Loess Accumulation Research Articles

Neogene–Quaternary Channel Evolution and Provenance Shift of the Middle Yellow River

AbstractThe formation age of the middle Yellow River and the existence of a northward‐flowing river have been fiercely debated. The age distribution of detrital zircon varied spatiotemporally and produced contradictory provenance interpretations. The Jinshaan Gorge, the main part of the middle Yellow River and key to studying fluvial evolution and clarifying disputes, developed its topography during the late Cenozoic. In this study, we systematically review the Cenozoic tectonic evolution of the North China Craton, perform detrital zircon U–Pb dating in the Neogene−Quaternary sediments and investigate the topography along the Jinshaan Gorge, and the sedimentology and chronological framework of these sediments. We propose that the Gorge of the middle Yellow River could have developed since the Neogene, controlled by the tectono‐geomorphologic evolution of the North China Craton in a dominantly extensional environment. No evidence supports a northward‐flowing river during the Early Pleistocene or even earlier in the Jinshaan Gorge. We attribute the provenance variations of the Cenozoic sediments to detrital mixing of diverse geological units, local and distant, and especially highlight the systematic provenance shift between the Neogene and Quaternary sediments caused by bedrock downcutting and recycling aeolian sediments. The increased 1.5−0.33 Ga component of the lower Yellow River during the Early Pleistocene was likely caused by enhanced loess accumulation and should not be individually used as a proxy for the Yellow River formation. We emphasize the significance of a comprehensive study of river evolution.

Dynamic landscape response to Younger Dryas and earliest Holocene cooling events in the European Eastern Alps (Austria)

In classic loess areas research into dust deposition and concomitant environmental changes has a long history and numerous well-investigated loess-palaeosol sequences provide insights into Late Quaternary landscape responses to climatic change on orbital to centennial time scales. This contrasts with mountain regions, where an understanding of dust deposition under rapidly changing climatic and environmental conditions is much less developed. Here we describe two sediment records from the Austrian Alps that provide rare evidence for intramontane loess accumulation. Dust deposition has been numerically constrained to the Younger Dryas (YD) to earliest Holocene interval, making these sites the first proof of significant intramontane aeolian activity during this time interval in the Eastern Alps.At study site 1, located in the Northern Calcareous Alps, a loess layer 10–20 cm in thickness and laterally exposed over more than 300 m is sandwiched into an alluvial-fan succession. Two optically-stimulated luminescence ages of quartz and four radiocarbon ages of charcoals indicate loess accumulation during the Younger Dryas to earliest Holocene. This laterally extensive loess drape suggests much drier climatic conditions compared to today, which is corroborated by palynological investigations. Macro- and micro-charcoal particles within the loess indicate regional wildfires that might have exaggerated climatically induced sedimentary processes. The second site is a Mesolithic site located ∼30 km southeast of site 1. At site two, redeposited till and pebbly scree are sharply overlain by a few centimetre thick light-grey loess layer, which is capped by the archaeological living floor hosting 14C dated fireplaces suggesting human presence as early as 10.9 ± 0.2 cal ka BP. These radiocarbon ages in combination with single-grain IRSL dating of feldspar at site two suggests concomitant aeolian deposition at site 1 and 2.Recently, a widespread drape of loess deposited immediately subsequent to the LGM was described for the same sector of the Eastern Alps (Gild et al., 2018). The present study expands on these findings and provides evidence for the recurrence of loess deposition also during the YD to earliest Holocene, and suggests a highly sensitive response of the geomorphic system in mountain ranges to abrupt post-LGM climate fluctuations. We conclude that, in addition to moraine records of Alpine glaciers and speleothems that accurately chronicle Late Glacial temperature fluctuations, the spatio-temporal pattern of inner-Alpine loess deposits records the mode and sensitivity of landscape responses to such cooling events. Because such aeolian sediment layers can be redeposited or pedologically overprinted, they are often overlooked, and are thus still severely under-researched.

