Pseudorbitolina Douvillé, 1910

Rashidi, Felix Schlagintweit Koorosh & Babadipour, Movlud, 2016, Orbitolinid Foraminifera From The Late Maastrichtian Of The Tarbur Formation (Zagros Zone, Sw Iran), Acta Palaeontologica Romaniae 12 (2), pp. 29-46 : 38-41

Genus Pseudorbitolina Douvillé, 1910

Remarks: The genus Pseudorbitolina is monospecific with the type species being Pseudorbitolina marthae Douvillé, 1910 .

Pseudorbitolina cf. marthae Douvillé, 1910

Figs. 3e–f , 11

*1910 Pseudorbitolina marthae n. gen., n. sp. – Douvillé, p. 57, text-fig. 1–4.

1948 Pseudorbitolina marthae Douvillé – Henson, p. 102, pl. 6, fig. 17, pl. 11, fig. 6?, text-fig. 16 (Maastrichtian Simsima Formation of Qatar, see Sugden and Standring, 1975).

1978 Pseudorbitolina marthae Douvillé – Neumann, p. 198, figs. 1–3, pls. 1–2 (with synonymy).

1979 Pseudorbitolina marthae Douvillé – Radoičić, pl. 8, figs. 1-3.

Non 2008 Pseudorbitolina cf. marthae Douvillé – Al-Kubaysi, fig. 2-12 = random section of Loftusia sp. (Maastrichtian Aqra Formation of Iraq).

2008 Pseudorbitolina marthae Douvillé – Boudagher-Fadel, pl. 5.7, figs. 8, 14 (Maastrichtian of Dukhan no. 1 well, Qatar; original material of Henson, 1947).

Non 2016 Pseudorbitolina marthae Douvillé – Al-Kubaysi and Abid, fig. 6-1 to 6-3 = random section of Loftusia sp. (Maastrichtian Aqra Formation of Iraq) (see Fig. 12 ).

Description: Test mostly low, more rarely high conicoconcave and irregularly curved. The specimens display a rather wide range of apical angle and consequently the ratio test diameter to height. The chambers do not cover the complete basal cone surface but exhibit marginal annuli only (type annular-concentric, e.g., Hottinger, 2008, fig. 37.4), becoming slightly broader during ontogeny. Adult specimens consist of up to 35 chambers (specimen in Fig. 11a ). The chambers display a marginal zone with a fine subepidermal network of intercalary beams and rafters ( Fig. 11f , lower part). There are up to two rafters; numbers of vertical partitions unknown. As can be seen in tangential sections, the primary beams are radially aligned between successive chambers ( Fig. 11e, h ). Towards the central part, an undivided zone connects the chamberlets of each chamber. Large foramina (tubular aperture of Henson, 1947) connect these undivided zones of succeeding chambers.

Dimensions (in mm):

Test diameter (D): ~ 1.6 mm to 4.6 mm (Douvillé, 1910: ~ 2–3 mm)

Test height (H): 0.75–1.2

D/H: 2.0–6.0

Diameter proloculus: 0.1 mm (1 value)

Remarks: First of all we have to stress that the available sections are not convenient for a detailed description of the test architecture. In any case, with its annular-concentric chambers more or less throughout the complete ontogeny, Pseudorbitolina represents a rather unusual chamber arrangement among the orbitolinids. According to the drawing of Douvillé (1910, fig. 3), the monospecific genus Pseudorbitolina shows a subspherical proloculus in apical position displaying a septulated supraembryonic zone at its top (like in Palorbitolina , see Schroeder, 1963, fig. 1). The thin-section specimens illustrated by Neumann (1978, pl. 1, fig. 7, pl. 2, fig. 6) in transverse sections instead shows an embryo in apical position consisting of a spherical proloculus and a hemispherical septulated deuteroconch arranged laterally to the former. In the Maastrichtian material, only one specimen was cut passing the proloculus ( Fig. 11a ).

In the revision of the species provided by Neumann (1978), the author concludes that it represents a good marker for the Campanian. Obviously there is a stratigraphic discrepancy of the occurrence of Pseudorbitolina marthae between the western Europe type region and Iran / Iraq (see synonymy). In the Campanian-Maastrichtian deposits of Turkey, P. marthae is restricted to the southeastern part belonging to the Arabian platform ( Özer et al., 2009). In the Maastrichtian of the Iraqian Aqra Formation, random sections of Loftusia sp. have been confounded with Pseudorbitolina marthae Douvillé (see synonymy) ( Fig. 12 ).

Figures

Fig. 3 Microfacies of some charactersistic samples from the Mandegan (a) and Naghan sections (b–f). a Packstone with benthic foraminifera Omphalocyclus macroporus (Lamarck) (O), and oblique transverse section of Dictyoconella? minima Henson on the right. Thin-section Rt 105. b Grainstone/packstone with debris of rudist shells, and larger benthic foraminifera Loftusia sp. (L), and transverse section of Dictyoconella? minima Henson (D). Thin-section 2NG 17. c Wackestone/packstone with benthic foraminifera among two specimens of Dictyoconus bakhtiari n. sp. (see also Fig. 10c, e). d Floatstone with corals, rudists, and tangential section of Dictyoconus bakhtiari n. sp. (Di). Thin-section 2NG 87-2. e–f Packstone with Pseudorbitolina cf. marthae Douvillé, and Omphalocyclus macroporus (Lamarck) (O) in f. Thin-sections 2NG 47 and NG 47-1.

Fig. 11 Pseudorbitolina cf. marthae Douvillé from the late Maastrichtian of the Tarbur Formation, Naghan section, SW Iran. a–b Axial section. Detail of protoconch in b. c Subaxial section of a low convexo-concave specimen. d Subaxial section of a high convexo-concave specimen. e, j Tangential sections showing the vertically aligned arrangement of main septules (beams). f–g Oblique sections. Note the undivided chamber zone sensu Neumann (1978). h Subaxial section of a juvenile specimen. i Detail of a specimen in axial section showing the “undivided zone” sensu Neumann (1978) connected by radial foramina (= tubular aperture sensu Henson, 1948). Abbreviation: tu = tubular aperture, uz = undivided zone. Thin-sections: 2NG 47 (a–c, f), 2NG 43 (d), Ng 47-1 (e, g), Ng 65-1 (h), 2NG 47 (i), 2NG 116 (j).

Fig. 12 Loftusia sp. from the late Maastrichtian of the Tarbur Formation, Naghan (a) and Mandegan (b) sections, SW Iran. a Oblique section. b Random section. This type of section has been confounded in the literature with Pseudorbitolina marthae Douvillé (see synonymy). Thin-sections: 2NG 207 (a), Rt 79-3 (b).