probability of transportation of loose particles in suffusion assessment by self filtration criteria suffusion occurs when soil particles are loosened detached and transported away by seepage flow through a series of pores and pore constrictions while traditional suffusion assessment methods are often based on particle size distribution analysis only modern assessment methods are focused on constriction size distributions which are derived from particle size distributions based on certain assumptions this paper provides a new assessment method which employs the probability of loose particles being transported to the next pore the new approach can introduce the influence of an overlapping zone between the two fractions of loose particles and soil primary fabric this overlapping zone was often overlooked in prior studies the constriction size distribution of the primary fabric can be calculated approximately by two dimensional or three dimensional methods the three dimensional method used in the presented study even offers the opportunity to study the influence of particle arrangements on suffusion the results of the new assessment methods show satisfactory agreement with experimental results

a theoretical envelope for internal instability of cohesionless soil the nature of seepage induced internal stability is characterised with reference both to effective stress in the finer fraction of the grain size distribution curve and also to hydraulic gradient within the soil the concept of a hydromechanical envelope is proposed in stress gradient space the onset of instability is triggered by a critical value of hydraulic gradient that is found consistent with the observations of terzaghi on piping in uniform sand and the observations of skempton and brogan on segregation piping in widely graded sandy gravels the envelope takes the form of a linear relation that for a particular soil is governed by the proportion of effective stress in the finer fraction of soil grains

effects of hydraulic loading history on suffusion susceptibility of cohesionless soils abstractsuffusion is a selective erosion of fine particles under the effect of seepage flow within the matrix of coarser particles this complex phenomenon appears as a combination of three process

influence of initial fines content on fabric of soils subjected to internal erosion seepage induced internal erosion often happens in earth structures this paper presents experimental investigations on the influence of initial fines content on fabric of soils subjected to interna

experimental investigation of initiation of backward erosion piping in soils experiments were conducted on field and laboratory mixed soils in a new true triaxial test apparatus to assess factors that influence initiation of piping in non cohesive and cohesive soils three modes of piping behaviour were recognised concentrated leak erosion backward erosion and suffusion the amount and type of the fines present in the soils significantly influenced the initiation and mode of piping the presence of non plastic fines significantly reduced the required seepage velocity to initiate piping critical seepage velocity whereas the presence of plastic fines greatly increased the hydraulic gradient required to initiate piping concentrated leak erosion occurred along the soil apparatus interface in soils with plastic fines at very low seepage velocity but required very high hydraulic gradients backward erosion was the primary mode of failure in non cohesive soils and this mode required a seepage velocity of 0 8 1 1 cm s to initiate piping in uniform sand the critical seepage veloc

experiments on piping in sandy gravels tests on internally unstable sandy gravels show that a significant proportion of the sand content is washed out by piping at hydraulic gradients far lower than the critical gradient given by a classical theory the probable explanation is that a major part of the overburden load is carried on a framework of gravel particles leaving the sand under relatively small pressures by contrast piping of the sand from stable sandy gravels occurs at approximately the full theoretical gradient the tests broadly confirm kenney s criterion for the internal stability of granular materials des essais realises sur des graves sableuses a instabilite interne importante montrent qu une proportion non negligeable du sable est lessivee pour des gradients hydrauliques bien inferieurs au gradient critique donne par les theories classiques l explication la plus probable est que la majeure partie de la surcharge des couches subjacentes est transmise au reseau des particules graveleuses le sable n etant alors plus soumis qu

effect of seepage on shallow landslides in consideration of changes in topography case study including an experimental sandy slope with artificial rainfall abstract many studies on shallow landslides have focused on seepage mechanisms however most of these studies assumed that the hillslope was parallel to the seepage direction and force they did not consider how the seepage was changed by the topography during failure to investigate the seepage mechanism particularly the influence of the topographic change during failure flume experiments using a 30 sandy slope were performed with artificial rainfall the factor of safety fs equation which considers the seepage direction and force and the numerical simulation were also applied to analyze the effect of topographic change on the seepage mechanism the experiments were divided into two stages rainfall induced experiment rie and seepage induced experiment sie with rainfall in the rie with a rainfall intensity of 80 mm h seepage erosion occurred followed by undercutting which resulted from seepage erosion to upward direction of sandy slope the analysis of fs in rie are showing an instability when seepage direction is be a slope parallel with theoretical value i hydraulic gradient in the numerical model when topographic changes of the surface of the sandy flume were applied seepage flow concentrated from failure surface of the toe of flume to middle part of flume which is affected by saturation in sie multiple failures caused by the seepage in the vertically upward direction occurred with a high seepage force and the failure mass then moved in the downward direction with the seepage flow fs for sie showed a high instability than those of rie when seepage direction with high force already changed from vertically downward seepage flow to increasing slope parallel seepage flow applying changed topography more deep from sandy flume surface in numerical model is showing concentrated seepage flow at the bottom of failures this is one of mechanism developing failure mass to downward direction to the toe of flume because soil moisture sensors installed near failures 25 cm depth show high value than porosity value indicating soil mobilization therefore the seepage direction and force play important roles in landslide mechanism and these factors should be considered in landslide studies

laboratory modeling of the mechanisms of piping erosion initiation a laboratory modeling program has been conducted to assess the mechanics of initiating the piping erosion process in sandy soils the models were performed on several soils differing in gradation grain size grain shape and specific gravity observations and monitoring of pore pressures within the samples during the modeling identified four stages in the development of piping initiation initial movement progressive heave boil formation and total heave by linking the observed behavior with the measured pore pressure regime in the sample a model for the mechanics of piping development has been developed finite element seepage analyses were performed to model the progression of piping development in the laboratory models and corroborate the developed model of mechanics the findings of the study identified a new model for the initiation of piping development that can be applied to the assessment of piping in the field

the alpine tethys rifted margins reconciling old and new ideas to understand the stratigraphic architecture of magma poor rifted margins this study focuses on the assessment of the stratigraphic architecture of the proximal and distal jurassic alpine tethys rifted margins the aim of the study was to reconcile the major observations performed in the alps through time with what is observed in present day magma poor rifted margins the proximal and distal rifted margins reflect two evolutionary phases of rifting involving different structures and isostatic evolutions leading to different stratigraphic records the proximal rifted margins formed from upper triassic to pliensbachian times and resulted in the formation of classical half graben basins rift evolution changed drastically during pliensbachian to toarcian times when extension started to localize in the future distal rifted margins low angle detachment faults become the new elementary structure controlling final crustal tapering and eventually mantle exhumation to the sea floor new structural elements controlling the stratigraphic architecture of the distal rifted margins include extensional allochthons and breakaway blocks both resulting from the delamination of a keystone block also referred to as hangingwall block during hyper extension processes to define the stratigraphic architecture of the proximal and distal rifted margins three stratigraphic marker horizons are used namely the top of the pre rift sequences the top of the proximal margin syn tectonic sequence and the base of post rift sequences based on the distribution of these stratigraphic marker horizons across the alpine units and a structural re evaluation of the rift structures a synthetic tectono stratigraphic evolution of the alpine tethys domain is proposed that reconciles old and new ideas about how rift systems may evolve in space and time

numerical modelling of internal erosion process in gravel soils based on the percolation analytical method internal erosion is a common form of damage in geomaterial structures that is caused by the migration of soil particles under a seepage flow the geometrical characteristics of soil particles is regarded as the intrinsic factor for internal instability thus in this study a network modelling technique is formulated for this purpose the soil particles and pores are generalised into a network model according to their fractal gradations thereafter the percolation theory is applied to analyse this conceptual probabilistic model the percolation and erosion backbones are simulated in the direct square bond percolation model through the extended hoshen kopelman algorithm and direct electrifying algorithm monte carlo experiments are conducted to analyse the internal erosion process in this network model the extent of internal instability can be calculated quantitatively and the deposition rate of transported particles in the mass conservation equation can be evaluated for further analysis compared with internal erosion tests the percolation analytical method is in accordance with experimental results this method provides fresh insights on the nature of internal erosion from a statistical perspective

coarse carbonate breccias as a result of water wave cyclic loading uppermost jurassic south east basin france in the uppermost jurassic of the central part of the south east basin of france an association of lime mudstone beds calcarenite beds and coarse carbonate breccia bodies form an informal stratigraphical unit called the barre tithonique in the barre tithonique gradual transitions from lime mudstone or calcarenite to breccia show different stages of deformation leading to progressive brecciation of the original lithologies the study of the breccia facies and the observed gradual transitions as a whole document a new early diagenetic process in carbonate environments resulting from water wave and seabed interaction water wave induced brecciation and its abundance in the barre tithonique indicate that sea seabed interaction was significant comparison with modern studies of the mechanics of wave seabed interaction suggests that water depth was less than 200 m it is demonstrated that sedimentary features such as channel like structures previously interpreted as being the result of erosion and deposition of mud flows were in fact produced by wave induced in situ reworking of lime mud without any significant unidirectional flow or gravity induced displacement