Phosphorus dynamics across a 450 ka vertical chronosequence of loess derived (paleo)soils in central US

Pedogenesis entails profound changes in terrestrial phosphorus (P) dynamics, yet means to understand how time- and climate-induced soil weathering impacts P-cycling over geologic timescales remain relatively limited to space-for-time substitution approaches with multi-site chronosequences. We tested an alternative approach for evaluating terrestrial P dynamics described by the Walker-Syers model by measuring P pools in a ~ 450 ka loess–paleosol sequence. This vertical chronosequence reflects episodic proglacial loess deposition during multiple glaciations and interglacial soil development in central North America in a four-stage loess–paleosol sequence that initiated with the pre-Illinois Episode glaciation. Changes in P pools estimated by sequential fractionation aligned with the Walker-Syers P model for interglacial periods but not glacial periods, possibly reflecting limited soil weathering in cooler and drier conditions of the latter. Total P decreased from 797 to 328 mg/kg with depth and was higher in paleosols than underlying loess parent materials. During glacial periods, primary P increased due to loess deposition and decreased during interglacial periods concomitantly with increased non-occluded and occluded secondary P pools, the extent of which reflected differences in weathering environments of paleoclimatic conditions and loess accumulation rates. That P fractions reflected the Walker-Syers model demonstrates that single-site vertical chronosequences have potential for evaluating long-term soil P dynamics.

High resolution luminescence and radiocarbon dating of Holocene Aeolian silt (loess) in west Greenland

Loess–palaeosol sequences serve as valuable archives of changes in climate and atmospheric mineral dust deposition. However, little work has been conducted on Holocene loess in the Arctic, despite the sensitivity of this region to climate changes. Aeolian silt/loess profiles in the ice-free region of western Greenland near Kangerlussuaq were sampled to develop a robust age framework using both luminescence and bulk organic matter radiocarbon dating. Radiocarbon ages generally show consistent age increases with depth but are likely offset to younger ages due to sediment mixing in the upper 10–20 cm of the profiles. Quartz OSL signals exhibit insensitivity, while low-temperature infrared stimulated luminescence performed at 50 °C (IR50) and the post-IR IRSL at 180 °C (pIRIR180) signals of polymineral fine grain revealed a consistent natural inherited dose of approximately 5 Gy for pIRIR180 and an unbleachable residual of around 2 Gy for IR50, with substantial fading rates in the latter. This led to a notable age overestimation when compared with bulk organic matter radiocarbon ages. To develop an appropriate dating approach, we evaluated the differential bleaching rates of feldspar IR50 and pIRIR180 signals, and corrected for modern inherited doses. Radiocarbon ages measured on the bulk organic carbon oxidised at 400 °C (LT 14C) increased very consistently with depth, allowing calculation of accumulation rates. The presence of the atmospheric radiocarbon bomb signal at depth indicated down-mixing of surface material into the profile, which caused negative (younger) age offsets. The offset-corrected radiocarbon-based age-depth model could be compared to the luminescence results.We show that a combination of LT 14C with polymineral pIRIR180 dating allows the development of age models for these deposits. This multi-chronological approach reveals that loess accumulation in the region was initiated around 4 ka, probably consisting of two main phases of loess accumulation at 4–3 ka and <1 ka. The initial phase matches the proposed onset of aeolian sand activity in the wider region, but post-dates local ice retreat by c. 3 kyr. The more recent phase of accumulation also matches the timing of increased sand accumulation in the region and likely coincides with Neoglacial to Little Ice Age ice advances, or even enhanced dust activity in the last decades.

Sub- and supra-moraine loesses in the Vistula catchment (Poland) with regard to the age and extentof the Scandinavian ice-sheets

The study focuses on the geochronology and correlation between loesses and glacial tills in the Vistula catchment in Poland, in an area covered by all Scandinavian ice-sheets and characterized by thick loess successions. The basis for this correlation was a litostratigraphic analysis of selected loess sites in the uplands, which are well-documented in the literature, and the occurrences of loess and loess-like deposits under the cover of glacial deposits in the lowland part of the Vistula catchment, characterized by a much sparser documentation. The nomenclature of loess horizons follows Maruszczak (2001) and Kukla (1987), but sometimes is significantly changed, according to modern Quaternary stratigraphical schemes. According to the analysis, accumulation of almost all loess horizons distinguished so far has been documented in the Pleistocene succession of the Vistula catchment: the oldest – lower (LNd), middle (LNs), and upper (LNg); older: lower (LSd), middle (LSs), and upper (LSg); and younger: lowest (LMn), lower (LMd), middle (LMs), and upper (LMg). In most cases loess accumulation took place in steppe-tundra conditions preceding the maximum ice-sheet development during the succeeding Scandinavian glaciations. For selected sites, the loess occurrence is presented in superposition to glacial tills and interglacial deposits. The distinguished loesses and glacial tills are tied to the stratigraphic schemes of the Pleistocene in Poland (Marks et al. 2016, 2019) and correlated with Ukrainian loess horizons (Łanczont et al. 2019).

