external dose rate determinations for esr dating at bau de l aubesier provence france abstract at bau de l aubesier provence france mousterian artefacts and human teeth occur in inhomogeneous lumpy sedimentary deposits that include bone and tooth fragments due to uranium u uptake by the bones and teeth the external dose rate experienced by the teeth has changed over time such changes must be considered when calculating thermoluminescence tl ages for burnt flint artefacts or electron spin resonance esr ages for the teeth therein here we assess the external dose rates using three methods in situ tl dosimetry gives the modern dose rate whereas volumetrically averaged geochemical analysis is used to estimate time averaged dose rates that consider u uptake by u rich sedimentary components blackwell and blickstein 2000 quarternary international 68 71 329 343 in esr isochron analysis blackwell and schwarcz 1993 applied radiation and isotopes 44 243 252 multiple subsamples with variable u concentrations measure the external dose rate experienced by the tooth regardless of reworking but do depend on the uptake model assumed the methods each suggest significantly different dose rates tl dosimetry for two combustion horizons measured external dose rates at 0 143 0 012 mgray y in layer iv and 0 184 0 016 mgray y in layer h geochemical analysis when volumetrically averaged to account for the influence from different sedimentary components indicates external dose rates ranging from as low as 0 094 0 024 mgray y assuming ru for u rich sedimentary components to a maximum of 0 251 0 048 mgray y assuming eu for the u rich components isochron analyses suggest more variable dose rates ranging from a minimum of 0 009 0 040 mgray y lu in the lower layers to a high of 1 103 0 160 mgray y eu in layer h1 three isochrons indicated that the teeth had experienced u leaching or a second uptake event which would affect the accuracy of the dose rate determinations for those teeth other teeth may have experienced similar processes quaternary researchers who want reliable dates in the age ranges for esr or tl must carefully consider both the nature of the sediment especially u rich bone fragments and its geometric arrangement around the samples to be dated corresponding results using more than one analytic method may be required for a reasonable confidence level

snowball earth ocean chemistry driven by extensive ridge volcanism during rodinia breakup the cryogenian snowball earth glaciations were followed by the deposition of massive cap carbonates geochemical modelling suggests that shallow ridge volcanism supplied much of the alkalinity and cations that fuelled this deposition

the problems in esr dating of tooth enamel of early pleistocene and the age of longgupo hominid wushan china abstract quite often esr dating of tooth enamel provides underestimated ages the factors which may account for the age suppression are studied for dating of the samples of early pleistocene thermal fading of the g 2 0018 signal during the burial time may also lead toage underestimation isothermal annealing of the g 2 0018 line was studied in this work and a mixed first and second order kinetics was observed its implication to the practical dating purpose is discussed it is suggested that if no uranium leakage is detected esr eu ages of early pleistocene enamel samples should be considered only as the lower limits of the true ages combined esr and magnetic dating of the longgupo profile wushan china assigns the olduvai subchron to the fossil hominid bearing layers of 7 8 of this profile

poisson s ratio and porosity at coso geothermal area california high resolution three dimensional compressional and shear wave velocity models derived from microearthquake traveltimes are used to map the distribution of poisson s ratio and porosity at coso geothermal area inyo county california spatial resolution of the three dimensional poisson s ratio and porosity distributions is estimated to be 0 5 km horizontally and 0 8 km vertically model uncertainties 1 in the interior and 2 3 around the edge of the model are estimated by a jackknife method we use perturbations of r vp vs ratio and vp vs product to derive distributions of poisson s ratio and porosity which are then used to constrain and delineate possible zones of intense heat fracture accumulation and fluid saturation poisson s ratio at coso ranges from 0 15 to 0 35 with an average of 0 224 lower than the crustal average of 0 25 high poisson s ratios are more extensive in shallower depths 1 5 km while lower poisson s ratios are found in the deeper section 1 5 3 0 km of the target area two major features with low poisson s ratio are identified at geothermal production depth 1 3 km around stations s2 s6 and s1 s3 s4 the two low features are separated by a northwest southeast trending high belt with variable width of 1 3 km a high body is found around s2 and s6 and extends down in depth a circular low belt corresponding to the high belt is located around s2 s6 and is linked to a previously reported structure in vs tomography this low highly porous belt is probably a horizontal conduit reservoir of geothermal fluid a vertical low and high channel beneath triangle s1 s3 s4 corresponds to a high attenuation dome like feature we propose an upwell and spread magma intrusion model for the last major magmatism in the coso region the magmatic upwelling is centered in the s1 s3 s4 area the model predicts potential geothermal resources to the south and west of triangle s1 s3 s4 based on local faulting patterns

lithium isotope evidence for enhanced silicate weathering during oae 1a early aptian selli event an abrupt rise in temperature forced by a massive input of co2 into the atmosphere is commonly invoked as the main trigger for oceanic anoxic events oaes global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas stimulating biological productivity the end result was widespread anoxia and deposition of black shales the hallmarks of oaes in order to assess the role of weathering as both an oae initiator and terminator via co2 sequestration during the early aptian oae 1a selli event 120 ma the isotopic ratio of lithium isotopes was analysed in three sections of shallow marine carbonates from the pacific and tethyan realms and one basinal pelagic section from the tethyan domain because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high and low temperature alteration of basaltic material a shift to lighter 7li values is expected to characterize oaes the studied sections illustrate this phenomenon 7li values decrease to a minimum coincident with the negative carbon isotope excursion that effectively records the onset of oae 1a a second negative 7li excursion occurs coeval with the minimum in strontium isotopes after the event the striking similarity to the strontium isotope record argues for a common driver the formation and destruction weathering of an oceanic lip could account for the parallel trend in both isotope systems the double spike in lithium isotopes is probably related to a change in weathering congruencies such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering in conjunction with organic carbon burial led to drawdown of atmospheric co2 during the early aptian oae 1a

considering sedimentary u uptake in external dose rate determinations for esr and luminescent dating abstract at many archaeological sites including bau de l aubesier la quina and la chaise de vouthon artefacts teeth and bones occur in heterogeneous lumpy sedimentary deposits that include bone and tooth fragments due to uranium u uptake by the bones and teeth in the adjacent sediment the external dose rate experienced by teeth bones or the sediment itself will have changed over time such changes must be considered when calculating dose dependent ages whether thermoluminescent tl age for burnt flint artefacts optically stimulated luminescent osl or radioluminescent rl ages for sediment or electron spin resonance esr ages for the teeth therein u uptake or loss in the sedimentary bone and tooth fragments can be modelled in the same manner as u uptake or loss in the dated teeth compared to dose rates derived from single bulk sedimentary geochemical analyses volumetrically averaged sedimentary dose rates at bau de l aubesier show significant differences depending on the model adopted for the u uptake in order to calculate the dosimetric contribution from the sedimentary components that had absorbed u

rock properties of the upper crust in central apennines italy derived from high resolution 3 d tomography 1 high resolution 3 d p and s wave velocity models of a central sector of the apennines central italy are computed by inverting first arrival times from an aftershock sequence september december 1997 following the mw 5 7 and mw 6 0 umbria marche earthquakes that occurred on september 26 1997 the high quality of the data set especially for the s wave allows us to compute 3 d variations in vp vp vs and vp vs the anomalies can be interpreted as lateral changes in rock type and fracturing which control fluid diffusion and variation in pore pressure this is in agreement with a poro elastic view that can be inferred from the spatio temporal evolution of the seismic sequence

the age of the nantuo formation and nantuo glaciation in south china a u pb sensitive high resolution ion microprobe shrimp age of 654 5 3 8 ma from an ash bed immediately below the nantuo formation in south china provides the lowest age constraint for the nantuo glaciation which has been correlated with the global marinoan glaciation a u pb shrimp age of 636 3 4 9 ma from a fallout tuff within the basal layer of the nantuo formation along with the existing age of 635 2 0 6 ma from its overlying doushantuo cap carbonate suggests that the traditionally defined nantuo formation may have been deposited in a short time period at the end of the nantuo glaciation in combination with available ages globally the data support a relatively short duration and rapid termination of marinoan glaciations

assessing the utility of fe al and fe speciation to record water column redox conditions in carbonate rich sediments abstract geochemical proxies based on fe abundance fe al and fe speciation have been widely applied to marine sediments in order to unravel paleo depositional redox conditions though geological time to date however these fe proxies have only been calibrated in relation to modern and ancient fine grained siliciclastic marine sediments this clearly limits their use particularly in relation to carbonate rich sediments and rocks to address this we here explore the applicability of fe based redox proxies in carbonates through three approaches first we have compiled fe al data for modern marine sediments to investigate variability in fe enrichments as a function of carbonate content and depositional setting second we have expanded this approach with a compilation of new and existing fe speciation data for modern and ancient marine sediments deposited under oxic and euxinic anoxic sulfidic water column conditions finally we show new data from paired limestone and dolomite sample sets to demonstrate the potential significance of deep burial dolomitization on the fe speciation redox proxy modern marine sediments deposited under oxic conditions show no relationship between fe al and carbonate content these sediments have an average fe al ratio of 0 55 0 11 with some higher values potentially being attributable to steady state early diagenetic remobilization of fe towards the sediment water interface in contrast significant fe al enrichments occur as a consequence of water column fe mineral formation and deposition either under anoxic conditions or due to input of anoxic hydrothermal fluids into oxic seawater iron speciation data also show no direct correlation with carbonate content and instead three groups can be distinguished based on total fe fe t and organic c contents sediments deposited under oxic water column conditions with fe t 0 5 wt generally plot below the lower fe hr fe t siliciclastic reference threshold 0 38 for distinguishing anoxic environments regardless of carbonate content also consistent with siliciclastic calibrations carbonate rich sediments deposited under anoxic water column conditions tend to have fe hr fe t ratios 0 38 in contrast oxic carbonate rich sediments with low fe t hr fe t ratios suggesting that the use of fe speciation for such samples is not appropriate for evaluating water column redox conditions taken together our data suggest that an fe t content of 0 5 wt rather than carbonate content represents the most suitable basis for identifying whether carbonate rich sediments are appropriate for fe based redox proxy analyses analysis of burial dolostones suggests that the fe speciation proxy may also be compromised by deep burial dolomitization where there has been a source of mobile fe to enrich rocks during recrystallization however pre screening can identify such samples this new assessment expands the utility of fe based redox proxies to also incorporate appropriate carbonate rich rocks provided that care is taken to assess the possible impact of deep burial dolomitization

