Shallow water marine environment

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Shallow water Shallow water.jpg
Shallow water

Shallow water marine environment refers to the area between the shore and deeper water,[ clarification needed ] such as a reef wall or a shelf break. [ clarification needed ]This environment is characterized by oceanic, geological and biological conditions, as described below. The water in this environment is shallow and clear, [1] [ clarification needed ] allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.

Contents

Sediment

The sediment itself is often composed of limestone, which forms readily in shallow, warm, calm waters. While siliciclastic and carbonaceous sediments can coexist, shallow marine environments can also contain only one or the other. Shallow water marine sediment primarily features larger grain sizes because smaller grains have washed out to deeper water. Within carbonaceous sedimentary rock, evaporite minerals such as gypsum, anhydrite, and halite may be present. [2] The most common evaporite minerals found within modern and ancient deposits are gypsum, anhydrite, and halite. These minerals can occur as crystalline layers, isolated crystals, or clusters of crystals. [2]

Approximately 75% of surface sediments are in shallow marine environments, holding most Phanerozoic and Precambrian sedimentary rock. [3] This is visible in the North American and Caribbean regions. However, shallow marine sediment quantity varies significantly over geologic time due to supercontinent breakup and shifting tectonic plate processes. [4]

Sedimentary Structures

Palimpsest ripples - National Museum of Nature and Science, Tokyo Palimpsest ripples - National Museum of Nature and Science, Tokyo - DSC07689.JPG
Palimpsest ripples - National Museum of Nature and Science, Tokyo

Shallow Marine Environments

Shallow marine environments are characterized by various types of sedimentary structures, including: [1]

Carbonaceous Rocks in SMEs

Carbonaceous sedimentary rock in SMEs contain significant amounts of non-skeletal matter along with siliciclastic or chemical constituents and can exhibit a range of sedimentary structures, including: [1]

Water composition

Characteristics

Shallow marine environments are typically characterized by clear and shallow water. The distributional patterns of marine organisms in these environments can be used to define different types of shallow marine environments based on temperature, which can also provide insights into past patterns in paleolithic zones. [5]

The boundaries between different shallow marine environment types in terms of climatic zones are not always agreed upon. However, three major criteria are used to define SME types: faunal provinces, faunal elements, and latitude. [5]

Carbonate factory zones

Carbon dioxide is removed from the atmosphere when it dissolves in seawater and turns into carbonic acid. The acid then weathers rocks, creating bicarbonate and other ions. Calcium carbonate is a precipitate from calcium and the bicarbonate ions, while the carbon is precipitates as limestone. [1] Many shallow marine environments are associated with carbonate factory zones, where processes that remove CO
2
from the water change bicarbonate ions into carbonate ions, supporting lime precipitation. These processes include increasing temperature, intense evaporation, and mixing water that is high in CO
3
and low in calcium cations with seawater.

Changes in limestone composition over geologic time

Over geologic time, the composition of limestone has changed from calcite-rich to aragonite-rich. This change is influenced by the presence of magnesium ions, which can inhibit calcite precipitation. Aragonite and calcite have the same chemical formula but a different crystal system, although aragonite is less prone to magnesium inhibition. Changes in the Mg/Ca ratio over geologic time, influenced by seafloor spreading and tectonic plate movement, have also increased aragonite abundance. [1]

Organisms

Echinoderms Echinoderms 600.jpg
Echinoderms

Shallow marine environments, particularly the intertidal zone, are home to a diverse range of organisms, including starfish, sea anemones, sponges, marine worms, clams, mussels, predatory crustaceans, barnacles and small fish. [6]

Hydrozoa and microinvertebrates

Hydrozoa, also known as hydroids, inhabit SMEs and feed on surrounding algae and zooplankton. Species of isopods and amphipods are found in intertidal zones, creating complex burrows and surface tracks in the sediment. Brittle stars may bury themselves in sediment with their arms exposed. [7]

Carbonate reefs

SMEs are characterized by carbonate reefs, which support many species. Estimates suggest that coral reefs alone may host between 1-9 million species. The three main types of reef formations are: [8]

Reef Organisms

Organisms that inhabit these reefs include red algae, green algae, bivalves and echinoderms. Many of these organisms contribute to reef formation. [1] Furthermore, unicellular dinoflagellates live in coral tissues, engaging in a mutualistic relationship where they provide corals with essential organic molecules. [6]

Fossils

Stromatolites in Sharkbay Stromatolites in Sharkbay.jpg
Stromatolites in Sharkbay

The majority of the fossil record has been discovered in lithified SMEs, which were once home to diverse organisms. Many of these fossils date to periods when much of the Earth was covered in shallow seas.

