Aeolian Sand Accumulation Research Articles

Grain-size and geochemical investigations on the Novyi Tik site (NW Ukraine) and their significance for understanding the local sedimentary environment in the Pleistocene


 
 
 Grain size and geochemical composition of the loess-palaeosol sequences are important evidence of the sedimentary environment in the Pleistocene, which enables to revela- tion of the sedimentation rates, the origin of deposits, and the sources of material that contributed to the loess accumulation and pedogenesis. The Kd index (10-50 μm / <5 μm), and the Ti/Zr, Ti/Nb and Ce/Y ratios considered to be indicators of aeolian silt accumulation, whereas the ratio of physical sand to physical clay have been suggested to reveal the relationship between sedimentation and pedogenesis. The grain size and geochemical analysis were applied at the Novyi Tik section (Volyn’ Upland), which is characterized by detailed stratigraphy and lateral diversity of palaeosols and deposits. Based on grain size and geochemical data from the section, four main units have been distinguished, which represent periods with similar sedimentary environment such as MIS 10-7, MIS 6, MIS 5 and MIS 4-2. During MIS 9 and 7, pedogenesis pre- vailed with a slight sedimentary contribution; during short-term cooling, thin loess beds were formed. High loess accumulation rates occurred during MIS 6, however, the source of aeolian dust material was different from those to other loess units. At the end of MIS 6, a period of dynamic sedimentation began, which resulted in the sandy grain-size composition of soils and non-soil deposits of MIS 5. The highest sedimentation rates presumably occurred during the stadials, therefore the soils could inherit the grain-size composition of the parent material. Moreover, during MIS 5 in the valley of the Styr River, episodes of aeolian sand accumulation could take place, since the sandy grain-size composition of soils of that time is widespread throughout the basin of the modern Khrinnyky reservoir. At the end of MIS 5, abrupt changes occurred in the sedimentary environment: sand sedimentation almost ceased and a period of aeolian silt accumulation began, and proceeded until the Holocene.
 
 

Timing and implications of aeolian sand accumulation in a alpine basin of Qilian Shan, NE Tibetan Plateau

The reconstruction of regional moisture and climate changes during the Holocene has been intensively carried out over the NE Tibetan Plateau, based on different geological archives. However, owing to either the lack of robust independent chronology or ambiguous interpreting of climate proxies as well as complex geographic settings within the plateau, the nature of Holocene environmental changes and their influence factors remain controversial, particularly on whether the optimal climate condition (effective moisture peak) has prevailed during the early- or mid-Holocene. In this study, we reported a new well-dated sand dune accumulation record from the Shawotou sand field in the Babao River drainage area in the southeast Qilian Mountains, to unravel the late glacial and Holocene moisture variation history. The robust chronologies of aeolian sands and palaeosols from two sections were established based on densely collected 49 samples using post-infrared (IR) IR-stimulated luminescence dating of coarse-grained K-feldspar. Based on stratigraphic investigation of the sand dune/palaeosol sections, the results show that the climatic condition was very dry during the late glacial and early Holocene (14–8 ka), characterized by sand dune formation, and then the moisture peaked in the middle Holocene (8–4 ka) with the strongest pedogenesis, followed by a relatively dry condition in the late Holocene (since 4 ka). The regional comparison suggested that the Holocene moisture variation pattern seems synchronous over the NE Tibetan Plateau, that is, the dry early Holocene and late Holocene but with peaked moisture in the middle Holocene, which is likely attributed to the precipitation changes of the East Asian summer monsoon.

