Luminescence chronology of aeolian deposits from the Qinghai Lake area in the Northeastern Qinghai-Tibetan Plateau and its palaeoenvironmental implications

Qinghai Lake, on the northeastern Qinghai-Tibetan Plateau, is the largest extant closed-basin lake in China, and has been the subject of numerous palaeoclimatological and palaeoenvironmental studies. In this study, 32 samples of aeolian sand, loess and palaeosol at six sites, and 1 sample of shoreline deposits underlying aeolian deposits were dated using optically stimulated luminescence (OSL). Where available, OSL ages are in agreement with previously published ¹⁴C ages. Our dating results, in combination with previous published ages on aeolian deposits showed that: (1) The oldest aeolian deposits around Qinghai Lake are in excess of 165 ka. (2) Aeolian deposition then began at ∼14 ka in the Qinghai Lake area. Periods of palaeosol formation occurred at ∼16.9 ka, ∼12.2–11 ka, ∼10–9 ka, ∼5.2–4 ka, and ∼3.9–0.7 ka. (3) The accumulation intervals of palaeosols are generally consistent with drilling-core-based environmental change proxies, indicating that palaeosols were formed during wet periods with higher vegetation cover. (4) A depositional hiatus period of ∼40–50 ka exists between the surface mantle aeolian deposits and underlying gravel deposits. (5) Lake levels during the Holocene did not exceed 3205.2 m elevation (11.8 m above recent lake level of April, 2010).     

Luminescence chronology of fluvial and aeolian deposits in the Russian Altai (Southern Siberia)

Geomorphological investigations in the Russian Altai Mountains provide evidence for the extent and timing of Late Quaternary glaciations and aeolian sediments. Infrared optically stimulated luminescence (IR-OSL) and thermoluminescence (TL) dating of aeolian sediments from the central part of the Russian Altai were carried out on silty and sandy sediments that cover fluvial and glacio-fluvial terraces. Most samples from loess, loess-like sediments and sandy loess taken from different terrace sequences within the Altai Mountains provide IRSL ages suggesting a main aeolian deposition period between 25 and 15 ka. These data are consistent with those from the adjacent Mongolian Altai. Sand and silt layers within moraines yielded IRSL age estimates between 22 and 19 ka and correlate to the ice margins of the Last Glacial Maximum. Aeolian dune sands overlying or neighbouring the loess-like sediments and the fluvial terraces at some places provide evidence for Late Glacial (around 15 ka) and Early Holocene (around 9 ka) aeolian activity. The youngest sand sheets gave deposition ages of about 1.5 ka. These sediments covered graves and are related to overgrazing. They provide evidence for the significant human impact on the environment. Fluvial sediments, including silt and sandy gravel intermingled with charcoal, yielded contradicting radiocarbon and luminescence ages. IRSL age estimates obtained for the silty layers range from 19 to 18 ka and are significantly older than the radiocarbon ages, which gave sub-recent ages between 1170 and 910 BP. These data indicate fluvial sedimentation of debris and mudflows in a period of deforestation and strong soil erosion related to mining activities during the 9th and 10th century.     

Luminescence dating of the late Quaternary sediments in Hangzhou Bay,China

Coastal plain of Hangzhou Bay, to the south of the present Yangtze Estuary, is closely linked to the evolution of the Yangtze River delta. However, absolute age of Pre-Holocene sediments is limited, which hinders the understanding of this area's environmental evolution. In this study, using optically stimulated luminescence (OSL), single aliquots and single grains of quartz and K-feldspar were used to date the late Quaternary sediments in coastal plain on the southern Hangzhou Bay. The vertical difference in particle size composition render either silt- or sand-sized quartz for dating. Cross-checking of multiple OSL dating methods indicated that the upper ∼65 m recorded the Holocene part of the succession; sediment from a depth of 136.6 m was dated to ∼180 ka. It was found that the single-grain method was more reliable in comparison to single-aliquot age, the former minimized the effect of signal components. Single-grain quartz and K-feldspar luminescence yielded consistent ages at sample depth of 136.6 m (∼160–180 ka), while the latter gave robust age at depth of 115.5 m (∼150 ka). This chronology is in general in accordance with neighbouring cores and can constrain paleomagnetic dating results in those cores. Taking together, the study site has thickest Holocene deposits in comparison to the highland centered around Taihu Lake on the southern Yangtze delta. Moreover, the luminescence characteristics of quartz from different sample depths, behaved differently with respect to luminescence sensitivity, signal components and saturation level, perhaps reflecting varied provenance and weathering characteristics caused by climate change.     

