Loess Of China Research Articles

The anti-erosion potential of taproots and fibrous roots in alluvial loess of north China: a pot experiment

The anti-erosion potential of taproots and fibrous roots in alluvial loess of north China: a pot experiment

Loess accumulation in the Tian Shan piedmont: Implications for palaeoenvironmental change in arid Central Asia

Whilst correlations have been made between the loess of Europe and China, deposits in Central Asia have remained largely overlooked by scientific investigation. The nature of the relationship between loess accumulation and palaeoclimate at the core of the Eurasian loess belt is particularly poorly understood.Here we reconstruct palaeoenvironmental change in Central Asia over the last 40 ky based on data from the Remizovka loess profile, in the northern foothills of the Tian Shan in southern Kazakhstan. Our interpretations are based on synthesis of chronostratigraphic, colour and magnetic susceptibility data, supported by chronostratigraphies from two additional sites nearby, Maibulak and Valikhanova. All three sites record substantially increased loess accumulation during late MIS 3 into the global last glacial maximum (gLGM). At Remizovka, increased loess flux occurred in two pulses at c. 38-25 ka and 22-18 ka, with the intervening period involving incipient pedogenesis. At Maibulak, two loess pulses at c. 40-30 ka and c. 28-22 ka are separated by a weakly developed paleosol which may date to the same time as pedogenesis at Remizovka. There is additional possible periglacial influence at Maibulak from c. 40–33.5 ka. At Valikhanova, there is some age overlap between paleosol and loess samples, but overall loess accumulation appears to have increased at c. 42-35 ka, c. 30 ka and the gLGM, with pedogenesis occurring >40 ka and c. 32 ka. At all three sites, Holocene loess accumulation is minimal; this period is characterised by pedogenesis.The chronostratigraphic variability between our sites highlights a need to interrogate climate-driven models for loess formation in piedmont environments. We interpret our data in the context of regional palaeoenvironmental archives to indicate that loess accumulation increased coeval with MIS 3 glacial advance in the Tian Shan, which was facilitated by northward expansion of the Asian monsoon and associated increase in precipitation. We hypothesise that increased ice volume impeded teleconnections with the temperate zone westerlies to the north; these were compressed against the piedmont resulting in increased wind strength and facilitating increased loess flux. Peak loess accumulation during the gLGM occurred under colder, drier climatic conditions, with reduced but sustained glacial ice volume and persistent influence of the westerlies in the arid Central Asian piedmont loess belt. In the absence of more widespread, reliably dated palaeoenvironmental records from the region, our data become of critical importance for understanding past environmental conditions in Central Asia, relative to elsewhere in Eurasia and globally.

Bearing Behavior Study of Rammed Cement-Soil Pile Compounded Foundation in Collapsible Loess

The rammed cement-soil pile compounded foundation is widely used in collapsible loess of northwest China. There are many factors influencing the bearing capacity of compounded foundation. The calculation result with empirical formula are usually not accurate. The influence factors on bearing capacity of compounded foundation are analyzed with finite element method based on the static load results. The result show that pile body elastic modulus has little effect on the bearing capacity of compounded foundation. This is quite different from bearing behavior of single pile. However, the soil parameters, such as soil elastic modulus, soil internal friction angle and soil cohesion have significant impact on compounded foundation bearing capacity.

Stepped-irradiation SAR: A viable approach to circumvent OSL equivalent dose underestimation in last glacial loess of northwestern China

The equivalent dose ( D e) obtained with the continuous irradiation SAR (CI-SAR) protocol for fine-grained quartz from loess of northwestern China is found to be lower than the expected value for samples older than 70 ka based on the regional stratigraphy. This is attributed to the difference in the response of the quartz to natural radiation and laboratory beta irradiation whose rates vary by ∼10 8 times. A stepped irradiation SAR protocol was employed to evaluate the influence of such a ‘dose rate effect’ on the equivalent dose determination. After investigating the effects of thermal treatment and ‘unit-dose’ on OSL signal and D e, we refined the stepped irradiation strategy with a ‘unit-dose’ of ∼25 Gy and successive thermal treatments at 250 °C for 10 s, and applied it to the SAR protocol. This stepped irradiation SAR (SI-SAR) protocol led to a 20%–70% increase in D e value for loess deposited during the early last glacial period.

