internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

three dimensional modelling of a holocene tufa system in the lathkill valley north derbyshire using ground penetrating radar unlithified and partly lithified carbonate sequences are ideally suited to the application of ground penetrating radar gpr augmented by percussion augering and shallow seismic techniques all tied to present day topography using global positioning system gps methods this methodology provides the first clear information on the distribution and geometry of lithofacies within buried tufa complexes the approach has been applied to a thick succession of holocene tufas filling a gorge site along a 3 5 km length of the river lathkill north derbyshire earlier studies have demonstrated the presence of up to 16 m of tufas and sapropels associated with two transverse tufa dams barrages these strata have been accumulating throughout the holocene although tufa developments at present are of minor extent internal tufa morphologies are recorded by gpr as bright laterally continuous reflections for lithified concretionary and lithoclast rich horizons the brightest reflectors occur within well cemented barrages and delineate core areas and prograding buttress zones in contrast unlithified lime muds and sapropels produce low contrast reflections lithostratigraphic control and depth calibration of the gpr profiles was provided by percussion augering at selected sites six distinct lithofacies and four secondary barrages are identified in the study constructional and destructional events can be identified and correlated within the gpr profile network and the internal growth morphologies of the barrages are apparent gpr profiles also clearly define the evolution of the facies geometries three phases of tufa development can be recognized within the gpr data and greatly extend our understanding of holocene tufa forming processes in valley sites a early holocene barrage build ups but with limited paludal deposition b middle holocene ponding and sapropel accumulation under warm conditions and c late holocene barrage termination and valley levelling probably coincidental with anthropogenic activity this type of multidisciplinary approach should be considered as an essential prerequisite to all biostratigraphic and geochemical studies of holocene freshwater carbonate sites

radar reflections from sedimentary structures in the vadose zone ground penetrating radar gpr is a suitable technique for imaging sedimentary structures in the vadose zone because small texture related capillary pressure variations lead to changes in water content and electromagnetic properties to study exactly how gpr reflections are generated by sedimentary structures gpr profiles of an aeolian sedimentary succession are combined with measurements of textural electromagnetic and water retention characteristics from a trench time domain reflectometry indicates that small variations in texture in the high angle dune sediment are associated with changes in water content synthetic modelling shows that these changes cause clear gpr reflections in an experimental approach to estimate the radar response of structures below the wave resolution i e features smaller than 4 variations in grain size distribution and porosity in a thin section were used to reconstruct water retention curves and impedance models of the thinly layered sediment synthetic radar records calculated from the impedance models show that reflections from the studied subcentimetre scale structures are composites of interfering signals although these low amplitude interfering signals will commonly be overprinted by more prominent reflections they may cause reflection patterns that change with frequency and do not represent primary bedding

the sedimentary structure of linear sand dunes linear sand dunes dunes that extend parallel to each other rather than in star like or crescentic forms are the most abundant type of desert sand dune1 but because their development and their internal structure are poorly understood they are rarely recognized in the rock record2 models of linear dune development2 3 4 5 6 have not been able to take into account the sub surface structure of existing dunes but have relied instead either on the extrapolation of short term measurements of winds and sediment transport or on observations of near surface internal sedimentary structures from such studies it has not been clear if linear dunes can migrate laterally2 7 8 here we present images produced by ground penetrating radar showing the three dimensional sedimentary structure of a linear dune in the namib sand sea where some of the world s largest linear dunes are situated these profiles show clear evidence for lateral migration in a linear dune moreover the migration of a sinuous crest line along the dune produces divergent sets of cross stratification which can become stacked as the dune height increases and large linear dunes can support superimposed dunes that produce stacked sets of trough cross stratification these clear structural signatures of linear dunes should facilitate their recognition in geological records

tephrochronological dating of varved interglacial lake deposits from pianico sellere southern alps italy to around 400 ka the sediment record from the pianico palaeolake in the southern alps is continuously varved spans more than 15 500 years and represents a key archive for interglacial climate variability at seasonal resolution the stratigraphic position of the pianico interglacial has been controversial in the past the identification of two volcanic ash layers and their microscopic analysis provides distinct marker layers for tephrochronological dating of these interglacial deposits in addition to micro facies analyses reconstructing depositional processes of both tephra layers within the lake environment their mineralogical and geochemical composition has been determined through major element electron probe micro analysis on glass shards comparison with published tephra data traced the volcanic source regions of the pianico tephras to the campanian volcanic complex of roccamonfina italy and probably the puy de sancy volcano in the french massif central available dating of near vent deposits from the roccamonfina volcano provides a robust tephrochronological anchor point at around 400 ka for the pianico interglacial these deposits correlate with marine oxygen isotope stage mis 11 and thus are younger than early to middle pleistocene previously suggested by k ar dating and older than the last interglacial as inferred from macrofloral remains and the geo logical setting copyright 2006 john wiley sons ltd

