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1.
Quaternary glacial stratigraphy and relative sea-level changes reveal at least two glacial expansions over the Chelyuskin Peninsula, bordering the Kara Sea at about 77°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences mapped to altitudes of at least up to ca. 80 m a.s.l. Chronological control is provided by accelerator mass spectrometry 14C dating, electron-spin resonance and optically stimulated luminescence geochronology. Major glaciations, followed by deglaciation and marine inundation, occurred during marine oxygen isotope stages 6–5e (MIS 6–5e) and stages MIS 5d–5c. These glacial sediments overlie marine sediments of Pliocene age, which are draped by fluvial sediment of a pre-Saalian age, thereby forming palaeovalley/basin fills in the post-Cretaceous topography. Till fabrics and glacial tectonics record expansions of local ice caps exclusively, suggesting wet-based ice cap advance, followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains and the Severnaya Zemlya archipelago, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with the exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice neither impacted the Chelyuskin Peninsula nor Severnaya Zemlya, and barely touched the northern coastal areas of the Taymyr Peninsula.  相似文献   

2.
天山阿特奥依纳克河流域冰川沉积序列   总被引：1，自引：0，他引：1  
阿特奥依纳克河位于我国天山的最西段,最大现代冰川作用中心托木尔峰的南麓。在第四纪冰期与间冰期的气候旋回中,该处留下了形态较为完整的6套冰川沉积。应用ESR测年技术 (辅以OSL测年技术) 对冰碛物及其相应的冰水沉积物进行了定年,测得6套冰碛年龄分别为7.3±0.8ka BP (OSL,冰水沙);12.3±1.2ka BP (OSL) 与15~29ka BP;46~54ka BP;56~65ka BP;155.8±15.6ka BP与234.8±23.5ka BP;453.0±45.3ka BP,测年结果表明它们分别形成于新冰期、海洋同位素阶段(MIS)2、3b、4、6、12。第三套冰碛测年结果表明该处MIS3b冰进规模较大,其规模基本上与末次盛冰期 (MIS2) 的规模相当。此处最老冰碛测年结果与我国中段天山乌鲁木齐河源高望峰冰碛的测年结果 (459.7±46ka BP与477.1ka BP) 遥相呼应,老冰碛的年龄显示我国天山西段与中段至少于MIS12进入了冰冻圈,开始发育冰川。  相似文献   

3.
Interpreting past glacial dynamics from the glacial record requires that the depositional environments of glacial sediments and landforms be understood. In the case of interlobate deposits, models that incorporate various components of pro, supra and subglacial deposition have been developed and tested in the northern Kettle Moraine (nKM), Wisconsin; a large interlobate deposit that formed between the Green Bay and Lake Michigan lobes of the Laurentide Ice Sheet during the last deglaciation. In this paper, we interpret a new genesis for the nKM using sediment analysis and distribution along with landform distribution. In Sheboygan County, the nKM consists of two steep-sided, high-relief, hummocky ridges separated by a low elevation and low-relief central axis. Gravel in the bounding hummocky ridges is well-sorted and well-rounded. Some bedding is collapsed. Large, isolated moulin kames are restricted to the axis area and composed of relatively poorly sorted, more angular gravel and diamicton. The distribution of these different sediments and landforms are explained by the accumulation of supraglacial debris that insulated the ice below the axis of the nKM, while the melting of cleaner ice on either side formed channels on the ice surface. As deglaciation proceeded, a substantial thickness of well-rounded, stream-deposited sand and gravel accumulated on ice in the bounding channels. Eventual collapse of this sediment formed the two hummocky ridges. Poorly sorted debris along the axis fell and slid into moulins and larger collapse areas in the ice. Thus, differential debris insulation and ice ablation controlled the mainly supraglacial deposition of this part of the nKM.  相似文献   

4.
中国东部沙区表层沉积物粒度特征   总被引：4，自引：4，他引：0  
通过分析中国东部沙区表层沉积物粒度特征及其与风力、植被覆盖的相关性,探讨了东部沙区现代风沙沉积环境及其区域差异性。结果显示:东部沙区各沙漠/沙地粒径级配相对一致,均以细沙、中沙为主,粒度分布整体呈单峰形态,中等分选,粒度分布和分选性均与西部沙区有较大不同。风力和植被覆盖状况的差异决定了各沙地所处的风沙环境性质和风沙活动强度不同,导致东部沙区表层沉积物粒度特征存在明显的区域差异性。其中,库布齐沙漠粒度特征与该区风蚀、搬运、堆积过程频繁交替的风沙活动方式密切关联;呼伦贝尔沙地粒度特征反映了风蚀主导的风沙环境;科尔沁沙地、浑善达克沙地,毛乌素沙地粒度特征和风沙活动方式相对复杂,与这3个沙地内部风蚀主导区和沙尘沉降主导区镶嵌分布的格局有关。东部沙区表层沉积物平均粒径和分选系数均与沙地年均风速和植被总盖度双因素之间具有显著的非线性相关性。  相似文献   

