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

an isotopic study of soils in chronological sequences of alluvial deposits providence mountains california the carbon sup 14 c and sup 13 c and oxygen isotopic composition of pedogenic carbonate was determined for two soil chronosequences on limestone and granitic alluvium in the providence mountains area in the mojave desert california the measured sup 14 c ages of pedogenic carbonate coating on clasts were interpreted in the light of a diffusion reaction model developed in our recent studies model ages of soil formation calculated from the measured sup 14 c ages of pedogenic carbonate are in correct relative order as determined by geomorphic evidence and are also consistent with model ages from the measured sup 14 c ages of soil organic matter sup 14 c model ages suggest that the order geomorphic surfaces we studied are of late pleistocene age ca 47 17 ka and the younger surfaces formed during the holocene ca 11 4 ka these age estimates of the geomorphic surfaces are older than the previously assigned ages based on a combination of soil development geomorphic relationships and several infrared stimulated luminescence dates but they are within a few thousand years of these other age estimates stable carbon isotopic composition of the soil carbonate indicates either a slight increase in c sub 4 or cam crassulacean acid metabolism plants or a decrease inmore plant density in this area during the holocene both the carbon and oxygen isotopic composition of soil carbonates suggests that the climate in the eastern mojave desert has in general become warmer and drier during the holocene 57 refs 9 figs 5 tabs less

origin and significance of calcium carbonate in soils of southwestern patagonia abstract a soil chronosequence spanning the last 0 76 1 0 ma shows a progressive increase in calcium carbonates based on 1 thickness of the bk bck horizons 2 maximum carbonate stage 3 profile accumulation of pedogenic carbonates and 4 mass flux of ca from a geochemical mass balance we favor a dust origin of the carbonates because 1 the till parent materials contain low amounts of caco3 2 there is minimal evidence for weathering of ca bearing minerals in the soil 3 the amount of caco3 in the profile is far in excess of what could be released by weathering 4 dust collected from the study area is enriched in caco3 and 5 a source area for the carbonates was identified although there likely were changes in dust deposition rates during the quaternary our calculations suggest that the current deposition rate of 0 18 g caco3 m 2 yr 1 is comparable to the long term profile accumulation rate of 0 16 g caco3 m 2 yr 1 230th u disequilibrium ages of carbonate pendants are consistent with cosmogenic surface exposure ages indicating that this method has potential for dating other geomorphic surfaces in patagonia cryogenic processes have affected many of the pedons particularly during the last glacial maximum

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

late quaternary slip rates for the southern elsinore fault in the coyote mountains southern california from analysis of alluvial fan landforms and clast provenance soils and u series ages of pedogenic carbonate abstract offset alluvial fans along the elsinore fault in the south central coyote mountains were studied to resolve an average late quaternary slip rate for this major western strand of the san andreas fault system in southern california alluvial fans and their offsets were mapped using high resolution dems combined with field observations of fan surface morphology and the character of the soils developed in each fan remnant clast assemblage data was used to determine the source of each alluvial fan upstream of the fault and u series dating of pedogenic carbonate was used to estimate minimum ages of the alluvial fan surfaces forty u th dates on pedogenic carbonate confirm the utility of the technique for dating late pleistocene alluvium in arid regions and suggest that age variation among late pleistocene fans grouped on the basis of soils and geomorphic criteria may be significant based on these data the southernmost segment of the elsinore fault has sustained a slip rate of 2 4 0 4 mm y for the past 60 70 ka and probably for the past 150 ka because displacement in the most recent surface rupture increases northwest of our slip rate sites this rate is likely a minimum for the southern elsinore fault with the actual rate more likely close to 3 mm y in the central part of the range these new data confirm that slip gradients along individual fault segments must be considered when estimating pre holocene slip rates for seismic hazard estimates these new results show that the southern elsinore fault accounts for about 6 of the total relative motion between north america and the pacific lithospheric plates in southernmost california assessment of previous estimates of slip in the most recent event suggests earthquakes of about mw 6 8 and when combined with the slip rate data a recurrence of such events about every thousand years

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

230th u dating of a late pleistocene alluvial fan along the southern san andreas fault u series dating of pedogenic carbonate clast coatings provides a reliable precise minimum age of 45 1 0 6 ka 2 for the t2 geomorphic surface of the biskra palms alluvial fan coachella valley california concordant ages for multiple subsamples from individual carbonate coatings provide evidence that the 238 u 234 u 230 th system has remained closed since carbonate formation the u series minimum age is used to assess previously published 10 be exposure ages of cobbles and boulders all but one cobble age and some boulder 10 be ages are younger than the u series minimum age indicating that surface cobbles and some boulders were partially shielded after deposition of the fan and have been subsequently exhumed by erosion of fine grained matrix to expose them on the present fan surface a comparison of u series and 10 be ages indicates that the interval between final alluvial deposition on the t2 fan surface and accumulation of dateable carbonate is not well resolved at biskra palms however the time lag inherent to dating via u series on pedogenic carbonate can be no larger than 10 k y the uncertainty of the 10 be derived age of the t2 fan surface dating of the t2 fan surface via u series on pedogenic carbonate minimum age 45 1 0 6 ka and 10 be on boulder top samples using forward modeling preferred age 50 5 ka provides broadly consistent constraints on the age of the fan surface and helps to elucidate its postdepositional development

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

chronology of pleistocene glacial advances in the central rocky mountains the distribution and ages of moraines in the wyoming type localities for pre pinedale rocky mountain glacial deposits are not well known through morphostratigraphic mapping river terrace longitudinal profile analysis and tephrochronology we place the age of sacagawea ridge moraines in the dinwoody lakes type area at about 660 ka outwash and river terrace deposits in the bull lake type area previously considered to be sacagawea ridge are actually older by one or two glacial cycles in the bull lake type locality 15 individual moraines are divided into 4 groups on the basis of relative age criteria using 36cl 10be cosmogenic dating of boulders the two older groups must be 130 ka the younger groups are given age ranges of 130 to 100 ka and 120 to 95 ka a terrace along wind river can be morphostratigraphically traced to the youngest of these moraine groups 36cl dating of boulders on the terrace provides an age range of 125 to 100 ka the combined relative age and cosmogenic nuclide chronology is consistent with previously published evidence from yellowstone national park demonstrating that mountain glaciers advanced not only prior to and during the later portion of marine isotope stage 6 but also during marine isotope stage 5d in contrast with some other areas of the rocky mountains we found no evidence for advances during marine isotope stage 4 at bull lake pinedale moraines that have a 36cl 10be age range of 23 to 16 ka suggest that glacial advances were limited to the later part of marine isotope stage 2 a river terrace that can be traced to these moraines has an age range of 23 to 16 ka a possible glacial advance during early marine isotope stage 2 is indicated by a river terrace whose age range is estimated by incision rate modeling at 46 to 28 ka but no moraines were identified along wind river there are eight terrace levels capped with outwash that are older than sacagawea ridge although the terraces are the record of early to middle pleistocene climatic cycles there are no correlative moraines preserved at the land surface

mechanics of formation of the gold bearing quartz fuchsite vein at the dome mine timmins area ontario the highest grade orebody in the dome mine is a steeply dipping 500 m long 550 m high and 3 5 m wide banded quartz fuchsite vein qfv accompanied by subsidiary veins in the adjacent wall rock t

