Helicolithus varolii


Classification: ntax_mesozoic -> Eiffellithales -> Eiffellithaceae -> Helicolithus -> Helicolithus varolii
Sister taxa: H. anceps, H. trabeculatus, H. leckiei, H. tectufissus ⟩⟨ H. turonicus, H. varolii, H. compactus, H. blairiae, H. sp.

Distinguishing features: Helicolithus with axial cross bars. Cross bars similar in length, and longitudinal bar does not reach ends of central area.


Taxonomy:

Citation: Helicolithus varolii Blair & Watkins 2009
Rank: Species

Farinacci & Howe catalog pages: H. varolii *

Distinguishing features: Helicolithus with axial cross bars. Cross bars similar in length, and longitudinal bar does not reach ends of central area.


Morphology: This ellipsoidal coccolith has a bicyclic rim and an axial cross. The proximal rim cycle exhibits pronounced birefringence in LM while the distal cycle remains dull. The central area is demarcated with an axial cross composed of four overlapping elements. The axial cross does not reach to the ends of the central area. These elements are triangular and contain a medial suture. The medial suture does not span the entire length of the crossbar. [Blair & Watkins 2009]

It differs from most Helicolithus species by having an axial cross instead of a diagonal cross. Helicolithus turonicus contains a near-axial cross that is offset from both the major and minor axes. It superficially resembles Eiffellithus eximius, but differs in having triangle-shaped crossbar elements and a suture that does not span the entire crossbar length. [Blair & Watkins 2009]

Size: 4.5-6.5 µm long (Blair & Watkins 2009)

Search data:
TagsLITHS: murolith, elliptical, CA: cross-axial, ca_disjunct, closed, CROSS-POLARS: rim-bicyclic, V-prominent, R-prominent,
MetricsLith size: 5->8µm;
Data source notes: holotype+/-1.5µm
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within Santonian Stage (83.64-86.26Ma, top in Santonian stage). Data source: Blair & Watkins 2009
First occurrence (base): within Coniacian Stage (86.26-89.77Ma, base in Coniacian stage). Data source: Blair & Watkins 2009

Plot of occurrence data:

References:

Blair, S. A. & Watkins, D. K. (2009). High-resolution calcareous nannofossil biostratigraphy for the Coniacian/Santonian Stage boundary, Western Interior Basin. Cretaceous Research. 30(2): 367-384. gs


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Helicolithus varolii compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 6-3-2021

Taxon Search:
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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=11352 Go to Archive.is to create a permanent copy of this page - citation notes



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