The continental slope in areas with an active tectonic regime is a zone dominated by gravitational processes. 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 over a large extent with hemipelagic and (or) chemogenic-diagenetic sediments. The latter include glauconite sands and silts. In the Peruvian sector of the outskirts of South America, they are widespread not only in the upwelling zone, but can also be traced north of it to a depth of 500 m and more. Glauconite sediments are characteristic of gentle slope areas. On the Oregon slope, glauconite sands form thin interlayers among silty-clayey hemipelagic silts, which compose in depressions that complicate the slope, a stratum of 100 meters thick. At the mouths of the canyons on the outskirts of Oregon, rather large fan fans have formed. The Astoria underwater cone is especially well studied. ДСДП) reaches from 2 to 7 m. They occur among silty-clayey sediments. In the interchannel spaces of the cone, turbidites are widespread, 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. Bowm): aleurite overlain by homogeneous silty clay. Similar sediments are widespread in the depths of the abyssal plain, which is generally characterized by carbonate pelagic sediments - nannoils. Volcanic formations play a secondary role. [...]
Continental slope and its foot. Quite different processes dominate on the continental slope of the underwater margins of the continents. If on the shelf the main role is played by hydrodynamic factors, then on the slope and its foot the processes of sedimentation are largely determined by a single factor - gravitational. It is associated with a number of phenomena that are diverse in scale and nature, from underwater landslides - rockfalls and breakdowns of large rock blocks and ending with the formation of huge landslides and various flows of matter, both laminar and turbulent. [...]
Shelf is a coastal area of the sea, bordering the continent, the depth of water above which does not exceed 200 m. The outer edge of the shelf is a continental slope, which descends to the bottom of the sea. [...]
Shelf - coastal oceanic shallow water, bounded by the coast and the crest 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 the sediment columns, thin interlayers of sands (2-6 cm each), with erosion or by indistinct 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 - the underwater and surface parts are distinguished. The submarine includes a shelf, a continental slope and a 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 floor of the abyssal ocean basins. In most areas, this border is drawn at depths from 3000 to 4500 m. It is more difficult to define the border 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, which flooded the previously drained shelves. [...]
Within the outer shelf (Delaware County), carbonate-terrigenous sands enriched with feldspars become the main type of sediments. It is also relict sand, which in the Georges Bank area contains micro-nodules of manganese. On the continental slope, sands are replaced by silty or sandy silts, containing, according to L. Doyle and other researchers, obtained in 1979, from 50 to 80% of silty material. Silts, as a rule, are distinguished by high Corg concentrations. The admixture of sandy particles does not exceed 15%, and in addition to quartz, feldspars, and glauconite, the shells of planktonic foraminifera and pyrite microcontractions play a significant role in the composition of the sandy fraction. In the section of the sediment columns raised in the lower part of the slope, there are small (up to 1 cm) layers and lenses of sand, often with gradational bedding. In landslide zones, these layers often lie at an angle to the general bedding. Lumps of harder and older clays, randomly dispersed in a finely dispersed mass, are described. The CaCO3 content in the sediments of the continental slope north of Cape Hatteras does not exceed 10%. Down the slope, the content of silt (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 sediments of the foot, and the content of clay particles increases. The main type of sediment is clay-silt silt. [...]
In the 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, Holocene sands disappear and the outermost shelf zone is occupied by sands of the Late Pleistocene age, under which a layer of pebbles with gravel is found everywhere, which is exposed in places at the shelf edge. [...]
The concept of the edge of a continent or a continental margin, which was born as a purely geographical one, later acquired a deep geological meaning. A bright morphostructural manifestation, manifested in the existence of an underwater marine terrace - a shelf, a ledge of a continental slope and, finally, a vast deep-sea foot, as well as a huge length of continental margins, equal, according to K.O. Emery (1977), to 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 differences of which reach 10-15 thousand and (Peru) in the zone of transition from the mainland to the ocean, a sharp change in geophysical characteristics, reflecting the different composition of the crust, and, possibly, of the upper mantle, a 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 of the 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, there are: a continental shelf, or shelf (shelf), - a shallow part 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 scarp to a depth of 2500 m and the ocean floor, which occupies most of the bottom with depths of up to 6000 m. [...]
For modern sediments of the open part of the South Primorye shelf, a different facies series is characteristic: sands and silty sands occupy the upper part of the subligoral, below the 30-40 m isobath, they are replaced by silts, which quickly turn at a depth of 50-60 m into silty-clayey and fine-silty silts. Silty-clayey sediments form vast 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 arriving from land (and this part of the shelf is mainly reached by clay particles) are carried out by the Primorsky Current, which is most active at the shelf bend on the continental slope. Holocene facies are almost everywhere represented by fine-grained silty sands with a content of 4-5.5% of pelitic admixture. [...]
