a geochemical multi proxy approach for anthropogenic processes in a middle upper pleistocene endokarstic deposit abstract deciphering human activities in archaeological sites is a priority issue in archaeological studies nevertheless its geochemical fingerprints on sediments are poorly known in sites belonging to the recent prehistory these geochemical signals have been taken into account but in oldest sites this subject has not been studied sufficiently the aim of this paper consists on tracking geochemical proxies that can be attributed to anthropogenic processes in endokarstic pleistocene deposits recognize these elements can be a key factor in order to explore the potential of non excavated archeological levels and find out activities performed in those sediments more accurately for that purpose a middle upper pleistocene endokarstic deposit cueva del angel belonging to the iberian peninsula has been chosen this site provides numerous evidences of human activities as butchering and cooking of predated animals or the habitual use of fire throughout its main stratigraphic sequence this geochemical archaeological approach highlights that the upper units consist of anthropogenic influenced sediments while the lower unit shows a greater percentage of geogenic inputs based on p and zn cu sr several levels with higher anthropogenic inputs have been identified these two attributes can be suggested as proxies of human activities for this site high values of p appear to be linked with butchering highly occupied levels and high levels of zn cu sr seem to be related with fires this geochemical information has been compared and tested with previous archeological information

evolution of the eastern volcanic ridge of the canary islands based on new kar data the results of 64 new k ar age determinations together with 32 previously published ages show that after a period of erosion of the basal complex miocene volcanic activity started around 20 ma in fuerteventura and 15 ma in lanzarote forming a tabular succession of basaltic lavas and pyroclastics with a few salic dykes and plugs this series includes five separate volcanic edifices each one with its own eruptive history in fuerteventura several miocene eruptive cycles have been identified in the central edifice one around 20 17 ma followed by two others centred around 15 and 13 ma in the southern edifice the maximum of activity took place around 16 14 ma whereas in the northern one the main activity occurred between 14 and 12 ma in lanzarote a first cycle of activity took place in the southern edifice between 15 5 and 14 1 ma followed by another between 13 6 and 12 3 ma in the northern edifice three pulses occurred 10 2 8 3 6 6 5 3 and 3 9 3 8 ma an important temporal gap greater in fuerteventura than in lanzarote separates series i from the plio quaternary series ii iii and iv formed by multi vent basaltic emissions in fuerteventura the following eruptive cycles have been identified 5 2 9 2 4 1 8 1 7 0 8 0 4 and 0 1 ma in lanzarote the activity was fairly continuous from 2 7 ma to historic times with a maximum in the lower pleistocene eruptive rates in the series i edifices were on the average 0 1 0 01 km3 ka comparable but slightly smaller than in similar edifices in tenerife and la gomera but much lower than in gran canaria average post miocene eruptive rates were about 0 013 0 027 km3 ka in lanzarote and 0 003 0 007 km3 ka in fuerteventura all these volcanic edifices show a similar general sequence fissural eruptions erosion multi vent volcanism repeated at different periods in different parts of the eastern islands of the canaries the model of growth of the series i edifices is comparable to those in tenerife and la gomera long periods of activity sometimes greater than 6 m y with pulses separated by gaps however salic and intermediate differentiates frequent in tenerife and la gomera are very scarce in these islands the fuerteventura lanzarote ridge shows a decrease in volcanic activity with time and also a certain ssw nne polarity in the temporal development of volcanism

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

dust raising in the dustiest place on earth the bodele in northern chad is the dustiest place on earth it is dusty because of the co location of strong near surface winds and a large exposure of low density friable diatomite data are reported from three kinds of observation on dust generation in the bodele a two automatic weather stations and pilot balloon tracking complemented with reanalysis data measuring and estimating wind velocities b sun photometers measuring atmospheric dust concentrations c a vacuum pump dust sampler and an array of mwac sediment samplers measuring in situ sediment transport with these data we develop four hypotheses about dust generation 1 the pulsing of dust output from the bodele depends primarily on the varying strength of a low level jet llj i e at this scale dust production is transport limited 2 the most prolific mechanism of dust production is the breakdown of saltating diatomite flakes as they collide with each other and with the surface 3 disturbance of flow around the large barchans particularly turbulence and convergence on their horns is a major contributor to dust production i e the dunes are dust mills 4 in consequence dust production is localised within the main exposure of diatomite to places where there are the most dunes as on the eastern and northern fringes of the exposure

