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951.
《International Geology Review》2012,54(17):2164-2183
ABSTRACTTephra fallout beds in marine sediments provide chronologically precise and highly resolved records of volcanism at time scales relevant to Quaternary climate cycles. While the record of discrete (visible) thin tephra beds is readily accessible, the significance of the dispersed (invisible) tephra record remains unclear. Here we evaluate the role of dispersed tephra for orbital-scale volcanic time variations in the Quaternary (<1.2 Ma) carbonate mud of IODP Hole U1437B (Northwest Pacific). The carbonate mud contains cyclic series of discrete fallout tephra beds from the oceanic Izu Bonin (~85% of tephra beds) and the continental Japan (~15%) volcanic arcs, respectively. Our results show the inorganic aluminosilicate (lithogenic) fraction is a mixture of dispersed Izu Bonin and Japan ash, and Asian dust. The time distribution of the Izu Bonin ash with its distinct composition appears to confirm and enhance the cyclic time variation of the discrete ash beds at Hole U1437B. Dispersed Japan ash resembles Asian dust in trace elements and is only distinguishable in Sr-Nd isotope space. Collectively, our results confirm the existence of periodic, orbital-scale fluctuations of arc volcanic frequency. Orbital-scale time variations of marine ash may be best established by series of discrete marine ash beds, yet the concomitant dispersed ash flux must also be recorded in order to understand the total flux of arc volcanic ash into the ocean basins and thus the role of the volcanism-climate link. 相似文献
952.
Effect and Prospect of Basic Geological Survey Based on Airborne Gravimetry in China 总被引:1,自引:0,他引:1
LI Wenyong ZHOU Jianxin XIONG Shengqing GUO Zhihong LU Wenfen XU Jianchun LIU Yanxu 《《地质学报》英文版》2012,86(1):38-47
The airborne gravimetry was an important leap and innovation in the world’s history of geophysical exploration. China's first test of the airborne gravity geological survey in the onshore-offshore transitional area of the western and southern part of the Bohai Sea was successful and effective in geology. Based on the airborne gravity data, and combining previous ground gravity, seismic and drilling data etc., we carried out the geological interpretation by forward and inverse methods. The result shows that the airborne Bouguer gravity anomaly was clear, the fracture interpretation was reliable, and the inversion depth of the main geological interfaces was relatively accurate. This airborne gravity geological survey not only filled the exploring gaps in the onshore-offshore transitional area, and realized the geological and tectonic junction between the sea and the land, but also discovered four local gravity anomalies, 11 fractures and three sags or subsags, and so on. The good geological effect of airborne gravimetry not restricted by terrain condition shows that it can be served as a new geophysical method in the exploration of complex terrain physiognomy area such as mountain, jungle, desert, marsh, onshore-offshore transitional area and so on, and has an extensive application prospect in China in the future. 相似文献
953.
Ryan L. Kobrick David M. Klaus Kenneth W. Street Jr. 《Planetary and Space Science》2011,59(14):1749-1757
Unexpected issues were encountered during the Apollo era of lunar exploration due to detrimental abrasion of materials upon exposure to the fine-grained, irregular shaped dust on the surface of the Moon. For critical design features involving contact with the lunar surface and for astronaut safety concerns, operational concepts and dust tolerance must be considered in the early phases of mission planning. To systematically define material selection criteria, dust interaction can be characterized by two-body or three-body abrasion testing, and sub-categorically by physical interactions of compression, rolling, sliding, and bending representing specific applications within the system. Two-body abrasion occurs when a single particle or asperity slides across a given surface removing or displacing material. Three-body abrasion occurs when multiple particles interact with a solid surface, or in between two surfaces, allowing the abrasives to freely rotate and interact with the material(s), leading to removal or displacement of mass. Different modes of interaction are described in this paper along with corresponding types of tests that can be utilized to evaluate each configuration. In addition to differential modes of abrasion, variable concentrations of dust in different zones can also be considered for a given system design and operational protocol. These zones include (1) outside the habitat where extensive dust exposure occurs, (2) in a transitional zone such as an airlock or suitport, and (3) inside the habitat or spacesuit with a low particle count. These zones can be used to help define dust interaction frequencies, and corresponding risks to the systems and/or crew can be addressed by appropriate mitigation strategies. An abrasion index is introduced that includes the level of risk, R, the hardness of the mineralogy, H, the severity of the abrasion mode, S, and the frequency of particle interactions, F. 相似文献
954.
The movement of small dust particles due to electrostatic forces, seismic activity and micrometeoroid bombardment has been hypothesized to occur on the Moon and asteroids. There currently exists significant uncertainty in the method of launching these small dust particles, which in turn makes the selection of accurate initial conditions for numerical simulations difficult. We evaluate the electric field strength required to launch small particles given surface gravitation, cohesion and seismic shaking. We find that the electric field strength required for dust particle launching is dominated by the cohesive force for micron-sized dust particles. There exists an intermediate dust particle size that requires the least electric field strength to launch. We see that the inclusion of the cohesive force significantly influences our understanding of dust lofting. 相似文献
955.
We report on the results of the Cosmic Dust Experiment (CDE) onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite, collected during eight months of operation between May 2007 and February 2008. CDE is an impact detector designed to measure the variability of the cosmic dust influx of grains with radius, . CDE consists of 14 permanently polarized polyvinylidene fluoride (PVDF) channels that produce an electrical signal when impacted with hyper-velocity dust particles. The instrument has a total surface area of 0.11 m2 and a time resolution of 1 s. CDE experienced higher noise levels than expected on-orbit, triggering the need for new laboratory experiments, as well as the development of new data reduction approaches. We present the first eight months of reduced CDE data, highlighting the observed spatial and temporal variability of the cosmic dust influx. 相似文献
956.
沙尘暴对大气环境和人类健康造成严重影响,查明沙尘来源对防沙治沙具有重要意义。选择中国北方7地2021年“3·15”沙尘暴期间降尘样品,分析粒度组成和核素(235U、232Th、226Ra、137Cs)含量差异。结果表明:西宁、兰州、西安、北京、济南和临沂6地降尘以粉粒为主,核素含量特征表明降尘是远距离搬运的风尘沉积或吹蚀起的附近黄土。除中卫和西安外,其余5地沙尘的137Cs比活度远高于农耕地,低于植被覆盖度高的草地,沙尘的主要来源应不是农耕地,而是覆盖度低的侵蚀草地。西安沙尘的137Cs比活度与农耕地相近,农耕地可能是沙尘的主要来源。中卫沙尘粒度粗,137Cs比活度极低,沙尘来源于毗邻的腾格里沙漠。 相似文献
957.
为了解某化工厂附近土壤铬污染状况及其生物有效性,研究了该化工厂周边的土壤、粉尘、排污底泥、工业废渣和水等不同介质中重金属含量及Cr的化学形态特征。结果显示,该区域土壤出现以化工厂为中心的大面积Cr异常;废渣和部分底泥中Cr的含量是土壤背景值的近100倍乃至上万倍;表层土壤和粉尘中Cr元素含量与化工厂距离变化曲线的一致性,表明化工厂粉尘是引起大面积Cr异常的主要污染源;不同介质中Cr元素主要以残渣态(生物不可利用态)存在,但底泥中Cr的潜在可利用态、废渣中Cr的可利用态存在一定的比例,会对当地的动植物和人体产生负面的生态效应,应重视其可能引起的生态后果。 相似文献
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