episodic fluid migration in the fennoscandian shield recorded by stable isotopes rare earth elements and fluid inclusions in fracture minerals at forsmark sweden abstract drilling through the palaeoproterozoic bedrock at forsmark central sweden during the site investigation for a potential geological repository of highly radioactive nuclear waste has provided high quality drill core material from the upper 1 km of the fennoscandian shield analyses of stable isotopes 13c 18o 34s 87sr 86sr rare earth elements and fluid inclusions in fracture filling calcite and pyrite from these drill cores have resulted in the discrimination of several episodes of fracture mineralisations these events represent migration of fluids during a wide range of conditions ranging from high temperature hydrothermal to present day groundwater circulation four major events have been distinguished 1 precipitation of epidote chlorite and quartz under hydrothermal conditions t 150 200 c during the proterozoic sometime between 1 8 and 1 1 ga 2 hydrothermal circulation at temperatures close to 200 c with precipitation of adularia albite prehnite laumontite calcite and chlorite most of these minerals precipitated during a tectonothermal event between 1 1 and 1 0 ga possibly in response to far field effects of the sveconorwegian orogeny 3 precipitation of mainly quartz calcite pyrite and asphaltite occurred during the palaeozoic at temperatures between 60 and 190 c mainly at

the timing of last glacial periglacial and aeolian events twente eastern netherlands sequences of last glacial age contain valuable palaeoclimatic information but are often difficult to date because the environment has been unfavourable for deposition of datable organic material this paper presents age estimates determined by optically stimulated luminescence for sediments from the type site of the so called coversands periglacial aeolian deposits in the netherlands these improve the chronology of this type site considerably allowing age limits 22 17 kyr bp to be set for the first time for the important phase of widespread permafrost degradation and aeolian deflation recorded in these deposits aeolian deposition occurred intermittently for most of the last glacial maximum and the late glacial phases based on luminescence dating sand sheet deposition was concentrated between ca 17 14 kyr ago and dune formation was dominant during the younger dryas the younger dryas was sufficiently cold to allow the first stages of ice wedge cast development in the netherlands copyright 1999 john wiley sons ltd

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

micro topographic analysis of shell pavements formed by aeolian transport in a wind tunnel simulation 1 beach surfaces containing shell materials represent one end member of a range of environments in which armoring is the primary control on wind erosion unlike spheres and cylinders which have formed the basis of theoretical model formulation and much of the early work in wind tunnels mollusc shells have complex and non uniform shapes which vary with their orientation identification of shell perimeter height and frontal area relative to the bed area roughness density is therefore a formidable task but nonetheless is essential for modeling sediment entrainment from beach surfaces a methodology is suggested in this paper for capturing and analyzing these geospatial data in the context of a wind tunnel simulation designed to improve understanding of the geophysical processes involved in armoring for deposits where non erodible shells represent half of the volume of the parent material the surface appears to be highly stable to wind erosion from the outset although minor reworking of the intervening erodible sediment does occur in comparison the shell coverage must increase to approximately 30 during wind erosion events in order for any given beach surface to stabilize especially beach deposits with a low concentration of shells by volume with suitable calibration the raupach shear stress partitioning model can be forced to perform well in predicting the threshold conditions for particle entrainment however this approach overlooks the pivotal involvement of particle impact and ricochet in the creation and sculpting of the armored bed as a case in point when the shells are removed from digital elevation models of armored beach surfaces formed in aeolian systems the adjusted topography is not suggestive of the presence of coherent flow structures e g horseshoe vortices and wedge shaped shelter areas as assumed to exist in the stress partitioning approach for isolated flows this would suggest that future work on the armoring of natural surfaces affected by wind erosion must allow for more complexity in the flow perturbation

a new model of wind erosion in the presence of vegetation 1 vegetation is known to impact strongly the erosion of soil by the wind lateral cover is the primary parameter used to represent the amount of vegetation in aeolian research and in particular shear stress partitioning research although lateral cover provides a simple means for representing how much vegetation is in an area it is not capable of characterizing how vegetation is distributed a new nonequilibrium model for the representation of nonerodible roughness elements is presented that uses the size distribution of erodible gaps between plants to characterize the ratio of the maximum shear stress to the average shear stress at the surface the model shows very good agreement with measured shear stress ratios from the laboratory and field experiments the model also satisfactorily explains relatively high horizontal aeolian sediment flux at high lateral cover the relationship between this model and another shear stress partitioning model is explored and the new model is found to be superior to the existing model because it 1 utilizes parameters with physical meaning that are measurable in the field or laboratory 2 explains observations of horizontal flux at high cover 3 overcomes difficulties inherent in the use of lateral cover to characterize vegetation on the surface 4 is scale explicit and 5 can be used at multiple scales from an individual unvegetated gap to an entire landscape

transpressive shear related to arc magmatism the paleoproterozoic storsjon edsbyn deformation zone central sweden 1 the polyphase 15 30 km wide and 200 km long storsjon edsbyn deformation zone sedz apparently separates two major paleoproterozoic provinces in central sweden four main phases of deformation have been recognized along the zone associated high strain rocks are characterized by their mineralogy microstructures kinematic patterns magnetic signatures and relative ages the mineral and stretching lineations are consistently steeply to moderately plunging analysis of mesoscopic shear zone populations of different generations suggests that most displacements are compatible with north south to northeast southwest bulk regional shortening the structural analysis suggests that the main ductile deformation along the sedz was due to dextral transpression with a steep coaxial component field evidence combined with published age data constrain the main deformation to the time interval circa 1 7 1 3 ga synkinematic titanite from a ductile protomylonite in the sedz yields an u pb age of 1674 6 ma the combined results imply transpressive deformation broadly synchronous with and spatially related to volcanism and plutonism in a continental margin magmatic arc setting

migratory tectonic switching western svecofennian orogen central sweden constraints from u pb zircon and titanite geochronology abstract the forsmark area in the western part of the svecofennian orogen central sweden is situated between two major palaeoproterozoic tectonic domains that show contrasting histories with respect to timing of igneous activity ductile deformation and metamorphism geological features common to both the adjacent domains are found at forsmark which consequently is a key area for understanding the tectonic evolution of the svecofennian orogen in this region new sims and tims geochronological data from several samples in a limited area at forsmark constrain the timing of igneous activity ductile deformation and metamorphism in this area u pb zircon dating in combination with field studies reveals the existence of two calk alkaline igneous suites at forsmark the older and most voluminous plutonic suite intruded at 1 89 1 87 ga and is affected by penetrative yet variably intense ductile deformation with the development of a ductile grain shape fabric under amphibolite facies metamorphic conditions and folding the younger and less voluminous hypabyssal suite intruded at 1 86 1 85 ga during the waning stages of this penetrative deformational phase furthermore u pb titanite dating shows that the area has been affected by one or more tectonothermal events after regional fabric development and possibly even after 1 83 ga the deformation during these events involved more restricted strain along discrete zones the forsmark data in combination with a compilation and evaluation of available geochronological data from the time interval 1 91 1 84 ga in central sweden points to the existence of at least two major tectonic cycles in this region each cycle is characterised by igneous activity associated at least partly with extension a short interval of compressional deformation and migration of the tectonic activity in this paper we discuss two highly contrasting tectonic models that may explain the cyclic tectonic evolution of the western part of the svecofennian orogen in central sweden the favoured model involves continuous subduction with a constant polarity beneath a single active continental margin combined with alternating subduction hinge retreat and advance the model involves migration of what has been described as tectonic switching in the younger accretionary orogenic systems of eastern australia palaeozoic lachlan orogen and new zealand

