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1.
福建晋江海岸带老红砂多期发育模式初步研究 总被引：3，自引：0，他引：3
我国东南沿海广泛分布的老红砂是海岸环境演变的产物.通过对福建晋江海岸带科任(KR)老红砂剖面加密采样进行OSL测年和粒度分析,初步确定了老红砂发育期次及其形成时代.以OSL测年值为基础,在统一的时间标尺上综合对比全球海平面和东亚季风变化序列,探讨了老红砂发育模式及其环境意义.研究表明:科任老红砂主要是晚更新世末次间冰期以来发育的,主要发生在约125 ～ 9ka期间,可以划分为6个沉积期,分别为125 ～115ka,105～97ka,84 ～ 74ka,61.5 ～52.0ka,39～29ka和15 ～9ka,期间可能存在至少5次明显的沉积间断.结合台湾海峡的水深变化特点分析,当海平面低于-70m时,由于研究区远离古海岸线,因而不可能有海岸风沙沉积;当海平面低于-15m高于-70m时,受到较强冬季风吹扬搬运海滩砂再沉积过程的影响,研究区可能有海岸风沙发育;当海平面高于-15m时,古今海岸线位置接近,在各种强度的冬季风作用下,研究区都会有海岸风沙广泛发育,并经历强烈的红化作用.即,科任老红砂主要发育于晚更新世末次间冰期以来气候暖湿的高海面和较高海面时期,而在末次冰期的低海面时期多次缺失海岸风沙沉积,尤其是末次盛冰期(LGM)的最低海面时期,现代海岸带所在区域老红砂发生沉积间断. 相似文献
2.
基于成因-环境原则和多指标综合原则,依据昆仑山垭口地区的冰川地貌特征、冰碛物特征和孢粉信息,重建了该地区古环境演化历史。其中,冰碛物中的石英砂扫描电镜结果揭示了冰川、流水、风等地质营力对冰碛物的影响,孢粉分析结果在一定程度上可以恢复当时的植被类型。根据垭口冰碛ESR年龄280 ka B.P.和冰碛剖面特征,将其时代暂定为300~260 ka B.P.;根据纳赤台地区的冰川地貌和沉积物特征,确定纳赤台后沟沉积为冰水扇沉积,纳赤台冰期为600~400 ka B.P.;根据玉虚峰U形谷两道侧碛垄的ESR和OSL年龄将其时代暂定为末次冰期早-中期。结合前人的研究成果,将昆仑山垭口地区的冰期序列厘定为望昆冰期（700~500 ka B.P.）、纳赤台冰期（600~400 ka B.P.）、垭口冰期（300~260 ka B.P.）、玉虚峰冰期（115~44 ka B.P.）、本头山冰期（20~13 ka B.P.）。 相似文献
3.
经过在若尔盖盆地进行全面野外考察,在黄河第一弯岸边发现了沉积序列清晰的、具有代表性的完整沉积地层剖面。通过沉积学和地层学特征和沉积相的观测分析,结合实验室粒度分析、数据处理和测年断代,其结果表明：该剖面底部蓝灰色古湖相沉积层反映出盆地内部在OSL年龄35 ka之前为较深的湖泊。其上覆盖的风沙与泥炭互层,反映出在该区域湖水消失之后,在30 ka之前古湖底出现泥炭沼泽,同时风沙作用盛行。而浊黄橙色古洪水沉积层（OFD1）则反映出在30~27 ka之间,曾经有来自于黄河源区流域的规模巨大的洪水进入若尔盖盆地,在古湖底泛滥并且将其携带的分选良好的细沙与粉沙质泥沙堆积下来。该剖面中部厚度达5~7 m的河漫滩-风沙层,沿着河岸追索,则可见其表现为高低起伏的古沙丘。这表明在末次冰期盛期和冰消期,气候干旱寒冷,黄河已经下切形成其河槽,其河漫滩沉积物被强劲的风力吹扬,形成连绵起伏的沙丘。该层之上所覆盖的浊黄橙色古洪水沉积层（OFD2）,则反映出在全新世初期9.86~8.28 ka之间,来自于黄河源区流域的大洪水再次进入盆地,在黄河第一湾两岸的古湖底沉积了分选良好的细沙质与粉沙质的泥沙。到了全新世中期后,若尔盖盆地风沙作用依然盛行,黄河河槽深切,第一湾两岸接受沙尘暴沉积。在全新世中期的相对温暖湿润气候条件之下,沙尘暴沉积物被改造为亚高山草甸黑土类土壤,成熟度极高。到了全新世晚期以来,风沙作用与沙尘暴沉积过程持续,沙尘暴沉积物也被改造为亚高山草甸黑土层。本文研究对于深入理解黄河源区末次冰期以来环境变化与地表过程演变,以及晚更新世以来的气候水文变化规律具有重要的科学意义。 相似文献
4.
