growth by extension and reworking of a south western kalahari linear dune optically stimulated luminescence osl dating studies of linear longitudinal dunes have been used extensively to elucidate late quaternary environments and climates in arid or formerly arid regions yet understanding of the development of such dunes is incomplete in particular conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally the degree to which they rework their own sediment during accumulation and whether they form primarily by extension as opposed to lateral sand movement from adjacent interdunes this study focuses on this last point although the importance of the other controversies is discussed in context a simple linear dune in the south western kalahari which has a prominent termination on a pan playa surface provides an opportunity to directly test hypotheses of dune extension chronostratigraphy along a 600 m transect along the crest of the dune constrained by 42 osl ages reveals that the dune grew by extension on occasions in the late pleistocene and early holocene but has also been subject to reworking along its length which has continued until recent times dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation whereas reworking is largely independent of conditions throughout the last 18 ka and may represent seasonal fluctuations in the position of the dune crest the relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change copyright 2011 john wiley sons ltd

past tree cover of the congo basin recovered by phytoliths and δ 13 c along soil profiles abstract the tropical moist forests tmf of the congo basin are extremely diverse in terms of structure and functional diversity previous paleoecological work suggests that these forests have experienced dramatic changes over the last millennia related to climate or humans these disturbances still influence today s repartition of forests and savannas as well as species distributions the objective of this study is to explore the sensitivity of phytolith assemblages compared to the 13 c of soil organic carbon soc to reconstruct past tree cover of the present tmf large transects across different geological substrata and forest communities were explored in total 18 soil profiles were investigated for pedogenic features and 53 radiocarbon dates from soc and charcoals were obtained phytolith extractions from modern soils and along four soil profiles were performed the 13 c of soc and phytolith assemblages were interpreted in terms of tree cover changes one of the most interesting results highlighted by this study was the strong match between phytolith tree cover and the 13 c signal as it not only aids the interpretation of 13 c soil signals but also puts into question the transport behavior of phytoliths in soil by processes that are still poorly understood the 13 c soc method has been successfully used to study major vegetation changes in africa but has never been previously constrained with another proxy of tree cover this study confirms the value of a multi proxy approach to investigate past vegetation changes in african tropical moist forests and shows that soc 13 c and phytolith signatures in soil profiles display the same dynamics and are complementary they suggest that the majority of the present forested sites never experienced a true savanna phase

a volumetric approach for the resistivity response of freshwater shaly sandstones the dc electrical response of freshwater saturated shaly sandstone is analyzed on the basis of effective volume conductivity concepts for a concentrated mixture of solid grains in a continuous electrolyte the bulk conductivity of this model is physically controlled by 1 the effective porosity and the average electrical tortuosity of its free pore electrolyte and 2 the amount and concentration of bound water that coats charged solid surfaces mainly of clays and a corresponding averaged electrical surface tortuosity the latter is combined in an equivalent volume conductivity that is mainly due to the electrical double layers of charges developed at the clay electrolyte interfaces analytical expressions based on effective medium and general mixture theories are developed to describe both the whole rock conductivity and the specific conductivities of its constituent elements the derived equations for the bulk conductivity of the system describe with sufficient precision experimental core dat

bioturbation and the upward movement of sediment particles and archaeological materials comments on bueno et al the literature on bioturbation both from the biological and archaeological points of view is growing steadily available data suggests that ants and termites are responsible for the upward movement of soil sediment particles and archaeological materials it is argued that this could be the most parsimonious explanation for the stratigraphic data presented by bueno et al 2013 given the size range of displaced materials and the environmental setting composed of a sandy soil in a savannah region

impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir the case of the oolithe blanche formation bathonian paris basin france the oolithe blanche formation was studied in three quarries located at the south eastern edge of the paris basin france heterogeneities in reservoir properties were assessed through a sedimentological diagenetic and petrophysical study the relationships between depositional settings diagenesis and petrophysical properties were analysed using detailed petrographic studies image analysis nano ctscans and petrophysical measurements the carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso and macroporosity early cementation vs early compaction processes mainly grain interpenetration may have considerable influence on fluid flow properties and parameters such as permeability acoustic velocities and tortuosity better reservoir properties are found when compaction processes begin before cementation from statistical analyses e g principal component analysis and linear discriminant analysis a sedimentological diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work

a simple effective medium model for water saturation in porous rocks a general equation for water saturation is derived from effective medium theory a simpler low frequency equation is also derived both equations are directly solvable for water saturation the model should be applicable to any granular water wet formation additional relationships are derived specifically for application to shaly sandstones but the model should be applicable to a wide range of rock types water conductivities and tool frequencies in the derivation hydrocarbons are included in the matrix component of the equation and the combined matrix elements are treated as resistors in parallel the low frequency equation is compared to various approaches to calculation of water saturation such as dual water waxman smits and bussian the general equation is compared to three component effective medium porosity index and complex refractive index models crim the model is proven to work on experimental data under a wide range of frequencies and water conductivities it is recommended that

electrical efficiency a pore geometric theory for interpreting the electrical properties of reservoir rocks knowledge of the way pore geometry affects the conductivity of rocks is important for the evaluation of sedimentary rocks for hydrocarbon potential virtually all formation evaluation from logs however uses the empirical archie equation that has never been given a satisfactory physical basis as an alternative we have formulated a new model based on the efficiency with which water bearing rocks conduct electric currents as determined by the conducting phase geometry electric current densities are not uniform throughout the conducting phase in the pore system of a rock numerical model studies show high current density in pore throats and low current density in nearly stagnant volumes in isolated parts of the pore system the electrical efficiency of a rock is the ratio of the average power developed in all water bearing parts of the pore system to the power developed in a straight tube with the same length and water volume as the rock it is inherently independent of the bulk volume of water in the ro

quaternary ichnofacies model for paleoenvironmental and paleosealevel interpretations a study from the banas river basin western india abstract integration of data from ichnological and other interdisciplinary sources from the quaternary banas river basin india has permitted the reconstruction of a composite ichnofacies model for the interpretation of paleoenvironments and paleosealevels a glacioeustatic transgressive regressive system tract of the ancient arabian sea has been recognized from the superposition of ichnofacies the pleistocene shallow marine psilonichnus ichnofacies ichnogenus psilonichnus skolithos arenicolites and thalassinoides of infaunal polychaete crab and bivalve origin developed in the vadpag vend segment of the lower banas sequence corresponds to interglacial high sea stands the overlying late pleistocene holocene continental coprinisphaera scoyenia mixed ichnofacies paleosol association of delicate surficial traces of terrestrial insects and river floodplain association of aquatic traces of worms and crustaceans formed in the radhanpur varahi segment of the upper banas sequence represents the last glacial regressive mode of sealevel levee bound oriented crustacean burrows may be used as new ichnological tools to locate buried paleochannels and aquifers the juxtaposition of levees with alternate worm burrow and barren zones and floodplains with gastropod and barren zones indicates monsoonal lows and highs in the holocene the overprinting of the coprinisphaera elements on the scoyenia forms has resulted from the recent sub recent environmental degradations rising temperature spread of desert shrinking saltmarshes and weakened fluvial forces probably related to global warming and other greenhouse processes the readable ichnological signatures of the quaternary glacioeustatic sealevel fluctuations and consequent climatic changes qualify the banas model for wider application

