26al 26mg systematics in d orbigny and sahara 99555 angrites implications for high resolution chronology using extinct chronometers abstract we report on an investigation of the 26al 26mg isotope systematics in the d orbigny and sahara 99555 angrites high precision mg isotope compositions and al mg ratios were measured in mineral separates and whole rock samples from d orbigny and sahara 99555 using multiple collector inductively coupled plasma mass spectrometry mc icpms plagioclase separates from both angrites have resolvable excesses in 26mg 26mg that correlate with their respective al mg ratios 26al 26mg systematics in the mineral separates and whole rocks define precise isochrons that correspond to 26al 27al ratios of 5 06 0 92 10 7 and 5 13 1 90 10 7 and initial 26mg values of 0 006 0 040 and 0 016 0 047 for d orbigny and sahara 99555 respectively the slopes and initial 26mg values are identical for these two meteorites within errors and the data for both angrites considered together define an isochron corresponding to a 26al 27al ratio of 5 10 0 55 10 7 and initial 26mg value of 0 012 0 019 relative to the efremovka e60 cai the 26al 27al values reported here for these angrites imply 26al 26mg ages of 4562 42 0 29 ma and 4562 43 0 53 ma for d orbigny and sahara 99555 respectively these 26al 26mg ages are concordant with model ages determined using other extinct radionuclide chronometers e g 53mn 53cr and 182hf 182w but are 2 myr younger than the absolute 207pb 206pb ages that have been reported recently for these angrites the reason for this discrepancy is not presently known but may imply disturbance of one or more of the isotope systems under consideration or a possible bias in the 207pb 206pb ages of the angrites resulting from natural or analytical causes

unraveling the evolution of chondrite parent asteroids by precise u pb dating and thermal modeling u th pb isotopic data are reported for mineral fractions individual chondrules and fractions of chondrule fragments from the equilibrated ordinary chondrite richardton h5 chondrules and milligram sized fractions of pyroxene rich chondrule fragments contain highly radiogenic pb and concordant or nearly concordant u th pb isotopic systems and are suitable for precise pb pb age determinations olivine and sulfide have low u concentrations and contain less radiogenic pb the ages of individual chondrules pyroxene rich and phosphate fractions are determined using u pb and pb pb isochron and model date calculations the pb pb isochron date of 4562 7 1 7 ma of the richardton chondrules and chondrule fragments is resolved from the pb pb isochron date of 4550 7 2 6 ma obtained from multiple phosphate fractions possible biases of the isochron dates due to single stage approximation of multi stage evolution contamination with modern common pb and disturbance to the system by reheating are examined and are found to be insignificant the chondrule and phosphate dates are interpreted as the timing of cessation of pb diffusion during cooling following metamorphism in chondrite parent bodies the difference in estimated closure temperatures 950 1150 k for pyroxenes and 700 800 k for phosphates temperature estimates are based on published diffusion rates for pb in pyroxenes and apatite allows evaluation of the average cooling rate at 26 13 k million years for the richardton parent body over the period of 4563 4551 my thermal modeling of the h chondrite parent body which is assumed to be asteroid 6 hebe heated by decay of 26al suggests a scenario in which accretion initiated at 1 7 m y after formation of calcium aluminum rich inclusions and continued for 3 5 m y

modern carbonate marine sands in estuaries of southwest england large deposits of marine sand occur in the taw camel and hayle estuaries of north devon and cornwall total carbonate concentrations reach 67 in the hayle 62 in the camel and 40 in the taw well mixed the sands contain modern skeletal debris of consistent composition which persists up to 18 km and 12 km landward from the mouths of the taw and camel estuaries although primarily a molluscan sand remains of barnacles bryozoans echinoids foraminifera sponge spicules decapods and coralline algae are common carbonate mineralogy provided by these components on a 100 carbonate basis consists of 45 aragonite 38 low mg calcite and 17 high mg calcite two estuaries of the southeast coast of devon the exe and teign contain smaller carbonate concentrations of up to 9 and 14 values are low there owing to dilution by readily eroded cliff talus from local exposures of new red sandstone these permo triassic sediments provide carbonate lithoclasts however which supplement the modern biogenic supply strontium values have been used to estimate the extent of carbonate lithoclasts supplied to the exe and teign the present source of marine sand of estuaries in southwest england is considered to be mostly near shore detritus supplemented by eroded cliff talus derived largely from local outcrops once this material enters the estuarine regime it is available as a supply of sediment for further up estuary transport

fine sediment and its sources severn estuary and inner bristol channel southwest britain abstract a comparison of the clay mineral assemblages of 22 samples from the estuary with 22 samples from river floodplains strongly suggests that the fine sediment present in the contemporary severn estuary and inner bristol channel come almost exclusively from the river catchments that feed the system the catchments are geologically diverse and the clay minerals particularly expandable clays kaolinite and chlorite seem to come from preferred parts of the drainage area although the estuary is flood dominated and some fine sediment is supplied from seaward the amount appears negligible in comparison with the fluvial supply the sands however seem largely to have an immediate western origin

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

geochemical correlation in deltaic successions a reality check whole rock geochemical analysis can aid the stratigraphic correlation of faunally barren successions compared to petrographic techniques or heavy mineral separations such analysis is quick and objective yet rarely has the reliability of the method been tested against unequivocal correlations we have applied it to the kenilworth member of the upper cretaceous blackhawk formation a well exposed and easily correlated 100 m thick unit in the deltaic successions of the book cliffs utah united states this is the first evaluation of geochemical analysis as an aid to sequence stratigraphic interpretation at the parasequence scale from the geochemistry alone it is not possible with statistical confidence to separate individual parasequences or systems tracts nor the fluvial incised valley from the marine shoreface units the magnitude of geochemical variation in a single sandstone bed over a 30 m lateral traverse is as great as vertically through an entire parasequence y nb rb and ti abundances are inversely correlated with grain size thus geochemical signatures follow sedimentological trends and distal parts of a parasequence appear distinct from proximal parts y ratios compensate for this grain size effect but introduce confusing distortions for elements such as zr that are not correlated with grain size contrary to some predictions zr is as common in the finest grained units as the coarsest and sr is not correlated with ca in some sections sr is also inversely correlated to grain size and cannot be used as an indicator for cement abundance

impact history of the hed parent body ies clarified by new 40ar 39ar analyses of four hed meteorites and one anomalous basaltic achondrite abstract we investigate the thermal impact histories of four hed meteorites one cumulate eucrite lake carnegie two brecciated basaltic eucrites camel donga millbillillie one howardite old homestead 003 and an anomalous basaltic achondrite deakin 010 we have measured eight convincing new 40ar 39ar ages for three hed meteorites laser incremental 40ar 39ar analyses of carefully separated small grains two concordant 40ar 39ar plateau ages were obtained for plagioclase separates from lake carnegie resulting in a weighted mean age of combined plateau ages of 4507 20 ma millbillillie recorded three impact events at 3722 55 ma 3579 28 ma and 3313 174 ma from plagioclase matrix and pyroxene respectively this highlights the power of the k ar system to record impacts of different magnitudes experienced by a single meteorite two aliquots from camel donga returned concordant plateau ages interpreted to represent a single significant impact event at 3693 51 ma the anomalous basaltic achondrite deakin 010 did not yield any plateau and resulted in a series of minimum apparent ages with an oldest minimum age of 3 66 ga for the largest impact recorded cosmic ray exposure ages yielded apparent 38arc ages ranging from 6 to 40 ma two clusters of ages that represent significant impacts into the hed parent body may have been identified the first high temperature event is recorded by lake carnegie and other unbrecciated eucrites at 4 5 ga and is interpreted as a mega impact although it is also possible that this age is recording magmatic crystallisation due to the similarity of published sm nd and pb pb ages additionally from statistically reliable isotopic ages provided in this study it appears that the age range of major impact heating events post 4 5 ga might be more tightly restricted 3 8 3 5 ga than previously suggested 3 4 4 1 ga however a larger dataset is required before comparison with the range of the lunar heavy bombardment is justified if hed are indeed from 4 vesta we raise the possibility that the impact at 4 5 ga might be associated with the formation of the south polar veneneia basin whereas an age at 3 7 ga may represent the formation age of either veneneia or the younger rheasilvia impact structure

rio tinto estuary spain 5000 years of pollution mining of massive sulfide deposits in southwestern spain extending back to the copper and bronze ages has resulted in the pollution of the rio tinto fluvial estuarine complex the site of columbus departure for the new world in 1492 additional sources of potential pollution include the large industrial complex at huelva near the lower portion of the estuary extensive analysis of surface sediment samples and cores has established that there are no geographic trends in the distribution of the pollutants which include cu fe pb zn ti ba cr v and co these data have however demonstrated that tidal flux within the estuary carries phosphorus and perhaps other elements from the industrial complex at huelva to the tidal limit of the system several kilometers upstream from the discharge site radiometric analysis of short cores shows that sedimentation rates over at least the past couple of centuries have been about 0 3 cm year these data and that from a single deep core demonstrate that the estuary was polluted from mining activity long before the large scale operations began in the late nineteenth century

landslide susceptibility assessment by bivariate methods at large scales application to a complex mountainous environment statistical assessment of landslide susceptibility has become a major topic of research in the last decade most progress has been accomplished on producing susceptibility maps at meso scales 1 50 000 1 25 000 at 1 10 000 scale which is the scale of production of most regulatory landslide hazard and risk maps in europe few tests on the performance of these methods have been performed this paper presents a procedure to identify the best variables for landslide susceptibility assessment through a bivariate technique weights of evidence woe and discusses the best way to minimize conditional independence ci between the predictive variables indeed violating ci can severely bias the simulated maps by over or under estimating landslide probabilities the proposed strategy includes four steps i identification of the best response variable rv to represent landslide events ii identification of the best combination of predictive variables pvs and neo predictive variables npvs to increase the performance of the statistical model iii evaluation of the performance of the simulations by appropriate tests and iv evaluation of the statistical model by expert judgment the study site is the north facing hillslope of the barcelonnette basin france affected by several types of landslides and characterized by a complex morphology results indicate that bivariate methods are powerful to assess landslide susceptibility at 1 10 000 scale however the method is limited from a geomorphological viewpoint when rvs and pvs are complex or poorly informative it is demonstrated that expert knowledge has still to be introduced in statistical models to produce reliable landslide susceptibility maps

the influence of geology and land use on the geochemical baselines of the east river basin china abstract a geochemical baseline refers to the concentration of an element or any chemical property of a naturally occurring substance in the earth s near surface materials originating from both natural and non natural sources in this study the tukey boxplot approach was adopted to develop geochemical baselines for 42 analytes in the east river basin south china data subset analyses change ratios and factor analyses were used to explore the anthropogenic effects and the influence of land use and geology on the spatial distribution of the geochemical baselines the sample medium was active fine grained 2 n 137 although considerable variation in elemental concentration was exhibited by the dataset the geochemistry of the study basin was generally consistent with the upper crustal abundance for china and with world average fluvial suspended matter concentrations median concentrations of the heavy metals lay within the limits of sediment quality guidelines and the bed sediment of this macro scale basin was relatively unpolluted the results revealed that whilst base cations were depleted background levels of as pb w and some rare earth elements were elevated relative to the crustal values subset analysis and factor analysis indicated that as pb and w were associated with anthropogenic activities whereas rare earth elements were affiliated with the igneous geology in the study basin

modelling groundwater fluctuations and the frequency of movement of a landslide in the terres noires region of barcellonnette france onn the basis of measurements of hydrological parameters and field monitoring of a landslide in the terres noires in the basin of barcelonnette france a hydrological model was developed describing groundwater fluctuations in relation to precipitation these groundwater fluctuations can be used as input to a stability model in order to assess the temporal frequency of instability of the landslide the calculated groundwater fluctuations which can forecast years with landslide incidents were roughly calibrated against dated movements obtained by dendrochronological research the hydrological system of the landslide can be understood through a three layer sequence a rather permeable colluvial top layer underlain by a less permeable colluvial second layer both overlying the nearly impermeable in situ non weathered black marls terres noires the mean ksat value for the matrix flow in the top layer is 15 7 cm day and in the underlying layer 0 7 cm day however water fluxes in these layers occur by two types of groundwater flow matrix flow obeying darcy s law and more rapid gravitational flow through preferential flow paths increasing the conductivity by a factor of 10 to 100 as cube method ksat measurements revealed the model shows long term yearly fluctuations of the phreatic surface with peaks at the end of winter as well as at the beginning of spring and minimum values during the dry summer period these long term fluctuations are explained by the high drainage capacity of the top colluvial layer and the relatively low vertical water fluxes within the underlying colluvial layer the model shows that maximum critical peak height conditions of the groundwater causing instability occur in wet seasons with at least six consecutive months with high amounts more than 60 mm of precipitation 1997 by john wiley sons ltd

