The continental shelf is the area of the ocean floor located between the average level of low tide and the site of a sharp change in the slope of the ocean floor, limiting the inner edge of the continental slope.
The steepening of the submarine slope occurs on average at a depth of about 430 feet below present sea level (Shepard, 1963). It is believed that in the past this line was at a depth of about 600 feet, so neo-oceanologists usually refer to the 600-foot isobath as the outer edge of the continental shelf. Average slope of the shelf zone the globe is less than one-eighth of a degree, or about 12 feet per mile, and has an average width of about 42 miles, with a minimum of less than 1 mile and a maximum of over 750 miles (Shepard, 1963). The distribution of continental shelves on the globe is shown in fig. 13.
Rice. 13. Continental shelves of the World Ocean (shaded).
Between the shelf edge and the deep-water area of the ocean floor there is a continental slope.
Its average width is about 10-20 miles, and its slope is about 4°. Slopes are not uncommon, characterized by a steepness of 25°, and sometimes even 45° (Trumbull, 1958).
Continental shelves can be considered as an underwater continuation of the marginal areas of the adjacent land, because, as a rule, their geological structure has many similarities with adjacent regions of the continent. Despite the fact that the continental shelf is usually considered a flat, devoid of remarkable features, a plain, canyons, depressions and underwater heights are often found in this part of the ocean. Glaciers, rivers, coral structures take part in the transformation of the slope and depth of the continental shelf. In some parts of the shelf area there is an intensive accumulation of sediments, in others - their erosion. Nowhere in other areas of the ocean are such sharp changes in the surface layer of sediments observed.
There are two types of continental shelves: wide, relatively shallow and monotonously even, found near the stable coasts of vast land plains, and narrow, steeply sloping, with complex relief, associated with coasts along which folded mountains extend. The continental shelf of the first type borders the eastern coast of the United States, the second type is developed along the western margin of the American mainland.
Precipitation within the shelf area is unevenly distributed, without a clear relationship with depth and distance from the coast. However, some generalizations are still possible. Thus, sand is usually distributed in the open shelf zone, while clay silts predominate in closed bays and inland seas. In the outer parts of the open shelves, coarser-grained sediments are common and bedrock is exposed. In the marine zone of extensive beaches, sandy deposits predominate.
The rocks of the shelf zone, as a rule, are very similar to the strata developed in adjacent areas of the land.
Therefore, the mineral deposits of the continental shelf have much in common with the deposits of the same minerals on the mainland both in terms of the nature of occurrence and the quality of raw materials. This assumption seemed to be confirmed by the study of deposits in the Gulf of Mexico and deposits of offshore areas near the California coast and other areas. However, since these conclusions are drawn from oil reserves statistics in the Gulf of Mexico and California regions, they cannot be generalized to solid mineral deposits. The only exceptions seem to be the sulfur deposits in the Gulf of Mexico, which are associated with salt domes.
History of shelf development
HYDROTECHNICAL STRUCTURES
CONTINENTAL SHELF
There is another area (both geographical and water management industry) in which hydraulic structures are used - this is the continental shelf of the oceans.
Basic concepts
The continental shelf (eng. Shelf - shelf) is a continental shelf, a leveled part of the underwater margin of the mainland, adjacent to land and characterized by a common geological structure with it. The shelf is limited on one side by the coast of the sea or ocean, on the other - by the so-called crevice, a sharp bend in the surface of the seabed, the transition to the continental (continental) slope.
The depth above the crest is close to 100–200 m (but in some cases reaches 500–1500 m, for example southern part Sea of Okhotsk, edge of the New Zealand shelf).
The part of the mainland (continent) covered by the waters of the ocean is its underwater margin and, in its geological structure and relief, continues the adjacent part of the land. Beyond the outer boundary of the underwater margin of the continent is the ocean floor (abyssal platform).
The underwater margin has, as a rule, three parts:
a) continental shelf - an underwater continuation of the continent, adjacent to land, characterized by a gradual slope of the bottom and shallow depths of the sea covering it;
b) the continental slope, into which the continental shelf passes, is characterized by a sharp and significant slope of the seabed;
c) continental rise (foot) - an elevation that is formed due to sedimentary rocks sliding off the continental slope.
The total area of the continental shelf on the planet is about 32 million km2. According to various authors, the total area of oceanic shallow water (up to 200 m deep) ranges from 7.5 to 12.1% of the water surface area.
The most extensive is the shelf of the Eurasian continent, covering 10 million km 2, while the shelves of the Northern and Western Europe occupy 2.6 million km 2, near the northern outskirts of Eurasia, its width reaches 1.5 thousand km. The second place in terms of area (up to 6 million km 2) is occupied by shelves North America and Greenland. On the third (4.5 million km 2) - shelves along the Pacific coast and the islands of Indonesia. This is followed by the shelves of South America (2.2 million km 2, of which almost 2 million km 2 are on the east coast and only 0.2 million km 2 are on the west coast), Australia, New Zealand and Tasmania (more than 2 million km 2). km 2) and Africa (1 million km 2).
In the Northern Hemisphere, the area of the coastal zone enclosed between isobaths (an isobath is a line connecting points of equal depths) of 0 and 200 m occupies 12.1% of the water surface (10.7 million km 2). In the southern, more oceanic hemisphere, the surface of the ocean is larger, and here similar sections of the bottom make up only 3.9% of the water area (8 million km 2).
The average depth of the outer edge of the shelf of the World Ocean is 130-132 m, the average width is about 40 nautical miles (73-78 km). The most extensive in the world are the shelves of the Barents Sea (1300-1700 km) and other Arctic seas, as well as the coast of Argentina. In the center of the sea shelf of the Barents Sea, depths reach 300–400 m, and on the crest in the trenches left by the glacier, 600 m. The maximum depths on the narrower shelves of the Labrador Peninsula (200 km wide) and Newfoundland Island (500 km wide) are respectively 1000 m. On the shelf of Patagonia - the southern tip of the South American continent - there are traces in the form of potholes (troughs - from German das Trog - trough) - with depths of 200–700 m, which were left by the glacier. By the “fault” of the glacier, by the way, the Strait of Magellan arose, which is a system of fiords between Tierra del Fuego and the continent.
The legal status of the continental shelf, its belonging to a certain state is regulated by international agreements.
The first such agreement was the Geneva Convention of 1958, which for the first time defined the concept of the continental shelf and the basis of the legal regime for its use. The convention determined that the coastal seabed to a depth of 200 m is considered the continental shelf. One of the specific principles for the implementation of this convention was the conclusion of bilateral agreements between bordering countries on the procedure for using the shelf.
In 1982, the UN Convention on the Law of the Sea was signed (entered into force in November 1994). Universal in terms of the number of participants and the set of objects subject to regulation, it determines the legal status of the continental shelf and the legal regime for its use as a spatial sphere and as a reservoir of natural resources. The 1982 UN Convention on the Law of the Sea has been signed by more than 160 countries and ratified by more than 60 of them. Interestingly, the United States refused to sign this document, reserving "the right to act at its own discretion." In August 1984, England, France, Italy, Germany, Belgium, the Netherlands, Japan and the United States signed an agreement providing for these states the possibility of extracting seabed resources without any obligations in relation to other countries and decisions of the UN Convention on the Law of the Sea.
The main principles of the UN Convention on the Law of the Sea are as follows.
The outer limit of the continental shelf, according to the 1982 Convention, runs along the outer limit of the continental margin or at a distance of 200 nautical miles from the baselines if the outer limit of the continental margin does not extend to such a distance.
If, on the other hand, the outer boundary of the underwater margin of the continent is located beyond 200 nautical miles, then the outer boundary of the continental shelf is established along the line that connects the fixed points determined by counting from the foot of the continental slope. Such points shall not be more than 350 miles from the baselines from which the breadth of the territorial sea is measured, or 100 miles from the 2500-meter isobath.
The outer limit of the continental shelf beyond 200 miles is established using a special international procedure, which consists in the fact that the coastal state sends data on the boundaries of its continental shelf to a special international body - the Commission on the Limits of the Continental Shelf. The Commission makes recommendations to this coastal State on the establishment of the outer limits of its continental shelf.
The outer limits of the continental shelf established on the basis of such recommendations are final and obligatory for all states. The coastal state exercises sovereign rights over the continental shelf for the purpose of its exploration and exploitation of its natural resources.
