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991.
992.
利用1961—2018年中国地面气象台站2 400站中广东省和广西壮族自治区(两广地区)134站逐日降水资料、英国Hadley中心逐月海表温度资料、NCEP/NCAR逐月再分析资料,筛选了两广地区前汛期降水正(负)异常、后汛期降水负(正)异常的年份,即前、后汛期降水异常反位相年份。结果表明,近60 a来,两广地区前、后汛期降水反位相现象与热带西太平洋海温异常存在密切联系。前汛期期间,当热带西太平洋海温为负异常时,大气对该冷源的Rossby波响应引起西北太平洋反气旋环流异常,且水汽由热带西太平洋向两广地区输送并辐合,同时两广地区为水汽的湿平流区域、风场异常辐合区域,其上空受异常上升运动控制,这样的环流配置有利于两广前汛期期间降水正异常。热带西太平洋海温负异常可持续至后汛期期间,大气的Rossby波响应所致的西太平洋反气旋较前汛期偏西北,两广地区为水汽异常辐散区域,同时水汽干平流且风场异常辐散,受异常下沉运动控制,不利于两广地区降水的产生。反之亦然。 相似文献
993.
开展地震资料解释,分析上超、下超、顶超等地震反射终止关系、不整合面以及沉积趋势,识别出北康-曾母盆地中中新世以来14个三级层序界面。在层序界面内部,通过层序地层内幕结构刻画和原形剖面恢复,并结合地层堆砌方式,在北康-曾母盆地中中新世以来的层序地层内,划分了海进、高位正常海退、强制海退和低位正常海退4种成因单元。通过进一步研究该4种成因单元内地层结构和相分布关系,提出北康-曾母盆地中中新世以来的3种层序地层样式,即陆架边缘富砂型三角洲进积楔、退积型生物礁和陆架边缘富砂-富泥型退积楔,其中,沉积物源供应量充足且可容空间减小时,发育富砂的三角洲进积楔,陆架边缘-斜坡-盆地区域发育含砂深水扇;而可容空间增量远大于沉积物供应量时,发育退积型生物礁和富砂-富泥退积楔,斜坡-盆地区域含砂深水扇欠发育。 相似文献
994.
Evolution of Quaternary groundwater system in North China Plain 总被引:4,自引:0,他引:4
Zonghu Zhang Dehong Shi Fuhong Ren Zhengzhou Yin Jichao Sun Cuiyun Zhang 《中国科学D辑(英文版)》1997,40(3):276-283
The Quaternary groundwater system in the North China Plain is formed mainly through the terrestrial water flow action on the
united geological and tectonic backgrounds. The analysis of groundwater dynamic field, simulation of groundwater geochemistry,
and the14C dating and extraction of isotope information have provided more evidence for recognizing and assessing the evolution of
groundwater circulation system and studying the past global changes. The exploitation and utilization of groundwater on a
large scale and overexploitation have given rise to the decline of regional groundwater level, change of flow field, decrease
of water resources and downward movement of saline water body. The water environment has entered a new evolution stage in
which it is intensely disturbed by the mankind’s activities.
Project supported by the National Natural Science Foundation of China. 相似文献
995.
996.
997.
Fine round gravel soil is widely employed in the subgrade of high speed railways in cold regions to prevent frost heaving
and thawing. The lower the fines content in fine round gravel soil, the smaller the quantities of frost heaving and thawing,
but compaction difficulty increases. This study is to obtain the optimum fines content and limited frost heaving and
thawing. The fine round gravel soil filling (FRGSF) used in the Harbin-Qiqihaer Passenger Dedicated Line is taken as the
study object. Influence of fines content on optimum water content, maximum dry density and frost heaving properties of
FRGSF were studied by means of compaction and frost heaving tests. Results show that the maximum dry density of the
FRGSF increases first and then decreases with an increase of fines content, namely there is an optimum fines content for
easy compaction. The method of surface-vibratory instrument is fit for coarse-grained soils, and wet state of
coarse-grained soil is in favor of compaction. Considering the relationship of fines content with maximum dry density and
the frost heaving ratio of FRGSF, the fines content should be limited to within the range of 9%-10%, so that the frost
heaving ratio is less than 1%, and the FRGSF is easily compacted. Water supply is proved to be an important factor influencing
the amount of frost heaving of FRGSF. We also conclude that in the field, it is imperative to control waterproofing
and drainage measures. 相似文献
998.
We used long term monitoring data to evaluate changes in abundance and species dominance of small-jellyfish (collected with zooplankton net whose bell diameter was less than 5 cm) between 1991 and 2009 in the Jiaozhou Bay, China. Zooplankton samples were vertically towed with conical plankton net from near-bottom to surface, identified microscopically, and mapped in time-space using Grapher 7.0 and Surfer 8.0. Results show that the abundance of small-jellyfish throughout the bay had been increasing during 2001-2009 on average of 15.2 ind./m 3 , almost 5 times higher than that between 1991 and 2000. The occurrence of peak abundance shifted from spring to summer after 2000, and two peaks appeared in spring and summer, respectively, after 2005. Both the abundance and the frequency of blooms of small-jellyfish increased after 2000 in the bay. In addition, the biodiversity of jellyfish has increased significantly in recent years with a change in dominant species. Several new dominant species appeared after 2000, including Rathkae octopunctata in winter, Phialidium hemisphaericum in spring, summer, and autumn, Phialucium carolinae in spring, and Pleurobrachia globosa in summer and autumn, while some previous dominant species throughout the 1990s (Eirene ceylonensis, Zanclea costata, Lovenella assimilis, and Muggiaea atlantica) were no longer dominant after 2000. The abundance of small-jellyfish was positively correlated with the density of dinoflagellates, and the abundance of zooplankton. We believe that the changes in smalljellyfish abundance and species composition were the result of eutrophication, aquaculture and coastal construction activities around the bay. Concurrently, seawater warming and salinity decrease in recent decades promoted the growth and reproduction of small-jellyfish in the bay. 相似文献
999.
1000.
克拉通盆地内古隆起是了解板内变形机制的重要窗口,也是油气、煤、盐、铀等矿产勘查的主要对象,一直是盆地分析的热点领域。本文以鄂尔多斯盆地中央古隆起为例,利用新的高精度反射地震剖面与深探井资料,解剖古隆起的地质结构,刻画构造演化过程,探讨其形成机制。研究表明,鄂尔多斯盆地古生代隆起带发育在华北克拉通地块中西部,自伊盟—杭锦旗、乌审旗—定边,南延至镇原—正宁一带,呈“工”字形,面积达7.5×104 km2以上;伊盟凸起为基底隆起,镇原隆起为多阶段、间隙性发育的剥蚀与沉积型隆起,定边凸起为沉积型隆起。它是基底分异构造格局与周缘板块构造事件共同控制的产物,为在中元古代裂陷基础上早古生代被动大陆边缘背景下发育演化的古隆起;古生代早期,邻接周缘洋盆表现为台缘隆起;石炭纪晚期—二叠纪早期,因差异升降而具陆缘隆起性质;印支晚期—燕山期以来,隐伏于天环坳陷之下埋藏沉没。鄂尔多斯盆地中央隆起带为多机制复合成因,伊盟凸起为基底强烈伸展、长期剥露剥蚀型隆起;镇原凸起为西缘断阶迁移、南缘前缘隆起叠加的复合隆起;定边凸起为断阶迁移、挤压叠加的继承性隆起。鄂尔多斯盆地中央隆起带对盆地内部的构造—沉积分异施加了重要影响,其两翼斜坡带是油气聚集的有利区带。 相似文献