晚第四纪MIS6以来柴达木盆地成盐作用对冰期气候的响应 总被引：2，自引：0，他引：2
气候是控制柴达木盆地盐类沉积的主要因素之一,但是其作用机制尚待明确。作者以柴达木盆地察汗斯拉图盐湖的3个含盐剖面为研究对象,采用多接收电感耦合等离子质谱(MC-ICP-MS)铀系测年测定其沉积时代,并通过X射线粉晶衍射(XRD)分析测定其盐类矿物种类。铀系测年显示D18剖面石盐和芒硝层的沉积时代为13.1±2.0 ka BP～15.9±2.5 ka BP,其中芒硝沉积年代属于末次冰期MIS2晚期;MXK2剖面芒硝层的沉积时代分别为131.7±39.5 ka BP和158.3±10.8 ka BP,D12剖面芒硝层的沉积时代分别为166.6±20.2 ka BP和198.0±20.6 ka BP,可以对应于倒数第二次冰期MIS6。XRD分析确定了3个剖面的盐类矿物主要为芒硝、石盐和石膏。综合多个盐湖晚第四纪成盐数据,本文认为倒数第二次冰期MIS6和末次冰期MIS2是柴达木盆地晚第四纪重要的成盐期,冰期的冷干气候有利于石盐和芒硝等盐类沉积。柴达木盆地"冰期成盐"的根本原因,是由于冰期环境下盆地周边山体冰川规模的扩张以及干冷的冰期气候,共同造成了盐湖补给水量的减少。此外,晚第四纪MIS6和MIS2的冰期降温也是导致盆地中冷相盐类沉积的直接原因。 相似文献
5.
对河北平原中部保定西伯章厚20.74 m的剖面进行实测,系统采集粒度和光释光（OSL）样品进行分析,以期获得其沉积特征及环境演变信息。光释光测年显示该剖面为102~8.69 ka的沉积,时代属于晚更新世到早全新世。岩性和粒度分析表明该剖面为曲流河冲积沉积,可以进一步划分为河道沉积和河漫滩沉积。河道沉积以含云母碎片的中粗砂为主,发育斜层理,频率曲线以正偏双峰频率曲线为主,分选中等到较差,概率累积曲线以跳跃组分为主的两段式为主。河漫滩沉积以黏土质粉砂为主,含保存良好的腹足类化石和钙质结核,频率曲线以负偏双峰为主,分选差,概率累积曲线以悬浮组分占比大的两段式为主。C-M图显示该剖面以均匀悬浮沉积为主,属典型曲流河沉积。实测剖面与黄土剖面对比分析显示西伯章剖面可以分为三个阶段,下部20.74~16.14 m为末次间冰期晚期沉积,气候温暖湿润,以粉砂质沉积为主;中部16.14~3.18 m为末次冰期沉积,气候干冷,沉积物显示细—粗—细的特征,与末次冰期早冰阶—间冰阶—盛冰阶一一对应;上部3.18~0.2 m为冰后期沉积,与末次间冰期晚期沉积环境类似,以黏土和黏土质粉砂沉积为主。粒度成因分析揭示了河北平原中部保定凹陷区晚第四纪沉积环境主要为河流冲积环境,粒度阶段性分布特征是晚第四纪以来冰期-间冰期气候的物质响应。 相似文献
6.
