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1.
The lacustrine deposits of lakes in arid central Asia (ACA) potentially record palaeoclimatic changes on orbital and suborbital time scales, but such changes are still poorly understood due to the lack of reliable chronologies. Bosten Lake, the largest freshwater inland lake in China, is located in the southern Tianshan Mountains in central ACA. A 51.6‐m‐deep lacustrine succession was retrieved from the lake and 30 samples from the succession were used for luminescence dating to establish a chronology based on multi‐grain quartz OSL and K‐feldspar post‐IR IRSL (pIRIR290) dating. Quartz OSL ages were only used for samples from the upper part of the core. The K‐feldspar luminescence characteristics (dose recovery test, anomalous fading test, first IR stimulation temperature plateau test) are satisfactory and from the relationship amongst the quartz OSL, IR50 and pIRIR290 doses we infer that the feldspar signals are likely to be well bleached at deposition. Bacon age‐depth modelling was used to derive a chronology spanning the last c. 220 ka. The chronology, lithology and grain‐size proxy record indicate that Bosten Lake formed at least c. 220 ka ago and that lake levels fluctuated frequently thereafter. A stable deep lake occurred at c. 220, 210–180, c. 165, 70–60, 40–30 and 20–5 ka, while shallow levels occurred at c. 215, 180–165, 100–70, 60–40 and 30–20 ka. Bosten Lake levels decreased by at least ~29 m and possibly the lake even dried up between c. 160 and c. 100 ka. We suggest that the water‐level fluctuations in the lakes of ACA may not respond directly to climatic changes and may be affected by a number of complex factors.  相似文献   

2.
In this study, we report standard quartz SAR OSL and post‐IR infrared (IR) stimulated luminescence (post‐IR IRSL; pIRIR290) measurements made on sand‐sized quartz and K‐feldspar extracts from the loess‐palaeosol sequence at Niuyangzigou in northeastern China. The quartz OSL characteristics are satisfactory. Extensive pIRIR50,290 dose recovery tests were performed by adding doses on top of the natural dose. We found that dose recovery ratios improve significantly when the test dose ranges between ~15 and ~80% of the total dose, and good dose recovery (within ±5% of unity) can be obtained up to ～800 Gy. Otherwise, the dose recovery ratio deviates from unity. The De values also depend on the test dose size and so we conclude that the effect of test dose size should be routinely considered in pIRIR dating. First IR stimulation plateau pIRIR290 results are compared with multiple elevated temperature ‐pIRIR (MET‐pIRIR) data. It appears that the low temperature MET‐pIRIR data are strongly affected by poor dose recovery, but this is not the case for the pIRIR290 results. Natural signal measurements at the highest (first IR) stimulation temperature on a sample expected to be in field saturation suggest that ~10% signal loss occurs in pIRIR signals. Long‐term laboratory bleaching experiments (>80 days) show that a constant (or very difficult to bleach) residual pIRIR290 signal is reached after ~300 h, corresponding to a dose of 6.2±0.7 Gy. Quartz OSL and feldspar pIRIR50,290 ages are in good agreement at least back to c. 70 ka. Beyond this the quartz ages begin to underestimate but the feldspar ages are in agreement with the expected Last Interglacial age palaeosol.  相似文献   

