Radar Facies Research Articles

Application of GPR in the study of shallow subsurface sedimentary architecture of Modwa spit, Gulf of Kachchh

The coastline constitutes a very sensitive geomorphic domain constantly subjected to dynamic coastal processes. The study of its ever-changing physiography and stratigraphy provides a wealth of information on its history and evolution, in many cases at decadal and annual scales. The present study was carried out on the Modwa beach complex between Rawal Pir and Modwa, about 10 km east of Mandvi on the northern coast of the Gulf of Kachchh. The Modwa spit is a 7-km long WNW-ESE trending prograding amalgamated beach ridge complex that is about 0.5 km wide at its western end and 1.5 km wide at its eastern end. This Ground-Penetrating Radar (GPR) survey delineated a variety of the radar surfaces and radar facies which reflects not only large scale sedimentary architecture, but depositional facies of the beach ridge complex. These are bounding surfaces separating the radar facies outline beach ridge (br), washover (wo), coastal dune (cd) and swale (sw) depositional environments. The internal sedimentary structures like tangential, parallel, concave and convex upward stratifications could also be visualized from the GPR profiles. The architecture suggests the formation of this complex due to a combined process of eastward littoral drift of locally derived sediments and its onshore deposition by storms and eolian activities.

3-D Architecture and Sequence Stratigraphic Evolution of a Forced Regressive Top-Truncated Mixed-Influenced Delta, Cretaceous Wall Creek Sandstone, Wyoming, U.S.A.

Abstract Ground-penetrating radar (GPR) is used to delineate the 3-D facies architectural elements and examine the evolution of a top-truncated, forced-regressive, mixed-influenced delta front in the Cretaceous Wall Creek Member of the Frontier Formation, Wyoming. The GPR data provide a bridge between outcrop facies architecture and recently published high-resolution 2-D seismic studies of Quaternary delta systems. The GPR data were integrated with outcrops, photomosaics, cores, and GPS data. Two orthogonal grids of 2-D GPR profiles provide information on the 3-D facies architecture and stratigraphy of the deltaic deposits. Three main GPR architectural elements are identified within the delta front: (1) mouth bars are characterized by seaward-dipping reflections (foreset beds) in dip view, and mounded bidirectionally downlapping reflections in strike view; (2) shallow delta-slope channels show truncation and onlap and also show low-angle landward (northwest) dipping reflections. The mouth bars are locally interrupted by (3) sub-horizontal radar reflections that are interpreted as tidally modulated bars. Within the mouth-bar radar facies, both top-preserved (proximal) and top-truncated (distal) examples are observed. Top-preserved proximal bars show evidence of mounded bar crests and landward accretion, as is observed in the upstream end of mouth bars on the modern Atchafalaya Delta in the Gulf of Mexico. Distal bar deposits primarily comprise the top-truncated, seaward-dipping foresets. The GPR interpretation shows two laterally overlapping delta lobes, interpreted to represent autocyclic delta switching. The older lower lobe forms a fan-shaped delta lobe composed of top-truncated coalesced mouth bars. The second phase of bars is largely top-preserved, building over the older bars. The presence of thicker bedsets and upstream accretion suggests that the younger lobe was quickly abandoned, as seen in the overlying transgressive ravinement. Although marine erosion during transgression was less effective on these later-stage bar deposits, ravinement increased landward. A comparison of the architectural elements at a more regional scale in two separate Wall Creek delta lobes (Murphy Creek and Raptor Ridge, ~ 30 km apart) indicates that the bar complexes were deposited on the delta fronts as accretionary forced-regressive deposits during a relative sea-level fall; the older river-dominated deltaic deposits at the Murphy Creek site prograded southeastward (~ 124°), whereas the younger and more tidally influenced Raptor Ridge bar deposits expanded southward (~ 171°) before final abandonment and regional transgression. The most distal lowstand lobe sediments within the offlapping parasequence at Raptor Ridge are more completely preserved and also show the greatest tidal influence, compared to the more severely top-truncated Murphy Creek, which is in an otherwise more landward location. This challenges the notion that tidal facies are predominantly associated with transgressive or highstand systems tracts. Greater preservation of deltaic facies in forced-regressive and lowstand deltas, as shown here, has also been documented in Quaternary shelf-edge deltas, such as the Lagniappe in the Gulf of Mexico and the Mahakham in Kalimantan.

