application of microfocus computed tomography in carbonate reservoir characterization possibilities and limitations normally thin section petrography by which observations are made in two dimensions forms the basis of sedimentpetrological reservoir appraisal studies in reservoir characterization however insight in the three dimensional mineral and porosity distribution is necessary in this study microfocus computed tomography ct which is a non destructive technique has been used for 3d characterization of the mineral phases i e calcite dolomite anhydrite and porosity in carbonate reservoir rocks in order to obtain quantitative information on density and atomic number of the scanned reservoir samples as well as about their rock texture a dual energy scanning technique has been used additional beam artifact correction and a segmentation algorithm focused on differentiating calcite dolomite and anhydrite have been implemented to validate the developed methodology thin sections of scanned samples of the khuff formation oman have also been analyzed petrographically and compared to corresponding ct sections and to the results of the dual energy algorithms despite the lower resolution when compared to thin section analysis the accuracy of the dual energy technique is in the range of the standard point counting technique and estimations can be made concerning the microporosity of the samples since the developed dual energy methodology provides a fast and objective determination of the percentages of the mineralogical phases ct becomes a very powerful tool in the evaluation of the reservoir potential and in the quantification of mineralogical changes in sedimentary systems e g cycles in addition images are acquired visualizing and quantifying the spatial distribution of these phases in three dimensions which is a major advantage compared to classic 2d thin section petrography

non destructive fabric analysis of prehistoric pottery using high resolution x ray microtomography a pilot study on the late mesolithic to neolithic site hamburg boberg abstract the characterisation of prehistoric pottery fragments presents a quite complex task in provenance studies petrographic and chemical analyses of the ceramic materials are employed to investigate potential production areas in respect to the geolocial background moreover also the production technology of the firing process as well as the forming techniques used by the prehistoric potters are of great interest their investigation is most often accompanied by a destructive preparation of the samples in this paper we want to present high resolution x ray microtomography ct a non destructive and non invasive method as a supplementary research tool in the study of prehistoric pottery ceramic fragments from the endmesolithic neolithic site hamburg boberg 15 northern germany were analysed by x ray microtomography ct inspection combines quantification and shape analysis of fabric components by means of computer aided image processing as the ct method is sensitive to material densities qualitative and quantitative analyses of different temper materials are possible furthermore the ct method permits the characterisation of the connectivity within the porous system as well as the analysis of the orientation of the pore structures which are indicative for vessel forming techniques although limited by the resolution of the reconstructed images distribution analysis of heavy minerals in the clay matrix can offer distinctive features to discriminate various clay sources moreover x ray microtomography can be used to infer the nature of organic temper even with all plant remains completely burnt out during the firing process the visualisation of the high resolution true volume renderings and their detailed morphometric characterisation enables new avenues in the study of ceramic technology

quantitative analysis of reservoir rocks by microfocus x ray computerised tomography abstract microfocus computer tomography ct is a non destructive imaging technique that allows visualisation of internal features within non transparent objects such as sedimentary rocks with resolution as good as 10 m in three dimensions this technique is highly superior to medical ct widely used in geology and material sciences superior resolution is achieved by decreasing the x ray spot size which allows a decrease in the penumbra effect and an increase in primary magnification by placing the sample close to the x ray source since polychromatic x ray sources are used the technique is not free of artefacts application of filtering techniques is recommended to circumvent these artefacts and to achieve good quality images for quantitative analysis application of a dual energy approach allows quantification of density as well as effective atomic number distribution of internal features as the technique acquires data in 3d ct provides an ideal tool to link 2d thin section petrography to 3d petrophysical measurements or to be used within an upscaling approach a number of applications and the use of dual energy density and effective atomic number characterisations are presented attention is also paid to some of the limitations of this technique

bedload path length and point bar development in gravel bed river models low sinuosity meandering gravel bed flume experiments were employed to investigate spatial patterns of deposition which point to patterns of channel development related to the pool and bar morphology at channel forming discharges fluorescent bedload tracers indicate that deposition is typically focused around the point bar apex downstream of the apex contributing to downstream bar migration and at the bar head riffle surface seven flume experimental runs illustrate a sequence of point bar development related to the spatial patterns of tracer deposition and the related path length distribution at early stages of bar formation transport is from the scour zone across the point bar head to the bar apex and bar margin downstream of the apex as the point bar develops bedload transport across the bar decreases as transport along the channel thalweg increases and sediment is deposited along the bar margin deposition cells appear to move from downstream to upstream of the bar apex as this sequence of bar formation progresses at low non channel forming discharges transport occurs to the bar head riffle surface with very little material being transported to the apex region or point bar interior the implication is that there is an inherent connection between the loci of particle deposition and point bar formation largely controlled by the morphology of the channel

automated statistical method to align 2d chemical maps with 3d x ray computed micro tomographic images of soils abstract recent 2 dimensional measurements reveal that soils are chemically very heterogeneous at nanometric and micrometric scales direct measurement techniques are still lacking to extend these observations to 3 dimensions sequential sectioning of soils followed by 2 dimensional mapping of chemical elements and geometric interpolation to 3d appears to be the only available alternative unfortunately sectioning of soil samples suffers from geometric distortions that are difficult to avoid in practise in this regard the objective of the research described in this article was to develop a procedure enabling one to locate in a 3d x ray microtomographic image of a soil sample a physical surface that is obtained by sectioning and for which a number of chemical maps are available this procedure involves three steps 1 the reconstitution of the physical structure of the soil layer surface 2 the alignment of the chemical maps with the reconstituted soil surface image and 3 the 3d alignment of the 2d chemical maps with the internal structure of the soil cube visual comparison of the c and si maps and of the reconstituted ct images of the layer surfaces suggests a good correspondence between them which is supported by pearson correlation coefficients of 0 57 0 58 0 45 and 0 43 for the different surfaces and elements considered relative to the original 3d x ray ct image of the soil sample the planes associated with the c and si maps respectively are nearly superposed which further confirms the validity of the alignment procedure

geometry and grain size characteristics of the basal surface of a braided river deposit description of the three dimensional geometry and grain size patterns of fluvial deposits and their relationship to the morphodynamics of the river has been an elusive objective in sedimentology hindered by limited exposure and the time scale of fluvial dynamics in small scale physical models the time scales are short enough to map river morphology and sedimentology during significant and continuous morphological development of the river and its deposits especially for braided rivers using close range digital photogrammetry the dynamics of the river morphology and resulting deposit geometry and sedimentology were captured using digital elevation model differencing techniques combined with automated grain size mapping from image texture analysis using these novel methods we show the temporal development and characteristics of braided river deposit geometry and for the first time map the characteristics and development of the basal surface of braided river deposits in relation to river morphodynamics and formative processes the basal surface has considerable relief wide variation in grain size similar to that of the river as a whole develops progressively over time by switching of channels producing adjacent patches and ribbons of basal incision of different ages and is only partially related to bed scour associated with laterally migrating channel confluences

