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90-650: The Northern Carnarvon Basin includes the Exmouth Plateau , Wombat Plateau (on the northern part of the Exmouth Plateau), Investigator Sub-basin, Rankin Platform, Exmouth Sub-basin, Barrow Sub-basin, Dampier Sub-basin, Beagle Sub-basin, Enderby Terrace, Peedamullah Shelf and the Lambert Shelf. The main sub-basins for petroleum exploration in the basin have been Dampier, Exmouth and Barrow. The Southern basin consists of

180-444: A Petri dish. In areas where diatoms are abundant, the underlying sediment is rich in silica diatom tests, and is called diatomaceous earth . Radiolarians are planktonic protozoans (making them part of the zooplankton), that like diatoms, secrete a silica test. The test surrounds the cell and can include an array of small openings through which the radiolarian can extend an amoeba-like "arm" or pseudopod. Radiolarian tests often display

270-421: A change in conditions, such as a change in temperature, pressure, or pH, which reduces the amount of a substance that can remain in a dissolved state. There is not a lot of hydrogenous sediment in the ocean compared to lithogenous or biogenous sediments, but there are some interesting forms. In hydrothermal vents seawater percolates into the seafloor where it becomes superheated by magma before being expelled by

360-449: A few millimetres per million years. For that reason, they only form in areas where there are low rates of lithogenous or biogenous sediment accumulation, because any other sediment deposition would quickly cover the nodules and prevent further nodule growth. Therefore, manganese nodules are usually limited to areas in the central ocean, far from significant lithogenous or biogenous inputs, where they can sometimes accumulate in large numbers on

450-408: A few millimetres to several tens of kilometres. Near the surface, the sea-floor sediments remain unconsolidated, but at depths of hundreds to thousands of metres (depending on the type of sediment and other factors) the sediment becomes lithified . The various sources of seafloor sediment can be summarized as follows:  The distributions of some of these materials around the seas are shown in

540-443: A global scale. So cosmogenous and hydrogenous sediments can mostly be ignored in the discussion of global sediment patterns. Coarse lithogenous/terrigenous sediments are dominant near the continental margins as land runoff , river discharge , and other processes deposit vast amounts of these materials on the continental shelf . Much of this sediment remains on or near the shelf, while turbidity currents can transport material down

630-473: A higher proportion of O18 isotope. This means the ratio of O16:O18 in shells is low during periods of colder climate. When climate warms, glacial ice melts releasing O16 from the ice and returning it to the oceans, increasing the O16:O18 ratio in the water. When organisms incorporate oxygen into their shells, the shells will contain a higher O16:O18 ratio. Scientists can therefore examine biogenous sediments, calculate

720-567: A location in Western Australia is a stub . You can help Misplaced Pages by expanding it . This article about a specific Australian geological feature is a stub . You can help Misplaced Pages by expanding it . Exmouth Plateau The Exmouth Plateau is an elongate northeast striking extensional passive margin located in the Indian Ocean roughly 3,000 meters offshore from western and northwestern Western Australia . The plateau makes up

810-422: A much faster rate, so they accumulate below their point of origin before the currents can disperse them. Most of the tests do not sink as individual particles; about 99% of them are first consumed by some other organism, and are then aggregated and expelled as large fecal pellets , which sink much more quickly and reach the ocean floor in only 10–15 days. This does not give the particles as much time to disperse, and

900-504: A number of interlocking CaCO 3 plates (coccoliths) that form a sphere surrounding the cell. When coccolithophores die the individual plates sink out and form an ooze. Over time, the coccolithophore ooze lithifies to becomes chalk. The White Cliffs of Dover in England are composed of coccolithophore-rich ooze that turned into chalk deposits. Foraminiferans (also referred to as forams ) are protozoans whose tests are often chambered, similar to

990-476: A number of rays protruding from their shells which aid in buoyancy. Oozes that are dominated by diatom or radiolarian tests are called siliceous oozes . Like the siliceous sediments, the calcium carbonate, or calcareous sediments are also produced from the tests of microscopic algae and protozoans; in this case the coccolithophores and foraminiferans. Coccolithophores are single-celled planktonic algae about 100 times smaller than diatoms. Their tests are composed of

