Seminar

The early Cambrian was an important period of environmental change and biological evolution, however, redox states and chemical features of the coeval ocean are still matters of debate. The Nanhua Basin in South China was connected to an open sea during this period, sedimentary successions deposited in the basin are thus ideal for paleoclimatic and paleoecologic reconstruction.

The phosphorite successions in the Nanhua Basin are divided into lower and upper units by a series of ~536 Ma tuff layers. Rocks from the lower unit show organic-related textures, suggesting the early Cambrian phosphogenesis was intimately linked to proliferation of primary producers. Distinctly high Zn, Cd and Pb concentrations and negative δ13Ccar excursions present in the upper phosphorite unit indicates extensive upwelling aftermath the ~536 Ma volcanisms.

Black shales deposited in the deep basin have extremely high V concentrations and low δ98Mo values. Substantial V enrichment in early Cambrian black shales elsewhere in the world indicates the presence of large marine vanadium reservoirs within the well- oxygenated ocean. Negative correlation between V concentrations and δ98Mo values reflects a significant burial of Fe-oxide during the early Cambrian which may have resulted in the termination of the ferruginous ocean existed since the early Archean.