thermochronology of the south cyclades shear zone ios greece effects of ductile shear in the argon partial retention zone micas and potassium feldspars from the south cyclades shear zone ios cyclades greece yield varied and complex 40ar 39ar apparent age spectra a correlation exists between 40ar 39ar apparent ages and the relative timing of different episodes of recrystallization and grain growth as indicated by fabric and microstructural analysis the 40ar 39ar apparent age spectra record the effects of variation in the degree of recrystallization and grain growth and partial to complete resetting of argon systematics in potassium bearing minerals during hercynian m0 alpine m1 and late oligocene early miocene m2 metamorphism deformation was strongly partitioned within the shear zone and this led to localized recrystallization and heterogeneous resetting of argon systematics within preexisting minerals modeling suggests the oligo miocene thermal events were of insufficient magnitude and or duration to completely reset the isotopic systematics in these samples our data lead to the concept of the argon partial retention and resetting zone prz defined as that portion of the crust where temperatures are insufficient to completely reset argon systematics within preexisting potassium bearing minerals within the prz some radiogenic argon in preexisting potassium bearing minerals will be outgassed and only partially retained tectonic exhumation of the prz involves movement on crustal scale ductile shear zones accompanied by strongly partitioned deformation and localized recrystallization recrystallization leads to resetting of argon systematics and thus will result in heterogeneous 40ar 39ar age distributions within these ductile shear zones e g in the south cyclades shear zone

topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus abstract the impact of signal crayfish pacifastacus leniusculus on the topography and fabric of six narrowly graded gravel substrates was investigated using repeat laser scanning of sediment surfaces in still water aquaria digital elevation models dems of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods the impact on the substrate was quantified by establishing topographic and volumetric changes using dems of difference dod the presence of an individual medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 giving a sediment displacement of 1 7 kg m 2 d 1 the majority 78 of this volume change was associated with small scale 1 median grain diameter movements of surface grains this fabric adjustment altered grain orientations and friction angles crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains crayfish were able to move material up to 38 mm in diameter that had a submerged weight six times that of the individuals used in this study by modifying the arrangement of grains on the surface of fluvial substrates signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material the results of this study suggest that signal crayfish an internationally widespread invasive species may have substantial impacts on the physical environment of streams and rivers as well as on local benthic ecological communities

a transferable method for the automated grain sizing of river gravels 1 the spatial and temporal resolution of surface grain size characterization is constrained by the limitations of traditional measurement techniques in this paper we present an extremely rapid image processing based procedure for the measurement of exposed fluvial gravels and other coarse grained sediments defining the steps required to minimize the errors in the derived grain size distribution this procedure differs significantly from those used previously it is based around a robust object detection algorithm that produces excellent results on images exhibiting a wide range of sedimentary conditions crucially without any user intervention or site specific parameterization the procedure is tested using a data set comprising 39 images from three rivers with contrasting grain lithology shape roundness and packing configuration and representing a very wide range of textures it is shown to perform more consistently than the best existing automated method achieving a precision equivalent to that obtainable by wolman sampling but taking between one sixth and one twentieth of the time the error in area by number grain size distribution percentiles is typically less than 0 05

effective discharge in small formerly glaciated mountain streams of british columbia limitations and implications episodic sediment supply past glaciation and slow responses to disturbance make small mountain streams transitional alluvial regimes in which nonequilibrium conditions are common bed load effective discharge in these streams is on average a low magnitude high frequency event but is highly variable using a two phase sediment transport model and long term discharge records we distinguish between three types of streams streams in which gravel sediment 8 mm diameter moves frequently and effective discharge occurs during gravel transport frequently mobile gravel fmg streams in which gravel moves infrequently but effective discharge nonetheless occurs during gravel transport infrequently mobile gravel img and streams in which sand sediment 8 mm diameter moves over largely immobile gravel and effective discharge occurs frequently during sand phase transport sand over immobile gravel sg using only effective discharge frequency or magnitude to characterize a stream without information on mobile sediment type is insufficient to distinguish between fmg and sg streams only the img streams have large rare effective discharges that approximate the bankfull discharge in fmg and sg streams the effective discharge is much more frequent and smaller than the bankfull only in the img streams does the effective discharge approximate a channel forming discharge in fmg and sg streams the effective discharge bears little relation to the size or dimensions of the channel and is at best a channel maintaining flow at worst it is geomorphically meaningless effective discharge should not therefore be used in isolation as a proxy for channel forming discharge for mountain stream channel design or management

sampling surficial fluvial gravels the precision of size distribution percentile sediments abstract grid by number wolman sampling is commonly used to characterize the texture of surficial fluvial sediments assessments of sampling precision have concentrated on the median grain size but adequate representation of other grain size percentiles is paramount in a number of sedimentological contexts the field effort required to construct percentile sampling distributions by replication is prohibitive and the absence of any general size distribution for fluvial sediments precludes theoretical calculation of percentile standard errors bootstrapping is used in this paper to determine percentile standard errors for large samples from two gravel bar surfaces the improvement of percentile precision with sample size follows the theoretical expectation hence improvement in percentile recision is achieved only at the expense of much greater sampling effort once sample sizes reach about 400 stones however absolute percentile standard errors differ significantly from theoretically derived values of particular interest is the stability of coarser percentile estimates in coarse skewed distributions d95 estimates may be as precise as d50 estimates for a given sample size the sensitivity of the precision of estimated percentiles to distribution shape is examined using synthetic skewed and bimodal grain size distributions the absolute precision of percentile estimates is shown to vary with the grain size distribution of a particular sediment our field results provide a reference for further work

grain size and topographical differences between static and mobile armour layers a series of laboratory flume experiments under conditions of sediment starvation zero sediment feeding and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers the experiments were carried out in an 8 m long flume using a bimodal grain size mixture d50 6 2 mm and a range of shear stresses ranging from 4 0 to 8 6 n m 2 the results confirm that a static armour layer is coarser than a mobile one and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength an analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges the topography of mobile armour layers created by rising discharges differed they exhibited a greater roughness length scale and were less organized despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation also the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges these differences were mainly due to the transport of the coarser fraction of bed sediments which diminished to zero over the static armour because of being hidden within the bed whereas in the mobile armour the coarser particles protruded into the flow and were actively transported increasing the vertical roughness length scale overall the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness detailed elevation models of exposed surfaces of gravel bed rivers are required to provide critical insight on the sediment availability and sedimentation processes copyright 2011 john wiley sons ltd

the geological significance of 40ar 39ar and rb sr white mica ages from syros and sifnos greece a record of continuous re crystallization during exhumation the attic cycladic crystalline belt in the central aegean region records a complex structural and metamorphic evolution that documents cenozoic subduction zone processes and exhumation a prerequisite to develop an improved tectono metamorphic understanding of this area is dating of distinct p t d stages to evaluate the geological significance of phengite ages of variably overprinted rocks 40ar 39ar and rb sr analyses were undertaken on transitional blueschist greenschist and greenschist facies samples from the islands of syros and sifnos white mica geochronology indicates a large age variability 40ar 39ar 41 27 ma rb sr 34 20 ma petrologically similar samples have either experienced greenschist facies overprinting at different times or variations in ages record variable degrees of greenschist facies retrogression and incomplete resetting of isotopic systematics the 40ar 39ar and rb sr data for metamorphic rocks from both islands record only minor localized evidence for miocene ages c 21 ma that are well documented elsewhere in the cyclades and interpreted to result from retrogression of high pressure mineral assemblages during lower pressure metamorphism field and textural evidence suggests that heterogeneous overprinting may be due to a lack of permeability and or limited availability of fluids in some bulk compositions and that retrogression was more or less parallel to lithological layering and or foliation as a result of possibly deformation enhanced channelized fluid ingress published and new 40ar 39ar and rb sr data for both islands indicate apparent age variations that can be broadly linked to mineral assemblages documenting transitional blueschist to greenschist and or greenschist facies metamorphism the data do not record the timing of peak hp metamorphism but may accurately record continuous partial resetting of isotopic systematics and or re crystallization of white mica during exhumation and greenschist facies retrogression the form of 40ar 39ar phengite age spectra are complex with the lowest temperature steps yielding middle to late miocene ages the youngest rb sr ages suggest maximum ages of 20 6 0 8 ma syros and 22 5 0 6 ma sifnos for the timing of greenschist facies overprinting the results of this study further accentuate the challenges of interpreting isotopic data for white mica from polymetamorphic terranes particularly when mixing of populations and or incomplete resetting of isotopic systematics occurs during exhumation these data capture the full range of isotopic age variations in retrogressed hp rocks documented in previous isotopic studies and can be interpreted in terms of the geodynamic evolution of the aegean

precise eclogitization ages deduced from rb sr mineral systematics the maksyutov complex southern urals russia abstract the maksyutov complex southern urals russia is a well preserved example of subduction related high pressure metamorphism one of its two litho tectonic units consists of rocks that experienced eclogite facies conditions published 40ar 39ar data on phengite u pb data on rutile and sm nd mineral data define a cluster of ages around 370 to 380 ma nevertheless no consensus exists as to the detailed interpretation of data and the exact age of eclogitization we present new high precision internal mineral rb sr isochrons for eclogite facies metabasites felsic eclogites and eclogite facies quartz veins nine isochrons mainly controlled by omphacite and white mica phases give concordant ages with an average value of 375 2 ma 2 microtextural features such as prograde growth zoning in eclogite facies phases suggest that the assemblages dated formed at a stage of prograde metamorphism sr isotopic equilibria among eclogite facies phases and among eclogite facies fluid veins and the host rocks indicate that our ages reflect crystallization ages related to the prograde metamorphic probably fluid mediated eclogitization reactions this interpretation is reinforced by data from fluid precipitated quartzitic eclogites whose modal composition together with intergrowth relationships conclusively imply closed system behavior after crystallization the possible occurrence of a pre 375 ma event of ultra high pressure metamorphism uhpm in the maksyutov complex is disproved by isotope systematics microtextures and mineral zoning patterns

a hybrid 3 d electromagnetic method for induction detection of hydraulic fractures through a tilted cased borehole in planar stratified media as one of the most important nondestructive characterization techniques electromagnetic em methods can be used in the subsurface fracture detection especially for hydraulic fracture evaluation in unconventional petroleum exploration and development the multiscale nature of long but extremely thin 3 d fractures is difficult for conventional em modeling methods such as the finite element method fem in numerical simulation the problem becomes even more challenging when the effects of tilted borehole casing and planar stratified media need to be considered so far modeling a tilted borehole in layered media is still a major challenge for conventional methods in this paper we present the hybrid numerical mode matching method with the stabilized biconjugate gradient fast fourier transform method as the forward modeling algorithm that can efficiently model 3 d fractures in planar stratified media with a cased borehole environment numerical results validate the accuracy of the hybrid forward method and show orders of magnitude higher efficiency of this forward solver than the fem

