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Calcareous nannofossil is the informal name for any
fossil remains composed of calcium carbonate and smaller than about
30 µm. The fossil may be an ascidian spicule, a juvenile foraminiferan
or an algal "calcisphere". The name is most commonly applied
to circular calcite plates or scales called coccoliths that are
produced by a subgroup of single-celled haptophyte algae called
Coccolithophores.
Coccolithophores first appear in the fossil record
in the Late Triassic and are one of the most important groups for
Mesozoic and Paleozoic biostratigraphy.
In ancient sediments the plate-like coccoliths often
occur with more variably-shaped calcite nannoliths , which are thought
to be derived from fossil species closely related to coccolithophores
but have no living representatives.
 Coccolithophores
Coccolithophores belong to the Phylum Haptophyta, Division Prymnesiophyceae,
which are algae with golden-brown chloroplasts and a unique flagella-like
structure called the haptonema..
Coccolithophores are oceanic phytoplankton that live in the photic
zone They are cosmopolitan in distribution, with their highest diversity
in the low latitudes and becoming rare in polar seas (>70°
latitude). The fossilised remains, or coccoliths, are produced at
various stages of their lifecycle
Coccoliths
Coccolith morphology may vary during the lifecycle of the coccolithophore,
with complex crystal structures (heterococcoliths) alternating with
simpler structures (holococcoliths).
 Heterococcoliths
are typically circular or elliptical and constructed from radial
arrays (cycles) of complexly shaped calcite crystals. They are grown
within the cell and extruded onto the cell surface to form an interlocking
skeleton.
 Holococcoliths
are typically simple discs or domed shapes formed by tiny similar-sized
calcite crystals. Holococcolith formation is still poorly understood
but is believed to occur outside the cell.
 Nannoliths
Nannoliths are a group of nannofossils with a wide range of
shapes. They have no living representatives but most have radial
symmetry and a complex crystal structure.
Nannoliths probably represent an artificial grouping as they include
both heterococcolith and holococcolith morphologies along with other
types of calcification.
Nannofossil Research at GNS
Nannofossil biostratigraphy has been an important tool in mapping
and hydrocarbons exploration of New Zealand's Late Cretaceous and
Cenozoic sedimentary basins for thirty years, beginning with pioneering
studies by Tony Edwards of the New Zealand Geological Survey. Tony
Edwards continues to be active as a consultant, focussing primarily
on late Cenozoic biostratigraphy.
Craig Jones undertakes nannofossil research at GNS
and has a primary focus on Paleogene biostratigraphy.
Nannofossil Links
Calcite
Palace - nannofossil taxonomy page
INA
- International Nannofossil Association
Varol Research
(nannofossil biostratigraphy consultancy)
Nannofossils at the USGS
Key References
Bown, P. R. (ed.) 1998. Calcareous nannofossil biostratigraphy,
Chapman and Hall (Kluwer Academic Publishers), 315 pp.
Edwards, A. R. 1971. A calcareous nannoplankton zonation of the
New Zealand Paleogene. In A. Farinacci (ed), Proceedings II Planktonic
Conference, Roma, 1970, 2, pp. 381-419
Hornibrook, N. de B. and Edwards, A. R. 1971. Integrated planktonic
foraminiferal and calcareous nannoplankton datum levels in the New
Zealand Cenozoic. In A. Farinacci (ed), Proceedings II Planktonic
Conference, Roma, 1970, 2, pp. 649-657
Perch-Nielsen, K. 1985. Chapters on Mesozoic calcareous nannofossils
& Cenozoic calcareous nannofossils. In Bolli, H. M., Saunders,
J. B., and Perch Nielsen, K. (eds.), Plankton Stratigraphy,
Cambridge University Press, pp. 329-554.
Siesser, W. G. 1993. Calcareous nannoplankton. In Lipps, J. H. (Ed)
Fossil Prokaryotes and Protists, 169-201, Blackwell Scientific Publishing
Young, J. R. et al. 1997. Guidelines for coccolith and calcareous
nannofossil terminology. Paleontology 40 (4): 875-912.
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