Advances and Issues in Luminescence Dating of Loess Deposits in Arid Central Asia
Wang Leibin1, , Wei Haitao1, Jia Jia1, Li Guoqiang1, Chen Fahu1, 2, *,
1.Key Laboratory of West China’s Environmental System, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China2.CAS Center for Excellence in Tibetan Plateau Earth Sciences of the Chinese Academy of Sciences, Beijing 100101, China
中图分类号:
P597.3
文献标识码:
A
文章编号:
1001-8166(2018)01-0093-10
通讯作者: *Corresponding author:Chen Fahu(1962-), male, Danfeng County, Shaanxi Province, Professor. Research areas include environmental change and the evolution of human civilization.E-mail:fhchen@itpcas.ac.cn
First author:Wang Leibin(1989-), female, Lingqiu County, Shanxi Province,Ph. D student. Research areas include optical dating.E-mail:wanglb15@lzu.edu.cn
High-resolution loess deposits are widely distributed in Arid Central Asia (ACA) and provide important records associated with dust transportation, paleoenvironmental and paleoclimatic evolution. The chronology is the foundation of the research into loess deposits as an environmental archive. In recent decades, the gradually developed optical dating method has been increasingly matured and become an important approach to establishing the loess-paleosol sequences. Here, we summarized and discussed previous work on loess chronology mainly based on optical dating approach in ACA. The following understandings have been listed: ① In comparison with optical dating method, the suitable material for 14C dating is uncommon in ACA. However, the dating range of luminescence dating is more extensive, and the dating materials are accessible. Thus, the optical dating is widely applicable in the establishment of loess framework in this area. ② Until now, the quartz Single Aliquot Regeneration (SAR) method can be applied to the establishment of loess-paleosol sequence since last glacial period. But several issues remain unaddressed. For example, the Optically Stimulated Luminescence (OSL) signal sensitivity of quartz grains are low in some areas. Furthermore, the results of OSL dating of different grain sizes within a single sample are inconsistent in some areas. The solution of these problems still requires more methodological research. ③ The post-IR IRSL (pIRIR) and multiple elevated temperature stimulation (MET-pIRIR) protoCols of feldspar have basically overcome the anomalous fading issue in the traditional IRSL dating process. In ACA, the framework since MIS 7 can be established with K-feldspar luminescence dating method. Compared with quartz luminescence characteristics, the K-feldspar luminescence signals are more sensitive and exhibit a high saturation level. In specific applications, it is necessary to establish the age frame according to the luminescence sensitivity, the age of samples or other factors.
Keywords：Arid central Asia
;
Loess deposits
;
Quartz OSL dating
;
K-feldspar pIRIR and MET-pIRIR dating.
WangLeibin, WeiHaitao, JiaJia, LiGuoqiang, ChenFahu. Advances and Issues in Luminescence Dating of Loess Deposits in Arid Central Asia[J]. Advances in Earth Science, 2018, 33(1): 93-102 https://doi.org/10.11867/j.issn.1001-8166.2018.01.0093
Fig.1 Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48]
Fig.2 The quartz OSL dating results and 14C results from three loess section in the arid central Asia (a)Zeketai (ZKT) loess section in Xinjiang Uygur Autonomous Region of China[18,19]. (b) Nilka (NLK) section in Xinjiang Uygur Autonomous Region of China[21,46]. (c) Bishkek loess section in Kyrgyz Republic[49]
Abstract The climates of Asia are affected significantly by the extent and height of the Himalayan mountains and the Tibetan plateau. Uplift of this region began about 50 Myr ago, and further significant increases in altitude of the Tibetan plateau are thought to have occurred about 10-8 Myr ago, or more recently. However, the climatic consequences of this uplift remain unclear. Here we use records of aeolian sediments from China and marine sediments from the Indian and North Pacific oceans to identify three stages of evolution of Asian climates: first, enhanced aridity in the Asian interior and onset of the Indian and east Asian monsoons, about 9-8 Myr ago; next, continued intensification of the east Asian summer and winter monsoons, together with increased dust transport to the North Pacific Ocean, about 3.6-2.6 Myr ago; and last, increased variability and possible weakening of the Indian and east Asian summer monsoons and continued strengthening of the east Asian winter monsoon since about 2.6 Myr ago. The results of a numerical climate-model experiment, using idealized stepwise increases of mountain-plateau elevation, support the argument that the stages in evolution of Asian monsoons are linked to phases of Himalaya-Tibetan plateau uplift and to Northern Hemisphere glaciation.
[2]
Dodonov AE, Zhou LP.
Loess deposition in Asia: Its initiation and development before and during the Quaternary
姝he initial desertification in the Asian interior is thought to be one of the most prominent climate changes in the Northern Hemisphere during the Cenozoic era.But the dating of this transition is uncertain,partly because desert sediments are usually scattered,discontinuous and difficult to date.Here we report nearly continuous aeolian deposits covering the interval from 22 to 6.2 million years ago,on the basis of palaeomagnetic measurements and fossil evidence.A total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils.This new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of Asia by the early Miocene epoch,at least 14 million years earlier than previously thought.Regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in Asia.
Abstract The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-340002Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 340002Myr ago.
[5]
Dodonov AE, Baiguzina LL.
Loess stratigraphy of Central Asia: Palaeoclimatic and palaeoenvironmental aspects
The loess-palaeosol succession of Central Asia is comparable with that of the Loess Plateau in North China. Palaeomagnetic investigations and palaeontological studies in South Tadjikistan suggest a date of 2-2.5 Ma for the oldest loess, indicating that dust storms became frequent in the region since 2-2.5 Ma BP. Under the prevalently arid and semi-arid environments of Central Asia, aeolian processes had a gradually increasing influence on subaerial sedimentation during the Pleistocene. However, atmospheric aeolian processes in Central Asia have mainly developed in accordance with Pleistocene climatic cyclicity, without extremely high intensification during the late Pleistocene as implied by the previous TL dating results. The identification of loess and palaeosol horizons with respective glaciations and interglacials is sometimes disputable. Nevertheless the available data, in spite of limited evidence, characterise well-developed palaeosols of the middle and late Pleistocene, as warm and wet intervals associated with interglacials. Palynological studies of loess sections show that loess and palaeosol horizons have palynological spectra that are sometimes difficult to interpret. Interregional loess-palaeosol correlation with glacial-interglacial events as well as with oxygen isotope records should be supplied by multidisciplinary investigations.
正Loess on the northern slope of Kunlun Mountains is the synchronous deposition of the Taklimakan Desert. The paleomagnetism and climatic records of an over 80 m loess-paleosol sequence on the highest river terrace at the foot of Kunlun Mountains show that the loess formed at - 880 ka B.P., suggestin
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Tectono-climatic implications of Eocene Paratethys regression in the Tajik Basin of Central Asia
[J]. Earth and Planetary Science Letters, 2015, 424: 168-178.
61We date the regression of the Paratethys at ca. 39 Ma in Tajikistan.61The marine connection between the Tarim and Tajik basins was disrupted between ca. 39 and 37 Ma.61A foreland basin was in place by ca. 40 Ma indicating active tectonics in the Pamir.61The regression followed and north-westward trend consistent with Pamir growth.61Uplift of the Pamir severed the seaway connection and aridified central Asia.
[10]
WangX, KraatzB, MengJ, et al.
Central Asian aridification during the late Eocene to early Miocene inferred from preliminary study of shallow marine-eolian sedimentary rocks from northeastern Tajik Basin
[J]. Science in China (Series D), 2016, 59(6): 1 242-1 257.
Abstract Arid central Asia (ACA) is one of the most arid regions in the mid-latitudes and one of the main potential dust sources for the northern hemisphere. The lack of in situ early Pleistocene loess/dust records from ACA hinders our comprehensive understanding of the spatio-temporal record of aeolian loess accumulation and long term climatic changes in Asia as a whole. Here, we report the results of sedimentological, chronological and climatic studies of early Pleistocene loess-palaeosol sequences (LPS) from the northeastern Iranian Golestan Province (NIGP) in the western part of ACA. Our results reveal that: 1) Accumulation of loess on the NIGP commenced at ~2.4-1.8芒聙聣Ma, making it the oldest loess known so far in western ACA; 2) the climate during the early Pleistocene in the NIGP was semi-arid, but wetter, warmer, and less windy than during the late Pleistocene and present interglacial; 3) orbital-scale palaeoclimatic changes in ACA during the early Pleistoceneare in-phase with those of monsoonal Asia, a relationship which was probably related to the growth and decay of northern hemisphere ice sheets.
[12]
ZanJinbo.
Loess on West Kunlun Mountains and Aridification of Asian Inland[D].
姝he Asian interior has the largest mid-latitude arid zone in the Northern Hemisphere,and so has become increasingly attractive for studying the initiation and the past extent of aridiflcation in this zone.Given the enormousness of the Asian interior,it remains unclear how old and extensive the eolian deposits might have been,and what wind regimes have been responsible for the formation of the mid-latitude arid zone.Here we report new eolian records of widespread Tertiary eolian deposits in a region far from the Chinese Loess Plateau,the giant Junggar inland basin of northwestern China.Our results demonstrate that the earliest eolian deposition initiated ca.24 Ma.We interpret that the Tertiary eolian dust in the Junggar Basin was transported by westerly winds,possibly from areas in Kazakhstan;the dust differs from the airborne dust transported by winter monsoon winds from the deserts of Mongolia and northern China that accumulated on the Loess Plateau.These results further reveal that the climate pattern,similar to that of the present,has prevailed at least since the latest Oligocene in Central Asia.
[16]
Zheng HB, Wei XC, TadaR, et al.
Late Oligocene-early Miocene birth of the Taklimakan Desert
[J]. Proceedings of the National Academy of Sciences, 2015, 112(25): 7 662-7 667.
Abstract As the world's second largest sand sea and one of the most important dust sources to the global aerosol system, the formation of the Taklimakan Desert marks a major environmental event in central Asia during the Cenozoic. Determining when and how the desert formed holds the key to better understanding the tectonic-climatic linkage in this critical region. However, the age of the Taklimakan remains controversial, with the dominant view being from 090804 3.4 Ma to 090804 7 Ma based on magnetostratigraphy of sedimentary sequences within and along the margins of the desert. In this study, we applied radioisotopic methods to precisely date a volcanic tuff preserved in the stratigraphy. We constrained the initial desertification to be late Oligocene to early Miocene, between 090804 26.7 Ma and 22.6 Ma. We suggest that the Taklimakan Desert was formed as a response to a combination of widespread regional aridification 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.
The distribution and genesis of Uzbekistan loess rocks, their composition, properties and conditions are naturally changing from mountains to the piedmont plains. For the piedmont plains and intermontane depressions the occurrence of alluvial and deluvial loess types is typical, and in the high mountains eluvial, deluvial, eluvial-deluvial and fluvioglacial ones. This can be explained by the difference of tectonic activity as well as by climatic humidity. The study and analyss of the accumulated data of loess of various genetic type, composition and properties show that the initial material of loess formation comes from the mountainous and alpine areas. The primariy sources of the parent rocks are ancient sediments above the limit of loess occurrence. As a result of intensive developments and irrigation in the territory of the republic, loess areas are decreasing, losing their properties, while they are transforming into the loess-like rocks. It was also determined that their structural and textural properties such as porosity, density, salt composition and filtration coefficient are changing simultaneously. The same changes are also noted in the mineralogical and granulometric composition.
[18]
Feng ZD, RanM, Yang QL, et al.
