Aeolian Systems Research Articles

A test of a climatic index of dune mobility using measurements from the southwestern United States

The climatic index of dune mobility developed by Lancaster (1988) has been applied to a variety of different environments. The index is, however, untested and unverified. We tested the index by comparison of values of the dune mobility index calculated from climate data with rates of sand transport measured at three stations in Arizona and New Mexico over the period 1985 to 1997. Our results show that changes in measured rates of sand transport closely parallel temporal changes in the dune mobility index. The mobility index is, however, a relatively poor predictor of the magnitude of actual sand transport on a year-to-year basis. This discrepancy is probably due to the fact that sand transport rates at these sites are strongly influenced by vegetation cover, the state of which may lag changes in annual precipitation. There is, however, a good relation between the mean annual mobility index and mean annual rates of sand transport. This indicates that the dune mobility index is a valid predictor of the long-term state of the aeolian system and can be used confidently for the purposes for which it was originally intended. Copyright © 2000 John Wiley & Sons, Ltd.

A test of a climatic index of dune mobility using measurements from the southwestern United States

The climatic index of dune mobility developed by Lancaster (1988) has been applied to a variety of different environments. The index is, however, untested and unverified. We tested the index by comparison of values of the dune mobility index calculated from climate data with rates of sand transport measured at three stations in Arizona and New Mexico over the period 1985 to 1997. Our results show that changes in measured rates of sand transport closely parallel temporal changes in the dune mobility index. The mobility index is, however, a relatively poor predictor of the magnitude of actual sand transport on a year-to-year basis. This discrepancy is probably due to the fact that sand transport rates at these sites are strongly influenced by vegetation cover, the state of which may lag changes in annual precipitation. There is, however, a good relation between the mean annual mobility index and mean annual rates of sand transport. This indicates that the dune mobility index is a valid predictor of the long-term state of the aeolian system and can be used confidently for the purposes for which it was originally intended. Copyright © 2000 John Wiley & Sons, Ltd.

Sedimentological maps of the typical loessic units in North Pampa, Argentina

Application of grain size data allowed the construction of maps of two typical loessic formations of North Pampa . A Sand Sea covering the central Argentine plain and a Peripheral Loess Belt to the northeast, compose the Pampean Aeolian System. A region of 20,000 km 2 in the Loess Belt (Santa Fe and Córdoba provinces) was studied. Thick loess outcrops are located in this region. The Tezanos Pinto Loess, Upper Pleistocene-Lower Holocene in age, and the San Guillermo Fm, Late Holocene in age, are analysed in this article. The silt content has been taken as the main parameter for mapping. In general, the pattern of the isoplethic curves is similar in both maps. These maps show that the silt content in both loessic units progressively increases from SSW to NNE. In the Loess Belt, the silt content increases from 55 to 60% in the SSW (at the transition belt to the Sand Sea) up to 75–80% in the NNE (along a distance of 120–200 km). Other sedimentological data of the outcropping loess-paleosols sequences are presented as complementary information.

Climate, sediment supply and tectonics as controls on the deposition and preservation of the aeolian-fluvial Etjo Sandstone Formation, Namibia

Deposition and subsequent preservation of the Jurassic-Cretaceous Etjo Sandstone Formation of Namibia represents a complex interplay between climatic and tectonic factors and related variations in extrabasinal sediment supply. The aeolian and fluvial deposits indicate semi-arid to arid climatic conditions throughout the deposition of four distinct sedimentary units. The succession records either an upward increase in aridity or an upward increase in aeolian sediment supply, represented by a transition from a fluvially dominated basal unit, through a marginal fluvial-aeolian unit to an exclusively aeolian unit. A combination of inherited palaeotopography and syndepositional extensional faulting provided the space necessary for the accumulation of much of the succession. A basinwide unconformity (super surface) divides the succession. This hiatus resulted partly from a lack of available preservation space and partly from a shutdown in aeolian activity related to a regional climatic reorganization. A subsequent shift in the palaeowind direction from northwesterly to southwesterly exploited sand reserves in the Paraná Basin of South America and led to the resumption of aeolian sedimentation across the region. Variations in preserved bedform thickness were directly controlled by differential amounts of tectonic subsidence across the basin. A second major super surface towards the top of the succession resulted from the regional shutdown of large tracts of the aeolian system following the eruption of Etendeka flood basalts across the region.

