sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

aeolian abrasion and modes of fine particle production from natural red dune sands an experimental study a series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles 125 m by 1 the release of resident fines 2 spalling chipping and breakage of particles and 3 the removal of grain surface coatings parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass test tube chamber for up to 120h the fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle size analyses using a coulter multisizer the abrasion of untreated parent samples produced fine particles in one of two main size classes 50 m but when the parent sample was sieved to exclude particles 250 m relatively more material in the range 10 50 m was produced for unsieved parent samples the size range associated with the dominant mode varied according to the length of the abrasion time the coarsest mode 63 m was dominant during the first 16 h of abrasion then became less significant and is thought to be associated with the release of resident fines into suspension the finest mode 10 m was absent or very weak during the first 16h of abrasion then became more significant and in some instances dominated the distribution as abrasion continued removal of grain surface coatings is the main source of fine material 10 m and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles by comparison with previous studies of aeolian particle abrasion these natural dune sands produced very low quantities of fine material by weight but their spatial extent makes them potentially a significant source of dust sized particles at the global scale

calcrete profile development in quaternary alluvial sequences southeast spain implications for using calcretes as a basis for landform chronologies a detailed study of the morphology and micro morphology of quaternary alluvial calcrete profiles from the sorbas basin shows that calcretes may be morphologically simple or complex the simple profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface the complex profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation these complex calcrete profiles are consequently described as composite profiles the exact morphology of the composite profiles depends upon 1 the number of calcrete forming events occurring during terrace sediment aggradation 2 the amount of sediment accretion that occurs between each period of calcrete formation and 3 the degree of pedogenesis after terrace formation simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation composite profiles are more problematic pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments in addition erosion may lead to the exhumation of older calcretes within the terrace sediment calcrete inheritance may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age composite profiles are therefore only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete forming events thus a detailed morphological micro morphological study is required before any chronological study is undertaken this is the only way to establish whether particular calcrete profiles are suitable for dating purposes copyright 2003 john wiley sons ltd

longevity of aeolian megaripples abstract megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain size distributions the interplay between wind grain size and ripple morphology height and wavelength controls their development two main mechanisms limit megaripple height the first megaripple flattening due to winds that are above the fluid threshold of the coarse grains destroys the armoring layer of the megaripple the second is megaripple erosion by the impacts of fast moving fine saltating grains that propel the coarse grains constituting the armoring layer for any given wind regime and grain size distribution the potential megaripple dimensions are limited by these two mechanisms here we study the first mechanism and estimate the duration of strong winds sustained above the fluid threshold needed to flatten megaripples strong gusts of wind in contrast cannot destroy the megaripples but can cause ripple migration based on data from previous works on megaripples we find a scaling law between the ripple morphology and the coarse mode of grains at the crest using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening in general the coarser the particles at the megaripple crest the stronger the wind needed to flatten the megaripples moreover the greater the strength of the wind required to flatten the megaripples the lower the recurrence probability taken together these findings increase the longevity of megaripples we apply the results for a megaripple field in the southern arava valley israel

calcrete fossilisation of alluvial fans in se spain the roles of groundwater pedogenic processes and fan dynamics in calcrete development abstract dryland alluvial fans developed along the northern flanks of the sierra lisbona in the north western vera basin almeria region southeast spain display negligible amounts of incision despite distal base level lowering of 30 m by the modern drainage network the fans are of early middle quaternary age and are graded to a coeval river terrace now isolated from the modern drainage network the negligible incision is due to the encasement and fossilisation of the alluvial fans by calcrete this paper explores the reasons for such fossilisation and assesses the relative importance of pedogenic and groundwater mechanisms for calcrete formation within an alluvial fan setting a single fan was selected for detailed examination the geomorphological and sedimentological features of the fan its catchment area and their relationship to the distal river terrace were documented qualitative and semi quantitative petrographic and scanning electron microscope analyses of calcrete samples collected from transects across the fan surface and within its distal top river terrace surface enabled the style pattern and relative timing of calcrete development to be assessed calcrete fabrics comprised initial micritic grain coating cements pellets and glaebular carbonate nodules with interstitial spaces infilled by equant sparite and microsparite mosaics it is proposed that the early phases of calcrete development were dominated by pedogenic processes with increasing groundwater calcretisation over time point count data indicated increased quantities of interstitial sparite and microsparite cement within near surface proximal fan calcretes and at depth across the fan suggesting that groundwater processes played a more important role in calcrete formation in these locations the contribution of groundwater to calcrete development can be best explained by the intrinsic funnelling of groundwater from the catchment through the proximal fan head area a zone where the fan gravels are thinnest calcrete fossilisation appears to have followed a reduction in the fan catchment area as a result of rockfalls and watershed stream capture which reduced water and sediment supply to the fan and enabled surface stabilization and calcrete development to take place the reduced sediment water supply combined with calcrete fossilisation appears to have protected the alluvial fans from regional base level lowering the implications of these results for existing pedostratigraphic models of calcrete development in alluvial fans are subsequently explored

sorting out abrasion in a gypsum dune field 1 grain size distributions in eolian settings are the result of both sorting and abrasion of grains by saltation the two are tightly coupled because mobility of particles determines abrasion rate while abrasion affects the mobility of particles by changing their mass and shape few field studies have examined this quantitatively we measured grain size and shape over a 9 km transect downwind of a line sediment source at white sands national monument a gypsum dune field the sediment source is composed of rodlike elongate coarse particles whose shapes appear to reflect the crystalline structure of gypsum dispersion in grain size decreases rapidly from the source coarse particles gradually become less elongate while an enrichment of smaller more elongate grains is observed along the transect transport calculations confirm that white sands is a threshold sand sea in which 1 the predominant particle diameter reflects grains transported in saltation under the dune forming wind velocity and 2 smaller elongate grains move in suspension under this dominant wind size selective transport explains first order trends in grain size however abrasion changes the shape of saltating grains and produces elongate smaller grains that are spallation and breaking products of larger particles both shape and size changes saturate 5 6 km downwind of the source as large particles become more equant abrasion rates slow down because protruding regions have been removed such asymptotic behavior of shape and abrasion rate has been observed in theory and experiment and is likely a generic result of the abrasion process in any environment

