the geohydrologic setting of yucca mountain nevada abstract this paper provides a geologic and hydrologic framework of the yucca mountain region for the geochemical papers in this volume the regional geologic units which range in age from late precambrian through holocene are briefly described yucca mountain is composed of dominantly pyroclastic units that range in age from 11 4 to 15 2 ma the principal focus of study has been on the paintbrush group which includes two major zoned and welded ash flow tuffs separated by an important hydrogeologic unit referred to as the paintbrush non welded ptn the regional structural setting is currently one of extension and the major local tectonic domains are presented together with a tectonic model that is consistent with the known structures at yucca mountain streamflow in this arid to semi arid region occurs principally in intermittent or ephemeral channels near yucca mountain the channels of fortymile wash and amargosa river collect infrequent runoff from tributary basins ultimately draining to death valley beneath the surface large scale interbasin flow of groundwater from one valley to another occurs commonly in the region regional groundwater flow beneath yucca mountain originates in the high mesas to the north and returns to the surface either in southern amargosa desert or in death valley where it is consumed by evapotranspiration the water table is very deep beneath the upland areas such as yucca mountain where it is 500 750 m below the land surface providing a large thickness of unsaturated rocks that are potentially suitable to host a nuclear waste repository the nature of unsaturated flow processes which are important for assessing radionuclide migration are inferred mainly from hydrochemical or isotopic evidence from pneumatic tests of the fracture systems and from the results of in situ experiments water seeping down through the unsaturated zone flows rapidly through fractures and more slowly through the pores of the rock matrix although capillary forces are expected to divert much of the flow around repository openings some may drip onto waste packages ultimately causing release of radionuclides followed by transport down to the water table

devils hole nevada δ18o record extended to the mid holocene abstract the mid to late pleistocene devils hole 18 o record has been extended from 60 000 to 4500 yr ago the new 18 o time series in conjunction with the one previously published is shown to be a proxy of pacific ocean sea surface temperature sst off the coast of california during marine oxygen isotope stages mis 2 and 6 the devil hole and sst time series exhibit a steady warming that began 5000 to 10 000 yr prior to the last and penultimate deglaciations several possible proximate causes for this early warming are evaluated the magnitude of the peak 18 o or sst during the last interglacial lig is significantly greater 1 per mill and 2 to 3 c respectively than the peak value of these parameters for the holocene in contrast benthic 18 o records of ice volume show only a few tenths per mill difference in the peak value for these interglacials statistical analysis provides an estimate of the large shared information variation between the devils hole and eastern pacific sst time series from 41 to 2 n and enforces the concept of a common forcing among all of these records the extended devils hole record adds to evidence of the importance of uplands bordering the eastern pacific as a source of archives for reconstructing pacific climate variability

improved spatial resolution for u series dating of opal at yucca mountain nevada usa using ion microprobe and microdigestion methods two novel methods of in situ isotope analysis ion microprobe and microdigestion were used for 230th u and 234u 238u dating of finely laminated opal hemispheres formed in unsaturated felsic tuff at yucca mountain nevada proposed site for a high level radioactive waste repository both methods allow analysis of layers as many as several orders of magnitude thinner than standard methods using total hemisphere digestion that were reported previously average growth rates calculated from data at this improved spatial resolution verified that opal grew at extremely slow rates over the last million years growth rates of 0 58 and 0 69 mm m y were obtained for the outer 305 and 740 m of two opal hemispheres analyzed by ion microprobe and 0 68 mm m y for the outer 22 m of one of these same hemispheres analyzed by sequential microdigestion these pleistocene growth rates are 2 to 10 times slower than those calculated for older secondary calcite and silica mineral coatings deposited over the last 5 to 10 m y dated by the u pb method and may reflect differences between miocene and pleistocene seepage flux the microdigestion data also imply that opal growth rates may have varied over the last 40 k y these data are the first indication that growth rates and associated seepage in the proposed repository horizon may correlate with changes in late pleistocene climate involving faster growth during wetter cooler climates glacial maximum slower growth during transition climates and no growth during the most arid climate modern data collected at this refined spatial scale may lead to a better understanding of the hydrologic variability expected within the thick unsaturated zone at yucca mountain over the time scale of interest for radioactive waste isolation

lunar surface rock abundance and regolith fines temperatures derived from lro diviner radiometer data 1 surface temperatures derived from thermal infrared measurements provide a means of understanding the physical properties of the lunar surface the contrasting thermophysical properties between rocks and regolith fines cause multiple temperatures to be present within the field of view of nighttime multispectral data returned from the lunar reconnaissance orbiter lro diviner radiometer between 60 n s latitudes regolith temperatures are influenced by the presence of rocks in addition to factors such as the thermophysical properties of the regolith fines latitude and local slopes and radiative heating from adjacent crater walls preliminary comparisons of derived rock concentrations with lro camera images show both qualitative and quantitative agreement although comparisons of derived rock concentrations with circular polarization ratio radar data sets display general similarities there are clear differences between the two data sets in the relative magnitude and areal extent of rocky signatures several surface units can be distinguished based on their regolith temperature and rock concentration values and distributions including maria and highlands surfaces rocky impact craters rilles and wrinkle ridges dark mantled deposits and isolated cold surfaces rock concentrations are correlated with crater age and rocks are only preserved on the youngest surfaces or where steep slopes occur and mass wasting prevents mantling with fines the presence of rocky surfaces excavated by young impacts allows for the estimation of minimum regolith thickness from the size of the impact the derived rock concentrations confirm the presence of thicker regolith cover in the highlands and in locations of radar dark haloes

late holocene climate of the eastern mediterranean inferred from diatom analysis of annually laminated lake sediments abstract diatoms from the annually laminated sediments of nar crater lake in central turkey are used to investigate climatic changes throughout the last 1720 years at decadal time resolution a diatom conductivity transfer function is employed to infer past water balance further information has been extracted from the palaeo record through calculation of diatom biovolume rarefaction species diversity and concentration and through the identification of diatom bloom events in core thin sections the nar diatom sequence is compared with oxygen isotope 18 o and pollen records from the same sediment cores in order to test the respective roles of changes in climate and land cover diatom inferred di conductivity excluding bloom taxa and 18 o show very good correspondence for the first half of the record and demonstrate that this region experienced a period of century scale drought prior to ad 540 with a subsequent rapid and simultaneous shift to fresher lake conditions and wetter climate after a drier phase in the nar record from ad 800 950 the period of the medieval climate anomaly ad 950 1400 was generally well watered during the subsequent little ice age ad 1700 1900 di conductivity and 18 o become decoupled thin sections reveal between 20 and 40 distinct diatom bloom events per century since ad 1100 with increasing frequency between ad 1700 and 2000 human land use changes evident in the pollen sequence may have influenced the diatom relationship with lake water conductivity in the later part of the record none the less diatom dca axes do show a clear response to multi decadal drought events within the last six centuries differences between the proxy climate records from nar lake may be associated with the dissimilar thresholds to environmental fluctuations and non stationarity in the response of different proxies through time the palaeoclimate records from nar show that arid periods occurred in the eastern mediterranean during the last two millennia that were more prolonged and extreme than those experienced in the last century

the miniature radio frequency instrument s mini rf global observations of earth s moon abstract radar provides a unique means to analyze the surface and subsurface physical properties of geologic deposits including their wavelength scale roughness the relative depth of the deposits and some limited compositional information the nasa lunar reconnaissance orbiter s lro miniature radio frequency mini rf instrument has enabled these analyses on the moon at a global scale mini rf has accumulated 67 coverage of the lunar surface in s band 12 6 cm radar with a resolution of 30 m pixel here we present new mini rf global orthorectified uncontrolled s band maps of the moon and use them for analysis of lunar surface physical properties reported here are readily apparent global and regional scale differences in lunar surface physical properties that suggest three distinct terranes namely a 1 nearside radar dark region 2 orientale basin and continuous ejecta and the 3 highlands radar bright region integrating these observations with new data from lro s diviner radiometer rock abundance maps as well clementine and lunar prospector derived compositional values show multiple distinct lunar surface terranes and sub terranes based upon both physical and compositional surface properties previous geochemical investigations of the moon suggested its crust is best divided into three to four basic crustal provinces or terranes feldspathic highlands terrane an and outer procellarum kreep terrane and south pole aitken terrane that are distinct from one another however integration of these geochemical data sets with new geophysical data sets allows us to refine these terranes the result shows a more complex view of these same crustal provinces and provides valuable scientific and hazard perspectives for future targeted human and robotic exploration

a new type of pyroclastic deposit on the moon containing fe spinel and chromite 1 we present details of the identification of sites that show an absorption band at visible wavelengths and a strong 2 m band using the selene spectral profiler all the sites exhibiting the visible feature are found on the regional dark mantle deposit dmd at sinus aestuum all the instances of the visible feature show a strong 2 m band suggestive of fe and cr rich spinels which are different from previously detected mg rich spinel since no visible feature is observed in other dmds the dmd at sinus aestuum is unique on the moon the occurrence trend of the spinels at sinus aestuum is also different from that of the mg rich spinels which are associated with impact structures this may suggest that the spinel at sinus aestuum is a different origin from that of the mg rich spinel

model near infrared optical constants of olivine and pyroxene as a function of iron content the imaginary coefficients of the complex index of refraction of olivine low ca orthopyroxene and high ca clinopyroxene are derived as a function of iron content and wavelength over the spectral region 0 4 to 2 5 m from reflectance spectra of powders and hapke radiative transfer theory reflectance spectra as a function of composition and grain size are computed and compared i find that while spectral effects of variations in these parameters are similar they are distinguishable variations in iron content do not explain all the observed spectral variations in the spectra of the samples investigated

an ostracode based paleolimnologic and paleohydrologic history of death valley 200 to 0 ka death valley a complex tectonic and hydrologic basin was cored from its lowest surface elevation to a depth of 186 m the sediments range from bedded primary halite to black muds continental ostracodes found in the black muds indicate that those sediments were deposited in a variety of hydrologic settings ranging from deep relatively fresh water to shallow saline lakes to spring discharge supported wetlands the alkaline enriched calcium depleted paleolake waters indicate extrabasinal streamflow and basin margin spring discharge the alkaline depleted calcium enriched paleowetland waters indicate intrabasinal spring discharge during marine isotope stage 6 mis 6 ca 180 140 ka the hydrologic settings were highly variable implying that complex relations existed between climate and basin hydrology termination ii mis 6 to mis 5e was a complex multicyclic sequence of paleoenvironments implying that climates oscillated between high and low effective moisture mis 4 ca 73 61 ka was a spring discharge supported wetland complex during mis 2 ca 20 12 ka the hydrologic settings were variable although they are not fully understood because some black muds deposited during that time were lost during coring

pristine lunar glasses criteria data and implications major element analyses of several thousand glasses from all of the apollo landing sites have resulted in the identification of 25 groups of pristine i e volcanic glass the nickel in these pristine glasses is shown to be indigenous not meteoritic contamination and to be correlated with mg the chemical data indicate that these glasses are consistently better candidates for primary magmas than the majority of crystalline mare basalts the pristine glasses support the view that assimilative processes ringwood and kesson 1976 involving two cumulate systems in the differentiated mantle operated during mare petrogenesis the reality of those assimilative interactions is evident by the occurrence of two linear arrays among the chemistries of the glasses data suggest that these cumulate components in the differentiated mantle persist for lateral distances of at least 1000 km and therefore appear to be products of a vast magma ocean that existed early in lunar history alternative hypotheses claiming that the highlands crust and mare source regions were produced by serial magmatism without a magma ocean have not yet considered all of the constraints derived from the pristine glasses

