文章快速检索    
 
  中国地质 2022, Vol. 49 Issue (2): 643-654  
0
引用本文
许云, 张宁, 赵存良, 梁汉东, 孙玉壮. 2022. 鄂尔多斯盆地侏罗纪煤中古野火事件及其对古气候的影响[J]. 中国地质, 49(2): 643-654.  
Xu Yun, Zhang Ning, Zhao Cunliang, Liang Handong, Sun Yuzhuang. 2022. Wildfires in Jurassic Coal Seams from Ordos Basin and its impact on Paleoclimate[J]. Geology in China, 49(2): 643-654. (in Chinese with English abstract).  

鄂尔多斯盆地侏罗纪煤中古野火事件及其对古气候的影响
许云1, 张宁2, 赵存良1, 梁汉东3, 孙玉壮1    
1. 河北工程大学河北省资源勘测研究重点实验室,河北 邯郸 056038;
2. 中国煤炭地质总局第一勘探局地质勘查院,河北 邯郸 056004;
3. 中国矿业大学(北京)煤炭资源与安全开采国家重点实验室,北京 100083
摘要[研究目的] 野火是陆地生态系统的一个重要组成部分,燃烧产生的温室气体会对气候环境产生影响。对地史时期古野火的研究可以获得野火对生态系统的潜在长期影响。[研究方法] 采集了鄂尔多斯盆地侏罗纪延安组5个主采煤层的56个样品,并对其进行了宏观煤岩观察、煤岩显微组分定量、惰质组反射率测定、微观形貌观察。[研究结果] 结果显示在煤层的顶底板中存在大量的宏观化石木炭(Charcoal),且细胞间层均为同质化; 煤中惰质组含量分布范围为45.23%~56.81%,且大部分惰质组反射率低于2%。[结论] 这表明在泥炭沉积时期发生过高频率的野火事件且以中低温的地表火为主。根据现代森林火灾碳排放模型和煤中的惰质组由燃烧成因理论,计算出仅在鄂尔多斯盆地延安组泥炭系统中野火释放的总碳量为443 Gt,其中CO2的量为1377 Gt,CO的量为86.7 Gt,CH4的量为8.2 Gt,CO2的释放量相当于目前大气圈中CO2总量的45.9%。延安组时期陆地生态系统中野火释放的巨量温室气体可能是导致这一时期气候变暖的原因之一。
关键词CO2排放    古野火    煤炭    煤田    侏罗纪    古气候    煤炭勘查工程    鄂尔多斯盆地    
中图分类号:P534.52;P618.11;P532            文献标志码:A             文章编号:1000-3657(2022)02-0643-
Wildfires in Jurassic Coal Seams from Ordos Basin and its impact on Paleoclimate
XU Yun1, ZHANG Ning2, ZHAO Cunliang1, LIANG Handong3, SUN Yuzhuang1    
1. Key Laboratory of Resource Exploration Research of Hebei, Hebei University of Engineering, Handan 056038, Hebei, China;
2. First Exploration Bureau, China National Administration of Coal Geology, Handan 056004, Hebei, China;
3. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology (Beijing), Beijing 100083, China
Abstract: This paper is the result of coalfield geological survey engineering.
[Objective] Wildfire is an important part of the earth system. The greenhouse gases produced by combustion will have an impact on the climate and the biosphere. One way to obtain information about the potential long term influences of wildfires on ecosystems and the climate system itself is to study palaeo-wildfires. [Methods] A total of 56 Jurassic coal samples from 5 main coal seams were collected from Northern Ordos Basin. The samples were analyzed by macropetrography, microscope, scanning electron microscope in order to study the evidences of wildfire and their impact on the paleoclimate. [Results] The results showed that a great deal of charcoal has been found in the roof and floor of the middle Jurassic coal from Ordos Basin and the cell walls of charcoal observed under SEM were homogenized. The average proportions of inertinite in the coal samples ranged from 45.23% to 56.81%, and the reflectance of most inertinite in coal is less than 2%, which indicated that the frequency wildfires occurred during the peat deposition period and the fires type were dominated by surface and ground fires with low temperature. [Conclusions] According to a carbon emission model for modern forest fires, the total carbon and gas emissions from wildfires in peat swamps of the Middle Jurassic in Northwest China were calculated. The total carbon released from peat-swamp forest wildfires was at least 443 Gt, corresponding to emissions of CO2, CO and CH4 of 1377 Gt, 86.7 Gt, and 8.26 Gt, respectively. The large amount of greenhouse gases released by wildfires may lead to changes of the atmospheric, which may have accelerated the process of climate warming in the Middle Jurassic.
Key words: CO2 reduction    Paleowildfire    coal    coal field    Jurassic    paleoclimate    coal exploration engineering    Ordos Basin    

1 引言

古野火指的是发生在第四纪之前的燃烧事件(Scott, 2000)。自从泥盆纪植物登陆以来,野火就开始在陆地广泛存在,成为地球系统中一个重要组成部分(Scott and Jones, 1994; Finkelstein et al., 2005; Bowman et al., 2009; Scott et al., 2010; 占长林等,2011; 沈文杰等,2012; Brown et al., 2012; Glasspool et al., 2015; 宋建中等,2015; Sun et al., 2017;刘红叶等, 2018)。研究表明燃烧释放的温室气体和颗粒物对气候变化有着重要的影响,如1997年的印度尼西亚森林大火释放了0.8~2.6 Gt的CO2,可能导致了全球变暖(Page et al., 2002)。将今论古,在地史时期由古野火释放的温室气体也将会对古气候产生影响。指示古野火事件的指标——黑炭是由不完全燃烧产生的一系列粒径连续的固体残留物,由于黑炭具有稳定的芳香性结构和抗氧化性,因此可以长期保存在沉积地层中(Scott and Jones, 1991)。古生态学将保存在地层中的粒径在mm和μm级别的黑炭称为化石木炭(Charcoal)(Masiello,2004),通过对化石木炭的研究可以重建古野火历史和恢复古环境,微观化石木炭(< 180 μm)常被用来进行孢粉计数统计分析古野火的发生频率(Clark,1996; Scott,2010),宏观化石木炭(>180 μm)在扫描电镜下可以提供早期植物的解剖学特征,为植物的演化过程提供信息(Schönenberger,2005),通过对炭化的叶片中的气孔密度研究可以反演古大气中的CO2浓度(Royer, 2001; Yan et al., 2009),通过对宏观化石木炭反射率的测定可以反演古野火类型,从而推测地史时期大气中O2的浓度(Petersen and Lindström,2012;Glasspool et al., 2015)。通过对化石木炭的定量研究和放射性碳同位素有助于了解生态系统中的碳循环和形成年代(Bird,1999)等。

