燕辽地区下马岭组内基性岩床侵位过程中CO_2释放量估算及对表生环境影响的探讨

大火成岩省对全球性环境巨变及大规模生物灭绝的影响是国际地学界关注的主要前缘科学问题之一。一般认为大火成岩省中熔岩流喷发所释放的温室及有毒气体、火山灰及其它流体是导致环境巨变及生物灭绝的最主要原因之一。但近年来研究表明,作为大火成岩省重要组成部分之一的大规模基性岩床(辉绿岩为主),其侵位到黑色页岩、煤层、蒸发岩及碳酸盐岩中释放出了巨量的温室及有毒气体,并对表生环境及生物灭绝有重要的驱动作用。在华北克拉通北缘近年来发现的约1.32Ga燕辽大火成岩省由大规模辉绿岩床群组成,这些辉绿岩床主要侵位于下马岭组黑色页岩(TOC含量0.6～20%,平均值约6.0%)中,部分侵位到雾迷山组及高于庄组白云岩或白云质灰岩中。野外调查结果表明,受岩床侵位的影响,辉绿岩床与下马岭组接触带附近黑色页岩有强烈的角岩化及脱碳现象。在接触带厚度及辉绿岩岩床与黑色页岩分布范围调查的基础上,根据受不同程度影响黑色页岩内总有机碳(TOC)含量分析结果,初步估算出岩床侵位到下马岭组黑色页岩过程中CO_2的释放量可达1.10×10~(12)t。如果考虑到华北克拉通燕辽地区侵入到高于庄组和雾迷山组碳酸盐岩中的岩床,以及北澳大利亚克拉通麦克阿瑟盆地Velkerri组中1.32Ga的大规模代里姆辉绿岩床群,这一时期辉绿岩岩床侵位所释放的CO_2等温室气体量可能会更大。华北克拉通燕辽及北澳大利亚克拉通代里姆1.32Ga大规模辉绿岩床侵位热接触变质中CO_2等气体的释放可能对大气—海洋环境有显著的影响,但由于华北及北澳大利亚克拉通缺少这一时期的沉积,其地质记录(如碳同位素负漂移,元素或其它同位素异常、生物量指标的差异等)可能存在于全球其它克拉通(如西伯利亚、波罗地等)约1.32Ga沉积地层中,需要开展更为深入的研究工作。     

