A calcite sea is one in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-magnesium calcite are the primary inorganic carbonate precipitates; the Early Paleozoic and the Middle to Late Mesozoic oceans were predominantly calcite seas, whereas the Middle Paleozoic through the Early Mesozoic and the Cenozoic are characterized by aragonite seas. The most significant geological and biological effects of calcite sea conditions include rapid and widespread formation of carbonate hardgrounds, calcitic ooids, calcite cements, the contemporaneous dissolution of aragonite shells in shallow warm seas. Hardgrounds were common, for example, in the calcite seas of the Ordovician and Jurassic, but absent from the aragonite seas of the Permian. Fossils of invertebrate organisms found in calcite sea deposits are dominated by either thick calcite shells and skeletons, were infaunal and/or had thick periostraca, or had an inner shell of aragonite and an outer shell of calcite.
This was because aragonite dissolved on the seafloor and had to be either avoided or protected as a biomineral. Calcite seas were coincident with times of rapid seafloor spreading and global greenhouse climate conditions. Seafloor spreading centers cycle seawater through hydrothermal vents, reducing the ratio of magnesium to calcium in the seawater through metamorphism of calcium-rich minerals in basalt to magnesium-rich clays; this reduction in the Mg/Ca ratio favors the precipitation of calcite over aragonite. Increased seafloor spreading means increased volcanism and elevated levels of carbon dioxide in the atmosphere and oceans; this may have an effect on which polymorph of calcium carbonate is precipitated. Further, high calcium concentrations of seawater favor the burial of CaCO3, thereby removing alkalinity from the ocean, lowering seawater pH and reducing its acid/base buffering. Cherns, L.. P.. "Missing molluscs as evidence of large-scale, early skeletal aragonite dissolution in a Silurian Sea".
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Utah is a state in the western United States. It became the 45th state admitted to the U. S. on January 4, 1896. Utah is the 13th-largest by area, 31st-most-populous, 10th-least-densely populated of the 50 United States. Utah has a population of more than 3 million according to the Census estimate for July 1, 2016. Urban development is concentrated in two areas: the Wasatch Front in the north-central part of the state, which contains 2.5 million people. Utah is bordered by Colorado to the east, Wyoming to the northeast, Idaho to the north, Arizona to the south, Nevada to the west, it touches a corner of New Mexico in the southeast. 62% of Utahns are reported to be members of The Church of Jesus Christ of Latter-day Saints, making Utah the only state with a majority population belonging to a single church. This influences Utahn culture and daily life; the LDS Church's world headquarters is located in Salt Lake City. The state is a center of transportation, information technology and research, government services, a major tourist destination for outdoor recreation.
In 2013, the U. S. Census Bureau estimated. St. George was the fastest-growing metropolitan area in the United States from 2000 to 2005. Utah has the 14th highest median average income and the least income inequality of any U. S. state. A 2012 Gallup national survey found Utah overall to be the "best state to live in" based on 13 forward-looking measurements including various economic and health-related outlook metrics. A common folk etymology is that the name "Utah" is derived from the name of the Ute tribe, purported to mean "people of the mountains" in the Ute language. However, the word for people in Ute is'núuchiu' while the word for mountain is'káav', offering no linguistic connection to the words'Ute' or'Utah'. According to other sources "Utah" is derived from the Apache name "yuttahih" which means "One, Higher up" or "Those that are higher up". In the Spanish language it was said as "Yuta", subsequently the English-speaking people adapted the word "Utah". Thousands of years before the arrival of European explorers, the Ancestral Puebloans and the Fremont people lived in what is now known as Utah, some of which spoke languages of the Uto-Aztecan group.
