controls on erosional retreat of the uplifted rift flanks at the gulf of suez and northern red sea the gulf of suez and red sea rifts are currently bordered by large asymmetric uplifts that are undergoing erosion we find that the amount and timing of erosion vary systematically along the strike of the margin and have been controlled by variations in the prerift stratigraphy the prerift strata are composed of cliff forming eocene cretaceous carbonates overlying the easily eroded cretacous cambrian nubian sandstone this lithologic succession promotes scarp retreat of the sedimentary section followed by dissection of the underlying basement the prerift section thins from over 2000 rn at the northern end of the rift to less than 400 rn at its junction with the red sea thus at the northern part of the gulf of suez the nubian sandstone is minimallyexposed and the carbonates form a scarp at the rift border fault farther south undercutting of the carbonates by erosion of the sandstone has resulted in scarp retreat the escarpment cuts diagonally away from the border fault and is over 100 km inland from the border fault at the southernmost gulf of suez the amount of retreat varies inversely with the sediment thickness exposure and erosion of basement are initiated by the retreat of the escarp ment and the depth of erosion as indicated by fission track ages increases with distance from the escarpment these observations are explained by a model in which erosion along the gulf of suez is initiated as rift flank uplift becomes sufficiently large to expose the friable sandstones undercutting of the escarpment and exhumation of basement has been propagating northward and westward for at least 20 m y the average rate of scarp retreat has been 6 km m y and the along strike propagation of the erosion has been 12 km m y the diachronous erosion of the the rift flanks at the gulf of suez highlights the importance of distinguishing between the timing of uplift and of erosion both thermochronometric and stratigraphic data primarily indicate the timing of erosion which may differ significantly from the timing of the uplift that initiates it they must be interpreted carefully to avoid erroneous conclusions about rift tectonics

influence of vegetation on aeolian sand transport rate from a backshore to a foredune at hasaki japan the influence of vegetation on aeolian sediment transport rate in the region from a backshore to a foredune was investigated at the hasaki coast in japan where an onshore wind was predominant and the creeping beach grasses carex kobomugi and calystegia soldanella were major species the comparison of cross shore distributions of the cross shore component of aeolian sand transport rate with and without vegetation which were estimated on the basis of the beach profile changes and a mass conservation equation showed that the creeping grasses influenced the aeolian sand transport rate the landward aeolian sand transport rate rapidly decreased landward from the seaward limit of vegetation when the grasses grew the aeolian sand transport rate reduced by 95 with a vegetation cover of 28 on the other hand when the grasses were absent the landward aeolian sand transport rate did not decrease near the seaward vegetation limit but near the foot of the foredune

a field quantification of coastal dune perennial plants as indicators of surface stability erosion or deposition dune plants both modify the wind field around them and are impacted by various stress factors among them sand erosion and sand deposition as coastal dunes are being either stabilized or remobilized in response to the changes in the rates of sand and dune movement the vegetation cover and composition are expected to vary reflecting the differences in the sedimentary conditions in this field study 315 quadrats of 100 m2 in which the perennial plant species were sampled were analysed with respect to annual rates of sand erosion and deposition that were measured using erosion pins a visual exploratory data analysis was introduced based on selective filtering of samples according to their vegetation cover this method combined with established statistical tools enabled the authors to uncover the inclination and indicative power of nine perennial dune plants to either a stabilized or a mobile environment and to establish whether they are more prevalent in places undergoing sand erosion or sand burial two species were found to be clear indicators of a stabilized environment stipagrostis lanata and retama raetam of the species indicating a mobile environment only one may be stated as a clear indicator of sand erosion silene succulenta with cyperus macrorrhizus coming close to being an indicator of a less mobile erosive environment the best indicator species for sand burial was found to be as expected ammophila arenaria with artemisia monosperma also indicating high rates of sand mobility especially when its relative cover is higher than 80 such information can be used to monitor natural processes of dune stabilization or reactivation or to assess the success of a management plan that aims at stabilizing a dune or at remobilizing it by removing vegetation

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

biogeomorphic model of dunefield activation and stabilization on the northern great plains abstract a conceptual model is proposed for the activity of sand dune systems on the northern great plains that incorporates vegetation growth theory and geomorphic system theory dunefield activity is modeled as a cyclic phenomenon alternating between active and stable states with the latter as the system state attractor the model is divided into two constituent parts an activation model and a stabilization model the activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover the intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover the stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth small perturbations during stabilization can prolong the duration of recovery enabling dunes to remain active well after the initial perturbation despite the geographic focus of this study the model appears applicable to a variety of environments where dune activity is limited in part by vegetation cover

variation in grain size and morphology of an inland parabolic dune during the incipient phase of stabilization in the hobq desert china abstract a significant increase in rainfall in the summer of 2012 on the southern fringe of the hobq desert inner mongolia resulted in the vegetation and thus stability of dunes in this area our research focuses on a typical parabolic dune which was active in 2011 and became stabilized after vegetation colonization topographic surveys and surface sediment analysis of the morphology and surface sands of the parabolic dune indicate that decreasing mean grain size and sorting values better sorting slightly more positive skewness and increasing kurtosis occurred over the dune surface during the incipient phase of stabilization there was a strong relationship between grain size sorting and dune mobility surface sand from the stabilized dune was generally finer and better sorted than at the same location when the dune was active during 2011 2012 the dune head had moved eastwards by approximately 2 3 m while its two arms expanded outward by approximately 3 2 m the height of the dune decreased and the dune became larger with a decreasing volume once anchored 2013 2014 the overall morphology and the grain size and sorting characteristics of the dune became more constant and quite different than when the dune was active

cooling history and tectonic exhumation stages of the south central tibetan plateau china constrained by 40ar 39ar and apatite fission track thermochronology between the qiangtang block and yalung zangpo suture zone in the south central tibetan plateau the following geological units and suture zones have been identified from south to north the gangdese granitic belt the lhasa block the nyainqentanghla shear zone the dangxiong sangxiong tectono granitic belt and the bangong nujiang suture zone to better constrain the tectonic evolution and cooling histories of these units 40 ar 39 ar muscovite biotite and k feldspar as well as apatite fission track dating and thermochronological analysis have been carried out the analytical results indicate that the south central tibetan plateau with the exception of the nyainqentanghla shear zone provides a record of three cooling stages at 165 150 130 110 and 45 35 ma fission track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks very different cooling phases occurred in the south central tibetan plateau compared with southern tibet as well as along the yalung zangpo suture zone there is no thermochronological evidence to indicate that the south central part of tibetan plateau was influenced by the underthrusting of indian plate the three stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the bangong nujiang suture zone along its eastern segment during middle late jurassic 165 150 ma and its western segment in the early late cretaceous 130 110 ma as well as by the collision between the indian and asian plates in the paleogene 45 35 ma 2005 elsevier ltd all rights reserved

