continuous porosity characterization metric scale intervals in heterogeneous sedimentary rocks using medical ct scanner abstract although computed tomography ct scanning has been regularly applied to core analyses in petroleum geology there is still a need to improve our ways to document porosity and porosity distribution in the entire pore scale spectrum from the tens of nanometer to the meter scale porosity imaging is particularly crucial for complex and heterogeneous rocks such as hydrothermally altered and fractured carbonates the present work proposes an improved method using medical ct to reliably estimate reservoir porosity an in house core flooding setup allowed to analyse several individual core samples scanned simultaneously dry and saturated as well as continuous core sections up to 1 5 m long without any prior knowledge of samples three dimensional alignment and subtraction of the two data sets dry and saturated states results in the generation of 3d porosity matrices the methodology tested on a large set of reference core material shows a strong correlation between conventional gas porosimetry techniques and porosity from ct scan the added value of the porosity measurements by ct scan is first of all the generation of 3d images of pore network allowing to assess spatial attributes of macropores their distribution and connectivity secondly the ct scan method also provides continuous porosity profile at the millimetric scale both developments are crucial for the understanding of reservoir rock properties

tomodensitometrie axiale relation entre l intensite tomographique et la densite de la matiere the calibration of an axial tomodensitometer used in sedimentology was carried out on minerals and liquid samples this study taking into consideration the interactions between x rays and matter revealed i a good correlation between the density of samples containing elements with low atomic number which undergo only compton scattering and the intensity readings obtained by computer tomography and ii readings higher than predicted by linear correlation for samples containing elements with high atomic number which undergo both compton scattering and photoelectric absorption an empirical model is used to correct the readings and correlate them with the density

palaeoenvironmental change during the end guadalupian permian mass extinction in sichuan china abstract the end guadalupian mass extinction has been investigated in sichuan province sw china in the south of the province the platform carbonates of the maokou formation are overlain by the emeishan flood basalts a possible factor in the extinction event and in the north of the province the formation is succeeded by shallow marine carbonates of the wuchiaping formation late permian the extinction event is primarily recorded by the loss of fusulinaceans and possibly by species level turnover amongst calcareous algae the high diversity middle permian microfossil assemblages are last seen beneath a surface recording widespread emergence and karstification in northern sichuan emergence occurred early in the capitanian stage and the succeeding strata record restricted hypersaline deposition that preceded the deposition of a thick ash horizon the wangpo bed these mid capitanian arid conditions are replaced by humid conditions towards the end of the stage as indicated by the development of a widespread coal seam in southern sichuan only a thin development of this humid coaly facies is seen developed atop the maokou karstic surface and below the oldest flood basalt the guadalupian interval saw the development of large c isotope excursions in the carbonate record these include a positive then negative swing late in the capitanian and a newly discovered negative spike superimposed on an early capitanian heavy interval this spike may be a global phenomenon but the magnitude 8 may have been exaggerated by an increased contribution from light respired c derived from soils during relative sea level fall a plethora of environmental factors approximately coincide with the extinction event including regression acidic volcanism and flood basalt volcanism making it difficult to unravel the relative significance of each

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

a comparison of micro ct and thin section analysis of lateglacial glaciolacustrine varves from glen roy scotland abstract despite the prevalence of thin section analysis in studies of quaternary sediments there are limitations associated with the production of thin sections sediment modification and the inherently 2d view that a thin section affords non destructive and rapid scanning technologies such as x ray computed microtomography ct enable material samples to be visualised and analysed in 3d in a quaternary context however such techniques are in their infancy this paper assesses the optimum approach to ct analysis of quaternary sediments applying the method on lateglacial glaciolacustrine varves from glen roy scotland scan datasets are examined at each stage of the thin section process and comparisons are made between 2d ct images and thin sections for the recognition of 2d sediment features with further appraisal of 3d models to identify 3d sediment structures comparable sediment features are observed in 2d ct images and thin sections however the ct imaging resolution determines the precision of microfacies descriptions additional 3d structures are distinguished from volumetric models that are otherwise impossible to identify in thin section slides these 3d structures can locally alter sediment properties e g layer thickness as seen in 2d thin sections and or digital images although such variation cannot be detected with these media it has been demonstrated that clear benefits exist in understanding the 3d structure of quaternary sediments both prior to thin sectioning to avoid complicating e g deformation structures and after thin sectioning to establish the complex 3d context of 2d datasets it is recommended that ct and thin section techniques are applied in parallel in future studies which will profit from the integration of true 3d data it is also advised that samples are scanned soon after field sampling due to the significant modification of in situ sediment structures that can occur during thin section processing

facies analysis and sea level change at the guadalupian lopingian global stratotype laibin south china and its bearing on the end guadalupian mass extinction abstract the guadalupian lopingian boundary stratotype at penglaitan and the nearby tieqiao section near laibin south china record a series of major environmental changes within the jiangnan basin during a mid permian biotic crisis the sequence stratigraphic petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea level fall that led to the establishment of mid ramp conditions laibin limestone in settings that were previously dominated by radiolarian mudstones the regression also coincides with a low point of 87 sr 86 sr ratios the lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the emeishan flood basalt province 800 km to the west of laibin thus unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event subsequent environmental changes included transgression spread of dysoxic waters indicated by populations of small pyrite framboids and a major negative c isotope excursion all these phenomena have been previously related to the end guadalupian extinction but they in fact post date the crisis because a post extinction fauna of foraminifers is encountered at this time

