广西东攀二叠系-三叠系界线剖面基于岩石磁参数的米兰科维奇旋回特征和地层对比

二叠纪-三叠纪之交发生了地质历史上最大的生物集群绝灭。通过对广西东攀二叠系-三叠系界线剖面不同的磁学数据进行频谱分析,其结果均具一致的功率谱峰,对比煤山剖面的同位素年龄将厚度频率35.7∶15.6∶7.7cm/cycle换算为时间周期95∶41.6∶20.5kyr/cycle,分别与米兰科维奇旋回偏心率、斜度、岁差相当,从而将地层研究的精度提高到万年级,为生物绝灭和众多地质事件提供时间上的约束。不同的磁学参数分别受控于不同的天文周期,磁性矿物种类主要受偏心率旋回控制,同时也受斜度周期的影响,而岁差周期则是促使岩石携磁能力高频变化的原因。不同二叠系—三叠系剖面(集中在界线附近)的磁化率曲线具有一致特征,可作为界线点确定的辅助依据。     

浙江长兴地区长兴组放射虫化石及其指相意义

浙江省长兴地区的长兴组煤山剖面一直作为中国乃至世界研究二叠系-三叠系界线的经典剖面之一。在该剖面,长兴组主要由灰黑、黑色碳酸盐组成,厚度约为30-45m。依据沉积岩性特征大致可划分上下2段:下段以灰黑或黑色的纹层状粒泥岩和泥粒岩为主,厚度约13m;上段由薄一中层状灰黑或黑色泥粒岩和粒泥岩组成,其中夹有极薄层的黑色钙质泥岩或泥岩和细条带状或透镜状硅质岩,厚27m左右。     

广西来宾蓬莱滩二叠纪瓜德鲁普统—乐平统界线剖面元素和同位素地球化学研究及地质意义

广西来宾蓬莱滩二叠系瓜德鲁普统-乐平统界线剖面已被国际地质科学联合会确定为国际界线层型标准剖面,在该界面附近发生了一次重要的全球性生物绝灭事件。蓬莱滩剖面样品采自乐平统合山组底部(由硅质岩和透镜状灰岩组成)和瓜德鲁普统茅口组上部来宾灰岩(由硅质灰岩、灰岩和少量硅质岩组成)。它们具有高的SiO2含量(除3个样品低于10%以外,其余样品均大于17%,平均为43.44%)、m值(>50)与Sr/Ba值(>1.0)和低的MgO/CaO(绝大部分低于02)与 V/(V+Ni)值(<046); Ce和Eu亏损明显。这些地球化学特征反映它们是在相对氧化的浅海环境中形成的,硅的来源非常丰富。样品的εNd(t)值(-7.5~-3.3)和(87Sr/86Sr)i值(0.70705~0.70739)都位于全球大洋Nd、Sr同位素演化曲线晚二叠纪时期区域内。有机碳的δ13Corg值变化明显(-26.7‰~-23.2‰),尤其是在瓜德鲁普统与乐平统以及茅口组与合山组界线附近发生显著的负漂移(达34‰),而且与无机碳的δ13C值呈现大致平行的变化趋势,证实在该界线附近发生过生物绝灭事件。虽然对瓜德鲁普统—乐平统交替时期发生的生物绝灭事件已提出过包括海平面下降在内的多种假设,但本文认为,由地幔柱上升引起的、以峨嵋山玄武岩喷发为代表的超级火山活动以及由此引起的环境效应是该时期生物绝灭的主要原因。     

地层单位与全球界线层型:概念、术语、有关规定与研究实例

全球二叠系-三叠系界线(PTB)层型及点("金钉子")定位我国浙江省长兴县煤山D剖面,极大地推动了PTB及二叠系和三叠系研究进展。在简要介绍地层单位与全球界线层型与点建立的相关概念、术语和有关规定、地层划分的主要种类及其地层单位术语的基础上,以全球二叠系—三叠系界线层型及点(中国浙江省长兴县煤山D剖面)为研究实例,综述了该金钉子剖面牙形石生物地层和年代地层研究现状。煤山D剖面构建了目前全球最完整的PTB地层牙形石带序列,为研究二叠纪末大灭绝后生物残存和复苏过程提供了重要的时间坐标系,也为相关的地质事件研究奠定了坚实的基础。     