Several types of fossils can be found in these environments, including:

See also

Related Research Articles

<span class="mw-page-title-main">Limestone</span> Type of sedimentary rock

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.

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and cementation of particles

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.

<span class="mw-page-title-main">Aragonite</span> Calcium carbonate mineral

Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate, the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation from marine and freshwater environments.

<span class="mw-page-title-main">Reef</span> Shoal of rock, coral, or other material lying beneath the surface of water

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. These 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.

<span class="mw-page-title-main">Ooid</span> Small sedimentary grain that forms on shallow tropical seabeds

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.

<span class="mw-page-title-main">Oolite</span> Sedimentary rock formed from ooids

Oolite or oölite is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. 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.

<span class="mw-page-title-main">Cay</span> Small island formed on the surface of a coral reef

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.

<span class="mw-page-title-main">Carbonate rock</span> Class of sedimentary rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as dolostone), which is composed of mineral dolomite (CaMg(CO3)2). They are usually classified based on texture and grain size. Importantly, carbonate rocks can exist as metamorphic and igneous rocks, too. When recrystallized carbonate rocks are metamorphosed, marble is created. Rare igneous carbonate rocks even exist as intrusive carbonatites and, even rarer, there exists volcanic carbonate lava.

<span class="mw-page-title-main">Calcareous</span> Adjective meaning mostly or partly composed of calcium carbonate

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.

<span class="mw-page-title-main">Carbonate platform</span> Sedimentary body with topographic relief composed of autochthonous calcareous 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.

<span class="mw-page-title-main">Depositional environment</span> Processes associated with the deposition of a particular type of sediment

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.

<span class="mw-page-title-main">Marine sediment</span> Accumulated material on seafloor

Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles either 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, or they are biogenic deposits from marine organisms or from chemical precipitation in seawater, as well as from underwater volcanoes and meteorite debris.

<span class="mw-page-title-main">Beachrock</span> Sedimentary rock cemented with carbonates, formed along a shoreline

Beachrock is a friable to well-cemented sedimentary rock that consists of a variable mixture of gravel-, sand-, and silt-sized sediment that is cemented with carbonate minerals and has formed along a shoreline. Depending on location, the sediment that is cemented to form beachrock can consist of a variable mixture of shells, coral fragments, rock fragments of different types, and other materials. It can contain scattered artifacts, pieces of wood, and coconuts. Beachrock typically forms within the intertidal zone within tropical or semitropical regions. However, Quaternary beachrock is also found as far north and south as 60° latitude.

<span class="mw-page-title-main">Calcite sea</span> Sea chemistry favouring low-magnesium calcite as the inorganic calcium carbonate precipitate

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.

<span class="mw-page-title-main">Sedimentary structures</span> Geologic structures formed during sediment deposition

Sedimentary structures include all kinds of features in sediments and sedimentary rocks, formed at the time of deposition.

<span class="mw-page-title-main">Aragonite sea</span> Chemical conditions of the sea favouring aragonite deposition

An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic calcium carbonate precipitates. The chemical conditions of the seawater must be notably high in magnesium content relative to calcium for an aragonite sea to form. This is in contrast to a calcite sea in which seawater low in magnesium content relative to calcium favors the formation of low-magnesium calcite as the primary inorganic marine calcium carbonate precipitate.

<span class="mw-page-title-main">Shell growth in estuaries</span>

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.

<span class="mw-page-title-main">Egg taphonomy</span> Study of the decomposition and fossilization of eggs

Egg taphonomy is the study of the decomposition and fossilization of eggs. The processes of egg taphonomy begin when the egg either hatches or dies. Eggshell fragments are robust and can often travel great distances before burial. More complete egg specimens gradually begin to fill with sediment, which hardens as minerals precipitate out of water percolating through pores or cracks in the shell. Throughout the fossilization process the calcium carbonate composing the eggshell generally remains unchanged, allowing scientists to study its original structure. However, egg fossils buried under sediments at great depth can be subjected to heat, pressure and chemical processes that can alter the structure of its shell through a process called diagenesis.

<span class="mw-page-title-main">Marine biogenic calcification</span> Shell formation mechanism

Marine biogenic calcification is the production of calcium carbonate by organisms in the global ocean.

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.

References

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