casing effects in the sea to borehole electromagnetic method the sea to borehole controlled source electromagnetic csem method has the potential of becoming a useful new exploration and monitoring technique modeling shows that the electromagnetic fields at reservoir depths can be 1 2 orders of magnitude larger than those on the seabed thus opening up the possibility to see deeper or detect and monitor smaller targets in the case of measurements inside metal casing the use of reciprocity to interchange the source and receiver allows the casing conductortobeconsideredasanantenna thisantennaisexcited by a source inside the casing which induces a current flowing along the casing conductor based on the current distribution a casing dipole moment and an equivalent length were derived for thetransversemagnetictmmode inthefrequencyrangeofinterest 0 1 10 hz the increase in field strength resulting from sea to borehole measurements is not lost to the casing attenuation for either the tm or the transverse electric te mode the ratio of the dipole moment of the casing antenna to that of the sourcecurrentcanbeconsideredasthecasingattenuationeffect thisratioisnotfarfromunityforfrequenciessmallerthan1 hz but it decreases rapidly with frequency the equivalent length of the casing antenna can be of the order of a few hundred meters as a consequence the field distribution changes significantly in the presence of casing and the vertical resolution of tm measurementsisdegraded thehorizontalresolutionisnotdegraded significantly measurementofthetmmodehastheadvantageof being sensitive to thin resistive targets and being less affected by sea air interactions in shallow water the te mode measurement having a localized casing effect contributes valuable informationaboutthebackgroundresistivity

estimating the settling velocity of bioclastic sediment using common grain size analysis techniques most techniques for estimating settling velocities of natural particles have been developed primarily for siliciclastic sediments therefore to understand how these techniques apply to bioclastic environments measured settling velocities ws of bioclastic sedimentary deposits sampled from a nearshore fringing reef in western australia were compared with settling velocities calculated using results from several common grain size analysis techniques sieve laser diffraction and image analysis and established models the effects of sediment density and shape were also examined by using a range of density values and three different models of ws sediment density was found to have a significant effect on calculated ws causing a range in normalized root mean square error of up to 28 depending upon settling velocity model and grain size method accounting for particle shape improved errors in predicted ws by 3 to 6 and removed any velocity dependent bias which is particularly important for the fastest settling fractions when shape was accounted for and measured density was used normalized root mean square errors were 4 10 and 18 for laser diffraction sieve and image analysis respectively the results of this study show that established models of ws that account for particle shape can be used to estimate settling velocity of irregularly shaped sand sized bioclastic sediments from sieve laser diffraction or image analysis derived measures of grain size with a limited amount of error collectively these findings will allow for grain size data measured with different methods to be accurately converted to settling velocity for comparison this will facilitate greater understanding of the hydraulic properties of bioclastic sediment which can help to increase our general knowledge of sediment dynamics in these environments this article is protected by copyright all rights reserved

controls on downstream variation in surficial sediment size of an outwash braidplain developed under high arctic conditions kaffioyra svalbard abstract the changes in morphology and surficial sediments of an outwash braidplain developed under high arctic conditions are closely related to geomorphic processes tectonic conditions and climate variations and are affected by the existence of permafrost these factors control the changes in river channel slope their morphology and active braidplain width which influence the downstream variation in grain size of outwash surficial sediments interdependence between these parameters has not previously been considered in relation to the spatial distribution of surficial sediments of outwash braidplain developed in the forefield of a retreating subpolar glacier in this study controls affecting the surficial lithology of the waldemar river outwash nw spitsbergen svalbard were recognised and indicated multiple correlations between the downstream changes in sediment texture the geomorphometry of distributary channels and outwash surface slope due to this the techniques of multivariate regression modelling artificial neural network and multivariate adaptive regression splines were used results show that observed relations between the sedimentary and morphological features indicate the existence of thresholds for downstream variation in bed material size which are not constant moreover the processes of sediment transport in an outwash braidplain are strictly related to shields stress which is proportional to changes in braidplain slope median grain diameter and sediment sorting in the proximal and middle zones of the outwash but is inversely proportional to median grain diameter in the distal zone contrary to shields bed material threshold entrainment model the results of this study will help understand outwash fan and plain evolution in paraglacial landscapes under conditions of changeable rate and source of sediment supply and transport capacity

morphological effects of different channel forming discharges in a gravel bed river the study analyses the morphological response of a gravel bed river to discharges of different magnitude from moderate events that occur several times a year to a 12 year flood and so defines the range of formative discharges for single morphological units channels bars islands and a range of magnitude of morphological activity from the threshold discharges for gravel transport and minor bar modification up to flows causing major morphological changes the study was conducted on the tagliamento river a large gravel bed river in north eastern italy using two different methods analysis of aerial photographs and field observation of painted gravel particles the available photographs five flights from august 1997 to november 2002 and the two commissioned flights june 2006 and april 2007 do not define periods with a single flood event but the intervals are short enough 11 to 22 months to have a limited number of flood events in each case the fieldwork which involved cross section survey grain size analysis and observation of painted sediments complemented the aerial surveys by allowing analysis of channel response to single flood events substantial morphological changes e g bank erosion of several tens of metres up to more than 100 m associated with flood events with a recurrence interval between 1 1 year and 12 years have been documented multiple forming discharges were defined based on the activity of different morphological units discharges equal to 20 50 of the bankfull discharge are formative for the channels whereas the bankfull discharge 1 1 year flood in this case of the tagliamento river is formative for low bars larger floods but still relatively frequent with a recurrence interval less than five years are required for full gravel transport on high bars and significant morphological changes of islands copyright 2009 john wiley sons ltd

40ar loss in experimentally deformed muscovite and biotite with implications for 40ar 39ar geochronology of naturally deformed rocks abstract the effects of deformation on radiogenic argon 40ar retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite cylindrical cores 15 mm in length and 6 25 mm in diameter were drilled from granite collected from the south armorican massif in northwestern france loaded into gold capsules and weld sealed in the presence of excess water the samples were deformed at a pressure of 10 kb and a temperature of 600 c over a period 29 of hours within a solid medium assembly in a griggs type triaxial hydraulic deformation apparatus overall shortening in the experiments was approximately 10 transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking cracking and grain segmentation of the micas infrared ir laser co2 heating of individual 1 5 2 5 mm diameter grains of muscovite and biotite separated from the undeformed granite yield well defined 40ar 39ar plateau ages of 311 2 ma 2 identical experiments on single grains separated from the experimentally deformed granite yield results indicating 40ar loss of 0 35 in muscovite and 2 3 40ar loss in biotite intragrain in situ ultraviolet uv laser ablation 40ar 39ar ages 4 10 1 of deformed muscovites range from 309 13 to 264 7 ma consistent with 0 16 40ar loss relative to the undeformed muscovite the in situ uv laser ablation 40ar 39ar ages of deformed biotite vary from 301 to 217 ma consistent with up to 32 40ar loss no spatial correlation is observed between in situ 40ar 39ar age and position within individual grains using available argon diffusion data for muscovite the observed 40ar loss in the experimentally treated muscovite can be utilized to predict average 40ar diffusion dimensions maximum 40ar 39ar ages obtained by uv laser ablation overlap those of the undeformed muscovite indicating argon loss of

the effect of hydrographs on bed load transport and bed sediment spatial arrangement 1 field measurements of sediment transport in gravel bed rivers often reveal hysteretic effects due to differences in sediment availability between the rising and falling limbs of a flood hydrograph however only a small number of flume studies have analyzed the dynamics of sediment transport during hydrographs three types of stepped hydrographs with contrasting durations and magnitudes are simulated here under sediment recirculation conditions bed load transport rate and grain size have been measured continuously the dynamic behavior of the surface armor layer has been explored by analyzing digital photographs and laser scanner surveys of the bed surface taken during hydrographs the results indicate that sediment transport during the falling limb was lower than during the rising limb in all of the three types of hydrographs this reduction is more evident for the low magnitude hydrographs the grain size of the bed remained virtually constant throughout the hydrographs but the grain size of transported sediments exhibited a counterclockwise hysteresis also a significant increase in the reference shear stress for sediment entrainment was measured during the falling limb of hydrographs additionally a detailed analysis of partial transport dynamics of the bed surface sediments reveals a reduction in sediment mobility during the falling limb of the hydrographs the difference in sediment entrainment and transport before and after the peak of the hydrographs appears to be caused by a change in the organization of the surface sediments an analysis of detailed laser scan bed surveys reveals a phase of bed restructuring lower vertical roughness clast rearrangement during the falling limb of hydrographs consequently changes in the degree of organization and complexity of the bed surface are likely the cause of the reduced mobility of sediments and thus of the reduced sediment transport rate during the falling limb of the hydrographs

the bed morphology of upland single thread channels in semi arid environments evidence of repeating bedforms and their wider implications for gravel bed rivers single thread gravel bed streams of moderate slope in the northern negev are characterized by three channel units bars exhibit steeper than average slopes and poorly sorted mixtures of small medium cobbles and coarse very coarse pebbles flats are associated with more gentle slopes and well sorted medium fine pebbles and granules and transitional units have intermediate slopes and grain size in general all three units are planar span the full channel width and have well defined boundaries bars and flats are more common than the transitional units and alternate downstream for distances of several hundred metres forming sequences that are reminiscent of the riffle pool structure commonly observed in humid temperate gravel bed rivers a notable contrast is the absence of significant bed relief bars lack crests and flats lack depressions the relative lack of bed relief in bar flat sequences is attributed to the high rate of sediment supply from the sparsely vegetated hillslopes which promotes the infilling of depressions and to the erosion of crests under conditions of intense transport this reduction of bed relief lowers channel roughness which in turn increases flow velocity and therefore the ability of the channel to transmit the large sediment loads it receives although our analyses pertain to a semi arid river system the results have wider implications for understanding the adjustment of channel bedform to high sediment loads in other fluvial environments copyright 2012 john wiley sons ltd

mapping sub pixel fluvial grain sizes with hyperspatial imagery this paper presents an investigation of image texture approaches for mapping sub pixel fluvial grain size features from airborne imagery allowing for the rapid acquisition of surface sand and coarse fraction 1 41 mm grain size information imagery at 30 mm resolution was acquired over four gravel bars from the fraser river british columbia canada combined first order and second order image texture approaches windowed standard deviation filter and the grey level co occurrence matrix were used first order image texture through the application of a standard deviation filter and subsequent thresholding was used to detect the presence of surface sand with optimal accuracy achieved at 91 1 9 a wide ranging parameter space investigation was used to derive optimum parameters for the grey level co occurrence matrix subsequently first and second order image textures were used in multiple linear regression to achieve good calibrations with several sub pixel grain size percentiles relative error at 1 44 3 18 6 80 and 10 6 for d5 d16 d35 and d50 respectively the larger percentiles of d84 and d95 had relative errors of 24 7 and 29 7 respectively the breakdown of calibration precision for larger percentiles is attributed to a pixel averaging effect it is concluded that multispectral imagery is not required because sufficient image texture information can be derived from standard colour imagery recommendations are suggested for application of this method to other localities and datasets thus reducing exhaustive parameter searches in future studies

