sedimentary facies of the eastern pacific s northernmost reef like setting cabo pulmo mexico abstract cabo pulmo mexico is often cited as the eastern pacific s northernmost coral reef we investigated sedimentary dynamics to verify whether the system functions sedimentologically as a reef which would mean that it retained internal sediment in a framework and exported peri reefal sediment creating clearly identifiable facies dominated by reefal fauna we mapped distribution of sediments using grab samples the acoustic ground discrimination systems qtc view and echo plus at 50 khz signal frequency and an ikonos satellite image morphologically the bay of cabo pulmo can be divided into intrusive dikes and rocky hardgrounds in less than 10 m depth and a sandy interior with rocky outcrops sloping to over 40 m reefal fauna without lasting framework building but with production of typically reef associated carbonate sediments as well as a patch reef facies were found on the dikes and hardgrounds sediments in the bay were a mixture of carbonates and siliciclastics and were influenced by a seasonal river near the bay s center that imported siliciclastic material to the north and south sediments had a higher carbonate content although overall the bay was characterized by 50 siliciclastics the shallower subtidal sands were dominated by mollusk fragments whereas in depths 30 m planktonic foraminiferal sand was found acoustically and optically remote sensed maps were used to differentiate between the rocky and sandy areas and to identify the presumed off shelf transport pathway of reef derived carbonates overall the sedimentary system is characterized by carbonate production but the coarser reef derived carbonates coral and reef dwelling mollusks are transported off shelf along a steep depth gradient and little typical peri reef sediment remains this transport is likely aided by storms since no sediment retaining frameworks are formed the dikes cannot retain internal sediment and the reefal fauna was not dominant in sediments throughout the bay we conclude that cabo pulmo sedimentologically functions only in a limited way like a coral reef

the adjustment of mantle plumes to changes in plate motion the relative motion of hotspots and lithospheric plates implies a velocity shear in the underlying mantle causing horizontal advection of mantle plumes as they rise toward the lithosphere consequent tilting of plumes parallel to the direction of plate motion indicates that plumes must undergo a period of readjustment after the velocity vector for plate motion is altered thus the shape of bends in the surface tracks of hotspots resulting from changes in plate motion will reflect the plume adjustment laboratory experiments as well as computations using a simple theory developed in richards griffiths 1988 for the dynamics of continuous plume conduits demonstrate that the bend in the surface track has a radius of curvature approximately equal to the maximum horizontal deflection of the conduit thus the sharpness of the bend at an age of 43ma in the hawaiian emperor volcanic chain implies that the deflection of the underlying plume in that case was small 200 km this small deflection is expected for plumes carrying large buoyancy fluxes and it indicates that tilting of the conduit is unlikely to be sufficient to cause diapiric instability

chemostratigraphy a method to improve interwell correlation in barren sequences a case study using onshore duckmantian stephanian sequences west midlands u k abstract chemostratigraphy has been applied to onshore duckmantian stephanian successions encountered in outcrop and penetrated by two boreholes from the west midlands u k these successions represent the onshore equivalents of the barren red measures which are important hydrocarbon bearing sequences in the southern north sea much is known about the onshore successions in terms of sedimentology mineralogy and provenance and thus they provide the ideal test for the validity of chemostratigraphy as a stratigraphic tool reliable inorganic geochemical data have been acquired from geochemical analyses of core sidewall core and cuttings samples with 19 elements being determined stratigraphic variations in elemental concentrations are compared with known variations in the mineralogical data the established lithostratigraphic units of the duckmantian stephanian intervals can also be recognized from the geochemical data and by using these data can be subdivided further this results in an independent chemostratigraphic correlation being established for the two boreholes which has been assessed statistically by discriminant function analysis from the geochemical and mineralogical data distinct changes in provenance are identified within the upper carboniferous successions the sediments of the coal measures were derived from a north westerly and westerly source caledonian whereas the etruria formation sediments came from the wales brabant massif the sediments having mixed caledonian and cadomian characteristics eventually these sediments were replaced by sediments from a southern hercynian source halesowen and salop formations

assessment of groundwater contamination around active dumpsite in ibadan southwestern nigeria using integrated electrical resistivity and hydrochemical methods investigation of groundwater contamination due to leachate migration in a solid waste disposal site was done using both geophysical and hydrochemical methods the main goals were to delineate groundwater contamination due to leachate percolation and thus assessment of quality of groundwater from nearby hand dug wells bordering the dumpsite for drinking purpose a total of ten resistivity traverses were acquired within and outside the dumpsite using wenner configuration with constant electrode separation ranging from 5 to 25 m the 2d resistivity data were processed and inverted using res2dinv and res3dinv softwares respectively geochemical assessment of groundwater samples were carried out according to apha standards while hydrochemical facies of the sampled groundwater was evaluated using piper trilinear software the inverse resistivity models of the subsurface from 2d and 3d imaging revealed low resistivity value less than 10 m suspected to be leachate while 3d inverse sections allowed delineation of leachate weathered layer bedrock and seepage path from the dumpsite the extent of migration was more pronounced in the southern part of the dumpsite hence possible contamination of shallow groundwater system as dumpsite ages the results of physico chemical analyses showed the groundwater samples to be within the limits of who nsdwq for drinking purpose however higher values of concentrations of most analyzed parameters were noticed in well 1 due to its nearness to dumpsite and well 10 due to agricultural activities respectively interpretation of piper diagram showed cahco3 to be dominant facie in the area while alkaline earth metals text ca 2 text mg 2 and weak acids hco3 co3 are dominant cations and anions during both climatic seasons groundwater in the study area is of hard fresh and alkaline in nature

sea bottom classification across a shallow water bar channel and near shore shelf using single beam acoustics an acoustic ground discrimination system qtc view series iv was used to identify and map the bottom acoustic diversity in the bar channel of ria de aveiro western portugal the majority of the survey area presented shallow depth for this type of equipment ranging mainly from 5 to 15 m depth occasionally reached 25 m in specific areas located across the entrance channel dug by the strong tidal currents reaching 3 m s the acoustic data were submitted to manual and auto cluster and the results obtained from both procedures were coherent using aids to the acoustic classification and ground truth sediment data a final solution consisting of four acoustic classes was reached their geographical distribution was coincident with the spatial distribution of the major bottom types and sediment groups hard bottom coarse sand medium sand and fine sand identified through multivariate analysis of the grain size data and reflected the complex hydrodynamics of the entrance channel the acoustic pattern was coincident at the intersections of the acoustic survey lines assuring the repeatability of the acoustic procedure overall the acoustic approach showed consistent results for the assessment and mapping of the benthic habitats in this shallow water coastal area providing a very valuable tool in an area where conventional sediment sampling is less favourable namely due to strong tidal currents and frequent ship traffic such as the entrance channel of ria de aveiro and the near shore adjacent shelf