Aeolian sand accumulation and land desertification over the past 1,500 years as revealed by two aeolian dunes in the Beiluhe Basin on interior Qinghai-Tibet Plateau, SW China

As an important region of desertification in China, the Qinghai-Tibetan Plateau (QTP) has attracted great attention. However, the study of land desertification history at the millennia-scale on the interior plateau is grossly inadequate. In a severely and rapidly desertifying area in the Beiluhe Basin on the interior QTP, grain-size distributions, sand particle morphologies, and 7 available optically stimulated luminescence (OSL) ages of sand sediment from two fixed aeolian dunes were obtained by several laboratory tests. Combining these results with plateau paleoclimate and contemporary aeolian sand activities in several adjacent regions, two phases of evident enhanced aeolian sand accumulation corresponding to desert expansion over the past 1500 years in the study region were identified. The first enhanced phase (850–700 a B.P.) might have been closely related to suitable trapping of denser vegetation cover and degradation of permafrost on the QTP as a consequence of warm and wet climates. Reactivation of local older sediments caused by cold and dry climates might have been responsible for the second enhanced phase (1400–1200 a B.P.). Permafrost plays an important role in aeolian sand accumulation and desertification on the QTP. However, expansion (or degradation) of permafrost has not always prevented (or promoted) aeolian desertification development on the QTP since the Last Glaciation Maximum (LGM, 21–14–12 ka B.P.). The effects of permafrost on aeolian desertification are governed by numerous factors such as preceding and current climate conditions, locations of permafrost and aeolian sand activity, and trap conditions due to vegetation and topography.

Quantitative analysis of the sedimentary architecture of eolian successions developed under icehouse and greenhouse climatic conditions

AbstractThe continental terrestrial record preserves an archive of how ancient sedimentary systems respond to and record changes in global climate. A database-driven quantitative assessment reveals differences in the preserved sedimentary architectures of siliciclastic eolian systems with broad geographic and stratigraphic distribution that developed under icehouse versus greenhouse climatic conditions. Over 5600 geological entities, including architectural elements, facies, sediment textures, and bounding surfaces, have been analyzed from 34 eolian systems of Paleoproterozoic to Cenozoic ages. Statistical analyses have been performed on the abundance, composition, preserved thickness, and arrangement of different eolian lithofacies, architectural elements, and bounding surfaces. Results demonstrate that preserved sedimentary architectures of icehouse and greenhouse systems differ markedly. Eolian dune, sand sheet, and interdune architectural elements that accumulated under icehouse conditions are significantly thinner relative to their greenhouse counterparts; this is observed across all basin settings, supercontinents, geological ages, and dune field physiographic settings. However, this difference between icehouse and greenhouse eolian systems is exclusively observed for paleolatitudes <30°, which suggests that climate-induced changes in the strength and circulation patterns of trade winds may have partly controlled eolian sand accumulation. These changes acted in combination with variations in water table levels, sand supply, and sand transport, ultimately influencing the nature of long-term sediment preservation. During icehouse episodes, Milankovitch cyclicity resulted in deposits typified by glacial accumulation and interglacial deflation. Greenhouse conditions promoted the accumulation of eolian elements into the geological record due to elevated water tables and biogenic- and chemical-stabilizing agents, which could protect deposits from wind-driven deflation. In the context of a rapidly changing climate, the results presented here can help predict the impact of climate change on Earth surface processes.

Late Quaternary seasonal process variations in lake basins on the NE Tibetan Plateau

