Coskinolina sistanensis, Schlagintweit & Hadi, 2018

Schlagintweit, Felix & Hadi, Mehdi, 2018, Coskinolina Sistanensis N. Sp., A New Larger Benthic Foraminifera From The Early Eocene Of Eastern Iran, Acta Palaeontologica Romaniae 14 (1), pp. 47-55 : 47-50

Coskinolina sistanensis n. sp.

( Figs. 4–5 , 6a , 7a–c pars)

1983 Lituonella cf. roberti Schlumberger – Rahagi, pl. 1, figs. 8–13, upper part of Lower Eocene of Iran (Sistan Suture Zone).

2017 Coskinolina liburnica Stache – Sirel & Deveciler, pl. 4, figs. 18–19, Cuisian of Turkey.

2017 Coskinolina liburnica Stache – Almansinia, pl. 10.2, fig. F–H, Eocene of Zagros Zone.

?2018 Daviesiconus sp. – Boudagher-Fadel, pl. 6.2, fig. 6, Early Eocene of Pakistan.

Derivation of name. The name refers to the Sistan Suture Zone, Eastern Iran.

Holotype. Subaxial section shown in Figure 4a . Thinsection CH 4.

Horizon and locality. Middle Ilerdian to late Cuisian carbonates of the Chenesht section ( Fig. 2–3 ).

Diagnosis. Medium-sized representative of the genus (maximum diameter up to 2.0 mm, height up to 1.85 mm) with slightly convex to almost plane test base. Often the tests are as broad as high, roughly triangular with plane sides in axial sections. Rarely they display a bell-shaped outline. High conical megalospheric forms with small eccentric embryo (protoconch and deuteroconch). Microspheric forms broader than high, with convex base. Initial trochospire of up to 10 chambers. There are about 6–8 chambers per 1 mm axial length. Adult test with up to 10 uniserial comparably high chambers. The pillars display a regular pattern, are comparably widely spaced, and alternate between successive chambers. Foramina numerous (cribrate distribution). Wall with pseudokeriothecal texture.

Remarks. Most specimens being almost equally wide as high correspond to megalospheric specimens. In accordance with other species of Coskinolina (see Hottinger and Drobne 1980), larger low-conical forms are assumed to correspond to the microspheric generation. The pseudokeriotheca, one characteristic of the genus, is only rarely discernible in Coskinolina sistanensis as fine striation of the wall. As Vicedo et al. (2013) remarked, diagenetic processes often mask this structure.

Rahagi (1980, pl. 1, figs. 1–4) described Coskinolina n. sp. from the Middle Eocene of the Sabzewar area, Central Iran. It displays a high conical comparably large test (height up to 2.5 mm, diameter up to 3 mm), plane base and up to 16 uniserial adult chambers. With its marginal zone subdivided by short exoskeletal beams of first order the illustrated taxon however does not belong to Coskinolina but to Daviesiconus Hottinger & Drobe 1980 or Barattolites Vecchio & Hottinger, 2007 . From the upper part of the Lower Eocene of the Sistan Zone, Rahagi (1983, pl. 1, figs. 8–13) reported Coskinolina sistanensis n. sp. as Lituonella cf. roberti . This taxon however a form that is clearly different (see Fig. 6d ). Coskinolina sistanensis n. sp. has also been reported as Coskinolina liburnica from the Cuisian of the Hayman-Polatli Basin in Central Anatolia, Turkey by Sirel & Deveciler (2017, pl. 4, figs. 17-18) ( Fig. 6a ).

Comparisons. For comparison of Coskinolina sistanensis with other species of the genus, the most important distinct characteristics are other species are mainly due to the comparably small size of both test and embryo, and the rather coarse and regular endoskeleton. It is worth mentioning that others like Coskinolina floridana Cole, 1941 belong to different genera such as Coskinon Hottinger & Drobne, 1980 or Fallotella Mangin ( Bowen Powell, 2010), among others because of the subdivided marginal zone. Coskinolina elongata Cole (Late early Eocene of Jamaica), 1941, has been designated the type-species of Coleiconus Hottinger & Drobne, 1980 .

