风成沉积石英绿光释光测年的单片技术

运用再生法进行单片技术测年所面临的主要问题是感量变化。论文探讨了石英绿光释光测年中对感量变化进行校正的方法,然后运用单片技术对沙漠黄土边界带风成沉积沙样进行等效剂量测定。结果表明,单片技术是石英绿光释光测年的理想手段。     

光释光测年单个黄土样品测片个数选取问题的统计学研究

光释光测年多颗粒实验中单个样品的测片个数选取没有一定标准,从几十到一百多个不等。通过分析7个黄土中颗粒(38~63 μm)样品,分别进行了不同测片个数的等效剂量的实验及统计分析研究。每个样品的等效剂量由SAR法和SGC法得到,每个样品不同测片数的等效剂量结果进行了多种统计分析和检验。认为在风成沉积物的光释光测年实验中,当一个样品进行实验的测片数达到20~30个测片时,样品的等效剂量分布形态就趋于稳定;即此测片数较合理——既能较准确反映统计意义上的样品的古剂量,又不至于进行大量重复性工作;这对于水成沉积物光释光测年中单个样品的测片个数选取也有一定的参考价值。     

腾格里沙漠两万年以来典型沉积物钾长石和石英光释光测年对比研究

沙漠内部保存的晚第四纪沉积序列,是重建过去气候环境变化的重要材料。近年来,不同测年方法被用于测定风成、湖相等各类沉积物的年龄,特别是光释光测年技术在沙漠地区的应用越来越多。然而,对不同光释光测年技术能否获得相对年轻样品的可靠年龄等问题,仍存在一些不确定性。本研究在腾格里沙漠不同点位采集了沉积物样品,开展了石英单片再生剂量法(SAR-OSL)和钾长石红外后释光法(pIRIR₁₅₀)对比测试,尤其是针对钾长石pIRIR₁₅₀进行了剂量恢复实验、衰退系数(g-值)以及残余剂量测定,进而探究钾长石pIRIR₁₅₀技术在该地区沉积物测年中的适用性与可靠性。结果表明：钾长石pIRIR₁₅₀释光信号总体晒退良好,30 h晒退后的残余剂量仅为0.07～0.27 Gy,并且在60 Gy的剂量范围内(对应研究区约两万年以内的样品),剂量恢复比率基本为1。经g-值校正后的钾长石pIRIR₁₅₀年代结果总体上出现高估,而未校正的年代则与石英SAR-OSL年代结果具有较好的一致性,表明研究区沉积物样品的...     

新疆阿尔泰山东段冰碛物光释光测年研究

冰川是塑造地表形态最积极的外营力之一,对冰川地貌的年代学研究是重建古冰川发展史的关键,也是研究气候变化的重要途径。冰碛物是冰川作用的直接产物,代表过去发生的冰川事件,对冰碛物进行准确测年能够为重建古冰川的进退、理解区域古气候变化提供年代学支撑。本文在新疆阿尔泰山东段采集了8个冰碛物样品以进行光释光测年,利用单片再生剂量法对90~125 μm的石英颗粒进行等效剂量的测定。通过等效剂量值频率分布特征及De（t）坪区图分析得出大部分冰碛物的光释光信号晒退不彻底,所以利用一阶动力学公式对持续激发的光释光信号晒退曲线（CW-OSL）进行多组分拟合拆分,得到快速、中速、慢速3种组分,依据分离出的快速组分确定等效剂量值。研究结果显示,距今32 ka以来阿尔泰山东段区域在MIS3阶段、MIS2阶段、8.2 ka左右、全新世大暖期及新冰期等5个时段有冰川发育,冰川发育与气候变化密切相关。     

长江三角洲全新世沉积物光释光测年研究

长江三角洲是研究古海岸沉积环境演化的理想区域。选取长江三角洲平原一支长岩芯钻孔上部55 m层位的沉积物进行光释光(optically stimulated luminescence,OSL)测年研究。根据沉积物粒度特性,在实验前处理过程中,提取100~200 μm或63~100 μm粗颗粒石英矿物进行OSL测年。测年样品的预热坪与剂量恢复实验表明选择180℃作为预热条件较为合适,石英OSL信号衰退曲线以快组分为主。条件实验结果、等效剂量分布以及各测片的循环比、热转移等方法学层面的实验结果表明,OSL测年技术对该孔的沉积物测年具有适应性和可靠性。通过年代—深度关系模型,建立该段地层中全新世以来的年龄框架。依据该孔的年代地层序列并结合前人工作,探讨全新世以来长江三角洲的沉积演化。     

