Blackites minusculus, 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 : 348-350

Blackites minusculus n. sp.

( Fig. 18 S-V)

urn:lsid:zoobank.org:act:9B705E57-195D-405F-A8C0-51A169BE9B57

Blackites perlongus – King et al. 2013: 187 (non B. perlongus Deflandre in Grassé, 1952).

HOLOTYPE. — Fig. 18V ( IRSNB b7114) (negative stored in the collections of the RBINS).

PARATYPES. — 3 figured specimens (l = 7.2-8.8 µm, w = 1.0 µm) from the Brussel Sand Formation, 1 from the Mont-des-Récollets (Unit B1) ( Fig. 18S ) ( IRSNB b7111) and 2 from Vossem (Unit B3) ( Fig. 18 T-U) ( IRSNB b7112, b7113).

DIAGNOSIS. — Tiny rhabdoliths, without a basal enlargement or collar, including a tapering stem wirh irregular surface surmounting a thin basal plate.

DERIVATIO NOMINIS. — Refers to the thin and delicate rhabdoliths,which are minuscule compared to most of the other representatives of the genus.

LOCUS TYPICUS. — Vossem:otolith sample taken in middle of the quarry by D. Nolf in 1974, about 1.50 m beneath a conspicuous sandstone (map 32/1, x = 164.175, y = 169.290; 50°50’01.96”N, 4°34’08.96”E) .

STRATUM TYPICUM. — Brussel Sand Formation, middle of Unit B 3; lower middle part of NP14.

DIMENSIONS. — Length = 7.5 to 10.4 µm; Maximum width of stem = 1.0 to 1.1 µm; Maximum width of basal plate = 1.7 to 2.1 µm (holotype: l = 8.6 µm, wm = 1.1 µm, wbp = 1.8 µm).

DISTRIBUTION. — At the Mont-des-Récollets B. minusculus n. sp. ranges from the top of the Aalter Formation (upper part of Unit A4) up to the upper part of the Brussel Sand Formation (top Unit B3), although inconsistently and in low numbers. It has not been recorded in Unit B4, and rarely in the overlying Lede Sand Formation at this locality. It occurs in many outcrops of the Brussel Sand Formation in its type-area (Vossem, Neerijse, St-Lambrechts-Woluwe, Nederokkerzeel, etc.), essentially in Unit B3 and is known from Unit B 4 in the Vlakte van de Raan BH (Steurbaut unpublished). This species is consistenly present in the ‘Chaumont-en-Vexin sands’ of the Paris Basin, attributable to the base of NP14. Hence, its range in the North Sea Basin seems to be restricted to NP14 and the lower part of NP15, with a major influx in the lower middle part of NP14 (Unit B3). B. minusculus n. sp. has been encountered in west Kazakhstan, also in low numbers, but appearing at a slightly lower position (middle of NP13) ( King et al. 2013).

DESCRIPTION

The rhabdoliths of this new taxon are tiny, ranging from 7.5 to 10.4 µm in length. They consist of a slender tapering stem, without a collar, surmounting a thin basal plate. The stem is slightly inflated in its upper part, reaching its maximum thickness at about 1/5 of its length, measured from the rounded distal tip. Its surface is rugose. The basal plate consists of 1 layer of radially oriented elements.

DISCUSSION

The presence of an elongated stem, rising vertically from a rather small and thin basal plate, and its optical characteristics (typical vertical extinction line and interference colours of the stem) allow this taxon to be attributed to the genus Blackites . It is distinct from all other described Blackites taxa by its tiny rhabdoliths (generally around 8.5 µm in length, maximum width c. 1 µm). Its silhouette resembles that of B. perlongus , although the latter is twice as long (17- 18 µm for holotype, see Deflandre & Fert 1954: pl. XII, figs 34-35, text fig. 86) and has its maximum thickness in a more central position (c. at the middle of the stem) (see also Bown 2005: pl. 24).

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).