昆仑山垭口地区"望昆冰期"冰碛宇宙成因核素10Be测年   总被引：4，自引：2，他引：2  

陈艺鑫  李英奎  张梅  张敬春  刘耕年 《冰川冻土》2011,33(1):101-109

昆仑山垭口地区是东昆仑山现代冰川作用中心之一,在第四纪冰期间冰期旋回中保留了多套较为完整的冰川沉积.位于垭口盆地西侧山脊上的望昆冰碛,是本区已知最老的冰川沉积.应用宇宙成因核素10Be暴露年龄方法对望昆冰碛进行年代测定,5个样品中有4个介于(56.9±5.6)～(38.2±3.5)ka BP之间,相当于MIS3阶段,明显年轻于前人所测ESR和古地磁年代,且与地貌系列不符.这一结果不能代表望昆冰碛的实际年代,而应为所测漂砾后期暴露的年代,反映了MIS3阶段昆仑山垭口地区曾遭受过强烈地表剥蚀过程.望昆冰碛10Be暴露年龄显著地年轻,表明应用宇宙核素暴露年代测定冰碛物形成时代具有复杂性,应充分考虑后期剥蚀等地表过程,并应使用其他测年方法进行相互验证.  相似文献   

Systems Theory in Physical Geography     

Arthur N. Strahler 《自然地理学》2013,34(1):1-27

Information used in systems is organized into a hierarchy of five levels, following W. H. Terjung; first, collected data; second, sets of morphological variables; third, flow systems of energy and matter; fourth, process-form systems; fifth, systems regulated by cybernetic feedback. System variables, rigorously defined by dimensional analysis, are grouped into four classes: A. dynamic variables related to energy force, and stress; B. mass-flow variables expressing rates of flow of matter; C. geometry variables describing size and form within systems; D. material-property variables, including environmental constants and regulator variables. The second level of systems analysis interrelates a set of morphological elements in a meaningful way in terms of system origin or function. Correlation and regression methods establish significant relationships among variables, which may be stated as empirical or rational equations based on field or laboratory observations. Open energy flow systems and open or closed material flow systems of the third level can be described by dimensionally correct equations or by schematic flow diagrams. Process-form systems of the fourth level are characterized by self-regulation through physical feedback loops. Cybernetic feedback characterizes the fifth level and links natural systems to those regulated or disturbed by human intervention.  相似文献   

Till fabric and grain-size analysis of glacial sequences in the Upper Sil River Basin,Cantabrian Mountains,NW Spain     

Javier Santos-González  João A. Santos  Rosa Blanca González-Gutiérrez  José María Redondo-Vega  Amelia Gómez-Villar 《自然地理学》2013,34(6):471-490

Fabric and grain-size analysis of eight deposits present in the Upper Sil River Basin palaeoglacial system of northwest Spain were used to interpret till types and to reconstruct the glacial paleoprocess history of this region. They are represented by lodgement, deformation, and melt-out tills. The first, representative of glacial advance stages, present cluster fabrics and are generally composed of poorly sorted and finer sediments. Melt-out and deformation tills, representative of stages of glacial stability followed by fast recession, present transitional to girdle fabrics and are composed of poorly sorted coarser sediments. In any case, multiple criteria, including lithological, clast-shape, or structural data, support these directional and grain-size observations. These sequences, most of them located in the snout area of the Sil palaeoglacier, are important in the reconstruction of glacial dynamics due to poor preservation of landforms related to the maximum glacial advance. This palaeoglacial system was formed by multiple tributaries and had an extension of over 450 km², with the Sil paleoglacier being 51 km long during its maximum glacial advance.  相似文献   

辽北震旦系殷屯组层位归属及其区域对比问题探讨     

曲洪祥  刘杰  郝明  曲若达  李红梅  李升东  全秀杰 《地质与资源》2013,22(4):296-298

辽北殷屯组分布于铁岭大甸子盆地西部,角度不整合于长城-蓟县系不同层位之上.该组以发育冰碛砾岩为其特征,相当于“南沱冰期”形成的产物,其岩性组合基本可以与鄂西峡东地区南华系南沱组对比.本文将殷屯组时代置于南华纪.  相似文献   

