factors affecting the durability of selected weak and clay bearing rocks from turkey with particular emphasis on the influence of the number of drying and wetting cycles weathering can induce a rapid change of rock material from initial rock like properties to soil like properties the resistance of a rock to short term weathering is described through a durability parameter called the slake durability index as durability is an important engineering parameter particularly for weak and clay bearing rocks it was assessed by a number of tests the main purpose of this study is to assess the influence of the number of drying and wetting cycles and controls of mineralogical composition and strength on durability for this purpose 141 samples of different types of weak and clay bearing rocks were selected from different parts of turkey and relationships between the above mentioned rock characteristics were statistically investigated the samples were subjected to multiple cycle slake durability testing x ray diffraction xrd analysis and uniaxial compression testing in addition to assess the influence of mineralogical composition on durability the mineral contents of the original material and the material passing from the drum of the slake durability apparatus after each cycle were also determined by xrd the results indicate that the type and amount of clay minerals are the main factors influencing the variations of the slake durability index in all samples the durability of the clay bearing rocks studied correlates best with the amount of expandable clay minerals a strong relationship between the uniaxial compressive strength and the fourth cycle slake durability index is found only for the marls among the rock types studied assessment of gradation results of the spoil pile materials consisting of clay bearing rocks also reveals that the increase in percentage of fines in old piles is indicative of material degradation as is evident by multiple cycle slaking it is emphasized that two cycle conventional slake durability testing did not appear to offer an acceptable indication of the durability of weak and clay bearing rocks when compared with multiple cyclic wetting and drying comments on the performance of the test are made that aim to make the testing process and interpretation of the results more reliable

the structure of reactive grain boundaries under stress containing confined fluids we present numerical experiments on structure development in grain boundaries during dissolution precipitation creep two solids that are represented by an elastic spring configuration are pressed together with a compressible fluid in the grain boundary the solid can dissolve or precipitate depending on elastic and surface energy as well as fluid pressure and concentration of dissolved material in the fluid we perform a number of numerical experiments with different starting configurations that represent a large scale island channel interface with solid solid contacts across the islands a rough grain boundary interface with a fluid along the whole interface and a smooth thin film interface the simulations suggest that the solid solid islands become unstable by necking and anti cracking so that the island channel interface will develop into a grain boundary interface the rough interface of the grain boundary will coarsen with time so that in the extreme case a smooth thin film interface will emerge however the thin film interface is also not necessarily stable but may develop into a rough grain boundary where the roughness is initiated by heterogeneous dissolution of the solid our numerical experiments suggest that interface structures during dissolution precipitation creep are transient and that the dominance of one interface structure depends on material properties the displacement rate purity of the reacting solid and the scale of observation

evolution of the western amazon lowland relief impact of andean foreland dynamics the congruency in the depositional origin and age of the uppermost sedimentary strata forming non flooded rainforest ground terra firme in the western and central amazon lowlands is a much debated subject here we conclude from the study of remote sensing imagery that active andean foreland dynamics have played a major role in the evolution of the plio pleistocene fluvial landscape in the western amazon foreland dynamics have resulted in a terra firme composed of late tertiary alluvium and younger alluvial terraces and plains in peru thermoluminescence and 14c dating show local aggradation of this younger alluvium between 180 and 30 ka the documented high age heterogeneity of the terra firme has implications for considerations of the biogeography of the amazon forest

mineralogical and isotopic record of biotic and abiotic diagenesis of the callovian oxfordian clayey formation of bure france abstract the callovian oxfordian cox clayey unit is being studied in the eastern part of the paris basin at depths between 400 and 500 m depth to assess of its suitability for nuclear waste disposal the present study combines new mineralogical and isotopic data to describe the sedimentary history of the cox unit petrologic study provided evidence of the following diagenetic mineral sequence 1 framboidal pyrite and micritic calcite 2 iron rich euhedral carbonates ankerite sideroplesite and glauconite 3 limpid calcite and dolomite and celestite infilling residual porosity in bioclasts and cracks 4 chalcedony 5 quartz calcite pyrite in bioturbations shows a wide range of 34s 38 to 34 5 providing evidence of bacterial sulphate reduction processes in changing sedimentation conditions the most negative values 38 to 22 measured in the lower part of the cox unit indicate precipitation of pyrite in a marine environment with a continuous sulphate supply the most positive pyrite 34s values 14 up to 34 5 in the upper part of the cox unit indicate pyrite precipitation in a closed system celestite 34s values reflect the last evolutionary stage of the system when bacterial activity ended however its deposition cannot be possible without sulphate supply due to carbonate bioclast dissolution the 87sr 86sr ratio of celestite 0 706872 0 707040 is consistent with deposition from jurassic marine derived waters carbon and oxygen isotopic compositions of bulk calcite and dolomite are consistent with marine carbonates siderite only present in the maximum clay zone has chemical composition and 18o consistent with a marine environment its 13c is however lower than those of marine carbonates suggesting a contribution of 13c depleted carbon from degradation of organic matter 18o values of diagenetic chalcedony range between 27 and 31 suggesting precipitation from marine derived pore waters late calcite crosscutting a vein filled with chalcedony and celestite and late euhedral quartz in a limestone from the top of the formation have lower 18o values 19 suggesting that they precipitated from meteoric fluids isotopically close to present day pore waters of the formation finally the study illustrates the transition from very active biotic diagenesis to abiotic diagenesis this transition appears to be driven by compaction of the sediment which inhibited movement of bacterial cells by reduction of porosity and pore sizes rather than a lack of inorganic carbon or sulphates

the effect of the negative pressure of capillary water on atmospheric noble gas solubility in ground water and palaeotemperature reconstruction abstract atmospheric derived noble gases he ne ar kr and xe dissolved in ground waters record the temperature at the moment of their recharge palaeotemperature reconstructions should include all the parameters affecting the soil air ground water thermodynamic equilibrium particularly the occurrence of excess air that is ang in excess compared to the equilibrium concentrations and often mass fractionated compared to the atmospheric pattern is likely produced by air entrapment during water infiltration in the nonsaturated zone nsz here we show that water persisting in the nsz has peculiar capillary properties controlled by the internal water pressure which decreases even down to negative pressures with decreasing soil air humidity decreasing water pressure induces mass dependent increasing solubility of ang from he to xe in addition in nonsaturated soils where water and air coexist air entrapment is favored allowing nonfractionated excess air this capillary approach has been coded in an inverse method program called thermo inver and tested on two well characterized noble gas datasets used to constrain palaeotemperatures in midwestern united states and brazil during the last glacial maximum quat res 43 1995 209 science 269 1995 379 results of these simulations highlight that under suitable climatic conditions and in fine porous media the capillary pressure of water may be a prominent parameter controlling the addition of ang to ground waters under these conditions the recharge zone for ang is the nzs and this water air coexistence zone easily produces excess air

