dating till using thermoluminescence abstract total thermoluminescence tl is commonly used in tl dating of till this paper presents a technique to isolate a post depositional tl component of subglacially derived mineral grains during glacial transport polymineralic grains are broken down to individual minerals which may then be further comminuted it is postulated that this process creates silt sized grains in which new electron traps can be populated by the external alpha radiation an equivalent dose has been measured on samples of subglacially derived till of known relative age using a modified subtraction technique where larger grains instead of being etched are reduced to the fine silt size by artificial grinding this experiment shows that the thermoluminescence of till is complex however the alpha induced tl is thought to reflect post depositional tl regeneration

late pleistocene holocene climatic and vegetational history of the brazilian caatinga the fossil dunes of the middle sao francisco river palynological studies of a peat bog sequence with a basal date of 10 990 80 yr b p provide a history of vegetational and climatic changes in the icatu river valley located inside a large system of stabilized sand dunes at the middle sao francisco river at 10o24 0 s 43o13 0 w in northeastern brazil the present day vegetation of the valley is vereda a mauritia vinifera palm swamp forest bordered by a narrow strip of semi deciduous tropical forest the adjacent dunes are stabilized by arboreal caatinga and cerrado vegetation in some areas the palynological profile of the saquinho locality within this valley was divided into five pollen zones zone sa1 10 990 10 540 yr b p contains pollen of taxa found in present amazonian and atlantic forests as well as from montane taxa thus suggesting very humid climatic conditions synchronous with more reduced temperatures zone sa2 10 540 6790 yr b p has pollen spectra from a vegetation type dominated by mauritia suggesting progressive warming and high humidity levels the period between 8920 and 8910 yr b p has rapid sedimentation rate few thermoluminescence tl dates pronounced increase of mauritia and ilex pollen suggesting a very moist climate from 8910 to 6790 yr b p there is a progressive decline in forest taxa and a gradual increase of caatinga and cerrado taxa on the landscape zone sa3 6790 ca 6230 yr b p does not contain palynomorphs possibly indicating semi arid conditions zone sa4 ca 6230 ca 4535 yr b p marks the return of mosaic vegetation composed of gallery forest cerrado and caatinga taxa indicating moister climatic conditions a marked decline in moisture levels characterizes the period between 4240 yr b p and present as suggested by an increase in caatinga and cerrado species and a decline in gallery forest taxa zone sa5 ca 4535 yr b p present establishes the present vegetational and climatic pattern of the icatu river valley 1999 elsevier science b v all rights reserved

determination of recent 238u 234u and 230th mobility in granitic rocks application of a natural analogue to the high level waste repository environment abstract the isotope activity ratios 234u 238u and 230th 234u have been investigated in drill core samples up to 1300 m depth in three granitoids from australia to identify the nature of possible recent 1 0 which has generated excess 230th these enriched ground waters do not appear to have penetrated below 530 m depth and 230th excess indicates bulk loss of u the observed disequilibria indicate that significant radionuclide mobilisation has occurred in these rocks during the recent past

alignment of stone pavement clasts by unconcentrated overland flow implications of numerical and physical modelling the crucial role of stone pavements in arid environments for aeolian or alluvial processes and as numerical dating tools is increasingly acknowledged this role is based on the assumption that stone pavements are stable landforms formed gradually over time and predominantly by vertical processes however this is challenged by evidence of stone pavement clast reworking or burial bimodal mostly slope aspect symmetrical clast orientation is a frequent phenomenon in various study areas it implies that stone pavements may be influenced by unidirectional lateral processes besides vertical ones here the finding of lateral processes contributing to stone pavement evolution is supported by numerical modelling and physical experiments these unequivocally show that unconcentrated overland flow can transport clasts to form a closely packed stone mosaic with characteristics similar to those of natural stone pavements the commonly observed length axes orientation angle of 40 14 for natural stone pavement clasts is consistently reproduced by angle dependent force equilibrium monte carlo runs confirm the natural scatter and allow characterization of the control parameters of clast orientation the model explains up to 70 of the natural variance it is further validated by flume experiments which confirm model predictions of single object orientation angles experiments with multiple objects yield artificial stone pavements with properties similar to those found in the field the unidirectional lateral process acting on natural stone pavements requires the presence of a vesicular horizon this underlines the tight genetic coupling of this common epipedon feature and the clast cover the presented findings highlight the role of stone pavements as process and environment proxies however stone pavements represent information since the last surface disturbance only this has to be considered when using them as age indicators copyright 2013 john wiley sons ltd

review of the modelling of radionuclide transport from u series disequilibria and of its use in assessing the safe disposal of nuclear waste in crystalline rock abstract u series disequilibia from crystalline rocks and u deposits have been used to estimate the timing of hydrogeological events for u and ra mobility and to model the transport rates of u and ra both with some sucess unfortunately activity ratio data alone are not unique to a given process or model and it is shown how inappropriate choice of the model can have quite diverse consequences for interpretation of the data information from other sources is needed to help minimise these non uniqueness problems but as yet the state of methodology is unadequate to assess completely the validity of the models in particular the rate of deposition of u in fractures seems highly dependent upon the availability of trivalent fe and other low temperature minerals whose rates of formation are largely unknown this review reinforces the need to assess closely the suggestion that chemisorption is an effective retardant of fracture borne borne repository source radionuclides

cracks in desert pavement rocks further insights into mechanical weathering by directional insolation the formation of cracks is a fundamental first step in the physical weathering of rocks in desert environments in this study we combine new field data from the mojave u s gobi mongolia and strzelecki australia deserts that collectively support the hypothesis that meridional cracks cracks with orientations not readily attributable to rock anisotropies or shape in boulders or cobbles form due to tensile stresses caused by directional heating and cooling during the sun s daily transit the new studies indicate that rock size surface age and latitude play important roles with respect to their influence on rock fracture rock size and pavement surface age exert an influence on the development of rock cracks as the average clast size of mature desert pavements may be at or below the threshold clast size for thermal cracking of rocks latitude controlled seasonal temperature variations play a key role as demonstrated by 1 tightly clustered mean resultant orientations that differ by latitude as predicted in mcfadden et al 2005 and 2 very cold wintertime temperatures and strong diurnal gradients that may favor crack development in wintertime given the likelihood for strong clast heating during early morning hours the consistent evidence for meridional cracks in surfaces of diverse age and desert environments climate vegetation and distance of clast transport indicate that directional insolation may play the key role in initially generating and propagating rock fractures rather than a secondary role as implied in recent field and modeling studies of physical weathering in deserts

tl dating of river terraces with fossil soils in the mediterranean region abstract fossil soils especially the red soils linked with interstadial conditions in the terraces of mediterranean rivers can be important chronoclimatostratigraphic markers the lack of organic remains makes them generally unsuitable for palaeobiological studies and thus palaeomorphological dating has been the main method applied to determine their relative age we present the first results of tl dating of fossil soils and water lain sediments from the catchment area of the turia jucar and serpis rivers in the region of valencia spain the regeneration method was used to determine the palaeodoses in fine silt grains extracted from the bulk samples and nal tl gamma spectrometry was used for determination of the dose rates a blind test on a radiocarbon dated 20 ka old sample from the po plain italy and tl ages for the eemian palaeolithic site in cova negra valencia spain indicate that the method can give correct results within the whole of the last glacial interglacial period the specific sedimentation regime interspersed with strong erosional processes in mediterranean valleys coarse grain and stony sediments frequent erosional contacts are not very favourable for tl dating or interpretation of the results also post sedimentation changes e g carbonate leaching and accumulation inside the dated horizon could affect the dose rate and consequently the tl age

a 22 000 year record of vegetation change in the north central sonoran desert abstract plant macrofossils from eleven packrat neotoma sp middens provide a history of vegetation change over the last 22 140 years at eagle eye mountain near the northern border of the sonoran desert in arizona this site is located in the arizona upland subdivision departures and arrivals of various perennial plant species during the holocene were similar to other records from more southerly sites and support earlier generalizations of van devender van devender t r 1990 late quaternary vegetation and climate of the sonoran desert united states and mexico in betancourt j l van devender t r martin p s eds packrat middens the last 40 000 years of biotic change university of arizona press tucson pp 134 165 regarding the tempo and mode of late quaternary changes in the arizona upland evergreen woodland containing pinus monophylla singleleaf pinyon juniperus osteosperma utah juniper and quercus turbinella shrub live oak occupied the site during full glacial times the latter two species but not p monophylla persisted into the early holocene and were joined by a limited number of desertscrub species including acacia greggii catclaw carnegiea gigantea saguaro and several other succulents with the arrival of many other species during the middle holocene a desertscrub community that differed considerably from the modern vegetation developed acacia greggii and cercidium floridum blue paloverde were the principal large woody species on exposed hillslopes assemblages similar in composition to the modern desertscrub did not appear until approximately 4000 years ago when the more xerophytic cercidium microphyllum foothills paloverde arrived and c floridum disappeared from hillslopes the delayed arrival of c microphyllum in comparison to other sonoran desertscrub species with similar climatic tolerances is attributed to the limited dispersal distance of its seeds by seed eating heteromyid rodents at 4540 and 6425 yr b p the cold intolerant shrub encelia farinosa was present on northeasterly aspect exposures where it is absent today suggesting slightly warmer winter conditions during the middle holocene the presence of the tree cercidium floridum and the perennial c 4 grass setaria leucopila on exposed slopes during the middle holocene indicates substantially moister conditions during that time than in the late holocene or today at sites on the xeric limits of the modern distributions of both species average annual precipitation is from 50 to 100 greater than that presently received at eagle eye mountain in particular the responses of s leucopila and cacti during the middle holocene indicate substantial increases in warm season precipitation

first evidence of an interglacial lake of eemian age in northeast italy this paper assesses the age of the tagliamento morainic amphitheatre northeast italy one of the largest morainic bodies in the piedmont area of northern italy using new stratigraphical and thermoluminescence tl data obtained from a site located on the inner flank of the amphitheatre two samples from a 12 m thick stratum of fluviolacustrine non varved fine sand provided tl ages of approximately 110 16 ka bp this sandy layer lies below a 6 m thick massive non laminated clayey stratum it is hypothesised that a large but short lived lake formed during the interglacial phase separating the penultimate and last glaciations assigning a riss age to the southeastern part of the amphitheatre therefore regains credence 1998 john wiley sons ltd

comparison of 226ra 238u and 228th 228ra disequilibrium with weathering indices in beach sand sediments from greece weathering indices can be used to quantify weathering of rocks at various stages of weathering processes and provide a better understanding of element mobility during weathering various weathering indices have been proposed in the literature worldwide in the present work radioactive secular disequilibrium has been used to determine weathering extent thirty seven samples from kavala and thirty from sithonia beach sands all of them being the weathering products of the local granitic plutons are studied for their secular disequilibrium in both 238u and 232th series 226ra 238u and 228ra 228th respectively the results are compared to weathering indices already in use worldwide and suggest a consistent correlation with wip alkaline and alkaline earth element leaching and pwi silica leaching for the well and very well sorted sands and for the heavy minerals of kavala this study suggests that with an appropriate choice of the weathering index and samples both u series and weathering index can recover the extent of chemical weathering

radioactive disequilibria in mineralised fracture samples from two uranium occurrences in northern sweden abstract mineralised fractures from two uranium occurrences in northern sweden were examined mineralogically and isotopically to establish the presence or absence of radioactive equilibrium that may indicate recent rock water interaction processes based on the natural mobility of uranium i e during the last 0 5 ma the results show evidence of radioactive disequilibrium in six of the nine samples investigated disequilibria are attributable to solution to solid 234 u recoil gain weakly mineralised zones adjacent to the main mineralisation and solid to solution 234 u recoil loss moderate to highly mineralised zones the absence of significant 238 u loss in the samples emphasises the reducing conditions at the sampled depths