论二叠系-三叠系界线定义

<正> 一个合理的二叠系-三叠系界线定义对于正确划分它的界线和选择它的层型剖面是十分必要的。自1971年国际二叠系-三叠系界线会议(Calgary,Canada)以来,二叠系-三叠系界线研究有了很大的进展。在1984年莫斯科国际地质大会召开期间举行的二叠系-三叠系界线工作会议上,多数委员赞同以Otoceras 带的底为三叠系底界的传统定     

西秦岭地区二叠—三叠系界线地层研究

在西秦岭地区南秦岭带广泛发育碳酸盐岩型二叠、三叠系。本文以选部益哇沟剖面为例，对该区界线地层进行研究，从岩石地层划分、生物地层划分以及地球化学元素最优分割研究出发，确定了二叠、三叠系界线点，证明牙形石Ｈｉｎｄｅｏｄｕｓｐａｒｖｕｓ可作为三叠系开始的标志，并且二叠、三叠系是连续的。沉积环境分析表明，三叠纪初期相对于二叠纪末发生了一次海侵。     

湖北恩施三岔口二叠系-三叠系界线附近黏土岩锆石U-Pb年龄及地质意义

通过对恩施地区二叠系-三叠系界线附近含凝灰质黏土岩的野外地质学特征调查,采用锆石U-Pb同位素测试分析,取得其206Pb/238 U加权平均年龄为251.6±1.2Ma,该年龄值为二叠系-三叠系界线附近的火山喷发事件的年龄。结合碳和氧同位素分析,二叠系-三叠系界线附近黏土层之上碳同位素明显负偏,这与该时期生物绝灭事件关系密切。通过区域对比,发现该套黏土岩在区域上可进行连续追踪,不同地区界线附近岩石组合差异性明显,二叠系顶部自西向东总体表现为碳酸盐岩比例逐渐减少、碳硅质岩逐渐增加的特征。     

西藏海相三叠系—侏罗系界线及晚三叠世生物绝灭事件研究

1998—2004年间在西藏聂拉木、林周、墨竹工卡和洛扎等地进行的三叠系/侏罗系界线地层研究表明,西藏隆子县和洛扎县尚未发现具有连续菊石层序的三叠系/侏罗系界线地层剖面。拉萨以北地区广泛分布的火山岩时代确定为晚三叠世—早侏罗世早期,这有助于解释晚三叠世末期生物绝灭与晚三叠世岩浆侵入和大规模的火山活动有关,但T/J界线尚待精确限定。聂拉木县格米格剖面是特提斯地区唯一未曾“压缩”的三叠系/侏罗系界线地层剖面,具有瑞替阶MARSHI菊石带、赫塘阶Tibeticum、Callyphyllum和Pleuro-notum菊石带。格米格剖面三叠系/侏罗系界线碳稳定同位素曲线记录了晚三叠世瑞替阶末期(Marshi菊石带)突然的负偏移,它很有可能和晚三叠世末期的由超级温室效应所产生的生物绝灭事件相对应。     

桂西南柳桥地区深水相二叠系-三叠系界线剖面

桂西南柳桥地区上二叠统为厚约84m的浅灰—灰白色块状海绵蓝藻生物灰岩(生物礁),之上为浅灰绿色—暗灰色薄层状含远洋浮游生物硅质岩、含泥质硅质岩、硅质泥岩(大隆组),这套深水相的沉积岩夹有大量浅灰白色的粘土岩。上覆的三叠系罗楼组底部为黄色泥岩,夹多层灰白色粘土岩,往上渐变为灰色薄层状含大量双壳类、菊石化石的钙质泥岩、泥灰岩。柳桥地区晚二叠世末期沉积岩和中基性火山岩的特征显示其是在地壳裂解、快速沉降、相对海平面快速上升过程中迅速淹没台地边缘的生物礁而形成的深水相海盆,造成深水盆地与浅水台地并存,具有多岛洋的地理分布格局。东攀二叠系-三叠系界线剖面的露头完整,对剖面的岩石学特征、生物化石组合特征等方面的详细研究显示,该地区一直处于连续沉积的深水环境中,没有发生沉积间断,界线上下的岩石特征和生物组合特征较清楚。     