Coskinolina liburnica Stache, 1875 (Cuisian of Croatia) ( Fig. 6 b-c): Medium- to large-sized test with distinctly convex base. Marginal chamber cavity narrow, slightly compressed or isometric. Megalosphere up to 0.4 mm. Bforms with more than 20 juvenile chambers. Chambers low in height (6–7 per mm axial length). Pillars densely arranged. There are 6–7 chambers per 1 mm axial length. Reference: Stache (1875), Schubert (1912), Hottinger & Drobne (1980), Hottinger (2007), Serra Kiel et al. (2016). Stratigraphy: SBZ 11–SBZ 12 (Serra Kiel et al., 1998: Late Ypresian = Middle–Late Cuisian); Late Ypresian to Priabonian, SBZ 11–SBZ 20 (Serra Kiel et al., 2016). C. sistanensis has been confounded with C. liburnica in the literature (see synonymy).

Coskinolina roberti ( Schlumberger, 1905; Eocene of France) ( Fig. 6d ): High-conical, large test (diameter up to> 3 mm) with large initial trochospire (see Poignant 1961; Hottinger and Drobne 1980). This species has reliably been recorded only from high-energy deposits (e.g. rudstones) of western France. Proloculus large (diameter 0.35–0.4 mm). There are 5–6 chambers per 1 mm axial length.

Coskinolina perpera Hottinger & Drobne, 1980 (Eocene of Croatia) ( Fig. 6e ): Chambers comparably high giving rise to often irregularly twisted pillars. The pillars display a general loose and irregular pattern. Marginal chamber cavities are distinctly inflated. There are 4 to 5 chambers per mm axial length (2 to 3 in microspheric forms). Embryo large consisting of a protoconch (diameter 0.35–0.45 mm) and deuteroconch (> 0.5 mm). Occurrences: Late Cuisian to Early Lutetian of Croatia ( Hottinger and Drobne, 1980); Middle Eocene of Somalia (Azzaroli 1950 fide Hottinger, 2007); Bartonian of Iran ( Hottinger, 2007); Lutetian-Priabonian of Oman (Serra Kiel et al., 2016).

Coskinolina douvillei ( Davies, 1930; Cuisian of Pakistan) ( Fig. 6f ): Medium-sized cone, slightly higher than wide (base mean 2.19 mm, height mean 2.64 mm, Davies 1930). Microspheric specimens attain a size of more than 7 mm ( Hottinger and Drobne 1980, pl. 10, fig. 2). Diameter protoconch 0.3–0.35 mm. Adult specimen with more than 15 uniserial chambers (e.g., Davies 1930, pl. 2, fig. 3). There are 5–6 chambers per 1 mm axial length.

Coskinolina depressa ( Azzaroli, 1952; Lutetian of Somalia): Large-sized (cone diameter up to 3.5 mm, cone height up to 3 mm, A-forms), low-conical species of the genus, often displaying convex base. Occurrences: Small sized Coskinolina with distinctly convex base were described by Serra-Kiel et al. (2016) as C. cf. depressa from the uppermost Bartonian to the Priabonian (SBZ 18–SBZ 20) of Oman. C. depressa is very close to C. douvillei if not a junior synonym ( Hottinger and Drobne, 1980, p. 44).

Stratigraphic distribution. In the Chenesht section Coskinolina sistanensis n. sp. occurs from the middle Illerdian to the early late Cuisian (= SBZ 8 to SBZ 12, basal part, of Serra Kiel et al., 1988). The occurrence of C. sistanensis n. sp. in older strata however cannot be excluded (see Fig. 2 ).

