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11.
While there are numerous thick loess–palaeosol sequences preserved across the Carpathian Basin, well dated sites that provide terrestrial palaeoenvironmental records extending beyond last glacial–interglacial cycle are scarce. Robust chronologies are essential for correlations of loess with other long-term Quaternary records and to further understanding of the palaeoenvironment and climate of this important region beyond the last 125 ka. Here a new geochronology based on 13 post-infrared infrared stimulated luminescence ages focused on the lower part of the loess–palaeosol sequence at Erdut is presented. The results show that the lower part of the Erdut profile spans the penultimate glacial cycle (MIS 7 to MIS 5). The considerable sediments overlaying the investigated part of the profile suggest that this section spans two glacial cycles, rather than the previously suggested one. The most likely source of the discrepancy is the use of uncorrected infrared stimulated luminescence signal, which can cause age underestimation if not accounted for. This study demonstrates the need to revisit sites such as Erdut, re-date them using updated measurement protocols, and update existing palaeoenvironmental interpretations. 相似文献
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Richard Christopher Chiverrell Geoff Stephen Powell Thomas Matthew Burke Alicia Medialdea Rachel Smedley Mark Bateman Chris Clark Geoffrey A. T. Duller Derek Fabel Geraint Jenkins Xianjiao Ou Helen Marie Roberts James Scourse 《第四纪科学杂志》2021,36(5):752-779
Here we reconstruct the last advance to maximum limits and retreat of the Irish Sea Glacier (ISG), the only land-terminating ice lobe of the western British Irish Ice Sheet. A series of reverse bedrock slopes rendered proglacial lakes endemic, forming time-transgressive moraine- and bedrock-dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, optically stimulated luminescence (OSL) bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples. This chronology constrains what is globally an early build-up of ice during late Marine Isotope Stage 3 and Greenland Stadial (GS) 5, with ice margins reaching south Lancashire by 30 ± 1.2 ka, followed by a 120-km advance at 28.3 ± 1.4 ka reaching its 26.5 ± 1.1 ka maximum extent during GS-3. Early retreat during GS-3 reflects piracy of ice sources shared with the Irish-Sea Ice Stream (ISIS), starving the ISG. With ISG retreat, an opportunistic readvance of Welsh ice during GS-2 rode over the ISG moraines occupying the space vacated, with ice margins oscillating within a substantial glacial over-deepening. Our geomorphological chronosequence shows a glacial system forced by climate but mediated by piracy of ice sources shared with the ISIS, changing flow regimes and fronting environments. 相似文献
14.
人工合成硅灰石的发光性质与发光机理的初步研究 总被引:2,自引:0,他引:2
在254nm紫外光照激发条件下,对人工合成掺入不同激活离子的低温TC型和高温型假硅灰石的发光性质进行了实验测定,从微观原子能量谱项讨论了在全的硅灰石基质中Eu^3+和Gd^3+的发光机理,分析了Bi^3+对Eu^3+与Pb^2+对Mn^2+的敏化发光条件,初步探讨了掺放Eu^3+的高温型假硅灰石发光强度减弱的原因。 相似文献
15.
In two of the perennially ice-covered lakes in the McMurdo Dry Valleys, lakes Hoare and Bonney in the Taylor Valley, bottom water has 14C ages of 2.7 ka and 10 ka (respectively), rendering 14C ages of bottom sediments highly problematic. Consequently, we tested the effectiveness of thermoluminescence (TL) zeroing in polymineral fine silt material from several depositional environments around and on the lake (stream suspensions, ice-surface sand dune, and silty sand from near the top of the more-than-3m-thick ice). We also conducted TL and infrared-stimulated-luminescence (IRSL) dating tests on material from three box cores recovered from the bottom of Lake Hoare, in a transect away from the abutting Canada Glacier. We observed effective zeroing of light-sensitive TL in suspended silt from one input stream and less effective zeroing from another stream. We observed effective zeroing of light-sensitive TL also in silt from a glacier-proximal eolian ice-surface dune and from sand from within the upper 5 cm of ice. In contrast, in box-core 1, the bottom sediment yielded minimum TL apparent ages of 1500-2600 yrs, with no discernable stratigraphic depth trend. IRSL dating applied to the same box-core samples produced significantly lower age estimates, ranging from ~600 ± 200 yrs to 1440 ± 270 yrs top-to-bottom, an improvement over the depth-constant ~2200 yrs TL ages. In two other cores closer to the Canada Glacier, IRSL ages from ~600 ± 200 yrs (top) to ~ 2900± 300 yrs (at depth) were measured. Not only are the IRSL ages a significant improvement over the TL results, but the near-core-top IRSL ages are also a dramatic improvement over the 14C results (~2.7 ka). IRSL dating has a demonstrated potential to supplant 14C dating for such antarctic lacustrine deposits. 相似文献
16.