magnetic investigations of the west hawk deep bay and clearwater impact structures canada due to the effects of erosion tectonism and burial impact structures are often obscured or destroyed geophysical methods are increasingly being used in detecting the signatures of impact structures while gravity lows associated with impact structures are well understood associated magnetic anomaly lows are not in this study drill cores from three canadian impact structures were analyzed for rock magnetic properties and mineralogy in order to explain the magnetic anomaly lows associated with these structures samples from the drill cores were cut and measured for anisotropy of magnetic susceptibility ams and natural remanent magnetization nrm parameters drill cores from the twin impact craters of the clearwater structure exhibited different nrm characteristics and samples from their respective drill cores were subject to demagnetization by alternating field and thermal techniques the difference noted in their nrm characteristics was attributed to the acquisition of a viscous remanent magnetization vrm at depth in clearwater east at all three structures both magnetic susceptibilities and remanent magnetizations are well below regional values in impact generated breccias melt rocks shocked crystalline rocks and in postimpact sedimentary infill the processes of brecciation alteration shock and infill by nonmagnetic sediments contribute to the development of the magnetic lows however a significant contribution to the observed magnetic anomalies was found by first order forward modelling to arise from basement rocks beneath the impact structures this zone of reduced magnetization may be caused by the partial demagnetization of magnetite by the impact induced transient stress wave traveling away from the point of impact

factors affecting the nature and rate of dust production from natural dune sands this paper evaluates the influence of natural sand particle characteristics on the amount and particle size distributions of dust produced by aeolian abrasion it contrasts with previous studies of aeolian abrasion by conducting experiments using i whole sand samples as opposed to selected size fractions ii natural mature dune sands rather than artificial or freshly crushed material and iii weathered sands that have acquired a superficial clay coating instead of grains with clean surfaces whilst previous research has found clear positive relationships between particle size sorting roundness and the amount of dust produced by aeolian abrasion the relationships determined in this study show some variation according to the geomorphological context from which the original samples were obtained the most important factor affecting the amount and particle size characteristics of the dust produced was the presence of a clay coating on the grain surface that is removed by the abrasion process the dust produced by this mechanism had a modal size of 2 5 m and material 10 m comprised up to 90 of the particles produced

making loess sized quartz silt data from laboratory simulations and implications for sediment transport pathways and the formation of desert loess deposits associated with the sahara abstract results from a series of laboratory simulations designed to investigate quartz silt generation by a number of geomorphic mechanisms are reviewed these findings are then used to discuss potential sediment pathways involved in the formation of desert loess deposits and a pathway is presented to show a proposed sequence of events involved in the formation of the loess deposits associated with the sahara the results indicate that both fluvial and aeolian systems can be very effective at producing quartz silt it is suggested that fluvial systems within hot desert environments may play a central role in both the production and distribution of loessic silt first the highly energetic but periodic fluvial regimes associated with arid and semi arid environments may be responsible for considerable quantities of particle comminution second the intermittent nature of these systems will help maintain geomorphologically active surfaces from which silt sized material can be easily deflated as well as fluvial comminution a range of weathering mechanisms and aeolian abrasion may also be responsible for the generation of silts in desert loess consequently silt sources and mechanisms of silt generation are likely to be much more diverse for desert loess than those associated with glacial loess

use of soils and colluvial deposits in analyzing tectonic events the southern arava rift israel abstract buried soils in colluvium units developed on downthrown fault blocks have been presumed to form during periods of tectonic quiescence this assumes however that all colluvial units on a fault scarp are tectonically induced particularly for a multiple event fault scarp to test this hypothesis we compared the colluvial stratigraphy and pattern of soil development on two non tectonic scarps terrace risers and a nearby multiple event fault scarp on the same alluvial fan surface both slopes developed under extremely and climatic conditions the colluvial stratigraphy and soil catenary relationship developed on terrace risers were found to be substantially different from those on the multiple event fault scarp the fault scarp colluvium contained several colluvial units separated by soils whereas only two colluvial units without buried soils were found on the terrace risers the colluvial units on the fault scarp were triangular in shape while those on the terrace riser were concave and overlapped up the slope cumulic soils indicating a continuous and low rate of deposition during pedogenesis were formed along the terrace riser in contrast buried soils indicating episodic deposition occurred on the downthrown block of the multiple event fault scarp accordingly the colluvial stratigraphy developed on the fault scarp can be viewed as a record of distinct tectonic events with no climatically controlled deposition the data indicate that soils and sedimentary stratigraphy can serve as useful indicators to distinguish terrace risers and single event fault scarps from multiple event fault scarps these indicators can be helpful in distinguishing phases of tectonic activity and in evaluating recurrence intervals on a multiple fault scarp

the timing of quaternary calcrete development in semi arid southeast spain investigating the role of climate on calcrete genesis quaternary aged calcrete horizons are common weathering products in arid and semi arid regions it is however unclear how calcrete forming processes respond to the major oscillations in climate that occur over the quaternary period this paper presents a u series based calcrete age database from the sorbas basin southeast spain the study constructs an age frequency distribution of these ages which is consequently compared to a range of palaeoenvironmental records from the mediterranean the age distribution presented here suggests that the formation of pedogenic calcrete horizons in the sorbas basin primarily occurs during warm isotope stages mis 1 and 5 with very few calcrete ages occurring during cold glacial stadial stages mis 2 3 and 4 it is suggested that this is a function of the environments that existed during warm isotope stages being more conducive to calcrete development than those that existed during cold climate episodes in a semi arid region such as the sorbas basin it is likely that increased aridity during glacial stages coupled with reduced vegetation and accelerated landscape instability was crucial in reducing rates of calcrete formation in a semi arid region such as southeast spain calcrete formation during the quaternary therefore oscillates with climate change but is primarily a warm episode phenomenon it is suggested that further studies are required to see how calcrete genesis responds to environmental change in more humid parts of the mediterranean

