鄂尔多斯地区晚古生代沉积体系及古地理演化

采用新的地层划分方案,在野外露头、钻井剖面的综合研究和室内编图基础上,提出陆表海碳酸盐台地-碎屑堡岛-浅水三角洲复合沉积体系是鄂尔多斯地区晚古生代重要的古地理格局。受区域构造背景影响,晚古生代盆地充填经历了裂陷海湾和陆表海浅陷共存、统一陆表海、近海内陆坳陷和内陆湖盆四个阶段,区域古地理格局由陆表海碳酸盐台地-碎屑堡岛-浅水三角洲复合体系沉积演变为三角洲-河流体系沉积,最终被河流-湖泊体系沉积取代。砂质储集体发育受控于沉积环境,主要展布在中、北部地区,以河流、三角洲砂体为主。     

First‐year post‐fire erosion rates in Bitterroot National Forest,Montana

Accelerated runoff and erosion commonly occur following forest fires due to combustion of protective forest floor material, which results in bare soil being exposed to overland flow and raindrop impact, as well as water repellent soil conditions. After the 2000 Valley Complex Fires in the Bitterroot National Forest of west‐central Montana, four sets of six hillslope plots were established to measure first‐year post‐wildfire erosion rates on steep slopes (greater than 50%) that had burned with high severity. Silt fences were installed at the base of each plot to trap eroded sediment from a contributing area of 100 m². Rain gauges were installed to correlate rain event characteristics to the event sediment yield. After each sediment‐producing rain event, the collected sediment was removed from the silt fence and weighed on site, and a sub‐sample taken to determine dry weight, particle size distribution, organic matter content, and nutrient content of the eroded material. Rainfall intensity was the only significant factor in determining post‐fire erosion rates from individual storm events. Short duration, high intensity thunderstorms with a maximum 10‐min rainfall intensity of 75 mm h^?1 caused the highest erosion rates (greater than 20 t ha^?1). Long duration, low intensity rains produced little erosion (less than 0·01 t ha^?1). Total C and N in the collected sediment varied directly with the organic matter; because the collected sediment was mostly mineral soil, the C and N content was small. Minimal amounts of Mg, Ca, and K were detected in the eroded sediments. The mean annual erosion rate predicted by Disturbed WEPP (Water Erosion Prediction Project) was 15% less than the mean annual erosion rate measured, which is within the accuracy range of the model. Published in 2007 by John Wiley & Sons, Ltd.     

最近50年来莱州湾东部典型砂岸潮上带土地利用变化研究

以不同时期测量和成像的地形图和高分辨率遥感影像为数据源,综合使用野外调查、遥感(RS)、全球定位系统(GPS)和地理信息系统(GIS)等方法,对最近50多年来莱州湾东部砂岸典型岸段(界河口—刁龙嘴)的土地利用变化进行研究。结果表明,最近50多年来,莱州湾东部海岸土地利用/土地覆被变化显著,土地利用类型转化的总趋势是风沙地、林地、耕地向养殖池及居民地转化。从20世纪90年代初以来,该岸段潮上带风沙地大部分已为养殖池(塘、大棚)等所覆盖,在沿海防护林和海域之间新出现了一条平行于岸线、基本连续展布的水产养殖设施带,其外侧建有高出当地最高潮位的防浪堤。潮上带土地覆被的如此深刻变化,必然深刻地改变风暴潮作用时的水动力边界条件,导致风暴潮作用过程中沿水下岸坡—海滩—潮上带方向的能量分布发生调整,进一步会对海岸地貌及冲淤发生的范围、强度、性质和形式等带来变化。因此,大面积的潮上带土地利用可能是莱州湾东部砂岸,最近30年来海岸地貌冲淤演变的重要影响因素之一,这为今后深入研究并预测该段海岸地貌冲淤变化提供了新的视角。     

