onset of recent rapid sea level rise in the western atlantic ocean a high resolution record of sea level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2 m thick salt marsh peat sequence at chezzetcook nova scotia canada former mean tide level positions are reconstructed with a precision of 0 055 m using a transfer function derived from distributions of modern salt marsh foraminifera our age model for the core section older than 300 years is based on 19 ams 14c ages and takes into account the individual probability distributions of calibrated radiocarbon ages the past 300 years is dated by pollen and the isotopes 206pb 207pb 210pb 137cs and 241am between ad 1000 and ad 1800 relative sea level rose at a mean rate of 17 cm per century apparent pre industrial rises of sea level dated at ad 1500 1550 and ad 1700 1800 cannot be clearly distinguished when radiocarbon age errors are taken into account furthermore they may be an artefact of fluctuations in atmospheric 14c production in the 19th century sea level rose at a mean rate of 1 6 mm yr between ad 1900 and ad 1920 sea level rise accelerated to the modern mean rate of 3 2 mm yr this acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming 2005 elsevier ltd all rights reserved

the use of jadammina macrescens brady and balticammina pseudomacrescens bronnimann lutze and whittaker protozoa foraminiferida as sea level indicators in studies of foraminiferal distributions in saltmarshes in new england and atlantic canada balticammina pseudomacrescens and jadammina macrescens have formerly been grouped as trochammina macrescens this study recognises them as distinct species and shows that they have significantly different distributions on the surface of saltmarshes in maine here relative abundances of j macrescens correlate with tidal elevation r2 0 55 p 0 00 whereas those of b pseudomacrescens do not r2 0 03 p 0 34 therefore j macrescens is a better sea level indicator in maine marshes than b pseudomacrescens in menunketesuck river marsh connecticut a clear vertical zonation of saltmarsh foraminifera is absent which hinders interpretation of fossil data this study shows that in maine separating b pseudomacrescens and j macrescens in counts of fossil data facilitates the detection of transgressional and regressional events in the biostratigraphical record and hence the reconstruction of local sea level histories regional variability between northern and southern new england saltmarshes necessitates the establishment of local reference sets of modern analogue data to aid palaeoecological interpretations

implications for sea level research of salt marsh and mudflat accretionary processes along paraglacial barrier coasts abstract paraglacial coastlines with dynamic coarse clastic barrier beaches are common in mid to high latitudes today and have been during the holocene sediments that have been deposited along these coastlines often in back barrier locations have been used to reconstruct relative sea level rsl movements and tendencies usually through the use of sea level index points derived frequently from salt marsh and mudflat deposits however the asymptotic relationship between minerogenic marsh mudflat accretion rates and time will produce regressive stratigraphies with a negative sea level tendency signature even within regimes of rising rsl the influence of gravel barriers on sedimentation will also tend to encourage regressive stratigraphies furthermore organogenic sediment production may release marsh accretion rates from the control of tidal inundation and result in succession to reed swamp despite rsl rise episodic minerogenic sediment supply to the marsh can trigger switches between marsh emergence and submergence which may result in stratigraphic sequences corresponding to negative and positive tendencies of rsl respectively although submergence may be prevented by organogenic sediment supply forcing by rsl rise may result in marsh emergence following initial submergence as a result of renewed accretion on the submerged marsh

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

spatial correlation length of normalized cone data in sand case study in the north of denmark the main topic of this study is to assess the anisotropic spatial correlation lengths of a sand layer deposit based on cone penetration testing with pore pressure measurement cptu data spatial c

