Study On Oligocene Plant Remains In The Huatugou Area Of Qaidam Basin,China

As the largest inland basin in thein the northeastern Tibetan Plateau,the Qaidam Basin is directly affected by the climatic and environmental change effect during the uplift of the Tibetan Plateau because of its special geographical location.Plant fossils are often used as indicators to discuss the paleoenvironment because they record the environmental and climatic information of their growth period;it is significant to analysis the study of paleoclimate and paleoenvironmental changes on the Tibetan Plateau by using plant fossil materials.Compared with those well-preserved plant fossils which have complete morphology,plant remains fossils have the characteristics of wide distribution,rich quantity,complex and diverse fossil types,which can be used as a good symbol to restore the paleoenvironment.This paper mainly focuses on the study of Oligocene plant remains in the Huatugou area of Qaidam Basin.After indoor chemical treatment and analysis,and observation and classification by stereomicroscope,biological microscope and scanning electron microscope,a variety of plant fossil residues including charcoal fossil,dispersed cuticle fossil,spherical fossil with special shape and other organic matter with certain structure were obtained.Based on the tracheid decoration characteristics,charcoal fossils are divided and a new morphological classification system is established,that is,rough with wood rays and smooth without wood rays among the non pit categories;Single row pits,double row pits,threaded cracks,threaded thickening,cross field and ladder pits;Based on the morphological differences of pits,single row pits are further divided into four subclasses,and double row pits are divided into three subclasses.The preservation characteristics of charcoal fossils show that wildfires occurred in the Oligocene in the Qaidam Basin,and the activity of fire belongs to canopy fire with high intensity;Based on the morphological analysis of carbon chips,it is speculated that the source plants are mainly woody plants,followed by herbaceous plants.According to the morphological characteristics,the dispersed stratum corneum is classified,and seven subclasses of straight wall non stomata and two subclasses of curved wall non stomata are obtained.Through the morphological characteristics and energy spectrum test of globular fossils,the systematic classification position and preservation state of globular fossils are discussed.It is considered that globular fossils belong to algae,and the element composition of fossils shows that pyritization occurred in the later burial preservation of fossils.Through the study of plant remnant fossils,the deficiency of the microscopic study of plant fossils in this area is supplemented.Combined with the study of other large plant fossils,it is speculated that there are more abundant plant types in the Oligocene of Qaidam Basin,which is helpful to restore the ancient vegetation appearance of this area in the Oligocene and indicates the warm and humid climate environment at that time.