computerized x ray tomography analysis of sandbox models examples of thin skinned thrust systems computerized x ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution as well as the three dimensional geometry of models that simulate tectonic deformations most of the plastic or viscous analog materials generally used in a normal gravity field for such models have x ray attenuations compatible with medical scanner images models using soft cohesionless granular materials were studied faults in granular materials corresponding to dilatant zones with lower by 30 50 x ray attenuation are thus clearly visible in the tomography images kinematic analysis was done on imbricate thrust propagation in materials with an internal friction angle of 30 thrust propagation is controlled mainly by a triangular pop up structure resulting from the nucleation of two conjugate thrusts at the basal decollement the pop up structure is created immediately in front of the previous thrust three dimensional geometry analysis was tested on lateral ramps parallel to the transport direction lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model though the lateral ramps strike almost parallel to the transport direction their dip angle is comparable to the dip angle of frontal ramps

evolution of a plume influenced source to sink system an example from the coupled central emeishan large igneous province and adjacent western yangtze cratonic basin in the late permian sw china abstract source to sink paleogeography in a time constrained sequence stratigraphic framework has been reconstructed for the non marine to marine transitional lopingian strata late permian in the western yangtze cratonic basin wycb and the adjacent inner zone of the emeishan large igneous province elip in order to reveal the evolution of a mantle plume influenced cratonic basin the lopingian coal bearing strata can be subdivided into seventeen 4th order sequences and three 3rd order composite sequences representing 6 76 myr paleogeographic reconstructions of the wycb demonstrate the existence of n s trending terrestrial transitional and marine facies belts distributed west to east away from the central elip geomorphological analysis indicates that the western boundary of the source area coincided with the major axis of the uplifted central elip based on sediment flux estimates and modeling bqart model relief of the central elip increased from near sea level in the earliest late permian and reached equilibrium at about 200 m in the latest permian sediment volume backfilling analysis indicates that total tectonic uplift of the central elip in the late permian was more than 500 m evolution of the coupled central elip and wycb can be subdivided into three stages pre eruptive uplift stage pre and syn eruptive subsidence stage and syn and post eruptive uplift stage post eruptive basin filling was controlled by sediment supply that was related to tectonic uplift drainage topography and climate change and basin accommodation that was related to sea level fluctuations and plume induced syn sedimentary tectonics

sedimentation and lithofacies paleogeography in southwestern china before and after the emeishan flood volcanism new insights into surface response to mantle plume activity abstract investigations into permian sedimentation and reconstruction of paleogeography in sw china are aimed at characterizing sedimentary responses to the emeishan mantle plume in addition to erosional features on the sediments underlying the uplifted emeishan basalts unusual depositions of permian age are also present in the emeishan large igneous province lip specifically carbonate gravity flows and submarine incised canyon fillings were developed in the western margin of the postulated uplifted area and rifting trenches were developed along the eastern margin alluvial fan deposits occur at the boundary between the inner and intermediate zones these depositions all rest on the maokou formation and are in turn covered by the emeishan basalts implying synchronism between crustal uplift and depositional events these deposits and the associated extension and normal faulting along the margin of and within the lip represent sedimentary features resulting from dynamic behavior of mantle plume com

sedimentary evidence for a rapid kilometer scale crustal doming prior to the eruption of the emeishan flood basalts biostratigraphic and sedimentologic investigations in 67 sections have been carried out for the middle permian maokou formation that immediately underlies the emeishan flood basalts in southwest china the results suggest a domal crustal thinning before the emplacement of the emeishan large igneous province variably thinned carbonates in the maokou formation are capped by a subaerial unconformity which is generally manifested by karst paleotopography paleoweathering zone or locally by relict gravels and basal conglomerates provenance analysis indicates that these gravels and conglomerates were mainly derived from the uppermost maokou formation therefore the stratigraphic thinning likely resulted from differential erosion due to regional uplift iso thickness contours of the maokou formation delineate a subcircular uplifted area in accordance with the crustal doming caused by a starting mantle plume as predicted by experimental and numerical modeling the duration of this uplift is estimated to be less than 3 myr and the magnitude of uplift is greater than 1000 m the sedimentary records therefore provide independent supporting evidence for the mantle plume initiation model for the generation of the emeishan flood basalts

quaternary cave levels in peninsular florida abstract the hypothesis that caves in the florida peninsula are tied to quaternary sea levels was proposed by hydrogeologists without data some 40 years ago the hypothesis is a version of glacial control of cave levels which is the logical combination of the water table theory of speleogenesis and the concept that base level positions the water table at the usa type example of glacial control of cave levels mammoth cave in the paleozoic rocks of kentucky the intermediary is base level determined by rivers by hypothesis the intermediary for florida is glacioeustatic sea level this paper presents elevation data that supports this hypothesis recent cave surveys in the air filled caves and spot elevations from archived maps reveal prominent levels of passages centered at 5 12 21 and 30 m above sea level over broad areas they do not follow the large scale structure of the floridan aquifer instead they align with nearby coastal marine terraces identified as modal peaks on frequency plots from various topographic data bases levels matching with the three highest terraces wicomico penholoway and talbott are particularly clear lower levels if they accord with sea level stands are likely composites data from cavities encountered in drilled wells e g bit drops and spot elevations from archived underwater cave maps demonstrate passage levels at depths of 15 30 70 and 90 120 m below the modern water table the depths below water table are similar to the depths below sea level of distant submerged terraces and paleoshoreline features identified using multibeam bathymetric data in the gulf of mexico the cave bit drop and terrace data are all consistent with the concept that quaternary sea level is the fundamental control on the cave scale porosity within the floridan aquifer this conclusion does not rule out the possibility that lithologically favored positions paleokarst features and confining units and mixing zones are also involved in the location of caves levels in this near coastal environment

