陆相盆地古气候变化与环境演化、聚煤作用
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摘要
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( δ13CO) and the paleoclimatic significance of main mining coal seam of the Middle Jurassic Upper Dameigou Formation( Bajocian stage) in northern Qaidam Basin. The average value of δ13CO 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 δ13CO value. The δ13CO 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 peatification) : Wet-warm paleoclimate is conducive to the carbon isotope fractionation of the coal-forming plants and the formation of poor13 C humus( predecessor of vitrinite),and the δ13CO 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 δ13CO value of coal increases. From the point of the relationship between the climate change reflected by the δ13CO 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 environment and coal accumulation in the terrestrial basin is proposed. It points out in the process of coal measures deposition 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 evolution of plants,and then cause the alternating evolution of swamp and terrigenous system in the basin.
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( δ13CO) and the paleoclimatic significance of main mining coal seam of the Middle Jurassic Upper Dameigou Formation( Bajocian stage) in northern Qaidam Basin. The average value of δ13CO 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 δ13CO value. The δ13CO 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 peatification) : Wet-warm paleoclimate is conducive to the carbon isotope fractionation of the coal-forming plants and the formation of poor13 C humus( predecessor of vitrinite),and the δ13CO 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 δ13CO value of coal increases. From the point of the relationship between the climate change reflected by the δ13CO 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 environment and coal accumulation in the terrestrial basin is proposed. It points out in the process of coal measures deposition 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 evolution of plants,and then cause the alternating evolution of swamp and terrigenous system in the basin.
引文
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[14]王谋,李勇,黄润秋,等.青藏高原腹地植物碳同位素组成对环境条件的响应[J].山地学报,2005,23(3):274-279.Wang Mou,Li Yong,Huang Runqiu,et al.The responses of floral carbonate isotopic compositions of the central Qinghai-Tibet plateau plants to environmental conditions[J].Journal of Mountain Science,2005,23(3):274-279.
[15]Stuiver Minze,Braziunas F Thomas.Tree cellulose13C/12C isotope ratios and climatic change[J].Nature,1987,328:58-60.
[16]Leary O M H.Carbon isotopes fractionation plants[J].Phytochemistry,1981,20(4):553-567.
[17]Wilson T A,Grinsted J M.12C/13C in cellulose and lignin as palaeothermometers[J].Nature,1977,26:133-135.
[18]Smith N Bruce,Epstein Samuel.Two categories of12C/13C ratios for higher plants[J].Plant Physiol,1971,47:380-384.
[19]Grocke R Darren.Distribution of C3and C4plants in the Late Pleistocene of South Australia recorded by isotope biogeochemistry of collagen in megafauna[J].Australian Journal of Botany,1997,45:607-617.
[20]Stach E.Stach’s textbook of Coal petrology,third revision.[M].Beijing,China Coal Industry Publishing House,1990.
[21]Park R,Epstein S.Metabolic fractionation of13C&12C in plants[J].Plant Physiology,1961,36:133-138.
[22]Rimmer S M,Rowe H D,Taulbee D N.Influence of maceral content onδ13C andδ15N in a Middle Pennsylvanian coal[J].Chemical geology,2006,225:77-90.
[23]谢庆宾,管守月.从岩相古地理看柴达木盆地侏罗系的油气前景[J].古地理学报,2003,5(4):475-484.Xie Qingbin,Guan Shiyue.Hydrocarbon potential of the Jurassic in Qaidam basin from the viewpoint of lithofacies palaeogeography[J].Journal of Palaeogeography,2003,5(4):475-484.
[24]Whiticar M J.Stable isotope geochemistry of coals,humic kerogens and related natural geses[J].International Journal of Coal Geology,1996,32:191-215.
[25]Rigby D,Batts B D,Smith J W.The effect of maturation on isotopic composition of fossil fuels[J].Organic Geochemistry,1981(3):29-36.
[26]Hesselbo S P,Morgans Bell H S,Mc Elwain J C.Carbon-cycle perturbation in the Middle Jurassic and accompanying changes in the terrestrial paleoenvironment[J].The Journal of Geology,2003,111(3):259-276.
[27]黄曼,邵龙义,鲁静,等.柴北缘老高泉地区侏罗纪含煤岩系层序地层特征[J].煤炭学报,2007,32(5):485-489.Huang Man,Shao Longyi,Lu Jing,et al.The sequence stratigraphy of the Middle Jurassic coal measures in the Laogaoquan region of the Northern Qaidam basin[J].Journal of China Coal Society,2007,32(5):485-489.
[2]邵龙义,鲁静,汪浩,等.中国含煤岩系层序地层学研究进展[J].沉积学报,2009,27(5):904-914.Shao Longyi,Lu Jing,Wang Hao,et al.Developments of coal measures sequence stratigraphy in China[J].Acta Sedimentologica Sinica,2009,27(5):904-914.
[3]桑树勋,陈世悦,刘焕杰.华北晚古生代成煤环境与成煤模式多样性研究[J].地质科学,2001,36(2):212-221.Sang Shuxun,Chen Shiyue,Liu Huanjie.Study on diversity of Late Paleozoiv coal-forming environments and models in North China[J].Chinese Journal of Geology,2001,36(2):212-221.
[4]梅冥相,刘少峰.基于陆生植被对河流沉积作用的影响论上三叠统须家河组的冲积构架:以重庆永川普安剖面为例[J].古地理学报,2013,15(2):5-11.Mei Mingxiang,Liu Shaofeng.Discussion of alluvial architecture for the Upper Triassic Xujiahe Formation in terms of sendimentological impact of terrestrial vegetation on fluvial sedimentation:A case study at Pu’an Section in Yongchuan of Chongqing[J].Journal of Palaeogeography,2013,15(2):5-11.