3.
The Heidelberg Basin (HDB) hosts one of the thickest Quaternary sediment successions in central Europe. To establish a reliable Middle and Upper Pleistocene chronology for a recently drilled core from the depocentre of the Heidelberg Basin, we applied multiple luminescence dating approaches, including quartz optically stimulated luminescence (OSL), two feldspar post‐IR IRSL protocols using second IR stimulation temperatures of 225 °C (pIRIR225) and 290 °C (pIRIR290), and two fading correction models. Relatively high anomalous fading was observed for both the pIRIR225 and pIRIR290 signals, with mean fading rates of 2.13±0.27 and 2.08±0.49%/decade, respectively. Poor dose recovery behaviour of the pIRIR290 signal suggests that the pIRIR290 ages are not reliable. The comparison of two fading correction methods for the K‐feldspar ages indicates that the correction method proposed by Kars et al. (2008) Radiation Measurements 43, 786, yields reliable ages, whereas the dose‐rate correction method proposed by Lamothe et al. (2003) Radiation Measurements 37, 493, does not. A chronology for the HDB is established using the quartz ages and reliable fading corrected feldspar pIRIR225 ages. Our chronology shows that the sediments in the upper Mannheim Formation were deposited during Marine Isotope Stage (MIS) 4 (c. 70 ka), constrained by two quartz ages in the upper 20 m of the core. Four fading corrected pIRIR225 ages of c. 400 ka show that the upper Ludwigshafen Formation was deposited during MIS 12–11, correlated with the Elsterian‐Holsteinian stage. Two ages of 491±76 and 487±79 ka indicate that the Middle and Upper Ludwigshafen Formation were probably deposited during the Cromerian Complex. This luminescence chronology is consistent with palynological results. It also indicates that the IR‐RF ages reported earlier are probably underestimated due to anomalous fading.  相似文献   

4.
The extensive aeolian deposits of the Tibetan Plateau (TP) represent important environmental archives, recording information about the past interplay between the Asian monsoon and Westerlies and the link between dust accumulation and Quaternary glaciations. In the northeast TP, mantles of sandy loess form a distinct belt lying between 3500 and 4500 m a.s.l. on the east‐facing slopes of the Anyemaqen Mountains. However, there is little chronological information about the loess deposits in this region. This study provides a detailed chronology for loess formation in the region using luminescence dating. A total of 29 samples were collected from an 8‐m‐thick homogeneous loess section at Hebei (HB) in order to date sand‐sized (63–90 μm) quartz and K‐feldspar fractions using optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL and pIRIR) signals, respectively. The resulting quartz and feldspar ages are in good agreement over the last 40 ka; beyond this (i.e. De >120 Gy), the quartz age is underestimated, and the pIRIR170 feldspar ages are considered more reliable. The HB loess section records continuous environmental information from c. 50 to c. 30 ka, i.e. throughout Marine Isotope Stage (MIS) 3. Mass accumulation rates (MARs) varied considerably over this period with increased dust accumulation around c. 38 ka and after c. 32 ka; in between, and at the beginning of MIS 3 (50–40 ka), the dust accumulation rate was ~50% lower. Finally, the HB section also records a MIS 2 hiatus of c. 17 ka duration, probably resulting from deflation. This study implies that loess deposition on the TP is predominantly an interglacial/interstadial phenomenon and the TP may be deflating at the same time as the Chinese Loess Plateau is accumulating, at least during MIS 2.  相似文献   

5.
The loess–palaeosol sequence of Batajnica (Vojvodina region, Serbia) is considered as one of the most complete and thickest terrestrial palaeoclimate archives for the Middle and Late Pleistocene. In order to achieve a numerical chronology for this profile, four sets of ages were obtained on 18 individual samples. Equivalent doses were determined using the SAR protocol on fine (4–11 μm) and coarse (63–90 μm) quartz fractions, as well as on polymineral fine grains by using two elevated temperature infrared stimulation methods, pIRIR290 and pIRIR225. We show that the upper age limit of coarse quartz OSL and polymineral pIRIR290 and pIRIR225 techniques is restricted to the Last Glacial/Interglacial cycle due to the field saturation of the natural signals. Luminescence ages on coarse quartz, pIRIR225 and pIRIR290 polymineral fine grains are in general agreement. Fine quartz ages are systematically lower than the coarse quartz and pIRIR ages, the degree of underestimation increasing with age. Comparison between natural and laboratory dose response curves indicate the age range over which each protocol provides reliable ages. For fine and coarse quartz, the natural and laboratory dose response curves overlap up to ~150 and ~250 Gy, respectively, suggesting that the SAR protocol provides reliable ages up to c. 50 ka on fine quartz and c. 100 ka on coarse quartz. Using the pIRIR225 and pIRIR290 protocols, equivalent doses up to ~400 Gy can be determined, beyond which in the case of the former the natural dose response curve slightly overestimates the laboratory dose response curve. Our results suggest that the choice of the mineral and luminescence technique to be used for dating loess sediments should take into consideration the reported limited reliability.  相似文献   

