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1.
通过对天山乌鲁木齐河源冰川底床基岩与沉淀物显微结构构造分析,对大陆性山岳冰川冰下过程的认识更加深入.沉积物微观结构和构造特性显示冰川底部存在较大的挤压应力作用,由显微滞碛等现象来看,压应力在微观上的空间分布很不均匀.沉淀物中块体碎裂和基岩上冰成裂隙反映,冰川底部冰体对基岩面有巨大的剪切应力作用.滑塌构造说明,冰川底部在微小的区域内压力分布不均匀,局部有重力作用过程存在.沉淀物中块体断裂和同生变形构造的存在说明沉淀物的形成过程为先期沉淀、后期受压.通过对冰川底部各种动力作用特征的阐述及沉淀物结构、构造的成因及特性的总结,认为大陆性山谷冰川底部冰岩界面处存在水膜,且冰川运动亦有滑动性. 相似文献
2.
贡嘎山海螺沟冰川沉积特征与冰下过程研究 总被引：4，自引：3，他引：1
贡嘎山海螺沟冰川是典型的海洋性冰川,粒度分析表明:冰下融出碛的细粒组分中粉砂占优势,压碎组分与磨碎组分界线在0.5 mm附近,说明其经历充分的研磨细化.与西藏枪勇冰川和天山乌鲁木齐河源冰川的矿物组成和化学成分对比,海螺沟冰川沉积物的经历的化学风化作用更强,即海洋性冰川冰下化学作用比大陆性冰川活跃.显微层理构造、正粒序层理和沉积透镜体反映海洋性冰川底部存在周期性沉积机制和明显的流水作用,显微滞碛是较常见的冰下融出碛类型.沉积物中显微褶皱和断层等反映海洋性冰川强烈滑动、剪切变形过程机制. 相似文献
3.
祁连山老虎沟12号冰川冰下形态特征分析 总被引：4，自引：1，他引：3
利用探地雷达对老虎沟12号冰川进行了多个剖面观测,分析了雷达图像反映的冰川内部特征.结果表明通过分析雷达图像中的纹理和位置,雷达波形的振幅和极性变化等信息能够有效的辅助识别冰川内部介质的变化界面位置和估算其规模.在老虎沟12号冰川的部分剖面内部存在冰内空洞、冰内融水空洞、冰下裂隙、冰下河等地貌形态,在冰岩界面和冰川边缘存在规模不等的碎屑层.这说明即使在典型的大陆型冰川,冰川内部结构也可能较为复杂,在冰岩界面处可能存在较强的冰川作用. 相似文献
4.
温冰川冰内及冰下水系季节演化及其水文学分析 总被引：5，自引：3，他引：2
针对温冰川冰内及冰下水系(又称冰川排水系统)演化及其水力过程,回顾了我国20世纪90年代在典型温冰川海螺沟冰川开展钻孔试验及关于冰下河堵溃问题的水文学分析,主要从水文学角度,探讨了消融期温冰川冰内及冰下水系的演化过程及其在径流过程曲线上的反映.利用径流-气温交叉相关分析方法,计算了海螺沟冰川2003—2005年逐日Q-T时滞,其季节变化在一定程度上指示了冰内及冰下水系季节演化过程及其水力状况,并针对典型时段,重点探讨了二者之间的相关性. 相似文献
5.
简要回顾和介绍了示踪试验方法在冰内及冰下水系演化研究中的应用, 并以ADM模型为例, 对示踪剂扩散模型进行了敏感性试验分析, 分析了不同参数组合条件对示踪剂浓度变化过程的影响. 在海螺沟冰川消融区下游冰舌段开展了示踪试验, 通过对一个固定入水口消融期整个过程的重复投放试验, 获取了每次独立示踪试验示踪剂的浓度变化过程, 并用ADM扩散模型反演了示踪剂传播速度、 水力扩散系数以及平均排水通道面积等相关指标, 揭示了海螺沟冰川此冰舌段冰下排水系统的季节变化过程. 相似文献
6.
针对冰川沉积系列细砂粉砂在埋藏前的曝光问题,笔者等人在帕米尔阿依直苏冰川做了观察.本文结合这些观察结果从沉积学角度讨论冰川沉积系列在产生、搬运、沉积过程中的曝光问题,并参考前人研究,将各类冰川沉积进行归纳.认为组成冰碛3个来源的细粒物质中,风成的全部曝光、岩壁风化碎屑部分曝光、冰川侵蚀岩屑不曝光;3个沉积系列中,冰水沉积完全曝光、冰川接触沉积中冰砾阜完全曝光、蛇形丘基本不曝光;冰碛物在沉积过程中,冰面融出碛基本上曝光、冰下滞碛和融出碛不曝光.本文根据分析,给出了冰川沉积系列曝光评估参考值. 相似文献
7.