mesozoic and cenozoic tectonics of the northern edge of the tibetan plateau fission track constraints abstract fission track analysis on zircons and apatites yields new information about the timing of deformation of the northern tibetan plateau ages on zircons ranging from 221 22 to 96 4 ma are indicative of a general late triassic early jurassic cooling probably driven by the collision between the qiantang and kunlun blocks mid jurassic slow cooling is recorded also in the apatites in regions not affected by later cenozoic deformation this jurassic denudation was followed by a period of sedimentation during the cretaceous except along the altyn tagh fault atf zone and in some restricted areas of the western and eastern qilian shan this long and relatively quiet period ended at about 40 10 ma along the major altyn tagh and kunlun strike slip fault zones which were activated by the india asia collision this first movement along lithospheric faults resulted in the eastward extrusion of the tibet plateau which was followed in late oligocene miocene times by a major compression event initiating the formation of the high relief of north tibet a final compressional event took place at 9 5 ma and is well correlated with high sedimentation rates in the basins of this region this compression induced continental subduction in the kunlun ranges the altun shan belt and possibly the qilian shan belt

late cretaceous exhumation and uplift of the harz mountains germany a multi method thermochronological approach the harz mountains represent one of the most prominent surface expressions of late cretaceous intraplate shortening in central europe we present a comprehensive low temperature thermochronological data set zircon and apatite fission track and u th he covering the exhumed paleozoic basement of the harz mountains and the adjacent kyffhauser block as well as lower triassic sedimentary rocks of the western and southern rim of the harz mountains integration of results with sedimentological data from the syntectonic late cretaceous subhercynian basin allows for a detailed reconstruction of the timing of uplift and erosion of the harz mountains the data reveal that i tectonic reorganization and initial exhumation started at around 90 ma ii uplift and emergence caused erosion of the mesozoic sedimentary cover between 86 85 ma and 83 82 ma and iii erosion of at least 3 4 km of underlying paleozoic rocks followed and continued into the paleogene the thickness of removed overburden amounts to at least 6 km and most erosion occurred in santonian to campanian time at minimum rates of 0 5 km myr the southwestern rim of the harz has exhumed slower over a longer period of time and may record a phase of late cretaceous syntectonic sediment accumulation

radiation enhanced fission track annealing revisited and consequences for apatite thermochronometry apatite fission track aft analyses for granitoid and metamorphic bedrock samples from the western superior province ontario the churchill rae province melville peninsula and southampton islan

dehydration induced damage and deformation in gypsum and implications for subduction zone processes 1 experimental heating tests were performed on volterra gypsum to study the micromechanical consequences of the dehydration reaction the experimental conditions were drained at 5 mpa fluid pressure and confining pressures ranging from 15 to 55 mpa one test was performed with a constantly applied differential stress of 30 mpa the reaction is marked by 1 a porosity increase and homogeneous compaction 2 a swarm of acoustic emissions 3 a large decrease in p and s wave velocities and 4 a decrease in vp vs ratio wave velocity data are interpreted in terms of crack density and pore aspect ratio which modeling pores as spheroids is estimated at around 0 05 crack like spheroid complementary tests performed in an environmental scanning electron microscope indicate that cracks first form inside the gypsum grains and are oriented preferentially along the crystal structure of gypsum most of the visible porosity appears at later stages when grains shrink and grain boundaries open extrapolation of our data to serpentinites in subduction zones suggest that the signature of dehydrating rocks in seismic tomography could be a low apparent poisson s ratio although this interpretation may be masked by anisotropy development due to preexisting crystal preferred orientation and or deformation induced cracking the large compaction and the absence of strain localization in the deformation test suggests that dehydrating rocks maybe seen as soft inclusions and could thus induce ruptures in the surrounding nonreacting rocks

a process based hypothesis for the barchan parabolic transformation and implications for dune activity modelling the introduction of vegetation to bare barchan dunes can result in a morphological transformation to vegetated parabolic dunes models can mimic this planform inversion but little is known about the specific processes and mechanisms responsible here we outline a minimalist quantitative and process based hypothesis to explain the barchan parabolic transformation the process is described in terms of variations in the stabilization of wind parallel cross sectional dune slices we hypothesize that stabilization of individual dune slices is the predictable result of feedbacks initiated from colonization of vegetation on the slipface which can only occur when slipface deposition rates are less than the deposition tolerance of vegetation under a constant vegetation growth regime the transformation of a barchan dune into a parabolic dune is a geometric response to spanwise gradients in deposition rates initial vegetation colonization of barchan horns causes shear between the anchored sides and the advancing centre of the dune which rotates the planform brinkline angle from concave to convex downwind this reduces slipface deposition rate and allows vegetation to expand inward from the arms to the dune centre the planform inversion of bare barchans dunes into vegetated parabolic dunes ultimately leads to complete stabilization our hypothesis raises several important questions for future study i are parabolic dunes transitional landforms between active and vegetation stabilized dune states ii should stabilization modelling of parabolic dune fields be treated differently than linear dunes and iii are stabilized parabolic dune fields armoured against re activation copyright 2012 john wiley sons ltd

permeability control on transient slip weakening during gypsum dehydration implications for earthquakes in subduction zones a conflict has emerged from recent laboratory experiments regarding the question of whether or not dehydration reactions can promote unstable slip in subduction zones leading to earthquakes although reactions produce mechanical weakening due to pore fluid pressure increase this weakening has been associated with both stable and unstable slip here new results monitoring strength permeability pore fluid pressure reaction progress and microstructural evolution during dehydration reactions are presented to identify the conditions necessary for mechanical instability triaxial experiments are conducted using gypsum and a direct shear sample assembly with constant normal stress that allows the measurement of permeability during sliding tests are conducted with temperature ramp from 70 to 150 c and with different effective confining pressures 50 100 and 150 mpa and velocities 0 1 and 0 4 m s 1 results show that gypsum dehydration to bassanite induces transient stable slip weakening that is controlled by pore fluid pressure and permeability evolution at the onset of dehydration the low permeability promoted by pore compaction induces pore fluid pressure build up and stable slip weakening the increase of bassanite content during the reaction shows clear evidence of dehydration related with the development of r1 riedel shears and p foliation planes where bassanite is preferentially localized along these structures the continued production of bassanite which is stronger than gypsum provides a supporting framework for newly formed pores thus resulting in permeability increase pore fluid pressure drop and fault strength increase after dehydration reaction deformation is characterized by unstable slip on the fully dehydrated reaction product controlled by the transition from velocity strengthening to velocity weakening behaviour of bassanite at temperature above 140 c and the localization of deformation along narrow y shear planes this study highlights the generic conditions required to trigger instabilities during dehydration reactions it shows that pore fluid pressure build up during dehydration reactions associated with the localization of a velocity weakening reacting or dehydrated phase along shear planes is necessary for earthquake triggering

