statistical properties of armored gravel bed surfaces 1 roughness of successively developed armor layers in a large laboratory flume is analyzed considering gravel surfaces as two dimensional random fields of bed elevations statistically derived roughness parameters are evaluated from precise digital elevation models dems of bed surfaces and are discussed with respect to successive development of stable armor layers the key results relate to evolution of the probability distribution of bed elevations and its moments and structure functions of various orders with respect to armoring discharge our results suggest that statistical analysis of bed elevations is a helpful tool for defining roughness parameters quantifying armoring effects and identifying particle orientation flow direction and surface forming processes

chemical sedimentology and paleoenvironmental history of lake olduvai a pliocene lake in northern tanzania lake olduvai was a saline highly alkaline closed basin lake in which lacustrine sediments of bed i and lower bed ii of olduvai gorge were deposited between ca 1 92 and 1 70 ma the lake consisted of a lacustrine area the central basin cb surrounded by lake margin terrain that was alternately flooded and dried the lacustrine deposits consist largely of authigenic clay and carbonate minerals zeolites k feldspar chert and pyrite claystones of the cb and most of the eastern lake margin elm terrain consist chiefly of mg rich authigenic illite smectite and interlayered illite smectite i s these clays were formed penecontemporaneously with detrital clay deposition by interaction of the detrital clays with the saline highly alkaline water the lake olduvai clays average 65 70 mg 2 sio 2 and alkali ions from lake water and the remaining 30 35 is detrital clay lacustrine clays of the elm indicate that this area was flooded by saline water for substantial periods of time hominids occupied the elm at times of lower lake levels when the clays were dried calcite is the most abundant carbonate mineral and occurs chiefly as sand size euhedral crystals dispersed in claystone and less commonly as calcite crystal limestones and nodules the sand size calcite crystals were formed diagenetically at shallow depths possibly from a gaylussite and or micritic calcium carbonate precursor dolomite occurs chiefly in the form of dolostones some of which are probably of replacement origin the oxygen isotope composition of lake water and pore fluid of the cb varied over 11 as determined from calculated delta 18 o h 2 o values of authigenic minerals clay minerals were formed chiefly in the more saline waters sand size calcite crystals were generated mostly from less saline pore fluids and limestone nodules were formed chiefly from dilute pore fluid dolostones were formed from fluids of varying salinity hydrogeology of the central basin was complex and postdepositional fluid movements are documented by differing delta 18 o h 2 o values for different authigenic minerals of the same samples pore fluids moved within the lake deposits for a considerable period of time after deposition as shown by 18 o values of quartz and k feldspar formed at different times downward flow of lacustrine fluids is indicated by zeolitic alteration of the underlying tuffaceous alluvial deposits lake olduvai became overall shallower during the deposition of bed i and the subaerial exposure increased leading to occasional playa conditions these changes very likely resulted from increasing aridity and tectonic activity the lake that deposited lower bed ii was larger than that responsible for upper bed i and episodes of wetter climate alternated with drier periods in which salinity and probably temperatures were higher than in the bed i lake

remote laser induced breakdown spectroscopy analysis of east african rift sedimentary samples under mars conditions abstract laser induced breakdown spectroscopy will be used by the chemcam instrument on the curiosity rover to obtain chemical analyses of the martian surface surficial and deeper hydrothermal processes on mars have produced a diverse family of chemical and clastic sedimentary lithologies from primary igneous rocks through physical and chemical transport deposition and diagenesis this study uses 16 samples from the east african rift ear as martian analogues to assess use of libs to evaluate weathering reactions in sedimentary rocks data were acquired at 9 m distance with samples under conditions designed to simulate mars use of external validation in which a few sedimentary samples are added to the validation set coupled with choice of the first local minimum in the root mean square value in all the components of the validation model provides optimal results in this data set accuracy is measured using root mean square error predictions for major elements in the sedimentary rocks as expressed in wt oxides even lower errors can be obtained by using a more focused training set these results are sufficiently accurate to usefully characterize the four competing kinds of chemical weathering reactions in paleosols hydrolysis oxidation hydration and salinization

structural properties of mobile armors formed at different flow strengths in gravel bed rivers differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume the temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size microtopography and bed organization at both grain and mesoscales measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds structured mobile armors formed quickly in each experiment at the grain scale 1 45 mm 9 ds50 17 mm where ds50 is the median surface particle size surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor particles comprising the armor also became flow aligned and developed imbrication at a larger scale 100 200 mm the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations metrics of mobile armor structure showed remarkable consistency over prolonged periods of near constant transport demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure bed structuring was least developed in the experiments conducted at the lowest flow strength however little difference was observed in the structural metrics of the mobile armors generated at higher flows although the range of transport rates studied was limited the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low 0 03 where is the dimensionless shear stress

