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1.
选择中国不同地区的冲洪积相等水成相沉积物样品,根据其简单多片再生法(SMAR)测量数据建立了细颗粒石英光释光信号的综合生长曲线(Standardised growth curves,SGC)。对未知年龄的水成相沉积物细颗粒石英样品,通过测量其天然光释光信号和试验剂量响应信号,并利用上述SGC方程可计算出其等效剂量值。将此值与简单多片再生法(SMAR)测量结果相比较,统计得出对于天然等效剂量为12~65Gy的样品,其误差可达19%;对于天然剂量>65Gy的样品,其误差更大;对于等效剂量<12Gy的样品,最大误差也达25%。实验表明,应用这个SGC估计未知年龄样品的等效剂量值范围,再对样品采用简单多片再生法(或单片再生法)进一步测量,可大大节省测量时间  相似文献   

2.
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3.
Luminescence dating has become a key tool in studies of the Quaternary. The typically stable luminescence response of quartz grains and the absence of a significant internal dose, make quartz minerals the preferred dosimeter for monitoring the burial dose in sediments. Unfortunately, the reliability of conventional OSL (optically stimulated luminescence) dating, based on blue stimulation, can be compromised when the luminescence decay is not dominated by a rapidly decaying and stable part of the luminescence signal (i.e. the fast component). On the other hand, standard methods in luminescence dating are limited to ages of a few hundred kiloyears. In this study, violet stimulated luminescence (VSL) has been used as a means to overcome both problems, applied to a series of colluvial deposits in the Atacama Desert, Chile. Quartz from this region, characterized by poor blue-OSL response, showed a reproducible and stable VSL signal capable of recovering given doses up to ∼500 Gy and a saturation dose twice as high as conventional OSL. The VSL response from these samples has been studied in detail and the estimated ages have been compared with an already established chronology for the same site, based on IRSL of potassium feldspar single grains. Results agree for the dose range of the profile studied, ∼100–250 Gy, equivalent to ages of 29–79 ka confirming the suitability of VSL for dating sedimentary quartz with unreliable blue-OSL response and to extend the age range of conventional OSL dating.  相似文献   

4.
Fossil oyster reefs are indicators of past sea levels, and their formation is usually dated by means of radiocarbon. However, radiocarbon dating of the shells from coastal areas may be complicated by the varying sources of carbon. Here we applied optical dating methods to date the samples from above and below a fossil oyster bed in a section on the coast of Bohai Bay, China. The optical ages of the sediments were used to constrain the oyster bed. Single-aliquot regenerative-dose procedures using the OSL signal from fine grain quartz, the IRSL and post-IR OSL signals from polymineral fine grains were employed to determine equivalent dose (De). The behaviors of the different luminescence signals from quartz and polymineral grains during De measurements were examined. The results showed that the quartz OSL signal is more reliable than the polymineral IRSL and post-IR OSL signals with respect to dating for these coastal samples. The optical ages indicated that the oyster reef formed between ca. 6.2 and 5.0 ka.  相似文献   

5.
Quartz optically stimulated luminescence (OSL) forms the basis for the chronology of Weichselian ice advances in Arctic Eurasia developed over the last few years. There is almost no age control on this chronology before 40 ka, except for some marine sediments correlated with marine isotope stage (MIS) 5e on the basis of their palaeofauna. Results from more southern latitudes have shown that dose estimates based on quartz OSL and the single aliquot regenerative (SAR) dose procedure may underestimate the age of MIS 5e deposits. Here we use the same method to date well-described marine sediments, thought to have been deposited during the very beginning of the Eemian interglacial at 130 ka, and exposed in two sections on the river Sula in northern Russia. Various quality-control checks are used to show that the OSL behaviour is satisfactory; the mean of 16 ages is 112±2 ka (σ=9 ka). This represents an underestimate of 14% compared to the expected age, a discrepancy similar to that reported elsewhere. In contrast to SAR, the single aliquot regeneration and added (SARA) dose procedure corrects for any change in sensitivity during the first OSL measurement. The SARA results are shown to be 10% older than those from SAR, confirming the geological age estimate and suggesting that SAR ages may underestimate older ages (larger doses), despite their good performance in the younger age range.  相似文献   

6.
Endorheic basins, filled by a rhythmic stratification of fluvio-lacustrine sediments, are useful archives for studying the interaction of palaeoenvironment and prehistoric development. Archaeological evidence indicates an occupational maximum during the Early to Mid-Holocene humid phase that can be linked to geochronological dates. A wadi has cut these sediments and a wadi profile of about 6 m was sampled for luminescence dating.