The late Quaternary climate history along the north-eastern Tibetan Plateau (NETP) is still a matter of debate with respect to signals in lake deposits and related catchment processes. Here we summarize the current knowledge based on lake development and eolian accumulation in catchments on the NETP. Interlinked processes between selected lakes and their catchments on the NETP show a relatively clear division into summer and late autumn/winter/early spring (October to April) dominated activities based on lake hydrological and eolian variations. Investigated lakes on the NETP experienced seldom water cover or pond/playa status during the Late Glacial with long ice cover periods. Eolian sand deposited in lake beds and/or the eastern parts of the respective catchments as a constant process during the colder season. These processes continued during the early Holocene despite climate warming and increased moisture supply as lake levels still remained relatively low, mainly fed by spring/summer glacier and snow melt. Eolian sand activity dominated in the catchments during the cold periods, while coarse sediments in the lake centers were mainly deposited by fluvial input in spring/summer and/or randomly distributed eolian material in ice cracks after melt in spring. During the mid-Holocene high lake levels occurred due to intensified multiple moisture supply sources. Eolian sand accumulation diminished and was eroded by precipitation thus more fluvial suspension was transported to the lake center. Subsequently, lake level decline until around 3 ka BP signaled a reduction in moisture availability and related surface runoff. Eolian sediment was less preserved due to surface erosion in line with lake level increase during the succeeding period. Fluvial material mixed with eolian sand was transported to the lake center during unfrozen periods. Afterwards fluctuating lake levels and intensive eolian deposits were frequently documented for the last 2 ka demonstrating climate variations similar to present.Fluctuations between the Asian summer monsoon (ASM) and Mid Latitude Westerlies (MLW)/Asian winter monsoon (AWM) influences were recorded with respect to season shifts for the entire Holocene with general dominance of north-westerly surface winds at investigated sites. Inspected periodicities of one lake record and eolian material demonstrate that local effects are of significance for eolian accumulations however, both records react to regional/global climatic changes but with different extend.

Effects of desertification on permafrost environment in Qinghai-Tibetan Plateau

Soil thermal state exerts an important role in soil physicochemical properties, nutrient content, soil carbon losses, and hydrological processes in cold regions. In the Qinghai-Tibet Plateau, desertification and aeolian sand accumulation greatly change the surface cover types and simultaneously alter the surface energy budget. However, the quantification of their impacts on the soil thermal state hasn't been studied methodically. Here, a laboratory experiment was conducted to investigate the impact of surface cover types, including bare surface, grass-coved surface, dry and wet (3%) aeolian sand-covered surface, on underlying soil thermal state. Our results demonstrate that there is a reciprocal relationship between environment change and permafrost degradation. The amount of heat entering the active layer was determined by the surface cover types and soil water content. Using the bare surface case as a reference, vegetation layer acted as a buffer to reduce the amount of heat propagation downwards the ground by 20% and to lower the near surface temperature by 0.7 °C. In contrast, dry aeolian sand acted as an insulation layer and warmed the ground by about 2 °C. Also, wet aeolian sand with high thermal conductivity facilitated the heat exchange with the atmosphere and warmed the ground about 1.5 °C. Our results have implications for thermal and hydrological processes in the atmosphere-ground-permafrost system and thermal stability of infrastructure under the effect of the desertification and aeolian sand accumulation. The hydrothermal interaction of desertification and permafrost needs to be quantified in the further study through long-term field observations and a fully-coupled water flow and heat transport model under a changing climate.

A new approach in reducing sand deposition on railway tracks to improve transportation

Abstract Aeolian particle transport involves uplift from the ground, dispersion and deposition back to the surface. Integrated effects of these processes, in general, are of great importance for a wide range of reasons mostly because of their unwanted deposition on the railway tracks, environmental impact, degradation of air quality and risks to human health. In sandy dry lands Aeolian sand accumulation on railway tracks is a major problem, since it directly affects safety of railway transportation, apart from decreasing the speed in railway transportation. The most common methods for preventing sand deposition on railway tracks like, building galleries (Gallery is a short length tunnel-shape cover which is built and installed over the railway track to avoid sand deposition. It is commonly applied in regions which are more probable of sand storm.), fences or increasing plant varieties around railway are restricted to special situations and not as effective. Efficient prevention of sand deposition is a great challenge that requires a comprehensive knowledge of wind-sand flow behavior. In the present study, an efficient 2D and 3D CFD model for simulation of two-phase gas-particle problems, as the sandy air flow, is developed. Conventional methods for preventing sand deposition on the railway track as well as an innovative method for avoiding sand deposition are presented and their effectiveness is evaluated by the proposed CFD model. It has been shown both by the CFD model and the accomplished empirical works that galleries cannot prevent sand deposition effectively. Instead, the innovative proposed method is proved to reduce sand deposition near the embankment, along with decreasing sand content of flowing wind.