[5]Berner R A.The effect of the rise of land plants on atmospheric CO2during the Paleozoic[A].Gensel P G,Edwards D.Plant invade the land[C].New York:Columbia University Press,1997:173-178.
[6]秦勇,王文峰,李壮福,等.海侵作用影响下的高分辨煤相序列及其古泥炭沼泽发育模式:以山西北部安太堡上石炭统太原组11号煤层为例[J].地质学报,2008,82(2):234-246.Qin Yong,Wang Wenfeng,Li Zhuangfu,et al.High resolution coal facies sequence and peat paleo-bog pattern during the transgression[J].Acta Geological Sinica,2008,82(2):234-246.
[7]孙枢,王成善.“深时”(Deep Time)研究与沉积学[J].沉积学报,2009,27(5):792-810.Sun Shu,Wang Chengshan.Deep time and sedimentology[J].Acta Sedimentologica Sinica,2009,27(5):792-810.
[8]杨永泰,张宝民,席萍,等.柴达木盆地北缘侏罗系展布规律新认识[J].地层学杂志,2001,25(2):154-158.Yang Yongtai,Zhang Baomin,Xi Ping,et al.New knowledge about distribution of the Jurassic Strata along North Margin of Qaidam basin[J].Journal of Stratigraphy,2001,25(2):154-158.
[9]刘天绩,邵龙义,曹代勇,等.柴达木盆地北缘侏罗系煤炭资源形成条件及资源评价[M].北京:地质出版社,2013.
[10]鲁静,邵龙义,王占刚,等.柴北缘侏罗纪煤层有机碳同位素组成与古气候[J].中国矿业大学学报,2014,43(4):599-605.Lu Jing,Shao Longyi,Wang Zhangang,et al.Organic carbon isotope composition and paleoclimate evolution of Jurassic coal seam in Northern Qaidam basin[J].Journal of China University of Mining&Technology,2014,43(4):599-605.
[11]Hesselbo P Stephen,Robinson A Stuart,Surlyk Finn,et al.Terrestrial and marine extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbation:A link to initiation of massive volcanism[J].Geology,2002,30:251-254.
[12]Freyer D H.Recent13C/12C trends in atmospheric CO2and tree rings[J].Nature,1981,293:679-680.
[13]Berner,R A.Geocarbsulf:a combined model for Phanerozoic atmospheric O2and CO2[J].Geochimica et Cosmochimica Acta,2006,70:5653-5664.
[14]王谋,李勇,黄润秋,等.青藏高原腹地植物碳同位素组成对环境条件的响应[J].山地学报,2005,23(3):274-279.Wang Mou,Li Yong,Huang Runqiu,et al.The responses of floral carbonate isotopic compositions of the central Qinghai-Tibet plateau plants to environmental conditions[J].Journal of Mountain Science,2005,23(3):274-279.
[15]Stuiver Minze,Braziunas F Thomas.Tree cellulose13C/12C isotope ratios and climatic change[J].Nature,1987,328:58-60.
[16]Leary O M H.Carbon isotopes fractionation plants[J].Phytochemistry,1981,20(4):553-567.
[17]Wilson T A,Grinsted J M.12C/13C in cellulose and lignin as palaeothermometers[J].Nature,1977,26:133-135.
[18]Smith N Bruce,Epstein Samuel.Two categories of12C/13C ratios for higher plants[J].Plant Physiol,1971,47:380-384.
[19]Grocke R Darren.Distribution of C3and C4plants in the Late Pleistocene of South Australia recorded by isotope biogeochemistry of collagen in megafauna[J].Australian Journal of Botany,1997,45:607-617.
[20]Stach E.Stach’s textbook of Coal petrology,third revision.[M].Beijing,China Coal Industry Publishing House,1990.
[21]Park R,Epstein S.Metabolic fractionation of13C&12C in plants[J].Plant Physiology,1961,36:133-138.
[22]Rimmer S M,Rowe H D,Taulbee D N.Influence of maceral content onδ13C andδ15N in a Middle Pennsylvanian coal[J].Chemical geology,2006,225:77-90.
[23]谢庆宾,管守月.从岩相古地理看柴达木盆地侏罗系的油气前景[J].古地理学报,2003,5(4):475-484.Xie Qingbin,Guan Shiyue.Hydrocarbon potential of the Jurassic in Qaidam basin from the viewpoint of lithofacies palaeogeography[J].Journal of Palaeogeography,2003,5(4):475-484.
[24]Whiticar M J.Stable isotope geochemistry of coals,humic kerogens and related natural geses[J].International Journal of Coal Geology,1996,32:191-215.
[25]Rigby D,Batts B D,Smith J W.The effect of maturation on isotopic composition of fossil fuels[J].Organic Geochemistry,1981(3):29-36.
[26]Hesselbo S P,Morgans Bell H S,Mc Elwain J C.Carbon-cycle perturbation in the Middle Jurassic and accompanying changes in the terrestrial paleoenvironment[J].The Journal of Geology,2003,111(3):259-276.
[27]黄曼,邵龙义,鲁静,等.柴北缘老高泉地区侏罗纪含煤岩系层序地层特征[J].煤炭学报,2007,32(5):485-489.Huang Man,Shao Longyi,Lu Jing,et al.The sequence stratigraphy of the Middle Jurassic coal measures in the Laogaoquan region of the Northern Qaidam basin[J].Journal of China Coal Society,2007,32(5):485-489.