the camera and the geomorphologist abstract the methods we use to produce geomorphic data are deeply interwoven with the geomorphic questions we choose to ask and with the geomorphic theories we construct authors have described major changes in the history of geomorphology in terms of theoretical shifts and or social cultural changes but it seems clear that shifts in methodological practices also can produce deep changes in geomorphology as a whole the camera has had a long illustrious and complex history as a geomorphic tool and as such is useful for assessing larger geomorphological concerns and themes the camera is also a symbol of the ongoing revolution in geomorphology from a data poor to a data rich subject this revolution is built upon many methodological changes and it has had many side effects the interrelated history of cameras and fluvial geomorphology provides an illuminating case study in past and present changes in the geomorphic sciences some past geomorphic practices such as using photos as descriptive evidence for verifying geomorphic theory remain as important approaches today other camera based practices have dwindled to some degree such as the production of large area topographic maps through traditional aerial photogrammetry which have been overtaken by alternative methods such as lidar and interferometric radar and newer camera based techniques such as structure from motion photogrammetry are at the heart of the recent democratization of geomorphic data as the modern data revolution progresses it is important to ask questions such as who has been part of the data revolution and what have been their motivations and have winners and losers been produced as part of the data revolution not all effects of the data revolution have been completely positive many geomorphologists feel overwhelmed by big data expectations and methodological concerns from a philosophy of science perspective the moves toward population like geomorphic data have strained normal inductive inference procedures and recent research has brought to light inferential alternatives such as advanced data mining and the hypothetico deductive approach even so most current analytical techniques appear to be lagging behind the newly introduced big data producing new wine in old bottles new data for old analyses beyond pure geomorphic research the camera and its derivatives are also part of profound shifts in educational and outreach expectations and practices clearly the data revolution in geomorphology is still in its infancy and much of that revolution has been wrought by the humble camera

information on grain sizes in gravel bed rivers by automated image analysis abstract the time required in the field to characterize textural variation over gravel surfaces can be reduced by taking vertical photographs for subsequent image analysis we present modified edge detection algorithms which combine edge seeding with an image porosity concept and partial watershed segmentation the methods allow quick reliable and operator independent size analysis from a wide range of vertical bed surface images they are tested using 24 naturally lit images of an exposed river bed with mixed lithologies and partial burial of gravel by sand grain size percentiles derived by automated image analysis correlate closely with those from manual image analysis with only small and consistent degrees of bias they also correlate well with percentiles from field measurements with substantial bias which however is consistent so that it can be corrected for leaving a residual scatter of 0 25 where log2 mm over a wide range of bed conditions the bias depends somewhat on sand cover and the biggest residual discrepancies are for tail percentiles

preservation of sub microscopic structural relicts in micas from the gran paradiso massif western alps implications for 40ar 39ar geochronology abstract permian igneous biotite and white mica that were re heated at 500 550 c in the middle late eocene were investigated by laser step heating and in situ 40ar 39ar techniques in conjunction with scanning electron microscopy sem electron microprobe emp and transmission electron microscopy tem to assess the influence of short lived metamorphism on k ar systematics large intra and inter grain age variations ranging from the triassic to the late eocene are primarily related to the extent of metamorphic re equilibration brown biotite porphyroclasts from weakly re equilibrated samples are characterized by core to rim zoning in major element composition mineral structure and 40ar 39ar ratios titanium concentration and fe mg fe ratios decrease from crystal cores towards the rims which are compositionally indistinguishable from green biotite aggregates in metamorphic coronas compositional changes are coupled with structural modifications towards the crystal edges where the disordered igneous 1m 2m1 stacks are replaced topotactically by highly ordered metamorphic 1m polytypes apparent ages up to 66 ma were determined in crystal cores by in situ laser probe analyses while ages as young as 45 ma are typical of crystal rims step heating experiments of these zoned biotites yielded a discordant saddle shaped age spectrum with a concordant central segment yielding an error weighted mean age of 44 9 0 3 ma biotite porphyroclasts from a more re equilibrated specimen gave markedly different results with uniform major elements compositional profiles homogeneous argon distribution throughout the crystals and a flat age spectrum at 36 5 0 3 ma tem investigations of these optically homogeneous porphyroclasts revealed that the original igneous structure had been replaced by highly ordered 1m polytypes during alpine metamorphism white mica yielded comparable results with spot ages up to 218 ma in domains characterized by high na na k ratios and low si and ti content representing the best preserved igneous relicts significantly younger apparent ages down to 44 39 ma are typical of domains affected by partial metamorphic re equilibration at high pressure conditions as indicated by increasing si and ti contents or by exhumation related exsolution of amoeboidal quartz these results indicate that different intra grain and inter grain ar concentration patterns arise primarily from the relative amount and distribution of relict igneous and metamorphic crystal chemical domains core to rim age gradients in biotite result from inward directed recrystallization from the crystal edges eventually leading to flat age profiles as metamorphic replacement of pre existing porphyroclasts runs to completion this study calls for caution when estimating thermal histories from apparent age gradients or from age vs grain size correlations unless the presence of pre metamorphic mineral relicts can be ruled out

kinks in mica role of dislocations and 001 cleavage abstract kinking in natural and experimentally deformed biotite and muscovite has been investigated by transmission electron microscopy tem it is found that complex microstructures exist in the vicinity of kink band boundaries kbbs gentle bending of 001 planes plays an important role in the kinking process where 001 planes are bent several degrees edge dislocations are observed in complex walls between active slip planes together with broad bands of dislocations parallel to 001 microfracturing and dilation occur parallel to 001 planes and the kbb a model is presented to explain the origin of observed kbbs which may be applicable to other crystalline materials with only one active slip plane

sedimentological characterization of antarctic moraines using uavs and structure from motion photogrammetry in glacial environments particle size analysis of moraines provides insights into clast origin transport history depositional mechanism and processes of reworking traditional methods for grain size classification are labour intensive physically intrusive and are limited to patch scale 1m2 observation we develop emerging high resolution ground and unmanned aerial vehicle based structure from motion uav sfm photogrammetry to recover grain size information across an moraine surface in the heritage range antarctica sfm data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning and were found to be accurate to within 1 7 and 50mm for patch and site scale modelling respectively grain size distributions were obtained through digital grain classification or photo sieving of patch scale sfm orthoimagery photo sieved distributions were accurate to 2mm compared to control distributions derived from dry sieving a relationship between patch scale median grain size and the standard deviation of local surface elevations was applied to a site scale uav sfm model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0 3 km2 area of moraine this highly automated workflow for site scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis

occurrence of cluster microforms in mountain rivers the occurrence of cluster microforms in natural rivers is examined using data collected from three mountain streams the study was conducted under the premise that the occurrence of clusters is strongly tied to local reach scale conditions and that prediction of clustered sites therefore can be made through identification of particular reach conditions that are conducive to cluster development for the study reach scale variables were measured at 50 sites and the presence or absence of clusters at each of these sites was recorded a statistical analysis using logistic regression was performed to examine the correlation between the occurrence of clusters and various combinations of reach scale parameters it was found that clustering was best predicted by the bankfull channel width scaled with the d84 of the bed sediment w d84 and the non dimensional parameter wq2 gd it is thought that these variables work best at predicting the presence of clusters because they are descriptive of the reach hydraulic and sedimentary conditions and work well at discriminating between reach morphology types it was found that clustering was most strongly tied to riffle pool type reaches observations from this study suggest that clusters can be described as bed features that form out of the structural organization of grains in cobble size sediment within depositional mountain reaches for which the majority of the sediment can become mobilized by yearly peak flows copyright 2008 john wiley and sons ltd

on the loss of 40ar from muscovite during polymetamorphism abstract recent laser studies have documented 40ar concentration gradients in micas that correspond to age variations of tens to hundreds of millions of years a fundamental problem to interpretation of such variations is to evaluate whether they represent loss via lattice diffusion or alternatively loss during chemical reactions and deformation new data of this study and comparisons with previous work suggest that muscovite is far less prone to lose accumulated 40ar via lattice diffusion during overprinting events than has been inferred previously kyanite muscovite assemblages in proterozoic schist along the eastern flank of the green mountain massif central vermont appalachians formed during proterozoic metamorphism at ca 1 1 ga and were remetamorphosed in the greenschist facies during both taconian ca 465 ma and acadian ca 390 ma events the overprinting events resulted in deformation of earlier kyanite and muscovite growth of chemically and isotopically distinct rims on earlier muscovite and growth of neoblastic muscovite and chloritoid with each event at inferred minimum temperatures of ca 425 c laser spot analyses of the grenville muscovite range from 988 11 ma in the centers of porphyroclasts to 397 7 ma along rims ages younger than 750 ma occur only on the deformed edges of porphyroclasts and in highly deformed areas within crystals parts of early formed muscovite that escaped late deformation and chemical reaction seem remarkably retentive of accumulated 40ar laser spot analyses along the outer 100 m of an undeformed growth face yield ages close to the timing of proterozoic metamorphism and cooling the present study suggests episodic heating events are ineffective for producing measurable diffusive argon loss along the edges of large muscovite crystals ca 1 mm in diameter particularly in comparison with deformation and reaction mechanisms and are unlikely to result in complete 40 ar 39 ar age resetting of such crystals the results of this study further emphasize that the argon diffusivity in muscovite is lower than commonly considered in previous work

catchment scale mapping of surface grain size in gravel bed rivers using airborne digital imagery 1 this study develops and assesses two methods for estimating median surface grain sizes using digital image processing from centimeter resolution airborne imagery digital images with ground resolutions of 3 cm and 10 cm were combined with field calibration measurements to establish predictive relationships for grain size as a function of both local image texture and local image semivariance independently acquired grain size data were then used to assess the algorithm performance results showed that for the 3 cm imagery both local image semivariance and texture are highly sensitive to median grain size with semivariance being a better predictor than image texture however in the case of 10 cm imagery sensitivity of image semivariance and texture to grain size was poor and this scale of imagery was found to be unsuitable for grain size estimation this study therefore demonstrates that local image properties in very high resolution digital imagery allow for automated grain size measurement using image processing and remote sensing methods

geomorphological effectiveness of floods to rework gravel bars insight from hyperscale topography and hydraulic modelling bars are key morphological units in river systems fashioning the sediment regime and bedload transport processes within a reach reworking of these features underpins channel adjustment at larger scales thereby acting as a key determinant of channel stability despite their importance to channel evolution few investigations have acquired spatially continuous data on bar morphology and sediment size to investigate bar reworking to this end four bars along a 10 km reach of a wandering gravel bed river were surveyed with terrestrial laser scanning tls capturing downstream changes in slope bed material size and channel planform detrended standard deviations z were extracted from tls point clouds and correlated to underlying physically measured median grain size d50 across a greater range of z values than have hitherto been reported the resulting linear regression model was used to create a 1 m resolution median grain size map a fusion of airborne lidar and optical empirical bathymetric mapping was used to develop reach scale digital elevation models dems for rapid two dimensional hydraulic modelling using jflow software the ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events 2 33 100 year recurrence intervals to entrain sediment and rework bar units results show that multiple bar forming discharges exist whereby frequent flood flows rework tail and back channel areas whilst much larger less frequent floods are required to mobilise the coarser sediment fraction on bar heads valley confinement is shown to exert a primary influence on patterns of bar reworking historical aerial photography hyperscale dems and hydraulic modelling are used to explain channel adjustment at the reach scale the proportion of the bar comprised of more frequently entrained units tail back channel supra platform relative to more static units bar head exerts a direct influence upon geomorphic sensitivity

