Components Of Loess Research Articles

Geochemistry and Provenance of Loess on the Miaodao Islands, China

Loess deposits are widely distributed across the globe and provide detailed records of climatic changes since the Quaternary period. Their geochemical element characteristics are important indicators of paleoenvironmental evolution and provenance. Therefore, four typical loess sections from four different islands of the Miaodao Islands were selected for systematically geochemical analysis of major and trace elements. The geochemical data of major and trace elements are very similar, indicating that the loess of all islands on the Miaodao have a common provenance. The geochemical test results show that t SiO2, Al2O3, Fe2O3 and CaO are the major chemical components of loess, with an average total content of 85–90%. The average Eu/Eu*, ΣLREE/ΣHREE, LaN/YbN, GdN/YbN values of the Miaodao Islands loess range from 0.65 to 0.69, 7.84 to 8.31, 8.02 to 9.99, 1.40 to 1.76. These data are similar to and different from those of the Chinese Loess Plateau, indicating the diversity of Miaodao Islands Loess provenance. The CIA (Chemical Index of Alteration) (50–65) and Na/K results suggest that the loess here had experienced incipient chemical weathering. The A-CN-K (Al2O3-CaO* + Na2O-K2O) diagram indicates that the weathering trend of the loess sections is consistent with that of continental weathering. The local loess data points are close and parallel to the A-CN line, suggesting that the loess dust material on the Miaodao Islands originated from the extensive upper continental crust, and was highly mixed in the process of wind transport and deposition. The relationships of Log[(CaO + Na2O)/K2O] versus Log(SiO2/Al2O3), Na2O/Al2O3 versus K2O/Al2O3, LaN/YbN versus Eu/Eu*, Sc-Th-La and Zr-Sc-Th plots of major and trace elements reveal that the loess sources for the Miaodao Islands are similar to those of the Loess Plateau, which were derived from alluvial fan deposits flanking the Qilian Shan in China, the Gobi Altay and Hangayn Mountains in Mongolia. However, the loess of the Miaodao Islands is coarser in average grain size and contains abundant marine fossils, with gravel layers, indicating it is allochthous and near-source, which suggests it mainly originated from the adjacent exposed sea floor sediments of the Bohai Sea during glacial periods. Finally, we conclude that the loess of the Miaodao Islands is the result of a gradual accumulation process, in which the relative amount of distant-source material decreased and the near-source material increased in response to changes in sea level and paleoclimate. Our findings support that the loess of the Miaodao Islands was formed by mixing material from distant and proximal sources.

Loess or lake sediments: Resolving the origin of massive beds in the Lower Jurassic of southern Africa

Throughout Earth's history, dust deposits have been considered sensitive markers of fluctuations in global atmospheric circulation patterns. However, the identification of ancient dust deposits remains problematic, as their massive (structureless) nature impedes an unequivocal classification. In southern Africa, the Lower Jurassic Clarens Formation is dominated by intriguing structureless sandy siltstones that have been interpreted as loess even though classical diagnostic outcrop‐scale loess features are not observed. In this study, we utilized grain characteristics such as size, shape, sorting and fabric to assess the origin of these ubiquitous massive beds, as compared to strata with a known origin in the unit. Based on these grain characteristics, the massive beds can be grouped into six different facies types (Facies 1–6). Facies 1 has very similar grain features to the large‐scale cross‐bedded strata and thus it is interpreted as migrating dune deposits, only apparently massive. The dominant grain size with a large proportion of very fine‐grained sand and the random grain fabric suggests that Facies 2 resulted from sandy dust fall (short‐term suspension), whereas Facies 3 is interpreted as aeolian dust, having features consistent with modern and ancient loess due to its dominant silt grain size and random grain fabric. Features in Facies 4 are undiagnostic and could reflect a range of aeolian processes, although a dominant silt grain size may suggest an overwhelming loess component. Facies 5 and 6 show primary aeolian signatures with the preferred grain orientation being evidence of reworking in an aqueous setting (e.g., lake, stream). These six facies types represent a spectrum of depositional processes that occurred in response to erg migration and climatic changes along this Early Jurassic erg margin. Their facies diversity is evidence for: (1) dry and windy conditions in SW Gondwana during the Sinemurian to Pliensbachian, and (2) reworking of the aeolian sediments in various fluvial and lacustrine settings during the development of one of the largest known sand seas in Earth's history.

