The continental slope is between the continental shelf and the ocean floor. The continental shelf is part of the continent, and the ocean floor is the real oneseabedTherefore, the continental slope is connected with sea and landbridge, which is connected at one endlandThe edge of the sea is connected to the sea at one end.
Although the continental slope is distributed on the seabed with a water depth of 200m to 2000m, the upper crust of the continental slopeGraniteMainly, usually belonging toContinental crustOnly a few of them belong to transitional crust.
Deep sea beyond the foot of the continental slopeOceanic crustwithbasaltMainly, where is typicaloceanic crust Therefore, the foot of the continental slope is the real boundary between continental crust and oceanic crust.
structure
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Structure diagram
Because the continental slope is hidden in the deep water area, it is rarely damaged, and basically maintains the original shape when the ancient continent was broken.In 1965,britaingeophysicsThe home computer drew a picture of the Atlantic Ocean with a depth of 1000 metersBathymetric chart。Graphic display ofa bathymetric contourIt fits perfectly.This proves from another angleContinental drift theoryIs correct.
On the seaward side, the slope descends from the outer edge of the shelf to the deep seabed.It spreads around all continents and is globalTopographic unit。The water depth at the upper boundary of the continental slope is mostly between 100 and 200 meters;The lower boundary is often gradual, about 1500~3500 meters deep in water, but in the adjacent zone, the continental slope extends down to deeper.The width of the continental slope is about 20 to 100 kilometers, with a total area of 28.7 million square kilometers, accounting for 5.6% of the global area.
The slope of the continental slope is steep.Pacific continental slopeAverage slopeIt is 5 degrees and 20 minutes, the gradient of the Atlantic continental slope is 3 degrees and 5 minutes, and the depth of the Indian Ocean continental slope is 2 degrees and 55 minutes.The gradient varies from several degrees to more than 20 degrees.The surface of the continental slope is extremely uneven, and many large and deepSubmarine canyon。Largest on landThe Yarlung Zangbo RiverandLancang RiverCompared with the Grand Canyon, the Grand Canyon can only be seen from a small perspective.Some submarine canyons cross the slope, and some branch like branches, cutting the continental slope into pieces.The surface of the continental slope also has relatively flat areas, which are calledDeep sea platform。Sometimes, multiple submarine platforms with different depths will be formed on a continental slope.
features
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The slope of the continental slope is mostly 3~6 degreesAverage slopeIs 417 '.In the Atlanticcontinental margin, the continental slope often becomes slower with the increase of water depth, and extends downward to;stayPacific type continental marginThe continental slope often becomes steeper with the increase of water depth and extends down to the trench.The average slope of the Pacific continental slope is 520 ', the average slope of the Atlantic continental slope is 305', and the average slope of the Indian Ocean continental slope is 255 '.The slope outside the large delta is the smallest, with an average of 1.3.Coral reef islandThe outer continental slope is the steepest, with a maximum slope of 45.
The continental slope can be a single slope or a step, forming a flat surface of the deep sea or a marginal platform.The continental slope is eroded by gullies, plusfaultCliff walls, scarps formed by slumping and diapir uplifts, etc., result in very rugged slope shape.
terrain
The bottom material of the continental slope is mainly mud, with a small amount of gravel andBioclastic。The sediment is finer than that of adjacent continental shelf and continental uplift, but during the sea level decline in the ice age, most of thecontinental shelfExposed as land, the river advances to the sea near the top of the continental slope, increasing the coarse sediment on the continental slope.Rock outcrops are common on steep slopes outside the narrow shelf adjacent to the mountain coast.The continental slope sediments are mainlyTerrigenous clast There are also sediments formed by biological and chemical reactions.
The continental slope basement is thinnedContinental crust。Granite was found in the continental slope area by trawling and drilling;Seismic survey shows that the lower part of the continental slopeGranite layerGradually thinning to the ocean sidePinch out；There are also foldsFault structureSome continental tectonic lines can extend to the continental slope.
origin
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The continental slope is the contact transition zone between the light and floating continents and the heavy and deep sinking ocean floor.As the continents split, narrow juvenile oceans formed between them.according toPrinciple of crustal isostasyThe elevation of the new oceanic crust should be significantly lower than that of both continents, and a steep new continental slope must be formed between the mainland and the new ocean floor.
Sketch map of geographical location of continental slope
atlantic type continental marginThe continental slope ofSedimentationIt is further shaped.Not long after generation, not yetExternal force actionThe strongly reconstructed continental slope,Sedimentary caprockThe microtectonic terrain and volcanic terrain are very significant and steep.The developed Atlantic continental slope, with irregular original terrain covered by huge thick sedimentary layer, has a gentle slope.
In the Pacificcontinental marginThe development of the continental slope is related to the subduction or underthrusting of the plate. The lower part of the continental slope can have the fold and fracture of the accretionary melange formed by subduction and scraping. The terrain is very complex.
type
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The division and convergence of plates have established the basic framework of continental slope morphology and structure.The further development of the continental slope can lead to many different types of continental slope depending on the difference of control factors:
① The fault type or escarpment type continental slope is mainly affected byFaultingControl, while the transformation of erosion accumulation is weak, and rock steps and escarpments are common, such asIberian PeninsulaThe northwest continental slope.
② The forespread accumulation continental slope has sufficient supply of terrigenous materials, and the continental slope is stronglySedimentationThe lower part of the continental slope gradually moves toward the ocean. Some continental slopes have sedimentary layers up to about 10 kilometers thick, and the continental slope on the Atlantic side of the United States mostly belongs to this type.
③ Erosive continental slope, weak sedimentation, turbidity current and collapse, etcErosionThe bedrock is exposed and the terrain is complex, such asSubmarine canyonAnd landslide development areas.
