Geochemical significance of the relative enrichment of pristane and the negative excursion of δ^(13)C_(Pr) across the Permian-Triassic Boundary atMeishan, China  

作　　者：WANG Chunjiang LIU Yimei LIU Hongxiu ZHU Lei SHI Quan 

机构地区：[1]Laboratory of Geochemistry and Environmental Sciences, Faculty ofGeosciences, China University of Petroleum, Beijing 102249, China

出　　处：《Chinese Science Bulletin》2005年第19期2213-2225,共13页

基　　金：This work was supported by the National Natural Science Foundation of China (Grant No, 40272056).

摘　　要：Changes in the distribution of isoprenoid hy-drocarbons and in δ 13Ckero or δ 13CPr 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 δ 13Ckero and δ 13Cmole near the boundary are revealed. A possible mecha-nism for the abnormal accumulation of pristane near PTB is suggested: Lipids in some marine animals and their metabo-lites, rich in pristane, can be preserved and accumulate in some suitable depositing facies under certain special condi-tions, such as the catastrophic death of animals and/or de-veloping of an anoxic water column, and thus the pristane enrichment occurs in the sediment. The occurrences of iso-prenoid 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 sup-port to a certain extent the above mechanism that interprets the genesis of a high Pr/Ph ratio in some typical marine an-oxic sediments. The synchronous sharp negative shifts in δ 13Cmole, δ 13Ckero and δ 13Ccarb from Beds 24 to 26 of the Me-ishan 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 δ 13Ckero and δ 13CPr may well indicate the importance of the release of methane hydrates and marine anoxia in the end-Permian mass extinc-tion.Changes in the distribution of isoprenoid hydrocarbons and in δ^13Ckero or δ^13Cpr 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 δ^13Ckero and δ^13Cmole 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 δ^13Cmole, δ^13Ckero and δ^13Ccarb 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 δ^13Ckero and δ^13CPr may well indicate the importance of the release of methane hydrates and marine anoxia in the end-Permian mass extinction.

关 键 词：地球化学 碳氢化合物 同位素 油脂 PTB 

分 类 号：P534.46[天文地球—古生物学与地层学]