multiple dust sources in the sahara desert the importance of sand dunes 1 we determine the current sources of dust in the sahara desert using quantitative correlation between the number of days with dust storms nds derived from remote sensing data of high temporal resolution with the distribution of the soil types and geomorphic units during 2006 8 the source of over 90 of the nds was found to be sand dunes leptosols calcisols arenosols and rock debris in contrast to previous studies only few dust storms originated from playas and dry lake beds land erodibility was estimated by regressing the nds to the number of days with high speed wind events and was found to be high for sand dunes clay and fine silt grains and aggregates are scarce in sand dunes which most likely produce dust particles through aeolian abrasion of sand grains thus saltating sand grains impacting clay aggregates on playa surfaces cannot be the sole process for generating dust in the sahara

dust production and the release of iron oxides resulting from the aeolian abrasion of natural dune sands global dust trajectories indicate that significant quantities of aeolian transported iron oxides originate in contemporary dryland areas one potential source is the iron rich clay coatings that characterize many sand sized particles in desert dunefields this paper uses laboratory experiments to determine the rate at which these coatings can be removed from dune sands by aeolian abrasion the coatings impart a red colour to the grains to which previous researchers have assigned variable geomorphological significance the quantities or iron removed during a 120 hour abrasion experiment are small 99 mg kg 1 and difficult to detect by eye however high resolution spectroscopy clearly indicates that ferric oxides are released during abrasion and the reflectance of the particles alters one of the products of aeolian abrasion is fine particles 10 mum diameter with the potential for long distance transport copyright c 2004 john wiley sons ltd

geochemical evidence for airborne dust additions to soils in channel islands national park california there is an increasing awareness that dust plays important roles in climate change biogeochemical cycles nutrient supply to ecosystems and soil formation in channel islands national park california soils are clay rich vertisols or alfi sols and mollisols with vertic properties the soils are overlain by silt rich mantles that contrast sharply with the underlying clay rich horizons silt mantles contain minerals that are rare or absent in the volcanic rocks that dominate these islands immobile trace elements sc th la and ta nd cr and rare earth elements show that the basalt and andesite on the islands have a composition intermediate between upper continental crust and oceanic crust in contrast the silt fractions and to a lesser extent clay fractions of the silt mantle have compositions closer to average upper continental crust and very similar to mojave desert dust island shelves exposed during the last glacial period could have provided a source of eolian sediment for the silt mantles but this is not supported by mineralogical data we hypothesize that a more likely source for the silt rich mantles is airborne dust from mainland california and baja california either from the mojave desert or from the continental shelf during glacial low stands of sea although average winds are from the northwest in coastal california easterly winds occur numerous times of the year when santa ana conditions prevail caused by a high pressure cell centered over the great basin the eolian silt mantles constitute an important medium of plant growth and provide evidence that abundant eolian silt and clay may be delivered to the eastern pacifi c ocean from inland desert sources

spatial soil variability in the cajon pass chronosequence implications for the use of soils as a geochronological tool abstract spatial variation of soil properties on a single geomorphic surface has a significant influence on surface correlations and age determinations made on the basis of soil properties few chronosequence studies have been based on a sufficient number of soils to evaluate the influence of soil variability we described and evaluate 35 soils on four terrace surfaces which constitute part of a previously described well dated soil chronosequence in cajon pass in southern california soils were described on both bar and swale sites removed from the influence of deposition adjacent slopes the influence of eolian silt on the rate of pedogenesis in cajon pass indicates that this sequence of soils cannot be considered a chronosequence in the strict sense of the term furthermore the evidence for a pedogenic threshold in these soils indicates that the soils do not develop monotonically with time and that soil development cannot be defined by a continuous univariant chronofunction the discrete nature of the data from a chronosequence and the complex nature of soil development are better analyzed by multivariate statistical procedures systematic variation in soil properties between soils from bar sites and soils from swale sites is attributed to geomorphic processes which affect either the rate or duration of eolian dust accumulation soils from bar sites were less variable and generally less strongly developed that soils from swale sites from the same surface the degree of variation of soil properties determined for a given landscape position on a surface is sufficient to raise questions concerning the usefulness of chronofunctions for determining the nature of time dependent pedogenic changes and for providing numerical age determinations multivariate statistical methods were used to differentiate among soils developed on three surfaces which differ in age by only 1500 years

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

can active sands generate dust particles by wind induced processes abstract mineral dust emission is a major process in determining the global dust cycle at a global scale there is still uncertainty about the absolute and relative contribution of dust from different source areas and landforms dust sources are mainly considered as surfaces containing relatively high percentages of fine particles e g playas yet active dune sands have been identified recently by remote sensing studies as dust sources in northern africa china and elsewhere previous studies on dust emission from active sands suggested that dust can be generated by different aeolian mechanisms that are related to i re emission of settled dust particles ii clay coating removal and iii abrasion of the sand grains however there is only limited information of the relative importance of the different mechanisms for producing this dust under natural aeolian wind conditions this study integrates wind tunnel experiments and high resolution laboratory sand analyses to explore aeolian dust emission from active sands with conditions simulating the natural processes of saltation and explores the role of the different dust emission mechanisms sand samples from three sites with different characteristics of grain size dust content morphology and mineralogy were used in the experiments no dust emission was recorded for shear velocities below the saltation threshold the initial content of dust sized particles 63 m in the sand sample was found to influence pm10 emission pm10 concentrations were increased with the initial content of dust sized particles in the sand the experiments identify clay coatings removal as the dominant mechanism over time of dust emission in typical active sand dunes 40 m the dust emission observed in this study indicates that in addition to the classic dust sources of non sandy soils sand bodies should also be taken into consideration in determining global dust emission

investigation of the controls on dune colour in the namib sand sea using mineral magnetic analyses abstract the geological and environmental controls upon the pattern of increasing dune redness inland in the namib sand sea are investigated using mineral magnetic measurements satellite imagery and dithionite extractable iron results suggest whole grains or inclusions within grains dominate the iron oxide assemblage but the sediment colour is more strongly influenced by a second component which consists of haematite within the grain coatings the magnetic data suggest that source materials exert at least a partial control on dune colour in this field setting evidence for the influence of other factors e g age and climatic gradient is also present

