Aeolian Sand Accumulation Research Articles

Age and significance of aeolian sediment reworking on high plateaux in the Scottish Highlands

Holocene aeolian sand sheets at the margins of high-level deflation surfaces in the Scottish Highlands commonly comprise two units: a lower weathered unit representing slow accumulation throughout much or all of the Holocene, and an upper unit of structureless sand that is inferred to represent recent erosion of aeolian deposits and aeolisols from adjacent plateaux. OSL dating of samples from above and below the upper—lower unit contact at three sites in NW Scotland places the onset of upper unit sediment accumulation within the interval AD 1550—1700. Accumulation rates calculated from OSL ages confirm rapid accumulation of upper-unit deposits. The timing of the onset of upper-unit sand accumulation excludes expansion of sheep grazing, intrinsic instability and atmospheric pollution as triggers of plateau-surface vegetation degradation and consequent erosion, but favours climatic deterioration (increased wind stress and possibly prolonged snow-lie) during the `Little Ice Age' as the likely cause. This explanation does not, however, apply in all cases; at an OSL-dated site in the Grampian Highlands upper-unit aeolian sand accumulation commenced around AD 1900.

Arid climate 2.5 Ma in the Plio-Pleistocene Valdarno Basin (Northern Apennines, Italy)

Distinctive, eolian-dominated sandy deposits 35 m thick exposed along the SW margin of the Plio-Pleistocene Valdarno Basin in the Northern Apennines, Italy, reflect an unusually arid period in the region. Paleomagnetic investigation and 40Ar/ 39Ar dating of a tephra layer, 10 m above the eolian sand, suggest that the sand was deposited between about 2.7 and 2.4 Ma. This age is coeval with the global climatic deterioration that occurred at the Middle–Upper Pliocene transition. Eolian sediments are represented by cross-bedded sand, rippled sand and horizontal-bedded sand. The alluvial deposits, associated with the eolian sediment, consist of sheet-like beds of coarse sand and erosively based, pebbly sand bodies. Eolian sand, together with fluvial sandy deposits, was formed in the medial–distal portion of an alluvial system, and represents the Rena Bianca Sand Unit. The eolian and alluvial deposits are arranged into sedimentary cycles (2–6 m thick), displaying a wetting–drying–wetting upward trend recording second-order climatic oscillations of ca. 40 ka. Each cycle is enclosed between major bounding surfaces, defined by iron mineral encrustations. These bounding surfaces represent periods of reduced eolian sand accumulation caused by a rising water table. During the 2.5 Ma global cooling, the Valdarno Basin experienced a period of arid conditions owing to the influence of cold and dry easterly and northeasterly winds. In contrast, during the Pleistocene, the uplift of the Pratomagno Ridge protected the Valdarno Basin from easterly and northeasterly winds, giving rise to relatively warm and wet conditions, and mitigating the regional and global climatic changes.

Influence of high water levels on aeolian sand transport: upper beach/dune evolution on a macrotidal coast, Wissant Bay, northern France

Aeolian sand transport measurements and detailed topographic surveys were carried out during 1 year along a macrotidal upper beach/dune system experiencing rapid coastal retreat. Aeolian transport measurements, coupled with wind records, showed extreme spatial and temporal variability along a spatially limited upper beach sector. Analysis of wind velocity, rainfall, and water level showed that aeolian sand transport may occur all year long on the upper beach with the most energetic conditions occurring during winter and spring. Analysis of volume change revealed that aeolian sedimentation on the upper beach occurred only during the summer period, while the rest of the year was characterised by upper beach and dune scarp erosion. This erosion, due to storm events combined with high water levels, completely eliminated summer aeolian sand accumulation. Our results show that aeolian transport and upper beach/dune evolution on this macrotidal beach is strongly controlled by the magnitude and frequency of occurrence of high water levels. This study illustrates the fact that upper beach/dune evolution cannot be completely understood and satisfactorily modelled if only potential aeolian sand transport is considered.

Ages of periods of sand movement in Hungary determined through luminescence measurements

The Late Glacial and Holocene climatic oscillations in Hungary are manifested by changing fluvial and aeolian sand deposition, as well as by intercalated soil formations. The sand-blown territories have special interest since the buried fossil soils provide detailed information about climate and environment changes. During the past two decades the time of the sand-moving periods was studied exclusively by radiocarbon age determination, but by now, thanks to the latest investigations, these results have been controlled and completed by the thermoluminescence and infrared optically stimulated luminescence dating methods. These techniques have been applied to provide a more detailed chronological framework for Late Pleistocene and Holocene sand accumulation periods. Five aeolian sand accumulation periods can be recognized covering the Late Glacial and Holocene time period at 14.0±2.3, 12.0±1.9, 9.2±1.7, 6.0±0.5 and 0.6±0.07 ka. The sand-blown formations are intercalated by soil horizons. The radiocarbon age estimates provide evidence for Late Glacial (Bölling, Alleröd) and Lower-Atlantic soil-forming periods.

