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==Calcareous foraminifera==

==Calcareous foraminifera==

Calcareous foraminifera are a group of unicellular organisms (protists) that secrete a rigid calcite or aragonite shell (or test). Fossils of these forms are found in sediments of brackish to marine origin from Silurian to Holocene in age. Most are benthic (bottom dwelling), but a significant group in the late Mesozoic and Cenozoic are planktonic (floating) forms.

Calcareous foraminifera are a group of unicellular organisms (protists) that secrete a rigid calcite or aragonite shell (or test). Fossils of these forms are found in sediments of brackish to marine origin from Silurian to Holocene in age. Most are benthic (bottom dwelling), but a significant group in the late Mesozoic and Cenozoic are planktonic (floating) forms.

Because many species have limited and well-known environmental ranges, they are excellent paleobathymetric and paleoenvironmental indicators, especially in younger Phanerozoic rocks.

Because many species have limited and well-known environmental ranges, they are excellent paleobathymetric and paleoenvironmental indicators, especially in younger Phanerozoic rocks.

The illustration below shows some typical calcareous foraminifera.

[[:file:applied-paleontology_fig17-1.png|Figure 1]] shows some typical calcareous foraminifera.

[[file:applied-paleontology_fig17-1.png|thumb|{{figure number|17-1}}See text for explanation.]]

 

[[file:applied-paleontology_fig17-2.png|thumb|{{figure number|2}}See text for explanation.]]

Ostracodes are microscopic crustaceans whose fossils are found in Cambrian to Holocene rocks. They occur in most marine and nonmarine depositional environments and are generally excellent environmental indicators. The paleontologic application of ostracodes is limited because (1) they are rare in many sections and (2) many species are endemic to local basins, so their age and environmental ranges are poorly understood. Ostracodes typically have rapid evolutionary rates and are useful biostratigraphic tools in some situations:

Ostracodes are microscopic crustaceans whose fossils are found in Cambrian to Holocene rocks. They occur in most marine and nonmarine depositional environments and are generally excellent environmental indicators. The paleontologic application of ostracodes is limited because (1) they are rare in many sections and (2) many species are endemic to local basins, so their age and environmental ranges are poorly understood. Ostracodes typically have rapid evolutionary rates and are useful biostratigraphic tools in some situations:

Ostracodes may also indicate thermal maturation of source rocks (see “Thermal Maturation”).

Ostracodes may also indicate thermal maturation of source rocks (see “Thermal Maturation”).

The illustration below shows some typical ostracodes.

[[:file:applied-paleontology_fig17-2.png|Figure 2]] shows some typical ostracodes.

[[file:applied-paleontology_fig17-2.png|thumb|{{figure number|17-2}}See text for explanation.]]

 

[[file:applied-paleontology_fig17-3.png|left|thumb|{{figure number|3}}See text for explanation.]]

The term ''calcareous nannofossils'' includes both fossil coccoliths and nannoliths. '''Coccoliths''' are minute (

The term ''calcareous nannofossils'' includes both fossil coccoliths and nannoliths. '''Coccoliths''' are minute (

Calcareous nannofossils are an excellent biostratigraphic tool because of their rapid evolution and geographic dispersal (i.e., their entire life cycle is in the photic zone of the ocean) as well as their varied and distinct morphologies. The oldest known calcareous nannofossils are Late Triassic; they are a crucial microfossil group in calibrating the Jurassic-Holocene marine record. Relatively little has been published about the paleogeographic distributions of calcareous nannofossils; less is known about their exact paleoenvironmental preferences, although they have been shown occasionally to penetrate into shallow marine environments. Their main industrial application is their calibration to published time scales and sequence stratigraphic records, especially the association of high abundance with condensed marine sections.

Calcareous nannofossils are an excellent biostratigraphic tool because of their rapid evolution and geographic dispersal (i.e., their entire life cycle is in the photic zone of the ocean) as well as their varied and distinct morphologies. The oldest known calcareous nannofossils are Late Triassic; they are a crucial microfossil group in calibrating the Jurassic-Holocene marine record. Relatively little has been published about the paleogeographic distributions of calcareous nannofossils; less is known about their exact paleoenvironmental preferences, although they have been shown occasionally to penetrate into shallow marine environments. Their main industrial application is their calibration to published time scales and sequence stratigraphic records, especially the association of high abundance with condensed marine sections.

[[:file:applied-paleontology_fig17-3.png|Figure 3]] shows some typical calcareous nannofossils.

 

[[file:applied-paleontology_fig17-3.png|thumb|{{figure number|17-3}}See text for explanation.]]

==See also==

==See also==