High resolution OSL dating of aeolian activity at Qinghai Lake, Northeast Tibetan Plateau

Qinghai Lake is the largest lake on the Tibetan Plateau (TP), located between the extremely arid Qaidam Basin to the west and the severely desertified Gonghe Basin to the south. Extensive aeolian sediment at Qinghai Lake is ideal material to reconstruct regional aeolian activity, and to better understand the relationship between desertification and climatic change in the lake basin. Aeolian sand accumulation is usually accompanied by erosion, hence, depositional hiatuses and disconformities must be identified for reliable reconstruction of regional aeolian activity. To date, the low density of age sampling around Qinghai Lake has hindered identification of hiatuses. In this study we report the first high density OSL dating; 41 OSL ages were obtained from two aeolian sand sections, Dongwei (DW) and Niaodao (ND). Sand accumulation trends recorded in the high-density OSL sampling sections were consistent with previously published probability density function (PDF) ages for the northeast TP. The middle Holocene (~7 to ~4 ka) was characterized by very low accumulation rates, with rapid sedimentation in the Late Glacial to Early Holocene (~14 to ~7 ka) and the Late Holocene (after ~4 ka). A ~3 ka hiatus in accumulation between ~7 to ~4 ka was identified in the DW section, but the ND section showed successive accumulation since the Late Glacial (~14 ka), on sub-orbital and millennial scales. Our environmental reconstructions are consistent with previously published aeolian data and paleoshorelines records. The combined evidence shows: strong aeolian activity since ~14 ka to ~9 ka; initiation of pedogenesis at ~9 to 7 ka; intensified soil development between ~7 ka and ~4 ka (with the most intense pedogenesis and least aeolian activity between ~6 to ~4 ka); relatively weak paleosol formation from ~4 to ~2 ka; and renewed aeolian activity after ~2 ka.

Factors Responsible for Rapid Diminishing of Endangered Grass Plant Elymus farctus subsp. boreoatlanticus in Phytocoenoses on Dunes Coast of Baltic Sea

Sand couch-grass Elymus farctus (Viv.) Runemark ex Melderis subsp. boreoatlanticus (Simonet & Guin.) Melderis is a species of psammophytic perennial grass which grows on low embryo dunes, less frequently on white dunes, on a sandy substrate which is rich in chlorides, with a neutral or alkaline pH. The occurrence of E. farctus subsp. boreoatlanticus was confirmed on the Polish Baltic coast only in six stands out of 20 quoted in the 19th century and at the beginning of the 20th century, and the species is classified as critically endangered (CR). One of the largest populations of that species is situated on the Wolin Island (the Baltic Sea, west coast of Poland). The population of this species was monitored between 2015-2017 in the habitat of initial white coastal dunes (Nature 2000 site, code 2110), where the sand couch-grass is a characteristic species of Honckenyo-Agropyretum juncei R.Tx. 1955 plant association. The results of the conducted research show that the main reason for the rapid decline of the population of Elymus farctus subsp. boreoatlanticus on the western coast of Poland is recreational use of beaches, which is growing in an uncontrollable manner and puts pressure on this habitat, followed by complete destruction of psammophilous and halophilous vegetation. In addition, impact from marine abrasion inhibits the development of white coastal dunes where E. farctus subsp. boreoatlanticus occurs, and intensive aeolian sand accumulation hinder the regenerative ability of shoots and significantly limit vegetative reproduction.

