaturated zone is sufficiently deep profiles from cyprus and northern senegal appear to record changes in recharge rate over periods up to 400 years the profiles are well correlated with known variations in rainfall and fluctuations in lake levels the model provides limiting conditions to be applied to the interpretation of profiles

computer simulation of the influence of basin physiography on condensed section deposition and maximum flooding abstract sequence stratigraphic analysis commonly involves the correlation of condensed sections which are widely used as chronostratigraphic markers condensed sections represent periods of very slow deposition due to sediment starvation and have generally been equated with the maximum flooding surface which is most commonly inferred to occur at sometime between the maximum rate of relative base level rise and the highest point of relative base level however similar sediment starvation can be produced by a rapid landward shift in the shoreline over large distances during the early stages of a base level rise over a very low gradient surface condensed section deposition therefore does not always correspond to a period between the maximum rate of relative base level rise and the highest point of relative base level but can be initiated earlier than the maximum rate of relative base level rise or conclude after the highest point of relative base level the initial timing and the duration of condensed section deposition is therefore influenced by basin physiography basin physiography can also contribute to a diachronous maximum flooding horizon lying at different levels throughout a basin because the rate of change in accommodation during fluctuating base level is partially dependent on the slope of the basin surface these principles are illustrated in the paper by computer simulations

evidence for chlorine recycling hydrosphere biosphere atmosphere in a forested wet zone on the canadian shield abstract the ability to measure environmental levels of 36 cl by accelerator mass spectrometry and 3 h by 3 he ingrowth mass spectrometry has made it possible to use the pulses of these two isotopes released into the atmosphere during nuclear weapons testing as tracers of cl and water movement in soils and groundwater the authors have investigated the movement of these tracers below a forested wet zone and have found that both are retarded to a differing extent in the near surface because of vegetative uptake and recycling adsorption by clay particles followed by slow release to the groundwater may also be significant the data accumulated in this region of near vertical recharge have gone a considerable distance towards explaining the anomalously low concentrations of 36 cl measured in the 5 laurentian great lakes as well as indicating possible mechanisms for large scale cl recycling in the atmosphere and biosphere identification of the near term non conservative behaviour of the cl is significant since such a phenomenon could introduce errors in many watershed calculations e g water residence times evaporation rates and mixing calculations

evaluation of evaporation rate from forested soil surface using stable isotopic composition of soil water in a headwater basin the stable isotopic composition of rain water and soil water was analysed and the soil surface evaporation rate was evaluated using the isotope value of soil water taken from a forested headwater basin in central japan rainfall throughfall soil water groundwater and discharge water were sampled at intervals of one month to determine the isotopic compositions of deuterium d and oxygen 18 18 o therein in addition tensiometric observation of soil water was performed continuously the stable isotopic ratio of soil water was homogenized between the soil surface and a depth of 100 cm by means of active soil water movement above 100 cm in depth the mean 18 o in deep soil water below a depth of 100 cm was 0 24 higher than the volume weighted mean 18 o in throughfall consequently the mean evaporation rate from the soil surface was calculated as 5 of the evapotranspiration rate using the difference between the 18 o in throughfall and in deep soil water based on the rayleigh equation under equilibrium condition

morphology and isotope heterogeneity of late quaternary pedogenic carbonates implications for paleosol carbonates as paleoenvironmental proxies abstract stable isotope values and radiocarbon ages were determined for pedogenic carbonate microsamples from relict soils and palaeosols from the rio grande rift region of new mexico carbonate nodules and clusters were sampled from fluvial and piedmont soils and palaeosols with widely varying exposure durations 7 900 ky pedogenic carbonates from individual soils exhibited irregular relationships between age and depth ranging in radiocarbon age by 13 ky at individual depths 18 o values and to a lesser extent 13 c values likewise had wide ranges within soils however comparing the stable isotope values of carbonates with similar radiocarbon ages within and between soils revealed consistent trends in stable isotope values over time 18 o values of pedogenic carbonates tended to decrease with decreasing age 25 17 radiocarbon ka and increased with decreasing age 13 c values with either depth or age although the oldest palaeosol piedmont carbonates radiocarbon ages of 24 5 19 2 ka are 1 more negative than the younger piedmont palaeosol carbonates pedogenic carbonates in the relict fluvial soil which has by far the longest exposure period showed the greatest range in 13 c values comparing the 13 c values of samples of similar radiocarbon age from the relict fluvial soil indicates a transition from a mixed c 3 c 4 ecosystem at 11 ka to an effectively pure c 3 ecosystem at 9 ka followed by a return to mixed vegetation by 5 ka thus although c 4 vegetation persisted in southern new mexico through the last glaciation drought resistant c 3 vegetation became dominant at 9 ka prior to significant strengthening of the summer monsoon this study illustrates that the stable isotope values of carbonate nodules and clusters from relict soils and or slowly buried palaeosols can be used for palaeoenvironmental reconstructions in the context of a detailed chronologic framework

