乌鲁木齐河源冰碛物的ESR测年研究

应用ESR测年技术对采自乌鲁木齐河源区上望峰、下望峰与高望峰的冰碛物进行了测年, 上望峰冰碛年代为(35±3.5) ka BP; 下望峰冰碛3个年代分别为(171.1±17) ka BP、 (176±18) ka BP、 (184.7±18) ka BP; 高望峰冰碛年代为(459.7±46) ka BP. 经对ESR测年结果的可靠性讨论并结合地貌地层与已有的14C年代、 ESR年代数据得出: 上望峰冰碛沉积于MIS 2相对应的末次冰期晚期; 下望峰冰碛系两次冰川作用沉积的, 公路之上冰碛于MIS 4相对应的末次冰期早期沉积的, 以下老的冰碛沉积于MIS 6相对应的冰期; 河源区最老的冰碛高望峰冰碛形成于MIS 12相对应的冰期. 高望峰冰碛年代同时还表明本段天山至少于此时已经上升到与当时冰川气候相耦合的高度, 进入了冰冻圈, 开始发育冰川.     

山东蒙山第四纪冰川遗迹光释光测年研究及冰期划分与对比

针对蒙山发育的第四纪冰川遗迹,采用光释光(Optic Stimulated Luminescence)的测年方法,对遗迹较新的冰碛垄进行了采样与测试,首次在我国东部中低山区获得了8.2ka BP与18.2~22.2ka BP两个时间段的冰期年龄值,对应于8.2ka BP早全新世全球冷事件与末次冰盛期。根据冰碛垄的特征与测定年龄值,结合我国以往其他地区冰期的对比研究,在蒙山建立了拦马冰期与蒙山冰期。本项研究,确认并发展了李四光关于我国东部第四纪冰川理论。     

青藏高原东北缘玛雅雪山晚第四纪冰川发育的气候和构造耦合

青藏高原东北缘的玛雅雪山(海拔4 447 m)保存着确切的第四纪冰川遗迹. 野外地貌调查与光释光测年方法相结合, 确认玛雅雪山晚第四纪主要经历3次冰川作用: 第Ⅰ组冰碛时代为新冰期; 第Ⅱ组冰碛物年龄为(23.2±1.0)ka, 其上覆泥石流年龄为(2.9±0.3)~(2.3±0.1)ka, 上层土壤年龄为(3.6±0.2)ka, 对应于深海氧同位素2阶段(MIS 2)的末次冰盛期(LGM); 第Ⅲ组冰碛年龄为(42.6±1.9)~(45.7±3.0) ka, 属于末次冰期中冰阶, 对应MIS 3中期. 采用最新综合因子法计算玛雅雪山现代冰川物质平衡线为海拔4 605 m. 依据冰川地貌形态, 计算末次冰期平衡线为海拔3 800 m. 通过庄浪河阶地的拔河高度及各级阶地的年代, 以河流的下切速率代表玛雅雪山的抬升速率, 计算得到末次冰期中期以来玛雅雪山抬升了50~60 m. 利用玛雅雪山周边的达里加山和太白山冰川漂砾的¹⁰Be 数据近似代表流域侵蚀速率, 推算出玛雅雪山剥蚀速率大约为29 mm·ka^-1, 推断MIS 3以来流域的剥蚀量为1~2 m. 综合末次冰期中期以来的构造抬升量和剥蚀量, 恢复末次冰期中期时的流域高度为海拔4 200 m, 平衡线高度为海拔3 750 m. 研究结果显示: 研究区在MIS 3时, 流域平均高度已经在平衡线之上, 在流域平均高度到主峰之间冰川开始积累, 发育冰川. 结合其他环境指标综合推断, 玛雅雪山晚第四纪冰川的发育是气候和构造耦合的产物.     

