a further study on seismic response of a set of parallel rock fractures filled with viscoelastic materials the purpose of this study is to further investigate the seismic response of a set of parallel rock fractures filled with viscoelastic materials following the work by zhu et al dry quartz sands are used to represent the viscoelastic materials the split hopkinson rock bar shrb technique is modified to simulate 1 d p wave propagation across the sand filled parallel fractures at first the displacement and stress discontinuity model dsdm describes the seismic response of a sand filled single fracture the modified recursive method mrm then predicts the seismic response of the sand filled parallel fractures the shrb tests verify the theoretical predictions by dsdm for the sand filled single fracture and by mrm for the sand filled parallel fractures the filling sands cause stress discontinuity across the fractures and promote displacement discontinuity the wave transmission coefficient for the sand filled parallel fractures depends on wave superposition between the fractures which is similar to the effect of fracture spacing on the wave transmission coefficient for the non filled parallel fractures

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

holocene environmental variability the record from lago grande di monticchio italy abstract the holocene pollen record from lago grande di monticchio reveals environmental changes throughout the holocene comparison of this record with other records of holocene environmental variability indicates that there is a temporal correlation between these changes and north atlantic events however the nature of this relationship and the underlying mechanism s is yet to be determined it is evidently complex with the apparent coincidence of sea surface temperature cooling events with both species expansions and disappearances the picture is further complicated by the interaction between human activity and natural environmental changes

influence of paleotopography base level and sedimentation rate on estuarine system response to the holocene sea level rise the example of the marais vernier seine estuary france the response of coastal systems to allogenic forcing factors is of interest to diverse research communities including those interested in global change sequence stratigraphy and modelling quaternary systems are of particular interest because they provide analogues for ancient rock records to understand the processes responsible for the sedimentary evolution of estuarine systems it is necessary to study as many fluvial systems as possible the objective of this review of the sedimentary evolution of a coastal marsh is to describe the influence of glacial paleotopography on the record of climatic and sea level changes the marais vernier located at the interface between the marine and fluvial parts of the estuary is a part of the lower seine valley wetland network which formed after the last glacial maximum previous studies have described the holocene filling which is composed of peat and detrital material deposited following climatic and sea level changes to understand the sedimentary evolution a paleotopographical based on drillings and electromagnetic surveys and a chronological framework based on radiocarbon dates for the southern peat marsh were defined the peat marsh paleotopography has three erosional surfaces the s1 surface is the oldest and also the highest topographically the s2 surface is younger wider and incised below the s1 surface the s3 surface the youngest of the three is narrow and deeply incised radiometric ages were considered on the basis of their geographical position in relation to the s3 surface prior to 7 5 ka cal bp sediments accumulated only above the narrow area described by the s3 surface at a rate of 5 5 mm yr 1 after 7 5 ka cal bp shortly after the flooding of the seine estuary sediments accumulated as peat deposits over the entire peat marsh at a rate of 3 mm yr 1 in response to the sea level rise the paleotopography delimits the area of deposition during the holocene and thus plays a critical role in determining the vertical accretion rate expressed as a thickness prior to 7 5 ka cal bp the vertical accretion rate 5 5 mm yr 1 was less than that observed for the seine estuary 6 8 mm yr 1 however rate of sea level rise and sediment supply which also affects sediment accumulation rates vary in northwestern europe during the holocene therefore although the marais vernier is a good illustration of paleotopographic influence the effects of autocompaction sea level and sediment supply complicate efforts to quantify the degree to which it controls sediment accumulation

using rock eval 6 pyrolysis for tracking fossil organic carbon in modern environments implications for the roles of erosion and weathering this work relates to the debate on the fossil organic carbon foc input in modern environments and its possible implication for the carbon cycle and suggests the use of rock eval 6 pyrolysis as a relevant tool for tracking foc in such environments considering that such a delivery is mainly due to supergene processes affecting the continental surface we studied organic matter in different reservoirs such as bedrocks alterites soils and rivers in two experimental catchments at draix alpes de haute provence france samples were subjected to geochemical rock eval 6 pyrolysis investigations and artificial bacterial degradations after comparing the geochemical fingerprint of samples geochemical markers of foc were defined and tracked in the different reservoirs our results confirm the contribution of foc in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of foc during its exchange between these pools in addition the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter fom bedrock to river fluxes controlled by gully erosion are characterized by a qualitative and quantitative preservation of fom bedrock to alterite fluxes governed by chemical weathering are characterized by foc mineralization without qualitative changes in deeper alterites alterite to soils fluxes controlled by bio chemical weathering are characterized by strong foc mineralization and qualitative changes of fom thus weathering and erosional processes induce different fom evolution and affect the fate of foc towards the global carbon cycle in this study gully erosion would involve maintenance of an ancient sink for the global carbon cycle while bio chemical processes provide a source of co2 finally this study suggests that rock eval 6 pyrolysis can be considered as a relevant tool for tracking foc in modern environments copyright 2006 john wiley sons ltd

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

spectrocolorimetric interpretation of sedimentary dynamics the new q7 4 diagram colour is a fundamental property of sediment and is often used for lithographic description to determine sedimentological structures facies etc however the sedimentary information contained in this parameter is difficult to extract because it is difficult to quantify colour can be quantified by spectrocolorimetry which provides very high resolution data quickly and non destructively when adapted to sedimentology spectrocolorimeters prove to be powerful tools due to their low purchase and maintenance costs and some are portable and easily used in the field several methods have been used to extract sedimentological data from colorimetric spectra first derivatives factorial analysis etc in the present study we first provide a review of the sedimentological application of spectrophotometers and after having described these methods their advantages and disadvantages we then describe a new tool called the q7 4 diagram abscissa l ordinates 700 400 ratio this new technique permits sedimentological units to be defined allows the identification of different sediment components and provides 5 distinct poles clayey deposits organic rich deposits chlorophyll a and by products altered organic matter deposits iron rich deposits carbonated deposits coupled with the analysis of first derivative spectra it is possible to distinguish different pigments linked to the degradation and or nature of the organic material chlorophyll a melanoidin etc the state of iron oxidation for example hematite and goethite like signatures and the nature of clays the q7 4 diagram permits rapid acquisition of high resolution data on changes of sediment dynamics in geosystems that have been subjected to highly varied climatic environmental conditions the instrument is non destructive easy to use and maintain portable for use in the field fast to implement is capable of high resolution and has a vast range of possible applications spectrocolorimetry appears to provide many advantages and could become an essential and robust tool for preliminary sedimentological studies