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1080-457: A system of listric normal faults near the eastern region of the Exmouth Plateau. These listric faults were a product from the development of a major low angle detachment fault between a sedimentary base of Permian-Triassic upper crust and the mid-crustal horizon. As a result, brittle deformation and crustal thinning in the upper crust of the eastern Exmouth Plateau occurred, while in the west,

1170-434: Is a bioessential element and is efficiently recycled in the marine environment through the silica cycle . Distance from land masses, water depth and ocean fertility are all factors that affect the opal silica content in seawater and the presence of siliceous oozes. The term calcareous can be applied to a fossil, sediment, or sedimentary rock which is formed from, or contains a high proportion of, calcium carbonate in

1260-454: Is a common mineral in terrestrial rocks, and it is very hard and resistant to abrasion. Over time, particles made from other materials are worn away, leaving only quartz behind. Beach sand is a very mature sediment; it is composed primarily of quartz, and the particles are rounded and of similar size (well-sorted). Marine sediments can also classified by their source of origin. There are four types:  Lithogenous or terrigenous sediment

1350-403: Is a form of calcium carbonate derived from planktonic organisms that accumulates on the sea floor . This can only occur if the ocean is shallower than the carbonate compensation depth . Below this depth, calcium carbonate begins to dissolve in the ocean, and only non-calcareous sediments are stable, such as siliceous ooze or pelagic red clay . Where and how sediments accumulate will depend on

1440-406: Is a low-energy, offshore-marine deposit in a period when input of the terrigenous sediments to the offshore was low minimal. Marine sediment Marine sediment , or ocean sediment , or seafloor sediment , are deposits of insoluble particles that have accumulated on the seafloor . These particles either have their origins in soil and rocks and have been transported from the land to

1530-777: Is a type of biogenic pelagic sediment located on the deep ocean floor . Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians . Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules. Siliceous oozes are composed of skeletons made from opal silica Si(O 2 ) , as opposed to calcareous oozes , which are made from skeletons of calcium carbonate organisms (i.e. coccolithophores ). Silica (Si)

1620-483: Is another way to categorize sediment texture. Sorting refers to how uniform the particles are in terms of size. If all of the particles are of a similar size, such as in beach sand , the sediment is well-sorted. If the particles are of very different sizes, the sediment is poorly sorted, such as in glacial deposits . A third way to describe marine sediment texture is its maturity, or how long its particles have been transported by water. One way which can indicate maturity

1710-475: Is highly variable in composition. Seafloor sediment can range in thickness from a few millimetres to several tens of kilometres. Near the surface seafloor sediment remains unconsolidated, but at depths of hundreds to thousands of metres the sediment becomes lithified (turned to rock). Rates of sediment accumulation are relatively slow throughout most of the ocean, in many cases taking thousands of years for any significant deposits to form. Sediment transported from

1800-474: Is how round the particles are. The more mature a sediment the rounder the particles will be, as a result of being abraded over time. A high degree of sorting can also indicate maturity, because over time the smaller particles will be washed away, and a given amount of energy will move particles of a similar size over the same distance. Lastly, the older and more mature a sediment the higher the quartz content, at least in sediments derived from rock particles. Quartz

1890-414: Is primarily composed of small fragments of preexisting rocks that have made their way into the ocean. These sediments can contain the entire range of particle sizes, from microscopic clays to large boulders, and they are found almost everywhere on the ocean floor. Lithogenous sediments are created on land through the process of weathering, where rocks and minerals are broken down into smaller particles through

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1980-465: Is thought to have come from river discharge, particularly from Asia. Most of this sediment, especially the larger particles, will be deposited and remain fairly close to the coastline, however, smaller clay particles may remain suspended in the water column for long periods of time and may be transported great distances from the source. Wind: Windborne (aeolian) transport can take small particles of sand and dust and move them thousands of kilometres from

2070-429: Is very resistant to abrasion, so it is a dominant component of lithogenous sediments, including sand. Biogenous sediments come from the remains of living organisms that settle out as sediment when the organisms die. It is the "hard parts" of the organisms that contribute to the sediments; things like shells, teeth or skeletal elements, as these parts are usually mineralized and are more resistant to decomposition than

