排序方式： 共有20条查询结果，搜索用时 15 毫秒
1.
在长江河口潮滩、分流河道和水下三角洲共获得18个柱样,进行沉积学分析和210Pb测定,并对其中6根柱样进行137Cs测定。经研究发现,长江口外在水深25～30m,122°30′N,31°00′E附近存在一个泥质沉积中心,沉积速率达2.0～6.3cm/yr。另外,在潮滩和涨潮槽也获得较高沉积速率,其中南汇和横沙岛潮滩沉积速率(1.03～1.94cm/yr)高于崇明东滩(0.51～0.76cm/yr),涨潮槽沉积速率也达0.86cm/yr。此外,在石洞口、南汇、九段沙潮滩和三角洲前缘有部分柱样未获沉积速率,推测为沉积环境不稳定或沉积速率过快所致。 相似文献
2.
JINSONG PING KOJI MATSUMOTO KOSUKE HEKI AKINORI SAITO PHILIP CALLAHAN LARAMIE POTTS 《Marine Geodesy》2013,36(3-4):741-752
The Jason-1 dual-frequency nadir ionosphere Total Electron Content (TEC) for 10-day cycles 1–67 is validated using absolute TEC measured by Japan's GPS Earth Observation Network (GEONET), or the GEONET Regional Ionosphere Map (RIM). The bias estimates (Jason–RIM) are small and statistically insignificant: 1.62 ± 9 TECu (TEC unit or 1016 electrons/m2, 1 TECu = 2.2 mm delay at Ku-band) and 0.73 ± 0.05 TECu, using the along-track difference and Gaussian distribution method, respectively. The bias estimates are –3.05 ± 10.44 TECu during daytime passes, and 0.02 ± 8.05 TECu during nighttime passes, respectively. When global Jason-1 TEC is compared with the Global Ionosphere Map (GIM) from the Center for Orbit Determination in Europe (or CODE) TEC, the bias (Jason–GIM) estimate is 0.68 ± 1.00 TECu, indicating Jason-1 ionosphere delay at Ku-band is longer than GIM by 3.1 mm, which is at present statistically insignificant. Significant zonal distributions of biases are found when the differences are projected into a sun-fixed geomagnetic reference frame. The observed biases range from –7 TECu (GIM larger by 15.4 mm) in the equatorial region, to +2 TECu in the Arctic region, and to +7 TECu in the Antarctica region, indicating significant geographical variations. This phenomena is primarily attributed to the uneven and poorly distributed global GPS stations particularly over ocean and near polar regions. Finally, when the Jason-1 and TOPEX/Poseidon (T/P) TECs were compared during Jason-1 cycles 1–67 (where cycles 1–21 represent the formation flight with T/P, cycles 22–67 represent the interleave orbits), the estimated bias is 1.42 ± 0.04 TECu. It is concluded that the offset between Jason/TOPEX and GPS (RIM or GIM) TECs is < 4 mm at Ku-band, which at present is negligible. 相似文献
3.
A. N. KROT A. MEIBOM M. I. PETAEV K. KEIL M. E. ZOLENSKY A. SAITO M. MUKAI K. OHSUMI 《Meteoritics & planetary science》2000,35(6):1249-1258
Abstract— The CH carbonaceous chondrites contain a population of ferrous (Fe/(Fe + Mg) ? 0.1‐0.4) silicate spherules (chondrules), about 15–30 μm in apparent diameter, composed of cryptocrystalline olivinepyroxene normative material, ±SiO2‐rich glass, and rounded‐to‐euhedral Fe, Ni metal grains. The silicate portions of the spherules are highly depleted in refractory lithophile elements (CaO, Al2O3, and TiO2 <0.04 wt%) and enriched in FeO, MnO, Cr2O3, and Na2O relative to the dominant, volatile‐poor, magnesian chondrules from CH chondrites. The Fe/(Fe + Mg) ratio in the silicate portions of the spherules is positively correlated with Fe concentration in metal grains, which suggests that this correlation is not due to oxidation, reduction, or both of iron (FeOsil ? Femet) during melting of metal‐silicate solid precursors. Rather, we suggest that this is a condensation signature of the precursors formed under oxidizing conditions. Each metal grain is compositionally uniform, but there are significant intergrain compositional variations: about 8–18 wt% Ni, <0.09 wt% Cr, and a sub‐solar Co/Ni ratio. The precursor materials of these spherules were thus characterized by extreme elemental fractionations, which have not been observed in chondritic materials before. Particularly striking is the fractionation of Ni and Co in the rounded‐to‐euhedral metal grains, which has resulted in a Co/Ni ratio significantly below solar. The liquidus temperatures of the euhedral Fe, Ni metal grains are lower than those of the coexisting ferrous silicates, and we infer that the former crystallized in supercooled silicate melts. The metal grains are compositionally metastable; they are not decomposed into taenite and kamacite, which suggests fast postcrystallization cooling at temperatures below 970 K and lack of subsequent prolonged thermal metamorphism at temperatures above 400–500 K. 相似文献
4.