2005년 동아시아 지역에서 발생한 모래폭풍과 먼지침전(황사)의 관측

2005년 1월부터 12월까지 지속적으로 몽골과 중국 북부의 사막과 건조지대에서 모래폭풍의 발생, 이동 그리고 한국에서 먼지침전(황사)을 모니터링하였다. NOAA 위성의 AVHRR(Advanced Very High Resolution Radiometer) 관측 자료를 직접 수신하여 false colour 합성영상을 만들어 모래폭풍의 발생과 이동 사례를 중점 분석하였다. 또한 모래폭풍 발원지의 풍하측에 위치한 한국 중부의 청원에서 PM10 농도가 <TEX>$190{\mu}g\;m^{-3}$</TEX> 이상인 황사 사례에 대한 PM10, PM2.5농도와 시정 그리고 <TEX>$O_3,\;NO_2,\;CO,\;SO_2$</TEX> 농도의 변동을 분석하였다. 2005년에는 발원지에 적설과 강력한 고기압, 저기압의 이동이 미흡하여 강한 모래폭풍의 발생이 적었고 한국에서도 황사의 발생 빈도가 1997-2005년의 평균과 비교하여 적었다. 한국에는 2005년 총 7회, 11일간의 황사 사례가 발생하였다. 여름에는 발원지가 습하고 바람이 약해 모래폭풍의 발생이 적었으며, 한국에서도 황사의 발생이 없었다. 발원지에서 발생한 모래폭풍이 중국의 대도시와 산업지대를 거치지 않고 한국으로 직접 이동할 경우, 먼지침전에 따른 PM2.5 농도는 PM10 농도의 20% 이하였다. 그러나 모래폭풍이 중국 동부의 산업지역을 거쳐 한국으로 이동할 경우 인위적 대기오염 물질이 함께 유입되어 PM2.5 농도가 증가하여 PM10농도의 25%이상을 나타내었다. 또한 2005년에는 사막에서 날아온 모래 먼지의 PM10농도가 <TEX>$190{\mu}g\;m^{-3}$</TEX> 이하여서 황사로는 미흡한 5개 이상 사례를 관측 및 분석하였다. Occurrences of sandstorms in the deserts and loess of Mongolia and northern China and associated dustfall episodes in the Korean Peninsula were monitored during the period January through December, 2005. False colour images were made by directly receiving the NOAA Advanced Very High Resolution Radiometer (AVHRR) data, and the distribution and transport of sandstorms were analyzed. The ground concentrations for PM10, PM2.5 and visibility of the dustfall episodes (PM10 concentration over <TEX>$190{\mu}g\;m^{-3}$</TEX>) were analyzed at Cheongwon, located midway in South Korea, and in the leeward direction of the place of origin of the sandstorms. Variations in the concentrations of <TEX>$O_3,\;NO_2$</TEX>, CO and <TEX>$SO_2$</TEX> were also compared with dust concentrations in the dustfall episodes. Fewer occurrences of strong sandstorms in the place of origin were observed in 2005, due largely to the accumulation of snow and mild fluctuations of high and low pressure systems in the place of origin, thereby accounting for a low frequency of dustfall episodes in Korea, compared with those during the period 1997-2005. A total of 7 dustfall episodes were monitored in Korea in 2005 that lasted 11 days. In summer, sandstorms occurred less frequently in the source region in 2005 due to high humidity and milder winds, thereby causing no dustfall episodes in Korea. In case the sandstorms occurring at the place of source head directly to Korea without passing through large cities and industrial areas of China, the PM2.5 concentrations were measured at 20% or lower than the PM10 concentrations. However, when the sandstorms headed to Korea via the industrial areas of eastern China, where they pick up anthropogenic air pollutants, the PM2.5 concentrations were at least 25% higher of the PM10 concentrations. On the other hand, over 5 cases were observed and analyzed in 2005 where the PM10 concentrations of sand dust originating from the deserts were measured at <TEX>$190{\mu}g\;m^{-3}$</TEX> or lower, falling short of the level of a dustfall episode.

Formation mechanism of ferromagnetic minerals in loess of China: TEM investigation

The results of TEM investigation indicate that magnetite and maghemite are the major ferromagnetic minerals in loess-paleosol sequences. Primary magnetite has the similar morphology and surface characteristics as eolian detrital particles. The magnetite can be classified into two categories, high-titanium and low-titanium, which may be the indicators of magmatic rocks and metamorphic rocks, respectively. TEM investigation at nanometer scale shows that primary detrital magnetite of micron scale had been partially weathered to maghemite of 5–20 nanometer during the pedogenic process, which maintain the pseudomorphism of the aeolian debris. Some chlorite particles were also weathered to nanometer scale magnetite or maghemite in the pedogenic process. So weathering of the two minerals leads to formation of superparamagnetism, which may be the important mechanism of magnetic-susceptibility increase in paleosols. The magnetite or maghemite resulting from the weathering of chlorite contains a small amount of P and S, which is the signal of microbe-mineral interaction, and indicates that microbes may play a certain role in chlorite weathering and formation of superparamagnetic particles.