The provenance of Gansu Group in Longxi region and implications for tectonics and paleoclimate

The Neogene sediments of Gansu Group from northwestern China contain eolian and fluvial deposits.The origins of these sediments are very important for exploring the onset of Asian inland aridification,the pattern of paleo-atmospheric circulation,and the regional tectonics and geomorphic evolution during the Miocene.Here we present detrital-zircon age spectra of typical eolian and fluvial deposits from highlands and subsidence basin,and compare them with those of surrounding eroded mountain(such as the West Qinling Mountains and Liupan Mountains)materials and Quaternary loess derived from the Asian inlands.The results reveal that(1)the detrital-zircon age spectrum of the Miocene eolian sample is remarkably different from the eroded materials of the West Qinling Mountains and the Miocene fluvial deposits from Tianshui region,but very similar to the Quaternary loess deposits.This indicates that the provenance of Miocene eolian sediments is similar with the Quaternary loess,and thus further confirms the previous conclusions that the distribution of Asian arid lands and the pattern of atmospheric circulation during the Miocene are broadly similar with the Quaternary.(2)The detrital-zircon age spectrum of the fluvial deposits(with age about 11.5 Ma)from Tianshui region is different from the eroded materials of West Qinling Mountains,but similar with that of the Liupan Mountains to the east,which may suggest that the Liupan Mountains have already been exhumed by11.5 Ma.     

根据历史地震和应变能积累释放过程分析山东地区近期地震活动趋势

根据历史地震和应变能积累释放过程对山东地区地震活动特征进行分析,认为该区目前处于地震活跃时段后期的能量剩余释放阶段,在此期间将以中等或中强地震活动为主。由现代地震活动特点分析认为,该区目前处于最近的一个应变能积累—释放过程中的释放阶段,这一阶段还可能持续4年左右,在此释放阶段中有可能发生多次4～5级乃至6级地震,但发生6级以上地震的可能性不大。     

Sedimentary evolution of a foreland basin from the northeastern Qilian Mountains based on the integration of geomorphological and luminescence dating of alluvial conglomerates and fluvial terrace sediments

Sedimentary deposits in the foreland basin of the northeastern Qilian Mountains are crucial documents recording tectonic activity and climate changes on the Tibetan Plateau. In this study, luminescence dating was used to date alluvial conglomerates and fluvial terrace sediments collected from the Beida River in the Jiuquan Basin, a foreland basin in the Hexi Corridor, northeastern Qilian Mountains. Detailed sedimentology and luminescence ages reveal that alluvial conglomerates accumulated from before 620 ka to 12 ka and that sediment accumulation rates increased at ∼330 ka and ∼35 ka, coinciding with the dates of two tectonic events (∼350 and ∼50 ka) and followed by climate cooling (from marine isotope stage (MIS) 9 to MIS 8 and from MIS 3 to MIS 2). This reveals that variations in the sediment accumulation rates are controlled by the coupling of tectonic uplift and climate cooling. The highest terrace (T7) that developed on the alluvial conglomerate base formed at ∼ 12 ka. The incision rate in the early Holocene was ∼2.1 mm/yr and increased to ∼14.6 mm/yr during the middle and late Holocene. The variations in the river incision rate provide geomorphic evidence for Holocene climate patterns in arid and semiarid areas. Luminescence dating offers a credible temporal framework for the deposits and reveals climate and tectonic effects on the evolution of the foreland basin, northeastern Qilian Mountains.     

