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排序方式: 共有873条查询结果,搜索用时 15 毫秒
1.
层状出溶结构导致拉长石晕彩形成——来自透射电镜的证据 总被引:1,自引:1,他引:0
从拉长石出溶结构的形态特征、成分差异和出溶结构的取向研究出发,采用TEM、STEM 以及SAED等手段对其进行测试,发现拉长石出溶结构层的厚度符合理论计算值,结构层的成分由富钙和贫钙两相长石组成,具备了产生干涉作用的必要条件.研究结果表明,拉长石的晕彩色是因其内部的层状出溶结构对光的干涉所致,结构层的厚度主要受富钙相长石的控制.随着钙(An)含量的增加,结构层相应地增厚,且富钙层的增大幅度大于贫钙层,从而导致晕彩色波长也随之增大.出溶结构层的取向为(153),近于平行晶体的(010)面,但不同产地的拉长石,尽管晕彩色相同,其出溶条纹中的钙含量和条纹的具体取向也不尽相同. 相似文献
2.
黄河口水下底坡微地貌及其成因探讨 总被引:3,自引:2,他引:3
高分辨率的回声测深、旁侧声纳及浅地层剖面记录首次直观地揭示了黄河口水下底坡上发育有大量形态不同的微地貌类型。据其形态特征和规模的差异,将它们划分为平滑海底、凹坑与洼地、冲沟、残留岗丘及扰动复合海底等五种类型。这些微地貌分布在不同水深条件下的不同水下三角洲单元上,并存在着相互联系和相互转化。黄河口海域特殊的沉积环境和复杂的动力条件是导致水下底坡微地貌形成发育的主要机制。 相似文献
3.
4.
Reinhardt L. Kudrass H.-R. Lückge A. Wiedicke M. Wunderlich J. Wendt G. 《Marine Geophysical Researches》2002,23(4):335-351
About 6000 km of both bathymetric and high-resolution acoustic profiles were acquired on the shelf and upper slope offshore Peru between 9° S and 14° S. Two new sediment echosounder systems – SEL-96 and SES-2000DS – provided details of the sedimentary structures of the Quaternary sequences within the Sechura-Salaverry, Huacho and Pisco Basins. To a great extent, the poleward undercurrent determines the distribution of sediments. The undercurrent has generated numerous erosional unconformities, it has winnowed hardgrounds and has created mudwaves common between 250 m and 400 m water depth. Distinct subbottom reflectors within sedimentary units represent hiatuses due to periods of intensified winnowing or non-deposition. Erosional unconformities usually marked by pronounced reflectors suggest shifts of the undercurrent system related to climatic changes and eustatic variations of sea level. On a larger scale, the stacked prograding depositional sequences reflect the sea-level cycles of the Middle Pleistocene to the Holocene. Based on the stratigraphy of our piston cores and that of Ocean Drilling Program (ODP) Site 680, the depositional sequences limited by extended unconformities were assigned to oxygen isotope stages 1 to 7. Other sedimentary structures are small straight channels that were conduits for downslope sediment transport. Deformed sediments associated with synsedimentary normal faults result from creep movements indicating beginning slope failure. 相似文献
5.
1990年7~8月,舟山地区的对虾养殖场暴发了流行性对虾黑鳃褐斑综合症,造成对虾大量死亡。作者根据这一病情,对病虾的主要器官组织进行了电镜观察。结果发现,病虾鳃丝细胞中有支原体感染。寄生部位为鳃呼吸上皮细胞的细胞质和核周腔。支原体多形态,呈近圆形、细长条形不等,无细胞壁,仅有单一膜包围,中心为一电子密度较低的区域。 相似文献
6.