黑炭在煤岩学分类中属于惰质组(Scott and Glasspool, 2007; Sun et al., 2017)。对于煤中惰质组的成因有两种观点,一种观点认为惰质组是有机质在泥炭化作用阶段经氧化蚀变形成(韩德馨等,1996; Hower et al., 2011, 2013),另一种观点认为惰质组是由不完全燃烧形成。近年来很多学者通过实验证明煤中的惰质组为不完全燃烧产物,等同于化石木炭(Scott, 1991, 1994; Guo and Bustin, 1998; Scott and Glasspool, 2007)。经过20多年的争论,惰质组是植物不完全燃烧的产物这一观点得到了越来越多学者的认同(Diessel,2010; Scott,2010; Shao et al., 2012; Yan et al., 2016; Sun et al., 2017)。随着对煤中惰质组成因的重新认识,蕴含在煤中的古野火信息越来越受到重视。

目前对古野火的研究主要集中在大的生物灭绝时期,如二叠纪—三叠纪、白垩纪—古近纪界限时期(Uhl et al., 2004, 2014;Jasper et al., 2008; Shen et al., 2011; Brown et al., 2012; Kauffmann et al., 2016; Shivanna et al., 2017; Sun et al., 2017),而对侏罗纪时期的古野火事件研究较少,对于来自煤中的古野火信息更是寥寥无几。侏罗纪是全球重要的成煤期,我国的侏罗纪煤占全国煤炭资源总量的2/3(韩德馨等,1996; 黄文辉等,2010),这为研究蕴含在煤中的侏罗纪野火信息提供了条件。侏罗纪全球大气中CO2浓度是目前大气中CO2浓度的4倍(Berner,2006; Sellwood and Valdes, 2008),属于典型的温室气候时期。目前对计算古野火释放的温室气体量和野火对侏罗纪气候环境影响等领域研究较少,基于此本文通过对鄂尔多斯盆地的中侏罗统延安组的煤层进行采样对上述问题进行了探讨。

2 地质背景

鄂尔多斯盆地位于华北克拉通西部,是中国重要的能源及矿产基地。根据构造形态和盆地演化历史,鄂尔多斯盆地可划分为伊盟隆起、渭北隆起、西缘冲断带、晋西挠褶带、天环坳陷、陕北斜坡等6个构造单元。研究区位于鄂尔多斯盆地东北部东胜和神木地区(图 1),区内岩浆活动不发育,出露地层以中、新生代地层为主(张泓等,1995)。盆地内侏罗纪地层较为稳定,为一套内陆湖泊相沉积。由下而上为富县组、延安组、直罗组、安定组和芬芳河组,其中主要含煤地层为延安组。延安组主要为一套河流、湖泊三角洲和湖泊沉积,岩石粒度总体表现较细,除底部常有砂砾岩、砾岩外,很少有粗碎屑岩,少数地区尚有泥灰岩及菱铁质岩透镜体(王双明等,1999)。鄂尔多斯盆地北缘的延安组地层普遍含煤5组且多为中、厚煤层; 南部可采煤层少,通常为1~2层。王双明等(1999)根据鄂尔多斯盆地不同区域地层的垂向变化,根据岩石的粒度特征,岩性组成,煤层的发育特征等将延安组自下而上分为五段(图 2),前人通过对鄂尔多斯盆地侏罗纪时代划分认为延安组对应中侏罗统早期的阿伦阶—巴柔阶,时间跨度为174.10~168.3 Ma(邓胜徽等,2017)。

图 1 鄂尔多斯盆地构造纲要图(据刘池洋等,2006) Fig. 1 Tectonic outline of Ordos Basin (after Liu Chiyang et al., 2006)
图 2 鄂尔多斯盆地延安组地层柱状图(据邓胜徽等,2017 Fig. 2 Stratigraphic section of the Yan'an Formation in Ordos Basin (after Deng Shenghui et al., 2017)
3 采样与测试方法

本次工作采集了神木—东胜矿区的7个主采煤层的顶底板及煤层样品共56个,其中52煤层煤样采自红柳林煤矿,51煤层煤样采自郭家湾煤矿,43和42煤层煤样采自凉水井煤矿,31煤层煤样采自寸草塔二矿,22煤层煤样采自哈拉沟煤矿,12煤层煤样采自补连塔煤矿。

根据显微煤岩类型测定方法(GB/T 15590-2008)对显微煤岩类型的测试要求对煤光片进行镜下显微组分观测,偏反光显微镜型号为Leica DM2500P,并用CRAIC软件对煤中的镜质组和惰质组分进行反射率测定。

用场发射扫描电镜(FE-SEM,FEI QuantaTM 650 FEG)观察煤层顶底板中化石木炭的植物细胞的炭化程度。煤样被喷金镀膜,在60~90 Pa的低真空条件下观测,工具距离是10 mm,射束电压20 kV。