gpr in sediments advice on data collection basic processing and interpretation a good practice guide within sedimentological studies ground penetrating radar gpr is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non destructive method the purpose of this paper is to provide an introduction to the collection processing and interpretation of gpr data so that future sedimentary studies can be improved with gpr equipment now being lightweight robust and portable proper data collection and survey design methods need to be followed in order to acquire high resolution subsurface digital data various factors are discussed including reflection profiling velocity soundings test surveys topography logistics data quality and extreme environments basic data processing and visualization are then reviewed followed by a discussion on gpr interpretation strategies including a background to radar stratigraphy for the sedimentary geologist or geomorphologist gpr offers unique data of the shallow subsurface including stratigraphy geometry architecture and structure

ground penetrating radar antennae frequencies and transmitter powers compared for penetration depth resolution and reflection continuity1 twelve ground penetrating radar gpr experiments were conducted on the modern wave influenced william river delta on the southern shore of lake athabasca in northern saskatchewan canada the delta is a well sorted quartzoserich clean sand dominated water saturated geomorphic feature which provided an ideal site to test gpr penetration depths resolution and continuity of reflections were compared for different antennae frequencies 25 50 100 200 mhz and transmitter powers pulser voltage 400 v 1000 v the data show significant variations in vertical resolution from 0 15 m to 0 76 m 200 25 mhz depth of penetration from 14 m 28 m 200 25 mhz and continuity of reflections increasing the transmitter power from 400 v to 1000 v increases the depth of penetration by 5 to 14 and improves the continuity of reflections with little effect on the resolution

ground penetrating radar a near face experience from washington county arkansas digital ground penetrating radar gpr is an emerging technology for detecting locating and or mapping features in the shallow subsurface it has application to geology civil engineering environmental science engineering soil science and many other fields this case history describes a high quality gpr survey performed in very close proximity to a vertical limestone rock face at a roadcut site in northwest arkansas the configuration allowed interpretation of the gpr results with the maximum of amount of geologic control the rock face itself our experience suggests that gpr has significant potential as a high resolution tool for mapping shallow structure and stratigraphy in carbonate rocks

sedimentology of an upper mesotidal 3 7 m holocene barrier willapa bay sw washington u s a in coastal southwest washington there is an unusually large largest along the pacific coast and thick holocene sand barrier 38 km long by 2 0 to 3 5 km wide by 17 to 25 m thick the barrier is 2 to 8 times thicker than previously described holocene barriers along the north american coast all of which have lower magnitude tidal regimes the willapa barrier is influenced by 1 a 3 7 m upper mesotidal regime 2 high 4 7 m winter storm waves and 3 a high sediment influx via northward longshore transport in winter from the nearby columbia river mouth from the perspective of oil reservoir modeling assuming 20 porosity and 40 recovery the barrier has a potential reservoir of recoverable fluids of one billion barrels

ground penetrating radar used to assess aggregate in catastrophic flood deposits northeast alberta canada coarse grained aggregate deposited by a catastrophic flood located north of fort mcmurray alberta was examined using ground penetrating radar gpr and lithostratigraphic logging techniques gpr transects were acquired from an upper scoured zone of flood deposits sedimentary structures cross beds and plane beds within the coarse sand and gravel and determinations of depth to bedrock sediment thickness of the aggregate were recognized in the gpr profiles by their varying dielectric properties fine grained conductive underlying oil sand till or glaciolacustrine sediment silt and clay attenuated the radar signal the sedimentary structures mapped from the gpr transects were confirmed in adjacent trench exposures we suggest that gpr is an efficient methodology for determining volumes of aggregate reserves thicknesses of aggregate deposits and mapping sedimentary structures of high energy fluvial sediments key words aggregate ground penetrating radar alberta spillway