vertical saltmarsh accretion and its relationship to sea level in the severn estuary u k an investigation using foraminifera as tidal indicators saltmarsh vertical accretion has been used as a proxy for sea level rise in previous studies on the assumption that accretion is in quasi equilibrium with sea level rise this assumption requires verification in each case as accretion may lag or exceed sea level rise leading to under or over estimates of sea level rise respectively verification may be provided by biostratigraphic analysis where biological remains in saltmarsh sediments may be related to former tide levels foraminifera are well suited as studies of modern saltmarshes have demonstrated distinct tidal relationships which may be used to calibrate downcore temporal foraminifera sequences it is hypothesized that depending on the relationship between sea level rise and accretion quasi equilibrium submergence and emergence foraminifera sequences may be recognized these are explored here in a severn estuary u k saltmarsh where an emergence foraminifera sequence is identified suggesting that previous sea level rise rates for the severn estuary based on saltmarsh accretion rates may be over estimates wider consequences of this may include over estimation of regional crustal subsidence rates required to accommodate artificially high sea level rise rates saltmarsh accretion rates are clearly not a suitable proxy for sea level rise in all cases and as such each saltmarsh requires biostratigraphic evaluation to establish sea level rise accretion relationships preferably independent sea level index points slips should be used over saltmarsh accretion rates in constructing sea level histories

organic carbon isotope systematics of coastal marshes abstract measurements of nitrogen organic carbon and 13c are presented forspartina dominated marsh sediments from a mineral marsh in sw netherlands and from a peaty marsh in massachusetts u s a 13c of organic carbon in the peaty marsh sediments is similar to that ofspartinamaterial whereas that in mineral marshes is depleted by 9 12 it is argued that this depletion in 13c of organic matter in marsh sediments is due to trapping of allochthonous organic matter which is depleted in13c the isotopic composition and concentration of organic carbon are used in a simple mass balance to constrain the amount of plant material accumulating in marsh sediments i e in terms of the so called net ecosystem production net ecosystem production 2 100 g c m 2year 1 is a small fraction 1 5 of plant production 2000 g c m 2year 1 this small amount of plant material being preserved is nevertheless sufficient to support marsh accretion rates similar to the rate of sea level rise

salt marsh accretion and sea level movement in the inner severn estuary southwest britain the archaeological and historical contribution the sea defences of the inner severn estuary may be dated partly by reference to historical sources and partly by the detection through field walking of early settlements on the reclaimed wetlands largely as the result of an intensive programme of levelling from reclaimed to active tidal marshes across dated defences it is shown that relative sea level c mean high water spring tides has risen in the area by at least 1 3 m since the later roman period the rise since c 1945 is given by a geochemical method which exploits the presence of metal pollutants in the deposits of the active marshes a marked acceleration in the upward movement of the relative level is suggested by the assembled data the minimum average rate of rise is apparently 0 40 mm a 1 between the later roman period and the medieval period 0 79 mm a 1 from then to the start of the modern period 1 49 mm a 1 through the modern period to c 1945 and 4 65 mm a 1 since c 1945 depending on the extent to which the severn estuary has experienced marine transgression over the period covered by the measurements the relative rise of mean high water spring tide level to the present could amount to about 1 75 m

long term accretion rates on tidal salt marshes abstract long term variations in salt marsh accretion rates were estimated using data collected on the marshes of the north norfolk coast england fourteen discrete marsh areas were sampled all lying within a 20 km stretch of coast the age of each marsh had previously been determined using radiocarbon or archival evidence for the date of vegetation inception on each marsh surface marsh ages ranged from 10 years to 2000 years the elevation of each marsh surface was determined in the field using levelling techniques the relationship between age and surface elevation was assumed to be a function of the rate of marsh accretion within this area of coast statistical tests showed this to be a highly significant relationship while the accretion rates calculated from the age height curve agree closely with field measurements on these marshes accretion rates were found to vary from 1 7 cm yr on 10 year old marshes to less than 0 002 cm on marshes older than 500 years the age height relationship describes an asymptotic curve with the asymptote lying 0 8 m below the level of the highest spring tides and appears to be controlled by the frequency of tidal maxima which peaks at 0 8 m below the maximum value and declines sharply above that height

