Some Early Jurassic Fossils In Santanhu Basin,Xinjiang And Their Geological Significance

The climate of Europe and Asia was warm and humid in the Early Jurassic.So the ferns,horsetails and gymnosperms were prosperous.However,the incident of sea level rise and lack of oxygen around the world in the late Early Jurassic brought about a certain change in the appearance of paleontology.Studies of paleobotany show that comparing with the early period of the Early Jurassic flora was degraded and southern molecules emerged at the late period of Early Jurassic.The climate became hot.The study of the Early Jurassic paleobotany will allow us to have a better understanding of climate change events during this period.At present,the study on paleobotany in this area remains at the level of morphological description.There is little research on the microstructure of plants,which is hindering species identifying and obtaining information of paleoclimate and palaeoenvironment.Using the methods of macroscopical and microscopic features observation and numerical analysis identifies 7 genera,5 species,and 4 indeterminate species by fossils collected in the Badaowan and Sangonghe formations in the Early Jurassic of the Santanghu Basin,Xinjiang.We discussed that the climate in the Santanghu Basin during the early and middle Early Jurassic period should be moist and well-watered.However,in the late period of the Early Jurassic,the climate turned to partial heat and drought.Through the combination of large plant fossils,the contrast between the tracheids of Coniopteris gaojiatianensis and the living Cibotium,and the upper epidermis features of the Ginkgoites sp..It provides evidence for the climate change in the late Early Jurassic around the world.The stomata index of fossil plants is sensitive indicators of environmental changes.It is widely used by paleontologists and geologists to trace the changes of paleoatmospheric CO₂concentration of the geological history.In this paper,we used the stomata index of Ginkgoites sp.,which is very sensitive to atmospheric CO₂,and the living Ginkgo biloba L to rebuild paleoatmospheric CO₂ concentration in late Early Jurassic.The concentration is 1189±71ppmv,which is within the scope of GEOCARB III.In this paper,Coniopteris gaojiatianensis was the main research object,and its spores in situ were observed by the first time.Combining the existing records of the world's Coniopteris,we think that the Coniopteris gaojiatianensis is one of the earliest species of Coniopteris.We discussed that Coniopteris originates from China in early period of Early Jurassic.Based on the results of others'research,this article discussed the evolution of the genus Coniopteris.It is believed that the plants of the genus Coniopteris become stronger and have stronger survivability during the evolution process.According to the distribution characteristics of the fossil in the world,combining with the palaeogeography of the Early Jurassic,it can be speculated that this genera migrated from south of China.Then it migrated northernmost towards Russia,and migrated west towards Central Asia,West Asia,all the way to Europe,North America,Africa,and Oceania.According to paleontological evidence such as Coniopteris gaojiatianensis,Zamites,Ferganoconcha,Waagenoperna,etc.,we think that the age of the Badaowan Formation is the Early Jurassic,and may be early in the Early Jurassic.