volumetric analysis of a new england barrier system using ground penetrating radar and coring techniques ground penetrating radar gpr profiles calibrated with core data allow accurate assessments of coastal barrier volumes we applied this procedure successfully to the barrier system along saco bay maine usa as part of a sediment budget study that focused on present day sand volumes in various coastal shoreface and inner shelf lithosomes and on sand fluxes that have affected the volume or distribution of sand in these sediment bodies through time on gpr profiles the components of the barrier lithosome are readily differentiated from other facies except where the radar signal is attenuated by brackish or salty groundwater significant differences between dielectric properties of the barrier lithosome and other units commonly result in strong boundary reflectors the mostly sandy barrier sediments allow deep penetration of gpr waves in contrast to finer grained strata and till covered bedrock within the saco bay barrier system 22 pm 3 times 10 6 m 3 of sediment are unevenly distributed

the use and application of gpr in sandy fluvial environments methodological considerations ground penetrating radar gpr is a popular technique for imaging and interpreting sedimentary architecture however current literature shows a wide range in the quality of information provided on the gpr methodology and processing technique it is therefore difficult to judge the validity of the gpr interpretations and this produces inherent difficulties for comparison between surveys this paper describes the key steps required to collect process and interpret gpr surveys in sandy fluvial sediments gpr data from the south saskatchewan river canada are used to illustrate each stage of data collection and processing particular attention is given to the appropriate set up conditions for the gpr software and hardware the selection of data processing techniques and velocity analysis methods for the interpretation of gpr reflectors are also investigated using ground truth control provided by a cut face exposure this paper presents recommendations for a systematic and rigorous methodology for the collection processing and interpretation of gpr data in sandy fluvial environments the paper suggests that all data collection parameters and processing steps should be recorded or tabulated in any gpr publication to facilitate comparisons between surveys

iron isotopic evolution during fractional crystallization of the uppermost bushveld complex layered mafic intrusion we present 56fe 56fe 54fe relative to standard irmm 014 data from whole rock and magnetite of the upper and upper main zones uumz of the bushveld complex with it we assess the role of fractional crystallization in controlling the fe isotopic evolution of a mafic magma the uumz evolved by fractional crystallization of a dry tholeiitic magma to produce gabbros and diorites with cumulus magnetite and fayalitic olivine despite previous experimental work indicating a potential for magnetite crystallization to drastically change magma 56fe we observe no change in whole rock 56fe above and below magnetite saturation we also observe no systematic change in whole rock 56fe with increasing stratigraphic height and only a small variation in 56fe in magnetite separates above magnetite saturation whole rock 56fe errors twice standard deviation 2 throughout the uumz ranges from 0 01 0 03 to 0 21 0 09 56feaveragewr 0 10 0 09 n 21 isotopically light outlier 56fewr 0 15 and magnetites range from 0 28 0 04 to 0 86 0 07 56feaveragemgt 0 50 0 15 n 20 similar to values previously reported for other layered intrusions we compare our measured 56fewr to a model that incorporates the changing normative mineralogy calculated temperatures and published fractionation factors of fe bearing phases throughout the uumz and produces 56fewr values that evolve only in response to fractional crystallization our results show that the fe isotopic composition of a multiply saturated multiple phases on the liquidus magma is unlikely to change significantly during fractional crystallization of magnetite due to the competing fractionation of other fe bearing cumulus phases this article is protected by copyright all rights reserved

combining multi scale geophysical techniques for robust hydro structural characterisation in catchments underlain by hard rock in post glacial regions summary accurate conceptual models of groundwater systems are essential for correct interpretation of monitoring data in catchment studies in surface water dominated hard rock regions modern ground and surface water monitoring programmes often have very high resolution chemical meteorological and hydrological observations but lack an equivalent emphasis on the subsurface environment the properties of which exert a strong control on flow pathways and interactions with surface waters the reasons for this disparity are the complexity of the system and the difficulty in accurately characterising the subsurface except locally at outcrops or in boreholes this is particularly the case in maritime north western europe where a legacy of glacial activity combined with large areas underlain by heterogeneous igneous and metamorphic bedrock make the structure and weathering of bedrock difficult to map or model traditional approaches which seek to extrapolate information from borehole to field scale are of limited application in these environments due to the high degree of spatial heterogeneity here we apply an integrative and multi scale approach optimising and combining standard geophysical techniques to generate a three dimensional geological conceptual model of the subsurface in a catchment in ne ireland available airborne lidar electromagnetic and magnetic data sets were analysed for the region at field scale surface geophysical methods including electrical resistivity tomography seismic refraction ground penetrating radar and magnetic surveys were used and combined with field mapping of outcrops and borehole testing the study demonstrates how combined interpretation of multiple methods at a range of scales produces robust three dimensional conceptual models and a stronger basis for interpreting groundwater and surface water monitoring data