late holocene sea level changes in eastern quebec and potential drivers abstract late holocene sea level changes can be reconstructed from salt marsh sediments with decimetre scale precision and decadal scale resolution these records of relative sea level changes comprise the net sea level contributions from mechanisms that act across local regional and global scales recent efforts help to constrain the relative significance of these mechanisms that include sediment dynamics and isostasy which cause relative sea level changes via vertical land motion ocean atmosphere processes that influence regional scale ocean mass redistribution and ocean cryosphere and steric interactions that drive global scale ocean volume changes there remains a paucity of high resolution late holocene sea level data from eastern canada this precludes an interrogation of the mechanisms that define sea level changes over recent centuries and millennia in a region sensitive to oceanic atlantic multidecadal variability atlantic meridional overturning circulation atmospheric north atlantic oscillation arctic oscillation and cryospheric ice mass balance changes we present new relative sea level data that span the past three millennia from baie des chaleurs in the gulf of st lawrence generated using salt marsh foraminifera supported with plant macrofossil analyses the accompanying chronology is based on radiocarbon and radionuclide analyses which are independently verified using trace metal and microcharcoal records relative sea level has risen at a mean rate of 0 93 1 25 mm yr 1 over the past 1500 years residual structure within the reconstruction internal variability has contributed up to an additional 0 61 0 46 mm yr 1 of short lived rsl rise prior to 1800 ce following a sea level low stand during the little ice age acceleration in relative sea level rise is identified between 1800 and 1900 ce within the estimates of internal variability and from 1950 ce to present in both the secular and residual trends phases of relative sea level changes in the gulf of st lawrence are concomitant with periods of glacier mass loss following the little ice age phase periods of the north atlantic oscillation and the atlantic meridional overturning circulation and northern hemisphere warming quantifying the individual effects of these different mechanisms is important for understanding how ocean atmosphere processes redistribute ocean mass upon larger scale background ocean volume changes

reconstructing relative sea level change using uk salt marsh foraminifera abstract the position of past sea levels can be reconstructed using a series of sea level index points that possess information on age location altitude and a quantified vertical relationship with a former tidal frame the indicative meaning whilst these points fix the altitude of relative sea level at one instant in time they provide no information on its variation between them here a foraminiferal transfer function is used to reconstruct changes in water depth from fossil assemblages preserved within salt marsh sediments the transfer function performs reliably in the high marsh zone where agglutinated foraminiferal species are dominant in lower marsh environments where calcareous species are prevalent postmortem test dissolution alters the fossil assemblages and leaves them without modern analogues to circumvent this problem a new transfer function based on agglutinated foraminifera and utilising preserved test linings is developed this new transfer function significantly reduces the number of samples without modern analogues but at the expense of diminished sensitivity in the low marsh environment additionally the transfer function is used to establish a series of sea level index points that place observed lateral shifts in depositional environment into a vertical and temporal context the combination of age altitude and high resolution water level reconstructions offers the potential to obtain more detailed and reliable records of relative sea level change from salt marsh sediments

influence of spatial variability of permeability property on steady state seepage flow and slope stability analysis in recent years spatial variability modeling of soil parameters using random field theory has gained distinct importance in geotechnical analysis in the present study commercially available finite difference numerical code flac 5 0 is used for modeling the permeability parameter as spatially correlated log normally distributed random variable and its influence on the steady state seepage flow and on the slope stability analysis are studied considering the case of a 5 0 m high cohesive frictional soil slope of 30 degrees a range of coefficients of variation cov from 60 to 90 in the permeability values and taking different values of correlation distance in the range of 0 5 15 m parametric studies using monte carlo simulations are performed to study the following three aspects i e i effect ostochastic soil permeability on the statistics of seepage flow in comparison to the analytic dupuit s solution available for the uniformly constant permeability property ii strain and deformation pattern and iii stability of the given slope assessed in terms of factor of safety fs the results obtained in this study are useful to understand the role of permeability variations in slope stability analysis under different slope conditions and material properties c 2009 elsevier b v all rights reserved

modelling spatial variability of soil parameters the purpose of this study is to show that geostatistics can help in finding the structure of the spatial variability of the undrained shear strength within a clay deposit the site under study b 6 owes its name to the earth dam that will be constructed on it the site is located on the shore of the broadback river in the james bay area of quebec the geostatistical analysis is carried out on the unaltered zone of the b 6 clay it shows an anisotropic structure for the spatial variability the knowledge of the structure variogram of the undrained shear strength is used in the kriging theory to compute estimations at points of the deposit where experimental measurements are not available kriging is also used to identify weak zones within the b 6 clay the geostatistical analysis of the b 6 clay gives the opportunity to test the capability of the method even if the errors of measurements were small the variogram has permitted detection and correction of a bias that affected a certain number of vane pr

