Aeolian Loess Deposits Research Articles

Increased late Holocene dust activity revealed by loess accumulation rates in Central Asia

Dust from the vast arid and semi-arid regions of arid Central Asia (ACA) makes a large contribution to global-scale dust cycles. However, systematic and regional-scale reconstructions of dust activity in ACA are lacking, thus hindering the exploration of its relationship with climate change. Aeolian loess deposits provide valuable records of past dust activity and its linkages to climate. We constructed a stacked, normalized dust mass accumulation rate (MAR) record from 17 loess sections with high-resolution dating, together with a probability density record based on 189 absolute ages from 39 Holocene loess sections. These records were used to reconstruct the temporal pattern of Holocene dust activity in ACA, which shows a pronounced increase during the late Holocene. After evaluating the temporal variation of moisture conditions at different altitudes in ACA, we conclude that while dust activity during the early and middle Holocene was driven predominantly by climate change, this was not the case in the late Holocene. Taking the mountain-basin system of the Yili Basin in Xinjiang as an example, we propose that dust activity on a large spatial scale was not completely controlled by changes in moisture conditions, and that regional factors, such as fluvial geomorphic processes, played an important role in increasing the materials supply to the areas of dust accumulation. We speculate that dust activity may intensify in ACA under future global warming scenarios.

Tracking the Provenance of Aeolian Loess in Northeastern China by Uranium Isotopes

AbstractThe aeolian loess deposits in northeastern China have substantial potential for reconstructing the paleoclimate in the East Asian monsoon boundary zone. Identifying the source of the aeolian dust is crucial to interpret the paleo‐proxies recorded in the loess deposits in northeastern China; however, traditional geochemical tracers such as Nd and Sr isotopes cannot discriminate between the potential source areas, that is, the Otindag Sandy Land, Horqin Sandy Land, and Hulun Buir Sandy Land regions. In this study, the (234U/238U) activity ratio is used to constrain the provenance of the loess deposits in northeastern China. The (234U/238U) of the studied loess‐paleosol sequences (from 0.935 to 0.910) decreases with increasing depositional age (from 10 to ∼1,000 ka), which is consistent with predictions from uranium isotope comminution age model. A derived (234U/238U) of 0.935 ± 0.003 for the newly deposited loess (zero depositional age) is most similar to that of the Otindag Sandy Land positioned at a proximal upwind direction, suggesting that the Otindag Sandy Land is the most likely source of the aeolian dust that formed the loess deposits in northeastern China. A transportation time of 432 ± 65 ka was calculated for these deposits, indicating extensive mixing of the fine dust in the source regions, which could partially explain the relative homogeneity of loess deposits in northeastern China. The transportation time longer than several glacial‐interglacial cycles suggests that reconstructions of regional paleoclimate on orbital timescales should be viewed with caution because the potential influence of climatic changes could largely be buffered.

Experimental Investigation of Helical Pile Performance for Loess Deposits Improvement

Collapsible loess is classified as problematic soil found on most continents. The loess immediately collapses under stresses induced by axial compressive loading or the soil weight when exposed to moisture. In Iran, vast areas of the Golestan province are covered with Aeolian loess deposits. This paper investigates whether the simultaneous effect of inundation and pre-loading in helical pile installation is operative and effective in improving Golestan loess. The effect of installation conditions on loess collapsibility is studied via two main approaches, i.e., field investigations and physical modeling. The experimental studies include the installation of ten single and triple helix piles in the Amirkabir University of Technology Frustum Confining Vessel, i.e., FCV-AUT. Also, ten single and double helix piles with embedment depth of 3 to 6 m and a helix diameter of 250 mm were installed in Golestan province, and full-scale pile static loading tests were performed. The results indicated that the simultaneous application of crowd loading and water pressure during the installation of helical piles results in collapsibility potential reduction due to the soil treatment. Moreover, high or low crowd loads accompanied by water pressure during pile installation bring about similar load-displacement behavior of model piles installed in FCV-AUT and full-scale helical piles. Eventually, it was illustrated that the applied improvement technique is effective on loess soils since it uses the least amount of material, machinery, and equipment while attaining the highest possible bearing capacity ratio regarding sustainability.