computer tomography a nondestructive high resolution technique for investigation of sedimentary structures abstract knowledge of sedimentary structures is very important to many marine geoscientific disciplines however the conventional method of detection x radiography is of limited value wherever full round samples are used although the resolution may be enhanced by the use of high resolution radiographs of sediment slabs with thicknesses of 7 10 mm this method is destructive and not really suitable for full round sediment cores or when slabbing is impossible as in the case with small diameter cores these problems can be avoided by the use of computer tomography a nondestructive method for the investigation of sedimentary structures besides not disturbing the sample material a higher resolution image of the structures can be achieved further computer storage of the data permits postprocessing such as the generation of 3d images

tidal hydrodynamics and fine grained sediment transport on the radial sand ridge system in the southern yellow sea abstract the large radial sand ridge rsr system located in the southern yellow sea off the jiangsu coast is characterized by a radial current field and high suspended sediment concentrations sscs significant rectilinear currents are present over the northern sand ridge area whereas rotary currents prevail over the southern area the transition between the two being dominated by a locally generated trapped wave observations undertaken in 2006 and 2007 indicate a seasonal pattern in the ssc and associated dynamic characteristics the results of a calibrated hydrodynamic model show that the m2 tide dominates the rsr area the maximum tidal amplitude in the core region close to land being approximately 2 m an amphidromic point is located some distance north of the rsr off the abandoned yellow river mouth 121 686 e 34 6 n specifically the eulerian and lagrangian residual currents flow southward in both summer and winter whereas the stokes drift is directed southward in the north and northward in the south moreover in deep water the lagrangian residual current is mainly determined by the eulerian residual current whereas it is strongly influenced by the stokes drift in shallow water the seasonal variation in the residual current in the southern yellow sea is a good indicator for the location of the yellow sea warm current yswc in both summer and winter measurements show that a ssc peak appears off the abandoned yellow river delta in response to the strong currents and plentiful supply of fine grained sediment from coastal erosion another ssc peak lying close to the north branch of the changjiang river mouth is related to the abundant suspended sediment supplied by the river seasonal variations in ssc are observed in the study area maximum average values and widest diffusion from land occurring in winter this being contrasted by minimum mean values in summer sensitivity experiments demonstrate that the main factor influencing the distribution of ssc is the tide while river discharge wind and wave effects are small and very localized to explain the seasonal variation in ssc the role of hydrodynamics initial conditions and temperature are tested in the model the results show that the hydrodynamics play a significant role whereas the initial conditions only have a minor regional influence temperature on the other hand is also shown to greatly influence the seasonal variation in ssc because of substantial changes in the viscosity of the water and the erosion shear stress the modeled results are used to calculate sediment fluxes which are shown to be consistent with the lagrangian residual current pattern while wind waves can significantly change the fluxes in winter bed elevations change substantially on a monthly time scale in general the deep channels are undergoing erosion while the shallow ridges and coastal tidal flats are accreting the net sediment transport being directed towards the coastal tidal flat and the changjiang yangtze river subaqueous delta

cat scan in marine stratigraphy a quantitative approach abstract computed axial tomography cat scan gives a pseudo 3d representation of sedimentary cores sediments may be described and numerically processed from digitized high resolution images a 150 m long borehole was drilled and sampled at ile aux coudres middle estuary of the st lawrence quebec and analysed by a tomodensitometer cat scanner this borehole represents mainly the illinoian sangamonian transition series isotopic stage 5e 130 80 kyr b p of a post glacial glacioisostatic marine invasion and the subsequent regressive prodelta four representative samples 900 mm long were chosen for analysis from a transition zone between glacial and prodeltaic sediments they have been described from tomographic longitudinal and transversal sections from ct number series and also from classical analysis such as grain size organic matter and carbonates ct numbers reflect sedimentary characteristics and are closely linked to grain size and to organic matter carbonates are only weakly correlated probably because of its low concentration bed thickness and numerical processing of ct number series are used to characterize lamina and allow for depicting sub annual annual and longer periodicities clay facies fine and thick rhythmites and isolated diamicton beds were identified from bottom to top the first sample contains homogeneous clay rhythmites typical of a distal environment the second is composed of diamictons and thin alternating light dark annual lamina sets in the third sample annual light dark rhythmites are slightly thicker and display subtle semi annual cyclicities in the fourth sample annual rhythmites are several centimetres in thickness and contain preserved sub annual events of possible seasonal cyclicity this succession of facies and associated stratal periodicities may be typical of transgressive sedimentation in a basin such as the st lawrence estuary during the transition from glacial to non glacial conditions

thin tephra layers in peat revealed by x radiography x radiography has been found to provide a rapid economical non destructive method of locating very thin fine grained tephra of icelandic origin in scottish peats tephra layers form time parallel marker horizons or isochrones that are of great archaeological significance because they cover large areas offer precise chronological control for associated material and occur at times of significant cultural and environmental changes not all of the discrete deposits of recent volcanic fallout in scotland are sufficiently dense to show clearly on x radiographs but those which do provide particularly clear easily located marker horizons with many applications in palaeoenvironmental studies the tephra layer in caithness produced by fallout from a c 4000 by eruption of hekla provides a particularly good example of the use of x radiography to locate volcanic ash the method also reveals other structures of archaeological and palaeoenvironmental significance butler 1992 journal of archaeological science 19 151 161