台湾环岛海岸带除火山、新构造事件外,新发现晚更新世风沙一土壤层相互叠置序列、洪江成因的复合洪积扇、风暴流旋回序列、湖泊成生一兴盛一衰亡旋回序列,反映出事件沉积作用类型多、多发性强、出现频率高的特点。晚更新世风沙一土壤层相互叠置序列以北岸的福隆剖面（图版1照片1）和东岸的港仔剖面（图版1照片2）出露最好,前者发现5个土壤层分隔出6期风沙沉积,中下部风沙层的ESR年龄值分别为96900aB.P和98900aB.P.;后一剖面序列由7个土壤层和两个洪泛砂砾层分隔出10期风沙沉积。 相似文献
7.
通过对六盘山西侧黄土地区进行详细的野外调查，在甘肃庄浪县城北水洛河第三级阶地平坦地面发现出露厚度3 m的全新世风成黄土古土壤剖面。确定以此为基础进行黄土古土壤物源分析及古气候恢复重建研究。在对该剖面土壤与沉积学宏观特征观察分析描述的基础上，从上向下，以每2 cm连续采样，共获得170个样品。在实验室进行理化指标分析和OSL测年、粒度成分端元分析和时间过程小波分析。结果表明，该剖面全新世黄土古土壤中可以识别出4个端元组分。它们分别代表了沉积物沉积后就地风化成壤改造作用、后期的淋溶淀积作用、西北冬季风和区域北风作用下的沙尘暴沉积作用。其中反应短尺度气候变化比较敏感的端元1组分在时间尺度上呈现出0.3 ka、0.7 ka、1.2ka、1.5 ka、1.8 ka以及2.4 ka的震荡周期。该研究结果对于推动量化分析六盘山西黄土高原全新世黄土古土壤物源和恢复重建该区域气候变化规律具有重要意义，也可为其他地区全新世气候变化过程恢复重建和区域对比提供参考材料。 相似文献
8.
西藏拉萨昌果沟遗址位于雅鲁藏布江中游支流的阶地上,是重要的新石器时代遗址.为探讨昌果沟遗址附近的古环境,对遗址附近开展地貌调查,在遗址北面约1 km处选取1个全新世风成沉积剖面进行光释光测年和环境指标分析,在雅鲁藏布江中游选2个阶地剖面进行光释光测年分析;此外,还总结了雅鲁藏布江中游23个全新世古土壤/泥炭的测年数据,进行概率密度分析,试图揭示区域的环境演化特征.研究表明:全新世古土壤/泥炭年代的概率密度可以较好地反映区域气候变化,9.0~6.0 ka古土壤/泥炭发育在波动中增强,气候由冷干向暖湿转换;6.0~2.9 ka古土壤/泥炭发育最强,气候相对温干;2.9 ka后鲜有古土壤/泥炭发育,气候变得冷干,史前人类活动受限.4.5 ka之后雅鲁藏布江中游及其支流一级阶地的形成为新石器时期先民提供农业耕作的场所,古土壤的发育为农作物提供了丰富的营养.1.4~1.1 ka期间(吐蕃王朝时期)局部地区有古土壤发育,气候好转. 相似文献
9.