reduction in soil aggregation in response to dust emission processes abstract dust emission by aeolian wind soil erosion depends on the topsoil properties of the source area especially on the nature of the aggregates where most dust particles are held although the key role of soil aggregates in dust emission the response of soil aggregation to aeolian processes and its implications for dust emission remain unknown this study focuses on aggregate size distribution asd analyses before and after in situ aeolian experiments in semiarid loess soils that are associated with dust emission wind tunnel simulations show that particulate matter pm emission and saltation rates depend on the initial asd and shear velocity under all initial asd conditions the content of saltator sized aggregates 63 250 m increased by 10 34 due to erosion of macro aggregates 500 m resulting in a higher size ratio sr between the saltators and macro aggregates following the aeolian erosion the results revealed that the saltator production increases significantly for soils that are subjected to short term anthropogenic disturbance of the topsoil the findings highlight a decrease in soil aggregation for all initial asd s in response to aeolian erosion and consequently its influence on the dust emission potential changes in asd should be considered as a key parameter in dust emission models of complex surfaces

an exceptionally long paleoseismic record of a slow moving fault the alhama de murcia fault eastern betic shear zone spain most catastrophic earthquakes occur along fast moving faults although some of them are triggered by slow moving ones long paleoseismic histories are infrequent in the latter faults here an exceptionally long paleoseismic record more than 300 k y of a slow moving structure is presented for the southern tip of the alhama de murcia fault eastern betic shear zone which is characterized by morphological expression of current tectonic activity and by a lack of historical seismicity at its tip the fault divides into a splay with two main faults bounding the gonar fault system at this area the condensed sedimentation and the distribution of the deformation in several structures provided us with more opportunities to obtain a complete paleoseismic record than at other segments of the fault the tectonic deformation of the system was studied by an integrated structural geomorphological and paleoseismological approach stratigraphic and tectonic features at six paleoseismic trenches indicate that old alluvial units have been repeatedly folded and thrusted over younger ones along the different traces of the structure the correlation of the event timing inferred for each of these trenches and the application of an improved protocol for the infrared stimulated luminescence irsl dating of k feldspar allowed us to constrain a paleoseismic record as old as 325 ka we identified a minimum of six possible paleoearthquakes of m w 6 7 and a maximum mean recurrence interval of 29 k y this provides compelling evidence for the underestimation of the seismic hazard in the region

demagnetization signatures of lunar impact craters research at the university of california berkeley was supported by nasa through subcontract lri 99 101 from the lunar research institute

genesis and climatic interpretation of paleosols and calcretes in a plio pleistocene alluvial fan of the costa blanca se spain abstract a plio pleistocene alluvial fan near la regia in the southeast coast of spain contains a vertical series of 7 fossil soils and 7 calcrete complexes the soil stratigraphy reflects recurring alternation of sedimentation and soil formation suggesting numerous pedogenically effective cyclical climatic changes during the late pliocene and early pleistocene the differentiated composition of calcretes near la regia is a polygenetic product surface erosion and sedimentary fossilization were followed by secondary carbonatization and subsequent induration at least 15 stages of soil formation are reconstructed red paleosols and pedogenic calcretes are well developed and reflect humid subtropical and mediterranean conditions during soil genesis with geomorphodynamic stability in contrast the accumulation of sediments and synsedimentary calcretes correlates with geomorphodynamic activity under considerably drier mediterranean conditions

fan surface dynamics and biogenic calcrete development interactions during ultimate phases of fan evolution in the semiarid se spain murcia abstract pleistocene alluvial fan surfaces of the campo de cartagena mar menor basin murcia se spain are capped by thick mature calcretes calcrete profiles consist mainly of six different horizons prismatic chalky nodular massive laminar and coated gravels petrographic study of the calcretes has shown the occurrence of features such as alveolar septal structures calcified filaments coated grains spherulites calcified root cells and calcispheres that indicate the biogenic origin of the calcretes mainly induced by plant root related microbial activity the calcretes studied were formed initially in the soil and represented the k horizon development of the calcrete profiles took place in six main stages and was driven by multiple phases of soil formation erosion and reworking the relationships between these processes caused the formation of different calcrete profiles in proximal and distal fan areas in the distal areas which are controlled by limited distal fan aggradation episodic sediment input buried previously developed calcretes and generated new space for calcrete growth by plants growing in the overlying unconsolidated materials this allowed the renewal of calcrete formation and it led to the development of complex composite profiles which are thicker than in proximal areas where surface stabilisation and or dissection enabled calcrete reworking and brecciation these processes of erosion sedimentation reworking and renewed calcrete formation initiated by vegetation were repeated through time they explain the complex macro and microstructures of these calcretes and indicate that calcrete development even reaching mature stages can start before the fan surface is completely abandoned but it requires episodic sedimentation eventually distal fan aggradation and continuous calcrete development throughout the entire fan surface led to the ultimate fan surface induration controlling subsequent landscape evolution so fan surface calcretes cannot be envisaged as simple top surface carbonate accumulations but as complex feedback systems in which pedogenic biogenic and sedimentary processes interact in response to the evolving fan surface dynamics during the terminal phases of fan development in semiarid environments

mapping of crustal magnetic anomalies on the lunar near side by the lunar prospector electron reflectometer lunar prospector lp electron reflectometer measurements show that surface fields are generally weak in the large mare basalt filled impact basins on the near side but are stronger over highland terranes especially those lying antipodal to young large impact basins between the imbrium and nectaris basins many anomalies correlate with the cayley and descartes formations statistical analyses show that the most strongly magnetic nearside terranes are cayley type light plains terra materials and pre imbrian craters light plains and terrae include basin impact ejecta as a major component suggesting that magnetization effects from basin forming impacts were involved in their formation the magnetization of pre imbrian craters however may be evidence of early thermal remanence relatively strong small scale magnetic anomalies are present over the reiner gamma feature on western oceanus procellarum and over the rima sirsalis rille on the southwestern border of procellarum both apollo subsatellite and lp data show that the latter anomaly is nearly aligned with the rille though lp magnetometer and reflectometer data show that the anomaly peak is actually centered over a light plains unit this anomaly and the reiner gamma anomaly are approximately radially aligned with the center of imbrium suggesting an association with ejecta from this basin