If you go deeper towards the open sea, then the continental slope goes beyond the shelf, then the continental foot, which together form a transition region from the continents to the ocean floor. 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 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 lies mainly between 3000 and 4000 m isobaths. [...]
The phenomena of salt diapirism, very characteristic of the continental slope and foot of Northwest Africa, are also observed in the Gibraltar zone, at the base of the continental slope of the United States 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 above, it can be concluded that sedimentation within the continental slope is very active during periods of high sea level, mainly due to the sedimentation of hemipelagic normal sedimentary silts. During periods of a decrease in the level of ocean waters, the maximum of sedimentation is shifted to its lower part and to the foot, which is due to both 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 one is the alternation of variegated clays and siltstones. The latter, according to W. Dean, J. The duration of the formation of single cyclotems was about 50,000 years. The origin of such cyclically constructed 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, located in the upwelling zone. [...]
Avandelta can extend to the middle shelf plain and even to the shelf edge. However, even outside the shelf, the profile of the margin 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 r. Niger. A somewhat different situation has developed in the delta of the river. Amazon. Avandelta in this case extends only to a depth 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 confluence of the river into the ocean. The modern Amazonian sediments, according to L.A. Zakharov's data, are represented by carbonate biomorphic-detrital formations. This, however, does not mean that the influence of the Amazon on sedimentary processes is limited only to the area of the delta and delta. As in most other cases, the bulk of sediments accumulated in the distal part of the transition zone, where a giant deep-sea fan was formed in the Late Cenozoic. On other margins of continental rifts, to which the deltas of large rivers are confined, there are also known powerful submarine alluvial fans associated with developed systems of canyons, which are located on the continuation of underwater river channels, for example, the Amazon, Indus, Congo canyons. [...]
The more sedimentologically active zone is the outer part of the shelf. 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 shoal, due to the rise of deep waters or, in other words, upwelling, which to one degree or another occurs along most of the continental slopes. On the modern margins of cratons, grouped along the western contour of the Atlantic and Indian Ocean, it is especially active in the regions of cyclonic gyres, in the sphere of which the Atlantic outskirts of Canada and partly the USA are located. [...]
The transition zones of this ooze are characterized by a reduced coastal plain, a short shelf, a rocky coast with small bays and bays, a relatively steep continental slope, often complicated by gentle uplifts and banks, and narrow underwater fan cones. As a rule, these are the outskirts of young folded structures in zones with increased seismicity. They are often located close to the centers of active volcanism. So, the Calabrian outskirts in the Ionian Sea are in the zone of influence of Etna and Vesuvius. [...]
The main factor that differentiates the marine biota is the depth of the sea (see Fig. 7.4): the continental shelf is abruptly replaced by the continental slope, smoothly turning into the continental foot, which sinks lower to the flat ocean floor - the abyssal plain. These morphological parts of the ocean roughly correspond to the following zones: neritic - the shelf (with the littoral - the tidal zone), bathyal - the continental slope and its foot; abyssal - an area of ocean depths from 2000 to 5000 m. The abyssal region is cut by deep depressions and gorges, the depth of which is more than 6000 m. The area of the open ocean beyond 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 suspended matter and bottom sediments show that the bulk of sedimentary materials are deposited not on the shelf, as it was believed until recently, but at the base of the continental slope. [...]
The outgoing branch of the geo cycle 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 cones, swamps, etc. [...]
Silty and silty-clayey silts 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 lat.). They are 80% composed of quartz grains, the rest falls on fragments of metamorphic rocks (10%), plagioclase (1%) and potassium feldspars (7%). Silty-clayey silts are composed 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 (the outskirts of Peru) also volcanic glass. [...]
Allen gave an overview of other stationary circulation models. Interesting effects are noted that arise when taking into account the bottom topography on the shelf, especially when the slope of the dia sharply increases during the transition of the shelf to the continental slope (see). [...]
As shown by detailed geophysical studies of recent years, and partly by the materials of deep-sea drilling, the outer edge of the Jurassic shelf was located, probably, 60-100 km from 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 outskirts of the United States. The expansion of the oceanic bed was accompanied by the fragmentation of the peripheral areas of the continental crust and the subsidence of individual blocks. Continuous subsidence, which covered the edge of the continent, favored active reef building along the outer edge of the ancient continental shoal in the arid climate that prevailed on many Jurassic margins. Only in coastal areas, in the immediate vicinity of the slopes of epirift uplifts, terrigenous marine, mainly sandy sediments accumulated. Reconstruction of the sedimentogenesis settings characteristic of passive continental margins located in tropical and subtropical climatic zones is shown in Fig. 37. [...]