three dimensional reverse time migration of ground penetrating radar signals three dimensional 3d ground penetrating radar gpr systems and 3d seismic imaging techniques have been developing fast and evolving rapidly in the last decade ray based migration methods have been successfully applied to processing 3d gpr signals based on the similarity between electromagnetic and seismic waves however reverse time migration rtm of 3d gpr signals has not been well studied in the past in this paper we present a 3d rtm based on maxwell s equations for 3d gpr surveys migration recovers the true subsurface structure from a distorted and unfocused time profile and suppresses common electromagnetic clutter and noise rtm based on maxwell s equations can consider conductivity directly and compensate for the attenuation within a high conductivity zone compared with 2d rtm 3d rtm back propagates both in line and cross line signals simultaneously and can include complex 3d permittivity and conductivity models we have integrated a parallel finite difference time domain fdtd algorithm based on a hybrid mpi and openmp scheme to reduce the computational cost of 3d problems the 3d rtm experiments on an anomaly of em shape and a realistic sand dune model demonstrate the effective recovery of 3d subsurface structures

anatomy of a bioclastic grainstone megashoal middle silurian southern ontario revealed by ground penetrating radar porous grainstones deposited as offshore carbonate sand shoals are important hydrocarbon reservoirs but little is known about their internal architecture and its effect on reservoir heterogeneity the middle silurian amabel formation exposed along the niagara escarpment of southern ontario provides an unparalleled opportunity to examine such a deposit in three dimensions with photomosaics and ground penetrating radar the amabel is a dolomitized bioclastic grainstone unit up to 25 m thick composed mainly of crinoid ossicles it thins and grades westward to thin bedded argillaceous dolostones although previously assumed to be reefal the undulating and oblique bedding that dominates the internal geometry was caused by vertical and lateral accretion on hummocky topography and scour surfaces some scours are huge as much as 15 m deep and attest to the dramatic nature of sediment movement by storms and hurricanes ground penetrating radar successfully detects the large scale bedding pattern and in conjunction with outcrop observations has potential for mapping the three dimensional architecture of ancient lithified deposits

sand deposition during the last millennium at aberffraw anglesey north wales as determined by osl dating of quartz abstract ground penetrating radar gpr was used to identify sediment units at the terminus of a small dune field at aberffraw nine samples were taken from boreholes sample locations were based on the stratigraphy established by gpr quartz grains were dated using a single aliquot regenerative dose protocol that allows for sensitivity changes sand deposition at llyn coron aberffraw occurred three times in the last 700 years with initial sand movement occurring around 1331 ad when historical documents record sand being mobilised in a strong storm

listric versus planar normal fault geometry an example from the eisenstadt sopron basin e austria in a gravel pit at the eastern margin of the eisenstadt sopron basin a satellite of vienna basin austria neogene sediments are exposed in the hanging wall of a major normal fault the anticlinal structure and associated conjugated secondary normal faults were previously interpreted as a rollover anticline above a listric normal fault the spatial orientation and distribution of sedimentary horizons and crosscutting faults were mapped in detail on a laser scan of the outcrop wall subsequently in order to assess the 3d distribution and geometry of this fault system a series of parallel ground penetrating radar gpr profiles were recorded behind the outcrop wall both outcrop and gpr data were compiled in a 3d structural model providing the basis for a kinematic reconstruction of the fault plane using balanced cross section techniques however the kinematic reconstruction results in a geologically meaningless normal fault cutting down and up section additionally no evidence for a weak layer serving as ductile detachment horizon i e salt or clay horizon can be identified in stratigraphic profiles instead the observed deflection of stratigraphic horizons may be caused by a displacement gradient along a planar master fault with a maximum displacement in the fault centre decreasing towards the fault tips accordingly the observed deflection of markers in the hanging wall and in a nearby location in the footwall of the normal fault is interpreted as large scale fault drag along a planar fault that records a displacement gradient instead of a rollover anticline related to a listric fault