spatial heterogeneities in a bioclastic shoal outcrop reservoir analogue architectural cyclical and diagenetic controls on lateral pore distribution abstract the distribution of pores in carbonate rocks is controlled by the synergy of different factors such as the initial sediment environment processes and diagenesis prediction of the texture related pore distribution to evaluate reservoir quality is still a challenging task in geothermal and hydrocarbon exploration in order to degrease these uncertainties 3d facies models are produced on the basis of facies types and their relationship to petrophysical properties however several studies have shown that these relationships are often rather controlled by diagenesis that is often described as a sequence for an entire reservoir two outcrops as part of the same bioclastic shoal reservoir analogue present two different architectural styles i layer cake architecture and ii high angle foreset architecture in order to identify petrophysical trends and related controlling factors both outcrops were mapped and studied in detail based on the investigation of 41 thin sections microfacies types were defined and diagenesis was analysed in addition permeability porosity was measured and pores were digitally characterized although both outcrop successions studied are associated with the same reservoir interval varied architecture leads to fundamental differences in the porosity permeability distribution petrophysical trends in the layer cake architecture are mainly controlled by cyclicity and channel features compared to layer cake architecture trends in the high angle foreset architecture are dominantly controlled by the depositional environment both outcrops show differences in their diagenesis while layer cake architecture suffered the entire sequence large parts of the high angle foreset architecture were not influenced by late burial and telogenetic processes as a consequence primary porosity is persevered within the high angle foreset architecture in addition results of this investigation indicate that primary porosity has a bigger influence on good permeability values compared to telogenetic associated vug enhancement this investigation therefore demonstrates that individual carbonate reservoirs can suffer different diagenetic pathways moreover the study highlights the potential of outcrop studies to improve the principal understanding of fundamental trends within potential subsurface reservoirs

water films at grain grain contacts debye huckel osmotic model of stress salinity and mineralogy dependence abstract water film diffusion is one of the mechanisms proposed to explain the deformation of rocks by pressure solution during geological processes in the upper crust this mechanism assumes that matter is dissolved inside the contact between two grains the resulting solutes are transported in the pore fluid through diffusion in an adsorbed water film the main problem of this theory is that it requires the presence of a water film that is believed to be stable under large deviatoric stresses inside the contact between two grains in this paper we show that the electrically charged surface of a mineral can attract counter ions from the pore and by the related change of osmotic pressure keep water within the contact this is due to the counter ions in the water film that increase the salinity in the film relative to that in the pore this lowers the free energy of water in the contact zone to a degree that balances the increase in free energy of water due to the elevated pressure in the film these notions are made more precise by combining the theory of the debye huckle double layer with equations of osmotic pressure the resulting d h o theory predicts the dependence of the water film thickness on stress across the contact composition of the pore fluid and the identity of the minerals involved

weathering processes and the composition of inorganic material transported through the orinoco river system venezuela and colombia abstract the composition of river borne material in the orinoco river system is related primarily to erosion regime which in turn is related to tectonic setting especially notable is the contrast between material derived from tectonically active mountain belts and that from stable cratonic regions for a particular morpho tectonic region the compositional suites of suspended sediment bed material overback deposits and dissolved phases are fairly uniform are are typically distinct from whose of other regions for each region a consistent set of chemical weathering reactions can be formulated to explain the composition of dissolved and solid loads in developing these formulations erosion on slopes and storage of solids in soils and alluvial sediments are important considerations compositionally verymature sediment is derived from areas of thick soils where erosion is transport limited and from areas where sediments are stored for extended periods of time in alluvial deposits compositionally immature sediments are derived from tectonically active mountain belts where erosion is weathering limited weathering limited erosion also is important in the elevated parts of the guayana shield within areas of sleep topography compared to the mountain belts sediments derived from elevated parts of the shield are more mature a greater degree of chemical weathering seems to be needed to erode the rock types typical of the shield the major element chemistry and mineral composition of sediment delivered by the orinoco river to the ocean are controlled by rivers that have their headwaters in mountain belts and cross the llanos a region of alluvial plains within the foreland basin the composition of sediments in rivers that drain the shield seems to be established primarily at the site of soil formation whereas for rivers that drain the mountain belts additional weathering occurs during s episodes of storage on alluvial plains as sediments are transported across the llanos to the main stem of the orinoco after mixing into the main stem there seems to be little subsequent alteration of sediment

the impact process in aeolian saltation two dimensional simulations a critical event in the trajectory of a sand grain saltating in air is its interaction with the surface we examine the phenomenon of grain bed impacts in two dimensions using a combination of dynamical computer simulations analytical models and physical reasoning the results indicate that the grain bed collisions can be treated as two body collisions with the bed particle assuming an effective mass greater than its true mass also the presence of geometrical surface irregularities has a strong bearing on the interaction between saltating and surface grain populations as well as on the formation of small scale bedforms

dunes on pluto the surface of pluto is more geologically diverse and dynamic than had been expected but the role of its tenuous atmosphere in shaping the landscape remains unclear we describe observations from the new horizons spacecraft of regularly spaced linear ridges whose morphology distribution and orientation are consistent with being transverse dunes these are located close to mountainous regions and are orthogonal to nearby wind streaks we demonstrate that the wavelength of the dunes 0 4 to 1 kilometer is best explained by the deposition of sand sized 200 to 300 micrometer particles of methane ice in moderate winds

equilibrium partial pressure of co 2 in callovian oxfordian argillite as a func tion of relative humidity experiments and modelling having previously demonstrated that the mineral assemblage of claystone can impose its pco2 under saturated conditions we here study the effect of rock desaturation i e the evaporation of pore water on the partial pressure of co2 pco2 in callovian oxfordian argillite from the paris basin france in this new study which combines experiments at room temperature and geochemical modelling we examine the primary role of capillary forces on chemical equilibria for relative humidity values ranging between 50 and 100 in particular we are able without any fitting parameters to model the experimental decrease of pco2 as a function of decreasing water content in the argillite this application to a complex natural system not only confirms the theoretical concepts of geochemistry in capillary contexts but is promising with respect to other systems both natural soil rock and industrial ceramics granular material