Under natural resources refers to the mineral and other non-living resources of the seabed and its subsoil, as well as "sessile species" of living organisms (organisms that, during their commercial development, are attached to the bottom or move only along the bottom - crayfish, crabs, corals, sponges, shells, etc.). P.). The rights of the coastal state in relation to the exploration and exploitation of the continental shelf are exclusive, which means that without the consent of the coastal state, no other state can explore on it and develop its natural resources. The rights of a coastal state to the continental shelf do not affect the legal status of the waters covering it and the airspace above them. Since the maritime space above the continental shelf continues to be the open sea, all states have the right to carry out navigation, flights, fisheries, lay submarine cables and pipelines.
The coastal state has the right, for the purpose of exploration and development of natural resources of the shelf, to erect appropriate structures and installations, to create security zones around them (up to 500 m). The exercise of the rights of a coastal state should not infringe on the rights of navigation and other rights of other states.
The coastal state has the right to determine the routes for laying cables and pipelines, to allow the construction of installations and drilling operations, and the construction of artificial islands.
Why is so much attention paid to the continental shelf?
The fact is that the coasts of the seas and oceans have always been attractive for human activity.
At present, 60% of the world's inhabitants live in a sixty-kilometer strip along the ocean shores. The population density here is 2.5 times higher than the average on the planet. Land plots along the coasts are rightfully considered the "golden land", and their natural environment regarded as priceless wealth. No less rich in natural resources is the oceanic shallow water bordering the coast, the very one that is called the continental shelf.
The attractive power of the sea coast as a habitat is determined not only by the climate favorable for life, but mainly by the food, mineral, energy resources, as well as the means of communication that the ocean provides. Cities such as Hamburg, Rotterdam, St. Petersburg, Shanghai, Calcutta, Amsterdam, Buenos Aires, New York, New Orleans and many other world centers of industry and trade arose in the most attractive land areas for settlement - in estuary zones ( confluence of rivers into the sea) and the lower reaches of large lowland rivers connected by water arteries with the deep parts of the mainland.
Of the more than 181 thousand species of bottom marine organisms living in the World Ocean, 180 thousand live in the coastal zone.
Their total biomass is estimated at 8-9 billion tons. Many species of marine animals have been used by humans for food since time immemorial. Up to 80 - 90% of 1 billion tons of the total biomass of higher marine organisms of the World Ocean is concentrated in coastal waters. 92% of all fish and 100% of shellfish and algae are currently harvested from the continental shelf.
On the seabed coastal shallow waters contain a large number of minerals. The riches of the continental shelf include oil, gas, sulfur, coal, iron ore, tin, sand, placers of ilmenite, rutile, zircon, magnetite, diamonds, gold, platinum, amber. 1,700 oil and gas fields have already been discovered on 50% of the area of the continental shelf (more than 100 billion tons of oil are extracted per year). The share of "offshore oil" produced on the continental shelf accounts for 20% of world production. The search for and preparation for exploitation of deposits of placer minerals: titanium, magnesium, diamonds, gold and others. The reserves of many shelf minerals are still simply not estimated.
History of shelf development
There is written evidence that since ancient times, people not only used the biological resources of the shelf, but were also interested in its nature. So, in 450 BC. e. the ancient Greek historian and geographer Herodotus gave the first description of the Mediterranean shelf: “The nature of the Egyptian land is such that if, approaching it on a ship, one day’s journey from it, throw a lot, you will get silt even at a depth of 11 fathoms (20 m).” Herodotus also noted the fact that powerful sandy formations - deltas - usually develop in the estuarine sections of rivers. This term, by the way, comes from the name capital letter Greek alphabet Δ (delta), after which the triangular delta of the Nile was named in antiquity.
Herodotus even suggested that Egypt was a gift from the Nile, referring to the fact that the river carried such a huge amount of solid material (140 megatons per year, now 88 megatons) that would be enough to form not only its delta, but the entire territory of Egypt.
The ancient Romans guessed to take into account the peculiarities of the sea roughness regime when creating coastal aqua farms. In the vicinity of Rome, located on the Tiber River, 27 km from its confluence with the Tyrrhenian Sea, the remains of three fish ponds were found. In ancient times, when the sea level was much higher than the modern one, their aeration was periodically carried out by the surf at the moments of strong storms.
In 1502, during the construction of the port of Cesenatico, knowledge of the features of the sea coast and the mode of movement of sediments helped the engineering genius of the Renaissance, Leonardo da Vinci, to take into account the alongshore movement of sediments and avoid siltation of the port through the construction of enclosing breakwaters. Obviously, it was in this connection that he uttered the wisest advice for marine researchers of all times and peoples: “When studying the movement of water, do not forget to draw a conclusion for practice from each discovered phenomenon so that your science does not remain useless.”
Already in the 19th century, knowledge of the nature of bottom sediments helped the fishermen of the North Atlantic to determine their location on the shelf with the help of the so-called "Yorkshire beans" - small pebbles raised by a lot from the bottom of shallow water. If it was possible to gnaw the pebbles, then, then, the ship was located to the west of the Dogger Bank, and if it was not possible, then to the east.
The problem of the use of marine resources, and the problem of the economic division of the seabed that followed from it, also arose in the Middle Ages and went through a certain path of development.
Also in Ancient Rome there was a doctrine of the "business sea" ("mare nostrum"), the economic status of the territories of the seabed. However, then it did not reach the point of dividing it between states. In the 17th century, the Dutch legal scholar Hugo Grotius stated that "the sea cannot be exhausted either by navigation on it or by fishing, that is, by none of the ways in which it can be used." For the economic development of the World Ocean, he proposed the concept of "res communis" - a thing that belongs to everyone. But already in 1911, making sure that stocks of, for example, fur seals can be destroyed in just a few years, the United States, Russia, Japan and Great Britain (Canada) concluded the first agreement in the history of maritime law on the protection of ocean resources.
Then there were many such agreements and unilaterally adopted acts. Thirty-third US President Harry Truman declared that all mineral resources (primarily oil) of the surrounding continental shelf belong to the United States. In 1947, Peru declared its property fish living within 200 miles from the coast, and included the water area in the country's territorial waters. By 1973, eight more states had joined Peru. In response to such claims, in 1970, one of the UN resolutions stated that "the bottom of the seas and oceans ... as well as resources ... belong to all mankind."
In 1977, the US also declared a 200-mile fishing zone. Japan, Australia, New Zealand followed.
These countries, unlike Peru, did not include such zones in the territory of the state. At the same time, the water area of the economic zone of Japan, for example, is 12 times larger than the territory of the country itself. By 1987, 114 coastal countries had already adopted similar laws - there was, in essence, a political and economic division of 40% of the World Ocean, or 26% of the surface of the globe. Legal confusion arose in relations between states regarding the use of marine resources.
In 1968, the USSR, by the Decree of the Presidium of the Supreme Council, established sovereign rights for exploration and exploitation natural resources on its continental shelf.
And only the 1982 UN Convention on the Law of the Sea brought order to this issue.
By the way, and in a question of the sizes of territorial waters. For a long time, the width of the territorial waters of coastal and island states was limited by the limits established since the Middle Ages, and amounted to 3 miles - the maximum distance a cannonball can fly. The 1982 UN Convention extended this limit to 12 miles (the range of visibility of the horizon from the bridge of a medium-sized ship).
As already noted, the United States and some other countries refused to sign this convention, reserving "the right to act at their own discretion."
The industrial development of the continental shelf for mining began in the 20th century. The construction of hydraulic structures on the shelf is the youngest type of water management construction.
The first oil wells in the Caspian Sea were drilled in the USSR in 1924 from artificial territories.
In 1933, the United States established oil production in the Gulf of Mexico. Norway produces oil in the North Sea. The greatest development of work on the development of the continental shelf was in the 60s of the XX century.
SHELF (a. shelf; n. Schelf; f. plateforme сontinentale, plateau сontinental; and. plataforma, plataforma сontinental) - relatively shallow (up to several hundred meters) sections of the bottom of the oceans, marginal and inland seas, bordering continents and islands. The coastline serves as the boundary of the shelf from the land side, the outer boundary is drawn along the edge - an inflection on the ocean side, below which the depth of the bottom increases sharply. The depth of the edge varies widely from tens of meters (islands, such as Cuba) to 400-500 (Labrador Peninsula) and even 600-700 m (Sea of Japan). Where the edge is not pronounced in the relief (for example, the deltas of large rivers, such as the Ganges), the 200 m isobath is taken as the outer boundary of the shelf - the approximate average depth of the bend. The shelf area is 31,194 thousand km 2 (about 8% of the area of the ocean floor), the average depth is 132 m, the width is from 1-3 to 1500 km.