地球氧逸度

地球是一个"氧化性"的星球。在太阳系所有行星中,只有地球大气中含有高浓度的O_2(约占21%)。研究表明,地球演化的早期,其大气组成与火星等类地行星相似,都是以CO_2为主,O_2含量可以忽略不计。在大约24-21亿年前,地球大气中O_2含量突然大幅度升高,一度超过现今O_2含量的1%,而后又在中元古代回落到现今O_2含量的0.1%以下。沉积物中氧化还原敏感元素的含量变化显示,大约6.3亿年前雪球地球结束之后,地球大气中的O_2含量再次大幅度升高至20%左右,而后在显生宙经历一系列复杂变化并最终演化至现今的水平。Re/Os比值显示,硅酸盐地球的氧逸度远高于月球,也高于火星。考虑到月球与地球分异发生在45亿年前,月球的低氧逸度暗示地球早期的氧逸度可能也较低。可以影响地球氧逸度的元素主要有O、H、Fe、S和C等。控制地球氧逸度变化的主要过程包括:核幔分异、板块俯冲和火山喷发去气等。在核幔分异以前,金属Fe可能是控制硅酸盐地球及其表生环境低氧逸度的关键因素。核幔分异过程中,Fe是控制氧逸度变化的关键元素。核幔分异将金属Fe与铁氧化物分开,造成地幔Fe~(3+)/Fe~(2+)比值升高。尤其是在下地幔,Fe~(2+)在高压下发生歧化反应,形成金属Fe和Fe~(3+)。其中Fe~(3+)赋存在布里奇曼石中,导致下地幔氧逸度低。在板块俯冲过程中,当有板片进入下地幔时,布里奇曼石会因体积补偿,被运移到上地幔,并发生分解,释放出Fe~(3+),导致周围地幔氧逸度的升高。但是,V/Sc和Zn/Fe等元素比值则显示在过去30多亿年以来,地幔的氧逸度变化不大,可能与上、下地幔间氧化还原缓冲层或者是上述元素比值对氧逸度不够敏感有关。在地球演化早期,金刚石是最早形成的矿物。由于金刚石的密度在上地幔高于地幔橄榄岩熔体,而在下地幔小于地幔橄榄岩熔体,因此在岩浆海阶段,金刚石倾向于在上地幔底部富集,成为一个富金刚石的储层。在板块俯冲阶段,这些金刚石会被布里奇曼石分解所释放的Fe~(3+)所氧化,形成富碳酸盐和CO:的层位,同时起到稳定上地幔氧逸度的作用。俯冲带地幔橄榄岩和岛弧火山岩的氧逸度均高于板内环境,因此一般认为板块俯冲会导致氧逸度升高。在板块俯冲过程中,氧逸度主要受到Fe和H_2O(水分解释放出H_2)的控制。蚀变大洋岩石圈中含有大量的H_2O,板块俯冲过程中脱水会导致地幔楔蛇纹石化。蛇纹石化过程会形成磁铁矿,释放出味,使局部在短时间内氧逸度降低。但是,由于H_2很容易逸散到大气中,而磁铁矿则保留在地幔楔中,其结果导致岩石中Fe~(3+)/Fe~(2+)比值升高,从而在发生部分熔融时形成高氧逸度岩浆。板块俯冲对氧逸度的影响是多方面的,还与俯冲板块的年龄、沉积物的性质等有关。对于富含有机物的沉积物俯冲过程,C是主要的氧逸度控制元素。在板块俯冲的浅部,有机物分解,释放出CH_4等还原性气体,造成上覆岩石圈氧逸度下降。富含铁锰结核等氧化性沉积物的俯冲则可以导致地幔楔氧逸度的升高,这一过程中Fe和Mn是控制氧逸度的主要元素。火山喷发可以释放出CH_4、CO_2、H_2S和SO_2等气体,也可以影响大气中O_2的含量。有研究认为,火山气体中的H_2S随岩浆房压力增加而增加,SO_2则随压力的增加而减少,因此岩浆房压力可以影响其排气的氧化-还原性,进而影响大气的O_2含量。一种观点认为,正是由于太古宙末期大量出现陆相火山岩,导致了大氧化事件,在这一模型中,S是控制氧逸度的关键。氧逸度对多种成矿作用均具有重要的控制作用。其中,斑岩铜金矿床的形成往往与高氧逸度的埃达克岩有关。这是由于当岩浆的氧逸度高于AFMQ+1.5时,岩浆中S主要以硫酸盐的形式存在。由于硫酸盐在岩浆中的溶解度远远高于硫化物,因此,在俯冲洋壳部分熔融过程中形成的高氧逸度埃达克质岩浆可以熔出更多的亲硫元素,有利于成矿。锡矿床的形成则往往与还原性岩浆有关。这是因为在高氧逸度岩浆中,Sn主要呈Sn~(4+),易于在岩浆结晶早期进入矿物中;而在还原性岩浆中,Sn主要以Sn~(2+)形式存在,表现为不相容元素,倾向于在岩浆中富集,并在岩浆期后热液阶段富集成矿。其他氧化还原敏感元素,如U、V、Mo、Re、Sb和Fe等,可以在表生过程中富集,有利于进一步富集成矿。     