26al 26mg isotope systematics of the first solids in the early solar system high precision bulk aluminum magnesium isotope measurements of calcium aluminum rich inclusions cais from cv carbonaceous chondrites in several laboratories define a bulk 26al 26mg isochron with an inferred initial 26al 27al ratio of approximately 5 25 10 5 named the canonical ratio nonigneous cv cais yield well defined internal 26al 26mg isochrons consistent with the canonical value these observations indicate that the canonical 26al 27al ratio records initial al mg fractionation by evaporation and condensation in the cv cai forming region the internal isochrons of igneous cv cais show a range of inferred initial 26al 27al ratios 4 2 5 2 10 5 indicating that cai melting continued for at least 0 2 ma after formation of their precursors a similar range of initial 26al 27al ratios is also obtained from the internal isochrons of many cais igneous and nonigneous in other groups of carbonaceous chondrites some cais and refractory grains corundum and hibonite from unmetamorphosed or weakly metamorphosed chondrites including cvs are significantly depleted in 26al at least some of these refractory objects may have formed prior to injection of 26al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk bulk aluminum and magnesium isotope measurements of various types of chondrites plot along the bulk cv cai isochron suggesting homogeneous distribution of 26al and magnesium isotopes in the protoplanetary disk after an epoch of cai formation the inferred initial 26al 27al ratios of chondrules indicate that most chondrules formed 1 3 ma after cais with the canonical 26al 27al ratio

landslide inventory maps new tools for an old problem landslides are present in all continents and play an important role in the evolution of landscapes they also represent a serious hazard in many areas of the world despite their importance we estimate that landslide maps cover less than 1 of the slopes in the landmasses and systematic information on the type abundance and distribution of landslides is lacking preparing landslide maps is important to document the extent of landslide phenomena in a region to investigate the distribution types pattern recurrence and statistics of slope failures to determine landslide susceptibility hazard vulnerability and risk and to study the evolution of landscapes dominated by mass wasting processes conventional methods for the production of landslide maps rely chiefly on the visual interpretation of stereoscopic aerial photography aided by field surveys these methods are time consuming and resource intensive new and emerging techniques based on satellite airborne and terrestrial remote sensing technologies promise to facilitate the production of landslide maps reducing the time and resources required for their compilation and systematic update in this work we first outline the principles for landslide mapping and we review the conventional methods for the preparation of landslide maps including geomorphological event seasonal and multi temporal inventories next we examine recent and new technologies for landslide mapping considering i the exploitation of very high resolution digital elevation models to analyze surface morphology ii the visual interpretation and semi automatic analysis of different types of satellite images including panchromatic multispectral and synthetic aperture radar images and iii tools that facilitate landslide field mapping next we discuss the advantages and the limitations of the new remote sensing data and technology for the production of geomorphological event seasonal and multi temporal inventory maps we conclude by arguing that the new tools will help to improve the quality of landslide maps with positive effects on all derivative products and analyses including erosion studies and landscape modeling susceptibility and hazard assessments and risk evaluations

differentiation history of the mesosiderite parent body constraints from trace elements and manganese chromium isotope systematics in vaca muerta silicate clasts abstract we report here the results of a study of trace element microdistributions and 53mn 53cr systematics in several basaltic and orthopyroxenitic clasts from the vaca muerta mesosiderite ion microprobe analyses of selected trace and minor element abundances in minerals of the silicate clasts indicate that following igneous crystallization these clasts underwent extensive metamorphic equilibration that resulted in intra and inter grain redistribution of elements there is also evidence in the elemental microdistributions that these clasts were subsequently affected to varying degrees by alteration resulting from redox reactions involving the indigenous silicates and externally derived reducing agents such as phosphorus derived from the mesosiderite metal at the time of metal silicate mixing furthermore our results suggest that the varying degrees of alteration by redox reactions recorded in the different clasts were most likely facilitated by different degrees of remelting induced by heating during the metal silicate mixing event after taking into account the effects of these postmagmatic secondary processes comparison of the trace and minor element concentrations and distributions in minerals of basaltic and orthopyroxenitic clasts with those of noncumulate eucrites and diogenites respectively suggests that the primary igneous petrogenesis including parent magma and source compositions of vaca muerta silicates were similar to those of achondritic meteorites of the howardite eucrite diogenite hed association internal 53mn 53cr isochrons obtained for two basaltic pebble 16 and 4679 and two orthopyroxenitic 4659 and 4670 clasts show that chromium isotopes are equilibrated within each clast nevertheless just as for noncumulate eucrites and diogenites 53cr excesses in whole rock samples of the basaltic clasts 1 01 e in pebble 16 1 07 e in 4679 are significantly higher than in the orthopyroxene rich clasts 0 62 e in 4659 0 53 e in 4670 as in the case of the hed parent body this suggests that mn cr fractionation in the parent body of the vaca muerta silicate clasts occurred very early in the history of the solar system when 53mn was still extant however the slope of the 53mn 53cr isochron defined by the whole rock samples of vaca muerta clasts corresponding to a 53mn 55mn ratio of 3 3 0 6 10 6 is distinctly lower than that defined by the hed whole rock samples corresponding to a 53mn 55mn ratio of 4 7 0 5 10 6 indicating that the global mn cr fractionation event that established mantle source reservoirs on the parent body of the vaca muerta silicate clasts occurred 2 ma after a similar event on the hed parent body

sediment dynamics of the severn estuary and inner bristol channel net sediment transport pathways have been determined in many environments by studying grain size trends this approach is extended here to an inner shelf environment with improved statistical techniques patterns of net surficial sediment transport are proposed indicating that the area is dominated by up estuary transport exceptions exist in the form of radial mud transport at the river mouths and clockwise sand circulation around linear sandbanks six different sedimentary environments are defined on the basis of the shape of the transfer function and its relationship to the grain size distributions erosion takes place along the axis of the estuary dynamic equilibrium is reached around the linear sandbanks whilst accretion occurs at the head of the estuary and where there are riverine inputs the results are compared with numerical model outputs representing water movement and sediment transport over the seaward part of the study area there is agreement between the two approaches contradictions increase however towards the upper reaches of the estuary the discrepancies can be attributed to 1 inherent differences between patterns of water and sediment movement 2 difficulties in modelling intertidal boundary conditions 3 inadequate representation of river influences in the models and 4 time scale differences associated with sediment transport processes

pb pb dating of individual chondrules from the cb a chondrite gujba assessment of the impact plume formation model the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the cba chondrite gujba are interpreted to reflect a single stage impact origin here we report high precision internal isochrons for four individual chondrules of the gujba chondrite to probe the formation history of cb chondrites and evaluate the concordancy of relevant short lived radionuclide chronometers all four chondrules define a brief formation interval with a weighted mean age of 4562 49 0 21 myr consistent with its origin from the vapor melt impact plume generated by colliding planetesimals formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4 8 0 3 myr finally given the well behaved pb pb systematics of all four chondrules a precise formation age and the concordancy of the mn cr hf w and i xe short lived radionuclide relative chronometers we propose that gujba may serve as a suitable time anchor for these systems

a new source of basaltic meteorites inferred from northwest africa 011 eucrites are a class of basaltic meteorites that share common mineralogical isotopic and chemical properties and are thought to have been derived from the same parent body possibly asteroid 4 vesta the texture mineralogy and noble gas data of the recently recovered meteorite northwest africa nwa 011 are similar to those of basaltic eucrites however the oxygen isotopic composition of nwa011 is different from that of other eucrites indicating that nwa011 may be derived from a different parent body the presence of basaltic meteorites with variable oxygen isotopic composition suggests the occurrence of multiple basaltic meteorite parent bodies perhaps similar to 4 vesta in the early solar system

hf w evidence for rapid differentiation of iron meteorite parent bodies abstract new high precision w isotope data on iron meteorites are presented that provide important constraints on the timing of silicate metal segregation in planetesimals magmatic iron meteorites all have e 182 w within error or less radiogenic than initial e 182 w estimated by studies of chondritic meteorites at face value this implies that iron meteorites are as old and older than refractory calcium aluminium rich inclusions cai which are widely thought to be the oldest solar system objects moreover different meteorites from the same magmatic groups believed to be derived from the same planetissimal core display a range of e 182 w we suggest that the paradoxical e 182 w values more negative than initial solar system initial ssi are most readily explained as a result of secondary spallation reactions with cosmic rays during transit between parent body and the earth this is supported by the most negative e 182 w being found in meteorites with the oldest exposure ages and the magnitude of the effect is shown to be consistent with known nuclear reactions on the other hand it is also striking that none of the magmatic iron group meteorites have e 182 w analyses outside error more radiogenic than the estimated solar system initial ratio this suggests that core formation in parent bodies of magmatic iron meteorites occurred 1 5 myr after the formation age of cai y amelin a n krot i d hutcheon and a a ulyanov lead isotopic ages of chondrules and calcium aluminum inclusions science 297 1678 1683 2002 this extremely early metal silicate differentiation is coeval with the first chondrules m bizzarro j a baker and h haack mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions nature 431 275 278 2004 a n krot y amelin p cassen and a meibom young chondrules in cb chondrites from a giant impact in the early solar system nature 436 989 992 2005 formation of later chondrules and hence the parent bodies of some chondritic meteorites must therefore have occurred in the presence of planetesimals large enough to possess iron cores we conclude that early planetary accretion and differentiation was sufficiently fast for 26 al decay to be an important heat source non magmatic iron meteorites however display more radiogenic and varied w isotope signatures this is in keeping with them being generated later by impact melting during which the metal partially re equilibrated with the then more radiogenic silicate fraction

modern u pb chronometry of meteorites advancing to higher time resolution reveals new problems in this paper we evaluate the factors that influence the accuracy of lead pb isotopic ages of meteorites and may possibly be responsible for inconsistencies between pb isotopic and extinct nuclide timescales of the early solar system instrumental mass fractionation and other possible analytical sources of error presence of more than one component of non radiogenic pb migration of ancient radiogenic pb by diffusion and other mechanisms possible heterogeneity of the isotopic composition of uranium u uncertainties in the decay constants of uranium isotopes possible presence of freshly synthesized actinides with short half life e g 234u in the early solar system possible initial disequilibrium in the uranium decay chains and potential fractionation of radiogenic pb isotopes and u isotopes caused by alpha recoil and subsequent laboratory treatment we review the use of 232th 238u values to assist in making accurate interpretations of the u pb ages of meteorite components we discuss recently published u pb dates of calcium aluminum rich inclusions cais and their apparent disagreement with the extinct nuclide dates in the context of capability and common pitfalls in modern meteorite chronology finally we discuss the requirements of meteorites that are intended to be used as the reference points in building a consistent time scale of the early solar system based on the combined use of the u pb system and extinct nuclide chronometers