mineralogy of nitrogenous guano on the bounty islands sw pacific ocean by far the commonest consituents of insular phosphate deposits are calcium phosphates of the apatite series of minerals especially varieties that contain structural carbonate in their crystal lattices e g francolite and dahllite this reflects the fact that the vast majority of described insular phosphate deposits occur in low latitudes where they have formed in a tropical environment by metasomatic replacement of carbonate in coral substrates by phosphate derived either from avian excrement or from phosphorus enriched lagoonal lacustrine waters thin recently formed guano accumulations on islands of the subantarctic bounty group differ radically in that they consist principally of struvite a hydrated ammonium magnesium phosphate that is better known as a component of human mammalian urinary stones and enteroliths and of bat guano in sheltered speleothems apatite occurs only in an accessory role in the bounty islands guano this contrast in mineralogy and the somewhat anomalous survival of soft unstable struvite in a totally exposed environment on the bounty islands are attributed to climatic factors and to the nature of the granodioritic rock substrate

hydraulic modeling of bed load transport in gravel bed laba river on the basis of a field study of a piedmont braided reach of the gravel bed laba river in the northern caucasus russia an undistorted 1 50 scale mobile bed hydraulic model was constructed in an outdoor experimental plot of the state hydrological institute st petersburg russia channel and hydraulic regimes of the laba river were studied in this model attention was paid to the regime of bed load transport and its relation to the hydraulic characteristics of the flow the same problems were investigated in an 100 m long 1 m wide flume with glass walls also located at the state hydrological institute and in an 18 m long 2 46 m wide steel tilting flume at hr wallingford ltd u k quantitative characteristics of bed load transport were obtained from the laboratory experiments and compared with the field data proximity of the field and scaled up laboratory data demonstrates that the processes of bed load transport of gravel bed rivers can be faithfully reproduced in small scale models and flumes

small is beautiful upscaling from microscale laminar to natural turbulent rivers 1 the use of microscale experimental rivers with flow depths of the order of a few millimeters to investigate natural processes such as alluvial fans dynamics knickpoints migration and channel morphologies such as meandering and braiding has become increasingly popular in recent years this raises the need to address the issue of how to extrapolate results from the experimental microscale at which flow is laminar to the scale of natural turbulent rivers we address this question by performing measurements of average flow velocity and sediment transport in an experimental laminar river the average flow velocity is correctly predicted from the navier stokes equation solved for a steady uniform laminar flow laminar sediment transport is found to be consistent with the law of meyer peter and muller 1948 commonly used to describe sediment transport in natural turbulent rivers we also show that surface tension is important only if the microscale river width is on the order of or smaller than the capillary length these results allow us to demonstrate that the evolution of longitudinal bed profiles of turbulent and laminar rivers are governed by identical dimensionless equations and therefore follow the same dynamics differences of time and length scales at work in experimental and natural rivers are mainly encoded in the expression of two parameters a diffusion coefficient and a threshold slope on the basis of this analysis we derive a set of equations allowing us to rescale bed elevation downstream distance time and uplift rate from an experimental microscale river to the field scale finally we show how this set of equations can be used to rescale these same parameters in the case of a temporally varying discharge

net local removal of floodplain sediment by river meander migration abstract erosion from the banks of meandering rivers causes a local influx of sediment to the river channel most of the eroded volume is usually replaced in nearby point bars however the typical geometry of river bends precludes the local replacement of all eroded material because i point bars tend to be built to a lower elevation than cutbanks and ii point bars tend to be shorter than the eroding portion of cutbanks because of channel curvature in a floodplain that is in equilibrium i e neither increasing nor decreasing in volume sediment eroded from cut banks must be replaced elsewhere on the floodplain the local imbalance caused by differences in bank height should be balanced primarily by overbank deposition while the local imbalance caused by curvature should be balanced primarily by deposition in abandoned stream courses or oxbow lakes estimates of these local imbalances based on remotely sensed measurements of bank geometry and channel migration have been made on four systems in the united states a 91 km reach of the pearl river in louisiana and mississippi a 62 km reach of the bogue chitto river in louisiana a 35 km reach of the neuse river in north carolina and a 2 7 km reach of the vermillion river in minnesota for these systems the total local imbalance integrated over many bends ranged from 0 36 to 2 27 m 3 yr m of valley length 0 15 to 1 32 m 3 yr m of channel length or 7 to 45 of gross cutbank erosion with a typical value of about 17 when compared with gauged suspended sediment data the measurements provide estimates of the relative importance of floodplains for storing material transported by a river system the data suggest that even if the studied systems are near long term mass balance equilibrium as opposed to undergoing net deposition or erosion almost all of the sand and in some cases much of the silt and clay in transit through these systems is likely to have spent some time stored in an upstream floodplain

predicting downstream hydraulic geometry a test of rational regime theory 1 the classical equations of hydraulic geometry are purely empirical but the widespread similarity of the scaling downstream form of them suggests that they express some important underlying regularities in the morphology of stream channels through the drainage network a successful physical theory of river regime must be able to reproduce and explain this regularity in this paper we test the regime theory of eaton et al 2004 using selected data of hydraulic geometry we first use data from environments in which bank strength presumably does not vary greatly such as in anabranched channel systems and deltas regime models parameterized by assuming uniform relative bank strength plausibly describe the observed bankfull channel geometries in these systems we then test a modified bank strength formulation for vegetated gravel bed rivers against downstream hydraulic geometry data sets in which relative bank strength is supposed to vary with channel scale assuming a uniform effective cohesion due to riparian vegetation the regime model is again able to reproduce details of the channel geometry both analyses show that the classical hydraulic geometry represents only an approximation of the variation of channel form if we have confidence in the theory we may infer information about bank strength and bed material transport the pattern of variation in these quantities as well as discharge through the drainage system lends approximate regularity to stream channel scaling that is summarized in the empirical relations

quantifiable effectiveness of experimental scaling of river and delta morphodynamics and stratigraphy laboratory experiments to simulate landscapes and stratigraphy often suffer from scale effects because reducing length and time scales leads to different behaviour of water and sediment classically scaling proceeded from dimensional analysis of the equations of motion and sediment transport and minor concessions such as vertical length scale distortion led to acceptable results in the past decade many experiments were done that seriously violated these scaling rules but nevertheless produced significant and insightful results that resemble the real world in quantifiable ways here we focus on self formed fluvial channels and channel patterns in experiments the objectives of this paper are 1 to identify what aspects of scaling considerations are most important for experiments that simulate morphodynamics and stratigraphy of rivers and deltas 2 to establish a design strategy for experiments based on a combination of relaxed classical scale rules theory of bars and meanders and small scale experiments focussed at specific processes we present a number of small laboratory setups and protocols that we use to rapidly quantify erosional and depositional types of forms and dynamics that develop in the landscape experiments as a function of detailed properties such as effective material strength and to assess potential scale effects most importantly the width to depth ratio of channels determines the bar pattern and meandering tendency the strength of floodplain material determines these channel dimensions and theory predicts that laboratory rivers should have 1 5 times larger width to depth ratios for the same bar pattern we show how floodplain formation can be controlled by adding silt sized silicaflour bentonite medicago sativa alfalfa or partially hydrolyzed polyacrylamide a synthetic polymer to poorly sorted sediment the experiments demonstrate that there is a narrow range of conditions between no mobility of bed or banks and too much mobility the density of vegetation and the volume proportion of silt allow well controllable channel dimensions whereas the polymer proved difficult to control the theory detailed methods of quantification and experimental setups presented here show that the rivers and deltas created in the laboratory seem to behave as natural rivers when the experimental conditions adhere to the relaxed scaling rules identified herein and that required types of fluvio deltaic morphodynamics can be reproduced based on conditions and sediments selected on the basis of a series of small scale experiments