deep volcanic morphology below lanzarote canaries from gravity inversion new results for timanfaya and implications abstract the deep roots of oceanic island volcanoes are poorly known and geophysical models can help to constrain processes such as magma storage and transport before and during eruptions lanzarote canary islands is a volcanic island in post erosional phase where in the 18th century one of the most important historical eruptions considering duration and volume of the canary islands took place in the timanfaya area to improve the knowledge on the structure of lanzarote and in timanfaya area we carry out a gravity determination of the subsurface anomalous 3d density structure using an improved quasi automatic inversion methodology the obtained model presents a 3d morphology of anomalous density bodies we describe the improvements of the inversion methodology the adjusted model and interpretative conclusions corresponding to the structure and the long term cumulative magmatic plumbing system of the island three high density sources are described as resulting in the inference of three main volcanic complexes a large central complex san bartolome and two smaller complexes one in the ne and a third smaller one located in the sw close to the timanfaya area the outcrops of miocene lava flows from the center of the island can be attributed to the top of the central intrusive model we infer the local plumbing system for timanfaya volcano area by means of strongly tilted successive branches of magma departing from the sw intrusive body the structural results show no evidence of any magma chamber below timanfaya as proposed by previous works we also present a comparison of the gravity results and geological observations showing different cases of correlation in the island they go from a good match between the gravity anomaly and the position of the central volcanic structure to no anomaly associated to the fissural quaternary volcanic activity

diagenesis in prehistoric caves the use of minerals that form in situ to assess the completeness of the archaeological record an interpretation of the archaeological record in particular that of a prehistoric cave site is complicated by the diversity of depositional and post depositional processes that affect the material deposited here we propose to use the authigenic minerals that form in situ within the cave sediments to reconstruct the ancient chemical environments in the sediments this can be done by experimentally determining the conditions under which each of the authigenic minerals are stable although this information is not available to date for minerals formed in a prehistoric cave we present calculated stability field data for the relevant minerals the results clearly demonstrate the feasibility of this approach this information particularly if based on measurements of real authigenic cave minerals will facilitate an assessment of the completeness of the cave archaeological record this is particularly important for determining whether or not the distributions of archaeologically important materials such as bones teeth plant phytoliths charcoal and ash reflect their original burial distributions or were altered as a result of secondary diagenetic processes

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

the emission and vertical flux of particulate matter 10 mum from a disturbed clay crusted surface arid and semi arid environments are important sources for the atmospheric loading of pm10 particulate matter 10 lm although the emission of this material is often limited by surface crusts this study investigates the emission and vertical flux of pm10 from a clay crusted playa with and without saltating grains to abrade the surface using a portable field wind tunnel it was found that despite disturbance to the surface the emission of pm10 decays rapidly without abrasion only in the presence of saltating grains was pm10 continuously liberated from the surface such that the emission rate the total amount of pm10 emitted from the surface expressed as a horizontal flux varied linearly with the saltation transport rate although the emission of pm10 was found to depend on saltation abrasion past studies have tended to focus on the relationship between the vertical flux of pm10 the amount of pm10 being transported vertically through the boundary layer and the shear velocity in this study the vertical flux of pm10 was found to vary with the shear velocity to the power of 2ae14 although the vertical pm10 flux is a proportion of the emission rate the horizontal flux no statistically significant relationship was observed between the emission rate and the shear velocity the disparity of these results is explained by the lack of a consistent relationship between the shear velocity and the saltation transport rate in this supply limited environment this suggests that the observed relationship between the vertical pm10 flux and the shear velocity is a spurious correlation resulting from the use of shear velocity to calculate the vertical dust flux it is thus concluded that shear velocity is not an appropriate variable for emission modelling in supply limited environments and that improvements in dust emission modelling will only be realized if the abrasion process is the focus of a concerted research effort

grain size characteristics of sediment transported during dust storms abstract the grain size characteristics of sediment transported by wind in creep saltation and suspension during 15 dust storms in the slims river valley yukon territory were investigated grain size analysis of the transported sediment indicated that the suspended sediment is significantly finer and better sorted than the sediment transported in either surface creep or saltation the data also show that during dust storms the mean particle size of the suspended sediment decreases as a power function of height the grain size distributions of the sediment transported in suspension and surface creep are characterized by strong positive skewness which results from the selective removal of surface particles small enough to be transported by the wind at a given velocity in contrast the grai size distribution of the saltation samples are negatively skewed which is thought to result from the selective removal of the finer particles into suspension from those particles initially lifted from the surface into the air stream thus the proportion of sediment initially entrained into the air stream which returns to the surface in saltation will lack the fine grains removed in suspension and will therefore tend to be less positively or negatively skewed