4 结果 4.1 煤层顶底板中的化石木炭和煤中的丝炭

根据Scott(2010)对地层中化石木炭的宏观鉴定特征,在采集的7层煤的顶底板中均发现了大量的宏观化石木炭(图 3),煤层顶底板中的化石木炭呈黑色,少数具有丝绢光泽,其形态多样,有立方块状、条带状、长条状等,这些粒径较大的宏观化石木炭是植物燃烧时释放水分,收缩开裂形成的不完全燃烧碎块被水流携带到低洼处和碎屑物同期沉积形成。

图 3 煤层顶底板中的化石木炭 a—12煤层顶板中的化石木炭;b—12煤层底板中的化石木炭;c—22煤层顶板中的化石木炭;d—22煤层底板中的化石木炭;e—31煤层顶板中的化石木炭;f—31煤层底板中的化石木炭;g—42煤层顶板中的化石木炭;h—42煤层底板中的化石木炭;i—43煤层顶板中的化石木炭;j—43煤层底板中的化石木炭;k—51煤层顶板中的化石木炭;l—51煤层底板中的化石木炭 Fig. 3 Charcoal in the rock of roof/floor of the middle Jurassic coal in Ordos Basin a-Charcoal in the roof of 12 coalseam; b-Charcoal in the floor of 12 coalseam; c-Charcoal in the roof of 22 coalseam; d-Charcoal in the floor of 22 coalseam; e-Charcoal in the roof of 31 coalseam; f-Charcoal in the floor of 31 coalseam; g-Charcoal in the roof of 42 coalseam; h-Charcoal in the floor of 42 coalseam; i-Charcoal in the roof of 43 coalseam; j-Charcoal in the floor of 43 coalseam; k-Charcoal in the roof of 51coalseam; l-Charcoal in the floor of 51 coalseam

煤层中的丝炭在剖面上呈薄层状、透镜状分布在煤层中(5~20 mm)(图 4a~c),平面上丝炭还以块状分布在煤层中,具有无定向排列的特征,粒度大,具有明显的原地堆积或微异地堆积的特征(图 4d~f)。丝炭层在外力敲击下极易开裂并碎成粉末,黑色,污手,部分具有丝绢光泽。

图 4 煤中的丝炭和丝炭的扫描电镜图片 a、b、c—煤层中呈薄层状的丝炭;d、e、f—平面上块状的丝炭;g、h、i、j、k、l分别为12, 22, 31, 42, 43和51煤中丝炭在扫描电镜下呈均质化的细胞间层 Fig. 4 Fusian (Charcoal) in the coal and the scanning electron microscope micrographs of fusian a, b, c-Fusain layer in vertical coalseam; d, e, f-Fusain in horizontal coalseam. g, h, i, j, k, l were the scanning electron micrograph of homogeneous cell walls of charcoal, which were taken from the 12, 22, 31, 42, 43 and 51 coal seams, respectively
4.2 煤中的惰质组

在本次研究的各煤层中镜质体反射率平均值分布范围为0.46%~0.55%(表 1),变质程度较低属于低-中煤级煤。在三大显微组分中,镜质组含量分布范围为39.85%~53.77%,惰质组含量分布范围为45.23%~56.81%,壳质组含量分布范围为0.85%~1.73%。在研究的煤层中惰质组主要以半丝质体和丝质体为主,其次为惰屑体、粗粒体,少量微粒体,菌类体少见。在丝质体中大多细胞结构保存完好,大部分丝质体被压扁破坏,部分被挤压破碎形成“弧形”或“星状”,少数丝质体胞腔中被矿物质充填(图 5a~c)。半丝质体的颜色比丝质体颜色偏暗,其胞腔结构比丝质体保存差。研究区煤中惰质组反射率的分布范围为0.7%~5.23%;除31煤中反射率在0.7%~2%的惰质组占总惰质组含量小于70%外,其余煤层中反射率在0.7%~2%的惰质组占总惰质组含量均大于70%,各煤层惰质组反射率的分布特征和对应的温度见表 2

表 1 煤中显微煤岩组分含量(%) Table 1 Maceral composition of the coals from the studied areas (%)
图 5 煤中的丝质体、天然木炭和天然焦 a、b、c—煤中的丝质体;d、e、f—煤中的天然木炭;g—22煤中的天然焦颗粒;h—31煤中的天然焦颗粒 Fig. 5 Inertinite, nature char and nature coke in coal seams a, b, c—Inertinite; d, e, f—Nature char; g—Nature coke in 22 coal seam; h—Nature coke in 31 coalseam
表 2 研究区煤中惰质组反射率及燃烧温度 Table 2 The inertinite reflectance and combustion temperature of coal from studied area
5 讨论 5.1 古野火存在的证据

宏观煤岩组分中的丝炭、显微煤岩组分中的惰质组和煤层顶底板中大量分布的化石木炭均表明在泥炭沉积时期发生过广泛的野火事件。与中国北方晚石炭系(< 25%;韩德馨,1996)和中二叠统(40%~51%;韩德馨,1996)煤中惰质组的含量相比,研究区煤中的惰质组含量(45.23%~56.81%)明显偏高,同时也明显高于南方晚二叠世煤中惰质组的含量(< 30%;Diessel,2010)。在当前的环境下泥炭中的惰质组含量为4.27%(Glasspool et al., 2015),而研究区煤中的惰质组含量远远高于这一数值,这表明在延安组泥炭沉积时期,野火的发生频率要远高于当前环境下泥炭中的野火发生频率。

Kwiecińska and Petersen(2004)认为natural char是煤或泥炭中的有机质受野火的影响热变质形成,其反射率不仅高于煤中的镜质组和壳质组的反射率,而且还要明显高于煤中惰质组的反射率,且natural char具有多孔性,这些孔洞大小、形态均不规则。现代研究表明natural char等同于化石木炭(Scott, 2010; Degani-Schmidt et al., 2015)。广泛分布在煤中的具有高反射率的nature char(图 5d~f)表明在泥炭形成时期均发生过古野火事件。

