University of Isfahan Journal of Stratigraphy and Sedimentology Researches 2008-7888 37 3 2021 09 23 The biotic crisis of end-Guadalupian in the Hambast Valley section, Abadeh, southwest Iran and its comparison with coeval deposits in eastern Tethys The biotic crisis of end-Guadalupian in the Hambast Valley section, Abadeh, southwest Iran and its comparison with coeval deposits in eastern Tethys 91 112 25812 10.22108/jssr.2021.126921.1197 FA Sakineh Arefifard Assistant professor, Geology Department, Faculty of Basic sciences, Lorestan University, Khorramabad, Iran Sima Shahinfar Geology Department, Faculty of Basic Sciences, Lorestan University Khorramabad Journal Article 2021 01 11 Abstract The study of Faunal biodiversity distribution in the strata close to the Middle and Upper Permian boundary in the Hambast Valley section was carried out. Considering obvious environmental and faunal changes in the topmost horizon of the subunit 4a of the Abadeh Formation, the end-Guadalupian extinction has happened before Guadalupian–Lopingian boundary. The significant changes near the Guadalupian-Lopingian boundary in this section are the presence of dolomite and stromatolitic limestone at the topmost part of the subunit 4a, implying the shallowness of the depositional environment as well as the noticeable decline of faunal biodiversity. The cause of end-Guadalupian bio-crisis in the Hambast Valley section is more likely due to the falling sea level. The examination of the end-Guadalupian extinction horizon in South China and Japan shows its position at the end of Capitanian. In South China (Penglaitan section) and Abadeh (Hambast Valley section), the end-Guadalupian eustatic regression has only left shallowing effects with environmental and faunal changes implying the end-Guadalupian extinction evidence. In the Hambast Valley section, the latest Capitanian Hemigordius irregulariformis Zone with some Codonofusiella species in the basal part of the subunit 4b are representative of the re-occurrence of the foraminiferal fauna after the end-Guadalupian extinction, while fusulinid Zone of early Wuchiapingian Codonofusiella-Reichelina is indicative of post-extinction foraminiferal recovery. Keywords: Hambast Valley section, Biodiversity, End-Guadalupian extinction, End-Guadalupian regression, Tethys Introduction The biotic crisis at the end of Permian was the biggest event throughout of Phanerozoic life history as Paleozoic faunas were replaced by new ones (Ervin 2006). This event occurred in two phases, one at Guadalupian–-Lopingian boundary, ca. 260 m.y. ago, and the other at Permian-Triassic boundary about 252 m.y. ago (Stanly and Yang 1994; Bambach 2006). The Permian-Triassic extinction was the most severe Phanerozoic extinction, which gave rise to the loss of more than 90% of the marine species (Shen et al. 2011). It has been thought that the main cause of this extinction was linked to the high environmental disturbances caused by the Siberian Large Igneous Province (Bond and Wignall 2014). Compared to the Permian–-Triassic extinction, the end-Guadalupian extinction was less severe. Its effects were mostly selective (Payne and Clapham 2012) so that algal-symbiont organisms including large-test fusulinids, rugose corals and large bivalves Alatochochidae were the most affected faunas (Isozaki et al. 2007a,b). Other organisms such as brachiopods, crinoids, ostracods and bryozoans were less influenced by end-Capitanian extinction. Recent studies (Ota and Isozaki 2006; Retallack et al. 2008) reveal that despite previous thoughts, biodiversity decline at the Guadalupian-Lopingian boundary was not fast and the main extinction happened in late Guadalupian and before Guadalupian-Lopingian boundary. There are different opinions about the cause of end-Guadalupian extinction including global regression (Jin et al. 1994; Arefifard 2012; Kolodka et al. 2012), the gigantic eruptions of Emeishan basaltic lavas in South China (Wignall et al. 2009; Bond et al. 2010; He et al. 2010), widespread methane emissions (Retallack et al. 2008) and global cooling (Isozaki 2007a) but no definitive cause has been proposed for it. However, the incidence of massive eruptions both in Permian–-Triassic boundary and end-Capitanian is a common feature that might be the most effective cause of these two extinctions. On the other hand, the volcanic events as the main causal mechanism of the extinction at end-Changhsingian and end-Capitanian might have influenced the regions close to these two activities and for the areas further away the other causes should be invoked. The continuous Permian–Triassic deposits in Iran crop out in the NE flank of the Hambast Mountain at 60 km East of Abadeh. In order to examine the end-Guadalupian extinction in the Hambast Valley, one stratigraphic section has been measured and samples which include the middle and upper parts of the unit 3 of the Surmaq Formation of Capitanian in age, and the upper Capitanian subunit 4a and uppermost Capitanian and Wuchiapingian subunit 4b of the Abadeh Formation. The main objective of this research is the study of effect of the end-Guadalupian extinction on faunal diversity in the Hambast valley section and its comparison with other coeval deposits within the Tethys basin, especially in South China and Japan. Materials & Methods In order to examine the end-Guadalupian extinction in strata before, after and across Guadalupian–Lopingian boundary in the Hambast Valley section, a stratigraphic section was measured and 274 samples