possible microbial origin of phosphorites on error seamount northwestern arabian sea abstract petrographical mineralogical and microprobe analysis of phosphorites from error seamount in the northwestern arabian sea demonstrates that microbial processes played an important role in the early diagenetic formation of the phosphorites during subaerial exposure of the seamount the phosphorites on error seamount occur as laminated crusts and massive slabs low magnesium calcite and carbonate fluorapatite are the major minerals of the phosphorites with goethite being important only in the massive slab phosphorites elemental sulphur pyrrhotite gypsum and chlorite are the mineral phases present in the acid insoluble residues of the phosphorites elemental sulphur which is exclusively formed by microbial processes occurs as submicrometre sized granules on gypsum surfaces the laminated crust phosphorites consist of organic rich and organic poor laminae interlayered with ghost pellets index fossils of oligocene to lower miocene age peloids and coated grains massive slab phosphorites are fine grained and consists of goethitic and non goethitic zones non goethitic zones comprise mainly microsphorite with oligocene to lower miocene fossils and microfossils goethitic zones contain abundant quaternary skeletons microprobe analyses of the error seamount phosphorites indicate that the geochemistry of these phosphorites is similar to that of the tertiary seamount phosphorites in the atlantic and pacific ocean and that they are enriched in ca and depleted in p compared to other seamount and island phosphorites in the indian ocean microbial activity is evident in both types of phosphorites and occurs in the form of microborings in peloids and on skeletal fragments encrustation of phosphate crystals on hollow globular microstructures and phosphate sheaths enclosing organic filaments the presence of calcite rim cements microspar filled patches and recrystallised grains indicates exposure of the seamount under subaerial conditions during which phosphatisation took place

ash bones and guano a study of the minerals and phytoliths in the sediments of grotte xvi dordogne france abstract very few prehistoric cave deposits in western europe contain visible hearth remains even though there is abundant evidence of fire use by cave inhabitants grotte xvi dordogne france is exceptional in this respect in that it contains a most conspicuous layer couche c characterized by a series of brightly coloured bedded sediments the formation of couche c has previously been ascribed to the ash and charcoal produced by the cave s mousterian occupants burning mainly lichens the mousterian sedimentary layers below couche c and the upper palaeolithic sediments unconformably overlying couche c are quite different in texture and colour and show no visible evidence of ash deposits analyses of the minerals microstructures and phytoliths in couche c are consistent with the notion that these sediments were derived mainly from ash produced by burning wood and to a lesser extent grass the original calcite component of the ash has been diagenetically altered to carbonated apatite around the cave periphery and to even more insoluble phosphate minerals in the centre one such mineral newberyite most likely formed by the reaction between guano degradation products and the ash under these circumstances bone preservation is also affected the overlying upper palaeolithic sediments contain calcite one of these layers abb contains much more calcite than all the other layers as well as abundant phytoliths derived from wood and grass this layer also contained many artifacts and bones it is thus concluded that ash is a major component of layer abb even though it is not visible to the maked eye in the form of hearths

beam hardening artifact reduction in microfocus computed tomography for improved quantitative coal characterization microfocus computed tomography ct is a non destructive technique allowing visualization of the internal microstructure of objects this technique can be used to quantify the maceral content and to define the cleat system within coal samples however a number of artifacts intrinsic to the technique hamper the optimal quantitative use of ct one of the most important artifacts is beam hardening which generates streaks on the images near dense inclusions such as ankerite or pyrite and makes the border of the sample appear denser than in reality these artifacts can be minimized by using a dual energy method in which two sets of scans taken at a different energy level are combined in this study existing dual energy methods are combined into a new technique and adapted to be more ideally suitable for coal samples the method is calibrated with an artificial sample made of a plexiglas cylinder in which two aluminum rods are built in plexiglas and aluminum were selected since their x ray attenuation properties are similar to those of vitrinite and dense phases such as ankerite respectively the method is tested on a coal sample bearing relatively high percentages of iron minerals the corrected and uncorrected images from one representative slice through the sample are compared with reflected light microscopy images from the corresponding polished surface the results show that the applied approach creates images in which the border does not appear denser than in reality and in which the artificial streaks near dense inclusions are removed in addition size measurements of the ankerite veins and grains in the sample are much more accurate based on the corrected images it is therefore assumed that the proposed dual energy algorithm minimizes the beam hardening artifact however the corrected images have a lower signal to noise ratio than the uncorrected images consequently this approach magnifies to some extent other artifacts noise scatter and partial volume effect which are also present in the uncorrected images some solutions to correct for these artifacts and to improve the developed dual energy method are proposed

modeling high sinuosity meanders in a small flume meandering channels with exposed point bars and sinuosities near 2 0 can spontaneously develop in a mix of diatomaceous earth and kaolinite clay the experimental streams that were studied were as small as 4 cm wide they showed many of the characteristics found in large meandering streams such as migration of channels formation of point bars clay plugs chutes and bar scrolls most of the meander series began as a first sharp bend that induced subsequent bends down stream sediment transport specifically bed load together with the slope of the floodplain were the dominant influences if not the cause of the channel instabilities that led to channel migration and bend formation bank cohesion allowed migrating channels to assume sinuous shapes and to maintain fairly uniform widths the experiments were conducted in a small flume and used simple equipment the use of light fine grained materials in flume experiments may prove to be valuable in learning more about the conditions of soil slope and flow which produce various meandering planforms

petrophysical characterization of tight oil sandstones by microscale x ray computed tomography abstract tight oil sandstones have complex pore structure due to multiple pore types and multiscale pore size ranging from several nanometers to dozens of microns in this study petrophyiscal properties of tight oil sandstones were quantified based on microscale x ray computed tomography xct imaging techniques the pore types in gray scale images were identified porosity pore size distribution psd and pore connectivity were analyzed from segmented image stacks and their permeability was calculated by representative elementary volume rev scale lattice boltzmann method lbm three types of pores including residual interparticle pores grain dissolution pores and micro fractures were identified a multi threshold segmentation algorithm was applied to segment the image stacks into three constituents namely pore matrix and clay the calculated volumetric fraction of the pore constituent from the segmented image stacks was smaller than experimental porosity because a certain amount of porosity was also contributed by clay constituent the psd of the samples was found to be unimodal in the range of 3 69 m with the peak at around 10 15 m the clay constituent led to the increase in the overall connectivity of the images stacks indicating that clays bridged the isolated pores by assigning appropriate porosity and permeability to the clay constituent calculated permeability of the samples using rev scale lbm well matched the experimental data this study provides new insight into characterization of pore structure of tight oil sandstones by xct technique

