Ordovician Cephalopod Biofacies of South China and Its Provincialization

The research on biofacies and its provincialization is of important significance not only for the increasing of precision of stratigraphic subdivision and correlation in South China,the reconstruction of ancient environment and paleogeography and even the guiding of oil and gas exploration,but also for the study of paleobiogeogrphy and sea level changes of southern China in Ordovician. On the basis of the studies of the ecological characteristics of Ordovician cephalopods from South China,eighteen cephalopod biofacies are recognized and described : (1) Open platform Proterocameroceras biofacies; (2) Restricted platform Pseudoectenolites-Xiadongoceras biofacies; (3) Open platform Retroclitendoceras-Pararetroclitendoceras biofacies; (4) Open platform Pronajaceras-Mamagouceras biofacies; (5) Shelf slope-basin Cyclostomiceras biofacies; (6) Open platform Cameroceras-Cyrtovaginoceras biofacies; (7) Open platform Coreanoceras-Manchuroceras biofacies; (8) Shelf slope-basin Kaipingoceras-Kyminoceras biofacies; (9) Inner shelf Bathmoceras-Protocycloceras biofacies; (10) Middle shelf Dideroceras-Ancistroceras biofacies; (11) Deep-water shelf Lituites-Cyclolituites biofacies; (12) Stagnant basin Lituites-Trilacinoceras biofacies; (13) Deep-water basin Paraendoceras-Sactorthoceras biofacies; (14) Deep-water shelf Sinoceras-Michelinoceras-Disoceras biofacies; (15) Deep-water shelf Beloitoceros-Jiangshanoceras biofacies; (16) Deep-water shelf-basin Eurasiaticoceras biofacies; (17) Shelf-slope Jiangxiceras-Yushanoceras biofacies; (18) Deep-water basin Michelinoceras biofacies. The cephalopods of these biofacies,their ecological characteristics,and living conditions are elucidated in this article. The association law of cephalopod biofacies in time and space shows that there were three cephalopod biofacies provinces in South China during the Ordovician,i.e.,Yangtze biofacies province,East Guizhou (贵州)-West Hunan (湖南) biofacies province (mixed-type biofacies province),and Central Hunan-West Zhejiang (浙江) biofacies province. It is suggested that differentiation of cephalopod biofacies was mainly controlled by sea level changes and tectonic evolution. The differentiation is obvious during lower sea level and not developed during high sea level.