late quaternary geomorphology and soils in crater flat yucca mountain area southern nevada crater flat is an alluvium filled structural basin on the west side of yucca mountain nevada which is under consideration for a high level nuclear waste repository north trending late quaternary faults offset alluvium in crater flat both along the canyons of the western flanks of yucca mountain and out on the piedmont slope we believe the initial lack of young offsets at yucca mountain was in part due to unrecognized late quaternary stratigraphy we hypothesize that alluviation in the yucca mountain region was more active during the late quaternary than previously thought several techniques were tried to test this hypothesis results are compared with previous soils and surface exposure dating studies and correlated to stratigraphy of other late quaternary units in the southern nevada death valley and mojave desert areas and provide new stratigraphic data relevant to understanding climatic alluvial processes in the basin and range province during the late quaternary 76 refs 7 figs 6 tabs

quantification of the late quaternary throw rates along the yadong rift southern tibet abstract southern tibet is characterized by seven main n s trending rifts bounded by normal faults which accommodate e w extension quantifying the throw and extension rates along these rifts is essential to understand their activity onset timing regional seismic hazard and kinematic role in the tectonic evolution of the tibetan plateau the yadong gulu rift ygr near lhasa is the longest and most prominent rift in southern tibet and one of the few that crosses the himalayas however it remains poorly studied and understood here we focus on the yadong rift i e the southern section of the ygr south of the yarlung zangbo suture we determine the late quaternary holocene throw rates at four sites where the active yadong normal fault vertically offsets glacial and fluvial geomorphic surfaces using terrestrial lidar uav and kinematic gps we precisely measured vertical offsets up to 17 m and constrained the age of abandoned surfaces using 32 10be cosmogenic surface exposure ages 10 20 ka one optically stimulated luminescence age and two travertine samples dated using u series dating the offset age reconstructions yield uniform throw rates of 0 9 0 3 mm yr along the entire yadong rift taking a fault dip of 50 as measured in the field we obtain late quaternary e w extension rates of 0 8 0 3 mm yr which is similar to but at the lower end of those along other rifts in southern tibet 1 2 mm yr

cosmogenic 3he exposure ages of pleistocene debris flows and desert pavements in capitol reef national park utah abstract the quaternary history of the capitol reef area utah is closely linked to the basaltic andesite boulder deposits that cover much of the landscape understanding the age and mode of emplacement of these deposits is crucial to deciphering the quaternary evolution of this part of the colorado plateau using cosmogenic 3 he exposure age dating we obtained apparent exposure ages for several key deposits in the capitol reef area coarse boulder diamicts capping the johnson mesa and carcass creek terraces are not associated with the bull lake glaciation as previously thought but were deposited 180 15 to 205 17 ka minimum age and are the result of debris flow deposition desert pavements on the johnson mesa surface give exposure ranging from 97 8 to 159 14 ka and are 34 96 kyears younger than the boulder exposure ages the offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition incision rates for the capitol reef reach of the fremont river calculated from the boulder exposure ages range from 0 40 to 0 43 m kyear 1 maximum rates and are some of the highest on the colorado plateau

geochemistry and evolution of ore forming fluids of the yueshan cu au skarn and vein type deposits anhui province south china abstract the yueshan mineral belt is geotectonically located at the centre of the changjiang deep fracture zone or depression of the lower yangtze platform two main types of ore deposits occur in the yueshan orefield cu au fe skarn deposits and cu mo au pb zn hydrothermal vein type deposits almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the yueshan dioritic intrusion in the vicinity of the zongpu and wuhen intrusions there are many cu pb zn au s vein type and a few cu fe au skarn type occurrences fluid inclusion studies show that the ore forming fluids are characterised by a cl s na k chemical association hydrothermal activity associated with the above two deposit types was related to the yueshan intrusion the fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water in comparison the hydrothermal activity related to the zongpu and wuhen intrusions was characterised by low salinity fluids chlorine and sulphur species played an important role in the transport of ore forming components hydrogen and oxygen isotope data also suggest that the ore forming fluids in the yueshan mineral belt consisted of magmatic water mixed in various proportions with meteoric water the enrichment of ore forming components in the magmatic waters resulted from fluid melt partitioning the ore fluids of magmatic origin formed large cu au deposits whereas ore fluids of mixed magmatic meteoric origin formed small to medium sized deposits the sulphur isotopic composition of the skarn and vein type deposits varies from 11 3 to 19 2 and from 4 2 to 10 0 respectively these variations do not appear to have been resulted from changes of physicochemical conditions rather due to compositional variation of sulphur at the source s and by water rock interaction complex water rock interaction between the ore bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore forming fluids hydrodynamic calculations show that magmatic ore forming fluids were channelled upwards into faults fractures and porous media with velocities of 1 4 m s 9 8 10 1 to 9 8 10 7 m s and 3 6 10 7 to 4 6 10 7 m s respectively a decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the triassic sedimentary rocks led to the deposition of the ore forming components the major species responsible for cu transport are deduced to have been cucl cucl2 cucl32 and cucloh whereas au was transported as au2 hs 2s2 au hs 2 auhs and auh3sio4 complexes cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of cu deposition gold deposition was related to decrease of ph total sulphur concentration and fo2 which resulted from fluid boiling and mixing geological and geochemical characteristics of the two deposit types in the yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 ma and represent a continuous process during the yanshanian time the cooling of the intrusions and the mineralisation event might have lasted about 6 ma the cooling rate of the magmatic intrusions was 80 to 120 c my 1 which permitted sufficient heat supply by magma to the ore forming system

numerical dating of a late quaternary spit shoreline complex at the northern end of silver lake playa mojave desert california a comparison of the applicability of radiocarbon luminescence terrestrial cosmogenic nuclide electron spin resonance u series and amino acid racemization methods a late quaternary spit shoreline complex on the northern shore of pleistocene lake mojave of southeastern california usa was studied with the goal of comparing accelerator mass spectrometry ams radiocarbon luminescence electron spin resonance esr terrestrial cosmogenic radionuclide tcn surface exposure amino acid racemization aar and u series dating methods the pattern of ages obtained by the different methods illustrates the complexity of processes acting in the lakeshore environment and highlights the utility of a multi method approach tcn surface exposure ages mostly 20 30 ka record the initial erosion of shoreline benches whereas radiocarbon ages on shells determined in this and previous studies within the spit supported by aar data record its construction at fluctuating lake levels from 16 to 10 ka luminescence ages on spit sediment 6 7 ka and esr ages on spit shells 4 ka are anomalously young relative to radiocarbon ages of shells within the same deposits the significance of the surprisingly young luminescence ages is not clear the younger esr ages could be a consequence of post mortem enrichment of u in the shells high concentrations of detrital thorium in tufa coating spit gravels inhibited the use of single sample u series dating detailed comparisons such as this provide one of the few means of assessing the accuracy of quaternary dating techniques more such comparisons are needed

revealing the pace of river landscape evolution during the quaternary recent developments in numerical dating methods during the last twenty years several technical developments have considerably intensified the use of numerical dating methods for the quaternary the study of fluvial archives has greatly benefited from these enhancements opening new dating horizons for a range of archives at distinct time scales and thereby providing new insights into previously unanswered questions in this contribution we separately present the state of the art of five numerical dating methods that are frequently used in the fluvial context radiocarbon luminescence electron spin resonance esr 230th u and terrestrial cosmogenic nuclides tcn dating we focus on the major recent developments for each technique that are most relevant for new dating applications in diverse fluvial environments and on explaining these for non specialists therefore essential information and precautions about sampling strategies in the field and or laboratory procedures are provided for each method new and important implications for chronological reconstructions of quaternary fluvial landscapes are discussed and where necessary exemplified by key case studies a clear statement of the current technical limitations of these methods is included and forthcoming developments which might possibly open new horizons for dating fluvial archives in the near future are summarised