role of pore fluid pressure on transient strength changes and fabric development during serpentine dehydration at mantle conditions implications for subduction zone seismicity abstract to further investigate the dehydration embrittlement hypothesis and its possible link to subduction zone seismicity we conducted deformation experiments on antigorite serpentinite in a griggs type apparatus at conditions below and above antigorite stability temperature ramps crossing the antigorite thermal stability were used in conjunction with a new experimental method that allows fluid produced during dehydration reactions to be drained partially drained or undrained during temperature ramps weakening coupled with transient slip initiated at 650 c coincident with the predicted phase transition of antigorite to olivine and talc at 1 gpa the weakening rate and steady state strength were dependent on drainage conditions undrained samples weakened over a few minutes and supported the lowest shear stress 50 mpa while drained samples weakened over a few hours and supported the highest shear stress 210 mpa the coefficient of friction shear stress over normal stress in drained samples decreased from 0 4 to 0 16 after the temperature ramp the strengths of samples that were first annealed at 700 c for 12 h then deformed were similar to those observed in the temperature ramp experiments strain localization along fractures occurred in all samples during temperature ramping regardless of the drainage conditions however microstructural observations indicate deformation by ductile mechanisms at higher strain under both undrained and drained conditions the rheology and microstructures suggest dehydrating serpentinite deforms via semibrittle flow with grain scale ductile deformation more active at high pore fluid pressures our results suggest that earthquakes in serpentinized mantle do not nucleate as a direct result of unstable frictional sliding along fractures generated at the onset of dehydration reactions

dehydration induced weakening and fault slip in gypsum implications for the faulting process at intermediate depth in subduction zones 1 high pressure fluids generated by metamorphic dehydration reactions can have profound effects on both rock strength and the stability of faults a decrease in effective pressure so produced could induce earthquakes at intermediate depth in the subducting slab either by embrittlement of an intact rock mass or by the reactivation of preexisting faults the purpose of this study was to experimentally investigate both processes using gypsum as an analog material constant strain rate relaxation and friction tests were performed on both intact cylindrical samples and saw cut aggregates both room temperature and dehydration conditions were investigated for comparison the maximum confining pressure and temperature were 50 mpa and 150 c respectively and the strain rate was varied between 1 5 10 6 and 1 5 10 5 s 1 this investigation shows that dehydrating gypsum is an excellent analog material for studies on reaction induced weakening however the lack of important brittle features like shear fractures and stress drops implies that intact gypsum aggregates do not show dehydration embrittlement in contrast this study demonstrates that depending on both the level of fault normal stress and the strain history dehydration induced unstable slip on preexisting faults is possible although some of the observations might be particular to gypsum the results also indicate that strong mechanical locking of the fault may continue to promote ductile flow unless new more favorably oriented faults are formed

effects of reaction kinetics and fluid drainage on the development of pore pressure excess in a dehydrating system abstract fluid is released by dehydration reactions during prograde metamorphism if the claperyron slope for the dehydrating reaction is positive then there is a net decrease in the total solid volume which implies an irreversible increase in porosity if the dilation of the pore space is insufficient to provide storage for all the released fluid then pore pressure excess is generated and if it becomes sufficiently high it may lead to brittle fracturing the time scale for pressure generation and the pore pressure excess can be maintained over long duration hinge on the interplay of reaction kinetics and fluid drainage motivated by experimental and microstructural observations a hydrological model is developed that incorporates dehydration kinetics and its pressure dependence analytic solutions were derived for the undrained development of pore pressure whether lithostatic pressure may be exceeded hinges on magnitude of the overstep in temperature and corresponding equilibrium pressure the time scale for development of pore pressure depends on the trade off between poroelasticity and the pressure sensitivity of reaction rate a finite difference model was also developed to simulate the progressive development of pore pressure excess dehydration and porosity development the model captures the experimental observation in gypsum of a reaction front that progressively propagates from the drained end toward the undrained end of a laboratory sample it is also in reasonable agreement with experimental data on fluid drainage and porosity production

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

episodic exhumation and related tectonic controlling during mesozoic in the eastern tian shan xinjiang northwestern china abstract the eastern tian shan ets which is located in the southern margin of the central asian orogenic belt experienced multiple cooling episodes during the mesozoic however the topography and cooling pattern of the region have been extensively affected by complex structural deformations here we combined a detailed structural analysis with new and existing low temperature thermochronological data from the eastern ets moqingwula range to constrain the process of deformation and exhumation during the mesozoic our results indicate that two phases deformation occurred in the late jurassic and the late cretaceous to the paleocene that transformed the landscape of the moqingwula range the first phase tilted the northern moqingwula range coinciding with folding and thrusting the second phase of deformation disrupted planation surfaces which dominantly formed in the early cretaceous and were preserved on the summit of the ranges our new data reveals three prominent cooling episodes during the 222 ma 138 113 ma and 68 57 ma as well as another subdued cooling phase during 113 92 ma in addition through integration of the regional cooling history and topographic evolution we discuss the geodynamics of the deformations and exhumations associated with tectonism within the central asian orogenic belt

constraining long term denudation and faulting history in intraplate regions by multisystem thermochronology an example of the sudetic marginal fault bohemian massif central europe 1 the rychlebske hory mountain region in the sudetes ne bohemian massif provides a natural laboratory for studies of postorogenic landscape evolution this work reveals both the exhumation history of the region and the paleoactivity along the sudetic marginal fault smf using zircon u th he zhe apatite fission track aft and apatite u th he ahe dating of crystalline basement and postorogenic sedimentary samples most significantly and in direct contradiction of traditional paleogeographic reconstructions this work has found evidence of a large cretaceous sea and regional burial to 6 5 km of the carboniferous permian basement in the late cretaceous 95 80 ma during the burial by sediments of the bohemian cretaceous basin system the smf acted as a normal fault as documented by offset zhe ages across the fault at 85 70 ma the basin was inverted cretaceous strata eroded and basement blocks were exhumed to the near surface at a rate of 300 m ma as evidenced by late cretaceous paleocene aft ages and thermal modeling results there is no appreciable difference in aft and ahe ages across the fault suggesting that the smf acted as a reverse fault during exhumation in the late eocene oligocene the basement was locally heated to 70 c by magmatic activity related to opening of the eger rift system neogene or younger thermal activity was not recorded in the thermochronological data confirming that late cenozoic uplift and erosion of the basement blocks was limited to less than 1 5 km in the study area