Ancestral Pueblo peoples built their homes through excavations in mountains, the Fremont people built houses of straw before disappearing from the region around the 15th century. Another group of Native Americans, the Navajo, settled in the region around the 18th century. In the mid-18th century, other Uto-Aztecan tribes, including the Goshute, the Paiute, the Shoshone, the Ute people settled in the region; these five groups were present. The southern Utah region was explored by the Spanish in 1540, led by Francisco Vásquez de Coronado, while looking for the legendary Cíbola. A group led by two Catholic priests—sometimes called the Dominguez-Escalante Expedition—left Santa Fe in 1776, hoping to find a route to the coast of California; the expedition encountered the native residents. The Spanish made further explorations in the region, but were not interested in colonizing the area because of its desert nature. In 1821, the year Mexico achieved its independence from Spain, the region became known as part of its territory of Alta California.
European trappers and fur traders explored some areas of Utah in the early 19th century from Canada and the United States. The city of Provo, Utah was named for one, Étienne Provost, who visited the area in 1825; the city of Ogden, Utah was named after Peter Skene Ogden, a Canadian explorer who traded furs in the Weber Valley. In late 1824, Jim Bridger became the first known English-speaking person to sight the Great Salt Lake. Due to the high salinity of its waters, He thought. After the discovery of the lake, hundreds of American and Canadian traders and trappers established trading posts in the region. In the 1830s, thousands of migrants traveling from the Eastern United States to the American West began to make stops in the region of the Great Salt Lake known as Lake Youta. Following the death of Joseph Smith in 1844, Brigham Young, as president of the Quorum of the Twelve, became the effective leader of the LDS Church in Nauvoo, Illinois. To address the growing conflicts between his people and their neighbors, Young agreed with Illinois Governor Thomas Ford in October 1845 that the Mormons would leave by the following year.
Young and the first band of Mormon pioneers reached the Salt Lake Valley on July 24, 1847. Over the next 22 years, more than 70,000 pioneers settled in Utah. For the first few years, Brigham Young and the thousands of early settlers of Salt Lake City struggled to survive; the arid desert land was deemed by the Mormons as desirable as a place where they could practice their religion without harassment. The Mormon settlements provided pioneers for other settlements in the West. Salt Lake City became the hub of a "far-flung commonwealth" of Mormon settlements. With new church converts coming from the East and around the world, Church leaders assigned groups of church members as missionaries to establish other settlements throughout the West, they developed irrigation to support large pioneer populations along Utah's Wasatch front. Throughout the remainder of the 19th century, Mormon pioneers established hundreds of other settlements in Utah, Id
Crinoids are marine animals that make up the class Crinoidea, one of the classes of the phylum Echinodermata, which includes the starfish, brittle stars, sea urchins and sea cucumbers. Those crinoids which in their adult form are attached to the sea bottom by a stalk are called sea lilies, while the unstalked forms are called feather stars or comatulids, being members of the largest crinoid order Comatulida. Adult crinoids are characterised by having the mouth located on the upper surface; this is surrounded by feeding arms, is linked to a U-shaped gut, with the anus being located on the oral disc near the mouth. Although the basic echinoderm pattern of fivefold symmetry can be recognised, in most crinoids the five arms are subdivided into ten or more; these are spread wide to gather planktonic particles from the water. At some stage in their life, most crinoids have a stem used to attach themselves to the substrate, but many live attached only as juveniles and become free-swimming as adults.
There are only about 600 living species of crinoid, but the class was much more abundant and diverse in the past. Some thick limestone beds dating to the mid- to late-Paleozoic era are entirely made up of disarticulated crinoid fragments; the name "Crinoidea" comes from the Greek word κρίνος, "a lily", with the suffix –oid meaning "like". They live in depths as great as 9,000 meters; those crinoids which in their adult form are attached to the sea bottom by a stalk are called sea lilies. The unstalked forms are called feather stars or comatulids, being members of the largest crinoid order, Comatulida; the basic body form of a crinoid is a stem and a crown consisting of a cup-like central body known as the theca, a set of five rays or arms branched and feathery. The mouth and anus are both located on the upper side of the theca, making the dorsal surface the oral surface, unlike in the other echinoderm groups such as the sea urchins and brittle stars where the mouth is on the underside; the numerous calcareous plates make up the bulk of the crinoid, with only a small percentage of soft tissue.