柴达木盆地西台吉乃尔盐湖沉积的年代学研究

柴达木盆地中部西台吉乃尔盐湖成因及其年代框架还存在争议。通过应用光释光测年法（OSL）和放射性碳测年法（AMS¹⁴C）测定两支分别来自该盐湖中部及东部边缘区域的岩芯,获得4个OSL和5个AMS¹⁴C年代数据。结果表明：（1） 对于老于30 ka的样品放射性碳测年法存在明显的年代低估,而对于年轻样品则存在约4.0 ka的碳库效应,相对而言光释光测年方法具有一定的合理性。（2） 两支岩芯顶部粉砂质粘土层形成于约0.3 ka,中部含粉砂质粘土盐层形成于大约4.0 ka,底部粉砂质粘土层则至少形成于70 ka 之前。     

OSL测年中CGC法求D_e均值的计算方法之比较分析

光释光测年中等效剂量是计算样品埋藏年龄的一个重要参数,一般通过求多个实验测量值的均值得出。标准生长曲线法是求等效剂量的一种常用且有效的方法,分析讨论了此法计算的等效剂量存在小幅度的系统性的偏大及其原因,提出了改进的方法;展望了CGC法求De均值更优的估计——极大似然估计。     

Ris. NaI γ谱仪在不同类型沉积物中环境剂量率的应用研究

光释光测年被广泛的应用于地球科学和考古学等领域的年代学研究,而如何准确测量环境剂量率是光释光测年的关键问题之一。研究利用丹麦 Ris. Nutech所提供的铀( U)、钍( Th)、钾( K)等标样,标定了实验室的 RGS-19A型 NaIγ谱仪。选择不同类型沉积物,进行了不同测量时间对实验结果的影响研究,结果显示随着测量时间增加,测量误差减小,在测量时间达到 6h就可满足其要求,可作为测试样品的固定测量时间;进一步对于岩性均一以及岩性不均一的 36个地质样品开展了 Ris. NaIγ谱仪法与 ICP-MS法, Ris. NaIγ谱仪法与中子活化法测定环境剂量率的对比研究。研究结果表明,对于大部分样品两组不同方法测量结果在误差范围内基本一致(±1σ),NaIγ谱仪与 ICP-MS法及中子活化法的剂量率平均之比为 1.13±0.03(n=36)。说明研究仪器测量结果是可靠的,此仪器 Ris.NaIγ谱仪可以广泛应用于不同类型沉积物光释光测年的环境剂量率测量中。     

汉江上游郧西郧县段古洪水事件光释光测年及其对气候变化的响应

通过对汉江上游的野外考察,发现汉江上游郧西-郧县段第一级阶地前沿全新世土壤剖面中夹有多层古洪水滞流沉积物,选择该河段的归仙河口（GXH）剖面进行了详细野外观察,结合粒度成分和磁化率指标分析,证明它们是典型的古洪水滞流沉积物。采用石英的单片再生剂量法（SAR）获得了该剖面中9 个样品的光释光年龄值。基于测定的光释光年龄、考古断代和地层对比结果,确定这四期洪水事件分别发生在距今12500-12000 a、7500-7200 a、3100-2800 a,1000-900 a。通过与汉江上游地区、国内和世界各地的多种指标气候变化记录的对比分析,进一步探讨了汉江上游郧西郧县段全新世以来发生的多期古洪水事件发生的气候背景,这一认识有助于深入理解区域洪涝灾害对全球气候变化的响应规律。     

湖泊碳库效应及校正方法

湖泊作为过去环境变化的信息载体,可以很好地提供高分辨率的连续记录,因此常被用来进行定年研究。湖泊沉积物放射性碳定年由于缺乏陆源植物残体、碳屑等可靠的定年材料,多选用其他材料（如全样有机质、水生残体及各类壳体）,但是这些材料通常受到“碳库效应”（The reservoir effect）的影响,而使得年代结果失真,导致难以建立高精度的年代框架,成为这一领域研究放射性碳年代应用的瓶颈。因此,如何对湖相沉积物¹⁴C年代结果进行有效的碳库效应校正,对高精度年代序列的建立具有重要意义。本文综览了近几十年来针对湖泊碳库效应进行研究所取得的一系列研究成果,详细总结了影响湖泊碳库效应的各种因素,讨论了碳库效应对湖泊沉积物定年结果的影响;分析了目前对湖泊碳库的各类校正方法,包括使用同一测年手段、不同测年材料建立点上碳库大小以及采用不同测年手段对碳库的校正等。本文为湖泊沉积物高精度年代序列的建立提供了一定的参考。     

