Late pleistocene evolution of Lake Manas in western China with constraints of OSL ages of lacustrine sediments

Lake Manas, located in northwestern China, has been formed in a structure depression since early Quaternary. Optically stimulated luminescence (OSL) dating is applied to the lacustrine and aeolian deposits collected from the lake to construct a chronological frame for lake level fluctuations since the last inter-glacial period. The results yielded two stages of high lake stands (∼20 m above the present lake bed) occurred before 66 ka and 38–27 ka ago. No evidence for Holocene high lake level was found in the studying area.     

Age determination for a Neolithic site in northeastern Qinghai-Tibetan Plateau using a combined luminescence and radiocarbon dating

The archaeological Shaliuheqiaodong site, located at the junction between the estuary of Shaliu River and the northeast bedrock terrace of Qinghai Lake, is one of the earliest Neolithic Age sites in the Qinghai-Tibetan Plateau (QTP), which is critical for understanding patterns of prehistoric human inhabitation in the high plateau extreme environments. There are only two published radiocarbon ages by far for chronological control. Recently, a new section (Gangcha section) was found, with abundant charcoals and fish bones well-preserved in the matrix of aeolian sediments, providing a good opportunity for a combined study of luminescence and radiocarbon dating. In the current study, we obtained three luminescence ages on aeolian sediment, six radiocarbon ages (three on charcoals and three on fish bones). Our results showed that the luminescence ages (average of 3.2 ± 0.2 ka) are in agreement with charcoal radiocarbon ages (3165–3273 cal a BP) where applicable, and that the lake reservoir effect age of radiocarbon dating was approximately 0.3–0.7 cal ka BP and an average of 0.4 cal ka BP at ∼3.2 cal ka BP (age difference between that of charcoals and fish bones). The prehistoric residence in Qinghai Lake area seemed to be sequenced from 15 ka BP to 3.1 ka BP, based on our data and previously published data altogether. The obvious baked vestiges on the bones of fish and animals, as well as a number of artifacts, indicate that naked carps had become a food resource for prehistoric people at least since 3.2 cal ka BP.     

Timing for high lake levels of Qinghai Lake in the Qinghai-Tibetan Plateau since the Last Interglaciation based on quartz OSL dating

Qinghai Lake is situated in the northeast of the Qinghai-Tibetan Plateau (QTP). Its size and proximity to the junction of three major climate systems make it sensitive to climate changes. Some investigations on shorelines of Qinghai Lake suggested highstands during MIS 3, but to what extent the lake level was higher than today is yet undetermined. Others proposed that the maximum highstands probably dated to MIS 5. It has also been shown that the lake level 120 m higher than today occurred at around 12 ka. Most of these previous ages were obtained using ¹⁴C dating or multiple-aliquot IRSL/OSL dating. For ¹⁴C dating, because of the dating limit (<40 ka) and the lack of suitable dating materials in this arid area, it is difficult to establish reliable chronological control. In the present study, seven samples collected from lacustrine deposits (five samples) and sand wedges (two samples) were dated using quartz optically stimulated luminescence (OSL) with the single aliquot regenerative-dose (SAR) protocol. OSL dating results showed that (1) the lake had experienced two high lake levels, one was in MIS 5 and another in early to middle MIS 3; (2) no evidence of high lake levels in MIS 4 has been found; (3) the alluvial gravels, whose surface is at an elevation of ～3246 m, were formed at least 28.8 ± 2.3 ka ago, and the widespread sand wedges within the alluvial gravels were formed during the period of 15.1–28.8 ka, which implied that the lake level had not reached an elevation of ～3240 m after 28.8 ± 2.3 ka.     

Luminescence chronology of loess-palaeosol deposits in the Central Shandong Mountains region: Provenances and paleoclimate implications

