Larger Benthic Foraminifera) from the Maastrichtian Tarbur Formation of SW Iran (Zagros Fold-Thrust-Belt)

Geopersia 6 (2), 2016, PP. 169-185 First record of Gyroconulina columellifera Schroeder & Darmoian, 1977 (larger benthic foraminifera) from the Maastrichtian Tarbur Formation of SW Iran (Zagros Fold-Thrust-Belt) Felix Schlagintweit1*, Koorosh Rashidi2, Farzaneh Barani2, 1 Lerchenauerstr. 167, 80935 München, Germany 2 Department of Geology, Payame Noor University, Po Box 19395-3697 Tehran, Iran. *Corresponding author, e-mail: [email protected] (received: 11/04/2016 ; accepted: 29/08/2016) Abstract The larger benthic foraminifera Gyroconulina columellifera Schroeder & Darmoian, 1977 (type-locality: Maastrichtian Aqra Formation of Iraq) is described for the first time from two sections of the Maastrichtian Tarbur Formation of the Zagros Fold-Thrust-Belt, SW Iran. New details on its wall microstructure are provided. The microfacies is represented by bioclastic wacke-/pack-/grainstones with benthic foraminifera (e.g., Loftusia ssp., Neobalkhania bignoti, Omphalocyclus macroporus) and dasycladalean algae. The Iranian discoveries give further evidence for the biostratigraphic importance of the taxon. The biostratigraphy of the Tarbur Formation based on larger benthic foraminifera is reviewed and critically discussed. Both Gyroconulina columellifera Schroeder & Darmoian, and the dasycladale Pseudocymopolia anadyomenea (Elliott), which have been first described from the Maastrichtian of Iraq, are now also reported from the Tarbur Formation of Iran. Their restricted occurrences along the southeastern northern margin of the Arabian plate and the Taurides of Turkey (Anatolian plate) are indicative for a Late Cretaceous provincialism, partly coinciding with the larger Loftusia bioprovince. Keywords: Benthic Foraminifera, Dasycladales, Zagros Zone, Biostratigraphy, Palaeobiogeography Introduction Douvillé, 1904; Kühn, 1932; Khazaei et al., 2010). The Late Cretaceous Tarbur Formation, named after In contrast, the micropalaeontological composition the village of Tarbur (Fars Province), and cropping of the Tarbur Formation is still poorly constrained. out in the SW Zagros basin, represents a Some taxa of calcareous algae and benthic predominantly carbonate lithostratigraphic unit that foraminifera are indicated and illustrated in various contains rich microfauna and microflora associated recently papers (Vaziri-Moghadam et al., 2005; with rudists (James & Wynd, 1965). It extends from Afghah, 2009; Maghfouri-Moghaddam et al., 2009; the northwest to the southeast of the Zagros basin Rajabi et al., 2011; Abyat et al., 2012, 2015; along the western edge of the imbricated Zagros Afghah and Farhoudi, 2012; Pirbaluti and Abyat, zone, between the main Zagros fault and the 2013; Pirbaluti et al., 2013; Afghah and Yaghmour, Shabazan fault to the east (Alavi, 2004). Towards 2014). Several determinations however are the southwest the Tarbur Formation interfingers incorrect and therefore need revision (e.g., with the Gurpi Formation that usually underlies the Schlagintweit et al., 2016). In the present paper, former. The type section of the Tarbur Formation Gyroconulina columellifera Schroeder & Darmoian, with a thickness of ~527 m is located at Kuh-e Darmoian, 1977, a taxon previously unrecorded Gadvan about 1.2 km north of Tarbur village from Iran is described from two sections of the (James and Wynd, 1965). Noteworthy, a new type- Tarbur Formation (Fig. 1). The well preserved locality southeast of Shiraz city has been proposed material of this taxon merits a separate publication; by Bakhtiyar et al. (2008a), but according to our the detailed analyses and micropalaeontological knowledge a publication with details on lithology, description of the microfauna and microflora and biostratigraphy is still lacking. In the (including some new taxa) will be described stratigraphic chart of Iran provided in 1995 by the separately later. Geological Society of Iran, the Tarbur Formation is assigned to the Campanian-Maastrichtian interval, Studied sections following the pioneer work of James and Wynd Mandegan section: The study area, located in the (1965). High Zagros Belt, is situated north of Mount Dena, The rudist fauna of the Tarbur Formation has about 65 km south of the town of Semirom. The already been described by several authors (e.g., section of the Tarbur Formation is exposed about 170 Schlagintweit et al. Geopersia, 6 (2), 2016 10 km south of the village of Mandegan. Here the the upper part of unit 1, persisting through units 2 Tarbur Formation with a thickness of ~272 m and 3, not reaching the topmost parts of the Tarbur overlies conformably the Gurpi Formation (Fig. 2). Formation as several other taxa. The Greenwich The top of the section is unconformably overlain by coordinates of the