Ground-penetrating radar profiling on embanked floodplains

AbstractManagement of the Dutch embanked floodplains is of crucial interest in the light of a likely increase of extreme floods. One of the issues is a gradual decrease of floodwater accommodation space as a result of overbank deposition of mud and sand during floods. To address this issue, sediment deposits of an undisturbed embanked floodplain near Winssen along the river Waal were studied using ground-penetrating radar (GPR). A number of radar facies units were recognized. Boreholes were used to relate radar facies units to sedimentary facies and to determine radar velocity. The GPR groundwave is affected by differences in moisture and texture of the top layer and probably interferes with the first subsurface reflector. The architectural elements recognized in the GPR transects confirm earlier reported insights on human-influenced river behaviour. This is testified in the development of sand bars during flood regimes that are probably more widespread than previously established.

Three-dimensional facies architecture and three-dimensional calcite concretion distributions in a tide-influenced delta front, Wall Creek Member, Frontier Formation, Wyoming

Ground-penetrating radar (GPR) has been used to image the three-dimensional (3-D) internal structure (and, thus, the 3-D facies architecture) of a top-truncated delta front in the topmost parasequence in the Wall Creek Sandstone Member of the Frontier Formation in Wyoming and to estimate the distribution of low-permeability concretions throughout the 3-D GPR volume. The interpretation of the 3-D GPR data is based both on correlations with outcrop and on calibration with core data from holes within the survey grid. Two main radar facies (RF) are identified. Radar facies 1 corresponds to tide-influenced mouth bars formed by a unidirectional flow during delta progradation or bidirectional flow during tides, whereas RF2 is correlated with laterally migrating channels developed on previous bar deposits. The delta-front foreset beds dip in the same direction as the dominant paleocurrent indicators. The GPR interpretation is consistent with the outcrop interpretation that, following a regressive period, bars and channels were developed at the Raptor Ridge site before subsequent transgressive ravinement. The individual 3-D deltaic facies architectures were reconstructed from the 3-D GPR volume and indicate that the depositional units are larger than the survey grid. Cluster analysis of the GPR attributes (instantaneous amplitudes and wave numbers) calibrated with the cores and the outcrop was used to predict the distribution of near-zero permeability concretions throughout the 3-D GPR volume; clusters of predictive attributes were defined and applied separately in the bars and channels. The predicted concretions in the bars and the channels are 14.7 and 10.2% by volume, respectively, which is consistent with those observed in the cores (14.7 and 10.5%, respectively), and their shape and thickness are also generally in consonance with those in the outcrop and cores. The estimated concretions are distributed in an aggregate pattern with irregularly shaped branches within the 3-D GPR volume, indicating that the cementation does not follow a traditional center-to-margin pattern. The concretions and 3-D geological solid model provide cemented flow baffles and a 3-D structural framework for 3-D reservoir modeling, respectively.

Bedrock detection and talus thickness assessment in the European Alps using geophysical methods