玉龙雪山冰川沉积序列OSL定年

位于青藏高原东南缘的玉龙雪山分布有欧亚大陆纬度最低的海洋型冰川,其主峰及周边地区保存了大量清晰完整的第四纪冰川遗迹。研究该区第四纪冰川作用遗迹及其冰川作用史,具有重要的理论与实际价值。应用光释光（OSL）测年技术对玉龙雪山冰川沉积物进行了定年,结合前人研究资料,重建玉龙雪山冰川作用史。研究结果表明：玉龙雪山东麓的末次冰期冰碛物主要形成于晚更新世末次冰期最盛时期,其平均年代约在25ka,西麓末次冰期冰碛物形成年代约为50ka,对应于深海氧同位素3阶段中期（MIS3b）。而倒数第二次冰期的年代在240ka左右,处于中更新世晚期,对应于MIS8阶段,当时玉龙雪山存在多条复式山谷冰川。该研究可为玉龙雪山第四纪冰川作用历史的重新认识以及光释光测年技术在该区的应用提供基础资料。     

中国第四纪冰期划分改进建议

由刘东生主持1位研究者提出的"以气候变化为标志的中国第四纪地层对比表"一文发表已近2a,其中由施雅风执笔第四纪冰期与海洋同位素对比部分.由于新情况的出现,需作适当改进:1)周尚哲等应用ESR测年确定祁连山北坡摆浪河源中梁赣海拔299m,高出现代河床500m处冰碛年代为42.9ka BP,天山乌鲁木齐河上游高出河床200～300m的高望峰阶地冰碛样品ESR测年为477.1ka BP和459.7ka BP,均相当于MIS 12阶段,该阶段国际上对应Kansan-Mindel冰期,与MIS 2、MIS和MIS 1都是100ka周期δ¹⁸O值特低时期;2)古里雅冰芯记录中相当于MIS3b阶段,δ¹⁸O值折算温度比现代低5℃左右,已经发现台湾雪山山庄期冰碛TL年代为(44.25±3.72)ka BP,天山乌鲁木齐河谷一处冰碛ESR年代45.9ka BP,喜马拉雅山、喀喇昆仑山和兴都库什南坡测定对应此时段冰川前进更为显著,初步检查亚、欧、北美、南美和澳洲12个地区23个地点相应于MIS 3b冷期冰川前进规模均超过MIS 2阶段,即常说LGM时,推测MIS 3b的降温值虽不及MIS 2,但降水较多,有利于冰川发展;3)MIS 3a暖期,不仅青藏高原异常暖湿,而且中国全境的降水量普遍高于现代,并有较大范围的海侵与仅低于现代海面8～10m的高海面,气候环境实际达到间冰期程度.上述3点应补充入中国冰期划分表.     

西藏东南部末次冰期早阶段冰川作用及其古气候意义

西藏东南部的“古乡冰期”和“白玉冰期”是划分中国第四纪冰期的蓝本。其中,白玉冰期即末次冰期,分为早阶段和晚阶段,相对应的冰川沉积广泛分布于本区的波堆藏布谷地。已有的冰川数值年代结果显示,末次冰期晚阶段的冰川作用发生于海洋氧同位素阶段（MIS）2。然而,关于早阶段的冰进记录,目前却未有确切的年代学证据,此次冰川作用究竟发生于MIS 4还是MIS 3,是一个悬而未决的问题。在前人研究及野外地貌调查的基础上,运用光释光测年手段对波堆藏布谷地疑似形成于末次冰期早阶段的冰碛垄进行测年,年代结果介于（56.4±4.2）~（65.9±3.9） ka之间,相当于MIS 4。藏东南地区MIS 4冰期冰川作用年代与青藏高原及其周边山地具有可比性,表明该阶段冰川作用发生的普遍性。通过对比北半球低纬度地区夏季太阳辐射及亚洲季风区古气温与古降水指标记录,认为藏东南地区MIS 4冰期冰川作用可能是对北半球低纬度地区夏季太阳辐射减弱及气温下降的响应,与季风降水无关。     