Aeolian system sediment state: theory and Mojave Desert Kelso dune field example

The sediment state of aeolian dune fields and sand seas at a basinal scale is defined by the separate components of sediment supply, sediment availability and the transport capacity of the wind. The sediment supply for aeolian systems is the sediment that contemporaneously or at some later point serves as the source material for the aeolian system. Numerous factors impact the susceptibility of grains on a surface to transport, but these are cumulatively manifested by the actual transport rate, which serves as a proxy for sediment availability. Transport capacity is the potential sediment transport rate of the wind. Because the three aspects of sediment state can be given as a volumetric rate, they are directly comparable. Plotted simultaneously against time, the generated curves define nine possible classes of sediment state. Sediment supply that is stored occurs because it is transport or availability limited, or generated at a rate greater than the potential or actual transport rates respectively. Contemporaneous or lagged influx to an aeolian system may be limited by sediment availability, but cannot exceed the transport capacity of the wind. For the Kelso dune field in the Mojave Desert of California, a variety of stratigraphic and geomorphic evidence is used to approximate the sediment state of the system. The sediment supply was generated during the latest Pleistocene and earliest Holocene during humid periods of enhanced discharge by the Mojave River to form the Lake Mojave fan delta or terminal fan, and has been calculated over time from the sedimentation rate and the frequency of floods. Estimation of transport capacity over time was based upon modern wind data, with an allowance for greater winds during the Pleistocene based upon climatic models. Sediment availability was approximated by calculation of a modern dune mobility index, with variation over time based upon climatic inferences. While quantifying the Kelso or any natural system is subject to numerous uncertainties, the sediment state approach reflects the temporal and spatial disjointed nature of accumulations at Kelso, as well as illuminating questions for future research.

Upper Quaternary geology of the lower Carcarañá Basin, North Pampa, Argentina

The geological evolution of the lower Carcarañá Basin reflects a sequence of dry and humid climates. From a geomorphological point of view, the area belongs to the Pampean Eolian System. The geomorphological units comprise several fluvial geoforms, partially masked by a loess carpet, on which eolian erosive forms developed. The sedimentary record is not simple. The typical profile begins with a predominantly eolian unit, composed of silty sand and including two pedogenic levels (Carcarañá Fm). The formation is the result of the reworking of a dune field in the Pampean Sand Sea (IS4). It is upper Pleistocene in age (IS 3). Another, somewhat different, climatic deterioration followed (related to the begining of the Last Glacial Maximum -IS 2), which caused the deposition of a loessic mantle (Tezanos Pinto Fm). Subsequent evolution of the climate involved a shift to humid conditions during the Hypsithermal period, generating a well-developed soil at the top of the formation. An upper Holocene eolian layer (San Guillermo Fm) covers the whole sequence. At the river margins of the basin the late Pleistocene/lower Holocene eolian deposits are replaced by a complex silty–clayey sequence, mainly paludal, with a soil complex in the middle of the section (Lucio Lopez Fm).

Holocene aeolian phases and human settlements along the Atlantic coast of southern Spain

A combined geomorphological, radiocarbon dating, archaeological and historical approach permits a refining of the age of the coastal dune systems related to estuaries in the Gulf of Cádiz. Three dune systems are distinguished in this paper. The oldest one, D1, which accumulated under prevailing WSW winds during the first millennium bc, overlays both the occupational horizons of Late Neolithic-Early Copper Age (fourth millennium bc) and the‘lithic workshop levels' (fourth to second millennia bc). The middle dune system, D2, containing both Roman and medieval remains, accumulated between the thirteenth or fourteenth centuries and the seventeenth century ad. The youngest D3 system is associated with the time of building of watchtowers in the seventeenth century ad but extends to the present; it is related to SW prevailing winds. We explain the absence of aeolian deposits prior to 2700 cal. BP as the result of trapping of a large part of the sediment supply in the estuaries, which starved the neighbouring beaches and aeolian settings. Aeolian accumulation reached significant values when sedimentation in the coastal zone changed from being mainly aggradational in the estuaries (6500–2700 cal. BP) to mainly progradational in spit barriers and related dunes (post 2700 cal. BP). The present analysis of aeolian systems suggests a non-direct correlation, at least in some cases, between coastal progradation of spit barriers and aridity.