evaluation of groundwater quality in coastal areas implications for sustainable agriculture seawater intrusion is a problem in the coastal areas of korea most productive agricultural fields are in the western and southern coastal areas of the country where irrigation predominantly relies on groundwater seawater intrusion has affected agricultural productivity to evaluate progressive encroachment of saline water the korean government established a seawater intrusion monitoring well network especially in the western and southern part of the peninsula automatic water levels and ec monitoring and periodic chemical analysis of groundwater help track salinization salinization of fresh groundwater is highly associated with groundwater withdrawal a large proportion of the groundwaters are classified as na cl and ca cl types the na cl types represent effects of seawater intrusion the highest ec level was over 1 6 km inland and high cl values were observed up to 1 2 km inland lower ratios of na cl and so4 cl than seawater values indicate the seawater encroachment a linear relation between na and cl represents simple mixing of the fresh groundwater with the seawater the saline na cl typed groundwaters showed br cl ratios similar to or less than seawater values the ca hco3 type groundwaters had the highest br cl ratios substantial proportions of the groundwaters showed potential for salinity and should be better managed for sustainable agriculture

demarcating saline water intrusion pathways using remote sensing gis and geophysical techniques in structurally controlled coastal aquifers in southern india application of remote sensing and geographical information system gis with the help of ground truth studies like vertical electrical soundings ves and water quality measurements gave a comprehensive picture on saline water intrusion pathways in the structural controlled aquifers of uppanar and cauvery river systems located in sirkazhi and mannanpandal coastal areas of southern india the detailed geomorphic units and lineaments were mapped using irs liss iii 1 50 000 scale and srtm elevation digital data under gis environment the area is mainly alluvial deposits of holocene age and classified into three major geomorphic units i e fluvial fluviomarine and marine geomorphic units the identified lineaments are mostly trending north northeast nne south southwest ssw northeast ne southwest sw northwest nw southeast se east west ew and east northeast ene west southwest wsw directions some of them are potential for fresh groundwater occurrence and movement the lineaments trending ne sw nne ssw and ene wsw act as pathways for saline water intrusion to the inland the lineament l1 nne ssw trending conformed as a sinisterly shifted fault played a significant role in saline water intrusion the area within the parallel lineaments l2 and l3 oriented ene wsw direction indicates low topography beach ridges paleo channel sinuosity large aerial extent of tidal flats and backwater inundation all the above geomorphic units gave indirect evidence of land subsidence which was confirmed with the help of sub surface geo electrical signals obtained through ves and in situ groundwater quality measurements integrating all the above results the saline water spread and fresh water pockets were identified

aquifer characterization using shallow geophysics in the keritis basin of western crete greece effective management of groundwater resources is a well known problem in several areas around the world it is especially important to areas suffering from an intrinsic lack of fresh water such as islands detailed study of available aquifers is of particular interest in the highly touristic greek island of crete the increasing water demand makes water resources management extremely important for sustainable development this is the case in the prefecture of chania in western crete where there has been a lack of success of many different groundwater management plans that have been produced over the years and submitted for application to water management authority the inefficiency of the management plans is verified by the continuous water shortage reported every year which forces the public authorities to transfer water from far away sources and wells until today there are only geological data as well as information from the borehole logs therefore the current work is focused to study in detail the tectonic and hydrogeological characteristics of the keritis watershed to make a correlation of the available geoenvironmental information with the geophysical data of the study aquifer transient electromagnetic soundings were conducted to obtain detailed information about the tectonic hydrogeological hydrolithological and geometrical characteristics of the aquifer under investigation in addition optimum areas of water well drilling were identified to minimize the uncertainty and the total cost economical managerial etc of future groundwater surveys

delineating the fresh and brackish saline aquifer interface in neill island of andaman nicobar from india a prelude geoelectrical investigation for delineation of the interface between fresh and brackish saline aquifers 25 resistivity soundings using schlumberger configuration were made in neill island of andaman nicobar from india a fence diagram was prepared using the results obtained from the soundings interpretation together lithology of nearby well cross section and measurements made near out cropping materials groundwater levels and electrical conductivity this diagram displays various litho units down to conductive stratum saturated with brackish saline water and also clearly depicted the occurrence of fresh water aquifer the depth to interface between fresh and brackish saline water aquifers varies 1 9 to 9 3 meters below ground level in the neill island

case study a 3d resistivity and induced polarization imaging from downstream a waste disposal site in brazil a contaminated site from a downstream municipal solid waste disposal site in brazil was investigated by using a 3d resistivity and induced polarization ip imaging technique this investigation purpose was to detect and delineate contamination plume produced by wastes the area was selected based on previous geophysical investigations and chemical analyses carried out in the site indicating the presence of a contamination plume in the area resistivity model has successfully imaged waste presence 31 mv v water table depth and groundwater flow direction a higher chargeability zone m 31 mv v outside wastes placement and following conductive anomaly was interpreted as a contamination plume normalized chargeability mn m confirmed polarizable zone which could be an effect of a salinity increase contamination plume and the clay presence in the environment

benthic habitat mapping of sorted bedforms using hydroacoustic and ground truthing methods in a coastal area of the german bight north sea abstract the continuously influence of human impacts on the seafloor and benthic habitats demands the knowledge of clearly defined habitats to assess recent conditions and to monitor future changes in this study a benthic habitat dominated by sorted bedforms was mapped in 2010 using biological sedimentological and acoustic data this approach reveals the first interdisciplinary analysis of macrofauna communities in sorted bedforms in the german bight the study area covered 4 km2 and was located ca 3 5 km west of island of sylt sorted bedforms formed as sinuous depressions with an east west orientation inside these depressions coarse sand covers the seafloor while outside predominantly fine to medium sand was found based on the hydroacoustic data two seafloor classes were identified acoustic class 1 was linked to coarse sand type a found inside these sorted bedforms whereas acoustic class 2 was related to mainly fine to medium sands type b the two acoustic classes and sediment types corresponded with the macrofauna communities 1 and 2 the aoinides paucibranchiata goniadella bobretzkii community on coarse sand and the spiophanes bombyx magelona johnstonii community on fine sand a transitional community 3 scoloplos armiger ophelia community with species found in communities 1 and 2 could not be detected by hydroacoustic methods this study showed the limits of the used acoustic methods which were unable to detect insignificant differences in the fauna composition of sandy areas

