Chute channels in the Holocene high‐sinuosity river deposits of the Firenze plain,Tuscany, Italy     

MASSIMILIANO GHINASSI 《Sedimentology》2011,58(3):618-642

This paper focuses on Holocene deposits of the Firenze alluvial plain (Northern Apennines, Italy) and deals with the sedimentary features of chute channels draining the down‐river edges of the meander neck formed by 70 to 100 m wide and 1 to 1·5 m deep sinuous channels. Two main types of chute channels have been recognized. Type 1 is represented by 3 to 6 m wide and 0·5 to 1 m deep straight channels filled with mud aggregates overlying a basal gravel lag made of reworked caliches. These channels drained the point bar top during floods, and are thought to have been initiated as small rills when a shallow flow overpassed the downstream side of the point bar. Type 2 channels, 3 to 6 m wide and 1 to 1·5 m deep, are moderately to highly sinuous and filled with well‐stratified sand and gravels sourced from nearby rocky highlands. Type 2 channels were connected to the main river channel also during the base flow stage. The transition from Type 1 to Type 2 channels is documented and is interpreted as the result of the meander cut‐off process. Type 1 chute channels represent the early stage of the cut‐off phase, when a headcut is incised on the down‐river edges of the meander neck. The headcut migrates up‐river across the meander neck during floods, when fast currents shape the chute channels into a straight route. The transition from Type 1 into Type 2 channels is linked to the connection of the up‐river migrating headcut with the main channel and the termination of the cut‐off process. At this stage, the cut‐off channel is drained permanently and receives bedload from the main channel. The progressive shaping of the newly formed channel will convert it into the main channel and lead to the formation of an oxbow lake in the abandoned meander branch. Development of chute channels in the Firenze alluvial plain is thought to have heralded a decrease in sinuosity of the main channels, triggered by a climate‐driven increase in water discharge.  相似文献   

Be data from meltwater channels suggest that Jameson Land, east Greenland, was ice-covered during the last glacial maximum     

Lena Håkansson  Jason P. Briner  Ala Aldahan  Göran Possnert 《Quaternary Research》2011,76(3):452-459

Along the northeast Greenland continental margin, bedrock on interfjord plateaus is highly weathered, whereas rock surfaces in fjord troughs are characterized by glacial scour. Based on the intense bedrock weathering and lack of glacial deposits from the last glaciation, interfjord plateaus have long been thought to be ice-free throughout the last glacial maximum (LGM). In recent years there is growing evidence from shelf and fjord settings that the northeast Greenland continental margin was more extensively glaciated during the LGM than previously thought. However, little is still known from interfjord settings. We present cosmogenic ¹⁰Be data from meltwater channels and weathered sandstone outcrops on Jameson Land, an interfjord highland north of Scoresby Sund. The mean exposure age of samples from channel beds (n = 3) constrains on the onset of deglaciation on interior Jameson Land to 18.5 ± 1.3–21.4 ± 1.9 ka (for erosion conditions of 0–10 mm/ka, respectively). This finding adds to growing evidence that the northeast Greenland continental margin was more heavily glaciated during the LGM than previously thought.  相似文献   

Sediment waves and depositional implications for fine-grained rocks in the Cerro Toro Formation (upper Cretaceous), Silla Syncline, Chile   总被引：1，自引：0，他引：1  

Kirt M. Campion  Barrett T. Dixon 《Marine and Petroleum Geology》2011,28(3):761-784

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d:\PDF\.pdf地震共中心点道集的瞬时基准面静校正和动校正   总被引：2，自引：2，他引：2  

刘江平 《物探与化探》1997,21(1):15-22

对地震野外共炮点记录进行浮动基准面静校正后的每一个共中心点道集记录而言,其基准面仍是一局部曲面,如何使之动校正后达到同相迭加,必须作所谓瞬时基准面静、动校正处理。本文从理论上阐述了共中心道集记录的瞬时基准面静、动校正的方法和技术,并用理论模型试算验证了该方法能够消除由于局部起伏对共中心点道集记录的影响,提高时间剖面的质量、速度和解释精度,确保在山区中采用地震反射波法多次覆盖技术勘探的成功。  相似文献   

