CHANGES IN ICE-MARGIN PROCESSES AND SEDIMENT ROUTING DURING ICE-SHEET ADVANCE ACROSS A MARGINAL MORAINE     

PETER G. KNIGHT  CARRIE E. JENNINGS  RICHARD I. WALLER  ZOE P. ROBINSON 《Geografiska Annaler: Series A, Physical Geography》2007,89(3):203-215

Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice‐marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice‐proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris‐rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations.  相似文献   

Glacial geomorphology of Teesdale,northern Pennines,England: Implications for upland styles of ice stream operation and deglaciation in the British-Irish Ice Sheet     

David J.A. Evans  Matthew Dinnage  David H. Roberts 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(6):697-735

The glacial geomorphology of Teesdale and the North Pennines uplands is analysed in order to decipher: a) the operation of easterly flowing palaeo-ice streams in the British-Irish Ice Sheet; and b) the style of regional deglaciation. Six landform categories are: i) bedrock controlled features, including glacitectonic bedrock megablocks or ‘rubble moraine’; ii) discrete mounds and hills, often of unknown composition, interpreted as weakly streamlined moraines and potential ‘rubble moraine’; iii) non-streamlined drift mounds and ridges, representing lateral, frontal and inter-ice stream/interlobate moraines; iv) streamlined landforms, including drumlins of various elongation ratios and bedrock controlled lineations; v) glacifluvial outwash and depositional ridges; and vi) relict channels and valleys, related to glacial meltwater incision or meltwater re-occupation of preglacial fluvial features. Multiple tills in valley-floor drumlin exposures indicate that the subglacial bedform record is a blend of flow directions typical of areas of discontinuous till cover and extensive bedrock erosional landforms. Arcuate assemblages of partially streamlined drift mounds are likely to be glacially overridden latero-frontal moraines related to phases of “average glacial conditions” (palimpsests). Deglacial oscillations of a glacier lobe in mid-Teesdale are marked by five inset assemblages of moraines and associated drift and meltwater channels, named the Glacial Lake Eggleshope, Mill Hill, Gueswick, Hayberries and Lonton stages. The Lonton stage moraines are thought to be coeval with bedrock-cored moraines in the central Stainmore Gap and likely record the temporary development of cold-based or polythermal ice conditions around the margins of a plateau-based icefield during the Scottish Readvance.  相似文献   

Fractal and Multifractal Properties of Geochemical Fields   总被引：12，自引：0，他引：12  

Shuyun Xie  Zhengyu Bao 《Mathematical Geology》2004,36(7):847-864

A fractal model, introduced by De Wijs to study the distribution, redistribution, or enrichment/depletion of element concentrations in a region, has become widely accepted. This paper uses it to simulate various geochemical fields for element concentration values. The frequency distribution and spatial pattern of the simulated values or concentrations are analyzed by the method of moments and the concentration–area (C–A) model. The spatial pattern of the original De Wijs model is shown to be intrinsically characterized by -shaped and symmetrical multifractal spectrum curves, whose center and width change systematically with the enrichment factors set in the simulation. The corresponding frequency distribution pattern on the log–log plot of frequency versus concentrations is called simple continuous multifractal (SCM) by the authors. In other experiments, when a De Wijs model is locally superimposed by another De Wijs model of different enrichment factors, the symmetry of the multifractal spectrum graph is broken and a different pattern of frequency distribution is found. It is referred to as highly accumulated continuous multifractals (HACM). Concentrations of 12 elements in 1448 rock samples from Shaoguan district, North Guangdong Province, South China, and 12 oil/gas indexes in surface soils from Sangtamu region, Tarim Basin, Northwest China, have been applied. The real geochemical fields, both metallic and oil/gas, are found to be remarkably compatible to those simulated patterns of De Wijs models with backgrounds of various enrichment and different degrees of superimposition, indicating that the frequency and spatial distribution patterns revealed by the authors are most possibly universal features of geochemical fields. It is particularly interesting to note that the major geochemical indicators of oil/gas geochemical fields are closer to the results of De Wijs models with a small enrichment factor, either with or without local superimposition, whereas those of the metallic geochemical field correspond more closely to De Wijs models with a background field of larger enrichment factors. The results obtained herein potentially have important implications in mineral and oil/gas resource assessment.  相似文献   

