Geochemical significance of the relative enrichment of pristane and the negative excursion of δ13CPr across the Permian-

Changes in the distribution of isoprenoid hydrocarbons and in δ13Ckero or δ13CPr across the section from the Changxing Formation to the lower Yinkeng Formation at Meishan (the GSSP of PTB) are studied, in which a relative enrichment of pristane and a sharp shift in both δ13Ckero and δ13Cmole near the boundary are revealed. A possible mechanism for the abnormal accumulation of pristane near PTB is suggested: Lipids in some marine animals and their metabolites, rich in pristane, can be preserved and accumulate in some suitable depositing facies under certain special conditions, such as the catastrophic death of animals and/or developing of an anoxic water column, and thus the pristane enrichment occurs in the sediment. The occurrences of isoprenoid enrichment and high Pr/Ph ratios have been found in other typical marine anoxic sediments accompanied by mass extinction in various extent during the most important geological periods, such as Late Ordovician, end of Devonian, Early Jurassic and Late Cretaceous. These occurrences support to a certain extent the above mechanism that interprets the genesis of a high Pr/Ph ratio in some typical marine anoxic sediments. The synchronous sharp negative shifts in δ13Cmole, δ13Ckero and δ13Ccarb from Beds 24 to 26 of the Meishan profile indicate that a sudden and strong variation of carbon source in the atmosphere-ocean system occurred during the quick but equable evolution from the end-Permian to Early Triassic, and the coupling between the pristane enrichment and negative shift in δ13Ckero and δ13CPr may well indicate the importance of the release of methane hydrates and marine anoxia in the end-Permian mass extinction.

作 者：   作者單位：   刊 名： 科學通報（英文版）  SCI 英文刊名： CHINESE SCIENCE BULLETIN  年，卷(期)： 2005 50(19)  分類號： P3  關鍵詞： PTB   pristane   carbon isotope ratio   animal lipids   marine anoxia  

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