isotopic and noble gas study of chalk groundwater in the london basin england abstract the chemical and isotopic composition of groundwater from 52 sites in the london u k area was determined as part of a project aimed at assessing the spatial variation in the age of chalk groundwater and in determining the relationship between fracture and matrix groundwater in this dual porosity system systematic changes in groundwater chemistry take place in the downgradient direction in response to several chemical processes these processes include early concentration by evaporation and congruent dissolution of calcite followed by widespread incongruent dissolution and ion exchange in addition to local oxidation reduction reactions gypsum dissolution and saline intrusion as a result of the above processes chalk groundwater follows an evolutionary path from ca bicarbonate type to na bicarbonate type the age of chalk groundwater was modelled using14c 13c 3h 2h and 180 there is a general increase in the groundwater age in a downgradient direction with the oldest water found in n central areas of the basin groundwater in the unconfined zones and in areas s of the greenwich fault is almost entirely of unevolved modem composition carbon 14 modelling suggests that chalk groundwater in the s basin is generally less than 10000 a old while that in the north is generally between 10000 and 25000 a old the presence of3h in concentrations of up to 7 tu in groundwater which yields ages of several 1000 a however indicates that mechanisms exist for the rapid introduction of recent groundwater to the confined aquifer results of palaeorecharge temperature determinations using 2h 180 and noble gas analytical results suggest that significant devensian recharge did indeed occur in the aquifer a model of the development of the chalk recognizes that it is a classic dual porosity aquifer in which groundwater flow occurs predominantly in the fracture system the upper 50 m of the aquifer was flushed with fresh water during the 2 3 106 a of the quaternary and therefore meteoric water largely replaced the tertiary and cretaceous marine water that previously saturated the system most processes which control the chemistry of the groundwater occur in the matrix where the surface area is exceptionally high although fracture flow dominates the flow regime diffusion from the matrix into the fracture porosity controls the chemistry of chalk groundwater

the effects of historic abstraction of groundwater from the london basin aquifers on groundwater quality abstract the basal sands and chalk aquifers in the lee valley and enfield haringey areaas of north london have considerable potential for artificial recharge having been dewatered by groundwater abstraction since the late 1800s trials have been undertaken periodically since the mid 1950s however one of the drawbacks is the potential for developing poor quality groundwater as a result of pyrite oxidation in the basal sands analysis of pumped groundwaters from the basal sands has confirmed the presence of relatively high concentrations of dissolved so4 along with k ca total fe and li porewater chemistry profiles have been obtained from fresh cores through the basal sands and underlying chalk at four sites the site with the highest so4 concentration up to 33 000 mg 1 1 had a porewater ph of 3 45 and has remained dewatered owing to overpumping for more than 70 a water pumped from the chalk showed little evidence of these extreme conditions there was no overall correlation between the bulk pyrite or gypsum content of the sediment and the porewater so4 concentration within the sediment the principal mechanism governing the generation of so4 is the oxidation of pyrite which is present in small amounts the extremely high concentrations of so4 in the porewaters indicate that the extent of oxidation is controlled by the entry of air rather than the input of dissolved oxygen or nitrate in the groundwater or recharge water abstraction from the chalk aquifer over many decades has resulted in the dewatering of the overlying basal sands aquifer allowing air entry and has led to the localized oxidation of pyrite and the accumulation of poor quality porewater in the basal sands the rate of oxidation is probably greatest near to wells and boreholes which allow ready access of air the solutes produced are only available for abstraction after the water table has risen dilution with native chalk groundwater will tend to minimize potential water quality problems future oxidation will be minimized by maintaining a high water table

modelling the influence of solution enhanced conduits on catchment scale contaminant transport in the hertfordshire chalk aquifer catchment scale 40 km2 contamination of the chalk aquifer of hertfordshire by bromate emanating from a disused industrial site north of st albans represents the largest occurrence of point source groundwater contamination in the uk the influences of double porosity diffusive exchange and rapid transport along solution enhanced conduits complicate predictive modelling of contaminant transport to threatened public supply wells tracer testing indicates that solution enhanced flow routes exist beyond the surface distribution of dissolution features in hertfordshire more extensively than previously thought a quantitative conceptual understanding of this flow system has been incorporated into a spatially distributed equivalent porous media representation in modflow and mt3d ms the calibrated model reproduces essential features of the aquifer system including heads and flows seasonal responses and the timing and spatial distribution of observed tracer breakthroughs in the solution enhanced aquifer but does not fully capture the magnitude and form of tracer and bromate advance due to the influence of local solution enhancement and matrix effects detailed breakthroughs at receptors cannot be resolved at the coarse grid scale however the model is able to simulate general trends

characterisation of fractured carbonate aquifers using ambient borehole dilution tests abstract fractured carbonate aquifers derive their transmissivity essentially from a well developed network of solutionally enhanced fractures and conduits that can lead to high groundwater velocities and high vulnerability to contamination of water quality characterisation of the variation of hydraulic properties with depth is important for delineating source protection areas characterising contaminant fate and transport determination of the effectiveness of aquifer remediation and parameter estimation for models in this work ambient open borehole uniform and point injection dilution tests were conducted on observation boreholes in the unconfined cretaceous chalk aquifer of east yorkshire uk and interpreted in conjunction with other data via the implementation of a new work flow this resulted in the characterisation of flow in these boreholes and the inference of properties such as groundwater flow patterns and velocities in the surrounding aquifer formation our workflow allowed sections of open boreholes showing horizontal versus vertical flow to be distinguished and the magnitude of such flows and exchanges with the aquifer to be determined flow within boreholes were then used to characterise i presence and direction of vertical hydraulic gradients ii nature and depth distribution of flowing features iii depth interval porosity and permeability estimation of the flowing features from overall borehole transmissivity and geophysical image or caliper logs iv groundwater velocity estimation in the surrounding aquifer discrete flowing features were distributed across the range of depths sampled by the observation boreholes typically up to 45 60 mbgl but the majority were located in the zone of water table fluctuation marked by solutionally enlarged flow features quantitative interpretation of both uniform injection tracer distributed throughout the open borehole section and point injection slug of tracer introduced at targeted depth yielded vertical velocities within the borehole water column in broad agreement with those measured by flow logging depth specific fracture kinematic porosities inferred from the ambient dilution data combined with long interval pump test and geophysical log data ranged between 3 7 10 4 4 1 10 3 with an average of 2 1 10 3 these values were in excellent agreement with those from other methods applied to the same aquifer such as larger scale pumping tests a new approach to estimation of groundwater velocities from the dilution test data using externally measured hydraulic gradients gave inferred horizontal groundwater velocities ranging between 60 and 850 m day in full agreement with those from previously conducted borehole to borehole tracer tests these results confirm that the studied aquifer is karstic with rapid preferential pathways which have implication for flow and transport modelling and pollution vulnerability our study results indicate that ambient single borehole dilution approaches can provide an inexpensive and reliable approach for the characterisation of fractured and karstic aquifers