pedogenesis of siliceous calcretes at yucca mountain nevada abstract siliceous calcretes in faults near yucca mountain nevada have been interpreted by some observers as evidence of seismically triggered eruptions of deep water such an origin could have important consequences if yucca mountain is developed as an unsaturated site for disposal of high level nuclear waste at odds with this hypothesis are the absence of features that should be present at fault fed springs e g fissure ridge mounds with microterraces and the preservation within root casts of delicate pedogenic microfossils such as calcified filaments and needle fiber calcites chemical evidence of pedogenic origin is found in fe and sc enrichments that require prior weathering of detritus in the calcretes as opposed to direct incorporation of adjacent unweathered bedrock carbonate and silica abundances and accumulation rates are well within the scope of pedogenic processes sources of carbonate are eolian whereas silica is derived in part by dissolution of local volcanic glasses but also by extensive dissolution of unstable silica minerals tridymite and cristobalite that are abundant in the local tuffs the siliceous calcretes at yucca mountain are pedogenic and provide no evidence in support of conjectured spring activity

moon near infrared spectral reflectance a first good look a positive identification of the minerals olivine plagioclase and several types of pyroxenes were made at several locations on the lunar surface by using remote measurements for example the crater aristarchus is found to have an average pyroxene composition of augite and plagioclase is obviously present a dark mantle deposit in the crater j herschel is at least partly composed of a mixture of 70o7o olivine and 30o7o pyroxene these determinations were possible because the reflectance spectra for 10 20 km diameter lunar areas have been measured for the first time in the ir spectral region 0 65 2 5 m with sufficient spectral resolution and photometric precision to define mineral electronic absorption bands the reflectance for all lunar regions observed over 100 to present continues to increase toward longer wavelengths to at least 2 5 m and several mineral absorption bands appear the telescopic spectra are of similar quality and contain features similar to laboratory spectra of lunar samples the absorption features in several spectra have been quantitatively analyzed using newly developed computer processing techniques including thermal flux removal and absorption band fitting to produce these mineral identifications detection and quantitative analysis of these absorptions provide a much improved basis for remotely determining and mapping surface mineralogy quantitatively from the ground or using airborne or spacecraft platforms

u and sr isotopes in ground water and calcite yucca mountain nevada evidence against upwelling water hydrogenic calcite and opaline silica deposits in fault zones at yucca mountain nevada have created considerable public and scientific controversy because of the possible development of a high level nuclear waste repository at this location strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep seated waters the vein deposits are isotopically distinct from ground water in the two aquifers that underlie yucca mountain indicating that the calcite could not have precipitated from ground water the data are consistent with a surficial origin for the hydrogenic deposits

500 ka precipitation record from southeastern australia evidence for interglacial relative aridity 230 th 234 u dating of speleothems from southeastern australia documents changes in effective precipitation over the past 500 k y at a temporal resolution not previously achieved results show that the highest effective precipitation for the southeastern interior of australia occurred during stadials and cool interstadials of the past four glacial cycles interglacials and warm interstadials as well as glacial maxima are comparatively arid we suggest that lower regional temperatures over the continent and changes in atmospheric circulation stronger walker circulation produced the observed periods of increased effective precipitation

the compositional and physical properties of localized lunar pyroclastic deposits abstract lunar localized pyroclastic deposits are low albedo deposits with areas 2 these deposits were difficult to study before the turn of the millennium because of the lack of available high spatial resolution data with the launch of the lunar reconnaissance orbiter kaguya and chaandrayan 1 new sets of diverse high spatial resolution data are now available using several of these data sets we conducted a study of 34 localized pyroclastic deposits globally for each localized pyroclastic deposit we examined topography to estimate pyroclastic volume and juvenile proportions s band radar backscatter thermal infrared derived measures of surficial rock abundance and regolith density and mineral abundances our goals are to 1 quantitatively characterize the physical and mineralogical properties of each localized pyroclastic deposit 2 investigate the physical and mineralogical variations among localized pyroclastic deposits 3 compare these properties of localized 2 to regional pyroclastic deposits 2500 km 2 and 4 provide useful parameters for future volcanological modeling from this study we find that 1 localized pyroclastic deposits exhibit low relief structures 2 the surface rock abundance and circular polarization ratio of localized pyroclastic deposits display a wide range of values 0 2 0 5 and 0 3 0 6 respectively 3 the glass abundance of localized pyroclastic deposits vary between 0 and 80 wt 4 there are four types of localized pyroclastic deposits based upon the surface rock abundance and glass abundance parameters 5 pyroclastic deposits within the same floor fractured crater tend to have similar properties and 6 localized pyroclastic deposits are diverse with respect to regional pyroclastic deposits but a subset of localized pyroclastic deposits have similar physical and mineralogical properties to regional pyroclastic deposits

radiative transfer modeling of compositions of lunar pyroclastic deposits 1 while over 100 lunar pyroclastic deposits have been identified remotely their compositions remain poorly constrained in this work we determine the compositions of three lunar regional pyroclastic deposits which are likely to contain large amounts of glass and for which we have high quality ground based spectra the aristarchus plateau mare humorum and sulpicius gallus we use radiative transfer theory and employ measured optical constants of glasses to predict the bidirectional reflectance of a particulate glass surface as a function of fe and ti concentration particle size and maturity in order to find the best spectral match to the remotely observed deposits tools are not available to model the optical effects of the unusual geometries of the ilmenite laths in the black beads so we address their effects on spectra of the regional pyroclastic deposits using computational mixing we find that model spectra of pure glass as opposed to devitrified black beads provide good matches to all three regions radiative transfer modeling predicts iron contents of 21 20 and 17 wt feo for aristarchus humorum and sulpicius gallus respectively and suggests that all three regions are low in titanium a result supported by lunar prospector neutron spectrometer data however we find that a moderate ti glass mixed with a small fraction of black beads cannot be ruled out for the sulpicius gallus region

optical effects of space weathering the role of the finest fraction the optical properties of lunar softs are different than those of rocks from which they are derived as a consequence of lunar space weathering soils are darker and exhibit a distinctive red sloped continuum and weaker mineral absorption bands the accumulation of dark glass welded aggregates agglutinates has been thought to account for these optical effects of space weathering on lunar soils spectroscopic analyses of agglutinate separates and size fractions for a suite of lunar softs presented here indicate that the agglutinate paradigm is insufficient to fully account for lunar optical alteration it is the finest fraction of lunar soils 25 gm which constitute 25 wt that dominates the optical properties of the bulk soil unlike size fractions of most silicates for which the finest fraction is the brightest the lunar soil size fractions all have comparable albedos in the short wavelength visible in the near infrared however it is the finest fraction that exhibits the steep red continuum and weak absorption bands the properties of the finest fraction cannot be duplicated by preparing a fine fraction by grinding larger agglutinate rich soil particles these results suggest space weathering on airless bodies is dominated by surface correlated processes perhaps associated with the development of fine grained fe o on or near the surface of grains and the accumulation of the larger agglutinates is not necessarily required to account for lunar optical alteration

influence of eolian deposition and rainfall amounts on the u isotopic composition of soil water and soil minerals 230th u dating of secondary deposits such as speleothems and pedogenic carbonate and opal provides information about the original 234u 238u composition of the waters the minerals precipitated from as a result these types of deposits often display temporal variations in initial 234u 238u that could reflect environmental variability past variations in soil water 234u 238u may reflect changes in the flux of water through the soil weathering rates or dust inputs in order to evaluate these potential influences we analyzed modern soil water chemistry and u isotopic compositions of fluids and solids from three soil sequences in nevada modern soil pore waters from diamond valley newark valley and fish lake valley nevada show significant 234u 238u differences between sites as a result of differing soil parent material newark valley pore waters are more heavily influenced by carbonate weathering and display much more enriched 234u 238u values than diamond and fish lake valley pore waters which are dominated by silicate weathering newark valley and diamond valley although located very near to each other have significantly different pore water 234u 238u values suggesting that deposition of distantly sourced dust does not exert a dominant influence on pore water 234u 238u at these sites pore water 234u 238u values also vary systematically along a rainfall gradient at fish lake valley where sites with lower rainfall display higher soil water 234u 238u values the results of this modern soil water chemistry study were used to parameterize two models that investigate the relative influence of dust content recoil and weathering on pore water 234u 238u in the upper layer of the soil and at depth under changing infiltration rates these models suggest that while the composition of soluble dust entering a soil profile is an important consideration the pore water 234u 238u at depth and thus the initial 234u 238u of minerals that precipitate from pore waters should be highly sensitive to changes in the infiltration flux through the soils as infiltration flux is closely tied to rainfall the initial 234u 238u of soil minerals at these sites should provide information about past rainfall variability

examining spectral variations in localized lunar dark mantle deposits the localized lunar dark mantle deposits dmds in alphonsus j herschel and oppenheimer craters were analyzed using visible near infrared spectroscopy data from the moon mineralogy mapper spectra of these localized dmds were analyzed for compositional and mineralogical variations within the deposits and were compared with nearby mare basalt units spectra of the three localized dmds exhibited mafic absorption features indicating iron rich compositions although the dmds were spectrally distinct from nearby mare basalts all of the dmds contained spectral signatures of glassy materials suggesting the presence of volcanic glass in varying concentrations across the individual deposits in addition the albedo and spectral signatures were variable within the alphonsus and oppenheimer crater dmds suggesting variable deposit thickness and or variations in the amount of mixing with the local substrate two previously unidentified localized dmds were discovered to the northeast of oppenheimer crater the identification of high concentrations of volcanic glass in multiple localized dmds in different locations suggests that the distribution of volcanic glass across the lunar surface is much more widespread than has been previously documented the presence of volcanic glass implies an explosive vulcanian eruption style for localized dmds as this allows volcanic glass to rapidly quench inhibiting crystallization compared to the larger hawaiian style eruptions typical of regional dmd emplacement where black beads indicate a higher degree of crystallization improved understanding of the local and global distributions of volcanic glass in lunar dmds will further constrain lunar degassing and compositional evolution throughout lunar volcanic history

lunar floor fractured craters classification distribution origin and implications for magmatism and shallow crustal structure 1 floor fractured craters ffcs are a class of lunar craters characterized by anomalously shallow floors cut by radial concentric and or polygonal fractures additional interior features are moats ridges and patches of mare material two formation mechanisms have been hypothesized floor uplift in response to shallow magmatic intrusion and sill formation and floor shallowing in response to thermally driven viscous relaxation this study combines new lunar orbiter laser altimeter lola and lunar reconnaissance orbiter camera lroc data to characterize and categorize the population of ffcs and map their distribution on the moon and uses variations in floor fractured crater morphology and regional distribution to investigate the proposed formation mechanisms the population of ffcs was categorized according to the classes outlined by schultz 1976 the distribution of these ffc categories shows an evolution of crater morphology from areas adjacent to lunar impact basins to areas in the lunar highlands we propose that this trend is supportive of formation by shallow magmatic intrusion and sill formation crustal thickness determines the magnitude of magmatic driving pressure and thus either piston like floor uplift for high magnitude or a convex floor profile for low magnitude predictions from previous studies modeling viscous relaxation are inconsistent with the observed altimetric profiles of ffcs hence our analysis favors ffc formation by shallow magmatic intrusion with the variety of ffc morphologies being intimately linked with location and crustal thickness and the driving pressure of the intrusion data from the grail gravity recovery and interior laboratory mission will help to test these conclusions

