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1.
祁连山西段之近代运动 总被引：1，自引：0，他引：1
祁连山西段之地形,水理,构造,以及代沉积之性质,气候之变迁表现近代地壳运动之迹象至为明显,兹撮要述之如次: 一、祁连山南北两麓各河谷口均在广大之冲积扇堆积 相似文献
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北京山区泥石流灾害预警方法研究 总被引：1，自引：0，他引：1
赵忠海 《地质灾害与环境保护》2014,25(4):14-19
北京山区泥石流灾害较为频繁,总体以暴雨型沟谷泥石流为主,受地形、地貌、地质、降雨以及松散物类型等因素的影响比较明显。在调查分析北京山区泥石流灾害发育特征的基础上,从泥石流的形成和启动条件入手,对泥石流灾害的预警方法进行研究与探讨。 相似文献
4.
广西横县六景火车站南侧,角度不整合覆盖下泥盆统莫丁组和那叫组下段、被新近系大面积覆盖而呈两部分远距离割裂状态的一套“二元结构”特征显著的红色泥砂基底碳酸盐岩粗—巨砾岩,长期以来未被学者们看作一个冲积扇的有机统一体进行研究。经两次实地踏勘、系统采样和测量,以现代山麓冲积扇鉴别特征为主,辅以古冲积扇特征,综合分析得出结论:该套沉积的系列相关分割露头分别为一古近纪冲积扇之残存扇根、扇中及扇缘。该冲积扇为一典型的古近纪早期干旱气候条件下、母岩区为陡峻碳酸盐岩山体的古山麓冲积扇。 相似文献
5.
羌塘盆地地处藏北高原,其南、北边界分别为班公错一怒江缝合带与拉竹龙一金沙江缝合带,盆地面积约18×104km2,可进一步分为羌北坳陷、中央隆起带和羌南坳陷3个二级构造单元.双湖托纳木地区地处羌北坳陷南部,与中央隆起带毗连,广泛发育上侏罗统雪山组沉积,垂向上由3个沉积旋回组合构成,总体显示为一个向上变粗的充填序列.雪山组发育扇三角洲相和冲积扇相,其中雪山组一段为前扇三角洲亚相沉积;二段为扇三角洲前缘亚相和扇三角洲平原亚相沉积,扇三角洲前缘亚相分为水下分流河道、河口坝和远砂坝沉积,扇三角洲平原亚相发育天然堤和分流河道沉积;三段为冲积扇相沉积,包括扇端和扇中沉积.雪山组沉积的物源来自西南部的中央隆起带. 相似文献
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大理冲积扇含水层非均质性分布规律研究 总被引：4，自引：0，他引：4
洪-冲积扇的非均质性分布规律对含水层渗流和污染物迁移研究、地下水污染管理、控制及修复具有重要意义。本文以大理点苍山东麓隐仙溪洪-冲积扇为例,对其水动力条件、沉积构造模型、地形坡度与运移距离的关系进行探讨。研究表明,冲积扇沉积非均质受水动力条件影响,当水动力较好时,沉积颗粒物为砾石和漂砾,填充泥质和粉砂质,水动力较弱时沉积多为砂质和粘土颗粒,扇面整体以水流河道为中心轴呈扇形沉积;冲积扇沉积颗粒物的分选性和磨圆度受地形坡度的影响,地形坡度大沉积颗粒物分选性和磨圆度差,搬运距离越远分选性和磨圆度越好;扇顶因水动力强,坡度大,沉积物分选性和磨圆度差,层理不发育,扇中扇缘随着水动力条件及地形坡度减弱,沉积物分选性和磨圆度逐渐变好,层理较为发育,沉积为水平或均匀层理。 相似文献
8.
