Depositional system constrained by the high-precision sequence framework and the source to sink systems: A case study from the First Member of the Liushagang Formation in the Weixinan Sag

Abstract

Objective The exploration direction of the Weixinan Sag in the Beibuwan Basin has shifted from structural traps to lithological traps, and the key problem in searching for lithological traps is to clarify the distribution of sandstones. Methods In this study, the high-frequency sequence division and depositional system of the First Member of the Liushagang Formation in the Weixinan Sag were analyzed using zircon dating, logging, core and seismic data. Results Then, the types and distributions of depositional facies in the First Member of the Liushagang Formation in the Weixinan Sag were clarified. The results show that the First Member of the Liushagang Formation was deposited as a third-order sequence, which can be divided into three system tracts and eight parasequence sets. Based on the analysis of the source to sink systems and sedimentary facies, the sediments in the Weixinan Sag mainly sourced from the Wanshan provenance in the northwest, the Qixi provenance in the east, the Wexinan provenance in the southeast, and the Xinan provenance in the southwest. The First Member of the Liushagang Formation in the Weixinan Sag mainly contains three sedimentary facies types: delta, lacustrine and sublacustrine fan. The lowstand system tract is dominated by mid-deep lake and sublacustrine fan deposits, including turbidity channels, natural levee, and sheet lobes. The expanding system tract mainly contains the sedimentary microfacies of deep lacustrine mud. The highstand system tract consists of front-delta deposition, among which the subaqueous distributary channel and subaqueous distributary interchannel are widely developed, and sedimentary microfacies such as mouth bar and sheet sand are less developed. Conclusion Three types of sublacustrine fan are mainly developed in the B subsag, including the western delta progradation slump type, southern near source fault slope belt type, and eastern far source gentle slope type.Among them, the southern provenance system with large-scale and good reservoir-forming conditions is the most promising target for further exploration.

Keywords

• weixinan sag
• the first member of the liushagang formation
• sequence stratigraphy
• depositional system
• source to sink system
• high-precision sequence framework