The loess-palaeosol deposits of the Central Shandong Mountains (CSM) to the east of the Chinese Loess Plateau (CLP) potentially provide valuable archives for the reconstruction of East Asian monsoon patterns. However, compared to the abundant attention given to the loess layer, fewer studies have explored the palaeosols documenting the processes and characteristics of interglacial climate changes. The high-resolution chronologies and provenances of the palaeosol in the CSM area are still unclear. In this work, the luminescence ages and paleoclimate proxies in the Shaozhuang (SZ) and Focun (FC) sections were studied, by combining detrital zircons U–Pb ages from the loess-palaesosol in Jingbian, Licheng, Focun, Pianguan and Dongming Yellow River sediments. Quartz single-aliquot regenerative dose protocol (SAR) and K-feldspar post-infrared IRSL (pIRIR₂₉₀) dating results were obtained in the SZ (8.0 ± 1.1 ka −50.8 ± 2.7 ka) and FC (3.8 ± 0.3 ka—144.0 ± 7.8 ka) sections to develop the most detailed CSM region chronologies to date. The analyzed grain sizes and detrital zircon U–Pb ages suggest that the provenance of the CSM loess was dominated by local Yellow River sediments. The palaeosols observed in the field in these two sections were composed of both aggradation soils deposited in the interglacial period and non-aggradation soil formed by the weathering and leaching of the underlying loess. We found evidences for the presence of non-aggradation soils as indicated the relatively high 5–16 μm particle percentages, relatively low chemical index of alteration (CIA) values and the percentages of >63 μm particles compared to those of the overlying palaeosol layers. Nevertheless, the loess-palaeosol deposits in the CSM are still the product of the East Asian monsoon and global climatic variations, as the deposits have recorded the glacial-interglacial cycles.     

Luminescence dating of a hearth from the archaeological site of Jiangxigou in the Qinghai Lake area of the northeastern Qinghai-Tibetan Plateau

Archeological research over the past several years has started to provide evidence relevant to understanding both the timing of and processes for human colonization of the high Qinghai-Tibetan Plateau. Much of this research has been in the Qinghai Lake area and the Qaidam Basin in the northeastern Qinghai-Tibetan Plateau. However, chronological data are still limited. Recently, a hearth was discovered in the Jiangxigou site in the south of the Qinghai Lake area, which was likely used by prehistoric hunters. The site is in the mouth of a canyon approximately 4.5 km from Qinghai Lake. Previous ages in this site are based on ¹⁴C dating only. The current study provides additional OSL dates for the hearth. The ages of four OSL samples bracketing the hearth range from 12.9 ± 0.9 to 14.4 ± 1.0 ka, but standard deviations overlap extensively and they likely represent the same age. The OSL ages show that by about 14.3 ± 1.0 ka prehistoric peoples were living in the Qinghai Lake area.     

Luminescence dating of a megaflood event on a terrace of the Jinsha River,China

The numerical dating of megaflood sediments is a worldwide challenge, a fact that has impeded a full understanding of Late Quaternary dam-outburst flood processes that occurred along the river courses of the Tibetan Plateau. Optically stimulated luminescence (OSL) dating has been widely used on such sediments. Due to their short transportation distances prior to deposition, the OSL signals of megaflood sediments are often partially bleached, resulting in age overestimations. Here, we report on a comparison of OSL ages obtained using both quartz (4–11 μm FG; 90–125, 180–250 μm CG) and K-feldspar (180–250 μm CG) extracted from sediments taken from the Binghong-Bingnong Neolithic-Bronze Age site on the second Jinshan River terrace (T2), in Yunnan Province, southwestern China. Contrary to previous experience suggesting that CG fractions are usually better bleached than FG fractions prior to deposition, our results showed that the OSL ages for the FG quartz fraction were generally younger than those for the CG fraction. This would suggest that the two fractions may have come from different sources, and may have been subject to different geomorphological processes prior to deposition. FG quartz fractions may be suitable to define the maximum age of sediments located in alpine gorge regions. CG quartz fractions can be used by applying the minimum age model (MAM) to select relatively well-bleached grains yielded ages close to the ‘true’ burial ages of the sediments. The results showed that the post-IR IRSL₂₂₅ ages of single grain K-feldspar were overestimated by > 3 ka, suggesting K-feldspar may not be suitable dating material for megaflood sediments <30 ka. The OSL dates suggest that the T2 terrace was formed ∼8.4 ka, that aeolian sediments were deposited during ∼2.6–1.5 ka, and that the megaflood event occurred after ∼1.5 ka.     