biotite and muscovite 40ar 39ar geochronological constraints on the post svecofennian tectonothermal evolution forsmark site central sweden in order to characterize the post svecofennian tectonothermal evolution of the fennoscandian shield 40ar 39ar biotite and some 40ar 39ar muscovite geochronological data are reported from a total of 30 surface outcrop and 1000 m long borehole samples at forsmark central sweden the thirteen surface samples were collected across three branches of a major wnw to nw trending system of deformation zones whereas the boreholes were drilled within a tectonic lens in between two of these zones the 40ar 39ar biotite ages indicate that the present erosion surface in central sweden cooled below 300 c at 1 73 1 66 ga and that the rocks could respond to stress by brittle deformation between 1 8 and 1 7 ga the variation in surface ages is suggested to be due to faulting along the large wnw to nw trending deformation zones following the establishment of a sub cambrian peneplain the minor variation of ages within a single crustal block may be due to disturbance along ene to nne trending fracture zones possible cooling paths derived from 40ar 39ar hornblende muscovite and biotite ages were calculated for the time interval from 1 80 to 1 66 ga when the area cooled from 500 c to 300 c between 1 70 and 1 64 ga uplift rates of c 22 m m y were calculated from borehole 40ar 39ar biotite data tectonothermal histories inferred from the combined cooling and uplift rates are related to simple slow cooling after the svecofennian orogeny to crustal movement in response to far field effects of c 1 7 ga orogenic activity further to the west or to a combination of these possibilities less

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

quantifying relationships of burning roughness and potential dust emission with laser altimetry of soil surfaces at submeter scales abstract decrease in surface roughness by the reduction of vegetation is one mechanism by which fire can promote aeolian transport in a variety of landscapes the extent to which fire might alter the roughness of the soil surface at fine spatial scales and the effect of this alteration on post fire aeolian response is not well known we examined relationships in the field between dust emissions and subcentimeter level soil surface roughness at submeter spatial scales with a terrestrial laser scanner and portable wind tunnel analog based on aeolian theory we hypothesized that observed relationships would differ from those determined in previous studies with laser altimetry at landscape scales meter kilometer length scales we examined four semiarid shrublands in southern idaho usa containing a distinct pattern of undershrub and interspace microsites including recently burned and unburned conditions mixed models were used to determine effects of burning on surface roughness and the response of dust emissions to changes in surface roughness results indicated that burned soil surfaces were rougher than unburned soil surfaces dust emissions were enhanced by increases in roughness on burned soil surfaces and in the absence of nonerodible roughness elements i e plants this finding is expectedly in contrast to previous work that demonstrated an inverse relationship between soil erosion and surface roughness determined with lidar light detection and ranging at landscape scales vegetated and unvegetated surfaces relationships of lidar derived roughness and aeolian emissions are scale dependent and vary with environmental factors of fire and vegetation these findings are integral for future research that attempts to parameterize model based predictions of aeolian emissions with lidar derived roughness

pleistocene cryostructures and landslide at petit bost southwestern france 45 n abstract remnants of a pleistocene landslide have been observed during field investigations of quaternary alluvial formations of the isle river at petit bost southwestern france the main features of the landslide induced deformation give a good indication of its size and depth the surface of rupture is located in a 0 5 m thick very plastic mottled clay at the top of an alluvial gravel the clay is overlain by 1 7 m thick loamy colluvial deposits with a polygonal net of bleached wedges that testify to past permafrost conditions the mechanical parameters used in stability calculations for the case of an infinite planar sliding surface that fits well the geomorphological data are given by triaxial tests stability calculation indicates that the slope is very stable at present and that rupture can only have occurred in fully unconsolidated and undrained conditions this likely happened during permafrost degradation and subsequent thawing of ice rich soil layers oedometric tests indicate post sliding over consolidation of the clay with regards to the debate on permafrost distribution in france during the pleistocene this study gives support to a wide extent of permafrost at least to the latitude 45 n southward during the coldest periods it also points out that frost induced slope instability may have played a major but still underestimated role in many french regions north to this latitude

neocrystallization or cooling 40ar 39ar ages of white micas from low grade mylonites abstract 40 ar 39 ar data for white micas from quartzite mylonites from a thrust system are evaluated with respect to whether the minerals record cooling ages or alternatively ages of deformation induced neocrystallization to address these interpretations three types of information are needed 1 the effective diffusion length scale controlling volume diffusion of argon in white micas 2 an estimate of the diffusion parameters for volume diffusion of argon and 3 the thermal history completely recrystallized quartzites exhibit smooth grain size distributions for white micas with good exponential or power law fits suggesting that the grains grew under similar conditions the microstructures indicate that the grains grew over a narrow range in time near the end of the deformation history measured grain size distributions provide a maximum limit for the diffusion length scale thermal histories are estimated by 40 ar 39 ar diffusion experiments on k feldspars using the multi diffusion domain method of lovera lovera o m richter f m harrison t m 1989 the 40 ar 39 ar thermochronometry for slowly cooled samples having a distribution of diffusion domain sizes j geophys res 94 17917 17935 these results are consistent with the expected temperature time path for the thrusting environment and predict maximum temperatures of 250 350 c during the time span recorded by the white micas experimentally and empirically calibrated diffusion parameters for white micas are applied to a cylindrical diffusion geometry to explore the question of cooling ages versus neocrystallization ages forward modeling of the passage of the white micas through the closure window for argon diffusion using the thermal histories derived from the k feldspars indicates that the white micas record neocrystallization rather than cooling and supports the idea that the white micas record the timing of when ductile deformation ceased

regular and irregular patterns in semiarid vegetation vegetation in many semiarid regions is strikingly patterned forming regular stripes on hillsides and irregular mosaics on flat ground a simple model of plant and water dynamics based on ecologically realistic assumptions and with reasonable parameter values captures both of these types of patterns the regular patterns result from a turing like instability the irregular patterns arise when the ecological dynamics amplify slight small scale topographic variability because of the close agreement between observations and these theoretical results this system provides a clear example of how nonlinear mechanisms can be important in determining the spatial structure of plant communities

a simple method to estimate threshold friction velocity of wind erosion in the field 1 this study provides a fast and easy to apply method to estimate threshold friction velocity tfv of wind erosion in the field wind tunnel experiments and a variety of ground measurements including air gun pocket penetrometer torvane and roughness chain were conducted in moab utah and cross validated in the mojave desert california patterns between tfv and ground measurements were examined to identify the optimum method for estimating tfv the results show that tfvs were best predicted using the air gun and penetrometer measurements in the moab sites this empirical method however systematically underestimated tfvs in the mojave desert sites further analysis showed that tfvs in the mojave sites can be satisfactorily estimated with a correction for rock cover which is presumably the main cause of the underestimation of tfvs the proposed method may be also applied to estimate tfvs in environments where other non erodible elements such as postharvest residuals are found

