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1.
OSL (optically stimulated luminescence) sensitivity of quartz has been shown to either (1) record downstream sediment transport related to increased number and duration of light exposure cycles or (2) be a function of source geology, presenting a potential tool to track sediment provenance. To test these competing models this study leverages a suite of modern river samples from an extensional basin system in the Rocky Mountains of western USA (Bear River) and a retroarc foreland basin system in the southern Central Andes of Argentina (Río San Juan) to understand the relationships among quartz luminescence sensitivity, sediment transport distance, and catchment lithologies. We compare our results with petrographic analysis of the river sand composition, and characterization of the lithology and morphometrics of the river catchments. Samples taken along the Bear River and its major tributaries in the Rocky Mountains show a progressive downstream decrease in quartz OSL sensitivity that records variation in sediment provenance and steady contribution of lower OSL sensitivity quartz recycled from Palaeozoic passive margin stratigraphy. Andean river sand samples from the Rio San Juan network exhibit pervasive low sensitivity quartz derived from Andean arc volcanic rocks and recycled Neogene foreland basin strata. These modern river sand data do not show increased sensitivity with transport distance and instead indicates that in these landscapes, quartz OSL sensitivity is an intrinsic property of the source rock. Our study shows that river sands primarily composed of older, recycled low-strained quartz derived from quartzite lithologies exhibit the highest quartz sensitivity values. Moderate quartz OSL sensitivity values are observed in rivers with young igneous quartz derived directly from the volcanic and intrusive rocks. Conversely, microcrystalline quartz in chert lithic grains or polycrystalline quartz found in composite metamorphic lithic grains record the lowest quartz OSL sensitivity values. Determining the controlling factors of quartz sensitivity in river sand provides a current baseline for resolving paleogeographic and paleodrainage histories in the sedimentary record and provides further understanding of how sediments are eroded, transported, and deposited in fluvial systems with diverse tectonic settings and geologic source rocks. 相似文献
2.
The signal properties of quartz optically stimulated luminescence (OSL) vary from sample to sample, and even from grain to grain, in terms of, for example, signal intensity or the composition of OSL signal components. However, the cause of the variation in quartz OSL properties is not well understood. Here, we report our experimental observations of continuous wave and linearly modulated OSL signals in quartz grains from fresh bedrocks, saprolites, and sediments in Korea. The OSL signals in quartz grains from both fresh bedrocks and saprolites in the granitic and metamorphic rocks are dominated by slower OSL components, with no fast OSL component. By contrast, the OSL signals in quartz extracts from sandstones are predominantly composed of fast OSL components. Quartz extracts derived from thermally metamorphosed or diagenetically recrystallised sandstones, however, tend to emit weaker OSL signals, a property related to intense slower OSL components. Along the fluvial transportation path, slower OSL components dominate near the host granite, but their absolute/relative intensity decreases with a simultaneous increase in the fast OSL component with transportation distance. OSL signal characteristics suitable for dating appear to be acquired during sedimentary processes after the liberation of quartz grains from granitic and metamorphic bedrock. Therefore, granitic and metamorphic quartz grains should be transported a sufficient distance for the fast OSL component to be sensitised. However, unless they have been affected by post-thermal metamorphism and recrystallisation, the OSL signal properties of quartz grains released from Cretaceous sedimentary rocks seem to be suitable for OSL dating, regardless of the transportation distance. 相似文献
3.
The provenance of loess in Chinese Loess Plateau, including origin, transport pathways and source areas, has long been one of the most important questions. In this study, the vertical variations of the luminescence sensitivity of quartz grains from the central Chinese Loess Plateau were investigated by using optically stimulated luminescence (OSL) techniques. Our results indicate that the luminescence sensitivity of quartz grains of paleosols can be much higher than that of loess beds. In addition, the quartz grains from the loess-paleosol sequence exhibit a temporal trend in the strength of luminescence sensitivity, characterized by higher values in soils and lower values in loess beds. The OSL sensitivity of quartz grains of the loess-paleosol sequence also shows very similar trend to the magnetic susceptibility and particle size fluctuations, implying that the luminescence sensitivity might be climatic dependent. The possible factors affecting the variations of luminescence sensitivity were discussed including particle size, natural radioactivity, and the provenance of eolian deposits. We suggest that the temporal variations of luminescence sensitivity can be attributed to the retreat-advance of deserts, the different contributions of glacial origin quartz particles associated with mountain processes, and wind patterns during glacial/interglacial cycles. Therefore, the secular variations of luminescence sensitivity of quartz grains are ultimately influenced by past climatic change through its controlling on sediment provenance changes. 相似文献
4.