history and dynamics of the greater yellowstone glacial system during the last two glaciations abstract the greater yellowstone glacial system gygs covered about 20 000 km2 at its maximum pleistocene extent the initiation culmination and ultimate decay of the gygs involved complex interactions between several coalescent ice masses flowing from glacial source areas adjoining and including the yellowstone plateau here we present an updated review of the history and dynamics of the gygs during the penultimate bull lake and last pinedale glaciations drawing upon an integration of glacial geologic mapping with 130 cosmogenic 10be and 3he exposure ages bull lake glacial deposits in greater yellowstone are dated to ca 150 140 ka and correlate with marine isotope stage 6 the bull lake glaciation extended well beyond the pinedale along the southern and western gygs margins but pinedale glaciers overrode bull lake ice limits on the north and east sides the northeastward shift of the center of ice mass from bull lake to pinedale time may be explained by uplift on the leading edge of the yellowstone hotspot and subsidence on the trailing margin in early pinedale time 22 18 ka ice buildup culminated in the high terrain of the beartooth uplift and high absaroka range glaciers from these source regions flowed onto the northeastern margin of the yellowstone plateau and advanced to terminal moraines beyond clarks fork canyon and in jackson hole by middle pinedale time 18 16 ka the yellowstone plateau ice cap surface had risen above the equilibrium line altitude stimulating orographic glacial buildup nourished by storms funneled eastward through the snake river plain the plateau ice cap eventually thickened to 1000 m and joined glaciers from the beartooth uplift and gallatin range to form the northern yellowstone outlet glacier terrain east and downwind of the ice cap crest was placed in a precipitation shadow resulting in glacial recession in these regions during the late pinedale 16 13 ka the plateau ice cap prograded southwestward toward the direction of moisture supply leading to advances along the southern and western margins of the gygs northern sectors of the plateau ice cap were nearly stagnant at this time the yellowstone region experienced widespread deglaciation ca 15 14 ka in response to warming climate unloading of the 1 km thick plateau ice cap and consequent release of pressure on the magmatic system beneath yellowstone was not accompanied by volcanism indicating that the magma chamber was not primed to erupt via decompression during the last deglaciation

quantifying glacial moraine age denudation and soil mixing with cosmogenic nuclide depth profiles 1 glacial boulders and soils on moraines are often dated to quantify the timing of glaciations and or rates of chemical weathering in moraine chronosequences a common assumption is that moraine crest erosion and soil mixing are unimportant however several studies suggest moraine denudation may be substantial we evaluate the magnitude of moraine denudation and soil mixing in the pinedale 21 ka and bull lake 140 ka moraines at fremont lake wyoming united states using cosmogenic nuclide depth profiles and a numerical model of moraine erosion and nuclide production and decay depth profiles indicate mixing of the surface layer from 40 to 60 cm depth age constraints from depth profile dating of cosmogenic nuclides result in ages of 17 24 ka for the pinedale moraine and 70 127 5 ka for the bull lake moraine these ages are comparable to ages based on the lal and chen approach which uses a sample from the mixed layer and the unmixed layer however the lal and chen approach is difficult to apply in real environments as the mixing depth needs to be determined independently we find our best fit model based ages for the bull lake moraine are younger than independent age constraints from boulder exposure dating due to incomplete mixing exposure age constraints from boulders are more straightforward for moraines than ages based on depth profile dating finally we find that moraine crests do significantly erode and are mixed suggesting that previous weathering and dust accumulation rate studies on moraines provide minimum estimates for these processes

role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes the central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings in the light of these general models we discuss the information that can be derived about geomorphic processes utilizing concentrations of in situ produced cosmogenic radionuclides 10be half life 1 5 ma and 26a1 half life 0 7 ma in a variety of geomorphic contexts glacial polish and tills meteorite impact craters alluvial fans paleo beach ridges marine terraces sand dunes and bedrock slopes we also compare 10be 26al data with results obtained by other dating methods we conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time scales in a wide range of geomorphological problems

a glacial chronology for the fish creek drainage of boulder mountain utah usa abstract boulder mountain located in south central utah is one of several mountain ranges on the colorado plateau that was glaciated during the late pleistocene using 3he exposure age dating corrected for non cosmogenic 3he with shielded samples we determined 3he exposure ages for boulders from the most well preserved moraines in the fish creek drainage of boulder mountain 3he exposure ages indicate a last glacial maximum lgm advance 23 100 1300 to 20 000 1400 yr ago and a later and smaller advance 16 800 500 to 15 200 500 yr ago this chronology is very similar to other cosmogenic glacial chronologies from the western u s and suggests that the timing of glacial advance and retreat on the colorado plateau was generally in phase with the rest of the western u s during the late pleistocene

the probable importance of snow and sediment shielding on cosmogenic ages of north central colorado pinedale and pre pinedale moraines abstract eight uncorrected 36 cl ages for pinedale boulders in north central colorado fall in the range 16 5 to 20 9 kyr 10 be age determinations on four of five boulders are in close agreement 6 difference with 36 cl determinations hypothetical corrections for snow shielding increased the 36 cl ages of pinedale boulder surfaces by an average of 12 most ages for pre pinedale bull lake boulders fall within marine isotope stage mis 5 a time when continental and sierran ice accumulations were small or nonexistent under the assumption that these boulders were deposited on moraines that formed before the end of mis 6 140 kyr bp calculations indicated that rock surface erosion rates would have had to range from 5 9 to 10 7 mm kyr 1 to produce the observed 36 cl values when compared to rates that have been documented for the past 20 kyr these erosion rates are extremely high snow shielding accounts for 0 48 of the additional years needed to shift pre pinedale dates to mis 6 this suggests that some combination of snow shielding sediment shielding or 36 cl leakage has greatly decreased the apparent ages of most pre pinedale boulders inability to account for the effects of these processes seriously hinders the use of cosmogenic ages of pre pinedale boulders as estimators of the timing of alpine glaciation