中国北方晚中生代陆相盆地红-黑岩系耦合产出对砂岩型铀矿成矿环境的制约

为研究中国北方陆相盆地红层-黑色岩系对砂岩型铀成矿的制约,文章研究了国内外红-黑岩系与砂岩型铀矿赋存岩层的时空关系,筛选了10万余m岩心钻探资料,选择准噶尔、鄂尔多斯和松辽盆地这3个典型产铀盆地,通过编制盆地钻孔柱状图、典型地区连井剖面图及关键岩层的地球化学测试等方法,对红-黑岩系和砂岩型铀矿的赋存岩层进行了垂向、横向上综合分析与对比。研究发现:北方陆相盆地自西向东铀矿赋存地层的时代由中侏罗世过渡到晚白垩世;晚中生代至少存在6次大规模的富氧红层沉积事件:Ⅰ中侏罗世—晚侏罗世早期(BathonianOxfordian),Ⅱ早白垩世早中期(Berriasian-Barremian),Ⅲ早白垩世中期(Barremian),Ⅳ晚白垩世早期(Cenomanian),Ⅴ晚白垩世中期(Coniacian)和Ⅵ晚白垩世晚期(Campanian)。其中第Ⅰ、Ⅴ和Ⅵ期红层之下沉积了时代相近的黑色层,与之构成"红-黑岩系"的沉积结构,是北方砂岩型铀成矿的3个重要层位。典型盆地内地球化学表明,红层与黑色层的B、Sr和Cu元素含量及Fe~(2+)/Fe~(3+)、B/Ga、Sr/Cu和FeO/MnO比值具有明显的差异,结合黑色岩层中草莓状黄铁矿、碳屑、油斑和红层中碳酸盐岩的发育,认为红层为相对较强氧化环境,黑色层为相对较还原环境。连井剖面资料显示红层、黑色层与砂岩型铀矿空间关系密切,铀矿多产于红层与黑色层之间过渡带上,呈板状矿体赋存于灰色、绿灰色砂岩和细砂岩中。一般红层与黑色层垂向距离超过500 m不利于成矿。晚中生代陆相盆地内耦合产出的黑色岩系和红色岩系是古沉积环境由还原向氧化转变形成的垂向分带,前者为铀矿物质沉淀提供了"障",后者为表生流体溶解铀矿提供了"场"。文章初步提出了红-黑岩系垂向环境变化制约着北方陆相盆地砂岩型铀大规模成矿作用的新认识。这些认识不仅对砂岩型铀矿成矿环境、成矿规律及成矿模式研究具有重要意义,更对目前正在开展的砂岩型铀矿勘查工作具有实践指导意义。     

白垩纪古海洋气候变化及主要问题

白垩纪并非一直处于温室气候状态,存在着冰室气候间断。白垩纪古海洋气候也是如此。通过收集已经发表的古海洋气候资料,综合分析研究显示,该期全球古海洋气候可以分为早白垩世低温气候、中白垩世温室气候、晚白垩世冰室气候3个阶段;早白垩世可进一步识别K_1-Ⅰ温暖干燥气候、K_1-Ⅱ冷湿气候、K_1-Ⅲ温暖气候回升3个次级变化旋回;中白垩世整体处于温暖状态,不过,虽然极热气候在全球出现和结束的时间不尽一致,但总体上出现在赛诺曼一土仑期,局部地区如赤道太平洋早可以在阿尔布期,南极地区晚可推迟到晚白垩世坎潘早期;晚白垩世可划分为K_3-Ⅰ大幅降温冰室期、K_3-Ⅱ浅幅气候回升期、K_3-Ⅲ低温冰室期、K_3-Ⅳ短暂温室期4个次级气候变化旋回。还介绍了白垩纪古海洋温度计、冷赤道与低温度梯度、中白垩世黑色页岩、气候变冷及旋回、大气CO_2作用几方面重大问题,并做了简要讨论。     