Birth of the Taklamakan Desert: When and How?

<abstract> <p>The Taklimakan Desert is one of the largest deserts and sand seas in the world and plays a critical role in the global aerosol (eolian dust) system, impacting both climate and ecosystems on continents and over oceans. Geological evidence suggests that much of the western part of the Tarim Basin, which is now covered by the vast sandy desert, was once the eastern fringe of the Paratethys Sea. After the retreat of the sea, the area transformed into a fluvial system before becoming an mountain front alluvial fan system due to the uplift of the northern Tibetan Plateau. Deserts developed during this period, as sand dunes and eolian loess deposits were formed and buried to become part of the sedimentary sequence. Dating of these sequences suggests that the Taklimakan Desert, in a similar form to what we observe today, came into existence no later than 25 million years ago. Taklimakan Desert was formed as a response to a combination of widespread regional aridification due to the rain shadow effect and increased erosion in the surrounding mountain fronts, both of which are closely linked to the tectonic uplift of the Tibetan-Pamir Plateau and Tian Shan, which had reached a climatically sensitive threshold at this time.</p> </abstract>

Intensified Northern Hemisphere Glaciation Facilitates Continuous Accumulation of Late Pliocene Loess on the Western Margin of the Pamir

AbstractThick eolian loess sequences in arid Central Asia (CA) contain a wealth of information on the intensity variations of midlatitude westerlies and the aridification history of the nearby deserts. In this study, detailed lithologic and magnetostratigraphic investigations suggest that loess deposits on the western margin of the Pamir Plateau began to accumulate at around 2.7 Ma, representing the most complete and oldest loess‐paleosol sequence in western CA. The widely distributed continuous loess deposition in the region suggests a rapid desiccation of CA during the late Pliocene. A synthesis of the initial timing and spatial distribution of late Cenozoic eolian deposits on the Eurasian continent further demonstrates that the dramatic increase in global ice volume exerted a dominant role in the expansion of eolian loess deposits in CA, China, and Europe, and middle Pleistocene expansion is a crucial precondition for the establishment of modern distribution patterns of the Eurasian loess belt.

Characteristics of a Benchmark Loess–Paleosol Profile in Northeast China

The Chaoyang profile represents a rare multi-period, continuous and complete sequence of aeolian paleo-deposits with a stable sedimentary origin and multi-stage paleoclimatic cycles. Benchmark profiles including soil types at different pedogenic stages can be used for the recognition and classification of paleosols and paleoclimate reconstruction. The loess–paleosol sequence benchmark profile (LBP) is also helpful in comparing the results of paleoenvironment reconstruction from different ecological regions. In this study, a loess–paleosol profile derived from thick loess in Chaoyang city of Liaoning province, Northeast China, was investigated as a well-preserved LBP that included various paleosol types. To determine the nature and origin of the Chaoyang profile, the geographic, stratigraphic and morphological characteristics were described in the field. Bulk samples from 42 horizons were collected for chemical and physical analysis, and sub-sampling of 946 samples at 2 cm intervals from the surface to the bottom were taken to measure grain size distributions and magnetic susceptibility. Results showed that the 19.85 m thick loess–paleosol profile had been continuously deposited since 423 ka BP. The upper part (0–195 cm), or UPP, was predominantly of aeolian loess deposition origin but was mixed with water-reworked materials from a nearby secondary loess source. The middle part (195–228 cm), or MIP, was also indirectly affected by the water-reworking process through the leaching of materials from the overlying UPP. The lower part (228–1985 cm), or LOP, was characterized by four reddish stratigraphic layers interbedded with five yellowish ones, indicating several types of paleosols developed under different ecological environments. The multi-stage paleoclimatic cycles as evidenced by morphological and physical characteristics as well as age dating and magnetic susceptibility correlated well with the Lingtai section and LR04 benthic δ18O. Because of these attributes, the Chaoyang profile can be deemed as a benchmark loess–paleosol profile for the recognition and classification of paleosols and paleoclimate reconstruction in Northeast China. The differences in morphological and physical properties between paleosols and loess suggest different soil fertility and agronomic properties and need further studies to assess their functionality with climate fluctuation.

