Key tectonic changes, deformation styles and hydrocarbon preservations in Middle-Upper Yangtze region

Controlled by different geodynamic backgrounds and tectonic stress fields,the Middle-Upper Yangtze region had experienced stages of tectonic movements,resulting in styles of faults,folds and unconformities.There were 4 key tectonic movements including the Guangxi,the Indosinian,the Yan-shanian and the Himalayan.During the Guangxi Movement,large-scale NE-trending tectonic deformations were formed in the study area.The changes from marine to continent took place in the Indosinian Movement.Large terrestrial facies sedimentary was well developed during the Yanshanian period.The study area was extruded from 3 directions during the Himalayan period.The 4 key tectonic movements played important roles in development and preservation of mudstone cap formations.The Guangxi Movement made a large destruction of the Silurian mudstones which were important cap formations in the Middle-Upper Yangtze region.The Middle-Lower Triassic mudstones suffered extensive erosion during the Indosinian Movement.Tectonic movements during the middle Yanshanian period strongly destroyed the regional cap formations of the early Yanshanian period except for those in the Sichuan Basin.Due to the Himalayan Movement,the Middle-Upper Mesozoic and the Cenozoic mudstone cap formations in the uplift were completely destroyed,only preserved in some regional depressions.Besides the mudstone cap formations,tectonic deformation styles of the key tectonic movements also controlled-hydrocarbon preservation in the study area.Chevron anticlines and relieved synclines were well developed in the east of Sichuan.Detachments in the west of Hunan and Hubei(mainly composed of the Silurian and the Lower Cambrian mudstones)were deeper than those in the east of Sichuan.The Xuefeng Uplift thrusted from SE to NW,resulting in large amounts of high-angle breakthroughs in the northwestern periphery.Meanwhile,in the west of Hunan and Hubei,low-angle thrusts matched with the Lower Cambrian and the Silurian cap formations,providing good conditions for hydrocarbon preservation.