The nature of the Chuxiong Basin and evolution of sedimentary sequences

The Chuxiong Basin was a foreland basin on the southwestern margin of the Yangtze platform during the Late Triassic.The basin-floor deformation of the foreland upwarped basin in the western part once led to a relative rise in sea level,and thus to three-phase marine flood- ings during the Camian and Rhaetian.Then these marine floodings prograded gradually toward the uplifted zone and eratonie margin in the eastern part,resulting in the deposition of the flooding sediments of carbonate ramps and dark mudstones and shales.The progradation of the marine-flooding bodies and coastal downlap in turn allow the formation of the composite depositional systems consisting of the Chuxiong delta and subaqueous sandy and gravelly lobes.
The delta complexes in the foreland basin appeared during the falling phases of sea level, and are quite different from the passive continental marginal sequences.In the ease of the conposite depositional systems,the condensed sections are less developed due to the covering of the transgressive surfaces by the dowrdap surfaces.These depositional systems are well represented by wedges and lobes.The sequence correlation is based on such indicators as three key boundaries,exposed unconformities,marine-flooding onlaps and downlaps plus the features and types of subaqucous lobes and flooding bodies.Three sub-second-order sequences have been identified just by these indicators.