show Abstracthide AbstractHB1, HB2, HB3, and HB4 are pit mud from the 20-year pit in the Hubei region, while SCT1, SCT2, SCM1, SCM2, SCB1, and SCB2 are pit mud from the 20-year pit in the Sichuan region. SCT1 and SCT2 are from the upper layer, SCM1 and SCM2 are from the middle layer, and SCB1 and SCB2 are from the bottom layer.