The properties of the quartz luminescence signal have been shown to be a useful tool for sediment provenance analysis. These provenance studies are based on the sensitivity of the fast optically stimulated luminescence (OSL) component, which is also used for sediment dating. Besides the widespread occurrence of quartz in terrigenous sediments, OSL sensitivity can be acquired using relatively fast and low-cost measurements compared to sediment provenance analysis methods based on accessory minerals or isotopes. Additionally, laboratories worldwide already have an extensive database of recorded quartz OSL signals primarily measured for dating studies, and these data could potentially be repurposed for provenance analysis of Quaternary sedimentary systems through OSL sensitivity calculation. Here, we investigate the use of OSL quartz signals measured in sediment dating surveys for OSL sensitivity calculation and evaluation of changes in sediment sources. The OSL sensitivity was calculated and expressed as %BOSLF, which corresponds to the percentage of the fast OSL component signal (blue stimulation) to the total OSL curve; such approach is advantageous as it does not require any normalisation of the measured signal intensity to dose or aliquot size (weight). Three sets of samples from Amazonian fluvial sediments are investigated: two sets of Holocene floodplain sediments representing different sediment sources to the Amazonian fluvial system, i.e. the Amazon craton and the Andes Mountain belt, and a set of samples from the Içá Formation, a paleo-fluvial system active during the Pleistocene whose provenance is not fully known. Results show that the quartz OSL signal derived from the first test doses (Tn) applied in dating protocols had the best performance for %BOSLF calculation when compared to results from a measurement protocol designed specifically for sediment provenance analysis. There is significant correlation (R2 = 88) between sensitivities derived from Tn and a specific OSL provenance analysis protocol. The proposed approach indicates to be appropriate for sediment provenance analysis since it is able to discriminate signal differences among samples from known sources: Brazilian cratonic quartz yield high sensitivity values (mean %BOSLF >70), in contrast to the relatively lower values from Andean quartz (mean %BOSLF <50). In general, quartz OSL sensitivities from the Içá Formation samples fall into the same range of modern sediments transported by the Içá and Japurá rivers draining the Andean Eastern Cordillera of Colombia and Ecuador. We also observe a decrease in quartz OSL sensitivity during the Holocene, notably after 4 ka, with younger deposits showing lower sensitivity. Sediment provenance variations are discussed in terms of watershed rearrangement and/or precipitation-driven changes during the Late Pleistocene and Holocene across Amazonia. 相似文献
5.
Quartz is a preferred mineral which is widely used for optically stimulated luminescence (OSL) and cosmogenic radionuclide (CRN) dating methods. Any contamination in the sample may mislead and result in erroneous results for both the dating methods (e.g. OSL or CRN). Therefore it is essential to get pure quartz before the measurements of OSL and CRN. Presence of other minerals can introduce unaccounted luminescence signal in the case of OSL, similarly in the case of CRN unaccounted concentration of 10Be and 26Al may be introduced. Therefore, in order to get reliable ages from CRN and OSL, extraction of pure quartz from the sediment becomes necessary. Protocols have been developed to extract pure quartz from the sediment, e.g., the separation of quartz from feldspar and other heavy minerals can be achieved by applying 2-step density separation. This is followed by HF leaching which usually removes the feldspar contamination from the quartz (if any left). However, in some cases, this method is not successful, especially in the case of feldspar rich samples or in the samples with intergrowth of feldspar in quartz crystals. This paper reports a method that is effective in separating quartz and feldspar. A small amount of fine grained iron powder was used to make feldspar as magnetic mineral and it is separated from quartz using isodynamic magnetic separator effectively. Efficacy of the method was tested with different analytical instruments such as scanning electron microscope (SEM), OSL/TL reader and inductively coupled plasma mass spectromete (ICP-MS). The analytical tests showed that the proposed method eliminates feldspar by ~95%. 相似文献
6.