probabilistic landslide risk analysis considering direct costs in the area north of lisbon portugal abstract the purpose of the present study is the analysis of landslide risk for roads and buildings in a small test site 20 km 2 in the area north of lisbon portugal for this purpose an evaluation is performed integrating into a gis information obtained from multiple sources i landslide hazard ii elements at risk and iii vulnerability landslide hazard is assessed on a probabilistic basis for three different types of slope movement shallow translational slides translational slides and rotational slides based on some assumptions such as i the likelihood of future landslide occurrence can be measured through statistical relationships between past landslide distribution and specified spatial data sets considered as landslide predisposing factors and ii the rainfall combination amount duration responsible for past slope instability within the test site will produce the same effects i e same type of landslides and similar total affected area each time they occur in the future when the return period of rainfall triggering events is known different scenarios can be modelled each one ascribed to a specific return period therefore landslide hazard is quantitatively assessed on a raster basis and is expressed as the probability for each pixel 25 m 2 to be affected by a future landslide considering a rainfall triggering scenario with a specific return period elements at risk within the test site include 2561 buildings and roads amounting to 169 km values attributed to elements at risk were defined considering reconstruction costs following the guidelines of the portuguese insurance institute vulnerability is considered as the degree of loss to a given element resulting from the occurrence of a landslide of a given magnitude vulnerability depends not only on structural properties of exposed elements but also on the type of process and its magnitude i e vulnerability cannot be defined in absolute terms but only with respect to a specific process e g vulnerability to shallow translational slides therefore vulnerability was classified for the three landslide groups considered on hazard assessment taking into account i landslide magnitude mean depth volume velocity ii damage levels produced by past landslide events in the study area and iii literature finally a landslide risk analysis considering direct costs was made in an automatic way crossing the following three layers i probabilistic hazard map for a landslide type z considering a particular rainfall triggering scenario whose return period is known ii vulnerability map values from 0 to 1 of the exposed elements to landslide type z and iii value map of the exposed elements considering reconstruction costs

reassessing the origin and chronology of the unique achondrite asuka 881394 implications for distribution of 26al in the early solar system abstract the achondrite asuka 881394 has mineralogy broadly similar to that of eucrites but is isotopically chemically and texturally distinct from them previous u pb chronology shows that it is very old forming within the first 0 8 ma of the formation of calcium aluminum rich inclusions cais however the age difference between asuka 881394 and other very old solar system materials cais quenched angrites measured with the 26al 26mg and 53mn 53cr extinct radionuclide chronometers and 207pb 206pb chronometer is not the same this could be interpreted to reflect heterogeneity in the distribution of 26al and 53mn in the early solar system given the significant implications for the early solar system chronology if 26al and 53mn are indeed heterogeneously distributed in this study we further investigate the origin of asuka 881394 and the apparent age discordance between short lived and absolute chronometers by focusing on measurement of its e54cr composition renewed measurements of the absolute pb pb age and new high precision measurements of its 26al 26mg systematics new cr isotope data places additional constraints on the origin of asuka 881394 its e 54cr value of 0 37 0 10e is resolvable outside of uncertainty from hed meteorites 0 72 0 10e reinforcing evidence from oxygen isotopic analyses that suggest it originated from a distinct parent body unlikely to be 4 vesta new pb pb analyses combined with using a directly measured 238u 235u ratio for age calculation result in a recalculated pb pb age of 4564 95 0 53 ma 1 5 ma younger than the previously reported age with this age asuka 881394 remains one of the oldest known achondrites in our solar system new high precision 26al 26mg data produce an initial 26al 27al ratio of 1 48 0 12 10 6 within error of previous data this ratio corresponds to an al mg age of 4563 69 0 36 ma or 4564 83 0 21 ma relative to cais and the d orbigny angrite respectively thus depending on which age anchor is used the 26al 26mg age is either 1 26 ma or 0 12 ma younger than the new pb pb age the latter being unresolved within analytical uncertainty though a potential age discrepancy between 26al 26mg and pb pb could be a result of heterogeneous distribution of 26al we demonstrate with our new high precision mg isotope data in conjunction with petrographic evidence that the mg isotope system has been disturbed in asuka 881394 we suggest that the 26al 26mg system closed to diffusion after the u pb system either due to slow cooling on the parent body or low grade metamorphic re equilibration of mg thus we can satisfactorily explain the observed age discrepancy between 26al 26mg and u pb systems in asuka 881394 without invoking heterogeneous distribution of 26al 27al ratio in the early solar system comparison of the asuka 881394 data with that of other anomalous achondrites from distinct parent bodies suggests that these could also have evolved from a source region with a canonical 26al 27al ratio because these achondrites have significant differences in their e54cr 17o systematics which could be indicative of location within the early protoplanetary disk it is consistent with homogeneous distribution of 26al in the early solar system angrites remain an outlier either because they evolved from a source with a lower 26al 27al ratio or because their 26al 26mg or pb pb data are problematic in either case this suggests that basaltic angrites are questionable as the age anchor for the entire solar system as a whole and other very old well preserved achondrites should be considered for that role

new constraints on early solar system chronology from al mg and u pb isotope systematics in the unique basaltic achondrite northwest africa 2976 abstract we report elemental abundances and the isotopic systematics of the short lived 26 al 26 mg half life of 0 73 ma and long lived u pb radiochronometers in the ungrouped basaltic meteorite northwest africa nwa 2976 the bulk geochemical composition of nwa 2976 is clearly distinct from that of the eucrites and angrites but shows broad similarities to that of the paired nwa 001 and 2400 ungrouped achondrites indicating that it is likely to also be paired with these two samples the major and trace element abundances in nwa 2976 further indicate that it formed by extensive melting and magmatic fractionation processes on its parent body the al mg and pb pb isotope systematics indicate that this meteorite represents the earliest stages of crust formation on a differentiated parent body in the early solar system the absolute pb pb internal isochron age of nwa 2976 obtained from acid leaching residues of three whole rock samples and two pyroxene separates is 4562 89 0 59 ma mswd 0 02 this pb pb age is calculated using the measured 238 u 235 u ratio of a nwa 2976 whole rock of 137 751 0 018 2 which was determined relative to the recently revised value of 137 840 0 008 for the srm 950a u isotope standard the al mg systematics reveal the presence of 26 mg isotopic anomalies produced by the decay of 26 al with an 26 al 27 al 0 of 3 94 0 16 10 7 and indicate a time of formation of 0 26 0 18 ma after the d orbigny angrite using the revised pb pb age of 4563 36 0 34 ma for the d orbigny anchor corrected for its u isotopic composition we deduce an al mg model age of 4563 10 0 38 ma for nwa 2976 which is consistent with its pb pb internal isochron age the concordance of the pb pb and al mg chronometers when taking into account the differences in the u isotopic compositions of the d orbigny and nwa 2976 achondrites whose parent bodies likely formed in distinct regions of early solar system as indicated by their different oxygen isotopic compositions implies that 26 al was homogeneously distributed in the early solar system it also suggests that igneous processes on planetesimals as represented by the formation of various basaltic meteorite groups that likely originated on distinct parent bodies e g eucrites and angrites as well as ungrouped achondrites were widespread throughout the protoplanetary disk within the first 5 ma of the history of the solar system

the age of the solar system redefined by the oldest pb pb age of a meteoritic inclusion the age of the solar system is defined by the formation of the first solid grains in the solar nebula pb pb age dating of these solids which were later trapped in a meteorite indicates that the solar system is 0 34 1 91 million years older than previously thought the age of the solar system can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto sun this age is estimated by dating calcium aluminium rich inclusions in meteorites these inclusions are considered as the earliest formed solids in the solar nebula their formation marks the beginning for several long and short lived radiogenic clocks that are used to precisely define the timescales of solar system events such as the formation and evolution of planetary bodies1 2 3 here we present the 207pb 206pb isotope systematics in a calcium aluminium rich inclusion from the northwest africa 2364 cv3 group chondritic meteorite which indicate that the inclusion formed 4 568 2 million years ago this age is between 0 3 refs 4 5 and 1 9 refs 1 6 million years older than previous estimates and is the oldest age obtained for any solar system object so far we also determined the 26al 26mg model age of this inclusion and find that it is identical to its absolute pb pb age implying that the short lived radionuclide 26al was homogeneously distributed in the nebular disc surrounding the proto sun from the consistently old ages in the studied inclusion we conclude that the proto sun and the nebular disc formed earlier than previously thought

transport of clay minerals and anthropogenic compounds into the german bight and the provenance of fine grained sediments se of helgoland a large mud body 500 km 2 and up to 21 m thick se of helgoland has been investigated using geochemical mineralogical and sedimentological methods the analysis of 27 sediment cores from this area revealed that overlying older fine grained sediments there is a 9cake9 of muddy polluted sediments up to 3 m thick which has accumulated over the last 100 years it is assumed that human activities like dredging and dumping are responsible for this rapid rate of deposition generally it has been estimated that all of this mud has been supplied by rivers entering this part of the north sea but analyses of sediments from the ems weser and the elbe rivers show that under normal conditions the river sediments do not enter the open sea but are trapped in the estuaries it may therefore be concluded that much of the underlying unpolluted sediments of the mud area were derived from elsewhere or were laid down during an earlier period one possibility is that the lower sediments were deposited when the german bight was a sheltered area protected by a barrier of morainic sediments in the north between helgoland and schleswig holstein this barrier must have been breached more than 2000 years ago

continental marine ratio changes in suspended and settled matter across a macrotidal estuary the seine estuary northwestern france abstract suspended matter movements in the macrotidal seine estuary france are mainly controlled by tidal currents during high river spates suspended matter is carried out of the estuary into the english channel a large part of the estuarine suspended matter comes from continental inputs throughout the year suspended matter is trapped in the turbidity maximum zone and on the estuarine tidal flats marine particles which are concentrated in the turbidity maximum zone can be transported upstream into fresh water conditions physical and chemical measurements as well as grain size analysis associated with scanning electron microscopy techniques are used to study the characteristics of silty sediments and suspended matter in the turbidity maximum zone of the seine estuary particulate tracers such as diatoms indicate a continental marine ratio more than 90 in the suspended matter these results are similar with those from radiotracers sedimentary analyses on fine deposits from the estuarine tidal flats show close similarities with suspended matter coming from the turbidity maximum zone the sedimentological processes of the seine estuary are compared with those in some other estuaries

u pb systematics of the unique achondrite ibitira precise age determination and petrogenetic implications abstract ibitira is an unbrecciated equilibrated vesicular basaltic achondrite that is considered to have originated on a parent body distinct from all other known meteorites we present the first combined high precision u and pb isotopic data for this unique meteorite the 238 u 235 u value of 137 777 0 013 determined for the whole rock is comparable to values determined for bulk chondrites and other basaltic achondrites this value results in corrections of 1 1 ma for pb pb dates calculated using the previously assumed invariant 238 u 235 u value of 137 88 using the determined 238 u 235 u value the 7 most radiogenic pb isotopic analyses for acid leached pyroxene rich and whole rock fractions yield an isochron pb pb age of 4556 75 0 57 ma in excellent agreement with the results of mn cr chronology which give the ages of 4557 4 2 5 ma and 4555 9 3 2 ma using the u corrected pb pb age of d orbigny as a time anchor along with the previously proposed thermal history of ibitira and our closure temperature estimates for pb diffusion the pb pb age is interpreted as the timing of the last chemical equilibration and coarse pyroxene exsolution that occurred during high temperature metamorphism the metamorphism may have been caused by burial of ibitira lava under successive lava flows and if so the pb pb age should post date the crystallization by a short time interval the pb isotopic data for acid leachates suggest partial re equilibration of pb between plagioclase and phosphate perhaps during an impact event at 4 49 ga as recorded by k ar systematics the whole rock 238 u 204 pb indicates that compared to ci chondrites ibitira is less depleted in pb than in some alkali elements despite a lower condensation temperature of pb than the alkali elements the restricted pb depletion may reflect preferential concentration of metals with high fluid melt partition coefficients including pb and zn as a result of fluid exsolution and migration within the parent magma we discuss the implications of the u pb systematics for the origin and differentiation of the parent body

caesium from former dartmoor volcanism its incorporation in new red sediments of sw england high concentrations of caesium occur in the new red sandstone of devon england values are most abundant in breccias at the base of the permian and decrease upwards through the sandstones and marls caesium resides in the clay fraction extensive volcanic activity on the south eastern edge of the cornubian massif provided a supply of cs due to its low ionic potential this alkali was concentrated at source under extreme weathering in the hydrolysate fraction of red bed sediments the source area was largely exhausted by late permian reflected by a reduction in cs content of new red sandstone detritus

