Reconstruction of the Tectonic Palaeogeomorphology of Longwangmiao Formation during the Caledonian-Hercynian Period in Moxi-Gaoshiti Area, Sichuan Basin and Its Geological Significance

Key words: 
• tectonic palaeogeomorphology /
• sedimentary palaeogeomorphology /
• Longwangmiao Formation /
• Sichuan Basin /
• Moxi-Gaoshiti area

Abstract: Based on 3-D seismic material and drill-hole data in Moxi-Gaoshiti area, the variation trend of the thickness from the bottom of Longwangmiao to the bottom of Permian was chosen to represent the tectonic palaeogeomorphology of the lower bottom of Longwangmiao Formation. Since the analysis found that the deposition of the overlying Gaotai Formation could fill and level up the Longwangmiao Formation at the end of Longwangmiao sedimentation, and there is a positive correlation between the thickness from the bottom of Longwangmiao to the bottom of Permian and the thickness of Gaotai Formation, the tectonic palaeogeomorphology of the lower bottom of Longwangmiao Formation could represent the Longwangmiao sedimentary palaeogeomorphology before the deposition of Gaotai Formation approximately. Meanwhile, the relatively low position at the southern margin of the palaeogeomorphology highland was the area where the grain beach of Longwangmiao Formation was most developed, it suggested that the palaeogeomorphology during the Longwangmiao sedimentation was similar to this palaeogeomorphology. After further analysis, we believe that palaeogeomorphology controlled the activity routines of the bedding flowing karst water which was supplied by the erosion window during the Caledonian-Hercynian period, and then determined the differences in development and quality change of the karst reservoirs:in the slope belt and the ravine area where the karst water converge, the karst reformation is the strongest, the reservoirs formed here are the best; in the isolated highlands, the reformation is relatively weak, and the reservoir quality is poor. The results show that this palaeogeomorphology was the result of inheritance developing of sedimentary palaeogeomorpholog during Longwangmiao depositon, and the newly drilled wells and development wells have proven its controlling action on sedimentation and reservoirs. This method and thought is helpful and referential for the same genre in similar geological background.