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

architectural complexity of a carbonate transgressive systems tract induced by basement physiography three dimensional exposure of the plio pleistocene calcarenite di gravina formation around matera horst italy permits analysis of the architecture and internal complexities of carbonate sedimentary bodies around a palaeoisland spatial organization of the different lithosomes along with their skeletal composition sedimentary structures and bedding patterns helps decipher the key factors that controlled platform architecture and distribution of heterogeneities basement physiography type and loci of carbonate production bottom currents and changes in accommodation relative sea level changes resulted from high frequency glacioeustatic cycles that punctuated an overall tectonically induced transgression topographic relief fragmentation of the limestone basement and wave energy controlled lithoclastic supply basement physiography and relative sea level changes determined the area available for carbonate producing biotas and thus the amount and type of skeletal sediments on the moderately dipping south western margin waves and associated currents re distributed the lithoclasts derived from coastal abrasion bioclasts mostly derived from epiphytic seaweed production in the shoreface infralittoral prisms resulted from downdip transport progradation and longshore transport which controlled along strike continuity of the prisms where basement continuity was interrupted at the margin of the palaeoisland a lithoclastic fan was deposited from dumping sediments carried by shore parallel currents fan shaped skeletal bodies coalesced to form an apron on the steeper northern side of the palaeoisland when a structural platform was flooded and epiphytic carbonates were shed red algae contribution depended on the available oligophotic area which in turn was controlled by high frequency sea level cycles basement physiography and apron aggradation the internal architecture of this apron resembles a low stand wedge but it accumulated during transgression deeper water contour parallel currents formed a lithosome at the foot of the structural relief interpreted as drift deposits it is composed of shallow water benthonic skeletal components planktonic foraminifera and some limeclasts

laboratory impact splash experiments to simulate asteroid surfaces abstract granular material that is bound by the low gravity of a small asteroid is mobilized by slow velocity impacts these splashes generated by impacts might play an important role in sculpting the asteroid s surface in laboratory experiments we characterize the ejecta generated by spherical 150 m diameter basalt grains impacting a granular bed at 0 8 m s we find that such an impact typically leads to less than 10 particles being ejected from the granular bed with typical ejecta trajectories rising to less than one particle diameter above the surface that is the observed impacts are highly dissipative and only a small fraction of the impact energy is imparted onto the ejecta while the impactor itself still rebounds it typically slows down significantly to an average of about 20 of its impact velocity scaled to asteroids impactor and ejecta generated from impacts of sand sized grains are not able to spread over the asteroid s surface but will stay close to the impact site therefore these highly inelastic impacts into soft granular beds efficiently trap grains in contrast to more elastic impacts on bare rocky surfaces confirming suggestions by shinbrot et al 2017 this is also in agreement to observed features on asteroids as this topological elasticity bias suggests that redistribution of grains leads to a size segregation

disobedient sediments can feedback on their transportation deposition and geomorphology abstract most sediments are obedient to the winds waves and currents which direct their transportation and deposition it has long been recognized however that the grain size and or grain kind of sediments can feedback on the processes of their own transportation deposition and geomorphology as well as that of succeeding deposits this note is to review three examples of marine sediments in which a single grain size or grain kind produces multiple feedbacks tidal bars of holocene ooid sands on great bahama bank are an example of multiple feedbacks of one grain kind on tidal currents wave action and accumulations these feedbacks are responsible for the distinctive pattern of elongated bars and channels which in turn amplify tidal currents the near constant movement of grains on the shallow bars and in the channels is where pellet nuclei are coated to form ooids thus the development and growth of bars feeds back to produce more ooids regional encrinites which consist predominantly of the disarticulated highly porous skeletons of crinoids are common from ordovician to jurassic during blooms of these filter feeders the resulting grains which are equivalent to quartz grains a tenth of their size can be entrained by currents as low as a knot ca 0 5 m s the resulting mobile substrate deters other invertebrates taphonomic feedback and results in the prevalence of layering produced by traction transport of low velocity the belt of mud extending for some 1600 km between the amazon and orinocco rivers is a special example of the feedback of mud on depositional processes sedimentary structures and geomorphology of the accumulations the clay rich mud from the amazon produces fluid mud which dampens and transforms wave action from the open sea to promote its own accumulation in giant bars in the inner shelf and shoreline with a variety of familiar laminations the result is a wedge of mud rich deposits some 24 m thick and 30 km wide capped with cheniers of sand which has prograded seaward in some 6000 years

controls on morphology and sedimentology of carbonate tidal deltas abacos bahamas abstract although the physical processes controlling siliciclastic shoal bodies are reasonably well understood the sedimentary processes that shape carbonate tidal shoal systems are poorly constrained the tidal deltas of the northwestern abaco islands bahamas provide a unique opportunity to explore the relationships between physical and sedimentary processes in a variety of sizes and shapes of tidal deltas the length of tidal deltas range in size from 350 m to 2 km from the inlet to the termination of the delta lobe and shoal crests consist primarily of well sorted ooid sands mean grain size between 400 and 500 m mcmanus sorting factor 0 70 coated grains are rare off the shoals and sorting decreases with distance from the shoal crests velocities in the rocky inlets can exceed 2 m s in the daily tidal cycles and the systematic distribution of grain types reflects tidal velocity variations areas with the highest velocities 0 80 m s correspond to hard rocky bottoms with some skeletal grains these regions of elevated velocities are focused within the inlets where jets of high velocity currents form during each tidal cycle these current jets extend outward from the inlet throat and velocities decrease outwards as the flow disperses velocities between 40 and 80 cm s occur in the regions with abundant ooids and peloids are most abundant in the lowest velocity regions the results of this study illustrate a clear relationship between quotidian physical processes and their geomorphic and sedimentologic products in a carbonate system in this context carbonates appear to share many geomorphic similarities with siliciclastic analogs the results represent an important step beyond qualitative facies interpretations and towards quantitative specified environmental and sedimentologic characterizations for carbonate systems

near at eros imaging and spectral results eros is a very elongated 34 kilometers by 11 kilometers by 11 kilometers asteroid most of the surface of which is saturated with craters smaller than 1 kilometer in diameter the largest crater is 5 5 kilometers across but there is a 10 kilometer saddle like depression with attributes of a large degraded crater surface lineations both grooves and ridges are prominent on eros some probably exploit planes of weakness produced by collisions on eros and or its parent body ejecta blocks 30 to 100 meters across are abundant but not uniformly distributed over the surface albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith on scales of 200 meters to 1 kilometer eros is more bland in terms of color variations than gaspra or ida spectra 800 to 2500 nanometers are consistent with an ordinary chondrite composition for which the measured mean density of 2 67 0 1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent

an unsaturated hydro mechanical modelling of two in situ experiments in callovo oxfordian argillite abstract the unsaturated behaviour of callovo oxfordian argillite is investigated through the modelling of 2 in situ experiments the first test studies the influence of ventilation in a gallery on the hydro mechanical behaviour of the rock mass the second test consists in a gas injection in the rock mass from an experimental borehole a hydro mechanical model is described and used in the modelling of the experiments a review of the main hydro mechanical parameters of argillite is presented the numerical results highlight the need of a flow boundary condition reproducing the fluid transfers between the surroundings and the rock mass the influence of dissolved gas on the compressibility of the liquid phase is also emphasised