辐照绿柱石的色心与赋色机制 总被引:4,自引:1,他引:4
在不同辐照剂量的带电粒子作用下,四川无色绿柱石因赋色而呈现浅蓝色,蓝绿色,黄绿色,浅黄色及橙黄色,紫外可见吸收光谱(UV-VIS)和阴极发光光谱(CLS)研究表明,辐照绿柱石中存在两组与赋色密切相关的色心组合,其一为相对稳定的[Fe^3 ]OH和[Fe^3 4]心,其二则为不稳定的[H^0]i心和F^ 心,二者对可见光的能量分别具有不同程度的选择性吸收和发射,由此产生特征的吸收与发射光谱。低温退火处理(210℃),有助于消除辐照绿柱石中不稳定的色心,使相对稳定的[Fe^3 ]OH心黉度再度聚集,并形成新的缺陷(二次缺陷),进而提高稳定色心的主波长和饱和度。研究证实,二次缺陷形成的初始温度,可近似代表辐照绿柱石的最佳热固色温度点,经辐照与热固色作用而形成的黄色,橙黄色绿柱石的颜色相对稳定,并不因长期日照或低温受热(<280℃)而褪色。 相似文献
17.
Optically stimulated luminescence (OSL) dating of sand samples from stabilized (or inactive) coastal dunes in Denmark provides information on the age of the termination phase of the last major aeolian activity period. A total of 26 sand samples were taken from four different coastal dunefields around the North Sea, Skagerrak and Kattegat coasts of Denmark. The OSL dates indicate that the last major phase of aeolian activity terminated between ad 1860 and 1905. Most of the dunes examined in this study were active around 1820, during a period documented to have been very stormy. A dune management scheme started around 1792, and this no doubt was a major cause of dunefield stabilization, but an overall decline of storminess, particularly spring and summer storminess, around the end of the 19th century must also have contributed to the increasing inactivity of coastal dunes. The new OSL dates on aeolian sand movement agree well with historical data and data from topographic maps on dune movement. This agreement supports the observation from earlier work that OSL dating of recent aeolian sand movement is accurate over the last few decades to centuries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
18.
钨酸铅晶体是一种非化学计量化合物,缺陷丰富,蕴含着利用掺杂产生新效应和开发新功能的广泛可能性。探讨了不同浓度La3 掺杂对于钨酸铅晶体发光性能的影响,如热释光、X射线激发发光、光致发光等。La3 掺杂有效地抑制了陷阱中心,使发光受到强烈的抑制,在高浓度掺杂的钨酸铅中,激发机制有所改变,通过XPS测试的结果分析了不同浓度La3 掺杂机制。低浓度掺杂中,La3 取代Pb2 ,形成缺陷复合体[2(La3Pb ).-(VPb)″];高浓度掺杂晶体中,La3 离子不但占据Pb2 位置,而且也会占据W6 位置(La3W ),产生La3 的自补偿机制,形成La3 的自补偿对[(La3W )-(La3Pb ).]-(VO)..或缺陷聚集体[3(LaP3b ).-(La3W )]。 相似文献
19.
20.
In an effort to better understand chronology of alluvial episodes in Cuyama Valley in the western Transverse Ranges of California, USA, we employed optically stimulated luminescence, radiocarbon and cosmogenic radionuclide surface exposure dating methods. Twenty-one optical dates ranging from 0.01 to 27 ka were obtained from exposures of late-Holocene axial-fluvial deposits, Pleistocene–Holocene alluvial-fan deposits, and axial-fluvial sands interbedded within a late Pleistocene alluvial fan. These were cross-checked with 37 AMS radiocarbon dates from charcoal and wood from within a and five 10Be surface exposure dates from boulders on alluvial-fan surfaces. The OSL results show generally good stratigraphic consistency, logical comparison with the radiocarbon and cosmogenic data, and appear to be the best method for accurate dating within deposits of this nature because suitable material is fairly easy to find in these environments. The radiocarbon data contained numerous “detrital ages”, but well-bedded lenses of apparently in situ or minimally transported charcoal provide reliable age estimates for the associated alluvium. Radiocarbon dating of detrital charcoal in the older alluvial fan deposits was problematic. Our cosmogenic surface-exposure dating was consistent stratigraphically and with our other data, but we were unable to determine its accuracy due to the limited number of samples and the possibility of inherited radionuclides and post-depositional erosion. In light of our results, we suggest that OSL dating using the latest analytical techniques combined with rigorous methods for estimation of paleodase is reliable and of increasing utility in otherwise difficult-to-date coarse alluvial environments in the southwestern United States and elsewhere. 相似文献