OSL chronology of Quaternary terraced deposits outcropping between Mt. Etna volcano and the Catania Plain (Sicily,southern Italy)

In this paper we tested the applicability of the Optically Stimulated Luminescence (OSL) technique through Single-Aliquot Regenerative-dose (SAR) protocol, on single grain quartz extracted from alluvial–coastal sediments. Five samples were collected from deposits belonging to a flight of seven orders of coastal–alluvial terraces outcropping in the area between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy), at the front of the Sicilian fold and thrust system. After various performance tests, we obtained OSL ages ranging between 240 ± 12 and 80 ± 4 ka, consistent with the normal evolutionary model of a terraced sequence, moving from the highest to the lowest elevation. Obtained data allowed us to determine a mean uplift rate of 1.2 mm/year during the last 240 ka, mostly related to regional uplift processes coupled with sea-level changes. Moreover, terraces belonging to the two highest orders are folded, forming a large anticline. According to our results, the frontal thrust of the Sicilian chain was active between 236 and 197 ka ago, even though seismological and geodetic data suggest current activity to the back.     

Fault-generated mountain fronts in the central apennines (Central Italy): Geomorphological features and seismotectonic implications

The morphotectonic framework of the Central Apennines is given by faulted blocks bounded by normal faults, mostly trending NW–SE, NNW–SSE and NE–SW, which cut previous compressive structures. Such a structural setting is consistent with the focal mechanisms of the earthquakes which often occur in this area. In this paper, three lithologically different normal fault-generated mountain fronts are analysed in order to assess the relations between their geomorphic features and active tectonics. They border the Norcia depression (Sibillini Mts, Umbria), the Amatrice–Campotosto plateau (Laga Mts, Lazio) and the Fucino basin (Marsica Mts, Abruzzi). The Norcia depression is bounded by a N20°W trending normal fault to the east and by a parallel antithetic fault to the west. The main fault has a 1000 m throw and gives rise to a wide fault escarpment, characterized by: (1) sharp slope breaks due to low angle gravity faults; (2) important paleolandslides; and (3) several fault scarplets on the piedmont belt affecting Quaternary deposits. The Amatrice–Campotosto plateau is delimited by the western slope of Mt Gorzano which runs along a N20°W trending normal fault having a 1500m throw. Minor parallel faults dislocate Quaternary landforms. Large-scale massmovements also occur here. The Fucino basin was struck by the 1915 Avezzano earthquake (I=XI MCS) which produced extensive surface faulting along two parallel NW trending normal fault escarpments on the eastern border of the basin. There is paleoseismic evidence including buried gravity graben in Late Glacial gravels and tectonic dip-slip striations on Holocene calcitic crusts covering bedrock normal fault planes. These data suggest that active extensional tectonics plays a major role in the slope morphogenesis of the Central Apennines and they indicate the importance of geomorphic analysis in seismic zonation of this area.     

Luminescence dating without sand lenses: An application of OSL to coarse-grained alluvial fan deposits of the Lost River Range,Idaho, USA

Optically stimulated luminescence (OSL) dating is increasingly used to estimate the age of fluvial deposits. A significant limitation, however, has been that conventional techniques of sampling and dose rate estimation are suitable only for thick (>60 cm) layers consisting of sand size or finer grains. Application of OSL dating to deposits lacking such layers remains a significant challenge. Alluvial fans along the western front of the Lost River Range in east-central Idaho, USA are one example. Deposits are typically pebble to cobble sheetflood gravels with a sandy matrix but thin to absent sand lenses. As a result, the majority of samples for this project were collected by excavating matrix material from gravelly deposits under light-safe tarps or at night. To examine the contributions of different grain-size fractions to calculated dose-rates, multiple grain-size fractions were analyzed using ICP–MS, high resolution gamma spectrometry and XRF. Dose rates from bulk sediment samples were 0.4–40% (mean of 18%) lower than dose-rate estimates from the sand-size fractions alone, illustrating the importance of representative sampling for dose rate determination. We attribute the difference to the low dose-rate contribution from radio-nuclide poor carbonate pebbles and cobbles that occur disproportionately in clast sizes larger than sand. Where possible, dose rates were based on bulk sediment samples since they integrate the dose-rate contribution from all grain sizes. Equivalent dose distributions showed little evidence for partial bleaching. However, many samples had significant kurtosis and/or overdispersion, possibly due to grain-size related microdosimetry effects, accumulation of pedogenic carbonate or post-depositional sediment mixing. Our OSL age estimates range from 4 to 120 ka, preserve stratigraphic and geomorphic order, and show good agreement with independent ages from tephra correlation and U-series dating of pedogenic carbonate. Furthermore, multiple samples from the same deposit produced ages in good agreement. This study demonstrates that with modified sampling methods and careful consideration of the dose rate, OSL dating can be successfully applied to coarse-grained deposits of climatic and tectonic significance that may be difficult to date by other methods.     

