Sequence Stratigraphy of the Permian--Triassia Boundary Section of Changxing, Zhejiang, Southern China

Three third-order sequences and about one hundred high-frequency cycles or Milankovitchcycles within the Late Permian Changxingian to Early Triassic Griesbachian are identified in theMeishan Section of Changxing, Zhejiang Province, southern China, the candidate stratotype sec-tion of the global Permo-Triassic boundary, based on a detailed study of the biological,ecological and high-resolution allochthonous cyclic events, microfacies and depositional systems.Furthermore, the stacking pattern of the depositional systems across various Changxingian andGriesbachian sedimentary facies of the Lower Yangtze and the sequence stratigraphic frameworkare outlined with the Meishan section as the principal section. In this paper the habitat types offossil biota are applied to semiquantitative palaeobathymetry and the study of relative sea levelchanges.     

南非陆相二叠系-三叠系界线研究进展

从岩石地层研究着手,介绍了南非卡鲁盆地内综合地层研究的相关成果.在生物地层方面,脊椎动物和植物化石的研究在该区具有传统优势,孢粉化石的研究则是在最近几年才取得较大进展,在陆相界线地层研究中菌孢化石在二叠系-三叠系界线处约1 m厚的地层内的富集事件属首次报道.在地球化学地层方面,南非有机碳同位素在二叠系-三叠系界线附近的变化趋势与海相二叠系-三叠系界线地层存在相似的对应关系,可以作为海、陆相界线地层对比的辅助标志.在磁性地层方面,南非卡鲁盆地内的磁极性存在从反向到正向然后再反转(R-N-R)的变化,二叠系-三叠系界线则位于第一反向极性带的顶部.同时,结合目前全球陆相二叠系-三叠系界线的研究现状及特点,分析了陆相界线地层研究中存在的基本问题,指出华南地区可能为突破传统观念的研究地区,陆地事件地层研究意义重大.     

广西东攀P-T界线深水相剖面与煤山剖面地层学对比

从放射虫生物地层学、黏土矿物事件地层学和有机碳同位素地层学方面对广西柳桥地区东攀二叠系-三叠系深水相剖面进行了研究,并与浙江煤山剖面(GSSP)同期地层进行了对比.结果表明,东攀剖面上二叠系-三叠系界线处与煤山剖面具有较好的可比性:①东攀剖面放射虫A.yaoi带可以与煤山剖面的Clarkina changxingensis-C.postwangi-C.postsubcarinata-C.deflecta组合带对比;②两剖面都具有性质相似、延伸稳定的界线黏土岩;③在两剖面界线黏土岩中,有机碳同位素组成都发生了巨减.     

Absence of extraterrestrial He in Permian-Triassic age sedimentary rocks

Helium concentration and isotopic composition were measured in a suite of samples across the Permian-Triassic boundary at Opal Creek, Canada, to determine whether high extraterrestrial helium concentrations are associated with a possible extinction-inducing impact event at this time. No extraterrestrial ³He was detected, implying that neither fullerene-hosted nor IDP-hosted He is present at or near the boundary. This observation is consistent with similar studies of some Permian-Triassic sections, but contrasts sharply with reports of both fullerene- and IDP-hosted extraterrestrial ³He at other sections.Step-heat experiments indicate rapid diffusion of extraterrestrial helium from sediments heated to temperatures above ∼ 70 °C. Given the likelihood of burial and associated heating in Permian-Triassic age rocks, the initially unexpected absence of IDP-hosted ³He likely indicates thermally induced diffusive loss. Indeed one of the key sections (Graphite Peak, Antarctica) from which extraterrestrial ³He has been reported at and near the Permian-Triassic boundary has been sufficiently heated that the reported preservation of extraterrestrial helium, in both IDPs and fullerenes, is inexplicable. Recent contamination provides a plausible explanation for extraterrestrial ³He in these samples.While no extraterrestrial ³He was detected at Opal Creek, there is a sharp increase in nucleogenic ³He very close to or at the Permian-Triassic boundary. This presumably arises from the major lithologic change at this time, from cherts in the Permian to shales and siltstones in the Triassic. Increased nucleogenic ³He is associated with increases in both lithium and organic carbon content into the Triassic. Either the production rate or the retention of this ³He is higher in the shales and siltstones than in the cherts. Care must be taken to eliminate such artifacts before interpreting changes in ³He concentration in terms of fluctuations in the delivery of ³He from space.     

