Sphenolithus recolletensis, Steurbaut, Etienne & Nolf, Dirk, 2021

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, Geodiversitas 43 (11), pp. 311-363 : 353

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.

Figures

FIG. 18. — New or less known calcareous nannofossil taxa from the Eocene of the Mont-des-Récollets and other localities in Belgium;a, b, c, views of the same specimen, in transmitted light or cross-polarized light or vice versa, and in different positions with respect to the polarisation directions. Numbers (e.g. IRSNB bXXXX) refer to the collections of the Royal Belgian Institute of Natural Sciences (Brussels).Pars 1: A-D, Braarudosphaera stylifera Troelsen & Quadros,1971,Mont-des-Récollets,122.85 m (IRSNB b7093,b7094,b7096);A, wm = 13 µm;B, wm = 12 µm;D, wm = 14.5 µm;C, Mont-des-Récollets,124.10 m (IRSNB b7095),wm = 13 µm;E, Lanternithus minutus Stradner, 1962, Mont-des-Récollets, 122.85 m, l = 5.6 µm (IRSNB b7097); F, G, Martiniaster cecellanoriae n. sp.: F, Chaumont-en-Vexin, sample 11, 0.55 m above base of the Lutetian, paratype,d = 13 µm (IRSNB b7098);G, Leuven BH,23.70 m depth, holotype,d = 14 µm (IRSNB b7099);H, Discoaster praebifax Wei & Wise,1989, Mont-des-Récollets,116.45 m, d = 7 µm (IRSNB b7100);I-M, Discoaster sublodoensis Bramlette & Sullivan,1961,Mont-des-Récollets,116.45 m (IRSNB b7101,b7102); J, d = 15.2 µm; I, d = 16 µm; K, Mont-des-Récollets, 118.35 m, d = 11.6 µm (IRSNB b7103); L, Vossem, otolith sample Nolf 1974, d = 7 µm (IRSNB b7104); M, Gisors, Bassin de Paris,sample 3,d = 14 µm (IRSNB b7105);N, Martiniaster fragilis (Martini,1961), Mont-des-Récollets,122.85 m, wm = 12 µm (IRSNB b7106);O-R, Discoaster wemmelensis Achuthan & Stradner,1969;O, Mont-des-Récollets, 122.85 m, d = 5.6 µm (IRSNB b7107); P-R, Vossem,otolith sample Nolf 1974 (IRSNB b7108, b7109, b7110);P, d = 5.3 µm; Q, d = 4.4 µm; R, d = 4.3 µm;S-V, Blackites minusculus n. sp.; S, Mont-des-Récollets,117.46 m, paratype, l = 8.8 µm (IRSNB b7111); T-V, Vossem, otolith sample Nolf 1974; T, U, paratypes (IRSNB b7112, b7113); T, I = 8.2 µm;U, I = 7.2 µm;V, holotype,I = 8.56 µm (IRSNB b7114); W-Y, Trochoaster nodosus n. sp.; W, Chaumont-en-Vexin,sample 16, 0.80 m above base of the Lutetian,holotype, d = 16 µm (IRSNB b7115);X, Vilvoorde BH, 5.80 m depth,paratype,d = 15 µm (IRSNB b7116); Y, Oedelem BH, 11.70 m depth, paratype, d = 15 µm (IRSNB b7117); Z-AA, Sphenolithus recolletensis n. sp.; Z, Mont-des-Récollets, 116.45 m, paratype, htot = 20 µm (IRSNB b7118);AA, Mont-des-Récollets, 117.46 m, holotype (a, c, parallel to the polarization directions;b, at 45°), htot = 11.4 µm (IRSNB b7119).