吐哈盆地WM油田辫状河三角洲前缘砂体分析   总被引：22，自引：2，他引：20  

周丽清  吴胜和  熊琦华  马晓芬  郭燕华  林双运 《沉积学报》2000,18(2):248-252

湖盆可容空间较小时,辫状河三角洲相对发育,水下分支河道横向迁移频繁,易形成席状分布的砂体 (水下分支河道复合体 )。可容空间增大时,辫状河三角洲相对不发育,水下分支河道延伸不远,河道砂体较孤立,河口坝相对比较发育。文中根据水流和波浪强弱提出九种水下分支河道与河口坝的关系图,基本上总结了吐哈盆地WM油田三间房组河口坝的形态;并对水下分支河道复合体的形成机制提出了独特的推理。  相似文献   

Erosion of a cyclic saltmarsh in Morecambe Bay,North-West England     

Ada W. Pringle 《地球表面变化过程与地形》1995,20(5):387-405

This paper presents results of investigations (1983–1992) into rates of change, morphology and processes occurring during the current erosional phase in a Morecambe Bay cyclic saltmarsh, in which it has narrowed from c. 1000 m (1975) to c. 150 m (1992). Monthly monitoring of marsh edge erosion and creek knickpoint retreat has revealed temporal and spatial variations. Highest frequency changes of low magnitude coincided with non-storm conditions and overmarsh tides above 5·80 m OD, which submerged the whole marsh. Less frequent changes of greater magnitude were associated with both overmarsh tides and strong onshore winds over 15 ms^?1, which generated high energy waves. The lowest frequency change of greatest magnitude occurred during an extreme onshore storm event and surge. Morphologically, during the erosional phase, a low angled landward slope was generated as erosion of the c. 0·5 m high active seaward cliff coincided with vertical accretion of 0·07 ma^?1 of relatively coarse sediment on the marsh surface immediately landward. Tidal hydrodynamics strongly influence the saltmarsh, which is confined to the upper 2·5 m of the macrotidal range (maximum c. 10·5 m). During overmarsh spring tides (maximum creek flood flow rate 0·13 ms^?1, up to bankfull level), flooding begins over lower landward creek banks before submerging the higher marsh edge. During ebb tides, water trapped by this higher edge can escape seaward only via the creeks (maximum ebb velocities 2·07 ms^?1 below bankfull level). Wave erosion also is limited to spring tides. Monthly mapping of the Kent Estuary channel pattern seaward of the saltmarsh showed that medium term higher erosion rates were related to the presence of a large channel, which lowered the adjacent creek base level and allowed larger waves to attack the marsh edge than when a sandbank flanked the marsh. Major River Kent channel shifts appear to initiate accretional or erosional phases of cyclic saltmarsh development.  相似文献   

青藏高原夏季云水含量及其水汽输送年际异常分析     

刘菊菊  游庆龙  王楠 《高原气象》2019,38(3):449-459

利用欧洲中期天气预报中心(ECMWF)提供的1979-2016年ERA-Interim再分析资料分析了青藏高原(下称高原)夏季云水含量及其水汽输送情况。结果表明:高原夏季云水含量占全年48%,东南向西北减少。影响高原云水含量的水汽通道有印度洋通道、南海通道、孟加拉湾北部及伊朗西部通道(依次简称通道1、2、3、4)。高原云水含量和各水汽通道强度均有明显年际变化。云水含量年际变化与通道2,4基本一致。云水含量与各水汽通道强度均呈增加趋势。通道1偏强时,来自印度洋北部和南海的异常水汽在孟加拉湾交汇向高原输送,主要使高原西北部云水含量增多。通道2偏强时,南海、中南半岛的异常偏南通量及孟加拉湾北部的异常西南通量向高原东南部输送更多水汽。通道3偏强时,西风带水汽和来自印度洋水汽更多输送到高原,主要使高原东北部云水含量偏多。通道4偏强时,来自南海-孟加拉湾南部的水汽向高原异常输送,使高原中部、东南部云水含量偏多。此外,西太平洋副热带高压(下称副高)偏西南偏强时,水汽通道2、4强度偏强,有利于水汽向高原输送。  相似文献   