黔南克脚二叠纪末生物群特征及其地质意义

贵州惠水克脚剖面是南盘江盆地北缘二叠系-三叠系界线剖面,地层连续,产不同门类的化石,对古生代-中生代之交黔南古地理和生物演化研究具有重要意义。剖面主要包括上二叠统大隆组和下三叠统大冶组下部。大隆组岩性主要为硅质泥岩、钙质泥岩和炭质页岩,夹火山灰黏土岩与薄层硅质灰岩,泥岩发育水平层理。大隆组主要产游泳生物菊石、浮游生物放射虫,另外产小个体腕足类、双壳类和腹足类等,少数层位含植物化石。大冶组下部主要为薄层泥质灰岩夹钙质泥岩。通过岩性、古生物组合、沉积构造等分析,认为本剖面在二叠纪末为离古陆较近的深水沉积。     

Facies analysis of the Semanggol Formation,South Kedah,Malaysia: A possible Permian–Triassic boundary section

Although the Permian–Triassic Semanggol Formation is widely distributed in northwestern Peninsula Malaysia and is made of various lithofacies, its sedimentology and possible relation with the Permian–Triassic boundary (PTB) were not considered before. In this study, detailed facies analysis was conducted for two sections of the Semanggol Formation at the Bukit Kukus and Baling areas, South Kedah to clarify its sedimentology and relation to the PTB. Four facies from the Permian part of the Semanggol Formation that were identified at the Bukit Kukus section include laminated black mudstone, interbedded mudstone and sandstone, volcanogenic sediments, and bedded chert. In Baling area, the Triassic part of the formation is classified into three members. The lower member comprises of claystone and bedded chert facies, while the middle member is composed of sandstone and claystone interbeds (rhythmite). On the other hand, the upper member is grouped into two main units. The lower unit is mainly claystone and includes two facies: the varve-like laminated silt and clay and massive black claystone. The upper unit is composed of various sandstone lithofacies ranging from hummocky cross stratified (HCS) sandstone to thinly laminated sandstone to burrowed sandstone facies. The HCS sandstones occur as two units of fine-grained poorly sorted sandstone with clay lenses as flaser structure and are separated by a hard iron crust. They also show coarse grains of lag deposits at their bases. The laminated black mudstone at the lowermost part of the Semanggol Formation represents a reducing and quite conditions, which is most probably below the fairweather wave base in offshore environment that changed upwards into a fining upward sequence of tide environment. Abundance of chert beds in the volcanogenic sediments suggests the deposition of tuffs and volcanic ashes in deep marine setting which continues to form the Permian pelagic bedded chert and claystone. The bedded chert in the lower member of the Triassic section suggests its formation in deep marine conditions. The rhythmic sandstone and claystone interbeds of the middle member are suggestive for its formation as a distal fan of a turbidite sequence. Lithology and primary sedimentary structure of the upper member suggest its deposition in environments range from deep marine represented by the varve-like laminated silt and clay to subtidal environment corresponds to the massive black claystone to coastal environment represented by the hummocky sandstone units and reaches the maximum regression at the hiatus surface. Another cycle of transgression can be indicated from the second hummocky unit with transgressive lag deposits that develops to relatively deeper conditions as indicated from the formation of relatively thick laminated sandstone and bioturbated massive sandstone facies that represent tidal and subtidal environment, respectively. Late Permian lithological variation from the radiolarian chert into early Triassic claystone probably resulted from a decrease in productivity of radiolarians and might represent a PTB in the Semanggol Formation. Volcanogenic sediments in the studied section can be used as an evidence for volcanic activities at the end of the Permian, which is probably connected to the nearby volcanic ash layers in the eastern China, the ultimate cause of the PTB in this area. Black mudstone in the Permian part of the studied section may be interrelated to the Latest Permian Anoxia that started to build in the deep ocean well before the event on shallow shelves.     

鄂西地区上二叠统的牙形石及其分带意义

湖北恩施天桥剖面发育有完好的二叠系大隆组下段硅质岩层。对其下伏吴家坪组灰岩及上覆大隆组上段灰岩中牙形石的研究表明,吴家坪组灰岩自下而上可分为Clarkina postbitteri postbitteri带、Clarkina dukouensis带、Clarkina asymmetrica带以及Clarkina guangyuanensis—Clarkina transcaucasica带,属吴家坪阶中下部牙形石带;大隆组上段灰岩可划分出两个牙形石带,即Clarkina subcarinata—Clarkina wangi带和Clarkina changxingensis changxingensis—Clarkina deflecta带,为长兴阶底部牙形石带。认为鄂西地区大隆组下段硅质岩的时代应归属于二叠纪吴家坪中期至长兴早期。     

