Platform (geology)
Encyclopedia
In geology, a platform is a continental area covered by relatively flat or gently tilted, mainly sediment
ary strata
, which overlie a basement
of consolidated igneous or metamorphic rocks of an earlier deformation. Platforms, shields
and the basement rocks
together constitute craton
s.
It is also common practice to use the term platform as a general term for a sequence of shallow water carbonate platform
s. Carbonate platforms can develop in almost any tectonic setting, but they are particularly common along passive margin
s. Many oilfields produce from sediments deposited along carbonate platforms.
Various types of carbonate platforms are recognised, including (but are not restricted to) rimmed shelf, ramp, epiric platforms, isolated platforms and drowned platforms.
An example of carbonate "bahamian type" platform, in a paleotectonic context of continental rifting during the Lias is the high Atlas
of Morocco
(Septfontaine, 1985). The coastal and lagoonal to supratidal "chotts" deposits of southern Tunisia
(Zarzis area) is also a good recent equivalent model (Davaud & Septfontaine, 1995).
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
ary strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
, which overlie a basement
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
of consolidated igneous or metamorphic rocks of an earlier deformation. Platforms, shields
Shield (geology)
A shield is generally a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. In all cases, the age of these rocks is greater than 570 million years and sometimes dates back 2 to 3.5 billion years...
and the basement rocks
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
together constitute craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
s.
It is also common practice to use the term platform as a general term for a sequence of shallow water carbonate platform
Carbonate platform
A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonous 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...
s. Carbonate platforms can develop in almost any tectonic setting, but they are particularly common along passive margin
Passive margin
A passive margin is the transition between oceanic and continental crust which is not an active plate margin. It is constructed by sedimentation above an ancient rift, now marked by transitional crust. Continental rifting creates new ocean basins. Eventually the continental rift forms a mid-oceanic...
s. Many oilfields produce from sediments deposited along carbonate platforms.
Various types of carbonate platforms are recognised, including (but are not restricted to) rimmed shelf, ramp, epiric platforms, isolated platforms and drowned platforms.
An example of carbonate "bahamian type" platform, in a paleotectonic context of continental rifting during the Lias is the high Atlas
Atlas Mountains
The Atlas Mountains is a mountain range across a northern stretch of Africa extending about through Morocco, Algeria, and Tunisia. The highest peak is Toubkal, with an elevation of in southwestern Morocco. The Atlas ranges separate the Mediterranean and Atlantic coastlines from the Sahara Desert...
of Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
(Septfontaine, 1985). The coastal and lagoonal to supratidal "chotts" deposits of southern Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
(Zarzis area) is also a good recent equivalent model (Davaud & Septfontaine, 1995).