modelling of crustal anomalies of lanzarote canary islands in light of gravity data the application of a gravity inversion method enables us to obtain a 3 d density contrast model of the upper crustal anomalies of the volcanic island of lanzarote canary islands for this we use a network of 296 gravity stations distributed over the whole island and a digital terrain model of about 45 000 terrestrial and oceanic data to determine the corresponding terrain correction a density value of 2480 kg m 3 is chosen for this correction by means of a new approach the resulting bouguer anomaly is analysed by means of a least squares prediction which gives us a mean level of uncorrelated observational noise of about 1 2 mgal this anomaly is considered in order to obtain independent information about the inner anomalous mass density distribution by means of a 3 d gravity inversion based on a systematic exploration on a prismatic partition of the subsoil volume and adopting et priori values of the density contrast positive and negative to determine the geometry of the anomalous bodies the problem of non uniqueness of the solution is avoided by using a minimization mix condition on the weighted residuals and the weighted whole anomalous mass the structural solution is finally presented by means of horizontal sections and vertical profiles a main intrusive body is located under the central eastern area and could correspond to a dilated volcanic activity of shield formation it shows a prismatic form of more than 15 km depth subducted with only the ridges remaining as horst blocks moreover the sw and ne extreme areas of the island show smaller and shallower positive bodies interpreted as less developed magmatic intrusions conversely several density lows offer interesting shallow alignments 45 degreesn ene wsw and 125 degreesn wnw ese which could be associated with a fracture system corresponding to structural stress and also correlate with historic eruptions such as for instance the timanfaya eruption the monitoring of several geophysical parameters at two underground geodynamic stations in the ne zone of the island and timanfaya shows characteristic differences between the two zones which confirm crustal anomalies in the second station

eolian suspension above the saltation layer the concentration profile abstract the acquisition of a new set of data on dust emission obtained at owens lake california was used to assess the performance of a previously published theoretical model that describes the normalized concentration profile of material in suspension above an actively emitting surface as a logarithmic function the normalized concentration profile has more commonly been modeled as a power law least squares regression was used to fit both the logarithmic and the power law model to approximately 20 hours of data on 10 minute average concentration profiles results for all these data combined and for each individual profile indicated that the logarithmic model better explains the concentration gradient profile than the power law model the predicted behavior of the model parameters including a concentration scaling parameter and a transfer coefficient for suspended particles was examined it was observed that divided by a defined reference concentration was relatively invariant during emission events as predicted by the model and had a value of 0 18 0 02 for the reference heights at which particle concentration and wind speed were measured 1 7 and 9 m the transfer coefficient for suspended particles was approximately 0 22 0 05 of the calculated momentum transfer coefficient defined here as the wind speed at the reference height divided by the friction velocity

structure of reunion island indian ocean inferred from the interpretation of gravity anomalies abstract reunion is a volcanic edifice whose origin is related to a hot spot in the indian ocean only 3 of its volume is emergent many geological and geophysical studies were carried out on reunion island during the 1980 s but few of them allow study of the internal structure of the edifice several gravity surveys have been carried out on the island since 1976 and we have compiled the available data set the lack of data on the western side of the island led us to conduct a regional survey in 1993 to obtain a more homogeneous distribution of the stations computation of bouguer anomalies for different correction densities accounts for the variable density of the rocks constituting the edifice and provides a distribution of gravity anomalies interpreted as dense bodies of intrusive rocks inside the edifice two very large intrusive complexes can be unambiguously recognised one beneath piton des neiges and one beneath the grand brule area both have been penetrated by geothermal exploration drill holes and the first is also known from outcrop observations 2 5d simple models were constructed to reveal the geometry and extent of the buried intrusives they are deeply rooted extending several kilometres below sea level and extensive 20 25 km long and 10 13 km wide for the piton des neiges complex 12 15 km long and some kilometres wide for the grand brule complex the development of such complexes implies that the activity of the two volcanic centres was long lasting and remained stable while the volcanoes were growing the grand brule complex has been interpreted as relics of an old volcano named alizes volcano the interpretation of the gravity maps suggests the presence of a ridge of dense rocks to the north of the axis joining the centres of piton des neiges and piton de la fournaise volcanoes by analogy with the other structures 2 5d models show that this structure would culminate between 0 and 1 km below sea level and be 15 km wide this complex induces a maximum anomaly in takamaka valley and we thus propose to name it takamaka volcano no geological evidence of the nature of these dense rocks is available but the ridge coincides with structures revealed by magnetic and seismic data interpretation of the bouguer anomaly maps suggests that the inner gravity structure of piton de la fournaise is not characterised by the presence of a voluminous dense body but probably by more restricted concentrations of dense rocks some structures can be recognised along the present ne and se rift zones and in the previous central part of piton de la fournaise to the west of the present summit the recent eastward migration of the centre of activity of piton de la fournaise accounts for the lack of a large positive anomaly beneath the active craters