Response of aeolian systems to Holocene climatic and hydrologic changes on the northern margin of the Sahara: a high-resolution record from the Chott Rharsa basin, Tunisia

Four millennial-scale latest Pleistocene to Holocene climatic cycles are recorded by aeolian-lacus trine strata along the southern margin of Chott Rharsa, a playa situated within an active tectonic basin along the northern margin of the Sahara Desert in Tunisia. Cycles are characterized by (1) a humid phase of dunefield stabilization and high lake levels, and (2) an arid phase of playa desiccation and deflation with dunefield construction. The cycles overall define a progressive drying trend and correlate well with a detailed chronology from Morocco and with the Sahara region in general for the latest Pleistocene and early Holocene. Climatic events appear more regional in nature for the later Holocene. An isolated outcrop of aeolian deposits dated at >86 ka BP argues for records of older cycles in the Chott Rharsa Basin that were subsequently removed by long-term deflation in the area.

High-precision provenance determination using detrital-zircon ages and petrography of Quaternary sands on the eastern Snake River Plain, Idaho

The Big Lost trough is an upper Pliocene to Holocene sedimentary basin containing volcanic sills in the northeastern Snake River Plain, Idaho. The basin receives sediment primarily from Basin and Range fluvial systems of the Big Lost River, Little Lost River, and Birch Creek. The Big Lost trough contains a >200-m-thick succession of lacustrine, fluvial, eolian, and playa sediments, recording high-frequency Quaternary climatic fluctuations interbedded with basalt flows. Alternating deposition of clay-rich lacustrine sediments and sandy fluvial and eolian sediments in the central part of the basin was in response to the interaction of fluvial and eolian systems with Pleistocene Lake Terreton. The source areas for modern sands from the fluvial systems can be differentiated by using both petrography and U/Pb age spectra from detrital-zircon populations. Provenance data from subsurface sands indicate that the Big Lost trough was supplied with sand largely deposited by the Big Lost River, with local redeposition by eolian processes, similar to the modern depositional system. Provenance and stratigraphic data suggest that during Pleistocene wet climate cycles, the center of the basin was dominated by lacustrine sedimentation; during dry climate cycles, the base level dropped, the Big Lost River prograded across the basin, and the eolianmore » system became active. At least seven climate oscillations are recorded in strata deposited between {approximately}140 and {approximately}1250 ka.« less

Relating eolian bounding-surface geometries to the bed forms that generated them: Etjo Formation, Cretaceous, Namibia

The Cretaceous Etjo Formation is a 200-m-thick eolian and fluvial sandstone succession exposed in the Huab Basin of northwestern Namibia. Eolian sedimentation was terminated abruptly by the emplacement of flood basalts of the Etendeka igneous province across much of the basin at 132 ± 1 Ma. The lavas “drowned” the dunes and, in doing so, preserved bed forms with heights and wavelengths of up to 100 m and 1.3 km, respectively. Subsequent erosion has resulted in the exposure of these bed forms and provides a rare opportunity to accurately reconstruct the three-dimensional geometry of an ancient eolian system and to relate bed-form morphology to bounding-surface geometries. Some bed forms lacked a single active slipface but instead were characterized by a dome form over which smaller transverse dunes migrated. Other bed forms were characterized by an active slipface and a stoss slope over which smaller, superimposed bed forms migrated. One bed form records a transitional evolution between these two end-member types. Preserved bed sets exhibit a positive (but stoss-erosional) angle of downwind bed-form climb of 1°. Bed forms of the Etjo Formation provide an opportunity to directly relate bed-set thickness to original bed-form height via the angle of climb.

