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{{short description|Sedimentary body with topographic relief composed of autochthonous calcareous deposits}}
[[File:Bahamabank.jpg|thumb|The [[Bahama Banks]] are an example of a carbonate platform]]
A '''carbonate platform''' is a [[Sedimentary rock|sedimentary]] body which possesses [[topographic]] relief, and is composed of [[Autochthon (geology)|autochthonic]] calcareous deposits.<ref name="geologic">{{cite book|title=Carbonate facies in geologic history|last=Wilson|first=James Lee|date=1975|publisher=Springer-Verlag|isbn=978-0387072364|location=Berlin|oclc=1366180}}</ref> Platform growth is mediated by [[Sessility (zoology)|sessile]] organisms whose [[skeleton]]s build up the [[coral reef|reef]] or by organisms (usually [[microbes]]) 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 (optics)|transparency]] and pH-Value. For example, carbonate sedimentation along the [[Atlantic]] [[South America]]n coasts takes place everywhere but at the mouth of the [[Amazon River]], because of the intense [[turbidity]] of the water there.<ref>{{cite journal|last1=Carannante|first1=G.|last2=Esteban|first2=M.|last3=Milliman|first3=J. D.|last4=Simone|first4=L.|date=1988-11-01|title=Carbonate lithofacies as paleolatitude indicators: problems and limitations|journal=Sedimentary Geology|series=Non-tropical shelf carbonates-modern and ancient|volume=60|issue=1|pages=333–346|doi=10.1016/0037-0738(88)90128-5|bibcode=1988SedG...60..333C |issn=0037-0738}}</ref> Spectacular examples of present-day carbonate platforms are the [[Bahama Banks]] under which the platform is roughly 8&nbsp;km thick, the [[Yucatan Peninsula]] which is up to 2&nbsp;km thick, the [[Florida]] platform,<ref>[https://archive.today/20110515100222/http://geology.about.com/library/bl/maps/blfloridamap.htm?terms=geologic+map+of+Florida Geologic Map of Florida<!-- Bot generated title -->]</ref> the platform on which the [[Great Barrier Reef]] is growing, and the [[Maldive]] [[atoll]]s.<ref>{{cite web |title=Bahamas Introduction |url=http://www.tamug.edu/cavebiology/Bahamas/BahamaIntro.html |website=www.tamug.edu |access-date=2006-03-09 |archive-url=https://web.archive.org/web/20091122081312/http://www.tamug.edu/cavebiology/Bahamas/BahamaIntro.html |archive-date=2009-11-22 |url-status=dead }}</ref> All these carbonate platforms and their associated [[reef]]s are confined to [[tropical]] latitudes.<ref>{{cite web|url=http://reefgis.reefbase.org/mapper.asp |title=ReefGIS - Location of Coral Reefs - Reef Basemap |access-date=2007-03-12 |url-status=dead |archive-url=https://web.archive.org/web/20080516101415/http://reefgis.reefbase.org/mapper.asp |archive-date=2008-05-16 }}</ref> Today's reefs are built mainly by [[scleractinia|scleractinian corals]], but in the distant past other organisms, like [[archaeocyatha]] (during the [[Cambrian]]) or extinct [[cnidaria]] ([[tabulata]] and [[rugosa]]) were important reef builders.

==Carbonate precipitation from seawater==
What makes carbonate platform environments different from other depositional environments is that carbonate is a product of precipitation, rather than being a sediment transported from elsewhere, as for sand or gravel.<ref name="geologic" /><ref name="Concepts" /> This implies for example that carbonate platforms may grow far from the coastlines of continents, as for the Pacific atolls.

The [[mineral]]ogic composition of carbonate platforms may be either [[calcite|calcitic]] or [[aragonite|aragonitic]]. [[Seawater]] is oversaturated in carbonate, so under certain conditions CaCO<sub>3</sub> precipitation is possible. Carbonate precipitation is [[Thermodynamics|thermodynamically]] favoured at high temperature and low [[pressure]]. Three types of carbonate precipitation are possible: ''biotically controlled'', ''biotically induced'' and ''abiotic''. Carbonate precipitation is biotically controlled when organisms (such as corals) are present that exploit carbonate dissolved in seawater to build their calcitic or aragonitic skeletons. Thus they may develop hard reef structures. Biotically induced precipitation takes place outside the cell of the organism, thus carbonate is not directly produced by organisms, but precipitates because of their metabolism. Abiotic precipitation, by definition,  involves little or no [[biological]] influence.<ref name="Concepts" />