the spatial and temporal patterns of aggradation in a temperate upland gravel bed river intensive field monitoring of a reach of upland gravel bed river illustrates the temporal and spatial variability of in channel sedimentation over the six year monitoring period the mean bed level in the channel has risen by 0 17 m with a maximum bed level rise of 0 5 m noted at one location over a five month winter period these rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2 6 times and overbank flow time increasing by 12 8 hours this work raises the profile of coarse sediment transfer in the design and operation of river management specifically engineering schemes it emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic exploration of the sediment supply and transfer system can explain patterns of channel sedimentation the complex spatial seasonal and annual variability in sediment supply and transfer raise uncertainties into the system s response to potential changes in climate and land use thus there is a demand for schemes that monitor coarse sediment transfer and channel response copyright 2009 john wiley sons ltd

practical aspects of avo modeling avo amplitude variation with offset modeling contributes significantly in seismic data acquisition design and prestack seismic data processing and interpretation it has become a common practice in prestack seismic analysis it is also used for verifying and developing avo theories conducting avo modeling is by nature an exercise of multidiscipline integration it thus enhances reservoir characterization and reduces the risk in hydrocarbon exploration

stability morphology and surface grain size patterns of channel bifurcation in gravel cobble bedded anabranching rivers this study presents the first detailed field based analysis of the morphology of bifurcations within anabranching cobble gravel rivers bifurcations divide the flow of water and sediment into downstream anabranches thereby influencing the characteristics of the anabranches and the longevity of river islands the history morphology bed grain size and flow vectors at five bifurcations on the renous river new brunswick canada were studied in detail the angles of bifurcations within five anabranching rivers in the miramichi basin were investigated the average bifurcation angle was 47 within the range of values cited for braided river bifurcations bifurcation angle decreased when anabranches were of similar length shields stresses in channels upstream of bifurcations were lower than reported values for braided rivers stable bifurcations displayed lower shields stresses than unstable bifurcations contrary to experimental results from braided river bifurcations bifurcations in anabranching rivers are stabilized by vegetation that slows channel migration and helps to maintain a uniform upstream flow field the morphology of stable bifurcations enhances their stability a large bar shaped like a shallow ramp that increases in elevation to floodplain level forms at stable bifurcations floodplains at stable bifurcations accrete upstream at rates between 0 9 and 2 5 m a 1 bars may also form within the entrance of an anabranch downstream of the bifurcation node these bars are associated with bifurcation instability forming after a period of stability or an avulsion channel abandonment occurs when a bar completely blocks the entrance to one anabranch the stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term copyright 2006 john wiley sons ltd

using avo for fracture detection analytic basis and practical solutions tight low porosity reservoirs can produce significant amounts of hydrocarbons if fracture networks provide the necessary permeability characterization of naturally fractured reservoirs using surface seismic data is an important exploration problem that has attracted much attention in the literature tle for example had an entire issue august 1996 on this subject while the data and modeling in existing publications demonstrate that fracturing causes significant azimuthal variation in recorded seismic signatures the problem is how to infer fracture parameters from these data

3d seismic imaging of volcanogenic massive sulfide deposits in the flin flon mining camp canada part 2 forward modeling abstractwe applied seismic modeling for a detailed 3d geologic model of the flin flon mining camp canada to address some imaging and interpretation issues related to a 17 km2 3d survey acquired in the camp and described in a complementary paper part 1 a 3d geologic volumetric model of the camp was created based on a compilation of geologic data constraints from drillholes surface geologic mapping interpretation of 2d seismic profiles and 3d surface and grid geostatistical modeling techniques the 3d modeling methodology was based on a hierarchical approach to account for the heterogeneous spatial distribution of geologic constraints elastic parameters were assigned within the model based on core sample measurements and correlation with the different lithologies the phase screen algorithm used for seismic modeling was validated against analytic and finite difference solutions to ensure that it provided accurate amplitude variation with offset behavior for dipping strata synthetic data were gener