oxygen isotope composition of syngenetic inclusions in diamond from the finsch mine rsa oxygen isotope data have been obtained for silicate inclusions in diamonds and similar associated minerals in peridotitic and eclogitic xenoliths from the finsch kimberlite by laser fluorination oxygen isotope analyses of syngenetic inclusions weighing 20 400 g have been obtained by laser heating in the presence of clf3 18o 16o ratios are determined on oxygen converted to co2 over hot graphite and for samples weighing less than 750 g producing 12 moles o2 enhanced co production in the graphite reactor causes a systematic shift in both 13c and 18o that varies as a function of sample weight a pressure effect correction procedure based on the magnitude of 13c co2 depletion relative to 13c graphite is used to obtain corrected 18o values for inclusions with an accuracy estimated to be 0 3 for samples weighing 40 g syngenetic inclusions in host diamonds with similar 13c values 8 4 to 2 7 have oxygen isotope compositions that vary significantly with a clear distinction between inclusions of peridotitic 4 6 to 5 6 and eclogitic paragenesis 5 7 to 8 0 the mean 18o composition of olivine inclusions is indistinguishable from that of typical peridotitic mantle 5 25 0 22 whereas syngenetic purple garnet inclusions possess relatively low 18o values 5 00 0 33 reversed oxygen isotope fractionation between olivine and garnet in both diamond inclusions and diamondiferous peridotite xenoliths suggests that garnet preserves subtle isotopic disequilibrium related to genesis of cr rich garnet and or exchange with the diamond forming fluid garnet in eclogite xenoliths in kimberlite show a range of 18o values from 2 3 to 7 3 but garnets in diamondiferous eclogites and as inclusions in diamond all have values 4 7

groundwater recharge estimation using chloride deuterium and oxygen 18 profiles in the deep coastal sands of western australia the depth distributions of environmental chloride deuterium and oxygen 18 in the deep sands 20 m were monitored with a view to estimate average recharge to groundwater the investigated area is located on the southwestern coast of western australia and supports a perennial native woodland vegetation by using a steady state model based on the conservation of chloride the average areal recharge was estimated to be approximately 15 of the average precipitation 775 mm yr 1 whilst the cl concentration of groundwater was relatively uniform there was a considerable spatial variability in the depth distribution of cl in the unsaturated zone an approximate method of data analysis is developed application of this to cl data shows that possibly some 50 of the total annual recharge occurs via movement of water through preferred pathways thus bypassing the soil matrix stable isotope deuterium and oxygen 18 data show that there has been some isotopic enrichment due to evaporation of the rainfall but the extent of enrichment appears to be too small to estimate recharge rates reliably it is argued that relatively small isotopic enrichment occurs in the system studied since the direct evaporation from soil is a rather small component of the total evapotranspiration the observations on the depth distribution of isotopes qualitatively support the presence of a bimodal system for water movement through the profile as was suggested by the analysis of chloride data

early proterozoic oceanic crust and the evolution of subcontinental mantle eclogites and related rocks from southern africa seven eclogitic nodules from kimberlites in southern africa have been studied in detail for whole rock major and trace element geochemistry petrography and mineral chemistry by electron microprobe high purity mineral separates from six of these samples have been analyzed for trace elements and for the isotopic composition of sr nd and oxygen three eclogite groups are recognized group a eclogites have very high mg fe low na in pyroxene moderate 18o 4 7 to 5 3 and low 87sr 86sr and 143 144nd olivine and enstatite may also be present as accessory phases in this group group b eclogites have moderate to high mg fe ratios high na in pyroxene low 18o 3 0 to 3 4 high 87sr 86sr and 143nd 144nd ratios and extremely lree depleted hree enriched garnets with no eu anomalies group c eclogites have low mg fe ratios high na in pyroxene and variable sr nd and o isotope compositions accessory feldspar is present in one sample that may be of crustal origin mineral separates of garnet and pyroxene have positive eu anomalies the group a eclogites are too refractory to represent magma compositions and must have formed as cumulate dike rocks in the upper mantle that contain a minor trapped liquid component this is supported by the presence of accessory olivine and enstatite and by their ksm and knd which are similar to empirical pyroxene garnet partition coefficients the group b eclogites are extremely depleted in incompatible elements and have ndvalues 10x to 20x morb the high 87sr 86sr of these eclogites is not consistent with their strongly depleted lree and high nd and cannot be primary it must have been imposed on the protolith the low 18o of these eclogites cannot form by mantle fractionation processes and must also be inherited from the protolith both the sr and oxygen isotope data are consistent with high temperature hydrothermal alteration of a basaltic protolith followed by partial melting to form the refractory compositions observed now the hydrothermal fluid may have been sea water but secondary enrichment of the protolith in rb is required to generate the observed high sr ratios the high na content of the pyroxenes supports a spilitic alteration event the major and trace element characteristics of the group c eclogites are consistent with recrystallization of a cumulate gabbro protolith one group c rock is probably a garnet granulite derived from the lower crust the other may represent the plutonic portion of oceanic crust a reconstructed whole rock isochron for the three bellsbank eclogites yields an age of 2 1 0 1 b y this implies that plate tectonic processes involving the generation and subduction of oceanic crust have been active since the early proterozoic the early proterozoic ocean crust consisted of two components a plutonic section of gabbro cumulates group c eclogites and a volcanic section of basalt group b eclogites the volcanic component has undergone substantial hydro thermal alteration and subsequent partial melting to form a refractory residue the plutonic component is less modified

eclogite facies fluid infiltration constraints from δ 18 o zoning in garnet in situ analysis reveals that eclogite facies garnets are zoned in 18o with lower values in the core and rims that are 1 5 to 2 5 higher this pattern is present in 9 out of 12 garnets analyzed by sims from four orogenic eclogite terranes and correlates with an increase in the mole fraction of pyrope and mg fe ratio from core to rim indicating prograde garnet growth at the maximum temperatures and the time scales experienced by these garnets calculated intragranular diffusion distances for oxygen are small 5 from two kimberlites are homogeneous in 18o possibly due to diffusive exchange which is possible for prolonged periods at higher mantle temperatures homogeneity of 18o in garnets outside the normal mantle range 5 6 may be common in kimberlitic samples

