Sphenolithus spiniger Bukry, 1971

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 : 353

Sphenolithus spiniger Bukry, 1971

( Fig. 19P )

Sphenolithus spiniger Bukry, 1971: 321 , pl. 6, figs 10-12; pl. 7, figs 1-2.

DISTRIBUTION. — The lowest occurrence of typical Sphenolithus spiniger (as defined below) is in the lower part of the Brussel Sand Formation (at Mont-des-Récollets in Unit B2). It is known from many outcrop and borehole sections of the Brussel Sand Formation and increases in numbers during the Sphenolithus bloom, as recorded in the Diegem and Zaventem outcrop sections (Steurbaut, detailed in forthcoming study). It occurs rarely in the Lede Sand Formation.

DISCUSSION

This sphenolith differs from the other Sphenolithus taxa described herein by its small triangular outline and very distinctive extinction pattern under crossed nicols. Viewed parallel to the polarisation directions it consists of 4 lobes separated by an extinction cross. The 2 proximal lobes are large and oval; the upper 2, which correspond to the lateral elements and spine, are much smaller and triangular. The extinction cross is much broader at its proximal end, so that the separation between the two lower lobes increases in proximal direction. Forms with a similar outline, but with a clearly different extinction pattern, are attributed to Sphenolithus aff. spiniger , known from the upper part of the Aalter Sand Formation and the Brussel Sand Formation. In these foms the lower 2 lobes are also triangular and the extinction cross is not enlarged proximally.

Figures

FIG. 19. — New or less known calcareous nannofossil taxa from the Eocene of the Mont-des-Récollets and other localities in Belgium. Pars 2: A, Nannoturba jolotteana Steurbaut, 2011, Mont-des-Récollets, 104.35 m, d = 15.2 µm (IRSNB b7120); B, C, Luminocanthus eolutetiensis n. gen., n. sp.; B, Vlakte van de Raan BH, 81.45 m depth, holotype, d = 9 µm (IRSNB b7121); C, Vlakte van de Raan BH, 79.95 m depth, paratype, d = 9 µm (IRSNB b7122); D-F, Nannoturba joceliniae n. sp., Mont-des-Récollets; D, 122.85 m, holotype, wm = 17 µm (IRSNB b7123); E, 123.50 m, paratype, wm = 13 µm (IRSNB b7124); F, 122.85 m, paratype, wm = 13 µm (IRSNB b7125); G-J, Luminocanthus plenilutetiensis n. gen., n. sp.; G, Mont-des-Récollets, 122.26-122.21 m, holotype, d = 8.4 µm (IRSNB b7126);H, Vossem, otolith sample Nolf 1974, paratype, d = 5.2 µm (IRSNB b7127); I, Prémontré, sample 12, paratype, d = 9.6 µm (IRSNB b7128); J, Knokke BH, 71.95 m depth, paratype, d = 6.7 µm (IRSNB b7129); K-N, Toweius brusselensis Steurbaut, 2011; K, Knokke BH, 97.50 m, paratype, d = 8.4 µm (IRSNB b6403); L, Mont-des-Récollets 122.85 m, l = 6 µm (IRSNB b7130); M, N, Vossem,otolith sample Nolf 1974, l = 4.6 µm (IRSNB b7131, b7132); O, Cribrocentrum sp. Isnes, sample 8, l = 5.9 µm (IRSNB b7133); P, Sphenolithus spiniger Bukry, 1971, Vossem,otolith sample Nolf 1974, h = 6.2 µm (IRSNB b7134); Q, Sphenolithus radians Deflandre in Grassé, 1952, Vossem, otolith sample Nolf 1974, h = 4.2 µm (IRSNB b7135); R, Sphenolithus moriformis (Bronnimann & Stradner, 1960), Vossem, otolith sample Nolf 1974, h = 3.3 µm (IRSNB b7136); S-V, Pemma spp.; S, Mont-des-Récollets, 115.50 m, d = 9 µm (IRSNB b7137); T-V, Vossem, otolith sample Nolf 1974 (IRSNB b7138, b7139, b7140); T, d = 8.3 µm; U, d = 8.4 µm; V, d = 6.5 µm.