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

the importance of bed sediment sand content for the structure of a static armor layer in a gravel bed river the surface structure of static armor layers generated from water worked gravel bed channels was investigated with primary focus on the influence of sand content and flow rate flume experiments were conducted in which four sediment mixtures with sand contents between 1 and 38 were armored under one of three different flow rates first and second order statistical analyses were applied to digital elevation models of unarmored armored and clustered bed surface areas to identify changes in surface structure results were combined with data from previous research to create an extended data set of armored bed surfaces water worked unarmored bed surfaces established under a dynamic equilibrium flow rate impacted the topographic variability and structure of the armored beds surface complexity decreased with armor formation as surface grains preferentially aligned with the flow direction the bed surface became smoother and where sediment mixture sand content was constant there was greater smoothing of the surface during higher armoring flows as grains rearranged more easily as bulk sand content increased statistical analyses of the expanded data set showed that beds with very little sand content developed static armor layers that remained rough and had greater topographic variability than armor layers from sediments with higher sand contents the bulk sediment sand content exerted a stronger influence over the change in surface roughness and structure upon armoring than that of the flow rate during armor formation when combined with the knowledge of the local flow regime the sand content may aid in predictions related to armored bed surface structure

weighted stacking for rock property estimation and detection of gas amplitude versus offset concepts can be used to generate weighted stacking schemes here called geo stack which can be used in an otherwise standard seismic data processing sequence to display information about rock properties the zoeppritz equations can be simplified and several different approximations appear in the literature they describe the variation of p wave reflection coefficients with the angle of incidence of a p wave as a function of the p wave velocities the s wave velocities and the densities above and below an interface using a smooth representative interval velocity model from boreholes or velocity analyses and assuming no dip the angle of incidence can be found as a function of time and offset by iterative ray tracing in particular the angle of incidence can be computed for each sample in a normal moveout corrected cmp gather the approximated zoeppritz equation can then be fitted to the amplitudes of all the traces at each time sample of the gather and certain rock properties can be estimated the estimation of the rock properties is achieved by the application of time and offset variant weights to the data samples before stacking the properties which can be displayed by geo stack are p wave reflectivity or true zero offset reflectivity s wave reflectivity and the reflectivity of p wave velocity divided by s wave velocity or pseudo poisson s ratio reflectivity if assumptions are made about the relation between p wave velocity and s wave velocity for water bearing clastic silicate rocks then it is possible to create a display which highlights the presence of gas

evolution of seismic interpretation during the last three decades the ingredients of seismic interpretation include the right mix of geological and geophysical knowledge together with a liberal dose of imagination tempered with a considerable amount of patience seismic interpretation is a skill that one acquires with experience but is constantly reinvigorated with new ideas and tools provided by younger university graduates the prime ingredients for seismic interpretation are seismic reflection data coupled with a geologic depositional and tectonic model which together provide the framework for integrating borehole microseismic and production data resulting in a good reservoir model although commonly used in both engineering and environmental applications most seismic reflection surveys are acquired for oil and gas exploration in both land and offshore areas around the world hydrocarbon accumulations are found at varying depths of a few thousand meters below the earth s surface which are ultimately confirmed by drilling because the cost of drilling closely sp

reducing 3 d acquisition footprint for 3 d dmo and 3 d prestack migration the acquisition patterns of 3 d surveys often have a significant effect on the results of dip moveout dmo or prestack migration when the spatial distribution of input traces is irregular results from dmo and migration are contaminated by artifacts in many cases the footprint of the acquisition patterns can be seen on the migrated section and may result in incorrect interpretation this phenomena also has a very significant effect on the feasibility of conducting amplitude variation with offset avo analysis after 3 d prestack migration or after 3 d dmo and also may affect velocity analysis we propose a simple enhancement to migration and dmo programs that acts to minimize acquisition artifacts

isolating roughness scales of gravel bed patches there is a growing consensus that gravel bed roughness should be parameterized based on bed surface topography not only sediment size one benefit is the possible identification of various spatial scales of surface roughness and evaluation of their respective contributions to flow resistance and also to bedload transport the absence of relationships between roughness at the different scales is apparent in previous work which currently limits roughness parameterization from topography and application in flow modeling this study examines the use of moving window detrending on gravel bed digital elevation models dems for isolating roughness scales and their respective signatures a large dataset of 35 water worked gravel bed patches from both the laboratory and the field was used for the analysis the measured bed topography was separated into two distinct dems one representing grains the other representing small bedforms for all dems bed elevation parameters measuring vertical roughness imbrication and spatial correlations were determined our results show distinct topographic signatures between grain and bedform dems we show strong positive linear relationships between grain vertical roughness and the size of the bed surface material surface sediment arrangement also determined bedform shape with groupings of coarse sediment forming humps on the surface and finer sediment sheltered in hollows patch scale vertical roughness could not be estimated simply as the sum of grain and bedform vertical roughness instead our results suggest weighted summation and the existence of universal weighting coefficients practical applications for studies on gravel bed roughness and flow modeling using dems are discussed

