Geol. Mag.: page 1 of 23 c Cambridge University Press 2017 1 doi:10.1017/S0016756816001199 Sea level drop, palaeoenvironmental change and related biotic responses across Guadalupian–Lopingian boundary in southwest, North and Central Iran ∗ SAKINEH AREFIFARD Department of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Lorestan 68151-44316, Iran (Received 16 September 2016; accepted 5 December 2016) Abstract – The Capitanian to Wuchiapingian deposits in Zagros (southwest Iran), Alborz (North Iran) and Central Iran display important information about the end-Guadalupian extinction. According to lithological characteristics in the studied sections, the Guadalupian–Lopingian boundary (G-LB) interval can be subdivided into three units: the Capitanian unit, the latest Capitanian unit or interval unit (i.e. deposits in the topmost portion of the Capitanian strata) and the Wuchiapingian unit. The G- LB horizon is set at the base of Wuchiapingian deposits based on the first appearance datum (FAD) of the Late Permian diagnostic small foraminifers. The Capitanian unit was deposited subtidally, but the latest Capitanian unit was in the intertidal zone. The Wuchiapingian unit shows the return of subtidal conditions. A remarkable subaerial exposure occurs at the top of the Ruteh Formation, in Alborz, which is a laterite/bauxite horizon followed by continental deposits. The overall facies change in the G-L boundary intervals in the sections under study indicates a sea level drop around the G-LB which was at its lowest level in the Ruteh section. The decline and elimination of shallow marine biota in the G-LB interval took place in two steps in the Zagros and Alborz sections and in one step in Central Iran. These are indicative of the appearance of the stressful environment during the late Capitanian shallowing trend before the G-LB. The sea level drop and regression in the late Capitanian can be considered the major causes of end-Guadalupian extinction in the Iranian sections, but in the Alborz area volcanic activity is another feasible cause of this crisis. Keywords: end-Guadalupian extinction, Iran, sea level drop, facies changes, biotic responses. 1. Introduction 1996). Clapham, Shen & Bottjer (2009) demonstrated that the end-Guadalupian extinction was not sharp, and A mass extinction is considered as a globally rapid loss in fact it was a protracted but gradual decline in di- of species diversity in both marine and terrestrial envir- versity from the Wordian to end-Changhsingian. They onments. The big five extinctions of the Phanerozoic also argued that end-Guadalupian extinction shows no are those in which more than 50 % of the biota were peak in extinction rate, and is provoked by a sharp de- eliminated (Raup & Sepkoski, 1982; Sepkoski, 1994, crease in origination rates during the Capitanian and 1996). The end-Capitanian biota losses can also be Wuchiapingian. considered as one of the major extinctions in earth his- Besides the decline in taxonomic diversity, the tory. They comprise decline in diversity, with an elev- Guadalupian–Lopingian boundary (G-LB) interval ated extinction rate. They preceded the Permo-Triassic was associated with an environmental change. An- mass extinction, the largest extinction event in the oxic conditions have been reported both from the mid- Phanerozoic, and some researchers consider the end- oceanic deep sea (Isozaki, 1997) and deeper epicon- Guadalupian biotic losses as a first step in the double- tinental basins (Nielsen & Shen, 2004) as the prelude phased Permo-Triassic mass extinction (Jin, Zhang & to ocean stratification which would finally play a ma- Shang, 1994; Stanley & Yang, 1994; Erwin, Bowring jor role in the end-Permian mass extinction. Clapham, & Yugan, 2002; Bambach, 2006; Bottjer et al. 2008; Shen & Bottjer (2009) suggested that the gradual re- Clapham, Shen & Bottjer, 2009;Alroy,2010). The duction in diversity rather than a sharp (‘sudden’) ex- end-Guadalupian extinction was relatively severe, as tinction in end-Capitanian time eliminates the need to c. 58 % of marine vertebrates were eliminated during find the catastrophic cause of the extinction mechan- the Capitanian (Knoll et al. 1996). This crisis was also isms for the late Capitanian. Indeed it implies that severe for large-test fusulinids with losses at the gen- the main biotic loss at the end of the Palaeozoic was eric level (Sepkoski, 1994; Stanley & Yang, 1994). the end-Changhsingian mass extinction which eradic- The standing marine invertebrate diversity declined ated more than 78 % of marine vertebrates. While sev- >75 % during the end-Guadalupian crisis (Knoll et al. eral biostratigraphic studies have been carried out on Middle and Late Permian deposits in Zagros (SW Iran) ∗ Author for correspondence: sarefi[email protected] (Szabo & Kheradpir, 1978; Baghbani, 1997; Gaillot Downloaded from https:/www.cambridge.org/core. IP address: 91.98.90.48, on 27 Jan 2017 at 06:58:08, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0016756816001199 2 S. AREFIFARD & Vachard, 2007; Davydov & Arefifard, 2013), Cent- cludes some evaporites and is composed of three units: ral Iran (Jenny-Deshusses, 1983; Kobayashi & Ishii, Lower Dalan Member(carbonates), Middle Nar Mem- 2003; Leven & Vaziri Moghaddam, 2004;Arefifard, ber (predominantly anhydrite) and Upper Dalan Mem- unpub. Ph.D. thesis, Shahid Beheshti Univ., 2006) and ber (anhydrite interbedded with carbonate) (Szabo & Alborz (N Iran) (Arefifard, unpub. M.Sc. thesis, Shahid Kheradpir, 1978). Beheshti Univ., 1997; Gaetani et al. 2009) and signi- The section under study for the G-LB analysis in ficantly improved our knowledge of Permian palaeo- Zagros is located in the Ile-Beyk section on Zard biogeography in Iran, they did not address the G-LB Kuh Mountain (270 km west of Shar-e Kurd city) interval and its taxonomic and causal environmental (Fig. 1). The thickness of the Dalan Formation in change. Kolodka et al. (2012) studied the Middle to High Zagros varies from 932 m in the Il-e Beyk Late Permian deposits (Dalan Formation) in the Kuh- section in Zard Kuh Mountain to 332 m in Kuh-e e Gakhum anticline (SE Iran). They documented the Dena. This section was first studied by Setudehnia palaeontological changes in the G-L interval, which (1975), who assigned the Dalan Formation to the include a foraminifera diversity decline (70 %) and Middle to Late Permian according to its fossil con- changes in algal associations such as Gymnocodiaceae tent (smaller foraminifers, few fusulinids and corals) and Dasycladaceae. They proposed that the G-L inter- in the Lower Dalan Member. In this section, due to val records an important environmental change from the missing Lower Permian Faraghan Formation, the a bioclastic ramp in the Guadalupian to a shelf in Dalan Formation unconformably overlies the Ordovi- the Late Permian which is coeval with significant fo- cian shales of the Zard Kuh Formation and conform- raminifer extinction. The top of the Guadalupian de- ably underlies Lower Triassic dolomites of the Kangan posits in the Kuh-e Gahkum section is reported as a Formation. drop in sea level coinciding with global regression at The most detailed fusulinid-based biostratigraphic the end-Capitanian (Kolodka et al. 2012). This study biozonation and microfacies study of the Dalan aims to clarify the detailed stratigraphy and fossil con- Formation in the Il-e Beyk section was carried out tent immediately below and above the G-LB interval by Davydov & Arefifard (2013). The lower part and analyse the trend of the faunal and palaeoenviron- of the Dalan Formation (484.5 m thick, including mental changes characterizing end-Gudalupian extinc- units 1–18, Fig. 2) mainly consists of medium- to tion in Iranian sections. thick-bedded, partly cliff-forming wackestone, pack- stone and grainstones with few horizons of mud- stone (Davydov & Arefifard, 2013). Four fusulinid 2. Materials biozones are identified in the Lower Dalan Mem- The database for this contribution originates from the ber which are, in ascending order, Praeskinnerella author’s many years’ field work in different parts of parviflucta – Chusenella? pseudocompacta, Eopoly- Iran, and also published literature. The sections in diexodina persica, Chusenella schwagerinaeformis – this study have been revisited for detailed sampling Rugososchwagerina zagroensis and Monodiexodina and more field information. This study deals with kattaensis. The age of the Lower Dalan Member, based detailed lithostratigraphy, biostratigraphy, microfacies on these fusulinid biozones, is referred to the Road- and fossil record change in the G-LB interval in the ian to early Capitanian. Cream-coloured thickly bed- Middle to Late Permian Dalan Formation, Zagros; ded dolomite and dolomitic limestones with occasional Middle to Late Permian Jamal Formation, Central Iran; chert nodules form the main lithological components and Middle Permian Ruteh Formation and Late Per- of the upper part of the Dalan Formation (442.5 m mian Nesen Formation, Alborz, to provide plausible thick, including units 19–28, Fig. 2). The only fu- lines of evidence for end-Guadalupian extinction in Ir- sulinid biozone recognized in the Upper Dalan Mem- anian sections and their geological implications. ber is Afghanella schencki – Sumatrina brevis.Rare small foraminifers are found, including Paraglobivalv- ulina sp. and Dagmarita sp. in the uppermost part of 3. Lithostratigraphy and biostratigraphy of the G-L the Upper Dalan Member. Therefore, the