uranium isotopes in soils as a proxy for past infiltration and precipitation across the western united states the intermittent presence of large pleistocene lakes in the southwestern interior of north america a region that is now a semi arid desert suggests repeated oscillations between profoundly different climatic conditions the origin of these shifts is still unresolved due to inconsistencies in existing climate proxy data for example pollen lake levels and oxygen isotopes in speleothems to resolve the inconsistencies in the water balance over the last 10 to 60 kyr we use uranium isotopic variations in secondary soil minerals to quantify net infiltration and precipitation along a north south transect in western north america we show that winter infiltration increased by 30 to 100 percent and precipitation by a lesser amount in the valleys of the great basin and mojave deserts between 60 and 26 ka this increase in infiltration and precipitation preceded the last glacial maximum lgm and the timing of most lake highstands in the region by 5 to 10 kyr respectively suggesting a possible last precipitation maximum lpm that coincided with a minimum in winter insolation subsequent decreases in infiltration and precipitation after the lgm can be reconciled with the timing of lake highstands if colder summer temperatures due to a minimum in summer insolation reduced lake evaporation the soil records combined with a range of proxy data suggest that seasonal insolation is the long term driver for large shifts in both precipitation and surface water variability in the region

hydrology of yucca mountain nevada yucca mountain located in southern nevada in the mojave desert is being considered as a geologic repository for high level radioactive waste although the site is arid previous studies indicate net infiltration rates of 5 10 mm yr 1 under current climate conditions unsaturated flow of water through the mountain generally is vertical and rapid through the fractures of the welded tuffs and slow through the matrix of the nonwelded tuffs the vitric zeolitic boundary of the nonwelded tuffs below the potential repository where it exists causes perching and substantial lateral flow that eventually flows through faults near the eastern edge of the potential repository and recharges the underlying groundwater system fast pathways are located where water flows relatively quickly through the unsaturated zone to the water table for the bulk of the water a large part of the travel time from land surface to the potential repository horizon 300 m below land surface is through the interlayered low fracture density nonwelded tuff where flow is predominately through the matrix the unsaturated zone at yucca mountain is being modeled using a three dimensional dual continuum numerical model to predict the results of measurements and observations in new boreholes and excavations the interaction between experimentalists and modelers is providing confidence in the conceptual model and the numerical model and is providing researchers with the ability to plan further testing and to evaluate the usefulness or necessity of further data collection

compositional analyses of small lunar pyroclastic deposits using clementine multispectral data clementine ultraviolet visible uvvis data are used to examine the compositions of 18 pyroclastic deposits 15 small three large at 13 sites on the moon compositional variations among pyroclastic deposits largely result from differing amounts of new basaltic or juvenile material and reworked local material entrained in their ejecta upon eruption characterization of pyroclastic deposit compositions allows us to understand the mechanisms of lunar explosive volcanism evidence for compositional differences between small pyroclastic deposits at a single site is observed at atlas crater at all sites compositional variation among the small pyroclastic deposits is consistent with earlier classification based on earth based spectra three compositional groups can be observed and the trend of increasing mafic absorption band strength from group 1 to group 2 to group 3 is noted as redefined here group 1 deposits include those of alphonsus west alphonsus southeast alphonsus northeast 2 atlas south cruger franklin grimaldi lavoisier oppenheimer orientale and riccioli group 1 deposits resemble lunar highlands with weak mafic bands and relatively high uv vis ratios group 2 deposits include those of alphonsus northeast 1 atlas north eastern frigoris east and west and aristarchus plateau group 2 deposits are similar to mature lunar maria with moderate mafic band depths and intermediate uv vis ratios the single group 3 deposit j herschel has a relatively strong mafic band and a low uv vis ratio and olivine is a likely juvenile component two of the deposits in these groups orientale and aristarchus are large pyroclastic deposits the third large pyroclastic deposit apollo 17 taurus littrow has a very weak mafic band and a high uv vis ratio and it does not belong to any of the compositional groups for small pyroclastic deposits the observed compositional variations indicate that highland and mare materials are also present in many large and small pyroclastic deposits and they suggest that volcanic glasses or spheres may not be dominant juvenile components in all large pyroclastic deposits

volcanic glass signatures in spectroscopic survey of newly proposed lunar pyroclastic deposits moon mineralogy mapper spectroscopic observations are used to assess the mineralogy of five sites that have recently been proposed to include lunar dark mantle deposits dmds volcanic glasses have for the first time clearly been identified at the location of three of the proposed pyroclastic deposits this is the first time that volcanic glasses have been identified at such a small scale on the lunar surface from remote sensing observations deposits at birt e schluter and walther a appear to be glassy dmds deposits at birt e and schluter show 1 morphological evidence suggesting a likely vent and 2 mineralogical evidence indicative of the presence of volcanic glasses the walther a deposits although they show no morphological evidence of vents have the spectroscopic characteristics diagnostic of volcanic glasses the deposits of the freundlich sharonov basin are separated in two areas 1 the buys ballot deposits lack mineralogical and morphological evidence and thus are found to be associated with mare volcanism not with dmds and 2 the anderson crater deposits which do not exhibit glassy dmd signatures but they appear to be associated with possible vent structures and so may be classifiable as dmds finally dark deposits near the crater kopff are found to be associated with likely mare volcanism and not associated with dmds the spectral identification of volcanic glass seen in many of the potential dmds is a strong indicator of their pyroclastic origin

modification and preservation of environmental signals in speleothems speleothems are primarily studied in order to generate archives of climatic change and results have led to significant advances in identifying and dating major shifts in the climate system however the climatological meaning of many speleothem records cannot be interpreted unequivocally this is particularly so for more subtle shifts and shorter time periods but the use of multiple proxies and improving understanding of formation mechanisms offers a clear way forward

uranium series dating of pedogenic silica and carbonate crater flat nevada a 230th 234u 238u dating study on pedogenic silica carbonate clast rinds and matrix laminae from alluvium in crater flat nevada was conducted using small sample thermal ionization mass spectrometry tims analyses on a large suite of samples though the 232th content of these soils is not particularly low mostly 0 1 9 ppm the high u content of the silica component mostly 4 26 ppm makes them particularly suitable for 230th u dating on single 10 to 200 mg totally digested samples using tims we observed that 1 both micro within rind and macro stratigraphic mappable deposit order of the 230th u ages were preserved in all cases 2 back calculated initial 234u 238u fall in a restricted range typically 1 67 0 19 so that 234u 238u ages with errors of about 100 kyr 2 could be reliably determined for the oldest 400 to 1000 ka rinds and 3 though 13 of the samples were 350 ka only three showed evidence for an open system history even though the sensitivity of such old samples to isotopic disruption is very high an attempt to use leach residue techniques to separate pedogenic from detrital u and th failed yielding corrupt 230th u ages we conclude that 230th u ages determined from totally dissolved multiple sub mm size subsamples provide more reliable estimates of soil chronology than methods employing larger samples chemical enhancement of 238u 232th or isochrons

origin timing and temperature of secondary calcite silica mineral formation at yucca mountain nevada the origin of secondary calcite silica minerals in primary and secondary porosity of the host miocene tuffs at yucca mountain has been hotly debated during the last decade proponents of a high level nuclear waste repository beneath yucca mountain have interpreted the secondary minerals to have formed from cool descending meteoric fluids in the vadose zone critics citing the presence of two phase fluid inclusions argued that the minerals could only have formed in the phreatic zone from ascending hydrothermal fluids understanding the origin temperature and timing of these minerals is critical in characterizing geologically recent fluid flux at the site and has significant implications to whether waste should be stored at yucca mountain petrographic and paragenetic studies of 155 samples collected from the exploratory studies facility esf and repository block cross drift ecrb tunnels indicate that heterogeneously distributed calcite with lesser chalcedony quartz opal and fluorite comprise the oldest secondary minerals these are typically overgrown by intermediate aged calcite often exhibiting distinctive bladed habits the youngest event recorded across the site is the deposition of mg enriched up to 1 wt and depleted growth zoned calcite intergrown with u enriched opal the cyclical variation in mg enrichment and depletion is probably related to climate changes that have occurred during the last few million years the distribution of secondary minerals is consistent with precipitation in the vadose zone fluid inclusion petrography of sections from the 155 samples determined that 96 of the fluid inclusion assemblages fias contained liquid only inclusions that formed at ambient temperatures 35 c however 50 of the samples n 78 contained relatively rare fia that contain both liquid only and liquid plus vapor inclusions herein termed two phase fias that formed at temperatures above 35 c virtually all of these two phase fias occur in paragenetically old calcite rare two phase inclusion assemblages were also observed in early fluorite and quartz and early intermediate calcite homogenization temperatures trapping temperatures across yucca mountain are generally 45 to 60 c but higher temperatures reaching 83 c were recorded in calcite from the north portal and ramp of the esf cooler temperatures of 35 to 45 c were recorded in the intensely fractured zone multiple populations of two phase fias from lithophysal cavities in the esf and ecrb cross drift indicate early fluid cooling with time from temperatures 45 c in early calcite to 35 to 45 c in paragenetically younger calcite freezing point depressions range from 0 2 to 1 6 c indicating trapping of a low salinity fluid the majority of intermediate calcite and all outermost mg enriched calcite contains rare all liquid inclusions and formed from ambient temperature 35 c fluids carbon and oxygen isotope data reveal a consistent trend of decreasing 13 c from 9 5 to 8 5 and increasing 18 o from 5 2 to 22 1 values from paragenetically early calcite to mg enriched growth zoned calcite depleted d values 131 to 90 of inclusion fluids from intermediate and the youngest mg enriched calcite indicate derivation from surface meteoric fluids recalculation of 18 oh2o values of 12 to 10 is consistent with derivation from paleometeoric fluids results of integrated u pb dating opal and chalcedony and fluid inclusion microthermometry indicate that two phase fias that trapped fluids of 50 c are older than 6 29 0 30 ma two phase fias in parage netically later calcite which formed from fluids of 35 to 45 c are older than 5 32 0 02 ma there is no evidence for trapping of fluids with elevated temperatures during the past 5 32 my the youngest mg enriched calcite intergrown with opal began to precipitate between about 1 9 to 2 9 ma and has continued to precipitate within the past half million years the presence of liquid only inclusions and the consistent occurrence of mg enriched calcite and opal as the youngest event indicate a minor but chemically distinct ambient temperature 35 c fluid flux during the past 2 to 3 my copyright 2003 elsevier science ltd

quaternary redox transitions in deep crystalline rock fractures at the western margin of the greenland ice sheet when planning for long term deep geological repositories for spent nuclear fuel knowledge of processes that will influence and change the sub surface environment is crucial for repositories in nor

lunar central peak mineralogy and iron content using the kaguya multiband imager reassessment of the compositional structure of the lunar crust ryder and wood 1977 suggested that the lunar crust becomes more mafic with depth because the impact melts associated with the large imbrium and serenitatis basins are more mafic than the surface composition of the moon in this study we reexamine the hypothesis that the crust becomes more mafic with depth we analyze the composition of crater central peaks by using recent remote sensing data and combining the best practices of previous studies we compute the mineralogy for 34 central peaks using 1 nine band visible and near infrared data from the kaguya multiband imager 2 an improved version of hapke s radiative transfer model validated with spectra of lunar soils with well known modal mineralogy and 3 new crustal thickness models from the gravity recovery and interior laboratory data to examine the variation in composition with depth we find that there is no increase in mafic mineral abundances with proximity to the crust mantle boundary or with depth from the current lunar surface and therefore that the crust does not become more mafic with depth we find that anorthosite with very low mafic abundance purest anorthosite or pan is a minority constituent in these peaks and there is no clear evidence of a distinct pan rich layer in the middle crust as previously proposed the composition of most of the central peaks we analyze is more mafic than classically defined anorthosites with an average noritic anorthosite composition similar to that of the lunar surface

