Confirmation of an Early Cretaceous age for the Qihulin Formation in eastern Heilongjiang Province, China: constraints from a new discovery of radiolarians   总被引：1，自引：0，他引：1  

Gang Li  Qun Yang 《Cretaceous Research》2003,24(6):691-696

The coal-bearing, alternating marine and non-marine Longzhaogou Group in eastern Heilongjiang, northeastern China, has long been considered as Jurassic, or mainly Jurassic, in age. However, recent studies have demonstrated that the ammonites and dinoflagellate cysts are of Early Cretaceous age. This has now been confirmed by new radiolarian evidence. The radiolarian fauna recovered from the upper Qihulin Formation of the Longzhaogou Group consists of nine poorly preserved species referable to nine genera. Novixitus is a Cretaceous genus, and the specimens of Archaeodictyomitra sp. and Xitus sp. recovered resemble A. vulgaris Pessagno and X. spicularius (Aliev), respectively.  相似文献   

Sedimentary Facies Architectures of Third-Order Sequences from Early to Middle Triassic in Nanpanjiang Basin     

MeiMingxiang MaYongsheng DengJun GaoJinhan ChenHuijun MengQingfen LiDonghai 《中国地质大学学报(英文版)》2003,14(2):103-118

There are complex and regular changes on sedimentary facies from the Early to the Middle Triassic in the Nanpanjiang basin. After the obvious drowned event of carbonate platforms in the transitional period between Permian and Triassic, carbonate platforms have evolved into the ramp type from the rimmed-shelf type. The differentiation of sedimentary facies becomes dearer in space, which are marked by the changes from an attached platform to a turbidity basin and several isolated platforms in the basin. The striking characteristics are the development of oolitic banks on isolated platforms in Nanning and Jingxi and the reef- and bank-limestones in the margin of the attached platform in the Early Triassic. Despite the difference of the time-span and the architectnre of fades succession of third-order sedimentary sequences, the process of the third-order relative sea-level changes reflected by the sedimentary facies succession of the third-order sequences is generally synchronous. Therefore, six third-order sequences could be discerned in the strata from the Early to the Middle Triassic in the Nanpanjiang basin. Using two types of facies changing surfaces and two types of diachronisms in stratigraphic records as the key elements, the sedimentary facies architectures of the third-order sequences that represent sequence stratigraphic frameworks from the Early to the Middle Triassic in the Nanpanjiang basin could be constructed.  相似文献   

A review of the geodynamic setting of large-scale Late Mesozoic gold mineralization in the North China Craton: an association with lithospheric thinning   总被引：22，自引：0，他引：22  

Jin-Hui Yang  Fu-Yuan Wu  Simon A. Wilde 《Ore Geology Reviews》2003,23(3-4):125-152

Abundant gold deposits are distributed along the margins of the North China Craton (NCC). Occurring throughout the Precambrian basement and located in or proximal to Mesozoic granitoids, these deposits show a consistent spatial–temporal association with Late Jurassic–Early Cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock. Their ages are mainly Early Cretaceous (130–110 Ma) and constrain a very short period of metallogenesis. Sr–Nd–Pb isotopic tracers of ores, minerals and associated rocks indicate that gold and associated metals mainly were derived from multi-sources, i.e., the wall rocks (Precambrian basement and Mesozoic granites) and associated mafic rocks.Previous studies, including high surface heat flow, uplift and later basin development, slow seismic wave speeds in the upper mantle, and a change in the character of mantle xenoliths sampled by Paleozoic to Cenozoic magmas, have been used to suggest that ancient, cratonic mantle lithosphere was removed from the base of the NCC some time after the Ordovician, and replaced by younger, less refractory lithospheric mantle. The geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization (130–110 Ma) indicate that they were derived from an ancient enriched lithospheric mantle source; whereas, the mafic dikes and volcanic rocks younger than 110 Ma were derived from a relatively depleted mantle source, i.e., asthenospheric mantle. According to their age and sources, relation to magmatism and geodynamic framework, the gold deposits were formed during lithospheric thinning. The removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature. The fluids derived from the lower crust were mixed with magmatic and meteoric waters, and resulted in the deposition of gold and associated metals.  相似文献   

震后震型早期判定的人工神经网络方法     

杨仕升 《华南地震》1997,17(4):42-47

应用人工神经网络的方法，利用３０次强震震后１天和２天内的地震资料作为学习样本，对广西及其邻区发生的４次地震的震型作了早期预测判定，结果表明应用效果较好，正确率达７５％。该方法值得进一步研究。  相似文献   

Palynological dating of infra- and intertrappean sediments in the Mesozoic succession of Borehole PGD-6, Domra Sub-basin, West Bengal, India     

Vijaya 《Cretaceous Research》1997,18(6):833-847

Palynofloras have been examined from infra- and intertrappean sediments of the Panchet and Rajmahal Formations in the Domra Sub-basin of the Damodar Basin, West Bengal, India. Three distinct palynological assemblages are identified and referred to the following palynozones: (i)Lundbladispora–Verrucosisporites(506.60–505.00 m, late Early Triassic, (ii)Murospora florida(501.65–422.20 m. Late Jurassic, Kimmeridgian–Tithonian), and (iii)Cicatricosisporites australiensis(342.00–229.6 m. Early Cretaceous, Tithonian–Berriasian). The first occurrences ofCallialasporites turbatusandC. dampieriare at 501.65 m.Callialasporitesis a dominant element of the succeeding assemblages from the Panchet Formation and indicates a Jurassic age. The FAD ofCicatricosisporites australiensisandC. augustusat 342.00 m, and inconsistent occurrences ofAequitriradites spinulosus,Crybelosporites stylosusin the overlying sediments indicate Jurassic–Cretaceous transition.  相似文献   