early late pliocene biochronology and surface water temperature variations in the mediterranean a high resolution magnetobiostratigraphy is presented for the early late pliocene in sicily paleomagnetic measurements on samples from 100 stratigraphic levels provide an unprecedented high quality polarity sequence which extends from the upper reversed gilbert to the upper normal gauss subchron the resultant chronology for the early late pliocene provides ages for the following principal mediterranean bioevents 1 fodgloborotalia crassaformis at 3 40 ma 2 prolonged absence ofgloborotalia puncticulata between 3 38 and 3 16 ma 3 loduvigerina rutila at 3 16 ma 4 lodsphaeroidinellopsis seminulina at 3 07 ma 5 lodgloboquadrina altispira at 3 04 ma 6 lodcibicides italicus at 2 96 ma summer and winter surface water temperature estimates for the period 3 50 to 2 92 ma are based on the abundances ofglobigerinoides sacculifer andgloborotalia puncticulata in 111 samples with an average resolution of some 5000 years short term variations in temperature of the surface water and in colour and carbonate content of the sediment are primarily controlled by the equinoxal precession a higher seasonality during deposition of the grey coloured carbonate poor facies suggests that at that time the summer solstice occurred near perihelion whereas an inverse alignment occurred at the time of deposition of white coloured carbonate rich layers this phase relationship between the precession cycle and grey coloured layers is also valid for the sapropels which began to intercalate in the grey coloured layers at 2 94 ma long term changes in surface water temperatures include a warming between 3 38 and 3 18 ma followed by a cooling from 3 18 to 3 03 ma the warming of mediterranean surface waters at 3 38 ma is believed to be associated with the final closure of the isthmus of panama consequent strengthening of the gulf stream injected larger volumes of warm surface water into the north atlantic drift and eastern boundary current and this caused surface water temperatures in the mid to high latitude northeast atlantic and mediterranean to rise the subsequent climatic cooling at 3 18 ma is linked to a first stage of northern hemisphere continental ice growth

the origin of rhythmic bedding in the pliocene trubi formation of sicily southern italy abstract foraminiferal palynological stable isotope geochemical clay mineralogical and granulometric data have been gathered for the successive layers of four rhythmic alterations of relatively carbonate poor and carbonate rich beds in the early pliocene trubi formation of sicily southern italy the marly rhythmites consist of a grey layer and a white more indurated layer in which an additional beige less indurated layer is intercalated they are therefore more complex than the well known marl limestone couples elsewhere these rhythmites probably originate from the alternate predominance of increased dilution of river supplied terrigenous material grey and decreased carbonate production in the surface waters beige the grey layers are considered to correspond to periods of increased local run off and higher surface water temperatures and productivity the beige layers signal more arid and cooler climatic conditions lower surface water productivity and stronger or more frequent dust loaded southern winds the white layers apparently reflect intermediate climatic and environmental conditions these periodical changes probably brought about by astronomical precession appear to have occurred not only during the pliocene but also during the late miocene

characteristic trace fossil associations in oxygen poor sedimentary environments the sedimentologic record of oxygen poor depositional environments typically includes trace fossils produced by deposit feeding organisms we propose an oxygen controlled trace fossil model in which increasing oxygen concentration of interstitial water in sediment parallels a transition from fodinichnia dominated through pascichnia dominated to domichnia dominated trace fossil associations in certain places such as parts of the late paleozoic oquirrh basin in utah this model provides a reasonable alternative to the more traditional depth controlled model of trace fossil distribution

plio pleistocene sedimentation on the walvis ridge southeast atlantic dsdp leg 75 site 532 influence of surface currents carbonate dissolution and climate an investigation of the quantitative composition of the coarse 40 m and clay 2 m fraction of hpc 532 dsdp leg 75 in 1300 m water depth on the eastern walvis ridge off southwest africa yielded the following results 1 1 the sediments reflect a complete latest miocene to recent depositional history sedimentation rates vary between 2 3 and 7 8 cm 10 3 years 2 2 preservation of calcium carbonate is subject to strong variations short term 100 000 years and long term about 1 m y cycles in carbonate dissolution have been observed with strongest dissolution occurring during periods of lowered sea level 3 3 upwelling influence from the near coastal upwelling centre has been detected by means of the opal content interglacial periods show high opal contents because the benguela current turned westward at about 20 s and carried opal laden upwelled water to the west sediments from glacial periods however show opal minima besides these short term cyclic variations in opal content long term cycles have been found with maximum upwelling influence in the latest pliocene early quaternary 4 4 each caco3 dissolution minimum maximum is correlated with an opal maximum minimum throughout the sediment sequence 5 5 the oceanographic system off southwest africa remained essentially unchanged since the latest miocene sea level rose and fell periodically on a small and on a large scale and the benguela current flowed southeast northwest and turned to the west at the latitude of site 532 during interglacial periods when sea level was high 6 6 the climate in the near coastal area of southwest africa in the latitude of site 532 has probably been arid throughout the investigated period

oxygen isotopes in coexisting garnets clinopyroxenes and phlogopites of roberts victor eclogites implications for petrogenesis and mantle metasomatism abstract 18 o values of coexisting garnet clinopyroxene and phlogopite for twelve compositionally and texturally diverse roberts victor eclogite xenoliths range from 3 8 to 7 1 4 0 to 7 4 and 5 9 to 7 4 respectively differences between the 18 o values of coexisting garnets and clinopyroxenes are normally zero however there is some variation in the 18 o values of different fractions of the same mineral in four samples which suggests the presence of isotopic zonation and inhomogeneity possibly resulting from the introduction of a secondary fluid which metasomatized the eclogites and resulted in the formation of phlogopite amphibole and celsian the 18 o value of the metasomatic fluid is generally buffered by the isotopic composition of the primary garnet and clinopyroxene as indicated by a correlation between the isotopic composition of phlogopite and the primary pyroxene and garnet the large range in 18 o values of the eclogites and the similarity in the isotopic composition of coexisting pyroxene and garnet support the interpretation that the roberts victor eclogites represent metamorphosed altered basalts the eclogites were subjected to infiltration metasomatism in the mantle prior to their incorporation in the kimberlite and the source of this fluid was probably unrelated to the eclogite