These ossicles fossilise well and there are beds of limestone dating from the Lower Carboniferous around Clitheroe, formed exclusively from a diverse fauna of crinoid fossils. The stem of sea lilies is composed of a column of porous ossicles which are connected by ligamentary tissue, it attaches to the substrate with a flattened holdfast or with whorls of jointed, root-like structures known as cirri. Further cirri may occur higher up the stem. In crinoids that attach to hard surfaces, the cirri may be robust and curved, resembling birds' feet, but when crinoids live on soft sediment, the cirri may be slender and rod-like. Juvenile feather stars have a stem, but this is lost, with many species retaining a few cirri at the base of the crown; the majority of living crinoids have only a vestigial stalk. In those deep-sea species that still retain a stalk, it may reach up to 1 m in length, fossil species are known with 20 m stems; the theca is homologous with the body or disc of other echinoderms. The base of the theca is formed from a cup-shaped set of ossicles, the calyx, while the upper surface is formed by the weakly-calcified tegmen, a mebranous disc.
The tegmen is divided into five "ambulacral areas", including a deep groove from which the tube feet project, five "interambulacral areas" between them. The mouth is near the centre or on the margin of the tegmen, ambulacral grooves lead from the base of the arms to the mouth; the anus is located on the tegmen on a small elevated cone, in an interambulacral area. The theca is small and contains the crinoid's digestive organs; the arms are supported by a series of articulating ossicles similar to those in the stalk. Primitively, crinoids had only five arms, but in most modern forms these are divided into two at ossicle II, giving ten arms in total. In most living species the free-swimming feather stars, the arms branch several more times, producing up to two hundred branches in total. Being jointed, the arms can curl up, they and lined, on either side alternately, by smaller jointed appendages known as "pinnules" which give them their feather-like appearance. Both arms and pinnules have tube feet along the margins of the ambulacral grooves.
The tube feet come in groups of three of different size. The grooves are equipped with cilia which facilitate feeding by moving the organic particles along the arm and into the mouth. Crinoids are passive suspension feeders, filtering plankton and small particles of detritus from the sea water flowing past them with their feather-like arms; the arms are raised to form a fan-shape, held perpendicular to the current. Mobile crinoids move to perch on rocks, coral heads or other eminences to maximise their feeding opportunities; the food particles are caught by the primary tube feet, which are extended and held erect from the pinnules, forming a food-trapping mesh, while the secondary and tertiary tube feet are involved in manipulating anything encountered. The tube feet are covered with sticky mucus. Once they have caught a particle of food, the tube feet flick it into the ambulacral groove, where the cilia propel the mucus and food particles towards the mouth. Lappets at the side of the groove help keep the mucus stream in place.
The total length of the food-trapping surface may be large.
Bryozoa are a phylum of aquatic invertebrate animals. About 0.5 millimetres long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia. Most marine species live in tropical waters, but a few occur in oceanic trenches, others are found in polar waters. One class lives only in a variety of freshwater environments, a few members of a marine class prefer brackish water. Over 4,000 living species are known. One genus is solitary and the rest are colonial; the phylum was called "Polyzoa", but this term was superseded by "Bryozoa" in 1831. Another group of animals discovered subsequently, whose filtering mechanism looked similar, was included in "Bryozoa" until 1869, when the two groups were noted to be different internally; the more discovered group was given the name Entoprocta, while the original "Bryozoa" were called "Ectoprocta". However, "Bryozoa" has remained the more used term for the latter group. Individuals in bryozoan colonies are called zooids, since they are not independent animals.
All colonies contain autozooids, which are responsible for excretion. Colonies of some classes have various types of non-feeding specialist zooids, some of which are hatcheries for fertilized eggs, some classes have special zooids for defense of the colony; the class Cheilostomata have the largest number of species because they have the widest range of specialist zooids. A few species can creep slowly by using spiny defensive zooids as legs. Autozooids supply nutrients to non-feeding zooids by channels. All zooids, including those of the solitary species, consist of a cystid that provides the body wall and produces the exoskeleton and a polypide that contains the internal organs and the lophophore or other specialist extensions. Zooids have no special excretory organs, the polypides of autozooids are scrapped when the polypides become overloaded by waste products. In autozooids the gut is U-shaped, with the mouth inside the "crown" of tentacles and the anus outside it. Colonies take a variety of forms, including fans and sheets.
