摘要
【目的】现代陆地植物叶片碳同位素值(δ^(13)C_(现代植物))的变化受大气CO_(2)浓度和大气CO_(2)同位素(δ^(13)CCO_(2))以及陆表气温、降水量的控制,δ^(13)C_(现代植物)与这些参数之间已经建立了数学函数关系式,这为应用古植物叶片碳同位素(δ^(13)C_(古植物))定量重建古气候参数提供了可能。然而,δ^(13)C_(古植物)分析资料稀少,且古植物化石在地层中间断分散出现,难以建立连续的δ^(13)C_(古植物)随剖面深度或时间的曲线,同时成岩埋藏过程中温度和压力的变化还可能对古植物叶片的碳同位素值产生干扰。来源于陆生木本和草本植物叶片的长链高碳数正构烷烃单体分子碳同位素(δ^(13)C_(正构烷烃))记录了陆地δ^(13)C_(古植物)变化过程,但两者之间缺乏系统的对比研究。【方法】系统采集了柴达木盆地侏罗纪、古近纪植物化石叶片和茎秆样品14件,同步测量了古植物化石和化石围岩的正构烷烃的碳同位素。【结果】古植物化石围岩样品的长链正构烷烃单体分子nC_(27)、nC_(29)、nC_(31)碳同位素平均值(δ^(13)Cn_(C27-nC29-nC31))比14件植物化石叶片同位素偏负约为-5.0‰,侏罗系大煤沟组与煤层互层产出的沼泽相黑色泥岩δ^(13)Cn_(C27-nC29-nC31)较全岩有机质碳同位素δ^(13)C_(TOC)偏负-5.3‰,古近纪下干柴沟组与盐湖相蒸发岩共生的黑色泥岩δ^(13)Cn_(C27-nC29-nC31)较干酪根有机质碳同位素δ^(13)C_(干酪根)偏负-5.1‰。【结论】鉴于全岩有机质中存在一定量的腐泥质组分,而干酪根组分中镜质体、惰质体和壳质组碳同位素存在差异,提出地质历史时期古植物叶片的碳同位素可按下式简化计算获得,即δ^(13)C_(古植物)=δ^(13)Cn_(C27-nC29-nC31)+5.0‰。
[Objective]The change in carbon isotope value of modern terrestrial plant leaves(δ^(13)C_(modern plants))is controlled by atmospheric carbon dioxide(CO_(2))concentration,atmospheric CO_(2)isotopic composition(δ^(13)CCO_(2)),continental surface temperature,and precipitation,and the mathematical relationship has been established betweenδ^(13)Cmodern plants and those climatic environmental elements,rendering an importance reference for the quantitative recon⁃struction of paleoclimate change using the carbon isotopic composition(δ^(13)C_(ancient plants))of ancient plant leaves.Current⁃ly,owing to scare analyticalδ^(13)C_(ancient plants)data and intermittent dispersion of paleoplant fossil-producing horizons in stratigraphic sections,establishing a continuous change curve ofδ^(13)C_(ancient plants)with depth or time is difficult,and the change of temperature and pressure in diagenetic burial process may disturb the carbon isotope value of ancient plant leaves.The compound-specific carbon isotope(δ^(13)C_(n-alkane))of long-chain high carbon number normal alkane(n-alkane)from terrestrial woody and herbaceous plant leaf blades records the change process of leaves from ancient terrestrial plants(δ^(13)Cn_(C27-nC29-nC31)average values).[Methods]Fourteen samples of Jurassic and Paleogene plant fossils,including leaves and stems,were collected from the Qaidam Basin.The carbon isotopic composition of n-alkanes was measured simultaneously in both the fossilized plants and their surrounding rock matrix.[Results]The carbon isotopic composition of n-alkanes(nC_(27),nC_(29),and nC_(31))derived from ancient plant leaves is approximately-5.0‰more negative than the isotopic composition of the plant fossil leaves themselves.Theδ^(13)Cn_(C27-nC29-nC31)average values of the Jurassic Daheigou Formation swamp-phase black mudstone interbedded with coal seams is-5.3‰more negative than the bulk organic carbon isotope value(δ^(13)C_(TOC))of the whole rock organic matter.Moreover,in the Paleo⁃gene Xiaganchaigou Formation,theδ^(13)Cn_(C27-nC29-nC31)average values of black mudstone associated with evaporites of the sa⁃line lake phase is-5.1‰more negative than the kerogen carbon isotope(δ^(13)C_(kerogen)).[Conclusions]In consideration of certain sapropelic components in the whole rock organic matter,as well as the carbon isotope difference among vitrinite,inertinite,and exinite in kerogen,the carbon isotopes of ancient plant leaves during the geological histori⁃cal period could be determined through a simplified calculation as per the following formula,namelyδ^(13)C_(ancient plants)=δ^(13)Cn_(C27-nC29-nC31)+5.0‰.Well Shi-68 from Yingxi area of Qaidam Basin is taken as an example to probe into the error change of continental strata whole rock organic matter and kerogen with ancient plant leaf carbon isotopes and calcu⁃lated n-alkanes.
作者
伊海生
伊帆
田康志
石宇翔
徐学敏
YI HaiSheng;YI Fan;TIAN KangZhi;SHI YuXiang;XU XueMin(Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;College of Geography and Planning,Chengdu University of Technology,Chengdu 610059,China;Key Laboratory of Petroleum Resources Research,Lanzhou 730000,China;Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences,Lanzhou 730000,China;College of Earth and Planetary Sciences,Chengdu University of Technology,Chengdu 610059,China;National Research Center for Geoanalysis,Beijing 100037 China)
出处
《沉积学报》
北大核心
2025年第5期1743-1757,共15页
Acta Sedimentologica Sinica
基金
国家自然科学基金项目(42172121)
甘肃省油气资源研究重点实验室开放课题基金(SZDKFJJ2022002)。
关键词
陆生古植物
叶片化石
长链正构烷烃
碳同位素差值
校正计算
侏罗纪
古近纪
柴达木盆地
ancient terrestrial plants
leave fossils
long-chain n-alkanes
carbon isotope differences
correction calculation
Jurassic
Paleogene
Qaidam Basin