a sea level rise curve from guilford connecticut usa abstract high resolution stratigraphic studies based on sediment chemistry lithology macroflora and benthic foraminiferal assemblages in three peat cores from coastal salt marshes at guilford connecticut show that coastal marshes are ephemeral environments marsh wide environmental variations were common and century long episodes of relative submergence alternated with emergence despite about 2 m of relative sea level rise rslr in connecticut over the last 1500 years the marshes have expanded both landwards and seawards and marsh accretion has been outpaced only marginally by rslr we used radiocarbon dating and the level of anthropogenic markers metal pollution as dated with 210 pb in the cores for age control for most of the last 1000 years the rate of rslr was between 1 3 and 1 8 mm yr but over the last 300 400 years it increased to 2 9 3 3 mm yr and has been faster than the accretion rate especially in the middle marsh the net submergence rate or submergence index ratio of the rate of rslr and marsh accretion rate averaged about 1 15 over the last 1000 years and increased to about 1 5 over the last 200 years the rate of rslr was very sluggish during the early part of the little ice age but we found a slightly higher rate during the little climate optimum this excursion is close to the noise level however the most significant observation is that rslr increased strongly around a d 1650 the onset of this acceleration falls in the middle to end of the little ice age and thus preceded the period of modern global warming that started late last century and that has been tentatively correlated with anthropogenic emissions of greenhouse gases

mid and late holocene sea level changes in roudsea marsh northwest england a diatom biostratigraphical investigation diatoms vascular vegetation sediment data and water salinity from contemporary intertidal environ ments in roudsea marsh northwest england are used to define altitudinal relationships between diatom assem blages and reference water levels comparison of these data with the high resolution diatom biostratigraphy of a fossil marsh sequence allows identification of fluctuations of relative sea level in the mid and late holo cene two oscillations in relative sea level are recorded a rise in sea level 0 6 m led to the inundation of the site after 6000 bp and was followed by a fall in sea level c 1 m around 4700 bp a second rise in sea level 0 5 m occurred before 2420 bp and was followed by a relatively stable or smaller rise of sea level during the last millennium the use of diatom groups based on marsh altitude was successful

probabilistic stability analysis of rainfall induced landslides considering spatial variability of permeability abstract many regions around the world are vulnerable to rainfall induced landslides a variety of methods have been proposed for revealing the mechanism of landslide initiation current analysis methods however do not consider the effects of non homogeneous soil profiles and variable hydraulic responses on rainfall induced slope failures in korea where the depth of weathering is very shallow many slope failures occur in the layer of weathered residual soil that overlays the bedrock these failures are characterized by shallow failure surfaces located near the interface between the weathered soil and the underlying bedrock in this study probabilistic stability analyses were conducted for a weathered residual soil slope with shallow impermeable bedrock to study the failure mechanism of rainfall related landslides a series of seepage and stability analyses of an infinite slope based on one dimensional random fields were performed to study the effects of uncertainty due to the spatial heterogeneity of hydraulic conductivity on the failure of unsaturated slopes due to rainfall infiltration the results showed that a probabilistic framework can be used to efficiently consider various failure patterns caused by spatial variability of hydraulic conductivity in rainfall infiltration assessment for a shallow infinite slope

ground and tunnel responses induced by partial leakage in saturated clay with anisotropic permeability abstract finite element analysis was conducted to study the ground and tunnel response to partial tunnel leakage coupled with anisotropic soil permeability a novel and little known approach that was developed from in situ inspections of shield tunnel leakage in the shanghai metro system the ground and tunnel settlements which were caused by water leaking into the tunnel significantly degraded both the serviceability and safety of the tunnel and its surroundings in a typical analysis such leakage is commonly assumed to be uniform along the tunnel circumference with a soil permeability that is isotropic numerical simulation results obtained in this paper indicated that partial tunnel leakage in only one side of the shield tunnel caused a greater pore pressure reduction at the tunnel spring line and a larger ground surface settlement than otherwise caused by uniform tunnel leakage with the same rate of water inflow indeed observations showed that partial leakage in only one side of the shield tunnel caused remarkable lateral movements of the tunnel our analysis showed that coupling leakage boundary conditions with favorable soil permeability anisotropy could significantly decrease the maximum ground settlements induced by the leakage which leads to an increase in the width of the surface settlement trough furthermore the effect of soil permeability anisotropy on ground settlement was found more profound for cases involving partial tunnel leakage boundary conditions