the impact of migration on avo amplitude variation with offset avo analysis is often limited to areas where multidimensional propagation effects such as reflector dip and diffractions from faults can be ignored migration inversion provides a framework for extending the use of seismic amplitudes to areas where structural or stratigraphic effects are important in this procedure sources and receivers are downward continued into the earth using uncollapsed prestack migration instead of stacking the data as in normal migration the prestack migrated data are used in avo analysis or other inversion techniques to infer local earth properties the prestack migration can take many forms in particular prestack time migration of common angle sections provides a convenient tool for improving the lateral resolution and spatial positioning of avo anomalies in this approach a plane wave decomposition is first applied in the offset direction separating the wavefield into different propagating angles the data are then gathered into common angle sections and migrated one angle at a time the common angle migrations have a simple form and are shown to adequately preserve amplitude as a function of angle normal avo analysis is then applied to the prestack migrated data examples using seismic lines from the gulf of mexico show how migration improves avo analysis in the first set of examples migration is shown to improve imaging of subtle spatial variations in bright spots subsequent avo analysis reveals dim spots associated with dry hole locations that were not resolvable using traditional processing techniques including both conventional avo and poststack migration a second set of examples shows improvements in avo response after migration is used to reduce interference from coherent noise and diffractions a final example shows the impact of migration on the spatial location of dipping avo anomalies in all cases migration improves both the signal to noise ratio and spatial resolution of avo anomalies

comparison of avo indicators a modeling study a worldwide collection of 25 sets of velocity and density measurements from adjacent shales brine sands and gas sands was acquired with full waveform sonic dipole sonic and conventional well logging devices and or in the laboratory these data provide theoretical shale over brine sand and shale over gas sand p wave and s wave normal incidence reflection coefficients r p and r s avo intercepts a avo gradients b the avo indicators r p r s reflection coefficient difference and a b avo product the reflection coefficient difference is found to be a more universal indicator than the avo product in clastic stratigraphic intervals for shale over brine sand re flections the average r p r s tends to be near zero and relatively invariant with depth irrespective of gas sand impedance r p r s is always negative for shale over reservoir quality gas sand reflections and more negative than for the corresponding brine sand reflections in comparison the avo product may be positive near zero or negative for gas sands depend ing on the impedance contrast with the overlying shale these measurements also verify that r p r s is well approximated by a simple linear combination of a and b

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

estimating local bed shear stress from velocity observations replicate velocity observations using conventional equipment under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements the bed shear velocity u can be estimated within 3 using the depth averaged velocity in the vertically averaged logarithmic velocity profile to be accurate this method is limited to relatively simple flow geometries which may be expected to have the appropriate velocity structure estimates of u made using a single near bed velocity observation are less precise by a factor of 3 because of the larger uncertainty associated with a single observation accuracy of this method requires appropriate flow conditions only near the bed so it may be applied in a wider range of flow conditions including spatially variable flow estimates of u from the slope of the near bed velocity profile are the least precise and require the most restrictive flow conditions for accuracy but offer the advantage that they may be made without independent knowledge of the bed roughness different methods for estimating roe should be useful in judging the precision of estimates made under similar conditions these estimates of precision together with considerations of convenience and model accuracy provide the basis for select ing the most appropriate or advantageous method for different conditions and purposes

an integrated target oriented prestack elastic waveform inversion sensitivity calibration and application an integrated target oriented prestack elastic wave form inversion procedure is implemented to estimate lithology fluid type and pay thickness of a layered target zone from surface seismic pp reflection data the integrated inversion procedure consists of three parts data processing and preparation iterative seis mic inversion and rock property integration in the data processing and preparation the seismic field gathers are processed and transformed into plane wave seismograms and the well logs are prepared for establishing a well tie the well tie is established using synthetics from a layered model obtained from block ing sonic shear sonic and density logs the layered model is later used as the a priori starting model for the iterative seismic inversion based on the a priori starting model and using the processed plane wave seismograms as input p wave velocity vp s wave velocity vs density p and thickness h of each layer in the layered target zone are estimated at each cdp location in the iterative seismic inversion

mars surface diversity as revealed by the omega mars express observations the observatoire pour la mineralogie l eau les glaces et l activite omega investigation on board the european space agency mars express mission is mapping the surface composition of mars at a 0 3 to 5 kilometer resolution by means of visible near infrared hyperspectral reflectance imagery the data acquired during the first 9 months of the mission already reveal a diverse and complex surface mineralogy offering key insights into the evolution of mars omega has identified and mapped mafic iron bearing silicates of both the northern and southern crust localized concentrations of hydrated phyllosilicates and sulfates but no carbonates and ices and frosts with a water ice composition of the north polar perennial cap as for the south cap covered by a thin carbon dioxide ice veneer

