Cyclostratigraphy Research On The Upper Devonian Of Baisha-1 Well In Yangshuo,Guilin,Guangxi

The Late Devonian is one of an important periods in the Earth history.Many major global geological events occurred,such as the F-F event at the Frasnian/Famennian boundary and the large-scale positive excursion of carbon isotopes.These large-scale geological and biological events had a profound impact on the Devonian climate,and its genetic mechanism and internal connections are also hot spots to study.The high-resolution chronostratigraphic framework is an important basis for understanding these large-scale geological events.Cyclostratigraphic research can establish a high-precision astronomical time scale with a resolution of 0.02⁰.4 Myr by identifying the Milankovitch signals recorded in the strata,which provides an important methodology for accurately constraining major global geological events and conducting global comparisons.At present,the progress has been achieved in the Mesozoic and Cenozoic by the virtue of the stability of 405 kyr long eccentricity,while the Devonian in the Paleozoic is less advanced due to the lack of astronomical solution.In this thesis,cyclostratigraphy study was carried out on the Upper Devonian of the Baisha-1 well in Yangshuo,Guangxi.Through the measurement of more than 15,000susceptibility data,a spectrum analysis of a total of 300 m core was carried out,and a good Milankovitch signal was identified.The ratios of long eccentricity,short eccentricity,obliquity and precession are roughly 24:6:2:1,and the deposition cycles of the long eccentricity signals in the depth of 4.55²50 m,250²75 m,and 275³00 m are 7.3¹2.01m,1.91².78 m,and 3.2³.85 m,respectively.A"floating"astronomical time scale of up to 20.7 Myr was established using the filtered 405 kyr long eccentricity,and the duration of the Liujiang formation was estimated as 8.5 Myr.Since the F-F boundary corresponds to the starting position of the positive shift of?¹³C_carb,this study combines the carbon isotope data and the cycle data results to define the location of the F-F boundary at the core of 203.8 m.The durations of carbon isotope excursions are⁹0 kyr and¹20 kyr,respectively.This result is basically close to the duration of the Kellwasser event corresponding to black shales in Poland,Canada,the United States and Belgium,confirming the global isochronism of the event.