Palaeodose estimates are based on single aliquot measurements of the sand-sized quartz fraction using the regenerative dose technique. The comparison of equivalent dose results from different aliquot sizes (<100 and >1000 grains) provides interesting insights into heterogeneous degrees of bleaching. Problems arising from substantial variations in environmental dose rates of such heterogeneous sediments are discussed.

The luminescence ages indicate two major phases of deposition, both of Holocene age. The lower 2 m of sediments were deposited about 9400 years ago. The sedimentation of the upper 2 m started about 7200 and terminated around 6300 years ago. Radiocarbon ages of charcoals contained in the upper part of the section disagree with that OSL dating. This discrepancy is explained by re-deposition of the charcoal fragments.  相似文献   


7.
The Wulanmulun site found in 2010 is an important Paleolithic site in Ordos (China), from which lots of stone and bone artifacts and mammalian fossils have been recovered. It was previously dated by radiocarbon and optically stimulated luminescence (OSL) techniques on quartz. To further confirm the reliability of the chronology constructed based on OSL ages and test the applicability of the recently developed pIRIR procedure on sediments from northern China, twenty-four sediment samples (including eolian, lacustrine and fluvio-eolian sands) from the site were determined using the multi-elevated-temperature post-IR IRSL (MET-pIRIR or pIRIR) procedure on potassium feldspar. The results show that the studied samples have two MET-pIRIR De preheat plateaus (280–320 and 340–360 °C), and the bleaching rates of the luminescence signals are associated with sample ages and stimulation temperatures. All the pIRIR ages (7–155 ka) corrected for anomalous fading and residual dose obtained after solar bleaching for 15 h are larger than the corresponding quartz OSL ages (4–66 ka) previously determined, even for the young eolian samples (<10 ka). But the corrected IRSL(50 °C) ages (6–85 ka) are broadly consistent with the quartz ages. It appears that the IRSL(50 °C) ages are more reliable, although this contradicts the previously results obtained by other people. On the other hand, we also obtained an extended age plateau between the stimulation temperatures of 50 and 290 °C in the plot of age versus stimulation temperature (A-T plot) by subtracting different residual doses obtained after different bleaching times. The reliability of the plateau ages requires further investigation. For the sediment samples from this site, quartz should be more suitable for dating than K-feldspar, and the quartz OSL ages of 50–65 ka for its cultural layer should be reliable.  相似文献   

8.
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.  相似文献   

9.
This study applies single-grain optically stimulated luminescence (SG OSL) dating of quartz sand temper to Intermountain Ware ceramics recovered from four archaeological sites in northwestern Wyoming, USA. We show that SG OSL dating can strengthen and further refines existing archaeological site chronologies in certain settings. The SG OSL results are compared to multi-grain infrared stimulated luminescence (IRSL) dating of the polymineral (feldspar and quartz) silt fraction in the ceramic paste of the same sherds. Results from the two methods are statistically indistinguishable, although coarse-grained quartz SG OSL ages have consistently lower standard error terms due to higher relative sensitivity and avoidance of anomalous fading calculations. Moreover, the SG OSL results produced precision at two-sigma standard error greater than or equal to associated calibrated radiocarbon ages. SG OSL dating of quartz temper from Intermountain Ware ceramics provides more reliable site occupation timing than radiocarbon dating, which can be conditioned by incorporation of old wood and contamination from young soil carbon. This study highlights the importance of SG OSL dating on sherds from buried contexts when exposure to wildfires may have occurred, as ceramics recovered from the ground surface of one site after a high-intensity fire produced near-modern apparent ages, suggesting they were thermally reset during the fire. We suggest SG OSL should be applied to date similar ceramics with quartz temper to determine site age and bolster regional chronologies.  相似文献   