changes in vp vs with depth implications for appropriate velocity models improved earthquake locations and material properties of the upper crust properties associated with the arrival times of shallow microearthquakes are determined for three tectonically different sites soviet central asia the central united states and southern california simple graphical presentations of the earthquake data including wadati and riznichenko diagrams are used to resolve the trade off in origin time and focal depth estimates of the average half space velocities for p and s waves and of the travel time ratio ts tp are also obtained that are relatively free of any model constraints used to initially locate the earthquake in all cases p and s arrivals exhibit a systematic decrease in ts tp with depth in the upper few kilometers this decrease is significant and matches similar variations observed in situ for the velocity ratio vp vs based on laboratory and theoretical studies such observations are consistent with the closing of saturated microcracks with increasing confining pressure independent determinations of velocity structure and rock properties from both refraction studies and borehole experiments show analogous results by specifying separate velocity models for both p and s waves that reflect this variation rather than assuming a constant value of vp vs we find improved stability in hypocenter determination and increased resolution of shallow seismicity patterns

esr and mass spectrometric uranium series dating studies of a mammoth tooth from stanton harcourt oxfordshire england abstract the age of the channel deposits at stanton harcourt oxfordshire england has been a topic of debate with important implications for british pleistocene stratigraphy recent excavations led by k scott reveal ample evidence for ancient environmental conditions characteristic of an interglacial however the question remains on the assignment of its age at present it is thought to represent an interglacial corresponding to either marine oi stage 7 or 5e in an attempt to constrain the chronology of the site and to assess the techniques reliability we have made electron spin resonance esr measurements on enamel and mass spectrometric u series measurements on both enamel and dentine from a mammoth tooth buried in the channel deposits at stanton harcourt four dentine samples gave u series dates between 65 4 0 4 and 146 5 1 0 ka and two enamel samples between these dentine layers were dated to 53 3 0 2 and 61 1 0 6 ka the corresponding esr age estimates for the enamel samples are 59 6 and 62 4 ka early u uptake eu and 95 11 and 98 7 ka linear u uptake lu the recent u uptake ru dates are 245 38 and 238 31 ka but in light of the u series data we would not expect these to represent realistic age estimates similar esr results were obtained from two other adjacent enamel samples the effect of the large size of the mammoth tooth on the external gamma dose and the internal gamma contribution from the high u content of the dentine are considered while the recent uptake esr dates appear to coincide with oi stage 7 all the early and linear uptake esr and mass spectrometric u series dates are younger than the expected age estimation based on recent geological interpretation and amino acid racemisation measurements 200 ka and optical dating studies 200 450 ka possible causes of the unexpected dating results are discussed we conclude that our mass spectrometric u series and eu and lu esr measurements represent minimum age estimates for the tooth analysed our results seem to suggest that the tooth and hence the channel deposits are at least 147 ka in age i e predating the last interglacial

esr dating in quaternary geology abstract electron spin resonance esr a relatively new dating technique was first suggested by zeller et al 1967 zeller 1968 and levy 1968 it has made substantial progress in frequent applications in the last few years esr dating is based on the direct measurement of the amount of radiation induced paramagnetic electrons trapped in crystal defects these free electrons were generated by alpha beta and gamma radiation of natural radioelements e g u th k and have accumulated in the minerals over geologic time the esr age is obtained by dividing the total amount of accumulated radiation dose archaeological dose ad by the dose per year annual dose this review comprises four major parts the principles of the method the determination of the archaeological dose ad the determination of the annual dose and a compilation of datable materials several questions remain the evaluation of the ad the determination of the annual dose and particularly with respect to the nature and stability of the electron traps used for dating

glacial effects on weathering processes new insights from the elemental and lithium isotopic composition of west greenland rivers greenland is by far the dominant source of glacial runoff to the oceans but the controls on the chemical and isotopic composition of this runoff are poorly known to better constrain glacial effects on weathering processes we have conducted elemental and lithium isotope analyses of glacial and non glacial rivers in gneiss catchments in west greenland the glacial rivers have high total suspended solids 0 5 g l 1 and low total dissolved solids 12 scm 1 relative to the non glacial rivers and they contain a higher proportion of dissolved ca2 and k because of subglacial preferential weathering of trace carbonates and biotite the glacial rivers also have high so42 because of the oxidation of trace sulphides under the ice both glacial and non glacial rivers have high 7li respectively not vert similar 26 and not vert similar 30 relative to the rocks from which the li is derived not vert similar 8 saturation state modelling suggests that this is due to the formation of fe oxyhydroxides in the non glacial rivers with preferential uptake of 6li during inner sphere sorption of li on the fe oxyhydroxide surface glacial rivers however are undersaturated with respect to clay minerals and fe oxyhydroxides nevertheless leaching of suspended sediments indicates that not vert similar 65 of the li in these sediments is associated with fe oxyhydroxide phases and the 7li value of this li is low not vert similar 5 these results suggest that these fe oxyhydroxides formed under the ice as a product of sulphide oxidation with preferential uptake of 6li onto the mineral surface solubilisation of li from these fe oxyhydroxide phases is unlikely to represent a significant flux of li to the oceans moreover because the difference between the 7li values of glacial vs non glacial rivers is small glaciation has not had a significant impact on the li isotopic composition of the riverine flux delivered to the oceans in the past even at the height of the last deglaciation

enhanced chemical weathering triggered an expansion of euxinic seawater in the aftermath of the sturtian glaciation abstract the cryogenian period comprised two episodes of global glaciation sturtian and marinoan glaciations separated by a non glacial interval which was characterized by early radiations of eukaryotic algae and putative metazoans geochemical data indicate that the non glacial interval might be marked by a transient marine oxygenation nevertheless oceanic redox conditions varied both in time and space further the links between non glacial climate and marine redox variations are not well constrained here we present high resolution lithium isotope 7 li fe speciation and trace element mo and u data for clastic sedimentary rocks from the cryogenian interglacial datangpo formation south china in order to track the evolution of continental chemical silicate weathering and driving factors behind marine redox variability during the cryogenian non glacial interval a significantly negative 7 li excursion of 5 is observed in the basal datangpo formation suggesting a dramatic increase in chemical silicate weathering intensity in the aftermath of the sturtian glaciation expansion and contraction of anoxic sulfidic conditions as demonstrated by fe speciation and trace element mo and u data mirror changes in silicate weathering intensity our study provides evidence that greater nutrient and sulfate availability due to high silicate weathering intensity associated with increased exposure of fresh rocks and a warm climate facilitated the spread of euxinic waters over the continental margins of the otherwise ferruginous cryogenian ocean

seismological evidence for magmatic and hydrothermal structure in long valley caldera from local earthquake attenuation and velocity tomography we compare the results of six different tomographic inversions for the three dimensional seismic attenuation and velocity structure in long valley caldera california in order to constrain interpretations on the location and character of magmatic and geothermal structure in the caldera crust p and s wave amplitudes and arrival times obtained in previous studies from seismograms of local earthquakes recorded on vertical and three component seismographis were inverted for q sv 1 q sh 1 q s 1 q p 1 and v p v s in the upper 9 km of teh caldera crust detailed comparisons of the results of the inversions suggest significant locations of high temperatures and perhaps magma and hydrothermal zones in the caldera a region of low q s with locally variable q p and v p v s is imaged in the 7 9 km depth range beneath the resurgent dome overlying and adjacent to this anomaly are significant low q p and low v p v s anomalies as well as smaller zones of low q s and high v p v s together these suggest zones of high temperature magma below and adjacent to zones of supercritical hydrothermal fluids at 4 5 km depth along the southern rim of the caldera just east of mammoth mountain a significant anomaly with relatively low q p and relatively low v p v s is imaged and is interpreted as a supercritical hydrothermal zone poorly resolved relatively low q p and relatively high v p v s are seen at 4 5 km depth beneath the inyo craters suggesting possible high temperatures and perhaps magma because of lack of data in the individual inversions the resultant images have spatially variable error and resolution however by comparing multiple images of different seismic parameters we have improved our ability to determine the significance of an constrain interpretation of seismic structure anomalies

oxygen minimum zone type biogeochemical cycling in the cenomanian turonian proto north atlantic across oceanic anoxic event 2 abstract oceanic anoxic events oaes in earth s history are regarded as analogues for current and future ocean deoxygenation potentially providing information on its pacing and internal dynamics in order to predict the earth system s response to changes in greenhouse gas concentrations and radiative forcing a sound understanding of how biogeochemical cycling differs in modern and ancient marine environments is required here we report proxy records for iron fe sulfur and nitrogen cycling in the tarfaya upwelling system in the cretaceous proto north atlantic before during and after oae2 93 ma we apply a novel quantitative approach to sedimentary fe speciation which takes into account the influence of terrigenous weathering and sedimentation as well as authigenic fe non terrigenous precipitated onsite rain rates on fe based paleo redox proxies generally elevated ratios of reactive fe i e bound to oxide carbonate and sulfide minerals to total fe fehr fet throughout the 5 million year record are attributed to transport limited chemical weathering under greenhouse climate conditions trace metal and nitrogen isotope systematics indicate a step wise transition from oxic to nitrogenous to euxinic conditions over several million years prior to oae2 taking into consideration the low terrigenous sedimentation rates in the tarfaya basin we demonstrate that highly elevated fehr fet from the mid cenomanian through oae2 were generated with a relatively small flux of additional authigenic fe evaluation of mass accumulation rates of reactive fe in conjunction with the extent of pyritization of reactive fe reveals that authigenic fe and sulfide precipitation rates in the tarfaya basin were similar to those in modern upwelling systems because of a smaller seawater nitrate inventory however chemolithoautotrophic sulfide oxidation with nitrate was less efficient in preventing hydrogen sulfide release into the water column as terrigenous weathering and sediment flux determine how much authigenic fe is required to generate an anoxic euxinic or ferruginous proxy signature we emphasize that both have to be taken into account when interpreting fe based paleo redox proxies