台湾东部峡谷的研究程度较低,对其沉积特征及成因缺乏系统的论述.利用近年来在台湾东部海域获得的地震剖面,对台东峡谷的形态特征、沉积充填以及成因进行了详细的分析.台东峡谷主体位于花东海盆,该部分水深在4 000~5 500 m范围内,以NE方向为主,长度约为160 km,宽度为0.2~14 km.根据峡谷的平面延伸特征,可以将台东峡谷分为3个区段:上游段为NE-NEE走向段、中游段为NE-NNW走向段、下游段为NE走向段直到峡谷嘴部;下切谷剖面形态从上游段的"V"型、中游段的复合形态（"UV"并行）逐渐过渡到下游段的"U"型.台东峡谷上游段-中游段滑塌构造发育,峡谷转弯处的侧翼可见波状沉积,其下游段则以沉积充填为主.台东峡谷的成因与构造作用、地形特征和深水沉积作用关系密切.受西南高东北低的地形特征及基底隐伏断裂控制,峡谷总体呈现NE向延伸;重力流作用为峡谷的下切侵蚀和充填提供了动力与物质来源,峡谷从上游段到下游段下切侵蚀能力减弱,谷底充填增厚;峡谷中游段受海山的阻挡,发生转向;峡谷下游段因多条峡谷携带的沉积物汇入和"喇叭状"地形的影响,输送的沉积物在出加瓜脊末端后,形成了大型深水扇. 相似文献
9.
洞庭盆地古沅江砾石层的沉积特征及沉积环境 总被引：3，自引：0，他引：3
以野外调查中发现的2处出露较好的古沅江沉积砾石层剖面,即河袱山剖面和黄土山剖面为研究对象,分析了所出露沉积物的沉积特征和沉积环境并建立了沉积序列。结果表明,古沅江砾石层在地貌上表现为古冲积扇,但该古冲积扇并不是一期冲积扇。依据2个剖面的岩性特征与沉积特征,以岩性层作为对比标志层,将剖面划分为3期冲积扇。河袱山剖面第2层与黄土山剖面第2层构成第Ⅰ期冲积扇,表现为扇顶-扇中相;河袱山剖面第3、4层与黄土山剖面第3~6层构成第Ⅱ期冲积扇,该期冲积扇较完整,表现为完整的扇顶-扇中相以及部分扇缘相;河袱山剖面第5层与黄土山剖面第7~9层构成第Ⅲ期冲积扇,表现为以扇顶相为主的扇顶-扇中相。该古冲积扇的成因类型表明冲积扇形成时的气候较为湿润;以砾质为主的沉积物则说明当时洞庭盆地周缘的地形较现在陡峻,古沅江也具有更强的搬运能力。 相似文献
10.
苏北盆地高邮-海安地区晚白垩世泰州组沉积相及物源分析 总被引：4，自引：2，他引：4
发生在晚白垩世的仪征运动,使泰州组不整合覆盖于赤山组或紫红色浦口组之上.促使了本区南断北超、南陡北缓的箕状断陷的形成与发展,由此导致本区泰一段冲积扇、扇三角洲、辫状河三角洲、半深湖泊沉积相当发育.从盆地边缘到盆地中心,沉积相逐渐由冲积扇沉积渐变为扇三角洲、浅湖、半深湖相沉积.泰二段沉积时期是本区最大湖侵期,半深水湖泊相最为发育.通过对重矿物组合、砂(砾)岩百分含量等值线图及沉积相展布格局等分析认为,本区泰州组沉积时期的物源主要来自南部的苏南隆起、北部的建湖隆起. 相似文献
11.