Three different geophysical techniques (ground-penetrating radar (GPR), 2D-resistivity, seismic refraction) were applied to measure sediment thickness of alpine talus slopes. The eight study areas covered a range of different rock types, aspects and elevations and are mainly situated in the north-eastern part of the European Alps. A total of more than 30 scree slopes were investigated. The emphasis was on the application of GPR. The other two methods were used additionally in five areas to verify the GPR results and to check the concurrence of the results. With all the techniques applied, certain difficulties of bedrock detection arose. GPR surveys using several frequencies seem to be the most powerful tool for detecting the bedrock surface and internal structures in these high-alpine environments. However, there frequently is no radar wave reflection at the debris–bedrock interface due to the rather similar dielectrical properties. This problem was overcome by using the characteristic reflection patterns of the subsurface units for delimitating debris from glacigenic sediments and bedrock. Typical radar facies are presented. The other two methods applied were impeded by the broad overlap between resistivity and seismic velocity values, respectively, of the subsurface layers. The widespread presence of compacted and/or glacigenic debris layers between surficial scree and bedrock rendered the interpretation difficult. The three methods coincide well in straightforward settings (e.g. debris superimposing bedrock). Additional sediment units like till, wet or compacted debris lead to considerable ambiguities and deviations between the results. Thus, the combined application of two or three techniques is strongly advisable to verify and improve the interpretation. The calculated Holocene rockwall retreat rates lay between 200 and 850 mm/ka which is well within the framework of previous measurements. The weathering rates at north faces seem to be roughly two times higher than at south faces in the areas of investigation.

A ground-penetrating radar survey of late Holocene fluvial sediments in NW Namibian river valleys: characterization and comparison

Fine-grained terraces and coarse-grained channel fills that represent episodes of late Holocene valley aggradation are used as geoarchives for palaeohydrological reconstructions in many arid regions of the world (e.g. southwestern USA, Australia, Israel and the Namib Desert). In Namibia, previous work on the sediment texture and facies of these valley fills has led to diverse interpretations of the depositional environment, including river-end, palaeoflood and floodout. Here we show, using ground-penetrating radar (GPR) profiles across four complex river channels to image sedimentological and stratigraphical structures, that the GPR images can be grouped into eight ’radar facies’ (reflection patterns). A combination of radar facies analysis and groundcheck (exposures, boreholes) has been used to interpret the radar profiles. By considering the geomorphological–sedimentological features and age determinations of the fluvial deposits described by earlier researchers and supplemented by our own investigations, we explain the late Holocene fine-grained terraces and coarse-grained channel fills as deposits accumulated during floods. Although the GPR results alone cannot conclusively resolve the fine-grained terrace deposits either as river-end or as slackwater accumulation, the novel combination of GPR, geomorphological findings and results from the literature provides evidence for our interpretation.

Texture-based classification of ground-penetrating radar images

Image texture is one of the key features used for the interpretation of radar facies in ground-penetrating radar (GPR) data. Establishing quantitative measures of texture is therefore a critical step in the effective development of advanced techniques for the interpretation of GPR images. This study presents the first effort to evaluate whether different measures of a GPR image capture the features of the data that, when coupled with a neural network classifier, are able to reproduce a human interpretation. The measures compared in this study are instantaneous amplitude and frequency, as well as the variance, covariance, Fourier-Mellin transform, R-transform, and principle components (PCs) determined for a window of radar data. A [Formula: see text] GPR section collected over the William River delta in Saskatchewan, Canada, is used for the analysis. We found that measures describing the local spatial structure of the GPR image (i.e., covariance, Fourier-Mellin, R-transform, and PCs) were able to reproduce human interpretations with greater than 93% accuracy. In contrast, classifications based on image variance and the instantaneous attributes agreed with the human interpretation less than 68% of the time. Among the textural measures that preserve spatial structure, we found that the best ones are insensitive to within facies variability while emphasizing differences between facies. For the specific case of the William River delta, the Fourier-Mellin transform, which retains information about the spatial correlation of reflections while remaining insensitive to their orientation, outperformed the other measures. Our work in describing radar texture provides an important first step in defining quantitative criteria that can be used to aid in the classification of radar data.

Nass River on the move: radar facies analysis of glaciofluvial sedimentation and its response to sea-level change in northwestern British Columbia