西藏隆格尔铁矿床成岩成矿时代及对区域多期铁成矿作用的启示:地球化学、锆石U⁃Pb及金云母Ar⁃Ar同位素定年约束

为了查明冈底斯成矿带隆格尔富铁矿床的成矿时代、形成环境及其对区域铁成矿作用的指示,对该矿床开展了岩石地球化学、锆石U-Pb年代学和Lu-Hf同位素及金云母Ar-Ar定年分析,结果表明:(1)矿区存在早白垩世花岗闪长岩(116.3 Ma)和晚白垩世闪长岩(94.3~93.8 Ma)两个阶段的岩浆活动,主矿体金云母40Ar/39Ar等时线年龄为93.71±2.96 Ma,表明该铁矿形成于晚白垩世;(2)与主矿体成矿相关的闪长岩具较低SiO₂含量(52.17%~55.32%),富集LREE及Rb、Ba、Pb等大离子亲石元素,亏损HREE和Nb、Ta、Ti等高场强元素,属于高钾钙碱性和准铝质岩石系列,锆石ε_Hf(t)介于1.4~3.6,Mg#指数极高(0.59~0.64),暗示成矿岩体有较多的幔源物质加入,具有壳幔混合特征;(3)结合冈底斯带其他铁矿床时代,可以将冈底斯铁成矿作用划分为~115 Ma、~94 Ma和50~65 Ma三期,隆格尔铁矿床属于冈底斯带新一期(晚白垩世)富铁成矿作用;(4)对比冈底斯成矿带多阶段矽卡岩型铁成矿作用发现,隆格尔铁矿成矿岩体与其他时期铁矿具有明显的地球化学差异,幔源物质较多的中基性岩浆相对于酸性岩浆可能更容易形成富铁矿床.      

地球圈层之间相互作用对白垩纪大洋缺氧与富氧过程的制约

白垩纪诸多地质事件中,以黑色页岩为特征的大洋缺氧事件和以红层为特征的大洋富氧环境尤其引人关注。本文探讨了白垩纪大洋从缺氧到富氧转化的过程与机制,认为上述沉积事件是地球圈层之间相互作用的结果。白垩纪岩石圈剧烈的岩浆活动,是缺氧、富氧事件发生的源动力,水圈、大气圈、生物圈的共同作用是沉积事件发生的结果。具体过程为:白垩纪大规模的火山喷发,改变了海陆面积的对比,并引起地球内部大量热能释放和大气中CO_2气体浓度的升高,最终导致大气温度的升高。海水温度的升高和CO_2浓度的增加导致海洋环境中溶解O_2的降低,缺氧事件随之而产生。同时,海底岩浆喷发在海底产生大量的富含铁元素的基性和超基性岩石,通过海底风化和热液活动,铁元素从岩石圈进入水圈。海水中的铁元素是海洋浮游植物宝贵的营养盐类,其含量的增加可激发浮游植物的大规模繁盛,而这一生命过程可以吸收海水中大量的CO_2,并且产生等量的O_2。随着海水中O_2浓度的不断升高,以富含Fe3+的红色沉积物为特征的海洋富氧环境出现。藏南和深海钻探、大洋钻探典型剖面的数据证实大洋缺氧和富氧发生的韵律性,即缺氧事件之后往往伴随富氧环境的出现。研究认为,白垩纪大洋缺氧和富氧事件是同一原因导致的不同结果,地球圈层相互作用是其根本制约因素。由岩浆活动引起的缺氧事件和同样由其造成的富氧环境,其机制存在明显的差异,前者以物理、化学过程为主,后者除此之外还演绎了更为复杂的生物-海洋地球化学过程。     

深部碳循环的环境气候效应SCIEI北大核心CSCD

地球表层温度主要由接收的太阳辐射能量及大气温室气体的保温能力共同控制。CO_(2)等温室气体通过对大气温度的调节影响着全球环境气候变化,工业革命以来全球CO_(2)排放量的增加被认为是全球变暖的重要原因,地质历史时期大气CO_(2)浓度的波动与温室和冰室气候的交替出现相对应。地球超过90%的碳赋存于深部,因此地球深部过程的些许波动便会影响到地表碳含量,进而深刻影响着地球的环境气候变化。以往的研究注重地表碳循环对环境气候的影响,对深部碳的贡献考虑不足。最近十余年全球开展了详细的深部碳循环研究,基于已经取得的重要成果,本文从大火成岩省、裂谷和俯冲带的视角对深部碳循环驱动的环境气候效应进行了系统回顾。认为未来的研究需要对地球深部碳循环通量和碳同位素组成进行更精确的定量,这是我们认识深部碳循环对地表环境气候影响的基础;除了碳元素本身我们还需要关注其他挥发性元素和有害金属元素的综合效应;俯冲带作为全球壳-幔相互作用和物质交换循环最重要的场所,应该是进行深部碳循环观察和环境气候效应研究的重点。     