6.
Buylaert, J.‐P., Huot, S., Murray, A.S. & Van den haute, P.: Infrared stimulated luminescence dating of an Eemian (MIS 5e) site in Denmark using K‐feldspar. Boreas, 10.1111/j.1502‐3885.2010.00156.x. ISSN 0300‐9483. Infrared stimulated luminescence (IRSL) dating of K‐feldspars may be an alternative to quartz optically stimulated luminescence (OSL) dating when the quartz OSL signal is too close to saturation or when the quartz luminescence characteristics are unsuitable. In this paper, Eemian (MIS 5e) coastal marine sands exposed in a cliff section on the coast of southern Jutland (Denmark) are used to test the accuracy and precision of IRSL dating using K‐feldspars. This material has been used previously to test quartz OSL dating ( Murray & Funder 2003 ): a small systematic underestimation of <10% compared to the expected age of ～130 ka was reported. In our study, a single‐aliquot regenerative‐dose (SAR) IRSL protocol is used to determine values of equivalent dose (De) and the corresponding fading rates (g values). A significant age underestimation (of up to ～35%) is observed; this is attributed to anomalous fading. Using a single site‐average fading rate of 3.66 ± 0.09%/decade to correct the IRSL ages for all samples provides good agreement between the average fading‐corrected K‐feldspar age (119 ± 6 ka) and the independent age control (132–125 ka). This is despite the reservations of Huntley & Lamothe (2001) that their fading correction method is not expected to work on samples older than ～20–50 ka. This fading‐corrected feldspar result is not significantly different from the overall revised quartz age (114 ± 7 ka) also presented here. We conclude that fading‐corrected IRSL ages measured using K‐feldspar may be both precise and accurate over a greater age range than might be otherwise expected.  相似文献   

7.
Optically stimulated luminescence (OSL) dating of polymineral fine-grained loess samples collected from the southern Loess Plateau of China was conducted using the single-aliquot regenerative-dose (SAR) protocol. A ‘Double-SAR’ procedure in which aliquots are subjected to both infrared (IR) and blue stimulations was used, and two sets of equivalent dose (D e ) determinations were produced. These doses are assumed to be predominantly related to the feldspathic and quartz fine grain populations, respectively. The results revealed that the OSL ages estimated by infrared stimulated luminescence (IRSL) signals and those estimated by [post-IR] stimulated luminescence ([post-IR] OSL) signals disagreed. Specifically, the ages estimated using the IRSL signals were smaller than those estimated using [post-IR] OSL signals. The results of an anomalous fading test of the two types of OSL signals revealed that the [post-IR] OSL signals from the etched sub-sample (by H2SiF6 and HF) and the un-etched sub-sample did not fade significantly. However, the IRSL signals from the un-etched sub-sample showed obvious signs of fading. These findings indicate that the lower age estimated by IRSL is due to the anomalous fading of feldspar IR signals in the polymineral fine grains. For samples collected from greater than 100 cm, the estimates of their OSL ages using two types of luminescence signals generally agreed with their pre-estimated ages, especially those of the [post-IR] OSL signals. However, for the three samples that were collected from a depth of less than 100 cm, their OSL ages were remarkably underestimated, possibly due to the enhanced human activity (such as soil cultivation) that has occurred in the region since 3000 a B.P.  相似文献   

