Late Paleozoic Conodont Biostratigraphy,Sr-O Isotopic Composition And Its Paleoclimate Significance In The Taiyuan Formation Of Southern North China

The late Paleozoic ice age is the last time that the earth changed from the icehouse to greenhouse since there were plants landing,which is of great significance for understanding the driving mechanism and impact of global warming.Multiple researchers have contributed to investigating and understanding the far-field climate change mechanisticals that to glacioeustasy and high-latitude ice changes in this critical transition.A high-precision biostratigraphy is essential to assess temporal relationships in the context of changing paleoclimates and land-sea configurations.Presently,our knowledge of ancient oceans is largely inferred from sedimentary successions deposited in shallow inland seas.There is increasing evidence,however,for the spatially and temporally variable nature of environmental dynamics in these semi-restricted,broad,shallow paleo-seas that can lead to the decoupling of epicontinental-based isotope records from those of more open-marine settings.During the Carboniferous-Permian transition,extensive epicontinental depositions were recorded in North China,which is an island block in the eastern tropical Tethyan region.Fundamental to understanding the local-to-regional environmental processes of the late Paleozoic is a high-resolution biostratigraphical and geochronologic framework.In this thesis,high-resolution conodont biostratigraphy from the Wenwan,Baipohe and Wuzhi sections in North China during the Carboniferous-Permian transition,combined with the oxygen isotope and strontium isotope of the conodont in the latter two sections,has been investigated in detail in order to evaluate the open-ocean sources and connect epicontinental isotope variability.And achieved some understanding as follows.1)The conodont Streptognathodus is the dominant genus and 2 genera and 20species,including 1 unidentified species and 1 similar species were identified though a sample-population approach in the studied sections.Five conodont zones are recognized in the studied successions of the Taiyuan Formation.They are Streptognathodus wabaunsensis,S.isolatus,S.sigmoidalis,S.constrictus and S.fusus in ascending order.2)Based on Unitary Association（UA）analysis of Carboniferous-Permian conodonts collected from North China,and combined with previously published tuff zircon U-Pb ages.The bottom of the Taiyuan Formation in North China can be constraint in the late Gzhelian,representing a large-scale transgression event at the end of the Carboniferous.And the top Taiyuan Formation is diachronous from the early Asselian in northern North China to the late Asselian in southern North China,which indicates the gradual southward movement of the sedimentary center and the uplift of the northern margin of North China.3)Based on conodont biostratigraphy and published tuff zircon U-Pb data,an updated stratigraphic framework of Late Carboniferous to Early Permian in North China was revised.Combine climate-sensitive sedimentation and plant fossil assemblages,a diachronous north-to-southclimate drying trend is indicated for North China.4)The difference between the North China and global conodontδ¹⁸O and ⁸⁷Sr/⁸⁶Sr records indicates that the seawater freshening and temperature under humid and hot climate conditions will greatly affect the seawater isotopic composition.While fresh water input can significantly reduce theδ¹⁸O value,the input from North Qinling orogen and Inner Mongolia uplift of the North China Craton can lead to a significant increase in the ⁸⁷Sr/⁸⁶Sr of sea water.5)The conodontδ¹⁸Oin the North China epicontinental sea responds to sea level change,which corresponds to the expansion and melting of glaciers.Even under the strong influence of regional hydrological factors,the variation of conodontδ¹⁸O is still indicative of global climate change.