“深时环境、气候与生命”主题专辑目次

<正>当前由于全球变暖趋势不断加剧,逐渐升高的大气CO_2浓度使地球向更温暖的气候状态发展,可能在未来百年尺度内达到"温室气候"。这种气候恰好不属于人类演化过程中和当前所处的"冰室"气候状态。因此,国际科学界面临的重大科学命题就是,地球如何从冷变暖进入"温室气候"状态?变暖过程中地表环境-气候-生物体系的变化及其相互关系如何?为了深入理解这种变化,以探究"深时(Deep     

深时古气候对未来气候变化的启示

当前人类活动引起大气中二氧化碳(CO_2)的浓度逐渐升高,地球气候可能将发生不可逆的变化,从目前的冰室气候进入温室气候状态。文中通过对现在地球气候系统与深时温室气候时期的大气CO_2浓度与气候变化临界点、温度与温度梯度、海平面变化与水循环、大洋水体氧化还原状态几个方面进行对比和分析,提出对地球在这种温室气候状态中的气候动力系统的认识亟待提高。尽管深时温室气候并不严格等同于未来地球的气候,但深时时期形成的地质记录为我们提供了全尺度洞察在温室气候状态下地球系统是如何运行的一个天然实验室。     

地球气候的变化不可逆转

美国犹他州人盐湖的创记录水位以及海平面的上升(高达一呎)可能都与化石燃料使用量的增加有关。这些变化可能出自于一个共同的原因,即大气中CO_2的增加。地球大气中CO_2含量的增加,通过“温室效应”导致地球气候的逐渐变暖。我们设想地球就是一座以CO_2作屋顶的巨人温室。太阳能量会很容易地进入温室,而大部分热量却不能散发到地球大气圈外,引起气温缓慢而持续的上升。     

中国东北地区显生宙岩浆作用和洋-陆格局及其与气候演变的关系SCIEI北大核心CSCD

显生宙期间,地球经历了温室-冰室气候的周期性交替变化。在数百万年的时间尺度,这种古气候的转变被认为是碳源和碳汇过程耦合的结果,但一直以来关于两者贡献程度的认识尚不明确。通过全球统计分析,不同学者提出大陆弧火山脱气模型和热带弧-陆碰撞模型用于解释整个显生宙古气候的演变,分别强调了碳源和碳汇的一级控制作用。为了检验上述模型,更好地理解古气候的转变机制和演化细节,本文系统总结了中国东北地区显生宙岩浆作用-矽卡岩型矿床的时空展布和构造背景,以及弧-陆碰撞的时代、规模和古地理位置,通过数据统计和作图对比,发现东北地区岩浆作用-矽卡岩成矿峰期、弧-陆碰撞缝合带的时空迁移与大气圈CO_(2)浓度和大陆冰川沉积有很好的对应关系,暗示东北显生宙构造-岩浆过程和古气候演变的内在联系。综合东北地区及全球的研究进展,本文提出如下倾向性认识:1)洋-陆俯冲过程中火山-变质脱气的强度决定了CO_(2)排放量,而热带区域弧-陆碰撞缝合带的规模决定了全球硅酸盐风化速率和CO_(2)吸收量,在地质演化过程中两者紧密联动,共同控制了显生宙古气候的演变;2)大陆弧岩浆作用的全球爆发不一定能造成温室气候的出现,如果缺乏充分矽卡岩变质脱碳反应,大陆弧CO_(2)排放通量与岛弧、大洋中脊和板内并无显著区别;3)SO_(2)属于短期效应气体,理论和实例研究均暗示爆发式火山作用难以诱发大冰期的形成,火山作用之于长期气候应该仍是促使地球升温而非变冷。     