The complexity of luminescence dating of tidal sand body revealed by the discrepancy of paired quartz OSL ages

Optically stimulated luminescence (OSL) dating is becoming a useful technique to yield absolute age of organic-poor sandy deposits. The buried tidal sand body (BTSB) in the coastal zone of northern Jiangsu Province, China, has been suggested to have the same origin as the offshore radial sand ridge in the Yellow Sea. However, chronological constrain of the BSTB is still quite limited. In this study, OSL measurements were conducted using silt-sized multi-grain and coarse-grained single-grain quartz to constrain the depositional history of a 25.6 m core from the BTSB. A low luminescence sensitivity of quartz was observed, and only ∼1.04% of the grains passed the standard rejection criterion for single-grain measurement. Analysis of paired OSL ages from two grain-size fractions using different protocols showed that silt-sized quartz ages were underestimated of 0.14–1.35 ka in comparison to coarse-grained quartz in the depth interval of 5.8–22.4 m. We interpret such an age discrepancy as the effects of lateral infiltration of fine-grained sediment into the sand body due to dynamic feature of channel-ridge system on the shelf. As far as we know, it is the first time that such infiltration is demonstrated through OSL dating. Our OSL data indicated that there is a significant hiatus between the Late Pleistocene stiff clay layer (50–18 ka) and the Holocene sequence. Holocene deposits only occurred in the last 2 ka, with rapid accumulation of ∼17 m-thick sediments at ∼2–1 ka, a slower accumulation between ∼1 and 0.1 ka and rapid land emergence through an accretion of ∼4 m-thick sediment over the past ∼0.1 ka. This study highlights the complexity of OSL dating in highly dynamic sedimentary environments. Therefore, examining different grain size fractions and comparing different measurement protocols are highly deserved in carrying out OSL dating in such environments.     

A short-lived aeolian event during the Early Holocene in southeastern Norway

The Starmoen dune field is part of a larger aeolian system in the Jømna and Glomma river valleys in southeastern Norway. It is believed to have formed just after the last deglaciation in the area, but no absolute ages have been available to support this. Here, we present a set of quartz optically stimulated luminescence (OSL) ages from the aeolian sediments and the underlying glacifluvial deposits. The results show that the main dune-building phase was a short-lived event ∼10 ka ago, likely with a duration less than a few hundred years. This suggests a rapid stabilisation of an initially unstable environment in newly deglaciated terrain. A much younger event with limited and surficial reworking of sand is dated to 770 ± 110 years ago, and the modern age of an active dune provide additional OSL quality control. Age overestimation is found for glacifluvial sediments, probably due to incomplete bleaching as indicated by e.g. scattered dose distributions from small aliquots. OSL measurements were conducted using coarse quartz grains (180–250 m), which show a dominance of a fast signal component.     

Late Quaternary evolution of lower reaches of the Volga River (Raygorod section) based on luminescence dating

The normally-closed Caspian Sea is known for large changes in relative sea-level (of ∼170 m) during the late Quaternary. These transgressive/regressive events influenced the topography, sedimentation and ecosystems of a large area, of up to 1 million km². The Volga River has played an important role in the water balance of the Caspian Quaternary basins but our understanding of the temporal evolution is poorly constrained. Recent studies on the evolution of the Lower Volga have focused mainly on the subaerial sequence of loess-palaeosol series corresponding to a long-duration Caspian low stand (the so-called “Atelian regression” from ∼90 to ∼25 ka). In this study we address, for the first time, the temporal evolution of the Volga River during the late Quaternary, as recorded in the many layers of alluvial sands at the Raygorod reference section. This 50 m high outcrop contains a complicated sequence of different types of interlayered alluvium (channel and floodplain facies), a loess-palaeosol sequence with a weakly developed palaeosol, and marine sediments of the Khvalynian transgression (Chocolate Clay facies). The new chronology, based on 35 samples, is derived using optically stimulated luminescence (OSL) analysis of sand-sized quartz, with support from post-infra-red infra-red stimulated luminescence (post-IR IRSL) from K-rich feldspar grains to date the older parts of the section. The new ages identify five stages of the topography development in the northern parts of the Lower Volga: (1) an MIS 5a flood-plain in deltaic/estuary environments (>90 ka) during a high-stand of the Caspian Sea (Hyrcanian transgression); (2) a transition from deltaic/estuary conditions to a river valley with normal alluvial sedimentation and sporadic stabilization reflected in palaeosol development (80–70 ka); (3) a palaeo-Volga channel migration at elevations of 4–8 m msl during 69–62 ka, evidence of a brief increase in Caspian Sea-level and blocking of the Volga flow; (4) a subaerial stage with high-speed accumulation of loess during MIS 4 to MIS 2, containing one weakly developed palaeosol (MIS 3c) and pedocomplex of three combined palaeosols of the beginning of MIS2 (30–24 ka); (5) a rapid Khvalynian transgression, starting at the Raygorod location at ∼18.3 ka, with relatively weak marine erosion of the top 40–60 cm of loess cover, presumably because of the rapid migration of the coastline in the flat Northern Caspian Lowland.     