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

using a genetic algorithm for 3 d inversion of gravity data in fuerteventura canary islands the use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the non linearity inherent in such applications we have implemented a genetic algorithm to efficiently invert a set of gravity data employing several fixed density contrasts this algorithm determines the geometry of the sources of the anomaly gravity field in a 3 d context the genetic algorithms based on darwin s theory of evolution seek the optimum solution from an initial population of models working with a set of parameters by means of modifications in successive iterations or generations this searching method traditionally consists of three operators selection crossover and mutation acting on each generation but we have added a further one which smoothes the obtained models in this way we have designed an efficient inversion gravity method confirmed by both a synthetic example and a real data set from the island of fuerteventura in the latter case we identify crustal structures related to the origin and evolution of the island the results show a clear correlation between the sources of gravity field in the model and the three volcanic complexes recognized in fuerteventura by other geological studies

gravity fields and the interpretation of volcanic structures geological discrimination and temporal evolution abstract a review of gravity data reflecting shallow concealed structures on volcanoes demonstrates that valuable information may be derived on the geological development of such structures and on the dynamic evolution of active volcanoes to a first approximation all recorded examples of anomalous gravity fields associated with volcanoes are concentric with and have sources that lie within the volcanic edifice positive anomalies with wavelengths less than 20 km and amplitudes up to ca 30 mgal characterise mainly basaltic volcanoes from various tectonic settings and are caused by a relatively dense intrusive complex magma body which contrasts with its surroundings either because the body is more mafic than average or more likely because near surface previously erupted materials are uncompacted negative anomalies with wavelengths up to 100 km and amplitudes up to ca 60 mgal occur over much larger volcanic calderas many of which have erupted highly silicic pyroclastic ash and pumice uncompacted silicic caldera infill with a possible contribution from low density magma bodies is responsible for the observed anomalies there is some evidence for a continuum of gravity anomaly types that corresponds to the geological evolution of volcanic systems generally from primitive rift or subduction related basaltic andesite to mature high level silicic calderas repeated microgravity observations over active volcanoes enable magma movements variations in magma input and changes in magma density to be monitored closely dynamic modelling of volcanic systems is providing new evidence on the behaviour of concealed magma bodies and could have considerable potential for predicting eruptive events

crustal structure gravity anomalies and flexure of the lithosphere in the vicinity of the canary islands summary simple elastic plate models have been used to calculate the flexure of the lithosphere caused by volcanic loading at the canary islands and sediment loading at the moroccan continental margin by comparing the calculated flexure to observations based on seismic refraction and free air gravity anomaly data constraints have been placed on the long term 106 years elastic thickness of the lithosphere te the best fit between the calculated and observed flexure in the vicinity of the canary islands is for te 20 km this value of te also explains seismic reflection data in regions that flank the island provided that the lithosphere underlying the moroccan margin is sufficiently weak te 5 km for sediment loading to contribute little to the island flexure a backstripping study in which gravity data are used to constrain the value of te supports the suggestion that the lithosphere underlying the moroccan margin like its conjugate at the baltimore canyon trough is weak although sediment loading at the moroccan margin appears therefore to have exerted little influence on the structure of the canary islands there is evidence that island flexure may have influenced the stratigraphic development of the moroccan margin especially in the region of the slope anticline a te of 20 km is about 15 km lower than would be expected on the basis of the thermal age of the oceanic lithosphere that underlies the canary islands similar low values have been reported from oceanic islands in the pacific superswell region of french polynesia where they have been attributed to re heating of the lithosphere by one or more hotspots a general e w age progression of the volcanic rocks suggests that the canary islands were also generated by a hotspot they lack however the topographic swell and gravity geoid high which usually accompanies these features one possibility is that the low te values are the result of a pre existing weakness in the oceanic crust a te of 20 km is large enough however for a significant part of the mantle to still be involved in the support of the island loads a more likely explanation is thermal weakening by a hotspot which has been localized enough to reduce te but not to produce a swell or gravity geoid high irrespective of its cause the low te suggests that oceanic lithosphere does not necessarily progressively increase its strength with age so that even 140 ma old lithosphere is vulnerable and can in some regions be significantly weakened by later thermal and mechanical processes

analysis of gravimetric anomalies in furnas caldera sao miguel azores abstract furnas volcano sao miguel island azores is a steep sided caldera complex resulting from several collapses in this paper we analyse and interpret the gravity survey carried out by the instituto de astronomia y geodesia spain and the gravity data published by the instituto nacional de meteorologia e geofisica portugal the resulting bouguer anomaly reveals the presence of a regional trend several local features and a component of noise in separating the regional trend we use a robust polynomial fitting further a covariance analysis and a least squares prediction are applied to filter the noise and to model the local anomaly a first signal map represents the main local anomaly while the secondary signal map shows superficial anomalies this distribution reveals a local main minimum close to the 1630 a d and gaspar craters several possible alignments are shown that lead to a model mainly with sw ne and se nw orientations of the negative anomaly with the pattern of the low density zones showing a relationship with the volcanic features applying a stabilized linear method of gravimetric inversion we obtain a density contrast distribution of the sources of the filtered local bouguer anomaly considering as unknowns the anomalous densities of a fixed discrete distribution of rectangular prisms which represents the subsoil volume a mixed minimization criteria for the weighted residuals and the weighted density contrast allow us to obtain a solution as a discrete three dimensional density contrast model the obtained anomalous densities model shows a clear relation with the structure of the caldera complex and tectonic trends with the principal body of negative contrast density being associated with the subsurface structure of the caldera