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

surface properties of stabilizing coastal dunes combining spectral and field analyses the coastal dunes of israel have been undergoing a process of stabilization since 1948 one of the major features of this process is a change in the surface properties of the dunes the development of a biological soil crust bsc and a change in the properties of the sand grains themselves in ashdod at the southern coastal plain of israel sand properties that include the bsc their fines silt and clay content and free iron oxide indicating their degree of rubification have been analysed in detail using field and lab spectroscopy methods in addition sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above mentioned factors it was found that the bsc over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust especially in the blue band the crust was found to be particularly developed in the stable areas mainly the interdunes and on the north facing slopes rather than on the south facing slopes a positive correlation was found between the crust fines and chlorophyll content with stable areas showing more developed bsc the stable areas showed also a lower albedo and slightly more developed reddish colour indicating a slightly higher rate of rubification this study demonstrates that the intensity of sand erosion deposition rates affects soil properties with the bsc being the fastest to react to the stabilization process months to several years followed by the content of fine particles several years to a decade whereas the rubification process is a much weaker marker and may need much longer time periods to develop decades to centuries

experimental evidence of reaction induced fracturing during olivine carbonation author s zhu w fusseis f lisabeth h xing t xiao x de andrade v karato si abstract 2016 american geophysical union all rights reserved mineral carbonation a process that binds co2 in the form of carbonates by silicate weathering is widespread on the earth s surface because of the abundance of silicate rocks and the permanence of the carbonated solids sequestering co2 via mineral carbonation has generated lots of interests however it is unclear how the fluid rock reaction proceeds to completion in spite of an increasing solid volume we conducted a mineral carbonation experiment in which a sintered olivine aggregate reacted with a sodium bicarbonate solution at reservoir conditions time resolved synchrotron x ray microtomographic images show cracks in polygonal patterns arising in the surface layers and propagating into the interior of the olivine aggregate the nanotomography data reveal that the incipient cracks intersect at right angles we infer that stretching due to nonuniform volume expansion generates polygonal cracking of the surfaces our data shed new lights on the processes that control hydration and carbonation of peridotite

remote sensing and spatial analysis of aeolian sand dunes a review and outlook abstract for more than four decades remote sensing images have been used to document and understand the evolution of aeolian sand dunes early studies focused on mapping and classifying dunes recent advances in sensor technology and software have allowed investigators to move towards quantitative investigation of dune form evolution and pattern development these advances have taken place alongside progress in numerical models which are capable of simulating the multitude of dune patterns observed in nature the potential to integrate remote sensing rs spatial analysis sa and modeling to predict the future changes of real world dune systems is steadily becoming a reality here we present a comprehensive review of significant recent advances involving rs and sa our objective is to demonstrate the capacity of these technologies to provide new insight on three important research domains 1 dune activity 2 dune patterns and hierarchies and 3 extra terrestrial dunes we outline how several recent advances have capitalized on the improved spatial and spectral resolution of rs data the availability of topographic data and new sa methods and software we also discuss some of the key research challenges and opportunities in the application of rs and sa dune field including the integration of rs data with field based measurements of vegetation cover structure and aeolian transport rate in order to develop predictive models of dune field activity expanding the observational evidence of dune form evolution at temporal and spatial scales that can be used to validate and refine simulation models the development and application of objective and reproducible sa methods for characterizing dune field pattern and expanding efforts to quantify three dimensional topographic changes of dune fields in order to develop improved understanding of spatio temporal patterns of erosion and deposition overall our review indicates a progressive evolution in the way sand dunes are studied whereas traditional field studies of airflow and sand transport can clarify event based process form interactions investigators are realizing a synoptic perspective is required to address the response of dune systems to major forcings the integration and evolution of the technologies discussed in this review are likely to form a foundation for future advances in aeolian study

metamorphic record of high pressure dehydration of antigorite serpentinite to chlorite harzburgite in a subduction setting cerro del almirez nevado filabride complex southern spain

geochemistry and geochronology of gneiss pebbles from foreland molasse conglomerates geodynamic and paleogeographic implications for the oligo miocene evolution of the eastern alps abstract gneiss pebbles deposited in foreland fans during the miocene epoch were studied with geochemical and thermochronological methods to reconstruct the paleodrainage evolution of the eastern alps and the geodynamic behavior of the source areas clear discrimination between upper plate austroalpine and lower plate penninic gneiss pebbles was achieved by single pebble paleocooling paths austroalpine gneisses showed highly variable and regionally distinctive paleocooling paths which record variscan to cretaceous rb sr and k ar cooling ages penninic gneisses showed paleogene to lower miocene high temperature rb sr k ar and miocene low temperature zircon and apatite fission track cooling ages cooling rates of penninic gneisses indicate maximum exhumation rates at 17 ma during the climax of lateral tectonic extrusion recording dominance of tectonic unroofing the paleodrainage evolution was characterized by a relatively stable catchment configuration in the western part of the eastern alps wh

the formation and expansion of the eastern proto tibetan plateau insights from low temperature thermochronology abstract we report new apatite fission track aft ages and thermal modeling results from the central songpan ganzi central and easternmost lhasa and eastern qiangtang blocks to provide robust constraints on the extent and expansion of the proto tibetan plateau our results reveal two main stages of rapid cooling events in different geological units the central songpan ganzi central lhasa and eastern qiangtang blocks underwent a phase of rapid cooling event during the paleocene early eocene 62 40 ma followed by extremely slow cooling since then such a sharp transition from relatively rapid to very slow cooling in approximately 40 ma in a large area suggest the eastern part of the proto tibetan plateau had formed since 40 ma the easternmost lhasa block experienced a stage of rapid cooling during the late eocene oligocene 40 24 ma this stage of rapid cooling event was coeval with the first stage of rapid cooling event in the longmen shan thrust belt suggestive of the eastward expansion of the eastern part of the proto tibetan plateau our paleogene aft ages and their corresponding rapid exhumation synthesized with other thermochronological and paleoaltimetry data are not consistent with those of the predictions from the channel flow model instead these observations favor the outward extrusion model the eastward expansion of the proto tibetan plateau improved the previous northward and southward growth model