fluvial architecture of early permian barakar rocks of korba gondwana basin eastern central india abstract the early permian barakar formation of the korba basin represents repeated deposition of fining upward sequences of coarse to medium grained sandstone fine grained sandstone shale shale and coal the sandstones are channel sheet like multistory and profusely cross bedded the shale beds are lens as well sheet like and laminated coal facies is thin to moderately thick and shows splitting paleocurrent analysis suggests a northwesterly paleoslope during barakar sedimentation however the deflection of paleoslope towards northeast in the eastern part of the basin supports the existence of a watershed in the depositional area the barakar paleochannel were 4 05 m deep and 176 m wide single channel with an average sinuosity of 1 27 the average flow velocity and sediment load during flood stage are in the order of 1 77 m s and 4 15 these results indicate bed load braided to mixed load nature of the barakar streams of the korba basin the study suggests that the early permian braided barakar streams deposited the coal measure sequence subsequent to deglaciation in a northwesterly slopping paleovalley the basin floor was highly uneven marked by the presence of a basement high in the northwestern part that bifurcates the paleostreams into northwestern and northeastern branches

structure and dynamics of sheared mantle plumes 1 an extensive series of laboratory experiments is used to investigate the behavior of sheared thermal plumes the plumes are generated by heating a small circular plate on the base of a cylindrical tank filled with viscous fluid and then sheared by rotating a horizontal lid at the fluid surface the motion of passive tracers in the plumes is visualized by the release of several dye streams on the hot plate we systematically examine the dependence of the convective flow on four dimensionless numbers a velocity ratio a rayleigh number the viscosity ratio and an aspect ratio we identify and delineate two transitions in the convective behavior from a regime where the plume can spread upstream against the shear to a regime where the entire plume is advected downstream and from a regime of negligible cross stream circulation to a regime with significant cross stream circulation and thermal entrainment our analysis of the steady profiles of the plumes shows that they initially rise with a constant vertical rise velocity this rise velocity depends on the buoyancy flux and ambient viscosity but is almost independent of the centerline plume viscosity which suggests that most of the thermal plume has a viscosity that is much closer to the ambient viscosity than the centerline viscosity as the plumes approach the lid they decelerate as the viscous drag on them steadily increases the lateral spreading of the plumes under the lid is found to be well described by similarity solutions derived for the spreading of compositional plumes on a rigid surface if the effective viscosity of the thermal plumes is taken to be the ambient viscosity rather than the centerline viscosity a similar theoretical model is found to roughly predict the upstream spreading of thermal plumes at low shear but it breaks down at moderate to high shear where the entire plumes are advected downstream when our results are applied to the earth we find that mantle plumes are mostly divided into only two flow regimes in the upper mantle plumes under slow moving plates experience upstream flow and negligible cross stream circulation while plumes under faster moving plates including all pacific plumes experience significant cross stream circulation and are advected downstream we also demonstrate that geochemical heterogeneities in a plume s source region will result in an azimuthally zoned plume and in an asymmetric geographical distribution of geochemical heterogeneities in the erupted hot spot basalts as is seen in the hawaiian galapagos marquesas and tahiti society island chains for individual mantle plumes we determine their diameter and vertical rise velocity as well as the extent of upstream spreading and the rate of lateral spreading under the lithosphere

weak thermal convection within tilted plume conduits 1 shear from flow in the mantle tilts the conduits of mantle plumes the density stratification at the top of the plume conduit is then unstable in cross section with cold material over hot this stratification drives cross stream convection such convection including the stokes law rise of the plume conduit through the ambient mantle readily mixes isoviscous thermal plumes with their surroundings laboratory experiments by kerr and meriaux 2004 indicate that cross stream convection is weak within plumes with strongly temperature dependent viscosity and significant 56 viscosity contrasts analogy with stagnant lid convection provides scaling relationships with a rayleigh number for cross stream convection within tilted plume conduits only material within a factor of a few e of the central viscosity of the plume convects significantly the scaling analysis shows that the laboratory experiments by kerr and meriaux 2004 had the proper parameter range for the hawaiian plume the petrological conclusion that the plume conduit has been only mildly stirred by cross stream convection is reasonable cross stream convection is less likely for low flux plumes like galapagos than high flux plumes and plumes in the deep mantle compared with those in the upper mantle

quaternary stratigraphy and trace element indices of the yangtze delta eastern china with special reference to marine transgressions the quaternary stratigraphy of the yangtze delta has been revealed by a deep 344 64 m continuous borehole the sediments of which are divided into four sections the early q1 middle q2 and late pleistocene q3 and the holocene q4 six lithofacies include lacustrine fluvial coastal drowned river channel deltaic and shallow marine in these time periods the fluvial and lacustrine lithofacies prevailed during q1and q2 coastal and drowned river channel lithofacies periodically appeared in q1 q2 and q3 shallow marine lithofacies dominated q3 and deltaic lithofacies occurred in q4 based on stratigraphy four transgressive events are inferred trace element sr ba b ga v content and ratios of sr ba and b ga are considered with regard to their distribution in the various lithofacies geochemical facies criteria are established based on combined diagnostic indices sr 160 ppm b 90 ppm sr ba 0 35 b ga 4 0 for the shallow marine lithofacies sr 90 ppm b 50 ppm sr ba 0 2 b ga 2 5 for the terrigenous lithofacies these indices correspond well to paleosalinity data obtained using the sedimentary phosphate method ca ca fe transgressive events identified by the geochemical indices are mostly the same as reflected by marine fossils nevertheless geochemical indices can indicate the occurrence of a weak transgression where marine fossils are rare

crustal thickness along the western galapagos spreading center and the compensation of the galapagos hotspot swell wide angle refraction and multichannel reflection seismic data show that oceanic crust along the galapagos spreading center gsc between 97 w and 91 25pw thickens by 2 3 km as the galapagos plume is approached from the west this crustal thickening can account for v52 of the 700 m amplitude of the galapagos swell after correcting for changes in crustal thickness the residual mantle bouguer gravity anomaly associated with the galapagos swell shows a minimum of 325 mgal near 92 15pw the area where the gsc is intersected by the wolf darwin volcanic lineament wdl the remaining depth and gravity anomalies indicate an eastward reduction of mantle density estimated to be most prominent above a compensation depth of 50 100 km melting calculations assuming adiabatic passive mantle upwelling predict the observed crustal thickening to arise from a small increase in mantle potential temperature of v30 c the associated thermal expansion and increase in melt depletion reduce mantle densities but to a degree that is insufficient to explain the geophysical observations the largest density anomalies appear at the intersection of the gsc and the wdl our results therefore require the existence of compositionally buoyant mantle beneath the gsc near the galapagos plume possible origins of this excess buoyancy include melt retained in the mantle as well as mantle depleted by melting in the upwelling plume beneath the galapagos islands that is later transported to the gsc our estimate for the buoyancy flux of the galapagos plume 700 kg s 31 is lower than previous estimates while the total crustal production rate of the galapagos plume 5 5 m 3 s 31 is comparable to that of the icelandic and hawaiian plumes