5.
Above the marine limit in Gangdalen, Nordenskiold Land, a 20 m thick sequence of unconsolidated sediments occurs. On the top of striated bedrock it is composed of a 2m thick till bed, 15m gravel interpreted to be deposited as a sandur, and another till bed on the top. A solifluction deposit is capping the section. Fabric analyses and erratics in the two tills indicate a similar development in glacial transport directions during the two glaciations, starting with a local glaciation which subsequently turns into a larger glaciation centred over the eastern part of Svalbard. Co-existence of different ice domes over Spitsbergen is suggested. The sandur was deposited during an ice free period with a sea-level 40–80 m higher than at present. The section is undated.  相似文献   

6.
During the late Wisconsin, glacial flour from alpine glaciers along the east side of the Cascade Range in southern Oregon was deposited in Upper Klamath Lake. Quantitative interpretation of magnetic properties and grain-size data of cored sediments from Caledonia Marsh on the west side of the lake provides a continuous record of the flux of glacial flour spanning the last 37 000 calendar years. For modeling purposes, the lake sediments from the 13-m core were divided into three sedimentary components defined from magnetic, geochemical, petrographic, and grain-size data. The components are (1) strongly magnetic, glacial flour made up of extremely fine-grained, fresh volcanic rock particles, (2) less magnetic lithic material made up of coarser, weathered volcanic detritus, and (3) non-magnetic biogenic material (largely biogenic silica). Quantitative interpretation is possible because there has been no significant postdepositional destruction or formation of magnetic minerals, nor alteration affecting grain-size distributions. Major steps involved in the interpretation include: (1) computation of biogenic and lithic components; (2) determination of magnetic properties and grain-size distributions of the non-glacial and glacial flour end-members; (3) computation of the contents of weathered and glacial flour components for each sample; (4) development of an age model based on the mass accumulation of the non-glacial lithic component; and (5) use of the age model and glacial flour contents to compute the flux of glacial flour. Comparison of the glacial flour record from Upper Klamath Lake to mapped glacial features suggests a nearly linear relation between flux of glacial flour and the extent of nearby glaciers. At 22 ka, following an extended period during which glaciers of limited size waxed and waned, late Wisconsin (Waban) glaciers began to grow, reaching their maximum extent at 19 ka. Glaciers remained near their maximum extent for 1000 years. During this period, lake sediments were made up of 80% glacial flour. The content of glacial flour decreased as the glaciers receded, and reached undetectable levels by 14 ka.  相似文献   

7.
The sedimentological characteristics of in situ and paraglacially reworked till are compared at recently deglaciated sites in Norway. Glacigenic deposits reworked by debris flows are shown to retain many of the characteristics of the parent sediments, and cannot readily be distinguished from in situ till in terms of fabric strength or type, clast imbrication, shape, angularity or texture, matrix granulometry or packing. Paraglacially re-worked sediments appear to differ from in situ tills only in terms of preferred clast orientation (down flow rather than downvalley) and their structural and lithofacies characteristics. These criteria are employed to differentiate paraglacial sediments from unre-worked tills exposed in valley-side sections. The stratigraphic relations between these indicate glacial reworking of earlier paraglacial sediments as well as paraglacial remobilisation of glacigenic deposits, indicating cyclic alternation of glacial and paraglacial sediment transport.  相似文献   

8.
Terrace remnants close to the marine limit as well as two separate moraine ridges are observed in front of the glacier Albrechtbreen. The stacking of marine sediments from an original elevation of ca. 60–80 m a.s.l. into the Little Ice Age Moraine gives evidence for a considerably smaller glacier following the early Holocene deglaciation compared to that of the present. The outer moraine is composed of glacial diamicton. Radiocarbon datings of whale ribs, shell fragments and a log taken from sediment in front of Albrechtbreen indicate that the initial deglaciation occurred before 9, 400 B.P. and that the outer moraine was formed during a younger Holocene glacial advance. Lithological differences between the two moraine ridges suggest that the first ice advance occurred during a period with limited permafrost, whereas permafrost was more extensive during the Little Ice Age.  相似文献   

