Origin of the penecontemporaneous sucrosic dolomite in the Permian Qixia Formation, northwestern Sichuan Basin, SW China

LU Feifan,TAN Xiucheng,ZHONG Yuan,LUO Bing,ZHANG Benjian,ZHANG Ya,LI Minglong,XIAO Di,WANG Xiaofang,ZENG Wei

Fig. 8. Petrological evidence of dolomitization time in Qixia Formation, northwestern Sichuan Basin. (a) Well D6, 7745.60-7745.70 m, Qi-1 Member, core sample, eogenetic exposed surface at the top of the tidal flat sedimentary sequence (purple dotted line, similarly hereinafter), and gray matrix dolomite above the exposed surface; (b) Well D6, 7745.20 m, Qi-1 Member, karren cutting bedrock in the dark red dolomite below the exposed surface; (c) Well D6, 7745.20 m, Qi-1 Member, the lower left side is matrix very finely to finely crystalline dolomite with weak karst influence, and the upper right side is the area with strong karst influence, that is, the dolomite grains shrinking in size due to dissolution and insoluble residues (PPL); (d) Hejialiang section, upper part of Qi-1 Member, limy sucrosic dolomite, the areas with fine grains suffered strong diffuse dissolution (indicated by blue arrow), the stained red part is dedolomitization calcite in the karren, and the karstification in the area with large grains is weak (yellow arrow) (Alizarin Red Staining on the left 1/2) (PPL); (e) Well D2, 2437.85 m, Qi-2 Member, karst cave filling (PPL); (f) Well D6, 7745.20 m, Qi-1 Member, below the exposed surface, ferric dolomite with pores or fractures partially filled with autochthonous-semiautochthonous medium-coarse crystalline dolomite (PPL); (g) Well D6, 7745.20 m, magnification of local part of Fig. 8f, clay fillings from the initial transgression deposition of the late stage between dolomite crystals (PPL); (h) Well D6, 7745.20 m, Qi-1 Member, cross-polarized light picture of Fig. 8g.