evidence for 1 82 ga transpressive shearing in a 1 85 ga granitoid in central sweden implications for the regional evolution abstract two crustal scale shear zone systems the storsjon edsbyn deformation zone and the hassela shear zone join in the western part of central sweden and form an anastomosing pattern of ductile shear zones several of these up to 1 km wide zones truncate an intrusion previously defined as a component of the major ca 1 80 1 77 ga magmatic suite the revsund granitoids in north central sweden however within the southern part of the intrusion titanites that are components of the fabric in a pervasively deformed shear zone forsaan have a u pb tims age of 1816 2 ma zircon porphyroclasts in the same fabric yield a u pb sims age of 1849 14 ma overlapping with the u pb tims age of 1851 2 ma for titanites from an undeformed granitoid these results are interpreted to define the ages of ductile shearing and magma emplacement respectively this interpretation is supported by microstructures as well as the regional structural pattern characterised by shear zones enveloping virtually undeformed pods of the granitoid previously reported and locally existing magmatic flow structures indicate some syn emplacement deformation the kinematic results characterised by a high proportion of pure shear within the granitoid and oblique dextral shearing along its margin reflect strain partitioning under transpressive conditions the kinematic and geochronological results fit into the regional framework of late orogenic localised deformation along crustal scale shear zones recent absolute datings of shear fabrics defines ca 1 82 1 80 ga as a period of shear zone activity in central sweden temporally this period overlaps with the emplacement of s type granites and granitoids derived from deeper crustal levels a similar situation exists in southern finland structural geochronological and geophysical data suggest that the crustal scale shear zones in central sweden and southern finland may be related temporally and spatially the age and the post tectonic nature on a regional scale of the dated 1 85 ga granitoid have important regional implications as both the age of the intrusion and the ductile shearing are older than the established age range 1 80 1 77 ga of the revsund granitoids either an extended intrusive history for the suite is indicated or the granitoids in this part of the type areas should be excluded from the revsund suite their post tectonic nature implies that the pervasive svecokarelian deformation in the area occurred earlier than generally assumed 1 85 1 80 ga on the other hand approximately coeval calc alkaline granitoids to the south east of the investigated area are folded and foliated pervasively indicating a later svecokarelian evolution in that area i e that the granitoids are located in domains with separate orogenic evolutions

brittle tectonic evolution and paleostress field reconstruction in the southwestern part of the fennoscandian shield forsmark sweden 1 six hundred fault slip data have provided robust paleostress fields within an approximately 35 km3 volume of paleoproterozoic 1 9 ga rocks in the southwestern fennoscandian shield forsmark sweden these rocks were affected by penetrative ductile strain from 1 87 to 1 86 ga folding ductile strain along discrete zones around 1 8 ga and semibrittle or brittle deformation around and after 1 8 ga compatible paleostress fields have been identified using site by site and merged data sets from outcrops and oriented drill cores transpressive deformation with a regional nnw sse 1 axis associated with clockwise stress deviation inside a tectonic lens resulted in dextral slip along regionally significant steep wnw ese and nw se deformation zones the semibrittle and most of the brittle structures including specifically the epidote bearing fractures were established during this oldest regime around 1 8 ga latest svecokarelian a younger paleostress field with a ne sw 1 axis which was also transpressive in character is inferred to have been active at 1 7 1 6 ga the best defined paleostress field is transpressive in character with a wnw ese 1 axis that resulted in sinistral reactivation along the wnw ese and nw se zones the main set of laumontite stepped faults developed at this stage at 1 1 0 9 ga sveconorwegian it is impossible to exclude fully the influence of reactivation during even younger phanerozoic tectonic events subordinate extensional paleostress fields were related either to the latest svecokarelian and sveconorwegian transpressive regimes due to 1 and 2 stress permutations or to regional extensional tectonic regimes during the meso or neoproterozoic or later during the permo carboniferous and or mesozoic

aeolian processes and the biosphere ravi s d odorico p breshears d d field j p goudie a s huxman t e li j okin g s swap r j thomas a d pelt s v whicker j j zobeck t m 2011 aeolian processes and the biosphere reviews of geophysics 49 3

penetrative ductile deformation and amphibolite facies metamorphism prior to 1851 ma in the western part of the svecofennian orogen fennoscandian shield the svecofennian orogen in the fennosandian shield consists of several palaeoproterozoic meta igneous provinces that generally young progressively southwards and westwards the understanding of the tectonic evolution of these different provinces is linked to the ability to constrain the timing of ductile deformation and metamorphism within them in the western part of the orogen in central sweden ductile deformation and metamorphism is conventionally thought to have occurred after 1 85 ga and mainly around 1 82 1 80 ga at forsmark in central sweden we have dated two undeformed granite dykes that cross cut the tectonic fabric in their host rocks to 1851 15 and 1855 6 ma respectively since the former shows an unequivocal field relationship with respect to the tectonic fabric we establish that penetrative ductile deformation under amphibolite facies metamorphic conditions occurred prior to 1851 5 ma this u pb zircon minimum age for the timing of ductile deformation is supported by a u pb titanite age of 1844 4 ma these data as well as the field relationships at forsmark indicate that an early phase of penetrative deformation and metamorphism affected the svecofennian bedrock in the western part of the fennoscandian shield and was overprinted after 1851 5 ma by spatially more confined deformational events in conjunction with earlier results our data help to establish the presence of tectonic domains with contrasting tectonothermal histories in the western part of the svecofennian orogen c 2006 elsevier b v all rights reserved less

characteristics of cryogenic soils along a latitudinal transect in arctic alaska the morphological chemical and physical properties of arctic tundra soils were examined along a 200 km latitudinal gradient in northern alaska which includes two major physiographic provinces the arctic coastal plain and the arctic foothills annual air temperature and precipitation increase along the gradient from north to south soils on the arctic coastal plain support wet nonacidic tundra vegetation and have high carbonate contents soil on the arctic foothills support moist nonacidic tundra in the northern part and moist acidic tundra in the southern part most arctic tundra soils are characterized by medium texture poor drainage and high organic matter content from north to south along the transect the base saturation of the active layer decreases and exchangeable aluminum increases from north to south most soils have strongly developed cryogenic features including warped and broken horizons ice lenses thin platy structure and organic matter frost churned into the ice rich upper permafrost horizons

brittle tectonothermal evolution in the forsmark area central fennoscandian shield recorded by paragenesis orientation and 40ar 39ar geochronology of fracture minerals in this paper we show how studies of fracture mineral paragenesis their orientation and ar 40 ar 39 geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area samples were selected from nearly 18 km of drill cores from the upper i km of the fennoscandian shield obtained during the site investigation for a repository of spent nuclear fuel in forsmark central sweden four major events of fracturing and or reactivation of fractures associated with fracture mineralisation have been distinguished the first event was characterised by precipitation of epidote quartz and chlorite along preferably sub horizontal and gently dipping fractures or steep wnw ese to nw se fractures precipitation occurred between 1 8 and 1 1 ga possibly during the late stage of the svecokarelian orogeny close to 1 8 1 7 ga the second event is associated with precipitation of hematite stained adularia and albite prehnite laumontite calcite and chlorite preferably along steep ene wsw to nne ssw and nnw sse fractures precipitation occurred around 1107 7 to 1034 3 ma probably due to effects from the sveconorwegian orogeny this event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite quartz pyrite and asphaltite during the palaeozoic the formation fluid emanated from an overlying organic rich sedimentary cover precipitation occurred during reactivation of proterozoic fractures but formation of new fractures is also inferred possibly due to far field effects of the caledonian orogeny or elevated hydrostatic pressure due to its foreland basin the latest event is dominated by clay minerals chlorite and calcite along hydraulically conductive fractures these minerals are prominent along sub horizontal and gently dipping fractures but also occur in sets of steeply dipping fractures it is inferred that the hydraulically conductive fractures are proterozoic structures in which mineral precipitation has occurred during a long period however some of the near surface sub horizontal fractures may be quaternary in age c 2009 elsevier b v all rights reserved less

