Reconfirmation of Neoproterozoic intra-cratonic rift in northeast Sichuan Basin and its significance of deep oil and gas

The discovery of Anyue Sinian-Cambrian giant gas field in Sichuan Basin has greatly encouraged relevant scholars to explore new fields of deep oil and gas in Sichuan Basin. However, there are still many controversies about the understanding of deep paleogeographic pattern in Northeast Sichuan. In this paper, the Neoproterozoic-Cambrian stratigraphic profiles in the north and northeast margin of Sichuan Basin are investigated and correlated, and stratigraphic framework of the Neoproterozoic-Cambrian prototype basin is reconstructed based on the key event records of sedimentary sequence.At the same time, combined with the latest deep drillings and geophysical data analyses in the basin, the evolution time, development range, filling sequence, paleogeographic pattern and evolution process of the intra-craton rift in Northeast Sichuan have been determined preliminarily. The study displays that the formation and evolution of the intra-craton rift in Northeast Sichuan can be divided into three stages:(1) The extensional faulting during Banxi period to early Sinian of Neoproterozoic, which coincides with the opening of the South China rift system, showing rapid filling, large sedimentary thickness and significant regional sedimentary differentiation; (2) The extensional settlement from the late Doushantuo period of Sinian to Qiongzhusi period of Cambrian, whose strata thickness is small, but the source rock is relatively developed; (3) The compression disturbance and depression from Canglangpu period to the end of Cambrian, in which the facies of limited platform and lagoon are developed with thick layer argillaceous rocks, argillaceous dolomite and gypsum-bearing rock series. Different from the short evolution of Mianyang-Changning intra-craton rift, the northeast Sichuan intra-craton rift occurs earlier, its early stage is compensatory rift filling, and the middle and late stages are composed of undercompensated fine clastic rocks and carbonate rocks. This new discovery may be of great significance to the prediction and exploration of deep oil and gas in Northeast Sichuan.