Loess in Pleistocene periglacial slope deposits and Holocene colluvium of European low mountain ranges: Mixing processes and spatial variations

Loess, as an allochthonous material, plays a significant role in the formation of Pleistocene periglacial slope deposits (PPSD), and thus also for Holocene soil formation, in the central European low mountain range. Although the differing loess proportions in different layers of the PPSD have been well recognized, quantitative distribution and mixing processes of loess in PPSD are still not fully understood. Detailed particle-size distribution was applied for quantifying loess proportions in PPSD in a sandstone area in central Germany. The bimodal pattern of the particle-size distribution curves clearly reflected loess and sandstone-weathering material as two components of the loess-affected layers, which allowed for the quantification of these two components by applying a two-endmembers unmixing model. By inspecting variations of particle-size distribution curves both vertically and spatially, we gained insights into the mixing processes of loess in PPSD and Holocene colluvium. Our results suggest that the loess component in upper layers most likely results from the incorporation of preexisting loess. Holocene colluvium and upper layers were thoroughly homogenized by various earth-surface processes. Radiocarbon dating of charcoal indicated strong human impact during historic times. Close correlation between the overall thickness of loess-containing layers and the depth-weighted loess content pointed to the erosional-depositional history at each site. Our research demonstrates the utility of detailed particle-size data for detecting and interpreting geomorphological processes and landscape evolution. It shows that the spatial distribution patterns of loess are subjected not only to topographic factors controlling primary loess deposition, but also to erosional-depositional histories and anthropogenic impact.

Satellite ASTER Mineral Mapping the Provenance of the Loess Used by the Ming to Build their Earthen Great Wall

The earthen border wall (Great Wall) built by the Ming is largely made of wind-blown loess. However, does the composition of this loess change along the length of the wall in response to variations in regional sediment transport pathways and impacting on the wall’s erosional durability? To date, defining these sediment transport pathways has been a challenge because of the paucity of spatially-comprehensive, compositional information. Here, we show that satellite ASTER mineral maps, combined with field sample measurements along a 1200 km section of the Ming’s earthen wall, reveal both the compositional heterogeneity of loess as well as the complexity of the sediment transport pathways of individual loess components, including: (i) quartz sand from Cretaceous sandstones in the Gobi Desert; (ii) gypsum from evaporative lakes in the Tengger Desert; (iii) kaolinite from Devonian Molasse in the Qilian Shan; and (iv) chlorite and muscovite from meta-volcanic rocks exposed across the Alashan Block. Sediment transport pathways involve a combination of colluvial, aeolian and fluvial (ephemeral and permanent) processes shaped by the topography. ASTER enabled mapping of compositional gradients related to two pathways, namely: (i) quartz sand driven by aeolian saltation in concert with the Yellow River; and (ii) clay and fine silt travelling large distances (>500 km) by long-term wind suspension. The most intact section of wall is found along the Hexi Corridor, which is poor in quartz sand and rich in (kaolinitic) clay and fine-silt, driven by wind-shielding by the Alashan Block. We also found evidence that the Ming: (i) mined loess from close by the wall (<1 km); (ii) targeted loess richer in finer fractions; and (iii) routinely applied a Ca-rich additive (probably lime).