integrating satellite observations and modern climate measurements with the recent sedimentary record an example from southeast alaska 1 assessments of climate change over time scales that exceed the last 100 years require robust integration of high quality instrument records with high resolution paleoclimate proxy data in this study we show that the recent biogenic sediments accumulating in two temperate ice free fjords in southeast alaska preserve evidence of north pacific ocean climate variability as recorded by both instrument networks and satellite observations multicore samples ew0408 32mc and ew0408 43mc were investigated with 137cs and excess 210pb geochronometry three dimensional computed tomography high resolution scanning xrf geochemistry and organic stable isotope analyses ew0408 32mc 57 162 n 135 357 w 146 m depth is a moderately bioturbated continuous record that spans ad 1930 2004 ew0408 43mc 56 965 n 135 268 w 91 m depth is composed of laminated diatom oozes a turbidite and a hypopycnal plume river flood deposit a discontinuous event based varve chronology indicates 43mc spans ad 1940 1981 decadal scale fluctuations in sedimentary br cl ratios accurately reflect changes in marine organic matter accumulation that display the same temporal pattern as that of the pacific decadal oscillation an estimated sitka summer productivity parameter calibrated using seawifs satellite observations support these relationships the correlation of north pacific climate regime states primary productivity and sediment geochemistry indicate the accumulation of biogenic sediment in southeast alaska temperate fjords can be used as a sensitive recorder of past productivity variability and by inference past climate conditions in the high latitude gulf of alaska

pre eruptive uplift in the emeishan in their correspondence he and colleagues question our conclusion of little or no uplift preceding emeishan volcanism that we reported in our letter1 debate concerns the nature of the contact between the maokou limestone and emeishan volcanics the depositional environment and volumetric significance of mafic hydromagmatic deposits mhds and evidence for symmetrical domal thinning mhds in the daqiao section are separated from the maokou limestone by 100 m of subaerial basaltic lavas but elsewhere mhds previously interpreted as basal conglomerates2 3 directly overlie the maokou2 3 mhds thus feature strongly in basal sections of the emeishan lava succession as also recently shown4 elsewhere in the emeishan an irregular surface at the top of the maokou limestone has been interpreted as an erosional unconformity2 3 but clastic deposits presented as evidence of this erosion2 3 are mhds produced by explosive magma water interaction1 a clear demonstration that this irregular top surface is an erosional truncation of limestone reef facies slope rim flat lagoonal is currently lacking but is critical because reefs and carbonate platforms show considerable natural relief of tens of metres the persistent hot wet climate since the oligocene has produced well developed weathering profiles on exposed palaeozoic marine sedimentary sequences5 but weathering and karst relief of the uppermost maokou limestone underlying the flood basalts have not been properly documented nor shown to be of middle permian age and immediately preceding emplacement of the large igneous province

giant radiating mafic dyke swarm of the emeishan large igneous province identifying the mantle plume centre in many continental large igneous provinces giant radiating dyke swarms are typically interpreted to result from the arrival of a mantle plume at the base of the lithosphere mafic dyke swarms in the emeishan large igneous province elip have not received much attention prior to this study we show that the geochemical characteristics and geochronological data of the mafic dykes are broadly similar to those of the spatially associated lavas suggesting they were derived from a common parental magma based on the regional geological data and our field observations we mapped the spatial distribution patterns of mafic dyke swarms in the elip and recognized six dyke sub swarms forming an overall radiating dyke swarm and converging in the yongren area yunnan province this location coincides with the maximum pre eruptive domal uplift and is close to the locations of high temperature picrites our study suggests that the yongren area may represent the mantle plume centre during the peak of emeishan magmatism

chronology and sedimentology of a new 2 9 ka annually laminated record from south sawtooth lake ellesmere island abstract few annually laminated varved lacustrine records exist in the arctic but these high resolution climate archives are needed to better understand abrupt climate change and the natural mode of climate variability of this sensitive region this paper presents a new high resolution 2900 year long varved lake sediment record from the fosheim peninsula ellesmere island the varve chronology is based on multiple varve counts made on high resolution scanning electron microscope images of overlapping sediment thin sections and is supported by several independent dating techniques including 137cs and 210pb analysis one optically stimulated luminescence age located close to the bottom of the composite sequence and comparison between paleomagnetic variations of this record and the longest high arctic varve record lower murray lake which confirms the reliability of the sawtooth chronology high resolution backscattered images examined under a scanning electron microscope sem were crucial to giving a more detailed view of sedimentation processes in the lake and thus help to delineate varves more precisely than in conventional image analysis fine scale geochemical analysis reveals that lake sedimentation is mainly clastic and that elemental geochemistry is influenced by grain size principal component analysis of multiple proxies and the coarse grain size fraction of south sawtooth lake display similar fluctuations to the nearby agassiz ice cap 18o record including lower values during the little ice age cold period these results show this new high resolution and continuous record has a reliable varve chronology and is sensitive to temperature variability south sawtooth lake s mean sedimentation rate of 1 67 mm a 1 is higher than any other sedimentary sequence in the high arctic providing a unique opportunity for extracting new high resolution paleoclimatological and paleoenvironmental record in a region where few other records currently exist

a rapid method for converting medical computed tomography scanner topogram attenuation scale to hounsfield unit scale and to obtain relative density values medical computed tomography scanners permit to rapidly obtain qualitative and quantitative information on objects in a non destructive manner in both longitudinal and transversal directions ct scan scales used to express attenuation on the images are different for longitudinal topograms and transversal tomograms views restraining the complementary use of the information extracted from both views moreover topograms are of full use in core analysis as they reveal fine scale information on stratigraphical sedimentological and physical properties of the material this paper presents a method to convert ct scan topogram intensity scale to hounsfield unit hu scale used on tomograms and to later extract a relative density from it the method is based on relationships between topogram and tomogram values absolute density and effective atomic numbers obtained on a series of minerals results show excellent correlations between converted topogram values and hu values obtained on the tomograms as well as between relative densities derived from the converted topogram values and the absolute density of the minerals