The Nass Valley of northwestern British Columbia is a glacial fiord containing extensive glaciomarine and glaciofluvial sediments. Two parallel braidplains, separated by a bedrock ridge, were deposited within the fiord. Mapping of these deposits led to the hypothesis that the braidplains must have terminated at deltas. However, a lack of surface exposures meant that ground-penetrating radar was needed to investigate these deposits. Radar facies analysis aided in the identification of braidplain, braid delta and glaciomarine depositional environments, as well as underlying bedrock. Several deltas graded to different sea levels were discovered, allowing inferences to be made about the relationship of falling sea level to sediment architecture. The upper section of the western braidplain is graded to a sea level of 185 m above sea level (asl), indicating that the proto-Nass River flowed on the western side of the bedrock ridge when the sea was at that level. However, the river moved to the east side of the ridge as sea level fell, depositing the extensive Aiyansh Braidplain – Braid Delta, which is graded to a 152 m sea-level stand. Several other deltas also formed at this sea-level stand. Avulsion occurred and the river flowed on the west side of the ridge again when sea level fell to 134 m asl. The river remained in this position throughout late glacial time and eventually evolved into the modern Nass River. The coarse-grained deposits are indicative of forced regression, with both stepped-top attached and detached stratal architecture present.

Estudo de depósitos da formação barreiras com base em reflexão por ondas de radar

This paper integrates radar reflection sections (GPR - Ground Penetrating Radar) with lithologic profiles based on sounding logs in deposits of the Barreiras Formation at selected points in the northern part of Rio de Janeiro State and southern part of Espirito Santo State. Three radar survey lines were investigated by common-offset mode using PulseEkko IV radar system and 50 MHz antennas. Based on interpretation of the main radar facies and units evident in the GPR lines, sampling points were selected for obtaining sounding logs using a mechanical auger. The Barreiras Formation deposits here described correspond to fining-upward sandy successions. In the geophysical survey, these sandy deposits are associated with more-or-less continuos wavy reflection patterns presenting a cross-bedded aspect and concave-upward geometry (radar facies II). Argillaceous mudstone layers interbedded with the sandy deposits are associated with a continuous, parallel reflection pattern (radar facies I). The Barreiras Formation sediments are interpreted as fluvial channel deposits, with little contribution of suspended sediments or gravitational flow deposits, in agreement with previous interpretations based on outcrop deposits in these regions.

Cyclical Evolution of a Modern Transgressive Sand Barrier in Northwestern Spain Elucidated by GPR and Aerial Photos

Abstract The internal structure of a modern baymouth barrier is analyzed in detail, including its historical evolution and the factors controlling it. Historical evolution was reconstructed using available aerial photographs from 1956 to 2003. Detailed geophysical data were acquired using ground-penetrating radar (GPR) and analyzed along with airphotos to reconstruct the recent evolution of a barrier located in northwestern Spain. The GPR data reveal the internal architecture of the barrier, which consists of two main radar facies: (1) washover deposits associated with landward barrier migration and vertical aggradation, and (2) beach deposits associated with seaward barrier progradation. The reconstruction of the stratigraphic sequence indicates the occurrence of two erosive periods followed by an accretionary period. The erosion along the barrier is outlined by the presence of three well-defined bounding surfaces. The stratigraphic record of the subsequent recovery phase depends on the impact level of the erosive phase, which is controlled by the presence of ephemeral inlets along the barrier. This alternating behavior implies a discontinuous shoreline trajectory in spite of a net landward migration. This trend is consistent with regional sea-level rise albeit being intensified locally by the interplay of sediment starvation and storm regime. Landward barrier retreat occurs by overwash and inlet breaching, which permits barrier preservation of volume due to a continuous constructive-destructive cycle. The results acquired from this example expand our understanding of the internal structure and evolutionary trends of transgressive sand barriers.

Geometry and evolution of Holocene transgressive and regressive barriers on the semi-arid coast of NE Brazil