8.
The continuing development of analytical methods for investigating sedimentary records calls for iterative re-examination of existing data sets obtained on loess-palaeosol sequences (LPS) as archives of palaeoenvironmental change. Here, we re-investigate two LPS (Hecklingen, Zilly) in the northern Harz foreland, Germany, being of interest due to their proximity to the Scandinavian Ice Sheet (SIS) and the position between oceanic climatic influence further west and continental influence towards the east. First, we established new quartz OSL and polymineral IRSL chronologies. Both methods show concordant ages in the upper part of the Hecklingen profile (~20–40 ka), but in the lower part IRSL underestimates OSL ages by up to ~15 ka for the period 40–60 ka. Interpretations hence refer to the OSL data set. Second, we applied Bayesian age-depth modelling to data sets from Hecklingen to resolve inversions in the original ages, also reducing averaged 1σ uncertainty by ~19% (OSL) and ~12% (IRSL). Modelled chronologies point out phases of increased (MIS 2, early MIS 3) and reduced (middle and late MIS 3) sedimentation, but interpretation of numerical rates is problematic because of intense erosion and slope wash particularly during MIS 3. Finally, previously obtained grain-size data were re-investigated by end member modelling analyses. Three fundamental grain-size distributions (loadings) explain the measured data sets and offer information on intensity and – combined with modelled OSL ages – timing of geomorphic processes. We interpret the loadings to represent (i) primary loess accumulation, (ii) postdepositional pedogenesis and/or input of aeolian fine fractions, and (iii) input of coarse aeolian material and/or slope wash. The applied modelling tools facilitate detailed understanding of site-formation through time, allowing us to correlate a strong peak in mean grain size at ~26–24 ka to the maximum extent of the SIS and increased influence of easterly winds.  相似文献   

9.
Sand wedges and ice‐wedge casts in the Qinghai Lake area on the northeastern Qinghai‐Tibetan Plateau (QTP) occur within alluvial gravel or river terrace deposits. In this study, we report the results of quartz Optically Stimulated Luminescence (OSL) dating of the infill of five relict sand wedges and one ice‐wedge cast. Combining our dating results with previously published luminescence ages of permafrost wedges in the Qinghai Lake area, we show that sand/ice wedges formed at c. 62 ka, c. 45 ka and between 30 and 15 ka, and that the mean annual air temperature (MAAT) was depressed by at least ～3°C relative to present during the sand/ice‐wedge formation periods. This new work is partially corroborated by post‐LGM proxy records from lakes and aeolian deposits reported from the northeastern QTP. It also significantly extends the palaeoenvironmental record in the region in the period before the LGM, when other proxy records are rare, allowing a better understanding of the palaeoenvironmental conditions on the northeastern QTP.  相似文献   

10.
Optical Stimulated Luminescence (OSL) is a technique that can be used for dating geological materials deposited within the last half‐million years, including sediments transported by air, water or gravity, as well as rocks heated at high temperatures. Recently, several studies have shown that OSL can also provide information on sediment transport. The pulsed photon‐stimulated luminescence (PPSL) unit (also known as a portable OSL reader) developed by the Scottish Universities Environmental Research Centre is an instrument designed to read luminescence signals from bulk (untreated) sediment samples comprising poly‐mineral and poly‐grain fractions. In this contribution, we evaluate the potential of the PPSL unit to assess the degree of OSL signal resetting in 27 young deposits (<2 ka) transported by different geomorphic agents in volcanic, coastal and fluvial depositional settings located in Mexico. Our results are in agreement with previous findings that used the Risø TL/OSL reader, confirming that sediments transported by debrisflows contain the highest inherited luminesce signals. Infrared stimulation (IRSL) values in volcanic ash, lavas, and sand beach and dune deposits exhibit low scatter. However, with blue stimulation (BLSL) these samples reveal a large degree of scattering, attributed to charge transfer in the case of the coastal deposits and to the low sensitivity of quartz in the case of volcanic material. The luminescence signals of fluvial sediments exhibit a highly scattered distribution in both IRSL and BLSL. We conclude that the use of a PPSL unit is a simple approach to assess the degree of OSL signal resetting in deposits sourced from different geological environments. This research contributes to previous studies that have investigated new applications of the PPSL unit to assist in OSL dating of geological materials.  相似文献   