mapping the architecture of glaciofluvial sediments with three dimensional georadar three dimensional 3 d ground penetrating radar georadar mapping offers new opportunities for determining the geometries and facies of surficial sedimentary units to investigate the potential of this high resolution technique and at the same time study the architecture of quaternary glaciofluvial deposits georadar data have been collected on a dense grid established across a sequence of braided river gravels and sands in northeastern switzerland results of this survey are striking 3 d images that provide many more details and much more reliable information on the heterogeneities of the shallow underground than are afforded by conventional georadar profile data continuous subhorizontal and oblique reflections can be traced throughout vertical sections and horizontal slices of the georadar data block to a depth of approx 15 m clearly defined are the dominant flow direction of the ancient braided river system the boundaries between different sedimentary facies and the level of the ground water table trough fill sediments and subhorizontal channel deposits observed on 7 m high quarry walls can be followed confidently in the subsurface the orientation shape and size of the troughs and the strike and dip of the cross bedding are all well resolved

ground penetrating radar characterization and porosity evolution of an upper pleistocene oolite capped depositional cycle red bays northwest andros island great bahama bank abstract linkages among surface sediments depositional processes geomorphic forms stratigraphic architecture and pore distribution in bahamian sand bodies and oolite capped depositional successions have been characterized in recent studies an understanding of how these parameters especially porosity are preserved or modified in the eogenetic environment is essential in bridging the gap between modern and ancient analogs two complementary 3d 200 mhz and 400 mhz ground penetrating radar surveys and three shallow cores reveal that the uppermost part of the upper pleistocene marine isotope stage 5e lucayan formation at red bays andros island great bahama bank comprises a single 6 m thick upward shallowing parasequence six radar packages p1 p6 bounded by radar surfaces s1 s6 have been identified in the two 3d radar volumes the stratigraphic succession indicates development of a burrowed backshoal lagoon during early flooding of the bank top followed by deposition of flood tide driven low angle sheet sands and sigmoidal subaqueous dune deposits as the shelf margin sand shoal moved bankward as a function of continued sea level rise constructional accommodation on the front of the prograding subaqueous dune in the northwest part of the survey area and erosional accommodation created by downcutting of a shallow tidal channel into the upper part of the subaqueous dune depositional unit in the northeast part of the study area were filled with peloid and ooid dominated carbonate sands as sea level stabilized the uppermost radar package is a thin 0 15 to 0 55 m partially calichified carbonate sand sheet that mantles the entire survey site and that reflects late highstand and fall of sea level exposure of the studied interval to meteoric vadose diagenesis over the past 100 000 years has resulted in partial stabilization of the largely aragonitic precursor sediment through selective partial dissolution of aragonitic grains mainly ooid cortical layers peloids and mollusk shells accompanied by precipitation of patchily distributed low magnesium calcite cement core data demonstrate a relationship between stratigraphically controlled sedimentological attributes diagenesis and pore distribution three distinctive zones of porosity were present upon deposition a lower zone of relatively high interparticle porosity 21 3 to 33 2 in the medial part of p1 a low porosity zone

ground penetrating radar investigation of a lake bonneville deita provo level brigham city utah field experiments carried out in the brigham sand and gravel company pit near brigham city utah show an impressive similarity between observed gravelly deltaic foreset facies in highwall exposures and inclined reflections detected by ground penetrating radar gpr beneath the pit floor the radar indicates additional inclined strata more than 30 m deep in a test to compare different antenna frequencies 50 100 and 200 mhz using a 400 v transmitter 50 mhz antennas are capable of detecting gravel facies in excess of 30 m whereas signal loss for the 100 and 200 mhz antennas occurs below 23 and 17 m respectively though providing higher resolution

beachrock a tool for reconstructing relative sea level in the far field abstract today s understanding of sea level change developed through a combination of process based physical modelling and observational data observational data of sea level change derives from coral reefs in the far field of the former ice sheets where a geographically variable relative sea level signal is expected as a response of the earth to ocean loading given this variability and the limited geographical distribution of coral reefs there is a need to explore other non coral based sea level markers to further understand sea level change and for example to fingerprint melt water here we present beachrock as a coastal deposit suitable for relative sea level rsl observations in the far field beachrock is an intertidal deposit forming in the zone where carbonate saturated meteoric and marine water mix and p co 2 decreases we provide the conceptual framework for beachrock analysis and describe techniques suitable for analysing and dating the deposit the approach is standardised by outlining the sediment characteristics in terms of rsl indicative meaning and indicative range and is tested against published data a study conducted on coasts of the mediterranean sea exemplifies the utility of beachrock for rsl reconstruction it is shown that the precision of the reconstruction is derived from the combined uncertainty of age and tidal amplitude or tidal range the uncertainty can be reduced to half the tidal amplitude when a deposit can be ascribed to the upper or lower intertidal zone beachrock based data benefit from the lack of non quantifiable error terms such as post depositional compaction due to the instantaneous formation and high preservation potential of the deposit this underlines the high precision of beachrock based rsl reconstruction which is a prime requirement for testing and extending coral based records

