Biogenous ooze is marine sediment that accumulates on the seafloor and is a byproduct of the death and sink of the skeletal remains of marine organisms. [1]
Biogenous ooze consists of organic compounds, usually in the form of microorganism tests that fall from closer to the ocean surface to the ocean floor after death. For marine sediment to receive this classification, it must be composed of more than 30% skeletal material which also includes teeth and shells. [1]
The two primary types of ooze are siliceous, which is composed primarily of silica (SiO2), and calcareous or carbonate, which is mostly calcium carbonate (CaCO3). [1] In an area in which biogenous is the dominant sediment type, the composition of microorganisms in that location determines to which category it is classified. The primary types of microorganisms used to classify ooze are radiolarians and diatoms (siliceous), and coccolithophores and foraminifera (calcareous). The presence of these organisms can lead to sub-classifications based upon their dominance. [1]
Along some areas of terrigenous sediment are siliceous ooze. This is due to siliceous ooze being more abundant in areas of cooler, more nutrient rich water. The nutrients allow for the abundant growth of microorganisms, and silica dissolves slower in cooler water, allowing adequate time for deposition. [2]
Radiolarians and diatoms are the primary plankton used to classify siliceous ooze. Radiolaria is a part of a diverse group of plankton with transparent skeletons and come in a variety of shapes. They range in size from 20–400 μm (0.020–0.400 mm). They are most abundant in regions near the equator as well as subpolar regions. Diatoms are single-celled siliceous algae that are a major part of phytoplankton. They come in pinnate and centric shapes and range in size from 10–100 μm (0.010–0.100 mm). [1]
Siliceous oozes lean towards dissolution in warmer waters with lower pressures, meaning they are best preserved in deep ocean. [3]
Calcareous sediments are more common in the deep ocean, comprising about half of its surface area. [4] However, the deepest parts of the ocean are dominated by abyssal clay instead.
Calcareous debris are mostly composed of forminiferal ooze and make about almost 50% of sediments on the seafloor. Calcareous oozes also have a terrigenous fraction made up of quartz and clay minerals. [1]
This is because calcareous ooze is limited by the calcite compensation depth (CCD). The CCD refers to the depth at which the rate of supply of calcareous deposits equal the rate of dissolution and varies around the world and is based upon temperature. [1] The CCD occurs at approximately 4000-5000 meters deep [4] because calcium carbonate dissolves faster in cooler water, so as water temperature decreases with depth, its deposition rate also decreases. The temperature dependence also means that calcareous ooze is more likely to be present in warmer waters, which also leads to its dominance in shallow areas surrounding tropical and subtropical islands that do not have much terrigenous sediment runoff.
Another important depth is the lysocline, also known as the depth where well preserved calcareous grain are separated from poorly preserved ones. The lysocline occurs at approximately 3,000–5,000 metres (1.9–3.1 mi) deep. Calcareous grains above the lysocline are able to accumulate without threat of dissolution.
Despite the common association between shallow water and high productivity, biogenous ooze is not as common around continental shelves. This is due to the transport of terrigenous sediments by methods such as rivers and wind from the continents. The terrigenous sediment buries most accumulated organic material, preventing enough biological material from being present for it to be classified as biogenous.
Distribution of biogenous sediments is determined by three factors: [1]
Accumulation rate of biogenous ooze is about 1cm per 1000 years.
In the fields of paleoceanography and paleoclimatology, biogenous ooze and other pelagic sediments can be collected form the seafloor and used to reconstruct Earth's climate for the last 100 million years.
Reconstruction can be done through analysis of biogeography, stable isotopes along with important oxygen and carbon isotopes. [5]
Chert is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood.
The Radiolaria, also called Radiozoa, are protozoa of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ectoplasm. The elaborate mineral skeleton is usually made of silica. They are found as zooplankton throughout the global ocean. As zooplankton, radiolarians are primarily heterotrophic, but many have photosynthetic endosymbionts and are, therefore, considered mixotrophs. The skeletal remains of some types of radiolarians make up a large part of the cover of the ocean floor as siliceous ooze. Due to their rapid change as species and intricate skeletons, radiolarians represent an important diagnostic fossil found from the Cambrian onwards.
The lysocline is the depth in the ocean dependent upon the carbonate compensation depth (CCD), usually around 3.5 km, below which the rate of dissolution of calcite increases dramatically because of a pressure effect. While the lysocline is the upper bound of this transition zone of calcite saturation, the CCD is the lower bound of this zone.
The seabed is the bottom of the ocean. All floors of the ocean are known as 'seabeds'.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
Calcareous is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.