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

visualizing three dimensional root networks using computed tomography abstract we describe a method to reconstruct the root network from a three dimensional image generated with computed tomography the x ray absorption of roots and the interface of the air soil material is very similar and the contrast extremely low the method consists of three steps contrast enhancement using a non linear diffusion filter thresholding based on rosin s method and extraction of the main features using a morphological connectivity algorithm with this approach we are also capable of reconstructing fine roots with high fidelity which is shown with a performance experiment using artificial images with increasing noise the method is applied to an x ray microtomography data set of two alder roots grown for 4 months in a natural moraine soil to simplify the soil material the bare roots were transferred into a plexiglas receptacle filled with quartz sand the reconstructed image is compared with a photograph of the real roots

correlation of 3d computerized tomographic scans and 2d colour image analysis of westphalian coal by means of multivariate statistics abstract core material containing westphalian vitrinite rich coal from the north of belgium campine basin has been investigated by colour image analysis and computerized tomography the relative 3d density distribution of the investigated core material was determined by non destructive x ray computerized tomography colour image analyses of polished sections of the same piece of core material provided data concerning the corresponding maceral composition and mineral content of the coal the application of both methods to the same piece of rock allowed for a first order cross correlation of different rock properties by multivariate statistical analysis density estimates of macerals were made the combination of both techniques is very useful in a study of fracture systems in core material and density calibration of computerized tomographic scans of rock constituents

computer axial tomography investigation of polymetallic nodules abstract polymetallic nodules collected from the clarion clipperton region of the north pacific ocean have been investigated by using a siemens somatrom hiq computer tomograph the reconstructed tomographies show much details in the internal structure of the nodules such as nucleus shape and origin primary and secondary growth surfaces highly mineralized areas and the fracture network in addition reconstructed 3d images of nodules have been obtained computer axial tomography proves to be a remarkably useful method for this typed of investigation

analysis of the internal structure of rocks and characterization of mechanical deformation by a non destructive method x ray tomodensitometry abstract tomodensitometry is a new non destructive method which reveals the internal structure of rocks through analysis of x ray images without any damage to the sample the scanner gives a radiological density which is a function of gravimetric density and mineralogy for limestones and sandstones an attempt is made to quantify the relation between radiological density and porosity spatial variations in the values of the radiological density measured on rock core specimens that are deformed and fractured in a triaxial cell are then related to the intensity of experimental volumetric deformation

numerical modelling of a mantle plume the plume head lithosphere interaction in the formation of an oceanic large igneous province abstract the thermomechanical processes associated with formation of large igneous provinces lips remain poorly understood owing to fundamental difficulties in simulating plume lithosphere interactions in current numerical models these models which aim to simulate the rise of mantle plume and the spread of plume head material imply a mechanically over simplified lithosphere and commonly a flat lithosphere zero vertical displacement as the upper boundary condition we propose a new numerical model derived from lithospheric scale models it has a high numerical resolution in the lithospheric domain and explicitly accounts for 1 free upper surface boundary condition 2 elastic plastic ductile lithospheric rheology including surface faulting and 3 vertical strength variations in the lithosphere we study the final stages of plume ascent and we focus on surface and lithospheric evolution and intra plate strain localisations the experiments predict that the first surface elevation occurs in less than 0 2 ma after plume initiation at 400 km depth variation of rheological parameters results in different surface elevations 500 2500 m ascent 2 10 m yr and base plate strain rates 10 12 10 15 s 1 fast 0 2 0 3 m yr plume head flattening starts at the moment when the plume head reaches the base of the lithosphere it leads to large scale extension and deep normal faulting at the centre of the plateau and to strong thermomechanical erosion at its base the erosion is maximal not under the plume centre as was predicted before but in two large bordering zones our study locally is the igneous province of the caribbean plate where the pre existing farallon lithosphere has been affected by the galapagos hotspot activity that generated thermal perturbations and crustal thickening with two main episodes of volcanism and underplating

