Upper Permian To Lower Triassic Conodont Successions From Pakistan And Armenia

The devastating Permian-Triassic mass extinction（PTME）marks the most severe biotic and environmental catastrophes in Earth’s history.Following this event,perturbed conditions accompanied with several minor extinction events persisted throughout the Early Triassic.The marine ecosystem went through a protracted recovery and did not fully recover until the mid-late Anisian,～8 Myr after the PTME.In studying biotic and environmental changes of the PTME and its aftermath,a high-resolution biochronostratigraphic framework is essential in providing a reliable timescale for reconstructing event sequences and correlating various events worldwide.Conodonts are believed to have survived the PTME without major diversity and abundance losses,thus have played an unparalleled role in establishing the Early Triassic timescale.Their rapid evolution,worldwide distribution,and usually good preservation have made them an ideal biostratigraphic tool in stratigraphic subdivision and correlations worldwide.Meanwhile,due to these advantages,conodonts have played an essential role in define the key chronostratigraphic boundaries of Triassic.The Salt Range,Pakistan,which was located in the southern Neo-Tethys Ocean during the Early Triassic,is a classical area in studying the Lower Triassic biostratigraphy and environmental events.Yet,the conodont data from this area has not been updated since the 1980s.A series of Upper Permian to Lower Triassic marine strata are well-exposed in Armenia,which was located in the western Paleo-Tethys Ocean and serves as an important reference in stratigraphic correlations worldwide,but conodont studies are lacking from this area.Hence,several sections of the above-mentioned localities were chosen to conduct systematic conodont studies,as well as carbon isotopic studies.A high-resolution conodont succession and carbon isotopic curve were thus established,which highly improved the resolution of the strata subdivision and correlation of the studied area.At the meantime,some key boundaries,such as the Permian-Triassic boundary（PTB）,Induan-Olenekian boundary（IOB）and the Smithian-Spathian boundary（SSB）,are defined and correlated with other well-studied sections from South China（Meishan and Chaohu）and India（Mud）using the detailed paleontological and isotopic data obtained in this study.In addition,the ontogeny and evolution of Griesbachian-Dienerian conodonts were studied based on the abundant specimens obtained.Main conclusions are as follows:1.The Early Triassic conodont zonal framework and organic carbon isotopic curve have been established in the Zaluch section,Pakistan.Conodont P1 elements assigned to67 species（including 13 new species）in 19 genera were recognized and formed the basis of 12 conodont zones.In ascending order,they are Hindeodus parvus Zone,Isarcicella lobata Zone,Is.isarcica Zone,Neoclarkina krystyni Zone,Sweetospathodus kummeli Zone,Neospathodus dieneri-Ns.cristagalli Zone,Novispathodus waageni eowaageni Zone,Nv.posterolongatus Zone,Foliella-Smithodus Zone,Ns.spitiensis Zone,Nv.pingdingshanensis Zone,and Triassospathodus homeri Zone.A series of positive and negative excursions ofδ¹³C were also recognized and can be used for global correlations.The PTB was placed at the base of Mianwali Formation based on the first occurrence（FO）of H.parvus.The IOB was placed at the horizon 11.45 m above the base of the Mianwali Formation（in the middle part of the Ceratite Marls Unit）based on the FO of Nv.w.eowaageni.The SSB was placed at the horizon 34.75 m above the base of the Mianwali Formation（base of the Bivalve Beds）based on the FO of Nv.pingdingshanensis.2.Conodont biostratigraphy and organic carbon isotopes from the Nammal section,Pakistan,were studied.Conodont P1 elements assigned to 22 species（including 7 new species）in 8 genera were recognized and formed the basis of 8 conodont zones.In ascending order,they are H.typicalis Zone,Nc.krystyni Zone,Nc.discreta Zone,Sw.kummeli带、Scythogondolella narmiaensis Zone,Ns.dieneri Zone,Ns.cristagalli Zone,and Nv.w.eowaageni Zone.The IOB was placed at the middle part of