improvement of hole erosion test and results on reference soils abstractunderstanding the factors that control the transport of soil particles detached by water is essential in predicting the contingency of internal and surface erosion of embankments during storms and floods it is particularly useful to be able to evaluate the sensitivity of the available soils to erosion at an early stage of a project and the risk assessment of an existing earthwork the presented study is based on laboratory tests with a hole erosion test apparatus and tries to characterize the internal erosion of soils the test consists of eroding a drilled soil specimen by water flow with a constant pressure drop at the boundaries of the specimen while recording the flow rate and studying the hole enlargement a new version of the apparatus with improved instruments and an interpretation method is proposed estimating the erosion rate based on the turbidity of the outflow and independent of hydraulic charge several remolded kaolinite sand mixtures are tested as reference soil textures and the

flume scale experiments on suffusion at the bottom of cutoff wall in sandy gravel alluvium this paper presents a series of flume scale experiments to investigate suffusion at the bottom of a cutoff wall in an internally unstable sandy gravel alluvium the initiation progression and potential failure of suffusion and the interactive effects of geomechanical and hydraulic conditions with the evolution of suffusion were investigated in this particular application temporal and spatial development of pore pressure earth pressure and settlement demonstrated suffusion was a multi phase involving pore water fine and coarse fractions and multi field involving seepage seepage induced fine fraction variation and stress deformation coupling phenomenon suffusion initiated at the downstream side of the tip of the cutoff wall and then generally progressed backward to the upstream side the monitored earth pressure provided an evidence of the heterogeneous stress distribution in internally unstable soil two linear empirical formulas for average hydraulic gradients at the initiation of suffusion a

spatial and temporal progression of internal erosion in cohesionless soil permeameter tests were performed on four widely graded cohesionless soils to study their susceptibility to in ternal erosion test specimens were reconstituted as a saturated slurry consolidated and then subjected to multi stage seepage flow under increasing hydraulic gradient the occurrence of internal instability is described qualitatively from vis ual observations through the wall of the permeameter during a test and from post test observations it is also described quantitatively from change of hydraulic gradient within the specimen and from axial displacement during a test the re sults provide a novel insight into the spatial and temporal progression of seepage induced internal instability this insight yields an improved characterization of suffusion and suffosion in cohesionless soils the progression of which appears gov erned by a critical combination of hydraulic gradient and effective stress resume des essais en permeametre ont eterealises sur quatre sols sans cohesion et agranulometrie etalee afin d etudier leur susceptibilitea l erosion interne les echantillons ont etereconstitues sous forme de pulpe saturee consolidee et en suite soumise aun ecoulement multi etapes sous un gradient hydraulique qui augmente l apparition de l instabiliteinterne est decrite de facon qualitative a partir d observations visuelles a travers la paroi du permeametre durant l essai ainsi que par des observations post essai l instabiliteinterne est aussi decrite quantitativement apartir des variations du gradient hydraulique al interieur des echantillons et du deplacement axial durant l essai les resultats offrent une vision nouvelle de la progression spatiale et temporelle de l instabiliteinterne causee par l infiltration ces resultats apportent une meil

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

pulses of plagioclase laden magmas and stratigraphic evolution in the upper zone of the bushveld complex south africa cumulate rocks of the upper main zone and upper zone uumz of the bushveld complex south africa contain the world s major resources of fe ti v hosted in ti magnetite and apatite and are commonly considered as having crystallized from the last major injection of magma into the magma chamber in this study we present the petrography modal proportions whole rock major element chemistry 260 samples electron microprobe data 10 000 analyses for plagioclase olivine and pyroxene and compiled analyses of cr in magnetite 239 samples for the uumz sampled over 2 1 km of the bierkraal drill cores in the western limb of the complex the uumz section exhibits a broad normal fractionation trend upwards but a series of reversals to more primitive anorthite contents in plagioclase mg in pyroxenes and olivine cr in whole rocks and cr in magnetite separates are observed accompanied by the appearance or disappearance of various minerals anorthosite or leucogabbro layers are closely linked to these reversals the reversals in an of plagioclase are used as boundaries to divide the uumz into 18 cycles these cycles are interpreted as indications of magma chamber replenishment by plagioclase laden magmas up to 20 vol plagioclase and are also marked by spikes in cr content in addition abundant fe ti oxide bearing plagioclase rich rocks are identified in the lower half of the uumz these have crystallized from a hybrid melt produced by the mixing of a new plagioclase bearing magma batch and the resident magma further crystallization of this hybrid liquid may lead to the formation of magnetite layers in the lower part of the uumz the bushveld uumz therefore grew by multiple emplacements of crystal laden magmas coming from deep seated chambers slow cooling in a shallow chamber explains the systematic bottom up compositional evolution in the cumulate pile within individual cycles the residual melt reached silicate liquid immiscibility soon after the saturation of apatite thereafter segregation of conjugate fe rich and si rich melts and crystallization of the paired melts produces cumulates with a smooth upward decrease in fe ti oxides whereas plagioclase mode increases in each apatite bearing cycle a comparison of systematic geochemical analyses and a detailed lithological stratigraphy between the bushveld limbs demonstrates the possible connectivity between the western and eastern upper zone but indicates notable differences from the bellevue section of the northern limb

critical hydraulic gradients of internal erosion under complex stress states abstractinternal erosion involves selective loss of fine particles within the matrix of coarse soil particles under seepage flow which affects the hydraulic and mechanical behavior of the soil in this research extensive laboratory internal erosion tests were conducted under complex stress states following three stress paths isotropic drained triaxial compression and triaxial extension stress paths these tests were designed to investigate the initiation and development of internal erosion and the effect of stress state on critical hydraulic gradients the entire erosion process can be divided into four phases stable initiation development and failure accordingly three critical gradients termed as initiation skeleton deformation and failure hydraulic gradients can be defined these critical gradients correspond to the onset of erosion of the fine particles filling the large pores of the skeleton the buckling of the strong force chains formed by the coarse particles and the soil failure re

determination of maximum paleotemperatures of burial mptb of sedimentary rocks from pyrolysis data on the associated organic matter basic principles and practical application the balazuc 1 borehole drilled in the frame of the geologie profonde de la france programme and the work carried out by various specialists provided the samples and the independent paleotemperature assessment data both needed to check a model aiming to the straightforward determination of maximum paleotemperatures of burial mptb from rock eval pyrolysis data basically the model supposes that laboratory e g rock eval pyrolysis resumes the successive elimination of kerogen moieties of increasing thermal stability where it had stopped during burial diagenesis then the temperature tmin determined at the onset of the s2 rock eval pyrolysis peak supposed to correspond to a peculiar kerogen moiety which was just undergoing cracking when maximum burial depth was reached might be used to calculate the corresponding mptb taking into account the different values of the experimental and natural thermal gradients the good agreement between calculated mptb values and results of fission track and fluid inclusion studies carried out on balazuc 1 borehole samples supports the validity of the model according to fundamental considerations the application of this approach is limited to samples having at least reached the onset of the metagenetic stage other possible limitations and the causes of uncertainty on the obtained results are discussed a detailed operating procedure is presented

visualisation of seepage induced suffusion and suffosion within internally erodible granular media a rigid walled transparent soil permeameter has been developed to study visually the mechanisms occurring during seepage induced internal erosion in susceptible granular media under upward flow

effect of seepage flow on incipient motion of sand particles in a bed subjected to surface flow abstract understanding the interaction of the groundwater seepage flow and sediment transport along permeable boundaries is essential for managing soil beds and bank erosion a significant bank failure may occur due to sediment transport under the boiling condition in the present study an experiment is conducted to investigate the effects of injection or upward seepage on the critical shear stress of a cohesionless soil bed subjected to surface flow the upward seepage force acting on the soil bed particles may reduce the virtual weight of the particles in turn it may also reduce the critical shear stress acting on the particles a theoretical analysis examines how the upward seepage force acts to modify the critical shear stress for the sediment entrainment due to the increase in the hydraulic gradient of the seepage flow a force analysis reveals that the ratio of the critical shear stress with seepage to that without seepage is dependent on the ratio of the hydraulic gradient of seepage to its value at the quicksand condition a test apparatus was built and the effects of injection on the critical shear stress of cohesionless soil bed particles were measured an acrylic channel with a rectangular cross section was prepared and a section of a cohesionless soil bed subjected to an upward seepage flow was installed at the bottom of the channel the experiment demonstrates that the induced seepage affects the dynamics of the channel flow even though the magnitude of the seepage flow velocity is significantly smaller than that of the free surface water flow the test results show that the dimensionless critical shear stress of the cohesionless soil bed particles decreases slightly as the hydraulic gradient of the seepage flow is increased when critical shear stress is determined at the upstream edge of the seepage zone furthermore the dimensionless critical shear stress decreases sharply with the increment of the hydraulic gradient of the seepage flow when critical shear stress is determined in the seepage zone however it does not decrease in either case as was theoretically assumed even when the hydraulic gradient approaches to the critical hydraulic gradient or the quicksand condition