Features of isostatic gravity anomaly and seismic activity in the Central Asian region

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The vertical influence of temperature and precipitation on snow cover variability in the Central Tianshan Mountains,Northwest China

Seasonal snow cover in mountainous regions will affect local climate and hydrology. In this study, we assessed the role of altitude in determining the relative importance of temperature and precipitation in snow cover variability in the Central Tianshan Mountains. The results show that: (a) in the study area, temperature has a greater influence on snow cover than precipitation during most of the time period studied and in most altitudes. (b) In the high elevation area, there is a threshold altitude of 3,900 ± 400 m, below which temperature is negatively correlated whereas precipitation is positively correlated to snow cover, and above which the situation is the opposite. Besides, this threshold altitude decreases from snow accumulated period to snow stable period and then increases from snowmelt period to snow‐free period. (c) Below 2,000 m, there is another threshold altitude of 1,400 ± 100 m during the snow stable period, below (above) which precipitation (temperature) is the main driver of snow cover.     

山东中西部及邻近地区震源参数和场地响应的反演

利用山东数字地震台网10个地震台自2004年6月至2007年8月记录的数字波形资料,采用Atkinson（1992）方法反演了山东中西部及邻近地区的非弹性衰减,得到该地区Q值与频率的关系是Q（f）=382．2·f^0.443。运用Moya（2000）方法反演了10个台站的场地响应,得到了26个地震的震源参数,并对所得结果进行了初步讨论。     

Nd and Sr isotopic variations in Chinese eolian deposits during the past 8 Ma: Implications for provenance change

A record of changes in Nd and Sr isotopic composition of the eolian deposits from the central Loess Plateau has been determined for the past 8 Ma. The isotopic records of the silicate fraction of the Quaternary and Tertiary eolian deposits allow interpreting the interplay between the Sr isotopic variations in the eolian deposits and the late Cenozoic tectonic and climatic changes. The results indicate that the temporal variations of Nd and Sr isotopes show remarkable changes around the beginning of the Quaternary. The lower values of the ¹⁴³Nd/¹⁴⁴Nd and the decreasing trend of the ⁸⁷Sr/⁸⁶Sr ratios after 2.58 Ma ago are attributed to the additions of relatively younger crust materials in response to the climatic cooling and the late Cenozoic uplift induced glacial grinding in the high orogenic belts in central Asia. In this context, the substantial changes in climate and tectonics have modified dust sources significantly, and the Quaternary loess forming processes are preferentially sampling relatively younger and high relief crust materials than that of the Tertiary Red Clay.     

Luminescence chronology of the Sankosh river terraces in the Assam- Bhutan foothills of the Himalayas: Implications to climate and tectonics