The optically stimulated luminescence (OSL) signals from quartz have been widely used to estimate the equivalent dose (De) of environment radiation after the deposition of mineral grains. However, the usage of quartz is often limited due to the lower saturation behavior compared with feldspar. Saturation limits among quartz (defining the upper dating range) vary significantly. It is important to better understand the reason for various dose saturation behaviors of the quartz OSL signals. In this study, coarse quartz grains were extracted from the Taklimakan Desert and the Hunshandake sandy land in north China and the dose saturation behavior of quartz OSL signals were studied. Our results suggest that the quartz grains produce very different aliquot-specific dose response curves, showing the significant variability in dose saturation characteristics for OSL signals. Laboratory dosing, optical bleaching and heating experiments were designed to simulate their effects on the dose saturation behavior for the quartz OSL. The results demonstrate that cycles of dosing and optical bleaching have insignificant impact on the OSL dose growth curves, while the heating to high temperature (above 400 °C) can significantly change the dose saturation characteristics for the quartz OSL. Such results suggest that the different heating history of quartz might be an important factor for the variability in dose saturation characteristics for OSL signals. Additionally, the quartz grains from the Hunshandake sandy land exhibit lower dose saturation level for OSL signals, compared with that from the Taklimakan Desert. This can be explained that the quartz grains from Hunshandake sandy land are mainly of igneous origin, while the quartz grains from Taklimakan Desert are mainly of metamorphic origin. 相似文献
7.
Optically stimulated luminescence (OSL) is used to determine the age of a rockfall event that removed part of the pictograph figures at the Great Gallery rock art panel in Canyonlands National Park, Utah, USA. Analyses from the outer millimeter of the buried surface of a rockfall boulder and quartz grains from the underlying sediment both provide consistent ages that also agree with an AMS radiocarbon age of a cottonwood leaf found immediately between the clast and underlying sediment. Measurement of the OSL signals as a function of depth into the surface of the boulder clearly shows that there is no detectable increase in the OSL signal to a depth of at least 3 mm suggesting that the OSL signal was fully reset to this depth before burial. Consistent OSL and radiocarbon ages for this rockfall event provide a minimum age of ∼900 a for the Great Gallery, which is the type locality of Barrier Canyon Style rock art with a controversial and unknown origin. 相似文献
8.
Middle to late Holocene alluvium, identified as Quaternary alluvial unit 4 (Qa4), along Kanab Creek in southern Utah, USA was dated using optically stimulated luminescence (OSL) on quartz sand, and by radiocarbon dating of detrital charcoal. Entrenchment beginning in 1882 AD created arroyo walls that expose up to 35 m of the Qa4 alluvium. The stratigraphy and sedimentology suggest that fluvial aggradation along the study reach occurred rapidly. Due to the high sediment supply, short transport distances and semi-arid climate with flashy discharge, partial bleaching (zeroing) of the luminescence signal was expected to be a problem for OSL dating. We approached this problem by first using small-aliquot (∼20 grains) and single-grain dating of quartz sand to reduce the number of grains contributing to the OSL signal. Second, we used statistical parameters based on single-grain and small-aliquot equivalent dose (De) distributions of bleached sediment to help identify partial bleaching and to inform if a minimum age model (MAM) should be used for age calculation. Comparison of results with radiocarbon ages demonstrates the success of OSL dating on Kanab Creek arroyo-fill deposits, although careful attention should be paid to the sedimentary facies and stratigraphy of the targeted sample horizon to minimize the effects of partial bleaching. Thin, decimeter-scale plane-bedded and ripple cross-bedded sandy lithofacies were found to be the best target for OSL dating, as these sediments showed minimal evidence for incomplete solar resetting. Additionally, results generally indicate that better-bleached sediments are found in downstream reaches. Age control from these arroyo-fill deposits was acquired in order to fulfill larger research goals of understanding regional arroyo incision and aggradation cycles. 相似文献
9.