age origin and climatic controls on vegetated linear dunes in the northwestern negev desert israel abstract the stabilized northwestern nw negev vegetated linear dunes vld of israel extend over 1300 km 2 and form the eastern end of the northern sinai nw negev erg this study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology stratigraphy and optically stimulated luminescence osl dating thirty five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and osl dating enabling spatial and temporal elucidation of the nw negev dunefield evolution in a global perspective the nw negev dunefield is relatively young though sporadic sand deposition has occurred during the past 100 ka dunes began to accumulate over large portions of the dunefield area only at 23 ka three main chronostratigraphic units corresponding to three osl age clusters were found throughout most of the dunefield indicating three main dune mobilizations late to post last glacial maximum lgm at 18 11 5 ka late holocene 2 0 8 ka and modern 150 8 years the post lgm phase is the most extensive and it defined the current dunefield boundaries it involved several episodes of dune incursions and damming of drainage systems dune advancement often occurred in rapid pulses and the orientation of vld long axes indicates similar long term wind directions the late holocene episode included partial incursion of new sand reworking of late pleistocene dunes as well as limited redeposition the modern sand movement only reactivated older dunes and did not lengthen vlds this aeolian record fits well with other regional aeolian sections we suggest that sand supply and storage in sinai was initiated by the late pleistocene exposure of the nile delta sands late pleistocene winds substantially stronger than those usually prevailing since the onset of the holocene are suggested to have transported the dune sands across sinai and into the northwestern negev our results demonstrate the sensitivity of vegetated linear dunes located along the northern fringe of the sub tropical desert belt to climate change i e wind and sediment supply

paleoethologic implications of zoophycos from late cretaceous and paleocene limestones of the venetian prealps northeastern italy large specimens of zoophycos are abundant in paleocene pelagic limestone successions in the vicinity of feltre and belluno in northeastern italy these burrow systems are familiar examples of the strongly ribbed downwardly spiralling version of the ichnogenus containing well developed primary and secondary lamellae marginal tunnels and poorly preserved axial structures some of the specimens contain fecal pellets rich in non carbonate mud and carbonized phytodetritus suggesting surface deposit feeding and organized subsurface storage of fecal material by the zoophycos producer other examples of the burrows record a departure from the normal behavioral pattern in the form of conspicuous radial tunnels that diverge from the axial region cut across structural elements and follow the laminae exactly to the outer margin this special feature of fully developed zoophycos appears to represent the last time the trace producers recycled the banks of fecal material possibly during long intervals of meager food supply at the deep ocean floor

subterranean ant nests trace fossils past and future many species of ants excavate complex species typical nests in soil the basic structural units of many nests are descending tunnels connecting flattened generally horizontal chambers of oval to lobed outline the species typical structure of many nests results from variation in the size shape number and arrangement of these basic elements nest architecture can be rendered by filling subterranean nests with a thin slurry of orthodontal plaster then excavating and reconstructing the hardened cast photographs of such nest casts of nine species of ants from northern florida show the range and type of variation of architecture preservation conditions under which ant nests could form complex trace fossils are discussed and reports of such traces reviewed the images presented in this paper will help to alert trace fossil specialists to the potential range of appearance of such nest fossils 2002 elsevier science b v all rights reserved

on the role of spatially correlated heterogeneity in determining mudrock sealing capacity for co2 sequestration abstract storing co2 in depleted hydrocarbon reservoirs is a common practice world wide mudrocks often serve as seals above these reservoirs due to their small pore throats and low permeability but they can fail if the buoyant pressure of the trapped fluid overcomes the threshold pressure of the seal mudrocks are primarily made of silt sized and clay sized particles and sufficiently high silt concentrations can create situations where the silt grains create a connected stress chain through the rock matrix which preserves the large pore throats under compaction this phenomenon termed silt bridging can reduce the threshold pressure of the mudrock causing seal failure we used grain scale modeling to create computer generated grain packs with and without the effect of gravity to understand the effects of deposition and compaction on the petrophysical properties like capillary pressure tortuosity permeability capillary drainage curves and spatial correlation of heterogeneities we found that when the fraction of silt sized grains exceeded 40 the percolation length the length of the first path of the non wetting fluid through a medium and the tortuosity suddenly decreased this was supported by the results from the throat size variograms where the same type of correlations between throats were observed at greater lag distances signifying increased intergranular distances our work provides an insight into the role of different grain sizes concentrations and spatial distributions on the flow properties and sealing capacity of mudrocks

coupled hydrogeophysical inversion to identify non gaussian hydraulic conductivity field by jointly assimilating geochemical and time lapse geophysical data abstract reliable inversion of spatial heterogeneity of hydraulic conductivity is crucial to understand subsurface fluids migration the ensemble smoother direct sampling method es ds has proven to be an effective method to identify non gaussian hydraulic conductivity distributions by incorporating a variety of traditional hydrodynamic measurements e g piezometric head however inversion problems for non gaussian parameters often suffer from a sparsity of the available data from direct sampling in boreholes as a non intrusive cost effective and high sampling density method time lapse geophysical technique has not yet drawn much attention as a useful source of information for delineating the underlying non gaussian heterogeneity in this study we integrated coupled hydrogeophysical modeling and the es ds algorithm to estimate non gaussian hydraulic conductivity field by assimilating both geochemical and time lapse geophysical datasets four synthetic cases for a salt injection experiment monitored by both sampling analysis and electrical resistivity tomography are conducted to assess the ability of the proposed approach to characterize hydraulic properties by assimilating different types of data results show that using geochemical or geophysical data alone only allow a rough reconstruction of subsurface heterogeneity of aquifers but might lose the fine structure by incorporating multi source datasets the main patterns of the non gaussian reference fields can be reflected with an improved resolution the time lapse geophysical methods open up new opportunities to accurately characterize non gaussian aquifers and monitor the dynamic processes of subsurface fluids

buried in ashes site formation processes at lapa do santo rockshelter east central brazil few archaeological sites in the americas contain high concentrations of human burials dating back to the early holocene the tropical karstic region of lagoa santa in central brazil state of minas gerais is one of the richest bioanthropological records available to study the behaviors and funerary practices of early holocene south americans with more than 200 skeletons found so far one of the key locations to examine the history of human settlement in lagoa santa is the site of lapa do santo a rockshelter known to contain the oldest rock art and the earliest evidence of funerary complexity in the continent in this geoarchaeological investigation we focus on the early holocene settlement at lapa do santo 7 9 12 7 cal kybp applying high resolution geoarchaeological techniques such as micromorphology organic petrology and ftir on both archaeological modern reference and experimental samples this is the first time that a micro contextual approach integrated with experimental geoarchaeology has been applied to study the formation of rockshelter deposits in a tropical setting our results show that the stratigraphic sequence formed under the dual influence of anthropogenic sedimentation through continuous combustion activities and geogenic sedimentation in the form of oxisol aggregates which fell from above the limestone cliff into the rockshelter intact hearths and remobilized combustion debris possibly hearth rake out are close to the graves suggesting repeated burning activities as part of the ritual behavior of early holocene south americans large amounts of ash are intermixed with heated and unheated oxisol aggregates heated termite mound fragments were also found mixed within the sediments post depositional alteration of the site includes limited bioturbation and localized low energy surface water and sub surface concentrations of moisture leading to precipitation of dense secondary carbonates the age inversions can be attributed to the human action of reworking the ashy sediments and not to post abandonment processes despite this the overall preservation of the sediments is good and most human burials can be considered to be in primary context

a new non archie model for pore structure numerical experiments using digital rock models summary tortuosity is a key parameter for investigating the pore structure of sedimentary rock the conventional model for calculating the tortuosity is derived from archie s law which is only valid for one conductive phase contained in a porous rock however there have been increasingly cases to show the non archie phenomenon in instances where the rock matrix has extra conductive phases such as surface conductivity caused by the electrical double layer therefore such model may be inapplicable in these cases and in calculations involving partial melting we investigated the relation between formation factor and porosity f o ver aw ide range of porosities by the lattice gas automata method lga with the electrical double layer the digital rock samples were constructed by packing up solid grains with different shapes and size distribution as previously measured in the laboratory on real rock specimens our purpose was to identify the origin of non archie behaviour of the f relation sometimes observed the simulations show that archie s law may only be an approximation of the f relation in a high porosity range based on our lga simulations and additional laboratory experimental data we developed new equations for non archie f relation and tortuosity potentially useful for improving the evaluation of pore structure