the iron paleoredox proxies a guide to the pitfalls problems and proper practice oceanic anoxia including euxinic settings defined by the presence of water column hydrogen sulfide h2s is minor in the ocean today such conditions however were common or even dominant in the past particularly during the precambrian and phanerozoic oceanic anoxic events the latter are associated with massive petroleum and mineral reserves and many of the major extinction events in the paleontological record our ability to recognize ancient oxygen deficiencies relies strongly on paleontological data viewed in combination with geochemical tracers and geochemistry is typically our only window onto ancient marine redox during the precambrian when diagnostic skeletal and behaviorial traces of oxygen dependent animals are mostly missing so far no approach has gained wider acceptance than the iron proxies which rely generally on quantification of the extent to which reactive iron as oxides principally is converted to pyrite the promise of these approaches lies in part with the relative ease of measurement but it is this ease and the corresponding widespread use that has also led to misuses much of the recent confidence in the iron paleoredox proxies lies with sophisticated deconstruction of the reactive fe pool via mineral calibrated wet chemical speciation these validations and calibrations mostly in the modern ocean expose the challenges while at the same time opening other doors of opportunity as the catalog of controlling factors extends beyond water column redox to include sedimentation rate sedimentary fe remobilization signals of oscillatory redox and hydrothermal versus other primary fe inputs to the ocean among other factors also key is a deep understanding of the limitations imposed or at least the due diligence required as linked to mineral transformations during burial and metamorphism this review seeks to highlight many of the key issues including appropriate sample choices as a roadmap for those keen to apply fe proxies in their studies of ancient oceans and their relationships to co evolving life among the critical messages to take away is the value of robust fe based measures of local redox that when combined with elemental mass balances and isotopic proxies dependent on those local conditions can shed light on the global redox state of the oceans through time and related implications for the history of life on earth

grain size control of river suspended sediment geochemistry clues from amazon river depth profiles residual solid products of erosion display a wide range of size density shape mineralogy and chemical composition and are hydrodynamically sorted in large river channels during their transport we characterize the chemical and isotopic variability of river sediments of the amazon basin collected at different water depths as a function of grain size absolute chemical concentrations and sr and nd isotopic ratios greatly varies along channel depth the al si ratio tightly linked to grain size distribution systematically decreases with depth mostly reflecting dilution by quartz minerals a double normalization diagram is proposed to correct from dilution effects elements define fan shaped patterns and can be classified in three different groups with respect to hydrodynamic sorting during transport in the amazon 1 poorly sorted insoluble elements like al fe th and rees 2 well sorted insoluble elements like zr and ti mainly carried by heavy minerals and 3 alkali na to cs and alkali earth elements mg to ba for which a large variety of patterns is observed related for alkali to their variable affinity for phyllosilicates sr isotopes show that the amazon river at the mouth is stratified the madeira and solimoes derived sediments being preferentially transported near the channel surface and at depth respectively the comparison between the solimoes and madeira rivers shows how the interplay between grain sorting weathering and crustal composition controls the composition of the suspended river sediments

development of a sequential extraction procedure for iron implications for iron partitioning in continentally derived particulates abstract the development of a sequential extraction procedure for iron in modern and ancient sediments is presented the scheme recognizes seven operationally derived iron pools 1 carbonate associated fe fe carb including siderite and ankerite 2 easily reducible oxides fe ox1 including ferrihydrite and lepidocrocite 3 reducible oxides fe ox2 including goethite hematite and akaganeite 4 magnetite fe mag 5 poorly reactive sheet silicate fe fe prs 6 pyrite fe fe py and 7 unreactive silicate fe fe u as such this is the first extraction scheme specifically developed to allow the separate identification of magnetite and the first to allow a complete evaluation of fe carbonate phases such as siderite and ankerite the scheme was developed following tests on pure mineral phases to evaluate the minerals solubilized by each technique and to determine optimum extraction times further tests on mixtures of pure minerals and on grain size separated sediments from two major us rivers and two glacial meltwaters validate the specificity of the scheme for different pools of iron minerals and demonstrate a high degree of reproducibility for each analytical stage the data obtained for the riverine and glacial sediments are additionally discussed in relation to the dominant modes of transport of different iron minerals in fine grained continental sediments

assessing the role of climate on uranium and lithium isotope behaviour in rivers draining a basaltic terrain this study presents uranium u and lithium li isotope and major and trace element data for the dissolved load suspended particles and bedload from rivers draining dominantly basaltic catchments on the island of sao miguel in the azores archipelago uranium activity ratios are at secular equilibrium in the bedload but are higher for suspended material suggesting sorption of uranium from the solution onto particle surfaces the 234u 238u of the riverine dissolved phase varies between 1 02 and 1 86 and lies on a mixing trend between the values expected from chemical weathering of basalt high u 234u 238u at secular equilibrium and an endmember with low u and high 234u 238u which probably reflects recoil effects associated with physical weathering and or soil formation lithium isotope ratios are consistently lighter in suspended material than the corresponding bedload suggesting preferential retention of 6li in the suspended load in turn the 7li of the dissolved load is always isotopically heavier ranging from 5 9 to 36 2 although the lightest values are affected by hydrothermal input the lithium isotopic composition of the dissolved load reflects the balance of primary mineral dissolution to secondary mineral formation comparison of the behaviour of u and li isotopes between sao miguel iceland and other basaltic terrains suggests that whilst u isotopes are dominated by weathering regimes dependent on factors such as weathering rates temperature runoff and climate neither weathering intensity nor climate exerts a direct influence on li isotope behaviour rather the formation of secondary minerals which is indirectly controlled by climate weathering primary mineralogy and biology appears to play the dominant role

viscoelastic relaxation and long lasting after slip following the 1997 umbria marche central italy earthquakes summary we combine global positioning system gps measurements with forward modelling of vis coelastic relaxation and after slip to study the post seismic deformation of the 1997 umbria marche central apennines moderate shallow earthquake sequence campaign gps mea surements spanning the time period 1999 2003 are depicting a clear post seismic deformation signal our results favour a normal faulting rupture model where most of the slip is located in the lower part of the seismogenic upper crust consistent with the rupture models obtained from the inversion of strong motion data the preferred rheological model obtained from viscoelastic relaxation modelling consists of an elastic upper crust underlain by a transition zone with a viscosity of 10 18 pa s while the rheology of deeper layers is not relevant for the observed time span shallow fault creep and after slip at the base of the seismogenic upper crust are the first order processes behind the observed post seismic deformation the deep after slip below the fault zone at about 8 km depth acting as a basal shear through localized time dependent deformation identifies a rheological discontinuity decoupling the seismogenic upper crust from the low viscosity transition zone

new perspectives on the li isotopic composition of the upper continental crust and its weathering signature abstract lithium isotopes are increasingly used to trace both present day and past weathering processes at the surface of the earth and could potentially be used to evaluate the average degree of past weathering recorded by the upper continental crust ucc yet the previous estimate of average 7li of the ucc has a rather large uncertainty hindering the use of li isotopes for this purpose new 7li for desert and periglacial loess deposits windblown dust from several parts of the world europe argentina china and tajikistan demonstrate that the former are more homogeneous than the latter and may therefore serve as excellent proxies of the average composition of large tracts of the ucc the li isotopic compositions and concentrations of desert loess samples are controlled by eolian sorting that can be quantified by a binary mixing between a weathered fine grained end member dominated by phyllosilicates and having low 7li and an unweathered coarse grained end member that is a mixture of quartz and plagioclase having higher 7li we use correlations between insoluble elements ree nd hf and fe2o3 sio2 li concentrations henceforth referred as li and 7li to estimate a new more precise average li isotopic composition and concentration for the ucc li 30 5 3 6 2 ppm and li 7 0 6 0 6 2 the 7li for desert loess deposits is anti correlated with the chemical index of alteration cia using this relationship along with our average 7li we infer that 1 the present day cia of the average ucc is 61 2 4 2 higher than the common reference value of 53 and 2 the average proportion of chemically weathered components is as high as 37 10 17 2 at the surface of the earth

lithium isotopes in global mid ocean ridge basalts abstract the lithium isotope compositions of 30 well characterized samples of glassy lavas from the three major mid ocean ridge segments of the world spanning a wide range in radiogenic isotope and elemental content and sea floor physical parameters have been measured the overall data set shows a significant range in 7li 1 6 to 5 6 with no global correlation between li isotopes and other geochemical or tectonic parameters the samples with the greatest lithophile element depletion n morb k2o tio2

li and δ7li in mudrocks from the british caledonides metamorphism and source influences mudrocks from three lower paleozoic basins in the british caledonides southern lake district northern lake district and southern uplands were investigated to determine the influence of sub greenschist facies metamorphism on li and the factors that control li in fine grained terrigenous sedimentary rocks metamorphic grade as determined by ki kubler index does not correlate with li content li and 7li indicating that sub greenschist facies metamorphism has negligible effect on li in these rocks collectively the data for all three basins show a negative correlation between li and 7li and a positive correlation between li and the chemical index of alteration cia suggesting that provenance exerts the greatest control on li in mudrocks samples from the northern lake district which were deposited in an extensional basin have homogeneous ree patterns similar to shale composites paas the highest cia th u and li and the lowest 7li and end consistent with their derivation from a highly weathered ancient continental source by contrast mudrocks from the southern uplands range to the lowest cia th u and li and have the highest 7li and end these samples were deposited in a forearc basin on the southern margin of the laurentian craton and contain volcanic detritus their ree patterns are the most variable ranging from average shale like patterns to less lree enriched patterns the compositional heterogeneity within the southern uplands mudrocks is consistent with a mixed provenance that includes juvenile crustal materials lower li end and th u higher 7li likely derived from the arc as well as more highly weathered continental detritus mudrocks from the southern lake district were deposited in a foreland basin and exhibit geochemical characteristics intermediate between the northern lake district and the southern uplands mudrocks indicating their derivation from a mixed source our study shows that li concentrations and 7li can provide additional information on the degree of weathering of the provenance of mudrocks

crustal structure and seismotectonics of central sicily southern italy new constraints from instrumental seismicity summary in this paper we propose a new model of the crustal structure and seismotectonics for central sicily southern italy through the analysis of the depth distribution and kinematics of the instrumental seismicity occurring during the period from 1983 to 2010 and its comparison with individual geological structures that may be active in the area the analysed data set consists of 392 earthquakes with local magnitudes ranging from 1 0 to 4 7 we defined a new detailed 1 d velocity model to relocate the earthquakes that occurred in central sicily and we calculated a moho depth of 37 km and a mean vp vs ratio of 1 73 the relocated seismic events are clustered mainly in the area north of caltanissetta e g mainland sicily and in the northeastern sector madonie mountains of the study area only minor and greatly dispersed seismicity is located in the western sector near belice and along the southern coast between gela and sciacca the relocated hypocentral distribution depicts a bimodal pattern 50 per cent of the events occur within the upper crust at depths less than 16 km 40 per cent of the events occur within the middle and depth crust at depths between 16 and 32 km and the remaining 10 per cent occur at subcrustal depths the energy release pattern shows a similar depth distribution on the basis of the kinematic analysis of 38 newly computed focal plane solutions two major geographically distinct seismotectonic domains are distinguished the madonie mountain domain with prevalent extensional and extensional oblique kinematics associated with upper crust late pliocene quaternary faulting and the mainland sicily domain with prevalent compressional and compressional oblique kinematics associated with thrust faulting at mid to deep crust depth along the north dipping sicilian basal thrust sbt the stress inversion of the mainland sicily focal solutions integrated with neighbouring mechanisms available in the literature highlights a regional homogeneous compressional tensor with a subhorizontal nnw sse striking 1 axis in addition on the basis of geodetic data the mainland sicily domain may be attributed to the sse ward thrusting of the mainland sicily block along the sbt plane seismogenic shearing along the sbt at mid crustal depths was responsible for the unexpected belice 1968 earthquake mw 6 1 with evident implications in terms of hazard assessment