Application of single-grain OSL dating to ice-proximal deposits,glacial Lake Benson,west-central Minnesota,USA

Glacial Lake Benson formed in west-central Minnesota as the Des Moines lobe of the Laurentide ice sheet retreated north of a small moraine in the Minnesota River lowland. Although previous research has constrained the timing of glacial Lake Agassiz immediately to the north, little age control is available for the formation of glacial Lake Benson and ice-marginal positions to the south. In order to constrain the age of glacial Lake Benson and test the application of single-grain optically stimulated luminescence (OSL) dating to ice-marginal deposits, seven OSL samples were collected from a variety of depositional settings. These included deltaic deposits linked to specific lake levels, pro-glacial fluvial, ice-contact and supra-glacial deposits. Single-grain OSL results indicate evidence for incomplete resetting (partial bleaching) of the luminescence signal, as expected for glacial environments, and therefore ages were calculated using a minimum age model. OSL results constrain the timing of ice-margin retreat and lake formation to 14.4–14.8 ka. Analysis of single-grain equivalent dose distributions indicates that deposits created by glacial-dominated processes typically had higher over-dispersion (>50%) and greater positive skew (>0.9) than deposits originating from fluvial processes. These results suggest that water-lain deposits should be targeted for OSL sampling over those created by glacial processes when dating ice-proximal settings.     

Holocene moist period recorded by the chronostratigraphy of a lake sedimentary sequence from Lake Tangra Yumco on the south Tibetan Plateau

Palaeolimnological studies together with geomorphological investigations of exposed lacustrine sections on the Tibetan Plateau provided valuable palaeoclimate records. Radiocarbon dating is the most commonly used method for establishing chronologies of lake sediments. However, ¹⁴C dating of such sediments could be problematic due to the lack of organic matter or a reservoir effect, which commonly appears in radiocarbon ages of lacustrine sediments from the Tibetan Plateau. OSL dating is an alternative for dating the lake sediments and also provides the opportunity to independently test radiocarbon chronologies. The current study tries to compare OSL and ¹⁴C dating results in order to evaluate the reservoir effect of ¹⁴C dating, and then based on quartz OSL dating and stratigraphic analysis, to construct the chronostratigraphy of a lacustrine sedimentary sequence (TYC section), an offshore profile from Tangra Yumco lake on the southern Tibetan Plateau. Results suggest that: (1) it is possible to obtain robust OSL age estimates for these lake sediments and the OSL ages of the three samples range from ca. 7.6 ka to ca. 2.3 ka; (2) The discrepancy between the OSL and ¹⁴C ages is ca. 4–5 ka, which possibly results from the age overestimate of ¹⁴C dating due to a reservoir effect in the studied lake; (3) the chronostratigraphy of TYC section and sedimentological environmental analysis show a large lake with a lake level distinctively above the present during ca. 7.6–2.7 ka indicating a wet mid-Holocene in the study area.     

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

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

High resolution OSL and post-IR IRSL dating of the last interglacial–glacial cycle at the Sanbahuo loess site (northeastern China)

Northeastern China is located in the East Asian monsoon region; it is sensitive to both high and low latitude global climate systems. Loess deposits in the region have considerable potential as sensitive archives of past climate changes. However, research into loess deposition and climate change in this region is restricted by the lack of independent age control. In this study, coarse-grained quartz SAR OSL and K-feldspar post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR₂₉₀) methods have been used to date the Sanbahuo loess site in northeastern China. The quartz OSL characteristics are satisfactory. The measured pIRIR₂₉₀ D_e's do not vary significantly with IR stimulation temperatures between 50 °C and 260 °C; a first IR stimulation temperature of 200 °C was adopted. Dose recovery tests were performed by adding different laboratory doses to both laboratory bleached (300 h SOL2) samples and natural samples; the results are satisfactory up to ∼800 Gy. Resulting quartz OSL and feldspar pIRIR₂₉₀ ages are in good agreement at least back to ∼44 ka; beyond this feldspar pIRIR₂₉₀ ages are older. The feldspar ages are consistent with the expected age of the S1 palaeosol (MIS 5). There appears to have been a period of fast loess deposition at ∼62 ka, perhaps indicative of winter monsoon intensification with a very cold and dry climate that lead to a serious desertification of dunefields in northeastern China.     