天然焦是用来描述受侵入体的热影响而产生局部变质的煤,除此之外天然焦也可以由燃烧形成(Kwiecińska and Petersen, 2004)。在采集的所有煤层中仅在31煤和22煤中发现了少量的天然焦颗粒。受侵入体影响形成的天然焦一般沿接触带分布,分布范围在几公里到几米之间,而在31煤和22煤中出现的天然焦以较小的且孤立的颗粒状分布在煤中(图 5, g~h),这表明这些天然焦颗粒是在泥炭沉积时期形成。地质资料显示研究区在泥炭形成时期和成煤后期均未发现岩浆活动,且煤中镜质体反射率在0.5%左右,属于低煤阶煤,因此煤中的天然焦颗粒是由高温燃烧形成而非受岩浆热变质而成。吴传荣等(1995)也发现在中国西北地区中侏罗世未受岩浆活动影响的煤中出现了小球体、热解碳、镶嵌体等各向异性体。Kwiecińska and Petersen(2004)认为这些小球体、热解碳、镶嵌体同样为天然焦颗粒,这表明在中侏罗世中国西北地区发生过大范围的古野火事件,研究区的古野火可能是其中的一部分。

5.2 古野火类型

根据燃料在空间的分布特征分为空中燃料,地表燃料和地面燃料,对应的燃料类型分为树冠火,地表火和地面火(Scott et al., 1994)。树冠火温度较高可达到800℃以上,主要产生微观的化石木炭。地表火温度一般在200~700℃,产生大量的宏观化石木炭。地面火的燃烧温度一般比较低(< 350℃),燃烧产物以宏观化石木炭为主(Petersen and Lindström,2012;Brown et al., 2012)。目前对古野火的燃烧温度及类型的研究主要来自于对不完全燃烧产生的化石木炭反射率的测定、木质细胞的均质化程度来大致估算。

实验表明煤中惰质组的反射率与燃烧温度呈正相关,即燃烧温度越高,形成的惰质组反射率越高(Guo and Bustin, 1998; Scott and Glasspool, 2007)。尽管惰质组反射率和燃烧温度不是完全的线性关系,但是燃烧温度大致可以通过公式(1)进行计算(Petersen and Lindström,2012)。

(1)

T为燃烧温度,Ro为测量出的惰质组反射率。在研究区的5层煤中惰质组反射率的分布基本一致,以低反射率(< 2%)的惰质组为主(表 2),这表明野火主要以中低温的地表火和地面火为主。尽管有高反射率的惰质组出现,如在31煤层中反射率>4%的惰质组含量最高,但也仅为4%,这表明在31层泥炭沉积形成时期发生的高温野火频率相对于其他泥炭层较高,但主要还是以地面火及地表火为主。在煤层顶底板中发现的大量的宏观化石木炭(图 3)也表明在泥炭沉积时期的野火以中低温的地面火和地表火为主。

在炭化过程中植物细胞壁的形态也会发生明显的变化,当燃烧温度低于300℃时,在扫描电镜下能够看到细胞的胞间层,当温度高于325℃时绝大部分植物细胞壁都变为均质化,当温度超过600℃时细胞壁会变成碎片,这些细小的碎片就是煤岩显微组分中的碎屑惰质组(Scott and Jones, 1991; Scott,2000; Scott and Glasspool, 2007)。本次采集的煤样在扫描电镜下观察发现细胞间层均为同质化(图 4,g~l),这表明中侏罗世在鄂尔多斯盆地北部泥炭沉积时期发生的古野火的温度在325~600℃,以中低温的地面火和地表火为主。

5.3 古野火释放的温室气体

燃烧过程中产生的大量温室气体对区域乃至全球碳平衡具有不可忽视的作用,同时也是现代大气中温室气体的主要来源之一(Crutzen et al., 1990; Moraes et al., 2004),目前计算森林野火导致的碳排量是在Seiler(1980)提出的公式基础上逐步完善的,生物质燃料燃烧过程中排放的总碳量计算公式为:

(2)

Ct为可燃物燃烧过程中排放的总碳量(t),M为在火灾事件中损失的可燃物载量(t),fc为可燃物中的含碳率,β为生物质燃料的燃烧效率,即单位面积森林燃烧过程中燃烧损失的可燃物占燃烧前可燃物的比例,是决定燃烧碳排放量的重要系数。

(3)

Es为某种含碳气体的排放量(g),Efs为某种含碳气体的排放因子(g/kg)。式(2)为燃烧过程中排放的总碳量,则不完全燃烧形成的残余固体物应为:

(4)

R为不完全燃烧残留物的总碳量(t),实验证明煤中的惰质组为不完全燃烧产生的固体残留物(Guo and Bustin, 1998; Scott and Glasspool, 2007),燃烧效率β取政府间气候变化专门委员会(IPCC)的经验估计值0.45(王效科等,1998; 常禹等,2015); 含碳率fc取国内外通用值0.5(刘晓东和王博,2017); 在侏罗纪成煤期中国北方地区主要处于亚热带—暖温带气候区域,植被类型主要为针、阔叶混交林(钟筱春等,2003),气体的排放因子Efs参考胡海清等(2012)测量的针叶-阔叶混交林排放因子的平均值计算,CO2排放因子取值3107.9 g/kg,CO排放因子取值为195.7 g/kg,CH4的排放因子取值为18.6 g/kg。中国鄂尔多斯盆地侏罗纪煤炭资源量为1487.66 Gt(黄文辉等,2010),煤中惰质组含量按最低值36.4%计算(韩德馨等,1996),将上述参数带入到公式(2)(3)(4)中,经计算侏罗纪煤中惰质组形成时向大气中排放的总碳量为443 Gt,其中CO2的量为1377 Gt,CO的量为86.7 Gt,CH4的量为8.2 Gt。在本次计算采用的煤炭资源量仅为鄂尔多斯盆地侏罗纪2000 m以浅地层中的煤炭储量,不包含不具备工业开采价值的薄煤层资源量和2000 m以深的煤炭资源量,因此实际释放量应该比计算数值更大。