section base are N 31º, 25', 8.13'' conglomerates of the Pliocene Bakhtiari Formation and E 51º, 24', 34.58''. (see Bahrami, 2009, for details). Based on the Fasa Section: It is located in the interior Fars lithostratigraphy, the section has been divided into (Folded Zagros Belt), about 20 km southwest of the three units (from base to top): unit 1 is dominated town of Fasa, close to the village Khane Nahar. The by thick-bedded limestones, unit 2 mostly contains exposed thickness of the Tarbur Formation is about medium-bedded limestones with intercalated marly 257 m. At the base, it is covered by alluvium and limestone layers, and unit 3 consists of marly the Gurpi Formation is not exposed. limestones. Gyroconulina columellifera appears in Figure 1. Location maps of the studied areas of the Tarbur Formation, and location of the Fasa and Mandegan sections. First record of Gyroconulina columellifera Schroeder & Darmoian, 1977… 171 Figure 2. Distribution (total vertical range) of selected larger benthic foraminifera in the Tarbur Formation of the Mandegan section. The Tarbur Formation can be subdivided into 3 top of the section is represented by the Paleocene lithostratigraphic units: medium- to thick-bedded Sachun Gypsum. The coordinates of the section limestones (73.1 m) (unit 1) followed by 124.4 m base are N 28º, 51', 2.49'', and E 53º, 30', 55.82''. medium-bedded limestones with Loftusia (unit 2) and some intercalated dolomitic layers in the lower Systematic palaeontology part, and finally unit 3 (74.5 m) consisting of The high-rank classification follows Pawlowski et medium- to thick-bedded limestones, yellow marls, al. (2013). For the low-rank classification see and thick-bedded dolomites (uppermost part). The Kaminski (2014). For glossary, report to Hottinger 172 Schlagintweit et al. Geopersia, 6 (2), 2016 (2006). forms, two to three chambers are discernible (e.g., Phylum Foraminifera d´Orbigny, 1826 Fig. 3B, D-F, N). Following a spherical proloculus, Class Globothalamea Pawlowski et al., 2013 the first post-embryonic chambers lack any Order Loftusiida Kaminski & Mikhalevich, 2004 subdivisions (Fig. 4B, 4J). The arched outermost Suborder Orbitolinina Kaminski, 2004 part of the following chambers (marginal zone of Superfamily Pfenderinoidea Smout & Sudgen, 1962 Schroeder & Darmoian, 1977) all bear an Family Pfenderinidae Smout & Sudgen, 1962 exoskeleton that consists of two generations of Subfamily Anatoliellidae Sirel, 2013 beams (beams and intercalary beams) and up to 3 Remarks. The genus Gyroconulina was previously (4?) rafters in the adult test part. In shallow placed in various families: Ataxophragmiidae tangential sections, the beams (primary and Schwager (Schroeder and Darmoian, 1977), secondary) and rafters display a polygonal network Pfenderinidae Smout and Sudgen, 1962 (subfamily (Fig. 3J-K). Deeper tangential sections only cut the Kurnubiinae) (Loeblich and Tappan, 1987; secondary beams revealing a pattern of rectangular Kaminski, 2014), and Anatoliellidae Sirel (Sirel, chamberlets distinctly higher than wide (Fig. 3I, 2013). In 2013, Sirel introduced the Anatolliellidae 4F). The endoskeleton is characterized by numerous for the two genera Gyroconulina Schroeder & comparably thick pillars (compared to thickness of Darmoian, 1977, and Anatoliella Sirel, 1988, both rafters and septa) that follow the foraminal axes, having high-conical serial tests with complex thereby being almost in line (subcontinuous) from exoskeleton and endoskeletal pillars. one chamber to the next. In the central part of the Genus Gyroconulina Schroeder & Darmoian, 1977 test, the pillars are densely set (Fig. 4L). The wall is (type-species: Gyroconulina columellifera thin and exhibits a finely friable hyaline structure Schroeder & Darmoian, 1977) limited to the spiral side of the test (e.g., Fig. 3A, Gyroconulina columellifera Schroeder & K). The innermost part appears somehow darker. Darmoian, 1977 Externally, it is sealed by a very thin microgranular (Figs. 3-5, 6B pars) micritic layer (or coating) (Fig. 4H, 5; = epiderm 1977 Gyroconulina columellifera n. gen., n. sp. sensu Hottinger, 2006). In contrast hereto, the Schroeder & Darmoian, p. 120, pl. 1, figs. 1-4, pl. microstructure of the exo- and endoskeleton is 2, figs. 1-7, text-fig. 2. micritic (Fig. 5). Wall and septa are equal in 1985 Gyroconulina columellifera Al-Rawi and Al- thickness. It is worth mentioning that any kind of Hamadani, pl. 4, fig. 3 (?), 4. test dimorphism was not mentioned in the original 1986 Gyroconulina columellifera Farinacci and description and is also not evident in the Iranian Yeniay, p. 260, not figured. material. 1986 Gyroconulina aqraensis n. sp. Lawa et al., p. Dimensions (data of Schroeder and Darmoian, 77, pl. 1, figs. 3-6, pl. 2, figs. 7-10, pl. 4, figs. 16-17. 1977, in brackets).

Load more