a depositional model for seismo turbidites in confined basins based on ionian sea deposits abstract this study investigates ionian sea seismo turbidite st deposits that we interpret to be triggered by major historic earthquakes and tsunamis in the calabrian arc st beds can be correlated with the ad 1908 mw 7 24 messina ad 1693 mw 7 41 catania and ad 1169 mw 6 6 eastern sicily earthquakes while two previously unknown turbidites might have been generated by the ad 1818 mw 6 23 catania and ad 1542 mw 6 77 siracusa earthquakes textural micropaleontological geochemical and mineralogical signatures of sts reveal cyclic patterns of sta stb stc and std sedimentary units for each earthquake with an associated tsunami the sta unit contains multiple st stacks with different mineralogy geochemistry foraminiferal assemblages and sedimentary structures that are deposited from synchronous multiple slope failures and turbidity currents the stb homogenite graded mud unit overlying the sta unit is deposited by the waning flows of the multiple turbidity currents that are trapped in the ionian sea confined basin the stc laminated and marine sourced unit results from seiching of the confined water mass that appears to be generated by earthquake ruptures combined with tsunami waves the std unit is a tsunamite cap deposited by the slow settling suspension cloud created by tsunami wave backwash erosion of the shoreline and continental shelf this tsunami process interpretation is based on the textural gradation of the upper unit and a more continental source of the tsunamite cap which includes c n 10 and the presence of inner shelf foraminifera with a lack of abyssal species this interpretation is in agreement with the lack of a tsunamite cap for the turbidite likely linked to the ad 1542 historic earthquake that is not associated with a tsunami the new sedimentologic criteria identifies the final seiche and tsunamite cap deposits of sts and provides a model that can now be tested in other locations to better understand the different depositional processes of seismo turbidites in confined basins

effects of tube sampling in soft clay a microstructural insight this paper analyses the effects of tube sampling in soft clay with particular emphasis on the modifications that occur in the clay fabric for tube specimens retrieved using open samplers shelby a

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

the guadalupian lopingian boundary mudstones at chaotian sw china are clastic rocks rather than acidic tuffs implication for a temporal coincidence between the end guadalupian mass extinction and the emeishan volcanism abstract previous studies on the temporal link between the end guadalupian mass extinction event and emeishan flood volcanism were mainly based on geochronological and bio and chemostratigraphic correlation techniques wignall et al 2009 the absence of material based hard evidence that directly links the extinction with the emeishan volcanism remains a major obstacle regardless of the indication of coincidence in timing isozaki et al 2007 the emeishan basalts overlie permian platform carbonates that may contain a record of the end guadalupian mass extinction and erosional product of this province this paper presents mineralogy and geochemistry of mudstones from the guadalupian lopingian boundary g lb at chaotian sw china results indicate that these g lb mudstones are not air fall acidic tuff as previously thought but likely represent clastic rocks derived from erosional deposits of the emeishan large igneous province elip mudstones of the lower part group 1 have a geochemical affinity to the emeishan felsic volcanic rocks whereas mudstones of the upper part group 2 are compositionally akin to mafic components of the emeishan traps this chemostratigraphic sequence resembles the xuanwei formation which sits on the emeishan basalts he et al 2007 these data therefore indicate that the lower part of the mudstones at the chaotian g lb section the lowermost part of xuanwei and longtan formations and the emeishan felsic extrusives broadly constitute an isochron horizon throughout the elip and adjacent region suggesting a short duration for the emeishan volcanism a temporal coincidence between emeishan volcanism and the end guadalupian mass extinction are therefore inferred thus providing support for a cause and effect relationship

quantitative 3d strain analysis in analogue experiments simulating tectonic deformation integration of x ray computed tomography and digital volume correlation techniques abstract the combination of scaled analogue experiments material mechanics x ray computed tomography xrct and digital volume correlation techniques dvc is a powerful new tool not only to examine the 3 dimensional structure and kinematic evolution of complex deformation structures in scaled analogue experiments but also to fully quantify their spatial strain distribution and complete strain history digital image correlation dic is an important advance in quantitative physical modelling and helps to understand non linear deformation processes optical non intrusive dic techniques enable the quantification of localised and distributed deformation in analogue experiments based either on images taken through transparent sidewalls 2d dic or on surface views 3d dic x ray computed tomography xrct analysis permits the non destructive visualisation of the internal structure and kinematic evolution of scaled analogue experiments simulating tectonic evolution of complex geological structures the combination of xrct sectional image data of analogue experiments with 2d dic only allows quantification of 2d displacement and strain components in section direction this completely omits the potential of ct experiments for full 3d strain analysis of complex non cylindrical deformation structures in this study we apply digital volume correlation dvc techniques on xrct scan data of solid analogue experiments to fully quantify the internal displacement and strain in 3 dimensions over time our first results indicate that the application of dvc techniques on xrct volume data can successfully be used to quantify the 3d spatial and temporal strain patterns inside analogue experiments we demonstrate the potential of combining dvc techniques and xrct volume imaging for 3d strain analysis of a contractional experiment simulating the development of a non cylindrical pop up structure furthermore we discuss various options for optimisation of granular materials pattern generation and data acquisition for increased resolution and accuracy of the strain results three dimensional strain analysis of analogue models is of particular interest for geological and seismic interpretations of complex non cylindrical geological structures the volume strain data enable the analysis of the large scale and small scale strain history of geological structures

no pre eruptive uplift in the emeishan large igneous province new evidences from its inner zone dali area southwest china abstract the permian emeishan large igneous province elip in southwest china has been considered a typical example of crustal domal uplift caused by mantle plume upwelling prior to the onset of volcanism however this model has been questioned by the discovery of hydromagmatic volcaniclastic deposits formed in a marine environment located near the central elip area the inner zone which is inferred to be the zone of maximum uplift the volcanology of the inner zone has thus far been poorly documented fueling the debate about whether or not pre eruptive uplift occurred prior to plume upwelling understanding the volcanology of this inner zone is therefore critical in constraining the eruption environment of the central elip our work has revealed new volcanological observations in the inner zone dali area which can systematically constrain volcanism and paleoenvironment the basal succession of the sequence is a thick pillow lavas pile with hyaloclastites implying an initial deeper submarine stage of eruptions limestones and submarine fallout tuffs are interbedded with these pillow lavas above that abundant mafic volcaniclastic products developed which contain palagonite rimmed lapilli tuffs base surge deposits and peperites suggesting hydroclastic volcanism in a shallower submarine environment the upper succession of the sequence preserves columnar jointed lava flows and subaerial fallout tuffs reflecting subaerial volcanism after the volcanic center emerged above the sea level these abundant and systematic natures of this evidence suggest that the initial volcanism of the central elip occurred in a deep submarine environment the submarine to subaerial transition is caused by progressive emplacement of voluminous magmatic products infilling the inner zone during the continuous emplacement of elip rather than by crustal doming prior to the onset of volcanisms

