Rational regime model of alluvial channel morphology and response

A theoretical model is developed for predicting equilibrium alluvial channel form. The concept of greatest relative stability, achieved by maximizing resistance to ?ow in the ?uvial system, is presented as the basis for an optimization condition for alluvial systems. Discharge, sediment supply (quantity and calibre) and valley gradient are accepted as independent governing variates. The model is used to de?ne a dimensionless alluvial state space characterized by aspect ratio (W/d), relative roughness (D/d), and dimensionless shear stress (τ*) or, equivalently, channel slope (S). Each alluvial state exhibits unique values of Froude number and sediment concentration. The range of alluvial states for constant values of relative bank strength (parameterized by an apparent friction angle, ?′) forms a single plane in the state space (W/d, D/d, τ* or S). The scaling relations produced by the model are consistent with laboratory channels exhibiting a range of bank strengths, and with the behaviour of natural channels. Copyright © 2004 John Wiley & Sons, Ltd.     

Strata反演技术在柳屯洼陷沙三2-3亚段储层描述中的应用

地震波阻抗反演技术已日益成为油气藏勘探、开发中储集层横向预测的重要手段。柳屯洼陷沙三^2-3亚段同时发育浊积砂体和厚层盐岩,横向相变剧烈。笔者论述了Strata反演的原理及其在该区的应用,在大量统计的基础上建立了不同岩性与波阻抗之间的解释标准。通过对反演剖面的解释,明确了深水浊积扇向盐湖相的渐变关系,做出了各体系域的砂体等厚图,描述了储层的空间展布特征。     

南秦岭镇安盆地泥盆纪沉积体系与古地理演化

通过对南秦岭镇安盆地泥盆系露头剖面的详细研究，将该区泥盆系划分为海岸、陆棚、斜坡-盆地及碳酸盐岩四种沉积体系，沉积体系及岩相组合具有南北向分异、东西向展布的特点。从地层由南向北超覆，相类型由北部的近源相至南部的远源相，以及碎屑搬运方向总体从北向南的变化趋势，更加确定了以前认为北部存在一个消失的古陆的认识。根据沉积体系及岩相组合的演化，把研究区的沉积盆地演化归纳为初始坳陷、拗陷和强裂断陷三个发展阶段，在不同的发展阶段具不同的环境格局，由北向南表现为：D2吉微特期古陆-海岸-陆棚；D2弗拉斯期古陆-碳酸盐台地-陆棚；D3法门期块断隆起-海岸-陆棚-斜坡-盆地-台地。     

Environmental reconstructions of a late devensian terrace sequence. Some preliminary findings

Facies analysis of Severn Main terrace sediments at Eardington, Shropshire is instructive in determining aspects of the sedimentary environment at a ‘proximal’ location in the terrace. Evaluation of the structural and directional properties of the gravels indicates that the terrace is a composite feature comprising two units. The lower unit is notable for the widespread occurrence of large sandy facies, a near absence of massive gravel facies, and the presence of large, locally derived, lithoclasts in excess of 1 m in diameter. Facies associations observed indicate the existence of in-channel bars and large channels with bedforms at the dune-plane bed transition. The directional properties of the unit indicate flows parallel to the main valley axis and although the unit is unlike previously reported examples it is interpreted as being the product of a proximal low sinuosity environment. The upper unit is composed mainly of multistorey, coarse, massive gravel units with limited interbedded sand facies. Fabric analysis indicates progradation of the unit from the west. The facies sequence is similar to those encompassed by facies models proposed for proximal alluvial fan deposits and therefore, on structural and directional grounds, the upper unit is interpreted as an alluvial fan deposit which prograded into the main Severn valley from the adjacent Mor Brook tributary. The implications of the composite nature of the terrace at this point are considered both in terms of terrace correlation and palaeohyrological estimation.     

Adjustment and recovery of unstable alluvial channels: Identification and approaches for engineering management

The management of riverine environments is shown to require a knowledge and awareness of the complex interactions between fluvial and mass-wasting processes, riparian vegetation, and channel form. Identification of the cause of instability rather than the local symptoms, and knowledge of the temporal and spatial aspects of channel adjustment are central to the application of (1) appropriate analyses to estimate future channel changes, (2) appropriate mitigation measures, and (3) the protection of river-crossing structures and adjacent land. Conceptual models of channel evolution and bank-slope development are particularly valuable for interpreting past and present processes, applying appropriate computational techniques to estimate future channel changes, and implementing strategies to mitigate the impacts of processes likely to dominate the channel in the future. Techniques for identification and analysis of channel instability are interdisciplinary and provide a mechanism for estimating changes in channel-bed elevation and channel width with time. Features of channel form and associated riparian vegetation can be used as diagnostic criteria to identify channel processes, the stage of channel evolution and the magnitude and extent of instability. Changes in bed elevation with time can be represented using an exponential function; changes in channel width with time can be calculated using slope stability equations and (or) projection of a temporary angle of stability from a low-angle surface termed the ‘slough line’ that supports re-establishment of woody vegetation. These techniques, in combination with knowledge of the state of channel evolution, can then be used to assess the appropriateness of various mitigation measures to control on-going channel adjustments and to protect river-crossing structures.     