Re-evaluating the origins of sands in the Gurbantunggut Desert and its role as an aeolian dust contributor

We analyzed the trace and rare earth element contents of the desert sands and loess deposits in the Junggar Basin. Combined with previously published data, and using principal component analysis, our results provide insights into the sand provenances of the Gurbantunggut Desert in eastern Central Asia (CA); the genetic links between deserts and loess deposits in CA; and the specific sources in CA for the aeolian dust in North Pacific Ocean sediments. The results demonstrate the spatial heterogeneity of the geochemistry of sand across the Gurbantunggut Desert. The desert sands in the northern and western parts of this desert are mainly derived from the Altai and Junggar mountains, respectively, as supported by the directions of sand fluxes. However, Beitashan Mountain makes a negligible contribution due to the lack of fluvial transport and westward sand fluxes. However, more sediment samples need to be collected to confirm the contribution of Tianshan Mountains. Our findings also indicate that the Gurbantunggut Desert did not contribute significantly to loess accumulation on the northern slopes of the Tianshan Mountains, in accordance with the weak genetic relationships between loess deposits and deserts in western CA. We attribute this to the limited ability of the CA deserts to produce and supply dust-sized particles. Additionally, using the Metropolis-Hastings sampling approach, we find that the Gurbantunggut Desert is not the source region in CA for the fine dust particles in North Pacific Ocean sediments. Overall, our results contribute to a deeper understanding of the aeolian systems in CA and their impacts on the dust cycle at a hemispheric scale.

Updated chronology for Peoria Silt (loess) accumulation in Illinois and western Indiana from radiocarbon dating of terrestrial gastropod shells

AbstractBased on calibrated radiocarbon ages of terrestrial gastropod shells (Succineidae, Discus, Stenotrema, Webbhelix), the chronology of Peoria Silt (loess) deposition in the Central Lowlands is updated. These taxa provide reliable ages (within ~0.2 ka), based on historical shell dating, shell-organic age comparisons, and stratigraphic consistency. A compilation of 53 new and 36 published Peoria Silt shell ages (calibrated), from 12 localities, date from 30.0 to 17.4 ka. Proximal (fossiliferous) loess from 10 sections had mean loess accumulation rates of 0.6–2.2 mm/yr. Study sites along the upper Mississippi, Illinois, to mid-Mississippi, and Ohio-Wabash Valleys suggest Peoria loess accumulated from ~27 to 15 ka, ~29 to 18 ka, and ~30 to 18 ka, respectively. The cessation age for Peoria Silt, based on surface extrapolations, is ~1–6 ka earlier than some prior Illinois estimates, even assuming slower loess accumulation in the modern solum. Younger loess in northwestern Illinois likely reflects, in part, Superior and Des Moines Lobe glacial-meltwater sediment, and Iowan Erosion Surface inputs to the upper Mississippi Valley, after the Lake Michigan Lobe receded. Furthermore, stronger winds, drier conditions, and reduced vegetation cover in valley deflation areas may have favored higher accumulation rates and later loess deposition in northwestern relative to southeastern areas.

Early Holocene occurrence of loess in Folldal, east-central southern Norway: Identification, origin and palaeoclimatic significance

Identified for the first time in Norway, windblown yellowish-brown dust in Folldal, east-central southern Norway, fulfils physical and geochemical criteria for sensu stricto loess, including a high carbonate content. Two extant and one relict marl pond located on low-carbonate rocks are investigated. An allochthonous origin for the marl ponds is suggested and explained by the deposition of suspended clastic carbonate as loess by aeolian processes. The scattered geographical distribution of loess and the need for a calcareous source area suggest a W-SW provenance from a relict valley sandur/existing flood plain in upper Grimsdalen. The mean grain size (~22.4 µm) of the aeolian silt is in the finer range of average loess, explained by the up to 25–30 km long transport and approximately 250–300 m airborne uphill move from the suggested source area to the marl ponds. Based on age-depth modelling using 9 AMS radiocarbon dates, loess deposition occurred from ca. 10,390 to 9780 cal. yr BP (610 years). Two prominent periods of loess accumulation occurred from ca. 10,390 to 10,190 (200 years) and ca. 10,020–9950 (70 years) cal. yr BP. Loess deposition results from W-SW wintertime winds in a dry to semi-arid climate. In southern Norway, W-SW winds in winter are associated with a positive mode of the North Atlantic Oscillation (NAO). From source to deposition, the response time to erode, transport and accumulate loess is suggested to be seasonal to 1 year. An immediate increase in organic production followed loess deposition as early initiation of a warmer and wetter Holocene climatic optimum.