Milestones in the evolution of the atmosphere with reference to climate change

The history of life on Earth is critically dependent on the carbon, sulfur and oxygen cycles of the lithosphere – hydrosphere – atmosphere – biosphere system. An Archean oxygen-poor greenhouse atmosphere developed through: (i) accumulation of CO₂ and CH₄ from episodic injections of CO₂ from volcanic activity, volatilised crust impacted by asteroids and comets, metamorphic devolatilisation processes and release of methane from sediments; and (ii) little CO₂ weathering-capture due to both high temperatures of the hydrosphere (low CO₂ solubility) and a low ratio of exposed continents to oceans. In the wake of the Sturtian glaciation, enrichment in oxygen and appearance of multicellular eukaryotes heralded the onset of the Phanerozoic where greenhouse conditions were interrupted by periods of strong CO₂-sequestration through intensified capture of CO₂ by marine plants, onset of land plants and burial of carbonaceous shale and coal (Late Ordovician; Carboniferous – Permian; Late Jurassic; Late Tertiary – Quaternary). The progression from Late Mesozoic and Early Tertiary greenhouse conditions to Late Tertiary – Quaternary ice ages was related to the sequestration of CO₂ by rapid weathering of the emerging Alpine and Himalayan mountain chains. A number of peak warming and sea-level-rise events include the Late Oligocene, mid-Miocene, mid-Pliocene and Pleistocene glacial terminations. The Late Tertiary – Quaternary ice ages were dominated by cyclic orbital-forcing-triggered terminations which involved CO₂-feedback effects from warming seas and the biosphere and albedo flips due to ice-sheet melting. Since ca AD 1750 human emissions were ～305 Gt of carbon, as compared with ～750 Gt C in the atmosphere. The emissions constitute ～12% of the terrestrial biosphere and ～10% of the known global fossil fuel reserve of ～4000 Gt C, whose combustion would compare to the ～ 4600 Gt C released to the atmosphere during the K – T impact event 65 million years ago, with associated ～65% mass extinction of species. The current growth rate of atmospheric greenhouse gases and global mean temperatures exceed those of Pleistocene glacial terminations by one to two orders of magnitude. The relationship between temperatures and sea-levels for the last few million years project future sea-level rises toward time-averaged values of at least 5 m per 1°C. The instability of ice sheets suggested by the Dansgaard – Oeschinger glacial cycles during 50 – 20 ka, observed ice melt lag effects of glacial terminations, spring ice collapse dynamics and the doubling per-decade of Greenland and west Antarctic ice melt suggest that the Intergovernmental Panel on Climate Change's projected sea-level rises (<59 cm) for the 21st century may be exceeded. The biological and philosophical rationale underlying climate change and mass extinction perpetrated by an intelligent carbon-emitting mammal species may never be known.     

试论全球气候变化与沙漠化的关系

本文通过全球气候变化对沙漠化的影响和沙漠化对沙区气候的反馈作用两方面,论述在气候变暖条件下,全球气候变化与沙漠化的关系,例如我国东部沙区降水增多,沙漠化逆转,西部沙区降水减少,沙漠化发展等原因。     

Early Cretaceous atmospheric pCO2 levels recorded from pedogenic carbonates in China

Pedogenic carbonates were collected from Early Cretaceous strata in Sichuan and Liaoning, China. These paleosol carbonates and calcareous paleosols were evaluated in order to reconstruct atmospheric CO₂ concentrations during the Early Cretaceous using a paleosol barometer. Using the isotopic ratios of pedogenic carbonates from Early Cretaceous (early-middle Berriasian, early Valanginian) strata in Sichuan Basin, averaged atmospheric pCO₂ is estimated to have been 360 ppmv in the early-middle Berriasian and a mean value of 241 ppmv in the early Valanginian. In the late Barremian in western Liaoning, however the average was 530 ppmv, with a range of 365 ppmv and 644 ppmv, lower than previous estimates of pCO₂ for these time periods, consistent with the suggestion of overall climate cooling and paleotemperature fluctuation during the Early Cretaceous. This indicates that not all of the Cretaceous was a high or continuous CO₂ greenhouse, especially during Early Cretaceous.     