As achieves of regional environmental changes in the past, alluvial fans have received extensive attention from geoscience community. Tectonic activity and climate change are two of the main factors affecting the development of alluvial fans. The Qilian Mountains, which is located on the northeastern edge of the Tibetan Plateau, experienced severe uplift since the Cenozoic. With the huge relief from surrounding areas, a series of alluvial fans developed at the northern foot of the Qilian Mountains. That makes it become an ideal area to study the relationships between tectonic uplift, climate change, and alluvial fan development. In order to explore how climate and tectonic changes have effect on the formation and development of alluvial fans, based on stream power model and diffusion equations, a numerical model of the drainage basin-fan system was built. Xigou River and Dayekou River with their fans in Qilian Mountains were simulated by using the above-mentioned numerical model. The results show that both the change in precipitation and the uplift rate affect the fan slope. Either the increase in the uplift rate or the decrease in precipitation causes the increment of fan slope, and vice versa. Fan slope changes linearly with the uplift rate variation, while the effect of precipitation on fan slope is relatively small. The response of catchment to tectonic activity and precipitation disturbances, as the change of sedimentary flux, is also in different patterns. The research will provide a new perspective for understanding the influence of regional tectonic activities and climate change on the geomorphological process. 相似文献
12.
The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors on sedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonically active area, soils were weakly developed in aggrading alluvial fans, dominated by mass flows, reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed; the former were associated with Mg-poor fan sediments while the latter formed on Mg-rich lake clays exposed during minor lake lowstands. The north-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream flood deposits, sourced by carbonate terrains. Floodplain and freshwater lake deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential development of calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quaternary fans, which are characterized by climatically induced periods of stability and instability. 相似文献
13.
Chonglong Gao Youliang Ji Chenliang Wu Jun Jin Ying Ren Zhao Yang Dawei Liu Zhijun Huan Xiaobing Duan Yuqi Zhou 《Sedimentology》2020,67(4):1750-1796
Alluvial fans are usually constructed through episodic flood events. Despite the significance of these ephemeral floods on the morphodynamics of alluvial fans, depositional responses to the variations in flood conditions are still poorly documented. This greatly limits the ability to interpret ancient sedimentary successions of fans and the associated flood hydrodynamics. The Quaternary Poplar Fan from endorheic Heshituoluogai Basin provides an optimal case for addressing this issue. Based on the variations in facies associations and flood conditions, three depositional stages – namely; lobe building stage, channel building stage and the abandonment stage – are identified. During the lobe building stage the Poplar Fan is predominately constructed through incised channel flood, sheetflood and unconfined streamflood, with coeval development of distal surficial ephemeral ponds. The channel building stage is characterized by the development of gravelly braided rivers. However, only scour pool fill deposits are preferentially preserved in the Poplar Fan. During the abandonment stage, erosional lags and aeolian sands randomly occur throughout the fan, while gully deposits can only be found in the distal fan. The distinctive facies architecture of the Poplar Fan is likely to be the result of periodicity of climate fluctuations between wetter and drier conditions during the Late Pleistocene to Holocene. The ephemeral floods formed under wetter conditions usually show high discharge and sediment concentrations which facilitate the lobe building processes. During the drier periods, only gravelly braided rivers can be developed through ephemeral floods as the intensity and frequency in precipitation, discharge and sediment concentrations of the flood flows significantly decrease. The abandonment stage of the fan may occur between recurring flood episodes or during the driest periods. Furthermore, the long-term (105 to 106 year) geomorphic evolution of the Poplar Fan shows the influence of tectonic activities. The ongoing thrust uplift tectonic activities have caused destruction of the fan but can also facilitate the fan-head trench/incision of the fan, which in turn facilitate the progradation of the fan. This study proposes a new depositional model for alluvial fans constructed through episodic flood events, which shows the character of both sheet-flood dominated and stream-flow dominated end members of alluvial fans. These findings supplement the understanding of the variability of the alluvial fans and provide means to characterize rock record of alluvial fans and their associated flood and climate conditions. 相似文献
14.