The Identification of Eolian Sands and Sandstones

This paper presents a brief review of criteria used for identifying eolian sands and sandstones. Many features of eolian sand grains are not unique to eolian environments, and therefore one must be very careful in making environmental interpretations based only upon sand grain characteristics. The identification of stratification types provides another potential means of identifying eolian sands and sandstones. In particular, ripple laminae are very different in eolian and subaqueous systems, and the proper identification of wind-ripple laminae is an excellent method of identifying eolian sands and sandstones.

Event detection and conditional averaging in unsteady aeolian systems

Traditional models of sediment flux ignore wind unsteadiness, and there are sound empirical and theoretical arguments that implicate this deficiency as being fundamental to explaining their limited predictive abilities. Drawing on concepts and theories from the fluid mechanics literature on turbulent boundary layers, and with the implementation of fast-response instrumentation (hot-film anemometers and continuously-weighing sand traps) this study begins to address a series of inter-related questions regarding the character of wind and transport events. Foremost among these is whether an event-based analysis of wind speed time series bears close resemblance to sediment flux events.The research demonstrates that fluid ‘ejection’ events identified by the Variable-Interval Time Averaging (VITA) method are only crudely associated with those identified using the quadrant-threshold method. Moreover, VITA events show poor correspondence with sediment flux events. The reasons for this are unclear, although it is likely that the character of events in this beach boundary layer differ substantively from the character of structural events typically associated with the sublayer bursting process. Additional unresolved issues include whether the inner/outer layer model applies to the grain-laden/grain-free zones of a saltation system, and whether the structural events evident in velocity time series from wind tunnels and natural beaches are analogous. Event-detection and conditional-averaging techniques hold promise for characterizing the fundamental nature of unsteadiness in aeolian systems.

Getting to the source: aeolian influx to the Permian Delaware basin region

Although an aeolian origin for the siliciclastics of the Permian (Guadalupian) Delaware and adjacent basins and shelf has been recognized, their source has remained elusive. An Ancestral Rockies source to the west and northwest has been traditionally favored. We propose instead that these sediments were derived from aeolian systems to the northeast and represented by the Whitehorse Group in the Anadarko Basin. This hypothesis is based upon (1) recognition of the aeolian nature of the Whitehorse, (2) regional correlation of the Whitehorse Group with portions of the Artesia Group, (3) paleoclimatic model-predicted and measured southwestward sediment transport for the Whitehorse, and (4) a proposed transport corridor over emergent mudflats along the northern margins of basisins in the Texas Panhandle and onto the New Mexico shelf. Potentially, a Whitehorse-Artesia link could show the formation of this mixed carbonate/siliciclastic system as the result of the interactions of diverse and distant environmental systems under eustatic and climatic forcing factors.

Abstract: Critical Heterogeneities in Aeolian Systems and Their Effect on Flow Performance in Reservoirs.

Abstract: Critical Heterogeneities in Aeolian Systems and Their Effect on Flow Performance in Reservoirs.

Carbonate ramps and the Pleistocene-Recent depositional systems of the Arabian Gulf

Abstract The term ramp was devised to be helpful. It was to provide an interpretative model with genetic significance for a specific category of carbonate body and one with predictive value in oil exploration. The present-day southern Arabian Gulf is commonly cited as a ramp but it fails to provide a good example. In contrast with most of its pre-Miocene history, the Arabian Gulf is a foreland basin with a tectonically, climatically and glacioeustatically controlled mixed carbonate-clastic fill. Because of glacioeustasy and its relatively shallow depth, the Gulf has spent much of the last 2.5 Ma emergent. Three separate and equally important sedimentary systems currently contribute to its development: the Arabian Gulf marine carbonate system, the Mesopotamian fluviodeltaic system and the Arabian continental aeolian system. The Arabian Gulf carbonate system is a ‘high stress’ regime that is in tectonic, eustatic and depositional disequilibrium. Its structural, morphological and sedimentological diversity discount it as a Recent analogue for the thick carbonate bodies in the geological record that show persistent accumulation of depth-related facies developed across gentle slopes lacking a marked shelf-slope break. The Arabian Gulf fails some fundamental tests for whether it should be regarded as a stable carbonate ramp depositional system and its use as an example of a ramp is not helpful.

