bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoluminescence dating of periods of sand movement and linear dune formation in the northern Negev, Israel
Authors: Rendell H. M. , Yair A. , Tsoar H. 
Published: April 2008

AbstractThe dating of periods of sand movement and dune formation in the Negev has, until the present study, been based on the presence of stone artefacts on, within or beneath sand dunes, or upon14C dating of associated deposits. We present the results of a preliminary thermoluminescence (TL) dating study of sand and interdune-playa deposits from the Sede Hallamish area of the northern Negev. The results appear to indicate that: (a) sediments in the interdune area were deposited over a period from at least 43 ka to 9 ka and include several depositional cycles; and (b) the lower parts of the linear dunes were formed 6–10 ka and the dune flanks have been stabilized since then. These results are placed in the context of existing studies of the palaeoclimate of the Negev during the Late Pleistocene.
A chronostratigraphic re-evaluation of the Tusayan Dunes, Moenkopi Plateau and southern Ward Terrace, Northeastern Arizona
Authors: Stokes Stephen , Breed Carol S. 
Published: April 2008

AbstractOptical dating of the Tusayan Dunes of northeastern Arizona indicates that at least three distinct late Holocene phases of aeolian reactivation took place in the area, partly upon pre-existing, Pleistocene linear dunes. The reactivation phases occurred approximately 400, 2000–3000, and 4700 years ago. We hypothesize that the large discrepancy in age between the basal and upper parts of the linear dunes relates to the reactivation of only the linear ridge crests, leaving an undisturbed plinth. If so, linear dunes hold a potential for preserving long-term records of successive aeolian depositions. Evidence of regional alluvial-fill episodes and palaeoclimatic data for the area indicate that sediment supply, in addition to aridity and effective sand-transporting winds, is a key factor in determining the timing of aeolian reactivation.
Modes of linear dune activity and their palaeoenvironmental significance: an evaluation with reference to southern African examples
Authors: Livingstone Ian , Thomas David S. G. 
Published: April 2008

Abstract
Supposedly relict continental desert sand dunes have frequently been used as palaeoenvironmental indicators. Often the argument has been, first, that vegetated dunes are fixed relicts, and second, that fixed dunes indicate past aridity. Recent work suggests that neither of these maxims is necessarily true. Using the example of the linear dunes of southern Africa, this paper examines the extent to which we can continue to support a simple assumption that vegetated dunes are inactive relicts. In particular, it addresses the problem of what constitutes activity on linear dunes, and suggests some hypotheses for investigating the ‘grey’ area between active, unvegetated dunes and densely wooded, inactive dunes. The concept of episodic activity is introduced in the context of partially vegetated linear dune forms.
Fluvial-aeolian interactions in a Proterozoic alluvial plain: example from the Mancheral Quartzite, Sullavai Group, Pranhita-Godavari Valley, India
Authors: Chakraborty Tapan , Chaudhuri A. K. 
Published: April 2008

Abstract
The coarse-grained alluvial succession of the Proterozoic Mancheral Quartzite encloses within it a few 2–6 m-thick, typically salmon red, fine-grained, very well-sorted sandstone units. Some 25–400f the fine-grained sandstone units is aeolian — mostly adhesion laminae with subordinate adhesion cross-laminae and wind-ripple strata. The remainder of the sequence is aqueous; either massive or with faintly-developed trough cross-bedding. Based on their grain size, sorting and roundness, the bulk of the aqueous deposits appear to be reworked aeolian deposits. Thick adhesion laminated units within them show a number of superimposed drying-upwards sequences, represented by an upward decrease in laminae spacing within each of the sequences. Individual drying-upwards sequences, 5–15 cm thick, are in places bounded by disconformity surfaces marked by iron crusts.
Stratigraphic relationships with associated fluvial facies indicate that these aeolian sandstones formed in the distal part of the floodplain. An arid climate, vegetation-free landscape, quickly avulsing channel behaviour and rapid basin subsidence favoured development and preservation of these rather thick alluvial plain aeolian deposits. Fluvial dynamics, in contrast to the erg dynamics as interpreted from other interlayered aeolian-fluvial deposits, was the primary control on the depositional features and their internal organization within these aeolian sandstone units.
A complex dune system in Baix Empordà (Catalonia, Spain)
Authors: Cros Lluisa , Serra Jordi 
Published: April 2008

Abstract

The dune system of Baix Empordà, Catalonia, Spain is composed of sediments supplied by the Ter and Daró rivers, transported by the effective north-northwesterly local wind called the
Tramuntana
.

