Albian extrusion evidences of the Triassic salt and clues of the beginning of the Eocene atlasic phase from the example of the Chitana-Ed Djebs structure (N.Tunisia): Implication in the North African Tethyan margin recorded events, comparisons   总被引：1，自引：0，他引：1  

Mohamed-Montassar Ben Slama  Amara Masrouhi  Mohamed Ghanmi  Mohamed Ben Youssef  Fouad Zargouni 《Comptes Rendus Geoscience》2009,341(7):547-556

In the northern part of Tunisia, close to Testour/Slouguia, new observations and updated biostratigraphy make it possible to highlight the relation between the Triassic saliferous mass and the surrounding Mesozoic beds (T. M.). Near the (T. M.) boundary, the formations observed consist dominantly of Triassic evaporites reworked in the Early and Late Albian deep-water sedimentary deposits. Throughout the studied area, Jurassic rocks are absent. We propose to interpret the Chitana-Ed Djebs structure originally emplaced as gravitational stretch masses in a passive margin in the same way as the salt bodies of widespread salt province in the Gulf of Mexico. A reconstructed schematic position of the Chitana-Ed Djebs salt body displays a scenario of setting of the salt mass on a submarine palaeo-slope. Moreover, the starting clues of the paroxysmal event of the Late Mesozoic tectonic inversion clearly fossilized through the discordance of the Middle Eocene–Early Lutetian limestone on the Albian series.  相似文献   

某水电站坝前左岸古滑坡成因机制分析     

廖锦  张进林 《四川地质学报》2009,29(2):191-194

古滑坡坐落于Ⅱ级阶地台面上,堆积物最大厚度可达50m余。利用FLAC^3D数值模拟得到的滑面在前缘位于基覆界面附近,与野外调查的结果一致。结合雅砻江河谷演化历史,从斜坡演化机制、边坡岩体的变形破坏模式,分析了古滑坡成因机制。研究表明：雅砻江快速下切使岸坡岩体浅表改造程度较为剧烈,不断增加的重力堆积静荷载与崩塌形成的瞬时冲击荷载加速了岩体的弯曲一拉裂变形进程,造成Ⅱ级阶地基座岩体发生突发性折断破坏．从而导致古滑坡失稳。  相似文献   

How green was my valley: forest canopy density in relation to topography and anthropogenic effects in Manipur valley,India     

Kiran Sharma 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):137-150

Forest canopy density (FCD) is a major factor in the evaluation of forest status and is an important indicator of possible management interventions. The study uses the FCD model with Landsat TM and Landsat 8 OLI images to assess canopy density in India’s Manipur valley and surrounding hills. Normalized difference built-up index (NDBI) was used to extract built-up areas and population density was retrieved from LandScan data, while elevation and slope were obtained from ASTER DEMs (30 m). Four types of canopy density were delineated with crown cover above 71%, 41–70%, 11–40%, below 10% and areas with no canopy cover, that is 0%. A sharp decline in forest area occurred during 1989–2016 at a rate of loss of 2.9 % year-1 with an average rate of deforestation of 3051 ha year-1. Dense forests exhibited remarkable degradation, especially towards the central valley. The variation in the topographical (elevation and slope) gradient resulted in significant differences in the canopy density over the study area barring some hill slopes. Population pressure and various developmental activities in recent decades led to forest degradation in this fragile yet rich Eastern Himalaya biodiversity hotspot.  相似文献   

Calibrating a FDR sensor for soil moisture monitoring in a wetland in Central Kenya     