Micro-hole and multigrain quartz luminescence dating of Paleodeltas at Lake Fryxell,McMurdo Dry Valleys (Antarctica), and relevance for lake history

Relict (perched) lacustrine deltas around the perennially ice-covered lakes in the Taylor Valley, Antarctica, imply that these lakes were up to 40 times larger in area than at present since the last glacial maximum (LGM). These deltas have been used to constrain ice-margin positions in Taylor Valley, and the boundaries of the proposed LGM ice-damned Glacial Lake Washburn. The timing of these high lake levels has depended on ¹⁴C chronologies of algal layers within relict lacustrine deltas. To provide additional geochronometric data for the post-LGM lake-level history, we applied photon-stimulated-luminescence (PSL) sediment dating to polymineral fine silt and sand-size quartz from 7 perched-delta and 3 active-delta sites of different elevations along 3 major meltwater streams entering Lake Fryxell. Our PSL dating of 4 quartz-sand samples from core tops in the seasonal ice-free moat of Lake Fryxell (elevation ∼18 m a.s.l.) and two core-top moat samples from the seasonal moat of Lake Vanda in nearby Wright Valley establish that adequate PSL clock zeroing (by daylight) occurs in regional, modern shoreline deposits. Minimum-age micro-hole PSL results from the moats are consistently near 100 a. Minimum-age micro-hole age estimates for the deltas range from ∼50 to 100 a near the present lake level up to 13.4 ± 1.3 ka at 240 m. These are systematically younger than the comparable, reservoir-uncorrected, ¹⁴C ages that range from 7 ka (cal yr BP) to 13 ka (cal yr BP) near lake level up to 20 ka (cal yr BP) at 220–240 m elevation. Our results indicate the occurrence of a dramatic discrepancy between PSL minimum-age and ¹⁴C age estimates that is presently unresolved.     

Shedding light on the timing of the largest Late Quaternary transgression of the Caspian Sea

The Late Quaternary history of the Caspian Sea remains controversial. One of the major disagreements in this debate concerns the stratigraphic correlation of various deposits in the Caspian Basin. In this paper we identify and date, for the first time, the Enotaevka regression, lying between the two major phases of the largest Late Quaternary Caspian Sea transgression, the Khvalynian transgressive epoch, and provide a minimum estimate of sea level decrease during this regression. The River Volga is the major source of water to the Caspian; the Lower Volga region is unique in its record of palaeogeographic events, and this provides the opportunity to build a single stratigraphic and palaeogeographic history for the Pleistocene of Central Eurasia. Here we use luminescence to establish a new chronology for the largest Late Quaternary transgressive epoch of the Caspian Sea. The existing radiocarbon chronology does not allow the resolution of the two transgressive phases of this epoch (Early and Late Khvalynian). Based on clear palaeontological and geomorphological evidence, these must be very different in age, but shells associated with both transgressions gave very scattered ages of between 8 and 50 ka. This ambiguity has led to considerable discussion concerning the existence or otherwise of a deep Enotaevka regression phase between the two Khvalynian transgressions. Recently we have again identified these deposits at Kosika, on the right valley side of the Volga River. The new luminescence chronology described here, based on quartz OSL and K-feldspar pIRIR₂₉₀ ages, allows us to reconstruct the complicated history of Late Quaternary sedimentation in the southern part of the Lower Volga valley. The Kosika section reflects the following major stages: (1) the earlier Khazarian transgressive epoch; (2) a decrease in the sea level with the development of a freshwater lake/lagoon in the Volga valley; and (3) the Khvalynian transgressive-regressive epoch, including both the Early and Late Khvalynian transgressive periods, and the intercalated Enotaevka regression. Sea level during the early stage of the Khvalynian transgression reached Kosika at about 23–22 ka (approx. −1 to −2 m asl). This event is of the same age as the “grey clay” strata at the base of the Leninsk section marine unit (Kurbanov et al., 2021), also formed at the beginning of the Early Khvalynian transgression. Around 15–14 ka the Khvalynian basin moved to a regressive stage, and in the northern part of the Lower Volga the top part of the well-known ‘Chocolate Clay’ accumulated. In the southern part of the valley marine accumulation stopped at about 12–13 ka. This allows us to reconstruct a decrease in Early Khvalynian basin sea level between 15–14 ka and 13–12 ka ago, of about ∼15 m. At the Kosika section sediments derived from the Enotayevka regression are visible as a weakly developed palaeosol with evidence of surficial erosion, and these sediments are now dated to 13–12 ka. At 8.6 ± 0.5 ka, during the period of the Mangyshlak regression, aeolian deflation processes reworked sediments deposited by immediately preceding Late Khvalynian transgression.     

