CHAPTER I ALLUVIAL SYSTEM 1.1. Introduction Alluvial fans are conical deposits of sediment that build up proximal to mountains/canyons (Figure 1). Alluvial fans form when drainage basins transition into a single feeder channel. The feeder channel exits the drainage basin and deposits sediment onto flat/wide plains, resulting in a lose of stream competence and rapid deposition of sediment (Blair and McPherson, 1994). Fans typically have a semicircular shape from map view, but appear convex up in cross section view. Alluvial fans form when channels enter a valley or canyon.The fan shape forms due to the change in channel morphology down slope. As fluids saturated with sediment leave the confined channel flow, an increase in area will result in thinning of the flow and velocity will decrease (Blair and McPherson, 1994). Sedimentation will occur gradually down fan. Alluvial fans are typically found in tectonic settings which create variations in topography, such as fans controlled by normal faulting in the Basin and Range of Arizona/Nevada (Harvey, 2002). Fans are commonly found in arid conditions, such as deserts. Alluvial fan sedimentation vs dissection is dependent on climatic and tectonic conditions. Aggradation will occur when water saturated with sediment is transported down fan (typically wet conditions), whereas dissection occurs when fluids are sediment starved (dry conditions) (Harvey, 2002). There are three main depositional processes that form alluvial fans: debris flows, mudflow, and stream flow. Debris flow deposits are dominated by gravitational processes, stream flow by fluvial processes, and mudflow by a combination of both factors. Debris flow and sheet flood facies associations are the most common depositional facies in alluvial fans (Miall, 1984). Figure 1. Alluvial Fan, Taklamakan Desert, Ximjiang (China?) Photo Credit: University of Maryland. 1.2. Geomorphology and Modern Analog Alluvial Fan geomorphology and anatomy is described in Blair and McPhearson, (1994), and Blair and McPhearson, (2009). Alluvial fans are found in the piedmont zone proximal to high elevations (Figure 2). This can include mountain ranges, rift margins, impact craters, etc. Alluvial fans require an inflow of sediment and fluids from an upper catchment area, with occasionaal sporadic water discharge by flooding to transport and deposit sediment down fan. Alluvial fans are fed by drainage basins, which consist of high order fluvial channels that contain fluid and sediment. The drainage basin drains into a central channel called the feeder channel. The point where the feeder channel exits the mountain and enters the fan is called the apex. The feeder channel cuts into the fan forming an incised channel, which can be a single channel or expand into multiple channels. If the fan is incised enough, the channel can cut through older alluvial fan deposits, depositing sediment further down fan (Blair, 1999). The confined flow of the channel will eventually end down fan, and flow will expand at the intersection point. As flow expands, velocity will decrease and sediment will be deposited on the depositional lobe. The angle of the depositional lobes vary, and can be between between 15 and 180 degrees. When alluvial fans intersect each other, they merge into what is called a Bajada, which form a broad apron of alluvial sediment. This will typically vary the angle of the depositional lobe of the fan, making it difficult to determine where one fan begins and another ends. Eventually active erosion may occur on the surface, leaving debris flow lobes (Blair, 1999). Alluvial fans tend to aggrade upward, and prograde away from the site of deposition. Typically alluvial fans will be bounded by aeolian, marine, lacustrine, or fluvial environments at their distal extent (Harvey, 2002). Figure 2. Aerial photograph of alluvian fan surface. Alluvial fans are conical in shape. They are fed from drainage basins at high elevations, typically mountains (top). The fan spreads out at the apex, and sediment is deposited due to a rapid loss in veolocity, forming the depositional lobe. Photo from Blair, McPhearson, (2009). 1.3. Modern Analog (Warm Spring Canyon Alluvial Fan, California. The sedimentology of the Warn Spring Canyon alluvial fan was described in Bair, T, (1999). Death valley is formed in a north south trending active rift basin. It consists of multiple half grabens, with the hanging wall block down dropping to the west along the oblique- slip North and South Death Valley fault zone. Alluvial fans are common along the Panamint Range, which feeds in the badwater Playa. The Warm Spring Canyon Alluvial Fan is located in Death Valley, and has an area of 32.6 square kilometers. It is an example of an arid alluvial fan, with annual rainfall of 42 mm a year. The fan is conical in shape similar to most alluvial fans, but it is influenced by several strike slip faults, which have offset incised channels along the fan (Figure 3). The fan is fed from catchments in the Panamint Range, which overlies andesites, dolomites, shale, and quartzite. The alluvial fan contains two major sections: An uplifted older section, and a distal younger section with active deposition in the salt playa. The incised channel passes through the older section. The older fan surface has been segmented due to active faulting. Desert pavement and soil development has started to form on the older fan section.The incised channel trends parallel to the fan apex, until it is offset by a transform fault along the fan surface. Deposition on the fan lobe is characterized by coarse cobbles. The fan terminates at the Badwater playa. 