10.
The most recent high magnitude seismic events, e.g. the Mw 8.2 Iquique earthquake (April 1st, 2014) and the Mw 8.8 Maule earthquake (February 27th, 2010) are reminders of the pronounced vulnerability of the Chilean coast to the impact of natural hazards like earthquakes and tsunamis. Therefore it is crucial to understand the complex tsunami history of Chile which can be deciphered by studying the geological record of former tsunamis in the form of tsunami deposits.At the coastal locality of Tirúa (Central Chile) six distinct, successive tsunamigenic sand layers are intercalated in fine grained floodplain sediments. We present the optically stimulated luminescence (OSL) analysis of quartz from samples of this sedimentological river marsh profile of 1.5 m depth.After the assessment of the applicability of OSL to these samples, it could be noted that despite of an expected low OSL sensitivity of the quartz from the South American Cordillera, most of the sampled quartz yielded a detectable natural signal. After performance tests according to the SAR-protocol, the measurements of the different tsunami sand layers were conducted with small (2.5 mm) aliquots of quartz with the preheat temperature 180 °C. The calculation of De was provided by applying both the central age and minimum age models. All samples are heterogeneous in their De distributions due to incomplete or absent significant bleaching during transport by tsunami. The resulting ages of the tsunami sediments yield an offset of nearly 200 years for CAM ages and less than 50 years for MAM ages, consequently favouring MAM ages for true burial age determination. In some tsunami sand layers and their surrounding river marsh sediments age inversions occur. They were caused by the initial deposition of well bleached sediments derived from beach and dunes followed by older sediments redeposited from beach and intertidal environments during tsunami flow. Despite the offset and age inversion six different tsunami events were dated in the Tirúa profile. Three of these events extend the historical record to pre-Columbian time with the oldest tsunami dated to over 1500 years before present.  相似文献   

11.
Panxian Dadong Cave located in the western Guizhou is a very important Paleolithic site in China. At this site bone and stone artifacts, human teeth and mammalian fossils (known as Ailuropoda-Stegodon fauna) were found, and the site was previously dated to 120–300 ka using ESR/uranium-series methods. In this study, we successfully extracted fine quartz grains from flowstone and silty carbonate-rich sediments in the excavated area. The quartz extracts displayed excellent luminescence properties, and satisfied the SAR (single-aliquot regenerative dose method) acceptance criteria. The sensitivity-corrected OSL signals are not saturated at a dose up to about 1400 Gy. The cultural unit was OSL dated to 190–300 ka, corresponding to MISs 7–8. The flowstone deposits overlying the cultural unit were determined to be 13–190 ka and the silty carbonate-rich sediments underlying the cultural unit to be 300–360 ka. The optical ages are in general agreement with the coupled ESR/U-series and U-series ages.  相似文献   

12.
We test the applicability of quartz optically stimulated luminescence (OSL) dating on clastic lake sediments to investigate whether this dating method can be applied to study the timing and rate of deposition in Holocene fluvio-deltaic lakes. Our study concerns the filling of a lake by the Angstel-Vecht system, part of the Rhine delta in the western Netherlands. Age constraints are provided by radiocarbon dates on the development and abandonment of the fluvial channels debouching into the lake. Results indicate that light exposure prior to deposition and burial was sufficient to reset the OSL signal of the vast majority of the quartz grains. Special attention was given to accurate estimation of the dose rate in the laminated and bedded deposits. The OSL ages obtained are in good agreement with the age constraints, especially for the relatively coarse sediments. OSL results indicate that the filling of the lake took about 700 years, with a sedimentation rate of ～3 mm per year. This study is a demonstration of the use of OSL dating of sand-sized quartz to determine the timing and rate of sedimentation in a Holocene fluvio-deltaic environment.  相似文献   

13.
Modern Mississippi Delta sediments were analyzed to investigate quartz OSL signal resetting in large river deltas and test the accuracy of OSL dating on a decadal time scale with the early background subtraction and a recently proposed burial dose estimation procedure. Both fine silt-sized and sand-sized quartz were measured with a modified single-aliquot regenerative dose (SAR) protocol and equivalent dose (De) was calculated using different background subtraction methods. Evidence of insufficient bleaching was observed, but the residual signal is equivalent to ∼100 a on average for both sandy quartz and fine silt-sized quartz. It is shown that dose distributions of sandy quartz are affected by the background subtraction. The proportion of aliquots that have De in agreement with expectation is significantly larger when an early background is subtracted compared to the late background subtraction. This is, in contrast, not observed for fine silt-sized quartz. Accurate OSL ages were obtained by employing the unlogged minimum age model to Des of sandy quartz obtained with the early background subtraction method.  相似文献   

14.
The Qinghai-Tibetan Plateau is an important area for the study of Quaternary glaciation. Optically stimulated luminescence (OSL) dating has the potential to contribute to the chronology of glaciation in this region, but it is important to assess the accuracy of OSL dating of these glacial sediments. In this study, single grain quartz OSL signals are examined for five glacial samples collected from the moraines outside the Baiyu Valley, southeastern Tibet. The quartz grains exhibit poor luminescence characteristics, with a small proportion of grains passing the screening criteria. Grains which pass the screening criteria have relatively low signal intensity, leading to De values with large uncertainties. MAM and CAM were used to determine De values for these samples. The OSL ages are consistent with the sequence of events derived from the geomorphological relationship of the samples, and also with previous published radiocarbon ages. However, it is more difficult to reconcile the OSL ages and the terrestrial cosmogenic nuclide (TCN) 10Be ages. Analysis of both single grain quartz OSL data and TCN 10Be data is complex in this area. Further work is required to increase confidence in the OSL ages generated for the glacial sediments from this region.  相似文献   