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

crustal differentiation in the early solar system clues from the unique achondrite northwest africa 7325 nwa 7325 the unique achondrite nwa 7325 is an unusual olivine gabbro composed chiefly of calcic plagioclase an85 93 diopsidic pyroxene en50 1 54 0 wo44 8 49 3 fs0 6 1 3 and forsteritic olivine fo97 it is al and mg rich and fe and na poor and displays very low concentrations of incompatible trace elements much below 0 3 x ci abundances for many of them it is also characterized by huge eu and sr anomalies eu eu 65 srn cen 240 although the o isotopic composition of nwa 7325 and some ureilites those with olivine cores in the range fo75 to fo88 are similar a genetic relationship between them is unlikely due to the fe poor composition of nwa 7325 it is almost certainly derived from a distinct planetesimal not previously sampled by other achondrites the low na al ga al zn al ratios as well as the low k rb and cs shown by nwa 7325 suggest a volatile depleted parent body this unique gabbro is demonstrably a cumulate but the composition of its parental melt cannot be precisely assessed however the liquid from which nwa 7325 crystallized would have been very poor in incompatible trace elements yb in the range of 0 25 to 1 5 x ci abundance with a very large positive eu anomaly such a melt cannot be the product of the early magmatic activity on a small parent body instead we propose that the parental melt to nwa 7325 formed as a consequence of the total melting of an ancient gabbroic lithology possibly upon impact in agreement with the systematics of 26al 26mg based on recent dating the crustal material that was parental to nwa 7325 must have been older than 4562 8 ma and formed possibly 4566 ma ago if this scenario is correct nwa 7325 provides evidence of one of the earliest crusts on a differentiated body so far studied

differentiation of vesta and the parent bodies of other achondrites 1 numerical simulations have been performed to understand the planetary differentiation of vesta and other differentiated asteroids the short lived nuclides 26al and 60fe were used as the heat sources for the differentiation of asteroids of sizes 20 270 km the essential aim was to simulate the two proposed differentiation scenarios associated with the formation of the basaltic achondrites one of these scenarios deals with their origin by partial melting of silicates the other scenario involves the origin of basalts from the residual melt left subsequent to crystallization in a convective and cooling magma ocean the core mantle differentiation in both the scenarios was commenced subsequent to 40 silicate melting the partial melt scenario seems to contradict the general trend in the chronological sequence of core mantle and mantle crust differentiations observed in various differentiated meteorites unless the irons meteorite parent bodies differentiated rapidly compared to prolonged accretion and differentiation of distinct parent bodies of achondrites even though the geochemical records of siderophile elements in eucrites favor the residual melt scenario based on our simulations it is difficult to rapidly and globally cool the magma oceans to produce residual basaltic melts subsequent to crystallization within initial 10 million years this is in contradiction with the chronological records of the basalts that suggest their early origin in order to make this scenario viable by invoking rapid and global cooling of the magma ocean it would be essential to substantially remove the insulating crust of the planetesimal by continuous bombardment of small planetesimals in the early solar system

53mn 53cr and 26al 26mg ages of a feldspathic lithology in polymict ureilites abstract we report 53 mn 53 cr and 26 al 26 mg isotopic data obtained by in situ sims analysis for feldspathic clasts in polymict ureilites dag 319 and dag 165 the analyzed clasts belong to the albitic lithology the most abundant population of indigenous feldspathic materials in polymict ureilites and are highly fractionated igneous assemblages of albitic plagioclase fe rich pyroxenes phosphates ilmenite silica and fe mn k p ti enriched glass glass in dag 165 clast 19 has extremely high and variable 55 mn 52 cr ratios 500 58 000 and shows correlated 53 cr excesses up to 1500 clearly indicating the presence of live 53 mn at the time of formation the slope of the well correlated isochron defined by glass and pyroxenes from this clast corresponds to 53 mn 55 mn 2 84 0 10 10 6 2 data for less 55 mn 52 cr enriched glasses from dag 319 clast b1 as well as phosphates from several other clasts are consistent with this isochron the 53 mn 55 mn ratio obtained from the isochron implies that these clasts are 0 70 0 18 ma younger than the d orbigny angrite corresponding to the absolute age of 4563 72 0 22 ma plagioclase in dag 319 clast b1 has a fairly constant 27 al 24 mg ratio of 900 and shows resolvable 26 mg excesses of 2 the slope of the isochron defined by pyroxene and plagioclase in this clast is 3 0 1 1 10 7 2 corresponding to a time difference of 5 4 0 3 0 5 ma after cai assuming the canonical initial 26 al 27 al ratio of 5 10 5 and an age 0 5 0 3 0 5 ma younger than d orbigny its absolute age relative to d orbigny is 4563 9 0 4 0 5 ma in agreement with the 53 mn 53 cr age from clast 19 these data provide the first high precision age date 5 4 ma after cai for ureilites giving a minimum estimate for the age of differentiation of their parent asteroid interpretation of this age for the thermal and physical history of that asteroid depends on a number of currently unknown or model dependent parameters including its size bulk composition and oxidation state and the petrologic relationship between the feldspathic clasts and main group ureilites

landslides and climatic conditions in the barcelonnette and vars basins southern french alps france research into the climatic causes behind the triggering and reactivation of landslides has been carried out in two basins in the southern french alps where a great many landslides have occurred over more than a century correlations between landslides and climate are sometimes precise and closely related in time at other times imprecise and more distant the better known the type of landslide and the date of its occurrence the greater the correlation may appear be this as it may climate is never the sole cause this paper deals with the limits of the effects of climate

pb diffusion in cr diopside augite and enstatite and consideration of the dependence of cation diffusion in pyroxene on oxygen fugacity abstract chemical diffusion of pb under anhydrous po2 buffered conditions has been measured in natural pyroxenes of three different compositions a chromian diopside an augitic clinopyroxene and a near end member enstatite sources of diffusant consisted of pbs powder and ground pyroxene mixed together pre reacted in evacuated silica capsules at 1050 c and re ground prepared sample capsules were annealed for times ranging from several hours to a few months at temperatures from 850 c to 1050 c the pb distributions in the pyroxene specimens were profiled by rutherford backscattering spectrometry rbs the following arrhenius relations are obtained for pb diffusion in the pyroxenes when buffered at qfm d c 8 7 10 7 exp 351 36 kj mol 1 rt m 2 s 1 cr diopside d a 3 8 10 5 exp 372 15 kj mol 1 rt m 2 s 1 augite d e 6 6 10 7 exp 366 29 kj mol 1 rt m 2 s 1 enstatite in all cases diffusion is measured perpendicular to the c axis diffusion in cr diopside does not appear to be strongly anisotropic as diffusion rates for transport parallel to c are similar to the 110 results above diffusion in the augite is faster by nearly an order of magnitude than pb diffusion in the cr diopside diffusion tends to be faster in pyroxenes with higher iron contents as was evident in our earlier work chemical geology 150 1998a 105 but simple correlations are not obvious pb diffusion in enstatite is considerably slower than in the clinopyroxene compositions studied to investigate the fo2 dependence of pb diffusion in pyroxene experiments using the cr diopside augite and enstatite as well as the near end member diopside and a more iron rich clinopyroxene employed in a recent diffusion study chemical geology 150 1998a 105 were run at 950 c under oxygen fugacities ranging from 10 6 to 10 16 all of the pyroxenes exhibited a positive dependence of pb diffusion rate on fo2 with values of m ranging from 0 14 to 0 20 given d fo2 m interestingly the exponential term for diopside is 0 19 in good agreement with the value 3 16 determined from point defect models for diffusion mechanisms controlled by cation vacancies j geophys res 99 1994 9423 the activation energies for pb diffusion in all of the pyroxenes studied are relatively high and pb diffusivities slow when compared with the extant diffusion data for most other minerals it follows as consequence of these comparatively slow diffusivities that pb closure temperatures are higher in pyroxenes than for the majority of minerals with the exception of a few phases such as zircon monazite and garnet the slightly faster diffusivities that characterize fe rich clinopyroxenes will lead to somewhat depressed closure temperatures but pyroxenes in general should be fairly retentive of pb isotopic information when subjected to all but the most extreme thermal events

alkali metals in the permo triassic as geochemical indicators of surficial processes abstract techniques established as most successful in the examination of widely variable but mainly oxidised geological materials require separation and isolation of components prior to analysis these methods reduce the number of variables involved in the production of clastic debris and enable conclusions to be drawn from a practical reversal of rock manufacture alkali metals prove successful as indicators of the surficial processes operative during permo triassic times they demonstrate enrichment by igneous material during early breccia production and subsequent dilution by wider sedimentation in basins to the east of cornubia england alkalis in recent soils river estuarine and beach sediments of southwest england are concentrated in the fine grained m fraction soils developed over permo triassic bedrock modern river estuarine sediments and beach sands all show anomalous enrichment of trace alkali metals they reflect the abundance of li rb and cs in parent material geochemical analyses of clays from deep boreholes in the wessex and central somerset basins enable inter basin comparisons with the high alkali deposits of devon absolute trace alkali levels are broadly similar to those of correlated beds at outcrop concentrations of cs prove higher in the upper permian than in the triassic of the wessex basin whilst values show devonian old red sandstone sediments to be un enriched in li and cs enrichment of li over rb in triassic mercia mudstones of the south devon coast suggests some li capture from sabkha brines by clays during evaporite production

an extension of the bus asteroid taxonomy into the near infrared the availability of asteroid spectral measurements extending to the near infrared resulting from the development of new telescopic instruments such as spex rayner 2003 provides a new basis for classifying asteroid reflectance spectra we present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0 45 to 2 45 microns this system of 24 classes is constructed using principal component analysis following most closely the visible wavelength taxonomy of bus 1999 which itself builds upon the system of tholen 1984 nearly all of the bus taxonomy classes are preserved with one new class sv defined for each class we present boundary definitions spectral descriptions and prototype examples a flow chart method is presented for classifying newly acquired data spanning this wavelength range when data are available only in the near infrared range 0 85 to 2 45 microns classification is also possible in many cases through an alternate flow chart process within our sample several classes remain relatively rare only 6 objects fall into the a class 349 dembowska and 3628 boznemcova reside as the only objects in their respective r and o classes eight q class objects are all near earth asteroids we note 1904 massevitch as an outer main belt v type while 15 other v type objects have inner main belt orbits consistent with an association with vesta

triggering conditions and mobility of debris flows associated to complex earthflows landslides on black marl slopes of the french alps are in most cases complex catastrophic failures in which the initial structural slides transform into slow moving earthflows under specific hydrological conditions these earthflows can transform into debris flows due to their sediment volume and their high mobility debris flow induced by landslides are far much dangerous than these resulting from continuous erosive processes a fundamental point to correctly delineate the area exposed to debris flows on the alluvial fans is therefore to understand why and how some earthflows transform into debris flow while most of them stabilize in this paper a case of transformation from earthflow to debris flow is presented and analysed an approach combining geomorphology hydrology geotechnics and rheology is adopted to model the debris flow initiation failure stage and its runout postfailure stage using the super sauze earthflow alpes de haute provence france as a case study the objective is to characterize the hydrological and mechanical conditions leading to debris flow initiation in such cohesive material results show a very good agreement between the observed runout distances and these calculated using the debris flow modeling code cemagref 1 d the deposit thickness in the depositional area and the velocities of the debris flows are also well reproduced furthermore a dynamic slope stability analysis shows that conditions in the debris source area under average pore water pressures and moisture contents are close to failure a small excess of water can therefore initiate failure seepage analysis is used to estimate the volume of debris that can be released for several hydroclimatic conditions the failed volumes are then introduced in the cemagref 1 d runout code to propose debris flow hazard scenarios results show that clayey earthflow can transform under 5 year return period rainfall conditions into 1 km runout debris flow of volumes ranging between 2000 to 5000 m 3 slope failures induced by 25 year return period rainfall can trigger large debris flow events 30 000 to 50 000 m 3 that can reach the alluvial fan and cause damage

