Late Devonian Conodont Biostratigraphy,Event Stratigraphy And Chemostratigraphy In South China And Western Junggar,NW China

The Devonian was a crucial period in Earth history and is marked by the colonization of land by large vascular plants,radiation of fishes,and the first occurrence of amphibians.The Late Devonian is characterized by numerous bio-environmental events,notably the Frasnian-Famennian?F-F?bio-crisis or Upper Kellwasser Event,which wiped out the shallow water coral and sponge reef ecosystems and is considered one of the“big five”faunal crises of the Phanerozoic.The Hangenberg Event at the Devonian-Carboniferous?D-C?boundary,which affected both marine and terrestrial ecosystems within a span of 100–300 kyr,may have been as severe as the Kellwasser Event.Besides,the late-latest Famennian glaciation in Gondwana was a major glaciation event in the Late Paleozoic.The Upper Devonian is well-developed in South China and Western Junggar,Northwestern China,which provide an excellent georgical background to explore the co-evolution of organisms and environments during Late Devonian.The offshore facies Lali section in South China comprised of a 220-m-thick,continuously exposed carbonate succession of Upper Devonian strata.160 samples were collected throughout the upper part of the Laoyefen Formation,the entire Wuzhishan Formation,and the lower part of the Wangyou Formation which yielded27865 P1 platform elements.12 Frasnian and 20 Famennian biozones are recognized.189 species or subspecies that belong to 10 genus,including Ancyrodella?Ancyrognathus?Bispathodus?Icriodus?Mesotaxis?Polygnathus?Palmatolepis?Siphonodella?Branmehla and Ancyrognathus.11 new species and subspecies are established in this study:Palmatolepis yizhouensis n.sp.,Pa.po.laliensis n.subsp.,Pa.gl.chengyuani n.subsp.,Pa.rh.jiqiangi n.subsp.,Pa.siyunae n.sp.,Pa.protoperlobata n.sp.,Polygnathus protobeulensis n.sp.,Icriodus al.laliensis n.subsp.,Ic.de.jiqiangi n.subsp.,Ic.io.chengyuani n.subsp.,Ic.siyunae n.sp..The nearshore facies Bulongguoer section in Western Junggar is characterized by the exposure of the famous Hongguleleng Formation which consists of bioclastic argillaceous limestones and marls with abundant shallow water faunas.The Hongguleleng Formation also represents typical shallow water tempestite facies formed in the archipelagic context of the Paleo-Asian Ocean.67 conodont samples were collected in the Lower and Upper Member of the Hongguleleng Formation,912 P1platform elements are obtained,Relative high abundance?about 40%?of endemic taxa?13 taxa?indicates isolation of the Junggar Basin in the early Famennian.Most no-endemic species suggest that the Lower Member of the Hongguleleng Formation has a Famennian prima Zone to utahensis Zone age,and the Frasnian-Famennian boundary does not exist in its bottom.The Upper member of the Hongguleleng Formation may be late Famennian-early Tournaisian age.The microfacies and conodont biofacies analysis recovered the Late Devonian paleoenvironment changes at the Lali and the Bulongguoer sections.At the Lali section,8 microfacies type are recognized,and the Wuzhishan Formation mainly develops the Palmatolepis-biofacies.Microfacies analyses and the abundance of Palmatolepis indicate that the highest Frasnian sea level lies in FZ 13?Upper rhenana Zone?,whereas the highest Famennian sea level was in the utahensis Zone.The Kellwasser and annulata events are characterized by transgressive black carbonates,while the Hangenberg Event is represented by black shale deposits.Other transgressive events recognized at Lali include the Middlesex,Nehden,Enkeberg,and Dasberg,as well as the Strunian transgression.Four regressive events were recognized on the basis of lithological and microfacies changes,i.e.,the linguiformis regression,Condroz Event,velifer regression,and the Derwer regression.These sea-level change events were of short duration and globally isochronous based on