Thus, the most intense sedimentation processes are currently confined to Bay. Martaban and the adjacent part of the open shelf, where the avandelta of the r. The Irrawaddy, and also to the southeastern shelf region north of the Malacca Peninsula. In the first area, there is an accumulation of finely dispersed clayey pilaf, in the second - carbonate sands and clay-carbonate sediments. Most of the solid runoff of the river. The Irrawaddy enters through the canyons to halistazu. However, the slope itself is over a considerable extent filled with clayey silts of a peculiar cream or reddish color, very thin, with a high content of iron oxide. This is a rare case of accumulation of non-central marine sediments containing products of washout of laterite and ferralite weathering crusts. The latter are common on the slopes of the coastal ridges and on the high plateaus of Burma. Terrigenous components are represented in the first type of sediments by aleurite, in the second - by clayey material. Accumulation of sediments of landslide and turbidite origin is assumed at the foot of the continental slope. Thus, on the continental margin in the Anadaman Sea, sedimentary processes differ in different intensities and directions: areas of purely terrigenous sedimentation here are adjacent to zones of carbonate sedimentation-accumulation. The wide distribution of relict formations and the relatively small role of biogenic substances can be considered unexpected for this tropical region. [...]
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 silt silts enriched in glauconite and containing relic material in the form of fragments of algal structures, less often oolites. The terrigenous part is usually represented by aeolian quartz. These are silty-pelitic sediments of brown or beige color, indistinctly layered 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 particles forming the sediment decreases. Carbonate micrite (pelitic particles) with a more uniform color predominates. The role of clay matter increases somewhat. The uniformity of the sections is disturbed by the presence of interlayers of green-woo-gray ash, compacted, with a lumpy texture, as well as dark gray to black (wet) sapropels. In the depression that separates the slopes of North Africa from the deep-water part of the Ionian Sea, there are more frequent layers of white carbonate sand (2-3 cm thick), indicating the manifestation of some kind of gravitational processes. [...]
The accumulation of modern sediments is confined to the zone of "land-sea struggle", and mainly to the deep-water parts of the outskirts: the lower half of the continental slope and the foot. These are areas of avalanche sedimentation, where the rates of accumulation of sedimentary material exceed 100 Bubnov units, otherwise 100 B. The significant width of the shelf with extremely small slopes of the seabed surface (only 0.6 m / km) is the reason that any even not very large rise in ocean level is reflected by a significant advance of the sea, which covers the areas of the coastal plain adjacent to the shelf. On the contrary, the drop in the level is accompanied by a sharp reduction in the area of the shelf zone. Accordingly, during periods of transgressions, the processes occurring in the coastal part of the shelf acquire the greatest importance, and during periods of regressions, processes of continental and submarine-slope sedimentation [...]
The modern development of the country's gas industry is associated with the development in the near future of natural gas fields on the continental shelf. One of the largest such objects will be the Shtokman gas condensate field. The structure of the interposition of technological objects of offshore fields is significantly different from fields onshore. Some of them are located on the sea surface (directly on drilling platforms), and the other on the mainland. Moreover, offshore technological objects can be located both at a sufficiently large and at a rather 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 between land and ocean (zero mark) does not record the transition of the continental crust to the oceanic one. On the hypsographic curve, the continental shelf, or shelf, is a water-flooded low-lying edge of the continents, as well as the continental slope, at the foot of which, on average, at a depth of 2450 m, the continental crust of the oceanic is replaced. 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 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 [...]
The third layer of the oceanic crust is traced from the center of the abyssal basins to the outer edge of the magnetic anomaly of the east coast. Thus, the oceanic nature of the crust under the continental foot in many areas is beyond doubt. However, the detailed structure of the zone in the 50-100 km strip to the east of the edge of the magnetic anomaly on the east coast of North America is still unknown. The presence of unfolded 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 sediment cover (8-14 km), is divided into blocks and thinned. [...]
Formed tectonically and morphologically dissimilar elements, which are united by a common geographic 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 completely deciphered. 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 undisturbed magnetic field zone, as, for example, F. Rabinovich (1978) does, or with the inner edge of this field. In the area of the Atlantic slope of the outskirts of the United States, there is a magnetic anomaly of the east coast, which has a width of 50 to 70 km. South of 36 ° N. NS. this anomaly is divided into two branches, of which the outer one can be 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 that intruded into the sedimentary strata in the Early Cretaceous [...]
Great prospects in the use of submarine groundwater by sea water intakes are opening up in connection with the significant development of technical means for drilling and testing wells on the shelf, continental slope and the seabed. Wells drilled offshore Australia, near the Atlantic coast of the United States, on the continental slope of the Gulf of Mexico and elsewhere, have exposed 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 to the east of Jacksonville. A well drilled from a ship, at a depth of 250 m below sea level, exposed 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 Eniplate-shaped orogeny, it was established that at the base of the sedimentary cover of the passive continental margins, more precisely, within the shelf and coastal plain, there are surprisingly similar lithologically complexes of ancient deposits. These are, as a rule, clastic red-colored formations of continental genesis, among which sandstones, conglomerates and siltstones with layers of clays (mudstones), evaporites, less often limestones, interlayered with lava sheets and horizons of volcanic ash, prevail. Similar geoformations were found on many margins in the Atlantic and Indian Ocean, in areas separated from each other by thousands and tens of thousands of kilometers, which makes it possible to consider them as complexes of deposits associated with a common stage of evolution for most of the margins under consideration. [...]