coarse bed material patch evolution in low order ephemeral channels abstract in river channel beds composed of a wide range of grain sizes the bed material is often arranged in discrete patches discernable by relative texture these bed material patches are the primary source of entrainable coarse sediment within the channel system and their composition and size have been found to influence the composition and rate of sediment transport twelve coarse gravel cobble sediment patches distributed throughout the channel network within a 4 53 ha watershed in southeastern arizona were monitored for 2 years changes in patch area and grain size were measured and painted patch grains were monitored to confirm that patch grains were mobilized during flow individual coarse bed material patches exhibited variable persistence during flows with return frequencies ranging from approximately 1 year to 4 6 years while no patch fully dispersed during the study period two new patches formed most coarse patches remained relatively stable in area and grain size distribution despite the entrainment of patch grains as lost grains were sufficiently replaced with sediment from upstream because of the grain replacement process and the effect of other sediment supply dynamics the changes in patch area and grain size distribution display a complex relationship with the magnitude of predicted grain mobilization within each patch results indicate that relative stability varies from patch to patch influenced by the balance of patch grains transported out of the patch and the deposition of new grains into the patch predictive models of coarse sediment transport and yield that assume the channel bed is a fixed source of sediment supply may not adequately capture the sediment dynamics within patchy channel beds and should be used with caution when applied to these environments due to the possibility of patch instability as documented in this study

bed material transport estimate in large gravel bed rivers using the virtual velocity approach this paper reports on a first attempt of using the virtual velocity approach to assess sediment mobility and transport in two wide and complex gravel bed rivers of northern italy displacement length and virtual velocity of spray painted tracers were measured in the field also the thickness of the sediment active layer during floods was measured using scour chains and post flood morphological changes as documented by repeated survey of channel cross sections the effects of eight and seven floods were studied on the tagliamento and brenta rivers where 259 and 277 spray painted areas were surveyed respectively in the tagliamento river 36 of the spray painted areas experienced partial transport whereas in the brenta river this accounted for 20 whereas full removal gravel deposition was observed on 37 and 26 of these areas on the tagliamento and brenta rivers respectively the mean displacement length of particles the thickness of the active layer and the extent of partial transport are well correlated with the dimensionless shear stress the virtual velocity approach allowed calculation of bed material transport over a wide range of flood magnitudes annual coarse sediment transport was calculated up to 150 for the tagliamento and 30 103 m3 yr 1 for the brenta the outcomes of this work highlight the relevance of partial transport condition as it could represent more than 70 of the total bed material transported during low magnitude floods and up to 40 for near bankfull events results confirm that bed material load tends to be overestimated by traditional formulas copyright 2016 john wiley sons ltd

automatic grain sizing of vertical exposures of gravelly deposits abstract the grain size distribution gsd is a key indicator in stratigraphy and morphology it is a basic tool used by a variety of disciplines geology geomorphology archeology ecology and engineering automatic grain sizing ags has been developed to estimate the gsd of surfaces in a rapid and effortless manner yet the traditional bulk method time consuming and laborious is still in use for the determination of the gsd of coarse grained sedimentary deposits and of the near subsurface of landforms principally river beds the ags technique is examined here in its application to the stratigraphic record and to the subsurface images processed by ags and manual samples of coarse grained deposits in section were compared for evaluation of accuracy and determination of the extent of validation of the ags technique the ags often achieves results very similar to field counting especially when the largest grains are accounted for in the size of the sampling area and when photographs are taken afar without flash best results are provided when two images of the same sediment are taken at close range and also from afar to combine their gsds hence overcoming errors generated by resolution sampling area and grain size the computed errors are larger than those in prior studies yet remain reasonably small even though results are not bias corrected axes exposed in an outcrop very likely differ from those exposed on the surface and sediment properties and lighting conditions vary although results indicate a 25 burial effect the performance of the ags for sections is high unlike prior application of ags for riverbed surface openwork gravels conglomerate sections and the near subsurface include a matrix resulting in a somewhat larger mean irreducible error the technique may be utilized in studies of conglomerate texture allowing the evaluation of entire gsds under difficult sampling conditions an example use of ags to subsurface gsd evaluation is provided among others enabling an easy and fast method to calculate extent of armoring

transient electromagnetic finite difference time domain earth modeling over steel infrastructure including highly conductive steel infrastructure into electromagnetic em earth modeling is motivated by the fact that long metal cased boreholes have the potential to be used as boosting antennas that enable larger source dipole moments and greater signal penetration depths unfortunately geophysical algorithms designed to simulate em responses over rather regional scales are complicated by material property contrasts and structure geometries that are more typical for em engineering applications hence the great majority of earth modeling algorithms that consider em responses from steel cased boreholes use integral equation methods to be able to model complex casing scenarios we revisited the finite difference time domain fdtd method to advance the modeling of transient em field responses from steel cased boreholes a time dependent function that allows for larger fdtd time steps in the dufort frankel method was developed alleviating the generally large computational overhead we compared our method against three different kinds of benchmark solutions to demonstrate the reliability of the fdtd field solutions these test cases were carried out to check the feasibility of a final hydraulic fracturing study images of the electric current distribution in a sheetlike rock fracture were calculated for the cases with and without the presence of a connecting borehole casing demonstrating the casing s potential of illuminating deep target zones

rb sr isotopic and compositional retentivity of muscovite during deformation abstract permian metapegmatite muscovite from the upper austroalpine matsch unit in southern tyrol italy was investigated regarding its rb sr and compositional retentivity during cretaceous upper greenschist facies deformation the data imply that microstructurally relic permian magmatic muscovite largely maintained its major and trace element compositions during deformation whereas the rb sr geochronometer is strongly affected by a net loss of sr lower sr concentrations of muscovite correlate with higher 87rb 86sr and 87sr 86sr ratios in most samples the muscovite grain size and magnetic fractions with the lowest 87rb 86sr and 87sr 86sr ratios preserve a permo triassic muscovite whole rock rb sr apparent age interpreted as to reflect formation during or cooling after pegmatite emplacement contrastingly muscovite fractions with higher 87rb 86sr and 87sr 86sr ratios are arranged along a roughly linear array with a positive correlation of the 87rb 86sr and 87sr 86sr ratios in the 87rb 86sr vs 87sr 86sr space they yield successively lower muscovite whole rock rb sr apparent ages we explain the variations in the rb sr isotopic character of microstructurally relic muscovite by a presumably deformation related loss of sr during the cretaceous event contemporaneously only very limited amounts of isotopically different sr from the matrix reservoir might possibly have entered the muscovite consequently the rb sr of the relic muscovite is affected by a net loss of sr the results imply that at temperatures of

estimation of grain size distributions and associated parameters from digital images of sediment abstract a new technique to estimate the grain size distribution gsd from a digital image of sediment is proposed advancing the applicability of a suite of sedimentary look up catalogue approaches originated by rubin rubin d m 2004 a simple autocorrelation algorithm for determining grain size from digital images of sediment journal of sedimentary research 74 1 160 165 the outputs of an automated procedure to estimate the gsd from digital images of sediment are examined with reference to the distributions obtained from both manually sieving the corresponding sediment samples and axial measurements made on the grains in the images measures of grain size obtained from the imaging procedure correlate very well with grain size measures derived from both the number frequency and mass frequency curve as expected the gsd obtained from the new automated approach based on kernel density compared better with point counts because of a shared two rather than three dimensionality the gsd shape is not always mimicked exactly however the percentiles obtained from the cumulative gsd compare well with those from sieved distributions which allow for the first time computation of graphical sorting and skewness from digital images of sediment which are accurate reflections of those measures obtained for point count and sieved samples the new approach allows for realistic gsds from which the residual can be computed thus a numerical criterion upon which the grain size distribution from an image can be accepted or rejected finally a method is presented whereby two dimensional autocorrelogram fields are derived from image power spectra ellipsoids are fitted to isolines of autocorrelation coefficients and from this the dominant axial lengths and orientation of these isolines which could facilitate computation of major and minor axis lengths of grains in sample images as well as their dominant orientation in turn this could allow for parameterisation of axial ratios for parameterisation of 2d shape such analysis is completely automated rapid and non intrusive

observations on sediment mobility in a large gravel bed river article this study investigates sediment mobility in a large gravel bed river tagliamento river northeastern italy field data were used to identify the morphological effectiveness of a range of flows floods with recurrence interval b1 to 3 5 year and for a detailed analysis of the partial transport condition the analyses were carried out on three cross sections where a number of areas representative of different morphological units main and secondary channels low and high bars islands were painted grain size of the painted area was measured using a photographic method monitoring of bed mobility during the study period supplied new photographs of the painted areas measurements of size and travel distance of the mobilized particles and estimate of flow depth after each flood event our analyses have shown that with dimensionless shear stress around 0 073 17 n m 2 the morphological effect over the painted areas was primarily partial transport while with stresses n0 1 25 n m 2 the bed experienced full mobility i e all the painted particles were transported or totally buried full sediment mobility was observed on lower morphological units i e main and secondary channels under floods with very high frequency rib1 y whereas on the low bars full mobility occurred under floods with a recurrence interval slightly n1 year instead fine deposition and partial transport conditions were observed on the higher bars even after the largest of the monitored floods ri 3 5 y the analysis of the partial transport condition relies on more than 3500 measurements of particle travel distance travel distances range from a few centimetres up to 22 m the transported particles were generally finer than the painted sediments and the analysis of the sediment transport ratio revealed that partial transport occurred under equal mobility conditions for particles finer than 32 mm and under size selective mobility for coarser fractions this appears to be corroborated for db32 mm by the insensitiveness of particle transport distance to particle sizes even if the exponent 1 of the relationship between the dimensionless shear stress and the maximum transported diameter would suggest that all fractions are transported under equal mobility conditions

surface to underground transient electromagnetic detection of water bearing goaves water bearing goaves are one of the main causes for water inrush accidents in chinese coal mines at present both the surface and subsurface geophysical technologies cannot fully meet the technical requirements of high precision detection for coal mines safety development and production based on the surface to borehole electromagnetic method we propose a surface to underground transient electromagnetic prospecting sutem in which the large rectangular loop is laid on the surface as the transmitting source and the receivers are laid in the subsurface roadways of the coal mines first we describe and discuss the sutem signal response using numerical simulation for a homogeneous half space the numerical results show that the curve of the induced electromotive force emf first increases to a peak and then decreases gradually till the end of the time window the shape of the curve closely reassembles a parabolic so the conductive bodies can be identified with the characters of the emf curve second we conducted a numerical simulation using the 3 d unstructured tetrahedral grids vector finite element total field electromagnetic forward modeling algorithm for the response of typical 1 d layered models and 3 d models the results show that the relative sensitivity is no relation with the depth of the abnormal layer when receiving points are under the layer the deeper the abnormal layer is the more obvious the advantage of sutem is finally the field experiment was carried out at a coal mine where the positions of water bearing goaves are known the sutem detection results do not exhibit a clear trend in the variation of electrical properties in the vertical direction of the formation however the variation in the lateral electrical properties is clear the expression of the low resistivity goaves is much clearer than the results from the surface tem the field experiment result is in agreement with the suggestions of the computer simulation and confirms the effectiveness of sutem

