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

Table 2 Major graptolitic belts and their development characteristics of bentonite on the Qiliao section in Shizhu.

Stage Graptolitic belt No. Sedimentary time/Ma Thickness/m Sedimentary rate/ (m·Ma-1) Development characteristics of bentonite Number of beds Cumulative thickness Single-bed thickness/cm Development rate / (cm·Ma-1) Remarks Aero- nian Stimulograptus sedgwickii LM8 0.27 >52.43 >72.82 Dense vegetation coverage Lituigrapatus convolutus LM7 0.45 2 10.80 0.50-10.00/5.40 24.0 10 m vegetation coverage, top sur- face undefined Demirastrites triangulatus LM6 1.56 31.94 20.47 5 16.80 0.50-10.00/3.40 10.8 Rhud- danian Coronograptus cyphus LM5 0.80 27.00 33.75 16 19.95 0.50-4.00/1.20 24.9 1.5 m vegetation coverage at the base Cystograptus vesiculosus LM4 0.90 1.14 1.27 1 0.75 0.50-1.00/0.75 0.8 Parakidograptus acuminatus LM3 0.93 4.67 2.38 Akidograptus ascensus LM2 0.43 Hirnan- tian Normalograptus persculptus LM1 0.60 Hirnantia-Dalmanitina O3g 0.73 0.89 3.32 Normalograptus extraordinarius WF4 9.71 Katian Paraorthograptus pacificus WF3 1.86 2 6.00 2.00-4.00/3.00 3.2 Dicellograptus complexus WF2 0.60 5 10.00 0.50-5.00/2.00 16.7