equivalence of abrupt grain size transitions in alluvial rivers and eolian sand seas a hypothesis gravel bed rivers organize to a threshold state in which the fluid stress during dominant flow conditions slightly exceeds the critical value these channels change fairly abruptly to sand dominated beds facilitated by a paucity of sediment in the range of 1 10 mm eolian sediments are also bimodal sand seas often transition rapidly downwind to silty loess deposits in this paper we hypothesize that both transitions result from the same processes 1 production of fine sediment by spallation from saltation abrasion of coarse grains and 2 segregation of fine and coarse modes by suspension and saltation transport respectively we demonstrate that gravel rivers and eolian dune fields are dynamically equivalent in terms of threshold transport shields stress and collision dynamics stokes number while abrasion may not be the dominant cause of downstream fining of fluvial gravels the reduction of collision efficiency with grain diameter sets a lower limit on gravel size leading to a grain size gap the collision efficiency hypothesis potentially reconciles conflicting studies on the importance of sorting and lithology in downstream fining shields and stokes similitude in rivers and deserts may be used to design appropriately scaled experiments to test and refine our hypothesis

particle size fractionation of eolian sand along the sinai negev erg of egypt and israel eolian sand fractions along the west east transport system of the northern sinai peninsula northwestern negev erg of egypt and israel were analyzed in this study with regard to source dune geomorphology eolian transport and paleoclimate the studied erg is composed of active linear seif dunes in northern sinai western part and stabilized vegetated linear dunes in the nw negev dune field eastern part linear seif dunes differ from vegetated linear dunes in their vegetation cover linearity internal structure and dynamics sand samples were analyzed for sand grain morphology and particle size distribution although both dune types are continuous landforms with similar orientations and sand grain roundness values the linear dunes of sinai are coarser grained than the negev vegetated linear dunes the vegetated linear dunes have a variable but higher proportion of very fine sand 50 125 m content and a varying but lower sand fining ratio defined as the ratio of fine sand percentage to very fine sand percentage from these observations we infer that fractionation of sand occurred along the studied eolian transport path during periods of enhanced windiness very fine sands are suggested to have been transported by saltation and low suspension from source deposits and sand sheets we suggest that a significant proportion of the very fine sand fraction of nile delta sands has been transported downwind through northern sinai during the late pleistocene especially when linear dunes reached the nw negev due to last glacial period windiness and probably larger sediment supply generally decreasing wind velocities and increasing precipitation along the west east dune transport path enhanced vegetative cover in the northern negev and enabled deposition of the very fine sand component within the dunes and probably further downwind our results suggest that particle size distribution can elucidate much about erg history over time scales of a glacial interglacial cycle especially in cases where the sand provenance is of a single dominant source

landscape response to strike slip faulting linked to collisional settings quaternary tectonics and basin formation in the eastern betics southeastern spain abstract neotectonic behaviour of the eastern betics southeastern spain has been controlled by the presence of a large left lateral shear zone this is an intraplate transcurrent zone probably decoupled by a mid crustal detachment horizon the morphological expression of this crustal structure is a sigmoidal corridor in which the main quaternary basins are located three types of morphostructural domains can be distinguished in the sigmoidal corridor the central segment and the northern and southern terminal splays the central segment is characterized by wrench tectonics whilst the southern and northern terminal splays are controlled by transtensional and transpressional tectonics respectively the quaternary morphostructural pattern is only the more recent picture of the tectonic processes that have controlled the late orogenic evolution of the eastern betics the indentation of the aguilas arc accompanied by thin skinned thrusting and tectonic escape in its easternmost sector and extensional collapse accompanied by thin skinned stretching in its westernmost sector

plio pleistocene drainage development in an inverted sedimentary basin vera basin betic cordillera se spain abstract the vera basin is one of a series of interconnected neogene quaternary sedimentary basins located within the internal zone of the betic cordillera southeast spain since the pliocene the vera basin has been subjected to low uplift rates 11 21 m ma 1 and inverted via compressive tectonics that are related to the ongoing oblique collision between the african and iberian plates within this paper the sedimentary and geomorphic response to basin inversion is explored sedimentary processes and environments are established for key stratigraphic units of the pliocene plio pleistocene basin fill and pleistocene dissectional landscape these data are subsequently utilised to reconstruct an evolving basin palaeogeography fault and uplift data are employed to discuss the role of tectonically driven basin inversion for controlling the resultant palaeogeographic changes and associated patterns of drainage development during the early mid pliocene the vera basin was characterised by shallow marine shelf conditions cuevas formation a major palaeogeographic reorganisation occurred during the mid late pliocene strike slip movement along the eastern basin margin coupled with uplift and basin emergence created a protected partially enclosed marine embayment that was conducive for gilbert type fan delta sedimentation from fluvial inputs along the northern and eastern basin margins espiritu santo formation the vera basin then became fully continental and internally drained through the development of a consequent drainage network that formed following the withdrawal of marine conditions during the late pliocene to early pleistocene alluvial fans developed along the northern and western basin margins grading to a bajada and terminating in a playa lake in central basin areas salmeron formation during the early mid pleistocene a switch from basin infilling to dissection took place recorded by alluvial fan incision a switch to braided river sedimentation and fluvial incision into the underlying basin fill sediments and basin margin mountainous topography fluvial incision headwards erosion expansion and modification of the consequent drainage network is documented within a series of up to four major inset river terrace levels and associated landforms fluvial incision and drainage network expansion are attributed to differential uplift and the creation of regional gradients between adjacent basins the relatively low plio pleistocene uplift rate of the vera basin 11 21 m ma 1 in comparison to adjacent basins sorbas 80 160 m ma 1 huercal overa 50 m ma 1 resulted in a switch from internal to external basin drainage ancestral forms of the principal drainage systems within the vera basin the rios almanzora aguas and antas captured basins and mountain catchment areas to the north huercal overa basin southwest sorbas basin and west sierra de los filabres range the switch from basin infilling to fluvial dissection is coincident with a phase of early mid pleistocene compressional tectonics expressed by extensional faulting this deformation is probably linked to accelerated strike slip movement along the palomares fault zone the faulting is superimposed onto the longer term pattern of plio pleistocene uplift and basin inversion