problems associated with reworked teeth in electron spin resonance esr dating a single radiation sensitive esr signal at g 2 0018 occurs in well crystallized fossil tooth enamel but not in modern teeth in dating fossil teeth the equivalent radiation dose a needed to produce the observed esr signal is the integral with respect to time of the natural environmental dose rate experienced by the tooth after its deposition regardless of the uranium u uptake history assumed a reliable age estimate requires a good estimate for the external dose rate during the tooth s history if teeth in a stratigraphic unit have been reworked from older units or are post depositional intrusions external dose rates measured in situ do not accurately reflect those experienced by the tooth for teeth from a single unit significant variations in the calculated ages a s enamel or dentine u concentrations all indicate mixed sample collections where enough subsamples can be collected from single teeth isochron analyses negate the need for a separate external dose measurement while calculating the sample age and the external dose rate experienced by the tooth failing that modelling the sedimentary dose rates using time averaged total external dose calculations becomes necessary these principles are illustrated using teeth from the australopithecine sites sterkfontein and swartkrans south africa

highly dynamic marine redox state through the cambrian explosion highlighted by authigenic δ238u records abstract the history of oceanic oxygenation from the late neoproterozoic to the early cambrian is currently debated making it difficult to gauge whether and to what extent environmental triggers played a role in shaping the trajectory of metazoan diversification uranium isotope 238 u records from carbonates have recently been used to argue for significant swings in the global marine redox state from the late neoproterozoic to the early cambrian however geochemical signatures in carbonates the u isotope archive most commonly employed to argue for redox shifts are susceptible to diagenetic alteration and may have variable offsets from seawater values therefore there is an impetus to reconstruct seawater u isotopic evolution using another sedimentary archive in order to verify that these excursions can indeed be linked to global shifts in marine redox landscape here we report new u isotope data from two fine grained siliciclastic upper ediacaran to lower cambrian ca 551 515 ma successions in south china we find large 238 u swings between 0 63 and 0 39 for calculated values of authigenic u in the siliciclastic rocks consistent with correlative records from the carbonates the replication of these patterns in both carbonate and siliciclastic units provides confirmatory evidence that the early cambrian seawater was characterized by highly variable u isotope compositions these new 238 u data also provide higher resolution records of global oceanic redox conditions during cambrian age 3 coeval with a critical interval of the cambrian explosion these 238 u data bolster the case that the ediacaran cambrian transition experienced massive swings in marine redox state providing a dynamic environmental backdrop for and potentially even a key driver of the emergence and radiation of metazoans

proterozoic ocean redox and biogeochemical stasis the partial pressure of oxygen in earth s atmosphere has increased dramatically through time and this increase is thought to have occurred in two rapid steps at both ends of the proterozoic eon 2 5 0 543 ga however the trajectory and mechanisms of earth s oxygenation are still poorly constrained and little is known regarding attendant changes in ocean ventilation and seafloor redox we have a particularly poor understanding of ocean chemistry during the mid proterozoic 1 8 0 8 ga given the coupling between redox sensitive trace element cycles and planktonic productivity various models for mid proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients with potential ecological constraints on emerging eukaryotic life here we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates we find that the metal enrichment record implies a proterozoic deep ocean characterized by pervasive anoxia relative to the phanerozoic at least 30 40 of modern seafloor area but a relatively small extent of euxinic anoxic and sulfidic seafloor less than 1 10 of modern seafloor area our model suggests that the oceanic mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of mo and chromium enrichments through time is consistent with the possibility of a mo n colimited marine biosphere during many periods of earth s history

seismic velocity variations along the rupture zone of the 1989 loma prieta earthquake california 1 we revisit the rupture zone of the 1989 mw6 9 loma prieta earthquake central california by developing high resolution three dimensional 3 d vp and vp vs models we apply the simul2000 inversion method and algorithm to a set of composite events which have greater number of picks per event and reduced random picking errors compared with traditional master events our final p wave velocity model generally agrees with previous studies showing a high velocity body of above 6 7 km s in the southeast rupture zone of the main shock the 3 dvp vs model however has different features with low vp vs in the upper crust and high vp vs anomalies in deeper layers of the rupture zone we interpret the low vp vs at shallow depths to be granitic rocks whereas at greater depths the areas of higher vp vs around 1 725 1 75 presumably are mafic rocks the resulting 3 d velocity model was used to improve absolute locations for all local events between 1984 and 2010 in our study area we then applied a similar event cluster analysis waveform cross correlation and differential time relocation methods to improve relative event location accuracy over 88 of the seismicity falls into similar event clusters a dramatic sharpening of seismicity patterns is obtained after using these methods the medians of the relative location uncertainties calculated by using the bootstrap approach are 5 m for horizontal and 8 m for vertical differential times from cross correlation are used to estimatein situnear sourcevp vsratio within each event cluster the high resolutionvp vs method confirms the trend of the velocity variations from the tomographic results although absolute values are slightly different

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

three dimensional p wave velocity structure of mt etna italy the three dimensional p wave velocity structure of mt etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs results show a near vertical low velocity zone that extends from beneath the central craters to a depth of 10 km this low velocity region is coincident with a band of steeply dipping seismicity suggesting a magmatic conduit that feeds the summit eruptions the most prominent structure is an approximately 8 km diameter high velocity body located between 2 and 12 km depth below the southeast flank of the volcano this high velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting

how tillite weathering during the snowball earth aftermath induced cap carbonate deposition the development and aftermath of a snowball earth during precambrian time still raise questions particularly the process involved in the deposition of the associated cap carbonates and the time required for the earth to return to more stable and less extreme climatic conditions we present numerical simulations modeling the chemical weathering of regolith exposed to a co 2 rich atmosphere after deglaciation we consider the effects of an early cation proton exchange reaction that promotes fast initial dissolution of the regolith a reaction often omitted in the modeling approach but one that becomes particularly important under acidic conditions and in environments where glacial erosion can substantially refresh the rock surfaces calculations show that this dissolution step may contribute significantly to the riverine ionic input and may promote the deposition of thick cap carbonates over a short period of time the long term weathering of the regolith becomes predominant representing an efficient way of removing atmospheric co 2 over periods ranging from tens to hundreds of thousands of years depending on the grain size of the regolith material

esr dating of tooth enamel comparison with 230th234u speleothem dates at la chaise de vouthon charente france abstract one way to assess a new dating method s reliability is by comparing its results with those from well established independent techniques a controlled test of the electron spin resonance esr dating method as it is currently being applied to teeth was attempted for the time range 100 250 ka beyond that of 14 c at the archaeological site of la chaise de vouthon charente france although absent in modern enamel a single esr signal with g 2 0018 in fossil tooth enamel hydroxyapatite increases in amplitude with increasing irradiation doses esr ages are derived from the ratio of the ad the radiation dose needed to produce the observed esr signal relative to the natural environmental dose rate ed experienced by the tooth after deposition since the age depends on the uranium u uptake history assumed three ages are calculated assuming 1 early u uptake eu 2 continuous linear uptake lu 3 recent uptake ru generally the lu age agrees best with known ages determined by other methods although the ru model is better for some teeth esr dating assumes that the fossil has not suffered recrystallization or significant diagenetic alteration in the preliminary test three teeth were dated in bourgeois delaunay a bovid molar associated with palaeolithic artefacts was collected from layers dated at 101 12 to 114 7 ka by 230 th 234 u dating of the over and underlying stalagmitic floors from suard two equus teeth were collected from beneath a stalagmitic floor dating 112 12 ka esr dating teeth significantly underestimated the true age for the teeth the mean esr ages range from 37 to 94 ka with standard errors of 2 6 ka and good replicability although more teeth at la chaise need to be tested to ascertain that the underestimation does not result from random variation commonly seen among teeth within one unit the consistent underestimation suggests a fault in one of the assumptions underlying the dating method the most obvious source of error lies in the difficulty in modelling the external dose only u leaching not incorrectly modelled u uptake would cause the underestimation diagenetic alteration may also cause anomalous fading thermal instability variation in k or esr signal suppression more study into the effects of diagenesis alteration on enamel esr signals is needed as is a reevaluation of the mean signal life and efficiency for several more enamel samples

redox condition in the nanhua basin during the waning of the sturtian glaciation a chromium isotope perspective abstract the neoproterozoic oxygenation event noe is often considered to be synchronously and possibly causally associated with the cryogenian glaciations reconstructing early cryogenian redox conditions is therefore essential for understanding the onset of the noe we analyzed cr isotope compositions 53cr as well as major and rare earth element ree concentrations of the banded iron formations bifs in the basal fulu formation of the xiajiajiang section nanhua basin which are thought to have been deposited during the waning stage of the sturtian glaciation strongly positively fractionated authigenic 53cr values were obtained after detrital correction ranging from 0 64 to 1 22 and averaging at 0 91 0 40 2 n 10 or after detrital evaluation 0 71 this suggests extensive oxidative cr cycling occurred at the earth s surface and implies that the po2 was probably higher than 1 pal during this period the lack of ce anomalies 0 90

uranium isotope evidence for limited euxinia in mid proterozoic oceans abstract reconstructing earth s oxygenation history is key to deciphering environmental controls on early biospheric evolution during the mid proterozoic eon low but potentially variable atmospheric po2 led to highly heterogeneous marine redox conditions with most studies indicating a relatively shallow depth of oxygen penetration the relative proportion of oxic anoxic and iron rich ferruginous and anoxic and sulfide rich euxinic conditions on the global seafloor is difficult to quantify however due to a general reliance on local redox proxies applied to the temporally discontinuous black shale record it is particularly important to constrain the global prevalence of euxinic bottom waters because sulfide toxicity has been implicated as a primary constraint on evolution in mid proterozoic oceans and limits the solubility of bioessential trace metals such as copper zinc and molybdenum here we present a suite of new uranium u isotope data from marine carbonate rocks that span the entire mid proterozoic interval 1 8 to 0 8 ga u isotopes in well preserved carbonate rocks represent a powerful new proxy that can be used to quantitatively constrain the global extent of marine euxinia the median 238 u value for mid proterozoic carbonate samples is 0 43 which is lower than the median value for modern post depositional carbonate sediments from the bahamas yet significantly higher than carbonate 238 u values recorded during other times of expanded anoxia in earth history such as during the end permian mass extinction when paired with a three sink isotope mass balance model our data indicate that no more than 7 of the global seafloor was euxinic during the mid proterozoic eon although transient pulses of expanded euxinia are recorded although these results challenge early expectations of a sulfide rich mid proterozoic ocean they are consistent with more recent inferences from the black shale trace metal record evidence therefore indicates that euxinic bottom waters were relatively limited in their spatial extent in the mid proterozoic oceans

a 300 600 ka esr u series chronology of acheulian sites in western europe for a long time the establishment of the chronology of acheulian settlements in western europe was restrained by the lack of reliable dating methods during the middle pleistocene the archaeological sites in this area are generally associated with fluvio lacustrine and karstic contexts the main geochronological methods e g k ar ar ar u series osl and tl could not be applied because of a lack of suitable material for dating or the expected ages were beyond the upper limit of the dating technique for several years the combination of esr and u series data has allowed the direct dating of palaeontological remains from the entire middle pleistocene period combined esr u series dating was applied to several major acheulian sites in spain italy and france this paper presents the dating results their implications for the chronology of the acheulian in western europe as well as the methodological limits of the esr u series dating method caused by the effect of weathering on the uranium uptake into the teeth

