APPLICATION OF BIOMARKER PARAMETERS TO QUANTITATIVE DISCRIMINATION OF THE HYDROTHERMAL SEDIMENTARY PALEOENVIRONMENT

By means of the computerized gas chromatography-mass spectrometry (GC-MS), the characteristics and significance for hydrothermal sedimentary paleoenvironment of biomarkers from the typical hydrothermal siliceous rocks in the Xicheng Orefield of Qinling Mineralization Belt are studied preliminarily. Then a functional model based on biomarker parameters is established according to the result of multivariate statistic analysis. The results show:① By comparison with the normal sedimentation, the organic matters from the hydrothermal rocks show the particular features:(a) the mean value of saturates/aromatics goes up to 4.64,indicating the characteristics of high saturates and low aromatics abundance; (b) the distribution of carbon-number varies confinedly with a single main peak, C₁₇ or C₁₈; (c) the mean value of carbon predominance index i.e. CPI is 1.35, which indicates an obvious odd-carbon predominance; (d) the mean values of ΣnC₂₂^-/ΣnC₂₂⁺ and nC₂₁₊₂₂/nC₂₈₊₂₉ go up to 3.17 and 4.29, respectively; (e) the mean value of Pr/Ph is only 0.44, but C₂₉^-/C₃₀⁺ and C₂₁Tri/αβC₃₀ go up to 7.41 and 4.32, respectively. These characteristics suggest that the hydrothermal rocks must have experienced an exceptional high-temperature environmental condition, and the depositional environment might be a high-temperature, hypersaline, anoxic, deep-water and close sea basin.② The result of Q-type cluster analysis shows that the samples of hot-water rocks and normal sedimentary rocks can be classified correctly according to the biomarker parameters. And based on the four indicies i.e. ΣnC₂₂^-/ΣnC₂₂⁺, nC₂₁₊₂₂/nC₂₈₊₂₉, Pr/Ph and αβC₃₀-hopane/ΣC₂₉-sterane, a recovery model for discrimination of hydrothermal vs. normal aqueous sedimentary paleoenvironment is established by the stepwise discriminant analysis. The research results can provide evidences for recovery and reconstruction of ancient hydrothermal depositional environment, and supply a new approach for investigation to the basic paleoenvironmental settings on hydrothermal sedimentation and organic biomineralization.