Aeolian landform processes since the last deglaciation revealed by OSL chronology and stratigraphy in the Hulunbuir dune field in NE China

The Hulunbuir dune field (HLB) is situated near the northern limit of the East Asian summer monsoon (EASM), and vulnerable to climate change. The aeolian sand–paleosol sequences of this region are crucial for understanding the past landform processes in response to climate change, but not yet understood well due to chronological controversies. Here, we presented 20 optically stimulated luminescence (OSL) ages from five aeolian sand–paleosol profiles in the HLB, and reconstructed the aeolian landform processes since 18 ka. The findings of this study suggested that the HLB was probably dominated by mobile dunes before 18 ka, as 10 out of 11 aeolian samples were dated to 18–12 ka. Two strong sandy paleosol layers were found and dated to ∼9 ka and 5–0.5 ka, indicating that strong in situ pedogenic process on the accumulative sand could occur during the Holocene. The OSL ages of samples near the top of three profiles were >9.5 ka, indicating two possible surface processes. First, the land surface was stable since 9.5 ka after stabilization, with no accumulation or erosion. Alternatively, the surface could have been erosive with the eroded sediments feeding downwind active dunes. The latter explanation is consistent with the current local landforms, which has widespread blowout pits, indicators of strong wind erosion. We emphasized that the OSL age of a sand layer sample in fossil dunes implied the onset of mobile dune stabilization, not the age of dune activity, as previously stated.     

Comparison between luminescence and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia

Dust depositions are critical archives for understanding interior aridification and westerly climatic changes in Central Asia. Accurate and reliable dating of loess is very important for interpreting and correlating environmental records. There remains a disparity between luminescence ages and radiocarbon dating of late Quaternary loess from the Ili Basin in Central Asia. In this study, we establish a closely spaced quartz optically stimulated luminescence (OSL) chronology for the 20.5-m-thick Nilka loess section in the Ili Basin. Based on OSL ages, two intervals of higher mass accumulation rate occurred at 49–43 ka and 24–14 ka. We further compare these OSL ages with 23 accelerator mass spectrometry (AMS) ¹⁴C ages of bulk organic matter. The results indicate that the OSL and radiocarbon ages agree well for ages younger than ca. 25 ¹⁴C cal ka BP. However, beyond 30 cal ka BP, there is no consistent increase in AMS ¹⁴C age with depth, while the OSL ages continue to increase. These differences confirm the observation that the AMS ¹⁴C ages obtained using conventional acid–base–acid (ABA) pretreatment are severely underestimated in other terrestrial deposits in Central Asia, which could be due to 2–4% modern carbon contamination. However, OSL dating is applicable for constructing an accurate chronology beyond 30 cal ka BP. We suggest caution when interpreting paleoenvironmental changes based on radiocarbon ages older than 25 cal ka BP.     

Lake level changes of Nam Co since 25 ka as revealed by OSL dating of paleo-shorelines