mechanisms limiting the growth of aeolian megaripples megaripples are distinguished from regular ripples by their larger size and bimodal sediment distribution the interplay between wind grain size and morphology controls their development but the exact mechanisms that limit the size of megaripples have been unclear using wind tunnel experiments we found two main mechanisms that limit the height of megaripples the first mechanism is megaripple flattening due to strong enough winds that drive the coarse grains into saltation the second mechanism is megaripple deflation by impacts of faster saltation grains in this latter mechanism the coarse grains are propelled by the impacts of fine saltating grains the occurrence of both these mechanisms depends on the grain size distribution and increases with both megaripple height and wind speed thus for a given wind environment and grain size distribution there exists a limit on the size of megaripples which is determined by these two mechanisms

quaternary tectonic activity of the carboneras fault in the la serrata range se iberia geomorphological and chronological constraints the eastern betic shear zone ebsz in southern iberia is known to accommodate part of the 4 5 mm yr convergence between africa and iberia but its seismic hazard is not sufficiently understood for an accurate risk assessment one of the main structures of the ebsz the left lateral 150 km long carboneras fault displays no clear instrumental and historical activity despite being morphologically expressive detailed geomorphological mapping geochronological analysis and structural observation on the la serrata segment of the carboneras fault were designed to investigate its recent evolution quaternary sediments and geomorphic features were targeted and 42 new numerical ages were obtained based on 66 samples thermoluminescence u series 14c 10be the chronological framework of la serrata was constructed by combining these numerical ages with a conceptual model previously developed in the region which assumes that alluvial fan aggradation was produced during cold and dry periods glacials and stadials whereas stability and phases of calcrete formation were favored during warm and wetter periods interglacials and interstadials the spatial distribution of dated alluvial fans suggests an early phase of uplift that probably occurred between 1 ma and 56 6 ka in the northeastern portion of the study area whereas in the southwest sector the main uplift phase occurred later than 110 3 ka a decline in fault activity would have taken place after 30 8 ka vertically offset dated units indicate minimum dip slip rates of 0 05 mm yr and 0 18 mm yr averaged for the last 1 ma and the last 110 3 ka respectively deflected channels and associated dated units yield a minimum left lateral strike slip rate of 1 31 mm yr averaged for the last 110 3 ka the most recent fault movement of the fault could be younger than ad 637 our results suggest therefore that the carboneras fault is among the fastest in iberia and should be considered in future hazard analyses

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

modelling earthquake rupture rates in fault systems for seismic hazard assessment the eastern betics shear zone abstract earthquake surface fault ruptures can show very complex geometries and involve different faults simultaneously consequently modern fault based probabilistic seismic hazard assessments psha need to account for such complexities in order to achieve more realistic modellings that treat fault systems as a whole and consider the occurrence of earthquake ruptures as aleatory uncertainties we use sherifs a recent approach of modelling annual rates of complex multi fault ruptures to obtain system level magnitude frequency distributions mfds for the eastern betics shear zone ebsz spain considering four fault rupture hypotheses we then analyze the consistency of each scenario based on data from the earthquake catalogue and paleoseismic studies the definition of the different rupture hypotheses was discussed within the frame of fault2sha esc working group and critical fault input data is extracted from previous published studies the four rupture hypotheses are defined as incremental scenarios based on fault geometry and kinematics with lengths varying from minimal fault sections to a rupture of nearly the whole system the results suggest that multi fault ruptures involving lengths up to single to several whole faults are consistent with the annual rates from both the instrumental catalogue and paleoseismic record the method does not allow to completely discard any hypothesis but it allows to weight the different models in a logic tree for seismic hazard assessment the approach is revealed as a practical tool for obtaining fault system mfds and as a useful tool for highlighting limitations and uncertainties in geological and paleoseismic data to be assessed this study aims to constitute a step forward in the consideration of complex multi fault ruptures for future seismic hazard assessments in the region

origin of desert loess from some experimental observations a longstanding problem of quaternary geology has been the origin of the silty deposit known as loess of the many explanations for its formation and distribution1 2 the most commonly accepted is that the silt is produced by subglacial grinding processes1 3 4 followed by redistribution and deposition by the wind the large expanses of loess in central europe are therefore considered to be the consequence of quaternary glaciation5 there is however a view6 7 that loessic silt may also originate as the product of processes in hot deserts some proponents of the desert loess hypothesis consider that silt size material is the product of weathering processes7 which may include salt weathering8 or weathering down incipient cracks9 an alternative mechanism is aeolian attrition of sand grains although probably as a result of the experimental work of kuenen10 smalley and krinsley11 consider that only fine silt 2 6 m is produced in large quantities by the abrasion of quartz grains we have simulated aeolian attrition of angular quartz grains previously produced by weathering in deserts the products of abrasion show that both coarse and fine silt sizes are produced these findings suggest that desert aeolian processes can produce loess we also suggest that much of this material from many deserts has been deposited in the sea but that the chinese loess could have been produced in the gobi desert the finest particles produced by such attrition may be a source of silica for silcrete formation