identifying causes of ground penetrating radar reflections using time domain reflectometry and sedimentological analyses ground penetrating radar gpr is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves however little is known about the exact cause of gpr reflections because few studies have coupled wave theory to petrophysical data in this study a 100 and 200 mhz gpr survey was conducted on aeolian deposits in a quarry time domain reflectometry tdr was used to obtain detailed information on the product of relative permittivity er and relative magnetic permeability lr which mainly controls the gpr contrast parameter in the subsurface combining tdr data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr synthetic radar traces constructed using the tdr logs and sedimentological data from the lacquer peels were compared with the actual gpr sections numerous peaks in erlr which are superimposed on a baseline value of 4 for dry sand are caused by potential gpr reflectors these increases in erlr coincide with the presence of either organic material having a higher water content and relative permittivity than the surrounding sediment or iron oxide bands enhancing relative magnetic permeability and causing water to stagnate on top of them sedimentary structures as reflected in textural change only result in possible gpr reflections when the volumetric water content exceeds 0ae055 the synthetic radar traces provide an improved insight into the behaviour of radar waves and show that gpr results may be ambiguous because of multiples and interference

ground penetrating radar of northern lacustrine deltas ground penetrating radar gpr was used in several selected deltaic sedimentary environments to better understand subsurface stratigraphy and reconstruct former depositional environments the profiles provide high resolution continuous subsurface data on facies thickness and depths orientation of major sedimentary structures postdepositional failure planes and depth of peat deposits field experiments were carried out on six river deltas records from four of the deltas exhibit sedimentary facies a record from one delta shows a possible slump and records from another delta reveal the thickness and stratigraphic relationships of peat deposits the delta types are i sandy wave influenced ii sandy immature wave influenced steeper middle and lower shoreface iii sandy braided and iv gravelly fan foreset in areas of limited subsurface control stratigraphic logs from drill core cutbank exposure or geophysical logs radar profiles can provide big picture perspectives of the subsurface

ground penetrating radar application in a shallow marine oxfordian limestone sequence located on the eastern flank of the paris basin ne france abstract a ground penetrating radar gpr survey has been carried out in upper jurassic limestones located on the eastern flank of the paris basin ne france the potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface the fundamentals of the gpr technique are described penetration depth and vertical resolution depends on the soil conditions the characteristics of input signal and the configuration of the transmitter receiver assembly in the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum i e approximately 55 m several depositional units are outlined on the gpr profiles six different lithological units are recognised with distinct gpr reflection characteristics the profiles illustrate the internal 3d organisation of the carbonate platform and its geometry they provide detailed insight into the nature of an oxfordian reefal build up the high resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3d depositional working model the gpr method is a non destructive remote sensing technique that is cost effective the method is considered complementary to other conventional high resolution reservoir characterisation studies it represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface

influence of organic matter in soils on radar wave reflection sedimentological implications abstract soils are excellent reflectors of ground penetrating radar gpr signals because of the ability of organic matter to hold water in this paper gpr profiles of an eolian sedimentary succession are combined with textural dielectric and moisture retention characteristics to illustrate the influence of soil moisture on radar wave reflection organic matter in this succession varies strongly from lt 0 15 for clean sand to 7 for the most prominent soil whereas grain size distributions are comparable moisture retention curves show a complex relationship between suction potential pf and volumetric water content as a result of their uniform pore size distribution clean sand and weakly developed soils with lt 1 organic matter experience a sudden loss of water between pf 1 5 and pf 1 8 going directly from saturated to almost dry conditions in contrast the most prominent soil shows a more gradual decrease in with increasing suction potential it follows that the dielectric contrast between clean sand and this soil increases sharply above pf 1 5 reaches a maximum value at field capacity conditions and then decreases slowly synthetic gpr images for different suction potentials show that field capacity conditions when reflection coefficients are high are favorable for tracing one single soil dry sediments are preferable when imaging widely spaced soils whereas saturated sediments are best when imaging closely spaced soils

