ECOSTRATIGRAPHY OF THE MIDDLE YANGTZE PLATFORM AND ITS SOUTHERN MARGIN DURING THE DAOBAOWANIAN (EARLY ORDOVICIAN)

Seven ecostratigraphic facies tracts (EFT) have been distinguished,for the Daobaowa-nian ecostratigraphy of the Middle Yangtze platform and its southern margin.They are:(1)Batostoma-Calathium platform organic reef ecostratigraphic facies tract,characterized by benthic reef-building communities;(2)Calathium-Archaeoscyphia platform organic reef ecostratigraphic facies tract;(3)Sinorthis inner shelf ecostratigraphic facies tract;(4)Came-roceras mid-outer shelf ecostratigraphic facies tract characterized by nektonic organisms; (5)Endoceras deep-water slope ecostratigraphic facies tract also characterized by nektonic organisms;(6)Tetragraptus basin-margin ecostratigraphic facies tract characterized by planktonic organisms,and (7)Didymograptus deep-sea basin ecostratigaphic facies tract characterized by planktonic organisms as well.According to the assemblages of ecostrati-graphic facies tracts,four ecostratigraphic facies regions have also been established.(1) Batostoma-Calathium and Calathium-Archaeoscyphia platform organic reef ecostratigraphic facies region;(2)Sinorthis and Cameroceras shelf ecostratigraphic facies region dominated by benthic and nektonic organisms;(3)Endoceras deep-water slope ecostratigraphic facies region including the transitional-type organisms,and (4)Tetragraptus and Didymograptus deep-water basin ecostratigraphic facies region composed of the Jiangnan-type organisms, all of which are arranged into one ecostratigraphic facies system,i.e.BCA,SC,E and TD platform-shelf-slope-basin ecostratigraphic facies system,The results of research on ecos-tratigraphy in this paper have disclosed the ecological,palaeobiogeographic,tectono-paiaeo-geographic,sedimentary facies and palaeogeographic characteristics of the study area dur-ing the Daobaowanian(Early Ordovician).