2160-423: The continental margins where they can be over 10 km thick. This is because the crust near passive continental margins is often very old, allowing for a long period of accumulation, and because there is a large amount of terrigenous sediment input coming from the continents. Near mid-ocean ridge systems where new oceanic crust is being formed, sediments are thinner, as they have had less time to accumulate on

2250-421: The diatoms (algae) and the radiolarians ( protozoans ). Diatoms are particularly important members of the phytoplankton, functioning as small, drifting algal photosynthesizers. A diatom consists of a single algal cell surrounded by an elaborate silica shell that it secretes for itself. Diatoms come in a range of shapes, from elongated, pennate forms, to round, or centric shapes that often have two halves, like

2340-435: The start of this article ↑ shows the distribution of the major types of sediment on the ocean floor. Cosmogenous sediments could potentially end up in any part of the ocean, but they accumulate in such small abundances that they are overwhelmed by other sediment types and thus are not dominant in any location. Similarly, hydrogenous sediments can have high concentrations in specific locations, but these regions are very small on

2430-465: The Bahamas. Methane hydrates are another type of hydrogenous deposit with a potential industrial application. All terrestrial erosion products include a small proportion of organic matter derived mostly from terrestrial plants. Tiny fragments of this material plus other organic matter from marine plants and animals accumulate in terrigenous sediments, especially within a few hundred kilometres of shore. As

2520-666: The Gascoyne, Merlinleigh, Bidgemia and Byro Sub-basins and Bernier Platform and is flanked to the east by the Archaean Pilbara Block. The Gnargoo structure , which has remarkable similarities to Woodleigh crater , is a proposed 75 km impact crater on the Gascoyne Platform, Southern Carnarvon Basin with an estimated age of 100-300 Ma. 24°48′24″S 115°13′29″E  /  24.80667°S 115.22472°E  / -24.80667; 115.22472 This article about

2610-637: The Mediterranean Sea. Beginning around 6 million years ago, tectonic processes closed off the Mediterranean Sea from the Atlantic, and the warm climate evaporated so much water that the Mediterranean was almost completely dried out, leaving large deposits of salt in its place (an event known as the Messinian Salinity Crisis ). Eventually the Mediterranean re-flooded about 5.3 million years ago, and

2700-743: The Mungaroo laid down only for a short period of time between the beginning of the Rhaetian to the Early Hettangian . Due to the thickness of fluvial deltaic deposits from the Mungaroo Formation, the transgressional sequence of the Brigadier Formation is correlated with the subsidence of sub-basins across region during the Middle and Late Triassic . The distribution of sediment packages throughout

2790-829: The Northern Carnarvon Basin and Exmouth Plateau varies with location during the Jurassic. By the Pliensbachian , the general beginning structure of the Northern Carnarvon Basin was formed, creating the Exmouth, Barrow, and Dampier sub-basins along the proximal end of the northwestern Australian margin. Rapid subsidence of the Northern Carnarvon sub-basins ensued the deposition of the Dingo Claystones. These Claystones are thick marine shale deposits separated into two sequence,

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2880-550: The O16:O18 ratios for samples of known ages, and from those ratios, infer the climate conditions under which those shells were formed. The same types of measurements can also be taken from ice cores; a decrease of 1 ppm O18 between ice samples represents a decrease in temperature of 1.5°C. The primary sources of microscopic biogenous sediments are unicellular algaes and protozoans (single-celled amoeba-like creatures) that secrete tests of either calcium carbonate (CaCO 3 ) or silica (SiO 2 ). Silica tests come from two main groups,

2970-622: The Permian extension that occurred just prior to the late Triassic extension event across the northwestern margin of Australia. Lying atop unconformable unit of Paleozoic sediments, the Locker Shale is composed of marine sediments deposited in a transgressional environment during the Late Permian extension. These marine sediments were deposited at the base of the Late Triassic and continued up until

3060-547: The Upper and Lower Dingo Claystones. The Lower Dingo sequence cannot be found in the Exmouth Plateau, because deposition During the Early to Middle Jurassic was restricted to sediments filling in the empty troughs of the Northern Carnarvon sub-basins. As deposition continued through the Middle and Late Jurassic , the troughs of sub-basins filled allowing more of the Dingo sediment overflow into

