Trochastrites pyramidalis, 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 : 347-348

Trochastrites pyramidalis n. sp.

( Fig. 20 T-W)

urn:lsid:zoobank.org:act:1A5F4964-D75A-4631-A0A4-E948EF2E29FF

HOLOTYPE. — Fig. 20U ( IRSNB b7161) (negative stored in the collections of the RBINS).

PARATYPES. — Three figured specimens from the upper part of the Oedelem Sand Member (top of the Aalter Formation) in the Oedelem BH ( Fig. 20T, V ) ( IRSNB b7160, IRSNB b7162) and the Vlakte van de Raan BH ( Fig. 20W ) ( IRSNB b7163); all from the lower part of NP14.

DIAGNOSIS. — Three irregularly bifurcated arms interconnected with a fourth arm to form a pyramidal construction surrounded by a weblike structure.

DERIVATIO NOMINIS. — Refers to the outline of the solid inner structure of these globular bodies, representing a triangular pyramid.

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

STRATUM TYPICUM. — Brussel Sand Formation, base of Unit B3; (sample 122.16 - 122.21 m), lower middle part of NP14 .

DIMENSIONS. — Diameter = 10 to 13 µm (holotype: d = 12 µm).

DISTRIBUTION. — Trochastrites pyramidalis n. sp. is restricted to the lower part of the Brussel Sand Formation at the Mont-des- Récollets, with rare records in Unit B1 and Unit B3 (lower NP14). It is also known from Unit BE in the Leuven BH (base of NP14) and from the Aalter-Oedelem area and the offshore Vlakte van de Raan borehole, where it has been identified in the upper part of the Aalter Sand Formation (Unit A4, base of NP14). In this offshore borehole it seems to range up to the base of Unit B4 (sample 79.15 m, Steurbaut unpublished).

DESCRIPTION

These nannoliths present a pyramidal structure consisting of three irregularly bifurcated arms lying in a plane and interconnected with a fourth arm almost perpendicular to that plane ( Fig. 20U ). This structure is surrounded by a weblike network. The bifurcated part of the arms is quite large compared to the total length of the arms.

DISCUSSION

This taxon differs from Trochastrites hohnensis ( Fig. 20S ) by its pyramidal outline and the greater length of the bifurcated parts of the arms. In T. bramlettei ( Martini, 1958) the bifurcation of the arms starts much earlier, not far from the central point where the arms meet.

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).