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. 3. Photos of outcropped bentonite-rich members on the Qiliao section in Shizhu (the geological hammer in the photos is 33 cm long and arrow indicates the bentonite bed). (a) Dicellograptus complexus belt, bentonite-rich member ①, about 1.3 m thick, interlayer of carbonaceous shale and thin-bedded siliceous shale, with 4 bentonite beds; (b) Paraorthograptus pacificus belt, bentonite-rich member ②, about 1.0 m thick, thin-bedded siliceous shale intercalated with 2 bentonite beds; (c) base of the Coronograptus cyphus belt, bentonite-rich member ③, about 0.3 m thick, moderate-bedded siliceous shale intercalated with 2 bentonite beds; (d) upper part of the Coronograptus cyphus belt, bentonite-rich member ④, 1.5 m thick, argillaceous and siliceous mixed shale intercalated with 7 bentonite beds; (e) lower part of the Demirastrites triangulatus belt, bentonite-rich member ⑤, Demirastrite belt thick-bedded bentonite bed, 8.0-10.0 cm thick; (f) upper part of the Lituigrapatus convolutus belt, bentonite-rich member ⑥, 10.0 cm thick, lead grey.