Types of biogenic quartz and its coupling storage mechanism in organic-rich shales: A case study of the Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation in the Sichuan Basin, SW China

GUAN Quanzhong,DONG Dazhong,ZHANG Hualing,SUN Shasha,ZHANG Surong,GUO Wen

Fig. 2. Types and characteristics of biogenic quartz in Wufeng-Longmaxi Formation shale. (a) Well W202, 2 566.21 m, siliceous shale, with sponge spicules of 15-45 µm in diameter accounting for 40%, and type I microcrystalline quartz aggregates filling in the sponge spicules (red arrow), cast thin section; (b) Well W202, 2 568.74 m, calcareous-siliceous hybrid shale, with pyrite (red dashed area) associated with Type I quartz aggregates (red arrow) and pyritized calcareous biological shells, SEM; (c) Well W202, 2 566.21 m, siliceous shale, with subhedral type I microcrystalline quartz filling in the organic matter, the red dots are points of EDS analysis, all of which are Si and O elements, SEM; (d) Well W201, 1540.77 m, calcareous shale, with "powdered" type II quartz aggregate on the matrix (red dashed area), unpolished-SEM; (e) Well W202, 2 568.03 m, siliceous shale, with nano-scale type II quartz grains "floating" on the organic matter inside the radiolarian, SEM; (f) Enlarged view of figure (e) shows type II quartz grains, SEM.