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

test of thermoluminescence dating of loess from new zealand and alaska abstract the accuracy of thermoluminescence tl ages for loess and sediments in general greater than 100 ka is disputed we tested the accuracy of three common tl sediment dating techniques applied to 4 11 m sized polymineral grains from known age loess using 16 samples from north island and south island new zealand and 2 samples from central alaska estimated sample ages range from 20 26 to 800 ka we varied the optical bleaching spectrum the selected window of the emission spectra ultraviolet or uv blue and green wavelengths the pre readout heat treatment and the tl equivalent dose measurement technique most of the 20 26 ka samples gave tl age underestimates of 3 6 ka that may be attributed to post burial open system behavior for the older samples the partial bleach tl method gave expected ages up to 300 ka and the total bleach tl method produced expected ages above 100 ka the partial bleach regeneration tl method gave significant age underestimates for samples older than 100 ka with a maximum tl age of 250 ka for samples having expected ages up to 350 ka two 300 360 ka samples which gave total bleach age underestimates with use of uv tl and green tl gave expected ages with use of blue tl these results demonstrate that reliable tl ages for loess from new zealand and alaska up to 800 ka can be obtained if uv and green emissions and the various regeneration methods are avoided this age range is well above the former putative 80 100 ka upper age limit for tl dating of loess from other regions which was thought to be a global limit application of our successful procedures to such loess is encouraged

tl analysis of loess samples from achenheim abstract we have investigated four loess samples from achenheim sample j2a and l1 were collected above and below a horizon with a supposed age of 30 ka sample o1 was collected below the last interglacial soil and t1 below the next interglacial soil for the determination of eds the additive dose and regeneration techniques were applied using different filters the additive dose technique was complicated by the observation that the dose response could not be described by a single saturation function we have applied two saturation functions and used only the values below the intercept dose for ed determination nearly all calculated ages are younger than expected given the uncertainties there is not a significant difference between results obtained by the additive dose and the regeneration methods the use of the bg12 and ug11 filters seem to give slightly lower results than the 5 58 filter we have calculated mean lives for the tl signals of samples l1 o2 and t1 assuming the youngest possible estimates 30 130 and 240 ka our measurements imply that the thermal stability of the recorded signals is somewhere in the 100 200 ka region for the 5 58 filter and around 100 ka for the other filters due to the uncertainty of the geological age estimates these values are more likely upper limits of the thermal stability

fluctuations in the thermoluminescence signal of suspended sediment in an alpine glacial meltwater stream abstract analysis of the thermoluminescence tl signal from suspended sediment samples from the dora di ferret river in northern italy reveals two scenarios for entrainment transport and bleaching of the tl signal in clear weather a simple diurnal fluctuation in luminescence intensity is apparent but the correlation with sediment concentration in the stream is very low storm events in contrast cause large amounts of unbleached sediment to be mobilised and entrained in the flow producing a significant positive correlation between tl intensity and sediment concentration such storm events may be identified by an initial dip in the intensity of the tl signal believed to be due to zeroed grains on the surface of valley slopes being washed off the slopes followed by a major rise in signal as erosion starts to incorporate previously unbleached sediment into the flow

soil horizon development and the tempo and modes of vegetation change during the holocene in a sonoran desert basin usa silt rich and clay rich vesicular horizons v horizons that develop beneath desert pavements limit infiltration and plant available soil moisture a radiocarbon date from buried charcoal constrains the timing of emplacement of a sonoran desert alluvial fan deposit to the very end of the pleistocene approximately 12 7 ka the surface of the fan is dotted with 1 5 3 m light colored plant scars that mark places once occupied by larger perennial plants a few very large ring like clones of larrea tridentata have persisted on the surface and represent plants that may have initially established as long ago as the early holocene the gravelly fan deposit initially would have possessed high infiltration capacities and fostered the establishment of vegetation two principal sets of factors have driven vegetation change over the course of the holocene during the first part of the holocene differences in life history attributes of various species dispersal and colonization vs competitive abilities would have contributed to a succession of perennial plant occupants culminating with the predominance of the slow growing long lived but competitively dominant l tridentata during the latter part of the holocene and continuing to the present continued development of the pavement and associated v horizon has increasingly diminished the capacity of the surface to absorb precipitation and is responsible for the more recent phase involving progressive elimination of vegetation development of soil features that markedly influence soil hydrology is a major component of vegetation change during the late quaternary in the more arid portions of the sonoran and mojave deserts

thermoluminescence dating studies of glacial silts from ontario to develop procedures for the direct dating of glacially related silts by thermoluminescence tl i have applied previously proposed techniques to three polymineralic 4 11 m samples from the toronto area furthermore one of these samples was studied in detail by isolating some mineral fractions the principal conclusion is that the tl of the lodgment halton till from woodbridge was not significantly reset during deposition whereas the tl of the waterlaid upper thorncliffe silt from the scarborough bluffs was reset as was the tl of the third sample wc st a massive silt from woodbridge that has been generally correlated with the glaciolacustrine sunnybrook diamict at the bluffs this conclusion follows from the observation of feldspar tl apparent ages of 140 ka for the 12 ka bp halton till and of 36 and 66 ka for the upper thorncliffe and wc st samples respectively the four laboratory factors that contributed most to inaccuracies in the tl apparent ages were 1 anomalous fading in the felds

luminescence dating of quaternary sediments in the himalaya and high asia a practical guide to its use and limitations for constraining the timing of glaciation abstract knowledge of the glacial history of high asia is of critical importance for scientific understanding of the palaeoclimate of this region the lack of absolute age controls on glacial landforms of the himalaya and high asia region is arguably the greatest problem facing the construction of a history of quaternary glaciation in these areas a major reason for this lack of dates has been the absence of a suitable dating method this paper reviews the use of optically stimulated luminescence osl dating in the himalaya critical examination of existing data is used to suggest guidelines for the collection of suitable sediments for dating using osl in order to constrain the timing of glaciations osl has been shown to provide reproducible and apparently accurate ages which constrain glacial advances however the correct selection of sediments is of critical importance in spite of developments in the technique there remain limitations to its applicability reasons for this are considered as is the potential of osl for constraining the timing of glacial expansion

soil heterogeneity in mojave desert shrublands biotic and abiotic processes 1 geological and ecological processes play critical roles in the evolution of desert piedmonts feedback between fast cyclic biotic and slow cumulative pedogenic processes on arid alluvial fan systems results in a heterogeneous landscape of interspace and canopy microsites defining the spatial extent between these processes will allow a better connection to ecosystem service and climate change we use a soil chronosequence in the mojave desert and high spatial resolution infiltrometer measurements along transects radiating from canopies of perennial shrubs to assess the extent of biotic and abiotic processes and the heterogeneity of soil properties in arid shrublands results showed higher saturated conductivity under vegetation regardless of surface age but it was more conspicuous on older developed soils at proximal locations to the shrub bulk density soil structure grade silt and clay content significantly increased radially from the canopy while sand and organic material decreased soil properties at distal locations 2 5 times the canopy radius had no significant spatial correlation the extent of the biotic influence of the shrub was 1 34 0 32 times the canopy radius hydraulic properties were weakly correlated in space but 75 of the variance could be attributed to sand content soil structure grade mean particle diameter and soil organic material none of which are exclusively biotic or abiotic the fast cyclic biotic processes occurring under vegetation are clearly overprinted on slow cumulative abiotic processes resulting in the deterministic variability observed at the plant scale

transport of 234u in the opalinus clay on centimetre to decimetre scales the opalinus clay formation in north switzerland is a potential host rock for a deep underground radioactive waste repository the distribution of u 238 u 234 and th 230 was studied in rock samples of the opalinus clay from an exploratory borehole at benken canton of zurich using mc icp ms the aim of u 234 was to assess the in situ long term migration behaviour in this rock very low hydraulic conductivities of the opalinus clay reducing potential of the pore water and its chemical equilibrium with the host rock are expected to render both u 238 and th 230 immobile if u is heterogeneously distributed in the opalinus clay gradients in the supply of u 234 from the rock matrix to the pore water by the decay of u 238 will be established diffusive redistribution separates u 234 from its immobile parent u 238 resulting in bulk rock u 234 u 238 activity disequilibria these may provide a means of estimating the mobility of u 234 in the rock if the diffusion rate of u 234 is significant compared to its decay rate sampling was carried out on two scales drilling of cm spaced samples from the drill core was done to study mobility over short distances and elucidate possible small scale lithological control homogenized 25 cm long portions of a 2 m long drill core section were prepared to provide information on transport over a longer distance variations in u and or th content on the cm scale between clays and carbonate sandy layers are revealed by beta scanning which shows that the dominant clay is richer in both elements samples were digested using aqua regia followed by total hf dissolution yielding two fractions in all studied samples u was found to be concentrated in the hf digestion fraction it has a high u th ratio and a study by sem eds points to sub mu m up to several mu m in size zircon grains as the main u rich phase this fraction consistently has u 234 u 238 activity ratios below unity the minute zircon grains constitute the major reservoir of u in the rock and act as constant rate suppliers of u 234 into the rock matrix and the pore water the aqua regia leach fraction was found to be enriched in th and complementary to the hf fraction having u 234 u 238 activity ratios above unity it is believed that these u activity ratios reflect the surplus of having u 234 delivered from the zircon grains some cm spaced samples show bulk rock u 234 u 238 activity ratios that are markedly out of equilibrium in most of them a striking negative correlation between the total u content and the bulk rock u 234 u 238 activity ratios is observed this is interpreted to indicate net u 234 transfer from regions of higher supply of u 234 towards those of lower supply which is in most cases equivalent to transfer from clayey towards carbonate sandy portions of the rock in contrast the 25 cm averaged samples all have uniform bulk rock u 234 u 238 activity ratios in equilibrium indicating u immobility in the last 1 1 5 ma on this spatial scale it is concluded that the small scale lithological variations which govern u spatial distribution in the opalinus clay are the major factor determining u 234 in situ supply rates regulating its diffusive fluxes and controlling the observed bulk rock u 234 u 238 activity ratios a simple box model is presented to simulate the measured bulk rock u 234 u 238 activity ratios and to give an additional insight into the studied system c 2008 elsevier ltd all rights reserved