《Physics and Chemistry of the Earth》2013

The recent transformation of wetlands into farmland in East Africa is accelerating due to growing food-demand, land shortages, and an increasing unpredictability of climatic conditions for crop production in uplands. However, the conversion of pristine wetlands into sites of production may alter hydrological attributes with negative effects on production potential. Particularly the amount and the dynamics of plant available soil moisture in the rooting zone of crops determine to a large extent the agricultural production potential of wetlands. Various methods exist to assess soil moisture dynamics with Frequency Domain Reflectometry (FDR) being among the most prominent. However, the suitability of FDR sensors for assessing plant available soil moisture has to date not been confirmed for wetland soils in the region. We monitored the seasonal and spatial dynamics of water availability for crop growth in an inland valley wetland of the Kenyan highlands using a FDR sensor which was site-specifically calibrated. Access tubes were installed within different wetland use types and hydrological situations along valley transects and soil properties affecting soil moisture (organic C, texture, and bulk density) were investigated. There was little variation in soil attributes between physical positions in the valley, and also between topsoil and subsoil attributes with the exception of organic C contents. With a root mean squared error of 0.073 m³/m³, the developed calibration function of the FDR sensor allows for reasonably accurate soil moisture prediction for both within-site comparisons and the monitoring of temporal soil moisture variations. Applying the calibration equation to a time series of profile probe readings over a period of one year illustrated not only the temporal variation of soil moisture, but also effects of land use.  相似文献   

芦山7.0级地震宏观场地效应   总被引：1，自引：0，他引：1  

齐文浩  陈龙伟  单振东  汪云龙 《地震工程与工程振动》2013,33(4)

继汶川地震之后,2013年4月20日四川省庐山县又发生了7.0级强烈地震,其场地条件对震害的影响目前认识较少.通过专项工作,考察了雅安雨城区、芦山县、天全县、宝兴县等地区的结构震害及其场地条件,包括软土场地、老河床、不利地段、潜在滑坡等,分析了不同场地条件与震害的关系.结果表明,此次地震震害与场地条件有较密切关系,震害形式主要表现为软土震陷、河谷地形控制震害分布、不利地段加重震害、潜在滑坡的威胁、地质灾害堵塞交通等,其中软土震陷、河谷地形震害分布、不利地段处理都是值得深入研究的问题.  相似文献   

MOISTURE STRESS,MID-TROPOSPHERIC PRESSURE PATTERNS,AND THE FOREST/GRASSLAND TRANSITION IN THE SOUTH CENTRAL STATES     

William T. Corcoran 《自然地理学》2013,34(2):148-159

The climatic causes of the major forest/grassland ecotone in the south central United States (Kansas, Missouri, Oklahoma, Texas) are still poorly understood. Grassland and forest vegetation types differ markedly in their ability to withstand water stress induced by vapor pressure deficit (VPD), the difference between saturation vapor pressure and actual vapor pressure in the atmosphere. VPD is an airmass characteristic induced by ambient temperatures higher than dewpoint temperature. Mean summer airmass movement is from the Gulf of Mexico onto the continent in the central states area, but mean VPD displays a strong gradient approximately parallel to the ecotone. A subset of days having the strongest VPD gradients across the ecotone also had a 500 mb pressure height pattern identical to the long-term mean (modal) pattern. This 500 mb pattern, with a ridge over the Rocky Mountains and a trough over the Great Lakes, induces subsidence, stability, warming, and high VPD in Great Plains airmasses. Farther east, away from the zone of maximum subsidence, VPD is much lower. The grassland region coincides with the area of highest VPD. Because of the importance of the daily configuration of mid-tropospheric windflow patterns in controlling the distribution of VPD, moisture, and precipitation, more frequent occurrence of the modal 500 mb pattern is one mechanism for the occurrence of drought.  相似文献   

雅鲁藏布江河谷盛夏降水年际变化及其与环流的联系          下载免费PDF全文

边巴卓嘎  赤曲  周顺武  吴萍  孙阳 《大气科学学报》2022,45(3):469-479

基于近57 a （1961—2017年）西藏雅鲁藏布江中游河谷地区（简称雅江河谷）4个站（拉萨、日喀则、泽当和江孜）盛夏（7—8月）月平均降水和同期NCEP/NCAR再分析资料,采用合成、相关分析等统计诊断方法,分析了雅江河谷盛夏降水的年际变化特征及其与大气环流的联系。结果表明：1）近57 a雅江河谷盛夏降水无显著线性趋势,降水主要以3～4 a显著周期的年际振荡为主。2）雅江河谷盛夏降水年际波动与区域内水汽收支的变化直接相关,其中印度半岛-东南亚异常反气旋引起的水汽输送通量和水汽在高原腹地辐合上升的动力过程是盛夏降水年际变化的主要原因。3）对流层中低层印度半岛-东南亚异常反气旋环流是该地区盛夏降水年际异常的重要水汽输送通道,该通道将西太平洋、南海和孟加拉湾等地水汽不断输送到高原,期间西太副高和伊朗高压等大尺度系统异常对水汽输送过程起到了重要作用,同时高原盛夏季风低压和南亚高压异常给水汽在高原腹地辐合抬升提供了动力条件。  相似文献   