A Very Old Sahara

In the News Focus article “A wobbly start for the Sahara” by Mark Sincell (16 July, p. [325][1]), it is stated that the Sahara region has only existed as a desert for 4000 years. To the contrary, there is substantial geologic evidence for widespread desert conditions in the Sahara before 4000 years ago. The most detailed and comprehensive Saharan record of Quaternary eolian sediments is present in the Chott Rharsa Basin in southern Tunisia ([1][2]). This record is one of eolian sands and sandstones that interfinger with lacustrine (lake) and sabkha (salt flat) deposits. Thermoluminescence dates from the sands and sandstones indicate that there were distinct phases of eolian sand accumulation around 12,200, 10,000, 7500, and 6200 to 5600 years ago. Lacustrine deposition occurred sometime between the eolian accumulations of 10,000 and 7500 years ago, sabkha deposition occurred sometime between the eolian accumulations of 7500 and 6200 years ago, and a gypsum crust developed by pedogenic (soil) processes after the eolian accumulation that occurred between 6200 and 5600 years ago but before the onset of the desert conditions that prevail today. Each phase of eolian sand accumulation was followed by eolian sediment burial by lacustrine or sabkha deposits and eolian sediment stabilization by vegetation and pedogenic crusts. Furthermore, a comparison of this reord with other eolian records ([2][3]) shows that the Tunisian record follows a pattern of regionally synchronous changes in eolian sediment behavior across the Sahara region. Thus, the statement by Sincell that the Sahara started only 4000 years ago, and his statement that “grasses and shrubbery covered what is now the Sahara until some unknown environmental catastrophe dried up all the water, leaving nothing but sand” consider only a limited time period. If one views the Saharan record for a longer time period, then it is clear that the Sahara region was desert well before 4000 years ago and that the episode of more abundant vegetation described by Sincell is simply the most recent of a series of episodes when eolian sands were temporarily covered by vegetation. As for the age of the initial onset of desert conditions in the Sahara, an isolated eolian sandstone in southern Tunisia has yielded a thermoluminescence date of greater than 86,000 years ago ([1][2], [2][3]), suggesting that desert conditions have been present for much longer than the time period considered by Sincell. 1. [↵][4]1. C. Swezey 2. et al. , Holocene 9, 141 (1999). [OpenUrl][5][Abstract/FREE Full Text][6] 2. [↵][7]1. C. Swezey , thesis (University of Texas at Austin, 1997). [1]: /lookup/doi/10.1126/science.285.5426.325 [2]: #ref-1 [3]: #ref-2 [4]: #xref-ref-1-1 View reference 1 in text [5]: {openurl}?query=rft.jtitle%253DThe%2BHolocene%26rft.stitle%253DThe%2BHolocene%26rft.issn%253D0959-6836%26rft.aulast%253DSwezey%26rft.auinit1%253DC.%26rft.volume%253D9%26rft.issue%253D2%26rft.spage%253D141%26rft.epage%253D147%26rft.atitle%253DResponse%2Bof%2Baeolian%2Bsystems%2Bto%2BHolocene%2Bclimatic%2Band%2Bhydrologic%2Bchanges%2Bon%2B%2B%2B%2B%2B%2B%2B%2B%2Bthe%2Bnorthern%2Bmargin%2Bof%2Bthe%2BSahara%253A%2Ba%2Bhigh-resolution%2Brecord%2Bfrom%2Bthe%2BChott%2BRharsa%2B%2B%2B%2B%2B%2B%2B%2B%2Bbasin%252C%2BTunisia%26rft_id%253Dinfo%253Adoi%252F10.1191%252F095968399670329816%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [6]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NToic3Bob2wiO3M6NToicmVzaWQiO3M6NzoiOS8yLzE0MSI7czo0OiJhdG9tIjtzOjI0OiIvc2NpLzI4Ni81NDM4LzIzOS45LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ== [7]: #xref-ref-2-1 View reference 2 in text

The geomorphology of Sugar Loaf Mound: Prehistoric cemeteries and the formation of loess cones in the lower Wabash Valley

Burial mounds found on bluff crests in the Midwest United States overlap in scale with conical shaped Peoria Loess hills along the valley margins of the lower Wabash River. Coring of Sugar Loaf Mound, a feature thought to be an artificial mound for some 200 years, indicates that it is a 9 m eolian feature that contains prehistoric human remains. Analysis indicates that a sharp-edged till ridge resulted in a zone of eolian sand and silt accumulation forming both a climbing and a perched dune. A streamline body resulted. Grain-size analysis indicates a bimodal population, suggesting a dust suspension from an outwash source and a local saltation sand source, with a time transgressive shift in dominance. Three other loess cones of comparable scale, shape, lithostratigraphy, and landscape position that were also used as late prehistoric cemeteries indicate a similar pattern of both formation and prehistoric mortuary use in the lower Wabash valley. © 1998 John Wiley & Sons, Inc.

