Permian integrative stratigraphy,biotas,paleogeographical and paleoclimatic evolution of the Qinghai-Tibetan Plateau and its surrounding areas

The Permian Period was a critical time interval during which various blocks of the Qinghai-Tibetan Plateau have experienced profound and complex paleogeographical changes.The supercontinent Pangea was formed to its maximum during this interval,hampering a global east-to-west trending equatorial warm ocean current.Meanwhile,a semi-closed Tethys Ocean warm pool formed an eastward-opening oceanic embayment of Pangea,and became an engine fostering the evolutions of organisms and environmental changes during the Paleozoic-Mesozoic transition.Stratigraphy and preserved fossil groups have proved extremely useful in understanding such changes and the evolutionary histories of the Qinghai-Tibetan Plateau.Widely distributed Permian deposits and fossils from various blocks of the Qinghai-Tibetan Plateau exhibited varied characteristics,reflecting these blocks’different paleolatitude settings and drifting histories.The Himalaya Tethys Zone south to the Yarlung Zangbo suture zone,located in the northern Gondwanan margin,yields fossil assemblages characterized by cold-water organisms throughout the Permian,and was affliated to those of the Gondwanaland.Most of the exotic limestone blocks within the Yarlung Zangbo suture zone are Guadalupian(Middle Permian)to Early Triassic in age.These exotic limestone blocks bear fossil assemblages that have transitional affinities between the warm Tethys and cold Gondwanan regions,suggesting that they most probably represent seamount deposits in the Neo-Tethys Ocean.During the Asselian to Sakmarian(Cisuralian,also Early Permian),the Cimmerian microcontinents in the northern part of Gondwana preserved glacio-marine deposits of Asselian to Sakmarian,and contained typical Gondwana-type cold-water faunas.By the middle Cisuralian(~290-280 Ma),the Cimmerian microcontinents rifted off from the Gondwanaland,and drifted northward allometrically due to the active magmatism of the Panjal Traps in the northern margin of the Indian Plate.Two slices of microcontinents are discerned as a result of such allometic drifting.The northern Cimmerian microcontinent slice,consisting of South Qiangtang,Baoshan,and Sibuma blocks,drifted relatively quickly,and preserved widespread carbonate deposits and warm-water faunas since Artinskian.By contrast,the southern Cimmerian microcontinent slice,consisting of Lhasa,Tengchong,and Irrawaddy blocks,drifted relatively slowly,and were characterized by widespread carbonate deposits containing warm-water faunas of late Kungurian to Lopingian(Late Permian).As such,these blocks rifted off from the northern Gondwanan margin since at least the Kungurian.Thus,it can be inferred that these blocks were incorperated into the low latitude,warm-water regions later than the northern Cimmerian slice.Such discrepancies in depositional sequences and paleobiogeography imply that the rifting of Cimmerian microcontinents resulted in the formation of both Meso-Tethys and Neo-Tethys oceans during the Cisuralian.By contrast,the North Qiangtang block,because of its further northern paleogeographical position,contains warm-water faunas throughout the whole Permian Period that are affiliated well with the faunas from the South China,Simao,and Indochina blocks.Together,these blocks belonged to the members of the northern Paleo-Tethys Ocean.Thus,an archipelagic paleogeographical framework divided by Paleo-,Meso-,and Neo-Tethys oceans was formed,fostering a global biodiversity centre within the Tethys warm pool.Since most of the allochthonous blocks assembling the Qinghai-Tibetan Plateau were situated in the middle to high latitude regions during the Permian,they preserved most sensitive paleoclimate records of the Late Paleozoic Ice Age(LPIA),the Artinskian global warming event,and the rapid warming event at the end-Permian.Therefore,sedimentological and paleontological records of these blocks are the unique window through which we can understand global evolutions of tectonic movement and paleoclimate,and their impacts on spatiotemporal distributions of comtemporaneous biotas.