detailed internal architecture of a fluvial channel sandstone determined from outcrop cores and 3 d ground penetrating radar example from the middle cretaceous ferron sandstone east central utah ideally characterization of hydrocarbon reservoirs requires information about heterogeneity at a submeter scale in three dimensions detailed geologic information and permeability data from surface and cliff face outcrops and boreholes in the alluvial part of the ferron sandstone are integrated here with three dimensional 3 d ground penetrating radar gpr data for analysis of a near surface sandstone reservoir analog in fluvial channel deposits the gpr survey covers a volume with a surface area of 40 x 16 5 m and a depth of 12 m five architectural elements are identified and described in outcrop and well cores using a sixfold hierarchy of bounding surfaces internally the lower four units consist of fine grained parallel laminated sandstone and the upper unit consists of medium grained trough cross bedded sandstone the same sedimentary architectural elements and associated bounding surfaces are distinguished in the gpr data by making use of principles developed in seismic stratigraphic analysis to facilitate comparison of geologic features in the depth domain and radar reflectors in the time domain the radar data are depth migrated the gpr interpretation is carried out mainly on migrated 100 mhz data with a vertical resolution of about 0 5 m measures of the spatial continuity and variation of the first and second order bounding surfaces are obtained by computing 3 d experimental variograms for each architectural element each radar begin page 1584 facies the maximum correlation length of the dominant internal features ranges between 4 and 6 m and the anisotropy factor ranges between 0 6 and 0 95

gpr survey of a lobate rock glacier in yankee boy basin colorado usa abstract the internal structure of a lobate rock glacier located in the san juan mountains of southwest colorado was investigated using ground penetrating radar gpr a 440 m 25 mhz longitudinal profile oriented along the central axis of the rock glacier shows moderate to strongly coherent reflection horizons or layers that can be recognized clearly to a depth of 30 35 m the layers are interpreted as representing ice supersaturated sediments and coarse blocky rockslide debris that are the result of flow perhaps generated by seasonal snow pack covered by episodic debris flows or high magnitude discharges of talus from the cirque headwall profiles collected at 50 mhz indicate that in the upper 20 m thickness of the rock glacier many of these layers are laterally continuous the total depth of penetration 40 m at 25 mhz was sufficient to detect the rock glacier cirque floor contact which is composed of underlying moraine several prominent reflection events that subdivide the profile into broad 10 15 m thick layers represent contacts between major depositional units these units are believed to be individual flow lobes that were initiated at various cirque headwall locations we interpret this rock glacier to be a composite feature that formed by a process involving the development and subsequent overlap of discrete flow lobes that have over ridden older glacial moraine and protalus rampart materials the latter materials have been incorporated into the present flow structure of the rock glacier

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

evidence for dune reactivation from gpr profiles on the maputaland coastal plain south africa the maputaland area of northeastern south africa is characterized by extensive dune fields which developed during polyphase reworking of regional aeolian cover sand from the mid pleistocene to the holocene extended parabolic dunes many preserved only as wind rift trailing limbs as well as areas of sinuous crested dunes hummocky dune systems and the high composite accretionary coastal barrier dune cordon are the dominant dune forms there are few natural sections exposing the stratigraphic succession and unequivocal relative age relationships between dune systems are uncommon a ground penetrating radar gpr survey of dunes and representative aeolian sand stratigraphic units was undertaken in order to investigate the internal structure of the different dune forms and identify stratigraphic relationships between buried sedimentary units the gpr profiles revealed that the trailing limbs of almost all the parabolic dunes that were surveyed comprise stacked sand units separated by low angle reflections interpreted as bounding surfaces which accumulated through polyphase vertical accretion most extended parabolic dunes are aligned north south and the upper parts of the dunes are characterized by inclined reflections in gpr profile interpreted as large scale sets of cross stratification with apparent dips toward the west a hummocky dune revealed cross stratified aeolian sand superimposed on a truncated dune form and probably formed through deflation of pre existing dunes using 100 mhz and 200 mhz antennae it is clear that gpr is capable of imaging very fine sedimentary structures and buried erosional surfaces in the homogeneous aeolian sand of maputaland at some of the sites investigated the buried sand units identified were sampled by hand augering for infrared stimulated luminescence dating the age determinations on these samples suggest that vertical accretion of up to 7 m of sand occurred intermittently over variable time scales up to 25 000 years on some parabolic dune limbs during the late pleistocene in some complex dunefields adjacent dunes were mobilized at different times suggesting that remobilization was localized the implications of the complex internal structure and vertical accretion of extended parabolic dunes are discussed in the context of changes in vegetation cover and water table due to seasonal and short term cyclical climate variations as well as long term climate change patterns during the last glacial cycle and the holocene