Stratigraphies and chronologies of late quaternary loess-paleosol sequences in the core area of the central Asian arid zone
The sporadic distribution of the Quaternary loess in Central Asia makes it hard to establish a regional pedostratigraphy through visual tracing of marker strata. The pedostratigraphic correlation presented here is thus completely based on the radiocarbon chronologies of the four studied sections. The first noticeable feature is that poorly-drained conditions predominated in the period between 6548,000 and 6530,000 14C BP, during which three entisols developed at 6545,000 14C BP, 6540,000 14C BP, and 6535,000 14C BP. After a period of loess deposition between 6530,000 and 6518,000 14C BP under poorly-drained conditions, an entisol at the westernmost site (Valikhanov, south-central Kazakhstan) developed between 6518,000 and 6510,000 14C BP, also under poorly-drained conditions. The time equivalent deposits at Romantic and Zeketai sections to the east do not exhibit any soil-forming characteristics, although poorly-drained conditions are also imprinted in the time-equivalent loess. The Holocene sequences in the Central Asian domain consist of an early Holocene loess unit deposited between 6510,000 and 655,000 14C BP and a late Holocene soil formed during the past 655000 years. In comparison, the climate was also wet between 6548,000 and 6520,000 14C BP, during which three mollisols developed under well-drained conditions in the Chinese Loess Plateau of the East Asian domain. The loess deposited between 6523,000 and 6510,000 14C BP in the Chinese Loess Plateau has neither observable marks of soil formation nor imprints of poorly-drained conditions. The Holocene sequence in the East Asian domain exhibits an out-of-phase relationship with that in the Central Asian domain, consisting of an early Holocene soil formed between 659000 and 654000 14C BP and a late Holocene loess unit deposited during the past 654000 years.
[19]
E CY, Lai Z P, Sun Y J,et al.
A luminescence dating study of loess deposits from the Yili River Basin in Western China
The loess deposits surrounding the high mountainous regions of Central Asia play an important role in understanding environmental changes in Eurasia on orbital and sub-orbital timescales. However, problems with dating Central Asian loess have limited the interpretation of climatic and environmental data, especially on sub-orbital timescales. We selected a controversial loess section, Zeketai (ZKT, with a thickness of 23m), in the Yili basin in Xinjiang Province in western China, to establish a detailed and systematic Optically Stimulated Luminescence (OSL) chronology. Quartz grains of 38–63μm were isolated from 15 samples and the single-aliquot regenerative-dose (SAR) protocol was employed for D e determination. OSL ages are in stratigraphic order and range from 13.8±1 to 72±6ka, suggesting continuous loess accumulation during the last glaciation. We compared these dating results with that of the previously published fine-grain sized quartz (4–11μm) using simplified multiple aliquot regenerative-dose (SMAR) protocol, and with the previous published radiocarbon dating ( 14 C) ages on snail shells. With the exception of three young samples from the upper 6m of the section, the SMAR dating results are basically consistent with the results using the SAR protocol. Both the SMAR and SAR OSL ages are consistently older than the 14 C ages, and the radiocarbon date results should be used with caution since they appear to have been underestimated.
[20]
Song YG, Li CX, Zhao JD, et al.
A combined luminescence and radiocarbon dating study of the Ili Loess, Central Asia
Similar to the loess in the Chinese Loess Plateau (CLP), the loess deposits in the Ili basin of Central Asia arid area play an important role in understanding the climate and environmental changes. However, in contrast to the intensively investigated loess deposits in the CLP, the Ili loess is still insufficiently known and poorly understood. The geochronology study of the Ili loess remains controversial. In order to examine the potential of optically stimulated luminescence (OSL) dating for the Ili loess, we carry out a combined luminescence and radiocarbon dating study on a 6.9聽m loess section in the south margin of the Ili basin. Polymineral fine grains were investigated by post infrared (IR) OSL using a Multiple-Aliquot Regenerative-dose (MAR) protocol. Radiocarbon dating of organic carbon were carried in a 3 Megavolt (MV) multi-element Accelerator Mass Spectrometry (AMS). The results indicate that the OSL ages are in agreement with the observed stratigraphy in the field, which is well correlated with that of the CLP, but the AMS 14C ages are much younger than the OSL and assumed stratigraphical ages. Thus, the OSL dating technique may provide an absolute chronology in this loess section. Further methodological approaches and more samples analysis will lead to the improvement of this chronology for high-resolution paleoclimatic interpretation.
[21]
Song YG, Lai ZP, LiY, et al.
Comparison between luminescence and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia
61OSL and radiocarbon dating of late Quaternary loess from Central Asia.61Modern carbon contamination causes saturation of radiocarbon ages at 3002cal02ka02BP.61OSL dating is applicable for constructing an accurate loess chronology beyond 3002ka.61Two intervals of higher mass accumulation rate occurred at 49–4302ka and 24–1402ka.
[22]
Huntley DJ,
Godfrey-Smith D I, Thewalt M L W. Optical dating of sediments
The last glacial period was characterized by abrupt, millennial-scale climate change. These climate fluctuations are particularly pronounced in records of the East Asian monsoon system and seem to be linked to changes in North Atlantic circulation. Here we present records of grain size variations from the northwestern Chinese Loess Plateau, dated using optically stimulated luminescence. We reconstruct changes in the strength of the East Asian winter monsoon over the past 60,000 years and find reconstructed millennial-scale variations that are broadly correlated with temperature variations over Greenland, suggesting a common forcing. We investigate the effect of a slow-down of Atlantic meridional overturning circulation on the monsoon system using a coupled climate model simulation with added freshwater flux into the northern North Atlantic, and find a strengthening winter monsoon circulation over the regions that supply dust to the Loess Plateau and a reduction in summer monsoon precipitation over East Asia. We conclude that Atlantic meridional overturning circulation is a driver of abrupt change in the East Asian winter and summer monsoon systems, and that the northern westerlies play a role in transmitting this signal from the North Atlantic to the Asian monsoon regions.
[25]
Zhang JF, Liu CL, Wu XH, et al.
Optically stimulated luminescence and radiocarbon dating of sediments from Lop Nur (Lop Nor), China
Lop Nur is a playa lake occupying the lowest part of the Tarim Basin, northwestern China, and is now a desolate and barren region. In the past decades, the ages of the lacustrine sediments from the lake were determined mainly by radiocarbon dating on bulk sediment. In this study, both optically stimulated luminescence (OSL) and radiocarbon methods were used to date the sediments from a pit in the central part of the lake. The OSL ages obtained for ten samples range from 0.5 to 9.4 ka, and are in stratigraphic order except for one sample. The 14 C ages obtained for twenty-two bulk sediment samples range from 5.8 to 30.2calkaBP with erratic distribution. Based on the comparison of 14 C with OSL ages and their age-depth models, we argue that the OSL ages are relatively reliable. The disequilibria in the U decay chain for some samples are deduced from the comparison of the NAA and TSAC results. We suggest that the OSL dating technique should preferably be applied to the playa sediments from Lop Nur, but the disequilibria in the U decay chain should be considered in evaluating dose rates. Additionally, radiocarbon reservoir effects in lakes in western China are reviewed.
[26]
LongH, ShenJ, WangY, et al.
High-resolution OSL dating of a late Quaternary sequence from Xingkai Lake (NE Asia): Chronological challenge of the “MIS 3a Mega-paleolake” hypothesis in China
[J]. Earth and Planetary Science Letters, 2015, 428(5): 281-292.
61We conducted a combined OSL and14C dating for a late Quaternary lake sequence.61The reliability and robustness of OSL dates are confirmed.6114C dating may significantly underestimate age of sediments of beyond 30 cal ka BP.61This paper challenges the14C-based “MIS 3a Mega-paleolake” hypothesis in China.61Sedimentation rate of Xingkai Lake related to global climatic changes on orbital timescales.
[27]
FuchsM, Owen LA.
Luminescence dating of glacial and associated sediments: Review, recommendations and future directions
Dating glacial and associated sediments is essential to provide a temporal framework for accurate reconstructions of past climatic conditions and for helping to determine the nature and magnitude of glaciation for landscape evolution studies. There are few widely applicable, accurate and precise methods available to date Quaternary landforms and sediments, despite the numerous numerical dating methods that are currently available. Furthermore, there are few methods that can be utilized for the whole of the late Quaternary ( c . 125 kyr ago to present). Recent developments in luminescence dating, however, are providing opportunities to date a broad range of late Quaternary glacial and associated landform sediments. The application of luminescence methods requires an understanding of the nature of glacial and associated environments to select the most appropriate sediment samples for dating. Problems associated with luminescence dating of glacial sediments include insufficient bleaching, low sensitivity of quartz, and variable dose rates during the history of the sediment due to changing water content or nuclide leaching. These problems can be overcome by careful sampling and descriptions of the sampling site, testing for insufficient bleaching and modelling dose rate variability.
[28]
Bateman MD, Swift DA, Piotrowski JA, et al.
Investigating the effects of glacial shearing of sediment on luminescence
Previously reported low luminescence of basal glacial sediment has raised the possibility that processes operating at the ice–bedrock interface have the potential to reset (or ‘bleach’) natural luminescence signals (Swift et02al., 2011). This finding indicates that certain types of glacial sediment (for example, sub-glacial diamicts) might be amenable to dating using luminescence-based techniques. Using a purpose-built ring-shear apparatus situated in a light-controlled environment, we have investigated the potential for mineral grains to be reset when subjected to conditions similar to those experienced by sediment that has undergone transport at the ice–bedrock interface. Reported here are the preliminary results of an initial experiment that used medium quartz sand with a naturally-acquired palaeodose of 654.302Gy that had been obtained from a relict dune system. Incremental sampling during the shearing experiment and measurements were made to track changes in the luminescence properties of the sand as strain/shearing increased. The results indicate that increased strain/shearing resulted in an increase in the number of zero-dose grains and evolution of the De distribution from unimodal to multimodal. In light of the very much longer shearing distances that sub-glacial sediment would endure in nature, these results would appear to suggest that geomechanical processes at the ice–bed interface of glaciers and ice sheets may be a viable mechanism for resetting sediment.
[29]
Duller G AT.
Single grain optical dating of glacigenic deposits
Determining the age of glacigenic sediments is difficult for many geochronological methods because of the lack of suitable materials for analysis. Luminescence dating can be applied to the mineral grains making up the glacigenic sediments. However a major source of uncertainty in previous studies has been whether the mineral grains were exposed to sufficient daylight prior to deposition for the luminescence signal to be reset. Measurements of the optically stimulated luminescence signal from single sand-sized quartz grains offers the potential for explicitly identifying if a sediment contains grains that were not exposed to sufficient daylight to reset their signal. Statistical analysis of the resulting data can then reject those grains to allow the age of the sample to be determined. This study is the first to apply single grain optical dating to glacigenic sediments, and demonstrates the issues involved by analysis of samples from Chile and Scotland. Ages from 2.4卤0.5 to 17.3卤1.5 ka are produced. Comparison of the results with independent age control suggests that the ages are reliable. The results also show that the extent of bleaching at deposition varies considerably from one sample to another. For the most incompletely bleached sample, luminescence measurements based on the average of many hundreds or thousands of grains would have overestimated the age of the sample by 鈭60 ka, but the single grain method proposed here was able to reliably date it.
[30]
ZhaoHua, WangChengmin, MaoHongliang, et al.