3150-748: The Winning Group atop the Valanginian unconformity. The Winning Group consists of Muderong Shale, Windalia Radiolarite, and Gearle Siltstone. The Muderong Shale is actually considered a siltstone and was deposited in a low energy, offshore-marine environment. The deposition of these sediments makes a good seal for gas buildups in the Exmouth Plateau and the surrounding sub-basins of the Northern Carnvon Basin. The Windalia Radiolarite are primarily carbonate marine deposits commonly containing poorly preserved radiolarians and forminiferas. The Gearle Siltstone

3240-405: The action of wind, rain, water flow, temperature- or ice-induced cracking, and other erosive processes. These small eroded particles are then transported to the oceans through a variety of mechanisms:  Streams and rivers: Various forms of runoff deposit large amounts of sediment into the oceans, mostly in the form of finer-grained particles. About 90% of the lithogenous sediment in the oceans

3330-448: The amount of material coming from a source, the distance from the source, the amount of time that sediment has had to accumulate, how well the sediments are preserved, and the amounts of other types of sediments that are also being added to the system. Rates of sediment accumulation are relatively slow throughout most of the ocean, in many cases taking thousands of years for any significant deposits to form. Lithogenous sediment accumulates

3420-403: The atmosphere that eventually settle back down to Earth and contribute to the sediments. Like spherules, meteor debris is mostly silica or iron and nickel. One form of debris from these collisions are tektites , which are small droplets of glass. They are likely composed of terrestrial silica that was ejected and melted during a meteorite impact, which then solidified as it cooled upon returning to

3510-400: The bottom! Given that slow descent, a current of only 1 cm/sec could carry the test as much as 15,000 km away from its point of origin before it reaches the bottom. Despite this, the sediments in a particular location are well-matched to the types of organisms and degree of productivity that occurs in the water overhead. This means the sediment particles must be sinking to the bottom at

3600-420: The bottom. While calcite is insoluble in surface water, its solubility increases with depth (and pressure) and at around 4,000 m, the carbonate fragments dissolve. This depth, which varies with latitude and water temperature, is known as the carbonate compensation depth . As a result, carbonate oozes are absent from the deepest parts of the ocean (deeper than 4,000 m), but they are common in shallower areas such as

3690-473: The central and southern margins of the Exmouth Plateau now known as the Gascoyne and Cuvier Abyssal Plains. As Australia continued to diverge away from the Antarctic land mass, it migrated in a northeastern direction and rotated counterclockwise to it present location, leaving the Exmouth Plateau along the continent's western margin. In the begin of the late Triassic , high volumes of sediments accumulate off of

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3780-492: The climate-change implications of its extraction and use can see that this would be folly. Cosmogenous sediment is derived from extraterrestrial sources, and comes in two primary forms; microscopic spherules and larger meteor debris. Spherules are composed mostly of silica or iron and nickel, and are thought to be ejected as meteors burn up after entering the atmosphere. Meteor debris comes from collisions of meteorites with Earth. These high impact collisions eject particles into

3870-409: The coccolithophores that also produced calcium carbonate tests. Discoaster tests were star-shaped, and reached sizes of 5-40 μm across. Discoasters went extinct approximately 2 million years ago, but their tests remain in deep, tropical sediments that predate their extinction. Because of their small size, these tests sink very slowly; a single microscopic test may take about 10–50 years to sink to

3960-452: The continental break up at the southern margin of the Exmouth Plateau. This followed seafloor spreading at the Gascoyne and Cuvier Abyssal Plains and erosion at the surface of the Exmouth, Dampier and Barrow sub-basins and an unconformity at the top of the early to middle Valanginian . By the middle to late Valanginian and through the Cretaceous major transgression occurred with deposit of

4050-453: The continental shelf and reach the deep ocean floor. Lithogenous sediments usually reflect the composition of whatever materials they were derived from, so they are dominated by the major minerals that make up most terrestrial rock. This includes quartz, feldspar, clay minerals, iron oxides, and terrestrial organic matter. Quartz (silicon dioxide, the main component of glass) is one of the most common minerals found in nearly all rocks, and it