geologic mapping of vesta from 1994 hubble space telescope images we utilize the 56 images of asteroid 4 vesta obtained through four mineralogically diagnostic filters by the hubble space telescope zellneret al 1997 icarus to construct a geologic map vesta s surface is found to be geologically diverse and to be dichotomous at a hemispheric scale the eastern hemisphere longitude definition from thomaset al 1997 icarus is dominated by units interpreted to be impact excavated plutonic material composed of magnesium rich and calcium poor pyroxene the mineralogy of this region is most analogous to diogenite meteorites several eastern hemisphere units which have the deepest and broadest 1 m absorption bands may contain a substantial olivine component the locations of these units are consistent with a previous map based on rotationally resolved groundbased spectroscopy gaffey 1997 icarus the western hemisphere is dominated by units interpreted to consist of a single component of iron rich and relatively calcium rich pyroxene analogous to surface basalts such as eucrite meteorites we investigate the spectral properties of 20 representative surface regions and find a correlation between the 1 m absorption band depth and albedo the units with lower albedos have shallower band depths such a relation could arise from differences in lithologies differences in surface particle sizes or from a weathering effect which decreases albedo and band depth over time because of vesta s geologic diversity and hemispheric dichotomy it is apparent that any major impact events such as those possibly related to the formation of the vesta family binzel and xu 1993 science260 186 191 did not globally resurface the planet the spectral evidence for remnants of a basaltic crust implies that the oldest units on the surface date back to the time of their emplacement most likely 4 5 byr ago if a weathering process exists which alters the albedo then the lowest albedo units such as the feature with the proposed name olbers most likely represent remnants of vesta s ancient basaltic crust

differentiation and magmatic activity in vesta evidenced by 26al 26mg dating in eucrites and diogenites abstract the 26 al 26 mg short lived chronometer has been widely used for dating ancient objects in studying the early solar system here we use this chronometer to investigate and refine the geological history of the asteroid 4 vesta ten meteorites widely believed to come from vesta 4 basaltic eucrites 3 cumulate eucrites and 3 diogenites and the unique achondrite asuka 881394 were selected for this study all samples were analyzed for their 26 mg and 27 al 24 mg ratios in order to construct both whole rock and model whole rock isochrons mineral separation was performed on 8 of the hed s in order to obtain internal isochrons while whole rock al mg analyses of hed s plot on a regression that could be interpreted as a vestan planetary isochron internal mineral isochrons indicate a more complex history crystallization ages obtained from internal 26 al 26 mg systematic in basaltic eucrites show that vesta s upper crust was formed during a short period of magmatic activity at 2 66 0 58 1 39 million years ma after calcium aluminum inclusions after cai we also suggest that impact metamorphism and subsequent age resetting could have taken place at the surface of vesta while 26 al was still extant cumulate eucrites crystallized progressively from 5 48 0 60 1 56 to 7 25 ma after cai model ages obtained for both basaltic and cumulate eucrites are similar and suggest that the timing of differentiation of a common eucrite source from a chondritic body can be modeled at 2 88 0 12 0 14 ma after cai i e contemporaneously from the onset of the basaltic eucritic crust based on their cumulate texture we suggest cumulate eucrites were likely formed deeper in the crust of vesta diogenites have a more complicated history and their 26 al 26 mg systematics show that they likely formed after the complete decay of 26 al and thus are younger than eucrites this refined chronology for eucrites and diogenites is consistent with a short magma ocean stage on 4 vesta from which the basaltic eucrites rapidly crystallized in order to explain the younger age and the complex history of diogenites we postulate that a second episode of magmatism was possibly triggered by a mantle overturn we bring a refined chronology of the geological history of vesta that shows that the asteroid has known a more complex differentiation than previously thought

high calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites our analyses of high quality spectra of several s type asteroids 17 thetis 847 agnia 808 merxia and members of the agnia and merxia families reveal that they include both low and highcalcium pyroxene with minor amounts of olivine 0 4 high calcium pyroxene is a spectrally detectable and petrologically important indicator of igneous history and may prove critical in future studies aimed at understanding the history of asteroidal bodies the silicate mineralogy inferred for thetis and the merxia and agnia family members requires that these asteroids experienced igneous differentiation producing broadly basaltic surface lithologies together with 4 vesta and its smaller vestoid family members and the main belt asteroid 1489 magnya these new asteroids provide strong evidence for igneous differentiation of at least five asteroid parent bodies based on this analysis of a small subset of the near infrared asteroid spectra taken to date with spex at the nasa irtf we expect that the number of known differentiated asteroids will increase consistent with the large number of parent bodies inferred from studies of iron meteorites

end of the kiaman superchron in the permian of sw england magnetostratigraphy of the aylesbeare mudstone and exeter groups the chronology of permian strata in sw england is fragmentary and largely based on radiometric dating of associated volcanic units magnetostratigraphy from the c 2 km of sediments in the exeter and aylesbeare mudstone groups was undertaken to define a detailed chronology using the end of the kiaman superchron and the overlying reverse and normal polarity in the middle and upper permian as age constraints the palaeomagnetic directions are consistent with other european permian palaeopoles with data passing fold and reversal tests the end of the kiaman superchron in the wordian occurs in the uppermost part of the exeter group the overlying aylesbeare mudstone group is early capitanian to latest wuchiapingian in age the changhsingian and most of the lower triassic sequence is absent magnetostratigraphic comparison with the southern permian basin shows that the exeter and aylesbeare mudstone groups are closely comparable in age with the havel and elbe subgroups of the rotliegend ii succession the altmark unconformities in these successions appear similar in age to the sequence boundaries in sw england indicating that both may be climate controlled clasts in the exeter group from unroofing of the dartmoor granite first occurred at a minimum of c 8 myr after formation of the granite supplementary material additional sampling magnetic fabric and palaeomagnetic data are available at http doi org 10 6084 m9 figshare c 3283400

ancient relative and absolute ages for a basaltic meteorite implications for timescales of planetesimal accretion and differentiation abstract asuka 881394 is a unique basaltic meteorite that originated in the crust of a differentiated planetesimal in the early solar system we present high precision pb mg and cr isotopic compositions of bulk samples and mineral separates from this achondrite a 207pb 206pb internal isochron obtained from the radiogenic pyroxene and whole rock fractions of asuka 881394 yields an absolute age of 4566 5 0 2 ma which we consider to be the best estimate for the crystallization age of this basaltic achondrite the 26al 26mg systematics show some evidence of disturbance but 5 of the 6 analyzed whole rock and mineral fractions define an isochron corresponding to a 27al 26al ratio of 1 28 0 07 10 6 comparison with the 26al 26mg and pb pb systematics in the d orbigny achondrite translates to a 26al 26mg age of 4565 4 0 2 ma for asuka 881394 the 53mn 53cr systematics in whole rock silicate and chromite fractions correspond to a 53mn 55mn ratio of 3 85 0 23 10 6 compared to the most precise 53mn 53cr and pb pb systematics available for the d orbigny angrite this translates to a 53mn 53cr age of 4565 3 0 4 ma similarly a comparison with the nwa 4801 angrite yields a 53mn 53cr age of 4565 5 0 4 ma in agreement with the age obtained relative to d orbigny while the 26al 26mg and 53mn 53cr ages appear to be concordant in asuka 881394 these ages are 1 ma younger than its 207pb 206pb age this discordance might have been caused by one or more of several reasons including differences in the closure temperatures for pb versus cr and mg diffusion in their host minerals combined with slow cooling of the parent body as well as differential resetting of isotopic systems by a process other than volume diffusion e g shock metamorphism the ancient age of asuka 881394 suggests that basaltic volcanism on its parent planetesimal occurred within 3 ma of the formation of earliest solids in the solar system essentially contemporaneously with chondrule formation this requires that the asuka 881394 parent body was fully accreted within 500 000 yrs of solar system formation

geological and geotechnical properties of the terres noires in southeastern france weathering erosion solid transport and instability abstract the geological formation known as the terres noires covers large areas of southeastern france between the rhone valley and the pre alpine hills this formation consists mainly of dark marls of the basal upper jurassic these marls are very susceptibility to weathering and are particularly prone to erosion resulting in high solid transport this paper attempts to quantify this transport in experimental catchment areas and shows that a forest cover can play a major role in preventing this type of phenomenon weathering of this formation may also lead to gravity instabilities in fresh marl although this is rare and much more frequently in the surficial weathered material

distinguishing between natural and anthropogenic sources of metals entering the irish sea international agreements e g ospar on the release of hazardous substances into the marine environment and environmental assessments of shelf seas require that concentrations and bioavailability of metals from anthropogenic sources can be distinguished from those originating as a result of natural geological processes the development of a methodology for distinguishing between anthropogenic and natural sources of metals entering the irish sea through river inputs is described the geochemistry of stream river and estuarine sediments has been used to identify background geochemical signatures related to geology and modifications to these signatures by anthropogenic activities the british geological survey bgs geochemical database based on stream sediments from 1 to 2 km2 catchments was used to derive the background signatures where mining activity was present the impact on the signature was estimated by comparison with the geochemistry of sediments from a geologically similar but mining free area river sediment samples taken upstream and downstream of major towns were used respectively to test the validity of using stream sediments to estimate the chemistry of the major river sediment and to provide an indication of the anthropogenic impact related to urban and industrial development the geochemistry of estuarine sediments from surface samples and cores was then compared with river and offshore sediment chemistry to assess the importance of riverine inputs to the irish sea studies were undertaken in the solway ribble wyre and mersey estuaries the results verify that catchment averages of stream sediments and major river samples have comparable chemistry where anthropogenic influences are small major urban and industrial including mining development causes easily recognised departures from the natural multi element geochemical signature in river sediment samples downstream of the development and enhanced metal levels are observed in sediments from estuaries with industrial catchments stream sediment chemistry coupled with limited river and estuarine sampling provides a cost effective means of identifying anthropogenic metal inputs to the marine environment investigations of field and laboratory protocols to characterise biological impact bioaccumulation of metals in sediments of the irish sea and its estuaries show that useful assessments can be made by a combination of surveys with bioindicator species such as clams scrobicularia plana selective sediment measurements that mimic the biologically available fractions and laboratory mesocosm studies

reconciliation of the excess 176 hf conundrum in meteorites recent disturbances of the lu hf and sm nd isotope systematics abstract the long lived 176 lu 176 hf and 147 sm 143 nd radioisotope systems are commonly used chronometers but when applied to meteorites they can reveal disturbances specifically lu hf isochrons commonly yield dates up to 300 myr older than the solar system and varying initial 176 hf 177 hf values we investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible minerals scatter away from isochron regressions for both meteorite classes with low hf phases such as plagioclase and olivine typically being most displaced above or left of reference isochrons relatively hf rich pyroxene is less disturbed but still to the point of steepening lu hf errorchrons using our lu hf and sm nd data we tested various hf and lu redistribution scenarios and found that decoupling of lu hf from 176 hf 177 hf must postdate the accumulation of significant radiogenic 176 hf therefore early irradiation or diffusion cannot explain the excess 176 hf instead disturbed meteorite isochrons are more likely caused by terrestrial weathering contamination or common laboratory procedures the partial dissolution of phosphate minerals may predominantly remove rare earth elements including lu leaving relatively immobile and radiogenic hf behind robust lu hf and improved sm nd meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic hf and silicate hosted terrestrial contaminants without disturbing parent daughter ratios

instability conditions of marly hillslopes towards landsliding or gullying the case of the barcelonnette basin south east france abstract black marl hillslopes in the french alps are strongly affected either by mass movements or by gully erosion due to their susceptibility to weathering processes this paper presents experimental data geomorphological geotechnical geomechanical and hydrological on the parameters of the material of three well known earthflows and of the two stratigraphic parts of the callovo oxfordian black marl the main objectives are to define the geomechanical behaviour of the various formations using different characterisations grain size distribution mineralogy retention capacity consolidation test direct shear test and triaxial test and to demonstrate how such soils can affect the stability of natural slopes particular care must be taken when interpreting the geomechanical tests on this evolving and very heterogeneous clay rich material there are strong relationships between the parent rock and the landslide materials this paper presents a conceptual model of the development of strength over a period of time and investigates the parameters of the material for use in slope stability analysis and risk assessment

