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1.
释光测年是可对冰川地貌进行直接定年的一种测年技术,已被广泛应用于冰川沉积测年中,推动了第四纪冰川研究的深入发展。但冰川沉积释光测年还没有达到标准化的程度,实际应用中仍有不少问题需要探究,其中最受关注的是冰川沉积物释光信号晒退不完全的问题,即样品在埋藏前因曝光机会有限导致信号没有归零或仅部分归零。冰川沉积释光信号晒退程度与地貌部位和沉积环境密切相关。冰川沉积释光采样需注意几个方面：（1）详细的地貌学和沉积学调查及对采样点的选择;（2）较适合释光测年的冰水沉积和冰缘风成沉积采集及其与冰川作用期次的联系;（3）冰碛夹层中的冰水砂透镜体的选取;（4）冰碛垄采样时垂直与水平方向上的考量;（5）岩石释光测年的发展使砾石成为当前第四纪冰川释光测年采样的一种选择。室内进行释光等效剂量测试时,也有几个关键的选择：（1）粗颗粒石英光释光测年是末次冰期以来冰川作用的首选方法;（2）如果样品年代老于石英测年上限,或者石英不适合测试,则可考虑钾长石后红外高温释光测年方法;（3）单颗粒、小测片和岩石释光埋藏测年技术可以鉴别样品的晒退情况,是目前最适合冰川沉积释光测年的几种选择;（4）如有条件,尝试用不同矿物、不同粒径、不同方法进行测试对比和交叉检验。要获得第四纪冰川释光测年的最佳年代学结果,地貌学、沉积学和年代学的结合是非常必要的。 相似文献
2.
冰川事件是气候波动最直接的地质证据,利用冰川作用过程中形成的冰碛物的年代数据建立冰川事件的时间顺序,是反演冰川演化历史以及区域古气候和古环境的有效途径。然而,由于冰川沉积环境的复杂性,很大程度限制了冰川年代数据的获取。近年来,随着光释光测年技术的不断完善,其应用范围已经扩展到冰川沉积物的年代测定。本文利用光释光(OSL)测年技术对青藏高原东南部稻城冰帽库照日地区系列冰碛垄进行年代测定,试图建立库照日地区冰川事件的年代序列。然而,光释光(OSL)年代结果与先前发表的ESR和宇生核素10Be暴露年代数据不一致,且个别数据与地貌新老关系不符。通过对比分析显示:冰碛物样品埋藏前释光信号的部分晒退以及样品提取的石英不纯,可能导致冰碛物光释光测年的较大误差和不准确性,应该引起足够的注意。 相似文献
3.
冰川事件是气候波动最直接的地质证据,利用冰川作用过程中形成的冰碛物的年代数据建立冰川事件的时间顺序,是反演冰川演化历史以及区域古气候和古环境的有效途径.然而,由于冰川沉积环境的复杂性,很大程度限制了冰川年代数据的获取.近年来,随着光释光测年技术的不断完善,其应用范围已经扩展到冰川沉积物的年代测定.本文利用光释光(OSL)测年技术对青藏高原东南部稻城冰帽库照日地区系列冰碛垄进行年代测定,试图建立库照日地区冰川事件的年代序列.然而,光释光(OSL)年代结果与先前发表的ESR和宇生核素10Be暴露年代数据不一致,且个别数据与地貌新老关系不符.通过对比分析显示:冰碛物样品埋藏前释光信号的部分晒退以及样品提取的石英不纯,可能导致冰碛物光释光测年的较大误差和不准确性,应该引起足够的注意. 相似文献
4.
准确获得水成沉积物的年龄是第四纪年代学重要的前沿问题之一。随着释光技术的发展,水成沉积物释光测年在如下方面有新的进展:具体释光技术的选择、释光测量方法、测年矿物的种类、矿物的粒级和获得等效剂量的统计方法等。线性调整光释光技术能够提取光释光信号中衰退快的组分;单片再生法应用广泛;单颗粒技术在挑选沉积时晒退充分的颗粒方面具有一定的优势;水成沉积物中的石英比长石更易晒退;较多的实验表明水成沉积物中的粗颗粒比细颗粒更易晒退;获得等效剂量的统计模型很多,但尚无一种统计模型适用于所有样品。在此基础上探讨了水成沉积物释光测年在气候、构造运动、冰川进退历史和人类活动主导的土壤侵蚀量变化研究中的意义及今后的研究方向,为全面了解该领域的最新研究进展提供参考。 相似文献
5.