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

framework for avo gradient and intercept interpretation amplitude variation with offset avo interpretation may be facilitated by crossplotting the avo intercept a and gradient b under a variety of reasonable petrophysical assumptions brine saturated sandstones and shales follow a well defined background trend in the a b plane generally a and b are negatively correlated for background rocks but they may be positively correlated at very high vp vs ratios such as may occur in very soft shallow sediments thus even fully brine saturated shallow events with large reflection coefficients may exhibit large increases in avo deviations from the background trend may be indicative of hydrocarbons or lithologies with anomalous elastic properties however in contrast to the common assumptions that gas sand amplitude increases with offset or that the reflection coefficient becomes more negative with increasing offset gas sands may exhibit a variety of avo behaviors a classification of gas sands based on location in the a b plane rather than on normal

causal fracture prediction curvature stress and geomechanics we propose scaling volume curvature measurements with material property estimates to produce a superior prediction of natural fractures curvature is one of many indirect fracture inferring attributes it does not detect fractures but is causally related to them through the assumption that increasing curvature relates to increasing strain there are many other variables that are causally related to fractures we propose that it would be advantageous to create combinations of these causal variables with curvature some of the most well known and important causes of variations in natural fracture density are material properties relating to brittleness material properties are critical geologically at all scales from large scale regional studies to prospect level inquiries because the properties may vary significantly within individual formations and between formations these vertical and lateral changes in material properties may be important and should be considered in fracture estimation along with c

estimation of effective roughness for water worked gravel surfaces abstractthere is no accepted standard equation for predicting flow resistance in gravel rivers this is mainly because of the lack of an effective approach for describing the roughness of the gravel surface this paper aims at describing the roughness of gravel surfaces based on characteristics of the elevation field rather than conventionally used grain size distribution a new parameter the coarseness parameter in addition to the steepness parameter and standard deviation of the elevation field is proposed for characterizing the roughness of gravel surfaces two groups of rough surfaces a and b were generated using unconditional gaussian simulation to study the influence of the coarseness and steepness parameters on effective roughness the effective roughness of groups a and b was calculated by a two equation turbulence model and a quantitative relationship between the effective roughness and proposed parameters was derived the resulting relationship derived from groups a and b was validated using

quantitative geochemical approach to pedogenesis importance of parent material reduction volumetric expansion and eolian influx in lateritization abstract using mass balance techniques we test the prevalent view that laterite genesis is dominated by in situ residual enrichment during chemical weathering of bedrock through calculation of net mass fluxes through the laterite soils in mali west africa we show that residual enrichment by removal of mobile elements with a corresponding increase in bulk porosity and decrease in bulk density contributes only a very minor fraction of the enrichment of al fe si and au instead we demonstrate that the abundance of these elements is due to the influx and accumulation by selective retention of chemically mature detritus of local and foreign origin clearly evident in micromorphological infilling features at the same sample depths that accumulation reaches extreme values we show that volumetric expansion in excess of 200 has occurred locally we infer that these spatially coincidental zones of mass influx of rock forming metals fe al si and also au with dilational hyperstrains result from a mutually reinforcing mechanical interaction between material influx and the effects of subsurface deformational processes such as shrink swell cycles and root growth and decay we propose that with progressive infilling of available connected voids by illuvial microsedimentary deposits of insoluble resistate and neoformed minerals the capacity for the combined skeleton and plasma to remain isovulumetric is exceeded we speculate that the resultant space problem is relieved by upwards expansion towards the overlying free surface continued translocation and void infilling occur and are limited to the depth where the size of translocational particles is smaller than that of the connected voids consequently progressive hyperstrains accumulate above this critical depth by the long term influence of a proposed translocational wedge of chemically resistant minerals against which numerous generations of plant roots have exerted stresses eclectic surficial contaminants involved are continuously derived from above leaving no indication of a relict source region within the present soil profile from which they might have been extracted instead the source region is largely the existing regolith column itself which releases local material and in addition is supplemented by deposition of colluvial detritus shed nearby by escarpment retreat

