Heliolithus margarita
Set number: 2446
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Holotype in the mobile mount
Set number: 2445
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In the mobile mount.
Set number: 2444
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Set number: 2443
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Set number: 2442
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In the mobile mount
Set number: 2441
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Set number: 2440
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In the mobile mount
Set number: 2439
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In the mobile mount
Set number: 2438
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In the mobile mount
Set number: 2477
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Set number: 2476
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Set number: 2475
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Set number: 2474
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Set number: 2473
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Heliolithus? margarita Bowman & Varol, 2021
A medium to large-sized and circular species of Heliolithus featuring a strangely formed disc and a vestigial and/or undetectable column. The relatively wide central canal is closed by the plug/tube cycle. In plan view, the bizarre disc gives a “daisy-like” appearance. The species appears birefringent in all views.
From Latin margarita, meaning daisy—referring to the daisy-like appearance of the species in plan-view.
Overall height: 3.61μm; Disc diameter: 9.56μm.
Medium to large (6.0–10.0μm) circular species composed of one disc and a vestigial column [very low or undetectable column]. The disc is moderately wide and appears relatively flat or very slightly convex. The relatively wide central canal is closed by a plug/tube cycle but often removed by adverse paleoenvironmental conditions. The disc is comprised of about 24–40 segments, but the segments of the plug/tube cycle are indistinct.
A distinct depression is present on one side of the disc. In plan view, the disc's character produces a daisy-like appearance in the species. The distal side is associated with dextrogyre extinction lines (e.g. Pl. 79, figs. 10, 14 in Bowman & Varol, 2021), whereas laevogyre extinction lines characterise the proximal side (e.g. Pl. 79, figs. 11–15 in Bowman & Varol, 2021). The horizontal axis relates to the blue sector on the distal side; however, the vertical axis relates to the blue sector on the proximal side (observed using the gypsum plate). The disc and column are birefringent in side-view and plan-view. More specifically, the disc and column show a whiteish-yellowish birefringence colour in plan-view, and the disc displays a reddish-yellowish birefringence colour in the side-view.
Heliolithus? margarita represents a strange and atypical form; therefore, assigning this species to Heliolithus is questionable. Heliolithus? margarita possesses a vestigial column, which is the diagnostic feature used to separate this species from other Heliolithus species. In addition, this species differs from the species of Caycedoa based on the diagnostic birefringent pattern of its disc. The disc is non-birefringent in plan-view in the species of Caycedoa.
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.
Holotype
Heliolithus? margarita
Bowman & Varol, 2021
Late Paleocene
DSDP Leg 25, Site 245, Mozambique Channel (Davie Ridge), Indian Ocean