characterization of previously unidentified lunar pyroclastic deposits using lunar reconnaissance orbiter camera data 1 we used a lunar reconnaissance orbiter camera lroc global monochrome wide angle camera wac mosaic to conduct a survey of the moon to search for previously unidentified pyroclastic deposits promising locations were examined in detail using lroc multispectral wac mosaics high resolution lroc narrow angle camera nac images and clementine multispectral ultraviolet visible or uvvis data out of 47 potential deposits chosen for closer examination 12 were selected as probable newly identified pyroclastic deposits potential pyroclastic deposits were generally found in settings similar to previously identified deposits including areas within or near mare deposits adjacent to highlands within floor fractured craters and along fissures in mare deposits however a significant new finding is the discovery of localized pyroclastic deposits within floor fractured craters anderson e and f on the lunar farside isolated from other known similar deposits our search confirms that most major regional and localized low albedo pyroclastic deposits have been identified on the moon down to 100 m pix resolution and that additional newly identified deposits are likely to be either isolated small deposits or additional portions of discontinuous patchy deposits

potential effects of alpha recoil on uranium series dating of calcrete abstract evaluation of paleosol ages in the vicinity of yucca mountain nevada at the time the site of a proposed high level nuclear waste repository is important for fault displacement hazard assessment uranium series isotope data were obtained for surface and subsurface calcrete samples from trenches and boreholes in midway valley nevada adjacent to yucca mountain 230 th u ages of 33 surface samples range from 1 3 to 423 thousand years ka and the back calculated 234 u 238 u initial activity ratios ar are relatively constant with a mean value of 1 54 0 15 1 which is consistent with the closed system behavior subsurface calcrete samples are too old to be dated by the 230 th u method u pb data for post pedogenic botryoidal opal from a subsurface calcrete sample show that these subsurface calcrete samples are older than 1 65 million years ma old enough to have attained secular equilibrium had their u th systems remained closed however subsurface calcrete samples show u series disequilibrium indicating open system behavior of 238 u daughter isotopes in contrast with the surface calcrete where open system behavior is not evident data for 21 subsurface calcrete samples yielded calculable 234 u 238 u model ages ranging from 130 to 1875 ka assuming an initial ar of 1 54 0 15 the mean value calculated for the surface calcrete samples a simple model describing continuous recoil loss predicts that the 234 u 238 u and 230 th 238 u ars reach steady state values 2 ma after calcrete formation potential effects of open system behavior on 230 th u ages and initial 234 u 238 u ars for younger surface calcrete were estimated using data for old subsurface calcrete samples with the 234 u loss and assuming that the total time of water rock interaction is the only difference between these soils the difference between the conventional closed system and open system ages may exceed errors of the calculated conventional ages for samples older than 250 ka but is negligible for younger soils

a compositional study of the aristarchus region of the moon using near infrared reflectance spectroscopy newly obtained near infrared reflectance spectra for features on or near the aristarchus plateau demonstrate the diversity of compositions in the region highland units are of three probable compositions a feldspar and clinopyroxene assemblage a probable clinopyroxene olivine and possibly feldspar assemblage and an assemblage composed of olivine or olivine and feldspar the feldspar clinopyroxene assemblage is tentatively correlated with the major th anomaly centered on aristarchus crater the regional pyroclastic deposits on the plateau are composed of greater than 90 fe2 bearing glass the aristarchus cratering event fully penetrated any mare or pyroclastics in the target evidence for mare related material is found in the ejecta on the mare side of the mare plateau contact

quantification of unsaturated zone alteration and cation exchange in zeolitized tuffs at yucca mountain nevada usa abstract zeolitized horizons in the unsaturated zone uz at yucca mountain nevada usa are an important component in concepts for a high level nuclear waste repository at this site the use of combined quantitative x ray diffraction and geochemical analysis allows measurement of the chemical changes that accompanied open system zeolitization at yucca mountain this approach also provides measures of the extent of chemical migration that has occurred in these horizons as a result of subsequent cation exchange mass balance analysis of zeolitized horizons with extensive cation exchange drill hole uz 16 and with only minimal cation exchange drill hole sd 9 shows that al is essentially immobile although zeolitization occurred in an open system the mass transfer of constituents other than water is relatively small in initial zeolitization in contrast to the larger scales of cation exchange that can occur after zeolites have formed cation exchange in the clinoptilolite mordenite zeolitized horizons is seen in downward diminishing concentration gradients of ca mg and sr exchanged for na and to lesser extent k comparison with data from drill hole sd 7 which has multiple zeolitized horizons above the water table shows that the upper horizons accumulate ca mg and sr to such an extent that transport of these elements to the deepest uz zeolitized horizon can be blocked quantitative analysis of zeolite formation yields insight into processes that are implied from laboratory studies and modeling efforts but are otherwise unverified at the site such analysis also yields information not provided by or contradicted by some models of flow and transport the results include the following 1 evidence of effective downward flow through zeolitic horizons despite the low permeability of these horizons 2 evidence that alkaline earth elements accumulated by zeolites are mostly derived from eolian materials in surface soils 3 validation of the very effective operation of unsaturated zeolitic horizons as cation exchange barriers 4 independent support of models that indicate average water infiltration rates of 5 mm yr over the past 10 ma and 5 evidence that the presence or absence of cation exchange profiles can be used to identify those portions of the site where transport through the uz is concentrated this last point is relevant to repository design because a knowledge of where transport takes place can be used to advantage in defining the boundaries of a repository such that high flux portions of the site can be avoided

potential for water table excursions induced by seismic events at yucca mountain nevada the possibility that 100 200 m changes in water table elevation can be mechanically induced by earthquakes is a consideration in site studies of a potential high level nuclear waste repository at yucca mountain nevada however numerical simulations of tectonohydrologic coupling involving earthquakes typical of the basin and range province produce 2 3 m excursions of a water table that is 500 m below the land surface even displacements corresponding to extraordinary seismic events drive water table excursions of less than 20 m flow resulting from earthquake induced pore pressure fields below the water table tends to be mainly horizontal vertical flows that cause changes of the level of the water table are secondary strongly anisotropic permeability intended to enhance vertical flow within fault zones only doubles water table rise in the models considered these simulations of water table rise compare well with observations following large earthquakes in the basin and range the authors models suggest that exceptional hydrologic and or tectonic conditions would be required to produce substantially larger water table rises

overview of calcite opal deposits at or near the proposed high level nuclear waste site yucca mountain nevada usa pedogenic hypogene or both calcite opal deposits cod at yucca mountain were studied with respect to their regional and field geology petrology and petrography chemistry and isotopic geochemistry and fluid inclusions they were also compared with true pedogenic deposits tpd groundwater spring deposits gsd and calcite vein deposits cvd in the subsurface some of the data are equivocal and can support either a hypogene or pedogenic origin for these deposits however sr c and o isotope fluid inclusion and other data favor a hypogene interpretation a hypothesis that may account for all currently available data is that the cod precipitated from warm co2 rich water that episodically upwelled along faults during the pleistocene and which upon reaching the surface flowed downslope within existing alluvial colluvial eluvial or soil deposits being formed near or on the topographic surface the cod acquired characteristics of pedogenic deposits this subject relates to the suitability of yucca mountain as a high level nuclear waste site

volcanic and impact deposits of the moon s aristarchus plateau a new view from earth based radar images lunar pyroclastic deposits reflect an explosive stage of the basaltic volcanism that filled impact basins across the nearside these fine grained mantling layers are of interest for their association with early mare volcanic processes and as possible sources of volatiles and other species for lunar outposts we present earth based radar images at 12 6 and 70 cm wavelengths of the pyroclastic deposit that blankets the aristarchus plateau the 70 cm data reveal the outlines of a lava flow complex that covers a significant portion of the plateau and appears to have formed by spillover of magma from the large sinuous rille vallis schroteri the pyroclastics mantling these flows are heavily contaminated with rocks 10 cm and larger in diameter the 12 6 cm data confirm that other areas are mantled by 20 m or less of material and that there are numerous patches of 2 cm and larger rocks associated with ejecta from aristarchus crater some of the radar detected rocky debris is within the mantling material and is not evident in visible wavelength images the radar data identify thick rock poor areas of the pyroclastic deposit best suited for resource exploitation

ascent and eruption of a lunar high titanium magma as inferred from the petrology of the 74001 2 drill core abstract an analysis of the orange glasses and crystallized beads from the 68 cm deep 74001 2 core has been conducted to understand the processes occurring during ascent and eruption of the apollo 17 orange glass magma equilibrium between melt and metal blebs fe85ni14co1 within the core along with cr contents in olivine phenocrysts suggest there was an oxidation of c and a reduction of the melt at an o fugacity of iw 1 3 and 1320 c to form co gas at 200 bars or 4 km depth this was followed by development of more oxidized conditions during ascent also during ascent there was formation of euhedral homogeneous fo81 olivine crystals and spinel crystals with higher al and mg contents than the smaller spinels in the crystallized beads both the metal blebs and al rich spinels were trapped inside the fo81 olivine phenocrysts as they grew prior to eruption the composition of the orange glasses are homogeneous throughout the core except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking a few glassy melt inclusions of orange glass composition trapped in the fo81 phenocrysts contain 600 100 ppm s and 50 ppm cl compared to the 200 ppm s and 50 ppm cl in the orange glass melt when quenched these inclusions therefore document the addition of 400 ppm s to the co rich volcanic gas during the eruption the size and distribution of different volcanic beads in the apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume the development of a brown texture in the orange glasses at the bottom of the core where the black beads dominate is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface the change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time which consequently would increase the plume optical density and favor slower cooling rates

limited hydrologic response to pleistocene climate change in deep vadose zones yucca mountain nevada abstract understanding the movement of water through thick vadose zones especially on time scales encompassing long term climate change is increasingly important as societies utilize semi arid environments for both water resources and sites viewed as favorable for long term disposal or storage of hazardous waste hydrologic responses to pleistocene climate change within a deep vadose zone in the eastern mojave desert at yucca mountain nevada were evaluated by uranium series dating of finely layered hyalitic opal using secondary ion mass spectrometry opal is present within cm thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface uranium concentrations in opal fluctuate systematically between 5 and 550 g g age calibrated profiles of uranium concentration correlate with regional climate records over the last 300 000 years and produce time series spectral peaks that have distinct periodicities of 100 and 41 ka consistent with planetary orbital parameters these results indicate that the chemical compositions of percolating solutions varied in response to near surface climate driven processes however slow micrometers per thousand years relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates

evaluation of pleistocene groundwater flow through fractured tuffs using a u series disequilibrium approach pahute mesa nevada usa abstract groundwater flow through fractured felsic tuffs and lavas at the nevada national security site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at pahute mesa to help evaluate fracture flow and matrix water exchange we have determined u series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces breccia zones and interiors of unfractured core the u series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium series decay chain due to preferential mobilization of 234 u relative to 238 u and u relative to th samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays silica fe mn oxyhydroxides and zeolite intact core interiors and breccia fragments were sampled in bulk in addition profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture matrix water exchange samples of rock matrix have 234 u 238 u and 230 th 238 u activity ratios ar closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix greater u mobility was observed in welded tuff matrix with elevated porosity and in zeolitized bedded tuff samples of brecciated core were also in secular equilibrium implying a lack of long range hydraulic connectivity in these cases samples of discrete fracture surfaces typically but not always were in radioactive disequilibrium many fractures had isotopic compositions plotting near the 230 th 234 u 1 1 line indicating a steady state balance between u input and removal along with radioactive decay numerical simulations of u series isotope evolution indicate that 0 5 to 1 million years are required to reach steady state compositions once attained disequilibrium 234 u 238 u and 230 th 238 u ar values can be maintained indefinitely as long as hydrological and geochemical processes remain stable therefore many pahute mesa fractures represent stable hydrologic pathways over million year timescales a smaller number of samples have non steady state compositions indicating transient conditions in the last several hundred thousand years in these cases u mobility is dominated by overall gains rather than losses of u