comparison of fractal models using nmr and ct analysis in low permeability sandstones abstract fractal geometry provides an effective method for characterization of the complex and irregular pore structure of eocene shahejie low permeability sandstones in the raoyang sag the bohai bay basin china laboratory measurements including porosity permeability scanning electron microscope sem thin sections nuclear magnetic resonance measurements nmr and x ray computed tomography ct technology are used to provide insights into the fractal characteristics of pore structure in sandstones of eocene shahejie formation in the bohai bay basin china quantitative ct analysis reveals the pore radius is not always linear to t2 transverse relaxation time value obtained from the nmr tests but instead power function of t2 fractal analysis was performed on the t2 distribution using various fractal models and the related fractal dimensions are calculated the fractal dimensions calculated using various fractal models are correlated with nmr parameters and permeability the fractal curves break into two segments at the t2cutoff t2 separating the immovable and movable fluids value or smaller when using fractal model and fractal model and only the large scale pore networks can be described by the fractal geometry mostly the entire pore size distributions micro pores to large scale pore networks can be described by the fractal model and the calculated fractal dimensions are in accordance with the ct scanning and thin section data and are strongly correlated with the t2gm geometric mean of t2 permeability and bvi bulk volume of immovable fluids the fractal behaviors of pore size distributions from nmr analysis have implications for pore structure evaluation in low permeability sandstones with similar geological settings

mechanisms of anabranch avulsion within gravel bed braided rivers observations from a scaled physical model the physical modelling of gravel bed braided rivers using a 1 20 froude scale model permits analysis of the types and relative occurrence of different avulsion mechanisms anabranch avulsion within braided rivers involves three main mechanisms choking avulsion caused by blockage of one channel by a sediment lobe constriction avulsion produced by deflection confinement and subsequent diversion of the flow by a barform and apex avulsion following erosion at the outside of sinuous thalwegs and confined meander bends each avulsion mechanism is described and analysis of the abundance of each type illustrates choking avulsion to be predominant without braided rivers three factors are found to control anabranch avulsions namely flow discharge sediment flux and floodplain topography these are briefly discussed together with the implications of avulsion type for the alluvial architecture of gravelly braided alluvium

pore structure and fractal characteristics of ordovician majiagou carbonate reservoirs in ordos basin china fractal analysis was performed on carbonate core plug samples from the ordovician majiagou carbonate reservoirs in the ordos basin using mercury intrusion capillary pressure micp nuclear magnetic resonance nmr and the x ray computed tomography ct measurements to improve our understanding of the pore structure characteristics the relationships between pore structure parameters and the fractal dimensions were investigated the pore systems are dominated by secondary intercrystalline pores and enlarged dissolution pores as well as microfractures the fractal curves from micp analysis break into two segments at the swanson s parameter the small pore throat systems can be described by the fractal theory whereas pores connected by relatively large throats greater than the pore throat radius at the pittman s hyperbola s apex are not cylindrical in shape cannot be described by a capillary tube model and tend to have apparent fractal dimensions larger than 3 0 the fact that the entirety of the capillary curve cannot be fit by a single fractal dimension implies that there are multiple pore systems present with different fractal dimensions the ct analysis shows that the pores are dispersed in the three dimensional spaces mainly with elliptical shapes the nmr measurements are sensitive to pore body size and micp probes pore throat dimensions the latter being complementary to the pore body size distribution none of the ct micp and nmr techniques provide right or wrong answers to the pore throat systems but they probe different aspects of the pore systems this study assumes the pore shapes to be spherical in general and then the fractal dimension is calculated from the nmr transverse relaxation time t2 spectrum the fractal dimensions of all the samples are calculated and the accuracy of the fractal model is verified by the high regression coefficients almost all the pore systems can be described by fractal theory and the fractal dimensions are strongly correlated with the t2 values separating the immovable fluid and the free fluid microfractures may bias t2 toward larger values making it hard to derive fractal dimensions from nmr measurements the coexistence of small pores pore radius 50 m results in a heterogeneous pore distribution and a high fractal dimension reservoir quality increases with the complexity degree of the microscopic pore structure conversely samples that are dominated by small pore systems tend to have a lower fractal dimension and a less complex pore structure

applications of x ray computed tomography in the geosciences x ray computed tomography ct is a technique that allows non destructive imaging and quantification of internal features of objects it was originally developed as a medical imaging technique but it is now also becoming widely used for the study of materials in engineering and the geosciences x ray ct reveals differences in density and atomic composition and can therefore be used for the study of porosity the relative distribution of contrasting solid phases and the penetration of injected solutions as a non destructive technique it is ideally suited for monitoring of processes such as the movement of solutions and the behaviour of materials under compression because large numbers of parallel two dimensional cross sections can be obtained three dimensional representations of selected features can be created in this book various applications of x ray ct in the geosciences are illustrated by papers covering a wide range of disciplines including petrology soil science petroleum geology geomechanics and sedimentology

measurement of aperture distribution capillary pressure relative permeability and in situ saturation in a rock fracture using computed tomography scanning we develop an experimental technique that uses computed tomography ct scanning to provide high resolution measurements of aperture distribution and in situ saturation along with capillary pressure and relative permeability for the same rough walled fracture we apply this technique to an induced fracture in a cylindrical basalt core undergoing water drainage we find that the sum of the water and gas relative permeabilities is much 1 at intermediate saturations and the water relative permeability shows a sharp change over a narrow range of average water saturation in situ saturation maps show channeling of gas and significant retention of the wetting phase water the capillary pressure initially increased and then decreased with decreasing water saturation although this type of capillary behavior is atypical for unsaturated flows we find that the sizes of the gas filled apertures are consistent with the measured capillary pressure

swiftness of biomorphodynamics in lilliput to giant sized rivers and deltas physical experiments of self formed river channels and floodplains with live vegetation are pathways for understanding that complement numerical modelling recent experiments succeeded in creating braided rivers and dynamic meandering systems with clastic and vegetated floodplains however application of the insights gained from such experiments to natural systems depends on understanding potential scale effects temporal and spatial here we combine review analysis and experiments to identify fundamental problems of biomorphological river pattern formation that are open for further research in experiments we first show by review and analysis that physics based linear bar theory predicts negligible spatial scale effects in bar and bend wavelength relative to channel width time scaling on the other hand remains problematic because it integrates multiple processes of sediment transport floodplain formation and bank failure affected by bank stratigraphy and riparian vegetation as a tentative solution we secondly present experimental methods to assess bank strength effects that can be used in the design of river pattern experiments the third issue is that riparian vegetation has often been represented in experiments by uniformly seeded sprouts of a single plant species whilst spectacularly different patterns are obtained with contrasting seeding protocols showing the need for other experimental procedures and alternative riparian species the main challenge for future experiments is better understanding of temporal scaling of biomorphodynamics

length scale of braided river morphology 1 pool bar topography in single channel rivers has a length scale proportional to channel width in braided rivers confluence bifurcation units are analogous to pool bar morphology and in some cases develop from initial alternate bars consequently confluence bifurcation units are expected to have length that scales with the central anabranch width and that constitutes a basic length scale braided channel morphology this idea was tested using measurements from a physical model of a gravel bed braided river and from aerial photographs of braided rivers length distance from confluence to bifurcation anabranch width and confluence angle of confluence bifurcation units were measured a simple length scaling is evident across the range of scales confluence bifurcation length is 4 5 times the channel width this scaling is a fundamental element of braided river morphology and suggests that braided patterns are created by processes and have morphological regularity similar to pool bar units of low sinuosity single thread rivers