Very high-frequency marine multichannel seismic reflection data generated by small-volume air- or waterguns allow detailed, high-resolution studies of sedimentary structures of the order of one to few metres wavelength. The high-frequency content, however, requires (1) a very exact knowledge of the source and receiver positions, and (2) the development of data processing methods which take this exact geometry into account. Static corrections are crucial for the quality of very high-frequency stacked data because static shifts caused by variations of the source and streamer depths are of the order of half to one dominant wavelength, so that they can lead to destructive interference during stacking of CDP sorted traces. As common surface-consistent residual static correction methods developed for land seismic data require fixed shot and receiver locations two simple and fast techniques have been developed for marine seismic data with moving sources and receivers to correct such static shifts. The first method – called CDP static correction method – is based on a simultaneous recording of Parasound sediment echosounder and multichannel seismic reflection data. It compares the depth information derived from the first arrivals of both data sets to calculate static correction time shifts for each seismic channel relative to the Parasound water depths. The second method – called average static correction method – utilises the fact that the streamer depth is mainly controlled by bird units, which keep the streamer in a predefined depth at certain increments but do not prevent the streamer from being slightly buoyant in-between. In case of calm weather conditions these streamer bendings mainly contribute to the overall static time shifts, whereas depth variations of the source are negligible. Hence, mean static correction time shifts are calculated for each channel by averaging the depth values determined at each geophone group position for several subsequent shots. Application of both methods to data of a high-resolution seismic survey of channel-levee systems on the Bengal Fan shows that the quality of the stacked section can be improved significantly compared to stacking results achieved without preceding static corrections. The optimised records show sedimentary features in great detail, that are not visible without static corrections. Limitations only result from the sea floor topography. The CDP static correction method generally provides more coherent reflections than the average static correction method but can only be applied in areas with rather flat sea floor, where no diffraction hyperbolae occur. In contrast, the average static correction method can also be used in regions with rough morphology, but the coherency of reflections is slightly reduced compared to the results of the CDP static correction method. 相似文献
7.
Simulation of Formation and Spreading of Salinity Minimum Associated with NPIW Using a High-Resolution Model 总被引:1,自引:2,他引:1
A series of numerical experiments were conducted with a high-resolution (eddy-permitting) North Pacific model to simulate
the formation and spreading of the salinity minimum associated with the North Pacific Intermediate Water (NPIW). It was found
that two factors are required to simulate a realistic configuration of the salinity minimum: a realistic wind stress field
and small-scale disturbances. The NCEP reanalyzed wind stress data lead to better results than the Hellerman and Rosenstein
wind stress data, due to the closer location of the simulated Oyashio and Kuroshio at the western boundary. Small-scale disturbances
formed by relaxing computational diffusivity included in the advection scheme promote the large-scale isopycnal mixing between
the Oyashio and Kuroshio waters, simulating a realistic configuration of the salinity minimum. A detailed analysis of the
Oyashio water transport was carried out on the final three-year data of the experiment with reduced computational diffusivity.
Simulated transport of the Kuroshio Extension in the intermediate layer is generally smaller than the observed value, while
those of the Oyashio and the flow at the subarctic front are comparable to the observed levels. In the Oyashio-Kuroshio interfrontal
zone the zonally integrated southward transport of the Oyashio water (140–155°E) is borne by the eddy activity, though the
time-mean flow reveals the existence of a coastal Oyashio intrusion. In the eastern part (155°E–180°) the zonally integrated
transport of the Oyashio water indicates a southward peak at the southern edge of the Kuroshio Extension, which corresponds
to the branching of the recirculating flow from the Kuroshio Extension.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
9.
Jonathan M. Bull Martin Gutowski Justin K. Dix Timothy J. Henstock Peter Hogarth Timothy G. Leighton Paul R. White 《Marine Geophysical Researches》2005,26(2-4):157-169
Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce
decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp
system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and
precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity
was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz)
that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive
array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with
each hydrophone group containing four individual elements and a pre-amplifier.
After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver
geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real
Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown
that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal
positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software
aboard the acquisition vessel.
The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that
the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface. 相似文献
10.