reply to comments by taylor and neal on trace element crystal chemistry of mantle eclogites in summary there are no existing clinopyroxene liquid ree distribution data obtained under appropriate conditions to permit numerical modeling of trace elements to constitute a critical test of the pyroxene fractionation process there are however numerous clinopyroxeneliquid partitioning data in the literature that give qualitatively similar patterns to those observed in grospydites further the high pressure fractionation model accounts for the major element and exsolution phenomena in a manner directly consistent with experimental petrologic studies and can qualitatively account for the trace element and isotopic characteristics of the rocks in a manner consistent with the crystal chemistry of the phases we therefore continue to prefer the high pressure clinopyroxene fractionation model over a low pressure plagioclase fractionation model for the origin of the grospydites

thermodynamics and lattice vibrations of minerals 5 applications to phase equilibria isotopic fractionation and high pressure thermodynamic properties in previous papers in this series a model that uses available elastic structural and spectroscopic data on minerals has been used to predict the thermodynamic functions cv heat capacity s entropy e internal energy and f helmholtz free energy in this paper four applications to problems of current geochemical and geophysical interest are presented 1 interpretation of complex trends of calorimetric data 2 calculation of phase equilibria 3 calculation of oxygen isotopic fractionation factors and 4 estimation of the effect of pressure on thermodynamic functions the model demonstrates that trends in high temperature thermodynamic properties of silicates are determined by the position and relative numbers of high frequency modes generally antisymmetric si al o stretching modes the position of these modes varies systematically with degree of polymerization of tetrahedra and therefore high temperature calorimetric behavior is relatively systematic as a function of crystal structure and mineral composition trends at low frequency are much more complex because the low frequency optic modes that most strongly influence the low temperature thermodynamic functions depend in a complex way on the size coordination and mass of cations and various polyhedra in the minerals the heat capacity curves of kyanite andalusite and sillimanite and of quartz coesite and stishovite show crossovers that cannot be explained by debye theory which accounts only for acoustic mode behavior but can be explained by the model spectra proposed because proper account is taken of the changing low and high frequency optic modes upon polymorphic transformations the proposed model is sufficiently accurate that phase equilibrium problems can be addressed the quartz coesite stishovite equilibrium curves the kyanite andalusite sillimanite triple point and the breakdown of albite to jadeite plus quartz are cited as specific examples for each example predicted slopes of equilibrium curves agree moderately well to excellently with slopes determined experimentally the calculated slopes are sensitive to spectroscopic parameters particularly to the distribution of optic modes in the far infrared this sensitivity is discussed in detail for the albite breakdown reaction the model can be used for prediction of isotopic fractionation factors if spectra of the isotopic forms of the mineral are known or postulated a simple set of rules for generating hypothetical spectra of 18o minerals from measured spectra of the 16o forms is given reduced partition functions are calculated for 13 minerals at 298 k the model values of reduced partition function 1000 ln of these minerals decrease in the order quartz calcite albite muscovite clinoenstatite anorthite diopside pyrope grossular zircon forsterite andradite rutile in good agreement with experimental data at 1000 k the first six minerals show small crossovers so that the order becomes calcite muscovite albite quartz anorthite and clinoenstatite the differences in 1000 ln at high temperature for these minerals are so small that the model probably cannot address the deviations from experimental trends the model clearly defines the region in which the fractionation factors do not follow a 1 t trend and should be useful for extrapolation of experimental data to low temperatures finally a modified gruneisen parameter model is proposed for shift of the lattice vibrational frequencies under compression and thermodynamic properties to 1000 kbar 1000 k are given for nine minerals at 1 mbar the predicted decrease in entropy at 298 k ranges from 54 of the 1 bar value for periclase to 25 for stishovite

the response of infiltration depth evaporation and soil water replenishment to rainfall in mobile dunes in the horqin sandy land northern china to understand the relationships among rainfall infiltration evaporation replenishment in mobile dunes in the semi arid areas of china we used the container of water distribution 100 100 120 cm3 to examine rainfall infiltration soil water redistribution and soil surface evaporation under natural and simulated rainfall conditions the results showed that infiltration depth was linearly related to rainfall amount and intensity rainfall amounts larger than 13 4 mm could replenish soil water at 60 cm depth after redistribution while with rainfalls larger than 39 8 mm infiltration depth could exceed 120 cm rainfall amounts larger than 50 mm produced saturated soil water at 120 cm depth and replenishment amount accounted for 40 4 of the total amount of rainfall soil surface evaporation exhibited a relatively minor change with increases in rainfall when rainfall was larger than 11 8 mm the amount of evaporation and soil water content were significantly correlated at 0 60 cm soil depth but not below these results suggest that the maximum effective depth of evaporation is 60 cm below the ground surface and that rainfall of 13 4 mm is a threshold distinguishing effective from ineffective rainfall in the mobile dunes of the horqin sandy land

