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, [1] allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.
The sediment itself is often composed of limestone, which forms readily in shallow, warm calm waters. The shallow marine environments are not exclusively composed of siliciclastic or carbonaceous sediments. While they cannot always coexist, it is possible to have a shallow marine environment composed solely of carbonaceous sediment or one that is composed completely of siliciclastic sediment. Shallow water marine sediment is made up of larger grain sizes because smaller grains have been washed out to deeper water. Within sedimentary rocks composed of carbonaceous sediment, there may also be evaporite minerals. [2] The most common evaporite minerals found within modern and ancient deposits are gypsum, anhydrite, and halite; they can occur as crystalline layers, isolated crystals or clusters of crystals. [2]
In terms of geologic time, it is said that most Phanerozoic sedimentary rock was deposited in shallow marine environments as about 75% of the sedimentary carapace is made up of shallow marine sediments; it is then assumed that Precambrian sedimentary rocks were too, deposited in shallow marine waters, unless it is specifically identified otherwise. [3] This trend is seen in the North American and Caribbean region. [4] Also, as a result of supercontinent breakup and other shifting tectonic plate processes, shallow marine sediment displays large variations in terms of quantity in the geologic time. [4]
Various types of structures form in shallow marine environments. For example, Graded-bedding, which occurs when beds have vertical gradation in grain size, with the smallest grains at the top. Also, Ripples, which are the smallest bedform type, and dunes, which are similar to ripples except are larger. [1]
Carbonaceous sedimentary rocks with several kinds of sedimentary structures within them can be found in shallow marine environments; they are a group of rocks that have a significant amount of non-skeletal matter along with siliciclastic or chemical constituents. [1] Some examples include:
Cross stratification is a layering structure found in gravel, sand, and coarse silt-sized sediment; the strata are distinct layers of sediment that are steeply inclined to the underlying surfaces of the deposit. [2]
Desiccation cracks are cracks formed due to drying out of newly deposited mud; these form in sub-aerial climates. [2]
Syneresis cracks are cracks in mud formed by mechanisms other than sub-aerial climate exposure. These mechanisms include Contraction caused by the clumping of settled clay sediment, contraction due to the deposition/compaction of a settling clay layer during faulting, compaction of smectitic clay because of lost interlayer water due to a change in salinity in surrounding water, compaction dewatering under sediment causing injection from below or collapsing from above, and tensional openings due to down-sloping of a surface mud layer. [2]
Fenestrae is an open or partially filled space occupied by different sediment or cement in the rock. [2]
Flame structures is mud shaped like flames that intrude the overlying layer of rock. [1]
Convolute folds are complicated folds in beds into irregular anticlines and/or synclines. [1]
Flutes are outstretched ridges that are rounded at one end and flared at the other. [1]
Groove casts are outstretched, almost straight grooves in sediment caused by the dragging of an object such as a rock, piece of wood, etc. [1]
Chevron structures are a type of groove cast that is v-shaped as a result of two or more stress directions; they occur on the bottoms of beds deposited in shallow water environments. [1]
The water in this environment is mostly clear and shallow. It is said that if shallow marine environments can be defined by their distributional patterns of marine organisms in terms of temperature, then deductions can be made from that of the past patterns in terms of paleolithic zones. Today, there are 3 major defining criteria used in defining shallow marine environments, these are The faunal provinces, the faunal elements, and the degree of latitude. However, the limits of different present-day shallow marine environments in terms of climatic zones are seldom agreed on. [5]
Also, many shallow marine environments are often associated with carbonate factory zones. In these zones, processes that remove the CO₂ from water to cause the bicarbonate ions to change into carbonate ions are important and support lime precipitation. Increasing temperature, intense evaporation, and mixing water that is high in CO₃ and low in calcium cations with seawater are some examples of processes that change bicarbonate ions to carbonate ions. Carbon dioxide is removed from the atmosphere by being dissolved in water and is turned into carbonic acid. The carbonic acid then weathers rocks, creating bicarbonate and other ions. Then the calcium carbonate is a precipitate from calcium and the bicarbonate ions that formed through organisms like coral, and then the carbon is stored in layers of limestone on the seafloor. In terms of geologic