u pb ages of secondary silica at yucca mountain nevada implications for the paleohydrology of the unsaturated zone abstract uranium th and pb isotopes were analyzed in layers of opal and chalcedony from individual mm to cm thick calcite and silica coatings at yucca mountain nevada usa a site that is being evaluated for a potential high level nuclear waste repository these calcite and silica coatings on fractures and in lithophysal cavities in miocene age tuffs in the unsaturated zone uz precipitated from descending water and record a long history of percolation through the uz opal and chalcedony have high concentrations of u 10 to 780 ppm and low concentrations of common pb as indicated by large values of 206pb 204pb up to 53 806 thus making them suitable for u pb age determinations interpretations of u pb isotope systems in opal samples at yucca mountain are complicated by the incorporation of excess 234u at the time of mineral formation resulting in reverse discordance of u pb ages however the 207pb 235u ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0 6 and 9 8 ma for chalcedony subsamples showing normal age discordance these ages may represent minimum times of deposition typically 207pb 235u ages are consistent with the microstratigraphy in the mineral coating samples such that the youngest ages are for subsamples from outer layers intermediate ages are from inner layers and oldest ages are from innermost layers 234u and 230th in most silica layers deeper in the coatings are in secular equilibrium with 238u which is consistent with their old age and closed system behavior during the past 0 5 ma the ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the topopah spring tuff yield slow long term average growth rates of 1 to 5 mm ma these data imply that the deeper parts of the uz at yucca mountain maintained long term hydrologic stability over the past 10 ma despite significant climate variations u pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from fractures in the shallower part of the uz welded part of the overlying tiva canyon tuff indicate larger long term average growth rates up to 23 mm ma and an absence of recently deposited materials ages of outermost layers are 3 5 ma these differences between the characteristics of the coatings for samples from the shallower and deeper parts of the uz may indicate that the nonwelded tuffs ptn located between the welded parts of the tiva canyon and topopah spring tuffs play an important role in moderating uz flow

evolution of the conceptual model of unsaturated zone hydrology at yucca mountain nevada abstract yucca mountain is an arid site proposed for consideration as the united states first underground high level radioactive waste repository low rainfall approximately 170 mm yr and a thick unsaturated zone 500 1000 m are important physical attributes of the site because the quantity of water likely to reach the waste and the paths and rates of movement of the water to the saturated zone under future climates would be major factors in controlling the concentrations and times of arrival of radionuclides at the surrounding accessible environment the framework for understanding the hydrologic processes that occur at this site and that control how quickly water will penetrate through the unsaturated zone to the water table has evolved during the past 15 yr early conceptual models assumed that very small volumes of water infiltrated into the bedrock 0 5 4 5 mm yr or 2 3 percent of rainfall that much of the infiltrated water flowed laterally within the upper nonwelded units because of capillary barrier effects and that the remaining water flowed down faults with a small amount flowing through the matrix of the lower welded fractured rocks it was believed that the matrix had to be saturated for fractures to flow however accumulating evidence indicated that infiltration rates were higher than initially estimated such as infiltration modeling based on neutron borehole data bomb pulse isotopes deep in the mountain perched water analyses and thermal analyses mechanisms supporting lateral diversion did not apply at these higher fluxes and the flux calculated in the lower welded unit exceeded the conductivity of the matrix implying vertical flow of water in the high permeability fractures of the potential repository host rock and disequilibrium between matrix and fracture water potentials the development of numerical modeling methods and parameter values evolved concurrently with the conceptual model in order to account for the observed field data particularly fracture flow deep in the unsaturated zone this paper presents the history of the evolution of conceptual models of hydrology and numerical models of unsaturated zone flow at yucca mountain nevada flint a l flint l e kwicklis e m bodvarsson g s fabryka martin j m 2001 hydrology of yucca mountain reviews of geophysics in press this retrospective is the basis for recommendations for optimizing the efficiency with which a viable and robust conceptual model can be developed for a complex site

physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada abstract calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at yucca mountain the potential site of a high level radioactive waste repository these secondary mineral deposits are heterogeneously distributed in the unsaturated zone uz with fewer than 10 of possible depositional sites mineralized the paragenetic sequence compiled from deposits throughout the uz consists of an early stage assemblage of calcite fluorite zeolites that is frequently capped by chalcedony quartz intermediate and late stage deposits consist largely of calcite commonly with opal on buried growth layers or outermost crystal faces of the calcite coatings on steep dipping fractures usually are thin 3 mm with low relief outer surfaces whereas shallow dipping fractures and lithophysal cavities typically contain thicker more coarsely crystalline deposits characterized by unusual thin tabular calcite blades up to several cms in length these blades may be capped with knobby or corniced overgrowths of late stage calcite intergrown with opal the observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips fluid inclusion studies have shown that most early stage and some intermediate stage calcite formed at temperatures of 35 to 85 c calcite deposition during the past several million years appears to have been at temperatures 18 o values although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository the authors conclude that the temperatures and fluid inclusion assemblages are consistent with deposition in a uz environment that experienced prolonged heat input from gradual cooling of nearby plutons the physical restriction of the deposits and therefore fluid flow to fracture footwalls and cavity floors and the heterogeneous and limited distribution of the deposits provides compelling evidence that they do not reflect flooding of the thick uz at yucca mountain the textures and isotopic and chemical compositions of these mineral deposits are consistent with deposition in a uz setting from meteoric waters percolating downward along fracture flow paths

thermal history of the unsaturated zone at yucca mountain nevada usa abstract secondary calcite silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry temperatures and timing of past fluid movement in the unsaturated zone at yucca mountain nevada the proposed site of a high level radioactive waste repository the distribution and geochemistry of these deposits are consistent with low temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone however the discovery of fluid inclusions in calcite with homogenization temperatures th up to 80 c was construed by some scientists as strong evidence for hydrothermal deposition this paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition mineral precipitation temperatures in the unsaturated zone are estimated from calcite and fluorite hosted fluid inclusions and calcite 18o values and depositional timing is constrained by the 207pb 235u ages of chalcedony or opal in the deposits fluid inclusion th from 50 samples of calcite and four samples of fluorite range from 35 to 90 c calcite 18o values range from 0 to 22 smow but most fall between 12 and 20 the highest th and the lowest 18o values are found in the older calcite calcite th and 18o values indicate that most calcite precipitated from water with 18o values between 13 and 7 similar to modern meteoric waters twenty two 207pb 235u ages of chalcedony or opal that generally postdate elevated depositional temperatures range from 9 5 to 1 9 ma new and published 207pb 235u and 230th uages coupled with the th values and estimates of temperature from calcite 18o values indicate that maximum unsaturated zone temperatures probably predate 10 ma and that the unsaturated zone had cooled to near present day temperatures 24 26 c at a depth of 250 m by 2 4 ma the evidence of elevated temperatures persisting in ash flow tuffs adjacent to parent calderas for as much as 8 ma is a new finding but consistent with thermal modeling simulations using the heat code demonstrate that prolonged cooling of the unsaturated zone is consistent with magmatic heat inputs and deep seated sub water table hydrothermal activity generated by the large magma body 8 km to the north that produced the 15 11 ma ash flows and ash falls that make up yucca mountain the evidence discussed in this and preceding papers strongly supports unsaturated zone deposition of the secondary minerals from descending meteoric waters although depositional temperatures reflect conductive and possibly vapor phase convective heating of the unsaturated zone related to regional magmatic sources until perhaps 6 ma depositional conditions similar to the present day unsaturated zone have prevailed for at least the past 2 4 ma

reply to the comment on origin timing and temperature of secondary calcite silica mineral formation at yucca mountain nevada by y v dublyansky s z smirnov and g p palyanova

overview of calcite opal deposits at or near the proposed high level nuclear waste site yucca mountain nevada usa pedogenic hypogene or both by c a hill y v dublyansky r s harmon c m schluter

18o 16o evidence for an early short lived 10 yr fumarolic event in the topopah spring tuff near the proposed high level nuclear waste repository within yucca mountain nevada usa abstract 18 o 16 o analyses of rock samples from the exploratory studies facility esf and from three other locations in the vicinity of yucca mountain nevada suggest that the uppermost 5 20 m of the 12 8 ma topopah spring tuff displays a characteristic 18 o 16 o pattern that is indicative of short lived 10 yr high temperature 500 c fumarolic meteoric hydrothermal activity hydrothermally altered rock is characterized by 1 3 m thick zones of 18 o depleted groundmass down to 18 o 5 5 located above and locally within the upper vitrophyre as well as complementary 2 4 m thick overlying zones of 18 o enriched as high as 18 o 13 7 mineralogically altered groundmass thirty four samples of the topopah spring tuff collected below the upper vitrophyre are not hydrothermally altered and correspondingly display a more uniform set of 18 o values 18 o 8 6 to 11 1 sanidine phenocrysts from fumarolically altered tuff in the upper cooling unit are petrographically pristine and also display uniform 18 o values 18 o 7 80 0 45 which are in isotopic equilibrium with other phenocryst phases at magmatic temperatures the 18 o 16 o signature displayed by the upper part of the topopah spring tuff is analogous to that produced by short lived 10 25 yr high temperature 500 c fumarolic activity in the bishop tuff and in the 1912 ash flow sheet in the valley of ten thousand smokes alaska the remarkable preservation of a fragile fumarolic 18 o 16 o signature in the upper part of the topopah spring tuff indicates that no subsequent hydrothermal alteration of this part of the tuff has occurred

200 k y paleoclimate record from death valley salt core a 186 m long core dv93 1 from death valley california composed of interbedded salts and muds contains a 200 k y record of closed basin environments and paleoclimates interpreted on the basis of sedimentology ostracodes homogenization temperatures of fluid inclusions in halite and correlation with shoreline tufa the 200 k y paleoclimate record is dominated by two dry and or warm and wet and cold cycles that occurred on a 100 k y time scale these cycles begin with mud flat deposits 192 ka to bottom of core and 60 ka to 120 ka wetter and or colder conditions produced greater effective moisture saline pan and shallow saline lake evaporites overlie mud flat sediments 186 ka to 192 ka and 35 ka to 60 ka eventually enough water entered death valley to sustain perennial lakes that had fluctuating water levels and salinities 120 ka to 186 ka and 10 ka to 35 ka when more arid conditions returned mud flat deposits accumulated on top of the perennial lake sediments completing the cycle 120 ka and 10 ka of particular significance are the major lacustrine phases 10 ka to 35 ka and 120 ka to 186 ka oxygen isotope stages 2 and 5e 6 which represent markedly colder and wetter conditions than those of modern death valley of the two major lake periods the penultimate glacial lakes were deeper and far longer lasting than those of the last glacial

improved discrimination of volcanic complexes tectonic features and regolith properties in mare serenitatis from earth based radar mapping radar images at 70 cm wavelength show 4 5 db variations in backscatter strength within regions of relatively uniform spectral reflectance properties in central and northern mare serenitatis delineating features suggesting lava flow margins channels and superposition relationships these backscatter differences are much less pronounced at 12 6 cm wavelength consistent with a large component of the 70 cm echo arising from the rough or blocky transition zone between the mare regolith and the intact bedrock such deep probing is possible because the ilmenite content which modulates microwave losses of central mare serenitatis is generally low 2 3 by weight modeling of the radar returns from a buried interface shows that an average regolith thickness of 10 m could lead to the observed shifts in 70 cm echo power with a change in tio2 content from 2 to 3 this thickness is consistent with estimates of regolith depth 10 15 m based on the smallest diameter for which fresh craters have obvious blocky ejecta the 70 cm backscatter differences provide a view of mare flow unit boundaries channels and lobes unseen by other remote sensing methods a localized pyroclastic deposit associated with rima calippus is identified based on its low radar echo strength radar mapping also improves delineation of units for crater age dating and highlights a 250 km long east west trending feature in northern mare serenitatis that we suggest is a large graben flooded by late stage mare flows

