Rock salt precipitates directly from seawater. Anhydrite was originally deposited as gypsum with thin layers of organic matter before it looses its water content. A sabkha is a desert coastal environment is where salts, including halite and gypsum , are commonly deposited. Polygons of salt crystals halite being deposited on a salt pan on a dry lake bed in Death Valley National Park, California.
An iron-manganese nodule forms very, very slowly from direct precipitation on the seafloor. Iron-manganese nodules on the deep seafloor near the Puerto Rico Trench.
Lithogenous Sediments Lithogenous sediments form through the processes of weathering and erosion of materials exposed on land and along coastlines. Lithogenous sediments consist of solid fragments of inorganic or organic material that come from the weathering of rock and soil erosion, and are carried and deposited by wind, water, or ice.
Volcanoes and coastal mountain ranges are major sources of lithogenous sediments. Volcanic ash clouds from erupting volcanoes and sediments carried by rivers in flood dump large quantities of sediment into ocean basins. In addition, shoreline erosion by wave action is also a major source of lithogenous sediments in some regions. Lithogenous sediments are also commonly called terrigenous sediments because they are derived dominantly from continental sources. They are also called clastic sediments because they are made up of rock fragments derived from other rocks—a clast is a Greek word for a rock fragment discussed in Chapters 8 and 9.
Sand and gravel on SoCal beaches are typical lithogenous sediments. Lithogenous sediments accumulate offshore, building up continental shelves and flooding int deep ocean basins along continental margins.
Continental-Derived Lithogenous Sediments Continents shed vast quantities of sediments into adjacent ocean basins. Rivers in flood transport vast quantities of gravel, sand, silt, and clay mud into ocean basins. River deltas are vast accumulations of sediment along the boundary between coastal plains and continental shelve, however the deltas exposed on land are only a small fraction of the material deposited at sea.
Most of the sediment is carried to sea by flood waters where they are redistributed offshore by wave and currents, especially during major tropical storms.
For example, the Ganges River floods each year as annual monsoonal storms drench to Himalayan Mountains and Indian subcontinent. Flood waters dump vast quantities of sediment into the Bay of Bengal in between India and Bangladesh Figure The influx of sediments supplied by the Ganges River supports a large mangrove forest which traps some sediment to form new land. However, most of the mud continues to move off shore to contribute to a massive accumulation of sediments, many miles deep, along the outer continental margin beneath the Bay of Bengal.
Volcanoes also contribute large quantities of sediments to ocean basins. Thick accumulations of volcanic sediment build up along the volcanic island chains along the margin of the Pacific Ocean such as the Andes Mountains of South America, the Aleutian Island Chain, Japan, Philippines, Indonesia, and others.
Volcanoes in the western Pacific region are also subject to severe erosion from tropical storms. Heavy rains from tropical storms produce lahars volcanic mud flows and floods that move vast quantities of sediment. For example, the volcanic eruptions of Mount Pinatubo in the summer of released an estimated 8 to 10 cubic kilometers of ash and erupted materials Figure The ash clouds rose to 35, feet into the atmosphere and spread ash and sediments both across the landscape and into adjacent Pacific Ocean basin.
The eruption occur the same time that Typhoon Yunka struck. Storm flood waters and mudflows during and after the eruption also dumped vast quantities of volcanic material into the sea. The Ganges River transports large quantities of sediments derived from the Himalayan Mountains region into the Indian Ocean. A massive eruption of Mount Pinatubo volcano in the Philippines. Turbidity Currents and Development of Submarine Canyons and Fans A turbidity flows is a turbid, dense current of sediments in suspension moving along downslope and along the bottom of a ocean or lake.
In the ocean, turbidity currents can be massive episodic events. They typically form and flow down through a submarine canyon carved by previous turbidity flows and accumulate near the base of the continental slope on deep-sea fans.
Turbidity flows produces deposits showing graded bedding Figure Slowing turbid currents drop their coarser fractions first gravel and sand and the finer silt and clay fractions settle out last. Sediments deposited by turbidity currents are called turbidites. A deep-sea fan is a fan- or delta-shaped sedimentary deposit found along the base of the continental slopes, commonly at the mouth of submarine canyons.