Microfacies, association, and palaeoenvironment: Coskinolina sistanensis n. sp. occurs in AlveolinaOpertorbitolites packstone and nummulitids - Alveolina rudstone, microfacies types restricted to the basal to middle parts of the Chenesht section ( Fig. 7 ). The first microfacies type is characterized by an abundance of Alveolina decipiens Schwager, A. ex gr. guidonis Drobne, A. elliptica nuttalli Davis , A. cf. citrea Drobne , with globular to slightly elongated forms and diameters less than 5 mm, Opertorbitolites (e.g., O. douvillei Nuttall , O. cf. ibericus Lehmann ), Orbitolites (e.g., Orbitolites sp. cf. O. minimus Henson ). Besides larger benthic foraminifera, small miliolids ( Quinqueloculina , Triloculina , Biloculina ), small rotaliids ( Neorotalia sp. ) occur. Detrital quartz grains are present in varying amounts with fine to medium sizes. The nummulitids- Alveolina rudstone microfacies is distinguished by small nummulitids i.e. Nummulites cf. atacicus Leymerie , Assilina sublaminosa Gill , N. tauricus de la Harpe , N. pratti d'Archiac & Haime , N. cf. distans Deshayes associated with Alveolina (e.g., A. cf. minuta Checchia-Rispoli , A. elliptica nuttalli Davies , A. cf. decastroi Scotto Di Carlo ) together with a decrease of abundance of Coskinolina sistanensis n. sp. Other subordinate components are encrusting foraminifera (acervulinids), orthophragminids, miliolids, orbitolitids, small tests of undetermined rotaliids, green algae, echinoids and quartz grains. With a predominance of larger porcelaneous taxa associated with agglutinating conical forms this microfacies type can be assigned to a proximal inner ramp setting (e.g., Vecchio and Hottinger, 2007). With the occurrence of alveolinids and conical agglutinating taxa in the lower two third of the section and the dominance of nummulitids in the last third, a deepening upward trend is documented ( Vecchio and Hottinger, 2007; Zamagni et al., 2008) ( Figs. 2–3 ).

Figures

Fig. 4 Coskinolina sistanensis n. sp., Illerdian-Cuisian of Iran: a, d–e, g (sub)axial sections showing small initial spire. Holotype specimen in a. b, h oblique sections of megalospheric form. c, f tangential-oblique sections. i–k transverse slightly-oblique sections. l tangential section showing undivided marginal zone and pseudokeriotheka (right side). Thinsections: CH 4 (a–c, e), CH 12 (d, f, j–l), CH 2 (g–h), CH 7 (i). Abbreviations: fo = foramen, ma = marginal aperture, pr = proloculus, pi = pillar.

Fig. 5 Coskinolina sistanensis n. sp., Illerdian-Cuisian of Iran: a oblique section of a low-conical specimen (?microspheric form). b, oblique section showing embryo. c–d, g–h, subaxial sections. e, tangential-oblique section. f, i, slightly oblique axial sections; embryo shown in (i). j axial section of a small megalospheric specimen showing embryo. k–l slightly oblique transverse sections. Thin-sections: CH 2 (a, c–h), CH 7 (b), CH 12 (i, k–l), CH 4 (j). Abbreviations: deu = deuteroconch, fo = foramen, m.a. = marginal aperture, pi = pillar, pr = proloculus.

Fig. 6 a Coskinolina sistanensis n. sp., compared to the type-species Coskinolina liburnica Stache in b–c, d Coskinolina roberti Schlumberger, e Coskinolina perpera Hottinger & Drobne, f Coskinolina douvillei (Davies).

Fig. 7 Microfacies and selected alveolinids from the Chenesht section. a–c Alveolina-Opertorbitolites pack- stone with Coskinolina sistanensis n. sp. (C), Alveolina elliptica (Sowerby) (arrows in b), Alveolina frumen- tiformis Schwager (arrow in c). d Alveolina elliptica nuttali Davies. e Alveolina oblonga d’Orbigny. Sam- ples CH 2 (a), CH 6 (b, e), CH 12 (c), CH 5 (d). Scale bars 1 mm.

Fig. 2 Field view of the Chenesht section with schematic distribution of main groups of larger benthic foraminifera.

Fig. 3 Log of the Chenesht section with distribution of larger benthic foraminifera.