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1.
冲绳海槽的形成与发展   总被引：1，自引：0，他引：1  
路应贤 《海洋学报》1981,3(4):589-600
冲绳海槽是位于东海大陆架外缘、东海陆架边缘隆褶带与琉球岛弧之间的一个狭长带状弧间盆地.关于它的成因,已有古琉球弧直接张裂和断裂下陷两种观点,而笔者认为,它是由于菲律宾海板块从早中新世末以来,向欧亚大陆板块下俯冲所形成的沟-弧-盆系列的一个组成部分,在其生成和发展过程中,先后经历了拗陷、断陷和扩张三个阶段.然而,扩张刚刚开始.今后它将进一步裂开,琉球弧将更加向菲律宾海方向推进.因受调查程度的限制,本文将以冲绳海槽北半部的资料为主要依据.  相似文献   

2.
Concentrations of minerals on the sea floor around New Zealand occur in a manner which makes them economically significant as future mineral resources.

Three major environments of interest are beaches, the continental shelf, and the adjacent deep‐sea floor. New Zealand's west coast beaches are well known as mineral resources containing large quantities of iron and titanium ores. Similar concentrations representing fossil beaches are also known from the continental shelf. The deep‐sea floor adjacent to the continental shelf is formed around New Zealand by the New Zealand Plateau, an extensive submarine platform in 500–1,500 m. Terrigenous sedimentation is negligible in this environment where, as a result, pure calcareous oozes are common. Vigorous bottom currents and suitable reducing micro‐environments encourage glauconite formation. In the past, possibly from warmer waters of the early and mid Tertiary, phosphates were precipitated from seawater to form phosphorite nodules, a potential resource of phosphates. During late Tertiary or Quaternary, volcanicity at the Antipodes Islands and on the Macquarie Ridge resulted in the formation of manganese deposits. Manganese minerals also occur in bulk on the floor of the Southwestern Pacific Basin away from the New Zealand Plateau.

The origin, bulk, and significance of these deposits are discussed.  相似文献   

3.
In recent years significant interest has emerged regarding bottom currents and sediment dispersal over continental shelves and shallow marine waters. Although many papers have been written on sediment dispersal mechanisms, they include relatively few long-term observations of bottom currents and/or sediment transport. Lack of observational data is related to the hostile nature of the environment, and the difficulty associated with placing and retrieving instruments on the floor of the continental shelf during some seasons and environmental conditions.This paper describes an instrumentation system designed for use on the floor of the continental shelf. It can remain submerged for periods of one month continuously recording water speed and direction 1 m from the sea bed, differential pressure, and bed nature by means of half-hourly photographs. Four of these systems are presently in use in arrays across the continental shelf of Washington.  相似文献   

4.
A sea floor magnetometer for the continental shelf   总被引：1，自引：0，他引：1  
Measurement of temporal magnetic variations on the sea floor is desirable in order to extend the technique of geomagnetic depth sounding into the oceans. This paper describes a recording three-component sea floor magnetometer and its use in continental shelf depths. The orientation and tilt of the instrument on the sea floor are recorded using gelatine solutions to freeze a compass card and a ball-bearing, respectively. A backing-off procedure initially nulls the magnetic field components along each of the three mutually orthogonal fluxgate sensors. Magnetic variations along each sensor axis are then recorded within a range of ± 300 nT of these nulled positions. The resolution is ± 1 nT, and with a power drain of 800 mW the magnetometer can record continuously for 30 days. The instrument capsule is moored to surface buoys for recovery in continental shelf applications. The buoys may have marker flags, radar reflectors or radio beacons attached to them to aid in relocation.  相似文献   

5.
Abstract

The continental margin of northern Sinai and Israel consists of a seaward‐inclined wedge, made up predominantly of foreset beds of mainly Nile‐derived clastics. They overlie seaward‐thickening Messinian (Upper Miocene) evaporites. Detailed bathymetric and seismic surveys reveal large areas of sea floor disturbances off northern Sinai and in several places off Israel, expressed by a complex block topography of the outer continental shelf and slope. These disturbed areas appear to be gigantic, deep‐seated, compound rotational slumps over down‐slope flowing evaporites. Many of the disturbances are above landward lobes of evaporites which fill buried Late Miocene erosion channels of the pre‐Messinian retreat of the sea. Flowage of the evaporites was presumably caused by excessive pore pressures, generated by the Pliocene‐Quaternary overload, in confined layers of the elastics interbedded within the evaporites.  相似文献   

