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The Precambrian/Cambrian boundary marks a critical interval in Earth history. Paleoenvironmental changes of the oceans have been suggested as a possible explanation for some significant events such as the marine biological evolution (“Cambrian explosion”). Here we report a remarkable variation range in trace element, iron speciation and molybdenum isotope signatures of black shales from the Early Cambrian Dingtai profile (Guizhou province) and three synsedimentary polymetallic Ni–Mo–(PGE–Au) sulfide ore deposits (Dazhuliushui and Maluhe in Guizhou province, and Sancha in Hunan province) on the Yangtze Platform, South China. Based on the (isotope) geochemical features, we classify the Dingtai profile into three intervals: interval 1 (0–1m) has extreme metal and TOC enrichment and heavy δ^98/95Mo values. This unit has all features of a euxinic environment, and is then followed by interval 2 (1 …