Optically stimulated luminescence (OSL) thermochronometry is an emerging application, whose capability to record sub-Million-year thermal histories is of increasing interest to a growing number of subdisciplines of Quaternary research. However, several recent studies have encountered difficulties both in extraction of OSL signals from bedrock quartz, and in their thermochronometric interpretation, thus highlighting the need for a methodological benchmark. Here, we investigate the characteristic OSL signals from quartz samples across all major types of bedrock and covering a wide range of chemical purities. High ratios of infrared to blue stimulated luminescence (IRSL/BLSL), an insensitive ‘fast’ OSL component, and anomalously short recombination lifetimes seen in time-resolved luminescence (TR-OSL), are often encountered in quartz from crystalline (magmatic and metamorphic) bedrock, and may hamper successful OSL dating. Furthermore, even when the desirable signal is present, its concentration might be indistinguishable from its environmental steady-state prediction, thus preventing its conversion to a cooling or heating history. We explore the saturation properties and the thermal activation parameters of various OSL signals in quartz to outline the capabilities and limitations for their use in low-temperature thermochronometry. 相似文献
10.
Sediments of river deltas provide valuable records of past coastal environments. Optically-stimulated luminescence (OSL) dating has become an alternative to radiocarbon dating for constraining the sediment chronology in large deltas that allow for sufficient sunlight bleaching of sediments during the fluvial transport. However, its applicability to smaller deltas with mountainous riverine systems has not been confirmed yet. To check this, we examine multiple signals from two Holocene sediment cores in the wave-dominated Thu Bon River delta in central Vietnam. Two cores were collected, respectively, 3.9 km and 1.2 km inland from the present shoreline and both show a >-25-m thick succession of coarsening-upward mud to sand deposits. Coarse grains (180–250 μm in diameter) of quartz and K-feldspar, and fine grains (4–11 μm in diameter) of quartz and polymineral were extracted from the upper and lower parts of the cores for multi-grain measurements of quartz OSL, and of feldspar infrared-stimulated luminescence (IRSL) at 50 °C (IR50) and post-IR IRSL at 175 °C (pIRIR175) to determine burial ages. In addition, facies analysis and radiocarbon dating were conducted. The landward core consists of transgressive to early regressive estuarine and prodelta facies, which is overlain by a sandy beach-shoreface facies. The seaward core consists of a relatively simple shallowing-upward succession from muddy prodelta facies to sandy beach-shoreface facies. All luminescence ages except for pIRIR175 of fine grains are mostly consistent with the radiocarbon ages. Instead, pIRIR175 ages of fine grains are significantly overestimated with variable offsets. OSL and IR50 of fine grains provide reasonable age estimates, as these grains were likely well bleached during the transport even along a short and steep mountainous river. Consistent age estimates of all signals from sand indicate that sand was well-bleached in the beach and shoreface owing to the frequent sediment reworking by waves and currents. These results support the hypothesis that luminescence dating is applicable to Holocene wave-dominated deltas and reiterate that comparing different luminescence signals is an effective way to check reliability of the age estimates in environments where the sunlight bleaching is not ensured. 相似文献
11.
The success of optically stimulated luminescence (OSL) dating relies to a large extent on suitable characteristics of the analysed mineral, in this case quartz. Previous OSL dating of Quaternary sediments in Scandinavia has shown that quartz characteristics vary widely across the region, resulting in dating studies with varied success. The aim of this study is to provide an overview of quartz luminescence characteristics in Sweden and Norway, evaluate their effect on dating results and discuss the underlying causes of their variability.A qualitative assessment of luminescence signal characteristics of quartz from Late Quaternary sediment deposits, from a range of geological and geographical settings, has been made by re-analysing data from samples previously dated at the Lund Luminescence Laboratory, Sweden. This allowed a general characterisation of signals and a study of the relationship of these properties to dating result ‘quality’. To quantify the results, selected samples were further analysed with single-grain measurements and with small aliquots.The results show that the average luminescence signal from quartz is fairly dim but dominated by a fast signal component and changes little during measurement. Dose determination precision is ∼4% for 8-mm aliquots and ∼6% for 2-mm aliquots. However, the luminescence signal characteristics have a spatial variation across Sweden and Norway, which appears to correlate with large-scale bedrock units. In areas of sedimentary bedrock outside the Scandinavian mountains and within the Blekinge-Bornholm province, the quartz is brighter and has a stronger fast signal component, while in the Caledonian orogenic belt, the signal is very weak and lacks a fast component. These differences lead to a range in precision of doses, from ∼2% to >40% (for doses in the order of 5–400 Gy), and in the number of rejected aliquots (0–100%) depending on location, but also implies that quartz luminescence can be used as a provenance indicator in part of Sweden and Norway. 相似文献
12.