cobble cam grain size measurements of sand to boulder from digital photographs and autocorrelation analyses a new application of the autocorrelation grain size analysis technique for mixed to coarse sediment settings has been investigated photographs of sand to boulder sized sediment along the elwha river delta beach were taken from approximately 1 2 m above the ground surface and detailed grain size measurements were made from 32 of these sites for calibration and validation digital photographs were found to provide accurate estimates of the long and intermediate axes of the surface sediment r2 0 98 but poor estimates of the short axes r2 0 68 suggesting that these short axes were naturally oriented in the vertical dimension the autocorrelation method was successfully applied resulting in total irreducible error of 14 over a range of mean grain sizes of 1 to 200 mm compared with reported edge and object detection results it is noted that the autocorrelation method presented here has lower error and can be applied to a much broader range of mean grain sizes without altering the physical set up of the camera 200 fold versus 6 fold the approach is considerably less sensitive to lighting conditions than object detection methods although autocorrelation estimates do improve when measures are taken to shade sediments from direct sunlight the effects of wet and dry conditions are also evaluated and discussed the technique provides an estimate of grain size sorting from the easily calculated autocorrelation standard error which is correlated with the graphical standard deviation at an r2 of 0 69 the technique is transferable to other sites when calibrated with linear corrections based on photo based measurements as shown by excellent grain size analysis results r2 0 97 irreducible error 16 from samples from the mixed grain size beaches of kachemak bay alaska thus a method has been developed to measure mean grain size and sorting properties of coarse sediments copyright 2009 john wiley sons ltd

quantifying the scale of gravel bed clusters with spatial statistics clustering of large surficial particles affect the critical shear stress bedload transport rate and ecological processes of gravel rivers particle clusters have been the subject of careful study and taxonomy but would benefit from new quantitative reproducible statistical analysis particularly in the gravel size classes where clusters are difficult to reliably resolve by visual gestalt methods this study quantified a clustering length scale for a gravel and cobble bed the size orientation and location of 7726 gravel and cobble particles were measured from 100 photographic samples of a symmetrical bar on the navarro river california nearest neighbor spatial statistics were used to analyze particle associations clustering was identified between gravel particles throughout the river bar clustering was also identified for large d84 of the sample and medium between the d50 and d84 of the sample particles relative to the local gradation the spatial scale of these large and medium particle clusters were 1 75d84 and 3 0d50 respectively

grain size sorting within river bars in relation to downstream fining along a wandering channel the textural variability of river bed gravels at bar scales is poorly understood as are the relations between variability at this scale and at reach and river scales surface and subsurface grain size distributions were therefore examined at reach bar and bedform scales along lower fraser river british columbia canada grain size variations within compound bars are conditioned by longitudinal position elevation and morphological setting surface and subsurface sediments tend to decrease in median size from bar head to bar tail by 33 and 17 respectively sediment size is constrained at some upper limit that is inversely related to bar surface elevation and which is consistent with competence considerations the surface sediments on unit bars are finer and better sorted than the bed materials in bar top channels and along the main bar edges secondary unit bars tend to have a lower sand content than other features a consequence of sediment resorting individual unit bars and gravel sheets exhibit streamwise grain size fining and lee side sand deposition over time significant amounts of cut and fill do not ipso facto cause changes in surface grain sizes yet sediment characteristics can change without any significant morphological adjustment taking place at the reach scale there is a clear downstream fining trend but local variability is consistently high due to within bar variations the surface median grain size range on individual bars is on average 25 of that along the entire 50 km reach but is 68 on one bar while the overall fining trend yields a downstream change in surface median size of 0 76 mm km 1 the average value for head to tail size reduction on individual bars is 6 3 mm km 1 an order of magnitude difference that highlights the effectiveness of bar scale sorting processes in gravel bed rivers possibilities for modelling bar scale variability and the interaction of the different controls that are identified are discussed

sensitivity analysis for the appraisal of hydrofractures in horizontal wells with borehole resistivity measurements abstractwe numerically evaluate the possibility of using borehole electromagnetic measurements to diagnose and quantify hydraulic fractures that have been artificially generated in a horizontal well hydrofractures are modeled as thin disks perpendicular to the well and filled with either sand based or electrically conductive proppant the study focuses on the effect of thickness and length radius of hydrofractures to assess their effects on specific configurations of borehole resistivity instruments numerical results indicate that several measurements e g those obtained with low and high frequency solenoids could be used to assess the thickness of a fracture however only low frequency measurements performed with electrodes and large spacing between transmitter and receivers 18 m exhibit the necessary sensitivity to reliably and accurately estimate the length of long hydrofractures up to 150 m in open hole wells in the case of steel cased wells the casing acts as a long electrode whereby

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

a new and practical method to obtain grain size measurements in sandy shores based on digital image acquisition and processing abstract modern methods for the automated evaluation of sediment size in sandy shores relay on digital image processing algorithms as an alternative to time consuming traditional sieving methodologies however the requirements necessary to guarantee that the considered image processing algorithm has a good grain identification success rate impose the need for dedicated hardware setups to capture the sand surface images examples are specially designed camera housings that maintain a constant distance between the camera lens and the sand surface tripods to fix and maintain the camera angle orthogonal to the sand surface external illumination systems that guarantee the light level necessary for the image processing algorithms and special lenses and focusing systems for close proximity image capturing in some cases controlled image capturing conditions can make the fieldwork more laborious which incurs in significant costs for monitoring campaigns considering large areas to circumvent this problem it is proposed a new automated image processing algorithm that identifies sand grains in digital images acquired with a standard digital camera without any extra hardware attached to it the accuracy and robustness of the proposed algorithm are evaluated in this work by means of a laboratory test on previously controlled grain samples field tests where 64 samples spread over a beach stretch of 65 km and with grain size ranging from 0 5 mm to 1 9 mm were processed by both the proposed method and by sieving and finally by manual point count on all acquired images the calculated root mean square rms error between mean grain sizes obtained from the proposed image processing method and the sieve method for the 64 samples was 0 33 mm and for the image processing method versus manual point counts comparison with the same images was 0 12 mm the achieved correlation coefficients r were 0 91 and 0 96 respectively

depositional and erosional architectures of gravelly braid bar formed by a flood in the abe river central japan inferred from a three dimensional ground penetrating radar analysis abstract we conducted a ground penetrating radar gpr survey of gravelly braid bars in the abe river central japan to clarify the three dimensional 3d variations in their depositional facies under various geomorphologic conditions in september 2011 a ten year return period flood in the study area reworked and deposited braid bars after the flood we surveyed three bars with different geomorphologies using a gpr system with a 250 mhz antenna and identified seven fundamental radar depositional facies inclined reflections facies ia and ib horizontal to subhorizontal reflections facies iia and iib discontinuous reflections facies iiia and iiib and facies assemblage with a large scale channel shaped lower boundary facies iv combinations of these facies in dicate bar formation processes channel filling lateral aggradation and lateral and downstream accretion in the abe river aerial photographs and airborne laser scanning data were obtained before and after the flood the observed changes of the surface topography are consistent with the subsurface results seen in the gpr sections this study demonstrated that the erosional and depositional architecture observed among bars with different channel styles was related to river width and represented depositional processes for high sediment discharge the quantitative characterizations of the sedimentary architecture will be useful for interpreting gravelly fluvial deposits in the rock record

a theoretical study of surface to borehole electromagnetic logging in cased holes a new electromagnetic logging method in which the source is a horizontal loop coaxial with a cased drill hole and the secondary axial fields are measured at depth within the casing has been analyzed the analysis which is for an idealized model of an infinite pipe in a conductive whole space has shown that the casing and formation are uncoupled at the low frequencies that would be used in field studies the field inside the casing may be found by first finding the field in the formation and then using this field as an incident field for the pipe alone this result permits the formation response to be recovered from the measured field in the borehole by applying a correction for the known properties of the casing if the casing response cannot be accurately predicted a separate logging tool employing a higher frequency transmitter could be used to determine the required casing parameters in the vicinity of the receiver this logging technique shows excellent sensitivity to changes in formation conduct

digital grain size analysis based on autocorrelation algorithm abstract grain size is one of the most important parameters in geology and coastal engineering however all traditional methods are time consuming laborious and expensive in this study the autocorrelation technique which was first expounded by rubin 2004 was extended to estimate the size of well sorted sediments and the grain size distribution of mixed size sediments long and intermediate axes of well sorted sediments ranging from 1 to 20 mm obtained from applying the autocorrelation method are compared with the corresponding results measured using a vernier caliper using the autocorrelation technique the sediment mean size was calculated and was found to compare better with point counts than sieving regarding the mixed size sediment a nonlinear programming method which is different from the conventional least squares with non negativity method the kernel density method and the maximum entropy method was used to obtain the representative grain sizes and associated sediment inherent parameters such as mean diameter median diameter sorting skewness and kurtosis image pre processing was used in the present analysis to enhance the contrast of the recorded image and a conversion method applied to take into account the difference between the two dimensional digital image method and the three dimensional sieving method using the modified fitting points and the improved gaussian function fitting method the cumulative grain size distribution curve and the probability density curve of the mixed size sediments were obtained the enhanced autocorrelation technique that was developed from the traditional look up catalogue approach provided a more accurate estimation of the grain size distribution as well as the relevant physical parameters of the mixed size sediment

deformation induced resetting of rb sr and 40ar 39ar mineral systems in a low grade polymetamorphic terrane eastern alps austria a paradox in dating metamorphic events in low grade polymetamorphic terranes is exemplified by the eastern lower austroalpine nappes of the eastern alps here the last metamorphic event best recorded in post variscan cover rocks is dated as late cretaceous in age c 80 85 ma by white mica rb sr and 40 ar 39 ar systems within the underlying polymetamorphic basement 40 ar 39 ar and rb sr ages of phengitic white mica record only early and or late variscan ages 375 270 ma indicating that the alpine greenschist facies metamorphic overprint virtually caused no rejuvenation of variscan mineral ages based on these results the timing of a penetrative ductile top to wnw simple shear deformation recorded within both basement and cover rocks was contradictory deformation within the post variscan cover rocks had to be alpine in age whereas phengite 40 ar 39 ar ages from basement mylonites yield variscan ages to date this deformation directly we isolated different mineral size fractions 63 30 and 30 10 m from highly strained shearbands within the wechsel basement nappe a resulting rb sr errorchron pointed to an upper cretaceous age c 85 ma for the deformation consistent with the timing of alpine metamorphism in the cover rocks coarser grained white mica 150 300 im from similar basement mylonites do not reflect any alpine overprint of either k ar and or rb sr systems it follows that dynamic re and or neocrystallization induced by ductile deformation within the shearbands was the dominant process by which the rb sr system locally virtually re equilibrated this is valid even for overprinting metamorphic conditions below the temperatures required for ar diffusional loss in phengitic white mica c 40 ar 39 ar should be considered with caution

morphotextural characterization of dryland braided channels braided streams have been extensively studied in humid environments or in flumes that simulate them dryland rivers have bare catchments rapid recession hydrographs and unarmored beds resulting in high bed load discharges our objective was to characterize the morphotexture of the morphological elements bar anabranches chutes and confluences in a dryland braided system morphological elements measured in wadis ze elim rahaf and roded located in southeast israel were scanned using terrestrial laser scanning from which digital elevation models were generated roughness was evaluated from the standard deviation of detrended surfaces or from wolman sampled surface texture armoring of the bar and the adjacent anabranch was also evaluated scour chains were deployed in confluences to measure scour and fill during flow events dryland anabranches were finer grained and less armored than the adjacent bars bed load deposited as midchannel bars or on top of existing bars and thus associated with the depositional braiding process was enriched by the coarser fractions while the remaining bed load was deposited in the anabranches during the rapid flow recession chutes associated with erosional braiding processes were formed as topographic features with high local gradients enabling winnowing of fines deposited immediately downstream or transported further away scour chains inserted in the confluence zones demonstrated the formation and obliteration of a scour hole during a flow event the terrestrial laser scanning based digital elevation models and roughness analyses suggest that the hydrological regime of ephemeral channels with short lived recessions is responsible for the morphotextural setting of braid systems in arid environments