Outskirts of South Primorye in the Sea of Japan. The outskirts of South Primorye are heterogeneous in structure. It is characterized by a rocky coastline, 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 as steep as in the northern section. [...]
From lines 1a-b table. 6.4 it can be seen that the primary production of plant biomass (expressed in terms of the amount of carbon) in the ocean is approximately half that on land. Almost all of these products are phytoplankton. The distribution of the biological productivity of the ocean for different types of organisms is shown in table. 6.6 (according to the data of the Institute of Oceanology of the Academy of Sciences of the USSR). [...]
Glauconite is not a mineral specific only to upwelling regions (in ancient geological epochs, glauconitites were also formed in epicontinental water bodies), but it is here that it acquires regional sediment-forming significance. In thin sections of samples taken from some parts of the slope in the central part of the outskirts of Peru, one can see variously transformed rock fragments, whose angular shape and lack of sorting indicate that they are submarine talus and did not move over long distances. Many of these fragments still retained relics of the previous structure, while others acquired the aggregate structure characteristic of glauconite, while others are chloritized or have fouling edges. Another source of glauconite could be oolite-like concretions in the above-described silty-clayey silts. [...]
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 present day 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 the roof of a sedimentary stratum, the upper surface of which falls steeply to the east to a depth of 4.5-5 km. This massif is identified with a thick carbonate platform formed in the Late Mesozoic. The massif serves as a limitation for a large trough, confined to the inner regions of the shelf and filled with Mesozoic and Cenozoic deposits up to 10 km thick. The depth of the basement below the carbonate platform itself has not been established. In the area of the foot, the acoustic basement (the roof of the oceanic crust) is located at a depth of 7-8 km below sea level, i.e., the thickness of sediments, mainly Cenozoic, here ranges 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 V. Ryan and other researchers in 1976, by reef limestones of the Neocomian age, is extended to the east from the modern one by only a few kilometers. [...]
In conclusion, it should be avenged that the upper half of the margins of the epiplatform orogeny regions, especially the land-sea conflict zone, are distinguished by the greatest variety of sedimentation environments. Diverse sediments are formed here: from carbonaceous diatomaceous silts of fjords in high latitudes to bichrocks and mangrove swamp deposits in low latitudes. Modern and relict bioherms are widespread on the open shelf of arid zones, and large reef structures in areas of recent rifting. The continental slopes are associated with the formation of monotonous silty-pelitic oozes, prone to flow and sliding. At the foot, they are replaced by cyclically constructed series of sediments, among which on mature margins of this type, along with common turbidites, a significant role is played by sediments of flows of liquefied clastic material and grain flows. [...]
In the Barremian age, another activation of the relief and rejuvenation took place. The climate was probably more and more approaching the humid tropical climate, and on some uplifts and elevated plateaus, rather thick weathering crusts were formed, the erosion of which led to the intensive removal of a finely dispersed suspension enriched in iron oxides and silica. Due to this, horizons of variegated clays were deposited in the central regions of the Atlantic Ocean, but mainly at the continental foot. Bauxites of this age are known within the so-called Ebro land in the Iberian Peninsula and within the Toulouse land. In the Aptian, the spreading of the ocean floor in the southern trough of the Atlantic Ocean became more active. To the south of the Kitovy and Rio Grande ridges, at the site of rift troughs and their feathering grabens, an oceanic depression appeared 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 clayey sediments, enriched in organic matter, accumulated. In the Aptian age, the gradual complexes of underwater deltaic sandy-silty-clayey sediments were formed here, which accumulated the ancient shelf and slope of Africa in the Cape Basin. The presence of a structural threshold along the ridge line. The Rio Grande impeded the exchange of water between this sea trough and the vast epicontinental basins to the north, which were formed in place 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 transition zones, not the least role is played by the age and composition of the strata eroded on elevations and high plateaus framing narrow coastal plains. Paleocene clays are exposed on the Arabian side of the Gulf of Aden near the Hadhramaut plateau. In severely arid climates, clay particles are blown off the slopes by the wind. However, the bulk of the fine material is transported to the coast in dry, 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 remnants of volcanic structures of the Late Cenozoic age - are put forward to the side of the ocean. These are dilapidated cones of volcanoes of the central type, preserved from the time of active rifting (Fig. 15). Separate volcanic structures are connected to the coast by narrow sandy barrows separating large bays and bays from the shelf. A large amount of clayey suspension accumulates here. Towards the open sea, clayey silts are replaced by carbonate-clayey sediments, the clastic part of which is represented by terrigenous aeolian material and skeletal remains of carbonate-building organisms. In the lower part of the sediment columns, uplifted 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 patchy texture and silty-clayey silts with almond-like inclusions of carbonate detritus. The sediment columns taken at the foot were represented by homogeneous carbonate-clayey silty-pelitic silts with indistinctly pronounced bedding. 