Abstract:

 In order to understand stratigraphy characteristics and contact relationship, it's necessary to establish sequence framework of Palaeogene in the Qikou Sag.On the basis of the theory of sequence stratigraphy, sequences are subdivided and the boundaries of different orders of sequences are discussed. The sequence framework for different orders of stratigraphic successions in the Palaeogene has been established with an integrated analysis of seismic, logging and core data. The Palaeogene consists of 1 first-order, 3 second-order sequences and 11 third-order sequences in the Qikou Sag. First-order and second-order sequences are tectonic ones, which correspond to tectonic movements. Third-order sequences are bounded by unconformities at basin margin and conformities in basin center. And third-order sequences can be identified in the whole basin. By the studies, it is proposed that the abrupt change of the depositional slopes resulting from the structural slope break zone or flexure slope break zone, has an important effect on the accommodation and sedimentation in the basin. The structural slope break zone or flexure slope break zone controls the development of the sequence and the lowstand sand bodies. Two models of slope break zones and sequences have been established and the areas below the slope break zones are favorable for the deposition of lowstand sand bodies.

Key words: Qikou Sag, Huanghua Depression, Palaeogene, sequence stratigraphy, sequence model