role of filling materials in a p wave interaction with a rock fracture the purpose of this study is to investigate the role of filling materials e g quartz sand and kaolin clay in the interaction between a p wave and a rock fracture the specific fracture stiffness reflects the seismic response of a filled fracture while the wave transmission coefficient describes p wave transmission across the filled fracture a series of experimental tests using a split hopkinson rock bar technique are conducted on artificial rock fractures that are filled with pure quartz sand sand clay mixtures with 30 50 and 70 clay weight fractions and a pure clay matrix the boundary conditions of the filled fracture i e the displacement and stress discontinuities are used in the method of characteristic lines to calculate the wave transmission coefficient in the time domain the analytical results agree well with the experimental results the specific fracture stiffness and the wave transmission coefficient decrease with increasing filling material thickness when the clay matrix completely fills the void space of the quartz sand the filled fracture exhibits the largest specific fracture stiffness and promotes p wave transmission in general the wave transmission coefficient is strongly related to the specific fracture stiffness regardless of the filling material composition or the filling material thickness c 2014 elsevier b v all rights reserved

correction for the siderite effect on rock eval parameters application to the sediments of lake barombi southwest cameroon abstract originally developed for use in the petroleum industry rock eval pyrolysis is a technique commonly applied to lake sediments to infer paleoenvironmental reconstructions the standard rock eval parameters provide information on the amount of total organic and inorganic carbon toc and minc respectively and are usually interpreted as proxies for the source aquatic or terrestrial of the primary production of organic matter hydrogen index vs oxygen index although this method usually provides valuable evidence the common presence of siderite in tropical lake sediments can alter the primary signal of the sedimentary organic matter som indeed the co2 and co released by the pyrolysis of siderite are integral to the calculation of the som related standard rock eval parameters in this study we analyze sediments from a core collected in the lake barombi southwest cameroon and describe the impact of siderite on standard rock eval parameters we propose a workflow that allows standard rock eval parameters to be corrected based on the analysis of thermograms the proposed corrections provide siderite effect free parameters accurately reflecting the changes in sedimentary organic matter composition

introduction groundwater resources modelling a case study from the uk ion on a nearby wetland in shepley m g whiteman m i hulme p j grout m w eds groundwater resources modelling a case study from the uk geological society london special publications 364 333 351 gooddy d c besien t 2007 introduction to the nitrate papers quarterly journal of engineering geology and hydrogeology 40 333 hughes a g van wonderen j j rees j g seymour k j manful d karl h 2012 how to get your model results used a guide to stakeholder engagement in shepley m g whiteman m i hulme p j grout m w eds groundwater resources modelling a case study from the uk geological society london special publications 364 39 48 hulme p j jackson c r atkins j k hughes a g mansour m m seymour k j wilson k 2012 a rapid model for estimating the depletion in river flows due to groundwater abstraction in shepley m g whiteman m i hulme p j grout m w eds groundwater resources modelling a case study from the uk geological society london special publications 364 289 302 hutchinson m j ingram r g s grout m w hayes p j 2012 a successful model 30 years of the lincolnshire chalk model in shepley m g whiteman m i hulme p j grout m w eds groundwater resources modelling a case study from the uk geological society london special publications 364 173 191 ingram r g s stone n carey m smart p l 2012 catchment scale water balance modelling in a carboniferous limestone aquifer in shepley m g whiteman m i hulme p j grout m w eds groundwater resources modelling a case study from the uk geological society london special publications 364 249 267 jones m a hughes a g jackson c r van wonderen j j 2012 groundwater resource modelling for public water supply management in london in shepley m g whiteman m i hulme p j grout m w eds groundwater resources modelling a case study from the uk geological society london special publications 364

influence of large scale inhomogeneities on a construction dewatering system in chalk large scale anisotropy and inhomogeneities resulting from the presence of fissures fractures and high permeability zones can have a major impact on local groundwater flows and affect significantly the performance of a construction dewatering system a groundwater model for the hs1 channel tunnel rail link thames tunnel southern approach excavation is used to show that the observed performance of the construction dewatering system cannot adequately be explained unless such features are incorporated while experience suggested that such features were likely to be present in this geological setting at the design stage there was significant uncertainty regarding their scale groundwater flow modelling enabled the location and extent of the inhomogeneities present to be deduced in some detail features such as highly permeable zones might be identified by more thorough site investigation including the more widespread use of pumping tests however the influence of anisotropy is harder to establish primari

heterogeneous behaviour of unconfined chalk aquifers infer from combination of groundwater residence time hydrochemistry and hydrodynamic tools chalk groundwater is an important aquifer resource in france and also in much of northwestern europe large areas between the paris basin the london basin denmark and the northwest of germany as it is intensively exploited for human use with a large proportion reserved for drinking water the improvement of the knowledge on chalk aquifer hydrodynamical functioning and groundwater geochemistry is essential for the management of this resource to achieve this aim we developed a methodology based on a combination of hydrodynamic hydrochemistry and groundwater dating tools a study site of about 500 km2 was selected in ne france where chalk outcrops at 15 sampling points including boreholes and rivers mainly from chalk aquifer drainage groundwater geochemistry were monitored monthly for 2 years from june 2017 to june 2019 groundwater level in boreholes were monitored hourly with in situ water loggers in addition two sampling campaigns for the analysis of cfcs and sf6 have been conducted in boreholes in high and low water level periods to define the groundwater residence time the aquifer at the majority of sampling sites has an inertial behavior with respect to recharge as no impact of individual rainfall event was observed rapid piezometric response following rainfalls was observed at one site suggesting the presence of locally highly developed fracture network contrariwise high spatial and temporal heterogeneities of geochemistry was observed on the study area according to the mixing process piston flow exponential or binary mixing defined at each sampling site groundwater dating indicated rather heterogeneous ages ranging from less than 20 years to more than 50 years a combination of hydrogeological setting residence time and land use information was used to explain the hydrochemical heterogeneities highlighting the main factors governing the chalk groundwater geochemistry including water level fluctuation thickness of the unsaturated zone superficial formations distribution of fracture network aquifer river relations and human activities a conceptual model was proposed to clarify the hydrogeosystem functioning of unconfined chalk aquifers the proposed methodology can be used for the study of other worldwide aquifers chalk or not with the aim to provide appropriate recommendations in terms of water management