chaos fractals and self organization in coastal geomorphology simulating dune landscapes in vegetated environments complex nonlinear dynamic systems are ubiquitous in the landscapes and phenomena studied by earth sciences in general and by geomorphology in particular concepts of chaos fractals and self organization originating from research in nonlinear dynamics have proven to be powerful approaches to understanding and modeling the evolution and characteristics of a wide variety of landscapes and bedforms this paper presents a brief survey of the fundamental ideas and terminology underlying these types of investigations covering such concepts as strange attractors fractal dimensions and self organized criticality their application in many areas of geomorphological research is subsequently reviewed in river network modeling and in surface analysis amongst others followed by more detailed descriptions of the use of chaos theory fractals and self organization in coastal geomorphology in particular these include self organized behavior of beach morphology the fractal nature of ocean surface gravity waves the self organization of beach cusps and simulation models of ripples and dune patterns this paper further presents a substantial extension of existing dune landscape simulation models by incorporating vegetation in the algorithm enabling more realistic investigations into the self organization of coastal dune systems interactions between vegetation and the sand transport process in the model such as the modification of erosion and deposition rules and the growth response of vegetation to burial and erosion introduce additional nonlinear feedback mechanisms that affect the course of selforganization of the simulated landscape exploratory modeling efforts show tantalizing results of how vegetation dynamics have a decisive impact on the emerging morphology and conversely how the developing landscape affects vegetation patterns extended interpretation of the modeling results in terms of attractors is hampered however by want of suitable state variables for characterizing vegetated landscapes with respect to both morphology and vegetation patterns d 2002 elsevier science b v all rights reserved

thermochronology of the torlesse accretionary complex wellington region new zealand the torlesse complex comprises several mesozoic accretionary prism complexes together forming continental basement over large parts of new zealand this study focuses on the thermal history of relatively low grade graywacke rocks exposed in a transect in southern north island that crosses the structural grain of the torlesse complex including its older and younger parts zircon fission track ft ages for the late triassic rakaia terrane which is the most inboard of the accretionary complexes are partially annealed some possibly reset and may indicate early cretaceous 134 10 ma cooling from maximum temperatures tmax probably related to imbrication of younger complexes of the pahau terrane numerical modeling of the zircon ft ages and published 40ara 39ar muscovite and biotite ages for the rakaia terrane suggest tmax values of 265 310 c and exhumation from depths of 10 12 km the rocks underlying the aorangi range and involving the youngest accretionary complex have experienced much lower tmax values of 210 and 110 c bracketed by reset apatite ft ages and detrital zircon ft ages the occurrence of a circa 100 ma component of zircon ft ages in both the weakly and highly indurated rocks beneath the aorangi range as well as in remnants of an overlying albian accretionary slope basin whatarangi formation imply multistorey accretion and incorporation of sediment into the youngest prism this circa 100 ma zircon ft age component also places a maximum age on the termination of mesozoic subduction beneath the new zealand region the occurrence of reset apatite ft ages across the whole of the wellington transect indicates that at least 4 km of exhumation occurred during the late miocene

eo alpine metamorphism and the mid miocene thermal event in the western carpathians slovakia new evidence from multiple thermochronology a combination of zircon u th he zhe apatite fission track aft and apatite u th he ahe dating methods is applied to constrain the metamorphic and exhumation history of the tatric part of the branisko mountains in the western carpathians zhe ages from the basement samples prove the basement experienced a very low grade to low grade eo alpine metamorphic overprint in mid cretaceous times miocene aft and ahe ages found in the basement and in the palaeogene sediments conclusively demonstrate that the branisko mts experienced a mid miocene thermal event this thermal event had a regional character and was related to magmatic and or burial heating that exposed the sediment and basement samples to 120 130 c and 100 190 c respectively

thermal petrological controls on the location of earthquakes within subducting plates we find that in young and warm subducting plates earthquakes occur just below the moho in older plates earthquakes occur throughout the subducting oceanic crust as well as the subducting mantle we document this behavior in several subduction zones where there are independent constraints on earthquake locations and slab structure specifically for northern and southern japan alaska and cascadia the differences in earthquake depth relative to subducting crust may reflect large differences in temperature and thus locations of major dehydration reactions in colder slabs the crust passes through blueschist facies dehydration reactions while in cascadia and nankai the major dehydration reactions in crust may be due to zoisite and amphibole breakdown or associated melting the cold paths allow more mineral bound h2o to be retained within the crust at shallow depths eventually released upon dehydration over shorter time intervals than warm paths the cold path dehydration reactions also result in net positive volume changes of solid fluid with solid volume decreasing less than the volume of h2o produced on hot paths the net volume changes are negative with solid volumes decreasing more than the volume of h2o produced the difference in behavior could drive a net increase in pore pressure upon dehydration for the cold but not the hot crustal paths the difference in rate of release in h2o and difference in sign of net system volume change may promote seismogenesis in cold subduction zones but inhibit it in the crust of warm slabs within the mantle of the downgoing plate earthquakes mostly occur where serpentine is stable or breaks down in both settings

the cooling history of silurian to cretaceous alkaline ring complexes south eastern desert egypt as revealed by fission track analysis abstract forty fission track ages of apatite zircon and sphene and nine horizontal confined track length distribution patterns in apatite have been used to establish the cooling history of nine silurian to late cretaceous alkaline ring complexes which intrude precambrian basement in the southern eastern desert of egypt zircon or sphene fission track ages were determined from three complexes for whichk ar andrb sr ages on the same samples were also available these ages are concordant and are interpreted as emplacement ages resulting from rapid cooling following high level crustal intrusion into relatively thick volcanic piles average apatite ages for each of the eight ring complexes range from 33 to 167 m y track length distribution patterns for apatites taken together with their ages invite subdivision into two groupings those complexes yielding early oligocene apparent apatite ages suggest cooling from the total track annealing zone followed by a relatively lengthy residence near the base of the partial annealing zone whereas those with late cretaceous ages indicate cooling from a shallower level in the partial annealing zone variations in cooling history resulted from differential uplift between fault bound blocks one block that containing the late cretaceous abu khruq complex was relatively stable and the different degrees of partial resetting recorded in apatites of this complex are attributed to the thermal effect of localised tertiary dyke intrusion fission track analysis in combination with geologic data indicates that in the south eastern desert of egypt a phase of uplift commenced in late oligocene time and was accompanied by paleogeothermal gradients of ca 40 50 c km uplift was more pronounced at least 2 2 5 km in areas within about 100 km from the present red sea coast this uplift which is viewed as part of a broader regional tectonism related to the opening of the red sea occurred along a northwest fracture pattern and was controlled by pre existing lines of weakness in the basement complex