Discussion of the paper “Loess genesis and worldwide distribution” by Yanrong Li, Wenhui Shi, Adnan Aydin, et al.

Different origins of loess deposits in northern and southern Central Asia are not only associated with Central Asian topography, but also with aeolian dust dynamics. However, the latter has received far less attention so far. This review focuses on atmospheric dust dynamics for loess deposition in Central Asia, aiming to heal this knowledge gap. Comparisons of loess grain size data from the Chinese Loess Plateau, and the northern and southern Central Asia suggested that the Siberian High-pressure system largely controlled dust mobilization and loess accumulation in northern Central Asia, instead of southern Central Asia. The North Atlantic Oscillation (NAO) mode also provided an additional promising solution to trigger of loess accumulation in the North Tianshan Mountains. In southern Central Asia, intensity of dust activity was majorly determined by the Caspian Sea-Hindu Kush Index (CasHKI), with stronger dust dynamics under higher CasHKI modes. However, the causes of variations in the CasHKI intensity represent a future challenge. The CasHKI values also influenced the wind dynamics controlling dust mobilization in the Fergana Valley. Therefore, the Central Asia can be divided into two parts regarding the aeolian dust dynamics, with a boundary located in the North Tianshan Mountains and the south of Aral Sea. The Siberian High and NAO phase appeared to affect the dust activity and loess accumulation in the northern part; while dust entrainment and deposition were mostly determined by the CasHKI mode in the southern part. However, precisely determining the boundary highlights the necessity of investigations on loess deposits in the Tashkent region. In addition, we further recommend that the dynamic linkages between the mid-latitude Westerlies and aeolian loess deposition constitute a future critical research topic in Central Asia.

Accuracy of ESR dating of small gastropods from loess and fluvial deposits in the Bavarian Alpine Foreland

This study focuses on the accuracy of the Electron Spin Resonance (ESR) dating method applied to small land snail shells from eolian loess deposits, and from shell bearing clods of sandy loam and marl in fluvial gravel deposits in the Bavarian Alpine Foreland. Due to the small size of land snail shells and lack of specimens available for ESR analysis it was necessary to reduce individual aliquot sample weights to 0.02–0.07 g. While the reduction in sample weight inevitably lowers the signal-to-noise ratio and thus may also negatively influence the precision on the equivalent dose due to even smallest weight variations between the single aliquots, the dating results are in good agreement with independent age control. In general, the ESR ages are mostly within the age interval of previous and new luminescence or radiocarbon dating results. We show that ESR dating of small terrestrial gastropods in most cases allows differentiating between shells of Holocene, Late or Middle Würmian (last glacial, MIS 3, 2), penultimate glacial (MIS 6) or penultimate interglacial (MIS 7) age with errors between c. 10%–15%.

Stable carbon and oxygen isotopic composition of modern land snails along a precipitation gradient in the mid-latitude East Asian monsoon region of China

