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 Author Steurbaut, Etienne Royal Belgian Institute of Natural Sciences, OD Earth and History of Life, Vautierstraat 29, B- 1000 Brussel (Belgium) and Department of Earth, and Environmental Sciences, KU Leuven, Celestijnenlaan 200 E, B- 3001 Leuven (Belgium) etienne.steurbaut@naturalsciences.be Author Nolf, Dirk Royal Belgian Institute of Natural Sciences, OD Earth and History of Life, Vautierstraat 29, B- 1000 Brussel (Belgium) text Geodiversitas 2021 2021-05-25 43 11 311 363 journal article 10.5252/geodiversitas2021v43a11 fc56a00d-cf6b-4fda-aa56-d0492e4781cb 1638-9395 4891107 urn:lsid:zoobank.org:pub:07D1F5A8-98E2-40F1-A716-D25CB975EA4C Nannoturba joceliniae n. sp. ( Fig. 19 D-F) urn:lsid:zoobank.org:act: 86C68780-D532-4C0E-9AB7-8C5749A5D19A HOLOTYPE . — Fig. 19D ( IRSNB b7123) (negatives stored in the collections of the RBINS ). PARATYPES . — 2 figured specimens from the Mont-des-Récollets (lmax = 17.6 µm ): 1 from the sample that yielded the holotype (Unit B4, sample 122.85 m ) ( Fig. 20F ) ( IRSNB b7125) and 1 from the base of the Lede Sand Formation ( 123.50 m ) ( Fig. 20E ) ( IRSNB b7124). DIAGNOSIS. — Large, irregular network of calcite laths, joining at the centre in a central protruding x- shaped wedge. DERIVATIO NOMINIS. — The name is a combination of the Christian names Joachim and Celine, introduced to commemorate and celebrate the wedding day of these two lovely persons. LOCUS TYPICUS . — Mont-des-Récollets , ‘ Grande Carrière’, N France ; 50°48’02.74”N , 2°30’23.06”E . STRATUM TYPICUM. — Brussel Sand Formation, Unit B4 (sample 122.85 m ); upper part of NP14. DIMENSIONS. — Height = 16.8 to 17.6 µm ; width = 15.6 to 14.6 µm ( holotype : h = 16.8 µm , w = 15.2 µm ). DISTRIBUTION. — At the Mont-des-Récollects this species is consistently present from the upper part of the Brussel Sand Formation (Unit B4), and ranges through the Lede Sand Formation up to the base of the Wemmel Sand Member (upper NP14 to lower NP15). However, there are earlier records from the Oedelem borehole ( 13.50 m depth, middle of Oedelem Sand Member), assignable to the extreme top of NP13, and from the Mont-des-Récollets (Unit B2) and the Nederokkerzeel and Vossem outcrops (upper Unit B3 of the Brussel Sand Formation), all assignable to the lower middle part of NP 14. DESCRIPTION This taxon is composed of an irregular complex network of several long calcite laths (up to 7), meeting at different angles in the centre of a more or less cubic structure. The dimensions are highly variable, as the different laths are often broken off. The longest diagonal reaches up to 17.6 µm , the second is generally slightly shorter. The centre is marked by an x-shaped protruding wedge. All calcite laths are strongly birefringent in cross-polarized light. DISCUSSION Similar lathlike networks with central X-shaped to diamond-shaped wedges were described from upper Ypresian deposits of the southern North Sea Basin ( Steurbaut 2011 ). Nannoturba joceliniae n. sp. differs from all previously described Nannoturba species ( N. robusta , N. spinosa and N. jolotteana ) by a reduced number (up to 7) of long, almost completely free, irregularly distributed laths, which only meet at the centre in an x-shaped to diamond-shaped wedge. In all others taxa the laths are joined over most of their length with different configurations, according to the species ( N. robusta with quadrangular disposition and laths meeting at 90°; N. spinosa with triangular disposition with laths meeting at 120°; N. jolotteana ( Fig. 19A ) resembling a flattened octahedron, with rhombic cross-section). It differs from specimens described as Nannotetrina nitida by Aubry (1983 : pl. 5, figs 13-14), as well as from the latter’s holotype (originally described as Tetralithus nitidus by Martini 1961 : pl. 1, fig. 5, pl. 4, fig. 41), by its large number of different sized laths. In fact, the specimens figured by Aubry also seem to belong to the genus Nannoturba , but probably represent another new species, different from Tetralithus nitidus Martini, 1961 .