广州S波段双线偏振天气雷达双通道一致性测试及分析     

胡东明  张羽  傅佩玲  田聪聪  刘畅 《气象科技》2019,47(3):373-379

双线偏振天气雷达双通道的一致性,是新一代天气雷达双线偏振升级的技术关键。本文分别采用机外仪表和机内测试信号,测试分析了广州CINRAD/SA-D双线偏振雷达接收机双通道的一致性。结果表明:①接收机双通道的动态范围、噪声系数、强度定标等满足设计指标,但测试结果也存在一定的差异,导致偏振参量差分反射率因子ZDR和差分相移ΦDP产生误差,需要对这种差异进行定期检查和修正,以确保双通道一致性;②旋转关节对整个接收链路的信号幅度和相位一致性有影响,这种影响随着方位的变化呈现出一定的周期变化规律,因此随着双线偏振雷达的长期运行,方位旋转关节的影响不可忽略。  相似文献   

新疆红枣消费者购买行为:包装偏好、购买渠道与支付水平   总被引：1，自引：0，他引：1  

李凤  马惠兰  苏洋 《干旱区地理》2015,38(2)

基于北京和上海429位消费者的抽样调查,采用Logistic模型,研究消费者对新疆红枣的购买行为及影响因素.结果表明:北京和上海消费者都偏好购买超市的袋装红枣,年支出水平多在300元以下.年龄、收入、购买目的均影响两地消费者购买新疆红枣,此外,外观和质量认知对北京消费者购买行为有显著影响,上海消费者还受性别、受教育程度及营养认知的影响.最后为新疆红枣产业的市场拓展提出建议,包括加大宣传力度、明确市场定位和保证红枣质量.  相似文献   

Bank erosion in agricultural drainage networks: new challenges from structure‐from‐motion photogrammetry for post‐event analysis          下载免费PDF全文

Massimo Prosdocimi  Simone Calligaro  Giulia Sofia  Giancarlo Dalla Fontana  Paolo Tarolli 《地球表面变化过程与地形》2015,40(14):1891-1906

Drainage channels are an integral part of agricultural landscapes, and their impact on catchment hydrology is strongly recognized. In cultivated and urbanized floodplains, channels have always played a key role in flood protection, land reclamation, and irrigation. Bank erosion is a critical issue in channels. Neglecting this process, especially during flood events, can result in underestimation of the risk in flood‐prone areas. The main aim of this work is to consider a low‐cost methodology for the analysis of bank erosion in agricultural drainage networks, and in particular for the estimation of the volumes of eroded and deposited material. A case study located in the Veneto floodplain was selected. The research is based on high‐resolution topographic data obtained by an emerging low‐cost photogrammetric method (structure‐from‐motion or SfM), and results are compared to terrestrial laser scanning (TLS) data. For the SfM analysis, extensive photosets were obtained using two standalone reflex digital cameras and an iPhone5® built‐in camera. Three digital elevation models (DEMs) were extracted at the resolution of 0.1 m using SfM and were compared with the ones derived by TLS. Using the different DEMs, the eroded areas were then identified using a feature extraction technique based on the topographic parameter Roughness Index (RI). DEMs derived from SfM were effective for both detecting erosion areas and estimating quantitatively the deposition and erosion volumes. Our results underlined how smartphones with high‐resolution built‐in cameras can be competitive instruments for obtaining suitable data for topography analysis and Earth surface monitoring. This methodology could be potentially very useful for farmers and/or technicians for post‐event field surveys to support flood risk management. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献