the Ceratite Marls Unit based on the FO of Nv.w.eowaageni,and this level coincides with theδ¹³C positive excursion maximum P2.The newly established Sc.narmiaensis Zone is useful for improving the subdivision resolution of the Dienerian,and it can be correlated with the counterpart found in Narmia section and Canadian Arctic.3.At the Narmia section,Pakistan,Conodont P1 elements assigned to 28 species（including 5 new species）in 6 genera were recognized and formed the basis of 7 conodont zones.In ascending order,they are H.postparvus Zone,Nc.krystyni Zone,Sw.kummeli Zone,Sc.narmiaensis Zone,Ns.dieneri Zone,Ns.cristagalli Zone,and Ns.pakistanensis Zone.Of these,the new species Sc.narmiaensis was first described from the Narmia section,and the corresponding zone is useful for improving the subdivision resolution of the Dienerian.4.From the Akhura Formation and the Karabaglyar Formation at Chanakhchi,Armenia,conodont P1 elements assigned to 20 species in 5 genera were recognized and formed the basis of 8 conodont zones belonging to Late Permian and Early Triassic.In ascending order,they are Clarkina yini Zone,C.abadehensis Zone,H.praeparvus Zone,H.parvus Zone,Is.staeschei Zone,H.postparvus Zone,H.sosioensis Zone,and Ns.dieneri Zone.The PTB was placed at the horizon 1.3 m above the base of the Karabaglyar Formation.The carbonate carbon isotopic curve in this section is highly consistent with that at Meishan,thus it can serve as a good auxiliary proxy for strata subdivision and correlation.5.From the Akhura Formation and the Karabaglyar Formation at Vedi,Armenia,conodont P1 elements assigned to 22 species in 3 genera were recognized and formed the basis of 7 conodont zones belonging to Late Permian and Early Triassic.In ascending order,they are C.bachmanni Zone,C.nodosa Zone,C.yini Zone,C.meishanensis Zone,H.praeparvus Zone,Is.isarcica Zone,and H.postparvus Zone.The PTB is temporarily undefined at this section due to the unexpected high occurrence of H.parvus and the scarcity of conodont yielding in the lower part of the Karabaglyar Formation.A negativeδ¹³C excursion occurs in the Is.isarcica Zone at this section,which is consistent with the record at Meishan.6.From the Karabaglyar Formation at OgbinⅡsection,Armenia,only one conodont species assigned to Ns.dieneri was recognized,which indicates a Dienerian age for the main part of the section.Theδ¹³C shows a continuous positive excursion and reaches a maximum peak in the upper part of the section,which may correspond to the P2maximum recognized in global records,and this implies a Smithian age for the upper part of the section.7.Our acknowledgements of the conodont faunas and the carbon isotopic excursions obtained from the Upper Permian to Lower Triassic of Pakistan and Armenia provide a solid foundation for the correlation of conodont successions between the studied area and the well-known sections in South China（Meishan and Chaohu）and India（Mud）.These data are of great value for improving the resolution of strata subdivision and correlation in the studied area and providing plentiful materials for the study of conodont diversification and evolution.8.Based on the abundant specimens collected from the Salt Range and Surghar Range of Pakistan,the ontogenetic patterns were reconstructed and described in detail for Dienerian zonal species Sweetospathodus kummeli,Neospathodus dieneri,Neospathodus cristagalli and Neospathodus pakistanensis,with the flange development being the most striking feature during ontogeny.The ontogenies of several Griesbachian platform-bearing conodonts were also described briefly.Some long-standing taxonomic uncertainties were clarified,and the taxonomic definitions were thus improved.The evolutionary relationships among these key taxa were established based on phylogenetic analysis,and some important evolutionary trends were recognized.A comparison of the ontogenetic trajectories revealed complex heterochronic processes of conodont development during the late Griesbachian to Dienerian.The reduction of conodont platform during the Griesbachian to Dienerian may reflect a major change of the global oceanic climates and environments.