5.4 古野火对侏罗纪古气候的影响

在鄂尔多斯盆地中侏罗世大气中CO2的浓度在1.2×10-3~1.6×10-3,为目前大气圈中CO2浓度的3~4倍(Yan et al., 2009; Wu et al., 2016; 金培红,2017)。根据Sellwood and Valdes(2008)的大气环流模型,在早、中侏罗世全球气温比现代高5~10℃,海水温度比现代高8℃。中国北方在侏罗纪发生了显著的升温事件,从早侏罗世的普林斯巴赫期开始至中侏罗世巴通期结束,高峰发生在中侏罗世阿伦期至巴柔期(钟筱春等,2003),与此同时大气中的CO2含量持续上升(Diessel,2010; 鲁静等,2016),这与延安组泥炭沉积时期一致(图 6)。温室气体特别是CO2被认为是在较短的时期内影响气候变化的主要原因,除此之外燃烧释放的黑碳气溶胶能够强烈吸收太阳辐射,影响辐射平衡,被认为是仅次于温室气体的全球变暖因素(Bowman et al., 2009)。鄂尔多斯盆地侏罗纪仅由泥炭沼泽系统中的野火释放的CO2量就相当于目前大气圈中CO2(3000 Gt)总量的45.9%。中国侏罗纪煤炭资源量丰富,约占全国煤炭资源总量的2/3;侏罗纪时期在全球范围内煤主要发育在南、北纬40度至极地地区,主要分布在华北陆块、西伯利亚板块、北美洲板块、澳大利亚板块及南极洲板块,寒带地区的西伯利亚北部也有分布(李江海,2013),因此在侏罗纪成煤期仅由泥炭沼泽区域的森林燃烧释放的温室气体应该是巨量的,同时陆地其他生态系统中野火也会释放大量的温室气体。尽管Ciarapica et al.(2006)认为晚三叠世—早侏罗世的气候变暖与中央大西洋岩浆区的火山活动以及其他导致甲烷水合物的排放增加的因素有关,但是在中侏罗世全球范围内由野火释放的温室气体量也是导致气候变化不可忽视的因素之一。

图 6 侏罗纪古大气CO2含量变化(据Diessel, 2010; 鲁静等, 2016 Fig. 6 Changing pattern of carbon dioxide in Jurassic palaeo-atmosphere (after Diessel, 2010; Lu Jing et al., 2016)
6 结论

(1)鄂尔多斯盆地延安组煤中高含量的惰质组、顶底板中的化石木炭均表明在延安组泥炭沼泽沉积时期发生过广泛的古野火事件,野火类型以中低温的地面火和地表火为主。

(2)根据现代森林火灾碳排放模型计算出仅在鄂尔多斯盆地中侏罗世泥炭沼泽中森林野火释放的CO2的量为1377 Gt,为目前大气圈中CO2总量的45.9%。考虑到鄂尔多斯盆地的侏罗纪煤炭资源量仅为全球侏罗纪煤炭资源量的一小部分,因此在全球范围野火释放的温室气体应该是巨量的。野火释放的CO2可能是导致中侏罗世大气中CO2浓度上升,气候变暖的因素之一。

