The Comparative Study Of Standard Stratotype-Section In Lower Devonian At East And West Of Junggar,Xinjiang

There are five typical rock strata units in the Lower Devonian in the eastern and western Junggar regions of Xinjiang.The master's thesis comprehensively conducts the field geological survey and relative regional comparative studies,mainly focusing on four aspects,i.e.the rock associations,biofossils and contact relationships of each unit from bottom to top,as well as the sedimentary environment.This paper has achieved the following results :1.This paper systematically discusses the term,evolution,and layer profiles of the standard stratotype-sections of the Lower Devonian five rock strata in the eastern and western Junggar regions.Based on the comparison of both profiles and histograms,we further discuss the geological characteristics and formation ages for these units.Based on a series of studies,we revised standard Stratotype-Section of the Kalamaili Formation profile,and the Tuoranggekuduke,Wulusubasitao,Hebukesaier and Malasu Formations were newly established as substratotype-sections in this paper.2.During this comparative study,LA-ICP-MS zircon U-Pb age of 403±12 Ma was obtained from the basalt of the Tuoranggekuduke Formation which pertains to the Beitashan stratum in the East Junggar,suggesting that the erupted time of this formation is in the Early Devonian.Moreover,these basalts from Tuoranggekuduke Formation are geochemically similar to the high alumina basalt.3.The Tuoranggekuduke Wulusubasitao Kalamaili Hebukesaier Formation and the Malasu Formations in the East and West Junggar are obviously different in rock associations mainly due to large regional spans and from different source areas.Accordingly,the mutural comparisons are relatively weak.However,Brachiopoda fossils(Paraspirfer-Leptaenopyxis)are found in all five formations of the biofossil assemblage,showing a littoral-shallow marine sedimentary environment,which is in part comparable to some extent.In addition,there is a lack of comparability in the top,bottom boundaries and contact relationships of the five formations due to fracture damage.4.Based on a comprehensive study of rock assemblages and regional data,the early Devonian oceanic-continental tectonic framework in the eastern and Western Junggar regions is discussed.