Chemical weathering of the loess deposits in the lower Changjiang Valley, China, and paleoclimatic implications

Loess deposits (Xiashu Loess) are widely distributed in the lower Changjiang Valley, East China, and are considered to be of eolian origin with a similar provenance to the well-documented loess of north-central China. The Xiashu Loess is characterized by strong dissolution of carbonate, and considerable weathering of some silicate minerals, especially plagioclase. Chemical mobility of Ca>Sr>Na>Mg was observed in the Xiashu Loess sediments, whilst most transition metals are relatively enriched. Chemical index of variation (CIA) and element ratios of K/Na and K/Ca record several paleoclimate events in the lower Changjiang Valley during the mid-late Quaternary, corresponding with isotopic records in deep-sea sediments. East China might be governed by stronger summer monsoons than north-central China during interglacial periods of the mid-late Quaternary, which may somewhat obscure the record of winter monsoons during glacial periods.

Formation mechanism of ferromagnetic minerals in loess of China: TEM investigation

Formation mechanism of ferromagnetic minerals in loess of China: TEM investigation

Dust storms in China: a case study of dust storm variation and dust characteristics

The paper discusses the nature of dust storms, which have inherent environmental implications. The physical, chemical and mineralogical properties of dust sediments collected in Kashi, Taklimakan desert, Kunlun mountains, Donghuang, Lanzhou, Ningxia, Xi'an, Inner Mongolia and Beijing from 1990 to 1994 were studied. The texture of most aeolian deposits ranges from silty clay to clay loam with median particle diameters (Mds) generally between 5 and 63 µm; similar to the loess of central China and the silt/fine sand in western and northern China. The dust sediments were characterized by a predominance of SiO2 and Al2O3 and a high amount of K2O with molar ratios for SiO2/Al2O3 and K2O/SiO2 from 5.17 to 8.43 and 0.009 to 0.0368 respectively. The triple peak spectrum is the main form of mass concentration in a clear sky. In a dust storm it shows as a single peak, with quartz, feldspar, chlorite, illite, calcite and dolomite being the dominant minerals. The physical, chemical and mineralogical properties of the present atmospheric dust are similar to those of wind-blown soils in western and central China. The results suggest that aeolian deposits and the fine-grained fractions of dust sediments collected in northern China are mainly soils transported from the arid and semi-arid regions of China and Mongolia by the prevailing winds.

Can relative paleointensities be determined from the normalized magnetization of the wind‐blown loess of China?

Although the wind‐blown loess and interbedded paleosol sequence in the Loess Plateau of China has been extensively studied and regarded as one of the most complete terrestrial records of both the geomagnetic field and climatic changes during the Quaternary, little attention has been paid to it as a source of relative paleointensity. In this study, we examine the Malan loess (L1), the last glacial sediments, in the Lingtai section to determine whether loess is able to reliably record the relative paleointensity. Toward that end both the conventional normalizing method as well as the pseudo‐Thellier method [Tauxe et al., 1995] were used in conjunction with the examination of the rock magnetic properties and natural remanent magnetization (NRM). Rock magnetic properties of L1 show the uniformity in terms of magnetic mineralogy and grain size, suggesting that they may be suitable for relative paleointensity studies. Normalized remanences derived from L1 show highs between both 72–66 ka and 62–51 ka and lows near 63 ka, 42 ka and between 20 and 10 ka. Comparable results using different normalization parameters suggest that large‐amplitude variation of normalized magnetization may reflect the intensity variation of the geomagnetic field. However, comparisons of the normalized magnetization with contemporaneous marine records show some dissimilarities. In particular, the intensity low at 20–10 ka, corresponding to the last glacial maximum, is not compatible with the Sint‐800 composite record. On the other hand, spectral coherence analyses of middle‐ and high‐frequency components of the normalized magnetizations suggest some climatic influence. Thus this apparent discrepancy may be explained by climatic changes in the Loess Plateau and the resulting effect on the NRM.

