A comparison of the effectiveness of the roots of two grass species in reducing soil erosion on alluvial fans in south-east China

The effects of root systems on soil detachment by overland flow are closely related to vegetation types. The objective of this study was to quantify the effects of two gramineous roots (Paspalum mandiocanum with shallow roots and Pennisetum giganteum with deep roots) on soil detachment capacity, rill erodibility, and critical shear stress on alluvial fans of benggang in south-east China. A 4-m-long and 0.12-m-wide flume was used. Slope steepness ranged from 9% to 27%, and unit flow discharge ranged from 1.39 × 10⁻³ to 4.19 × 10⁻³ m² s⁻¹. The mean detachment capacities of P. mandiocanum and P. giganteum lands were 18% and 38% lower than that of bare land, respectively, and the effects of root on reducing soil detachment were mainly reflected in the 0- to 5-cm soil layer. The most important factors in characterizing soil detachment capacity were root length density and soil cohesion, and soil detachment capacity of the two grass lands could be estimated using flow shear stress, soil cohesion, and root length density (NSE = 0.90). With the increase in soil depth, rill erodibility increased, whereas shear stress decreased. The mean rill erodibilities of P. mandiocanum and P. giganteum lands were 81% and 61% as much as that of bare land, respectively. Additionally, rill erodibilities of the two grass lands could be estimated as an exponential function by root length density and soil cohesion (NSE = 0.88). The mean critical shear stress of P. mandiocanum and P. giganteum lands was 1.29 and 1.39 times that of bare land, respectively, and it could be estimated with a linear function by root length density (NSE = 0.76). This study demonstrated that planting of the two grasses P. mandiocanum and P. giganteum could effectively reduce soil detachment and enhance soil resistance to erosion on alluvial fans, with the deep roots of P. giganteum being more effective than the shallow roots of P. mandiocanum. The results are helpful for understanding the influencing mechanism of root systems on soil detachment process.     

恒河深海扇东北区域晚第四纪气候和海平面变化对沉积作用的控制

通过对恒河深海扇沟道间均质细粒沉积物的氧同位素地层划分,本文讨论了晚更新世以来冰川—气候旋回和海平面变化对印度洋北部大陆坡地带各种活跃的沉积因素（陆源和碳酸盐物质的沉积通量、浊流活动的强度和频度、粘土矿物分布、碳酸盐浓度和钙质生物壳的溶解度）的控制作用和因素间的相互关联。     

广丰松峰盆地的扇三角洲特征

本文通过对盆地岩性组合和沉积的构造特点的分析,得出丰松峰盆地的沉积体系为扇三角洲。     

湖盆扇三角洲河口坝发育程度及粒度韵律特征:以滦平盆地桑园剖面下白垩统西瓜园组为例*

扇三角洲作为重要的油气储集场所,其成因单元类型及分布特征控制着油气的差异分布及采出效率。关于扇三角洲分流河道沉积特征已有共识,但河口坝沉积特征尤其是韵律特征尚存在争议。以滦平盆地桑园剖面下白垩统西瓜园组湖盆扇三角洲沉积体为例,通过人工实测及无人机观测相结合的方法,对河口坝沉积特征、尤其是韵律特征进行研究,利用水槽模拟实验阐明河口坝韵律特征的形成机理。结果表明,河口坝在整个剖面中占砂(砾)岩体的45.27%,分流河道和席状砂分别占53.42%和1.31%。河口坝在剖面上呈底平顶凸状,通常由多期增生体组成。当增生体主要由砂岩组成时,呈粒度反韵律特征; 而当增生体主要由砾岩组成时,呈粒度正韵律特征。河口坝整体韵律受控于增生体的垂向叠置样式,既可呈反韵律特征又可呈正韵律特征。当流量、沉积底形坡度等地质条件一定时,河口坝内部增生体韵律性主要受沉积物粒度控制。当沉积物粒度较细时,河口水流扩散模式为底床摩擦力主控,增生体呈现反韵律特征; 而当沉积物粒度较粗时,河口水流扩散模式为惯性力主控,河口坝增生体则呈现正韵律特征。     

中国中西部大型湖盆沉积体系域研究进展及页岩油气勘探*

中国陆相大型湖盆碎屑岩—碳酸盐岩沉积区分布广泛,含油气盆地内新发现了多个油气田,特别是近年来在致密油/页岩油勘探方面获得了突破。根据沉积体系域演化和可容纳空间演变解释层序地层单元,建立层序演化模式,预测油气储集体,适合于研究有成因联系的异旋回地层序列。深水体系的沉积层序体系域研究进展表现为引入强制海退(湖退)的概念,从经典的层序地层学格架三分体系域发展为四分体系域和二分体系域,不同尺度的相对整合序列和体系域分布与命名具有紧密联系。强制海(湖)退条件下形成的下降期体系域(FSST)和强制海(湖)退楔体系域(FRW)有内涵细节上的差异。采用A-P-D(加积-进积-降积)准层序叠加分析方法,分析体系域格架下薄层细粒沉积砂体的沉积搬运机理,提高了体系域识别和油气储集体预测的准确度。柴达木盆地古近系和四川盆地侏罗系研究实例表明,湖侵体系域随湖平面上升,浅湖和半深湖范围扩大,沉积中心地区发育三角洲前缘薄层砂体和深水浊积扇及多旋回泥页岩—泥灰岩组合,有利于页岩油气储集体的发育,成为“甜点”勘探目标区。展望未来,与页岩油气勘探有关的沉积层序体系域领域研究在以下几个方面将取得重要进展: (1)咸化湖盆深水沉积体系的高频旋回体系域研究; (2)与页岩型和混积型页岩油类型相关的湖侵体系域混积体系研究; (3)体系域级别的层序—古地理研究; (4)体系域格架下的源-汇系统及其古湖泊分布特征研究; (5)湖泊古水深、古气候和古环境的地球化学指标分析; (6)富有机质页岩发育的微纳米级孔—缝体系储集能力研究; (7)煤系环境纯湖相泥岩和沼泽相(湖沼或河沼)泥岩对规模天然气生烃贡献率的沉积基础研究。     