The Navajo Sandstone

The Navajo Sandstone is the remnant of an early Jurassic (Pliensbachian‐Toarcian) aeolian (wind‐blown) system that stretched over most of the western United States for several million years. Interpretation of these deposits suggests that the Navajo erg (sand sea) was one of the most extensive desert systems ever to have existed in the history of the Earth, and probably contained the largest sand dunes that have ever moved across the surface of the planet.

On the prediction of bed‐load sand transport rate in air

ABSTRACTThis paper discusses the parameterization of aeolian mass transport rate beginning with a critical discussion of four different forms of the prediction equation. Following this, recent progress in understanding the physics of the aeolian system is used to suggest an alternative approach which provides some new insights into the prediction of mass flux. The primary object of the paper is not to add another transport rate equation to those already present in the literature but rather to discuss the transport system in relation to the physical processes showing, to some extent, why reliable transport rate prediction has so far been elusive.

Doñana National Park (south-west Spain): geomorphological characterization through a soil-vegetation study

The geographical history of the Doñana National Park during the Quaternary is viewed as a necessary background to understanding the actual morphology and principal processes. At present, the geomorphology of the Doñana National Park is classified into three morphogenetic systems: aeolian, estuarine and littoral. This paper describes the geomorphological classification of the aeolian system (the eldest one) down to the level of morphoedaphic elements, which are recognized through a soil classification and vegetation study.

Nature of environmental changes in South America at the Last Glacial Maximum

A review is given of geomorphological evidence suggesting the nature of environmental changes in South America during the Last Glaciation Maximum (LGM). The data are from glacial, geocryogenic, alluvial, colluvial and aeolian systems and span 68° of latitude, making the most complete land transect of major climatic systems in the Southern Hemisphere. Glaciers in the northern and central Andes may have reached their maximal extent by 27,000 yr B.P.; reduced precipitation at the LGM, caused by lower temperatures and lower atmospheric humidity, probably led to slight glacier recession in the tropical Andes. Icefields in the Southern Andes were most expansive when global temperature and sea level were lowest, because Pacific westerlies supplied abundant moisture, and western outlets advancing across the continental shelf were constrained by sea level. Low-gradient river networks became incised by at least 100 m into narrow channels as global sea level fell by 120 m during the LGM. “Draw-down” of water-tables possibly impacted the forest cover, enhancing the drying influence of reduced sea surface temperature and atmospheric humidity. As forest and grass covers diminished in extent, effecting greater atmospheric cooling because of reduced evapotranspiration and convective condensation, colluvial and aeolian processes became more active and widespread. Almost 25% of the continent is covered with palaeo-aeolian features, presumed to have been active when airflow was stronger due to steeper atmospheric pressure and temperature gradients at the LGM. Substantial changes in precipitation totals and incidence, and in ground-water availability, probably eliminated modern-type tropical rainforest except in areas currently receiving ca. 5000 mm of annual rainfall. Equivalent changes in vegetation cover spread across much of the Guyana and Brazilian highlands and throughout the southern temperate regions.

About this title

Sedimentological research has traditionally produced geological models primarily relevant to hydrocarbon exploration, focusing predominantly on location and external geometry of sediment bodies and underplaying the importance of the internal reservoir framework. This failure severely inhibits the application of new and sophisticated technologies to improve recovery efficiencies. It-is reservoir architecture, the internal fabric and structure of a reservoir, that ultimately controls the paths of fluid migration during oil and gas emplacement and subsequent extraction. This architecture is, in turn, the product of the depositional and diagenetic processes that created the reservoir. If an understanding of the origin of the reservoir is developed, reservoir architecture, and hence fluid-flow paths, becomes predictable. This volume assesses the current position of predictive geoscience for fluvial and aeolian systems, documents recent advances in methods and understanding and highlights outstanding problems. The authors form a wide spectrum of geoscientists from industry and academia, with leaders in the science providing review papers in their field of specialization. The volume naturally divides into four sections: fluvial reservoirs, aeolian reservoirs, structure and methods.