断层与幔源二氧化碳气藏的形成和分布——以渤海湾盆地济阳坳陷为例

幔源CO_2气的形成和分布与不同级别断层早白垩世以来的活动密切相关。郯庐断裂带是研究区最主要的成气断层,拆离断层和变换断层这些地壳断层是次要的成气断层,二者于早白垩世143Ma、124Ma、新生代~43Ma、~24Ma和~8Ma的走滑或伸展活动,以及与之准同时的新生代碱性玄武岩浆活动,控制了幔源CO_2气的分散和聚集。它们与基底断裂、盖层断裂共同组成运移通道,其中拆离滑脱处的低速带和盖层断裂中的顺层断层是重要的水平运移通道。早白垩世古太平洋板块俯冲脱水脱气,产生的幔源CO_2气沿着郯庐断裂带向上分散聚集;新生代以来受控于太平洋板块俯冲方向和速度的改变以及印欧板块碰撞的远程效应,形成幔源CO_2气。与此同时郯庐断裂带切割深度亦逐渐加大,~43Ma碱性岩浆活动亦开始形成幔源CO_2气并主要位于断裂带,24Ma和8Ma(5Ma)为新近纪碱性岩浆活动脱气两个主要形成时期。郯庐断裂带的活动使地幔脱气形成的CO_2沿断层走向向上运移,并在作为重要横向运移通道的拆离断层拆离滑脱处,与因岩浆脱气形成的CO_2汇合,再通过陡倾斜、缓倾斜基底断层、盖层断层的接力传递在浅部聚集成藏。预测郯庐断裂带附近是无机成因油气重要的聚集分布区带。     

Global warming and long-term climatic changes: a progress report

The authors believe that recent global warming of Earth’s atmosphere is not due to an increase in anthropogenic carbon dioxide emission but rather to long-term global factors. The human contribution to the CO₂ content in the atmosphere and the increase in temperature is negligible in comparison with other sources of carbon dioxide emission. Discussed in this paper are sources, avenues of migration, and the amounts of naturally produced carbon dioxide and methane (greenhouse gases) and long-term changes in the Earth’s climate, which are necessary for understanding the causes of current temperature trends.     

Role of low solar luminosity in the history of the biosphere

It was shown that the history of the biosphere is closely related to processes caused by low solar luminosity. Solar radiation is insufficient to maintain the Earth’s surface temperature above the freezing point of water. Positive temperatures are kept owing to the presence of greenhouse gases in the atmosphere: CO₂, CH₄, and others. Certain stages in the development of the biosphere and climate are related to these effects. Methane was the main carbon-bearing gas in the primordial atmosphere. It compensated the low solar luminosity. Life originated under the reduced conditions of the early Earth. Methane-producing biota was formed. Methane remained to be the main greenhouse gas in the Archean. The release of molecular oxygen into the atmosphere 2.4 Ga ago resulted in the disruption of the established mechanism of the compensation of the low solar luminosity. Methane ceased to cause a significant greenhouse effect, and the content of carbon dioxide was insufficient to play this role. A global glaciation began and had lasted for approximately 200 million years. However, the increasing CO₂ content in the atmosphere reached eventually a level sufficient for the compensation for the low solar luminosity. The glaciation period came to an end. Simultaneously, a conflict arose between the role of CO₂ as a gas controlling the thermal regime of the planet and as an initial material for biota production. As long as the resource of biotic carbon was inferior to that of atmospheric CO₂, the uptake of atmospheric CO₂ related to sporadic increases in biologic production was insufficient for a significant change in the thermal regime. This was the reason for a long-term climate stabilization for 1.5 billion years. By 0.8 Ga, the resource of oceanic biota reached the level at which variations in the uptake of atmospheric CO₂ related to variations in the production of organic and carbonate carbon became comparable with the resource of atmospheric CO₂. Since then, an oscillatory equilibrium has been established between the intensity of biota development and climate-controlling CO₂ content in the atmosphere. Glaciation and warming periods have alternated. These changes were triggered by various geologic events: intensification or attenuation of volcanism; growth, breakup, or migration of continents; large-scale magmatism; etc. A new relation between atmospheric CO₂ and biotic carbon was established in response to the emergence of terrestrial biota and the appearance of massive buffers of organic carbon on land. The interrelation of the biosphere and climate changed.     