Influences of soil moisture and salt content on loess shear strength in the Xining Basin, northeastern Qinghai-Tibet Plateau

Moisture and salt content of soil are the two predominant factors influencing its shear strength. This study aims to investigate the effects of these two factors on shear strength behavior of loess in the Xining Basin of Northeast Qinghai-Tibet Plateau, where such geological hazards as soil erosion, landslides and debris flows are widespread due to the highly erodible loess. Salinized loess soil collected from the test site was desalinized through saltleaching in the laboratory. The desalinized and ovendried loess samples were also artificially moisturized and salinized in order to examine how soil salinity affects its shear strength at different moisture levels. Soil samples prepared in different ways (moisturizing, salt-leaching, and salinized) were measured to determine soil cohesion and internal friction angle. The results show that salt-leaching up to 18 rounds almost completely removed the salt content and considerably changed the physical components of loess, but the soil type remained unchanged. As salt content increases from 0.00% to 12.00%, both the cohesion and internal friction angle exhibit an initial decrease and then increase with salt content. As moisture content is 12.00%, the salt content threshold value for both cohesion and internal friction angle is identified as 3.00%. As the moisture content rises to 16.0% and 20.00%, the salt content threshold value for cohesion is still 6.00%, but 3.00% for internal friction angle. At these thresholds soil shear strength is the lowest, below which it is inversely related to soil salinity. Beyond the thresholds, however, the relationship is positive. Dissimilar to salinity, soil moisture content exerts an adverse effect on shear strength of loess. The findings of this study can provide a valuable guidance on stabilizing the engineering properties of salinized loess to prevent slope failures during heavy rainfall events.

대두직물의 황토염색

The purpose of this study is to investigate the loess dyeability of soybean fabric using loess as colorants. Recent days, various textile products such as inner wears, sheets and interior goods are manufactured using materials dyed with loess emphasizing its improved metabolism, anti-bacterial, deodorizing properties, and far infrared ray emissions. Soybean fabric was dyed with loess solution according to concentration of loess, dyeing temperature and dyeing time. To improve washing fastness, soybean fabric and dyed soybean fabric with loess were mordanted by mordanting agents such as sodium chloride(NaCl), Acetic acid(CH₃COOH) and Aluminium Potassium Sulfate(AlK(SO₄)₂·12H₂O). Dyeability and color characteristics of dyed soybean fabric were obtained by CCM observation. Particle size distribution of loess, the dyeability(K/S) of soybean fabric, morphology and washing durability of loess dyed soybean fabric were investigated. The results obtained were as follows; Mean average diameter of loess was 1.08µm. The main components of loess used in this study were silicon dioxide(SiO₂), aluminium oxide(Al₂O₃), and iron oxide(Fe₂O₃). The content of these three component was above 75 weight %. The dyeability of soybean fabric was increased gradually with increasing concentration of loess. The optimum dyeing temperature and dyeing time were 90℃ and 60minutes expectively. The fastness to washing according to concentration of loess and mordanting method indicated good grade result as more than 4 degree in all conditions.

Loess-like deposits in the Pearl River delta area, southeast China

A layer of yellow silt is widely distributed in the late Quaternary succession of the Pearl River delta, southeast China. A representative section at Xi Lingang was analyzed using particle size analysis, scanning electron microscope observation, geochemical analysis and OSL dating to determine the characteristics and genesis of the yellow silt. Grain size composition of the yellow silt is homogeneous and comparable to typical north China loess (10–50 μm as “basic grain size group”, <5 μm as “secondary grain size group”). Grain size parameters and frequency distribution curves of the yellow silt also indicate an aeolian origin. Aeolian micro-textures with subangular–subrounded grains characterized by dished surface collision pits during wind transportation. Homogeneous major element composition of the yellow silt suggests that the dust has been well mixed and sorted prior to deposition, a typical feature of aeolian origin, but Chemical Index of Alteration values indicate that the yellow silt has suffered intense weathering after deposition. Five OSL dates obtained in this study and other geochronological data indicate that the yellow silt has a Last Glacial Maximum age. The grain size of loess across China becomes finer from northwest to southeast because of increasing transportation distance, and implies that the loess component of the yellow silt in the Pearl River delta area is also derived from a northwest China provenance.