The Chitral district of northern Pakistan lies in the eastern Hindu Kush Range. The population in this high-relief mountainous terrain is restricted to tributary-junction fans in the Chitral valley. Proximity to steep valley slopes renders these fans prone to hydrogeomorphic hazards, including landslides, floods and debris flows.This paper focuses on debris-flow hazards on tributary-junction fans in Chitral. Using field observations, satellite-image analyses and a preliminary morphometry, the tributary-junction fans in the Chitral valley are classified into (1) discrete and (2) composite. The discrete fans are modern-day active landforms and include debris cones associated with ephemeral gullies, debris fans associated with ephemeral channels and alluvial fans formed by perennial streams. The composite fans are a collage of sediment deposits of widely different ages and formed by diverse alluvial-fan forming processes. These include fans formed predominantly during MIS-2/Holocene interglacial stages superimposed by modern-day alluvial and debris fans. Composite fans are turned into relict fans when entrenched by modern-day perennial streams. These deeply incised channels discharge their sediment load directly into the trunk river without significant spread on fan surface. In comparison, when associated with ephemeral streams, active debris fans develop directly at composite-fan surfaces. Major settlements in Chitral are located on composite fans, as they provide large tracts of leveled land with easy accesses to water from the tributary streams. These fan surfaces are relatively more stable, especially when they are entrenched by perennial streams (e.g., Chitral, Ayun, and Reshun). When associated with ephemeral streams (e.g., Snowghar) or a combination of ephemeral and perennial streams (e.g., Drosh), these fans are subject to frequent debris-flow hazards.Fans associated with ephemeral streams are prone to high-frequency (∼10 years return period) debris-flow hazards. By comparison, fans associated with perennial streams are impacted by debris-flow hazards during exceptionally large events with return periods of ∼30 years. This study has utility for quick debris-flow hazard assessment in high-relief mountainous regions, especially in arid- to semi-arid south-central Asia where hazard zonation maps are generally lacking. 相似文献
15.
Alluvial fans in southern Monglia occur along a group of narrow discontinuous mountain ranges which formed as transpressional uplifts along a series of strike-slip faults. They provide information on the nature of neotectonic activity in the eastern Gobi Altai range and on palaeoclimate change. Alluvial fan formation was dominated by various geomorphological processes largely controlled by climatic changes related to an increase in aridity throughout late Quaternary times. Their sedimentology shows that initially they experienced humid conditions, when the sedimentary environments were dominated by perennial streams, followed by a period of increasing aridity, during which coarse fanglomerates were deposited in alluvial fans by ephemerial streams and active-layer structures were produced by permafrost within the alluvial fan sediments. With climatic amelioration during early Holocene times, the permafrost degraded and fan incision and entrenchment dominated. Sedimentation was then confined to the upper reaches of the fans, adjacent to steep mountain slopes, and within the entrenched channels. The alluvial fans have been neotectonically deformed, faulted and their surface warped by small thrust faults that propagate from the mountain fronts into their forelands. Localised uplift rates are in the order of 0.1 to 1 m Ka−1. © 1997 John Wiley & Sons, Ltd. 相似文献
16.
Tectonic controls on the geomorphic evolution of alluvial fans in the Piedmont Zone of Ganga Plain,Uttarakhand, India 总被引：3，自引：0，他引：3
Pradeep K. Goswami Charu C. Pant Shefali Pandey 《Journal of Earth System Science》2009,118(3):245-259
The Piedmont Zone is the least studied part of the Ganga Plain. The northern limit of the Piedmont Zone is defined by the
Himalayan Frontal Thrust (HFT) along which the Himalaya is being thrust over the alluvium of the Ganga Plain. Interpretation
of satellite imagery, Digital Terrain Models (DTMs) and field data has helped in the identification and mapping of various
morphotectonic features in the densely forested and cultivated Piedmont Zone in the Kumaun region of the Uttarakhand state
of India. The Piedmont Zone has formed as a result of coalescing alluvial fans, alluvial aprons and talus deposits. The fans
have differential morphologies and aggradation processes within a common climatic zone and similar litho-tectonic setting
of the catchment area. Morphotectonic analysis reveals that the fan morphologies and aggradation processes in the area are
mainly controlled by the ongoing tectonic activities. Such activities along the HFT and transverse faults have controlled
the accommodation space by causing differential subsidence of the basin, and aggradation processes by causing channel migration,
channel incision and shifting of depocentres. The active tectonic movements have further modified the landscape of the area
in the form of tilted alluvial fan, gravel ridges, terraces and uplifted gravels. 相似文献
17.