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 the island-arc transition zones are concentrated in its western half, while the eastern half-ring is made up of the margins of the Andean and Nevada types, has also led to a certain asymmetry of sedimentological nature. This can be seen in the example of latitudinal climatic zoning, reflected in the composition of precipitation, which spread 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 most studied are the processes of sedimentation in the area of the West Aleutian volcanic arc and the Bering Sea located behind it. According to A.P. Lisitsyn and D.E. Gershanovich, the accumulation of terrigenous sandy and silty sediments predominates on the continental shelf of the Bering Sea, to a greater or lesser extent enriched in pebble and boulder material of ice drift. Large aleurite sediments descend on the continental slope, where, in the zone of their distribution, numerous spots and areas of sandy and gravel-pebble deposits are found. The bottom of the deep-water basins is occupied by diatom and weakly diatom aleurite-pelitic and pelitic oozes enriched by layer-by-layer volcanic ash. [...]
Judging by the abundance of ignimbrites and volcanogenic-sedimentary rocks of continental genesis in the Sierra Nevada sections, the stage corresponding to the period of the development of the island volcanic arc on the continental substrate (submerged state of the margin) was completed already in the Early Jurassic period in the Californian transition zone, and folded mountain structures began to grow. This stage is similar to the Late Cretaceous in the Peruvian Andes. Formations of the Mesozoic age are absent here. It is easy to notice a certain similarity with the modern zoning on the Pacific margin of South America, where the eugeosynclinal complex of the Western Cordillera itself borders on the ocean side with the area of distribution of predominantly Paleozoic formations, which apparently compose the core of the margin in the shelf region and the upper half of the continental slope (Table 2) ...
- a part of the continental crust, flooded by the ocean. Due to the good illumination and warmth of the water on the shelf, an abundance of marine organisms is characteristic. This is the most productive part of it, since it is here that 90% of seafood and many minerals are mined, primarily oil and natural gas.
Continental slope, Continental foot
Transition zone from shelf to ocean bed
Mid ocean ridges
Ø These are underwater mountain ranges that are located almost in the middle of the oceans. That is why they are called mid-oceanic. Only in the Pacific Ocean the ridge does not occupy a middle position and is called the East Pacific Rise.
Ø are formed in places where lithospheric plates move apart. where the lithospheric plates move apart, lava flows to the surface along the faults. It solidifies and forms underwater ridges
Ø The width of the ridges is 1000 km, and in some places even more. The height above the level of the surrounding plains is 2-3 km.
Ø Some of the ridge peaks rise above the water level and form islands. Iceland is an example of such an island.
Gutter
Deep and long hollow at the bottom of the ocean
formed at the site of the collision of plates of oceanic and continental
Mariana trench(or Mariana Trench) - the deepest known on Earth, 11 km deep oceanic deep-sea trench in the west of the Pacific Ocean,
PARTS OF THE WORLD OCEAN
PROPERTIES OF WORLD OCEAN WATER
| density.- | the density of salt water is greater than that of fresh water, so it is easier to stay on the surface when swimming in salt water | |
| salinity | amount of salts in grams dissolved in 1 liter of seawater | Expressed in ppm. The average salinity of the ocean is 35 g / l. Ocean water has a bitter-salty taste, determined in it by chlorides and sulfates. |
| Depends | 1) on the ratio of atmospheric precipitation and evaporation, which varies depending on the geographic latitude, less salinity can be where the amount of precipitation exceeds evaporation, where the influx of river waters is large, where ice is melting; 2) from the depth. Salinity also changes with depth. to a depth of 1500 m salinity is somewhat decreases compared to the surface. Deeper changes in water salinity are insignificant, it is almost everywhere Z6% o. ppm 3) FROM THE NUMBER of rivers flowing into the seas, oceans (they desalinate the water) 4) from the outlet at the bottom of the mantle substance, which increases salinity | |
| Sources of | 1) most of the salts on the surface of the earth dissolve surface waters and washed away from land rivers and rains. 2) from substance mantle | |
| Meaning | conducts electric current well, freezes at a lower t, and boils at a higher t compared to fresh water. | |
| Geography | 1.mach - in tropical latitudes 2.min - in polar Minimum salinity - 5% - in the Baltic Sea, maximum - up to 41%- in the Red Sea. The maximum salinity of the Red Sea is explained by the fact that there is a rift zone. Young basaltic lavas are observed at the bottom, the formation of which indicates the rise of matter from the mantle and the expansion of the earth's crust in the Red Sea. In addition, the Red Sea is located in tropical latitudes - high evaporation and low rainfall, no rivers flow into it. | |