Development and age structure of Holocene coastal sand dunes at Horn Head, near Dunfanaghy, Co Donegal, Ireland

Two areas of Holocene coastal sand dunes on the western side of the Horn Head peninsula extend from low ground immediately inland of their respective source beaches onto flanking higher ground (> 100 m OD). Stratigraphic investigations supported by 14C dating of buried organic-rich horizons and shells demonstrate several phases of sand accumulation in the Pollaguill-Croaghadara system in contrast to the larger Tramore-Anloge Hill system, where the available evidence points to relatively recent dune emplacement. A broadly synchronous phase of dune development occurred during the thirteenth to fourteenth centuries AD and is viewed as part of a regional (northwestern Europe) dune-building episode resulting from climatic deterio ration. Earlier phases (pre-3300-2800 14C years BP) of aeolian sand deposition at Pollaguill-Croaghadara have no apparent equivalents at Tramore-Anloge Hill and repeated fluvial incision and sand reworking during the last 2000 14C years is also evident at the former site. Dated organic horizons, in combination with site location, sand source and transport direction, suggest the earliest phase of aeolian sand accumulation and subsequent stabilization was time-transgressive. The respective roles of relative sea-level change, climatic change and anthropogenic influence in dune evolution are difficult to evaluate in the absence of detailed information, although documentary evidence indicates human-induced destabilization of the Tramore-Anloge Hill dunes during the 1920s and 1930s. Thus, despite similar topographic settings and close proximity, the dunes do not share entirely similar histories and caution against the development of regional dune chronologies from investi gations of single systems. The observations and data suggest that a mix of local and regional controls have combined in the construction of these dunes.

Luminescence dating of late quaternary aeolian deposits at Dale Lake and Cronese Mountains, Mojave Desert, California

Relict aeolian deposits and landforms that can provide important information on the timing, geographical extent and intensity of periods of aeolian sand accumulation are widespread in the Mojave Desert. California. The Pleistocene part of the record is mostly undated. The stratigraphy and sedimentology of sites near Dale Lake (Dale Lake sand ramp) and the Cronese Mountains (Cat Dune) were studied, and luminescence dating techniques used to try to establish a chronological framework for the deposits. The dating of these sites proved difficult, with major disparities between the results of quartz and feldspar thermoluminescence (TL) dating, particularly where the sediments comprised a mixture of aeolian and colluvial meterial. However, initial results, based on quartz TL and feldspar infra-red stimulated luminescence dating, indicate the existence of two main periods of Late Pleistocene aeolian deposition between >35 to 25 ka and 15 to 10 ka.

Loess Buried in the Paleo-sand Dunes in San' in andHokuriku along the Coast of Japan Sea

The eolian sand members along the coast of Japan represent at least five major periods of accumulation in the last Glacial age and Holocene. These deposits include well-defined paleosols which divide individual eolian sand members into five parts. The five major periods of eolian sand accumulation can be classified as follows : 4, 000-5, 000 y.B.P. (the young est); 18, 000-20, 000 y.B.P. ; 30, 000 y.B.P. ; 50, 000 y.B.P. ; 70, 000 y.B.P. (the oldest).In Izumo, Kumihama, Amino and Fukui along the coast of Japan Sea, Paleo-sand dunes developed noticeably and five paleosols were buried in these eolian dune sand.The purpose of this paper is to point out that eolian dust deposited much in paleosol horizons and that silt and clay fractions in paleosols originated in eolian dust which came from China in the last Glacial age.The seven samples were collected from the outcrops of paleo-sand dunes in Izumo, Kumihama, Amino and Fukui. Three Chinese loess samples were collected in Chuhua and Manchouli in China. Two desert soils from Wuwei in China and one tephric loess sample from New Zealand were collected.The results from our research are summarized as follows : 1) The mean diameter of paleosols in these areas in Japan is ranging from 0.001 to0.011 mm. Texture of paleosols differentiates from light and heavy clay. The clay fractions of paleosols are characterized by predominance of 14A minerals, illite, kaolinite and quartz. Contents of quartz in the silt fraction (5-20μ) of paleosols are 32-74%. According to the amount of SiO2, Al2O3and -H2O·IL in the <0.02 mm fraction of paleosols, Japanese samples belong to the eolian dust group. These results are very much consistent with those of the author's previous analysis of loess from Northern Kyushu and Yonaguni Island in Japan, Chinese loess and desert soils, and New Zealand loess.2) Based on the analyses of size distribution, chemical properties and X ray diffraction, we can conclude that silt and clay fraction in paleosols had originated in eolian dust from China, and paleosols had been formed from loess which compose major part of them in the last Glacial age.3) Eolian dust had been not only much deposited on the paleosol horizon, but also had less mixed with the eolian sands. This indicates that eolian dust had come continuously from China in the last Glacial age. Following the interruption of dune formation, formation of paleosols had taken place. Simultaneously eolian dust had began to deposit thickly on the dune surface.