factors and processes governing the 14c content of carbonate in desert soils epsl elsevier earth and planetary science letters 125 1994 385 405 factors and processes governing the 14c content of carbonate in desert soils ronald amundson a yang wang a oliver chadwick b susan trumbore c leslie mcfadden d eric mcdonald d steven wells e michael deniro f a division of ecosystem sciences 108 hilgard university of california berkeley ca 94720 usa b earth sciences division jet propulsion laboratory pasadena ca 91109 usa c department of geosciences university of california irvine ca 92717 usa d department of earth and planetary sciences university of new mexico albuquerque nm 87131 usa e department of earth sciences university of california riverside ca 92521 usa f department of geological sciences university of california santa barbara ca 93106 usa received 1 september 1993 revision accepted 14 april 1994 abstract a model is presented describing the factors and processes which determine the measured 14c ages of soil calcium carbonate pedogenic carbonate forms in isotopic equilium with soil co 2 carbon dioxide in soils is a mixture of co 2 derived from two biological sources respiration by living plant roots and respiration of microorganisms decomposing soil humus the relative proportion of these two co z sources can greatly affect the initial 14c content of pedogenic carbonate the greater the contribution of humus derived co 2 the greater the initial 14c age of the carbonate mineral for any gwen mixture of co 2 sources the steady state co 2 distribution vs soil depth can be described by a production diffusion model as a soil ages the 14c age of soil humus increases as does the steady state 14c age of soil co 2 and the initial 14c age of any pedogenic carbonate which forms the mean 14c age of a complete pedogenic carbonate coating or nodule will underestimate the true age of the soil carbonate this discrepancy increases the older a soil becomes partial removal of outer and younger carbonate coatings greatly improves the relationship between measured 14c age and true age although the production diffusion model qualitatively explains the 14c age of pedogenic carbonate vs soil depth in many soils other factors such as climate change may contribute to the observed trends particularily in soils older than the holocene 1 introduction r a d i o c a r b o n d a t i n g o f s e d i m e n t a r y d e p o s i t s in d e s e r t s is h i n d e r e d by a lack o f o r g a n i c carbon paradoxically most o f the d e p o s i t s in t h e s e re mk gions a r e b l a n k e t e d with i n o r g a n i c c a r b o n in the f o r m o f p e d o g e n i c c a r b o n a t e since t h e early 1960s 14c ages have b e e n c a l c u l a t e d for t h e s e c a r b o n a t e s 1 fig 1 illustrates t h a t an a p p r o x i m a t e 1 1 r e l a t i o n s h i p exists b e t w e e n 14c ages of soil c a r b o n a t e a n d coexisting o r g a n i c m a t e r i a l s a n d ages d e t e r m i n e d by o t h e r m e a n s see also 2 3 t h e s e r e l a t i o n s h i p s a r e n o t perfect s o m e c a r b o n a t e is y o u n g e r t h a n i n d e p e n d e n t ages sug 0012 821x 94 07 00 1994 elsevier science b v all rights reserved ssdi 0012 821x 94 00097 i

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

reply to comment by j l diaz hernandez and r julia on quaternary landscape evolution and erosion rates for an intramontane neogene basin guadix baza basin se spain abstract we demonstrate that the age of 43 ka obtained for the topmost calcrete layer in the guadix baza remains the only reliable numerical dating of the flat geomorphic surface that marks the end of the sedimentation in the basin consequently the late pleistocene to holocene erosion rates derived from the incision of the present day drainage network into the flat geomorphic surface remain valid the calcrete radiometric ages reported by diaz hernandez and julia 2012 in their comment are untenable due to the contamination with detrital 230 th not corrected with the applied u th technique and the possible mix of textural elements with different ages older inherited grains and newly formed grains diaz hernandez and julia also quote u th ages for travertine terraces formed later than the calcrete layer these ages lack internal consistency probably due to systematic contamination and or weathering of the samples the archaeological ages reported by diaz hernandez and julia are subjected to great uncertainties but independently of the age assumed as most realistic they are completely compatible with the age of 43 ka that we obtained for the topmost calcrete layer in the guadix baza basin

reinterpretation of the cedar ridge section wind river range wyoming implications for the glacial chronology of the rocky mountains the cedar ridge stratigraphic section in the escarpment north of bull lake wind river range wyoming may be the most significant section of quaternary sediments in the rocky mountains this section contains a thick sequence of bull lake till but its greater significance is as the type section or a reference section for the deposits of three pre bull lake glaciations washakie point oldest cedar ridge and sacagawea ridge reference section type section at dinwoody lakes however after reexamining the tills lake sediments and buried soils in this section we conclude that the stratigraphic record is best interpreted as the result of two glaciations not the four of previous investigations buried soils are especially useful in deciphering the stratigraphy of this section through the contrast between well developed interglacial soils and weakly developed interstadial soils we conclude that only the bull lake and sacagawea ridge glaciations are represented by deposits in the cedar ridge section deposits formerly called cedar ridge are reinterpreted as representing an early stade of the sacagawea ridge glaciation a paleomagnetic study reveals that all the sediments have normal polarity and thus are probably younger than the brunhes matuyama boundary of ca 770 ka although the deposits of the cedar ridge section have been correlated with moraines and terraces this procedure should be done only by direct tracing or with the use of all available dating control the best record of quaternary glaciations in the area however is in the river terraces of glacial outwash origin in the wind river basin not the moraines and stratigraphic sections along the mountain front

cosmogenic 36cl and 10be ages of quaternary glacial and fluvial deposits of the wind river range wyoming we measured cosmogenic 36 cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the wind river range wyoming we also measured 10 be in 10 of the same samples most of the 10 be ages were in good agreement with the 36 cl ages indicating that rock surface erosion rates were very low the oldest moraine investigated the type sacagewea ridge site yielded only a limiting minimum age of 232 ka the oldest moraines in the type bull lake complex also could be constrained only to 130 ka the main sequence of type bull lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka the best estimates are closer to the upper limits of these ranges and associated uncertainties are in the range of 10 to 15 these uncertainties could permit deposition in either marine isotope stage 6 or stage 5d we found no evidence of glacial deposits dating to marine isotope stage 4 both bull lake age moraines from fremont lake on the opposite side of the wind river range and boulders on a fluvial terrace above the wind river gave age distributions very similar to that of the second oldest bull lake advance ca 130 to 100 ka the distribution of boulder ages for pinedale moraines at bull lake indicated deposition between 23 and 16 ka nearly identical to the distribution of 10 be ages previously reported for the type pinedale moraines at fremont lake

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

from sedimentary records to sediment budgets multiple approaches to catchment sediment flux this paper reviews the traditional approach to sediment budget studies in geomorphology new approaches and more specifically the potential impact of new methodological advances each component of the budget is discussed including the spatial and volumetric estimations of erosion deposition and storage and the precision and accuracy of flux rate estimation examples are used from recent work in germany the netherlands and the uk and include the pedogenic approach to erosion estimation remote sensing lidar geophysics and sediment based dating techniques for flux rate estimation the precision and accuracy of catchment sediment flux estimates based upon sediment storage is not only dependant upon volumetric accuracy but also on the precision and accuracy of sediment dating in this area there has been a revolution with direct sediment dating techniques tl osl esr freeing budget studies from the constraints and biases of radiocarbon of particular importance is the use of cosmogenic nuclides for dating but which can also be used to derive long term erosion rates but only using a steady state assumption finally a tentative initial application of the sediment budget approach to pleistocene terrace staircase in unglaciated basins is discussed it is argued that only now do we have the techniques available to be able to produce accurate sediment budget estimations at spatial scales greater than that of zero order basins and over time periods greater than that covered by direct observations

