Characteristics of Sequence-based Lithofacies and Paleogeography,and Prediction of Oolitic Shoal of the Feixianguan Formation in the Northeastern Sichuan

The Feixianguan Formation of Lower Triassic in the northeast Sichuan can be divided into 2 third-order sequences, six system tracts in terms of sedimentary facies and sequence interfaces. Characteristics of sequence stratigraphy of the Feixianguan Formation are analyzed, sequence-palaeogeography maps compiled and development regularity of oolitic shoal predicted. It is indicated that, during the development of SQ1 sequence, the effect of transgression brings about such distribution framework of facies zones as platform basin-platform margin-open-limited-evaporate platform. Of the system tracts, the platform margin and oolitic shoal are the most developed ones. The effects of large scale descent of sea level and dry and hot climate during the development stage of SQ2 translates the original open platform into limited one and eventually into evaporate platform with dominant deposition of dolomite, forming the first important regional tight caprock of the Feixianguan Formation which is favorable for the accumulation of oil and gas.