Response of dune mobility and pedogenesis to fluctuations in monsoon precipitation and human activity in the Hulunbuir dune field, northeastern China, since the last deglaciation

The Hulunbuir dune field is located at the northern margin of the temperate monsoon zone in East Asia, and changes in dune activity and pedogenesis in the dune field are highly sensitive to the advance and retreat of the East Asian summer monsoon (EASM) and to human activity. Thus, the stratigraphic sequences of paleosol and aeolian sand of the dune field have great potential for reconstructing the history of dune activity and pedogenesis and their response to past fluctuations in monsoon precipitation and the intensity of human activity. However, our knowledge of the evolution of the landscape and paleoclimate of the dune field is limited. Here, we present the results of analyses of quartz optically stimulated luminescence (OSL), grain size and magnetic susceptibility (MS) from 13 representative sections in the Hulunbuir dune field. The grain-size analysis indicates that the sand layers are composed of typical aeolian sand, and the MS variations of the aeolian sand and sandy paleosol sequences mainly reflect changes in the intensity of pedogenesis. We combine our new OSL dating results with previously published OSL ages to refine the chronology of sand dune development. An OSL age hiatus in both aeolian sand and paleosol during the 5–7 ka indicates that aeolian deposition in Hulunbuir ceased almost completely during this period, which corresponds to the peak in EASM strength. Thus, our study provides new evidence for a delayed response of the EASM maximum to peak insolation forcing (11–10 ka) in the mid-latitude monsoon margin. In addition, we speculate that peaks in probability density (PD) from 1.2–0.7 ka and from 0.25–0 ka of aeolian sand accumulation correspond to population increases and the development of cultivation and animal husbandry in the Hulunbuir dune field.

Holocene eolian sand deposition linked to climatic variability, Northern Great Plains, Canada

The Bigstick and Seward Sand Hills are possibly two of the oldest dune fields within the late Wisconsin glaciated regions of the Northern Great Plains. As with most Northern Great Plains dune fields, source sediments are former proglacial outwash sands. Thus, Holocene dune construction is primarily related to spatial–temporal variations in surface cover and transport capacity, rather than renewed sediment input. However, eolian landscape reconstructions on the Northern Great Plains have been temporally constrained to recent periods of activity, as older episodes of deposition are typically reworked by younger events. In this study, sediment cores from shallow lacustrine basins and interdune areas provide an improved record of Holocene eolian sand deposition. Eolian sand accumulation in the interdunes and basins occurred between 150 and 270 years ago, 1.9 and 3.0 ka, 5.4 and 8.6 ka, and prior to ca. 10.8 ka. These episodes of sand accumulation were bracketed by lacustrine deposition and soil formation, which represented wetter conditions. Other than mid-Holocene dune activity, which may be related to peak warmth and aridity, most periods of eolian sand accumulation coincided with cooler but drier climatic events such as the Younger Dryas, late-Holocene cooling prior to the Medieval Climatic Anomaly, and the ‘Little Ice Age’. These depositional episodes are also spatially represented by other dune fields in the region, providing a broad-scale view of the connections between past climatic events and eolian landscape evolution on the Northern Great Plains.

The north-eastern aeolian ‘European Sand Belt’ as potential record of environmental changes: A case study from Eastern Latvia and Southern Estonia

Abstract The Latvian and Estonian inland dunes belong to the north-eastern part of the ‘European Sand Belt’ (ESB). These dunes are widely distributed over broad glaciolacustrine plains and Late Glacial alluvial deltas, considered to be potential sources for the aeolian material. Little is known about these aeolian sediments and their substratum; here we present a detailed sedimentary structural and textural characterisation together with a luminescence-based chronology. Through a comparison between grain-size, rounding of quartz grains and surface characteristics in medium/coarse (0.5–0.8 mm) sand, and the light mineral content, we found an alternation of aeolian and periglacial components. Further, short-lasting aeolian abrasion and/or transportation periods, and a significant contribution of a nearby sediment source are suggested. Luminescence dating points to aeolian sand accumulation and dune formation between ∼16 ka and ∼9 ka. However, we also observed some presumably watertable controlled environmental conditions at ∼13 ka; this corresponds with the occurrence of an ice-dammed/proglacial lake.