An integrated study based on ground penetrating radar (GPR) profiles, vibracore descriptions, water-well logs, and radiocarbon dating in a coastal deposit located in the northern region of Rio Grande do Norte State, northeastern Brazil, allowed us to identify Holocene transgressive and regressive barriers. The construction process for the studied coastal barrier is different from that proposed for the Holocene coastal plains along the eastern Brazilian coast, where the hydraulic barrier set up by large rivers for sediments transported by longshore currents has caused a strongly positive longshore sediment imbalance. In the study area, interpretation of the GPR images, within the constraints of vibracores data, allowed us to interpret five radar facies and four radar boundary sequences for these coastal deposits, which were built up during the Holocene coastal evolution of the region. As a result, the geometry of the coastal barrier was reconstructed. Based on barrier geometry, sediment ages, stratigraphic records, and sedimentation patterns, we propose a barrier evolutionary model for the Holocene for the study region. During the Holocene highstand, a transgressive barrier was deposited and a lagoon extended landward. During the sea-level fall soon after the Holocene highstand, the deposition of a regressive barrier (forced regression) started. This deposition was induced by the coastal geometry and high amounts of eolian sediments supplied by east-northeast winds. Also during this period of sea-level fall, the beach face became wider, and thus more subjected to wind action, facilitating the deposition of the first eolian deposits. These sediments were transported to the nearly formed embayment, providing a surplus for the construction of the regressive barrier. During the regressive phase, tidal channels closed and the lagoon became isolated from the open sea. The geometry of both the regressive and transgressive barriers as well as the stratigraphic relation between the sedimentary deposits suggest that the Holocene highstand in this region was not more than 1.4 m above present-day mean sea level.

The sedimentology and alluvial architecture of the sandy braided South Saskatchewan River, Canada

AbstractGround penetrating radar (GPR) surveys of unit and compound braid bars in the sandy South Saskatchewan River, Canada, are used to test the influential facies model for sandy braided alluvium presented by Cant & Walker (1978). Four main radar facies are identified: (1) high‐angle (up to angle‐of‐repose) inclined reflections, interpreted as having formed at the margins of migrating bars; (2) discontinuous undular and/or trough‐shaped reflections, interpreted as cross‐strata associated with the migration of sinuous‐crested dunes; (3) low‐angle (< 6°) reflections, interpreted as formed by low‐amplitude dunes or unit bars as they migrate onto bar surfaces; and (4) reflections of variable dip bounded by a concave reflection, interpreted as being formed by the filling of channel scours, cross‐bar channels or depressions on the bar surface. The predominant vertical arrangement of facies is discontinuous trough‐shaped reflections at the channel base overlain by discontinuous undular reflections, overlain by low‐angle reflections that dominate the deposits near the bar surface. High‐angle inclined reflections are only found near the surface of unit bars, and are of relatively small‐scale (< 0·5 m), but can be found at a greater range of depths within compound bars. The GPR data show that a high spatial variability exists in the distribution of facies between different compound bars, with facies variability within a single bar being as pronounced as that between bars. Compound bars evolve as an amalgamation of unit bars and other compound bars, and comprise a facies distribution that is representative of the main bar types in the South Saskatchewan River. The GPR data are compared with the original model of Cant & Walker (1978) and reveal a much greater variability in the scale, proportion and distribution of facies than that presented by Cant & Walker (1978). Most notably, high‐angle inclined strata are over‐represented in the model of Cant and Walker, with many bars being dominated by the deposits of low‐ and high‐amplitude dunes. It is suggested that further GPR studies from a range of braided river types are required to properly quantify the full range of deposits. Only by moving away from traditional, highly generalized facies models can a greater understanding of braided river deposits and their controls be established.

The Architecture of Prograding Sandy-Gravel Beach Ridges Formed During the Last Holocene Highstand: Southwestern British Columbia, Canada

This study was conducted to establish the sedimentary architecture of a beach-ridge system that developed in response to rising and then stabilizing sea level in a macrotidal setting. The beach ridges document a shift from transgressive to highstand depositional conditions. A beach-ridge complex is being deposited on the Boundary Bay tidal flats that flank the Fraser River delta in southwestern British Columbia. The delta onlapped an offshore island, during the Holocene, and partially incorporated it into its delta plain; sand and gravel eroded from this island is the sediment source for the beach ridges. Four depositional–geomorphic environments are identified: beach ridges, lagoon and swales, washover fans, and tidal flats. The beach ridges prograded over the tidal flats of the Fraser delta when sea level stabilized and the late-Holocene highstand was established. The very earliest beach ridges were deposited about 5200 to 4800 years BP, but most were formed after 2250 years BP with the establishment of the Holocene highstand. Beach-ridge progradation rates varied between 1.6 m a −1 to 0.48 m a −1 . Ground penetrating radar (GPR) was used to provide continuous two- and three-dimensional images of the facies in order to delineate the depositional architecture of the sandy-gravel beach ridges. We supplemented the customary use of well logs and cores for ground truthing GPR lines with cone penetration testing (CPT), which provided a detailed suite of logs invaluable for correlating radar reflections with subtle lithologic variations unidentifiable in core. A synthesis of geomorphic environments, lithologic logs, and radar facies is used to construct a depositional model of the beach-ridge complex.