pedogenic carbonate stable isotope record of environmental change during the neogene in the southern great plains southwest kansas usa oxygen isotopes and paleoclimate during the evolution of c4 dominated grasslands neogene strata in the meade basin southwest kansas preserve numerous superposed calcareous paleosols in sections that range in age from the clarendonian north american land mammal age nalma 12 0 9 0 ma early late miocene to the early irvingtonian nalma ca 2 5 ca 1 ma early pleistocene the carbon isotope compositions 13 c relative to vienna peedee belemnite vpdb of pedogenic carbonates from these sections record the protracted regional increase in the abundance of grasses using the c 4 photosynthetic pathway over this interval with the first appearance of a modern like grassland ecosystem having 70 c 4 biomass around 1 3 ma we use the stable oxygen isotope composition 18 o relative to vienna standard mean ocean water vsmow of 194 paleosol carbonates from 19 measured sections to reconstruct the climatic conditions in the meade basin during the rise of c 4 grasses to ecological dominance in the region pedogenic carbonate 18 o values are sensitive to soil temperature and the 18 o of soil water and hence they are a paleoclimate proxy carbonate 13 c values do not exhibit consistent trends in relation to 18 o values indicating no consistent relationship between short term climatic conditions in terms of temperature or aridity and the abundance of c 4 biomass mean carbonate 18 o values within biostratigraphic intervals decrease from the clarendonian 25 3 0 72 to the early and middle blancan 21 8 0 87 and 22 1 0 69 respectively and they also exhibit a decreasing trend in the late blancan early irvingtonian from 25 to 21 the increase in 18 o values between the end of the middle blancan and the beginning of the late blancan early irvingtonian sections could reflect the onset of northern hemisphere glaciation and a change in the isotope composition of the hydrosphere due to increased ice volume the long term trend in 18 o values suggests that c 4 biomass increased coincident with some combination of decreasing temperature increasing proportion of winter precipitation recharge of soil water and or increasing soil moisture thus the ecological dominance of c 4 grasses in the region today does not seem to be linked to warmer temperatures or increased aridity

identification of probable groundwater paths in the amargosa desert vicinity in this study the hydrogeochemical program phreeqc was used to determine the chemical speciation and mineral saturation indices sis of groundwater in the vicinity of the proposed high level nuclear waste repository at yucca mountain nevada usa in turn these data were used to interpret the origin and recharge mode of groundwater to elucidate the mechanisms of flow and transport and to determine potential sources of groundwater contamination phreeqc was run to determine aqueous dissolved species and minerals that would be in equilibrium with the study area s groundwater selected major ions associated si f and ca na ion exchange were then examined using the multivariate statistical methods of principal component factor analysis and k means cluster analysis analysis of dissolved ion concentrations sis and ca na ion exchange allows simultaneous consideration of arithmetic raw concentrations and logarithmic si ion exchange variables that describe the hydrochemical system and therefore can provide further insight into the system s behavior the analysis indicates that the dominant processes and reactions responsible for the hydrochemical evolution in the system are 1 evaporative concentration prior to infiltration 2 carbonate equilibrium 3 silicate weathering reactions 4 limited mixing with saline water 5 dissolution precipitation of calcite dolomite and fluorite and 6 ion exchange principal component factor analysis and k means cluster analysis of factor scores allow the reduction of dimensions describing the system and the identification of hydrogeochemical facies and the processes that defined and govern their evolution statistical analysis results indicate that the northern west face and southern yucca mountain groundwater is fresh water with low concentrations of ca2 mg2 cl ca2 na 2 and caf2 the fortymile wash groundwater is dilute the carbonate signature is shown in the ash meadows and death valley waters with high fluorite si finally the crater flat stripped hills and skeleton hills are dominated by ca na ion exchange mg and ca the hydrochemical and statistical analyses showed three main groundwater signatures or hydrochemical processes indicating groundwater evolution potential flowpaths and recharge areas the flowpaths are the trace of the amargosa river the trace of fortymile wash and its convergence with the amargosa river this appears to represent not just a groundwater flow path but traces of surface runoff infiltration as well

influx and efflux of moisture in a desert soil during a 1 year period spatial and temporal variation of moisture flux in soil over a 1 year period was studied in the thar desert of india tritium was injected at a depth of 0 8 m at 18 sites distributed over an area of 50 km2 and at 20 adjacent points at a single site over a sand dune before the 1994 monsoon vertical soil profiles were collected from the 18 sites after the end of monsoon and at the end of the year and from the multiple injections site at different time intervals throughout the year moisture flux values computed from tritium and moisture distribution in soil profiles show that the moisture influx at a site depends upon the grain size of the top 20 cm layer and that about 68 of the total influx of water below the injection depth is lost during the summer months the data for the multiple injections site show that the tritium spike was displaced to a depth of 4 m by the end of the monsoon and it remained stationary during the postmonsoon period of 8 months although about 64 of the soil moisture was lost the spiked layer showed enrichment in the specific activity of tritium during summer months these observations suggest that vapor diffusion is the dominant process for moisture loss from the thar desert soil the net input natural recharge to groundwater due to 1994 precipitation was 62 mm

tracing infiltration and recharge using stable isotope in taihang mt north china the groundwater in headwater region is an important recharge source for the adjacent mountain front plain in order to reveal the relationship among precipitation soil water and groundwater from june to september in 2004 stable isotopes deuterium and oxygen 18 in precipitation and soil waters at the depths of 10 20 30 50 70 90 and 110 cm were analyzed at two sites covered by black locust robinia pseudoacia l site a and grass predominated by themeda triandra t japonica willd tanaka and bothriochloa ischaemum b ischaemum l keng site b in an experimental catchment at taihang mt north china respectively the 18o of precipitation in daily rain events shows large variations 13 3 to 4 3 with a mean of 8 1 the 18o and d of soil waters along profiles in two sites suggest that the influence of canopy cover was just up to 10 cm in top soil water the soil water moved over the zero flux plane at 70 cm in depth is expected to escape the evaporative effect at the end of september in both sites the results show that the stable isotope instead of tritium as tradition can be used to trace the soil water behaviors based on the movement of isotopic peak along the vertical profiles in this semi arid and semi humid mountainous region the infiltration depths of soil water in taihang mt are 12 and 10 mm day from june to september in 2004 in site a and site b respectively tracing by stable isotope recharge fluxes of soil water to local groundwater are of 3 8 and 3 2 mm day in site a and site b respectively the results provide desirable information for assessment of local groundwater resources