There is no generally accepted classification of the shelf. There are continental and insular shelves. Island shelves, as a rule, are less deep, not wide, and are specific in terms of relief and precipitation. In addition, the shelves of active and passive continental margins are distinguished. The shelves of active margins are distinguished by high seismicity, increased heat flow, intense magnetic anomalies, and manifestations of volcanism. Morphologically, they are less pronounced than the shelves of passive margins: they are narrower, have a steep stepped slope, and are often fragmented by tectonic faults (for example, the borderland off the coast of California). OK Leontiev (1982) divides the shelves into 3 unequal distribution groups: transgressive, abrasion (or depleted), and accumulative. Other classifications (G.S. Ganeshin et al., 1975) are based on geostructural criteria: platform, folded, and geosynclinal shelves. It was proposed to classify the shelves according to the type of their heterogeneities: tectonic, lithogenetic (oceanic in the area of large swell, oceanic in the area of constant storms, inland tidal and tidal seas, in the zone of calm dominance, etc., P. A. Kaplin, 1977) . The classifications reflect the different approaches of their authors to the origin, position, and morphology of the shelf. Some consider it a completely continental morphostructure and define it as a submerged part of the land, while others consider it a part of the ocean that develops under the influence of oceanic structures. There is also an approach to the shelf as a transitional (intermediate) but independent morphostructure, which is influenced by the processes of tectonogenesis, sedimentogenesis, relief formation both from the land side and from the ocean side.
The process of formation of relief and sediments on the shelf is mainly subject to geographical zoning, although there are also azonal facies and landforms (volcanic, tectonic and tidal). The relief of the shelf is mostly leveled. Shelf plains are almost everywhere complicated by various forms of meso- and microrelief of tectonic (tectonic steps, fault ledges), subaerial (flooded river valleys, moraine ridges, denudation remnants and ridges, etc.), subaerial (formed by waves and currents of a sand wave, ridges, ripples , channels for the flow of compensatory and discontinuous currents) and coastal-marine or coastal genesis (elements of ancient coastlines - abrasion terraces, relict accumulative forms). The specific relief forms of the shelf are submarine canyons, the problem of the origin of which is debatable. The dimensions of the canyons are extremely large, some of them start within the coastal zone, cross the shelf, cut through the continental slope and end on the abyssal plains (for example, the length of the canyons of the Congo River is about 800 km, the cut into the bottom is 1100 m).
Sedimentary deposits on the shelf are represented by thick strata of terrigenous, carbonate, sometimes salt-bearing, continental and coastal-marine (passive margins), volcanogenic, marine and coastal-marine (active margins) deposits aged from the Jurassic and younger. In part, these deposits are deformed and, as a rule, are lowered along faults by 1–10 km (Atlantic coast of the USA). Late Pleistocene and Holocene sediments belong to the latest shelf deposits. As a result of the Flanders transgression (17-6 thousand years ago), a complex stratum of deposits was formed on the shelf, consisting of subaerial (comprising 50-70% of all shelf deposits), coastal-marine (lagoonal, estuary, bar) and modern marine sediments. In the thickness of these sediments, relics of the coastal relief and sediments formed at various hypsometric levels turned out to be buried. Subaerial sediments are relict. Sediments caused by the activity of ice and marine organisms also play a significant role. As a result of the activity of various kinds of currents and waves, the clastic material (mainly large-clastic) of the shelf experiences constant movement, migrating to the shore or to the crest. Within the shelf (especially near the mouths of the rivers) the process of "avalanche sedimentation" is carried out, as a result of which a significant amount of detrital material accumulates.
In the Quaternary, processes associated with glacioeustatic transgressions and regressions appeared on the shelf. During the regression, the shelf was drained to approximately 100 m depth, subaerial sediments were deposited on the dried part, and a subaerial relief was formed. Subsequent transgressions, the amplitude of which reached 100-110 m, partially destroyed the sediments and relief of previous regressive epochs. Due to the fact that the coastline repeatedly migrated along the upper shelf, the subaerial relief and sediments of the early and middle Pleistocene are poorly preserved. During periods of glaciation, huge masses of detrital glacial, fluvioglacial, and alluvial material were brought to the shelf and accumulated. During fast transgressions, this material was processed by waves and a significant part of it was thrown onto land in the waterfront zone, and then formed into huge dune massifs and coastal accumulative forms.
Numerous deposits of various minerals are known on the shelf.
Of greatest importance are oil and gas, whose reserves within the shelf are estimated at 100 billion tons and 15 trillion cubic meters, respectively. m 3. Placer deposits, which are sources of titanium, zirconium, tin, chromium, diamonds, gold, platinum, etc., are also of great industrial importance. Of non-metallic minerals, phosphorites have been identified within the shelf, as well as huge reserves of non-metallic building materials - sand and gravel, shell rock, coral limestone, which are widely used in construction. About 30 countries carry out trial and industrial exploitation of minerals on the shelf.
On the international legal regime of the shelf, see Art. World Ocean.
Sheelf (eng.shelf) - a flattened area of the underwater margin of the mainland, adjacent
ksushe and characterized by a common geological structure with it.
The boundaries of the shelf are the coast of the sea or ocean and the so-called edge (a sharp bend in the surface of the seabed - the transition
to the continental slope). The depth above the crest is usually 100-200 meters (but in some cases it can reach 500-1500 m, for example, in the southern part of the Sea of Okhotsk or the crest of the New Zealand shelf).
The total shelf area is about 32 million km². The most extensive shelf is near the northern margin of Eurasia, where its width reaches 1.5 thousand kilometers, as well as in the Bering Sea, the Hudson Bay, the South China Sea, and off the northern coast of Australia.
The UN Convention on the Law of the Sea of 1982 grants coastal states the right to control the continental sea shelf (the seabed and subsoil of submarine areas located outside the territorial waters of the state). To exercise this right, a country must submit an application to a special international body - the UN Commission on the Limits of the Continental Shelf.
Bottom relief of the Barents Sea
HE gave Norway the waters and shelf of the Barents Sea.
Shelf (English shelf) - a leveled area of the underwater margin of the mainland, adjacent to the land and characterized by a common geological structure with it.
The boundaries of the shelf are the coast of the sea or ocean and the so-called edge (a sharp bend in the surface of the seabed - the transition to the continental slope). The depth above the crest is usually 100-200 meters (but in some cases it can reach 500-1500 m, for example, in the southern part of the Sea of Okhotsk or the crest of the New Zealand shelf). The total shelf area is about 32 million km². The shelf is most extensive near the northern margin of Eurasia, where its width reaches 1.5 thousand kilometers, as well as in the Bering Sea, Hudson Bay, the South China Sea, off the northern coast of Australia. The 1982 United Nations Convention on the Law of the Sea grants coastal states the right to control the continental sea shelf (the seabed and subsoil of submarine areas located outside the territorial waters of the state). To exercise this right, a country must submit an application to a special international body - the UN Commission on the Limits of the Continental Shelf. Shtokman Development AG operates in Russia on the shelf of the Barents Sea. Oil is produced on the shelf of the Baltic Sea near the coast of the Kaliningrad region, oil, gas and other minerals are produced on the shelf of the Caspian Sea, and gas is produced off the coast of Sakhalin.
Shelf (English shelf) - a leveled area of the underwater margin of the mainland, adjacent to the land and characterized by a common geological structure with it. Wikipedia rules
I don't know myself...
The shelf is the outskirts of the mainland flooded by the ocean, and therefore there, there are the same minerals as on land
Part of mainland earth's crust
Shelf - a leveled area of the underwater margin of the mainland. The boundaries of the shelf are the coast of the sea or ocean.
