Lateroglacial valleys and landforms in the Karakoram Mountains (Pakistan)   总被引：1，自引：0，他引：1  

Lasafam Iturrizaga 《GeoJournal》2001,54(2-4):397-428

Lateroglacial landforms play a major role in the geomorphological landscape assemblage of the Karakoram Mountains. Nevertheless, in the past they have received only little attention in the glacial-geomorphological literature. In this article, the lateroglacial landscape will be presented as a geomorphological landscape unit. The Karakoram glaciers with lengths of up to 60 km are accompanied by lateroglacial sediment complexes over tens of kilometers. Besides their large horizontal distribution, they are spread over a considerable vertical range and occur between 2500 m–5000 m.The traditional view is that primary processes of rock disintegration such as ice avalanches and freeze-thaw processes as well as glaciofluvial sediments are the main debris suppliers for the formation of lateroglacial sediment complexes. However, the investigation of the lateroglacial sediment landscape of the Karakoram glaciers showed, that firstly the secondary debris supply in form of reworking of older glacigenic deposits (Late glacial slope moraines) represents a major debris source. Secondly, the lateroglacial sediments are composed to a major part of debris supplies from the tributary valleys. In this regard, the sediment input by mudflow events accords a prominent role. Therefore a considerable proportion of the lateroglacial sediments is of non-glacial origin. This fact has to be taken into consideration regarding glacier reconstruction in recent unglaciated mountain valleys. Further on, resedimented mudflow deposits could be identified as important parent material for recent lateral moraine formation. The distribution of lateroglacial valleys (`lateral moraine valleys') was traditionally closely linked to differences in insolation, which are in the subtropical latitude very high (`ablation valleys'). Therefore the S-faced valley flank was seen as the favourable location for lateroglacial valleys. However, field observations on more than 20 glaciers in the Karakoram Mountains proved that lateroglacial valleys occur in all exposures, and can be even absent in S-exposure. Topographical factors seem to be more important than insolation differences for the distribution pattern. Only the distribution of `true ablation valleys' can be regarded as a result of insolation differences. In fact, they can act as initial form for the formation of lateral moraine valleys.  相似文献   

柴达木盆地第四纪盐湖演化   总被引：11，自引：2，他引：11       下载免费PDF全文

魏新俊  姜继学 《地质学报》1993,67(3):255-265

本文讨论了柴达木盆地第四纪沉积分布及盐矿物产出特征、新构造运动分期及其在区内的表现;指出盆地西部第三系背斜构造带之上分布的四级湖成阶地的形成与距今10万年前发生的新构造运动有关,其分布形态记录了第四纪盐湖演化的历史;结合第四纪沉积分布及盐类沉积特征把盆地第四纪盐湖演化分为4个时期,对应4个盐类沉积阶段。  相似文献   

福建武夷山风景名胜区及其附近地区的地貌研究   总被引：2，自引：0，他引：2  

刘尚仁 《热带地理》2004,24(3):216-220,241

武夷山风景名胜区及其附近地区由花岗岩、火山熔岩、变质岩和砂页岩等构成的中山、低山占最大面积.最高海拔约1800m,在海拔350～1200m,有7级剥蚀夷平面,形态有山顶缓坡型、山坡肩膀型、谷底裂点型(占绝大多数).丹霞地貌的顶面坡以圆弧形为主,陡崖坡有罕见的切层洞穴群和最大的晒布岩,崖麓缓坡多由红层组成.河流纵谷常沿着NNE走向较软的中生界砂页岩发育,断层谷断续长数十公里;横谷常沿着NWW的走向节理发育.据6个TL年龄认定河流阶地的沉积年代:第一级阶地Q3 ,第二级阶地Q2或Q2为主,第三级阶地Q2.  相似文献   

西江的河流阶地与洪冲积阶地   总被引：1，自引：1，他引：0  

刘尚仁  彭华 《热带地理》2003,23(4):314-318

西江第一级阶地主要由Q3沉积构成,三水青歧以上属于可被洪水淹没的半埋藏阶地,与Q4河漫滩共同组成冲积平原,青歧以下属于西江三角洲下面的埋藏阶地.第二级阶地主要由Q2末期的冲积物组成,少量可延续到Q3初期;第三级阶地多由Q2中期的冲积物组成;第四级阶地仅在封开发现,是目前广东最高的河流阶地,由Q1末期或Q2初期的冲积物构成.西江两旁有老和新的两级洪冲积阶地,老阶地高出山前倾斜平原,主要由Q2洪冲积物组成,新阶地在山前倾斜平原呈埋藏和半埋藏状态,主要由Q3洪冲积物组成,与少量的Q4洪冲积物共同组成该山前倾斜平  相似文献   

对华北山地低山麓面形成时代之新认识   总被引：2，自引：2，他引：0  

吴忱 《地理与地理信息科学》2004,20(2):105-108

华北山地太行山东麓和燕山南麓的低山麓面比较发育。前人研究成果中,均把其与地文期中的"××期侵蚀"对比,形成于晚上新世。但不少研究资料表明,它向山地内部延伸,逐渐以喇叭口状收缩与河流谷地内的第三级阶地面相连。低山麓面和阶地面上的组成物质是红色砂、粘土砾石和红色土。古生物化石和测年数据表明其形成于中更新世。因此,它与地文期中的"××期侵蚀"是不同时期的面,二者不能对比。  相似文献   