Contrasting dust supply patterns across the north-western Chinese Loess Plateau during the last glacial-interglacial cycle

Loess grain-size distributions of four loess-paleosol sequences, located on a west to east transect from the north-eastern Tibetan Plateau (TP) to the north-western Chinese Loess Plateau (CLP), are unmixed with the end-member modelling algorithm EMMA. The unmixing results indicate that the loess is a mixture of three components representing very fine sandy, coarse silty and medium silty loess. The proportional contributions of these loess components in conjunction with loess mass accumulation rate estimates reveal that during the last glacial-interglacial cycle two contrasting dust supply patterns were active over the north-eastern TP and the north-western CLP: a constant supply of medium silty loess and an episodic supply of coarse silty loess and fine sandy loess. The variable input of the two coarse dust components is the main cause for the variation in grain-size patterns and mass accumulation rates between the studied sites. Alluvial fans and river floodplains in the intra-mountainous basins of the Tibetan Plateau and the deserts of northern China and Inner Mongolia are the main dust source areas for loess deposits of the north-eastern TP and the CLP, respectively. The sensitivity of these dust source areas to climate variations determines the timing of dust transport and deposition. In general, high dust fluxes are recorded during the last glacial period (Marine Isotope Stages (MIS) 2–4) and low dust fluxes during the last interglacial (MIS-5). The loess sections in the two regions (TP, CLP) show contrasting dust flux patterns during MIS-3. The records from the CLP show a relatively low dust input in this period, most likely related to increased humidity in the northern dust sources (deserts) where an increased vegetation cover minimized dust deflation. In contrast to this, the Tibetan Plateau records appear to show increased and highly variable dust fluxes for MIS-3. Alternating periods of increased humidity and aridity on the Tibetan Plateau (during MIS-3) have resulted in an overall increase in fluvial/alluvial activity. Hence, the enhanced availability of exposed fine-grained fluvial/alluvial sediments on the Tibetan Plateau facilitated dust entrainment which resulted in an increased dust supply towards the Tibetan Plateau sites during this period.

Clay minerals in the major Chinese coastal estuaries and their provenance implications

A sea-survey was carried out along the Chinese coast from the Bohai Sea to South China Sea, and 15 surficial samples were taken from major coastal estuaries, i.e., from north to south, the Yellow, abandoned Yellow, Yangtze, Qiantang, Ou, Min, Han, and Pearl River estuaries. On the basis of clay mineral analysis and published data collection, this paper discusses the characteristics of clay minerals of each coastal river and potentials of implications of sediment sources. The results show that the change of diagnostic clay minerals from smectite to kaolinite from the Yellow to the Pearl River estuaries is southward, as clearly shown by the ratios of smectite to chlorite (S/Ch) and kaolinite to illite (K/I). S/Ch decreases southward, while K/I moves reversely, implying change in climate setting from cool/dry to humid/hot with intensified weathering processes. Besides, these two indicators in the estuaries are also linked with the derivation of parent-rock of each river-basin and coastal hydrodynamics. The disproportional higher ratio of K/I in the Yellow and abandoned Yellow River estuaries is ascribed to their sediment sources with abundant loess component in the north-central China. The K/I decrease offshore from the Pearl River estuary is primarily due to hydrodynamic sorting. Therefore, the S/Ch and K/I of the present study comprehensively reflect the controls of climate, parent-rock, and sediment transport along the coast.

Do fine-grained components of loess indicate westerlies: Insights from observations of dust storm deposits at Lenghu (Qaidam Basin, China)

The hyper-arid Qaidam Basin is a major dust source area in China. Mineral materials that settled during 11 dust storms from November 2003 to April 2005 in the northern Qaidam Basin were comprised of an amount of fine particles. The particles <20 μm varied between 11.4 and 19.4 vol.-%, while the mean volume percentages of <2, 2–5, 5–10 and 10–20 μm particles were 2.9, 3.6, 4.0 and 5.3 vol.-%, respectively. The deposits were characterised by very similar multi-modal grain size distributions. Stronger winds (>14 m s −1 at a height of 10 m above ground) during these dust storms were unfavourable for the gravitational settling of single fine mineral grains. Fine particles might instead settle either by forming aggregates or by adhering to larger grains. As such, the great amount of clay and fine silt in Chinese loess deposits can largely be correlated with dust storm processes and are likely derived from proximal source areas. Fine dust records from the Chinese Loess Plateau (CLP) therefore have to be interpreted cautiously as climatic proxies for changes in the westerlies.

Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau

AbstractThe Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Glacial and interglacial eolian dust dispersal patterns across the Chinese Loess Plateau inferred from decomposed loess grain‐size records

Previous studies have indicated that a genetically meaningful decomposition (unmixing) of loess grain‐size distributions can be accomplished with the end‐member modeling algorithm EMMA. The independent decomposition of two series of loess grain‐size records from the NE Tibetan Plateau and Loess Plateau spanning the last glacial‐interglacial cycle indicates that the two data sets are described by very similar mixing models. The average mixing model presented here is regarded as representative for the vast loess region in northern China and allows quantification of the contribution of three loess components to the loess grain‐size distributions. A genetic interpretation and the paleoclimatic significance of the average mixing model have been provided by comparison of the modeled loess components with modern dust samples in terms of their grain‐size distribution and flux rates, and by the distribution patterns of the loess components across the Loess Plateau reconstructed for the last two glacial‐interglacial cycles. The sandy and silty loess components represent the coarse dust fraction supplied by saltation and short‐term suspension processes over the proximal part of the Loess Plateau during major dust outbreaks in spring and early summer. The low‐level winter monsoon (northwesterly wind system) is the likely transporting agent for these dust events. A clayey loess component represents the fine dust component supplied over the entire Loess Plateau by long‐term suspension processes during major dust outbreaks and as part of a background supply system. The clayey loess component in the glacial loess deposits is dominantly supplied during major dust outbreaks by the northwesterly winter monsoon, whereas the clayey loess component in the interglacial paleosols is mainly supplied by non‐dust‐storm processes, possibly with a significant contribution by the high‐level subtropical jet stream (westerly winds).

Late Quaternary aeolian dust input variability on the Chinese Loess Plateau: inferences from unmixing of loess grain-size records

The grain-size distributions (GSDs) of loess–paleosol sequences may provide valuable information on provenance, transport and paleoclimate variability, and consequently, a wide range of methods to extract genetic information from loess GSDs has been proposed. Here it is shown that a genetically meaningful decomposition of a series of Late Quaternary loess grain-size records extending across the Chinese Loess Plateau can be accomplished with the end-member modelling algorithm (EMMA). The unmixing results in conjunction with loess accumulation rate estimates reveal that two contrasting dust supply patterns were active over the Loess Plateau during the last glacial–interglacial cycle: (i) a background sedimentation pattern that was dominant during interglacial periods, especially over the central and southern parts of the Loess Plateau, is reflected by the constant flux of the fine-grained loess component, (ii) an episodic, highly variable dust input pattern, that was dominant during glacial periods throughout the Loess Plateau and noticeable during interglacial periods mainly over the northern Loess Plateau and almost disappearing over the southern Loess Plateau, is reflected in the admixture of two coarse-grained loess components. A genetic interpretation and the paleoclimatic significance of the mixing model are provided by comparison of the modelled end members with modern dust samples in terms of their GSD and flux rates.

Adsorption of polycyclic aromatic hydrocarbon onto the components of loess and Aeolian dust

Adsorption of polycyclic aromatic hydrocarbon onto the components of loess and Aeolian dust

Chemical equilibrium modeling of copper precipitation in a hyper-concentrated solid-liquid system

Rapid progress has been made recently in the understanding of heavy metal sorption and speciation on sediment and soils. One aspect that was overlooked in the previous studies was the process of pollutant transformation and transportation in hyper-concentrated solid-liquid systems. In this paper, batch experiments on copper sorption in association with loess at high sediment concentrations were conducted. However, some reaction mechanisms were difficult to determine experimentally due to the limitations of speciation extraction methods. In an additional study, the MINTEQA2 chemical equilibrium model was used to calculate the speciation and precipitation of copper sorption by loess to give quantitative predictions and detailed information about the reaction process. The experiments and the modeling simulation were made under the same sorption conditions, with sediment concentrations ranging from 50 to 200 kg/m3 and adsorbates of CuSO4 and Cu(NO3)2, in order to compare their results. The modeling results clearly supported the experimental results, fully explained the mechanisms of the effects of chemical form and sediment concentration on the copper sorption, and strengthened the dominant role of carbonates among the main components of loess in the process of copper sorption.