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

cosmogenic exposure age chronologies of pinedale and bull lake glaciations in greater yellowstone and the teton range usa abstract we have obtained 69 new cosmogenic 10be surface exposure ages from boulders on moraines deposited by glaciers of the greater yellowstone glacial system and teton range during the middle and late pleistocene these new data combined with 43 previously obtained 3he and 10be ages from deposits of the northern yellowstone outlet glacier establish a high resolution chronology for the yellowstone teton mountain glacier complexes boulders deposited at the southern limit of the penultimate ice advance of the yellowstone glacial system yield a mean age of 136 13 10be ka and oldest ages of 151 157 10be ka these ages support a correlation with the bull lake of west yellowstone with the type bull lake of the wind river range and with marine isotope stage mis 6 end moraines marking the maximum pinedale positions of outlet glaciers around the periphery of the yellowstone glacial system range in age from 18 8 0 9 to 16 5 1 4 10be ka and possibly as young as 14 6 0 7 10be ka suggesting differences in response times of the various ice cap source regions moreover all dated pinedale terminal moraines in the greater yellowstone glacial system post date the pinedale maximum in the wind river range by 4 6 kyr indicating a significant phase relationship between glacial maxima in these adjacent ranges boulders on the outermost set and an inner set of pinedale end moraines enclosing jenny lake on the eastern teton front yield mean ages of 14 6 0 7 and 13 5 1 1 10be ka respectively the outer jenny lake moraines are partially buried by outwash from ice on the yellowstone plateau hence their age indicates a major standstill of an expanded valley glacier in the teton range prior to the younger dryas followed closely by deglaciation of the yellowstone plateau these new glacial chronologies are indicative of spatially variable regional climate forcing and temporally complex patterns of glacier responses in this region of the rocky mountains during the pleistocene

radiocarbon dating of thin pedogenic carbonate laminae from holocene archaeological sites radiocarbon dating has been previously suggested to be applicable to pedogenic carbonate however until now the validity of radiocarbon dates from pedogenic carbonate remained poorly understood because of the relatively low resolution of chronological controls in this study we compared the radiocarbon dates a total of 21 of thin 0 2 0 3 mm in thickness laminae of pedogenic carbonate coatings on clasts from holocene archaeological sites in the eastern mediterranean and south siberia with independently estimated age ranges for these sites we obtained a high correlation between the oldest laminae of coatings with the site ages the 14 c ages of pedogenic carbonate were systematically younger by c 0 3 1 6 ka mean c 0 75 ka compared with archaeological sites this finding suggests that pedogenic carbonate despite potential complicating factors can be dated more accurately with 14 c than has been generally appreciated

geochronological position of badlands and geomorphological patterns in the guadix baza basin se spain abstract the guadix baza basin is one of a number of intramontane depressions located within the betic cordillera se spain where the geological and geomorphological evolution is controlled by tectonic activity the basin ceased to be closed after capture by the atlantic network when five main land systems developed late pleistocene geological evolution basically consisted of erosional modelling when badlands were deeply incised in highly erodible materials marls and silts three travertine platforms and several palaeolithic sites were used to determine that this main incision period fell within a 115 000 48 000 yr range there are few signs of geomorphological evolution of this basin in the last 48 000 yr based on these geomorphological data and soil development tectonic uplift of the basin probably played a secondary role in its evolution and climatic conditions in southern iberia in the 144 000 48 000 yr period were more humid and variable than later

asynchronous maximum advances of mountain and continental glaciers the last maximum glacier advance in many mountain ranges appears to have predated the last maximum advance of the wisconsinan continental ice sheets 20 000 years b p published evidence from widely spaced localities in north and south america europe asia and hawai i suggests that some mountain glaciers extended farther during one or more stades early in the last glaciation roughly 115 000 30 000 years b p than at its end when low global temperature and high precipitation presumably were most favorable for the growth of glaciers variations in the timing of glacier advances in different mountain ranges suggest that alpine glaciers are dependent on regional climate as well as global conditions their study might provide sensitive tests for theories of global climate change glacial deposits are often used as time markers in neotectonic and geomorphic studies and their ages sometimes are inferred from distant measurements or from proxy histories of global climate change undated geomorphic features such as moraines sharply incised streams and river terraces which commonly have been associated with the last maximum glacier advance 20 000 years b p or last deglaciation 13 000 years b p may actually be older by a factor of 2 to 4 or more conversely deposits assigned to the maximum advances of the penultimate global glaciation 130 000 years b p may actually date from early in the most recent glacial cycle and be younger by a comparable factor rates of faulting or folding estimated from displacements or deformation and the assumed ages of such geomorphic features might be too great or too small by corresponding factors

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

dating constituent formation in soils to determine rates of soil processes a review abstract rates of soil processes are poorly known one approach to determine them could be through the radiogenic isotopic dating of soil constituents such methods have been recently used to date minerals in soils and weathering profiles thanks to the development of high resolution techniques such as 40ar 39ar u series of micro drilled samples u series by laser ablation and u th he and to the development of suitable methodology expanding application of the techniques to a variety of supergene minerals e g fe and mn oxihydroxides carbonates etc in this paper we identify i the main soil constituents that can be dated through these isotopic methods that are mainly fe oxides mn oxides pedogenic carbonates and organic matter ii the main pedogenic processes that leads to their formation in soils and iii the different soil settings that allow transforming soil constituent ages into rates of soil processes namely growth bands transformation fronts and chronosequences

ages and significance of glacial and mass movement deposits on the west side of boulder mountain utah usa abstract using air photos satellite images and field observations we mapped quaternary glacial and mass movement deposits on the west side of boulder mountain in south central utah usa prominent glacial moraines were deposited by outlet glaciers that emanated from an ice cap that existed atop boulder mountain cosmogenic 3 he exposure ages of these deposits range from 20 2 1 5 to 22 5 2 5 ka and indicate maximum ice advance during the global last glacial maximum lgm three 3 he exposure ages of boulders from the pine creek slump deposit indicate that the slumping likely occurred at or before 125 ka eight 3 he exposure ages of boulders from the miller creek potholes debris flow deposit range from 20 2 2 0 to 50 4 3 0 ka five of those boulders yielded ages in the range of 26 33 ka and suggest emplacement of the debris flow deposit during that time both of these mass movement features cover prominent fault traces related to the thousand lakes fault but do not appear to be offset suggesting that major faulting has not occurred since 125 kyr ago in this area

duration and structure of the past four interglaciations reanalysis and additional dating of the devils hole 18o paleotemperature record confirm that the last interglaciation in the great basin the continental analog of marine isotopic substage 5e lasted 22 000 yr consistent with the vostok paleotemperature record which suggests a duration of 19 000 yr for this event in antarctica the three preceding interglaciations in the devils hole record analogs of marine isotopic substages 7e 9c and 11c range from 20 000 to 26 000 yr in duration a 20 000 yr duration for the last interglaciation is consistent with tims uranium series dated sea level high stands thus the widely held view that interglaciations were of 11 000 to 13 000 yr duration and constituted only about 10 of mid to late pleistocene climatic cycles needs reexamination the warmest portion of each interglaciation in the devils hole time series is marked by a 18o plateau signifying apparent climatic stability for periods of 10 000 to 15 000 yr duration

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

oxygen isotope composition of annually banded modern and mid holocene travertine and evidence of paleomonsoon floods grand canyon arizona usa abstract holocene and modern travertine formed in spring fed havasu creek of the grand canyon arizona was studied to determine the factors governing its oxygen isotope composition analysis of substrate grown travertine indicates that calculated calcite formation temperatures compare favorably with measured water temperatures and include silt rich laminae deposited by monsoon driven floods ancient spring pool travertine is dated by u series at 7380 110 yr and consists of 14 travertine silt couplets of probable annual deposition one hundred eighty high resolution 18o analyses of this mid holocene sample average 11 0 pdb the average value for modern travertine is 0 5 lower perhaps because mid holocene temperature was higher or there was proportionally greater summer recharge 18o cyclicity in the mid holocene travertine has average amplitude of 1 9 0 5 pdb slightly less than the inferred modern day annual temperature range of havasu creek the annual temperature range might have been reduced during the 14 yr interval compared to present although other non temperature factors could account for the muted annual variation silt rich laminae within isotopically lower calcite in the modern and mid holocene travertine verifies the seasonal resolution of both samples and suggests that similar temperature precipitation conditions as well as monsoon generated summer floods prevailed in the mid holocene as they do throughout the grand canyon region today