参考文献
Berner R A. 2006. GEOCARBSULF: A combined model for Phanerozoic atmospheric O2 and CO2[J]. Geochimica et Cosmochimica Acta, 70(23): 5653-5664. DOI:10.1016/j.gca.2005.11.032
Bowman D M J S, Balch J K, Artaxo P. 2009. Fire in the Earth System[J]. Science, 324(5926): 481-484. DOI:10.1126/science.1163886
Brown S A E, Scott A C, Glasspool I J, Collinson M E. 2012. Cretaceous wildfires and their impact on the Earth system[J]. Cretaceous Research, 36: 162-190. DOI:10.1016/j.cretres.2012.02.008
Bird M I, Moyo C, Veenendaal E M. 1999. Stability of elemental carbon in a savanna soil[J]. Global Biogeochemical Cycles, 13(4): 923-932. DOI:10.1029/1999GB900067
Chang Yu, Huang Wentao, Hu Yuanman, Li Yuehui, Bu Rencang, Liu Yongyao. 2015. Contemporary research advances on carbon emissions by forest fires and future prospects[J]. Chinese Journal of Ecology, 34(10): 2922-2929 (in Chinese with English abstract).
Ciarapica F E, Giacchetta G. 2006. Managing the condition-based maintenance of a combined-cycle power plant: An approach using soft computing techniques[J]. Journal of Loss Prevention in the Process Industries, 19(4): 316-325. DOI:10.1016/j.jlp.2005.07.018
Crutzen P J, Andreae M O. 1990. Biomass burning in the tropics: Impact on atmospheric chemistry and biogeochemical cycles[J]. Science, 250: 1669-1678. DOI:10.1126/science.250.4988.1669
Degani-Schmidt I, Guerra-Sommer M, Mendonça J, Filho J, Jasper A. 2015. Charcoalified logs as evidence of hypautochthonous autochthonous wildfire events in a peat-forming environment from the Permian of southern Paraná Basin (Brazil)[J]. International Journal of Coal Geology, 146: 55-67. DOI:10.1016/j.coal.2015.05.002
Deng Shenghui, Lu Yuanzheng, Zhao Yi, Fan Ru, Wang Yongdong, Yang Xiaoju, Li Xin, Sun Bainian. 2017. The Jurassic palaeoclimate regionalization and evolution of China[J]. Earth Science Frontiers, 24(1): 106-142 (in Chinese with English abstract).
Diessel C F K. 2010. The stratigraphic distribution of inertinite[J]. International Journal of Coal, Geology, 81(4): 251-268. DOI:10.1016/j.coal.2009.04.004
Finkelstein D B, Pratt L M, Curtin T M, Brassell S C. 2005. Wildfires and seasonal aridity recorded in Late Cretaceous strata from south-eastern Arizona[J]. USA Sedimentology, 52(3): 587-599. DOI:10.1111/j.1365-3091.2005.00712.x
Glasspool I J, Scott A C, Waltham D, Pronina N, Shao L. 2015. The impact of fire on the Late Paleozoic[J]. Earth System Frontiers in Plant Science, 6: 756.
Guo Y, Bustin R M. 1998. Fire spectroscopy and reflectance of modern charcoals and fungal decayed woods: implications for studies of inertinite in coals[J]. International Journal of Coal Geology, 37(1-2): 29-53. DOI:10.1016/S0166-5162(98)00019-6
Han Dexin, Ren Deyi, Wang Yanbin, Jin Kuili, Mao Heling, Qin Yong. 1996. Coal Petrology of China[M]. Xuzhou: China Mining University Press, 140-146 (in Chinese with English abstract).
Hower J C, Misz-Keenan M, O"Keefe J M K, Mastalerz M, Eble C F, Garrison T M. 2013. Macrinite forms in Pennsylvanian coals[J]. International Journal of Coal Geology, 116/117: 172-181. DOI:10.1016/j.coal.2013.07.017
Hower J C, O"Keefe J M K, Eble C F, Raymond A, Valentim B, Volk T J. 2011. Notes on the origin of inertinite macerals in coal: Evidence for fungal and arthropod transformations of degraded macerals[J]. International Journal of Coal Geology, 86(2/3): 231-240.
Hu Haiqing, Wei Shujing, Sun Long. 2012. Estimation of carbon emissions due to forest fire in Daxing'an mountains from 1965 to 2010[J]. Chinese Journal of Plant Ecology, 36(7): 629-644 (in Chinese with English abstract).
Huang Wenhui, Ao Weihua, Weng Chengmin, Xiao Xiuling, Liu Dameng, Tang Xiuyi, Chen Ping, Zhao Zhigen, Wan Xin, Finkelman Bob. 2010. Characteristics of coal petrology and genesis of Jurassic coal in Ordos Basin[J]. Geoscience, 24(6): 1186-1197 (in Chinese with English abstract).
Jasper A, Uhl D, Guerra-Sommer M, Mosbrugger V. 2008. Palaeobotanical evidence of wildfires in the Late Palaeozoic of South America - Early Permian, Rio Bonito Formation, Paraná Basin, Rio Grande do Sul, Brazil[J]. Journal of South American Earth Sciences, 26(4): 435-444. DOI:10.1016/j.jsames.2008.08.002
Jin Peihong, Dong Junling, Wang Zixi, Yuan Jidong, Mao Ziqiang, Li Yuqiong, Sun Bainian. 2017. Middle Jurassic ginkgophyte fossils from the Gucheng coal mine of the Junger Banner, Inner Mongolia and indications of the paleo-CO2 concentration[J]. Journal of Lanzhou University: Natural Sciences, 53(1): 1-9 (in Chinese with English abstract).
Kauffmann M, Jasper André, Uhl D, Meneghini J, Osterkamp I C, Zvirtes G. 2016. Evidence for palaeo-wildfire in the Late Permian palaeotropics-Charcoal from the Motuca Formation in the Parnaíba Basin, Brazil[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 450: 122-128. DOI:10.1016/j.palaeo.2016.03.005
