Faulted Structure And Its Controlling The Sedimentation Filling Of Wenchang Sag In The Pearl River Mouth Basin

Wenchang sag,is an important part of the formation in the Zhu-3 Depression,the Pearl River Mouth Basin, and its evolution through the complex geodynamic processes, outside by the Pacific Plate, the Indian Plate and the Philippine plate impact, which are subject to the Pearl River South Fault and other fault activities effects. The region experienced a stretch, twist, reverse and other tectonic stress, through the complex process of formation and evolution, in the region formed a large number of different types of fault systems, complex structural pattern. In this paper, study the faults of the Wenchang sag and its control of sediment filling.Combined with 30 years exploration and development of regional research, in the tectonic setting, structural framework and tectonic units, stratigraphic features and understanding of basin evolution, based on the use of seismic logging, stratigraphic, lithologic reservoir and other areas basic geological information on the geological interpretation of Wenchang tectonic, sedimentary strata knowledge and summarized ,and then come to understand the following key:1. Faults have the feature of grading and staging in Wenchang sag. The faults can be divided into 4 to 5 level. Zhu-3 South faults is the Level-1 fault; the Zhu-3 1 and Zhu-3 2 faults are the Level-2 faults; the Zhu-3 3, 4, 5 and 6 are the Level-III faults; other faults in the sag are the Level-4 to 5 faults. There are three active periods in the active of the faults: early active period, late active period and long-term active period.2. Faults’trend follows the rules: from the basement to the T40, bounded by T81 and T71. From Tg to T81 before, the main faults are NE; from T81 to T71 before, the faults near the NE and NWW are the main faults; from T71 to T40, the EW and NWW-trending faults developed a lot, and over time,proportion of the total of the nearly NWW faults are increasing, reflecting nearly SN direction tension gradually dominant. after the T71. From early to late, D-Stress of the region controls the trend of dextral faults. In the end deposition stage of Member 2 of Enping Formation and Member 2 of Wenchang Formation, the twice rapid adjustment of the D-stress direction, makes torsional stress component aggregation on turning point near the compression faults, and then formed two inversion structure, after formed synsedimentary anticline in the deposition stage of Member 1 of Enping Formation and Member 1 of Wenchang Formation.3. The fault activity feature is characterized by: A). the mian faults basically are syndeposit faults in Paleogene period; B). the southern part of the faults activitie more strength than han that in the north. C). formation and evolution of the controlling-sag faults is very complex, with a fault at different time with the same part of activities vary different, with a fault at the same time also different in different parts of the activities, such as Zhu-3 south faults.D). deposit-center and fault activity center of Wenchang sag migrated from WS to NE. E). there exist muti-caracteristics(feature)in the fault activity, such as subsection, linkage, replace and separation,which is impacted by tectonic stress field.4. Fault’s formation has the closely relationship with the geological structure history. During Late Cretaceous - Middle Miocene, there were five tectonic events, which had different impact on the direction of the fault system, fault distribution, fault number, fault activity ration. Faults control the framework of Wenchang sag, distribution and evolution of faults activity controls pattern of faulted in its south and overlapping to the north and the difference of N-S zoning and E-W partitioning.5. Tectonic features and style in Wenchang A and B sag includes seven parts, which in Wenchang C sag includes four sections. This difference is controlled by the break point of the faults, continuity, and transfer zones, and in section, controlled by the activities of fault intensity and plane morphology.6. Faults activity is episodic and cyclic. Which in Wenchang sag control the developing sytle of long-term cycles and systems tract in the level-III sequence. The fault activity is intense in depression period, and then decreses until now. This is the same evolution process in each period. And then, affects the sequence development style in different parts of depression.7. The features Zhu-3 south faults’activity control the Wenchang sag "seesaw" type deposit-center migration. Evolution history of faults controls the sedimentary fan distribution, we can predict the fans and the good reservoirs by reconstructing the fault evolution, ancient tectonic stress field, ancient strcture, and conbining the sedimentory featrue.