The holocenic evolution of a stretch of an eastern italian alpine valley

The morphological evolution of a stretch of an alpine valley located in the Eastern Italian Alps is described. This has been conditioned by a great alluvial fan that was formed as a consequence of interconnected events, deriving from large rockfalls which occurred in the late glacial period at the head of the Missiaga–Bordina valley, on the left side of the Agordo basin. The aggradation of the alluvial fan blocked the Cordevole valley south of the Agordo basin and produced a lake that is documented by lacustrine sediments. Age determination by ¹⁴C techniques on wood remnants found in these sediments fixes the life of the lake at between approximately 5880 and 5300 years BP . This represents, indirectly, the age of the main phase of the development of the fan. After the building up of the alluvial fan, an erosional phase began, leading to the formation of the present landscape. A series of illustrations depicts the sequence of the fan's development.     

The multivariate controls of hydraulic geometry: A causal investigation in terms of boundary shear distribution

Most downstream hydraulic geometry exponents have been found to be very close to the classic values reported by Leopold and Maddock (1953). These have been viewed as the simplified cases to general trends because the hydraulic geometry of alluvial channels is actually the product of ‘multivariate controls’ (Richards, 1982). This paper is an attempt to develop a soundly based foundation for the explanation of the physical mechanisms of these controls. A quantitative relationship between channel shape and boundary shear distribution developed from experimental flume results is found to be applicable in some instances to alluvial channels, particularly to stable canals. On the basis of this relationship, it is shown that downstream hydraulic geometry is determined not only by flow discharge, but also by channel slope, channel average roughness and sediment composition of the channel boundary. This is strongly supported by our analysis of 529 observations from both stable canals and natural rivers in the U.S.A. and the U.K. The difference between regime relations in canals and the hydraulic geometry of rivers appears to be caused mainly by channel slope and average roughness, which can be regarded as constants only in stable canals. The close relationship between discharge and channel average roughness observed in canals is not repeated in natural channels, partly because of the variety of flow values used to define the channel-forming discharge. Furthermore, it is indicated that the effects of the sediment composition of the channel boundary on hydraulic geometry are significant and need further investigation.     

胜利油田渤南洼陷沙四上段沉积环境分析

通过地质和物探手段相结合，宏观和微观方法相结合，对渤南洼陷构造发育特征和沙四上段沉积相特征进行了深入的研究。根据沉积旋回性、韵律性等特征，确定渤南洼陷沙四上段沉积环境为滨（浅）湖－半深湖和湖底扇。根据沉积学标志，测井相标志和地震相标志，对沙四上段沉积环境为滨（浅）湖－半深湖和湖底扇。根据沉只学标志，测井相标志和地震相标志，对沙四上段湖底扇沉积微相进行了详细划分和描述，将湖底扇划分为内扇、中扇和外扇3个亚相，并进一步划分为5个微相。在上述基础上，揭示了湖底扇的平面展布规律，建立了沙四上段湖底扇的沉积模式。     

鄂尔多斯盆地早侏罗世富县期岩相古地理特征

在综合研究钻井剖面、野外露头基础上，结合室内编图、比层对比资料，指出早侏罗世富县期冲积扇－河流相沉积与古地貌密切相关，其古地理格局受印支运动后古构造面上的五条河谷控制；区内存在的冲积扇，分布于深沟河谷的陡壁一侧，为进积型冲积扇；富县期5条河流除晋陕河流为网状砂质河流外，其余均为低弯度砾砂质河流，边滩与洪泛平原微相沉积分布较广，并认为甘陕主河道流向为由西向东，“杂富县”为富县晚期洪泛平原微相产物。     

Submarine fan environment inferred from turbidite thickness distributions

Recent studies of turbidite bed thickness distributions have demonstrated power-law as well as log-normal statistical distributions. The different distributions may reflect different fan processes and environments and, therefore, could be used as a quantitative method to help identify those environments, including those devoid of sequential patterns. The cumulative distributions of well-known turbidite deposits spanning a range of interpreted fan subenvironments are used to illustrate the potential correlation between cumulative distribution and environments. Assuming that power-law distributions may, for some systems, be the primary input signal, one-dimensional modelling allows semi-quantitative characterization of the effects of different fan processes such as erosion and bed amalgamation. Environments indicative of different fan processes may be characterized based on the degree to which processes have acted as a 'filter' to modify the assumed power-law distribution systematically. This model of the effect of fan processes on the power-law distribution is used to help to account for bed thickness distributions observed in several field sites.