末次盛冰期以来冲绳海槽中段岩心中黏土粒级沉积物地球化学特征及物质来源的阶段性 总被引：4，自引：2，他引：4
测定了冲绳海槽DGKS9603孔21个样品中黏土粒级沉积物的常、微量元素组分,利用因子分析的方法,识别出对冲绳海槽中段沉积物物源有重要影响的陆源成因因子、生物成因因子及火山作用和海底热液因子.陆源成因因子的元素组合为Fe2O3,Al2O3,V等惰性元素及K2O,MgO等氧化物;生源因子的元素组合为CaO,Sr,Ba,Mn,P;火山和海底热液成因因子的元素组合为Na,Co,Ni.据样品的因子得分将柱样由上而下划分出物源的4个不同阶段:A段生物成因因子得分高,沉积物质主要是本地生物沉积,但也有富含生物成因物质的陆源物质的贡献;B段火山作用所产生的沉积物质特征显著,Na,Co,Ni呈现高含量;C段以陆源物质和生源物质沉积混杂为特征,元素垂向上变化不大;D段主要为陆源物质,其他来源物质相对较少,且可能主要来自在末次冰期最盛期所出露的陆架沉积.提出了冲绳海槽物源具有阶段性的论点.由于末次盛冰期以来全球气候呈现冷暖交替的阶段性变化,本区物源的阶段性变化是这一时期气候和古环境阶段性变化的良好反映. 相似文献
5.
ASAHIKO TAIRA SANEATSU SAITO KAN AOIKE SUMITO MORITA HIDEKAZU TOKUYAMA KIYOSHI SUYEHIRO NARUMI TAKAHASHI MASANAO SHINOHARA SCHOICHI KIYOKAWA JIRO NAKA & ADAM KLAUS 《Island Arc》1998,7(3):395-407
The bulk composition of the continental crust throughout geological history is thought by most previous workers to be andesitic. This assumption of an andesitic bulk composition led to an early hypothesis by 72 ) that the continental crust was created by arc magmatism. This hypothesis for the origin of continental crust was challenged by several authors because: (i) the mean rate of arc crust addition obtained by 50 ) is too small to account for some certain phases of rapid crustal growth; and (ii) the bulk composition of ocean island arcs, the main contributor to the Archean and early Proterozoic crust, is basaltic rather than andesitic ( 4 ; 49 ). New data from the Northern Izu–Bonin arc are presented here which support the 72 ) hypothesis for the origin of the continental crust by andesitic arc magma. A geological interpretation of P wave crustal structure obtained from the Northern Izu–Bonin arc by 66 ) indicates that the arc crust has four distinctive lithologic layers: from top to bottom: (i) a 0.5–2-km-thick layer of basic to intermediate volcaniclastic, lava and hemipelagite (layer A); (ii) a 2–5-km-thick basic to intermediate volcaniclastics, lavas and intrusive layer (layer B); (iii) a 2–7-km-thick layer of felsic (tonalitic) rocks (layer C); and (iv) a 4–7-km-thick layer of mafic igneous rocks (layer D). The chemical composition of the upper and middle part of the northern Izu–Bonin arc is estimated to be similar to the average continental crust by 73 ). The rate of igneous addition of the Northern Izu–Bonin arc since its initial 45-Ma magmatism was calculated as 80 km3/km per million years. This rate of addition is considered to be a reasonable estimate for all arcs in the western Pacific. Using this rate, the global rate of crustal growth is estimated to be 2.96 km3/year which exceeds the average rate of crustal growth since the formation of the Earth (1.76 km3/year). Based on this estimate of continental growth and the previously documented sediment subduction and tectonic erosion rate (1.8 km3/year, 24 ), several examples of growth curves of the continental crust are presented here. These growth curves suggest that at least 50% of the present volume of the continental crust can be explained by arc magmatism. This conclusion indicates that arc magmatism is the most important contributor to the formation of continental crust, especially at the upper crustal level. 相似文献
6.
Grain size records reveal variability of the East Asian Winter Monsoon since the Middle Holocene in the Central Yellow Sea mud area,China 总被引：3，自引：0，他引：3
Yoshiki SAITO 《中国科学:地球科学(英文版)》2012,(10):1656-1668
Three cores(ZY-1,ZY-2 and ZY-3) retrieved from the Central Yellow Sea mud(CYSM) were analyzed in sensitive grain size and AMS 14 C dating to reconstruct the history of the East Asian Winter Monsoon(EAWM) since the Middle Holocene in the study area.The results show that these data provide a continuous history of the EAWM over the past 7.2 ka and that the EAWM can be divided into three periods:strong and highly fluctuating during 7.2-4.2 ka BP;moderate and relatively stable during 4.2-1.8 ka BP;and weakened during 1.8-0 ka BP.Compared with the East Asian Summer Monsoon(EASM) recorded in the previous studies,the evolutionary history of the EAWM broadly follows the orbital-derived winter insolation with a similar long-term step-decreased trend as the EASM.At the centennial scale,however,the EAWM intensified events correlate well with the EASM weakened events and the North Atlantic climatic variations(Bond events 0 to 5) within the dating error,most likely forced by the reduction of solar irradiance through changes in the oceanic-atmospheric circulation patterns. 相似文献
7.