寒武纪早期澄江生物群小细丝海绵属新材料     

杨继媛  马海丹  陈爱林  侯先光 《高校地质学报》1997,25(3):474

文章描述了云南寒武纪早期澄江生物群小细丝海绵属一新种——螺旋小细丝海绵（Leptomitella spiralis sp. nov.）。新种 具有横向骨针束围绕海绵体呈螺旋状排列的典型特征，明显区别于属内其他种；此外，在外部形态和骨针类型上与属内其他种 也存在较大差异。新种的发现增加了Leptomitella种间形态结构的多样性，也为海绵动物的早期演化及寒武纪海绵动物辐射演 化研究提供新的化石资料。  相似文献   

北淮阳金寨—苏仙石地区中生代花岗岩类岩石学及地球化学特征   总被引：4，自引：4，他引：4  

李家振  刘文灿 《现代地质》1997,11(1):102-110

位于大别山北麓的北淮阳金寨—苏仙石地区广泛发育花岗岩类侵入岩，同位素年龄为１４０～９７Ｍａ，时代属Ｊ３—Ｋ１。根据侵入岩的地质、岩石学和岩石地球化学特征，将本区侵入岩划分为３个超单元（包括１０个单元）和３个独立单元，分属中性岩和酸性岩两大类，岩石类型有闪长岩、二长岩和花岗岩等。根据岩石化学的判别结果，侵入岩均属亚碱性系列中的钙碱性岩石，并属于普通型和钾质型  相似文献   

北祁连造山带东段老虎山石英闪长岩成因及其地质意义     

张海瑞  赵姣龙  于汇洋 《高校地质学报》1997,25(5):641

以北祁连造山带东段老虎山石英闪长岩体为研究对象，进行了锆石U-Pb年龄及全岩元素与Sr-Nd同位素组成的系统 测定，据此探讨了岩石的成因及其对北祁连构造演化的启示。锆石LA-ICP-MS U-Pb定年结果表明，石英闪长岩体的形成 年龄为440 Ma。岩石具有亚碱、准铝以及贫钙、镁、铁的特征，碱铝指数（AKI值） 均低于0.85，铝饱和指数（A/NKC 值） 多小于1.0，属钙碱性I型花岗岩类岩石。在稀土和微量元素组成上，岩石富集轻稀土和大离子亲石元素（如Rb、Cs、 Th和U），亏损高场强元素（如Nb和Ta），显示弧岩浆岩的地球化学特征。岩体具有相对均一的Sr-Nd同位素组成，初始Sr同 位素值为0.7058~0.7071，εNd(t)值为-1.06~-0.31。综合分析表明，老虎山石英闪长岩应起源于玄武质下地壳物质的部分熔 融，并在成岩过程中有少量幔源物质的混入。对区内火成岩地质地球化学特征与产出背景的全面分析，表明受北祁连洋俯 冲及随后岛弧与祁连—柴达木陆块碰撞拼贴影响，弧后盆地的北向俯冲消减作用可能是诱发民乐窑沟和老虎山弧岩浆岩以 及导致毛藏寺—老虎山花岗岩带内埃达克质岩石侵位的基本动力机制。  相似文献   

吉林东南部早寒武含铜层及其形成的古地理分析     

常建平 《吉林大学学报(地球科学版)》1996,(4)

吉林省东南部早寒武世晚期地层中含有数层含铜层，它们主要赋存在红色岩层所夹的灰绿黄绿色岩层之中。本区含铜层的形成与当时富氧阶段中的缺氧时期息息相关；而且该类型含铜层主要产自滨海或滨浅海地带，受当时古地理严格控制  相似文献   

南天山北缘麻粒岩残迹与辉石相韧性变形研究   总被引：9，自引：4，他引：9       下载免费PDF全文

舒良树  王赐银 《地质科学》1996,31(4):375-383

对新疆北部南天山北缘蛇绿混杂岩带中麻粒岩的岩石学、矿物学、岩石化学、矿物化学、稀土元素地球化学特征及辉石相韧性变形构造的研究表明,榆树沟麻粒岩的共生矿物组合为透辉石-次透辉石-紫苏辉石-石榴石-斜长石,属基性岩类暗色麻粒岩,以低硅高钙为特征,稀土总量低,轻稀土与铕弱亏损,反映高温高压熔融环境和岩浆分异差的特点。麻粒岩及超镁铁岩中的辉石经历了强烈的韧性剪切变形作用,不对称辉石残斑系、动态重结晶辉石亚颗粒集合体、辉石变形双晶纹、鱼尾构造、核幔构造等显微韧变构造广泛发育。宏观和微观运动学分析揭示了一期从南向北的推覆构造。麻粒岩的形成与早古生代大陆地壳拉伸作用有关,辉石相韧性变形则与早古生代末南天山边缘海的挤压关闭和推覆逆冲有关。  相似文献