Discoaster sublodoensis Bramlette & Sullivan, 1961

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 : 345

Discoaster sublodoensis Bramlette & Sullivan, 1961

( Fig. 18 I-M)

Discoaster sublodoensis Bramlette & Sullivan, 1961: 162 , pl. 12, fig. 6a-b.

DISTRIBUTION. — Typical 5-rayed specimens.of Discoaster sublodoensis are recorded at the base of Unit A 4 in the well-preserved assemblages of the Vlakte van de Raan borehole and at the base of the ‘Chaumont-en-Vexin sands’ in the Paris Basin, although always in very low numbers. They co-occur with numerous 6-rayed specimens with straight rays (considered herein as ‘late form’ of D. lodoensis ) and other, although more rarely, 6-rayed forms with straight rays without ridges ( D. strictus and alies). In the less well preserved assemblages of the Mont-des-Récollets the typical 5-rayed specimens seem to pop up only from the middle of Unit A4. D. sublodoensis remains quite rare within the totality of its range at the Mont-des- Récollets, although it is consistently found up to the top of Unit B3. It is extremely rare from the base of B4 onward and has not been observed in the base of the overlying Lede Sand Formation.

DISCUSSION

Specimens from the Paris Basin and the Hampshire Basin ( Aubry 1986) are almost identical to these from Belgium, but slightly differ from the holotype (Lodo Formation, California, Bramlette & Sullivan 1961: pl. 12/6), material collected in DSDP holes ( Wei & Wise 1989a: fig. 3/2), and some of the forms recorded at the Ypresian/Lutetian GSSP in Spain ( Molina et al. 2011: plate 1, fig. 2). The latter are marked by a rather wide central area rapidly narrowing and extending into 5 or 6 (exceptionally 7) slender rays and by ray margins, which are slightly bowed inwards near the base of each ray. The area where the rays meet is not sharp and angular, but, on the contrary, distinctly rounded (see Fig. 18M ). The rays of the North Sea Basin specimens have triangular free ends, with straight margins, which meet at clear angles (see Fig. 18 I-K). The central disk, which is marked by a small low stem and low crests along the margin of the rays, ending at the interstices between the rays, is similar within the total population range of the species.

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).