==Classification==
The three types of precipitation (abiotic, biotically induced and biotically controlled) cluster into three "carbonate factories". A carbonate factory is the ensemble of the [[Sedimentary depositional environment|sedimentary environment]], the intervening organisms and the precipitation processes that lead to the formation of a carbonate platform. The differences between three factories is the dominant precipitation pathway and skeletal associations. In contrast, a carbonate platform is a geological structure of parautochotonous carbonate sediments and carbonate rocks, having a morphological relief.<ref name="Concepts" />

=== Platforms produced by the "tropical factory" ===
In these carbonate factories, precipitation is biotically controlled, mostly by [[autotrophic]] organisms. Organisms that build this kind of platforms are today mostly [[coral]]s and [[green algae]], that need sunlight for photosynthesis and thus live in the [[euphotic zone]] (i.e., shallow water environments in which sunlight penetrates easily). Tropical carbonate factories are only present today in warm and sunlit waters of the tropical-subtropical belt, and they have high carbonate production rates but only in a narrow depth window.<ref name="Concepts">{{cite book|title=Carbonate sedimentology and sequence stratigraphy|last=Schlager|first=Wolfgang|publisher=SEPM Concepts in Sedimentology and Paleontology|year=2005|isbn=978-1565761162}}</ref> The depositional profile of a Tropical factory is called "rimmed" and includes three main parts: a [[lagoon]], a [[reef]] and a slope. In the reef, the framework produced by large-sized skeletons, as those of corals, and by encrusting organisms resists wave action and forms a rigid build up that may develop up to sea-level.<ref name="Pomar2001" /> The presence of a rim produces restricted circulation in the back reef area and a lagoon may develop in which carbonate mud is often produced. When reef accretion reaches the point that the foot of the reef is below wave base, a slope develops: the sediments of the slope derive from the erosion of the margin by waves, storms and gravitational collapses.<ref name="Concepts" /><ref name="Pomar2001" /> This process accumulates coral debris in clinoforms. The maximum angle that a slope can achieve is the settlement angle of gravel (30–34°).<ref name="angle sediment">{{cite journal|last=Kenter|first=Jeroen A. M.|date=1990|title=Carbonate platform flanks: slope angle and sediment fabric|journal=Sedimentology|volume=37|issue=5|pages=777–794|doi=10.1111/j.1365-3091.1990.tb01825.x|bibcode=1990Sedim..37..777K |issn=1365-3091}}</ref>

=== Platforms produced by the "cool-water factory" ===
In these carbonate factories, precipitation is biotically controlled by [[heterotroph]]ic organisms, sometimes in association with photo-autotrophic organisms such as [[red algae]]. The typical skeletal association includes [[Foraminifera|foraminifers]], red algae and [[Mollusca|molluscs]]. Despite being autotrophic, red algae are mostly associated to heterotrophic carbonate producers, and need less light than green algae. The range of occurrence of cool-water factories extends from the limit of the tropical factory (at about 30◦) up to polar latitudes, but they could also occur at low latitudes in the thermocline below the warm surface waters or in upwelling areas.<ref name="conundrum">{{cite journal |last1=Pomar |first1=L. |last2=Hallock |first2=P. |author-link2=Pamela Hallock |date=2008-03-01 |title=Carbonate factories: A conundrum in sedimentary geology |journal=Earth-Science Reviews |volume=87 |issue=3–4 |pages=134–169 |doi=10.1016/j.earscirev.2007.12.002 |bibcode=2008ESRv...87..134P |issn=0012-8252}}</ref> This type of factories has a low potential of carbonate production, is largely independent from sunlight availability, and can sustain a higher amount of nutrients than tropical factories. Carbonate platforms built by the "cool-water factory" show two types of geometry or depositional profile, i.e., the homoclinal ramp or the distally-steepened ramp. In both geometries there are three parts: the inner ramp above the fair weather [[wave base]], the middle ramp, above the storm wave base, the outer ramp, below the storm wave base. In distally steepened ramps, a distal step is formed between the middle and outer ramp, by the in situ accumulation of gravel-sized carbonate grains <ref name="conundrum" />

=== Platforms produced by the "mud-mound factory" ===
These factories are characterised by abiotic precipitation and biotically induced precipitation. The typical environmental settings where "mud-mound factories" are found in the Phanerozoic are dysphotic or [[Aphotic zone|aphotic]], nutrient-rich waters that are low in oxygen but not [[Anoxic waters|anoxic]]. These conditions often prevail in the thermocline, for example at intermediate water depths below the ocean's [[mixed layer]].<ref name="Concepts" /> 
The most important component of these platforms is fine-grained carbonate that precipitates in situ ([[automicrite]]) by a complex interplay of biotic and abiotic reactions with microbes and decaying organic tissue.<ref name="Concepts" /> 
Mud-mound factories do not produce a skeletal association, but they have specific [[facies]] and microfacies, for example [[stromatolite]]s, that are laminated [[microbialite]]s, and [[thrombolite]]s, that are [[microbialite]]s characterized by clotted peloidal fabric at the microscopic scale and by dendroid fabric at the hand-sample scale.
The geometry of these platforms is mound-shaped, where all the mound is productive, including the slopes.<ref name="Concepts" />