Previously reported low luminescence of basal glacial sediment has raised the possibility that processes operating at the ice–bedrock interface have the potential to reset (or ‘bleach’) natural luminescence signals (Swift et al., 2011). This finding indicates that certain types of glacial sediment (for example, sub-glacial diamicts) might be amenable to dating using luminescence-based techniques. Using a purpose-built ring-shear apparatus situated in a light-controlled environment, we have investigated the potential for mineral grains to be reset when subjected to conditions similar to those experienced by sediment that has undergone transport at the ice–bedrock interface. Reported here are the preliminary results of an initial experiment that used medium quartz sand with a naturally-acquired palaeodose of ∼4.3 Gy that had been obtained from a relict dune system. Incremental sampling during the shearing experiment and measurements were made to track changes in the luminescence properties of the sand as strain/shearing increased. The results indicate that increased strain/shearing resulted in an increase in the number of zero-dose grains and evolution of the De distribution from unimodal to multimodal. In light of the very much longer shearing distances that sub-glacial sediment would endure in nature, these results would appear to suggest that geomechanical processes at the ice–bed interface of glaciers and ice sheets may be a viable mechanism for resetting sediment. 相似文献
13.
Rock fragment distributions and regolith evolution in the Ouachita Mountains,Arkansas, USA 总被引：2，自引：0，他引：2
Rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls, erosion, deposition, bioturbation, and weathering. The distribution of rock fragments in regoliths of the Ouachita Mountains, Arkansas, shows that sandstone fragments are common in all layers, even if sandstone is absent in parent material. Shale and sandstone fragments are produced at the bedrock weathering front, but the shale weathers rapidly and intact fragments are rare in the solum. Sandstone is weathered from ridgetop outcrops and transported downslope. Some of these fragments are moved downward, by faunalturbation and by transport into pits associated with rotting tree stumps. Upward movement by treethrow is common, resulting in a net concentration of rocks near the surface. However, the highest fragment concentrations are in the lower regolith, indicating active production at the weathering front. The regolith is a dynamic feature, reflecting the influences of vertical and horizontal processes, of active weathering at the bedrock interface, and of surficial sediment movements. The role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities, and that forest soils have likely been extensively mixed within Holocene and historic time. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
14.
Employing a portable luminescence reader in a novel approach for studying soil mantles can help to both better our understanding of and determine the relative importance of the different erosional processes operating on a given landscape. By measuring bulk IRSL signal intensity of unprepared regolith samples as a function of depth, a portable reader has been used to rapidly explore patterns and rates of soil mixing within the actively uplifting San Gabriel Mountains, southern California, USA. Both IRSL and OSL measurements were taken from three different hillslope soil profiles collected within a 100 m radius, as well as a number of bedrock samples. To gauge the rates of grain mixing, bulk IRSL signals are converted to dose values by measuring IRSL growth as a function of dose in a conventional luminescence reader using smaller subsamples from key locations. These data are combined with dose rate determinations based on both in-situ NaI gamma spectrometer measurements and chemical determinations of U, Th and K, in order to convert dose values into “effective age” estimates; these values represent mixed regolith and soil, and not age of sediment deposition. This approach has generated soil turn-over histories much more complex than our simple, signal saturation-with-depth model predicts. 相似文献
15.
