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Continental shelf

About: Continental shelf is a research topic. Over the lifetime, 17169 publications have been published within this topic receiving 551422 citations.


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Journal ArticleDOI
TL;DR: In this article, the relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, pyrophyllite, mixed-layer clay minerals, feldspars, and dolomite were determined.
Abstract: Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 μ- and 2–20 μ-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite(?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, feldspars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted: Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean. Mineralogical analysis of the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin. Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface. Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa. The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety of pedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation. In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea arc mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator.

2,001 citations

OtherDOI
01 Jan 1979
TL;DR: The plate-tectonic evolution of a region can be deduced by following the as-sumptions that subduction zones are characterized by ophiolite, melange, wildflysch, and blueschist, that intermediate and silicic calc-alkaline igneous rocks form above Benioff zones, and that truncations of orogenic belts indicate rifting as mentioned in this paper.
Abstract: The plate-tectonic evolution of a region can be deduced by following the as­ sumptions that subduction zones are characterized by ophiolite, melange, wildflysch, and blueschist, that intermediate and silicic calc-alkaline igneous rocks form above Benioff zones, and that truncations of orogenic belts indicate rifting. Interrelatioships provide cross­ checks, as do marine geophysical data. Southeast Asia and "Sundaland" are an aggregate of small continental fragments. Late Paleozoic subduction westward beneath Malaya and Thailand (recorded by granites in eastern Malaya, and by melanges in western Laos and Cambodia) ended when Indochina collided with them. Early and Middle Triassic subduction was eastward, beneath the west side of the aggregate. Late Triassic and Jurassic subduction from the north ended in collision of the aggregate with China. Early Cretaceous subduction was again from the west. Late Cretaceous subduction was beneath the east side of the aggregate and followed continental rifting there. Cenozoic subduction, from the west once more, ended in the north when the aggregate collided with India, but subduction still continues in the south. Borneo similarly reflects changing subduction patterns. The Philippines, Sulawesi, and Halmahera consist wholly of upper Mesozoic(?) and Cenozoic island-arc subduction and magmatic complexes and lack old continental founda­ tions. The scrambled fragments of the Philippines came from several arc systems, including two extending to Borneo. Sulawesi and Halmahera record primarily subduction from the east and may be rifted and contorted fragments initially continuous with southeast Borneo and central Java. In the early Tertiary, Australia and New Guinea, which then had a stable-shelf northern margin, moved northward until they collided with a southward-migrating island arc, behind which had formed the Caroline oceanic plate. Late Cenozoic tectonics in New Guinea have been dominated by southward subduction fo the Caroline oceanic plate beneath the Austra­ lian New Guinea continent, and by left-lateral strikeslip faulting. Such faulting tore the Sula Islands from northwest New Buinea and carried them to Sulawesi. The islands of the outer Banda arc are formed of melanges of the shallow-water sedi­ ments of the New Guinea and Australian continental shelf, which is now disappearing be­ neath the active arc.

1,603 citations

Journal ArticleDOI
TL;DR: In this paper, it is proposed that mountain belts develop by deformation and metamorphism of the sedimentary and volcanic assemblages of Atlantic-type continental margins, resulting from the events associated with the rupture of continents and the expansion of oceans by plate generation at oceanic ridges.
Abstract: Analysis of the sedimentary, volcanic, structural, and metamorphic chronology in mountain belts, and consideration of the implications of the new global tectonics (plate tectonics), strongly indicate that mountain belts are a consequence of plate evolution. It is proposed that mountain belts develop by the deformation and metamorphism of the sedimentary and volcanic assemblages of Atlantic-type continental margins. These assemblages result from the events associated with the rupture of continents and the expansion of oceans by lithosphere plate generation at oceanic ridges. The earliest assemblages thus developed are volcanic rocks and coarse clastic sediments deposited in fault-bounded troughs on a distending and segmenting continental crust, subsequently split apart and carried away from the ridge on essentially aseismic continental margins. As the continental margins move away from the ridge, nonvolcanic continental shelf and rise assemblages of orthoquartzite-carbonate, and lutite (shelf), and lutite, slump deposits, and turbidites (rise) accumulate. This kind of continental margin is transformed into an orogenic belt in one of two ways. If a trench develops near, or at, the continenal margin to consume lithosphere from the oceanic side, a mountain belt (cordilleran type) grows by dominantly thermal mechanisms related to the rise of calc-alkaline and basaltic magmas. Cordilleran-type mountain belts are characterized by paired metamorphic belts (blueschist on the oceanic side and high temperature on the continental side) and divergent thrusting and synorogenic sediment transport from the high-temperature volcanic axis. If the continental margin collides with an island arc, or with another continent, a collision-type mountain belt develops by dominantly mechanical processes. Where a continent/island arc collision occurs, the resulting mountains will be small (e.g., the Tertiary fold belt of northern New Guinea), and a new trench will develop on the oceanic side of the arc. Where a continent/continent collision occurs, the mountains will be large (e.g., the Himalayas), and the single trench zone of plate consumption is replaced by a wide zone of deformation. Collision-type mountain belts do not have paired metamorphic belts; they are characterized by a single dominant direction of thrusting and synorogenic sediment transport, away from the site of the trench over the underthrust plate. Stratigraphic sequences of mountain belts (geosynclinal sequences) match those asciated with present-day oceans, island arcs, and continental margins.

1,462 citations

Journal ArticleDOI
13 Jun 2008-Science
TL;DR: The ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area, and seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf is observed.
Abstract: The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of approximately 40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO2 has increased the areal extent of the affected area.

1,336 citations

Journal ArticleDOI
TL;DR: P Paleoindicators in dated sediment cores indicate that hypoxic conditions likely began to appear around the turn of the last century and became more severe since the 1950s as the nitrate flux from the Mississippi River to the Gulf of Mexico tripled.
Abstract: The second largest zone of coastal hypoxia (oxygen-depleted waters) in the world is found on the northern Gulf of Mexico continental shelf adjacent to the outflows of the Mississippi and Atchafalaya Rivers. The combination of high freshwater discharge, wind mixing, regional circulation, and summer warming controls the strength of stratification that goes through a well-defined seasonal cycle. The physical structure of the water column and high nutrient loads that enhance primary production lead to an annual formation of the hypoxic water mass that is dominant from spring through late summer. Paleoindicators in dated sediment cores indicate that hypoxic conditions likely began to appear around the turn of the last century and became more severe since the 1950s as the nitrate flux from the Mississippi River to the Gulf of Mexico tripled. Whereas increased nutrients enhance the production of some organisms, others are eliminated from water masses (they either emigrate from the area or die) where the...

1,185 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023292
2022669
2021373
2020466
2019399
2018417