Cyclostratigraphy Study On The Early Cambrian Of Huize-1 Core,Yunnan

Cambrian is the first period of Phanerozoic,when biological explosion,carbon isotope excursions and geomagnetic polarity reversal occurred.An high precision and resolution geochronology is significant for understanding major geological events.Milankovitch signals extracting using cyclostratigraphy can be used to establish the astronomical time scale with a temporal resolution of kiloyears to estimate the duration and rate of biological and geological events.Cyclostratigraphy for the Paleozoic is more difficult than Cenozoic and Mesozoic,due to the absence of high-resolution temporal constraints,e.g.,radioisotopic ages,biostratigraphy,magnetostratigraphy.In this thesis,the high-precision cyclostratigraphy on Early Cambrian Shiyantou and Yuanshan formations at Huize-1 drilling core from Huize,Yunnan was studied.The reliable Milankovitch cycles were identified by Multi-Taper Mehtod(MTM)and Average Spectral Misfit(ASM)on 11737 measured magnetic susceptibility data.After band-pass filtering and astronomical calibration on 405 kyr long eccentricity,a floating astronomical time scale was established with a duration of~9.83 Myr.The duration of Shiyantou Formation,Yuanshan Formation and carbon isotope excursion in the Shiyantou Formation was estimated as ~5750 kyr,~4080 kyr and ~530 kyr,respectively.Anchoring a CA-TD-TIMS U-Pb dating age(526.86 ±0.16 Ma)from the Shiyantou Formation at Meishucun section,the approximate age of the base of the Second Series of Cambrian was estimated as 521.11 ± 0.16 Ma,which is consistent to that in Geological Time Scale 2018(~521 Ma).Modulation in eccentricity and obliquity has period of ~1900 kyr and of ~1370 kyr,respectively.