stable carbon and oxygen isotopes of pedogenic carbonates ajo mountains southern arizona implications for paleoenvironmental change abstract in this study we compare the stable isotope composition of late holocene pedogenic carbonate from a late holocene soil developed on the pediment below the ajo mountains in southern arizona usa with measurements of the 18 o of the soil water throughout the seasonal cycle and with 18 o and 13 c measurements on older dated soils the comparison with the soil water composition shows that the pedogenic carbonate is forming in equilibrium with highly evaporated soil water at the highest summer temperatures the 13 c of the carbonate apparently reflects equilibrium with co 2 of an isotopic composition consistent with the present mixture of c3 desert shrubs and cam cactus comparison with glacial period soil carbonates shows that there has been little change in the 18 o but that the 13 c was about 4 5 heavier independent evidence indicates that glacial period summer temperatures were probably much cooler and that the 18 o of precipitation was also lighter the increase in the carbonate water fractionation factor with decreasing temperature probably counteracted the decrease in the 18 o of precipitation producing little net change in the 18 o of the soil carbonate we attribute the decrease in the 13 c to replacement of a glacial period c4 grassland by holocene c3 cam desert shrubs and succulents this replacement was probably in response to an increase in temperature and reduction in summer precipitation at the end of the last glacial period the 13 c of older soil carbonates indicates that landscape was dominated by grassland for most of the past 700 ka and that the present vegetation likely represents a relatively brief anomaly

uncertainties around modelling of steady state phreatic evaporation with field soil profiles of δ18o and chloride summary the application of the general advection diffusion equation to model phreatic evaporation flux rates from solute concentration soil profiles has been applied to a variety of arid zone locations but the effects of heterogeneous and uncertain field data on modelling performance are rarely described we revisit and extend the model by accounting for the effects of variable water content and sediment type on the impedance factor and in turn effective diffusion coefficient we explore the local sensitivity of the extended model to its major assumptions and parameter values the mean diffusion coefficient of the soil profile data is most sensitive to the volumetric water content close to the evaporation front and so modelled evaporation results can be very sensitive to uncertainty around the position of the evaporation front the uncertainty in the position of the groundwater reservoir and its concentration has little effect where the lower part of the profile shows an asymptotic trend towards a representative value of groundwater concentration but can vary substantially with different values of groundwater depth and concentration if this is not the case field data from the southern margin of the great artesian basin are shown to exhibit considerable uncertainty around the boundary conditions of the advection diffusion model e g position of evaporation front depth and concentration of lower groundwater boundary condition resulting phreatic evaporation flux estimates show a wide range that needs to be considered when using these data in water balance studies of groundwater systems

magnitude of climate variability during middle pliocene warmth a palaeoclimate modelling study abstract the nature and magnitude of climatic variability during the period of middle pliocene warmth ca 3 29 2 97 ma is poorly understood we present a suite of palaeoclimate modelling experiments incorporating an advanced atmospheric general circulation model gcm coupled to a q flux ocean model for 3 29 3 12 and 2 97 ma bp astronomical solutions for the periods in question were derived from the berger and loutre bl2 astronomical solution boundary conditions excluding sea surface temperatures ssts which were predicted by the slab ocean model were provided from the usgs prism2 2 2 digital data set the model results indicate that little annual variation 0 5 c in ssts relative to a control experiment occurred during the middle pliocene in response to the altered orbital configurations annual surface air temperatures also displayed little variation seasonally surface air temperatures displayed a trend of cooler temperatures during december january and february and warmer temperatures during june july and august this pattern is consistent with altered seasonality resulting from the prescribed orbital configurations precipitation changes follow the seasonal trend observed for surface air temperature compared to present day surface wind strength and wind stress over the north atlantic north pacific and southern ocean remained greater in each of the pliocene experiments this suggests that wind driven gyral circulation may have been consistently greater during the middle pliocene the trend of climatic variability predicted by the gcm for the middle pliocene accords with geological data however it is unclear if the model correctly simulates the magnitude of the variation this uncertainty is derived from a the relative insensitivity of the gcm to perturbation in the imposed boundary conditions b a lack of detailed time series data concerning changes to terrestrial ice cover and greenhouse gas concentrations for the middle pliocene and c difficulties in representing the effects of climatic history in snap shot gcm experiments

magnetostratigraphy based astronomical tuning of the early pliocene lacustrine sediments of ptolemais nw greece and bed to bed correlation with the marine record continental deposits from the early pliocene lacustrine ptolemais basin in nw greece display rhythmical alternations of lignite and marl beds three parallel sections from this area are studied using magnetostratigraphy and cyclostratigraphy the presence of the greater part of the gilbert chron enables the recognition of astronomical periodicities in the succession especially the precessional influence is evident as it determines the lithological cycles the continental ptolemais composite section is correlated to the most recent astronomical time scale and thus to the marine reference section the rossello composite from sicily c g langereis f j hilgen the rossello composite a mediterranean and global reference section for the early to early late pliocene earth planet sci lett 104 1991 211 225 on a bed to bed scale it is concluded that lignite corresponds to an insolation minimum beige layer in the rossello composite and marl to an insolation maximum grey layer in the rossello composite this implies a precipitation increase during insolation maxima in early pliocene continental greece 1998 elsevier science b v all rights reserved