deflection of plumes by mantle shear flow experimental results and a simple theory summary linear hotspot tracks indicate relative motion between some hotspot sources and the overlying lithosphere in order to better understand the effects of plate motions and mantle convection on mantle plumes and associated hotspots we consider the path of a continuous plume of buoyant material in a shear flow laboratory experiments show that steady plumes bent over by a linear velocity profile follow parabolic trajectories plume trajectories are also shown to evolve quadratically in time toward a new steady shape after a change in the ambient flow a remarkably simple description of plume dynamics provides good agreement with the experimental data the plume trajectory is determined by the combination of horizontal advection by mantle flow and vertical rise according to a modified stokes law these results are applied to some idealised examples which demonstrate effects of depth dependent mantle viscosity and return flow at least some mantle plumes are likely to be sufficiently robust that they remain close to vertical and therefore stable

the bent hawaiian emperor hotspot track inheriting the mantle wind bends in volcanic hotspot lineaments best represented by the large elbow in the hawaiian emperor chain were thought to directly record changes in plate motion several lines of geophysical inquiry now suggest that a change in the locus of upwelling in the mantle induced by mantle dynamics causes bends in hotspot tracks inverse modeling suggests that although deep flow near the core mantle boundary may have played a role in the hawaiian emperor bend capture of a plume by a ridge followed by changes in sub pacific mantle flow can better explain the observations thus hotspot tracks can reveal patterns of past mantle circulation

mobile sand deposits and shoreface sediment dynamics in the inner german bight north sea abstract this paper presents a conceptual model for the net bedload transport regime on the shoreface of the german bight the model is based on the spatial distribution of the surficial sediment cover north sea sands which is identical to the uppermost layer in the seismic recordings sediment thickness was measured using very high resolution seismic profiling chirp sonar and vibrocoring the three dimensional sediment distribution was estimated using geostatistical methods cokriging the results demonstrate a longshore sand distribution with three distinct zones in zone 1 0 10 m water depth the sediments attain their maximum thickness of 10 2 5 m between 10 and 15 m water depth a relatively thin sand layer of 0 4 1 5 m is observed within zone 2 the seaward adjacent zone 3 15 20 m water depth is characterized by an averaged sand thickness of 2 3 m with local maxima of 5 6 m further offshore the sand layer decreases to about 1 2 m thickness the net bedload transport directions inferred from this sediment zonation comprise a longshore sediment bypassing in zone 1 which results in a substantial sediment supply to the innermost part of the german bight due to bedload convergence shore normal bedload transport shifts sand to and fro across the coastal profile although the net directional transport is seawards this results in sediment depletion between the 10 and 15 m isobaths zone 2 and an adjacent sediment accumulation in deeper waters zone 3

channeling at the base of the lithosphere during the lateral flow of plume material beneath flow line hot spots chains of volcanic edifices lie along flow lines between plume fed hot spots and the thin lithosphere at ridge axes discovery and euterpe musicians seamounts are two examples an attractive hypothesis is that buoyant plume material flows along the base of the lithosphere perpendicular to isochrons the plume material may conceivably flow in a broad front or flow within channels convectively eroded into the base to the lithosphere a necessary but not sufficient condition for convective channeling is that the expected stagnant lid heat flow for the maximum temperature of the plume material is comparable to the half space surface heat flow of the oceanic lithosphere two dimensional and three dimensional numerical calculations confirm this inference a second criterion for significant convective erosion is that it needs to occur before the plume material thins by lateral spreading scaling relationships indicate spreading and convection are closely related mathematically the nusselt number ratio of convective to conductive heat flow in the plume material scales with the flux volume per time per length of flow front of the plume material a blob of unconfined plume material thus spreads before the lithosphere thins much and evolves to a slowly spreading and slowly convecting warm region in equilibrium with conduction into the base of the overlying lithosphere three dimensional calculations illustrate this long lasting and hence observable state of plume material away from its plume source a different flow domain occurs around a stationary hot plume that continuously supplies hot material the plume convectively erodes the overlying lithosphere trapping the plume material near its orifice the region of lithosphere underlain by plume material grows toward the ridge axis and laterally by convective thinning of the lithosphere at its edges the hottest plume material channels along flow lines geologically the regions of lithosphere underlain by either warm or hot plume material are likely to extend laterally away from the volcanic edifices whether or not channeling occurs

petrography and geochemical indices of the lagos lagoon coastal sediments dahomey basin southwestern nigeria sea level change implications abstract the lagos lagoon part of the barrier lagoon geomorphic zone of the nigerian coastal system is underlain by quaternary coastal plain sands of the dahomey basin the study involves sedimentological and geochemical study of the three georeferenced wells to evaluate the lithotopes distribution provenance environment of deposition and the resulting marine transgression regression episodes from previous sea level changes a total of twenty nine core samples were used for this study eighteen of the samples sandstones were subjected to granulometric petrography analyses heavy mineral separation and inductively coupled plasma mass spectrometry icp ms analysis geochemical facies criteria were established based on diagnostic indices the quaternary lithosome indicates the presence of clay siltstone sandstone and conglomerate the sandstones are fine to coarse grained poorly sorted to moderately well sorted negatively to positively skewed and mesokurtic to leptokurtic the heavy mineral assemblage is characterized by zircon rutile tourmaline garnet staurolite sillimanite apatite epidote hornblende and kyanite this assemblage suggests sediments derived from both igneous and metamorphic provenance probably from the ibadan craton the average ztr index is 27 84 indicating mineralogically immature sediments petrographic analysis shows that the most abundant detrital minerals are quartz average of 88 7 feldspar average of 4 37 and rock fragments average of 7 3 the qfr ternary plots revealed that the sands are super mature quartz arenite derived from the uplifted continental block under a humid climatic setting which have undergone moderate transportation and have been subjected to moderate mechanical and chemical weathering the ratios of k 2 o na 2 o and sio 2 suggest passive and active continental margin settings linear discriminant analysis revealed that the sediments were deposited within fluvial to shallow marine lithosomes this corroborated the bivariate plots of the statistical parameter the results of the trace element and ratios considered with regard to their distribution in the diverse lithofacies showing the range of sr from 50 to 120 ppm ba 180 340 ppm ga 5 14 ppm b 25 48 ppm v 53 125 ppm sr ba 0 20 0 39 and ba ga 1 86 7 00 all indicating fluvial shallow and marginal marine lithosomes the lithofacies are derived from a mixed provenance have undergone chemical weathering during transportation and are deposited in the fluvio marine environment these indices indicate the occurrence of weak marine transgressions