中国第四纪冰川演化序列与MIS对比研究的新进展

近年来,随着多种可对冰川地形进行直接定年的测年技术的发展与应用,中国第四纪冰川研究取得了新进展,较为突出的是获得了大量与地貌地层关系相符的年代学资料、建立了冰川演化若干典型范例以及进一步确立了青藏高原构造隆升与冰川发育的耦合关系。中国第四纪冰川演化序列与海洋氧同位素阶段(Marine Oxygen Isotope Stage,MIS) 比较经历了2000 年、2002 年两次立案与改进。笔者基于近年来新测得的年代学数据、已建立的冰川演化序列以及青藏高原隆升与冰川发育的耦合关系等新的研究资料,提出了中国冰期与海洋氧同位素阶段比较的2011 年改进方案,包括近百万年冰川变化的15 个特征时段及其对应的时间与中国冰期名称等信息。     

Paleoenvironmental implications of new OSL dates on the formation of the “Shell Bar” in the Qaidam Basin,northeastern Qinghai-Tibetan Plateau

A geological feature in the Qaidam Basin known as the “Shell Bar” contains millions of freshwater clam shells buried in situ. Since the 1980s, this feature in the now hyper-arid basin has been interpreted to be lake deposits that provide evidence for a warmer and more humid climate than present during late marine isotope stage 3 (MIS 3). Global climate during late MIS 3 and the last glacial maximum, however, was cold and dry, with much lower sea levels. We re-investigated the feature geomorphologically and sedimentologically, and employed optically stimulated luminescence (OSL) dating to verify the chronology of the sediments. We interpret the Shell Bar to be a remnant of a river channel formed by a stream that ran across an exposed lake bed during a regressive lake phase. Deflation of the surrounding older, fine-grained lacustrine deposits has left the fluvial channel sediments topographically inverted, indicating the erosive nature of the landscape. Luminescence ages place the formation of the Shell Bar in MIS 5 (~113–99 ka), much older than previous radiocarbon ages of <40 ka BP, but place the paleoclimatic inferences more in accord with other regional and global climate proxy records. We present a brief review of the age differences derived from ¹⁴C and OSL dating of some critical sections that were thought to represent a warmer and more humid climate than present during late MIS 3. We attribute the differences to underestimation of ¹⁴C ages. We suggest that ¹⁴C ages older than ~25 ka BP may require re-investigation, especially dates on samples from arid regions.     

Comparison of radiocarbon and OSL dating methods for a Late Quaternary sediment core from Lake Ulaan,Mongolia

Both radiocarbon and optically stimulated luminescence (OSL) dating methods were applied to test their suitability for establishing a chronology of arid-zone lacustrine sediments using a 5.88-m-long core drilled from Lake Ulaan, southern Mongolia. Although the radiocarbon and OSL ages agree in some samples, the radiocarbon ages are older than the corresponding OSL ages at the 550-cm depth horizon (late Pleistocene) and in the 100–300-cm interval (early to late Holocene). In the early to late Holocene, radiocarbon ages are consistently older than OSL ages by 4,100–5,800 years, and in the late Pleistocene by 2,700–3,000 years. Grain-size analysis of early to late Holocene sediments and one late Pleistocene sediment sample (550-cm depth) indicates that eolian processes were the dominant sediment-transport mechanism. Also, two late Pleistocene sediments samples (from 400- to 500-cm depths) are interpreted to have been deposited by both eolian and glaciofluvial processes. Accordingly, the radiocarbon ages that were older than the corresponding OSL ages during the Holocene seem to have been a consequence of the influx of ¹⁴C-deficient carbon delivered from adjacent soils and Paleozoic carbonate rocks by the westerly winds, a process that is also active today. In addition to the input of old reworked carbon by eolian processes, the late Pleistocene sediments were also influenced by old carbon delivered by deglacial meltwater. The results of this study suggest that when eolian sediment transport is suspected, especially in lakes of arid environments, the OSL dating method is superior to the radiocarbon dating method, as it eliminates a common ‘old-carbon’ error problem.     

蓬莱黄土剖面光释光年代学及其沉积特征研究

对山东半岛北部蓬莱林格庄黄土剖面进行了系统的野外考察,并进行了光释光测年以及粒度、磁化率指标分析。研究表明,磁化率的变化与不同粒级的百分含量具有一定的相关性,频率磁化率与粗颗粒含量基本呈一定的负相关。结合野外地层划分与光释光年代学测试可以将该剖面划分为3个黄土层和3个古土壤层,该剖面记录了末次间冰期以来该区气候和环境变化的历史。     

Luminescence geochronology for sediments from Lake El’gygytgyn,northeast Siberia,Russia: constraining the timing of paleoenvironmental events for the past 200 ka