The Cheilostomata produce mineralized exoskeletons and form single-layered sheets which encrust over surfaces. Zooids of all the freshwater species are simultaneous hermaphrodites. Although those of many marine species function first as males and as females, their colonies always contain a combination of zooids that are in their male and female stages. All species emit sperm into the water; some release ova into the water, while others capture sperm via their tentacles to fertilize their ova internally. In some species the larvae have large yolks, go to feed, settle on a surface. Others feed for a few days before settling. After settling, all larvae undergo a radical metamorphosis that destroys and rebuilds all the internal tissues. Freshwater species produce statoblasts that lie dormant until conditions are favorable, which enables a colony's lineage to survive if severe conditions kill the mother colony. Predators of marine bryozoans include nudibranchs, sea urchins, crustaceans and starfish.
Freshwater bryozoans are preyed on by snails and fish. In Thailand, many populations of one freshwater species have been wiped out by an introduced species of snail. A fast-growing invasive bryozoan off the northeast and northwest coasts of the US has reduced kelp forests so much that it has affected local fish and invertebrate populations. Bryozoans have spread diseases to fish fishermen. Chemicals extracted from a marine bryozoan species have been investigated for treatment of cancer and Alzheimer's disease, but analyses have not been encouraging. Mineralized skeletons of bryozoans first appear in rocks from the Early Ordovician period, making it the last major phylum to appear in the fossil record; this has led researchers to suspect that bryozoans arose earlier but were unmineralized, may have differed from fossilized and modern forms. Early fossils are of erect forms, but encrusting forms became dominant, it is uncertain. Bryozoans' evolutionary relationships to other phyla are unclear because scientists' view of the family tree of animals is influenced by better-known phyla.
Both morphological and molecular phylogeny analyses disagree over bryozoans' relationships with entoprocts, about whether bryozoans should be grouped with brachiopods and phoronids in Lophophorata, whether bryozoans should be considered protostomes or deuterostomes. Bryozoans and brachiopods strain food out of the water by means of a lophophore, a "crown" of hollow tentacles. Bryozoans form colonies consisting of clones called zooids that are about 0.5 millimetres long. Phoronids resemble bryozoan zooids but are 2 to 20 centimetres long and, although they grow in clumps, do not form colonies consisting of clones. Brachiopods thought to be related to bryozoans and phoronids, are distinguished by having shells rather like those of bivalves. All three of these phyla have a coelom, an internal cavity lined by mesothelium; some encrusting bryozoan colonies with mineralized exoskeletons look like small corals. However, bryozoan colonies are founded by an ancestrula, round rather than shaped like a normal zooid of that species.
On the other hand, the founding
Marker horizons or chronohorizons or marker beds are stratigraphic units of the same age and of such distinctive composition and appearance, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age and of common origin. Such clear markers facilitate the correlation of strata, used in conjunction with fossil floral and faunal assemblages and paleomagnetism, permit the mapping of land masses and bodies of water throughout the history of the earth. Palynology, the study of fossil pollens and spores works out the stratigraphy of rocks by comparing pollen and spore assemblages with those of well-known layers - a tool used by petroleum exploration companies in the search for new fields; the fossilised teeth or elements of Conodonts are an useful tool. The ejecta from volcanoes and bolide impacts create useful markers, as different volcanic eruptions and impacts produce beds with distinctive compositions. Marker horizons of tephra are used as a dating tool in archaeology, since the dates of eruptions are well-established.
