Luminocanthus eolutetiensis, 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 : 344

Luminocanthus eolutetiensis n. gen., n. sp.

( Fig. 19B, C )

urn:lsid:zoobank.org:act:B9D3C0AA-736A-4785-9B04-D58126482E0E

HOLOTYPE. — Fig. 19B ( IRSNB b7121) (negatives stored in the collections of the RBINS).

PARATYPES. — 1 figured specimen (d = 9 µm) from the upper part of the Aalter Sand Formation in the Vlakte van de Raan BH, 79.95 m depth ( Fig. 19C ) ( IRSNB b7122).

DIAGNOSIS. — Circular coccoliths consisting of two appressed shields and including a central disk covered by a series of radially oriented calcite laths and a smaller outer rim with numerous almost indistinct slightly curved elements. Only the outer rim is highly birefringent in cross-polarized light.

DERIVATIO NOMINIS. — Refers to the total range of this species, which seems to be restricted to the earliest part of the Lutetian.

LOCUS TYPICUS. — Vlakte van de Raan borehole, 81.45 m depth, 51°29’08”N, 03°09’50”E.

STRATUM TYPICUM. — Aalter Sand Formation, upper part of Oedelem Sand Member; base of NP14.

DIMENSIONS. — Diameter = all around 9 µm (holotype: d = 9 µm). DISTRIBUTION. — Luminocanthus eolutetiensis n. gen., n. sp. is known from boreholes in the Belgian sector of the North Sea (SEWB and Vlakte van de Raan, see Appendix 1), where it seems to be retricted to the top of the Aalter Sand Formation (base of NP 14). Up to now it has not been recorded in coeval deposits from onshore Belgium.

DESCRIPTION

These medium-sized (d= c. 9 µm)rather thick subcircular forms consist of a prominent outer rim including numerous (probably c. 50) vaguely visible elements and an inner area with radially oriented elements. Both zones are sharply delimited in distal view.The outer rim is rather thick and exhibits high birefringence under crossed nicols, especially the outer rim of the proximal shield ( Fig. 19 Ba). The inner area is only faintly birefringent, although shows a clear extinction cross with laevogyre curvation in distal view.It widens and is somewhat blurry in the outer rim.

D ISCUSSION

This taxon differs from L. plenilutetiensis n. gen., n. sp. ( Fig. 19 G-J) by the configuration of the outer rim and the central area. The outer rim of L. eolutetiensis n. gen., n. sp. is much more elevated, smaller and sharply separated from the central area. This rim is also highly birefringent as in L. plenilutetiensis n. gen., n. sp., but contrarely to the latter, the central area remains only faintly illuminated in cross-polarized light. The extinction lines are rather sharp in the central area and become wider and vague in the outer rim.

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.