Late Sinian and Early Cambrian strata are well developed at the Maidiping Section, Emei County, Sichuan province. Here, the Sinian-Cambrian boundary ( China C point ) is defined by a marked lithological change from carbonate rocks to shale.High-resolution geochemical studies of the Maidiping section show that a ca-30-cm-thick layer at the base of the Jiulaodong Formation from the Sinian-Cambrian boundary upward can be divided into phosphorite, greyish black shale and mudstone. phosphorite and the lower part of black shale are enriched in Ir, Ni, Co, Cr and Fe as well as Cs, Hf, Rb, Ba, Th and U.Therefore, it is more reasonable to take the China C point as the Sinian-Cambrian boundary at the Maidiping section rather than the China A, China B or China D points.