The evolution of the terrestrial-terminating Irish Sea glacier during the last glaciation

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.     

Coleopteran evidence for a mosaic of environments at high altitude in the eastern Pyrénées,France, during the climatic transition between the Allerød and Younger Dryas

Late‐glacial environmental and climatic implications are inferred from an insect fauna from organic sediments infilling a palaeochannel on the banks of the River Têt, eastern Pyrénées, France. A pine cone in association with the insect fauna has been radiocarbon dated to 10 920 ± 60 yr BP, namely close to the Allerød – Younger Dryas boundary. Two distinct insect associations appear to be recognisable here. One is an assemblage typical of the high altitude forest and a second is characteristic of an alpine grassland. The close coexistence of these two assemblages is attributed to the climatic cooling towards the start of the Younger Dryas Stadial, when the forest cover broke up into remnant patches interspersed by alpine grassland. It is suggested that in a region of such high relief a mosaic of habitats may have been caused by patchy differences in insolation aspect, especially during a period of climatic deterioration. Copyright © 1999 John Wiley & Sons, Ltd.     

2013年西藏嘉黎县“7.5”冰湖溃决洪水成因及潜在危害

冰湖溃决洪水（泥石流）是西藏自治区主要自然灾害之一. 2013年7月5日,西藏自治区嘉黎县忠玉乡发生“7.5”冰湖溃决洪水灾害事件,导致人员失踪,房屋被毁,桥梁、道路等基础设施遭到严重破坏,直接经济损失高达2.7亿元. 基于不同时间段地形图和遥感影像资料,利用地理信息技术,发现导致“7.5”洪灾的溃决冰湖为然则日阿错. 该冰湖溃决的直接诱因可能是雪崩和冰崩的共同作用,溃决前的强降水过程及气温的快速上升是其间接原因,而冰湖长期稳定的扩张导致水量聚集是其溃决并造成巨大灾害的基础. 然则日阿错溃决后形成2个冰湖,面积分别为0.25 km²和0.01 km²,再次发生溃决的概率极小. 这次溃决洪水和泥石流灾害事件阻塞了尼都藏布的罗琼沟及衣布沟,并形成2处面积分别为0.33 km²和0.13 km²堰塞湖,且存在溃决风险,在今后一段时间内应加强监测工作与排险工程实施.     

Aragonite and calcite preservation in sediments from Lake Iznik related to bottom lake oxygenation and water column depth

This study examines the forcing mechanisms driving long‐term carbonate accumulation and preservation in lacustrine sediments in Lake Iznik (north‐western Turkey) since the last glacial. Currently, carbonates precipitate during summer from the alkaline water column, and the sediments preserve aragonite and calcite. Based on X‐ray diffraction data, carbonate accumulation has changed significantly and striking reversals in the abundance of the two carbonate polymorphs have occurred on a decadal time scale, during the last 31 ka cal bp . Different lines of evidence, such as grain size, organic matter and redox sensitive elements, indicate that reversals in carbonate polymorph abundance arise due to physical changes in the lacustrine setting, for example, water column depth and lake mixing. The aragonite concentrations are remarkably sensitive to climate, and exhibit millennial‐scale oscillations. Extending observations from modern lakes, the Iznik record shows that the aerobic decomposition of organic matter and sulphate reduction are also substantial factors in carbonate preservation over long time periods. Lower lake levels favour aragonite precipitation from supersaturated waters. Prolonged periods of stratification and, consequently, enhanced sulphate reduction favour aragonite preservation. In contrast, prolonged or repeated exposure of the sediment–water interface to oxygen results in in situ aerobic organic matter decomposition, eventually leading to carbonate dissolution. Notably, the Iznik sediment profile raises the hypothesis that different states of lacustrine mixing lead to selective preservation of different carbonate polymorphs. Thus, a change in the entire lake water chemistry is not strictly necessary to favour the preservation of one polymorph over another. Therefore, this investigation is a novel contribution to the carbon cycle in lacustrine systems.     