element mobility studies of two drill cores from the gotemar granite krakemala test site southeast sweden abstract a pilot study was carried out on two relatively deep drill cores 600 m from the gotemar granite massif in s e sweden this granite is typical of the 1400 ma anorogenic granites of the northern hemisphere samples from representative unfractured parts of the cores together with four samples taken along a profile tangential to a fracture plane at 280 m depth were investigated chemically mineralogically and isotopically the results show that after crystallisation subtle and pervasive open system modifications of the trace element chemistry of the granite took place whereas the major element chemistry and minera logical data emphasised the relative homogeneity of the gotemar granite samples investigated trace elements such as u rb and pb revealed irregular distributions which are probably the result of large scale hydrothermal alteration processes this conclusion is supported by isotopic studies which indicate that whole rock samples were open to a gain or loss of pb and possibly u at 420 171 ma ago in addition isotopic data for u pb and u ra are consistent with a recent minor loss of u the pervasive alteration and the more recent mobilisation of u are evident to a depth of at least 600 m the effects are most prevalent along major fracture zones and within the upper 250 300 m of one drill hole where a high frequency of crush zones has been noted higher fe oxidation ratios higher rb contents lower u contents and correspondingly higher th u ratios all characterise this zone

tl dating of partially bleached sediments by the regeneration method abstract thermoluminescence dating of sediments in the warsaw laboratory is based on blue to green emission the partial bleach regeneration method is proposed for dating sediments which have not been completely bleached at the time of burial correct tl ages are reported for sediments covering organic deposits of the eemian interglacial and also for glacial sediments of wurm and riss age we obtained good results for dating till using the partial bleach regeneration method the tl zeroing in till is explained by the rubbing or compression of grains beneath the glacier and by the freeze thaw activity occurring during glacial transport and deglaciation

apparent osl ages of modern deposits from fabergstolsdalen norway implications for sampling glacial sediments the application of optically stimulated luminescence osl dating within glacial settings can be limited where sediments have not had their osl signal fully reset by sunlight exposure heterogeneous bleaching can result in age overestimations and although it is recognized that certain depositional settings are more likely to have experienced sufficient sunlight exposure to bleach the osl signal no comprehensive study has empirically investigated the processes of sediment bleaching or the variability in bleaching between deposits of the same type and within the same glacial catchment a suite of modern glacial and glaciofluvial sediments from fabergstolsda len southern norway have been analysed to explore the controls that sedimentary processes and depositional setting have on bleaching of the osl signal of quartz there is considerable variability in the residual osl ages of similar modern deposits which reflects high sensitivity of the osl signal to sediment source sedimentary process transport distance and depositional setting overdispersion values are greatest for the sediments which have been most heterogeneously bleached and these sediments have the lowest residual ages sampling strategies that incorporate sufficient consideration of the depositional framework of sample settings can minimize the effects of unbleached residuals on osl age determinations copyright 2013 the authors journal of quaternary science published by john wiley sons ltd on behalf of quaternary research association

late pleistocene c4plant dominance and summer rainfall in the southwestern united states from isotopic study of herbivore teeth abstract patterns of climate and c4plant abundance in the southwestern united states during the last glaciation were evaluated from isotopic study of herbivore tooth enamel enamel 13c values revealed a substantial eastward increase in c4plant consumption formammuthusspp bisonspp equusspp andcamelopsspp the 13c values were greatest inbisonspp 6 9 to 1 7 andmammuthusspp 9 0 to 0 3 and in some locales indicated c4 dominated grazing the 13c values of antilocaprids were lowest among taxa 12 5 to 7 9 and indicated c3feeding at all sites on the basis of modern correlations between climate and c4grass abundance the enamel data imply significant summer rain in parts of southern arizona and new mexico throughout the last glaciation enamel 18o values range from 19 0 to 31 0 and generally increase to the east this pattern could point to a tropical or subtropical source of summer rainfall at a synoptic scale the isotope data indicate that interactions of seasonal moisture temperature and lowered atmospheric pco2determined glacial age c4abundance patterns

the role of isotope geochemistry studies in the canadian nuclear fuel waste management program abstract the objective of the canadian nuclear fuel waste management program is to develop and assess a method for the safe disposal of used nuclear fuel wastes from canadian nuclear power generating facilities the concept that is being developed involves the disposal of these wastes in a cavity mined at a depth of 500 1000 m in a plutonic rock formation both in the assessment of this concept and in any possible future site selection the geochemistry of the rock formation and of the groundwater plays a significant role isotope geochemistry studies involve the determination of the distribution and behaviour of stable and radioactive isotopes in the groundwater and in the rock matrix this information can be used to shed light on the geochemical history of the rock formation under investigation and increase the understanding of the geochemical processes that govern the evolution of these rock formations the information can in principle also be used to date the various geological events and processes that have led to the distribution of radioactive isotopes in the rock and in the groundwater

co development of alluvial fan surfaces and arid botanical communities stonewall flat nevada usa arid alluvial fan and fluvial dry wash surfaces in stonewall flat nevada usa are characterized using surface geomorphic surveys soil pits botanical line surveys and varnish microlamination dating techniques active and abandoned washes and active fan surfaces are dominated by primary geomorphic processes of high energy sedimentation from flash floods these surfaces are characterized by bar and swale topography a lack of stone pavements soil horizons and rock varnish younger terraces and slightly older intermediate fan surfaces are in transition from primary sedimentation processes to lower energy secondary surface modifying processes of sheet wash and eolian transport and deposition these surfaces are characterized by faint to no bar and swale topography incipient to moderately well developed pavements and soil horizons and abundant coppices old and stable fan surfaces are dominated by lower energy secondary processes and manifest well developed pavements soils and sparse coppices around widely distributed shrubs varnish microlamination dating yields ages of 13 15 ka for intermediate fan surfaces and 25 55 to 86 75 ka for stable fan surfaces plant communities co developing with these surfaces affect and are affected by both primary and secondary geomorphic fan processes relatively active surfaces contain few woody species co dominance of shrubs and annuals with abundant annuals between the shrubs is characteristic of surfaces transitional from primary processes to secondary processes stable surfaces dominated by secondary processes are characterized by woody perennials with long lived woody species inhabiting the oldest surfaces feedback mechanisms between early botanical communities and eolian deposition affect coppice and pavement development in turn these surface features control both the composition and distribution of botanical communities on older more stable surfaces published 2012 this article is a u s government work and is in the public domain in the usa

late pleistocene climatic variations at achenheim france based on a magnetic susceptibility and tl chronology of loess abstract new field investigations of the achenheim sequence alsace france allow for the characterization of variations in the low field magnetic susceptibility over most of the last climatic cycle i e the past 130 000 yr new stratigraphic data and thermoluminescence measurements permit reassessment of the previous chronological interpretation of the upper pleistocene at achenheim a high resolution analysis of magnetic susceptibility discloses the occurrence of a fine grained marker horizon which was also found recently in another section this horizon is interpreted as a small scale dust layer deposited prior to the main interval of loess deposition the horizon deposited at the marine isotope stage mis 5 4 boundary has been found in other loess sequences and is especially prevalent in central europe it is characterized by low susceptibility values and a grayish color new thermoluminescence dates indicate that the loess deposition took place after the mis 5 4 boundary i e after 70 000 yr these results are consistent with the greenland grip ice core dust record which also demonstrates a dusty atmosphere after 72 000 yr ago on a more regional scale the achenheim loess sequence demonstrates a reliable correlation between the western side of the eurasian loess belt and the dust record of the greenland ice cores

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

devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last british irish ice sheet this contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last british irish ice sheet a task undertaken as part of a larger community based project britice chrono that aims to improve understanding of the ice sheet s deglacial evolution as accurate reconstructions depend on the quality of the available data some form of assessment is needed of the reliability and suitability of each given age s in our dataset we outline the background considerations that informed the quality assurance procedures devised given our specific research question we describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty when these criteria were applied to an existing database of all geochronological data relating to the last british irish ice sheet they resulted in a significant reduction in data considered suitable for synthesis the assessed data set was used to test a bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models

decouverte de concretions calcaires striees dans le till de gentilly basses terres du saint laurent quebec la decouverte de concretions striees dans le till de gentilly renforce l hypothese de l existence d une phase ancienne de concretionnement en milieu glacio lacustre dans les basses terres du saint laurent qui serait anterieure a la derniere englaciation generale des datations 14c obtenues sur deux d entre elles confirment les datations anterieures des concretions des varves du lac de deschaillons elle conduit a suggerer un ge maximal de l ordre de 35 000 bp pour la mise en place du till de gentilly compte tenu de l ge des sediments sous jacents de saint pierre 75 000 bp les basses terres du saint laurent n auraient pas connu d englaciation generale pendant une tres grande partie du wisconsinien the discovery of striated calcareous concretions in the gentilly till supports the hypothesis of an early episode of carbonate precipitation in a glaciolacustrine environment that occurred before the st lawrence lowlands became covered by the last ice advance finite 14c ages have been obtained on two such concretions these ages are in agreement with several others obtained previously on concretions from lake deschaillon varves they suggest a maximum age of ca 35 000 bp for the gentilly till deposition inasmuch as the underlying st pierre sediments have been dated at ca 75 000 bp the st lawrence lowlands would have been ice free during a large part of the wisconsinan stage