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

continental flood basalt weathering as a trigger for neoproterozoic snowball earth abstract atmospheric co2 levels and global climate are regulated on geological timescales by the silicate weathering feedback however this thermostat has failed multiple times in earth s history most spectacularly during the cryogenian c 720 635 ma snowball earth episodes the unique middle neoproterozoic paleogeography of a rifting low latitude supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo under these primed conditions the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios 13 c of neoproterozoic seawater due to their elevated p contents in order to test these hypotheses we have compiled new and previously published neoproterozoic nd isotope data from mudstones in northern rodinia north america australia svalbard and south china and sr isotope data from carbonate rocks the nd isotope data are used to model the mafic detrital input into sedimentary basins in northern rodinia the results reveal a dominant contribution from continental flood basalt weathering during the ca 130 m y preceding the onset of cryogenian glaciation followed by a precipitous decline afterwards these data are mirrored by the sr isotope record which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early middle neoproterozoic ocean including a pulse of unradiogenic sr input into the oceans just prior to the onset of cyrogenian glaciation hence our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average 13 c of seawater in the neoproterozoic and to the initiation of the first sturtian snowball earth

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

behaviour of lithium and its isotopes during weathering in the mackenzie basin canada we report li isotopic compositions for river waters and suspended sediments of about 40 rivers sampled within the mackenzie river basin in northwestern canada the aim of this study is to characterize the behaviour of li and its isotopes during weathering at the scale of a large mixed lithology basin the mackenzie river waters display systematically heavier li isotopic compositions relative to source rocks and suspended sediments the range in delta li 7 is larger in dissolved load from 9 3 parts per thousand to 29 0 parts per thousand compared to suspended sediments from 1 7 parts per thousand to 3 2 parts per thousand which are not significantly different from delta li 7 values in bedrocks our study shows that dissolved li is essentially derived from the weathering of silicates and that its isotopic composition in the dissolved load is inversely correlated with its relative mobility when compared to na the highest enrichment of li 7 in the dissolved load is reported when li is not or poorly incorporated in secondary phases after its release into solution by mineral dissolution this counterintuitive observation is interpreted by the mixing of water types derived from two different weathering regimes producing different li isotopic compositions within the mackenzie river basin the incipient weathering regime characterizing the rocky mountains and the shield areas produces li 7 enrichment in the fluid phase that is most simply explained by the precipitation of oxyhydroxide phases fractionating li isotopes the second weathering regime is found in the lowland area and produces the lower delta li 7 waters but still enriched in li 7 compared to bedrocks and the most li depleted waters compared to na fractionation factors suggest that the incorporation of li in clay minerals is the mechanism that explains the isotopic composition of the lowland rivers the correlation of boron and lithium concentrations found in the dissolved load of the mackenzie rivers suggests that precipitation of clay minerals is favoured by the relatively high residence time of water in groundwater in the shield and rocky mountains li isotopes suggest that clay minerals are not forming and that secondary minerals with stronger affinity for li 7 appear although the weathering mechanisms operating in the mackenzie basin need to be characterized more precisely the li isotope data reported here clearly show the control of li isotopes by the weathering intensity the spatial diversity of weathering regimes resulting from a complex combination of factors such as topography geology climate and hydrology explains in fine the spatial distribution of li isotopic ratios in the large drainage basin of the mackenzie river there is no simple relationship between li isotopic composition and chemical denudation fluxes in the mackenzie river basin

upper crust tomographic structure of the central apennines italy from local earthquakes abstract we derived a three dimensional p and s waves velocity model of the first 9 km of crust in the central apennine from local earthquakes the data set used for the tomographic inversion was recorded from three component regional and local networks which operated in the region from 1979 to 1998 and consists of 984 earthquakes for these earthquakes we have at least eight phases a gap smaller than 200 and a total rms residual smaller than 0 6 s giving a total of 13190 p and 10257 s phases first arrivals the inversion is performed using the simulps12 code this technique iterates the estimated velocity model parameters defined at the nodes of a grid relocating the earthquakes with an approximate 3 d ray tracing a large positive p and s wave velocity anomaly is observed in correspondence to the main seismogenetic volume of the central apennines a synthetic test demonstrates that this anomaly is not artificially produced by the substantially higher density of earthquakes within the seismic velocity anomaly this anomaly corresponds to the carbonatic rocks that form the core of the fold and thrust central apennines belt these rocks are underlain by ductile evaporite formations which were justaposed during the tectonic evolution of the belt we suggest that the evaporite layers effectively decouple the upper crustal seismogenetic volume from the middle and lower crust we conclude that the accumulation of seismic energy could be induced by gravitational tectonic processes explaining the fact that most of the seismicity is confined above the evaporites

esr dating of pleistocene fossil teeth from alberta and saskatchewan teeth collected from pleistocene surficial sediments in southeastern alberta and western saskatchewan have been dated by electron spin resonance esr the dates generally agree with the previously

cryogenian aspidella from northwestern canada abstract the ediacaran period saw the appearance of the first widespread ecosystems dominated by complex multicellular forms with the earliest examples inhabiting deep waters below the photic zone contrary to expectation the first appearance of large members of the ediacara biota is sudden and no definitive precursors have been described from earlier neoproterozoic rocks this sudden appearance has long been an enigma cryogenian fossils from deep water deposits immediately pre dating marinoan glacial deposits within the mackenzie mountains nw canada document the earliest stages of the growth of subphotic benthic communities among the previously described twitya discs from this locality are at least two examples of the ediacaran form taxon aspidella billings 1872 these fossils represent a nearly 80 ma range extension of aspidella and possible forerunners of the benthic communities of the ediacara biota

lithium isotope evidence for enhanced weathering during oceanic anoxic event 2 the ocean anoxic event 2 oae2 about 93 5 million years ago was marked by high atmospheric co2 concentration rapid global warming and marine anoxia and euxinia the event lasted for about 440 000 years and led to habitat loss and mass extinction the marine anoxia is thought to be linked to enhanced biological productivity but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery here we use lithium isotope measurements from carbonates spanning the interval including oae2 to assess the role of silicate weathering we find the lightest values of the li isotope ratio 7li during oae2 indicating high levels of weathering and therefore atmospheric co2 removal which we attribute to an enhanced hydrological cycle we use a geochemical model to simulate the evolution of 7li and the ca sr and os isotope tracers our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric co2 concentrations and rapid global warming which initiated oae2 the simulated warming was accompanied by a roughly 200 000 year pulse of accelerated weathering of mafic silicate rocks which removed co2 from the atmosphere the weathering also delivered nutrients to the oceans that stimulated primary productivity we suggest that this process together with the burial of organic carbon allowed the rapid recovery and stabilization from the greenhouse state

uranium isotope evidence for temporary ocean oxygenation in the aftermath of the sturtian snowball earth abstract the appearance and radiation of animals are commonly attributed to neoproterozoic oceanic oxygenation yet independent geochemical evidence for such an event remains equivocal strata deposited between the sturtian and marinoan snowball earth glaciations 660 to 640 ma contain the earliest animal biomarkers and possible body fossils to quantify the extent of seafloor oxygenation during this critical interval we present uranium isotope ratios 238u 235u denoted as 238 u from limestone of the taishir formation in mongolia through two stratigraphic sections that are separated by 75 km within the same depositional basin above the sturtian glacial deposits through 150 m of stratigraphy 238 u compositions have a mean value of 0 47 this interval is followed by a 0 3 decrease in 238 u coincident with the taishir negative carbon isotope excursion thereafter 238 u values remain relatively low until the erosional unconformity at the base of the marinoan glacial deposits using a box model we show that the best explanation for the higher 238 u values of the post sturtian limestones is extensive but temporary oxygenation of the seafloor and is inconsistent with a scenario involving only increased delivery of uranium to the oceans due to post snowball weathering the decline in 238 u in overlying strata coincident with the taishir negative 13 c excursion indicates a subsequent decrease in seafloor oxygenation the u isotopic data combined with modeling results challenge the notion of a simple unidirectional oxygenation of neoproterozoic oceans

a global transition to ferruginous conditions in the early neoproterozoic oceans eukaryotic life expanded during the proterozoic eon1 2 5 to 0 542 billion years ago against a background of fluctuating ocean chemistry2 3 4 after about 1 8 billion years ago the global ocean is thought to have been characterized by oxygenated surface waters with anoxic and sulphidic waters in middle depths along productive continental margins and anoxic and iron containing ferruginous deeper waters5 6 7 the spatial extent of sulphidic waters probably varied through time5 6 but this surface to deep redox structure is suggested to have persisted until the first neoproterozoic glaciation about 717 million years ago8 9 10 11 here we report an analysis of ocean redox conditions throughout the proterozoic using new and existing iron speciation and sulphur isotope data from multiple cores and outcrops we find a global transition from sulphidic to ferruginous mid depth waters in the earliest neoproterozoic coincident with the amalgamation of the supercontinent rodinia at low latitudes we suggest that ferruginous conditions were initiated by an increase in the oceanic influx of highly reactive iron relative to sulphate driven by a change in weathering regime and the uptake of sulphate by extensive continental evaporites on rodinia we propose that this transition essentially detoxified ocean margin settings allowing for expanded opportunities for eukaryote diversification following a prolonged evolutionary stasis before one billion years ago