6.
An inexpensive Pull-Up Shallow Water Seismometer (PUSS) has been designed and built to conduct long range seismic refraction experiments in the North Sea and the continental shelf around Britain, with the particular goal of studying the crustal and lithospheric structure under the epeirogenic basin of the North Sea. Signals from a gimbal-mounted 3-component geophone and a hydrophone are frequency modulated and mixed with clock and flutter correction signals before being recorded on a standard speed cassette tape recorder, with one hour of recording time. A 100 hour programmable timer allows the interval between the time of reset of the clock and each shot window of optional 5 or 10 min duration, to be preselected. The PUSS is launched and recovered using a pull-up technique originally developed for current meters. The replay system is also described.In May 1976 sea trials of 5 PUSSes were conducted along a 200 km refraction line in the North Sea. The encouraging performance of the equipment resulted in the decision to build a further 10 units and to proceed with a 400 km refraction line planned for the summer of 1977.  相似文献   

7.
The formation of incised valleys on continental shelves is generally attributed to fluvial erosion under low sea level conditions. However, there are exceptions. A multibeam sonar survey at the northern end of Australia's Great Barrier Reef, adjacent to the southern edge of the Gulf of Papua, mapped a shelf valley system up to 220 m deep that extends for more than 90 km across the continental shelf. This is the deepest shelf valley yet found in the Great Barrier Reef and is well below the maximum depth of fluvial incision that could have occurred under a − 120 m, eustatic sea level low-stand, as what occurred on this margin during the last ice age. These valleys appear to have formed by a combination of reef growth and tidal current scour, probably in relation to a sea level at around 30–50 m below its present position.

Tidally incised depressions in the valley floor exhibit closed bathymetric contours at both ends. Valley floor sediments are mainly calcareous muddy, gravelly sand on the middle shelf, giving way to well-sorted, gravely sand containing a large relict fraction on the outer shelf. The valley extends between broad platform reefs and framework coral growth, which accumulated through the late Quaternary, coincides with tidal current scour to produce steep-sided (locally vertical) valley walls. The deepest segments of the valley were probably the sites of lakes during the last ice age, when Torres Strait formed an emergent land-bridge between Australia and Papua New Guinea. Numerical modeling predicts that the strongest tidal currents occur over the deepest, outer-shelf segment of the valley when sea level is about 40–50 m below its present position. These results are consistent with a Pleistocene age and relict origin of the valley.

Based on these observations, we propose a new conceptual model for the formation of tidally incised shelf valleys. Tidal erosion on meso- to macro-tidal, rimmed carbonate shelves is enhanced during sea level rise and fall when a tidal, hydraulic pressure gradient is established between the shelf-lagoon and the adjacent ocean basin. Tidal flows attain a maximum, and channel incision is greatest, when a large hydraulic pressure gradient coincides with small channel cross sections. Our tidal-incision model may explain the observation of other workers, that sediment is exported from the Great Barrier Reef shelf to the adjacent ocean basins during intermediate (rather than last glacial maximum) low-stand, sea level positions. The model may apply to other rimmed shelves, both modern and ancient.  相似文献   


8.
A seismic refraction survey along nine profiles has been carried out on the Norwegian continental shelf in the area between Andøya and Fugløybanken (69°–71°N). In all but one of the profiles the shelf is found to be covered with layered sediments. Average velocities are 1.85, 2.20, 2,55, 3.25, and 3.90 km/s probably representing sediments of Cenozoic and Mesozoic ages. An average velocity of 5.25 km/s represents a basement, which probably is the seaward continuation of the onshore Caledonian rocks. Except for an apparent depressional area just north of Andøya the sedimentary layers appear to dip towards the shelf edge. On the outer part of the shelf the 2.20 km/s layer appears at the sea-floor while more complex structures are found on the inner part of the shelf.Publication No. 3 in NTNF's Continental Shelf Project.  相似文献   

