Abstract: A series of layered black chert was deposited in the lower Yangtze region during the Ediacaran-Cambrian (E-C) transition period. In the western Zhejiang, the Diben section consists of the Piyuancun Formation, which corresponds roughly to the Liuchapo Formation or the Laobao Formation in the upper Yangtze region. The chert generally has highly organic carbon content, and is highly enriched in uranium (U), vanadium (V), molybdenum (Mo) and other redox sensitive elements. The chert, together with the black mudstone deposited in early Cambrian, is called black rock series. But there is still some debate about its genesis. The major and trace (rare earth) elements in the black chert are measured and analyzed to probe into the source and origin of the chert of the Piyuancun Formation in the western Zhejiang. The results show that: (1) It is not possible for chert deposited in such a large range of deep water to be formed only by hydrothermal sources. (2) The late Ediacaran biodegradation products have a significant impact on the formation of chert. However, it is still not possible to determine whether the materials that constitute chert is mainly derived from organisms due to the lack of reliable palaeontological evidence. We infer that biological activities exerted certain influence on the formation of chert. (3) The chert of Piyuancun Formation was mainly products of chemical deposition, and silica mainly came from the weathering of continental silicate minerals.

Key words: Ediacaran-Cambrian, chert, Piyuancun Formation, major and trace elements