An Analysis on Sequence Stratigraphy and Sedimentary System of Early Neocene in Qikou Sag

The paper discusses the features of Early Neocene's sequence stratigraphy and sedimentary system of Qikou sag by employing large mount of materials such as seismic data, logging data, observation results of rock cores and new rule. There are one secondary sequence and six third level sequences of Early Neocene in Qikou sag. Based on studies of controlling factors of sequence development, we conclude that there are two kinds of sequence developed in Qikou sag, which are tectonic sequence and climate sequence. Sequence 1, sequence 3,sequence 4, sequence 5 and sequence 6 are tectonic sequence because the action of the boundary faults controls the space of sedimentation. Sequence 2 is the climate sequence. During the sedimentation of sequence 2, the primary controlling factor on the sequence model is climate and the changes of lake level are not influenced by the uplift of basement rock and the action of boundary faults. During progression period, fan head, mid fan and far end of alluvial fan or fan delta developed on different fault terraces, turbidity fan and gravity flow deposits developed in deeply depressed position. During high stand, wedge and lenses shaped deposits of delta occured on the whole basin. The development of sequence controls the rock's reservoir proporty. The sag's tectonic feature influences the distribution of the sequence and the third level fault has eminent influence on sand bodies. For example, fan head, mid fan and far end of alluvial fan or fan delta developed near the lower part of the faults. These findings could be used to predict the location of sand bodies and have great significances in directing the petroleum exploration.