Calculites


Classification: Mesozoic -> Holococcoliths -> Common genera -> Calculites
Sister taxa: Calculites, Lucianorhabdus, Orastrum, Owenia,

Distinguishing features: Holococcoliths with a proximal plate of four blocks; ridged and pitted distal surface; and short, narrow, hollow spines. Entire coccolith bright in xpl in plan view


Daughter taxa: ss (blue => in age window 0-800Ma)
formed of single block
Small Calculites with short, hollow central stem and small basal plate with one to seven pores.
Formed of 4 or 5 blocks
Calculites with four blocks divided along diagonal sutures that bend sharply where they meet the rim. The transverse and longitudinal blocks are in opposing crystallographic orientation.
Sutures nearly aligned with the axes of the ellipse, low birefringence. May have a stem.
Calculites with four blocks divided along broadly diagonal sutures.
Calculites with four blocks divided along near axial sutures.
Formed of 4 blocks like C. obscurus, but with a perforation in each block, and blocks go into extinction separately
Formed of five bocks, with pores and central spine
continuous rim
Small with irregular elongate central opening
Calculites with a single, relatively wide, central perforation 
Small (holotype 3.3 µm), with wide central plate with multiple perforations.
Medium sized (holotype 5.3 µm) with a small central perforation and kinked isogyres.
Very small (holotype 2.6 µm) Calculites with a long, narrow, central perforation
Small Calculites with four blocks divided along near axial sutures (extinction lines) at 0˚ and diagonal sutures (extinction lines) at 45˚ to the polarising directions.
Small (holotype 4µm) species with a long, narrow central perforation.
Small with very small central perforation
Early Cretaceous species
Small elliptical holococcolith forming single block with low birefirngence; process and several depressions
Small holococcoliths with a rim, and central-area plate divided by a distinct, longitudinal suture.
Specimens not identified to species level

Taxonomy:

Citation: Calculites Prins & Sissingh in Sissingh, 1977
Rank: Genus
Type species: Calculites obscurus (Deflandre, 1959) Prins & Sissingh in Sissingh, 1977

Farinacci & Howe catalog pages: Calculites *

Distinguishing features: Holococcoliths with a proximal plate of four blocks; ridged and pitted distal surface; and short, narrow, hollow spines. Entire coccolith bright in xpl in plan view


Morphology remarks: At present Calculites includes two main types of holococcoliths. (1) Disk-shaped holococcoliths formed of a few blocks - i.e. the holococcoliths crystallites are aligned over large areas and these areas go into extinction as single pseudo-crystals (with overgrowth they may actually turn into large crystals). As the holococcolith is rotated in xpl the blocks go in and out of extinction but the sutures between them do not move. Most of these holococcoliths also show rather high birefringence and broadly radial c-axis orientation. Well-preseved specimens may be hollow and may have a thin rim with more continuous radial extinction orientations. The typical shape is a roughly elliptical disk but this may have a central process and/or sculpted surface and/or depressions (which appear as dark 'pores' in lm). This group includes the type species C. obscurus.
(2)   Disk-shaped holococcoliths with a continuous rim - i.e. holococcoliths with a rim formed of crystallites of continuously varying orientation. This rim is bright in xpl with clear isogyres which move around the coccolith as the coccolith orientation changes. In most cases the isogyres are aligned axially when the coccolith is parallel to the polarisers and form a pair of V-shaped wedges at the ends of the coccolith when it is in the 45° position. The rim width varies and the central part is usually darker, and although it is probably only occasionally a true opening it is typically described as a perforation. [my interpretation - JRY 2020]

Search data:
TagsLITHS: holococcolith, elliptical, hollow, CA: pores, vacant, process, closed, V-UNITS: V-prominent, R-UNITS: R-prominent, DETAILS: ca_conjunct, 1ou, rim-unicyclic,
MetricsLith size: 2->9µm;
Sources: size range of included species
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): at top of Maastrichtian Stage (100% up, 66Ma, in Maastrichtian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Hauterivian Stage (0% up, 133.9Ma, in Hauterivian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Early Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 86-131. gs :: ::

Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs :: ::

Sissingh, W. (1977). Biostratigraphy of Cretaceous calcareous nannoplankton. Geologie en Mijnbouw. 65(1): 37-65. gs :: ::


nannotaxlogo400px

Calculites compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 29-5-2020

Taxon Search:
Advanced Search

Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10163 Go to Archive.is to create a permanent copy of this page - citation notes



Comments (0)

No comments yet on this page. Please do add comments if you spot any problems, or have information to share

Add Comment

* Required information
1000
Captcha Image
Powered by Commentics