4 facies associations were developed by Bair, T, (1999). to describe the Warn Spring alluvial fan. Facies association 1 consists of debris flow and washed debris flow depositions, which dominated the alluvial fan surface. Facies ranged from A (matrix supported, muddy, pebble gravel) , to B (clast supported, gravel bed deposits). Facies Association 2 are incised channel deposits that are present within the incised fan surface. Facies ranged from poorly sorted, pebble-cobble beds (C), to poorly sorted, gravely-sandy mud with some planar beds (D). Incised channel deposits are eroded into the Facies association 1. Facies association 3 are lake Manly shoreline deposits influenced by wave action along the playa lake, which includes well sorted gravel sands will low angle planar beds. The Warm Springs Canyon Alluvial fan was interpreted to have been dominated by debris flows during its history, with constant winnowing of fines due to flood waters (Blair, T, 1999). Older segments of the fan are separated by an incised channel. A marine transgression in the late Pleistocene deposited beach influenced sediment up fan and a barrier beach system formed parallel to the fan. Eventually water level fell, and distal fan deposition continued. The Warm Spring Canyon Alluvial Fan serves as a model for alluvial fan deposition in arid climates, with variable changes due to climate and tectonics. Figure 3. Morphology of the debris flow dominated Warm Spring Canyon Alluvial Fan. White represents Depositional load, where sediment exits the confinement of the channel walls, and flow expands, resulting in deposition. Former depositional lobes border the active lobe. These deposits were pushed aside as newer deposits enter the fan. The shoreline represents the maximum lake level of the Lake Manly shoreline. Active transform and normal faults cut perpendicular to the fan surface, often trapping sediment within the channel. Photo from Blair, T, (1999). 1.4. Depositional Processes and Depositional Facies 1.4.1. Depositional Processes Alluvial fans require an inflow of sediment and fluids from a drainage basin, with occasional overland flow by high discharge events to build an alluvial fan. Sediment is derived from the drainage basin or proximal lithology. Flow conditions required to move large volumes of sediment can typically come from heavy precipitation, rapid snowmelt, or anthropogenically through human induced flood events (Miall, 1981) . 1.4.2. Flow Regine Deposition on the fan surface will occur from either from a decrease in fan slope, a decrease in flow depth/velocity, or an increase in the channel volume as the fluid leaves the confined flow (Blair, and McPherson, 1994). Alluvial fans are conical in shape, with a gradual transition from high angle (up to 15 degrees) that decreases down fan. Slope is dependent on source material, with larger clasts supporting steeper cliffs. Alluvial fans typically transport sediment in super critical flow (turbulent flow, high Reynolds number).Supercritical flow will be more prevalent at higher angles, with lower water depth. As competance is lost downslope, the coarser materials will be deposited up fan, while the finer material is deposited down fan (Blair, and McPherson, 1994). Figure 4. Model of subcritical vs supercritical flow conditions. Subcritical flow (laminar flow conditions) occur at lower water depths, decreased slope, and low water velocities. Supercritical flow typically occurs at steep gradients, deep water depth, and high velocities. Alluvial fans are almost always super critical, and occupy the top left portion of the graph (large slope, low water depth). Photo from Blair, T., McPhearson, 1994). 