form function and feedbacks in a tidally dominated ooid shoal bahamas although the general aspects of oolitic depositional systems are well documented seascape scale 10 3 10 6 m 2 patterns of oolitic shoals and the details of processes acting on them are not well understood or quantified to begin to fill this basic gap in understanding this paper describes the morphology and hydrodynamics of lily bank a modern tidally dominated bahamian ooid shoal in this study integrating remote sensing imagery with quantitative geo located bathymetrical hydrological and granulometric data in a geographic information system documents geomorphic and sedimentological patterns and facilitates interpreting these patterns in the context of the processes operating in this system the results of these analyses reveal that parabolic bars up to several kilometres in wavelength and several metres in height form a common morphologic motif although there is considerable variation on that general theme the seascape scale configuration of bars and superimposed sedimentary structures is closely linked to spatial patterns of tidal movements and includes the presence of mutually evasive flood and ebb channels sedimentologically bars are neither homogenous nor random bodies instead granulometric parameters such as sorting and percentage mud vary systematically as shaped by hydro geomorphic controls the best sorted coarsest ooids are on bar crests whereas the finest grains are found in the lower energy deeper interior and flanking regions in short results clearly document hydrodynamic bathymetrical influences on these ooid shoals and their granulometry linkages akin to siliciclastic analogues sedimentological hydrodynamic and geomorphic observations are consistent with a conceptual model for the formation of parabolic bars in which initial irregularities in nonparabolic bars are enhanced through their effect of focusing flow constricted flow leads to higher flow velocities tidal flow velocity asymmetries differential net sediment transport and growth of bathymetrical highs this bathymetrical divergence creates separate paths for flood and ebb tides facilitating emergence of better developed parabolic forms the resultant parabolic geometries and component bedforms appear to be either in dynamic equilibrium with both ebb and flood tide flows or evolving toward that state in exploring patterns and processes within carbonate shoals this study illustrates some of the first documented insights on quantitative details of morphology and dynamics and in the links between geomorphic framework and grain size and sorting in an oolitic carbonate system assuming a

a late atokan regional encrinite early late moscovian middle pennsylvanian in the sierra agua verde sonora state nw mexico

quantitative study of geochemical processes in the dogger aquifer paris basin france the quantification of geochemical reactions in hydrothermal aquifers requires an exhaustive approach because of their interdependence all chemical elements likely to have a quantitative influence on dissolution or precipitation reactions have to be taken into account geochemical constraints the number of which equals the number of the chemical elements were determined with the help of chemical analyses of the solution in the case study of the dogger aquifer paris basin france 12 elements are taken into account al c cl ca f h k mg na o s si three constraints apply to water activity neutrality and conservation of chloride in aqueous solutions the determination of the remaining constraints was based on saturation indices stability diagrams of minerals and partial pressure of carbon dioxide pco2 the present day solutions are at equilibrium with respect to nine minerals albite anhydrite chalcedony calcite dolomite fluorite kaolinite k feldspar and illite or chlorite thus it was demonstrated that the composition of these solutions including computed pco2 is only a function of temperature and chloride content moreover it was possible to test the validity of the geochemical system by computing its speciation and comparing these theoretical results with actual chemical analyses ph and concentrations finally geochemical simulations were used in predicting what quantities would be dissolved or precipitated as either the temperature or the chlorinity varied although the rock is predominantly calcareous these quantities could not be determined if the influence of the aluminosilicates were neglected this chemical component approach with which one can pose and solve rigorously the chemical equilibrium problem constitutes a prerequisite for the quantitative study of geochemical processes related to fluid flow

stable isotope composition of co2 outgassed from cores of argillites a simple method to constrain δ18o of porewater and δ13c of dissolved carbon in mudrocks abstract stable isotope characterization of porewater and dissolved species in mudrocks and argillaceous rocks is notoriously difficult techniques based on physical or chemical extraction of porewater can generate significant analytical artefacts the authors report a novel simple approach to determine the 18o of porewater and 13c of dissolved c in argillites the method uses core samples placed in specifically designed outgassing cells sealed shortly after drilling and stored in well controlled conditions after 1 2 months co2 naturally outgassed by argillite porewater is collected purified and analyzed for c and o isotopes porewater 18o and dissolved c 13c are calculated from co2 isotope data using appropriate fractionation factors this methodology was successfully applied to the callovo oxfordian argillites from bure eastern paris basin france and the opalinus clay formation from mont terri switzerland in both clay formations results indicate that porewater is meteoric and dissolved c is of marine origin the main advantage of the approach is that it does not induce any major physical or chemical disturbance to the clay water system investigated further testing on argillaceous rocks of variable composition and organic content is needed to assess extent of applicability

facies model on the modern isolated carbonate platform in the xisha archipelago south china sea abstract the xuande atoll with a discontinuous reef rim caused by platform drowning is a typical ellipse isolated platform on the northern slope of the south china sea based on the data of drilling holes the analysis of surface sediments and high resolution acoustic data six sedimentary facies are identified in the xuande atoll including reef outer slope reef front reef flat aeolianite sand island back reef slope and lagoon facies map shows that the elevated reef rimmed margins with islands are more noticeable on the windward of the platform with an elevated and discontinuous reef rimmed margin as well as coarse grained sediment in the interior platform xuande can serve as a case of a leaky bucket atoll which is characterized by initially drowning scenarios the facies architecture of the xuande atoll is evidently influenced by complex and interacting parameters including antecedent topography sea level wind driven currents water depth and tectonic subsidence different controlling factors exist in the drowning of the windward and leeward sides of the platform margin the study of modern depositional settings in the xuande atoll will provide insight on predictions for ancient carbonate provinces

decoding the mechanism of formation in marine ooids a review abstract ooid shoals sedimentary structures consisting of carbonate grains are often used as proxies to explore changes in seawater chemistry over earth history despite their importance as contributors to the global carbonate budget and as paleo environmental indicators for water depth ph temperature and water energy the mechanism of formation of these concentric sub spherical concretions of tangentially or radially arranged aragonite or calcite crystals is still the subject of intense debate unlike oncoids whose microbial origins are well acknowledged ooids are traditionally viewed as abiotic grains mainly produced in suspension by agitated warm waters that are supersaturated with respect to caco3 yet there is considerable evidence including geochemical bio signatures and detection of viable microbes capable of mineralization and biofilm production and degradation to suggest otherwise the emergence of new and sophisticated technologies reveals that the level of microbial diversity of these sedimentary grains exceeds that of some microbialite systems these findings have refined our understanding of ooid genesis and ooid accretion processes and argue toward microbial mediation both as a direct result of metabolic activities inducing changes in the environment conducive to precipitation and by a passive mechanism in which mucilaginous extracellular polymeric substances eps act as a template for mineral nucleation furthermore new developments in the field indicate that carbonate mineralization in marine ooids occurs through sequential precipitations that involve an amorphous calcium carbonate phase acc which some argue are of biotic origins herein we discuss the most relevant theories of ooid formation including some of the early pioneering studies that laid the groundwork for new theories attempting to decode the origins of these controversial grains