evolution of salt marsh cliffs in muddy and sandy systems a qualitative comparison of british west coast estuaries salt marsh cliffs in the muddy severn estuary are mostly strong and tall they are retreating in response to the erosive attack of wave and tidal currents chiefly through toppling failures and rotational slips in the sandy solway firth and morecambe bay systems marsh cliffs are strong only in their upper parts where a dense root mat of marsh grasses binds the sediments here cantilever and toppling failures are the main response of the cliffs to tidal and wave erosion the differences between the three estuarine systems in the mechanisms of marsh cliff erosion are partly reflected in the mode of preservation of the cliffs on the restoration of the conditions leading to renewal of marsh growth

flandrian sea level changes in the fenland i the geographical setting and evidence of relative sea level changes the flandrian sediments of the fenland record the infilling of the wash embayment on the east coast of england uk since at least 6500 bp changes in sea level have been a major control on the rate and pattern of sediment accumulation new data are presented from the area which together with published information allow the reconstruction of palaeoenvironments from 6500 to 2500 bp the major environmental changes involved alternations between freshwater fen and intertidal marine sedimentation each episode was characterised by transitional changes as vegetation and sediment zones shifted over large areas marine brackish sediments are found up to 45 km inland of the present coast radiocarbon dated sea level index points with relevant stratigraphic and micropalaeontological data ranging from 6415 bp at 8 17m od to 2595 bp at 1 45m od are described

large scale textural patterns and sedimentary processes on tidal salt marshes in the severn estuary southwest britain abstract approximately 840 km2 of largely reclaimed estuarine alluvium border the severn estuary and inner bristol channel today using a direct measure of grain size and the proxy evidence of sediment controlled early land use medieval early modern it is shown that the grain size of the tidal mud deposited on the marshes prior to reclamation declined outward from the main and larger tidal channels toward the bedrock limit of the alluvium variations in the altitude of the marsh surfaces as they survive after reclamation suggest that the deposition rate of this sediment also decreased outward from these sources at elmore a representative narrow ca 1 km marsh grain size change is steep and well defined in contrast at hill in a representative sector from a large and broad ca 5 km marsh the measured change is gradual and disorderly and disturbed by an extensive arcuate belt of relatively coarse sediments based on a review of processes and sedimentation and appealing to a broad geomorphological and hydraulic analogy between tidal wetlands and river floodplains it is suggested that marshes of the elmore type may be supplied with sediment largely by transverse diffusion from the tidal channel whereas hill type marshes may receive considerable mud by convection as well as diffusion

on the minimum amplitude of regional sea level fluctuations during the flandrian the mathematical form of a time height sea level curve representing intermediate frequency fluctuations superimposed on an underlying upward trend yields a simple method for estimating the minimum amplitude of fluctuations from field measurements of the thickness of silt peat couplets drawing on data from the thames estuary and the fenland basin fluctuations of relative sea level with minimum amplitudes between 0 08 m and 0 91 m seem to have occurred in the southeast british region during the mid flandrian 1997 john wiley sons ltd