absolute dating of hominids and palaeolithic artifacts of the cave of la chaise de vouthon charente france abstract two adjacent chambers of the cave of la chaise grotte de bourgeois delaunay b d and grotte suard have been studied both were partly filled with detrital sediments containing lower and middle palaeolithic artifacts and skeletal remains of pre neanderthalian hominids layers of stalagmitic calcite occur interstratified in the sediments of both chambers dates obtained by 230th 234u ratios have provided a time scale for hominid and cultural evolution as represented in this cave in b d the lower travertine rests on a breccia containing cranial remains of juvenile neanderthals the base of the travertine dates to 151 15 ky ky 1000 years bp the top of the travertine yields a date of 112 5 ky the travertine contains pollen of an interglacial flora overlying detrital sediments 1 2 m in thickness contain artifacts transitional from acheulian to mousterian industries they are capped by a travertine layer 7 whose base is dated at 100 6 ky and which is capped by stalagmites ranging in age down to 58 7 ky overlying the travertine is sediment containing first mousterian and then aurignacian artifacts near the base of the sediments filling grotte suard is a stalagmite layer dated to 249 30 ky it contains interglacial pollen and presumably dates to the beginning of the isotope stage 7 interglacial neanderthaloid hominid teeth and cranial fragments are found scattered through the overlying sediments up to a capping stalagmitic layer whose base is dated at 101 7 ky the best described hominids from suard are from a section that was probably overlying the capping stalagmite the capping stalagmite is temporally correlated with layer 7 of b d

stratified oceans and oxygenation of the late precambrian environment a post glacial geochemical record from the neoproterozoic of w mongolia the late neoproterozoic 750 545 ma was a time of revolutionary environmental change recurrent glaciation and tectonic upheaval which culminated in the evolution of metazoans and animal biomineralization geochemical data are presented for a post glacial 700 ma limestone succession from w mongolia 87 sr 86 sr is used to constrain the timing of early diagenetic exchange stratigraphic trends to high d 13 c carb and d 13 c org mirror sea level fluctuations which we argue is consistent with the hypothesis that late precambrian ocean chemistry was controlled by vertical stratification repeated establishment of stratification 700 545 ma would have led to greater oxygen availability in the surface environment a causal link between this oxygenation and the further evolution of animals is proposed

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

lithium and lithium isotope profiles through the upper oceanic crust a study of seawater basalt exchange at odp sites 504b and 896a abstract ocean drilling program odp hole 504b near the costa rica rift is the deepest hole drilled in the ocean crust penetrating a volcanic section a transition zone and a sheeted dike complex the distribution of li and its isotopes through this 1 8 km section of oceanic crust reflects the varying conditions of seawater alteration with depth the upper volcanic rocks altered at low temperatures are enriched in li 5 6 27 3 ppm and have heavier isotopic compositions 7li 6 6 20 8 relative to fresh mid ocean ridge basalt morb due to uptake of seawater li into alteration clays the li content and isotopic compositions of the deeper volcanic rocks are similar to morb reflecting restricted seawater circulation in this section the transition zone is a region of mixing of seawater with upwelling hydrothermal fluids and sulfide mineralization li enrichment in this zone is accompanied by relatively light isotopic compositions 0 8 2 1 which signify influence of basalt derived li during mineralization and alteration li decreases with depth to 0 6 ppm in the sheeted dike complex as a result of increasing hydrothermal extraction in the high temperature reaction zone rocks in the dike complex have variable isotopic values that range from 1 7 to 7 9 depending on the extent of hydrothermal recrystallization and off axis low temperature alteration hydrothermally altered rocks are isotopically light because 6li is preferentially retained in greenschist and amphibolite facies minerals the 7li values of the highly altered rocks of the dike complex are complementary to those of high temperature mid ocean ridge vent fluids and compatible to equilibrium control by the alteration mineral assemblage the inventory of li in basement rocks permits a reevaluation of the role of oceanic crust in the budget of li in the ocean on balance the upper 1 8 km of oceanic crusts remains a sink for oceanic li the observations at 504b and an estimated flux from the underlying 0 5 km of gabbro suggest that the global hydrothermal flux is at most 8 109 mol yr compatible with geophysical thermal models this work defines the distribution of li and its isotopes in the upper ocean crust and provides a basis to interpret the contribution of subducted lithosphere to arc magmas and cycling of crustal material in the deep mantle

lithium isotope systematics in a forested granitic catchment strengbach vosges mountains france abstract over the last decade it has become apparent that li isotopes may be a good proxy to trace silicate weathering however the exact mechanisms which drive the behaviour of li isotopes in surface environments are not totally understood and there is a need to better calibrate and characterize this proxy in this study we analysed the li concentrations and isotopic compositions in the various surface reservoirs soils rocks waters and plants of a small forested granitic catchment located in the vosges mountains strengbach catchment france ohge http ohge u strasbg fr li fluxes were calculated in both soil profiles and at the basin scale and it was found that even in this forested basin atmospheric inputs and litter fall represented a minor flux compared to input derived from the weathering of rocks and soil minerals which together represent a minimum of 70 of dissolved li li isotope ratios in soil pore waters show large depth dependent variations average dissolved 7 li decreases from 1 1 to 14 4 between 0 and 30 cm but is 30 7 at 60 cm this range of li isotopic compositions is very large and it encompasses almost the entire range of terrestrial li isotope compositions that have been previously reported we interpret these variations to result from both the dissolution and precipitation of secondary phases large isotopic variations were also measured in the springs and stream waters with 7 li varying from 5 3 to 19 6 7 li increases from the top to the bottom of the basin and also covaries with discharge at the outlet these variations are interpreted to reflect isotopic fractionations occurring during secondary phase precipitation along the water pathway through the rocks we suggest that the dissolved 7 li increases with increasing residence time of waters through the rocks and so with increasing time of interaction between waters and solids a dissolution precipitation model was used to fit the dissolved li isotopic compositions it was found that the isotopic compositions of springs and stream waters are explicable by an isotopic fractionation of 5 to 14 best fit 10 8 in agreement with li incorporation into clay in soil solutions it was found that isotopic fractionation during secondary precipitation is larger at least 23 suggesting a major role for different secondary phases such as iron oxides that maybe incorporate li with a higher isotope fractionation

detailed mass spectrometric u series analyses of two teeth from the archaeological site of pech de l aze ii implications for uranium migration and dating abstract we report th u ages obtained by thermal ionization mass spectrometry of cross sections of two teeth from the archaeological site of pech de l aze ii the aim of this study is to reconstruct the pathways and time dependency of uranium uptake into different constituents of the two teeth a previous esr dating study of the two teeth yielded age estimates in the range of about 130 000 to 200 000 years which was in agreement with the geological assignment of riss for layers from which the specimens were recovered the closed system u series ages of all analyses range from 48 to 137 ka thus yielding age estimates which are between 30 and 90 ka too young the apparent closed system u series ages of the dentine and cement fractions at the top of the teeth are the oldest becoming gradually younger towards the interior of the two teeth the difference between apparent u series ages of dentine at the outer and inner parts of the two teeth is about 35 ka the enamel sections show the same patterns in u concentration and progression of apparent th u ages as the adjacent dentine samples but with generally younger ages our results indicate that uranium migrates both from the top and the base into the dentine of the teeth and from there into the adjacent enamel depending on the position of the sample significant uranium uptake appears to have taken place over many tens of thousands of years modelling the u uptake histories using a parametric model shows that for the cement and dentine components uptake is intermediate between linear uptake lu and early uptake eu closed system the enamel although often assumed to approximate more closely a closed system shows evidence of more recent u uptake these results also imply that it is not possible to use a simple single parameter u uptake model for all components of a given tooth either for u series or esr dating

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

the effect of hydrothermal spring weathering processes and primary productivity on lithium isotopes lake myvatn iceland lithium isotopes are rapidly becoming one of the most useful tracers of silicate weathering processes but little is known on their behaviour in groundwaters and hydrothermal springs and how these sources might influence the weathering signal in surface waters this study presents lithium isotope compositions 7li for cold groundwaters 3 7 c and hydrothermal springs that were at geothermal temperatures 200 300 c but have cooled during transport 17 44 c both represent an important source of water and nutrients for lake myvatn iceland we also present a time series from the laxa river which is the single outflow from the lake the 7li values in the input springs to lake myvatn are highly variable 5 27 and correlate inversely with temperature and total dissolved solids these co variations imply that even in such waters the processes controlling 7li variations during weathering still operate that is the ratio of primary rock dissolution to secondary mineral formation where the latter preferentially incorporates 6li with a temperature dependent fractionation factor in high temperature geothermal waters 300 c secondary mineral formation is inhibited and has a low fractionation factor leading to little 7li fractionation even in waters that have cooled considerably over several months from their geothermal temperatures fractionation is still low and 7li values are similar to those reported from waters measured at 350 c in contrast cooler groundwaters promote relatively high proportions of clay formation which scavenge dissolved solids including 6li the time series on the laxa river the single outflow from lake myvatn shows little 7li variation with time over the 12 month sampling period 17 21 demonstrating that in contrast to tracers such as si isotopes li isotopes are unaffected by the significant seasonal phytoplankton blooms that occur in the lake thus these results clearly illustrate that li isotopes are ideally suited to constrain silicate weathering processes because fractionation by secondary mineral formation operates even when groundwater and hydrothermal inputs are significant and because li isotopes are demonstrably unaffected by phytoplankton or plant growth

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

a three dimensional crustal seismic velocity model for southern california from a composite event method we present a new crustal seismic velocity model for southern california derived from p and s arrival times from local earthquakes and explosions to reduce the volume of data and ensure a more uniform source distribution we compute composite event picks for 2597 distributed master events that include pick information for other events within spheres of 2 km radius the approach reduces random picking error and maximizes the number of s wave picks to constrain absolute event locations and shallow velocity structure we also use times from controlled sources including both refraction shots and quarries we implement the simulps tomography algorithm to obtain three dimensional 3 d v p and v p v s structure and hypocenter locations of the composite events our new velocity model in general agrees with previous studies resolving low velocity features at shallow depths in the basins and some high velocity features in the midcrust using our velocity model and 3 d ray tracing we relocate about 450 000 earthquakes from 1981 to 2005 we observe a weak correlation between seismic velocities and earthquake occurrence with shallow earthquakes mostly occurring in high p velocity regions and midcrustal earthquakes occurring in low p velocity regions in addition most seismicity occurs in regions with relatively low v p v s ratios although aftershock sequences following large earthquakes are often an exception to this pattern

esr dating of tooth enamel from karain excavation antalya turkey abstract samples of fossil tooth enamesl taken from different depths of karain cave antalya turkey were studied by the esr method the accumulated doses d e s of the samples were determined using the paramagnetic center at g 2 0020 0 0003 by means of three different microwave power conditions it is found that the dating signal at g 2 0020 h pp 0 34 mt is disturbed significantly by the isotropic signal at g 2 0007 0 0003 at high microwave power the lifetime of this signal is significantly smaller than the lifetime of the dating signal however the statistical uncertainty caused by different microwave powers is still within the total uncertainty in the age determination of the tooth enamels under investigation the esr ages of the samples were calculated using early uranium eu and linear uranium lu uptake models the ages due to eu and lu models are in agreement within an error of 10 due to the low uranium content of the samples