Scour depth under pipelines placed on weakly cohesive soils

We here study the scouring processes that evolve around a submarine pipeline placed on a weakly cohesive seabed. We first analyze some laboratory tests carried out by Vijaya Kumar et al. [21], Xu et al. [25] and Zhou et al. [28] that focused on the scouring around a horizontal cylinder lying on a cohesive bed, subject to waves and currents. The specific purpose is that of finding a new formula for the prediction of the equilibrium scour depth under submarine pipelines. After a theoretical analysis of the main parameters, the sought formula has been found to be a function of: (i) the hydrodynamic forces acting on the cylinder (through the Keulegan–Carpenter parameter KC), (ii) the clay content of the soil C_c, and (iii) the burial depth e₀/D. In the presence of small amounts of clay (C_c< 5 %), the scour depth depends directly on KC (as confirmed by many literature works for pipelines lying on sandy soils, e.g. [18]) and inversely on C_c (as already seen for bridge abutments on cohesive soils, e.g. [1]), the best-fit law being characterized by a coefficient of determination R² = 0.62. If some burial depth is accounted for, this being a novelty of the present work, a more general formulation can be used, valid in the presence of weakly-cohesive soils and with burial depths of the pipe smaller than 0.5 (R² = 0.79). For large clay-content ranges (2% < C_c < 75 %), the scour depth depends directly on both KC and C_c, this giving R² = 0.79 (no burial depth) and 0.91 (some burial depth). However, this finding is at odds with the main literature, because, for large amounts of clay, it is fundamental to consider the liquidity index LI, which accounts for some important clay properties, like the plasticity. We argue that the absence of LI is balanced by the direct dependence of the scour depth on C_c. Notwithstanding the small number of available data, a formula for the prediction of the scour depth under pipelines lying on cohesive soils is fundamental for several engineering applications. The present contribution represents the first attempt to build such a formula, when the pipeline is subject to the wave-current forcing and the seabed is characterized by a relatively small clay content.     

重力驱动作用——滦平盆地下白垩统西瓜园组沉积时期主要的搬运机制

通过对冀北滦平盆地下白垩统西瓜园组沉积地层的实地考察,发现盆地内发育丰富的重力驱动作用沉积物。文中描述西瓜园组发育的滑动和滑塌现象,指出露头剖面中存在的挤压变形现象并非构造成因,而是由于滑动块体和滑塌块体前端的挤压应力环境造成的。在介绍西瓜园组重力流沉积发育环境的基础上,对露头中存在的若干重力流沉积进行了描述,并使用砂质碎屑流这一概念对这些现象进行了较为合理的成因解释。通过对滑动和滑塌(重力块体运动)和砂质碎屑流—浊流(重力流)沉积物研究,结合前人对该地区冲积扇—扇三角洲的研究成果,认为重力驱动作用是滦平盆地下白垩统西瓜园组沉积时期主要的搬运机制。     

珠江口盆地荔湾井区珠江组深水扇沉积特征

珠江口盆地白云凹陷荔湾深水区为油气勘探有利区域,通过岩石学和古生物组合特征研究,认为该区珠江组下部属于典型的深水扇沉积,可划分为早期盆地扇和晚期斜坡扇两种类型,两类深水扇都以发育颗粒流、砂质碎屑流及低密度浊流等顺坡重力流沉积为主,同时夹有少量内波和等深流等深水牵引流改造沉积。砂质碎屑流为两类深水扇水道砂体的主要沉积类型,发育有逆-正粒序层理、平行层理和水平层理,粒序层内可见各种丰富的液化变形和生物逃逸构造,而水平层内发育有更多的生物钻孔和扰动现象。两类深水扇的沉积构造和古生物特征有明显差异,其中盆地扇水道砂岩中普遍含硅质小砾石,水道间泥岩中含有较多保存完好的抱球虫化石,斜坡扇水道砂岩以富含炭泥屑为典型特征,水道间泥岩含有更丰富的颗石藻和抱球虫化石,其中部分抱球虫和颗石具有遭受海底溶蚀作用的现象,指示斜坡扇相对盆地扇有更大的水体深度。平面上两类深水扇具有相似的重力流沉积的分带性,都具有自陆架坡折向盆地方向由颗粒流沉积逐渐向砂质碎屑流和近源高密度浊流、远源低密度浊流等单向演化的特点。     