4140-584: The deepest parts of the ocean, and most of this clay is terrestrial in origin. Siliceous oozes (derived from radiolaria and diatoms) are common in the south polar region, along the equator in the Pacific, south of the Aleutian Islands, and within large parts of the Indian Ocean. Carbonate oozes are widely distributed in all of the oceans within equatorial and mid-latitude regions. In fact, clay settles everywhere in

4230-440: The diagram at the start of this article ↑ . Terrigenous sediments predominate near the continents and within inland seas and large lakes. These sediments tend to be relatively coarse, typically containing sand and silt, but in some cases even pebbles and cobbles. Clay settles slowly in nearshore environments, but much of the clay is dispersed far from its source areas by ocean currents. Clay minerals are predominant over wide areas in

4320-529: The distal margins of Exmouth Plateau. In the Late Jurassic , Gondwanaland begins to break apart creating Western Gondwana, which was composed of the South American and African continental land masses, and Eastern Gondwana. The Eastern Gondwanian continent was composed of Madagascar, Greater India, Antarctica, and Australia. During this period of time Australia shared its southern margin with Antarctica and

4410-539: The distal margins of the region. This depositional sequence characterizes the Upper Dingo Claystones, which are found as thick proximal sequences in the Northern Carnarvon sub-basins and thinner distal sequences in the Exmouth Plateau. During the late Tithonian to early Valanginian there were major changes in depositional patterns, specifically associated with the Barrow Group. At this period of time there

4500-426: The distal portions of the Northern Carnarvon Basin furthest offshore. One of the primary gas source for the Exmouth Plateau and Northern Carnarvon Basin, the Mungaroo Formation contains thick successions of siltstone , sandstone , and coal . The Mungaroo Formation is capped by thin transgressive sequence of shallow marine claystone and limestone called the Brigadier Formation. This is a much thinner formation than

4590-438: The earth. In turn, molten material from the interior returns to the surface of the earth in the form of lava flows and emissions from deep sea hydrothermal vents , ensuring the process continues indefinitely. The sediments provide habitat for a multitude of marine life , particularly of marine microorganisms . Their fossilized remains contain information about past climates , plate tectonics , ocean circulation patterns, and

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4680-555: The end of Anisian age when it transitioned in the Mungaroo Formation. The Mungaroo Formation is an intricate fluvial environment of meandering and braided stream deposits laid down in the Ladinian (~241 Mya) to Norian ages (~209 Mya) during the pre-rift active margin of the Northwestern Australian Shelf. It is one of the thickest formations in the region and becomes progressively thicker (approximately 3,000 m thick) in

4770-425: The extraction of these non-renewable resources. Evaporites are hydrogenous sediments that form when seawater evaporates, leaving the dissolved materials to precipitate into solids, particularly halite (salt, NaCl). In fact, the evaporation of seawater is the oldest form of salt production for human use, and is still carried out today. Large deposits of halite evaporites exist in a number of places, including under

4860-557: The fastest, on the order of one metre or more per thousand years for coarser particles. However, sedimentation rates near the mouths of large rivers with high discharge can be orders of magnitude higher. Biogenous oozes accumulate at a rate of about 1 cm per thousand years, while small clay particles are deposited in the deep ocean at around one millimetre per thousand years. As described above, manganese nodules have an incredibly slow rate of accumulation, gaining 0.001 millimetres per thousand years. Marine sediments are thickest near

4950-464: The fleshy "soft parts" that rapidly deteriorate after death. Macroscopic sediments contain large remains, such as skeletons, teeth, or shells of larger organisms. This type of sediment is fairly rare over most of the ocean, as large organisms do not die in enough of a concentrated abundance to allow these remains to accumulate. One exception is around coral reefs ; here there is a great abundance of organisms that leave behind their remains, in particular

5040-415: The form of calcite or aragonite . Calcareous sediments ( limestone ) are usually deposited in shallow water near land, since the carbonate is precipitated by marine organisms that need land-derived nutrients. Generally speaking, the farther from land sediments fall, the less calcareous they are. Some areas can have interbedded calcareous sediments due to storms, or changes in ocean currents. Calcareous ooze