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

carbonate porosity from s p traveltime ratios a twenty mile s wave seismic line was acquired on the northeastern shelf of the anadarko basin by the 1977 1978 conoco p wave s wave group shoot the resolution of the s wave section is at least as good as the resolution of a coincident p wave section acquired in 1975 the top and bottom of a collection of paleozoic carbonates called the hunton group can be identified on both sets of data p and s traveltimes and traveltime ratios delineate lateral variations in the thickness and average porosity of the hunton where the pore space is saturated with liquid a systematic increase in average porosity from less than 2 percent to about 11 percent correlates with an increase in the s p traveltime ratio from 1 84 to 1 96 the ratio decreases to values between 1 65 and 1 80 at two places along the line probably indicating that the pore space is partially gas saturated at these locations the data are consistent with the seismic response of a petrophysical model of the hunton in which a majority of the pore shapes are elongated rather than round

glacial weathering sulfide oxidation and global carbon cycle feedbacks connections between glaciation chemical weathering and the global carbon cycle could steer the evolution of global climate over geologic time but even the directionality of feedbacks in this system remain to be resolved here we assemble a compilation of hydrochemical data from glacierized catchments use this data to evaluate the dominant chemical reactions associated with glacial weathering and explore the implications for long term geochemical cycles weathering yields from catchments in our compilation are higher than the global average which results in part from higher runoff in glaciated catchments our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals to evaluate the effects of glacial weathering on atmospheric pco 2 we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon dic generated by weathering reactions compared with nonglacial weathering glacial weathering is more likely to yield alkalinity dic ratios less than 1 suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of co 2 to the atmosphere back of the envelope calculations indicate that oxidative fluxes could change ocean atmosphere co 2 equilibrium by 25 ppm or more over 10 ky over longer timescales co 2 release could act as a negative feedback limiting progress of glaciation dependent on lithology and the concentration of atmospheric o 2 future work on glaciation weathering carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals

oxygenation of a cryogenian ocean nanhua basin south china revealed by pyrite fe isotope compositions abstract the nature of ocean redox chemistry between the cryogenian sturtian and marinoan glaciations ca 663 654 ma is important for understanding the relationship between environmental conditions and the subsequent emergence and expansion of early animals the cryogenian to ediacaran stratigraphic succession of the nanhua basin in south china provides a nearly complete sedimentary record of the cryogenian including a continuous record of interglacial sedimentation here we present a high resolution pyrite fe isotope record for a 120 m long drill core zk105 through sturtian glacial diamictites and the overlying interglacial sediments in the nanhua basin to explore changes in marine chemistry during the late cryogenian our pyrite fe isotope profile exhibits significant stratigraphic variation interval i comprising middle to upper tiesi ao diamictites correlative with the sturtian glaciation is characterized by light modern seawater like fe isotope compositions interval ii comprising uppermost tiesi ao diamictites and the basal organic rich datangpo formation is characterized by an abrupt shift to heavier fe isotope compositions and interval iii comprising organic poor grey shales in the middle datangpo formation is characterized by the return of lighter seawater like fe isotope compositions we infer that interval i pyrite was deposited in a predominantly anoxic glacial nanhua basin through reaction of dissolved fe2 and h2s mediated by microbial sulfate reduction msr the shift to heavier pyrite fe isotope values in interval ii is interpreted as partial oxidation of ferrous iron to ferric iron and subsequent near quantitative reduction and transformation of fe oxyhydroxides to pyrite through coupling with oxidation of organic matter in the local diagenetic environment in interval iii near quantitative oxidation of ferrous iron to fe oxyhydroxides followed by near quantitative reduction and conversion to pyrite in the local diagenetic environment was likely responsible for the return of lighter seawater like fe isotope compositions in pyrite our pyrite fe isotope profile thus records increased oxygenation in the nanhua basin between the sturtian and marinoan glaciations the increased oxygenation of nanhua basin seawater deduced from pyrite fe isotopes could have resulted from either local or global controls further work will be needed to determine whether this increasing oxygenation extended to the global scale

riverine li isotope fractionation in the amazon river basin controlled by the weathering regimes we report li isotope composition 7li 7li of river borne dissolved and solid material in the largest river system on earth the amazon river basin to characterize li isotope fractionation arl a continental scale the 7li 7li in the dissolved load 1 2 to 32 is fractionated toward heavy values compared to the inferred bedrock 1 to 5 and the suspended sediments 6 8 to 0 5 as a result of the preferential incorporation of 66li into secondary minerals during weathering despite having very contrasted weathering and erosion regimes both andean headwaters and lowland rivers share similar ranges of dissolved 7li 7li 1 2 to 18 correlations between dissolved 7li 7li and li na and li mg ratios suggest that the proportion of li incorporated in secondary minerals during weathering act as the main control on the 7lidiss 7lidiss across the entire amazon basin a batch steady state fractionation model for andean and lowland rivers satisfactorily reproduces these variations with a fractionation factor between weathering products and dissolved load sec dis sec dis of 0 983 two types of supply limited weathering regimes can be identified for the lowlands clearwaters with dominant incorporation of li in secondary minerals and black waters e g rio negro where dissolution of secondary minerals enhanced by organic matter produces low 7li 7li apart from the black waters the 7li 7li of andean and lowland rivers is negatively correlated to the denudation rates with the lowest 7li 7li corresponding to the rivers having the highest denudation rates in contrast the main tributaries draining both the andes and the lowlands have higher 7li 7li compared to other rivers we propose that part of the dissolved li derived from weathering in the andes is re incorporated in sediments during transfer of water and sediments in floodplains and that this results in an increase of the dissolved 7li 7li along the course of these rivers unlike other rivers the dissolved 7li 7li in the main tributaries is best described by a rayleigh fractionation model with a fractionation factor sec dis sec dis of 0 991 altogether the control imposed by residence time in the weathering zone and floodplain processes results in i a non linear correlation between dissolved 7li 7li and the weathering intensity defined as w d and ii a positive relationship between the dissolved li flux and the denudation rate these results have important implications for the understanding of past ocean 7li 7li and its use as a paleo weathering proxy

on the limits of using combined u series esr method to date fossil teeth from two early pleistocene archaeological sites of the orce area guadix baza basin spain abstract article history received 6 june 2011available online 9 february 2012keywords combined u series esr dating methodfossil teethfuente nueva 3barranco leonorceearly pleistocene the combined u series electron spin resonance esr dating method was applied to nine teeth from twoearly pleistocene archaeological sites located in the orce area guadix baza basin southern spain fuentenueva 3 fn 3 and barranco leon bl the combination of biostratigraphy and magnetostratigraphy placesboth sites between the olduvai and jaramillo subchrons 1 78 1 07 ma our results highlight the dif culty of dating such old sites and point out the limits of the combined u series esr dating method based on the us model we identi ed several sources of uncertainties that may lead toinaccurate age estimates seven samples could not be dated because the dental tissues had 230 th 234 u ac tivity ratios higher than equilibrium indicating that uranium had probably leached from these tissues it washowever possible to calculate numerical estimates for two of the teeth both from fn 3 one yielded a middlepleistocene age that seems to be strongly underestimated the other provided an age of 1 19 0 21 ma inagreement with data obtained from independent methods the latter result gives encouragement thatthere are samples that can be used for routine dating of old sites 2012 university of washington published by elsevier inc all rights reserved

temporal changes of medium properties during explosive volcanic eruption volcanic evolutions typically accompany significant changes in medium properties monitoring the seismic properties may be useful in identifying the state of volcanic evolution temporal variation of shallow crustal vp vs ratios before and during the 2009 eruption of redoubt volcano alaska is investigated using the p and s traveltimes of local earthquakes high vp vs ratios of 1 9 are observed over a wide region in the precursory phase suggesting the presence of partial melts in the medium at least several months before explosive eruptions the high v p v s ratios decrease until the early effusive phase with rates of 0 179 year 1 in the precursory phase 65 days and 2 147 year 1 in the explosive phase 40 days which is equivalent to a decrease in the bulk modulus of fluids by 1 1 and 7 9 gpa respectively the decreasing v p v s ratios in the precursory phase may be due to increasing amounts of overpressurized gas and water vapor in the medium the rapid decrease in vp vs ratios during the explosive phase may be caused by melt eruption and gas emission the vp vs ratios were observed to be nearly stationary since the early effusive phase suggesting rare presence of melts and low levels of pore pressures with degassing these observations suggest that monitoring vp vs ratios may be useful to identify the eruption state

absolute dating by uranium series disequilibrium of bones from the cave of la chaise de vouthon charente france animal bones associated with palaeolithic artefacts and skeletal remains of early hominids from the cave of la chaise de vouthon have been dated using a new approach to uranium series dating of bone speleothem cave calcite interstratified with bone bearing sediments in the two chambers of grotte bourgeois delaunay and grotte suard have previously been dated by the 230th 234 u method this provides a chronological control for the bone ages for which the method is still at an experimental stage a good agreement is shown in most cases between the calcite and the bone ages showing the cave to have been a stable environment for the deposition of bone and the acquisition of uranium

lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion abstract the erosion of major mountain ranges is thought to be largely cannibalistic recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift despite this recognition it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean here we have analyzed the li content and isotope composition li 7 of suspended sediments sampled along river depth profiles and bed sands in three of the largest earth s river systems amazon mackenzie and ganga brahmaputra rivers the li 7 values of river sediments transported by these rivers range from 5 3 to 3 6 and decrease with sediment grain size we interpret these variations as reflecting a mixture of unweathered rock fragments preferentially transported at depth in the coarse fraction and present day weathering products preferentially transported at the surface in the finest fraction only the finest surface sediments contain the complementary reservoir of li solubilized by water rock interactions within the watersheds li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks a mass budget approach based on li isotopes li al and na al ratios solved by an inverse method allows us to estimate that for the large rivers analyzed here the part of solid weathering products formed by present day weathering reactions and transported to the ocean do not exceed 35 li isotopes also show that the sediments transported by the amazon mackenzie and ganga brahmaputra river systems are mostly sourced from sedimentary rocks 60 rather than igneous rocks this study shows that li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present day weathering processes overall li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering

