The origin of Ediacaran phosphogenesis event: New insights from Doushantuo Formation in the Danzhai phosphorite deposit, South China

Abstract

The Ediacaran-early Cambrian period is not only the key period of global climate and life evolution, but also recorded the occurrence of the second large-scale phosphogenesis event in history of the Earth. South China records a large number of phosphorus-forming events of that period, which the late Ediacaran Doushantuo Formation (Doushantuo Fm.) is the most important example. Although the Ediacaran Doushantuo Fm. of China contains only 5 % of global reserves, it accounts for 45 % of the world’s phosphorous (P) production. Therefore, the study on the formation of phosphorite in the Ediacaran Doushantuo Fm., South China will help in our better understanding of the role of the phosphorus-forming event in that period. Here, we present a detailed study of geology, petrology, and geochemistry and CO isotopes of the Doushantuo Fm. phosphorite, shale and dolomite samples at Danzhai, southwest Guizhou. The rare earth element + Y (REY) signature of phosphorites display a “hat-shaped” post-Archean Australian Shale (PAAS)-normalized REY distributions, with systematically lower Ce/Ce* ranging from −0.56 to −0.60 (average −0.58, n = 4). The δ13CVPDB δ18OVPDB and δ18OV-SMOW values range from −12.88 to 4.39 ‰, −10.3–7.18 ‰, and 20.29 – 23.51 ‰, respectively. Our field, petrologic, geochemical and isotopic data suggest that: (1) The ore-forming materials of the Danzhai phosphorite deposit may have an input of marine hydrothermal and the organic-rich water brought by up-welling; (2) The Ce/Ce* and pyrite speciation data suggest that the Danzhai phosphorite deposit was formed in a suboxic-oxic conditon; (3) The phosphogenesis of the late Doushantuo phosphate deposit is mainly the result of growth and mineralization of microorganisms, accompanied by the mechanical dynamic action of seawater.