fracture related hydrothermal alteration of metagranitic rock and associated changes in mineralogy geochemistry and degree of oxidation a case study at forsmark central sweden red staining of rocks due to fluid rock interaction during hydrothermal circulation in fractures is a common feature in crystalline sequences in this study red stained metagranitic rock adjacent to fractures in forsmark central sweden has been studied with emphasis on the mineral reactions and associated element mobility occurring during the alteration the main mineral reactions associated with the hydrothermal alteration are an almost complete saussuritization of plagioclase accompanied by total chloritization of biotite magnetite has been partly replaced by hematite whereas quartz and k feldspar were relatively unaffected by the hydrothermal alteration we show that redistribution of elements on the whole rock scale was very limited and is mainly manifested by enrichment of na2o and volatiles and depletion of cao feo and sio2 in the red stained rock however on the microscale element redistribution was more extensive with both intragranular and intergranular migration of e g ca k na al si fe ba cs rb sr ti and rees the altered rock shows a shift towards higher total oxidation factors but the change is smaller than 1 and the red staining of the rock is due to hematite dissemination rather than a significant oxidation of the rock an increase in the connected porosity is also observed in the altered rock

albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository hydrothermal alteration resulting in albitization and quartz dissolution has been identified in paleoproterozoic metagranites down to 1000 m elevation at forsmark sweden the alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository in general albitization occurs extensively but it is also observed locally adjacent to minor intrusive bodies of amphibolite the altered rocks show a marked decrease in k feldspar and an increase in quartz relative to the unaltered equivalents resulting in an epitonalitic composition plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks it is inferred that albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1 87 1 86 ga the mineralogy of the epitonalites gives rise to an increased thermal conductivity and thereby a positive influence for the design and safety of a deep geological repository for spent nuclear fuel however the increased frequency of low conductive amphibolite in the albitized volumes consistent with the proposed mechanism for alteration gives a negative influence in sharp contrast to the albitization a majority of the occurrences of quartz dissolution which resulted in the formation of episyenite are located along fracture zones quartz dissolution took place between or after 1 8 1 7 ga when the bedrock was able to respond to deformation in a brittle manner most of the vugs left after the removal of quartz are to a variable extent refilled by hydrothermal assemblages including quartz albite k feldspar hematite chlorite and calcite the geometry and spatial distribution of episyenite argue against an extreme fluid rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 degrees c the dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe like volumes the close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and thereby reduce the negative mechanical and hydrogeological aspects for a deep geological repository c 2012 elsevier b v all rights reserved

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

timing of magmatism and migmatization in the 2 0 1 8 ga accretionary svecokarelian orogen south central sweden the palaeoproterozoic 2 0 1 8 ga svecokarelian orogen in central sweden consists of a low pressure predominantly medium grade metamorphic domain central part of bergslagen lithotectonic unit enclosed to the north and south by low pressure migmatite belts two periods of metamorphism 1 87 1 85 and 1 83 1 79 ga are known in the migmatite belts in this study new u th pb ion microprobe data on zircon and monazite from twelve samples of locally migmatized gneisses and felsic intrusive bodies determine both protolith and metamorphic ages in four sample areas north of stockholm inside or immediately adjacent to the medium grade metamorphic domain two orthogneiss samples from the rimbo area yield unusually old protolith ages of 1909 4 and 1908 4 ma while three orthogneisses from the skutskar and forsmark areas yield more typical protolith ages between 1901 3 and 1888 3 ma migmatized paragneiss samples from this and two earlier studies contain a significant detrital component sourced from this 1 9 ga magmatic suite they are interpreted to be deposited contemporaneously with or shortly after this magmatism migmatization of the paragneiss at rimbo was followed by intrusion of leucogranite at 1846 3 ma even in the other sample areas to the north hedesunda tierp skutskar and forsmark metamorphism including migmatization is constrained to the 1 87 1 85 ga interval and penetrative ductile deformation is limited by earlier studies in the forsmark area to 1 87 1 86 ga however apart from a metamorphic monazite age of 1863 1 ma precise ages were not possible to obtain due to the presence of only partially reset recrystallized domains in zircon or highly discordant u rich metamict and altered metamorphic rims migmatization was contemporaneous with magmatic activity at 1 87 1 84 ga in the bergslagen lithotectonic unit involving a mantle derived component and there is a spatial connection between migmatization and this magmatic phase in the hedesunda tierp sample area the close spatial and temporal interplay between ductile deformation magmatism and migmatization the p t metamorphic conditions and the continuation of similar magmatic activity around and after 1 8 ga support solely accretionary rather than combined accretionary and collisional orogenic processes as an explanation for the metamorphism the generally lower metamorphic grade and restricted influence of the younger metamorphic episode at least at the ground surface level distinguishes the central part of the bergslagen lithotectonic unit from the migmatite belts further north and south

reflection seismic investigations in the dannemora area central sweden insights into the geometry of polyphase deformation zones and magnetite skarn deposits the bergslagen region is one of the most ore prospective districts in sweden presented here are results from two nearly 25 km long reflection seismic profiles crossing this region in the dannemora

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

tracing the palaeoredox conditions at forsmark sweden using uranium mineral geochronology abstract u pb isotope systems have been used to constrain the timing of formation alteration and oxidation of u minerals from the meta granitic bedrock at forsmark eastern sweden secondary ion mass spectrometry sims has been used to collect u pb data from uraninite discordant data suggest a 1 8 ga emplacement of uraninite bearing pegmatites and an event of uraninite alteration at 1 6 ga the latter age is contemporaneous with the gothian orogeny in scandinavia which was associated with hydrothermal fluid circulation in the fennoscandian shield ca uranyl silicates haiweeite and uranophane predominately formed 1 3 1 2 ga contemporaneous with the emplacement of the satakunta complex of the central scandinavian dolerite group a palaeozoic group of ca u vi silicates is also present which indicates that the geochemical composition of geologic fluids was heterogeneous throughout the fracture network during this time low pb concentrations in the u vi silicates of several samples are compatible with a recent

improving the large scale modeling of the saltation flux of soil particles in presence of nonerodible elements stress partition between nonerodible obstacles and the underlying particle bed greatly influence erosion by wind in dry areas several studies have already been dedicated to this problem but their results cannot be used in large scale modeling of the saltation flux because they always involve microscale parameters experiments are carried out in a wind tunnel to find a simplified expression of the stress partition coefficient defined by arya marbles of three different diameters are used to constitute nonerodible elements arrays of various densities they are successively laid on three substrates of varying roughness results deduced from wind profile analysis then show that can be expressed simply as a function of the roughness lengths of the overall terrain and of the underlying substrate which can be determined relatively simply the determination of allows us to propose a more accurate calculation of the saltation flux for large scale models of dust production