v p v s and lithology published laboratory investigations suggest an association exists between the ratio of seismic compressional and shear wave velocities vp vs and sedimentary rock lithology comparisons of some theoretical models with these laboratory studies suggest that crack or pore geometry has a stronger effect on observed vp vs values than elastic constants of the minerals comprising the matrix further it can be inferred that the observed association between lithology and vp vs is a result of an association between lithology and distribution of pore and crack shapes direct observation of crack shapes for a variety of lithologies is a next step in strengthening these inferences the present study reviews the empirical relations between vp vs and lithology and examines two published theoretical models of cracked elastic media the models suggest that seismic velocities of sandstones may be controlled by cracks and pores with aspect ratios in the range of 10 1 to 1 dolomite in the range of 10 2 to 10 1 and dens

bootstrap inversion for vertical and lateral variations of the s wave structure and the υp υs ratio from shallow earthquakes in the rhinegraben seismic zone germany using s wave arrival times of 400 earthquakes in the southern rhinegraben 1 d and 3 d inversions for the shear s wave crustal structure of that region are performed these models are then combined with previously obtained 1 d and 3 d p wave models to compute vertical and lateral variations of the p s poisson s ratio such an independent p and s wave inversion approach circumvents many of the limitations of the classical wadati diagram method usually used for the determination of crustal p s ratios for the statistical evaluation of the 1 d models we have used a new monte carlo bootstrap resampling technique which has been found useful in many statistical estimation problems where the underlying statistics of the data is poorly known the 1 d bootstrap p s crustal models exhibit significant vertical variations whereas the upper sedimentary and crystalline layer of the crust is characterized by a significant increase of p s over the reference value p s in the upper and middle crust is lowered this correlates well with several findings from wadati diagrams for p s in other seismically active zones and might be explained through the gradual closing of saturated microcracks in that depth range however the p s reduction can also be interpreted in terms of a particular petrological composition such as orthoclase feldspar without the indispensable need for fluids a lowering of p gus is also observed for the lower crust which might reflect the strong lamination found here from previous deep seismic sounding experiments for the upper mantle a strong increase of p s is observed which is primarily triggered by a decrease of s and is best explained by an eclogite petrological assemblage for the 3 d s wave models significant reductions of more than 100 were obtained for the unexplained travel time residuals variations of p s in the upper and middle crust are mostly induced by changes in p rather than s for the upper crust slight decreases of p s are observed for the rhinegraben but increases are detected for the adjacent vosges and black forest areas in the middle crust the refraction seismic deduced reduction of p s under parts of the black forest can neither be corroborated nor rejected however because of some experimental ambiguity on the effects of petrological composition and interstitial pore fluids this does not rule out the presence of the latter in the lower crust a local reduction of p s is observed under the kaiserstuhl and graben black forest shoulder and has been explained in terms of a metamorphic dehydrating phase change of the hydrous amphibolite facies to the anhydrous granulite facies depending on the pore pressure of the dehydrated water and the fractional amount of interstitial co2 granulite facies metamorphism occurs in the 650 800 c temperature range temperatures at the upper end of this interval can be generated by the mechanism of accretionary magmatic underplating as it has been proposed for some extensional rift zones where asthenospheric upwelling as in the rhinegraben occurs

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

lithium isotope behaviour during weathering in the ganges alluvial plain the ganges river system is responsible for the transportation of a large flux of dissolved materials derived from himalayan weathering to the oceans silicate weathering driven cooling resulting from uplift of the himalayas has been proposed to be a key player in cenozoic climate variation this study has analysed li isotope 7li ratios from over 50 ganges river waters and sediments in order to trace silicate weathering processes sediments have 7li of 0 identical to bulk continental crust however suspended sediment depth profiles do not display variations associated with grain size that have been observed in other large river systems dissolved 7li are low 11 in the ganges headwaters but reach a constant value of 21 1 6 within a relatively short distance downstream which is then maintained for almost 2000 km to the ganges mouth given that li isotopes are controlled by the ratio of primary mineral dissolution to secondary mineral formation this suggests that the ganges floodplain is at steady state in terms of these processes for most of its length low 7li in the mountainous regions suggest silicate weathering is therefore at its most congruent where uplift and fresh silicate exposure rates are high however there is no correlation between 7li and the silicate weathering rate in these rivers suggesting that li isotopes cannot be used as a weathering rate tracer although they do inform on weathering congruency and intensity the close to constant 7li values for the final 2000 km of ganges flow also suggest that once the size of the alluvial plain reached more than 500 km the flow distance after which riverine 7li stops varying the ganges exerted little influence on the changing cenozoic seawater 7li because riverine 7li attained a near steady state composition

the challenge of dating early pleistocene fossil teeth by the combined uranium series electron spin resonance method the venta micena palaeontological site orce spain the palaeontological site of venta micena orce andalusia spain lies in the eastern sector of the guadix baza basin one of the best documented areas in europe for plio pleistocene biostratigraphy the combination of biochronological and palaeomagnetic results combined with the radiometric data obtained for atapuerca sima del elefante indicated that the venta micena stratum was formed between the jaramillo and olduvai palaeomagnetic events most likely between 1 22 and 1 77 ma five fossil teeth from two outcrops sites a and b were selected to assess the potential of combined uranium series electron spin resonance us esr dating of early pleistocene sites although the us esr results of the first outcrop showed a large scatter between the three teeth the mean age of 1 37 0 24 ma can be considered a reasonable age estimate for venta micena the mean esr age of 0 62 0 03 ma obtained for site b seems to be a severe underestimation when compared with the independent age control this underestimation is attributed to a relative recent u mobilization event that led to some u leaching the results show that any esr age calculations of old samples are extremely sensitive to variations in the measured 230th 234u ratios in dental tissues although the results demonstrate that esr can in principle be applied to early pleistocene sites they also reveal the complexity of dating such old teeth it is necessary to continue research in several directions such as study of the behaviour of esr signals in old teeth and understanding recent u mobilization processes to improve the reliability of the combined us esr dating method applied to early pleistocene times a period for which the number of available numerical dating techniques is very limited copyright 2011 john wiley sons ltd

riverine behaviour of uranium and lithium isotopes in an actively glaciated basaltic terrain this study presents u and li isotope and major and trace element data for the dissolved load suspended particulates and bedload for icelandic rivers draining predominantly basaltic catchments physical erosion rates range from 920 to 2084 t km2 yr with the higher values associated with glacier fed rivers chemical erosion rates range from 45 to 91 t km2 yr with lower rates being associated with glacier fed rivers uranium activity ratios 234u 238u are close to secular equilibrium in the suspended and bedloads but all dissolved load samples show values greater than unity ranging from 1 13 to 2 41 the highest 234u 238u values are found in glacier fed rivers and can be attributed to recoil effects as grinding by glaciers locally enhances rates of physical weathering activity ratios in glacial rivers decrease with distance from the glacial source due to input from non glacial tributaries which have high levels of dissolved uranium and lower activity ratios in contrast in non glacial rivers uranium activity ratios increase with distance downstream due to continued weathering in soils and of bedrock the 7li value of the suspended load is always lower than that of the bedload due to preferential retention of 6li in secondary minerals during weathering in turn the 7li value of the dissolved load is always greater than that of the bedload ranging from 17 0 to 43 7 7li for the dissolved load decreases with increasing levels of dissolved silicon and the saturation index of secondary minerals which suggests that 7li decreases with increasing chemical weathering there is no correlation between 7li values and uranium activity ratios for the dissolved load for non glacial rivers but for glacier fed rivers there is an increase in 7li with increasing 234u 238u suggesting that where physical comminution of mineral grains by glaciers is high chemical weathering is suppressed and vice versa

v p v s from mode converted p sv reflections p sv reflections are generated by a compressional wave source and result from p waves that are converted to shear sv waves upon reflection recording both the p and sv components yields compressional and shear data simultaneously verifying that the easily detected events really are p sv reflections is accomplished by noting the good correlation of surface cdp data with vertical seismic profile vsp reflections stacking velocities from p sv cdp gathers determine the vpvs product when source to receiver offset is less than the depth of the reflector but data from synthetic models show that p sv reflections are nonhyperbolic for shallow reflections or when source to receiver offset is too large shear velocity vs can be calculated from p sv reflections by one of two techniques comparison of stacked section p p and p sv reflection times or by using the p p and p sv stacking velocities unfortunately most p sv reflections on a p sv seismic section do not necessarily originate from exactly the same dep

velocity and attenuation tomography of the umbria marche 1997 fault system evidence of a fluid governed seismic sequence abstract the 1997 umbria marche is probably the best ever monitored normal faulting seismic sequence seismicity migration and multiple main shocks characterize the activation of a 40 km long system of contiguous fault segments as documented by seismological data many authors as indicative of fault weakening by fluids migration have interpreted this behaviour in this study we create a new catalogue of high quality p and s wave arrival times merging data recorded by permanent and temporary stations to improve the resolution of velocity and attenuation models and earthquake locations we show that the relocated earthquakes and the joint interpretation of p and s wave velocity and attenuation models help in understanding the faulting processes revealing new details of the geometry of the main faults and physical state of fluids within the crustal volume we observe that large aftershocks occur on the top and within the triassic evaporitic layer a rock volume locally characterised by fluid over pressured as evidenced by high vp vs and low qp qs anomalies velocity and attenuation heterogeneities are evidence that the migration of fluid pressure along the fault system is the driving mechanism of the prolonged earthquake sequence

tracing weathering regimes using the lithium isotope composition of detrital sediments lithium li isotopes are a promising tracer of chemical weathering processes for both modern and ancient times in order to improve the use of li isotopes in the sedimentary record here we calibrate the relationship between weathering intensity and detrital li isotope composition 7li using the fine fraction of modern large river sediments through independent estimates for sediment provenance to calculate the li isotope signature of the rock from which the sediments derive through weathering we show that source rock variability in particular the relative contribution of sedimentary versus igneous rocks must be corrected for before using li isotopes as a weathering proxy we also show that for rivers draining mountain ranges the contribution to river sediments of particles derived from sedimentary rocks is correlated to their li al ratio making it possible to use li contents to estimate the average source rock composition once corrected for bedrock variability the li isotope signature defines a negative relationship with the weathering intensity ratio between silicate weathering rate and total denudation rate with highest li isotope fractionation for the highest weathering intensity altogether we propose a set of new relationships between weathering erosion provenance and li isotopes that can be used to quantify present day and paleo weathering using detrital sediment