effects of climate change on soils in glacial deposits wind river basin wyoming abstract soil chronofunctions are often quasilinear but those relationships may be only gross fortuitous generalizations that ignore changes in soils resulting from climatic and other cyclic external influences that govern soil formation or soil degradation in the rocky mountains soil development has been extensively used to estimate the age of sediments but the number of soils is usually few and large ranges in values for soil data may be dismissed as normal variation in a detailed study of soils in the wind river range and wind river basin characteristics of near surface horizons do not follow age trends however the underlying carbonate bearing horizons do have age related characteristics this soil paradox may be related to glacial interglacial cycles in which 1 wind erodes near surface horizons and then provides new parent material and 2 cryoturbation disrupts carbonate horizons remobilizing carbonate and changing carbonate morphology but with only minimal loss of carbonate from the soil

diagenesis and distribution of acyclic isoprenoid hydrocarbons in late miocene to pliocene marine siliceous rocks from horonobe hokkaido japan abstract a sequence of late miocene to pliocene siliceous mudstones from boreholes hdb 3 and hdb 4 from horonobe hokkaido japan is homogeneous and useful for the study of diagenetic degradation and transformation of sedimentary organic matter using these siliceous mudstones the diagenetic change in acyclic isoprenoid hydrocarbons was investigated the palaeotemperatures of the samples were estimated to be in the range 30 60 c on the basis of the silica mineral transformation and the present day geothermal gradient in the region the relative abundances of pristane to pristenes and phytane to phytenes increase drastically with depth the remarkable changes in pristane pristene and phytane phytene occur in a temperature range of about 35 50 c the relative abundances could be potential parameters for palaeotemperature analysis of immature sedimentary rocks remarkable increases in pristane and phytane concentration with maturity show that in addition to extractable free pristenes and phytenes bound acyclic isoprenoids are the major source of pristane and phytane pristane phytane and pristenes phytenes are nearly constant through the entire boreholes showing that the relative abundance of the precursor c 19 c 20 acyclic isoprenoids was determined at the time of deposition and or in the early stage of diagenesis pristene phytene as well as pristane phytane could be useful parameters for assessing palaeodepositional environment

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

interpretation of the conolly contour diagram of fault related veins the conolly diagram is a section or plan on which the distances from the vein to an arbitrary reference plane are contoured this graphical technique makes it possible to depict the shape of the vein in a form which resembles topographic contour maps the conolly diagram can be used to analyse the relation between oreshoot development in fault related veins the attitude of the irregular fault plane and slip direction of the fault

rock varnish microlamination dating of late quaternary geomorphic features in the drylands of western usa abstract varnish microlamination vml dating is a correlative age determination technique that can be used to date and correlate various geomorphic features in deserts in this study we establish a generalized late quaternary i e 0 300 ka varnish layering sequence for the drylands of western usa and tentatively correlate it with the specmap oxygen isotope record we then use this climatically correlated varnish layering sequence as a correlative dating tool to determine surface exposure ages for late quaternary geomorphic features in the study region vml dating of alluvial fan deposits in death valley of eastern california indicates that during the mid to late pleistocene 5 15 ky long aggradation events occurred during either wet or dry climatic periods and that major climate shifts between glacial and interglacial conditions may be the pacemaker for alteration of major episodes of fan aggradation during the holocene interglacial time however 0 5 1 ky long brief episodes of fan deposition may be linked to short periods of relatively wet climate vml dating of alluvial desert pavements in death valley and the mojave desert reveals that pavements can be developed rapidly

230th u dating of surficial deposits using the ion microprobe shrimp rg a microstratigraphic perspective abstract we used the sensitive high resolution ion microprobe reverse geometry shrimp rg to date pedogenic opal using the 230 th u system due to the high spatial resolution of an ion microprobe typically 30 m regions of pure opal within a sample can be targeted and detrital material can be avoided in addition because the technique is non destructive the sample can be preserved for other types of analyses including electron microprobe or other stable isotope or trace element ion microprobe measurements the technique is limited to material with u concentrations greater than 50 ppm however the high spatial resolution small sample requirements and the ability to avoid detrital material make this technique a suitable technique for dating many pleistocene deposits formed in semi arid environments to determine the versatility of the method samples from several different deposits were analyzed including silica rich pebble coatings from pedogenic carbonate horizons a siliceous sinter deposit and opaline silica deposited as a spring mound u concentrations for 30 m diameter spots ranged from 50 to 1000 ppm in these types of materials the 230 th 232 th activity ratios also ranged from 100 to 10 6 eliminating the need for detrital th corrections that reduce the precision of traditional u th ages for many milligram and larger sized samples in pedogenic material layers of high u opal ca 500 ppm are commonly juxtaposed next to layers of calcite with much lower u concentrations 1 2 ppm if these types of samples are not analyzed using a technique with the appropriate spatial resolution the ages may be strongly biased towards the age of the opal comparison with standard tims thermal ionization mass spectrometry measurements from separate microdrilled samples suggests that although the analytical precision of the ion microprobe shrimp rg measurements is less than tims the high spatial resolution results in better accuracy in the age determination for finely layered or complex deposits the ion microprobe approach also may be useful for pre screening samples to determine the age and degree of post depositional alteration analyzing finely layered samples or samples with complex growth histories and obtaining simultaneous measurements of trace elements

middle pleistocene formation of the rio grande gorge san luis valley south central colorado and north central new mexico usa process timing and downstream implications abstract the rio grande is the fourth longest river in north america extending over 3 000 km from the rocky mountains to the gulf of mexico the pleistocene evolution of this river from individual subbasins into a coalesced fluvial system has been long debated herein we constrain the middle pleistocene evolution of the northernmost and largest rio grande basin the san luis basin and the timing of incision of the rio grande gorge based on new geologic mapping 3he surface exposure dating and u series dating on pedogenic carbonates 3he dating of shoreline deposits of closed basin lake alamosa and fluvially scoured bedrock along the rio grande gorge rim indicate the san luis basin was connected with southerly rio grande basins and progressively incised since 400 ka waning tectonic activity coupled with the hydrologic response to intensified middle pleistocene glaciation drove southward spillover of lake alamosa 400 ka expanding the river s drainage basin by nearly 24 000 km2 and adding recharge areas in the high altitude glaciated san juan tusas and sangre de cristo mountains geologic barriers to streamflow on the taos plateau were breached and basin tributary drainages were integrated and inset into their present canyons 250 200 ka with approximately 120 m of incision during 400 200 ka previous work demonstrates that southerly streamflow through basins south of the slb terminated into a large rift related bolson complex until the middle pleistocene and most axial rio grande river incision has occurred since 630 ka we propose that middle pleistocene integration of the slb was the major geomorphic event that eroded plio pleistocene tectonic and volcanic barriers and re established flow of the rio grande from the rocky mountains to the gulf of mexico

from mass wasting to slope stabilization putting constrains on a tectonically induced transition in slope erosion mode a case study in the judea hills israel calcrete coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the soreq drainage judea hills israel these remnants indicate that a transition from landslide dominated terrain to dissolution controlled hillslope erosion had occurred this transition possibly occurred due to the significant decrease in tectonic uplift during the late cenozoic the study area is characterized by sub humid mediterranean climate the drainage hillslopes are typically mantled by thick calcrete crusts overlying upper cretaceous marine carbonate rocks using tt osl dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit we conclude that incision of 100 m occurred from 1056 262 to 688 86 ka due to 0 3 westward tilt of the region such incision invoked high frequency of landslide activity in the drainage the ages of a younger landslide remnant alluvial terrace and alluvial fan all situated only a few meters above the present level of the active streambed range between 688 86 ka and 244 25 ka and indicate that since 688 86 the soreq base level had stabilized and that landslide activity decreased significantly by the middle pleistocene copyright 2012 john wiley sons ltd