a three dimensional gravity inversion applied to sao miguel island azores gravimetric studies are becoming more and more widely acknowledged as a useful tool for studying and modeling the distributions of subsurface masses that are associated with volcanic activity in this paper new gravimetric data for the volcanic island of sao miguel azores were analyzed and interpreted by a stabilized linear inversion methodology an inversion model of higher resolution was calculated for the caldera of furnas which has a larger density of data in order to filter out the noncorrelatable anomalies least squares prediction was used resulting in a correlated gravimetric signal model with an accuracy of the order of 0 9 mgal the gravimetric inversion technique is based on the adjustment of a three dimensional 3 d model of cubes of unknown density that represents the island s subsurface the problem of non uniqueness is solved by minimization with appropriate covariance matrices of the data resulting from the least squares prediction and of the unknowns we also propose a criterion for choosing a balance between the data fit which in this case corresponds to residues with rms of the order of 0 6 mgal and the smoothness of the solution the global model of the island includes a low density zone in a wnw ese direction and a depth of the order of 20 km associated with the terceira rift spreading center the minimums located at a depth of 4 km may be associated with shallow magmatic chambers beneath the main volcanoes of the island the main high density area is related to the nordeste basaltic shield with regard to the caldera furnas in addition to the minimum that can be associated with a magmatic chamber there are other shallow minimums that correspond to eruptive processes

the pleistocene clastic sediments in the divje babe i cave slovenia geochemical characterisation and provenance part 2 different grain size fractions of clastic sediments 40 65 0 5 3 and 0 5 mm from the divje babe i cave were chemically analysed in the chemical composition of the medium and fine fractions four groups of variables were revealed 1 mgo loi tot c dolomite autochthonous terrigenous component 2 p2o5 tot s mo sr cu cao and so on bones apatite cement biochemical chemical components 3 sio2 al2o3 ree rb zr k2o th tio2 fe2o3 and so on non carbonate allochthonous terrigenous components and 4 u cd mno more mobile chemical components vertical distributions of p2o5 sio2 and u in the fine fraction suggest five geochemical boundaries the origin of p2o5 is attributed mainly to the cave bear a negative correlation between the content of sio2 and cavernously corroded clasts indicating a humidity indicates a dominant aeolian transport of non carbonate material into the cave vertical distribution of u indicates the migration of u and its enrichment in the deeper parts of the sedimentary sequence the mobilization of u was influenced by the duration of exposure of the sediments on the cave floor the chemical characteristics of non carbonate material indicate that source rocks probably belong to the triassic volcanic volcanogenic and terrigenous sedimentary rocks

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

effects of temperature and humidity upon the transport of sedimentary particles by wind aeolian transport of sedimentary particles is a well recognized phenomenon in cold regions but the effect of low temperature t and specific humidity q upon particle entrainment has not previously been investigated this study reports on wind tunnel experiments 12 c t 32 c and 1 g kg 1 q 10 g kg 1 that suggest the aerodynamic drag required to entrain sand sized particles can be 30 lower in cold or high latitude settings as compared to hot deserts for any given regional wind velocity this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature

wind tunnel and field calibration of five aeolian sand traps the efficiency of five aeolian sand samplers was tested via wind tunnel experiments and field measurements the samplers were the big spring number eight bsne sampler the modified wilson and cooke mwac sampler the suspended sediment trap sustra the pollet catcher polca and the saltiphone in the wind tunnel the samplers were calibrated against an isokinetic sampler a modified sartorius sm 16711 sampler with adjustable flow rate and this for three sand types median diameter 132 194 and 287 m and five wind speeds ranging from 6 6 to 14 4 m s 1 in the field seven calibration tests of two weeks each were conducted the absolute efficiencies of the bsne mwac and polca are more or less comparable and vary between 70 and 120 depending on sediment size and wind speed for the sustra the efficiency is somewhat lower for fine sands and for wind speeds above 11 m s 1 finally the saltiphone can accurately detect the periods of saltation transport but in its current version the instrument is not accurate when measuring the absolute saltation flux the most recommendable sampler in the test is the mwac not only because of its high efficiency but also because its efficiency is independent of wind speed

threshold friction velocities and rupture moduli for crusted desert soils for the input of soil particles into the air desert soils having clay crusts mostly from the mojave desert were tested for threshold friction velocity the friction velocity at which soil erosion begins with an open bottomed wind tunnel the soils were also tested for content of clay water soluble material calcium carbonate organic material mineralogy of clay and of salts soil moisture modulus of rupture and crust thickness if no loose material existed on the soil surface crusts having modulus of rupture greater than 0 7 bar and crust thickness of 0 7 cm to 0 3 cm were effective in protecting against wind erosion disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1 9 cm did not experience significant wind erosion modulus of rupture was related to composition of soil but was shown to depend mostly on clay content soil composition is related to modulus of rupture in an empirical equation