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment

a process based model for colluvial soil depth and shallow landsliding using digital elevation data a model is proposed for predicting the spatial variation in colluvial soil depth the results of which are used in a separate model to examine the effects of root strength and vertically varying saturated conductivity on slope stability the soil depth model solves for the mass balance between soil production from underlying bedrock and the divergence of diffusive soil transport this model is applied using high resolution digital elevation data of a well studied site in northern california and the evolving soil depth is solved using a finite difference model under varying initial conditions the field data support an exponential decline of soil production with increasing soil depth and a diffusivity of about 50 cm 2 yr the predicted pattern of thick and thin colluvium corresponds well with field observations soil thickness on ridges rapidly obtain an equilibrium depth which suggests that detailed field observations relating soil depth to local topographic curvature could further test this model bedrock emerges where the curvature causes divergent transport to exceed the soil production rate hence the spatial pattern of bedrock outcrops places constraints on the production law the infinite slope stability model uses the predicted soil depth to estimate the effects of root cohesion and vertically varying saturated conductivity low cohesion soils overlying low conductivity bedrock are shown to be least stable the model may be most useful in analyses of slope instability associated with vegetation changes from either land use or climate change although practical applications may be limited by the need to assign values to several spatially varying parameters although both the soil depth and slope stability models offer local mechanistic predictions that can be applied to large areas representation of the finest scale valleys in the digital terrain model significantly influences local model predictions this argues for preserving fine scale topographic detail and using relatively fine grid sizes even in analyses of large catchments

temporal variations in the trace element content of stream sediments an example from a tropical rain forest regime solomon islands abstract a stream sediment geochemical anomaly in a tropical rain forest environment on the island of guadalcanal was monitored at monthly intervals over a period of 15 months major changes in stream sediment chemistry took place after heavy rainfall associated with the passage of the tail of a cyclone through the region these changes were directly linked to changes in the mineralogical composition of the sediments significant chemical variations also occurred in the period before the cyclone but these appear to have been related to variations in hydromorphic dispersion processes the data suggest that common exploration practices such as the use of threshold values should be applied with caution in tropical rain forest terrain the use of element fe ratios in exploration work and smoothing techniques in regional geochemical mapping may help eliminate some of the more pronounced effects of temporal variations in the trace element contents of stream sediments

26al 26mg deficit dating ultramafic meteorites and silicate planetesimal differentiation in the early solar system abstract meteorites with significantly sub chondritic al mg that formed in the first 2 million years of the solar system should be characterised by deficits in the abundance of 26mg 26mg due to the absence of in growth of 26mg from the decay of short lived 26al t1 2 0 73 myr however these 26mg deficits will be small 26mg 0 037 even for material that formed at the same time as the solar system s oldest solids calcium aluminium rich inclusions and thus measurement of these deficits is analytically challenging here we report on a search for 26mg deficits in three types of ultramafic meteorites pallasites ureilites and aubrites by multiple collector inductively coupled plasma mass spectrometry a range of analytical tests were carried out including analysis of 1 a range of synthetic mg solution standards 2 mg gravimetrically doped with a high purity 26mg spike 3 mg cuts collected sequentially from cation exchange separation columns with fractionated stable mg isotope compositions 4 mg separated from samples that was bracketed by analyses of both dsm 3 and mg separated from a natural olivine sample subjected to the same chemical processing as the samples these tests confirm it is possible to resolve differences in 26mg from the terrestrial materials that are 0 005 however if mg yields from chemical separation are low or an inappropriate equilibrium isotopically fractionated standard is used this will generate analytical artefacts on 26mg when this is calculated with the kinetic exponential mass fractionation law as is the case when correcting for instrumental mass bias during mass spectrometric analysis olivine from four different main group pallasites and four bulk ureilites have small deficits in the abundance of 26mg with 26 mg dsm 3 0 0120 0 0018 and 26 mg dsm 3 0 0062 0 0023 respectively relative to terrestrial olivine 26 mg dsm 3 0 0029 0 0028 six aubrites have 26 mg dsm 3 0 0015 0 0020 which is identical to terrestrial olivine model ages from these deficits can be calculated by assuming that 26al was homogeneously distributed in the planetesimal forming regions of the proto planetary disc at the same level as calcium aluminium rich inclusions cais the absence of 26mg deficits in aubrites means these can only be constrained to have formed relatively late 2 9 myr after cai formation model ages calculated from pallasite olivine deficits would suggest that pallasite olivine crystallised and was diffusively isolated on its parent body 1 24 0 28 0 40 myr after formation of cais similarly ureilites would have experienced silicate partial melting and lowering of their bulk al mg ratios 1 9 0 7 2 2 myr after cai formation the model ages for silicate differentiation on the main group pallasite parent body are intermediate between those for metal silicate fractionation for core formation obtained from magmatic iron meteorites and those for asteroidal silicate magmatism obtained from basaltic meteorites

carbonaceous achondrites northwest africa 6704 6693 milestones for early solar system chronology and genealogy abstract northwest africa nwa 6704 6693 are medium to coarse grained achondrites with unique petrologic and geochemical traits that are distinct from the currently established meteorite groups here we report on the extinct 26al 26mg and 53mn 53cr systems to establish fine scale chronology of its formation and cr and ti isotopic anomalies to constrain the composition of the source reservoir of nwa 6704 6693 excesses in the neutron rich 54cr and 50ti isotopes due to nucleosynthetic anomalies separate nwa 6704 6693 from the vast majority of established achondrites and instead resemble the excesses seen among the carbonaceous chondrites specifically the cr type chondrites the excesses in these isotopes indicate a common feeding zone during accretion in the protoplanetary disk between the source of nwa 6704 6693 and that of the carbonaceous chondrites the 26al 26mg data for pyroxene and plagioclase from nwa 6704 yield a 26al 27al 0 3 15 0 38 10 7 mswd 0 49 and an initial 26mg 0 004 0 005 at the time of isotopic closure this initial 26al 27al 0 translates to an absolute age of 4563 14 0 38 ma relative to the d orbigny angrite however given the potential heterogeneity of 26al the d orbigny angrite might not be a good age anchor for the purpose of calculating 26al 26mg ages the 26al 26mg age relative to another carbonaceous achondrite nwa 2976 is 4562 66 0 60 ma the 53mn 53cr systematics of nwa 6704 6693 indicate a 53mn 55mn 0 of 2 59 0 34 10 6 mswd 1 2 with an evolved initial e53cr of 0 14 0 03 the 53mn 55mn 0 yields an 53mn 53cr age of 4562 17 0 76 ma relative to the d orbigny angrite concordant ages determined using the short lived 26al 26mg and 53mn 53cr systems and extant 207pb 206pb system 4562 60 0 30 ma for nwa 6704 6693 amelin et al 2019 indicate rapid cooling and nearly contemporaneous closing of multiple isotope systems the ancient crystallization ages and positive 54cr and 50ti anomalies of nwa 6704 6693 indicate widespread melting and differentiation processes occurring in both non carbonaceous nc and carbonaceous chondrite cc regions of the protoplanetary disk additionally we report the cr and ti isotopic composition for a petrologic range of cr type materials cr2 cr6 and achondrites the additional cr and ti isotopic data for these cr type materials indicates a range in isotopic composition not previously observed based on cr2 chondrites alone

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

evaluation of cold water carbonates as a possible paleoclimatic indicator abstract the common belief currently shared by many geoscientists concerning the climatic interpretation of limestones is that a warm water environment is essential this concept is not necessarily true because the rate and extent of terrigenous sediment dilution rather than water temperature is the primary factor determining whether or not a limestone forms at nearshore or continental shelf depths because carbonate productivity is lowest in cold climates however caco3 abundance and the thickness of carbonate accumulations tend to be least at high latitudes in this regard present day continental shelves and beaches offer a poor model for comparing cold water and warm water carbonates because of the generally emergent continental tectonic framework recent eustatic sea level changes and the presence of ice caps at the modern poles typically the influence of climate on non reef continental shelf and beach environments cannot be clearly distinguished by the presence or absence of major taxonomic groups faunal diversity and equitability are more sensitive in this regard the absence of shelf depth inorganic carbonate precipitates micrite envelopes and peloids may also point to the cold water origin of a rock skeletal mineralogy and oxygen isotopes of certain unrecrystallized carbonates may be good paleoclimatic indicators however trace elements and physical textural attributes of the carbonate fraction are probably temperature insensitive previous studies of high latitude continental shelves have concentrated merely on the abundance of calcareous material and there is seemingly a disproportionate amount of information with respect to low latitude carbonate studies further research on cold water carbonates may open up new avenues for alternative paleoenvironmental and paleoclimatic interpretations

long term modelling of landslides for different forest management practices long term effects of different forest management practices on landslide initiation and volume were analysed using a physically based slope stability model the watershed based model calculates the effects of multiple harvesting entries on slope stability by accounting for the cumulative impacts of a prior vegetation removal on a more recent removal related to vegetation root strength and tree surcharge four sequential clearcuts and partial cuts with variable rotation lengths were simulated with or without leave areas and with or without understorey vegetation in a subwatershed of carnation creek vancouver island british columbia the combined in nite slope and distributed hydrologic models used to calculate safety factor revealed that most of the simulated landslides were clustered within a 5 to 17 year period after initial harvesting in cases where suf cient time c 50 years lapsed prior to the next harvesting cycle partial cutting produced fewer landslides and reduced landslide volume by 1 4 to 1 6 fold compared to clearcutting approximately the same total landslide volume was produced when 100 per cent of the site was initially clearcut compared to harvesting 20 per cent of the area in successive 10 year intervals a similar nding was obtained for partial cutting vegetation leave areas were effective in reducing landsliding by 2 to 3 fold retaining vigorous understorey vegetation also reduced landslide volume by 3 8 to 4 8 fold the combined management strategies of partial cutting increasing rotation length provision of leave areas and retention of viable understorey vegetation offer the best alternative for minimizing landslide occurrence in managed forests copyright 2003 john wiley sons ltd

a view on some hydrological triggering systems in landslides abstract in this paper different types of hydrological triggering systems for debris flows shallow and deeper landslides are described the generation of surface run off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows failure conditions in shallow landslides can occur when at a critical depth which is determined by the cohesion of the soil and the slope angle the moisture content in the soil becomes close to saturation resulting in a considerable reduction of soil strength deeper landslides 5 20 m depth are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level the assessment of meteorological threshold conditions for shallow landslides 1 2 m needs more detailed meteorological information than for deeper landslides in the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration

finding the most suitable slope stability model for the assessment of the impact of climate change on a landslide in southeast france the response of a landslide near barcelonnette southeast france to climatic factors was simulated with three slope stability models a fully empirical gross precipitation threshold a semi empirical threshold model for net precipitation and a fully conceptual slope stability model the three models performed with similar levels in reproducing the present day temporal pattern of landslide reactivation using dendrogeomorphological information as test data the semi empirical and conceptual models were found to be overparameterized because more than one parameter setting matching the test data was identified in the case of the conceptual model this resulted in strongly divergent scenarios of future landslide activity using downscaled climate scenarios as inputs to the model the uncertainty of the landslide scenarios obtained with the semi empirical model was much lower in addition the simulation of strongly different scenarios by the fully empirical threshold was attributed to its incomplete representation of the site specific landslide reactivation mechanism it is concluded that the semi empirical model constitutes the best compromise between conceptual representation and model robustness copyright 2000 john wiley sons ltd