Geotechnical thresholds in the Lanzhou loess of China

Abstract Failure of cementation bonds leading to soil structure collapse and slope failure is a major problem encountered in loess slopes in the Lanzhou region of China. Typical physical properties (low plasticity indices, short-range bonds, decrease in shear strength upon saturation) show little variation throughout the loess strata. However, important variations in the modes of failure and collapse potential exist which are related to varying thresholds of cementation bond failure and packing transformations. When geotechnical thresholds are exceeded, metastable loess can rapidly transform from an open to close particle packing; a phenomenon enhanced by leaching processes and degradation of cementation bonds. Geotechnical parameters from laboratory and in situ tests provide an insight into the variation of cementation bond ‘condition’ which, in turn, provides enhanced understanding of processes underlying slope instability development and the triggering of catastrophic mass movements in loess.

Climate extremes in Loess of China coupled with the strength of deep-water formation in the North Atlantic

The loess-paleosol sequences of the last 1.2 Ma in China have recorded two kinds of climate extremes: the strongly developed S4, S5-1 and S5-3 soils (corresponding to the marine δ 18O stages 11, 13, and 15, respectively) as evidence of three episodes of great warmth and two coarse-grained loess units (L9 and L15, corresponding to the marine δ 18O stages 22, 23, 24 and 38, respectively) which indicate severest glacial conditions. The climatic and geographical significance of these events are still unclear, and their cause remains a puzzle. Paleopedological, geochemical and magnetic susceptibility data from three loess sections (Xifeng, Changwu and Weinan) suggest that the S4, S5-1 and S5-3 soils were formed under sub-tropical semi-humid climates with a tentatively estimated mean annual temperature (MAT) of at least 4–6°C higher and a mean annual precipitation (MAP) of 200–300 mm higher than for the present-day, indicating a much strengthened summer monsoon. The annual rainfall was particularly accentuated for the southern-most part of the Loess Plateau, suggesting that the monsoon rain belt (the contact of the monsoonal northward warm-humid air mass with the dry-cold southward one) might have stood at the southern part of the Plateau for a relatively long period each year. The loess units L9 and L15 were deposited under semi-desertic environments with a tentatively estimated MAT and MAP of only about 1.5–3°C and 150–250 mm, indicating a much strengthened winter monsoon, and that the summer monsoon front could rarely penetrate into the Loess Plateau region. Correlation with marine carbon isotope records suggests that these climate extremes have large regional, even global, significance rather than being local phenomena in China. They match the periods with greatest/smallest Atlantic–Pacific δ 13C gradients, respectively, indicating their relationships with the strength of Deep Water (NADW) production in the North Atlantic. These results suggest that the monsoon climate in the Loess Plateau region was significantly linked with the North Atlantic thermohaline circulation on timescales of 10 4 years.

Changes in water chemistry and loess porosity with leaching: implications for collapsibility in the loess of north China: T. Muxart, A. Billard, A. Andrieu, E. Derbyshire & X. Meng, in: Genesis and properties of collapsible soils. Proc. workshop, Loughborough, 1994, ed. E. Derbyshire & others, (Kluwer; NATO ASI Series C, 468), 1995, pp 313–331

Changes in water chemistry and loess porosity with leaching: implications for collapsibility in the loess of north China: T. Muxart, A. Billard, A. Andrieu, E. Derbyshire & X. Meng, in: Genesis and properties of collapsible soils. Proc. workshop, Loughborough, 1994, ed. E. Derbyshire & others, (Kluwer; NATO ASI Series C, 468), 1995, pp 313–331

Molluscan assemblages from the loess of North Central China

Although molluscan faunas are the most widespread fossil remains in the Chinese loess. there have been very few attempts to use their potential for climatic reconstruction, or to develop cIimato-stratigraphic schemes. This paper reports assemblages of Mollusca from three sites in the North and South Central parts of the Loess Plateau, and evaluates the uses of molluscan faunas as climatic proxies in the S 1 palaeosol, the Malan Loess and S o palaeosol. The molluscan sequence is compared with the record obtained from pedological and magnetic techniques. The current study shows that major peaks in magnetic susceptibility, thought to be due to pedogenesis under warm, humid conditions, can be matched by levels of high molluscan abundance. The occurrence of a sharp molluscan peak within the Malan Loess, otherwise only indicated by a slight increase in magnetic susceptibility, is held to be due to the existence of a short-lived humid episode and demonstrates the sensitivity of Mollusca as indicators of relatively low magnitude climatic shifts not well indicated by other lines of evidence.

