江西省鄱阳湖信江决口三角洲沉积特征及模式

利用实地考察、浅钻孔、探槽及卫星影像等方法,对鄱阳湖信江决口三角洲进行了系统研究。该决口三角洲是洪水冲破信江西岸天然堤流入附近的河漫湖泊形成的,其平面形态为鸟足状,总体延伸方向与主河道近垂直。在横切剖面上整个决口三角洲沉积体呈透镜状覆盖在早期的湿地或河漫湖泊沉积之上。鄱阳湖信江决口三角洲可分为3个亚相:决口三角洲平原、决口三角洲前缘和决口前三角洲。决口三角洲平原主要发育决口河道、决口天然堤、废弃决口河道和湿地,其中决口河道又可以进一步划分为决口水道、边滩、汊口滩;决口三角洲前缘主要发育河口坝、支流间湾。河漫湖泊规模小、深度浅、波浪能量弱,对河口坝和决口河道砂体的改造较弱,不易形成连片分布的席状砂;决口前三角洲不发育。决口三角洲沉积受河流作用和河漫湖泊作用的共同控制,其演化可以划分为主河道天然堤生长阶段、决口初期阶段、进积分汊阶段及分汊—废弃阶段4个阶段。     

Cascades of sub-decadal,channel-floodplain changes in low-gradient,non-vegetated reaches near a dryland river terminus: Salar de Uyuni,Bolivia

The terminus of the ephemeral Río Colorado is located at the margins of Salar de Uyuni, Bolivia, the world's largest salt lake. The low-gradient (<0.0006 m m^-1), non-vegetated reaches approaching the terminus provide an excellent natural laboratory for investigating cascades of channel-floodplain changes that occur in response to quasi-regular flows (at least once annually) and fine-grained sediment supply (dominantly silt and clay). High-resolution satellite imagery (<0.65 m, various dates from 2004 onwards) and field data reveal widespread, pronounced and rapid morphodynamics on sub-decadal timescales, including channel erosion and chute cutoff formation, and development of crevasse channels and splays, floodouts (unchannelled surfaces at channel termini), and erosion cells (floodplain scour-transport-fill features). In particular, following high annual precipitation (>400 mm) in 2004–2005 and two subsequent high magnitude daily precipitation events (~40 mm), all of which led to widespread flooding, numerous crevasse splays formed between 2004 and 2016, avulsions occurred at nearby floodouts, and erosion cells downstream of the splays and floodouts underwent striking morphological changes. High-precision GPS data reveal two preferential localities for erosion cell development: partially or fully abandoned channels with crevasse splay remnants, and topographic lows between channels. In this overall low-gradient setting, comparatively high gradients (up to ~0.0006 m m^-1) at the edge of splay deposits and topography created by crevasses and abandoned channels may initiate knickpoint retreat and thereafter erosion cell development. Abandoned channels with splays tend to give rise to narrow, deep erosion cells, while topographic lows promote relatively shallow, wide erosion cells. In both situations, erosion cells may extend upslope and downslope, and eventually connect to form straight channels. The channel-floodplain morphodynamics near the Río Colorado terminus extend previous analyses of low-gradient, dryland river systems, particularly because the lack of vegetation and quasi-regular floods drive cascades of rapid changes on sub-decadal timescales. © 2018 John Wiley & Sons, Ltd.     

鄂尔多斯盆地南部延安组水下分流河道型湖泊三角洲体系的沉积构成

采用过程沉积学和成因地层分析相结合的方法,在鄂尔多斯盆地南部延安组中识别出了一种新的湖泊三角洲沉积体系。它与普通河控型湖泊三角洲的主要区别是下三角洲平原部分不是由典型的分流河口坝和前三角洲沉积组成,而是由多分支的水下分流河道、水下决口扇和湖泊沉积组成。在边缘三角洲部分,时常受波浪作用的改造,并形成各种类型的湖滨沉积。本文比较详细地讨论了这类湖泊三角洲的沉积构成及其发育的边界条件。     

综合物探方法在上海市防汛墙检测中的应用

上海市防汛墙的坚固与否,关系到上海市人民生命与财产的安全,而传统的钻孔取芯方法,由于具有技术与经济方面的不合理,通过物探的方法对防汛墙体进行了检测,取得了较好的应用效果。     

一个典型的水下分流河道砂体展布与油气富集规律

三角洲一般位于海(湖)陆之间的过渡地带，是海(湖)陆相的重要组成部分。鄂尔多斯盆地三叠系延长组储层，由于其特殊的沉积环境．湖底坡降小．河控占主导地位．水下分流河道极为发育．最典型的是白120井区长33储层，由一个单一的水下分流河道组成。该区沉积规律强，各沉积单元发育，中间为河道沉积区，两侧为高于河道的天然堤，外部为漫溢沉积区，末端有4个朵体，中部发育一个小型决口水道。砂体呈指状展布，左右对称，具有三角洲水下分流河道典型的双凸特点。该区的沉积环境控制了砂体的展布和油气的富集程度。通过对该区块的研究，建立了一个完整的水下分流河道的沉积模式，这对于丰富三角洲沉积相的内容具有一定的意义。     

Formation and reorientation of structure in the surge‐type glacier Kongsvegen,Svalbard