holocene environmental change and vegetation contraction in the sonoran desert abstract two types of microtopographic features plant scar mounds and plant scar depressions on surfaces of barren desert pavements provide a unique record of the former presence of large perennial plants evidence of bioturbation by burrowing animals extends more than 1 m beneath each type of plant scar indicating that both features originated as large bioturbation mounds formation of bioturbation mounds in desertscrub environments is generally restricted to areas beneath widely separated large perennial plants the contrasting forms of plant scars mounds vs depressions represent time dependent changes following disappearance of the large plants and eventual cessation of bioturbation plant scar mounds represent a geologically recent episode of plant mortality whereas plant scar depressions represent the disappearance of plants at a considerably earlier time possibly at the pleistocene holocene transition contrasting spatial distributions of the two kinds of plant scars indicate that vegetation on alluvial fans has progressively contracted from a more diffuse former vegetation cover yielding the wide barren pavement surfaces present today in less arid portions of the sonoran desert spatial distribution of recent plant mortality due to persistent severe drought provides an analog of the progressive loss of plants from different parts of the landscape in the past

zeroing of the tl signal in sediment undergoing fluvioglacial transport an example from austerdalen western norway abstract study of levels of natural tl in sediment undergoing fluvial transport in austerdalen norway shows that bleaching does occur but does not follow a regular pattern this is attributed to the incorporation of older unbleached material into the sediment load as a result of riverbank erosion levels of residual tl are high enough to raise doubts about the accuracy of fine grain tl dating of fluvioglacial sediments which have experienced only a short distance of transport

application of a soil water balance model to evaluate the influence of holocene climate change on calcic soils mojave desert california u s a abstract we used a process based soil water balance model to simulate the downward flux of soil water under varied conditions of climate vegetation and soil texture to determine the potential impact of episodic periods of wetter pluvial climate during the holocene on calcic soils in the mojave desert that have a bimodal distribution of carbonate daily weather data associated with a relatively wet climate years with extreme increases in annual rainfall 33 cm yr and dry climate historic average annual rainfall 15 cm yr was used to simulate the affects of pleistocene and holocene climate change on soil water balance linkages among atmospheric circulation patterns regional increases in precipitation and historic flooding in the mojave desert california suggest that historic wet years provide an analog for wetter climates that occurred during the last glacial period latest pleistocene and episodically during holocene periods of pluvial activity modeling results indicate that soil water balance for dry and wet years strongly corresponds with the upper and lower zones of carbonate accumulation respectively soil water only reached the lower zone of carbonate during a wet year when extreme increases in winter spring storm activity resulted in a significant increase in precipitation and the downward flux of soil water the linkage between increases in frontal storm activity and pluvial events suggests that the shallow zone of the bimodal distribution of carbonate is a result of periods of significant decreases in winter and spring rainfall and not primarily due to increases in holocene temperature or the development of clay rich horizons calculation of carbonate solubility and accumulation rates suggests that the bimodal distribution of carbonates in soils may have also been impacted by episodic periods of extreme increases in precipitation associated with perennial lakes during the holocene results suggests that much of the carbonate in the upper 75 cm of pleistocene soils may have accumulated during the late holocene rather than throughout the entire holocene

thermoluminescence dating tests of pleistocene sediments from uplifted marine shorelines along the southwest coastline of the calabrian peninsula southern italy abstract this paper presents tl age estimates of pleistocene raised marine terraces from southern calabria southern italy it focuses on the dating of last interglacial shallow marine sand deposits including several tyrrhenian key reference deposits whose stratigraphic assignment is based on biostratigraphic evidence presence of a strombus bubonius fauna and geochronometric data amino acid data calibrated with u th dates on coral the tl age estimates are obtained on alkali feldspar coarse grains using their blue tl emission they are in good agreement with the ir osl age estimates obtained on the same feldspar samples our feldspar tl method is tested on two tyrrhenian key reference sites ravagnese and bovetto in the reggio di calabria area their measured tl age estimates 97 11 ka and 100 10 ka are lower than their estimated geological age i e oxygen isotope substage 5e the correction for long term fading suggested by mejdahl 1988 is tested on these two samples using a lifetime of 446 ka as estimated from both calabrian and miocene sand collected within the same area this correction would yield preliminary tl ages 116 13 ka and 116 12 ka that are in better agreement with the expected geological age the application of our tl method to paleoshorelines lying below the tyrrhenian reference shoreline of ravagnese bovetto yields stratigraphically consistent tl age estimates the tl method is also applied to two supposedly pre last interglacial paleoshorelines which are geomorphologically older than the tyrrhenian reference shorelines they remain however chronologically undifferentiated both by the tl and the amino acid methods finally the preliminary feldspar tl results obtained on the miocene and the calabrian sand deposits 1 ma suggest that our feldspar tl method is limited in the sw calabrian area to about 200 ka

history of actinide and minor element mobility in an archean granitic batholith in manitoba canada abstract surface and borehole core samples from the lac du bonnet granite manitoba canada have been analysed for major element concentrations fe 3 fe total ratios rare earth element ree content and actinide isotopic abundances this work forms part of the geological investigations of the canadian nuclear fuel waste management program performed by atomic energy of canada limited aecl the study attempts to understand the history of and processes governing mobilisation of elements and naturally occurring radionuclides during high and low temperature alteration events in fluid bearing fractures in the granite one surface sample and two core samples from 150 m and 730 m are each in contact with fractures in the granite and show evidence of alteration events that penetrated the rock matrix over distances of at least 3 cm loss of ca and na is seen in cores from a depth of 150 m from the highly altered hematite rich rock adjacent to sub horizontal fracture zones at the underground research laboratory url of aecl near lac du bonnet in contrast k fe fe 3 fe and u concentrations increase towards the fracture surface due to formation of illite and association of u with hematite and the illite at the fracture surface u continues to increase but fe and thefe 3 fe ratio decrease indicating fe removal by reduction the ree also show some enrichment in more altered rock at intermediate depths but the total ree concentration is lower than in the surface and deep core samples no clear trends are visible for parent and fracture surface ree in surface and deep core samples however disequilibrium values of 234 u 238 u and 230 th 234 u ratios in surface and intermediate depth core samples indicate that u has been mobilised in recent geological time the last ma but th has remained relatively immobile high th u and 230 th 234 u ratios in surface samples are indicative of rapid leaching of u but little isotopic fractionation probably within the last 10 5 a apparently unaltered rock several centimetres distant from the fracture in surface and intermediate depth samples has lost appreciable u but evidence from u series disequilibrium studies suggests that this process occurred more than one million years ago perhaps during deuteric or hydrothermal alteration core from a fracture at depth in the granite shows little hematite or clay formation and lacks evidence of ree and recent or ancient actinide mobilisation the u series results are correlated with the observed concentrations and isotope activity ratios of u in groundwaters sampled from the same or adjacent fractures analyses of samples of highly altered rubble recovered from centre portions of fracture zones at the url show both excesses and deficiencies of 234 u and 230 th in neighbouring locations possibly due to the presence of a redox front whose position is controlled by modern groundwater composition the implications of these results are discussed for the concept of disposal of nuclear fuel waste at depth in plutonic rock on the canadian shield

geomorphological evidence and 10be exposure ages for the last glacial maximum and deglaciation of the velka and mala studena dolina valleys in the high tatra mountains central europe abstract 10be exposure age chronology of the last glaciation was established in a key area at the southern slopes of the high tatra mts western carpathians in situ produced 10be in moraine boulders glacially transformed bedrock surfaces and rockfall accumulations constrains the timing of the last glacial maximum lgm glacier expansion and provides chronological evidence for the post lgm decay of one of the largest paleoglaciers in the range the uncertainty weighted mean age of 22 0 0 8 ka obtained for the terminal moraine in the forefield of the velka studena dolina valley indicates that the oldest moraine was deposited close to the global lgm this finding confirms that well preserved moraines in the range were formed during the last glacial cycle and that glaciation on the southern flank of the range was more extensive than earlier in the last glacial cycle the maximum glacier extent correlates with late wurmian weichselian glacier phases in the alps the bavarian bohemian forest and the krkonose mts but probably postdates the period of maximum glaciation in the southern carpathians re advance moraines at the mouth of the velka studena dolina valley and in the middle part of the mala studena dolina valley were deposited no later than around 20 5 ka and 15 5 ka respectively the timing of these advances is broadly synchronous within the high tatra mts as well as with glacier advances in the alps bavarian bohemian forest and krkonose mts 10be exposure ages obtained from glacially transformed bedrock surfaces range between 20 5 1 7 ka and 10 7 0 3 ka constraining the onset and the final phase of the deglaciation surface exposure dating of four rockfall accumulations produced uncertainty weighted mean ages of 20 2 1 2 ka 17 0 0 7 ka 16 5 0 4 ka and 15 6 0 7 ka these ages indicate that activation of rock slope failures occurred under paraglacial conditions within a few centuries up to 1400 years after the formation of re advance moraines

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

the relative mobility of u th and ra isotopes in the weathered zones of the eye dashwa lakes granite pluton northwestern ontario canada radioisotope activity ratios of weathered surface rocks from the eye dashwa lakes granite pluton show that in the 238u decay series 226ra has been leached more rapidly than the grandparent 234u and 238u isotopes the observation of 238th232th disequilibria in the 232th decay series shows that either 228th half life of 1 9 yrs or 228ra half life of 5 75 yrs have been removed from these rocks very rapidly indeed isotope ratios of separated mineral fractions appear to show that whereas uranium tends to be removed from all mineral fractions ra is strongly readsorbed onto feldspars presumably as these undergo alteration to clay minerals this necessitates making a distinction between intermineral mobility of u or ra and the net loss of u or ra from the whole rock an attempt has been made to model quantitatively the transport rate of ra though with little success failure of the modelling appears to indicate that the mobility of 228ra is higher than might be predicted by the mobility of 226ra that is the two isotopes are not strict analogues of one another in their response to initial weathering

