Sinian-Early Cambrian Tectonic-Sedimentary Evolution in Sichuan Basin

There are many different opinions on Sinian-Early Cambrian tectonic-sedimentary evolution in Sichuan Basin.Based on the previous studies, the latest seismic, drilling and outcrop data and the sedimentary evolution characteristics of Sinian-Early Cambrian tectonics in Sichuan Basin are discussed systematically.The analysis shows that the Sichuan Basin has a structural framework with alternative depressions and upheavals before the deposition of Doushantuo Formation.The high point of the Hannan ancient land structure continued migration to the northeast in the sedimentary period of Doushantuo to Early Cambrian.The Kaijiang-Xuanhan ancient uplift in the first and second phase of Dengying Formation sedimentary period is the main developing period, and the top of the ancient uplift may be no longer covered by water.During the third and fourth phase of Dengying Formation sedimentary period, the development of the ancient uplift decreased and turned into the underwater uplift.In the Early Cambrian period, it merged with the ancient uplift in central Sichuan.Based on the analysis of the well connection profile, typical well element logging, field outcrop characteristics and previous research results, our analysis suggests that there is deep-water deposit in the Deyang-Anyue ancient rifting during the third and fourth phase of Dengying Formation sedimentary period.On this basis, the development pattern of ancient rifting is summarized.The Deyang-Anyue ancient rifting has obvious characteristics of multiple stages of development.The edge of the ancient rifting continues to move northeast, the edge of the ancient rifting of the second phase of Dengying Formation sedimentary period is located in the Shuangtan area, while the edge of the ancient rifting of the fourth phase is located in the west of Yuanba.At the same time, the ancient rifting has the development characteristics of "early in the north and late in the south, first fault depression second depression".The ancient rifting developed from the middle to the north of Sichuan during the sedimentary period of Dengying Formation and had the development characteristics of fault depression.In Early Cambrian, the ancient rifting changed into depression, and the South Sichuan area began to develop on a large scale, the edge of the ancient rifting continues to move northeast in the middle to the north of Sichuan.The hydrocarbon source rock of Qiongzhusi Formation was developed as a result of transformation of Yuanba-Renhechang-Malubei area into deep water deposits in northern Sichuan Basin.By the end of the Early Cambrian, the ancient rift had died out and was filled up.