OSL dating of volcanic baked sediments in Datong area, Shanxi Province of China
Abstract Loess deposits preserve important records of Quaternary climate change and atmospheric dust flux; however, their full significance can only be revealed once a reliable chronology is established. Our understanding of loess-palaeosol sequences and the development of luminescence dating techniques have progressed hand-in-hand over the past 25 years, with each subject informing the advancement of the other. This article considers the development and application of luminescence dating techniques to loess deposits from the early days of thermoluminescence (TL) to the optically stimulated luminescence (OSL) methods utilized today. Recent technological and methodological advances have led to a step-change in the accuracy and precision of quartz OSL ages; this has led to an expansion of high-resolution luminescence studies, which in turn are informing loess studies and challenging some of the basic ideas regarding the nature of loess records, their formation and their significance. Future luminescence research efforts are likely to focus on extending the age range of luminescence techniques, possibly by utilizing new luminescence signals; this, again, will allow investigation of the long-term variability of loess records in comparison with other long records of climate change to which they are frequently compared.
[35]
StevensT, Armitage SJ, Lu HY, et al.
Sedimentation and diagenesis of Chinese loess: Implications for the preservation of continuous, high-resolution climate records
Chinese loess has been extensively utilized to produce continuous and high-resolution climate records of the late Cenozoic. Such work assumes uninterrupted loess deposition and limited diagenesis. Here, closely spaced optically stimulated luminescence (OSL) dates are used to characterize the Holocene and Late Pleistocene sedimentation histories of three sites across a NW-SE transect of the Chinese Loess Plateau. The results suggest that sedimentation is episodic at subglacial-interglacial time scales, with rates rapidly varying within units and between sites. Unconformities, noneolian deposition, and mixing of sediments also appear to be common. Existing understanding of loess deposition therefore requires reexamination, while previous reconstructions of rapid climate change, not dated using absolute methods, should be regarded with caution. Loess deposits may still yield detailed climate records from specific high-sedimentation-rate strata, and evidence for rapid climate change may yet be obtainable by targeting these units through absolute dating. The rapid changes in sedimentation presented here indicate the East Asian Monsoon has the capacity to vary on millennial scales.
[36]
Lai ZP.
Testing the use of an OSL Standardised Growth Curve (SGC) for DE determination on quartz from the Chinese Loess Plateau
A sensitivity-corrected Multiple Aliquot Regenerative-dose protocol has been developed for fine-grained quartz OSL dating of Chinese loess. Its reliability has been assessed on the basis of the methodology and by dating reference samples of known age close to the transition from the last interglacial paleosol (S 1 ) to the last glacial loess (L 1 ), which corresponds to the Marine Oxygen Isotope Stage (MIS) 5/4 transition. On the basis of the fine-grained quartz OSL-age estimates for 33 loess samples from the upper part of the Luochuan profile, a detailed chronostratigraphy of continuous dust accumulation in the past 130ka has been proposed. Changes in the accumulation rate occurred during the last glacial period (MIS 4 to MIS 2); unexpectedly, high accumulation rates were found in the weakly developed L 1–2(S) paleosol of the last interstadial (MIS 3), rather than in the classic L 1–1 and L 1–3 loess of the cold–dry glacial condition (MIS 2 and 4). The OSL ages show some disagreement with the previous numerical chronology for the loess–paleosol sequence based on correlation of variations in grain size with sedimentation rate; the latter method resulted in an almost constant accumulation rate from 72 to 12ka.
[38]
Zhou LP, Dodonov AE, Shackleton NJ.
Thermoluminescence dating of the Orkutsay loess section in Tashkent region, Uzbekistan, Central Asia
The chronology of loess in Central Asia was investigated by means of thermoluminescence dating (TL) in the 1970s, when age estimates ranging from 20 ka to over 800 ka were taken as providing an absolute chronology. This has caused major misinterpretation of Central Asian loess stratigraphy and palaeoclimatic reconstruction. We present a new TL study of a loess section at Orkutsay in the Tashkent Region, Uzbekistan. Nine samples spreading over a large stratigraphic interval yield apparent TL ages ranging from 20 ka to 134 ka. We interpret our TL results with reference to recent TL dating studies of loess from other regions. We consider most of our TL age estimates obtained by the regeneration method to be underestimated. A single TL date of 92.8 ka obtained by the total bleach method for loess just below the first pedocomplex (PC 1) of the last interglacial is also significantly younger than expected. We attribute the underestimation to sensitivity change induced by the laboratory optical bleach and instability of the TL signal. We conclude that the current TL techniques as employed in this study cannot provide a reliable absolute chronology for the sequence below PC 1 and cannot provide even a relative chronology for the loess below PC2. For the Orkutsay section the dating limit is around 130 ka. The results of this study suggest that the previous Central Asian loess chronology based on early TL studies is not valid.
[39]
Zhou LP, Fu DP, Zhang JF.
An analysis of the components of the luminescence signals of selected polymineral and quartz samples from loess in western China and southern Tajikistan, and their suitability for optical dating
Previous luminescence dating studies on loess from China and Tajikistan have focused on the establishment of the regional chronology of the loess sequences. In order to improve the precision and accuracy of optical ages derived from the loess of the last glacial period in these regions, we have examined the components of luminescence signals in three loess samples from western China and southern Tajikistan. Our results show that the polymineral IRSL and post-IR OSL, and quartz OSL signals from loess of the two regions are represented by three components, which display different bleaching and growth characteristics. While the composition of the polymineral IRSL signals is similar between samples with the same age from the two regions, in the case of quartz there is significant discrepancy in the proportion of the fast and medium components of the OSL signals. Greater difference is observed in the composition of the polymineral post-IR OSL signals for the loess from the two regions. The three components of polymineral IRSL signals yield almost identical equivalent dose values as that derived from the total IRSL signal. An apparent agreement in equivalent dose is observed between the fast component of the polymineral post-IR OSL and the quartz OSL for the loess of western China but not in the loess of the same age from southern Tajikistan. The fast component of the quartz OSL yields an equivalent dose 25% higher than that based on the total signal for the sample from the base of the Late Pleistocene loess in southern Tajikistan. This demonstrates the importance of signal selection for an accurate luminescence dating of Central Asian loess.
[40]
FrechenM, KehlM, RolfC, et al.
Loess chronology of the Caspian Lowland in Northern Iran
The loess/palaeosol sequences of the Caspian Lowland in Northern Iran provide detailed archives of climate and environmental change showing a close relationship to global cooling and warming trends for the Quaternary period. The magnitude of these changes is under discussion owing to uncertainties in the chronologies for individual sites. A chronological frame was set up for the last glacial loess record for three Upper Pleistocene key sections by infrared optically stimulated luminescence (IRSL). In the Caspian Lowland, IRSL dating gives reliable ages for sediments covering at least the past 60聽ka. However, for sediments older than 60聽ka, a significant age underestimation is likely. The first strongly developed buried Bt/Bwt horizons or pedocomplexes at the three sections under study correlate most likely with the last interglacial (MIS 5). At least four periods of increased sediment accumulation were determined for the last glacial period intercalated by periods of weak soil formation. The loess/palaeosol sequences in Northern Iran recorded coeval and similar major climatic changes as in South-Eastern Central Europe and Central Asia.
[41]
Li GQ, Rao ZG, Duan YW, et al.
Paleoenvironmental changes recorded in a luminescence dated loess/paleosol sequence from the Tianshan Mountains, arid Central Asia, since the Penultimate Glaciation
[J]. Earth and Planetary Science Letters, 2016, 448(15): 1-12.
Mid-latitude arid central Asia (ACA) is one of the driest regions in the world and is a key source area of global atmospheric dust. Loess records of paleoclimatic changes in ACA are complex and interpretations are problematic due primarily to the lack of robust chronologies. Quartz OSL and K-feldspar pIRIR dating methods were employed to date 8 quartz and 30 K-feldspar samples from a 30 m loess sequence (BYH10 section) on the northern slope of the Tianshan Mountains, central ACA, northwest China. The reliability of quartz and K-feldspar ages was monitored by internal checks of luminescence characteristics and by comparison of the quartz and K-feldspar ages. The section lithology, proxy indexes of grain size and magnetic susceptibility, and the high resolution OSL chronology together indicate: (1) Quartz OSL dating can be used to date ACA loess samples less than 40 ka, while K-feldspar pIRIR dating is reliable for loess samples at least as old as 鈭150 ka from ACA; (2) Aeolian loess began to be deposited on the northern slope of Tianshan Mountains beginning at least 鈭145 ka ago, and was deposited primarily during the penultimate and last glaciation periods; (3) Rapid loess deposition occurred during MIS 6, MIS 4 to early-mid MIS 3, and MIS 2, but little or no loess deposition occurred during MIS 5, MIS 3a and MIS 1; (4) This loess depositional sequence is comparable to previously published stalagmite growth records in the region on glacial-interglacial cycles. Rapid dust deposition and lack of stalagmite growth during glacials, and lack of loess deposition and stalagmite growth during interglacials, indicate a climatic pattern of wet-warm (interglacial) and dry-cold (glacial) climatic regimes on orbital cycles in ACA; (5) Variation in the loess deposition rates in ACA was much larger than in the central loess plateau during the last glaciation; (6) Depositional hiatuses of >50 kyr occur in ACA loess sequences, and high resolution chronologies are needed when reconstructing past climatic changes.
[42]
Kang SG, Wang XL, Lu YC, et al.
A high-resolution quartz OSL chronology of the Talede loess over the past ~30 ka and its implications for dust accumulation in the Ili Basin, Central Asia
61A fine-grained quartz SAR OSL chronology of the Talede loess over the past 3002ka.61Age discrepancy of14C when compared with quartz OSL.61Potential of fine-grained quartz OSL dating of Central Asian loess.61Rapid dust accumulation during the LGM.61Slow but increasing dust accumulation during the Holocene.
[43]
ZhaoH, Li SH, LiB, et al.
Holocene climate changes in westerly-dominated areas of central Asia: Evidence from optical dating of two loess sections in Tianshan Mountain, China
Optical dating was applied to two loess-paleosol sections (Lujiaowan and Shuixigou) from the northern piedmont of Tianshan Mountain, Xinjiang province, China. The two sections are over 20002km apart and have a similar depositional sequence, which consists of two paleosol layers embedded by one loess layer. Two difficulties were met in optical dating. First, because the sections are located on the slope of the mountain, it was found that some cliff debris, with coarse grains (>20002μm), were mixed with the eolian sediments by rainfall, especially in the paleosol layers. Second, the optically stimulated luminescence (OSL) signals of quartz grains from the deposits were too dim to obtain a reliable equivalent dose (De). The 63–9002μm K-feldspar grains were separated to decrease the debris portion, and they yielded bright infrared stimulated luminescence (IRSL) signals. A multiple-elevated-temperature post-IR IRSL (MET-pIRIR) procedure was applied to determine De. Comparing the optical dating ages of the two sections, the Lujiaowan (LJW) and Shuixigou (SXG) sections recorded almost the same depositional process during the Holocene. The ages of the two loess layers (2.44–3.3802ka at LJW; 2.47–4.3602ka at SXG) suggested that one drought event happened widely in this westerly dominated area. The same drought event 2.5–3.502ka ago also happened in the Chinese Loess Plateau (CLP), where the summer monsoon dominated. However, the paleosol development period (6.6–402ka) in the study area was distinguished from the monsoon dominated area (8–402ka), which suggests an arid early Holocene in the westerly area.
[44]
FrechenM, Dodonov AE.