The stable oxygen and carbon isotope composition (δ18Oshell and δ13Cshell) of land snail shells preserved in Chinese eolian loess deposits have the potential to reconstruct past changes in the East Asian Summer Monsoon (EASM) since the late Oligocene. To assess the potential of δ18Oshell and δ13Cshell for the semi-quantitative reconstruction of past variations of the EASM, we studied modern snails and the corresponding vegetation composition of three distinct ecosystems (woodland, grassland and mountains), spanning a large rainfall gradient (178–1403 mm) in the mid-latitude East Asian monsoon region. The results show that different snail species in the three ecosystems have significantly different values of δ18Oshell and δ13Cshell. The snails in woodland from the eastern plain area have significantly lower δ18Oshell and δ13Cshell values than those of snails in grassland from the Chinese Loess Plateau, and the snails from the Qinba Mountains region have values intermediate between the two. Systematic variations of the δ13C of snail shells, body tissues and local plants are evident along the rainfall gradient, indicating that δ13Cshell is mainly influenced by the δ13C of ingested plants, which is controlled by the EASM. We confirm that δ13Cshell is a reliable precipitation proxy and we obtained a new empirical equation (δ13Cshell = −0.0030(±0.0003) MAP − 8.80(±0.32), r = −0.76, n = 74, p < 0.001) for the relationship between δ13Cshell and mean annual precipitation, which is based on the results of the present study, together with those of Bao et al. (2018). We infer that δ18Oshell is influenced by precipitation δ18O, and that here is a significant relationship between δ18Oshell and mean annual precipitation (δ18Oshell = −0.0028(±0.0008) MAP − 1.32(±0.58), r = −0.65, p < 0.05, n = 21), possibly because of the rainfall amount effect in the study region. In addition, temperature and evaporation associated with relative humidity play non-negligible roles in determining δ18Oshell, and their effects should be considered before using the δ18O of fossil snail shells to reconstruct precipitation δ18O and/or rainfall amount.

Identification of aeolian loess deposits on the Indo-Gangetic Plain (India) and their significance

Aeolian loess deposits contain abundant information about the evolution of the paleoenvironment. For example, paleoclimate changes recorded in Chinese loess area obtained significant achievement in the past few decades. Compared to Chinese loess, research on Indian loess is lacking. Currently, most studies focus on the Kashmir area located in the southern Himalayas, and studies on other areas are rare. However, field observations demonstrate that the sediments around the New Delhi-Agra-Jaipur Plain are similar to Chinese loess-paleosol sequences. For example, the boundary between two strata is transitional and without horizontal bedding. Moreover, obvious pedogenic horizons developed among sediment sequences, probably indicating unrecognised aeolian deposits in the Indo-Gangetic Plain (IGP). To confirm this, pilot samples were obtained from the IGP and detailed indoor measurements conducted. The results indicate that the distribution patterns of particle size and rare earth elements (REE) of the pilot samples are similar to Chinese loess. Furthermore, the scanning electronic microscopy (SEM) images of pilot samples show obvious conchoidal fractures, dash-shaped concavities, and abundant small pits that usually form through mechanical impact. These are typical characteristics of aeolian particles. In addition, environmental and rock magnetic measurements indicate that the dominant magnetic minerals in the pilot samples are magnetite and maghemite, and that they likely contain small amounts of hematite. Furthermore, conventional magnetic parameters are comparable with Chinese loess. Based on this, aeolian loess deposits are widely distributed in the IGP, which may have promoted the development of Indian farming and contributed towards the prosperity of ancient Indian civilisation. This study also provides a new and valuable record for the research on paleoclimate changes in the study area in the future.

Onset of aridification by 34 Ma across the Eocene-Oligocene transition in Central Asia

Cenozoic climate has changed markedly from a warm, wet climate to the present cool, dry glacial-interglacial cycles. The largest of these cooling steps is thought to have taken place across the Eocene-Oligocene transition. Terrestrial airborne eolian loess is a direct result of land aridification; therefore, the prolonged formation of thick eolian loess deposits provides a key to aridification history in the geological past. However, the oldest eolian loess in the Asian interior has been dated to only 25–22 Ma. Here we present new sedimentological, geochemical, and magnetostratigraphic data from Cenozoic sections in southwestern Mongolia to show that the earliest eolian dust accumulation occurred by 34 Ma, ∼10 m.y. earlier than currently believed. We suggest that this oldest eolian dust accumulation provides direct evidence for enhanced aridification across the Eocene-Oligocene transition in Central Asia; this is explicable by reduced moisture transport caused by prevailing westerlies during retreat of the Neotethys Ocean. These climatic changes were related to the changing regional plate configuration as well as to global cooling and ice-sheet growth in Antarctica.

