Molecular Isotope Geochemistry Of Peat Deposits During 27kaB.P To 15KaB.P In Baoxiu Basin, Yunnan Province: Paleoclimatic Implications

In the thesis, we study a peat profile with the length of about 200cm sampled from Baoxiu Basin in Yunnan province by application with some relative alkanes' distributions and compounds-specific stable carbon/hydrogen isotope to discuss the changes of paleoclimate and paleoenvironment from 27kaB.P to 15kaB.P in this region.Peat's n-alkane has distinct distribution patterns with a strong odd-even preference between n-C23 to n-C33 which reflect land plants are main source of the n-alkanes. The n-alkanes' carbon isotopic values ranging -29‰~-36‰ support above viewpoint and suggest that C3 plants are main in land plants. C19 n-alkane is main in short-chain n-alkanes which indicate autochthonal algae is it's main source. We can reconstruct initial changes of climate and environment from 27kaB.P to 15kaB.P in this region by the indices of CPI, ALC, Paq , δ 13Ctoc and compounds-specific stable carbon/hydrogen isotope :Phase Ⅰ (198cm-162cm,about27-23kaB.P):cold-wet;Phase Ⅱ (162cm-120cm, about23-22kaB.P):warm-dry to cold-wet to warm-dry;PhaseⅢ(120cm-96cm,about22-15kaB.P): cold-wet to warm-dry.The carbon isotopic datum of n-alkane of n-C27, n-C29 and n-C31 display their indication to climate and environment in large degrees, namely their less negative datum indicate the warm-dry period, while their more negative datum indicate the cold-wet period. Besides, we find that the hydrogen's isotopic datum of the n-alkanes of n-C27 and n-C19 are also good proxy of climate and environment: their less negative datum in warm-dry phase, while their more negative datum in cold-wet phase. We use hydrogen isotope of n-C19 n-alkane to indicate the 5D changes of sedimental water and find the less negative 8D of sedimental water always appear in warm-dry phase. The estimation results of bi-mode's application indicate that C3 plants are main in land plants from 27kaB.P to 15kaB.P in this region and also support the C4 plants' expansion in LGM in the region.