One particular bolide impact 66 million years ago, Chicxulub, is controversially held to have led to a major extinction event and produced an iridium anomaly that occurs in a thin, global layer of clay marking the Cretaceous–Paleogene boundary. Iridium layers are associated with bolide impacts and are not unique, but when occurring in conjunction with the extinction of specialised tropical planktic foraminifera and the appearance of the first Danian species, signal a reliable marker horizon for the Cretaceous–Paleogene boundary. Fossil faunal and floral assemblages, both marine and terrestrial, make for distinctive marker horizons; some marker units are distinctive by virtue of their magnetic qualities. The Water Tower Slates, forming part of the Hospital Hill Series in the Witwatersrand Basin, include a fine-grained ferruginous quartzite, magnetic. From the same series a ripple-marked quartzite and a speckled bed are used as marker horizons. On a much smaller time scale, marker horizons may be created by sedimentologists and limnologists in order to measure deposition and erosion rates in a marsh or pond environment.
The materials used for such an artificial horizon are chosen for their visibility and stability and may be brick dust, sand, glitter or feldspar clay. Historical Geology of South Africa - JF Truswell International Stratigraphic Guide - Geological Society of America - Amos Salvador
Limestone is a carbonate sedimentary rock, composed of the skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. A related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. About 10% of sedimentary rocks are limestones; the solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as foraminifera; these organisms secrete shells made of aragonite or calcite, leave these shells behind when they die. Other carbonate grains composing limestones are ooids, peloids and extraclasts. Limestone contains variable amounts of silica in the form of chert or siliceous skeletal fragment, varying amounts of clay and sand carried in by rivers; some limestones do not consist of grains, are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters; this produces speleothems, such as stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance; the primary source of the calcite in limestone is most marine organisms. Some of these organisms can construct mounds of rock building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone does not form in deeper waters.
Limestones may form in lacustrine and evaporite depositional environments. Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors with weathered surfaces. Limestone may be crystalline, granular, or massive, depending on the method of formation. Crystals of calcite, dolomite or barite may line small cavities in the rock; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble. Limestone is a parent material of Mollisol soil group. Two major classification schemes, the Folk and the Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems and cement; the Folk system uses two-part names. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample; the Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains. Robert J. Dunham published his system for limestone in 1962.
Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are for rock families, his efforts deal with the question of whether or not the grains were in mutual contact, therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock; the Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright, it adds some diagenetic patterns and can be summarized as follows: See: Carbonate platform About 10% of all sedimentary rocks are limestones. Limestone is soluble in acid, therefore forms many erosional landforms; these include limestone pavements, pot holes, cenotes and gorges. Such erosion landscapes are known
Hederellids are extinct colonial animals with calcitic tubular branching exoskeletons. They were most common in the Devonian period, they are more properly known as "hederelloids" because they were defined as a suborder by Bassler, who described about 130 species. Although they have traditionally been considered bryozoans, they are not because of their branching patterns, lack of an astogenetic gradient, skeletal microstructure, wide range in tube diameters. Work continues on assessing the true affinities of hederelloids, but they appear to be most related to phoronids and other lophophorates. Family Hederellidae Genus Diversipora Genus Hederella Family Reptariidae Genus Cystoporella Genus Hederopsis Genus Hernodia Bassler, R. S; the Hederelloidea. A suborder of Paleozoic cyclostomatous Bryozoa. Proceedings of the United States National Museum, 87:25-91. Taylor, Paul D.. "Evolution of biomineralization in'Lophophorates'". Special Papers in Palaeontology. 84: 317–333. Doi:10.1111/j.1475-4983.2010.00985.x.
Taylor, P. D. and Wilson, M. A. Morphology and affinities of hederelloid "bryozoans", p. 301-309. In: Hageman, S. J. Key, M. M. Jr. and Winston, J. E. Bryozoan Studies 2007: Proceedings of the 14th International Bryozoology Conference, North Carolina, July 1–8, 2007. Virginia Museum of Natural History Special Publication 15. Wilson, M. A. and Taylor, P. D. "Pseudobryozoans" and the problem of encruster diversity in the Paleozoic. PaleoBios, 21:134-135. Wilson, M. A.. "Predatory drillholes and partial mortality in Devonian colonial metazoans". Geology. 34: 565–568. Doi:10.1130/G22468.1