④ Reef type continental slope, related to the growth of coral reefs, is steep, such asYucatan PeninsulaThe continental slope of.
⑤ Diapiric continental slope: low-density evaporite or mud layer forms diapir after deep burial, so the sedimentary layer on the continental slope is deformed, and the seabed is irregular, such as in the Gulf of Mexico.
resources
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Because of the riverrunoffAnd marine processes, the continental slope sediments may contain richOrganic matter, the continental slope is very thickSedimentary layerIt has good oil and gas prospects.
fromcontinental shelfExtending outward, the sea bottom suddenly falls, forming a steep slope, which is called the continental slope.It is like the wall of a basin, and like a long belt around the ocean bottom.The width of the continental slope is different in the oceans, ranging from more than ten kilometers to several hundred kilometers, with an average width of about 70 kilometers. The slope ranges from several degrees to more than 20 degrees, with an average of 4 ° 30 '.It is the longest and most spectacular slope on the earth. The total area of the global continental slope is about 28 million square kilometers, accounting for about 12% of the total ocean area.At the foot of the slope, there are many deep canyons calledSubmarine canyonIt is deeper and larger than the mountain streams and canyons across mountains on land.
type
According to the topographic characteristics, there are two types of continental slopes.
One is that the terrain is relatively simple and the slope is relatively uniform, such as the North Atlantic along North America, Europe andBarents SeaAnd other places.The upper half of this kind of continental slope is a steep wall, and the exposed rocks are lack of sediment. About 2000 meters down, the slope of the continental slope suddenly becomes very gentle, and the depth gradually increases, becoming a concave piedmont zone.Along the slope of the continental slope, there are a series of parallel“Submarine canyon"Cut the continental slope.
Location of continental slope
Another kind of continental slope, with complex terrain and many uneven terrain on the slope, is mainly distributed in the Pacific Ocean.The continental slope of the South China Sea belongs to this category. The slope surface often presents a series of steps, which are angular highlands with flat top and steep wall, alternating with some closed flat bottomed depressions.There are some largeGraveldebris, and there are some messysand, stone and ooze.On this kind of continental slopeSubmarine canyonThe valley bottom is also ladder shaped.In addition to these two types, the continental slope around the estuary of a big river is usually flat, and the whole slope is covered with sediment brought from the river.
sediment
The sediments on the continental slope mainly come from the continent.The sediment brought into the sea by the river passes throughcontinental shelfTransport to the continental slope.In addition, a considerable part is the ooze of marine biological remains.To sum up, about 25% of the whole continental slope coverssand10% are exposed rocks.The remaining 65% is covered with a kind of cyanOrganic matterOoze.This kind of ooze is often maroon because of oxidation, and its accumulation speed is much slower than that of continental shelf.
In the volcanic activity zone, there areashThe high latitude area is mixed with rocks and coarse sand brought by the continental current.Near the tropical estuary, there is a kind of red ooze composed of tropical red weathered soil.[2]
canyon
Geographical map
The most special terrain on the continental slope is the deep Grand Canyon, known asSubmarine canyon。It is generally straight, and the valley bottomSlope ratioThe valley bottom slope of mountain rivers is much larger. The two walls of the canyon are stepped steep walls, and the cross section is in a "V" shape.The scale of submarine canyon is often larger than that of river canyon on land.The Three Gorges of the Yangtze River in China is a world-famous grand canyon. The height difference between the two sides of the canyon is nearly 800 meters, and there are nearly 100 meters high steep walls at the bottom, which form a box canyon at the bottom of the valley. This steep wall was formed by the uplift of the crust in the Three Gorges area during the latest geological period, causing the erosion and cutting of the Yangtze River channel. So when people navigate in the Three Gorges, the first impressive thing is the vertical steep walls on both sides of the river,The flow of the Yangtze River is confined between rock walls one or two hundred meters wide. This is the crustNeotectonic movementCaused by.
U.S.AColorado Grand CanyonIt is also the world famous Grand Canyon,Colorado RiverIt cuts through the Mesozoic sandstone stratum. The rock walls on both banks are nearly 1000 meters high. The two walls of the canyon are in the form of steps. One layer narrows to the bottom of the valley, and there is also a layer of valley bottom steep wall caused by the latest tectonic movement. Today, the Colorado River flows between the steep wall canyons.imageThree Gorges of the Yangtze RiverThe Grand Canyon of Colorado is one of the few grand canyons on the mainland.andSubmarine canyonIt is much larger than the grand canyon on land. Hundreds of submarine canyons have been found, which are distributed on the continents all over the world.
Corals on the continental slope
Most submarine canyons have only one section on the continental slopecontinental shelfIt disappears when it goes down to the bottom of the ocean, and has nothing to do with rivers on land.But there are also someSubmarine canyonIt can be connected with rivers on land.Like the East Coast of North AmericaHudson submarine canyonIts source isHudson River , rivers flow into the ocean.
There is a shallow and flat underwater valley at the bottom of the continental shelf, with a depth of 30 meters below the sea floor, but a width of 7 kilometerscontinental shelfAt the edge, the depth of the underwater valley (below the seabed) is 40 meters, and the width of the valley reaches 25 kilometers. Obviously, the underwater valley is straight and shallow on the continental shelflow-lying land。Connected with this underwater valley is the submarine canyon on the continental slope, which starts from the top with a water depth of 150 meters and goes down along the continental slope to the ocean bottom with a depth of 2400 meters.The depth of its incision at the bottom of the sea is more than 1000 meters for almost the entire submarine canyon. After its tail enters the ocean floor more than 2000 meters deep, it gradually disappears.
