Cyclostratigraphy Of The Serpukhovian(Carboniferous) In Narao Section,Guizhou Province

The Late Paleozoic Ice Age(LPIA)is the longest ice age during the Phanerozoic.The Serpukhovian in the Early Carboniferous is an important interval during the LPIA,when several significant climatic and biological events occurred.High-precision geochronology is the base of evolution history of the earth to decipher the environment chages.Narao section in Luodian area,is located in Qian-Gui Basin,southwest of South China Block.Continuous and complete deposits in the Narao was sensitive to paleoclimate change.It is an ideal area to study the development of the glacial history of Serpukhovian.Here,magnetic susceptibility and natural gamma ray were used as the paleoclimate proxies to carry out a detailed cyclostratigraphy study on Narao section,for identifying the accurate astronomical orbital periods and establishing a correlatable high-resolution astronomical time.In this way,the geochronology of the Serpukhovian would be refined to explore the orbital driving mechanism of climate change.Magnetic susceptibility(MS)and natural gamma ray(GR)series of Narao show the hierarchy of sedimentary cycles.The identified sedimentary cycles of GR are3.01-2.44 m,0.72-0.69 m,0.34 m and 0.19-0.11 m thick with the ratio of22.73:6.36:3.1:1.72:1,which is similar with that from MS series.This ratio is consistent with the that of the periods of orbital parameters.Using the 405 kyr calibration,the periods of 405 kyr(long eccentricity),98 kyr(short eccentricity),30.8kyr(obliquity),19 kyr and 17.8 kyr(precession)are identified,and the sedimentation rate is calculated to ?0.6 cm/kyr.A "floating" astronomical time scale has been established with a duration of ?7.68 Myr.In addition,the cyclostratigraphic correlation with Naqing and Luokun sections in South China confirms that the duration of Serpukhovian stages is 7.68 Myr,consistent with the result of GTS2012.405 kyr long eccentricity and 1.2 Myr obliquity cycle may be the driving force of sea level change at low latitudes.