the hydrogeochemistry of methane evidence from english groundwaters the presence of methane ch4 in groundwater is usually only noticed when it rises to high concentrations to date rather little is known about its production or natural baseline conditions evidence from a range of non polluted groundwater environments in england including water supply aquifers aquicludes and thermal waters reveals that ch4 is almost always detectable even in aerobic conditions measurements of potable waters from cretaceous jurassic and triassic carbonate and sandstone aquifers reveal ch4 concentrations of up to 500 g l but a mean value of 10 g l however aquiclude and thermal waters from the carboniferous and triassic typically contain in excess of 1500 g l such high concentrations have so far only been found at redox eh potentials below 0 mv but in general ch4 concentration and eh value are poorly correlated this suggests a lack of thermodynamic equilibrium which is confirmed by comparing pe values calculated from the redox couple c 4 c 4 with those derived from eh genesis of ch4 appears to occur on two timescales a rapid if low rate of production from labile carbon in anaerobic microsites in the soil and a much longer millennium scale of production from more refractory carbon methane is rarely measured in groundwater there is no single ionic determinand which acts universally as a proxy but a combination of high hco3 and low so4 concentrations or the reverse is an indication that high amounts of ch4 may be present

advances in modelling groundwater behaviour in chalk catchments groundwater in chalk catchments is a major resource that also helps support internationally important habitats and ecosystems its dual porosity and dual permeability properties coupled with large scale structural features such as hard rock layers and marls produce a highly complex hydrogeological system recent impacts from groundwater flooding as well as vulnerability to drought have raised questions over the ability of traditional approaches to model these aquifers current work on near surface hydrological processes has highlighted the importance of the soil and weathered zone for controlling recharge rates in addition karst like features sedimentary deposits and valley bottom processes govern stream aquifer interaction and present a challenge in their representation in any modelling system methods that have and are being developed to incorporate these features and their use in modelling chalk catchments are described these are required in order to address major challenges such as groundwater flooding and drought impacts both of which could become more frequent and intense as a result of climate change

groundwater resource modelling for public water supply management in london in london groundwater abstractions for public supply are predominantly from the chalk aquifer however water resource pressures put existing abstractions at risk and often require complex analysis to support new source development thames water develops and uses regional groundwater models for such analysis to support communication with stakeholders such as the environment agency the environmental regulator of england and wales using two case studies the importance of regional models as thames water assets is demonstrated while thames water has developed regional models as a context for sub catchment scale analysis of groundwater source development they are subsequently used to address other issues as a result the models are updated regularly enhancing both conceptual understanding and calibration these models cost less than 1 of the capital cost of new water source schemes however as they are enhanced and applied more widely the models accrue further value as active decision support tools regional model usage to investigate a range of local systems and interactions is of particular value to thames water in this regard it is important to appreciate and promote the clarity and consistency generated when stakeholder specific issues can be analysed within an agreed regional model framework

systems tracts sedimentology in the lagoon of mayotte associated with the holocene transgression twelve gravity cores from various settings within the mayotte barrier reef lagoon complex were studied to determine the sedimentology of the sequence stratigraphic systems tracts that formed during the holocene transgression our studies focussed on the determination of physical chemical mineralogical and biological parameters of the sediments from specific systems tracts these parameters determine the thickness and facies of each systems tracts and are controlled by the rate and amplitude of sea level rise lagoonal topography and environmental changes the lowstand systems tract lst before 11 5 ka bp comprises ferralitic or organic rich paleosoils in the proximal and middle lagoon and karstified pleistocene reefal carbonates in the distal lagoon the transgressive systems tract tst 11 5 7 ka bp consists of a lower terrigenous and an upper mixed terrigenous carbonate or carbonate dominated unit locally mangrove muds were deposited the highstand systems tract hst can be divided into an early highstand ehst 7 1 ka bp and a late highstand systems tract lhst after 1 ka bp in the proximal lagoonal wedge the early highstand systems tract consists of terrigenous or mixed terrigenous carbonate muds to sandy muds in the middle lagoon it shows carbonate mud to sandy mud and carbonate gravel to reefal carbonates in the distal lagoons terrigenous muds dominate the late highstand systems tract in the proximal lagoonal wedge in the mid lagoonal plain mixed terrigenous carbonate or carbonate mud to sandy mud dominates while carbonate gravel to reefal carbonate prevails in the distal lagoon for the last 9 ka sedimentation in the lagoon of mayotte has been spatially divided into a proximal terrigenous and a distal carbonate dominated province maximum carbonate concentrations between 4 and 1 ka bp coincide with the time of maximum solar insolation after 1 ka bp a general decrease in carbonate concentrations can be observed this coincides with increased terrigenous sediment input which results from a reduction in accommodation space and to some extent is of anthropogenic origin

karstic behaviour of groundwater in the english chalk although the chalk is only weakly karstified tracer testing from stream sinks has demonstrated groundwater flow velocities comparable to those observed in highly karstic aquifers field survey of surface karst features in the catchments of the pang and lambourn rivers in southern england demonstrates the importance of overlying and adjacent palaeogene strata in the development of karst features tracer techniques employed within the catchments enable further characterisation of the range and connectivity of solutional voids in this area of the chalk and allow assessment of the relative importance of different mechanisms of contaminant attenuation quantitative tracer test results suggest that groundwater flow may be through a complex combination of small conduits typically 10 1000 mm in diameter and more laterally extensive fissures with apertures of 1 50 mm evidence of connectivity between conduits and fissures suggest that in areas of the chalk with rapid groundwater flow fissures supplying abstraction boreholes may be connected to karst conduit networks with low potential for contaminant attenuation

organic carbon sources and transformations in mangrove sediments a rock eval pyrolysis approach abstract a rock eval pyrolysis study was carried out on sedimentary cores and leaf and woody tissue of vascular plant species from the mangroves of french guiana these forests develop on moving mudbanks and have a lifetime limited to few decades before being eroded our main purpose was to complete the understanding of carbon cycling in this specific environment using a method that allows monitoring the depth evolution of sources and transformation of organic matter om within a tight depth span leaf and woody tissue showed clearly distinct rock eval parameters however these parameters strongly varied with om decomposition rapidly limiting their efficiency as mangrove plant tracers the decrease in values of tps2 pyrolysis temperature corresponding to the maximum release of hydrocarbons with depth clearly showed a line between a pedogenetic layer enriched in autochthonous om and marine sediments enriched in allochthonous om this allochthonous om originated from the particulate discharge of the amazon river which is partly deflected northwestwards by the current of the guianas within the soil layer decay processes induced a strong dehydrogenation and slight oxidation of om the two processes occurring simultaneously the deeper layers were characterized by a very strong increase in oico2 quantity of pyrolysed co2 relative to total organic carbon beneath both the young and the senescent forests this trend resulted rather from an increasing content of authigenic carbonate than from increasing concentration of oxidized allochthonous debris carbonate can form as a result of the more anoxic conditions prevailing in buried layers vs the upper suboxic ones beneath the senescent mangrove a greater increase in oico2 probably reflected greater carbonate precipitation resulting from the decomposition of higher amounts of om

