{{Short description|Type of marine environment}} {{expert|Limnology and Oceanography|reason=Scope poorly defined|date=July 2024}} thumb|Shallow water
'''Shallow water marine environment''' refers to the neritic marine environment between the shore and the shelf break. This environment is characterized by oceanic, geological and biological conditions, as described below, and water in this environment is shallow and clear,<ref name="Boggs">{{cite book |last1=Boggs |first1=Sam |title=Principles of Sedimentology and Stratigraphy |date=2012 |publisher=Pearson |isbn=978-0-321-64318-6 |edition=fifth |location=New Jersey}}</ref>{{clarify|How deep is shallow? What happens if the water is not clear??|date=July 2024}} allowing the formation of different sedimentary structures, carbonate rocks, coral reefs, and allowing certain organisms to survive and become fossils.
==Sediment== {{see also|Marine 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;<ref name="lib book">{{cite book |last1=Demicco, Robert V. |first1=Hardie, Lawrence A. |title=Sedimentary Structures and Early Diagenetic Features of Shallow Marine Carbonate Deposits |date=1994 |publisher=Society of Sedimentary Geology |isbn=1-56576-013-1 |edition=First |location=Tulsa, Oklahoma}}</ref> these are the most common evaporite minerals found within modern and ancient deposits and can occur as crystalline layers, isolated crystals, or clusters of crystals.<ref name=" lib book" />
Approximately 75% of surface sediments are in shallow marine environments, holding most Phanerozoic and Precambrian sedimentary rock.<ref name="rise&fall of strom">{{cite journal |last1=Peters |first1=Shanan |display-authors=etal |date=2017 |title=The rise and fall of stromatolites in shallow marine environments |url=https://pubs-geoscienceworld-org.qe2a-proxy.mun.ca/geology/article-lookup/45/6/487#ref-25 |journal=Geology |volume=45 |issue=6 |pages=487–490 |bibcode=2017Geo....45..487P |doi=10.1130/G38931.1|url-access=subscription }}</ref> 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.<ref name="sed cycling">{{cite journal |last1=Peters |first1=Shanan |date=2017 |title=Sediment cycling on continental and oceanic crust |url=https://pubs-geoscienceworld-org.qe2a-proxy.mun.ca/geology/article-lookup/45/4/323 |journal=Geology |volume=45 |issue=4 |pages=323–326 |bibcode=2017Geo....45..323P |doi=10.1130/G38861.1|url-access=subscription }}</ref>
==Sedimentary Structures== thumb|Palimpsest ripples - National Museum of Nature and Science, Tokyo
=== Shallow marine environments === Shallow marine environments are characterized by various types of sedimentary structures, including:<ref name="Boggs" />
* Graded bedding: characterized by a vertical gradation in grain size, with the smallest grains at the top * Ripples: the smallest bedform type * Dunes: larger and similar in shape to ripples
=== 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:<ref name="Boggs" />
* Cross stratification: a layering structure found in gravel, sand, and coarse silt-sized sediment, characterized by distinct layers that are steeply inclined to the underlying surface. * Desiccation cracks: cracks formed by the drying of newly deposited mud in sub-aerial climates. * Flame structures: mud shaped like flames that intrude into the overlying layer of rock. * Convolute folds: sediment folded into irregular anticlines and/or synclines. * Flutes: outstretched ridges that are rounded at one end and flared at the other. * Groove casts: outstretched, almost straight grooves in sediment caused by the dragging of an object. * Chevron structures: a v-shaped type of groove cast, resulting from stress applied in two or more directions, found on the bottoms of beds deposited in shallow water environments. * Syneresis cracks: cracks formed by means other than sub-aerial climate exposure, including contraction by clay clumping, contraction from settling during faulting, smectitic clay compaction from dewatering due to a salinity change in surrounding water, compaction dewatering under sediment causing injection from below or collapsing from above, and tensional opening due to down-sloping of a surface mud layer.<ref name="lib book" /> * Fenestrae: open or partially filled spaces occupied by different sediment or cement<ref name="lib book" />
==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.<ref name=":0">{{cite journal |last1=Hall |first1=Clarence A. |date=1964 |title=Shallow-Water Marine Climates and Molluscan Provinces |journal=Ecology |volume=45 |issue=2 |pages=226–234 |doi=10.2307/1933835 |jstor=1933835|bibcode=1964Ecol...45..226H }}</ref>
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.<ref name=":0" />
==== 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.<ref name="Boggs" /> Many shallow marine environments are associated with carbonate factory zones, where processes that remove {{Chem|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 {{Chem|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.<ref name="Boggs" />
==Organisms== thumb|Echinoderms {{see also|Marine coastal ecosystem}}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.<ref name="biology">{{cite book |last1=Reece |first1=Jane |title=Campbell Biology |date=2015 |publisher=Pearson |isbn=978-0-13-418911-6 |edition=second |location=Ontario |display-authors=etal}}</ref>
=== 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.<ref name="ichnology">{{cite journal |last1=Gingras |first1=Murray K. |display-authors=etal |date=2008 |title=Biology of shallow marine ichnology: a modern perspective |url=https://www.int-res.com/articles/ab2008/2/b002p255.pdf |journal=Aquatic Biology |volume=2 |issue=3 |pages=255–268 |doi=10.3354/ab00055 |doi-access=free|bibcode=2008AquaB...2..255G }}</ref>
=== 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:<ref>{{cite journal |last1=Dumont |first1=H.J. |date=2009 |title=Marine Biodiversity of Costa Rica, Central America |journal=Monographiae Biologicae |volume=86 |doi=10.1007/978-1-4020-9726-3 |isbn=978-1-4020-9725-6}}</ref>
* Fringing Reefs: attached to the shore * Barrier Reefs: separated from the mainland by a lagoon * Atoll Reefs: ring-shaped reefs surrounding a lagoon
=== Reef Organisms === Organisms that inhabit these reefs include red algae, green algae, bivalves and echinoderms. Many of these organisms contribute to reef formation.<ref name="Boggs" /> Furthermore, unicellular dinoflagellates live in coral tissues, engaging in a mutualistic relationship where they provide corals with essential organic molecules.<ref name="biology" />
==Fossils== thumb|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:
* Skolithos ichnofacies: vertical, cylindrical, or U-shaped burrows created by organisms for protection. These are classified as trace fossils.<ref name="Boggs" /> * Glossifungites Ichnofacies: vertical, cylindrical, U-shaped, or tear-shaped borings or burrows created by organisms such as shrimp, crabs, worms, and bivalves. These are also classified as trace fossils. * Stromatolites: laminated sedimentary structures formed when cyanobacteria create microbial mats, trapping clay, silt sediment, and organic materials. These mats eventually lithify, embedding fossils.
==See also== * Tides in marginal seas
==References== {{reflist}}
==External links== * [http://www.mnh.si.edu/exhibits/darwin/images/burgessshale_250.jpg Example of marine fossil - Burgess Shale]
Category:Oceans