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 Discoaster wemmelensis Achuthan & Stradner, 1969 ( Fig. 18 O-R) Discoaster wemmelensis Achuthan & Stradner, 1969: 5 , 6, text-fig. 2; pl. 4, figs 3-4. DISTRIBUTION. — D. wemmelensis is consistently recorded in Lutetian nannofossil assemblages worldwide, although generally in low concentrations (Perch-Nielsen 1985; Aubry 1986 ; Varol 1998 ; Tori & Monechi 2013 ; Franceschi et al. 2015 ). It occurs in very low numbers at the Mont-des-Récollets, from the base of the Brussel Sand Formation (its LO is at the base of Unit B1, lower NP14) up to the base of the Wemmel Sand Member (middle NP15). A few isolated specimens have been recorded slightly earlier at the top of the Aalter Sand Formation in boreholes north of the Mont-des- Récollets, but not at the Mont-des-Récollets itself ( 2 in the Vlakte van de Raan borehole and 1 specimen in the Oedelem borehole, a few meters above the base of NP14 as defined herein). This might not correspond to its total range, as in Belgium D. wemmelensis is known to occur throughout the Wemmel Sand Member (middle NP15) up to the Ursel Clay Member (base of NP16) (Steurbaut 1986). DISCUSSION This small (d = c. 5 µm ) discoaster with serrate outline is marked by two superimposed cycles of elements, consisting of 20 to 30 wedge-shaped rays, and lacks a central knob.