time, the composition of limestone has changed from calcite rich limestone to aragonite rich limestone. The presence of magnesium ions at certain concentrations inhibits the ability to precipitate calcite. Aragonite, however, has the same chemical formula as calcite but it is in a different crystal system that is much less prone to the magnesium preventing the precipitation of this mineral, which would prevent it from forming carbonate rocks. At times in geologic history where the Mg and Ca ratio were different, and the seas were more abundant in calcite and this was as a result of the high rates of seafloor spreading because of tectonic plate movement and action. The more spreading, the more the Magnesium gets removed, so more calcite is precipitated, and calcite will be more abundant than aragonite. [1]
Some organisms in this environment, specifically those in the intertidal zone, are starfish, sea anemones, sponges, marine worms, clams, mussels, predatory crustaceans, barnacles and small fish. [6] Hydrozoa, or hydroids, also live in shallow marine ecosystems and eat surrounding algae and zooplankton. [7] Some species of isopods and amphipods are found in the intertidal zones and create several different burrows and surface tracks in the sediment. [8] Brittle stars have been seen buried in sediment with their arms showing through the sediment; this behaviour has been noted in several shallow marine areas. [8]
As well, carbonate reefs can be found in the depositional environment that is shallow marine areas; they are host to reefs and organisms that reside in reefs. Recent estimates regarding the numbers of species on coral reefs range from 1–9 million. [9] There are 3 main types of reef formations: fringing reefs, these reefs are attached to the shore, barrier reefs, which are separated from mainland by a lagoon, and atoll reefs. [1] Organisms that live in this environment include red algae, green algae, bivalves and echinoderms. [1] Many of these organisms contribute to the formation of reefs. [1] Also, unicellular dinoflagellates live in the tissues of corals, and have a mutualistic relationship in which the dinoflagellates provide the corals with organic molecules. [6]
The vast majority of the fossil record has been found after the shallow water marine environment has been lithified. Many of these fossils were deposited at times when much of Earth was covered with shallow seas, supporting a wide variety of organisms.
Several fossils can be found/formed in this environment. Some examples include:
Skolithos Ichnofacies are trace fossils that are vertical, cylindrical or U-shaped burrows created by organisms for protection. [1]
Glossifungites ichnofacies are trace fossils that are vertical, cylindrical, U or tear-shaped borings or burrows created by organisms like shrimp, crabs, worms and bivalves. [1]
Stromatolites are fossils that are laminated sedimentary structures that form when cyanobacteria form microbial mats which then trap clay and/or silt sediment and organic materials to form the fossil. [1]
Limestone is a common 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 calcium carbonate. 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, and these 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.
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 processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but there are also reefs such as the coral reefs of tropical waters formed by biotic processes dominated by corals and coralline algae, and artificial reefs such as shipwrecks and other anthropogenic underwater structures may occur intentionally or as the result of an accident, and sometimes have a designed role in enhancing the physical complexity of featureless sand bottoms, to attract a more diverse assemblage of organisms. Reefs are often quite near to the surface, but not all definitions require this.
Ooids are small, spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals. Ooids usually form on the sea floor, most commonly in shallow tropical seas. After being buried under additional sediment, these ooid grains can be cemented together to form a sedimentary rock called an oolite. Oolites usually consist of calcium carbonate; these belong to the limestone rock family. Pisoids are similar to ooids, but are larger than 2 mm in diameter, often considerably larger, as with the pisoids in the hot springs at Carlsbad in the Czech Republic.
Oolite or oölite is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Ancient Greek word for egg (ᾠόν). Strictly, oolites consist of ooids of diameter 0.25–2 millimetres; rocks composed of ooids larger than 2 mm are called pisolites. The term oolith can refer to oolite or individual ooids.
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.
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.
Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than 1⁄16 mm and are too small to study readily in the field. At first sight, the rock types appear quite similar; however, there are important differences in composition and nomenclature.
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, and in sediment deposits.