Deep sea fans form from sediments carried by turbidity flows density currents that pour into the deep ocean basin from the continental shelf and slope regions and then gradually settle to form graded beds of sediment on the seafloor.
Deep-sea fans can extend for many tens to hundreds of miles away from the base of the continental slope and an coalesce into a broad, gently sloping region called a continental rise. Graywacke is a fine-to-coarse-grained sedimentary rock consisting of a mix of angular fragments of quartz, feldspar, and mafic minerals set in a muddy base commonly called a dirty sandstone or mudstone because of its mixed size fractions and brown appearance.
Graywacke is the general term applied to sediments deposited by turbidity flows, and they commonly show graded bedding. Graywacke is common in the Coast Ranges of California and other active continental margin regions. It is exposed on land where tectonic forces push up rocks that originally formed in the deep ocean example in Figure Turbidites deposits associated with turbidity flows commonly appear as inter-bedded layers of graywacke sandstone and shale.
Conglomerate typically occurs in thicker beds and were originally deposited as gravel and mud on ancient submarine fans closer to the mouths of submarine canyons or in channels carved into the seabed. Turbidity flows are essentially underwater landslides or density-driven currents. Sediments laden with sediment are heavier than clear seawater. Seas stacks composed of submarine channel deposits mostly conglomerate exposed at Gazos Creek State Beach, California.
Turbidity currents scour canyons in the deep offshore environment and deposit sediments in the deep ocean. Deep-sea fans build up the continental rise region at the base of the continental slope and spread for hundreds of miles seaward.
Each layer represents an undersea storm turbidity flow that spread across a deep sea fan on a continental rise. They were pushed up by tectonic uplift along the coast. Abyssal Clays Abyssal clays are very fine-grained sediments, mostly clay minerals and iron-rich mineral dust that are blow in by the wind from distant terrestrial sources. Much of the abyssal clay components are derived from dust storms in the world's desert regions and from explosive volcanic eruptions that can blow fine particles high into the atmosphere.
Abyssal clays are also fine-grained material carried and redistributed by ocean currents such as tail end of far-turbidity currents that can travel hundreds to even thousands of miles away from continental margins. Abyssal clays in the deep ocean basins accumulate very slowly relative to other ocean sediments. Abyssal clays dominate sediments on the seafloor in the northern Pacific Ocean basin see discussion on volume and distribution of marine sediments in section Biogenous Sediments Biogenous sediments include sediments formed by accumulation of organic materials.
Biogenous sediments are mostly composed of the remains of organisms—including skeletal remains of microplankton both plants and animals , plant remains algae, wood, roots, and leaves and remains of larger animals including shells of invertebrates, such as shells, coral fragments, and fish and other vertebrate teeth, bone, and scales, and fecal material left behind by any type of organism.
Biogenous sediments can form in both terrestrial and marine environments. Biogenous sediments may be partly mixed with lithogenous sediments continental-derived sediments in coastal regions, particularly where streams and rivers contribute sediments.
For instance, quartz beach sand is not biogenous, but ground up an worn fragments of shells is biogenous. Some beach sands consist entirely of shell and coral fragments. Biogenous Sediments In the Marine Environment Bioaccumulation is the buildup of organic remains , such as deposits associated with coral reefs, shell or bone beds, and algae and ooze calcareous and siliceous. On land bioaccumulation in swampy environments produces peat beds with burial and time, peat eventually can be converted to coal.
In many passive margin regions in tropical regions, carbonate sediments form and accumulate forming massive deposits along continental margins. Carbonate Reefs or Coral Reefs A reef is a general name for a ridge of jagged rock, coral, or sand just above or below the surface of the sea. A carbonate reef is one that is made of skeletal material composed of coral, coralline algae, and other carbonate skeletal material. Carbonate reefs are commonly called coral reefs, but not all organisms that look like corals are actually corals—other organisms that create solid structure branching or not include coralline algae, bryozoans, sponges, stromatoporoids, and many other types of invertebrates.
Figure illustrates the variety of settings and features associated with carbonate depositional environments. Carbonate coral reefs form in clear shallow, warm, tropical marine waters.
