藏南泽当卡多地区中生代放射虫动物群研究及其地质意义

雅鲁藏布江蛇绿岩带一直以来被认为是新特提斯洋岩石圈的残留,其与雅鲁藏布江缝合带内相关的海相地层共同记录了新特提斯洋的演化过程以及印度—欧亚板块的碰撞过程。位于藏南泽当西南卡多附近的硅质岩剖面中发现有保存较好的中生代放射虫化石,鉴定出放射虫31属39种,识别出4个放射虫组合,并将之与邻区及西特提斯地区放射虫化石带进行对比确定其时代:Alievium longispineum-Transhsuum maxwelli组合,晚巴通期—早卡洛夫期;Hsuum maxwelli-Triactoma mexicana组合,晚卡洛夫期—牛津期;Holocryptocapsa hindei-Hiscocapsa grutterinki组合,晚巴雷姆期—早阿普特期;Hemicryptocapsa polyhedra-Obeliscoites giganteus组合,晚阿尔布期—赛诺曼期。卡多硅质岩中所含放射虫组合可为泽当蛇绿岩的形成时限及新特提斯洋的演化提供重要的微体古生物依据。     

滇西北独龙江岩浆弧和丙中洛地块的划分与特征

为查明滇西北贡山地区大地构造单元的划分与特征,系统收集整理了不同比例尺的区域地质调查资料,得出4方面新认识:1该区大地构造单元划分为独龙江岩浆弧和丙中洛地块,二者分界为向东倾斜的高黎贡山逆冲推覆断裂;2独龙江岩浆弧属腾冲造山带,丙中洛地块属三江造山带,其间被中特提斯洋所分隔;3中特提斯洋于中侏罗世打开,晚侏罗世—早白垩世早期向西俯冲消减,早白垩世晚期—晚白垩世闭合;4班公错—东巧缝合带在该区已被向西逆冲推覆的高黎贡山岩群(Pt_1G.)所压覆。     

拉孜县幅地质调查新成果及主要进展

在雅鲁藏布江缝合带(中段)南部发现中、晚三叠世放射虫动物群,提供了该地区深水动物群新资料和混杂岩地层的年代依据.从原修康群(T3X)解体出中贝混杂岩(T2-3ZM)和破姆弄混杂岩(J3K1PM),前者形成于中-晚三叠世,后者形成于晚侏罗世-早白垩世,并由此揭示缝合带具有多旋回碰撞演化特征.冈底斯地块昂杰组(C2P1a)玄武岩的发现,表明藏南晚古生代超级冈瓦纳古大陆开始裂解.     

拉孜县幅地质调查新成果及主要进展

在雅鲁藏布江缝合带(中段)南部发现中、晚三叠世放射虫动物群，提供了该地区深水动物群新资料和混杂岩地层的年代依据。从原修康群(T3X)解体出中贝混杂岩(T2-3Z^M)和破姆弄混杂岩(J3K1P^M)，前者形成于中-晚三卺世，后者形成于晚侏罗世-早白垩世．并由此揭示缝合带具有多旋回碰撞演化特征：冈底斯地块昂杰组(C2P1a)玄武岩的发现，表明藏南晚古生代超级冈瓦纳古大陆开始裂解：     

试论西藏二叠纪(竹蜓)类及非(竹蜓)有孔虫的生物地理区系与古地理及古构造的关系

本文通过对西藏二叠系(竹蜓)类及非(竹蜓)有孔虫的研究认为,早二叠世早期(竹蜓)类以冷温型的Monodiexodina动物群为主,属冈瓦纳—特提斯生物区,冈瓦纳大陆与欧亚太陆及扬子地块的分界分别为昆仑山南坡断裂和金沙江断裂。早二叠世晚期(竹蜓)类Neoschwagerina-Polydiexodina动物群仍限于冈瓦纳北缘区,其生物区系以及扬子地块的分界与早二叠世早期相同,而冈瓦纳大陆北缘西部首先与欧亚大陆塔里木等地块接近,该动物群才越过了昆仑山北坡。晚二叠世晚期(竹蜓)类以Palaeofusulina动物群为主,与扬子地块相似属华夏—特提斯生物区,冈瓦纳与欧亚大陆的界线转为班公湖—怒江断裂,而冈底斯带与喜马拉雅带至今未见Palaeofusulina,该二带仍属冈瓦纳—特提斯生物区。     

