SEQUENCE STRATIGRAPHY ON NEOPROTEROZOIC OUTCROPS, IN NORTHWEST HUNAN, SOUTH CHINA

The Neoproterozoic successions in northwest Hunan,South China belong to a stable sedimentary region of paleo-continental margin along the southeast border of Yangtze platform.The paper deals with the sequence stratigraphy on Neoproterozoic (1000-57OMa) outcrops in the area.Adopting a dividing plan of gallery-typed section and comprehensive sequence stratigraphy,14 Ⅲ order sequences are divided from Neoproterozoic successions in the stable shallow marine area,based on careful field investigations on outcrops,i.e.4 sequences in Laoshanya Formation (equal to Banxi Group);2 in Dieshuihe Formation (equal to Liantuo Formation);1 in Dongshanfeng (equal to Jiangkou Formation)——Xiangmeng Formations;1 in Nantuo Formation;2 in Doushantuo Formation and 4 in Dengying Formation.Altogether 7 type-I sequence boundaries and 7 type-II sequence boundaries and 1 immersed uncomformity are identified on outcrops.By a orrelation of sequence stratigraphy over the whole area (including Dongkou area in central Hunan),a Sinian (800-570Ma) synchronous stratigraphic framework is established in norhtwest Hunan.It is concluded that a synthetic approach suitable to the Neoproterozoic sequence stratigraphy on outcrops across the area should be adopted.And further the paper ptosposed new concepts about the location of stratigraphy,lithofacies-paleogeography and the evolution of paleo-tectonics.