Loess chronology of the middle and upper Pleistocene in Tadjikistan
The loess/paleosol sequences of Central Asia are continuous terrestrial records of the Quaternary period and enable detailed comparison with paleoclimatic archives such as marine and ice core records in order to reconstruct regional and global paleoclimatic and paleoecological development during the past 130 000 years. Thermoluminescence (TL) and infrared stimulated luminescence (IRSL) dating methods are applied to the extensively studied loess/paleosol sequence of the section at Darai Kalon/Chashmanigar, Tadjikistan, in order to determine a more accurate chronological framework and climatostratigraphic reconstruction for the last interglacial/glacial cycle. Luminescence dating suggests that the loess above the first pedocomplex from the top, PC1, accumulated during the last glacial period. A high accumulation rate of up to 1.20m per 1000 years was determined for the last glacial loess, especially for the uppermost 5-8m. PC1 formed during the last interglacial period (oxygen-isotope stage 5). The loess between PC1 and PC2 is designated to be of penultimate glacial deposition age. Infrared stimulated luminescence and TL age estimates are in agreement to 80 000 years before present (BP), indicating a long-distance transport of the aeolian dust prior to deposition. The upper numerical age-limit range is between 300 000 and 450 000 years. However, reliable dating of the loess older than 130 000 years is not possible due to age scatter between samples and an inadequate increase of paleodose with depth. This high-resolution dating study underlines the importance of the section at Darai Kalon and indicates that it is one of the most continuous loess/paleosol records of the Northern Hemisphere. The chronological results are particularly important for the reconstruction of the human evolution in Central Asia, suggesting much older age estimates than previously obtained for most of the archeological key sites associated with PC5 and PC4 in Tadjikistan.
[45]
MachalettB, FrechenM, HambachU, et al.
The loess sequence from Remisowka (northern boundary of the Tien Shan Mountains, Kazakhstan) Part I: Luminescence dating
Similar to the Chinese loess, the loess deposits surrounding the high mountain regions of Central Asia play an important role in understanding the climate and environmental change during the Pleistocene in Eurasia. Despite their thickness and widespread distribution, the loess deposits in southeast Kazakhstan have so far not been investigated in detail. The Remisowka loess-損alaeosol sequence is located in the vicinity of the North Tien Shan Mountains at an altitude of 1070聽m above sea level. In the profile under study nine loess layers were distinguished, intercalated by eight pedocomplexes and so indicating a similar cyclicity like the loess-損alaeosol sequences in Central Asia and China. At the Remisowka section, 12 loess samples were taken to set up a more reliable chronological model for the section, using a luminescence dating approach. Polymineral fine grains were investigated by infrared optically stimulated luminescence applying the multiple aliquot additive dose protocol. Preliminary fading experiments were carried out for one sample taken from the uppermost loess layer. While the results of the uppermost layer are in agreement with geological age estimates and indicate a correlation to the Late Glacial, age underestimation is very likely for the samples below the first weak palaeosol. No significant age increase with depth was recognised. The reason for this age underestimation is not yet fully understood but could be related to anomalous fading. Further methodological approaches are necessary as well as a combination of different chronometric techniques for improvement of the results.
[46]
Yang SL, Forman SL, Song YG, et al.
Evaluating OSL-SAR protocols for dating quartz grains from the loess in Ili Basin, Central Asia
61OSL ages show loess in the Ili Basin, China was deposited ca. 70 to 1402ka ago.61Equivalent dose values show high overdispersion (38–66%), thus we use Maximum Age Model.61Overall OSL ages for Basin provide more credible chronology than 14C ages.
[47]
LiY, Song YG, Lai ZP, et al.
Rapid and cyclic dust accumulation during MIS 2 in Central Asia inferred from loess OSL dating and grain size analysis
Abstract Due to lack of reliable proxies from the Westerlies-dominant region, the strength change of Northern Hemisphere Westerlies remains poorly understood. The aim of this study is to provide a reliable paleoclimatic proxy about the Northern Hemisphere Westerlies change. Here we report a 30.7芒聙聣m thick loess section from the Ili basin directly controlled by the Westerlies. Based on optically stimulated luminescence (OSL) and high resolution grain-size records, we reconstruct the change history of the Westerlies strength during the last glacial period (mainly Marine Isotope Stages 2, MIS2), being similar with the Westerlies index recorded in the Qinghai Lake sediments. Within error limits, all ages are in stratigraphic order. We further compare the climatic records among the Ili loess, Qinghai Lake and the NGRIP, their similarity shows a good climatic coupling relationship among the Central Asia, East Asia and the North Atlantic, and the Westerlies plays a critical influence in transporting the North Atlantic signal to Central and East Asia.
[48]
Li GQ, Wen LJ, Xia DS, et al.
Quartz OSL and K-feldspar pIRIR dating of a loess/paleosol sequence from arid central Asia, Tianshan Mountains, NW China
61K-feldspar pIRIR 17002°C signal can be used to date Holocene loess in ACA.61The K-feldspar pIRIR ages are consistent with their corresponding quartz OSL ages.61Loess deposition started 651602ka ago with paleosol formation between 65602ka and present.61ACA was arid during the early Holocene and humid during the mid-late Holocene.
[49]
Youn JH, Seong YB, Choi JH, et al.
Loess deposits in the northern Kyrgyz Tien Shan: Implications for the paleoclimate reconstruction during the Late Quaternary
Loess deposits on the northern slopes of the Kyrgyz Tien Shan were examined. Their particle size characteristics show silt size dominancy (>聽80%) with minor contribution from sand (12%) and clay (7%). The loess was dated using optically stimulated luminescence (OSL) and radiocarbon methods to define the timing of deposition. The OSL ages of fine and coarse quartz fractions were consistent with each other within 2蟽 uncertainty level, except several samples deposited during MIS 2. Based on the OSL ages, four major loess depositional periods are recognized in the northern Kyrgyz Tien Shan during the Late Quaternary: the Holocene, MIS 2, MIS 3, and MIS 4. The rate of dust accumulation in the northern Tien Shan during MIS 2 was greater than that during MIS 3 or MIS 4. This implies that cold-揹ry conditions varied significantly during the Late Quaternary in the study area. The accumulation patterns of the Kyrgyz loess deposits in the northern Tien Shan are closely related to climate fluctuations during the Late Quaternary, influenced by changes in the mid-latitude westerlies, Asian summer monsoons, and Siberian High Pressure (SHP) systems, during which there was no significant cessation of deposition.
[50]
LauerT, FrechenM, VlaminckS, et al.
Luminescence-chronology of the loess palaeosol sequence Toshan, Northern Iran—A highly resolved climate archive for the last glacial-interglacial cycle
Loess-palaeosol sequences are highly resolved archives for palaeoenvironmental reconstruction and build an important link to correlate European and Central Asian loess sequences. For the loess palaeosol sequence at Toshan, Northern Iran, a luminescence-based chronological framework was established. The timing of dust accumulation and soil formation was investigated and thereby information on changes in palaeoenvironmental conditions in the region obtained. For luminescence dating, the 4–11μm grain size fraction was used and the pIRIR 290 approach was applied to polyminerals. Tests concerning bleachability, dose recovery and anomalous fading were conducted. The results show that residual doses have only minor influence on the determination of the equivalent dose. The Eemian (MIS 5e) soil seems to be preserved but a chronological classification based on luminescence ages for this soil remains difficult. The pIRIR 290 age estimates from the lower part of the profile range from 104±9 to 127±8ka. Luminescence ages from the central profile-part point to an increase in dust accumulation starting around the MIS 4/MIS 3 transition. Furthermore, a chronological framework for interstadial soils was developed indicating e.g. soil formation at around 40ka during MIS 3 and 26ka during MIS 2. The top part of the profile was dated to about 22ka. The age estimates show that the Toshan loess profile is a highly resolved loess record providing a valuable climate archive for the last glacial–interglacial cycle reflecting several climatic shifts represented by dust accumulation or enhanced degrees of soil formation (stadials and interstadials).
[51]
JanosHormata.Central Asian Civilization History[M]. Beijing:China Translation and Publishing Corporation, 2002.
Precipitation and snow distribution, melt of glaciers and snow, and runoff formation in two basins in the northern Tien Shan are calculated and described. Major climatic features are a spring-summer precipitation maximum occurring simultaneously with ice and snow melt. Precipitation increases with altitude except in winter when an air temperature inversion occurs. Air temperature is a good predictor of glacial melt. Typical hydrographs have two floods: one is formed from melt of seasonal snow cover, and the other is formed from melt of glacial ice. The second flood is usually larger than the first. In mountain basins of the northern Tien Shan direct runoff from rainfall averages about 7-12% of annual volume. The glacial runoff is 18-28% of average annual runoff in basins with area of glaciation not less than 30-40%, but during summer it can increase to 40-70% of average annual runoff. Surface runoff from seasonal snow melt during spring and summer is 18% of average annual runoff, the groundwater component is 34-38% of average annual runoff.
[54]
HuRuji.Physical Geography of the Tianshan Mountains in China[M].Beijing:China EnvironmentaI Science Press,2004.
[胡汝骥. 中国天山自然地理[M].北京:中国环境科学出版社,2004.]
[55]
Dodonov AE.
Loess records|Central Asia—Encyclopedia of Quaternary Science
[J]. Encyclopedia of Quaternary Science, 2007, 26: 1 418-1 429.
Mineralogical, textural, geochemical, and weathering characteristics of loess deposits in Golestan province of Iran suggest that they are mostly derived from felsic igneous rocks and are related to Quaternary palaeoclimate. Whole-rock analyses indicate heavy minerals such as zircon, tourmaline and phyllosillicate minerals (e.g. muscovite, chlorite, illite) exert a significant control on the chemical composition. The loess samples display uniform chemical composition, indicative of similar alteration history. Chemical index of alteration suggests a weak to moderate degree of weathering in a felsic source area. Scanning electron micrographs of quartz grains reveal abundant silt-sized quartz particles, a result of glacial grinding during the Late Pleistocene in Central Asia. Subsequently, these silt particles were transported from Central Asia to their depositional site by wind and paraglacial processes. Local topography of northeast Iran (Alborz Mountains) acted as a major barrier, entrapping the airborne particles on the plains of Golestan province. Copyright 漏 2012 John Wiley & Sons, Ltd.
[60]
KehlM, SarvatiR, AhmadiH, et al.
Loess paleosol-sequences along a climatic gradient in Northern Iran
[J]. Eiszeitalter und Gegenwart, 2005, 55(1): 149-173.
Im südlichen Kaspischen Tiefland und seinen umliegenden Gebieten treten L02sse in verschiedenen geomorphologischen Positionen entlang eines rezenten Klimagradienten von subhumiden zu semiariden Verh01ltnissen auf. Drei L02ss-Pal01obodenabfolgen werden beschrieben, die im n02rdlichen Vorgebirge des Alborz (Profile Neka und Now Deh) und im L02sshügelland n02rdlich Gondbad-e Kavus (Profil Agh Band) aufgeschlossen sind. Das Profil Neka besteht aus feink02rnigem L02ss, der von zwei kr01ftig entwickelten Pal01obodenkomplexen aus Bwk-, Bt- und AhBt-Horizonten durchzogen wird. Erste Lumineszenzdatierungen weisen darauf hin, dass der obere Pedokomplex w01hrend der Sauerstoff-Isotopen-Stadien (OIS) 5a und/oder 5c gebildet wurde, w01hrend der untere das OIS 5e oder ein 01lteres Interglazial repr01sentieren k02nnte. Neun hell braune oder dunkel braune bis r02tlich-braune Pal01ob02den (CBk-, Bwk- und Bt-Horizonte) des L02sses bei Now Deh spiegeln unterschiedliche Verwitterungsintensit01ten von Interglazialen und Interstadialen des Mittleren bis Oberen Pleistoz01ns wider. W01hrend der obere Bt-Horizont von Now Deh wahrscheinlich mit dem OIS 5e korreliert, bilden die unteren Bt-Horizonte einen Pedokomplex, der das Interglazial des OIS 7 repr01sentiert. Die Pedo-komplexe in Neka und Now Deh weisen jeweils auf polyzyklische Bodenentwicklung hin, die Bodenbildung, Bodenabtrag, L02ssaufwehung und erneute Bodenbildung umfasste. In den L02sshügeln bei Agh Band bedeckt ein 40 m m01chtiges, weitgehend homogenes, gipshaltiges und feinsand- sowie grobschluffreiches L02sspaket einen braunen Pal01ob02den (Bw(t)), der vermutlich in das letzte Interglazial zu stellen ist. Die beschriebenen L02ss-Pal01obodenabfolgen dokumentieren den mehrfachen Wechsel von trocken-kalten zu feucht-warmen Klimaverh01ltnissen mit L02ssablagerung bzw. Bodenbildung. Sie stellen ausgezeichnete terrestrische Archive des quart01ren Klima- und Umweltwandels Nordirans dar.