哈尔滨荒山剖面是东北地区第四纪典型剖面，因缺乏绝对年龄数据，关于其地层划分及时代还有不同认识.对荒山剖面进行了系统的磁性地层学研究，并与AMS14C、OSL等年代学数据相结合，重新厘定了荒山剖面第四纪地层的年代框架.结果表明，荒山剖面记录了Matuyama负极性时晚期至Brunhes正极性时的沉积，B/M界线位于剖面下部46.7 m，剖面起始沉积年龄早于0.90 Ma.根据AMS14C和OSL年龄确定了全新统和上更新统的底界，对第四纪岩石地层单位的分层标志及顶、底年龄进行了分析，确定第四纪各个岩石地层单位的时代分别为:坦途组的年龄为~12 ka BP，顾乡屯组的年龄为12~79 ka BP，哈尔滨组的年龄为79~138 ka BP，上荒山组的年龄为138~580 ka BP，下荒山组的年龄>900 ka BP.据此建立了荒山剖面第四纪地层系统，为区域地层对比提供依据. 相似文献
10.
我国内陆干旱区在末次冰期(含深海氧同位素第3阶段)是否存在古大湖近年来持续存在争论.居延泽是黑河的尾闾湖之一,位于我国典型干旱区,是开展这项研究的理想区域.依据居延泽盆地最低处的JYZ11A钻孔(全孔长61.13m,本文侧重上部27m岩芯),使用石英光释光测年获得3个可靠释光年龄并据此建立年代框架.全孔10cm间距测量沉积物粒度,钻孔上部16.7m以2cm间距测量低频磁化率,本文侧重分析JYZ11A钻孔上部10m的指标记录.综合岩性地层、沉积物粒度分布特征和粒度、磁化率指标记录,并与前人已有研究进行对比,本研究发现末次冰期时居延泽盆地主要堆积棕色冲洪积物和风沙沉积物,早全新世为风沙沉积,中全新世出现浅灰色湖相沉积与风沙交替沉积,而稳定湖泊只在约3ka时才逐渐形成,可能存在多次湖面波动并留下古湖岸堤.因此,居延泽盆地在末次冰期包括深海氧同位素第3阶段晚期并不存在稳定大湖.居延泽早全新世干涸、中晚全新世湖泊较稳定发育的全新世成湖模式与季风区湖泊演化模式明显不同,而与许多中亚干旱区的湖泊、风成沉积等古环境记录相似,它们可能共同指示了一种有别于中国季风区的全新世区域湿度演化模式. 相似文献
11.
Age,origin and climatic controls on vegetated linear dunes in the northwestern Negev Desert (Israel) 总被引：1，自引：0，他引：1
Joel Roskin Naomi Porat Haim Tsoar Dan G. Blumberg Anja M. Zander 《Quaternary Science Reviews》2011,30(13-14):1649-1674
The stabilized northwestern (NW) Negev vegetated linear dunes (VLD) of Israel extend over 1300 km2 and form the eastern end of the Northern Sinai – NW Negev Erg. This study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology, stratigraphy and optically stimulated luminescence (OSL) dating. Thirty-five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and OSL dating, enabling spatial and temporal elucidation of the NW Negev dunefield evolution.In a global perspective the NW Negev dunefield is relatively young. Though sporadic sand deposition has occurred during the past 100 ka, dunes began to accumulate over large portions of the dunefield area only at ～23 ka. Three main chronostratigraphic units, corresponding to three (OSL) age clusters, were found throughout most of the dunefield, indicating three main dune mobilizations: late to post last glacial maximum (LGM) at 18–11.5 ka, late Holocene (2–0.8 ka), and modern (150–8 years). The post-LGM phase is the most extensive and it defined the current dunefield boundaries. It involved several episodes of dune incursions and damming of drainage systems. Dune advancement often occurred in rapid pulses and the orientation of VLD long axes indicates similar long-term wind directions. The late Holocene episode included partial incursion of new sand, reworking of Late Pleistocene dunes as well as limited redeposition. The modern sand movement only reactivated older dunes and did not lengthen VLDs.This aeolian record fits well with other regional aeolian sections. We suggest that sand supply and storage in Sinai was initiated by the Late Pleistocene exposure of the Nile Delta sands. Late Pleistocene winds, substantially stronger than those usually prevailing since the onset of the Holocene, are suggested to have transported the dune sands across Sinai and into the northwestern Negev.Our results demonstrate the sensitivity of vegetated linear dunes located along the (northern) fringe of the sub-tropical desert belt to climate change (i.e. wind) and sediment supply. 相似文献
12.