Quartz OSL and K-feldspar pIRIR dating of a loess/paleosol sequence from arid central Asia, Tianshan Mountains, NW China

Loess deposits surrounding the high mountainous regions of arid central Asia (ACA) play an important role in understanding environmental changes in Eurasia on orbital and sub-orbital time scales. However, problems with dating loess in ACA have limited the interpretation of climatic and environmental data, especially Holocene data. We selected a typical loess/paleosol sequence (LJW10) on the northern slope of the Tianshan Mountains in ACA consisting of 280 cm of loess with multiple paleosols formed in the upper 170 cm of the section. We applied quartz OSL dating to coarse-grained (63–90 μm) fractions, and newly developed K-feldspar pIRIR dating protocols to both coarse-grained and medium-grained (38–63 μm) fractions of the samples from LJW10 section. Internal checks of the quartz OSL dating indicate that the single-aliquot regenerative-dose protocol on large aliquots (5 mm) is appropriate for equivalent dose (De) determinations and that the quartz ages of the loess samples are likely to be reliable. Luminescence characteristics and internal checks of the pIRIR dating indicate the pIRIR signal at a 170 °C stimulation temperature with a 200 °C preheat can be used for both coarse-grained and medium-grained De determinations. Anomalous fading tests for the pIRIR 170 °C signal indicate the pIRIR signals are stable and the anomalous fading of the pIRIR 170 °C signal can be ignored. Sunlight bleaching tests of the loess indicate the residual dose for the pIRIR 170 °C signal can also be ignored as it corresponds to only ∼9 years for the medium-grained K-feldspar and ∼85 years for the coarse-grained K-feldspar. The pIRIR ages of five medium-grained and coarse-grained K-feldspar samples are consistent with coarse-grained quartz OSL ages, and both the medium-grained and coarse-grained ages increase uniformly with depth, indicating these pIRIR ages are reliable. Based on the coarse-grained quartz OSL ages, and on coarse-grained and medium-grained K-feldspar pIRIR ages, an age-depth model for the paleosol-loess sequence was established by using a Bacon age-depth model. This model suggests eolian loess deposition began by at least ∼16 ka ago and that paleosol development on these eolian loess deposits began ∼5.5 ka, continuing to the present, with periods of high effective moisture at 5.5–4.9, 4.6–4.1, and 3.4–3.1 ka. This sequence suggests overall relative aridity during the early Holocene and an increase in effective moisture beginning ∼5.5 ka during the mid-late Holocene in ACA.

Geochronological reconsideration of the eastern European key loess section at Stayky in Ukraine

Abstract. Event-stratigraphical correlations between regional terrestrial sedimentary archives and marine or ice-core records that provide climate history are highly desirable for a deeper understanding of the effects of global climate change. However, such correlations are not simple, as the terrestrial records tend to be floating and fragmentary, and usually show varying sedimentation rates. Therefore, a reliable chronometric framework is a prerequisite for any event stratigraphy involving terrestrial archives. We propose that the age model underlying the event-stratigraphical approach for the eastern European key loess section at Stayky in Ukraine needs revision. Here we explore why it is unlikely that the Middle Pleniglacial Vytachiv Soil developed during Greenland interstadial (GIS) 8, and why the embryonic soils in the upper part of the Upper Pleniglacial part of the loess section most likely post-date the Heinrich 2 event. As a consequence, the revised age-model challenges the earlier suggested correlation of the suite of incipient soils above the Vytachiv Soil with Greenland Interstadials, which was supposed to start with GIS7 but for which matching from after GIS5 seems more likely. The revised chronology suggests that the transition from Middle to Upper Pleniglacial environmental conditions at the eastern European key section occurred during the final phase of marine isotope stage (MIS) 3. Thus, the picture appears to be in accordance with that of the western European key section at Nussloch. This points to a common driver of palaeo-environmental change in both regions, such as early late glacial maximum (LGM) advances of the Arctic ice shield or changes of the North Atlantic circulation and sea-ice distribution associated with changes in the palaeowind field relevant to aeolian loess deposition and soil formation. To test and substantiate the alternative age model, more chronologies for well-stratified loess sections throughout the European loess belt are required.