Sediment mobility and bed armoring in the St Clair River: insights from hydrodynamic modeling     

Xiaofeng Liu  Gary Parker  Jonathan A. Czuba  Kevin Oberg  Jose M. Mier  James L. Best  Daniel R. Parsons  Peter Ashmore  Bommanna G. Krishnappan  Marcelo H. Garcia 《地球表面变化过程与地形》2012,37(9):957-970

The lake levels in Lake Michigan‐Huron have recently fallen to near historical lows, as has the elevation difference between Lake Michigan‐Huron compared to Lake Erie. This decline in lake levels has the potential to cause detrimental impacts on the lake ecosystems, together with social and economic impacts on communities in the entire Great Lakes region. Results from past work suggest that morphological changes in the St Clair River, which is the only natural outlet for Lake Michigan‐Huron, could be an appreciable factor in the recent trends of lake level decline. A key research question is whether bed erosion within the river has caused an increase in water conveyance, therefore, contributed to the falling lake level. In this paper, a numerical modeling approach with field data is used to investigate the possibility of sediment movement in the St Clair River and assess the likelihood of morphological change under the current flow regime. A two‐dimensional numerical model was used to study flow structure, bed shear stress, and sediment mobility/armoring over a range of flow discharges. Boundary conditions for the numerical model were provided by detailed field measurements that included high‐resolution bathymetry and three‐dimensional flow velocities. The results indicate that, without considering other effects, under the current range of flow conditions, the shear stresses produced by the river flow are too low to transport most of the coarse bed sediment within the reach and are too low to cause substantial bed erosion or bed scour. However, the detailed maps of the bed show mobile bedforms in the upper St Clair River that are indicative of sediment transport. Relatively high shear stresses near a constriction at the upstream end of the river and at channel bends could cause local scour and deposition. Ship‐induced propeller wake erosion also is a likely cause of sediment movement in the entire reach. Other factors that may promote sediment movement, such as ice cover and dredging in the lower river, require further investigation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

青藏高原东缘山地古冰川沉积物磁化率特点及其影响因素分析   总被引：1，自引：1，他引：0  

张威  李媛媛  冯骥  毕伟力  刘鸽 《地理科学进展》2012,31(11):1415-1425

湖泊、黄土与古土壤、深海沉积物等连续沉积体的磁化率变化作为环境变化的替代性指标被广泛应用,然而对于非连续、能够反映特定时段气候变化的沉积体,如冰川沉积物的磁化率却较少涉及.本文通过对青藏高原东缘8 个典型冰川发育山地冰碛物磁化率进行研究,并与黄土、湖泊、深海沉积物以及不同区域的表土磁化率进行对比,采用质量磁化率和频率磁化率探讨冰碛物的磁化率特点及其影响因素.结果表明：青藏高原东缘山地的冰碛物质量磁化率呈宽幅波动,介于(3.01~1808.80)×10^-8 m³·kg^-1,平均值147.84×10^-8 m³·kg^-1;频率磁化率值较低、且波动幅度小,介于0~6.89%,平均值为1.37%.不同时空条件下冰碛物的磁化率特点不同,即不同地点同一冰期磁化率的差异显著;同一地点不同冰期冰碛物的磁化率变化不明显.影响冰碛物磁化率的主导因素是母岩的岩性条件,气候因素起次要作用.  相似文献   

EARLY PLIOCENE EXPANSION OF THE EAST ANTARCTIC ICE SHEET, UPPER WRIGHT VALLEY, ANTARCTICA     

JAMES BOCKHEIM  MALCOLM MCLEOD 《Geografiska Annaler: Series A, Physical Geography》2008,90(3):187-199