Kwiecińska B, Petersen H I. 2004. Graphite, semi-graphite, natural coke, natural char classification—ICCP system[J]. International Journal of Coal Geology, 57(2): 99-116. DOI:10.1016/j.coal.2003.09.003
Li Jianghai, Jiang Hongfu. 2013. Global Paleoplate Reconstruction, Lithofacies Paleogeography and Paleoenvironment Atlas[M]. Beijing: Geological Publishing House, 43 (in Chinese).
Liu Chiyang, Zhao Hongge, Gui Xiaojun, Yue Leping, Zhao Junfeng, Wang Jianqiang. 2006. Space-time coordinate of the evolution and reformation and mineralization response in Ordos Basin[J]. Acta Geologica Sinica, 80(5): 617-638 (in Chinese with English abstract).
Liu Hongye, Gu Yansheng, Cheng Shenggao, Huang Ting, Xiao He. 2018. Research advancement on the paleofire occurrences and its significance of global change since the last deglaciation[J]. Advances in Geosciences, 8(1): 106-119 (in Chinese with English abstract). DOI:10.12677/AG.2018.81012
Liu Xiaodong, Wang Bo. 2017. Review on the main emission products released by forest combustion[J]. Journal of Beijing Forestry University, 39(12): 118-124 (in Chinese with English abstract).
Lu Jing, Yang Minfang, Shao Longyi, Chen Shucong, Li Yonghong, Zhou Kai, Wang Wanqing. 2016. Paleoclimate change and sedimentary environment evolution, coal accumulation: A Middle Jurassic terrestrial[J]. Journal of China Coal Society, 41(7): 1788-1797 (in Chinese with English abstract).
Marynowski L, Simoneit B R T. 2009. Widespread Upper Triassic to Lower Jurassic wildfire records from Poland: Evidence from charcoal and pyrolytic polycyclic aromatic Hydrocarbons[J]. Palaios, 24(12): 785-798. DOI:10.2110/palo.2009.p09-044r
Masiello C A. 2004. New directions in black carbon organic geochemistry[J]. Marine Chemistry, 92(1/4): 201-213.
Moraes E C, Franchio S H, Rao V B. 2004. Effects of biomass burning inAmazonia on climate: A numerical experiment with a statistical-dynamical model[J]. Journal of Geophysical Research, 109: 1-12.
Page D S, Boehm P D, Douglas G S, Bence A E, Burns W A, Mankiewicz P J. 1999. Pyrogenic polycyclic aromatic hydrocarbons in sediments record past human activity: A case study in Prince William Sound, Alaska Marine[J]. Pollution Bulletin, 38: 247-260. DOI:10.1016/S0025-326X(98)00142-8
Page S E, Siegert F, Rieley J O, Boehm H D V, Jaya A, Limin S. 2002. The amount of carbon released from peat and forest fires in indonesia during 1997[J]. Nature (London), 420(6911): 61-65. DOI:10.1038/nature01131
Petersen H I, Lindström S. 2012. Synchronous wildfire activity rise and mire deforestation at the Triassic-Jurassic boundary[J]. PLoS ONE, 7(10): e47236. DOI:10.1371/journal.pone.0047236
Qin S, Gao K, Wang J, Li Y, Lu Q. 2016. Organic geochemistry of the Late Permian coals from the Huoshaopu and Jinjia Mines, Liupanshui Coalfield, China[J]. Energy Exploration & Exploitation, 34(6): 881-898.
Royer D L. 2001. Stomatal density and stomatal index as indicators of paleoatmospheric CO2 concentration[J]. Review of Palaeobotany and Palynology, 114(1): 1-28.
Schönenberger J. 2005. Rise from the ashes—the reconstruction of charcoal fossil owers[J]. Trends in Plant Science, 10(9): 436-443. DOI:10.1016/j.tplants.2005.07.006
Scott A C, Glasspool I J. 2007. Observations and experiments on the origin and formation of inertinite group macerals[J]. International Journal of Coal Geology, 70(1/3): 53-66.
Scott A C, Jones T P. 1991. Fossil charcoal: a plant-fossil record preserved by fire[J]. Geology Today, 7(6): 214-216. DOI:10.1111/j.1365-2451.1991.tb00806.x
Scott A C, Jones T P. 1994. The nature and influence of fire in carboniferous ecosystems[J]. Palaeogeography Palaeoclimatology Palaeoecology, 106: 91-112. DOI:10.1016/0031-0182(94)90005-1
Scott A C, Kenig F, Plotnick R E. 2010. Evidence of multiple late Bashkirian to early Moscovian (Pennsylvanian) fire events preserved in contemporaneous cave fills[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 291(1/2): 72-84.
Scott A C. 2000. The Pre-Quaternary history of fire[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 164(1): 281-329.
Scott A C. 2010. Charcoal recognition, taphonomy and uses in palaeoenvironmental analysis[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 291(1/2): 11-39.
Seiler W, Crutzen, P J. 1980. Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere from biomass burning[J]. Climatic Change, 2(3): 207-247. DOI:10.1007/BF00137988
Sellwood B W, Valdes P J. 2008. Jurassic climates[J]. Proceedings of the Ueologists Association, 119(1): 1-17. DOI:10.1016/S0016-7878(08)80256-8
Shao Longyi, Wang Hao, Yu Xiaohui, Liu Jing, Zhang Mingquan. 2012. Paleo-fires and atmospheric oxygen levels in the latest permian: Evidence from maceral compositions of coals in eastern yunnan, southern China[J]. Acta Geologica Sinica, 86(4): 949-962. DOI:10.1111/j.1755-6724.2012.00719.x
