A Study Of Meso-micro Fossil Plants From The Shangganchaigou Formation In The Northwestern Qaidam Basin

The Qinghai-Tibet Plateau is famous as `the roof of the world' because itsaverage elevation is above 4000 m.Since the Cenozoic era,the strongly uplifted qinghai-tibet plateau has influenced the climate and environmental changes in northwest China.Under such geological changes,the Qinghai-Tibet Plateau has also formed a unique plateau ecological environment.Geological and climatic changes in the Cenozoic era have always been a focus of geological research.As an important sedimentary basin in the northern part of the Qinghai-Tibet Plateau,the Qaidam basin in the study area of this paper is an important object of study because good Cenozoic strata have developed in the basin.In recent years,more and more fossils of plants and animals have been found in the Shangganchaigou formation of the Oligocene in the northwestern margin of the Qaidam basin in the study area.However,there are few studies on the meso-micro fossil plants,so this paper makes some supplements for this part.In this paper,the meso-micro fossil plants found in the Shangganchaigou Formation of the Oligocene in the Qaidam Basin are mainly divided into three types: charcoal fossils,dispersed cuticles and other plant meso-micro fossils fragments.Compared with macrofossils,the meso-micro fossil plants are more difficult to study,but more extensive conclusions can be drawn.Through chemical processing analysis,observation under microscope,biological microscope and scanning electron microscopy(SEM)indoors,the external morphologys and internal structures of the meso-micro fossil plants were studied.As for charcoal fossils,because of their small size,they can be divided into three types according to their tracheid or vessel thickening: single-row porous charcoal fossils,double-row or multi-row porous charcoal fossils and threaded or annular fossil charcoals.For charcoal fossils,due to their small size,a new classification system was established according to the thickening of tracheid or catheter.The formation of charcoal fossils is related to wildfires.Charcoal is the oxidation product of incomplete combustion of plants under anoxic conditions.Studying the formation of fossil charcoals is helpful to understand the history of ancient fires.Meanwhile,the occurrence of wildfires may be related to the climate of the Qaidam Basin during the Oligocene.By studying fossil charcoal,it can be used as evidence to restore paleoenvironment.There is no dispersed cuticle preserved in situ,which plays a certain role in the study of burial and transportation.The dispersed cuticle is of great significance for the restoration of Oligocene environment in the western margin of Qaidam Basin.By studying meso-micro fossil plants,the paleoenvironment,paleofires and paleovegetation at that time were further understood,which is a new supplement to the research results of large fossils.At that time,the climate in the western margin of Qaidam basin was warmer and wetter than now,and vegetation types were more abundant.Wildfires occur during short periods of drought.It is concluded that the seasonal drought in Qaidam basin at that time may be affected by the monsoon.