THE STORM DEPOSITS AND CHANNEL FACIES IN GUANSHAN FORMATION, WUTONG GROUP FROM SOUTH JIANGSUAND EAST ANHUI

The sedimentary environments of Guanshan Formation in South Jiangsu puzzled the geologists for decades because of lacking identifiable body fo-ssils and other depositional features in the sandy deposits.But both trace fossils and sedimentary structures are abundent after carefully looking into the well displayed section in Kongshan,Jiangsu and Taihushan,Auhui.In contrast to the previous studies,seven clastic shoreline depositional types have been recognized in the region for the first time.The first depositional type is intertidal bar,which is characterized by herringbonecross-bedding and swash cross-bedding as well as reverse graded bedding;The Zndtypeof Submerged bar is composed of quartz fine grained sandstone at the lower part,planar cross-bedding in the middle and follo-wed by troughcross-bedding and reverse graded quartz sandstone at the top.The 3rd type is recorded by storm surge deposits of basal lag Pebbles,graded coarse sandstones and suspension deposits of mud layers after the storm was over.This depositional type is suggested to be produced in an area near the fair wheather wave base.The fourth sandy depositional type of the studied district contains lag conglomerates,two clay layers and trace fossils of Arenicolites implying a shallow subtidal channel origin.Finally,the fifth one of deposition has lower subunit of medium to coarse grained sandstones with pebbles,and middle subunit of large planar cross-bedding and herringbone cross-bedding,as well as thin bedded fine to medium grained sandstones alternating with sandy mud layers in which trace fossils of Arenicolites,cf.Cruziana have been found.The sedimentary texture,structure and biogeneic structure imply its sedimentary environment were of deep subtidal channel.