sm nd isotope systematics of high ree accessory minerals and major phases id tims la icp ms and epma data constrain multiple permian triassic pegmatite emplacement in the koralpe eastern alps abstract detailed sm nd mineral id tims empa and la icp ms analysis of meta pegmatite minerals from the koralpe stubalpe area austria involving single crystal separation step wise dissolution and acid leaching techniques yielded i information about the partitioning of ree between accessory and major mineral phases in meta pegmatites and ii age constraints on the long lasting permian triassic event in the austroalpine basement units of the eastern alps internal sm nd mineral isochrons performed on porphyroclast domains from the three localities rostockbach kuppergrund and wildbachgraben including garnet xenotime apatite monazite and feldspar indicate multiple emplacement of pegmatoid melts between 273 2 and 258 3 ma other localities yielded younger ages indicating that magmatic garnet crystallisation persisted from 251 7 to c 230 ma ages calculated between high ree accessories monazite apatite xenotime and the low ree major phases feldspar and garnet are largely consistent zircon however plots clearly off the internal regression line h 2 so 4 leaching experiments on meta pegmatite garnet rich in micron sized xenotime and apatite inclusions locally affected by dynamic recrystallisation yielded information about the behaviour of the sm nd system during strong tectono metamorphic overprinting the data suggest multiple injections of pegmatite melts at distinctly different times during protracted crustal thinning and heating in the permian triassic ky paramorphs after andalusite and micro inclusions of kyanite staurolite and sillimanite in magmatic garnet indicate crystallisation of the garnet at moderately high but variable pressure conditions during subsequent eclogite facies overprinting peak pt c 700 c 2 2 gpa and intense deformation in cretaceous time the magmatic chemical and isotopic signatures of porphyroclasts were largely preserved except for localized within grain micro shear zones and outermost rim domains whereas part of the feldspar rich matrix recrystallised during pervasive mylonitisation along the eclogite to amphibolite facies grade exhumation path

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

characterization of river delta shorelines 1 coastline shape is among the basic geometric properties of the earth s surface yet defining and quantifying coastline shape precisely remains challenging here we propose new methods based on the dilation and erosion operators of mathematical morphology mm for the characterization of delta shorelines a class of open coasts we demonstrate the suitability of mm based methods for noise removal and shoreline identification from digital images of river deltas of varying geometric complexity we also show that a global a regional and a local shoreline parameter provide a first step in distinguishing among river wave and tidal dominated delta shapes

through casing hydraulic fracture evaluation by induction logging ii the inversion algorithm and experimental validations evaluation of hydraulic fractures has been under intensive study since the last decade among published works only a few have included casing effects this paper focuses on the through casing electromagnetic em induction imaging method that evaluates hydraulic fractures with enhanced contrasts an experimental system and an inverse scattering algorithm are presented the laboratory scaled experimental system is built for the feasibility study of the em induction imaging method for the through casing hydraulic fracture evaluation to develop the inverse scattering algorithm fractures outside boreholes with metallic casing are modeled by a novel hybrid approximation method this method combines the distorted born approximation and the mixed order stabilized bi conjugate gradient fast fourier transform method to solve the forward scattering problem the variational born iterative method is applied to solve the nonlinear inverse problem iteratively experimental results show that the inverse scattering algorithm is effective for em contrast enhanced through casing hydraulic fracture evaluation

interactions between a cushion plant azorella selago and surface sediment transport on sub antarctic marion island on sub antarctic marion island cushions of the dominant vascular plant species azorella selago interact with the geomorphology of fellfield landscapes by affecting sediment distribution and ultimately terrace formation here to understand the consequences of azorella cushions for substrate movement and sorting we quantified the size and shape of azorella cushions and the grain size distribution of sediment surrounding these cushions using a combination of image analysis approaches results show that as cushions become larger they tend to become more elongated and grow more perpendicular to the slope mean and variance of grain size were greater upslope of azorella cushions while the number of particles was higher downslope of cushions although these differences were not significant at all sites studied differences between upslope and downslope particle sizes were however not related to cushion elongation or growth angle as had been expected the observed sediment partitioning is likely caused by a combination of frost related sediment transport and azorella cushions acting as sediment obstructions understanding these interactions between azorella cushions and the landscape is especially important in the light of recent warming and drying on the island as particle size affects soil properties such as water holding capacity and frost susceptibility

time temperature relation of mineral isochrons a thermodynamic model and illustrative examples for the rbsr system abstract we have developed a thermodynamic model for the determination of the closure temperature t c at which the minerals defining an internal isochron in rb sr or similar geochronological system were set with a geochronological clock it is shown that the equilibrium fractionation of 87 rb and 87 sr between a pair of minerals at t c k d 87 rb 87 sr c is given by the ratio of the quantity 87 rb 86 sr in the two minerals as measured at the present time k d 87 rb 87 sr which equals the element distribution coefficient k d rb sr under equilibrium condition can be calibrated as a function of temperature and compared with the retrieved value of k d 87 rb 87 sr c in a natural pair to obtain t c the various mineral pairs defining an internal isochron will yield concordant or discordant values of t c depending on whether or not they closed simultaneously with respect to the diffusion of rb and sr both types of results are expected and are important in the analyses of the evolutionary history of the host rocks preliminary analyses of the published data in the rb sr system suggest a fairly wide range of t c even for the same mineral pair reflecting differences in the cooling rates and physico chemical environments of the host rocks

the relative stability of salmon redds and unspawned streambeds where female salmon build nests redds streambed material is mixed fine sediment is winnowed and bed material is moved into a tailspill mound resembling the shape of a dune completed redd surfaces are coarser and better sorted than unspawned beds which is thought to increase redd stability because larger grains are heavier and harder to move and sorting increases friction angles for mobility however spawning also loosens sediment and creates topography that accelerates flow which can increase particle mobility we address these factors controlling the relative stability of redds and unspawned beds in flume experiments where redds were constructed with a technique that mimics the nesting behavior of female salmon although redds exhibited relatively coarse surfaces measured entrainment forces indicate particle loosening by spawning lowered grain resistance to motion by 12 37 on average compared to unspawned beds in addition for the same discharges boundary shear stress was 13 41 higher on a redd due to flow convergence on the tailspill visual measurements of particle entrainment further indicated redd instability as bed average shear stress was 22 lower at incipient motion and 29 lower at the discharge that mobilized all grain sizes on a redd overall results demonstrate redds are unstable compared to unspawned beds which increases the risk of scour for buried eggs but may facilitate fine sediment flushing and improve the quality of spawning gravels for future generations of spawners therefore managing salmon returns to increase streambed disturbance may be an effective tool for reducing sedimentation impacts on salmon reproduction this article is protected by copyright all rights reserved

rb sr microchrons of synkinematic mica in mylonites an example from the dav fault of the eastern alps abstract a technique for texturally controlled microsampling from rock thick sections and subsequent rb sr dating of g sized samples has been developed it allows direct dating of minerals unequivocally related to deformation the technique has been applied to strictly synkinematically grown white mica prepared from mylonites related to the defereggen antholz vals dav fault south of the tauern window eastern alps control of deformation ages is provided by field relationships with independently dated plutons and dykes dated here by single mineral rb sr the field observations and isotopic ages are fully consistent and demonstrate that this is a reliable method for sub mm scale geochronology the ages obtained establish that sinistral strike slip shearing associated with the dav fault lasted from at least 33 ma to 30 ma followed by an abrupt change to dextral transpression related to the adjacent periadriatic fault

a stacked late quaternary fluvio periglacial sequence from the axe valley southern england with implications for landscape evolution and palaeolithic archaeology the current model of mid latitude late quaternary terrace sequences is that they are uplift driven but climatically controlled terrace staircases relating to both regional scale crustal and tectonic factors and palaeohydrological variations forced by quasi cyclic climatic conditions in the 100 k world post mid pleistocene transition this model appears to hold for the majority of the river valleys draining into the english channel which exhibit 8 15 terrace levels over approximately 60 100 m of altitudinal elevation however one valley the axe has only one major morphological terrace and has long been regarded as anomalous this paper uses both conventional and novel stratigraphical methods digital granulometry and terrestrial laser scanning to show that this terrace is a stacked sedimentary sequence of 20 30 m thickness with a quasi continuous i e with hiatuses pulsed record of fluvial and periglacial sedimentation over at least the last 300 400 k yrs as determined principally by osl dating of the upper two thirds of the sequence since uplift has been regional there is no evidence of anomalous neotectonics and climatic history must be comparable to the adjacent catchments both of which have staircase sequences a catchment specific mechanism is required the axe is the only valley in north west europe incised entirely into the near horizontally bedded chert crypto crystalline quartz and sand rich lower cretaceous rocks creating a buried valley mapping of the valley slopes has identified many large landslide scars associated with past and present springs it is proposed that these are thaw slump scars and represent large hill slope failures caused by vauclausian water pressures and hydraulic fracturing of the chert during rapid permafrost melting a simple 1d model of this thermokarstic process is used to explore this mechanism and it is proposed that the resultant anomalously high input of chert and sand into the valley during terminations caused pulsed aggradation until the last termination it is also proposed that interglacial and interstadial incision may have been prevented by the over sized and interlocking nature of the sub angular chert clasts until the lateglacial when confinement of the river overcame this immobility threshold one result of this hydrogeologically mediated valley evolution was to provide a sequence of proximal palaeolithic archaeology over two mis cycles this study demonstrates that uplift tectonics and climate alone do not fully determine quaternary valley evolution and that lithological and hydrogeological conditions are a fundamental cause of variation in terrestrial quaternary records and landform evolution

how round is round a new approach to the topic roundness by fourier grain shape analysis numerous methods for roundness measurement have been developed none however has been generally accepted because of conceptual and practical deficiencies modern image processing and fourier grain shape analysis have eliminated the practical shortcomings but the conceptual ones remained single higher harmonics of the fourier series for example fail to serve as reliable equivalents for roundness evaluation the concept outlined in this paper recognizes three criteria for the evaluation of roundness 1 all curvatures convex as well as concave or plane elements must be considered 2 the positions of morphological elements are significant because salient parts of a particle are more easily abraded than protected ones consequently the curvatures have to be weighted by their relative position on the particle 3 positions and curvatures of morphological elements have to be compared with the particle s ultimate abraded shape which is assumed to be an ellipsoid the ellipsoid reflects the aspect of form or sphericity the distinction between sphericity and roundness is retained because there is no evidence that sphericity changes significantly during transport the measurement is based on the outline of a particle s maximum projection plane which is transformed to a fourier series roundness data are derived from the complete amplitude spectrum the aspect of sphericity is eliminated by subtracting the amplitude spectrum of the best approximating ellipse from the spectrum of the empirical shape the residual amplitudes are normalized and summed in a final step the resulting values are rescaled this guarantees reasonable boundaries and a normal distribution of roundness values the procedure is automated and its efficiency permits the calculation of large samples tests on fluvial and coastal gravel populations demonstrate that the method is sensitive to abrasional wear during all stages of roundness

