Changes

Calcareous microfossils have shells composed of calcite or aragonite. These organisms are present in most marine and in some nonmarine environments. At great oceanic depths characterized by low temperature and high hydrostatic pressure, however, calcareous remains are largely or completely dissolved. The depth below which this occurs, which varies in different oceanographic settings, is termed the '''carbonate compensation depth''' (CCD).

Calcareous microfossils have shells composed of calcite or aragonite. These organisms are present in most marine and in some nonmarine environments. At great oceanic depths characterized by low temperature and high hydrostatic pressure, however, calcareous remains are largely or completely dissolved. The depth below which this occurs, which varies in different oceanographic settings, is termed the '''carbonate compensation depth''' (CCD).

There are three principal types of calcareous microfossils: calcareous foraminifera, ostra-codes, and calcareous nannofossils.

There are three principal types of calcareous microfossils: calcareous foraminifera, ostracods, and calcareous nannofossils.

==Calcareous foraminifera==

==Calcareous foraminifera==

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

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

==Ostracodes==

==Ostracods==

[[file:applied-paleontology_fig17-2.png|300px|thumb|{{figure number|2}}Typical ostracodes.]]

[[file:applied-paleontology_fig17-2.png|300px|thumb|{{figure number|2}}Typical ostracods.]]

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:

Ostracods 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 ostracods 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. Ostracods typically have rapid evolutionary rates and are useful biostratigraphic tools in some situations:

* In Paleozoic sequences

* In Paleozoic sequences

* In lacustrine environments, where they are frequently one of the few microfossils present

* In lacustrine environments, where they are frequently one of the few microfossils present

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

Ostracods may also indicate [[thermal maturation]] of source rocks.

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

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

==Calcareous nannofossils==

==Calcareous nannofossils==