Abstract:

The analysis of sedimentary history indicates that, paleocontinental mar-gin in South China underwent multistage plate tectonic evolution of rift, pas-sive margin and clousure orogeny from Late Presinian to Silurian. A series of grabens stretching NE developed during the rift stage(Presinian-Early Sinian). they were filled with a series of coarse clastic rocksmainly by gravity flow and intercalated beds of basaltic volcanic breccia whichbelongs to A- series or T-series on the diagram of Na₂O+K₂O versus SiO₂and tuff. Isolated carbonate platforms and ambient deeper-water basins weredeveloped inside the young passive margin(Middle Sinian-middle Early Camb-riam), and then sedimentary filling made it an extensive shallow-water car-bonate platform: deep-water starved basins appeared rapidly after the rifting. In the outer side of the young passive margin, only silicalite of tens ofmeters thick was developed. Matured passive Margin(late Early Cambrian-Early Ordovician) was characterized by the development of a huge carbona-te wedge along the shelf break zone. In the outer shelf and shelf margin,algal reefs and carbonate banks usually developed well: the associationof slope and slope-toe was dominated by various kinds of gravity flow se-diments in the early stage and was characterized by contourites in the latestage; pelagic laminated marls and shales developed in the basin. Ano-ther important character was that the shelf margin migrated towards sea,leading to distictive prograding sedimentation on the slope. During theclousure orogeny stage of the Middle Ordovician-Silurian, the direction ofsediment transportation changed opposite, and coarse clastics prograded pro-gressively from southeast to northwest even overlapped onto the central partof the paleo-Yangzi Plate. This process formed a shallowing-upward se-quence which composed of a thick clastic rock that changed from turbidites inbottom to coastal sediments in top till continental deposits. This orogenyfinally ended up with the widespread uplift in the end of the Silurian.