Establishment of the Delta Sandbody Framework Model in a 3^rd Order Baselevel Cycle: taking Shanbei Ansai delta outcrop as example

Key words: 
• sequence stratigraphic framework /
• baselevel cycle /
• river delta /
• Ordos Basin /
• sandbody framework model

Abstract: Delta sandbody is one of the most important continental-basin hydrocarbon reservoir in China. The establishment of delta sandbody framework model in sequence stratigraphic framework is very important to the prediction of delta sandbody. Detailed high-resolution sequence stratigraphy study has been carried out on the Upper Triassic fluvial delta outcrops along the eastern margin of Ordos Basin. The basal surface of incised fluvial valley has been recognized as the boundary of a 3^rd order base level cycle. Furthermore, delta sandbody framework prototype model and the evolutionary model of deltaplain distributary channel style in a 3^rd order base level cycle have been established. This study demonstrate that the incision, aggradation, migration, overflow and style change of delta plain distributary channel or fluvial channel should be happen regularly in response to different base-level rise and fall rate in a 3^rd order base level cycle, which make difference to the type, shape, scale and connectivity of delta sandbody in sequence stratigrphic framework. The discovery of this rule is important to the prediction of delta sandbody and the stratigraphic-trap forming condition analysis. Furthermore study of sandbody distribution in sequence stratigrphic framework under different geological conditions is helpful to the realization of the study object of sequence stratigrphy-“interpretable in genesis and predictable in space-time”.