粤北地区的河流阶地——广东河流阶地研究之三     

刘尚仁  黄进 《热带地理》2011,31(1):3-7

依据粤北至少16条河流、34处河流阶地、30个14C或热释光测龄数据等情况,探讨该区阶地的分布与特征:粤北最多有6级河流阶地,其最大阶地高度60 m,低于粤东和粤西5～16 m;第一级阶地变形最明显:乐昌峡以上属于常态阶地,乐昌峡以下属于半埋藏阶地;三水以下进入珠江三角洲属于埋藏阶地.第一级阶地冲积物时代为晚更新世至中...  相似文献   

A Karst Connection model for Grand Canyon, Arizona, USA   总被引：2，自引：1，他引：1  

C.A. Hill  N. Eberz  R.H. Buecher   《Geomorphology》2008,95(3-4):316-334

Along the Asturian coast of northern Spain an uplifted wave-cut platform extends for  100 km east–west. The steep cliff which bounds the gently seaward-dipping platform to the north increases in height from 30 m in the west to 100 m in the east and reflects the overall eastward increase in platform elevation. The southern edge of the 2–4 km-wide platform runs along the foothills of the Cantabrian Mountains, as constrained by a high-resolution digital elevation model. The marine platform, which was carved into deformed Paleozoic bedrock with abundant quartzite beds, is largely covered by weathered marine and continental sediments. Quartzite samples from flat bedrock outcrops which are currently not covered by sediment or soil yield cosmogenic nuclide concentrations (²¹Ne, ¹⁰Be and ²⁶Al) that demonstrate a long and complex exposure history, including periods of burial with partial or complete shielding from cosmic rays. The combination of multiple cosmogenic nuclides yields a minimum age of 1–2 Ma for the platform. Taking into account (i) the horizontal and vertical extent of the platform, (ii) the high resistance to erosion of the quartzitic bedrock, and (iii) published data on the magnitude of past sea level fluctuations, we suggest that the wave-cut platform formed in the Pliocene. Subvertical faults cutting the platform at high angles to the coastline offset the southern edge of the platform by 20 to 40 m and reactivate the pre-existing anisotropy in the Paleozoic bedrock. Uplift and crustal deformation of the coastal region have occurred after platform formation in the Pliocene and may still be active. The slow deformation of the northern edge of the Iberian plate including the Cantabrian Mountains may result from the ongoing slow convergence at an incipient subduction zone extending along the coast of northern Spain.  相似文献   

Holocene debris-flow deposits and their implications on the climate in the upper Jinsha River valley, China     

Jian Chen  Fuchu Dai  Xin Yao 《Geomorphology》2008,93(3-4):493-500

Major debris-flow deposits occur along the xerothermic valley of the upper Jinsha River. The debris-flow deposits, ranging in thickness from 1 to 20 m, invariably occupy gently inclined piedmont slopes. The sediments are presently deeply dissected by gullies, and the process of mass movement has almost ceased. Detailed textural, stratigraphical, and geochemical studies reveal the formation processes of the debris flows. Seven debris-flow incidents are noted based on the unit combination characteristics of debris-flow deposits. The age estimates of optically stimulated luminescence (OSL) show that the occurrence of debris flows started at around 10.6 kyr BP and weakened until 4.5 kyr BP, corresponding to the obvious strengthened phase of the summer monsoons in the region. The ages of the debris-flow deposits indicate that the occurrence of a mass of debris flows was a response to the intensified summer monsoon in the SE fringe of the Tibetan Plateau since the early Holocene.  相似文献   

哀牢山区梯田景观多功能的综合评价   总被引：3，自引：0，他引：3  

角媛梅 《云南地理环境研究》2008,20(6):7-10

景观多功能的概念、研究内容和评价是景观生态学的研究热点之一。以哀牢山区梯田景观为例,从景观的生产价值、生态价值、文化价值与美学价值等4个方面提出其多功能价值综合评价的体系和标准,并分析和评价了梯田景观的多功能价值。结果表明：（1）梯田景观美学价值的6个指标均处于比较高的水平,美学价值高;（2）梯田景观生产价值的7个指标说明其生产功能低下;（3）梯田景观生态功能的7个指标说明其生态功能良好;（4）梯田景观文化价值的6个指标说明其文化社会功能很高;（5）梯田景观四种价值的顺序是文化价值〉美学价值〉生态价值〉生产价值,而从景观价值的总体水平看,其价值仅为良好状态,可见高层的综合评价结果是其下一级水平的平均状态。  相似文献   

天山北麓河流阶地序列及形成年代   总被引：4，自引：1，他引：3  

吕红华  李有利  南峰  司苏沛  刘运明  钱蟒  赵洪壮 《地理学报》2008,63(1):65-74

天山北麓河流阶地序列及其年代一直是悬而未决的问题。根据详细的野外工作, 确定天山北麓发育7 级河流阶地, 其中T₇、T₆、T₅ 及T₂ 等主要阶地为河流切割先期冲积扇而形 成, 与4 级阶地对应的4 期冲积扇分别为F₁、F₂、F₃ 与F₄。由于天山北麓构造隆升向盆地方 向迁移, 冲积扇呈串珠状发育, 背斜带间发育的冲积扇平面形态则由于南北背斜的限制而变 得不规则。基于黄土-古土壤序列对比分析、ESR 与OSL 测年以及前人研究成果, 确定天山 北麓河流下切形成T₇、T₆、T₅ 及T₂ 等阶地的时间分别为约0.54 Ma BP、0.3~0.2 Ma BP、 28~8 ka BP 和全新世早期。阶地年代表明, 天山北麓3 级主要阶地T₇、T₆、T₅ 及对应冲积扇 发育与天山更新世3 个冰期间冰期旋回基本对应。  相似文献