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Impagidinium obscurum

From Fensome et al., 2019:
Vieira et al., 2020, p.384, pl.1, figs.1–9; pl.2, figs.1–6. Holotype: Vieira et al., 2019, pl.1, figs.1–2. Age: Late Paleocene.

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Original description Vieira et al., 2020:

Derivation of name. From the Latin obscurus, which means hidden, indistinct, unclear, dim – with reference to the often-obscured view of the full tabulation of the cyst.

Holotype. Plate 1, figures 1 and 2 at 1742.48 m (core sample), well 25/8-4 (dorsal view). EF coordinates: V50.1/2. Polar axis length 63 mm and equatorial axis length 58 mm.

Type locality. Norwegian North Sea, well 25/8-4, latitude 5915031.3100N, longitude 236042.9700E (Figure 3, location A).

Stratigraphic horizon. Late Paleocene (Thanetian).

Diagnosis. This species of Impagidinium which is characterised by distinctive folding of the surface between septa, giving rise to ridges that often intersect and converge without a clear pattern. The folding of the surface often obscures a clear visualisation of the tabulation.

Description. Intermediate size, proximate dinoflagellate cyst with subpolygonal ambitus and strong preference for polar compression, lacking an apical horn or any polar projection. The wall comprises two closely appressed layers. Both the peri- and endophragm are thin. However, the endophragm is slightly thicker than the periphragm. The periphragm forms sutural crests or septa with more or less uniform height and smooth to slightly undulate margins. Septum height varies from 2 to 6 mm. Areas between septa are scabrate and considerably wrinkled/folded. Although the tabulation is often obscured by the dense folding of the walls combined with a tendency for preservation in polar compression, the tabulation formula has been deciphered based on the organisation of sutural crests in exceptionally well-preserved specimens. The interpreted tabulation is 3–4', 0a, 5–6'', 5–6c, 5–6'''', 1p, 1'''' (see Plate 1, figures 3, 6, 9). Three apical plates are identified. A fourth one may be also present, although it has not been clearly observed, possibly as a result of its merging with plate 10, with no obvious sutural crest between them.

Plate 6'' is either absent or extremely reduced, as is usual within the genus Impagidinium. The archeopyle is precingular, formed by the displacement of plate 300. The operculum is free.
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