cenozoic exhumation and deformation of northeastern tibet and the qinling is tibetan lower crustal flow diverging around the sichuan basin apatite fission track thermochronology data elucidate the cooling exhumation history of the qinling qin mountains which contain a paleozoic mesozoic orogenic collage north of the sichuan basin and northeast of the tibetan plateau in particular we examine the extent to which the qinling were affected by the rising plateau the northern and eastern qinling show continuous cooling and slow exhumation since the cretaceous in contrast in the southwestern qinling rapid cooling initiated at 9 4 ma a few million years later than in the eastern tibetan plateau a compilation of major cenozoic faults in the eastern tibetan plateau and the qinling and their kinematic and dynamic characterization shows that deformation in the qinling has predominantly been strike slip active sinistral and dextral strike slip faults delineate an area of eastward rock flow and bound the area of rapid late cenozoic cooling outlined by apatite fission track thermochronology these data can be interpreted to indicate that lower crustal flow has been diverted around the longmen shan and beneath the southwestern qinling causing active plateau uplift in this area alternatively northeastern tibet may be growing eastward faster in the western qinling than the entire south china block is extruding to the east

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

analysis of coastal dune dynamics shoreline position and large woody debris at wickaninnish bay pacific rim national park british columbia large woody debris lwd and colonizing vegetation alter the sediment budgets and stability of coastal dune systems in british columbia lwd on beaches consists largely of historical escape logs f

vegetation and sedimentation on coastal foredunes on a timescale of years to decades vegetated foredunes may show various modes of morphological development vegetation is one of the factors that determine the sedimentation pattern and thus morphology on the foredune in turn the vegetation pattern may be controlled by the sedimentation pattern although these effects have been quantified for short timescales there is relatively little information on the interaction between vegetation and sedimentation for timescales of over a year for the island of ameland the netherlands elevation measurements and aerial photographs between 2002 and 2012 were used to derive changes in elevation and vegetation patterns on a year to year basis this was done for a range of stable to accreting foredunes sedimentation increases from the beach to a maximum halfway up the seaward slope of the foredune and then decreases again when going landward this trend is further modified by the vegetation s spatial pattern on a timescale of years there is no correlation between the density of vegetation cover and the amount of accretion however by accounting for the gradual depletion of the sand load over the foredune a relationship can be defined between vegetation cover and its trapping efficiency foredune vegetation spreads mainly by lateral expansion of existing patches no strong effect was found of the sedimentation balance on the expansion of vegetation it is suggested that other growth limiting factors are of similar importance masking any possible dependency of vegetation growth on sand accretion

assessment of highly active dune mobility in the medium short and very short term abstract dune activity or stability has usually been studied over long time periods however this may not reflect changes that occur in the short term especially for highly active dunefields extreme wind conditions that are generated near the strait of gibraltar sw spain have given rise to the transgressive valdevaqueros dunefield the current work focuses on analyzing the sand drift potential and the evolution of the dune profile in the medium term months the short term days and the very short term hours topographic data which were collected with a differential gps were interpreted from reconstructed empirical orthogonal functions eof the results showed that generally the dune profile presented shifting morphologies especially around the crest and brink and a trend towards migration to a gentler steady state as a result the leeward side adopted continuous slope variations during the different survey periods whereas the windward slope did not undergo any significant change lateral and vertical displacements were analyzed during a severe easterly sandstorm when the dune brink experienced an advance migration rate of 1 75 m in 24 h sand transport rates of 25 5 36 5 m 3 m 1 month 1 22 52 m 3 m 1 day 1 and 0 93 m 3 m 1 h 1 were measured for the medium term short term and very short term respectively these values were compared to the theoretical sand transport rate for valdevaqueros dune based on the classic bagnold equation as well other more recent formulae to obtain a ratio between the real and the theoretical rates for each study period these results together with the sand drift potential up to 10 000 vector units demonstrate that valdevaqueros tarifa is a dunefield with one of the highest sand transport capacities in europe

tectonic response of the central chilean margin 35 38 s to the collision and subduction of heterogeneous oceanic crust a thermochronological study along strike geological segmentation in the andean chain has been recognized at various scales and is usually attributed to changes in plate motion vectors as well as the upper plate expression of differing subducted slab age strength and composition we present new multi phase 40ar 39ar apatite fission track and zircon and apatite u th he data from a north south oriented traverse between 35 and 38 s along the principal andean cordillera of chile that reveal 1 rapid cooling at 18 and 15 ma which can be attributed to both thermal relaxation following magmatic intrusion and regional scale exhumation and 2 along strike differences in the extent of exhumation since 7 5 ma that may be a consequence of the subduction of the juan fernandez ridge above the flat slab segment at 32 since 10 ma a comparison of the response of the south american plate to the collision of the carnegie nazca and juan fernandez ridges suggests that slab flattening is not the dominant driving force that exhumes the upper plate in these settings rather the extent of exhumation is controlled by pre existing structural weaknesses the time duration of the dynamically supported topography and climate

comparison of experimental techniques to increase the number of measurable confined fission tracks in zircon abstract we compared three experimental techniques for increasing the number of measurable horizontal confined fission tracks hcts in annealed and unannealed zircon these techniques are irradiation of 252 cf spontaneous fission fragments irradiation of heavy ions 58 ni 11 using a tandem van de graaff accelerator and artificial fracturing of the zircon grains all these techniques increased the number of measurable hcts and they introduced no significant change in the measured length of annealed hcts for the samples with low track density 10 5 cm 2 heavy ion irradiation was far more effective than irradiation of 252 cf fission fragments because relatively long artificial tracks could be formed by the heavy ion irradiation the artificial fracturing method is recommended when an accelerator facility is not easily available because its effect was comparable to heavy ion irradiation and it is practicable in ordinary laboratories using these techniques a preliminary comparison of annealing characteristics was performed for three zircon samples with different spontaneous track densities of 4 10 5 4 10 6 and 2 10 7 cm 2 with fission track ages of 3 1 22 8 and 367 6 ma respectively the length reduction due to the thermal annealing of these zircons appeared to be different with the possibility that the thermal stability of spontaneous fission tracks depends on the initial spontaneous track density i e the higher the initial spontaneous track density of a sample the slower the rate of track annealing