on the postglacial isostatic adjustment of the british isles and the shallow viscoelastic structure of the earth summary observations of postglacial relative sea level rsl history at sites beyond the margins of the main accumulations of wu rm wisconsin devensian ice may be invoked to test the accuracy of global models of the glacial isostatic adjustment process the existing database of rsl time series for the british isles forms a continuous network of sites that sample the coasts of scotland england and wales fairly uniformly and which may be especially important in this regard not only are these 14c data for the holocene epoch of very high quality in terms of our knowledge of the coastal environment and relationship to palaeo sea level of each age measurement but they are especially numerous and relate to an island that was itself partly glaciated in the north essentially ice free in the south and located well outboard of the massive ice sheet that covered fennoscandia at the last glacial maximum lgm taken together the time series from 55 distinct locations allow us to perform a fairly stringent test of the recently formulated ice 4g vm2 global model of the isostatic adjustment process even without modification this model has been shown to fit most of the time series in the uk data set rather well in order to satisfy very recently published a priori constraints on the maximum thickness of the scottish ice sheet however we find that the lithospheric thickness the feature of the radial viscoelastic structure to which the rebound data from scotland are most sensitive must be somewhat reduced whereas the assumed thickness of the lithosphere in ice 4g vm2 was near to 120 km best fits to the scottish data require a lithospheric thickness near to 90 km this reduced value for lithospheric thickness agrees exceedingly well with the latest estimates of this earth property based on the inversion of oceanic geoid and topography data as the asymptotic thickness characteristic of the oldest ocean floor this would appear to be the best possible a priori estimate for the thickness of the cratonic lithospheres upon which the largest ice sheets of the late pleistocene are known to have rested we also demonstrate explicitly that inferences of the shallow viscoelastic structure beneath the british isles are strongly influenced by the details of the history of deglaciation at remote locations at antarctica in particular

a 17 yr record of sediment accretion in the salt marshes of maine usa abstract marker horizons of brick dust were established in 1986 in 26 salt marshes along the coast of maine usa in 2003 we measured the sediment accumulation rates for the 17 year period in 11 relocated sites and obtained results varying from 1 4 to 4 2 mm yr the mean accretion rate for all marshes was 2 8 mm yr accretion rates measured from 1986 to 2003 were comparable to those measured at the sites in 1987 and 1990 indicating that marsh accretion rates are similar on annual and decadal time scales inorganic material was found to be the primary constituent of maine salt marsh sediments several marshes show clear evidence of transgression since 1986 in the form of landward moving plant zones or encroachment of mudflat onto salt marsh indications for regressive changes were not observed marsh sediment accumulation rates are generally higher than mean rates of relative sea level rise indicating that most salt marshes are currently keeping pace with sea level rise however if relative sea level rise were to exceed rates of 4 mm yr many salt marshes in maine may not survive

constraints on measurement of sea level movements from salt marsh accretion rates the use of sediment accretion rates measured on coastal and estuarine salt marshes as a surrogate for rates of sea level change rests on the usually implicit assumption that marsh maturity is unchanged over the measurement period this assumption is inherently difficult to test empirically but a simple mathematical analysis shows that it is true only in a severely restricted case under most practical conditions measured accretion rates either over estimate or under estimate the rate of sea level change under certain circumstances they may indicate an upward trend when the tendency is actually downward a knowledge of marsh history is critical to the evaluation of such measurements sea level movements estimated from accretion rates are theoretically most reliable in the case of relatively old marshes and comparatively short measurement periods

milankovitch cyclicity and the boom clay formation an oligocene siliciclastic shelf sequence in belgium the boom clay formation of northeast belgium consists of a sequence of alternating laterally persistent beds of silt and clay power spectral analysis of grain size variations indicates regular sedimentary cycles with wavelengths of about 100 and 46cm that had periods of 124 and 57 thousand years ka or less the lateral continuity ofthe beds combined with the regularity and estimated periods of the cycles suggests an indirect link to the 100 and 41 ka orbital milankovitch cycles the variations in meangrain size were caused by changing bottom water turbulence as controlled by storms and or glacio eustatic water depth fluctuations this study confirms that certain marinesiliciclastic sequences can provide proxy records of palaeoclimatic variance

failure mechanism and bearing capacity of footings buried at various depths in spatially random soil abstract the objective of this paper is to demonstrate how the spatial variability of random soil affects the failure mechanism and the ultimate bearing capacity of foundations buried at various depths a nonlinear finite element analysis combined with random field theory is employed to explore the vertical capacity of foundations embedded at different depths in random soil different possibilities of shear failures resulting from spatial patterns of soil are demonstrated and are used to explain the significant discrepancy between the bearing capacity of the random soil and that of uniform soil the effect of the spatial pattern of the soil on the development of shear planes is also investigated with the coefficients of variation for the bearing capacity demonstrated to be closely related to the shear plane length the results of the statistical variation in the bearing capacity are provided for different embedment depths and these are also reported as the failure probability of the footing compared wit

