Abstract:

Two Kinds of deltas-meandering stream-shallow sea delta and braided stream-shallow lake delta-developed in Permo-carboniferous Systems in Ordos Basin.The deltas differ from typical deltaic model.Deltaic front subaqueous distributary channel sand bodies and deltaic plain distributary channel sand bodies are the skeleton sand bodies of meandering stream-shallow sea delta and braided streain-shallow lake delta respectively but not tranditional deltaic front river mouth sand bars.The two kinds of deltas are controlled by river types,ground slope,water depth,water density differentia,river sedimentation and lake dispersion.The first kind of delta mainly developed in meandering stream water system;the second kind of delta developed in braided river water system.Two depositional models were built according to their characteristics.It is pointed out that the subaqueous distributary channel sand bodies of the first type of delta and the lensing and zonal distributary clannel sand bodies of the second type are favourable oil and gas exploration targets.

Key words: Ordos Basin, meandering stream-shallow sea delta, braided river-shallow lake delta, sedimental feature, mechanism, depositional model