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.

The indicative significance of grain size end-members and quartz surface microtextural features in Beglitsa loess sections at the Sea of Azov

The loess accumulation processes in the Azov Sea region leaves a record of atmospheric circulation trends in southern Russia, which can be used to explore aeolian dynamics and atmospheric circulation evolution. However, the historical aeolian transportation and accumulation processes of the loess deposits in this region remain controversial, which limits our understanding of aeolian dust dynamics. In the present study, based on grain size analysis and scanning electron microscopy imaging, grain size end-member and microtextural characteristics of loess sediments in the Beglitsa section of the Sea of Azov were studied to reveal their sedimentary environments and processes. According to the results, the Beglitsa section exhibits typical characteristics of aeolian sediment. EM analysis revealed that the Sea of Azov loess is composed of materials from both distant and proximal sources transported by high-altitude westerly and mesoscale regional winds, respectively. Particle shape and morphology indicated that the Azov loess materials have experienced wind and flow action. The application of the two methods revealed that the formation of the Azov loess is a complex process from source to sink. It results from the combined effects of high-altitude westerly winds, low-altitude local wind systems, and near-surface air flow in the course of development, which is also influenced by sea-level rise and fall. The results of the present study lay a foundation for the interpretation of historical aeolian dynamics and environmental significance of the Azov loess.

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

&#x0D; &#x0D; &#x0D; 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 / &lt;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.&#x0D; &#x0D; &#x0D;

A categorical quantification of the effects of vegetation restorations on streamflow variations in the Loess Plateau, China

The Loess Plateau is the world’s largest and most typical loess accumulation area, and its recent change in vegetation cover has had significant hydrological effects. Understanding the impact of vegetation restorations in this region is essential for local water security and the sustainable development of Loess regions. This investigation concentrates on the upper basin of the Beiluo River, a representative watershed on the Loess Plateau. Using the coupled application of the hydrological model and the DFI baseflow segmentation method, as well as the analysis of extreme land cover transfer scenarios, the impact of typical land cover transition categories on the watershed runoff process on the Loess Plateau is systematically evaluated. Depending on the change in runoff introduced by the unit transfer area, a rapid estimation method for river runoff in the Loess Plateau is proposed. The results show that base flow contributes considerably to river runoff on the Loess Plateau, and the SWAT-DFI coupling has substantially improved the hydrological model’s simulation accuracy during the dry season. From 1985 to 2020, the primary land cover transfer categories in the upper basin of the Beiluo River were agricultural land to the forest (AL2F), agricultural land to pasture (AL2P), pasture to agricultural land (P2AL), and pasture to the forest (P2F), of which P2AL is the only form of transfer that increases discharge. From a spatial perspective, the intensity of the impact of AL2F and AL2P on runoff is greater in the upstream region than in the downstream region. From the standpoint of land cover transfer type, the intensity of runoff depth change caused by transfer per unit area varied, which was primarily manifested by the fact that the impact of AL2F was greater than that of AL2P, both of which were greater than that of P2AL and significantly higher than that of P2F. The proposed rapid estimation method based on land cover transfer equivalents can rapidly estimate river runoff changes and spatial distribution under various land cover change conditions, which is critical for understanding the hydrological effects of vegetation restoration on the Loess Plateau. The quantified effect of land cover change on runoff and the proposed quick estimation approach can serve as benchmarks for water security and ecological restoration on the Loess Plateau and other loess accumulation areas around the globe.

