Developmental characteristics and geological significance of the bentonite in the Upper Ordovician Wufeng - Lower Silurian Longmaxi Formation in eastern Sichuan Basin, SW China

WANG Yuman,LI Xinjing,WANG Hao,JIANG Shan,CHEN Bo,MA Jie,DAI Bing

Fig. 4. Thin sections of black shale in (or overlying) the bentonite-rich members on the Qiliao section in Shizhu. (a) Bentonite-rich member ①, siliceous shale, with less-developed laminae; (b) bentonite-rich member ①, with abundant radiolarians; (c) bentonite-rich member ②, siliceous shale, with no lamina; (d) bentonite-rich member ②, with abundant radiolarians in star- or dot-like distribution; (e) bentonite-rich member ③, siliceous shale, with horizontal fine laminae; (f) bentonite-rich member ③, with abundant radiolarians; (g) bentonite-rich member ④, argillaceous and siliceous mixed shale, with rich laminae; (h) bentonite-rich member ④, bright-colored grains in the lamina are quartz and radiolarian; (i) bentonite-rich member ⑤, overlain by argillaceous shale, with horizontal laminae; (j) bentonite-rich member ⑤, bright-colored grains in the laminae are quartz and radiolarian; (k) bentonite-rich member ⑥, overlain by argillaceous shale, with well-developed laminae; (l) bentonite-rich member ⑥, bright-colored grains in the laminae are quartz and radiolarian.