9.
本文利用电镜扫描方法 (SEM)对比分析了南极乔治王岛无冰区海滩沉积、冰碛物以及阿德雷岛湖泊沉积等典型沉积环境中的石英砂表面结构特征 ,得出了乔治王岛各典型沉积环境中石英砂表面结构特征的颗粒频率曲线。结果表明 :不同沉积环境下的石英砂颗粒表面结构特征具有相似性 ,这主要和南极地区广泛发育的冰川作用有关 ,同时 ,它们也有各自典型的特征组合 ,这些典型特征组合的不同反映了石英砂后期的搬运历史和沉积环境的差异。本文还依据石英砂表面特征的颗粒出现频率 ,利用聚类分析方法对研究区内三级海岸阶地上的沉积物和一个未知成因的样品进行了沉积环境的判别分析 ,结果证明石英砂微形貌特征可以作为南极地区沉积环境识别的有效手段  相似文献   

10.
巢湖沉积物粒度特征及其沉积学意义   总被引：1，自引：0，他引：1  
徐利强  徐芳  周涛发 《地理科学》2015,35(10):1318-1324
对采自西巢湖湖心的一根长为143 cm的沉积柱进行了粒度分析,重建了粒度组成的演变过程。湖心沉积物主要为粉砂和黏土,粒度参数（平均粒径、标准偏差、偏度、尖度、分维值）分析表明沉积物分选程度较好,均为正偏态,峰态为很窄到非常窄,且具有一定的分形特征。C-M图解和概率累积曲线揭示了较弱的水动力环境,颗粒的搬运方式主要为跃移和悬移,比例分别约为70%和25%~30%。结合因子分析,识别出第一主因子（PC1）对细粒物质含量存在显著影响,其值反映了碎屑物质在湖泊中的搬运距离,PC1因子与平均粒径Mz可作为巢湖湖泊水位的替代性指标。  相似文献   

11.
The scientific study of quartz grains is a powerful tool in deciphering the depositional environment and mode of transportation of sediments, and ultimately the origin and classification of sediments. Surface microfeatures, angularity, chemical features, and grain-size analysis of quartz grains, collectively reveal the sedimentary and physicochemical processes that acted on the grains during different stages of their geological history. Here, we apply scanning electron microscopic (SEM) analysis to evaluating the sedimentary provenance, modes of transport, weathering characteristics, alteration, and sedimentary environment of selected detrital quartz grains from the peripheral part of two epi-shelf lakes (ESL-1 and ESL-2) of the Schirmacher Oasis of East Antarctica. Our study reveals that different styles of physical weathering, erosive signatures, and chemical precipitation variably affected these quartz grains before final deposition as lake sediments. Statistical analysis (central tendencies, sorting, skewness, and kurtosis) indicates that these quartz-bearing sediments are poorly sorted glaciofluvial sediments. Saltation and suspension seem to have been the two dominant modes of transportation, and chemical analysis of these sediments indicates a gneissic provenance.  相似文献   

12.
Based on grain-size analysis of sediment samples from a delta at Altermarka, it has previously been suggested that two tills were deposited on the delta surface as a glacier planed off the delta topsets and created its adverse surface slope. In this reinvestigation of the delta, there was no evidence that a glacier overrode the surface: the topset beds remain intact and no appreciable till was found. Sediments resembling the ‘till’ samples were located, but soil processes and other sedimentary processes easily account for the wide grain-size distributions of these sediments. As a result, this study cautions against using grain-size analysis, on its own, to interpret the genesis of sediments. Other processes potentially responsible for the adverse surface slope include differential isostatic rebound, recent differential slip along ancient thrust faults, and failure of the delta surface to reach sea level. Based on the sedimentology of the topset beds and the local relative sea level history (indicating the delta (9495±70 14C yr BP) formed about the time of the local marine limit (9560–9375 14C yr BP) 17 m higher than the delta surface), the feature is determined to have built up below sea level with an adverse surface slope.  相似文献   

13.
云南东北部拱王山末次冰期   总被引：1，自引：0，他引：1  
1 Introduction The Gongwang mountains constitute one of the few high m ountains of irrefutable late Pleistocene glaciation in eastern China. This area is one of the m ost extensively studied Quaternary geologicallocationsin eastern China and the interpret…  相似文献   