Shen W, Sun Y, Lin Y, Liu D, Chai P. 2011. Evidence for wildfire in the Meishan section and implications for Permian-Triassic events[J]. Geochimica et Cosmochimica Acta, 75(7): 1992-2006. DOI:10.1016/j.gca.2011.01.027
Shen Wenjie, Zhang Hua, Sun Yongge, Lin Yangting, Liang Ting, Yang Zhijun, Zhou Yongzhang. 2012. Evidences for the Permian-Triassic wildfire event: Review and appraisal[J]. Advances in Earth Science, 27(6): 613-623 (in Chinese with English abstract).
Shivanna M, Murthy S, Gautam S. 2017. Macroscopic charcoal remains as evidence of wildfire from Late Permian Gondwana sediments of India: Further contribution to global fossil charcoal database[J]. Palaeoworld, 26(4): 638-649. DOI:10.1016/j.palwor.2017.05.003
Song Jianzhong, Hu Jianfang, Peng Pingan, Wan Xiaoqiao. 2015. Black carbon record in ancient geological samples and its responses to the paleoclimate and paleoenvironment[J]. Chinese Journal of Nature, 37(2): 86-92 (in Chinese with English abstract).
Wang Shuangming, Zhang Yuping. 1999. Study on the formation, evolution and coal-accumulating regularity of the Jurassic Ordos basin[J]. Earth Science Frontiers, 6(1): 147-155 (in Chinese with English abstract).
Wang Xiaoke, Zhuang Yahui, Feng Zongwei. 1998. Estimation of carbon containing gases released from forest fire[J]. Advances in Environmental Science, 6(4): 1-15 (in Chinese with English abstract).
Wu Chuanrong, Zhang Hui, Li Yuanlu, Li Xiaoyan, Wang Chengsheng. 1995. Reserche on Coal Petrology Properties and Coal Metamorphism of Early-middle Jurassic Coal in Northwest China China[M]. Beijing: China Coal Industry Publishing House, 22-32 (in Chinese with English abstract).
Wu Jingyu, Ding Suting, Li Qijia, Sun Bainian, Wang Yongdong. 2016. Reconstructing paleoatmospheric CO2 levels based on fossil Ginkgoites from the Upper Triassic and Middle Jurassic in Northwest China[J]. PalZ, 90(2): 377-387. DOI:10.1007/s12542-016-0300-1
Xia Yangqing, Wang Chunjiang, Meng Qianxiang, Wang Hongyong, Du Li. 1998. The simulation of the formation of condensed nucleus and polycyclic aromatic hydrocarbons[J]. Acta Sedimentologica Sinica, 16(2): 1-4 (in Chinese with English abstract).
Yan Defei, Sun Bainian, Xie Sanping, Li Xiangchuan, Wen Wenwen. 2009. Response to paleoatmospheric CO2 concentration of Solenites vimineus (Phillips) Harris (Ginkgophyta) from the Middle Jurassic of the Yaojie Basin, Gansu Province, China[J]. Science in China: Earth Sciences, 52(12): 2029-2039. DOI:10.1007/s11430-009-0181-1
Yan M, Wan M, He X, Hou X, Wang J. 2016. First report of Cisuralian (early Permian) charcoal layers within a coal bed from Baode, North China with reference to global wildfire distribution[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 459: 394-408. DOI:10.1016/j.palaeo.2016.07.031
Zhan Changlin, Cao Junji, Han Yongming, An Zhisheng. 2011. Research progress on reconstruction of paleofire history[J]. Advances in Earth Science, 12: 1248-1259 (in Chinese with English abstract).
Zhang Hong, Bai Qingzhao, Zhang Xiaowei. 1995. Formation and Evolution of Ordos Coal-accumulcting Basin[M]. Xi' an: Shannxi Science and Technology Press, 1-15 (in Chinese with English abstract).
Zhong Xiaochun, Zhao Chuanben, Yang Shizhong. 2003. Jurassic System in the North of China Volum Ⅱ Paleoenvironment and Oil and Gas[M]. Beijing: Petroleum Industry Press, 53-65 (in Chinese with English abstract).
常禹, 黄文韬, 胡远满, 李月辉, 布仁仓, 刘永耀. 2015. 林火碳排放研究概况及展望[J]. 生态学杂志, 34(10): 2922-2929.
邓胜徽, 卢远征, 赵怡, 樊茹, 王永栋, 杨小菊, 李鑫, 孙柏年. 2017. 中国侏罗纪古气候分区与演变[J]. 地学前缘, 24(1): 106-142.
韩德馨, 任德贻, 王延彬, 金奎励, 毛鹤龄, 秦勇. 1996. 中国煤岩学[M]. 徐州: 中国矿业大学出版社, 26-28.
胡海清, 魏书精, 孙龙. 2012. 1965-2010年大兴安岭森林火灾碳排放的估算研究[J]. 植物生态学报, 36(7): 629-644.
黄文辉, 敖卫华, 翁成敏, 肖秀玲, 刘大锰, 唐修义, 陈萍, 赵志根, 万欢, Finkelman Bob. 2010. 鄂尔多斯盆地侏罗纪煤的煤岩特征及成因分析[J]. 现代地质, 24(6): 1186-1197. DOI:10.3969/j.issn.1000-8527.2010.06.022
金培红, 董俊玲, 王姿晰, 远继东, 毛子强, 李玉琼, 孙柏年. 2017. 内蒙古准格尔旗古城煤矿中侏罗世银杏类化石及其对古大气CO2的指示[J]. 兰州大学学报: 自然科学版, 53(1): 1-9.
李江海, 江洪福. 2013. 全球古板块再造、岩相古地理及古环境图集[M]. 北京: 地质出版社, 43.
刘池洋, 赵红格, 桂小军. 2006. 鄂尔多斯盆地演化-改造的时空坐标及其成藏(矿)响应[J]. 地质学报, 80(5): 617-638. DOI:10.3321/j.issn:0001-5717.2006.05.001
刘红叶, 顾延生, 程胜高, 黄庭, 肖河. 2018. 末次冰消期以来火灾发生及全球变化意义[J]. 地球科学前沿, 8(1): 106-119.
刘晓东, 王博. 2017. 森林燃烧主要排放物研究进展[J]. 北京林业大学学报, 39(12): 118-124.
鲁静, 杨敏芳, 邵龙义, 陈恕聪, 李永红, 周凯, 王万青. 2016. 陆相盆地古气候变化与环境演化、聚煤作用[J]. 煤炭学报, 41(7): 1788-1797.
沈文杰, 张华, 孙永革, 林杨挺, 梁婷, 杨志军, 周永章. 2012. 二叠纪—三叠纪界线大火燃烧的地层记录: 研究进展回顾与评述[J]. 地球科学进展, (6): 613-623.
宋建中, 胡建芳, 彭平安, 万晓樵. 2015. 古老地质样品的黑碳记录及其对古气候、古环境的响应[J]. 自然杂志, 37(2): 86-92.
王双明, 张玉平. 1999. 鄂尔多斯侏罗纪盆地形成演化和聚煤规律[J]. 地学前缘, 6(S1): 147-15.
王效科, 庄亚辉, 冯宗炜. 1998. 森林火灾释放的含碳温室气体量的估计[J]. 环境工程学报, 6(4): 1-15.
吴传荣, 张慧, 李远滤, 李小颜, 汪程生. 1995. 西北早—中侏罗世煤岩煤质与煤变质研究[M]. 北京: 煤炭工业出版社, 22-32.
夏燕青, 王春江, 孟仟祥, 王红勇, 杜丽. 1998. 稠环芳烃和多环芳烃成因模拟[J]. 沉积学报, 16(2): 1-4.
占长林, 曹军骥, 韩永明, 安芷生. 2011. 古火灾历史重建的研究进展[J]. 地球科学进展, (12): 1248-1259.
张泓, 白清昭, 张笑薇. 1995. 鄂尔多斯聚煤盆地形成与演化[M]. 西安: 陕西科学技术出版社, 1-15.
钟筱春, 赵传本, 杨时中. 2003. 中国北方侏罗纪二古环境与油气[M]. 北京: 石油工业出版社, 53-65.