Holocene climate and landscape change in the northeastern Tibetan Plateau foreland inferred from the Zhuyeze Lake record

Pollen and grain-size data from the Holocene Zhuyeze Lake record in arid Central Asia were re-assessed and combined with new ostracod species assemblage data to improve inferences of the lake history and controlling climate conditions. Zhuyeze Lake was a perennial freshwater–oligohaline lake since its establishment ca. 13 cal. ka BP. The lake level fell below the position of the QTL02 section site at 2.1 cal. ka BP after the beginning of the Han Dynasty, and we assume that significantly intensified land use upstream of Zhuyeze Lake was at least partly causing the lake-level decline. Most stable lake conditions and lowest salinities were recorded in the mid Holocene between 7.5 and 5.5 cal. ka BP, providing additional evidence for the inference of the highest moisture availability in the mid Holocene in arid Central Asia. The most striking feature of analyses of grain-size and ostracod data is the inference of more or less unchanged lake levels and lake water chemistry during a period of aeolian sand accumulation in the lake between 7.8 and 7.5 cal. ka BP. Similar conspicuous and apparently contemporaneously formed sand layers were recorded in other sections in the ancient lake basin and farther upstream, and mobilization of aeolian sands must have occurred for a few hundred years in the region. Indications for the 8.2 ka event from our section and other climate records in Central and eastern Asia support the hypothesis that a short-lived cold-dry climate initiated the increased activation of aeolian sands which was later on gradually enhanced as a result of burial of previously vegetated land by dunes and sand sheets. Further work is required to determine the regional extent of sand mobilization at ca. 7.5 cal. ka BP in the northeastern Tibetan Plateau foreland and to examine the timing and controls of the self-enhancing aeolian sand mobilization, vegetation degradation and subsequent recovery.

Extreme monsoon aridity episodes recorded in South China during Heinrich Events

Geological records of climate change since the last glaciation in South China, a core area of the East Asian monsoon, are key to understanding secular variation in the monsoon system. However, with the exception of the speleothems, records from this area with independent age control are few. We investigated aeolian sand deposition on a sand hill on the shore of Poyang Lake in South China and reconstructed the chronological sequence of aeolian deposition using Optically Stimulated Luminescence (OSL) dating. Without exception, all aeolian sediments were deposited within seven periods that generally match the timing of Heinrich events and other cold periods in Greenland. We argue that aeolian sand accumulation in this region is most likely forced by extreme aridity driven by weakening of the summer monsoon, while the characteristics of this deposition are influenced by winter monsoon intensity. The monsoon shifts revealed here suggest a possible link between North Atlantic cooling and summer monsoon strength in South China, and support the intensities of cooling phases recorded in Greenland ice cores.

Climate-driven changes to dune activity during the Last Glacial Maximum and deglaciation in the Mu Us dune field, north-central China

One significant change of terrestrial landscapes in response to past climate change has been the transformation between activity and stability of extensively distributed wind-blown sand dunes. The relations between the dynamics of the aeolian landscape and its drivers are not yet completely understood, however. Evidence of aeolian sand deposition during the Last Glacial Maximum (LGM) is scarce in many mid-latitude dune fields, whereas abundant evidence exists for aeolian sand accumulation during the deglaciation, i.e. after about 15 ka. Whether this contrast actually reflects changes in dune activity is still unclear, making paleoclimatic interpretation uncertain. Comprehensive field investigation and luminescence dating in the Mu Us dune field, north-central China, demonstrates that aeolian sands deposited during the LGM are preserved as fills in periglacial sand wedges and beneath loess deposits near the downwind dune field margin. The scarcity of LGM dune sand elsewhere in the dune field is interpreted as the result of intensive aeolian activity without substantial net sand accumulation. Increasing sand accumulation after 15 ka, reflected by much more extensive preservation, signals a change in sand supply relative to sand transportation through the dune field. Reduced wind strength and other environmental changes including regional permafrost degradation after 15 ka transformed the dune field state from net erosion to net accumulation; the dunes, however, remained largely mobile as they were in the LGM. Similar diverging patterns of dune sand accumulation and preservation before and after 15 ka in many mid-latitude dune fields imply broad climatic controls linked to the changes in high-northern-latitude forcing.

