List the two primary chemical compounds found in the majority of biogenic sediment, as well as examples of the organisms that make them. Calcium carbonate (made by foraminifers and coccolithophores) and silica are the two most abundant chemical components in biogenous sediment (produced by diatoms and radiolarians). Animals including crabs, shrimp, and snails consume diatoms and radiolarians and so their shells are made of calcium carbonate. Sea lettuce is a green alga that produces an organic material called silica glass which builds up in layers around marine animals' exoskeletons. This layer insulates them from heat loss during cold-water winters and reduces friction when they move through water.
Calcium carbonate is also used to make concrete, chalk, and eggshells. Silica is used in manufacturing tools, abrasives, and some types of glass.
Organic matter is another important component of biogenous sediment. It consists of the remains of plants and animals that have died and decomosed over time. Organic matter includes things like leaves, twigs, flowers, fruits, seeds, meat, bone, skin, fur, and any other organ or tissue that can be broken down by bacteria or fungi. Bacteria and fungi play a large role in the decomposition process of organic matter, breaking it down into its basic chemicals (carbon, hydrogen, oxygen, nitrogen, and phosphorus).
Biogenous sediments are sediments formed from the skeletal remains of once-living creatures (bio = life, generare = to generate). These hard portions contain a wide range of objects, including microscopic creature shells (called tests), coral fragments, sea urchin spines, and mollusc shell fragments. Tests are hollow tubes left by single-cell organisms such as bacteria or algae. Coral is the solidified tissue of marine plants called corals. Sea urchins are members of a large group of animals called echinoderms. They have a covering of spiny plates and can swim by moving their arms back and forth like a fish. Molluscs include snails and mussels. They are aquatic animals that live in water-filled shells or other protective structures. Biogenic materials are useful markers for tracing environmental changes over long periods of time.
All biogenic sediments are composed of dead organisms, but they can be classified into two broad groups based on their chemical composition: organic sediment and mineral sediment. Organic sediments consist mainly of carbon compounds such as cellulose and chitin. They may also contain some minerals such as calcium carbonate (shell) or magnesium phosphate (moss). In contrast, mineral sediments contain only minerals such as silicon dioxide or aluminum oxide. Neither type of sediment can be directly used to identify living organisms because they could have come from recently deceased organisms.
By far the most prevalent chemical sedimentary rock is limestone. Chert, banded iron formations, and a variety of rocks formed when bodies of water evaporate are among the others. Some chemical sedimentary rocks, particularly limestone and chert, are formed as a result of biological activity. Limestone caves are often filled with fossils that lived in ancient seas that covered much of North America.
Chemical sediments can also contain evidence of past life processes. For example, coal forms when plants die and decompose in shallow waters or on land. The remains of these plants become encrusted with minerals that later become cemented together to form coal. Coals can be burned to generate electricity and the by-products include carbon dioxide, which is one of the main greenhouse gases responsible for global warming.
Chemical sedimentary rocks are found everywhere in nature. They make up the Rocky Mountains, the Appalachian Mountains, the Mississippi River basin, and many other regions around the world.
Limestone is the most common sedimentary rock in Europe. It makes up the cliffs of England, France, and Ireland, among other countries. Limestone is made up of thin layers of calcium carbonate (the same ingredient in chalk) that were once living organisms. As these organisms died, they sank to the bottom of the ocean and were buried in mud.
Sediment is classified into four types: cosmogenous (from space), volcanogenous (ash from volcanic eruptions), terrigenous (from continental erosion and river runoff), and biogenous (skeletons of marine creatures). Sediments are categorised based on their size. Coarse sediment is anything bigger than.5 millimetres (mm), such as sand, gravel, or rubble. Medium-sized sediment is between.5 mm and 2 mm in diameter, such as silt or clay. Fine sediment is less than 2 mm in diameter, such as pollen or seeds.
Cosmogenic sediment is material that comes from space and impacts Earth at a high speed to form a coarse deposit over large areas. This type of sediment includes meteorites and comet fragments. Astronomical objects with masses greater than 10,000 tons (or 5 million pounds) impact the Earth about every 50 years on average. The impact creates a crater up to 300 miles (500 km) wide and generates a cloud of dust and gas that blocks out sunlight for many years. This causes climate changes and can cause biological disasters if a planetoid is large enough to cause a mass extinction.
Volcanogenic sediment is material that forms when molten rock bubbles its way through Earth's crust until it hits water, which freezes into glassy droplets that are carried by the flow back to land. As these rocks cool they harden into stones, sand, and clays.
Abstract Chemical sediments are all minerals generated by inorganic processes in the sedimentary environment. They provide evidence for the type and age of the rock from which they are derived, as well as the conditions under which the rocks were deposited.
Mineral deposits on Earth are classified into three main groups: mineral veins, beds, and structures. Mineral veins contain a single type of mineral, whereas beds consist of a single layer of closely spaced crystals of a single species. Structures are defined as aggregates of mineral grains held together by a cementing material or matrix. The three main types of sedimentary structures are sills, dikes, and reefs. Sills are thin layers of rock that can be seen in outcrops and that often contains quartz or sandstone.
Dikes are steeply inclined sheets of rock that often contain quartz or sandstone. Reefs are large patches of rock that grow upward from the bottom of a body of water. Reefs may contain fossils or not; if they do, they can be used to determine the age of the ocean floor. All three of these structures are made of silicon dioxide (quartz) because it is one of the most abundant elements found in the Earth's crust.
1 Terrigenous Sediments: These sediments are created on the continents by erosion, volcanism, and wind transport. These are the most plentiful sediments. 2 Biogenous Sediments: These are sediments that have been generated by organisms. Most biogenic sediments are decomposed mineral particles from which organic material has been removed. However, there are also sediments composed of intact biological matter such as shells or bones that can be very large if they are preserved in well-drained areas where they do not accumulate waterlogging deposits.
Terrigenous sediments contain some of the same components found in terrestrial sediment: rock, sand, and clay. However, terrigenous sediment may also contain other materials in smaller amounts including metal ores, fossil fuels, and human-made objects. Marine fossils are commonly found in terrigenous sediment. In contrast, biogenic sediment does not contain any solid particles from the outside environment. Instead, it consists entirely of remains of plants and animals. Biogenic sediment is important for reconstructing past environments because it can provide information about what species were present during different times periods.
Terrigenous sediment is most common in bays, beaches, and estuaries. Fluvial sediment is carried by rivers to the sea. A mixture of fluvial and marine sediment is called allochthonous.