Early Changhsingian (Late Permian) Ammonoids from NW Iran
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N. Jb. Geol. Paläont. Abh. 293/1 (2019), 37–56 Article E Stuttgart, July 2019 Early Changhsingian (Late Permian) ammonoids from NW Iran Dieter Korn, Abbas Ghaderi, and Nahideh Ghanizadeh Tabrizi With 25 figures Abstract: Early Changhsingian ammonoids from the Transcaucasus-NW Iranian region are poorly known. Here we revise the ammonoids of this interval based on new findings in sections of the Aras Valley and Ali Bashi Mountains of the Julfa region, NW Iran. We revise the ceratitid genera Phisonites, Iranites, Shevyrevites and Dzhulfites. We introduce the new genus Araxoceltites with the three new species A. sanestapanus, A. laterocostatus and A. cristatus. Key words: Late Permian, Ammonoidea, Iran, stratigraphy, diversity. 1. Introduction a high species richness, those from the Transcaucasus are comparatively poor. In their monograph describing Late Permian (Lopingian) ammonoids are remarkable the sections in Armenia and Azerbaijan, for instance, for their high overturn rates, which stand in contrast to Ruzhencev & Shevyrev (1965) listed only eight the Early and Middle Permian, during which the group xenodiscid species from this interval. This is in strik- evolved considerably slowly on the substage and stage ing contrast to the late Changhsingian, from where levels (e.g., Miller & Furnish 1940; Ruzhencev alone nearly 30 species are known from the Paratiro- 1952; Ruzhencev 1956; Leonova 2002). The Late lites Limestone of NW Iran (Korn et al. 2016). A Permian is, after the end-Guadalupian extinction event diversity analysis showed that the ammonoid diver- that caused a significant extinction of the goniati- sity is increasing towards the top of the formation tid ammonoids, characterized by the presence of am- (Kiessling et al. 2018). monoid assemblages dominated by the order Cera- During our field study of the Permian-Triassic titida (e.g., Ruzhencev 1962; Ruzhencev 1963; boundary beds of NW Iran (Fig. 1), we measured Zhao et al. 1978). Wuchiapingian ammonoid assem- and sampled several sections (Aras Valley, several blages are dominated by members of the superfam- parallel sections in the Ali Bashi Mountains, Zal) in ily Otoceratoidea, while the Changhsingian assem- great detail (applying bed-by-bed sampling) with the blages are almost entirely composed of the superfam- focus on petrography and microfacies characteristics ily Xenodiscoidea (e.g., Ruzhencev & Shevyrev (Leda et al. 2014), conodont stratigraphy (Ghaderi 1965; Zhao et al. 1978; Leonova 2002). During the 2014; Ghaderi et al. 2014b; Isaa et al. 2016), sta- Changhsingian, the otoceratids existed only as a ghost ble isotopes (Schobben et al. 2014; Schobben et al. lineage (e.g., Kummel 1972). The abrupt change in 2015; Schobben et al. 2016; Schobben et al. 2019), the composition of ammonoid assemblages between brachiopods (Ghaderi et al. 2014a) and ammonoids the two stages has not been explained so far. (Ghaderi et al. 2014b; Korn et al. 2016). Within this Early Changhsingian ammonoids are known in multidisciplinary project, we also collected a num- greater diversity from only two regions worldwide, the ber of ammonoids from the early Changhsingian Zal Transcaucasian-NW Iranian region and South China. Member of the Ali Bashi Formation, which are de- However, while the South Chinese assemblages show scribed below. © 2019 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/njgpa/2019/0829 0077-7749/2019/0829 $ 5.00 eschweizerbart_xxx 38 D. Korn et al. Fig. 1. Geographic position of Permian-Triassic boundary sections in the Transcaucasus-NW Iran region (after Arakelyan et al. 1965) and palaeogeographic position of the Julfa region (after Stampfli & Borel 2002). 2. Material A nearly complete Wuchiapingian and Changhsingian suc- cession is exposed at this locality with a good outcrop of the The studied material comes from the early Changhsingian Zal Member over an extension of 200 m. The member has a Zal Member (i.e. the lower part of the Ali Bashi Forma- thickness of 9.35 m; we collected 77 specimens. tion), which has a position between two units of nodular or platy limestone: the upper part of Julfa Formation below Ali Bashi 1 section (38.9397° N, 45.5197°E): It corre- and Paratirolites Limestone above (Ghaderi et al. 2014b). sponds to Locality 1 described in some detail by Teichert The Zal Member is mainly composed of light to dark grey, et al. (1973). The entire Changhsingian succession is ex- reddish or purple shales with the intercalation of marly posed in this section and allows a detailed study. The Zal limestone beds or packages of thin bedded limestone beds Member has a thickness of about 12 m; we collected five (Fig. 2). Several of the beds yielded macrofossils, but am- specimens. monoids could be collected only occasionally from a few Ali Bashi 4 section (38.9416° N, 45.5158°E): Locality 4 levels. The member is, geographically, restricted to a rather of Teichert et al. (1973) is the section described in detail small