帕米尔东北部木吉断层晚第四纪运动性质和滑动速率的约束     

邓金花  韩非  李涛  张博譞  许建红  姚远 《第四纪研究》2020,(1):114-123

帕米尔造山带是印度-欧亚大陆会聚带的西构造结。木吉断层作为中-西帕米尔与东帕米尔的最北部边界转换断层,其运动性质和滑动速率的准确限定对于理解帕米尔现今应力状态和运动学特征等具有重要意义。本文以木吉断层东段布拉克村北位错特征显著的冰碛台地(39.2020°N,74.3910°E)为研究对象,基于高分辨率卫星影像解译、野外地质地貌调查、差分GPS测量和冰川漂砾宇宙成因核素10Be暴露测年,获得布拉克北冰碛台地形成(16.8±3.5 ka)以来木吉断层的累积右旋位错量、垂直位错量、南北向拉张量以及最小速率分别为约190 m、105±12 m、34±12 m和11.3±2.4 mm/a、6.3±1.5 mm/a、2.0±0.8 mm/a;三者的比值约为6:3:1,水平向的总滑动速率为11.5±2.3 mm/a。与位于断层中部近乎纯走滑的阿克萨依处相比,木吉断层在布拉克北以右旋走滑为主的同时,具有明显的正断分量。断层在布拉克北的水平向总滑动速率11.5±2.3 mm/a与阿克萨依处右旋走滑速率的最大值(9.4±0.9 mm/a)大致相当;因此尽管断层沿走向的运动性质发生了显著变化,其水平向滑动速率大致保持恒定。  相似文献   

西藏终碛湖溃决形式研究   总被引：1，自引：0，他引：1       下载免费PDF全文

刘晶晶  程尊兰李泳 罗曦 《地学前缘》2009,16(4):372-380

西藏终碛湖众多,一旦发生溃决,将造成巨大损失。冰湖溃决机制的研究对冰湖溃决预测和溃后灾害评估是十分必要的。将冰湖终碛堤视为天然堆石坝,用水力学和土力学理论研究冰湖溃决的力学机制。重点研究溢流型溃决形式和管涌型溃决形式,根据野外观测数据和前人的研究,发现溢流型溃决的溃口多呈梯形或圆弧状形,对比真实数据发现溃口顶宽与坝高的关系,并且所有冰川终碛堤都表现为局部溃决。通过实地考察、取样分析,判断光谢措终碛堤的可能渗透破坏形式。  相似文献   

Exact solution for horizontal displacement at center of the surface of an elastic half space under horizontal impulsive punch loading     

Bo Jin  Hua Liu 《Soil Dynamics and Earthquake Engineering》1999,18(7):1198

The exact analytical solution for the horizontal displacement at the center of the surface of an elastic half space under an impulsive loading having the same spatial distribution as the contact stresses that arise underneath a rigid disk when subjected to a static, horizontal load, is obtained using the Cagniard–De Hoop method. The solution can be used to study the dynamical interaction between soil and structures, and can also be used to assess numerical computations with a finite element or a boundary element program.  相似文献   

Occurrence,evolution and ice content of ice-debris complexes in the Ak-Shiirak,Central Tien Shan revealed by geophysical and remotely-sensed investigations     