[61]
Buylaert JP, VandenbergheD, Murray AS, et al.
Luminescence dating of old (>70 ka) Chinese loess: A comparison of single-aliquot OSL and IRSL techniques
Chinese loess is regarded as one of the most detailed and complete terrestrial archives of late Cenozoic climate change. However, high-resolution optically stimulated luminescence (OSL) dates presented here reveal that the suborbital chronological framework of Chinese loess used in many previous climate reconstructions requires reassessment. Chronological uncertainty of as much as 10-15 k.y. for the late Pleistocene is largely a result of the widespread use of nonradiometric dating techniques that fail to account for site-specific depositional conditions associated with loess emplacement and diagenesis. OSL-based age models that account for these processes are used to examine detailed records of past sedimentation, as well as grain size and magnetic susceptibility proxies for late Pleistocene East Asian monsoon variation. Abrupt shifts in monsoon proxies occur over 10(2)-10(3) yr time scales, potentially forced by a variety of factors and influenced by site location and site-specific changes in sedimentation.
[63]
FrechenM.
Loess in Europe
[J]. E & G Quaternary Science Journal, 2011, 60(1): 3-5.
In Hungary, many loess/palaeosol sequences have been found to be discontinuous. In order to allow for correlations with other Quaternary records, reliable chronologies are needed. We therefore apply post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR 290 ) dating to the uppermost 20m of the loess sequence at Paks. The pIRIR 290 ages are compared with blue quartz OSL ages to test for potential age overestimation due to poor signal re-setting, and the observed good agreement is taken to imply that the more difficult to bleach pIRIR 290 signal was reset prior to deposition. Our pIRIR 290 based chronology reveals that most of the Late Pleistocene loess was deposited during marine isotope stage (MIS) 3 and during the Last Glacial Maximum (LGM). This is in disagreement with formerly published ages. The discrepancy can most likely be explained by anomalous fading (resulting in an age underestimate); this conclusion is supported by our uncorrected ‘standard’ IRSL ages. We further confirm that the Basaharc Double soil complex can be correlated with MIS 7; the underlying loess and soils cannot be dated accurately because the pIRIR 290 signal approaches saturation.
[65]
Forman SL, PiersonJ.
Late Pleistocene luminescence chronology of loess deposition in the Missouri and Mississippi River valleys, United States
The loess stratigraphy of the mid-continental U.S. is an important proxy record for the advance of the North American ice sheet into the catchment of the Mississippi, Missouri and Ohio rivers. One of the most outstanding problems is deciphering the age of the loess deposits in this area during the Late Pleistocene. We used multiple-aliquot additive dose procedures under infrared stimulated luminescence (IRSL) and single aliquot regeneration (SAR) protocols to resolve ages of loess at the Loveland Silt type locality, Iowa, the Pleasant Grove School section, Illinois, and the Bonfils Quarry section, Missouri. Radiocarbon dated levels in the Peoria Loess and Roxana Silt were used to test the accuracy of the IRSL and SAR methods. SAR on polymineral and quartz extracts yielded underestimates in age by 20–55%, whereas IRSL gave concordant ages to the 14 C control and was used to date the loess sequences. The oldest loess, the Bonfils Silt, gave IRSL ages between 159 and 264 ka and are considered non-finite estimates because the luminescence response was near saturation with additive β dose. The Loveland Silt at the type locality exhibited considerable luminescence in growth with additive β dose and yielded the mean age of 159±14 ka ( n =4). The Teneriffe Silt gave a mean IRSL age of 93±5 ka ( n =4) which, overlaps at two σ with a previous TL age and indicates deposition sometime between 100 and 80 ka. The Roxana Silt yielded stratigraphically consistent IRSL ages between ca. 60 and 30 ka. Luminescence and radiocarbon dating indicate that there were four distinct periods of loess deposition in the Mississippi and Missouri river basins at ca. 180–140 ka, 100–80 ka, 60–30 ka, and 25–12 ka which are concordant with periods of meltwater input to the Gulf of Mexico, another proxy of glaciation in mid-continental North America.
[66]
Berger GW.
Luminescence chronology of late pleistocene loess-paleosol and tephra sequences near Fairbanks, Alaska
Thermoluminescence (TL) and infrared-stimulated luminescence (IRSL) sediment-dating methods have been applied to paleosol- and tephra-bearing loess sequences younger than marine oxygen isotope stage (MIS) 7 at three important sites. TL ages indicate the development of significant paleosols 09080475,000 and 09080430,000 yr ago in the loess sequence at the Gold Hill site. Relatively minor soil development occurred 09080470,000 and 09080448,000 yr ago. Like the 09080475,000-yr-old soil, the 30,000-yr-old soil is apparently of global extent, and consistent in timing with inferred warm intervals elsewhere (e.g., Greenland, Europe, western and central China). At Birch Hill, replicate TL dating of primary loess combined with two earlier TL results from the same site, and with an earlier mean fission-track-glass-shard age of 140,000 00± 10,000 yr for the associated Old Crow tephra, yield a more precise numeric age of 142,300 00± 6600 yr for this Alaska/Yukon chronostratigraphic marker ash bed. Three of the TL ages at the Halfway House site are difficult to interpret, but combined with other evidence, they indicate: (1) the upper 50900096 m of loess from Halfway House is not part of the Gold Hill Loess (equivalent to pre-MIS 5 age) as long thought by T.L. P0108w0108, but rather is much younger; (2) the regionally significant variegated tephra, found in the Fairbanks and Klondike areas and previously thought to be older than MIS 5, has an age of 77,800 00± 4100 yr (late MIS 5).
[67]
Miao XD, Hanson PR, WangH, et al.
Timing and origin for sand dunes in the Green River Lowland of Illinois, upper Mississippi River Valley, USA
OSL and radiocarbon ages also indicate that dunes were reactivated during the early, middle and late Holocene. Some eolian activation occurred within well-defined dry intervals in the upper Midwest, suggesting that increased aridity may have been the primary driver in mobilizing sand. However, many ages do not correspond to drier periods. In contrast to the relative coherency of the Pleistocene OSL ages from multiple study sites, the Holocene OSL ages do not overlap from one site to another, suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the Holocene. Therefore, we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the Holocene. The multiple periods of eolian activity during the Holocene suggest a high potential for future sand activation in the region, and these results are informative for environmental prediction and potential future mitigation.
Optically stimulated luminescence (OSL) dating technique is a reliable method to determine the ages of sand dune sediments. While it seems logical to assume that for these windblown materials (such as sand dune sediments) grains from different sized fractions are suitable for optical dating and would yield identical ages, this was not previously explicitly demonstrated yet. In this study, six samples were selected from the sand dunes intercalated in loess strata near Lanzhou, western Chinese Loess Plateau, and different grain-size quartz fractions (e.g. 38–6302μm, 90–15002μm, 150–20002μm, 200–25002μm and 250–30002μm) were extracted to compare the OSL ages of different grain-size quartz. The results show that: (1) quartz OSL ages derived from different grain-size fractions produce identical ages within errors, confirming that the ages resulting from both coarse silt-sized (or middle grain of 38–6302μm) and sand-sized (90–30002μm) quartz can represent the periods of sand dune accumulation; (2) the OSL ages of the selected sand dune samples fall into ca. 28–1802ka, suggesting that the sand dune accumulation occurred during the marine isotope stage 2 (MIS 2) in current study area, which might imply regional increased aridity on the western Chinese Loess Plateau.
[70]
Kang SG, Wang XL, Lu YC.
Quartz OSL chronology and dust accumulation rate changes since the Last Glacial at Weinan on the southeastern Chinese Loess Plateau
The fine-grained (4–1165μm) quartz Optically Stimulated Luminescence (OSL) dating technique was applied to the Weinan section on the southeastern Chinese Loess Plateau (CLP) with a high luminescence sampling resolution (10- and 20-cm intervals). Fifty-eight OSL ages, spanning c. 1–7465ka, were obtained for the 10-m loess–palaeosol sequences. The reliability of the OSL dating and the constructed chronology was confirmed by comparing the OSL ages with independent dates from other studies and by correlation with palaeoclimatic time series. The closely spaced OSL ages at Weinan indicate that the mean dust accumulation rate (DAR) of L1–1 (MIS 2, 7.0±0.965cm65ka611) is lower than those of L1–3 (MIS 4, 19.1±6.165cm65ka611) and L1–2 (MIS 3, 16.0±0.765cm65ka611) and that the mean DAR61c. 30–2065ka ago (11.4±2.465cm65ka611) is higher than that c. 20–1065ka ago (3.0±0.165cm65ka611) in L1–1. The subsequent calculation of the mass accumulation rate (MAR) indicates that the MAR of L1–1 (10765g65m61265a611) is much lower than those of L1–2 (24765g65m61265a611) and L1–3 (30765g65m61265a611). By comparing the mean DAR results during the Last Glacial at Weinan with those at a further six sites from other studies, we observed that the mean DAR of L1–2 is higher (lower) than that of L1–1 on the eastern (western) CLP, and that the mean DAR during MIS 2 has an evident transition from high to low at c. 2065ka on the entire CLP. Possible mechanisms for the above mean DAR changes at orbital and sub-orbital time scales are presented.
[71]
LiChuanxiang, SongYougui, QianLinbo, et al.
The history of climate change recorded by the grain size at the Zhaosu loess section in the central Asia since the last glacial period
The optically stimulated luminescence (OSL) sensitivity of quartz has a significant influence on luminescence dating procedures. Furthermore, identifying the natural controls of quartz OSL sensitivity is an important step towards new applications of OSL in geology such as provenance tracing. We evaluate the OSL sensitivity (total and the proportion of the informally assigned fast, medium and slow components) of single grains of quartz extracted from 10 different igneous and metamorphic rocks with known formation conditions; and from fluvial and coastal sediments with different sedimentary histories and known source rocks. This sample suite allows assessment of the variability of the OSL sensitivity of single quartz grains with respect to their primary origin and sedimentary history. We observed significant variability in the OSL sensitivity of grains within all studied rock and sediment samples, with the brightest grains of each sample being those dominated by the fast component. Quartz from rocks formed under high temperature (>500掳C) conditions, such as rhyolites and metamorphic rocks from the amphibolite facies, display higher OSL sensitivity. The OSL sensitivity of fluvial sediments which have experienced only a short transport distance is relatively low. These sediments show a small increase in OSL sensitivity downstream, mainly due to a decreasing fraction of -渄im- grains. The quartz grains from coastal sands present very high sensitivity and variability, which is consistent with their long sedimentary history. The high variability of the OSL sensitivity of quartz from coastal sands is attributed more to the mixture of grains with distinct sedimentary histories than to the provenance from many types of source rocks. The temperature of crystallization and the number of cycles of burial and solar exposure are suggested as the main natural factors controlling the OSL sensitivity of quartz grains. The increase in OSL sensitivity due to cycles of erosion and deposition surpasses the sensitivity inherited from the source rock, with this increase being mainly related to the sensitization of fast OSL components. The discrimination of grains with different sedimentary histories through their OSL sensitivities can allow the development of quantitative provenance methods based on quartz.