This study focused on the luminescence dating of sediments from Lake El’gygytgyn, a meteorite impact crater 100 km north of the Arctic Circle in northeast Siberia, formed 3.58 Ma ago. The sediment is principally eolian deposited in to a lake with nearly permanently ice. The fine-grained polymineral and quartz extracts taken from nine distinct levels from the upper 12.3 m of sediment core PG1351 were dated by infrared stimulated (IRSL) and green stimulated luminescence (GSL) using multiple aliquot additive dose procedures. The veracity of these ages is evaluated by comparing to an age model for the core derived from magnetic excursions and from correlation of variations of the magnetic susceptibility record to similar magnitude variations in δ ¹⁸O in the Greenland Ice core record. The IRSL ages from the upper 9 m of core correspond well with the independent age control for the past ca. 200 ka. However, sediments deeper in the core at 12.3 m with an inferred age of ca. 250 ka age yield a saturated IRSL response and therefore a non-finite OSL age. The youngest sediment dated from 0.70 m depth yielded the IRSL age of ca. 11.5 ka, older than the corresponding age of 9.3–8.8 ka, indicating a discrepancy in dating the youngest sediments in the upper 1 m of core. This study confirms the utility of IRSL by the multiple aliquot additive dose method to date sediments <200 ka old from eastern Siberia. This is the sixth in a series of eleven papers published in this special issue dedicated to initial studies of El’gygytgyn Crater Lake and its catchment in NE Russia. Julie Brigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.     

Chronology of the Holocene loess-paleosol section and its deposition and pedogenesis on the south of Chinese Loess Plateau

Optically stimulated luminescence (OSL) dating for polymineral fine-grained loess samples, collected in Laoguantai (LGT) section on the south of the Chinese Loess Plateau, was made by application of 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 (De) determinations were produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively. The OSL ages estimated from IRSL signals are smaller than those estimated from [post-IR] OSL signals due to the anomalous fading of feldspar IR signals, based on fading experiment. The young ages of the samples near ground surface may be originated from the post-depositional disturbance by the intensifying humanity’s cultivation since 3.0 ka BP in the Guanzhong Basin, south of the Chinese Loess Plateau. Based on OSL dating, as well as field observations and stratigraphic correlation, we determine the chronology of the LGT loess-paleosol sequence. In combination with climate proxy records, it is indicated that aeolian loess deposition and pedogenesis underwent polyphase changes during the Holocene, likely to have been driven by shifts in the East Asian monsoon. This suggests that aeolian loess deposition is episodic and highly variable, with contributions from non-aeolian processes such as alluvial deposition found in the area.     

班戈错盐湖古湖岸堤石英光释光年代学及其古环境指示意义研究

古湖岸堤是湖泊湖面变化的地貌学证据,通过古湖岸堤沉积年代学研究可重建地质时期湖泊演化历史。青藏高原内陆湖泊众多,保存了大量的第四纪时期古湖岸堤,是研究过去湖泊演化和气候变化信息的重要载体。对青藏高原班戈错盐湖北岸和东岸的低位连续古湖岸堤开展了地貌调查和光释光年代学研究。结果表明班戈错自末次冰消期(13. 5±1. 2 ka BP)以来,湖面整体呈波动下降过程,期间出现了4期湖面稳定阶段,分别在末次冰消期(13. 5±1. 2～11. 2±1. 0 ka BP)、全新世早中期(10. 1±0. 8～6. 5±0. 5 ka BP)、全新世后期(4. 2±0. 4～3. 1±0. 2 ka BP)以及全新世晚期(1. 7±0. 1～1. 2±0. 1 ka BP)。全新世晚期约1. 7 ka BP以后湖面迅速退缩,湖泊蒸发浓缩进入盐湖阶段。在末次冰消期班戈错高湖面形成主要与北半球太阳辐射强度增加引起气温升高,导致区域冰雪融水量增加相关,而在全新世湖面变化主要受印度季风强度变化控制。     

云南千湖山第四纪冰川发育特点与环境变化

千湖山(4249 m) 是横断山脉中段保存确切第四纪冰川遗迹的山地,受西南季风影响强烈。对于研究青藏高原边缘山地冰川发育与气候和构造之间的耦合关系具有十分重要的科学意义。在千湖山海拔3500 m以上保存着古冰川侵蚀与堆积地貌,冰川发育依托海拔4000~4200 m的夷平面及其支谷地形。冰川形态类型为小型的冰帽以及由冰帽边缘溢流进入山谷的山谷冰川。应用相对地貌法,光释光(OSL) 年代测试,本文确定千湖山地区的冰进系列:末次冰盛期(LGM,22.2±1.9 ka BP)、末次冰期中期(MIS3b,37.3±3.7 ka BP、45.6±4.3 ka BP45.6±4.3 ka BP)、末次冰期早期(MIS4)。千湖山冰川前进规模是MIS3b 阶段大于末次冰盛期,主要原因是末次冰期中期(MIS3b) 时本区气候相对湿润,而在末次冰盛期(MIS2) 时气候条件比较干燥。在总体相似的气候背景下,与横断山其它存在多期次冰川作用的山地相比,千湖山只发育末次冰期的冰川作用,其差异性说明该地区冰川发育主要受山体构造抬升控制。