《Quaternary Science Reviews》2003,22(10-13):1067-1076
This study is concerned with the Late Quaternary climatic chronology of the Strzelecki Desert dunefields in central Australia. The sand ridges comprise layers of quartz sand, some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence (OSL). Deduced from the OSL age of the oldest aeolian layer dated, we conclude that the onset of aridity dates back to at least ∼65 ka. Older phases of aeolian activity though, following a fluvial depositional phase 160 ka ago, cannot be excluded, although no aeolian layers giving evidence for this have been found in the two dunes dated here. Unconsolidated dune sands in the upper part of one section with Late Holocene (4 ka to modern) depositional ages indicate a reactivation of the dunefield in recent times.From the crosscheck of 14C ages of the carbonated rootlets with OSL results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development. 相似文献
13.
Optical stimulated luminescence (OSL) study on sand and fossil soils from Hulun Buir Dunefield in Eastern China is reported in this paper. Aeolian dune sequences responded to the climate change by alternations of aeolian sand and dark sandy soils, which corresponded to arid and humid conditions, respectively. Optical dating using the single aliquot regeneration technique with quartz was applied to the deposits. The results indicate that the soils and underlying aeolian sand correspond to the Holocene optimum (HO) and the last late glacial, respectively. Combined with studies of OSL dating of 13 profiles and grain-size, magnetic susceptibility, total organic carbon, sediment color and scanning electron microscopy measurements for two representative sections, indicate the expansion in the last late glacial sand was 10 times that of today. The dune field was not totally stabilized by vegetation cover until HO (10–5 ka BP). 相似文献
14.
Dam Quang-Minh Manfred Frechen Tran Nghi Jan Harff 《International Journal of Earth Sciences》2010,99(8):1731-1740
In Vietnam, the coastal sand barriers and dunes located in front of the steep slopes of the high rising Truong Son Mountains
are sensitive to climate and environment change and give evidence for Holocene sea-level rise. The outer barrier sands were
deposited shortly before or contemporaneous with the local sea-level high stand along the Van Phong Bay postdating the last
glacial maximum (LGM). Optically stimulated luminescence (OSL) dating yielded deposition ages ranging from 8.3 ± 0.6 to 6.2 ± 0.3 ka
for the stratigraphically oldest exposed barrier sands. Further periods of sand accumulation took place between 2.7 and 2.5 ka
and between 0.7 and 0.5 ka. The youngest period of sand mobilisation was dated to 0.2 ± 0.01 ka and is most likely related
to reworked sand from mining activities. At the Suoi Tien section in southern central Vietnam, the deposition of the inner
barrier sands very likely correlate with an earlier sea-level high stand prior to the last glaciation. OSL age estimates range
from 276 ± 17 to 139 ± 15 ka. OSL dating significantly improves our knowledge about the sedimentary dynamics along the coast
of Vietnam during the Holocene. 相似文献
15.
本研究利用石英光释光测年的单片再生法(Singlealiquot Regenerativedose Protocol,简称SAR)对毛乌素沙地内部西北－东南方向5个风成砂－砂质古土壤剖面进行了年代测定,结合年代框架和剖面沉积相、磁化率及粒度特征探讨了晚第四纪以来毛乌素沙地演化和气候变化。研究表明毛乌素沙地在晚第四纪以来经历了多次沙地固定与活化的交替演化： 距今91.0ka,71.0ka,48.0ka,22.0ka,11.6ka,5.0ka,1.1ka,1.0ka和0.4ka前后风成砂沉积,沙地活化,指示气候干旱,植被覆盖度低; 在距今65ka和全新世适宜期(8.5～5.0ka),沙地固定成壤,砂质古土壤发育,指示气候湿润。另外,剖面中风成砂层数变多、厚度增加、粒径变粗指示了晚第四纪以来毛乌素沙地干旱化趋势加强。 相似文献
16.