drag and shear stress partitioning in sparse desert creosote communities most research to characterize the wind erosion susceptibility and the degree of surface roughness required to suppress erosion on erodible surfaces has been empirical however a recently proposed shear velocity ratio model attempts to place shear stress partitioning in an entirely theoretical framework the purpose of this study was to directly measure components of shear stress in a sparsely vegetated environment in order to evaluate the model for the field study new instrumentation was developed to measure drag on a creosote shrub and irwin sensors were modified to measure surface shear stress in the field simultaneous measurements of total shear stress and surface shear stress were taken at four sites of different roughness densities in the eldorado valley nevada results indicate that porous shrubs had greater drag coefficients cd 0 485 than did solid elements sphere cd 0 3 and are more effective at protecting a surface values of the ratio of element to surface drag coefficients we

structural evolution of the accretional continental margin of the paleoproterozoic svecofennian orogen in southern sweden abstract volcanic and sedimentary rocks of the vastervik and valdemarsvik groups along the southern margin of the 1 90 1 85 ga south svecofennian crustal province in sweden have been migmatised and intruded by granitoids and gabbros during extension deformation phase d1 at a depth of at least 10 km peak metamorphic conditions were reached around 1825 ma extension switched to compression before cooling the partially molten middle crust facilitated shortening and thickening by isoclinal and sheath folds on scales from a decimetre to 10 km d2 a pervasive mylonitic s2 foliation developed these structures were refolded into eastward plunging crustal scale upright folds with e se w nw trending axial planes d3 d2 d3 deformation structures are colinear and developed during top to the wnw slip along s2 locally zones of high ductile strain in garnet bearing migmatite assemblages record considerable vertical displacement from 850 to 300 mpa possibly in nappe roots some major d2 sheath folds are embraced by d3 like but nnw trending megafolds d4 apparently resulting from shortening around the former d2 d4 deformations are interpreted to be broadly coeval and related to transpressive crustal shortening against the northern svecofennian continental back stop after cooling to high greenschist facies conditions early structures underwent renewed transpression in north south direction expressed in localized retrogressive shear zones phase d5 much d5 strain was accommodated by the 10 km wide nw se striking right lateral loftahammar linkoping deformation zone lldz operative around 1800 1780 ma regional strain partitioning caused transverse shortening in 15 20 km wide border zones of the lldz later overprints d6 involve narrow subparallel nw se striking and steeply ne dipping low greenschist facies mylonite zones some of which merge into the regional polyphase asbro norrkoping deformation zone d6 was transpressive oblique left lateral ne block up slip suggests a w sw e ne orientation of 1 peak metamorphism and partial melting in the supracrustal rocks was approximately coeval with 1800 1835 ma old subduction related magmatism in the oskarshamn jonkoping belt ojb 100 km to the south west seismic reflection profiling off the baltic coast babel line b suggests northward polarity of subduction beneath the ojb and a back arc environment of the vastervik and valdemarsvik groups between the ojb arc and the margin of the 1850 ma old svecofennian orogen we suggest that d1 d5 deformation was caused by intracontinental back arc extension and subsequent closure of the back arc basin by oblique accretion of the ojb marginal arc onto the northern continent accretion involved northward indentation by mid crustal wedges one of which coincides with and possibly caused the nucleation of the d5 stage lldz 40ar 39ar data from hornblende and white mica identify a prolonged cooling history of the area 1810 1490 ma influenced by the nearby late and postorogenic transscandinavian igneous belt and possibly by largely hidden c 1530 ma old anorogenic rapakivi type intrusions

coal derived rates of atmospheric dust deposition during the permian despite widespread evidence for atmospheric dust deposition prior to the quaternary quantitative rate data remains sparse as dust influences both climate and biological productivity the absence of quantitative dust data limits the comprehensiveness of models of pre quaternary climate and biogeochemical cycles here we propose that inorganic matter contained in coal primarily records atmospheric dust deposition to test this we use the average concentration of inorganic matter in permian coal to map global patterns and deposition rates of atmospheric dust over pangea the dust accumulation rate is calculated assuming permian peat carbon accumulation rates in temperate climates were similar to holocene rates and accounting for the loss of carbon during coalification coal derived rates vary from 0 02 to 25 g m 2 year 1 values that fall within the present day global range a well constrained east west pattern of dust deposition corresponding to expected palaeoclimate gradients extends across gondwana with maximum dust deposition rates occurring close to arid regions a similar pattern is partially defined over the northern hemisphere patterns are consistent with the presence of two large global dust plumes centred on the tropics the spatial patterns of dust deposition were also compared to dust cycle simulations for the permian made with the community climate system model version 3 ccsm3 key differences between the simulations and the coal data are the lack of evidence for an antarctic dust source higher than expected dust deposition over n and s china and greater dust deposition rates over western gondwana this new coal based dust accumulation rate data expands the pre neogene quantitative record of atmospheric dust and can help to inform and validate models of global circulation and biogeochemical cycles over the past 350 myr

a process based model for aeolian sediment transport and spatiotemporal varying sediment availability aeolian sediment transport is influenced by a variety of bed surface properties like moisture shells vegetation and nonerodible elements the bed surface properties influence aeolian sediment transport by changing the sediment transport capacity and or the sediment availability the effect of bed surface properties on the transport capacity and sediment availability is typically incorporated through the velocity threshold this approach appears to be a critical limitation in existing aeolian sediment transport models for simulation of real world cases with spatiotemporal variations in bed surface properties this paper presents a new model approach for multifraction aeolian sediment transport in which sediment availability is simulated rather than parameterized through the velocity threshold the model can cope with arbitrary spatiotemporal configurations of bed surface properties that either limit or enhance the sediment availability or sediment transport capacity the performance of the model is illustrated using four prototype cases the simulation of two wind tunnel experiments from literature and a sensitivity analysis of newly introduced parameters

high frequency sediment transport responses on a vegetated foredune wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and wenglor laser particle counters the foredune had a compound seaward slope with a wave cut scarp about 0 5 m high separating the upper vegetated portion from the lower dune ramp which was bare of vegetation wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction but overall magnitudes were similar over the whole length ten minute average transport intensity correlates strongly with mean wind speed measured at the dune crest and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique but for wind angles 45 from shore perpendicular some sand is transported onto the lower slope copyright 2012 john wiley sons ltd

estimating total horizontal aeolian flux within shrub invaded groundwater dependent meadows using empirical and mechanistic models 1 wind erosion is a significant environmental problem that removes soil resources from sensitive ecosystems and contributes to air pollution in regions of shallow groundwater friable puffy soils are maintained through capillary action surface evaporation of solute rich soil moisture and protection from mobilization by groundwater dependent grasses and shrubs when a reduction in vegetation cover occurs through any disturbance process there is potential for aeolian transport and dust emission we find that as mean gap size between vegetation elements scaled by vegetation height increases total horizontal aeolian sediment flux increases and explains 58 of the variation in total horizontal aeolian sediment flux we also test a probabilistic model of wind erosion based on gap size between vegetation elements scaled by vegetation height the okin model which predicts measured total horizontal aeolian sediment flux more closely than another commonly used model based on the average plant area observed in profile raupach model the threshold shear velocity of bare soil appears to increase as gap size between vegetation elements scaled by vegetation height increases reflecting either surface armoring or reduced interaction between the groundwater capillary zone and surface sediments this work advances understanding of the importance of measuring gap size between vegetation elements scaled by vegetation height for empirically estimating q and for structuring process based models of desert wind erosion in groundwater dependent vegetation