streaming potential measurements 2 relationship between electrical and hydraulic flow patterns from rock samples during deformation streaming potential and resistivity measurements have been performed on fontainebleau sandstone and villejust quartzite samples in a triaxial device during compaction uniaxial compression and rupture measurements on individual samples do not show any clear intrinsic dependence of the streaming potential coefficient with permeability an apparent dependence of the streaming potential coefficient with permeability is however observed during deformation the effect of surface conductivity is taken into account and is small compared with the observed changes in the streaming potential coefficient the observed dependence is therefore interpreted in terms of a difference in the evolution of the electrical and hydraulic connectivity patterns during deformation this effect causes the streaming potential coefficient and consequently the inferred potential to be reduced by a geometrical factor r g representing the electrical efficiency of the hydraulic network estimates of the r g factor varying between 0 2 and 0 8 for electrolyte resistivity larger than 100 m are obtained by comparing the values of the potential inferred from intact rock samples with the values obtained from crushed rock samples where the geometrical effects are assumed to be negligible the reduction of the streaming potential coefficient observed during compaction or uniaxial compression suggests that the tortuosity of the hydraulic network increases faster than the tortuosity of the electrical network before rupture an increase in the streaming potential coefficient associated with the onset of dilatancy was observed for three samples of fontainebleau sandstone and one sample of villejust quartzite the changes in streaming potential coefficient prior to failure range from 30 to 50 during one experiment an increase in the concentration of sulfate ions was also observed before failure these experiments suggest that observable streaming potential and geochemical variations could occur before earthquakes

structure kinematics and composition of fluid controlled brittle faults and veins in lower cretaceous claystones lower saxony basin northern germany constraints from petrographic studies microfabrics stable isotopes and biomarker analyses abstract investigation of fault rocks is crucial for the evaluation of sealing properties of rock formations considered as oil and gas storage or for the disposal of heat generating radioactive waste even in tight rock formations fluid flow may concentrate along brittle faults the present study focuses on the sealing properties of faulted lower cretaceous clay and siltstones encountered in drill cores from the central and eastern lower saxony basin germany our investigations are based on a multidisciplinary approach including microstructural mineralogical geochemical stable isotope and biomarker analyses the new data suggest that preexisting discontinuities and or sedimentary heterogeneities played a significant role for the increase in fluid pressure and formation of mode i veins within low permeability claystones high strain domains of fault cores consist of fine grained fault gouge a scaly fabric of varying deformation intensity is present around larger faults calcite precipitation in faults and complex mineralized veins and the differences in trace element concentrations of various veins reflect several phases of palaeofluid activity calcite precipitation in the fault rocks led to elevated amounts of mn ba and or sr isotope signatures indicate a local carbonate source for the origin of thin calcite coatings of fault planes but a more complex palaeofluid interaction for the larger faults and for complex veins consistent with the microfabrics biomarker signatures reveal the presence of mature hydrocarbons pointing to hydrocarbon migration in sections where steep only weakly mineralized faults occur the new results suggest that faulted claystones represent critical zones with a potentially reduced barrier capability consistent with published data

determining the porosity exponent m and lithology factor a for sandstones and their control by overburden pressure a case study from the gulf of suez egypt the porosity exponent m represents an important parameter in archie s equation it is routinely used in well logging interpretation and formation evaluation it reflects some petrophysical rock properties such as the petrofabrics pore fabrics and overburden pressure obp data measured at ambient conditions for a total of 55 sandstone core samples were obtained from 8 wells varying in depositional facies geologic age degree of consolidation and cementation material and then measured again at obp similar to the actual reservoir conditions to check the effect of obp on archie s parameters and to introduce a model of high reliability other published data sets were also used to confirm the study results based on the best fit regression analysis several empirical relationships were introduced to relate the porosity exponent to pore volume lithology factor and permeability the effect of obp on the porosity exponent was also investigated in relation to the petrophysical parameters given the above a new statistical model is proposed to relate the porosity exponent to the permeability of the studied sandstone samples in the gulf of suez egypt the effect of confining pressure on the studied porosity exponent m and the lithology factor a is significant when porosity is less than or equal to 10 from the present study categorization of the studied samples into flow units and rock types using the hydraulic flow unit and the discrete rock types increased the reliability of the obtained relationships and increased the applicability of the obtained equations in addition the value of the lithology factor a fluctuates around 1 0 92 1 04 regardless of the applied processing method whereas the value of the porosity exponent m fluctuates around 1 83 the obtained relationships between the formation resistivity factor and porosity have a very high reliability 0 949 correlation coefficient 0 969

palaeo environmental implications derived from lake and sabkha deposits of the southern rub al khali saudi arabia and oman abstract shallow lakes and sabkha deposits are evidence of past periods of higher groundwater table than today and hence reflect increased humidity in the rub al khali the large desert in the southern part of the arabian peninsula reported here are the observations made during four expeditions into this remote area in combination with luminescence dating constraining the age of the deposits the results presented extend the spatial coverage of evidence and show that most of the deposits correlate to mis 5 ca 130 70 ka and the early mid holocene ca 11 5 5 ka a single sample points towards potentially more humid conditions during the transition mis 4 3 ca 65 55 ka the presence of the mussel unio in some of the deposits attributed to mis 5 is indirect evidence for the presence of fish in the lakes which must have supported a rich and diverse fauna and probably also flora together with other evidence this demonstrates that a number of small persistent lakes were spread across the rub al khali for at least some of the time these lakes would not only have been a potential source of freshwater but could also have provided an additional and easy accessible food source via the fish for humans migrating through the area the presented palaeoenvironmental data underlines that parts of mis 5 represent a time window of opportunity for a potential expansion of modern humans across arabia

soil morphology of an alluvial chronosequence from the little river north carolina coastal plain usa abstract a soil chronosequence on terraces of the little river in the north carolina coastal plain was characterized to evaluate age related trends in pedogenesis five representative pedons per landform were studied from six late quaternary fluvial surfaces and temporal trends were assessed by regression of morphological parameters against previously reported terrace optical age estimates solum b horizon and bt horizon thickness subsoil clay content and buntley westin index rubification have strong positive correlations with age and together distinguish between soils of the floodplain 200 yr bp the first terrace 9 9 2 0 ka intermediate surfaces t2 t3b t4 17 4 4 2 74 6 10 4 ka and the oldest terrace t5b 94 0 15 9 ka over time soils develop from entisols with respective a c and a e bw c profiles on the floodplain and first terrace to ultisols with increasing argillic horizon thickness rubification and clay content on t2 t5b solum thickness bt horizon thickness and clay content display linear increases through time with soil thickening reflective of downward pedogenesis through permeable coarse grained alluvium increasing argillic horizon clay content is attributable to illuviation and possibly also to a combined bioturbation translocation process whereby clays scattered throughout sandy parent sediments are delivered to the surface by bioturbation then concentrated in b horizons by eluviation illuviation rubification increases with age and reflects transformation and subsoil concentration of inherited free iron rather than iron oxide formation from primary mineral weathering t5b pedons display morphologies comparable to those of 200 ka to 1 ma soils along coastal plain rivers that also drain the appalachian piedmont probably because sandy coastal plain derived little river alluvium has a higher hydraulic conductivity that promotes faster rates of downward weathering clay translocation and rubification than the more finely grained sediments of piedmont draining rivers thus textural differences related to sedimentary provenance should be recognized when interpreting chronosequences from the region although rates of pedogenesis differ among coastal plain alluvial soils linear trends in the 100 ka little river chronosequence may nonetheless correspond to the early more linear phases of development in studies from the region that span much longer intervals of time

