东北地区向海湖泊沉积物正构烷烃单体碳同位素特征及其古环境意义

摘要

The section of 1 420 cm lake sediment from Xianghai in the western of Songnen Plain was investigated.According to the AMS 1 4 C dating,the chronology of lake sediment since Last Deglaciation was established;combined with the types of sediment and the abundance of organic matter,molecular organic geochemical characteristics including carbon isotopic compositions of n-alkanes and long-chain n-alkanes in the samples were analyzed;compared with the climatic indicators of sediment core, the changes of paleovegetation and paleoclimate since Last Deglaciation were evaluated.The results show that the organic matters in lake sediment are mainly derived from algae and higher plant according to the distribution of n-alkanes from lake sediment in Xianghai;the n-alkanes exhibit strong odd-carbon number predominance,and the main peak of high carbon number of n-alkanes is nC3 1 ,so that the organic matters are mainly derived from terrestrial higher plants,especially herbaceous higher plants;the carbon isotopic compositions of long-chain n-alkanes (nC2 7 ,nC2 9 and nC3 1 )are positive in whole,and the main higher vegetation type in the lake is C3 plant dominantly by the means of binary pattern,and the relative biomass of C4 plant increases from Last Deglaciation to the megathermal of Holocene;the change of climate fluctuates since Last Deglaciation,and the climatic and environmental changes in the study area can be divided into five stages including cold and dry in Last Deglaciation,cold and wet in Early Holocene,warm and dry in the early megathermal of Holocene,warm and wet in the late megathermal of Holocene,and warm-cool and drying in Late Holocene.%以松嫩平原西部向海1420 cm 湖泊沉积物剖面为研究对象,根据 AMS 14 C 年代信息建立末次冰消期以来的年代序列；结合沉积物类型、有机质丰度,重点对样品中正构烷烃及长链正构烷烃碳同位素等分子有机地球化学特征进行研究；通过综合对比各气候指标,重建该地区末次冰消期以来的古植被、古气候变化。结果表明：向海湖泊沉积物中正构烷烃的分布特征表明其主要来源于低等菌藻类生物和高等植物；正构烷烃的高碳数部分呈现明显的奇碳优势,高碳数部分主峰碳主要为 nC31,指示有机质主要来源于陆生高等植物,且草本高等植物输入丰富；长链正构烷烃(nC27、nC29、nC31)稳定碳同位素整体呈偏正的趋势,并利用二元模式估算出湖区主要高等植被类型以 C3植物占绝对优势,末次冰消期到全新世大暖期 C4植物相对生物量增加；末次冰消期以来,研究区气候环境变化较不稳定,可分为5个阶段,分别为气候冷干的末次冰消期,气候冷湿的早全新世,气候暖干的中全新世大暖期前期,气候温暖湿润的中全新世大暖期后期以及气候温凉变干的晚全新世。