冰川冰内及冰下水系研究综述 总被引：1，自引：0，他引：1
冰内及冰下水系的形成与演化具有时空变化性,对冰川汇水储水及径流过程产生影响,与之紧密联系的冰下水文过程(水力状况)与冰川运动、冰川侵蚀及冰川洪水形成等过程息息相关。冰内及冰下水系空间结构和形态复杂,且不同于一般喀斯特水文系统,具有明显的季节变化性,其空间分布和水力状况会因外界水体输入(降水和冰雪融水)的变化而改变。冰内及冰下水系的变化通过影响汇流对冰川融水的径流过程产生影响,冰川区一些溃决洪水事件的发生与冰内及冰下蓄水的突然释放有很大关系。冰川蓄排水还通过改变冰下水力条件来影响冰川运动,反之冰川运动不仅影响蓄排水过程的转换效率,且通过改变冰川消融强度(冰体向下游消融区输送速率的变化)影响冰川排水系统的空间分布范围。在气候变暖及冰川变化的背景下,研究冰内冰下水系演化的时空特征及其影响具有重要科学意义。综述了目前国内外针对冰川冰内及冰下水系相关研究的进展及主要成果,并对该领域的研究前景进行了展望。 相似文献
8.
3号冰川消融区下部有4个主要的剪切面,这些剪切面伴随着5—40厘米厚的富含岩屑冰。在每个富含岩屑冰区域采集了内碛样品以便考察它的特征和来源。 冰内碛巨砾具有极其明显的棱角状,泥沙和粘土的含量低于温冰川磨蚀过程产生的冰碛的泥沙和粘土含量。用电子扫描显微镜观察到的石英颗粒表面特征表明: (1)所有颗粒都具有典型的“冰川作用”特征。 (2)5—20%的颗粒显示出在“冰川作用”特征之上附加有二氧化硅溶解沉淀物特征。 (3)水下机械作用的标志如撞击痕和磨圆现象很少观察到。(1)意味着石英颗粒是机械研磨或挤压作用的产物;(2)和(3)意味着某些颗粒在被挤压后曾在水中停留过,但颗粒并没有在湍流水流中被搬运。 这些结果暗示3号冰川内碛主要是由冰川底部挤压或拔蚀作用所产生,而不是磨蚀作用的产物。在内碛产生的冰川底部,温度一直或以前保持在融点,但水量小于温冰川底部的水量。 相似文献
9.
南极大陆冰下基岩岩心对研究南极大陆地质构造及成因具有重要意义,目前尚没有任何一个国家在南极内陆成功钻取冰下基岩样品,研制可快速钻至冰岩界面并完成基岩采样的钻进设备迫在眉睫。针对极地冰下基岩取样技术难题,提出了一种可结合热水钻系统使用的采用热水驱动的冰下基岩取心钻具概念设计。该钻具系统采用常规热水钻完成南极大陆上覆冰层钻进,然后更换热水取心钻具穿过已有钻孔快速到达冰岩界面,完成冰下沉积物和基岩取心钻进,大大缩短基岩取心时间,提高钻进效率。结合中国自主研发的热水钻系统参数,对螺杆马达压力损失和输出扭矩进行理论计算,提出了螺杆马达选择依据。该技术有望在未来极地冰下基岩取心钻进中发挥重要作用。 相似文献
10.
冰川底部滑动是冰川运动重要的组成部分,是冰川动力过程的底部边界条件.底部滑动速度的估算,对于研究青藏高原及周边地区冰川运动规律、冰川内部应力分布和冰川异常变化机制等具有重要意义.系统总结了冰川底部滑动速度的影响因素及其估算模型的发展现状,其模型从单纯考虑底部剪切应力与冰床特性的关系逐渐扩展到考虑底部有效压力和冰下水文过程等综合影响,剖析了现有模型的结构和功能.进而分析了现有模型存在的主要问题和挑战,为进一步完善模型提供参考.未来冰川底部滑动研究需基于遥感大数据、新技术等进一步强化观测,着重耦合冰下水文过程的影响,进而促进气候变化—冰川物质平衡—冰川动力学响应过程的集成研究. 相似文献
11.