benthic habitat mapping concerns using a combined approach acoustic sediment and biological data abstract near shore benthic biotopes in the 2 30 m depth range were analyzed and mapped using a combination of biological sedimentary and acoustic data to interrogate the utility of these methods the surveyed area covered approximately 270 km 2 along 80 km of the southeast coast of portugal the acoustic data were acquired with a single beam ground discrimination system qtc view series v connected to a dual frequency echo sounder 50 and 200 khz sediment grain size and macrofaunal community data were obtained by grab sampling at 88 sites the sedimentary and the biological data were subjected to classification and ordination analysis and the acoustic data obtained with the two frequencies were analyzed individually with the qtc impact v3 4 software and classified into acoustic classes the affinity groups obtained with the three datasets were mapped using a geographic information system the study area showed an inshore offshore pattern with sands ranging from very fine to very coarse revealing a sediment distribution in the near shore shelf comprised by two main areas a very fine fine sand area up to 7 10 m depth and a very coarse coarse sand area offshore in turn the biological data also showed an inshore offshore pattern identifying two main biological assemblages fine very fine sand and coarse very coarse sand communities furthermore the biological pattern clearly reflected the hydrodynamic conditions of the area from highly hydrodynamic shallow depth to the calmer deeper areas accordingly species richness and densities were lower at shallow areas than at deeper depth the acoustic data identified the prevailing biosedimentary gradients along the inshore offshore direction overall the results obtained here showed that the acoustic system could identify two main areas based on sediment grain size which closely related to the two main biological communities groups a and b this study indicates the importance of combining several layers of information in order to increase the spatial resolution of the main biotope distribution validating the acoustic data and detail their sub divisions ground truth sampling furthermore we show that designing ground truth samples on the basis of the acoustic diversity data allows the biological data to speak for itself in general acoustic techniques are used as a means to optimize ground truth sampling this will only be valid if acoustics can capture all the essence of biotope heterogeneity if this is not the case special attention should be given when using broad scale methods acoustic remote sensing devoted to biotope mapping

salt water intrusion mapping by geoelectrical imaging surveys the geoelectrical imaging method is a tool for mapping the intrusion boundary between fresh water and saline water due to its inherent capability to delineate the lateral changes in pore water salinity a new field survey technique that can be used for environmental and geotechnical investigations has been developed this study evaluates the multiscale survey technique as a tool employed in electrical imaging to detect the salt water intrusion boundary in yan state of kedah northwest malaysia the technique was incorporated into these surveys and it has proved to be a robust method for accurately mapping the fresh water saline water boundary the resulting resistivity sections from these surveys were consistent with both the available geological and borehole information from the area and the previous resistivity surveys conducted by the geological survey of malaysia at those sites

aquifer boundaries explored by geoelectrical measurements in the coastal plain of yemen a case of equivalence until 216 vertical electrical schlumberger soundings were made little was known about the subsurface geology at the wadi surdud area in the coastal plain of the yemen arab republic these soundings provide information on the distribution of aquifers aquitards and impermeable rocks and the salinity of the groundwater a first qualitative interpretation of the geoelectrical sounding curves gives a general impression of the hydrogeologic setting and the aquifer boundaries however a more detailed quantitative interpretation shows that no single resistivity model completely satisfies all the hydrogeologic and geologic facts and theories basically two different models are possible in one the thickness of the aquifer is fixed in the other its resistivity is fixed several geologic and hydrogeologic hypotheses may be put forward to support each model varying from relying upon tectonic events and sedimentary depositional environments to influences of agriculture and water abstraction both models are

application and evaluation of electromagnetic methods for imaging saltwater intrusion in coastal aquifers seaside groundwater basin california developing effective resource management strategies to limit or prevent saltwater intrusion as a result of increasing demands on coastal groundwater resources requires reliable information about the geologic structure and hydrologic state of an aquifer system a common strategy for acquiring such information is to drill sentinel wells near the coast to monitor changes in water salinity with time however installation and operation of sentinel wells is costly and provides limited spatial coverage we studied the use of noninvasive electromagnetic em geophysical methods as an alternative to installation of monitoring wells for characterizing coastal aquifers we tested the feasibility of using em methods at a field site in northern california to identify the potential for and or presence of hydraulic communication between an unconfined saline aquifer and a confined freshwater aquifer one dimensional soundings were acquired using the time domain electromagnetic tdem and audiomagnetotelluric amt methods we compared inverted resistivity models of tdem and amt data obtained from several inversion algorithms we found that multiple interpretations of inverted models can be supported by the same data set but that there were consistencies between all data sets and inversion algorithms results from all collected data sets suggested that em methods are capable of reliably identifying a saltwater saturated zone in the unconfined aquifer geophysical data indicated that the impermeable clay between aquifers may be more continuous than is supported by current models

application of gis and hydrogeochemistry of groundwater pollution status of nagapattinam district of tamil nadu india this study evaluated groundwater quality of the coastal aquifer in nagapattinam district with intensive agricultural activities in the southern part of india chemical components such as ph ec tds major cations and anions were used to identify seawater intrusion fifty two groundwater samples were collected from dug and bore wells in this region during summer and monsoon seasons 2011 ec tds na and cl were higher in summer than in monsoon the correlation and two way joining cluster analyses clearly show that groundwater quality is mainly controlled by seawater intrusion and other anthropogenic sources modified hill piper exhibits that most of the samples belong to water contaminated with gypsum sector the interpretation of gibbs plot represents the groundwater samples that fall in evaporation and rock weathering zone and other samples are affiliated to various anthropogenic activities based on na sar chloride hardness and wilcox classification the groundwater is moderately suitable for agriculture this region is vulnerable to seawater intrusion during summer due to the severe pumping of groundwater in groundwater quality maps produced by inverse distance weighting of arcgis some good and medium patches could be used for agriculture to a certain extent the northern southern and central parts of the study area fell in poor quality regions because of seawater intrusion and infiltration of irrigation water contaminated with pesticides and fertilizers

imaging of contaminant plumes using ert in qinhuai river water and its bed caused by urban effluents at nanjing china this paper presents the imaging of contaminant plumes in qinhuai river and its bed for the remediation strategies of the river qinhuai meets with yangtze river at nanjing area via inner and outer channels coursing through urban districts of the city the discharge of urban effluents has badly affected the water quality of the river generally contamination assessment is carried out through traditional point based sampling methods however these methods are often inadequate to estimate accurately the spatial distribution of contaminants and their extension therefore electrical resistivity tomography ert is applied because of its high quality imaging to investigate contamination and its extension in qinhuai river and its bed eight sites were selected at outer and inner channels of the river a 2 d inversion of the perceived data was carried out and the obtained resistivity values were converted into salinity after temperature correction the acquired images of resistivity and salinity show that in low streaming conditions the river has large zones of low resistivity in the water body which are extending toward underlying bed corresponding to high contamination conversely in high streaming conditions the low resistivity zone shrinks significantly at almost all the studied sites except xishan bridge site e which still showed high plume of contamination this phenomenon reveals that in low streaming conditions the contamination level is high while in high streaming conditions salts are flushed out from the river this study further demonstrates that ert method can be a useful technique for the environmental studies of rivers canals and surface water environments