10 be exposure age chronology of the last glaciation of the rohacska valley in the western tatra mountains central europe abstract 10 be exposure ages from moraines and bedrock sites in the rohacska valley provide chronology of the last glaciation in the largest valley of the western tatra mts the western carpathians the minimum apparent exposure age of 19 4 2 1 ka obtained for the oldest sampled boulder and the mean age of 18 0 0 8 ka calculated for the terminal moraine indicate that the oldest preserved moraine was probably deposited at the time of the global last glacial maximum lgm the age of this moraine coincides with the termination of the maximum glacier expansion in other central european ranges including the adjacent high tatra mts and the alps the equilibrium line altitude ela of the lgm glacier in the rohacska valley estimated at 1400 1410 m a s l was 50 80 m lower than in the eastern part of the range indicating a positive ela gradient from west to east among the north facing glaciers in the tatra mts lateglacial glacier expansion occurred no later than 13 4 0 5 ka and 11 9 0 5 ka as indicated by the mean exposure ages calculated for re advance moraines this timing is consistent with the exposure age chronology of the last lateglacial re advance in the high tatra mts alps and lower mountain ranges in central europe the ela in the rohacska valley estimated at 1690 1770 m a s l in this period was located 130 300 m lower than in the north facing valleys in the high tatra mts 10 be exposure ages obtained for a rock glacier constrains the timing of this landform stabilization in the salatinska valley and provides the first chronological evidence for the lateglacial activity of rock glaciers in the carpathians

a comparison of different tl techniques on loess samples from rheindahlen f r g abstract 9 tl samples of the loess profile rheindahlen lower rhine area germany covering the time span of the last 300 ka were studied systematic investigation was carried out using different filters and preheating procedures ed determinations were done by the additive dose and the regeneration method the annual dose was determined by aas alpha counting naa and gamma spectrometry in the laboratory and in the field the results show that the weichselian loess is datable whereas no tl age differentiation between loesses of stage 6 and stage 8 is possible if the accumulated dose ed is in the 600 gy region every apparent tl age between 100 and 300 ka can be obtained this leads to the conclusion that in rheindahlen no reliable tl ages are available for loess deposits underneath the eemian soil stage 5e

biogeomorphology of a mojave desert landscape configurations and feedbacks of abiotic and biotic land surfaces during landform evolution abstract terrestrial ecosystems can be more holistically understood by investigating the morphology of landscape mosaics the assemblage of their ecological communities and the linkages and feedbacks between the mosaics and communities the overarching objectives of this study were to 1 study the abiotic and biotic configurations of landform units as mosaics within a mojave desert chronosequence and 2 elucidate their potential feedbacks interactions and dynamics during landform evolution seven landform units distributed over three geomorphic ages were identified including young bars and swales intermediate aged flattened bars flattened swales and bioturbation units and old desert pavements and shrub zones these landform units were characterized according to abiotic and biotic land surface properties landform units were statistically distinct and predictable based on a specific suite of abiotic and biotic properties vascular plant functional group and biological soil crust community diversity varied with geomorphology with greatest diversity associated with bars and shrub zones and lowest diversity associated with desert pavements biological soil crust communities were controlled by geomorphic age surface rock size and protruding rocks with young bar units having the highest abundance and diversity perennial forbs were observed in old shrub zones with small rocks and few protruding rocks a high clast density and a finer sized clast distribution were found particularly in desert pavements and flattened swales and generally inhibited biological soil crust and plant cover evolutionary trajectories for landforms of a lower piedmont landscape can be dominated by either abiotic and biotic landform processes these two trajectories are distinctly different and are associated with their own unique linkages feedbacks and dynamics of abiotic and biotic land surface properties producing a highly diverse desert landscape

apparent thermoluminescence ages of st pierre sediments at pierreville quebec and the problem of anomalous fading this work reports a case study in thermoluminescence tl dating in which a delayed measurements procedure has been used in order to circumvent the problem of anomalous fading in sediments the pro

a review of current research on tl dating of loess abstract the thick loess deposits of china central europe and north america are particularly suitable for the application of the thermoluminescence tl dating method because individual grains are likely to have travelled large distances and thus been well exposed to light before deposition wind blown silt grains collected close to glacial rivers in alaska have been shown to give a zero age of not more than 2 ka demonstrating the efficiency of the zeroing mechanism differences in laboratory procedures can cause differences in the tl ages reported particularly for loess over 100 ka tl ages for interstadial soils in europe are in agreement with the very few radiocarbon dates on reliable material such as charcoal on the other hand tl dates from sites in belgium and north western germany indicate that the previously accepted chronology which was based on two radiocarbon dates on humic rich sediments is incorrect the use of the last interglacial palaeosol for assessing the tl dates on loess above and below it is limited by the uncertainty in the timing of termination of soil forming processes 107 and 71 ka are the limits suggested by the astronomically derived time scale results on deposits from china north america alaska and europe are discussed in this context

pedogenic evolution on the arid bishop creek moraines eastern sierra nevada california abstract soil chronosequences on alpine moraine complexes have been used to help unravel the glacial histories of the eastern sierra nevada the moraine sequence along bishop creek includes well preserved moraines that have been previously dated using cosmogenic 36cl surface exposure ages the goal of this study was to interpret pedogenesis within a soil geomorphic context on these quantitatively dated moraines soil development surface clast cover and moraine morphology were studied on seven of the moraines ranging in age from 15 to 170 ka older moraines had gentler slopes broader crests and decreased surface rock cover soils showed weak development across the chronosequence of moraines pedogenesis involved slight increases in clay the formation of clay lamellae development of a vesicular horizon in a surface layer of aeolian dust and weathering of surface and subsurface granitic clasts soil reddening and structure development were minimal soil formation was likely inhibited by the arid to semi arid climate and intermittent wind and water erosion during the time span of the chronosequence

can glacial shearing of sediment reset the signal used for luminescence dating abstract understanding the geomorphology left by waxing and waning of former glaciers and ice sheets during the late quaternary has been the focus of much research this has been hampered by the difficulty in dating such features luminescence has the potential to be applied to glacial sediments but requires signal resetting prior to burial in order to provide accurate ages this paper explores the possibility that rather than relying on light to reset the luminescence signal glacial processes underneath ice might cause resetting experiments were conducted on a ring shear machine set up to replicate subglacial conditions and simulate the shearing that can occur within subglacial sediments luminescence measurement at the single grain level indicates that a number albeit small of zero dosed grains were produced and that these increased in abundance with distance travelled within the shearing zone observed changes in grain shape characteristics with increasing shear distance indicate the presence of localised high pressure grain to grain stresses caused by grain bridges this appears to explain why some grains became zeroed whilst others retained their palaeodose based on the observed experimental trend it is thought that localised grain stress is a viable luminescence resetting mechanism as such relatively short shearing distances might be sufficient to reset a small proportion of the luminescence signal within subglacial sediments dating of previously avoided subglacial sediments may therefore be possible

large near surface nitrate pools in soils capped by desert pavement in the mojave desert california we found exceptionally high nitrate levels up to 12 750 kg ha 1 at shallow depths 1 m in soils mantled by desert pavement a common land surface feature in arid regions nearby soils without desert pavement had nitrate contents that were one to two orders of magnitude lower the soil conditions coincident with desert pavement i e stability antiquity and virtually no leaching favor the retention and accumulation of nitrate delivered by atmospheric deposition or in situ fixation the nitrate stored in soils under desert pavement is a previously unrecognized pool of nitrogen that has the potential to increase the global nitrogen inventory for near surface desert soils to five times previous estimates its near surface occurrence makes this labile nitrogen pool particularly susceptible to mobilization by climate change or human disturbance risking contamination of surface and groundwaters

predictive mapping of soil landscape relationships in the arid southwest united states abstract multi scale geospatial and absolute variation of surface and near surface soil physical and chemical properties can be mapped and quantified by coupling digital soil mapping techniques with high resolution remote sensing products the goal of this research was to advance data driven digital soil mapping techniques by developing an approach that can integrate multi scale digital surface topography and reflectance derived remote sensing products and characterize multi scale soil landscape relations of quaternary alluvial and eolian deposits the study area spanned the arid landscape encompassed by the barry m goldwater range west bmgrw which is administered by the marine corps air station yuma in southwestern arizona usa an iterative principal component analysis ipca was implemented for lidar elevation and landsat etm derived soil predictors termed environmental covariates principal components that characterize 95 of covariate space variability were then integrated and classified using an isodata iterative self organizing data unsupervised technique the classified map was further segmented into polygons based on a region growing algorithm yielding multi scale maps of soil landscape relations that were compared with maps of soil landforms identified from aerial photographs satellite images and field observation the approach identified and mapped the spatial variability of soil landscape relationships in alluvial and eolian deposits and illustrated the applicability of coupling covariate selection and integration by ipca isodata classification of integrated data layers and image segmentation for effective spatial prediction of soil landscape characteristics the approach developed here is data driven applicable for multi scale mapping allows incorporation of a wide variety of covariates and maps spatially homogenous soil landscape units that are necessary for hydrologic models land and ecosystem management decisions and hazard assessment

differences between the last two glacial maxima and implications for ice sheet δ18o and sea level reconstructions studies of past glacial cycles yield critical information about climate and sea level ice volume variability including the sensitivity of climate to radiative change and impacts of crustal rebound on sea level reconstructions for past interglacials here we identify significant differences between the last and penultimate glacial maxima lgm and pgm in terms of global volume and distribution of land ice despite similar temperatures and radiative forcing our analysis challenges conventional views of relationships between global ice volume sea level seawater oxygen isotope values and deep sea temperature and supports the potential presence of large floating arctic ice shelves during the pgm the existence of different glacial modes calls for focussed research on the complex processes behind ice age development we present a glacioisostatic assessment to demonstrate how a different pgm ice sheet configuration might affect sea level estimates for the last interglacial results suggest that this may alter existing last interglacial sea level estimates which often use an lgm like ice configuration by several metres likely upward

changing uranium distributions during weathering of granite abstract changes in uranium distribution during chemical weathering were investigated in three granitoid types from the new england district new south wales australia over a range of samples from unweathered rock to profoundly weathered material uranium fission track micromapping was used to characterise the three principal modes of u abundance in unweathered granitoid rock low concentrations of background u in fine fractures in quartz and in deuterically altered feldspar biotite and hornblende interstitial u in concentrations between 140 and 1500 g g 1 principally in hydrated fe oxide mn oxide and clay minerals and the greatest proportion as resistate u 90 4000 g g 1 located in the accessory minerals during low temperature chemical weathering a significant net u loss occurs and the remaining u is redistributed amongst the three modes background u is depleted and the mobilised u is adsorbed by interstitial aggregates thereby increasing interstitial u concentrations resistate u is also depleted as sphene zircon monazite and acicular apatite retain their initial u concentrations but are reduced in modal abundance prismatic apatite fluorite and allanite are progressively removed the significant net loss of u during chemical weathering provides uranium for potential secondary sedimentary mineralisation and implies that weathered granitoid rock is not an appropriate element in the geological barrier for nuclear waste