Shelf - coastal shallow marine or oceanic zone with depths up to 200 meters.
coastal shallow zone
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shelf (continental shelf, continental shelf), a shallow part of the underwater margin of continents and islands, which has a relatively leveled surface and slight slopes. confined to the area of development of the earth's crust of the continental type. The geomorphological boundaries of the shelf are the coastal zone and the edge of the shelf - an inflection below which the continental slope begins and the depths increase sharply. In the absence of a visible inflection, the outer boundary of the shelf is drawn along the 200 m isobath. The actual depths of the crest vary considerably, from 50 to 2000 m. - from 1 to 1500 km. The widest shelf in the north of Eurasia, in the Bering Sea, near the north. coast of Australia, in the Yellow, East China and South China seas. Total sq. shelf 31,194 thousand km², or 8.6% of the area. World Ocean. In Russia - approx. 5154 thousand km². has a complex history, went through a long path of development in the Mesozoic and Cenozoic eras; its relief was formed in the Holocene and in the modern era.
Watch value Shelf in other dictionaries
Shelf- shelf, m. (English shelf) (geographic). A shallow part of the sea formed from a submerged part of the land.
Explanatory Dictionary of Ushakov
Shelf M.- 1. The coastal part of the bottom of the world ocean, bordering the continents; continental shelf.
Explanatory Dictionary of Efremova
Continental Shelf- - the seabed and
the subsoil of the underwater regions of a coastal State, located outside its territorial sea throughout the natural prolongation ........
Economic dictionary
Shelf— coastal shallow marine or oceanic
zone with depths up to 200 meters.
Economic dictionary
Outer Continental Shelf- - under US law, this is the continental shelf, defined in accordance with international law, to which the areas of the bottom of the territorial sea are added. For two........
Law Dictionary
Shelf- -a; m. shelf] Spec. Coastal shallow zone of the ocean (with depths up to 200 m); continental shelf.
◁ Shelf, th, th. III zone. Sh-th waters. Sh. ice. th islands.
Explanatory Dictionary of Kuznetsov
Continental Shelf- - an area of the seabed (including its subsoil) of a certain width adjacent to the territorial waters, in which the coastal state exercises sovereign rights in ........
Law Dictionary
Continental Shelf of Russia- - this is a coastal, marine (oceanic) shallow water, which has a similar geological structure to the neighboring land; the most productive and productive for economic ........
Law Dictionary
Continental Shelf-, a gently inclined part of the underwater margin of the continent, extending from the edge of the coast to the CONTINENTAL SLOPE, going into the sea to depths of about 150 m. maybe ........
Scientific and technical encyclopedic dictionary
Continental Shelf- see Art. Shelf.
Shelf- (English shelf) (mainland shallow) - a leveled part of the underwater margin of the continents, adjacent to the shores of the land and characterized by a common geological structure. Depths........
Big encyclopedic dictionary
Shelf- (a. shelf; N. Schelf; f. plateforme continentale, plateau continental; and. plataforma, plataforma continental) - relatively shallow (up to several hundreds of meters) areas of the bottom of the oceans, marginal and inland seas, bordering ..... ...
Mountain Encyclopedia
Continental Shelf- Marginal regions of the continents, flooded by shallow seas. The outer edge steeply goes into the depths of the ocean. It is covered with thick layers of sea and river sediments. On the shelf....
Historical dictionary
Shelf- - continental shelf - a leveled part of the underwater margin of the continents, adjacent to the coast of the land and characterized by a common geological structure with it. Sh. apply ........
Historical dictionary
Shelf- the leveled part of the underwater margin of the continents, adjacent to the shores of the land and characterized by a common geological structure with it. Underwater plains with a relatively small bottom slope, which are the margins of the continents lowered below sea level with a relatively weak dissected relief and a depth of 1 to 200 meters (shallow shelf), less often up to 500 m (deep shelf). The shelf existed in all geological periods, in some of them growing sharply in size (for example, in the Jurassic and Cretaceous), in others occupying small areas (Permian, Devonian). The modern geological epoch is characterized by moderate development of shelf seas.
The depths of the shelf edge are usually 100-200 m, in some cases reaching 1500-2000 m. The total shelf area is about 8% of the area of the World Ocean. Within the shelf:
- oil and gas fields are being developed;
- the possibility of extracting some other minerals is being explored;
- are the most important fishing areas of the world.
There are continental and insular shelves. Island shelves, as a rule, are less deep, not wide, and are specific in terms of relief and precipitation. In addition, the shelves of active and passive continental margins are distinguished. The shelves of active margins are distinguished by high seismicity, increased heat flow, intense magnetic anomalies, and manifestations of volcanism. Morphologically, they are less pronounced than the Shelves of the passive margins: they are narrower, have a steep stepped slope, and are often fragmented by tectonic faults (borderlands off the coast of California). OK. Leontiev (1982) divides the shelves into 3 unequal distribution groups: transgressive, abrasion (or depleted), and accumulative. Other classifications (G.S. Ganeshin et al., 1975) are based on geostructural criteria: platform, folded, and geosynclinal shelves. It was proposed to classify the shelves according to the type of their heterogeneities: tectonic, lithogenetic (oceanic in the area of large swell, oceanic in the area of constant storms, internal tidal and tidal seas, in the zone of calm dominance, etc. (P.A. Kaplin, 1977) "The classifications reflect different approaches of their authors to the origin, position, morphology of the shelf. Some consider it to be a completely continental morphostructure and define it as a flooded part of the land, others - a part of the ocean developing under the influence of oceanic structures. There is also an approach to the shelf, as a transitional (intermediate ), but an independent morphostructure that is influenced by the processes of tectonogenesis, sedimentogenesis, relief formation both from the land side and from the ocean.
Sedimentary deposits on the shelf are represented by thick strata of terrigenous, carbonate, sometimes salt-bearing, continental and coastal-marine (passive margins), volcanogenic, marine and coastal-marine (active margins) deposits aged from the Jurassic and younger. In part, these deposits are deformed and, as a rule, are lowered along faults by 1–10 km (Atlantic coast of the USA). The latest shelf deposits include late Pleistocene and Holocene sediments. As a result of the Flanders transgression (17-6 thousand years ago), a complex stratum of deposits was formed on the shelf, consisting of subaerial (comprising 50-70% of all shelf deposits), coastal-marine (lagoonal, estuary, bar) and modern marine sediments. In the thickness of these sediments, relics of the coastal relief and sediments formed at various hypsometric levels turned out to be buried. Subaerial sediments are relict. Sediments caused by the activity of ice and marine organisms also play a significant role. As a result of the activity of various kinds of currents and waves, the clastic material of the shelf experiences constant movement, migrating to the coast or to the crest. Within the shelf (especially near the mouths of rivers) the process of "avalanche sedimentation" occurs, as a result of which a significant amount of detrital material accumulates.
Within the shelf, the main mass of sediments is deposited, from which sedimentary rocks subsequently arise.
The rate of sedimentation in the shelf area is many times greater than on the continental slope, and even more so on the ocean floor. Within the shelf, the first place in terms of abundance, diversity and thickness is occupied by detrital, the second by organogenic, and the third by chemical sediments. The latter are deposited in their pure form only in the most coastal areas of the sea and in lagoons.
The origin of the shelf is usually associated with eustatic fluctuations in the water level of the World Ocean, caused by global climate change. To a lesser extent, shelves are formed when the coast retreats under the action of abrasion or during the underwater accumulation of thick layers of sediments near the edge of the continent. The current position of the shelf edge, beyond which the continental slope begins, is not the same due to the manifestation of vertical movements of the earth's crust and varies in the depth range of 90-500 m with an average value of 132 m. The relief of the shelf indicates the manifestation of surface erosion processes - river and glacial forms are known here relief (underwater riverbeds and proluvial valleys), fossil ice and peat bogs with the remains of mammoths and other terrestrial animals, which confirms the former position of land on the shelf.
Irregularities on the surface of the shelf have been preserved from the time when the shelves were raised above sea level. Such a time was the era of the Quaternary glaciation, when significant masses of atmospheric water were connected in continental ice and the level of the World Ocean was 100-150 m lower than the modern one. Subaerial erosional forms include, for example, underwater valleys at the bottom of the North Sea. A deep underwater valley is dug in the shelf against the mouth of the river. Hudson on the Atlantic margin of North America, similar submarine valleys are found opposite the mouths of many other rivers.
Other irregularities on the shelf surface are associated with uneven accumulation of sediments. But in general, the shelf is characterized by a very gentle relief due to the washing of sediments by waves and the leveling of their surface at the level of the wave action basis.