Evolution of loess-paleosol sequence from the perspectives of thermodynamics and microstructure

The process of entropy increase can promote the formation and transformation of natural structures, and also provide information on the evolution process of some inherently complex structures in nature. However, this process has rarely been discussed in the evolution of loess-paleosol sequences. In this study, taking the Xiushidu section of Jingyang as an example, we deciphered the evolution process of a loess-paleosol sequence from the perspective of thermodynamics and microstructure. The configuration entropy of microstructure was found to be sensitive to subtle differences and can be regarded as a new climate indicator. In other words, entropy values changed periodically in the loess strata, with paleosol layers showing lower values than the adjacent loess layers. In addition, the relationship between configuration entropy and external entropy flow induced by climatic change played an important role in the evolution of loess-paleosol sequence. During the paleosol development period, the soil structure underwent continuous change driven by strong weathering and pedogenic processes. The significant structural changes might have entered a new orderly state of the system. In contrast, during the loess accumulation period, the external conditions did not satisfy the threshold of qualitative change, and the soil structure continued to develop toward a disordered state. In the context of thermodynamic entropy, the evolution of the loess-paleosol sequence is a result of alternation between the “near disordered state” and “dissipative structure”. Macroscopically, the change process of the geological system was a dynamic cycle: an open system that constantly experienced a cycle of “external entropy input”-“self-adjustment”-“external entropy input”. We define the above entropy change process as a thermodynamic conceptual model of the loess-paleosol sequence evolution. These findings provide a new thermodynamics approach for deciphering loess-paleosol sequences.

Experimental study on strain accumulation characteristics of saturated remolded loess under pure rotation of the principal stress axis

The study conducted a pure rotation test of 720° for saturated remolded Q2 loess under principal stress axis (PSA) rotation when deviatoric stress and the intermediate principal stress ratio are different, also paying attention to examining the changes of strain accumulation and pore pressure of such loess. According to the test, as the PSA rotates continuously, the pore water pressure exhibited by saturated remolded loess presents a normal cyclic accumulation elevation, and under the same deviatoric stress conditions, the pore water pressure accumulation trend of different principal stress ratios is the same; however, the magnitude is different. The increment of pore water pressure becomes smaller as the number of cycles increases. When the deviatoric stress level is low, the material hardening is in a cyclic stable state, the strain component remains stable with the continuous rotation of the PSA, and the strain path area is reduced, together with a stable final size. In case of higher deviatoric stress, the material strength cycle becomes weaker and the strain component accumulates slowly as the PSA (the spiral line of the strain path) continuously rotates in the γzθ−(ϵz−ϵθ) plane, and gradually expands until failure. The increased intermediate principal stress is accompanied by accelerated strain development speed and advanced failure.

Characterization and sources of water-soluble inorganic ions during sulfate-driven and nitrate-driven haze on the largest loess accumulation plateau

With the rapid reduction of anthropogenic SO2 emissions, the critical driver of haze in China has shifted from being dominated by sulfate to alternating sulfate and nitrate. Haze induced by different driver species may differ in the chemical forms of water-soluble inorganic ions (WSIIs). The unique topography and high-emission industrial agglomeration of the Loess Plateau determine its severe local PM2.5 pollution and influence global weather patterns through the outward export of pollutants. PM2.5 samples were conducted in Pingyao, on the eastern Loess Plateau of China, in autumn and winter. The average mass of PM2.5 was 88.82 ± 57.37 μg/m3; sulfate, nitrate, and ammonium were the dominant component. The chemical form of the ion was dominated by (NH4)2SO4, NH4NO3, NaNO3 and KNO3 during the nitrate-driven (ND) haze, while (NH4)2SO4, NH4HSO4, NH4NO3, NaNO3 and KNO3 were predominant species during the sulfate-driven (SD) haze. Heterogeneous oxidation reactions dominated the mechanism of sulfate formation. Primary sulfate emissions or other generation pathways contributed to sulfate formation during the SD haze. The gas-phase homogeneous reaction of NO2 and NH3 dominates the nitrate generation during the ND haze. The heterogeneous reactions also played an essential role during the SD haze. Nitrate aerosol (42.30%) and coal and biomass combustion (23.23%) were the dominant sources of WSIIs during the ND haze. In comparison, nitrate aerosol (31.80%) and sulfate aerosol (25.08%) were considered the primary control direction during the SD haze. The chemical characteristics and sources of aerosols under various types of haze differ significantly, and knowledge gained from this investigation provides insight into the causes of heavy haze.