subaerial gravel size measurement using topographic data derived from a uav sfm approach fluvial grain size plays a fundamental role in determining the condition and availability of aquatic habitats remote sensing provides rapid and objective methods of quantifying fluvial grain size and typically provide coarse grain size outputs c 1m at the catchment scale up to 80km channel lengths or fine resolution outputs c 1mm at the patch scale c 1m2 recently drone based approaches have started to fill the gap between these scales providing hyperspatial resolution data 10cm over reaches up to a few hundred metres in length this mesoscale is of importance to habitat assessments and is aligned with the ideals of the riverscape concept most drone based grain size measurement approaches use textural variables computed from drone orthoimagery to date however no published works provide quantitative evidence of the success of this approach despite significant differences in platform stability and the image quality obtained by manned aircraft versus drones with interest in drone surveys growing rapidly such error quantification is essential for making reliable evidence based recommendations about the suitability of drones for routine management of fluvial environments here we provide an initial assessment of the accuracy and precision of grain size estimates produced using two different drone based methods 1 the image textural variable negative entropy and 2 the roughness of point clouds derived from drone imagery processed using structure from motion photogrammetry data is collected from a small gravel bed river in cumbria uk results from jack knife analyses show that the point cloud roughness method gives more accurate and precise measures of grain size at this site as indicated by the mean 0 0002m and standard deviation 0 0184m of residual errors however both methods struggle to provide grain size measures with sub centimetre precision we suggest that blur within the drone imagery prevents better precision resulting from an inadequate camera gimbal

granulometric study of the hanaupah fan death valley california we applied new granulometric techniques to the various surfaces of the hanaupah fan death valley california namely the q1 surface with an estimated age of 800 490 ka the younger q2 170 105 ka and q3 50 14 ka surfaces the 14 ka deposits of the incised channel and to a c 14 ka lake manly shoreline deposit at the northern periphery of the fan we used these techniques to generate quantitative information on surface clast grain size distributions clast sphericity roundness and clast orientation to provide a data set that could be used to define fan segment surfaces and to help interpret fan genesis grain size analyses were carried out by photo sieving of 139 surface pictures by petrographic identification of samples taken in the incised channel and by identification and measuring of the largest clasts 1452 measurements on the q3 surface the results show that all fan segment surfaces regardless of age have similar size distributions with a well defined gravel mode of 2 3 to 3 0 phi and are poorly to moderately sorted samples from the incised channel have distributions that are very similar to each other regardless of distance from the apex but display reduced sorting compared to the fan surfaces which largely lack fines perhaps from winnowing by secondary overland flow only the shoreline deposit is different from the other elements showing a much narrower well defined gravel mode 3 0 phi and is moderately well sorted sphericity and roundness of clasts on all surfaces show only minor differences similar to the other sedimentary parameters indicating a remarkable homogeneity of the surfaces of the sediment body in addition measurements of the largest clasts 100 cm long axis on the q3 surface showed no discernible trend either with radial distance or with rock type these data suggest large depositional episodes that produce extensive sedimentary units without differentiation relative to distance from the source of the examined parameters clast orientation is the best predictor of relative age of fan surfaces clast orientation in the main channel is bimodal i e the long axes of clasts are either at right angles or parallel to transport direction this bimodality disappears with increasing age and the preferred orientation becomes unimodal long clast axes normal to transport direction on the q1 surface although the causes of this change are still in debate use of this parameter as a relative age dating tool seems possible 1998 john wiley sons ltd

granulometric characterization of paleosols in loess series by automated static image analysis abstract an automated image analysis method is proposed here to study the size and shape of siliciclastic sedimentary particles of paleosols of central european loess sequences several direct and indirect measurement techniques are available for grain size measurements of sedimentary mineral particles indirect techniques involve the use of some kind of physical laws however all requirements for calculations are in many cases not known even so the direct manual microscopic observation and measurement of large representative number of grains is time consuming and sometimes rather subjective therefore automated image analyses techniques provide a new and perspective way to analyse grain size and shape sedimentary particles here we test these indirect laser diffraction and direct automated static image analysis techniques and provide new granulometric size and shape data of paleosols our results demonstrate that grain size data of the mineral dust samples are strongly dependent on shape parameters of particles and shape heterogeneity was different between different size classes due to the irregular grain shape parameters uncertainties have arisen also for determination of grain sizes in this paper we present a possible correction procedure to reduce the differences among the results of the laser diffraction and image analysis methods by applying new correction factors results of the two approaches could become closer but the unknown thickness of particles remains a problem to solve the other presented correction procedure to assess the uncertain 3rd dimension of particles by their intensity size relationships makes us able to reduce further the deviations of the two sizing methods

compositional changes of minerals associated with dynamic recrystallizatin the rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously the enhanced exchange rate may result from a reduction in grain size shorter distance for volume diffusion dissolution and growth of grains by diffusion creep pressure solution or the movement of high angle grain boundaries through strained grains during recrystallization in the dislocation creep regime the migration of high angle grain boundaries provides high diffusivity paths for the rapid exchange of components during recrystallization the operation of the latter process has been demonstrated by deforming aggregates consisting of two plagioclases an1 and an79 at 900 c 1 gpa confining pressure and a strain rate of 2x10 6s 1 the polygonal recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable but often intermediate composition at the conditions of these experiments the volume interdiffusion rate of nasi caal is too slow to produce any observable chemical change and microstructural chemical relations indicate that the contribution from diffusion creep was insignificant except for initially fine grained 2 10 m aggregates these results indicate that strain induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for resetting the isotope systematics of minerals such as feldspars pyroxenes and amphiboles

analysis of electromagnetic induction for hydraulic fracture diagnostics in open and cased boreholes in this paper the sensitivity and detectability of an electromagnetic induction tool for hydraulic fracture detection are analyzed by calculating the electromagnetic response from an orthogonal transverse fracture otf in an open or cased borehole using the improved numerical mode matching method the otf is modeled as a slim circular disk which is axially symmetric with respect to the borehole axis and filled with a conductive or magnetic proppant the feasibility of the induction tool for fracture diagnostics was validated via scaled down experimental measurements we then quantitatively analyze the induction response sensitivity to different proppant parameters such as conductivity and permeability to evaluate the effectiveness of the induction logging tool for fracture detection the analysis reveals that the short spaced receiver can accurately locate the fracture position and distinguish small sized fractures while the long spaced receiver can differentiate fractures with large dimension casings with different thicknesses conductivities and permeabilities are modeled together with the fracture to investigate their effects in fracture detection finally the application of the induction tool to a fracture network is evaluated

photogrammetric monitoring of small streams under a riparian forest canopy the recent advent of digital photogrammetry has enabled the modeling and monitoring of river beds at relatively high spatial resolution 0 01 to 1 m through the extraction of digital elevation models dems the traditional approach to image capture has been to mount a metric camera to an aircraft although non metric cameras have been mounted to a variety of novel aerial platforms to acquire river based imagery e g helicopters radio controlled motorized vehicles tethered blimps and balloons however most of these techniques are designed to acquire imagery at flying heights above the riparian tree canopy in relatively narrow channels e g 20 m bankfull width streamside trees can obscure the channel and limit continuous photogrammetric data acquisition of both the channel bed and banks while still providing useful information regarding the riparian canopy and even spot elevations of the channel this paper presents a technique for the capture and analysis of close range photogrammetric data acquired from a vertically mounted non metric camera suspended 10 m above the channel bed by a unipod the camera is positioned under the riparian forest canopy so that the channel bed can be imaged without obstruction the system is portable and permits relatively rapid image acquisition over rough terrain and in dense forest the platform was used to generate dems with a nominal ground resolution of 0 03 m dems generated from this platform required post possessing to either adjust or eliminate erroneous cells introduced by the extraction process overhanging branches and by the effects of refraction at the air water interface for submerged portions of the channel bed the vertical precision in the post processed surface generally ranged from 0 01 to 0 1 m depending on the quality of triangulation and the characteristics of the surface being imaged copyright 2010 john wiley sons ltd

grain size information from the statistical properties of digital images of sediment abstract the autocorrelation technique for estimating grain size from digital images ofsand beds has been extended and validated for use on coarse sand 0ae7 mm and gravel up to 20 mm a number of aspects of the technique have beenexplored and some potential improvements suggested autocorrelation is justone suitable statistical method sensitive to the grain size of sediment in digitalimages four additional techniques are presented and their relative meritsdiscussed a collective suite of techniques applicable to the general problem ofgrain size estimation from digital images of sediment might broaden theapplicability to more sedimentary environments as well as improve itsaccuracy these techniques are compared using a large data set from a gravelbarrier beach in southern england based on over 180 samples mean grain sizeof sieved and imaged sediments correspond to within between 8 and 16 some theoretical aspects of the spatial arrangement of image intensity indigital images of natural sediments are addressed including the fractal natureof sediments in images which has potential implications for derivation ofgrain size distributions from images of sand sized material throughsegmentation and thresholding the methods outlined in this contributionmay also nd application in further uncovering the geometric structure ofsediment beds as well as in the simulation of sedimentation processes keywordsgrain size analysis digital images statistical models gravel beach introductiongrain size information from natural environ ments traditionally is obtained using methodssuch as sieving laser diffraction and settling which do not help measure equivalent propertiesof the sample in addition the slow and labour intensive nature of these methodologies has lim ited the spatial and temporal resolution at whichgrain size data are obtained where grain size isan important parameter such as in determiningsediment transport studies can be limited funda mentally by the dif culty in sampling for sedi ment at the required frequency a furtherdisadvantage is that sediment must be removedfrom the natural environment potentially alteringsubsequent system development in contrast photographic methods can be used to measuresediment size at a resolution comparable withmeasurements of hydraulic hydrodynamic andmorphological topographical conditions withoutdisrupting the sediment body by direct sampling the problem of deriving sediment size infor mation from digital images of sediment has beenapproached using two different families of tech niques the rst is based on edge detection andimage segmentation principles e g butler et al 2001 sime ferguson 2003 graham et al 2005 such techniques rely on marked image intensity contrasts between grains and gapsbetween grains interstices such that thresholdscan be speci ed to discriminate individual grainsfrom the background intensity levels e g sime ferguson 2003 thus far these methods aresedimentology 2009 56 421 438

flow regimes bed morphology and flow resistance in self formed step pool channels received 3 july 2008 revised 28 december 2008 accepted 13 january 2009 published 25 april 2009 1 we used a mobile bed flume with scaled grain size distribution channel geometry and flow to examine morphology and hydraulics of stepped channels we hypothesized that 1 step geometry and flow resistance differs significantly as a function of the range of grain sizes present 2 a transition from nappe to skimming flow occurs in stepped channels with mobile beds for conditions similar to stepped spillways and 3 the partitioning of flow resistance changes significantly when flow passes from nappe to skimming conditions results support each of these hypotheses and help to illuminate the complexity of v q relationships in stepped channels in which a dramatic decrease in flow resistance and increase in velocity accompany the transition from nappe to skimming flow near step forming events therefore a single flow resistance equation applicable to both ordinary and large floods may not be ideal in stepped channels nonetheless models based on dimensionless velocity and unit discharge appear more robust compared to those based on the darcy weisbach friction factor