episodic struvite deposits in a northern great plains flyway lake indicators of mid holocene drought a series of 34 layers of struvite hydrous mg ammonium phosphate were deposited in laminated sediments of kettle lake north dakota in the northern great plains usa sedimentologic mineralogic and nitrogen isotopic evidence suggest that struvite was deposited during nutrient enriched eutrophication events within a mg rich lacustrine environment the struvite layers are dispersed between 4650 and 8700 cal yr bp with particularly high frequency between 8068 and 8700 cal yr bp the youngest struvite layer dates to 2734 cal yr bp key features of the struvite forming events were a relatively low water stage and consequent ele vated water salinity associated with the dry mid holocene b disappearance of most lakes and wetlands in the region and c focused but brief visitations by large populations of migratory waterfowl the lack of more fre quent occurrence of struvite is ascribed to the rarity with which this combination of conditions was achieved in combination with difficulty of preservation for this salt 15 n isotopes in struvite mean 7 51 are heavy rel ative to 15 n in sediment and also extremely uniform over time the isotopes are interpreted to reflect a water fowl waste source without extensive nh4 volatilizaton the timing of the struvite events does not closely correspond to century scale mid holocene drought cycles inferred from oscillating aragonite concentrations although there is a weak preferred occurrence in the humid phase of these cycles thus the struvite events are ephemeral prairie features of this generally arid period but tend not to occur at precisely the most arid intervals

scales of lateral petrophysical heterogeneity in dolomite lithofacies as determined from outcrop analogs implications for 3 d reservoir modeling petrophysical data from dolomite outcrops of the mississippian madison formation at sheep canyon wyoming exhibit three scales of lateral variability in single rock fabric units these include a near random component nugget effect a short range structure and a long range cyclic trend hole effect the nugget effect is high and accounts for 31 39 and 48 50 of the variance in porosity and permeability respectively short range lateral variability is reflected by correlation lengths of 6 5 16 ft 2 5 5 m laterally long range periodicities are equivalent to approximately 10 of the petrophysical variance and have wavelengths of 31 and 140 ft 9 5 and 42 6 m for porosity and permeability 55 ft 16 8 m for log10 permeability respectively cross sectional and plan view petrophysical models and streamline simulations explore the effects of these scales of heterogeneity on fluid flow although short range variability accounts for most of the petrophysical heterogeneity the longer range trends can significantly affect fluid flow behavior results indicate that breakthrough time and sweep efficiency vary depending on the magnitude of the lateral long range petrophysical variability that exists in a dolomite reservoir as the component of the long range periodicity hole effect increases from approximately 0 to 25 of the total petrophysical variability a corresponding increase in breakthrough time and sweep efficiency occurs however as the magnitude of the lateral long range petrophysical variability increases beyond 25 of the total petrophysical variability e g from 25 to 50 a corresponding reduction in breakthrough time occurs because the spatial continuity of permeability is greater results indicate that heterogeneity caused by lateral petrophysical cyclicity should be incorporated into dolomite reservoir models for hole effect magnitudes that are greater than 10 of the petrophysical variance to properly characterize and model these scales of variability in a petroleum reservoir outcrop analogs are essential to provide accurate quantitative descriptions of lateral variability in dolomite rock fabrics

experimental delta formation in crater lakes and implications for interpretation of martian deltas 1 the morphology of delta deposits in crater lakes on mars is indicative of upstream e g flow discharge and sediment properties and downstream e g basin characteristics parameters from which the hydrological conditions at the time of formation can be inferred to investigate the influences of these parameters on delta morphology we experimentally created deltas in crater shaped basins by feeding a range of constant flow discharges over a feeder channel of various sand textures we reproduced three categorically different types of deltas including most of the types that have been identified on mars our most striking observation is that water level behavior itself a unique function of flow discharge basin size and hypsometry and basin floor permeability can explain most delta morphologies observed on mars stepped retrograding deltas formed during water level rise prograding deltas formed during water level still stand and during water level fall deltas were partially destroyed by erosion on mars numerous retrograding and prograding deltas were preserved most of them without indications of channel incisions or other fluvial modification we conclude that the main difference between a single foreset prograding delta and a multiple foreset retrograding delta is the behavior of the water level in the basin these simple delta morphologies cannot be reconciled with long duration hydrological activity because that would imply crater lake fluctuations due to inherent complex water level histories along with complex sediment delivery histories our experiments and numerical verifications demonstrate that such deltas preferentially form during one aqueous event which parsimoniously argues for short duration hydrological activity

one dimensional modeling of a recent ganga avulsion assessing the potential effect of tectonic subsidence on a large river abstract river avulsion as studied in small sized and medium sized rivers is partly explained by the water surface gradient advantage of a new channel course over the old course caused by spatial differences in aggradation and compaction recently the effect of meandering upstream of the avulsion node or bifurcation was shown to have an equally large effect on avulsion duration as gradient advantage these effects remain poorly understood for the largest rivers on earth where gradients are very small subtle gradient advantages are affected by tectonics and often several anabranches remain active simultaneously our objective was to assess the relative importance of these factors in the river ganga in determining the pacing of an avulsion we used a combination of historical data remote sensing and one dimensional modeling the course of the ganga in historical times was through the present ganga bhagirathi system but then there was either a gradual or sudden shift to the present ganga padma system historical evidence and remnant paleochannels as observed in satellite sensor data corroborate the changing pattern of the ganga river system but the exact causes of the shifting and of the short avulsion duration remain unclear based on generalized data using a one dimensional model we ran idealized scenarios bracketing different tectonic subsidence estimates for long term morphodynamic evolution of the upstream channel and the two downstream bifurcates the model predicts flow and sediment partitioning at the bifurcation node and includes the effect of migrating meanders at the bifurcation and width adjustment of the bifurcates our modeling demonstrates that the old and the new branches can remain open and morphologically active for a long time because of the large backwater effect and the high mobility of the sediment the bifurcation stabilizes at an asymmetrical flow and sediment division which in smaller rivers such as the river rhine would be followed by residual channel filling but in the much larger ganges results in morphologically active anabranches the model results reveal that neither a gradient advantage nor a bend upstream of the bifurcation leads to an avulsion within centuries as has been observed in some large rivers in tectonically inactive regions on the other hand a realistic tectonic uplift of the old branch or subsidence of the new branch may force an avulsion to take place quickly and historical data show that the study area is seismically active the combination of these factors leads to a realistic modeled avulsion duration of less than three centuries historical data indicate that these general conclusions might also apply to other large rivers in this region e g the brahmaputra and the teesta we conclude that large rivers may avulse quickly in response to tectonics but attain an anabranching pattern because of the large dimension of the residual channel and backwater effects

partial transport of a sand gravel sediment grains of a single size within a mixed size bed are entrained over a range of flows within this range some grains exposed on the bed surface are active entrained at least once over the duration of a transport event while the remaining surface grains are immobile a condition we define as partial transport we demonstrate the existence and domain of partial transport using observations of grain entrainment on time series of bed photographs of flume experiments with a widely sorted sand gravel mixture the active proportion of the bed surface increases with bed shear stress 0 at a given 0 90 of the active grains are entrained when the cumulative mass transported exceeds approximately 4 times the active mass on the bed mobilization of grains in a size fraction increases from 10 to 90 over a range of 0 of a factor of 2 the bounds of this range increase with grain size di so that at a given 0 sizes over a range of a factor of 4 are in a state of partial transport fractional transport rates are independent of di for fully mobilized fractions and decrease rapidly with di for partially mobile fractions partial transport is associated with substantial transport rates of finer fully mobile sizes limits both the rate and size distribution of grain exchange with the bed subsurface and may be the dominant transport condition in many gravel bed rivers