Loess microstructure indication indexes for the study of palaeoclimatic conditions in northwest China

AbstractThe Loess Plateau of China, located to the west of the Liupan Mountains and north of the Qinling Mountains stretching across the Yellow River, is the main loess deposit area in Northwest China. The loess in the northwest of China has deposits with large thickness and extensive distribution. Scanning electron microscopy (SEM) and energy spectrum analysis of loess have been performed to study the relationship between the loess microstructures and the forming climates Era. The relevant indexes were evaluated including the sand‐dropping speed (Vn), certain sedimentary depths (hn sand particle volume (Vd) and element ratios of Ca/Fe, K/Al, Si/Al and Ca/Mg. The microstructure indexes of loess accumulation and evolution reflect paleoclimate conditions and time scales to a certain extent. The important discovery is the microscopic sand‐dropping speed (Vn) and the sedimentary depth hn) calculation method of different sedimentary ages. These indices are compared with the record of major aeolian‐forming climates from the Guliya ice core, and provide a reliable benchmark for studying climate change It also can be used as important indicators of monsoonal change and environmental evolution reconstruction. The index of sand sedimentation speed (Vn) got from loess microstructure could reflect sand‐dropping speed and loess deposition course. According the article can serve as new indicators of climatic changes of different forming loess layers. It can also be concluded that the climatic indexes obtained from loess microstructure can reflect climate conditions of loess forming. The loess forming climatic parameters are synchronous correspond to Tengger Desert and Guliya ice core for studying climate change, then microscopic parameters can also be used for preliminary analysis of loess climate formation and has be found corresponding evidence, and the loess climatic parameters correspond to the other two indexes. The analysis of loess microstructure indexes is very useful in researching climate change. Loess microstructure indexes can find new indicators and information about the monsoon climate evolution and paleoclimate changes.

The origin and transformation of soil lamellae in calcareous and non-calcareous loess soils in the Central European loess belt – A case study from southern Poland

Loess in Europe is heterogeneous due to differences in paleoenvironmental conditions during sedimentation and pedogenesis. In many regions of Europe, including southern Poland, loess accumulation was followed by the leaching of carbonates followed by clay translocation, which is typical in silty soils in humid climates. Loess soils in the temperate climate zone are characterized by the presence of well-developed or well-preserved microfabrics of different origin but with similar morphology, among which lamellae can be distinguished. Lamellae commonly occur in loess soils; however, detailed studies focused on their origin and evolution are lacking. The main aim of the present study was to determine the origin and transformation of lamellae both in calcareous and non-calcareous loess soils in the Central European loess belt, using an example from southern Poland. The following three hypotheses were tested: (1) decalcification of the upper part of loess soils is a necessary condition for soil lamellae formation, while frost action is not a key factor shaping their morphology and properties in the Central European loess belt, (2) occurrence of carbonate in the lower part of calcareous loess soils inhibits lamellae formation, (3) soil lamellae are transformed due to bioturbation and shrinking-swelling processes in both calcareous and non-calcareous loess soils. The obtained results indicate that decalcification of the upper part of calcareous loess soils enables the translocation of clay particles and lamellae formation. Field observations and micromorphological analysis indicate that the presence of carbonate limits the development of soil lamellae and constitutes a barrier to deeper clay translocation in loess soils. This finding suggests a pedogenic origin of lamellae in the loess soils of southern Poland. Soil lamellae show a number of signs indicating their mechanical degradation due to swelling and shrinking, bioturbation, and dissolution driven by eluviation and redox processes. The progressive evolution of lamellae leads to an enhancement of their expression in the illuvial Bt and transitional BC horizons.

Aeolian process and climatic changes in loess records from the eastern Tibetan Plateau: Implications for paleoenvironmental dynamics since MIS 3

The Tibetan Plateau (TP) is extremely sensitive to climate change. However, climate variability during the last glaciation in the TP is not well-understood. The widely distributed loess deposits on the eastern TP serve as a significant archive for retrieving past climate changes and aeolian dust dynamics. Through detailed quartz optically stimulated luminescence and radiocarbon dating and the analysis of environmental proxies, we have established a reliable chronology of the Maerkang loess sequence in the eastern TP and reconstructed well-constrained histories of dust activities and environmental variation. Our results demonstrate that the accumulation of aeolian loess in this region occurred at least 60 thousand years ago. The dust mass accumulation rate (MAR) varied highly in the last glacial period, with high MARs in the Last Glacial Maximum and relatively low MARs in marine isotope stage (MIS) 3. Humid conditions occurred in MIS 3 (approximately 50–32 ka) due to the intensified Indian summer monsoon. The rapid climate variations of the Maerkang loess might be correlated to the Dansgaard–Oeschger cycles and the Heinrich events, which implies the significant impact of the North Atlantic climatic system on the TP. Our findings provide new evidence for a better understanding of the history of environmental variations since MIS 3 in the eastern TP.

