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→Calcareous nannofossils
[[file:applied-paleontology_fig17-3.png|left|thumb|{{figure number|3}}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 (<25μm) calcite objects produced by unicellular marine plants (golden-brown algae). The origin of nannoliths is uncertain, but these calcite bodies are associated with fossil coccoliths assemblages in marine sediments and are also organically derived.
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.