Dune formation is mostly related to the vegetation on the plains area and to topographic obstacles in the Begur Massif zone. Morphologically, these dunes are mainly parabolics and blowouts. Climbing, falling and ‘passadis’ dunes are present in the mountainous zone, the latter being a newly proposed name for a type of lee dune.
The sands are differentiated into distinct groups according to their sedimentological features and marine faunal content. Their evolution and age have been determined by mapping, and by geological and historical information, respectively.
Late Holocene dune formation on the Sefton coast, northwest England
Authors: Pye Kenneth , Neal Adrian 
Published: April 2008

Abstract
Coastal dunes fringe the coast between Southport and Liverpool in northwest England, forming a natural barrier which prevents marine flooding of low-lying agricultural land in West Lancashire and north Merseyside. The dunes are best developed at Formby Point, where they reach 25 m above sea-level and blown sand extends some 4 km inland. This paper presents the results of an initial programme of field drilling, sediment analysis and radiocarbon dating which suggest that the dune complex developed from a large offshore sandbank, which was in existence by 6800 years ago. Behind the bank lay a large area of intertidal mudflats and sandflats with fringing saltmarsh. Dunes may have first become established on the emergent sand bank around 6000 years ago, but the oldest dunes for which there is direct dating evidence formed between 5700 and 5800 years ago. A period of dune stability, possibly associated with seaward progradation of beach and foredune ridges, appears to have occurred between 2500 years ago and the early Middle Ages. During the earlier part of this period oak and alder woodland covered the dunes and the sands were deeply podsolized. Historical and documentary evidence indicates that extensive sandblowing occurred all along the coast during the early Middle Ages, which was a period of exceptional storminess and rapid coastal erosion. Several settlements and farms were lost to the sea or were overwhelmed by blown sand as the coast eroded. Active sand tongues extended across the full width of the barrier and buried the backbarrier peats and silts along the western margin of Downholland Moss. Dune instability has continued intermittently until the present, although on a smaller scale, and consequently most of the present dune forms are relatively recent. Sand stabilization and foreshore reclamation measures undertaken in the second half of the nineteenth century were highly effective and contributed to a net seaward progradation of the entire Formby coastline between 1850 and 1900. Abandonment of these measures around the time of the First World War contributed to, but did not ultimately cause, a return to shoreline erosion and a new phase of frontal dune instability which is still in progress.
Progressive vadose diagenesis in late Quaternary aeolianite deposits?
Authors: Gardner Rita A. M. , McLaren Susan J. 
Published: April 2008

Abstract

Since the mid-1960s a number of models (as exemplified by Gavish & Friedman (1969) and Land
et al.
(1967)) have been developed which suggest that a progressive sequence of morphological, mineralogical and chemical changes occurs during carbonate diagenesis in the vadose zone. The models raise the possibility that the degree of cementation and diagenetic alteration can be used as a guide to interpreting the relative, and even the absolute, age of deposits. A study of the early vadose diagenesis of a wide range of late Quaternary age aeolianites from Oman, South India, the Bahamas, Tunisia and Mallorca has been undertaken to assess the wider applicability of the models. The results presented in this paper indicate that the rigid application of such models to areas outside those for which they have been developed is inappropriate. In the aeolianites analysed, spatial and temporal heterogeneity is the key characteristic. All tend towards an end point of low-Mg calcite allochems and meniscus, rim and pore-filling cement types but at different rates in different places, both locally and regionally, and via several different diagenetic routes.
Contrasting origin and character of Pleistocene and Holocene dust falls on the Canary Islands and southern Morocco: genetic and climatic significance
Authors: Coudé-Gaussen Geneviève , Rognon Pierre 
Published: April 2008

Abstract
Various surficial calcitizations and laminar calcretes overlie non-carbonate basement rocks in southern Morocoo (Ifni and Anti-Atlas areas) and basalt outcrops or biodetrital sands in the eastern Canary Islands (mainly Fuerteventura). Geomorphological, sedimentological and micromorphological data provide evidence for their origin by deposition of Pleistocene calcitic dust and syn- to post-depositional colluvial reworking. These dusts were derived from the comminution of marine and local biodetrital sands mobilized by the westerlies on the emergent offshore shelves during times of Pleistocene low sea-level.
An opposite aeolian system related to Holocene and present-day Saharan dusts explains the formation of silts resting on the slopes of Fuerteventura and the fine fraction of the colluvial soils of southern Morocco. These deposits often lie unconformably on the calcitic bodies and their sedimentological and micromorphological characters are similar to those of the modern Saharan dusts. This suggests opposite major climatic conditions for the two aeolian dust systems: the calcitic dust system was controlled by a southerly shift of the midlatitude circulation in the Pleistocene; the later Saharan dust contribution seems to be related to the re-establishment of the trade wind circulation and Saharan air outbreaks, particularly in the early Holocene when the continuance of blocking situations in the midlatitude Atlantic may have been notable.
The magnetic mineralogy of a loess section near Lanzhou, China
Authors: Rolph Timothy C. , Shaw John , Derbyshire Edward , Jingtai Wang 
Published: April 2008