OSL dating of offset streams across the Altyn Tagh Fault: Channel deflection, loess deposition and implication for the slip rate

Two deflected streams flowing across the Altyn Tagh Fault (ATF) were investigated at the Aksay segment, NW China. Due to strike of the ATF, stream channels are deflected and elongated by adding new sections along the fault line. After subsequent water erosion and fluvial refreshment, banks of these deflected streams are overlain by aeolian loess. Geomorphological features suggest that stream deflections along the fault were developed as a result of faulting activities and displacements were progressively accumulated from multiple faulting cycles. Each faulting cycle is composed of faulting event triggered elongation of channels, creation of stream banks or risers and subsequent aeolian loess deposition on the banks. A model is proposed to illustrate the relationship between fault movement and loess deposition, which is supported by OSL dating of the loess on the offset stream channels. Our results demonstrated that: (1) loess deposits along deflected streams can be used to trace fault slip history, given specific geomorphic assumptions discussed in the text; and (2) based on stream channel offsets and loess ages, the Holocene slip rate of the ATF is estimated to be 11±2mm/year along the Aksay segment.

Reconstruction of Late Neogene paleoenvironmental changes in the area of Pannonhalma (Western Hungary) using granulometric methods

A generalized section of the Pannonhalma Hills has been compiled and analysed. The stratigraphic column of the section represents the paleoenvironmental and paleoclimatic changes of the last ca. 7–8 million years. The elevated old strata also comprise the deposits of the Lake Pannon, overlain by Plio-Pleistocene terrestrial sediments. The generalized section consists of shallow freshwater, fl uvial sediments and Pleistocene eolian loess deposits. These strata can be correlated with Austrian outcrops (e.g. at Gollersdorf), situated at the northern margin of the Little Hungarian Plain. The black freshwater clay strata differ markedly from other clay horizons, and can be considered and applied as marker horizons in correlative studies. This black clay is the product of fi rst appearance of rivers in the region. A detailed granulometric analysis has been performed to refi ne the results of paleoenvironmental reconstructions for Transdanubia.

Paleoclimatic evolution of Holocene loess and discussion of the sensitivity of magnetic susceptibility and median diameter

Climate changes are closely related to peoples' livelihoods. Holocene climate changes are therefore particularly important to humans. It is known that eolian loess deposits in China are one of the best geological records for paleoclimatic change. As it is the top layer of loess sequence, Holocene loess may be easily disturbed by human activities. For that reason, it has not been studied thoroughly. Recently, a continuously deposited, high-resolution and well-preserved Holocene loess section has been found in Baicaoyuan, Huining County, Gansu Province, located in the northwest edge of the Chinese Loess Plateau. The magnetic and grain size signals of the section reflect Holocene paleoclimate variations and are comparable to the stalagmite oxygen isotope records of Sanbao and Hulu caves. They consistently record the general evolution process of Holocene paleoclimate in Eastern Asia. During the period 14.2–12.8 ka BP, Last Glacial Maximum turned into Holocene transition phase. During 12.8–11.5 ka BP, the climate was cold and dry, dominated by the Younger Dryas. Between 11.5 and 10.5 ka BP, the climate rapidly turned warm and wet, and 10.5–5.2 ka BP was the Holocene Optimum Period, during which some relatively dry-cold events could be observed. Since 5.2 ka BP, the climate slowly became dry and cold. In summary, the climate showed a general drying trend from the early Holocene to the late Holocene, which was controlled by variation of solar radiation. Compared with magnetic susceptibility, the median diameter curve fluctuates frequently. Some climate events were recorded by the median diameter curve, but not observed in the magnetic susceptibility curve. It is suggested that the grain size parameter is more sensitive to paleoclimate changes than susceptibility at the Baicaoyuan section during the Holocene.