1.4.3. Processes on Alluvial Fans (Primary and Secondary) Primary Processes on Alluvial Fans include processes that deposit colluvium and eroded rocks downslope, often due to failure on the fan surface. The material is transported down fan by either water or gravity. Primary and Secondary processes on Alluvial fan development are explored in Hooke, A., (1967), Wells and Harvey, (1987), and Blair and McPhearson, (2009). Depositional processes on a fan include 1.3.3. Deposits due to gravity Rockfall/rock slides/rock avalanche: Rockfalls occur due to the erosion of bedrock material and transportation due to gravity. Failure can occur for a number of reasons, but is often due to gravity/weathering. Rock slides can be differentiated from rock falls due to their larger block size, and sliding motion along a curved surface. When large boulders are disintegrated during transport downslope, it is called a rock avalanche. Rock Fall deposits are typically massive, with large clasts and brecciated texture. Earth flows: Earthflows occur to due a combination and gravity and muddy colluvium. Earthflows can occur when water percolates into bedrock, and lowers the internal friction. Further loading and the force of gravity may induce failure on the surface along a basal plane. Earthflow deposits are slow processes that move material downfan. When the transported material consits of colluvium, it is called a colluvial slip. 1.3.4. Deposits due to water Braided stream deposits: The upper surface of an alluvial fan is dominated by braided stream deposition. These channels are incised, but overbank flooding can occur during high discharge events. It typically contains well sorted, well stratified, and cross bedded sandstone with coarse grained material at the channel thalweg. Debris Flows: A debris flows occurs when a viscous combination of sediment saturated with water moves and is transported down fan and is deposited. Failure occurs when hydrostatic pore pressure increases due to water saturation, which lowers the shear stress. Sediment varies in size, althought ypically contains large pebbles and boulders. Debris composed predominately of mud are called mudflows. Debris flows are believed to behave as a non-newtonian fluid, and will migrate down slope as a laminar flow with little erosion. They are deposited as conglomerate facies with little to no bedding (Figure 5). Reverse grading often forms due to sieving and density differentials during transport, which forces large clasts to the top. The bottom of the fan is slowed due to friction, and the coarse part on top will have a higher velocity, depositing down fan in front of the slower flow. Debris flows are typically deposited as clast or mud rich levees that give way to lobes down fan as energy decreases. Levees are typically coarse grained, and are deposited as coarse grained material is pushed out of the way as the material moves down fan. Coarse grained levees will dominate on high angle fans, where coarse grained and fine grained lobes will dominate on low angle fans. Debris flow deposits can be either mud rich or clast rich. Figure 5. Example of a debris flow deposit. Taken from University of Maryland. Sheet flow: Sheet flows form from shallow, short-lived, unconfined flow that moves across an inclined surface (Figure 6). Sheet flows are often deposited as flood water over channel levees, leading to unconfined flow.The decrease in water depth, and expansion of area will result in sediment deposition down fan as slope decreases. Sheet flow deposits are typically stratified with sand ripples and cross beds. Alternating low angle beds of pebble/sand couplets in the direction of flow are common. Back dipping beds are sometimes present due to supercritical flow. In some instances, sheet floods with low sediment composition can errode the fan, forming sinuous troughs/crests with no sediment infill. These are called transverse ribs. Figure 6. Typical sheet flood deposit. stratified sandstone. May contain cross beds and ripples. Typically coarse grained deposits are present at the bottom of deposits. Photo from the University of Maryland. 1.5. Controls on Depositional System Evolution 1.5.1. Tectonics Alluvial fans typically form in regions of large vertical relief. They are often found in tectonically active areas, including foreland basins, rift zones, and mountain belts (DeCelles et al, 1991) (Blair, 1999). Tectonically areas actively create and maintain relief. Fans can have short or long lifespans, depending on the episode of tectonics. Convergent zones create relief that is constantly modified, where rift basins result in relief in fans that can aggrade for millions of years (Blair, 1999). Fans adjacent to the tectonically active side of a rift fan will be larger due to increased subsidence. 1.5.2 Climate Alluvial fans have proven to be useful indicators of climate (Hooke, 1967) (Harvey, 2002) (Doom, 2009). Some authors have speculated on how climate may influence depositional processes, with wet climates dominated by sheet floods, and arid conditions dominated by debris flow deposits. This has been disproven to be uniformly untrue, as debris flows can occur in any fan environment, as well as sheet floods. Alluvial fan models must consider both gravitational and fluid origin for alluvial fan facies. Authors speculate that fan aggradation occurs during moist periods due to greater sediment production, where fan erosian occurs during arid periods (Doom, 2009). It is argued that fan erosian occurs due to fluids exiting the catchment area without sediment. Arid conditions are dominated by rock fall deposits. The lack of rainfall also results in fewer episodes of channel breaching, resulting in fewer episodes of deposition. Decreased vegetation during arid periods will result in lower slope stability and increased incision. Secondary processes on alluvial fans are believed to form irrespective of climate. 