温室气体浓度变化及其源与汇研究进展

对工业革命以来大气中主要温室气体浓度变化和增长趋势作了简介。概述了冰芯研究的最新成果:420 ka BP以来CO2浓度变化情况及其揭示的气候变化机制;全新世期间CH4浓度的波动;气候事件中N2O浓度的快速波动及工业化前的水平。总结了全球温室气体源与汇的研究现状,重点介绍了全球碳循环研究中的未知汇问题,列举了根据不同资料和模型估计的陆地碳汇位置和幅度以及影响因素对陆地碳汇的贡献等认识上的差异。简单介绍了国内有关温室气体源与汇研究,如稻田CH4排放、岩溶系统碳循环和黄土中温室气体组分特征等方面的研究成果和认识。     

Sedimentary manganese metallogenesis in response to the evolution of the Earth system

The concentration of manganese in solution and its precipitation in inorganic systems are primarily redox-controlled, guided by several Earth processes most of which were tectonically induced. The Early Archean atmosphere-hydrosphere system was extremely O₂-deficient. Thus, the very high mantle heat flux producing superplumes, severe outgassing and high-temperature hydrothermal activity introduced substantial Mn²⁺ in anoxic oceans but prevented its precipitation. During the Late Archean, centered at ca. 2.75 Ga, the introduction of Photosystem II and decrease of the oxygen sinks led to a limited buildup of surface O₂-content locally, initiating modest deposition of manganese in shallow basin-margin oxygenated niches (e.g., deposits in India and Brazil). Rapid burial of organic matter, decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the Archean-Proterozoic transition. Concurrently, a massive drawdown of atmospheric CO₂ owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused Paleoproterozoic glaciations (2.45-2.22 Ga). The spectacular sedimentary manganese deposits (at ca. 2.4 Ga) of Transvaal Supergroup, South Africa, were formed by oxidation of hydrothermally derived Mn²⁺ transferred from a stratified ocean to the continental shelf by transgression. Episodes of increased burial rate of organic matter during ca. 2.4 and 2.06 Ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere. Black shale-hosted Mn carbonate deposits in the Birimian sequence (ca. 2.3-2.0 Ga), West Africa, its equivalents in South America and those in the Francevillian sequence (ca. 2.2-2.1 Ga), Gabon are correlatable to this period. Tectonically forced doming-up, attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric CO₂ drawdown causing glaciation on the Neoproterozoic Rodinia supercontinent. Tectonic rifting and mantle outgassing led to deglaciation. Dissolved Mn²⁺ and Fe²⁺ concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation. During the Sturtian glacial-interglacial event (ca. 750-700 Ma), interstratified Mn oxide and BIF deposits of Damara sequence, Namibia, was formed. The Varangian (≡ Marinoan; ca. 600 Ma) cryogenic event produced Mn oxide and BIF deposits at Urucum, Jacadigo Group, Brazil. The Datangpo interglacial sequence, South China (Liantuo-Nantuo ≡ Varangian event) contains black shale-hosted Mn carbonate deposits. The Early Paleozoic witnessed several glacioeustatic sea level changes producing small Mn carbonate deposits of Tiantaishan (Early Cambrian) and Taojiang (Mid-Ordovician) in black shale sequences, China, and the major Mn oxide-carbonate deposits of Karadzhal-type, Central Kazakhstan (Late Devonian). The Mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans. During the Early Jurassic OAE, organic-rich sediments host many Mn carbonate deposits in Europe (e.g., Úrkút, Hungary) in black shale sequences. The Late Jurassic giant Mn Carbonate deposit at Molango, Mexico, was also genetically related to sea level change. Mn carbonates were always derived from Mn oxyhydroxides during early diagenesis. Large Mn oxide deposits of Cretaceous age at Groote Eylandt, Australia and Imini-Tasdremt, Morocco, were also formed during transgression-regression in greenhouse climate. The Early Oligocene giant Mn oxide-carbonate deposit of Chiatura (Georgia) and Nikopol (Ukraine) were developed in a similar situation. Thereafter, manganese sedimentation was entirely shifted to the deep seafloor and since ca. 15 Ma B.P. was climatically controlled (glaciation-deglaciation) assisted by oxygenated polar bottom currents (AABW, NADW). The changes in climate and the sea level were mainly tectonically forced.