Dissocladella? chahtorshiana, Rashidi & Schlagintweit

SCHLAGINTWEIT, FELIX, RASHIDI, KOOROSH, YARAHMADZAHI, HAMED, HABIBIMOOD, SHARAM, AMIRSHAHKARMI, MAHNAZ, AHMADI, HOSSAIN & KHOKAN, HOSSAIN, 2019, Dissocladella? Chahtorshiana Rashidi & Schlagintweit N. Sp., A New Dasycladale (Green Algae) From The Paleocene Of Iran, Acta Palaeontologica Romaniae 15 (2), pp. 3-13 : 7-9

Dissocladella? chahtorshiana n. sp.

Figs. 5A–D pars, 6–8

Origin of the name: The name refers to the type-locality Mount Chah Torsh, Central Iran ( Figs. 1–3 ).

Holotype: Oblique section shown in Figure 8C , thin-section CT 4 .

Horizon and locality: Selandian carbonates from Mount Chah Torsh, lithostratigraphically not defined (= no formation name assigned).

Description: A medium-sized, well calcified Dasycladale with a cylindrical to slightly clavate thallus ( Fig. 7A–B , Fig. 8D ). The large main axis of roughly two third of diameter is bordered by a rather smooth surface except common widenings of the proximal part of the laterals, assumed of secondary origin ( Fig. 6A, F ) (compare Pl. 1, Fig. 3 in Radoičic et al., 2005). The primariy laterals are numerous and regularly alternating between consecutive verticils. In shallow tangential sections they are close-set and of round outline ( Fig. 7A–B , lower part). In deep tangential sections they appear of triangular outline (with rounded edges) ( Fig. 7B , middle part). The primaries are usually arranged perpendicular to the axis in cylindrical morphologies ( Fig. 7B ); in slightly claviform morphologies they are slightly inclined upwards ( Fig. 8D ). The shape of the primaries is variable: slightly widening outwards and without detectable secondaries ( Fig. 6A–B ) or with a distinct swelling (club-shaped morphology) and secondaries ( Fig. 6E–F ). Sometimes the swollen part of the primaries are almost touching (or do so) with neighbouring ones. The different morphologies might refer to different parts of the thallus (sterile? fertile?). In transverse or longitudinal sections, two secondaries distinctly shorter than the primaries and widening distally are detectable ( Fig. 7C–D, E–G ). The exact number of secondaries per primary however lateral is unknown. Often they appear as a united micritic diverging masse upon the distal surface of the primaries ( Fig. 7C, E, G ).

Comparisons: From the Paleogene, the following species of Dissocladella have been described (data from Barattolo, 2002):

D. deserta Elliott (Selandian-Ypresian): D. deserta from the Paleocene of Iraq, and lower Eocene of Egypt ( Elliott, 1968) is a very small species (D = 0.39-0.47 mm), and about twelve primaries.

D. gracilis Radoičić (Thanetian of Slovenia, Radoičić, 1991): as name already implies, it represents a very small alga (D: 0.16-0.290 mm, max. 0.368 mm) with four primaries.

D. longjangensis Mu & Wang (Lutetian of China, Mu and Wang, 1985): medium-sized species (D up to 0.65 mm, see Kuss and Herbig, 1993, Paleogene of Egypt), and a main axis occupying about half the diameter (d/D 0.50-0.55).

D. lunata Segonzac ( Thanetian of France, Segonzac, 1979): small sized species (D: 0.282 -0.415 mm) with four to six primaries.

D. savitriae Pia (Danian-Thanetian): large-sized and annulated representative of the genus (D: 1.5-2.0 mm) with more than 40 primaries per verticil ( Rao and Pia, 1936).

D. turnsekae Radoičić (Danian-Selandian of Slovenia, Radoičić, 1998): it represents a very small species (D = 0.24-0.35 mm) with about eight primaries aligned vertically between successive whorls.

We may also note some resemblances of the lateral morphology with the poorly known Jodotella volpensis described by Segonzac (1976) with two sections from the Thanetian of France. The transverse section shown in plate 3, fig. 1, shows primaries that are widened proximally, displaying distinct swelling in the middle part, and two secondaries. This alga is distinctly smaller, displays a much lower d/D ratio (about 0.38), a reduced number of laterals (w = 16). Jodotella is different by its fertile ampullae set in clusters laterally to the primaries ( Deloffre and Génot, 1982).