evidence for the stability of the potential nuclear waste host sphene over geological time from uranium lead ages and uranium series measurements abstract a sphene based glass ceramic material is being investigated as a potential host for canadian nuclear fuel recycle waste the ability of sphene to retain certain radionuclides over geological time is examined using observed properties and age measurements of natural sphenes the long term stability of sphene is determined by comparing u th pb isotopic age data for sphene from the literature with ages determined for zircon and other minerals better internal agreement is found between u th pb sphene ages than for zircon ages indicating the resistance of sphene to daughter radionuclide loss over periods as long as 3000 ma excellent agreement was observed between sphene ages and the estimated age of crystallization of the host rocks or vein infillings except where subsequent metamorphim had reset the sphene age complete lead loss was generally found to accompany high grade metamorphic conditions when temperatures exceeded 500 c stability over shorter periods of geological time was found for vein infilling and mineral separates of sphene using uranium series disequilibrium analysis conditions of secular equilibrium in the decay chain 238 u 234 u 230 th 226 ra were observed for most of the 21 sphenes studied indicating that no radionuclide migration had occurred over periods as long as the last 1 ma exceptions to this were four sphenes that had 234 u deficiencies between 6 and 24 and two sphenes that showed 226 ra 230 rh disequilibrium no correlation was found between the extent of radiation damage suffered by the sphenes and the presence of uranium series disequilibrium the presence of alteration products in three sphenes did correlate however with measured disequilibrium indicating that some 234 u and 226 ra had been lost or gained by these samples in the last 1 ma and 8 ka respectively

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

luminescence dating of glaciofluvial deposits a review abstract for glacigenic sediments optically stimulated luminescence osl dating offers an opportunity to date the time of deposition of quartz and feldspar minerals that are ubiquitous within the sediment matrix rather than relying upon the chance occurrence of organic material for radiocarbon dating the osl dating signal or charge accumulates in crystal defects of individual quartz and feldspar minerals through exposure to environmental radiation within their depositional setting the osl signal within individual grains can be reset or bleached through exposure to daylight during transportation processes thus osl dating of sediments attempts to determine the time elapsed since burial glacigenic sediments present considerable challenges for osl dating not only in terms of poor bleaching of the osl signal during the transport and deposition cycle but also poor quartz luminescence characteristics which are often related to sediment provenance the nature of the bedrock or source material and the freshly eroded nature of many such deposits this paper reviews luminescence dating techniques as applied to glaciofluvial sediments and explores the challenges that such deposits present to the technique successful application of osl techniques can be judged in a number of ways comparison with the independent chronologies is prevalent in the literature but recently the movement towards measurement of large numbers of small aliquots and single grains allows a more robust assessment of luminescence properties and behaviour for individual samples and ultimately more precise luminescence ages to be determined for glaciofluvial sediments in particular it is important to investigate the depositional sub environment of each sample in relation to the chance of sufficient bleaching during transport and deposition a lithofacies based approach to sampling for optically stimulated luminescence dating of these sediments is suggested whereby hypothetically well bleached deposits are targeted after a detailed investigation into possible environments of deposition this approach together with small aliquot single grain analysis methodologies should further enhance the likelihood of obtaining a sufficiently bleached sample for osl dating

towards successful osl sampling strategies in glacial environments deciphering the influence of depositional processes on bleaching of modern glacial sediments from jostedalen southern norway the optically stimulated luminescence osl signals of quartz and k feldspar are known to bleach poorly within some glacial settings and can present a major challenge to dating applications however because the osl signal is extremely sensitive to sunlight exposure history the residual luminescence signals of modern glacial sediments also encode information about transport and depositional processes through examination of the residual luminescence properties equivalent dose de and overdispersion values of a suite of modern glacial sediments from different depositional settings sandar proglacial delta and main meltwater channel this study provides insights not only into which sediments are likely to be fully bleached within glacial settings but also into how osl can be used to trace different depositional processes across sedimentary landforms improved understanding of the processes of sediment bleaching will enable better sample selection and may improve the accuracy and precision of osl dating of glacial sediments the luminescence signals of both coarse grained quartz and k feldspar with similar sediment sources are found to be sensitive to both depositional process and specific depositional setting whereas modern braid bar head deposits from the nigardsdalen ice proximal proglacial delta typically have ages of 3 ka similar depositional features from the fabergstolsgrandane sandur have residual ages of 26 ka exploration of changing residual luminescence signals across individual sandur and proglacial delta braid bar features shows that braid bar head deposits can retain large residual d e values while the partner braid bar tail deposits are almost completely bleached the quartz osl signal and k feldspar irsl50 and post ir irsl250 signals are shown to bleach at the same rate across the same bar feature and the irsl50 k feldspar signal is also shown to be completely bleached for bar tail deposits in nigardsdalen therefore the irsl50 k feldspar signal is suitable for dating some glacial deposits circumventing the challenges associated with dim quartz signals 2014 the authors published by elsevier ltd this is an open access article under the cc by license

thermoluminescence dating of late devensian loesses in southern england scattered across southern england are many isolated deposits of loess like material1 a few such as that at pegwell bay in kent are highly calcareous and unweathered but most have been reworked by fluvial or colluvial processes there is good stratigraphical evidence for a few pre devensian loesses also in kent but dating of more recent loess has so far been based on indirect evidence much work has been done on the pegwell bay loess as it is the most extensive truly aeolian loessic deposit in britain kerney2 compared the late devensian deposits in the isle of thanet and at pegwell bay with similar deposits in holland and belgium where radiocarbon dates have been obtained for interstadial deposits correlation of the east kent deposits with these in northern europe indicates that the loesses in kent were formed between 30 000 and 14 000 yr ago i report here dates for six of the more recent deposits in southern britain from the scilly isles to kent the dates have been obtained on the loess itself using a recently developed thermoluminescence tl dating technique3 4 and confirm the ages as being late devensian

timing of past glaciations in kanchenjunga himal nepal by optically stimulated luminescence dating of tills abstract optically stimulated luminescence osl was used to date glacial sediments to elucidate the ages of past glacial advances in kanchenjunga himal eastern nepal seven glacial sediments samples were collected from four different moraines and quartz grains were extracted from samples however the luminescence from feldspars existing as minor contamination and or microinclusion in the quartz grains was so bright it masked the quartz signal after etching the fraction 20 min extra with hf the natural infrared stimulated luminescence irsl signal which indicates the existence of feldspar almost disappeared equivalent dose de values were estimated by the single aliquot regenerative dose protocol using two different quartz fractions fraction a which was etched 20 min extra and fraction b which was prepared by the standard procedure still had a strong feldspar signal although the natural irsl intensity for fraction a was so weak the regenerated irsl was relatively strong and not negligible for most of the aliquots such aliquots were omitted because the sensitivity of the feldspar is much higher than quartz and the difference in the sensitivity can cause de underestimation out of 42 aliquots from four samples for fraction a only six aliquots from two samples were remained the de values for single aliquots were uniformly distributed for fraction b moreover the calculated osl ages for fractions a and b from the two samples agreed with each other it is suggested that both quartz and feldspars grains or microinclusions in quartz grains were likely to have been bleached while glacial debris has been transported on the glacier the resulting osl ages suggest that the glaciers expanded at 5 6 8 10 and 20 21 ka in the kanchenjunga himal

226ra 238u and 228th 228ra disequilibrium as weathering indices in beach sand sediments associated with granitoids from cyclades greece abstract radioactive secular disequilibrium measured as the absolute difference from 1 of the 226ra 238u and 228ra 228th ratios have been used to determine weathering extent twenty eight samples from beach sands of cyclades islands all of them being the weathering products of the local granitic plutons are studied for their secular disequilibrium in both 238u and 232th series 226ra 238u and 228th 228ra respectively the results are compared to weathering indices already in use worldwide and suggest a significant linear correlation of u series disequilibrium with wip alkaline and alkaline earth element leaching and pwi silica leaching for the beach sands studied and significant non linear correlations with cia chemical index of alteration and pia plagioclase index of alteration considering only the heavy mineral enriched samples significant correlations exist between u series disequilibrium and cia ciw chemical index of weathering and pia therefore with an appropriate choice of the weathering index and samples both u series and weathering index can recover the extent of chemical weathering on the other hand the use of th series disequilibrium as a weathering index is limited due to 228th and 228ra geochemistry and especially due to their short radionuclide half lives u series disequilibrium can therefore be used as a relatively sensitive weathering index in sediments consistent with cia ciw and pia indices however the mineralogical composition must be considered more specifically the mineral content of the sediments should involve considerable amounts of sensitive to weathering minerals e g fe mg minerals as well as feldspars

in situ radionuclide transport and preferential groundwater flows at ineel idaho decay series disequilibrium studies uranium and thorium decay series disequilibria in groundwater occur as a result of water rock interactions and they provide site specific natural analog information for assessment of in situ long term migration of radionuclides in the far field of a nuclear waste disposal site in this study a mass balance model was used to relate the decay series radionuclide distributions among solution sorbed and solid phases in an aquifer system to processes of water transport sorption desorption dissolution precipitation radioactive ingrowth decay and recoil isotopes of u 238u 234u th 232th 230th 228th 234th ra 226ra 228ra 224ra and rn 222rn were measured in 23 groundwater samples collected from a basaltic aquifer at the idaho national engineering and environmental laboratory ineel idaho the results show that groundwater activities of th and ra isotopes are 2 4 orders lower than those of their u progenitors which average 1 35 0 40 dpm 238u l with 234u 238u ratios of 1 6 3 0 222rn activities range from 20 to 500 dpm l modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water rock interaction at ineel 1 time for sorption is minutes for ra and th time for desorption is days for ra and years for th and time for precipitation is days for th years for ra and centuries for u 2 retardation factors due to sorption average 106 for 232th 104 for 226ra and 103 for 238u 3 dissolution rates of rocks are 70 to 800 mg l y 4 ages of groundwater range from 10 to 100 years contours of groundwater age as well as spatial patterns of radionuclide disequilibria delineate two north south preferential flow pathways and two stagnated locales relatively high rates of dissolution and precipitation and recoil of 222rn occur near the groundwater recharging sites as well as in the major flow pathways decay of the sorbed parent radionuclides e g 226ra and 228ra on micro fracture surfaces constitutes an important source of their daughter 222rn and 228th activities in groundwater