spatial structure of near bed flow properties at the grain scale abstract expanding the existing knowledge of the role of roughness on near bed flow properties is vital to provide deeper insights into the interactions between the flow sediment transport morphology and ecology this study uses four fixed beds from both the laboratory and the field to characterise the structure of near bed flow properties dense measurements over a grid of 6 mm spacing were conducted across each cast using an acoustic doppler velocimeter these measurements followed the line of the bed topography with the sampling location being 2 mm away from the maximum bed elevations near bed flow properties were calculated across the surface including velocity turbulence intensity turbulent kinetic energy reynolds stress and quadrant analysis improved visualisation of flow properties involves contour plots of the spatial distribution of flow over the dem of the gravel bed to facilitate attributions of flow patterns to roughness and topography using the standard deviation of elevations as a proxy for grain roughness of each surface we observed that a decrease in roughness led to an increase in the average near bed velocity in contrast an increase in roughness resulted in an increase in both turbulence intensity and turbulent production tke analysis of quadrant events dominating across the surface can provide indications into the potential for erosion and or deposition across the natural mobile surfaces finally second order structure function analysis is used to quantify the spatial structure of flow properties presenting novel isopleth maps of flow properties for the majority of flow properties across all surfaces the range in the spatial extent of flow structures is between 1 and 2 25 d50a except for transverse and vertical velocities which have a wider range up to 3 5 d50a

do alternate bars affect sediment transport and flow resistance in gravel bed rivers in natural gravel bed streams the complex topography of the bed can cause variation of flow resistance and sediment transport previous studies have shown that in addition to grain resistance skin friction flow resistance is also caused by bank roughness channel bars bed undulations and channel curvature sediment transport is similarly influenced by the complex topography and the transport rate can vary spatially a three dimensional 3d numerical model was used to generate a detailed description of the flow and bedload transport fields in gravel bed rivers here we quantify the reach averaged hydraulic resistance and sediment transport regime that prevails when self formed alternate river bars are present and compare with the regime that would prevail were no bars are present we do this by comparing the results of i a 3d morphodynamic model in which bars form as a consequence of flow bed interaction and ii an equivalent one dimensional 1d case which refers to flat bed conditions but otherwise corresponding to identical average velocity and bed slope the 3d numerical model is applied to generate different bed topographies of alternate bars at regime morphological equilibrium then extended to non equilibrium conditions for decreasing shear stress within a sensitivity analysis context the contribution of grain resistance is estimated with the local values of the bed shear stress while bar resistance results from the overall deviation of the flow field from that occurring in the flat bed configuration the local sediment transport in both the longitudinal and transverse directions is computed with the local shields stress and local bed inclination the calculations result in a method for correcting 1d models to account for the total sediment transport and resistance in a cross section due to 3d effects of alternate bars we term the resulting relations morphologically averaged sediment transport and resistance equations copyright 2012 john wiley sons ltd

water worked gravel beds in laboratory flumes a natural analogue an investigation has been conducted to identify the key parameters that are likely to scale laboratory sediment deposits to the field scale two types of bed formation were examined one where sediment is manually placed and screeded and the second where sediment is fed into a running flume this later technique created deposits through sequential cycles of sediment transport and deposition detailed bed surface topography measurements have been made over a screeded bed and three fed beds in addition bulk subsurface porosity and hydraulic conductivity have been measured by comparing the four beds results revealed that certain physical properties of the screeded bed were clearly different from those of the fed beds the screeded bed had a random organization of grains on both the surface and within the subsurface the fed beds exhibited greater surface and subsurface organization and complexity and had a number of properties that closely resembled those found for water worked gravel beds the surfaces were water worked and armoured and there was preferential particle orientation and direction of imbrication in the subsurface this suggested that fed beds are able to simulate in a simplified manner both the surface and subsurface properties of established gravel bed river deposits the near bed flow properties were also compared it revealed that the use of a screeded bed will typically cause an underestimation in the degree of temporal variability in the flow furthermore time averaged streamwise velocities were found to be randomly organized over the screeded bed but were organized into long streamwise flow structures over the fed beds it clearly showed that caution should be taken when comparing velocity measurements over screeded beds with water worked beds and that the formation of fed beds offers an improved way of investigating intragravel flow and sediment water interface exchange processes in gravel bed rivers at a laboratory scale copyright 2008 john wiley sons ltd