water saturations in a wilcox shaly reservoir sandstone fordoche field point coupee parish louisiana abstract a new model has been derived for calculation of water saturation in shaly reservoir sandstones the model is based on effective medium theory emt and has been used successfully on a wide range of clayey low resistivity reservoirs a further independent test of saturations calculated by the model was made for a deep wilcox shaly reservoir at a depth of 13 176 ft 4016 m in fordoche field the reservoir w8 has a low average resistivity of about 2 5 ohm m and an estimated 18 clay as compared to an average resistivity of 1 5 ohm m in an underlying wet sandstone w 10 of similar clay content for the reservoir calculated water saturations are in the range of 35 to 50 increasing downward and suggest that the shaly sandstone should produce water free oil other shaly sand models generally give water saturations in excess of 50 for the reservoir water saturations calculated by the emt model agree well with other parameters for sandstones reported production core analysis and synthetic capillary pressures the reservoir w8 had an initial potential of 213 bbl of oil per day confirming water free oil production which could have been predicted by the emt model

seismic and mechanical properties of opalinus clay comparison between sandy and shaly facies from mont terri switzerland for the safe disposal of high level radioactive waste different host rocks are currently being considered the favorable properties of clay are low permeability some retention capacity concerning radionuclides and the ability to self seal cracks and fissures e g by swelling or time dependent compaction creep in switzerland the jurassic opalinus clay is envisaged as a potential host rock which at mont terri is subdivided into the sandy shaly and carbonate rich facies the latter being less abundant for long term safety assessments the understanding of the relations of properties e g mineralogical composition and microstructure and performance e g mechanical behavior of clays and claystones is essential in the case of the sandy opalinus clay the mechanical strength increases with increasing carbonate content because carbonates form the matrix the mineralogical investigation of a set of sandy facies samples proved a significantly larger carbonate content 20 40 mass when compared to the shaly facies 10 20 mass the carbonates of the shaly opalinus clay on the other hand are mostly localized fossils aligned parallel to the bedding acting as predetermined breaking points image analysis of sem images of polished sections proved the determined microstructural differences in addition carbonate particles of the sandy facies are mostly isometric whereas carbonate particles of the shaly facies cover a greater range of shapes the mechanical tests were accompanied by investigations of the p and s wave velocities which revealed that the anisotropy of the sandy facies is less pronounced than sedimentological analyses would suggest the mechanical strength which for the first time presents results of real triaxial tests of the sandy facies the samples of the sandy facies exhibit a failure strength of eff b approximately twice as high as was found for the shaly facies considering the deformation axis parallel to the bedding similar values were obtained when measuring perpendicularly to the bedding

moisture expansion as a deterioration factor for sandstone used in buildings the expansion processes that develop in building stones upon changes of moisture content may be an important contributing factor for their deteriorations until recently few data could be found in the literature concerning this parameter and weathering processes moreover the processes that may be responsible for the moisture related expansion of natural building stones are not yet completely understood to further elucidate this process extensive mineralogical petrophysical and fabric investigations were performed on eight german sandstones in order to obtain more information regarding the weathering process and its dependence on the rock fabric the analysed sandstones show a wide range of pore size distributions and porosities a positive correlation with the fabric and the pore space can be found for all studied petrophysical parameters the intensity of the expansion and related swelling pressure cannot be attributed only to the swelling of clay minerals the investigations suggest that the micropores and the resulting disjoining pressure during wet dry cycles also play an important role the results obtained suggest that the mechanism is related to the presence of liquid water within the porous material

evaluating natural site formation processes in eolian dune sands a case study from the krmpotich folsom site killpecker dunes wyoming abstract eolian dune sands commonly contain archaeological material in both surface and buried contexts however because of the dynamic nature of dunes the original context of an archaeological site can be severely modified or destroyed as a result of post occupational geomorphic processes this paper examines a folsom occupation associated with a buried soil in the killpecker dunes in southwestern wyoming field and labortory data are compared to determine the likely scenario of natural site formation processes responsible for the current context of the archaeological assemblage two primary eolian stratigraphic units are present at the site and are separated by the buried artefact bearing soil radiocarbon and optical luminescence ages indicate that the folsom artefacts occur across a temporal hiatus and that the buried soil is late holocene in age sedimentological data indicate that the highest frequencies of artefacts by depth are associated with an erosional contact characterized by a concentration of coarse grained material thus the folsom assemblage appears to have been vertically displaced as a result of post occupational erosion and deflation this case study indicates that evaluating the context of an archaeological occupation in a dune setting is best carried out utilizing multiple lines of evidence derived from both field and laboratory work

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

electrical and fluid flow properties of carbonate microporosity types from multiscale digital image analysis and mercury injection electrical and fluid flow properties of porous media are directly related to the morphology of pores and the connectivity of the pore network both are closely linked to the amount and type of intrinsic microporosity in carbonate rocks which is not resolved by conventional techniques broad ion beam bib milling produces high quality true two dimensional cross sections for scanning electron microscopy sem and enables accurate quantification of carbonate microporosity for the first time the combination of bib sem mosaics with optical micrographs yields a multiscale digital image analysis msdia spanning six orders of magnitude in this paper the pore structures of 12 different carbonate rock samples from various rock types are quantified using msdia mercury injection capillary pressure measurements are used to assess pore throat properties the quantified pore structure parameters are correlated with plug measurements of electrical resistivity and permeability results indicate that petrophysical properties are closely linked to the type of microporosity which is distinctive for a certain rock type rock types with crystalline microporosity such as mudstone and dolomite generally show good connectivity in which the size of the pore network determines if the rock favors either hydraulic or electric flow rock types with intercement or micromoldic microporosity such as bindstone and travertine show variations in connectivity due to layering and moldic micropores of biological origin furthermore pore size distributions psd follow a power law in all samples despite their depositional and diagenetic differences the slope of the psd correlates with the electric properties in which samples with a steeper slope show lower cementation factors the linearity of the power law distribution enables predictions of pore populations outside the investigated length scales

influence of carbonate content and micro fabrics on the failure strength of the sandy facies of the opalinus clay from mont terri underground rock laboratory abstract the relationship between micro fabric failure strength and mineralogical composition is studied on representative samples of the sandy facies of the opalinus clay mont terri an approximately 7 m long drill core of the bore hole blt a2 sandy facies mont terri was investigated on different scales mainly with respect to carbonate distribution image analysis showed that the carbonates of the sandy facies mainly occur as i matrix which in turn acts as cement ii in the fine sand fraction and iii as biogenic carbonates being present in minor amounts mechanical testing indicated a clear relation the failure strength increased with increasing carbonate content the carbonates of the sandy facies therefore appear to be similar to the carbonates of the callovo oxfordian clay with respect to their possible influence on failure strength

bulk electric conductivity response to soil and rock co2 concentration during controlled co2 release experiments observations and analytic modeling abstractto develop monitoring technologies for geologic co2 storage controlled co2 release experiments at the zero emissions research and technology zert site in bozeman montana usa were carried out in 2009 2011 to understand the impact on the electric properties of soil and sediment rock due to possible co2 leakage we have developed an analytical model to explain and predict the electric conductivity ec for co2 impacted soil and sedimentary rock results from the model were compared with the measurements at the zert site during 2009 2011 and the co2 vadose project site in france in 2011 2012 after model calibration at each site the model was calibrated using the saturation n and cementation m exponents contained in archie s equation and a chemistry coefficient pkc as tuning parameters that minimized the misfit between observed and modeled soil rock bulk conductivity data the calibration resulted in n 3 15 m 2 95 and pkc 4 7 for the zert site which was within the range of values in t

