Studies Of The Denudation, Resumption And The Deposite System Of QianJiang Formation In The QianJiang Depression

This thesis, for the first time, carefully analyzes the erosion of each section of Qianjiang depression using Seismic Sequence Stratigraphy Method (SSSM) to study the erosion depth data in a systematic way. This method indicates that the maximum erosion depth after the settlement of Jinghezhen Formation exceeds 2000 meters.After processing a large amount of drilling and seismic data,,SSSM method is employed effectively for the restoration study of the total erosion depth of the lower third system of Qianjiang Depression and its major sections.There erosion zones can be obtained clearly based on the total erosion strength, the strong erosion zone of the northeast, the stable erosion zone in the middle and the slope erosion zone of the southwest.In this thesis, the following tectonic motion is discovered after using our SSSM method to restore the stratum depth of the studies zones. In the last phase of the geological settlement of Jinghezhen Formation, uplifting the basin was eroded, and the fault activities of Qianbei Fault forced to raise the front of its descending basin layer, which leads to elevated erosion. This indicates that Qianbei Fault had been already formed by this time. Following this is the early phase of the settlement of the lower stratum of Section Qian4, and this is the time when Qianbei Fault had strong activities, and the lower layer of Section Qian4 facing the fault is obviously thickened resulting in a wedged form. A groove was also formed along the fault layer under the influence of Qianbei Depression, and this was the rudiment of the current Bunghu syncline. From the seismic section plane it can be noticed clearly that the lower stratum of Section Qian4 is thickened where it is facing the fault. This was the time when Qianjing Depression entered its strong fault period, and it concurred with the activities of Haokou Fault, Fanwanhu Fault and Zhouji Fault. The entire system is along a northeast direction, and the fault activity is weakened from north towards south.In this thesis, it is proposed for the first time that the main structural units of Qianjiang Depression did not develop successionally. After adopting erosion restoration and compaction correction technique to reconstruct the Qianjiang salt lake paleostructure and ancient geomorphology, we claim that the largest negative formation of Qianjiang Depression—Banghu Syncline—was not successional. During the settlement period of Qianjiang Formation, the depression center was located between Wangchang and Banghu, and it migrated towards southwest, while the largest positive formation—Wangchang Syncline—was a negative formation originally, but it rose slowly after the second section of Qianjiang Formation had finished its first phase of salt tectonics and then rose sharply during the last phase of Jinghe Formation until it reached its final formation during the last phase of the settlement of Guanghuasi Formation of the upper Tertiary. This theory is used to better explain the formation mechanism of Wangchang Syncline in Qianjiang Depression, as well as the formation of large scale accumulation of oil and gas. It will dramatically change people’s understanding of the settlement system of Qianjiang Formation and sand distribution.Distribution of lithologic or hidden reservoirs is affected by factors such as basin palaeogeomorphics, sedimentary basin system development and basin settlement characteristics, etc. Therefore, we studied the ancient landscape restoration, balanced cross-section and sandstone distribution for each section of Qianjiang Formation in Qianjiang Depression.