Lake-Level Fluctuations and Small-Scale Vegetation Patterns During the Late Glacial in The Netherlands

Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS ¹⁴C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands.     

云南省东北部拱王山第四纪冰川遗迹研究

云南省东北部的拱王山海拔３１００ｍ以上的山地发生过第四纪冰川作用，典型的冰川遗迹集中分布在轿子山峰附近和妖精塘－牛洞坪两个地区，遗存的冰川地貌主要有冰斗，冰蚀岩盆和侧碛堤。根据冰川地貌的组合特征，以及它们生成的先后顺序，将拱王山第四纪冰川作用划分为末次冰期的倒数第二期冰期。     

基于手绘图件的考古遗址三维建模方法

考古遗址是研究古代人类活动的重要场所。重建考古遗址三维模型对于历史回溯、古环境恢复和古迹保护等考古工作均具有重要的意义。传统考古发掘过程中普遍采用的手绘图件难以实现考古现场环境的模拟与再现,也不能准确地反映出遗址中文化层与其所包含地物的空间关系。近年来,考古学家引入各类勘察新技术用于考古文化层与遗迹的三维建模,但这些方法无法应用于已完成发掘工作的遗址三维重建。针对这一问题,本文提出一种以考古发掘过程中普遍采用的手绘图件为数据源的考古遗址三维建模方法。该方法以探方为基本建模单元,将考古文化层与遗迹分开建模,利用探方分布图及探方图建立考古文化层三维模型,利用遗迹图建立考古遗迹三维模型,并以三维实体布尔运算方法,将两者无缝整合,构建完整的田野考古遗址三维模型。最后,以湖南澧县八十垱东区为研究区,验证了本文相关研究成果的有效性与实用性。实践证明,该方法能够充分利用传统考古过程中积累的大量资料,有助于将传统考古学在宏观尺度下的定性描述转化为现代"数字考古"中微观尺度的定量描述。     

黄土堆积与冰期事件

黄土高原早期环境 ,应该同其周边环境大体相似 ,也存在冰期问题 :三套“砂质黄土”是冰期遗物的唯一表象 ,这是因为冰体夹在黄土层中间 ,基本丧失了冰川形成条件 ,故虽有冰期而无冰川 ,自然也就没有山岳冰川所形成的各类遗物 ,当然也包括冰川地貌的形踪     

北京潭柘寺地区第四纪冰川遗迹的宏观和微观特征

以北京西山潭柘寺地区第四纪冰川遗迹的宏观特征研究为基础,对管坨岭冰期和赵家台冰期的古冰川沉积进行了石英颗粒表面结构形貌组合特征的分析。结果表明,管坨岭冰期的管坨岭冰碛层和大富庄冰碛层,以及赵家台冰期的太平庄冰碛层中的石英颗粒表面结构,以冰川成因的形貌组合占优势,而赵家台冰期鲁家滩冰水沉积中的石英颗粒表面结构,则以冰川和流水共有成因的形貌占优势。所以,据冰川遗迹的宏观和微观特征,可以肯定该区分别在早更新世和中更新世曾发育过两次古冰川作用。      

Saprolite Remnants as Indicators of Pre-Glacial Landform Genesis in Southeast Sweden

Twenty‐six sites with remnants of gravelly saprolites (grus) have been located in southeast Sweden. Joint block hills (castle kopjes) and steep rock walls with weathered joints as well as rounded boulders are documented to have an origin in deep weathering and subsequent stripping of saprolites. The saprolite remnants and landforms result from the fragmentation of the re‐exposed sub‐Cambrian peneplain along fracture systems. Only shallow saprolites occur on the elevated intact parts of the sub‐Cambrian peneplain, while saprolites up to 20 m thick are encountered in areas where the sub‐Cambrian peneplain is fractured and dissected. Neogene uplift with reactivation of the weathering system is thought to be the main cause of saprolite formation. Deep weathering is thus judged to have been the major agent of landform formation in the study area, while glacial and glaciofluvial erosion has contributed mainly by stripping saprolites, detaching corestones, and plucking joint blocks along weathered joints.