SEDIMENTARY ENVIRONMENT ANALYSIS OF ANCIENT SAND RIDGES FROM ZK23 HOLE IN THE EAST CHINA SEA

Based on the analysis of core samples from the hole of Zk23 in the East China Sea Continental Shelf and by means of sedimentary stratigraphy, biostratigraphy and chronostratigraphy, the authors consider that the fine-sand deposition in borehole was part of buried ancient estuary sand ridges of the Yangtze River.The deposition history of study area around the hole before and after the glacial period as well as postglacial period is made clear after our research:(1)the estuarine sublayer -undersea delta facies was deposited during the fast sea level rise around 15 kaBP;(2)sand ridges mostly consisting of fine sand, were formed when the sea level was the fluctuation range of 60~80 m of isobath during the deglacial period around 15~12 kaBP;(3)first silty clay and clay silt strata above the sand ridges were deposited during the period when the sea level rose fast from 12 to 7 kaBP and then it keeps stable to the present.