Shallow water marine environment refers to the area between the

shore A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past a ...

and deeper water, such as a

reef 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 out ...

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.

Sediment

The

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

itself is often composed of

limestone Limestone ( calcium carbonate ) 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 . Limestone forms whe ...

, which forms readily in shallow, warm calm waters. The shallow marine environments are not exclusively composed of

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone Sandstone is a clastic ...

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

aceous 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 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 ...

is made up of larger

grain size Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refer ...

s because smaller grains have been washed out to deeper water. Within sedimentary rocks composed of carbonaceous sediment, there may also be

evaporite An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocea ...

minerals. 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. 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. This trend is seen in the North American and Caribbean region. 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.

Sedimentary Structures

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 Ripple may refer to: Science and technology * Capillary wave, commonly known as ripple, a wave traveling along the phase boundary of a fluid ** Ripple, more generally a disturbance, for example of spacetime in gravitational waves * Ripple (electri ...

, which are the smallest bedform type, and

dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...

s, which are similar to ripples except are larger. 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. 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. Desiccation cracks are cracks formed due to drying out of newly deposited mud; these form in

sub-aerial In natural science, subaerial (literally "under the air"), has been used since 1833,Subaerial
in the Merriam- ...

climates.

Syneresis crack Syneresis cracks (also known as subaqueous shrinkage cracks) are a sedimentary structure developed by the shrinkage of sediment without desiccation – not to be confused with desiccation cracks. Syneresis is the expulsion of a liquid from a g ...

s 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. Fenestrae is an open or partially filled space occupied by different sediment or cement in the rock.

Flame structure A flame structure is a type of soft-sediment deformation that forms in unconsolidated sediments. The weight of an overlying bed forces an underlying bed to push up through the overlying bed, generally when both strata are saturated with water. T ...

s is mud shaped like flames that intrude the overlying layer of rock. Convolute folds are complicated folds in beds into irregular anticlines and/or synclines.

Flutes The flute is a family of classical music instrument in the woodwind group. Like all woodwinds, flutes are aerophones, meaning they make sound by vibrating a column of air. However, unlike woodwind instruments with reeds, a flute is a reedless ...

are outstretched ridges that are rounded at one end and flared at the other. Groove casts are outstretched, almost straight grooves in sediment caused by the dragging of an object such as a rock, piece of wood, etc.

Chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock lay ...

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.

Water composition

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. 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.

Organisms

Some organisms in this environment, specifically those in the

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

, are

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

marine worm Any worm that lives in a marine environment is considered a marine worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida (segmented worms), Chaetognatha, Hemichordata, and Phoronida. For a ...

clam Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two she ...

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

s, predatory

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

s and small

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

Hydrozoa Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specializ ...

, or hydroids, also live in shallow marine ecosystems and eat surrounding

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

and

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

. Some species of

isopods Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

and

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...

are found in the intertidal zones and create several different burrows and surface tracks in the sediment.

Brittle star Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomo ...

s have been seen buried in sediment with their arms showing through the sediment; this behaviour has been noted in several shallow marine areas. As well,

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

reefs can be found in the

depositional environment 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 ...

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 reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. Co ...

s range from 1–9 million. There are 3 main types of reef formations:

fringing reef 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 direc ...

s, these reefs are attached to the shore,

barrier reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. Co ...

s, which are separated from mainland by a

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

, and

atoll reef An atoll () is a ring-shaped island, including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. Atolls are located in warm tropical or subtropical oceans and seas where corals can gro ...

s. Organisms that live in this environment include

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s and

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

s. Many of these organisms contribute to the formation of reefs. Also,

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

s live in the tissues of

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

s, and have a mutualistic relationship in which the dinoflagellates provide the corals with organic molecules.

Fossils

The vast majority of the

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

has been found after the shallow water marine environment has been

lithified Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificati ...

. Many of these

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s 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 An ichnofacies is an assemblage of trace fossils that provides an indication of the conditions that their formative organisms inhabited. Concept Trace fossil assemblages are far from random; the range of fossils recorded in association is constra ...

are trace fossils that are vertical, cylindrical or U-shaped burrows created by organisms for protection. 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.

Stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

s 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.

References

{{reflist

External links

Example of marine fossil - Burgess Shale
Oceans