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

modelling palaeosol preservation in aeolian dunes in some of the world s desert and desert marginal areas e g simpson strzelecki australia dunefields preserve well developed palaeosols whereas in other regions with broadly similar climatic regimes and topography e g southwest kalahari the dunes are characterized by very poorly developed internal stratigraphy it has been postulated that dunes such as those in the kalahari may never have had conditions conducive to soil formation or that soils once formed but any evidence of palaeosols has been lost due to reworking this study develops and applies a one dimensional numerical model to simulate dune development soil formation and soil preservation variables in the model allowed experimentation on the influence of sediment supply the time taken for soil to form and the additional resistance to erosion offered by the soil reduced sediment supply plays a vital role in landscape development during periods of initial pedogenesis although re exhumed palaeosols influence sediment supply the effect is minimal although under almost all parameterized conditions more than half and up to 80 90 of those soils initially formed are lost due to reworking evidence of their past formation remains in the large majority of profiles and the dominant factor in controlling the preservation of palaeosols is the frequency of their formation the implication is that where dunes are found without palaeosols the most likely albeit not certain inference is that they have never formed counter intuitively the limited sediment supply means their additional resistance to erosion becomes almost inconsequential to their preservation at least until the unit approaches complete invulnerability short chronostratigraphic hiatuses around palaeosols are normal and although long gaps can occur they are extremely infrequent where such gaps are observed in field studies external forcing factors e g climatic or environmental changes are implied as they are highly unlikely to result from stochastic net preservation copyright 2014 john wiley sons ltd

long term morphotectonic evolution in sweden abstract a morphotectonic interpretation of the relief of sweden is presented based on an analysis of the gross forms of the topography computer made topographic profiles covering 76 375 km have been examined together with contour maps new maps of relief and layers of height have also been used three main aspects considered are the relation between the surface of the precambrian basement and its cover rocks the erosional new surfaces developed in both caledonian basement and reexposed precambrian basement and the evolution of the valley pattern the analysis produced the following results the surface of the precambrian basement is a mosaic of old exhumed surfaces and new surfaces formed after erosion of the cover rocks the exhumed surfaces include 1 a sub jotnian surface mainly below cover rocks in downfaulted positions 2 the sub cambrian peneplain and 3 sub mesozoic etch surfaces block faulting was identified in relation to the different exhumed surfaces after the formation of the caledonides a post caledonian surface was cut across the caledonian basement and the precambrian basement with its cover the subsequent evolution of the swedish part of this surface has been traced through several new surfaces in stepped sequences and in relation to the exhumed surfaces five main denudation intervals are distinguished that result in characteristic relief they are preceded by intervals of orogeny uplift and faulting and followed by subsidence and or deposition of sedimentary strata the valley patterns the distribution of new and exhumed surfaces as well as remmants of cover rocks give some fundamental clues to where and when uplift and subsidence occurred historical geomorphology has mainly been based on theories of erosion cycles the relief of the cratons are difficult to fit exclusively into such a system the importance of long lasting covers and of exhumed surfaces have not been considered enough neither the movements of uplift and subsidence reconstruction of geomorphic events appears to be more important for understanding relief evolution than any model as every phase is unique the methods used in this study are worth testing within other cratons

coversand and pleistocene palaeosols in the landes region southwestern france new sections in the coversand of the landes region southwestern france show at least two main depositional phases corresponding to the upper pleniglacial and the lateglacial which are separated by palaeosols the lower palaeosol a gleyic to histic cryosol overlying a net of sand wedges and dated to ca 23 14c ka bp testifies to a short occurrence of permafrost impeded drainage due to the frozen subsoil is assumed to be the main factor involved in lowered aeolian transport and soil formation pollen analysis indicates a shrub tundra type environment the overlying coversand unit is associated with small transverse ridges or sheet like deposits and corresponds to the maximal extension of the sands upper pleniglacial in age an incipient podzol developed on the dunes under a boreal pine forest and has been dated to 11 5 12 14c ka bp i e to the allerod period this has been buried by the second coversand unit during the younger dryas typified by abundant denivation features and root imprints although preliminary the chronology of sand deposition in the landes region appears thus to be roughly similar to that found for the other european coversands showing that all were the result of similar western european climatic changes i e repeated episodes of increasing aridity related to the upper pleniglacial and the younger dryas episode copyright 2008 john wiley sons ltd

pressure temperature time paths the past decade has been a time of unprecedented improvement in our ability to reconstruct the thermal evolution of orogenic belts like many instances of rapid advancement in science this achievement can be traced to the convergence of disparate research directions the new field of thermochronology the study of the time temperature evolution of rocks derived from the realization by geochronologists that many mineral iso topic systems could be used to determine the time of cooling of a terrain through a series of predictable temperatures e g armstrong 1966 wagner et ai 1977 harrison mcdougali 1980 berger york 1981 petrologists have made great progress in their ability to discern the pressure tem perature history of metamorphic rocks through the improvement of con ventional thermobarometric techniques see bohlen lindsley 1987 and essene 1989 for reviews and the development of important new approaches to relating changes in mineral chemistry to changes in environ mental parameters spear selvcrstonc 1983 st onge 1987 from a theoretical standpoint several geophysical papers in the midto late 1970s and early 1980s explored heat transfer processes in orogenic belts and the role of these in the development and preservation of metamorphic mineral assemblages oxburgh england 1974 bickle et a1 1975 bird et a1 1975 england richardson 1977 toksoz bird 1977 england thompson 1984 among others the integration of geochronologic and petrologic techniques aliows us

ar 40 ar 39 hornblende geochronology from the forsmark area in central sweden constraints on late svecofennian cooling ductile deformation and exhumation at forsmark ca 120 km north of stockholm in central sweden ductile high strain belts with wnw to nw trend anastomose around tectonic lenses with an inferred lower degree of ductile strain previous studies of ductile deformation zones with wnw to nw trend elsewhere in the western part of the svecofennian orogen in central sweden have yielded estimates for the timing of at least one phase of discrete ductile deformation that fall in the time interval 1 82 1 78 ga most of these ages were determined by the u pb dating of titanite and for this reason provide no information on the thermal evolution in this paper we make use of ar 40 ar 39 hornblende geochronology to address late svecofennian cooling ductile deformation and exhumation the data demonstrate the presence of three ar 40 ar 39 hornblende age generations all ages have been adjusted to take account of ca 1 systematic bias between ar 40 ar 39 and u pb ages recently reported in the literature the oldest age ca 1 87 ga and the intermediate age generation 1 85 1 84 ga are spatially restricted to the tectonic lenses by contrast the youngest age generation 1 83 1 81 ga occurs both within the tectonic lenses and the enveloping high strain belts one explanation for the structurally controlled age distribution involves regional cooling beneath the closure temperature for argon isotopic mobility around or above 500 degrees c by 1 84 ga as represented in the oldest and intermediate age generations followed by resetting of the argon isotope system in hornblende between 1 83 and 1 81 ga as represented in the youngest age generation this resetting occurred in response to retrograde lower amphibolite to upper greenschist facies deformation along discrete high strain zones within the broader high strain belts and was associated with regional exhumation an alternative explanation involves no resetting of the ages instead it is suggested that a period of slow cooling of hornblendes with slightly different closure temperatures from ca 1 87 to 1 82 ga may have caused the age variation observed within the tectonic lenses whereas locally maintained higher temperatures due to activity along the discrete high strain zones can explain the consistently younger ages in the broad enveloping high strain belts in this explanation an increase in cooling rate in response to regional exhumation finally closed the argon isotope system in hornblende throughout the area at 1 83 1 81 ga it is suggested that the regional exhumation at 1 83 1 81 ga which is included in both explanations is related to far field effects of the deformation that ended an accretionary tectonic cycle in adjacent tectonic domains c 2008 elsevier b v all rights reserved less