conodont correlations.At the Bulongguoer section,5 microfacies type are recognized,and the Hongguleleng Formation develops an Icriodus-Polygnathus biofacies.Storm-sequence are extremely developed in its Lower Member,the carbonate grains mainly comprise bryozoan and echinoderm,no peloids,ooid,bacteria and algae are found,and indicate typical cold-water carbonates.The possible Nehden,Condroz and Enkeberg events are recognized on the basis of lithological and microfacies changes.A new biostratigraphically constrained carbon isotope record from the Lali section?South China?is presented to document perturbations in the Late Devonian carbon cycle.Positive carbon isotope excursions?PCIEs?are most important components of the Late Devonian long-term carbon isotope cycle:Frasnes?+2‰?,Middlesex?+1‰?,Lower Kellwasser?+3‰?,Upper Kellwasser?+3‰?and Upper annulata?+1‰?events,as well as a small positive PCIE?+1‰?in the Famennian expansa-aculeatus zones were recorded.It is noteworthy that no significant carbon isotope shifts are found for the Rhinestreet,Nehden,Condroz and Enkeberg events.The Late Devonian long-term carbon isotope curve from South China is in agreement with contemporaneous world-wide trends in Euramerica?Europe and North America?and Gondwana.Global data suggests a higher Famennian?¹³C_carbarb baseline?about+2.5‰?than that of the Frasnian?about+1‰?,which correspond to higher ⁸⁷Sr/⁸⁶Sr ratio at a same time.Previous studies believed that the PCIEs are caused by ocean anoxia which is related to enhanced continental weathering.But the ultimate driver remains unclear,spread of land plants or increased tectonic activity may be responsible,but these explanations are still questionable due to the relative short durations of the PCIEs compared to long-term processes of plant evolution and plant cover extension as well as tectonic movements.A new conodont apatite oxygen isotopes records were measured from the Lali section to reconstruct variations in the marine palaeotemperature and ice volume during the Late Devonian in eastern Palaeotethys.The early-middle Frasnian is marked by a warming trend(-1.5‰negative shift of?¹⁸O_apatite),and hottest part lies in late Frasnian FZ 11.Late Devonian greenhouse-icehouse transition dates back to middle-late Famennian due to a large positive shift?+2‰?of?¹⁸O_apatite from the velifer Zone to the ultimus Zone in the Lali section,and this shift corresponds to similar?¹⁸O_apatite increase in the Rheic Ocean and can explain wide-developed glacier sediments in Gondwana and Euramerica during the late-latest Famennian.Besides,the?¹⁸O_apatitepatite exhibit simultaneous short-term positive excursions as well as?¹³C_carb records for the Late Devonian bio-events:the Middlesex(punctata,+0.5‰?¹⁸O_apatite),Lower Kellwasser(+1‰?¹⁸O_apatite)and Upper annulata events(+0.8‰?¹⁸O_apatite).These short-term cooling pulsed changes during bio-events are believed to be controlled by the global carbon cycle.Here,based on species list provided by Becker and Hartenfels?2016?,taxonomy and phylogeny of Late Devonian conodont genus Palmatolepis are revised.There are total 210 names of Late Devonian palmatolepid species which are based on P1 elements.After excluding nomen dubius,synonym,homonym and species need to be revised or should not be placed into genus Palmatolepis,only 58 and 78 species are valid for entire Frasnian and Famennian palmatolepid species separately,and 122 of them are found at the Lali section?including 5 new species and subspecies?.Frasnian palmatolepid conodonts contain 6 evolution stocks:“transitans-stock”,“hassi-stock”,“nasuta-stock”,“feisti-stock”,“ljaschenkoae-stock”and“yizhouensis-stock”.And Famennian palmatolepid conodonts contain 12 evolution stocks::“ultima-stock”,“subperlobata-stock”,“werneri-stock”,“regularis-stock”,“sandbergi-stock”,“minuta-stock”,“glabra-stock”,“delicatula-stock”,“clarki-stock”,“rhomboidea-stock”,“basilicus-stock”and“perlobata-stock”?...