Characteristics Of Biomarkers In Selected Samples From Different Environments: Their Implications For Climatic And Environmental Variations

This study examines the types, features and significance of biomarkers and their applications to climatic and environmental changes using the GC-MS method ,we analyzed peat and swamp sediments from Ruoer Gai plateau, modern soils from different climate regions in China. Lacustrine sediments from Linxia basin and lipid compounds extracted from crude oil from Yaerxia oil field, Jiuxi basin. The results of this study indicate that different biomarkers occur in different environments. These are summarized below.(1) In the sediment samples from different dephs of the peat, predominant even-carbon numbers distributions of major peaks of long-chain n-alkanes, and lowΣnC₂₁^-/ΣnC₂₂⁺,nC₁₇/nC₃₁ and (nC₁₅+nC₁₇+nC₁₉)/(nC₂₇+nC₂₉+nC₃₁) indicate that grassland vegetation was important during peat formation and the climate was cold and wet. Higher abundances of nC₂₇ and nC₂₉ in some of the samples suggest that materials derived from plateau shrubs are present in the samples. Variation of CPI of long-chain n-alkanes with depth of the samples is related to diagenetic evolution of organic materials in the peat profiles.(2) Variations in high-carbon numbers(nC₂₉, nC₃₁, nC₃₃) and low-carbon numbers (nC₁₆, nC₁₇, nC₁₈) of n-alkanes in morden soil samples are related to climatic changes in different regions. The ratios of (nC₁₆+nC₁₇+nC₁₈) / (nC₂₉+nC₃₁+nC₃₃) change with humidity and temperature. The ratios ofΣnC₂₁^-/ΣC₂₂⁺, nC₁₇/nC₃₁ and (nC₁₅+nC₁₇ + nC₁₉) / (nC₂₇+nC₂₉+nC₃₁) with the sources of organic materials from different regions, particularly changes in vegetations in different climaticzones.(3) The major components of n-alkanes and their bimodal distributions vary with dephs of lacustrine sediments in Linxia basin. The main carbon peaks of n-alkanes in sample L1 and L2 are nC₁₈ and nC₂₉. The ratios of nC_17-21/ nC_27-31 and nC_{27/ nC31} in these 2 samples are higher than sample L3. The organic materials from sample L1 and L2 were derived from primitive algae and highly-evolved plants (forest) in warm and humid climate. The main carbon peaks of n-alkane in sample L3 are nC₁₈ and nC₂₅. The abundance of nC₂₉ and nC₃₁ in sample L3 is higher than the other 2 samples, indicating that the climate of sample L3 was warmer and more humid than the other 2 samples. The changes of peak variations of n-alkyl-2-ketone in the samplesvary with climatic an vegetational changes.(4) The hydrocarbon components in 3 crude oil samples from Jiuxi basin have similar paraffin, terpanes and steranes which indicates that their organic materials have similar biological origins and similar diagenetic conditions. The distributional patterns of high-carbon and low-carbon numbers and high concentrations of C₂₉ sreranes in n-alkanes indicate that the parental organic matters of the crude oil are of highly evolved plants. Loe pristine / phtane (Pr/Ph value) and high gammaceranes / C₃₀ hopanes values indicate that depositional conditions were reduced, low saline water.