Chronology of the Holocene loess-paleosol section and its deposition and pedogenesis on the south of Chinese Loess Plateau

Optically stimulated luminescence (OSL) dating for polymineral fine-grained loess samples, collected in Laoguantai (LGT) section on the south of the Chinese Loess Plateau, was made by application of single-aliquot regenerative-dose (SAR) protocol. A ‘Double-SAR’ procedure in which aliquots are subjected to both infrared (IR) and blue stimulations was used, and two sets of equivalent dose (De) determinations were produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively. The OSL ages estimated from IRSL signals are smaller than those estimated from [post-IR] OSL signals due to the anomalous fading of feldspar IR signals, based on fading experiment. The young ages of the samples near ground surface may be originated from the post-depositional disturbance by the intensifying humanity’s cultivation since 3.0 ka BP in the Guanzhong Basin, south of the Chinese Loess Plateau. Based on OSL dating, as well as field observations and stratigraphic correlation, we determine the chronology of the LGT loess-paleosol sequence. In combination with climate proxy records, it is indicated that aeolian loess deposition and pedogenesis underwent polyphase changes during the Holocene, likely to have been driven by shifts in the East Asian monsoon. This suggests that aeolian loess deposition is episodic and highly variable, with contributions from non-aeolian processes such as alluvial deposition found in the area.

Paleomagnetic dating of the topmost terrace in Kouma, Henan and its indication to the Yellow River’s running through Sanmen Gorges

In the east of Xiaolangdi, many river terraces are developed at the exit of the Yellow River Gorges. Among them the terraces in Kouma, Yanshi of Henan Province are most typical, where the Yellow River developed three staircase terraces, among which the altitude of gravel stratum of the topmost terrace is 30-35 m higher than the river level. The top of the gravel stratum was covered by 60 m eolian loess deposits which have many brownish-red paleosol strips. And the paleosol S-14 is at its bottom. Research on systematic magnetostratigraphy and paleosol-loess matching indicates that the bottom age of the loess on the topmost terrace is 1165 ka. Therefore, it can be concluded that the terrace develops no later than 1.165 Ma and the situation that the Yellow River runs through Sanmen Gorges and inpours into East China Sea happened at least before 1.165 Ma.

Geochemical and isotopic studies of aeolian sediments in China

AbstractThe Sr and Nd isotopic, rare earth element (REE) and major element compositions, together with mineral and grain‐size proportions, are reported for aeolian loess deposits and desert sands from several Chinese localities. The study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments, and to constrain the provenance of Chinese loess. Samples include loesses from the Tarim and Junggar basins and desert sands from the Taklimakan desert in north‐west China, loess from the Ordos area and desert sands from the Tengger and Mu‐us deserts in north‐central China, as well as loess and desert sands from the Naiman area, north‐east China. REE distributions show minimal variation among the Chinese loess deposits, whereas those for the desert sands show regional variations. New isotopic data document a latitudinal variation in Sr and Nd isotopic features for the loesses and desert sands. The Naiman and Junggar loesses have distinctly lower 87Sr/86Sr ratios and higher εNd(0) values than the loesses from the Tarim Basin, the Ordos area and the Loess Plateau. Among the desert sands, the Naiman samples have higher εNd(0) values than the Taklimakan, Tengger and Mu‐us samples. Isotopic data suggest that loesses of the Loess Plateau were supplied from the Tarim Basin loesses and Taklimakan Desert sand, and that the Naiman loesses were supplied from the Junggar Basin loesses. The latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the Tianshan and west Kunlun Mountains, which are possible sources for the loesses and desert sands. These inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over East Asia.

Heavy mineral record of the Holocene environment on the Loess Plateau in China and its pedogenetic significance

Three, sections of Holocene loess on the Loess Plateau were studied to document environmental and pedogenetic changes in heavy minerals in the fine sand to fine silt fraction (0.25-0.01 mm). The sections were in a north-south transect and ranged in age from 10 000 ± 200 year B.P. to the present. The heavy minerals consist mainly of homblende, epidote and opaque minerals. However, there are differences in the content of unstable minerals and in the surface characteristics of grains. Indices based on mineral ratios and grain surface characteristics suggest that the so-called Heilutu soil, which has been recognized as a modern soil, was subjected to variations in natural weathering conditions, aeolian loess deposition and human impacts. Its profile indicates that it is a polygenetic soil.