用OSL方法确定雅鲁藏布江大拐弯第四纪晚期冰川堰塞湖年龄

雅鲁藏布江是青藏高原上的一条大河, 其河谷地貌和地质环境演化的发育历史对于青藏高原地质研究有重要意义。前人用ESR和14C测年方法对雅鲁藏布江河谷两岸广泛分布河湖相沉积物、冰碛物测年确定了有四期堰塞湖。作者用光释光(OSL, Opically Stimulated Luminesecence)测年方法分析采集到的湖相样品年龄为(50.9±2.1) ka BP和(1.8±0.1) ka BP, 证明雅鲁藏布江大拐弯处末次冰期早冰阶和新冰期存在 古堰塞湖。     

冰川沉积释光测年： 采样策略与测试选择

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。     

天山夏特河流域晚第四纪冰川沉积序列与地貌演化

夏特河源于天山最大现代冰川作用中心托木尔—汗腾格里峰的东北坡,流域内保存有形态较为清晰的四套冰川沉积。这些地形记录了夏特河流域的古冰川变化,对它们进行研究可获得该地晚第四纪以来的冰川时空演化规律。在第三套冰碛夹层中的砂质透镜体里采集了5个OSL年代学样品,应用单片再生（SAR）测年技术测得它们的年龄为（13.3±0.8）~（20.1±1.3） ka。基于测年结果、各套冰碛距现代冰川的远近、冰碛垄的完整程度、冰碛物的风化胶结状况及接触关系,并参阅托木尔—汗腾格里峰南坡与东南坡以及东、中、西段天山其他流域的年代学资料,可初步得出：第一套和第二套冰碛分别沉积于小冰期和新冰期;第三套冰碛形成于末次盛冰期及随后的冰消期,可对应于海洋氧同位素阶段（MIS） 2;保存在河口的第四套冰川沉积及与其相关联的宽阔且长达数十千米的“U”形谷共同指示,它应形成于冰川规模较大的倒数第二次冰期,时间上可对应于MIS 6。     

基于年代学约束的白马雪山晚第四纪冰川作用

白马雪山(5429m)地处横断山脉腹地,海拔3800m以上保存着确切的第四纪冰川遗迹,对其进行深入研究,可以为重建西南季风影响区的环境演变历史以及区域冰期-间冰期系列对比提供依据.本文采用野外地貌调查与电子自旋共振测年(ESR)相结合的方法,查明白马雪山第四纪冰川发育的地貌特点,并对研究区的冰期系列进行划分.结果显示,白马雪山晚第四纪以来至少发生5次冰川作用,分别为中梁赣冰期(475±62ka,MIS 12);倒数第二次冰期(MIS 6),年代分别为166±22ka、142±17ka、209±23ka、153±15ka、120±16ka和180±20ka;末次冰期早期(MIS 4),年代分别为57±6.8ka、67±8.7ka、81±11ka、77±11ka和64±7.7ka;末次盛冰期(19±2.5ka,LGM,MIS 2)以及全新世新冰期/小冰期(MIS 1).研究区的冰川作用与青藏高原的脉动式抬升具有一定的对应关系.     

Cosmogenic nuclide constraints on glacial chronology in the source area of the Urumqi River,Tian Shan,China

