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Continental Margins – zone of transition between continent and adjacent ocean basin
Atlantic - Covered with thick layers of undisturbed sediments. This region has very little volcanic or earthquake activity.
Not associated with plate boundaries.
Pacific – The Pacific Ocean crust is plunging beneath continental crust. This is caused by volcanic and earthquake activity. The result of this activity is a narrow continental margin .
Not all coastlines have a continental shelf.
It extends from the shoreline to approximately 80 kilometers. It is approximately 130 meters in depth on its seaward side.
Large mineral deposits
Oil and natural gas
Sand and gravel deposits
Important fishing grounds
Marks the edge of the continental shelf. Is a steeper drop to the ocean floor, between 50 and 250.
Submarine canyons: Formed by erosion at least in part by turbidity currents . They form when sediments are disturbed by volcanic or earthquake activity. The muddy sediment that is now mixed in the water flows down the continental shelf and slope.
Or they could have formed????????
Another possibility is that when sea level was much lower some rivers crossed the continental shelf causing erosion to form submarine canyons.
What could have caused this…….
Glaciers forming……… REALLY!!!!!!!
Areas at the base of the continental slope when sediments have accumulated. They may be hundreds of miles wide.
Trenches: subduction zones, sites of plate convergence
Deepest is Mariana Trench = 11,022 meters in depth
are very wide and may occupy ½ of the ocean floor, site of divergent plate boundary or sea floor spreading sites. They are broken into segments by transform faults.
form along mid-ocean ridges. The water here is mineral rich; the hot newly formed crust comes in contact with cold ocean water causing minerals like sulfur, iron, copper, and zinc precipitate out and are deposited.
Atoll formation and corals
terrigenous – originates on land.
They consist primarily of mineral grains that were eroded from continental rocks and transported to the oceans.
Coarse grain materials like sand settle quickly near the shore. Fine grained sediments like clay may take years to settle.
1centimeter of clay may take 50,000 years to form.
Terrigenous sediments accumulate much quicker in areas like the Gulf of Mexico where the Mississippi enters the ocean. Deposits there may be several kilometers thick.
biogenous – consists of shells and skeletons of marine animals and algae.
The most common type is calcareous ooze which forms from calcium carbonate shells and corals. The shells dissolve as the sink to lower depths.
This sediment has the consistency of thick mud.
Other sediments include siliceous ooze which is composed mostly of diatom shells made of silica. Phosphate rich biogenous sediments come from teeth, bones and scales of fish.
hydrogenous – consists of minerals that crystallize directly from ocean water through various chemical reactions.
Manganese nodules – made also of iron and other metals, they form around grains of sand and are scatter across large areas of the deep ocean floor.
Calcium carbonates – form by precipitation directly from ocean water in warm climates. If this sediment is buried it can form limestone.
Evaporites – form where evaporation rates are high and ocean circulation is restricted. As water evaporates the remaining water becomes saturated with dissolved minerals which begin to precipitate. These sediments are generally called “salts.” Three common minerals that form this way are halite, gypsum, and calcium sulfate .
Resources from the Seafloor
Oil and natural gas – ancient remains of microscopic organisms that were buried before they could decompose. Exposed to pressure of overlying rocks and the Earth’s internal heat the remains were transformed into oil and natural gas.
Major offshore reserves: Persian Gulf, Gulf of Mexico, off southern California, North Sea, and the East Indies.
Possible new reserves may be off the coast of Alaska and the Canadian Arctic, Asian seas, Africa, and Brazil
Problems: pollution of the oceans
Gas hydrates – occurs as methane hydrate or methane.
Gas Hydrate is an ice-like crystalline solid formed from a mixture of water and natural gas, usually methane. They occur in the pore spaces of sediments, and may form cements, nodes or layers.
These occur beneath permafrost areas on land and under the ocean floor at depths below 525 meters. Most oceanic gas hydrates are created when bacteria break down organic matter trapped in ocean floor sediments. Other gases include ethane and propane.
Chunks of gas hydrates look like metals and evaporate quickly when exposed to warm temperatures and less pressure.
An estimated 20 quadrillion cubic meters of methane are locked in sediments. This is double the Earth’s coal, oil, and natural gas reserves combined.
Where are gas hydrates found?
Sand and gravel – used in construction and some are gem quality. Diamonds, platinum, titanium, and gold are found in these deposits.
Manganese nodules – they include iron, copper, nickel, and cobalt.
Cobalt – used to make strong allows of other metals. Can make cutting tools, magnets, and jet engine parts.
Evaporative salts – Of economic use is halite which is used in table salt, seasoning of food, curing, preserving food, agriculture, dying fabrics and de-icing roads.
Problems include …
developing the tools to get them from the ocean floor