Distinguishing features: Parent taxon (Common genera): The four most commonly recorded genera This taxon: 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
ss (time control age-window is: 0-800Ma)
formed of single block
Calculites favosus Small Calculites with short, hollow central stem and small basal plate with one to seven pores.
Formed of 4 or more blocks
Calculites anfractus 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.
Calculites axosuturalis Sutures nearly aligned with the axes of the ellipse, low birefringence. May have a stem.
Calculites obscurus Calculites with four blocks divided along broadly diagonal sutures.
Calculites ovalis Calculites with four blocks divided along near axial sutures.
Calculites rosalyniae Formed of 4 blocks like C. obscurus, but with a perforation in each block, and blocks go into extinction separately
Calculites paulus Very small (holotype 2.6 µm) Calculites with a long, narrow, central perforation
Calculites percernis 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.
Calculites proscissus Small (holotype 4µm) species with a long, narrow central perforation.
Distinguishing features: Parent taxon (Common genera): The four most commonly recorded genera This taxon: 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: 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]
Lith size: 2->9µm; Data source notes: 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 Danian stage). Data source: Total of ranges of the species in this database First occurrence (base): within Early Hauterivian Substage (130.60-132.60Ma, base in Hauterivian stage). Data source: Total of ranges of species in this database
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
Neptune data: This is a higher taxon page so Neptune data is not plotted. See also: customisable plot Parent: Common genera
References:
Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Lower Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 86-131. gsO
Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 132-199. gsO
Sissingh, W. (1977). Biostratigraphy of Cretaceous calcareous nannoplankton. Geologie en Mijnbouw. 65(1): 37-65. gs
Missing or ambiguous references: Heck 1980;
Calculites compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 15-9-2024
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