Limestone is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of CaCO3. Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life.
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.
An atoll is a ring-shaped island, including a coral rim that encircles a lagoon. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical parts of the oceans and seas where corals can develop. Most of the approximately 440 atolls in the world are in the Pacific Ocean.
A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic (non-living) processes such as deposition of sand or wave erosion planing down rock outcrops. However, reefs such as the coral reefs of tropical waters are formed by biotic (living) processes, dominated by corals and coralline algae. Artificial reefs such as shipwrecks and other man-made underwater structures may occur intentionally or as the result of an accident, and are sometimes designed to increase the physical complexity of featureless sand bottoms to attract a more diverse range of organisms. Reefs are often quite near to the surface, but not all definitions require this.
A cay, also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef. Cays occur in tropical environments throughout the Pacific, Atlantic, and Indian oceans, including in the Caribbean and on the Great Barrier Reef and Belize Barrier Reef.
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxide (P2O5). Marketed phosphate rock is enriched ("beneficiated") to at least 28%, often more than 30% P2O5. This occurs through washing, screening, de-liming, magnetic separation or flotation. By comparison, the average phosphorus content of sedimentary rocks is less than 0.2%. The phosphate is present as fluorapatite Ca5(PO4)3F typically in cryptocrystalline masses (grain sizes < 1 μm) referred to as collophane-sedimentary apatite deposits of uncertain origin. It is also present as hydroxyapatite Ca5(PO4)3OH or Ca10(PO4)6(OH)2, which is often dissolved from vertebrate bones and teeth, whereas fluorapatite can originate from hydrothermal veins. Other sources also include chemically dissolved phosphate minerals from igneous and metamorphic rocks. Phosphorite deposits often occur in extensive layers, which cumulatively cover tens of thousands of square kilometres of the Earth's crust.
A sabkha is a coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coastal plains just above normal high-tide level. Within a sabkha, evaporite-saline minerals sediments typically accumulate below the surface of mudflats or sandflats. Evaporite-saline minerals, tidal-flood, and aeolian deposits characterize many sabkhas found along modern coastlines. The accepted type locality for a sabkha is at the southern coast of the Persian Gulf, in the United Arab Emirates. Evidence of clastic sabkhas are found in the geological record of many areas, including the UK and Ireland. Sabkha is a phonetic transliteration of the Arabic word used to describe any form of salt flat. A sabkha is also known as a sabkhah,sebkha, or coastal sabkha.
Cyclic sediments are sequences of sedimentary rocks that are characterised by repetitive patterns of different rock types (strata) or facies within the sequence. Processes that generate sedimentary cyclicity can be either autocyclic or allocyclic, and can result in piles of sedimentary cycles hundreds or even thousands of metres thick. The study of sequence stratigraphy was developed from controversies over the causes of cyclic sedimentation.
In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record. In most cases, the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the further back in geological time sediments were deposited, the more likely that direct modern analogues are not available.
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.
A fringing reef is one of the three main types of coral reef. It is distinguished from the other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows directly from the shoreline, then the reef flat extends to the beach and there is no backreef. In other cases, fringing reefs may grow hundreds of yards from shore and contain extensive backreef areas within which it contains food and water, examples are Philippines, Indonesia, Timor-Leste, the western coast of Australia, the Caribbean, East Africa, and Red Sea. Charles Darwin believed that fringing reefs are the first kind of reefs to form around a landmass in a long-term reef growth process. The largest fringing coral reef in the world is the Ningaloo Reef, stretching to around 260 km (160 mi) along the coastline of Western Australia.