广西横县六景火车站南侧,角度不整合覆盖下泥盆统莫丁组和那叫组下段,被新近系大面积覆盖而呈两部分远距离割裂状态的一套“二元结构”特征显著的红色泥砂基底碳酸盐岩粗巨砾岩及其横向相变部分,长期以来未被将其作为一个冲积扇的有机统一体进行研究。经笔者两次实地踏勘,系统采样和分析,以现代山麓冲积扇鉴别特征为主,辅以古冲积扇特征,综合分析认为该套沉积系列相关分割露头分别为一古近系冲积扇所残存扇根、扇中和扇缘。该冲积扇为一典型的古近纪早期干旱气候条件下,母岩区为陡峻碳酸盐岩山体的古山麓冲积扇。 相似文献
18.
Dredging the alluvial fans for repaving the international road located in the bottom of the Wadi Watir valley produced vertical cliff faces of different heights, and at different locations of the fans. The heights of the cliff faces resulted in considerable elevation differences between the surface of the dredged alluvial fans and the local base level provided by the Watir trunk valley. The principal geomorphic response to this anthropogenic intervention is triggering upstream channel incision waves at different intensities in the fluvial systems of the downstream reaches of the Watir drainage basin. The channel incision processes resulted in subsequent geomorphic adjustment scenarios that vary from widening the active channels on the surface of the dredged fans, triggering rockfalls from the adjacent hillslopes, and transporting coarse alluvial deposits from the main sediment sources of the fluvial systems, and eventually re-depositing them as sheetform gravel, channelform gravel, and new fan lobes. The major outcome of the various geomorphic adjustment processes was changing the role of the alluvial fans within the fluvial systems from buffer zones where fan aggradation was dominant into dynamic coupled zones. Being coupled zones, the dredged alluvial fans allowed high potential of mass transmission from the feeder catchment areas into the Watir trunk valley. Under such conditions, it could be stipulated that considerable changes in the morphology of landscapes are highly anticipated in response to flash flood events that intermittently occur in the Watir drainage basin. 相似文献
19.
We describe and test a method for identifying alluvial fans likely to be affected by debris flows. It is based on identifying
catchment parameters by geographical information system interrogation of a digital elevation model, using the Melton ratio
as the discriminating parameter. The method was calibrated using data from debris-flow-generating catchments in Coromandel
and the adjacent Kaimai Ranges, North Island, NZ, and tested against data from the rest of New Zealand. The procedure is remarkably
(but not completely) reliable for identifying debris-flow-capable catchments, and thus fans, across the wide range of climates
and lithologies in New Zealand mountains. A case study illustrates the potential of the method for avoiding future hazards
and emphasises the need for a precautionary approach when field investigations do not detect evidence for past debris flows. 相似文献
20.
An archaeological survey and geomorphological investigation were conducted over a period of three years in the Tol and Kipsing River valleys, both located in the Mukogodo Hills‐Upper Ewaso Ng'iro Plains region of Central Kenya. Eleven alluvial‐stratigraphic sections were studied, and five late‐Quaternary alluvial stratigraphic units were identified on the basis of lithology, chronology, and soil stratigraphy. The locations of 63 archaeological sites recorded during the reconnaissance were compared with the distribution of the alluvial units. These data were used to predict where sites of different cultural periods are most likely to be found and to determine the relationship between site location and alluvial deposition. Since natural processes of deposition and erosion do not fully account for the distribution of Middle and Later Stone Age sites in the study area, the hypothesis that these differences reflect human choices, not the operation of natural processes, cannot be rejected. © 2004 Wiley Periodicals, Inc. 相似文献