Himalaya is an active fold and thrust belt formed due to continent-continent collision between the Eurasian and Indian plates. It comprises a 3000 km long chain of mountains that span ∼1000 km across, with major boundary thrusts viz., Main Central Thrust (MCT), Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). MFT is marked as mountain front and is the most active thrust; however, evidence of tectonic activity along MCT and MBT also exists.Tectonic activity along MFT created uplifted terraces which now serve as geomorphic archives of past tectonic events. The present study focussed on a glacial-fed river Sankosh that originates in northern Bhutan, and crosses MCT, MBT and MFT before joining the Brahmaputra River in Assam. Due to tectonic uplift, the river shows a deflection at MFT, incising and thus forming four levels of strath terraces. Luminescence chronology, geomorphic studies and analysis of satellite images suggest four levels of terraces T4 (highest level, 195 m asl), T3, T2 and T1 (lowest level, 120 m asl).The quartz was found insensitive for luminescence dating, and thus fading corrected Infra-Red Stimulated Luminescence (IRSL) ages on feldspar minerals were measured that provided ages of 143-77 ka (T4), 65-36 ka (T2) and 35-14 ka (T1), respectively. The T3 terrace was present only on the right bank of the river and could not be accessed. These ages accord with other studies at the Chalsa and Malbazar, North Bengal (west of the study area) and this regional disposition of similar ages suggest that these formed during glacial-interglacial periods. The strath terraces indicate a time-averaged tectonic uplift with a 0.5 mm/year rate over the past 150 ka.     

Radiocarbon and luminescence dating of the Wulanmulun site in Ordos,and its implication for the chronology of Paleolithic sites in China

After the Salawusu and Shuidonggou sites, the Wulanmulun site found in 2011 is another important Paleolithic site in Ordos, China, due to its numerous stone artifacts and animal fossils. Here, we carry out a combined luminescence and radiocarbon dating of the site. The luminescence dating was done on coarse-grained quartz from 24 sediment samples using a single-aliquot regenerative-dose (SAR) protocol. The radiocarbon dating was performed on ten charcoal samples and one bone sample using acid-base-acid (ABA) and acid–base-wet oxidation-stepped combustion (ABOx-SC) pretreatments. The results showed that: (i) although some samples show relative large (>20%) overdispersion in De distribution (small aliquots), the quartz grains are considered to be sufficiently bleached before burial; (ii) the quartz OSL ages of ∼4–65 ka obtained for the samples are generally stratigraphically consistent and reliable; (iii) the radiocarbon ages obtained using the ABA pretreatment procedure are much younger than the corresponding OSL ages, and the radiocarbon ages obtained using the ABOx-SC method are beyond or close to the laboratory background. The radiocarbon ages obtained using the ABA treatment were considered to be underestimated. This implication is that caution must be taken for dating Chinese Paleolithic (>25 ka) using the ABA pretreatment procedure on carbon samples. Finally, the cultural layers from the Wulanmulun site are deduced to be between 50 and 65 ka.     

Processes and environmental significance of the subglacial chemical deposits in Tianshan Mountains

The precipitation process of subglacial chemical deposits is closely related to the subglacial hydrologic processes and the physical, chemical reactions on the ice-bedrock interfaces. Thus the chemical deposits can serve as a nice proxy for the study of subglacial envi- ronment and a great deal of researches have been done on them during the 1970s and 1980s[1─7]. The alpine glaciers in Northwest China develop in the very continental environment with a comparatively slow subglacial process, du…     

Spatial and temporal variability in the stable isotope systematics of modern precipitation in China: implications for paleoclimate reconstructions

The stable isotopic composition of materials such as glacial ice, tree rings, lake sediments, and speleothems from low-to-mid latitudes contains information about past changes in temperature (T) and precipitation amount (P). However, the transfer functions which link δ¹⁸O_p to changes in T or P, dδ¹⁸O_p/dT and dδ¹⁸O_p/dP, can exhibit significant temporal and spatial variability in these regions. In areas affected by the Southeast Asian monsoon, past variations in δ¹⁸O and δD of precipitation have been attributed to variations in monsoon intensity, storm tracks, and/or variations in temperature. Proper interpretation of past δ¹⁸O_p variations here requires an understanding of these complicated stable isotope systematics. Since temperature and precipitation are positively correlated in China and have opposite effects on δ¹⁸O_p, it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions. Here, we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord. The strength of these transfer functions in China is investigated using multiple regression analysis of data from 10 sites within the Global Network for Isotopes in Precipitation (GNIP). δ¹⁸O_p is modeled as a function of both temperature and precipitation. The magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence. δ¹⁸O_p values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature, and therefore exhibit more negative values in the summer. In contrast, δ¹⁸O_p values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between δ¹⁸O_p and temperature. The sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation. Comparison with simple linear models (δ¹⁸O_p as a function of T or P) and a geographic model (δ¹⁸O_p as a function of latitude and altitude) shows that the multiple regression model is more successful at reproducing δ¹⁸O_p values at sites that are strongly influenced by the summer monsoon. The fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally. Since the Southeast Asian monsoon intensity is known to exhibit large variations on a number of timescales (annual to glacial–interglacial), and the magnitude and sign of the transfer functions is related to monsoon intensity, we suggest that as monsoon intensity changes, the magnitude and possibly even the sign of the transfer functions may vary. Therefore, quantitative paleoclimate reconstructions based on δ¹⁸O_p variations may not be valid.     

