藏北可可西里地区中新世湖相油页岩的生物分子标识及碳同位素异常  

BIOMARKERS AND CARBON ISOTOPIC ANOMALY FROM THE MIOCENE LACUSTRINE OIL SHALES IN HOH XIL BASIN OF NORTHERN TIBETAN PLATEAU

作　　者：伊海生[1] 林金辉[1] 王成善[1] 彭平安[2] 

机构地区：[1]成都理工大学沉积地质研究所,成都610059 [2]中国科学院广州地球化学研究所

出　　处：《成都理工学院学报》2002年第5期473-480,共8页Journal of Chengdu University of Technology

基　　金：国家重点基础研究发展计划项目 ( G19980 4 0 80 1 -5 ) ;中国科学院有机地球化学国家重点实验室项目 ( OGL-970 3)联合资助

摘　　要：对采自藏北可可西里地区中新世湖相油页岩样品进行了有机岩石学和分子地球化学实验分析 ,目的是通过生物分子生态学方法重建古湖泊系统的演化。两个层位油页岩抽提沥青的 GC-MS和 GC-IRMS分析表明 ,剖面下部的油页岩和泥质岩富含β胡萝卜烷和伽马蜡烷 ,沉积环境是一个水体分层的咸水古湖泊系统。色谱 -质谱分析中检出的短链正构烷烃来自于水生生物 ,而以奇数碳 C2 9为主峰且奇偶优势明显的长链 ( C2 3 ～ C3 1 )正烷烃是 C3 型陆生高等植物输入的。植烷和姥鲛烷被解释为来自生活在透光带上部的藻类和蓝细菌 ,β胡萝卜烷可能与栖居于透光带下部的喜盐性古细菌及光合细菌有关 ,藿烷和莫烷代表生活在氧跃面或缺氧底层水中的甲烷菌和化学自养细菌群落。作者发现上部层位油页岩比下部油页岩明显富集 1 3 C,干酪根 δ1 3 C高达 -1 7.76‰ ,正烷烃单体碳同位素 δ1 3 C平均值为 -2 1 .97‰ ,主峰 n C2 3 的 δ1 3 C值可达 -1 5 .0 1‰。经对比证实 ,这种罕见的 1 3 C异常是 C4型植被或绿藻 Botryococcus突然繁盛引起的 ,这预示着中新世末青藏高原隆升可能达到临界高度 ,古湖泊生态系统随着气候变化发生了转型和更新。The oil shale and lacustrine sediment samples from the Miocene Wudaoliang Formation sections of the Hoh Xil basin in northern Tibetan plateau are studied in order to rescontruct paleolake environment and to deduce paleoclimatic change information. Twelve samples are examined by total organic carbon analysis and Rock-Eval pyrolysis. The solvent extracts and kerogens from oil shales and marls are separated and examined by organic petrographic, GC-MS, and GC-IRMS methods. The relative abundances of biomarkers and carbon isotopic composition of individual hydrocarbons are used to explain organic source and paleoecosystem. The individual carbon isotopic compositions of short-chain n-alkanes suggest the input from aquatic organisms, and the long-chain n-alkanes characterized by maximum at n-C 29 and an odd-over-even predominance in the range C 23-C 31 are derived from terrestrial plants. Pristane and phytene commonly reflect the input from algae and cyanobacteria in the shallow photic zone. Hopanoid biomarker is produced by organisms inhabiting the lower part of the water column of paleolake. Hopanes and moretanes are likely from methanotrophic bacteria community and chemoautrophic bacteria living at the lacustrine oxycline interface or above anoxic bottom water. The authors oberserved that the oil shale and marl in the lower part of stratigraphic section show higher values in gammacerane and β-carotane, its depositional environment is interpreted as a stratified paleolake system. β-carotane could be related to halophilic archaebacteria or phototrsynthetic bacteria in deeper photic zone. Gammacerane is derived from primary producers and green sulfer bacteria living at or below chemocline and is an indicator for water column stratification. The upper oil shale samples are clearly rich in 13C compared to the lower oil shale samples, δ 13C in the kerogen is -17.76‰, the average value of δ 13C of the individual n-alkanes is -21.97‰, and δ 13C of the n-C 23 maximiumg peak is ab

关 键 词：碳同位素异常 青藏高原 中新世 油页岩 生物分子标志物 分子地球化学 有机岩石学 

分 类 号：P618.13[天文地球—矿床学] TE12[天文地球—地质学]