5130-562: The fragments of the stony skeletons of corals that make up a large percentage of tropical sand. Microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or tests . Although very small, these organisms are highly abundant and as they die by the billions every day their tests sink to the bottom to create biogenous sediments. Sediments composed of microscopic tests are far more abundant than sediments from macroscopic particles, and because of their small size they create fine-grained, mushy sediment layers. If

5220-419: The halite deposits were covered by other sediments, but they still remain beneath the seafloor. Oolites are small, rounded grains formed from concentric layers of precipitation of material around a suspended particle. They are usually composed of calcium carbonate, but they may also from phosphates and other materials. Accumulation of oolites results in oolitic sand, which is found in its greatest abundance in

5310-513: The isotopes). O16 is the most common form, followed by O18 (O17 is rare). O16 is lighter than O18, so it evaporates more easily, leading to water vapor that has a higher proportion of O16. During periods of cooler climate, water vapor condenses into rain and snow, which forms glacial ice that has a high proportion of O16. The remaining seawater therefore has a relatively higher proportion of O18. Marine organisms which incorporate dissolved oxygen into their shells as calcium carbonate will have shells with

5400-431: The land accumulates the fastest, on the order of one metre or more per thousand years for coarser particles. However, sedimentation rates near the mouths of large rivers with high discharge can be orders of magnitude higher. Biogenous oozes accumulate at a rate of about one centimetre per thousand years, while small clay particles are deposited in the deep ocean at around one millimetre per thousand years. Sediments from

5490-401: The land are deposited on the continental margins by surface runoff , river discharge , and other processes. Turbidity currents can transport this sediment down the continental slope to the deep ocean floor. The deep ocean floor undergoes its own process of spreading out from the mid-ocean ridge, and then slowly subducts accumulated sediment on the deep floor into the molten interior of

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5580-426: The largest with grain diameters of 256 mm or larger. Among other things, grain size represents the conditions under which the sediment was deposited. High energy conditions, such as strong currents or waves, usually results in the deposition of only the larger particles as the finer ones will be carried away. Lower energy conditions will allow the smaller particles to settle out and form finer sediments. Sorting

5670-622: The low temperatures typical of the seafloor (close to 4 °C), water and methane combine to create a substance known as methane hydrate. Within a few metres to hundreds of metres of the seafloor, the temperature is low enough for methane hydrate to be stable and hydrates accumulate within the sediment. Methane hydrate is flammable because when it is heated, the methane is released as a gas. The methane within seafloor sediments represents an enormous reservoir of fossil fuel energy. Although energy corporations and governments are anxious to develop ways to produce and sell this methane, anyone that understands

5760-521: The lower crystalline crust and lithosphere experienced shear stress and thinning. The formation of the fault system closer to the coast caused the initial development of the Exmouth, Barrow, and Dampier sub-basins of the Northern Carnarvon Basin. Carbonate marine sediment, primarily marls, continued to be deposited at this time on the central and western portions of the plateau. Closer to the shoreline siliciclastic mud and silt were deposited from marine and deltaic environments. As extension continued in

5850-465: The mid to late Jurassic, multiple pull-apart basins and oblique right-lateral strike-slip faulting in the eastern margin of the Exmouth Plateau continued to dominate. The simple shear stress of the Exmouth detachment fault between the base of the upper crust, and the lower crust had been reduced in the east plateau. This reduction in simple shear was in part caused by the deformation that developed series negative flower structures and half-graben systems in

5940-636: The mid-Atlantic ridge, the East Pacific Rise (west of South America), along the trend of the Hawaiian/Emperor Seamounts (in the northern Pacific), and on the tops of many isolated seamounts. Sediment texture can be examined in several ways. The first way is grain size . Sediments can be classified by particle size according to the Wentworth scale . Clay sediments are the finest with a grain diameter of less than .004 mm and boulders are

6030-411: The nodule to grow over time. The composition of the nodules can vary somewhat depending on their location and the conditions of their formation, but they are usually dominated by manganese- and iron oxides. They may also contain smaller amounts of other metals such as copper, nickel and cobalt. The precipitation of manganese nodules is one of the slowest geological processes known; they grow on the order of

