bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for dune reactivation from GPR profiles on the Maputaland coastal plain, South Africa
Authors: Botha Greg A. , Bristow Charlie S. , Porat Naomi , Duller Geoff , Armitage Simon J. , Roberts Helen M. , Clarke Brendan M. , Kota Mxolisi W. , Schoeman Philo 
Published: April 2008

Abstract
The Maputaland area of northeastern South Africa is characterized by extensive dunefields 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.
GPR investigation of multiple stage-5 sea-level fluctuations on a siliciclastic estuarine shoreline, Delaware Bay, southern New Jersey, USA
Authors: O’Neal Michael L. , Dunn Richard K. 
Published: April 2008

Abstract
Ground penetrating radar (GPR) surveys were used to identify three distinct sea-level highstands within the oxygen isotope stage (OIS) 5-equivalent sediments of the Quaternary Cape May Formation in southern New Jersey. The three units, QCM1a, QCM1b, and QCM1c, are designated as submembers of the Cape May 1 member. The transgressive ravinement surfaces (TRS) forming the bounding unconformities of these units are recognized as laterally extensive reflections on the radar records and have been corroborated as gravel lag deposits and associated lithological discontinuities in continuous vibracores and hand-augered boreholes. GPR and lithological data have been used to interpret these highstand deposits in a sequence-stratigraphic framework. These units are thin (3 m or less), lithologically similar and present limited geomorphic expression of their individual existence beneath a low terrace (+6 m to mean sea level/MSL) on the northern margin of Delaware Bay. In the upper two units, QCM1b and QCM1a, radar surveys across subtle, bay-margin parallel, sublinear topographic highs of 3 m relief or less in the Jones Island area reveal internal structures consistent with geomorphic interpretation as stranded estuarine shorelines. The newly identified shoreline complexes are located well bayward of, and lower in elevation than, the commonly accepted +5 m to +6 m MSL OIS 5e shoreline. This older shoreline abuts the Cedarville Scarp and is attributed to the sea-level highstand associated with QCM1a. GPR was also used to accurately place vibracores for gathering samples of the three units for optically stimulated luminescence dating. Together, these three highstand deposits record sea-level fluctuations within OIS 5, at time scales shorter than those commonly recognized in the mid-Atlantic region.
Sedimentary architecture and post-glacial evolution of Cheekye fan, southwestern British Columbia, Canada
Authors: Ékes Csaba , Friele Pierre 
Published: April 2008

Abstract
The purpose of this paper is to examine the internal architecture and post-glacial evolution of Cheekye fan, British Columbia, Canada. Analysis of a large database of ground penetrating radar (GPR) profiles has allowed the identification of ten reflection configurations that characterize this high-energy environment. GPR profiles augmented with test-pit, well-log and radiocarbon data provided detailed subsurface information and revealed the large-scale internal architecture and Holocene sedimentation history of Cheekye fan. Based on a shift in reflection configuration with depth, GPR data appears to record a change in the mode of deposition through time. This data suggests that Cheekye fan is a paraglacial fan, largely a product of the geological past. This fact should be taken into consideration when making future hazard estimates.
GPR survey of a lobate rock glacier in Yankee Boy Basin, Colorado, USA
Authors: Degenhardt John J. , Giardino John R. , Junck M. Brian 
Published: April 2008

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.
GPR images of periglacial slope deposits beneath peat bogs in the Central European Highlands, Germany
Authors: Leopold Matthias , Völkel Jörg 
Published: April 2008

Abstract

This research investigates the use of ground penetrating radar (GPR) to determine the continuity of periglacial slope deposits under peat bogs. In the Central European Highlands, periglacial slope deposits are a common parent material for soils and play a critical role in determining the nature of chemical and physical processes in soil development. There is a common agreement on the general distribution of these slope deposits, but there is an ongoing debate in German literature concerning the actual age of these deposits. In particular, the youngest head can usually be found under peat bogs of Late Glacial age (
14
C and pollen stratigraphy) and has lead to a minimum age determination of pre-Alleröd. Stratigraphic investigations were made using drill cores, and GPR was used to define the continuity of the head under the bog. Several examples from southeastern Bavaria are given.
Soil effects on GPR detection of buried non-metallic mines
Authors: Hendrickx Jan M. H. , Hong Sung-Ho , Miller Tim , Borchers Brian , Rhebergen Jan B. 
Published: April 2008

