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141.
Channel morphology and its impact on flood passage, the Tianjiazhen reach of the middle Yangtze River 总被引:1,自引:0,他引:1
The Tianjiazhen reach of the middle Yangtze is about 8 km long, and characterized by a narrow river width of 650 m and local water depth of > 90 m in deep inner troughs, of which about 60 m is below the mean sea level. The troughs in the channel of such a large river are associated with regional tectonics and local lithology. The channel configuration plays a critical role in modifying the height and duration of river floods and erosion of the riverbed. The formation of the troughs in the bed of the Yangtze is considered to be controlled by sets of NW–SE-oriented neotectonic fault zones, in which some segments consist of highly folded thick Triassic limestone crossed by the Yangtze River. Several limestone hills, currently located next to the river channel, serve as nodes that create large vortices in the river, thereby accelerating downcutting on the riverbed composed of limestone highly susceptible to physical corrosion and chemical dissolution. Hydrological records indicate that the nodal hills and channel configuration at Tianjiazhen do not impact on normal flow discharges but discharges > 50,000 m3s− 1 are slowed down for 2–3 days. Catastrophic floods are held up for even longer periods. These inevitably result in elevated flood stages upstream of prolonged duration, affecting large cities such as Wuhan and a very large number of people. 相似文献
142.
黑龙江鸡东盆地是受古、新近纪敦密断裂带作用而形成的断陷含煤盆地。依据该盆地91-205钻孔永庆组的岩性变化特点和盆地构造演化阶段,识别和阐述了中中新世湖盆发育的3个阶段,即早期湖泊形成发展阶段、中期湖泊扩张最大阶段和晚期湖泊收缩衰退阶段,并揭示湖泊阶段性发展的旋回性特征。根据孢粉资料,恢复湖盆各个不同发育阶段的古植被面貌,重建当时的古气候。结果表明植被经历了北亚热带含常绿阔叶成分的落叶阔叶林、暖温带—北亚热带落叶阔叶林以及含亚高山针叶树种的暖温带—北亚热带落叶阔叶林阶段,鸡东盆地中中新世湖泊的演变和植被更替存在着潜在的关联。 相似文献
143.
利用1:20万区域化探资料及1:2万化探普查资料,通过对母质(岩)常量元素、微量元素、土壤中重金属元素的分布分配特征的研究,结合区内地下水化学类型的分布特点,阐述了东海-新沂地区土壤农业地质背景及土壤环境质量,并对1:20万区域化探圈出的异常地段中元素的改良处理提出了相应的建议,为农业生产和产业结构调整指明了方向.充分说明了地球化学探矿资料作为基础性的资料,除了为找矿服务以外,更能象基础地质图一样,服务于农业、工业、环境等各个领域. 相似文献
144.
A geochemical baseline provides the means to distinguish between the pedogenic origin and the anthropogenic origin of the
trace element in the environmental compartments. We collected 271 soil samples representative of different parent rocks and
soil types from the whole territory of Hong Kong and analyzed the composition of clay mineralogy and the contents of 15 chemical
elements (Fe, Cd, As, etc.) for these samples. The baseline was predicted with the method of the normalization procedure combined
with the relative cumulative frequency curve. The result indicated that Fe was the best reference element for the normalization
procedure among the five potential reference elements (Fe, Al, Sc, Ti, and Mn), followed by Sc and Ti. A poor correlation
was found between Sc, Ti, and Cu. The predicted baseline was much lower than the A-value of the Dutch List used usually in screening the polluted soil of Hong Kong, implying that the extent of heavy metal
pollution might have been underestimated with respect to local lands. We also applied the cluster analysis to distinguish
the geochemical associations of the trace elements due to its importance to the baseline. Approximately three major associations
including the Fe–Mn-oxides related, Al oxides or Al-bearing-clay-mineralogy related and sulfide- related associations were
observed from the dendrogram. 相似文献
145.