Reconstruction of the climate and associated changes in the ocean level indicates that during the entire Phanerozoic, eustatic fluctuations did not stop, and in some periods the water level of the World Ocean increased by 300-350 m relative to its current position. At the same time, significant areas of land (up to 60% of the area of \u200b\u200bthe continents) were flooded.
The problem of substantiating the outer boundary of the Russian continental shelf (OGCS) using geological and geophysical methods has become one of the key tasks since the late 1980s, when the corresponding resolution was adopted by the USSR Council of Ministers. In connection with the entry into force federal law on the Continental Shelf and the ratification by Russia in 1997 of the "UN Convention on the Law of the Sea of 1982", by the decision of the Government of the Russian Federation, the work was intensified. The features of the relief and deep structure of the bottom of the Arctic Ocean (AO), its position on the planet, the insufficient level of knowledge and hence the ambiguity in the interpretation of the history of the formation of the subsoil determined the decisive role of bathymetric and geological and geophysical methods in solving the issue of the possibility of spreading the concept of "legal shelf of Russia" on a significant area of the bottom of the deep-sea region of the Arctic Ocean.
Literature
- V.B. Karaulov, M.N. Nikitina Geology. Basic concepts and terms, M, URSS, 2005
- N.V. Koronovsky, A.F. Yakushova Fundamentals of Geology
- Dobretsov V.B. Development mineral resources shelf. - L .: Nedra, 1980, p. 272.
- Avdonin V.V., Kruglyakov V.V., Ponamareva I.N., Titova E.V. Minerals of the World Ocean: Textbook, M.: Publishing House of Moscow State University, 2000.
- Bogdanov D.V. Regional Physical Geography of the World Ocean: Tutorial for universities, M.: Higher school, 1985.
- Gavrilov V.P. Geology and mineral resources of the World Ocean: Proc. for universities, M.: Nedra, 1990.
- Geology and minerals of the shelves of Russia. Ch. ed. M.N. Alekseev. – M.: 2002. S. 425.
The concept of "continental shelf" can be considered both from a geographical and legal point of view. If we talk about geography, then the shelf is called the seabed and subsoil, extending at a distance of 200 or more nautical miles from the territorial waters, to the underwater edge of the mainland.
This is a flat surface of the underwater continental part, which has a common geological structure with the land. The conditional boundaries of the shelf are the ocean coast on one side and the "edge" on the other (the place where the seabed passes into).
The shelf can have different depths, but most often the water column above the crest is up to 200 meters. Although there are places on the planet where the depth above the crest reaches 1500 meters, as, for example, off the coast of New Zealand. According to scientists, the total area of the continental shelves of the oceans is approximately 32 million square kilometers.
The most extensive continental shelf is famous for the northern coast of Eurasia (shelf width up to one and a half thousand kilometers), the northern coast of Australia, the Bering Sea. One of the narrowest places on the continental shelf is the west coast of South America.
Shelf relief
Continental shelves vary in structure. The shelf may have an undulating relief, as off the coast of Eurasia; can be almost smooth, as in the northern latitudes, where the shelf surface is "polished" by large blocks of ice. In the tropics and southern hemisphere shelves are often surrounded by coral reefs (the largest known - 
The Great Barrier Reef off the coast of Australia) that separates the coast from the ocean depths. Off the coast of California, the shelf is dotted with deep troughs, formed as a result of land erosion long before it sank under water. Where a powerful current passes close to the coast, the shelf can begin with a smooth slope, and then abruptly break off in depth.
Shelf control
Continental shelves are the main fishing areas: in this part of the world's oceans there is a huge supply of food for fish, so it is on the shelves that the main fish are caught. In addition, in the bowels of the shelf in different parts of the world there are rich reserves of gas and oil, such as, for example, in the Gulf of Mexico.
According to the UN Convention on the Law of the Sea, which has existed since 1982, coastal states have the right to control the sea shelf, that is, that part of the seabed and subsoil that is outside the territorial waters. 
A country can obtain the right to conduct research and mining on the shelf after its application is considered by the UN International Commission on the Limits of the Continental Shelf. These limits are also calculated in accordance with the norms of the aforementioned Convention.
For example, seven states have the right to develop the continental shelf in the North Sea: Norway, Great Britain, Denmark, the Netherlands, Germany, France, and Belgium. More than sixty natural gas and oil fields have already been discovered in this part of the shelf, the largest being in the zone of Norwegian and British influence.
Continental shelf and maritime law
The sovereign right of the coastal state to explore the shelf and develop resources in this area means that if the state does not conduct such work, then no one has the right to claim similar actions in this area.
In other words, no one can conduct exploration and development without first obtaining the consent of the coastal state that controls this part of the shelf. It is noteworthy that the rights to the shelf do not apply to the airspace and covering waters: here any state can lay pipelines and cables, coordinating the proposed route with the coastal state. 
The coastal state has the exclusive right to construct artificial islands on the continental shelf. If the development of mineral resources is carried out beyond 200 miles from territorial waters, then the UN Convention obliges the coastal state to transfer money or make contributions in kind to the International Seabed Authority.
The continental slope in areas with an active tectonic regime is a zone in which gravitational processes predominate. This is facilitated by the dissected underwater relief, high seismicity and a significant level of material supply from land and (or) shelf. Despite this, the slope of the Andean margins is covered for a large extent by hemipelagic and (or) chemogenic-diagenetic sediments. The latter include glauconite sands and silts. In the Peruvian sector of the margin of South America, they are distributed not only in the upwelling zone, but can also be traced to the north of it to a depth of 500 m or more. Glauconite sediments are characteristic of the gently sloping sections of the slope. On the Oregon slope, glauconite sands form thin pro-silt among silty-argillaceous hemipelagic oozes, which form 100-meter-thick strata in depressions that complicate the slope. Quite large alluvial fans formed at the mouths of canyons on the outskirts of Oregon. The underwater cone of Astoria is especially well studied. DSDP) reaches from 2 to 7 m. They occur among silty clayey sediments. In the interchannel spaces of the cone, turbidites are common, which are dominated by silts. The cyclite of such turbidite is usually incomplete, it contains only the upper horizons (T4 and T5 according to A. Boum): siltstone overlain by homogeneous silty clay. Similar sediments are also common in the depths of the abyssal plain, which is generally characterized by carbonate pelagic sediments - nannoils. Volcanogenic formations play a secondary role.[ ...]
Continental slope and its foot. Completely different processes dominate on the continental slope of the submarine margins of the continents. If hydrodynamic factors play the main role on the shelf, then on the slope and its foot the processes of sedimentation are largely determined by the only factor, gravitational. It is associated with a number of phenomena that are diverse in scale and nature, starting with underwater landslides - rockfalls and disruptions of large blocks of rocks and ending with the formation of huge landslides and various flows of matter, both laminar and turbulent.[ ...]
Shelf - a coastal area of the sea, bordering the mainland, the water depth above which does not exceed 200 m. The outer edge of the shelf is a continental slope, descending to the bottom of the sea.[ ...]
Shelf - coastal oceanic shallow water, limited by the coast and the ridge of the continental slope.[ ...]
Not only the shelf, but also a significant part of the continental slope of Socotra Island is devoid of a cover of unconsolidated sediments. In sediment cores, thin sand interlayers (2-6 cm each) with erosion or fuzzy contact lie on coccolith-foraminiferal sandy silts and are in turn overlapped by the same carbonate silts.[ ...]
As part of the continental margin - the most common form of the transition zone from the continent to the ocean - underwater and above-water parts are distinguished. The submarine includes the shelf, the continental slope and the foot, the edge of which, in areas not complicated by a deep-water trench, is the outer boundary of the margin and separates it from the bed of the abyssal ocean basins. In most areas, this boundary is drawn at depths from 3000 to 4500 m. It is more difficult to determine the boundary of the margin on the continent itself.[ ...]
The melting of continental ice sheets caused an increase in the level of the Ocean, a transgression (advance) of the seas, flooding the previously drained shelves.[ ...]