==Geometry of carbonate platforms==
Several factors influence the geometry of a carbonate platform, including inherited topography, synsedimentary [[tectonics]], exposure to currents and [[trade winds]]. Two main types of carbonate platforms are distinguished on the base of their geographic setting: isolated (as [[Atolls of the Maldives|Maldives atolls]]) or epicontinental (as the [[Belize]] reefs or the [[Florida Keys]]). However, the one most important factor influencing geometries is perhaps the type of carbonate factory. Depending on the dominant carbonate factory, we can distinguish three types of carbonate platforms: T-type carbonate platforms (produced by "tropical factories"), C-type carbonate platforms (produced by "cool-water factories"), M-type carbonate platforms ("produced by mud-mound factories"). Each of them has its own typical geometry.<ref name="Concepts" />

[[Image:CARBONATIC PLATFORM EN.PNG|500px|thumb|Generalized cross-section of a typical carbonate platform.]]

=== T-type carbonate platforms ===
The depositional profile of T-type carbonate platforms can be subdivided into several [[sedimentary environment]]s.<ref name="geologic" />

The carbonate hinterland is the most landward environment, composed by weathered [[carbonate rocks]]. The evaporitic [[tidal flat]] is a typical low-energy environment.

[[Image:FangoCarb1.jpg|thumb|An example of carbonate mud sedimentation in the internal part of the Florida Bay lagoon. The presence of young mangroves is important to entrap the carbonate mud.]]

The internal [[lagoon]], as the name suggests, is the part of platform behind the reef. It is characterised by shallow and calm waters, and so it is a low-energy sedimentary environment. Sediments are composed by reef fragments, hard parts of organisms and, if the platform is epicontinental, also by a terrigenous contribution. In some lagoons (e.g., the [[Florida Bay]]), [[green alga]]e produce great volumes of carbonate mud. Rocks here are [[mudstone]]s to [[grainstone]]s, depending on the energy of the environment.

The [[reef]] is the rigid structure of carbonate platforms and is located between the internal lagoon and the slope, in the platform margin, in which the framework produced by large-sized skeletons, as those of corals, and by encrusting organisms will resist wave action and form a rigid build up that may develop up to sea-level. Survival of the platform depends on the existence of the reef, because only this part of the platform can build a rigid, wave-resistant structure. The reef is created by essentially in-place, [[sessility (motility)|sessile]] organisms. Today's reefs are mostly built by [[hermatypic]] corals. Geologically speaking, reef rocks can be classified as massive [[Boundstone (rock)|boundstones]].

The [[slope]] is the outer part of the platform, connecting the reef with the basin. This depositional environment acts as sink for excess carbonate sediment: most of the sediment produced in the lagoon and reef is transported by various processes and accumulates in the slope, with an inclination depending on the grain size of sediments, and that could attain the settlement angle of gravel (30-34°) at most.<ref name="angle sediment" /> The slope contains coarser sediments than the reef and lagoon. These rocks are generally [[rudstone]]s or [[grainstone]]s.

The periplatform basin is the outermost part of the t-type carbonate platform, and carbonate sedimentation is there dominated by density-cascating processes.<ref>{{cite journal|last1=Roberts|first1=Harry H.|last2=Wilson|first2=Paul A.|date=1992-08-01|title=Carbonate-periplatform sedimentation by density flows: A mechanism for rapid off-bank and vertical transport of shallow-water fines|journal=Geology|volume=20|issue=8|pages=713–716|doi=10.1130/0091-7613(1992)020<0713:CPSBDF>2.3.CO;2|bibcode=1992Geo....20..713W|issn=0091-7613}}</ref>

The presence of a rim damps the action of waves in the back reef area and a lagoon may develop in which carbonate mud is often produced. When reef accretion reaches the point that the foot of the reef is below wave base, a slope develops: the sediments of the slope derive from the erosion of the margin by waves, storms and gravitational collapses. This process accumulates coral debris in clinoforms. Clinoforms are [[Bed (geology)|beds]] that have a sigmoidal or tabular shape, but are always deposited with a primary inclination.

