北京西山寒武纪海相红层的分布与时代     

李明  林宝玉 《地质学报》2022,96(6):1895-1921

本文参照北京西山及国内外寒武系相关地层资料，在古生物学和地层学研究的基础上，对北京西山寒武纪海相红层进行了初步研究。在西山寒武纪地层中，共识别出14层(套)海相红层，分别为：早寒武世下苇甸组1层B∈RB1(沧浪铺期)；早—中寒武世早期3层B∈RB2、B∈RB3及B∈RB4(馒头期—毛庄期)；中寒武世中期3层B∈RB5、B∈RB6及B∈RB7(徐庄期)；中寒武世晚期1层B∈RB8(张夏期)；晚寒武世早期2层B∈RB9、B∈RB10(崮山期)；晚寒武世中期3层B∈RB11、B∈RB12、B∈RB13(长山期)：晚寒武世晚期1层B∈RB14(凤山期)。所有14层海相红层形成于陆表海浅水环境，它们均属陆棚红层。红层分布模式说明，它们的形成与其附近的古陆有关。依据海相红层及其上下层位中所含的三叶虫化石，本文初步论述了各海相红层的大致时代，并与其他地区的同期海相红层进行了对比。此外，本文还讨论了山西东部寒武纪海相红层的层序和全球早寒武世沧浪铺期海相红层的广布事件。  相似文献   

The smallest of the largest: a new look at possible dwarfing in sauropod dinosaurs     

Jianu  Coralia-Maria  Weishampel  David B. 《Geologie en Mijnbouw》1999,78(3-4):335-343

Franz Baron Nopcsa recognised that the Late Cretaceous titanosaurid sauropod from Transylvania, Magyarosaurus dacus, was much smaller than the better known sauropods from the Upper Jurassic of the United States and even from Late Cretaceous deposits elsewhere in the world. In keeping with his biogeographic interpretations, Nopcsa viewed this difference as a consequence of body-size effects via island habitation. We present a preliminary re-evaluation of Nopcsa's claims and their heterochronic consequences using two approaches, viz. (1) regression analysis of humeral data as a means of establishing patterns in body size among titanosaurids, and (2) optimisation of humeral data onto titanosaurid cladograms to evaluate evolutionary trends within the clade. Our regression analysis is based on twenty species distributed among fourteen genera of neosauropods and uses length and mid-shaft mediolateral width of the humerus of presumed fully adult forms, and of growth samples that consist of postnatal to adult individuals. Linear regression analysis suggests that, among adult neosauropods, M. dacus appears to be represented by the smallest individuals; that M. dacus humeri appear to be more similar to those of subadults than to adults of other taxa; and that this juvenile morphology may constitute dwarfing in M. dacus by paedomorphosis. In order for these regressions to reflect their evolutionary context more fully, we also present optimisation analyses of humeral form within Titanosauroidea. Although many aspects of the phylogeny of this clade are relatively poorly resolved, preliminary results of our analyses are consistent with the conclusion that M. dacus was a heterochronic dwarf.  相似文献   

陕西黄土高原晚更新世环境变化   总被引：14，自引：3，他引：11  

赵景波  黄春长 《地理科学》1999,19(6):565-569

岐山剖面孢粉分析表明,黄土高原东南部晚更新世植被与气候变化可分为７个阶段和１３个小阶段。其中末次冰期的３个冷干阶段和２个温湿阶段被分别命名为秦家寨,岐山,坡头冰阶和尚家坡,杨家湾间冰阶。冰阶的植被以温带森林草原为主,间冰阶的植被以落叶阔叶林为主。  相似文献   

天山乌鲁木齐河源分选环的发育特征   总被引：1，自引：1，他引：1  

刘耕年  刘岳峰 《冰川冻土》1993,15(3):474-480

  相似文献   

滇东磷矿风化型矿石的判别指标讨论及次生风化富集作用   总被引：3，自引：0，他引：3  

戈定夷  刘永先 《矿物岩石》1994,14(3):29-42

风化型磷矿石－风化磷块岩是滇东最主要的磷矿石，为判别矿石为原生成风化磷块岩，前人已提出过１０余种作为判别标志的风化指标，但是这些指标的计算仅以矿石的化学组成为依据。笔者研究后指出，应以次生风化作用过程中磷块岩的组成和结构变化为基础，再合理使用上述某些判别指标，才能正确确定风化矿石，决定其利用价值和方法。笔者还指出，在次生风化作用中被溶蚀的不仅是碳酸盐，只要条件适当，石英和粘土矿物也可以溶蚀，使磷矿石品位增高，结构疏松，成为有利于洗选的优质矿石。  相似文献   