deep sea sediments in the eastern equatorial atlantic off the african coast and meteorological flow patterns over the sahel deep sea mineral dust deposits are a powerful tool allowing to deduct atmospheric flow patterns here deep sea sediments from the eastern tropical atlantic were used to derive climatic conditions over the african continent where in summer the dust is lifted in the transition zone of the sahara and the sahel the meteorological process causing this aeolian dust injection are the squall lines the rain bearing disturbances of the sahel they produce a high surface wind velocity area in their northern vicinity the deep sea deposits of sediments and their spatial patterns allowed to conclude that the dust raising mechanism connected with the squall lines were similar for present day conditions and for the time of the last glacial maximum the saharan trades and the african monsoon had about the same extension in either time slice coupled with an identical travel belt of the squall lines however the intensity and the frequency of the squall lines were lower in glacial times

kinky profiles effects of soil surface heating upon vertical dust concentration profiles in the channel country of western queensland australia 1 in rangelands unlike cultivated fields soil surface conditions and vegetation cover are far from uniform field measurements taken within rangeland environments show that the shape of vertical dust concentration profiles can vary significantly between wind erosion events regression fits used to analyze vertical dust concentration profiles are therefore better for some events than others such variability has usually been explained as experimental error or noise or as a result of the nonuniformity of surface conditions a computer simulation model dsism is used to examine this variability in terms of wind erosion processes analysis of these simulation results together with field observations shows that nonuniformity in surface conditions alone cannot explain variations observed in the vertical dust concentration profiles these same simulations suggest that much of the variability in vertical dust concentration profiles is the result of thermal heating of the soil surface

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

paleomagnetic determinations on lanzarote from magnetic and gravity anomalies implications for the early history of the canary islands the bouguer and aeromagnetic anomaly maps of lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island indicating one isolated source assuming that the structure responsible for both anomalies is the same a methodology has been designed to estimate the total magnetization vector of the source which is interpreted as a large intrusive body mafic core positioned as a result of magma rising to the surface during the early stages of growth of lanzarote considering its geometry to be known from a previous three dimensional 3 d gravity model the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced to the pole anomaly map comparison between the gravity and the pseudogravity anomalies and 3 d forward magnetic modeling the total magnetization vector obtained by this method is defined by a module of 4 5 a m 1 and a direction d 20 degrees and i 30 degrees comparing the paleomagnetic pole obtained from this direction with the apparent polar wander path of africa for the last 160 myr it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization nrm which could have been acquired between 60 and 100 ma this result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in lanzarote took place during the upper cretaceous thus providing the first evidence of a timeline for the early formative stages of this volcanic island

the crustal structure of the canary basin accretion processes at slow spreading centers multichannel seismic reflection and gravity data define the structure of mesozoic ocean crust of the canary basin formed at slow spreading rates single and multichannel seismics show a transition from smooth to rough basement topography from jurassic to cretaceous crust and a coeval change in crustal structure internal reflectivity of the rough basement area comprises upper upper middle or whole crust cutting discrete dipping reflections lower crustal reflectivity is almost absent and reflections from the crust mantle transition are short and discontinuous or absent for several kilometers in contrast crust in the smooth basement area is characterized by sparse lower crustal events and common reflections from the crust mantle boundary the crustal structure of fracture zones in the rough basement area is associated with depressions in the basement top and in most cases with thin crust in the smooth basement area fracture zones exhibit neither a clear topographic expression nor crustal thinning we interpret these characteristics as indicative of an increase in extensional tectonic activity and decrease in magmatic activity at the spreading ridge associated with a general decrease of spreading rate from jurassic to cretaceous times in addition the crust imaged across the path of the cape verde hot spot in the canary basin exhibits a widespread lower crustal reflectivity very smooth topography and apparently thick crust our data document significant changes in the structure of crust formed at slow spreading rates which we attribute to thermal changes in the lithosphere due either to variations in spreading rate or to the presence of a hot spot beneath the mesozoic mid atlantic ridge