6120-443: The ocean and begins to break apart or melt, these particles get deposited. Most of the deposition will happen close to where the glacier meets the water, but a small amount of material is also transported longer distances by rafting, where larger pieces of ice drift far from the glacier before releasing their sediment. Gravity: Landslides, mudslides, avalanches, and other gravity-driven events can deposit large amounts of material into

6210-489: The ocean are gastroliths. Gastrolith means "stomach stone". Many animals, including seabirds, pinnipeds, and some crocodiles deliberately swallow stones and regurgitate them latter. Stones swallowed on land can be regurgitated at sea. The stones can help grind food in the stomach or act as ballast regulating buoyancy. Mostly these processes deposit lithogenous sediment close to shore. Sediment particles can then be transported farther by waves and currents, and may eventually escape

6300-444: The ocean when they happen close to shore. Waves: Wave action along a coastline will erode rocks and will pull loose particles from beaches and shorelines into the water. Volcanoes: Volcanic eruptions emit vast amounts of ash and other debris into the atmosphere, where it can then be transported by wind to eventually get deposited in the oceans. Gastroliths : Another, relatively minor, means of transporting lithogenous sediment to

6390-452: The oceans, but in areas where silica- and carbonate-producing organisms are prolific, they produce enough silica or carbonate sediment to dominate over clay. Carbonate sediments are derived from a wide range of near-surface pelagic organisms that make their shells out of carbonate. These tiny shells, and the even tinier fragments that form when they break into pieces, settle slowly through the water column, but they don't necessarily make it to

6480-481: The overall structural morphology of the Exmouth Plateau had taken shape, aside from the post-breakup subsidence that occurred afterward from the Late Cretaceous to present day. Activity at the eastern Exmouth Plateau's detachment system had likely ceased which is reason for the completion of the plateau's morphology. The Locker Shale and Mungaroo formation are associated with the syn-rift and post-rift sequences of

6570-474: The sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea, or they are biogenic deposits from marine organisms or from chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris. Except within a few kilometres of a mid-ocean ridge , where the volcanic rock is still relatively young, most parts of the seafloor are covered in sediment . This material comes from several different sources and

6660-476: The seafloor (Figure 12.4.2 right). Because the nodules contain a number of commercially valuable metals, there has been significant interest in mining the nodules over the last several decades, although most of the efforts have thus far remained at the exploratory stage. A number of factors have prevented large-scale extraction of nodules, including the high costs of deep sea mining operations, political issues over mining rights, and environmental concerns surrounding

6750-435: The seafloor and the other half suspected from water column indicators and/or seafloor deposits. Manganese nodules are rounded lumps of manganese and other metals that form on the seafloor, generally ranging between 3–10 cm in diameter, although they may sometimes reach up to 30 cm. The nodules form in a manner similar to pearls; there is a central object around which concentric layers are slowly deposited, causing

6840-415: The sediment below will reflect the production occurring near the surface. The increased rate of sinking through this mechanism has been called the "fecal express". Seawater contains many different dissolved substances. Occasionally chemical reactions occur that cause these substances to precipitate out as solid particles, which then accumulate as hydrogenous sediment. These reactions are usually triggered by

6930-403: The sediment layer consists of at least 30% microscopic biogenous material, it is classified as a biogenous ooze. The remainder of the sediment is often made up of clay. Biogenous sediments can allow the reconstruction of past climate history from oxygen isotope ratios. Oxygen atoms exist in three forms, or isotopes, in ocean water: O16 , O17 and O18 (the number refers to the atomic masses of

7020-436: The sediments pile up, the deeper parts start to warm up (from geothermal heat), and bacteria get to work breaking down the contained organic matter. Because this is happening in the absence of oxygen (a.k.a. anaerobic conditions), the by-product of this metabolism is the gas methane (CH 4 ). Methane released by the bacteria slowly bubbles upward through the sediment toward the seafloor. At water depths of 500 m to 1,000 m, and at

7110-444: The shells of snails. As the organism grows, is secretes new, larger chambers in which to reside. Most foraminiferans are benthic, living on or in the sediment, but there are some planktonic species living higher in the water column. When coccolithophores and foraminiferans die, they form calcareous oozes . Older calcareous sediment layers contain the remains of another type of organism, the discoasters ; single-celled algae related to

