Abstract: Deep ancient strata system is getting more and more attention in the field of hydrocarbon exploration, among which the Sinian Doushantuo Formation of the Sichuan Basin is considered as one of the most potential source rock. During the past decades, few work aimed at this formation had been taken. To deepen understanding of the Doushantuo Formation as a set of potential source rock, taking well-sampled Minyuexiang Section of Chengkou County of northeastern of Sichuan Basin as a case, the geochemical characteristics and organic matter accumulation mechanism of Doushantuo shale are systematically discussed by means of comprehensive analysis of petrology, major, trace and rare earth elements. The results show that the organic-rich black shale developed in the Doushantuo Formation was mainly deposited in suboxic-anoxic environment, and significant positive Eu anomalies indicate that the Doushantuo Formation wasinfluenced by hydrothermal activity during the sedimentation process. The organic matter accumulation is strongly controlled by the anoxic sedimentary environment. Due to the low sedimentation rate, the organic matter gradually enriched with the increase of deposition rate from bottom to top. In addition, hydrothermal activity led to the elevated accumulation and burial of organic matter. Further, the Doushantuo Formation has certain oil and gas potential, but its heterogeneity is developed, which may be related to the eustatic change during the glacial-interglacial period.

Key words: ancient petroleum system, deep strata；element geochemistry, organic matter accumulation, Doushantuo Formation, Sichuan Basin