identifying seawater intrusion in coastal areas by means of 1d and quasi 2d joint inversion of tdem and ves data abstract seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes sea level rise extreme phenomena like flooding and droughts and groundwater depletion near to the coastline to evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion geophysical methods are the most appropriate tool to address these researches among all geophysical techniques electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater freshwater and geological layers the combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods in this investigation joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the ferragudo albufeira aquifer system algarve south of portugal for this purpose two profiles combining electrical resistivity tomography ert and time domain electromagnetic tdem methods were measured and the results were compared with the information obtained from exploration drilling three different inversions have been carried out single inversion of the ert and tdem data 1d joint inversion and quasi 2d joint inversion single inversion results identify seawater intrusion although the sedimentary layers detected in exploration drilling were not well differentiated the models obtained with 1d joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined finally the quasi 2d joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling this study demonstrates that the quasi 2d joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas

small scale mapping of sea bed assemblages in the eastern english channel using sidescan sonar and remote sampling techniques abstract a survey was conducted in the eastern english channel to investigate the use of sidescan sonar used in conjunction with traditional biological sampling methods to map the variety and distribution of benthic biotopes i e sea bed habitats and their associated biological communities an area of sea bed approximately 28 km 12 km in size offshore from shoreham u k was surveyed using a digital sidescan sonar system and a mosaic of the output was produced covering 100 of the survey area this was used to divide the area into acoustically distinct regions around which subsequent benthic ground truth surveys were designed benthic communities and sediment types within each of the these regions were sampled using a hamon grab fitted with a video camera and using a heavy duty 2 m beam trawl further information concerning the sea bed was obtained through the application of additional video and photographic techniques substrates within each acoustic region were generally homogeneous in distribution and sediment types ranged across the survey area from cobbles and coarse gravel through to muddy sands analysis of the faunal data revealed the presence of statistically distinct biological assemblages within most of the acoustic regions although species similarity between samples collected from within each acoustic area was often low using a combination of all the data sets five discrete biotopes could be identified and mapped across the area the application of acoustic techniques used in conjunction with biological sampling techniques to map the distribution of sea bed habitats and associated benthic communities is discussed

macrobenthic community structure of soft bottom sediments at the belgian continental shelf within the frame of different research projects a large number of sites at the belgian continental shelf bcs have been sampled for the macrobenthos between 1994 and 2000 these samples cover a diverse range of habitats from the sandy beaches to the open sea from the gullies between the sandbanks to the tops of the sandbanks and from clay to coarse sandy sediments to investigate the large scale spatial distribution of the macrobenthos of the belgian continental shelf the data of all these research projects 728 samples were combined and analysed by means of several multivariate techniques 10 sample groups with similar macrobenthic assemblage structure were distinguished each sample group is found in a particular physico chemical environment and has a specific species composition four sample groups differ drastically both in habitat and species composition and are considered to represent four macrobenthic communities 1 the muddy fine sand abra alba mysella bidentata community is characterized by high densities and diversity 2 the nephtys cirrosa community occurs in well sorted sandy sediments and is characterized by low densities and diversity 3 very low densities and diversity typify the ophelia limacina glycera lapidum community which is found in coarse sandy sediments and 4 the eurydice pulchra scolelepis squamata community is typical for the upper intertidal zone of sandy beaches these macrobenthic communities are not isolated from each other but are linked through six transitional species assemblages the transition between the a alba m bidentata community and the n cirrosa community is characterized by a reduction in the mud content and is dominated by magelona johnstoni the transition between the n cirrosa and the o limacina g lapidum community is distinctive by decreasing densities and coincides with a gradual transition between medium and coarse sandy sediments from the n cirrosa to the e pulchra s squamata community transitional species assemblages related to the transition from the subtidal to the intertidal environment were found each community or transitional species assemblages was found over a specific range along the onshore offshore gradient four types can be discerned 1 almost restricted to the near shore area but possible wider distribution 2 distributed over the full onshore offshore gradient 3 restricted to the near shore area and 4 restricted to the sandy beach environment the diversity pattern on the bcs follows this division with species rich and poor assemblages in the near shore area to only species poor assemblages more offshore the distribution and diversity patterns are linked to the habitat type distinguished by median grain size and mud content

an evaluation of acoustic seabed classification techniques for marine biotope monitoring over broad scales 1 km2 and meso scales 10 m2 1 km2 abstract acoustic seabed classification is a useful tool for monitoring marine benthic habitats over broad scales 1 km 2 and meso scales 10 m 2 1 km 2 its utility in this context was evaluated using two approaches by describing natural changes in the temporal distribution of marine biotopes across the broad scale 4 km 2 and by attempting to detect specific experimentally induced changes to kelp dominated biotopes across the meso scale 100 m 2 for the first approach acoustic backscatter mosaics were constructed using sidescan sonar and multibeam echosounder data collected from church bay rathlin island northern ireland in 1999 2008 and 2009 the mosaics were manually segmented into acoustic facies which were ground truthed using a drop video camera biotopes were classified from the video by multivariate exploratory analysis and cross tabulated with the acoustic facies showing a positive correlation these results were integrated with bathymetric data to map the distribution of seven unique biotopes in church bay kappa analysis showed the biotope distribution was highly similar between the biotope maps possibly due to the stability of bedforms shaped by the tidal regime around rathlin island the greatest biotope change in this approach was represented by seasonal and annual changes in the growth of the seagrass zostera marina in the second approach sidescan sonar data were collected before and after the removal of 100 m 2 of kelp from three sites comparison of the data revealed no differences between the high resolution backscatter imagery it is concluded that acoustic seabed classification can be used to monitor change over broad and meso scales but not necessarily for all biotopes its success depends on the type of acoustic system employed and the biological characteristics of the target biotope