area between the northern side of the Araxes (= Aras) by Stepanov et al. (1969) and Ghaderi et al. (2014b).It river and the village of Zal about 30 kilometres to the South is the most complete of all the sections in the Ali Bashi (Fig. 1). At most places, the member is covered by scree; Mountains. The Zal Member has a thickness of 12.40 m; we only occasionally the entire member is exposed. collected 14 specimens. Our material, consisting of 126 specimens, comes from the following localities (for a detailed outline of the strati- Ali Bashi N section (38.9456°N, 45.5137°E): This sec- graphic succession, see Ghaderi et al. 2014b; Leda et al. tion has only rarely been studied previously (Ghaderi et al. 2014): 2014b; Korn et al. 2016). It begins in the higher portion of Aras Valley section (39.0154°N, 45.4345°E): This sec- the Zal Member and ranges into the Triassic Elikah Forma- tion was described for the first time by Ghaderi et al. tion; we collected one specimen. (2014b) and Leda et al. (2014); it is situated about 19 km Zal section (38.7327° N, 45.5795°E): The type locality WNW of the towns of Dzhulfa and Julfa in a dry small side of the Zal Member shows a succession that resembles, in valley west of the Aras (Araxes) River. The outcrop has a po- spite of about twenty kilometres distance, the Ali Bashi and sition approximately 2 km north-west of the Dorasham I sec- Aras Valley sections. The Zal Member has a thickness of tion of Ruzhencev et al. (1965) and Kotlyar et al. (1983). 12.40 m; we collected 29 specimens. eschweizerbart_xxx 10 m Fig. 2. 0 m 5 m Columnar sections of the Zal Member with the in-situ collected ammonoid specimens. Zal Member Paratirolites Limestone Aras Valley shales limestone nodules platy limestone nodular limestone compact limestone Pseudogastrioceras relicuum Xenodiscus dorashamensis Iranites transcaucasius Phisonites triangulus Araxoceltites sanestepanus Araxoceltites cristatus Shevyrevites nodosus Dzhulfites spinosus Dzhulfites nodosus Early Changhsingian (Late Permian) ammonoids from NW Iran 15 m 10 m 0 m 5 m Zal Member Paratirolites Limestone Ali Bashi1 Iranites transcaucasius Araxoceltites cristatus Vedioceras sp. Dzhulfoceras sp. 15 m 10 m 0 m 5 m Zal Member Paratirolites Limestone Zal 39 Dzhulfites nodosus Araxoceltites cristatus eschweizerbart_xxx 40 D. Korn et al. In total, 126 ammonoid specimens of the Zal Member The study of the NW Iranian sections showed that were collected, of which only a few were collected in-situ the subdivision developed in the Dorasham section (Fig. 2). The specimens belong to the following species: can largely be confirmed, but modifications have to be Pseudogastrioceras relicuum Korn & –8specimens done (Fig. 2). Ghaderi (in Korn et al. 2016) Xenodiscus dorashamensis Shevyrev, –16specimens 1. Iranites transcaucasius–Phisonites triangulus 1965 Zone. – The lowermost part of the Ali Bashi Forma- Xenodiscus sp. –1specimen tion contains ammonoid assemblages in low diversity Phisonites triangulus Shevyrev, 1965 – 4 specimens Iranites transcaucasius (Shevyrev, –9specimens and rather poor preservation. Iranites transcaucasius 1965) and Phisonites triangulus occur, together with other Shevyrevites shevyrevi Teichert & –3specimens smooth ceratitic ammonoids, at the base of the Zal Kummel (in Teichert et al. 1973) Member in the Aras Valley section. According to our Shevyrevites nodosus Shevyrev, 1965 – 1 specimen collections, the two zones proposed by Ruzhencev & Araxoceltites cristatus n. gen. n. sp. – 37 specimens Araxoceltites sanestapanus n. gen. –13specimens Shevyrev (1965) cannot be separated. Phisonites n. sp. triangulus occurs, in the Aras Valley section, in a Araxoceltites laterocostatus n. gen. –2specimens single thin limestone bed 12.90 m below the extinction n. sp. horizon. Iranites transcaucasius was collected by us Dzhulfites spinosus Shevyrev, 1965 – 7 specimens already below this bed at −13.50 m, and hence the two Dzhulfites nodosus Shevyrev, 1965 – 23 specimens zones are merged here. Vedioceras sp. –1specimen Dzhulfoceras sp. –1specimen A fragment of Vedioceras sp. in shales at the base Unfortunately, most of the specimens are incomplete of of the Ali Bashi Formation in the Ali Bashi 1 sec- just whorl fragments. Even when the conch is rather com- tion demonstrates that the change from Vedioceras- plete, the specimens suffered from distortion. Many of them dominated faunas of the Wuchiapingian to the xeno- are weathered because they are float collections. discid-dominated assemblages of the Changhsingian is probably not abrupt. It can, however, not be ex- cluded that the specimen was reworked, as it is rather 3. Ammonoid zonation within the Zal strongly corroded. Member 2. Dzhulfites nodosus Zone. – The zone is best Ghaderi In accordance to previous articles ( et al. recorded in the Aras Valley and Zal sections. In the 2014b; Leda et al. 2014; Korn et al. 2016), we orien- Aras Valley section, Dzhulfites nodosus, D. spinosus tate the position of the respective fossil horizons at the and Araxoceltites sanestapanus occur at −9.50 m.