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

uranium series disequilibrium studies of granitic rocks abstract igneous plutons of the canadian shield which are to be considered as possible storage sites for radioactive waste should be free from any evidence of past mobility of chemical species through the rock however cores taken from some plutons to depths of up to 1 km reveal the presence of hydrous low temperature alteration along joints and fractures and within the body of the rock to test whether such rocks or any others have been subjected to chemical transport in geologically recent times we may study the state of radioactive equilibrium between 238 u 235 u and 232 th and their short lived daughterisotopes members of the decay series of these parent isotopes have half lives ranging from a few hours to 0 25 ma also the chemical characteristics of the various daughters vary significantly allowing us to test the mobility of isotopes of similar half life but differing chemistry if the rock has been chemically undisturbed for 10 ma or more then the activity in d p m g of each daughter in these decay schemes will be equal to that of its parent isotope conversely if the rock was chemically disturbed 10 n a ago then some daughter isotopes with half lives t 10 n a will be out of equilibrium with their parents preliminary results are presented showing disequilibrium effects in samples from atikokan ontario

glacial abrasion and sliding their dependence on the debris concentration in basal ice a model of bedrock abrasion by a temperate glacier is developed that takes into account the significant impeding effect of scattered rock fragments at the ice rock interface on glacier sliding an increase in the debris concentration above a relatively low value can reduce the abrasion rate by decreasing both the flux of rock fragments and the effective forces which press fragments against the bed abrasion of a simple wavy bed is shown to be most rapid for a relatively low debris concentration above which the abrasion varies inversely with the debris content a similar concentration dependence of abrasion is expected for beds of arbitrary geometry but low roughness sliding glaciers will tend to abrade until the basal ice is nearly stagnant at which point rocks of all sizes start to lodge against the bed

timing and distribution of alluvial fan sedimentation in response to strengthening of late holocene enso variability in the sonoran desert southwestern arizona usa abstract the integration of geomorphic mapping soil stratigraphy and radiocarbon dating of alluvial deposits offers insight to the timing magnitude and paleoclimatic context of holocene fan sedimentation near yuma arizona mapping of 3400 km2 indicates about 10 of the area aggraded in the late holocene and formed regionally extensive alluvial fan and alluvial plain cut and fill terraces fan deposits have weakly developed gravelly soils and yielded a date of 3200 2950 cal yr bp from carbonized wood alluvial plain deposits have weakly developed buried sandy soils and provided a date of 2460 2300 cal yr bp from a terrestrial snail shell precipitation records were analyzed to form historical analogues to the late holocene aggradation and to consider the role of climatic variability and extreme hydrologic events as drivers of the sedimentation the historical precipitation record indicates numerous above average events correlated to the southern oscillation index soi in the region but lacks any significant reactivation of alluvial fan surfaces the timing of aggradation from 3200 to 2300 cal yr bp correlates well with other paleoclimatic proxy records in the southwestern u s and eastern pacific region which indicate an intensification of the el nino southern oscillation enso climatic pattern and rapid climate change during this period

uranium series radionuclide and element migration around the sanerliu granite hosted uranium deposit in southern china as a natural analogue for high level radwaste repositories abstract the sanerliu uranium deposit located in hunan province south china has a number of features analogous to aspects considered in the performance assessment of concepts for the disposal of high level radwaste deep in granite the deposit is hosted by medium to coarse grained porphyritic granite with a rb sr isochron age of 215 2 6 3 ma the orebodies have a burial depth of more than 160 400 m under the surface of the ground the major uranium mineralizations have u pb ages pitchblende of 103 2 0 6 88 3 0 5 and 51 2 0 4 ma and a hydrothermal origin the isotopic data show that the rb sr systems in the whole rock samples of less and un fractured host granite around the orebodies have been little disturbed since the altered granite formed 132 ma ago such samples have close to secular equilibrium activity ratios for 234 u 238 u 230 th 234 u and 226 ra 230 th indicating that obvious water rock interactions have not taken place in them within the interval of at least the last 1 ma the migration of uranium thorium and most trace elements in the ores and the host granite are limited often less than 30 35 m over 51 ma the alpha activity ratios 234 u 238 u 230 th 234 u and 226 ra 230 th for the samples from the fracture zones show obvious deviations from secular equilibrium indicating the deposition of uranium during the last 1 ma and of radium during the last 10 3 yr the fracture zones are channels for groundwater flow however the migration of uranium series radionuclides along the fracture zones is limited by adsorption onto the clays this is confirmed by the absence of any hydrogeochemical indication on the ground surface of the orebodies the ores have been well preserved in a natural aquifer system without any specially designed artificial barriers the migration behavior of radionuclides in the ores of the sanerliu deposit may be termed a worse case scenario for the safety assessment of a high level radwaste disposal repository hosted by granitic rocks

complex patterns of glacier advances during the late glacial in the chagan uzun valley russian altai abstract the southern part of the russian altai mountains is recognized for its evidence of catastrophic glacial lake outbursts however little is known about the late pleistocene paleoglacial history despite the interest in such reconstructions for constraining paleoclimate in this study we present a detailed paleoglaciological reconstruction of the chagan uzun valley in the russian altai mountains combining for the first time detailed geomorphological mapping sedimentological logging and in situ cosmogenic 10be and 26al surface exposure dating of glacially transported boulders the chagan uzun valley exhibits the most impressive glacial landforms of this sector of the altai with extensive lobate moraine belts deposited in the intramontane chuja basin reflecting a series of pronounced former glacial advances observations of hillside scale folding and extensive faulting of pre existing soft sediments within the outer moraine belts together with the geomorphology strongly indicate that these moraine belts were formed during surge like events identification of surge related features is essential for paleoclimate inference because these features correspond to a glacier system that is not in equilibrium with the contemporary climate but instead largely influenced by various internal and external factors therefore no strict relationship can be established between climatic variables and the pronounced distal glacial extent observed in the chagan uzun valley chuja basin in contrast the inner up valley glacial landforms of the chagan uzun valley were likely deposited during retreat of temperate valley glaciers close to equilibrium with climate and so most probably triggered by a general warming cosmogenic ages associated with the outermost innermost and intermediate moraines all indicate deposition times clustered around 19 ka however the actual deposition time of the outermost moraine may slightly predate the 10be ages due to shielding caused by subsequent lake water coverage this chronology indicates a marine isotope stage mis 2 last maximum extent of the chagan uzun glacier and an onset of the deglaciation around 19 ka this is consistent with other regional paleoclimate proxy records and with the northern hemisphere glaciation chronology finally this study also highlights the highly dynamic environment in this area with complex interactions between glacial events and the formation and drainage of lakes

thermoluminescence dating of sediments abstract the potential for using the thermoluminescence behaviour of sediments for dating them was first recognized by soviet scientists g v morozov and v n shelkoplyas and for over a decade their tl dates obtained from a variety of sediments have appeared in the soviet literature since 1977 tl sediment dates have been published by six additional groups using a variety of methods in this review we describe the principles of tl dating the various methods used and contrast tl dating of sediments with the now well accepted tl dating of pottery we conclude that while tl dating has the potential to solve many sedimentary problems more fundamental research needs to be carried out before such dates should be accepted a set of criteria for acceptable dates is proposed

an analogue validation study of natural radionuclide migration in crystalline rocks using uranium series disequilibrium studies abstract concentrations and isotope ratios of natural decay series radionuclides have been studied in three contrasting crystalline rock drillcore sections intersecting water conducting fractures deep in the bedrock radioactive disequilibria resulting from rock water interactions were observed in two of the cores these indicated u migration along distances of 40 cm or more on a time scale of 1 myr in conjunction with th immobility under the same conditions fracture surface minerals showed a high affinity for radionuclide retardation and a limit of 3 cm is suggested for the migration of radionuclides from fracture fluids into the saturated rock this limit may correspond to enhanced matrix porosities resulting from earlier hydrothermal activity along the same channels

uranium series disequilibrium in tuffs from yucca mountain nevada as evidence of pore fluid flow over the last million years abstract samples of tuff from boreholes drilled into fault zones in the exploratory studies facility esf and relatively unfractured rock of the cross drift tunnels at yucca mountain nevada have been analysed by u series methods this work is part of a project to verify the finding of fast flow paths through the tuff to esf level indicated by the presence of bomb 36cl in pore fluids secular radioactive equilibrium in the u decay series i e when the radioactivity ratios 234u 238u 230th 234u and 226ra 230th all equal 1 00 might be expected if the tuff samples have not experienced radionuclide loss due to rock water interaction occurring within the last million years however most fractured and unfractured samples were found to have a small deficiency of 234u weighted mean 234u 238u 0 95 0 01 and a small excess of 230th weighted mean 230th 234u 1 10 0 02 the 226ra 230th ratios are close to secular equilibrium weighted mean 0 94 0 07 these data indicate that 234u has been removed from the rock samples in the last 350 ka probably by pore fluids within the precision of the measurement it would appear that 226ra has not been mobilized and removed from the tuff although there may be some localised 226ra redistribution as suggested by a few ratio values that are significantly different from 1 0 because both fractured and unfractured tuffs show approximately the same deficiency of 234u this indicates that pore fluids are moving equally through fractured and unfractured rock more importantly fractured rock appears not to be a dominant pathway for groundwater flow otherwise the ratio would be more strongly affected and the th and ra isotopic ratios would likely also show disequilibrium application of a simple mass balance model suggests that surface infiltration rate is over an order of magnitude greater than the rate indicated by other infiltration models and that residence time of pore fluids at esf level is about 400 a processes of u sorption precipitation and re solution are believed to be occurring and would account for these anomalous results but have not been included in the model despite the difficulties the u series data suggest that fractured rock specifically the sundance and drill hole wash faults are not preferred flow paths for groundwater flowing through the topopah spring tuff and by implication rapid flow within 50 a from the surface to the level of the esf is improbable