were collected from the middle and upper parts of the Unit 3 of the Surmaq Formation and Abadeh Formation. In addition to the identification of foraminifer genera and species to determine precise age assignments, foraminiferal faunas and other fossil groups abundance in thin sections were evaluated, especially before and after Guadalupian–Lopingian boundary. Discussion of Results & Conclusions The middle and upper parts of the unit 3 of the Surmaq Formation based on Altineria bacillaeformis-Baisalina pulchra-Hemigordiopsis luquensis biozone could be assigned to lower Capitanian. The examination of the foraminiferal content in subunits 4a and 4b and unit 5 of the Abadeh Formation reveal upper Capitanian Baisalina cf. guizhouensi, uppermost Capitanian Hemigordius irregulariformis and Wuchiapingian Pseudodunbarula-Codonofusiella-Reichelina biozones. In the Hambast Valley section, the most biodiversity is observed in the main part of the upper Capitanian subunit 4a of the Abadeh Formation; in contrast, its uppermost portion, which is composed of dolomite and stromatolitic limestone, lacks fossil. In the Panglaitan and Tieqiao sections in South China, fossil remains are traceable to the upper member of the Maokou Formation known as Laibin and only its uppermost parts have no fossil (Shen et al. 2007). In Japan, the upper part of the Akasaka Limestone is mainly composed of black limestone belongs to the late Capitanian (Kafukuda et al. 2014). The uppermost portion of the Akasaka Limestone is followed by a greenish very thin-bedded of extremely fine-grained claystone. In this thin-bedded clayed bed, no fossil remain is recorded. In the Hambast Valley section, the disappearance of the upper Capitanian biota considered as Barren Interval Zone occurred in one step and is documented in the dolomitic beds and stromatolitic limestones of the uppermost portion of the subunit 4a of the Abadeh Formation. This Barren Interval Zone is located in the uppermost part of the Laibin Member in South China and occurred in the very thin clayed bed in Japan, which is considered as a subaerial exposure at the top of the Akasaka Limestone resulting from the short time sea-level fall and as one of the possible causes of the end-Guadalupian extinction. Considering the faunal distribution and biodiversity in the Hambast Valley section, the extinction horizon is located before the latest Capitanian and within the uppermost portion of the subunit 4a of the Abadeh Formation where no fossil is found. The examination of extinction horizon in other coeval deposits with the Hambast Valley section in South China and Japan reveals its position at the latest Capitanian in the Penglaitan and Tieqiao sections in South China and Akasaka section in central Japan. Although evidence of shallowing has been reported at the end of Capitanian in both South Chinese sections and the Hambast Valley section, there is no indication of regression during this time interval in these two regions. However, there is a record of regression in Japan as a plausible cause of end-Guadalupian extinction. Abstract The study of Faunal biodiversity distribution in the strata close to the Middle and Upper Permian boundary in the Hambast Valley section was carried out. Considering obvious environmental and faunal changes in the topmost horizon of the subunit 4a of the Abadeh Formation, the end-Guadalupian extinction has happened before Guadalupian–Lopingian boundary. The significant changes near the Guadalupian-Lopingian boundary in this section are the presence of dolomite and stromatolitic limestone at the topmost part of the subunit 4a, implying the shallowness of the depositional environment as well as the noticeable decline of faunal biodiversity. The cause of end-Guadalupian bio-crisis in the Hambast Valley section is more likely due to the falling sea level. The examination of the end-Guadalupian extinction horizon in South China and Japan shows its position at the end of Capitanian. In South China (Penglaitan section) and Abadeh (Hambast Valley section), the end-Guadalupian eustatic regression has only left shallowing effects with environmental and faunal changes implying the end-Guadalupian extinction evidence. In the Hambast Valley section, the latest Capitanian Hemigordius irregulariformis Zone with some Codonofusiella species in the basal part of the subunit 4b are representative of the re-occurrence of the foraminiferal fauna after the end-Guadalupian extinction, while fusulinid Zone of early Wuchiapingian Codonofusiella-Reichelina is indicative of post-extinction foraminiferal recovery. Keywords: Hambast Valley section, Biodiversity, End-Guadalupian extinction, End-Guadalupian regression, Tethys Introduction The biotic crisis at the end of Permian was the biggest event throughout of Phanerozoic life history as Paleozoic faunas were replaced by new ones (Ervin 2006). This event occurred in two phases, one at Guadalupian–-Lopingian boundary, ca. 260 m.y. ago, and the other at Permian-Triassic boundary about 252 m.y. ago (Stanly and Yang 1994; Bambach 2006). The Permian-Triassic extinction was the most severe Phanerozoic extinction, which gave rise to the loss of more than 90% of the marine species (Shen et al. 2011). It has been thought that the main cause of this extinction was linked to the high environmental disturbances caused by the Siberian Large Igneous Province (Bond and Wignall 2014). Compared to the Permian–-Triassic extinction, the end-Guadalupian extinction was less severe. Its effects were