A New Approach in Studying Depositional System Within Riftsubsidence Basin: 〖WTBZ〗from paleogeomorphology, lithologic change and water depth to depositional system

Key words: 
• riftsubsidence basin /
• depositional system /
• single factor analysis /
• depositional regime /
• palaeogeomorphology reconstruction /
• water depth /
• waveform feature

Abstract: The single factor analysis which based on sedimentary dynamic mostly emphasizes the actions relating to transportation and depositional procedure, adopting one method from point to surface, from local to whole and from quantitative change to qualitative change, and the depositional regime which is based on morphology, present sedimentation and datum up and down, adopting other gradually penetrating method from surface to point and from whole to local, are different in research approach. The former is not prone to controlling the law of bulk distribution of depositional system in riftsubsidence basin, but the latter is opposite. The basic request of the method of depositional regime which includes three key technologies: palaeogeomorphology reconstruction, recognition of seismic reflection texture and waveform feature is provided with affluent and excellent seismic data. Through palaeogeomorphology reconstruction, combining the observation of present sedimentation, water depth and lithologic, the distribution law of depositional system can be ascertained. Furthermore, by researching seismic reflection texture and waveform feature, the types of sedimentary microfacies can be decided in a point. The law of plane distribution of depositional system which locates the middle part of middle submember of the 3rd member of Shahejie Formation in Gunan pothole, Zhanhua sag is studied by using the method of depositional regime. The braided rive delta front subfacies located on the south slop area is developed in the braided rive delta which progrades from south to north. The basin bottom fans located at the toe of Gunan fault are mostly distributed in the north pothole. Moreover, the basin bottom fan can be developed because the nearshore beach and bar in the shallow lake glides, too. The shallow lake subfacies with affluent nearshore beach and bar and sandsheet is mostly developed because the water depth is shallow.