the use of gpr to image three dimensional 3 d turbidite channel architecture in the carboniferous ross formation county clare western ireland

the structure and development of foredunes on a locally prograding coast insights from ground penetrating radar surveys norfolk uk the internal structure of coastal foredunes from three sites along the north norfolk coast has been investigated using ground penetrating radar gpr which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non destructive or geophysical technique combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution the radar profiles show the internal structures which include foreslope accretion trough cut and fill roll over and beach deposits foredune ridges contain large sets of low angle cross stratification from dune foreslope accretion with trough shaped structures from cut and fill on the crest and rearslope foreslope accretion indicates sand supply from the beach to the foreslope while troughs on the dune crest and rearslope are attributed to reworking by offshore winds bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement radar sequence boundaries within dunes have been traced below the water table passing into beach erosion surfaces these are believed to result from storm activity which erodes the upper beach and dunes in one example at brancaster a dune scarp and erosion surface may be correlated with erosion in the 1950s possibly the 1953 storm results suggest that dune ridge development is intimately linked to changes in the shoreline with dune development associated with coastal progradation while dunes are eroded during storms and where beaches are eroding a stable coast provides more time for dune development resulting in higher foredune ridges a model for coastal dune evolution is presented which illustrates stages of dune development in response to beach evolution and sand supply in contrast to many other coastal dune fields where the prevailing wind is onshore on the north norfolk coast the prevailing wind is directed along the coast and offshore which reduces the landward migration of sand dunes

geophysical investigation of underground water content zones using electrical resistivity tomography and ground penetrating radar a case study in hesarak karaj iran abstract this paper describes the successful application of an integrated geophysical survey to investigate the depth of underground water table and the location of probable cavity occurrences at a developing residential area to design the foundation of under constructing urban buildings located at hesarak karaj alborz province of iran the integrated shallow and non invasive geophysical survey consists of electrical resistivity tomography ert and ground penetrating radar gpr these methods could appropriately indicate the existence of the water table at a depth of approximately 12 m while processed gpr radargrams localized no cavity occurrences in the studied site a 100 mhz shielded gpr antenna has been used to conduct a high resolution shallow subsurface survey in order to delineate probable cavities of the area and two electrical arrays of gradient and wenner have been used as well to image resistivity variations of subsurface layers especially for prospecting water saturated zone the acquired results which were in good accordance with the reality of the studied area at locating water table and cavity occurrences could effectively provide guidance to builders in order to tackle water flow issue and not to concern about filling cavities during constructing any building in the site

radar facies of paraglacial barrier systems coastal new england usa analysis of a large data base of ground penetrating radar gpr profiles from both natural and developed paraglacial barriers along the coast of new england has allowed identification of eight reflection configurations that characterize this type of mid to high latitude coastal environment bedrock anchor points yield primarily hyperbolic configurations whereas glacial anchor points and sediment source areas are characterized by chaotic parallel and tangential oblique configurations beaches and dunes produce predominantly sigmoidal oblique hummocky reflection free and bounding surface configurations back barrier sediments may yield basin fill configurations but generally include abundant signal attenuating units the gpr data calibrated with information from cores were collected across swash aligned and drift aligned barriers in a variety of wave and tidal energy settings application of a 120 mhz antenna as used in this study enables portrayal of a range of sedimentary units from individual bedforms on single records to entire barrier elements using large numbers of intersecting gpr sections at maximum vertical resolutions that vary between 0 2 m and 0 7 m the most important drawback of gpr in the coastal environment is attenuation of the electromagnetic em signal by layers of salt marsh peat or by brackish or salty groundwater primarily along barrier edges this disadvantage is offset by many benefits data can be collected at rates of several km per day making gpr an excellent reconnaissance tool a core that is used in the calibration of gpr data can be matched with great accuracy to its position on the complementary gpr record allowing detailed correlation between lithostratigraphy and reflection configuration