analysis of faulted fan surfaces and paleosols in the palomares fault zone betic cordillera se spain paleoclimatic and paleoseismic implications abstract this study presents a multidisciplinary approach to the tectonic geomorphology and history of the palomares strike slip fault in the eastern betic cordillera se spain analysis combines geomorphological mapping of fan surfaces pedological studies of faulted sedimentary successions geoelectrical prospection and typical paleoseismological routines of structural analyses combined application of these methods together with the existing geochronological databases offer probable paleoclimatic and paleoseismic scenarios for the zone from middle pleistocene to holocene this study segments the palomares fault plf in three overlapping en echelon n s trends plf1 plf2 plf3 the older plf1 controls the main faulted almenara almagro range fronts the younger plf2 cuts and beheads crusted fan surfaces in the aljibejo zone abj the intermediate plf3 controls the development of intervening tectonic reliefs and offset paleosol sequences in alluvial colluvial deposits our analysis focuses on the plf3 at the la escarihuela site esch where outcrops display eight faulted paleosols developed on overlapped middle pleistocene colluvial alluvial deposits with variable vertical slip of between 21 and 12 cm bulk accumulated offset 33 cm evidence of two surface faulting events after the structural analysis of the fault planes striae plunges net left lateral displacements of 120 9 3 3 cm event 1 to 69 1 5 2 cm event 2 associated with maximum magnitudes of c 6 7 6 5 mw however the faulted sequence is sealed by a thick mature calcrete horizon of similar characteristics to that faulted at the abj1 site regional chronological data on calcic soils and calcretes in se spain assign this mature calcrete to oxygen isotopic stages ois 9 c 300 ka with this age fixed at the uppermost of the faulted paleosol sequence at the esch site plf3 soil development features clay and carbonate contents thickness reddishness etc were used as paleoclimatic proxies to correlate soil horizons with conventional ois correlation indicates that clayey bt soil horizons primarily occurred during warm isotopic stages followed by recalcification and carbonate accumulation btk bk ck horizons during latter warmer stages a proposed theoretical geochronological framework suggests that the sedimentary sequence at the esch site plf3 was deposited between ois 18 and 9 major environmental change towards the present semi arid climate occurred during ois 13 c 500 ka during this same stage paleoseismic event 1 also occurred but paleoseismic event 2 took probably place during ois 10 c 350 ka before development of the uppermost calcrete sealing the deformation in this fault segment however this ois 9 calcrete is faulted in the abj1 and a younger less developed calcrete is faulted in abj2 on the plf2 segment chronology proposed in this paper suggests theoretical ages for these events of between ois 8 ois 5 for abj1 c 200 ka and between ois 4 ois 2 for abj2 c 40 ka this last paleoseismic event triggered major landscape changes with still visible fault scarps linear tectonic reliefs alluvial fan beheading and active drainage shuttering this present work illustrates the use of soil paleosol analyses in paleoseismology as a useful tool to build paleoclimatic analogues and develop relative chronological frameworks from existing regional age data

influence of strike slip fault segmentation on drainage evolution and topography a case study the palomares fault zone southeastern betics spain abstract the palomares fault zone pfz is one of the main sinistral strike slip faults in the betics se spain with approximately 16 km of north south displacement the pfz initiated during the tortonian messinian as a transfer structure linking areas subject to nw se shortening during the plio quaternary the fault zone lengthened cutting previous fold structures and widened towards the east displacing the active mountain front to the western border of sierra almagrera sierra almenara these sierras which show moderate uplift rates of 0 05 0 15 m ka formed in response to the oblique slip regime of the pfz the drainage system in the vicinity of the pfz is asymmetric with respect to a main axial valley that runs parallel to the pfz on the downthrown fault block in this block the drainage density is lower and the streams are longer than in the uplifted block furthermore west of the main axial valley the streams describe eastward directed deflections indicating the progressive eastward migration of the main axial valley during the pleistocene the drainage system on the uplifted ranges shows a consequent pattern indicating recent uplift and folding under nnw sse convergence recent activity along segments of the pfz has increased topographical gradients favouring dissection of previous streams by headward erosion of streams transverse to the active fault segments

mechanisms of loess sized quartz silt production and their relative effectiveness laboratory simulations the production of loess sized quartz silt is frequently ascribed to glacial grinding mechanisms in this study a series of laboratory simulations was set up the purpose of which was to demonstrate that a range of geomorphic mechanisms are capable of producing silt under laboratory conditions the geomorphic mechanisms investigated were aeolian abrasion fluvial comminution glacial grinding salt weathering and frost weathering the results confirmed that under laboratory conditions all of these mechanisms were capable of producing silt the relative effectiveness of these mechanisms at producing silt under laboratory conditions was then calculated in order to provide a starting point for a consideration of their potential effectiveness within the natural environment these results indicate that fluvial and aeolian activity are highly effective at producing quartz silt over short time periods in a dust storm of four days duration 287 g of silt could potentially be produced from every kilogram of sand entrained while fluvial comminution in a turbulent fluvial environment could potentially produce 900 g of silt from every kilogram of sand entrained within 32 h over longer periods of time the glacial grinding and weathering mechanisms represent more continuous and hence more effective silt producing mechanisms although it is realised that the relative importance of each silt producing mechanism will differ spatially and temporally due to differences in climate relief geology and geomorphic history the findings from this work do have implications for the genesis of loess deposits they demonstrate that glacial and cold weathering processes are not solely responsible for fine particle formation and that efficient silt producing mechanisms can operate within a variety of environments under suitable conditions weathering together with episodic contributions from aeolian and fluvial mechanisms could be responsible for a considerable proportion of global quartz silt production

soil evolution indices in fluvial terrace chronosequences from central spain tagus and duero fluvial basins abstract soil development in central spain was studied through analysis of soil chronosequences from tagus and duero river valley terrace systems evolved under similar mediterranean climatic conditions throughout the pleistocene the most complete soil terrace sequence representative for our study developed in the tagus valley aranjuez toledo talavera sector we present soil textural data for argillic horizons developed in late to early pleistocene soils from five valleys we derive soil development indices from clay and silt content and thickness of argillic horizons global clay content gcc clay content cc and clay silt ratio c si ratio numerical indices related to clay illuviation reflect soil evolution explored by multiple regression of soil terrace height and soil age relative terrace heights above present river thalwegs i e 100 m were transformed to ages with a height age transfer function on the basis of preliminary statistical geochronological analyses for central spain the height age transfer function a 3rd order polynomial r 2 0 90 based on 60 published numerical ages and paleomagnetic data for terrace sequences describes the overall trend of valley downcutting for the last c 2 ma in central spain it assigns numerical ages to terrace levels at different relative elevations and gives an estimate of standardized ages for the related soils the explored age soil relationships logarithmic functions r 2 0 80 are sensitive to parent material clay content corresponding to geology of river catchments for most soil indices only the clay silt ratio minimizes this sensitivity and can thus be used for regional approaches tagus and duero basins central spain whereas the cc index is applicable only to individual river valleys or different river valleys with similar catchment geology i e tagus basin the c si ratio illustrates the logarithmic trend of weathering of soil particles into clay over time the generation of soil textural balances sustaining illuviation processes and therefore provides an estimate of soil ageing for the implementation of soil chronofunctions for regional analysis of river valleys evolving in similar climatic conditions and with similar base level history

pleistocene deposits at stoke goldington in the valley of the great ouse uk at stoke goldington in the valley of the great ouse in buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late middle pleistocene near the base of the succession at a level only 1 m above the modern floodplain a fossil assemblage including pollen plant macrofossils molluscs insects and ostracods provides evidence for the local development of herb rich grassland under temperate climatic conditions the fossil record amino acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during oxygen isotope stage 7 the deposits containing the temperate assemblage are immediately overlain by typical cold climate gravels of the great ouse these have been subjected to a later cut and fill episode with the fill accumulating in cool climatic conditions the cut and fill episode was succeeded by aggradation forming the overlying terrace surface amino acid racemisation ratios indicate that the fill was emplaced and the terrace surface created during or after oxygen isotope stage 5 1996 john wiley sons ltd