palaeohydrogeological reconstructions of the north lincolnshire chalk uk for the last 140 000 years abstract the influence of climatic change on hydrogeology is investigated by studying the evolution of the north lincolnshire chalk aquifer system during the last 140 000 years a numerical modelling approach is adopted using a density coupled finite difference model to reconstruct past groundwater environments two major controls on groundwater circulation are considered the position of sea level which determines the base level condition and the amount of recharge associated with different climates the quaternary history of the region is used to define aquifer boundary conditions and climate analogue data are used to determine likely recharge amounts model results cannot be compared against groundwater flow volumes or head other than for the present day situation and so hydrochemical evidence is used to constrain the model simulations the main finding is that recharge to the chalk aquifer during the last 140 000 years has been restricted to periods when the climate and sea level position have been similar to those of the present day the devensian cold period experienced very minor recharge with no chalk permeability development forest clearance since about 5000 years ago is predicted to have permitted an increase in the volume of freshwater recharge which increased the rate of chalk permeability development the presence of saline water at depth in the aquifer is argued on the basis of the model behaviour to be contributed by a component of upward cross formational flow

modifications of chalk microporosity geometry during burial an application of mathematical morphology abstract the diagenetic evolution of chalk during burial has previously been established and can be summarized as follows 1 ooze deposition and dewatering burial 1000 m moreover chalk particles tend to increase in size as a result of diagenesis i e recrystallization or cementation as a result of compaction and cementation the shape size and connectivity of chalk microporosity evolve during burial however if the evolution of bulk porosity during burial is well quantified actual modifications of pore space topology are less understood quantifying pore space properties such as pore and throat sizes aspect ratio and spatial distribution usually require costly instruments as well as long and complex experimental procedures instead this study documents the application of mathematical morphology to investigate chalk microporosity from two dimensional 2d scanning electron microscope sem chalk samples n 105 have been collected from onshore quarries and offshore oil and gas reservoirs six chalk lithotypes are defined based on their mineralogical composition i e clay and silica content as well as the average size of chalk particles and their apparent diagenetic impact which appears strongly related to the mean grain size the latter is used as a proxy for the diagenetic overprint while the burial diagenetic model offers a framework for the different lithotypes and their respective pore space properties during intermediate burial 1000 m pressure solution and cementation become pervasive and produce large clusters of coalescent calcite crystals 3 10 m mean 5 13 m total porosity is strongly reduced as a result 6 11 while pore body and throat dimensions drop to 1 58 and 0 03 m respectively a high aspect ratio 88 1 and lower proportion of rough porosity relative to total image porosity suggest that throats are proportionally more affected than pore bodies cementation leads to less dendritic more globular and isolated pores where processes such as overpressure and oil charge have helped preserve porosity during deep burial 20 30 pore and throat dimensions were locked to moderately high values 2 0 and 0 1 m respectively even in silica and clay rich chalk since the geometry of microporosity exerts a major control on fluid flow reservoir modelling and recovery predictions could benefit from a better understanding on the geological controls on chalk microporosity not only can mathematical morphology quantify pore space properties that are fundamental in pore network and flow modelling but by being applicable on large datasets it could provide a new insight into the geological modifications of chalk microporosity during burial

analysis of water level response to rainfall and implications for recharge pathways in the chalk aquifer se england summary water table response to rainfall was investigated at six sites in the upper middle and lower chalk of southern england daily time series of rainfall and borehole water level were cross correlated to investigate seasonal variations in groundwater level response times based on periods of 3 month duration the time lags in days yielding significant correlations were compared with the average unsaturated zone thickness during each 3 month period in general for cases when the unsaturated zone was greater than 18 m thick the time lag for a significant water level response increased rapidly once the depth to the water table exceeded a critical value which varied from site to site for shallower water tables a linear relationship between the depth to the water table and the water level response time was evident the observed variations in response time can only be partially accounted for using a diffusive model for propagation through the unsaturated matrix suggesting that some fissure flow was occurring the majority of rapid responses were observed during the winter spring recharge period when the unsaturated zone is thinnest and the unsaturated zone moisture content is highest and were more likely to occur when the rainfall intensity exceeded 5 mm day at some sites a very rapid response within 24 h of rainfall was observed in addition to the longer term responses even when the unsaturated zone was up to 64 m thick this response was generally associated with the autumn period the results of the cross correlation analysis provide statistical support for the presence of fissure flow and for the contribution of multiple pathways through the unsaturated zone to groundwater recharge

sedimentary environmental changes and millennial climatic variability in a tropical shallow lake lake ossa cameroon during the holocene abstract the holocene environmental evolution of the shallow ossa lacustrine complex in cameroon is analysed on the basis of the present day sedimentary dynamics and principally by the study of five well dated cores sediment accumulation rates lithofacies and mineral content changes and various tracers of flux provenance are considered in connection with the pollen data at the shallower sites 1 2 m water depth during the dry season a moderate rise in lake level may have induced the transition from hydromorphic marshy conditions gleys to lacustrine conditions muds ca 8000 cal bp at the easternmost site a moderate fall may have generated the opposite process ca 7000 cal bp in the near northern part a marked decrease in sediment accumulation rate between 5000 and 3000 cal bp is apparent in some cores coinciding with an increasing discontinuity of the particulate supply during this interval the weakening of monsoon rainfall is associated to an increasingly seasonal regime characterized by lower and sporadic fluxes this decrease corresponds to a northern shift of equatorial climatic conditions with the main dry season occurring during the boreal summer during the time interval between ca 2800 and 2000 cal bp the return of tropical climatic conditions induced the opening of the vegetation associated with more intensive erosion increasing cyperaceae may indicate flooding of areas suitable for colonisation until 2800 cal bp the first overflow of the sanaga river into lake ossa occurred after ca 5800 cal bp with a ne sw depositional axis of coarse material transport of suspended matter in the surface waters northward was probably induced by prevailing sw winds the timing of this climatic evolution is independently supported by other lake sediment records from the forest domain of west africa and can be compared with other cyclical phenomena such as bond and dansgaard oeschger as well as solar oscillations

recharge of the upper chalk aquifer at a site in hampshire england 1 water balance and unsaturated flow abstract measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of upper chalk at a site in southern england are described measured evaporation continued at the penman potential rate until the soil moisture deficit reached 175 mm this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used the field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed the mechanisms of water flow through the unsaturated zone of the chalk are examined and it is shown that at this upper chalk site matrix flow is the dominant recharge mechanism