thermoluminescence ages for three sections in hungary abstract samples were collected from sections at mende paks and tapiosuly ages for the loess above the mf1 soil at mende were in agreement with the radiocarbon dates on charcoal fragments from the soil ages for loess from tapiosuly were also in agreement with radiocarbon ages for younger soils however tl age estimates for loess above or below the mf2 soil at each of the three sites suggested that this soil had an age of around 76 ka it has not been confirmed whether these ages are underestimated however they are older than previously thought on the basis of other tl studies they imply that the underlying mb soil is much older than the last interglacial

mapping quaternary alluvial fans in the southwestern united states based on multiparameter surface roughness of lidar topographic data 1 quaternary alluvial fans have diverse surface morphologies related to both depositional and weathering processes numerous studies have demonstrated that the surface expression and morphometry of alluvial fans can be used as an indicator of their relative age of deposition but only recently has there been an effort to utilize high resolution topographic data to differentiate alluvial fans by surface age with automated and quantifiable routines we developed a quantitative model for mapping the relative age of alluvial fan surfaces based on multiparameter surface roughness values computed from 1 m resolution lidar topographic data roughness is defined as a function of observational scale and integration of slope curvature and aspect topographic parameters alluvial fan roughness values were computed across multiple observation scales 3 3 m to 150 150 m based on the standard deviation sd of slope curvature tangential and aspect topographic parameters plots of roughness value versus size of observation scale suggest that the sd of each parameter over a 7 7 m observation window best identified the signature of surface roughness elements roughness maps derived from slope curvature and aspect at this scale were integrated using fuzzy logic the integrated roughness map was then classified into five relative morphostratigraphic surface age categories active wash to 400 ka and statistically compared with a similar fivefold surface age map of alluvial fans developed using traditional field surveys and aerial photographic interpretation the model correctly predicted the distribution and relative surface age of 61 of alluvial fan landforms based on traditional mapping techniques

osl dating of late holocene coastal sediments and its implication for sea level eustacy in hainan island southern china abstract since the sea level rise is not geographically homogeneous but rather shows great regional differences optically simulated luminescence using quartz as a natural dosimeter has proved to be a powerful and reliable dating technique to determine depositional ages of young coastal sediments around the world the samples acquired from one beach ridge and two marine terraces in coastal hainan island southern china are detected osl dating for the investigation of sea level changes the results show 1 coastal sands in hainan island were well bleached before deposition and the quartz osl can date coastal sediments younger than 200 years which could be one of good indicators for paleo relative sea level highstand records 2 three coastal sediments with 4 m 3 7 m and 2 m higher than present sea level were deposited at 2 40 0 05 ka 2 92 0 17 ka and 4 26 0 10 ka respectively which indicate that the height of highstand relative sea level are higher than both mean global sea level eustacy and those records offshore southern china 3 comparisons with tropical cyclones observations around south china sea indicates that the late holocene coastal sediments of hainan island might have been reformed by tropical cyclones with a highstand sea level

thermoluminescence dating of glacially transported sediments some considerations abstract theoretical considerations imply that the suitability of glacially deposited sediments for thermoluminescence tl dating will be influenced by transport routes within the ice and by facies of deposition measurments on sediments obtained from the austerdalsbreen glacier in western norway indicate that zeroing of sediment does not occur at the base of a valley glacier but that englacial and supraglacial sediments showed evidence of bleaching but not total zeroing analysis of sediments from recent glacial and fluvioglacial landforms showed no evidence that they had been zeroed prior to deposition results indicate that the tl age of glacial landforms will be a function of the derivation and travel paths of the sediments of which it is composed rather than of the form itself it is concluded that as knowledge of the rates of bleaching associated with various facies of transport and deposition of glacial sediments improves so the potential of the technique to act as a diagnostic sedimentological tool will increase even when dating of glacial deposits by tl is impossible

extending the geochronometry of arctic lake cores beyond the radiocarbon limit by using thermoluminescence reconstructing detailed paleoclimatic paleoenvironmental histories from pleistocene sediments in the arctic is an ongoing challenge because of the difficulty of measuring accurate timescales beyond the range of radiocarbon 14c dating important archives of such histories are arctic lakes that exist outside the known extent of the last major glaciations to develop reliable geochronometry of sediment cores from arctic and other lakes we applied thermoluminescence tl sediment dating methods to 24 samples 8 reported earlier but some reanalyzed here selected from cores from squirrel and joe lakes in northwestern alaska a sequence of 23 14c ages from the upper parts of these cores permitted tests of the zeroing assumption of tl dating that all fine silt grains were exposed to daylight before final burial we performed multiple tl tests on most samples to isolate stable tl signals and measured tl emissions spectra to help characterize samples tl ages generally agree with the 30 kyr age depth trend derived from 14c dating and extend the timescale apparently to 180 ka for squirrel lake and to at least 60 ka for joe lake an anomalously old tl result from squirrel lake is attributed to failure of the tl zeroing assumption within that sediment horizon in the lower joe lake core we assign a timing of 45 ka to 50 ka for the beginning of an apparently climatic warming interval these results identify and quantify the main tl sources of tl age inaccuracy and the preferred tl protocols for accurate tl sediment dating in northern high latitude lake deposits they also provide the first direct chronology beyond the 14c dating range for these lakes

actinide and rare earth element characteristics of deep fracture zones in the lac du bonnet granitic batholith manitoba canada the history of major trace and actinide element mobility and fluid infiltration has been studied in two deep fractures 1 km in the lac du bonnet batholith as part of the canadian nuclear fuel waste management program core samples collected from two fracture zones fr1 and fr2 1175 m deep containing saline groundwater tds 50 g l were investigated mineralogically chemically and isotopically 238u series o and h several sequentially overprinting alteration stages were identified from early high temperature to later low temperature hydrothermal alteration k feldspar illite chlorite and later kaolinite formed during these stages subsequent infiltration of oxidizing fluids produced alteration of the chlorite to hydrous iron oxides fracture zone fr1 contains predominantly hematite coating fracture zone fr2 is characterized by the formation of a breccia and by an intense alteration of the granite in contact with this breccia to illitic clay alteration occurred during infiltration either of formation brines or of isotopically evolved meteoric water where 18o 8 to 12 and d 65 to 20 at calculated temperatures between 250 and 25 c loss of ca na and sr and to some extent ba was observed in all the altered samples relative to fresh granite a sharp increase in k mg u th and ree was observed in the illitic clay rich zone pronounced disequilibria of 234u238u 0 5 230th234u 0 7 and 226ra230th 0 9 exist in the illitic clay indicating loss of 234u 230th and 226ra to the groundwater within the last 1 5 ma in contrast an excess of 234u 230th and 226ra was measured in the brecciated samples the disequilibria are consistent with a model involving loss of 234u 230th and 226ra to groundwater by recoil from u deposited on the illitic clay surfaces these radionuclides were deposited subsequently in the nearby brecciated zone

formation mechanisms and control factors of vesicular soil structure abstract vesicular structure is a widespread feature of soils in arid environments typically associated with stone pavements it has a major control function for dust and water fluxes and hence for site ecology previous models of vesicular structure formation and stability are inconsistent and mostly focused on the investigation of isolated control parameters to test existing models to infer plausible mechanisms of vesicular structure formation and to unveil controlling environmental and sedimentological parameters we present quantitative data of vesicle properties of artificial and natural vesicles vesicles are not unstable but their changes in size are non linear with time they form due to surface sealing by puddling and by a wetting front which advances downward thereby elevating gas pressure within the sediment matrix translocation of clay or precipitation of calcium carbonate support vesicle stabilisation vesicular structure forms within a wide range of environmental and sedimentological settings at least 6 3 15 7 mm of water per wetting cycle 0 70 sand content 0 8 5 6 ms cm electric conductivity and 1 28 calcium carbonate content high sand contents favour larger and rounder vesicles whereas increasing calcium carbonate content has the opposite effect the concentration of dissolved ions does not considerably influence vesicle formation under an artificial cover stone vesicles could not be created at all whereas they were concentrated around stone margins the main limiting factor for vesicle formation in natural environments is root activity the type and density of surface cover determine fine material fluxes into the aggregates of vesicular horizons the shape of vesicles may be related to dust influx intensity accordingly horizons with spherical vesicles may indicate constant low dust influx on poorly vegetated surfaces and be therefore used as proxies of environmental conditions

uranium thorium series radionuclides in brines and reservoir rocks from two deep geothermal boreholes in the salton sea geothermal field southeastern california naturally occurring u and th series radionuclides have been analyzed in high temperature brines 300 c 25 wt dissolved solids and associated rocks from two deep geothermal wells located on the northeastern margin of the salton sea geothermal field ssgf these data are part of a study of the ssgf as a natural analog of possible radionuclide behavior near a nuclear waste repository constructed in salt beds and permit evaluation of some characteristics of water rock interaction in the ssgf rock brine concentration ratios rc dpm g rock dpm g brine were found to vary from near unity for isotopes of ra pb and rn to about 5 105 for 232th the high sorptivity of 232th is closely followed by that of 238u and 234u rc 5 104 suggesting that u is retained in the 4 oxidation state by the reducing conditions in the brines the relatively high solubility of 210pb and 212pb is attributed to formation of chloride complexes while the high ra solubility is attributed to chloride complexing a lack of suitable adsorption sites due to the high brine salinity and temperature and the reducing conditions that prevent mno2 and raso4 from forming the 228ra226ra ratios in the brines are approximately equal to those of their parents 232th230th in associated rocks indicating that ra equilibration in the brine rock system is achieved within the mean life of 228ra 8 3 years the 224ra228ra ratios in these brines are about 0 7 indicating that either 1 brine composition is not homogeneous and 224ra decays in fracture zones deficient in ra and th as the brine travels to the wellhead or 2 ra equilibration in the brine host rock system is not complete within the mean life of 224ra 5 2 days because the desorption of 224ra from the solid phase is impeded the 228ac228ra activity ratio in the ssgf brines studied is 0 1 and from this ratio the residence time of 228ac in the brine before sorption onto solid surfaces is estimated to be 70 minutes indicating the potential for rapid removal of reactive isotopes fom brines the brine is greatly enriched in 226ra 2 3 dpm g about 104 105 times that of its parent 230th while reservoir rocks are about 10 deficient in 226ra relative to 230th material balance calculations for 2226ra and 18o suggest that brines reside in the reservoir for 102 103 years that the ssgf formed 10 000 40 000 years b p and that porosity cannot be more than 20