a grain conductivity approach to shaly sandstones the effects of clay conduction on the electrical behavior of shaly sandstones at low frequencies are analyzed by considering self similar mixtures of conductive grains as representative of these porous rocks an essential step in this model is the representation of the surface conductivities of the clay platelets by an equivalent volume conductivity based on their pattern of occurrence the clays are treated either as a continuous coating over the sand grains or as individual detrital grains mixed with a nonconductive mineral matrix in the first case the solids are modeled as layered conductive particles taken as spheres to a first approximation in the second case we generalize from the results of a three component self similar mixture of spherical particles for linear approximations the models are described by expressions quite similar to the frequently used waxman smits and dual water equations but dependent upon the clay type concentration and its distribution in the rock the models are written in terms of geometric parameters readily available from well log measurements the derived analytical expressions are successfully applied to describe a set of available experimental core and geophysical log data the results clearly demonstrate the applicability of the equations to well log interpretation as a practical procedure for computing formation factors and shaliness of argillaceous sandstones

towards an estimation of sub sea ice platelet layer volume with multi frequency electromagnetic induction sounding ice platelet clusters modify the heat and mass balance of sea ice near antarctic ice shelves and provide a unique habitat for ice associated organisms the amount and distribution of these ice crystals below the solid sea ice provide insight into melt rates and circulation regimes in the ice shelf cavities which are difficult to observe directly however little is known about the circum antarctic volume of the sub sea ice platelet layer because observations have mostly been limited to point measurements in this study we present a new application of multi frequency electromagnetic em induction sounding to quantify platelet layer properties combining in situ data with the theoretical response yields a bulk platelet layer conductivity of 1154 271msm 1 and ice volume fractions of 0 29 0 43 calibration routines and uncertainties are discussed in detail to facilitate future studies our results suggest that multi frequency em induction sounding is a promising method to efficiently map platelet layer volume on a larger scale than has previously been feasible

comment on electrical conductivity of albite quartz water and albite water nacl systems and its implication to the high conductivity anomalies in the continental crust by guo x yoshino t shimojuku a in their otherwise excellent study of the electrical conductivity of mineral systems including albite and aqueous fluids in the continental crust guo et al 2015 note that when archie s law archie 1942 is fitted to the data for bulk conductivity as a function of fluid fraction the exponent values are negative for all measurements made between 500 k and 900 k they note that the negative values indicate that the bulk conductivity decreases with increasing fluid fraction and that this is opposite to the accepted behaviour e g glover 2015 guo et al 2015 attempt to explain the behaviour by noting that the melting point of the ab qtz h2o system varies with increasing water content however there is an underlying problem with their use of the simple archie s law archie s law is given by the equation

application of luminescence dating and geomorphological analysis to the study of landscape evolution settlement and climate change on the channel island of herm abstract the optically stimulated luminescence osl dating of sands and palaeosol horizons sampled as part of an archaeological investigation and supported by geomorphological analysis has been applied to identify critical stages in the development of the landscape on herm one of the channel islands that lies off the coast of guernsey on which megalithic monuments were constructed during the neolithic period in particular there were three phases of significant aeolian activity during the prehistoric period the onsets dated by osl in this study to ca 4 3 and 2 3 ka ago where the first phase marked a significant change in the long term trend of aggradation of soils that persisted during the next two millennia osl ages were also obtained for palaeosols in which there was evidence of ploughing placing this activity in the late 2nd millennium bc and the 4th and 13th centuries ad the osl ages for basal deposits of dune sands that cover the northern part of the island indicate that they were formed by phases of intense aeolian activity during the medieval period commencing in the 13th century ad and continuing for several hundred years which can be correlated with documented high intensity storms in the north atlantic within the period 13th 15th centuries ad the phases of significant aeolian activity dated by osl to ca 4 and 2 ka ago can be linked with those detected in different regions of the north atlantic coastal areas the availability of chronologies for aeolian horizons provides a valuable tool in the study of the evolution of coastal landscape and how past coastal communities responded to climate change

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

the formation process of a paleoindian open air site in central brazil integrating lithic analysis radiocarbon and luminescence dating abstract lithic analysis radiocarbon dating and luminescence dating are applied to a stratified open air paleoindian site in central brazil lending some balance to a published record dominated by rock shelter sites most lithics are found in two discrete occupation layers lithics found outside these layers are attributed to post depositional movement of small flakes mainly upwards single grain luminescence dating on quartz grains also suggest post depositional movement both wind and bioturbation are suspected mechanisms the luminescence analysis does not provide precise depositional dates in this situation but does support such dates suggested by radiocarbon

determination of effective grain geometry for electrical modeling of sedimentary rocks accurate electrical modeling of sedimentary rocks is crucial for the interpretation of electrical survey data and must take into account the geometric information of the rock grains we have developed an incremental model for the multiphase electrical conductivity of sedimentary rocks on the theoretical basis of differential effective medium models the developed incremental model was first validated on clean and clay rich sandstones and then applied to simulate the conductivity offive digitally created rock samples with different spectra of grain aspect ratios the conductivity is calculated as a function of water conductivity at full water saturation and an effective grain aspect ratio for a two phase medium is determined to reproduce the electrical behavior of the digital rocks it was found that the effectivegrain aspect ratio can either be determined analytically or estimated from the aspect ratio spectrum a link between the obtained effective grain aspect ratio and the cementation coefficient widely used in petrophysics has been established the cementation coefficient increases with the decrease of the grain aspect ratio increasing the z axis depolarization factor and grain conductivity and the increase of sample porosity it showed that the cementation coefficient can be interpreted as a measure of the connectivity of pores as well as the conductivity of the grains our results gave us new insights into the physical meanings of the grain aspect ratio and cementation coefficient which could be used to facilitate the electrical modeling or interpretation of reservoir rocks

pressure effects on the joint elastic electrical properties of reservoir sandstones we conducted a laboratory study of the joint elastic electrical properties of sixty three brine saturated sandstone samples to assess the likely impact of differential pressure confining minus pore fluid pressures in the range 8 60 mpa on the joint interpretation of marine seismic and controlled source electromagnetic survey data the samples showed a wide range of petrophysical properties representative of most sandstone reservoirs we found that a regression equation comprising both a constant and an exponential part gave a good fit to the pressure dependence of all five measured geophysical parameters ultrasonic p and s wave velocity attenuation and electrical resistivity electrical resistivity was more pressure sensitive in clay rich sandstones with higher concentrations of low aspect ratio pores and micropores than in clean sandstones attenuation was more pressure sensitive in clean sandstones with large open pores macropores than in clay rich sandstones pore shape did not show any influence on the pressure sensitivity of elastic velocity as differential pressure increases the effect of the low aspect ratio pores and micropores on electrical resistivity becomes stronger than the effect of the macropores on attenuation further analysis of correlations among the five parameters as a function of pressure revealed potentially diagnostic relationships for geopressure prediction in reservoir sandstones

an effective medium algorithm for calculating water saturations at any salinity or frequency an algorithmic approach is used to mix the conductivities and geometric factors of the disperse components the rock and hydrocarbon particles with the host conductivity formation water the theoretical basis for the algorithm is the hanai bruggeman hb equation which itself incorporates only one disperse component the new approach the incremental model accommodates geometric factors such as sand and shale porosity exponents saturation exponent and also accommodates the associated grain conductivities its advantage over previous methods is that it works at any water salinity or tool frequency while allowing saturation and porosity exponents to have values other than 1 5 the algorithm is general and is written to accommodate simultaneous mixing of up to three disperse components and the formation water but it can be extended to accommodate any number of disperse components in its application to shaley sands hydrocarbon and sand elements are set to zero conductivity at low frequency but they can be nonzero for calculating saturations at higher frequencies the reason for this is that hydrocarbon and sand conductivities are real and very close to zero at low frequencies but at high frequencies the dielectric constants become significant making the complex conductivities nonzero the incremental model compared well with the waxman smits model on multiple water conductivity saturation data from two published experimental data sets the model is adaptable to other rock conductivity problems such as vuggy porosity vuggy water saturation and clay coated sand grains the potential exists for the algorithm to be part of a comprehensive computer program for calculating rock conductivities and saturations using many different combinations of rock fabrics and compositions