stratigraphic record of the structural evolution of the western extensional margin of the subalpine basin during the triassic and jurassic ardeche france abstract the nature and the geometry of mesozoic deposits in the ardeche region reflect the different stages of structural evolution of the western extensional margin of the subalpine basin through stratigraphic analysis of a broad transect passing from the uzer block through the gpf geologie profonde de la france borehole balazuc 1 and two petroleum exploration wells on the different blocks of the margin it has been possible to integrate data from borehole bai in a sequential stratigraphic and regional dynamic framework and to attempt to specify the modes of tectonic control on the organization of the deposits along a profile of this extensional palaeomargin the triassic and jurassic deposits are composed of six major transgressive regressive cycles for which the geometric and stratigraphic characteristics indicate that they were controlled by the tectonic evolution of the basin and more specifically by variations in the type and rate of subsidence the first two cycles anisian early sinemurian in age correspond to the initial structural creation of the margin with a west east sedimentary polarity extensional tectonism which affected the palaeozoic basement in part controlled the duration and intensity of the transgressive phases with the regressive phases reflecting a decrease in regional subsidence the third and fourth cycles early sinemurian middle bathonian in age were contemporaneous with the tethyan rifting in particular they record evidence of decreasing regional subsidence and even uplift associated with block faulting this caused strong tectonic decoupling and highly variable subsidence along the margin profile episodes that are represented by that part of each sedimentary cycles deposited around the maximum regression i e end of the regressive phase and beginning of the transgressive phase sinemurian and aalenian a regional phase of subsidence followed which allowed maximum expansion of the transgression toarcian and bajocian transgressive peaks the fifth and sixth cycles middle bath on ian kimmeridgian in age were deposited during a period of widespread subsidence of the margin that was synchronous with the onset of tethyain oceanic spreading they preferentially record episodes of accelerated subsidence giving rise to transgressive phases generally associated with a synsedimentary tectonic activity that incurred relatively heterogeneous subsidence across the entire palaeomargin late bathonian and early oxfordian the regressive phases are subsequently marked by a decreased but uniform subsidence with no evidence of uplift the sediments of these last two cycles were deposited in a post rift context and are liable to record effects of geodynamic events outside the basin characterization of the different stages in the evolution of the ardeche palaeomargin by their stratigraphic expression provides geological constraints for modelling fluid migration throughout this extensional margin the objective of the gpf ardeche project

comparison of two criteria for internal stability of granular soil internal instability describes the loss of soil particles as a result of seepage two criteria are commonly used to determine the potential for such instability within a granular soil that is subje

multiscale modeling of flood induced piping in river levees a three dimensional transient fully coupled fluid particle model is utilized to simulate flood induced piping under river levees and taking into account the effects of soil fluid structure interactions the porous soil medium is modeled as a mixture of two phases namely the fluid phase water and the particulate solid phase the fluid is idealized as a continuum by using an averaged form of navier stokes equations that accounts for the presence of the solid particles these particles are modeled at a microscale using the discrete element method the interphase momentum transfer is modeled using an established relationship that accounts for the dynamic change in porosity and possible occurrence of nonlinear losses the hydraulic structure levee is modeled as an impervious rigid block and its motion is described by a combination of external and internal forces from the surrounding fluid and solid particles a computational simulation is conducted to investigate the response of a granular deposit when su

the applicability of microbially induced calcite precipitation micp for internal erosion control in gravel sand mixtures seepage induced internal erosion in earth filled embankment dams has been attracting the attention of civil engineering researchers and practitioners for decades microbially induced carbonate prec

sand production model in gas hydrate bearing sediments abstract this paper provides a comprehensive analytical formulation that entails the features of sand production in gas hydrate bearing sediments including grain detachment migration sediment deformation and hydrate dissociation the formulation is thermo hydro mechanically coupled such that grain detachment causes stress reduction sediment shear deformation induces grain detachment and grain flow alters multiphase fluid pressure and temperature profiles through a series of analyses the sensitivity of sand production related parameters on resulting solid volume changes is evaluated furthermore the effect of various operational methods on mitigating sand production in hydrate bearing sediments during gas production is numerically investigated it is found that out of the different operational methods investigated lowering depressurization rate was the most effective in reducing sand production for a given gas production

origin of anorthosite and magnetitite layers in the bushveld complex constrained by major element compositions of plagioclase the bushveld complex a layered mafic intrusion in south africa shows extreme vertical differentiation in terms of mineral compositions and modal proportions from dunite to ferrodiorite in a continuous borehole core drilled through the uppermost 2 8k m of the intrusion typical rocks range upwards from troctolite through gabbronorite and ferrogabbronorite to ferrodiorite with extreme examples of anorthosite magnetitite and feldspathic pyroxenite the an content of plagioclase has previously been determined for 420 samples and decreases upward from an78 to an36 with six minor slow reversals variations in modal proportions of plagioclase have been calculated based on 2200 density determinations on whole rocks forty five anorthosite layers have been identified ranging from 1 to 23 m thick none of these layers is associated with the abovementioned reversals in an content in plagioclase and nearly all have leucocratic rocks below and above with more than the likely cotectic proportions of plagioclase these observations argue against an origin for anorthosite related to magma addition or to supersaturation and oscillatory nucleation rhythmically pulsed crystallization possibly associated with pressure changes followed by crystal settling and sorting of minerals of different densities is a hypothesis consistent with all the observations twenty layers of magnetitite have been identified there is a significant reversal in an content in the overlying plagioclase compared with the underlying sample across only one such layer again this observation challenges hypotheses that such layers result from magma addition but is consistent with a pressure change hypothesis for triggering magnetite crystallization the upper contacts of magnetitite layers that grade into anorthosite over many centimetres possibly also reflect settling and sorting rocks forming the uppermost 100 m of the intrusion contain the most sodic plagioclase compositions demonstrating that there is no downward crystallizing roof facies furthermore this uppermost 100 m section is depleted in plagioclase relative to its cotectic proportions hence we find no evidence supporting flotation or prolonged suspension of plagioclase

capillary tube model for internal stability of cohesionless soil abstractkovacs criterion to assess the potential for internal instability of cohesionless soils that was proposed but never tested experimentally is verified with reference to a database of laboratory test results the inherent margin of safety is described and a threshold boundary between stable and potentially unstable gradations is established a variation on the method is then presented termed the simplified kovacs criterion

laboratory study on subgrade fluidization under undrained cyclic triaxial loading a long term issue that has hampered the efficient operation of heavy haul tracks is the migration of fluidized fines from the shallow soft subgrade to the overlying ballast i e mud pumping this

the ardeche palaeomargin of the south east basin of france mesozoic evolution of a part of the tethyan continental margin geologie profonde de la france programme abstract this paper incorporates the results of seismic and gravity investigations borehole data and studies of sedimentology biostratigraphy sequence stratigraphy and structural geology carried out in the framework of the deep geology of france programme the main purpose of the paper is to define the structure and to reconstruct the evolution of the ardeche palaeomargin of the south east basin of france from the stephanian to the end of the mesozoic the acquisition and processing of three seismic reflection profiles the drilling of two scientific boreholes ba1 and mm1 and subsequent structural modelling with the use of cross section balancing techniques applied to both the depth migrated seismic and geological sections provide new geometrical constraints which lead to the following hypothesis of the geodynamic evolution of the margin 1 1 late palaeozoic extension with the development of high angle basement faults asymmetrical permian half grabens pre extension sedimentary cover 2 2 during the middle triassic a pre rift stage with the creation of small fault blocks and in the late triassic the formation of an e w flexure 3 3 end lias early jurassic to middle jurassic formation of a major detachment in the carboniferous coal measures leading to complete decoupling of the mesozoic sedimentary cover from the basement this episode of extension coeval with the opening of tethys can be related to a phase of episodic rifting between the late sinemurian and the late bathonian i e during 30 ma 4 4 late jurassic to early cretaceous thermal subsidence with regional downwarping of the basement towards the east 5 5 after the late cretaceous the period of maximum burial pyrenean and alpine deformation in the south and east causing progressive uplift of the ardeche palaeomargin as much as two kilometres of mesozoic deposits subsequently being eroded from the section during the tertiary