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

the role of soil processes in δ18o terrestrial climate proxies a paleoclimate interpretation of a terrestrial hydrologic proxy such as the 18o of tree cellulose or speleothem calcite may be biased or misinterpreted if the isotopic composition of the soil water from which the proxy originated undergoes isotopic exchange or fractionation in this study we use a global isotope enabled land surface model to investigate how the 18o of precipitation may be altered in a soil column due to evaporation and vertical moisture transport in order to assess how precipitation and evaporation contribute to the soil water isotopic variability we compare seasonal and interannual changes in simulated xylem water 18o within a control simulation and in a suite of sensitivity experiments where the effects of precipitation 18o water vapor 18o and soil water evaporation are independently removed the simulations carried out for the period 1979 to 2004 reveal that in semiarid regions such as the southwest united states the seasonal cycle in xylem water 18o is strongly affected by evaporative loss during the dry season and evaporation can also constitute as much as 50 of the interannual 18o variance additional simulations including soil water tagging experiments indicate that upward fluxes of soil water occur during drier periods for soil water 18o profiles that are isotopically more depleted in 18o at depth this imparts a low isotopic signature to xylem water 18o during such dry intervals hence without taking into account vertical moisture transport in the soils low 18o years could be misinterpreted as wet conditions due to decreased evaporative enrichment when instead drier conditions are equally as likely

the rossello composite a mediterranean and global reference section for the early to early late pliocene a high resolution magnetostratigraphy planktonic foraminiferal biostratigraphy and cyclostratigraphy is presented for the pliocene trubi marls in the punta di maiata section on sicily the integrated stratigraphy of the rossello composite section of hilgen 1 newslett stratigr 17 1987 is thereby completed this composite section provides an unprecedented high quality reference section for the early to early late pliocene containing a continuous sequence ranging from below the thvera subchron into the matuyama chron 4 86 2 45 ma the punta di maiata section extends from the sidufjall subchron of the gilbert into the gauss chron 4 50 3 30 ma linear interpolation between paleomagnetic datum planes in this section yields first order age estimates of 3 72 0 01 and 3 59 0 01 ma for the last common occurrence lco and the actual last occurrence lo of globorotalia margaritae in addition this age of 3 59 ma provides an accurate age for the zanclean piacenzian z p boundary provided the lo of g margaritae is maintained as a criterion to define this boundary in the mediterranean irrespective however of the criterion used the punta di maiata and punta piccola subsections of the rossello composite are at present the most suitable sections to be designated as stratotypes for the z p boundary the global significance of the rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the trubi sedimentary cycles with the astronomical record

perchlorate accumulation and migration in the deep vadose zone in a semiarid region summary for 25 years a plant in israel manufacturing ammonium perchlorate disposed of untreated wastewater in four unlined ponds this study explores the transport mechanisms of perchlorate infiltrated from 1965 to 1990 from one of these active storage ponds into a deep 40 m layered vadose zone and the underlying israeli coastal aquifer perchlorate migration from 1990 when wastewater disposal ceased until today with infiltration due only to natural rain 500 mm y 1 was also studied several indirect methods were used including mass balance in the unsaturated zone profile 18 o and 2 h profiles below the pond and a comparison of the same sediment profiles in 2005 and 2007 the isotopic composition of the pore water could be divided into two separate groups lighter depleted and heavier enriched samples all samples in the lighter group were from the shallow vadose zone above two clayey layers and represent natural infiltration of rainwater the enriched samples were from the deeper section of the unsaturated zone 20 40 m and represent water used for perchlorate manufacturing 14 years prior to drilling consequently the overall maximum infiltration rate was estimated to be 1 4 m y 1 below the clayey layer almost identical perchlorate concentrations were found along the sediment profile in 2005 and 2007 two boreholes 3 m apart very different perchlorate profiles were observed above the clayey layers this suggests that perchlorate below the clay layers 20 40 m is practically stagnant under the current natural conditions the reduction in perchlorate concentration in groundwater below the ponds vs its increased concentration further downgradient supports the contention that the current migration of perchlorate from the vadose zone to the groundwater is very small we estimate that perchlorate concentration in the groundwater under the infiltration pond which was 187 mg l 1 in 2004 will reach 10 g l 1 within about 14 years the existence of a clayey layer crossing the thick vadose zone was thus found to significantly change the infiltration rate when ponded conditions were replaced with natural precipitation

water movement in desert soil traced by hydrogen and oxygen isotopes chloride and chlorine 36 southern arizona abstract understanding soil water movement is important for water resource management and for analyzing pollutant transport in the vadose zone seasonal variations in shallow soil profiles may have profound effects on deep soil water and solutes we have investigated seasonal soil water movement in the top meter of undisturbed desert soil in the southern arizona using 2 h 18 o cl and bomb 36 c1 six soil profiles were sampled from a young terrace holocene during 1991 to 1992 on a seasonal basis one soil profile was sampled from an older terrace latest pleistocene in october 1992 and one from a yet older fan surface late pleistocene in march 1992 the results indicate that repeated seasonal cyclic movement of soil water in the top 60 80 cm active zone tends to produce a consistent stable isotope composition for the soil water below the active zone in different seasons the deep 18 o on the oldest surface is about 6 heavier than on the younger surfaces probably resulting from greater evaporative loss due to the larger proportion of fines in the older soil this deep isotopic composition is closely related to the composition of the local average annual precipitation an annual average evaporation rate of 35 mm year 1 was estimated using a steady state diffusion model whereas the actual regional evapotranspiration rate is 175 250 mm year 1 this suggests that about 80 of the soil water is lost through transpiration and first stage evaporation before quasi steady state is reached the long term average infiltration rate below the active zone is about 4 mm year 1 for the younger terrace based on both chloride mass balance and bomb 36 cl and 0 02 mm year 1 for the older terrace and the fan surface based on chloride mass balance the correlation between the deep 18 o the reduction of downward flux and the surface age suggests that increasing soil development has resulted in a significant decrease of soil water infiltration and hence an increase in evaporation and surface runoff