RIVERS' FEATURES ON ALLUVIAL FANS IN NORTHWEST CHINA

IINTRODUCTIONAlluvialfanisakindofsedimentogeniclandform,whichisdevelopedwhereriverflowsoutofmountain.Holdingapositionalongfootsofmostmountains,itconstittltestheimportantpartofthefluvialsedimentarysystem.Hooke(1967)describedtraditionalriverformonalluvialfans.Riversinciseandformdeepstableandunstablechannelsonupperpartsofalluvialfans.Andbelowtheintersectionpoints,riversflowoutofthevalleysinformofbraidedchannelanddepositsmallsecondaryajlluvialfansonthesurfaceofthefan.Lobeck(1939,fromRochocki…     

古冲沟冲积扇体地震反射资料研究

利用地震资料研究古冲沟冲积扇体的反射特征、内部结构、剖面特征和分布特征等问题,研究结果为识别和确认古冲沟冲积扇体油气藏提供依据     

Late Eocene–early Miocene provenance evolution of the Crocker Fan in the southern South China Sea

There are many large-scale Cenozoic sedimentary basins with plentiful river deltas, deep-water fans and carbonate platforms in the southern South China Sea. The Crocker Fan was deposited as a typical submarine fan during the late Eocene–early Miocene, and stretches extensively across the entire Sarawak–Sabah of the northern Borneo area. However, systematic analyses are still lacking regarding its sediment composition and potential source suppliers. No consensus has been reached yet on the provenance evolution and sedimentary infilling processes, which seriously impeded the oil-and-gas exploration undertakings. By combining with sedimentary-facies identification, heavy mineral assemblages, elemental geochemistry and detrital zircon U-Pb dating, this paper aims to generalize an integrated analysis on the potential provenance terranes and restore source-to-sink pathways of the Crocker Fan. In general, the Crocker Fan was initially formed over the Cretaceous–lower/middle Eocene Rajang Group by an angular Rajang unconformity. The continual southward subduction of the proto-South China Sea resulted in magmatic activities and subsequent regional deformation and thrusting along the Lupar Line in the northern Borneo. The lowermost Crocker sequence is featured by a thick conglomerate layer sourced from in-situ or adjacent paleo-uplifts. From the late Eocene to the early Miocene, the Crocker Fan was constantly delivered with voluminous detritus from the Malay Peninsula of the western Sundaland. The Zengmu Basin was widely deposited with delta plain and neritic facies sediments, while the Brunei-Sabah Basin, to the farther east, was ubiquitously characterized by turbiditic sequences. The Crocker Fan successions are overall thick layers of modest-grained sandstones, which formed high-quality reservoirs in the southern South China Sea region.     

Submarine slope–fan sedimentation in an ancient forearc related to contemporaneous magmatism: The Upper Cretaceous Izumi Group,southwestern Japan

The Izumi Group in southwestern Japan is considered to represent deposits in a forearc basin along an active volcanic arc during the late Late Cretaceous. The group consists mainly of felsic volcanic and plutonic detritus, and overlies a Lower to Upper Cretaceous plutono‐metamorphic complex (the Ryoke complex). In order to reconstruct the depositional environments and constrain the age of deposition, sedimentary facies and U–Pb dating of zircon grains in tuff were studied for a drilled core obtained from the basal part of the Izumi Group. On the basis of the lithofacies associations, the core was subdivided into six units from base to top, as follows: mudstone‐dominated unit nonconformably deposited on the Ryoke granodiorite; tuffaceous mudstone‐dominated unit; tuff unit; tuffaceous sandstone–mudstone unit; sandstone–mudstone unit; and sandstone‐dominated unit. This succession suggests that the depositional system changed from non‐volcanic muddy slope or basin floor, to volcaniclastic sandy submarine fan. Based on a review of published radiometric age data of the surrounding region of the Ryoke complex and the Sanyo Belt which was an active volcanic front during deposition of the Izumi Group, the U–Pb age (82.7 ±0.5 Ma) of zircon grains in the tuff unit corresponds to those of felsic volcanic and pyroclastic rocks in the Sanyo Belt.     

深海弯曲水道内部一种特殊的沉积单元:凹岸坝

在深海水道研究过程中,识别出深海弯曲水道内部存在一种特殊的沉积单元--凹岸坝,基于尼日尔三角洲陆坡区浅层高频三维地震资料,利用地震相分析技术,探究了凹岸坝的沉积结构特征和形成机制,讨论了其与水道弯曲丘(nested mounds)、曲流河凹岸滩坝之间的差异。研究结果表明:凹岸坝是分布于曲率较大、以垂向加积为主的末期水道弯曲凹岸处的坝体沉积单元,该沉积单元在地震剖面上表现为强振幅、连续性较好的反射特征,其内部沉积界面倾向于水道弯曲凸岸处,倾角约1°~20°,且在凹岸弧顶处达到最大值。凹岸坝形成的关键在于惯性作用,其造成水道内部重力流流体在弯曲处发生溢岸,导致流量减少,流体动能相应降低,流体携砂能力小于沉积物负载,造成沉积物快速沉降,从而形成凹岸坝。由于凹岸坝是一种连续性较好的砂体沉积,所以其可成为潜在的、储集性能较好的油气储集体。