Testing ground‐penetrating radar for resolving facies architecture changes ‐ a radar stratigraphic and sedimentological analysis along a 30 km profile on the Karup Outwash Plain, Denmark

ABSTRACTKnowledge of the spatial distribution of lithofacies, obtained through detailed modelling of the movement of water and solutes, may improve precise predictions of an area's vulnerability towards contaminants. This calls for information on lithofacies variability on several scales. The possibilities for upscaling lithofacies distribution from excavation scale to field scale or to an even larger scale with the use of ground‐penetrating radar (GPR) is tested on one of the largest outwash plains in Denmark: the Karup Outwash plain in the western part of Jutland. The testing involves GPR surveys at 16 locations along a 30 km long profile following the ancient mean flow direction of the braided‐river system, as well as combined detailed sedimentological investigations at selected locations. The GPR testing is divided into several phases of which this paper reports on the first two.In the first phase, GPR surveys and sedimentary investigations at gravel‐pits and excavation sites are carried out at the same location with the aim of determining whether lithofacies can be related to GPR reflection sequences either directly or through facies architecture models. Studies of outcropping glaciofluvial deposits at a gravel‐pit and a shallow excavation in the proximal and intermediate parts of the outwash plain, respectively, show that the sand‐dominated outwash plain typically contains lithofacies types with bed thicknesses of up to 0.5 m and successions of beds of thicknesses up to 1 m. GPR surveys carried out at the same locations show that the observed lithofacies types typically have dimensions that, in a vertical direction, are the same as or less than the resolution obtained by a 200 MHz GPR system. In such sand‐dominated outwash deposits, the GPR reflections may more often be caused by the bedding structures in successions of beds and of larger erosion surfaces separating different lithofacies, rather than by the lithofacies boundaries themselves.In the second phase, tests are conducted to determine whether facies architecture changes along the ancient mean flow direction in the outwash plain can be recognized using radar stratigraphic analysis. Radar stratigraphic analysis, so far limited to two GPR sections orientated parallel and perpendicular to the ancient mean flow direction at 15 locations, reveals a systematic change in the pattern of radar sequence boundaries and the occurrence of radar facies. The changes in radar sequences seem to reflect changes in lithology and sedimentary structures related to the overall fall in the depositional energy from the proximal to the distal part of the outwash plain. The results clearly indicate that radar stratigraphic analysis reveals realistic facies architecture models for the outwash plain, provided densely spaced GPR data are acquired and locally calibrated against excavations and coreholes.It is concluded that GPR can be used for upscaling lithofacies distributions in sedimentological settings like the present Karup Outwash Plain.

Combining ground penetrating radar surveys and optical dating to determine dune migration in Namibia

Ground penetrating radar (GPR) profiles across a complex linear dune in the Namib Sand Sea have been used to image sets of cross-stratification and their bounding surfaces. A combination of radar facies analysis and radar stratigraphy has been used to interpret the radar profiles and define a relative chronology. Thick sets of cross-stratification indicate when the dune was most active, whereas thin sets of cross-stratification are interpreted to indicate the increased prevalence of wind reversals and lower rates of dune migration, with bounding surfaces formed during periods of stabilization, non-deposition or erosion. A drilling and dating campaign was designed on the basis of the dune stratigraphy as defined by the GPR survey. Sampling was targeted at large sets of cross-stratification formed when the dunes were most active, and avoiding bounding surfaces formed when the dune was stable or even eroded. The results from optical dating give ages between 0.34 ± 0.02 ka and 1.57 ± 0.07 ka, indicating a time-averaged dune migration rate of 0.12 m a −1 over the past 1600 years.