雅鲁藏布江缝合带南缘混杂岩放射虫组合及其地质意义

在西藏南部雅鲁藏布江缝合带南侧的吉隆地区出露有一套混杂岩,该混杂岩中见大量的放射虫化石。其研究成果可为恢复缝合带南缘混杂岩地层层序、探讨特提斯古海洋盆地演化、揭示印度-亚洲板块的全面碰撞过程等提供重要的生物地层学证据。将吉隆地区桑单林剖面自下而上划分为宗卓组、桑单林组和者雅组3个岩石地层单元;并在其中发现有晚白垩世-始新世放射虫化石,鉴定出50属、72种,划分了4个放射虫化石带：Immersothorax cyclops带(晚白垩世Campanian期),Spongurus irregularis带(早古新世,RP1-RP3),Buryella dumitricai带(古新世中晚期,RP4-RP6),Phormocyrtis turgida带(始新世早期,RP7-RP8)。通过对古近纪时期特提斯喜马拉雅北亚带的地层、沉积等特征进行横向上的对比分析,认为古新世时处于特提斯喜马拉雅沉积带北亚带西段的吉隆地区为前渊环境,东段的江孜地区则为滨浅海沉积环境,表明西藏境内特提斯洋的闭合并不是同时发生的,而是沿雅鲁藏布江缝合带自东向西发生。     

青藏高原西部班公湖蛇绿混杂岩带的基本特征与构造演化

班公湖蛇绿混杂岩带位于班公湖-怒江结合带西段,是中生代特提斯洋消亡的遗迹。根据西藏1∶25万日土县幅、喀纳幅地质填图成果,将班公湖蛇绿混杂岩带的时空结构划分为南、北两条亚带;综合分析研究认为,本区中特提斯洋的演化经历了三叠纪-早中侏罗世扩张,中晚侏罗世双向俯冲,晚侏罗世-早白垩世残余洋(海)盆和晚白垩世陆(弧)-陆碰撞等构造演化阶段。     

新疆库车地区放射虫新资料及其意义

在新疆库车地区硅质岩地层中发现了丰富的保存良好的放射虫化石，共计１７属３７种，包括一新种。并在此基础上，建立了５个放射虫组合带。该放射虫动物群的多数分子曾见于德国的Ｆｌａｎｄｋｅｎｗａｌｄ地区和美国Ａｌａｓｋａ和Ｏｈｉｏ页岩中以及我国广酉。通过大量资料的分析对比，确定该套放射虫组合时代为晚泥盆世—早石炭世，进而阐述了这套放射虫硅质岩的大地构造意义。     

青海可可西里大地构造基本特征

在可可西里地区发现的晚古生代蛇绿混杂岩及不整合于其上的晚二叠世—早三叠世海滩亚相石英砂岩表明此区曾存在过古特提斯洋,早二叠世末古特提斯基本闭合。晚二叠世—早三叠世为相对稳定阶段。中、晚三叠世海侵,沉积了巨厚复理石。三叠纪末—早侏罗世发生了强烈的造山作用,形成造山带,可可西里地区进入陆内演化阶段。     

班公湖-怒江结合带西段中特提斯多岛弧构造演化

本文根据1∶25万地质填图成果,将班公湖-怒江结合带西段弧-盆系时空结构自北向南划分为五峰尖-拉热拉新晚侏罗世—早白垩世陆缘火山-岩浆弧带、班公湖蛇绿混杂岩北、南亚带和昂龙岗日-班戈白垩纪—始新世岩浆弧带等,初步认为中特提斯洋经历了三叠纪—早侏罗世扩张,中—晚侏罗世往北、南双向俯冲,晚三叠世—早白垩世残余洋(海)盆和早—晚白垩世陆-弧(陆)碰撞等演化阶段。     

PALEOCEANOGRAPHY AND EVOLUTION OF THE CENO-TETHYS: MICROPALEONTOLOGICAL EVIDENCE FROM PELAGIC SEDIMENTS IN THE YARLUNG ZANGBO SUTURE ZONE, SOUTHERN TIBET

PALEOCEANOGRAPHY AND EVOLUTION OF THE CENO-TETHYS: MICROPALEONTOLOGICAL EVIDENCE FROM PELAGIC SEDIMENTS IN THE YARLUNG ZANGBO SUTURE ZONE, SOUTHERN TIBET     

Late Olenekian Radiolarians from Bedded Chert of Ashio Terrane, Northeast Japan,and Faunal Turnovers in Western Panthalassa during Early Triassic

Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Asisian faunas, respectively, and is herein named the Minowa fauna. Study of the literaure indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian-Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic.The first turnover is the Poalaozoie-type radiolarian extinction at the Permain-Triassic boundary,the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic-type radiolarian famas that are characterized by mulit0segmented Nassellaria.     