| Temperature | this is the degree of water heating | Ocean water freezes at a temperature of minus two degrees, the higher the salinity, the lower the freezing point. The average temperature is about 4 ◦ C. The ocean heats up slowly and slowly gives off heat, i.e. serves as a heat accumulator. The warmest sea is the Red |
| Heat sources | 1.The sun heats only the upper layer of the ocean, several meters thick. Heat is transferred to the bottom of this layer due to the constant stirring of the water. 2. from the depths of the planet through the faults comes hot magma, cold water, penetrating into these faults, combines with hot magma is saturated, salts and gases and rises from the bottom up. Scientists called these sources "black smokers" | |
| Heat distribution | A \ in latitude The sun irregularly illuminates and heats the Earth, therefore t surface water changes from the equator to the poles. B \ in depth- the deeper the colder (except in the mid-ocean ridges) |
PLAN CHARACTERISTICS OF THE SEA
| title | Barents Sea |
| Dimensions, depth | First place in Russia in terms of area, 200 - 1000 m - shallow |
| What washes | Mainland - NW Eurasia |
| Part of which ocean | Arctic |
| Sea view | Okrannoe |
| Bottom relief | Lies on the shelf |
| Water properties | Lies in polar latitudes - Salinity is low, temperature is low |
| Currents | Warm Norwegian current, therefore it is the only non-freezing sea in the Arctic Ocean, and warmer than the rest of the seas of S.L. ocean |
| Economic value | Transport, field, tidal power station, navy base, oil and gas production |
Water movement
| waves | vibrations of water particles about their equilibrium position under the influence of external forces, for example, wind. | while the waves run along the surface of the water, the water itself, or rather its particles, only fluctuates up and down, therefore, if you go out to sea on a boat and put it with its bow to the wave, you can see that the waves only raise and lower the boat, not bringing it closer to shore. |
| Structure | Each wave has a crest, slope and sole. | Outsole - Bottom, Ridge-Top The distance between 2 adjacent ridges is the wavelength. The distance from the sole to the crest - the height of the waves is more often 4 meters, up to 30 meters. \ storm \ |
| Views | deep, surface, Wind waves, surf, tsunami | |
| Deep | waves arise at the boundaries of water layers with different densities | Such waves are a frequent occurrence at any depth of the oceans; they are unsafe for divers, submarines, and large ocean liners with deep draft. |
| Surface | waves are generated by winds, underwater earthquakes, and tides. | |
| Wind waves | Wind waves arise from friction of wind against water | With a weak wind, small waves appear on the surface of the water - ripples. With a very strong wind - a storm - their height can reach the height of a five-story building. Most often storms occur in the northern parts of the Pacific and Atlantic oceans, as well as around Antarctica south of 40 ° S. NS. These latitudes are called the Roaring Forties. The height of the waves here is always greater than 3 m. The highest storm wave, 30 m, is also recorded in the Antarctic waters. |
| Surf | On the way to the gentle shallow shores, the waves touch the bottom, and their height increases. In this case, the crest of the wave tilts forward and overturns. This is how the surf appears | The surf washes away beaches and shallows of sand, pebbles and other sediments |
| tsunami | these are waves of gigantic proportions generated by an earthquake or seaquake, volcanism. | In the open ocean, almost invisible to ships. -30cm. But when the path of the tsunami blocks the mainland and the island, the wave hits the land with a height of 40m. , moving at a speed of -800 km / h |
| Sea currents | horizontal movement of water masses in a certain direction | |
| Causes | The main cause of sea currents is wind, but the movement of water can be caused by the accumulation of water in any part of the ocean, as well as the difference in water density in different parts of the ocean and other reasons. | Warm If the water in the current is warmer than the surrounding ocean water Cold If the water in the current is colder than the surrounding ocean water |
| MEANING | 1. Currents have a great influence on the climate, especially coastal areas, passing along the western or eastern coast of the continents. 2. have been used since antiquity for the movement of ships, "sea mail" | Cold - make the climate - drier and colder Warm - humidier and warmer |
| Direction of currents | determined by the general circulation of the atmosphere, the deflecting force of the Earth's rotation around the axis, the relief of the ocean floor, the outlines of the continents | |
| tides | periodic fluctuations in water level near the coast and in the open sea, water entry far towards the land. | |
| ebb | periodic fluctuations in water level near the coast and in the open sea, water retreat. | |
| cause | - the forces of mutual attraction between the Earth, the Moon and the Sun | |
| geography | tides with a height of 19 m are observed off the coast of North America in the Gulf of Fundy, and Russia in the Sea of Okhotsk. | |
| meaning | 1.When the tide is high you can fish and go boating. and collect seashells at low tide. 2. tidal power plants. | |
LIFE IN THE OCEAN
By way of life, they are grouped depending on their habitat..