remote sensing of lunar pyroclastic mantling deposits abstract mantling deposits on the moon are considered to be pyroclastic units emplaced on the lunar surface as a result of explosive fire fountaining these pyroclastic units are characterized as having low albedos having smooth fine textured surfaces and consisting in part of homogeneous febearing volcanic glass and partially crystallized spheres mantling units exhibit low returns on depolarized 3 8 cm radar maps indicating an absence of surface scatterers in the 1 to 50 cm size range a number of reflectance spectra from several regional pyroclastic deposits are presented for the first time these data support a previous interpretation that mantling units have a unique spectral signature which is indicative of the presence of a significant fe bearing volcanic glass component the rima bode region is discussed as an example of an area in which several types of remote sensing data including 3 8 cm radar spectral reflectance and multispectral vidicon data were used to reconstruct the geologic events surrounding the emplacement of a regional pyroclastic mantling deposit the recognition of numerous varieties of volcanic glass samples especially relatively high albedo e g green yellow glasses suggests the existence of additional unrecognized mantling deposits with albedos higher than those studied to date on the basis of the remote sensing data summarized and presented five new areas have been identified which may represent higher albedo regional pyroclastic deposits

local spectrophotometric properties of pyroclastic deposits at the lavoisier lunar crater we present a study of the lavoisier lunar crater combining photometric data from the amie camera smart 1 mission and hyperspectral data from the moon mineralogy mapper m3 chandrayaan 1 mission with a special emphasis on the pyroclastic deposits considered to be present on the crater floor the photometric parameters are in agreement with the general photometric behaviors of the lunar regolith especially the backscattering properties the assumed pyroclastic materials within lavoisier present at first order a rather homogeneous photometric behavior in favor of their surface state homogeneity however they are not significantly different from other non dark patches on the crater s floor whereas the assumed pyroclastic deposit of lavoisier f displays clearly different photometric parameters indicative of distinct physical surface properties from the pyroclastic materials within lavoisier using laboratory data to get hindsight on the reliability of results from orbital datasets we show that the use of more or less depleted phase curves for photometric inversions has a clear impact on the photometric parameters that are derived the hyperspectral analysis of lavoisier crater shows that the various pyroclastic deposits present the same mineralogical composition distinct from the floor of the crater and the mare basalts m3 spectra do not differentiate between the pyroclastic deposits within lavoisier and lavoisier f they have the same spectral signatures share a similar mineralogical composition and probably the same volcanic origin therefore the differences seen in the photometric analysis from the amie observations are indicative of variations in grain sizes and or roughness and or particles scattering properties and or compaction state the combined mineralogical and photometric analysis is a very useful approach to document the nature of the pyroclastic deposits of the moon and possibly of other objects of the solar system e g mercury as the combination of the mineralogy and the physical properties sets constraints on the origin and mode of emplacement of the deposits and characterizes the eruption styles

reply to the comment on physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada by y v dublyansky s e smirnov and g p palyanova

gld100 the near global lunar 100 m raster dtm from lroc wac stereo image data 1 we derived near global lunar topography from stereo image data acquired by the wide angle camera wac of the lunar reconnaissance orbiter camera lroc system from polar orbit tracks the lroc wac provides image data with a mean ground resolution at nadir of 75 m pixel with substantial cross track stereo overlap wac stereo images from the one year nominal mission and the first months of the science mission phase are combined to produce a near global digital terrain model dtm with a pixel spacing of 100 m the global lunar dtm 100 m or gld100 it covers 79 s to 79 n latitudes 98 2 of the entire lunar surface we compare the gld100 with results from previous stereo and altimetry based products particularly with the lunar orbiter laser altimeter lola altimetry which is the current topographic reference for the moon we describe typical characteristics of the gld100 and based upon the comparison to the lola data set assess its vertical and lateral resolution and accuracy we conclude that the introduced first version of the stereo based gld100 is a valuable topographic representation of the lunar surface complementary to the lola altimetry data set further improvements can be expected from continuative investigations

206pb 230th 234u 238u and 207pb 235u geochronology of quaternary opal yucca mountain nevada abstract u th pb isotopic systems have been studied in submillimeter thick outermost layers of quaternary opal occurring in calcite silica fracture and cavity coatings within tertiary tuffs at yucca mountain nevada usa these coatings preserve a record of paleohydrologic conditions at this site which is being evaluated as a potential high level nuclear waste repository the opal precipitated from groundwater is variably enriched in 234u measured 234u 238u activity ratio 1 124 6 179 and has high u 30 313 ppm low th 0 008 3 7 ppm and low common pb concentrations measured 206pb 204pb up to 11 370 it has been demonstrated that the laboratory acid treatment used in this study to clean sample surfaces and to remove adherent calcite did not disturb u th pb isotopic systems in opal the opal ages calculated from 206pb 238u and 207pb 235u ratios display strong reverse discordance because of excess radiogenic 206pb derived from the elevated initial 234u the data are best interpreted using projections of a new four dimensional concordia diagram defined by 206pb 238u 207pb 235u 234u 238uactivity and 230th 238uactivity ages and initial 234u 238u activity ratios have been calculated using different projections of this diagram and tested for concordance the data are discordant that is observed 207pb 235u ages of 170 32 2 to 1772 40 ka are systematically older than 230th u ages of 34 1 0 6 to 452 32 ka the age discordance is not a result of migration of uranium and its decay products under the open system conditions but a consequence of noninstantaneous growth of opal combined u pb and 230th u ages support the model of slow mineral deposition at the rates of millimeters per million years resulting in layering on a scale too fine for mechanical sampling in this case u pb ages provide more accurate estimates of the average age for mixed multiage samples than 230th u ages because ages based on shorter lived isotopes are nonlinearly biased by younger mineral additions use of the combined u th pb technique to date yucca mountain quaternary opals significantly extends the age range beyond that of the 230th u dating method and shows that selected fracture pathways in the unsaturated zone felsic tuffs of yucca mountain have been active throughout the quaternary

erratum to reply to the comment on physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada by y v dublyansky s e smirnov and g p palyanova applied geochemistry 19 2004 1879 1889

testing the relation between uv vis color and tio2 content of the lunar maria reflectance spectroscopy is important for placing lunar samples into a regional and global geologic context to this end the ultraviolet visible uv vis color ratio used to estimate the tio2 composition of mature mare basalts has been one of the most widely used spectral parameters in lunar exploration we examine the correlation between uv vis color and tio2 content using a combination of clementine lunar prospector and sample data to document the extent to which color is dependent upon tio2 examination of the remotely sensed data reveals that the correlation between uv vis ratio and tio2 composition is best represented by a sigmoidal trend rather than the canonical linear or curvilinear correlation with this information we are then able to evaluate between two models that propose different explanations for the relationship between uv vis color and tio2 the first model attributes the correlation between tio2 and uv vis color to spectrally neutral opaques i e ilmenite while the other emphasizes the effect of fe ti charge transfer in lunar glasses and dual scattering mechanisms between high and low ti basalts we do not find evidence in the spectral data to support the occurrence of fe ti charge transfer in lunar glass as the principal cause for color in high ti basalts the data also do not substantiate the existence of different scattering mechanisms e g volume v surface scattering between high and low tio2 basalts instead our analyses substantiate that the spectral effects of ilmenite exhibit a major influence over the uv vis ratio by including sample data we find that in addition to ilemenite tio2 content factors such as feo content ilmenite grain size modal abundance of plagioclase and the olivine to pyroxene ratio in a mare soils can influence the uv vis continuum these findings point to promising avenues of research that future uv vis spectral techniques can exploit in order to yield more accurate tio2 estimates and potentially additional petrologic information

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

lunar regional dark mantle deposits geologic multispectral and modeling studies clementine five channel uv visible uvvis data have been used to study seven regional dark mantle deposits dmds on the moon the dmds were mapped in distribution to determine their extent and stratigraphic relationship to other geologic units based upon the spectral properties for each dmd the crystallization of the beads in each deposit was inferred and used to estimate cooling rates in the volcanic plumes that emplaced the deposits deposits with a high concentration of glasses reflect volcanic plumes that had low optical densities and high cooling rates whereas deposits dominated by crystallized beads indicate plumes with slower cooling rates due to higher optical densities spectral data from each of the regional dmds show that their glass crystallized bead ratio can be estimated based upon their 415 750 and 750 950 nm values and comparison to laboratory spectra for the beads patches of young dark mantle in the sinus aestuum dmd represent one extreme with the bluest color highest 415 750 and weakest glass band absorption lowest 750 950 of all the dmds at the other extreme is the aristarchus plateau dmd with the reddest color and strongest glass band absorption the other nearside dmds including taurus littrow sulpicius gallus rima bode and mare vaporum lie between these two extremes due to intermediate mixtures of the crystallized beads and glasses with other local soils the orientale ring dmd on the western limb is dominated by volcanic glasses and is spectrally similar to the localized dmds found in alphonsus crater we have identified a central vent for the orientale ring dmd and model the eruption as degassing of a near surface dike to produce a 20 km high umbrella shaped plume with ejection velocities of 360 m s and deposition of the glasses at an average radius of 80 km from the vent although we cannot identify the exact sources for the other regional dmds probably because they are buried beneath younger mare the eruptions most likely resulted from dikes breaching the surface and producing a volcanic plume dominated by larger greater than submillimeter hot clasts that formed mare and sinuous rules the small percent of clasts that form the volcanic beads are carried by the expanding gas cloud to large distances in some cases 100 km to produce the observed continuous regional dmds the lack of basalt samples that can be petrologically related to the volcanic glasses may be a result of their spatial separation with the basalts flowing into the basins while the beads are deposited both into the basins and on the adjacent highlands

compositional analyses of lunar pyroclastic deposits abstract the 5 band clementine uvvis data at 100 m pixel were used to examine the compositions of 75 large and small lunar pyroclastic deposits lpds and these were compared to representative lunar maria and highlands deposits results show that the albedo spectral color and inferred composition of most lpds are similar to those of low titanium mature lunar maria these lpds may have consisted largely of fragmented basalt with substantial components of iron bearing mafic minerals pyroxenes olivine and smaller amounts if any of volcanic glass several smaller lpds also show substantial highland components three classes of very large deposits can be distinguished from most lpds and from each other on the basis of crystallinity and possible titanium content of their pyroclastic components one class has spectral properties that are dominated by high titanium crystallized black beads e g taurus littrow a second consists of a mixture of high titanium glasses and beads with a higher glass bead ratio sulpicius gallus than that of taurus littrow and a third has a significant component of quenched iron bearing volcanic glasses aristarchus with possible moderate titanium contents although areally extensive these three classes of very large pyroclastic deposits compose only 20 of the 75 deposits studied 27 and eruption of such materials was thus likely to have been less frequent on the moon

an evaluation of paired δ18o and 234u 238u 0 in opal as a tool for paleoclimate reconstruction in semi arid environments abstract authigenic opal deposits are widespread in semi arid and arid environments and often contain high uranium concentrations that facilitate high precision dating by u series and u pb geochronology however despite their ubiquity and utility for placing temporal constraints on surficial processes the potential for authigenic opal deposits to be used as archives of past climate variability remains largely unexplored compared with more frequently used authigenic carbonate deposits here we investigate the potential for authigenic opal deposits to provide records of paleoclimate and paleohydrologic variability through the development of a combined record of uranium 234 u 238 u 0 and oxygen 18 o isotope variability using in situ ion microprobe methods on opal deposits from pinnacles national park california that precipitated from approximately 16 to 3 ka pinnacles opal 234 u 238 u 0 suggests a moderate decrease in net infiltration from the early to middle holocene coincident with the timing of increasing aridity inferred from sierra nevada lake records while pinnacles opal 18 o indicates a relative increase in subtropical storms at the same time a shift to more north pacific sourced storms commenced after 5 ka coincident with the easing of aridity in northern california and increased storminess in the sierra nevada as indicated by lake sediment records these results suggest that useful insights about past hydrologic change can be gleaned from authigenic opal deposits and that these deposits have the potential to enhance the spatial and temporal coverage of paleoclimate reconstructions in regions where other archives might be scarce however further study of the influence of water in opal on 18 o variability and additional in situ analysis of 18 o variability on longer lived opal deposits with uniform growth histories are necessary to verify the controls on this potential proxy similarly further investigation into short term and spatial variability in 234 u 238 u sw will improve qualitative and quantitative applications of 234 u 238 u 0 in authigenic opal deposits enhancing our ability to use this promising new paleoclimate archive