风暴浪作用下沙质岸滩稳定机制物理模型试验研究

近年来风暴潮等海洋灾害日趋频发,沙质海岸侵蚀问题也愈发突出,沙滩稳定防护显得日益重要。为研究风暴浪作用下沙质岸滩稳定机制问题,设计了一系列的水槽试验,对风暴浪作用下沙质岸滩的稳定机制和演变过程进行了录像观察和研究分析。试验中采用图像处理技术,根据水和岸滩床面的像素值差异,对岸滩整体剖面进行实时动态提取;对比和分析了不同入射波高、波周期、水深、岸滩初始坡度以及波高连续变化下沙质岸滩演变过程。试验结果表明,岸滩稳定与岸滩初始坡度和沙坝的发育直接相关,而波参数主要影响岸滩扰动幅度和沙坝以及前滩侵蚀边界的位置变化。当入射波高连续变化时,沙坝迅速响应并向离岸迁移。岸滩变化幅值与入射波能流存在明显正相关关系,波能流越大对岸滩稳定性的危害越大。而水位升高会增强前滩向岸侵蚀风险。此外,在本试验尺度下,前滩以侵蚀为主。当岸滩初始坡度小于稳定坡度且波陡较小时,即Dean参数Ω''较小时,岸滩才发生明显的前滩淤积,这对于试验尺度下岸滩恢复工况研究至关重要。具体来说,当岸滩整体坡度为1:10且前滩坡度达到1:5~1:2.5时,岸滩稳定性最好,岸滩形态最接近最终平衡剖面,岸滩趋于稳定的时间最短。     

Formation and evolution of sand deserts in Xinjiang,Northwest China：Ⅰ. Provenances of desert sands

Sandy desert landscape is a geological product of arid climate and abundant sand materials supply in natural conditions, therefore the formation of sandy desert is an ideal studying object for understanding the interaction between various stratigraphic/epigenetic spheres of the earth system. However, until now, the knowledge about the provenance and formation of these deserts in Xinjiang, Central Asia is diverse and inconsistent, a systematic review is necessary. Ancient aeolian sand sediments in the internal areas of these deserts and their twin dust deposits in the Cenozoic strata surrounding the Xinjiang deserts are direct and indirect clues reflecting the provenance of sand materials and the formation and evolution of deserts. Based on the geochemical, mineralogical and isotopic evidences of desert sands and relevant deposits in the peripheral regions, this paper reviews the research progress on the development of the sandy deserts in Xinjiang, Northwest China. Many proofs proposed that desert sands in Xinjiang were mainly sourced from the ancient pluvial, alluvial and fluvial sediments and were eventually achieved because of the local sand supply. It pointed out that the settings of tectonic structure in Xinjiang had made sediments both in the Tarim Basin and the Junggar Basin being influenced greatly by regional hydrological system and aeolian processes originated from the planetary wind system of westerly, the East Asian winter monsoon and the topographical mountain-valley winds. However, the directions of transportation paths are different between the hydrological dynamics and the aeolian dynamics, which are decided by the slantwise structures of the basins tectonics and the regional atmospheric circulation routes, respectively, and have determined anisotropies of the transport pathway of these sediments delivered by different agents. This results in a geological cycle of detrital sediment transportation in the two large basins and thus largely increases the degree of sediment mixing, alternation and recycle between younger and older sediment sources, as well as the complexity and diversity of sand provenances.     

动应力对粉质土变形、强度的影响

研山铁矿设计采用露天开采,最终最大边坡高达600m。边坡上部为粉土和粉砂、中砂、卵石、粉质粘土,下部为砂质粘性土和砾质粘性土。由于边坡高,受环境动应力影响因素大,因此分析粉土和粉质粘土层在动应力作用下对变形和强度的影响,对边坡稳定分析具有重要意义。     

雅鲁藏布江深厚砂砾卵石覆盖层钻探工艺

为了开展雅鲁藏布江流域综合规划及其水资源开发利用与保护专题研究工作,在雅鲁藏布江干流里龙坝址和本宗坝址共布置了4个200~300 m深的钻孔。主要通过在西藏高寒地区4个深厚覆盖层钻孔的成功实施经验,对西藏高寒地区深厚覆盖层勘探成孔工艺与技术进行研究探讨。