Biomarkers of the phosphorites and their indicators of the sedimentary environments of the Doushantuo Formation in Weng’an,Guizhou

The fossil assemblages of the Weng’an biotas identified in the phosphorites from the Neoproterozoic Doushantuo Formation in Weng’an,Guizhou consist of multicelluar algae,cyanobacteria,Acritarchs,dormant eggs and embryos of metazoas,tabular metazoas and bilateral metazoas and so on.The organic geochemical analysis of the phosphorite samples collected from the Doushantuo Formation in Weng’an has disclosed that the hydrocarbon fractions contain n-alkanes,terpanes,steranes,and isoprenoid hydrocarbons.The distribution of n-alkanes displays the highest peak of nC₂₁,and a wide range of carbon atom numbers.The OEP value equals to 1.03,and the Pr/Ph ratio equals to 0.95,indicating the phytane dominance.The sterane contents of C₂₇ > C₂₉ > C₂₈ shows the distribution of asymmetrical "V" shape.The dominance of C₂₇ may be caused by abundant acritarchs.The biomarkers cited above indicate that the organisms in the phosphorites are mostly derived from algae and bacteria.Some of the biomarkers also suggest the reducing and high-salinity sedimentary environments of phosphorites.