9.
The Cenozoic margins of the Norwegian-Greenland Sea offer ideal conditions for passive margin studies. A series of structural elements, first observed on these margins, led to the concept of volcanic passive margins. Questions still remain about the development of such features and the location of the boundary between oceanic and continental crust. Despite the thin sediment cover of the margins, seismic reflection data are not able to image the deeper structures due to the occurrence of igneous rocks at shallow depth.This paper presents a 320-km long profile perpendicular to the strike of the main structural units of the Lofoten Margin in Northern Norway. A geological model is proposed, based on observations made with ocean bottom seismographs, which recorded seismic refraction data and wide angle reflections, along with a seismic reflection profile covering the same area. Ray-tracing was used to calculate a geophysical model from the shelf area into the Lofoten basin. The structures typical of a volcanic passive margin were found, showing that the Lofoten Margin was influenced by increased volcanic activity during its evolution. The ocean/continent transition is located in a 30-km wide zone landwards of the Vøring Plateau escarpment.The whole margin is underlain by a possibly underplated, high velocity layer. Evidence for a pre-rift sediment basin landwards of the escarpment, overlain by basalt flows, was seen. These structural features, related to extensive volcanism on the Lofoten Margin, are not as distinct as further south along the Norwegian Margin. Viewed in the light of the hot-spot theory of White and McKenzie (1989) the Lofoten Margin can be interpreted as a transitional type between volcanic and non-volcanic passive margin.  相似文献   

10.
Seismic and sequence stratigraphic architecture of the central western continental margin of India (between Coondapur and south of Mangalore) has been investigated with shallow seismic data. Seismic stratigraphic analysis defined nine seismic units, that are configured in a major type-1 depositional sequence possibly related to fourth-order eustatic sea-level changes, comprising regressive, lowstand, transgressive and highstand systems tracts. The late-Quaternary evolution of the continental margin took place under the influence of an asymmetric relative fourth-order sea-level cycle punctuated by higher frequency cycles. These cycles of minor order were characterised by rapid sea-level rises and gradual sea-level falls that generated depositional sequences spanning different time scales. During the regressive periods, dipping strata were developed, while erosional surfaces and incised valleys were formed during the lowstands of sea level. Terraces, v-shaped depressions, lagoon-like structures observed on the outer continental shelf are the result of the transgressive period. In the study area we have recognised a complex erosional surface that records a long time span during the relative sea-level fall (regressive period) and the following sea-level lowstand and has been reworked during the last transgression. We also infer that sedimentation processes changed from siliciclastic sedimentation to carbonate sedimentation and again to siliciclastic sedimentation, marking an important phase in the late-Quaternary evolution of the western continental shelf of India. We attribute this to an abrupt climate change at the end of the oxygen isotope stage 2, between the Last Glacial Maximum and the Bølling-Allerod event (14?000 yr BP). This sensitive climate change (warming) favoured the formation of reefs at various depths on the shelf, besides the development of Fifty Fathom Flat, a carbonate platform on the outer shelf off Bombay developed prior to 8300 yr BP. The highstand systems tracts were deposited after the sea level reached its present position.  相似文献   

11.
The distribution of samples containing the lucinid Divaricella (Divalucina) huttoniana (Vanatta) from the continental shelf of the North, South, Stewart and Chatham Islands (New Zealand) in the New Zealand Oceanographic Institute collection is discussed in relation to published records and museum collections. The paucity of living specimens and large shells in shelf samples contrasts with beach collections, and is partly related to sampling problems close inshore off sandy beaches. Southern distributional limits are probably related to winter temperatures on the sea floor.  相似文献   