Chronologies of sedimentary changes in the south Bohai Sea,China: constraints from luminescence and radiocarbon dating 总被引：1，自引：0，他引：1
Liang Yi Zhongping Lai Hongjun Yu Xingyong Xu Qiao Su Jing Yao Xulong Wang Xuefa Shi 《Boreas: An International Journal of Quaternary Research》2013,42(2):267-284
The alternation of terrestrial and marine deposits is an indicator of past environmental and sea‐level changes. The age of deposition is usually dated by means of radiocarbon. However, radiocarbon dates of molluscan shells from coastal areas may be complicated by various sources of carbon, and problematic for deposits of 40–50 ka or older. Herein, we apply the Optically Stimulated Luminescence (OSL) dating method to date samples from terrestrial and marine/coastal sediments extracted from three cores in the south Bohai Sea, China. Multiple‐ and single‐aliquot regenerative‐dose procedures using OSL signals from fine‐silt (4–11 μm), coarse‐silt (38–63 μm) and fine‐sand (63–90 or 90–125 μm) quartz were employed to determine the equivalent dose (D e). The results showed that: (i) OSL ages from quartz of different grain sizes and different protocols are consistent with each other; (ii) for Holocene samples, most of the radiocarbon dates agree well with OSL ages; (iii) for pre‐Holocene samples, radiocarbon dates cluster at 40–50 14 C ka BP, whereas OSL ages are in stratigraphic order from 11 ka to 176 ka. Because of the self‐consistency of the quartz OSL ages, the stratigraphic agreement in the three cores, and the clustering of the radiocarbon dates, we suggest that the quartz OSL ages are more reliable with respect to dating the samples from the south Bohai Sea. Finally, the four marine strata identified in the south Bohai Sea are likely to have formed during the Holocene, Marine Isotopic Stage (MIS) 3–5, MIS 6 and probably MIS 7, respectively. 相似文献
17.
Sedimentology, stratigraphy and landscape evolution of a Holocene coastal dune system, Lodbjerg, NW Jutland, Denmark 总被引：1，自引：0，他引：1
The stratigraphy and landscape evolution of the Lodbjerg coastal dune system record the interplay of environmental and cultural changes since the Late Neolithic. The modern dunefield forms part of a 40 km long belt of dunes and aeolian sand‐plains that stretches along the west coast of Thy, NW Jutland. The dunefield, which is now stabilized, forms the upper part of a 15–30 m thick aeolian succession. The aeolian deposits drape a glacial landscape or Middle Holocene lake sediments. The aeolian deposits were studied in coastal cliff exposures and their large‐scale stratigraphy was examined by ground‐penetrating radar mapping. The contact between the aeolian and underlying sediments is a well‐developed peaty palaeosol, the top of which yields dates between 2300 BC and 600 BC . Four main aeolian units are distinguished, but there is some lateral stratigraphic variation in relation to underlying topography. The three lower aeolian units are separated by peaty palaeosols and primarily developed as 1–4 m thick sand‐plain deposits; these are interpreted as trailing edge deposits of parabolic dunes that moved inland episodically. Local occurrence of large‐scale cross‐stratification may record the head section of a migrating parabolic dune. The upper unit is dominated by large‐scale cross‐stratification of various types and records cliff‐top dune deposition. The nature of the aeolian succession indicates that the aeolian landscape was characterized by alternating phases of activity and stabilization. Most sand transported inland was apparently preserved. Combined evidence from luminescence dating of aeolian sand and radiocarbon dating of palaeosols indicates that phases of aeolian sand movement were initiated at about 2200 BC , 700 BC and AD 1100. Episodes of inland sand movement were apparently initiated during marked climate shifts towards cooler, wetter and more stormy conditions; these episodes are thought to record increased coastal erosion and strong‐wind reworking of beach and foredune sediments. The intensity, duration and areal importance of these sand‐drift events increased with time, probably reflecting the increasing anthropogenic pressure on the landscape. The formation of the cliff‐top dunes after AD 1800 records the modern retreat of the coastal cliffs. 相似文献
18.
