Calcidiscus bicircus


Classification: Coccolithophores -> Coccolithales -> Calcidiscaceae -> Calcidiscus -> C. pacificanus group -> Calcidiscus bicircus
Sister taxa: C. bicircus, C. gerrardii, C. pacificanus, C. parvicrucis, C. parvus, C. scullyae, C. kamikurii,

Distinguishing features: Medium to large (5-9 µm) circular-subcircular placoliths with a non-birefringent distal shield and narrow to closed central area surrounded by a narrow, bright tube cycle.


Taxonomy:

Citation: Calcidiscus bicircus Bown, 2005
Rank: Species

Farinacci & Howe catalog pages: Calcidiscus bicircus *

Distinguishing features: Medium to large (5-9 µm) circular-subcircular placoliths with a non-birefringent distal shield and narrow to closed central area surrounded by a narrow, bright tube cycle.

Search data:
TagsLITHS: placolith, elliptical, sub-circular, RIM: rim-broad, CA: Placoliths: closed,
CSPH: spherical, monomorphic, V-UNITS: distal shield, tube, R-UNITS: prox shield, DETAILS: rim-bicyclic, isogyres oblique,
MetricsLith size: 5->9µm;
Sources:
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within NP17 zone (37.32-40.40Ma, top in Priabonian stage). Data source: Bown et al., 2007
First occurrence (base): within NP12 zone (50.50-53.70Ma, base in Ypresian stage). Data source: Shamrock & Watkins 2012

Plot of occurrence data:

  • (NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: C. pacificanus group

    References:

    Bown, P.R., (2005). Palaeogene calcareous nannofossils from the Kilwa and Lindi areas of coastal Tanzania (Tanzania Drilling Project 2003-4). Journal of Nannoplankton Research, 27(1): 21-95.GS

    Bown, P.R.; Dunkley-Jones, T. & Young, J.R., (2007). Umbilicosphaera jordanii Bown 2005 from the Paleogene of Tanzania: confirmation of generic assignment and a Paleocene origination for the family Calcidiscaceae. Journal of Nannoplankton Research, 29(1): 25-30.GS

    Shamrock, J.L. & Watkins, D.K., (2012). Eocene calcareous nannofossil biostratigraphy and community structure from Exmouth Plateau, Eastern Indian Ocean (ODP Site 762). Stratigraphy, 9(1): 1-11.GS

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    Calcidiscus bicircus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 24-4-2019

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    Comments (1)

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    Enis Kemal Sagular (Suleyman Demirel University, Turkey)
    Its images seem to Biscutum blackii from Late Cretaceous species. If being so and found within NP14-NP17 zone assemblage, it may have been reworked from old sediments.
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    Jeremy Young (UCL, UK)
    C. bicircus certainly does resemble Biscutum but it occurs in Tanzania in sites with negligible reworking and has a consistent range there so it probably is an example of homoeomorphy not reworking.
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