impact of floodplain gravel mining on landforms and processes a study case in orlat gravel pit romania understanding gravel mining a very common but aggressive activity as a morphogenetic action is fundamental for analyzing and assessing the impact on floodplain morphology and the dynamic of riverbeds on sediments budget and water balance assessment but also for floodplain planning and resources management field observations and gis analysis were performed in a gravel pit area from central romania to assess the impact of gravel harvesting during the last decade 2005 2015 on floodplain landscape landforms dynamic and fluvial processes field measurements diachronic analysis on maps channel sinuosity coefficient and braided coefficient were carried out to assess the riverbed pattern the results indicate that the intensive harvesting of gravels and sands in floodplain area leads to doubling of pit and pit ponds surfaces changes in floodplain morphology and landscape degradation and radical changes in land use land cover the channel analysis indicates that the natural conditions and gravel harvesting had an important role in riverbed mobility and reveals different patterns along the cibin river meandered disentangling and sinuous the main changes of the riverbed consist of meanders radius reduction meander loops migration northward and downstream increased sinuosity and decreased braided coefficient this study facilitates a better understanding of the geomorphologic consequences of off stream gravel harvesting the fluvial processes variability linked to flow and bedload and point to human action as morphogenetic and morphodynamic factors moreover this study may enhance the environmental significance in sustainable management of floodplain being a useful tool in applied ecology river remediation studies and territorial planning

mercury in the bushveld complex south africa and the skaergaard intrusion greenland abstract we present mercury concentrations for layered mafic rocks of the bushveld complex the skaergaard intrusion morb and a karoo dolerite sill as determined by combustion atomic absorption spectroscopy combustion aas with gold amalgamation pre concentration mercury in the bushveld complex and the skaergaard intrusion is generally low with about 1 1 and 0 8 ppb hg on average respectively the karoo dolerite sill chill margins and morb have average hg concentrations of 2 5 and 6 4 ppb respectively the reason for the low whole rock hg concentrations in layered mafic intrusions is that the element is incompatible with respect to the cumulus mineral assemblages our results show far lower hg concentrations for the skaergaard cumulates than previous measurements and we find no evidence for preferential enrichment in plagioclase rich rocks as previously reported we attribute this difference to inaccurate analytical methodology of the early measurements there are hg enrichments in distinct levels in both intrusions mercury enrichments in the bushveld complex are observed near the top of the lower zone 2 4 ppb in the merensky reef at 8 6 ppb the platreef at 3 ppb average and in the upper zone near the main magnetitite layer 4 7 ppb these enrichments are due to the concentration of hg by sulfides as suggested by a positive correlation between cu and hg there is no upward increase in hg with stratigraphic height or positive correlation between hg and zr in the bushveld complex as would be expected if hg acted as an immobile incompatible element the lack of correlation is explained by periodic degassing of the bushveld magma chamber in which volatile elements including hg and s escaped in contrast the skaergaard intrusion probably did not degas and there is hg enrichment in the sandwich horizon 53 ppb because of the combination of the incompatibility and the presence of sulfides

origin of rollover rollover is the folding of hanging wall fault blocks by bending or collapse in response to slip on nonplanar commonly listric normal faults the shapes of rollover folds are controlled by a number of variables including 1 the shape of the fault 2 the total fault slip after a bed is deposited 3 the direction of relative particle motion in hanging wall collapse 4 the history of sedimentation rate relative to fault slip rate and 5 compaction the importance and role of each of these variables is illustrated by a two dimensional balanced structural modeling technique that treats continuously curved faults as though composed of a large number of straight fault segments in this modeling an active axial surface oriented parallel to the direction of relative p rticle motion in hanging wall collapse emanates from each fault bend and is the instantaneous locus of folding the quantitative correctness of this theory of rollover is tested by modeling natural structures from the gulf of mexico for which both fault shape and fold shape are known from high quality seismic and well sections the direction of hanging wall collapse commonly is in the antithetic or synthetic normal fault or coulomb shear orientations although sliding along weak bedding planes also is an important collapse mechanism in some regions collapse is in the antithetic shear direction for concave fault bends and in the synthetic shear direction for convex bends these collapse directions can be observed directly in some high quality seismic images as axial surfaces emanating from fault bends the shapes of rollovers within growth strata depend strongly on the sedimentation rate relative to fault slip rate as well as the total slip after a bed is deposited the crests of classic gulf coast rollovers are growth axial surfaces along which are abrupt changes in sedimentation rate within the growth st atigraphic interval these changes are produced by deformation of the sediment water interface along active axial surfaces compaction can substantially modify the relationship between fault shape and rollover shape however under certain common conditions the history of compaction can be neglected if the folding is modeled in the compacted state

geometric models of listric normal faults and rollover folds existing geometric models allow master fault shapes to be constructed given the shape and heave or displacement of a deformed marker horizon in the hanging wall these models assist in projecting normal faults to depth where the fault geometry is poorly constrained by available seismic data currently it is unclear which model best predicts the actual relation between rollover and fault geometries to address this deficiency the relative accuracies of the constant heave constant displacement constant bed length slip line and inclined shear constructions are evaluated using clay model analogs and seismic examples each of the geometric models predicts a different fault shape and depth to detachment for the same rollover shape because different hanging wall deformat on mechanisms are assumed a construction is developed for determining the hanging wall geometry from a known fault geometry this construction is based on the inclined shear model and geometric constraints imposed by material displacement paths viewed from different reference frames fixed to the hanging wall and footwall blocks in clay models the inclined shear antithetic shear greek alpha 20 degrees and slip line constructions produce the best agreement between actual and modeled fault and marker bed shapes in rollovers for subsurface examples the inclined shear model antithetic shear greek alpha 20 40 degrees and the constant displacement model predict fault trajectories that are the most similar to the positions and shapes of the master fault segments interpreted fr m offshore norway and gulf of mexico seismic lines the shear angle required in the inclined shear model can often be estimated from the orientation of minor faults in the hanging wall the shear angle may also be determined through iterative modeling in which the shear angle is systematically varied and the resultant model fault shape is compared to the shape of the shallow segment of the master fault interpreted from the seismic record

equivalent state theory for mixtures of sand with non plastic fines a dem investigation the discrete element method dem was used to simulate constant volume undrained triaxial compression tests for coarse particles sand mixed with non plastic fines simulations were performed on

rare earth element abundances in apatite in the bushveld complex a consequence of the trapped liquid shift effect reply the concentrations of the rare earth elements rees in apatite from a 600 m thick sequence toward the top of the bushveld complex south africa have previously been published they show two ranges of compositions in a lower section and an upper section the data were interpreted in terms of liquid immiscibility the evidence for this model is reassessed and an alternative explanation offered that involves the trapped liquid shift effect in this process the true cumulus phase compositions reequilibrated with trapped liquid as it solidified and ree abundances in apatite were variably increased the extent of the change depends on the relative proportions of cumulus apatite and trapped liquid calculations show that if there was 5 apatite and 10 trapped liquid as found in the lower section the ree abundance in the final apatite would have only increased marginally relative to the original cumulus composition however in the upper section where there was only 2 apatite and 25 trapped liquid the ree abundances were increased by a factor of 3 most of the rees are essentially incompatible in the other cumulus phases except apatite and the other phases have little influence on the final concentrations of rees in apatite however for eu which partitions into plagioclase this mineral acts as a major buffering influence and relatively less eu than the other rees entered apatite during the solidification process as a result the calculated final apatite in the upper section developed a large negative eu anomaly as observed in the actual mineral analyses the concept of large scale liquid immiscibility in the upper part of the bushveld complex based on rees in apatite is challenged and an interpretation involving the trapped liquid shift effect is considered more plausible

hafnium isotopic composition of the bushveld complex requires mantle melt upper crust mixing new evidence from zirconology of mafic felsic and metasedimentary rocks

internal stability of crushed sands experimental study the current paper documents an experimental study conducted to evaluate the internal stability of sands subjected to seepage at high stresses a custom made one dimensional compression cell with fluid flow capabilities was used to load and flush saturated specimens composed of selected sands with heterogeneous mineral composition the degree of internal stability i e the extent to which a soil can retain its mobile particles was quantified with both the size distribution curves and the relative amounts of fragments collected in the effluent results indicate that a uniform internally stable sands become internally unstable at high stresses albeit temporarily and b internal instability features are dependent on mineral composition and the extent of particle breakage particle level force analyses suggest that the internal stability of crushed sands is dependent on the hydrodynamic conditions imposed