12.
The marine geological map n. 502 “Agropoli”, located offshore the Cilento Promontory, southern Italy, is here described and the regional geology interpreted, particularly referring to water depths between the 30 and 200 m isobaths. The geologic map has been constructed in the frame of a research program financed by the National Geological Survey of Italy (CARG Project), finalized to the construction of up-to-date cartography of the Campania region. Geological and geophysical data on the continental shelf and slope offshore of the Southern Campania region have been collected in the study area, bounded northwards by the Salerno Gulf and southwards by the Policastro Gulf. A high resolution multibeam bathymetry allowed for the construction of a marine digital elevation map; sidescan sonar profiles also have been collected and interpreted. The latter, merged to the bathymetry, have represented the base for the marine geologic cartography. The integrated geologic interpretation of seismic, bathymetric and sidescan sonar data has been calibrated by sea-bottom samples. The morpho-structures and the seismic sequences overlying the outcrops of acoustic basement reported in the cartographic representation have been studied in detail using single-channel seismics. The interpretation of seismic profiles has been a support for the reconstruction of the stratigraphic and structural setting of the Quaternary continental shelf successions and the outcrops of rocky acoustic basement in correspondence to the Licosa Cape morpho-structural high. These areas result from the seaward prolongation of the stratigraphic and structural units, widely cropping out in the surrounding emerged sector of the Cilento Promontory. The cartographic approach is based on the recognition of laterally coeval depositional systems, interpreted in the frame of the system tracts of the Late Quaternary depositional sequence. We present evidence of now subaqueous terraces inferred to be palaeoshorelines representing past sea-level positions and tentatively correlated these to oxygen isotopic stratigraphy.  相似文献   

13.
Multichannel seismic reflection profiles from the continental rise west of the Antarctic Peninsula between 63° and 69°S show the growth of eight very large mound-shaped sedimentary bodies. MCS profiles and long-range side-scan sonar (GLORIA) images show the sea floor between mounds is traversed by channels originating in a dendritic pattern near the base of the continental slope. The mounds are interpreted as sediment drifts, constructed mainly from the fine-grained components of turbidity currents originating on the continental slope, entrained in a nepheloid layer within the ambient southwesterly bottom currents and redeposited downcurrent.  相似文献   

14.
The relationship between spatial variations of the properties of sea-floor sediments and acoustic backscatter from the surface of the sea floor on the continental shelf off of Panama City, Florida, USA, is investigated using surficial sediment grab samples and digital side-scan sonar data. Acoustic backscatter strength has a high, direct correlation with the mean grain size of the sediments. Acoustic backscatter strength also correlates directly with the carbonate content of the sediments, particularly in medium-and coarse-sand facies, because large, irregularly shaped, carbonate particles affect both the mean grain size of the sediments and the roughness of the surface of the sea floor.  相似文献   

15.
海南岛东部陆架海底地貌   总被引：4，自引：0，他引：4  
通过二十多条测线的测深、旁测声纳和浅地层连续测量的调查以及底质等资料，概述了海南岛东部陆架海底堆积平原地貌及其上的地貌类型，其中海底沟，坎、岗阜等地貌类型的线性排列和古海岸线的位置相应。  相似文献   

16.
Australia׳s remote location and position on the vast Indo-Australian plate mean that possesses one of the largest continental shelf areas in the world. The criteria in Article 76 of the United Nations Convention on the Law of the Sea permit the claiming on continental shelf to 200 nautical miles from territorial sea baselines, and if certain criteria are met based on the configuration and content of the seabed, to distances beyond. During the negotiations at UNCLOS III, Australia was a strong proponent of this extended shelf regime, as it was likely to have large areas beyond 200 nautical miles. Article 76 provides for a number of requirements to be met for a coastal State to assert sovereign rights over areas of continental shelf beyond 200 nautical miles, including a ten year deadline from becoming a party. This placed a disproportionate burden upon Australia, as it faced the same ten year time frame to lodge data with the Commission on the Limits on the Continental Shelf (CLCS) as other States with much smaller areas in issue. Australia also chose not to rely upon measures agreed between State parties to effectively extend this deadline, and to limit the requirements to be met within it. This paper looks at how Australian authorities approached the difficult task, while maintaining the standards required for data by the CLCS, and how the task was ultimately implemented. It also examines how the extended continental shelf arrangements interacted with the rest of Australia׳s law of the sea practice and maritime boundaries with other States. For example, after the entry into force of the Convention, Australia negotiated two maritime boundaries with neighbouring States that each explicitly dealt with areas beyond 200 nautical miles. It concludes with consideration of what issues remain unresolved in respect of the Australian continental shelf beyond 200 nautical miles. The paper will conclude at how Australia׳s implementation has raised new issues with neighbouring States, including an unresolved dispute in the South Pacific Ocean.  相似文献   