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

the mont terri rock laboratory a new international research project in a mesozoic shale formation in switzerland abstract in many countries argillaceous formations are being considered as potential host rocks for repositories of radioactive waste therefore in 1995 several organisations decided to start an international research project in the reconnaissance gallery of the mont terri motorway tunnel in north western switzerland in a mesozoic shale formation the opalinus clay aalenian this project is under the patronage of the swiss national hydrological and geological survey the following organisations are also partners in the project andra and ipsn france bgr germany enresa spain nagra switzerland jnc and obayashi japan sckcen belgium the aims of the project are to analyse the hydrogeological geochemical and rock mechanical properties of an argillaceous formation the changes of these properties induced by the excavation of galleries and to evaluate and improve appropriate investigation techniques in january 1996 eight niches were excavated for the project and 15 experiments were started in boreholes of no more than 30 m in length in the winter of 1997 1998 a new research gallery was excavated to host further experiments different excavation drilling and investigation techniques have been tested and improved significant results of the different experiments are already available some of those dealing with hydrochemistry porewater pressure measurements and the evolution of the excavation disturbed zone edz are reported in this paper

holocene floodplain lake sediments in the amazon 14c dating and palaeoecological use abstract the holocene biostratigraphic record of amazon lowland rain forests is fragmentary and is based on restricted number of cores the majority representing sedimentation in a floodplain environment these biostratigraphic data have often been interpreted as demonstrating climatic oscillation between wetter and drier conditions and the subsequent vegetation changes here we survey and 14c date a further six western amazon floodplain lakes and examine their fluvially controlled sedimentation processes the lakes which are of the cutoff type are located along the rivers manu tambopata and amazon solimoes in the peruvian amazon lowlands all the lakes cored are under the influence of current overbank sedimentation of the parent suspension rich whitewater rivers and receive an annual fill of allochthonous inorganic suspension during the flood most of the cores collected were rich in minerogenic sediments gyttja clay loss on ignition we think that the observed bias towards older 14c ages documented in the gyttja clays is caused by the high proportion of old fine particulate organic matter being recirculated and resedimented within the suspension load the strong fluvial control of lake sedimentation and the unreliability of the 14c dates from the amazon suspension rich floodplains call for caution in palaeoecological interpretation furthermore owing to the low number of within lake replicate cores in the amazon holocene stratigraphy analyses we consider the postulated holocene climatic oscillation schemes to be tentative only

marine carbonate systems in the sarmatian middle miocene of the central paratethys the zsambek basin of hungary the study of eight stratigraphic sections at the margin of the semi enclosed zsa mbe k basin hungary allows the sedimentary anatomy of oolitic bioclastic systems in the sarmatian of the central paratethys to be reconstructed the mollusc foraminiferal and ostracod associations indicate that the carbonate systems are latest badenian to late sarmatian in age the lower upper sarmatian deposits are organized in superimposed subaqueous dunes prograding towards the basin on a low angle ramp during the late sarmatian the ramp underwent subaerial erosion linked to a moderate relative fall in sea level lagoonal deposits were later formed and microbial nubeculariid bryozoan serpulid buildups were emplaced the abnormal marine conditions of the sarmatian conducive to the development of a poorly diversified flora and fauna and dominant non skeletal grains are linked to fluctuating salinities mesotrophic to eutrophic conditions and perhaps high alkalinity

in situ interaction of cement paste and shotcrete with claystones in a deep disposal context in situ sampling was performed in the andra meuse haute marne france underground research laboratory url allowing the study of two cement based materials claystone interfaces that have undergone 4 to 5 years of interaction the first interface concerned a shotcrete that was sprayed on the wall of an access drift at the laboratory level and the second one a class g cement paste that was injected in a borehole filled from the surface and was intercepted during the excavation of a new gallery in the first case the hydrodynamic conditions were controlled by the ventilation of the drift while in the second the cement paste and claystone materials were considered saturated and far from any mechanical perturbation a multi scale investigation was carried out to identify any evidence of alkaline perturbation in the cement based materials and the claystone chemical mineralogical and textural measurements were thus performed on the different materials in contact at the nanometer to a centimeter scale results showed that all the perturbations resulting from the geochemical contrast between the cement materials and the claystone were limited to a m scale on each side of the interfaces carbonation was observed in the cement materials leading to an opening or a clogging of the porosity according to the hydrodynamic conditions and the formulation of the cement material the distribution of the cation exchange population was also modified in the claystone in contact with the cement paste where a potassium saturation of the exchangeable fraction was identified the originality of the present work is that realistic field controlled samples from the andra url were studied hereby allowing the evaluation of the impact of natural heterogeneities of the in situ experimental conditions that is hydrodynamic conditions engineered damage zone mineralogical variations on the perturbations at the cement paste claystone interfaces an important result is that the clogging of porosity was not homogenous along the interfaces

cation exchanged fe ii and sr compared to other divalent cations ca mg in the bure callovian oxfordian formation implications for porewater composition modelling abstract iron and sr bearing phases were thoroughly investigated by means of spectrometric and microscopic techniques in callovian oxfordian cox samples originating from the andra underground research laboratory url in bure france strontium was found to be essentially associated with celestite whereas fe was found to be distributed over a wide range of mineral phases iron was mainly present as fe ii in the studied samples 93 from mossbauer results most of the fe ii was found to be in pyrite sideroplesite ankerite and clay minerals iron iii if present was associated with clay minerals probably illite illite smectite mixed layer minerals and chlorite no fe iii oxy hydro xide could be detected in the samples strontianite was not observed either based on these observations it is likely that the cox porewater is in equilibrium with the following carbonate minerals calcite dolomite and ankerite sideroplesite but not with strontianite it is shown that this equilibrium information can be combined with clay cation exchange composition information in order to give direct estimates or constraints on the solubility products of the carbonate minerals dolomite siderite and strontianite as a consequence an experimental method was developed to retrieve the cation exchanged fe ii in very well preserved cox samples the very homogeneous cation exchange composition of the formation is completely in agreement with a homogeneous presence of calcite and dolomite minerals whose equilibrium reactions control part of the porewater composition amongst the broad range of values available for dolomite solubility products in thermodynamic databases the value of log kdolomite 3 57 is the most appropriate for the one present in the cox formation with regard to strontianite it appears that the equilibrium constant tabulated in the llnl database is not valid for natural clay systems the value given by busenberg et al used by most of the other available thermodynamic databases seems to be far more appropriate concerning fe ii and siderite ankerite equilibrium the measured fe ca ratio on the clay exchanger 0 01 could only be considered as a maximum value due to possible experimental bias leading to the following constraint for the solubility of the sideroplesite phase present in the cox fe0 7mg0 2ca0 1co3 h 0 7 fe2 0 2 mg2 0 1 ca2 hco 3 logksid cox this constraint is in agreement with the estimated solubility of this phase based on a solid solution model log ksid cox 0 23