The carbonate compensation depth (CCD) is the depth, in the oceans, at which the rate of supply of calcium carbonates matches the rate of solvation. That is, solvation 'compensates' supply. Below the CCD solvation is faster, so that carbonate particles dissolve and the carbonate shells (tests) of animals are not preserved. Carbonate particles cannot accumulate in the sediments where the sea floor is below this depth.
Pelagic sediment or pelagite is a fine-grained sediment that accumulates as the result of the settling of particles to the floor of the open ocean, far from land. These particles consist primarily of either the microscopic, calcareous or siliceous shells of phytoplankton or zooplankton; clay-size siliciclastic sediment; or some mixture of these. Trace amounts of meteoric dust and variable amounts of volcanic ash also occur within pelagic sediments. Based upon the composition of the ooze, there are three main types of pelagic sediments: siliceous oozes, calcareous oozes, and red clays.
Lithogenic silica (LSi) is silica (SiO2) derived from terrigenous rock (Igneous, metamorphic, and sedimentary), lithogenic sediments composed of the detritus of pre-existing rock, volcanic ejecta, extraterrestrial material, and minerals such silicate. Silica is the most abundant compound in the earth's crust (59%) and the main component of almost every rock (>95%).
Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plants.
Radiolarite is a siliceous, comparatively hard, fine-grained, chert-like, and homogeneous sedimentary rock that is composed predominantly of the microscopic remains of radiolarians. This term is also used for indurated radiolarian oozes and sometimes as a synonym of radiolarian earth. However, radiolarian earth is typically regarded by Earth scientists to be the unconsolidated equivalent of a radiolarite. A radiolarian chert is well-bedded, microcrystalline radiolarite that has a well-developed siliceous cement or groundmass.
Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles have their origins in soil and rocks and have been transported from the land to the sea, mainly by rivers but also by dust carried by wind and by the flow of glaciers into the sea. Additional deposits come from marine organisms and chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris.
Siliceous ooze 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 SiO2·nH2O, as opposed to calcareous oozes, which are made from skeletons of calcium carbonate (CaCO3·nH2O) organisms (i.e. coccolithophores). Silica (Si) 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.
Hemipelagic sediment, or hemipelagite, is a type of marine sediment that consists of clay and silt-sized grains that are terrigenous and some biogenic material derived from the landmass nearest the deposits or from organisms living in the water. Hemipelagic sediments are deposited on continental shelves and continental rises, and differ from pelagic sediment compositionally. Pelagic sediment is composed of primarily biogenic material from organisms living in the water column or on the seafloor and contains little to no terrigenous material. Terrigenous material includes minerals from the lithosphere like feldspar or quartz. Volcanism on land, wind blown sediments as well as particulates discharged from rivers can contribute to Hemipelagic deposits. These deposits can be used to qualify climatic changes and identify changes in sediment provenances.
Marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism is any microscopic living organism or virus, that is too small to see with the unaided human eye without magnification. Microorganisms are very diverse. They can be single-celled or multicellular and include bacteria, archaea, viruses and most protozoa, as well as some fungi, algae, and animals, such as rotifers and copepods. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses as microorganisms, but others consider these as non-living.
The Ruhpolding Formation is a sedimentary formation of the Northern Calcareous Alps deposited during the Upper Jurassic. The open marine radiolarite is very rich in silica.
Pelagic red clay, also known as simply red clay, brown clay or pelagic clay, is a type of pelagic sediment.
Takuyo-Daisan is a guyot in the Western Pacific Ocean off Japan. It is 1,409 metres (4,623 ft) deep and has a square-shaped flat top surrounded by a perimeter ridge. Several other seamounts lie nearby.
The silica cycle is the biogeochemical cycle in which biogenic silica is transported between the Earth's systems. Silicon is considered a bioessential element and is one of the most abundant elements on Earth. The silica cycle has significant overlap with the carbon cycle and plays an important role in the sequestration of carbon through continental weathering, biogenic export and burial as oozes on geologic timescales.
Madeira Abyssal Plain, also called Madeira Plain, is an abyssal plain situated at the center and deepest part of the Canary Basin. It is a north-northeast to south-southeast elongated basin that almost parallels the Mid-Atlantic Ridge. Its western boundary is marked by a chain of seamounts known as the either Seewarte Seamounts or Atlantis-Great Meteor Seamount Chain. Its eastern boundary is a distinct break of slope that marks the foot of the African Continental Rise. This abyssal plain occupies an area of about 68,000 km2 (26,000 sq mi). Across this basin, slope angles are generally less than 0.01°.
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