14.
Late Pleistocene glaciation was restricted to only a few high mountains in eastern China. The Gongwang mountains constitute one of the typical places once glaciated. Geomorphic mapping of the area and the TL dating provides evidence for at least four distinct glaciations. YJT-I glacial advance occurred about 100 ka BP and two TL absolute ages (101,100 ±7780 a BP; 104,000±8300 a BP) indicate this advance happened during the Penultimale Glaciation. The early stage glacial advance (YJT-II advance) during the last glaciation occurred about 40,920±3400 a BP. The last glacial maximum advance (YJT-III advance) about 18-25 ka BP, which sustained by two TL ages (18,230 ±1420 a BP; 25,420 ±2110 a BP). The Penultimale and the early stage glaciations were more extensive and the last glacial maximum (LGM) and the late-glacial period (YJT-IV advance, 10 ka BP) were progressively less extensive. Correlated with the other mountains in eastern China, these glacial advances in the Gongwang mountains just like the advances in the western part such as Diancang mountains, Yulong mountains of Yunnan Province and the glacier series are more complete than the adjacent mid-latitude regions such as Taibai mountain and Taiwan mountains and are roughly representative of climate changes during the last glacial cycle in Yunnan Province.  相似文献   

15.
On western Kongsøya, Svalbard, three coarsening-upwards sequences of marine to littoral sediments, separated by tills, are recognised in sections at ca 50-92 m above present sea level. These sequences show major glaciations in the northern Barents Sea, resulting in substantial glacioisostatic downpressing of Kongsøya. Till fabrics indicate ice movements controlled by the local topography, while glaciotectonic deformations suggest that ice moved from an ice divide northeast of Kongsøya. independent of the local topography. The stratigraphical evidences show two pre-Holocene ice-free periods, when the climate was similar to or slightly warmer than at present. The age of these periods is not clear. It is suggested that the elder ice free interval is older than isotope stage 5e. The younger ice free interval could be of Eemian or Early Weichselian age. The uppermost succession of sublittoral-littoral sediments is of early Holocene age. It relates to the high (≥100 m) postglacial marine limit, dated to approximately 10,000 bp.  相似文献   

16.
Interpretation of sediments in the floors of valleys opening into western McMurdo Sound has been so problematic that it has hindered understanding of the late Quaternary history of the Antarctic Ice Sheet. Lateral moraines and enclosed drift sheets so clearly exposed on the headlands are generally absent within the valleys themselves. Instead, valley-floor sediments and landforms consist of hummocky, stratified fine sediment generally capped by coarser, poorly sorted material, small cross-valley and longitudinal ridges, and lateral ridges that superficially resemble shorelines. One clue as to the origin of these deposits is that at least some of the valleys were occupied by large proglacial lakes during the last glacial maximum (e.g. Glacial Lakes Trowbridge and Washburn in Miers and Taylor Valleys, respectively). This paper describes a new mechanism observed in a modern perennially ice-covered proglacial lake that documents the movement of glacial debris beyond the grounding line across the surface of the lake. This mechanism accounts for the absence of moraines and other ice-contact features on the valley floors, as well as for the presence of the other deposits and landforms mentioned above.  相似文献   

17.
湖泊粉尘记录是研究区域大气粉尘演化历史的重要载体,而现代过程研究是定量提取湖泊沉积物中粉尘信号的重要基础。对山西公海湖泊沉积岩芯样品及周边不同类型的表土样品开展了粒度分析,并对岩芯样品进行粒度组分的定量分离。结果表明：全新世湖泊岩芯样品以黏粒（<2 μm）、细粉砂（2～19 μm）和粗粉砂（19～78 μm）为主,粗粉砂组分的粒度特征与湖泊沉积物中的石英颗粒、黄土样品中的粗粒组分及现代大气降尘的粒度特征相似,石英颗粒的表面微形态也具有典型风成特征。因此,公海湖泊沉积物中粒径19～78 μm的粗粉砂组分可用来代表大气粉尘的变化,这与湖泊沉积物中粗粉砂组分是大气尘暴降尘主要组分的认识一致。另外,公海湖泊冰面粉尘样品的平均粒径还具有从西北向东南递减的趋势,表现出与冬季风方向一致的特征,进一步表明公海湖泊沉积物中粗粉砂组分可以代表东亚冬季风强度的变化。因此,公海湖泊岩芯中的粗粉砂组分可用来重建全新世大气粉尘变化以及可能的东亚冬季风强度演化历史。  相似文献   