Debris flow deposits within the Palaeogene lava fields of NW Scotland: evidence for mass wasting of the volcanic landscape during emplacement of the Ardnamurchan Central Complex

Coarse fragmental rocks, previously interpreted as primary pyroclastic accumulations infilling flared vents (Richey JE 1938) “The rhythmic eruptions of Ben Hiant, Ardnamurchan, a tertiary volcano. Bull Volcanol” 2(3):1–21), are re-interpreted as predominantly debris flow deposits, with minor hyperconcentrated and stream-flow deposits, temporally and spatially associated with the Palaeogene Ardnamurchan Central Complex (ACC), NW Scotland. These volcaniclastic rocks are conglomerates and breccias, interbedded with siltstones and sandstones, which formed by surface processes on a dissected landscape, developed in response to shallow emplacement of the ACC. Clast-matrix and photo-statistical analyses allow the palaeo-topography and drainage system to be reconstructed and the development of a palaeo-geographic model for the volcanic landscape. Slabs of basalt, dolerite and sandstone were transported as megablocks during catastrophic, gravity-driven events. Lower energy intervals during volcanic hiatuses are marked by lacustrine-fluvial volcaniclastic siltstones and sandstones preserving palynomorph assemblages. We suggest that shallow intrusion is a plausible initiation mechanism for mass wasting in other large igneous provinces. Historically, deposits of the type described here may have been misidentified as vent facies pyroclastic materials.     

The form and function of headwater streams based on field and modeling investigations in the southern Appalachian Mountains

Headwater streams drain the majority of most landscapes, yet less is known about their morphology and sediment transport processes than for lowland rivers. We have studied headwater channel form, discharge and erosive power in the humid, moderate‐relief Valley and Ridge and Blue Ridge provinces of the Appalachian Mountains. Field observations from nine headwater (<2 km² drainage area), mixed bedrock–alluvial channels in a variety of boundary conditions demonstrate variation with respect to slope‐area channel initiation, basic morphology, slope distribution, hydraulic geometry, substrate grain size and role of woody debris. These channels display only some of the typical downstream trends expected of larger, lowland rivers. Variations are controlled mainly by differences in bedrock resistance, from the formation level down to short‐wavelength, outcrop‐scale variations. Hydrologic modeling on these ungauged channels estimates the recurrence of channel‐filling discharge and its ability to erode the channel bed. Two‐year recurrence discharge is generally larger and closer to bankfull height in the Valley and Ridge, due to low soil infiltration capacity. Discharge that fills the channel to its surveyed bankfull form is variable, generally exceeding two‐year flows at small drainage areas (<0·5 km²) and being exceeded by them at greater drainage areas. This suggests bankfull is not controlled by the same recurrence storm throughout a channel or physiographic region. Stream power and relative competence are also variable. These heterogeneities contrast relations observed in larger streams and illustrate the sensitivity of headwater channels to local knickpoints of resistant bedrock and armoring of channels by influx of coarse debris from hillslopes. The general lack of predictable trends or functional relationships among hydraulic variables and the close coupling of channel form and function with local boundary conditions indicate that headwater streams pose a significant challenge to landscape evolution modeling. Copyright © 2005 John Wiley & Sons, Ltd.