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

lapa das boleiras rockshelter stratigraphy and formation processes at a paleoamerican site in central brazil abstract lapa das boleiras rockshelter a paleoamerican archaeological site in central brazil was intensely occupied by humans from 10 000 14c bp 11 8 cal kyr bp until approximately 7500 14c bp 8 4 cal kyr bp in this paper we present some interpretations about the formation processes operating on the site one of our main conclusions is that the bulk of accumulated sediments at the site is of anthropogenic origin they are constituted by volumetrically significant quantities of plant ash remains what is somewhat unexpectedly in view of prevailing models about the lifestyle of paleoamerican hunter gatherers in south america the evidence we discuss below is also consistent with paleoenvironmental data that suggest a dry period during the mid holocene in the region probably leading to a decrease in human occupation araujo a g m neves w pilo l b atui j p 2005 holocene dryness and human occupation in brazil during the archaic gap quaternary research 64 298 307 we surmise that both factors underpin a surprising reduction in sediment accumulation at the site during the mid holocene

thalassinoides phycodes compound burrow systems in paleocene deep water limestone southern alps of italy abstract compound burrow systems consisting of branching horizontal tunnels in the core areas of the systems intergrading with fan like tunnels in distal areas are common in the paleocene scaglia cinerea limestone if preserved as isolated elements the cores would be identified as thalassinoides suevicus and the distal elements as phycodes cf palmatus these complex trace fossils are probably combination dwelling deposit feeding structures produced by endobenthic crustaceans that occupied and operated the systems for relatively long intervals of time compounds such as these may be more common than supposed and represent an important but essentially unexploited source of biologic information on marine invertebrate trace producers

late oligocene early miocene paleosols of distal fluvial systems ebro basin spain abstract the study of paleosols can be a vital tool in the paleoenvironmental interpretation of continental deposits because their physical and chemical characteristics are a reflection of variations in aspects of soil formation changes in paleosol characteristics can be used to determine the architecture and nature of parent material paleosol maturity topography climate and soil forming organisms including vegetation cover on the ancient floodplain and can be utilized to recreate a palaeocatena furthermore paleosols can provide quantitative data on paleoclimate where other sources such as organic matter and pedogenic carbonate are absent late oligocene early miocene strata exposed in the ebro basin spain have been identified as proximal alluvial fan fluvial and lacustrine continental facies in parts of the distal fluvial system pedogenically altered channel and overbank deposits interfinger with ephemeral lacustrine facies three main paleosol types developed in these sediments and have been described and compared to modern soils entisol like early successional soils inceptisol like young soils and alfisol like open woodland soils paleoenvironmental reconstructions suggest a mosaic of ecotypes with areas of open woodland composed of shrubs herbs and small trees and other plants of low stature and with each ecotype being controlled primarily by fluctuating paleohydrological conditions from field observations and geochemical analysis the climate was found to be humid continental mean annual temperature mat 10 14 c 4 c mean annual precipitation map 450 830 mm yr 1 200 mm yr 1 these results indicate that climatic conditions were wetter than the present day ebro basin mat 14 c map 320 mm yr 1 and differ from previous interpretations of an arid to semi arid environment based on sedimentological criteria alone

microstructural controls on electric and acoustic properties in tight gas sandstones some empirical data and observations quantitative interpretation of log data from tight gas sandstone reservoirs is almost always difficult and typically yields saturations that are inconsistent with results from various measurements of well performance this is an issue of economic importance as the ability to use log data to reliably identify completion zones and predict well performance could result in considerable cost savings for operators

localization and characterization of an active fault in an urbanized area in central guatemala by means of geoelectrical imaging article i nfo article history the polochic and motagua faults define the active plate boundary between the north american and caribbean plates in central guatemala a splay of the polochic fault traverses the rapidly growing city of san miguel uspantan that is periodically affected by destructive earthquakes this fault splay was located using a 2d electrical resistivity tomography ert survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built ert images show the fault as a 50 m wide near vertical low resistivity anomaly bounded within a few meters by high resistivity anomalies forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location geometry and internal structure of the fault zone as well as the affected lithologies our results indicate that the city is constructed on a 20 m thick surficial layer consisting of poorly consolidated highly porous water logged pumice this soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking the electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might at least in part be fed by water rising along the fault therefore the potential threat posed by this fault splay may not be limited to its seismic activity per se but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments the results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of san miguel uspantan and illustrate the potential of ert surveying for paleoseismic studies

combined geophysical and analytical methods to estimate offshore freshwater extent abstract offshore fresh groundwater is increasingly suggested as a potential water resource for onshore human demands in many cases onshore pumping already draws significant fresh groundwater from offshore however offshore aquifers and the extent of offshore freshwater are usually poorly characterised due to data scarcity this study combines geophysical data hydraulic information and a first order mathematical analysis to investigate offshore freshwater extent in the gambier embayment australia a large seismic data set combined with onshore and offshore bore log geological profiles are used to explore the regional offshore hydro stratigraphy aquifer hydraulic parameters and onshore heads are obtained from onshore investigations a novel application of archie s law geophysical data and onshore hydrochemical data provide useful insights into the salinity profiles within four offshore wells these are compared to steady state sharp interface estimates of the freshwater extent obtained from a recently developed analytical solution albeit using simplified conceptual models salinities derived from resistivity measurements indicate that in the south of the study area pore water with total dissolved solids tds of 2 2 g l 1 is found up to 13 2 km offshore offshore pore water salinities are more saline in the northern areas most likely due to thinning of the offshore confining unit the analytical solution produced freshwater saltwater interface locations that were approximately consistent with the freshwater saltwater stratification in two of the offshore wells although analytical uncertainty is high this investigation provides a leading example of offshore freshwater evaluation applying multiple techniques demonstrating both the benefit and uncertainty of geophysical interpretation and analytical solutions of freshwater extent

permeability models of porous media characteristic length scales scaling constants and time dependent electrokinetic coupling fluidpermeabilityisoneofthemostimportantcharacteristics of a hydrocarbon reservoir and is described by a number of empirical and theoretical models we have taken four of the most importantmodels eachofwhichisderivedfromadifferentphysicalapproach andhaverewrittentheminagenericformthatimplies a characteristic scale length and scaling constant for each model the four models have been compared theoretically and using experimental data from 22 bead packs and 188 rock cores from a sand shale sequence in the u k sector of the north sea thekozeny carmanmodeldidnotperformwellbecauseittakes no account of the connectedness of the pore network and should no longer be used the other three models schwartz sen and johnsonssj katzandthompsonkt andtherevil glover pezard andzamorargpzallperformedwellwhenusedwith their respective length scales and scaling constants surprisingly we found that the ssj and kt models are extremely similar such that their characteristic scale lengths and scaling constants arealmostidenticaleventhoughtheyarederivedusingextremely different approaches the ssj model by weighting the kozeny carman model using the local electrical field and the kt model by using entry radii from fluid imbibition measurements theexperimentallydeterminedscalingconstantsforeach model were found to be cssjckt8 3crgpz 3 use of these models with ac electrokinetic theory has also allowed us to showthatthesescalingconstantsarealsorelatedtotheavaluein the rgpz model and the m value in time dependent electrokinetictheoryandthentoderivearelationshipbetweentheelectrokinetic transition frequency and the rgpz scale length which we have validated using experimental data the practical implication of this work for permeability prediction is that the kt model should be used when fluid imbibition data are available whereasthergpzmodelshouldbeusedwhenelectricaldataare available