Ground‐penetrating radar facies as an aid to sequence stratigraphic analysis: application to the archaeology of Clonmacnoise Castle, Ireland

AbstractThis paper describes the advantages of interpreting ground‐penetrating radar (GPR) facies in a sequence stratigraphic context. These data have been collected adjacent to the River Shannon at Clonmacnoise Castle in central Ireland and demonstrate that stratigraphy is not necessarily made up of horizontal isochronous surfaces; some reflective surfaces are more important than others in interpretation and that two‐dimensional sections must be interpreted with caution. Radar facies analysis and thus sequence stratigraphy can be used to both interpret the sedimentary record in terms of palaeoenvironments as well as identify important (key) surfaces. Bright, continuous surfaces are often found at horizons of palaeoenvironmental change and have distinctive reflector shapes and terminations (or stratal patterns) above and below. Such stratal patterns define and reflect linked fluvial and human environments that have developed and been preserved through the creation of accommodation space. Key surfaces have been identified when sedimentation was altered, thus reflecting a natural or anthropogenic palaeoenvironmental change. In anthropogenically modified or created successions, such as those seen at Clonmacnoise, key surfaces have produced changes in dielectric constants in the sediments that are seen as radar reflections. Natural activity includes lateral migration of point‐bars and fluvial onlap. Anthropogenic activity has created accommodation space (the moat), a major sequence boundary and subdwelling surface disruption of reflectors. A pre‐moat fault can be observed on GPR data that is along strike of a surface scarp to the southwest of Clonmacnoise Castle. The results demonstrate the enhanced interpretive and predictive use of radar facies in sequence stratigraphy. Copyright © 2004 John Wiley & Sons, Ltd.

Neolithic flint mines in Arnhofen, southern Germany: a ground‐penetrating radar survey

AbstractGround‐penetrating radar (GPR) was used at an excavation site of a Neolithic flint mine in southern Germany to establish the subsurface geology of the mine and to aid in the location of mine shafts in unexcavated areas. Three radar facies were identified to characterize the geology of the study area. A test GPR line surveying known Neolithic mine shafts provided calibrated results for the identification of new shafts. Forty radar lines with a length of 40 m identified the locations of previously unknown shafts in unexcavated areas. The GPR results provide archaeologists with valuable additional information on the extent of the former flint mine. Copyright © 2004 John Wiley & Sons, Ltd.

Stochastic estimation of facies using ground penetrating radar data

Explicitly defining large-scale heterogeneity is a necessary step of groundwater model calibration if accurate estimates of flow and transport are to be made. In this work, neural networks are used to estimate radar facies probabilities from ground penetrating radar (GPR) images, yielding stochastic facies-based models that honour the large-scale architecture of the subsurface. For synthetic GPR images, a neural network was able to correctly identify radar facies with an accuracy of approximately 90%. Manual interpretation of a set of 450 MHz GPR field data from the Borden aquifer resulted in the identification of four radar facies. Of these, a neural network was able to identify two facies with an accuracy of near 80% and one with an accuracy of 44%. The neural network was not able to identify the fourth facies, likely due to the choice of defining facies characteristics. Sequential indicator simulation was used to generate facies realizations conditioned to the radar facies probabilities. Numerical simulations indicate that significant improvements in the prediction of solute transport are possible when GPR is used to constrain the facies model compared to using well data alone, especially when data are sparse.

