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Environmental record from the mud area on the inner continental shelf of the East China Sea since the midHolocene 总被引：1，自引：1，他引：0
Paleoclimate record was revealed in Core MZ01 covering the mid-Holocene in age, located in the mud area of the inner continental shelf of the East China Sea. The ancient environment featured low-energy shallow sea shelf deposition formed mainly by coastal currents. The results show that temporal variation in geochemistry corresponds with the climate changes inferred from historical record. Relatively low MgO/Al2O3, CaO/K2O and high Al2O3/Na2O, K2O/Na2O, MnO/CaO values reflected a warm and humid climate in general, and vice versa. Therefore, these chemical indices could be applied to identify the variation of palaeoclimate in eastern China. The authors reconstructed the history of mid-Holocene climatic variation of the inner continental shelf of the East China Sea. From 8 300 a BP to 4 200 a BP, the climate was moderately warm and humid. From 4 200 a BP to 2 000 a BP, the climate turned cool and dry, and the regional climate frequently fluctuated in alternation of cool-dry periods (3 700 a BP, 2 850 a BP and 2 400 a BP) and warm-wet periods (3 250 a BP and 2 650 a BP). After 2 000 a BP, the climate of the study area gradually turned warm again, while the Little Ice Age, a cold event centered at around 250 a BP was indicated by those geochemical indices as mentioned above. 相似文献
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This paper presents a paleoflood study to determine the flood frequency of the Changjiang River, based on core cj0702, taken from the Changjiang River subaqueous delta. We identified flood deposits by means of high-resolution grain-size variation, sensitive population, geochemical indexes and magnetic susceptibility. The core covers a time span of 120 years by 210 Pb dating and was sampled at 1–2 cm intervals. Grain size, geochemical elements, and physical parameters were analyzed. The results indicate that the sediment of the core is mainly composed of silt and clay, as well as groups of interbedded silt, clay silt, and clay. Vertically, the grain size pattern was controlled by seasonal variations in water discharge and by the sediment input in winter from the abandoned Huanghe River delta. River flooding caused extreme values in all our measured parameters. We identified more than 20 flood events that occurred since 1887 using the physical parameter analysis method. The environmentally sensitive component of sediment grain size(14.32–96.39 μm) contribution30%, Zr/Rb ratio1.5, and magnetic susceptibility16 were selected as the criteria for flood identification generally. We also found that floods that had taken place in the upstream, midstream, or downstream parts of the river were clearly identified by these indexes while the large-scale floods that covered the whole drainage area did not leave clear indications in the sediment record. This study for identification of flood events is of great significance for understanding hyperpycnal current sedimentation as well as for forecasting of floods. 相似文献
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塔里木盆地吐木休克断裂带断层封闭性研究 总被引：8，自引：3，他引：5
吐木休克断裂带位于塔里木盆地的西北部,是研究区规模最大、最具有研究意义的走滑断裂。油气勘探表明,吐木休克断裂带及邻区发育一系列大型背斜油气圈闭,它们受到了吐木休克断裂带的切割,所以对吐木休克断裂带断层封闭性研究对油气的勘探具有重要意义。根据断层封闭性影响因素的分析,选取断层的活动性、断层两盘地层的对置关系、断层断面图、断移地层的砂泥比、涂抹系数、断层面的压力与砂泥比的关系等6个参数作为断层封闭性研究综合评价指标,确定吐木休克断裂带中的主要断层都不具有封闭性,对先存的油气圈闭主要起破坏和改造作用。 相似文献
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贻贝养殖区底层鱼类群落结构特征分析 总被引：2，自引：0，他引：2
采用相对丰度、种类丰富度、多样性和均匀度以及相似性指数,结合丰度生物量比较曲线、等级聚类和生物与环境相关分析等多元统计方法对贻贝养殖和泥地生境中的鱼类组成、群落时空格局及其与环境因子间的关系作了比较研究。结果在两生境共采集鱼类41种,其中MF为35种,SB为25种。MF中以皮氏叫姑鱼(Johnius belangerii)和小黄鱼(Larimichthys polyactis)为代表的石首鱼科鱼类的优势度皆高于同期的SB,且褐菖鲉(Sebastiscus marmoratus)和星康吉鳗(Conger myriaster)成为MF的季节性优势种。但鲬(Platycephalus indicus)和黄鮟鮟(Lophius litulon)等泥地优势种在MF却较为少见。单变量分析表明两生境间各季度种类组成中等不相似。春夏季MF站位的群落丰度密度和物种多样性比SB高,但两生境间各指标并无显著差异。多变量分析显示3个站位的群落格局皆有显著的季节变化,且2生境间群落组成差异明显。ABC分析揭示幼小鱼类的数量优势在MF站位要比SB更明显,群落稳定性高于后者。BIOENV分析显示溶解氧皆为两生境鱼类群落组成的最大相关因子。研究表明,相对于同期的泥地生境,贻贝养殖对鱼类群落结构及其多样性并无显著影响,但养殖活动对石首鱼科鱼类和一些趋礁鱼类的种群可能起到了积极的养护作用,同时也为幼小鱼类提供了更多的人工庇护所。 相似文献
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