18.
Using a combination of geophysical and geotechnical data from Storfjorden Trough Mouth Fan off southern Svalbard, we investigate the hydrogeology of the continental margin and how this is affected by Quaternary glacial advances and retreats over the continental shelf. The geotechnical results show that plumites, deposited during the deglaciation, have high porosities, permeabilities and compressibilities with respect to glacigenic debris flows and tills. These results together with margin stratigraphic models obtained from seismic reflection data were used as input for numerical finite element models to understand focusing of interstitial fluids on glaciated continental margins. The modelled evolution of the Storfjorden TMF shows that tills formed on the shelf following the onset of glacial sedimentation (ca. 1.5 Ma) acted as aquitards and therefore played a significant role in decreasing the vertical fluid flow towards the sea floor and diverting it towards the slope. The model shows that high overpressure ratios (up to λ ca. 0.6) developed below the shelf edge and on the middle slope. A more detailed model for the last 220 kyrs accounting for ice loading during glacial maxima shows that the formation of these aquitards on the shelf focused fluid flow towards the most permeable plumite sediments on the slope. The less permeable glacigenic debris flows that were deposited during glacial maxima on the slope hinder fluid evacuation from plumites allowing high overpressure ratios (up to λ ca. 0.7) to develop in the shallowest plumite layers. These high overpressures likely persist to the Present and are a critical precondition for submarine slope failure.  相似文献   

19.
Rock magnetic properties of the maar lake sediments of Lac St Front (Massif Central, France) reflect environmental changes during the last climatic cycle. High magnetic concentrations are measured in the sediments deposited under glacial climatic conditions, while lower concentrations correspond with more temperate climatic periods. Low- and high-temperature measurements indicate that the remanence is carried by (titanium-poor) magnetite. However, some maghemite and haematite is present in sediments deposited under temperate conditions.
Normalized intensities and coercivities of the anhysteretic remanent magnetization (ARM) are clearly higher for the sediments deposited during the temperate climatic periods of the Eemian, St Germain I, II and Mid-glacial than for glacial sediments, but other magnetic parameters hardly differ between these groups. Due to slight differences in magnetic composition and possible effects of grain interactions, it is not straightforward to relate this different ARM behaviour to magnetic grain-size variations. For the Holocene sediments, rock magnetic parameters indicate a larger grain size. This trend is also suggested by granulometric experiments with an optical laser granulometer. Dissolution of smaller grains is the most likely explanation for this larger grain size.
Changes in magnetic composition and grain size are extremely limited for the glacial sediments, but magnetic concentration varies considerably. Magnetic concentration maxima in the glacial sediments of Lac St Front correlate with those of the nearby Lac du Bouchet (Thouveny et al. 1994). Correlating the susceptibility records of these sequences with the δ18O record of the GRIP ice cores (Thouveny et al. 1994) suggests that magnetic concentration maxima may correspond with short cold climatic episodes, associated with Heinrich events.  相似文献   

20.
The Kanas River originates on the southern slope of Youyi Peak, the largest center of modern glaciers in Altai Mountains, China. Three sets of moraines and associated glacial sediments are well preserved near the Kanas Lake outlet, recording a complex history and landscape evolution during the Last Glacial. Dating the moraines allows the temporal and spatial glacier shift and climate during the Last Glacial to be determined, and then constrains when and how the Kanas Lake basin was formed. Dating of the glacial tills was undertaken by utilizing the optically stimulated luminescence (OSL) method. Results date four samples from the three sets of moraines to 28.0, 34.4, 38.1, and 49.9 ka and one sample from outwash sediment to 6.8 ka. The Kanas Lake basin is a downfaulted basin and was eroded by glacier before 28.0 ka, and the glacial moraines blocked the glacier-melt water after the glacier retreat, which made the present-day Kanas Lake eventually form at least before 6.8 ka BP. In Altai Mountains, the glacier advance was more extensive in Marine Isotope Stage (MIS) 3 than MIS 2, probably because the mid-latitude westerlies shifted northward and/or intensified during the MIS 3, resulting in a more positive glacier mass balance. Nevertheless, the Siberian High dominated the Altai Mountains in MIS 2, resulting in a relative decrease in precipitation.  相似文献   

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