three dimensional flow and trace metal mobility in shallow chalk groundwater dorset united kingdom abstract the three dimensional groundwater flow and the hydrogeochemical regime have been determined in the bere stream valley north dorset downs southern england the dual porosity characteristics of the portsdown chalk have been established using geophysical and hydrochemical borehole logging chemical properties have been established using major and trace element analyses of depth samples and groundwaters the study site is located at the unconfined confined boundary of the chalk aquifer where it is overflowing in the observation boreholes the chalk dips locally at about 5 m km to the south east under palaeogene confining beds and three distinctive flow horizons may be recognised the chalk groundwater is of ca hco 3 type and three separate geochemical groundwater zones were also determined with depth having different oxygen levels and trace element characteristics 1 a shallow o 2 rich zone with around 80 dissolved o 2 and low trace element concentrations 2 a mixing and transition zone with significant concentrations of trace elements and high trace metal concentrations at its base manganese 29 g l nickel 55 g l cadmium 146 g l and zinc 214 g l 3 a deeper zone with depleted oxygen 5 20 dissolved o 2 and with longer water residence times shown by higher mg ca and k na ratios as well as higher sr and f the groundwater geochemistry in the chalk aquifer is dominated by incongruent reactions with the fine grained carbonate sediments which release trace element impurities to the water some of the metals are co precipitated with mn and fe oxide phases on fissure surfaces whilst producing a purer calcite during subsequent recrystallisation to purer iron and manganese oxides on fissure surfaces under specific geochemical and hydrodynamic conditions trace metals are released into the fissure water the results demonstrate the need to monitor quality stratification and the changes in the groundwater baseline chemistry in areas close to the redox boundary which in the dual porosity chalk is likely to be a diffuse zone with exchange between oxygen poor matrix waters and more oxic water flowing through the fissures

catchment scale tracer testing from karstic features in a porous limestone tracer testing was undertaken from sinking streams feeding the chalk a porous limestone aquifer characterised by frequent small scale surface karst features the objective was to investigate the nature and extent of sub surface karstic development in the aquifer previous tracer testing has demonstrated rapid flow combined with low attenuation of tracer in this study at two sites rapid groundwater flow was combined with very high attenuation and at two other sites no tracer was detected at springs within the likely catchment area of the stream sinks tested suggesting that tracer was totally attenuated along the flowpath it is proposed that the networks beneath stream sinks in the chalk and other mildly karstic aquifers distribute recharge into multiple enlarged fractures that divide and become smaller at each division whereas the networks around springs have a predominantly tributary topology that concentrates flow into a few relatively large cavities a morphology with similarities to that of the early stages of karstification tracer attenuation is controlled by the degree to which the two networks are directly connected in the first state there is no direct linkage and flow between the two networks is via primary fractures in which tracer attenuation is extreme the second state is at a percolation threshold in which a single direct link joins the two networks a very small proportion of tracer reaches the spring rapidly but overall attenuation is very high in the third state the recharge and discharge networks are integrated therefore a large fraction of tracer reaches the spring and peak concentrations are relatively high despite the large number of stream sinks that recharge the chalk aquifer these results suggest that sub surface conduit development may not always be continuous with flow down smaller fissures and fractures causing high attenuation of solutes and particulates providing a degree of protection to groundwater outlets that is not seen in more highly karstic aquifers bacteriophage tracers that can be detected at very large dilutions 1015 are recommended for investigating groundwater pathways where attenuation may be high

dynamic response of a rock fracture filled with viscoelastic materials rock fractures filled with viscoelastic materials such as sand usually contribute to rock mass instability under the influence of seismic waves and dynamic loads the purpose of this study is to verify that the specific fracture stiffness and the specific initial mass of the filling sand are two key fracture parameters in interrelating the physical mechanical and seismic properties of a rock fracture filled with dry sand a series of dynamic tests using a split hopkinson rock bar was conducted on a simulated sand filled fracture the experimental results show that stress wave attenuation across the filled fracture is strongly affected by wave reflection and transmission at the fracture interfaces and the dynamic compaction of the filling sand with the comparison between the analytical predictions by the displacement discontinuity model and the displacement and stress discontinuity model and the experimental results from the laboratory tests it is found that both models can predict a filled fracture with a smaller thickness i e less than 10 mm the displacement and stress discontinuity model may be used to predict a fracture with a larger thickness by considering the specific initial mass of filling materials the wave transmission coefficient for a filled fracture generally increases with increasing specific fracture stiffness

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

late holocene paleoclimatic changes in western central africa inferred from mineral abundance in dated sediments from lake ossa southwest cameroon abstract minerals derived from catchment soils were determined using ftir spectroscopy in the well dated core ow4 from lake ossa a lowland rainforest area in cameroon this quantification provides a hydrologic record indicating that the magnitude of runoff events and by inference rainfall pattern has varied during the late holocene the comparison between minerogenic inputs and vegetation changes improves the understanding of the inferred climate dynamics since at least 5400 cal yr b p the paleomonsoon rainfall intensity decreased as shown by a general decrease in mineral fluxes this observation is consistent with a gradual weakening of the boreal summer insolation in tropical latitudes however the major vegetational change lags behind the onset of the decrease in mineral fluxes from 2800 to ca 1000 cal yr b p the forest receded the amount of rainforest taxa decreased and is replaced by pioneer trees and poaceae when the mineral fluxes attained their lowest values this episode of maximum dryness is attributed to an abrupt climatic event of global significance which is superimposed onto the paleomonsoon variability it is related to a cold event which in turn produced a change in the lower atmospheric circulation that was characterized by a strengthening of northern trade winds probably correlated with sea surface temperature variations in the eastern tropical atlantic area

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

the nature and distribution of flowing features in a weakly karstified porous limestone aquifer the nature and distribution of flowing features in boreholes in an area of approximately 400 km2 in a weakly karstic porous limestone aquifer the chalk was investigated using single borehole dilution tests sbdts and borehole imaging one hundred and twenty flowing features identified from sbdts in 24 boreholes have densities which decrease from 0 3 m 1 near the water table to 0 07 m 1 at depths of more than 40 m below the water table the average density is 0 20 m 1 there is some evidence of regional lithological control and borehole imaging of three boreholes indicated that most flowing features are associated with marls hardgrounds and flints that may be developed at a more local scale borehole imaging also demonstrated that many flowing features are solutionally enlarged fractures suggesting that even in carbonate aquifers where surface karst is developed on only a small scale groundwater flow is still strongly influenced by dissolution fully connected solutional pathways can occur over 100s sometimes 1000s of metres however conduits tubules and fissures may not always be individually persistent along a flowpath instead being connected together and also connected to unmodified fractures to create a relatively dense network of voids with variable apertures 15 cm groundwater therefore moves along flowpaths made up of voids with varying shape and character local solutional development of fractures at significant depths below the surface suggests that mixing corrosion and in situ sources of acidity may contribute to solutional enhancement of fractures the study demonstrates that single borehole dilution testing is a useful method of obtaining a large dataset of flowing features at catchment regional scales the chalk is a carbonate aquifer with small scale surface karst development and this study raises the question of whether other carbonate aquifers with small scale surface karst have similar characteristics and what hydrological role small scale dissolutional features play in highly karstic aquifers