the 3d microscopic signature of strain within glacial sediments revealed using x ray computed microtomography abstract x ray computed microtomography ct a non destructive analytical technique was used to create volumetric three dimensional 3d models representing the internal composition and structure of undisturbed pro and subglacial soft sediment sample plugs for the purposes of identifying and analysing kinematic indicators the technique is introduced and a methodology is presented addressing specific issues relating to the investigation of unlithified polymineralic sediments six samples were selected based on their proximity to type brittle and ductile deformation structures or because of their perceived suitability for successful application of the technique analysis of a proglacial ideal specimen permitted the 3d geometry of a suite of micro faults and folds to be investigated and the strain history of the sample reconstructed the poor contrast achieved in scanning a diamicton of glaciomarine origin is attributable to overconsolidation under normal loading the sediment demonstrated to have undergone subsequent subglacial deformation another overconsolidated diamicton contains an extensive small scale the subglacial sample evidence indicates that complex polyphase brittle ductile deformation histories are common in such diamictic soft sediments and that the local micro scale environment composition structure shear forces and effective pressure controls rheology the sediment void ratio is a key indicator of strain three of the samples are tentatively placed at different points on the strain cycle for subglacially deforming soft sediment based on their void ratio characteristics and distribution it has been demonstrated that ct offers significant potential for elucidating glacial soft sediment kinematics the ability of the technique to both test a variety of hypotheses pertaining to mechanisms operating within the subglacial environment and evaluate efforts to replicate those processes under controlled laboratory conditions is therefore discussed along with solutions to the problems encountered within this project ct also permits the seamless linking of analytical techniques applied at the hand specimen mm micromorphological m mm scanning electron microscopy and x ray diffraction fluorescence nm m scales and the archiving duplication and dissemination of sample volumetric 3d data

three dimensional grain fabric measurements using high resolution x ray computed tomography abstract high resolution x ray computed tomography hrxct provides detailed imagery of the interiors of rocks up to hand sample size non destructively and in three dimensions new tools described here allow these data to be used for analysis of grain fabrics two separate sets of measurement techniques have been developed the first concentrates on quantifying individual crystals phenocrysts porphyroblasts or other discrete objects or void spaces within a sample quantifiable properties include location size shape orientation and contact relationships with adjacent objects the second set of techniques performs a more general fabric analysis on any distinguishable component in a sample a fabric tensor can be computed based on a number of metrics including the star volume distribution svd star length distribution sld and mean intercept length mil methods the fabric tensors provide principal component directions and magnitudes which in turn provide a measure of degree of anisotropy and shape indices because the svd and sld measure only the material of interest whereas the mil is also influenced by spatial distribution results can be divergent for sparse phases also introduced is a three dimensional rose diagram that can be viewed interactively and inspected to reveal further details about non orthogonal directional components these techniques are demonstrated through analysis of a garnet kyanite schist from mica dam british columbia

assessing the effect of vegetation related bank strength on channel morphology and stability in gravel bed streams using numerical models bank strength due to vegetation dominates the geometry of small stream channels but has virtually no effect on the geometry of larger ones the dependence of bank strength on channel scale affects the form of downstream hydraulic geometry relations and the meandering braiding threshold it is also associated with a lateral migration threshold discharge below which channels do not migrate appreciably across their floodplains a rational regime model is used to explore these scale effects it parameterizes vegetation related bank strength using a dimensionless effective cohesion cr the scale effects are explored primarily using an alluvial state space defined by the dimensionless formative discharge q and channel slope s which is analogous to the q s diagrams originally used to explore meandering braiding thresholds the analyses show that the effect of vegetation on both downstream hydraulic geometry and the meandering braiding threshold is strongest for the smallest streams in a watershed but that the effect disappears for q 106 the analysis of the migration threshold suggests that the critical discharge ranges from about 5 m3 s to 50 m3 s depending on the characteristic rooting depth for the vegetation the analysis also suggests that where fires frequently affect riparian forests channels may alternate between laterally stable gravel plane bed channels and laterally active riffle pool channels these channels likely do not exhibit the classic dynamic equilibrium associated with alluvial streams but instead exhibit a cyclical morphologic evolution oscillating between laterally stable and laterally unstable end members with a frequency determined by the forest fire recurrence interval copyright 2008 john wiley sons ltd

multi scale x ray tomography analysis of carbonate porosity the porosity from values of 1 up to more than 50 with a mean value of 36 5 and permeability from very low values to 20 4 d with a mean value around 800 md of 38 plugs with a diameter 40 mm have been measured these plugs were taken approximately every 1 5 m along a 100 m long core sampling a series of reefal carbonate platform lithofacies a non unique relationship between porosity and permeability is obtained in addition the porosity was measured from processing x ray micro tomography images with resolutions ranging from 0 42 to 190 0 m and sampling volumes ranging from less than 1 m3 to few cm3 depending on the structure of the pore network the computed porosity is in some cases controlled by the x ray image resolution and the sampled volume while high resolution is required to image micro porous material large samples with lower resolution images are necessary for identifying distributed vugs and millimetre scale structures this study shows that multi resolution x ray micro tomography is an effective tool for characterizing the multi scale pore structure of carbonate rocks and understanding how it may control key petrophysical parameters such as porosity and permeability

bank and near bank processes in an incised channel abstract gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion the interaction of these forces control streambank mechanics hydraulic forces exerted by flowing water on in situ bank toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower bank profiles seepage forces exerted on in situ bank material by groundwater downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength data from a study site on goodwin creek ms usa clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore water pressures negative pore water pressures matric suction have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear a stable bank can be transformed into an unstable bank during periods of prolonged rainfall through 1 increase in soil bulk unit specific weight 2 decrease or complete loss of matric suction and therefore apparent cohesion 3 generation of positive pore water pressures and therefore reduction or loss of frictional strength 4 entrainment of in situ and failed material at the bank toe and 5 loss of confining pressure during recession of stormflow hydrographs relatively small frequent flows during the winter have the ability to erode failed bank materials maintain oversteepened unstable bank surfaces and promote prolonged periods of bank retreat channel migration and high yields of fine grained sediment confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe which steepens the bank for example more than 2 m of bank retreat occurred during the study period at the research site on goodwin creek northern mississippi the loss of matric suction negative pore pressures due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability apparent cohesion friction angle soil bulk unit weight and moisture content were measured in situ matric suction was measured continuously in situ with a series of five pressure transducer tensiometers a bank failure algorithm which combines the mohr coulomb approach for saturated conditions and the fredlund modification for unsaturated conditions was developed for layered cohesive streambanks the resulting equation has been used successfully to investigate the role of matric suction positive pore water pressures and confining pressure for layered streambanks composed of cohesive materials