Ceno-Tethyan Jurassic Radiolarian Fauna from the Raskoh Arc, Balochistan, Pakistan

The Raskoh arc is about 250 km long, 40 km wide and trends in ENE direction. The arc is convex towards southeast and terminated by the Chaman transform fault zone towards east. This arc is designated as frontal arc of the Chagai-Raskoh arc system. The Late Cretaceous Kuchakki Volcanic Group is the most widespread and previously considered the oldest unit of the the Raskoh arc followed by sedimentary rock formations including Rakhshani Formation (Paleocene), Kharan Limestone (Early Eocene) and Nauroze Formation (Middle Eocene to Oligocene), Dalbandin Formation (Miocene to Pleistocene), and semi-unconsolidated Subrecent and Recent deposits. The Rakhshani Formation is the most widespread and well-exposed unit of the Raskoh arc. During the present field investigation the Rakhshani forma-tion in the southeastern part of the Raskoh arc, is identified as an accretionary complex, which is designated as Raskoh accretionary complex. The Raskoh accretionary comple is subdivided into three units: (a) Bunap sedimen-tary complex, (b) Charkohan radiolarian chert, and (c) Raskoh ophiolite melange. The Bunap sedimentary complex is farther divided into three tectonostratigraphic units viz., northern, middle and southern. Each unit is bounded by thrust faults, which is usually marked by sheared serpentinites, except northern unit, which has gradational and at places faulted contact with the Kuchakki Volcanic Group. The northern unit is mainly composed of allochthonous fragments and blocks of limestone, sandstone, mudstone and the volcanics in dark gray, greenish gray and bluish gray siliceous flaky shale. At places the shale is metamorphosed into phyllite. This unit is thrust over the middle unit, which exhibits relatively a coherent stratigraphy, represented by greenish gray calcareous flaky shale with intercalation of thin beds and lenticular bodies of mudstone, sandstone and limestone. The middle unit is again thrust over the southern unit, which is mainly composed of large exotic blocks of volcanic rocks, limestone, sand-stone, mudstone and conglomerate embedded in dark gray, greenish gray and bluish gray siliceous flaky shale which is generally moderately argillized. The unit is thrust over the Kharan Limestone. During the present field investigation about 350 meter thick sequence of thin-bedded maroon and green chert intercalated with the siliceous flaky shale of the same colour are discovered within this unit, which is found in the southeastern part of the Ras-koh arc. This chert sequence occurs on the margins of a large exotic block (350m X 3 km) of volcaniclastic rocks of unknown origin, which makes an overturned syncline. This chert sequence is developed on its both limbs and has lower faulted contact with the Bunap sedimentary complex. Two samples collected from this chert sequence yielded radiolarian fauna, which include Parvicingula sp., Laxto-rum sp., Parahsuum cf. simplum, Parahsuum sp., Nassellaria gen. et sp. indet., Hsuum cf. Matsuokai., Archaeo-spongoprunum sp., Nassellaria gen. et sp. indet. and Hagias gen. et sp. indet., Tricolocapsa sp., Hsuum sp., Ris-tola sp., Archaeospongoprunum sp. and Tritrabinate gen. et sp. indet. This radiolarian chert sequence represents the late Early to Middle Jurassic pelagic sediment deposited in Ceno-Tethyan ocean floor; prior to the inception of volcanism in the Raskoh arc and accreted with the arc during Late Cretaceous to Eocene along with the Bunap sedimentary complex of Late Jurassic age.     