释光技术在水成沉积物测年中的应用进展 总被引：1，自引：0，他引：1
准确获得水成沉积物的年龄是第四纪年代学重要的前沿问题之一。随着释光技术的发展,水成沉积物释光测年在如下方面有新的进展：具体释光技术的选择、释光测量方法、测年矿物的种类、矿物的粒级和获得等效剂量的统计方法等。线性调整光释光技术能够提取光释光信号中衰退快的组分;单片再生法应用广泛;单颗粒技术在挑选沉积时晒退充分的颗粒方面具有一定的优势;水成沉积物中的石英比长石更易晒退;较多的实验表明水成沉积物中的粗颗粒比细颗粒更易晒退;获得等效剂量的统计模型很多,但尚无一种统计模型适用于所有样品。在此基础上探讨了水成沉积物释光测年在气候、构造运动、冰川进退历史和人类活动主导的土壤侵蚀量变化研究中的意义及今后的研究方向,为全面了解该领域的最新研究进展提供参考。 相似文献
6.
冰碛石的形态和表面特征 总被引：3，自引：0，他引：3
沉积物中砾石的各种形态参数(磨圆度、球度和扁平度)及表面特征对研究搬运介质和沉积过程是很有用的。有些作者的工作表明,冰碛中的砾石随搬运距离的增加,其磨圆度和球度的提高是明显的;还有人用A.Cailleux的计算磨圆度的公式(2R/a×100)成功地揭示了冰碛、冰水沉积、冰川接触沉积和融冻泥流沉积之间的 相似文献
7.
冰水沉积是和冰川发育密切相关的,系由冰川融水造成的一种颗粒较细、磨圆较好、分选性好、有一定层理的沉积物。在冰水砾石中仔细观察,往往可以找到残留有某些冰碛砾石特征的条痕石、马鞍石、压凹石及碎裂石等。这些特征,使冰水沉积既区别于冰碛物,又区别于一般的流水沉积。在山区,特别是在高山区,冰水沉积并不是很难辨认的。 相似文献
8.
山地冰川沉积研究在中国有特殊重要性。因为欧、美对冰碛沉积研究多限于大陆冰盖,沉积环境比较单纯,冰水沉积比重很大,而中国山地冰川多限于山体内部,冰水沉积极不发育,且沉积环境很复杂,亚相变化也大。此外中国山地冰川多属大陆性,与欧、美海洋性冰川在物理性质和沉积特征上都有不同。如冰川磨蚀作用弱,冰碛中粉砂少,冰上融出碛发育而流碛和滞碛不发育,原生(同生)构造如粗糙斜层很发育等。这些都将丰富冰碛沉积学内容,并对科学地鉴别中国东部各种混杂堆积的成因有重要意义。如据现代冰川沉积指标庐山就没有任何冰川堆积。 相似文献
9.
电子自旋共振(ESR)技术是一种确定物质成分和结构的顺磁性质的分析方法,也能够用于沉积物定年。该方法的测量技术和测年的物理机制等还处于发展阶段。冰川作用过程十分复杂,形成各种类型的冰川沉积物,其顺磁信号的归零机制有显著差异,ESR测年的实验方案也有所差异。因此,识别冰碛物类型,采集合适的样品对于ESR测年的准确性十分重要。冰下融出碛和滞碛经过了冰下磨蚀过程,结构致密,细颗粒基质含量高,石英砂中的一些杂质芯的ESR信号能够衰退。许多冰上融出碛,结构疏松,但细颗粒基质含量高,不但经过了搬运过程中的冰下磨蚀过程使ESR信号衰退,又经历了沉积时的冰上阳光直射过程使信号衰退,一些样品的ESR信号能够完全晒退。冰水湖泊和冰水河流沉积的细砂和粉砂来源于冰下研磨的产物,信号会衰退;在搬运沉积过程中又可能被阳光直射,信号进一步衰退。其它类型的冰碛物的ESR信号衰退机制不明,或粒径不适合用ESR方法测年。采集冰碛物ESR年代样品时,最好同时采集信号衰退机制相同的现代冰碛物样品,以便对照,并用于扣除可能的残留信号。 相似文献
10.