Within the outer shelf (Delaware County), carbonate-terrigenous sands enriched in feldspars become the main type of sediments. These are also relict sands, which contain micronodules of manganese in the Georges Bank area. On the continental slope, the sands are replaced by silty or sandy silts, containing, according to the data of L. Doyle and other researchers obtained in 1979, from 50 to 80% of silty material. Sludges, as a rule, are distinguished by increased concentrations of Corg. The admixture of particles of sand size does not exceed 15%, and in addition to quartz, feldspars, and glauconite, shells of planktonic foraminifers and pyrite microconcretions play a significant role in the composition of the sand fraction. In the section of sediment columns raised in the lower part of the slope, there are small (up to 1 cm) layers and lenses of sand, often with gradation layering. In the areas of landslides, these interlayers often lie at an angle to the general stratification. Lumps of harder and more ancient clays randomly dispersed in a finely dispersed mass are described. The content of CaCO3 in sediments of the continental slope north of Cape Hatteras does not exceed 10%. Down the slope, the content of silty (from 10 to 50%) and clay (from 5 to 30%) particles increases. At the same time, the role of silty material remains constant in the foothill sediments, while the content of clay particles increases. Clay-silty silt becomes the main type of sediments.[ ...]
In areas of shelf expansion, they are replaced by sandy and silty silts (depth 55-90 m). The latter in the direction of the continental slope are again replaced by silty sands. Below the 100-120 m isobath, the Holocene sands disappear and the outermost zone of the shelf is occupied by late Pleistocene sands, under which a layer of pebbles with gravel is found everywhere, exposed in places at the edge of the shelf.[ ...]
The concept of the edge of a continent or continental margin, which was born as a purely geographical concept, later acquired a deep geological meaning. Bright morphostructural manifestation, manifested in the existence of an underwater sea terrace - a shelf, a ledge of the continental slope and, finally, an extensive deep-water foot, as well as a huge extent of the continental margins, equal, according to K. O. Emery (1977), almost 195 thousand km , allow us to consider them one of the most important features of the face of the Earth. The ubiquitous contrast of the relief, the drops of which reach 10-15 thousand and (Peru) in the transition zone from the mainland to the ocean, a sharp change in geophysical characteristics, reflecting the different composition of the crust, and, possibly, upper mantle, the bright specificity of geological, oceanographic and other processes on (and above) the continental margin - all this emphasizes the special position that it occupies in the relief earth's surface, being a reflection of the main geological boundary: the contact of the continental crust with the oceanic crust.[ ...]
In the relief of the ocean floor, the following are distinguished: the continental shelf, or shelf (shelf), is a shallow part up to a depth of 200 m, the width of which in some cases reaches many hundreds of kilometers; the continental slope is a rather steep ledge to a depth of 2500 m and the ocean floor, which occupies most of the bottom with depths up to 6000 m.[ ...]
Recent sediments of the open part of the Southern Primorye shelf are characterized by a different facies series: sands and silty sands occupy the upper part of the subligoral, below the 30–40 m isobath they are replaced by silts, which quickly change at a depth of 50–60 m into silty–argillaceous and fine silty silts. Silty-argillaceous sediments form extensive fields and are replaced at depths of 90-100 m by silty sands. At depths of 110–120 m, modern material is not deposited, since particles coming from the land (and clay particles reach this part of the shelf) are carried by the Primorsky Current, which is most active at the inflection of the shelf onto the continental slope. Holocene facies are almost everywhere represented by fine-grained silty sands with a content of 4-5.5% pelitic admixture.[ ...]
If you go deeper towards the open sea, then behind the shelf there is a continental slope, then a continental foot, which together form a transitional area from the continents to the ocean bed. The continental slope is the most steeply inclined part of the bottom, the slope of which is 10“2, but in some places it reaches 10-1. The outer boundary of the continental slope is the 3000 m isobath. At the continental foot, the bottom slope is an order of magnitude less than in the area of the continental slope. The outer boundary of the continental foot is located mainly between the isobaths of 3000 and 4000 m.[ ...]
The phenomena of salt diapirism, which are very characteristic of the continental slope and the foot of Northwest Africa, are also observed in the Gibraltar zone, at the base of the US continental slope south of Cape Lookout and in some parts of the Portuguese shelf. In the latter case, judging by the sections studied on land, the evaporites are of Early Jurassic age.[ ...]
From the foregoing, we can conclude that sedimentation within the continental slope is very active during periods of high ocean level, mainly due to the deposition of hemipelagic normal sedimentary silts. During periods of low levels ocean waters the maximum of sedimentation is shifted to its lower part and to the foot, which is due both to the supply of material directly from the shelf, and the gravitational movement of sedimentary masses accumulated by this moment on the slope itself.[ ...]
In the Paleocene-Early Eocene cyclically constructed series, the main feature is the alternation of variegated clays and siltstones. The latter, according to W. Dean, J. The duration of the formation of single cyclothemes was about 50,000 years. The origin of such cyclically built series was apparently associated with the removal of a significant amount of organic matter from the outer shelf and the upper half of the slope, which were in the upwelling zone.[ ...]
The delta front can extend to the middle shelf plain and even to the edge of the shelf. However, even outside the shelf, the margin profile is usually formed by the solid runoff of large rivers flowing into the ocean. Such, for example, is that part of the outskirts of the Gulf of Guinea, to which the delta of the river is confined. Niger. A somewhat different situation has developed in the delta of the river. Amazons. The fore-delta in this case extends only to depths of several tens of meters. The rest of the shelf is not fed by the suspension of the Amazon, as it is intercepted by the Guiana Current, which carries it along the continental slope of Northern Brazil. In the outer part of the shelf, at the site where the river flows into the ocean. Amazonian modern sediments, according to L. A. Zakharov, are represented by carbonate biomorphic-detritus formations. This, however, does not mean that the influence of the Amazon on sedimentary processes is limited only to the region of the delta and foredelta. As in most other cases, the bulk of the sediments accumulated in the distal part of the transition zone, where a giant deep-sea fan formed in the Late Cenozoic. On other outskirts of continental rifts, to which the deltas of large rivers are confined, powerful underwater fans are also known, associated with developed systems of canyons, which are located on the continuation of underwater river channels, for example, the canyons of the Amazon, Indus, Congo.[ ...]
The outer part of the shelf is the more active zone in terms of sedimentology. This is due to the weakening of the action of the main hydrodynamic factors: waves and swell. Of no small importance is the increase in the bioproductivity of surface waters over this part of the continental shelf, due to the rise of deep waters or, in other words, upwelling, which occurs to some extent along most continental slopes. On the modern margins of cratons, grouped along the western contour of the Atlantic and the Indian Ocean, it is especially active in the areas of cyclonic gyres, in the sphere of action of which is the Atlantic margin of Canada and partly the United States.[ ...]
The transition zones of this mud are characterized by a reduced coastal plain, a short shelf, a rocky coastline with small bays and bays, a relatively steep continental slope, often complicated by gentle rises and banks, and narrow underwater fans. As a rule, these are the outskirts of young folded structures in zones with increased seismicity. Often they are located near the centers of active volcanism. So, the Calabrian outskirts in the Ionian Sea is in the zone of influence of Etna and Vesuvius.[ ...]
The main factor that differentiates marine biota is the depth of the sea (see Fig. 7.4): the continental shelf is abruptly replaced by a continental slope, smoothly turning into a continental foot, which descends lower to a flat ocean bed - the abyssal plain. These morphological parts of the ocean approximately correspond to the following zones: neritic - to the shelf (with littoral - tidal zone), bathyal - to the continental slope and its foot; abyssal - the area of ocean depths from 2000 to 5000 m. The abyssal area is cut by deep depressions and gorges, the depth of which is more than 6000 m. The area of the open ocean outside the shelf is called oceanic. The entire population of the ocean, as well as in freshwater ecosystems, is divided into plankton, nekton, and benthos. Plankton and nekton, i.e. everything that lives in open waters forms the so-called pelagic zone.[ ...]
Studies of suspensions and bottom sediments show that the bulk of sedimentary materials are deposited not on the shelf, as was thought until recently, but at the base of the continental slope.[ ...]
The outgoing branch of the geo-circulation is located in areas of stable accumulation, i.e. in the ocean, especially within the shelf and other parts of the continental margin, as well as in closed water bodies of land and in places of stable accumulation such as deltas, alluvial fans, swamps, etc.[ ...]
Silty and silty-argillaceous oozes are displaced to the periphery of upwelling zones and are distributed either in the outer part of the shelf or in the lower half of the continental slope. Thus, fine silt silts are found in separate areas in the outer part of the Peruvian shelf (7-10 ° S). They are 80% composed of quartz grains, the rest falls on fragments of metamorphic rocks (10%), plagioclases (1%) and potassium feldspars (7%). Silty-argillaceous oozes consist of aggregates of clay minerals with low interference color and disordered texture. An abundance of thin micaceous scales and plates of hornblende is characteristic, and in areas of modern volcanism (outskirts of Peru) also volcanic glass.[ ...]