The Aganane Formation is a Pliensbachian geologic formation in the Azilal, Béni-Mellal, Ouarzazate, Tinerhir and Errachidia provinces, central Morocco, being the remnant of a local massive Carbonate platform, and known mostly for its rich tracksites including footprints of thyreophoran, sauropod and theropod dinosaurs. This formation has been dated to the Pliensbachian stage of the Lower Jurassic, thanks to the find of the ammonite Arieticeras cf. algovianum, indicator of Middle Domerian in the upper zone, and lower delimitation by the foraminifers Mayncina termieri and Orbitopsella praecursor. The dinosaur tracksites are all located a few metres below the Pliensbachian-Toarcian limit, being coeval and connected with the lowermost layers of the continental Azilal Formation. The Aganane Formation was also coeval with the Jbel Taguendouft Formation and the Tamadout 1 Formation, all developed along a local "platform-furrow" in the Middle Atlas Mountains, that act as a barrier controlling the western border of the Jurassic Atlas Gulf. The nearshore sections, including both carbonate platforms and close to sea terrestrial facies where located on an isolated internal domain thanks to the control of the barrier, allowing the Aganane Formation to develop on a hot and humid climate, where a local algal marsh had intermittent progradations, intercalated with a layer of terrigenous continental origin. The ichnosites were developed in tidal flats and coastal deposits suitable to sea flooding.
The Elk Point Group is a stratigraphic unit of Early to Middle Devonian age in the Western Canada and Williston sedimentary basins. It underlies a large area that extends from the southern boundary of the Northwest Territories in Canada to North Dakota in the United States. It has been subdivided into numerous formations, number of which host major petroleum and natural gas reservoirs.
In geology, intraclasts are irregularly-shaped grains that form by syndepositional erosion of partially-lithified sediment. Gravel grade material is generally composed of whole disarticulated or broken skeletal fragments together with sand grade material of whole, disaggregated and broken skeletal debris. Such sediments can contain fragments of early cemented limestones of local origin which are known as intraclasts.
Shallow water marine environment refers to the area between the shore and deeper water, such as a reef wall or a shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below. The water in this environment is shallow and clear, allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.
San Cassiano Formation (Anisian-Carnian) is a geologic formation located on the Southern Alps in the Dolomites. These Triassic dolomites are considered to be a classic example of ancient carbonate platforms. As the allochthonous elements in the Shale strata show a good preservation, fossils and microbialites contained in these elements are useful in detailed geochemical analyses.
The marine ecoregions of the South African exclusive economic zone are a set of geographically delineated regions of similar ecological characteristics on a fairly broad scale, covering the exclusive economic zone along the South African coast.
Automicrite is autochthonous micrite, that is, a carbonate mud precipitated in situ and made up of fine-grained calcite or aragonite micron-sized crystals. It precipitates on the sea floor or within the sediment as an authigenic mud thanks to physicochemical, microbial, photosynthetic and biochemical processes. It has peculiar fabrics and uniform mineralogical and chemical composition.
Darwin Guyot is a volcanic underwater mountain top, or guyot, in the Mid-Pacific Mountains between the Marshall Islands and Hawaii. Named after Charles Darwin, it rose above sea level more than 118 million years ago during the early Cretaceous period to become an atoll, developed rudist reefs, and then drowned, perhaps as a consequence of sea level rise. The flat top of Darwin Guyot now rests 1,266 metres (4,154 ft) below sea level.
The Azilal Formation, also known as Toundoute Continental Series and Wazzant Formation, is a geological unit in the Azilal, Béni-Mellal, Ouarzazate, Tinerhir and Errachidia provinces of the High Atlas of Morocco, that cover the Latest Pliensbachian to Middle Aalenian stages of the Jurassic Period. It is a terrestrial deposit which overlies marine dolomites of equivalent age to the Rotzo Formation of Italy, mostly part of the Aganane Formation. Dinosaur remains, such the sauropod Tazoudasaurus and the basal ceratosaur Berberosaurus are known from the unit, along with several undescribed genera. The Units inside the group have been considered individual on the past, being a division of the so-called "Couches rouges", and subdivided by a supposed geological scale. The strata of the group extends towards the Central High Atlas, covering different anticlines, and topographic accidents along the range of the Mountains. Although new studies have suggested that the strata is coeval in age, and should be referred to as a unique unit. The formation is best assigned to an alluvial environment occasionally interrupted by shallow marine incursions and marks a dramatic decrease of the carbonate productivity under increasing terrigenous sedimentation. The Azilal Formation consists mainly of claystones rich in continental plant debris and laminated microbial facies. The toarcian High Atlas is divided in 5 units: the continental layers with paralic deposits belong to the Azilal, along the shoreface layers of the Tagoudite Formation and Tafraout Formation, both connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation.