浙江长兴煤山地区晚二叠世末、早三叠世初的火山活动

<正> 近年来,不少学者分别从生物地层(赵金科等,1981;盛金章等,1983;王义刚,1984;Sheng Jinzhang et al.,1984),事件地层(孙亦因等,1984;何锦文,1985),岩相、生物相(杨万容等,1981;芮琳等,1984),粘土矿物(何锦文,1981),元素地球化学特征(柴之芳等,1986),构造岩浆活动(周瑶琪,1986)以及碳同位素(陈锦石等,1984)等方面对浙江     

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 …     

Restudy of conodont biostratigraphy of the Permian–Triassic boundary section in Zhongzhai,southwestern Guizhou Province,South China

New conodont samples have been systematically collected at high stratigraphic resolution from the upper part of the Longtan Formation through to the lower part of the Yelang Formation at the Zhongzhai section, southwestern Guizhou Province, South China, in an effort to verify the first local occurrence of Hindeodus parvus in relation to the Permian–Triassic boundary at this section. The resampled conodont fauna from the Permian–Triassic boundary interval comprises five identified species and two undetermined species in Hindeodus and Clarkina. Most importantly, the first local occurrence of Hindeodus parvus is found for the first time from the bottom of Bed 28a, 18 cm lower than the previously reported first local occurrence of this species at this section. Considering the previously accepted PTB at the Zhongzhai section, well calibrated by conodont biostratigraphy, geochronology and carbon isotope chemostratigraphy, this lower (earlier) occurrence of H. parvus suggests that this critical species could occur below the Permian–Triassic boundary. As such, this paper provides evidence that (1) the first local occurrences of H. parvus are diachronous in different sections with respect to the PTB defined by the First Appearance Datum (FAD) of this species at its GSSP section in Meishan, China and that (2) the lower stratigraphic range of H. parvus should now be extended to latest Permian.     

INVERSION OF STRIKE-SLIP MOVEMENTS ALONG THE YARLUNG ZANGBO SUTURE ZONE, TIBET

INVERSION OF STRIKE-SLIP MOVEMENTS ALONG THE YARLUNG ZANGBO SUTURE ZONE, TIBET     

西藏色龙西山色龙群的时代及二叠系与三叠系的界线

<正> 色龙群于1964年由希夏邦马峰登山队科学考察队(1982)命名,层型剖面在聂拉木县色龙村西北约1km的小山上,时代为二叠纪。穆恩之等(1973)认为色龙群的时代属早二叠世晚期。章炳高(1974)、吴望始(1975)、张守信、金玉玕(1976),王玉净、穆西南(1984)对色龙群的时代有类似的看法,均未提及它包含有长兴期地层的存在。饶荣标等(1985)将色龙群分为两组,上部为扒嘎组,下部为门多组。在色龙西山剖面,扒嘎组为生物碎屑灰岩,厚4.15m,含Gertholites curvatus,Thamnopora densa,Pseudofavosites irregularis,Trachypora sp.,Sinkiangopora sp.,时代属晚二叠世,与上覆下三叠统土隆组为整合接触。     

塔里木盆地阿克1井二叠纪孢粉地层及其地质意义

阿克 1井是塔里木盆地西南坳陷喀什凹陷乌恰构造带阿克莫木背斜北高点的第一口预探井 ,该井中二叠统比尤列提群 (P2 by)钻厚 2 5 5 .5 0 m(395 4— 4 2 0 9.5 0 m,未钻穿 ) ,为灰褐、灰、深灰色泥岩、粉砂质泥岩与同色灰质泥岩近等厚互层 ,偶夹薄层浅灰、灰色泥灰岩、泥晶含泥灰岩及灰色泥质粉砂岩、粉砂岩 ,产大量孢粉化石 ,可建立Florinites- Protohaploxypinus- Vittatina组合 ,地质时代为中二叠世。该井二叠纪地层的钻揭 ,具有非常重要的地质意义 ,不但完善了该地层小区的地层层序 ,而且丰富了二叠纪的孢粉化石资料 ,填补了该区二叠纪古生物研究的空白 ,还改变了对该区生油条件的评价 ,提高了对该区的含油气远景评价等级。