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- loess
- clay
- clastic rock
- sediment
- mud
terrigenous sediment
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What is sediment in geology?
Sediment in geology refers to solid matter that settles at the bottom of a liquid body. Sedimentary rocks are created when layers of sediment accumulate and solidify.
Terrigenous sediment is deep-sea sediment that rivers and wind transport to the oceans from land. Turbidity currents carry terrigenous sediments to the deep sea, forming sedimentary deposits called turbidites. Turbidites create deep-sea fans or abyssal cones, such as the Bengal Cone. Abyssal plains form from turbidites in locations with a large sediment supply.
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What does terrigenous mean?
Terrigenous sediment is deep-sea sediment that rivers and wind transport to the oceans from land.
Terrigenous sediments on the continental shelf often accumulate in submarine canyons on the continental slope. Turbidity currents then carry these sediments into the deep sea, creating sedimentary deposits called turbidites. Turbidites form sedimentary deep-sea fans near the base of the continental slope and abyssal cones below major river deltas, such as the Ganges Fan in the Bay of Bengal.
Abyssal plains result from turbidite accumulation beyond deep-sea fans and abyssal cones where sediment supply is high. Brown clays, a type of pelagic sediment mostly of terrigenous origin, consist of clay minerals like chlorite and kaolinite. These clays enter the oceans via rivers, with kaolinite also carried by wind from arid regions.
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What are terrigenous sediments?
Terrigenous sediments are deep-sea sediments transported to the ocean by wind and rivers from land sources.
These sediments often accumulate in submarine canyons on the continental shelf and are carried into the deep sea by turbidity currents, creating turbidites, which are sedimentary deposits with sediment particles that get finer from bottom to top. Turbidites form sedimentary deep-sea fans next to the continental slope's base and abyssal cones below major river deltas, such as the Ganges Fan in the Bay of Bengal.
Abyssal plains, prominent near the Atlantic margins and in the northeast Pacific, form from turbidite accumulation beyond deep-sea fans and abyssal cones where sediment supply is large. Brown clays, a type of pelagic sediment mostly of terrigenous origin, are widespread in the deeper ocean areas below 4 km and dominate the central North Pacific floor.
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How are terrigenous sediments formed and transported?
Terrigenous sediments are deep-sea sediments carried to the oceans from land by rivers and wind. They originate through the weathering of pre-existing rocks, with subsequent transportation and deposition of the weathering products.
Erosion transports the weathered material as solid matter or dissolved components, eventually depositing it as sediment. These sediments are then transported by various means, including gravity, mudflows, running water, glaciers, and wind, and are deposited in different environments like desert dunes, continental shelves, and river deltas.
Rivers play a crucial role in carrying sediment to the sea, with the amount of erosional debris exported from a drainage basin referred to as sediment yield. The sediment load is classified into bed load, suspended load, and dissolved load, depending on particle size and river competence.
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Where are terrigenous sediments commonly found in the ocean?
Terrigenous sediments, originating from land, are commonly found in several ocean environments. These sediments primarily accumulate on continental shelves, slopes, and rises, eventually merging into abyssal plains. Submarine canyons on the continental slope often store terrigenous sediments, which turbidity currents then carry into the deep sea, forming turbidites and deep-sea fans. Abyssal plains, prominent near the Atlantic margins and the northeast Pacific, form from turbidite accumulation. Additionally, brown clays, largely of terrigenous origin, are widespread in deeper ocean areas below 4 km. The immense sediment load from rivers emptying into the Indian Ocean is the highest among the major oceans, with a significant portion originating from the Indian subcontinent.
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How do terrigenous sediments affect ocean floor features and ecosystems?
Terrigenous sediments, transported by rivers and wind from land, significantly influence ocean floor features and ecosystems. These sediments, stored in submarine canyons, are carried into the deep sea by turbidity currents, forming turbidites that build sedimentary deep-sea fans and abyssal cones.
Accumulation of turbidites beyond deep-sea fans in areas with large sediment supply leads to the creation of flat, featureless abyssal plains.
Pelagic sediments of terrigenous origin, such as brown clays, accumulate slowly in deeper ocean areas, affecting the composition of the ocean floor. Volcanic ash sediments are commonly found near island arcs and marginal trenches. Glacial marine sediments, carried by icebergs, cover the ocean floor encircling Antarctica, influencing sediment distribution.
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terrigenous sediment, deep-sea sediment transported to the oceans by rivers and wind from land sources.
Terrigeneous sediments that reach the continental shelf are often stored in submarine canyons on the continental slope. Turbidity currents carry these sediments down into the deep sea. These currents create sedimentary deposits called turbidites, which are layers up to several metres thick composed of sediment particles that grade upward from coarser to finer sizes. The turbidites build sedimentary deep-sea fans adjacent to the base of the continental slope. Turbidites also are found below the major river deltas of the world where they build features called abyssal cones. The largest of these is the Ganges Fan (also called the Ganges Cone or Bengal Cone) in the Bay of Bengal east of the Indian subcontinent. It measures 3,000 km (about 1,900 miles) long (north-south) by 1,000 km (about 600 miles) wide (east-west) and is up to 12 km (about 7 miles) thick. The Bengal Cone continues to form from rock material eroded from the Himalayas and transported by the Ganges and Brahmaputra rivers.
Abyssal plains are formed by the accumulation of turbidites beyond the limits of deep-sea fans and abyssal cones in locations where there is a very large sediment supply. In contrast to fans and cones, abyssal plains are flat and featureless. They are prominent near both margins of the Atlantic and in the northeast Pacific. Tectonic and climate controls have influenced the formation of abyssal plains. The last major glaciation near the end of the Pleistocene Epoch about 11,700 years ago greatly increased erosion and sediment supply to the deep sea, but deep-sea trenches interrupted the flow of turbidity currents to the ocean floor. Off the Pacific Northwest coast of the United States, however, the trenches were filled by turbidites, and subsequent turbidity currents passed beyond them to form the Alaska and Tufts abyssal plains.
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Brown clays are a variety of pelagic sediment, mostly of terrigenous origin, which are composed largely of four different clay minerals: chlorite, illite, kaolinite, and montmorillonite. By definition, clays have less than 30 percent biogenic components. Quartz, volcanic ash, and micrometeorites are common as minor constituents. Brown clays are widespread in the deeper areas of the oceans below 4 km (about 2.5 miles). They dominate the floor of the central North Pacific. Clays accumulate very slowly, averaging about 1 mm (0.04 inch) per 1,000 years. The type of clay found in a given area is a function of the source region on land and the climate. For example, chlorite is dominant in polar regions and kaolinite in the tropics. Clays are introduced into the oceans by river transport, although kaolinite is also carried by the wind from the arid regions of Africa and Australia. Montmorillonite is an alteration product of volcanic material and can form from either wind-blown volcanic ash or basaltic glass on the seafloor.
Sediments composed mostly or entirely of volcanic ash are commonly found adjacent to the island arcs and marginal trenches. These are normally deposited as turbidites. Volcanic ash that has been ejected higher than 5 km (about 3 miles) during an eruption can be carried by wind and settle out through the atmosphere and oceans as pelagic sediment. The ocean floor encircling Antarctica is covered by glacial marine sediments. These sediments are carried by icebergs from the continent as far north as the Antarctic Convergence at 45° to 55° latitude.