a distributed slope stability model for steep forested basins a distributed physically based slope stability model dslam based on an infinite slope model a kinematic wave groundwater model and a continuous change vegetation root strength model is presented it is integrated with a contour line based topographic analysis and a geographic information system gis for spatial data extraction and display the model can be run with either individual rainfall events or long term sequences of storms these inputs can be either actual storm records or synthesized random events based on monte carlo simulation the model is designed to analyze rapid shallow landslides and the spatial distribution of safety factor fs in steep forested areas it can investigate the slope stability problem in both temporal and spatial dimensions for example the impact of timber harvesting on slope stability either at a given time or through an extended management period the probability of landslide occurrence for a given year and the delivery of landslide sediments to headwater streams the dslam model was applied in a steep forested drainage of cedar creek in the oregon coast ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975 simulated volume and number of failures were 733 m3 and 4 respectively these values agreed closely with field measurements following the 1975 storm however the effect of parameter uncertainty may complicate this comparison for example when soil cohesion values of 2 0 and 3 0 kpa were used the failure volume changed by factors of 2 04 and 0 41 respectively compared with the average condition of 2 5 kpa used in the simulation for soil depths 30 higher and lower than the standard condition the failure volume changed by factors of 2 0 and 0 27 respectively when maximum root cohesion changed from 12 5 kpa average condition to 10 kpa the failure volume increased 1 73 fold for the case of 15 kpa the failure volume changed by a factor of 0 55 the simulated failures caused by the storm were mostly in hollows the simulations show that the spatial distribution of fs is controlled mainly by topography and timber harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms most areas with fs 3 0 corresponded with the distribution of blocks clear cut in 1968 and all elements with fs 2 0 were in areas clear cut in 1968 areas with low fs 1 0 1 6 expanded dramatically during the rainstorm and decreased at a slow rate after the storm factors of safety in hollows declined sharply during the storm

sims pb pb and u pb age determination of eucrite zircons at 5 μm scale and the first 50 ma of the thermal history of vesta eucrites a subgroup of basaltic achondrites represent the remnants of the earliest magmatic stage of the solar system formation possibly on the asteroid 4 vesta the precise determination of their crystallization age is therefore important for constraining the evolutionary history of the asteroid including melting and differentiation processes of the parent body zircons would be the best mineral for such purpose however extra terrestrial zircons are rare and those found in eucrites are typically small 5 m using a cameca ims 1280 high resolution ion microprobe precise uranium lead u pb and pb pb ages of the non cumulate basaltic eucrite zircons in bereba cachari caldera camel donga and juvinas were determined successfully at scale of 5 m we obtained a weighted average 207pb 206pb age of 4541 11 ma and u pb concordia age of 4525 24 ma for the five eucrite samples studied a synthesis of available age data of howardites eucrites and diogenites indicate a protracted magmatic history on vesta with a most pronounced core mantle differentiation event marked at 4564 2 ma followed by a peak of basaltic magmatism at 4552 7 ma which gradually diminished over the next 50 ma thermal modeling of vesta suggests that partial melt fraction of greater than 10 with temperature well exceeding 1500 k could be maintained over this period throughout its interior this is consistent with the chronological records of eucrites suggesting persistent magmatism on vesta during the first 50 ma in the early solar system

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

flow behaviour and runout modelling of a complex debris flow in a clay shale basin identification of debris flow hazard areas necessitates the knowledge of the flow thickness and the runout distance both have been investigated using a numerical runout model on the faucon stream south french alps representative of clay shale basins results of various rheological tests and numerical experiments are presented and discussed the calibration of the model was undertaken using the results of both geomorphological surveys and sedimentological analyses rheological tests using either a parallel plate rheometer a coaxial rheometer slump tests and an inclined plane were carried out on several samples results have shown that the flow behaviour could be described by an herschel bulkley constitutive equation the rheological responses of several natural suspensions collected from surficial deposits sandstones moraines weathered black marls were also investigated in order to model the runout of the flow the model bing was used the model describes well the influence of each type of sediment on the behaviour runout distance deposit thickness of the flow although the velocities were significantly overestimated different risk scenarios are tested and discussed copyright 2005 john wiley sons ltd

the isotopic composition of uranium and lead in allende inclusions and meteoritic phosphates we measured the isotopic compositions of u and pb in eight ca al rich inclusions from the allende chondrite in whitlockite from the st severin chondrite and in a whitlockite and a whole rock sample from the angra dos reis achondrite ador the total range in 235 u 238 u in the acid soluble phases of the allende inclusions and meteoritic whitlockites is from 1 137 6 to 1 138 3 and to within the error limits 3 20 indistinguishable from normal terrestrial u the 235 u 238 u ratios for whitlockites from st severin and ador are the same as that in the bulk meteorites and are normal the pb isotopic compositions of the acid soluble phases of the allende coarse grained inclusions except c 1 give a mean 207 pb 206 pb model age of4 559 0 015ae which is consistent with the observation of normal u isotopic composition the pb isotopic compositions of coarse grained fun inclusion c 1 and of two fine grained inclusions from allende indicate that the u pb systems of these samples have evolved differently from the rest of the meteorite the 207 pb 206 pb model ages for the whitlockites and for bulk ador are the same as those for st severin whitlockite 4 551 0 004ae the pb results from st severin indirectly constrain the value of the u isotopic abundance to be within 7 4 of normal both the directly measured235u 238u and the pb data on st severin are in complete disagreement with claims of large 235 u excess reported by other workers on the same meteorite the th u ratios of some acid soluble phases of allende inclusions and of meteoritic whitlockite show varying degrees of enrichment of th relative to u by factors of 2 to 25 relative to the bulk meteorites previous studies have shown that 244 pu 238 u ratios in whitlockite are also fractionated relative to the bulk meteorites the observation of no isotopic effects in u reported here does not support the claims of either fractionation of 247 cm 238 u or of a large amount of live 247 cm at the early stage of formation of the solar system using the present data we obtain a limit of 247 cm 235 u 4 10 3 at the time of meteorite formation or differentiation this implies that the last major r process contribution to the material in the protosolar nebula was 10 8 years prior to 26 al formation and injection

mn cr isotope systematics of the d orbigny angrite we have conducted a detailed study of the mn cr systematics of the angrite d orbigny here we report cr isotopic abundances and mn cr ratios in olivine pyroxene glass chromite and bulk rock samples from d orbigny 53cr excesses in these samples correlate well with their respective mn cr ratios and define an isochron with a slope that corresponds to an initial 53mn 55mn ratio 3 24 0 04 x 10 6 and initial 53cr 52cr ratio of 53 0 30 0 03 at the time of isotopic closure the 53mn 55mn ratio of the d orbigny bulk rock is more than two fold the 53mn 55mn ratio of the angrites lewis cliff 86010 lew and angra dos reis ador and implies an older mn cr age of 4562 9 0 6 ma for d orbigny relative to a pb pb age of 4557 8 0 5 ma for lew and ador one of the most unusual aspects of d orbigny is the presence of glass a phase that has not been identified in any of the other angrites the mn cr data for glass and a pyroxene fraction found in druses indicate that they formed contemporaneously with the main phases of the meteorite since the mn cr age of d orbigny is 5 ma years older than the angrites lew and ador d orbigny likely represents an earlier stage in the evolution of the angrite parent body

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

discovery of a basaltic asteroid in the outer main belt visible and near infrared spectroscopic observations of the asteroid 1459 magnya indicate that it has a basaltic surface magnya is at 3 15 astronomical units au from the sun and has no known dynamical link to any family to any nearby large asteroid or to asteroid 4 vesta at 2 36 au which is the only other known large basaltic asteroid we show that the region of the belt around magnya is densely filled by mean motion resonances generating slow orbital diffusion processes and providing a potential mechanism for removing other basaltic fragments that may have been created on the same parent body as magnya magnya may represent a rare surviving fragment from a larger differentiated planetesimal that was disrupted long ago

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle to investigate whether magnesium isotopes are fractionated during basalt differentiation we have performed high precision mg isotopic analyses by multi collector inductively coupled plasma mass spectrometry mc icp ms on a set of well characterized samples from kilauea iki lava lake hawaii usa samples from the kilauea iki lava lake produced by closed system crystal melt fractionation range from olivine rich cumulates to highly differentiated basalts with mgo content ranging from 2 37 to 26 87 wt our results demonstrate that although these basalts have diverse chemical compositions mineralogies crystallization temperatures and degrees of differentiation their mg isotopic compositions display no measurable variation within the limits of our external precision average 26 mg 0 36 0 10 and 25 mg 0 20 0 07 uncertainties are 2sd this indicates that mg isotopic fractionation during crystal melt fractionation at temperatures of 1055 c is undetectable at the level of precision of the current investigation calculations based on our data suggest that at near magmatic temperatures the maximum fractionation in the 26 mg 24 mg ratio between olivine and melt is 0 07 two additional oceanic basalts two continental basalts bcr 1 and bcr 2 and two primitive carbonaceous chondrites allende and murchison analyzed in this study have mg isotopic compositions similar to the kilauea iki lava lake samples in contrast to a recent report u wiechert a n halliday non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 2007 360 371 the results presented here suggest that the bulk silicate earth has a chondritic mg isotopic composition 2007 published by elsevier b v

size of the group iva iron meteorite core constraints from the age and composition of muonionalusta the group iva fractionally crystallized iron meteorites display a diverse range of metallographic cooling rates these have been attributed to their formation in a metallic core approximately 150 km in radius that cooled to crystallization in the absence of any appreciable insulating mantle here we build upon this formation model by incorporating several new constraints these include i a recent u pb radiometric closure age of 2 5 myr after solar system formation for the group iva iron muonionalusta ii new measurements and modeling of highly siderophile element compositions for a suite of ivas and iii consideration of the thermal effects of heating by the decay of the short lived radionuclide 60fe our model for the thermal evolution of the iva core suggests that it was approximately 50 110 km in radius after being collisionally exposed this range is due to uncertainties in the initial abundance of live 60fe incorporated into the iva core our models define a relationship between cooling rate and closure age which is used to make several predictions that can be tested with future measurements in general our results show that diverse cooling rates and early u pb closure ages can only coexist on mantle free bodies and that energy released by the decay of 60fe reduces the core size necessary to produce diverse metallographic cooling rates the influence of 60fe on cooling rates has largely been neglected in previous core formation models accounting for this heat source can affect size estimates for other iron meteorite cores that cooled to crystallization in the presence of live 60fe candidates for such a scenario of early mantle free formation include the iron iiab iiiab and ivb groups

major and trace elements of zircons from basaltic eucrites implications for the formation of zircons on the eucrite parent body abstract the major and trace elements in zircons obtained from basaltic eucrites yamato y 75011 y 792510 y 82082 asuka a 881467 juvinas and stannern were determined using an electron microprobe analyzer and a sensitive high resolution ion microprobe and the formation of zircons on the parent body was discussed the maximum sizes of zircon grains in each sample are likely to be related to its metamorphic grade the least metamorphosed basaltic eucrite y 75011 contains zircons with sizes of a few m conversely the highly metamorphosed basaltic eucrites y 792510 and a 881467 include zircons larger than 20 m the relationship between the maximum grain size and metamorphic grade suggests that the formation process of zircons is related to metamorphic events the zr hf ratios of the zircons found in this study show a wide variation 31 6 71 7 as compared to the chondritic values zr hf 32 8 34 3 and bulk basaltic eucrites 34 0 34 7 the zr hf ratios of the zircons from y 792510 and a 881467 are relatively constant whereas those of the zircons from y 82082 juvinas and stannern show large variations the rare earth element ree content in the zircons from y 792510 and a 881467 is given by la 0 1 ci and lu 1000 ci on the other hand the zircons from stannern show higher ree content la 0 1 1 ci and lu 1000 10 000 ci than those from y 792510 and a 881467 the most reliable ree data of a large zircon from a 881467 show no ce anomaly and a distinct negative eu anomaly therefore it is presumed that the zircons formed under reducing condition in which ce 3 was stable the melt compositions coexisting with the studied zircons suggest that the zircons from highly metamorphosed eucrites might react with the ree enriched melt derived from partial melting of the mesostasis region during metamorphism