T. Bolch  N. Rohrbach  S. Kutuzov  B.A. Robson  A. Osmonov 《地球表面变化过程与地形》2019,44(1):129-143

Rock glaciers and large ice-debris complexes are common in many mountain ranges and are especially prominent in semi-arid mountains such as the Andes or the Tien Shan. These features contain a significant amount of ice but their occurrence and evolution are not well known. Here, we present an inventory of the ice-debris complexes for the Ak-Shiirak, Tien Shan's second largest glacierised massif, and a holistic methodology to investigate two characteristic and large ice-debris complexes in detail based on field investigations and remote sensing analysis using Sentinel-1 SAR data, 1964 Corona and recent high resolution stereo images. Overall, we found 74 rock glaciers and ice-debris complexes covering an area of 11.2 km² (3.2% of the glacier coverage) with a mean elevation of about 3950 m asl. Most of the complexes are located south-east of the main ridge of Ak-Shiirak. Ground penetrating radar (GPR) measurements reveal high ice content with the occurrence of massif debris-covered dead-ice bodies in the parts within the Little Ice Age glacier extent. These parts showed significant surface lowering, in some places exceeding 20 m between 1964 and 2015. The periglacial parts are characterised by complex rock glaciers of different ages. These rock glaciers could be remnants of debris-covered ice located in permafrost conditions. They show stable surface elevations with no or only very low surface movement. However, the characteristics of the fronts of most rock glacier parts indicate slight activity and elevation gains at the fronts slight advances. GPR data indicated less ice content and slanting layers which coincide with the ridges and furrows and could mainly be formed by glacier advances under permafrost conditions. Overall, the ice content is decreasing from the upper to the lower part of the ice-debris complexes. Hence, these complexes, and especially the glacier-affected parts, should be considered when assessing the hydrological impacts of climate change. © 2018 John Wiley & Sons, Ltd.  相似文献   

Outburst mechanism of Yindapu Glacial Lake in Tibet     

ZHUANG Shuyu  LI Guangjie  CHEN Guoyu  SHU Youfeng College of Construction Engineering  Jilin University  Changchun  China 《东北亚地学研究》2009,(4):200-203

At present, the mechanism research on glacial lake outburst mainly focuses on the ice quake and ice landslide, etc. To some glacial lakes, the seepage deformation is the dominant factor in outburst process. Taking the Yindapu Glacial Lake in Tibet as an example, using SEEP/W module of FEM software （ GEO-STUDIO）, the authors analyzed seepage stability of terminal moraine ridge dam. The leading role of seepage deformation in some glacial lake outburst mechanism is proposed and proved.  相似文献   

Late Quaternary glaciations and cosmogenic 36Cl geochronology of Mount Dedegöl,south‐west Turkey     

Ouzhan Kse  M. Ak&#x;f Sar&#x;kaya  Att&#x;la &#x;ner  Adem Canda 《第四纪科学杂志》2019,34(1):51-63

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Capture of comets from the Oort cloud into Halley-type and Jupiter-family orbits     

E. E. Biryukov 《Solar System Research》2007,41(3):211-219

This paper analyzes the capture of comets into Halley-type and Jupiter-family orbits from the nearparabolic flux of the Oort cloud. Two types of capture into Halley-type orbits are found. The first type is the evolution of near-parabolic orbits into short-period orbits (with heliocentric orbital periods P < 200 years) as a result of close encounters with giant planets. This process is followed by a very slow drift of cometary orbits into the inner part of the Solar System. Only those comets may pass from short-period orbits into Halley-type and Jupiter-family orbits, which move in orbits with perihelion distances q < 13 au. In the second type of capture, the perihelion distances of cometary orbits become rather small (< 1.5 au) during the first stage of dynamic evolution under the action of perturbations from the Galaxy, and then their semimajor axes decrease as a result of diffusion. The capture takes place, on average, in 500 revolutions of the comet about the Sun, whereas in the first case, the comet is captured, on average, after 12500 revolutions. The region of initial orbital perihelion distances q > 4 au is found to be at least as important a source of Halley-type comets as the region of perihelion distances q < 4 au. More than half of the Halley-type comets are captured from the nearly parabolic flux with q > 4 au. The analysis of the dynamic evolution of objects moving in short-period orbits shows that the distribution of Centaurs orbits agrees well with the observed distribution corrected for observational selection effects. Hence, the hypothesis associating the origin of Centaurs with the Edgeworth-Kuiper belt and the trans-Neptunian region exclusively should be rejected.  相似文献