The size of a T-type carbonate platform, from the hinterland to the foot of the slope, can be of tens of kilometers.<ref name="Concepts" />

=== C-type carbonate platforms ===
C-type carbonate platforms are characterized by the absence of early [[Cementation (geology)|cementation]] and [[lithification]], and so the sediment distribution is only driven by [[sea waves|waves]] and, in particular, it occurs above the [[wave base]]. They show two types of geometry or depositional profile, i.e., the homoclinal ramp or the distally-steepened ramp. In both geometries there are three parts. In the inner ramp, above the fair weather [[wave base]], the carbonate production is slow enough that all sediments may be transported offshore by waves, currents and storms. As a consequence, the shoreline may be retreating, and so in the inner ramp there may be a cliff caused by erosional processes. In the middle ramp, between the fair weather wave base and the storm wave base, carbonate sediment remains in place and can be reworking only by the storm waves. In the outer ramp, below the storm wave base, fine sediments may accumulate. In distally steepened ramps, a distal step is formed between the middle and outer ramp, by the in situ accumulation of gravel-sized carbonate grains (e.g., [[rhodolith]]s) only episodically moved by currents. Carbonate production occurs along the full depositional profile in this type of carbonate platforms, with an extra production in the outer part of the middle ramp, but carbonate production rates are always less than in the T-type carbonate platforms.<ref name="Pomar2001">{{cite journal |last1=Pomar |first1=L. |title=Types of carbonate platforms: a genetic approach |journal=Basin Research |date=September 2001 |volume=13 |issue=3 |pages=313–334 |doi=10.1046/j.0950-091x.2001.00152.x|bibcode=2001BasR...13..313P |s2cid=129859376}}</ref><ref name="Concepts" />

=== M-type carbonate platforms ===
M-type carbonate platforms are characterized by an inner platform, an outer platform, an upper slope made by microbial [[Boundstone (rock)|boundstone]], and a lower slope often made by [[breccia]]. The slope may be steeper than the angle of repose of gravels, with an inclination that may attain 50°.

In the M-type carbonate platforms the carbonate production mostly occurs on the upper slope and in the outer part of the inner platform.<ref name="Pomar2001" /><ref name="steep" />
[[File:Tafraout Formation.png|thumb|223x223px|(A) The Siliclastic-Carbonate [[Tafraout Group]] at Jebel Akenzoud ([[Dadès Gorges]], Central [[High Atlas]] Basin, Morocco). (B) Close-up view of the left-hand side of the panel. Lateral accretion within the ooidal shoal in the uppermost part of the infilling unit can be seen (white arrows). (C) Stratigraphic correlation. (D) Close up view on the right-hand side shoulder of the infilling unit. (E) Close up on the erosion surface.]]

