Cyclostratigraphy Study On The Base Of Cambrian Guzhangian Stage Of GSSP Section Of Guzhang,Hunan,China

Cambrian is the first period of Phanerozoic.It is characterized by the numerous significant geological and biological events including bloom of multicellular phyla,populated invertebrates especially Trilobite,carbon isotope excursion(TOCE,SPICE,BACE),and geomagnetic polarity reversal.Understanding of these geological events requires a high-resolution time framework.According to GTS2012,the Cambrian time scale is built on the fitting of radioisotope ages and biological zones with poor accuracy that is close to 3.0 Myr.It would hinder the estimations of the durations of geological,biological and environmental events.Cyclostratigraphy analysis provides an effective method to solve this problem by establishing a high-resolution time scale through identification of orbital cycles and astronomical calibration.It can provide an astro-chronological estimation for the major geological events.The Guzhang section,as a GSSP of basal Guzhangian Stage,ranges from the upper part of the Drumian Stage to the lower part of the Guzhangian Stage.Four important trilobite biozones have been identified at the studied section.The main scientific objectives of this study are: 1)to identify the Milankovitch cycles in the Guzhang Section,2)to establish a floating astronomical time scale(ATS)andthen estimate the average of sediment accumulation rate(SAR);and the durations of the trilobite biozones,3)to discuss the feasibility of Magnetic susceptibility(MS)and Natural gamma(GR)as paleoclimate proxies using handhold magnetic susceptibility meter and natural gamma spectrometer on the section.MS is measured directly on the section with an even spacing of 2 cm.GR is measured directly on the section with an even spacing of 5 cm.A MS series with 4340 data and a GR with 6944 data were obtained.The results of spectrum analysis and efft spectral analysis indicate that the whole package of Milankovitch cycles recorded at Guzhang Section.The long eccentricity,short eccentricity,obliquity and precession give rise of the sedimentary cycles of 24.8 m,7 m,1.8 m,and 1.2 m.3.5 long eccentricity cycles are identified and a floating ATS is established.The duration of Goniagnostus nathorsti biozones is estimated as 0.49 Myr,and Lejopyge armata is 0.14 Myr.In addition,the duration of the lower Huaqiao Formation is estimated as 1.33 Myr,with an average SAR of 6.5cm/kyr.