the canary islands swell a coherence analysis of bathymetry and gravity summary the canary archipelago is an intraplate volcanic chain located near the west african continental margin emplaced on old oceanic lithosphere of jurassic age with an extended volcanic activity since middle miocene the adjacent seafloor does not show the broad oceanic swell usually observed in hotspot generated oceanic islands however the observation of a noticeable depth anomaly in the basement west of the canaries might indicate that the swell is masked by a thick sedimentary cover and the influence of the canarian volcanism we use a spectral approach based on coherence analysis to determine the swell and its compensation mechanism the coherence between gravity and topography indicates that the swell is caused by a subsurface load correlated with the surface volcanic load the residual gravity geoid anomaly indicates that the subsurface load extends 600 km ssw and 800 km n and nne of the islands we used computed depth anomalies from available deep seismic profiles to constrain the extent and amplitude of the basement uplift caused by a relatively low density anomaly within the lithospheric mantle and coherence analysis to constrain the elastic thickness of the lithosphere t e and the compensation depth of the swell depth anomalies and coherence are well simulated with t e 28 36 km compensation depth of 40 65 km and a negative density contrast within the lithosphere of 33 kg m 3 the density contrast corresponds to a temperature increment of 325 c which we interpret to be partially maintained by a low viscosity convective layer in the lowermost lithosphere and which probably involves the shallower parts of the asthenosphere this interpretation does not require a significant rejuvenation of the mechanical properties of the lithosphere

wind erosion of crusted soil sediments saltating particles increase the rate of dust release from sediments in arid and semi arid areas they also break interparticle bonds in aggregated and crusted soils thereby increasing the number of particles available for entrainment this pilot study examines rates of erosion in relation to the flux of saltating grains for three crusted sediments of different strengths dislodgement of surface particles decreases with increasing crust strength as measured by a cylindrical flat ended penetrometer in addition initial dust release from craters formed by single impactors in unaggregated soil is examined in relation to the associated saltator the volume of material removed depends linearly on the kinetic energy of the abraders

tectonic evolution of the emergent part of a volcanic ocean island lanzarote canary islands abstract a reconstruction of the structural evolution of lanzarote confirms the existence of two principal stages of construction of the island separated by a main erosional event the first pre erosional is the shield stage miocene pliocene in age which is divided in three stratigraphic groups where different formations can be distinguished using unconformities mappable over the whole area of outcrop in the second post erosional stage developed during the quaternary nine stratigraphic levels are tentatively identified and are grouped in two phases of volcanic activity shields phase and pyroclastic cones phase data from 580 photogeologic lineaments as well as field data from 204 fault planes 195 with sense of movement 273 dykes and 45 volcanic alignments are presented the tectonic style of the deformations is brittle and polyphasic strike slip faults are dominant but normal and reverse faults are also present both the so called atlantic and african directions are well developed in trends of strike slip faults and volcanic indicators at least two deformation phases can be identified from the geometrical analysis of faults and from the stress tensor calculated using lineations on fault planes the reconstructed stress field responsible for the measured deformations changed orientation during the evolution of the island of lanzarote it is suggested that a permutation between principal stress axes 1 and 3 occurred subparallel to the length of the island between the pre erosional and post erosional stages

application of gravity and deep dipole geoelectrics in the volcanic area of mt etna sicily abstract the structural pattern of the basement of the mt etna volcano is studied by combining results from new gravity and deep dipole geoelectric field data at first the bouguer map was separated into regional and residual contour maps by a 50 km cut off wavelength then by the geoelectric interpretation n s and e w resistivity cross sections were elaborated which were used as guidelines for modelling gravity residuals after observing a close correspondence between bouguer anomalies and resistivity classes by a trial and error adjustment to the relationship between resistivity and density a 3 d block model of the basement was finally constructed which consistently matched with both gravity and geoelectric information content two main conclusions emerged from the combined interpretation the first is the presence of diffuse inhomogeneities in the upper portion of the basement down to an average depth of 2 km below sea level in contrast with the regularity of the explored underlying portion the second is the absence of geophysical markers suggesting the existence of a large magmatic chamber down to about 3 km below sea level

dust model intercomparison dmip study over asia overview 1 an intercomparison study involving eight dust emission transport models over asia dmip has been completed participating dust models utilize a variety of dust emission schemes horizontal and vertical resolutions numerical methods and different meteorological models two huge dust episodes occurred in spring 2002 and were used for the dmip study meteorological parameters dust emission flux and dust concentration diameter 20 m are compared within the same domain on the basis of pm and nies lidar measurements we found that modeled dust concentrations between the 25 and 75 percentiles generally agreed with the pm observations the model results correctly captured the major dust onset and cessation timing at each observation site however the maximum concentration of each model was 2 4 times different dust emission fluxes from the taklimakan desert and mongolia differ immensely among the models indicating that the dust source allocation scheme over these regions differs greatly among the various modeling groups this suggests the measurements of dust flux and accurate updated land use information are important to improve the models over these regions the dust vertical concentration profile at beijing china and nagasaki japan has a large scatter more than two times different among the models for beijing the scaled dust profile has a quite similar vertical profile and shows relatively good agreement with the lidar extinction profile however for nagasaki the scaled dust profiles do not agree these results indicate that modeling of dust transport and removal processes between china and japan is another important issue in improving dust modeling