[73]
MorenoE.
An assessment of the luminescence sensitivity of Australian quartz with respect to sediment history
This study provides a preliminary systematic characterisation of OSL sensitivity, with respect to sediment history, of single grains of Australian quartz from a variety of source rocks and depositional contexts. Samples from two distinct lithologies and with relatively short modern sedimentary histories were compared in an examination of the influence of rock type on OSL sensitivity. Sediments derived from weathered sandstone were found to be brighter than those from metamorphosed schists, suggesting that sensitivity may be inherited from the source rock and its earlier sedimentary history. Secondly, quartz from the same source, but different modes of deposition, was compared to assess the effect on sensitivity of nature of exposure to light during the most recent bleaching event. Quartz grain sensitivity appears not to vary depending on the mode of sediment deposition, suggesting that the nature of exposure to light during deposition is less important in the sensitisation process. This study highlights the complexity and variety of natural sedimentary quartz, demonstrating the limitations of an investigation based solely on OSL sensitivity. Further systematic investigation into the physical, geological and geomorphological characteristics of sediments is proposed to better understand the mechanisms of luminescence sensitisation in quartz.
[74]
Li SH.
Identification of well-bleached grains in the optical dating of quartz
A simple means of identifying poorly bleached samples is proposed for the dating of quartz using the single-aliquot additive-dose optically stimulated luminescence (OSL) protocol. For a well-bleached sample, it is shown that the equivalent dose ( D e ) does not change with the ratio of the natural OSL from a brief (0.1聽s) stimulation to the 110掳C thermoluminescence from a subsequent small test dose. In contrast, in a poorly bleached sample, the D e increases strongly at higher values of the ratio. These observations suggest that this ratio can be used as an indicator of whether or not a sample is well bleached. The OSL/TL ratio is also likely to be sensitive to such factors as thermal history and feldspar contamination.
[75]
Fan TL, Fan YX, ZhaoH,et al.
Investigations on the degree of bleaching of quartz OSL signals using modern aeolian dust from western Loess Plateau, China
Optically Stimulated Luminescence signal of quartz extracted from modern aeolian dust with known maximum age (about decades) was analyzed in terms of degree of bleaching. The results of dose recovery tests show that the modified double single-aliquot regenerative-dose protocol with the early background subtraction is robust for dating these modern dusts using small aliquots. Bleaching of these dusts is discussed based on the distribution of De values in histograms, scatter plots of D e versus sensitivity corrected natural OSL signal and comparison between measured D e and expected D e . The results indicate that most dusts were completely bleached but some dusts were not completely bleached. For those incompletely bleached dusts in Lanzhou area, the maximum OSL age overestimation is up to 鈭1 ka, which might be caused by fast deposition accompanied by heavy sand/dust storms. The research suggests that cautions should be given to OSL ages younger than 1 ka in the western China close to deserts.
[76]
ConstantinD, CameniA, PanaiotuC, et al.
Fine and coarse-quartz SAR-OSL dating of Last Glacial loess in Southern Romania
Previous single aliquot regenerative optically stimulated luminescence (SAR-OSL) dating studies of representative loess sections in southeastern Romania revealed severe discrepancies among the ages obtained on fine (4–11μm) and coarse (63–90μm) grains of quartz. The current study aims at expanding these investigations by extending the area of study to the more westerly loess deposits in the Lower Danube Basin. The luminescence properties of the grain sizes of quartz extracted from 18 samples collected from the Last Glacial loess layer at Lunca section (Wallachian Plain) are examined and compared. Investigations confirm the reliability of the SAR-OSL protocol previously applied to Romanian loess (preheat at 220°C for 10s, cutheat at 180°C and elevated temperature OSL). Despite this, the obtained equivalent doses on coarse quartz are higher than those obtained on fine material for most samples, as in the case of our previous studies. These results into fine quartz OSL ages that are significantly lower compared to the coarse quartz age results. However, the ages obtained for the uppermost two samples are in very good agreement. Ages spanning from 19±2 ka to 43±4 ka on fine quartz and from 20±2 ka to 54±6 ka on coarse quartz have been obtained for the loess deposited during Last Glacial period. Based on the fine as well as the coarse quartz chronology significantly low sedimentation rates were computed for the Last Glacial Maximum period and MIS 3. OSL ages and magnetic susceptibility measurements indicate that the loess layer corresponding to the Early Glacial period (MIS 4) is very thin at this site and affected by pedogenesis. Regarding the investigation into the cause of the observed age discrepancy we present evidence through time resolved investigations that the observed behaviour is typical of quartz and cannot be accounted by feldspar contamination. We confirm once more that the growth of the OSL signal in nature does not correspond to the laboratory generated SAR dose response curve that is best described by a sum of two saturating exponential functions. The differences observed between the natural and the laboratory dose response for the two quartz fractions are believed to be a cause for the different chronologies reported.
[77]
Fan YX, ZhaoH, Chen FH.
The equivalent dose of different grain size quartz fractions from lakeshore sediments in the arid region of north China
Equivalent dose ( D e) values were measured by using medium aliquots of different grain size quartz fractions of five lakeshore sediments from the arid region of north China. There are two different relationships between D e values and grain sizes of these five samples. The first relationship is that the D e02values obtained from various grain sizes are in agreement within 1 delta errors. The second relationship is that D e values are similar to each other for fractions between 125 and 300 μm, while the D e value of the 63–90 μm fraction is 406555% smaller than others. For example, the D e values obtained for sample #3 are 20.15 ± 1.19 Gy, 19.80 ± 0.83 Gy and 20.93 ± 1.06 Gy for fractions of 90–125, 125–150 and 250–300 μm respectively, but are 10.79 ± 0.84 Gy for the 63–90 μm fraction. The second relationship can't be interpreted by previous studies of both dosimetry and heterogeneous bleaching. It is deduced for sample #2, #3 and #6 that fine particles (<90 μm) intruded after the dominant sedimentation. Comparison of OSL ages from different grain size fractions of sample #2 with a radiocarbon age from the same lithologic layer supports that fractions coarser than 125 μm yield more reliable burial ages, while the fraction finer than 90 μm yields underestimated ages for some lakeshore sediments from this arid region.
[78]
Bateman MD, Boulter CH, Carr AS,et al.
Detecting post-depositional sediment disturbance in sandy deposits using optical luminescence
Post-depositional mixing or exhumation is common in surficial sediments, yet may be unobservable from field evidence. However, any disturbance may have significant consquences in terms of establishing a reliable luminescence age determination. Optically stimulated luminescence (OSL) measurements, particularly measurements at the single grain level, can be used to gain an insight into both contemporary and past post-depositional processes. This paper examines sites from Texas and Florida (USA) with independent chronological control to demonstrate the potential effects of varying degrees of bioturbation on OSL. Results show that contemporary soil forming processes clearly impact on the palaeodose ( D e) replicate distributions which are measured in order to derive an OSL age. Significant levels of scatter and apparently zero dose grains are observed in the upper-most sediments; declining with depth from the surface. D e replicates from undisturbed and fully bleached sediments are unskewed, show low overdispersion (OD) and comparable single grain and single aliquot OSL ages. Bioturbated sediments, however, may show highly skewed multi-model D e distributions with higher OD values, zero dose grains at depth, and significant diffences between single grain and single aliquot results. True burial ages may be derived from minimally bioturbated sediments through the application of statistical analysis such as finite mixture modelling to isolate D e components. However, for significantly bioturbated sediments, the latter approach, even at the single grain level, produces inaccurate ages. In such cases we argue that additional evidence (both dating and contexual) may be required to identify with confidence the burial D e population.
All Quaternary dating methods involve the measurement of one or more variables to estimate the age of a sample. Each measured quantity has an associated error and uncertainty, and may also be subject to natural variation. We review the statistical estimation of such uncertainties and variation for comparing and interpreting age estimates, with specific reference to the estimation of equivalent dose (De) values in the optically stimulated luminescence (OSL) dating of sediments. We discuss statistical aspects of OSL signal and background estimation, the determination of De values for multi-grain aliquots and individual mineral grains from the same and different samples, and the extent of variation commonly observed among such estimates. Examples are drawn from geological and archaeological contexts. We discuss the strengths and weaknesses of various graphical methods of displaying multiple, independent estimates of De, along with statistical tests and models to compare and appropriately combine them. Many of our recommendations are applicable also to the clear presentation of data obtained using other Quaternary dating methods. We encourage the use of models and methods that are based on well established statistical principles and, ideally, are validated by appropriate numerical simulations; and we discourage the adoption of ad hoc methods developed using a particular set of measurement conditions and tested on a limited number of samples, as these may not be applicable more generally. We emphasise that the choice of statistical models should not be made solely on statistical grounds (or arbitrary rules) but should take into account the broader scientific context of each sample and any additional pertinent information.
[81]
Huntley DJ, LamotheM.
Ubiquity of anomalous fading in K-feldspars and the measurement and correction for it in optical dating
[J]. Canadian Journal of Earth Sciences, 2001, 38(7): 1 093-1 106.
The Karewa deposits of the tectonic basin of Kashmir in India are overlain by eolian loess. This loess (up to 25 m thick) is divided by several paleosols, which have been recently studied and classified in detail. Thermoluminescence dating of these deposits in conjunction with micromorphological analysis enables the following conclusions:
[84]
BrongerA, Pant RK, Singhvi AK.
Pleistocene climatic changes and landscape evolution in the Kashmir Basin, India: Paleopedologic and chronostratigraphic studies
The Kashmir Basin is filled with Pliocene-Pleistocene fluvio-lacustrine sediments. On the flank of the Pir Panjal these sediments, called “Lower Karewas”, are covered with loess deposits up to 25 m thick that contain numerous middle and late Pleistocene paleosols, mostly polygenetic pedocomplexes, which were classified by micromorphological studies. Thermoluminescence dates provide a chronostratigraphy of the late Pleistocene loess-paleosol sequences. On the Himalayan flank, the “Upper Karewas” are covered only with late Pleistocene loess-paleosol sequences. Their base is the last interglacial soil, developed ca. 110,000 ± 10,000 yr B.P. This soil is genetically comparable to the modern soil and, therefore, is thought to have developed under a deciduous forest in a “xeric” soil moisture regime. The loesses of last glacial age on both flanks of the basin contain three humus-rich Ah, mostly Aht, horizons, indicating three warm and mostly humid climatic episodes between ca. 80,000 and 50,000 yr B.P. The middle Pleistocene loesses contain at least four Bwt, or thick Bt, horizons developed during four interglacial periods, having climates similar to the present. Large parts of the Karewa Lake must have lasted until the end of the penultimate glacial age.
[85]
Rendell HM.
Environmental changes during the Pleistocene in the Potwar Plateau and Peshawar Basin, northern Pakistan
[J]. Proceedings of the Indian National Science Academy, Part A: Physical Sciences,1988, 54(3): 390-398.