天山乌鲁木齐河源末次冰期冰川沉积光释光测年 总被引：6，自引：5，他引：1
乌鲁木齐河源地区是中国冰川遗迹保存最丰富、地貌最典型的区域之一,是根据冰川遗迹重建第四纪冰川历史的理想地区。大量的研究工作以及技术测年结果也使其成为试验冰川沉积光释光（optically stimulated luminescence,OSL）测年可行性的理想地点。共采集了6个冰碛及上覆黄土样品用于光释光测年。提取38~63 μm的石英颗粒,运用SAR-SGC法测试等效剂量。各种检验表明测试程序是适用的。通过地貌地层关系、重复样品、已有年代的对比等方法,检验该地冰川沉积OSL测年的可行性。结果表明,OSL年代结果与地貌地层新老关系非常吻合,与已有的其他测年技术的年代结果也具可比性,表明这些样品的OSL信号在沉积之前晒退较好,OSL年代是可信的。冰川观测站侧碛垄的OSL年代为14.8±1.2 ka;9号冰川支谷口附近冰碛的OSL年代为13.5±1.1 ka和17.2±1.3 ka;上望峰冰碛的OSL年代为20.1±1.6 ka。综合OSL年代结果与此前其他测年结果,这几套冰碛垄形成于深海氧同位素MIS 2阶段应该是比较统一的认识。上望峰冰碛上覆黄土的OSL年代（10.5±0.8 ka）也印证了该结论。OSL年代指示上望峰冰碛对应于末次冰期最盛期,冰川观测站和9号冰川支谷谷口冰碛对应于晚冰期。下望峰冰碛的OSL年代为36.3±2.8 ka,对应于MIS 3阶段。下望峰冰碛的形成时代,仍有待更多沉积学以及测年工作进一步确定。 相似文献
11.
The application of optically stimulated luminescence (OSL) dating within glacial settings can be limited where sediments have not had their OSL signal fully reset by sunlight exposure. Heterogeneous bleaching can result in age overestimations, and although it is recognized that certain depositional settings are more likely to have experienced sufficient sunlight exposure to bleach the OSL signal, no comprehensive study has empirically investigated the processes of sediment bleaching, or the variability in bleaching between deposits of the same type and within the same glacial catchment. A suite of modern glacial and glaciofluvial sediments from Fåbergstølsdalen, southern Norway, have been analysed to explore the controls that sedimentary processes and depositional setting have on bleaching of the OSL signal of quartz. There is considerable variability in the residual OSL ages of similar modern deposits, which reflects high sensitivity of the OSL signal to sediment source, sedimentary process, transport distance and depositional setting. Overdispersion values are greatest for the sediments which have been most heterogeneously bleached and these sediments have the lowest residual ages. Sampling strategies that incorporate sufficient consideration of the depositional framework of sample settings can minimize the effects of unbleached residuals on OSL age determinations. 相似文献
12.
Priscila E. Souza Reza Sohbati Andrew S. Murray Aart Kroon Lars B. Clemmensen Mikkel U. Hede Lars Nielsen 《Boreas: An International Journal of Quaternary Research》2019,48(4):841-855
Here we investigate the use of optically stimulated luminescence (OSL) for dating cobbles from the body of successive beach ridges and compare cobble surface‐derived ages to standard quartz OSL ages from sand. Between four and eight cobbles and sand samples (age control) were dated with the luminescence method, taken from the modern beach and from beach ridges on the south and north extremes of a prograding spit on the westernmost coast of Lolland, Denmark. Luminescence‐depth profiles perpendicular to the surfaces of the cobbles show that the feldspar infrared signals stimulated at 50 °C were fully reset to various depths into the cobbles prior to final deposition; as a result, the equivalent doses determined from close to the surface of such cobbles can be used to calculate burial ages. Beach‐ridge burial ages given by the average of ages of individual cobbles taken from the same site are consistent, within errors, with the ages derived from the sand samples. Cobble‐ and sand‐derived ages show that the southernmost beach ridge at Albuen was formed around 2 ka ago, indicating that this sandy spit is younger than other coastal systems in Denmark. The agreement between ages derived from clasts and from standard quartz OSL in this study confirms that, even in the absence of sandy sediments, we can reliably date sites using OSL by targeting larger clasts. In addition, the record of prior light exposure contained in the shape of the cobbles’ luminescence‐depth profile removes one of the major uncertainties (i.e. the degree of signal reset prior to burial) in the luminescence dating of high latitude sites. 相似文献
13.