Abstract
A collection of almost 500 hand samples from a 250 m loess section near Lanzhou, Gansu province, have been investigated to determine both the nature of the magnetic mineralogical differences between the loess and inter-bedded soils and the time variance of the magnetic mineralogy. Results indicate that the parent magnetic material, which is aeolian in origin, is cation-deficient magnetite/maghaemite and the strong magnetic susceptibility contrast, particularly in the younger material, between loess and soil, is mostly due to pedogenic enhancement of the magnetic content of soils by in situ formation of ultrafine magnetite, although we should not ignore possible changes in the nature of the available aeolian material during the warmer soil-forming periods. Compared to loess sections further to the east, the degree of enhancement in the soils is small, on average having a ferrimagnetic content which is only 17 0reater than that of the loess. Trends in the magnetic mineralogy of the section indicate a possible link with the long-term climate change of Northern China, the average ferrimagnetic grain size increasing with decreasing age in response to increased wind velocity and a colder, drier climate. At a point approximately 110 m above the base there is a dramatic change in the nature and concentration of the magnetic material. This change indicates either a rapid deterioration in the average climate or a sudden change in the provenance of the source material, although at this stage we cannot discount the possibility of some time gap at this position. The loess/palaeosol susceptibility contrast is noticeably reduced below this level, perhaps indicating less extremes of climate.
Fluvial scour and incision: models for their influence on the development of realistic reservoir geometries
Authors: Salter T. 
Published: April 2008

AbstractThe three-dimensional geometry of fluvial sandbodies may be very complicated. Factors influencing this complexity include the processes of fluvial scour and incision, both of which can promote local or widespread increases in sandbody thickness. Incision, as caused by downstream relative base-level fall, produces entrenched valleys that control the location of subsequent alluvial deposits. A simple model is presented that attempts to quantify the scale of this extrinsic incision and, in turn, highlights several sedimentary implications of base-level fall. In contrast, scour is an intrinsic process common to all fluvial systems, and is promoted by constriction, curvature or confluences within the major channels. Existing empirical relationships that predict fluvial sandbody width from thickness are oversimplistic, failing to consider the modification of sandbody dimensions by such intrinsic processes. At low aggradation rates sandbody thickness may exceed channel bankfull depth by 100%, due purely to the effects of scour.It is proposed that future fluvial width: thickness databases should stem from the classification of deposits according to the aggradational regime during their deposition. This will encourage the specific recognition of scour and incision, particularly in coastal plain alluvial deposits, and lead to an improved understanding of the controls upon sandbody deposition.
Dimensions and quality of reservoirs originating in low and high sinuosity channel systems, Lower Cretaceous Travis Peak Formation, East Texas, USA
Authors: Davies David K. , Williams Brian P. J. , Vessell Richard K. 
Published: April 2008

Abstract
Quantification of the dimensions and quality of fluvial reservoirs requires knowledge of channel style, depositional environment and diagenesis. Two styles of fluvial channel co-existed during the rapid aggradation of >600 m of Lower Cretaceous, Travis Peak sediments in East Texas: (1) high sinuosity (meandering) channels, and (2) low sinuosity (straight) channels. Each was restricted to a specific geographic area, the result of long-term, geomorphic stability. In both channel systems, reservoir sandstones originated principally in channel and crevasse splay environments.

Reservoir models developed through sedimentological analysis are similar to those developed independently through reservoir simulation studies. Reservoir sandstones originating as point bars in high sinuosity channel systems are relatively small (1.2 km
2
or less), thin (3.6 m), heterogeneous, and isolated within non-pay mudrocks. Reservoir sandstones originating as medial and transverse/oblique bars in the low sinuosity system are areally extensive (>20 km
2
) thick (3.6 to 13.7 m), homogeneous, and display complex pressure relationships due to avulsion of long stream segments, and the lateral and vertical stacking of successive channels in well-defined channel belts. The greatest volume of channel sandstone occurs in the low sinuosity channel system. The high sinuosity system is dominated by overbank deposits.