spatial distribution patterns of calcareous nannofossils across the callovian oxfordian transition in the french subalpine basin abstract callovian oxfordian calcareous nannofossils are documented from four sections distributed along a proximal distal slope to central basin transect in the french subalpine basin south eastern france the sections were dated and correlated using integrated ammonite dinoflagellate and nannofossil biostratigraphies the nannofossil assemblages are constantly dominated by watznaueria britannica however significant spatial changes in nannofossil assemblage composition are recorded nannofossil assemblages recovered in slope and slope to basin transition sections are characterized by high abundances lowest diversities highest percentages of smallest sized morphotypes of w britannica subordinated w britannica manivitiae a morphotype described in this study and are indicative of turbulent unstable and or eutrophic conditions towards the central part of the basin as the nutrient content and turbulence declined and paleoenvironmental stability increased the nannofossil assemblages become more diverse and characterized by lower relative abundances of w britannica but higher contribution of larger morphotypes and higher relative abundances of w barnesiae fossacincta biscutum dubium and zeugrhabdotus erectus these latter small coccoliths markers of high surface waters fertility for the cretaceous were probably not competitive with respect to smaller sized w britannica in unstable and eutrophic surface waters for the jurassic an increase in the surface water productivity is recorded both in proximal and distal sections at the callovian oxfordian transition and is demonstrated both by an increase in nannofossil total abundances and in the relative abundances of taxa adapted to high trophic levels thermal minimum in surface waters as indicated by an increase in the percentages of the cool water nannofossil taxa is associated to increased productivity further studies will be necessary to demonstrate whether surface water productivity changes already recorded in the eastern paris basin were global

hydromechanical modeling of granular soils considering internal erosion this paper attempts to formulate a coupled practical model in the framework of continuum mechanics to evaluate the phenomenon of internal erosion and its consequences on the mechanical behavior of

cyclicity in the main and upper zones of the bushveld complex south africa crystallization from a zoned magma sheet the major element composition of plagioclase pyroxene olivine and magnetite and whole rock sr sr data are presented for the uppermost 2 1 km of the layered mafic rocks upper main zone and upper zone at bierkraal in the western bushveld complex initial sr sr ratios are near constant 0 7073 0 0001 for 24 samples and imply crystallization from a homogeneous magma sheet without major magma recharge or assimilation the 2125 m thick section investigated in drill core comprises 26 magnetitite and six nelsonite magnetite ilmenite apatite layers and changes up section from gabbronorite an72 plagioclase mg 74 clinopyroxene to magnetite ilmenite apatite fayalite ferrodiorite an43 mg 5 clinopyroxene fo1 olivine the overall fractionation trend is however interrupted by reversals characterized by higher an of plagioclase higher mg of pyroxene and olivine and higher v2o5 of magnetite in the upper half of the succession there is also the intermittent presence of cumulus olivine and apatite these reversals in normal fractionation trends define the bases of at least nine major cycles we have calculated a plausible composition for the magma from which this entire succession formed forward fractional crystallization modeling of this composition predicts an initial increase in total iron near constant sio2 and an increasing density of the residual magma before magnetite crystallizes after magnetite begins to crystallize the residual magma shows a nearconstant total iron an increase in sio2 and decrease in density we explain the observed cyclicity by bottom crystallization initially magma stratification developed during crystallization of the basal gabbronorites once magnetite began to crystallize periodic density inversion led to mixing with the overlying magma layer producing mineralogical breaks between fractionation cycles the magnetitite and nelsonite layers mainly occur within fractionation cycles not at their bases in at least two cases crystallization of thick magnetitite layers may have lowered the density of the basal layer of melt dramatically and triggered the proposed density inversion resulting in close but not perfect coincidence of mineralogical breaks and packages of magnetitite layers

successive post variscan stress fields in the french massif central and its borders western european plate comparison with geodynamic data abstract structural analysis and particularly microtectonic methods have made it possible to define the different stages of brittle deformation of the massif central basement and the surrounding sedimentary cover from the end of the hercynian orogeny to the end of the tertiary during the stephanian a compressional tectonic regime prevailed regional faults appeared or were react vated reactivation as a result of initial n s compression becoming nw then e w these regional strike slip faults caused local extension which led to the formation of small coal bearing basins this compressional regime which marked the end of the formation of pangea was followed by a series of extension episodes permian triassic extension oscillating around n s e w to nw se extension in the early and middle jurassic and finally n s to ne sw extension in the late jurassic to cretaceous the normal faults formed during these episodes strongly influenced the distribution of emerging continents and sedimentary basins from the campanian 75 ma to the present the convergence of africa and eurasia involved the distribut on of stresses in the west european plate several tectonic episodes are distinguished in the massif central during the eocene approximately n s compression predominated general e w extension in the late eocene oligocene resulted in grabens with general northerly strike mainly in the centre of the massif central and on its east and southeast borders lastly compression varying from nw se to e w in the north and south of the massif central prevailed during the alpine orogenic phase at the end of the miocene these successive stages of brittle deformation are interpreted in the context of the evolution of the west european plate and its displacement in relation to the african plate the correspondences between the major geodynamic periods and the distribution of stresses over the west european continent are noted as well as the problems which remair to be resolved

palaeocirculation in the basin of southeastern france sub alpine range a synthesis from fluid inclusions studies abstract in the basin of southeastern france sub alpine range circulation of palaeofluids relates to the geodynamic evolution of the western tethyan margin alpine chain build up from the triassic to present recent reconstructions allow distinction of two main provinces 1 the western border of the basin where the jurassic extensional structures have not been affected by alpine compression and 2 the central and eastern parts of the basin subjected to a partial tectonic inversion during eocene and miocene compressional events in the oxfordian shales two main distinct areas are recognized on both sides of the digne fault grading from a diagenetic domain with temperatures lower than 150 c corresponding with aliphatic oil in fluid inclusions to a low grade metamorphism with temperatures up to 250 c and dry gas hydrothermal circulations are suspected but not yet evidenced during the oligocene rising triassic diapirs were the setting of intense fluid circulation with mineral neoformations fluid inclusions indicate a heterogeneous trapping of na ca k mgci solution up to 35 wt nacl equ saturated with co2 n2 at temperatures up to 350 c during successive episodes of fluid injection such gas may originate from deep sources pervasive flow of co2 n2 but local shallow reactions can not be rejected p t conditions of 250 c 1 5 kbars are deduced for the eastern diapirs and 250 c 1 5 kbars to 360 c 2 2 kbars for western diapirs geodynamic reconstructions indicate a palaeoburial depth for the brine of about 10 km corresponding to a mean thermal gradient of 35 c km this is in agreement with the burial depth of triassic evaporates exceeding 8 km during cretaceous before the main diapir rise in the oligocene mesozoic sediments were investigated by drilling near the uzer fault balazuc we recognize major diagenetic events involving mineral transformations at temperatures up to 150 c this can be explained by greater burial during the cretaceous with a post cretaceous erosion amounting to about 1 5 km late circulation of low temperature ca mg na ba rich solutions in all the series is indicated by intense fracturing according to its tectonic characteristics this episode may relate to fault reactivation during the eocene in conclusion the configuration of the basin and its western border allows trapping of connate fluids beneath the triassic evaporate and their mixing with deeper water all these fluids circulated between the hercynian crystalline basement and the triassic evaporates across lias and middle jurassic strata during the middle cretaceous in infra triassic sedimentary layers the estimated depth during this period is about 10 km in the basin a normal geothermal gradient account for oil and gas generation low temperature subsurface aqueous fluids did circulate along the basin border in the palaeogene during an episode of fault reactivation

assessing the potential of internal erosion and suffusion of granular soils this study presents a new empirical criterion for assessing the potential of internal erosion and suffusion of granular soils this method considers the bimodal structure of a soil having a primary coarse fabric and loose finer particles based on the porosities influenced by the particle size distribution and the degree of compaction by comparing the representative particle size of a loose finer fraction with the controlling constriction size of a primary coarse fabric a distinct boundary between internally stable and unstable soils with respect to internal erosion may be found

an experimental setup for fluid venting in unconsolidated sediments new insights to fluid mechanics and structures abstract focused outflow of water at the seafloor termed seepage or fluid venting is a widely recognized global phenomenon in an effort to better understand the mechanisms by which fluid flow related structures form we performed laboratory seepage experiments using samples representing a broad range of grain sizes and hydraulic conductivities 10e 3 to 10e 7 m s detailed observations led to the recognition of a typical often repeated progression of fluid flow structures that form during processes of increasing and decreasing hydraulic gradients the development of fluid flow structures like macro pores conduits and pipes is strongly dependant upon cohesion but is unrelated to grain size variations from sample to sample partial liquefaction leads to permanent changes in the grain fabric and to an increase in hydraulic conductivity our observations explain the longevity of seep sites and systematic relationships between hydraulic gradients grain fabric appearance and hydraulic conductivity that could be used to estimate flow rates based on structural findings

observations on internal stability of cohesionless soils introduction internal stability refers to the ability of the coarser fraction of a soil to prevent migration of its finer fraction as a result of seepage flow skempton brogan 1994 report findings from piping tests on four well graded to gap graded sandy gravels flow was imposed in an upward direction without surcharge loading and without vibration an abrupt transition was noted from stable to unstable states defined by the ratio d9 15 d9 85 1 4 4 as postulated by kezdi 1979 and attributed to work published in 1969 the latter concept was conceived independently by de mello 1975 advocated by sherard 1979 for a ratio 4 to 5 and recommended by lowe 1988 for a ratio of 5 it involves splitting the gradation at arbitrary points along the curve to yield d9 15 of the coarse fraction and d9 85 of the fine fraction as illustrated in fig 1 for gradation g3 c in this study we further evaluate the kezdi 1979 criterion through laboratory permeameter testing of five soils fig 1 and table 1 and compare the results with a dataset of 34 gradations extracted from kenney lau 1985 1986 and honjo et al 1996

