Stage boundaries of the Triassic in Northeast Asia

The International Union of Geological Science approved the stage boundaries suggested by the international working groups for the Tethyan Triassic. In this work we estimate the possibility of their establishment and correlation in the Boreal sections of Northeast Asia, based on the analyzed distribution of ammonoids and conodonts. As the conodonts of the Induan Stage have not been identified for sure in the region under study, the lower boundary of the Triassic System is defined here at the base of the Otoceras concavum Zone of the ammonoid scale. In addition to the ammonoids Hedenstroemia hedenstroemi (Keyserling), the first occurrence of the conodonts Pseudogondolella nepalensis (Kozur et Mostler) is suggested to be the biomarker of the Olenekian Stage base. The lower boundaries of the Anisian and Ladinian stages, defined respectively at the basal levels of the Paracrochordiceras-Japonites Beds in Northern Dobrogea and the Eoprotrachyceras curionii Zone in the Brescian Prealps are recognizable, though with some reservations, at the base of the Grambergia taimyrensis and Eonathorstites oleshkoi zones in Northeast Asia. According to the priority principle and similarity between the ammonoid faunas of the Daxatina cf. canadensis Subzone and Frankites regoledanus Zone, the lower boundary of the Carnian Stage is defined at the base of the Alpine Trachyceras aon Zone. In Northeast Asia, this boundary is established at the base of the “Protrachyceras” omkutchanicum Zone, as we take into account the fact that the Daxatina and Stolleyites ammonoid genera occur in sections of British Columbia below the stratigraphic level of the Trachyceras forms. The lower boundary of the Norian Stage is concurrent with the base of the Guembelites jandianus Zone in the Alps and equivalent Stikinoceras kerri Zone in North America and Striatosirenites kinasovi Zone in Northeast Asia. The conodont species Norigondolella navicula (Huckriede) that is most important for the Boreal-Tethyan correlation cannot be used as a biomarker of the Norian lower boundary because of its problematic diagnosis and rare occurrence in the Boreal sections. The Rhaetian Stage base is defined at the appearance level of the Misikella conodont genus in the Hallstatt region, Austria, that is simultaneously the disappearance level of the characteristic Norian bivalves (Monotis) and ammonoids (Metasibirites). In Northeast Asia, this boundary is established at the top of the Monotis ochotica Zone. The correlation between the biostratigraphic units of the Middle-Upper Triassic conodont scale established in Northeast Asia and standard ammonoid zonation is verified.     

华南二叠－三叠系的事件地层与生物地层界线

华南二叠－三叠系界线研究应严格区分事件地层界线与生物地层界线。“界线粘土”层的底界即为事件地层界线。生物地层界线定义不能与“混生层”或“过渡层”的概念连在一起。长兴煤山忠心大队剖面是最好的二叠－三叠系全球界线层型剖面点（ＧＳＳＰ）。二叠－三叠系生物地层界线定义为ＨｉｎｄｅｏｄｕｓｐａｒｖｕｓＭｏｒｐｈｏｔｙｐｅ１的首次出现,其位置就在长兴剖面界线层（混生层）２的内部,比事件地层界线高１５ｃｍ。ＨｉｎｄｅｏｄｕｓｐａｒｖｕｓＭｏｒｐｈｏｔｙｐｅ１的首次出现,即为长兴阶的顶界。     

华南二叠－三叠系的事件地层与生物地层界线

华南二叠－三叠系界线研究应严格区分事件地层界线与生物地层界线。“界线粘土”层的底界即为事件地层界线。生物地层界线定义不能与“混生层”或“过渡层”的概念连在一起。长兴煤山忠心大队剖面是最好的二叠－三叠系全球界线层型剖面点（ＧＳＳＰ）。二叠－三叠系生物地层界线定义为ＨｉｎｄｅｏｄｕｓｐａｒｖｕｓＭｏｒｐｈｏｔｙｐｅ１的首次出现,其位置就在长兴剖面界线层（混生层）２的内部,比事件地层界线高１５ｃｍ。ＨｉｎｄｅｏｄｕｓｐａｒｖｕｓＭｏｒｐｈｏｔｙｐｅ１的首次出现,即为长兴阶的顶界。     

High-resolution carbon isotope changes in the Permian–Triassic boundary interval, Chongqing, South China; implications for control and growth of earliest Triassic microbialites