Abstract
Landmines are a major problem in many areas of the world. In spite of the fact that many different types of landmine sensors have been developed, the detection of non-metallic landmines remains very difficult. The objective of this contribution is to synthesize our work related to the effects of soil texture and soil water content on the detection of non-metallic anti-tank landmines using ground penetrating radar (GPR). We present a model for the prediction of radar response under a wide range of soil texture and soil water content conditions. Next we present measurements from field experiments in a sand and a silt loam which validate the radar response model. The spatial variability of soil water content in field soils may strongly decrease the effectiveness of GPR for anti-tank mine detection. Uniform wetting of sand and loam soils by irrigation or rain will improve the radar signal. Radar detection in clay soils will be most effective under dry conditions.
The use of vertical radar profiling (VRP) in GPR surveys of ancient sedimentary strata
Authors: Pringle J. K. , Westerman A. R. , Clark J. D. , Guest J. A. , Ferguson R. J. , Gardiner A. R. 
Published: April 2008

Abstract
Vertical radar profiling (VRP) is an application of ground penetrating radar (GPR) technologies that can extract important subsurface information from suitable outcrops. Using standard GPR equipment, a site-specific time-depth calibration can be obtained, along with correlation of observed sedimentological horizons exposed on cliff-faces. These horizons may then be correlated with subsurface reflection events imaged on fixed-offset profiles. Summaries of six GPR study sites, where the VRP technique was used, are detailed. Where possible, CMP and VRP velocities have been compared, and show good correlations. Geochemical analysis of selected sedimentary rocks shows that increasing grain size and quartz mineral percentages generally lead to increased GPR velocities. Reflection events tend to be associated with sandstone/shale boundaries.
Downhole GPR for high-resolution analysis of material properties near Fairbanks, Alaska
Authors: Hunter Lewis E. , Delaney Allan J. , Lawson Daniel E. , Davis Les 
Published: April 2008

Abstract
In August 2000, we used cross-borehole ground penetrating radar (GPR) measurements to investigate sites on Fort Wainwright, Alaska, and east of the Cold Regions Research and Engineering Laboratory (CRREL) permafrost tunnel near Fox, Alaska. The sites are characterized by perennially frozen soils characteristic of much of interior Alaska. The purpose of this investigation was to define variations in GPR signal velocity and attenuation that may be indicative of hydrocarbon contamination and to determine if downhole GPR methods could detect petroleum contaminants. To acquire background information for comparison, we conducted detailed investigations in non-contaminated areas to define general conditions before we profiled at the Fort Wainwright Tank Farm where extensive contamination has been documented.

Results showed that cross-borehole GPR is a useful tool for detecting changes in electrical characteristics in permafrost and contaminated environments. Bulk electrical properties (velocity and attenuation) were observed to vary systematically between frozen and unfrozen materials, and produced distinct signal responses to frozen/unfrozen sediments, bedrock and massive ground ice. There is considerable overlap in both velocity and attenuation for soils and rock. Fine-grained silts exhibit higher attenuation (9–10 dB m
−1
) than coarser sand and gravel (1.5–2 dB m
−1
). Bedrock values are intermediate (2–7 dB m
−1
). Unfrozen sediment and rock exhibit velocities between 0.05 m ns
−1
and 0.1 m ns
−1
and attenuation ranges from 4 dB m
−1
to 11 dB m
−1
at 100 Mhz while frozen materials are between the velocities of 0.1 m ns
−1
and 0.18 m ns
−1
and 1.5 dB m
−1
and 10 dB m
−1
at −0.3 °C. The general trend is for frozen materials to have higher velocities than their unsaturated or saturated counterparts. Preliminary results where petroleum contamination was pervasive show that the attenuation decreases from 6 dB m
−1
to 7 dB m
−1
in uncontaminated schist to 4 dB m
−1
in the hydrocarbon-contaminated schist. Additional measurements are required to determine that the observed decrease in attenuation is primarily related to petroleum contamination.
The use of GPR to image three-dimensional (3-D) turbidite channel architecture in the Carboniferous Ross Formation, County Clare, western Ireland
Authors: Pringle J. K. , Clark J. D. , Westerman A. R. , Gardiner A. R. 
Published: April 2008