A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms which induce carbonate precipitation through their metabolism. Therefore, carbonate platforms can not grow up everywhere: they are not present in places where limiting factors to the life of reef-building organisms exist. Such limiting factors are, among others: light, water temperature, transparency and pH-Value. For example, carbonate sedimentation along the Atlantic South American coasts takes place everywhere but at the mouth of the Amazon River, because of the intense turbidity of the water there. Spectacular examples of present-day carbonate platforms are the Bahama Banks under which the platform is roughly 8 km thick, the Yucatan Peninsula which is up to 2 km thick, the Florida platform, the platform on which the Great Barrier Reef is growing, and the Maldive atolls. All these carbonate platforms and their associated reefs are confined to tropical latitudes. Today's reefs are built mainly by scleractinian corals, but in the distant past other organisms, like archaeocyatha or extinct cnidaria were important reef builders.
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.
Bioclasts are skeletal fossil fragments of once living marine or land organisms that are found in sedimentary rocks laid down in a marine environment—especially limestone varieties around the globe. some of which take on distinct textures and coloration from their predominate bioclasts—that geologists, archaeologists and paleontologists use to date a rock strata to a particular geological era.
Monte San Giorgio is a mountain and UNESCO World Heritage Site on the border between Switzerland and Italy. It is part of the Lugano Prealps, overlooking Lake Lugano in the Swiss Canton of Ticino.
A calcite sea is a sea 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.
Shell growth in estuaries is an aspect of marine biology that has attracted a number of scientific research studies. Many groups of marine organisms produce calcified exoskeletons, commonly known as shells, hard calcium carbonate structures which the organisms rely on for various specialized structural and defensive purposes. The rate at which these shells form is greatly influenced by physical and chemical characteristics of the water in which these organisms live. Estuaries are dynamic habitats which expose their inhabitants to a wide array of rapidly changing physical conditions, exaggerating the differences in physical and chemical properties of the water.
The geology of Germany is heavily influenced by several phases of orogeny in the Paleozoic and the Cenozoic, by sedimentation in shelf seas and epicontinental seas and on plains in the Permian and Mesozoic as well as by the Quaternary glaciations.
The geology of Ohio formed beginning more than one billion years ago in the Proterozoic eon of the Precambrian. The igneous and metamorphic crystalline basement rock is poorly understood except through deep boreholes and does not outcrop at the surface. The basement rock is divided between the Grenville Province and Superior Province. When the Grenville Province crust collided with Proto-North America, it launched the Grenville orogeny, a major mountain building event. The Grenville mountains eroded, filling in rift basins and Ohio was flooded and periodically exposed as dry land throughout the Paleozoic. In addition to marine carbonates such as limestone and dolomite, large deposits of shale and sandstone formed as subsequent mountain building events such as the Taconic orogeny and Acadian orogeny led to additional sediment deposition. Ohio transitioned to dryland conditions in the Pennsylvanian, forming large coal swamps and the region has been dryland ever since. Until the Pleistocene glaciations erased these features, the landscape was cut with deep stream valleys, which scoured away hundreds of meters of rock leaving little trace of geologic history in the Mesozoic and Cenozoic.
The geology of Georgia is the study of rocks, minerals, water, landforms and geologic history in Georgia. The country is dominated by the Caucasus Mountains at the junction of the Eurasian Plate and the Afro-Arabian Plate, and rock units from the Mesozoic and Cenozoic are particularly prevalent. For much of its geologic history, until the uplift of the Caucasus, Georgia was submerged by marine transgression events. Geologic research for 150 years by Georgian and Russian geologists has shed significant light on the region and since the 1970s has been augmented with the understanding of plate tectonics.
The calcium cycle is a transfer of calcium between dissolved and solid phases. There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils. Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate, which can deposit to form sediments or the exoskeletons of organisms. Calcium ions can also be utilized biologically, as calcium is essential to biological functions such as the production of bones and teeth or cellular function. The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes. Calcium moves through these different media as it cycles throughout the Earth. The marine calcium cycle is affected by changing atmospheric carbon dioxide due to ocean acidification.
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.