modelling the probability of occurrence of shallow landslides and channelized debris flows using geotop fs this paper describes a coupled distributed hydrological geotechnical model geotop fs which simulates the probability of occurrence of shallow landslides and debris flows we use a hydrological distributed model geotop which models latent and sensible heat fluxes and surface runoff and computes soil moisture in 3 d by solving richards equation numerically together with an infinite slope geotechnical model geotop fs the combined model allows both the hydraulic and geotechnical properties of soil to be considered and realistically modelled in particular the model has been conceived to make direct use of field surveys geotechnical characteristics and soil moisture measurements in the model the depth of available sediments is also used to characterize the hydraulic properties of the area examined to account for the uncertainty related to the natural variability in the factors influencing the stability of natural slopes the safety factor is computed with a probabilistic approach in order to determine the likelihood of slope failures soil parameters are assigned distributions instead of single deterministic values the analysis presented was carried out for an alpine watershed located in the friuli region italy for which some geological and geotechnical data were available in the past this watershed experienced landslides and debris flows during intense storms following long and moderate intensity rainfall events the distributed coupled geotop fs model was calibrated by reproducing some of these events and validated in order to map future failure probabilities

cr diffusion in orthopyroxene experimental determination 53mn 53cr thermochronology and planetary applications we have determined cr diffusion coefficients d in orthopyroxene parallel to the a b and c axial directions as a function temperature at f o2 corresponding to those of the wustite iron wi buffer diffusion is found to be significantly anisotropic with d c d b d a conforming to an earlier theoretical prediction increase of f o2 from wi buffer conditions to 4 5 log unit above the buffer at 950 and 1050 c leads to decrease of d cr by a factor of two to three possibly suggesting significant contribution from an interstitial diffusion mechanism we have used the diffusion data to calculate the closure tem peratures tc of the mn cr decay system in orthopyroxene as a function of initial temperature t0 grain size a and cooling rate for spherical and plane sheet geometries we also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of mn cr ages in orthopyroxene during cooling t0 and a application of these relations to the mn cr age data of the cumulate eucrite serra de mageyields a tc of 830 980 c and cooling rates of 2 27 c myr at tc and 1 13 c myr at 500 c it is shown that the cooling of serra de mageto the closure temperature of the mn cr system took place at its original site in the parent body and thus implies a thickness for the eucrite crust in the commonly accepted hed parent body vesta of greater than 30 km this thickness of the eucrite crust is compatible only with a model of relatively olivine poor bulk mineralogy in which olivine constitutes 19 7 of the total asteroidal mass

spatially distributed three dimensional slope stability modelling in a raster gis abstract we present a grass gis implementation of a three dimensional slope stability model capable of dealing with shallow and deep seated slope failures r rotstab it exploits a modified version of the revised hovland method and evaluates the slope stability over a large number of randomly selected slip surfaces ellipsoidal or truncated in shape for each raster cell in the modelling domain the factor of safety is taken from the most critical slip surface this results in an overview of potentially unstable regions without showing the individual sliding areas furthermore the model produces a susceptibility index for each cell based on the proportion of slip surfaces with a low factor of safety we test the model in the collazzone area umbria central italy where detailed information on shallow and deep seated landslides morphology and lithology is available the rate of true predictions landslide plus non landslide ranges from 54 7 to 81 2 for shallow landslides and from 58 5 to 87 4 for deep seated landslides depending on the adjustment of the uncertain geotechnical parameters in the same order the rate of true landslide predictions decreases from 80 2 to 19 9 shallow and from 64 3 to 3 6 deep seated so that an increase of the true landslide prediction rate can only be achieved at the cost of a significant increase of the false alarm rate the results for shallow landslides are very similar to those yielded with the infinite slope stability model in terms of the minimum factor of safety but differ substantially in terms of the spatial patterns the evaluation of the landslide susceptibility index yields areas under the roc curves of 0 68 0 70 shallow landslides r rotstab 0 61 0 65 shallow landslides infinite slope stability model and 0 59 0 63 deep seated landslides we conclude that the r rotstab model outperforms the infinite slope stability model

alice assessment of landslides induced by climatic events a single tool to integrate shallow and deep landslides for susceptibility and hazard assessment abstract the increasing evolution of urban areas in landslide prone regions and the modification of precipitation due to global climate change have led to a growing need for landslide hazard assessment lha for local land management and security services lha is based on the definition of the spatial and temporal probability of landslide occurrences and is split into three steps i a phenomenon inventory ii a landslide susceptibility analysis and iii a landslide hazard analysis nevertheless in practice essential information is often missing and lha corresponds most of the time to landslide susceptibility assessment acquired by expert knowledge this article presents a physical based model alice assessment of landslides induced by climatic events that can integrate different types of landslides shallow and deep with different sizes this tool can be used at the meso or broader scale 1 25 000 to 1 10 000 of work according to expert knowledge however a calibration must be carried out to fit observations and to take uncertainties into account thus a specific strategy is applied to the model on a study site located in the french south alps where numerous different landslide types were observed and analyzed after calibration on a small representative area the best fitted parameters are applied to a larger area for different types of landslides three landslide susceptibility maps shallow translational landslides rotational landslides and complex landslides are produced and the different susceptibility classes are compared with a landslide susceptibility map produced by a geomorphological approach the different susceptibility envelopes computed by the model are well integrated into the high susceptibility envelopes defined by the so called expert geomorphological approach thus the tool makes it possible to improve the mapping of potentially unstable areas by taking into account parameters such as the groundwater level in different surficial formations or the geotechnical values of landslide prone formations that experts are not always able to integrate alice is therefore proven to be a useful tool for mapping potential landslide prone areas if the tool is well calibrated taking into account the expert vision of the field different landslide types and different triggering factors including rainfall and seismic acceleration

estimation of annual bedload flux in a macrotidal estuary bristol channel u k sedimentological data from the bristol channel indicate that mutually evasive ebb and flood dominant zones of net bedload transport are present to test this hypothesis long term observations of currents from the channel are combined with empirical formulae to estimate annual bedload transport rates under the combined influence of tidal currents and surface wind waves extrapolating these values over the ebb and flood dominant zones sand flux to the upper part of the channel is estimated at about 64 105 t yr 1 with supply and removal being of nearly equal magnitude such patterns of sand and water movement may be typical of tidally dominated estuaries and embayments

geophysical geotechnical and hydrological investigations of a small landslide in the french alps abstract geophysical geotechnical and hydrological surveys were conducted in the french alps on a small landslide in black marl material to assess the stability the geophysical survey consisting of electromagnetic geo electric and relative differences in water content the data on the basal slip surface together with geotechnical parameters cohesion and angle of internal friction were used to make a stability analysis this analysis revealed that a groundwater level of 4 m below the ground surface is the critical threshold for reactivating the landslide the hydrological investigation which entailed measurements of saturated permeability and pressure heads indicated that instability depended on long term wet conditions with little evapotranspiration

u pb and al mg systematics of the ungrouped achondrite northwest africa 7325 abstract northwest africa nwa 7325 is a unique ungrouped gabbroic achondrite which has characteristics consistent with a possible link to the planet mercury in order to understand the origin of this meteorite and the nature of its parent body we have determined its crystallisation age using the long lived u pb and short lived al mg chronometers an internal pb pb isochron defined by six acid leached pyroxene fractions yields an age of 4563 4 2 6 ma assuming that the 238u 235u ratio for nwa 7325 is identical to the bulk earth and solar system value of 137 794 the al mg isotope analyses of seven fractions four plagioclase one pyroxene one olivine and one whole rock define a regression line corresponding to 26al 27al0 3 03 0 14 10 7 and an initial 26mg of 0 093 0 004 when anchored to the d orbigny angrite this initial 26al 27al yields an age of 4563 09 0 26 ma the pb pb age of 4563 4 2 6 ma and al mg age of 4563 09 0 26 ma are in complete agreement but the low u concentrations of nwa 7325 resulted in a relatively low precision pb pb age the observed excess in initial 26mg can be explained by 27al 24mg fractionation and subsequent mg isotopic evolution after planetary differentiation furthermore the parental magma of nwa 7325 most likely formed within 1 72 ma after calcium aluminium rich inclusion cai formation nwa 7325 formed near simultaneously with quenched angrites and a number of ungrouped achondrites at 4563 ma suggesting that a multitude of planetary bodies had formed and differentiated by 4 5 myr after cai formation this ancient age may be interpreted as an argument against nwa 7325 originating from mercury however it does not completely rule it out

the u pb systematics of angrite sahara 99555 abstract angrite sahara 99555 hereafter sah precisely dated by baker et al baker j bizzarro m wittig n connelly j and haack h 2005 early planetesimal melting from an age of 4 5662 gyr for differentiated meteorites nature 436 1127 1131 has been proposed as a new reference point for the early solar system timescale and for calculation of the revised minimum age of our solar system the pb pb age of sah of 4566 18 0 14 ma reported by baker et al differs from the pb pb age of d orbigny another basaltic angrite of 4564 42 0 12 ma amelin y 2008 u pb ages of angrites geochim cosmochim acta 72 221 232 despite the fact that the relative 53mn 53cr and 182hf 182w ages of these meteorites are identical here i report u pb data for 21 whole rock and pyroxene fractions from sah analyzed using the same approach as d orbigny amelin 2008 these fractions contain between 1 3 and 8 9 pg of total common pb slightly more than analytical blank measured 206pb 204pb ratios are between 625 and 2817 for d orbigny blank corrected 206pb 204pb ratios are between 1173 and 6675 eight acid washed whole rock fractions yielded an isochron age of 4564 86 0 38 ma mswd 1 5 data for pyroxene fractions plot mostly above the whole rock isochron and do not form a linear array in 207pb 206pb vs 204pb 206pb isochron coordinates the 207pb 206pb model dates of the pyroxene fractions vary from 4563 8 0 3 to 4567 1 0 5 ma the difference between whole rock and pyroxene u pb systematics may be a result of re distribution of radiogenic pb at a mineral grain scale several million years after crystallization complexities of sm nd lu hf and possibly 26al 26mg mineral systematics of sah described previously may be related to the same process that caused the re distribution of radiogenic pb disturbance of isotopic chronometers renders sah an imperfect anchor for the early solar system timescale the problems with age determination revealed by the studies of sah call for greater attention in pb isotopic dating of angrites and other achondrites

estimating the quality of landslide susceptibility models we present a landslide susceptibility model for the collazzone area central italy and we propose a framework for evaluating the model reliability and prediction skill the landslide susceptibility model was obtained through discriminant analysis of 46 thematic environmental variables and using the presence of shallow landslides obtained from a multi temporal inventory map as the dependent variable for statistical analysis by comparing the number of correctly and incorrectly classified mapping units it is established that the model classifies 77 0 of 894 mapping units correctly model fitting performance is investigated by comparing the proportion of the study area in each probability class with the corresponding proportion of landslide area we then prepare an ensemble of 350 landslide susceptibility models using the same landslide and thematic information but different numbers of mapping units this ensemble is exploited to investigate the model reliability including the role of the thematic variables used to construct the model and the model sensitivity to changes in the input data by studying the variation of the model s susceptibility estimate the error associated with the susceptibility assessment for each mapping unit is determined this result is shown on a map that complements the landslide susceptibility map prediction skill of the susceptibility model is then estimated by comparing the forecast with two recent event inventory maps the susceptibility model is found capable of predicting the newly triggered landslides a general framework for testing a susceptibility model is proposed including a scheme for ranking the quality of the susceptibility assessment

geochemistry and petrogenesis of volcanic clasts in the permian breccias around exeter geochemical comparisons between volcanic clasts from the late permian red beds and various granite plutons and granite porphyries 9elvans9 from sw england show that the clasts have closest affinity with the poorly megacrystic granite of dartmoor and the 9elvan like9 godolphin granite this affinity with the dartmoor granite backs up recently published nd data and age determinations it is concluded that the clasts represent volcanic material derived from an evolving subsurface granitic magma thereby conforming with conclusions ideas of earlier workers for the former presence of a dartmoor volcano

caesium in the up estuary transport of sediments abstract trace elements are used in the teign estuary of southwest england u k to identify the source of sediments barium present in clastic material derived from past mining activity characterises river input whilst strontium from skeletal debris marks the landward transport of marine derived sediments high caesium concentrations occurring in the estuary are traced to estuarine and coastal outcrops of permian sandstones significantly cs values reach a maximum 85 ppm in the middle and upper estuary where river and marine derived sediments mix caesium resides largely in both the clay fraction 40 230 ppm and argillaceous lithic material 60 180 ppm it proves a useful marker for sediment differentiation by indicating the status of up estuary sediment transport