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91.
The seismic expression of a salt-filled channel which cuts across the Mid North Sea High in Quadrant 37 is described, with features interpreted as being produced by salt-edge dissolution forming both eastern and western margins of the channel. The apparent half-graben nature of the channel is shown to be only superficial, and due to complex faulting associated with, but not defining, its western margin. The shallower faulting here is a Mesozoic to early Tertiary growth fault related to local dissolution of Zechstein salt. The dissolution effect appears in turn to have been localized by the presence of a deeper fault that was already downthrown to the east in Zechstein times, when it seems to have limited the eastward progradation of Zechstein shelf carbonates and anhydrites, and had probably ceased to move significantly before the onset of the Late Cimmerian erosional phase. The origin of this arcuate fault is tentatively ascribed to subsidence around a granite batholith. Zechstein salt originally spread some distance to the east and west of the channel; it was dissolved from the edges inwards, mainly before the Late Cretaceous, giving rise to a thicker Mesozoic sequence on parts of the flanks of the channel than in the middle. Besides providing an interesting structural case history, the features described have implications regarding Zechstein sedimentation, reservoir potential, the tectonic history of the North Sea, and the nature of the Mid North Sea High itself. 相似文献
92.
93.
环境演变研究时间序列的建立方法评述 总被引:3,自引:0,他引:3
对环境演变时间序列建立的几种主要方法的纪年原理、应用状况及应用的优点、范围、局限性进行了阐述和比较,包括长寿命宇宙成因核素在内的同位素纪年方法主要判别第四纪以来大时间尺主的沉积物的地质年龄,且能很好地应用于全球变化的研究,但百余年来沉积物的年龄及侵蚀历史变化的研究只能通过^210Pbex、^137Cs等半衰期相对较短的核素来进行;指出^210Pbex可望在现代流域侵蚀环境演变以及其效应评价的研究中获得新的突破。 相似文献
94.
W. R. Roest J. J. Dañobeitia J. Verhoef B. J. Collette 《Marine Geophysical Researches》1992,14(1):1-24
The data from a recent magnetic compilation by Verhoefet al. (1991) off west Africa were used in combination with data in the western Atlantic to review the Mesozoic plate kinematic evolution of the central North Atlantic. The magnetic profile data were analyzed to identify the M-series sea floor spreading anomalies on the African plate. Oceanic fracture zones were identified from magnetic anomalies and seismic and gravity measurements. The identified sea floor spreading anomalies on the African plate were combined with those on the North American plate to calculate reconstruction poles for this part of the central Atlantic. The total separation poles derived in this paper describe a smooth curve, suggesting that the motion of the pole through time was continuous. Although the new sea floor spreading history differs only slightly from the one presented by Klitgord and Schouten (1986), it predicts smoother flowlines. On the other hand, the sea floor spreading history as depicted by the flowlines for the eastern central Atlantic deviates substantially from that of Sundvik and Larson (1988). A revised spreading history is also presented for the Cretaceous Magnetic Quiet Zone, where large changes in spreading direction occurred, that can not be resolved when fitting magnetic isochrons only, but which are evident from fracture zone traces and directions of sea floor spreading topography.Deceased 11 November 1991 相似文献
95.
水成沉积与风成沉积及古土壤的磁组构特征 总被引:14,自引:2,他引:14
晚第四纪水成沉积、风成沉积、古土壤等的磁组构研究表明,不同成因的沉积物具有明显不同的磁组构特征。一般地,水成沉积的体积磁化率K受物源和水动力因素控制,P和F均>1.02,q<0.5;风成沉积的K受物源控制,内陆黄土的K明显高于沿海黄土及海岸风沙K,P和F均<1.02,q的平均值>0.55;古土壤的K受母质沉积类型和成土环境的氧化还原条件控制,内陆古土壤的K偏高,沿海古土壤的K偏低,内陆古土壤的K远高于沿海古土壤的K,P和F均<1.02,q的平均值在0.5左右。运用典型沉积的磁组构特征对比分析未知沉积物,可以得到未知沉积物的物源、沉积过程和环境信息。 相似文献
96.
97.
底部浮泥表层推移速度分布的ADCP—GPS估测方法 总被引:3,自引:0,他引:3
ADCP对底跟踪走航观测的流速数据中包含水体底部浮泥、底沙运动信息,对比GPS定位方法算出的水体流速数据可以分离出浮泥相对于GPS定位的运动信号,从而达到对底质推移观测的目的。 相似文献
98.
99.
The spring-spawning Baltic Sea herring spawn in coastal areas that also serve as nursery areas for the young fish during their first summer. In a bay known as a herring spawning and nursery area, the pelagic fish abundance was quantified using hydroacoustics every second week from late spring to autumn in 2000 and 2001. A dense system of survey transects allowed determination of the acoustic index (the nautical area scattering coefficient) for fish abundance with high precision. The variation, expressed as the geostatistical coefficient of variation, was on average 5% both years and ranged from 3–11% (2000) and 3–8% (2001). Through the hydroacoustic data intra-annual dynamics in acoustic fish abundance, densities and size composition could be followed, which showed similar trends in both years. In spring and early summer acoustic fish densities were low, followed by a drastic, 20-fold increase in late summer. Hydroacoustic data and biological samples suggest that the increase was caused mainly by the recruitment of young-of-the-year herring to the acoustically assessable pelagic fish community. This age class is commonly not well represented in catches when using traditional sampling gears such as gill nets and trawls, and hydroacoustics may help to improve quantitative estimates of small juvenile fish in order to increase the understanding of biological processes in coastal nursery areas. 相似文献
100.
Shinya Magome Tomohiro Yamashita Takeshi Kohama Atsushi Kaneda Yuichi Hayami Satoru Takahashi Hidetaka Takeoka 《Journal of Oceanography》2007,63(5):761-773
Jellyfish patch formation is investigated by conducting a drifter experiment combined with aerial photography of a sustained
patch of the moon jellyfish in Hokezu Bay, Japan. Jellyfish patches are aggregations of individuals that are caused by a combination
of swimming (active influence) and advection by currents (passive influence). The drifter experiment involved the injection
of 49 drifters around a distinct surface patch of jellyfish within an area of approximately 300 m × 300 m. The drifters’ motion,
caused only by the passive influence, was recorded in a series of 38 aerial photographs taken over approximately 1 h. The
ambient uniform current field larger than the patch scale was estimated from the movement of the centroid position of drifters,
while the distribution of horizontal divergence and relative vorticity around the patch was estimated from the time-derivative
in areas of triangles formed by the drifters. The centroid positions of both drifters and patches moved stably toward the
bay head at different speeds. The difference vector between the patch and drifter centroids was directed to the sun, and was
opposite to the ambient current. The distributions of vorticity and divergence around patches exhibited inhomogeneity within
the patch scale, and the drifters in this nonuniform current field aggregated near the convergence area within 1 h. The results
suggest that horizontal patch formation is predominantly influenced by passive factors at the surface of Hokezu Bay. Furthermore,
the upward swimming against downwelling may make sustained patch in surface layer. 相似文献