reaction fronts permeability and fluid pressure development during dehydration reactions abstract fluids released by prograde metamorphism are often invoked to explain a range of crustal processes from earthquake triggering to metasomatism these fluids can be either trapped and overpressured or released and channelized depending on the interplay between permeability reaction rate and compaction experimental data are presented measuring permeability porosity and microstructural evolution throughout the dehydration of gypsum to form bassanite reaction fronts regions over which the reaction largely occurs are used as a framework to explain the results experiments were conducted under hydrostatic conditions at a constant temperature of 115 c at two effective pressures of 60 mpa and 110 mpa and three pore fluid pressures of 20 40 and 60 mpa at high effective pressure creep of the gypsum solid framework results in low porosity and permeability producing high pore fluid pressure build up that slows the reaction rate a clearly defined narrow reaction front migrates along the sample and the average permeability remains low until the front sweeps across the entire sample conversely at low effective pressure the reaction front is wide producing a permeable drained network average permeability is enhanced significantly after only a small fraction of the reaction has completed by the interconnection of open pores this study shows that the width of reaction fronts and hence the permeability development is strongly controlled by compaction the reaction front velocity is broadly dependent on permeability and the reaction driving force a simple quantitative model for these relationships is developed

transport of low ah2o dehydration products to melt sites via reaction zone networks milford sound new zealand the gabbroic dioritic pembroke hornblende granulite phg of milford sound displays a geometrically simple mesoscopic network of sub planar garnet reaction zones grz in which the meta igneous hornblende granulite has been depleted of na si and h2o and c 25 vol almandine rich garnet has formed some studies postulate the initial presence of melt along the centres of all grz explaining the frequent absence of feldspathic veins by selective melt loss a more parsimonious model is necessitated by structural evidence and together with chemical data suggests a relationship between mid range metasomatic transport and anatexis the pembroke outcrops show a process of incipient melting of gabbro diorite in an environment of relatively low ah2o in lithologies that have limited free quartz a non equilibrium steady state is proposed in which a sodic dehydration fluid moves some distance via the grz network towards areas of partial melting only in these areas are na and si reconstituted as albite with more garnet as byproduct having avoided the need for melt percolation the combined structural and chemical evidence directs a focus on mass transport in low ah2o gabbroic environments in subsequent events of shearing and complete transposition both sets of garnet the atypical grz residue and partial melt melanosomes were inherited by the milford gneiss facies of the phg

dehydration of lawsonite could directly trigger earthquakes in subducting oceanic crust intermediate depth earthquakes in cold subduction zones are observed within the subducting oceanic crust as well as the mantle in contrast intermediate depth earthquakes in hot subduction zones predominantly occur just below the mohorovicic discontinuity these observations have stimulated interest in relationships between blueschist facies metamorphism and seismicity particularly through dehydration reactions involving the mineral lawsonite here we conducted deformation experiments on lawsonite while monitoring acoustic emissions in a griggs type deformation apparatus the temperature was increased above the thermal stability of lawsonite while the sample was deforming to test whether the lawsonite dehydration reaction induces unstable fault slip in contrast to similar tests on antigorite unstable fault slip that is stick slip occurred during dehydration reactions in the lawsonite and acoustic emission signals were continuously observed microstructural observations indicate that strain is highly localized along the fault r1 and b shears and that the fault surface develops slickensides very smooth fault surfaces polished by frictional sliding the unloading slope during the unstable slip follows the stiffness of the apparatus at all experimental conditions regardless of the strain rate and temperature ramping rate a thermomechanical scaling factor for the experiments is within the range estimated for natural subduction zones indicating the potential for unstable frictional sliding within natural lawsonite layers

tracking metamorphic dehydration reactions in real time with transmission small and wide angle synchrotron x ray scattering the case of gypsum dehydration we present a review of a unique non destructive method for the real time monitoring of phase transformations and nano pore evolution in dehydrating rocks transmission small and wide angle synchrotron x ray scattering saxs waxs it is shown how saxs waxs can be applied to investigating rock samples dehydrated in a purpose built loading cell that allows the coeval application of high temperature axial confinement and fluid pressure or flow to the specimen because synchrotron sources deliver extremely bright monochromatic x rays across a wide energy spectrum they enable the in situ examination of confined rock samples with thicknesses of 1 mm at a time resolution of order seconds hence fast kinetics with reaction completion times of about hundreds of seconds can be tracked with beam sizes of order tens to hundreds of micrometres it is possible to monitor multiple interrogation points in a sample with a lateral extent of a few centimetres thus resolving potential lateral spatial effects during dehydration and enlarging sample statistics significantly therefore the saxs waxs method offers the opportunity to acquire data on a striking range of length scales for rock samples with thicknesses of 10 3 m and widths of 10 2 m a lateral interrogation point spacing of 10 5 m can be achieved within each irradiated interrogation point volume information concerning pores with sizes between 10 9 and 10 7 m and the crystal lattice on the scale of 10 10 m is acquired in real time this article presents a summary of the physical principles underpinning transmission x ray scattering with the aim of providing a guide for the design and interpretation of time resolved saxs waxs experiments it is elucidated 1 when and how saxs data can be used to analyse total porosity internal surface area and pore size distributions in rocks on length scales from 1 to 300 nm 2 how waxs can be employed to track lattice transformations in situ and 3 which limitations and complicating factors should be considered during experimental design data analysis and interpretation to illustrate the key capabilities of the saxs waxs method we present a series of dehydration experiments on a well studied natural gypsum rock volterra alabaster our results demonstrate that saxs waxs is excellently suited for the in situ tracking of dehydration kinetics and the associated evolution of nano pores the phase transformation from gypsum to bassanite is correlated directly with nano void growth on length scales between 1 and 11 nm for the first time a comparison of the saxs waxs kinetic results with literature data emphasises the need for future dehydration experiments on rock specimens because of the impact of rock fabric and the generally heterogeneous and transient nature of dehydration reactions in nature it is anticipated that the saxs waxs method combined with in situ loading cells will constitute an invaluable tool in the ongoing quest for understanding dehydration and other mineral replacement reactions in rocks quantitatively