《Quaternary Science Reviews》2007,26(19-21):2617-2630
The linear dunes of the Kalahari, now largely inactive, have long been identified as having potential palaeoenvironmental significance. The application of optically stimulated luminescence (OSL) dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region, though field methodologies and time-consuming multiple-aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated.In order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records, this intensive study presents 71 OSL ages from the linear dunes of the southwestern Kalahari at Witpan, South Africa, sampled with coring equipment at regular and frequent intervals down to bedrock.The earliest sand accumulation recorded at Witpan is at 104 ka, and in spatially discrete locations, other evidence of dune activity is recorded at 77–76, 57–52 and 35–27 ka. Although an inherently discontinuous archive, the linear dunes of the southwestern Kalahari have the potential to record multiple phases of dune construction. Following the Last Glacial Maximum there is near continuous evidence of dune-building, with a peak of accumulation recorded from 15 to 9 ka at five individual sites. This latter period is generally recognised from other proxy evidence as being unusually arid in this region, and such periods of dune activity are likely to be related to intensification of the continental anticyclone. During the Holocene, accumulation has continued at most sites sampled, albeit at a lesser intensity. This may imply that these dunes are presently not far from thresholds of activation. 相似文献
19.
使用钾长石进行释光测年时,由于长石的释光信号存在异常衰减,会导致沉积事件年龄的低估。对中国北方4个全新世样品分别使用石英和钾长石矿物组分释光测年,通过测量钾长石的衰退系数(g值)对钾长石使用再生剂量法获得的表征年龄进行了校正。发现对于本文所研究的年轻样品钾长石表征年龄与石英年龄相比系统偏小约2％～9％,钾长石校正年龄与石英年龄相比则严重偏大约16％～40％,表明使用g值无法校正年轻样品的钾长石年龄。对于年轻样品,钾长石IRSL信号异常衰减现象对测年结果的影响是可以忽略的。 相似文献
20.
The northeastern Qinghai-Tibetan Plateau(QTP) of China is located at the triple junction of the Asian winter and summer monsoons and the westerlies, where paleoclimatic evolution has an important scientific significance for recognizing the spatial-temporal pattern of Asian monsoons in the past and predicting environmental change in the future. Nevertheless, the framework of the Holocene moisture variation and related mechanisms remain controversial, owing to complex hydroclimatic conditions triggered by the landform of the large mountain-arid basin. Here, we employed geochemical proxies from typical aeolian sand-palaeosol sequences in the Gonghe Basin, northeastern QTP, together with Optically Stimulated Luminescence(OSL) dating, to reconstruct the pattern of effective moisture variation and associated mechanisms in this region. Our results indicate that the regional effective moisture was at its lowest until 9–8 ka, and approached a maximum during 8–4/3 ka of the middle Holocene. Afterwards, the climate became relatively dry in general, but with a transient humid interval around 2–1 ka. Our geochemical evidence indicates that the dry early Holocene probably can be attributed to a strong winter monsoon forced by remnant ice sheet, combined with the high evaporation caused by solar insolation. Also, shifts of humid-dry are closely linked to the Asian summer monsoonal strength and therefore the balance of evaporation-precipitation in the middle and late Holocene. Thus, the pattern of the Holocene effective moisture variation is characterized as the ‘monsoon model' in a closed intermontane arid and semi-arid basin near the western Asian monsoonal limit. 相似文献