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

field measurement and analysis of climatic factors affecting dune mobility near grand falls on the navajo nation southwestern united states abstract aeolian sand covers extensive areas of the navajo nation in the southwestern united states much of this sand is currently stabilized by vegetation although many drier parts of these native lands also have active and partly active dunes current prolonged drought conditions that started in the mid 1990s are producing significant changes in dune mobility reactivation of regional aeolian deposits due to drought or increasing aridity from rising temperatures resulting from climate change could have serious consequences for human and animal populations agriculture grazing and infrastructure to understand and document the current and future potential for mobility seasonally repeated surveys were used to track the location of multiple active barchan dunes by utilizing real time kinematic gps field surveys and simultaneously collecting in situ meteorological data it is possible to examine climatic parameters and seasonal variations that affect dune mobility and their relative influences through analysis of the recorded data we examined the fit of various climate parameters and demonstrate that under the current prolonged drought wind power is the dominant factor controlling dune mobility

40ar 39ar geochronology and p t t paths from the cordillera darwin metamorphic complex tierra del fuego chile ar 39ar data collected from hornblende muscovite biotite and k feldspar constrain the p t t history of the cordillera darwin metamorphic complex tierra del fuego chile these data show two periods of rapid cooling the first between c 500 and c 325 c at rates 225 c ma and the second between c 250 and c 200 c for high t cooling 40ar 39ar ages are spatially disparate and depend on metamorphic grade rocks that record deeper and hotter peak metamorphic conditions have younger 40ar 39ar ages sillimanite and kyanite grade rocks in the south central part of the complex cooled latest 40ar 39ar hbl 73 77 ma ms 67 70 ma bt 68 ma and oldest kfs 65 ma thermobarometry and p t path studies of these rocks indicate that maximum burial of 26 30 km at 575 625 c may have been followed by as much as 10 km of exhumation with heating of 25 50 c staurolite grade rocks have intermediate 40ar 39ar ages hbl 84 86 ma ms 71 ma bt 72 75 ma and oldest kfs 80 ma thermobarometry on these rocks indicates maximum burial of 19 26 km at temperatures of 550 580 c garnet grade rocks have the oldest ages ms 72 ma and oldest kfs 91 ma peak p t conditions were 525 550 c and 5 7 kbar regional metamorphic temperatures for greenschist facies rocks south of the beagle channel did not exceed c 300 325 c from 110ma to the present although the rocks are only 2 km from kyanite bearing rocks to the north one dimensional thermal models allow limits to be placed on exhumation rates assuming a stable geothermal gradient of 20 25 c km i the maximum exhumation rate for the st grade rocks is c 2 5 mm yr i whereas the minimum exhumation rate for the ky sil grade rocks is c 1 0 mm yr uniform exhumation rates cannot explain the disparity in cooling histories for rocks at different grades and so early differential exhumation is inferred to have occurred petrological and geochronological comparisons with other metamorphic complexes suggest that single exhumation events typically remove less than c 20 km of overburden this behaviour can be explained in terms of a continental deformation model in which brittle extensional faults in the upper crust are rooted to shallowly dipping ductile shear zones or regions of homogeneous thinning at mid to deep crustal levels the p t r data from cordillera darwin 1 are best explained by a wedge extrusion model in which extensional exhumation in the southern rear of the complex was coeval with thrusting in the north along the margin of the complex and into the magallanes sedimentary basin 2 suggest that differential exhumation occurred initially with st grade rocks exhuming faster than ky sil grade rocks and 3 show variations in cooling rate through time that correlate both with local deformation events and with changes in plate motions and interactions

pleistocene periglacial eolian deposits in southwestern alaska sedimentary facies and depositional processes abstract pleistocene periglacial eolian sediments are widespread in the nushagak holitna and upper kuskokwim lowlands of southwestern alaska these sediments comprise mainly sand sheet deposits and sand loess intergrades with subordinate sand dune deposits and loess sand sheet deposits range from 1 sharply defined parallel low angle laminae formed by migrating wind ripples to 2 irregular subhorizontal strata which reflect migration of poorly segregated wind ripples accumulation on a sparsely vegetated surface adhesion on a quasi planar bed and or niveo eolian deposition sand loess intergrades represent alternating bed load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems the dominance of sand sheet deposits over deposits of well formed dunes in the pleistocene eolian record of southwestern alaska reflects the limited availability of loose dry sand in this former periglacial environment immobilization of sand after deposition as low relief sheets resulted from a seasonally variable combination of ice cementation sparse vegetation high water tables and snow cover

coupled topographic and vegetation patterns in coastal dunes remote sensing observations and ecomorphodynamic implications vegetation plays a key role in stabilizing coastal dunes and barrier islands by mediating sand transport deposition and erosion dune topography in turn affects vegetation growth by determining local environmental conditions however our understanding of vegetation and dune topography as coupled and spatially extensive dynamical systems is limited here we develop and use remote sensing analyses to quantitatively characterize coastal dune ecotopographic patterns by simultaneously identifying the spatial distribution of topographic elevation and vegetation biomass lidar derived leaf area index and hyperspectral derived normalized difference vegetation index patterns yield vegetation distributions at the whole system scale which are in agreement with each other and with field observations lidar derived concurrent quantifications of biomass and topography show that plants more favorably develop on the landward side of the foredune crest and that the foredune crestline marks the position of an ecotone which is interpreted as the result of a sheltering effect sharply changing local environmental conditions we conclude that the position of the foredune crestline is a chief ecomorphodynamic feature resulting from the two way interaction between vegetation and topography

the origin of horizontal alternating bedding in weichselian aeolian sands in northwestern europe abstract periglacial acolian sands of weichselian age are widespread in the lowlands of western and central europe one facies of this sediment type corresponding to the coversand sensu stricto is characterised by a wavy parallel bedding and a generally horizontal position of the strata since this layering results from an alternation of finer and coarser grained beds horizontal alternating bedding is the appropriate designation for it by a detailed analysis of representative lacquer peels eight characteristic stratification types could be distinguished these units are the smallest fundamental building blocks constituting the sediment under consideration an idealised annual cycle of sedimentation is proposed in summer light and variable winds carry silt in suspension to the site of deposition whilst the sandy saltation load is left behind in a throughput zone farther upwind upon settling the fines adhere to the surface which is wet or damp due to the thawing of the seasonally frozen ground in winter wind strength is generally greater so that deposition of sand prevails in the area whereas the fine grained suspension load settles downwind deposition by snow free winds results in the accretion of patches of well sorted sand snow flurries on the other hand produce niveo aeolian strata of generally more poorly sorted sand in the cycle it is implied that 1 the aeolian sedimentation basin must have been large and uniform enough to permit areal separation of sand and loess like material and 2 a seasonal shift in the centres of sand and silt deposition was inherent to the atmospheric pressure system of the formative period the exposed part of the northern and eastern north sea floor as it existed around the middle weichselian glacial climax assumedly was the principal source area for the deposits the relationships between the periglacial aeolian sands with horizontal alternating bedding loess and their integrades as described from the belgian lowlands and niedersachsen can be interpreted in the context of the proposed depositional cycle

