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151.
L. N. Andreicheva T. I. Marchenko-Vagapova 《Stratigraphy and Geological Correlation》2007,15(4):421-436
The Pleistocene sediments of North European Russia have been studied using different methods to establish their composition and identify the enclosed organic remains. The results obtained elucidate natural climatic environments of the Pleistocene and corresponding sedimentation cycles and development stages. Glaciation centers are identified for different Pleistocene epochs based on lithological criteria. The established secular trends characterizing spatial distribution and composition of different-age glacial horizons facilitate their regional correlation. Climatic conditions and paleogeographic settings of sedimentation during interglacial epochs of the middle-late Pleistocene and Holocene are reconstructed. Variations in development of vegetation, temperature, and humidity are detected for the first time in the Timan-Pechora-Vychegda, Arkhangel’sk and Vologda regions with parallel coordination of obtained data. As is concluded, there was a tendency of climate cooling in North European Russia during the Neopleistocene. 相似文献
152.
A study on two closed salt lake basins, Tal Chapar and Parihara in the eastern margin of the Thar Desert, Rajasthan, was carried
out to unravel late Quaternary geomorphic evolution of these saline lakes. Both lakes are elliptical in shape bordered by
stabilised dunes, and are oriented in a NE-SW direction, i.e., in the direction of the prevailing summer monsoon wind. Both
lakes have been formed in the wind-shadow zones of isolated hills of Precambrian quartzite. Our study indicates that the late
Quaternary sediments in the lakes began with the cyclic deposition of laminated fine silt layers (0.5 m thick), rich in organic
matter, alternating with ripple cross-bedded sand layers (each ∼1.5–2 m thick). Sand layers that are moderately sorted are
separated by laminated silt-clay layers with gypsum/calcite and this unit occurs in the upper most 4 m sequence in deeper
sections. The presence of gypsum crystals within the laminated sediments suggests a high concentration of Ca in the inflowing
water.
At Parihara Lake the organic carbon-rich sediments at 95 cm depth was dated to 7,375 + 155/−150 year BP. At Tal Chapar radiocarbon
dates of 7,190 + 155/−150 and 9,903 + 360/−350 was obtained from the sediments rich in organic carbon occurring at a depth
of 1.35 m and 1.80 m, respectively. The study reveals strong hydrologic oscillations during the past ∼14,000 year BP (13,090 + 310/−300 year
BP).
Quaternary geomorphic processes, especially the strong aeolian processes during dry climatic phases, played a major role in
the formation of the lake basins, as well as the fringing linear dunes. Geochemical and mineralogical analyses of the lacustrine
sediments, supported by radiocarbon dates indicate the existence of an ephemeral lake earlier than ∼13,000 year BP as sediments
began to be deposited in a lacustrine environment implying sustained runoff in the catchments. A freshwater lake formed between
9,000 year and 7,000 year BP. The lake dried periodically and this strong fluctuating regime continued until about ∼7,000 year
BP. Mid-Holocene was wet and this was possibly due to higher winter rains A saline lake existed between 6,000 year and 1,300 year
BP and finally present day semi arid conditions set in since 1,200 year BP. Remnants of a habitation site (hearth and charred
bones) on stabilised dune at Devani near Tal Chapar were dated to 240 ± 120 year, while that at Gopalpura was dated to 335 ± 90 year.
These historical sites on stabilised dunes were, according to the local accounts, settlements of people who used the lake
brine for manufacturing salt. 相似文献
153.
This paper includes an investigation of the influence of the soil–structure interaction (SSI) on the fundamental period of buildings. The behaviour of both the soil and the structure is assumed to be elastic. The soil‐foundation system is modelled using translational and rotational discrete springs. Analysis is first conducted for one‐storey buildings. It shows that the influence of the SSI on the fundamental frequency of building depends on the soil–structure relative rigidity Kss. Analysis is then extended for multi‐storey buildings. It allows the generalization of the soil–structure relative rigidity Ks to such complex structures. Charts are proposed for taking into account the influence of the SSI in the calculation of the fundamental frequency of a wide range of buildings. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
154.
主要论述了与地名相关的地球信息科学、数字地球、地理信息系统、数字地图与电子地图等现代科技的发展及利用现代科技进行地堍用字和读音规范、地名信息系统、地名标志、地名技术规范、地名科研与管理等现代化地名工作问题。 相似文献
155.
基于MEM1谱分析的水文时间序列隐含周期特性研究 总被引:13,自引:1,他引:13
水文时间序列的隐含周期(本文将简单周期、复合周期及近似周期等统称为隐含周期)的识别、判定是一个重要而又较为困难的问题,相对成熟和有效的做法是对其进行频谱分析。建立在最大熵原理(POME)基础之上的MEM1谱分析,克服了传统谱分析方法的诸多不足,具有频谱光滑、分辨率高等独特优势。为此,以黄河花园口(秦厂)测站年径流系列、月径流系列和年最大洪峰流量序列隐含周期特性的研究为例,探讨了MEM1谱分析在水文时间序列隐含周期特性中的应用。 相似文献
156.
157.
广西两系杂交稻制种安全期气候分析 总被引:1,自引:0,他引:1
根据两系杂交水稻制种对气象条件的要求 ,利用广西 80多站的气象资料 ,统计分析了广西各地两系杂交水稻制种的安全期 ,提出了广西杂交水稻安全制种应注意的一些气候问题 相似文献
158.
159.
四川地震工作三十年的进展与新世纪的展望 总被引:3,自引:0,他引:3
回顾了四川省过去30年的地震工作,包括地震观测技术、地震预报、地震地质、工程地震、地震灾害预测和防震减灾系统。指出存在的问题并提出建议。 相似文献
160.