FIG. 19. — New or less known calcareous nannofossil taxa from the Eocene of the Mont-des-Récollets and other localities in Belgium. Pars 2: A, Nannoturba jolotteana Steurbaut, 2011, Mont-des-Récollets, 104.35 m, d = 15.2 µm (IRSNB b7120); B, C, Luminocanthus eolutetiensis n. gen., n. sp.; B, Vlakte van de Raan BH, 81.45 m depth, holotype, d = 9 µm (IRSNB b7121); C, Vlakte van de Raan BH, 79.95 m depth, paratype, d = 9 µm (IRSNB b7122); D-F, Nannoturba joceliniae n. sp., Mont-des-Récollets; D, 122.85 m, holotype, wm = 17 µm (IRSNB b7123); E, 123.50 m, paratype, wm = 13 µm (IRSNB b7124); F, 122.85 m, paratype, wm = 13 µm (IRSNB b7125); G-J, Luminocanthus plenilutetiensis n. gen., n. sp.; G, Mont-des-Récollets, 122.26-122.21 m, holotype, d = 8.4 µm (IRSNB b7126);H, Vossem, otolith sample Nolf 1974, paratype, d = 5.2 µm (IRSNB b7127); I, Prémontré, sample 12, paratype, d = 9.6 µm (IRSNB b7128); J, Knokke BH, 71.95 m depth, paratype, d = 6.7 µm (IRSNB b7129); K-N, Toweius brusselensis Steurbaut, 2011; K, Knokke BH, 97.50 m, paratype, d = 8.4 µm (IRSNB b6403); L, Mont-des-Récollets 122.85 m, l = 6 µm (IRSNB b7130); M, N, Vossem,otolith sample Nolf 1974, l = 4.6 µm (IRSNB b7131, b7132); O, Cribrocentrum sp. Isnes, sample 8, l = 5.9 µm (IRSNB b7133); P, Sphenolithus spiniger Bukry, 1971, Vossem,otolith sample Nolf 1974, h = 6.2 µm (IRSNB b7134); Q, Sphenolithus radians Deflandre in Grassé, 1952, Vossem, otolith sample Nolf 1974, h = 4.2 µm (IRSNB b7135); R, Sphenolithus moriformis (Bronnimann & Stradner, 1960), Vossem, otolith sample Nolf 1974, h = 3.3 µm (IRSNB b7136); S-V, Pemma spp.; S, Mont-des-Récollets, 115.50 m, d = 9 µm (IRSNB b7137); T-V, Vossem, otolith sample Nolf 1974 (IRSNB b7138, b7139, b7140); T, d = 8.3 µm; U, d = 8.4 µm; V, d = 6.5 µm.

FIG. 20. — New or less known calcareous nannofossil taxa from the Eocene of the Mont-des-Récollets and other localities in Belgium.Pars 3: A-G, Blackites praeinflatus n. sp.; A, Mont-des-Récollets, 122.26-122.21 m, holotype, l = 23.0 µm (IRSNB b7141); B, paratype, Mont-des-Récollets, 122.16 m, paratype, l = 22.5 µm (IRSNB b7142); C, Mont-des-Récollets, 122.26-122.21 m, paratype, l = 24.0 µm (IRSNB b7143); D, Zaventem, sample 17, paratype, l = 24.0 µm (IRSNB b7144); E, Mont-des-Récollets,122.26-122.21 m, paratype,l = 29.0 µm (IRSNB b7145); F, G, Vossem, otolith sample Nolf, 1974, paratypes (IRSNB b7146, b7147); F, l = 23.05 µm; G, l = 15.2 µm;H-K, Blackites inflatus (Bramlette & Sullivan, 1961);H, Isnes,sample 8, l = 17.5 µm (IRSNB b7148);I, Gobertange,sample Go5, l = 28 µm (IRSNB b7149); J, Isnes, sample 8, l = 18 µm (IRSNB b7150); K, Gobertange, sample Go5, l = 26 µm (IRSNB b7151); L-M, Blackites aff. gladius (Locker, 1967), Isnes, sample 8 (IRSNB b7152, b7153); L, l = 10.46 µm; M, l = 11.76 µm; N-Q, Sphenolithus quadricornutus n. sp.; N, Mont-des-Récollets, 126.50 m, holotype, htot = 9 µm, hpc = hle = 2 µm (IRSNB b7154); O, Balegem, level 6, paratype, hpc + hle = 4 µm (IRSNB b7155); P, Mont-des-Récollets 126.50 m, paratype,htot = 6 µm, hpp + hle = 3 µm (IRSNB b7156); Q, Mont-des-Récollets, 122.85 m, paratype, htot = 9 µm, hpc + hle = 3 µm (IRSNB b7157); R, Sphenolithus perpendicularis Shamrock, 2010, Balegem, level 6, h = 5 µm (IRSNB b7158); S, Trochastrites hohnensis (Martini, 1958). Mont-des-Récollets, 122.85 m, wm = 12 µm (IRSNB b7159); T-W, Trochastrites pyramidalis n. sp.; T, Oedelem BH, 5.50 m, paratype, wm = 10 µm (IRSNB b7160); U, Mont-des-Récollets,122.16 m, holotype, wm = 12 µm (IRSNB b7161); V, Oedelem BH,5.50 m, paratype,wm = 13 µm (IRSNB b7162); W, Vlakte van de Raan BH,80.27 m, paratype, wm = 12 µm (IRSNB b7163).