Helenea


Classification: ntax_mesozoic -> Podorhabdales -> Cretarhabdaceae -> Helenea
Sister taxa: Mattiolia, Wisea ⟩⟨ Speetonia ⟩⟨ Cruciellipsis, Flabellites, Grantarhabdus, Helenea ⟩⟨ Cretarhabdus, Retecapsa, Pickelhaube, Miravetesina

Distinguishing features: Elliptical to subcircular cretarhabdids with bicylic rim - outer cycle darker in LM; central area typically narrow with axial or diagonal croos


Daughter taxa (time control age-window is: 0-800Ma)
Helenea chiastia
Medium-sized (5-8 µm) broadly elliptical to subcircular Helenea central area narrow with axial cross and distinctly blocky (square) short spine. Central area length <½ coccolith length (Bralower et al., 1989).
Helenea conus
Medium to large (6-10 µm) subcircular to broadly elliptical; central area with a vaulted axial cross and spine. The bars usually display a dark median line under XPL and flare at their ends.
Helenea quadrata
Medium-sized (5-8 µm) broadly elliptical cretarhabdid coccoliths with a central area spanned by diagonal cross bars. The bars may display median black lines under XPL.
Helenea staurolithina
Medium-sized (5-8 µm), normally to broadly elliptical; central area narrow with axial cross. Central area length ≥½ coccolith length.
Helenea sp.
Specimens not identified to species level

Taxonomy:

Citation: Helenea Worsley, 1971
Rank: Genus
Type species: Helenea staurolithina Worsley, 1971.
Synonyms: Microstaurus Black, 1971
Taxonomic discussion: "Helenea and Microstaurus were described in the same year by Worsley (1971) and Black (1971), and after recombinations, they include one shared species name for different coccoliths. The genus Microstaurus is regarded here as a junior synonym of Helenea, and Microstaurus quadratus Black, 1971, a junior synonym of Helenea staurolithina. Helenea quadrata Worsley, 1971 is included in the genus here and is distinguished by coccoliths with diagonal cross bars." [Bown 2005]
NB Bown (2005), Rutledge (1994) and Perch-Nielsen (1985) all state that Worlsey 1971 has priority over Black 1971 by a few months, but wothut providing further doumntaton. Black 1971 has a printed publciation date of 2nd July 1971, I have not been able to obtain a precise publication date for the Worslyey 1971 (which was a chapter in Farinacci 1971, Proceedings of the Second Planktonic Conference). [my notes - JRY 2020]

Farinacci & Howe catalog pages: Helenea + * , Microstaurus *

Distinguishing features: Elliptical to subcircular cretarhabdids with bicylic rim - outer cycle darker in LM; central area typically narrow with axial or diagonal croos


Morphology: Elliptical to subcircular cretarhabdid coccoliths that in LM show a change in birefringence toward the edge of the shield/rim, creating a diffuse bicyclic image; the outer cycle is narrowest. The central areas are typically narrow and spanned by structures dominated by primary cross bars rather than lateral bars or grills, although the former may be present. Both axial and diagonal cross structures occur. The bars often flare toward their ends.

Search data:
TagsLITHS: placolith, elliptical, CA: cross-axial, ca_disjunct, process, diagonal cross, CROSS-POLARS: rim-bicyclic, R-prominent,
MetricsLith size: 0->0µm;
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 Cenomanian Stage (100% up, 93.9Ma, in Cenomanian stage). Data source: Total of range of species in this database
First occurrence (base): in mid part of Oxfordian Stage (54% up, 160.1Ma, in Oxfordian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Black, M. (1971a). Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society. 38: 381-424. gs

Bown, P. R. & Cooper, M. K. E. (1998). Jurassic. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 34-85. gs

Bown, P. R. (2005c). Early to Mid-Cretaceous Calcareous Nannoplankton from the Northwest Pacific Ocean, Leg 198, Shatsky Rise. Proceedings of the Ocean Drilling Program, Scientific Results. 198: 1-82. gs V O

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

Lambert, B. (1987). Nannofossiles calcaires de l'Albien supérieur et du Vraconnien du Cameroun méridional. Cahiers de Micropaléontologie. 2(2): 33-60. gs V O

Perch-Nielsen, K. (1985b). Mesozoic calcareous nannofossils. In, Bolli, H. M., Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 329-426. gs

Rutledge, D. C. (1994). Calcareous nannofossils of the boreal Lower Cretaceous: Applications in biostratigraphy & palaeoceanography. PhD thesis, University College London. 1-324. gs

Worsley, T. R. (1971). Calcareous nannofossil zonation of Upper Jurassic and Lower Cretaceous sediments from the Western Atlantic. In, Farinacci, A. (ed.) Proceedings of the Second Planktonic Conference Roma 1970. Edizioni Tecnoscienza, Rome 2: 1301-1321. gs


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Helenea compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 25-2-2021

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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=10499 Go to Archive.is to create a permanent copy of this page - citation notes



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