contrasting hydrological response of coastal and desert biocrusts biocrusts abound in southern israel covering the hallamish dune field near nizzana niz in the negev mean annual precipitation of 95 mm and the coast of nizzanim nim near ashdod mean annual precipitation of 500 mm while the hydrological response of the niz crust to natural rain events was thoroughly investigated no data is available on the hydrological response of the nim crust runoff was monitored in runoff plots during the years 2005 2008 and in addition sprinkling experiments were carried out on nim and niz crusts for the evaluation of the possible factors that may control runoff initiation fine content of the parent material crust thickness compressional strength hydrophobicity surface microrelief organic matter biomass chlorophyll a and total carbohydrates and the crust s species composition of nim were studied and compared to that of niz the data showed that in comparison to the niz crust that readily generated runoff no runoff was produced by the nim crust this was so despite the fact that 1 microculeus vaginatus predominated in both crusts 2 the substantially higher rain intensities in nim 3 the greater thickness and higher chlorophyll content and 4 the lower microrelief at nim in comparison to niz the lack of runoff in nim was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation the absence of runoff and its consequences on the nim ecosystem are discussed copyright 2012 john wiley sons ltd

experimental investigation into the scale dependence of fluid transport in heterogeneous rocks we investigated the dependence of hydraulic properties on the spatial scale of intrinsic and artificial heterogeneity applying harmonic pore pressure testing to two varieties of fontainebleau sandstone at various periods and effective pressures blocks with porosities of about 5 and 8 were chosen exhibiting a permeability of about 2 10 19 and 1 10 13 m2 respectively the permeability of the less permeable variety strongly depends on sample size artificial heterogeneous rock samples were prepared by stacking pieces of the two sandstone varieties perpendicular and parallel to the main flow direction the perturbation of the fluid flow owing to the interfaces between pieces of the same variety is controlled by the orientation of and subordinately by the effective stress on the interfaces constraints on conduit geometry derived from the effect of interfaces indicate that interconnectivity is more important than pore radius at the lower porosity the effective permeability of alternating stacks of the two varieties differs tremendously for the two interface orientations arithmetic and harmonic averages coincide with the effective properties parallel and perpendicular to the main flow respectively when the oscillation period is varied two regimes are observed one with constant permeability at long periods and a second with decreasing permeability for decreasing period at short periods order of magnitude considerations of penetration depth suggest that this period dependence may be related to heterogeneity

low temperature thermal evolution of the azov massif ukrainian shield ukraine implications for interpreting u th he and fission track ages from cratons abstract the low temperature thermal evolution of the azov massif eastern part of the ukrainian shield ukraine is investigated by combined zircon fission track zft apatite fission track aft and apatite u th he ahe thermochronology the data help to better understand the geodynamic evolution of the azov massif and the adjacent intra cratonic rift basin dniepr donets basin as follows zft data reveal that the precambrian crystalline basement of the azov massif was heated to temperatures close to 240 c during the late palaeozoic the heating event is interpreted in terms of burial of the basement beneath a several kilometres thick pile of devonian and carboniferous sedimentary deposits of the adjacent dniepr donets basin during permo triassic times large parts of the basement were affected by a thermal event related to mantle upwelling associated magmatic activity and increased heat flow in the adjacent rift the major part of the basement cooled to near surface conditions in the early to middle triassic and since then was thermally stable as suggested by aft and ahe data further aft data confirm late triassic magmatic activity in the azov massif which however did not influence regional thermal pattern the northern part of the basement and its sedimentary cover record a cooling event in the jurassic which was probably related to erosion however although ar ar data of jurassic magmatic activity in the donbas foldbelt are about 20 my younger than the aft data thermal relaxation after elevated heat flow associated with this magmatic event cannot be completely ruled out our results reveal apparent inconsistencies between aft and ahe data the ahe ages corrected for alpha ejection according to the standard procedure farley k a wolf r a silver l t 1996 the effect of long alpha stopping distances on u th he ages geochim cosmochim acta 60 21 4223 4229 farley k a 2002 u th he dating techniques calibrations and applications mineral soc am rev mineral geochem 47 819 844 are older than corresponding aft ages in order to test the relevance of alpha ejection correction mechanical abrasion of several apatite grains was applied we found that in case of relatively slow cooling alpha ejection correction of raw u th he ages leads to erroneously high ages this shows that alpha ejection correction should be used with caution we propose that this correction should only be applied to samples with a fast cooling history whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means

dune mobility and vegetation cover in the southwest kalahari desert as part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest kalahari data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces and that the majority of surface activity occurs on the crests and upper slopes of the dunes the data suggest that the limiting variables on surface sediment movement vary on different parts of a dune on interdunes and lower dune slopes the primary limiting variable is available wind energy while on dune crests and upper slopes it is vegetation cover ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation from individual data points no evidence is found to support a threshold vegetation cover below which sediment movement occurs rather a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change however dunes with differing amounts of mean vegetation cover display differing degrees of surface activity and at this scale a vegetation cover threshold in the region of 14 per cent may be recognized

mobility of a remobilised parabolic dune in kennemerland the netherlands abstract a parabolic dune in the netherlands was remobilised in december 1998 by removing vegetation and soil the main aim of the experiment was ecological to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes if processes can be reactivated at coarse scale periodic rejuvenation of the landscape over the long term is possible without the need for managers to interfere further the experiment provides the opportunity to address another important question can large parabolic dunes in the netherlands be mobile in the present climate mobility of the dune is investigated by means of erosion pins aerial photography and measurement of cross sections activity indices are derived from erosion pin recordings and correlated to weather conditions from 1999 to 2001 displacement of the dune ranged from 0 to 12 m in east northeasterly direction activity of the dune is related to wind conditions but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods periods with extreme wind speeds resulted in much less geomorphic change than expected

measurements and numerical simulations of the degree of activity and vegetation cover on parabolic dunes in north eastern brazil in this work we present measurements of vegetation cover over parabolic dunes with different degrees of activation along the north eastern brazilian coast we extend the local values of the vegetation cover density to the whole dune by correlating measurements with the relative brightness index c of high resolution quickbird panchromatic satellite images of the dune field we then introduce the vegetation data into a continuous model for vegetated dunes coupling sand erosion and vegetation growth and perform simulations of the evolution of the morphology and vegetation cover of parabolic dunes finally from the comparison of both the measurements and the simulation results we show that the model is able to predict the dune shape and the vegetation distribution of real parabolic dunes as result of the evolution of a blow out