松辽盆地晚三冬期的黑碳记录及其古环境意义

The records of black carbon from Songliao Basin,Northeast China in Late Santonian,and their paleoenvironment implication

黑碳(BC)是生物质和化石燃料等不完全燃烧产生的含碳物质,古老沉积物中的黑碳记录可以重建过去的火灾事件和陆地植被演化历史。文中通过对晚三冬期松辽盆地姚家车站剖面、后金沟剖面和岳王城剖面的黑碳记录进行分析,来揭示嫩江组一段到二段下部的火灾事件、气候特征及植被变化信息。研究结果显示:嫩江组一段BC的含量较低,为0%~0.22%,表明可能存在的火灾事件规模很小;在该段时期有几次BC/TOC值较高,暗示着小规模的火灾事件。在嫩二段下部BC的含量突然升高,最高可达1.4%,反映了大规模火灾事件的发生。黑碳的稳定碳同位素(δ^(13) CBC)数据表明:在嫩一段,黑碳的δ^(13) CBC值(-29.4‰^-25.0‰)表现为逐渐偏正的趋势,可能是由大气CO_2浓度逐渐降低所导致;在嫩二段下部,δ^(13) CBC值先呈现突然偏负的趋势,可能是由于大规模的火灾事件以及火山活动引起的大气CO_2浓度短暂升高以及植被类型的变化所造成的,之后δ^(13) CBC值又表现为逐渐偏正的特征。综合来看,在嫩江组一段仅发生小规模火灾事件,嫩二段下部则发生大规模火灾事件,由嫩江组一段到二段下部大气CO_2浓度呈现降低—升高—再降低的变化趋势。

Black Carbon（BC）is a series of the carbonaceous materials mainly formed from the incomplete combustion of biomass and fossil fuels.BC signatures in ancient geological deposits can be used to record the history of fire activities,terrestrial plants,and paleoenvironment.In this study,the concentration and stable carbon isotopes（δ^（13） CBC）of BC in the outcrops of Yaojia Station profile,Houjingou profile and Yuewang Town profile in Songliao Basin were analyzed for recording the history of wild fire events,and to reconstruct the terrestrial vegetation types and paleoenvironments in Late Santonian.The results showed that the BC concentrations（0%-0.22%）in the sediments in the Member 1of Nenjiang Formation were relative lower,which may indicate that the wild fire scales were very small.In addition,several high BC/TOC values were observed in the Member 1of Nenjiang Formation,which suggested some small fire events.In the Lower Member 2of Nenjiang Formation,the BC concentrations increased abruptly and the highest value was up to 1.4%,which may be related to massive fire activities and volcanic eruption events.Theδ^（13） CBC values（-29.4‰--25.0‰）of BC exhibited positive excursion in the Member 1of Nenjiang Formation,which may be due to the decreasing of CO_2 concentrations in the atmosphere.Then an abrupt negative excursion ofδ^（13）CBC values was observed in the Lower Member 2of Nenjiang Formation,which could be explained by two reasons.One reason was the increasing CO_2 concentration caused by the fire activities and volcanic eruption events.The other one was the changes of the predominant vegetation types.And then theδ^（13） CBC values were positive excursion again.In summary,the record of BC concentrations indicated some small fire activities occurred in the Member1 of Nenjiang Formation and more massive fire activities happened in the Lower Member 2of Nenjiang Formation.And the record ofδ^（13） CBC values suggested that the atmospheric CO_2 concentrations were varied in different phase from the Member 1of Nenjiang Formation to the Lower Member 2of Nenjiang Formation.