high resolution seismic stratigraphy of a narrow bedrock controlled estuary the guadiana estuarine system sw iberia abstract the late quaternary sedimentary architecture of the guadiana estuary southwestern iberian peninsula a narrow bedrock controlled estuary with moderate sediment supply was studied by applying concepts of high resolution seismic stratigraphy the estuarine sedimentary infill consists of a discontinuous basal interval overlain by five seismic units bounded by laterally continuous seismic horizons the correlation between seismic facies and a stratigraphic section of the guadiana valley enables the proposal of a detailed sequence stratigraphic interpretation of the estuarine infill during the last glacial lowstand the guadiana was a subaerial valley with no significant accumulation of fluvial deposits because of increased sediment bypass towards the present day middle and outer shelf towards the end of the postglacial transgression the subaerial valley was transformed into an estuary and sediments began preferentially accumulating in structural depressions furthermore flood tidal currents constrained by basement highs enhanced sand deposition in the upper part of the estuary wave influence was reduced and confined to the lower estuarine system here the narrow morphology of the valley led to an increased sediment export to the shelf during the holocene highstand period the lower part of the estuarine infill consists of four fifth order depositional sequences composed of regressive deposits hst the last glacial maximum is recorded by a distinct stratigraphic surface representing simultaneously the sequence boundary and the transgressive surface a tidal ravinement surface is characterized by strong erosion and channel formation in the outer estuarine zones the maximum flooding surface is identified by change of stratal patterns between landward prograding transgressive deposits and downlapping highstand deposits both transgressive tst and regressive tracts hst were deposited during the final part of the postglacial transgression and subsequent highstand

understanding groundwater sources and movement using water chemistry and tracers in a low matrix permeability terrain the cretaceous chalk ulster white limestone formation northern ireland abstract the cretaceous chalk ulster white limestone formation uwlf in northern ireland has been diagenetically altered to a hard low porosity low matrix permeability rock it subcrops extensive beneath thick horizontal tertiary basalt lavas but has a restricted strip of outcrop approximately 80 km2 around the periphery of the overlying igneous rock despite its nature and location numerous springs issue from the chalk and are used for public and local supply although little is known about the origin of the groundwater or the type of flow within the chalk we have addressed these unknowns using hydrogeochemical data from both rock types and surface stream waters and fluorescent dye tracing we have demonstrated that leakage recharge from the basalt to the chalk accounts for less than 20 of the total water issuing from the chalk springs using geochemical mass balance of conservative species and discharge data the majority of the discharge derives from streams coming off the basalt and entering sink holes in the chalk aquifer field and water tracing evidence shows that groundwater flow in the chalk is dominated by conduit and fissure flow near to the outcrop areas karstification has been widespread near outcrop but has not ocurred in the sub basalt region beneath the basalts the chalk exhibits different hydraulic properties due to the reduced recharge and dissolution potential that has prevented extensive development of fissure permeability in the uwlf the chalk aquifer thus appears to be strongly zoned in terms of the source of water flow regime and recharge rate

decadal record of climate variability spanning the past 700 yr in the southern tropics of east africa biogenic silica profiles in varved sediments from northern lake malawi nyasa east africa span the past 700 yr and reflect past primary productivity in the overlying waters on a centennial scale this has been influenced by lake level and a consequent shift in the location of high diatom productivity within the lake basin primary production was higher during the little ice age an arid period from about a d 1570 to 1850 when lake level was about 120 m lower than during the previous three centuries or the past 150 yr

evidence for a shallow highly permeable zone in the chalk of hampshire u k abstract studies of the chalk in the u k in the last 10 15 years have shown that it is generally the top 20 50 m below the water table which provides most of the aquifer yield an investigation in hampshire in connection with a river augmentation scheme using seasonal groundwater abstraction shows the chalk in the area to have a particularly thin and well developed 6 m thick zone possessing both high transmissivity and storativity evidence is put forward to support its existence

environmental responses to lateglacial climatic fluctuations recorded in the sediments of pre alpine lake mondsee northeastern alps investigation of the sedimentary record of pre alpine lake mondsee upper austria focused on the environmental reaction to rapid lateglacial climatic changes results of this study reveal complex proxy responses that are variable in time and influenced by the long term evolution of the lake and its catchment a new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub annual resolution for mu xrf element scanning carbon geochemistry stable isotope measurements on ostracods pollen analyses and large scale thin sections for microfacies analysis the holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometric 14 c dating of terrestrial plant macrofossils whereas the lateglacial age model is based on delta 18 o wiggle matching with the greenland ngrip record using the gicc05 chronology microfacies analysis enables the detection of subtle salimentological changes proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing comparing periods of major warming at the onset of the lateglacial and holocene and of major cooling at the onset of the younger dryas reveals differences in proxy responses reflecting threshold effects and ecosystem inertia temperature increase vegetation recovery decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the holocene took place with only decadal leads and lags over a ca 100 a period whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the lateglacial interstadial by ca 500 750a cooling at the onset of the younger dryas is reflected by the simultaneous reaction of delta 18 o and vegetation but sedimentological changes reduction of endogenic calcite content increase in detrital flux were delayed by about 150 300 a three short term lateglacial cold intervals corresponding to greenland isotope substages gl 1d gl 1c2 and gl 1b also show complex proxy responses that vary in time copyright c 2011 john wiley sons ltd

spectrophotometer analysis of holocene sediments from an anoxic fjord saanich inlet british columbia canada abstract a borehole core through the holocene sediments of saanich inlet british columbia canada was analyzed using high resolution spectrophotometry to determine whether spectral signal variations can be used as environmental climatic proxies the effects of post drilling oxidation and water loss on the core sample were assessed by comparing spectral measurements taken onboard the research ship immediately after the core was opened with shore based measurements taken one year later for saanich inlet sediments the shore based measurements provided more reliable indications of the degree of basin anoxia our spectral analyses allowed us to identify all the major features of the saanich inlet sediment sequence mazama ash and fraser river drainage stratigraphic markers oxygenation state of the basin by using the first derivative value at 675 nm as a proxy for changes in organic matter content and the colorimetric parameter b as an indicator of diatom content we were able to recognize changes in terrestrially derived organic matter om and diatom concentrations in the sediment we suggest that these variations are due to changes in upwelling intensity and fluctuations in sea level during the holocene our results confirm the potential value of spectrophotometry in identifying sediment composition and in reconstructing paleoenvironments