a four component mixing model for water in a karst terrain in south central indiana usa using solute concentration and stable isotopes as tracers the study area lies in a highly karstified carbonate terrain in south central indiana sinkholes conduits and caves form large secondary pathways for the subsurface flow as a result the discharge from a main emergence point for the subsurface flow system the orangeville rise quickly responds to the storm events and shows wide variations in flow rate water chemistry and stable isotopic compositions these responses are attributed to the mixing of water in secondary pathways in the study area recharge occurs through the thick mantled karst plain and the sinkhole plains and the role of soil layer and epikarst in the recharge process is of great importance rain dic 2 hco3 mg l 13cdic 7 soil water dic 544 hco3 mg l 13cdic 14 7 epikarstic water dic 224 hco3 mg l 13cdic 13 6 and phreatic diffuse flow water dic 299 hco3 mg l 13cdic 11 8 generally showed unique and constant dissolved inorganic carbon dic and 13cdic values over time using dic and 13cdic as tracers a four component mixing model was established for the karstic flow system by constructing the discharge hydrograph separation curves the mixing ratio of each component rain 10 6 soil 3 1 epikarstic 52 3 and phreatic 34 0 water was determined for the orangeville rise discharge over the testing period of 104 h after the storm event of 10 4 90 vadose water occupied 55 4 of spring discharge and this demonstrates the importance of the unsaturated zone especially the epikarst in the karstic flow systems

sequence concepts at seismic and outcrop scale the distinction between physical and conceptual stratigraphic surfaces abstract the sequence stratigraphic terms maximum flooding surface and downlap surface as currently applied are ambiguous examples of these intra sequence surfaces are summarised from high frequency mid pleistocene sequences and from a cretaceous recent seismic megasequence both from new zealand at any one locality a mid pleistocene sequence contains up to four stratal discontinuities in ascending order the sequence boundary ravinement surface local flooding surface and downlap surface these physical surfaces which occur in outcrop are regionally diachronous and should be differentiated from theoretical isochronous horizons such as the time of maximum flooding horizon corresponding to maximum shoreline transgression and the time of peak eustatic or local relative sea level horizons corresponding to the highpoint of the eustatic and relative sea level cycles respectively in seismic studies the boundary between the transgressive and highstand systems tracts is usually located at the downlap surface on the basis of a major thermo tectonic sea level cycle in the canterbury basin it is shown that the downlap surface is not a single regional surface and that the change in slope associated with toes of successive prograding clinoforms rises in stratigraphic height basinwards the downlap surface therefore does not usually coincide with the maximum flooding horizon in plio pleistocene cyclothems a discrete unit the mid cycle shellbed straddles the contact between the transgressive and highstand systems tracts this unit might be classified within its own systems tract the condensed section systems tract csst alternatively the position of the boundary between the transgressive and highstand systems tracts can remain unspecified or unknowable

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

a chlorine 36 study of regional groundwater flow and vertical transport in southern nevada chlorine 36 data for groundwater from the death valley regional flow system is interpreted in the context of existing conceptual models for regional groundwater flow in southern nevada chlorine 36 end member compositions are defined for both recharge and chemically evolved groundwater components the geochemical evolution of 36cl is strongly controlled by water rock interaction with paleozoic carbonate rocks that comprise the regional aquifer system resulting in chemically evolved groundwater that is characteristically low in 36cl cl and high in cl groundwater from alluvial and volcanic aquifers that overlie the regional carbonate aquifer are generally characterized by high 36cl cl and low cl signatures and are chemically distinct from water in the regional carbonate aquifer this difference provides a means of examining vertical transport and groundwater mixing processes in combination with other geochemical and hydrogeologic data the end members defined here provide constraints on aquifer residence times and mixing ratios

eustatic signals in deep marine sedimentary sequences recovered at odp site 978 alboran basin western mediterranean sea abstract a continuous section of pliocene marine sediments was recovered at ocean drilling program site 978 located in the alboran sea between spain and morocco three pliocene subunits have been defined at site 978 the lowermost subunit ic 129 2 m thick is characterized by alternating beds of lighter more calcareous and darker less calcareous claystone with bioturbated upper and lower contacts type 1 cycles the middle subunit ib 67 1 m thick is composed of relatively homogeneous nannofossil claystone and the uppermost subunit ia 211 6 m thick contains abrupt based darker terrigenous layers interpreted as turbidites that are interstratified with lighter nannofossil claystone type 2 cycles the rhythmically bedded light and dark layers in subunit ic correlate with those in the rosello composite section of sicily a global reference standard for the pliocene time scale these sedimentary cycles are products of variations in precession and resulting continental runoff missing cycles occur during eustatic highstands the shift to more homogeneous sedimentation in subunit ib is represented in similar aged sequences throughout the mediterranean which display evidence of submarine mass wasting mediterranean wide slope degradation was likely a response to rapid sea level change at approximately 3 ma this change in sedimentation style was accompanied by an upsection increase in sediment accumulation rates associated with turbidite influx in subunit ia turbidite frequency throughout the pliocene section can be linked to eustatic changes in sea level with turbidite maxima corresponding with mid sequence downlap surfaces and their associated condensed sections