Temporal changes in meltwater abundance, distribution and characteristics (controlling subglacial processes and ice sheet dynamics) can be inferred from subglacial sediment successions. Field evidence for changes in subglacial meltwater characteristics over time is presented from two sites (Doonan, Drummee) near a former late Weichselian (Devensian) ice centre in the north of Ireland. On a macroscale, both sites investigated show subglacial diamicton overlying glacially planated bedrock platforms. In more detail, primary sedimentary structures and facies variability show a complex relationship between depositional processes and meltwater characteristics at the ice/bed interface (IBI). Sedimentary evidence suggests sediment transport and deposition took place by low-viscosity subglacial slurries (mobile sediment–meltwater admixtures), which are part of a continuum between the processes of subglacial sediment deformation and subglacial meltwater flooding. Subtle changes in meltwater abundance and distribution at the IBI controlled slurry rheology, mechanisms of particle support and detailed sediment depositional processes. 相似文献
12.
Subglacial and subaqueous sediments deposited near the margin of a Late-glacial ice-dammed lake near Achnasheen, northern Scotland, are described and interpreted. The subglacial sediments consist of deformation tills and glacitectonites derived from pre-existing glaciolacustrine deposits, and the subaqueous sediments consist of ice-proximal outwash and sediment flow deposits, and distal turbidites. Sediment was delivered from the glacier to the lake by two main processes: (1) subglacial till deformation, which fed debris flows at the grounding line; and (2) meltwater transport, which fed sediment-gravity flows on prograding outwash fans. Beyond the ice-marginal environment, deposition was from turbidity currents, ice-rafting and settling of suspended sediments. The exposures support the conclusion that the presence of a subglacial deforming layer can exert an important influence on sedimentation at the grounding lines of calving glaciers. 相似文献
13.
A multi-proxy approach involving a study of sediment architecture, grain size, grain roundness and crushing index, petrographic and clay mineral composition, till fabric and till micromorphology was applied to infer processes of till formation and deformation under a Weichselian ice sheet at Kurzetnik, Poland. The succession consists of three superposed till units overlying outwash sediments deformed at the top. The textural characteristics of tills vary little throughout the till thickness, whereas structural appearance is diversified including massive and bedded regions. Indicators of intergranular bed deformation include overturned, attenuated folds, boudinage structures, a sediment-mixing zone, grain crushing, microstructural lineations, grain stacking and high fabric strength. Lodgement proxies are grooved intra-till surfaces, ploughing marks and consistently striated clast surfaces. Basal decoupling by pressurized meltwater is indicated by undisturbed sand stringers, sand-filled meltwater scours under pebbles and partly armoured till pellets. It is suggested that the till experienced multiple transitions between lodgement, deformation and basal decoupling. Cumulative strain was high, but the depth of (time-transgressive) deformation much lower (centimetre range) than the entire till thickness ( ca 2 m) at any point in time, consistent with the deforming bed mosaic model. Throughout most of ice overriding, porewater pressure was high, in the vicinity of glacier floatation pressure indicating that the substratum, consisting of 11 m thick sand, was unable to drain subglacial meltwater sufficiently. 相似文献
14.
JASPER KNIGHT 《Boreas: An International Journal of Quaternary Research》2009,38(3):545-554
Subglacial erosional forms are commonly found on bedrock substrates inside the Late Weichselian ice margin in County Donegal, northwest Ireland, and can be used to provide detailed information on subglacial processes and environments. The erosional forms occur on spatial scales from whalebacks (tens of metres in scale), to asymmetric and channelized bedrock-cut scours (tens of cm in scale) and striations (mm scale). Processes responsible for development of subglacial erosional forms occur along a continuum, from free meltwater existing as a laterally extensive sheet at the ice-bed interface, to abrasion by basal ice. Channelized bedrock-cut scours are particularly common in County Donegal, and show asymmetric and meandering thalwegs, U-shaped cross-profiles and steep lateral margins. Innermost parts of the scours are highly polished and have striations that follow thalweg direction. In places, bedrock surfaces are overlain by a delicate polish and thin calcite cement, and are buried beneath glacial till. Based on their morphology, the bedrock scours are interpreted as s-forms caused by high-pressure subglacial meltwater erosion. Striations within the scoured channels reflect periods of ice-bed coupling and subglacial abrasion. The range of features observed here was used to consider relationships between subglacial topography, hydraulic processes and ice-bed coupling. Precipitation of calcite cement took place in depressions on the bedrock surface by CO2 degassing. Infilling of depressions by glacial till formed a new type of 'sticky spot' related to spatial variations in subglacial water pressure. The temporal evolution of sticky spots reflects interactions within the subglacial environment between subglacial relief, hydraulic regime and ice-bed coupling. 相似文献
15.
