没有脊梁也繁荣

告别了寒武纪,我们来到了奥陶纪。关于寒武纪—奥陶纪的分界线,并没有一个特别明确的时间点,但在这期间,发生了地球上第一次的生物集体灭绝事件。在那时候,绝大部分生物都生活在海洋里,这次生物灭绝事件使地球上大约一半的生物消失,消灭了很多腕足动物、牙形石、还有很多种类的三叶虫。由于年代太过久远,科学家们无法找出这次生物大灭绝的原因。于是,奥陶纪便在大约5亿年前,用灭绝生物的遗体书写了自己的历史。     

http://www.sciencedirect.com/science/article/pii/S1674987113001072

The late Permian Emeishan large igneous province(ELIP) covers ~0.3 x 106 km2 of the western margin of the Yangtze Block and Tibetan Plateau with displaced,correlative units in northern Vietnam(Song Da zone).The ELIP is of particular interest because it contains numerous world-class base metal deposits and is contemporaneous with the late Capitanian(~260 Ma) mass extinction.The flood basalts are the signature feature of the ELIP but there are also ultramafic and silicic volcanic rocks and layered maficultramafic and silicic plutonic rocks exposed.The ELIP is divided into three nearly concentric zones(i.e.inner,middle and outer) which correspond to progressively thicker crust from the inner to the outer zone.The eruptive age of the ELIP is constrained by geological,paleomagnetic and geochronological evidence to an interval of 3 Ma.The presence of picritic rocks and thick piles of flood basalts testifies to high temperature thermal regime however there is uncertainty as to whether these magmas were derived from the subcontinental lithospheric mantle or sub-lithospheric mantle(i.e.asthenosphere or mantle plume) sources or both.The range of Sr(I_(Sr) = 0.7040-0.7132),Nd(ε_(Nd)(t) ≈-14 to +8),Pb(~(206)Pb/~(204)Pb_1≈ 17.9-20.6) and Os(γ_(Os) =-5 to +11) isotope values of the ultramafic and mafic rocks does not permit a conclusive answer to ultimate source origin of the primitive rocks but it is clear that some rocks were affected by crustal contamination and the presence of near-depleted isotope compositions suggests that there is a sub-lithospheric mantle component in the system.The silicic rocks are derived by basaltic magmas/rocks through fractional crystallization or partial melting,crustal melting or by interactions between mafic and crustal melts.The formation of the Fe-Ti-V oxide-ore deposits is probably due to a combination of fractional crystallization of Ti-rich basalt and fluxing of C02-rich fluids whereas the Ni-Cu-(PGE) deposits are related to crystallization and crustal contamination of mafic or ultramafic magmas with subsequent segregation of a sulphide-rich portion.The ELIP is considered to be a mantle plume-derived LIP however the primary evidence for such a model is less convincing(e.g.uplift and geochemistry) and is far more complicated than previously suggested but is likely to be derived from a relatively short-lived,plume-like upwelling of mantle-derived magmas.The emplacement of the ELIP may have adversely affected the short-term environmental conditions and contributed to the decline in biota during the late Capitanian.     

“中国的乐平统及二叠纪末生物大灭绝研究”获2010年度国家自然科学二等奖

<正>由已故金玉玕院士领导的,沈树忠、王向东、王玕、曹长群研究员等参与完成的"中国的乐平统和二叠纪末生物大灭绝"获得2010年度国家自然科学二等奖。这项成果属于地球科学领域关于地质历史时期重大生物演化事件及其环境背景的国际前沿性基础研究。在整个地质历程中发生了5次生物大灭绝事件,二叠纪末期(2.5亿年前)的生物大灭绝代表显生宙地球生态系统     

Were Late Cretaceous extinctions of gastropods selective by generic longevity?

Many gastropod taxa went extinct during the Late Cretaceous.The stratigraphic ranges of 268 genera permit to establish the longevity of extinction victims for each stage of this epoch."Young" taxa (originated within 3 epochs before the extinction) prevailed among victims of the extinctions in all stages.The proportion of "old" taxa(originated before the Cretaceous) that went extinct was the highest in the Cenomanian,and it was the lowest in the Coniacian and the Maastrichtian.It appears that the end-Cretaceous mass extinction affected chiefly "young" taxa.However,the comparison with the earlier time intervals suggests that this pattern of selectivity by generic longevity was not specific for the noted catastrophe,but,in contrast,it was typical for the entire Late Cretaceous.The latest Cenomanian environmental perturbation(OAE2) caused a stronger extinction of "old" taxa,and thus,this biotic crisis was less selective by generic longevity.This hypothesis,however,is not proven by the statistical test.     