==Carbonate platforms in the geological record==
[[File:Jbel Bou Dahar early Mesozoic map.jpg|left|thumb|The [[Calcaires du Bou Dahar]] record a well preserved carbonate platform, including it´s sedimentary cycles and facies.]]
Sedimentary sequences show carbonate platforms as old as the [[Precambrian]], when they were formed by [[stromatolite|stromatolitic]] sequences. In the [[Cambrian]] carbonate platforms were built by [[archaeocyatha]]. During [[Paleozoic]] [[brachiopod]] (richtofenida) and [[stromatoporoidea]] reefs were erected. At the middle of the Paleozoic era corals became important platforms builders, first with [[tabulata]] (from the [[Silurian]]) and then with [[rugosa]] (from the [[Devonian]]). [[Scleractinia]] become important reef builders beginning only in the [[Carnian]] (upper [[Triassic]]). Some of the best examples of carbonate platforms are in the [[Dolomites]], deposited during the Triassic. This region of the Southern [[Alps]] contains many well preserved isolated carbonate platforms, including the [[Sella group|Sella]], [[Rosengarten group|Gardenaccia]], [[Sassolungo]] and [[Latemar]]. The middle [[Lias Group|Liassic]] "bahamian type" carbonate platform was notoriously widespread in the western [[Tethys Ocean]], including the [[Rotzo Formation]] on Italy, the [[Aganane Formation]] & the [[Calcaires du Bou Dahar]] of Morocco (Septfontaine, 1985) is characterised by the accumulation of autocyclic regressive [[Cyclic sediments|cycles]], spectacular supratidal deposits and [[vadose]] [[Diagenesis|diagenetic]] features with [[dinosaur]] tracks.<ref name="B&L2">{{cite journal |last1=Burgess |first1=C. J. |last2=Lee |first2=C. W. |title=The development of a Lower Jurassic carbonate tidal flat, central High Atlas, Morocco; 1, Sedimentary history |journal=Journal of Sedimentary Research |date=1978 |volume=48 |issue=3 |pages=777–793|url=https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/48/3/777/97153/The-development-of-a-Lower-Jurassic-carbonate |access-date=20 April 2023}}</ref> In the same area the overlying [[Tafraout Group]] (Toarcian-Aalenian) records a massive Siliclastic-Carbonate Platform.<ref>{{Cite journal |last=Krencker |first=F.-N. |last2=Fantasia |first2=A. |last3=El Ouali |first3=M. |last4=Kabiri |first4=L. |last5=Bodin |first5=S. |date=2022 |title=The effects of strong sediment-supply variability on the sequence stratigraphic architecture: Insights from early Toarcian carbonate factory collapses |url=http://dx.doi.org/10.1016/j.marpetgeo.2021.105469 |journal=Marine and Petroleum Geology |volume=136 |pages=105469 |doi=10.1016/j.marpetgeo.2021.105469 |issn=0264-8172|doi-access=free }}</ref> Other coeval records of platforms are seen in the [[Adriatic Sea|Adriatic Platform]], in areas such as the [[Dinaric Alps]] (The [[Budoš Limestone]] of [[Montenegro]]), Rotzo or the [[Podpeč Limestone]] of Slovenia.<ref name="PANTIC1">{{cite journal |last1=Pantić |first1=N. K. |title=Liassic flora from Budos mountain - Montenegro |journal=Glasnik Prir. Muzeja SRP. Zem |date=1952 |volume=5 |issue=1 |pages=293–308}}</ref>  Others regional records include examples like the [[Coimbra Formation]] (Sinemurian) in the Lusitanian Basin.<ref>{{Cite journal |last=Duarte |first=Luís Vítor |last2=Silva |first2=Ricardo Louro |last3=Azerêdo |first3=Ana Cristina |last4=Comas-Rengifo |first4=María José |last5=Mendonça Filho |first5=João Graciano |date=2023-01-13 |title=Shallow-water carbonates of the Coimbra Formation, Lusitanian Basin (Portugal): contributions to the integrated stratigraphic analysis of the Sinemurian sedimentary successions in the western Iberian Margin |url=http://dx.doi.org/10.5802/crgeos.144 |journal=Comptes Rendus. Géoscience |volume=354 |issue=S3 |pages=89–106 |doi=10.5802/crgeos.144 |issn=1778-7025|doi-access=free }}</ref> The Aalenian Iberian Platform includes Volcanic intrusions that led to ephemeral islands, like in the [[El Pedregal Formation]].<ref>{{Cite journal |last=Cortés |first=J. E. |last2=Gómez |first2=J. J. |date=2018-04-16 |title=The epiclastic barrier-island system of the Early‒Middle Jurassic in eastern Spain |url=http://dx.doi.org/10.1007/s41513-018-0061-7 |journal=Journal of Iberian Geology |volume=44 |issue=2 |pages=257–271 |doi=10.1007/s41513-018-0061-7 |issn=1698-6180|url-access=subscription }}</ref> The Cretaceous ([[Campanian]]) [[Calcare di Aurisina]] in Italy, records a series of islands adjacent to a shallow carbonate sea in a platform built by [[bivalvia]] ([[rudists]]).<ref>{{Cite journal |last1=Jurkovšek |first1=Bogdan |last2=Biolchi |first2=Sara |last3=Furlani |first3=Stefano |last4=Kolar-Jurkovšek |first4=Tea |last5=Zini |first5=Luca |last6=Jež |first6=Jernej |last7=Tunis |first7=Giorgio |last8=Bavec |first8=Miloš |last9=Cucchi |first9=Franco |date=2016-08-12 |title=Geology of the Classical Karst Region (SW Slovenia–NE Italy) |url=http://dx.doi.org/10.1080/17445647.2016.1215941 |journal=Journal of Maps |volume=12 |issue=sup1 |pages=352–362 |doi=10.1080/17445647.2016.1215941 |bibcode=2016JMaps..12S.352J |issn=1744-5647|hdl=11368/2888161 |hdl-access=free }}</ref> The Tunisian coastal "chotts" and their cyclic muddy deposits represent a good recent equivalent (Davaud & Septfontaine, 1995). Such cycles were also observed on the [[Mesozoic]] Arabic platform, Oman and Abu Dhabi (Septfontaine & De Matos, 1998) with the same microfauna of foraminifera in an almost identical biostratigraphic succession.
[[File:Bloc diagramme Lias Haut Atlas.jpg|thumb|[[Aganane Formation]] platform of Morocco with first order autocyclic regressive cycles]] [[File:Cycles régressifs de comblement.jpg|thumb|[[Aganane Formation]] metre-scale peritidal sedimentary cycles in two outcrops. The two outcrops are 230 km apart. Storm beds and possibly tsunamites include abundant reworked foraminifera. This image is an example of the continuity of peritidal cycles in a carbonate platform environment.]] [[File:Cycle virtuel émersif.jpg|thumb|Virtual metric "shallowing upward sequence" observed all along (more than 10,000 km) the south Tethyan margin during middle Liassic times. The (micro)fossils are identical till Oman and beyond.]]

