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.     

下扬子区早三叠世孤峰组层状硅质岩成因

下扬子区早三叠世孤峰组中产出的层状硅质岩厚度为近20—80m,含有数量不等的放射虫和海绵骨针。孤峰组剖面有硅质岩型、碳酸盐岩型和硅质岩-碳酸盐岩混合型3种类型。层状硅质岩主要产在第一、第三2种类型剖面中。硅质沉积中心是一些菱形或椭圆形小型(面积在数千平方公里以内)凹地,其形成受断裂控制。硅质岩中产出泥化火山岩,层薄,且层数很多。硅质岩富Fe贫Al,富集As,Sb,Bi,Ga,Au,Ag,Cr等微量元素。稀土元素总量低,Ce负异常,重稀土有不同程度的富集,具有热水硅质岩的特征。硅质岩中混有少量非热水成因的物质。硅质沉积时海水温度约为几十度至160余度。     

南天山洋古地理及构造演化：西南天山放射虫硅质岩与地层记录的再认识*

泥盆纪—石炭纪放射虫硅质岩在西南天山广泛分布,从东部的独库公路沿线到西部的阿合奇中—吉边境构成一条深水沉积带。独库公路沿线已发现中泥盆世晚期至早石炭世维宪早期的放射虫硅质岩,可用“库勒湖组”统称。从志留系顶统科克铁克达坂组经下泥盆统阿尔腾柯斯组到库勒湖组的生物地层和沉积相研究表明了南天山洋从浅海到深水洋盆的演化过程。南天山洋是塔里木北缘浅海陆架裂解产生的小洋盆。构造古地理和生物古地理研究表明,南天山洋是古特提斯的分支洋盆,不属古亚洲洋范围。塔里木以南的古特提斯分支洋盆,在早石炭世及之后的继续扩张,使塔里木北移,导致南天山洋和准噶尔—北天山区的古亚洲洋在早石炭世晚期和晚石炭世相继消亡。     

老挝西北部琅勃拉邦构造带放射虫硅质岩及其构造意义

琅勃拉邦构造带内放射虫硅质岩含有放射虫Entactinia vulgaris Won, Entactinosphaera palimpola Foreman和Belowea variabilis (Ormiston et Lane),时代为早石炭世,为老挝境内首次报告。硅质岩样品具有很高的SiO2质量分数(95.29%~98.17%),大部分样品表现出相类似的稀土配分模式,部分样品配分模式图表现为上凸状,具有中稀土富集,均具有明显的Ce负异常,Ce/Ce*值为0.64~0.74,其中部分样品具有Eu的负异常,为0.58~0.68。Y/Ho比值为31.05~40.96,类似日本Sasayama中-晚二叠世的远洋硅质岩。地球化学显示其为含酸性火山碎屑非热液成因的远洋硅质岩。这些研究证实了在思茅板块和印支板块之间存在一个开阔的石炭纪时期弧后盆地。     

Long-lived Paleotethyan pelagic remnant inside Shan-Thai Block: Evidence from radiolarian biostratigraphy

The Shan-Thai Block, regarded traditionally as awhole geotectonic unit by the geologists engaged inthe study of geotectonic evolution of Southeast Asia, issituated to the west of the Ailaoshan and Nan-UttaraditSutures and to the east of the Shan Boundary Faults,and covers southwestern Yunnan, eastern Myanmar,most of Thailand, northwestern Laos, western Malay-sia, and Sumatra[1,2] (fig. 1). However, recent researchshows that it consists of two continental terranes fromGondwana and Cathay…     

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).     

新疆南天山库尔干一带泥盆纪-早石炭世放射虫组合的发现

新疆南天山库尔干南阿尔腾柯斯组硅质岩地层中发现了丰富的保存良好的放射虫化石,共计21属34种,11个未定种,1个未定种属。研究表明,两个样品的放射虫组合时代分别为中—晚泥盆世和早石炭世。中—晚泥盆世放射虫组合的发现,丰富了库车地区泥盆纪放射虫生物群组合,为确定阿尔腾柯斯组的时代奠定了生物化石依据。结合前人对该组生物化石的研究,该组为跨时代岩石地层单元,应予解体。而具有早泥盆世—晚石炭世放射虫硅质岩的深水海相沉积地层为古南天山洋盆的演化过程提供了地层学证据。     

Radiolarian Age of Manganese Ore and Red Chert from the Ananai Stratiform Manganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. We obtain radiolarian fossils such as Follicucullus monacanthus, Pseudoalbaillella aff. globosa, Pseudoalbaillella cf fusiformis , and Pseudoalbaillella spp. belonging to the Pseudoalbaillella globosa and Follicucullus monacanthus Zones from manganese ore and associated red chert of the Ananai stratiform manganese deposit in the Northern Chichibu Belt, central Shikoku. The depositional age of the Ananai ore deposit is constrained as Guadalupian (Middle Permian) that is between 270.6 and 260.4 Ma in the updated geologic time scale.     

Pleistocene radiolarian biostratigraphy in the South China Sea*

Based on a quantitative radiolarian analysis, 5 radiolarian zones (NR1-NR5) have been defined at Core. 17957-2 from the South China Sea, considering radiolarian zonations from low latitudes. The absolute age assignment of the radiolarian zones and the ranges of the six marker species is based on the direct correlation with the paleomagnetic and isotopic record, respectively. A comparison of the radiolarian stratigraphic data obtained from Core 17957-2 from the South China Sea with those from the equatorial Pacific and the tropical Indian Ocean shows a close similarity to the ages defined in the equatorial Pacific. The obtained biostratigraphic data provide an excellent tool for further dating of Pleistocene sediments in the China Sea. Project supported by the National Natural Science Foundation of China (Grant No. 49291100) and by the German Federal Ministry for Education, Science, Research and Technology (BMBF) as part of a GermadChinese scientific cooperation program. This is Alfred Wegener Contribution No. 1473.     

南海南部上层水体中多孔放射虫的组成与分布特征

通过对2002年5月采自南海南部11个站位的28个浮游分层拖网样品的定量研究,初步分析了南海南部上层水体中多孔放射虫的组成与分布特征。共鉴定出116属221种多孔放射虫,其中泡沫虫目123种,占总种数的55．7％;罩笼虫目98种,占总种数的44．3％。罩笼虫目在个体数量上占优势,罩笼虫目与泡沫虫目个体数量之比平均达1．73。多孔放射虫的属种组成呈现明显的热带暖水动物群的组合面貌,优势种相当突出,其组成与南海中北部海区及其它低纬度大洋相比存在一定差异,反映了南海南部海区独特的多孔放射虫属种组成特征。多孔放射虫丰度在不同水层中因受到不同环境因素的影响而呈现不同的平面分布趋势,惟一相似之处是高值多出现于西南或东北部海区;在垂直方向上基本呈随深度增加而减小的分布趋势,丰度和属种数最高值均出现于0—50m水层,在50m以深丰度和属种数均明显减少。各站位间简单分异度S变化幅度较大,在75—140种之间;而复合分异度H(s)变化幅度较小．在3．5-4．0之间。总体来说分异度值均比较高,表明南海南部上层水体中多孔放射虫种类多样性程度比较高,种群比较繁盛。