排序方式： 共有5条查询结果，搜索用时 15 毫秒
1
1.
Characteristics of Clay Minerals in the Northern South China Sea and Its Implications for Evolution of East Asian Monsoon since Miocene 总被引：3，自引：0，他引：3
Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma. 相似文献
2.
The Okinawa Trough is a natural laboratory for the study of air-sea interaction and paleoenvironmental change. It has been demonstrated that present offshore export of particles in the bottom nepheloid layer occur primarily with downwelling from the northeast winter monsoon, which is inhibited by a transverse circulation pattern in summer. This current system was very different during the Last Glacial Maximum owing to low sea level(-120 m) and exposure of a large shelf area. We collected sediment core Oki01 from the middle Okinawa Trough during 2012 using R/V K exue No. 1 to elucidate the timing and cause of the current system transition in the East China Sea. Clay mineral, dry density, and elemental(Ti, Ca) composition of core Oki01 was analyzed. The results indicate that clay minerals derived mainly from the Huanghe(Yellow) and the Changjiang(Yangtze) Rivers during 16.0–11.6 ka, and the modern current system in the East China Sea formed beginning in the early Holocene. Therefore, mixing of East China Sea continental shelf, Changjiang River and partially Taiwan Island sediment are the major contributors. The decrease of log(Ti/Ca) and alternating provenance since the early Holocene indicate less sediment from the East China in summer because of resistance of the modern current system, i.e., a "water barrier" and upwelling. Conversely, sediment delivery persists in winter and log(Ti/Ca) indicates the winter monsoon signal since the early Holocene. Our evidence also suggests that sediment from Taiwan Island could be transported by the Kuroshio Current to the middle Okinawa Trough, where it mingles with winter monsooninduced export of sediment from the Changjiang River and East China Sea continental shelf. Although the present research advances understanding of the evolutionary history of paleoenvironmental change in the Okinawa Trough, more sediment cores should be retrieved over wide areas to construct a larger scenario. 相似文献
3.
南海北部中新世以来粘土矿物特征及东亚古季风记录 总被引：4，自引：0，他引：4
应用X射线衍射(XRD)、扫描电子显微镜(SEM) 和X射线能谱(EDS) 分析技术对南海北部ODP1146站中新世以来(~20 Ma) 粘土矿物的组成、结晶学特征、微形貌和化学成分进行了研究, 分析了粘土矿物的物质来源及其记录的东亚季风演化历史.1146站粘土矿物组合的总体特点是以伊利石和蒙脱石为主, 高岭石和绿泥石含量较低.物源分析表明, 1146站蒙脱石主要来自于吕宋岛, 伊利石和绿泥石来自于珠江和台湾(长江), 而高岭石则主要来自于珠江.1146站的粘土矿物不仅被南海周围物源的同时代气候所控制, 而且为相互消长的不同传输作用(表层洋流) 的强度所影响.1146站(伊利石+绿泥石) /蒙脱石比值可以用来作为东亚季风演化的矿物学标志.指标变化显示出东亚冬季风强度和冬季风相对夏季风的强度在15 Ma、8 Ma和3 Ma左右发生了3次显著加强, 结果可以与黄土、北太平洋风尘沉积、南海微体古生物记录等很好对比.青藏高原的阶段性隆升可能促进了东亚季风的这3次加强. 相似文献
4.
苔藓动物的群体是由生理上互相连系、以无性繁殖方法复制的称之为个虫的成员组成。幼虫变态后,绝大多数苔藓虫形成构成群体基础的单一个虫,称为初虫,这些单一的初虫通常为一摄食个虫,有时则为形态多样的无摄食功能的空个虫;另一些幼虫变态后则形成2个、3个或5个个虫,称之为初虫群,初虫群的每一个体均为摄食个虫。绝大多数苔藓虫群体都由单一的初虫或初虫群以无性出芽而成,只有极少数苔藓虫群体由休眠芽产生或由裂殖方式产生。按照苔藓动物学关于群体性质的一般概念,每一群体由若干类型的个虫和多个虫部分构成,而某些群体还包括个虫外部分。个虫是无性繁殖产生、分别执行如摄食、生殖、支撑、保护等主要生理或结构功能的自然连系的形态单位。多个虫部分包括既存个虫界限外面生长的连续体壁层及其包裹的体腔,随着群体发育,它们便成为个虫之一部分。个虫外部分在群体整个生命期间都位于个虫界限之外,包括体壁(有骨骼层或无骨骼层)、非体壁之一部分的骨骼以及相邻的体腔。群体是一个可与单体动物相比拟而与环境相互作用的完整生命机体,一般说来,群体是均匀一致的。组成群体的成员除初虫或初虫群是以有性生殖方式产生外,所有其他部分都是由细胞生理上连续的有丝分裂和非细胞部分的分泌作用产生的。如果假定它们的基因是均匀性的,那么就可以说在一群体内的个虫在形态上是同一的,然而一苔藓动物群体内的个虫在某些特征上通常是不同的。一群体内表征上不同的个虫表达了那些未必反映基因差异的形态变异,任一群体所显示的这种非遗传变异都可归于下述诱发群体内形态变异的四个非遗传因素:个虫和个虫外结构的个体发育、群体发育(或群育)、多形结构和微环境。 相似文献
5.
建立1种新的射影重建方法。该方法以全局性极小化射影三维空间点的二维反投影误差平方和为准则,相对于缩小SVD反投影误差的方法,具有更为明确合理的物理意义。实现过程是以奇异值分解为基本工具的分步线性迭代计算,避免了传统射影重建方法复杂的非线性优化环节。它无需估计投影深度,避免了基础矩阵计算的复杂性问题,因而也不受相机特殊运动的限制。文中利用虚拟物体图像和真实物体图像进行了实验验证,证明该方法具有计算简单、准确性和鲁棒性高等方面的特点,具有较高的实用价值。 相似文献
1