mostly selective (Payne and Clapham 2012) so that algal-symbiont organisms including large-test fusulinids, rugose corals and large bivalves Alatochochidae were the most affected faunas (Isozaki et al. 2007a,b). Other organisms such as brachiopods, crinoids, ostracods and bryozoans were less influenced by end-Capitanian extinction. Recent studies (Ota and Isozaki 2006; Retallack et al. 2008) reveal that despite previous thoughts, biodiversity decline at the Guadalupian-Lopingian boundary was not fast and the main extinction happened in late Guadalupian and before Guadalupian-Lopingian boundary. There are different opinions about the cause of end-Guadalupian extinction including global regression (Jin et al. 1994; Arefifard 2012; Kolodka et al. 2012), the gigantic eruptions of Emeishan basaltic lavas in South China (Wignall et al. 2009; Bond et al. 2010; He et al. 2010), widespread methane emissions (Retallack et al. 2008) and global cooling (Isozaki 2007a) but no definitive cause has been proposed for it. However, the incidence of massive eruptions both in Permian–-Triassic boundary and end-Capitanian is a common feature that might be the most effective cause of these two extinctions. On the other hand, the volcanic events as the main causal mechanism of the extinction at end-Changhsingian and end-Capitanian might have influenced the regions close to these two activities and for the areas further away the other causes should be invoked. The continuous Permian–Triassic deposits in Iran crop out in the NE flank of the Hambast Mountain at 60 km East of Abadeh. In order to examine the end-Guadalupian extinction in the Hambast Valley, one stratigraphic section has been measured and samples which include the middle and upper parts of the unit 3 of the Surmaq Formation of Capitanian in age, and the upper Capitanian subunit 4a and uppermost Capitanian and Wuchiapingian subunit 4b of the Abadeh Formation. The main objective of this research is the study of effect of the end-Guadalupian extinction on faunal diversity in the Hambast valley section and its comparison with other coeval deposits within the Tethys basin, especially in South China and Japan. Materials & Methods In order to examine the end-Guadalupian extinction in strata before, after and across Guadalupian–Lopingian boundary in the Hambast Valley section, a stratigraphic section was measured and 274 samples were collected from the middle and upper parts of the Unit 3 of the Surmaq Formation and Abadeh Formation. In addition to the identification of foraminifer genera and species to determine precise age assignments, foraminiferal faunas and other fossil groups abundance in thin sections were evaluated, especially before and after Guadalupian–Lopingian boundary. Discussion of Results & Conclusions The middle and upper parts of the unit 3 of the Surmaq Formation based on Altineria bacillaeformis-Baisalina pulchra-Hemigordiopsis luquensis biozone could be assigned to lower Capitanian. The examination of the foraminiferal content in subunits 4a and 4b and unit 5 of the Abadeh Formation reveal upper Capitanian Baisalina cf. guizhouensi, uppermost Capitanian Hemigordius irregulariformis and Wuchiapingian Pseudodunbarula-Codonofusiella-Reichelina biozones. In the Hambast Valley section, the most biodiversity is observed in the main part of the upper Capitanian subunit 4a of the Abadeh Formation; in contrast, its uppermost portion, which is composed of dolomite and stromatolitic limestone, lacks fossil. In the Panglaitan and Tieqiao sections in South China, fossil remains are traceable to the upper member of the Maokou Formation known as Laibin and only its uppermost parts have no fossil (Shen et al. 2007). In Japan, the upper part of the Akasaka Limestone is mainly composed of black limestone belongs to the late Capitanian (Kafukuda et al. 2014). The uppermost portion of the Akasaka Limestone is followed by a greenish very thin-bedded of extremely fine-grained claystone. In this thin-bedded clayed bed, no fossil remain is recorded. In the Hambast Valley section, the disappearance of the upper Capitanian biota considered as Barren Interval Zone occurred in one step and is documented in the dolomitic beds and stromatolitic limestones of the uppermost portion of the subunit 4a of the Abadeh Formation. This Barren Interval Zone is located in the uppermost part of the Laibin Member in South China and occurred in the very thin clayed bed in Japan, which is considered as a subaerial exposure at the top of the Akasaka Limestone resulting from the short time sea-level fall and as one of the possible causes of the end-Guadalupian extinction. Considering the faunal distribution and biodiversity in the Hambast Valley section, the extinction horizon is located before the latest Capitanian and within the uppermost portion of the subunit 4a of the Abadeh Formation where no fossil is found. The examination of extinction horizon in other coeval deposits with the Hambast Valley section in South China and Japan reveals its position at the latest Capitanian in the Penglaitan and Tieqiao sections in South China and Akasaka section in central Japan. Although evidence of shallowing has been reported at the end of Capitanian in both South Chinese sections and the Hambast Valley section, there is no indication of regression during this time interval in these two regions. However, there is a record of regression in Japan as a plausible cause of end-Guadalupian extinction.

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