utilisation de la scanographie pour l etude des sediments influence des parametres physiques chimiques et biologiques sur la mesure des intensites tomographiques in july 1996 a flash flood resulted in the input of 9 million m3 of sediment toward the bay of ha ha leading to the elimination partly or totally of the benthic fauna of the bay in this study the ct scanner has been used in a highly perturbed environment the bay of ha ha to both assess i the relationships between the variations of tomographic intensities and the sedimentologic parameters of the sedimentary column and ii to quantify the biogenic structures resulting from the activity of benthic organisms compaction caco3 contents and granulometry of sediments are the most important influences on the variation of tomographic intensities the scanner allowed the study and quantification in a non destructive way of the sediment occupation by biogenic structures and more particularly allowed to further assess most of the relative importance of the fine fraction of biogenic structures 0 250 1 mm in the surface sediment layer 0 5 cm sediment occupation by biogenic structures reached m

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

a novel sedimentological method based on ct scanning use for tomographic characterization of the galicia interior basin abstract non destructive techniques of core analysis especially of marine cores are being broadly employed for sedimentary paleoceanographic and paleoclimate research in particular computed tomography scanning ct scanning allows acquisition of 3d and 2d images according to desired planes and thus the identification of sedimentary structures large grains and their distributions as well as direct measurements of material densities the most significant contribution of this technique is the possibility of getting results before opening the core in this work ct scan data obtained for five cores from the galicia interior basin gib nw peninsula iberia are presented and discussed focussing on 1 methodology of the ct scan use 2 tomographic description of sedimentary facies identified in the gib 3 treatment of the numeric data obtained with ct scanning using specific software anidoc and 4 comparison of tomographic data with data obtained by conventional methodologies of core analysis the most singular feature of gib cores is the presence of ice rafted debris ird deposited during late pleistocene heinrich events he which can be easily recognized using the ct scan by the presence of high radio density grains immersed in a low radio density matrix comparison of ct scan data with analytical sedimentary data and he proxies performed on the cores validates the ct scanning method as a powerful tool to improve correlations identify well constrained events and make more accurate basin reconstructions without opening all the cores in an oceanographic study

identifying the sedimentary imprint of high frequency holocene river floods in lake sediments development and application of a new method abstract in an effort to improve the understanding of floods and how they relate to climate we have developed a method that objectively identifies the sedimentary imprint of individual river floods in downstream lake basins the method is applied to a high resolution lake sediment core retrieved from southern norway resulting in a detailed record of holocene river flood activity covering the last 10 000 years including floods also recorded by instrumental and historical data the minimum number of individual floods recorded for this period is 100 on multidecadal to centennial timescales significant change in flood frequency is observed that arguably can be attributed to large scale climatic changes such as the varying amount of winter precipitation and summer rainstorms flood frequency was low during the early holocene 9770 7700 cal yr bp and even lower for the period that followed lasting until 5500 cal yr bp for the next 2500 years a modest increase in flood activity followed this trend was truncated 2500 cal yr bp by a sudden shift towards increased flooding frequency with the exception of a short interval around 1000 cal yr bp when the number of floods again was low this tendency of increased flood activity prevailed until present including stor ofsen a large flood that occurred in ad 1789 and also three other historically documented river floods

reply to comment on paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism by bin he yi gang xu jun peng guan yu ting zhong lithos 119 1 9 2010 we welcome the comments of ukstins peate et al 2011 on our recent paper he et al 2010a which provide us with an opportunity to extend our discussion on paleokarst between themaokou formation and theemeishanbasalts ukstins peate et al 2011 question the existence of karstic surface of the maokou limestone described by he et al 2010a instead theycontend that the earliest emeishanmagmaswereeruptedat or below sea level in the center of the emeishan large igneous province elip rejecting the pre volcanic domal uplift model proposed by he et al 2003 their arguments are largely basedon their interpretations of field observations such as a sedimentary continuity across the guadalupian lopingian boundary g lb in the center of the elip and b the faulted contact between emeishan basalt andmaokou formation however aswewill showbelow wedispute thesefieldobservations and ukstins peate et al s interpretation of the temporal and spatial frameworks of our and others results in this reply we will clarify using specific examples some key aspects of their questions about the paleokarst on the maokou formation and its relationship to plumeinduced uplift in the elip

paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism abstract the 260 ma emeishan large igneous province elip in southwest china has previously been demonstrated to provide compelling evidence for pre volcanic crustal doming in support of the mantle plume hypothesis however this has been questioned by ukstins peate and bryan 2008 by showing hydrothermal magmatic activity at the daqiao section to solve this argument a detailed characterization of the contact between the emeishan basalts and the maokou formation was carried out the contact is shown to be an unconformity which is characterized by paleokarst on top of the maokou formation including paleokarst relief sinkholes caves tower karst and its corresponding rocks such as kaolinite bauxite and ferruginous duricrust and collapsed breccias etc this paleokarst unconformity was in turn covered or infilled by the emeishan basalts and tuffs suggesting that uplift and erosion occurred prior to the eruption of the elip the extent of erosion of the maokou formation indicates the elip can be divided into three roughly concentric zones the inner intermediate and outer zones the paleokarst features on the top of maokou formation vary across the elip in the inner zone a likely sinkhole and an incision valley with 450 m relief in height are found in the intermediate zone various paleokarst landforms such as karst relief sinkholes and tower karsts are well developed some sinkholes that developed in the qixia formation below the maokou formation imply that the paleorelief is more than 350 m in height in the outer zone the paleokarstic surface is a paleo weathering layer with minor karstification and development of caves at 10 50 m this spatial variation of the paleokarst reflects variation of uplift height across the elip the extent of minimal uplift is estimated to be at least 450 m in the inner zone 350 m in the intermediate zone whereas uplift is minor tens 50 m in the outer zone the magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models the paleokarst was formed after the deposition of the maokou formation and the eruption of the emeishan basalts at the end guadalupian and indicates a short duration of uplift thus this study lends further support to domal uplift prior to the emeishan flood volcanism but also to the mantle plume initiation model for the generation of the elip

tomographic study of paleoproterozoic carbonates as key to understanding the formation of molar tooth structure abstract x ray computed tomographic studies of relatively pure paleoproterozoic limestones from the george formation muskwa assemblage northern british columbia canada indicate that molar tooth structures developed along linked fractures in gel like semi plastic carbonate mud with a high organic content where pore fluid and or gas pressures matched confining loads mt blobs developed where pressure exceeded loads cracks propagated into adjacent semi elastic sediment and were rapidly filled by clusters of uniform equant microcrystalline carbonate where abundant carbonate was not precipitated incipient cracks and sheets collapsed leaving residual trains of microcrystalline carbonate with similar density to the molar tooth carbonate tomographic studies show that the density of calcite domains within petrographically uniform sheets of mt void filling calcite is uneven suggesting that precipitation was not instantaneous but was propagated from discrete centres it is here suggested that carbonate production and sediment rheology were both strongly influenced by organic matter during early sea floor diagenesis microcrystalline carbonate precipitated within organic rich sediment with high water content possibly within decomposing mats of microbial extracellular polymeric substances eps when pore pressures in the host sediment increased in response to cyclic loading by long period waves pore fluids containing eps were injected into newly created fractures allowing rapid precipitation of molar tooth carbonate because tomographic studies allow detailed resolution of minor density differences they provide a useful method of evaluating structures in relatively uniform carbonate rocks of any age

comment on paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism a department of geoscience 121 trowbridge hall university of iowa iowa city ia 52242 usa b biogeoscience queensland university of technology brisbane queensland 4001 australia c department of earth and environment university of leeds leeds ls2 9jt uk d dougalearth ltd 12 nevilles cross villas durham dh1 4jr uk e department of earth sciences university of hong kong pokfulam road hong kong china

geothermal constraints on emeishan mantle plume magmatism paleotemperature reconstruction of the sichuan basin sw china the middle late permian emeishan large igneous province elip in southwestern china represents a classic example of a mantle plume origin to constrain the thermal regime of the elip and contemporaneous magmatic activity in the northeastern sichuan basin maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance ro and apatite fission track data two heating patterns were identified 1 heating of the overlying lithosphere by magma storage regions and or magmatic activity related to the mantle plume which resulted in a relatively strong geothermal field and 2 direct heating of country rock by stock or basalt borehole ro data and reconstructed maximum paleotemperature profiles near the elip exhibit abrupt tectonothermal unconformities between the middle and late permian the profiles in the lower subsections i e pre middle permian exhibited significantly higher gradients than those in the upper subsections distal to the basalt province high paleo geotemperatures hereafter paleotemperatures were inferred despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes in contrast ro profiles from boreholes without igneous rocks i e late permian contained no break at the unconformity paleotemperature gradients of the upper and the lower subsections and erosion at the middle late permian unconformity revealed variations in the thermal regime the inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic thermal response to the emeishan mantle plume

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

re evaluating plume induced uplift in the emeishan large igneous province numerical and fluid dynamic modelling predicts that mantle plumes should generate a broad domal uplift 1 000 km wide 500 to 1 000 m high preceding volcanism in large igneous provinces the emeishan large igneous province southwest china has been offered as the best example of plume induced uplift where kilometre scale pre and syn volcanic relief was interpreted to develop in response to the impingement of a plume head here we document voluminous mafic hydromagmatic deposits and submarine extrusions that formed during the initiation and early stages of the emeishan large igneous province these deposits were previously interpreted to be alluvial fan sediments shed from a pre volcanic domal high the abundance of such deposits consisting of variable proportions of marine limestone and basaltic fragments strongly suggests that the bulk of this province was emplaced at sea level evidence for dynamic pre volcanic uplift as predicted by plume models is lacking and such a lack may be the more general case any positive relief that developed was more likely the result of the formation of a volcanic edifice and rapid accumulation of the volcanic pile thick alluvial fan sediments from the core of the emeishan large igneous province have been considered as critical field evidence in support of plume induced pre volcanic doming and uplift these sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level precluding dynamic pre volcanic uplift as predicted by mantle plume models