DENG Yi-nan1,2, GUO Qing-jun2, ZHU Mao-yan3, ZHANG Jun-ming3

1. MLR Key Laboratory of Marine Mineral Resources, Guangzhou Marine Geological Survey, Guangzhou 510075, China;
2. Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; 3. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China

Abstract: The Early Cambrian is a period with great change in Earth's history. In order to determine palaeoenvironment of black rock series in the deep sea area and the source of Ni-Mo-PGE layer, samples were systematically collected from the Longbizui section in the Lower Cambrian basin facies area, western Hunan. We analyzed trace element ratios in kerogen, correlations of TOC-(V, U and Mo) and Ni-Co-Zn diagram in bulk rocks. The results indicated that, Th/U, V/Sc and V/Cr values showed a same trend in the section. TOC-(V, U and Mo) correlation indicated euxinic conditions, and most samples were distributed in the hydrothermal area of the Ni-Co-Zn diagram. It suggested that a Ni-Mo-PGE polymetallic layer, which enriches trace elements and has relative negative δ13Corg values, might exist in the lower part of the section and this layer can serve as a marker for stratigraphic succession. The results indicated that the deep sea areas of early Cambrian had been through a short euxinic environment period and then turned into a widespread anoxic environment after oxygenated events in the bottom water. Hydrothermal activities existed during the deposition of black rock series. The extreme enrichment of some metals in the Ni-Mo-PGE layer might be resulted from reducing environment of bottom water and hydrothermal activities.

Keywords: early Cambrian trace element kerogen black rock series western Hunan Province

*Corresponding Author, E-Mail: guoqj@igsnrr.ac.cn

Bulletin of Mineralogy, Petrology and Geochemistry Vol. 34, No.2, 2015, page 410-418