Bottom organisms (benthos) live on the bottom surface or in bottom sediments.
Actively moving organisms live in the water column (nekton) and
those that are not able to resist the movement of waters ( plankton).
The distribution of life in the ocean depends on several factors: salinity of water, the depth of penetration of sunlight (light), the amount of oxygen dissolved in the water, the temperature of the water, the presence of nutrients in it.
Since light is the main condition for the existence of green algae that feed on other organisms, the upper 50-meter water column is the most populated by living organisms. Areas where waters of different properties and origins converge, such as cold and warm currents, as well as areas of the ocean with an intense rise of nutrient-rich deep waters, are also rich in life. A huge number of marine organisms are concentrated on the continental shelf - the shelf.
Option 1.
1. Which of the following countries are provided with almost all known resources:
1) Russia, Japan, USA 2) USA, South Africa, Brazil 3) Russia, USA, China
2. The main oil fields in the world are concentrated in:
1) Australia, South Africa, East Asia
2) Asia, North America, North Africa
3) Western Europe, Tropical Africa, Australia
3. Per capita arable land is best provided for:
1) India 2) Argentina 3) Australia
4. The main way to solve the problem of clean fresh water:
transportation of icebergs 3) recycling water supply
saving water in everyday life and in nature 4) transfer of river flows
5. Find the correct statement:
1) forests cover 65% of the land
2) Russia accounts for 20% of the world's total timber reserves
3) Half of all wood produced is burned as fuel
6. The main areas of oil and gas production on the shelf include:
1) North Sea 2) Persian Gulf 3) California Gulf
4) Gulf of Mexico 5) Black Sea 6) Red Sea
7. Select the correct statements:
1) the value of recreational resources is determined only in monetary form
2) wind energy resources are concentrated mainly in the temperate zone
3) objects of natural and anthropogenic origin used by humans for recreation, tourism, treatment are called recreational resources
8.Question on definitions:
What are natural resources, resource availability, water consumption, mariculture, nature management
Exhaustible non-renewable A) geothermal energy
Inexhaustible B) fish
Exhaustible renewable B) apatites
IN 2. Arrange lands as their share of the world's land stock decreases
Arable land, orchards 3) Unproductive land
Meadows, pastures 4) Forests
AT 3. Select from the listed countries three leaders in geological coal reserves
Indonesia 4) Venezuela
Libya 5) China
USA 6) Australia
AT 4. Choose three examples of unsustainable environmental management
Conversion of TPP to gas
Using waste as secondary raw materials
Terracing slopes
Burial of toxic substances in deep sea depressions
Increasing the size of the whaling industry
Creation of mine waste heaps
Theoretical question
What factors determine the location of natural resources on the planet? Can it be argued that it does not depend on a person at all?
Tests on the topic "Natural resources of the world" - grade 10
Option 2.
The largest ore deposits are concentrated in ore belts:
South American 2) Pacific 3) Mediterranean
The main centers of phosphate mining are located in:
Japan, Chile, USA, Canada 2) USA, China, Morocco, Russia
Kazakhstan, Brazil, Australia, Germany
Arable land per capita in the world:
decreases 2) does not change 3) increases
Russia's forests account for the world's total timber reserves:
35% 2) 20% 3) 50% 4) 95%
Choose the correct statement:
The main oil and gas resources associated with the shelf are found off the coast of Russia, the countries of the Near and Middle East, Africa, Southeast Asia, Latin America
Indian Ocean provides 56% of the world's fish catch
Due to the biological resources of the World Ocean, mankind satisfies its needs for proteins by 25%
Solar energy is most developed in:
Russia, UK 2) USA, France 3) Italy, Brazil
Group the countries below according to the following criteria:
A) countries where arable land occupies a leading place in the structure of agricultural land
B) countries where meadows and pastures occupy a leading place in the structure of agricultural land
1) Australia 2) Hungary 3) Afghanistan 4) Netherlands
5) Denmark 6) Monogoly
8. Question for definitions:
What is natural resource potential, resource-saving technology, forest cover, recreational resources, environmental policy?
IN 1. Establish a correspondence between the types of natural resources and the natural resources to which they belong
Type of natural resources Natural resources
Exhaustible non-renewable A) solar energy
Inexhaustible B) fresh water
Exhaustible renewable B) uranium
IN 2. Which three natural resources are inexhaustible?