very high resolution side scan sonar mapping of biogenic reefs of the tube worm lanice conchilega reefs of the tube building polychaete lattice conchilega are known to represent hotspots of biodiversity within inter and subtidal soft sediments of the north sea however because of their patchy distribution point sampling does not appropriately map their subtidal spatial distribution this study evaluated the feasibility to detect l conchilega reefs by very high resolution side scan sonar imagery a subtidal very high resolution 410 khz side scan survey combined with grab sampling revealed high densities of l conchilega up to 1979 ind m 2 to coincide with a higher reflectivity patchy and grainy acoustic facies from the side scan sonar imagery individual reefs were estimated to reach a maximum size of 15 m 2 to ground truth the acoustic facies the distribution of intertidal l conchilega reefs was mapped at low tide and side scan sonar imagery was recorded during the following high tide intertidal l conchilega reefs had a patch size of 0 8 m 2 up to 11 6 m 2 elevated 7 5 to 11 5 cm above the surrounding seafloor and covered approximately 10 of the selected area the very high 445 khz resolution side scan sonar imagery revealed a similar acoustic facies as in the subtidal lower resolution 132 khz side scan sonar imagery was less efficient to detect physically less developed l conchilega reefs we conclude that 1 there are no major technical restrictions to map l conchilega reefs using side scan sonar 2 the developmental stage of l conchilega reefs impacts the detectability of the reefs and 3 very high resolution side scan sonar imagery is considered a necessity when mapping small scale structures such as l conchilega reefs c 2008 elsevier inc all rights reserved

the dynamical and thermal structure of deep mantle plumes abstract if the interpretation of the d layer at the base of the mantle as a thermal boundary layer with a temperature increment in the order of 800 k is correct then the formation of deep mantle plumes to vent material from it appears inevitable we demonstrate quantitatively that the strong temperature dependence of viscosity guides the upward flow into long lived chimneys that are 20 km in diameter near the base of the mantle and decrease in width with progressive upward softening and partial melting of plume material the speed of flow up the axis of the plume is correspondingly fast 1 6 m y 1 at the base and 4 8 m y 1 at 670 km depth thermal diffusive spreading of a heated plume is compensated by a slow horizontal convergence of mantle material toward the chimney in response to the lower pressure there this convergence which contributes only a small increment to the flux of material up the plume also serves to throttle the flow in the chimney the global plume mass flux necessary to transport 1 6 10 12 w of core heat upward through the mantle is 1 8 10 6 kg s 1 at its base plume material is probably still significantly below its solidus or eutectic temperature but substantial partial melting is very likely as it rises we speculate that a small fraction of this fluid component eventually emerges at the surface in hot spots with the fate of the remainder being unknown the behaviour and properties of d and of plumes are closely coupled not only are plumes a necessary consequence of a thermal boundary layer but their existence is impossible without that layer

evaluating freshwater lens morphology affected by seawater intrusion using chemistry resistivity integrated technique a case study of two different land covers in carey island malaysia freshwater lenses are vital to small island communities but are susceptible to seawater intrusion due to the physical changes in the shoreline land cover the effect of seawater intrusion and irrigation water on a coastal unconfined aquifer beneath naturally preserved mangrove and deforested mangrove barren belt was investigated in carey island analysis of the total dissolved solids tds and earth resistivity er using a geochemistry electrical integrated technique gave a tds er relationship capable of predicting freshwater lens morphology affected by sea irrigation water the study result shows freshwater was fourfold thicker in close proximity of the mangrove forest than the mangrove barren area the further the shoreline from the mangrove thickest section the less vulnerable was the seawater intrusion and the more fresh the irrigation water and hence the greater the freshwater availability potential

review of electromagnetic induction for mapping barrier island framework geology abstract the geologic framework controls on modern barrier island transgression and the relationship of these controls to subsurface structure hydrology and island geomorphology are not well understood recent evidence suggests that alongshore variations in pre holocene geology of barrier islands modify nearshore hydrodynamic processes and sediment transport ultimately affecting how barrier islands will respond to relative sea level rise explorations of holocene barrier island geology are usually based on cores to supplement bathymetric onshore offshore seismic and or ground penetrating radar gpr surveys the advantages and limitations of these methods with respect to barrier island investigations are briefly described in this review alternative near surface geophysical methods including electromagnetic induction emi sensors are increasingly being used for coastal research because they are non invasive provide continuous subsurface information across a variety of sub environments and are capable of characterizing large areas in a short time although these emi sensors have shown promise in coastal applications a number of issues primarily related to subsurface hydrology need to be addressed to fully assess the limitations of this technique this paper reviews the theory methodology and applications of emi in support of geologic framework studies with particular reference to barrier islands resolution of these issues will allow emi sensors to complement and offer significant advantages over traditional methods in support of an improved understanding of large scale barrier island evolution

boron beryllium and sulfur in holocene sediments and peats of the nile delta egypt their use as indicators of salinity and climate abstract the concentrations of 14 major and trace elements b ba be co cr cu fe mn ni p s v zn and organic c in bulk sediment samples of holocene age from bore holes in the nile delta egypt are considered in terms of sediment grain size and depositional setting using this background information an attempt is made to evaluate paleosalinity and paleoclimatic change by geochemical analyses of peats in every sediment facies examined we find that grain size is a major controlling factor of geochemical composition but the b be ratio is helpful in paleoenvironmental interpretations organic matter content is the major factor affecting element concentrations in peats zn cr fe be cu mn concentrations on an organic matter free basis are lower in these organic rich layers than in other nile delta sediment facies the sulfur content of the peats indicates a decreased importance of freshwater input to holocene lagoons from about 8000 to 3400 years bp high boron beryllium ratios and the presence of gypsum in peats deposited between 6300 and 4900 years bp record the most evaporitic phase affecting this region this geochemical finding is in close agreement with results of other independent paleoclimatic studies which indicate the onset of arid conditions in northeast africa at about 5000 years bp

single beam acoustic ground discrimination of shallow water habitats 50 khz or 200 khz frequency survey the single beam acoustic ground discrimination system qtc view series v was used in the bay of cadiz southwest spain for the identification and mapping of the bottom acoustic diversity the acoustic data were obtained through two successive surveys each conducted with one of the following echo sounder frequencies 50 khz and 200 khz the performance of each survey frequency for the identification of the sedimentary gradients was analyzed the surveys were conducted during high tide given that the majority of the surveyed area is shallower than 5 m although depth may occasionally reach 20 m in specific areas located in a navigation channel the acoustic data obtained at the two different frequencies were individually submitted to manual clustering and a final solution consisting of three acoustic classes was reached for both datasets however only the geographical distribution of the acoustic classes obtained with 50 khz echo sounder frequency was coincident with the spatial distribution of the superficial sediment groups silty medium sand very silty fine sand and mud identified through multivariate analysis of the grain size data of ground truth sediment samples the results obtained with the 200 khz echo sounder frequency did not match the sedimentary gradients obtained for the area surveyed not even the separation of muddy and sandy areas

