Sphenolithus recolletensis Steurbaut & Nolf, 2021, n. sp.
Creators: name: Steurbaut, Etienne
name: Nolf, Dirk
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Chromista
Haptophyta
Coccolithophyceae
Discoasterales
Sphenolithaceae
Sphenolithus
Sphenolithus recolletensis

description: Sphenolithus recolletensis n. sp.
(Fig. 18 Z-AA)
urn:lsid:zoobank.org:act: C09F103A-DD50-4227-AE6E-3B228A020AC9
HOLOTYPE. — Fig. 18 AA (IRSNB b7119) (negatives stored in the collections of the RBINS).
PARATYPES. — 1 figured specimen from the upper part of the Aalter Sand Formation (Unit A4) at Mont-des-Récollets (sample 116.45- 116.50 m) (Fig. 18Z) (IRSNB b7118).
DIAGNOSIS. — Rather large sphenoliths, consisting of an almost cubical lower portion, including the proximal shield and lateral elements, and a conspicuous apical spine with particular optical characteristics, made up of a solid centre and two diverging sword-like blades, which remained joined together over more than half of their length, before diverging distally and finally ending in a long distal threadlike structure. Both blades diverge at an angle of about 70°.
DERIVATIO NOMINIS. — Named after the Mont-des-Récollets at Cassel (N France), refers to the type locality and unique locality record of this species.
LOCUS TYPICUS. — Mont-des-Récollets, ‘ Grande Carrière’, N France; 50°48’02.74”N, 2°30’23.06”E.
STRATUM TYPICUM. — Brussel Sand Formation, base of Unit B1 (sample 117.46-117.51 m); lower part of NP14.
DIMENSIONS. — Height = 11.2 to 13.6 µm (exceptionally 20 µm, see Fig. 18Z) with spine; Height body, without spine = 7.4 to 9 µm; Maximum width (wmab) = 4.4-5.2 µm (holotype: htotal = 11.4 µm, hpp = 3.0 µm, hab = 4.4 µm, hds = 4 µm, wpp = 3.2 µm, wmab = 4.4 µm).
DISTRIBUTION. — This species has a very restricted range, both in time and in space. Up to now it has only been recorded at Montdes-Récollets, and only in the top of the Aalter Sand Formation (upper part of Unit A4) and the base of the Brussel Sand Formation (Units B1 and B2) (lower middle of NP14).
DESCRIPTION
These sphenoliths are robust and rather large, ranging from 11.2 to 14.0 µm in height. Their proximal portion consists of an irregular lattice, almost quadrangular in lateral view (width slightly larger than height), including a basal layer of radial elements (proximal cycle) surmounted by layers of lateral elements (lateral cycle). The apical spine consists of a solid centre and two diverging sword-like blades. These blades remain joined together over more than half of their length, before diverging at an angle of c. 70°. The top of each blade is tapering and ends in a thin and moderately long distal threadlike structure. These structures, as well as the top of the blades, are fragile and are often abraded or broken off.
The outline of these sphenoliths is unique, as well as their optical behaviour. Viewed between crossed nicols at 0° (in position parallel to the polarization directions) the entire sphenolith shows maximum birefringence, with a conspicuous extinction cross in the proximal portion and a vertical extinction line in the apical spine, separating the two halves. Maximum birefringence occurs every 90°. When viewed at 45° the extinction lines in the proximal portion have shifted from a cross-pattern into an x-pattern, whereas only the central part of the apical spine remains strongly birefringent and the blades only faintly. At 32° from maximum birefringence one of the blades becomes completely extinct (also most of its centre). The other blade fades out at c. 26° further clockwise (at c. 58° from the initial starting point).
DISCUSSION
The outline, structure and optical behaviour of the proximal portion of this new Sphenolithus taxon is very similar to that of Sphenolithus radians (Fig. 19Q). Both differ by the outline of the apical spine, which consist of 2 diverging blades in S. recolletensis n. sp. The outline of the apical spine of the latter presents some similarities with these of S. furcatolithoides and S. perpendicularis (see Shamrock 2010a: pl. 1), but clearly differs from these by its massive strongly birefringent candle-shaped form, when viewed at 45°. The angle between the 2 diverging blades of the apical spine (c. 70°) is intermediate to that of S. furcatolithoides (c. 35°) (see Bown 2005: pl. 45) and that of S. perpendicularis (c. 96°) (Fig. 20R). The latter, which has been discovered in the middle Lutetian offshore W Australia (lower part of Zone NP15, restricted to Zone CP13a) (Shamrock 2010a, b), has not been identified at the Mont-des-Récollets. However, a single specimen has been encountered in the middle of the Lede Sand Formation at Balegem (Fig. 20R). This is the first record of S. perpendicularis in the Belgian Basin.
description: Published as part of Steurbaut, Etienne & Nolf, Dirk, 2021, The Mont-des-Récollets section (N France): a key site for the Ypresian-Lutetian transition at mid-latitudes - reassessment of the boundary criterion for the base- Lutetian GSSP, pp. 311-363 in Geodiversitas 43 (11) on page 353, DOI: 10.5252/geodiversitas2021v43a11, http://zenodo.org/record/4891107