Formation Of Phosphorite Deposit, Breakup Of Rodinia Supercontinent And Biology Explosion

Guizhou Province is rich in phosphorite resource, which was formed in the Doushantuoan of the Late Sinian and the Meishucunian of the Early Cambrian. The two stages phosphorit preserved the earliest Weng'an biota and Meishucun biota respectively. The two biotas are representative of two biology explosion events during the early evolvement of life. Based on the above, we may confer that there lie relationship between the formation of phosphorite and the biology explosion. In addition, studying indicate that the tillite of Nanruo Fm. and the "cap" carbonate of Dengying Fm. have relationships with the breakup of Rodinia supercontinent. The phosphorite deposited underlying Dengying carbonate and overlying Noutuo tillite, so the formation of phosphorite also has relationship with the breakup of Rodinia supercontinent.To study the relationships of the formation of phosphorite, the breakup of Rodinia supercontinent and the biology explosion is significant not only for revealing the source, environment, structure and mechanism of the deposit but also for resolving the problem to contrast Neoproterozoic strata, the events of several biology explosions and of glaciations world-wide.Analyses of petrography, paleontology, elemental-chemistry, isotopic geochemistry, organic geochemistry and isotope chronology are conducted on phosphorite of Doushantuo Formation and Early Cambrian from Weng'an, Kaiyang and Zhijjng deposit in Guizhou province, SW China. The purpose of this study is to advance our understanding of the relationships of the formation of phosphorite, the breakup of Rodinia supercontinent and the biology explosion by documenting and interpreting the geochemistry of the phosphorites. The studying gets some conclusions as follows:Study of the geology of three phosphorites indicate that the phosphorite of Doushantuoan is richer in P than that of Cambrian. The Weng'an and Zhijinphosphorites deposited on the oxidation zone, and the Kaiyang phosphorite deposited on the suboxidation zone.The mineralogenetic epoch of three phosphorites have been gained. The isochron age of the Doushantuoan phosphorite deposit is about 583±19Ma (Sm-Nd dating) and 588±8.6Ma, 582±7.7Ma (Rb-Sr dating). The isochron age of the Cambrian Meishucunian phosphorite deposit is about 542±23Ma(Sm-Nd dating) and 541±12Ma(Rb-Sr dating). These ages are coupled of that (600Ma-550Ma, 540Ma) of the breakup of South China block from the Rodinia supercontinent. So it gives a chronological proof to support the view that the breakup of Rodinia supercontinent is responsible for the formation of phosphorite.The contents of the ore-forming elements, trace element, rare earth elements and the isotopic compositions of Nd indicate that the breakup of Rodinia supercontinent provide hydrothermal and mantle's ore material for the phosphorite and lead to hypothermia metallogenesis in large-scale.Investigating the Weng'an biota in the Doushantuo stratum and the small-shell biota in the Cambrian stratum, suggest that the breakup of Rodinia supercontinent is responsible for these two biology explosions.The relations of biology and P in the stratum indicate that biology participated in phosphatization directly or indirectly. There are several proofs: geology, trace element, apatite mineral geochemistry and organic geochemistry. The biology participated in phosphatization directly mainly occurred during the process of assimilating P. Then the indirectly phosphatization occurred during the process of geochemical and physical enrichment.In conclusion, the breakup of Rodinia supercontinent initiated the biology explosion, and provided the hydrothermal and mantle's ore material. The biology enriched and accumulate P element and further formed the phosphorite.