desaturation and structure relationships around drifts excavated in the well compacted tournemire s argillite aveyron france this study aimed to explore the relationships between the extension of rock desaturation and the excavation damaged zone edz subsequent to the excavation of a century old tunnel and of recent drifts 1996 and 2003 at the tournemire underground research laboratory url located in the aveyron county south of the massif central france the other objective of this work was to assess the impact of desaturation on the hydraulic head profile measured around the tunnel one section was selected per drift two boreholes were drilled for each section one parallel and one inclined 45 with respect to the bedding for each borehole we performed on site drill core mapping petrophysical measurements pneumatic and hydraulic tests by means of a modular mini packer system mmps results indicate that the edz around drifts is mainly a combination of unloading joints mimicking the drift shape and of desaturation cracks parallel to the bedding the edz extension around the tunnel is twice to three times that of the drifts of 1996 and 2003 and is essentially composed of unloading joints resulting from the mechanical response of the rock the masonery covering the tunnel walls is assumed to have protected the rock from seasonal variations of air humidity thus limiting without excluding the formation of desaturation cracks the edz extension deduced from core mapping is in agreement with that deduced from pneumatic tests with permeabilities several orders of magnitude greater than in the undisturbed zone degrees of saturation for the three sections range between 0 9 and 1 in the edz area and reach 1 in the undamaged zone the head profile deduced from measurements recorded since 2002 indicates the occurrence of an excavation disturbed zone edz of about 40 m around the tunnel this edz is likely due to the existence of sub atmospheric water pressures clearly seen in the first meter around the tunnel we have tried to quantify the impact of the tunnel since its excavation on saturation degree and on hydraulic heads the simulation was performed by considering as a first approach the absence of fracturing in the edz a constant suction of 3300 m deduced from the mean annual values of relative humidity and temperature measured in the tunnel atmosphere since 2002 was applied at the tunnel wall the degrees of saturation simulated around the tunnel are underestimated in the edz area and consistent to experimental data in the unfractured zone the modelling of hydraulic heads is overestimated in the horizontal direction and is in the domain of experimental values in the vertical direction but the lack of intermediate data cannot enable us to conclude on this consistency this study demonstrated the role played by fracturing on the distribution of petrophysical parameters and of heads around drifts and the century old tunnel it has also demonstrated the necessity of coupling mechanic and hydraulic calculations by considering capillary forces

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

chemical and isotopic characterization of hydrocarbon gas traces in porewater of very low permeability rocks the example of the callovo oxfordian argillites of the eastern part of the paris basin abstract a methodology has been developed to determine chemical and carbon isotopic compositions of trace amounts of hydrocarbon gas compounds methane ethane propane iso and normal butane present as dissolved compounds in the porewater of the low permeability callovo oxfordian argillites in eastern paris basin france results indicate that the studied hydrocarbons contain significant amounts of ethane butane and propane in addition to methane carbon isotopic compositions reflect primarily thermogenic origin thermal cracking of organic matter and lack of any significant biodegradation because temperature did not exceed 50 c in the studied argillites investigated hydrocarbons must have originated in hotter deeper organic bearing formations possibly stephanian coals data supports the predominance of high maturity thermogenic gas in the upper part of the callovo oxfordian and low maturity thermogenic gas mixed with minor bacterially produced methane in the lower part of the formation a mixing between three end member gases models quite well the data one thermogenic gas with a low maturity 42 methane with a 13 c of 53 a gas with higher maturity 55 methane with a 13 c of 47 and a bacterial gas 99 45 methane with a 13 c of 80 this study illustrates that migration of hydrocarbon gases can take place in rocks with very low permeability and porosity such as compacted mudrocks given enough time it further suggests that the studied fluid migration and transfer in aquitards would help characterization and understanding of fluid movements in sedimentary basins as a complement to studies focused on water aquifers and hydrocarbon reservoirs chemical and isotopic composition of dissolved hydrocarbons in porewater can be used as natural tracers of fluid circulation in sedimentary basins in addition to more conventional tracers

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

biogeochemical processes in a clay formation in situ experiment part e equilibrium controls on chemistry of pore water from the opalinus clay mont terri underground research laboratory switzerland the chemistry of pore water particularly ph and ionic strength is an important property of clay rocks being considered as host rocks for long term storage of radioactive waste pore waters in clay rich rocks generally cannot be sampled directly instead their chemistry must be found using laboratory measured properties of core samples and geochemical modelling many such measurements have been made on samples from the opalinus clay from the mont terri underground research laboratory url several boreholes in that url yielded water samples against which pore water models have been calibrated following a first synthesis report published in 2003 this paper presents the evolution of the modelling approaches developed within mont terri url scientific programs through the last decade 1997 2009 models are compared to the composition of waters sampled during dedicated borehole experiments reanalysis of the models parameters and database enabled the principal shortcomings of the previous modelling efforts to be overcome the inability to model the k concentrations correctly with the measured cation exchange properties was found to be due to the use of an inappropriate selectivity coefficient for na k exchange the inability to reproduce the measured carbonate chemistry and ph of the pore waters using mineral water reactions alone was corrected by considering clay mineral equilibria re examination of the measured ca mg activity ratios and consideration of the mineralogical composition of the opalinus clay suggested that ca mg cation exchange rather than dolomite saturation may control the ratio of these ions in solution this re examination also suggests that the ca mg ratio decreases with increasing pore water salinity several possible reasons for this are proposed moreover it is demonstrated that feldspar equilibria must not be included in opalinus clay modelling because feldspars are present only in very small quantities in the formation and because na k ratios measured in pore water samples are inconsistent with feldspar saturation the principal need to improve future modelling is additional or better data on rock properties in particular i a more detailed identification of phases in the opalinus clay that include redox sensitive elements together with evaluation of their thermodynamic properties ii an improved understanding of the distribution of celestite throughout the opalinus clay for sr so4 concentrations control iii improvements in analytic and thermodynamic data for ca mg rock cation exchange and mineral chemical properties and iv the measurement of composition and stability constants of clay minerals actually present in the formation