Reza Sohbati Andrew S. Murray Jan‐Pieter Buylaert Nelson A. C. Almeida Pedro P. Cunha 《Boreas: An International Journal of Quaternary Research》2012,41(3):452-462
The burial age of an alluvially deposited cobble pavement at the Tapada do Montinho archaeological site (east‐central Portugal) is investigated using optically stimulated luminescence (OSL) dating. Measurements on the cobbles (quartzite clasts) were carried out on intact slices and large aliquots (～8 mm) of quartz grains (63–300 μm), both recovered from the outer 1.5‐mm surface of the cobbles. The recycling ratio, recuperation and dose‐recovery tests show that the single‐aliquot regenerative‐dose (SAR) protocol is applicable to both rock slices and quartz grains; both have similar luminescence characteristics. The variation in the natural OSL signal with depth below the cobble surface using intact slices from two different cobbles shows that both were bleached to a depth of at least ～2 mm before deposition. A model of the variation of dose with depth fitted to data from one of the cobbles gives a burial age of ～19 ka and also predicts the dose‐depth variation at the time of deposition. Ages based on rock slices suggest that one cobble surface, and the inner parts of two other cobbles experienced a resetting event at ～45 ka, consistent with the age control. However, the surfaces of the other cobbles all record light‐exposure events in the range 26 to 14 ka, suggesting that some of the cobbles were exposed to daylight perhaps more than once in this period. Given the shallow burial depth and unexpectedly young ages of the surrounding and overlying finer‐grained sediment, it is suggested that phases of light exposure following surficial erosion are probably responsible for this underestimate. Nevertheless, it is remarkable that we can identify and quantify four events (two light exposures of different durations and two sequential burial periods) in the dose record contained within a single clast, and this suggests that the luminescence dating of rock surfaces may prove, in the future, to be at least as important as sand/silt sediment dating. 相似文献
14.
《Journal of Asian Earth Sciences》2010,39(6):274-282
In an active fold-and-thrust belt, sediment is commonly transported in the form of debris and colluviums, and the ages of such deposits can be important for seismic hazard assessment. These sediments are mainly transported by high concentration flows that travel very short distances before burial, and therefore have very few opportunities for daylight exposure and bleaching, which limits the application of luminescence dating in such environments. Luminescence studies on modern debris flow deposits and channel sediments in central Taiwan indicate a mixed population of bleached and unbleached grains. The well bleached grains constitute a small proportion of the sediments and could only be identified using the single grain dating technique; doing single aliquot analysis may result in overestimation of the age of such sediments by 3–25 ka. The data reveal that outwash sediments are better bleached than debris flow sediments. Our results show that quartz that has experienced partial resetting can be used for luminescence dating only through the use of the single grain technique. 相似文献
15.
Romée H. Kars Tony Reimann Christina Ankjærgaard Jakob Wallinga 《Boreas: An International Journal of Quaternary Research》2014,43(4):780-791
Post‐infrared (pIR) stimulated luminescence dating of sedimentary feldspar largely avoids the effects of anomalous fading that affect conventional infrared stimulated luminescence (IRSL) dating. However, optical resetting of pIR signals is more difficult than resetting the conventional IRSL signal, which may undermine the crucial assumption that pIR signals were effectively bleached upon deposition and burial of sediment grains. In this study, we quantify the bleaching properties of several pIR signals on various samples using laboratory‐simulated bleaching in full sunlight and water‐attenuated sunlight. Our data show that bleaching is most efficient under full spectrum conditions for all pIR signals and that pIR signals measured at elevated temperature are increasingly harder to bleach than IR and pIR signals measured at low temperature (e.g. IR at 50°C). All bleaching curves exhibit a very slow and steady decrease, indicating that a fixed un‐bleachable residual level cannot be reached within the 11 days of solar simulator exposure undertaken here. We show that the magnitude of a laboratory‐determined residual dose depends on the adopted bleaching protocol and cannot be used as a proxy for the dose that remains in the sample at the time of burial (remnant dose). Our data emphasize the importance of finding a balance between sufficient signal stability and a minimized contribution of a remnant dose when using pIR procedures for feldspar luminescence dating. 相似文献
16.