Thomsen, K.J., Murray, A.S., Jain, M., B03tter-Jensen, L. [2008. Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts. Radiat. Meas. 43, 1474–1486] have identified a number of feldspar signals which show significantly less anomalous fading than the conventional IRSL signal stimulated at 5002°C and detected in the blue–violet region of the spectrum. One of these was the post-IR IR signal in which first an IR bleach is carried out at a low temperature (e.g. 10002s at 5002°C) and a remaining IRSL signal is measured at an elevated temperature (10002s at 22502°C; detection in the blue–violet region). It is the latter signal that is of interest in this paper. We test such a post-IR IR dating protocol on K-feldspar extracts from a variety of locations and depositional environments and compare the results with those from the conventional IR at 5002°C protocol. Based on laboratory tests (recycling ratio, recuperation, dose recovery) we show that our SAR protocol is suitable for these samples. The observed post-IR IR fading rates (mean g 2days02=021.6202±020.06%/decade, n02=0224; assuming logarithmic fading) are significantly lower than those measured at 5002°C (mean g 2days02=023.2302±020.13%/decade, n02=0224). The signal is bleachable in nature although residual doses of the order of a few Gy are to be expected. After fading correction the ages are indistinguishable from those measured by IR at 5002°C over an age range from a few ka to >26002ka. However, the correction factor for anomalous fading is only 6539% of that of the conventional IR at 5002°C signal. This smaller correction factor makes the new post-IR IR ages much less dependent on the inherent assumptions included in the fading correction model.
[89]
Huntley DJ, Lian OB.
Some observations on tunneling of trapped electrons in feldspars and their implications for optical dating
Anomalous fading in feldspars is now understood to be caused by the tunnelling of electrons from one defect site to another. Here we present some experimental observations concerning the phenomenon. The fading rates of a variety of feldspar crystals and K-feldspar separates from sediments are reported. It is found that (1) the fading rates of 77 K-feldspar extracts from sediments range from 1 to 10%/decade, with an average value of about 5%/decade, (2) the fading rates of K-feldspars extracted from sediments derived largely from volcanic bedrock are not higher than those from non-volcanic bedrock as is widely thought, (3) the fading rates of 31 individual feldspars range from 1 to 35%/decade, (4) in plagioclase feldspars the fading rate increases with increasing Ca and/or Fe content, (5) the fading rate increases with laboratory radiation dose at large doses, (6) for samples for which the time elapsed since burial is long enough for their luminescence to be in saturation, the fading rate is correlated with the ratio of the field saturation intensity to the laboratory saturation intensity; extrapolation to zero fading rate shows that trap emptying as a result of thermal eviction is not significant, and that the mean thermal lifetime in temperate environments of electrons in traps relevant to dating is 猢4 Ma., and (7), different aliquots of a sample can have fading rates that differ by a factor as large as two even if the aliquots contain several thousands of grains, thus it is necessary to ensure when correcting ages for anomalous fading that the fading rate used is that applicable to the aliquots on which the equivalent dose is measured.
[90]
ZhaoH, Li SH.
Luminescence isochron dating: A new approach with different grain sizes
Abstract A new approach to isochron dating is described using different sizes of quartz and K-feldspar grains. The technique can be applied to sites with time-dependent external dose rates. It is assumed that any underestimation of the equivalent dose (De) using K-feldspar is by a factor F, which is independent of grain size (90-350 microm) for a given sample. Calibration of the beta source for different grain sizes is discussed, and then the sample ages are calculated using the differences between quartz and K-feldspar De from grains of similar size. Two aeolian sediment samples from north-eastern China are used to illustrate the application of the new method. It is confirmed that the observed values of De derived using K-feldspar underestimate the expected doses (based on the quartz De) but, nevertheless, these K-feldspar De values correlate linearly with the calculated internal dose rate contribution, supporting the assumption that the underestimation factor F is independent of grain size. The isochron ages are also compared with the results obtained using quartz De and the measured external dose rates.
[91]
AuclairM, LamotheM, HuotS.
Measurement of anomalous fading for feldspar IRSL using SAR
Age underestimates and wide equivalent paleodose distributions are commonly observed in IRSL dating of feldspar minerals using both multiple and single aliquot methods. For well-bleached sediments, this is thought to be caused primarily by anomalous fading. This article explains how to assess a fading rate ( g value), which can be used to correct the measured optical ages. It also shows how different fading rates are obtained on single-aliquots using different protocols. It is found that the g value deduced from delayed L i/ T i measurements is strongly dependent on the timing of the preheat treatment. For the single-aliquot regenerative-dose protocol (SAR), best results are obtained using delayed L i/ T i ratios if the samples are preheated before storage.
[92]
LiB, Li SH, Wintle AG, et al.
Isochron measurements of naturally irradiated K-feldspar grains
The equivalent doses of K-feldspar grains in a range of grain sizes from 90 to 250 μ m mathContainer Loading Mathjax diameter were measured using a single-aliquot regenerative-dose protocol for the infrared stimulated luminescence (IRSL) signals for two samples of desert sand. The equivalent doses for each sample were compared with that for the 125 – 150 μ m mathContainer Loading Mathjax grains of quartz from the same samples. The results suggested that the K-feldspar equivalent doses were underestimated because of anomalous fading. Measurements of the decay of the IRSL signals following laboratory irradiation for these two samples, and an additional one from a previously published isochron study, showed anomalous fading during the period of laboratory storage. The decay rate was about 3% per decade for all samples and was independent of the grain size used. Using plots of equivalent doses for K-feldspars as a function of their calculated internal dose rate, and the quartz equivalent dose as a function of grain size, it was concluded that the IRSL signal derived from the internal dose rate had not faded over the 13,000 years that had elapsed since the grains were deposited.
[93]
LiB, Li SH, Wintle AG, et al.
Isochron dating of sediments using luminescence of K-feldspar grains
[J]. Journal of Geophysical Research: Earth Surface, 2008, 113(F2).DOI:10.1029/2007JF000900.
[1] A new method for dating well-bleached sediments is presented, with results for thirteen samples from China. The method uses an isochron constructed from the measurement of natural radiation doses received by potassium-feldspar grains in a range of grain sizes using the infrared stimulated luminescence (IRSL) signal. The age of deposition of the sediment is calculated from this isochron and from the internal dose rate to the grains from 40K and 87Rb in the crystal lattice. This procedure appears to overcome age underestimation due to anomalous fading, a phenomenon that has precluded conventional luminescence dating of K-feldspars and would be applicable to K-feldspars for which the natural dose is beyond the linear dose response region. Also, since the isochron IRSL method is reliant on only the internal dose rate, it overcomes problems related to (1) changes in past dose rate due to postdepositional migration of radionuclides, (2) changes in water content as water-lain sediments dry out, (3) spatial heterogeneity in the gamma dose rate, and (4) uncertainties in the cosmic ray dose rate during the period of sample burial.
[94]
Thomsen KJ, Murray AS, JainM, et al.
Laboratory fading rates of various luminescence signals from feldspar-rich sediment extracts
Feldspar as a retrospective dosimeter is receiving more and more attention because of its useful luminescence properties; in particular the dose response curve extends to significantly higher doses than quartz. However, feldspars have one major disadvantage; both the thermoluminescence (TL) and optically stimulated luminescence (OSL) signals exhibit anomalous (athermal) fading. Much of the OSL work carried out on feldspars in recent years has focussed on determining fading rates and correcting for them. Almost all work has been carried out using IR stimulation at 50 掳C detected in the blue region of the spectrum. In contrast, we have determined fading rates for various sedimentary feldspar samples using different stimulation and detection windows. If the initial part of the OSL signal is used the lowest fading rate is observed with post-IR blue stimulation (UV detection), but if a later part of the signal is used the lowest fading rate is obtained for IR stimulation (blue detection). Daylight bleaching experiments show that, unlike quartz, the initial and final parts of the feldspar OSL signal bleach at approximately the same rate. Stimulation at elevated temperatures significantly reduces the apparent fading rate. This signal appears to bleach more rapidly in daylight than the signal observed when stimulation is at 50 掳C (for IR stimulation and blue detection). We conclude that there are OSL signals from sedimentary feldspars which fade at a significantly lower rate than the signal used conventionally, and that further testing of these signals is warranted to see if they are dosimetrically useful.
[95]
Murray AS, Buylaert JP, Thomsen KJ, et al.
The effect of preheating on the IRSL signal from feldspar
It is difficult to relate the IRSL signal from feldspar to a particular region of the TL curve; prior IR stimulation reduces the TL signal over a wide range of temperatures. Such data are apparently consistent with the observation from pulse anneal experiments that a laboratory-induced IRSL signal is detectably eroded by a relatively low temperature preheat. These results can be explained by a distribution of trap depths of IR sensitive traps, and/or by changes in recombination probability induced by IR exposure. To investigate the relative importance of these processes, we first examine the relationship between the loss of blue IRSL and TL signals with preheating, and the effect of prior IRSL on the TL signal. Using IRSL measured at 50 °C and a SAR protocol, we then examine the dependence on preheat temperature of equivalent dose (D e), laboratory fading rate ( g), and the resulting luminescence age, from three sedimentary potassium-rich feldspar extracts. We demonstrate that there is no systematic increase in D e for a preheat temperature range from 6580 °C to 65320 °C (60 s duration). After fading correction, age plateaus vary slightly over the temperature range examined, but there is no evidence for an increase in age with preheat temperature. We therefore conclude that the main dosimetry trap(s) in feldspar are not significantly eroded by laboratory heating for up to 60 s at 320 °C, and we tentatively identify the source of this IRSL as a TL peak lying between 410 and 420 °C; this suggestion is consistent with a kinetic analysis of sensitivity-corrected IRSL data. The corollary to our observations is that shallow (unstable) traps do not give rise to a significant IRSL signal.
[96]
ThielC, Buylaert JP, MurrayA, et al.
Luminescence dating of the Stratzing loess profile (Austria)—Testing the potential of an elevated temperature post-IR IRSL protocol
Feldspar infrared stimulated luminescence (IRSL) signals saturate at 652000Gy, i.e. 65500–700ka (assuming a dose rate of 3–4Gy/ka, typical for loess) and it is therefore theoretically possible to date Middle Pleistocene loess. However, the accuracy of age estimates is hampered by anomalous fading, which leads to significant age underestimation. Fading corrections have been proposed but these corrections are reliant on inherent assumptions and in any case are inapplicable at large doses (as the growth curve approaches saturation). Recent studies have identified a post-IR IRSL signal that shows less fading and is thus less dependent on accurate fading corrections. This study builds upon these investigations and applies a post-IR IRSL SAR dating protocol to polymineral fine-grain samples of the loess/palaeosol sequence in Stratzing, Lower Austria. After a preheat at 320°C (60s) and an IR bleach at 50°C (200s) IRSL was measured at 290°C for 200s; the same set of conditions were used to measure the response to a test dose. Recycling ratios, recuperation and dose recovery tests show that this protocol is suitable for the loess under investigation, although finite residual doses of up to 20Gy are observed. For the oldest samples, the natural signal is in, or close to, saturation, indicating that fading is negligible in nature. This observation is inconsistent with the measured laboratory fading rates of 1–1.5%/decade and needs further investigation.
[97]
Buylaert JP, JainM, Murray AS, et al.