geochronology of late pleistocene to holocene speleothemsfrom central texas implications for regional paleoclimate a detailed chronology for four stalagmites from three central texas caves separated by as much as 130 km provides a 71 000 yr record of temporal changes in hydrology and climate mass spectrometric 238 u230 th and 235 u231 pa analyses have yielded 53 ages the accuracy of the ages and the closedsystem behavior of the speleothems are indicated by interlaboratory comparisons concordance of 230 th and 231 pa ages and the result that all ages are in correct stratigraphic order over the past 71 000 yr the stalagmites have similar growth histories with alternating periods of relatively rapid and slow growth the growth rates vary over more than two orders of magnitude and there were three periods of rapid growth 71 60 ka 39 33 ka and 24 12 ka these growth rate shifts correspond in part with global glacial interglacial climatic shifts paleontological evidence indicates that around the last glacial maximum 20 ka climate in central texas was cooler and wetter than at present this wetter interval corresponds with the most recent period of increased growth rates in the speleothems which is consistent with conditions necessary for speleothem growth the temporal shift in wetness has been proposed to result

consequences of slow growth for 230th u dating of quaternary opals yucca mountain nv usa thermal ionization mass spectrometry and data are reported for uranium rich opals coating fractures and cavities within the silicic tuffs forming yucca mountain nv the potential site of a high level radioactive waste repository high uranium concentrations up to 207 ppm and extremely high activity ratios up to about 106 make microsamples of these opals suitable for precise dating conventional ages range from 40 to greater than 600 ka and initial activity ratios between 1 03 and 8 2 isotopic evidence indicates that the opals have not experienced uranium mobility however wide variations in apparent ages and initial ratios for separate subsamples of the same outermost mineral surfaces positive correlation between ages and sample weights and negative correlation between ages and calculated initial are inconsistent with the assumption that all minerals in a given subsample was deposited instantaneously the data are more consistent with a conceptual model of continuous deposition where secondary mineral growth has occurred at a constant slow rate up to the present this model assumes that individual subsamples represent mixtures of older and younger material and that calculations using the resulting isotope ratios reflect an average age ages calculated using the continuous deposition model for opals imply average mineral growth rates of less than 5 mm m y the model of continuous deposition also predicts discordance between ages obtained using different radiometric methods for the same subsample differences in half lives will result in younger apparent ages for the shorter lived isotope due to the greater influence of younger materials continuously added to mineral surfaces discordant and u pb ages obtained from outermost mineral surfaces at yucca mountain support this model

ion probe u pb dating of authigenic and detrital opal from neogene quaternary alluvium abstract knowing depositional ages of alluvial fans is essential for many tectonic paleoclimatic and geomorphic studies in arid environments the use of u pb dating on secondary silica to establish the age of neogene quaternary clastic sediments was tested on samples of authigenic and detrital opal and chalcedony from depths of 25 to 53 m in boreholes at midway valley nevada dating of authigenic opal present as rinds on rock clasts and in calcite silica cements establishes minimum ages of alluvium deposition dating of detrital opal or chalcedony derived from the source volcanic rocks gives the maximum age of sediment deposition materials analyzed included 12 samples of authigenic opal one sample of fracture coating opal from bedrock one sample of detrital opal and two samples of detrital chalcedony uranium lead isotope data were obtained by both thermal ionization mass spectrometry and ion microprobe uranium concentrations ranged from tens to hundreds of g g relatively large u pb allowed calculation of 206 pb 238 u ages that ranged from 1 64 0 36 2 to 6 16 0 50 ma for authigenic opal and from 8 34 0 28 to 11 2 1 3 ma for detrital opal chalcedony three samples with the most radiogenic pb isotope compositions also allowed calculation of 207 pb 235 u ages which were concordant with 206 pb 238 u ages from the same samples these results indicate that basin development at midway valley was initiated between about 8 and 6 ma and that the basin was filled at long term average deposition rates of less than 1 cm ka because alluvium in midway valley was derived from adjacent highlands at yucca mountain the low rates of deposition determined in this study may imply a slow rate of erosion of yucca mountain volcanic strata underlying the basin are offset by a number of buried faults to a greater degree than the relatively smooth sloping bedrock alluvium contact these geologic relations indicate that movement on most faults ceased prior to erosional planation and burial therefore ages of the authigenic opal from basal alluvium indicate that the last movement on buried faults was older than about 6 ma

deep arid system hydrodynamics 1 equilibrium states and response times in thick desert vadose zones 1 quantifying moisture fluxes through deep desert soils remains difficult because of the small magnitude of the fluxes and the lack of a comprehensive model to describe flow and transport through such dry material a particular challenge for such a model is reproducing both observed matric potential and chloride profiles we propose a conceptual model for flow in desert vadose zones that includes isothermal and nonisothermal vapor transport and the role of desert vegetation in supporting a net upward moisture flux below the root zone numerical simulations incorporating this conceptual model match typical matric potential and chloride profiles the modeling approach thereby reconciles the paradox between the recognized importance of plants upward driving forces and vapor flow processes in desert vadose zones and the inadequacy of the downward only liquid flow assumption of the conventional chloride mass balance approach our work shows that water transport in thick desert vadose zones at steady state is usually dominated by upward vapor flow and that long response times of the order of 104 105 years are required to equilibrate to existing arid surface conditions simulation results indicate that most thick desert vadose zones have been locked in slow drying transients that began in response to a climate shift and establishment of desert vegetation many thousands of years ago

rise and fall of late pleistocene pluvial lakes in response to reduced evaporation and precipitation evidence from lake surprise california widespread late pleistocene lake systems of the basin and range province indicate substantially greater moisture availability during glacial periods relative to modern times but the climatic factors that drive changes in lake levels are poorly constrained to better constrain these climatic forcing factors we present a new lacustrine paleoclimate record and precipitation estimates for lake surprise a closed basin lake in northeastern california we combine a detailed analysis of lake hydrography and constitutive relationships describing the water balance to determine the influence of precipitation evaporation temperature and seasonal insolation on past lake levels at its maximum extent during the last deglaciation lake surprise covered 1366 km 2 36 of the terminally draining surprise valley watershed using paired radiocarbon and 230 th u analyses we dated shoreline tufa deposits from wave cut lake terraces in surprise valley california to determine the hydrography of the most recent lake cycle this new lake hydrograph places the highest lake level 176 m above the present day playa at 15 19 0 18 calibrated ka 14 c age this significantly postdates the last glacial maximum lgm when lake surprise stood at only moderate levels 65 99 m above modern playa similar to nearby lake lahontan to evaluate the climatic factors associated with lake level changes we use an oxygen isotope mass balance model combined with an analysis of predictions from the paleoclimate model intercomparison project 3 pmip3 climate model ensemble our isotope mass balance model predicts minimal precipitation increases of only 2 18 during the lgm relative to modern compared to an 75 increase in precipitation during the 15 19 ka highstand lgm pmip3 climate model simulations corroborate these findings simulating an average precipitation increase of only 6 5 relative to modern accompanied by a 28 decrease in total evaporation driven by a 7 c decrease in mean annual temperature lgm pmip3 climate model simulations also suggest a seasonal decoupling of runoff and precipitation with peak runoff shifting to the late spring early summer from the late winter early spring our coupled analyses suggest that moderate lake levels during the lgm were a result of reduced evaporation driven by reduced summer insolation and temperatures not by increased precipitation reduced evaporation primed basin and range lake systems particularly smaller isolated basins such as surprise valley to respond rapidly to increased precipitation during late heinrich stadial 1 hs1 post lgm highstands were potentially driven by increased rainfall during hs1 brought by latitudinally extensive and strengthened midlatitude westerly storm tracks the effects of which are recorded in the region9s lacustrine and glacial records these results suggest that seasonal insolation and reduced temperatures have been underinvestigated as long term drivers of moisture availability in the western united states

radiative transfer modeling of the effect of mineralogy on some empirical methods for estimating iron concentration from multispectral imaging of the moon 1 several empirical models for deriving feo concentration from multispectral imaging of the moon are tested using model spectra of lunar soil the spectra are computed from a radiative transfer model based on the work of bruce hapke and cover the system plagioclase orthopyroxene clinopyroxene olivine ilmenite and vary the mg number and maturity over lunar relevant ranges the high degree of correlation between measured and spectrally estimated feo when applied to lunar soils returned by apollo provides constraints on the abundance of certain rock types and these constraints are consistent with geochemical mixing models good feo estimates are yielded for mixtures of plagioclase clinopyroxene and ilmenite by all the algorithms it is found that all spectral algorithms show large errors in the presence of significant olivine and significant errors in the presence of ferroan orthopyroxene the best performance is shown by the lemouelic et al 2002 algorithm that is also insensitive to topographic shading in the absence of ilmenite previously noted differences between spectrally derived feo and that derived by other techniques are all consistent with reported mineralogical differences

geochemical and c o sr and u series isotopic evidence for the meteoric origin of calcrete at solitario wash crater flat nevada usa calcite rich soils calcrete in alluvium and colluvium at solitario wash crater flat nevada usa contain pedogenic calcite and opaline silica similar to soils present elsewhere in the semi arid southwestern united states nevertheless a ground water discharge origin for the solitario wash soil deposits was proposed in a series of publications proposing elevation dependent variations of carbon and oxygen isotopes in calcrete samples discharge of ground water in the past would raise the possibility of future flooding in the unsaturated zone at yucca mountain nevada site of a proposed high level nuclear waste repository new geochemical and carbon oxygen strontium and uranium series isotopic data disprove the presence of systematic elevation isotopic composition relations which are the main justification given for a proposed ground water discharge origin of the calcrete deposits at solitario wash values of 13c 4 1 to 7 8 per mil 18o 23 8 17 2 87sr 86sr 0 71270 0 71146 and initial 234u 238u activity ratios of about 1 6 in the new calcrete samples are within ranges previously observed in pedogenic carbonate deposits at yucca mountain and are incompatible with a ground water origin for the calcrete variations in carbon and oxygen isotopes in solitario wash calcrete likely are caused by pedogenic deposition from meteoric water under varying quaternary climatic conditions over hundreds of thousands of years

opal as a u pb geochronometer search for a standard we report structural geochemical and tims u th pb and u series isotopic data for several samples of precious and common opal which we tested as potential standards for ion microprobe and la icpms isotopic studies the precious opals are low in u contain high concentration of common pb and are not suitable for u pb age determinations in contrast all studied samples of common opal are enriched in uranium and contain sufficiently radiogenic pb for precise calculations of 206pb 238u and 207pb 235u dates complications in the u pb systematics are due to the presence of ubiquitous unsupported 206pb probably derived from initial excess 234u and possibly other intermediate products of 238u decay elevated concentrations and possibly anomalous isotopic composition of initial pb in some of the opals and the presence of two opal generations of different ages in one of the samples despite these imperfections two out of five studied common opals are acceptable as u pb and u series standards at least in the interim the data obtained in this study can be used to guide further search for a better opal standard