gently dipping fracture zones in paleoproterozoic metagranite sweden evidence from reflection seismic and cored borehole data and implications for the disposal of nuclear waste 1 the svecokarelian orogen in the coastal area north of stockholm central sweden is characterized by a complex deformation belt in this belt bedrock domains strike wnw nw dip steeply and are affected by high ductile strain these domains anastomose around tectonic lenses that are up to a few tens of kilometers in length and are a few kilometers wide the bedrock within the lenses is folded and in general affected by lower ductile strain site investigations for the disposal of highly radioactive nuclear waste are presently in progress within one of these lenses approximately 16 km of high resolution 10 m source and receiver spacing 100 channels seismic data were acquired in 2002 along five separate profiles 2 to 5 km in length within this lens in the southeast reflection orientations are well determined where profiles cross one another here there is a nearly one to one correlation of distinct reflections on the seismic sections with hydraulically conductive fracture zones in cored boreholes indicating that these fracture zones control the reflectivity however smaller lenses of amphibolite within the fracture zones may enhance the reflectivity the reflections dip gently to the sse and se and the zones in the boreholes are dominated by fractures that show the same dip direction or are subhorizontal a working hypothesis for the gently dipping fracture zones suggests that these structures formed as minor thrust faults during the later stages of the svecokarelian orogeny mineral fillings and coatings along fractures in these zones indicate later reactivation the current stress field a high intensity of fractures in the zones at a high angle to 3 high in situ stresses in the bedrock and rapid glacial unloading with the development of high differential stresses may explain the large volume of groundwater in these zones the reflection seismic data in combination with the verifying work presented in the cored borehole data have steered the subsequent focus in geoscientific studies to the northwestern part of the candidate area

the structure and genesis of weichselian to early hologene aeolian sand sheets in western europe abstract weischselian to early holocene aeolian sands are widespread in the lowlands of western europe to a large extent these deposits occur in the form of sheet like coversands with slipfaced dunes being much rarer whereas the latter type of landform corresponds to a single facies with dune foreset cross bedding aeolian facies 1 two structurally different facies are distinguishable in the sand sheets this paper concentrates on the two sand sheet facies which are referred to as aeolian facies 2 and aeolian facies 3 data on these two types are based on 1 a survey of existing literature and 2 a detailed analysis of lacquer peels and larger scale exposures in england the netherlands and the federal republic of germany aeolian facies 2 is defined by the spatial position of its beds which may be either horizontal inclined or oppositely dipping in the case of structures formed by fluctuating winds horizontal bedding is by far the most common type inclined bedding is related either to small isolated dome dunes or to scoop shaped deflation surfaces the structures resulting from fluctuating winds are rare and do not represent an inherently large measure of directional variability of the wind regime the internal structure of the beds is dominated by aeolian planebed lamination with or without concordantly infilled wind scours degradation of this stratification type because of interference by coarse particles is discussed aeolian facies 3 is uniquely typified by the alternation of coarser and finer grained horizontal thin beds that are either wavy or even in shape depositional models of facies 3 are given at both the local and regional scales in both cases the coarser grained layers result from tractional deposition of saltating and creeping grains whilst the finer grained strata were laid down by settling from suspension periodic changes in surface wind speed the presence of a damp depositional surface and the availability of both sand and silt in the source area are necessary conditions for the working of the models the large scale model is associated with specific environmental conditions of the weichselian upper pleniglacial the local scale model accounts for the fact that facies 3 is also found in units of weichselian late glacial or early holocene age the regional scale model involves stepwise tractional transport over long distances so that grains of distant provenance were mixed with material from sources nearer to the receiving site this process was an important control on the mineralogical composition of the resultant deposits the prevalence of aeolian planebed lamination in both facies 2 and the coarser grained layers of facies 3 is attributed to the interaction of three factors viz the rarity of topographic barriers the sparseness of vegetation cover and a high ratio between wind energy and sand availability during the processes of transport and deposition in the lowlands of europe sand sheets are gradually replaced in an easterly direction by coeval wind dunes the possible causes of this phenomenon are considered

land degradation in drylands interactions among hydrologic aeolian erosion and vegetation dynamics article i nfo land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality climate change shifts in vegetation composition accelerated soil erosion processes and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification even though the role of hydrologic aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized most studies have concentrated only on the role of one or two of these components and not on the interactions among all three drawing on relevant published studies here we review recent contributions to the study of biotic and abiotic drivers of dryland degradation and we propose a more holistic perspective of the interactions between wind and water erosion processes in dryland systems how these processes affect vegetation patterns and how vegetation patterns in turn affect these processes notably changing climate and land use have resulted in rapid vegetation shifts which alter the rates and patterns of soil erosion in dryland systems with the predicted increase in aridity and an increase in the frequency of droughts in drylands around the world there could be an increasing dominance of abiotic controls of land degradation in particular hydrologic and aeolian soil erosion processes further changes in climate may alter the relative importance of wind versus water erosion in dryland ecosystems therefore acquiring a more holistic perspective of the interactions among hydrologic aeolian erosion and vegetation dynamic processes is fundamental to quantifying and modeling land degradation processes in drylands in changing climate disturbance regimes and management scenarios

review of the deterministic modelling of deformation zones and fracture domains at the site proposed for a spent nuclear fuel repository sweden and consequences of structural anisotropy abstract this paper presents a review of the data sets and methodologies used to construct deterministic models for the spatial distribution of deformation zones and intervening fracture domains in 3 d space at forsmark fennoscandian shield sweden these models formed part of the investigations to characterize this site recently proposed as a repository for the storage of spent nuclear fuel in sweden the pronounced spatial variability in the distribution of bedrock structures formed under ductile lower amphibolite or greenschist facies and subsequently brittle conditions was controlled by two factors firstly the multiphase reactivation around and after 1 8 ga of older ductile structures with a strong anisotropy formed under higher temperature conditions at 1 87 1 86 ga and secondly by the release of rock stresses in connection with loading and unloading cycles after 1 6 ga the spatial variability in bedrock structures is accompanied by a significant heterogeneity in the hydraulic flow properties the most transmissive fractures being sub horizontal or gently dipping although the bedrock structures at forsmark are ancient features the present day aperture of fractures and their hydraulic tranmissivity are inferred to be influenced by the current stress state it is apparent that the aperture of fractures can change throughout geological time as the stress field evolves for this reason the assessment of the long term up to 100 000 years safety of a site for the storage of spent nuclear fuel in crystalline bedrock requires an evaluation of all fractures at the site not only the currently open fractures that are connected and conductive to groundwater flow this study also highlights the need for an integration of structural data from the ground surface and boreholes with magnetic field and seismic reflection data with high spatial resolution during the characterization of structures at a possible site for the storage of spent nuclear fuel in crystalline bedrock