Allen gave an overview of other stationary circulation models. Interesting effects are noted that arise when the bottom relief on the shelf is taken into account, especially when the dia slope increases sharply when the shelf passes into the continental slope (see).[ ...]
As detailed geophysical studies show recent years, and partly also the materials of deep-sea drilling, the outer edge of the Jurassic shelf was located, probably, 60-100 km seaward of the modern one. It is often identified with the submerged edge of ancient carbonate platforms, the position of which is clearly established by geophysical methods under the modern slope, and sometimes in the foot area in various regions of the Atlantic margin of the United States. The expansion of the oceanic floor was accompanied by the fragmentation of the peripheral sections of the continental crust and the subsidence of individual blocks. Continuous subsidence, which covered the edge of the continent, favored in the arid climate that prevailed on many outskirts jurassic, active reef building along the outer edge of the ancient continental shelf. Only in coastal areas, in the immediate vicinity of the slopes of epirift uplifts, did terrigenous marine, mostly sandy, sediments accumulate. Reconstruction of sedimentogenesis settings typical for passive continental margins located in tropical and subtropical climatic zones is given in Fig. 2. 37.[ ...]
Thus, the most intense sedimentation processes are currently confined to the bay. Martaban and the adjacent part of the open shelf, where the fore-delta of the river is located. Irrawaddy, as well as to the southeastern shelf area north of the Malay Peninsula. In the first area there is an accumulation of clay fine pilaf, in the second - carbonate sands and clay-carbonate sediments. Most of the solid runoff of the river. The Irrawaddy enters through the canyons into halistasa. However, the slope itself for a considerable extent is filled with clayey silts of a peculiar cream or reddish color, very thin, with a high content of oxide iron. This is a rare case of accumulation of non-stranded marine sediments containing washout products of lateritic and ferralitic weathering crusts. The latter are common on the slopes of the coastal ranges and on the high plateaus of Burma. Terrigenous components are represented in the first type of sediments by silty, in the second - by clayey material. At the foot of the continental slope, the accumulation of sediments of landslide and turbidity origin is assumed. Thus, on the continental margin in the Anadaman Sea, sedimentary processes differ in intensity and direction: areas of purely terrigenous sedimentation here are adjacent to zones of carbonate sedimentation-accumulation. Unexpected for this tropical region is the wide distribution of relict formations and the relatively small role of biogenic substances.[ ...]
In arid zones, the situation is largely different. The main sediment-forming element here is carbonate detritus. On the outer shelf of Africa in the Ionian Sea (Libyan area), it accumulates in the form of foraminiferal sandy silty silts enriched in glauconite and containing relict material in the form of fragments of algal structures, less often ooliths. The terrigenous part is usually represented by eolian quartz. These are brown or beige silty-pelitic sediments, indistinctly bedded and weakly spotted, enriched in pteropod remains at some levels. When dried, numerous traces of processing by silt-eaters are found. Their appearance is apparently associated with the drift of shelf material. Down the slope, the size of the sediment-forming particles decreases. Carbonate micrite (pelitic particles) with a more uniform color predominates. The role of the clay substance increases somewhat. The uniformity of the sections is disturbed by the presence of layers of green-vago-gray ash, compacted, with a lumpy texture, as well as dark gray to black (when wet) sapropels. In the depression that separates the layers of North Africa from the deep part of the Ionian Sea, layers of white carbonate sand (2-3 cm thick) become more frequent, indicating the manifestation of some kind of gravitational processes.[ ...]
The accumulation of modern sediments is confined to the zone of "struggle between land and sea", and mainly to the deep-water parts of the margin: the lower half of the continental slope and the foot. These are areas of avalanche sedimentation, where sedimentary material accumulation rates exceed 100 Bubnov units, otherwise 100 B. The significant width of the shelf with extremely small slopes of the bottom surface (only 0.6 m/km) is the reason that any even not very large rise in the ocean level is reflected by a significant advance of the sea, which captures the areas of the coastal plain adjacent to the shelf. On the contrary, the level drop is accompanied by a sharp reduction in the area of the shelf zone. Accordingly, during the periods of transgressions, the processes occurring in the coastal part of the shelf acquire the greatest importance, during the periods of regressions - the processes of continental and submarine-slope sedimentation.[ ...]
The current development of the country's gas industry is associated with the development of natural gas fields on the continental shelf in the near future. One of the largest such facilities will be the Shtokman gas condensate field. The structure of the mutual arrangement of technological objects of offshore fields differs significantly from onshore fields. One part of them is located on the sea surface (directly on the drilling platforms), and the other part is on the mainland. Moreover, offshore technological facilities can be located both at a fairly large and at a fairly small distance from the coastline of the mainland.[ ...]
The main structures of the ocean floor are ocean basins, ocean ridges, deep-sea trenches and continental margins, which in turn consist of a shelf, a continental slope and a continental foot.[ ...]
The boundary of land and ocean (zero mark) does not fix the transition of the continental crust into the oceanic one. On the hypsographic curve, there is a distinct morphological expression of the continental shelf, or shelf - the low-lying margin of the continents flooded with water, as well as the continental slope, at the foot of which, on average at a depth of 2450 m, the continental crust is replaced by oceanic. Noteworthy is the coincidence of the marks of the foot of the continental slope with the average (leveled) level of the earth's crust - 2430 m below the ocean level. If the leveled surface of the earth's crust is covered with water contained in the Ocean, the level of the latter will be 250 m higher than the present one.[ ...]
The third layer of oceanic crust is traced from the center of the abyssal basins to the outer edge of the magnetic anomaly on the east coast. Thus, the oceanic nature of the crust under the continental foot in many regions is not in doubt. However, the detailed structure of the zone in the band 50–100 km east of the edge of the magnetic anomaly on the east coast of North America is still unknown. The presence of developed blocks of sedimentary rocks and large diapirs suggests that it is composed mainly of sedimentary strata. The continental crust in the shelf zone is overlain by an even thicker cover of sediments 8-14 km long), broken into blocks and thinned.[ ...]
Formed by tectonically and morphologically heterogeneous elements that are united by a common geographical location and arose under the influence of the same geological events, the continental margin, regardless of its age, is a complex heterogeneous formation, which includes areas with continental and oceanic crust. The deep boundary between them has not yet been deciphered completely. On the Atlantic and Indian Ocean margins of the continents, it is identified either with the E anomaly located in the middle part of the zone of undisturbed magnetic field, as, for example, F. Rabinovich does (1978), or with the inner edge of this field. In the region of the Atlantic slope of the US margin, there is a magnetic anomaly of the east coast, which has a width of 50 to 70 km. South of 36° N. sh. this anomaly is divided into two branches, of which the outer one is traced along the 1200-1300 m isobath. In the shelf area at a depth of 7-10 km, sources of magnetic disturbances are found, which are believed to be either weakly magnetized blocks of basement rocks, or dike hairs and sills intruded into the sedimentary sequence in the Early Cretaceous.[ ...]
Great prospects for the use of submarine groundwater by marine water intakes are opening up in connection with the significant development technical means drilling and testing of wells on the shelf, the continental slope and the bottom of the seas. Wells drilled on the shelf of Australia, near the Atlantic coast of the USA, on the continental slope of the Gulf of Mexico and in other places, have revealed fresh low-mineralized submarine waters with significant pressure. Thus, while drilling in the Atlantic Ocean off the coast of Florida, fresh water was found 43 km from the coast east of Jacksonville. A well drilled from a ship at a depth of 250 m below sea level revealed water with a salinity of 0.7 g/l, while the water pressure reaches 9 m above sea level.[ ...]
According to the results of drilling, as well as the study of strata exposed in the zones of the Late Cenozoic and Quaternary eniplatform orogeny, it was established that at the base of the sedimentary cover of passive continental margins, more precisely, within the shelf and coastal plain, complexes of ancient sediments surprisingly similar in lithological terms occur. These are, as a rule, clastic red-colored formations of continental genesis, among which sandstones, conglomerates and siltstones with layers of clays (argillites), evaporites, less often limestones, interbedded with lava covers and horizons of volcanic ash, prevail. Similar geoformations have been found on many margins in the Atlantic and the Indian Ocean, in areas thousands and tens of thousands of kilometers apart from each other, which allows us to consider them as sediment complexes associated with a single stage of evolution for most of the margins considered.[ ...]