the formation of coastal peat marshes under an upward tendency of relative sea level the upward growth of a tidal mudflat marsh within the tidal frame is determined theoretically by the rates of minerogenic sediment supply organogenic sediment supply long range sediment compaction and movement of relative sea level where the movement of relative sea level is upward a marsh can achieve a state of dynamic equilibrium in which the composition of the sediment accumulating on its surface is governed by the balance between the rates of organogenic supply and sea level change a peat organogenic marsh should arise where the former rate roughly equals or exceeds the latter a minerogenic marsh should form where the rate of sea level rise is dominant even though the absolute availability of mineral fine sediment may be so high as to appear to suggest that build up to extreme tidal levels where vegetation would dominate should have occurred

vertical salt marsh accretion since the roman period in the severn estuary southwest britain abstract using three methods of measurement and averaging over the whole estuary the vertical sediment accretion on mature clastic salt marshes amounts to 1 22 m since the roman period ca a d 150 1 05 m since the medieval period ca a d 1250 0 54 m since ca a d 1845 and 0 21 m since ca a d 1945 these data are cautiously interpreted to mean that the trend of relative sea level in the severn estuary is continuing upward shorter term negative tendencies are not excluded and that the current rate of rise could be a few millimetres per year the measured sediment thicknesses cannot be equated directly with relative movements of sea level however because of effects related mainly to 1 changes in the tidal range with general deepening 2 the possible transgression up the severn vale of the estuary as a whole and 3 the possible raising of tidal levels due to wetland reclamation after estimating for all these factors the true relative rise since the roman period could have amounted to 1 6 1 7 m

influence of spatial variability of soil young s modulus on tunnel convergence in soft soils abstract field data have shown the fact that soil spatial variability could aggravate the uncertainty of tunnel convergence d a key indicator for serviceability and safety of tunnels this paper presents a detailed numerical analysis to investigate the probabilistic response of tunnel convergence in spatially varied soft soils the soil young s modulus es is highlighted and modeled with isotropic and horizontally stratified anisotropic random fields respectively the influence of scale of fluctuation sof of the es on convergence d is discussed in detail with respect to different directions i e the vertical and horizontal directions both for and d it is observed that ignoring the spatial variability of es i e disregarding the possibility of unfavorable soft soil low stiffness soil locally around tunnel can underestimate the mean value of d the horizontally stratified anisotropic random field is more appropriate than isotropic random field in the sense of an accurate prediction especially when extreme tunnel convergence occurs in horizontally stratified anisotropic random fields the influence of horizontal and vertical sof is different on tunnel convergence the surrounding soils near tunnel crown and invert or across tunnel horizontal diameter are very critical to the tunnel convergence in addition the effect of horizontal sof x on failure probability of the calculated d exceeding the specified allowable dlim is limited when the x is larger than 4 84 times of tunnel outer diameter

flandrian sea level changes in the fenland ii tendencies of sea level movement altitudinal changes and local and regional factors stratigraphic micropalaeontologic and radiocarbon data show that since c 6500 bp the fenland has been influenced by 7 periods of positive sea level tendencies and by 6 periods of negative sea level tendencies despite the numerous problems associated with the reconstruction of past altitudes of sea level the periods of positive sea level tendencies were clearly characterised by a rise in sea level the development of transgressive overlaps and a landward movement of the coastline the periods of negative sea level tendencies were characterised by the development of regressive overlaps a seaward movement of the coastline and a reduced or negative rate of sea level rise the various altitudinal errors do not permit the incontrovertible distinction of periods of falling sea levels all changes within the fenland were not synchronous and local factors influenced the exact nature of each sea level indicator dominant regional and local factors have been identified for different areas and different time periods the chronological and spatial characteristics of the sequences within the fenland are best explained by a palaeocoastline without supratidal barriers controlling sedimentation the data indicate an average crustal subsidence in the fenland of 0 9m 1000 years since c 6500 bp and the pattern of positive and negative tendencies of sea level movement is also seen in the chronologies for north west england and north east scotland