HOUYUAN LU ZHENXIA LIU NAIQIN WU SERGE BERNÉ YOSHIKI SAITO BAOZHU LIU LUO WANG 《Boreas: An International Journal of Quaternary Research》2002,31(4):378-385
Fossil rice phytoliths have been identified from a lateglacial to Holocene sequence of epicontinental sediments in the East China Sea that were probably transported by the Yangtze River from its middle and/or lower reaches. The rice phytoliths occurred first in the sequence at about 13900 cal. yr BP and disappeared during the period of 13000-10000 cal. yr BP, implying the earliest domesticated cereal crops of the world ever reported. Based on the records of phytoliths, pollen, diatoms and foraminifera from the sequence, the climate between 13000 and 10000 cal. yr BP was notably colder (Younger Dryas). The coincidence of disappearance of domesticated rice phytoliths with cold climate conditions may suggest a great climatic influence on human activities during that time. Warmer and wetter conditions during the period 13900 to 13000 cal. yr BP and after 10000 cal. yr BP have probably favoured rice domestication in the area. 相似文献
8.
TORU TAMURA FUTOSHI NANAYAMA YOSHIKI SAITO FUMITOSHI MURAKAMI REI NAKASHIMA KAZUAKI WATANABE 《Sedimentology》2007,54(5):1149-1162
This study documents lowering of the surf zone (i.e. the upper shoreface) leading to intra-shoreface erosion, following two rapid relative sea-level falls along a tectonically uplifted coast during the Holocene, and the characteristics of the resultant prograding shoreface deposits. These findings are based on high-resolution analysis and radiocarbon dating of three new drill cores obtained from the Kujukuri strand plain, Pacific coast of eastern Japan, combined with previously published borehole data and information on modern shoreline profile adjustments. A shallowing-upward sandy succession composed of lower and upper shoreface facies, foreshore and backshore facies was recognized in the drill cores. Two rapid falls in relative sea-level at 2·3 to 2·6 and 1·8 to 2·0 ka are recorded by downstepping of the base of the foreshore facies, and farther seawards by the lowering of an erosional boundary between the upper and lower shoreface facies. Superimposed bed profiles of an adjacent modern beach define an envelope, the base of which reflects shore-normal migration of longshore bars and troughs. The base of the envelope represents an erosional surface that divides the surface mobile layer above from preserved deposits beneath. The surface is concave upwards and steeper than the mean beach profile, and exhibits a flat platform approximately at the lower limit of the upper shoreface equating to the storm surf zone. The seaward transition of this surface, rather than the mean equilibrium profile, controls the metre-scale to decimetre-scale internal structure of the Kujukuri shoreface deposits. Depositional models for sea-level fall based on an exponential equilibrium profile do not adequately account for the presence and migration of longshore bars and troughs. 相似文献
9.
根据对越南红河三角洲的2个钻孔的孢粉分析结果，结合沉积特征和高精度的AMS^14C测年数据，恢复了近五千年来百年一千年尺度的气候变化，发现了3个分别开始于4530cal．aBP，2100cal．aBP和620cal．aBP的明显降温事件，其中4530cal．aBP和620cal．aBP降温事件可与全球全新世气候变冷事件中的“新冰期(Neoglacial)”和“小冰期(Little Ice Age)”相对应，可能与由北大西洋地区几个短期变冷事件的全球气候响应机制有关。3340cal．aBP以来，人类干扰性植物成分的增加，表明人类活动对自然植被的影响改造作用增强，因此，本研究中气候的降温事件不排除人类影响的因素，仍需要进一步深入研究。 相似文献
10.
N. SUZUKI S. KIMURA T. NAKADA C. KAITO Y. SAITO C. KOIKE 《Meteoritics & planetary science》2000,35(6):1269-1273
Abstract— Films condensed from vapors containing SiO, Fe, or Mg showed an amorphous structure. Infrared (IR) spectra and electron microscopic characterization have been carried out on these films. After the heat treatment of these films in air, IR peaks at approximately 18–23 μm appeared, in addition to peaks attributable to SiO2. These peaks can be attributed to metallic oxides such as FeO, Fe2O3, and MgO. It can be concluded that Fe‐ or Mg‐bearing silicate minerals cannot be produced by the rapid cooling of SiO, Fe, or Mg vapors. Although IR spectra of FeO have been discussed in order to match some spectra obtained with the Infrared Space Observatory, the identification of FeO as the impurity would be very important because the IR spectra of FeO grains are very dependent on the shape and size of the grains. These impurities can also influence the IR spectral feature of SiO2. 相似文献