A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments
Abstract Top of page Abstract Signal stability – physical model Sample preparation, analytical facilities and dose-rate determination Samples and published age control Additional quartz OSL age control Feldspar luminescence characteristics Results and discussion Conclusions Acknowledgements References Luminescence dating is used extensively to provide absolute chronologies for Late Pleistocene sediments. Nowadays, most optical dates are based on quartz optically stimulated luminescence (OSL). However, the application of this signal is usually limited to the last 6510065ka because of saturation of the quartz luminescence signal with dose. In contrast, the feldspar infrared stimulated luminescence (IRSL) dose–response curve grows to much higher doses; this has the potential to extend the datable age range by a factor of 4–5 compared with quartz OSL. However, it has been known for several decades that this IRSL signal is unstable, and this instability often gives rise to significant age underestimation. Here we test against independent age control the recently developed feldspar post-IR IRSL approach to the dating of sediments, which appears to avoid signal instability. A physical model explaining our observations is discussed, and the method is shown to be accurate back to 60065ka. The post-IR IRSL signal is reduced by exposure to daylight more slowly than that from quartz and low-temperature IRSL, preventing its general application to young (e.g. Holocene) sediments. Nevertheless, this new approach is widely applicable (feldspar of appropriate luminescence behaviour is even more ubiquitous than quartz). These characteristics make this a method of great importance for the dating of Middle and Late Pleistocene deposits.
[98]
LiB, Li SH.
Luminescence dating of K-feldspar from sediments: A protocol without anomalous fading correction
A protocol for optical dating of potassium-rich feldspar (K-feldspar) is proposed. It utilizes the infrared stimulated luminescence (IRSL) signal measured by progressively increasing the stimulation temperature from 50 to 250°C in step of 50°C, so-called multi-elevated-temperature post-IR IRSL (MET-pIRIR) measurements. Negligible anomalous fading was observed for the MET-pIRIR signals obtained at 200 and 250°C. This was supported by equivalent dose (D e ) measurements using the IRSL and MET-pIRIR signals. The D e values increase progressively from 50°C to 200°C, but similar D e values were obtained for the MET-pIRIR signal at 200 and 250°C. Measurement of modern samples and bleached samples indicates that the MET-pIRIR signals have small residual doses less than 5Gy equivalent to about 1–2ka. We have tested the protocol using various sedimentary samples with different ages from different regions of China. The MET-pIR IRSL ages obtained at 200 and 250°C are consistent with independent and/or quartz OSL ages.
[99]
KarimiA, FrechenM, KhademiH.
Chronostratigraphy of loess deposits in northeast Iran
Little information is available on the paleoclimate evolution of northeast Iran relating to global cold and warm stages. The loess/paleosol sequences from southern Mashhad and Kalat-e Naderi areas were studied to determine the landscape evolution and to set up the first chronological framework for the Pleistocene deposits in northeast Iran. The loess deposits in these areas are less thick (up to 12 m) and have a more patchy distribution than in the Caspian Lowland of northern Iran. Infrared stimulated luminescence (IRSL) dating of loess or loess derivatives from the Robat-e Khakestari, Tappeh Salam and Deh Gheybi sections (a) and (b) from southern Mashhad, as well as Kalat-e Naderi sections (a) and (b) in Kalat-e Naderi area provides a more reliable chronological framework for climate and environmental changes taken place over for the time period including the penultimate and last interglacial/glacial cycles. The Robat-e Khakestari section, the Kalat-e Naderi sections (a) and (b), and to some extent the Tappeh Salam section include loess/paleosol sequences, which are chronologically in excellent agreement with the loess record of the Caspian Lowland in northern Iran. The Deh Gheybi sections (a) and (b) include loess-like sediments and fluvial deposits that make their interpretation difficult. Loess accumulated during MIS 2 at the Robat-e Khakestari section and at the Kalat-e Naderi sections (a) and (b) suggesting a more windy and arid Last Glacial Maximum (LGM) in northeast Iran. Paleosols, correlating most likely with MIS 5, were covered by fluvial sediments at the Kalat-e Naderi section (a). The absence of loess deposits correlating to MIS 3 and MIS 4 at the Robat-e Khakestari section is very likely to have been caused by fluvial processes and water erosion.
[100]
LauerT, VlaminckS, FrechenM, et al.
The Agh Band loess-palaeosolsequence—A terrestrial archive for climatic shifts during the last and penultimate glacial-interglacial cycles in a semiarid region in northern Iran
The results show that the Agh Band profile yields a climate archive reaching from MIS 7 to MIS 2. Several chronological hiatuses of some 10ka show that periods of intense loess accumulation were interrupted by phases of only minor loess sedimentation and/or erosion. The Agh Band profile is subdivided by several shifts in grain-size distribution. The coarsening- and fining up trends correlate with increasing and decreasing wind-velocity, respectively. In the central part of the Agh Band loess sequence a weakly developed palaeosol is preserved which was developed at around 80ka. Furthermore, the loess deposits formed from about 100ka to 60ka ago show banded structures. A pedocomplex including two well-developed palaeosols consisting of Bw(y) horizons and a CB-horizon as well as intercalated loess can be found in the lower part of the sequence also evidenced by the increased values of magnetic susceptibility. The corresponding luminescence age estimates indicate that the palaeosols represent a period of increased humidity and landscape stability during late MIS 7 and MIS 6. Hence, in the Agh Band loess, various changes in the palaeo-sedimentary system, triggered by changes in climate can be observed. This yields important information on the sensitive response of sedimentary systems and landscapes within semi-arid regions to shifts in moisture and possibly temperature.
[101]
LiB, JacobsZ, Roberts RG, et al.
Review and assessment of the potential of post-IR IRSL dating methods to circumvent the problem of anomalous fading in feldspar luminescence
Quartz has been the main mineral used for optically stimulated luminescence (OSL) dating of sediments over the last decade. The quartz OSL signal, however, has been shown to saturate at relatively low doses of 鈭200-400 Gy, making it difficult to be used for dating beyond about 200 thou-sand years (ka), unless the environmental dose rate is low. The infrared stimulated luminescence (IRSL) from feldspars has been shown to continue to grow to higher dose levels than quartz OSL. The application of IRSL dating of feldspars, however, has long been hampered by the anomalous fading effect. Recent progress in understanding anomalous fading of the infrared stimulated luminescence (IRSL) signals in potassium-feldspar has led to the development of post-IR IRSL (pIRIR) protocols and also a multiple elevated temperature (MET) stimulation (MET-pIRIR) protocol. These procedures have raised the prospect of isolating a non-fading IRSL component for dating Quaternary deposits containing feldspars. In this study, we review the recent progress made on (1) overcoming anomalous fading of feldspar, and (2) the development of pIRIR dating techniques for feldspar. The potential and problems associated with these methods are discussed.
[102]
LiB, Roberts RG, BrummA, et al.
IRSL dating of fast-fading sanidine feldspars from Sulawesi, Indonesia
The chronology of dust deposition and climate during the last interglacial is poorly known on the Chinese Loess Plateau. Here, 51 samples were taken from the 655m S1 palaeosol (MIS5) at the desert marginal Jingbian site to develop what is currently the most detailed S1 chronology on the Plateau using instrumental dating techniques. We use the post-IR IRSL signal from sand-sized grains of K-rich feldspar. Signal resetting in the agricultural layer shows that it is possible to almost completely zero this signal in nature. First IR stimulation plateau measurements show that there is no clear dependence of D e on first IR stimulation temperature between 50 and 260°C suggesting negligible signal fading. Resultant ages are consistent with a last interglacial age (65130 to 6575 ka) and are also consistent within errors with continuous linear sedimentation rates. The average mass accumulation rate for S1 is 65150gm 612 a 611 , considerably higher than at many other sites but within the overall range of Loess Plateau estimates. The remarkably stable sediment accumulation at the site contrasts with a more complex record of environmental and monsoonal change recorded in grain-size and magnetic susceptibility.
Evolution of Asian monsoons and phased uplift of the Himalaya-Tibetan Plateau since Late Miocene times
Loess in Kunlun Mountains and its implications on desert development and Tibetan Plateau uplift in west China
0
2002
Tectono-climatic implications of Eocene Paratethys regression in the Tajik Basin of Central Asia
0
2015
Central Asian aridification during the late Eocene to early Miocene inferred from preliminary study of shallow marine-eolian sedimentary rocks from northeastern Tajik Basin
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... The quartz OSL dating results and 14C results from three loess section in the arid central Asia (a)Zeketai (ZKT) loess section in Xinjiang Uygur Autonomous Region of China[18,19]. (b) Nilka (NLK) section in Xinjiang Uygur Autonomous Region of China[21,46]. (c) Bishkek loess section in Kyrgyz Republic[49] ...
A luminescence dating study of loess deposits from the Yili River Basin in Western China
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... The quartz OSL dating results and 14C results from three loess section in the arid central Asia (a)Zeketai (ZKT) loess section in Xinjiang Uygur Autonomous Region of China[18,19]. (b) Nilka (NLK) section in Xinjiang Uygur Autonomous Region of China[21,46]. (c) Bishkek loess section in Kyrgyz Republic[49] ...
A combined luminescence and radiocarbon dating study of the Ili Loess, Central Asia
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... The quartz OSL dating results and 14C results from three loess section in the arid central Asia (a)Zeketai (ZKT) loess section in Xinjiang Uygur Autonomous Region of China[18,19]. (b) Nilka (NLK) section in Xinjiang Uygur Autonomous Region of China[21,46]. (c) Bishkek loess section in Kyrgyz Republic[49] ...
Godfrey-Smith D I, Thewalt M L W. Optical dating of sediments
High-resolution OSL dating of a late Quaternary sequence from Xingkai Lake (NE Asia): Chronological challenge of the “MIS 3a Mega-paleolake” hypothesis in China
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
An analysis of the components of the luminescence signals of selected polymineral and quartz samples from loess in western China and southern Tajikistan, and their suitability for optical dating
0
2010
Loess chronology of the Caspian Lowland in Northern Iran
Paleoenvironmental changes recorded in a luminescence dated loess/paleosol sequence from the Tianshan Mountains, arid Central Asia, since the Penultimate Glaciation
A high-resolution quartz OSL chronology of the Talede loess over the past ~30 ka and its implications for dust accumulation in the Ili Basin, Central Asia
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... The quartz OSL dating results and 14C results from three loess section in the arid central Asia (a)Zeketai (ZKT) loess section in Xinjiang Uygur Autonomous Region of China[18,19]. (b) Nilka (NLK) section in Xinjiang Uygur Autonomous Region of China[21,46]. (c) Bishkek loess section in Kyrgyz Republic[49] ...
Rapid and cyclic dust accumulation during MIS 2 in Central Asia inferred from loess OSL dating and grain size analysis
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
Quartz OSL and K-feldspar pIRIR dating of a loess/paleosol sequence from arid central Asia, Tianshan Mountains, NW China
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
... The quartz OSL dating results and 14C results from three loess section in the arid central Asia (a)Zeketai (ZKT) loess section in Xinjiang Uygur Autonomous Region of China[18,19]. (b) Nilka (NLK) section in Xinjiang Uygur Autonomous Region of China[21,46]. (c) Bishkek loess section in Kyrgyz Republic[49] ...
Luminescence-chronology of the loess palaeosol sequence Toshan, Northern Iran—A highly resolved climate archive for the last glacial-interglacial cycle
... Location of the study area and published loess record sites in the arid Central Asia a:Toshan section[50].b:Darai Kalon section[44].c:Orkutsay section[38].d:Bishkek section[49].e:Remsowka section[18].f:Zhaosuboma(ZSP) section[20].g:Talede (TLD) section[42].h:Xiaoerbulake (XEBLK) section[47].i:Nilka(NLK) section[21,46].j:Zeketai (ZKT) section[18,19].k:Lujiaowan (LJW) / Lujiaowan10 (LJW10) section[43].l:Shuixigou (SXG) section[43].m:Baiyanghe (BYH) section[48] ...
The Agh Band loess-palaeosolsequence—A terrestrial archive for climatic shifts during the last and penultimate glacial-interglacial cycles in a semiarid region in northern Iran
, 魏海涛
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