Permian integrative stratigraphy and timescale of China

A series of global major geological and biological events occurred during the Permian Period. Establishing a highresolution stratigraphic and temporal framework is essential to understand their cause-effect relationship. The official International timescale of the Permian System consists of three series(i.e., Cisuralian, Guadalupian and Lopingian in ascending order) and nine stages. In China, the Permian System is composed of three series(Chuanshanian, Yansingian and Lopingian) and eight stages, of which the subdivisions and definitions of the Chuanshanian and Yangsingian series are very different from the Cisuralian and Guadalupian series. The Permian Period spanned ～47 Myr. Its base is defined by the First Appearance Datum(FAD) of the conodont Streptognathodus isolatus at Aidaralash, Kazakhstan with an interpolated absolute age 298.9±0.15 Ma at Usolka, southern Urals, Russia. Its top equals the base of the Triassic System and is defined by the FAD of the conodont Hindeodus parvus at Meishan D section, southeast China with an interpolated absolute age 251.902±0.024 Ma. Thirty-five conodont, 23 fusulinid, 17 radiolarian and 20 ammonoid zones are established for the Permian in China, of which the Guadalupian and Lopingian conodont zones have been served as the standard for international correlation. The Permian δ13 Ccarbtrend indicates that it is characterized by a rapid negative shift of 3–5‰ at the end of the Changhsingian, which can be used for global correlation of the end-Permian mass extinction interval, but δ13 Ccarbrecords from all other intervals may have more or less suffered subsequent diagenetic alteration or represented regional or local signatures only. Permian δ18 Oapatitestudies suggest that an icehouse stage dominated the time interval from the late Carboniferous to Kungurian(late Cisuralian). However, paleoclimate began to ameriolate during the late Kungurian and gradually shifted into a greenhouse-dominated stage during the Guadalupian.The Changhsingian was a relatively cool stage, followed by a globally-recognizable rapid temperature rise of 8–10°C at the very end of the Changhsingian. The87 Sr/86 Sr ratio trend shows that their values at the beginning of the Permian were between 0.70800,then gradually decreased to the late Capitanian minimum 0.70680–0.70690, followed by a persistent increase until the end of the Permian with the value 0.70708. Magenetostratigraphy suggests two distinct stages separated by the Illawarra Reversal in the middle Wordian, of which the lower is the reverse polarity Kiaman Superchron and the upper is the mixed-polarity Illawarra Superchron. The end-Guadalupian(or pre-Lopingian) biological crisis occurred during the late Capitanian, when faunal changeovers of different fossil groups had different paces, but generally experienced a relatively long time from the Jinogondolella altudensis Zone until the earliest Wuchiapingian. The end-Permian mass extinction was a catastrophic event that is best constrained at the Meishan section, which occurred at 251.941±0.037 Ma and persisted no more than 61±48 kyr. After the major pulse at Bed 25, the extinction patterns are displayed differently in different sections. The global end-Guadalupian regression is manifested between the conodont Jinogondolella xuanhanensis and Clarkina dukouensis zones and the endChanghsingian transgression began in the Hindeodus changxingensis-Clarkina zhejiangensis Zone. The Permian Period is also characterized by strong faunal provincialism in general, which resulted in difficulties in inter-continental and inter-regional correlation of both marine and terrestrial systems.

Carboniferous and Permian integrative stratigraphy and timescale of North China Block

The Carboniferous-Permian strata in the North China Block(NCB) contain abundant fossils, coals and natural gases.Establishing a high-resolution timescale for the Carboniferous and Permian in the NCB is essential to understand the geologic events and explore the spatial and temporal distributions of the natural resources. The upper Carboniferous and the basal part of Permian are relatively well correlated because they yield marine conodont and fusuline fossils. However, the Permian terrestrial strata mostly rely on poorly constrained palynostratigraphy and phytostratigraphy and are short of the precise geochronologic constraints on the correlation with the marine strata. This study provides a critical review on the state-of-the-art of the latest Carboniferous and Permian chronostratigraphic and biostratigraphic frameworks and stratigraphic correlation in the NCB. The Penchi Formation ranges from lower Bashkirian to lower Gzhelian;the Taiyuan Formation is assigned to the upper Gzhelian to lower Asselian;the Shansi and Lower Shihhotse formations are from middle Asselian to lower Sakmarian;the Upper Shihhotse Formation is assigned to upper Artinskian to lower Kungurian, and the Sunjiagou Formation was assigned to Lopingian, respectively. A long hiatus up to ~20 Myr between the Upper Shihhotse and Sunjiagou formations, mainly marked by a large-scale erosional surface at the base of a coarse conglomeratic sandstone unit and/or multiple paleosol layers as well as significant differences of floras between these two lithostratigraphic units, is present probably due to tectonic uplift in association with the closure of the Paleo Asian Ocean(PAO) during the Cisuralian and Guadalupian. The possible amplitude of sea-level changes from Carboniferous to Permian on the NCB is estimated from 0 to 40 m.The floral succession, depositional records and organic carbon isotope profiles suggest that the latest Carboniferous and earliest Permian was a favorable period for coal accumulation under an ever-wet and warm climate, followed by a prominent shift to dry climate from early-middle Cisuralian. This climatic shift during the Permian was mainly resulted from northward migration of the Pangea and the closure of the PAO, which is comparable with the Carboniferous and Permian trends in central Europe.