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

laboratory piping tests on fine gravel results of an experimental study are presented in which the horizontal critical gradient required for backward erosion piping of fine gravel was measured a horizontal flume was constructed that a

cored section of the balazuc well southeastern basin of france geologic and geochemical approach deep geology of france programme abstract the ardeche project of the geologie profonde de la france gpf or deep geology of france programme aims at quantifying mass transfer along the margin of the southeastern basin of france using drilling data a very comprehensive geologic study has been made of the cores from the balazuc well including lithology sedimentology mineralogy and petrography this enabled the determination of several lithologic units and of the evolution of their depositional environment petrographic study showed that the diagenetic evolution can be divided into four phases from syn sedimentary diagenesis to a late faulting related phase in order to provide a framework for these observations at the scale of the units a geochemical investigation was carried out as well it consisted of the unusual procedure of total rock analyses on core slabs up to 60 cm long each sample representing a rocktype in this paper we compare the geologic results with the chemical logs that were obtained from these analyses the lithology and mineralogy of the formations give a specific chemical signature the evolution with depth of the major elements defines trends that can be correlated with first and second order major and minor stratigraphic cycles indicating that the base level evolution has been recorded by these logs through detrital control using minor elements fe mn sr and ba the evolution with depth of several specific mineralogical phases indicates that the depositional environment and tectonic control of the sedimentation remained guides for the chemical composition of diagenetic deposits comparison with petrographic results shows that diagenesis occurred extremely rapidly leading to a complete decrease in permeability of the series the results show that this type of geochemistry can be a powerful tool to complete geologic observations

incompatible trace element behavior in the bushveld complex borehole core from the uppermost 500 m of the rustenburg layered suite of the bushveld complex has been analyzed for rb sr zr y and nb plots of absolute trace element abundance and trace element ratios against stratigraphic height are presented these are used to test for multiple injection of magma and postcumulus migration of residual liquid these and previously published data are used to support the hypotheses that there was a new injection of magma above the merensky reef and that large scale infiltration metasomatism did not occur no evidence from incompatible element data exists for an addition of magma near the pyroxenite marker where a distinct reversal in cumulus mineral composition occurs however this may be the result of relatively small degrees of fractionation of the host magma prior to the addition of new magma the ability to recognize the entry of new magma may be restricted by the analytical precision the uppermost 500 m of the layered sequence appears to behave as a single broadly homogeneous magma in showing a systematic predictable upward increase in incompatible element abundances consistent with a model assuming 10 to 30 percent trapped liquid in the cumulate deviations from the predicted trends for zr y and nb are attributed to these elements being compatible in magnetite for zr and apatite for y and nb which are present in the uppermost rocks

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

cross section restoration and balancing as aid to seismic interpretation in extensional terranes structural cross sections in extensional terranes can be improved significantly by restoration and balancing principles originally developed for fold and thrust belts in rift basins and passive continental margins use of restoration techniques in analysis of growth faults elongate salt swells and other extensional structures results in geologically valid seismic interpretations sections must be in depth as opposed to two way time and oriented in the direction of material transport and decompaction must accompany restoration hanging wall deformation is characterized by different processes depending on the mechanical properties of the rocks being extended and can be approximated by various geometric and kinematic models antithetic faulting is analogous to antithetic shear combined antithetic and synthetic faulting is approximated by vertical shear domino style extension corresponds to rigid body rotation and flexural slip flow is modeled by bed length balance methods selection of the appropriate algorithm is crucial for proper restoration and balancing applications of these techniques illustrated here using seismic data from the gulf coast and north sea include 1 evaluating and adjusting seismic interpretations 2 projecting listric fault trajectories to depth 3 delineating more accurately the geometry and extent of hydrocarbon reservoirs 4 identifying new exploration leads 5 determining the deformation history of an area and 6 constraining the timing and direction of hydrocarbon migration and entrapment

the residual or roof zone of the bushveld complex south africa the geological succession of an area in the southeastern bushveld complex south africa is described here in which up to 700 m of monzonitic rocks more evolved than in currently proposed stratigraphic sections of the bushveld have been identified beneath the rooiberg group felsites the roof rocks to the intrusion a previous mass balance calculation for incompatible elements from the upper part of the bushveld complex indicated that some evolved rocks are missing from currently accepted sections through the stratigraphy most previous attempts to constrain the location of such evolved rocks have been based on one dimensional vertical modelling and the possibility of lateral magma migration within the complex has mainly been ignored by most researchers characterization of the currently accepted most evolved rocks is based on two challengeable assumptions that the crystallization surface was exactly parallel to the roof and that the bushveld granite was emplaced exactly at the contact between the uppermost rocks of the complex upper zone and the felsic volcanic roof rocks rooiberg group both assumptions are shown here to be questionable it is inferred that this body of monzonite represents this more evolved magma that migrated laterally not vertically these observations show that vertical summation of the compositions in the intrusion cannot give the correct answer for the original composition of the magma these evolved rocks contain abundant plagioclase up to 20 in total of quartz alkali feldspar plus hornblende and very minor olivine clinopyroxene and an oxide phase they contain up to 65 sio2 and can be called hornblende quartz monzonites they do not display good cumulate textures such rocks have been reported in the older pre 1970 literature but with different names from the eastern western and northern limbs of the bushveld and so potentially are volumetrically significant the more recent publications have focused on vertical sections where fairly melanocratic and oxide rich rocks form the top contact that contact is interpreted here to have been truncated by emplacement of the bushveld granite to emphasize that the present studied rocks are mineralogically and texturally distinctly different from those reported in previous sections it is proposed that they be designated as the residual or roof zone of the bushveld complex

where are the limits of mesozoic intracontinental sedimentary basins of southern france abstract reconstitution of the geometry of sedimentary basins is fundamental to understand the nature of present sedimentary rocks and the economic potential in hydrocarbon and mineral resources present day topography of southern france shows elevations growing between the meso cenozoic aquitaine basin to the south east basin across the variscan domain and the jurassic causses small basin with maximum relief in the cevennes area present day elevation offset is of approximately 1000 m this geometry questions the paleogeography and dynamics of these various domains and the relative elevation of the variscan domain during the subsidence of adjacent aquitaine and south east basins in this study we investigate the geological history of the variscan basement high and the causses small basin using paleotemperatures deduced from organic matter analysis low temperature thermochronology and regional geological constraints lower jurassic upper pliensbachian and toarcian marls sampled across the area from the aquitaine basin to the south east basin have similar depositional environments containing mainly type iii oganic matter and close tmax values ranging between 430 and 440 2 c these data show that the entire south massif central has undergone a similar burial history considering that these values are explained by burial low temperature thermochronology data have been acquired on basement rocks outcropping on the borders of sedimentary basins rouergue cevennes and margeride fission track ages are ranging between 74 5 and 187 6 ma and track lengths between 11 5 0 3 and 13 6 0 1 m apatite u th he corrected ages are ranging between 65 5 and 184 15 ma data inversion with the software qtqt indicates a cooling episode starting at the end of early cretaceous or beginning of late cretaceous from maximum temperature of 100 10 c in the rouergue and cevennes area and from 80 10 c in most of the margeride area thermal indicators are compatible with the erosion of a middle upper jurassic and cretaceous sedimentary cover of 1400 400 m assuming a thermal paleogradient of 35 c km the preserved sedimentary cover attests of a middle and upper jurassic lower cretaceous sedimentary cover of 1000 2000m in the aquitaine and south east basins this erosion phase occurred during mid cretaceous and is associated to a major geodynamical event characterized by large amplitude from the aquitaine basin to durancian doming in the south east basin and by kilometric offset we interpret also these data to show that marine connections have existed between the aquitaine basin and the south east basin during the jurassic and likely early cretaceous the present day morphology of the area has then been acquired after cretaceous times and may result from the pyrenean orogenic event during eocene times