delineation of saltwater intrusion into the freshwater aquifer of lekki peninsula lagos nigeria recently the deterioration of water quality in the coastal zones of lekki peninsula area of lagos due to saltwater infiltration into the freshwater aquifer has become a major concern with the aim of providing valuable information on the hydrogeologic system of the aquifers the subsurface lithology and delineating the groundwater salinity vertical electrical resistivity ves sounding survey was carried out utilizing surface schlumberger electrode arrays and electrode spacing varying between 1 and 150m the dc resistivity surveys revealed significant variations in subsurface resistivity also the ves resistivity curves showed a dominant trend of decreasing resistivity with depth thus increasing salinity in general the presence of four distinct resistivity zones were delineated viz the unconsolidated dry sand a having resistivity values ranging between 125 and 1 028 m represent the first layer the fresh water saturated soil zone b having resistivity values which correspond to 32 256 m is the second layer the third layer zone c is interpreted as the mixing transition zone of fresh with brackish groundwater the resistivity of this layer ranges from 4 to 32 m while layer four zone d is characterized with resistivities values generally below 4 m reflecting an aquifer possibly containing brine the rock matrix salinity and water saturation are the major factors controlling the resistivity of the formation moreover this investigation shows that saline water intrusion into the aquifers can be accurately mapped using surface dc resistivity method

acoustic habitat and shellfish mapping and monitoring in shallow coastal water sidescan sonar experiences in the netherlands sidescan sonar has been applied in a number of shallow water environments along the dutch coast to map and monitor shellfish and seabed habitats the littoral setting of these surveys may hamper data acquisition flying the towfish in zones of turbulence and waves but also offers valuable opportunities for understanding interpreting and validating sidescan sonar images because of the ability to ground truth during low water periods enabling easy identification and validation acoustical images of some of the mussel banks on the tidal flats of the wadden sea recorded at high tide show a marked resemblance with optical google earth images of the same banks these sonar images may thus serve as acoustic type signatures for the interpretation of sonar patterns recorded in deeper water where ground truthing is more difficult and more expensive similarly acoustic type signatures of japanese oyster banks were obtained in the estuaries in the southwest of the netherlands automated acoustic pattern recognition of different habitats and acoustical estimation of faunal cover and density are possible applications of sidescan sonar both require that the backscattering observed on the sidescan sonar images is directly caused by the biological component of the seafloor filtering offers a simple and effective pre processing technique to separate the faunal signals from linear trends such as emanating from wave ripples or the central tracks of the towfish acoustically estimating the faunal density is approached by in situ counting peaks in backscattering in unit squares these counts must be calibrated by ground truthing ground truthing on littoral mussel banks in the wadden sea has been carried out by measuring their cover along lines during low tide due to its capacity of yielding full cover high resolution images of large surfaces sidescan sonar proves to be an excellent cost effective tool for quantitative time lapse monitoring of habitats 2009 elsevier ltd all rights reserved

global basin classification system a proposed system classifies sedimentary basins worldwide into specific as well as general categories the geologic history of each basin may be subdivided into cycles using three parameters basin forming tectonics depositional sequences and basin modifying tectonics sedimentary basins may be simple with one or two tectonic sedimentary cycles or they may be complex polyhistory basins with many different cycles and events there are eight simple cycle types in this classification which cover continental continental margin and oceanic areas the eight basic cycle types their depositional fills and tectonic modifiers have been given letter and number symbols so that the specific geologic history of each basin may be written as a formula these formulas may then e compared and similarities or differences between basins noted

local lithospheric relief associated with fracture zones and ponded plume material 1 buoyant plume material ponds at the base of oceanic lithosphere it is a natural probe for the relief on the base of the lithosphere owing to plate age because it flows laterally along an upside down drainage pattern geomorphic and geochemical studies of near ridge and on ridge hot spots indicate as expected that the oceanic lithosphere thickens as it ages corridors of thin lithosphere channel plume material along the axis while the thick lithosphere at the end of ridge segments dams this along axis flow channel hot spots extend from plumes toward ridge axes however a good correlation between local lithospheric thickness and local age is not evident at fracture zones within the old ocean basins such a correlation would be expected if the lithosphere cooled only by conduction then pressure release melting and volcanoes would occur preferentially near fracture zones where plume material cascades from thick old to thin young lithosphere this concentration of volcanic edifices does not occur this lack of correlation between lithosphere thickness and plate age is an expected consequence of small scale convection at the base of the lithosphere scaling relationships and numerical models indicate that modestly vigorous convection of several milliwatt per meter squared is sufficient to perturb local lithospheric relief beneath fracture zones without changing the gross correlation of lithospheric thickness with plate age typically the step in lithospheric thickness moves toward the old side of the fracture zone

coseismic dehydration of serpentinite evidence from high velocity friction experiments abstract high velocity friction hvf experiments on serpentinite under conditions equivalent to large amounts of earthquake slip produced large volumes of water vapor derived from the frictional heating induced dehydration of serpentinite fourier transform infrared ftir and thermogravimetry tg differential scanning calorimetry dsc microspectroscopic analyses show that the water in the slip zone and its bounding zones was released due to dehydration during the hvf experiments our experimental results demonstrate that i the run product consists of 10 wt molten materials with abundant vesicles and 90 wt fine grained clasts ii both serpentine and olivine minerals were melted during high velocity slip 1 1 1 3 m s iii rapid serpentine dehydration occurred in a zone of up to 3 mm wide including the slip zone and its bounding zones accompanying frictional melting during high velocity slip and iv no distinct dehydration or frictional melting occurred during low velocity slip

electrical methods ves and ert for identifying mapping and monitoring different saline domains in a coastal plain region alt emporda northern spain summary the spatial variability through time of the degree of salinity of soils and groundwater is a major issue concerning the sustainable management of water resources the problem is accentuated in coastal plain areas where saline bodies of different origin coexist we present an extensive geoelectrical resistivity dataset collected in the alt emporda clastic coastal aquifer system ne spain integrating the results of field campaigns undertaken within a period of more than two decades the dataset is unique in the literature and comprises highly valuable information for the investigation of saline domains the joint application of vertical electrical sounding ves and electrical resistivity tomography ert methods allowed the identification of saline domains and monitoring their evolution through time geophysical data gathered during field campaigns in 1982 2002 and 2010 were calibrated and interpreted on the basis of soil and groundwater physico chemical analyses and hydrogeological stratigraphic and geomorphological data the results illustrate the potential of electrical resistivity methods at differentiating saline domains in coastal aquifer areas and at modelling their configuration and evolution although the ves data processing allows solving the one dimensional resistivity structure of the subsurface the inversion imposes a 1d layered model thus interpretation of two dimensional structures is subject to the interpolation between discrete measures in contrast ert data offer a continuous 2d image of the resistivity distribution both laterally and in depth given that the bulk resistivity of the medium is extremely sensitive to salt content the ert profiles permitted identifying and determining the geometry of hyper saline areas characterized by resistivities of less than 5 m the study demonstrates the efficiency of the electrical methods to map subsurface conductive zones and illustrates how the accurate knowledge of the hydrogeological pattern results critical to meet this objective