Tonromeinia deflandrei

Bowman & Varol, 2021 Dec 28, 2022

Set number: 2347

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10µm

Tonromeinia deflandrei, Late Paleocene, DSDP Leg 25, Site 245, Mozambique Channel (Davie Ridge), Indian Ocean

Holotype

Final Epithet

Tonromeinia deflandrei Bowman & Varol, 2021

Basionym

Tonromeinia deflandrei Bowman & Varol, 2021

Diagnosis

A large elliptical species of Tonromeinia consists of two narrow discs, a low column and a featureless central area lacking a tube cycle. The diameter and height/thickness of the two discs and a column all appear equal. The width of the central opening is greater than the width of the discs/a column, and this primary width ratio characterises the species.

Etymology

In honour of the late Prof. Dr G. Deflandre, the renowned French nannofossil specialist, a great pioneer of nannofossil taxonomy.

Dimensions Of Holotype

Overall length: 9.10μm; Overall width: 8.25μm; Central Opening width: 4.47μm; Central Opening length: 5.32μm; Discs/Column width:1.88μm.

Description

Large (8.0–11.0μm) elliptical species constructed of two discs and a column. The discs/a column are of equal diameter and height/thickness. The diameter of the large central opening (without tube cycle) is greater than the width of the discs/column.

Optical Properties

In cross-polarised light, the extinction lines are dextrogyre patterns on the distal side, whereas the proximal side exhibits laevogyre pattern extinction lines. When viewed using a gypsum plate, the distal side corresponds with the arrangement of the horizontal axis and the blue region. Still, the affiliation of the vertical axis and blue pattern relates to the proximal side. The discs/columns display whiteish birefringence colours in plan view.

Observation of this species is restricted to plan-view, as the limited height of the column prevents sufficient mass distribution along the height axis.

Remarks

The width ratio criteria associated with Tonromeinia deflandrei establishes that the width of the central opening is greater than the width of the discs/column. Tonromeinia deflandrei possesses a large central opening that is much greater than the width of the discs/column. By comparison, Tonromeinia noeliae displays a narrower central opening than the width of the discs/column. Moreover, in plan-view, the birefringence colours of Tonromeinia deflandrei are whiteish but yellowish in Tonromeinia noeliae. Finally, Tonromeinia deflandrei and Tonromeinia noeliae appear elliptical in overall shape, whereas all other species of Tonromeinia are circular.

References

Bowman, A. R. & Varol, O. 2021. A Taxonomic Revision of Heliolithaceae - Applications in Resolving the Problematic Calcareous Nannofossil Biostratigraphy of the Paleocene. In: M. Montenary, M. (Ed.). Calcareous nannofossil biostratigraphy of the Stratigraphy and timescales. 6: 43-223.