The nature, origin and accumulation of loess

Loess can be defined simply as a terrestrial clastic sediment, composed predominantly of silt-size particles, which is formed essentially by the accumulation of wind-blown dust. There are three fundamental requirements for its formation: (1) a sustained source of dust, (2) adequate wind energy to transport the dust, and (3) a suitable accumulation site. Most loess has been modified to some degree by local reworking, bioturbation and syn-depositional weathering, but a process of ‘loessification’ is not necessary for a dust deposit to qualify as loess. The terms ‘primary loess’ and ‘secondary loess’ have previously been used to described wind-deposited loess and redeposited loess, respectively, but it is more accurate to describe material reworked and redeposited by non-aeolian processes as ‘loess-derived colluvium’ or ‘loess-derived alluvium’. During the Quaternary, loess formed in three main situations: (1) mid-continental shield areas beyond the limits of ice sheets (periglacial loess), (2) on the margins of high mountain ranges (perimontane loess), and (3) on the semi-arid margins of some lowland deserts (peridesert loess). Peridesert loess is relatively poorly developed partly due to the limited efficiency of silt-generating mechanisms in low-land deserts compared with glaciation, but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition, particularly in areas which experience frequent climatic changes. The remarkably thick loess of China and Central Asia results from an unusual combination of conditions which has persisted for much of the last 2–3 million years, namely rapid uplift of the Tibetan Plateau and surrounding mountain ranges, high rates of sediment production and supply to adjacent basins, a strong northwesterly and westerly wind regime, and the existence of effective dust traps downwind of the source regions.

The loess of north-central China: geotechnical properties and their relation to slope stability : T. A. Dijkstra, C. D. F. Rogers, I. J. Smalley, E. Derbyshire, Li Yong Jin & Meng Xing Min, Engineering Geology, 36(3–4), 1994, pp 153–171

The loess of north-central China: geotechnical properties and their relation to slope stability : T. A. Dijkstra, C. D. F. Rogers, I. J. Smalley, E. Derbyshire, Li Yong Jin & Meng Xing Min, Engineering Geology, 36(3–4), 1994, pp 153–171

Neotectonics and mass movements in the loess of north-central China : T. Dijkstra, E. Derbyshire & Meng Xing Min, Quaternary Proceedings, 3, 1993, pp 93–110

Neotectonics and mass movements in the loess of north-central China : T. Dijkstra, E. Derbyshire & Meng Xing Min, Quaternary Proceedings, 3, 1993, pp 93–110

The loess of north-central China: Geotechnical properties and their relation to slope stability

Loess is an aeolian deposit consisting of predominantly silt-sized quartz particles, and containing variable amounts of clay-sized minerals. Loess is generally classified as a water-softening material, because upon wetting the loess fabric rapidly weakens or collapses. The strain hardening of Malan loess and the brittle failure of Lishi and Wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state. From tests carried out on samples with varying moisture contents, using a modified Bromhead ring shear apparatus, it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content. When the moisture content reaches a material-specific threshold, the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value. The frequent failure of loess slopes in the western part of the Chinese Loess Plateau is closely related to progressive weathering along zones in these slopes, which causes a dramatic decrease in strength from the peak strength condition. Progressive weathering is common in the loess slopes in the western part of the Chinese Loess Plateau. During the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts, destruction of cementation bonds, and redistribution of particles. Localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane. Therefore, the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed, and unweathered, central parts of the slopes. It is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes, many of which are steepand lie directly above domestic and industrial urban areas.

ESR dating and trapped electrons lifetime of quartz grains in loess of China

This paper reports the preliminary application of ESR dating to loess strata. The samples were collected from the 7th palaeosol layer (S7) of the Luochuan section, Shaanxi province in China. The ESR age of S7 is 736 ka (total dose 2945 Gy, annual dose 4 mGy/year). This age represents the original eolian accumulation age. The result is consistent with the palaeomagnetic data (730 ka). We have also carried out thermal annealing experiments on quartz grains from the S7 sample. ESR intensities ( g = 2.0005) increase from 25°C to 320°C. It may be that trapped electrons transfer into the E′ centre site. ESR intensities decrease from 340°C to 460°C due to thermal annealing. We obtained a mean-life of E′ centre electrons at 20°C of 6.66 × 10 8 years. The activation energy is 1.35 eV and frequency factor is 3.7 × 10 8 min −1.

The loes-like red yellow soil of the south western coastal area of Korea in comparison with the loess of China and Japan

The analyses of the physical and chemical properties including X ray diffraction analysis of the red yellow soil of the Hwangsan-Myun, Kimje County and Gamgok-Myun, Chungeup County, in the SW coastal area of Korea were carried out and the results were compared with those of the loess in China and Japan and the red soil of Korea.