Microbialite of anoxic condition from Permian-Triassic transition in Guizhou,China

Spherical microfossils are present in the Hindeodus parvus zone of the Lower Triassic in Ziyun,Guizhou Province. They generally range from 0.15 to 0.30 mm across,with micritic wall and filled by micro-sparry calcites,and are evenly scattered in micritic matrix. Their abundance makes the rock as-signed to microbialites. The accompanied organisms include ostracods and algal mat,but no gastro-pods or bivalves. Presence of small (<7 μm) pyrite framboids indicates that this bed formed in anoxic conditions. In some sections,this bed is overlain and underlain by tidal-flat micritic limestone with microgastropods and small burrows. Occurrence only in deposits on reef top indicates that the micro-bial organism was benthic,and needed sunlight in life. The size of the microbial fossil exceeds that of any bacteria or cyanobacteria. Thus,it does not belong to these two phyla. It may belong to lower green algae,and is assigned to a new species in a new genus,Ziyunosphaeridium sinensis gen. et sp. nov. Up to now,the rocks described as microbialites from the Permian-Triassic transition include six types: (1) porous micritic limestone such as that descried from Japan by Sano and Nakashima (1997),(2) limestone with rich globular microfossils such as that described from the Nanpanjiang Basin in China by Lehrmann (1999),(3) dendroidal limestone such as that described from the vicinity of Chongqing by Kershaw et al. (1999),(4) spherical microbial limestone adapted to anoxic environments described from Ziyun,Guizhou reported in this paper,(5) limestone with cyanobacterial fossils such as that described by Wang et al. (2005),and (6) stromatolites. All these microbialites are not reefs in the proper sense,and the argument that Permian reef ecosystems extended into the Mesozoic is incorrect.     

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 …     

鄂尔多斯盆地南缘上二叠统——中下三叠统地球化学特征及其古气候、古环境指示意义

为探索陆相湖泊环境记录中二叠纪—三叠纪之交古气候演化的信息,以鄂尔多斯盆地南缘陕西铜川石川河剖面上二叠统石千峰组(P3s)和三叠系的刘家沟组(T1l)、和尚沟组(T1h)、纸坊组(T2z)为研究对象,对界面上下地层开展了系统的矿物学、岩石学和地球化学研究。通过主量和微量元素、碳氧同位素以及TOC测试对古盐度、古氧化还原环境和古气候演化规律进行分析。测试结果显示在二叠系—三叠系(P/T)界线附近主、微量元素和碳、氧同位素发生较明显的变化,气候环境代用化学指标的波动指示了从晚二叠世至早中三叠世鄂尔多斯盆地的古气候、古环境的变化。研究结果表明上二叠统石千峰组形成于河流-三角洲沉积环境,氧化程度相对低,古气候相对温暖湿润;下三叠统刘家沟组与和尚沟组的紫红色砂泥岩代表水体较浅的河流-三角洲相,强氧化环境,气候干旱炎热;而到中三叠统纸坊组沉积期,湖平面上升,元素的迁移作用加强,氧化程度变弱,气温降低,气候转为半干旱半湿润气候。碳同位素分析结果显示,鄂尔多斯盆地陆相P/T界线上δ^13CPDB存在显著负偏,与全球范围内的海相P/T界线具有一致性,说明在华北地台陆相P/T界线上同样存在气候突变和生物灭绝等重大地质事件的沉积记录,与海相地层可对比。     

Sulfur Isotopes of Framboidal Pyrite in the Permian-Triassic Boundary Clay at Meishan Section

Pyrite framboids were found in the Permian-Triassic boundary at Meishan Section, while their sulfur isotopes were determined. The majority of framboids is less than 5 μm in diameter, with some large-sized framboids. Also, euhedral gypsums were observed in the boundary clay. The authors suppose that most of the pyrite framboids formed just below the redox boundary and stopped growing after entering the lower water column. The result indicates that it was probably lower dysoxia condition in the temporal ocean. Moreover, the authors also presume that some pyrite was oxidated to sulfates accompanying the fluctuation of redox condition, which would probably be the origin of the negative sulfur isotopes of gypsum and CAS reported before. In addition, sulfur isotope of framboidal pyrite suggests that sulfur is originated from bacterial sulfate reduction in anoxic condition. Therefore, this study confirms that the ocean was widely anoxic during the Permian-Triassic transitional period. However, the redox condition in temporal ocean was probably not stable, with short-term fluctuations.     

江西修水二叠系-三叠系界线地层树枝状微生物岩状岩石成因初解

江西修水二叠系-三叠系界线地层有一段特殊构造的地层，下部为灰色部分和红色部分组成的斑状构造，上部为灰色部分和黄色部分组成的树枝状构造。这种树枝状构造的岩石与前人报道自重庆老龙洞剖面的微生物岩非常相似。岩石薄片观察表明，树枝状构造的暗色部分为残留的灰泥岩；浅色部分为灰岩经过重结晶、白云石化去白云石化作用改造而成。在暗色的残留灰岩里有保存很好的丰富的球状微生物化石。研究认为，岩石中暗色部分和浅色部分的原始组分是同时沉积的；是成岩作用控制了浅色部分的形成。这一成果应当对认识老龙洞剖面树枝状微生物岩的成因有借鉴作用。