Abstract
Petroleum reservoir models are currently built from two-dimensional (2-D) information. An understanding of both the large-scale and internal three-dimensional (3-D) architecture of turbidite channel deposits is important for both hydrocarbon exploration and production. A ground penetrating radar (GPR) survey was undertaken on a study site exposing Upper Carboniferous Ross Formation deposits in western Ireland. Both channel margins and intrachannel fill were imaged in 3-D. Constant-offset, 2-D reflection sections were calibrated by vertical radar profiles. GPR data were integrated with sedimentary and survey data to produce a 3-D model of the study site.
Impact of periodicity on sediment flux in alluvial systems: grain to basin scale
Authors: Frostick Lynne E. , Jones Stuart J. 
Published: April 2008

Abstract
Periodicity is a common component of many sedimentological processes, but seldom is it considered across all scales of fluvial processes in order to understand the complete impact on sediment supply to basins. Temporal changes in sediment supply within drainage systems and sedimentary basins are a consequence of the inherent instability in transport processes. The causes of fluctuations are of 2 main types: (i) changes in factors endemic to the supply of sediment but which are at least partly independent of erosive forces and (ii) changes in the magnitude of forces available to transport sediment. Fluctuations at spatial scales from grain — through reach — to basin — scales and at temporal scales from minutes to millennia are discussed and evaluated. All fluctuations are reflected in sedimentary deposits in some way. For example, irregular patterns of bed break-up during erosion can generate bedforms that are recorded in deposits, the passage of waves of sediment can cause cycles of incision and aggradation in a reach; large flood events will flush sediment into coastal regions and will be recorded as an identifiable ‘package’ in the deposits. Many models of basin processes and products assume a consistent supply of sediment which is far from the case in nature. One of the challenges in the coming decade is to move away from using long-term averages of sediment supply and to link models directly into geomorphic processes.
Annual sediment budgets in an unstable gravel-bed river: the River Coquet, northern England
Authors: Fuller I. C. , Passmore D. G. , Heritage G. L. , Large A. R. G. , Milan D. J. , Brewer P. A. 
Published: April 2008

Abstract

Sediment budgeting procedures based on analysis of three-dimensional morphological change provide a useful mechanism by which rates and patterns of fluvial sediment erosion, transfer and deposition can be monitored. This paper presents results from an annual sediment budgeting programme established in a 1-km long piedmont reach of the gravel-bed River Coquet in Northumberland, northern England. The study reach has a locally braided channel planform and has experienced lateral instability over at least the past 150 years. Annual sediment budgets for 1997–1998 and 1998–1999 have been based on tacheometric survey of: (i) 15 monumented channel cross-profiles; and (ii) channel margins and gravel-bar morphology. Survey data have been analysed for each discrete morphological unit (differentiating channel and complex bar assemblages) within 17 sub-reaches of the study reach using Arc/Info
™
GIS. The morphological sediment budgeting techniques used to generate these reach-scale budgets may be particularly valuable in unstable gravel-bed rivers due to the inherent difficulties in measuring bed-load transport. The results show considerable variability in rates and patterns of within-reach sediment transfer between the successive surveys. The channel at Holystone is characterized by substantial within-reach sediment transfer, with minimal net export downstream. This behaviour appears to be characteristic of UK gravel-bed piedmont rivers.
Drainage basin structure, sediment delivery and the response to environmental change
Authors: Richards Keith 
Published: April 2008

Abstract
The purpose of this paper is to explore the role that drainage basins and networks play in filtering and modulating the effects of environmental change. The record of this change is often inferred from the properties of alluvial stratigraphy in river valleys. However, the variable time lags and smoothing effects caused during the flux of sediment through a drainage basin are very poorly understood, and need to be clarified before the depositional record can be linked to the causes of change. Interactions amongst drainage network elements — main valleys and tributaries — result in complex patterns of storage and delivery in time and space, and these interactions are reviewed in this paper. While the combination of cosmogenic isotopic dating of erosional records, and the use of shallow seismic and ground penetrating radar methods may provide data on the empirical linkages between sediment sources and sinks, a significant research need is for a modelling framework to enable cut-and-fill records to be simulated, and to provide a rigorous connection between the valley-fill depositional record and the environmentally-driven variations in sediment production. This will require a return to the long-neglected analysis of drainage network structure, and an improved understanding of the within-catchment variations in the sediment delivery ratio. Until this is achieved, it will be premature to assume direct connections between environmental change and the record of alluviation in many valleys.
Metamorphism and thermodynamics: the formative years
Authors: Fritscher Bernhard 
Published: April 2008