11.
Radiocarbon dating of bulk organic matter is the most commonly used method for establishing chronologies of lake sediments for palaeoclimate reconstructions on the Tibetan Plateau. However, this method is likely to be problematic because the dated material often suffers from old carbon contamination. Recently, advances in luminescence‐based chronological techniques have provided new options for dating lacustrine sediments. In the current study, we tested for the first time the applicability of a new post‐IR IRSL (pIRIR) measurement protocol for dating fine‐grained polymineral material from a deep‐lake sediment core from the central part of Tangra Yumco, on the southern Tibetan Plateau. Our results show that: (i) radioactive disequilibria in the uranium decay chain were observed in the studied lake sediments, and thus taken into account for dose rate calculation by using a dynamic modelling approach; (ii) the suitability and robustness of the pIRIR protocol measured at 150°C (pIRIR150) for our samples are confirmed by a set of luminescence characteristic tests as well as the agreement with an independent age control; (iii) turbidite deposition partly caused an insufficient resetting of luminescence signals and thus apparent overestimation in luminescence dating; (iv) compared with the luminescence‐based age‐depth model, the 14C ages of bulk organic matter from the studied core generally yielded an age difference of ～2 ka, which is attributed to hardwater reservoir effects in Tangra Yumco. This study highlights the need for multi‐dating approaches of lake sedimentary archives on the Tibetan Plateau.  相似文献   

12.
The alternation of terrestrial and marine deposits is an indicator of past environmental and sea‐level changes. The age of deposition is usually dated by means of radiocarbon. However, radiocarbon dates of molluscan shells from coastal areas may be complicated by various sources of carbon, and problematic for deposits of 40–50 ka or older. Herein, we apply the Optically Stimulated Luminescence (OSL) dating method to date samples from terrestrial and marine/coastal sediments extracted from three cores in the south Bohai Sea, China. Multiple‐ and single‐aliquot regenerative‐dose procedures using OSL signals from fine‐silt (4–11 μm), coarse‐silt (38–63 μm) and fine‐sand (63–90 or 90–125 μm) quartz were employed to determine the equivalent dose (D e). The results showed that: (i) OSL ages from quartz of different grain sizes and different protocols are consistent with each other; (ii) for Holocene samples, most of the radiocarbon dates agree well with OSL ages; (iii) for pre‐Holocene samples, radiocarbon dates cluster at 40–50 14 C ka BP, whereas OSL ages are in stratigraphic order from 11 ka to 176 ka. Because of the self‐consistency of the quartz OSL ages, the stratigraphic agreement in the three cores, and the clustering of the radiocarbon dates, we suggest that the quartz OSL ages are more reliable with respect to dating the samples from the south Bohai Sea. Finally, the four marine strata identified in the south Bohai Sea are likely to have formed during the Holocene, Marine Isotopic Stage (MIS) 3–5, MIS 6 and probably MIS 7, respectively.  相似文献   

13.
博斯腾湖湖泊沉积物光释光年代测量*   总被引：2，自引：0，他引：2  
使用光释光年代学的单片再生法测量了博斯腾湖沉积剖面中碳酸盐泥及粉砂质泥底部的浅湖相灰色粉细砂和风成沙的年龄,对剖面上部碳酸盐层中陆生植物残体进行了AMS 14 C测年。通过不同测片的等效剂量(De)值的分布状况评价了样品的晒褪程度,选择不随灵敏度校正后的自然释光信号变化的相对集中的等效剂量(De)值计算了样品的埋藏年龄。通过这些年龄结果的对比,发现石英矿物的OSL年龄和AMS 14 C年龄在地层上是一致的,表明尽管在浅湖相细砂中存在不完全晒褪,但根据相对较小而集中的De值计算得到的年龄结果是可靠的。这些年龄结果和地层资料揭示末次冰消期以来至早全新世,博斯腾湖处于无水干盆地向深水湖泊转化的浅水湖泊状态,现代深水博斯腾湖大约形成于距今8ka前后。  相似文献   