Over time, lime sediments are produced by biological activity in and around carbonate reefs. Carbonate reefs grow at rates of feet per thousand years. Wave action and currents will erode and redistribute lime sediments offshore where they may accumulate. Over time millions of years calcareous sediments build up, creating massive carbonate platforms becoming regions underlain by limestone that may become strata many thousands of feet thick.
Examples of carbonate platform regions include the Bahamas, South Florida, and the Yucatan Peninsula Figure and The world's largest reef system is the reef tracts, islands, and tidal shoals associated with the Great Barrier Reef located along the east coast of Australia Figure The Great Barrier Reef is composed of over 2, individual carbonate reefs and about islands stretching for over miles 2, km along the northeast coast of Australia and encompassing about , square miles , km 2.
It is the largest feature of biological origin on Earth. Similar reef tracts have formed throughout geologic history in other locations around the world. Calcium carbonate depositional environments include coral reefs, keys, shoals, tidal flats, bays, and other coastal and offshore features. South Florida is part of a growing carbonate platform with the Keys consisting of both ancient and modern reefs, forming a barrier reef complex. Massive carbonate platforms how in blue gray surround much of the Gulf of Mexico.
They include continental shelf regions around the Yucatan Peninsula, South Florida, and islands of the Caribbean where biogenous sediments form and accumulate over time. The Great Barrier Reef is the world's largest organic deposit light blue are keys. The growth of the great reef tract has kept pace with the global rise in sea level since the end of the last Wisconsin ice age.
Atolls are volcanic islands or seamounts covered or surrounded by fringing carbonate reefs that build up even long after the volcano stopped erupting. Lime mud , lime sand and larger skeletal fragments accumulate around living coral reefs.
Lime sediments are created mostly by organisms feeding on other reef organisms. Storms can erode reefs and redistribute carbonate sediments. Marine Ooze The oceans are full of many varieties of microscopic organisms, but only several varieties are responsible for generating vast quantities of biogenous sediments. Ooze is slimy mud sediment soft and mushy on the bottom of an ocean or lake bed formed from the accumulation of skeletal and organic remains of microscopic organisms: phytoplankton plants and zooplankton animals.
Components of oozes: calcareous, biosiliceous, and lithogenous materials. Calcareous Oozes Calcareous oozes are sediments dominantly composed dominantly of calcium carbonate CaCO 3. Two dominant groups of microorganisms that contribute carbonate remains: Coccolithopores phytoplankton and Foraminifera zooplankton. Coccolithopores Coccolithopores are single-celled marine phytoplankton microscopic plants that live in large numbers throughout the upper layers of the ocean.
Unlike any other plant in the ocean, coccolithopores secrete shells of microscopic plates made of calcite CaCO 3. These scales, known as coccoliths , are shaped like hubcaps and are only three one-thousandths of a millimeter in diameter Figure Coccolithopores are part of base of the food chain and contribute vast quantities of coccoliths as sediment to large regions of the ocean basins. Coccoliths are concentrated in calcareous ooze. Coccoliths first appear in the fossil record in Triassic time.
Because they are composed of low-magnesium calcite the most stable form they are easily fossilized and preserved in sedimentary rocks. What is a Coccolithopores? A Coccolithopores is covered with calcareous plates called coccoliths.
Foraminifera Forams Foraminifera or forams are a large group of single-celled zooplankton, most species have calcareous shells or tests. Their shells are commonly divided into chambers which are added during growth and form patterns including spirals, open tubes, or hollow spheres Figure Depending on the species, the shell may be made of crystalline calcite, organic compounds, or sand grains and other particles cemented together.
They are usually less than 1 mm in size, but some species grow much larger, reaching up to 20 cm. The majority of foraminifera species are benthic meaning they live on or within the seamounts sediment while typically smaller varieties are floaters planktonic in the water column at various depths. Foraminifera are found in all depths of the ocean, although deep ocean varieties do not have calcareous tests. They contribute a significant volume of sediments to carbonate reefs and a major component of carbonate oozes throughout ocean basins.
Over 10, species of foraminifera are recognized, both living and fossil. They first appeared in the fossil record in Cambrian time over million years ago. Examples of foraminifera tests. Pyramids of Giza, Egypt are constructed with foraminifera-rich limestone.