Fossil leaves resembling Nothofagaceae have been investigated from the Eocene of western Antarctica and a new form genus Nothofagofolia is proposed for these kinds of fossils. Some new specimens belonging to this form genus are described. They were collected
from the Fossil Hill locality of Fildes Peninsula, King George Island, South Shetland Islands, western Antarctica. Two new
species, two new combinations and an unnamed species are reported. A number of published Nothofagus leaf fossils from the same locality are discussed and revised. As a result of these studies of Nothofagus leaf morphology, we conclude that (1) Nothofagus probably originated in high latitudes of the Southern Hemisphere during the middle-late Late Cretaceous and diversified,
dispersed gradually to the lower latitudes of the same hemisphere; (2) leaf morphological characters are significant for the
systematics of the family Nothofagaceae, especially at the intrageneric level; and (3) extant species of Nothofagus known from southern temperate areas have more primitive leaf morphological characters and lower leaf ranks than those from
tropical mountains as well as those of the Fagaceae and Betulaceae.
Supported by the Foundation of State Key Laboratory of Palaeobiology & Stratigraphy, Nanjing Institute of Geology and Palaoentology,
Chinese Academy of Sciences (Grant No. 013106), the National Natural Science Foundation of China (Grant No. 30670159) and
the Fund of Innovation Program by Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences 相似文献
146.
147.
148.
The correlations of the δ18Omax in the shallow ice core from the Guliya ice cap on the Tibetan Plateau with the global sea surface temperatures (SST) and
height at the 500 hPa over the Northern Hemisphere were analyzed. The correlated regions on oceans that have a significant
influence on the δ18Omax in the Guliya ice core are all located in ocean currents, or convergent regions of currents. They are the eastern Equatorial
Pacific, the Northern Pacific Current, the Hot Pool in the eastern Indian Ocean, the Mozambique Current, the Northern Atlantic
Current, the Canary Current and the Atlantic Equatorial Current. The δ18Omax in the Guliya ice core has negative correlations with the SST located in the lower latitudes, and positive correlations with
the SST in the middle latitudes. The correlated areas at the 500 hPa that have a great impact on the δ18Omax are located in the subtropical highs over the mid-low-latitude oceans and the long-wave trough area over Balkhash Lake, where
there are marked negative correlations between the heights in those areas and the δ18Omax. The influencing mechanism is displayed by the diversity of the vapor origins transported to the Guliya region. The strengths
of the European ridge and the ridge over Baikal Lake have notable positive correlations with the δ18Omax. The two systems indirectly influence the vapor transportation towards the Guliya region by the adjustment of long-wave trough
and ridge. 相似文献
149.
影响事件层保存潜力的主要因素有 :纯粹的沉积速率、生物成因的混合速率以及机械改造的规模,可以从时间规模 (过渡时间和消除时间 )的角度来考虑事件层保存潜力。基底的机械改造同样对于事件层和正常天气下的沉积物的保存具有重要影响。综合分析影响事件层保存潜力的各种因素表明,在近基的临滨带中、上部及滨外带下部,事件层具有较高的保存潜力,而在近基及远基两端之间的临滨带下部及滨外带上部,事件层保存潜力较低. 相似文献
150.
利用贝类(Lamprotula)化石碳氧同位素再建山西丁村地区晚更新世气候环境 总被引:3,自引:0,他引:3
较大的湖泊中的贝类生长线的氧同位素可能记录了季节性的温度变化。对拔氏丽蚌 (楔丽蚌 )Lamprotula(Cuneolamprotula)bazini (Heude)和环带丽蚌 (丽蚌 )Lamprotula (Lamprotula)zonata (Heude)的生长线进行氧同位素研究表明,前者有较强的适应环境变化的能力。δ18O值记录的襄汾地区晚更新世的古温度为 2 0~ 2 4℃至 30~34℃,古降雨量多出现代 2 0 0~ 2 6 7mm,河水排泄不畅,积水成湖。这些结果给人的启示是:全球变暖后,该地区气温可能有较大升幅 ;降雨量的增加有可能在排水不畅地区形成水灾,应注意防患于未然。 相似文献