experimental investigation of global backward erosion and suffusion of soils in embankment dams many embankment dams constructed with a core of nonplastic or very low plasticity silt sand gravel typically of glacial fluvioglacial or alluvial origin have experienced internal erosion this h

erosion of silty sand tailings through a geomembrane defect under filter incompatible conditions at tailings storage facilities a geomembrane may be used to contain tailings from relatively more permeable foundation or embankment materials a filter incompatible condition may arise between the tailings and underliner materials in this study potential for piping erosion of tailings through a 1 cm diameter geomembrane defect was evaluated in a series of physical experiments the geomembrane defect was sandwiched between silty sand tailings and various underliners df15 db85 5 6 to 13 5 not meeting typical retention criteria for filtration the leakage rates and visual findings revealed that a critical stress condition existed where erosion continuously occurred for up to 24 hours this stress condition could be encountered during early deposition or development of a reclaim pond at a tailings storage facility when allowed to occur erosion during this stress condition resulted in subsequent leakage rates that were 2 to 3 orders of magnitude higher than previously observed with filter compatible c

palaeo stresses inferred from macro and microfractures in the balazuc 1 borehole gpf programme contribution to the tectonic evolution of the cevennes border of the se basin of france abstract the scientific borehole balazuc 1 was drilled on the ardeche margin of the se basin of france for the purpose of studying fluid rock interactions in stratiform reservoirs in a tectonically controlled area a structural study was made of oriented cores from the drill hole between the depths of 1218 and 1729 5 m the various types of fracture that could have been used during fluid transfers have been described and analysed four major faults and 335 minor faults and tension gashes mineralized in carbonates anhydrite and sulphides were intersected at the bottom of the hole one of the major faults brings into contact rocks of triassic age and a formation attributed to the upper palaeozoic the other faults have caused thinning of certain units of the lower middle triassic micro structural study of the fault planes has enabled characterization of the tectonic episodes by which the triassic and lower liassic sedimentary rocks were affected these episodes discussed in the context of the ligurian tethys were 1 e w synsedimentary extension during the early middle triassic that caused tilting to the southeast of the upper palaeozoic and lower middle triassic successions this continued into the late triassic 2 an episode of n s extension during the early lias characterized by hydroplastic type faults probably the result of a local variation of the stress field in a trans tensional regime 3 the major period of activity on the uzer fault with downthrow of more than 1000 m that continued from the lotharingian late sinemurian to the early bathonian it was not possible to calculate the stress tensor for this period because no secondary fault system developed in the lower block traversed by the borehole brittle deformation at this time seems to have been concentrated on the major structures 4 approximately n s extension possibly end jurassic to earliest cretaceous during which the tension gashes mineralized in carbonates and pyrite were formed in the rhaetian and hettangian deposits 5 three compressive and or strike slip episodes attributed to the cenozoic pyrenean and alpine phases of deformation the oligocene extensional phase was not recognized in the borehole

closure to fabric and effective stress distribution in internally unstable soils by t shire c o sullivan k j hanley and r j fannin the authors have performed numerical tests to determine the distribution of fabric and effective stresses in internally unstable soils different grain size distribution curves as well as different densities were investigated the authors have used the methods of kezdi 1979 and kenney and lau 1985 1986 to assess the internal stability the relative density has a significant effect on the internal stability ahlinhan et al 2012 icold 2013 accordingly it is important to use a method takes into consideration the effect of density to assess the internal stability neither kezdi s method nor kenney and lau s method takes the density in consideration a suitable method is the one suggested by dallo et al 2013 which takes the effect of soil density in consideration for instance the soil gap med 18 is classified as border line according to kezdi s method whereas it is classified as unstable according to kenney and lau s method regardless of its relative density according to dallo et al 2013 soil gap med 18 is unstable transition or border line and stable for the loose medium and dense relative densities respectively also the internal stability prediction accuracy of dallo et al 2013 s method is better than those of the kezdi or kenney and lau methods dallo et al 2013 the discusser used the method of dallo et al 2013 to assess the internal stability of the gap graded soils tested by the authors table 1 it can be seen that the soils gap wide xx are unstable the soils gap narrow xx are stable whereas the internal stability of the soils gap med xx depends on the relative density of the soil another discussion point is related to the authors adoption of the findings of skempton and brogan 1994 that the critical finer fraction s falls between narrow limits of finer fractions by mass ffine 1 4 24 29 for dense and loose samples respectively also the finer fraction smax at which the finer particles completely separate the coarse particles from one another is given as ffine 1 4 35 the discusser believes that the critical finer fraction can be computed more accurately according to indraratna et al 2011 eq 1 or dallo and wang 2012 eq 2 as smax 1 4 1 nl 1 nc nc 1

platinum group element distribution in the main zone and upper zone of the bushveld complex south africa abstract the platinum group element pge contents of the upper portions of the bushveld complex were investigated with three questions in mind a in natural systems does magnetite concentrate os ir ru and rh ipge as has been observed in experimental systems b is there a au pd enriched layer present such as observed in the upper parts of the skaergaard intrusion c can changes in metal ratios be used for prospecting for pge deposits in the sulfide poor main magnetite layer of the eastern bushveld ir and rh are enriched relative to pt pd and au and this could be because magnetite preferentially concentrated ir and rh over pt pd and au however in most other magnetite layers no enrichment was observed this could be because most magnetite layers contain approximately 1 sulfides and the pge budget is dominated by the sulfides these sulfides obscured the effects of magnetite collecting ipge because sulfides collect all the pge and the partition coefficients for the pge into a sulfide liquid are much greater than the partition coefficient for ipge into magnetite the weighted average of the platinum group elements pge and au over the 2000 m of sampled stratigraphy is au 2 1 ppb pd 1 7 ppb pt 1 7 ppb rh 0 18 ppb ru comparison of the composition of the marginal rocks of the bushveld with a weighted average for the complete 6 km of the bushveld cumulates shows that the cumulate pile is much richer in compatible elements ir rh cr and poorer in incompatible elements sm and hf than the marginal rocks two possible solutions to this are a the magma emplaced into the chamber was a crystal mush and thus more mafic than marginal rocks to the intrusion or b fractionated magma has been removed from the cumulate sequence and either irrupted or intruded the country rocks as granites and granophyres

two expressions of the transition from mafic cumulates to granitoids in the bushveld complex south africa examples from the western and eastern limbs 2020 elsevier b v in the bushveld complex of south africa numerous granitic and granophyric rocks termed the lebowa granite and rashoop granophyre suites respectively overlie the layered ultramafic mafic rocks of the rustenburg layered suite despite their close spatial and temporal association the granites and granophyres are often interpreted as being unrelated to the rustenburg layered suite this paper describes the transition from the uppermost rustenburg layered suite into overlying granite and granophyre at three locations in the western the bierkraal drill core and eastern diepkloof farm and stoffberg town limbs of the bushveld complex in the western limb a 60 m thick transition zone bridges the petrological gap between the overlying nebo granite lebowa granite suite and upper zone rustenburg layered suite across the transition zone the composition of olivine changes from fo6 to fo1 clinopyroxene from mg 25 to mg 2 and plagioclase from an45 to an16 at stoffberg in the eastern limb the upper zone dioritic cumulates grade into the overlying monzonitic roof zone across the roof zone plagioclase compositions change from an42 to an4 clinopyroxene from mg 30 to mg 11 and olivine from fo9 to fo5 based on geochemistry and petrography we correlate the lowermost stratigraphy at the farm diepkloof with the stoffberg roof zone at diepkloof the roof zone grades into the overlying stavoren granophyre rashoop granophyre suite all units are indistinguishable in terms of bulk rock nd end 6 4 to 5 4 and hf ehf 9 2 to 6 6 isotopes corrected to 2055 ma similarly the upper main zone upper zone and transition zone are indistinguishable in terms of bulk rock sr isotopes 87sr 86sr 2055 ma 0 7071 to 0 7076 except one transition zone outlier at 0 7058 we submit that the transition zone represents the fossil record of bulk and or diffusional mixing between coexisting upper zone and nebo granite magmas we test this hypothesis by combining field petrographic and geochemical observations with forward modelling using the rhyolite melts algorithm our work on the bierkraal core western limb shows that at least a portion of the granitic magma was emplaced before the residual liquid of the upper zone had solidified at stoffberg and diepkloof in the eastern limb where the granite is absent the roof zone underwent uninterrupted fractional crystallization