土耳其Sinop盆地晚白垩世大洋红层中的放射虫

在土耳其北部Sinop盆地Kayadibi剖面上发育了一套以红色灰岩及红色硅质岩为特征的,被称之为Kapanboˇgazi组的远洋或半远洋环境下的海相红色沉积。其中的硅质岩里产丰富且保存完好的放射虫化石。其放射虫组合以Crucella cachensis, Alievum superbum?, Patellula verteoensis, Patellula ecliptica, Dictyo mitra multicostata, Pseudodictyomitra pseudomacrocephala, Halesium triacanthum, Pessagnobrachia fabia nii, Pseudoaulophacus putahensis 和Paronaella communis 等属种同时出现为特征,可以与北美、西特提斯及俄罗斯等地建立的Alievum superbum 放射虫带对比,时代为土仑期。     

First direct age determination from the Jurassic radiolarian-bearing siliceous series (Jédidi Formation) of northwestern Tunisia

Our study presents preliminary biostratigraphic results from the Jurassic siliceous series of northwestern Tunisia. For the first time, radiolarians are extracted from the Jédidi formation and provide a direct age determination. They are the first radiolarian fauna documented from Tunisia. Two age assignments are comprised within the following intervals: (1) Late Bathonian–Early Callovian, (2) Late Bathonian–Early Oxfordian. These ages are compatible with recent stratigraphic synthesis proposed for the Jurassic series of Tunisia. The data suggest the correlation of the Jédidi formation with siliceous series of Middle–Late Jurassic age from the external zone of the Maghrebides belt rather than with true oceanic units from the Maghrebian flyschs or the internal zones of western Tethys. To cite this article: F. Cordey et al., C. R. Geoscience 337 (2005).     

滇西北金沙江带早石炭世深海沉积的发现

 70年代末以来,金沙江蛇绿岩带或金沙江缝合带受到人们的重视,其地质证据主要在滇西北德钦-川西南得荣一带(张之盂和金蒙,1979;陈炳蔚,1983;黄汲清等,1984;陈炳蔚等,1991)。由于该地区构造复杂,地形险峻,交通不便,研究程度不高。     

Radiolarian Age of Red Chert from the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. The radiolarian age of red chert from the Kunimiyama area of the Northern Chichibu Belt was determined in order to constrain the depositional age of the Kunimiyama deposit that is among the largest ferromanganese deposits in Japan. Pseudoalbaillella cf scalprata Holdsworth and Jones, Pseudoalbaillella cf longicornis Ishiga and Imoto and Pseudoalbaillella sp. belonging to the Ps. lomentaria Zone are found in the red chert, indicating an age of middle Early Permian (middle Wolfcampian). The red chert occurs immediately above the ferromanganese deposit, and the boundary between them is gradual. Based on their mode of occurrence and geochemical features, it is most likely that radiolarian chert and ferromanganese precipitate accumulated simultaneously to produce red chert during the waning stage of submarine hydrothermal activity that was responsible for the Kunimiyama deposit. Consequently, the age of Kunimiyama stratiform ferromanganese deposit is constrained as middle Early Permian (middle Wolfcampian).     

Study on the Tectonic Setting for the Ophiolites in Xigaze, Tibet

The Xigaze ophiolite is located in the middle section of the Yarlung Zangbo River ophiolite belt and includes a well-preserved sequence section of seven ophiolite blocks. The relatively complete ophiolitic sequence sections are represented by Jiding, Dejixiang, Baigang, and Dazhuqu ophiolites and consist of three–four units. The complete ophiolite sequence in order from the bottom to top consists of mantle peridotite, cumulates, sheeted sill dike swarms, and basic lavas±radiolarian chert. These cumulates are absent in the remaining blocks of Dejixiang and Luqu. The age of radiolaria in the radiolarian chert is Late Jurassic–Cretaceous. The basalt and ultramafic rock of the ophiolite also are overlaid by Tertiary Liuqu conglomerate, which contains numerous pebble components of ophiolite, indicating that the Tethys Ocean began to close at the end of Cretaceous Period. The isotopic data of gabbro, diabase, and albite granite in the Xigaze ophiolite are approximately 126–139 Ma, which indicates that the ophiolite formed in the Early Cretaceous. The K–Ar age of amphibole in garnet amphibolite in the ophiolite mélange is 81 Ma, indicating that tectonic ophiolite emplacement occurred at the end of Late Cretaceous.     

华南晚古生代硅质岩时空分布及再扩张残留海槽演化

根据硅质岩系的岩石组合和放射虫化石群的垂向变化,将华南泥盆系至中二叠统划分为５个构造层序,除早泥盆地的第１构造层序和晚石炭世的第４构造层序之外,其余每个构造层序对应出现一个放射虫生物群演替旋回,底部从无放射虫硅质泥岩带开始,向上变化为种属单调的中深海放射虫化石带,然后出现深海放射虫化石组合带,上部又出现了中深海放射虫化石组合带,这种演替旋回常常与海底火山喷发过程同步,代表残留海槽的一次再伸展扩张过