Class Foraminifera Eichwaldnext section
Order Lituolida Lankester
Superfamily Lituolacea de Blainville
Family Lituolidae de Blainville
Subfamily Lituolinae de Blainville
Genus Lituola Lamarck
Type species – Litulites nautiloidea Lamarck, 1816.
Lituola senoniensis (Hofker, 1949)
Pl. 1, fig. 10.
Description – Test planispiral with somewhat protruding chamber walls. Three to four tight, involute whorls, leaving a broad umbillicus. Chambers numerous, up to 24 in the last whorl, long and narrow. No canal system, agglutinated walls thick, microgranular. Diameter 0.3-0.8 mm, thickness 0.10-0.22 mm.
Stratigraphy – First appears in the Nekum Member and is more abundant in the Meersen Member. This species has also been found in Paleocene sedimentary rocks, but this occurrence probably represents reworked specimens.
Remarks – When first described, this species was placed in the genus Peneroplis because of the very similar internal and external morphology. In the original description, Hofker (1949) even considered that his new species was synonymous with an extant species, Peneroplis pertusus (Forskål). Only when better-preserved specimens became available did the micro-granular texture of the (agglutinated) test walls become clear.
Order Rotaliida Delage and Hérouard
Superfamily Orbitoidacea Schwager
Family Orbitoididae Schwager
Subfamily Orbitoidinae Schwager
Genus Orbitoides d’Orbigny
Type species – Lycophris faujasii Defrance , 1823.
Remarks – Orbitoides is characterised by a lenticular test shape, with a more or less acute test margin. The equatorial layer increases in thickness from the centre to the margin of the test.
Orbitoides apiculata Schlumberger, 1902
Pl. 2, figs. 1, 5.
Description – Test round, one side flattened, the other showing a distinct umbilicus. Surface on the outside with regularly spaced, small pustules. Macrosphere diameter 2.5-3.0 mm, thickness 1.2-1.8 mm. Microsphere diameter up to 13 mm, thickness 2.0 – 2.5 mm.
Stratigraphy – Orbitoides apiculata occurs in the top of the Nekum Member (Kanne Horizon) and base of the Meerssen Member (Caster Horizon), that is, zone L of Hofker (1966).
Remarks – Although the macrospheric generation has been extensively described and discussed in many studies, the much larger microspheric generation has received little attention. However, since both Orbitoides species regularly occur together in the type Maastrichtian deposits, it is difficult to separate the microspheric generation.
Orbitoides brinkae Visser, 1951
Pl. 2, fig. 2.
Description – Test round, one side more convex than the other. Periphery rounded. Surface ornamented with few, small pustules. In horizontal section most of the test is formed by the very large nucleoconch. Macrosphere: diameter 0.7-1.3 mm, thickness 0.35-0.7 mm. Microsphere: not known (see remark about the previous species).
Stratigraphy – Orbitoides brinkae occurs in the top of the section, in the upper part of the Nekum Member and the Meerssen Member.
Subfamily Omphalocyclinae Vaughan
Genus Omphalocyclus Bronn
Type species – Omphalocyclus macropora (Lamarck, 1816).
Omphalocyclus macropora (Lamarck, 1816)
Pl. 2, fig. 3.
Description – Test biconcave to discoidal, centrally depressed, with the thickest part at 67 to 75 % of the diameter. Test margin rounded, with a single or double row of apertures. In vertical section the equatorial and lateral chambers are hardly distinguishable. Only one row of lateral chambers is present on each side of the median layer. The test reaches its largest thickness at about two-thirds of the radius, giving it a typical ‘bow-tie’ appearance. Diameter of the macrospheric generation 0.8-2.0 mm, of the microspheric generation up to 5 mm.
Stratigraphy – Omphalocyclus occurs in the top of the Nekum Member and is locally abundant in the Meerssen Member.
Family Lepidorbitoididae Vaughan
Subfamily Lepidorbitoidinae Vaughan
Genus Daviesina Smout
Type species – Daviesina khatiyahi Smout, 1954.
Daviesina fleuriausi (d’Orbigny, 1826)
Pl. 1, fig. 1.
Description – Test round, biconvex; large specimens have a strongly flattened last whorl. The periphery of large specimens is thickened. Sutures distinct, elevated and curved backwards. The surface of the test is covered by pustules, which are largest in the centre and indistinct in the last whorl. Diameter 0.4-1.7 mm, thickness 0.2-0.5 mm.
Stratigraphy – The first occurrence of Daviesina is in the Laumont Horizon (Nekum Member) and it extends to the top of the Maastrichtian.
Genus Lepidorbitoides A.Silvestri
Type species – Lepidorbitoides socialis Leymerie, 1851.
Lepidorbitoides minor (Schlumberger, 1902)
Pl. 2, fig. 4.
Description – Test round, biconvex with a rounded to acute periphery. Surface covered by fine pustules. Equatorial layer very thin and of equal height in vertical section. The lateral chamberlets are equally well developed on either side of the equatorial layer and are very elongated. Micro- and macrosphere diameters 0.6-2.0 mm, thickness 0.5-0.9 mm.
Stratigraphy – Lepidorbitoides minor occurs in the Emael Member and above.
Remarks – Unlike Orbitoides spp. and many other larger benthic foraminifer genera, there is no size difference between the macro- and microspheric generation of L. minor. The microspheric generation can only be recognised by the arrangement of the initial chambers; only one in about one hundred specimens is microspheric.
Superfamily Rotaliacea Ehrenberg
Family Calcarinidae Schwager
Genus Siderolites Lamarck
Type species – Siderolites calcitrapoides Lamarck, 1799.
Siderolites calcitrapoides Lamarck in Faujas de Saint Fond, 1799
Pl. 1, figs. 2, 3, 5, 6, 8, 9.
Description – Test globular, with 2-10 round spines. Sides of the test rounded. Test covered by pustules (diameter 15-25 μm). Chambers and sutures are not visible from the outside. Spines commonly in one plane around the periphery and with longitudinal ribs. In vertical section chambers are arranged planispiral with 2-3 rows of lateral chamberlets. Diameter including spines up to 4 mm (microsphere) or up to 2 mm (macrosphere).
Stratigraphy – Siderolites calcitrapoides has been found in the Schiepersberg Member and above, but is especially abundant in the Nekum Member.
Siderolites laevigatus (d’Orbigny, 1826)
Pl. 2, figs. 4, 7.
Description – Test flattened, with 0-11 ventrally compressed spines, which commonly are fused together, forming a flange around the test. Sides of the test sharp. Test covered by coarse pustules (diameter 60-80 µm). Chambers and sutures are not visible from the outside. Spines in one plane around the periphery, covered with pustules in the central part and oblique striae on the sides and distal part. Proloculus of the macrosphere large (0.4-0.5 mm), diameter including spines up to 5 mm (microsphere) or up to 2.5 mm (macrosphere).
Stratigraphy – This species has only been found in Nekum Member, where it can be very abundant.
Remarks – Siderolites calcitrapoides and S. laevigata have variously been treated as one very variable or as two difficult to distinguish species. We treat them as two separate species, but do not exclude the possibility that they are end members of one variable plexus.