a simple way to model the pressure dependency of rock velocity abstract modeling the pressure dependency of rock velocity is important for interpreting and comparing the seismic and earthquake data from different depths this study develops a multicomponent differential effective medium model for the elastic properties of porous rocks with two types of pores in the grain background without mixing order the developed model is applied to modeling the pressure dependent elastic velocity of porous rocks by incorporating the variation of stiff and compliant porosity as a function of pressure the pressure dependent stiff and compliant porosity were inverted from the measured total porosity under pressure using a dual porosity model and the unknown constant stiff and compliant pore aspect ratios were inverted by best fitting the modeled velocity to the measured data application of the approach to a low porosity granite and a medium porosity sandstone sample showed that the pressure dependency of rock velocity can be satisfactorily modeled by the developed model using the pressure dependent stiff and compliant porosity and carefully estimated stiff and compliant pore aspect ratio values

holocene eolian activation as a proxy for broad scale landscape change on the gila river indian community arizona abstract eolian sediments are common within the middle gila river valley southern arizona and reflect variability in eolian and fluvial processes during the late holocene this study focuses on deciphering the stratigraphic record of eolian deposition and associated luminescence dating of quartz extracts by single aliquot regeneration sar protocols stratigraphic assessment coupled with luminescence ages indicates that there are four broad eolian depositional events at ca 3145 220 yr 1950 1360 yr 800 100 yr and 690 315 yr this nascent chronology correlated with regional archeological evidence and paleoclimate proxy datasets leads to two general conclusions 1 loess deposits transverse dune formation and sand sheet deposition in the late holocene are probably linked to flow variability of the gila river though the last two events are concordant with regional megadroughts and 2 the stability of eolian landforms since the 19th century reflects the lack of eolian sediment supply during a period of fluvial incision resulting in entisol formation on dunes the prime catalyst of eolian activity during the late holocene is inferred to be sediment supply driven by climate periodicity and variable flow within the gila river catchment

preserving the palaeoenvironmental record in drylands bioturbation and its significance for luminescence derived chronologies luminescence osl dating has revolutionised the understanding of late pleistocene dryland activity however one of the key assumptions for this sort of palaeoenvironmental work is that sedimentary sequences have been preserved intact enabling their use as proxy indicators of past changes this relies on stabilisation or burial soon after deposition and a mechanism to prevent any subsequent re mobilisation as well as a dating technique osl especially at the single grain level can be used to gain an insight into post depositional processes that may distort or invalidate the palaeoenvironmental record of geological sediment sequences this paper explores the possible impact of bioturbation the movement of sediment by flora and fauna on luminescence derived chronologies from quaternary sedimentary deposits in texas and florida usa which have both independent radiocarbon chronologies and archaeological evidence these sites clearly illustrate the ability of bioturbation to rejuvenate ancient weathered sandy bedrock and or to alter depositional stratigraphies through the processes of exhumation and sub surface mixing of sediment the use of multiple osl replicate measurements is advocated as a strategy for checking for bioturbated sediment where significant osl heterogeneity is found caution should be taken with the derived osl ages and further measurements at the single grain level are recommended observations from the linear dunes of the kalahari show them to have no bedding structure and to have osl heterogeneity similar to that shown from the bioturbated texan and florida sites the kalahari linear dunes could have therefore undergone hitherto undetected post depositional sediment disturbance which would have implications for the established osl chronology for the region

nonuniversality of the archie exponent due to multifractality of resistivity well logs archie s law expresses a relation between the formation factor f of porous media and their porosity f m where m is the archie or the cementation exponent despite widespread use of archie s law the value of m and whether it is universal and independent of the type of reservoir have remained controversial we analyze various porosity and resistivity logs along 36 wells in six iranian oil and gas reservoirs using wavelet transform coherence and multifractal detrended fluctuation analysis m is estimated for two sets of data one set contains the resistivity data that include those segments of the well that contain significant clay content and one without the analysis indicates that the well logs are multifractal and that due to the multifractality the exponent m is nonuniversal thus analysis of the resistivity of laboratory or outcrop samples that are not multifractal yields estimates of m that are not applicable to well logs in oil or gas reservoirs

neoichnology at lake margins implications for paleo lake systems abstract neoichnological studies provide significant information that can aid in the interpretation of ancient ichnological assemblages here we examine for the first time the pattern in both vertebrate and invertebrate trace distribution and abundance that can be seen in two geographically separate but broadly analogous contemporary semi arid climate lake margin settings in an effort to describe taphonomic processes relevant to paleo lake systems lake margin to supralittoral zone transects were made at ruby reservoir montana usa and la sotonera spain and vegetation cover trace cover trace diversity and substrate characteristics were recorded similar patterns in trace distribution were seen through the eulittoral to supralittoral zones with the majority of traces identified within a single transect present at both sites however a few traces attributed to larger organisms were found to be unique to each and in some instances could to be assigned to a specific trace maker the eulittoral zone was considered to have characteristics attributable to the scoyenia ichnofacies however analysis of the supralittoral zone shows some characteristics of both the coprinisphaera and the mermia ichnofacies in addition a transitional zone between a scoyenia like ichnofacies and a fully terrestrial assemblage was found which may enable continental ichnofacies to be further refined for application to paleo lake systems study of the distribution of traces with distance along the transects also suggests taphonomic biases against the preservation of certain types of traces e g avian due to seasonal fluctuations of the lake level and the subsequent reduced preservation potential for lake proximal traces

archaeology of the pleistocene holocene boundary in brazil abstract after a short history of brazilian research about pleistocene peopling the late pleistocene early holocene changes of climate and resources are discussed claims for a very ancient presence of man before 13 000 bp itaborai toca da esperanca pedra furada and lapa vermelha sites are polemic because putative structures and artifacts could have been made by natural processes in central and northeastern brazil some sites dated between 14 000 and 10 000 bp provide clear evidence of human activities and coexistence with huge pleistocene mammals in a synthesis of our present knowledge about the 12 000 8000 bp period biological aspects of the lagoa santa people and their subsistence are discussed the main regional traditions are umbu with bifacial projectile points and humaita with heavy implements in the southern part of brazil in the central and northeastern regions the itaparica tradition is characterized by typical retouched flakes and limaces although projectile points are generally thought to be absent in the earliest levels of this tradition some have been found in boquete cave in amazonia some cultural aspects seem to have been the same as in central brazil

self potential as a predictor of seawater intrusion in coastal groundwater boreholes abstract monitoring of self potentials sps in the chalk of england has shown that a consistent electrical potential gradient exists within a coastal groundwater borehole previously affected by seawater intrusion si and that this gradient is absent in boreholes further inland furthermore a small but characteristic reduction in this gradient was observed several days prior to si occurring we present results from a combined hydrodynamic and electrodynamic model which matches the observed phenomena for the first time and sheds light on the source mechanisms for the spatial and temporal distribution of sp the model predictions are highly sensitive to the relative contribution of electrochemical exclusion and diffusion potentials the exclusion efficiency in different rock strata geoelectric heterogeneity largely due to marls and hardgrounds with a relatively high exclusion efficiency was the key factor in controlling the magnitude of the modeled sp gradient ahead of the saline front and its evolution prior to breakthrough the model results suggest that where sufficient geoelectric heterogeneity exists borehole sp may be used as an early warning mechanism for si