== Sequence stratigraphy of carbonate platforms ==
With respect to the [[sequence stratigraphy]] of siliciclastic systems, carbonate platforms present some peculiarities, which are related to the fact that carbonate sediment is precipitated directly on the platform, mostly with the intervention of living organisms, instead of being only transported and deposited.<ref name="geologic" /> Among these peculiarities, carbonate platforms may be subject to drowning, and may be the source of sediment via highstand shedding or slope shedding.<ref name="Concepts" />

=== Drowning ===

Drowning of a carbonate platform is an event where the [[relative sea level]] rise is faster than the accumulation rate on a carbonate platform, which eventually leads to the platform to submerge below the [[euphotic zone]].<ref name="paradox">{{cite journal|last=Schlager|first=Wolgang|date=1981|title=The paradox of drowned reefs and carbonate platforms|journal=Geological Society of America Bulletin|volume=92|issue=4|pages=197|doi=10.1130/0016-7606(1981)92<197:tpodra>2.0.co;2|bibcode=1981GSAB...92..197S |issn=0016-7606}}</ref> In the [[geologic record]] of a drowned carbonate platform, [[neritic]] deposits change rapidly into deep-marine sediments. Typically [[hardground]]s with [[ferromanganese]] oxides, [[phosphate]] or [[glauconite]] crusts lie in between of [[neritic]] and deep-marine sediments.<ref name="paradox" />

Several drowned carbonate platforms have been found in the geologic record. However, it has not been very clear how the drowning of carbonate platforms exactly happen. Modern carbonate platforms and reefs are estimated to grow approximately 1,000 μm/yr, possibly several times faster in the past. 1,000 μm/yr growth rate of carbonates exceeds by orders of [[Order of magnitude|magnitude]] any [[relative sea level]] rise that is caused by long-term subsidence, or changes in [[eustatic sea level]]. Based on the rates of these processes, drowning of the carbonate platforms should not be possible, which causes "the paradox of drowned carbonate platforms and reefs".<ref name="paradox" />

Since drowning of carbonate platforms requires exceptional rise in the [[relative sea level]], only limited number of processes can cause it. According to Schlager,<ref name="paradox" /> only anomalously quick rise of [[relative sea level]] or [[benthic]] growth reduction caused by deteriorating changes in the environment could explain the drowning of platforms. For instance, regional downfaulting, submarine [[volcanism]] or [[Sea level|glacioeustasy]] could be the reason for rapid rise in [[relative sea level]], whereas for example changes in oceanic [[salinity]] might cause the environment to become deteriorative for the carbonate producers.<ref name="paradox" />

One example of a drowned carbonate platform is located in [[Huon Gulf]], [[Papua New Guinea]]. It is believed to be drowned by rapid sea level rise caused by [[deglaciation]] and subsidence of the platform, which enabled coralline algal-[[foraminifera]]l nodules and [[halimeda]] [[limestones]] to cover the [[coral reef]]s.<ref>{{cite journal|last1=Webster|first1=Jody M|last2=Wallace|first2=Laura |author-link2=Laura Wallace (scientist) |last3=Silver|first3=Eli|last4=Potts|first4=Donald|last5=Braga|first5=Juan Carlos|last6=Renema|first6=Willem|last7=Riker-Coleman|first7=Kristin|last8=Gallup|first8=Christina|date=2004-02-28|title=Coralgal composition of drowned carbonate platforms in the Huon Gulf, Papua New Guinea; implications for lowstand reef development and drowning|journal=Marine Geology|volume=204|issue=1|pages=59–89|doi=10.1016/S0025-3227(03)00356-6|bibcode=2004MGeol.204...59W |issn=0025-3227}}</ref>