14.
In this study we present optically stimulated luminescence (OSL) dating results obtained at one of the most important open‐air Middle Palaeolithic sites in the Sierra de Atapuerca foothills – Hotel California. We also assess the possibility of obtaining extended‐range OSL chronologies for a nearby Middle Pleistocene fluvial deposit using several novel methods, namely OSL dating of individual quartz ‘supergrains’, multi‐grain aliquot thermally transferred OSL (TT‐OSL) dating and the first application of a single‐grain TT‐OSL dating procedure. Four single‐grain OSL ages constrain the Middle Palaeolithic occupation of Hotel California to between 71±6 and 48±3 ka. The Hotel California single‐grain equivalent dose (De) distributions are highly overdispersed and contain several dose populations, which are probably attributable to post‐depositional sediment mixing, partial bleaching and intrinsic scatter. The reliability of multi‐grain aliquot OSL dating is compromised by the complex underlying De dispersion affecting these samples, as well as by biasing multi‐grain averaging effects. Extended‐range OSL and TT‐OSL chronologies for the nearby Pico River terrace are consistent with each other and with broad independent age control. These experimental approaches yield a weighted average age of 348±16 ka for terrace TA9 of the Arlanzón River sequence. Our results highlight the benefits of comparing ages obtained using several OSL methodologies to improve the robustness of luminescence chronologies. They also demonstrate the potential that single‐grain OSL techniques offer for establishing improved age constraints on the many other Middle Palaeolithic sites found at Atapuerca and elsewhere across north‐central Spain.  相似文献   

15.
《Quaternary Science Reviews》2003,22(10-13):1067-1076
This study is concerned with the Late Quaternary climatic chronology of the Strzelecki Desert dunefields in central Australia. The sand ridges comprise layers of quartz sand, some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence (OSL). Deduced from the OSL age of the oldest aeolian layer dated, we conclude that the onset of aridity dates back to at least ∼65 ka. Older phases of aeolian activity though, following a fluvial depositional phase 160 ka ago, cannot be excluded, although no aeolian layers giving evidence for this have been found in the two dunes dated here. Unconsolidated dune sands in the upper part of one section with Late Holocene (4 ka to modern) depositional ages indicate a reactivation of the dunefield in recent times.From the crosscheck of 14C ages of the carbonated rootlets with OSL results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development.  相似文献   

16.
The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by 40Ar/39Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations; (ii) varved clayey silts reflecting strong seasonality and an intralake oxic–anoxic boundary, for example, lake‐level highstands during interglacials/interstadials; (iii) CaCO3‐rich banded sediments which are representative of a lowering of the oxic–anoxic boundary, for example, lake level decreases during glacial inceptions; (iv) CaCO3‐poor banded and mottled clayey silts reflecting an oxic–anoxic boundary close to the sediment–water interface, for example, lake‐level lowstands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicating the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka bp . Although local environmental processes such as tectonic and volcanic activity influenced sedimentation, the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes, making Lake Van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years.  相似文献   