四川汶川县映秀镇红椿沟“8.14”特大泥石流形成条件与运动特征分析     

李德华  许向宁  郝红兵 《中国地质灾害与防治学报》2012,23(3):32-38

2010年8月14日,汶川县映秀镇强降雨导致红椿沟暴发特大泥石流灾害,冲出固体物质80.5×104m3,泥石流堰塞堵断岷江主河道,导致河水改道冲入映秀新区,淤埋了沟口213国道公路400m,掩埋了在建映(秀)-汶(川)高速公路引线路基及多个桥墩,造成17人失踪。据灾后调查,红椿沟泥石流为近几年暴发的较典型泥石流沟,地震诱发的集中物源特别丰富,暴发泥石流时一次冲出固体物质量巨大,沟内多点堵溃、拉槽下切集中启动物源的特征十分明显;本文重点分析了形成泥石流的三大条件及泥石流启动机理,反算运动特征参数,预测其发展趋势。  相似文献   

汶川地震区文家沟泥石流成因模式分析   总被引：3，自引：0，他引：3  

刘传正 《地质论评》2012,58(4):709-715

文家沟2008～2010年期间8次泥石流事件是在地震滑坡堆积体上因持续强降雨渗透变形溃决和后续侵蚀产生的,不同于一般的沟谷型和坡面型泥石流。文家沟滑坡堆积体上新生的泥石流沟共冲出松散固体物质总体积约180×104m3,2010年的"8.13"泥石流事件是其中规模最大的一次,冲出的松散固体物质体积约在115×104m3。文家沟泥石流的成因模式是,强降雨过程在滑坡堆积体上先期出现"渗流管涌、暂态壅水、溃决滑塌"的造沟作用模式,后期出现"溯源侵蚀、冲刷刨蚀、侧蚀坍塌、混合奔流(搅拌机)"的扩沟作用模式。2008年的"6.21"和2010年的"7.31"泥石流事件主要起因于前者,其他事件主要起因于后者。松散堆积体因排泄持续降雨入渗的能力不足而造成地下水滞留和水位升高是导致斜坡体稳定性降低的内在原因。当地下水壅高水位面达到水平时,堆积体内渗透动水压力达到最大,堆积斜坡的稳定性最低,成为堆积体表层发生滑塌溃决的临界条件。  相似文献   

阿尔泰山喀纳斯河流域末次冰期OSL年代学新证   总被引：2，自引：1，他引：1  

江合理  赵井东  殷秀峰  李忠勤  康剑  孙吉舟 《冰川冻土》2012,34(2):304-310

布尔津河支流喀纳斯河源于中俄蒙三国交界处友谊峰的南坡,为额尔齐斯河的重要源区.友谊峰连同奎屯峰等高峰形成了阿尔泰山最大的现代冰川作用中心.在第四纪期间,这些冰川都发生了规模较大的进退,在河谷中留下了形态较为清晰的冰川地形.应用OSL单片再生剂量测定技术对采自主U型谷两侧的高大侧碛垄进行了定年,测年结果分别为(27.2±2.0)ka(K-1)与(16.1±1.5)ka(K-2).基于地貌地层学原理、并结合已有的年代学资料(OSL与14 C)与古气候研究资料,末次冰期以来喀纳斯河流域共有5次规模较大的冰进,分别为小冰期、新冰期、末次冰期晚冰阶(MIS 2)、末次冰期中冰阶(MIS 3中期)与末次冰期早冰阶(MIS 4).  相似文献