Plate movements carrying carbonate platforms to [[latitude]]s unfavourable for carbonate production are also suggested to be one of the possible reasons for drowning{{explain|date=January 2019}}.<ref name="paradox" /><ref name="Pomar2001" /> For example, [[guyot]]s located in the Pacific Basin between [[Hawaii]]an and [[Mariana Islands]] are believed to be transported to low southern [[latitude]]s (0-10°S) where equatorial [[upwelling]] occurred.<ref name="Pomar2001" /> High amounts of [[nutrient]]s and higher productivity caused decrease in water transparency and increase in bio-eroders populations, which reduced carbonate accumulation and eventually led to drowning{{explain|date=January 2019}}.<ref name="Pomar2001" /><ref>{{cite journal|last1=Hallock|first1=Pamela|last2=Schlager|first2=Wolfgang|date=August 1986|title=Nutrient Excess and the Demise of Coral Reefs and Carbonate Platforms|journal=PALAIOS|volume=1|issue=4|pages=389|doi=10.2307/3514476|issn=0883-1351|jstor=3514476|bibcode=1986Palai...1..389H}}</ref>

=== Highstand shedding ===
[[File:SlopeShedding.png|alt=|thumb|464x464px|Highstand shedding and slope shedding]]
[[Highstand systems tract|Highstand]] shedding is a process in which a carbonate platform produces and sheds most of the sediments into the adjacent basin during highstands of sea level. This process has been observed on all rimmed carbonate platforms in the Quaternary, such as the [[Great Bahama Bank]]. Flat topped, rimmed platforms with steep slopes show more pronounced highstand shedding than platforms with gentle slopes and cool water carbonate systems.<ref>{{cite journal |first1=Wolfgang |last1=Schlager |first2=John J. G. |last2=Reijmer |first3=Andre |last3=Droxler |date=1994|title=Highstand Shedding of Carbonate Platforms|journal=SEPM Journal of Sedimentary Research|volume= 64B|doi=10.1306/D4267FAA-2B26-11D7-8648000102C1865D}}</ref>

Highstand shedding is pronounced on [[Carbonate platform#Tropical factory|tropical carbonate platforms]] because of the combined effect of sediment production and [[diagenesis]].<ref name="Concepts" /> Sediment production of a platform increases with its size, and during [[Highstand systems tract|highstand]] the top of the platform is flooded and the productive area is bigger compared to the [[Lowstand systems tract|lowstand]] conditions, when only a minimal part of the platform is available for production.<ref name="Concepts" /> The effect of increased highstand production is enhanced by the rapid [[lithification]] of carbonate during lowstands, because the exposed platform top is [[karstified]] rather than eroded, and does not export sediment.<ref name="Concepts" />

=== Slope shedding ===
Slope shedding is a process typical of [[Carbonate platform#Mud-mound factory|microbial platforms]], in which the carbonate production is nearly independent from sea level oscillations. The carbonate factory, composed of microbial communities precipitating [[microbialite]]s, is insensitive to light and can extend from the platform break down the slope to hundreds of meters in depth. Sea level drops of any reasonable amplitude would not significantly affect the slope production areas. Microbial boundstone slope systems are remarkably different from tropical platforms in sediment productions profiles, slope readjustment processes and sediment sourcing. Their [[progradation]] is independent from platform sediment shedding and largely driven by slope shedding.<ref name="steep">{{cite journal|date=2005-07-01|title=Steep microbial boundstone-dominated platform margins – examples and implications|journal=Sedimentary Geology|volume=178|issue=1–2|pages=5–30|doi=10.1016/j.sedgeo.2004.12.033|issn=0037-0738|last1=Kenter|first1=Jeroen A.M.|last2=Harris|first2=Paul M. (Mitch)|last3=Della Porta|first3=Giovanna|bibcode=2005SedG..178....5K }}</ref>

Examples of margins that may be affected of slope shedding that are characterized by various contributions of microbial carbonate growth to the upper slope and margin, are:
* the [[Canning Basin]] in Australia 
* the Guilin platform in the southern China
* the Permian of the [[Permian Basin (North America)|US Permian Basin]]
* the middle Triassic carbonate platforms of the [[Dolomites]].<ref name="steep" />