KENT M. SYVERSON DAVID M. MICKELSON 《Boreas: An International Journal of Quaternary Research》2009,38(1):132-145
Pleistocene lateral meltwater channels are commonly used as evidence of cold-based or polythermal ice. However, lateral meltwater channel formation has been observed for >40 years along the margins of a rapidly thinning temperate glacier in Glacier Bay, Alaska. Flights of nested linear lateral meltwater channels and in-and-out channels have formed on the sides of emerging nunataks. Nested channels at Burroughs Glacier are up to 200 m long; they are good proxies for the slope of the ice margin along the land surface and are terminated by subglacial chutes. A perched water table associated with precipitation and high ablation rates in the temperate ice causes surface meltwater to flow toward the margin above less permeable ice. The water flows along the margin and erodes lateral meltwater channels until a subglacial chute carries the water into the subglacial water system. Rates of channel formation range from 0 to 8 channels/year. Spacing and rates of channel formation are controlled by the land-surface slope, ablation rate, erodibility of the substrate and stream discharge. Because lateral meltwater channels have been observed forming along a temperate glacier margin, care must be exercised when using the presence of lateral meltwater channels as definitive evidence of cold-based or polythermal ice. 相似文献
16.
Emrys Phillips Jonathan R. Lee 《Proceedings of the Geologists' Association. Geologists' Association》2013
The efficiency of subglacial drainage is known to have a profound influence on subglacial deformation and glacier dynamics with, in particular, high meltwater contents and/or pressures aiding glacier motion. The complex sequence of Middle Pleistocene tills and glacial outwash sediments exposed along the north Norfolk coast (Eastern England) were deposited in the ice-marginal zone of the British Ice Sheet and contain widespread evidence for subglacial deformation during repeated phases of ice advance and retreat. During a phase of easterly directed ice advance, the glacial and pre-glacial sequences were pervasively deformed leading to the development of a thick unit of glacitectonic mélange. Although the role of pressurised meltwater has been recognised in facilitating deformation and mélange formation, this paper provides evidence for the subsequent development of a channelised subglacial drainage system beneath this part of the British Ice Sheet filled by a complex assemblage of sands, gravels and mass flow deposits. The channels are relatively undeformed when compared to the host mélange, forming elongate, lenticular to U-shaped, flat-topped bodies (up to 20–30 m thick) located within the upper part of this highly deformed unit. This relatively stable channelised system led to an increase in the efficiency of subglacial drainage from beneath the British Ice Sheet and the collapse of the subglacial shear zone, potentially slowing or even arresting the easterly directed advance of the ice sheet. 相似文献
17.
The general subject of this paper is subglacial deformation beneath Breiðamerkurjökull, a surging Icelandic glacier. More specifically it discusses the evolution and the role of fluid pressure on the behaviour of subglacial sediments during deformation. During Little Ice Age maximum, the two outcrops studied, North Jökulsarlon (N-Jk) and Brennhola-Alda (BA), were located at 2550 m and 550 m respectively from the front of the Breiðamerkurjökull. Sedimentological analysis at the forefield of the glacier shows thick, coarse glaciofluvial deposits interbedded with thin, fine-grained shallow lacustrine/swamp deposits, overlain by a deformed till unit at N-Jk. BA outcrop shows fine-grained shallow lacustrine/swamp deposits overlain by a deformed till unit. The sequence of deformation events from one outcrop to the other is similar. First, major thrust planes, which were rooted in shallow lacustrine/swamp deposits developed by glacially induced simple shear. Next, the thrusts were folded, indicating the deformation of hydroplastic sediment assisted by moderate fluid pressure. Then clastic dyke swarms crosscut the sedimentary succession, proving that fluid overpressure caused hydrofracturing associated with fluidisation. Finally, as water escaped from the glacier bed, fluid pressure dropped, and normal faulting occurred in brittle-state subglacial sediments. Fluid-pressure variations are related to glacier dynamics. They control the deformation sequence by modifying subglacial rheological behaviour and the nature of the subglacial tectonism. 相似文献