15.
A newly developed range-finder luminescence dating method is applied to samples from the eastern Punjab region of Pakistan. Overbank sediments from this area are the subject of an ongoing project into the demise of the Harappan civilization about 4.2 ka and the range-finder technique was used to ascertain whether samples from three pits are from this part of the Holocene. Luminescence measurements of raw sample gave a signal dominated by feldspars, even when using a [post-IR] optically stimulated luminescence (OSL) signal. Following etching in hydrofluoric acid samples gave OSL signals characteristic of quartz and these were used to calculate the equivalent dose. The total dose rate was estimated from beta counting. Eight range-finder OSL ages extend from 4000 to 6600 years ago and are consistent with two radiocarbon ages from the same pits demonstrating that these sediments do straddle the period of interest for this project. The range-finder approach provides a rapid means of informing future field sampling campaigns.  相似文献   

16.
Resetting of sediments mobilised by the LGM ice-sheet in southern Norway   总被引：3，自引：0，他引：3  
Former geological field investigations in the Rondane area, east-central southern Norway, have proposed that the maximum Fennoscandian ice-sheet coverage occurred during the Late Weichselian Glacial Maximum (LGM, ca. 20 ka) and that subsequent glaciofluvial sediments were first deposited in the early Holocene (after 10 ka). However, recent field investigations with ages from three internally consistent quartz optically stimulated luminescence (OSL) age series show an apparent deglaciation of northern Rondane in the period 20.0–13.8 ka. We examine here the possibility that these ages are too old because the sediment was not completely zeroed prior to deposition. Our investigations of incomplete bleaching use modern analogues, small aliquots, and single grains of quartz. First, the symmetric shape of small aliquot equivalent dose distributions suggests that the sediment was probably well bleached at deposition. This is supported by 5 modern analogue equivalent doses (De) of 0.6 Gy, 1.5% of the typical De from the deglaciation sediments. Finally, from single grain studies on three samples, we conclude that there is no evidence for poor bleaching in these samples; thus the weighted mean gives the best estimates of De, and these are completely consistent with both large and small aliquot estimates for these samples. These comparisons between large aliquots, modern analogues, small aliquots and single-grain analyses help to validate the OSL ages and confirm the complete resetting of these sediments prior to deposition.  相似文献   

17.
The paleogeography of Amazonia lowlands during the Pleistocene remains hampered by the lack of reliable absolute ages to constrain sediment deposition in the hundred thousand to few million years timescales. Optically stimulated luminescence (OSL) dating applied to quartz has provided important chronological control for late Quaternary sediments, but the method is limited to the last ∼150 ka. In order to extend the age range of luminescence dating, new signals from quartz have been investigated. This study tested the application of isothermal thermoluminescence (ITL) and thermally transferred optically stimulated luminescence (TT-OSL) signals of quartz for dating of fluvial terraces from eastern Amazonia. ITL and TT-OSL signals measured in a modern fluvial sediment sample have shown small residual doses (4 and 16 Gy), suggesting adequate bleached sediments for the target dose range (>150 Gy). This sample responded well to dose recovery test, which showed that the ITL and TT-OSL signals grow to higher doses compared to the doses estimated by the conventional OSL signal. The ITL signal saturated for doses significantly lower than doses reported in the literature. Most dating samples were beyond the ITL saturation doses and only TT-OSL signals were suitable to estimate equivalent doses. Burial ages ranging from 107 to 340 ka were estimated for the fluvial terraces in the lower Xingu River. The main ages uncertainties are related to dose rate changes through time. Despite the uncertainties, these ages should indicate a higher channel base level during the Middle Pleistocene followed by channel incision, possibly due to episodes of increased precipitation in the Xingu watershed.  相似文献   