Many lakes in the Tibetan Plateau (TP) experienced dramatic lake level changes in the late Quaternary, as suggested by well-preserved paleo-shorelines up to ∼200 m above present lake levels. These relic shorelines provide direct geomorphic record to reconstruct past lake level fluctuation history and water volume changes, linked closely to variations in paleo-climatic controls including Asian monsoon, westerlies and glacial meltwater. In this study, 27 near-shore sediment samples from three of eight paleo-shorelines at north of Nam Co were dated by Optically Stimulated Luminescence (OSL) technique, using coarse grains of quartz and potassium feldspar.Our results indicate that: 1) S1 is the highest/most developed shoreline (+26 m). Sediment from upper part of S1 has a consistent age of ∼25 ka (nine samples from 3 gullies), suggesting a high lake level of Nam Co occurred around 25 ka. An overflow point west of Nam Co has a close elevation to that of S1 and thus limits the presence of higher lake levels; 2) sediment profile from the slightly lower S2 (+22 m) contains two parts, silty sand (6.9–8.9 ka) at the bottom and shoreline deposits atop (∼2.3 ka), suggesting Nam Co maintained a relative high lake level in the early Holocene and such lake level occurred again at about 3.0–2.0 ka; 3) In contrast to the swift variations of monsoon precipitation and glacial meltwater in the late Quaternary, water level of Nam Co remained relatively stable during the period from ∼25 ka to about early Holocene (from +26 m to +22 m), implying a continuous outflowing stage and lake infill constantly exceeds evaporation; 4) S5 (+11 m) has an age of 0.7–1.4 ka. Nam Co showed a much accelerated pace of shrinkage since about 2.0 ka in the late Holocene in roughly two steps: it dropped from +22 m to +11 m from ∼2.0 ka to 1.4 ka, and subsequently dropped another 11 m after 0.7 ka.     

A detailed luminescence chronology of the Lower Volga loess-palaeosol sequence at Leninsk

We present a detailed luminescence chronology of the loess-palaeosol sequences in the Lower Volga region of Russia at the Leninsk site – an important palaeogeographic archive describing the climate and environmental conditions of regressive stages of the Caspian Sea. The chronology of these sediments has received very little attention compared to the under- and overlying marine deposits. The degree of bleaching was addressed by making use of the differential resetting rates of quartz and feldspar. Our results show that the quartz OSL and feldspar pIRIR_50,290 signals were sufficiently bleached before deposition and uncertainties in bleaching have a negligible impact on the reliability of the luminescence ages. The combined quartz OSL and K-feldspar pIRIR_50,290 chronology constrains the main stages of the Northern Caspian Lowland evolution during the Late Quaternary. During early MIS 5 (130–120 ka), the northern part of the Lower Volga was covered by a shallow brackish water estuary of the warm Late Khazarian Caspian Sea transgression. After ∼122 ka, the Volga incised the Northern Caspian Lowland surface following sea-level decrease and the start of subaerial conditions at Leninsk. Loess accumulation rate increased towards the end of MIS 5 and two palaeosols of presumably MIS 5с and MIS 5a age formed, exhibiting features evidencing a dry, cold climate, influenced by long seasonal flooding by the Volga River. Cryogenesis affecting the MIS 5a soil is a regional phenomenon and is dated to between ∼70 and 90 ka. The overlying thick Atelian loess unit formed during the cold periods of MIS 4 and MIS 3. Clear erosional features at the top of the Atelian loess are constrained by luminescence to ∼35 to ∼24 ka, allowing reconstruction of erosion of 150–200 cm of loess.     

Luminescence chronology of fossiliferous fluvial sediments along the middle Atbara River,Sudan

Fluvial sediments of the middle Atbara River Valley, eastern Sudan, contain abundant vertebrate fossils and stone tools. Previous work described two sedimentary units, the Butana Bridge Synthem (BBS) and the Khashm El Girba Synthem (KGS), with three divisions each (BBS1-3 and KGS1-3, from bottom to top, respectively). ²³⁰Th/U dating on bivalve shells suggested an age of ∼126 and ∼92 ka for the basal KGS2 and basal KGS3, respectively, and mammalian biochronology in combination with magnetostratigraphy suggested an age of late Early to early Middle Pleistocene for the underlying BBS. To establish a detailed chronology of this fluvial sedimentary sequence, we collected 17 luminescence samples from both sides of the Atbara River close to the Butana Bridge. Quartz OSL dating was applied to samples from the upper part of the profile (upper KGS2 and KGS3), but the signal reached saturation within the upper ∼10 m of the sequence. To select a suitable feldspar signal to date older samples beyond the limit of the quartz OSL, a comparison of the quartz OSL, feldspar post-IR IRSL at 225 and 290 °C, and pulsed IRSL signal at 50 °C was conducted for a sample from KGS3. The result showed that only the fading corrected pulsed IRSL yielded an age consistent with the quartz OSL, and the post-IR IRSL signals (both at 225 and 290 °C) overestimated the quartz age significantly. We therefore selected the pulsed IRSL signal to date the older deposits. The luminescence ages indicate that the entire BBS - KGS sequence was deposited between 224 ± 23 ka and <17 ± 1 ka, corresponding to marine isotope stages (MIS) 7–2, significantly revising previous conclusions.