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1.
Dwight E. Boegeman Gordon J. Miller William R. Normark 《Marine Geophysical Researches》1972,1(4):381-396
The Marine Physical Laboratory of the Scripps Institution of Oceanography has developed an acoustic relay transponder for precise relative positioning of near-bottom instruments and geologic sampling devices. Although specifically designed to position equipment lowered on standard wire ropes without a need to maintain direct electrical contact with the surface ship, the relay transponder may be used to track free vehicles, such as deep submersibles, from the surface. The relay transponder is positioned relative to an array of bottom-anchored acoustic transponders. It is interrogated acoustically from the surface ship; it then sequentially interrogates the bottom transponders which, in turn, reply to the ship. From the measurement of the total travel time (ship to relay transponder to bottom transponder to ship) and assuming, or knowing, the sound velocity of the water, we obtain a relayed range measurement. These relayed ranges, used in conjunction with ship to bottom-transponder ranges, allow us to calculate the position of the relay transponder. A recent application of this technique is described in which several gravity core samples from the crest of the Horizon Guyot were positioned with respect to the detailed bathymetry and the geology within the area. The estimated error in positioning the samples is less than 20 m inside a navigational net extending over 100 km2.Contribution of the Scripps Institution of Oceanography, new series. 相似文献
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Seismic reflection profiling in the South San Clemente Basin and the southern portion of the San Diego Trough has revealed at least six sedimentary units exhibiting varying stages of deformation. Four of the units are interpreted to be marine turbidites supplied by adjacent submarine canyons. Sediments comprising the Descanso Plain and correlative material within the South San Clemente Basin are attributed to a southerly source (Banda Canyon), while the more recent Quaternary turbidites from Coronado Canyon filled the southern San Diego Trough and then spilled over into South San Clemente Basin. The relatively high but intermittent rates of sedimentation, together with shifting sources and areas of deposition, have resulted in sedimentary units that were emplaced in comparatively short episodes but which were subjected to relatively continuous tectonic activity. Consequently, the sedimentary layers of each unit appear uniformly affected by deformation which increases in successively older units. 相似文献
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Navy Fan is a Late Pleistocene sand-rich fan prograding into an irregularly shaped basin in the southern California Borderland.
The middle fan, characterized by one active and two abandoned “distributary” channels and associated lobe deposits, at present
onlaps part of the basin slope directly opposite from the upper-fan valley, thus dividing the lower-fan/basin-plain regions
into two separate parts of different depths. Fine-scale mesotopographic relief on the fan surface and correlation of individual
turbidite beds through nearly 40 cores on the middle and lower fan provide data for evaluating the Late Pleistocene and Holocene
depositional processes.
Margin setting represents fan and/or source area 相似文献
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The 0.5- to 2-km thick Quaternary Laurentian Fan is built over Tertiary and Mesozoic sediments that rest on oceanic crust.
Two 400-km long fan valleys, with asymmetric levees up to 700-m high, lead to an equally long, sandy, lobate basin plain (northern
Sohm Abyssal Plain). The muddy distal Sohm Abyssal Plain is a further 400-km long. The sediment supplied to the fan is glacial
in origin, and in part results from seismically triggered slumping on the upper continental slope. Sandy turbidity currents,
such as the 1929 Grand Banks earthquake event, probably erode the fan-valley floors; but thick muddy turbidity currents build
up the high levees.
Margin setting represents fan and/or source area 相似文献
7.
The Delgada Fan, an irregularly shaped turbidite deposit extending more than 350 km offshore from northern California, consists
of two large leveed-valley units each fed by a separate complex of coalescing submarine canyons and slope gullies. Although
the leveed-valley units head within 25 km of each other, both appear to have developed independently during fan growth. The
larger southern leveed-valley system has not developed middle-fan distributary channels and appears to illustrate a period
of progressive valley abandonment. Although the lower-fan area is underlain by sandy sediments, little sand has been recovered
in piston cores from the leveed-valley unit.
Margin setting represents fan and/or source area 相似文献
8.
Comparison of modern submarine fans and ancient turbidite sequences is still in its infancy, mainly because of the incompatibility
of study approaches. Research on modern fan systems mainly deals with morphologic aspects and surficial sediments, while observations
on ancient turbidite formations are mostly directed to vertical sequences. The lack of a common data set also results from
different scales of observation.
To review the current status of modern and ancient turbidite research, an international group of specialists formed COMFAN
(Committee on Fans) and met in September 1982 at the Gulf Research and Development Company research facilities in Pennsylvania.
Margin setting represents fan and/or source area 相似文献
9.
A marine sampling program, utilizing the PISCES-5 submersible operated by the Hawaii Undersea Research Laboratory (NOAA), has confirmed the presence of a major submerged coral reef offshore from Ka Lae (South Point), Hawaii. The top of the reef is now 150–160 m below sea level. Radiocarbon and Useries dating indicates that it drowned about 13.9 ka by the combined effects of island subsidence (2.5 mm/year) and the rapid rise of sea level at the end of the last glaciation so that the relative submergence rate of more than 10 mm/year exceeded the upward growth rate of the reef. The submerged reef caps the offshore part of the southwest rift-zone ridge of Mauna Loa, which has apparently undergone little volcanic activity offshore since 170 ka, and possibly since 270 ka. This fact suggests that rift zone activity is becoming increasingly restricted toward the upper part of the volcano, a condition possibly heralding the end of the shield-building stage. 相似文献
10.
The Rhone Fan is a large Plio-Pleistocene turbidite deposit in the western Mediterranean Sea. The fan is fed from the broad Rhone River delta, but only one canyon, the Petit-Rhone, has fed most of the major turbidite depositional sequences that have been mapped. Slumping of sediment from intercanyon areas on the delta slope also has provided much sediment for the fan. The lack of Recent turbidite deposition on the fan suggests that turbidite sedimentation dominates during glacial low stands of sea level, building major leveed valley sequences, while surficial slumping of the valley levee deposits and pelagic sedimentation seem to mark high stands of sea level during interglacial periods. 相似文献