using the porosity exponent m and pore scale resistivity modelling to understand pore fabric types in coquinas barremian aptian of the morro do chaves formation ne brazil abstract the recent major discoveries of petroleum in pre salt carbonate reservoirs of mainly lacustrine origin offshore brazil has increased interest in studying these complex non marine reservoirs which present many production development challenges largely due to their heterogeneous nature some of the reservoir carbonate rock types present in brazil are limestones composed predominantly of bivalve shells which are known as coquinas the coquinas show a variety of pore types pore sizes pore shapes and pore connectivity which define their porosity and strongly influence the permeability and resulting electrical resistivity but this aspect of these relationships in these carbonates has been relatively poorly characterised particularly in a quantitative manner in the literature the petrophysical characterisation of the coquinas of the morro de chaves formation barremian aptian exposed in a quarry in ne brazil was carried out using the outcrop selected samples plugs and petrographic thin sections to investigate these aspects porosity permeability grain density and porosity exponent m measurements were carried out on the plugs x ray microtomography was performed to identify key characteristics of the pore system and for the basis of 3 d modelling significant variation in m was observed across the plug data set which is not unexpected in carbonates but it suggested that a range of fabrics and pore topology were present in these rocks which are described only as calcirudites modelling of the resistivity using 3d pore scale models was used to understand the role of disconnected macro pores and dissolution seams in controlling the more extreme variation in petrophysical properties observed in the coquinas this understanding of the controls on resistivity pathways in this outcrop coquina will help in understanding the pore types in the subsurface and the estimation of saturations in these complex rocks where they are found to be oil bearing

three dimensional miarolitic cavity distribution in the kakkonda granite from borehole wd 1a using x ray computerized tomography abstract three dimensional imaging of a granite core from the borehole wd 1a drilled at the kakkonda geothermal field ne japan was performed by x ray computerized tomography ct the ct images displayed miarolitic cavities possible geothermal reservoir felsic minerals mafic minerals and enclaves in the granite voxels with ct numbers less than 1500 were estimated to be the miarolitic cavities on the basis of i the ct imaging of the synthetic glass tubes and ii the detailed comparison between the ct image and the cut surface of the rock sample a three dimensional distribution of miarolitic cavities was reconstructed from a set of contiguous two dimensional ct images and showed a spatially heterogeneous distribution with a boundary that strikes n 20 e this trend is probably important as the regional distribution of the geothermal reservoir which demonstrates that x ray ct is a powerful tool in geothermal studies chemical fluctuations of na and k were found around the miarolitic cavity zone this may be useful for finding miarolitic cavity zones without coring

hyperspectral image analysis of different carbonate lithologies limestone karst and hydrothermal dolomites the pozalagua quarry case study cantabria north west spain ground based hyperspectral imaging combined with terrestrial lidar scanning is a novel technique for outcrop analysis which has been applied to early and late albian carbonates of the pozalagua quarry cantabrian mountains spain an image processing workflow has been developed for differentiating limestone from dolomite providing additional sedimentary and diagenetic information and the possibility to quantitatively delineate diagenetic phases in an accurate way spectral absorption signatures can be linked to specific sedimentary or diagenetic products such as recent and palaeokarst hydrothermal karst solution enlarged fractures and different dolomite types some of the spectral signatures are related to iron manganese organic matter clay and or water content ground truthing accessible parts of the quarry showed that the classification based on hyperspectral image interpretation was very accurate this technique opens the possibility for quantitative data evaluation on sedimentary and diagenetic features in inaccessible outcrops this study demonstrates the potential of ground based imaging spectroscopy to provide information about the chemical mineralogical distribution in outcrops which could otherwise not be established using conventional field methods

holocene coastal carbonates and evaporites of the southern arabian gulf and their ancient analogues abstract the holocene sediments of the coast of the united arab emirates in the southeastern arabian gulf are frequently cited in the literature as type examples for analogous assemblages of carbonates evaporites and siliciclastics throughout the geologic record this paper is intended as a convenient single source for the description of sediments of this region providing information on how to reach the classic localities and some of the analogs the holocene sediments of the region accumulate over an area that is 500 km long and up to 60 km wide the sediments collecting offshore are predominantly pelecypod sands mixed with lime and argillaceous mud with these latter fine sediments increasing as the water deepens the pelecypod rich sediments also collect east of abu dhabi island both in the deeper tidal channels between the barrier island lagoons and in deeper portions of the protected lagoons west of abu dhabi island the shallow water margin is the site of coral reefs and coralgal sands whereas to the east oolites accumulate on the tidal deltas of channels located between barrier islands grapestones accumulate to the lee of the reefs and the oolite shoals where cementation becomes more common they are particularly common on the less protected shallow water margins of the lagoons west of abu dhabi island pelleted lime muds accumulate in the lagoons in the lee of the barrier islands of the eastern abu dhabi lining the inner shores of the protected lagoons of abu dhabi and on other islands to the west are cyano bacterial mats and mangrove swamps landward of these a prograding north facing shoreline is formed by supratidal salt flats sabkhas in which evaporite minerals are accumulating this paper describes the localities associated with 1 the mangrove swamps of the west side of the al dhabaiya peninsula 2 the indurated cemented carbonate crusts cyanobacterial flats and sabkha evaporites on the shore of the khor al bazam south of qanatir island 3 the reef and oolitic sand flats on the coast just east of jebel dhana and 4 the marine travertine and aragonite coats associated with the beach sediments in a small bay south of jebel dhana and 5 the sabkha mutti between jebel barakah and al sila similar sedimentological associations of carbonate and evaporites to those of the holocene of the united arab emirates are to be found in the tertiary and mesozoic sedimentary rocks of the immediate subsurface in the arabian gulf other analogs to this setting include the paleozoic carbonates of the western usa europe and asia mesozoic carbonates of the gulf of mexico europe and middle east and tertiary sedimentary rocks in the middle east