Outskirts of Southern Primorye in the Sea of Japan. The outskirts of Southern Primorye are heterogeneous in structure. It is characterized by a rocky coast, a narrow open shelf and a very steep continental slope. Within the southern section there are bays deeply cut into the land: Amursky and Ussuriysky, as well as many other smaller bays and islands. The shelf here reaches a considerable width. The slope is also steep, as in the northern section.[ ...]
From lines 1a-b of Table. Figure 6.4 shows that the primary production of plant biomass (expressed as carbon) in the ocean is about half that on land. Almost all of these products are related to phytoplankton. The distribution of the biological productivity of the ocean for various types of organisms is given in Table. 6.6 (according to the Institute of Oceanology of the Academy of Sciences of the USSR).[ ...]
Glauconite is not a mineral specific only for upwelling regions (in ancient geological epochs, glauconites also formed in epicontinental water bodies), but it is here that it acquires a regional sediment-forming significance. In thin sections of specimens recovered from some areas of the slope in the central part of the margin of Peru, one can see rock fragments transformed to varying degrees, whose angular shape and lack of sorting indicate that they represent an underwater scree and did not move over long distances. Many of these fragments still retained relics of the former structure, while others acquired the aggregate structure characteristic of glauconite, and others are chloritized or have fouling rims. Another source of glauconite could be oolitic nodules in the silty-argillaceous muds described above.[ ...]
The most studied among the transition zones in areas with a passive tectonic regime is the Atlantic margin of the United States, the deep structure of which is shown in Fig. 3. Studies using multichannel seismic equipment have shown that in many areas of this margin, in addition to the modern continental slope, there is a paleoslope located to the east of the modern one and buried under a layer of sediments. In the area of the Georges Bank, under the outer part of the shelf and the slope at a depth of 1800 m from the bottom, there is a top layer of sedimentary rocks, the upper surface of which dips steeply to the east to a depth of 4.5-5 km. This massif is identified with a thick carbonate platform that formed in the Late Mesozoic. The massif serves as a limit for a large trough confined to the interior of the shelf and filled with Mesozoic and Cenozoic deposits up to 10 km thick. The depth of the basement under the carbonate platform itself has not been established. In the foot area, the acoustic basement (roof of the oceanic crust) is located at a depth of 7-8 km below sea level, i.e., the thickness of the sediments, mainly Cenozoic, here is from 3 to 4 km. The outer boundary of the ancient slope, formed, judging by the results of dredging carried out in the canyons of this zone by W. Ryan and other researchers in 1976, by neocomian reef limestones, is advanced to the east from the modern one by only a few kilometers.[ ...]
In conclusion, it should be noted that greatest variety The upper half of the margins of the regions of epiplatform orogenesis, especially the zone of struggle between land and sea, differs in sedimentation settings. A variety of sediments are formed here: from carbonaceous diatomaceous silts of fjords in high latitudes to bichrocks and mangrove swamp deposits in low latitudes. On the open shelf of arid zones, modern and relict bioherms are widespread, and in areas of recent rifting, large reef structures. The continental slopes here are associated with the formation of monotonous silty-pelitic silts, prone to flow and landslide. At the foot, they are replaced by cyclically built series of sediments, among which, on the mature margins of this type, along with ordinary turbidites, deposits of flows of liquefied clastic material and grain flows play a significant role.[ ...]
In the Barremian age, another activation of the relief and rejuvenation took place. The climate was probably approaching more and more humid tropical, and on some uplifts and elevated plateaus, rather thick weathering crusts were formed, the erosion of which led to the intensive removal of finely dispersed suspension enriched in iron oxides and silica. Due to this, in the central regions of the Atlantic Ocean, but mainly at the foot of the mainland, horizons of variegated clays were deposited. Bauxites of this age are known within the so-called Ebro land on the Iberian Peninsula and within the Toulouse land. In the Aptian, the spreading of the ocean floor in the southern basin of the Atlantic Ocean became more active. To the south of the Kitovy and Rio Grande ridges, at the site of rift troughs and the grabens feathering them, an oceanic-type basin arose in the Neocomian, in which, according to the data of V. Ludwig, V. Krasheninikov and I. Basov, obtained in 1980, a regime of marine terrigenous sedimentation was established and clay sediments accumulated, enriched organic matter. In the Aptian, progradational complexes of underwater-deltaic sandy-silty-argillaceous deposits formed here, building up the ancient shelf and slope of Africa in the Cape Basin. The presence of a structural threshold along the line xp. The Rio Grande made it difficult to exchange water between this sea basin and the vast epicontinental basins located to the north, which arose on the site of rift grabens.[ ...]
These include the outskirts of Africa and Arabia in the Gulf of Aden. Among the factors that determine the composition of sediments in the underwater part of these transitional zones, not the least role is played by the age and composition of the strata eroded on uplands and high plateaus framing narrow coastal plains. Paleocene clays are exposed on the Arabian side of the Gulf of Aden in the region of the Hadhramaut plateau. In conditions of a sharply arid climate, clay particles are blown out by the wind from the slopes. However, the bulk of the fine material is transported to the coast by drying up full streams, from where it spreads along the entire profile of the underwater margin of Arabia. The peculiar structure of the coast contributes to the capture of clay suspension in the coastal part of the shelf. The so-called "tombols" - the remains of volcanic structures of the Late Cenozoic age - are advanced here towards the ocean. These are semi-destroyed cones of central type volcanoes, preserved from the time of active rifting (Fig. 15). Individual volcanic structures are connected to the coast by narrow sandy barriers separating large bays and gulfs from the shelf. Here, in in large numbers clay sediment accumulates. Towards the open sea, clayey muds are replaced by carbonate-clayey sediments, the clastic part of which is represented by terrigenous eolian material and skeletal remains of carbonate-building organisms. In the lower part of the cores of sediments recovered at the base of the continental slope during the 8th cruise of the R/V Akademik Petrovsky, there is an alternation of sandy-silty terrigenous-carbonate silts with a spotted texture and silty-argillaceous silts with almond-shaped inclusions of carbonate detritus. Sediment cores taken at the foot were represented by homogeneous carbonate-argillaceous silty-pelitic silts with indistinct layering. Thus, there are no traces of active gradational movements in the surface layer of the sedimentary cover in this area.[ ...]
The tectonic asymmetry of the Pacific Rim, expressed primarily in the fact that its western half contains transition zones of the island-arc type, while the eastern half-ring consists of Andean and Nevadian margins, has also led to a certain sedimentological asymmetry. This can be seen in the example of latitudinal climatic zonality, reflected in the composition of precipitation that has become widespread in the transition zones in the east and west of the ocean. In this regard, let us consider the island-arc margins located along the western perimeter of the Pacific Rim. The processes of sedimentation in the area of the West Aleutian volcanic arc and the Bering Sea located behind it are the most studied. According to A.P. Lisitsyn and D.E. Gershanovich, the continental shelf of the Bering Sea is dominated by the accumulation of terrigenous sandy and silty sediments enriched to a greater or lesser extent by pebble and boulder ice-rafted material. Coarse aleurite sediments descend onto the continental slope, where numerous spots and areas of sandy and gravel-pebble deposits are found in their distribution zone. The bottom of deep-water basins is occupied by diatoms and weakly diatoms silty-pelitic and pelitic silts, enriched in layers of volcanic ash.[ ...]
Judging by the abundance of ignimbrites and volcanic-sedimentary rocks of continental genesis in sections of the Sierra Nevada, already in the Early Jurassic in the Californian transitional zone, the stage corresponding to the period of the development of an island volcanic arc on the continental substrate (submerged state of the margin) ended, and folded mountain structures began to grow. This stage is similar to the Late Cretaceous in the Peruvian Andes. There are no formations of the Mesozoic age. It is easy to see a certain similarity with modern zonality on the Pacific margin of South America, where the eugeosynclinal complex of the Western Cordillera itself borders on the ocean side with the distribution area of predominantly Paleozoic formations, which, apparently, form the core of the margin in the shelf area and the upper half of the continental slope (Table 2). .