Chalk Chalk is a soft, fine-grained, white to grayish variety of limestone that is composed of the calcareous skeletal remains of microscopic marine organisms including coccoliths and foraminifera.
Some of the purest varieties can have up to 99 percent calcium carbonate. The White Cliffs consist of Cretaceous-age chalk deposited about 89 to 85 million years ago in more tropical conditions than exist in the region today. The layers of chalk reach nearly meter thick. The sediment the chalk formed from was coccolithopore ooze. The White Cliffs of Dover, England are chalk.
Siliceous Oozes Siliceous oozes are sediments dominantly composed dominantly of SiO 2 silica. Two dominant groups of organisms that contribute siliceous remains: diatoms and radiolarians. Diatoms Diatoms are the most common plankton. Diatoms are phytoplankton single-celled microscopic marine plants Figure Example of diatoms. These are images taken with a microscope. Radiolarians A radiolarian is a single-celled aquatic animal zooplankton that has a spherical, amoeba-like body with a rigid spiny skeleton of silica.
There are hundreds of known species of radiolarians See a list on radiolaria. Figure is a photomicrograph depicting the siliceous tests of ten species of marine radiolarians. Upon death, their tests can accumulate on the seamounts and form siliceous marine sediments known as radiolarian ooze a form of siliceous ooze. Radiolarians first appear in the geologic record in early Cambrian time and have experienced several periods of proliferation and extinctions as recorded in the geologic record.
Today, radiolarians are more common in equatorial regions. Example of Radiolarian skeletons tests. Chert Chert is a fine-grained siliceous sedimentary rock. It is a hard, dense, and consist chiefly of interlocking microscopic crystals of quartz and may contain opal. It has a conchoidal fracture and may occur in a variety of colors. Most chert forms from compaction and recrystallization of siliceous microplankton remains—siliceous ooze eventually looses its water content and recrystallizes, and turns into layers of chert Figure Organic residues preserved as chert beds are known from rocks dating back to early Precambrian time.
Banded-iron formations BIFs are composed of inter-bedded layers of iron-oxide minerals and chert, and are thought to be biogenous in origin Figure Younger marine cherts are mostly formed from diatoms and radiolarian oozes. Layers of marine chert exposed in the Marin Headlands, California. Check your knowledge of ocean basins and continents by locating and labeling them on a world map.
This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Ocean Basins and Continents. The content and activities in this topic will work towards building an understanding of continents and ocean basins.
Continents and the Ocean There is one world ocean. The ocean is the most prominent feature on our planet. You can see this by tracing through the ocean on a map with your finger. On a globe, you can trace the ocean by moving your finger in a complete circle around the world without having to cross any land.
The world ocean can best be visualized by viewing a globe from the South Pole Fig. From this perspective, Antarctica is at the center of the world ocean.
Three ocean extensions reach northward from Antarctica and extend toward the South Pacific, South Atlantic, and Indian ocean basins between the continents. At lower latitudes, the ice melts during the summer months.
At polar latitudes, however, the ice cover is permanent. Another distinctive feature of the Arctic Ocean is the presence of islands composed of ice. These ice islands move, as does much of the ice cover, in the currents that exist in the underlying ocean water. Scientists have used the islands as research bases to study the arctic ice movements and other aspects of the far North.
Lee Lerner. Lebow, Ruth, and Tom S. Oceanus: the Marine Environment. Belmont, CA: Wadsworth Publishing, Earth's Oceans: An Introduction. Physiography of the Ocean Basins. Okanagan University College. The World Factbook Central Intelligence Agency.
Toggle navigation. Atlantic Ocean Basin The Atlantic Ocean is the second largest of Earth's five oceans, the most heavily traveled, and the most intensely studied, principally because of its importance in ship traffic between Europe and North America.
Southern Ocean A decision by the International Hydrographic Organization in the spring of delimited a fifth world ocean, the Southern Ocean. Brian D. Hoyle and K. Bibliography Lebow, Ruth, and Tom S. User Contributions:. Comment about this article, ask questions, or add new information about this topic: Name:. E-mail: Show my email publicly. Human Verification:.
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