17.
Here we present a multi‐proxy investigation of the Klein Klütz Höved (KKH) coastal cliff section in northeastern Germany, involving lithofacies analysis, micromorphology, micropalaeontology, palynology and luminescence dating of quartz and feldspar. We subdivide the local stratigraphy into three depositional phases. (i) Following a Saalian advance (MIS 6) of the Scandinavian Ice Sheet, the penultimate deglaciation (Termination II) at the site occurred between c. 139 and 134 ka, leading to the establishment of a braided river system and lacustrine basins under arctic‐subarctic climate conditions. (ii) In the initial phase of the Eemian interglacial lacustrine deposits were formed, containing warm‐water ostracods and a pollen spectrum indicating gradual expansion of woodlands eventually containing thermophile deciduous forest elements. A correlation of the local pollen assemblages with Eemian reference records from central Europe suggests that fewer than 750 years of the last interglacial period are preserved at KKH. The occurrence of brackish ostracods dates the onset of the Eemian marine transgression at the section at c. 300–750 years after the beginning of the last interglacial period. (iii) Directly above the Eemian record a ~10‐m‐thick sedimentary succession of MIS 2 age was deposited, implying a significant hiatus of c. 90 ka encompassing the time from middle and upper MIS 5e to late MIS 3. During the Late Weichselian, KKH featured a depositional shift from (glacio‐)lacustrine to subglacial to recessional terminoglacial facies, with the first documented Weichselian ice advance post‐dating 20±2 ka. Overall, the KKH section represents an exceptional sedimentary archive for palaeoenvironmental reconstructions, covering the period from the Saalian glaciation and subsequent Termination II to the early Eemian and Late Weichselian. The results refine the existing palaeogeographical and geochronological models of the late Quaternary history in the southwestern Baltic Sea area and allow correlations with other reference records in a wider area.  相似文献   

18.
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19.
《Quaternary Science Reviews》2003,22(10-13):1207-1211
The time-integrated slip rate in fault zones can be determined if the deformed deposits are reliably dated. Here, we report optically stimulated luminescence (OSL) ages of Late Pleistocene fluvial deposits cut by the Wangsan fault, southeastern Korea, which displaces a hanging wall block of about 28 m. Five sandy samples of the deformed Quaternary deposits were dated by quartz OSL using the single aliquot regenerative-dose (SAR) protocol. Three samples taken from the footwall block show stratigraphically consistent OSL ages of 54±7, 76±5 and 90±6 ka, from top to bottom. Two samples collected from the same layer in the hanging wall block show reproducible OSL ages of 81±5 and 82±5 ka, which are also in good agreement with the stratigraphic relationships. Our OSL ages yield an average sedimentation rate of the Quaternary deposits as around 0.04 mm a−1, and a minimum value of time-integrated slip rate as 0.52 mm a−1. This minimum slip rate is considerably higher than those reported earlier for Quaternary faults in southeastern Korea. The youngest OSL age (54±7 ka) constrains the maximum value of the recurrence interval of the fault movement.  相似文献   

20.
Carbon, oxygen and clumped isotope (Δ47) values were measured from lacustrine and tufa (spring)‐mound carbonate deposits in the Lower Jurassic Navajo Sandstone of southern Utah and northern Arizona in order to understand the palaeohydrology. These carbonate deposits are enriched in both 18O and 13C across the basin from east to west; neither isotope is strongly sensitive to the carbonate facies. However, 18O is enriched in lake carbonate deposits compared to the associated spring mounds. This is consistent with evaporation of the spring waters as they exited the mounds and were retained in interdune lakes. Clumped isotopes (Δ47) exhibit minor systematic differences between lake and tufa‐mound temperatures, suggesting that the rate of carbonate formation under ambient conditions was moderate. These clumped isotope values imply palaeotemperature elevated beyond reasonable surface temperatures (54 to 86°C), which indicates limited bond reordering at estimated burial depths of ca 4 to 5 km, consistent with independent estimates of sediment thickness and burial depth gradients across the basin. Although clumped isotopes do not provide surface temperature information in this case, they still provide useful burial information and support interpretations of the evolution of groundwater locally. The findings of this study significantly extend the utility of combining stable isotope and clumped isotope methods into aeolian environments.  相似文献   

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