Travis Peak sandstones have been extensively modified by compaction and cementation. Despite extensive diagenesis, permeability values reflect original depositonal environment and bedding style, even in rocks which have lost more than 80% of their original, depositional porosity. Channel sandstones have higher permeability than associated splay sandstones. Within a channel sandstone, the highest values of permeability occur in destratified, and flat- to low-angle cross-bedded sandstones: planar cross-bedded and ripple-bedded sandstones have the lowest values of permeability. Original depositional environment and bedding style exercise important control on permeability (particularly potential gas flow) even in rocks in which the pore systems have been modified significantly by diagenesis. A knowledge of depositional environment and bedding style is therefore important in predicting potential producibility in tight, gas sandstones such as the Travis Peak formation.
The complex nature of a Jurassic multistorey, alluvial sandstone body, Whitby, North Yorkshire
Authors: Alexander J. , Gawthorpe R. L. 
Published: April 2008

Abstract

The complex alluvial sandstone body of the Saltwick Formation (Aalenian) exposed in the town of Whitby, North Yorkshire is 700–1000 m wide, up to
c.
25 m thick and extensive in the palaeoslope direction (N-S). Exposed sections are approximately parallel and perpendicular to the palaeochannel orientation. The sandstone body is made up of a large number of channel storeys stacked in a complex vertical and lateral pattern and it is composed predominantly of fine- to medium-grained sandstone (> 85% by volume) with subordinate amounts of mudstone and siltstone. The sedimentary facies architecture indicates that channels repeatedly reoccupied the same site and that periods of erosion and incision alternated with periods of rapid bed aggradation. The sandstone facies patterns are related to migration of channel bars, dunes and ripples. Fine-grained sediment facies which occur between some of the storeys are laterally discontinuous because of their position within abandoned channels and their partial erosion by later channels.

Within the sandstone, permeability ranges from 0.8 to 682.1 mD with a geometric mean of 83.5 mD. Permeability heterogeneity is apparent from laminae to sandstone body scale. An attempt was made to characterize permeability on the basis of sedimentary facies. However, there is considerable scatter in the data and individual facies show a varying degree of heterogeneity of permeability. Two major sandstone storeys which appear very similar in origin and lithological character were found to have systematically different permeability distributions (geometric mean permeabilities of 36.0 and 108.5 mD). Facies variations can only partly explain this. There is a difference in the mean permeability of the same facies in the two sandstone storeys (e.g. geometric mean permeability of cross bedded sandstones in the two units are 63 mD and 100 mD respectively).
Production evidence for geological heterogeneities in the Anschutz Ranch East Field, western USA
Authors: Lewis Helen , Couples Gary D. 
Published: April 2008

Abstract
The Anschutz Ranch East Field is a large asymmetric anticlinal trap in the Wyoming-Idaho-Utah thrustbelt of the western USA. The aeolian Jurassic Nugget Sandstone reservoir unit is a layered sequence of dunes and stratigraphically flat interdunes. This interpretation is supported by patterns of reservoir performance in the gently-dipping, nearly planar backlimb of the fold where there is little structural deformation. Structural features which developed during emplacement of the Anschutz Ranch East truncation anticline are partially dependent on the distribution of lithofacies, and the changes in rock properties which result from the deformation are overprinted onto the pre-existing rock properties. An extensive coring programme demonstrates that most of the strain in the Nugget Sandstone is in the crest and forelimb of the fold. Throughout the structure, the deformation is primarily of the compactive (sealing) type, leading to lowered porosities and permeabilities, and thus both to degraded reservoir quality and to flow barriers. Structurally-created low-permeability zones are identified or interpreted at a range of scales, and production histories provide sufficient evidence to establish the role of the larger features as flow partitions.
Compartmentalization of an aeolian sandstone by structural heterogeneities: Permo-Triassic Hopeman Sandstone, Moray Firth, Scotland
Authors: Edwards H. Ewart , Becker Andrew D. , Howell John A. 
Published: April 2008

Abstract
Many excellent aeolian sandstones suffer a decline of reservoir quality associated with structural compartmentalization by tectonic features. An onshore analogue, the Permo-Triassic Hopeman Sandstone, which crops out along the Southern side of the Moray Firth, Scotland, has been studied due to the difficulty in quantifying tectonic heterogeneities in the sub-surface. A hierarchy of structural flow barriers, with impermeable fault rock, has been observed. These vary from solitary deformation bands, via compound zones of bands to major slip surfaces/faults. Episodic faulting leads to the growth from bands to larger fault zones. Increased cementation of the sandstones is seen adjacent to these tight fault zones, and a zone of enhanced cementation, spatially governed by the main fault in the region, has been mapped. Conjugate extensional systems of deformation bands decrease in density away from major faults. Porosity reduction is related to proximity to faults, with porosity increasing abruptly away from the tectonic barrier; the deformation producing low-quality reservoir and flow barriers. Tectonic features have, intermittently, acted as both fluid conduits and barriers: enhanced cementation of sedimentary features adjacent to ‘tight’ faults shows migration of diagenetic brines along fractures. The relatively well sorted aeolian Hopeman Sandstones display better developed flow barriers than the poorly-sorted, mixed facies fluviatile Burghead Beds. Interaction of fluid-flow, diagenetic cementation and structural deformation produce flow barriers that compartmentalize the sandstones on all scales.