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

iron and nutrient content of wind erodible sediment in the ephemeral river valleys of namibia abstract research concerning the global distribution of aeolian dust sources has principally focussed on salt clay pan and desiccated lacustrine emission areas in southern africa such sources are identified as etosha pan in northern namibia and makgadikgadi pans in northern botswana dust emitting from ephemeral river valleys however has been largely overlooked rivers are known nutrient transport pathways and the flooding regimes of ephemeral river valleys frequently replenish stores of fine sediment which on drying can become susceptible to aeolian erosion such airborne sediment may be nutrient rich and thus be significant for the fertilisation of marine waters once deposited this study investigates the dust source sediments from three ephemeral river valleys in namibia in terms of their particle size distribution and their concentrations of bioavailable n p and fe we compare the nutrient content of these sediments from the ephemeral river valleys to those collected from etosha and makgadikgadi pans and consider their relative ocean fertilising potential our results show that the ephemeral river valleys contain fine grained sediment similar in physical character to etosha and makgadikgadi pans yet they have up to 43 times greater concentrations of bioavailable iron and enriched n and p macronutrients that are each important for ocean fertilisation the known dust emitting river valleys of namibia may therefore be contributing a greater fertilisation role in the adjacent marine system than previously considered and not yet investigated given this finding a re assessment of the potential role of ephemeral river valleys in providing nutrient rich sediment into the aeolian and marine systems in other dryland areas is necessary

the crustal structure of el hierro canary islands from 3 d gravity inversion el hierro is the youngest and westernmost island of the canarian archipelago due to its singular and interesting characteristics with extensive landsliding studying its crustal structure can provide very useful information about its origin and evolution with this aim we use the gravity inversion methodology obtaining a crustal model of mass distribution we performed a gravity survey of the entire island completing the gravity anomaly map of this area with marine data from the united states geological survey the calculated bouguer gravity anomaly map was studied using a covariance analysis and the least squares technique to obtain crustal information from these data we used a 3d gravity inversion based on genetic algorithms ga thus our inversion technique aims to determine the geometry of the sources of the observed gravity field upon a prismatic partition of the subsoil volume and adopting a priori density contrast values the results of this gravity study of el hierro island show the correlation of several volcanic structures with the distribution of the gravity field sources the characteristic triple rift system of the island is associated with low density areas and the older volcanic stages with high density structures we also found differences among the structures related to the several landslides which helped the island takes shape

an estimation of the elastic thickness of the lithosphere in the canary archipelago using admittance function a recent compilation of shipborne gravity and bathymetry data has been used to determine the effective elastic thickness eet of the lithosphere beneath the canary islands volcanic complex by means of the admittance technique as a first approach we have computed the admittance which is interpreted in terms of isotropic elastic plate thickness with an eet of 23 km nevertheless the proximity of the west african continental margin wacm together with the lateral variability in lithosphere structure in part caused by the large volcanic history of the canaries require a slightly different approach to minimize the influence of the margin and to check whether or not any significant variation in eet occurs related to the known canary hotspot we have computed the admittance following the isochron lines the results show a higher eet 35 km than that obtained by the first approach but slightly smaller than that predicted by the cooling plate model

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

complete gravity study of piton de la fournaise volcano reunion island abstract we present an interpretation of all available gravity data on piton de la fournaise volcano including a new set collected in the summit area using a linear programming inversion method we determine the extension of the grand brule ultramafic body drilled in 1985 and we propose to interpret it as a frozen magma chamber related to a disappeared volcano we also present evidence for superficial mass excess under the enclos fouque and plaine des sables calderas that we link to the present piton de la fournaise volcanism the detailed gravity survey of the summit area allows us to emphasize the great importance of dyke complexes associated with the ne and se rift zones and with the shallow magma chamber a negative anomaly in the summit area is interpreted as a relative minimum between the positive anomaly of grand brule and those of the western part of the enclos fouque and plaine des sables calderas

dust emission and transport in mali west africa vertical dust fluxes were measured in the inland delta region of the niger river mali west africa during april june 1989 and 1990 measurements of dust flux represent for the most part non dust storm conditions or dust haze periods the observed concentration versus height relationships are similar to data presented by other investigators the relationship between wind shear velocity u m s 1 and vertical dust flux f g m 2 s 1 can be described by a relationship in which f is proportional to u 4 however there is considerable scatter within the data set which is attributable to textural controls and surface conditions the vertical dust fluxes measured in mali are compared to dust fluxes measured in texas usa and yukon territories canada the significantly different values for the constant of proportionality a in the f a u 4 relationship for these geographically diverse areas is a function of surficial controls on the release of sediments to the air stream dust concentrations measured in mali were found to be uniformly high and in general exceed who health standards for acceptable total suspended particulate loadings as a result background dust may be considered a long term stress on health for the people of this region of mali