late quaternary environmental and climatic changes in central brazil paleoenvironmental changes dating back to 30 000 yr b p documented in a pollen record from central brazil lat 19 s permit the reconstruction of climatic changes related to shifts of the antarctic polar fronts the paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution taking into account present day climatic parameters at 30 000 yr b p the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest from 17 000 to 14 000 yr b p the climate was drier although tree pollen percentages were relatively high after 12 000 yr b p araucaria forest elements increased suggesting a moister and cooler climate the araucaria forest disappeared during a short interval between 11 000 and 10 000 yr b p this could be related to the younger dryas event at the beginning of the holocene the climate became cool and moist again as indicated by the reexpansion of the araucaria forest the latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr b p at 5000 yr b p an arid interval was followed by the expansion of mesophytic semideciduous forest elements

modelling electrical conductivity for earth media with macroscopic fluid filled fractures modeling electrical conductivity for earth media with macroscopic fluid filled fractures james g berryman 1 and g michael hoversten 2 lawrence berkeley national laboratory one cyclotron road ms 90r1116 berkeley ca 94740 usa e mail jgberryman lbl gov chevron energy technology co 6001 bollinger canyon road san ramon ca 94583 e mail hovg chevron com

frictional stability permeability relationships for fractures in shales there is wide concern that fluid injection in the subsurface such as for the stimulation of shale reservoirs or for geological co2 sequestration gcs has the potential to induce seismicity that may change reservoir permeability due to fault slip however the impact of induced seismicity on fracture permeability evolution remains unclear due to the spectrum of modes of fault reactivation e g stable versus unstable as seismicity is controlled by the frictional response of fractures we explore friction stability permeability relationships through the concurrent measurement of frictional and hydraulic properties of artificial fractures in green river shale grs and opalinus shale ops we observe that carbonate rich grs shows higher frictional strength but weak neutral frictional stability the grs fracture permeability declines during shearing while an increased sliding velocity reduces the rate of permeability decline by comparison the phyllosilicate rich ops has lower friction and strong stability while the fracture permeability is reduced due to the swelling behavior that dominates over the shearing induced permeability reduction hence we conclude that the friction stability permeability relationship of a fracture is largely controlled by mineral composition and that shale mineral compositions with strong frictional stability may be particularly subject to permanent permeability reduction during fluid infiltration

conductivity models for archie rocks abstractthe petroleum industry s standard porosity resistivity model i e archie s law although it is fit for its purpose remains poorly understood after seven decades of use this results from the choice of the graphical display and trend formula used to analyze archie s seminal porosity resistivity data taken in the nacatoch sandstone a petroliferous clastic formation in the gulf of mexico coastal area archie s model accurately predicts the conductivity brine volume trend for this sandstone not all rocks follow the same porosity resistivity trends observed in the nacatoch sandstone but those that do are defined as archie rocks archie s nacatoch sandstone data set has significant irreducible scatter or noise data with significant scatter cannot be used to uniquely define a trend alternative graphical analyses of archie s nacatoch sandstone data indicates that archie could have analyzed these data differently had it occurred to him to do so a physics based porosity conductivity model a ge

approaches to middle stone age landscape archaeology in tropical africa the southern montane forest grassland mosaic ecosystem in the humid subtropics southern rift valley of africa comprised the environmental context for a large area in which modern human evolution and dispersal occurred variable climatic conditions during the late pleistocene have ranged between humid and hyperarid changing the character of the ecosystem and transforming it at different points in time into a barrier a refuge and a corridor between southern and eastern african populations alluvial fans presently blanket the areas adjacent to major river systems which were key areas of prehistoric human habitation these sets of variables have created conditions that are both challenging and advantageous to conduct archaeological research lateritic soil development has resulted in poor organic preservation and facilitated insect bioturbation which has demanded an integrated micro macro scale approach to building a reliable geochronology an integrated field and analytical methodology has also been employed to identify the nature and degree of post depositional movement in alluvial deposits which preserve a wide range of spatial integrity levels in buried stone artifact assemblages between 47 and 30 ka in karonga northern malawi this paper describes the methodological advances taken toward understanding open air middle stone age archaeology in sub tropical africa and explores the inferential potential for understanding pleistocene human ecology in the important southern rift valley region

identification remediation and analysis of karst sinkholes in the longest railroad tunnel in south korea abstract tunneling in karst terrains presents numerous challenges to the engineer including the unpredictable occurrence of cavities and well developed hydraulic conduits that could lead to sinkhole development during construction of the longest railroad tunnel in south korea excessive water inrushes and support collapses accompanying the formation of a couple of sinkholes and subsidence on the ground surface such cases of sinkhole formation during tunneling in south korea have been rarely reported various characterization methods were used at the tunneling site to identify the causes of the sinkholes and the subsidence on the ground surface especially noteworthy in this regard is that the massive limestone in this area contains a high degree of lime purity as high concentrations of lime are very corrosive a limestone micro scale cavity readily developed along the fault planes and joints due to weathering and chemical corrosion the data obtained from various types of geological and geophysical exploration methods identified the formation of micro scale cavity networks that served as conduits carrying reservoir water from the surface to the underground tunnel additional micro scale vertical cavity networks were detected for the unexcavated tunnel route through geophysical and horizontal probe core drilling methods ground reinforcement was applied to sinkhole and subsidence at the ground surface and the cavity inside the tunnel for remediation after the installation of underground waterproof grouting around the tunnel and of grouting walls around the sinkholes the groundwater level recovered and the ground surface settlement ceased seepage analyses were performed to provide an optimal drainage design for long term stability based on this case study and the lessons learned we suggest a risk reduction system for safe tunneling in karst terrains

influence of carbonate microfabrics on the failure strength of claystones claystones are currently being investigated as a potential host rock for radioactive waste disposal the relevant parameters are hydraulic conductivity swelling and shrinkage water uptake rheological and mechanical behavior much attention is paid to the opalinus clay opa in switzerland and the callovo oxfordian clay cox in france one of the scientific challenges is to develop numerical models to predict the mechanical behavior of claystones under repository like conditions recent studies have demonstrated the influence of carbonates on selected mechanical parameters e g failure strength in this study we show that opa and cox behave differently with respect to their failure strength the failure strength of opa decreases with increasing carbonate content whereas it increases with increasing carbonate content in case of the cox the different behavior is caused by microstructural variations results of carbonate microfabric investigations verify that opa mainly contains coarse grained shell fragments while cox shows a more homogeneous distribution of fine grained mainly non biogenic carbonates in conclusion not only the carbonate content but in addition their grain size distribution their shape and the spatial distribution control the mechanical behavior of both clays

what is the cementation exponent a new interpretation in 2003 182 billion barrels of oil reserves worth about us 4 5 trillion were discovered worldwide johnson et al 2004 moreover between 1950 and 2002 the total volume of reserves discovered has run to more than 1500 billion barrels for oil and 7 5 trillion cubic feet for gas bentley 2002 more than half of these resources have already been produced and have driven the global economy for the last 50 years

modelling the low frequency electrical properties of pyrite bearing reservoir sandstones abstract marine controlled source electromagnetic sounding has developed rapidly in recent years to complement conventional seismic method for better discrimination of pore fluid to obtain quantitative and reliable interpretation of the csem data a robust rock physics model is vital to link the bulk rock electrical conductivity to the electrical properties and microstructure of the rock constituents especially when some of the constituents exhibit extreme electrical behaviours e g pyrite a common mineral associated with reservoir rocks based on the multi phase incremental model validated on published experimentally measured electrical conductivity of pyrite bearing sandstones the effects of key parameters i e pyrite content porosity pyrite conductivity grain aspect ratio and water saturation on the electrical conductivity of pyrite bearing sandstones and their corresponding csem responses were comprehensively studied the results are expected to assist in the csem data interpretation when a pyrite bearing sandstone reservoir is encountered in the future