7200-530: The shoreline of western Australia to the northern extend of the Exmouth Plateau by the Mungaroo Deltas. The Carnian (237-228 Ma) to Norian (228-209 Ma) aged fluviodeltaic sediments deposited were siliciclastic claystones and sandstones, and detritus which would late make up the coals found in Mungaroo Formation. As extensional rifting between Greater Indian and the Australian continued, magmatic intrusion along

7290-416: The source. These small particles can fall into the ocean when the wind dies down, or can serve as the nuclei around which raindrops or snowflakes form. Aeolian transport is particularly important near desert areas. Glaciers and ice rafting : As glaciers grind their way over land, they pick up lots of soil and rock particles, including very large boulders, that get carried by the ice. When the glacier meets

7380-458: The surface. Cosmogenous sediment is fairly rare in the ocean and it does not usually accumulate in large deposits. However, it is constantly being added to through space dust that continuously rains down on Earth. About 90% of incoming cosmogenous debris is vaporized as it enters the atmosphere, but it is estimated that 5 to 300 tons of space dust land on the Earth's surface each day. Siliceous ooze

7470-463: The timing of major extinctions . Except within a few kilometres of a mid-ocean ridge , where the volcanic rock is still relatively young, most parts of the seafloor are covered in sediments. This material comes from several different sources and is highly variable in composition, depending on proximity to a continent, water depth, ocean currents, biological activity, and climate. Seafloor sediments (and sedimentary rocks ) can range in thickness from

7560-585: The vent. This superheated water contains many dissolved substances, and when it encounters the cold seawater after leaving the vent, these particles precipitate out, mostly as metal sulfides. These particles make up the "smoke" that flows from a vent, and may eventually settle on the bottom as hydrogenous sediment. Hydrothermal vents are distributed along the Earth's plate boundaries, although they may also be found at intra-plate locations such as hotspot volcanoes. Currently there are about 500 known active submarine hydrothermal vent fields, about half visually observed at

7650-434: The west plateau. By this time, the lithospheric thinning that had been initiated during the early Jurassic was now considerably thinner. At this period, a magmatic intrusion between the lower crystalline crest and the lithosphere been introduce, underplating this region. In Early Cretaceous , pure shear deformation at the ocean-continental boundary completed the final continental breakup and sea-floor spreading. By this time

7740-604: The western margin (now the Exmouth Plateau) with Greater India. The formation of the Exmouth's northern margin, the Argo Abyssal Plain, was not initiated until 155 million years ago when Australia broke apart from a continental fragment of the Burma Plate that's present location is argued to be subsumed under Asia. It wasn't until 20 million years later that the Greater Indian land mass broke from western Australia, forming

7830-570: The westernmost section of the Exmouth Plateau caused further rifting to the outer margins. By the end of the Late Triassic (209-201 Ma) tectonic activity had relatively slowed down and less deltaic sediments were deposited compared to the Carnian and Norian . More marine sedimentary deposit such as carbonates are found during this time period. During the early Jurassic, extension at the west Australian margin initiated simple shear mechanics creating

7920-587: The westernmost structural unit of the Northern Carnarvon Basin , which comprises the Exmouth, Barrow, Dampier, and Beagle Sub-basins, and the Rankin Platform. The Exmouth Plateau was once a part of the northern shore of eastern of Gondwanaland until it broke away during Late Jurassic to Early Cretaceous , leaving behind the oceanic crust of the Argo, Cuvier, and Gascoyne abyssal plains that now surround

8010-403: The younger crust. As distance increases from a ridge spreading center the sediments get progressively thicker, increasing by approximately 100–200 m of sediment for every 1000 km distance from the ridge axis. With a seafloor spreading rate of about 20–40 km/million years, this represents a sediment accumulation rate of approximately 100–200 m every 25–50 million years. The diagram at

8100-560: Was large uplift of the Cape Range Fracture Zone that provided sediments from the Barrow Delta prograde northward past Barrow Island and across the Exmouth Plateau. The sediments of the Barrow Group are composed of interbedded shale and fluvial-deltiac sands that were extensively deposited into Exmouth and Barrow sub-basins. Eventually, deposition of the Barrow Delta's sediment ceased during the early or middle Valanginian due to

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