Discoaster praebifax Wei & Wise, 1989

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 praebifax Wei & Wise, 1989 ( Fig. 18H )

Discoaster praebifax Wei & Wise, 1989b: 11 , fig. 3.

DISTRIBUTION. — In the southern North Sea Basin the LO of D. praebifax slightly precedes the LO of Discoaster sublodoensis (e.g. at Aalter, beds 4 to 9: Steurbaut & Nolf 1989, erroneously interpreted as D. bifax ), and is, consequently, within the top of NP13. At the Mont-des-Récollets, D. praebifax first occurs in the upper part of the Aalter Sand Formation (lower NP14) and ranges up to the base of the Wemmel Sand Member. Its earliest record is from Aktulagay (west Kazakhstan), where it appears at the base of NP13 ( King et al. 2013).

DISCUSSION

In their investigation of middle Eocene calcareous nannofossil associations of two DSDP holes, Wei & Wise (1989b) separated the discoasters with high numbers of rays (16-27) and one prominent central stem from similar forms with fewer rays (10-15), known as Discoaster bifax Bukry, 1971 , to which they previously have been attributed (e.g. in Perch- Nielsen 1985; Aubry 1986). The populations with high ray numbers were grouped into D. praebifax , which, in view of its morphological similarities and stratigraphic relationship, was suggested to be the ancestor of the latter. The number of rays in the Mont-des-Récollets specimens ranges between 20 and 22, evidencing the presence of D. praebifax only.

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).