== Gallery ==
<gallery>
File:Cycle émersif Maroc.jpg|"Shallowing upward" cycle in the [[Aganane Formation]] of the high Atlas (Morocco). Algal dolomitized laminations on top.
File:Cycle émersif Oman.jpg|"Shallowing upward" cycles in the lagoonal Lias of the Musandam Peninsula. (N-Oman).
File:Cycle émersif Musandam.jpg|"Shallowing upward" liassic cycles arranged in decametric sequences, Musandam Peninsula, (N-Oman).
File:Cycle émersif Laghdar.jpg|"Shallowing upward" cycle in the Middle Jurassic (Saghtan form.) of the jbel Laghdar Range (Oman).
File:Desiccation Rnim.jpg|[[Desiccation]] figures on top of a regressive sequence; [[Aganane Formation]], High Atlas, Morocco.
File:Calcretes et ammonites.jpg|Ammonites and belemnites washed over a supratidal surface (calcretes and "[[Teepee structure|teepees]]"); [[Aganane Formation]] of the High Atlas, Morocco.
File:Brèche de tempête.jpg|Hurricane breccia cemented (early diagenesis) at the surface of a bed, top of a regressive, metric, sequence. [[Aganane Formation]], High Atlas.
File:Pisolithes vadoses.jpg|Vadose ferrugenous pisolites (soil) and coastal (tempestite) sediment with birdseyes in an outer platform environment. Aerial diagenesis. [[Aganane Formation]], High Atlas, Morocco.
File:Keystone vugs meniscus.jpg|Meniscus and point contact cement in a marine grainstone with displaced foraminifera (by tide and hurricanes) on the supratidal flat of the middle liassic platform of Morocco. Top of emersive cycle. Middle Atlas.
File:Calcretes remaniés dolomie.jpg|Reworked calcretes concretions from the supratidal environment in a marine (dolomitised) sediment displaced by hurricanes on the inner platform flat. Top of emersive sequence. [[Aganane Formation]], High Atlas, Morocco.
File:Ciment stalactite vadose.jpg|Stalactitic cement in sediment from the supratidal zone, vadose environment, top of "shallowing upward" sequence. [[Aganane Formation]], High Atlas. Thin section. L = 0.3&nbsp;mm.
File:Traces dino géant.jpg|Giant dinosaur tracks (sauropod) on top of a regressive sequence, [[Aganane Formation]], High Atlas, Morocco.
File:Calcretes et birdseyes.jpg|Vadose stalactitic cement filling an horizontal cavity in a marine coastal sediment, outer platform. Birdseyes in the allodapic (tidal or tempestite) grainstone point to an aerial diagenesis. [[Aganane Formation]], High Atlas, Morocco.
File:Séquences Lias Todhra.jpg|Autocyclic filling (metric to hectometric) sequences in the Middle Liassic lagoon, South (Todhra) of the [[Aganane Formation]], High Atlas, Morocco.
File:Teepee supratidal flat.jpg|"Teepee" structure, due to increasing sediment volume by dolomitisation on the inner platform supratidal flat. Top of emersive cycle. Middle Lias, [[Aganane Formation]], High Atlas.
File:Carottes chott tunisien.jpg|Quaternary to recent equivalent of a "shallowing upward sequence", cores in a Tunisian "chott", intertidal laminations in yellow.
File:Tunisie teepee.jpg|Recent "teepee" structures in a Tunisian salt lagoon, "chott".
File:Tunisie carottes Zarzis.jpg|Recent equivalents of "shallowing upward sequences", cores in a Tunisian salt lagoon, "chott".
File:Tunisie gypse.jpg|Top of a regressive sequence with algal laminations (yellow) and crystallised gypsum, salt lagoon "chott", Tunisia.
File:Tunisie tempête.jpg|Eolian bioclastic (calcareous algae and porcellaneous foraminifera) sand dune on Tunisian shore.
</gallery>
{{clear}}

==See also==
*[[Ocean bank (topography)]]
*[[Bahama Banks]]

== Footnotes ==
<references/>

== References ==
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* Davaud E. & Septfontaine M. (1995): "Post-mortem onshore transportation of epiphityc foraminifera: recent example from the Tunisian coast line". ''Jour. Sediment. Research'', 65/1A, 136–142.
* Bosellini A., 1984, "Progradation geometries of carbonate platforms: examples from the Triassic of the Dolomites, northern Italy". ''Sedimentology'', Vol. 31, pp.&nbsp;1–24
* [https://web.archive.org/web/20091122081312/http://www.tamug.edu/cavebiology/Bahamas/BahamaIntro.html "Bahamas Introduction" (Accessed 3/8/06)]
* [https://archive.today/20110515100222/http://geology.about.com/library/bl/maps/blfloridamap.htm?terms=geologic+map+of+Florida About.com: "Geologic Map of Florida" (Accessed 3/8/06)]
* Pinet P. R., 1996, ''Invitation to Oceanography''. St. Paul: West Publishing Company, {{ISBN|0-314-06339-0}}
* Septfontaine M. 1985, "Depositional environments and associated foraminifera (lituolids) in the middle liassic carbonate platform of Morocco." ''Rev. de Micropal.'' 28/4 265–289. See also www.palgeo.ch/publications.
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{{Physical oceanography|state=collapsed}}

[[Category:Carbonates]]
[[Category:Sedimentology]]
[[Category:Marine geology]]
[[Category:Undersea banks|.]]
[[Category:Submarine topography]]
[[Category:Sedimentary rocks]]