automated analysis of imbrication and flow direction in alluvial sediments using laser scan data abstract an automated method for analysis of imbrication and flow direction in alluvial sediments is described that uses digital elevation models dems derived from three dimensional laser scanning of dry gravel river beds a global analysis of the dem is used that does not depend on location and analysis of individual grains the method is more convenient and quantitative than are existing techniques methods are described for determining the suitability of particular data sets for analysis by this method the method is applied to gravel river beds on the south island of new zealand

hydrothermal hydration of martian crust illustration via geochemical model calculations if hydrothermal systems existed on mars hydration of crustal rocks may have had the potential to affect the water budget of the planet we have conducted geochemical model calculations to investigate the relative roles of host rock composition temperature water to rock ratio and initial fluid oxygen fugacity on the mineralogy of hydrothermal alteration assemblages as well as the effectiveness of alteration to store water in the crust as hydrous minerals in order to place calculations for mars in perspective models of hydrothermal alteration of three genetically related icelandic volcanics a basalt andesite and rhyolite are presented together with results for compositions based on snc meteorite samples shergotty and chassigny temperatures from 150 c to 250 c water to rock ratios from 0 1 to 1000 and two initial fluid oxygen fugacities are considered in the models model results for water to rock ratios less than 10 are emphasized because they are likely to be more applicable to mars in accord with studies of low grade alteration of terrestrial rocks we find that the major controls on hydrous mineral production are host rock composition and temperature over the range of conditions considered the alteration of shergotty shows the greatest potential for storing water as hydrous minerals and the alteration of icelandic rhyolite has the lowest potential

morphology and surface sedimentary features of point bars in welsh gravel bed rivers two examples of point bars in single channel gravel bed rivers in wales illustrate some of the morphological and surface sedimentary features observed during a wider examination of 40 sites of recent less than 100 years channel sedimentation the point bars consist of predominantly sandy gravel bar platforms overlain by discontinuous sand bodies cut bank exposures show generally massive sandy gravels abruptly underlying a silt sand unit morphologically the bars are platformlike with primary inner attached or secondary medial chutes this relief together with the effects of seasonal vegetation determines the locations of finer grained non gravel material the frequency with which deposits produced by this type of channel sedimentation may be encountered in quaternary and pre quaternary successions is briefly discussed

the effect of interpolation on imaging and avo a viking case study the use of prestack interpolation prior to prestack migration to improve avo analysis on image gathers is demonstrated on an exploration play the interpolation achieves this improvement by reducing migration artifacts avo analysis attempts to estimate fundamental information from surface seismic data and likely will be used more frequently if the estimates can be more accurately produced land 3d seismic typically has poor and irregular sampling this poor sampling creates migration noise which is a material cause of inaccurate avo estimates prestack 5d interpolation is applied prior to prestack migration and avo analysis on the imaged gathers to address this noise problem the interpolation algorithm includes offset and azimuth dimensions that preserve avo information this method is evaluated bycomparing the results to those of alternate approaches such as superbinning that suppress this kind of noise in avo analysis the evaluation is determined by comparing our ability to predict the reservoir q

field application of close range digital photogrammetry crdp for grain scale fluvial morphology studies in situ measurement of grain scale fluvial morphology is important for studies on grain roughness sediment transport and the interactions between animals and the geomorphology topics relevant to many river practitioners close range digital photogrammetry crdp and terrestrial laser scanning tls are the two most common techniques to obtain high resolution digital elevation models dems from fluvial surfaces however field application of topography remote sensing at the grain scale is presently hindered mainly by the tedious workflow challenges that one needs to overcome to obtain high accuracy elevation data a recommended approach for crdp to collect high resolution and high accuracy dems has been developed for gravel bed flume studies the present paper investigates the deployment of the laboratory technique on three exposed gravel bars in a natural river environment in contrast to other approaches having the calibration carried out in the laboratory removes the need for independently surveyed ground control targets and makes for an efficient and effective data collection in the field optimization of the gravel bed imagery helps dem collection without being impacted by variable lighting conditions the benefit of a light weight three dimensional printed gravel bed model for dem quality assessment is shown and confirms the reliability of grain roughness data measured with crdp imagery and dem analysis evidences sedimentological contrasts between gravel bars within the reach the analysis of the surface elevations shows the effect variable grain size and sediment sorting have on the surface roughness by plotting the two dimensional structure functions and surface slopes and aspects we identify different grain arrangements and surface structures the calculation of the inclination index allows determining the surface forming flow direction s we show that progress in topography remote sensing is important to extend our knowledge on fluvial morphology processes at the grain scale and how a technique customized for use by fluvial geomorphologists in the field benefits this progress copyright 2016 john wiley sons ltd