High-resolution OSL dating of loess in Adventdalen, Svalbard: Late Holocene dust activity and permafrost development

There is considerable uncertainty over the nature and causes of Holocene dust activity in the Arctic, and its links to climatic changes. Loess deposits act as near-source archives of dust deposition and provide a means to address these uncertainties. Here we develop a fully independent age model for a loess core taken in Adventdalen, Svalbard, based on 136 quartz luminescence ages taken at 2 cm intervals. This represents the most detailed luminescence dating analysis undertaken to date on a sedimentary archive. Extensive laboratory tests and stratigraphic consistency indicate that the quartz luminescence ages are reliable. Together with grain size and cryostratigraphic analyses, as well as stratigraphic investigation of an adjacent loess exposure, the exceptional detail of the chronology combined with Bayesian age modelling uniquely allows changes in loess accumulation rates, particle size and permafrost development to be reconstructed over the last 3000 yrs on 101–103 yr timescales. The results show that loess deposition was mostly continuous over this interval, albeit with a short period of reworking or non-aeolian sedimentation during the Little Ice Age. Permafrost development in the loess is dominantly syngenetic, with ice contents increasing with depth. There is considerable variability in loess mass accumulation rate over the late Holocene, with peaks occurring during the last 250 yrs, as well as at 750–900, 1050–1200, 1400–1600, 1900–2450 and possibly 2700–3000 a. These peaks generally coincide with increased coarse silt deposition, potentially suggesting a link with greater wind activity. However, the peaks also seem to coincide with possible warm phases on Svalbard, which would rather imply that temperature-driven sediment availability in glaciofluvial source areas is the main control on dustiness in Adventdalen. In any case, the rates of loess deposition in the Adventdalen core are exceptionally high globally (up to 0.35 cm yr−1/2900 g m−2 yr−1 sedimentation and mass accumulation rates, respectively), and if representative of wider patterns across Svalbard, may suggest that the archipelago is a more important high latitude dust source than previously realised.

LOESS FORMATION IN NEW ZEALAND DURING THE LAST GLACIAL EPOCH AND UNDER MODERN CONDITIONS&lt;a href="#FN1"&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/a&gt;

The main territories for the development of Late Pleistocene loess are located in the inland regions of the Northern Hemisphere, so the very existence of loess in New Zealand, a region with a temperate maritime climate, is of undoubted scientific interest. The analysis of geological, geomorphological, paleogeographical and geochronological data on the distribution, structure and formation conditions of loess in New Zealand in the Late Pleistocene has been carried out. The study showed that in New Zealand, as in other regions of the temperate latitudes of the Southern Hemisphere, the accumulation of loess occurred mainly in the cold phases of the last climatic macrocycle: in the Early Pleniglacial, 80 (75)–(60) 55 ka BP; (2) during cooling within MIS 3, 45–40 ka BP on the South Island and 40–30 ka BP, with a peak of about 30 ka BP, on the North Island; (3) in the Late Pleniglacial, from 25 to 17–12 cal ka BP. Comparison of these stages with the Antarctica ice cores data shows their close relationship with global climate change. The article reviews data on the current conditions for the development of eolian processes and the formation of loess-like deposits in New Zealand. In contemporary conditions, eolian processes in New Zealand are concentrated within geomorphologically active territories, e. g. in river valleys with glacier feeding and an abundance of loose sediments, in areas with widespread coastal sand dunes, and in those territories where vegetation and soil disturbances promote wind erosion of the surface layers of unconsolidated sediments. Large-scale anthropogenic impact (destruction of forests, disruption of the herbaceous cover due to intensive grazing of livestock, especially sheep, ploughing of slopes on light weakly cohesive soils, etc.) to some extent makes the present interglacial conditions for the development of eolian processes in New Zealand similar to periglacial ones.