paragenesis of cretaceous to eocene carbonate reservoirs in the ionian fold and thrust belt albania relation between tectonism and fluid flow this paper examines the diagenetic history of dual i e matrix and fracture porosity reservoir lithologies in cretaceous to eocene carbonate turbidites of the ionian fold and thrust belt close to the oil producing centre of fier ballsh central albania the first major diagenetic event controlling reservoir quality was early cementation by isopachous and syntaxial low mg calcite these cements formed primarily around crinoid and rudist fragments which acted as nucleation sites in sediments in which these bioclasts are the major rock constituent this cement can make up 30 of the rock volume resulting in low effective porosity in strata in which these bioclasts are mixed with reworkedmicrite isopachous syntaxial cements stabilized the framework and matrixporosity is around 15 the volumetric importance of these cements their optical and luminescence character distribution and dull orange luminescence and stable isotopic signal 18o and 13c averaging respectively 0 5 vpdb and 2 vpdb all support a marine phreatic origin within these turbidites and debris flows several generations of fractures alternated with episodes of cementation a detailed reconstruction of this history was based on cross cutting relationships of fractures and compactional and layer parallel shortening lps stylolites the prefolding calcite veins possess orange cathodoluminescence similar to that of the host rock their stable isotope signatures 18o of 3 86 to 0 85 vpdb and 13c of 0 14 to 2 98 vpdb support a closed diagenetic rock buffered system a similar closed system accounts for the selectively reopened and subsequently calcite cemented lps stylolites 18o of 1 81 to 1 14 vpdb and 13c of 1 52 to 2 56 vpdb within the prefolding veins brecciated host rock fragments and complex textures such as crack and seal features resulted from hydraulic fracturing they reflect expulsion of overpressured fluids within the footwall of the frontal thrusts after folding and thrust sheet emplacement some calcite veins are still rock buffered 18o of 0 96 to 0 2 vpdb and 13c of 0 79 to 1 37 vpdb whereas others reflect external i e extraformational and thus large scale fluid fluxes some of these veins are linked to basement derived fluid circulation or originated from fluid flow along evaporitic decollement horizons 18o around 3 0 vpdb and 13c around 1 5 vpdb others are related to the maturation of hydrocarbons in the system 18o around 7 1 vpdb and 13c around 9 3 vpdb an open joint system reflecting an extensional stress regime developed during or after the final folding stage this joint system enhanced vertical connectivity this open joint network can be explained by the high palaeotopographical position and the folding of the reservoir analogue within the deformational front the joint system is pre burdigalian in age based upon a dated karstified discordance contact sediment filled karst cavity development is linked to meteoric water infiltration during emergence of some of the structures despite its sediment fill the karst network is locally an important contributor to reservoir matrix porosity in otherwise tight lithologies development of secondary porosity along bed parallel and bed perpendicular i e layer parallel shortening stylolites is interpreted as a late stage diagenetic event associated with migration of acidic fluids during hydrocarbon maturation development of porosity along the lps system enhanced the vertical reservoir connectivity

experimental steep braided flow application to flooding risk on fans flooding processes occurring on alluvial fans are considerably different from those occurring along single thread rivers with well defined floodplains active erosion rapid sedimentation and the uncertainty in flow path make the prediction of flood evolution and extent difficult based on a large scale experiment this study investigates the long term evolution of the flow on a steep noncohesive sediment surface resembling a complex of merged alluvial fans the results are pertinent to the assessment of flooding hazard on alluvial fans at any given time the average flow occupancy was 21 of the surface however the flow was characterized by active channel switching and overflow processes the percentage of the surface remaining dry was found to decay harmonically with time a reworking time was defined as the time at which half of the surface that was initially dry remained dry whereas the other half was inundated at least once an empirical expression was developed in which reworking time is proportional to the average cross sectional area of flow and inversely proportional to the sediment supply

3d quantification of mineral components and porosity distribution in westphalian c sandstone by microfocus x ray computed tomography abstract microfocus x ray computed tomography ct measurements were performed on deltaic sandstone samples from the diagenetically altered westphalian c strata campine basin north east belgium in order to collect three dimensional data on mineral quartz kaolinite ankerite etc and porosity distribution the acquired ct data were compared with point counting results of stained impregnated thin sections to qualify the sensitivity of ct comparison between techniques shows positive results with regard to the quantification of main mineral phases such as quartz and ankerite and porosity distribution however major discrepancies exist when studying the clay minerals this can be explained by the influence of microporosity associated with these clay minerals resulting in partial volume effects

formation of a cohesive floodplain in a dynamic experimental meandering river field studies suggest that a cohesive floodplain is a necessary condition for meandering in contrast to braided rivers however it is only partly understood how the balance between floodplain construction by overbank deposition and removal by bank erosion and chutes leads to meandering this is needed because only then does a dynamic equilibrium exist and channels maintain meandering with low width depth ratios our objective is to understand how different styles of floodplain formation such as overbank deposition and lateral accretion cause narrower channels and prevent chute cutoffs that lead to meandering in this study we present two experiments with a self forming channel in identical conditions but to one we added cohesive silt at the upstream boundary the effect of cohesive silt on bank stability was tested in auxiliary bank erosion experiments and showed that an increase in silt reduced erosion rates by a factor of 2 the experiment without silt developed to a braided river by continuous and extensive shifting of multiple channels in contrast in the meandering river silt deposits increased bank stability of the cohesive floodplain and resulted in a reduction of chute cutoffs and increased sinuosity by continuous lateral migration of a single channel overbank flow led to deposition of the silt and two styles of cohesive floodplain were observed first overbank vertical accretion of silt e g levee overbank sedimentation or splays and second lateral point bar accretion with silt on the scrolls and in the swales the first style led to a reduction in bank erosion while the second style reduced excavation of chutes we conclude that sedimentation of fine cohesive material on the floodplain by discharge exceeding bankfull is a necessary condition for meandering

alluvial fans formed by channelized fluvial and sheet flow i theory alluvial fans and fan deltas are of three basic types those built up primarily by the action of constantly avulsing river and stream channels those constructed by sheet flows and those resulting from the successive deposition of debris flows the present analysis is directed toward the first two types a mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean i e averaged over many avulsions bed slope and elevation in an axially symmetric fan an example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel in each example the case of channelized flow is compared to the case of sheet flow the model is applied to the tailings basin of a mine in the companion paper

microfabric and anisotropy of elastic waves in sandstone an observation using high resolution x ray microtomography abstract petrophysical experiments using acoustic velocities to characterise anisotropies of mechanical behaviour of rocks are of essential relevance to understand the geomechanical behaviour of sandstone reservoirs under changing stress fields here we present high resolution x ray microtomography ct as a supplementary research tool to interpret anisotropic ultrasound velocities in sandstones with variation of isotopic stress specimens of two lower cretaceous sandstones localities bentheim and obernkirchen both germany have been used in petrophysical laboratory experiments under dry conditions to study ultrasonic sound velocities frequency of signal input 1 mhz subsequently oriented micro plugs drilled from the sandstone samples were investigated using high resolution x ray microtomography by means of image processing of the reconstructed scan images geometric attributes such as mean structural thickness orientation and tortuosity were evaluated from the ct data for both pore space and grain skeleton our observations clearly indicate the different roles of pore space and grain skeleton in regard to the propagation of ultrasonic waves because the pores do not transmit the waves it was sufficient to investigate the average thickness of this fabric element in contrast as the ultrasonic waves traverse the rock via the adjacent grains it was necessary to survey the actual travel lengths of seismic waves in the sandstone grain skeleton

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

computer axial tomography in geosciences an overview abstract computer axial tomography cat is one of the most adequate non destructive techniques for the investigation of the internal structure of a large category of objects this method based on the attenuation of x or gamma ray generates digital images which map the numerical values of the linear attenuation coefficient of a section or of the entire volume of the investigated sample depending on the energy of the utilized radiation as well as on the effective atomic number of the sample cat can furnish with a spatial resolution of 0 01 0 5 mm quantitative as well as qualitative information concerning local density or chemical composition of the sample in geosciences cat has been successfully applied to the investigation of bulk density moisture content or macroporosity of the soil soil plant water system oil sand or shales small scale heterogeneities in siltstone or sandstone diamonds in kimberlite mineralization layers in manganese nodules local structure of marine sediments or coal composition the method has also been used for the investigation of the rock mechanical properties rock permeability fracture network two or three phase flow or residual oil distribution in carbonate cores a review of the actual applications of cat in soil science sedimentology coal geology as well as rock mechanics is presented all these applications reveal the great potential of cat in geoscience investigations