17.
The results of a single channel seismic reflection survey and of a micropaleontological examination of diatom remains in bottom sediment samples on the shelf and continental slope of the Peter the Great Bay area are presented. The composition and age of the sedimentary layer were studied using integrated seismic, micropaleontological and geological data. The continental slope was formed not later than at the beginning of the Early Miocene. The slope is covered with Middle Miocene-Pliocene sediments. The sedimentary thickness on most of the slope is 0.2–0.4 s. The maximum thickness (0.8–1.0 s) is observed within the areas of submarine canyons and valleys. The thickness of the Early Miocene-Pliocene sediments on the shelf is 0.2–0.4 s. On the shelf break and in a southwest-trending trough of the acoustic basement, it increases up to 1.0 s. Two uncomformities were identified in the sediments of the shelf area. The proposed age of the upper uncomformity is 10.0–8.5 My B.P.; it represents the result of a global sea level fall. The age of the lower uncomformity is unknown.  相似文献   

18.
The structure of the continental shelf off southern Morocco was studied by means of 2,100 km of seismic reflection profiles, magnetic and bathymetric surveys, and dredge samples. The research area lies off four geologic divisions adjacent to the coast: the Atlas Mountains; the Souss Trough; the Anti-Atlas Mountains; and the Aaiun Basin. The continental shelf, along with the western Atlas Mountains, the western Souss Trough, and the entire Aaiun Basin, has subsided along a normal fault-flexure system. This system runs along the shore at the Anti-Atlas Mountains, and cuts off this cratonic block from the shelf subsidence. The shelf is narrow and characterized by out-building off the Anti-Atlas range, whereas it is broader and characterized by upbuilding to the north and south. Deposition was essentially continuous at least from Early Cretaceous through Eocene time. Published work suggests that the last cycle of sedimentation began during Permian rifting. After Eocene time, most sediments carried to the shelf must have bypassed it and gone to construct the slope and rise or to the deep sea. Tertiary orogenies caused extensive folding of Mesozoic and early Tertiary deposits off the Atlas Mountains.  相似文献   

19.
《Marine Geology》2007,236(1-2):1-13
The direct record of Late Miocene–Early Pliocene Antarctic Peninsula Ice Sheet expansions from a previously published seismostratigraphic study of the outer shelf at Ocean Drilling Program Site 1097 is compared to the glacial history we deduced from published proxy evidence within coeval sections on the adjacent continental rise. The proxies are sedimentary structures (laminated vs. massive/bioturbated facies) and clay minerals (predominantly smectite and chlorite contents) from Ocean Drilling Program Site 1095 located on the distal part of a large drift. The comparison shows that more sedimentary cycles are evident on the continental rise for three of the four diatom biozones we considered. This indicates that the continental-rise sedimentology may indeed be related to local or regional paleoenvironmental variability, including Antarctic Peninsula Ice Sheet grounding events on the adjacent outer continental shelf. If correct, this would be a promising result because unlike the outer continental shelf sequences drilled thus far, the continental rise record is relatively continuous and can be dated using paleomagnetic and biostratigraphic data. However, our study also shows that no objective criteria provide direct linkages between the glacial history we deduced from the two continental rise proxies and that previously derived from the continental-shelf seismic stratigraphy. Furthermore, the two sedimentologic proxies on the continental rise do not always provide a consistent picture of glacial history when compared against each other.  相似文献   

20.
-On the basis of the data of geophysics and seismic activities, the analyses of the active faults, seismic activities and the sea floor unstable factors of the Zhujiang River Mouth Basin have been made so as to study the characteristics of the compressional subactive continental margin of Cathaysian system, arc littoral strongly active fracture zone, the division of seismic subzone and seismic zone of the continental margin of northern South China Sea, the potential focal area, and to analyze the regional stability. We consider that the Zhujiang River Mouth Basin belongs to a stable or a moderately stable region.  相似文献   

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