Sedimentary,Palaontological Characteristics And Their Geological Significance Of Lower Cretaceous Yantang Formation In Sourth Anhui Province

Several Mesozoic continental sedimentary basins occur in southern Anhui Procince.Tunxi basin is one of them.Mecozoic red layers well developed in the basin are basically exposed continuously.The basin is a representative one among the Mesozoic(Cenozoic)basins in southern China,which is an ideal aera to study strata,tectonic and basin evolution in that time.This study focus on Yantang Formation in lower cretaceous,which is exposed in Yantang Village of Huizhou district,Sanchong Village of Yanghu Town,and Dongguanying of Village Xintan Town in Huangshan city.The Formation has a thickness between 105-175m,and lithological types include mottled sandstone contained locally pyroclasts and conglomerates,mudstone and shale which contain ostracods,Estheria,insects,bivalves,gastropods,fishes and plants.The relation to the underlaying Shiling Formation is contacted disconformably or somewhere unconformably.The mudstone from Yantang Formation of lower cretaceous in Tunxi basin contains many kinds of fossils which were the important developmental evidence of the Jehol biota in this region.Because of several tectonic movement overlap in the basin,respecially of the Yanshan movement of Mesozoic,Yantang Formation was strongly influenced and exposed discontinuously.In addition,restricted from the outcrops and geological undersanding of that time,the whole tectonic environment and the stratigraphic relationship of Yantang Formation have not been fully considered.In this article the sedimentary and paleontological characteristics,as well as depositional evolution processes of Yantang Formation are discussed by using the lithostratigraphic,biostratigraphic,chronostratigraphic principles and some new conclusions are achieved.