deglaciation and postglacial environmental changes in the teton mountain range recorded at jenny lake grand teton national park wy abstract sediments contained in lake basins positioned along the eastern front of the teton mountain range preserve a continuous and datable record of deglaciation and postglacial environmental conditions here we develop a multiproxy glacier and paleoenvironmental record using a combination of seismic reflection data and multiple sediment cores recovered from jenny lake and other nearby lakes age control of teton lake sediments is established primarily through radiocarbon dating and supported by the presence of two prominent rhyolitic tephra deposits that are geochemically correlated to the widespread mazama 7 6 ka and glacier peak 13 6 ka tephra layers multiple glacier and climate indicators including sediment accumulation rate bulk density clastic sediment concentration and flux organic matter concentration flux 13c 15n and c n ratios and biogenic silica track changes in environmental conditions and landscape development sediment accumulation at jenny lake began centuries prior to 13 8 ka and cores from three lakes demonstrate that teton glacier extents were greatly reduced by this time persistent ice retreat in cascade canyon was slowed by an interval of small glacier activity between 13 5 and 11 5 ka prior to the end of glacial lacustrine sedimentation 11 5 ka the transition to non glacial sediments marks the onset of holocene conditions at jenny lake and reflects a shift toward warmer summers increased vegetation cover and landscape stability in the tetons we discuss the teton lake sediment records within the context of other regional studies in an effort to construct a comprehensive overview of deglaciation and postglacial environmental conditions at grand teton national park

dating fluvial terraces by 230th u on pedogenic carbonate wind river basin wyoming abstract reliable and precise ages of quaternary pedogenic carbonate can be obtained with 230th u dating by thermal ionization mass spectrometry applied to carefully selected milligram size samples datable carbonate can form within a few thousand years of surface stabilization allowing ages of quaternary deposits and surfaces to be closely estimated pedogenic carbonate clast rinds from gravels of glacio fluvial terraces in the wind river basin have median concentrations of 14 ppm u and 0 07 ppm 232th with median 230th 232th 270 making them well suited for 230th u dating horizons as thin as 0 5 mm were sampled from polished slabs to reduce averaging of long 105 yr and sometimes visibly discontinuous depositional histories dense translucent samples with finite 230th u ages preserve within rind stratigraphic order in all cases ages for terraces wr4 167 000 6 400 yr and wr2 55 000 8600 yr indicate a mean incision rate of 0 26 0 05 m per thousand years for the wind river over the past glacial cycle slower than inferred from cosmogenic nuclide dating terrace wr3 which formed penecontemporaneously with the final maximum glacial advance of the penultimate rocky mountain bull lake glaciation has an age of 150 000 8300 yr indicating that it is broadly synchronous with the penultimate global ice volume maximum

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

in situ u series dating by laser ablation multi collector icpms new prospects for quaternary geochronology the capabilities and potential applications of in situ dating of quaternary materials using laser ablation mc icpms are explored 234 u 238 u and 230 th 234 u can be measured with precision sufficient for dating at a spatial resolution of 100mm or better in samples that contain as a little as 1 ppm uranium moreover u and th concentrations and u series isotope ratios can be continuously profiled to determine changes in age that occur with sample growth e g in speleothems these capabilities additionally permit the dating of bones teeth and possibly molluscs which are subject to post mortem open system behaviour of useries isotopes and can be employed to elucidate processes of u series migration during weathering and diagenesis a drawback of laser ablation mc icpms is that it cannot in general provide u series age estimates with the high precision and accuracy of conventional tims or solution mc icpms methods however sample preparation is straightforward the amount of sample consumed negligible and it can be used to rapidly characterise or screen and select samples from which more precise and accurate dates can be obtained using conventional methods given further instrumental developments and the establishment of suitable matrix matched standards for carbonates and other materials we foresee that laser ablation mc icpms will play an increasingly important role in quaternary dating research r 2005 published by elsevier ltd

late quaternary slip rate of the southern elsinore fault southern california dating offset alluvial fans via 230th u on pedogenic carbonate 1 to understand how strain is accommodated along the pacific north american plate boundary and to assess the associated seismic hazard estimates of long term 103 105 year slip rates for strands of the san andreas fault system are needed the mean slip rate over the past 40 kyr for the southernmost elsinore fault one of the principal strands of the san andreas fault system in southern california was determined using offset alluvial fans dated by u series on pedogenic carbonate two displaced fans correlated with their source drainages using distinctive gravel clast assemblages define offsets of 60 20 and 83 31 m milligram size samples of dense carbonate clast coatings from fan soils provide 230th u based ages of 39 1 5 3 and 46 4 5 3 kyr all errors are 2 respectively for the offset fans our results indicate that the elsinore fault near its southern terminus slipped at a mean rate of 1 6 0 4 mm yr over the past 40 kyr however slip associated with the most recent earthquake on the southern elsinore fault increases northward from the study area and if this pattern has repeated through time the peak slip rate on the southern elsinore fault may significantly exceed our measured rate

dating fluvial terraces with and profiles application to the wind river wyoming abstract fluvial strath terraces provide a record of river incision and the timing of climatic perturbations to the fluvial system dating depositional surfaces like terraces that are older than the range of 14 c however is difficult we employ a cosmogenic radionuclide crn profile technique that addresses a major problem of crn dating on such surfaces nuclide inheritance by measuring 10 be and 26 al profiles we constrain the exposure age and the mean crn inheritance for the deposit the crn profile also yields a self check on the assumptions underlying the method we report our attempts to date terraces along the wind river wy like many sequences of western north american fluvial terraces these are inferred to reflect oscillation between glacial and interglacial conditions in the headwaters previous dating of some of these terraces and the associated terraces and glacial deposits makes this a unique location to compare dating methods dates from five sites along the bull lake glacial correlative terrace wr 3 are 118 125 ka which agrees with dates on bull lake age moraines and independent age estimates on the terrace and is consistent with the model of terrace glacial relationship crn inheritance is significant and highly variable requiring it be considered despite the additional sampling complexity assuming all inheritance in wr 3 deposits arises during exhumation in the headwaters we obtain minimum mean rates of exhumation of 13 130 m my for the source rocks alternatively assuming the crns are inherited during clast transport the time of fluvial transport from source to terrace is 10 ka it increases downstream and is lower for sand than cobbles the crn ages for older terraces wr 7 300 ka and wr 15 510 ka are lower by 50 than previous estimates based on tephrochronology the most plausible explanation is eolian deflation of a once thicker loess cover on the terrace surfaces mean thicknesses of loess of 0 5 1 5 m are required to reconcile these concentrations of crn with the previous estimates of age difficulty in dating the older terraces emphasizes that geologic caution independent estimates of age and multiple sample sites should still be part of dating depositional surfaces with crns even when employing the inheritance correction technique