Cosmogenic nuclide surface exposure dating of boulders and erratics provides new constraints for a glacial chronology in the source area of the Urumqi River, Tian Shan, China. ¹⁰Be exposure ages of 15.0 ± 1.3–17.1 ± 1.5 ka from the Upper Wangfeng (UWF) moraines agree well with their previous relative age assignments to marine isotope stage (MIS) 2, but are younger than published AMS ¹⁴C and electron spin resonance (ESR) ages (from 22.8 ± 0.6 to 37.4 ka). This difference may result from variations in techniques, or could reflect the impact of surface erosion and sediment/snow cover on surface exposure dating. ¹⁰Be ages from the Lower Wangfeng (LWF) moraines (18.7 ± 1.8 and 16.2 ± 1.5 ka) are indistinguishable from the UWF exposure ages, but are significantly younger than previously reported thermoluminescence (TL) and ESR ages (37.7 ± 2.6–184.7 ± 18 ka). Either these two groups were formed during the same period (MIS 2) and there are problems with TL and ESR ages, or the moraines were of very different ages and the similar exposure ages result from different degrees of degradation. Erratics on rock steps and a drumlin along >8 km of the main glacial valley above the UWF have internally consistent and slightly decreasing ¹⁰Be exposure ages indicating glacier retreat >2.5 m a^?1 after MIS 2 and before middle or late Holocene glacier re‐advances. This retreat rate is similar to rates observed from modern glaciers. Copyright © 2011 John Wiley & Sons, Ltd.     

稻城冰帽冰碛物光释光测年研究中遇到的问题及探讨

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。     

Late Quaternary glacial history of Khentey Mountains,Central Mongolia

Mongolian glaciers have been the subject of relatively little research, resulting in less geochronological constraint than other parts of Central Asia. The Khentey Mountains (latitude 47–51°N, longitude 105–112°E) are a typical landlocked mountain range exhibiting clear geomorphic evidence of late Quaternary glaciation. Yet, compared to western parts of Mongolia such as the Mongolian Altay, Gobi Altay, Khangay, and Khovsgol, glacial history of the Khentey Mountains is poorly understood. To address this, and permit comparison of the Khentey glacier–climate record with other alpine regions in Mongolia, we performed geomorphological mapping and cosmogenic ¹⁰Be surface‐exposure dating in two glaciated regions of the Khentey Mountains: Yestii and Khagiin Khar. Specifically, we measured ¹⁰Be in 34 samples collected from five moraine sequences, which, together with morphostratigraphy, correspond to four main glacial stages: (i) The M_y1 terminal moraine sequence for Yestii (21.0±4.9 ka) and the M_k1 moraine for Khagiin Khar (19.6±2.6 ka), both of which represent the Last Glacial Maximum; (ii) the Lateglacial M_k2 moraine, dated to 16.0±3.5 ka; (iii) the M_k3 moraine, dated to either 17.6±7.0 ka (Lateglacial) or 12.1±1.1 ka (Younger Dryas); and (iv) the currently undated M_k4 moraine (~2200 m a.s.l.), to which we assign a Holocene age. Our results suggest that the timing of maximum glacier extent in Mongolia was regionally variable. In the Khentey Mountains, maximum glaciation occurred during Marine Isotope Stage (MIS) 2, whereas the maximum occurred during MIS 3 in Khangay and Khovsgol and during MIS 4 in the Altay. The MIS 2 glacial maximum in the Khentey Mountains coincided with the global sea level minimum during the Last Glacial Maximum, and was followed by at least three glacial re‐advances during the Lateglacial to possibly the Holocene.     

阿尔泰山喀纳斯河流域末次冰期OSL年代学新证

布尔津河支流喀纳斯河源于中俄蒙三国交界处友谊峰的南坡,为额尔齐斯河的重要源区.友谊峰连同奎屯峰等高峰形成了阿尔泰山最大的现代冰川作用中心.在第四纪期间,这些冰川都发生了规模较大的进退,在河谷中留下了形态较为清晰的冰川地形.应用OSL单片再生剂量测定技术对采自主U型谷两侧的高大侧碛垄进行了定年,测年结果分别为(27.2±2.0)ka(K-1)与(16.1±1.5)ka(K-2).基于地貌地层学原理、并结合已有的年代学资料(OSL与14 C)与古气候研究资料,末次冰期以来喀纳斯河流域共有5次规模较大的冰进,分别为小冰期、新冰期、末次冰期晚冰阶(MIS 2)、末次冰期中冰阶(MIS 3中期)与末次冰期早冰阶(MIS 4).     