Abstract
Between 1890 and the 1920s petrologists and mineralogists began to apply concepts of theoretical chemistry — in particular, the concept of chemical equilibrium — to the study of metamorphic rocks. The majority of the petrological community, however, hesitated to apply the new method on a large scale to metamorphism. Focusing on the works of Becke, Goldschmidt and Eskola, some early approaches to a linkage of metamorphic petrology and theoretical chemistry are reviewed. The controversial discussion, particularly of Goldschmidt’s classical study of the Christiania area, led Miyashiro to distinguish two paradigms of early twentieth-century metamorphic petrology. With regard to the contemporary discussion, as well as to Miyashiro’s interpretation, this paper is concluded by an epilogue on ‘image and logic’, which is intended to relate the paradigms of early modern metamorphism to different cultures, and ‘national styles’ of Earth sciences in the nineteenth and early twentieth centuries.
Marie Tharp, oceanographic cartographer, and her contributions to the revolution in the Earth sciences
Authors: Barton Cathy 
Published: April 2008

Abstract
In the early 1950s, two American geologists, Bruce Charles Heezen (1924–1977) and Marie Tharp, began mapping the sea floor to improve understanding of ocean-basin geology and to connect the oceans to the continents theoretically. Both were researchers at the Lamont Geological Observatory of Columbia University, now Lamont-Doherty Earth Observatory. Heezen and Tharp used the ‘physiographic mapping’ technique, which makes it possible to relate topographic features to underlying geology. The diagrams mostly utilized light and texture, rather than colour, and were sketched using a hachuring technique. Heezen collected data for research purposes and Tharp used his information to compile their physiographic diagrams. During this process, she confirmed previous predictions when she made an important discovery: a rift on the Mid-Atlantic Ridge. Tharp’s visual interpretations of the sea-floor data contributed to the reintroduction of continental drift theory and the 1960s geological revolution. At a time when most women were excluded from scientific careers, Tharp, initially a research assistant, succeeded in this competitive arena. Working with Heezen as a geologist and cartographer, she had an unusual opportunity to participate in the era’s exciting discoveries; and her contributions were acknowledged. While their data-gathering activities and analyses stimulated change and contributed to the revolution in the Earth sciences, Heezen and Tharp were not directly involved in the plate-tectonics revolution, but favoured expanding-Earth theory.
Some personal thoughts on stratigraphic precision in the twentieth century
Authors: Torrens Hugh S. 
Published: April 2008

Abstract
Surprisingly, most of the major elements of today’s stratigraphic column were in place by 1850. By then, the ideas that stratigraphy concerned geological time relations, and that a palaeontological identity of ‘best’ fossils (like ammonites) was an indication of time-equivalence, were starting to be accepted. By 1900, thanks to the work of people like Henry Shaler Williams (USA) and Sydney Savory Buckman (UK) stratigraphy was starting to concern itself with the precision with which biochronological time-scales could be created, especially in the Jurassic. By then, Buckman had demonstrated the great extent to which particular lithologies could cross time-lines and equally how well such rapidly evolving fossils as ammonites could be used to discriminate time. But from 1960, facing new demands for energy, and the growth of new ‘earth science’, focussing on numerical methods in geophysics and geochemistry using computers, such field-based ‘historical geology’ was progressively perceived as boring, out-dated, and expensive. Many new techniques, which ignored, or worse, assumed time-equivalence, now evolved. Fossils by their unique nature had given unique signatures to discriminate time. But some of the new methods relied on binary repetitions, not unique to time, and may suggest a false precision. This paper attempts a, now near-impossible, investigation of the temporal precisions that stratigraphic methods, both old and new, might attain. It concludes that we need to pay greater attention to the incompleteness of the stratigraphic record and to the chronological precision with which we can investigate that record. It now seems almost axiomatic that the harder you look at a rock the more incomplete the record of its stratigraphy appears to become.