Sphenolithus quadricornutus, 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 : 352

Sphenolithus quadricornutus n. sp.

( Fig. 20 N-Q)

urn:lsid:zoobank.org:act:129C12D5-F3FE-47C6-849A-EE69215A1E64

HOLOTYPE. — Fig. 20N ( IRSNB b7154) (negatives stored in the collections of the RBINS).

PARATYPES. — 3 figured specimens (h without spines = 3.8-4.8 µm): 1 from the Lede Sand Formation, at Balegem ( Fig. 20O ) ( IRSNB b7155) and 2 from Mont-des-Récollets: 1 from the Lede Sand Formation ( Fig. 20P ) ( IRSNB b7156) and 1 from the Brussel Sand Formation (Unit B4) ( Fig. 20Q ) ( IRSNB b7157).

DIAGNOSIS. — Small hourglass-shaped sphenoliths, consisting of a conical proximal column, surmounted by a series of blocky distally widening lateral elements, both of almost equal height, supporting four equally spread diverging spines.

DERIVATIO NOMINIS. — Refers to the four conspicuous diverging spines which rise from the corners of the sphenolith.

LOCUS TYPICUS. — Mont-des-Récollets , ‘ Grande Carrière’, N France; 50°48’02.74”N, 2°30’23.06”E.

STRATUM TYPICUM. — Lede Sand Formation (sample 126.50 m); lower part of NP15.

DIMENSIONS. — Height = 11.2 to 12.8 µm with spine; Height body, without spine = 5 to 6.5 µm; Maximum width (wmab) = 4.4-5.2 µm (holotype: htotal = 11.2 µm, hpp = 2.5 µm, hle = 2.5 µm, hds = 6.2 µm; wpp = 3.4 µm).

DISTRIBUTION. — This species has a rather restricted range. It occurs in the top of the Brussel Sand Formation (Unit B4) and in the Lede Sand Formation at Mont-des-Récollets, and in several outcrops of the Lede Sand Formation (Balegem, Oosterzele) and the base of the overlying Wemmel Sand Member (Oedelem borehole). Its range seems thus to be restricted to the top of NP14 and lower NP15.

DESCRIPTION

These sphenoliths are very tiny, consisting of a conical proximal column and a series of blocky lateral elements, which seem to widen distally, producing the typical hourglass shape. The latter is also easily observed in cross polarized light (see discussion below). Both the proximal column and the area with the lateral elements are of almost equal height (each c. 2.5 µm). Half long diverging spines (maximum 1.5 times as long as the sphenolith’s body) emerge from each of the four corners.

DISCUSSION

Sphenolithus quadricornutus n. sp. bears a striking resemblance to Sphenolithus quadrispinatus , described from the Late Miocene (Tortonian, NN10) of the southern Atlantic (Perch-Nielsen 1980), especially in its dimensions and the length and the position of the spines. They essentially differ in general outline, which is cylindrical in S. quadrispinatus , but hourglass-shaped in S. quadricornutus n. sp. This is also clearly observed in cross-polarized light when seen at 0°. In this position S. quadrispinatus is highly birefringent, consisting of four almost equal rectangular blocks (height is greater than width), separated by extinction lines with cross pattern. S. quadricornutus n. sp. is also strongly birefringent in that position, but presents an x-shaped interference figure, of which the four bright parts are rather rhombic instead of rectangular and separated by extinction lines with cross pattern. Viewed at 45° this cross pattern turns into an x-pattern.

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).