Landforming processes are highly active in the Arctic, and luminescence dating can be used to establish a chronological framework for these processes. For example, luminescence ages of raised littoral and marine deposits provide the age control for many reconstructions of Pleistocene events in the Arctic. Due to the nature of the depositional environment (e.g. short transport distance, turbid water, long polar night) these types of sediment may not be completely zeroed at the time of deposition. To test the significance of incomplete bleaching in this type of environment, surface sediments were sampled along a transect from the margin of a glacier out into a nearby bay on NW Svalbard. The water in the bay is very turbid (secchi depth 0.1 m), but there is significant reworking by waves along the shores.Quartz optically stimulated luminescence (OSL) and feldspar infrared stimulated luminescence (IRSL) were measured using sand-sized grains. For quartz OSL and feldspar IRSL (50 °C) the ice-proximal sample showed relatively high doses (∼12 Gy) while nearby beach sand and shallow-marine deposits, as well as ice-distal sandur sediments, had much lower doses: most OSL doses were consistent with zero, while IRSL (50 °C) ranged from 0.5 to 6.5 Gy. Post-IR IRSL (290 °C) doses were overall much higher (∼20–55 Gy), which partly is due to a significant (∼12 Gy) unbleachable residual, and partly due to slower bleaching rates than for the IRSL (50 °C) signal.In this Arctic environment it appears that bleaching is limited in the first ∼100 m of meltwater transport from the glacier margin, but for material transported at least 3 km bleaching of OSL and IRSL (50 °C) signals is more or less complete. Given the very limited light penetration through the seawater in the bay, any bleaching must have occurred during fluvial/subaerial transport to the bay or by wave-reworking on the beach. Apart from the ice-proximal glacifluvial sediments, residual apparent doses recorded by quartz OSL and feldspar IRSL (50 °C) are negligible for the luminescence dating of Pleistocene-aged deposits of ice-distal, littoral and shallow-marine origin. 相似文献
16.
Geochemically-fingerprinted tephra beds provide unique chronostratigraphic markers for comparing Quaternary sedimentary records across eastern Beringia (Alaska and Yukon Territory). Establishing reliable numerical age control on these tephra horizons enables them to be placed within firm temporal frameworks and increases their potential as correlative tools for regional palaeoenvironmental reconstructions. To this end we present new single-grain and multi-grain quartz optically stimulated luminescence (OSL) chronologies for loess deposits bracketing three well-documented and regionally significant variants of the Sheep Creek tephra (SCt) at two sites in west-central Yukon Territory (Ash Bend and Quartz Creek). Single-grain OSL ages bracketing the SCt-A and SCt-K reveal that these tephras were deposited during late Marine Isotope Stage (MIS) 5 or early MIS 4. The SCt-C variant and associated organic-rich bed at Ash Bend were likely deposited during late MIS 5, based on a single-grain OSL age of ∼81 ka for the overlying sediments. The single-grain OSL ages obtained for these deposits are in stratigraphic order and in broad agreement with a fission track age estimate of ∼77 ka for the SCt-K. In contrast, comparative chronologies obtained using multi-grain aliquots are stratigraphically inconsistent and unexpectedly young when compared with the independent SCt-K age. Detailed examination of the single-grain OSL datasets reveal a range of unfavourable luminescent properties that could have contributed to the multi-grain aliquot age discrepancies; including, very low yields of luminescent grains, weak OSL signal sensitivities and large populations of aberrant grains (particularly 0 Gy grains and ‘dim’ grains with a tendency to sensitise during the equivalent dose (De) measurement sequence) that have similarly sized OSL signals as grains used for De analysis. Synthetic aliquot De datasets constructed from single-grain OSL measurements reveal that the large proportional light sum contributions of 0 Gy and dim grains could possibly account for multi-grain age underestimations in some of the Ash Bend samples. In light of these potentially problematic averaging effects, we do not consider the multi-grain OSL ages to be reliable and suggest that single-grain approaches may be preferable for dating sediments with similar quartz luminescence behaviours across this region. 相似文献
17.
Raised beach sand deposits along the southeastern coast of Norway were dated by optical (OSL) and infrared stimulated luminescence (IRSL) and the quartz and K-feldspar luminescence characteristics were described. Due to the poor quartz luminescence characteristics, only a limited number of samples were suitable for OSL dating. More promising are the K-feldspar extracts, with typical K-feldspar luminescence characteristics and no sign of fading. For equivalent dose (De) determination, sand-size quartz and feldspar extracts were used, applying a single aliquot regenerative (SAR) protocol. Both, OSL and IRSL De estimates show a wide distribution, unexpected for beach deposits. The calculated OSL and IRSL age estimates were generally in good agreement and the correctness of the ages was confirmed by independent age control. Because only a limited number of the quartz samples were suitable for OSL dating, IRSL dating of the K-feldspar represents an alternative to OSL quartz dating. 相似文献
18.