Dimensions (in mm): The main biometric parameters are compiled in Table 1 . The maximum observed length of a thallus fragment is about 17.5 mm ( Fig. 5E ).

Palaeoenvironment: Dissocladella ? chahtorshiana occurs in bioclastic packstones with various dasycladalean algae (e.g., Clypeina , Cymopolia ), among some rather large taxa such as Rostroporella oviformis Segonzac ( Fig. 5D ), halimedacean algae ( Fig. 5A–B ) gastropods, benthic foraminifera, and rare fragments of corals. The association generally points to an open marine, outer platform environment of moderate water energy. A similar association including Rostroporella , Clypeina , Cymopolia div. sp., has been reported by Deloffre and Radoičić (1978, p. 63) from the Paleocene of Slovenia and designated as "reefal environment".

Figures

Fig. 5 Typical microfacies of samples with Dissocladella? chahtorshiana n. sp. (D), from the Paleocene of the Kuh-e- Chah Torsh (a–c) and Kuh-e-Patorgi (d-e) sections. a–b Bioclastic packstone with dasycladalean (e.g., Acroporella? anceps Segonzac, A), halimedacean (ha) algae, gastropods, and porcelaneous benthic foraminifera (e.g., soritoidids). c Bioclastic packstone with dasycladalean algae (e.g., Clypeina elliotti Beckmann & Beckmann, Cl). d Bioclastic packstone with dasycladaleans (e.g., Rostroporella oviformis Segonzac, R). Thin-sections: Ah 185 (a–b), CT 4 (c), 2pz29 (d). e Weathered rock surface with thallus fragments of Dissocladella? chahtorshiana n. sp. The maximum observed length amounts for ~ 17.5 mm (arrow). Kuh-e-Patorgi area.

Fig. 1 Tentative location of the Kuh-e-Chah Torsh (1) and Kuh-e-Patorgi (2) sections plot- ted on the tectonic map of Iran (modified from Zanchi et al., 2009). Abbreviations: AA = Anatolian–Armenian Block, AMC = Anarak Metamorphic Complex, KDF = Kopeh Dagh Foredeep, MZT = Main Zagros Trust).

Fig. 2 Location (1) and field view (2) of Kuh-e-Chah Torsh, the type-locality of Dissocladella? chahtorshiana n. sp. For the position within the territory of Iran see figure 1. Larger Benthic Foraminifera in (2): Dictyoconus? pachymarginalis Schroeder (?late Bedoulian-Gargasian?, a), Orbitoides gensacicus (Leymerie) (late Maastrichtian, b), Sistanites iranicus Rahaghi (Selandian, c), Orduella sphaerica Sirel (Selandian, d).

Fig. 3 Simplified lithostratigraphic column of the Kuh-e-Chah Torsh section with position of samples and distribution of benthic foraminifera and calcareous algae. Inferred SBZ zones after Serra-Kiel et al. (1998), Sirel (2012), and Hottinger (2014) (modified from Schlagintweit & Rashidi, 2019, in press.). .

Fig. 8 Dissocladella? chahtorshiana n. sp. from Selandian carbonates of Kuh-e-Chah Torsh, Central Iran. a–f, variously oriented oblique sections. Note the claviform thallus in d, and the presence of short secondaries visible in a (right side) or f (upper side). The holotype is shown in c. Thin-sections: CT 4 (a–d, f), Ah 185 (e).

Fig. 7 Dissocladella? chahtorshiana n. sp. from Selandian carbonates of Kuh-e-Chah Torsh, Central Iran. a–b, longitudinal (upper part) and tangential (lower part) sections. Primaries are arranged in alternating position between successive verticils. In shallow tangential sections they are close-set and display rounded transverse outline. In deep tangential section (b, middle part) the transverse sections are rounded triangular. c–h, detailed views of the primaries, showing short secondaries. Thin-sections: Ah 185 (a–b), CT 4 (c–h).

Fig. 6 Dissocladella? chahtorshiana n. sp. from Selandian carbonates of Kuh-e-Chah Torsh, Central Iran. a–f, transverse sections, partly slightly oblique. Note the different morphologies of the primaries, only slightly widening (a–b), or clubshaped (e–f). Secondary laterals partly visible in c, e, and f. g, oblique section. Thin-sections: Ah 185 (a, c-d), CT 4 (b, e-g).