Surface exposure dating of the Great Aletsch Glacier Egesen moraine system,western Swiss Alps,using the cosmogenic nuclide 10Be

Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide ¹⁰Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The ¹⁰Be dates range from 10 460±1100 to 9040±1020 yr ago. Three ¹⁰Be dates between 9630±810 and 9040±1020 yr ago are based upon samples from the surfaces of granite boulders. Two ¹⁰Be dates, 10 460±1100 and 9910±970 yr ago, are based upon a sample from a quartz vein at the surface of a schist boulder. In consideration of the numerous factors that can influence apparently young ¹⁰Be dates and the scatter within the data, we interpret the weighted mean of four boulder ages, 9640±430 yr (including the weighted mean of two ¹⁰Be dates of the quartz vein), as a minimum age of deposition of the moraine. All ¹⁰Be dates from the Great Aletsch Glacier Egesen moraine are consistent with radiocarbon dates of nearby bog‐bottom organic sediments, which provide minimum ages of deglaciation from the moraine. The ¹⁰Be dates from boulders on the Great Aletsch Glacier Egesen moraine also are similar to ¹⁰Be dates from Egesen moraines of Vadret Lagrev Glacier on Julier Pass, in the eastern Swiss Alps. Both the morphology of the Great Aletsch Glacier Egesen moraine and the comparison with ¹⁰Be dates from the inner Vadret Lagrev Egesen moraine support the hypothesis that the climatic cooling that occurred during the Younger Dryas cold episode influenced the glacial advance that deposited the Great Aletsch Glacier Egesen moraine. Because of the large size and slow response time of Great Aletsch Glacier, we suggest that the Great Aletsch Glacier Egesen moraine was formed during the last glacial advance of the multiphased Egesen cold period, the Kromer stage, during the Preboreal chron. Copyright © 2004 John Wiley & Sons, Ltd.     

Luminescence dating of Quaternary alluvial successions,Sellicks Creek,South Mount Lofty Ranges,southern Australia

Abstract

Quaternary alluvial and colluvial sediments infill major river valleys and form alluvial fans and colluvium-filled bedrock depressions on the range fronts and within the Mount Lofty Ranges of southern Australia. A complex association of alluvial successions occurs in the Sellicks Creek drainage basin, as revealed from lithostratigraphy, physical landscape setting and optically stimulated luminescence (OSL) ages. Correlation of OSL ages with the Marine Oxygen Isotope record reveals that the alluvial successions represent multiple episodes of alluvial sedimentation since the penultimate glaciation (Marine Isotope Stage 6; MIS 6). The successions include a penultimate glacial maximum alluvium (Taringa Formation; 160?±?15?ka; MIS 6), an unnamed alluvial succession (42?±?3.2?ka; MIS 3), a late last glacial colluvial succession within bedrock depressions (ca 15?ka; MIS 2) and a late last glacial alluvium (ca 15?ka; MIS 2) in the lowest, distal portion of Sellicks Creek. In addition, the Waldeila Formation, a Holocene alluvium (3.5?±?0.3?ka; MIS 1), and sediments deposited during a phase of Post-European Settlement Aggradation (PESA) are also identified. The age and spatial distribution of the red/brown successions, mapped as the Upper Pleistocene Pooraka Formation, directly relate to different topographic and tectonic settings. Neotectonic uplift locally enhanced erosion and sedimentation, while differences in drainage basin sizes along the margin of the ranges have influenced the timing and delivery of sediment in downstream locations. Close to the Willunga Fault Scarp at Sellicks Creek, sediments resembling the Pooraka Formation have yielded a pooled mean OSL age of 83.9?±?7?ka (MIS 5a) corroborating the previously identified extended time range for deposition of the formation. Elsewhere, within major river valleys, the Pooraka Formation was deposited during the last interglacial maximum (128–118?ka; MIS 5e). In general, alluviation occurred during interglacial and interstadial pluvial events, while erosion predominated during drier glacial episodes. In both cases, contemporaneous erosion and sedimentation continued to affect the landscape. For example, in the Sellicks Creek drainage basin, which lies across an actively uplifting fault zone, late glacial age sediments (MIS 2) occur within the ranges and near the distal margin of the alluvial fan complex. OSL dating of the alluvial successions reported in this paper highlights linkages between the terrestrial and marine environments in association with sea-level (base-level) and climatic perturbations. While the alluvial successions relate largely to climatically driven changes, especially in major river valleys, tectonics, eustasy, geomorphic setting and topography have influenced erosion and sedimentation, especially on steep-sloped alluvial fan environments.