detection and quantification of three dimensional hydraulic fractures with horizontal borehole resistivity measurements this paper investigates the suitability of low frequency borehole resistivity measurements for detecting and appraising hydraulic fractures the effects of the borehole logging tool s transmitter receiver spacing orientation and operating frequency as well as the fracture s shape cross sectional area dip and electrical conductivity contrast with the embedding formation are quantified using an fast fourier transform fft accelerated integral equation solver simulation results for a logging tool that consists of one transmitter and two receivers in a homogeneous shale formation of 1 3 s m conductivity show the following 1 longer transmitter receiver spacings can differentiate larger fractures while shorter transmitter receiver spacings can detect smaller fractures specifically the tool can differentiate fractures up to 1000 m 2 in area if the receivers are 18 and 19 2 m away from the transmitter but this long spacing configuration cannot detect fractures smaller than 10 m 2 in area and requires the effective electrical conductivity of the fracture to be larger than 100 s m in comparison the tool can detect fractures as small as 1 m 2 in area if the receivers are 1 2 and 1 5 m away from the transmitter even if the effective electrical conductivity of the fracture is only 10 s m but this short spacing configuration cannot distinguish fractures larger than 10 m 2 in area 2 coaxial measurements are sensitive to the fracture cross sectional area but cannot differentiate fractures of the same area with different cross sectional shapes or dips transverse copolarized measurements can discern axially symmetric fractures from asymmetric ones for example in long spacing configuration they can differentiate elliptical fractures with an aspect ratio of 8 from circular or square fractures if their areas are within 1 m 2 to 1000 m 2 cross polarized measurements can quantify fracture dip and become more sensitive as the dip angle increases for example in long spacing configuration they can detect 15 dipping fractures that are larger than 100 m 2 in area but cannot distinguish them while they can detect and distinguish 60 dipping fractures if their areas are in the range of 100 1000 m 2 3 the measurements are mostly insensitive to the operating frequency in the 10 hz 1 khz range in the short spacing configuration and depend moderately on the operating frequency in the long spacing configuration 4 the relative strength of the measured signals is proportional to the fracture effective electrical conductivity when the fracture is more than ten times conductive compared to the embedding rock formation 5 short spacing measurements exhibit higher resolution the tool can differentiate two fractures as long as they are more than 1 m 4 m away from each other in the short spacing long spacing configuration 6 in complex fracture networks not only major branches but intermediate and small branches contribute to the shape and magnitude of measured signals the contributions depend mainly on the area and position of the branches

can high resolution 3d topographic surveys provide reliable grain size estimates in gravel bed rivers high resolution topographic surveys such as those provided by structure from motion sfm contain a wealth of information that is not always exploited in the generation of digital elevation models dems in particular several authors have related sub metre scale topographic variability or surface roughness to sediment grain size by deriving empirical relationships between the two in fluvial applications such relationships permit rapid analysis of the spatial distribution of grain size over entire river reaches providing improved data to drive three dimensional hydraulic models allowing rapid geomorphic monitoring of sub reach river restoration projects and enabling more robust characterisation of riverbed habitats however comparison of previously published roughness grain size relationships shows substantial variability between field sites using a combination of over 300 laboratory and field based sfm surveys we demonstrate the influence of inherent survey error irregularity of natural gravels particle shape grain packing structure sorting and form roughness on roughness grain size relationships roughness analysis from sfm datasets can accurately predict the diameter of smooth hemispheres though natural irregular gravels result in a higher roughness value for a given diameter and different grain shapes yield different relationships a suite of empirical relationships is presented as a decision tree which improves predictions of grain size by accounting for differences in patch facies large improvements in d50 prediction are possible sfm is capable of providing accurate grain size estimates although further refinement is needed for poorly sorted gravel patches for which c axis percentiles are better predicted than b axis percentiles

induction logging through casing by detecting lateral waves a numerical analysis induction logging through casing iltc is of significant importance to the evaluation of residual oils traditional induction logging fails to work in cased wells due to the shielding effect of metallic casings to date the feasibility of iltc remains an open question in this article we propose an iltc based on the detection of lateral waves that carry the formation information based on the analytical equations derived to describe the hybrid modes of total magnetic fields that can be detected inside cased wells numerical analyses aiming to describe the behavior of lateral waves were carried out in both frequency and time domains the obtained results comply with full wave simulations and existing scaled experiments our results indicate that if an iltc tool can be properly configured to work in a region dominated by lateral waves and the casing effect and the primary field of the lateral waves can be effectively compensated it is feasible to implement an iltc to detect formation conductivities ranging from 0 01 to 5 s m

dating deformation using rb sr in white mica greenschist facies deformation ages from the entrelor shear zone italian alps ages of deformation have been obtained by rb sr analysis of white micas whose microstructural and chemical characteristics indicate that they crystallized or recrystallized during shear fabric formation since white micas commonly define deformation fabrics in medium grade metamorphic rocks these ages can be directly related to structural geometries with regional context this direct method contrasts with estimates of midcrustal deformation ages derived from cooling histories because it does not rely on assumptions about the thermal structure of the crust it does require that the dated minerals attained isotopic equilibrium with the dominant sr reservoir at temperatures lower than the closure temperature this resetting was apparently achieved during dynamic recrystallization of white micas in greenschist facies metasediments and metagranitoid units in the western alps the results suggest that the sr isotopic composition of the new mica is buffered by the coexisting high sr phases calcite feldspar or epidote via the grain boundary network high strain rocks from the entrelor shear zone system of the western alps have yielded indistinguishable white mica rb sr ages along 30 km of individual and kinematically linked shear zones the age of the back thrusting event is constrained at 34 1ma the age yielded by the younger generation of synkinematically crystallized white micas this event was short lived involving at least 20 km of shortening in 1 m y or less an earlier variably overprinted component dating from 38 to 37 ma has been identified in the mica fabric but its kinematic significance is uncertain this method of dating strain fabrics offers a powerful tool for tectonic studies since isotopic resetting can be directly linked to structural geometries microstructural textures and pt conditions it allows testing of kinematic models in orogens and can provide important information on the rates of geological processes in the crust

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

increase in coarse sediment transport associated with disturbance of gravel river beds by signal crayfish pacifastacus leniusculus there is growing acknowledgement of the interaction between animals and the river bed on which they live and the implications of biological activity for geomorphic processes it has been observed that signal crayfish pacifastacus leniusculus disturb gravel substrates potentially promoting sediment transport and impacting ecological communities however the mechanisms involved and the extent of their impact remain poorly understood especially in relation to other processes that affect grain mobility in gravel bed rivers a series of flume experiments using loose and water worked gravel beds of narrowly graded grain sizes that were exposed to 6 h of crayfish activity under low velocity flows showed a substantial increase in the number of grains entrained by subsequent higher velocity flows when compared with control runs in which crayfish were never introduced crayfish alter the topography of their substrate by constructing pits and mounds which affect grain protrusion when walking and foraging they also alter gravel fabric by reorienting and changing the friction angle of surface grains in water worked surfaces this fabric rearrangement is shown to lead to a statistically significant partial reversal of the structuring that had been achieved by antecedent flow for these previously water worked surfaces the increase in entrainment arising from disturbance by crayfish was statistically significant with grain transport nearly twice as great this suggests that signal crayfish an increasingly widespread invasive species in temperate latitudes beyond their native nw north america have the potential to enhance coarse grained bedload flux by altering the surface structure of gravel river beds and reducing the stability of surface grains this study illustrates further the importance of acknowledging the impact of mobile organisms in conditioning the river bed when assessing sediment entrainment mechanics in the context of predicting bedload flux

rejuvenation of rbsr mica ages during shearing on the northwestern margin of the nanga parbat haramosh massif abstract the shear zone bordering the western margin of the nanga parbat haramosh massif nphm separates terranes with distinct but well documented cooling histories this study was undertaken in order to examine isotopic behaviour and if possible to date deformation or cooling within the contact zone itself rb sr muscovite and biotite ages and petrographic descriptions are presented for a range of metamorphic lithologies and granite sheets which have been affected to varying degrees by greenschist facies extensional crenulation this deformation has been kinematically linked to the differential uplift of the nphm ages for metamorphic lithologies and granite sheets are similar and are considered together determined muscovite ages mostly lie in the range 9 22 ma whilst the majority of biotite ages lie in the range 2 11 ma mica ages from the shear zone are significantly more variable than ages determined for unsheared lithologies from outside the shear zone even closely spaced samples yield variable mica ages and in some cases there is a significant difference between muscovite and biotite ages determined for the same sample muscovite ages yield a bimodal distribution with groups of ages in the range 17 21 ma and 8 12 ma the older group is thought to reflect the original purely thermostatic cooling of lithologies through the muscovite closure temperature prior to formation of the nphm structure in contrast the younger group of muscovite ages reflects variable degrees of isotopic resetting during shearing at temperatures below the muscovite closure temperature associated with the relative uplift of the nphm the majority of biotite ages also reflect partial to complete resetting during shearing however biotite samples from structurally competent amphibolite horizons preserve older 16 ma ages indicating that there was locally a strong lithological or fluid control on the degree of resetting the flanks of the nphm cooled through the muscovite closure temperature significantly earlier than the deeper structural levels presently exposed within the core of the nphm greenschist grade deformation was occurring within the shear zone at the same time that deeper levels of indian crust were passing through the muscovite closure temperature suggesting that the shearing reflects the relatively passive extensional movement of rocks sliding off the flank of the actively growing nanga parbat structure the results highlight the isotopic complexities of long lived shear zones present in orogenic belts but show that useful radiometric age information may be obtained if the regional tectonic history is well understood and if the samples for dating come from well constrained structural settings

photo sieving a method for grain size analysis of coarse grained unconsolidated bedding surfaces the photo sieving method enables the grain size analysis of particles 10 mm from unconsolidated openwork bedding surfaces the accuracy is equal to the machine sieving method the sediment surface is photographed in the field using a camera stand the enlarged print is digitized for computer processing by tracing the outlines of the pebbles from the size and shape of the projection area of the individual pebble images the computer determines the ellipsoids of revolution classifies these ellipsoids and establishes their grain size distribution in percentage by weight thus photo sieving differs distinctly from point counting techniques with the aid of photo sieving the surface grain size distributions of larger sedimentary systems may be regularly mapped alluvial fans braided rivers both onshore and offshore coasts or areas of relict sediments and manganese nodules are suitable for this method

application of image based granulometry to siliceous and calcareous estuarine and marine sediments abstract grain size analysis has long been used as a descriptor of transport and depositional processes this paper presents the possibility of using image based granulometries not yet widely used in the earth sciences to characterize granulometric composition of unconsolidated estuarine and marine sediments to test the method conventional sediment analysis of siliceous and calcareous sediments are compared to image based analysis of sediments obtained along the ore estuary northern sweden and the adriatic sea croatia and italy these grains have different textural characteristics composition roundness and specific surface area granulometric parameters are calculated using both a graphical method and the mathematical method of moments grains have been imaged using a microscope and mathematical granulometries have been applied to the digital data image based granulometric moment descriptors are compared with sieve coulter counter derived moments although it is not claimed that digital imaging should be the only method used in sedimentology the results show the potential of applying digital electronic imaging to granulometric analysis of sediments in this way sampling for granulometric analysis and sieving processes combined with coulter counter analysis of fraction