The optically stimulated luminescence (OSL) signals from quartz consist of several physically distinct components, which are commonly referred to as fast, medium and slow components. In this study, the OSL components of quartz from the Taklimakan Desert and the Hunshandake sandy land in north China are investigated. Our results show that the relative contributions of OSL components to the bulk OSL signal can be significantly different among quartz grains from both deserts. Laboratory dosing, optical bleaching and heating experiments are used to test their effects on the relative contributions of quartz OSL components. It is found that cycles of dosing and optical bleaching have insignificant impact on the relative contributions of quartz OSL components, while heating to high temperature (500 °C) can significantly enhance the contribution of the fast component to the bulk OSL signals, especially for quartz samples from the Taklimakan Desert. Such results suggest that the different heating history of natural quartz grains plays an important role in controlling OSL components. Additionally, the quartz grains from the Hunshandake sandy land can easily be distinguished from those of the Taklimakan Desert, by using a ternary plot of fast-medium-slow components. The quartz grains from the Hunshandake sandy land exhibit a much stronger fast component than those from the Taklimakan Desert. This can be explained by that the quartz grains from the Hunshandake sandy land are mainly of igneous origin, while most of the quartz grains from the Taklimakan Desert are of low grade metamorphic origin. 相似文献
19.
Esperanza Muñoz‐Salinas Paul Bishop David CW Sanderson Jose‐Juan Zamorano 《地球表面变化过程与地形》2011,36(5):651-660
Optically stimulated luminescence (OSL) is a technique that has been applied from the mid‐1980s, mainly for sediment dating. The OSL technique is based on sample stimulation by light to determine the luminescence signal that is stored in the crystal lattices of sediment grains after deposition, burial by later sediment and subsequent exposure to ionizing radiation from radioactive elements in the surrounding sediment. In such sediment dating, two parameters are required: the equivalent dose (i.e. the luminescence signal stored in the grains), and the dose rate (i.e. the ionizing energy from α, β and γ radiation emitted by naturally occurring radioisotopes in the deposit, plus the effects of cosmic radiation). In this research, the OSL technique is not used for dating. The study goal is to analyse only the luminescence signals (the total photon counts) in polymineral samples obtained after light stimulation in the blue (BLSL) and infrared (IRSL) wavelengths using a portable OSL reader designed and built at the Scottish Universities Environmental Research Centre (SUERC). Three fluvial case studies – from Cambodia, Australia and Mexico – are used to illustrate the geomorphological interpretations possible with the portable OSL reader data from sediments resulting from a range of different depositional processes. The case studies show that aspects of sediment's transport and depositional processes can be inferred from the portable OSL reader data, providing valuable insights into geomorphological history. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
20.
There is little geochonological data on sedimentation in dambos (seasonally saturated, channel-less valley floors) found throughout Central and Southern Africa. Radiocarbon dating is problematic for dambos due to (i) oxidation of organic materials during dry seasons; and (ii) the potential for contemporary biological contamination of near-surface sediments. However, for luminescence dating the equatorial site and semi-arid climate facilitate grain bleaching, while the gentle terrain ensures shallow water columns, low turbidity, and relatively long surface exposures for transported grains prior to deposition and burial. For this study, we focused on dating sandy strata (indicative of high-energy fluvial events) at various positions and depths within a second-order dambo in central Uganda. Blue-light quartz optically stimulated luminescences (OSL) ages were compared with infrared stimulated luminescence (IRSL) and thermoluminescence (TL) ages from finer grains in the same sample. A total of 8 samples were dated, with 6 intervals obtained at 35, 33, 16, 10.4, 8.4, and 5.9 ka. In general, luminescence ages were stratigraphically, geomorphically and ordinally consistent and most blue-light OSL ages could be correlated with well-dated climatic events registered either in Greenland ice cores or Lake Victoria sediments. Based upon OSL age correlations, we theorize that extreme fluvial dambo events occur primarily during relatively wet periods, often preceding humid-to-arid transitions. The optical ages reported in this study provide the first detailed chronology of dambo sedimentation, and we anticipate that further dambo work could provide a wealth of information on the paleohydrology of Central and Southern Africa. 相似文献