re evaluating dual porosity effects at the site of a seminal groundwater modelling study tilmanstone southern england the first numerical model of solute transport to incorporate fickian diffusive exchange between mobile fracture water and immobile porewater for an actual case of groundwater contamination at catchment scale was applied to the chalk aquifer at tilmanstone in se england by bibby water resources research 1981 17 1075 1081 the unconfined aquifer at tilmanstone had been contaminated by coalfield brine leaking from disposal lagoons operating throughout much of the twentieth century recent observations show that the bibby model underestimates dual porosity diffusive retardation and hence underestimates the persistence of contamination probably by several decades 2d representation of the aquifer in plan ignored the hydrostratigraphy and model calibration was limited by the lack of time variant paired profiles of fracture water and porewater vertical profiles through the chalk determined by packer testing borehole dilution testing and geophysical logging together with a new depth profile of chloride concentration in chalk matrix porewater are described the hydrostratigraphy is interpreted in relation to the chalk lithostratigraphy of se england and incorporated into a vertical section model of chloride transport along the axis of the valley consistent with the new and historical profiles of fracture water and porewater chloride concentrations new predictions of the longevity of the chloride contamination at tilmanstone are presented

characterisation of hydraulic head changes and aquifer properties in the london basin using persistent scatterer interferometry ground motion data in this paper persistent scatterer interferometry was applied to ers 1 2 and envisat satellite data covering 1992 2000 and 2002 2010 respectively to analyse the relationship between ground motion and hydraulic head changes in the london basin united kingdom the integration of observed groundwater levels provided by the environment agency and satellite derived displacement time series allowed the estimation of the spatio temporal variations of the chalk aquifer storage coefficient and compressibility over an area of 1360 km2 the average storage coefficient of the aquifer reaches values of 1 10 3 and the estimated average aquifer compressibility is 7 7 10 10 pa 1 and 1 2 10 9 pa 1 for the periods 1992 2000 and 2002 2010 respectively derived storage coefficient values appear to be correlated with the hydrogeological setting where confined by the london clay the storage coefficient is typically an order of magnitude lower than where the chalk is overlain by the lambeth group psi derived storage coefficient estimates agree with the values obtained from pumping tests in the same area a simplified one dimensional model is applied to simulate the ground motion response to hydraulic heads changes at nine piezometers the comparison between simulated and satellite observed ground motion changes reveals good agreement with errors ranging between 1 4 and 6 9 mm and being 3 2 mm on average

recent localised sulphate reduction and pyrite formation in a fissured chalk aquifer reply reduction oxidation reactions in the london basin aquifer system how may they be investigated

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

improved groundwater vulnerability mapping for the karstic chalk aquifer of south east england abstract the cretaceous age chalk of south east england forms an important aquifer within chalk the storage and transmission of groundwater is enhanced by subsurface karstic weathering the case study presented in this paper demonstrates that current approaches to assessing groundwater vulnerability to pollution and delineating source protection zones are flawed as they do not take proper account of the karstic nature of chalk improved techniques based on understanding the geological and geomorphological controls of karst development in chalk are proposed to overcome the shortcomings of published groundwater vulnerability maps the results also demonstrate the inadequacies of current groundwater modelling approaches for defining source protection zones the techniques follow european commission research recommendations by taking account of recharge presence of overlying cover deposits the nature of chalk karst and the way in which it influences the flow of groundwater the approach described allows for better informed decisions to be made about chalk aquifer management to ensure adequate protection and conservation of groundwater for example the published groundwater vulnerability map shows lambeth group deposits classified as being a minor aquifer of low groundwater vulnerability in the chosen study area however by applying the new techniques they are classified as having an aquifer vulnerability rating of moderate to very high when taking the karstic development of the underlying chalk into account

diagnostic tests for conceptualizing transport in bedrock aquifers transport in bedrock aquifers is complex because there is often substantial flow through fractures and the apertures and interconnectivity of these fractures are usually uncertain single porosity numerical models often give satisfactory results for simulating flow however simulating transport is more challenging and results based on single porosity assumptions can yield inaccurate results seven cases are reviewed where travel times were found to be unexpectedly short results show that dual porosity flow is common with advective flow through fracture networks and immobile storage in the matrix however in some cases a dual or multiple permeability or porosity approach provides better simulations of aquifer behavior fracture porosity of bedrock aquifers is usually 1 resulting in rapid groundwater velocities in many aquifers overestimation of the effective porosity is the most common reason for the overestimation of travel times residence times of artificial tracers in bedrock aquifers are typically two to three orders of magnitude less than residence times of environmental tracers because the latter are retarded by matrix diffusion fourteen diagnostic tests for determining the appropriate conceptual model for bedrock aquifers are described

influence of inherited paleotopography and water level rise on the sedimentary infill of lake ossa s cameroon inferred by continuous color and bulk organic matter analyses lacustrine records hold considerable archives providing access to valuable information however to decode this information it is necessary to know how the lake in question and its catchment area function in this study we propose to highlight the different factors that govern sedimentation by studying different core samples covering the holocene taken from lake ossa cameroon to do this we chose to use organic matter as a tracer of changes in sedimentation by coupling two complementary methods spectrophotometry for color measurement and rock eval pyrolysis for bulk geochemical analysis spectrophotometry is used classically to quantify color and obtain data very rapidly at very high resolution and non destructively rock eval data give geochemical indication on organic matter composition thus it was possible to highlight different types of organic matter at different stages of transformation including different sources that can be responsible of this transformation distal proximal autochtonous the synthesis of this information led to the formulation of a scenario of how lake ossa was filled although this lake had already been used for paleoclimatic environmental purposes we show here that most of the forcing responsible for the sedimentation in the lake was due to the paleotopography and the rise in the lake level during the holocene

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

a review of selected engineering geological characteristics of english chalk abstract chalk is a variable material the properties of which are dependent upon its composition textural features and diagenetic history with the exception of certain horizons in the lower chalk that contain appreciable amounts of clayey material the english chalk is a remarkably pure micritic carbonate rock that generally can be divided into coarse and fine fractions the latter comprises 70 80 of chalk cementation took place more or less contemporaneously with deposition so that the sediment was able to support relatively high overburden pressures hence high values of porosity were retained chalk varies appreciably in density and hardness the harder chalks are the result of diagenetic processes and bioturbation that brought about densification in soft chalks the grains are only bound together at the points of contact by thin films of calcite the latest classification of chalk is based on an assessment of intact dry density discontinuity aperture and discontinuity spacing chalk tends to vary from moderately weak to moderately strong and its strength is significantly reduced on saturation under triaxial loading conditions diagonal shear failure tends to occur at lower confining pressures but at higher confining pressures barrel shaped failure occurs indicating plastic deformation and textural disaggregation similarly at low loading chalk exhibits low volume compressibility but much more significant consolidation occurs if the yield stress is exceeded chalk undergoes dissolution and so solution features are found throughout its outcrop mineworkings in the chalk extend back into the distant past the most ancient being those excavated in the neolithic age for flint several types of workings exist collapse of old mineworkings most of which are unrecorded is difficult to predict the potential for subsidence caused by the collapse of both mineworkings and dissolution features affects development and its occurrence can lead to the abandonment of property or worse the loss of lives

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in