interaction between migrating bars and bifurcations in gravel bed rivers 1 in the present work we investigate the interaction between migrating alternate bars and the dynamics of river bifurcations laboratory experiments are carried out to study a y shaped bifurcation with fixed banks and erodible bed composed of well sorted sand the problem is also analyzed by developing a theoretical one dimensional model results show the occurrence of regular fluctuations in the discharge distribution at the bifurcation node which are strictly related to bar migration the effectiveness of bars in conditioning the bifurcation behavior increases with bar amplitude and decreases with bar migration speed four qualitatively different behaviors of the system are observed as the controlling parameters of the flow are varied within a range significant for gravel bed rivers the theoretical predictions are in good qualitative agreement with the experimental observations

interpretation of alluvial beds through bed elevation distribution moments 1 with equipment advances now enabling the measurement and processing of alluvial bed elevation data at high spatial and temporal resolutions the moments of measured bed elevation distributions can be used to characterize riverbed structure from analyses of a wide range of high quality data sets for a range of flows sediments and types of bed surface e g armoured gravels uniform sands ripples and dunes at laboratory and field scales the standard deviation of bed elevations is found to provide a robust integral measure of bed roughness height this approach has the statistical advantage of utilizing all relevant bed elevation information and also removes any potential need to subjectively identify valid individual roughness elements within the measured bed data in addition to defining the vertical roughness scale for a bed surface the general shape of the bed surface forms or elements can be characterized by the bed elevation distribution skewness sk with the distribution kurtosis ku providing a measure of the evenness or intermittency of these elements based on the present analyses a schematic sk ku plane is presented to aid interpretation of the structure of steady state and developing alluvial bed surfaces from measured bed elevation distributions where various bed surface types e g artificially smoothed beds armoured gravel beds planar beds of mobile uniform sediments ripples and dunes can be differentiated based on this diagram relatively large values of ku that can occur for a measured riverbed surface are associated with intermittent bed roughness elements as can arise for supply limited dunes or widely distributed pebble clusters or bed forms on an otherwise plane bed

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

measurement of gravel bed topography evaluation study applying statistical roughness analysis abstractin this two part study experiments are conducted to evaluate available topography measurement techniques for gravel beds in a laboratory flume and to study their suitability for statistical roughness analysis the available instruments for this study include 1 an acoustic bed profiler 2 a hand held laser scanner and 3 two digital consumer cameras forming a stereophotogrammetric system and are employed to obtain digital elevation models dems of water worked gravel beds in the first part of the study the three measurement techniques are reviewed and their feasibilities for future grain scale roughness work assessed based on the obtained elevation datasets water worked gravel bed topographies are measured with all three available measurement techniques the analysis of the dems concentrates on using probability distribution functions pdfs and second order structure functions of bed elevations roughness coefficients are determined and used as a benchmark for comparison of the three

modeling river bed morphology roughness and surface sedimentology using high resolution terrestrial laser scanning 1 recent advances in technology have revolutionized the acquisition of topographic data offering new perspectives on the structure and morphology of the earth s surface these developments have had a profound impact on the practice of river science creating a step change in the dimensionality resolution and precision of fluvial terrain models the emergence of hyperscale survey methods including structure from motion photogrammetry and terrestrial laser scanning tls now presents the opportunity to acquire 3 d point cloud data that capture grain scale detail over reach scale extents translating these data into geomorphologically relevant products is however not straightforward unlike traditional survey methods tls acquires observations rapidly and automatically but unselectively this results in considerable noise associated with backscatter from vegetation and other artifacts moreover the large data volumes are difficult to visualize require very high capacity storage and are not incorporated readily into gis and simulation models in this paper we analyze the geomorphological integrity of multiscale terrain models rendered from a tls survey of the braided river feshie scotland these raster terrain models are generated using a new computationally efficient geospatial toolkit the topographic point cloud analysis toolkit topcat this performs an intelligent decimation of point cloud data into a set of 2 5 d terrain models that retain information on the high frequency subgrid topography as the moments of the locally detrended elevation distribution the results quantify the degree of terrain generalization inherent in conventional fluvial dems and illustrate how subgrid topographic statistics can be used to map the spatial pattern of particle size grain roughness and sedimentary facies at the reach scale

benefiting from 3d avo by using adaptive supergathers 3d surface seismic data have many useful features e g fine sampling better resolution that coupled with the fact that 3d prestack time or depth migration yields accurate imaging of subsurface features are good reasons to conclude that performing avo analysis on 3d data will be beneficial as it is on 2d data

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s