Application of ground-penetrating radar, digital optical borehole images, and cores for characterization of porosity hydraulic conductivity and paleokarst in the Biscayne aquifer, southeastern Florida, USA

This paper presents examples of ground-penetrating radar (GPR) data from two study sites in southeastern Florida where karstic Pleistocene platform carbonates that comprise the unconfined Biscayne aquifer were imaged. Important features shown on resultant GPR profiles include: (1) upward and lateral qualitative interpretative distribution of porosity and hydraulic conductivity; (2) paleotopographic relief on karstic subaerial exposure surfaces; and (3) vertical stacking of chronostratigraphic high-frequency cycles (HFCs). These characteristics were verified by comparison to rock properties observed and measured in core samples, and identified in digital optical borehole images. Results demonstrate that an empirical relation exists between measured whole-core porosity and hydraulic conductivity, observed porosity on digital optical borehole images, formation conductivity, and GPR reflection amplitudes—as porosity and hydraulic conductivity determined from core and borehole images increases, formation conductivity increases, and GPR reflection amplitude decreases. This relation allows for qualitative interpretation of the vertical and lateral distribution of porosity and hydraulic conductivity within HFCs. Two subtidal HFCs in the uppermost Biscayne aquifer have significantly unique populations of whole-core porosity values and vertical hydraulic conductivity values. Porosity measurements from one cycle has a median value about two to three times greater than the values from the other HFC, and median values of vertical hydraulic-conductivity about three orders of magnitude higher than the other HFC. The HFC with the higher porosity and hydraulic conductivity values is shown as a discrete package of relatively low-amplitude reflections, whereas the HFC characterized by lower porosity and hydraulic-conductivity measurements is expressed by higher amplitude reflections. Porosity and hydraulic-conductivity values measured from whole-core samples, and vuggy porosity identified on digital borehole images from shallowing-upward, peritidal HFCs show that the highest porosity occurs at the base of the cycles, moderate porosity at the middle of the cycles, and lowest porosity occurs at the top of cycles. Hydraulic conductivity is also highest at the base of the peritidal cycles and lowest in the middle to upper parts of cycles. This change in porosity and hydraulic conductivity from bottom to top is visible as an upward variation in reflection amplitude on GPR profiles—lowest amplitudes at the base and highest at the cycle tops. This study demonstrates that GPR can be used to show the qualitative distribution of porosity and hydraulic conductivity within a cycle-stratigraphic framework composed of carbonate HFCs. The distribution of porosity and hydraulic conductivity within HFCs is related to depositional textures. The upward and lateral patterns of the rock facies within the HFCs can be translated to geophysical-log properties and radar facies configurations that could aid in interpretation and prediction of ground-water flow through a carbonate aquifer.

Ground-penetrating radar facies characterization of deepwater turbidite outcrops

High-resolution outcrop studies are becoming an increasingly important tool in building reservoir architectural models (Slatt, 2000). By providing attributes of strata in both the lateral and vertical directions, outcrop studies can help constrain reservoir characterization models (e.g., identify seals or barriers to fluid flow). Outcrop exposures, at best, are limited in their extent. Boreholes, even when they are spaced tightly together, may yield an inaccurate picture of sedimentary features. Because the type and scale of information important to hydrocarbon production can be beneath the resolution of 3D seismic data, there is a need for a geophysical method that yields a high-resolution, continuous image of the subsurface. Ground-penetrating radar (GPR) is one of the more recent geophysical technologies used in examining outcrops (Slatt, 2000;Young et al., 2001). GPR is an electromagnetic imaging procedure that generates reflections from boundaries between layers and can use modified seismic processing to create images (Young et al., 1995). The short wavelengths of GPR signal provide data, which is subseismic scale in resolution. The resulting profiles are good for interpreting small-scale sedimentary features of bed continuity, stratification patterns, and facies boundaries. This paper presents the results from a GPR study of the Lewis Shale turbidite outcrops in Wyoming. The objective of the project is to collect subseismic scale resolution data to aid in determining small-scale sedimentary features. The interpretations, in turn, could be used to provide a better understanding of fluid flow and reservoir production modeling. The Lewis Shale, a Cretaceous age turbidite deposit, is an active gas exploration target and analog for the lower Cretaceous sequences in South Africa and tertiary deposits in the Gulf of Mexico. The formation crops out along the western edge of the Rawlins-Sierra Madre uplift within southeast Wyoming. The geology of three areas along the Lewis Shale outcrop has been studied. …