Climatic
Energy of the flow
Wind energy
Soil
AT 3. Position regions as their share of the world's total geological natural gas reserves increases
Overseas Europe
Overseas asia
AT 4. An example of rational nature management is
Conversion of road transport to gas
Drainage of swamps
Creation of closed cycles in production
Construction of tall pipes at enterprises
Theoretical question
Why is a completely wasteless technology unrealistic?
It is a coastal part of the seabed with a relatively leveled surface. From a geological point of view, it is an underwater continuation of continental platforms. A characteristic feature of the underwater margin is the presence of ancient coastlines and submerged sea terraces attached to them, underwater extensions of river valleys (the Thames bed, the Churchill river bed in Hudson Bay) and various other forms of relief of continental genesis.
The underwater margin of the continents occupies about 20% of the bottom of the World Ocean and, in turn, consists of a shelf (or continental shelf), a continental slope, and a continental foot.
Shelf, or continental shelf, is an extensive shallow part of the bottom in the coastal strip of the oceans. Recently, the shelf is considered to be a relatively shallow and mostly flat part of the underwater margin of the continents, directly adjacent to the continents, and in geological terms, it is a continuation of the continental platform. From this point of view, narrow coastal shoals bordering the mountain coasts of geosynclinal areas (Cordillera) should not be attributed to the shelf zone. Until recently, it was believed that the shelf is limited from the sea by the 200 m isobath. However, in all likelihood, this issue should be resolved depending on specific conditions, and not mechanically, at some time given depth. The entire Barents Sea is a shelf, but depths of more than 400 m prevail here.The Middle Caspian, including its Derbent depression, is also a shelf sea in geological terms, although the depths here reach 800 m.In the shelf zone of the Sea of Okhotsk, depths of more than 1000 m prevail. Therefore, it is more correct draw the lower boundary of the shelf along the edge of the continental slope facing a deep sea trough or oceanic basin, regardless of the depth at which this edge lies.
The relics of accumulative and denudation relief on the bottom of the Baltic and Kara seas, the shelf of Labrador and other underwater margins of the continents adjacent to the regions of the Quaternary glaciation have long been known. Offshore New Zealand, there are ancient Lower Quaternary dunes buried under modern sediments. Flooded river valleys are known offshore Indonesia. Numerous glacial trough valleys have been found on the Norwegian shelf, off the coast of Iceland, Chile, and Canada. F. Nansen noted for the first time that the western coast of Norway is bordered by wide leveled areas, which are called the strandflat. Formation of strandflats, according to F. Nansen, is due to the combined actions of abrasion, tidal phenomena and frost weathering, which is most active in the harsh conditions of the north, which manifests itself in the zone of surf and ebb and flow.
All these features of the shelf indicate that, quite recently, the shelf was land and is indeed the submarine margin of the continent.
Continental slope. The inclusion of the continental slope into the submarine margin of the continent cannot be considered generally accepted. However, most American and French researchers include the continental slope in the submarine margin of the mainland. Indeed, given the peculiarity of the geological structure of the continental slope, it should be included in the underwater margin of the continents. In terms of its geological structure, it really is the edge of the continent, sharply expressed in the relief of the ocean floor.
The continental slope has been most thoroughly studied in the western part of the Atlantic Ocean. Here, the shelf of the US Atlantic coast ends with a steep scarp in the upper part to a depth of about 2000 m, and the cover of loose sediments is either absent or insignificant. The continental slope is cut by numerous deep hollows. Such deep-sea hollows (valleys) are called underwater canyons. The depth of some of them reaches 700 m, length - 240 km, width - from 400 to 500 m. The most common features of the underwater canyons are as follows. These are large hollows with steep slopes and steep falls. Most often they are V-shaped, but in some cases they are trough-shaped. In the mouths of some canyons, wide delta-like sediment fillings are found - a kind of underwater fan fans. Some scholars believe that underwater canyons represent flooded sections of river valleys.
Continental foot is an inclined plain adjacent to the lower part of the continental slope and falling towards the ocean floor. The continental foot as a relief element was identified relatively recently. Previously, it was attributed either to the continental slope or to the ocean floor, which explains the significant discrepancies in the newest and older definitions of the area of the continental slope. In the area of the continental foot, the greatest thickness of the loose layer of sediments is noted. Under this stratum, geophysicists discovered a thin crust of the continental type, and the surface of the granite layer is usually bent, which, possibly, should be associated with a strong load of loose sediments.
Along the very edge of the European continent, the continental foot is also presented in the form of an inclined plain, but it is much narrower here than on the North American mainland.
The presence of the continental crust under the sediments that compose the surface of the continental foot indicates that this part of the ocean floor with the shelf and continental slope should be attributed to the underwater margin of the continent.
Judging by the geophysical data, the change of the continental crust to the oceanic one at the outer boundary of the continental foot is carried out by the pinching out of the granite layer and the emergence of the basalt layer into direct contact with the sedimentary.