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石U－Pb年代学意义   总被引：1，自引：0，他引：1  

方中  李惠民 《地层学杂志》1994,18(3):168-172

苏南晚二叠世末期双峰次火山岩的发现和单颗粒锆石Ｕ－Ｐｂ年代学意义方中，李惠民，夏邦栋，楚雪君，刘寿和，王学锋（南京大学地球科学系，江苏南京，２１０００８；天津地质矿产研究所，天津，３００１７０）关键词晚二叠世，双峰火山岩，同生锆石，捕虏晶锆石，Ｕ－Ｐ...  相似文献   

内蒙古平庄─元宝山盆地群晚中生代地层   总被引：2，自引：0，他引：2  

商平  王宇林 《地层学杂志》1994,18(4):275-281

平庄─元宝山盆地的晚中生代地层可划分为下白垩统黑水组、元宝山组和杏园组，上侏罗统上那不打组与那不打组。杏园组和元宝山组中含有丰富的植物化石，属于ＲｕｆｆｏｒｄｉａＯｎｙｃｈｉｏｐｓｉｓ植物群的中部组合，可与邻区的主要含煤沉积的植物组合进行对比，时代属早白垩世Ｂｅｒｒｉａｓｉａｎ期至早Ａｐｔｉａｎ期。  相似文献   

吉林省大黑山条垒南段古生代晚期─中生代构造演化   总被引：2，自引：1，他引：2  

林建平  万天丰 《现代地质》1994,8(4):467-473

根据大黑山条垒南段的地质建造及构造形变特征，结合区域地质资料，将本区古生代晚期一中生代构造演化史划分为３个构造阶段，即海酉一印支期、燕山期和四川期。不同时期的构造变形、岩浆活动和应力场等特征不同：海西－印支期以ＳＮ向挤压为主；燕山期为ＮＷ－ＳＥ向挤压，平均差应力值为１１２．５ＭＰａ；四川期最大主压应力轴呈ＮＮＥ－ＳＳＷ向，平均差应力值为１０１．４ＭＰａ。四川期为本区构造格架基本定型的时期。  相似文献   

Review of Late Proterozoic sutures,ophiolitic mélanges and tectonics of eastern Egypt and north-east Sudan     

R. M. Shackleton 《International Journal of Earth Sciences》1994,83(3):537-546

The distribution, structural relations and ages of ophiolites and ophiolitic melanges in the Eastern Deserts of Egypt and north-east Sudan, and their relation to arc and post-arc magmatism, are used to infer the probable positions of sutures and the directions of obduction and subduction. The ages of the successive tectonic stages in the terranes decrease northwards, by about 100 Ma in the region discussed. Obduction was north-westwards. The obducted sheets of ophiolite and ophiolitic melange, extending about 500 km north from the Onib-Sol Flamed suture, may all represent a single back-arc basin. The direction of subduction is still not clearly proved: more geochemical evidence of arc-magmatic polarity is needed. The late tectonic north-westward thrusting, the NW - SE stretching lineation, the transpressional north-south Hamisama Shear Zone and the NW-SE sinistral Najd faults are all attributed to north-westward movement (present coordinates) of terranes towards the older craton west of the Nile. The Najd faults are interpreted as intracontinental transform faults.  相似文献   

华北地区南部晚古生代煤的变质成因——地下水热液对煤变质作用影响的进一步探讨   总被引：1，自引：0，他引：1  

钟宁宁  曹代勇 《地质学报》1994,68(4)

在分析造成华北地区南部晚古生代煤变质分带性的地质因素基础上,阐述了煤变质成因与区域构造格局演化的密切联系;从古地热异常形成机制出发,着重讨论了地下水热液对煤变质作用的影响,建立了煤的地下水效液变质作用地质模式;用古地热-煤变质系统的概念,根据热源、载热体和通道、聚热体3个要素的配置,分析了煤变质成因。  相似文献