Influence of slope and exposition on water balance of loess soils

AbstractLaboratory and field measurements as well as deterministic simulation models were used to determine the water components of loess derived soils with different expositions and slopes in the hilly region South of Hannover, Germany.Studies were investigated from 1987‐1990 on three positions of a loess slope with 8 % inclination, 200 m length and northern exposition. Crop rotation was sugar beet, winter wheat, sugar beet.Results show that the soil water budget is strongly related to slope position, relief and plant available water in the rootzone. It was found that drainage at the bottom of a slope is often higher than on top of the slope. On slopes with northern exposition groundwater recharge increases with inclination whereas actual evapotranspiration decreases. For slopes with southern exposition the opposite reaction can be expected. The thickness of loess deposits and the root depth determine the plant available water; a sensitivity study demonstrates how groundwater recharge decreases with the amount of plant available water. This reaction is independent of the exposition of the slope. Field and simulation studies show that runoff occurs under sugar beet whenever soil is bare or sparsely covered, rainfall intensity is high and topsoil is sealed. Moreover, in loess derived soils interflow may occur on sites with stagnic horizons. Sensitivity analyses show that this process probably takes place whenever saturated hydraulic conductivity of this horizon is less than 10cm/d.

Thermoluminescence dating of Dimlington Stadial deposits in eastern England

The loess component of a solifluction deposit of the Dimlington Stadial exposed at the inland site of Eppleworth in eastern England gave a thermoluminescence date of 17.5 ± 1.6 × 103 years. The solifluction deposit is overlain by a slightly weathered till correlated with the Skipsea Till of coastal exposures. which lies between organic horizons with radiocarbon dates of 18,500–18,240 B.P. and 13,045 B.P. Although the till must have been deposited during the Dimlington Stadial (after 18,240 B.P. at Dimlington and after 17,500 B.P. at Epplcworth), it gave apparent TL dates of 42.1 ± 3.6 × 103 years at Eppleworth and 102 ± 9 × 103 years at Dimlington, indicating that the components of the till were not exposed to light immediately before deposition.

The geomorphology and stratigraphy of the Lizard Loess in south Cornwall, England

The Quaternary deposits of south Cornwall are described with an emphasis placed on the loess component. A formal lithostratigraphic name – the Lizard Loess – is proposed for the loess formation with a holostratotype designated from the Lizard Peninsula. Two environments of loess deposition are distinguished on the basis of geomorphic position and degree of solifluction activity.

Pleistocene history of the Vale of St. Albans

The stratigraphy of the Pleistocene sequence in the area of the Vale of St Albans has been investigated and the results used to link the sequences in East Anglia and the Middle Thames region. Lithological units have been characterized using various methods and thirteen formal lithostratigraphical units are proposed. The bulk of the deposits are included in the Anglian glacial stage during which two major ice advances occurred. Both advances dammed the eastward-flowing river in the Vale causing, respectively, a minor and a more extensive proglacial lake. The river was finally diverted and after the ice retreat a westward-flowing river occupied the Vale. Organic remains fill kettle holes resting on the glacial deposits. A new site at London Colney shows a late Anglian to Hoxnian Ho1 pollen sequence. Wolstonian soliflucted gravels overlie the hollow fills. It is probable, since pre-Ipswichian and Ipswichian deposits occur near the present river level, that the modern river valleys were initiated during this stage. Overlying the Ipswichian deposits in river valleys and on interfluves is brown silt, containing a substantial loess component. This is considered to represent early Devensian river aggradation. A period of downcutting then occurred, before the accumulation of valley gravels which contain organic horizons radiocarbon-dated to the Late Devensian. The sequence is extended north to Stevenage and Hitchin and east into Essex. The Middle Thames Terrace sequence is equated with the Vale using relative heights and lithology, showing that the Thames flowed through the Vale until late Anglian times, when it was diverted southwards and took up a course close to that which it follows today.