《Russian Geology and Geophysics》2015,56(8):1162-1172
Sedimentary indicators of catastrophic glacial megafloods—plane-bedded angular gravel, cobbles, and boulders—are described in several sections of the high terraces of the Chuya River valley. The principal difference of these sediments from typical alluvium of this area is demonstrated. The clast roundness, grain size of clasts, and sedimentary structures of the high-terrace deposits of the Chuya and Katun’ valleys indicate the same facies originated through megaflood deposition. These results are at odds with ideas of alluvial, glacial, or glaciofluvial genesis of the high-terrace deposits of the Chuya River. 相似文献
17.
Georgina E. King David C. W. Sanderson Ruth A. J. Robinson Adrian A. Finch 《Boreas: An International Journal of Quaternary Research》2014,43(4):955-972
Analysis of a high‐resolution suite of modern glacial sediments from Jostedalen, southern Norway, using a portable optically stimulated luminescence (OSL) reader, provides insights into the processes of sediment bleaching in glacial environments at the catchment scale. High‐magnitude, low‐frequency processes result in the least effective sediment bleaching, whereas low‐magnitude, high‐frequency events provide greater bleaching opportunities. Changes in sediment bleaching can also be identified at the scale of individual bar features: tails of braid‐bars and side‐attached bar deposits have the lowest portable reader signal intensities, as well as the smallest conventional OSL residual doses. In addition to improving our understanding of the processes of sediment bleaching, portable reader investigations can also facilitate more rapid and comprehensive modern analogue investigations, which are commonly used to confirm that the OSL signals of modern glacial sediments are well bleached. 相似文献
18.
L. Alappat A. Vink M. Frechen 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(1):43-16
This paper provides insight into the fate of Late Weichselian and Early Holocene sediments accumulated in the German sector of the southern North Sea. A combination of optically stimulated luminescence (OSL) dating and radiocarbon dating was applied to set up the chronology. Seven cores were studied to obtain ten quartz OSL samples and ten radiocarbon samples. The core locations were chosen along a southeast to northwest transect along the western side of the Elbe palaeovalley, giving a good coverage of the entire German North Sea area. All samples for OSL dating showed a significant scatter in the equivalent dose (De) distribution of quartz due to heterogeneous bleaching. The Minimum Age Model (MAM-3) was found to be the most suitable to extract true burial ages. It was inferred from the study that sedimentation did still occur during the late deglaciation period in many areas. These are mainly Late Weichselian glaciofluvial or glaciolacustrine sediments directly overlain by early Holocene fluvial and/or transgressive deposits and followed by modern marine sands. However, considerable late Weichselian erosion or a possible period of non-deposition was observed in the highland area to the northeast of the Dogger Bank and a small discontinuity in the near-shore region was noticed, probably due to early Holocene fluvial erosion. Relicts of a palaeo-river bank or terrace were identified in core 14VC to the east of the Dogger Bank. A possible interpretation of the Pleistocene-Holocene interface along the core transect is provided based on lithology and measured OSL and radiocarbon ages. 相似文献
19.
A.M.D. Gemmell 《Quaternary Science Reviews》1988,7(3-4)
Theoretical considerations imply that the suitability of glacially-deposited sediments for thermoluminescence (TL) dating will be influenced by transport routes within the ice, and by facies of deposition. Measurments on sediments obtained from the Austerdalsbreen glacier in western Norway indicate that zeroing of sediment does not occur at the base of a valley glacier, but that englacial and supraglacial sediments showed evidence of bleaching but not total zeroing. Analysis of sediments from recent glacial and fluvioglacial landforms showed no evidence that they had been zeroed prior to deposition. Results indicate that the TL-age of glacial landforms will be a function of the derivation and travel paths of the sediments of which it is composed rather than of the form itself. It is concluded that as knowledge of the rates of bleaching associated with various facies of transport and deposition of glacial sediments improves, so the potential of the technique to act as a diagnostic sedimentological tool will increase, even when dating of glacial deposits by TL is impossible. 相似文献