Kongsvegen, a surge‐type glacier in Spitsbergen, Svalbard, shares a tide‐water margin with the glacier Kronebreen. The complex has been in retreat since a surge advance of Kongsvegen around 1948. The surface of Kongsvegen displays suites of deformational structures highlighted by debris‐rich folia. These structures are melting out to form a network of sediment ridges in the grounded terminal area. The structures are also visible in a marginal, 1 km long, 5–20 m high cliff‐face at the terminus. Current models for the evolution of deformational structures at Kongsvegen divide the structures into suites based on their orientation and dip, before assigning a mechanism for genesis based on structure geometry. Interpretation of aerial photographs and field mapping of surface structures suggest that many structures were reorientated or advected during the surge. We suggest that many of the deformational structures highlighted by debris‐rich folia represent reorientated, sediment‐filled crevasses. Some evidence of thrusting is apparent but the process is not as ubiquitous as previously suggested. Many deformational structures also appear to have been offset by more recent structures. Mechanisms of structural development must, therefore, be considered within the context of distinct stages of glacier flow dynamics and multiple surge episodes. Furthermore, evidence for thrusting and folding within the glacier systems of Svalbard has been used as the basis for interpreting Quaternary glacial landforms in the UK. The findings of this paper, therefore, have implications for interpretations of the Quaternary record. Copyright © 2002 John Wiley & Sons, Ltd.     

冰川表面水文过程研究进展

冰面水文过程是冰川径流过程的重要组成部分,对于冰川运动与物质平衡具有重要影响。冰川表面在太阳辐射、冰川物理性质、冰面地形和成冰带空间分布等多种因素影响下消融,形成以冰面水系为主线,锅穴、冰裂隙、冰面湖等为端点的冰面融水输送与分配体系。深入理解冰面水文过程,掌握冰川表面融水的输送、存储与释放,对于研究短时间尺度的冰川融水径流过程、探索冰川动态响应机理具有重要意义。总结回顾了目前国内外冰面水文过程的研究现状,提出了该领域有待解决的主要科学问题。     

Detection of crevasses over polar ice shelves using Satellite Laser Altimeter

Ice shelf breakups account for most mass loss from the Antarctic Ice Sheet as the consequence of the propagation of crevasses(or rift)in response to stress.Thus there is a pressing need for detecting crevasses’location and depth,to understand the mechanism of calving processes.This paper presents a method of crevasse detection using the ICESat-1/GLAS data.A case study was taken at the Amery Ice Shelf of Antarctica to verify the accuracy of geo-location and depth of crevasses detected.Moreover,based on the limited crevasse points,we developed a method to detect the peak stress points which can be used to track the location of the crack tips and to identify the possible high-risk area where an ice shelf begins to break up.The spatial and temporal distribution of crevasse depth and the spatial distribution of peak stress points of the Amery Ice Shelf were analyzed through 132 tracks in 16 campaign periods of ICESat-1/GLAS between 2003 and 2008.The results showed that the depth of the detected crevasse points ranged from 2 to 31.7 m,which were above the sea level;the crevasse that advected downstream to the front edge of an ice shelf has little possibility to directly result in breakups because the crevasse depth did not show any increasing trend over time;the local stress concentration is distributed mainly in the suture zones on the ice shelves.     

Anastamosing channels in the lower Neches River valley,Texas

Active and semi‐active anastomosing Holocene channels upstream of the delta in the lower valley of the meandering Neches River in southeast Texas represent several morphologically distinct and hydrologically independent channel systems. These appear to have a common origin as multi‐thread crevasse channels strongly influenced by antecedent morphology. Levee breaching leads to steeper cross‐valley flows toward floodplain basins associated with Pleistocene meander scars, creating multi‐thread channels that persist due to additional tributary contributions and ground water inputs. Results are consistent with the notion of plural systems where main channels, tributaries, and sub‐channels may have different morphologies and hydrogeomorphic functions. The adjacent Trinity and Sabine Rivers have similar environmental controls, yet the Trinity lacks evidence of extensive anastomosing channels on its floodplain, and those of the Sabine appear to be of different origin. The paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy. Copyright © 2014 John Wiley & Sons, Ltd.     

Crevasse splays from the rapidly aggrading, sand-bed, braided Niobrara River, Nebraska: effect of base-level rise

Base-level rise of ≈2·35 m on the Niobrara River has resulted in aggradation of the channel belt and a recent avulsion. Overbank areas have become flooded by rising groundwaters, and more than eight crevasse splays have formed between 1993 and 1997. Two crevasse splays, situated on the west and east sides of the Niobrara, have been studied using ground-penetrating radar (GPR), shallow boreholes and topographic surveys. The vibracores and GPR profiles provide a nearly three-dimensional view of the architecture of crevasse splay deposits. The east splay was initiated in the winter of 1993/94 and has expanded to cover an area ≈200 m by 1000 m, with sediment up to 2·5 m thick. The west splay, which was initiated by the opening of a crevasse channel through a levee in the autumn of 1995, covers an area ≈150 m by 250 m, with up to 1·2 m of sand deposited in a single year. The Niobrara splays are sand dominated and characterized by bedload deposition within channels, 5–30 m wide and 0·5–2 m deep, with the development of slipfaces where splays prograde into standing bodies of water. Sedimentary structures in cores include horizontal lamination, ripple lamination and sets of cross-stratification. There is a slight tendency for splays to coarsen up, but individual beds within the splays often fine up. The abundance of crevasse splays on the Niobrara River contrasts with other braided river floodplains. In the Niobrara, crevasse splay formation followed aggradation within the channel belt, which occurred in response to base-level rise. The link between crevasse splays, channel aggradation and base-level rise has important implications for the interpretation of ancient braided river and floodplain sequences. It is suggested that crevasse splay deposits should be an important component of aggrading fluvial sediments and, hence, should be preserved within the rock record. In this case, the aggradation and crevassing have been tied to a rise in base-level elevation, and it is suggested that similar deposits should be preserved where braided rivers are affected by base-level rise, for instance during transgression and filling of palaeovalleys.