1. KEY POINTS

2. Luminescence dating of the Sellicks Creek alluvial fan complex reveals that sedimentation occurred predominantly during the later stages of glacial cycles accompanying lower sea-levels than present.

3. Luminescence dating confirms that the stratigraphically lower portions of the Pooraka Formation are beyond the range of radiocarbon dating.

4. Upper Pleistocene alluvial fan sedimentation at Sellicks Creek correlates with pluvial events in southeastern Australia.

     

Lateglacial and early Holocene surface exposure ages of glacial boulders in the Taiwanese high mountain range

Glacial landforms and sediments mapped in three presently unglaciated mountain massifs, the Nanhuta Shan, the Hsueh Shan and the Yushan, support the concept of repeated, multi-stage glaciations in the Taiwanese high mountain range during the late Pleistocene. New results from surface exposure dating using in situ produced cosmogenic ¹⁰Be measured in samples taken from erratic and moraine boulders in Nanhuta Shan at altitudes between 3100 and 3500 m are presented here. The results confirm independent and previously reported Optically Stimulated Luminescence (OSL) ages and ¹⁰Be exposure ages from glacial deposits in the same area and suggest a Lateglacial and early Holocene glaciation, the so called Nanhuta glacier advance with two substages at about 12–15 ka and 9.5 ka BP. The respective equilibrium line altitudes (ELA) were calculated at 3340 m and 3440 m with corresponding ELA depressions of 610 ± 100 m and 510 ± 100 m relative to the present day (theoretical) ELA, which is estimated to be at about 3950 ± 100 m in Taiwan. Large-scale erosional landforms indicate a much wider glacier extent during an earlier stage, which is not dated in Nanhuta Shan so far. Luminescence dating from near Hsueh Shan suggests an age of marine isotope stage (MIS) 4 for this stage.     

东天山黑沟流域冰川沉积序列及OSL测年研究

黑沟源于东天山最大现代冰川作用中心博格达峰的南坡. 在第四纪冰期与间冰期旋回中,该流域的冰川均发生过多次规模较大的进退,在谷中留下了较为完整的冰川沉积序列. 这些冰川地形包含有重要的古气候变化信息,对其研究可重建黑沟流域的冰川演化史. 应用OSL对该流域的冰川沉积物进行定年,测定结果表明冰水沉积物（沙质透镜体）比冰碛物更适宜应用单片再生剂量（SAR）测年技术进行测定. 基于测得的年龄并结合地貌地层学原理可初步得出：晚第四纪期间,黑沟流域共发生了5次规模较大的冰川作用,分别为全新世期间的小冰期（16世纪以来冷期的冰进）与新冰期（距今3~4 ka的冰进）,末次冰期晚冰阶（MIS 2）与早冰阶（MIS 4）以及倒数第二次冰期（MIS 6）.     

Late Pleistocene and Holocene glaciation of the Fish Lake valley,northeastern Alaska Range,Alaska

We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using ¹⁰Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that ¹⁰Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between ¹⁰Be and lichenometric ages reveal that ¹⁰Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.