1.6. Facies Models Two general facies models exist for alluvial fans, depending on if the the alluvial fan is dominated by debris flow or sheet flood deposits (Figure 7). This is typically a direct result of climate (see above). Debris flows dominate in arid climate, while sheet floods dominate in wet climates. Figure 7. Model of debris flow dominated alluvial fan (A) vs sheet flood dominated alluvial fan (B). Debris flow dominated fans form as a result of gravitational processes. They are dominated by coarse grained, poorly sorted deposits. Sheet floods form from fluid dominated processes, and form fine-coarse slightly bedded material. Photo from Blair, T., McPherson, J., (2009). 1.6.1. Tellheim Type The Trollheim fan from Deep Springs Valley California has been used in the past for idealized alluvial fan facies models in an arid environment. It is dominated by debris flow deposits. The fan was initially studied by Hooke, who described the geomorphology and characterized the sedimentology of the fan. The fan formed as a result of dip slip motion in the Basin and Range of western California (Miall, 1981). The Trollheim fan was deposited under steep flow, abundant sediment supply, and infrequent flood conditions.The Trollheim fan consists of debris flow dominated fans, as well as braided stream and sheet flood deposits (Figure 8). The fan overlies stream flow channel deposits.Channel fill deposits are characterised by clast supported gravel lenses. Debris flow deposits facies consist of Gm(gravel debris flow deposits, massive or bedded gravel with some horizontal stratification) and Gms (channel gravels) (Miall, 1981) (Blair and McPhearson, 1993). Gm deposits are composed of poorly sorted, matrix supported coarse-fine grained matrial. It can be either gravel or matrix supported. Gravel supported are more prevalent proximal to the fan due to the transportation of the finer material down fan. Gms is characterized by flat, lobate geometry. Scours are infilled with finer grained Gm. Minor sheet floods result in deposition of St (cross bedded sand), Sr (ripple bedded sand), and Fm(overbank clay). These sheet floods are characterized by fining upward sequences. Some authors have speculated that the finer grained deposits were constructed from clay rich debris flows instead of sheet floods (Blair and McPhearson 1993). The surface is topped by Hummocky gravels. Fine grained sandsheets are also common near the base of the fan, formed due to aeolian processes. Figure 8. Ideal model of debris flow dominated fan, as proposed based on the Tollheim Alluvial Fan. Consists of massive boulders-mud, with possible reverse grading. Bedded sandstone-cobbles are present in sheet flood deposits. Photo Miall, A., (1981). 1.6.2. Scott Type The Scott type alluvial fan applies to fans beyound the limit of debris flows, or fans that lack debris flows. Unlike the Tellheim type, the Scott Type is dominated by fluid processes, and can also be applied to fluvial systems (Miall, 1981). It is dominated by Gm (massive, crudly bedded gravel with some horizontal stratification), forming longitudinal bars during floods (Figure 9). Gt (trough cross bedded gravel), and Gp (planar crossbedded gravel) are common during channel fill deposits on the fan. These are common debris flow deposits, similar to the Trollheim fan. It also contains Sp (planar crossbedded sand), Sh (horizontally laminated sand) and Sr (sand with ripples). These are commonly deposited during sheet floods, during high discharge events (Nichols and Fisher, 2007). after the discharge decreases. Unlike the Trollheim fan, sheet flood deposits dominate in the Scott Type. The Scott type accurately seperates debris flow from sheet flood deposits, however many of the facies seen in the Scott type are also apparent in other facies models describing coarse grained rivers, including the Donjek distal gravelly river model (Miall, 1981). Figure 9. Ideal model of sheet flood dominated alluvial fan. Consists of primarily sand-coarse cobble, bedded conglomerates. Photo from Miall, A., (1981). CHAPTER II EOLIAN DEPOSITIONAL SYSTEM 2.1. Introduction Figure: Crest of sand dune with traces of insect footsteps (Photo courtesy: http://www.wallpaperswa.com) The term eolian (or aeolian in European usage) represents the process of transporting sediments up to sand size by wind (Glennie, 1970; Nichols, 1999). Eolian depositional system is responsible for the deposits dominated by wind-driven sediments where the wind is strong enough to destabilize any surface. This depositional environment prevailed before the appearance of vegetation on earth surface and also active in modern beaches, glacial outwash plains and, both cold and hot climatic deserts (Greeley & Iverson, 1985). This website is concentrated towards the desert eolian depositional environment will provide a preliminary overview. “Deserts are vast areas of windblown sand” this popular concept proved incorrect today. Diverse tectonic settings, location, local climate, and antecedent condition facilitates a diverse array of desert environments. Modern day deserts are concentrated within 30° latitude belts, centered on Tropics of Cancer and Capricorn. These deserts are dominated by subtropical high-pressure wind cells. Another concentration of deserts occurred within the interior of the large continents, away from the oceanic moisture sources. Sandy eolian systems with dunes, erg (eolian sand sea) covers 20% of modern deserts. Figure: Distribution of modern deserts around the world ( Photo courtesy: Pearson Prentice Hall, Inc.) 2.2. Geomorphology & Modern Analog Desert environments range from sand-rich deserts of central Asia to sand-deficient deserts of North America. The desert plain is floored by exposed basement rocks or pavement where sand deposition ceased for a while. These pavement rocks are known as a different term in different geographic locations as reg, serir, hammada, gobi, or gibber plain (Kocurek, 1998). Yardangs are streamlined hills formed by the wind oriented bedrock deposits over the pavements. Irregular shaped hills are termed as demoiselles. Fluvial features are common in precipitation prone deserts. Arid alluvial fans formed with sediments derived from the upland. Ephemeral desert streams or wadis carry the sediments and they can extend up to the basin (Kocurek, 1998). Prevailing wind deflates fine-grained sediments and forms loess deposits which actually covers the 10 % of the earth surfaces. Figure: Processe of sediment accumulation to form dunes (Photo courtesy: www.geocoaching.com) Figure: Large scale cross-beddings generated by dune migration in Navajo Sandstone, Utah, USA (Photo courtesy: http://web.ncf.ca/aa456/sand/overview/index.html) Eolian bed forms are in some way similar to their subaqueous counterparts. Based on the particle size three bed forms are dominant in the deserts, they are eolian ripples, dunes, and drass (Wilson, 1972). Eolian ripples are series of an equally spaced pile of grains formed due to selective pickup and saltation by the wind (Nichols, 1998). Coarser grains concentrated on the crest and form inverse grading as the wind blow finer grains while the ripple migrate. The ripple crests are aligned perpendicular to wind direction. Ripple wavelength varies from few centimeters to several meters whereas the height range is between less than a centimeters to more than ten centimeters. Eolian dunes are larger bed forms with wavelengths ranges from 3 meters to 600 meters and 10 cm to 100 meters height ranges. The dunes migrate by saltation of sand up the stoss side where the saltation form ripples. Unstable grains cascade downs on the lee side initiating avalanches or grain flow. Multiple layers of avalanches will form trough to planar-cross bedding depends on the migration of different dune shape. Migration of transverse, linear, and star dunes form planar cross bedding whereas barchans dune migration form trough cross bedding. Darrs are large scale dunes featuring large sand sea or erg. These large scale undulations show wavelength of hundreds of meters to kilometers and height of tens to hundreds of meters. Darrs comprises of superimposed dunes on the stoss and lee sides. Figure: Types of eolian dunes 2.3. Depositional Process and Depositional facies Wind is the dominant process in the deserts. The wind flowing over loose sediment grains exerts a lifting force on the particles. With increasing velocity the force gain enough energy to roll or saltate the grains (Nichols, 1998). The average normal wind speed that flows over land is around 30 m/s and this velocity is strong enough to carry average grain size around half a millimeter in diameter (Pye, 1987; Nickling, 1994). This is the main reason behind the dominance of grain size less than coarse sand in the eolian deposits. Constant wind velocity will pick up the medium-grained sand and deposit them in equal distance forming eolian ripple crests. Well-developed ripple crest facilitates grain avalanche developing cross-lamination, less significant than subaqueous deposits. Repeated avalanche develop a set of large scale cross beddings which have ripple laminations on the lee side of the dune. Large trough and planar beddings are the significant structure of the eolian deposits. Such large-scale crossbedding is rare in the subaqueous deposits. All of these above-mentioned bed forms construct the arid zone facies dominated by eolian sand. Arid zone facies also includes ephemeral lake deposits and alluvial fan and/or ephemeral river sediments. These sediments generate by the weathering of the surrounding catchment areas and deposited as poorly sorted detritus carried by the rivers on an alluvial fan. Ephemeral channels or wadis also carry and deposits sediments over extended areas. These deposits are reworked subsequently by the wind and redeposit as eolian dune complexes in other parts of the basin. Ephemeral lakes in this extreme arid condition dry up and leave evaporate and mud deposits. Positions of the ephemeral lakes, sand dunes and the alluvial fans deposits in the stratigraphic record will change with time. These three sub-facies will be preserved as intercalated beds in succession and will comprise arid zone facies. Figure: Depositional environments in arid region (After Nichols, 1999). 