Calcareous nannofossils

[2] The nannofossils are a convenient source of geochronological data due to the abundance and rapid evolution of the single-cell organisms forming them (nannoplankton)[3] and ease of handling of the sediment samples.

[5] In 1861 George Charles Wallich and, independently, Henry Clifton Sorby, figured out the organic nature of coccoliths after observing their aggregations, coccospheres.

One of the goals of the Challenger expedition was to understand the nature of the Bathybius,[7] but the scientists aboard the ship reached the conclusion that the gel-like substance apparently holding the disks in a coccosphere together was a result of processing the samples[7] and later declared the coccoliths to constitute the defensive armor of tiny nannoplankton algae (the term was coined in 1909 by Hans Lohmann [de] to identify the tiniest plankton, less than 60 microns in size, that passed through the regular phytoplankton nets).

[4] Research of the nannoplankton systematics in the early 20th century (Erwin Kamptner, Georges Deflandre [fr], and Trygve Braarud[8]) enabled M. N. Bramlette and W. R. Riedel[9] to successfully use the nannofossils for biostratigraphy (1954).

Optical microscopes with cross-polarization and phase-contrast illumination, techniques introduced in 1952 by Kamptner and Braarud & Nordli respectively, are still used for routine field work.

Agnini et al. in 2017 had combined the scales, reintroducing the new biohorizons for the unreliable ones, resulting in schemes coded with CNP for Palaeocene, CNE for Eocene, CNO for Oligocene, CNM for Miocene, CNPL for Pliocene/Pleistocene (CN stands for Calcareous Nannofossils).