重大地质转折期的碳、硫循环与环境演变

碳、硫在表层储库和地质储库以不同的形式相互转换,在这个过程中都伴随着一定的同位素分馏。碳同位素的分馏主要受到光合作用以及海水溶解无机碳与大气CO2交换的控制,而硫同位素的分馏则主要受控于硫酸盐细菌还原作用。表层储库碳、硫同位素的组成通过地质作用被很好地保存在地质储库中,因此通过对地质储库中碳、硫同位素的分析和研究,可以很好地了解地球各圈层相互作用的规律,重塑地质历史特别是重大关键转折时期的演化过程。同时文中借助一些碳、硫同位素应用实例,进一步加深理解影响碳、硫同位素组成和变化的原因,以提高对不同时期全球环境变化的认知程度。     

黔西滇东地区二叠纪-三叠纪之交有机碳同位素和生物地层对比

二叠纪-三叠纪之交海、陆相地层对比研究对陆相二叠系-三叠系界线的定义以及全面认识该全球性重大生物与环境突变事件具有重要意义,是当前国际古生物学与地层学研究的重点和难点.选择贵州六盘水仲河二叠系-三叠系界线剖面为研究对象,系统研究了该剖面的化石面貌和有机碳同位素演变特征.结合黔西滇东地区二叠纪-三叠纪之交良好的陆相、海陆过渡相和浅海碎屑岩相地层记录,初步搭建了海、陆相生物地层与有机碳同位素地层对比框架.值得关注的是,综合已有研究的陆相和海陆过渡相剖面植物有机碳同位素和海相剖面无机碳同位素数据,发现均存在相同的碳同位素演变特征,且与生物地层对比方案一致.据此,认为高分辨率的有机碳同位素化学地层是实现海-陆相地层对比的有效手段之一.      

古海洋氧化还原条件的遗迹化石定量表征特征:以华南二叠纪末生物大灭绝事件为例*

地质历史时期的重大生物—环境事件往往伴随着古海洋海水氧化还原条件的改变,而遗迹化石作为原位保存的生物成因沉积构造,对于解读古海洋氧化还原条件具有显著的优势。通过对前人常用的遗迹学参数进行分析总结,发现遗迹化石多样性、生物扰动强度、潜穴直径、特征遗迹化石组合这4项定量参数可以表征古海洋氧化还原条件的变化。文中以华南二叠系乐平统遗迹化石及生物扰动构造作为研究对象,系统分析了二叠纪末生物大灭绝事件前后遗迹化石参数表征的古海洋氧化还原条件变化特征:自吴家坪期晚期华南古海洋开始出现缺氧,然而该缺氧状态在长兴期不具有持续性,而是呈现出周期性缺氧/贫氧→富氧/有氧的波动特征;在二叠纪末生物大灭绝之前,煤山剖面高精度的定量遗迹学参数指示长兴组24e层顶部存在缺氧事件,并与大灭绝事件有着良好的对应关系。这一实例具体展示了遗迹学参数在古海洋水体氧化还原条件重建中应用前景广阔。     

扬子板块西缘下志留统龙马溪组底部斑脱岩研究——锆石U-Pb测年、微量元素特征及地质意义

奥陶系—志留系之交斑脱岩分布广泛,且发育数层,是研究该时期地层年代学、地层对比、事件地层及生物大灭绝的良好载体.通过对扬子板块西缘永善地区上奥陶统—下志留统龙马溪组底部地层中的斑脱岩进行锆石U-Pb测年,获得年龄加权平均值443.5±1.7 Ma,限定了地层的沉积年龄,为扬子板块西缘奥陶系—志留系火山喷发事件及地层年代学研究提供了较可靠的依据,也为扬子板块周缘奥陶系—志留系高分辨率地层格架的建立提供基础信息.锆石微量元素特征显示其具有I型花岗岩类特征,形成于岩浆弧或造山带.晚奥陶世—早志留世多期次、高频率的火山活动可能是造成生物大灭绝的主导因素.     

重庆凉风垭剖面二叠-三叠系界线层碳同位素变化特征

重庆凉风垭二叠-三叠系界线剖面64个碳酸盐样品碳同位素值测试结果显示,在界线附近碳同位素值出现3次负异常,第1次负异常出现在第37层,考虑到该层是灰岩透镜体与黏土岩的混合层,此次异常有待进一步验证;第2次负异常出现在第40层,此次异常是δ(13C)值偏移幅度最大的1次(1.5‰),在该层大量生物灭绝;第3次负异常出现在第44层.凉风垭界线剖面碳同位素值的3次负异常与生物变化的对比表明,碳循环的多次变化与生物危机相伴,生物危机期间环境处于不稳定状态.     

菌藻类繁盛:晚泥盆世大灭绝的疑凶?

广西桂林杨堤剖面的地球化学数据显示晚泥盆世弗拉期末—法门期海平面波折上升、水体从富氧变为贫氧,同时无机、有机碳同位素(δ13Ccarb和δ13Ckerogen)分别从 0.43(‰V-PDB)→ 3.54(‰V-PDB)和-29.38(‰V-PDB)→-24.14(‰V-PDB),可以与北美、欧洲等地进行对比.通过对海平面变化、缺氧程度分析,并结合岩石薄片,我们认为这种快速正向波动是由以菌藻类生物为主要生产者的海洋生产力迅速增加引起的.镜下观察发现,F-F大灭绝中菌藻类不但未受影响反而更加繁盛.与之相对应,对营养盐P及菌藻类生长刺激元素Fe、Zn的研究也发现在晚弗拉期出现几次含量突增.更值得注意的是其来源主要由陆地输入,这就印证了晚泥盆世陆生植物大规模繁盛使得生物化学风化盛行,导致地表径流向陆表海输送的营养物质增加改变了海洋化学环境,富营养化的海水使菌藻类繁盛并造成其他生物灭绝的假说.