the amazon influenced muddy coast of south america a review of mud bank shoreline interactions the 1500 km long coast of south america between the amazon and the orinoco river mouths is the world s muddiest this is due to the huge suspended sediment discharge of the amazon river 106 754 tons yr 1 9 part of which is transported alongshore as mud banks mud bank formation is controlled by the physical oceanography of the continental shelf seaward of the amazon river mouth an initial seafloor storage area for much of the suspended sediment discharged from the river in this area rapid and sustained fluid mud concentration and trapping are associated with fresh water salt water interaction and estuarine front activity on the shelf due to the enormous amazon water discharge ca 173 000 m3 s 1 at obidos 900 km upstream of the mouth fluid mud is transported shoreward and then along the coasts of the guianas by a complex interaction of wave and tidal forcing and wind generated coastal currents the mud banks which may number up to 15 or more at any time are up to 5 m thick 10 to 60 km long and 20 to 30 km wide and each may contain the equivalent mass of the annual mud supply of the amazon as the banks migrate alongshore their interaction with waves results in complex and markedly fluctuating shorelines that are associated with space and time varying depositional bank phases and erosional inter bank phases bank zones are protected from wave attack as a result of wave energy dampening by mud and undergo significant albeit temporary coastal accretion accompanied by rapid mangrove colonization the dampening of waves in bank areas as they propagate onshore is accompanied by the shoreward recycling of mud commonly in the form of individual mud bars these bars progressively undergo desiccation and consolidation and thus constitute a major pathway for rapid and massive colonization by mangroves erosion by waves propagating across relatively mud deficient shoreface zones in inter bank areas can lead to muddy shoreline retreat rates of tens of metres to several kilometres over a few months to a few years accompanied by massive removal of mangroves notwithstanding the higher incident wave energy on inter bank shores inter bank shorefaces are permanently muddy due to the pervasive influence of the amazon muddy discharge inter bank and transitional bank to inter bank phases are associated with both periodic sandy chenier formation and extreme forms of rotation of rare headland bound sandy beaches the high mud supply from the amazon has been the overarching geological control on the quaternary evolution of the northeastern south american coast having led to the growth of a muddy shelf clinoform at the mouth of the amazon and more or less important progradation throughout this coast net progradation reflects an imbalance in favour of deposition during each mud bank inter bank cycle the high mud supply has presumably blanketed shelf sand deposited by smaller rivers during eustatic lowstand phases the shelf clinoform structure at the mouth of the amazon and the muddy coastal progradation throughout the coast of the guianas and into venezuela provide analogues of the geological record on muddy shorefaces

geomorphology of the gran sabana guayana shield southeastern venezuela abstract the forms of the gran sabana have been developed mainly on rocks of the gently folded precambrian roraima group a sequence of quartzites and siliceous conglomerates with intercalated jasper chert arkose siltstone and shale locally intruded by diabase dikes and sills two planation surfaces are preserved on the gran sabana the auyan tepui 2000 2900 m elevation and the wonken 900 1200 m surfaces with a speculative mesozoic initial age they are still extending table mountains dominate the landscape they comprise pediments foothills precipitous scarps hundreds of meters high a rim and a flattish summit the table mountain topography is controlled by joint systems water percolates along joints and bedding planes dissolves the siliceous cement the quartzite disaggregates and large blocks are isolated and collapse accumulating at the foot of the scarps and on top of the table mountain summits the percolating water forms large and intricate cave systems which frequently emerge in the scarp zone as high waterfalls these mark the lowest level of erosion of the table mountains karstic structures are prominent in the summit zone the evolution of the table mountain topography has been controlled by a combination of tectonic structural stratigraphic climatic and temporal factors

influence of reaction kinetics and mesh refinement on the numerical modelling of concrete clay interactions large quantities of cements and concretes need to be incorporated in geological disposal facilities for long lived radwaste an alkaline plume diffusing from an aged concrete ph 12 5 through argillite type rocks has been modelled considering feedback of porosity value variations on transport properties using the reactive transport code toughreact the mineralogical composition of the argillite is modified at the interface with the concrete diffusion of cementitious elements leads to rapid and strong porosity occlusion in the argillite numerical results show that both reaction rates and spatial refinement affect mineralogical transformation pathways the variations in porosity and the extension of the zone affected by the alkaline perturbation are compared at different times the major effects of mineral precipitation under kinetic constraints rather than local equilibrium are a delay in the porosity clogging and an increase in the extension of the alkaline perturbation in the clay formation the same time delay rise for the porosity occlusion also appears for the roughest spatial resolutions a simulation as representative as possible of temporal and spatial scales of cementation processes must then be supported by more comparative data such as long term experimental investigations or natural analogues

suspended sediments of the modern amazon and orinoco rivers abstract the amazon and orinoco rivers are massive transcontinental conveyance systems for suspended sediment they derive about 90 of their sediment from the andes that support their western headwaters transport it for thousands of kilometers across the breadth of the continent and deposit it in the coastal zones of the atlantic at their points of maximum suspended sediment discharge the amazon transports an average of 1100 1300 10 6 tons per year and the orinoco transports about 150 10 6 tons per year relations of sediment discharge to water discharge are complicated by unusual patterns of seasonal storage and remobilization increased storage and reduced transport of sediment in the middle orinoco during periods of peak water discharge and storage of suspended sediment in the lower amazon during rising discharge and resuspension during falling discharge spatial distributions of suspended sediment in cross sections of both rivers are typically heterogeneous not only in the vertical sense but also in the lateral the cross channel mixing of tributary inputs into the mainstem waters is a slow process that requires several hundred kilometers of downriver transport to complete considerable fine grained sediment is exchanged between rivers and floodplains by the combination of overbank deposition and bank erosion

