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Calcareous nannofossils [usually smaller than 35μm] include calcite-secreting haptophytes (Coccolithophores) and associated nannoliths (Discoasters, Nannoconids, Schizosphaerellids, Pithonellids etc.). Nannoliths may or may not be related to haptophytes (Coccolithophores).

Cocolith coccosphere
Salisia ovata
Discoaster kuepperi

The present day living organisms of the Cocolithophores are marine, unicellular, flagellate phytoplankton, belonging to the phylum Haptophyta and division Class Prymnesiophyceae.

The presence of coccoliths in the Coccolithophore cell is the most important feature.

Haptophytes display an alternation of two distinct cycles in their life history, named a dimorphic life cycle. During their motile phase they possess the haptonema, whereas during the alternating, non-motile phase they lack a haptonema.

The cell normally secretes coccoliths with heterococcolith morphologies in the non-motile phase. In the motile phase it is "naked" or bears coccoliths with holococcolith morphologies. Structurally, heterococcoliths are more complexly constructed than holococcoliths.

Homozygosphaera ponticullfera
Heterococcolith, placolith
Reticulofenestra pseudoumbilicus
Heterococcolith, discolith, zeugoid
Staurolithites aachenus
Heterococcolith, discolith, protolith
Placozygus fibuliformis
Heterococcolith, discolith, cribrilith
Pontosphaera callosa

The more complex heterococcoliths are formed internally during non-motile phase and secreted out to form a coccosphere which externally cover the entire coccolith. In the heterococcoliths, the crystal outline modified and the shapes more delicately molded. The crystal edges and faces may still be observed in the SEM. The placoliths [heterococcolith in structure], have two shields and a tube cycles begin calcification as a narrow ring which amalgamated into the tube cycle and then spreads laterally at the peripheries to form the two shield.

Rhabdosphaera clavigera
Scyphosphaera pulcherrima
Coccolithus palegicus
Helicosphaera intermedia
Scapholithus fossilis
Syracosphaera pulchra
Discosphaera tubifera

Composed of one or very few crystals and initially thought to be nannoliths but latter proved to be heterococcoliths.

Amaerolithus delicatus
Pemma basquense
Micula decussata
Scampanella sp.
Lithostromation perdurum
Triqeutrorhabdulus rioi
Discoaster surculus
Sphenolithus belemnos
Sphenolithus abies
Sphenolithus editus
Thoracosphaera heimii
Leonella granifera
Pernambugia tuberosa
Bonetia truncata
Micrascidites vulgaris
Rigaudia multiradiata
Monniotia fasciculata
Nannofossils first appeared in the Late Triassic; apparently confined to low latitudes. They flourished in all marine environments during the Jurassic and Cretaceous and attained their maximum diversity peak during the Late Cretaceous. Nannofossils had a mass extinction at the Cretaceous/Tertiary boundary, whenover 90% of species became extinct. During the Early Paleocene, nannofossils re-established rapidly and they reached another maximum peak in the Lower Eocene, especially at an event termed Zone NP12. Nannofossil diversity drastically reduced during the Oligocene but flourished again during the Miocene to Pliocene., folloed by a significant reduction in diversity during the Pleistocene. Taxonomic investigation was pioneered by Ehrenberg (1856) first discovered nannofossil, but their organic nature was proved by Wallich (1877). A comprehensive taxonomic study of nannofossils was published by Lohman (1902), supplemented by additional published research between 1920’s and 1850’s by Kamptner and Deflandre (references required) . The application of nannofossil to biostratigraphy was pioneered by Bramlette & Riedel (1954), Stradner (1959, 1961), Bramlette & Sullivan (1961), Bramlette & Wilcoxon (1967), Hay & Mohler (1967), Hay et. al.(1967), Gartner (1969). Numerous taxonomic and biostratigraphic papers were published in the 1970’s by Perch-Nielsen, Bukry and Reinhardt. In the 1970’s, the widely usedCenozoic zonation scheme by Martini (1971) and the Cretaceous zonation scheme by Sissingh (1977) were published.

Bramlette, M.N. & Riedel, W.R. 1954. Stratigraphic value of discoasters and some other microfossils related to Recent coccolithophores. Journal of Paleontology, 28: 385-403.

Bramlette, M.N. & Sullivan, F.R. 1961. Coccolithophorids and related Nannoplankton of the early Tertiary in California. Micropaleontology, 7: 129-188.

Bramlette, M.N., and Wilcoxon, J.A., 1967. Middle Tertiary calcareous nannoplankton of the Cipero Section, Trinidad, W.I. Tulane Stud. Geol, 5:93-132.

Ehrenberg, C. C. 1836. Bemerkungen uber feste mikroskopische, anorganische Formen in den erdigen und derben Mineralien. Ber. Disch. Akad. Wiss., 1836: 84-5

Gartner, S., 1969. Correlation of Neogene planktonic foraminifer and calcareous nannofossils zones. Trans. Gulf Coast Assoc. Geol. Soc., 19:585– 599.

Hay, W.W. & Mohler, H.P. 1967. Calcareous nannoplankton from early Tertiary rocks at Pont Labau, France, and Paleocene-Eocene correlations. Journal of Paleontology, 41: 1505-1541.

Hay, W.W., Mohler, H.P., Roth, P.H., Schmidt, R.R. & Boudreaux, J.E. 1967. Calcareous nannoplankton Zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean area, and transoceanic correlation. Transactions of the Gulf Coast Association of Geological Societies, 17: 428-480.Stradner (1959)

Lohmann, H., 1902. Die Coccolithophoridae, eine mongraphie der Coccolithen bildenden Flagellaten, zugleich ein Beitrag zur Kenntnis des Mittelmeer auftriebs. Arch. Protistenkd., 1:89-165.

Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In Farinacci, A. (Ed.), Proc. 2nd Int. Conf. Planktonic Microfossils Roma: Rome (Ed. Tecnosci.), 2:739-785.

Sissingh, W. 1977. Biostratigraphy of Cretaceous calcareous nannoplankton. Geologie en Mijnbouw 56, 37–65.

Stradner, H. 1959. Die fossilen Discoasteriden Osterreichs. II. Teil. Erdoël-Zeitschrift, 75: 472-488.

Stradner, H., 1961. Vorkommen von Nannofossilien I’m Mesozoikum und Alttertiar. Erdoël-Zeitschrift, 77: 77-88.

Wallich, G.C., 1877. Observations on the coccosphere. Ann. Mag. Natural History (Ser. 4) 19, 342–350.

Living coccoliths have a widespread marine distribution, living mainly in the photic zone and being most diverse at low latitudes. Their abundance and diversity increase with increasing water depth and distance to shore. Physical parameters affecting the distribution of coccoliths include depth of water, hydraulic energy, turbidity, temperature, salinity, calcium, magnesium, strontium, iron, light, photoperiod, oxygen, nitrogen, vitamins and heterotrophy.