1. State Key Laboratory of Coal Resources and Safety Mining,China University of Mining & Technology( Beijing),Beijing　 100083,China;2. Langfang Branch,Petroleum Exploration and Development Research Insitute,PetroChina,Langfang　 065007,China;3. Qinghai Coalfield Geologic Bureau,Xining 　810000,China

为了揭示陆相盆地古气候变化与沉积环境、聚煤作用耦合关系,应用同位素地球化学、煤岩学等理论和方法,进行了柴北缘中侏罗统大煤沟组上段(巴柔期)主采煤层煤岩组分、有机碳同位素组成(δ13CO)及其古气候意义研究。研究煤层(7号和F煤层)δ13CO值平均为-23.9‰,分别变化在-26.7‰~-21.6‰和-25.6‰~-22.9‰。根据沼泽、陆源碎屑体系交替演化特征和煤层有机碳δ13CO值变化规律,将大煤沟组上段划分为8个阶段并对应于1个长周期旋回(C1)和3个短周期旋回(C2)。认为低变质煤δ13CO值在反映古大气CO2同位素组成及其含量变化的同时,还记录了聚煤期(植物生长至泥炭化阶段末)古气候(温度和湿度)的变化:湿暖古气候有利于成煤植物对碳同位素分馏及贫13C腐殖质(镜质组前身)的形成,煤δ13CO值降低;干热古气候不利于植物对碳同位素的分馏,但有利于富集13C的惰质组(丝质体)形成,进而引起煤δ13CO值升高。从煤层δ13CO值所反映的气候变化与陆源碎屑体系废弃、复活及聚煤发生、终止关系角度提出了陆相盆地古气候与沉积环境、聚煤作用关系模型,指出在盆地构造活动、基底沉降较稳定和均匀的煤系沉积过程中,气候变化通过盆地和流域内径流深度(年平均降雨量减去年平均蒸发量)和植被发育演化控制了绝对湖平面变化、沉积物的产生和搬运(供给)速率,进而引起盆地内沼泽、陆源碎屑两种矛盾体系的交替与演化。

In order to reveal the relationship between paleoclimate change and sedimentary environment,as well as coal accumulation in the terrestrial basin,the principle of isotope geochemistry and petrology has been used to study the maceral,the isotope composition of organic carbon ( δ13 CO) and the paleoclimatic significance of main mining coal seam of the Middle Jurassic Upper Dameigou Formation (Bajocian stage) in northern Qaidam Basin. The average val- ue of δ13 CO of No. 7 coal and coal F is -23. 9‰,it varies from -26. 7‰ to -21. 6‰ and from -25. 6‰ to -22. 9‰respectively. The Upper Dameigou Formation is divided into eight stages corresponding to a long period cycle ( C1) and three short period cycles (C2) according to the characteristics of alternating evolution of swamp and terrigenous system and the variation of the organic carbon δ13 CO value. The δ13 CO value of low metamorphic coal is considered to not only reflect the isotope composition and content changes of palaeoatmospheric CO2 ,but also record the changes of paleoclimate (temperature and humidity) during the coal accumulating period ( plant growth to the end of peatifica- tion):Wet-warm paleoclimate is conducive to the carbon isotope fractionation of the coal-forming plants and the forma- tion of poor13 C humus (predecessor of vitrinite),and the δ13 CO value of coal decreased;dry-hot paleoclimate is not conducive to the carbon isotope fractionation of plants,but it is conducive to the formation of inertinite ( fusinite) in enrich13 C,and then cause the δ13 CO value of coal increases. From the point of the relationship between the climate change reflected by the δ13 CO values of the coal seam and the abandonment and revival of terrigenous system and the commencing and termination of coal accumulation,a model of the relationship between paleoclimate,sedimentary envi- ronment and coal accumulation in the terrestrial basin is proposed. It points out in the process of coal measures deposi- tion when the tectonic is active and basement subsidence is stable and uniform,the change of absolute lake level and the rate of sediment production and transportation ( supply) are controlled by the climate change through the runoff depth of drainage basin (annual average rainfall minus annual average evaporation) and the development and evolu- tion of plants,and then cause the alternating evolution of swamp and terrigenous system in the basin.

国家自然科学基金资助项目(41472131；41002049)；教育部新世纪优秀人才资助项目(2013102050020)；

Lu Jing,Yang Minfang,Shao Longyi,et al. Paleoclimate change and sedimentary environment evolution,coal accumulation:A Middle Juras- sic terrestrial[J]. Journal of China Coal Society,2016,41(7):1788-1797.