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Scientific sea-floor dredging is currently used in marine geology primarily by the hard-rock community interested in the recovery of basement rock samples from the unsedimented deep ocean floor. The technique has generally been eclipsed by ocean drilling for recovery of sedimentary rocks, because of perceived uncertainties in the location of sampling and in the representativeness of recovered material. This contribution reviews dredging equipment currently in use by marine geological institutions and refers to pinger attachments that allow precise information on the behaviour of the dredge to be telemetered back to the ship. We argue that improvements in ship navigation and transponder navigation at the seafloor, when used in conjunction with surface and/or deeply towed sidescan and swathemapping surveys, now allow for considerably less uncertainty on the location of dredge sampling. Refined sorting criteria for dredge hauls are now also available. Recent comparisons of regional sample recovery by ocean drilling and by dredge sampling indicate that the dredge hauls can usefully supplement the drilling data in the construction of sedimentary and tectonic histories of seafloor areas. 相似文献
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Jean-Marie Auzende Eiichi Honza Xavier Boespflug Satendra Deo Jean-Philippe Eissen Jun Hashimoto Philippe Huchon Junichiro Ishibashi Yo Iwabuchi Philip Jarvis Masato Joshima Kiyoyuki Kisimoto Yasuto Kuwahara Yves Lafoy Tsuyoshi Matsumoto Jean-Pierre Maze Kiyohiko Mitsuzawa Hiroyasu Monma Takeshi Naganuma Yukihiro Nojiri Suguru Ohta Kiyoshi Otsuka Yoshihisa Okuda Hélène Ondreas Akira Otsuki Etienne Ruellan Myriam Sibuet Manabu Tanahashi Takeo Tanaka Tetsuro Urabe 《Marine Geophysical Researches》1990,12(4):269-283
The aim of the Japanese-French Kaiyo 87 cruise was the study of the spreading axis in the North Fiji Basin (SW Pacific). A
Seabeam and geophysical survey allowed us to define the detailed structure of the active NS spreading axis between 16° and
22° S and its relationships with the left lateral motion of the North Fiji Fracture Zone. Between 21° S and 18°10′ S, the
spreading axis trends NS. From 18°10 S to 16°40 S the orientation of the spreading axis changes from NS to 015°. North of
16°40′ S the spreading axis trends 160°. These two 015° and 160° branches converge with the left lateral North Fiji fracture
zone around 16°40′ S to define an RRFZ triple junction. Water sampling, dredging and photo TV deep towing give new information
concerning the hydrothermal activity along the spreading axis. The discovery of hydrothermal deposits associated with living
communities confirms this activity. 相似文献
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This paper examines present and future resource utilization in the tidal section of the Georges River in the southern part of Sydney. Over the last 30 years, the physical characteristics of the river have changed as a result of urbanization, changed hydrologic regime and sand dredging. Urbanization has resulted in an increase in population from 190,000 in 1947 to 550,000. This has resulted in an increase in runoff, sediment input to the river and waste disposal. The change in hydrologic regime has resulted in a substantial increase in the magnitude and frequency of flooding which has increased erosion. Sand dredging has increased the channel capacity, enlarged the tidal prism and increased water turbidity. It has also resulted in extensive bank erosion in the upper part of the river and extensive deposition lower down as tailings are deposited. Although most of these changes have resulted in the deterioration of environmental quality, use of the river for recreation and as an urban amenity has increased. 相似文献
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A. S. Hill L. O. Veale D. Pennington S. G. Whyte A. R. Brand R. G. Hartnoll 《Estuarine, Coastal and Shelf Science》1999,48(6):739
From 1946 to 1951 Dr N. S. Jones sampled the benthos around the south of the Isle of Man from over 200 sites. Multivariate methods have been used here to compare subsets of this historical data with recent data from the same locations: of these locations some have been subject to heavy scallop dredging over the intervening 40 plus years and some to little dredging. Clear changes were apparent regardless of scallop dredging intensity. Some of the changes in the heavily dredged areas were those expected to result from extreme physical disturbance—an increased polychaete mollusc ratio, loss of some fragile species, and an increase in the predominance of scavenger/predator species. However, changes in the lightly dredged areas also included the loss of a number of species including some potentially fragile tube-dwellers. Reasons for these changes were not apparent. 相似文献