asymmetry in holocene river deltas patterns controls and stratigraphic effects abstract understanding controls on sediment distribution in river deltas is paramount to predicting facies relationships and stratal architecture most classifications of deltas have focused on subaerial plan morphology as a simplistic function of river tide and wave energy new work however is revealing the importance of subaqueous deposits and in particular shore parallel sediment redistribution in the shaping of delta planform delta asymmetry has emerged as an important characteristic reflective of patterns of alongshore sediment dispersal asymmetry has been described from onshore and offshore environments from several different types of modern deltas but aspects of asymmetry have not been fully documented and the degree to which these patterns are recorded in deltaic strata is not yet known this study is a comprehensive literature review of sediment distributions in modern deltas focusing on studies with high resolution geomorphic geophysical and geochronological datasets we reviewed 27 deltas using over 100 papers primarily from the past 15 20 years morphological facies and stratigraphic aspects were analyzed across the entire spectrum of deposits from the delta apex to the most distal muds of the prodelta we define quantifiable indices of asymmetry describing upcurrent vs downcurrent distribution of sediment volume sediment area sediment caliber and distributary channels most deltas are asymmetrical to some degree with respect to one or more of these parameters many deltas are increasingly skewed toward the downcurrent side from proximal to distal sub environments i e delta plain delta front prodelta some deltas are skewed toward the upcurrent side in one sub environment and toward the downcurrent side in another sub environment sand is preferentially deposited on the downcurrent side of most deltas but distributary channels tend to develop toward the upcurrent side the highest sand mud ratios are often on the upcurrent side in the lower delta plain but in the delta front these ratios are highest on the downcurrent side these complex patterns of asymmetry reflect different combinations of controls including discharge partitioning lobe abandonment and localized transgression plume deflection by coastal currents dominance of longshore current direction variable subsidence and other factors these processes may result in upcurrent downcurrent variations in clinoform geometry rates of progradation and stratal lapping relationships asymmetry has multiple aspects manifestations and controls even within a single delta but the long term preservation potential of these patterns likely varies depending on depositional setting and shoreline trajectory studies of ancient deltas will be better informed by recognizing the wide variety of controls on sediment distribution and avoiding the tendency toward a single model of delta asymmetry

a two species model of aeolian sand transport the transport of sand by wind results from the equilibrium between the erosion of grains dragged by the flow and the resulting slow down of the wind velocity the dynamical mechanisms governing the saturation of the sand flux are investigated theoretically we first demonstrate that previous models based on the assumption that all the grains have the same trajectory are either not self consistent or lead to unstable solutions a model based on a discrete number of states is derived which solves these problems two well defined species of grain appear which correspond to saltons high energy grains and reptons grains ejected from the sand bed by the impact of saltons they play specific roles the negative feedback of the transport on the wind is limited to the reptation layer while most of the transport is due to saltation the model is further simplified benefiting from the existence of these two species and the dependencies of the threshold velocity the saturated flux the aerodynamic roughness and the saturation length are derived and compared to experimental measurements

a mid tournaisian late visean carbonate ramp reconstructed from nappes and olistolites in the southern montagne noire france abstract the mainly calcareous succession from the mid tournaisian to the lower part of the upper visean in the southern montagne noire mont peyroux nappes and cabrieres slices is sedimentologically revised from the late visean the variscan orogeny affected the area and the studied mississippian part of the succession was considered as part together with the devonian of a period of tectonic quiescence later included as nappes and olistolites in a wildflysch this study presents the facies from pelagic limestones calciturbidites bioclastic limestones and microbial limestones and the relationship between platform and calciturbidites in the pre orogenic context of the montagne noire basin during the mississippian the differences in the lithostratigraphy is analyzed by means of four tectonostratigraphical units mont peyroux nappe roquessels band cabrieres area and la serre band previously defined by other authors that together with the deep water vieussan caragnas unit not studied here due to the poverty in chronostratigraphical data allow reconstructing the original carbonate platform the latter seems to correspond to a ramp for the latest tournaisian to early visean and a distally steppened ramp from the middle visean to the early late visean including basin plain to slope as the deepest water environments and middle ramp as the shallowest except for the uppermost part of the succession where the inner ramp is recognized during this period the shallowing tendency in the tectonostratigraphic units is well marked mont peyroux nappe roquessels band cabrieres area la serre band from deeper to shallower which differs from the shallowing trend defined by previous authors during the devonian strong similarities are observed with the preserved mississippian carbonates in the mouthoumet massif to the south which might represent the shallowest water deposits of the ramp not preversed in the cabrieres la serre areas

alteration of the callovo oxfordian clay from meuse haute marne underground laboratory france by alkaline solution ii modelling of mineral reactions abstract one of the french options for the final disposal of high level radioactive waste is a deep geological repository the callovo oxfordian formation in the meuse and haute marne france was proposed by the french agency for the management of radioactive wastes andra to be the site of a research laboratory in order to evaluate in situ the interaction between the host formation and the engineered barriers in the previous experimental part secondary minerals such as zeolites tobermorite and katoite have been observed after the alteration of the callovo oxfordian clay under alkaline conditions three different reactions of phyllosilicates alteration have been proposed as a function of both ph and chemical composition of the reacting solutions the aim of this work was to simulate the reaction between the callovo oxfordian clay and high ph solutions in order to validate the proposed alteration reactions from experimental data the thermodynamic modelling of stability relationships among minerals in the callovo oxfordian clay was performed using the solution speciation solubility modelling code kindis at 120 c for different chemical media naoh koh and ca oh 2 input data were the mineralogical composition of the

grain scale simulations of loose sedimentary beds the example of grain bed impacts in aeolian saltation sediment transport by wind is one of many processes of interest to the geomorphologist in which grain to grain contacts play an important role in order to illustrate the modelling of collections of frictional inelastic sedimentary grains with the particle dynamics method pdm we use the grain impact process in aeolian saltation as a specific example in pdm all the forces on each particle are evaluated at a sequence of small time steps and the newtonian equations of motion are integrated forward in time interparticle forces at grain contacts are treated as springs with prescribed stiffness normal force and by a coulomb friction law tangential force particle inelasticity is represented by spring damping the granular splash resulting from saltation impacts is assessed for sensitivity to the choice of grain properties and the integration time step we find that for the range of impact speeds and impactor masses relevant to aeolian settings grain splashes are relatively insensitive to grain stiffness grain inelasticity and grain friction and that the pattern of ejection from the bed is largely controlled by bed microtopography a large set of impact realizations involving a variety of impact points on a small set of target beds is used to collect the appropriate statistics for describing the stochastic splash process the splash function representing these statistics is then available for use in calculations over longer time scales such as the evolution of the saltation curtain the details given here will enable the interested reader to adapt pdm modelling to other types of clastic sedimentary systems

the global surface roughness of 25143 itokawa abstract surface roughness is an important metric in understanding how the geologic history of an asteroid affects its small scale topography and it provides an additional means to quantitatively compare one asteroid with another in this study we report the first detailed global surface roughness maps of 25143 itokawa at horizontal scales from 8 32 m comparison of the spatial distribution of the surface roughness of itokawa with 433 eros the other asteroid for which this kind of analysis has been possible indicates that the two asteroids are dominated by different geologic processes on itokawa the surface roughness reflects the results of down slope activity that moves fine grained material into geopotential lows and leaves large blocks in geopotential highs on 433 eros the surface roughness is controlled by geologically recent large impact craters in addition large longitudinal spatial variations of surface roughness could impact the role of yorp on itokawa