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

the influence of tectonics sea level fluctuations and river capture on the quaternary morphogenesis of the semi arid pulpi basin southeast spain abstract the semi arid pulpi basin is located within a 250 km long left lateral shear zone between alicante and almeria the pulpi basin itself is crossed by the n20e striking palomares fault active during the neogene and quaternary in the upper pliocene a major epeirogenic uplift occurred which caused emergence of the basins simultaneously a change from marine to terrestrial sedimentation started and the development of the present landscape began the quaternary relief development in the pulpi basin has been particularly influenced by tectonic disturbances and river captures which have had contrasting effects on different parts of the basin in the southern basin tectonically induced dissection of the oldest quaternary glacis level was accompanied by the influence of the fluctuations in sea level both factors have caused continuing erosion in the central pulpi basin mid quaternary fluvial capture processes were important for the morphogenesis since the loss of the catchment areas in the neighbouring huercal overa basin the fluvial activity of the rivers in the western part has been limited the transition from the distal end of the mid quatemary glacis to the present valley floor takes place without a noticeable step no younger fluvial terraces are missing in the eastern part the catchment area of the main river has hardly changed since its establishment during the upper pliocene besides the relics of the oldest glacis level no further glacis accumulation developed during the mid quaternary only a fluvial terrace was deposited

palaeoclimate and palaeoenvironmental responses in the western mediterranean over the last 140 ka evidence from mallorca spain climatic change in the western mediterranean basin over the last 140 ka has been investigated from sediment and soil sequences along the coast of the northeastern part of mallorca spain palaeoclimate and palaeoenvironments are reconstructed from sediment and soil structures marine and terrestrial molluscan fauna grain size distributions mineral magnetics sediment and soil chemistry sem and oxygen isotope values dating is by osl and amino acid geochronometry along with marine molluscan faunal assemblages all oxygen isotope stages and substages from ois 6 to 1 are recorded mean annual temperatures m a t of c 19 2 c for the climatic optimum of the last interglacial compare with c 17 3 c for the present and are associated with high sea level extensive woodland and stable soils although wide temperature ranges are detected during this stage with values as low as c 10 3 c through ois 5d to 5a m a t fluctuated from 8 2 c to 17 9 c low sea level open vegetation effective river activity and aeolian sand and dust deposition characterize 5d and 5b while relatively high sea level and soil development on stable landscapes dominate ois 5c and 5a ois 4 is represented by m a t of c 4 9 c with aeolian sand and loess deposition limited river activity and weak soil development loess deposition persisted into ois 3 but at this time the m a t was c 13 c and with higher humidity and vegetation growth during the lgm ois 2 m a t was c 8 1 c and effective river slope and aeolian processes along with associated with limited vegetation cover were responsible for the most extensive changes in the landscape major rates of change occur during periods of climatic deterioration when the high levels of geomorphic energy were imposed on a landscape undergoing a breakdown of vegetation cover

a scaling law for aeolian dunes on mars venus earth and for subaqueous ripples abstract the linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength at which the bed destabilises to form dunes should scale with the drag length l drag s f d this scaling law is tested using existing and new measurements performed in water subaqueous ripples in air aeolian dunes and fresh snow dunes in a high pressure co2 wind tunnel reproducing conditions close to venus atmosphere and in the low pressure co2 martian atmosphere martian dunes the difficulty is to determine the diameter of saltating grains on mars a first estimate comes from photographs of aeolian ripples taken by the rovers opportunity and spirit showing grains whose diameters are smaller than on earth dunes in addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds it confirms that the small grains visualised by the rovers should be grains experiencing saltation finally we show that within error bars the scaling of with ldrag holds over almost five decades we conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on mars

constraints on the depth of magnetized crust on mars from impact craters large diameter greater than 500 km martian impact basins are associated with observed magnetic fields which are statistically distinct from and smaller than fields associated with smaller craters we suggest that this effect arises because impacts cause shock heating and excavation reducing the magnetization of previously magnetized crust for a simple uniformly magnetized model the magnetic field at 100 km altitude is reduced by 50 when a crater shaped demagnetization zone reaches the base of the magnetized layer by analogy with terrestrial data we assume that in martian craters the zone of demagnetization extends to a depth of 0 04 0 15 crater diameters on the basis of this assumption the data suggest that the depth to the base of the magnetized layer on mars if uniform is 35 km with lower and upper bounds of 10 and 100 km respectively these bounds imply magnetizations of 5 40 a m 1 and are consistent with likely mars geotherms at 4 gyr b p

an integrated model for dune morphology and sand fluxes on mars the transport and deposition of sand is the most prevalent agent of landscape modification on mars today with fluxes comparable to some sand dunes on earth until now the relationship between sand flux and dune field morphology has been poorly constrained by tracking dune movement over 10 km long dune fields in herschel crater and nili patera representative of many dune fields on mars we find a downwind flux decrease that correlates with a sequence of changing morphology from barchans to barchanoids and seifs longitudinal dunes to isolated dome dunes and ending with sand sheets we show empirical consistency with atmospheric internal boundary layer ibl theory which can describe these broad flux and morphology changes in martian dune fields deviations from ibl flux predictions are from wind streamline compressions up slopes leading to a speedup effect by establishing a dune field morphology type example and correlating it with measured and predicted flux changes we provide an integrated morphology and flux model that can be applied to other areas of mars and be used to infer paleo environmental conditions from preserved sandstone

methane storms as a driver of titan s dune orientation titan s equatorial dunes propagate eastwards whereas titan s surface winds blow towards the west atmospheric simulations suggest that tropical methane storms generate strong eastward gusts that may dominate sand transport on titan s surface