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81.
本文主要阐述了乾安县浅层高氟地下水的分布规律;探讨了浅层高氟地下水的成因与构造、地貌、古气候、地层岩性和水文地质条件的关系,从而闸明了广泛分布的湖沼相松散沉积物的组成和水文地质条件是本区浅层高氟地下水的主要原因。 相似文献
82.
The primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in Kenya. Results indicated that transfer of sediments (‘inputs’) from primary source areas was minor in comparison to changes in storage. The major sediment source area within the Katiorin drainage basin was the colluvial hillslope zone. The net change in storage within this zone was approximately 2100 Mg yr?1. Surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments. Sediment storage within the in-channel reservoir increased by 60 Mg yr?1, which was minor when compared to the total store of sediment in this reservoir. During 1986, the channel network stored only a small fraction ( < 3 per cent) of the sediment delivered from the hillslope subsystem. Therefore, the in-channel reservoir had limited influence on sediment conveyance to the basin outlet. These data indicate that a static equilibrium condition cannot be assumed within the Katiorin drainage basin. Such an assumption would result in erosion estimates of approximately 5.5 mm yr?1 for the entire basin (based on a sediment output of 7430 Mg km?2 yr?1 and a measured bulk density of 1.35 Mg m?3). However, this masked the actual rates of 1.2 to 7.1 mm yr?1 in subbasin primary source areas, and rates of 0.6 to 17 mm yr?1 for colluvial material in the various subbasins. The extreme accelerated erosion rates resulted from minimal ground vegetation, steep slopes, soil crust formation, an erodible substrate, and a well-integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet. 相似文献
83.
Domenico Tropeano 《地球表面变化过程与地形》1984,9(3):253-266
The ‘Tertiary Basin of Piedmont’ is a hilly region, mainly composed of marine sediments, such as marls, silts and sands. The slopes, largely devoted to grape production, are usually kept bare of vegetation and are thus prone to soil erosion processes. For two years we have measured soil loss in relation to rainfall on experimental plots located in vineyards. In all the plots considered erosion started with low rainfall intensities (0·07 mm/min), and above 0·4 mm/min the amount of soil loss dramatically increased (to over 1800 g/m in one event). Most of the erosion occurs during summer rainstorms, but the behaviour of the soil under erosive rainfalls is very different from one site to another, depending only in part upon the various rainfall rates, soil and geometrical characteristics of the plots. It can be seen that soil loss varies from nearly negligible values (20 g/m/yr) to unacceptably high levels (to over 4·7 kg/m/yr), according to the different types of land cultivation. Deep ploughing and heavy herbicide treatment give rise to accelerated erosion processes leading to soil losses much higher than in other vineyard plots in Europe. 相似文献
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A large sample of radar reflectivity data from essentially a full summer of operation was analyzed to determine the horizontal
extents and internal structure of rain areas observed at altitude levels from 2 to 10 km. Results are given on the size distributions
of individual cells or patches defined by reflectivity thresholds approximately 4 dBz apart, on the dependence of mean size
on altitude and reflectivity threshold, and on the interior structure of the patches as characterized by the number and sizes
of higher-threshold patches contained in each echo. In a more detailed analysis of internal structure, the data were restricted
to convective echoes in which certain prescribed reflectivities, ranging from about 30 to 50 dBz, were exceeded. It was found
that the dependence of mean quantities, such as patch area, on reflectivity and altitude could be approximately described
by simple functions, but that the scatter of observations about the mean was usually large. 相似文献
86.
论中国含油气区的构造环境性质、分区及其成油气专属性 总被引:13,自引:0,他引:13
在前中生代,形成了华北、扬子和塔里木等较大的海相及海陆交互相含油气区(盆地),构造格架呈南北分异。经海西-印支运动,形成统一的中国大陆板块,且整体构造格架演变为东西分异。根据盆地结构、构造变形样式、岩浆活动、地温场、壳幔结构及壳幔连通程度等方面的特征,论述了中、新生代中国含油气区的大地构造环境性质与含油气特征。据此划分出 4个具有不同构造环境性质的含油气区:①东部裂谷伸展区,其西带为华夏裂谷系,以产下第三系和白垩系原油为主,东带为大陆架裂谷系,以产下第三系煤型气为主;②中部克拉通构造稳定区,以产古生界天然气为主;③西北构造反转区,含油气层系较多,油气成因类型也多样;④特提斯碰撞-走滑区,构造变形复杂,部分地区具有较好的油气资源前景。进一步讨论了油气形成的"构造环境专属性"问题。 相似文献
87.
88.
猪野泽记录的季风边缘区全新世中期 气候环境演化历史* 总被引:4,自引:16,他引:4
通过季风边缘区石羊河古终端湖猪野泽QTL剖面年代学及沉积物粒度、碳酸盐、有机碳、碳氮比和有机质稳定同位素等多项气候代用指标的综合分析,建立了季风边缘区9~3cal.kaB.P. 的古气候演化序列。结果表明,9cal.kaB.P. 到7.8cal.kaB.P. 期间,流域的水分条件和温度逐渐上升,植被状况好转,此时气候逐渐转暖湿;而在7.8~7.5cal.kaB.P. 出现了显著的百年尺度的干旱事件,沉积物主要以砂质沉积为主,此时湖泊生产力显著下降;全新世期间最为暖湿的气候适宜期出现在7.5~5.0cal.kaB.P.;约5.0cal.kaB.P. 以来,该区域出现了较为明显的干旱化趋势。另外,对猪野泽地区的白碱湖的湖泊地貌学和年代学研究表明该区域在7.5~5.0cal.kaB.P. 出现了3次高湖面,并且湖岸堤时序变化指示了全新世后半期湖泊逐渐退缩的过程进而指示该区域出现了显著的干旱化趋势。 相似文献
89.
90.