18.
We investigate the use of quartz optically stimulated luminescence (OSL) dating for determining fluvial overbank sedimentation rates over decades to centuries. For the study we took 11 samples from three cores from an embanked floodplain along the River Waal (Rhine) near Neerijnen (The Netherlands). We propose a measurement protocol for young fluvial quartz based on the single-aliquot regenerative dose procedure. Parameters for the protocol are chosen to isolate the fast OSL component, eliminate an ultrafast OSL component and avoid thermal transfer. The protocol shows excellent dose recovery and recycling ratios. For each sample, a Gaussian is fitted to the lower part of the equivalent dose distribution to obtain an estimate of the burial dose. We discuss the validity of the OSL ages using internal and external controls, and conclude that there is no evidence for large systematic offsets in the OSL ages. OSL based sedimentation rates are between ～3 and 8 mm/a, in line with previous estimates.  相似文献   

19.
This study reports on the first investigation into the potential of quartz luminescence dating to establish formation ages of ferruginous duricrust deposits (ironstones) of the Xingu River in Eastern Amazonia, Brazil. The studied ironstones comprise sand and gravel cemented by goethite (FeO(OH)), occurring as sandstones and conglomerates in the riverbed of the Xingu River, a major tributary of the Amazon River. The Xingu ironstones have a cavernous morphology and give origin to particular habitat for benthic biota in an area that hosts the largest rapids in Amazonia. So far, the Xingu ironstones have uncertain formation ages and their sedimentary origin is still poorly understood. In this way, seven samples of ironstones distributed along the lower Xingu River were collected for optically stimulated luminescence (OSL) dating of their detrital quartz sand grains. Additionally, the organic content of some samples was dated by radiocarbon (14C) for comparison with quartz OSL ages. The luminescence ages of the sand-sized quartz grains extracted from the ironstones were obtained from medium (100–300 grains) and small (10–20 grains) aliquots using the single aliquot regenerative-dose (SAR) protocol. Equivalent doses (De) distributions have varied overdispersion (OD) both for medium size aliquots (OD = 19–58 %) and small size aliquots (OD = 29–76 %). No significant trend was observed between De and aliquot size. The studied ironstones grow over the riverbed, but stay below or above water throughout the year due to the seasonal water level variation of the Xingu River. However, the effect of water saturation in dose rates is reduced due to relatively low porosity of ironstones. Water saturated dose rates (dry sample dose rates) range from 2.70 ± 0.21 (2.79 ± 0.22) Gy/ka to 12.34 ± 0.97 (13.26 ± 1.12) Gy/ka, which are relatively high when compared to values reported for Brazilian sandy sediments elsewhere (∼1 Gy/ka). Samples with high overdispersion (>40 %) are mainly attributed to mixing of grains trapped in different time periods by goethite cementation. The obtained OSL ages for water saturated (dry) samples range from 3.4 ± 0.3 (3.3 ± 0.4) ka to 59.6 ± 6.0 (58.1 ± 6.4) ka, using De determined from medium size aliquots and dose response curves fitted by an exponential plus linear function. Radiocarbon ages of the bulk organic matter extracted from selected ironstone varied from ca. 4 cal ka BP to ca. 23 cal ka BP. Significant differences were observed between OSL and radiocarbon ages, suggesting asynchronous trapping of organic matter and detrital quartz within the ironstone matrix. These late Pleistocene to Holocene ages indicate that ironstones of the Xingu River result from an active surface geochemical system able to precipitate goethite and cement detrital sediments under transport. The obtained ages and differences between OSL and radiocarbon ages point out that the ironstones have multiphase and spatially heterogeneous growth across the Xingu riverbed. Our results also expand the application of luminescence dating to different sedimentary deposits.  相似文献   

20.
This study presents results from 20 optically stimulated luminescence (OSL) ages from one of the world's largest beach ridge plains, the Jerup beach ridge plain at the base of the Skagen Spit in the northernmost part of Jutland, Denmark. The OSL ages were obtained using quartz and a SAR protocol, and used to establish a chronology for the beach ridge plain and for the underlying coastal plain. The accuracy of the chronology is tested both by laboratory tests (recuperation, recycling ratio and dose recovery) and by comparison with independent age controls, e.g. previously reported radiocarbon dates, map sources, anecdotal evidence and settlement names. It is concluded that the OSL signals are internally consistent, and that the derived OSL ages are in good agreement with a large range of independent age controls. The ridge plain is shown to cover a time span from 1000 to 2700 years ago; this chronology is more detailed and precise than those previously available, and gives an average beach ridge formation rate of 15 yr/ridge and an average lateral migration rate of 2.0 m/yr. This study adds to the growing knowledge that OSL dating has a large potential for establishing detailed and precise chronologies in coastal marine sediments, including beach ridges.  相似文献   

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