Blackites aff. gladius ( Locker, 1967 ) Varol, 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 : 352

Blackites aff. gladius ( Locker, 1967) Varol, 1989 ( Fig. 20L, M )

Rhabdosphaera gladius Locker, 1967: 766 , pl. 1, fig. 1; pl. 2, fig. 12.

Blackites gladius – Varol 1989: 286.

DISTRIBUTION. — Blackites aff. gladius is only known from three records, one in Belgium, one in the Paris Basin and one in the Aquitaine Basin. It rarely co-occurs with Blackites inflatus in the Isnes quarry in SW Belgium, where its presence seems to be restricted to the top of the Brussel Sand Formation. A few specimens have been identified in the Donzacq Marl (upper NP14) at Saint-Geoursd’Auribat (Aquitaine Basin) ( Lin et al. 2017) and in the upper part of the ‘Glauconie Grossière s.s.’ at Margival (Paris Basin, sample 3 in Steurbaut 1988), where it also co-occurs with B. inflatus . B. aff. gladius seems to indicate late Biochron NP14, also known as Biochon NP14b (sensu Berggren et al. 1995). It has not been recorded at the Mont-des-Récollets because of major erosion of the top of the Brussel Sand Formation in N France.

DISCUSSION

This medium-sized rhabdolith (c. 11 µm length) is marked by a very wide basal plate (c. 4.8 µm) and a lensiform stem, which maximum width is located in the upper half of the stem. The latter, which presents a basal collar, seems to be thin-walled ( Fig. 20L ) and rugose towards the top. These rhabdoliths bear great resemblance with those of B. gladius ( Varol 1989: pl. 4, fig. 5; Bown 2005: pl. 21, figs 10-14). However, they differ by certain features of the stem, which is relatively longer and more slender in B. aff. gladius , especially in the top part, as well as by the position of its maximum width. The latter is less distal compared to its position in B. gladius .

Figures

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).