dating silica sinter geyserite a cautionary tale abstract we describe a new effort to date hydrothermal silica sinter deposits geyserite from the upper geyser basin of yellowstone national park using 14c of co deposited organic matter u series and cosmogenic 10be methods a majority of the samples were collected from stratigraphic sections mainly at riverside giant and castle geysers ages obtained from 41 14c analyses range from modern to 12 1 cal ka bp nearly all the 14c ages show inconsistencies with their stratigraphic positions and several replicate 14c analyses from the same sample result in significantly different ages the 13c values of the organic material in the sinter range from 26 6 to 12 7 the more enriched values are attributed to microbial fixation of dissolved inorganic carbon dic which has heavier 13c values and is 14c depleted relative to atmospheric co2 leading to an apparent older age u series analyses on 4 samples yielded ages between 2 2 and 7 4 ka large 230th u age uncertainties in the sinter due to low uranium concentrations along with elevated 232th and associated initial 230th make these ages imprecise for use on holocene deposits a single cosmogenic 10be exposure age of 596 18 ka is considerably older than the age of underlying rhyolite and is thus unreliable this apparent old age results from contamination by meteoric 10be trapped in the opal that overprints the very small amount of cosmogenic 10be by presenting the problems we encountered and discussing their probable cause this paper highlights the difficulty in obtaining reliable high precision geochronological data necessary to use sinter deposits as paleoenvironmental and paleo hydrothermal archives

evidence for a hypogene paleohydrogeological event at the prospective nuclear waste disposal site yucca mountain nevada usa revealed by the isotope composition of fluid inclusion water abstract secondary calcite residing in open cavities in the unsaturated zone of yucca mountain has long been interpreted as the result of downward infiltration of meteoric water through open fractures in order to obtain information on the isotopic composition d and 18 o of the mineral forming water we studied fluid inclusions from this calcite water was extracted from inclusions by heated crushing and the d values were measured using a continuous flow isotope ratio mass spectrometry method the 18 o values were calculated from the 18 o values of the host calcite assuming isotopic equilibrium at the temperature of formation determined by fluid inclusion microthermometry the d values measured in all samples range between 110 and 90 similar to holocene meteoric water coupled 18 o d values plot significantly 2 to 8 to the right of the meteoric water line among the various processes operating at the topographic surface and or in the unsaturated zone only two processes evaporation and water rock exchange could alter the isotope composition of percolating water our analysis indicates however that none of these processes could produce the observed large positive 18 o shifts the latter require isotopic interaction between mineral forming fluid and host rock at elevated temperature 100 c which is only possible in the deep seated hydrothermal environment the stable isotope data are difficult to reconcile with a meteoric origin of the water from which the secondary minerals at yucca mountain precipitated instead they point to the deep seated provenance of the mineral forming waters and their introduction into the unsaturated zone from below i e a hypogene origin

two million year record of deuterium depletion in great basin ground waters fluid inclusions in uranium series dated calcitic veins from the southern great basin record a reduction of 40 per mil in the deuterium content of ground water recharge during the pleistocene this variation is tentatively attributed to major uplift of the sierra nevada range and the transverse ranges during this epoch with attendant increasing orographic depletion of deuterium from inland bound pacific storms

spectral characteristics of lunar impact melts and inferred mineralogy abstract two suites of lunar impact melt samples have been measured in nasa s reflectance experiment laboratory relab at brown university suite 1 comprises seven apollo 17 crystalline impact melt breccias and seven quenched glass equivalents suite 2 is made up of 15 additional impact melt samples from apollo 12 15 16 and 17 which exhibit a range of textures and compositions related to cooling conditions and glass abundance a few of these samples have cooled slowly and fully crystallized and thus have the same spectral properties as igneous rocks of similar texture and composition they cannot be uniquely distinguished without geologic context however most of the impact melts and melt breccias contain either quantities of quenched glass and or have developed microcrystalline nonequilibrium textures with well defined diagnostic spectral properties the microcrystalline textures are associated with a distinctive 600 nm absorption feature apparently due to submicroscopic ilmenite inclusions in a transparent host typically fine grained plagioclase the reflectance properties of these lunar sample suites contribute to and constrain the identification and characterization of impact melts in remote sensing data

radar remote sensing of pyroclastic deposits in the southern mare serenitatis and mare vaporum regions of the moon 1 we use polarimetric radar observations to study the distribution depth and embedded rock abundance of nearside lunar pyroclastic deposits radar images were obtained for mare vaporum and the southern half of mare serenitatis the imaged areas contain the large rima bode mare vaporum sulpicius gallus and taurus littrow pyroclastic deposits potential pyroclastic deposits at rima hyginus crater the tacquet formation and a dome in mare vaporum are also included data were acquired at s band 12 6 cm wavelength using arecibo observatory and the green bank telescope in a bistatic configuration the s band images have resolutions between 20 and 100 m pixel the pyroclastic deposits appear dark to the radar and have low circular polarization ratios at s band wavelengths because they are smooth easily penetrable by radar waves and generally contain few embedded blocks changes in circular polarization ratio cpr across some of the pyroclastic deposits show areas with increased rock abundance as well as deposits that are shallower radar backscatter and cpr maps are used to identify fine grained mantling deposits in cases where optical and near infrared data are ambiguous about the presence of pyroclastics the tacquet formation in southern serenitatis areas near hyginus crater and a dome in mare vaporum have lower backscatter cross sections than would be expected for mare basalts of similar estimated titanium content combined with very low cpr values this is strong evidence that these areas are covered in fine grained pyroclastic mantling material

northwest european palaeoclimate as indicated by growth frequency variations of secondary calcite deposits a compilationn for the northwest of europe of over 500 uranium series speleothen and travertine dates is presented using a cumulative distributed error frequency approach these secondary carbonate deposits require both significant groundwater supply and a biogenic soil carbon dioxide source for their growth during glacial periods soil co2 production is inhibited and the water supply is ice locked therefore growth is slowed significantly if not stopped thus deposits can be used on a chronological basis to give a signal of glacial and non glacial periods however sensitivity to the groundwater supply modifies this signal with growth also limited in times of high aridity the palaeoclimatic signal is thus complex the compilation presented is used both as a chronology for comparison with the orbitally tuned marine oxygen isotope record and as a palaeoclimatic indicator attention is focused on two periods of the last glacial interglacial cycle where the record provides a significantly different palaeoclimatic record to other terrestrial and oceanic records these are the isotope stages 5 4 transition for which a relatively low cumulative growth frequency indicates an earlier increase in aridity than observed elsewhere and isotope stage 3 the pleniglacial where both statistically significant high 49 62 ka and low 22 35 44 46 ka levels of growth are observed and can be used to constrain the timing of many of the interstadial events within this period

seasonal variations in modern speleothem calcite growth in central texas u s a variations in growth rates of speleothem calcite have been hypothesized to reflect changes in a range of paleoenvironmental variables including atmospheric temperature and precipitation drip water composition and the rate of soil co2 delivery to the subsurface to test these hypotheses we quantified growth rates of modern speleothem calcite on artificial substrates and monitored concurrent environmental conditions in three caves across the edwards plateau in central texas within each of two caves different drip sites exhibit similar annual cycles in calcite growth rates even though there are large differences between the mean growth rates at the sites the growth rate cycles inversely correlate to seasonal changes in regional air temperature outside the caves with near zero growth rates during the warmest summer months and peak growth rates in fall through spring drip sites from caves 130 km apart exhibit similar temporal patterns in calcite growth rate indicating a controlling mechanism on at least this distance the seasonal variations in calcite growth rate can be accounted for by a primary control by regional temperature effects on ventilation of cave air co2 concentrations and or drip water co2 contents in contrast site to site differences in the magnitude of calcite growth rates within an individual cave appear to be controlled principally by differences in drip rate a secondary control by drip rate on the growth rate temporal variations is suggested by interannual variations no calcite growth was observed in the third cave which has relatively high values of and small seasonal changes in cave air co2 these results indicate that growth rate variations in ancient speleothems may serve as a paleoenvironmental proxy with seasonal resolution by applying this approach of monitoring the modern system speleothem growth rate and geochemical proxies for paleoenvironmental change may be evaluated and calibrated

ten million years of activity within the eastern california shear zone from u pb dating of fault zone opal abstract reconstructions of long term fault activity are essential for understanding both the mechanisms controlling fault behavior and accurate earthquake hazard assessments increasing evidence for temporal variations in strain accumulation suggests non uniform strain rates over a range of historic to geologic timescales the paucity of long term records of fault activity has limited our ability to resolve these variations we present a method for constraining long term fault activity based on u pb dating of fault related opal from secondary fault segments within the eastern california shear zone ecsz the presence of sheared and breccia cemented opaline silica within well exposed faults at near surface conditions suggest that opal formation is associated with high magnitude earthquakes capable of surface rupture 6 m temporal constraints from massive and sheared syntectonic opal n 74 on related secondary faults from this study provide new insights on the timing of fault initiation reactivation and longevity the oldest dates obtained indicate that ecsz activity commenced at or before 10 ma multiple deformation events dated within a single structure on episodically deposited and sheared opal up to six generations demonstrate that fault reactivation occurred over 105 yr timescales 0 7 0 1 myr relative probabilities of dated deformation events can be used to evaluate changes in fault activity in the past 2 5 ma n 60 this analysis indicates enhanced fault activity starting at 2 ma and peaking around 1 ma possibly due to fault interactions and distribution of deformation between the ecsz and the san andreas fault

annually laminated sequences in the internal structure of some belgian stalagmites importance for paleoclimatology abstract fifteen stalagmites from four caves and one sealed tunnel in southern belgium are composed of alternations of annually deposited white porous and dark compact laminae this is demonstrated by comparing the number of laminae with the local history of the site for modern stalagmites and with radioisotopic ages for late glacial and holocene stalagmites annual cyclicity in the internal structure of these speleothems is explained by the highly seasonal variations of the water excess which influences underground water flow comparison between climatic data and modern stalagmites of a closed tunnel shows that growth laminae can record climatic variations 1 there is a good correlation r 0 84 between lamina thickness in a stalagmite and water excess 2 during years with a high water excess dark compact laminae are more developed which makes the speleothem darker vertical successions of several laminae represent microsequences that may have recorded climatic variations with a time resolution of 1 2 year in a late glacial stalagmite successive laminae microsequences form very regular cycles of 11 years separated by a thick darkcompact lamina it is supposed that as for modern stalagmites the thick dark compact lamina corresponds to a period of high water excess hence this 11 year cycle may reflect a climatic cycle

u pb shrimp dating of uraniferous opals abstract u pb and u series analyses of four u rich opal samples using sensitive high resolution ion microprobe shrimp demonstrate the potential of this technique for the dating of opals with ages ranging from several tens of thousand years to millions of years the major advantages of the technique compared to the conventional thermal ionisation mass spectrometry tims are the high spatial resolution 20 m the ability to analyse in situ all isotopes required to determine both u pb and u series ages and a relatively short analysis time which allows obtaining a growth rate of opal as a result of a single shrimp session there are two major limitations to this method determined by both current level of development of ion probes and understanding of ion sputtering processes first sufficient secondary ion beam intensities can only be obtained for opal samples with u concentrations in excess of 20 g g however this restriction still permits dating of a large variety of opals second u pb ratios in all analyses drifted with time and were only weakly correlated with changes in other ratios such as u uo this drift which is difficult to correct for remains the main factor currently limiting the precision and accuracy of the u pb shrimp opal ages nevertheless an assumption of similar behaviour of standard and unknown opals under similar analytical conditions allowed successful determination of ages with precisions of 10 for the samples investigated in this study shrimp based u series and u pb ages are consistent with tims dating results of the same materials and known geological timeframes