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event

late pleistocene climate inferred from the reconstruction of the taylor river glacier complex southern sawatch range colorado abstract ice surface topography of a late pleistocene glacier complex herein named the taylor river glacier complex trgc was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps during the last glacial maximum lgm the trgc covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and or upland ice fields equilibrium line altitudes elas for the glaciers of the trgc were estimated using the accumulation area ratio method assuming that ratio to be 0 65 0 05 elas thus derived ranged from about 3275 to 3400 m with a mean of 3340 60 m a degree day model ddm was used to infer the climatic significance of the lgm ela with no appreciable differences in precipitation with respect to modern climate the ela implies that mean summer temperatures during the lgm were 7 6 c cooler than today the ddm was also used to determine the temperatures required to maintain steady state mass balances for each of the reconstructed glaciers the required reductions in summer temperature vary little about a mean of 7 1 c the sensitivity of these results to slight 25 changes assumed for lgm precipitation are less than 0 5 c even under an lgm climate in which precipitation is assumed to be substantially different 50 than the present mean summer temperatures must be on the order of 7 0 to 8 5 c lower to depress equilibrium lines to lgm altitudes the greater sensitivity of the ela to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation

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

230th u burial dating of ostrich eggshell abstract obtaining precise and accurate dates for late quaternary terrestrial sequences containing middle stone age or middle paleolithic archaeological materials ca 30 300 ka can be challenging many such sequences lie beyond the limit of radiocarbon dating 50 ka and lack volcanic ashes suitable for 40ar 39ar dating we report a dating approach with about ten times the range of radiocarbon dating 500 ka based on a novel protocol for 230th u dating of ostrich eggshell a common component of african near eastern and asian archaeological sequences uranium in ostrich eggshell typically at levels of tens to hundreds of ppb is acquired after burial however accurate burial ages can be determined from measured 230th u ages when corrected for uranium uptake via diffusion using ostrich eggshells from a pleistocene holocene east african site we have 1 characterized the spatial distribution of uranium and common thorium 232th concentrations in ostrich eggshell by laser ablation icp ms 2 determined apparent 230th u ages on outer and inner layers of eggshells by solution icp ms analyses of selectively abraded eggshells and 3 calculated 230th u burial ages using a simple model for diffusive uptake of uranium we assess our method by comparing the 230th u burial ages median uncertainty 2 3 1 sd with radiocarbon dates on carbonate from the same eggshells we find good agreement in seven out of nine eggshells confirming the accuracy of their 230th u model ages eggshells that fail to yield reliable 230th u ages may be recognized by anomalous patterns of apparent 230th u ages providing a reliability criterion innate to the 230th u data ostrich eggshells are resistant to diagenesis simplifying 230th u dating compared to bones and teeth eggshells of ostrich emu rhea and other living and extinct ratites found on six continents share similar structure and composition suggesting our new approach to 230th u dating of eggshell may be applicable in diverse late quaternary terrestrial settings

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

isotopic evidence for shifts in atmospheric circulation patterns during the late quaternary in mid north america wyoming is now at the eastern margin of westerlies originating in the pacific but in the pleistocene appears to have received moisture from elsewhere possibly the gulf of mexico oxygen isotope ratios of pedogenic carbonate in postglacial terraces correspond to ratios in equilibrium with present meteoric waters which show a strong relation to precipitation seasonality and storm sources in contrast the oxygen isotope ratios of all pre holocene soils are significantly more positive even though the carbon isotope composition of coexisting organic matter suggests that the carbonate formed in temperatures cooler than today the oxygen isotope ratios of paleowaters in mid north america appear to be more useful for identifying past storm sources than for estimating paleotemperatures

ice ages the california current and devils hole at the end of an ice age climate changes across the globe but this response is not uniform in some parts of the world oceanic and atmospheric temperatures started to rise well before continental ice sheets began to melt in his perspective lea 1 highlights the report by herbert et al 2 who show that ocean temperatures in the california current led ice volume change by 10 000 to 15 000 years the data support earlier results from a terrestrial record at devils hole helping to reconcile them with the leading theory of ice age cycles 1 http www sciencemag org cgi content full 293 5527 59 2 http www sciencemag org cgi content short 293 5527 71

age calibration of carbonate rind thickness in late pleistocene soils for surficial deposit age estimation southwest usa abstract carbonate rinds have been used for cross correlation of landforms as well as a quantitative indicator of soil age using the measured rind thickness of clasts found within a deposit whose age has been independently determined allows the construction of a calibrated surface age proxy measurements were taken at sites within the mojave desert the northwestern sonoran desert the southern great basin and the western colorado plateau these sites are all within about 300 km of the intersection of the borders of the states of california arizona and nevada in the study area elevation varied from 200 to 1200 m map was from 95 to 195 mm and mat was from 18 4 to 23 3 c the calibrated proxy while not accounting for the effects of parent material or climate on rind development does show a strong correlation r 2 0 74 p

dating and characterization of polymorphic transformation of aragonite to calcite in pleistocene bivalves from rhodes greece by combined shell microstructure stable isotope and electron spin resonance study absolute dating of diagenesis is a challenging yet significant problem reconstructing the depositional and diagenetic history of a late pleistocene coralligene type red algal reef and overlying maerl red algal sand from the plimiri coastal cliff se island of rhodes greece is enabled using a combination of microstructure stable isotope analyses and electron spin resonance of large bivalve shells partially altered by diagenesis these shells consisting of both original shell aragonite and polymorphic transformed rims now consisting of neomorphic spar provide the opportunity to date the primary age when the shells were precipitated as well as the age of their polymorphic transformation the contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance esr alone however sample contamination was evaluated with quantitative xrd providing the opportunity to apply corrections which increased reliability of the ages the carbon and oxygen stable isotope values and the neomorphic spar microtexture suggested that the polymorphic transformation at plimiri took place in a meteoric environment with a high and increasing fluid rock ratio the electron spin resonance dates combined with the vertical sedimentary evolution allowed to assign the formation of the red algal reef to the marine isotope stages 6 to 5e transgressive event ca 135 to 120 ka and to identify meteoric diagenetic phases during possibly the marine isotope stage 5d and the upper marine isotope stage 5c to lower 3 the use of electron spin resonance dating of neomorphic spar and age correction for sample contamination is presented herein for the first time and the results suggest that it might provide a useful tool to date late pleistocene diagenesis

quaternary morphotectonic mapping of the wadi araba and implications for the tectonic activity of the southern dead sea fault 1 the dead sea strike slip fault accommodates the northward motion of arabia relative to sinai at a rate of 5 mm yr the southern segment of the fault the wadi araba fault runs along a valley blanketed in quaternary sediments we first focused on understanding the relative and absolute timing of emplacement of the alluvial surfaces we then determined the probable source of the sediments before assessing their lateral offset to constrain the late pleistocene fault slip rate seven successive morphostratigraphic levels were identified at two sites we recognized an alluvial sequence of five to seven successive levels with ages getting younger northward a pattern consistent with the western block moving southward relative to two fixed feeding channels located to the east surface samples were collected for10be cosmogenic radionuclide dating fans f3 and f5 were found to be synchronous from site to site at 102 26 ka and 324 22 ka respectively while f4 could be dated at 163 19 ka at one site only these are minimum ages assuming no erosion of the alluvial surfaces at least two of these periods are correlated with wet periods that are regionally well documented further analyses of tectonic offsets are affected in most cases by large uncertainties due to the configuration of the sites they indicate maximum offsets of 5 5 km for the oldest possibly 1 ma old surfaces they lead to bracketing of the fault slip rate between 5 and 12 mm yr with preferred values of 5 7 mm yr for the last 300 ka

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr