Provenance analysis of the first Member of the Middle Jurassic Shaximiao Formation in Central Sichuan Basin

Key words: 
• Sichuan Basin /
• Shaximiao Formation /
• Provenance analysis /
• andesite fragment /
• epidote

Abstract: [Objective] The Shaximiao Formation in the Middle Jurassic of the Sichuan Basin is an important tight gas exploration and development layer. Currently, the exploration and development of the first Member of the Shaximiao Formation is in its initial stage, with weak overall research, especially the lack of a systematic understanding of the controlling role of high-quality sand body distribution. [Methods] Based on petrological analysis and geochemistry, this article studied the provenance of the first Member of the Shaximiao Formation in the central Sichuan region. [Results] The results are as follows: (1) The sandstone of the first Member of the Shaximiao Formation in the central Sichuan region is mainly composed of feldspar litharenite and lithic feldspar sandstone. Igneous rock lithic fragments are mainly andesite, which are less developed in the underlying formations but commonly found in the northeast and southeast of Sichuan. (2) The dominant heavy minerals in the first Member of the Shaximiao Formation in the central Sichuan region are garnet and epidote. Epidote is rare in the underlying formations but highly developed in the northeast and southeast of Sichuan. (3) Discrimination diagrams, including F1-F2, SiO2-TiO2, La/Th-Hf, and Co/Th-La/Sc, show that the provenance of the first Member of the Shaximiao Formation in the central Sichuan region is mainly felsic volcanic rocks with a small amount of sedimentary rocks. [Conclusion] Based on the above analysis, the sandstone provenance of the first Member of the Shaximiao Formation in the central Sichuan Basin is mainly derived from the Daba Mountains in the northeast of Sichuan Basin, while other directions around the basin have limited provenance supply. These results provide strong support for the division of favorable areas for tight gas in the Sichuan Basin and for exploration and development activities.