2.4. Controls on Depositional System Evolution Like other depositional systems eolian system is vulnerable to tectonic changes, sea level, and climate. Any change in these factors will affect the overall stability and the whole system will change to maintain the balance resulting some unique deposits. Figure: Depositional environments in arid region (After Nichols, 1999) 2.5. Controls on Depositional System Evolution Like other depositional systems eolian system is vulnerable to tectonic changes, sea level, and climate. Any change in these factors will affect the overall stability and the whole system will change to maintain the balance resulting some unique deposits. Figure: Effects of wind on different courtesy: http://www.slideshare.net/wwlittle/eolian-systems) arid depositional deposits Photo The dominant factor in the eolian depositional system for distribution and extent of sandy deserts is climate. Aridity inhibits the development of plants and soil that would stabilize loose sediment. Moreover, an absence of abundant surface water constrain sediment reworking and removal by fluvial processes. The relation between wind speed and substrate susceptibility is not only depends on aridity but also wind energy and sand supply (Kocurek, 1998). Some large vegetated ergs will be an active eolian system under high energy wind (Wasson, 1984). Coastal dune field will develop on humid condition with a high supply of sand associated with higher wind energy. Sediment supply determines the degree of sand development in arid deserts, where depletion of sand supply will develop reg or desert pavement exposing the underlying basement rock. Figure: Isla Cancun barrier island off Yucatan Peninsula, Mexico with Holocene eolian dune development ( Loucks and Ward, 2001). Adjacent depositional environments will prevail over arid desert if waning of sand continued over time without any external force. Interaction between arid and other adjacent environments varies on different factors. The slope, nature of surface run-off, and sand extension dictates the degree of interaction between fluvial and arid environment. Marine-arid interaction relies on the marine processes (wave and tide), extension and development of eolian sand, and wind energy as well as direction. Facies Models Figure: Simplified model of an eolian facies dominated by trough cross-bedding ( Photo courtesy: http://www.slideshare.net/wwlittle/eolian-systems) Eolian facies model composed of three sub-facies representing ephemeral lakes, sand dunes and the alluvial fans deposits in the stratigraphic record. Although dominated by large scale planar and trough cross-bedding generated by dune migration, these three sub-facies will be intercalated in stratigraphic sections. Dunes and inter-dunes deposits show marked variation in texture, but in both deposits sorting is very well. Alluvial deposits are characterized by poorly sorted grains whereas lake deposits show a prominence of evaporates. Figure: Idealized eolian facies model with both dune and interdune deposits (Morad, 2010) References References Cited DeCelles, P., Gray, M., Ridgway, K., ColeR., Pivnik, D., Pequera, N., Srivastava, P.: Controls on Synorogenic Alluvial-Fan Architecture, Beartooth Conglomerate (Palaeocene), Wyoming and Montana: Sedimentology, 1991, v. 38, p. 567-590. Dorn, R., 2009, The Role of Climate Change in Alluvial Fan Development, Geomorphology of Desert Environments, 2nd edition. Blair, T., McPherson, 1993, The Trollheim Alluvial Fan and Racies Model Revisted: GSA Bulletin, v. 104, p. 762-769. Blair, T., 1999, Sedimentology of the Debris-Flow-Dominated Warm Spring Canyon Alluvial Fan, Death Valley, California: Sedimentology, v. 46, p. 941-965. Blair, T., McPherson,J., 1994, Alluvial Fans and Their Natural Distinction From Rivers Based on GeoMorphology, Hydraulic Processes, Sedimentary Processes, and Facies Assemblages:Journal of Sedimentary Research, V. A64, No. 3, P. 450-489. 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Pye, K., 1987, Aeolian dust and dust deposits: Academic Press, London Wasson, R.J., 1984, Late Quarternary paleoenvironments in the desert dunefields of Australia in: Late Caianozonic Paleoclimates of the Southern Hemisphere, Vogel. J.C., ed A.A. Balkema, Rotterdam, p. 419-432. Wilson, I.G.,1972, Universal discontinuities in bedforms produced by the wind: Journal of Sedimentary Petrology, v.42, p.667–669.