High-resolution δ¹³C_CARB analysis of the Permian–Triassic boundary (PTB) interval at the Laolongdong section, Beibei, near the city of Chongqing, south China, encompasses the latest Permian and earliest Triassic major facies changes in the South China Block (SCB). Microbialites form a distinctive unit in the lowermost 190 cm above the top of the Changhsing Formation (latest Permian) at Laolongdong, comparable to a range of earliest Triassic sites in low latitudes in the Tethyan area. The data show that declining values of δ¹³C_CARB, well-known globally, began at the base of the microbialite. High positive values (+3 to 4 ppt) of δ¹³C_CARB in the Late Permian are interpreted to indicate storage of ¹²C in the deep waters of a stratified ocean, that was released during ocean overturn in the earliest Triassic, contributing to the distinctive fall in isotope values; this interpretation has been stated by other authors and is followed here. The δ¹³C_CARB curve shows fluctuations within the microbialite unit, which are not reflected in the microbialite structure. Comparisons between microbialite branches and adjacent micritic sediment show little difference in δ¹³C_CARB, demonstrating that the microbialite grew in equilibrium with surrounding seawater. The Early Triassic microbialites are interpreted to be a response to upwelling of bicarbonate-rich poorly oxygenated water in low latitudes of Tethys Ocean, consistent with current ocean models for the PTB interval. However, the decline of δ¹³C_CARB may be due to a combination of processes, including productivity collapse resulting from mass extinction, return of deep water to ocean surface, oxidation of methane released from methane hydrate destabilisation, and atmospheric deterioration. Nevertheless, build-up of bicarbonate-rich anoxic deep waters may be expected as a result of the partial isolation of Tethys, due to continental geography; release of bicarbonate-rich deep water, by ocean upwelling, in the earliest Triassic may have been an inevitable consequence of this combination of circumstances.     

Problems of migration of Polish crude oils on the basis of geochemical correlation data and carbon isotope composition

A method for the correlation of crude oils has been worked out on the basis of analyses of 120 crude oils from 4 geological regions of Poland.     

川东北飞仙关组甲烷为主的TSR及其同位素分馏作用

川东北开江-梁平陆棚东北侧飞仙关组多孔鲕粒白云岩中发生了以甲烷为主的热化学硫酸盐还原作用(TSR),产生高达20%的H₂S;而西南侧鲕粒灰岩以低孔、低H₂S天然气为特征。东北侧白云岩主要发育白云石粒间溶孔或粒间扩大溶孔,这些溶孔可与方解石(δ¹³C=-10‰~-19‰)、储层沥青、元素硫、黄铁矿和石英紧密共生,可分布于片状储层沥青与白云石晶体之间,说明白云石溶解作用发生在沥青形成以后。白云石的溶解作用导致现今天然气以无机CO₂为主,δ¹³C_CO2主要介于-2‰~+2‰之间。这种溶解作用是在酸性条件下,硬石膏或天青石参与下发生的,可能先产生MgSO₄配对离子,而后MgSO₄又与甲烷反应产生H₂S,净增大了孔隙。研究还发现,普光气田及以东天然气的来源不同于河坝和元坝天然气;对普光气田及以东天然气分析显示,甲烷δ¹³C值与残余烃含量 之间存在对数相关关系。这表明TSR过程中,甲烷同位素分馏作用遵从封闭体系下瑞利分馏原理。据此计算显示,渡4井约有15%甲烷被氧化了。     

浙江长兴煤山地区二叠-三叠系界线底粘土中动物化石的发现及其意义

<正> 浙江长兴煤山地区是我国南部上二叠统长兴阶及二叠-三叠系界线候选层型剖面的所在地。近十年来,我们先后在本区测制了6条上二叠统长兴阶及二叠-三叠系界线剖面,即剖面A.B.C.D.E和Z(Sheng et al.,1984)把下三叠统下青龙组底部的混生动物群层自下而上分成混生层1、2和3三层,混生层1包括两部分,下部为伊利石-蒙脱石粘土层,亦称底粘土(basal clay),上部为黑色泥岩,当时没有在底粘土发现化石。此后,一     

贵州省黔西县官坝地区二叠系—三叠系地质界面碳、氧同位素特征及意义

研究了贵州省黔西县官坝地区二叠系—三叠系界线附近岩石样品的碳、氧同位素,结果表明,δ13C具有一个明显的负漂移,δ180也具有明显降低特点.在界线附近发现的3层凝灰岩表明,在晚二叠世—早三叠世该区发生过火山活动.火山活动导致了沉积环境突变,致使二叠纪末发生了生物集群灭绝事件.     