A review of Late Quaternary inland dune systems of South America east of the Andes

Inland dune systems of South America occur in a variety of environmental settings under different climatic conditions, from humid–subhumid to semiarid–arid. This contribution provides the state of the art on dune research of inland systems east of the Andes. Tropical northern (∼10°N–∼10°S), including the dune fields of Llanos del Orinoco and the Amazonian basin, are mainly formed from parabolic, blowout (or deflation basins) and linear dunes, developed on river floodplains. Aeolian activity was reported to occur near the late Pleistocene–Holocene boundary in Llanos del Orinoco, over the last ∼17 ka in the Branco river basin and ∼32.6 ka in the Negro river basin, both in the Amazonian region. In general, the attributed aeolian origin is controversial, the morphology difficult to determine, and the chronology still extremely limited and rather debatable in some cases. The southern tropical region (∼10°S–∼22°S) includes aeolian systems situated across the extensive lowlands of the Gran Chaco and those located in fluvial basins related to the cratonic Brazilian shield (São Francisco River, Pantanal and Mato Grosso). The oldest barchanoid–barchan ridges at the Gran Chaco were dated ∼36–33 ka and subsequent aeolian sand accumulation occurred at ∼18 ka, ∼14–12 ka, ∼10–9 ka and mid to late Holocene times. Parabolic dunes at the São Francisco River floodplain show an oldest episode generated between ∼28 and ∼11 ka, followed by eolian activity during the early to mid-Holocene. No chronological data is available for the linear and lunette dunes described at the Pantanal. Linear ridges were distinguished in the upper Paraná River (Mato Grosso) with associated sand accumulation at different intervals of the Holocene. The last reviewed region is the Andean Piedmont and western Pampas, at subtropical eastern South America, comprising a large variety of dune morphologies (barchan–barchanoid, linear, parabolic, transverse and lunette dunes, deflation basins, and sand sheets). Luminescence ages suggest the occurrence of aeolian activity intervals during late glacial times and the Holocene. The general understanding on the dynamic of South American dune systems is hampered by the paucity of chronological information and the representativeness of some dune records. Whether they reflect local or regional environmental conditions is still a matter of discussion in several areas that need further studies.

Sedimentary and OSL dating evidence for the development of the present Hobq desert landscape, northern China

The sedimentary sequence and landscape of the Hobq desert was observed through twelve profiles along five N-S sections extending through the entire desert. Aeolian sands were found to overlie the alluvial, diluvial, and lacustrine sediments in this desert. Optically stimulated luminescence (OSL) dating results were obtained from post-IR OSL signals of quartz fractions of sand samples at the bottom of sand dunes and hills by using the Double-SAR protocol. The OSL ages reveal that the latest sand accumulation began around 19 ka in the northwestern part and 9 ka in the eastern part of the Hobq Desert. Around 7 ka, the sand accumulation was strengthened and extended southward and northward 2 ka to develop the present desert landscape. Our study suggests that the aeolian sand accumulation around 19, 9 and 7 ka resulted from the weakening of the Asian summer monsoon over this region. However, the rapid development of the present Hobq desert landscape since 2 ka was likely triggered by human activities in this desert.

Fluvial and aeolian landscape evolution in Hungary – results of the last 20 years research