the origin of basic ultrabasic sills with s d and i shaped compositional profiles by in situ crystallization of a single input of phenocryst poor parental magma an attempt is made to develop an in situ crystallization model based on the concept of soret fractionation to explain the origin of commonly observed s d and i shaped compositional profiles in sills formed from a single pulse of phenocryst poor parental magma the model envisages that the various compositional profiles observed in sills can be interpreted in terms of different combinations of four principal units basal zone and layered series forming the floor sequence and top zone and upper border series constituting the roof sequence the basal and top zones represent mirror images of the layered and upper border series respectively and therefore are referred to as basal and top reversals it is proposed that the formation of basal and top reversals takes place through the non equilibrium soret differentiation of liquid boundary layers which form as a consequence of the temperature gradient imposed by the cold country rock in contrast the layered and upper border series originate predominantly through the crystal liquid boundary layers developing in equilibrium conditions the model permits the production of s d and i shaped compositional profiles from the same magma composition all that is necessary to produce a specific shape of compositional profile is an appropriate temperature gradient imposed by the cold country rock on the liquid boundary layers of a parental magma of a given composition

seismic precursor to instability induced by internal erosion in loose granular slopes fluidised landslides are one of the most dangerous types of mass movements as they can run over long distances at high velocity a flow like landslide can occur in both artificially designed and na

a new approach to soil characterisation for hydrology stability analysis models abstract landslide stability analysis increasingly utilises high resolution coupled hydrology slope stability models chasm to improve stability assessments in areas subject to dynamic pore pressure regimes in such environments the estimation of soil hydraulic conductivity k is a key parameter but one which is not always readily available or determined with the required resolution by using basic soil particle size distribution psd data we evaluate the microscopic composition of the actual soil and applying the analytical relations obtain by a self consistent method scm approach we determine an appropriate value of k this is of importance in that it allows within soil type variability to be reflected in terms of k and hence within the model structure the scm methodology is briefly reviewed and an illustrative application is undertaken for a slope typical of hong kong the results show model output sensitivity in terms of moisture content and factor of safety fos when comparing k values determined using the scm approach and the conventional field determination in attempting to determine slope hydrological processes and attendant stability conditions we conclude that the application of scm approach offers a novel methodology for potentially improving the parameterisation of hydrology slope stability models

assessing the potential of internal instability and suffusion in embankment dams and their foundations suffusion is the process by which finer soil particles are moved through constrictions between larger soil particles by seepage forces soils susceptible to suffusion are described as internally unstable this technical note describes a method for assessing the potential of internal instability of silt sand gravel or clay silt sand gravel soils based on their particle size distribution based on laboratory tests carried out by the writers and results published by others it is shown that some commonly used methods are conservative for these soils

palaeomagnetic dating of widespread remagnetization on the southeastern border of the french massif central and implications for fluid flow and mississippi valley type mineralization summary palaeomagnetic dating techniques have been applied to determine the age of fluid migration that produced the mississippi valley type mvt pb zn ba f deposits in the cevennes region of southern france 15 sampling sites in two gently deformed areas around the largentiere and croix de pallieres mines on the cevennes border were selected for palaeomagnetic study they yielded a very well defined direction of remagnetization corresponding to an early middle eocene age this remagnetization cannot be related to the formation of magnetite as a result of the transformation of smectite to illite because the latter has been well dated as a mesozoic event the magnetic overprint in this area is related to a chemical phenomenon during fluid migration the age of remagnetization corresponds to a major uplift in the pyrenees mountains located to the south of the cevennes this implies that fluid migration occurred from the south to the north as a result of hydraulic head established in the pyrenees orogenic belt during orogenesis and suggests that the mvt deposits in the cevennes region formed from a gravity driven fluid system as described by garven freeze 1984a b

suffusion susceptibility investigation by energy based method and statistical analysis internal erosion is one of the main causes of instabilities within hydraulic earth structures four internal erosion processes can be distinguished and this study deals with the process of suffusi

emplacement and crystallization time for the bushveld complex the bushveld complex formed by the crystallization of successive basaltic magmatism may be of the order of several million years for example the columbia river basalts hooper injections of magma which were sufficiently closely spaced in time that each previous magma had not cooled and differentiated 1988 were erupted in the period 17 12 ma with minor eruptions for a further 5 my although most outpouring significantly before the addition of the next one to constrain the emplacement and crystallization times a thermal model is presented occurred within the first 2 my it is now recognized that large intrusions were not emplaced in a single pulse but which permits the investigation of the rate of cooling of magma in an intrusion repeatedly subjected to magma addition and subresult from multiple magma injection the question is how rapidly were magma chambers such as the bc traction such modelling indicates that magmas injected into the bushveld complex were emplaced within 75 000 years at that filled and how much magma was involved answers are relevant to the dynamics of melt production storage and time injection into the complex ceased the volume of rock in the eastern and western limbs is 370 000 600 000 km however transport in the mantle and crust this paper describes a thermal modelling technique not previously applied a quantitative evaluation of the cr budget in the formation of chromitite layers indicates that large volumes of magma cannot be to magma chambers which can be used to analyse this process and to obtain an estimate of the emplacement accounted for in the preserved rock sequence similarly an evaluation of the incompatible trace element abundances such as those for zr time to present this model it is necessary to discuss the stratigraphy size and connectivity of the different limbs and k suggests that the chamber was open and that large volumes of differentiated magma escaped the volume of magma therefore of the bushveld complex and to consider the extent of tapping of the magma chamber as well as its filling greatly exceeded the preserved volume of cumulate rocks giving an estimated magma volume of over 1 10 km an average the term bushveld complex has been given several meanings in the literature and according to the south emplacement rate of 13 km year is indicated by these calculations african commission on stratigraphy 1980 includes not only the ultramafic mafic layered rocks but also the sills beneath the intrusion volcanic rocks which pre date the

noritic dykes of southern west greenland early proterozoic boninitic magmatism two major swarms of early proterozoic ca 2 1 ga basic dykes occur within the archaean craton of southern west greenland one swarm comprises ophitic and sub ophitic tholeiitic dolerites while the other the bn dyke swarm constitutes mainly norites in which pyroxenes and olivine are enclosed by plagioclase oikocrysts the close geochemical similarity between a quenched norite and the coarser grained varieties indicates that the composition of the latter type has not been significantly modified by crystal accumulation the bn dykes are geochemically distinctive most having high mgo ca 16 cr and ni contents in conjunction with relatively high sio2 light rare earth ree and large ion lithophile lil element concentrations the texture mineral chemistry and petrochemistry of the quenched noritic dyke all bear strong resemblances to those features in modern boninitic lavas the bn dykes also correspond to proposed parental liquids of the bushveld complex and other major layered basic igneous intrusions the two dyke swarms are petrogenetically distinct the tholeiitic dolerites were derived from a relatively undepleted primordial mantle while the noritic dykes originated from a metasomatized harzburgitic source the wide spread distribution of similar proterozoic intrusions suggests crustal underplating by harzburgitic mantle on a world wide scale at this time

monitoring of internal erosion processes by time lapse electrical resistivity tomography abstract internal erosion phenomena are a major threat to all earthen structures such as river levees and dams studying these phenomena has been limited because they occur concealed inside the material which makes them difficult to observe and monitor non destructive geophysical monitoring techniques are powerful tools that can provide insight into the processes involved for this reason a test rig has been specifically designed to conduct three dimensional electrical resistivity tomography of soil specimens undergoing internal erosion due to seepage two suffusion tests were conducted where the erosion evolution has been monitored the time series of eroded mass weight were then used to correlate the changes in three dimensional resistivity distribution to the porosity change in media by means of archie s law the results from the first suffusion test were used to calibrate archie s model parameters it was found that the resistivity variations were able to predict changes in the porous matrix structure the data obtained from the second test were used to validate the model parameters and confirmed that the time lapse three dimensional inverted resistivity images were able to successfully quantify the global erosion rate

a felsic end to bushveld differentiation the similarities in age c 2 06 ga and isotopic composition of the bushveld igneous complex and the overlying rooiberg group felsic volcanic rocks suggest the possibility that the two are cogenetic to investigate this possibility we derive a robust new estimate of the major and trace element bulk composition of the bushveld upper zone and upper main zone uumz using melts thermodynamic modeling we show that this composition fails to reproduce fundamental features of the cumulate sequence such as the presence of primary orthopyroxene at the base of the magma column we investigate the possibility that some amount of evolved magma escaped from the magma chamber and derive a new estimate of the uumz parent magma composition that reproduces generally the observed cumulate sequence our results constrain the amount and composition of the escaped magma and provide evidence of a genetic link between the uumz of the bushveld layered series and the felsic volcanic rocks immediately overlying it we conclude that between 15 and 25 of the original magma volume was expelled and is manifest either as part of the upper rooiberg group lava sequence or the rashoop granophyre distinction is hindered by their almost identical major and trace element compositions a parent magma in which 15 25 rooiberg or rashoop material is added back to the extant cumulate sequence is initially saturated in orthopyroxene and is in major and trace element equilibrium with the phases at the base of the uumz