川东北宣汉黄金口一带中三叠统雷口坡组底界划分

川东北宣汉黄金口一带能源、矿产资源丰富,中三叠统雷口坡组是该区钾、锂资源的赋矿层位之一,也是该区重要的天然气储层。黄金口一带雷口坡组底界多以岩性组合和测井曲线特征来划分,而不是以区域上广泛分布的“绿豆岩”作为其底界划分的标志。笔者在该区的1口钾盐探井中发现绿豆岩,其厚度2~3 cm,镜下鉴定其为富钾长石玻屑凝灰岩。XRD分析表明其主要矿物成分为石英、微斜长石、白云母。通过对岩性组合和测井曲线的对比研究,认为黄金口一带雷口坡组底界应下移,位于原划分的嘉陵江组中。     

Strontium isotope stratigraphy in the Late Cretaceous: intercontinentaI correlation of the Campanian/ Maastrichtian boundary

In the Boreal Chalk of northwestern Europe the base of the Maastrichtian Stage is defined by entry of the belemnite Belemnella . In the Kronsmoor section, in northwestern Germany, which is a standard section for the European Chalk, ⁸⁷Sr/⁸⁶Sr at the Campanian/ Maastrichtian (C/M) boundary is 0.707723±9 (10). An isotopic correlation of this boundary to the US Western Interior, for which a highly refined cephalopod biostratigraphy exists, suggests that this boundary, as defined at Kronsmoor, occurs within the Baculites jenseni zone. This correlationagrees with the latest placement based on biostratigraphic criteria. On⁸⁷Sr/⁸⁶Srcriteria the boundary at Kronsmoor correlates to the English Chalk at Trunch, Norfolk, UK, at a level 3.5 m lower than its position based on biostratigraphic criteria.
At Kronsmoor, ⁸⁷Sr/⁸⁶Sr increases in a quasi-linear manner through much of the section, suggesting that, averaged over intervals of 1 Myr, the gross sedimentation rate and temporal rate of change of ⁸⁷Sr/⁸⁶Sr were approximately constant through the section. For US samples, zonally-plotted values of ⁸⁷Sr/⁸⁶Sr define a quasi-linear trend, which suggests a moderate uniformity of zonal duration from the Baculites compressus zone (73.2±0.7 Ma, 10) to the Baculites grandis zone (70.1±0.7 Ma, 10).     

A Review on the Global Stratotype Section and Point of the Permian-Triassic Boundary

1 Introduction The Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary (PTB) has been ratified by IUGS in 2001 (Yin et al., 2001). It is defined at the base of the Hindeodus parvus horizon, i.e. the base of Bed 27c of Meishan Section D, Changxing County, Zhejiang Province, South China. The PTB is important because it is not only an erathem boundary but also a great turning point of geological history symbolized by profound global changes and the strongest …     

二叠系-三叠系界线全球层型剖面——回顾和进展

综合评述了5年来对二叠系—三叠系界线(PTB)全球层型剖面——煤山D剖面的研究进展。简要介绍剖面的研究历史、地理和地质背景,叙述了世界上最完整的二叠纪长兴期至三叠纪格里斯巴赫期的牙形石和菊石带,并简短讨论了Otoceras的年代。叙述了煤山与其他剖面长兴期至格里斯巴赫期磁性地层学的对比。介绍了δ13C和δ34S的化学地层学最新研究进展,特别是在PTB附近多个δ13C负漂移的发现。两项重要的分子地层学研究显示了基础生态系统的深刻变化——微生物生态系的灾变和在二叠纪—三叠纪生态系之交严重缺氧事件期间透光带的静海相环境。文章报道了自2001年以来PTB年代测定的进展。PTB之下14cm处火山成因的粘土层25层的年代,现在定为(252·4±0·3)Ma(Mundil等,2004)。文章还讨论了事件地层学,认为尽管在25-26层有一个主事件,煤山PTB附近的事件是多幕式的,并且开始于事件层25-26层之前。因此,PTB大绝灭主因是外星撞击导致的可能性是不大的。     

中国南方二叠-三叠纪过渡时期的碳同位素旋回地层与突变事件

在中国南方晚二叠世至早三叠世初碳酸盐岩的Ｃ 同位素演化基础上, 考察了长兴阶层型剖面的高分辨率Ｃ 同位素旋回地层,发现长兴阶有三个Ｃ 同位素四级旋回,与吴家坪阶晚期的一个四级旋回共同组成了一个完整的三级旋回。与这种缓慢变化形成强烈对比的是：Ｐ／ Ｔ 界线上在１ ．５ ～２．６ 万ａ 左右的地球年时间中δ１３ Ｃ 突变为高负值, 形成剧烈负异常, 其中生物集群绝灭因素可能占２／３ 以上,变负幅度约５‰～６ ‰。二叠纪末生物集群绝灭的原因可能与大规模的火山爆发引起的气体增加和缺氧事件有关。