Whereas the glacial geomorphology of lower and central Wright Valley is reasonably well understood, the upper valley region, including the North and South Forks and the Dais, has received little attention. Our studies suggest that a wet-based glacier overrode the area and deposited what has been mapped elsewhere as the Peleus till. While we did not observe this silt-rich till in the Labyrinth, it occurs on the Dais and in protected areas of the North and South Forks. Most importantly, our findings imply that the Wright Upper Glacier, an outlet glacier of the East Antarctic Ice Sheet, deposited lateral moraines and lateral-moraine segments along the north and south walls of both the North and South Forks following deposition of the Peleus till. We argue that this drift is correlative with Taylor IVa drift in central Taylor Valley and Alpine III drift in central Wright Valley, based on landscape features, surface-boulder weathering, soil development, and stratigraphy. The presence of meltwater channels, outwash, kame moraines, esker-like features, and kames suggests that ice-marginal or supraglacial water may have accompanied this glaciation.  相似文献   

冰内岩屑和新冰碛细粒组分的若干特征     

周尚哲 《冰川冻土》1991,13(1):43-50

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Till deposition by glacier submarginal,incremental thickening   总被引：1，自引：0，他引：1  

David J. A. Evans  John F. Hiemstra 《地球表面变化过程与地形》2005,30(13):1633-1662

Macro‐ and micro‐scale sedimentological analyses of recently deposited tills and complex push/squeeze moraines on the forelands of Icelandic glaciers and in a stacked till sequence at the former Younger Dryas margin of the Loch Lomond glacier lobe in Scotland are used to assess the depositional processes involved in glacier submarginal emplacement of sediment. Where subglacial meltwater is unable to flush out subglacial sediment or construct thick debris‐rich basal ice by cumulative freeze‐on processes, glacier submarginal processes are dictated by seasonal cycles of refreezing and melt‐out of tills advected from up‐ice by a combination of lodgement, deformation and ice keel and clast ploughing. Although individual till layers may display typical A and B horizon deformation characteristics, the spatially and temporally variable mosaic of subglacial processes will overprint sedimentary and structural signatures on till sequences to the extent that they would be almost impossible to classify genetically in the ancient sediment record. At the macro‐scale, Icelandic tills display moderately strong clast fabrics that conform to the ice flow directions documented by surface flutings; very strong fabrics typify unequivocally lodged clasts. Despite previous interpretations of these tills as subglacial deforming layers, micro‐morphological analysis reveals that shearing played only a partial role in the emplacement of till matrixes, and water escape and sediment flowage features are widespread. A model of submarginal incremental thickening is presented as an explanation of these data, involving till slab emplacement over several seasonal cycles. Each cycle involves: (1) late summer subglacial lodgement, bedrock and sediment plucking, subglacial deformation and ice keel ploughing; (2) early winter freeze‐on of subglacial sediment to the thin outer snout; (3) late winter readvance and failure along a decollement plane within the till, resulting in the carriage of till onto the proximal side of the previous year's push moraine; (4) early summer melt‐out of the till slab, initiating porewater migration, water escape and sediment flow and extrusion. Repeated reworking of the thin end of submarginal till wedges produces overprinted strain signatures and clast pavements. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Characterisation of glacial sediments using geophysical methods for groundwater source protection     

Matthew Kilner  L. Jared West  Tavi Murray 《Journal of Applied Geophysics》2005,57(4):43

A sequence of glacial and alluvial deposits overlying the Cretaceous Chalk in Eastern England was characterised using two geophysical techniques: electrical resistivity imaging and electromagnetic (EM) induction. Extensive geological data were available from trenching and boreholes. Synthetic modelling of the electrical resistivity imaging technique was undertaken to identify its limitations and to optimise survey design. The EM induction method provided a quick and cost-effective reconnaissance technique for identifying large-scale lateral variation in lithology, and for siting resistivity profiles and further boreholes. The resistivity imaging technique provided detailed information on the vertical continuity of permeable units, and was able to identify permeable pathways through the sequence. Certain limitations in detecting thin sand or gravel layers underlying electrically conductive clay were seen in both the synthetic and field data. Nevertheless, the study shows that knowledge of these limitations allows interpretation for the purpose of groundwater vulnerability assessment, given that an appropriate amount of invasive investigation has been conducted.  相似文献