AbstractPresent study provides a review of the latest results on fluvial and aeolian landscape evolution in Hungary achieved by our team during the last 20 years.– The Hungarian river terrace system and its chronology was described with special emphasise on the novel threshold concept. A revised terrace system was created by the compilation of novel terrace chronology and MIS data. Evolution of river terraces was not only governed by climatic factors but tectonic ones too. Incision rate of the Danube, and uplift rate of the Transdanubian Range (TR) was around 0.1-0.3 mm/a in the marginal zones of the TR (mostly based on the published U-series data) and was above 1 mm/a in its axial zone (based on 3He exposure age dating of strath terraces).– According to a detailed geomorphological investigation of the different channel-planform morphologies in the Middle Tisza region and Sajó-Hernád alluvial fan, six phases of river pattern change and four incision periods were detected during the last 20,000 years.– Wind polished rock surfaces dated by in situ produced cosmogenic 10Be suggest that deflation was active in Hungary as early as 1.5 Ma ago. According to these exposure age data, Pleistocene denudation rate of the study area (Balaton Highland) was 40-80 m/Ma.– In sand covered areas the alternations of wind-blown layers and buried fossil soils provide information about climate and environment changes. In this study, periods of sand movement were mostly determined by optically stimulated luminescence (OSL) dating methods and five aeolian sand accumulation periods were recognised during the last 25 000 years.– A new loess stratigraphical view was elaborated using the most recent dating methods (luminescence, AAR). The lower part of Mende Upper (MF1-2) pedokomplex is suggested to represent the last interglacial period (MIS 5e). During the last interglacial/glacial period (MIS 5 - MIS 2) several soil-forming periods existed but the preservation of these paleosoils is variable depending on their paleogeomorphological position.

Physical and chemical attributes of archaeological soils developed from shell middens in the Região dos Lagos, Rio de Janeiro, Brazil

In prehistoric times, innumerous shell middens, called "sambaquis", consisting mainly of remains of marine organisms, were built along the Brazilian coast. Although the scientific community took interest in these anthropic formations, especially since the nineteenth century, their pedological context is still poorly understood. The purpose of this study was to characterize and identify the physical and chemical changes induced by soil-forming processes, as well as to compare the morphology of shell midden soils with other, already described, anthropogenic soils of Brazil. Four soil profiles developed from shell middens in the Região dos Lagos - RJ were morphologically described and the physical and chemical properties determined. The chemical analysis showed that Ca, Mn, Mg, and particularly P and Zn are indicators of anthropic horizons of midden soils, as in the Amazon Dark Earths (Terras Pretas de Índio). After the deposition of P-rich material, P reaction and leaching can mask or disturb the evidence of in situ man-made strata, but mineralogical and chemical studies of phosphate forms can elucidate the apparent complexity. Lower phosphate-rich strata without direct anthropic inputs indicate P leaching and precipitation in secondary forms. The total and bioavailable contents of Ca, Mg, Zn, Mn, Cu, P, and organic C of midden soils were much higher than of regional soils without influence of ancient human settlements, demonstrating that the high fertility persisted for long periods, at some sites for more than 4000 years. The physical analysis showed that wind-blown sand contributed significantly to increase the sand fraction in the analyzed soils (texture classes sand, sandy loam and sandy clay loam) and that the aeolian sand accumulation occurred simultaneously with the midden formation.

Optically stimulated luminescence (OSL) dating of coastal aeolian sand accumulation in Sanday, Orkney Islands, Scotland

Optically stimulated luminescence (OSL) dating of sand has been used to identify periods of enhanced aeolian activity at two coastal archaeological sites in Orkney that coincide with periods of Holocene climatic deterioration recorded elsewhere in both Scotland and W Europe. Areas of Tofts Ness, Sanday were settled from the Neolithic, abandoned in the late Neolithic/early Bronze Age, reoccupied and permanently abandoned in the Iron Age. Sand layers above the Neolithic soils have been OSL dated to about 4000 BP, correlating well with a period of increased aeolian activity elsewhere in W Europe. OSL dating of aeolian sands above midden deposits and a Bronze Age burial at Lopness on Sanday suggest dune development by 3000 BP, although both sites also contain sand that was deposited during the `Little Ice Age'. Several possible mechanisms may have contributed to an increase in aeolian activity during the Holocene that led to the abandonment of these sites. Although volcanic eruptions in Iceland cannot be discounted as a contributory factor, a more likely driver of change in sand dune systems is the enhanced N Atlantic storminess suggested by ice core records from Greenland. During periods of climatic deterioration the declining productivity of other agricultural land places enhanced demands on agriculturally marginal sand dunes, leading to further destabilization and the potential for enhanced sand transport events.